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Sample records for accumulated shear strain

  1. Strain accumulation and rotation in the Eastern California Shear Zone

    USGS Publications Warehouse

    Savage, J.C.; Gan, Weijun; Svarc, J.L.

    2001-01-01

    Although the Eastern California Shear Zone (ECSZ) (strike ???N25??W) does not quite coincide with a small circle drawn about the Pacific-North America pole of rotation, trilateration and GPS measurements demonstrate that the motion within the zone corresponds to right-lateral simple shear across a vertical plane (strike N33??W??5??) roughly parallel to the tangent to that local small circle (strike ???N40??W). If the simple shear is released by slip on faults subparallel to the shear zone, the accumulated rotation is also released, leaving no secular rotation. South of the Garlock fault the principal faults (e.g., Calico-Blackwater fault) strike ???N40??W, close enough to the strike of the vertical plane across which maximum right-lateral shear accumulates to almost wholly accommodate that accumulation of both strain and rotation by right-lateral slip. North of the Garlock fault dip slip as well as strike slip on the principal faults (strike ???N20??W) is required to accommodate the simple shear accumulation. In both cases the accumulated rotation is released with the shear strain. The Garlock fault, which transects the ECSZ, is not offset by north-northwest striking faults nor, despite geological evidence for long-term left-lateral slip, does it appear at the present time to be accumulating left-lateral simple shear strain across the fault due to slip at depth. Rather the motion is explained by right-lateral simple shear across the orthogonal ECSZ. Left-lateral slip on the Garlock fault will release the shear strain accumulating there but would augment the accumulating rotation, resulting in a secular clockwise rotation rate ???80 nrad yr-1 (4.6?? Myr-1).

  2. Strain accumulation across the Eastern California Shear Zone at latitude 36°30'N

    USGS Publications Warehouse

    Gan, Weijun; Svarc, Jerry L.; Savage, J.C.; Prescott, W.H.

    2000-01-01

    The motion of a linear array of monuments extending across the Eastern California Shear Zone (ECSZ) has been measured from 1994 to 1999 with the Global Positioning System. The linear array is oriented N54°E, perpendicular to the tangent to the local small circle drawn about the Pacific-North America pole of rotation, and the observed motion across the ECSZ is approximated by differential rotation about that pole. The observations suggest uniform deformation within the ECSZ (strike N23°W) (26 nstrain yr−1 extension normal to the zone and 39 nstrain yr−1 simple right-lateral shear across it) with no significant deformation in the two blocks (the Sierra Nevada mountains and southern Nevada) on either side. The deformation may be imposed by right-lateral slip at depth on the individual major fault systems within the zone if the slip rates are: Death Valley-Furnace Creek fault 3.2±0.9 mm yr−1, Hunter Mountain-Panamint Valley fault 3.3±1.6 mm yr−1, and Owens Valley fault 6.9±1.6 mm yr−1. However, this estimate of the slip rate on the Owens Valley fault is 3 times greater than the geologic estimate.

  3. Shear-wave Velocity Structure and Inter-Seismic Strain Accumulation in the Up-Dip Region of the Cascadia Subduction Zone: Similarities to Tohoku?

    NASA Astrophysics Data System (ADS)

    Collins, J. A.; McGuire, J. J.; Wei, M.

    2013-12-01

    The up-dip region of subduction zone thrusts is difficult to study using land-based seismic and geodetic networks, yet documenting its ability to store and release elastic strain is critical for understanding the mechanics of great subduction earthquakes and tsunami generation. The 2011 Tohoku earthquake produced extremely large slip in the shallowest portion of the subduction zone beneath a region of the fore-arc that is comprised of extremely low-velocity, unconsolidated sediments [Tsuru et al. JGR 2012]. The influence of the sediment material properties on the co-seismic slip distribution and tsunami generation can be considerable through both the effects on the dynamic wavefield during the rupture [Kozdon and Dunham, BSSA 2012] and potentially the build up of strain during the inter-seismic period. As part of the 2010-2011 SeaJade experiment [Scherwath et al, EOS 2011], we deployed 10 ocean bottom seismographs (OBS) on the continental slope offshore of Vancouver Island in the region of the NEPTUNE Canada observatory. One goal of the experiment is to measure the shear modulus of the sediments lying above the subducting plate using the seafloor compliance technique. Using seafloor acceleration measured by broadband seismometer and seafloor pressure measured by Differential Pressure Gauge (DPG), we estimate the compliance spectrum in the infra-gravity wave band (~0.002-0.04 Hz) at 9 sites following the methodology of Crawford et al. [JGR, 1991]. We calibrated DPG sensitivities using laboratory measurements and by comparing teleseismic Rayleigh arrivals recorded on the seismometer and DPG channels [Webb, pers. comm]. We correct the vertical-component seismometer data for tilt using the procedure of Crawford and Webb [BSSA, 2000], Corrections for the gravitational attraction of the surface gravity waves [Crawford et al., JGR, 1998] are important at frequencies of 0.003-0.006 Hz only. Typically, the coherences are high (>0.7) in the 0.006 to 0.03 Hz range. We invert

  4. Strain patterns and strain accumulation along plate margins

    NASA Technical Reports Server (NTRS)

    Savage, J. C.

    1978-01-01

    Observations of strain accumulation along plate margins in Japan, New Zealand, and the United States indicate that: (1) a typical maximum rate of secular strain accumulation is on the order of 0.3 ppm/a, (2) a substantial part of the strain accumulation process can be attributed to slip at depth on the major plate boundary faults, and (3) some plastic deformation in a zone 100 km or more in width is apparently involved in the strain accumulation process.

  5. Rapid intraplate strain accumulation in the New Madrid seismic zone

    USGS Publications Warehouse

    Liu, L.; Zoback, M.D.; Segall, P.

    1992-01-01

    Remeasurement of a triangulation network in the southern part of the New Madrid seismic zone with the Global Positioning System has revealed rapid crustal strain accumulation since the 1950s. This area experienced three large (moment magnitudes >8) earthquakes in 1811 to 1812. The orientation and sense of shear is consistent with right-lateral strike slip motion along a northeast-trending fault zone (as indicated by current seismicity). Detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time.

  6. Rapid intraplate strain accumulation in the New Madrid seismic zone

    SciTech Connect

    Liu, L.; Zoback, M.D.; Segall, P. USGS, Menlo Park, CA )

    1992-09-01

    Remeasurement of a triangulation network in the southern part of the New Madrid seismic zone with the Global Positioning System has revealed rapid crustal strain accumulation since the 1950s. This area experienced three large (moment magnitudes greater than 8) earthquakes in 1811 to 1812. The orientation and sense of shear is consistent with right-lateral strike slip motion along a northeast-trending fault zone (as indicated by current seismicity). Detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time. 34 refs.

  7. 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.

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

    NASA Technical Reports Server (NTRS)

    Cheng, R. Y. K.

    1976-01-01

    The shearing resistance of cohesive soils subjected to a high rate of shearing strain was investigated. 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 to date, 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 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.

  9. Strain accumulation along the Cascadia subduction zone

    USGS Publications Warehouse

    Murray, M.H.; Lisowski, M.

    2000-01-01

    We combine triangulation, trilateration, and GPS observations to determine horizontal strain rates along the Cascadia subduction zone from Cape Mendocino to the Strait of Juan de Fuca. Shear-strain rates are significantly greater than zero (95% confidence) in all forearc regions (26-167 nanoradians/yr), and are not significant in the arc and backarc regions. The deformation is primarily uniaxial contraction nearly parallel to Juan de Fuca-North America plate convergence (N55??-80??E). The strain rates are consistent with an elastic dislocation model for interseismic slip with a shallow 100-km wide locked zone and a deeper 75-km transition zone along the entire megathrust, except along the central Oregon coast where relatively lower strain rates are consistent with 30-40 km wide locked and transition zones.

  10. Strain localization across main continental strike-slip shear zones

    NASA Astrophysics Data System (ADS)

    Boutonnet, E.; Leloup, P.; Rozel, A.

    2011-12-01

    Whether deformation within the deep continental crust is fundamentally concentrated in narrow shear zones or distributed in wide zones stays a major controversy of the earth sciences. This is in part because direct measurements of ductile shear or strain rate are difficult, especially when deformation is intense as it is the case in ductile shear zones. The QPSRM (quartz paleo strain rates metry) method allows indirect measurements of strain rates in natural rocks, using shear stress, an estimation of the temperature of deformation, and assuming a flow law. This method has been recently calibrated for ductile continental shear zones conditions, giving the users the best power flow law/ piezometer combination to calculate accurate local strain rates. By comparing the local strain rates with the equivalent global strain rates, measured by dividing the shear rates (mm/yr) by the shear zone width, we estimated the amount of strain localization across ductile shear zones. We applied this method to two major shear zones located in the India-Asia collision zone: the Ailao Shan Red River shear zone (ASRR, SE Asia) and the Karakorum shear zone (Ksz, SW Tibet). We used the Hirth et al. (2001) flow law and the Twiss (1977) piezometer. Within the ASRR, a gradient of strain rates is observed between the shear zone border (5.4 x10-15 s-1) and the shear zone center (3.6 x10-12 s-1). The equivalent global strain rates range between 8.0 x10-15 and 1.7 x10-13 s-1, assuming a shear rate of ~1 cm/yr and a homogenous deformation across the ~15 km-large shear zone. We interpret the local strain rates, which are higher than the global strain rates, as strain localization. The strain localization in the core of the ASRR shear zone had been observed by field studies, and also predicted by numerical models. This study brings a measurement of this strain localization. Within the Ksz, the equivalent shear rate is 4.4 x10-14 s-1, assuming a shear rate of ~11 mm/yr and a homogenous deformation

  11. A biaxial method for inplane shear testing. [shear strain in composite materials

    NASA Technical Reports Server (NTRS)

    Bush, H. G.; Weller, T.

    1978-01-01

    A biaxial method for performing inplane shear tests of materials using a shear frame is described. Aluminum plate and sandwich specimens were used to characterize the uniformity of shear strain imparted by the biaxial method of loading as opposed to the uniaxial method. The inplane stiffening effect of aluminum honeycomb core was determined. Test results for (+ or - 45) graphite-epoxy laminate are presented. Some theoretical considerations of subjecting an anisotropic material to a uniform shear deformation are discussed.

  12. Large-strain shear response of unidirectional boron/aluminum

    SciTech Connect

    Reedy, E.D. Jr.

    1982-01-01

    Data characterizing the shear response of unidirectionally reinforced boron/aluminum are presented. The symmetric rail shear test method was used to make the measurements. Results are given for 5.6 mil diameter boron fibers in either an 1100 or a 6061 aluminum matrix. The boron/6061 aluminum was tested in both the as-fabricated and a heat-treated condition. The composite data are used to define matrix shear stress-strain relations in a manner suitable for shear-lag analyses of flawed composites. Analyses of center-notched tensile specimens are in excellent agreement with experiment.

  13. On the Effect of Strain Gradient on Adiabatic Shear Banding

    NASA Astrophysics Data System (ADS)

    Tsagrakis, Ioannis; Aifantis, Elias C.

    2015-10-01

    Most of the work on adiabatic shear banding is based on the effect of temperature gradients on shear band nucleation and evolution. In contrast, the present work considers the coupling between temperature and strain gradients. The competition of thermal and strain gradient terms on the onset of instability and its dependence on specimen size is illustrated. It is shown that heat conduction promotes the instability initiation in the hardening part of the homogeneous stress-strain, while the strain gradient term favors the occurrence of this initiation in the softening regime. This behavior is size dependent, i.e., small specimens can support stable homogeneous deformations even in the softening regime. The spacing of adiabatic shear bands is also evaluated by considering the dominant instability mode during the primary stages of the localization process and it is found that it is an increasing function of the strain gradient coefficient.

  14. Himalayan Strain Accumulation 100 ka Timescales

    NASA Astrophysics Data System (ADS)

    Cannon, J. M.; Murphy, M. A.; Liu, Y.

    2015-12-01

    Crustal scale fault systems and tectonostratigraphic units in the Himalaya can be traced for 2500 km along strike. However regional studies have shown that there is variability in the location and rate of strain accumulation which appears to be driven by Main Himalayan Thrust (MHT) geometry and convergence obliquity. GPS illuminates the modern interseismic strain rate and the historical record of great earthquakes elucidates variations in strain accumulation over 103 years. To connect these patterns with the 106 year structural and thermochronometric geologic record we examine normalized river channel steepness (ksn), a proxy for rock uplift rate, which develops over 104 - 105 years. Here we present a ksn map of the Himalaya and compare it with bedrock geology, precipitation, the historic earthquake record, GPS, seismicity, and seismotectonic models. Our map shows significant along strike changes in the magnitude of channel steepness, the areal extent of swaths of high ksn channels, and their location with respect to the range front. Differences include the juxtaposition of two narrow (30 - 40 km) range parallel belts of high ksn in west Nepal and Bhutan coincident with MHT duplexes and belts of microseismcity, with a single broad (70 km) swath of high ksn and microseismicity in central and eastern Nepal. Separating west and central Nepal a band of low ksn crosses the range coincident with the West Nepal Fault (WNF) and the lowest rate of microseismicity in Nepal. To the west the orogen is obliquely convergent and has less high ksn channels, while the orthogonally convergent region to the east contains the highest concentration of oversteepened channels in the Himalaya supporting the idea that the WNF is a strain partitioning boundary. The syntaxes are characterized by locally high channel steepness surrounded by low to moderate ksn channels consistent with the hypothesis that rapid exhumation within the syntaxes is sustained by an influx of lower crust.

  15. The importance of strain localisation in shear zones

    NASA Astrophysics Data System (ADS)

    Bons, Paul D.; Finch, Melanie; Gomez-Rivas, Enrique; Griera, Albert; Llorens, Maria-Gema; Steinbach, Florian; Weikusat, Ilka

    2016-04-01

    The occurrence of various types of shear bands (C, C', C'') in shear zones indicate that heterogeneity of strain is common in strongly deformed rocks. However, the importance of strain localisation is difficult to ascertain if suitable strain markers are lacking, which is usually the case. Numerical modelling with the finite-element method has so far not given much insight in the development of shear bands. We suggest that this is not only because the modelled strains are often not high enough, but also because this technique (that usually assumes isotropic material properties within elements) does not properly incorporate mineral deformation behaviour. We simulated high-strain, simple-shear deformation in single- and polyphase materials with a full-field theory (FFT) model coupled to the Elle modelling platform (www.elle.ws; Lebensohn 2001; Bons et al. 2008). The FFT-approach simulates visco-plastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses in relations to the applied stresses. Griera et al. (2011; 2013) have shown that this approach is particularly well suited for strongly anisotropic minerals, such as mica and ice Ih (Llorens 2015). We modelled single- and polyphase composites of minerals with different anisotropies and strengths, roughly equivalent to minerals such as ice Ih, mica, quartz and feldspar. Single-phase polycrystalline aggregates show distinct heterogeneity of strain rate, especially in case of ice Ih, which is mechanically close to mica (see also Griera et al. 2015). Finite strain distributions are heterogeneous as well, but the patterns may differ from that of the strain rate distribution. Dynamic recrystallisation, however, usually masks any strain and strain rate localisation (Llorens 2015). In case of polyphase aggregates, equivalent to e.g. a granite, we observe extensive localisation in both syn- and antithetic shear bands. The antithetic shear bands

  16. Ismetpasa and Destek regions; Creeping or accumulating strain

    NASA Astrophysics Data System (ADS)

    Yavasoglu, Hakan; Alkan, M. Nurullah; Aladogan, Kayhan; Ozulu, I. Murat; Ilci, Veli; Sahin, Murat; Tombus, F. Engin; Tiryakioglu, Ibrahim

    2016-04-01

    The North Anatolian Fault (NAF) is one of the most destructive fault system all over the world. In the last century, many devastating seismic event happened on it and its shear zone (NAFZ). Especially, after the 1999 Izmit and Duzce earthquakes, the earth science studies increase to save human life. To better understand the mechanism of the active fault system, tectonic stress and strain are important phenomena. According to elastic rebound theory, the locked active faults release the accumulated strain abruptly in four periods; interseismic, preseismic, coseismic and postseismic. In the literature, this phase is called the earthquake cycle. On the other hand, there is another scenario (aseismic deformation or creep) to release the strain without any remarkable seismic event. For the creep procedure, the important subject is threshold of the aseismic slip rate. If it is equal or larger than long-term slip rate, the destructive earthquakes will not occur along the fault which has aseismic slip rate. On the contrary, if the creep motion is lower than long-term slip rate along the fault, the fault has potential to produce moderate-to-large size earthquakes. In this study, the regions, Ismetpasa and Destek, have been studied to determine the aseismic deformation using GPS data. The first and second GPS campaigns have been evaluated with GAMIT/GLOBK software. Preliminary results of the project (slip-rate along the NAF in this region and aseismic deformation) will be presented.

  17. Strain Relaxation in CVD Graphene: Wrinkling with Shear Lag.

    PubMed

    Bronsgeest, Merijntje S; Bendiab, Nedjma; Mathur, Shashank; Kimouche, Amina; Johnson, Harley T; Coraux, Johann; Pochet, Pascal

    2015-08-12

    We measure uniaxial strain fields in the vicinity of edges and wrinkles in graphene prepared by chemical vapor deposition (CVD), by combining microscopy techniques and local vibrational characterization. These strain fields have magnitudes of several tenths of a percent and extend across micrometer distances. The nonlinear shear-lag model remarkably captures these strain fields in terms of the graphene-substrate interaction and provides a complete understanding of strain-relieving wrinkles in graphene for any level of graphene-substrate coherency. PMID:26171667

  18. Strain accumulation across the Denali fault in the Delta River canyon, Alaska.

    USGS Publications Warehouse

    Savage, J.C.; Lisowski, M.; Prescott, W.H.

    1981-01-01

    Deformation along the Denali fault in the Delta River canyon was determined from geodetic surveys in 1941/1942, 1970, 1975, and 1979. The data were best for the 1975-79 interval; in that period the average strain accumulation was essentially pure right lateral shear at a rate of 0.6+-0.1 murad/a (a is years) (engineering shear) across a vertical plane striking N87oE. The plane of maximum shear is rotated about 30o countercloskwise from the local strike of the Denali fault but closely coincides with the strike of a major linear segment of the fault that begins 50 km farther W. The deformation between 1941-42 and 1970 is consistent with a similar rate of strain accumulation if one removes the coseismic strain step contributed by the 1964 Alaska earthquake. The 1970-75 deformation is poorly defined owing to uncertainties in the 1970 survey, but the strain accumulation during that period is certainly much less than during the 1975-79 interval. The 1975-79 strain accumulation is interpreted by means of a dislocation model which suggests that the Denali fault in the vicinity of the Delta River Canyon behaves as a leaky transform fault.-Authors

  19. Strain Accumulation in Montenegro Using GPS Measurements

    NASA Astrophysics Data System (ADS)

    Glavatovic, B.; Vucic, L.; D'Agostino, N.; D'Anastasio, E.; Selvaggi, G.

    2011-12-01

    In this work we present the preliminary results of the analysis of GPS measurements collected from continuous stations belonging to networks deployed for both sceintific and societal purposes. The area is particularly interesting in relationship with the large Mw 7.1 earthquake that affected the Montenegro coastal areas in 1979 and the large uncertainties associated with recurrence times of large events and the present-day rate of strain accumulation. The dataset from the MEPOS (Montenegro), MONTEPOS (Montenegro), AGROS (Serbia) and MAKPOS (Macedonia) networks, combined with data from the RING (http://ring.gm.ingv.it) and other continuous GPS networks in the Mediterranean, Eurasian and African regions, has been analyzed using the GIPSY-OASIS II software package and the precise point positioning method [Zumberge et al., 1997]. Carrier phase ambiguities have been successfully resolved across the entire network using an algorithm based on a fixed-point theorem that closely approximates a full-network resolution [Blewitt, 2008]. Satellite orbit and clock parameters, and daily coordinate transformation parameters into ITRF2005 were provided by the Jet Propulsion Laboratory (JPL). ITRF2005 positions were transformed into an Eurasia fixed reference frame by performing daily transformations into a frame that is defined by minimizing the horizontal velocities of 30 stations across the stable part of the Eurasian continent (away from areas affected by glacial isostatic adjustments). Common mode errors for this continental scale frame are further reduced by including an additional 60 stations as far away as Iceland, Eastern Eurasia, and Africa in a daily spatial (7 parameters) filter [D'Anastasio et al., 2008]. We estimate velocities from the continuous GPS time-series using the CATS software package [Williams, 2003] while accounting for annual and semi-annual constituents, simultaneously estimating rate uncertainties given the assumption that the error model is dominated by

  20. Critical scaling with strain rate in overdamped sheared disordered solids

    NASA Astrophysics Data System (ADS)

    Clemmer, Joel; Salerno, Kenneth; Robbins, Mark

    In the limit of quasistatic shear, disordered solids demonstrate non-equilibrium critical behavior including power-law distributions of avalanches. Using molecular dynamics simulations of 2D and 3D overdamped binary LJ glasses, we explore the critical behavior in the limit of finite strain rate. We use finite-size scaling to find the critical exponents characterizing shear stress, kinetic energy, and measures of temporal and spatial correlations. The shear stress of the system rises as a power β of the strain rate. Larger system size extends this power law to lower rates. This behavior is governed by a power law drop of the dynamic correlation length with increasing shear stress defined by the exponent ν. This finite-size effect also impacts the scaling of the RMS kinetic energy with strain rate as avalanches begin nucleating simultaneously leading to continuous deformation of the solid. As system size increases, avalanches begin overlapping at lower rates. The correlation function of non-affine displacement exhibits novel anisotropic power law scaling with the magnitude of the wave vector. Its strain rate dependence is used to determine the scaling of the dynamic correlation length. Support provided by: DMR-1006805; NSF IGERT-0801471; OCI-0963185; CMMI-0923018.

  1. Theory and Practice of Shear/Stress Strain Gage Hygrometry

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A.; Fenner, Ralph L.

    2006-01-01

    Mechanical hygrometry has progressed during the last several decades from crude hygroscopes to state-of-the art strain-gage sensors. The strain-gage devices vary from different metallic beams to strain-gage sensors using cellulose crystallite elements, held in full shear restraint. This old technique is still in use but several companies are now actively pursuing development of MEMS miniaturized humidity sensors. These new sensors use polyimide thin film for water vapor adsorption and desorption. This paper will provide overview about modern humidity sensors.

  2. Shear Weakening and Strain Localization in the Deeper Mantle?

    NASA Astrophysics Data System (ADS)

    Hernlund, J. W.

    2011-12-01

    Shear weakening and strain localization is an essential component of plate tectonics on Earth, and is ubiquitously observed in both crustal and mantle rocks exposed at Earth's surface at a variety of scales. However, it is commonly assumed that this process is only important in the lithosphere (because it would otherwise be strong and inhibit plate-like behavior), and that at greater depths the mantle's style of deformation is inherently diffuse and broadly distributed. This assumption strongly influences our view of processes in Earth's deep interior, such as styles of mantle mixing, and is the basis for the rheological formulation implemented in most mantle convection models. However, there are many possibilities that would permit shear localization at large scales, in a way that could alter our view of internal mantle deformation in important ways. One example is the possible presence of very weak rocks (e.g., owing to localized volatile enrichment) that may become sheared and stretched in flows to create effective weak zones between stronger bodies of rock. Another example is the possibility that weaker mineral phases in a rock can become sheared between stronger grains such that the weakest phase dominates the long-term dynamic processes operating in the mantle. Simple modeling of various scenarios reveals that differences in long-term behavior for shear localized mantle convection largely depend upon the scale of the shear zone. If the weak zones are large in scale, they acan persist over long time scales, and may be advected laterally away from the buoyancy centers where they are produced (giving rise to toroidal motion). On the other hand, if the weakening fabric occurs at the grain-scale, then the fabric can be healed by processes such as Ostwald ripening that operate on shorter time scales at higher temperatures. Regardless of the scale of shear zones, subduction of slabs through the lower mantle can occur relatively rapidly when accommodated by localized

  3. Surface strain measurements of fingertip skin under shearing.

    PubMed

    Delhaye, Benoit; Barrea, Allan; Edin, Benoni B; Lefèvre, Philippe; Thonnard, Jean-Louis

    2016-02-01

    The temporal evolution of surface strain, resulting from a combination of normal and tangential loading forces on the fingerpad, was calculated from high-resolution images. A customized robotic device loaded the fingertip with varying normal force, tangential direction and tangential speed. We observed strain waves that propagated from the periphery to the centre of the contact area. Consequently, different regions of the contact area were subject to varying degrees of compression, stretch and shear. The spatial distribution of both the strains and the strain energy densities depended on the stimulus direction. Additionally, the strains varied with the normal force level and were substantial, e.g. peak strains of 50% with a normal force of 5 N, i.e. at force levels well within the range of common dexterous manipulation tasks. While these observations were consistent with some theoretical predictions from contact mechanics, we also observed substantial deviations as expected given the complex geometry and mechanics of fingertips. Specifically, from in-depth analyses, we conclude that some of these deviations depend on local fingerprint patterns. Our data provide useful information for models of tactile afferent responses and background for the design of novel haptic interfaces. PMID:26888949

  4. Surface strain measurements of fingertip skin under shearing

    PubMed Central

    2016-01-01

    The temporal evolution of surface strain, resulting from a combination of normal and tangential loading forces on the fingerpad, was calculated from high-resolution images. A customized robotic device loaded the fingertip with varying normal force, tangential direction and tangential speed. We observed strain waves that propagated from the periphery to the centre of the contact area. Consequently, different regions of the contact area were subject to varying degrees of compression, stretch and shear. The spatial distribution of both the strains and the strain energy densities depended on the stimulus direction. Additionally, the strains varied with the normal force level and were substantial, e.g. peak strains of 50% with a normal force of 5 N, i.e. at force levels well within the range of common dexterous manipulation tasks. While these observations were consistent with some theoretical predictions from contact mechanics, we also observed substantial deviations as expected given the complex geometry and mechanics of fingertips. Specifically, from in-depth analyses, we conclude that some of these deviations depend on local fingerprint patterns. Our data provide useful information for models of tactile afferent responses and background for the design of novel haptic interfaces. PMID:26888949

  5. Strain localization driven by thermal decomposition during seismic shear

    NASA Astrophysics Data System (ADS)

    Platt, John D.; Brantut, Nicolas; Rice, James R.

    2015-06-01

    Field and laboratory observations show that shear deformation is often extremely localized at seismic slip rates, with a typical deforming zone width on the order of a few tens of microns. This extreme localization can be understood in terms of thermally driven weakening mechanisms. A zone of initially high strain rate will experience more shear heating and thus weaken faster, making it more likely to accommodate subsequent deformation. Fault zones often contain thermally unstable minerals such as clays or carbonates, which devolatilize at the high temperatures attained during seismic slip. In this paper, we investigate how these thermal decomposition reactions drive strain localization when coupled to a model for thermal pressurization of in situ groundwater. Building on Rice et al. (2014), we use a linear stability analysis to predict a localized zone thickness that depends on a combination of hydraulic, frictional, and thermochemical properties of the deforming fault rock. Numerical simulations show that the onset of thermal decomposition drives additional strain localization when compared with thermal pressurization alone and predict localized zone thicknesses of ˜7 and ˜13 μm for lizardite and calcite, respectively. Finally we show how thermal diffusion and the endothermic reaction combine to limit the peak temperature of the fault and that the pore fluid released by the reaction provides additional weakening of ˜20-40% of the initial strength.

  6. Shear strains in a graphite-PEEK beam by moire interferometry with carrier fringes

    NASA Technical Reports Server (NTRS)

    Post, Daniel; Czarnek, Robert; Joh, Duksung

    1986-01-01

    A multispan quasi-isotropic graphite-PEEK beam exhibited dramatic shear strains in the interlaminar region between plies. Shear strains in the plies themselves varied in basic accord with fiber direction. Large anomalous shear strains developed near the center of the beam height, where shear stresses were large. High-sensitivity moire interferometry with 2400 lines/mm was used. A new technique of data extraction was developed, using carrier fringes to transform the pattern to one in which fringe slopes are proportional to derivatives of displacement. It enhanced detection and measurement of highly localized shear-strain gradients.

  7. In-situ shear stress indicator using heated strain gages at the flow boundary

    NASA Astrophysics Data System (ADS)

    Yeh, Chi-An; Yang, Fuling

    2011-11-01

    This work borrows the concept of hot-wire anemometry and sketch a technique that uses local heat transfer to infer the flow field and the corresponding stress. Conventional strain gages were mounted at the flow solid boundary as the heat source and acrylic boundary was chosen for its low thermal conductivity ensuring heat accumulation when a gage is energized. The gage would now work in slightly overheated state and its self-heating leads to an additional thermal strain. When exposed to a flow field, heat is brought away by local forced convection, resulting in deviations in gage signal from that developed in quiescent liquid. We have developed a facility to achieve synchronous gage measurements at different locations on a solid boundary. Three steady flow motions were considered: circular Couette flow, rectilinear uniform flow, and rectilinear oscillating flow. Preliminary tests show the gage reading does respond to the imposed flow through thermal effects and greater deviation was measured in flows of higher shear strain rates. The correlation between the gage signals and the imposed flow field is further examined by theoretical analysis. We also introduced a second solid boundary to the vicinity of the gage in the two rectilinear flows. The gage readings demonstrate rises in its magnitudes indicating wall amplification effect on the local shear strain, agreeing to the drag augmentation by a second solid boundary reported in many multiphase flow literatures.

  8. Dislocation accumulation at large plastic strains -- An approach to the theoretical strength of materials

    SciTech Connect

    Embury, J.D. |; Han, K.

    1999-04-01

    The usual method of introducing engineers to the concept of dislocations and their role in plastic flow is to compare an estimate of the theoretical strength of solid (of order {micro}/30 where {micro} is the shear modulus) and the observed strength of either single crystals ({mu}/10{sup 4}) or practical engineering material such as structural steels where the yield stress in shear is of order {mu}/10{sup 3}. However, if one considers the problem in reverse, one can consider the accumulation of dislocations as an important mechanism by which one can produce engineering materials in which the strength level approaches the theoretical strength. If one assumes that the flow stress can be expressed in terms of te mean free path between stored dislocations or as the square root of the global dislocation density, then one can see the influence of dislocation density in a diagrammatic form. It is clear that the strengthening by dislocation accumulation due to large imposed plastic strains represents an important approach both to the development of new, potentially valuable, engineering materials and an important area of basic understanding in terms of the mechanical response of materials close to their theoretical strength. Thus, this article will survey some of the factors which influence dislocation accumulation at large strains and the consequences of such accumulation processes.

  9. A physical model for strain accumulation in the San Francisco Bay Region

    USGS Publications Warehouse

    Pollitz, F.F.; Nyst, M.

    2005-01-01

    Strain accumulation in tectonically active regions is generally a superposition of the effects of background tectonic loading, steady-state dislocation processes, such as creep, and transient deformation. In the San Francisco Bay region (SFBR), the most uncertain of these processes is transient deformation, which arises primarily in association with large earthquakes. As such, it depends upon the history of faulting and the rheology of the crust and mantle, which together determine the pattern of longer term (decade-scale) post-seismic response to earthquakes. We utilize a set of 102 GPS velocity vectors in the SFBR in order to characterize the strain rate field and construct a physical model of its present deformation. We first perform an inversion for the continuous velocity gradient field from the discrete GPS velocity field, from which both tensor strain rate and rotation rate may be extracted. The present strain rate pattern is well described as a nearly uniform shear strain rate oriented approximately N34??W (140 nanostrain yr-1) plus a N56??E uniaxial compression rate averaging 20 nanostrain yr-1 across the shear zone. We fit the velocity and strain rate fields to a model of time-dependent deformation within a 135-kin-wide, arcuate shear zone bounded by strong Pacific Plate and Sierra Nevada block lithosphere to the SW and NE, respectively. Driving forces are purely lateral, consisting of shear zone deformation imposed by the relative motions between the thick Pacific Plate and Sierra Nevada block lithospheres. Assuming a depth-dependent viscoelastic structure within the shear zone, we account for the effects of steady creep on faults and viscoelastic relaxation following the 1906 San Francisco and 1989 Loma Prieta earthquakes, subject to constant velocity boundary conditions on the edges of the shear zone. Fault creep is realized by evaluating dislocations on the creeping portions of faults in the fluid limit of the viscoelastic model. A priori plate

  10. Correlation of thrombosis growth rate to pathological wall shear rate during platelet accumulation.

    PubMed

    Bark, David L; Para, Andrea N; Ku, David N

    2012-10-01

    Local hemodynamics may strongly influence atherothrombosis, which can lead to acute myocardial infarction and stroke. The relationship between hemodynamics and thrombosis during platelet accumulation was studied through an in vitro flow system consisting of a stenosis. Specifically, wall shear rates (WSR) ranging from 0 to 100,000 s(-1) were ascertained through computations and compared with thrombus growth rates found by image analysis for over 5,000 individual observation points per experiment. A positive correlation (P < 0.0001) was found between thrombus accumulation rates and WSR up to 6,000 s(-1), with a decrease in growth rates at WSR >6,000 s(-1) (P < 0.0001). Furthermore, growth rates at pathological shear rates were found to be two to four times greater than for physiological arterial shear rates below 400 s(-1). Platelets did not accumulate for the first minute of perfusion. The initial lag time, before discernible thrombus growth could be found, diminished with shear (P < 0.0001). These studies show the quantitative increase in thrombus growth rates with very high shear rates in stenoses onto a collagen substrate. PMID:22539078

  11. Strain accumulation across the Coast Ranges at the latitude of San Francisco, 1994-2000

    NASA Astrophysics Data System (ADS)

    Savage, J. C.; Gan, W.; Prescott, W. H.; Svarc, J. L.

    2004-03-01

    A 66-monument geodetic array spanning the Coast Ranges near San Francisco has been surveyed more than eight times by GPS between late 1993 and early 2001. The measured horizontal velocities of the monuments are well represented by uniform, right-lateral, simple shear parallel to N29°W. (The local strike of the San Andreas Fault is ˜N34°W.) The observed areal dilatation rate of 6.9 ± 10.0 nstrain yr-1 (quoted uncertainty is one standard deviation and extension is reckoned positive) is not significantly different from zero, which implies that the observed strain accumulation could be released by strike-slip faulting alone. Our results are consistent with the slip rates assigned by the [2003] to the principal faults (San Gregorio, San Andreas, Hayward-Rodgers Creek, Calaveras-Concord-Green Valley, and Greenville Faults) cutting across the GPS array. The vector sum of those slip rates is 39.8 ± 2.6 mm yr-1 N29.8°W ± 2.8°, whereas the motion across the GPS array (breadth 120 km) inferred from the uniform strain rate approximation is 38.7 ± 1.2 mm yr-1 N29.0°W ± 0.9° right-lateral shear and 0.4 ± 0.9 mm yr-1 N61°E ± 0.9° extension. We interpret the near coincidence of these rates and the absence of significant accumulation of areal dilatation to imply that right-lateral slip on the principal faults can release the accumulating strain; major strain release on reverse faults subparallel to the San Andreas Fault within the Coast Ranges is not required.

  12. Strain accumulation across the Coast Ranges at the latitude of San Francisco, 1994-2000

    USGS Publications Warehouse

    Savage, J.C.; Gan, Weijun; Prescott, W.H.; Svarc, J.L.

    2004-01-01

    A 66-monument geodetic array spanning the Coast Ranges near San Francisco has been surveyed more than eight times by GIPS between late 1993 and early 2001. The measured horizontal velocities of the monuments are well represented by uniform, right-lateral, simple shear parallel to N29??W. (The local strike of the San Andreas Fault is ???N34??W. The observed areal dilatation rate of 6.9 ?? 10.0 nstrain yr-1 (quoted uncertainty is one standard deviation and extension is reckoned positive) is not significantly different from zero, which implies that the observed strain accumulation could be released by strike-slip faulting alone. Our results are consistent with the slip rates assigned by the Working Group on California Earthquake Probabilities [2003] to the principal faults (San Gregorio, San Andreas, Hayward-Rodgers Creek, Calaveras-Concord-Green Valley, and Greenville Faults) cutting across the GPS array. The vector sum of those slip rates is 39.8 ?? 2.6 mm yr-1 N29.8??W ?? 2.8??, whereas the motion across the GPS array (breadth 120 km) inferred from the uniform strain rate approximation is 38.7 ?? 1.2 mm yr-1 N29.0?? ?? 0.9?? right-lateral shear and 0.4 ?? 0.9 mm yr-1 N61??E ?? 0.9?? extension. We interpret the near coincidence of these rates and the absence of significant accumulation of areal dilatation to imply that right-lateral slip on the principal faults can release the accumulating strain; major strain release on reverse faults subparallel to the San Andreas Fault within the Coast Ranges is not required. Copyright 2004 by the American Geophysical union.

  13. Strain accumulation in southern California, 1973-1980.

    USGS Publications Warehouse

    Savage, J.C.; Prescott, W.H.; Lisowski, M.; King, N.E.

    1981-01-01

    Frequent surveys of seven trilateration networks in southern California over the interval 1973-1980 suggest that a regional increment in strain may have occurred in 1978-1979. Prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north-south compression. This secular trend was interrupted sometime in 1978-1979 by an increment in both north-south and east-west extension in five of the seven networks. The onset of this change appears to have occurred first in the networks farthest south. The changes occurred without any unusual seismicity within the networks, but the overall seismicity in southern California was unusually low prior to and has been unusually high since the occurrence. The average principal strain rates for the seven networks in the 1973-1980 interval are 0.17 mu strain/yr north- south contraction and 0.08 mu strain/yr east-west extension. Although the observed increment in strain could be related to unidentified systematic error in the measuring system, a careful review of the measurements and comparisons with three other measuring systems reveal no appreciable cumulative systematic error. -Authors

  14. Complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones

    NASA Astrophysics Data System (ADS)

    Coward, M. P.; Potts, G. J.

    Many of the complex strain patterns seen in shear zones and thrust zones, such as variable fabric orientations, refolded folds and fabrics, together with folds with hinges almost parallel to the main transport direction, can be explained in terms of differential movement within the shear zones. These strains are developed at the frontal and lateral tips of the zones as they propagate. Examples are taken from the Moine thrust zone of Scotland which show variations in strains particularly at the lateral tips. The form of differential movement described here may lead to complex strain paths and non-plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts.

  15. An octahedral shear strain-based measure of SNR for 3D MR elastography

    NASA Astrophysics Data System (ADS)

    McGarry, M. D. J.; Van Houten, E. E. W.; Perriñez, P. R.; Pattison, A. J.; Weaver, J. B.; Paulsen, K. D.

    2011-07-01

    A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, γ, is directly related to the shear modulus, μ, through the definition of shear stress, τ = μγ. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and the human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects.

  16. A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.

    PubMed

    Kang, Suk Hoon; Kim, Tae Kyu; Jang, Jinsung; Oh, Kyu Hwan

    2015-06-01

    In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.

  17. Cold work hardening of Al from shear deformation up to large strains

    SciTech Connect

    Les, P.; Zehetbauer, M.; Kopacz, I.; Rauch, E.F.

    1999-08-06

    Several deformation modes have been applied so far which exhibited stage IV and stage V hardening in large strain cold working. However, some deformation modes especially if applied to single crystals failed (1) because of limited deformation (tensile test and compression), (2) inhomogeneous deformation (torsion), (3) iterative deformation (wire drawing, rolling) allowing for recovery processes in between small deformation steps. Moreover, except for torsion test, none of the deformation modes is capable of measuring the strain rate sensitivity up to large strains at low deformation temperatures. Thus it was the aim of the present work to deform single and polycrystalline samples of Al 99.99% in a simple shear test which has been shown to achieve also the late stages of deformation. Moreover, it should make possible strain rate sensitivity measurements in parallel to the shear stress-strain characteristics. For single crystals at room temperature the shear test seems to be the only method which can provide such data.

  18. In vivo vascular wall shear rate and circumferential strain of renal disease patients.

    PubMed

    Park, Dae Woo; Kruger, Grant H; Rubin, Jonathan M; Hamilton, James; Gottschalk, Paul; Dodde, Robert E; Shih, Albert J; Weitzel, William F

    2013-02-01

    This study measures the vascular wall shear rate at the vessel edge using decorrelation based ultrasound speckle tracking. Results for nine healthy and eight renal disease subjects are presented. Additionally, the vascular wall shear rate and circumferential strain during physiologic pressure, pressure equalization and hyperemia are compared for five healthy and three renal disease subjects. The mean and maximum wall shear rates were measured during the cardiac cycle at the top and bottom wall edges. The healthy subjects had significantly higher mean and maximum vascular wall shear rate than the renal disease subjects. The key findings of this research were that the mean vascular wall shear rates and circumferential strain changes between physiologic pressure and hyperemia that was significantly different between healthy and renal disease subjects.

  19. Controlled High-Rate-Strain Shear Bands in Inert and Reactant Porous Materials

    NASA Astrophysics Data System (ADS)

    Nesterenko, Vitali

    1997-07-01

    Shear localization was considered as one of the main reasons for initiation of chemical reaction in energetic materials under dynamic loading (Dremin and Breusov 1968, Winter and Field 1975, Frey 1981, Kipp 1985, Iyer, Bennet et al., 1994) and for particles bonding during shock compaction (Nesterenko 1985). However despite of wide spread recognition of the importance of rapid shear flow the shear bands in porous heterogeneous materials did not become an object of research. The primary reason for this was a lack of appropriate experimental method. The "Thick-Walled Cylinder" method, which allows to reproduce shear bands in controlled conditions, was initially proposed by Nesterenko et al., 1989 for solid inert materials and then modified by Nesterenko, Meyers et al., 1994 to fit porous inert and energetic materials. The method allows to reproduce the array of shear bands with shear strains 10 - 100 and strain rate 107 s-1. Experimental results will be presented for inert materials (granular, fractured ceramics) and for reactant porous mixtures (Nb-Si, Ti-Si, Ti-C). Mechanisms of material deformation and shear induced chemical reactions inside shear localization zone as well as conditions for the initiation of the chemical reaction in the bulk of energetic material by array of shear bands will be considered.

  20. Shear-strain-induced chemical reactivity of layered molecular crystals

    SciTech Connect

    M. M. Kuklja; Sergey N. Rashkeev

    2007-04-01

    A density-functional-theory study of shear-related dissociation of two molecular crystals, diamino-dinitroethylene (FOX-7) and triamino-trinitrobenzine (TATB), is presented. A detailed explanation is proposed for the fact that FOX-7 is more sensitive than TATB while their sensitivities to initiation of chemistry have been expected to be comparable. We suggest that shear plays a crucial role in dissociation of molecules in organic energetic crystals and may be imperative in providing specific recommendations on ways for materials design.

  1. Strain localisation and thermal evolution of a thick ultramylonitic shear zone

    NASA Astrophysics Data System (ADS)

    Finch, M.; Hasalova, P.; Weinberg, R. F.

    2013-12-01

    Ultramylonites are the ultimate result of mylonitisation in a ductile shear zone. They accommodate high amounts of strain because they are the weakest rock in the shear zone and usually form thin bands within rocks of lower strain (mylonites and protomylonites). Thick ultramylonites are rare; where they are reported in the literature they are up to a few hundred metres thick and indicate inefficient localisation processes. This work describes an ultramylonitic shear zone within the Sierras Pampeanas of Argentina: the El Pichao shear zone. The shear zone is part of the 470 Ma Sierra de Quilmes, a metamorphic complex of the Famatinian orogeny. The El Pichao shear zone is >3.5-km thick and contains a 1-km core of continuous ultramylonite. Globally, shear zones of similar width are rare and where reported are related to major orogenic fronts. Shear zone width is determined by plate velocity and rock strength, such that greater widths occur at high velocities and lower rock strengths. Shear zones widen when the degree of strain localisation decreases which can be caused by weakening of the host rock, hardening of the shear zone, or a decrease in the yield stress of the rock due to an increase in temperature. Different mechanisms lead to each of these processes and their determination is difficult in studies of shear zones. El Pichao shear zone overprints amphibolite faces Grt-schists in the footwall, granites in the ultramylonitic shear zone core, and migmatites in the hanging wall. Syn-kinematic anatexis in the migmatitic hanging wall indicates that the migmatites should have been weaker during shearing than the crystallised granite which formed the protolith to the ultramylonitic core. Additionally, the migmatites are very heterogenous with mica-rich melanosomes and syn-kinematic Qtz-Fsp leucosomes, making them the ideal site for strain localisation and strain partitioning between weaker and stronger phases. However, strain localised to the granite of the

  2. Strain accumulation and rotation in western Nevada, 1993-2000

    USGS Publications Warehouse

    Svarc, J.L.; Savage, J.C.; Prescott, W.H.; Ramelli, A.R.

    2002-01-01

    The positions of 44 GPS monuments in an array extending from the Sierra Nevada at the latitude of Reno to near Austin, Nevada, have been measured several times in the 1993-2000 interval. The western half of the array spans the Walker Lane belt, whereas the eastern half spans the central Nevada seismic zone (CNSZ). The principal strain rates in the Walker Lane belt are 29.6 ?? 5.3 nstrain yr-1 N88.4??E ?? 5.4?? and -12.8 ?? 6.0 nanostrain yr-1 N01.6??W ?? 5.4??, extension reckoned positive, and the clockwise (as seen from above the Earth) rotation rate about a vertical axis is 13.6 ?? 4.0 nrad yr-1. The quoted uncertainties are standard deviations. The motion in the Walker Lane belt can then be represented by a zone striking N35??W subject to 16.8 ?? 4.9 nstrain yr-1 extension perpendicular to it and 19.5 ?? 4.0 nstrain yr-1 right-lateral, simple shear across it. The N35??W strike of the zone is the same as the direction of the local tangent to the small circle drawn about the Pacific-North America pole of rotation. The principal strain rates for the CNSZ are 46.2 ?? 11.0 nstrain yr-1 N49.9??W ?? 6.0?? and -13.6 ?? 6.1 nstrain yr-1 N40.1??E ?? 6.0??, and the clockwise rotation rate about a vertical axis is 20.3 ?? 6.3 nrad yr-1. The motion across the CNSZ can then be represented by a zone striking N12??E subject to 32.6 ?? 11.0 nstrain yr-1 extension perpendicular to it and 25.1 ?? 6.3 nstrain yr-1 right-lateral, simple shear across it. The N12??E strike of the zone is similar to the strikes of the faults (Rainbow Mountain, Fairview Peak, and Dixie Valley) within it.

  3. Strain pattern and deformational history in the eastern part of the Cauvery shear zone, southern India

    NASA Astrophysics Data System (ADS)

    Chetty, T. R. K.; Rao, Y. J. Bhaskar

    2006-10-01

    Regional structural mapping, guided by remote sensing interpretation, in the eastern part of the Cauvery shear zone (CSZ), southern Granulite Terrain, reveals a structural framework of two major boundary shear zones interlinked by a set of sigmoidal shear belts. The strain pattern and deformational history are manifest in terms of two major episodes; D1 and D2. While D1 structures are well preserved in low strain areas, the D2 fabrics are well reflected in high strain belts enveloping the low strain domains. Our multiscale structural observations can be modelled in terms of a plan view duplex showing a cross sectional flower structure related to regional transpression resulting from late Neoproterozoic collisional processes in the eastern Gondwana.

  4. Platelet Activation Due to Hemodynamic Shear Stresses: Damage Accumulation Model and Comparison to In Vitro Measurements

    PubMed Central

    Nobili, Matteo; Sheriff, Jawaad; Morbiducci, Umberto; Redaelli, Alberto; Bluestein, Danny

    2009-01-01

    The need to optimize the thrombogenic performance of blood recirculating cardiovascular devices, e.g., prosthetic heart valves (PHV) and ventricular assist devices (VAD), is accentuated by the fact that most of them require lifelong anticoagulation therapy that does not eliminate the risk of thromboembolic complications. The formation of thromboemboli in the flow field of these devices is potentiated by contact with foreign surfaces and regional flow phenomena that stimulate blood clotting, especially platelets. With the lack of appropriate methodology, device manufacturers do not specifically optimize for thrombogenic performance. Such optimization can be facilitated by formulating a robust numerical methodology with predictive capabilities of flow-induced platelet activation. In this study, a phenomenological model for platelet cumulative damage, identified by means of genetic algorithms (GAs), was correlated with in vitro experiments conducted in a Hemodynamic Shearing Device (HSD). Platelets were uniformly exposed to flow shear representing the lower end of the stress levels encountered in devices, and platelet activity state (PAS) was measured in response to six dynamic shear stress waveforms representing repeated passages through a device, and correlated to the predictions of the damage accumulation model. Experimental results demonstrated an increase in PAS with a decrease in “relaxation” time between pulses. The model predictions were in very good agreement with the experimental results. PMID:18204318

  5. Deformation and Shear Band Development in an Ultrahigh Carbon Steel During High Strain Rate Deformation

    SciTech Connect

    Lesuer, D R; Syn, C K; Sherby, O D

    2004-07-06

    The mechanical response of a pearlitic UHCS-1.3C steel deformed at approximately 4000 s{sup -1} to large strains ({var_epsilon} = -0.9) has been studied. Failure, at both the macroscopic and the microscopic levels has been evaluated, and the ability of the material to absorb energy in compression has been examined. Failure occurred by the development of a shear band. However before failure, extensive buckling of the carbide plates was observed and the UHCS-1.3C material exhibited significant potential for compressive ductility and energy absorption due to the distributed buckling of these plates. Strain localization during adiabatic shear band development resulted in the formation of austenite. Subsequent cooling produced a divorced-eutectoid transformation with associated deformation, which resulted in a microstructure consisting of 50 to 100 nm sized grains. The stress-strain behavior within the shear band has also been determined. The results are used to critically evaluate the maximum shear stress criterion of shear band development. New criteria for the development of shear bands are developed based on a strain energy concept.

  6. Room temperature shear properties of the strain isolator pad for the shuttle thermal protection system

    NASA Technical Reports Server (NTRS)

    Sawyer, J. W.; Waters, W. A., Jr.

    1981-01-01

    Tests were conducted at room temperature to determine the shear properties of the strain isolator pad (SIP) material used in the thermal protection system of the space shuttle. Tests were conducted on both the .23 cm and .41 cm thick SIP material in the virgin state and after fifty fully reversed shear cycles. The shear stress displacement relationships are highly nonlinear, exhibit large hysteresis effects, are dependent on material orientation, and have a large low modulus region near the zero stress level where small changes in stress can result in large displacements. The values at the higher stress levels generally increase with normal and shear force load conditioning. Normal forces applied during the shear tests reduces the low modulus region for the material. Shear test techniques which restrict the normal movement of the material give erroneous stress displacement results. However, small normal forces do not significantly effect the shear modulus for a given shear stress. Poisson's ratio values for the material are within the range of values for many common materials. The values are not constant but vary as a function of the stress level and the previous stress history of the material. Ultimate shear strengths of the .23 cm thick SIP are significantly higher than those obtained for the .41 cm thick SIP.

  7. Microstructural evolution in adiabatic shear bands of copper at high strain rates: Electron backscatter diffraction characterization

    SciTech Connect

    Tang Lin; Chen Zhiyong; Zhan Congkun; Yang Xuyue; Liu Chuming; Cai Hongnian

    2012-02-15

    The microstructural evolution of adiabatic shear bands in annealed copper with different large strains at high strain rates has been investigated by electron backscatter diffraction. The results show that mechanical twinning can occur with minimal contribution to shear localization under dynamic loading. Elongated ultrafine grains with widths of 100-300 nm are observed during the evolution of the adiabatic shear bands. A rotational dynamic recrystallization mechanism is proposed to explain the formation of the elongated ultrafine grains. - Highlights: Black-Right-Pointing-Pointer The microstructural evolution of ASB is studied by electron backscatter diffraction. Black-Right-Pointing-Pointer Twinning can occur in ASB while the contribution to shear localization is slight. Black-Right-Pointing-Pointer Elongated ultrafine grains are observed during the evolution process of ASB. Black-Right-Pointing-Pointer A possible mechanism is proposed to explain the microstructure evolution of ASB.

  8. The plane strain shear fracture of the advanced high strength steels

    SciTech Connect

    Sun, Li

    2013-12-16

    The “shear 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 predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear 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 operate 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 “shear 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 “shear fracture” in the component.

  9. Anisotropic Power Law Strain Correlations in Sheared Amorphous 2D Solids

    NASA Astrophysics Data System (ADS)

    Maloney, C. E.; Robbins, M. O.

    2009-06-01

    The local deformation of steadily sheared two-dimensional Lennard-Jones glasses is studied via computer simulations at zero temperature. In the quasistatic limit, spatial correlations in the incremental strain field are highly anisotropic. The data show power law behavior with a strong angular dependence of the scaling exponent, and the strongest correlations along the directions of maximal shear stress. These results support the notion that the jamming transition at the onset of flow is critical, but suggest unusual critical behavior. The predicted behavior is testable through experiments on sheared amorphous materials such as bubble rafts, foams, emulsions, granular packings, and other systems where particle displacements can be tracked.

  10. Anisotropic Power Law Strain Correlations in Sheared Amorphous 2D Solids

    SciTech Connect

    Maloney, C. E.; Robbins, M. O.

    2009-06-05

    The local deformation of steadily sheared two-dimensional Lennard-Jones glasses is studied via computer simulations at zero temperature. In the quasistatic limit, spatial correlations in the incremental strain field are highly anisotropic. The data show power law behavior with a strong angular dependence of the scaling exponent, and the strongest correlations along the directions of maximal shear stress. These results support the notion that the jamming transition at the onset of flow is critical, but suggest unusual critical behavior. The predicted behavior is testable through experiments on sheared amorphous materials such as bubble rafts, foams, emulsions, granular packings, and other systems where particle displacements can be tracked.

  11. Time-evolution and strain distribution of a major shear zone (SASZ, Brittany, France)

    NASA Astrophysics Data System (ADS)

    Augier, Romain; Raimbourg, Hugues; Bellanger, Mathieu; Turrillot, Paul; Monié, Patrick

    2014-05-01

    Mylonite-bearing crustal shear zones are exhumed extensions at depth of (potentially seismogenic) brittle faults at shallow structural level. By concentrating deformation, shear zones play a major role in the rheology and mechanical behavior of the continental crust. Analysis of shear zone geometry and microstructures is a useful tool to decipher deformation kinematics, though finite strain estimation is still relatively qualitative. Timing of the deformation has also been the focus of numerous studies using the complete spectrum of geochronometers. However, only rare examples provide geochronological data that can be unambiguously linked with deformation. Thus, time-scales over which major mylonite zones develop and remain active under ductile conditions as well as their strain rates often remain poorly documented. Several sections across the South Armorican Shear Zone (SASZ), a crustal-scale, several km-thick dextral shear zone were investigated by structural, petrological and Ar/Ar radiochronological methods. Finite strain profiles on these sections showed a strong deformation partitioning towards the ultramylonite core of the SASZ, with a decrease, of both the C'/S mean angle (from ca. 45° to less than 5°) and the Quartz grain-size (from ca. 150 to 5 µm). In parallel, conventional and in-situ Ar/Ar datings on the fabric-forming white micas were performed on compositionally complex white-micas. Inherited magmatic muscovites carried by the foliation and newly-formed, syn-tectonic substituted phengites located along the shear bands yielded 2 age groups for the less deformed samples. Along the shear zone cross-section, the difference between these two ages evolves from 10-15 Ma in weakly deformed domains to zero toward the SASZ core. In addition, the very fine-grained syn-tectonic phengites yielded the same ca. 300-298 Ma age irrespectively of their distance to the core of the shear zone, even in slightly deformed rocks distant by several km. These results

  12. Strain-rate dependent shear viscosity of the Gaussian core model fluid.

    PubMed

    Ahmed, Alauddin; Mausbach, Peter; Sadus, Richard J

    2009-12-14

    Nonequilibrium molecular dynamics simulations are reported for the shear viscosity of the Gaussian core model (GCM) fluid over a wide range of densities, temperatures and strain rates. A transition from Newtonian and non-Newtonian behavior is observed in all cases for sufficiently high strain rates. On the high-density side of the solid region where re-entrant melting occurs, the shear viscosity decreases significantly when the density is increased at constant temperature and Newtonian behavior persists until very high strain rates. This behavior, which is attributed to particle overlap, is in contrast to the monotonic increase in shear viscosity with density observed for the Lennard-Jones potential. Contrary to the behavior of normal fluids, the viscosity is observed to increase with increasing temperatures at high densities. This reflects a peculiarity of the GCM, namely the approach to the "infinite-density ideal-gas limit." The behavior is also consistent with viscosity measurements of cationic surfactant solutions. In contrast to other potentials, the shear viscosities for the Gaussian core potential at low to moderate strain rates are obtained with modest statistical uncertainties. Zero shear viscosities extrapolated from the nonequilibrium simulations are in good agreement with equilibrium Green-Kubo calculations.

  13. Interseismic Strain Accumulation Across Metropolitan Los Angeles: Puente Hills Thrust

    NASA Astrophysics Data System (ADS)

    Argus, D.; Liu, Z.; Heflin, M. B.; Moore, A. W.; Owen, S. E.; Lundgren, P.; Drake, V. G.; Rodriguez, I. I.

    2012-12-01

    Twelve years of observation of the Southern California Integrated GPS Network (SCIGN) are tightly constraining the distribution of shortening across metropolitan Los Angeles, providing information on strain accumulation across blind thrust faults. Synthetic Aperture Radar Interferometry (InSAR) and water well records are allowing the effects of water and oil management to be distinguished. The Mojave segment of the San Andreas fault is at a 25° angle to Pacific-North America plate motion. GPS shows that NNE-SSW shortening due to this big restraining bend is fastest not immediately south of the San Andreas fault across the San Gabriel mountains, but rather 50 km south of the fault in northern metropolitan Los Angeles. The GPS results we quote next are for a NNE profile through downtown Los Angeles. Just 2 mm/yr of shortening is being taken up across the San Gabriel mountains, 40 km wide (0.05 micro strain/yr); 4 mm/yr of shortening is being taken up between the Sierra Madre fault, at the southern front of the San Gabriel mountains, and South Central Los Angeles, also 40 km wide (0.10 micro strain/yr). We find shortening to be more evenly distributed across metropolitan Los Angeles than we found before [Argus et al. 2005], though within the 95% confidence limits. An elastic models of interseismic strain accumulation is fit to the GPS observations using the Back Slip model of Savage [1983]. Rheology differences between crystalline basement and sedimentary basin rocks are incorporated using the EDGRN/EDCMP algorithm of Wang et al. [2003]. We attempt to place the Back Slip model into the context of the Elastic Subducting Plate Model of Kanda and Simons [2010]. We find, along the NNE profile through downtown, that: (1) The deep Sierra Madre Thrust cannot be slipping faster than 2 mm/yr, and (2) The Puente Hills Thrust and nearby thrust faults (such as the upper Elysian Park Thrust) are slipping at 9 ±2 mm/yr beneath a locking depth of 12 ±5 km (95% confidence limits

  14. Interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles

    NASA Astrophysics Data System (ADS)

    Argus, Donald F.; Heflin, Michael B.; Peltzer, Gilles; Crampé, FréDeric; Webb, Frank H.

    2005-04-01

    We use global positioning system (GPS) geodesy and synthetic aperture radar (SAR) interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles. We establish a relationship between horizontal and vertical seasonal oscillations of the Santa Ana aquifer, use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management, and estimate horizontal interseismic velocities corrected for anthropogenic effects. Vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr-1 in the Santa Ana and San Gabriel aquifers and faster than 5 mm yr-1 in the Chino aquifer and in many oil fields. Inferred horizontal anthropogenic velocities are faster than 1 mm yr-1 at 18 of 46 GPS sites. Northern metropolitan Los Angeles is contracting, with the 25 km south of the San Gabriel Mountains shortening at 4.5 ± 1 mm yr-1 (95% confidence limits). The thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 ± 2 mm yr-1 beneath and north of a position 6 ± 2 km deep and 8 ± 8 km north of downtown Los Angeles. The model fault is near the Los Angeles segment of the Puente Hills thrust but south of the Sante Fe Springs segment of the thrust. Disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory; models with different stiffnesses of sedimentary basin and crystalline basement must be investigated.

  15. Interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles

    NASA Astrophysics Data System (ADS)

    Argus, D. F.; Heflin, M. B.; Peltzer, G.; Crampe, F.; Webb, F. H.

    2005-05-01

    We use global positioning system (GPS) geodesy and synthetic aperture radar (SAR) interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles. We establish a relationship between horizontal and vertical seasonal oscillations of the Santa Ana aquifer, use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management, and estimate horizontal interseismic velocities corrected for anthropogenic effects. Vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm/yr in the Santa Ana and San Gabriel aquifers and faster than 5 mm/yr in the Chino aquifer and in many oil fields. Inferred horizontal anthropogenic velocities are faster than 1 mm/yr at 18 of 46 GPS sites. Northern metropolitan Los Angeles is contracting, with the 25 km south of the San Gabriel mountains shortening at 4.5 ±1 mm/yr (95% confidence limits). The thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 ±2 mm/yr beneath and north of a position 6 ±2 km deep and 8 ±8 km north of downtown Los Angeles. The model fault is near the Los Angeles segment of the Puente Hills thrust but south of the Sante Fe Springs segment of the thrust. Disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory; models with different stiffnesses of sedimentary basin and crystalline basement must be investigated.

  16. Endothelial cell alignment as a result of anisotropic strain and flow induced shear stress combinations

    PubMed Central

    Sinha, Ravi; Le Gac, Séverine; Verdonschot, Nico; van den Berg, Albert; Koopman, Bart; Rouwkema, Jeroen

    2016-01-01

    Endothelial cells (ECs) are continuously exposed in vivo to cyclic strain and shear stress from pulsatile blood flow. When these stimuli are applied in vitro, ECs adopt an appearance resembling their in vivo state, most apparent in their alignment (perpendicular to uniaxial strain and along the flow). Uniaxial strain and flow perpendicular to the strain, used in most in vitro studies, only represent the in vivo conditions in straight parts of vessels. The conditions present over large fractions of the vasculature can be better represented by anisotropic biaxial strains at various orientations to flow. To emulate these biological complexities in vitro, we have developed a medium-throughput device to screen for the effects on cells of variously oriented anisotropic biaxial strains and flow combinations. Upon the application of only strains for 24 h, ECs (HUVECs) aligned perpendicular to the maximum principal strain and the alignment was stronger for a higher maximum:minimum principal strain ratio. A 0.55 Pa shear stress, when applied alone or with strain for 24 h, caused cells to align along the flow. Studying EC response to such combined physiological mechanical stimuli was not possible with existing platforms and to our best knowledge, has not been reported before. PMID:27404382

  17. Determining Sliding Velocity and Shear-Strain Magnitude From Basal Sediments of Past Ice Sheets

    NASA Astrophysics Data System (ADS)

    Iverson, N. R.; Hooyer, T. S.; Thomason, J. F.

    2004-12-01

    Ice sheets slide over their basal sediments and commonly deform them. Despite meticulous description of such sediments, they have not been used to estimate rates or magnitudes of basal motion. Thus, although a common assertion is that modeling of past ice sheets can benefit from studies of basal sediments, their actual utility in modeling studies has been minimal. We have developed methods for estimating sliding velocity and till shear-strain magnitude from basal sediments of past ice sheets. The first method involves balancing shear traction on clasts that have plowed through the bed surface with resistance to plowing provided by the bed. The shear traction on clasts is provided by the sliding theory of Lliboutry, and plowing resistance is estimated using a geotechnical theory of cone penetration. The result is an expression for sliding speed of a past ice sheet that depends only on the size distribution of clasts that plowed and the thermomechanical properties of ice and clasts. This method was applied to sizes of clasts that plowed through outwash near Peoria, Illinois, to estimate the sliding speed of the Illinoian ice sheet in that area: 60-170 m/a. The second method involves shearing till in laboratory experiments to study the evolution of till microstructural properties as a function of shear-strain magnitude. Microstructural anisotropy is quantified by collecting multiple intact samples (20 mm cubes) and determining the strength of fabric defined by principal directions of magnetic susceptibility. These directions depend on alignment of needle-shaped magnetite grains. Fabrics formed by directions of maximum susceptibility do not become steady until shear strains of 20-50. Therefore, laboratory calibrations of fabric strength to shear-strain magnitude allow the extent of bed deformation to be determined from susceptibility fabrics of basal till. These studies can provide quantitative inputs to ice-sheet models that have been unavailable previously.

  18. Strain Rate Sensitivity of Epoxy Resin in Tensile and Shear Loading

    NASA Technical Reports Server (NTRS)

    Gilat, Amos; Goldberg, Robert K.; Roberts, Gary D.

    2005-01-01

    The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about 5x10(exp 5), 2, and 450 to 700 /s. In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear both resins show a ductile response with maximum stress that is increasing with strain rate. In tension a ductile response is observed at low strain rate (approx. 5x10(exp 5) /s), and brittle response is observed at the medium and high strain rates (2, and 700 /s). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.

  19. Constraints on accumulated strain near the ETS zone along Cascadia

    NASA Astrophysics Data System (ADS)

    Krogstad, Randy D.; Schmidt, David A.; Weldon, Ray J.; Burgette, Reed J.

    2016-04-01

    Current national seismic hazard models for Cascadia use the zone of episodic tremor and slip (ETS) to denote the lower boundary of the seismogenic zone. Recent numerical models have suggested that an appreciable amount of long-term strain may accumulate at the depth of ETS and questions this assumption. We use uplift rates from leveling campaigns spanning approximately 50-70 yrs in Washington and Oregon to investigate the amount of potential long-term locking near the ETS zone. We evaluate the potential for deeper locking in Cascadia by exploring a range of locking parameters along the subduction zone, including the ETS zone. Of the four east-west leveling profiles studied, three show a reduction in the misfit when secondary locking near the ETS zone is included; however the reduction in misfit values is only statistically significant for one profile. This would suggest that models including a small amount of secondary locking are broadly indistinguishable from models without any secondary locking. If secondary locking is considered, the leveling data allow for locking up to ∼20% of the plate rate near the updip edge of the ETS zone. These results are consistent with, but less resolved, by GPS observations.

  20. In situ observation of shear zone microstructures and strain localization using a transparent rotary shear apparatus

    NASA Astrophysics Data System (ADS)

    Korkolis, Evangelos

    An important focus of Geophysics is why geologic faults experience multiple styles of failure, ranging from stable aseismic creep to unstable seismic slip. Previous studies suggest that microstructures within fault gouge, a granular layer of wear material, have a significant effect on macroscopic fault behavior. This thesis investigates the effects of particle angularity, particle size distribution, total displacement, slip rate, and fault wall roughness on microstructures and grain kinematics in simulated gouge assemblages using a transparent rotary shear apparatus. Gouge strength increases with particle angularity, as evidenced by rotation of force chains near the sliding interface. Variations in slip rate and fault wall roughness appear to have no effect on the macroscopic behavior of gouge. After some widening at low displacement, the width of the deforming zone is observed to scale with average particle size, eventually becoming wider for spherical particles, independent of the tested particle size distributions.

  1. Variability of polyploid strains of Candida scottii in accumulation of riboflavin in the medium.

    PubMed

    Imshenetsky, A A; Kondratieva, T F

    1977-01-01

    Polyploid strains of Candida scottii show a higher spontaneous and UV-induced variability in accumulation of riboflavin in the medium than the original haploid strain. UV irradiation affects the formation of variants and induces those which accumulate more riboflavin than any of the most productive variants resulting from spontaneous variability. In the polyploid strains the frequency of plus-variants increases. Therefore, polyploid strains of C. scottii are advantageous for selection processes. PMID:855365

  2. Observations of strain accumulation across the San Andreas fault near Palmdale, California, with a two-color geodimeter

    USGS Publications Warehouse

    Langbein, J.O.; Linker, M.F.; McGarr, A.; Slater, L.E.

    1982-01-01

    Two-color laser ranging measurements during a 15-month period over a geodetic network spanning the San Andreas fault near Palmdale, California, indicate that the crust expands and contracts aseismically in episodes as short as 2 weeks. Shear strain parallel to the fault has accumulated monotonically since November 1980, but at a variable rate. Improvements in measurement precision and temporal resolution over those of previous geodetic studies near Palmdale have resulted in the definition of a time history of crustal deformation that is much more complex than formerly realized. Copyright ?? 1982 AAAS.

  3. Stick-slip instabilities and shear strain localization in amorphous materials.

    PubMed

    Daub, Eric G; Carlson, Jean M

    2009-12-01

    We study the impact of strain localization on the stability of frictional slipping in dense amorphous materials. We model the material using shear transformation zone (STZ) theory, a continuum approximation for plastic deformation in amorphous solids. In the STZ model, the internal state is quantified by an effective disorder temperature, and the effective temperature dynamics capture the spontaneous localization of strain. We study the effect of strain localization on stick-slip instabilities by coupling the STZ model to a noninertial spring slider system. We perform a linear stability analysis to generate a phase diagram that connects the small scale physics of strain localization to the macroscopic stability of sliding. Our calculations determine the values of spring stiffness and driving velocity where steady sliding becomes unstable and we confirm our results through numerical integration. We investigate both homogeneous deformation, where no shear band forms, and localized deformation, where a narrow shear band spontaneously forms and accommodates all of the deformation. Our results show that at a given velocity, strain localization leads to unstable frictional sliding at a much larger spring stiffness compared to homogeneous deformation, and that localized deformation cannot be approximated by a homogeneous model with a narrower material. We also find that strain localization provides a physical mechanism for irregular stick-slip cycles in certain parameter ranges. Our results quantitatively connect the internal physics of deformation in amorphous materials to the larger scale frictional dynamics of stick-slip.

  4. Strain partitioning in the mid-crust of a transpressional shear zone system: Insights from the Homestake and Slide Lake shear zones, central Colorado

    NASA Astrophysics Data System (ADS)

    Lee, P. Elizabeth; Jessup, Micah J.; Shaw, Colin A.; Hicks, Gordon L.; Allen, Joseph L.

    2012-06-01

    Kinematic analysis and field mapping of the Homestake shear zone (HSZ) and Slide Lake shear zone (SLSZ) in central Colorado may provide insight into the interaction between subvertical and low-angle shear zones in the middle crust. The northeast-striking, steeply dipping HSZ comprises a ˜10-km-wide set of anastomosing ductile shear zones and pseudotachylyte-bearing faults. Approximately 4 km south of the HSZ, north-northeast-striking, shallowly dipping mylonites of the SLSZ form three 1-10-m-thick splays. Oblique stretching lineations and shear sense in both shear zones record components of dip-slip (top-up-to-the-northwest and top-down-to-the-southeast) and dextral strike-slip movement during mylonite development. Quartz and feldspar deformation mechanisms and quartz [c] axis lattice preferred orientation (LPO) patterns suggest deformation temperatures ranging from ˜280-500 °C in the HSZ to ˜280-600 °C in the SLSZ. Quartz [c] axis LPOs suggest plane strain general shear across the shear system. Based on the relative timing of fabric development, compatible kinematics and similar deformation temperatures in the SLSZ and the HSZ, we propose that both shear zones formed during strain localization and partitioning within a transpressional shear zone system that involved subvertical shuffling in the mid-crust at 1.4 Ga.

  5. Suppression of repeated adiabatic shear banding by dynamic large strain extrusion machining

    NASA Astrophysics Data System (ADS)

    Cai, S. L.; Dai, L. H.

    2014-12-01

    High speed machining (HSM) is an advanced production technology with great future potential. Chip serration or segmentation is a commonly observed phenomenon during high speed machining of metals, which is found to be ascribed to a repeated shear band formation fueled by thermo-plastic instability occurring within the primary shear zone. The occurrence of serrated chips leads to the cutting force fluctuation, decreased tool life, degradation of the surface finish and less accuracy in machine parts during high speed machining. Hence, understanding and controlling serrated chip formation in HSM are extremely important. In this work, a novel dynamic large strain extrusion machining (DLSEM) technique is developed for suppressing formation of serrated chips. The systematic DLSEM experiments of Ti-6Al-4V and Inconel 718 alloy with varying degrees of imposed extrusion constraint were carried out. It is found that there is a prominent chip morphology transition from serrated to continuous state and shear band spacing decreases with the constraint degree increasing. In order to uncover underlying mechanism of the imposed extrusion constraint suppressing repeated adiabatic shear banding in DLSEM, new theoretical models are developed where the effects of extrusion constraint, material convection due to chip flow and momentum diffusion during shear band propagation are included. The analytical expressions for the onset criterion of adiabatic shear band and shear band spacing in DLSEM are obtained. The theoretical predictions are in agreement with the experimental results.

  6. Kinematic, finite strain and vorticity analysis of the Sisters Shear Zone, Stewart Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Ring, Uwe; Bernet, Matthias; Tulloch, Andy

    2015-04-01

    The Sisters Shear Zone (SSZ) on Stewart Island, New Zealand, is a greenschist-facies extensional shear zone active prior to and possibly during the development of the Pacific-Antarctica spreading ridge at ∼76 Ma. We report quantitative kinematic and rotation data as well as apatite fission-track (AFT) ages from the SSZ. Early kinematic indicators associated with the NNE-trending stretching lineation formed under upper greenschist-facies metamorphism and show alternating top-to-the-NNW and top-to-the-SSE senses of shear. During progressive exhumation lowermost greenschist-facies and brittle-ductile kinematic indicators depict a more uniform top-to-the-SSE sense of shear in the topmost SSZ just below the detachment plane. Deformed metagranites in the SSZ allow the reconstruction of deformation and flow parameters. The mean kinematic vorticity number (Wm) ranges from 0.10 to 0.89; smaller numbers prevail in the deeper parts of the shear zone with a higher degree of simple shear deformation in the upper parts of the shear zone (deeper and upper parts relate to present geometry). High finite strain intensity correlates with low Wm and high Wm numbers near the detachment correlate with relatively weak strain intensity. Finite strain shows oblate geometries. Overall, our data indicate vertical and possibly temporal variations in deformation of the SSZ. Most AFT ages cluster around 85-75 Ma. We interpret the AFT ages to reflect the final stages of continental break-up just before and possibly during the initiation of sea-floor spreading between New Zealand and Antarctica.

  7. Effect of Strain on Microstructure Evolution of 1Cr18Ni9Ti Stainless Steel During Adiabatic Shearing

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Jiang, L. H.; Luo, S. H.; Hu, H. B.; Tang, T. G.; Zhang, Q. M.

    2016-01-01

    Dynamic shear test was conducted on the hat-shaped specimen of the thermo-mechanical-processed 1Cr18Ni9Ti stainless steel by using the split Hopkinson pressure bar at ambient temperature. The effect of the shear strain on the microstructure evolution was investigated during adiabatic shearing. The results revealed that the development of adiabatic shear localization went through three stages, including the incubation period, the development stage, and the maturity period. TEM observations showed that the grains in the shear region were elongated, and the elongated grains were gradually evolved into equiaxed nano-grains of 100 nm as shear strain increased. The rotational dynamic recrystallization kinetics calculation showed that subgrains had sufficient time to generate an equiaxed microcrystalline structure by rotation within the deformation time. Based on the observation of the evolution of dislocations and sub-grains in the adiabatic shear region, a model of the microstructure evolution was established during the adiabatic shearing.

  8. Strain-induced outgassing of three-phase magmas during simple shear

    NASA Astrophysics Data System (ADS)

    Shields, J. K.; Mader, H. M.; Pistone, M.; Caricchi, L.; Floess, D.; Putlitz, B.

    2014-09-01

    A major factor determining the explosivity of silicic eruptions is the removal of volatiles from magma through permeability-controlled outgassing. We studied the microstructural development of permeability during deformation of highly viscous magma by performing simple shear experiments on bubble (0.12-0.36 volume fraction) and crystal-bearing (0-0.42 volume fraction) silicate melts. Experiments were performed under torsion, at high temperature and pressure (723-873 K and 150-200 MPa) in a Paterson deformation apparatus at bulk shear strains between 0 and 10. The experimental setup allows for gas escape if bubble connectivity is reached on the sample periphery. Three-dimensional imaging and analysis of deformed bubbles was performed using X-ray tomography. The development of localized deformation in all samples, enhanced by crystal content, leads to brittle fracture at bulk strains > 2 and sample-wide fracturing in samples deformed to strains >5. A decrease in both bubble fraction and dissolved volatile content with increasing strain, along with strain-hardening rheological behavior, suggests significant shear-induced outgassing through the fracture networks, applicable to shallow conduit degassing in magmas containing crystal fractions of 0-0.42. This study contributes to our understanding of highly viscous magma outgassing and processes governing the effusive-explosive transition.

  9. Beyond linear elasticity: jammed solids at finite shear strain and rate.

    PubMed

    Boschan, Julia; Vågberg, Daniel; Somfai, Ellák; Tighe, Brian P

    2016-06-28

    The shear response of soft solids can be modeled with linear elasticity, provided the forcing is slow and weak. Both of these approximations must break down when the material loses rigidity, such as in foams and emulsions at their (un)jamming point - suggesting that the window of linear elastic response near jamming is exceedingly narrow. Yet precisely when and how this breakdown occurs remains unclear. To answer these questions, we perform computer simulations of stress relaxation and shear start-up tests in athermal soft sphere packings, the canonical model for jamming. By systematically varying the strain amplitude, strain rate, distance to jamming, and system size, we identify characteristic strain and time scales that quantify how and when the window of linear elasticity closes, and relate these scales to changes in the microscopic contact network. PMID:27212139

  10. [Dynamic accumulation regulation of curcumin, demethoxycurcumin and bisdemethoxyeurcumin in three strains of curcuma longae rhizome].

    PubMed

    Li, Qing-Miao; Yang, Wen-Yu; Tang, Xue-Mei; Zhang, Mei; Zhou, Xian-Jian; Shu, Guang-Ming; Zhao, Jun-Ning; Fang, Qing-Mao

    2014-06-01

    The paper is aimed to study the dynamic accumulation regulation of curcumin (Cur), demethoxycurcumin (DMC) and bisdemethoxyeurcumin (BDMC) in three strains of Curcuma longa, and provide scientific references for formalized cultivation, timely harvesting, quality control and breeding cultivation of C. longa. The accumulation regulation of the three curcumin derivatives was basically the same in rhizome of three strains. The relative contents decreased along with plant development growing, while the accumulation per hectare increased with plant development growing. The accumulation of curcuminoids per hectare could be taken as the assessment standard for the best harvest time of C. longa. A3 was the best strain in terms of Cur and BDMC content.

  11. Shear localization in high-strain-rate deformation of granular alumina

    SciTech Connect

    Nesterenko, V.F.; Meyers, M.A.; Chen, H.C.

    1996-05-01

    Dynamic deformation of densified granular alumina of two different particle sizes was investigated by the radial symmetric collapse of a thick-walled cylinder. The densified granular alumina was used to model the flow in ballistic impact and penetration of fragmented ceramic armor. Shear localization was a well developed deformation mode at an overall radial strain of {approximately}0.2--0.4 and strain rate of 10{sup 4}{sup {minus}1}. The following qualitative features of shear bands were established: (1) Shear bands have clear boundaries and their thickness does not depend on the initial particle size and has a typical value {approximately}10 {micro}m. (2) The structure of the shear bands was dependent on initial particle size, suggesting differences in the mechanisms of flow. For the {approximately}4 {micro}m alumina, comminution (break-up) and softening of particles were observed. For the {approximately}0.4 {micro}m particles, a peculiar structure consisting of a central crack with two lateral cracks was formed. (3) Distributions of shear bands and displacement magnitudes were dependent on initial particle size. The observed differences in powder behavior are associated with different mechanisms of powder repacking. For large particles ({approximately}4 {micro}m), additional hardening resulting from microfracture and subsequent repacking of different size particles in the powder takes place. The small-sized ({approximately}0.4 {micro}m) ceramic does not go through the particle fracturing stage and the hardening is due to ``classical`` repacking.

  12. Winged inclusions: Pinch-and-swell objects during high-strain simple shear

    NASA Astrophysics Data System (ADS)

    Grasemann, Bernhard; Dabrowski, Marcin

    2015-01-01

    In this study, we compare natural examples of isolated pinch-and-swell objects, which have been deformed in simple shear, with results of high-strain numerical models. Such structures, which have geometrical similarities with δ-clast systems and rolling structures, have been called winged inclusions. We suggest a new mechanical explanation for the evolution of winged inclusions, which form when pinch-and-swell shaped objects consisting of a core and pre-existing wings rotate out of the shear plane. The viscosity ratio, the stress exponent, and the shape of the winged inclusion have a significant influence on the rotation rate. The rotational behaviour of winged inclusions differs significantly from the rotational behaviour of simple elliptical objects with comparable aspect ratios. During the early stages of formation, winged inclusions may resemble mirror images of sigmoids and misinterpretations may lead to a wrong determination of the shear sense. During progressive shear to large strains, the structures may be approximately described as consisting of a pulsating rotating core and thinning wings that rotate with different rates. During rotation of the structure, the core of the winged inclusions records an overall decrease of the aspect ratio influencing the rotation rate of the inclusion. The wings are subject to ptygmatic folding, when they rotate through the field of instantaneous shortening and may unfold again in the field of instantaneous stretching. During ongoing shearing, the wings on both sides of the core rotate with the core, may change their positions and finally unfold after rotation about 180° resulting again in a pinch-and-swell shaped object. Therefore, winged inclusions record ambiguous information about the finite strain. Rotating winged inclusions create a significant flow perturbation in the matrix resulting in nucleation of folds, refolding and propagation of shear zones. Rootless intrafolial folds with opposing closures have strong

  13. Strain localization in shear zones during exhumation: a graphical approach to facies interpretation

    NASA Astrophysics Data System (ADS)

    Cardello, Giovanni Luca; Augier, Romain; Laurent, Valentin; Roche, Vincent; Jolivet, Laurent

    2015-04-01

    Strain localization is a fundamental process determining plate tectonics. It is expressed in the ductile field by shear zones where strain concentrates. Despite their worldwide distribution in most metamorphic units, their detailed characterization and processes comprehension are far to be fully addressed. In this work, a graphic approach to tectono-metamorphic facies identification is applied to the Delfini Shear Zone in Syros (Cyclades, Greece), which is mostly characterized by metabasites displaying different degree of retrogression from fresh eclogite to prasinite. Several exhumation mechanisms brought them from the depths of the subduction zone to the surface, from syn-orogenic exhumation to post-orogenic backarc extension. Boudinage, grain-size reduction and metamorphic reactions determinate strain localization across well-deformed volumes of rocks organized in a hierarchic frame of smaller individual shear zones (10-25 meters thick). The most representative of them can be subdivided in 5 tectono-metamorphic (Tm) facies, TmA to E. TmA records HP witnesses and older folding stages preserved within large boudins as large as 1-2 m across. TmB is characterized by much smaller and progressively more asymmetric boudins and sigmoids. TmC is defined by well-transposed sub- to plane-parallel blueschist textures crossed by chlorite-shear bands bounding the newly formed boudins. When strain increases (facies TmD-E), the texture is progressively retrograded to LP-HT greenschist-facies conditions. Those observations allowed us to establish a sequence of stages of strain localization. The first stage (1) is determined by quite symmetric folding and boudinage. In a second stage (2), grain-size reduction is associated with dense shear bands formation along previously formed glaucophane and quartz-rich veins. With progressively more localized strain, mode-I veins may arrange as tension gashes that gradually evolve to blueschist shear bands. This process determinates the

  14. Shear strain mediated magneto-electric effects in composites of piezoelectric lanthanum gallium silicate or tantalate and ferromagnetic alloys

    NASA Astrophysics Data System (ADS)

    Sreenivasulu, G.; Qu, P.; Piskulich, E.; Petrov, V. M.; Fetisov, Y. K.; Nosov, A. P.; Qu, Hongwei; Srinivasan, G.

    2014-07-01

    Shear strain mediated magneto-electric (ME) coupling is studied in composites of piezoelectric Y-cut lanthanum gallium silicate (LGS) or tantalate (LGT) and ferromagnetic Fe-Co-V alloys. It is shown that extensional strain does not result in ME effects in these layered composites. Under shear strain generated by an ac and dc bias magnetic fields along the length and width of the sample, respectively, strong ME coupling is measured at low-frequencies and at mechanical resonance. A model is discussed for the ME effects. These composites of Y-cut piezoelectrics and ferromagnetic alloys are of importance for shear strain based magnetic field sensors.

  15. Shear strain mediated magneto-electric effects in composites of piezoelectric lanthanum gallium silicate or tantalate and ferromagnetic alloys

    SciTech Connect

    Sreenivasulu, G.; Piskulich, E.; Srinivasan, G.; Qu, P.; Qu, Hongwei; Petrov, V. M.; Fetisov, Y. K.; Nosov, A. P.

    2014-07-21

    Shear strain mediated magneto-electric (ME) coupling is studied in composites of piezoelectric Y-cut lanthanum gallium silicate (LGS) or tantalate (LGT) and ferromagnetic Fe-Co-V alloys. It is shown that extensional strain does not result in ME effects in these layered composites. Under shear strain generated by an ac and dc bias magnetic fields along the length and width of the sample, respectively, strong ME coupling is measured at low-frequencies and at mechanical resonance. A model is discussed for the ME effects. These composites of Y-cut piezoelectrics and ferromagnetic alloys are of importance for shear strain based magnetic field sensors.

  16. Strain localization in the middle- to upper continental crust: examples from the Patos and Pernambuco shear zones (Borborema Province, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Viegas, G.; Archanjo, C. J.; Hollanda, M. H.; Vauchez, A. R.

    2014-12-01

    The accommodation of deformation in the Earth's lithosphere typically results in a heterogeneous distribution of strain in the continental crust, which is a function of effective pressure, temperature and strain rate at different structural levels. In Northeast Brazil, the Borborema Province is characterized by an interconnected, crustal-scale shear zone system associated with a widespread granitic plutonism. Two of the most prominent structures of this system, the Patos and Pernambuco shear zones, are characterized by ~ 600 km long E-W striking mylonite belts in which strain localization processes are observed either in association with partial melting in the Patos strike-slip fault, or as zones of overprinting brittle-ductile deformation in the Pernambuco shear zone. Deformation mechanisms are distinct across the Patos shear zone, mainly marked by crystalline plasticity and diffusion creep in the high-temperature northern border, magmatic flow in the central region and dislocation creep coupled with microfracturing in the southern sector. The Espinho Branco migmatite (~ 565 Ma) acts as a weak rheological layer that accumulates strain in the northern portion of the fault. Alternatively, the absence of partial melting and the dominant cataclastic/plastic flow regime lead to grain-size sensitive strain localization at the southern border. The Pernambuco shear zone was nucleated at the vicinities of two granitoid batholiths at c.a. 588 Ma. Low-temperature mylonites adjacent to the batholiths show several microstructures indicating coeval activity of brittle-ductile deformation. Recent zircon U-Pb (SHRIMP) data on these mylonites yielded mean ages of ~ 539 Ma, suggesting successive events of thermal input and shearing within the structure. These features suggest that strain localization processes exert an important control on the rheology of the continental lithosphere; the accommodation of deformation in the middle crust is mainly attained by the presence of weak

  17. Influence of shear strains on the phase of light transmitted through single-mode fiber optic strain sensors

    NASA Astrophysics Data System (ADS)

    Jensen, David W.; Pai, Suresh P.

    1995-04-01

    Since the well-known demonstration of a fiber-optic strain gage by Butter and Hocker in 1978, significant refinements have been made in the area of fiber optic sensing, enabling the measurement of many different physical quantities, including strain, displacement, linear and circular acceleration, temperature, degree of cure in plastics, chemical compositions, pressure, acoustic waves, and fluid flow rates. Both analytical and experimental efforts have contributed to our current understanding of the relationship between the elongation of a host medium and phase changes in the light passing through an optical fiber. This paper describes research which partially fills in the remaining gap by quantifying the influence of shear strains on the phase change of light passing through an embedded optical fiber. In this experiment, optical fibers were embedded in 18-inch long by 2.25-inch diameter composite tubes. Three tubes were fabricated with axial fibers and one with a helical fiber, using a hand layup fabrication technique. These tubes were also instrumented with two strain gage rosettes. The tubes were subjected to pure torsional loads while the surface strains and the fiber-optic phase changes were measured. A modified all-fiber Mach-Zehnder interferometer with active homodyne feedback was used to determine the phase changes in the optical fibers due to the applied strains. The phase changes were also predicted using fundamental concepts of structural mechanics and existing phase-strain models.

  18. Effect of strain rate on shear properties and fracture characteristics of DP600 and AA5182-O sheet metal alloys

    NASA Astrophysics Data System (ADS)

    Rahmaan, Taamjeed; Butcher, Cliff; Abedini, Armin; Worswick, Michael

    2015-09-01

    Shear tests were performed at strain rates ranging from quasi-static (.01 s-1) to 600 s-1 for DP600 steel and AA5182-O sheet metal alloys at room temperature. A miniature sized shear specimen was modified and validated in this work to perform high strain rate shear testing. Digital image correlation (DIC) techniques were employed to measure the strains in the experiments, and a criterion to detect the onset of fracture based on the hardening rate of the materials is proposed. At equivalent strains greater than 20%, the DP600 and AA5182 alloys demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the DP600 shows positive rate sensitivity while the AA5182 was not sensitive to strain rate. For both alloys, the equivalent fracture strain and elongation to failure decreased with strain rate. A conversion of the shear stress to an equivalent stress using the von Mises yield criterion provided excellent agreement with the results from tensile tests at elevated strain rates. Unlike the tensile test, the shear test is not limited by the onset of necking so the equivalent stress can be determined over a larger range of strain.

  19. Sub-micron strain analysis of local stick-slip motion of individual shear bands in a bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Binkowski, I.; Schlottbom, S.; Leuthold, J.; Ostendorp, S.; Divinski, S. V.; Wilde, G.

    2015-11-01

    Nanodot deposition on a side surface of a rectangular sample and digital image correlation are used to quantify the in-plane strain fields associated with the propagation of a shear band in a PdNiP bulk metallic glass, induced by rolling. Within the resolution of the method related to an average inter-dot distance of 100 nm, deformation is found to be highly localized at the shear bands, while alternating areas with a size of 100-400 nm with opposite local shear strains are found. This phenomenon substantiates a local stick-slip nature of shear band propagation during the metallic glass deformation, even during rolling.

  20. Cartilage nominal strain correlates with shear modulus and glycosaminoglycans content in meniscectomized joints.

    PubMed

    Song, Yongnam; Carter, Dennis R; Giori, Nicholas J

    2014-06-01

    Postmeniscectomy osteoarthritis (OA) is hypothesized to be the consequence of abnormal mechanical conditions, but the relationship between postsurgical alterations in articular cartilage strain and in vivo biomechanical/biochemical changes in articular cartilage is unclear. We hypothesized that spatial variations in cartilage nominal strain (percentile thickness change) would correlate with previously reported in vivo articular cartilage property changes following meniscectomy. Cadevaric sheep knees were loaded in cyclic compression which was previously developed to mimic normal sheep gait, while a 4.7 T magnetic resonance imaging (MRI) imaged the whole joint. 3D cartilage strain maps were compared with in vivo sheep studies that described postmeniscectomy changes in shear modulus, phase lag, proteoglycan content and collagen organization/content in the articular cartilage. The area of articular cartilage experiencing high (overloaded) and low (underloaded) strain was significantly increased in the meniscectomized tibial compartment by 10% and 25%, respectively, while no significant changes were found in the nonmeniscectomized compartment. The overloaded and underloaded regions of articular cartilage in our in vitro specimens correlated with regions of in vivo shear modulus reduction. Glycosaminoglycans (GAG) content only increased at the underloaded articular cartilage but decreased at the overloaded articular cartilage. No significant correlation was found in phase lag and collagen organization/content changes with the strain variation. Comparisons between postsurgical nominal strain and in vivo cartilage property changes suggest that both overloading and underloading after meniscectomy may directly damage the cartilage matrix stiffness (shear modulus). Disruption of superficial cartilage by overloading might be responsible for the proteoglycan (GAG) loss in the early stage of postmeniscectomy OA. PMID:24671447

  1. Repetitive differential finger motion increases shear strain between the flexor tendon and subsynovial connective tissue.

    PubMed

    Tat, Jimmy; Kociolek, Aaron M; Keir, Peter J

    2013-10-01

    Non-inflammatory fibrosis and thickening of the subsynovial connective tissue (SSCT) are characteristic in carpal tunnel syndrome (CTS) patients. These pathological changes have been linked to repetitive hand tasks that create shear forces between the flexor tendons and SSCT. We measured the relative motion of the flexor digitorum superficialis tendon and SSCT during two repetitive finger tasks using color Doppler ultrasound. Twelve participants performed flexion-extension cycles for 30 min with the long finger alone (differential movement) and with all four fingers together (concurrent movement). Shear strain index (SSI, a relative measure of excursion in flexion and extension) and maximum velocity ratio (MVR, the ratio of SSCT versus tendon during flexion and extension) were used to represent shear. A linear effect of exertion time was significant and corresponded with larger tendon shear in differential motion. The flexion SSI increased 20.4% from the first to the 30th minute, while MVR decreased 8.9% in flexion and 8.7% in extension. No significant changes were found during concurrent motion. These results suggest that exposure to repetitive differential finger tasks may increase the risk of shear injury in the carpal tunnel.

  2. Deriving strain from crystallographic preferred orientation for a ductile shear zone in north western Turkey.

    NASA Astrophysics Data System (ADS)

    Farrell, K.; Lloyd, G. E. E.; Wallis, D.; Phillips, R. J.

    2015-12-01

    Understanding the behaviour of active continental-scale fault zones at depth, and in particular how displacements observed at the Earth's surface are accommodated through the crust, is crucial to improving understanding of the earthquake cycle. This behaviour can be inferred by study of exhumed portions of ductile shear zones using methods such as recording strain profile(s) across the fault zone. However, due to the nature of mid-crustal rocks, strain markers tend to be rare and/or discontinuously distributed. The intensity (I) of crystallographic preferred orientation (CPO) of deformed minerals provides a proxy for strain that is continuous across fault zones. CPO are collected via electron back scattered diffraction in the scanning electron microscope. The strength of the CPO can be quantified using eigenvalue-based intensity parameters. Calibration of intensity with strain is achieved via comparison with visco-plastic self-consistency models of CPO evolution, although the temperature-dependent critical resolved shear stresses of potential crystal slip systems must be known. As an example, we consider the dextral strike-slip Eskişehir shear zone, NW Turkey, which was active during the Oligocene and accommodated ~100km of displacement, including a component of late oblique-normal slip. An exhumed mid-crustal section of this fault zone is exposed in the Uludağ Massif, comprising of high-grade metamorphic rocks of the Uludağ Group, intruded by the Central and South Uludağ granites. Sample transects focussed on the pure calcic marbles that dominate the stratigraphy. Fortunately, the availability of experimental data for calcite crystal slip behaviour at different temperatures makes the application of the CPO intensity strain proxy method relatively straightforward. The Uludağ Massif and Eskişehir shear zone provide a field based analogue for the ductile shear zone beneath the currently active North Anatolian Fault. The results of our CPO intensity-based strain

  3. Scaling of the critical slip distance for seismic faulting with shear strain in fault zones

    USGS Publications Warehouse

    Marone, C.; Kilgore, B.

    1993-01-01

    THEORETICAL and experimentally based laws for seismic faulting contain a critical slip distance1-5, Dc, which is the slip over which strength breaks down during earthquake nucleation. On an earthquake-generating fault, this distance plays a key role in determining the rupture nucleation dimension6, the amount of premonitory and post-seismic slip7-10, and the maximum seismic ground acceleration1,11. In laboratory friction experiments, Dc has been related to the size of surface contact junctions2,5,12; thus, the discrepancy between laboratory measurements of Dc (??? 10-5 m) and values obtained from modelling earthquakes (??? 10-2 m) has been attributed to differences in roughness between laboratory surfaces and natural faults5. This interpretation predicts a dependence of Dc on the particle size of fault gouge 2 (breccia and wear material) but not on shear strain. Here we present experimental results showing that Dc scales with shear strain in simulated fault gouge. Our data suggest a new physical interpretation for the critical slip distance, in which Dc is controlled by the thickness of the zone of localized shear strain. As gouge zones of mature faults are commonly 102-103 m thick13-17, whereas laboratory gouge layers are 1-10 mm thick, our data offer an alternative interpretation of the discrepancy between laboratory and field-based estimates of Dc.

  4. The growth and coalescence of ellipsoidal voids in plane strain under combined shear and tension

    NASA Astrophysics Data System (ADS)

    Scheyvaerts, F.; Onck, P. R.; Tekogˇlu, C.; Pardoen, T.

    2011-02-01

    New extensions of a model for the growth and coalescence of ellipsoidal voids based on the Gurson formalism are proposed in order to treat problems involving shear and/or voids axis not necessarily aligned with the main loading direction, under plane strain loading conditions. These extensions are motivated and validated using 3D finite element void cell calculations with overall plane strain enforced in one direction. The starting point is the Gologanu model dealing with spheroidal void shape. A void rotation law based on homogenization theory is coupled to this damage model. The predictions of the model closely agree with the 3D cell calculations, capturing the effect of the initial void shape and orientation on the void rotation rate. An empirical correction is also introduced for the change of the void aspect ratio in the plane transverse to the main axis of the void departing from its initially circular shape. This correction is needed for an accurate prediction of the onset of coalescence. Next, a new approach is proposed to take strain hardening into account within the Thomason criterion for internal necking, avoiding the use of strain hardening-dependent fitting parameters. The coalescence criterion is generalized to any possible direction of the coalescence plane and void orientation. Finally, the model is supplemented by a mathematical description of the final drop of the stress carrying capacity during coalescence. The entire model is developed for plane strain conditions, setting the path to a 3D extension. After validation of the model, a parametric study addresses the effect of shear on the ductility of metallic alloys for a range of microstructural and flow parameters, under different stress states. In general, the presence of shear, for identical stress triaxiality, decreases the ductility, partly explaining recent experimental results obtained in the low stress triaxiality regime.

  5. Large strain variable stiffness composites for shear deformations with applications to morphing aircraft skins

    NASA Astrophysics Data System (ADS)

    McKnight, G. P.; Henry, C. P.

    2008-03-01

    Morphing or reconfigurable structures potentially allow for previously unattainable vehicle performance by permitting several optimized structures to be achieved using a single platform. The key to enabling this technology in applications such as aircraft wings, nozzles, and control surfaces, are new engineered materials which can achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight). These materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations. In this work, we build upon previous efforts in segmented reinforcement variable stiffness composites employing shape memory polymers to create prototype hybrid composite materials that combine the benefits of cellular materials with those of discontinuous reinforcement composites. These composites help overcome two key challenges for shearing wing skins: the resistance to out of plane buckling from actuation induced shear deformation, and resistance to membrane deflections resulting from distributed aerodynamic pressure loading. We designed, fabricated, and tested composite materials intended for shear deformation and address out of plane deflections in variable area wing skins. Our designs are based on the kinematic engineering of reinforcement platelets such that desired microstructural kinematics is achieved through prescribed boundary conditions. We achieve this kinematic control by etching sheets of metallic reinforcement into regular patterns of platelets and connecting ligaments. This kinematic engineering allows optimization of materials properties for a known deformation pathway. We use mechanical analysis and full field photogrammetry to relate local scale kinematics and strains to global deformations for both axial tension loading and shear loading with a pinned-diamond type fixture. The Poisson ratio of the kinematically engineered composite is ~3x higher than

  6. Relationship of trehalose accumulation with ethanol fermentation in industrial Saccharomyces cerevisiae yeast strains.

    PubMed

    Wang, Pin-Mei; Zheng, Dao-Qiong; Chi, Xiao-Qin; Li, Ou; Qian, Chao-Dong; Liu, Tian-Zhe; Zhang, Xiao-Yang; Du, Feng-Guang; Sun, Pei-Yong; Qu, Ai-Min; Wu, Xue-Chang

    2014-01-01

    The protective effect and the mechanisms of trehalose accumulation in industrial Saccharomyces cerevisiae strains were investigated during ethanol fermentation. The engineered strains with more intercellular trehalose achieved significantly higher fermentation rates and ethanol yields than their wild strain ZS during very high gravity (VHG) fermentation, while their performances were not different during regular fermentation. The VHG fermentation performances of these strains were consistent with their growth capacity under osmotic stress and ethanol stress, the key stress factors during VHG fermentation. These results suggest that trehalose accumulation is more important for VHG fermentation of industrial yeast strains than regular one. The differences in membrane integrity and antioxidative capacity of these strains indicated the possible mechanisms of trehalose as a protectant under VHG condition. Therefore, trehalose metabolic engineering may be a useful strategy for improving the VHG fermentation performance of industrial yeast strains.

  7. Relationship of trehalose accumulation with ethanol fermentation in industrial Saccharomyces cerevisiae yeast strains.

    PubMed

    Wang, Pin-Mei; Zheng, Dao-Qiong; Chi, Xiao-Qin; Li, Ou; Qian, Chao-Dong; Liu, Tian-Zhe; Zhang, Xiao-Yang; Du, Feng-Guang; Sun, Pei-Yong; Qu, Ai-Min; Wu, Xue-Chang

    2014-01-01

    The protective effect and the mechanisms of trehalose accumulation in industrial Saccharomyces cerevisiae strains were investigated during ethanol fermentation. The engineered strains with more intercellular trehalose achieved significantly higher fermentation rates and ethanol yields than their wild strain ZS during very high gravity (VHG) fermentation, while their performances were not different during regular fermentation. The VHG fermentation performances of these strains were consistent with their growth capacity under osmotic stress and ethanol stress, the key stress factors during VHG fermentation. These results suggest that trehalose accumulation is more important for VHG fermentation of industrial yeast strains than regular one. The differences in membrane integrity and antioxidative capacity of these strains indicated the possible mechanisms of trehalose as a protectant under VHG condition. Therefore, trehalose metabolic engineering may be a useful strategy for improving the VHG fermentation performance of industrial yeast strains. PMID:24316480

  8. Accumulation of plastic strain in Zircaloy-4 at low homologous temperature

    NASA Astrophysics Data System (ADS)

    Matsunaga, Tetsuya; Satoh, Yuhki; Abe, Hiroaki

    2015-10-01

    Time-dependent strain accumulation in Zircaloy-4 was evaluated at 294 K, i.e., homologous temperature (T/Tm, where Tm is the melting temperature) of 0.14, to ascertain the mechanical response in fuel cladding material, even at the time of storage. Although diffusion processes are suppressed, considerable strain accumulation was observed at less than 0.2% offset stress. Transmission electron microscopy and electron backscattered diffraction analyses were used to investigate the dominant microstructural mechanism. Results showed that the heterogeneous dislocation structure generated strain accumulation, where straightly aligned dislocation arrays on the prismatic plane move freely and few deformation twins were formed in the grain interior. Furthermore, few dislocation tangles were observed because the slip systems were limited to one. Therefore, Zircaloy-4 shows weak work-hardening at the low homologous temperature because of the fewer interactions among dislocations, leading to unexpected strain accumulation under constant load conditions.

  9. Toward Quantitative, High-Shear Strain Deformation Experiments at Lower Mantle Conditions

    NASA Astrophysics Data System (ADS)

    Slivka, L.; Miyagi, L. M.; Amulele, G.; Otsuka, K.; Du, Z.; Karato, S.

    2010-12-01

    Relatively little is known about the deformation properties of lower mantle mineral phases. This is largely due to the fact that conventional deformation devices have been unable to reach pressure and temperature conditions beyond those of the transition zone. The Rotational Drickamer Apparatus (RDA) has been used successfully to perform quantitative, high shear strain deformation experiments at conditions of the transition zone. New technological advances such as beveling anvils to reduce cupping of the anvil tips at high pressures, and high precision laser machining of sample assemblies are allowing us to increase the available pressure range of the RDA toward lower mantle conditions. We have already performed deformation experiments on ringwoodite at ~23 GPa and 1800 K, conditions quite close to those of the top of the lower mantle. These experiments were performed at beamline X17B2 of the National Synchrotron Light Source, using white x-rays to collect energy-dispersive diffraction patterns at a fixed 2θ of 6.7° over ten azimuth angles. Determination of strain was made in-situ using x-ray radiography and a Pt strain marker. Equivalent strains of up to γ = 2 are achieved. Uniaxial and shear stresses were determined in-situ from the d-spacing of ringwoodite (311) and (400) lattice planes as a function of azimuth angle.

  10. Long Pathways for Outgassing Generated by a Rapid and Large Shear Strain of Bubbly Fluids Reducing Effective Viscosity and Affecting Eruption Styles

    NASA Astrophysics Data System (ADS)

    Namiki, A.; Tanaka, Y.

    2015-12-01

    The styles of basaltic explosive eruptions have a wide variety, which is usually attributed to the separation of volcanic gas from the surrounding silicate melt. As a mechanism of gas separation, shear deformation has been suggested. However, the bubble shape evolution under large strain at high strain rate and its effects on viscosity have not yet understood well. We thus performed shear deformation experiments of bubbly liquid under high shear rate and large strain with in situ observation of bubble deformation and viscosity measurements. We used syrup solution as a magma analogue whose viscosity of 3, 50, 500 Pa s, similar to that of basaltic magma. We rotated disc-shaped bubbly syrup at shear rates of 0.03-10 s-1 with strains of 3-1000. Experiments show that deformed bubbles coalesce into larger bubbles and finally generate concentric air rings, resulting that the striped shape of air and liquid parts appears. The widths of air rings greatly exceed the bubble sizes and can be long outgassing pathways if those exist in a volcanic conduit. During the evolution of air rings the measured effective viscosity decreases, while after reaching to a steady state, viscous resistance increases again. At this stage, bubble volume and size in the liquid parts become considerably small. Time evolution of bubble size distribution suggests that most of bubbles are assimilated into the air rings and the remnants in the liquid parts break up into small bubbles. Similar shear deformation of bubbly magma could occur in volcanic conduits, which generates large bubbles at a depth where the lower effective viscosity enhances the ascending velocity. The large bubbles may originate Strombolian eruption or suppresses the explosive eruption by making the long outgassing pathways reaching to the Earth's surface. In both cases, bubble free dense melt accumulates at a shallow conduit. Our experiments suggest that, for larger melt viscosity and narrower conduit, the gas separation occurs

  11. Rheological and microstructural evolution of Carrara marble with high shear strain: results from high temperature torsion experiments

    NASA Astrophysics Data System (ADS)

    Pieri, Marco; Burlini, Luigi; Kunze, Karsten; Stretton, Iona; Olgaard, David L.

    2001-09-01

    This study investigated the rheological and microstructural evolution of Carrara marble deformed to large shear strain to understand how dynamic recrystallization and lattice-preferred orientation (LPO) are related to strain softening processes. Solid cylinders of Carrara marble were deformed in torsion up to a shear strain of γ=11 at constant twist rates, which correspond to a shear strain rate of 3×10 -4 s -1 at the outer surface, and at temperatures of 1000 and 1200 K (727 and 927°C, respectively). For the initial grain size of 150 μm, these conditions are within the dislocation creep regime. Substantial changes in both rheology and microstructure were observed as the marble deformed to high shear strain at 1000 K (1200 K). A peak stress was reached at about γ=1 ( γ=0.5) followed by moderate strain weakening. An apparent steady-state flow stress was obtained at high shear strain of γ>5 ( γ>2). The stress exponent n decreased slowly with strain from 10 ( γ=1) to 6 ( γ=9) at 1000 K, but it remained approximately constant at 1200 K ( n around 10). At the maximum reached shear strain of γ=11 ( γ=8.5), the marble had almost completely recrystallized to a fine grain size of about 10 μm (20 μm). A secondary foliation developed in the recrystallized matrix, which is at a large oblique angle to the shear zone boundary (SZB). LPO was measured by electron backscatter diffraction (EBSD). For both temperatures, the LPO evolved from an oblique deformation texture to a very sharp and symmetric single orientation component with r{101¯4} parallel to the shear plane and a<1¯21¯0> parallel to the shear direction. It is concluded that strain weakening was associated with the development of a strong LPO during dynamic recrystallization to a finer grain size. Mechanical and microstructural steady-state is only reached at large shear strain. The steady-state lattice and grain shape fabrics can hardly be used as shear sense indicators in such recrystallized calcite

  12. Localisation of shear fracture networks in anisotropic materials: influence of strain rate and material strength

    NASA Astrophysics Data System (ADS)

    Gomez-Rivas, E.; Griera, A.

    2009-04-01

    This contribution presents an experimental study of deformation localisation and the formation of fracture networks in elastoviscoplastic layered materials under pure shear boundary conditions. The mechanical properties of the analogue mixtures, which are made of plasticine, have been used to analyse the transition from models in which deformation is accommodated by homogeneous viscous flow to systems controlled by a few active faults. Two series of experiments have been studied: (a) the same material was deformed at different strain rates and (b) four materials with different mechanical properties were deformed at a fixed strain rate. The results show that strain rate and viscous ductility define a change on the degree of deformation localisation and the geometry of fracture networks. The increase of deformation also produces changes on the mechanical behaviour of the systems and the type of deformation. Localisation of fracture networks is enhanced when strain rate is increased. Moreover, there is a progressive increment in the relationship between fracture displacement and fracture length related to the strain rate applied to the system. This experimental observation is also corroborated by a series of simple finite element linear elastoviscous simulations. In these models, a horizontal inclusion within a matrix simulates a pre-existing fracture. The displacement along this fracture is tracked at all times using some selected nodes located at the two walls. The results indicate that there is a dependency of fracture displacements on the strain rate. A deviation between shear strains registered by fractures and the one applied by the boundary conditions is also detected, especially at low strain. The degree of localisation and the nucleation of shear fractures also depend strongly on the viscous ductility and strength of the analogue material. The raise of the material stiffness causes an increase of the length of fractures and displacements along them. This fact

  13. Strain Accumulation and Release in the South Iceland Seismic Zone (Invited)

    NASA Astrophysics Data System (ADS)

    Arnadottir, T.; Hreinsdottir, S.; Geirsson, H.; Ofeigsson, B.

    2013-12-01

    Iceland is located on the Mid-Atlantic ridge, straddling the plate boundary of the North-American and Eurasian plates. Several active volcanic zones and two main transforms accommodate the plate spreading across the island. In the South, the South Iceland Seismic Zone (SISZ) forms the active plate boundary between the Hengill triple junction in the west, and the Eastern Volcanic Zone. The SISZ translates the E-W left lateral shear at depth by faulting on numerous N-S oriented faults in the brittle crust forming the southern margin of the proposed Hreppar micro-plate in South Iceland. In June 2000 and May 2008, two sets of magnitude 6.5 and 6.0 main shocks struck the SISZ. Both earthquake episodes consisted of a pair of main shocks of similar size rupturing closely spaced faults, where static and dynamic stress changes generated by the first event triggered the second main shock further west. The June 2000 earthquakes occurred in the central part of the SISZ, and the May 2008 events in the western part, close to the Hengill triple junction. Since June 2000 annual GPS measurements have been conducted in a geodetic network in South Iceland and a number of continuous GPS stations have been installed. We report strain rate variations in South Iceland derived from GPS observations during 2000 to 2013. In addition to plate motion, and post-seismic signals, the surface deformation is complicated by magma accumulation under active volcanoes at the eastern border of the SISZ - Hekla, and Eyjafjallajökull - as well as subsidence and contraction in the Hengill area caused by fluid withdrawal for geothermal energy production. We also note an increase in strain rates in the epicentral area of the May 2008 main shocks during 2004 to 2007. Previous studies have indicated that the seismic moment released in the June 2000 and May 2008 earthquakes is only half of the accumulated stress since the last major earthquake sequence in 1896-1912. Thus, magnitude 6-7 events may be expected

  14. Analysis of bonded joints. [shear stress and stress-strain diagrams

    NASA Technical Reports Server (NTRS)

    Srinivas, S.

    1975-01-01

    A refined elastic analysis of bonded joints which accounts for transverse shear deformation and transverse normal stress was developed to obtain the stresses and displacements in the adherends and in the bond. The displacements were expanded in terms of polynomials in the thicknesswise coordinate; the coefficients of these polynomials were functions of the axial coordinate. The stress distribution was obtained in terms of these coefficients by using strain-displacement and stress-strain relations. The governing differential equations were obtained by integrating the equations of equilibrium, and were solved. The boundary conditions (interface or support) were satisfied to complete the analysis. Single-lap, flush, and double-lap joints were analyzed, along with the effects of adhesive properties, plate thicknesses, material properties, and plate taper on maximum peel and shear stresses in the bond. The results obtained by using the thin-beam analysis available in the literature were compared with the results obtained by using the refined analysis. In general, thin-beam analysis yielded reasonably accurate results, but in certain cases the errors were high. Numerical investigations showed that the maximum peel and shear stresses in the bond can be reduced by (1) using a combination of flexible and stiff bonds, (2) using stiffer lap plates, and (3) tapering the plates.

  15. Reduced uptake and accumulation of norfloxacin in resistant strains of Neisseria gonorrhoeae isolated in Japan.

    PubMed Central

    Tanaka, M; Fukuda, H; Hirai, K; Hosaka, M; Matsumoto, T; Kumazawa, J

    1994-01-01

    OBJECTIVE--To investigate the alteration of cell permeability toward fluoroquinolones in Neisseria gonorrhoeae, which is a major quinolone-resistance mechanism along with the alteration of DNA gyrase in gram-negative bacteria. The prevalence of fluoroquinolone-resistant N gonorrhoeae strains is rapidly increasing in Japan. MATERIALS AND METHODS--The uptake and accumulation of norfloxacin by gonococcal cells, including six clinical and five World Health Organization (WHO) reference strains, were measured. Of the six clinical strains, two were highly resistant to norfloxacin (MIC 8.0 and 4.0 micrograms/ml), two were moderately resistant (MIC 1.0 and 0.5 microgram/ml), and two were sensitive (MIC 0.063 and 0.004 microgram/ml). All five WHO reference strains were sensitive to norfloxacin (MIC < or = 0.001 to 0.063 microgram/ml). RESULTS--Mean initial norfloxacin uptake in the four resistant strains (104 ng/mg of dry cells) was significantly lower than that in the seven sensitive strains (158 ng/mg of dry cells) (p < 0.05). The mean uptake after 20 minutes was also significantly lower in the four resistant strains (130 ng/mg of dry cells) than in the seven sensitive strains (194 ng/mg of dry cells) (p < 0.05). However, there was no significant difference in mean norfloxacin accumulation after 20 minutes between the four resistant strains (26 ng/mg of dry cells) and the seven sensitive strains (36 ng/mg of dry cells). The accumulation of norfloxacin after 20 minutes was almost zero in two of the four resistant strains, while the remaining two strains accumulated norfloxacin as well as the sensitive strains. CONCLUSIONS--These findings suggest that alteration of bacterial cell permeability is a quinolone-resistance mechanism in N gonorrhoeae isolated in Japan, and that this bacteria may exhibit other mechanisms such as alteration of DNA gyrase. PMID:7959709

  16. Why homogeneous boundary conditions lead to heterogeneous internal strain in analogue simple shear experiments - explained by numerical modeling

    NASA Astrophysics Data System (ADS)

    Exner, Ulrike; Frehner, Marcel; Mancktelow, Neil S.; Grujic, Djordje

    2010-05-01

    Analogue modeling of geological structures, investigating for example the rotation and interaction of rigid or weak inclusions in a matrix, single layer folding, or fold interference patterns, commonly employs a linear simple shear or general shear rig. While the boundaries of such deformation rigs theoretically prescribe a homogeneous isochoric (plane strain) flow, the internal deformation pattern of the analogue material (paraffin wax or silicone putties) may strongly deviate from the intended homogeneous strain conditions. For example, in simple shear experiments (x-y-coordinate system, simple shear in x-direction) the following observations can be made: (1) Close to model boundaries initially parallel to the y-direction of the apparatus a prominent deflection of passive marker lines develops during the experiment, indicating a strong perturbation strain. (2) The central part of the model rotates with the opposite sense of rotation compared to the imposed vorticity, documented by the imposed marker grid. We employ two-dimensional numerical finite element models to investigate the observed deviation from a homogeneous simple shear flow field in simple shear rig experiments. A Newtonian rheology is used to represent the analogue material. We tested different boundary conditions that do not represent perfect simple shear boundary conditions, but could possibly be present in analogue experiments. The numerical results show that neither traction-free slip nor free surface boundary conditions at the four walls, nor any combination of these boundary conditions produces the deformation pattern observed in analogue experiments. Therefore, we conclude that the imposed boundary conditions at the walls of the analogue rigs are not the reason for the observed heterogeneous strain field. In analogue experiments, the analogue material commonly lies on top of a weak viscous material (e.g. vaseline) or is sandwiched between two layers of such a material. These layers are also

  17. Strain localization across main continental strike-slip shear zones : a multi-methods approach for the case of the Karakorum shear zone

    NASA Astrophysics Data System (ADS)

    Boutonnet, E.; Leloup, P. H.; Rozel, A.; Arnaud, N.; Paquette, J. L.

    2012-04-01

    Whether deformation within the deep continental crust is fundamentally concentrated in narrow shear zones or distributed in wide zones stays a major controversy of the earth sciences. This is in part because direct measurements of ductile shear or strain rate are difficult, especially when deformation is intense, as it is the case in ductile shear zones. The Pangong range (India) is an 8km-wide shear zone, corresponding to the exhumed root of the central Karakorum fault zone (KFZ), one of the great continental strike-slip faults of the India-Asia collision zone. Ductile deformation is most intense in the Tangtse and Muglib mylonitic strands, which bracket the shear zone to the SW and NE, respectively. The relationships between dykes emplacement ages (U/Pb dating) and deformation indicate that deformation was not synchronous across the shear zone. Ar/Ar dating document that cooling was diachronic across strike and ductile deformation (~ 300°C) stopped earlier in the SW than in the NE. Deformation thus appears to have migrated / localized from the whole shear zone to the Muglib strand, the only locus showing evidence for brittle deformation and active faulting. We compared the strain rates measured at different spatial scales: (1) a global scale investigated by the geological fault rate estimation and (2) a local scale, investigated with the QSR (Quartz strain rate metry) method. The total offset (200-240 km) and the KFZ life span (18 to 25 Ma) yield an average fault rate of 1.1 ±0.2 cm/yr. this corresponds to a global shear rate of 4.4 x10-14 s-1, assuming an homogenous deformation in space and time within a 8 km wide shear zone. Five quartz samples provided deformation temperatures between 348 and 428°C and corresponding paleo-stresses between 24 and 65 MPa. The local strain rates measured within the two mylonitic strands of the fault zone (> 1 x10-13 s-1), are higher than those measured outside of these strands (≤ 1 x10-14 s-1), where deformation is weaker

  18. AN ANALYSIS OF THE SEGMENTATION THRESHOLD USED IN AXIAL-SHEAR STRAIN ELASTOGRAPHY

    PubMed Central

    Thittai, Arun K.; Xia, Rongmin

    2014-01-01

    Axial - shear strain elastography was introduced recently to image the tumor-host tissue boundary bonding characteristics. The image depicting the axial-shear strain distribution in a tissue under axial compression was termed as an axial-shear strain elastogram (ASSE). It has been demonstrated through simulation, tissue-mimicking phantom experiments, and retrospective analysis of in vivo breast lesion data that metrics quantifying the pattern of axial-shear strain distribution on ASSE can be used as features for identifying the lesion boundary condition as loosely-bonded or firmly-bonded. Consequently, features from ASSE have been shown to have potential in non-invasive breast lesion classification into benign versus malignant. Although there appears to be a broad concurrence in the results reported by different groups, important details pertaining to the appropriate segmentation threshold needed for – 1) displaying the ASSE as a color-overlay on top of corresponding Axial Strain Elastogram (ASE) and/or sonogram for feature visualization and 2) ASSE feature extraction are not yet fully addressed. In this study, we utilize ASSE from tissue mimicking phantom (with loosely-bonded & firmly-bonded inclusions) experiments and freehand –acquired in vivo breast lesion data (7 benign & 9 malignant) to analyze the effect of segmentation threshold on ASSE feature value, specifically, the “fill-in” feature that was introduced recently. We varied the segmentation threshold from 20% to 70% (of the maximum ASSE value) for each frame of the acquisition cine-loop of every data and computed the number of ASSE pixels within the lesion that was greater than or equal to this threshold value. If at least 40% of the pixels within the lesion area crossed this segmentation threshold, the ASSE frame was considered to demonstrate a “fill-in” that would indicate a loosely-bonded lesion boundary condition (suggestive of a benign lesion). Otherwise, the ASSE frame was considered not

  19. Biological Effects of Low-Frequency Shear Strain: Physical Descriptors.

    PubMed

    Carstensen, Edwin L; Parker, Kevin J; Dalecki, Diane; Hocking, Denise C

    2016-01-01

    Biological effects of megahertz-frequency diagnostic ultrasound are thoroughly monitored by professional societies throughout the world. A corresponding, thorough, quantitative evaluation of the archival literature on the biological effects of low-frequency vibration is needed. Biological effects, of course, are related directly to what those exposures do physically to the tissue-specifically, to the shear strains that those sources produce in the tissues. Instead of the simple compressional strains produced by diagnostic ultrasound, realistic sources of low-frequency vibration produce both fast (∼1,500 m/s) and slow (1-10 m/s) waves, each of which may have longitudinal and transverse shear components. Part 1 of this series illustrates the resulting strains, starting with those produced by longitudinally and transversely oscillating planes, through monopole and dipole sources of fast waves and, finally, to the case of a sphere moving in translation-the simplest model of the fields produced by realistic sources. PMID:26458790

  20. Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing.

    PubMed

    Bazant, Zdenek P; Caner, Ferhun C

    2013-11-26

    Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the -2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the -1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.

  1. Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

    PubMed Central

    Bažant, Zdeněk P.; Caner, Ferhun C.

    2013-01-01

    Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the −2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the −1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow. PMID:24218624

  2. Magnetic fabric of sheared till: A strain indicator for evaluating the bed deformation model of glacier flow

    USGS Publications Warehouse

    Hooyer, T.S.; Iverson, N.R.; Lagroix, F.; Thomason, J.F.

    2008-01-01

    Wet-based portions of ice sheets may move primarily by shearing their till beds, resting in high sediment fluxes and the development of subglacial landforms. This model of glacier movement, which requires high bed shear strains, can be tested using till microstructural characteristics that evolve during till deformation. Here we examine the development of magnetic fabric using a ring shear device to defom two Wisconsin-age basal tills to shear strains as high as 70. Hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility (AMS) develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller. At moderate shear strains (???6-25), principal axes of maximum magnetic susceptibility develop a strong fabric (S1 eignevalues of 0.83-0.96), without further strengthening at higher strains, During deformation, directions of maximum susceptibility cluster strongly in the direction of shear and plunge 'up-glacier,' consistent with the behavior of pebbles and sand particles studied in earlier experiments. In contrast, the magnitude of AMS does not vary systematically with strain and is small relative to its variability among samples; this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear. Although processes other than pervasive bed deformation may result in strong flow parallel fabrics, AMS fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model. Copyright 2008 by the American Geophysical Union.

  3. Strain accumulation and rotation in western Oregon and southwestern Washington

    USGS Publications Warehouse

    Svarc, J.L.; Savage, J.C.; Prescott, W.H.; Murray, M.H.

    2002-01-01

    Velocities of 75 geodetic monuments in western Oregon and southwestern Washington extending from the coast to more than 300 km inland have been determined from GPS surveys over the interval 1992-2000. The average standard deviation in each of the horizontal velocity components is ??? 1 mm yr-1. The observed velocity field is approximated by a combination of rigid rotation (Euler vector relative to interior North America: 43. 40??N ?? 0.14??, 119.33??W ?? 0.28??, and 0.822 ?? 0.057?? Myr-1 clockwise; quoted uncertainties are standard deviations), uniform regional strain rate (??EE = -7.4 ?? 1.8, ??EN = -3.4 ?? 1.0, and ??NN = -5.0 ?? 0.8 nstrain yr-1, extension reckoned positive), and a dislocation model representing subduction of the Juan de Fuca plate beneath North America. Subduction south of 44.5??N was represented by a 40-km-wide locked thrust and subduction north of 44.5??N by a 75-km-wide locked thrust.

  4. The large shear strain dynamic behaviour of in-vitro porcine brain tissue and a silicone gel model material.

    PubMed

    Brands, D W; Bovendeerd, P H; Peters, G W; Wismans, J S

    2000-11-01

    The large strain dynamic behaviour of brain tissue and silicone gel, a brain substitute material used in mechanical head models, was compared. The non-linear shear strain behaviour was characterised using stress relaxation experiments. Brain tissue showed significant shear softening for strains above 1% (approximately 30% softening for shear strains up to 20%) while the time relaxation behaviour was nearly strain independent. Silicone gel behaved as a linear viscoelastic solid for all strains tested (up to 50%) and frequencies up to 461 Hz. As a result, the large strain time dependent behaviour of both materials could be derived for frequencies up to 1000 Hz from small strain oscillatory experiments and application of Time Temperature Superpositioning. It was concluded that silicone gel material parameters are in the same range as those of brain tissue. Nevertheless the brain tissue response will not be captured exactly due to increased viscous damping at high frequencies and the absence of shear softening in the silicone gel. For trend studies and benchmarking of numerical models the gel can be a good model material.

  5. Ab initio study of shear strain effects on ferroelectricity at PbTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Van Truong, Do; Hung, Nguyen Tuan; Shimada, Takahiro; Kitamura, Takayuki

    2012-08-01

    Ferroelectric thin film with the perovskite ABO3 structure have been widely used in technology applications, e.g., actuators in MEMS/NEMS and nonvolatile random access memories (FeRAM). In order to clarify the effect of the shear strain on the ferroelectricity, the PbTiO3 thin film as a typical one is chosen. The focus of this study is to put on the PbO-terminated (1​ × ​1) and c(2​ × ​2) surfaces and the TiO2-terminated (1​ × ​1) surface. Based on ab initio density functional theory calculations with the local density approximation, we have found out that in both the PbO and TiO2-terminated (1​ × ​1) models, the ferroelectricity in the PbO layers was enhanced under the positive shear strain while it was suppressed under the negative one. For the TiO2 layers, the ferroelectricity was slightly enhanced and sharply suppressed under the positive and negative shear strains, respectively. In the PbO-terminated (2​ × ​2) model, the AFE phase was suppressed by the FE phase under the positive shear strain while the opposite trend was found under the negative shear strain. For the PbO layers, the ferroelectricity was enhanced under the positive and negative shear strains. For the TiO2 layers, the influence of the negative shear strain on the ferroelectricity was larger than that of the positive one. In addition, the ideal strength of the PbTiO3 thin film with the different terminations was investigated as well.

  6. Constraints on strain rates during large-scale mid-crustal shearing: An example from the basal Vaddas shear zone, northern Caledonides

    NASA Astrophysics Data System (ADS)

    Gasser, Deta; Stünitz, Holger; Nasipuri, Pritam; Menegon, Luca

    2013-04-01

    The Caledonian orogen in Scandinavia is characterized by large-scale crustal nappe stacks which were emplaced east-/southeast-wards onto the Baltica shield. Whereas original thrust relationships are generally obscured by syn- to post-collisional extensional deformation in the southern and central Scandinavian Caledonides, several large-scale thrust systems are well-preserved in the northern Scandinavian Caledonides in Troms and Finnmark. One example is the mid-crustal Vaddas shear zone, which emplaced the Vaddas nappe on top of the Kalak nappe complex. In this contribution we present a structural, petrological and geochronological analysis of the rocks under- and overlying the Vaddas shear zone in northern Troms, in order to estimate the strain rate associated with thrusting along this major shear zone. The Vaddas nappe above the investigated shear zone consists mainly of Upper Ordovician to Silurian metasediments, which were deposited in a marine environment and which were intruded by voluminous gabbroic intrusions, before they were sheared off from their substratum and transported on top of the Kalak nappe complex during the Caledonian orogeny. PT conditions from one of these gabbroic bodies indicate that the body intruded the metasediments at ~9 kbar (Getsinger et al., subm to G3), which corresponds to a depth of ~34 km. U-Pb SIMS dating of zircons from this gabbro indicate that intrusion occurred at 439±2 Ma. The Vaddas nappe is separated from the Kalak nappe by an at least ~150 m thick, amphibolite-facies shear zone with a subhorizontal fabric and top-to-the-SE shear sense. It has developed within the lowest part of the Vaddas nappe as well as the upper part of the Kalak nappe complex and PT calculations indicate that final shearing occurred at ~450° C and ~6 kbar (depth of ~23 km). U-Pb TIMS dating of titanites, which grow parallel to the shear fabric in the Kalak nappe complex, gives 206Pb/238U ages ranging from 442±1 to 429±1 Ma, indicating that

  7. Analysis of transverse shear strains in pre-twisted thick beams using variational asymptotic method

    SciTech Connect

    Ameen, Maqsood M.; Harursampath, Dineshkumar E-mail: dinesh@aero.iisc.ernet.in

    2015-03-10

    The cross-sectional stiffness matrix is derived for a pre-twisted, moderately thick beam made of transversely isotropic materials and having rectangular cross sections. An asymptotically-exact methodology is used to model the anisotropic beam from 3-D elasticity, without any further assumptions. The beam is allowed to have large displacements and rotations, but small strain is assumed. The strain energy is computed making use of the beam constitutive law and kinematical relations derived with the inclusion of geometrical nonlinearities and an initial twist. The energy functional is minimized making use of the Variational Asymptotic Method (VAM), thereby reducing the cross section to a point on the beam reference line with appropriate properties, forming a 1-D constitutive law. VAM is a mathematical technique employed in the current problem to rigorously split the 3-D analysis of beams into two: a 2-D analysis over the beam cross-sectional domain, which provides a compact semi-analytical form of the properties of the cross sections, and a nonlinear 1-D analysis of the beam ref-erence curve. In this method, as applied herein, the cross-sectional analysis is performed asymptotically by taking advantage of a material small parameter and two geometric small parameters. 3-D strain components are derived using kinematics and arranged in orders of the small parameters. Closed-form expressions are derived for the 3-D non-linear warping and stress fields. Warping functions are obtained by the minimization of strain energy subject to certain set of constraints that render the 1-D strain measures well-defined. The zeroth-order 3-D warping field thus yielded is then used to integrate the 3-D strain energy density over the cross section, resulting in the 1-D strain energy density, which in turn helps identify the corresponding cross-sectional stiffness matrix. The model is capable of predicting interlaminar and transverse shear stresses accurately up to first order.

  8. Microstructural characteristics of adiabatic shear localization in a metastable beta titanium alloy deformed at high strain rate and elevated temperatures

    SciTech Connect

    Zhan, Hongyi; Zeng, Weidong; Wang, Gui; Kent, Damon; Dargusch, Matthew

    2015-04-15

    The microstructural evolution and grain refinement within adiabatic shear bands in the Ti6554 alloy deformed at high strain rates and elevated temperatures have been characterized using transmission electron microscopy. No stress drops were observed in the corresponding stress–strain curve, indicating that the initiation of adiabatic shear bands does not lead to the loss of load capacity for the Ti6554 alloy. The outer region of the shear bands mainly consists of cell structures bounded by dislocation clusters. Equiaxed subgrains in the core area of the shear band can be evolved from the subdivision of cell structures or reconstruction and transverse segmentation of dislocation clusters. It is proposed that dislocation activity dominates the grain refinement process. The rotational recrystallization mechanism may operate as the kinetic requirements for it are fulfilled. The coexistence of different substructures across the shear bands implies that the microstructural evolution inside the shear bands is not homogeneous and different grain refinement mechanisms may operate simultaneously to refine the structure. - Graphical abstract: Display Omitted - Highlights: • The microstructure within the adiabatic shear band was characterized by TEM. • No stress drops were observed in the corresponding stress–strain curve. • Dislocation activity dominated the grain refinement process. • The kinetic requirements for rotational recrystallization mechanism were fulfilled. • Different grain refinement mechanisms operated simultaneously to refine the structure.

  9. Axial-shear strain elastography for breast lesion classification: further results from in vivo data.

    PubMed

    Thittai, Arun K; Yamal, Jose-Miguel; Mobbs, Louise M; Kraemer-Chant, Christina M; Chekuri, Srinivasa; Garra, Brian S; Ophir, Jonathan

    2011-02-01

    The purpose of this work was to investigate the potential of the normalized axial-shear strain area (NASSA) feature, derived from axial-shear strain elastograms (ASSE), for breast lesion classification of fibroadenoma and cancer. This study consisted of previously acquired in vivo digital radiofrequency data of breast lesions. A total of 33 biopsy-proven malignant tumors and 30 fibroadenoma cases were included in the study, which involved three observers blinded to the original BIRADS-ultrasound scores. The observers outlined the lesions on the sonograms. The ASSEs were segmented and color-overlaid on the sonograms, and the NASSA feature from the ASSE was computed semi-automatically. Receiver operating characteristic (ROC) curves were then generated and the area under the curve (AUC) was calculated for each observer performance. A logistic regression classifier was built to compare the improvement in the AUC when using BIRADS scores plus NASSA values as opposed to BIRADS scores alone. BIRADS score ROC had an AUC of 0.89 (95% CI = 0.81 to 0.97). In comparison, the average of the AUC for all the three observers using ASSE feature alone was 0.84. However, the AUC increased to 0.94 (average of 3 observers) when BIRADS score and ASSE feature were combined. The results demonstrate that the NASSA feature derived from ASSE has the potential to improve BIRADS breast lesion classification of fibroadenoma and malignant tumors. PMID:21208733

  10. Normal and Fibrotic Rat Livers Demonstrate Shear Strain Softening and Compression Stiffening: A Model for Soft Tissue Mechanics.

    PubMed

    Perepelyuk, Maryna; Chin, LiKang; Cao, Xuan; van Oosten, Anne; Shenoy, Vivek B; Janmey, Paul A; Wells, Rebecca G

    2016-01-01

    Tissues including liver stiffen and acquire more extracellular matrix with fibrosis. The relationship between matrix content and stiffness, however, is non-linear, and stiffness is only one component of tissue mechanics. The mechanical response of tissues such as liver to physiological stresses is not well described, and models of tissue mechanics are limited. To better understand the mechanics of the normal and fibrotic rat liver, we carried out a series of studies using parallel plate rheometry, measuring the response to compressive, extensional, and shear strains. We found that the shear storage and loss moduli G' and G" and the apparent Young's moduli measured by uniaxial strain orthogonal to the shear direction increased markedly with both progressive fibrosis and increasing compression, that livers shear strain softened, and that significant increases in shear modulus with compressional stress occurred within a range consistent with increased sinusoidal pressures in liver disease. Proteoglycan content and integrin-matrix interactions were significant determinants of liver mechanics, particularly in compression. We propose a new non-linear constitutive model of the liver. A key feature of this model is that, while it assumes overall liver incompressibility, it takes into account water flow and solid phase compressibility. In sum, we report a detailed study of non-linear liver mechanics under physiological strains in the normal state, early fibrosis, and late fibrosis. We propose a constitutive model that captures compression stiffening, tension softening, and shear softening, and can be understood in terms of the cellular and matrix components of the liver.

  11. Normal and Fibrotic Rat Livers Demonstrate Shear Strain Softening and Compression Stiffening: A Model for Soft Tissue Mechanics

    PubMed Central

    Cao, Xuan; van Oosten, Anne; Shenoy, Vivek B.; Janmey, Paul A.; Wells, Rebecca G.

    2016-01-01

    Tissues including liver stiffen and acquire more extracellular matrix with fibrosis. The relationship between matrix content and stiffness, however, is non-linear, and stiffness is only one component of tissue mechanics. The mechanical response of tissues such as liver to physiological stresses is not well described, and models of tissue mechanics are limited. To better understand the mechanics of the normal and fibrotic rat liver, we carried out a series of studies using parallel plate rheometry, measuring the response to compressive, extensional, and shear strains. We found that the shear storage and loss moduli G’ and G” and the apparent Young's moduli measured by uniaxial strain orthogonal to the shear direction increased markedly with both progressive fibrosis and increasing compression, that livers shear strain softened, and that significant increases in shear modulus with compressional stress occurred within a range consistent with increased sinusoidal pressures in liver disease. Proteoglycan content and integrin-matrix interactions were significant determinants of liver mechanics, particularly in compression. We propose a new non-linear constitutive model of the liver. A key feature of this model is that, while it assumes overall liver incompressibility, it takes into account water flow and solid phase compressibility. In sum, we report a detailed study of non-linear liver mechanics under physiological strains in the normal state, early fibrosis, and late fibrosis. We propose a constitutive model that captures compression stiffening, tension softening, and shear softening, and can be understood in terms of the cellular and matrix components of the liver. PMID:26735954

  12. Absence of strain accumulation in the Shumagin seismic gap, Alaska, 1980-1987 ( USA).

    USGS Publications Warehouse

    Lisowski, M.; Savage, J.C.; Prescott, W.H.; Gross, W.K.

    1988-01-01

    Measurements of the deformation of a trilateration network in the Shumagin seismic gap in the interval 1980-1987 failed to detect any significant strain accumulation (observed extension rate in the direction of plate convergence 0.00 + or - 0.03 mu strain/yr). Dislocation models of the subduction process and measurements at a comparable network at a known seismic subduction zone (Nankai Trough, Japan) suggest that a rate of the order of -0.2 mu strain/yr should have been observed if the main thrust zone beneath the Shumagin Islands were locked. The simplest explanation of the observed absence of strain accumulation in the Shumagin seismic gap is that the main thrust zone beneath the Shumagin Islands is not presently locked. Other possible explanations depend upon very particular circumstances.-Authors

  13. Fusarium proliferatum strains change fumonisin biosynthesis and accumulation when exposed to host plant extracts.

    PubMed

    Górna, Karolina; Pawłowicz, Izabela; Waśkiewicz, Agnieszka; Stępień, Łukasz

    2016-01-01

    Fumonisin concentrations in mycelia and media were studied in liquid Fusarium proliferatum cultures supplemented with host plant extracts. Furthermore, the kinetics of fumonisin accumulation in media and mycelia collected before and after extract addition was analysed as well as the changes in the expression of the FUM1 gene. Fumonisin content in culture media increased in almost all F. proliferatum strains shortly after plant extracts were added. The asparagus extract induced the highest FB level increase and the garlic extract was the second most effective inducer. Fumonisin level decreased constantly until 14th day of culturing, though for some strains also at day 8th an elevated FB level was observed. Pineapple extract induced the highest increase of fum1 transcript levels as well as fumonisin synthesis in many strains, and the peas extract inhibited fungal growth and fumonisin biosynthesis. Moreover, fumonisins were accumulated in mycelia of studied strains and in the respective media. PMID:27268248

  14. Research on novel MEMS shear beam strain gauge and PZT accelerometer based on deep RIE process

    NASA Astrophysics Data System (ADS)

    Wang, Yu

    2000-10-01

    In this thesis research, the design and processing of a shear beam strain gauge and a PZT accelerometer MEMS device have been investigated in order to understand the effects of chip geometry and processing methods on the performance of these two kinds of MEMS chips. The thesis provides a theoretical analysis using an area-moment method coupled with silicon piezoresistance characteristics to analyze the stresses and the strain state and the piezoresistance effect on the resistors that formed a Wheatstone bridge in the shear beam; the analysis also demonstrates the relation between the dimensions of key chip structures and the device sensitivity. A processing including ion implantation plus drive-in and metalization was investigated in order to attain high sensitivity and good ohmic contact characteristics for a single-step implantation process. A photolithography process, using photo resists of about 30 mum thickness, was developed and investigated for Deep RIE etching in order to form the microstructure. As a result of the design and processing work, the strain gauge device showed good linearity over a +/-300 mum/m range, good temperature characteristics over 13--54°C, low transverse sensitivity and a gauge factor 10 times larger than the foil gauge cousin. The thesis presents the processing research on PZT accelerometer. The research involved compatible process development in order to integrate a PZT capacitor structure (with thick PZT film) into the silicon microstructure. The thesis also presents investigation of wet bulk micromachining processes and Deep RIE process. The thesis discusses the process and behavior of different mask layers for different approaches. The factors that affect the aspect ratio of Si during the DRIE process are also discussed. Accelerometers showed good sensitivities (2.04 PC/g) with a bandwidth of 8kHz. Future work based on these investigations has been proposed to improve the devices performance.

  15. Shear strain in Nd0.5Ca0.5MnO3 at high pressures.

    PubMed

    Arulraj, Anthony; Dinnebier, Robert E; Carlson, Stefan; Hanfland, Michael; van Smaalen, Sander

    2005-04-29

    High-pressure x-ray powder diffraction has been measured on the half doped rare earth manganite Nd0.5Ca0.5MnO3 up to a pressure of 15 GPa. We report the presence of a quantifiable amount of shear distortion of the MnO6 octahedra in Nd0.5Ca0.5MnO3 at high pressures. The lattice strain of Nd0.5Ca0.5MnO3 is minimal at a crossover pressure of p* approximately 7 GPa, with the same lattice strain above and below this pressure achieved by shear and Jahn-Teller-type distortions, respectively. The increase in shear strain with increasing pressure provides a mechanism for the insulating behavior of manganites at high pressures that has not been considered before. PMID:15904242

  16. Implementation of Improved Transverse Shear Calculations and Higher Order Laminate Theory Into Strain Rate Dependent Analyses of Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Zhu, Lin-Fa; Kim, Soo; Chattopadhyay, Aditi; Goldberg, Robert K.

    2004-01-01

    A numerical procedure has been developed to investigate the nonlinear and strain rate dependent deformation response of polymer matrix composite laminated plates under high strain rate impact loadings. A recently developed strength of materials based micromechanics model, incorporating a set of nonlinear, strain rate dependent constitutive equations for the polymer matrix, is extended to account for the transverse shear effects during impact. Four different assumptions of transverse shear deformation are investigated in order to improve the developed strain rate dependent micromechanics model. The validities of these assumptions are investigated using numerical and theoretical approaches. A method to determine through the thickness strain and transverse Poisson's ratio of the composite is developed. The revised micromechanics model is then implemented into a higher order laminated plate theory which is modified to include the effects of inelastic strains. Parametric studies are conducted to investigate the mechanical response of composite plates under high strain rate loadings. Results show the transverse shear stresses cannot be neglected in the impact problem. A significant level of strain rate dependency and material nonlinearity is found in the deformation response of representative composite specimens.

  17. The influence of strain localisation on the rotation behaviour of rigid objects in experimental shear zones

    NASA Astrophysics Data System (ADS)

    ten Grotenhuis, Saskia M.; Passchier, Cees W.; Bons, Paul D.

    2002-03-01

    Mica fish and tourmaline fish from natural mylonites were analysed in thin section to determine their orientation distribution. They are oriented with their long axes tilted with respect to the mylonitic foliation, and fish with a small aspect ratio exhibit a slightly larger angle than fish with a large aspect ratio. This orientation seems to be a stable orientation for the mica and tourmaline fish. Analogue experiments with two rheologically different matrix materials were performed to explain the data. One material was PDMS, a linear viscous polymer. The other was tapioca pearls, a granular material with low cohesion and Mohr-Coulomb type behaviour. In contrast to a fairly homogeneous strain distribution in PDMS, distinct small-scale shear bands developed in tapioca pearls during deformation. Experiments modelled different vorticity numbers and parallelogram-shaped rigid objects with different aspect ratios were used. Rotation rates of objects in a viscous matrix are very similar to analytical solutions for ellipses in viscous flow, but stable orientations differ from data of natural examples. In all experiments with a Mohr-Coulomb matrix elongated objects had a stable orientation due to small-scale strain localisation. We therefore suggest that small-scale strain localisation (≤mm) that might be hidden by ongoing deformation and recrystallisation processes, is an important characteristic of the rheology of mylonites.

  18. Cones of localized shear strain in incompressible elasticity with prestress: Green's function and integral representations

    PubMed Central

    Argani, L. P.; Bigoni, D.; Capuani, D.; Movchan, N. V.

    2014-01-01

    The infinite-body three-dimensional Green's function set (for incremental displacement and mean stress) is derived for the incremental deformation of a uniformly strained incompressible, nonlinear elastic body. Particular cases of the developed formulation are the Mooney–Rivlin elasticity and the J2-deformation theory of plasticity. These Green's functions are used to develop a boundary integral equation framework, by introducing an ad hoc potential, which paves the way for a boundary element formulation of three-dimensional problems of incremental elasticity. Results are used to investigate the behaviour of a material deformed near the limit of ellipticity and to reveal patterns of shear failure. In fact, within the investigated three-dimensional framework, localized deformations emanating from a perturbation are shown to be organized in conical geometries rather than in planar bands, so that failure is predicted to develop through curved and thin surfaces of intense shearing, as can for instance be observed in the cup–cone rupture of ductile metal bars. PMID:25197258

  19. Mechanical anisotropy control on strain localization in upper mantle shear zones

    NASA Astrophysics Data System (ADS)

    Herwegh, Marco; Mercolli, Ivan; Linckens, Jolien; Müntener, Othmar

    2016-05-01

    Mantle rocks at oceanic spreading centers reveal dramatic rheological changes from partially molten to solid-state ductile to brittle deformation with progressive cooling. Using the crustal-scale Wadi al Wasit mantle shear zone (SZ, Semail ophiolite, Oman), we monitor such changes based on quantitative field and microstructural investigations combined with petrological and geochemical analyses. The spatial distribution of magmatic dikes and high strain zones gives important information on the location of magmatic and tectonic activity. In the SZ, dikes derived from primitive melts (websterites) are distributed over the entire SZ but are more abundant in the center; dikes from more evolved, plagioclase saturated melts (gabbronorites) are restricted to the SZ center. Accordingly, harzburgite deformation fabrics show a transition from protomylonite (1100°C), mylonite (900-800°C) to ultramylonite (<700°C) and a serpentine foliation (<500°C) from the SZ rim to the center. The spatial correlation between solid-state deformation fabrics and magmatic features indicates progressive strain localization in the SZ on the cooling path. Three stages can be discriminated: (i) Cycles of melt injection (dunite channels and websterite dikes) and solid-state deformation (protomylonites-mylonites; 1100-900°C), (ii) dominant solid-state deformation in harzburgite mylonites (900-800°C) with some last melt injections (gabbronorites) and ultramylonites (<700°C), and (iii) infiltration of seawater inducing a serpentine foliation (<500°C) followed by cataclasis during obduction. The change of these processes in space and time indicates that early dike-related ridge-parallel deformation controls the onset of the entire strain localization history promoting nucleation sites for different strain weakening processes as a consequence of changing physicochemical conditions.

  20. The Cora Lake Shear Zone: Strain Localization in an Ultramylonitic, Deep Crustal Shear Zone, Athabasca Granulite Terrain, Western Churchill Province, Canada

    NASA Astrophysics Data System (ADS)

    Regan, S.; Williams, M. L.; Mahan, K. H.; Orlandini, O. F.; Jercinovic, M. J.; Leslie, S. R.; Holland, M.

    2012-12-01

    Ultramylonitic shear zones typically involve intense strain localization, and when developed over large regions can introduce considerable heterogeneity into the crust. The Cora Lake shear zone (CLsz) displays several 10's to 100's of meters-wide zones of ultramylonite distributed throughout its full 3-5 km mylonitized width. Detailed mapping, petrography, thermobarometry, and in-situ monazite geochronology suggest that it formed during the waning phases of granulite grade metamorphism and deformation, within one of North America's largest exposures of polydeformed lower continental crust. Anastomosing zones of ultramylonite contain recrystallized grain-sizes approaching the micron scale and might appear to suggest lower temperature mylonitization. However, feldspar and even clinopyroxene are dynamically recrystallized, and quantitative thermobarometry of syn-deformational assemblages indicate high P and T conditions ranging from 0.9 -10.6 GPa and 775-850 °C. Even at these high T's, dynamic recovery and recrystallization were extremely limited. Rocks with low modal quartz have extremely small equilibrium volumes. This is likely the result of inefficient diffusion, which is further supported by the unannealed nature of the crystals. Local carbonate veins suggests that H2O poor, CO2 rich conditions may have aided in the preservation of fine grain sizes, and may have inhibited dynamic recovery and recrystallization. The Cora Lake shear zone is interpreted to have been relatively strong and to have hardened during progressive deformation. Garnet is commonly fractured perpendicular to host rock fabric, and statically replaced by both biotite and muscovite. Pseudotachylite, with the same sense of shear, occurs in several ultramylonitized mafic granulites. Thus, cataclasis and frictional melt are interpreted to have been produced in the lower continental crust, not during later reactivation. We suggest that strengthening of rheologically stiffer lithologies led to

  1. Real-time monitoring of high-intensity focused ultrasound treatment using axial strain and axial-shear strain elastograms.

    PubMed

    Xia, Rongmin; Thittai, Arun K

    2014-03-01

    Axial strain elastograms (ASEs) have been found to help visualize sonographically invisible thermal lesions. However, in most studies involving high-intensity focused ultrasound (HIFU)-induced thermal lesions, elastography imaging was performed separately later, after the lesion was formed. In this article, the feasibility of monitoring, in real time, tissue elasticity variation during HIFU treatment and immediately thereafter is explored using quasi-static elastography. Further, in addition to ASEs, we also explore the use of simultaneously acquired axial-shear strain elastograms (ASSEs) for HIFU lesion visualization. Experiments were performed on commercial porcine liver samples in vitro. The HIFU experiments were conducted at two applied acoustic power settings, 35 and 20 W. The experimental setup allowed us to interrupt the HIFU pulse momentarily several different times during treatment to perform elastographic compression and data acquisition. At the end of the experiments, the samples were cut along the imaging plane and photographed to compare size and location of the formed lesion with those visualized on ASEs and ASSEs. Single-lesion and multiple-lesion experiments were performed to assess the contribution of ASEs and ASSEs to lesion visualization and treatment monitoring tasks. At both power settings, ASEs and ASSEs provided accurate location information during HIFU treatment. At the low-power setting case, ASEs and ASSEs provide accurate lesion size in real-time monitoring. Lesion appearance in ASEs and ASSEs was affected by the cavitation bubbles produced at the high-power setting. The results further indicate that the cavitation bubbles influence lesion appearance more in ASEs than in ASSEs. Both ASEs and ASSEs provided accurate size information after a waiting period that allowed the cavitation bubbles to disappear. The results indicate that ASSEs not only improve lesion visualization and size measurement of a single lesion, but, under certain

  2. Frictional properties of DFDP-1 Alpine Fault rocks under hydrothermal conditions and high shear strain

    NASA Astrophysics Data System (ADS)

    Niemeijer, André R.; Boulton, Carolyn; Toy, Virginia; Townend, John; Sutherland, Rupert

    2015-04-01

    The Alpine Fault, New Zealand, is a major plate-bounding fault that accommodates 65-75% of the total relative motion between the Australian and Pacific plates. Paleoseismic evidence of large-displacement surface-rupturing events, as well as an absence of measurable contemporary surface deformation, indicates that the fault slips mostly in quasi-periodic large-magnitude earthquakes (< Mw 8.0). To understand the mechanics of earthquakes, it is important to study the evolution of frictional properties of the fault rocks under conditions representative of the potential hypocentral depth. Here, we present data obtained on drill core samples of rocks that surround the principal slip zone(s) (PSZ) of the Alpine Fault and the PSZ itself. The drill core samples were obtained during phase 1 of the Deep Fault Drilling Project (DFDP-1) in 2011 at relatively shallow depths (down to ~150 m). Simulated fault gouges were sheared under elevated pressure and temperature conditions in a hydrothermal ring shear apparatus. We performed experiments at temperatures of 25, 150, 300, 450 ° C, and 600 oC. Using the shallow geothermal gradient of 63 ° C/km determined in DFDP-1, our highest temperature corresponds to a depth of ~7 km (Sutherland et al. 2012); it would correspond to 10 km depth using a more moderate geotherm of 45 oC/km (Toy et al. 2010). All samples show a transition from velocity-strengthening behavior, i.e. a positive value of (a-b), to velocity-weakening behavior, i.e. a negative value of (a-b) at a temperature of 150 ° C. The transition depends on the absolute value of sliding velocity, with velocity-weakening dominating at lower sliding velocities. At 600 oC, velocity-strengthening dominates at low sliding velocity, whereas the high-velocity steps are all velocity-weakening. Moreover, shear stress depends linearly on effective normal stress at 600 oC, indicating that shearing is essentially frictional and that no transition to ductile (normal stress independent) flow

  3. Onset of failure in finitely strained layered composites subjected to combined normal and shear loading

    NASA Astrophysics Data System (ADS)

    Nestorović, M. D.; Triantafyllidis, N.

    2004-04-01

    A limiting factor in the design of fiber-reinforced composites is their failure under axial compression along the fiber direction. These critical axial stresses are significantly reduced in the presence of shear stresses. This investigation is motivated by the desire to study the onset of failure in fiber-reinforced composites under arbitrary multi-axial loading and in the absence of the experimentally inevitable imperfections and finite boundaries. By using a finite strain continuum mechanics formulation for the bifurcation (buckling) problem of a rate-independent, perfectly periodic (layered) solid of infinite extent, we are able to study the influence of load orientation, material properties and fiber volume fraction on the onset of instability in fiber-reinforced composites. Two applications of the general theory are presented in detail, one for a finitely strained elastic rubber composite and another for a graphite-epoxy composite, whose constitutive properties have been determined experimentally. For the latter case, extensive comparisons are made between the predictions of our general theory and the available experimental results as well as to the existing approximate structural theories. It is found that the load orientation, material properties and fiber volume fraction have substantial effects on the onset of failure stresses as well as on the type of the corresponding mode (local or global).

  4. Strain rate and shear stress at the grain scale generated during near equilibrium antigorite dehydration

    NASA Astrophysics Data System (ADS)

    Padrón-Navarta, José Alberto; Tommasi, Andréa; Garrido, Carlos J.; Mainprice, David; Clément, Maxime

    2016-04-01

    has not been previously reported and offers an unique opportunity to estimate a lower bound for the strain rates and local shear stresses generated during the grain growth and coeval compaction. Estimated values based on experimental creep rates on pyroxene aggregates [3] result in strain rates in the order of 10-12 to 10-13 s-1 and shear stresses of 60-70 MPa. Lower shear stress values (20-40 MPa) are retrieved using the thermodynamic model clinoenstatite inversion of Coe [4] in combination with the hydrostatic high-pressure experimental data on the stability of low clinoenstatite (P21/c). These data suggest that, under low deviatoric stress, fluid extraction and compaction near equilibrium in natural systems are only marginally higher than the strain rate of the solid matrix. These observations support the relatively long residence time of fluids in dehydration fronts and the necessity to further explore and quantify the feedback between mineral grain growth and fluid migration. [1] Connolly (2010) Elements 6(3):165-172; [2] Padrón-Navarta et al. (2015). Contrib Miner Petrol 169:35 [3] Raleigh et al. (1971). J Geophys Res 76(17): 4011-4022; [4] Coe (1970). Contrib Miner Petrol 26(3):247-264

  5. Evaluation Of Elastic Strain Accumulation In The Southern Indian Peninsula By GPS-Geodesy

    NASA Astrophysics Data System (ADS)

    Narayanababu, R.; Ec, M.; Tummala, C.

    2004-12-01

    The computed elastic strain accumulation in the southern Indian peninsula from the GPS derived velocity fields of the global network of GPS stations, in and around the Indian plate which includes Maitri, Indian Antarctic Station, show a significant departure from rigid plate behaviour in a manner consistent with the mapped intra plate stress field, observations of deformations and seismicity in the region. Our results of intraplate strain accumulation within Antarctica Plate covering three sites MAIT, CAS1 and DAV1 are 1.8x10-9yr-1, 1.6x10-9yr-1 and 1.1x10-9yr-1, respectively. Similarly, the estimates of interplate strain accumulation between Antarctica and other plates Somalia (SEY1), Africa (HARO), Australia (YAR1), and diffuse plate boundary between India and Australia (COCO) are found to be 1.1x10-9yr-1, 1.0x10-10yr-1, 1.27x10-8yr-1 and 1.18x10-8yr-1, respectively. These estimates are in good agreement with the earlier studies on estimation of global strain rate. The combined GPS and seismic analysis confirm the emergence of diffuse plate boundary between India and Australia and relates to the late Miocene Himalayan uplift. The calculated stress field in the West of the Indian Peninsula has a roughly N-S directed tensional and E-W oriented compressional character and the velocity vectors of all other sites throw a significant insight into the plausible causes of the strain accumulation processes in the Indian Ocean and the northward movement of Indian plate.

  6. Normal and shear strains of the left ventricle in healthy human subjects measured by two-dimensional speckle tracking echocardiography

    PubMed Central

    2014-01-01

    Background Animal studies have shown that shear deformation of myocardial sheets in transmural planes of left ventricular (LV) wall is an important mechanism for systolic wall thickening, and normal and shear strains of the LV free wall differ from those of the interventricular septum (IVS). We sought to test whether these also hold for human hearts. Methods Thirty healthy volunteers (male 23 and female 7, aged 34 ± 6 years) from Outpatient Department of the University of Tokyo Hospital were included. Echocardiographic images were obtained in the left decubitus position using a commercially available system (Aloka SSD-6500, Japan) equipped with a 3.5-MHz transducer. The ECG was recorded simultaneously. The peak systolic radial normal strain (length change), shear strain (angle change) and time to peak systolic radial normal strain were obtained non-invasively by two-dimensional speckle tracking echocardiography. Results The peak systolic radial normal strain in both IVS and LV posterior wall (LVPW) showed a trend to increase progressively from the apical level to the basal level, especially at short axis views, and the peak systolic radial normal strain of LVPW was significantly greater than that of IVS at all three levels. The time to peak systolic radial normal strain was the shortest at the basal IVS, and increased progressively from the base to the apical IVS. It gradually increased from the apical to the basal LVPW in sequence, especially at short axis views. The peak of radial normal strain of LVPW occurred much later than the peak of IVS at all three levels. For IVS, the shear deformation was clockwise at basal level, and counterclockwise at mid and apical levels in LV long-axis view. For LVPW, the shear deformations were all counterclockwise in LV long-axis view and increased slightly from base to the apex. LVPW showed larger shear strains than IVS at all three levels. Bland-Altman analysis shows very good agreement between measurements taken by the

  7. Impact comminution of solids due to local kinetic energy of high shear strain rate: I. Continuum theory and turbulence analogy

    NASA Astrophysics Data System (ADS)

    Bažant, Zdeněk P.; Caner, Ferhun C.

    2014-03-01

    The modeling of high velocity impact into brittle or quasibrittle solids is hampered by the unavailability of a constitutive model capturing the effects of material comminution into very fine particles. The present objective is to develop such a model, usable in finite element programs. The comminution at very high strain rates can dissipate a large portion of the kinetic energy of an impacting missile. The spatial derivative of the energy dissipated by comminution gives a force resisting the penetration, which is superposed on the nodal forces obtained from the static constitutive model in a finite element program. The present theory is inspired partly by Grady's model for expansive comminution due to explosion inside a hollow sphere, and partly by analogy with turbulence. In high velocity turbulent flow, the energy dissipation rate gets enhanced by the formation of micro-vortices (eddies) which dissipate energy by viscous shear stress. Similarly, here it is assumed that the energy dissipation at fast deformation of a confined solid gets enhanced by the release of kinetic energy of the motion associated with a high-rate shear strain of forming particles. For simplicity, the shape of these particles in the plane of maximum shear rate is considered to be regular hexagons. The particle sizes are assumed to be distributed according to the Schuhmann power law. The condition that the rate of release of the local kinetic energy must be equal to the interface fracture energy yields a relation between the particle size, the shear strain rate, the fracture energy and the mass density. As one experimental justification, the present theory agrees with Grady's empirical observation that, in impact events, the average particle size is proportional to the (-2/3) power of the shear strain rate. The main characteristic of the comminution process is a dimensionless number Ba (Eq. (37)) representing the ratio of the local kinetic energy of shear strain rate to the maximum possible

  8. Draft Genome Sequence of Arenibacter sp. Strain C-21, an Iodine-Accumulating Bacterium Isolated from Surface Marine Sediment

    PubMed Central

    Ito, Kohei; Nakajima, Nobuyoshi; Yamamura, Shigeki; Tomita, Masaru

    2016-01-01

    Arenibacter sp. strain C-21, isolated from surface marine sediment of Japan, accumulates iodine in the presence of glucose and iodide (I-). We report here the draft genome sequence of this strain to provide insight into the molecular mechanism underlying its iodine-accumulating ability. PMID:27738047

  9. A New Fungal Isolate, Penidiella sp. Strain T9, Accumulates the Rare Earth Element Dysprosium

    PubMed Central

    Horiike, Takumi

    2015-01-01

    With an aim to develop a highly efficient method for the recovery of rare earth elements (REEs) by using microorganisms, we attempted to isolate dysprosium (Dy)-accumulating microorganisms that grow under acidic conditions from environmental samples containing high concentrations of heavy metals. One acidophilic strain, T9, which was isolated from an abandoned mine, decreased the concentration of Dy in medium that contained 100 mg/liter Dy to 53 mg/liter Dy after 3 days of cultivation at pH 2.5. The Dy content in the cell pellet of the T9 strain was 910 μg/mg of dry cells. The T9 strain also accumulated other REEs. Based on the results of 28S-D1/D2 rRNA gene sequencing and morphological characterization, we designated this fungal strain Penidiella sp. T9. Bioaccumulation of Dy was observed on the cell surface of the T9 strain by elemental mapping using scanning electron microscopy-energy dispersive X-ray spectroscopy. Our results indicate that Penidiella sp. T9 has the potential to recover REEs such as Dy from mine drainage and industrial liquid waste under acidic conditions. PMID:25710372

  10. A new fungal isolate, Penidiella sp. strain T9, accumulates the rare earth element dysprosium.

    PubMed

    Horiike, Takumi; Yamashita, Mitsuo

    2015-05-01

    With an aim to develop a highly efficient method for the recovery of rare earth elements (REEs) by using microorganisms, we attempted to isolate dysprosium (Dy)-accumulating microorganisms that grow under acidic conditions from environmental samples containing high concentrations of heavy metals. One acidophilic strain, T9, which was isolated from an abandoned mine, decreased the concentration of Dy in medium that contained 100 mg/liter Dy to 53 mg/liter Dy after 3 days of cultivation at pH 2.5. The Dy content in the cell pellet of the T9 strain was 910 μg/mg of dry cells. The T9 strain also accumulated other REEs. Based on the results of 28S-D1/D2 rRNA gene sequencing and morphological characterization, we designated this fungal strain Penidiella sp. T9. Bioaccumulation of Dy was observed on the cell surface of the T9 strain by elemental mapping using scanning electron microscopy-energy dispersive X-ray spectroscopy. Our results indicate that Penidiella sp. T9 has the potential to recover REEs such as Dy from mine drainage and industrial liquid waste under acidic conditions.

  11. Magnetism and Raman Spectroscopy of Pristine and Hydrogenated TaSe2 Monolayer tuned by Tensile and Pure Shear Strain

    NASA Astrophysics Data System (ADS)

    Chowdhury, Sugata; Simpson, Jeffrey; Einstein, T. L.; Walker, Angela R. Hight

    2D-materials with controllable optical, electronic and magnetic properties are desirable for novel nanodevices. Here we studied these properties for both pristine and hydrogenated TaSe2 (TaSe2-H) monolayer (ML) in the framework of DFT using the PAW method. We considered uniaxial and biaxial tensile strain, as well as shear strain along the basal planes in the range between 1% and 16%. Previous theoretical works (e.g.) considered only symmetrical biaxial tensile. Pristine ML is ferromagnetic for uniaxial tensile strain along ◯ or ŷ. For tensile strain in ŷ, the calculated magnetic moments of the Ta atoms are twice those for the same strain in ◯. Under pure shear strain (expansion along ŷ and compression along ◯), a pristine ML is ferromagnetic, but becomes non-magnetic when the strain directions are interchanged. Due to carrier-mediated double-exchange, the pristine ML is ferromagnetic when the Se-Ta-Se bond angle is < 82° and the ML thickness is < 3.25Å. We find that all Raman-active phonon modes show obvious red-shifting due to bond elongation and the E2 modes degeneracy is lifted as strain increases. For a TaSe2-H ML, the same trends were observed. Results show the ability to tune the properties of 2D-materials.

  12. High Shear Strain Behavior of Synthetic Muscovite Fault Gouges Under Hydrothermal Conditions

    NASA Astrophysics Data System (ADS)

    van Diggelen, E. W.; de Bresser, H. H.; Peach, C. J.; Spiers, C. J.

    2008-12-01

    Phyllosilicates are common constituents of mid-crustal fault zones and are widely believed to exert a strong influence on the strength of fault rocks, in particular around the brittle-ductile transition. The present study aims to experimentally determine the mechanical strength and frictional behaviour of muscovite gouge, in order to establish whether the presence of muscovite might contribute to the long term weakness often inferred to hold for large scale crustal fault zones. Rotary shear experiments in the temperature range 20-700°C, at 100 MPa fluid pressure, have been performed on synthetic muscovite gouges (average grain size 13 μm, < 10% quartz). The effects of sliding velocity, normal stress and shear strain on the frictional behavior of the muscovite gouges have been studied. Microstructural analysis of the experimentally deformed samples has been done using SEM and XED in order to obtain insight in the operating microphysical processes. The mechanical behavior under the conditions applied is independent of sliding velocity in the range 0.03-3.8 μm/s. The results show frictional behavior in samples deformed in velocity stepping experiments under 100 MPa normal stress with coefficients of friction of ~0.34 at 20°C, in agreement with previous data, gradually increasing to values of ~0.55 at 300°C, remaining around this value up to 600°C. During shear, samples compact continuously (15-20% at γ~25) at low temperatures (20-300°C). At higher temperatures, similar compaction is preceded by initial dilatation of up to 10%. The low temperature microstructures (< 300°C) show strong grain size reduction to form a well- foliated muscovite matrix (grain size < 2 μm) enclosing quartz and widespread muscovite porphyroclasts (~10 μm). Numerous shear bands in the Riedel and Y-shear orientations are present. Towards higher temperature, the microstructures are increasingly characterized by dense, elongate lenses (20-50 by 10 μm) of fine, folded and kinked grains

  13. Comparison of game-farm and wild-strain mallard ducks in accumulation of methylmercury

    USGS Publications Warehouse

    Heinz, G.H.

    1979-01-01

    The accumulation of mercury was compared in game-farm and wild-strain mallard ducks fed a diet containing 0.5 ppm mercury in the form of methylmercury dicyandiamide. There were no significant differences between the two strains in levels of mercury that accumulated in blood, kidney, liver, breast muscle, brain, eggs, or ducklings. Mercury levels in blood were significantly correlated with levels in other tissues and eggs, as were levels in down feathers of ducklings with levels in carcasses of ducklings. The results indicate that game-farm mallards are probably suitable substitutes for wild mallards in toxicological work, that blood samples can be used to estimate levels of mercury in other tissues of adults, and that down feathers are predictive of mercury levels in duckling carcasses.

  14. Small breast lesion classification performance using the normalized axial-shear strain area feature.

    PubMed

    Thittai, Arun K; Yamal, Jose-Miguel; Ophir, Jonathan

    2013-03-01

    Breast cancers that are found and confirmed because they are causing symptoms tend to be larger and are more likely to have already spread to the lymph nodes and beyond. Thus, early detection and confirmation are of paramount importance. The normalized axial-shear strain area (NASSA) feature from the axial-shear strain elastogram (ASSE) has been shown to be a feature that can identify the boundary-bonding conditions that are indicative of the presence of cancer. Recently, we investigated and reported on the potential of the NASSA feature for breast lesion classification into fibroadenomas and cancers. In this article, we investigate the size distribution of the lesions that were part of the previous study and analyze classification performance specifically on small lesions (<10 mm diameter). A total of 33 biopsy-proven malignant tumors and 30 fibroadenomas were part of the study that involved three observers blinded to the Breast Imaging Reporting and Data System (BIRADS) ultrasound scores. The observers outlined the lesions on the sonograms and the lesion size (maximum circle-equivalent diameter in millimeters) was computed from this outline. The ASSE was automatically segmented and color-overlaid on the sonogram, and the NASSA feature from ASSE was computed semi-automatically. Receiver operating characteristic curves were then generated for the subset of cases involving small lesions. Box plots were produced for the two different lesion size groups, small and large, from a logistic regression classifier that was built previously. The results of our study show that approximately 38% and 22% of the fibroadenomas and cancers, respectively, were small. Furthermore, it was found that the NASSA feature resulted in a perfect classification of the small lesions, both in the training data and in the cross-validation. For lesions <10 mm the difference in fibroadenoma and cancer mean scores was 0.73 ± 0.13 (p < 0.001), whereas lesions >10 mm had a difference of 0.52 ± 0

  15. Draft Genome Sequence of Halomonas sp. HG01, a Polyhydroxyalkanoate-Accumulating Strain Isolated from Peru

    PubMed Central

    Cardinali-Rezende, Juliana; Nahat, Rafael Augusto Teodoro Pereira de Souza; Guzmán Moreno, César Wilber; Carreño Farfán, Carmen Rosa; Silva, Luiziana Ferreira; Taciro, Marilda Keico

    2016-01-01

    Halomonas sp. strain HG01, isolated from a salt mine in Peru, is a halophilic aerobic heterotrophic bacterium accumulating poly-3-hydroxybutyrate and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from different carbon sources. Here, we report the draft genome sequence of this isolate, which was found to be 3,665,487 bp long, with a G+C content of 68%. PMID:26798101

  16. ETS Related Uplift and Strain Accumulation in Northern Cascadia from Tidal Records

    NASA Astrophysics Data System (ADS)

    Alba, S. K.; Weldon, R. J.; Livelybrooks, D.; Schmidt, D. A.; Krogstad, R.

    2011-12-01

    Vertical displacements, uplift rates between events, and net uplift rates spanning the most recent 12 episodic tremor and slip events (ETS) on the northern Cascadia Subduction Zone (between 1997 and 2010) have been determined from hourly water level records from 4 NOAA tide gauges (Neah Bay, Port Angeles, Port Townsend, and Seattle). Dense GPS networks have thus far been the primary means to characterize displacements and inter ETS strain rates associated with ETS that occurred beneath the Olympic Peninsula, WA [McGuire & Segall, 2003; Szeliga et al., 2004; Melbourne et al., 2005; Wang et al., 2008; McCaffrey, 2009; Schmidt & Gao, 2010]. However, GPS generally has poor vertical resolution so we are exploring the use of tidal records are used to improve estimates of vertical deformation and extend the observations to the pre GPS era. Vertical displacements are particularly useful in locating the downdip (and therefore inland) extent of slip, variations in the magnitude of slip on the slip patch, and for determining long term rates that span many ETS cycles. Tidal records were analyzed by removing shared ocean noise so that uncertainties largely depend upon distance to neighboring sites. In northern Cascadia displacements during individual events are on the order of millimeters with near centimeter uncertainties, whereas 12 event average displacements by site are resolved to ~1mm ( -1.19+/-0.95mm at Neah Bay, 2.85+/-0.74mm, Port Angeles, -2.05+/-0.76mm, Port Townsend, and 0.39+/-1.08mm at Seattle), and individual site averages generally agree with displacements inferred from modeling GPS data. The relationship between long term uplift, average vertical displacements during ETS and average uplift which occurs between events can indicate the style and distribution of strain accumulation. Examination of water level trends between events show an interseismic deformation rate approximately equal in magnitude but opposite in sign (although with greater uncertainties). This

  17. Pseudomonas mutant strains that accumulate androstane and seco-androstane intermediates from bile acids.

    PubMed Central

    Leppik, R A; Sinden, D J

    1987-01-01

    Transposon mutant strains which were affected in bile acid catabolism were isolated from four Pseudomonas spp. Two of the mutant groups isolated were found to accumulate 12 alpha-hydroxyandrosta-1,4-diene-3,17-dione as the major product from deoxycholic acid. Strains in one of these two groups were able to grow on steroids such as chenodeoxycholic acid, which lacks a 12 alpha-hydroxy function, whereas the one member of the second group could not. With chenodeoxycholic acid, this latter strain accumulated a yellow muconic-like derivative, tentatively identified as 3,7-dihydroxy-5,9,17-trioxo-4(5),9(10)-disecoandrosta-1(10)2 -dien-4-oic acid. Members of two further mutant groups accumulated either 12 beta-hydroxyandrosta-1,4-diene-3,17-dione or 3,12 beta-dihydroxy-9(10)-secoandrosta-1,3,5(10)-triene-9,17-dione as the major product from deoxycholic acid. The relationship between the catabolism of m- and p-cresol, 3-ethylphenol and the bile acids was also examined. PMID:3038076

  18. Clast Rotation and Nature of Strain Localization in Thick Ultramylonites: the El Pichao Shear Zone (Sierra de Quilmes), NW Argentina.

    NASA Astrophysics Data System (ADS)

    Hasalova, Pavlina; Hunter, Nicholas James; Weinberg, Roberto; Finch, Melanie

    2013-04-01

    Ultramylonite formation is integral to understanding the accommodation of high strain in ductile shear zones, mountain building and crustal movement. The El Pichao Shear Zone (PSZ) is 3-7km thick ductile thrust zone in the Sierra de Quilmes, NW Argentina. Sinistral thrusting along the PSZ has placed granulite facies migmatites of the Tolombón Complex on top of amphibolite metasedimentary rocks of the Agua del Sapo Complex, separated by a sheared granitic body intruded by pegmatites. The fabric varies from protomylonite to ultramylonite. Ultramylonites in the core of the shear zone reach ~1km in thickness. Ultramylonites of this thickness are extremely rare, and thus the El Pichao Shear Zone provides a unique opportunity to investigate the origin of such high strain rocks. We used microstructural and quantitative textural analysis, quartz crystallographic preferred orientation (CPO), clast vorticity and geochemical data to investigate the origin of the thick ultramylonites, and variable strain accommodation associated with the mylonitization process. The mylonitic rocks have granitic composition and consist of a matrix of Bt+Qtz+Ms+Pl+Kfs, Qtz ribbons, mica bands and feldspar porphyroclasts. Feldspar clasts have been variably rotated and their deformation behaviour varies between brittle faulting and partial to complete dynamic recrystallisation. In the ultramylonite Qtz ribbons or strong S-C fabrics are lacking and the matrix tends to be homogeneous with only weak foliation defined by the preferred orientation of micas. There is also a systematic decrease in matrix grain size and mica connectivity towards ultramylonite. Quartz CPO suggests changes in deformation mechanisms associated with strain increase. The transition between mylonite and ultramylonite in the PSZ occurred due to a switch from dominant dislocation creep to dominant diffusion creep. Major and trace element data show no geochemical variation between samples, indicating that the mylonite

  19. Studies of Shear Band Velocity Using Spatially and Temporally Resolved Measurements of Strain During Quasistatic Compression of Bulk Metallic Glass

    SciTech Connect

    Wright, W J; Samale, M; Hufnagel, T; LeBlanc, M; Florando, J

    2009-06-15

    We have made measurements of the temporal and spatial features of the evolution of strain during the serrated flow of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass tested under quasistatic, room temperature, uniaxial compression. Strain and load data were acquired at rates of up to 400 kHz using strain gages affixed to all four sides of the specimen and a piezoelectric load cell located near the specimen. Calculation of the displacement rate requires an assumption about the nature of the shear displacement. If one assumes that the entire shear plane displaces simultaneously, the displacement rate is approximately 0.002 m/s. If instead one assumes that the displacement occurs as a localized propagating front, the velocity of the front is approximately 2.8 m/s. In either case, the velocity is orders of magnitude less than the shear wave speed ({approx}2000 m/s). The significance of these measurements for estimates of heating in shear bands is discussed.

  20. Investigation of high-speed free shear flows using improved pressure-strain correlated Reynolds stress turbulence model

    NASA Technical Reports Server (NTRS)

    Tiwari, S. N.; Lakshmanan, B.

    1993-01-01

    A high-speed shear layer is studied using compressibility corrected Reynolds stress turbulence model which employs newly developed model for pressure-strain correlation. MacCormack explicit prediction-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 prediction of the normalized streamwise stress and Reynolds shear stress. The computed results are in good agreement with the experimental data.

  1. Strain localization in brittle-ductile shear zones: fluid abundant vs fluid limited conditions (an example from Wyangala area, Australia)

    NASA Astrophysics Data System (ADS)

    Spruzeniece, L.; Piazolo, S.

    2015-04-01

    This study focuses on physiochemical processes occurring in a brittle-ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia), a coarse-grained two feldspar-quartz-biotite granite is transformed into a medium grained orthogneiss at the shear zone margins and a fine-grained quartz-muscovite phyllonite in the central parts. The orthogneiss displays cataclasis of feldspar and crystal-plastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized showing distinct crystallographic preferred orientation (CPO). Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts, in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data shows a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high and low strain fabrics represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. We suggest that the fabrics and mineralogical changes in the shear zone centre have formed due to fluid influx probably along an initially brittle fracture. Here, hydration reactions dramatically changed the rheological properties of the rock. In the newly produced muscovite-quartz layers creep cavitation associated with grain boundary sliding and

  2. Role of Cations in Accumulation and Release of Phosphate by Acinetobacter Strain 210A

    PubMed Central

    van Groenestijn, Johan W.; Vlekke, Gerard J. F. M.; Anink, Désirée M. E.; Deinema, Maria H.; Zehnder, Alexander J. B.

    1988-01-01

    Cells of the strictly aerobic Acinetobacter strain 210A, containing aerobically large amounts of polyphosphate (100 mg of phosphorus per g [dry weight] of biomass), released in the absence of oxygen 1.49 mmol of Pi, 0.77 meq of Mg2+, 0.48 meq of K+, 0.02 meq of Ca2+, and 0.14 meq of NH4+ per g (dry weight) of biomass. The drop in pH during this anaerobic phase was caused by the release of 1.8 protons per PO43− molecule. Cells of Acinetobacter strain 132, which do not accumulate polyphosphate aerobically, released only 0.33 mmol of Pi and 0.13 meq of Mg2+ per g (dry weight) of biomass but released K+ in amounts comparable to those released by strain 210A. Stationary-phase cultures of Acinetobacter strain 210A, in which polyphosphate could not be detected by Neisser staining, aerobically took up phosphate simultaneously with Mg2+, the most important counterion in polyphosphate. In the absence of dissolved phosphate in the medium, no Mg2+ was taken up. Cells containing polyphosphate granules were able to grow in a Mg-free medium, whereas cells without these granules were not. Mg2+ was not essential as a counterion because it could be replaced by Ca2+. The presence of small amounts of K+ was essential for polyphosphate formation in cells of strain 210A. During continuous cultivation under K+ limitation, cells of Acinetobacter strain 210A contained only 14 mg of phosphorus per g (dry weight) of biomass, whereas this element was accumulated in amounts of 59 mg/g under substrate limitation and 41 mg/g under Mg2+ limitation. For phosphate uptake in activated sludge, the presence of K+ seemed to be crucial. PMID:16347788

  3. Scaling of viscous shear zones with depth-dependent viscosity and power-law stress-strain-rate dependence

    NASA Astrophysics Data System (ADS)

    Moore, James D. P.; Parsons, Barry

    2015-07-01

    One of the unresolved questions concerning fault deformation is the degree and cause of localization of shear at depth beneath a fault. Geologic observations of exhumed shear zones indicate that while the motion is no longer planar, it can still be localized near the down-dip extension of the fault; however, the degree of localization is uncertain. We employ simple analytic and numerical models to investigate the structural form of distributed shear beneath a strike-slip fault, and the relative importance of the physical mechanisms that have the potential to localize a shear zone. For a purely depth dependent viscosity, η = η0 exp (-z/z0), we find that a shear zone develops with a half-width δ _w˜ √{z_0} for small z0 at the base of the layer, where lengths are non-dimensionalized by the layer thickness (d km). Including a non-linear stress-strain-rate relation (dot{ɛ }∝ σ ^n) scales δw by 1/√{n}, comparable to deformation length scales in thin viscous sheet calculations. We find that the primary control on the shear-zone width is the depth dependence of viscosity that arises from the temperature dependence of viscosity and the increase in temperature with depth. As this relationship is exponential, scaling relations give a dimensional half-width that scales approximately as tilde{δ}_w≈ T_{1/2}√{Rd/nQβ } km, where T_{1/2} (K) is the temperature at the midpoint of the layer, R (J mol-1 K-1) the gas constant, Q (J mol-1) the activation energy and β (K km-1) the geothermal gradient. This relation predicts the numerical results for the parameter range consistent with continental rheologies to within 2-5 per cent and shear-zone half-widths from 2 to 6 km. The inclusion of shear-stress heating reduces δw by only an additional 5-25 per cent, depending on the initial width of the shear zone. While the width of the shear zone may not decrease significantly, local temperature increases from shear-stress heating range from 50 to 300 °C resulting in a

  4. Characterization of a S-adenosyl-l-methionine (SAM)-accumulating strain of Scheffersomyces stipitis.

    PubMed

    Križanović, Stela; Butorac, Ana; Mrvčić, Jasna; Krpan, Maja; Cindrić, Mario; Bačun-Družina, Višnja; Stanzer, Damir

    2015-06-01

    S-adenosyl-l-methionine (SAM) is an important molecule in the cellular metabolism of mammals. In this study, we examined several of the physiological characteristics of a SAM-accumulating strain of the yeast Scheffersomyces stipitis (M12), including SAM production, ergosterol content, and ethanol tolerance. S. stipitis M12 accumulated up to 52.48 mg SAM/g dry cell weight. Proteome analyses showed that the disruption of C-24 methylation in ergosterol biosynthesis, a step mediated by C-24 sterol methyltransferase (Erg6p), results in greater SAM accumulation by S. stipitis M12 compared to the wild-type strain. A comparative proteome-wide analysis identified 25 proteins that were differentially expressed by S. stipitis M12. These proteins are involved in ribosome biogenesis, translation, the stress response, ubiquitin-dependent catabolic processes, the cell cycle, ethanol tolerance, posttranslational modification, peroxisomal membrane stability, epigenetic regulation, the actin cytoskeleton and cell morphology, iron and copper homeostasis, cell signaling, and energy metabolism.

  5. Patulin Accumulation In Apples During Storage by Penicillium Expansum and Penicillium Griseofulvum Strains

    PubMed Central

    Welke, Juliane Elisa; Hoeltz, Michele; Dottori, Horacio Alberto; Noll, Isa Beatriz

    2011-01-01

    A part of apples destined to juice production is generally of poor quality. Apples from cold storage or recently harvest (ground harvested or low quality apples) are stored under ambient conditions until they are processed. Since Penicillium expansum and P. griseofulvum are the principal fungal species isolated from stored apples in Brazil, the objective of this study was to investigate the ability of these strains to produce patulin in apples and report the consequences of this type of storage in loss of quality. The toxin was quantified using thin layer chromatography and charge-coupled device camera (TLC-CCD). The rate and quantities that P. expansum and P. griseofulvum can grow and produce patulin are highly dependent on the fungal strain and time. Lesion diameter resulted to be independent of the strain considered. The maximum period of time which apples were kept at cold storage (4 °C) without patulin accumulation was 27 days. When these apples were kept at 25 °C during 3 days, both factors lesion diameter and patulin production increased significantly. These results confirm that time in which apples are taken out from cold storage room before juice production is critical in order to prevent patulin accumulation. PMID:24031618

  6. Single myosin cross-bridge orientation in cardiac papillary muscle detects lever-arm shear strain in transduction.

    PubMed

    Burghardt, Thomas P; Josephson, Matthew P; Ajtai, Katalin

    2011-09-13

    Myosin motors transduce ATP free energy into mechanical work. Transduction models allocate specific functions to motor structural domains beginning with ATP hydrolysis in the active site and ending in a lever-arm rotating power-stroke. Myosin light chains, regulatory (RLC) and essential (ELC), bind IQ-domains on the lever-arm and track its movement. Strong evidence exists that light chains stabilize the lever-arm and that light chain mutation undermines stability. Human ventricular RLC tagged with photoactivatable GFP (HCRLC-PAGFP) replaces native RLC in porcine papillary muscle fibers, restores native contractility, and situates PAGFP for single molecule orientation tracking within the crowded fiber lattice. The spatial emission pattern from single photoactivated PAGFP tagged myosins was observed in z-stacks fitted simultaneously to maximize accuracy in estimated dipole orientation. Emitter dipole polar and azimuthal angle pair scatter plots identified an area where steric and molecular crowding constraints depopulated orientations unfavorable for actin interaction. Transitions between pre- and post-power-stroke states represent the lever-arm trajectory sampled by the data and quantify lever-arm shear strain in transduction at three tension levels. These data identify forces acting on myosin in the in situ fiber system due to crowding, steric hindrance, and actomyosin interaction. They induce lever-arm shear strain observed with single molecule orientation detection. A single myosin work histogram reveals discretized power-stroke substates reminiscent of the Huxley-Simmons model for myosin based contraction [Huxley and Simmons ( 1971 ) Nature 233 , 533]. RLC or ELC mutation, should it impact lever-arm shear strain, will be detected as changes in single myosin shear strain or power-stroke substate distribution.

  7. 20th-Century Strain Accumulation on the Lesser Antilles Megathrust Based on Coral Microatolls

    NASA Astrophysics Data System (ADS)

    Philibosian, B.; Feuillet, N.; Jacques, E.; Weil Accardo, J.; Meriaux, A. S. B.; Guihou, A.; Anglade, A.

    2015-12-01

    The Lesser Antilles subduction zone forms the eastern boundary of the Caribbean plate. The seismic potential of the megathrust remains poorly known, despite the hazard it poses to numerous island populations and its proximity to the Americas. As it has not produced any large earthquakes in modern times, the megathrust has often been assumed to be aseismic. However, historical records of great earthquakes in the 19th century and earlier, which were almost certainly megathrust ruptures, demonstrate that the subduction is not entirely aseismic. Recent occurrences of giant earthquakes in areas where such events were previously thought to be impossible have inspired the geoscience community to re-evaluate the seismic potential of other "low-hazard" subduction zones, such as the Lesser Antilles. Using the method of coral microatoll paleogeodesy developed in Sumatra, we examine 20th-century vertical deformation on the forearc islands of the Lesser Antilles and model the underlying strain accumulation on the megathrust. Our data indicate that the eastern coasts of the forearc islands have been subsiding relative to the arc islands, suggesting that on the time scale of the 20th century, a portion of the megathrust just east of the forearc islands has been locked. Our findings are in contrast to recent GPS-based models that suggest little or no strain accumulation anywhere along the Lesser Antilles megathrust. This discrepancy is potentially explained by the different time scales of measurement, as recent studies elsewhere have indicated that interseismic coupling patterns may vary on decadal time scales and that century-scale or longer records are required to accurately assess seismic potential. The accumulated strain we have detected will likely be released in future earthquakes, uplifting the previously subsiding areas as well as contributing to seismic and potentially to tsunami hazard in the region.

  8. Transient rheological behavior of natural polysaccharide xanthan gum solutions in start-up shear flow fields: An experimental study using a strain-controlled rheometer

    NASA Astrophysics Data System (ADS)

    Lee, Ji-Seok; Kim, Yong-Seok; Song, Ki-Won

    2015-08-01

    The objective of the present study is to experimentally investigate the transient rheological behavior of concentrated xanthan gum solutions in start-up shear flow fields. Using a strain-controlled rheometer, a number of constant shear rates were suddenly imposed to aqueous xanthan gum solutions with different concentrations and the resultant shear stress responses were measured with time. The main findings obtained from this study can be summarized as follows: (1) For all shear rates imposed, however low it may be, the shear stress is rapidly increased with time (stress overshoot) upon inception of steady shear flow before passing through the maximum stress value and then gradually decreased with time (stress decay) until reaching a steady state flow. (2) As the imposed shear rate is increased, a more pronounced stress overshoot takes place and the maximum stress value becomes larger, whereas both times at which the maximum stress is observed and needed to reach a steady state flow are shortened. (3) The maximum shear stress is linearly increased with shear rate in a double logarithmic scale and becomes larger with increasing concentration at equal shear rates. In addition, the time at which the maximum stress occurs exhibits a linear relationship with the inverse of shear rate in a double logarithmic scale for all xanthan gum solutions, regardless of their concentrations. (4) The shear stress is sharply increased with an increase in strain until reaching the maximum stress at small range of deformations. The maximum stress is observed at similar strain values, irrespective of the imposed shear rates lower than 10 1/s. (5) The Bird-Leider model can be successfully used with regard to quantitatively predicting the transient behavior of concentrated xanthan gum solutions. However, this model has a fatal weakness in terms of describing a decrease in shear stress (stress decay).

  9. Present-day Block Motions and Strain Accumulation on Active Faults in the Caribbean

    NASA Astrophysics Data System (ADS)

    Symithe, S. J.; Calais, E.; Freed, A. M.

    2014-12-01

    The quasi-frontal subduction of the north and south American plates under the Lesser Antilles and the left and right lateral strike-slip along the northern and southern margins of the Caribbean plate offer the opportunity to study the transition from subduction to strike-slip between major plates. In addition, the segmentation and degree of interplate coupling at the Lesser Antilles subduction is key to our understanding of the earthquake potential of a subduction whose length is similar to the rupture area of the Mw9.0, 2011, Tohoku earthquake in Japan. We used the block modeling approach described in Meade and Loveless (2009) to test the optimal block geometry for the northern, eastern and southern boundaries of the Caribbean plate. We solved for angular velocities for each block/plate and strain accumulation rates for all major faults in the region. Then we calculated the variations in interplate coupling along the subduction plate boundaries using the accumulated strain rates. We tested 11 different block geometries; they are all based on geological evidences unless they are suggested by discrepancies within the GPS and seismological data or by previously published results. We confirm the existence of the micro Gonave plate. The boundary between the Micro-Gonave plate and the Hispaniola crustal block is better suited along the Haitian-Thrust-Belt instead of the Neiba-Matheux fault. The interseismic GPS velocities do not show evidence for a distinct North Lesser Antilles block. We found a totally uncoupled section of the subduction starting from the Puerto-Rico trench to the end of the Lesser Antilles section. All the relative motion of the Caribbean block is lost aseismically along the boundary of that portion of the subduction. While we found strong coupling along the northern Hispaniola section, most of the deformation on this region is being accumulated along intrablock faults with very low strain (~2mm/yr) along the intraplate subduction interface. We also

  10. Strain accumulation in the Shumagin Islands: Results of initial GPS measurements

    NASA Technical Reports Server (NTRS)

    Larson, Kristine M.; Lisowski, Michael

    1994-01-01

    Deformation in the Shumagin seismic gap has been monitored with repeated trilateration (EDM) in the 1980-1987 interval and with the Global Positioning System (GPS) in the 1987-1991 interval. The geodetic network extends for 100-km across the Shumagin Islands to the Alaska Peninsula. Results from the GPS surveys are consistent with those previously reported for the EDM surveys: we failed to detect significant strain accumulation in the N30 deg W direction of plate convergence. Using the method of simultaneous reduction for position and strain rates, we found the average rate of extension in the direction of plate convergence to be -25 +/- 25 nanostrain/yr (nstrain/yr) during the 1987-1991 interval of GPS surveys compared with -20 +/- 15 nstrain/yr during the 1981-1987 interval of complete EDM surveys. We found a marginally significant -26 +/- 12 nstrain/yr extension rate in the 1981-1991 interval covered by the combined EDM and GPS surveys. Strain rates are higher, but not significantly so, in the part of the network closest to the trench. Spatial variation in the deformation is observed in the 1980-1991 average station velocities, where three of the four stations closest to the trench have an arcward velocity of a few mm/yr. The observed strain rates are an order of magnitude lower than the -200 nstrain/yr rate predicted by dislocation models.

  11. Using Local Second Gradient Model and Shear Strain Localisation to Model the Excavation Damaged Zone in Unsaturated Claystone

    NASA Astrophysics Data System (ADS)

    Pardoen, Benoît; Levasseur, Séverine; Collin, Frédéric

    2015-03-01

    The drilling of galleries induces damage propagation in the surrounding medium and creates, around them, the excavation damaged zone (EDZ). The prediction of the extension and fracture structure of this zone remains a major issue, especially in the context of underground nuclear waste storage. Experimental studies on geomaterials indicate that localised deformation in shear band mode usually appears prior to fractures. Thus, the excavation damaged zone can be modelled by considering the development of shear strain localisation bands. In the classical finite element framework, strain localisation suffers a mesh-dependency problem. Therefore, an enhanced model with a regularisation method is required to correctly model the strain localisation behaviour. Among the existing methods, we choose the coupled local second gradient model. We extend it to unsaturated conditions and we include the solid grain compressibility. Furthermore, air ventilation inside underground galleries engenders a rock-atmosphere interaction that could influence the damaged zone. This interaction has to be investigated in order to predict the damaged zone behaviour. Finally, a hydro-mechanical modelling of a gallery excavation in claystone is presented and leads to a fairly good representation of the EDZ. The main objectives of this study are to model the fractures by considering shear strain localisation bands, and to investigate if an isotropic model accurately reproduces the in situ measurements. The numerical results provide information about the damaged zone extension, structure and behaviour that are in very good agreement with in situ measurements and observations. For instance, the strain localisation bands that develop in chevron pattern during the excavation and rock desaturation, due to air ventilation, are observed close to the gallery.

  12. An Analysis of Strain Accumulation in the Western Part of Black Sea Region in Turkey

    NASA Astrophysics Data System (ADS)

    Deniz, I.; Avsar, N. B.; Deniz, R.; Mekik, C.; Kutoglu, S.

    2014-12-01

    Turkish National Horizontal Control Network (TNHCN) based on the European Datum 1950 (ED50) was used as the principal geodetic network until 2005 in Turkey. Since 2005, Turkish Large Scale Map and Map Information Production Regulation have required that that all the densification points have been produced within the same datum of Turkish National Fundamental GPS Network (TNFGN) put into practise in 2002 and based on International Terrestrial Reference Frame (ITRF). Hence, the common points were produced in both European Datum 1950 (ED50), and TNFGN.It is known that the geological and geophysical information about the network area can be obtained by the evaluation of the coordinate and scale variations in a geodetic network. For one such evaluation, the coordinate variations and velocities of network points, and also the strains are investigated. However, the principal problem in derivation of velocities arises from two different datums. In this context, the computation of velocities using the coordinate data of the ED50 and TNFGN is not accurate and reliable. Likewise, the analysis of strain from the coordinate differences is not reliable. However, due to the fact that the scale of a geodetic network is independent from datum, the strains can be derived from scale variations accurately and reliably.In this study, a test area limited 39.5°-42.0° northern latitudes and 31.0°-37.0° eastern longitudes was chosen. The benchmarks in this test area are composed of 30 geodetic control points derived with the aim of cadastral and engineering applications. We used data mining to investigate the common benchmarks in both reference systems for this area. Accordingly, the ED50 and TNFGN coordinates refer 1954 and 2005, respectively. Thus, it has been investigated the strain accumulation of 51 years in this region. It should be also noted that since 1954, the earthquakes have not registered greater than magnitude 6.0 in the test area. It is a considerable situation for this

  13. Elastic and Inelastic Strain Accumulation Along the Northern and Central Itoigawa-Shizuoka Tectonic Line, Central Japan

    NASA Astrophysics Data System (ADS)

    Teratani, N.; Sagiya, T.; Nishimura, T.; Yarai, H.; Suito, H.

    2014-12-01

    Itoigawa-Shizuoka Tectonic Line (ISTL) in central Japan is one of the most active fault systems in Japan. The Japanese government evaluated a M8 class earthquake may occur at the Gofukuji fault in the central ISTL with a possibility of 14% in the next 30 years. So we analyze GPS data around the northern and the central ISTL to monitor tectonic strain accumulation and to propose a fault model for future earthquake in this area. Along the northern and central ISTL, there exist active faults such as the Kamishiro fault (KF), the East Mathumoto Basin fault (EMBF) and the Gofukuji fault (GF). KF and EMBF are east-dipping reverse faults, and GF is a left-lateral strike slip fault. We analyzed GPS data of 34 campaign sites during 2002-2010 and 55 continuous sites during 1998-2013 to obtain 3-dimentional velocities in the ITRF 2008 reference frame. Around GF, the velocity field represents a typical inter-seismic pattern around a strike slip fault. By applying an elastic dislocation model, we estimate a fault slip rate as 5-7 mm/yr with a locking depth of over 5 km. These parameters are consistent with the seismogenic zone depth and the geological slip rate of GF. On the other hand, for KF and EMBF, we model the deformation pattern with faults in an elastic layer overlying a viscoelastic substratum to represent steady contraction. The modeling result shows KF dips at 30-40 degree and its locking depth is only 2 km, implying that the whole fault is creeping. EMBF dips at 40-50 degree with a locking depth of 2 km. The results indicate that there is ongoing stress accumulation around GF, but KF and EMBF accommodates contraction inelastically. GF at the central ISTL is considered to store strain energy more than 1.000 years and a future major earthquake should occur to release shear stress along the central part. The rupture may continue to the south, but more observation and modeling effect is necessary.

  14. Slip distribution, strain accumulation and aseismic slip on the Chaman Fault system

    NASA Astrophysics Data System (ADS)

    Amelug, F.

    2015-12-01

    The Chaman fault system is a transcurrent fault system developed due to the oblique convergence of the India and Eurasia plates in the western boundary of the India plate. To evaluate the contemporary rates of strain accumulation along and across the Chaman Fault system, we use 2003-2011 Envisat SAR imagery and InSAR time-series methods to obtain a ground velocity field in radar line-of-sight (LOS) direction. We correct the InSAR data for different sources of systematic biases including the phase unwrapping errors, local oscillator drift, topographic residuals and stratified tropospheric delay and evaluate the uncertainty due to the residual delay using time-series of MODIS observations of precipitable water vapor. The InSAR velocity field and modeling demonstrates the distribution of deformation across the Chaman fault system. In the central Chaman fault system, the InSAR velocity shows clear strain localization on the Chaman and Ghazaband faults and modeling suggests a total slip rate of ~24 mm/yr distributed on the two faults with rates of 8 and 16 mm/yr, respectively corresponding to the 80% of the total ~3 cm/yr plate motion between India and Eurasia at these latitudes and consistent with the kinematic models which have predicted a slip rate of ~17-24 mm/yr for the Chaman Fault. In the northern Chaman fault system (north of 30.5N), ~6 mm/yr of the relative plate motion is accommodated across Chaman fault. North of 30.5 N where the topographic expression of the Ghazaband fault vanishes, its slip does not transfer to the Chaman fault but rather distributes among different faults in the Kirthar range and Sulaiman lobe. Observed surface creep on the southern Chaman fault between Nushki and north of City of Chaman, indicates that the fault is partially locked, consistent with the recorded M<7 earthquakes in last century on this segment. The Chaman fault between north of the City of Chaman to North of Kabul, does not show an increase in the rate of strain

  15. Estimating Strain Accumulation in the New Madrid and Wabash Valley Seismic Zones

    NASA Astrophysics Data System (ADS)

    Craig, T. J.; Calais, E.

    2014-12-01

    The mechanical behaviour -- and hence earthquake potential -- of faults in continental interiors is a question of critical importance for the resultant seismic hazard, but no consensus has yet been reached on this controversial topic. The debate has focused on the central and eastern United States, in particular the New Madrid Seismic Zone, struck by three magnitude 7 or greater earthquakes in 1811--1812, and to a lesser extent the Wabash Valley Seismic Zone just to the north. A key aspect of this issue is the rate at which strain is currently accruing on those faults in the plate interior, a quantity that remains debated. Understanding if the present-day strain rates indicate sufficient motion to account for the historical and paleoseismological earthquakes by steady-state fault behaviour, or if strain accumulation is time-dependent in this area, is critical for investigating the causative process driving this seismicity in the plate interior, and how regional strain reflects the interplay between stresses arising from different geological processes. Here we address this issue with an analysis of up to 14 years of continuous GPS data from a network of 200 sites in the central United States centred on the New Madrid and Wabash Valley seismic zones. We find that high-quality sites in these regions show motions that are consistently within the 95% confidence limit of zero deformation relative to a rigid background. These results place an upper bound on regional strain accrual of 0.2 mm/yr and 0.5 mm/yr in the New Madrid and Wabash Valley Seismic Zones, respectively. These results, together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors, indicate that either tectonic loading rates or fault properties vary with time in the NMSZ and possibly plate-wide.

  16. Lipid accumulation by oleaginous and non-oleaginous yeast strains in nitrogen and phosphate limitation.

    PubMed

    Kolouchová, Irena; Maťátková, Olga; Sigler, Karel; Masák, Jan; Řezanka, Tomáš

    2016-09-01

    We investigated the possibility of utilizing both oleaginous yeast species accumulating large amounts of lipids (Yarrowia lipolytica, Rhodotorula glutinis, Trichosporon cutaneum, Candida sp.) and traditional biotechnological non-oleaginous ones characterized by high biomass yield (Kluyveromyces polysporus, Torulaspora delbrueckii, Saccharomyces cerevisiae) as potential producers of biofuel-utilizable and nutritionally valuable lipids. The main objective was to increase lipid accumulation by increasing C/P ratio together with higher C/N ratio, while maintaining high biomass yield. The C/N ratio of 30 was found to lead to higher biomass content and the total lipid content increased significantly with higher C/P ratio. With higher ratios of both C/N and C/P, the content of monounsaturated fatty acids (FAs) in cell lipids increased while polyunsaturated FAs decreased. Oleaginous yeast species had a lower proportion of unsaturated FAs (approx. 80 %) than non-oleaginous strains (approx. 90 %). At a C/N ratio of 30 and C/P ratio 1043, T. cutaneum produced a high amount of ω-6 unsaturated linoleic acid, the precursor of some prostaglandins, leukotrienes, and thromboxanes, while Candida sp. and K. polysporus accumulated a high content of palmitoleic acid.

  17. Rheology and microstructure of non-Brownian suspensions in the liquid and crystal coexistence region: strain stiffening in large amplitude oscillatory shear.

    PubMed

    Lee, Young Ki; Nam, Jaewook; Hyun, Kyu; Ahn, Kyung Hyun; Lee, Seung Jong

    2015-05-28

    Concentrated hard-sphere suspensions in the liquid and crystal coexistence region show a unique nonlinear behavior under a large amplitude oscillatory shear flow, the so-called strain stiffening, in which the viscosity or modulus suddenly starts to increase near a critical strain amplitude. Even though this phenomenon has been widely reported in experiments, its key mechanism has never been investigated in a systematic way. To have a good understanding of this behavior, a numerical simulation was performed using the lattice Boltzmann method (LBM). Strain stiffening was clearly observed at large strain amplitudes, and the critical strain amplitude showed an angular frequency dependency. The distortion of the shear stress appeared near the critical strain amplitude, and the nonlinear behavior was quantified by the Fourier transformation (FT) and the stress decomposition methods. Above the critical strain amplitude, an increase in the global bond order parameter Ψ(6) was observed at the flow reversal. The maximum of Ψ(6) and the maximum shear stress occurred at the same strain. These results show how strongly the ordered structure of the particles is related to the stress distortion. The ordered particles maintained a bond number of "two" with alignment with the compressive axis, and they were distributed over a narrow range of angular distribution (110°-130°). In addition, the ordered structure was formed near the lowest shear rate region (the flow reversal). The characteristics of the ordered structure were remarkably different from those of the hydroclusters which are regarded as the origin of shear thickening. It is clear that strain stiffening and shear thickening originate from different mechanisms. Our results clearly demonstrate how the ordering of the particles induces strain stiffening in the liquid and crystal coexistence region.

  18. Identifying shear transformation zones in amorphous solids via a virtual strain method

    NASA Astrophysics Data System (ADS)

    Falk, Michael; Patinet, Sylvain

    One outstanding problem in the mechanical response of amorphous solids is the identification of flow defect sites, so called shear transformation zones (STZs), a priori in the structure. Many methods have been utilized in order to predict local STZ sites including short-range order, soft-mode analysis and machine learning. Here we directly probe local regions of the material via shear in order to detect nearby saddle points that can result in transformations. This non-perturbative method gives excellent correlation with global shear of the system. It also provides a means to cross-correlate the existence of such local transition pathways with other proposed diagnostics such as the soft-spot method of Manning and Liu. We use the information gained by this method to consider the coarse-graining necessary to connect atomistic methods to continuum theories.

  19. Correlation of data on strain accumulation adjacent to the San Andreas Fault with available models

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald L.

    1986-01-01

    Theoretical and numerical studies of deformation on strike slip faults were performed and the results applied to geodetic observations performed in the vicinity of the San Andreas Fault in California. The initial efforts were devoted to an extensive series of finite element calculations of the deformation associated with cyclic displacements on a strike-slip fault. Measurements of strain accumulation adjacent to the San Andreas Fault indicate that the zone of strain accumulation extends only a few tens of kilometers away from the fault. There is a concern about the tendency to make geodetic observations along the line to the source. This technique has serious problems for strike slip faults since the vector velocity is also along the fault. Use of a series of stations lying perpendicular to the fault whose positions are measured relative to a reference station are suggested to correct the problem. The complexity of faulting adjacent to the San Andreas Fault indicated that the homogeneous elastic and viscoelastic approach to deformation had serious limitations. These limitation led to the proposal of an approach that assumes a fault is composed of a distribution of asperities and barriers on all scales. Thus, an earthquake on a fault is treated as a failure of a fractal tree. Work continued on the development of a fractal based model for deformation in the western United States. In order to better understand the distribution of seismicity on the San Andreas Fault system a fractal analog was developed. The fractal concept also provides a means of testing whether clustering in time or space is a scale-invariant process.

  20. Application of strain analysis to estimate pressure solution processes in regional shear zones

    NASA Astrophysics Data System (ADS)

    Voytenko, V. N.; Khlebalin, I. Yu.; Senotrusov, V. A.

    2016-01-01

    This paper considers the basic principles of the strain analysis method based on the analysis of antitaxial regeneration fibrous fringes around linear rigid inclusions in a low-viscosity rock matrix. This method has been developed for pressure shadows composed of fibrous minerals, whose orientation is controlled by the major elongation direction rather than the orientation of rigid inclusions. This approach is applicable only for rocks exposed to uniform coaxial straining. The strain ellipse is calculated in two ways: for three variably oriented strain markers, it is calculated using Mohr's circles, and for numerous strain markers by average body ellipse. The strain ellipsoid is calculated using the parameters of a few strain ellipses calculated with three and more non-parallel planes. This paper provides the data on the method testing in reference sites of Dora-Pil' ore field in the Upper Indigirka district and Vangash area in the Yenisei Range. Regeneration fibrous fringes around fragments of fern fossils and linear rutile metacrystals were used as markers. The results of strain analysis obtained for the reference sites in the Upper Indigirka district made it possible to describe the signs of variable strain stages of developing strike-slip zones making up the Adycha-Taryn Fault Zone. Sublatitudinal ore-bearing strike-slip zones are characterized by a subvertical orientation of the elongation axes X of elongated strain ellipsoids, which are subperpendicular to quartz-carbonate veins and slope kink zones. NW-trending strike-slip zones are characterized by subhorizontal orientation of the Z shortening axes of flattened strain ellipsoids, which are subparallel to the normals of quartz-carbonate veins and veinlets. The results of strain analysis obtained for reference sites in the Vangash area made it possible to describe the thrust strain environment following the metamorphism stage and to reveal specific features in the formation of the strain textures of ore

  1. Accumulation of a bioactive benzoisochromanequinone compound kalafungin by a wild type antitumor-medermycin-producing streptomycete strain.

    PubMed

    Lü, Jin; He, Qiang; Huang, Luyao; Cai, Xiaofeng; Guo, Wenwen; He, Jing; Zhang, Lili; Li, Aiying

    2015-01-01

    Medermycin and kalafungin, two antibacterial and antitumor antibiotics isolated from different streptomycetes, share an identical polyketide skeleton core. The present study reported the discovery of kalafungin in a medermycin-producing streptomycete strain for the first time. A mutant strain obtained through UV mutagenesis showed a 3-fold increase in the production of this antibiotic, compared to the wild type strain. Heterologous expression experiments suggested that its production was severely controlled by the gene cluster for medermycin biosynthesis. In all, these findings suggested that kalafungin and medermycin could be accumulated by the same streptomycete and share their biosynthetic pathway to some extent in this strain. PMID:25695632

  2. Accumulation of a Bioactive Benzoisochromanequinone Compound Kalafungin by a Wild Type Antitumor-Medermycin-Producing Streptomycete Strain

    PubMed Central

    Lü, Jin; He, Qiang; Huang, Luyao; Cai, Xiaofeng; Guo, Wenwen; He, Jing; Zhang, Lili; Li, Aiying

    2015-01-01

    Medermycin and kalafungin, two antibacterial and antitumor antibiotics isolated from different streptomycetes, share an identical polyketide skeleton core. The present study reported the discovery of kalafungin in a medermycin-producing streptomycete strain for the first time. A mutant strain obtained through UV mutagenesis showed a 3-fold increase in the production of this antibiotic, compared to the wild type strain. Heterologous expression experiments suggested that its production was severely controlled by the gene cluster for medermycin biosynthesis. In all, these findings suggested that kalafungin and medermycin could be accumulated by the same streptomycete and share their biosynthetic pathway to some extent in this strain. PMID:25695632

  3. Accumulation of a bioactive benzoisochromanequinone compound kalafungin by a wild type antitumor-medermycin-producing streptomycete strain.

    PubMed

    Lü, Jin; He, Qiang; Huang, Luyao; Cai, Xiaofeng; Guo, Wenwen; He, Jing; Zhang, Lili; Li, Aiying

    2015-01-01

    Medermycin and kalafungin, two antibacterial and antitumor antibiotics isolated from different streptomycetes, share an identical polyketide skeleton core. The present study reported the discovery of kalafungin in a medermycin-producing streptomycete strain for the first time. A mutant strain obtained through UV mutagenesis showed a 3-fold increase in the production of this antibiotic, compared to the wild type strain. Heterologous expression experiments suggested that its production was severely controlled by the gene cluster for medermycin biosynthesis. In all, these findings suggested that kalafungin and medermycin could be accumulated by the same streptomycete and share their biosynthetic pathway to some extent in this strain.

  4. SPONTANEOUS MUTATION ACCUMULATION IN MULTIPLE STRAINS OF THE GREEN ALGA, CHLAMYDOMONAS REINHARDTII

    PubMed Central

    Morgan, Andrew D; Ness, Rob W; Keightley, Peter D; Colegrave, Nick

    2014-01-01

    Estimates of mutational parameters, such as the average fitness effect of a new mutation and the rate at which new genetic variation for fitness is created by mutation, are important for the understanding of many biological processes. However, the causes of interspecific variation in mutational parameters and the extent to which they vary within species remain largely unknown. We maintained multiple strains of the unicellular eukaryote Chlamydomonas reinhardtii, for approximately 1000 generations under relaxed selection by transferring a single cell every ∼10 generations. Mean fitness of the lines tended to decline with generations of mutation accumulation whereas mutational variance increased. We did not find any evidence for differences among strains in any of the mutational parameters estimated. The overall change in mean fitness per cell division and rate of input of mutational variance per cell division were more similar to values observed in multicellular organisms than to those in other single-celled microbes. However, after taking into account differences in genome size among species, estimates from multicellular organisms and microbes, including our new estimates from C. reinhardtii, become substantially more similar. Thus, we suggest that variation in genome size is an important determinant of interspecific variation in mutational parameters. PMID:24826801

  5. Along-strike Variations in Active Strain Accumulation in the Northwest Himalaya

    NASA Astrophysics Data System (ADS)

    Morell, K. D.; Ahmad, T.; Sandiford, M.; Codilean, A. T.; Fulop, R. H.

    2015-12-01

    The spatial distribution of channel steepness, erosion rate, and physiographic data highlight pronounced along-strike changes in active strain accumulation in the northwest Himalaya. In particular, the data suggest that the mid-crustal ramp of the Main Himalayan Thrust could merge along-strike with an active portion of the Main Boundary Thrust near longitude ~77º E. This along-strike change in active fault geometry also coincides with the lateral termination of both lesser and greater Himalayan sequences, a significant reduction in total shortening within the wedge, and pronounced variations in regional seismicity. Recent activity along extensional structures in the high Himalaya of this same region appears to have led to significant reorganization, modification and capture of the Sutlej River basin, one of the largest Himalayan river systems. Given the recent 2015 Gorkha earthquake along a comparable section ~500-km along strike, these new constraints on active fault architecture could have regional implications for how strain is partitioned along seismogenic faults in the northwest Himalaya.

  6. Spontaneous mutation accumulation in multiple strains of the green alga, Chlamydomonas reinhardtii.

    PubMed

    Morgan, Andrew D; Ness, Rob W; Keightley, Peter D; Colegrave, Nick

    2014-09-01

    Estimates of mutational parameters, such as the average fitness effect of a new mutation and the rate at which new genetic variation for fitness is created by mutation, are important for the understanding of many biological processes. However, the causes of interspecific variation in mutational parameters and the extent to which they vary within species remain largely unknown. We maintained multiple strains of the unicellular eukaryote Chlamydomonas reinhardtii, for approximately 1000 generations under relaxed selection by transferring a single cell every ~10 generations. Mean fitness of the lines tended to decline with generations of mutation accumulation whereas mutational variance increased. We did not find any evidence for differences among strains in any of the mutational parameters estimated. The overall change in mean fitness per cell division and rate of input of mutational variance per cell division were more similar to values observed in multicellular organisms than to those in other single-celled microbes. However, after taking into account differences in genome size among species, estimates from multicellular organisms and microbes, including our new estimates from C. reinhardtii, become substantially more similar. Thus, we suggest that variation in genome size is an important determinant of interspecific variation in mutational parameters. PMID:24826801

  7. A Shearing-Stretching Device That Can Apply Physiological Fluid Shear Stress and Cyclic Stretch Concurrently to Endothelial Cells.

    PubMed

    Meza, Daphne; Abejar, Louie; Rubenstein, David A; Yin, Wei

    2016-03-01

    Endothelial cell (EC) morphology and functions can be highly impacted by the mechanical stresses that the cells experience in vivo. In most areas in the vasculature, ECs are continuously exposed to unsteady blood flow-induced shear stress and vasodilation-contraction-induced tensile stress/strain simultaneously. Investigations on how ECs respond to combined shear stress and tensile strain will help us to better understand how an altered mechanical environment affects EC mechanotransduction, dysfunction, and associated cardiovascular disease development. In the present study, a programmable shearing and stretching device that can apply dynamic fluid shear stress and cyclic tensile strain simultaneously to cultured ECs was developed. Flow and stress/strain conditions in the device were simulated using a fluid structure interaction (FSI) model. To characterize the performance of this device and the effect of combined shear stress-tensile strain on EC morphology, human coronary artery ECs (HCAECs) were exposed to concurrent shear stress and cyclic tensile strain in the device. Changes in EC morphology were evaluated through cell elongation, cell alignment, and cell junctional actin accumulation. Results obtained from the numerical simulation indicated that in the "in-plane" area of the device, both fluid shear stress and biaxial tensile strain were uniform. Results obtained from the in vitro experiments demonstrated that shear stress, alone or combined with cyclic tensile strain, induced significant cell elongation. While biaxial tensile strain alone did not induce any appreciable change in EC elongation. Fluid shear stress and cyclic tensile strain had different effects on EC actin filament alignment and accumulation. By combining various fluid shear stress and cyclic tensile strain conditions, this device can provide a physiologically relevant mechanical environment to study EC responses to physiological and pathological mechanical stimulation. PMID:26810848

  8. The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

    NASA Technical Reports Server (NTRS)

    Dembosky, Stanley K.; Sancaktar, Erol

    1985-01-01

    The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

  9. Design procedures for Strain Hardening Cement Composites (SHCC) and measurement of their shear properties by mechanical and 2-D Digital Image Correlation (DIC) method

    NASA Astrophysics Data System (ADS)

    Aswani, Karan

    The main objective of this study is to investigate the behaviour and applications of strain hardening cement composites (SHCC). Application of SHCC for use in slabs of common configurations was studied and design procedures are prepared by employing yield line theory and integrating it with simplified tri-linear model developed in Arizona State University by Dr. Barzin Mobasher and Dr. Chote Soranakom. Intrinsic material property of moment-curvature response for SHCC was used to derive the relationship between applied load and deflection in a two-step process involving the limit state analysis and kinematically admissible displacements. For application of SHCC in structures such as shear walls, tensile and shear properties are necessary for design. Lot of research has already been done to study the tensile properties and therefore shear property study was undertaken to prepare a design guide. Shear response of textile reinforced concrete was investigated based on picture frame shear test method. The effects of orientation, volume of cement paste per layer, planar cross-section and volume fraction of textiles were investigated. Pultrusion was used for the production of textile reinforced concrete. It is an automated set-up with low equipment cost which provides uniform production and smooth final surface of the TRC. A 3-D optical non-contacting deformation measurement technique of digital image correlation (DIC) was used to conduct the image analysis on the shear samples by means of tracking the displacement field through comparison between the reference image and deformed images. DIC successfully obtained full-field strain distribution, displacement and strain versus time responses, demonstrated the bonding mechanism from perspective of strain field, and gave a relation between shear angle and shear strain.

  10. Fabric transitions in quartz via viscoplastic self-consistent modeling part I: Axial compression and simple shear under constant strain

    NASA Astrophysics Data System (ADS)

    Morales, Luiz F. G.; Lloyd, Geoffrey E.; Mainprice, David

    2014-12-01

    Quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures, leading to the development of different types of crystallographic preferred orientation (CPO) patterns. In this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self-consistent (VPSC) approach. For that, we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems. We have performed these simulations in axial compression and simple shear regimes under constant Von Mises equivalent strain of 100% (γ = 1.73), assuming that the aggregates deformed exclusively by dislocation glide. Some of the predicted CPOs patterns are similar to those observed in naturally and experimentally deformed quartz. Nevertheless, some classical CPO patterns usually interpreted as result from dislocation glide (e.g. Y-maxima due to prism < a > slip) are clearly not developed in the simulated conditions. In addition we reported new potential preferred orientation patterns that might happen in high temperature conditions, both in axial compression and simple shear. We have demonstrated that CPOs generated under axial compression are usually stronger that those predicted under simple shear, due to the continuous rotation observed in the later simulations. The fabric strength depends essentially on the dominant active slip system, and normally the stronger CPOs result from dominant basal slip in < a >, followed by rhomb < a > and prism [c] slip, whereas prism < a > slip does not produce strong fabrics. The opening angle of quartz [0001] fabric used as a proxy of temperature seems to be reliable for deformation temperatures of ~ 400 °C, when the main slip systems have similar behaviors.

  11. Fabric Transitions in Quartz via Visco-Plastic Self-Consistent Modelling: Axial Compression and Simple Shear under Constant Strain

    NASA Astrophysics Data System (ADS)

    Morales, L. F. G.; Lloyd, G. E.; Mainprice, D.

    2014-12-01

    Quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures, leading to the development of different types of crystallographic preferred orientation (CPO) patterns. In this contribution we present the results of an extensive modelling of quartz fabric transitions via visco-plastic self- consistent (VPSC) approach. For that, we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems. We have performed these simulations in axial compression and simple shear regimes under constant Von Mises equivalent strain of 100% (γ=1.73), assuming that the aggregates deformed exclusively by dislocation glide. Some of the predicted CPOs patterns are similar to those observed in naturally and experimentally deformed quartz. Nevertheless, some classical CPO patterns usually interpreted as resulting from dislocation glide (e.g. Y-maxima due to prism slip) are clearly not developed in the simulated conditions. In addition we report potentially new preferred orientation patterns that might develop in high temperature conditions, both in axial compression and simple shear. We have demonstrated that CPOs generated under axial compression are usually stronger that those predicted under simple shear, due to the continuous rotation observed in the later simulations. The fabric strength depends essentially on the dominant active slip system, and normally the stronger CPOs result from dominant basal slip in , followed by rhomb and prism [c] slip, whereas prism slip does not produce strong fabrics. The opening angle of quartz [0001] fabric used as a proxy of temperature seems to be reliable for deformation temperatures of ~400°C, when the main slip systems have similar behaviours.

  12. Starch and lipid accumulation in eight strains of six Chlorella species under comparatively high light intensity and aeration culture conditions.

    PubMed

    Takeshita, Tsuyoshi; Ota, Shuhei; Yamazaki, Tomokazu; Hirata, Aiko; Zachleder, Vilém; Kawano, Shigeyuki

    2014-04-01

    The microalgae family Chlorella species are known to accumulate starch and lipids. Although nitrogen or phosphorous deficiencies promote starch and lipids formation in many microalgae, these deficiencies also limit their growth and productivity. Therefore, the Chlorellaceae strains were attempted to increase starch and lipids productivity under high-light-intensity conditions (600-μmol photons m(-2)s(-1)). The 12:12-h light-dark (LD) cycle conditions elicited more stable growth than the continuous light (LL) conditions, whereas the starch and lipids yields increased in LL conditions. The amount of starch and lipids per cell increased in Chlorella viscosa and Chlorella vulgaris in sulfur-deficient medium, and long-chain fatty acids with 20 or more carbon atoms accumulated in cells grown in sulfur-deficient medium. Accumulation of starch and lipids was investigated in eight strains. The accumulation was strain-dependent, and varied according to the medium and light conditions. Five of the eight Chlorella strains exhibited similar accumulation patterns.

  13. Development of a Plane Strain Tensile Geometry to Assess Shear Fracture in Dual Phase Steels

    NASA Astrophysics Data System (ADS)

    Taylor, M. D.; Matlock, D. K.; De Moor, E.; Speer, J. G.

    2014-10-01

    A geometrically modified sample capable of generating a triaxial stress state when tested on a standard uniaxial tensile frame was developed to replicate shear fractures observed during stretch bend tests and industrial sheet stamping operations. Seven commercially produced dual phase (DP) steels were tested using the geometrically modified sample, and the modified sample successfully produced shear fractures on a unique shear plane for all steels. For each steel, void densities were determined, based on metallographic analyses, as a function of imposed displacement. Microstructural properties of ferrite and martensite grain size, martensite volume fraction (MVF), retained austenite content, Vickers hardness, average nanoindentation hardness, average ferrite and martensite constituent hardness, and tensile properties were obtained in order to evaluate potential correlations with void data. A linear correlation was observed between Vickers hardness and the average nanoindentation hardness, verifying the ability of nanoindentation to produce data consistent with more traditional hardness measurement techniques. A linear relationship was observed between the number of voids present at 90% failure displacement and the martensite/ferrite hardness ratio, indicating that a decrease in relative hardness difference in a microstructure can suppress void formation, and potentially extend formability limits. The void population appeared independent of MVF, grain size, and tensile properties suggesting that constituent hardness may be a dominant parameter when considering suppression of void nucleation in DP steels.

  14. Oxidative stress is a mediator for increased lipid accumulation in a newly isolated Dunaliella salina strain.

    PubMed

    Yilancioglu, Kaan; Cokol, Murat; Pastirmaci, Inanc; Erman, Batu; Cetiner, Selim

    2014-01-01

    Green algae offer sustainable, clean and eco-friendly energy resource. However, production efficiency needs to be improved. Increasing cellular lipid levels by nitrogen depletion is one of the most studied strategies. Despite this, the underlying physiological and biochemical mechanisms of this response have not been well defined. Algae species adapted to hypersaline conditions can be cultivated in salty waters which are not useful for agriculture or consumption. Due to their inherent extreme cultivation conditions, use of hypersaline algae species is better suited for avoiding culture contamination issues. In this study, we identified a new halophilic Dunaliella salina strain by using 18S ribosomal RNA gene sequencing. We found that growth and biomass productivities of this strain were directly related to nitrogen levels, as the highest biomass concentration under 0.05 mM or 5 mM nitrogen regimes were 495 mg/l and 1409 mg/l, respectively. We also confirmed that nitrogen limitation increased cellular lipid content up to 35% under 0.05 mM nitrogen concentration. In order to gain insight into the mechanisms of this phenomenon, we applied fluorometric, flow cytometric and spectrophotometric methods to measure oxidative stress and enzymatic defence mechanisms. Under nitrogen depleted cultivation conditions, we observed increased lipid peroxidation by measuring an important oxidative stress marker, malondialdehyde and enhanced activation of catalase, ascorbate peroxidase and superoxide dismutase antioxidant enzymes. These observations indicated that oxidative stress is accompanied by increased lipid content in the green alga. In addition, we also showed that at optimum cultivation conditions, inducing oxidative stress by application of exogenous H2O2 leads to increased cellular lipid content up to 44% when compared with non-treated control groups. Our results support that oxidative stress and lipid overproduction are linked. Importantly, these results also suggest that

  15. Oxidative Stress Is a Mediator for Increased Lipid Accumulation in a Newly Isolated Dunaliella salina Strain

    PubMed Central

    Yilancioglu, Kaan; Cokol, Murat; Pastirmaci, Inanc; Erman, Batu; Cetiner, Selim

    2014-01-01

    Green algae offer sustainable, clean and eco-friendly energy resource. However, production efficiency needs to be improved. Increasing cellular lipid levels by nitrogen depletion is one of the most studied strategies. Despite this, the underlying physiological and biochemical mechanisms of this response have not been well defined. Algae species adapted to hypersaline conditions can be cultivated in salty waters which are not useful for agriculture or consumption. Due to their inherent extreme cultivation conditions, use of hypersaline algae species is better suited for avoiding culture contamination issues. In this study, we identified a new halophilic Dunaliella salina strain by using 18S ribosomal RNA gene sequencing. We found that growth and biomass productivities of this strain were directly related to nitrogen levels, as the highest biomass concentration under 0.05 mM or 5 mM nitrogen regimes were 495 mg/l and 1409 mg/l, respectively. We also confirmed that nitrogen limitation increased cellular lipid content up to 35% under 0.05 mM nitrogen concentration. In order to gain insight into the mechanisms of this phenomenon, we applied fluorometric, flow cytometric and spectrophotometric methods to measure oxidative stress and enzymatic defence mechanisms. Under nitrogen depleted cultivation conditions, we observed increased lipid peroxidation by measuring an important oxidative stress marker, malondialdehyde and enhanced activation of catalase, ascorbate peroxidase and superoxide dismutase antioxidant enzymes. These observations indicated that oxidative stress is accompanied by increased lipid content in the green alga. In addition, we also showed that at optimum cultivation conditions, inducing oxidative stress by application of exogenous H2O2 leads to increased cellular lipid content up to 44% when compared with non-treated control groups. Our results support that oxidative stress and lipid overproduction are linked. Importantly, these results also suggest that

  16. Oxidative stress is a mediator for increased lipid accumulation in a newly isolated Dunaliella salina strain.

    PubMed

    Yilancioglu, Kaan; Cokol, Murat; Pastirmaci, Inanc; Erman, Batu; Cetiner, Selim

    2014-01-01

    Green algae offer sustainable, clean and eco-friendly energy resource. However, production efficiency needs to be improved. Increasing cellular lipid levels by nitrogen depletion is one of the most studied strategies. Despite this, the underlying physiological and biochemical mechanisms of this response have not been well defined. Algae species adapted to hypersaline conditions can be cultivated in salty waters which are not useful for agriculture or consumption. Due to their inherent extreme cultivation conditions, use of hypersaline algae species is better suited for avoiding culture contamination issues. In this study, we identified a new halophilic Dunaliella salina strain by using 18S ribosomal RNA gene sequencing. We found that growth and biomass productivities of this strain were directly related to nitrogen levels, as the highest biomass concentration under 0.05 mM or 5 mM nitrogen regimes were 495 mg/l and 1409 mg/l, respectively. We also confirmed that nitrogen limitation increased cellular lipid content up to 35% under 0.05 mM nitrogen concentration. In order to gain insight into the mechanisms of this phenomenon, we applied fluorometric, flow cytometric and spectrophotometric methods to measure oxidative stress and enzymatic defence mechanisms. Under nitrogen depleted cultivation conditions, we observed increased lipid peroxidation by measuring an important oxidative stress marker, malondialdehyde and enhanced activation of catalase, ascorbate peroxidase and superoxide dismutase antioxidant enzymes. These observations indicated that oxidative stress is accompanied by increased lipid content in the green alga. In addition, we also showed that at optimum cultivation conditions, inducing oxidative stress by application of exogenous H2O2 leads to increased cellular lipid content up to 44% when compared with non-treated control groups. Our results support that oxidative stress and lipid overproduction are linked. Importantly, these results also suggest that

  17. Global Positioning System measurements of strain accumulation across the Imperial Valley, California - 1986-1989

    NASA Technical Reports Server (NTRS)

    Larsen, Shawn; Reilinger, Robert

    1992-01-01

    The Global Positioning System (GPS) data collected in southern California from 1986 to 1989 indicate considerable strain accumulation across the Imperial Valley. Displacements are computed at 29 stations in and near the valley from 1986 to 1988, and at 11 sites from 1988 to 1989. The earlier measurements indicate 5.9 =/- 1.0 cm/yr right-lateral differential velocity across the valley, although the data are heavily influenced by the 1987 Superstition Hills earthquake sequence. Some measurements, especially the east-trending displacements, are suspects for large errors. The 1988 to 1989 GPS displacements are best modeled by 5.2 =/- 0.9 cm/yr of valley crossing deformation, but rates calculated from conventional geodetic measurements (3.4 to 4.3 cm/yr) fit the data nearly as well. There is evidence from GPS and Very Long Base Interferometry (VLBI) observations that the present slip rate along the southern San Andreas fault is smaller than the long-term geologic estimate, suggesting a lower earthquake potential than is currently assumed. Correspondingly, a higher earthquake potential is indicated for the San Jacinto fault. The Imperial Valley GPS sites form part of a 183 station network in southern California and northern Baja California, which spans a cross-section of the North American-Pacific plate boundary.

  18. Dislocation pileup as a representation of strain accumulation on a strike-slip fault

    USGS Publications Warehouse

    Savage, J.C.

    2006-01-01

    The conventional model of strain accumulation on a vertical transform fault is a discrete screw dislocation in an elastic half-space with the Burgers vector of the dislocation increasing at the rate of relative plate motion. It would be more realistic to replace that discrete dislocation by a dislocation distribution, presumably a pileup in which the individual dislocations are in equilibrium. The length of the pileup depends upon the applied stress and the amount of slip that has occurred at depth. I argue here that the dislocation pileup (the transition on the fault from no slip to slip at the full plate rate) occupies a substantial portion of the lithosphere thickness. A discrete dislocation at an adjustable depth can reproduce the surface deformation profile predicted by a pileup so closely that it will be difficult to distinguish between the two models. The locking depth (dislocation depth) of that discrete dislocation approximation is substantially (???30%) larger than that (depth to top of the pileup) in the pileup model. Thus, in inverting surface deformation data using the discrete dislocation model, the locking depth in the model should not be interpreted as the true locking depth. Although dislocation pileup models should provide a good explanation of the surface deformation near the fault trace, that explanation may not be adequate at greater distances from the fault trace because approximating the expected horizontally distributed deformation at subcrustal depths by uniform slip concentrated on the fault is not justified.

  19. Interseismic strain accumulation in south central Chile from GPS measurements, 1996-1999

    NASA Astrophysics Data System (ADS)

    Ruegg, J. C.; Campos, J.; Madariaga, R.; Kausel, E.; de Chabalier, J. B.; Armijo, R.; Dimitrov, D.; Georgiev, I.; Barrientos, S.

    2002-06-01

    Two campaigns of Global Positioning System (GPS) measurements were carried out in the Concepción-Constitución area of Chile in 1996 and 1999. It is very likely that this area is a mature seismic gap, since no subduction earthquake has occurred there since 1835. In 1996, 32 sites were occupied in the range 35°S-37°S, between the Pacific coast of Chile and the Andes near the Chile-Argentina border. In 1999, the network was extended by the installation of 9 new points in the Arauco region whereas 13 points among the 1996 stations were reoccupied. The analysis of this campaign data set, together with the data recorded at eight continuous GPS sites (mostly IGS stations) in South America and surrounding regions, indicates a velocity of about 40 +/- 10 mm/yr in the direction N80-90°S for the coastal sites with respect to stable cratonic South America. This velocity decreases to about 20-25 mm/yr towards the Andes. We interpret this result as reflecting interseismic strain accumulation above the Nazca-South America subduction zone, due to a locked thrust zone extending down to about 60 km depth.

  20. GPS measurements of strain accumulation across the Imperial Valley, California: 1986-1989

    NASA Technical Reports Server (NTRS)

    Larsen, Shawn; Reilinger, Robert

    1989-01-01

    The Global Positioning System (GPS) data collected in southern California from 1986 to 1989 indicate considerable strain accumulation across the Imperial Valley. Displacements are computed at 29 stations in and near the valley from 1986 to 1988, and at 11 sites from 1988 to 1989. The earlier measurements indicate 5.9 +/- 1.0 cm/yr right-lateral differential velocity across the valley, although the data are heavily influenced by the 1987 Superstition Hills earthquake sequence. Some measurements, especially the east-trending displacements, are suspects for large errors. The 1988 to 1989 GPS displacements are best modeled by 5.2 +/- 0.9 cm/yr of valley crossing deformation, but rates calculated from conventional geodetic measurements (3.4 to 4.3 cm/yr) fit the data nearly as well. There is evidence from GPS and Very Long Base Interferometry (VLBI) observations that the present slip rate along the southern San Andreas fault is smaller than the long-term geologic estimate, suggesting a lower earthquake potential than is currently assumed. Correspondingly, a higher earthquake potential is indicated for the San Jacinto fault. The Imperial Valley GPS sites form part of a 183 station network in southern California and northern Baja California, which spans a cross-section of the North American-Pacific plate boundary.

  1. Experimental and Computational Study of the Shearing Resistance of Polyurea at High Pressures and High Strain Rates

    NASA Astrophysics Data System (ADS)

    Grujicic, Mica; Yavari, R.; Snipes, J. S.; Ramaswami, S.; Jiao, T.; Clifton, R. J.

    2015-02-01

    Mechanical response of polyurea, a nanophase segregated elastomeric co-polymer, is investigated using all-atom, equilibrium, molecular-dynamics methods and tools. Specifically, the effects of high pressure (1-30 GPa) and high strain rate (105-106 s-1) on the shearing resistance of polyurea are examined. Such loading conditions are encountered by polyurea coatings subjected to impact by high-velocity projectiles, shell shrapnel, and improvised explosive device fragments. Computed results are compared with their experimental counterparts obtained using the so-called pressure-shear plate impact experiments. Computed results have also been rationalized in terms of the nanosegregated polyurea microstructure consisting of rod-shaped, discrete, the so-called hard domains embedded in a highly compliant, the so-called soft matrix. By analyzing molecular-level microstructure and its evolution during high-rate deformation and under high imposed pressures, an attempt is made to identify and quantify main phenomena in viscous/inelastic deformation and microstructure-reorganization processes that are most likely responsible for the observed mechanical response of polyurea.

  2. Universal classification of twisted, strained and sheared graphene moiré superlattices

    NASA Astrophysics Data System (ADS)

    Artaud, A.; Magaud, L.; Le Quang, T.; Guisset, V.; David, P.; Chapelier, C.; Coraux, J.

    2016-05-01

    Moiré superlattices in graphene supported on various substrates have opened a new avenue to engineer graphene’s electronic properties. Yet, the exact crystallographic structure on which their band structure depends remains highly debated. In this scanning tunneling microscopy and density functional theory study, we have analysed graphene samples grown on multilayer graphene prepared onto SiC and on the close-packed surfaces of Re and Ir with ultra-high precision. We resolve small-angle twists and shears in graphene, and identify large unit cells comprising more than 1,000 carbon atoms and exhibiting non-trivial nanopatterns for moiré superlattices, which are commensurate to the graphene lattice. Finally, a general formalism applicable to any hexagonal moiré is presented to classify all reported structures.

  3. Shear strain determination of the polymer polydimethysiloxane (PMDS) using digital image correlation in different temperatures

    NASA Astrophysics Data System (ADS)

    de Oliveira, G. N.; Nunes, L. C. S.; dos Santos, P. A. M.

    2011-01-01

    In the present work a digital image correlation (DIC) method is used in order to analyze the adhesive shear modulus of poly-dimethylsiloxane (PDMS) submitted to different loads and temperatures. This is an optical-numerical full-field surface displacement measurement method. It is based on a comparison between two images of a specimen coated by a random speckled pattern in the undeformed and in the deformed states. A single lap joint testing is performed. This is a standard test specimen for characterizing adhesive properties and it is considered the simplest form of adhesive joints. For the single lap joint specimen, steel adherends are bonded using a flexible rubber elastic polymer (PDMS), which is a commercially available silicone elastic rubber

  4. Universal classification of twisted, strained and sheared graphene moiré superlattices

    PubMed Central

    Artaud, A.; Magaud, L.; Le Quang, T.; Guisset, V.; David, P.; Chapelier, C.; Coraux, J.

    2016-01-01

    Moiré superlattices in graphene supported on various substrates have opened a new avenue to engineer graphene’s electronic properties. Yet, the exact crystallographic structure on which their band structure depends remains highly debated. In this scanning tunneling microscopy and density functional theory study, we have analysed graphene samples grown on multilayer graphene prepared onto SiC and on the close-packed surfaces of Re and Ir with ultra-high precision. We resolve small-angle twists and shears in graphene, and identify large unit cells comprising more than 1,000 carbon atoms and exhibiting non-trivial nanopatterns for moiré superlattices, which are commensurate to the graphene lattice. Finally, a general formalism applicable to any hexagonal moiré is presented to classify all reported structures. PMID:27181495

  5. The Interaction between Fluid Wall Shear Stress and Solid Circumferential Strain Affects Endothelial Gene Expression.

    PubMed

    Amaya, Ronny; Pierides, Alexis; Tarbell, John M

    2015-01-01

    Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS) and circumferential stress (CS) that can be characterized by the temporal phase angle between WSS and CS (stress phase angle - SPA). Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180°) such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0°) are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 °) and synchronous hemodynamics (SPA=0 °). This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS) exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2) and CS (4 ± 4%) over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NFκB and other NFκB target genes. The up regulation of NFκB p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NFκB p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 °) can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease.

  6. The Interaction between Fluid Wall Shear Stress and Solid Circumferential Strain Affects Endothelial Gene Expression

    PubMed Central

    Amaya, Ronny; Pierides, Alexis; Tarbell, John M.

    2015-01-01

    Endothelial cells lining the walls of blood vessels are exposed simultaneously to wall shear stress (WSS) and circumferential stress (CS) that can be characterized by the temporal phase angle between WSS and CS (stress phase angle – SPA). Regions of the circulation with highly asynchronous hemodynamics (SPA close to -180°) such as coronary arteries are associated with the development of pathological conditions such as atherosclerosis and intimal hyperplasia whereas more synchronous regions (SPA closer to 0°) are spared of disease. The present study evaluates endothelial cell gene expression of 42 atherosclerosis-related genes under asynchronous hemodynamics (SPA=-180 °) and synchronous hemodynamics (SPA=0 °). This study used a novel bioreactor to investigate the cellular response of bovine aortic endothelial cells (BAECS) exposed to a combination of pulsatile WSS and CS at SPA=0 or SPA=-180. Using a PCR array of 42 genes, we determined that BAECS exposed to non-reversing sinusoidal WSS (10±10 dyne/cm2) and CS (4 ± 4 %) over a 7 hour testing period displayed 17 genes that were up regulated by SPA = -180 °, most of them pro-atherogenic, including NFκB and other NFκB target genes. The up regulation of NFκB p50/p105 and p65 by SPA =-180° was confirmed by Western blots and immunofluorescence staining demonstrating the nuclear translocation of NFκB p50/p105 and p65. These data suggest that asynchronous hemodynamics (SPA=-180 °) can elicit proatherogenic responses in endothelial cells compared to synchronous hemodynamics without shear stress reversal, indicating that SPA may be an important parameter characterizing arterial susceptibility to disease. PMID:26147292

  7. Prion Strain Differences in Accumulation of PrPSc on Neurons and Glia Are Associated with Similar Expression Profiles of Neuroinflammatory Genes: Comparison of Three Prion Strains

    PubMed Central

    Carroll, James A.; Striebel, James F.; Rangel, Alejandra; Woods, Tyson; Phillips, Katie; Peterson, Karin E.; Race, Brent; Chesebro, Bruce

    2016-01-01

    Misfolding and aggregation of host proteins are important features of the pathogenesis of neurodegenerative diseases including Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia and prion diseases. In all these diseases, the misfolded protein increases in amount by a mechanism involving seeded polymerization. In prion diseases, host prion protein is misfolded to form a pathogenic protease-resistant form, PrPSc, which accumulates in neurons, astroglia and microglia in the CNS. Here using dual-staining immunohistochemistry, we compared the cell specificity of PrPSc accumulation at early preclinical times post-infection using three mouse scrapie strains that differ in brain regional pathology. PrPSc from each strain had a different pattern of cell specificity. Strain 22L was mainly associated with astroglia, whereas strain ME7 was mainly associated with neurons and neuropil. In thalamus and cortex, strain RML was similar to 22L, but in substantia nigra, RML was similar to ME7. Expression of 90 genes involved in neuroinflammation was studied quantitatively using mRNA from thalamus at preclinical times. Surprisingly, despite the cellular differences in PrPSc accumulation, the pattern of upregulated genes was similar for all three strains, and the small differences observed correlated with variations in the early disease tempo. Gene upregulation correlated with activation of both astroglia and microglia detected in early disease prior to vacuolar pathology or clinical signs. Interestingly, the profile of upregulated genes in scrapie differed markedly from that seen in two acute viral CNS diseases (LaCrosse virus and BE polytropic Friend retrovirus) that had reactive gliosis at levels similar to our prion-infected mice. PMID:27046083

  8. Prion Strain Differences in Accumulation of PrPSc on Neurons and Glia Are Associated with Similar Expression Profiles of Neuroinflammatory Genes: Comparison of Three Prion Strains.

    PubMed

    Carroll, James A; Striebel, James F; Rangel, Alejandra; Woods, Tyson; Phillips, Katie; Peterson, Karin E; Race, Brent; Chesebro, Bruce

    2016-04-01

    Misfolding and aggregation of host proteins are important features of the pathogenesis of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, frontotemporal dementia and prion diseases. In all these diseases, the misfolded protein increases in amount by a mechanism involving seeded polymerization. In prion diseases, host prion protein is misfolded to form a pathogenic protease-resistant form, PrPSc, which accumulates in neurons, astroglia and microglia in the CNS. Here using dual-staining immunohistochemistry, we compared the cell specificity of PrPSc accumulation at early preclinical times post-infection using three mouse scrapie strains that differ in brain regional pathology. PrPSc from each strain had a different pattern of cell specificity. Strain 22L was mainly associated with astroglia, whereas strain ME7 was mainly associated with neurons and neuropil. In thalamus and cortex, strain RML was similar to 22L, but in substantia nigra, RML was similar to ME7. Expression of 90 genes involved in neuroinflammation was studied quantitatively using mRNA from thalamus at preclinical times. Surprisingly, despite the cellular differences in PrPSc accumulation, the pattern of upregulated genes was similar for all three strains, and the small differences observed correlated with variations in the early disease tempo. Gene upregulation correlated with activation of both astroglia and microglia detected in early disease prior to vacuolar pathology or clinical signs. Interestingly, the profile of upregulated genes in scrapie differed markedly from that seen in two acute viral CNS diseases (LaCrosse virus and BE polytropic Friend retrovirus) that had reactive gliosis at levels similar to our prion-infected mice. PMID:27046083

  9. A physical model for strain accumulation in the San Francisco Bay region: Stress evolution since 1838

    USGS Publications Warehouse

    Pollitz, F.; Bakun, W.H.; Nyst, M.

    2004-01-01

    Understanding of the behavior of plate boundary zones has progressed to the point where reasonably comprehensive physical models can predict their evolution. The San Andreas fault system in the San Francisco Bay region (SFBR) is dominated by a few major faults whose behavior over about one earthquake cycle is fairly well understood. By combining the past history of large ruptures on SFBR faults with a recently proposed physical model of strain accumulation in the SFBR, we derive the evolution of regional stress from 1838 until the present. This effort depends on (1) an existing compilation of the source properties of historic and contemporary SFBR earthquakes based on documented shaking, geodetic data, and seismic data (Bakun, 1999) and (2) a few key parameters of a simple regional viscoelastic coupling model constrained by recent GPS data (Pollitz and Nyst, 2004). Although uncertainties abound in the location, magnitude, and fault geometries of historic ruptures and the physical model relies on gross simplifications, the resulting stress evolution model is sufficiently detailed to provide a useful window into the past stress history. In the framework of Coulomb failure stress, we find that virtually all M ??? 5.8 earthquakes prior to 1906 and M ??? 5.5 earthquakes after 1906 are consistent with stress triggering from previous earthquakes. These events systematically lie in zones of predicted stress concentration elevated 5-10 bars above the regional average. The SFBR is predicted to have emerged from the 1906 "shadow" in about 1980, consistent with the acceleration in regional seismicity at that time. The stress evolution model may be a reliable indicator of the most likely areas to experience M ??? 5.5 shocks in the future.

  10. Complex Toxin Profile of French Mediterranean Ostreopsis cf. ovata Strains, Seafood Accumulation and Ovatoxins Prepurification

    PubMed Central

    Brissard, Charline; Herrenknecht, Christine; Séchet, Véronique; Hervé, Fabienne; Pisapia, Francesco; Harcouet, Jocelyn; Lémée, Rodolphe; Chomérat, Nicolas; Hess, Philipp; Amzil, Zouher

    2014-01-01

    Ostreopsis cf. ovata produces palytoxin analogues including ovatoxins (OVTXs) and a putative palytoxin (p-PLTX), which can accumulate in marine organisms and may possibly lead to food intoxication. However, purified ovatoxins are not widely available and their toxicities are still unknown. The aim of this study was to improve understanding of the ecophysiology of Ostreopsis cf. ovata and its toxin production as well as to optimize the purification process for ovatoxin. During Ostreopsis blooms in 2011 and 2012 in Villefranche-sur-Mer (France, NW Mediterranean Sea), microalgae epiphytic cells and marine organisms were collected and analyzed both by LC-MS/MS and hemolysis assay. Results obtained with these two methods were comparable, suggesting ovatoxins have hemolytic properties. An average of 223 μg·kg−1 of palytoxin equivalent of whole flesh was found, thus exceeding the threshold of 30 μg·kg−1 in shellfish recommended by the European Food Safety Authority (EFSA). Ostreopsis cells showed the same toxin profile both in situ and in laboratory culture, with ovatoxin-a (OVTX-a) being the most abundant analogue (~50%), followed by OVTX-b (~15%), p-PLTX (12%), OVTX-d (8%), OVTX-c (5%) and OVTX-e (4%). Ostreopsis cf. ovata produced up to 2 g of biomass per L of culture, with a maximum concentration of 300 pg PLTX equivalent cell−1. Thus, an approximate amount of 10 mg of PLTX-group toxins may be produced with 10 L of this strain. Toxin extracts obtained from collected biomass were purified using different techniques such as liquid-liquid partition or size exclusion. Among these methods, open-column chromatography with Sephadex LH20 phase yielded the best results with a cleanup efficiency of 93% and recovery of about 85%, representing an increase of toxin percentage by 13 fold. Hence, this purification step should be incorporated into future isolation exercises. PMID:24828292

  11. Strain anisotropy and shear strength of shock compressed tantalum from in-situ Laue diffraction

    NASA Astrophysics Data System (ADS)

    Wehrenberg, C.; Comley, A. J.; Rudd, R. E.; Terry, M.; Hawreliak, J.; Maddox, B. R.; Prisbrey, S. T.; Park, H.-S.; Remington, B. A.

    2014-05-01

    Laser driven shock experiments were performed at the Omega facility to study the dynamic yield strength of ~5 μm thick single crystal tantalum using in-situ Laue diffraction. Tantalum samples were shocked along the [001] direction to peak stresses up to 50 GPa and probed using a 150 ps pulse of bremsstrahlung radiation from an imploding CH capsule x-ray source timed for when the shock was halfway through the sample. The capsule implosion was monitored by a combination of pinhole cameras and DANTE x-ray diode scopes. Diffraction spots for both the undriven and driven regions of the sample were recorded simultaneously on image plate detectors. The strain state of the material was found by combining the strain anisotropy found from the driven diffraction pattern and with simultaneous VISAR measurements.

  12. Auxotroph Accumulation in Deoxyribonucleic Acid Polymeraseless Strains of Escherichia coli K-121

    PubMed Central

    Berg, Claire M.

    1971-01-01

    Spontaneous auxotrophs are found with high frequency in several strains of Escherichia coli K-12 deficient in Kornberg deoxyribonucleic acid polymerase. These include amino acid-, vitamin-, purine-, and pyrimidine-requiring strains. Although this was suggestive evidence that these strains might be mutators, reconstruction experiments demonstrate that auxotrophs possess a selective advantage over prototrophs in the same culture. Thus, despite the high frequency of auxotrophs in polymerase-deficient strains, it is not yet clear whether they have elevated mutation rates. PMID:4934065

  13. Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

    USGS Publications Warehouse

    Kirby, S.H.

    1985-01-01

    the general phenomenon of ductile faulting in which ductile strains are localized into shear zones. Ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant-strain-rate tests or as an accelerating-creep-rate stage at constant differential stress. A number of physical mechanisms have been identified that may be responsible for ductile faulting, including the onset of dynamic recrystallization, phase changes, hydrothermal alteration and hydrolytic weakening. Microscopic evidence for these processes as well as larger-scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere. ?? 1985.

  14. Comparison of ultrasound B-mode, strain imaging, acoustic radiation force impulse displacement and shear wave velocity imaging using real time clinical breast images

    NASA Astrophysics Data System (ADS)

    Manickam, Kavitha; Machireddy, Ramasubba Reddy; Raghavan, Bagyam

    2016-04-01

    It has been observed that many pathological process increase the elastic modulus of soft tissue compared to normal. In order to image tissue stiffness using ultrasound, a mechanical compression is applied to tissues of interest and local tissue deformation is measured. Based on the mechanical excitation, ultrasound stiffness imaging methods are classified as compression or strain imaging which is based on external compression and Acoustic Radiation Force Impulse (ARFI) imaging which is based on force generated by focused ultrasound. When ultrasound is focused on tissue, shear wave is generated in lateral direction and shear wave velocity is proportional to stiffness of tissues. The work presented in this paper investigates strain elastography and ARFI imaging in clinical cancer diagnostics using real time patient data. Ultrasound B-mode imaging, strain imaging, ARFI displacement and ARFI shear wave velocity imaging were conducted on 50 patients (31 Benign and 23 malignant categories) using Siemens S2000 machine. True modulus contrast values were calculated from the measured shear wave velocities. For ultrasound B-mode, ARFI displacement imaging and strain imaging, observed image contrast and Contrast to Noise Ratio were calculated for benign and malignant cancers. Observed contrast values were compared based on the true modulus contrast values calculated from shear wave velocity imaging. In addition to that, student unpaired t-test was conducted for all the four techniques and box plots are presented. Results show that, strain imaging is better for malignant cancers whereas ARFI imaging is superior than strain imaging and B-mode for benign lesions representations.

  15. Ti distribution in quartz across a heterogeneous shear zone within a granodiorite: the effect of deformation mechanism and strain on Ti resetting

    NASA Astrophysics Data System (ADS)

    Bestmann, Michel; Pennacchioni, Giorgio

    2015-04-01

    The study of a heterogeneous ductile shear zone developed at ca. 500 °C and 0.2 GPa during post-magmatic cooling of a granodiorite allows the effect of strain and recrystallization on Ti re-equilibration of quartz to be assessed. Understanding this effect is critical for applying Ti-in-quartz (TitaniQ) thermobarometry to mylonites. Differently strained quartz across the shear zone shows a heterogeneous distribution of Ti (measured by SIMS) with overall Ti range between 2 and 45 ppm. Quartz cathodoluminescence (CL) is proved by spectral analysis to be univocally correlated to Ti content and CL images were calibrated as Ti maps using SIMS measurements. Coarse grained weakly deformed domains consist of magmatic quartz extensively recrystallized by grain boundary migration (GBM) and mostly (65-75% area) contain 20-38 ppm Ti. Ti resetting to lower amounts occurred locally: (i) in haloes surrounding titanite and biotite inclusions (Ti as low as 6 ppm); (ii) along grain boundaries and healed microfractures; and (iii) towards the quartz domain boundary. With increasing strain quartz underwent progressive grainsize reduction and developed a bimodal microstructure with elongate grains (>100's µm long) surrounded by mantles of new grains (10-30 µm in size) recrystallized by subgrain rotation (SR). Dynamic recrystallization by SGR, associated with prism slip, became increasingly important over GBM as strain increased towards the shear zone core. Relevant resetting of Ti in quartz only occurred in high strain domains (shear strain gamma ≥ 10) in the shear zone core where fine recrystallization amounts at 50-60% area and coarser cores are strongly substructured. These domains are not compositionally homogeneous and still show a range of Ti content between 2 and 10 ppm. In all strain facies of the shear zone quartz-filled pressure shadows associated with feldspar show an almost constant Ti of ~ 2ppm. Therefore the pristine Ti content of the magmatic quartz mylonitized in

  16. Oil accumulation in the model green alga Chlamydomonas reinhardtii: characterization, variability between common laboratory strains and relationship with starch reserves

    PubMed Central

    2011-01-01

    Background When cultivated under stress conditions, many microalgae species accumulate both starch and oil (triacylglycerols). The model green microalga Chlamydomonas reinhardtii has recently emerged as a model to test genetic engineering or cultivation strategies aiming at increasing lipid yields for biodiesel production. Blocking starch synthesis has been suggested as a way to boost oil accumulation. Here, we characterize the triacylglycerol (TAG) accumulation process in Chlamydomonas and quantify TAGs in various wild-type and starchless strains. Results In response to nitrogen deficiency, Chlamydomonas reinhardtii produced TAGs enriched in palmitic, oleic and linoleic acids that accumulated in oil-bodies. Oil synthesis was maximal between 2 and 3 days following nitrogen depletion and reached a plateau around day 5. In the first 48 hours of oil deposition, a ~80% reduction in the major plastidial membrane lipids occurred. Upon nitrogen re-supply, mobilization of TAGs started after starch degradation but was completed within 24 hours. Comparison of oil content in five common laboratory strains (CC124, CC125, cw15, CC1690 and 11-32A) revealed a high variability, from 2 μg TAG per million cell in CC124 to 11 μg in 11-32A. Quantification of TAGs on a cell basis in three mutants affected in starch synthesis (cw15sta1-2, cw15sta6 and cw15sta7-1) showed that blocking starch synthesis did not result in TAG over-accumulation compared to their direct progenitor, the arginine auxotroph strain 330. Moreover, no significant correlation was found between cellular oil and starch levels among the twenty wild-type, mutants and complemented strains tested. By contrast, cellular oil content was found to increase steeply with salt concentration in the growth medium. At 100 mM NaCl, oil level similar to nitrogen depletion conditions could be reached in CC124 strain. Conclusion A reference basis for future genetic studies of oil metabolism in Chlamydomonas is provided. Results

  17. Analysis of Strains Lacking Known Osmolyte Accumulation Mechanisms Reveals Contributions of Osmolytes and Transporters to Protection against Abiotic Stress

    PubMed Central

    Murdock, Lindsay; Burke, Tangi; Coumoundouros, Chelsea; Culham, Doreen E.; Deutch, Charles E.; Ellinger, James; Kerr, Craig H.; Plater, Samantha M.; To, Eric; Wright, Geordie

    2014-01-01

    Osmolyte accumulation and release can protect cells from abiotic stresses. In Escherichia coli, known mechanisms mediate osmotic stress-induced accumulation of K+ glutamate, trehalose, or zwitterions like glycine betaine. Previous observations suggested that additional osmolyte accumulation mechanisms (OAMs) exist and their impacts may be abiotic stress specific. Derivatives of the uropathogenic strain CFT073 and the laboratory strain MG1655 lacking known OAMs were created. CFT073 grew without osmoprotectants in minimal medium with up to 0.9 M NaCl. CFT073 and its OAM-deficient derivative grew equally well in high- and low-osmolality urine pools. Urine-grown bacteria did not accumulate large amounts of known or novel osmolytes. Thus, CFT073 showed unusual osmotolerance and did not require osmolyte accumulation to grow in urine. Yeast extract and brain heart infusion stimulated growth of the OAM-deficient MG1655 derivative at high salinity. Neither known nor putative osmoprotectants did so. Glutamate and glutamine accumulated after growth with either organic mixture, and no novel osmolytes were detected. MG1655 derivatives retaining individual OAMs were created. Their abilities to mediate osmoprotection were compared at 15°C, 37°C without or with urea, and 42°C. Stress protection was not OAM specific, and variations in osmoprotectant effectiveness were similar under all conditions. Glycine betaine and dimethylsulfoniopropionate (DMSP) were the most effective. Trimethylamine-N-oxide (TMAO) was a weak osmoprotectant and a particularly effective urea protectant. The effectiveness of glycine betaine, TMAO, and proline as osmoprotectants correlated with their preferential exclusion from protein surfaces, not with their propensity to prevent protein denaturation. Thus, their effectiveness as stress protectants correlated with their ability to rehydrate the cytoplasm. PMID:24951793

  18. On the influence of dynamic stress variations on strain accumulation in fault zones

    NASA Astrophysics Data System (ADS)

    Grigoriev, A. S.; Shilko, E. V.; Astafurov, S. V.; Dimaki, A. V.; Vysotsky, E. M.; Psakhie, S. G.

    2015-10-01

    In this paper, a numerical study of the influence of the stress state of interface of the block medium structural elements on the deformation response of interface to the dynamic impacts. It is shown that the basic characteristics of the stress state determining the deformation response of the interface are the values of shear stress and mean stress. It is found that the dependence of the irreversible displacement at the interface zone initiated by dynamic impact on the reduced shear stress is described by the logistic function. Herewith, the influence of the mean stress and dynamic impact energy on the value of displacement initiated by dynamic impact can be taken into account by dependence of the logistic function numerator on these parameters.

  19. FE Analysis on Shear Deformation for Asymmetrically Hot-Rolled High-Manganese Steel Strip

    NASA Astrophysics Data System (ADS)

    Sui, Feng-Li; Wang, Xin; Li, Chang-Sheng; Zhao, Jun

    2016-09-01

    Shear deformation along the longitudinal cross section of the high-manganese steel strip has been analyzed in hot asymmetrical rolling process using rigid-plastic finite element model. The friction coefficient between the rolls and the strip surfaces, the diameter of the work rolls, the speed ratio for the lower/upper rolls, the reduction rate and the initial temperature of the billet were all taken into account. Influence of these process parameters on the shear stress, the shear strain and the related shear strain energy in the center layer of the hot-rolled strip was analyzed. It is indicated that increasing the speed ratio, the reduction rate and the work roll diameter is an effective way to accumulate more shear strain energy in the strip center. A mathematical model reflecting the relationship between the shear strain energy and the process parameters has been established.

  20. Shear-accelerated crystallization in a supercooled atomic liquid.

    PubMed

    Shao, Zhen; Singer, Jonathan P; Liu, Yanhui; Liu, Ze; Li, Huiping; Gopinadhan, Manesh; O'Hern, Corey S; Schroers, Jan; Osuji, Chinedum O

    2015-02-01

    A bulk metallic glass forming alloy is subjected to shear flow in its supercooled state by compression of a short rod to produce a flat disk. The resulting material exhibits enhanced crystallization kinetics during isothermal annealing as reflected in the decrease of the crystallization time relative to the nondeformed case. The transition from quiescent to shear-accelerated crystallization is linked to strain accumulated during shear flow above a critical shear rate γ̇(c)≈0.3 s(-1) which corresponds to Péclet number, Pe∼O(1). The observation of shear-accelerated crystallization in an atomic system at modest shear rates is uncommon. It is made possible here by the substantial viscosity of the supercooled liquid which increases strongly with temperature in the approach to the glass transition. We may therefore anticipate the encounter of nontrivial shear-related effects during thermoplastic deformation of similar systems.

  1. Identification of oleaginous yeast strains able to accumulate high intracellular lipids when cultivated in alkaline pretreated corn stover

    PubMed Central

    Sitepu, Irnayuli R.; Jin, Mingjie; Fernandez, J. Enrique; da Costa Sousa, Leonardo; Balan, Venkatesh; Boundy-Mills, Kyria L.

    2015-01-01

    Microbial oil is a potential alternative to food/plant-derived biodiesel fuel. Our previous screening studies identified a wide range of oleaginous yeast species, using a defined laboratory medium known to stimulate lipid accumulation. In this study, the ability of these yeasts to grow and accumulate lipids was further investigated in synthetic hydrolysate (SynH) and authentic ammonia fiber expansion (AFEX™)-pretreated corn stover hydrolysate (ACSH). Most yeast strains tested were able to accumulate lipids in SynH, but only a few were able to grow and accumulate lipids in ACSH medium. Cryptococcus humicola UCDFST 10-1004 was able to accumulate as high as 15.5 g/L lipids, out of a total of 36 g/L cellular biomass when grown in ACSH, with a cellular lipid content of 40% of cell dry weight. This lipid production is among the highest reported values for oleaginous yeasts grown in authentic hydrolysate. Pre-culturing in SynH media with xylose as sole carbon source enabled yeasts to assimilate both glucose and xylose more efficiently in the subsequent hydrolysate medium. This study demonstrates that ACSH is a suitable medium for certain oleaginous yeasts to convert lignocellullosic sugars to triacylglycerols for production of biodiesel and other valuable oleochemicals. PMID:25052467

  2. Identification of oleaginous yeast strains able to accumulate high intracellular lipids when cultivated in alkaline pretreated corn stover.

    PubMed

    Sitepu, Irnayuli R; Jin, Mingjie; Fernandez, J Enrique; da Costa Sousa, Leonardo; Balan, Venkatesh; Boundy-Mills, Kyria L

    2014-09-01

    Microbial oil is a potential alternative to food/plant-derived biodiesel fuel. Our previous screening studies identified a wide range of oleaginous yeast species, using a defined laboratory medium known to stimulate lipid accumulation. In this study, the ability of these yeasts to grow and accumulate lipids was further investigated in synthetic hydrolysate (SynH) and authentic ammonia fiber expansion (AFEX™)-pretreated corn stover hydrolysate (ACSH). Most yeast strains tested were able to accumulate lipids in SynH, but only a few were able to grow and accumulate lipids in ACSH medium. Cryptococcus humicola UCDFST 10-1004 was able to accumulate as high as 15.5 g/L lipids, out of a total of 36 g/L cellular biomass when grown in ACSH, with a cellular lipid content of 40 % of cell dry weight. This lipid production is among the highest reported values for oleaginous yeasts grown in authentic hydrolysate. Preculturing in SynH media with xylose as sole carbon source enabled yeasts to assimilate both glucose and xylose more efficiently in the subsequent hydrolysate medium. This study demonstrates that ACSH is a suitable medium for certain oleaginous yeasts to convert lignocellullosic sugars to triacylglycerols for production of biodiesel and other valuable oleochemicals.

  3. Accumulation of Amino Acids in Rhizobium sp. Strain WR1001 in Response to Sodium Chloride Salinity

    PubMed Central

    Hua, Sui-Sheng T.; Tsai, Victor Y.; Lichens, Georgia M.; Noma, Amy T.

    1982-01-01

    Rhizobium sp. strain WR1001, isolated from the Sonoran Desert by Eskew and Ting, was found to be able to grow in defined medium containing NaCl up to 500 mM, a concentration approaching that of sea water. Therefore, it is a valuable strain for studying the biochemical basis of salt tolerance. Intracellular free glutamate was found to increase rapidly in response to osmotic stress by NaCl. It accounted for 88% of the amino acid pool when the bacterium was grown in 500 mM NaCl. The role of glutamate dehydrogenase in glutamate biosynthesis was examined in several Rhizobium strains. Both NADH- and NADPH-dependent glutamate dehydrogenase activities in various Rhizobium strains were observed. The range of activity differed considerably depending on the particular strain. KCl (500 mM) did not stimulate glutamate dehydrogenase activity, as reported in a number of bacterial strains by Measures. The low activity of glutamate dehydrogenase in Rhizobium sp. strain WR1001 apparently cannot fulfill a biosynthetic function of glutamate formation in response to medium NaCl concentrations. PMID:16346049

  4. Two-dimensional strain-hardening membrane model for large deformation behavior of multiple red blood cells in high shear conditions

    PubMed Central

    2014-01-01

    Background Computational modeling of Red Blood Cell (RBC) flow contributes to the fundamental understanding of microhemodynamics and microcirculation. In order to construct theoretical RBC models, experimental studies on single RBC mechanics have presented a material description for RBC membranes based on their membrane shear, bending and area moduli. These properties have been directly employed in 3D continuum models of RBCs but practical flow analysis with 3D models have been limited by their computationally expensive nature. As such, various researchers have employed 2D models to efficiently and qualitatively study microvessel flows. Currently, the representation of RBC dynamics using 2D models is a limited methodology that breaks down at high shear rates due to excessive and unrealistic stretching. Methods We propose a localized scaling of the 2D elastic moduli such that it increases with RBC local membrane strain, thereby accounting for effects such as the Poisson effect and membrane local area incompressibility lost in the 2D simplification. Validation of our 2D Large Deformation (2D-LD) RBC model was achieved by comparing the predicted RBC deformation against the 3D model from literature for the case of a single RBC in simple shear flow under various shear rates (dimensionless shear rate G = 0.05, 0.1, 0.2, 0.5). The multi-cell flow of RBCs (38% Hematocrit) in a 20 μm width microchannel under varying shear rates (50, 150, 150 s-1) was then simulated with our proposed model and the popularly-employed 2D neo-Hookean model in order to evaluate the efficacy of our proposed 2D-LD model. Results The validation set indicated similar RBC deformation for both the 2D-LD and the 3D models across the studied shear rates, highlighting the robustness of our model. The multi-cell simulation indicated that the 2D neo-Hookean model predicts noodle-like RBC shapes at high shear rates (G = 0.5) whereas our 2D-LD model maintains sensible RBC deformations. Conclusion

  5. Theory of related to shear strain u6 physical properties of ferroelectrics and antiferroelectrics of the KH2PO4 family

    NASA Astrophysics Data System (ADS)

    Levitskii, R. R.; Lisnii, B. M.

    2004-05-01

    We propose an extension of the proton tunneling model in order to study related to the shear strain u6 dielectric, piezoelectric, and elastic properties of ferro- and antiferroelectrics of the KH2PO4 family. This strain is introduced into the proton Hamiltonian via the linear contributions into the configurational energies of protons surrounding an oxygen tetrahedron. In the four-particle cluster approximation for the short-range interactions and the mean field approximation for the long-range interaction we explore the phase transition and piezoelectric effect in the KH2PO4 ferroelectrics. In the paraelectric phase the dielectric, piezoelectric, and elastic characteristics of the NH4H2PO4 antiferroelectrics are calculated. At the proper choice of the theory parameters a good agreement between theoretical and experimental results is obtained. Taking into account of the piezoelectric coupling with the shear strain u6 allows one to calculate the static dielectric permittivities of free and clamped crystals as well as to obtain a good description of ferroelectric spontaneous shear strain u6.

  6. Inter-Rifting and Inter-Seismic Strain Accumulation in a Propagating Ridge System: A Geodetic Study from South Iceland

    NASA Astrophysics Data System (ADS)

    Travis, M. E.; La Femina, P. C.; Geirsson, H.

    2012-12-01

    The Mid-Atlantic Ridge, a slow spreading (~19 mm/yr) mid-ocean ridge boundary between the North American and Eurasian plates, is exposed subaerially in Iceland as the result of ridge-hotspot interaction. Plate spreading in Iceland is accommodated along neovolcanic zones comprised of central volcanoes and their fissure swarms. In south Iceland plate motion is partitioned between the Western Volcanic Zone (WVZ) and Eastern Volcanic Zone (EVZ). The EVZ is propagating to the southwest, while the WVZ is dying out from the northeast. Plate motion across both systems has been accommodated by repeated rifting events and fissure eruptions. In this study we investigate whether the WVZ is active and accumulating strain, and how strain is partitioned between the WVZ and EVZ. We also test how strain is accumulating along fissure swarms within the EVZ (i.e. is strain accumulation localized to one fissure swarm, or are multiple systems active?). We use GPS data and elastic block models run using the program DEFNODE to investigate these issues. GPS data are processed using the GIPSY-OASIS II software, and have been truncated to the 2000.5-2011 time period to avoid co-seismic displacement from the two June 2000 South Iceland Seismic Zone earthquakes. We also truncate the time series for sites within 20 km of Eyjafjallajökull to the beginning of 2010 to eliminate deformation associated with the March 2010 eruption of that volcano. We correct for co-seismic displacement from the two May 2008 SISZ earthquakes, inflation at Hekla volcano and the horizontal component of glacial isostatic rebound (GIA). Our best-fit model for inter-rifting and inter-seismic elastic strain accumulation suggests 80-90% of spreading is accommodated in the EVZ with the other 10-20% accommodated by the WVZ. The best-fit location of the EVZ is between Veidivotn and Lakigigar in an area of no Holocene volcanic activity. We suggest the WVZ is only active at Hengill and its associated fissure swarm. Geologic and

  7. Strain accumulation and fluid-rock interaction in a naturally deformed diamictite, Willard thrust system, Utah (USA): Implications for crustal rheology and strain softening

    NASA Astrophysics Data System (ADS)

    Yonkee, W. Adolph; Czeck, Dyanna M.; Nachbor, Amelia C.; Barszewski, Christine; Pantone, Spenser; Balgord, Elizabeth A.; Johnson, Kimberly R.

    2013-05-01

    Structural and geochemical patterns of heterogeneously deformed diamictite in northern Utah (USA) record interrelations between strain accumulation, fluid-rock interaction, and softening processes across a major fault (Willard thrust). Different clast types in the diamictite have varying shape fabrics related to competence contrasts with estimated effective viscosity ratios relative to micaceous matrix of: ˜6 and 8 for large quartzite clasts respectively in the Willard hanging wall and footwall; ˜5 and 2 for less altered and more altered granitic clasts respectively in the hanging wall and footwall; and ˜1 for micaceous clasts that approximate matrix strain. Within the footwall, matrix X-Z strain ratios increase from ˜2 to 8 westward along a distinct deformation gradient. Microstructures record widespread mass transfer, alteration of feldspar to mica, and dislocation creep of quartz within matrix and clasts. Fluid influx along microcracks and mesoscopic vein networks increased westward and led to reaction softening and hydrolytic weakening, in conjunction with textural softening from alignment of muscovite aggregates. Consistent Si, Al, and Ti concentrations between matrix, granitic clasts, and protoliths indicate limited volume change. Mg gain and Na loss reflect alteration of feldspar to phengitic muscovite. Within the hanging wall, strain is overall lower with matrix X-Z strain ratios of ˜2 to 4. Microstructures record mass transfer and dislocation creep concentrated in the matrix. Greater Al and Ti concentrations and lower Si concentrations in matrix indicate volume loss by quartz dissolution. Na gain in granitic clasts reflects albitization. Large granitic clasts have less mica alteration and greater competence compared to smaller clasts. Differences in strain and alteration patterns across the Willard thrust fault suggest overall downward (up-temperature) fluid flow in the hanging wall and upward (down-temperature) fluid flow in the footwall.

  8. Slip-rates along the Chaman fault: Implication for transient strain accumulation and strain partitioning along the western Indian plate margin

    NASA Astrophysics Data System (ADS)

    Ul-Hadi, Shams; Khan, Shuhab D.; Owen, Lewis A.; Khan, Abdul S.; Hedrick, Kathryn A.; Caffee, Marc W.

    2013-11-01

    The Chaman fault in Western Pakistan marks the western collision boundary between the Indian and Eurasian plates and connects the Makran subduction zone to the Himalayan convergence zone. Geomorphic-scale slip-rates along an active strand of the Chaman fault are added to the sporadic data set of this poorly investigated transform system. Field investigations coupled with high-resolution GeoEye-1 satellite data of an alluvial fan surface (Bostankaul alluvial fan) show ~ 1150 m left-lateral offset by the fault since the formation of the alluvial fan surface. A weighted mean 10Be exposure age of 34.8 ± 3 kyr for the Bostankaul alluvial surface yields a slip-rate of 33.3 ± 3.0 mm/yr. This rate agrees with the geologically defined slip-rates along the Chaman fault, but is approximately twice as large as that inferred from the decade-long global positioning system measurements of 18 ± 1 mm/yr. The contrast in geomorphic and geodetic slip-rates along the Chaman fault, like other major intra-continental strike-slip faults, has two major implications: 1) the geodetic rates might represent a period of reduced displacement as compared to the averaged Late Pleistocene rate because of transient variations in rates of elastic strain accumulation; or 2) strain partitioning within the plate boundary zone. While strain partitioning could be the reason of slip-rate variations within the western Indian plate boundary zone, transient strain accumulation could explain contrasting slip-rates along the Chaman fault at this stage in its poorly understood seismic cycle.

  9. Strain transfer at continental scale from a transcurrent shear zone to a transpressional fold belt: The Patos-Seridó system, northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Corsini, Michel; Vauchez, Alain; Archanjo, Carlos; de Sá, Emanuel F. J.

    1991-06-01

    During the Brasiliano-pan-African orogeny, a complex continental-scale pattern of east-west transcurrent shear zones and northeast-trending fold belts formed in the northern and central Borborema province of northeastern Brazil. The east-west shear zones have been usually regarded as slightly younger features, but the study of the most spectacular case of intersection between these two structures, the Patos shear zone and the Seridó transpressional belt, leads to a different tectonic model. Satellite imagery and structural, petro-logical, and geophysical data support the interpretation that these structures (1) are in structural continuity and (2) formed simultaneously under amphibolite facies metamorphic conditions that led to partial melting. This suggests a model of strain transfer at the scale of the orogen: at the eastern end of the Patos east-west dextral shear zone, the strain that accommodated the relative motion of the northern block was transferred to the northeast-trending Seridó belt, where it resulted in folding, strike-slip faulting, and stretching parallel to the strike of the belt.

  10. Cesium accumulation of Rhodococcus erythropolis CS98 strain immobilized in hydrogel matrices.

    PubMed

    Takei, Takayuki; Yamasaki, Mika; Yoshida, Masahiro

    2014-04-01

    Agarose gels were superior to calcium-alginate gels for immobilizing Rhodococcus erythropolis CS98 strain to remove cesium from water. Suitable incubation time of the immobilized cells in cesium solutions, cell number in the gels and volume ratio of the cesium solution to the gels for efficient cesium removal were identified.

  11. Selection of microalgae for high CO2 fixation efficiency and lipid accumulation from ten Chlorella strains using municipal wastewater.

    PubMed

    Hu, Xia; Zhou, Jiti; Liu, Guangfei; Gui, Bing

    2016-08-01

    As significant differences in cellular physiology, metabolic potential and genetics occur among strains with morphological similarity, the screening of appropriate microalgae species for effective CO2 fixation and biodiesel production is extremely critical. In this study, ten strains of Chlorella were cultivated in municipal wastewater influent (MWI) and their tolerance for MWI, CO2 fixation efficiency and lipid productivity were assessed. The results showed that the biomass concentrations of four strains (Chlorella vulgaris, Chlorella 64.01, Chlorella regularis var. minima and Chlorella sp.) were significantly higher than other strains. When the cultivation systems were aerated with 10% CO2, Chlorella sp. showed the highest CO2 fixation efficiency (35.51%), while the highest lipid accumulation (58.48%) was observed with C. vulgaris. Scanning electron microscopy images revealed that the cells of both Chlorella sp. and C. vulgaris kept their normal morphologies after 15day batch culture. These findings indicated that Chlorella sp. and C. vulgaris have fairly good tolerance for MWI, and moreover, Chlorella sp. was appropriate for CO2 fixation while C. vulgaris represented the highest potential for producing biodiesel.

  12. Selection of microalgae for high CO2 fixation efficiency and lipid accumulation from ten Chlorella strains using municipal wastewater.

    PubMed

    Hu, Xia; Zhou, Jiti; Liu, Guangfei; Gui, Bing

    2016-08-01

    As significant differences in cellular physiology, metabolic potential and genetics occur among strains with morphological similarity, the screening of appropriate microalgae species for effective CO2 fixation and biodiesel production is extremely critical. In this study, ten strains of Chlorella were cultivated in municipal wastewater influent (MWI) and their tolerance for MWI, CO2 fixation efficiency and lipid productivity were assessed. The results showed that the biomass concentrations of four strains (Chlorella vulgaris, Chlorella 64.01, Chlorella regularis var. minima and Chlorella sp.) were significantly higher than other strains. When the cultivation systems were aerated with 10% CO2, Chlorella sp. showed the highest CO2 fixation efficiency (35.51%), while the highest lipid accumulation (58.48%) was observed with C. vulgaris. Scanning electron microscopy images revealed that the cells of both Chlorella sp. and C. vulgaris kept their normal morphologies after 15day batch culture. These findings indicated that Chlorella sp. and C. vulgaris have fairly good tolerance for MWI, and moreover, Chlorella sp. was appropriate for CO2 fixation while C. vulgaris represented the highest potential for producing biodiesel. PMID:27521939

  13. Geodetic strain measurements in Washington.

    USGS Publications Warehouse

    Savage, J.C.; Lisowski, M.; Prescott, W.H.

    1981-01-01

    Two new geodetic measurements of strain accumulation in the state of Washington for the interval 1972-1979 are reported. Near Seattle the average principal strain rates are 0.07 + or - 0.03 mu strain/yr N19oW and -0.13 + or - 0.02 mu strain/yr N71oE, and near Richland (south central Washington) the average principal strain rates are -0.02 + or - 0.01 mu strain/yr N36oW and -0.04 + or - 0.01 mu strain/yr N54oE. Extension is taken as positive, and the uncertainties quoted are standard deviations. A measurement of shear strain accumulation (dilation not determined) in the epoch 1914- 1966 along the north coast of Vancouver Island by the Geodetic Survey of Canada indicates a marginally significant accumulation of right-lateral shear (0.06 + or - 0.03 mu rad/yr) across the plate boundary (N40oW strike). Although there are significant differences in detail, these strain measurements are roughly consistent with a crude dislocation model that represents subduction of the Juan de Fuca plate. The observed accumulation of strain implies that large, shallow, thrust earthquakes should be expected off the coast of Washington and British Columbia. However, this conclusion is not easily reconciled with either observations of elevation change along the Washington coast or the focal mechanism solutions for shallow earthquakes in Washington. -Authors

  14. Prediction of fracture healing under axial loading, shear loading and bending is possible using distortional and dilatational strains as determining mechanical stimuli

    PubMed Central

    Steiner, Malte; Claes, Lutz; Ignatius, Anita; Niemeyer, Frank; Simon, Ulrich; Wehner, Tim

    2013-01-01

    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 shear 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 predict 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 shear and asymmetrical bending loading conditions. PMID:23825112

  15. Factors affecting accumulation and degradation of curdlan, trehalose and glycogen in cultures of Cellulomonas flavigena strain KU (ATCC 53703).

    PubMed

    Siriwardana, Lakmal S; Gall, Aaron R; Buller, Clarence S; Esch, Steven W; Kenyon, William J

    2011-03-01

    Cellulomonas flavigena strain KU (ATCC 53703) is a cellulolytic, Gram-positive bacterium which produces large quantities of an insoluble exopolysaccharide (EPS) when grown in minimal media with a high carbon-to-nitrogen (C/N) ratio. Earlier studies proved the EPS is structurally identical to the linear β-1,3-glucan known as curdlan and provided evidence that the EPS functions as a carbon and energy reserve compound. We now report that C. flavigena KU also accumulates two intracellular, glucose-storage carbohydrates under conditions of carbon and energy excess. These carbohydrates were partially purified and identified as the disaccharide trehalose and a glycogen/amylopectin-type polysaccharide. A novel method is described for the sequential fractionation and quantitative determination of all three carbohydrates from culture samples. This fractionation protocol was used to examine the effects of C/N ratio and osmolarity on the accumulation of cellular carbohydrates in batch culture. Increasing the C/N of the growth medium caused a significant accumulation of curdlan and glycogen but had a relatively minor effect on accumulation of trehalose. In contrast, trehalose levels increased in response to increasing osmolarity, while curdlan levels declined and glycogen levels were generally unaffected. During starvation for an exogenous source of carbon and energy, only curdlan and glycogen showed substantial degradation within the first 24 h. These results support the conclusion that extracellular curdlan and intracellular glycogen can both serve as short-term reserve compounds for C. flavigena KU and that trehalose appears to accumulate as a compatible solute in response to osmotic stress.

  16. Radiation-induced pulmonary endothelial dysfunction and hydroxyproline accumulation in four strains of mice

    SciTech Connect

    Ward, W.F.; Sharplin, J.; Franko, A.J.; Hinz, J.M. )

    1989-10-01

    C57BL mice exposed to 14 Gy of whole-thorax irradiation develop significant histologic lung fibrosis within 52 weeks, whereas CBA and C3H mice do not exhibit substantial fibrosis during this time. The purpose of the present study was to determine whether this strain-dependent difference in radiation histopathology is associated with genetic differences in pulmonary endothelial metabolic activity or in endothelial radioresponsiveness. C57BL/6J, C57BL/10J, CBA/J, and C3H/HeJ mice were sacrificed 12 weeks after exposure to 0 or 14 Gy of 300-kV X rays to the whole thorax. Lung angiotensin converting enzyme (ACE) activity and plasminogen activator (PLA) activity were measured as indices of pulmonary endothelial function; and lung hydroxyproline (HP) content served as an index of pulmonary fibrosis. Lung ACE and PLA activities in sham-irradiated C57BL/6J and CB57BL/10J mice were only half as high as those in sham-irradiated CBA/J and C3H/HeJ mice. Exposure to 14 Gy of X rays produced a slight but nonsignificant reduction in lung ACE and PLA activity in the C57BL strains, and a significant reduction in the CBA/J and C3H/HeJ mice. Even after 14 Gy, however, lung ACE and PLA activities in CBA/J and C3H/HeJ mice were higher than those in sham-irradiated C57BL/6J and C57BL/10J mice. Lung HP content in all four strains increased significantly after irradiation, but this increase was accompanied by an increase in lung wet weight. As a result, HP concentration (per milligram wet weight) remained constant or increased slightly in both C57BL strains and actually decreased in the CBA/J and C3H/HeJ mice. These data demonstrate significant genetic differences in both intrinsic pulmonary endothelial enzyme activity and endothelial radioresponsiveness among the four strains of mice.

  17. Interseismic Strain Accumulation at the Northern Costa Rica Seismogenic Zone From Integration of InSAR and GPS

    NASA Astrophysics Data System (ADS)

    Schwartz, S. Y.; Xue, L.

    2012-12-01

    The presence of the Nicoya Peninsula directly above the seismogenic zone in northern Costa Rica has allowed detailed studies of its seismic and aseismic behavior. This segment of the Middle American Trench generates large earthquakes about every 50 years with the last event occurring in 1950. Abundant seismicity, multiple episodes of slow slip and tremor and years of surface deformation have been recorded here between 2000 and 2011, since the first GPS and seismic instruments were installed. Several models of interseismic strain accumulation have been produced using the GPS data. These models reveal different patterns of locking and variations in locking magnitude that range between 50% to 100% of the plate convergence rate. The GPS data provide excellent temporal coverage but relatively sparse spatial coverage and poor quality vertical measurements of ground deformation. To improve on this, we combine InSAR and GPS observations to produce the first interseismic deformation estimates obtained by InSAR at a subduction zone. We use 18 ALOS SAR acquisitions between 2007 and 2011 covering the Nicoya Peninsula and ROI_PAC software to construct 120 interferograms with perpendicular baselines under 1200m. GPS data are used to correct for orbital errors and corrected interferograms are stacked to produce a deformation rate map that strongly resembles a synthetic interferogram constructed using a GPS based interseismic deformation model. To detect accumulated interseismic deformation over a longer time period we use the small baseline subset (SBAS) method to construct InSAR time series. The resulting linear rate map agrees very well with the GPS measurements along two profiles perpendicular to the coast where GPS observations are the densest. Maximum displacements reach ~10-15 mm/yr near the coastline. Future work will integrate these results with GPS observations to obtain a high-resolution strain accumulation model for the Nicoya Peninsula.

  18. Strain-dependent evolution of garnets in a high pressure ductile shear zone using Synchroton x-ray microtomography

    NASA Astrophysics Data System (ADS)

    Macente, Alice; Fusseis, Florian; Menegon, Luca; John, Timm

    2016-04-01

    Synkinematic reaction microfabrics carry important information on the kinetics, timing and rheology of tectonometamorphic processes. Despite being routinely interpreted in metamorphic and structural studies, reaction and deformation microfabrics are usually described in two dimensions. We applied Synchrotron-based x-ray microtomography to document the evolution of a pristine olivine gabbro into a deformed omphacite-garnet eclogite in 3D. In the investigated samples, which cover a strain gradient into a shear zone from the Western Gneiss Region (Norway) previously described by John et al., (2009), we focused on the spatial transformation of garnet coronas into elongated clusters of garnets. Our microtomographic data allowed us to quantify changes to the garnet volume, their shapes and their spatial arrangement. We combined microtomographic observations with light microscope- and backscatter electron images as well as electron microprobe- (EMPA) and electron backscatter diffraction (EBSD) analyses to correlate mineral composition and orientation data with the x-ray absorption signal of the same mineral grains. This allowed us to extrapolate our interpretation of the metamorphic microfabric evolution to the third dimension, effectively yielding a 4-dimensional dataset. We found that: - The x-ray absorption contrast between individual mineral phases in our microtomographic data is sufficient to allow the same petrographic observations than in light- and electron microscopy, but extended to 3D. - Amongst the major constituents of the synkinematic reactions, garnet is the only phase that can be segmented confidently from the microtomographic data. - With increasing deformation, the garnet volume increases from about 9% to 25%. - Garnet coronas in the gabbros never completely encapsulate olivine grains. This may indicate that the reaction progressed preferentially in some directions, but also leaves pathways for element transport to and from the olivines that are

  19. Constraints on strain rate and fabric partitioning in ductilely deformed black quartzites (Badajoz-Córdoba Shear Zone, Iberian Massif)

    NASA Astrophysics Data System (ADS)

    Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio

    2013-04-01

    The Badajoz-Córdoba Shear Zone is a is 30-40 km wide and 400 km long, NW-SE trending structure located at the boundary between the Ossa-Morena and Central-Iberian Zones of the Iberian Massif. Two elongated domains can be differentiated inside: the Obejo-Valsequillo domain to the NE and the Ductile Shear Belt (DSB) to the SW. The former exhibits Precambrian to Cambrian volcano-sedimentary rocks unconformably overlaying a Neoproterozoic basement formed by the "Serie Negra". The latter, 5-15 km wide, is composed mainly of metamorphic tectonites including the "Serie Negra" and other units located structurally under it. The petrofabric of "Serie Negra" black quartzites from the DSB is analyzed in this study with the Electron Back-Scattered Diffraction technique (EBSD). Black quartzites represent originally siliceous, chemical-biochemical shallow-water marine deposits, currently composed almost exclusively of quartz and graphite. Macroscopically they exhibit an outstanding planolinear tectonic fabric. Petrographically, coarse- and fine-grained dynamically recrystallized quartz bands alternate. The former contain quartz grains with irregular shapes, mica inclusions and "pinning" grain boundaries. Oriented mica grains and graphite particles constrain irregular quartz grain shapes. Quartz ribbons with chessboard microstructures also occur, indicating recrystallization under elevated temperatures coeval with extreme stretching. Fine-grained recrystallized quartz bands are dominated by quartz grains with straight boundaries, triple junctions, a scarcer evidence of bulging, and a higher concentration of dispersed, minute graphite grains. Quartz lattice-preferred orientation (LPO) patterns permit to identify two well-developed maxima for [c] axes: one close to the Y structural direction and the other one around Z, and -axes girdles normal to Y and Z. Although both [c] axis maxima appear in the coarse- and fine-grained bands, subsets can be isolated with grain cluster

  20. Determining Recoverable and Irrecoverable Contributions to Accumulated Strain in a NiTiPd High-Temperature Shape Memory Alloy During Thermomechanical Cycling

    NASA Technical Reports Server (NTRS)

    Monroe, J. A.; Karaman, I.; Lagoudas, D. C.; Bigelow, G.; Noebe, R. D.; Padula, S., II

    2011-01-01

    When Ni(29.5)Ti(50.5)Pd30 shape memory alloy is thermally cycled under stress, significant strain can accumulate due to elasticity, remnant oriented martensite and plasticity. The strain due to remnant martensite can be recovered by further thermal cycling under 0 MPa until the original transformation-induced volume change and martensite coefficient of thermal expansion are obtained. Using this technique, it was determined that the 8.15% total accumulated strain after cycling under 200 MPa consisted of 0.38%, 3.97% and 3.87% for elasticity, remnant oriented martensite and creep/plasticity, respectively.

  1. Stimulation of pigment accumulation in Anabaena azollae strains: effect of light intensity and sugars.

    PubMed

    Venugopal, V; Prasanna, R; Sood, A; Jaiswal, P; Kaushik, B D

    2006-01-01

    The influence of high light intensity on the growth and pigment accumulating ability of Anabaena azollae was investigated. A. azollae responded positively to high light intensity (6 klx) and was further evaluated at higher intensities (10 and 15 klx), in the presence of glucose, sucrose and jaggery +/- DCMU. Significant enhancement in phycobiliproteins and carotenoids was observed in the sugar supplemented cultures at high light intensities. SDS-PAGE profiles of whole cell proteins revealed the presence of unique bands in such treatments. Sucrose supplementation induced a 30-90 % increase in carotenoids, phycocyanin and phycoerythrin content at 10 klx. Molecular analysis of the stimulatory and interactive role of sugars on pigment enhancement at high light intensity may aid in better exploitation of cyanobacteria as a source of pigments.

  2. Interseismic strain accumulation across the North Anatolian Fault measured using InSAR

    NASA Astrophysics Data System (ADS)

    Walters, R. J.; Parsons, B. E.; Wright, T. J.

    2010-12-01

    The North Anatolian Fault (NAF) is a major feature of Middle Eastern tectonics, facilitating the westwards 'escape' of the Anatolian block away from the Arabia-Eurasia continental collision. In order to understand the role that the NAF plays in regional tectonics it is important to accurately determine the slip rate across the fault. Many slip rate estimates for the NAF have been made over Quaternary and longer time-scales but few geodetic estimates currently exist, especially in eastern Turkey. Here we construct satellite radar interferograms using Envisat ASAR data to measure ground displacements around the NAF and hence estimate the slip rate across it. We make use of SAR data from two satellite tracks, one ascending and one descending, that overlap across the NAF, providing a check on the assumption of horizontal fault-parallel motion that has previously been used in interseismic modelling of the fault. We mitigate the effects of atmospheric errors by constructing multiple interferograms over the fault and summing them, effectively creating a longer timespan interferogram and improving the signal-to-noise ratio. We empirically correct for orbital errors by flattening the radar swaths on the Anatolian Plateau, an area with little expected deformation. Our measurements of rates of displacement are consistent with an interseismic model for the NAF where deformation occurs at depth on a narrow shear zone below a layer in which the fault is locked. We jointly invert data from both satellite tracks to solve for best fitting model parameters, estimating both the slip rate and the depth to which the fault is locked. Our best-fitting model gives a slip rate of 23 mm/yr and a locking depth of 19 km, which is in agreement with a previous estimate made from a single track of ERS SAR data (Wright et al., 2001, GRL 28, 2117-2120), and with existing GPS data. We also construct a velocity field using a combination of InSAR and GPS data for eastern Turkey.

  3. Shear avalanches in metallic glasses under nanoindentation: Deformation units and rate dependent strain burst cut-off

    SciTech Connect

    Bian, X. L.; Wang, G.; Gao, Y. L.; Zhai, Q. J.; Chan, K. C.; Ren, J. L.

    2013-09-02

    Indented metallic glasses at the nanoscale deform via strain bursts. Conventional continuum descriptions are not appropriate for such highly stochastic, intermittent deformations. In this study, after a statistical analysis of strain bursts in five metallic glasses, the dependence of the cut-off of the strain burst size on deformation units and loading rate is established. For soft metallic glasses with smaller deformation units, cut-off of the strain burst size truncates the scale-free behavior at larger strain burst sizes. For hard metallic glasses, scale-free behavior occurs in a wide range of strain burst sizes.

  4. InSAR observations of strain accumulation and fault creep along the Chaman Fault system, Pakistan and Afghanistan

    NASA Astrophysics Data System (ADS)

    Fattahi, Heresh; Amelung, Falk

    2016-08-01

    We use 2004-2011 Envisat synthetic aperture radar imagery and InSAR time series methods to estimate the contemporary rates of strain accumulation in the Chaman Fault system in Pakistan and Afghanistan. At 29 N we find long-term slip rates of 16 ± 2.3 mm/yr for the Ghazaband Fault and of 8 ± 3.1 mm/yr for the Chaman Fault. This makes the Ghazaband Fault one of the most hazardous faults of the plate boundary zone. We further identify a 340 km long segment displaying aseismic surface creep along the Chaman Fault, with maximum surface creep rate of 8.1 ± 2 mm/yr. The observation that the Chaman Fault accommodates only 30% of the relative plate motion between India and Eurasia implies that the remainder is accommodated south and east of the Katawaz block microplate.

  5. Interseismic strain accumulation in seismic gap of south central Chile from GPS measurements

    NASA Astrophysics Data System (ADS)

    Rudloff, A.; Vigny, C.; Ruegg, J. C.; Campos, J.

    2003-04-01

    Three campaigns of Global Positioning System (GPS) measurements were carried out in the Concepcion-Constitucion seismic gap in South Central Chile in 1996, 1999, and 2002. We observed a network of about 40 sites, made of 2 east-west transects roughly perpendicular to the trench ranging from the coastal area to the Argentina border and 1 north-south profile along the coast. Data sets were processed with MIT's GAMIT/GLOBK package. Horizontal velocities have formal uncertainties around 1 to 2 mm/yr in average. Vertical velocities are also determined and have uncertainties around 2 to 5 mm/yr. We find that the convergence between Nazca and South-America plates better matches the pole previously estimated by (Larson et al, 1997) than the Nuvel-1A estimate. Our estimate predicts a convergence of 72 mm/yr at N70 to be compared with Nuvel-1A 80 mm/yr at N79. With respect to stable South America, horizontal velocities decrease from 35 mm/yr on the coast to 14 mm/yr in the Cordillera. Vertical velocities help constraint lithospheric flecture. Partionning of the slightly oblique convergence will be investigated. The gradient of convergent parallel velocities reflects aseismic elastic loading on a zone of about 400 km width. Interestingly enough, this gradient exhibit a linear pattern, marginally compatible with the expected arctangent shape. 70 mm/yr of motion accumulated since the last big event in this area (1835 Earthquake described by Darwin) represent more than 10 m of displacement. Therefore, this area is probably mature for a next large earthquake, the magnitude of which could reach 8.5.

  6. Lead solubilization and accumulation by two strains of Pseudomonas obtained from a contaminated alfisol's effluent in southwestern Nigeria.

    PubMed

    Ekundayo, E O; Killham, K

    2001-10-01

    Two strains of Pseudomonas species (B2 and D5) selected from an array of lead solubilizing and accumulating bacteria obtained from the effluent contaminated soil samples of a battery manufacturing factory were studied. Increase in pH between 4.0 and 6.0 favoured the growth of isolates: Peak log10 cfu mL(-1) values of 7.1, 7.5 and 8.5 were obtained at pH 4, 5 and 6, respectively. Cell bound lead concentrations for B2 (0.34 mg mL(-1)) and D5 (0.30 mg mL(-1)) obtained by direct contact with Pbs were greater than lead concentrations of 0.89 and 0.25 mg mL(-1) for B2 and D5, respectively, obtained in dialyzed cultures. These cell bound lead concentration in undialyzed cultures were also greater than lead concentrations of 0.03 and 0.07 mg mL(-1) for B2 and D5 in culture supernatants. Glucose addition did nor improve lead accumulation in the isolates. Exploitation of such isolates for the biotreatment of lead laden effluent was conducted. PMID:11683230

  7. Lead solubilization and accumulation by two strains of Pseudomonas obtained from a contaminated alfisol's effluent in southwestern Nigeria.

    PubMed

    Ekundayo, E O; Killham, K

    2001-10-01

    Two strains of Pseudomonas species (B2 and D5) selected from an array of lead solubilizing and accumulating bacteria obtained from the effluent contaminated soil samples of a battery manufacturing factory were studied. Increase in pH between 4.0 and 6.0 favoured the growth of isolates: Peak log10 cfu mL(-1) values of 7.1, 7.5 and 8.5 were obtained at pH 4, 5 and 6, respectively. Cell bound lead concentrations for B2 (0.34 mg mL(-1)) and D5 (0.30 mg mL(-1)) obtained by direct contact with Pbs were greater than lead concentrations of 0.89 and 0.25 mg mL(-1) for B2 and D5, respectively, obtained in dialyzed cultures. These cell bound lead concentration in undialyzed cultures were also greater than lead concentrations of 0.03 and 0.07 mg mL(-1) for B2 and D5 in culture supernatants. Glucose addition did nor improve lead accumulation in the isolates. Exploitation of such isolates for the biotreatment of lead laden effluent was conducted.

  8. Brittle grain-size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Viegas, Gustavo; Menegon, Luca; Archanjo, Carlos

    2016-03-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse-grained (> 50 µm) feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (< 15 µm) localized in C' shear bands. Detailed microstructural observations and electron backscatter diffraction (EBSD) analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (˜ 1-2 mm) monomineralic veins transposed along the shear zone foliation or as thin ribbons ( ≤ 25 µm width) dispersed in the feldspathic mixture. The microstructure and c axis crystallographic-preferred orientation are similar in the thick monomineralic veins and in the thin ribbons, and they suggest dominant subgrain rotation recrystallization and activity of prism < a > and rhomb < a > slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the quartz monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 µm vs. 5 µm respectively). The fine-grained feldspar mixture has a weak crystallographic-preferred orientation interpreted as the result of shear zone parallel-oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Once C' shear bands were generated and underwent viscous deformation at constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate 1 order of magnitude faster than the monophase quartz monomineralic veins, as evidenced by applying experimentally and theoretically calibrated flow laws for dislocation creep in quartz and diffusion creep in

  9. Interseismic Strain Accumulation in Metropolitan Los Angeles Distinguished from Oil and Water management using InSAR and GPS

    NASA Astrophysics Data System (ADS)

    Argus, D. F.; Agram, P. S.; Rollins, C.; Avouac, J. P.; Barbot, S.

    2015-12-01

    Thesis.InSAR measurements from 1992 to 2012 are detecting deformation due to oil pumping and groundwater changes throughout metropolitan Los Angeles. This is allowing elastic strain build up on blind thrusts beneath the city to be accurately evaluated using GPS. Oil Fields.Pumping and repressurization of oil fields have generated substantial displacement in metropolitan Los Angeles, causing Beverly Hills, downtown, and Whittier to subside at 3-10 mm/yr and Santa Fe Springs and La Mirada to rise at 5-9 mm/yr. Aquifers.Displacements of the Santa Ana and San Gabriel Valley aquifers accumulate in response to sustained changes in groundwater over periods of either drought or heavy precipitation. Santa Ana aquifer has subsided nearly 0.1 m in response to lowering of the groundwater level by about 25 m over the past 18 years. Anthropogenic Vs. Tectonic Motion.We are assessing horizontal motions due to changes groundwater using an empirical relationship established on the basis of seasonal oscillations of Santa Ana aquifer. Anthropogenic horizontal motion is estimated to be proportional to the directional gradient in vertical motion inferred with InSAR. We are finding this rough approximation to be quite useful for evaluating deviations of GPS positions from a constant velocity. We are also constructing Mogi models of volume change in oil fields to evaluate GPS deviations. Earthquake Strain Buildup on Blind Thrust Faults.NNE contraction perpendicular to the big restraining bend in the San Andreas fault is fastest not immediately south of the San Andreas in the San Gabriel Mountains, but instead 50 km south of the fault in northern metropolitan Los Angeles. An elastic model of interseismic strain accumulation fit to GPS data and incorporating a 1D approximation of the rheology of the Los Angeles basin indicates the deep segment of the Puente Hills (-upper Elysian Park) Thrust to be slipping at 9 ±2 mm/yr beneath a locking depth of 12 ±5 km. Please see also our

  10. Plastic response and correlations in athermally sheared amorphous solids

    NASA Astrophysics Data System (ADS)

    Puosi, F.; Rottler, J.; Barrat, J.-L.

    2016-09-01

    The onset of irreversible deformation in low-temperature amorphous solids is due to the accumulation of elementary events, consisting of spatially and temporally localized atomic rearrangements involving only a few tens of atoms. Recently, numerical and experimental work addressed the issue of spatiotemporal correlations between these plastic events. Here, we provide further insight into these correlations by investigating, via molecular dynamics (MD) simulations, the plastic response of a two-dimensional amorphous solid to artificially triggered local shear transformations. We show that while the plastic response is virtually absent in as-quenched configurations, it becomes apparent if a shear strain was previously imposed on the system. Plastic response has a fourfold symmetry, which is characteristic of the shear stress redistribution following the local transformation. At high shear rate we report evidence for a fluctuation-dissipation relation, connecting plastic response and correlation, which seems to break down if lower shear rates are considered.

  11. Brittle grain size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Viegas, Gustavo; Menegon, Luca; Archanjo, Carlos

    2016-04-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse (> 50 μm) grained feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (< 15 μm in size) localized in C' shear bands. Detailed microstructural observations and EBSD analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (˜ 1-2 mm) monomineralic bands or as thin ribbons dispersed in the feldspathic mixture. The microstructure and c-axis crystallographic preferred orientation are similar in the thick monomineralic band and in the thin ribbons, and suggest dominant subgrain rotation recrystallization and activity of prism and rhomb slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 μm vs 5 μm, respectively).The fine-grained feldspar mixture has a weak crystallographic preferred orientation interpreted as the result of oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Assuming that the C' shear bands deformed under constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate one order of magnitude faster than the monophase quartz ribbons. Overall, our dataset indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystalline plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the feldspathic material

  12. Interseismic strain accumulation across an active thrust system: an InSAR case study in the Himalaya

    NASA Astrophysics Data System (ADS)

    Grandin, R.; Doin, M.; Ducret, G.; Bollinger, L.; Pinel-Puysségur, B.; Lasserre, C.; Jolivet, R.

    2011-12-01

    The major active thrust system underlying the Himalayan range produces recurrent large earthquakes, posing a significant threat to the densely populated Indo-Gangetic basin. Measuring the interseismic deformation associated with this fault system could provide important constraints on the geometry of the locked faults that are bound to rupture in future great earthquakes. This has so far been considered out of reach of InSAR techniques, due to decorrelation, prominent topographic features, and unfavourable climatic conditions. However, preliminary tests carried out with the archived ASAR data provided by ESA's ENVISAT satellite since 2002 have shown that recent advances in InSAR processing may now allow geodesists to tackle most of these perturbations. In this context, applying these advanced techniques to the case of the Himalayas is both a challenging and necessary task. We will present the methodology and the first results of an InSAR study of interseismic strain accumulation across the Himalayas. Small-baseline processing of ENVISAT data using a combination of ROI_PAC software, NSBAS processing chain and MulSAR technique yields a sufficient number of coherent interferograms to compute a preliminary average velocity map of interseismic uplift. Time-space variations of stratified tropospheric delay observed in these interferogrames are mitigated using a prediction deduced from outputs of the ECMWF global meteorological reanalysis ERA-Interim. Finally, a correction of DEM errors from the wrapped InSAR data set further improves the coherence of interferograms with a large perpendicular baseline. Comparison of the InSAR LOS velocity maps with microseismic activity detected near the transition zone at the base of the seismogenic portion of the Main Himalayan Thrust is expected to provide constraints on the process of elastic strain accumulation during the interseismic period. This will help in understanding the interaction between the construction of topography

  13. Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson's ratios and fluid expulsion under tensile loading.

    PubMed

    Ahmadzadeh, Hossein; Freedman, Benjamin R; Connizzo, Brianne K; Soslowsky, Louis J; Shenoy, Vivek B

    2015-08-01

    As tendons are loaded, they reduce in volume and exude fluid to the surrounding medium. Experimental studies have shown that tendon stretching results in a Poisson's ratio greater than 0.5, with a maximum value at small strains followed by a nonlinear decay. Here we present a computational model that attributes this macroscopic observation to the microscopic mechanism of the load transfer between fibrils under stretch. We develop a finite element model based on the mechanical role of the interfibrillar-linking elements, such as thin fibrils that bridge the aligned fibrils or macromolecules such as glycosaminoglycans (GAGs) in the interfibrillar sliding and verify it with a theoretical shear-lag model. We showed the existence of a previously unappreciated structure-function mechanism whereby the Poisson's ratio in tendon is affected by the strain applied and interfibrillar-linker properties, and together these features predict tendon volume shrinkage under tensile loading. During loading, the interfibrillar-linkers pulled fibrils toward each other and squeezed the matrix, leading to the Poisson's ratio larger than 0.5 and fluid expulsion. In addition, the rotation of the interfibrillar-linkers with respect to the fibrils at large strains caused a reduction in the volume shrinkage and eventual nonlinear decay in Poisson's ratio at large strains. Our model also predicts a fluid flow that has a radial pattern toward the surrounding medium, with the larger fluid velocities in proportion to the interfibrillar sliding. PMID:25934322

  14. The Lima-Peru seismic gap: a study of inter-seismic strain accumulation from a decade of GPS measurements

    NASA Astrophysics Data System (ADS)

    Norabuena, E. O.; Pollitz, F. F.; Dixon, T. H.

    2013-05-01

    The Peruvian subduction zone between the Mendaña Fracture zone and Arica, northern Chile, has been source of large megathrust earthquakes since historical to present times, The two last major events affecting the southern segment corresponds to Arequipa 2001 (Mw 8.3) and Pisco 2007 (Mw 8.1). A noteworthy event is the Lima 1746 earthquake with an assigned magnitude of Mw 8.5 and which is assumed to have broken several km of the seismogenic zone off Lima. The great shock was followed by a devastating tsunami that destroyed the main port of Callao, killing about 99 percent of its population. This extreme event was followed by quiescence of a few hundred years until the XX century when the Lima subduction zone was broken again by the earthquakes of May 1940 (Mw 8.0), October 1966 (Mw 8.0) and Lima 1974 (Mw 8.0). The broken areas overlap partially with the estimated area of the 1746 earthquake and put the region in a state of seismic gap representing a major hazard for Lima city - Peru's capital and its about 9 million of inhabitants. Our study reports the interseismic strain accumulation derived from a decade of GPS measurement at 11 geodetic monuments including one measurement in an island 80 km offshore and models variations of coupling along the plate interface.

  15. The Effects of Light, Temperature, and Nutrition on Growth and Pigment Accumulation of Three Dunaliella salina Strains Isolated from Saline Soil

    PubMed Central

    Wu, Zhe; Duangmanee, Promchup; Zhao, Pu; Juntawong, Niran; Ma, Chunhong

    2016-01-01

    Background: Developing algal industries in saline-alkali areas is necessary. However, suitable strains and optimal production conditions must be studied before widespread commercial use. Objectives: The effects of light, temperature, KNO3, and CO(NH2)2 on beta-carotene and biomass accumulation were compared and evaluated in order to provide scientific guidance for commercial algal production in northeastern Thailand. Materials and Methods: An orthogonal design was used for evaluating optimal conditions for the algal production of three candidate Dunaliella salina strains (KU XI, KU 10 and KU 31) which were isolated from saline soils and cultured in the column photobioreactor. Results: The optimal light and temperature for algae growth were 135.3 μmol m-2 s-1 and 22°C, while the conditions of 245.6 μmol m-2 s-1 and 22°C induced the highest level of beta-carotene production (117.99 mg L-1). The optimal concentrations of KNO3, CO(NH2)2, and NaHCO3 for algae growth were 0.5 g L-1, 0.36 g L-1, and 1.5 g L-1, respectively, while 0, 0.12 g L-1 and 1.5 g L-1 were best suited for beta-carotene accumulation. The highest beta-carotene rate per cell appeared with the highest light intensity (12.21 pg) and lowest temperature (12.47 pg), and the lowest total beta-carotene content appeared at the lowest temperature (15°C). There was not a significant difference in biomass accumulation among the three Dunaliella strains; however, the beta-carotene accumulation of KU XI was higher than that of the other two strains. Conclusions: Light and temperature were both relevant factors that contributed to the growth and beta-carotene accumulation of the three D. salina strains, and NaHCO3 had significantly positive effects on growth. The degree of impact of the different factors on cell growth was temperature > NaHCO3 > light intensity > KNO3 > CO (NH2)2 > strains; the impact on beta-carotene accumulation was temperature > light intensity > KNO3 > CO (NH2)2 > strains > NaHCO3 PMID

  16. Measurement of interseismic strain accumulation in the Southern Andes (25°-35°S) using Envisat SAR data

    NASA Astrophysics Data System (ADS)

    Ducret, G.; Doin, M. P.; Grandin, R.; Socquet, A.; Vigny, C.; Métois, M.; Béjar-Pizzaro, M.

    2012-04-01

    The Chilean subduction zone is one of the most active in the world. The Nazca plate subducts under the South America plate with a velocity around 7 cm/year. Along-strike and along-dip variations of interseismic coupling suggest that the subduction interface is divided into segments. Rupture of one or several consecutive segments may produce earthquakes of magnitude greater than 8.0. However, the definition of the segmentation in the particular case of the Chilean subduction and its relation to earthquake nucleation in general is a debated topic. We focus on an area extending over 1000 km in latitude, located between Taltal (~25°S) and Constitution (~35°S), which has been accumulating tectonic strain since the mid-20th century. Three main earthquakes occurred in the last decade around the boundaries of this segment : the 1995 Antogagasta (M=8.1) and the 2007 Tocopilla (M=7.7) earthquakes to the North and the 2010 Maule (M=8.8) earthquake to the South. A few seismic swarms occurred in recent years : the episode of Valparaiso (~33°S) in 1985, the Puntaqui (~30°S) crisis in 1997, and the swarms in the Copiapo (~27°S) region in 1973 and 2006. The 25-35°S part of the subduction zone experiences since 38 years a background seismicity (given by USGS catalog), that is mainly located along the plate interface and less frequently within the overriding plate. The seismicity rate is varying from South to North with a maximum seismicity located around La Serena area (~30°S). There, the coupling distribution is constrained by an important GPS dataset that indicate a lower coupling (less than 60%) compared with areas further North and South. Similarly, GPS data suggest that the Copiapo area also corresponds to a local minimum of coupling. However the GPS network is too sparse further North to constrain coupling variations between 28° and 25°S. We use InSAR (Interferometric Synthetic Aperture Radar) to provide additional insights on interseismic strain accumulation and the

  17. Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone. The case of the right-lateral Karakorum fault.

    NASA Astrophysics Data System (ADS)

    Leloup, P. H.; Boutonnet, E.; Arnaud, N.; Paquette, J. L.; Davis, W. J.; Hattori, K.

    2012-04-01

    quartz ribbon with the QSR method from 5 samples across the Tangtse shear zone are higher in the two mylonitic strands than in the surrounding rocks. The corresponding integrated shear rate is on the order of 5.7 E-14 s-1, which would corresponds to an integrated fault rate on the order of 1.45 cm yr-1. Such rate is close to, but somewhat higher, than the fault rate deduced from geological constraints. This study conducted in the frontal part of the Himalayan orogen shows that large continental strike-slip faults can be linked with magmatism and be stable for more than 20 Ma, even in the hottest part of the orogen where strain localization is supposed to be at a minimum. While de fault zone propagates along strike, deformation also migrates across-strike within the ~8km wide shear zone.

  18. ROS accumulation and oxidative damage to cell structures in Saccharomyces cerevisiae wine strains during fermentation of high-sugar-containing medium.

    PubMed

    Landolfo, Sara; Politi, Huguette; Angelozzi, Daniele; Mannazzu, Ilaria

    2008-06-01

    To further elucidate the impact of fermentative stress on Saccharomyces cerevisiae wine strains, we have here evaluated markers of oxidative stress, oxidative damage and antioxidant response in four oenological strains of S. cerevisiae, relating these to membrane integrity, ethanol production and cell viability during fermentation in high-sugar-containing medium. The cells were sampled at different fermentation stages and analysed by flow cytometry to evaluate membrane integrity and accumulation of reactive oxygen species (ROS). At the same time, catalase and superoxide dismutase activities, trehalose accumulation, and protein carbonylation and degradation were measured. The results indicate that the stress conditions occurring during hypoxic fermentation in high-sugar-containing medium result in the production of ROS and trigger an antioxidant response. This involves superoxide dismutase and trehalose for the protection of cell structures from oxidative damage, and protein catabolism for the removal of damaged proteins. Cell viability, membrane integrity and ethanol production depend on the extent of oxidative damage to cellular components. This is, in turn, related to the 'fitness' of each strain, which depends on the contribution of individual cells to ROS accumulation and scavenging. These findings highlight that the differences in individual cell resistances to ROS contribute to the persistence of wine strains during growth under unfavourable culture conditions, and they provide further insights into our understanding of yeast behaviour during industrial fermentation.

  19. A musculoskeletal modeling approach for estimating anterior cruciate ligament strains and knee anterior-posterior shear forces in stop-jumps performed by young recreational female athletes.

    PubMed

    Kar, Julia; Quesada, Peter M

    2013-02-01

    The central goal of this study was to contribute to the advancements being made in determining the underlying causes of anterior cruciate ligament (ACL) injuries. ACL injuries are frequently incurred by recreational and professional young female athletes during non-contact impact activities in sports like volleyball and basketball. This musculoskeletal-neuromuscular study investigated stop-jumps and factors related to ACL injury like knee valgus and internal-external moment loads, knee anterior-posterior (AP) shear forces, ACL strains and internal forces. Motion capture data was obtained from the landing phase of stop-jumps performed by eleven young recreational female athletes and electromyography (EMG) data collected from quadriceps, hamstring and gastrocnimius muscles which were then compared to numerically estimated activations. Numerical simulation tools used were Inverse Kinematics, Computed Muscle Control and Forward Dynamics and the knee modeled as a six degree of freedom joint. Results showed averaged peak strains of 12.2 ± 4.1% in the right and 11.9 ± 3.0% in the left ACL. Averaged peak knee AP shear forces were 482.3 ± 65.7 N for the right and 430.0 ± 52.4 N for the left knees, approximately equal to 0.7-0.8 times body weight across both knees. A lack of symmetry was observed between the knees for valgus angles (p < 0.04), valgus moments (p < 0.001) and muscle activations (p < 0.001), all of which can be detrimental to ACL stability during impact activities. Comparisons between recorded EMG data and estimated muscle activations show the relation between electrical signal and muscle depolarization. In summary, this study outlines a musculoskeletal simulation approach that provides numerical estimations for a number of variables associated with ACL injuries in female athletes performing stop-jumps.

  20. A Multiscale Model of Shear flow of Granular Materials with Breakable Particles: Role of Force Chain Instabilities and Implications for Strain Localization and Stability of Sliding

    NASA Astrophysics Data System (ADS)

    Elbanna, A. E.; Lieou, C.; Karimi, P.; Carlson, J.; Li, R.

    2014-12-01

    Quantitative prediction of the shear response and energy partitioning in granular layers with breakable particles remains a major challenge in earthquake physics. As a first step towards addressing this problem, we use the Shear Transformation Zone theory (STZ) to model irreversible plastic deformations in the gouge due to local rearrangements of the particles. To model grain breakage, we use an energy balance approach to augment the STZ theory with an equation for the grain size reduction as a function of the applied work rate and pressure. Previous numerical and experimental work on grain breakage was inconclusive regarding whether grain breakage was a softening or a hardening mechanism. The outcome depends on the competition between evolving grain angularity and reduced particle size with both processes affecting force chain dynamics. To account for local force chain instabilities, we develop a small scale model for force chain buckling that is integrated within the STZ formulation through variations of the minimum flow stress of the system. We idealize a typical force chain as an array of particles with both translational and rotational degrees of freedom. The relative motion between the particles is resisted by sliding and rolling friction. The sliding friction is provided by a rigid-plastic element. The rolling resistance is modeled by a torsional spring. The deflection of the force chain is resisted by an array of lateral springs representing the effective confinement provided by the rest of the granular medium Our results suggest that there exist a critical grain size below which the buckling stress for the force chain, and hence the flow stress, decreases linearly with the decrease of the particle size. Furthermore, we show that grain breakage is a potential weakening mechanism at high pressures and at strain rates high enough to reduce the grain size below the aforementioned critical limit. Grain breakage also promotes strain localization, particularly in

  1. Mineral reactions and strain localization in a sheared mafic granulite infiltrated by melt (Seiland Igneous Province, Norway)

    NASA Astrophysics Data System (ADS)

    degli Alessandrini, Giulia; Menegon, Luca; Malaspina, Nadia; Dijkstra, Arjan; Anderson, Mark

    2016-04-01

    This study investigates the deformation mechanisms of a metagabbroic dyke experiencing syn-kinematic melt-rock interaction in a continental lower-crustal shear zone in the Seiland Igneous Province (northern Norway). Solid state shearing occurred at T ≈750-820 °C, P ≈0.75-0.95 GPa and was coeval with melt infiltration from dehydration melting of adjacent metasediments, as evident from thin leucosome veinlets within the dykes. The mylonite consists of cpx [Ca0.47,Mg0.35,Fe0.18]SiO3 + opx [Ca0.1,Mg0.5,Fe0.4]SiO3 + pl (An77Ab22Or1) porphyroclasts with localized grt and ilm coronas, embedded in a fine grained matrix of cpx + opx + pl + qtz + ilm ± kfs. Porphyroclasts range in size (diameter) between 25 to 650 μm, whereas the fine grain matrix is consistently below 10 μm (average 4-7 μm). Porphyroclasts show varying degrees of elongation, with the opx reaching aspect ratios of 1:16 and the cpx reaching rare maxima of 1:7. Cpx and pl porphyroclasts are micro-fractured and micro-boudinaged with fine-grained material infill. Texturally, opx porphyroclasts display a marked crystallographic preferred orientation (CPO) and activity of the {100}<001> and minor {100}<010> slip systems, whereas cpx and pl porphyroclasts are randomly oriented. All porphyroclasts have strong internal misorientations (undulatory and sweeping extinction) and lack recovery features (subgrains). The fine-grained polyphase matrix wrapping the porphyroclasts displays weak to absent CPO, with the exception of opx that shows a {100} poles-to-planes maxima perpendicular to the foliation. Based on the microstructure, we argue that a large part of the matrix is the product of metamorphic reactions in the presence of melt. To test this hypothesis, the interaction between the studied mafic dyke and an adjacent felsic leucosome was modelled using PerpleX for P-T conditions ranging between 7-9 kbar and 700-1000°C. Results show that the syn-kinematic mineral assemblage (opx + cpx + pl + qtz + ilm ± kfs

  2. Three hen strains fed photoisomerized trans,trans CLA-rich soy oil exhibit different yolk accumulation rates and source-specific isomer deposition.

    PubMed

    Shinn, Sara E; Gilley, Alex D; Proctor, Andrew; Anthony, Nicholas B

    2015-04-01

    Most CLA chicken feeding trials used cis,trans (c,t) and trans,cis (t,c) CLA isomers to produce CLA-rich eggs, while reports of trans,trans (t,t) CLA enrichment in egg yolks are limited. The CLA yolk fatty acid profile changes and the 10-12 days of feeding needed for maximum CLA are well documented, but there is no information describing CLA accumulation during initial feed administration. In addition, no information on CLA accumulation rates in different hen strains is available. The aim of this study was to determine a mathematical model that described yolk CLA accumulation and depletion in three hen strains by using t,t CLA-rich soybean oil produced by photoisomerization. Diets of 30-week Leghorns, broilers, and jungle fowl were supplemented with 15% CLA-rich soy oil for 16 days, and eggs were collected for 32 days. Yolk fatty acid profiles were measured by GC-FID. CLA accumulation and depletion was modeled by both quadratic and piecewise regression analysis. A strong quadratic model was proposed, but it was not as effective as piecewise regression in describing CLA accumulation and depletion. Broiler hen eggs contained the greatest concentration of CLA at 3.2 mol/100 g egg yolk, then jungle fowl at 2.9 mol CLA, and Leghorns at 2.3 mol CLA. The t,t CLA isomer levels remained at 55% of total yolk CLA during CLA feeding. However, t-10,c-12 (t,c) CLA concentration increased slightly during CLA accumulation and was significantly greater than c-9,t-11 CLA. Jungle fowl had the smallest increase in yolk saturated fat with CLA yolk accumulation.

  3. The Ray Corner High Strain Zone of the Norumbega Fault System in Maine: A Complex History of Ductile Shear, Brittle Deformation, and Paleoseismicity

    NASA Astrophysics Data System (ADS)

    West, D. P., Jr.; Pollock, S. G.; Song, W. J.; Price, N.; Johnson, S. E.

    2014-12-01

    Recent detailed bedrock mapping in south-central Maine in the vicinity of the regionally extensive Norumbega fault system has revealed the presence of a previously unrecognized zone of overprinting ductile and brittle deformation herein referred to as the Ray Corner high strain zone. The nearly one km wide zone trends approximately 045o and can be mapped continuously for a distance of over 20 kms. Like nearly all previously mapped high strain zones of the Norumbega fault system, the Ray Corner high strain zone is contained within a single lithotectonic belt (Casco Bay Group) and thus while recording a polyphase history of high strain displacement at different structural levels, it does not represent a terrain boundary at the present erosional surface. The Ray Corner high strain zone is characterized by an older (likely Devonian) pervasive steeply dipping mylonitic foliation. Lineations, where observable, are sub-horizontal and a variety of kinematic indicators indicate dextral shear. Quartz microstructures are consistent with grain boundary migration and sub-grain rotation recrystallization processes, whereas feldspars are fractured. EBSD analysis of recrystallized quartz ribbons reveal strong CPO patterns in c-axis pole figures (both Y maxima and bipolar maxima between Y and Z) that are consistent with prism + romb slip. These finding are consistent with mylonitic deformation occurring at temperatures in the 400-500oC range. Superimposed on these earlier mylonitic fabrics in zones several 10s of meters across are a wide range of lower temperature brittle deformational features. These include spectacular pseudotachylyte fault and injection veins up to 3 cm thick, cataclastite breccia cored brittle faults up to 10 cm thick, and silicified fault breccia zones up to several meters across. While most of these brittle features cross-cut the earlier ductile fabrics, locally there is microstructural evidence of deformed pseudotachylyte layers within the mylonites

  4. Crustal strain accumulation on Southern Basin and Range Province faults modulated by distant plate boundary earthquakes? Evidence from geodesy, seismic imaging, and paleoseismology

    NASA Astrophysics Data System (ADS)

    Bennett, R. A.; Shirzaei, M.; Broermann, J.; Spinler, J. C.; Holland, A. A.; Pearthree, P.

    2014-12-01

    GPS in Arizona reveals a change in the pattern of crustal strain accumulation in 2010 and based on viscoelastic modeling appears to be associated with the distant M7.2 El Mayor-Cucapah (EMC) earthquake in Baja California, Mexico. GPS data collected between 1999 and 2009 near the Santa Rita normal fault in SE Arizona reveal a narrow zone of crustal deformation coincident with the fault trace, delineated by W-NW facing Pleistocene fault scarps of heights 1 to 7 m. The apparent deformation zone is also seen in a preliminary InSAR interferogram. Total motion across the zone inferred using an elastic block model constrained by the pre-2010 GPS measurements is ~1 mm/yr in a sense consistent with normal fault motion. However, continuous GPS measurements throughout Arizona reveal pronounced changes in crustal velocity following the EMC earthquake, such that the relative motion across the Santa Rita fault post-2010 is negligible. Paleoseismic evidence indicates that mapped Santa Rita fault scarps were formed by two or more large magnitude (M6.7 to M7.6) surface rupturing normal-faulting earthquakes 60 to 100 kyrs ago. Seismic refraction and reflection data constrained by deep (~800 m) well log data provide evidence of progressive, possibly intermittent, displacement on the fault through time. The rate of strain accumulation observed geodetically prior to 2010, if constant over the past 60 to 100 kyrs, would imply an untenable minimum slip rate deficit of 60 to 100 m since the most recent earthquake. One explanation for the available geodetic, seismic, and paleoseismic evidence is that strain accumulation is modulated by viscoelastic relaxation associated with frequent large magnitude earthquakes in the Salton Trough region, episodically inhibiting the accumulation of elastic strain required to generate large earthquakes on the Santa Rita and possibly other faults in the Southern Basin and Range. An important question is thus for how long the postseismic velocity changes

  5. Documentation of programs that compute 1) quasi-static tilts produced by an expanding dislocation loop in an elastic and viscoelastic material, and 2) surface shear stresses, strains, and shear displacements produced by screw dislocations in a vertical slab with modulus contrast

    USGS Publications Warehouse

    McHugh, Stuart

    1976-01-01

    The material in this report can be grouped into two categories: 1) programs that compute tilts produced by a vertically oriented expanding rectangular dislocation loop in an elastic or viscoelastic material and 2) programs that compute the shear stresses, strains, and shear displacements in a three-phase half-space (i.e. a half-space containing a vertical slab). Each section describes the relevant theory, and provides a detailed guide to the operation of the programs. A series of examples is provided at the end of each section.

  6. Project Hotspot: Linear accumulation rates of late Cenozoic basalt at Kimama, Idaho, and implications for crustal strain and subsidence rates of the central Snake River Plain

    NASA Astrophysics Data System (ADS)

    Rodgers, D. W.; Potter, K. E.; Shervais, J. W.; Champion, D. E.; Duncan, R. A.

    2013-12-01

    Project Hotspot's Kimama drill hole on the Snake River Plain, Idaho recovered a 1912 m thick section of basalt core that ranges in age from ~700 ka to at least 6.14 Ma, based on five 40Ar/39Ar analyses and twenty paleomagnetic age assignments. Fifty-four flow groups comprising 510 individual flows were defined, yielding an average recurrence interval of ~11,400 years between flows. Age-depth analysis indicate that, over thicknesses >150 m and age spans >500 k.y., accumulation rates were constant at 30 m/100 k.y. The existence and persistence of this linear accumulation rate for greater than 5 m.y. documents an external tectonic control on eruption dynamics. One conceptual model relates accumulation rates to horizontal crustal strain, such that far-field extension rate controls the periodicity of dikes that feed basalt flows. In this model, each of the 54 flow groups would have a deep-seated, relatively wide (1-10m) dike that branches upward into a network of narrow (10-100 cm) dikes feeding individual lava flows. Assuming an east-west lateral lava flow extent of up to 50 km, the Kimama data record a steady-state crustal strain rate of 10-9 to 10-10 y-1. This rate is comparable to modern, decadal strain rates measured with GPS in the adjacent Basin & Range province, but exceeds decadal strain rates of zero measured in the eastern Snake River Plain. Linear accumulation rates also provide insight into basalt subsidence history. In this model, the middle-upper crust subsides due to the added weight of lava flows, the added weight of mid-crustal sills/dikes, and thermal contraction in the wake of the Yellowstone hot spot. Isostatic compensation would occur in the (nearly) molten lower crust. Assuming constant surface elevation and a basalt density of 2.6 g/cm3, the lava flow weight would account for 87% of the burial through time, yielding a steady-state "tectonic" subsidence rate of 4 m/100 k.y. attributed to the driving forces of mid-crustal injection and/or thermal

  7. Strain localization and fluid infiltration during subduction initiation: the record from sheared mafic amphibolites at the base of the New Caledonian ophiolite

    NASA Astrophysics Data System (ADS)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Vitale-Brovarone, Alberto; Monié, Patrick; Chauvet, Alain; Whitechurch, Hubert

    2015-04-01

    Most of our knowledge on subduction inception and obduction processes comes from metamorphic soles structurally associated with peridotite tectonites at the base of many ophiolites, and from early-obduction, rarely deformed, magmatic dikes emplaced at different level of the mantle sequence. These dikes record a partial refertilization of obducted ophiolites through subduction-derived fluids. However, these dikes are rarely deformed and/or metamorphosed. Here, we study the base of the New Caledonian ophiolite, using a combination of structural field studies and petrological-geochemical-geochronological analysis, with the aim of linking deformation and metasomatism through fluid infiltration and recrystallization. We report the existence of strongly sheared mafic amphibolites within the base of the New Caledonian obducted ophiolite, ~ 50-100 m above the basal thrust contact and < 1000 m below the mantle-crust transition. These ~ N150-striking, hm-long and m- to several m-thick shear bands correspond to former small-scale intrusions (and surrounding peridotites), highly boudinaged and amphibolitized at high temperatures (750-800 °C), providing evidence that strain localized at the base of the ophiolite. Mafic protoliths of these amphibolites consisted of plagioclase and orthopyroxene (± olivine and calcic amphibole in places). We show that deformation is intimately associated to at least three major stages of fluid infiltration on mafic intrusions. The first stage of deformation and metasomatism coincides with amphibolitization and controlled the later channelization of fluids. The formation of calcic amphiboles records the percolation of Ca and Al-rich aqueous fluids. Amphibole-plagioclase geothermobarometry indicates high temperature and low pressure conditions (i.e. 750-800 °C; 3-5 kbar). Thermochronological data from hornblende (40Ar/39Ar) suggest that this deformation episode occurred at ~ 55 Ma, coinciding with E-dipping subduction initiation and incipient

  8. Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone

    USGS Publications Warehouse

    Frankel, K.L.; Brantley, K.S.; Dolan, J.F.; Finkel, R.C.; Klinger, R.E.; Knott, J.R.; Machette, M.N.; Owen, L.A.; Phillips, F.M.; Slate, J.L.; Wernicke, B.P.

    2007-01-01

    The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right-lateral strike-slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high-resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ???297 ?? 9 m of right-lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic 10Be and 36C1 geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/-20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on 36Cl depth profiles is 63 ?? 8 ka. Combining the offset measurement with the cosmogenic 10Be date yields a geologic fault slip rate of 4.2 +1.9/-1.1 mm yr-1, whereas the 36Cl data indicate 4.7 +0.9/-0.6 mm yr-1 of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ???8.5 to 10 mm yr-1. This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant. Copyright 2007 by the American Geophysical Union.

  9. InSAR time-series constraints on inter-seismic strain accumulation and creep distribution along North Anatolian and Chaman Faults

    NASA Astrophysics Data System (ADS)

    Havazli, E.; Fattahi, H.; Amelung, F.

    2013-12-01

    In many aspects, the San Andreas and the North Anatolian fault zones show many similarities. They are similarly right-lateral, strike-slip faults, at the same time, are transforms. However, they vary in the maximum amount of lateral displacement and show different topographic features. The maximum offset is nearly 300 km along the San Andreas Fault whereas it is approximately 85-90 km along the North Anatolian Fault. In recent years, interseismic crustal velocities and strains have been determined for North Anatolian Fault Zone through repeated measurements using the Global Positioning System and satellite radar interferometry. The Chaman Fault in Pakistan and Afghanistan is the only major fault along the western India-Eurasia plate boundary zone and probably accommodates the entire relative plate motion of 30-35 mm/yr. Recent GPS and InSAR studies on the Chaman fault yield slip rates of 18 × 1 mm/yr. The inconsistency in geologic, geodetic and seismic slip rates along the Chaman Fault need investigations to better understand the geodynamic responses of the Indo-Asia collision along its western boundary. We use InSAR time-series analysis using archived and new SAR imagery to constrain strain accumulation across the North Anatolian Fault and Chaman Faults. We expect a relative accuracy of InSAR measurements better than 1 mm/yr over 100 km, made possible by recent advances in flattening residual, orbital error and atmospheric correction strategies [Fattahi & Amelung, 2013]. After validation of the technique in Southern San Andreas Fault, using GPS observations, we apply the same InSAR time-series approach to constrain strain accumulation across the North Anatolian and Chaman Faults. We will use the InSAR data to establish the first-order fault properties of the Chaman and North Anatolian Faults (creep distribution, locking depth) using analytical two-dimensional elastic strain accumulation models along different transects across the faults. Our preliminary results

  10. Optimization of macroelement concentrations, pH and osmolarity for triacylglycerol accumulation in Rhodococcus opacus strain PD630

    PubMed Central

    2013-01-01

    The refinement of biodiesel or renewable diesel from bacterial lipids has a great potential to make a contribution for energy production in the future. This study provides new data concerning suitable nutrient concentrations for cultivation of the Gram-positive Rhodococcus opacus PD630, which is able to accumulate large amounts of lipids during nitrogen limitation. Enhanced concentrations of magnesium have been shown to increase the final optical density and the lipid content of the cells. Elevated phosphate concentrations slowed down the onset of the accumulation phase, without a clear effect on the final optical density and the cell’s lipid content. A robust growth of R. opacus was possible in the presence of ammonium concentrations of up to 1.4 g l-1 and sucrose concentrations of up to 240 g l-1, with an optimum regarding growth and lipid storage observed in the range of 0.2 to 0.4 g l-1 ammonium and 20 to 40 g l-1 sucrose, respectively. Moreover, R. opacus showed tolerance to high salt concentrations. PMID:23855965

  11. Strain accumulation in the New Madrid and Wabash Valley seismic zones from 14 years of continuous GPS observation

    NASA Astrophysics Data System (ADS)

    Craig, Timothy J.; Calais, Eric

    2014-12-01

    The mechanical behavior—and hence earthquake potential—of faults in continental interiors is an issue of critical importance for the resultant seismic hazard, but no consensus has yet been reached on this controversial topic. The debate has focused on the central and eastern United States, in particular, the New Madrid Seismic Zone, struck by four magnitude 7 or greater earthquakes in 1811-1812, and to a lesser extent the Wabash Valley Seismic Zone just to the north. A key aspect of this issue is the rate at which strain is currently accruing on those plate interior faults, a quantity that remains debated. Here we address this issue with an analysis of up to 14.6 years of continuous GPS data from a network of 200 sites in the central United States centered on the New Madrid and Wabash Valley seismic zones. We find that the high-quality sites in these regions show motions that are consistently within the 95% confidence limit of zero deformation. These results place an upper bound on strain accrual on faults of 0.2 mm/yr and 0.6 mm/yr in the New Madrid and Wabash Valley Seismic Zones, respectively. For the New Madrid region, where a paleoseismic record is available for the past ˜5000 years, we argue that strain accrual—if any—does not permit the 500-900 year repeat time of paleo-earthquakes observed in the Upper Mississippi Embayment. These results, together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors, indicate that either tectonic loading rates or fault properties vary with time in the New Madrid Seismic Zone and possibly plate wide.

  12. Relationship between Nitrite Reduction and Active Phosphate Uptake in the Phosphate-Accumulating Denitrifier Pseudomonas sp. Strain JR 12

    PubMed Central

    Barak, Yoram; van Rijn, Jaap

    2000-01-01

    Phosphate uptake by the phosphate-accumulating denitrifier Pseudomonas sp. JR12 was examined with different combinations of electron and carbon donors and electron acceptors. Phosphate uptake in acetate-supplemented cells took place with either oxygen or nitrate but did not take place when nitrite served as the final electron acceptor. Furthermore, nitrite reduction rates by this denitrifier were shown to be significantly reduced in the presence of phosphate. Phosphate uptake assays in the presence of the H+-ATPase inhibitor N,N′-dicyclohexylcarbodiimide (DCCD), in the presence of the uncoupler carbonyl cyanide 3-chlorophenylhydrazone (CCCP), or with osmotic shock-treated cells indicated that phosphate transport over the cytoplasmic membrane of this bacterium was mediated by primary and secondary transport systems. By examining the redox transitions of whole cells at 553 nm we found that phosphate addition caused a significant oxidation of a c-type cytochrome. Based on these findings, we propose that this c-type cytochrome serves as an intermediate in the electron transfer to both nitrite reductase and the site responsible for active phosphate transport. In previous studies with this bacterium we found that the oxidation state of this c-type cytochrome was significantly higher in acetate-supplemented, nitrite-respiring cells (incapable of phosphate uptake) than in phosphate-accumulating cells incubated with different combinations of electron donors and acceptors. Based on the latter finding and results obtained in the present study it is suggested that phosphate uptake in this bacterium is subjected to a redox control of the active phosphate transport site. By means of this mechanism an explanation is provided for the observed absence of phosphate uptake in the presence of nitrite and inhibition of nitrite reduction by phosphate in this organism. The implications of these findings regarding denitrifying, phosphate removal wastewater plants is discussed. PMID

  13. Construction of a Vibrio cholerae prototype vaccine strain O395-N1-E1 which accumulates cell-associated cholera toxin B subunit.

    PubMed

    Rhie, Gi-eun; Jung, Hae-Mi; Kim, Bong Su; Mekalanos, John J

    2008-10-01

    Because of its production and use in Vietnam, the most widely used oral cholera vaccine consists of heat- or formalin-killed Vibrio cholerae whole cells (WC). An earlier version of this type of vaccine called whole cell-recombinant B subunit vaccine (BS-WC) produced in Sweden also contained the B subunit of cholera toxin (CTB). Both WC and BS-WC vaccines produced moderate levels of protection in field trials designed to evaluate their cholera efficacy. V. cholerae cells in these vaccines induce antibacterial immunity, and CTB contributes to the vaccine's efficacy presumably by stimulating production of anti-toxin neutralizing antibody. Although more effective than the WC vaccine, the BS-WC vaccine has not been adopted for manufacture by developing world countries primarily because the CTB component is difficult to manufacture and include in the vaccine in the doses needed to induce significant immune responses. We reasoned this was a technical problem that might be solved by engineering strains of V. cholerae that express cell-associated CTB that would co-purify with the bacterial cell fraction during the manufacture of WC vaccine. Here we report that construction of a V. cholerae O1 classical strain, O395-N1-E1, that has been engineered to accumulate CTB in the periplasmic fraction by disrupting the epsE gene of type II secretion pathway. O395-N1-E1 induces anti-CTB IgG and vibriocidal antibodies in mice immunized with two doses of formalin killed whole cells. Intraperitoneal immunization of mice with O395-N1-E1 induced a significantly higher anti-CTB antibody response compared to that of the parental strain, O395-N1. Our results suggest that this prototype cholera vaccine candidate strain may assist in preparing improved and inexpensive oral BS-WC cholera vaccine without the need to purify CTB separately. PMID:18582519

  14. [Study of the Accumulation of Rec A from Bacillus subtilis in the Mitochondria of a Recombinant Strain of the Yeast Yarrowia lipolytica].

    PubMed

    Isakova, E P; Deryabina, Y I; Leonovich, O A; Zylkova, M V; Biriukova, Iu K

    2016-01-01

    No eukaryotic species has a system for homologous DNA recombination of the mitochondrial genome. We report on an integrative genetic systembased on the pQ-SRUS construct that allows the expression of the RecA recombinase from Bacillus subtilis and its transportation to mitochondria of Yarrowia lipolytica. The targeting of recombinant RecA to mitochondria is provided by leader sequences (5'-UTR and 3-UTR) derived from the SOD2 gene mRNA, which exhibit affinity to the outer mitochondrial membrane and provides cotranslational import of RecA to the inner space of mitochondria. The accumulation of RecA in mitochondria of the Y. lipolytica recombinant strain bearing the pQ-SRUS construct has been shown by immunoblotting of purified mitochondrial preparations.

  15. Differential accumulation of poly(A)+ RNA between virulent and double-stranded RNA-induced hypovirulent strains of Cryphonectria (Endothia) parasitica.

    PubMed Central

    Powell, W A; Van Alfen, N K

    1987-01-01

    The double-stranded RNA responsible for transmissible hypovirulence in Cryphonectria (Endothia) parasitica was found to affect the accumulation of specific poly(A)+ RNA. Using differential hybridization techniques, two genes were isolated, Vir1 and Vir2, which were specifically expressed as poly(A)+ RNAs in the virulent cells. The highly expressed RNA sequences from these genes were not found in total RNA isolated from either American or European hypovirulent strains, although the genes were present in their genomes. Other virulence- and hypovirulence-specific RNA sequences were also detected. One isolated hypovirulence-specific RNA sequence was expressed in both virulent and hypovirulent cells, but in a two- to fourfold-higher concentration in the hypovirulent cells. The results show that hypovirulence is associated with concurrent changes in a few highly expressed poly(A)+ RNAs, which suggests a specific effect of the double-stranded RNA on fungal gene expression. Images PMID:2446118

  16. [Study of the Accumulation of Rec A from Bacillus subtilis in the Mitochondria of a Recombinant Strain of the Yeast Yarrowia lipolytica].

    PubMed

    Isakova, E P; Deryabina, Y I; Leonovich, O A; Zylkova, M V; Biriukova, Iu K

    2016-01-01

    No eukaryotic species has a system for homologous DNA recombination of the mitochondrial genome. We report on an integrative genetic systembased on the pQ-SRUS construct that allows the expression of the RecA recombinase from Bacillus subtilis and its transportation to mitochondria of Yarrowia lipolytica. The targeting of recombinant RecA to mitochondria is provided by leader sequences (5'-UTR and 3-UTR) derived from the SOD2 gene mRNA, which exhibit affinity to the outer mitochondrial membrane and provides cotranslational import of RecA to the inner space of mitochondria. The accumulation of RecA in mitochondria of the Y. lipolytica recombinant strain bearing the pQ-SRUS construct has been shown by immunoblotting of purified mitochondrial preparations. PMID:27266246

  17. The French neurotropic vaccine strain of yellow fever virus accumulates mutations slowly during passage in cell culture.

    PubMed

    Holbrook, M R; Li, L; Suderman, M T; Wang, H; Barrett, A D

    2000-08-01

    This study of the yellow fever French neurotropic vaccine strain from the Institut Pasteur (FNV-IP) demonstrates that this viral genome is not as stable as that of the 17D-204 vaccine virus. FNV-IP was plaque-purified three times and then passaged eight times in Vero cells. Viral populations from the second and eighth passage post purification were sequenced and compared to the published sequences of FNV-IP. The passage-2 viral population had 31 nucleotide and nine amino acid changes compared to the parental virus while the passage-8 virus had six additional nucleotide changes encoding a single amino acid substitution. The plaque-purified virus also had two sequence deletions in the 3'-noncoding region. The plaque purification resulted in selection of a passage-2 virus that had a mouse LD(50) of 20 pfu/ml, 67-fold greater than parental FNV-IP which had an LD(50) of 0.3 pfu/ml. Subsequent passage in Vero cells resulted in a passage-8 virus which had increased neurovirulence with an LD(50) of 3.2 pfu/ml. The only amino acid difference between the passage-2 and passage-8 viruses was at amino acid 638 of NS5 which lies within domain V of the RNA-dependent-RNA polymerase. Overall, these data indicate that FNV-IP virus has an inherently less stable genome than 17D vaccine virus and a variable viral population.

  18. Escherichia coli rimM and yjeQ null strains accumulate immature 30S subunits of similar structure and protein complement

    PubMed Central

    Leong, Vivian; Kent, Meredith; Jomaa, Ahmad; Ortega, Joaquin

    2013-01-01

    Assembly of the Escherichia coli 30S ribosomal subunits proceeds through multiple parallel pathways. The protein factors RimM, YjeQ, RbfA, and Era work in conjunction to assist at the late stages of the maturation process of the small subunit. However, it is unclear how the functional interplay between these factors occurs in the context of multiple parallel pathways. To understand how these factors work together, we have characterized the immature 30S subunits that accumulate in ΔrimM cells and compared them with immature 30S subunits from a ΔyjeQ strain. The cryo-EM maps obtained from these particles showed that the densities representing helices 44 and 45 in the rRNA were partially missing, suggesting mobility of these motifs. These 30S subunits were also partially depleted in all tertiary ribosomal proteins, particularly those binding in the head domain. Using image classification, we identified four subpopulations of ΔrimM immature 30S subunits differing in the amount of missing density for helices 44 and 45, as well as the amount of density existing in these maps for the underrepresented proteins. The structural defects found in these immature subunits resembled those of the 30S subunits that accumulate in the ΔyjeQ strain. These findings are consistent with an “early convergency model” in which multiple parallel assembly pathways of the 30S subunit converge into a late assembly intermediate, as opposed to the mature state. Functionally related factors will bind to this intermediate to catalyze the last steps of maturation leading to the mature 30S subunit. PMID:23611982

  19. Geometry and kinematic evolution of Riedel shear structures, Capitol Reef National Park, Utah

    NASA Astrophysics Data System (ADS)

    Katz, Yoram; Weinberger, Ram; Aydin, Atilla

    2004-03-01

    Riedel shear structures are common fault patterns identified within shear zones and related to the embryonic stages of fault formation. This study focuses on the geometry of outcrop-scale natural shear zones consisting of different generations of Riedel structures, exposed in the Jurassic Navajo sandstone, Capitol Reef National Park, Utah. Geometric analysis of different structures shows that the spacing of synthetic R-deformation bands increases with the spacing of antithetic R'-deformation bands. Systematic correlation is found between the R-band spacing and the angles formed between R- and R'-bands. Examination of young Riedel structures shows their tendency to localize along narrow, elongated domains sub-parallel to the shear direction and create denser Riedel networks. We suggest that the evolution of Riedel structures is dominated by two mechanisms: (1) discrete faulting in the form of conjugate deformation bands, generally complying with the Mohr-Coulomb criteria, and (2) granular flow, which rotates mainly the R'-deformation bands. Both mechanisms are intensified with progressive strain, decreasing the deformation-band spacing and increasing the R- to R'-angles. The tendency of young Riedel structures to organize in dense elongated networks is related to strain localization during the shear-zone evolution. We suggest a kinematic explanation for the evolution of Riedel-structure networks, which relates the network geometry to the progressive accumulation and localization of shear strain.

  20. On the structure of the internal wave field: The impact of the distribution of shear and strain variance in wavenumber-frequency space on mixing estimates

    NASA Astrophysics Data System (ADS)

    Chinn, Brian

    Data from an archive of McLane Moored Profiler (MP) deployments are used to investigate the role of internal waves, and in general physical processes occupying this frequency range, on the dissipation of kinetic energy and to study how these processes work to shape the spectral characteristics of the wavefield. The data used come from 5 separate field programs, and by analyzing them as a set, provides the opportunity to not only compare and contrast an unprecedented range of different forcing regimes, but also supports the discovery of unique observations of physical processes at individual sites. This dissertation is composed of four separate chapters that address different aspects of this idea. First, two records, one to the North (MP1) and one to the South (MP2), of Mindoro strait, which lies between the South China Sea and the Sulu Sea, were used to study the processes driving mixing in the Strait. The records are dominated by near inertial variability and internal tides at both the diurnal and semidiurnal frequencies. Analysis of the velocity records from MP1 reveals suggestive evidence for the presence of parametric subharmonic instability of the diurnal tide as well as curious rectilinear bottom trapped near inertial waves. Diffusivities estimated via Thorpe scale analysis at MP1 reveal weak mixing over much of the water column that increases nearly an order of magnitude near the bottom and is strongly tied to the tides. Average mixing rates are found to be insufficient to produce observed changes in water mass properties suggesting additional processes are at play. Second, variability in the shear to strain ratio (Ro) is investigated with the goal of understanding the factors that influence Ro variability, quantifying its time and space scales, and determining how variability impacts estimates of parameterized diffusivity. Time mean Ro from each of the sites spans a range from 1 to 10 and within each record, temporal variability around the mean is

  1. Micromechanics of shear banding

    SciTech Connect

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  2. 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.

  3. The strain accumulation studies between India and Antarctica in the Southern Indian Peninsula with GPS/GNSS-Geodesy by geodetically tying the two continents

    NASA Astrophysics Data System (ADS)

    Narayana Babu, R. N.; EC, M.

    2011-12-01

    Two global networks (IND and ANT) have been chosen that geodetically connect the two continents to holistically understand the geodynamical and crustal deformation processes in the south of Indian peninsula between India and Antarctica,. Since the baseline length between HYDE, India and MAIT, Antarctica is more than 10,000 km, it is mandatory to form these two different networks to improve the accuracy of the baseline measurements by GPS and so the IGS Station at Diego Garcia (DGAR) is chosen as the common station between the two networks. 13 years of data from 1997 to 2010 were used. By these global networks' analyses, the stations HYDE and MAIT are geodetically tied through DGAR. Very long baselines have been estimated from HYDE and also from Kerguelen (KERG) to other chosen IGS stations in and around India and Antarctica. Our analysis and results using ANT network show an increase in the baseline lengths between Kerguelen in Antarctic plate and other stations such as SEY1, DGAR and COCO and shortening of baseline lengths between HYDE in Indian plate and all these above stations using IND network. The analysis using ANT network also shows lengthening of baselines from Kerguelen to the sites Yaragadee (YAR1) and Tidbinbilla (TID2) in Australian plate; and Seychelles (SEY1) in Male plate, COCO in the diffuse plate boundary between India and Australia and DGAR in Capricorn plate at the rates of 5.3cm/yr, 3.8cm/yr, 5.6mm/yr, 3.03 cm/yr and 5.5 cm/yr respectively. The high rate of movement of COCO Island in comparison to Seychelles could be the result of excessive strain accumulation due to the Indo-Australia diffuse plate boundary forces acting upon this region. The estimated elastic strain accumulation shows an increasing trend of 1.27x 10-8 yr-1 in the south of Indian peninsula. Our results show the precision of approximately 3-4mm (North), 5-6 mm (East), and 10-12mm (vertical) for the estimation of site coordinates. These results provide new information on the

  4. Geodetic Tying of Antarctica and India With 10 Years of Continuous GPS Measurements for Geodynamical and Strain Accumulation Studies in the South of Indian Peninsula

    NASA Astrophysics Data System (ADS)

    Ec, M.; N, R.

    2008-12-01

    To holistically understand the geodynamical and crustal deformation processes between India and Antarctica, two global networks (IND and ANT) have been chosen. The objective is to geodetically connect the two continents. The IGS Station at Diego Garcia (DGAR) is the common station between the two networks. 10 years of data from 1997 to 2007 were used. By these global networks' analyses, the stations HYDE in India and MAIT at Antarctica are geodetically tied through the station DGAR. Very long baselines have been estimated from HYDE and also from Kerguelen (KERG) to other chosen IGS stations in and around India and Antarctica. Our analysis and results using ANT network show an increase in the baseline lengths between Kerguelen in Antarctic plate and other stations such as SEY1, DGAR and COCO and shortening of baseline lengths between HYDE in Indian plate and all these above stations using IND network. The analysis using ANT network also shows lengthening of baselines from Kerguelen to the sites Yaragadee (YAR1) and Tidbinbilla (TID2) in Australian plate; and Seychelles (SEY1) in Male plate, COCO in the diffuse plate boundary between India and Australia and DGAR in Capricorn plate at the rates of 5.3cm/yr, 3.8cm/yr, 5.6mm/yr, 3.03 cm/yr and 5.5 cm/yr respectively. The high rate of movement of COCO Island in comparison to Seychelles could be the result of excessive strain accumulation due to the Indo-Australia diffuse plate boundary forces acting upon this region. The estimated elastic strain accumulation shows an increasing trend of 1.27x 10-8 yr-1 in the south of Indian peninsula. Our results show the precision of approximately 3-4mm (North), 5-6 mm (East), and 10-12mm (vertical) for the estimation of site coordinates. These results provide new information on the direction and rate of Indian plate motion, the driving mechanisms of Indian plate and intraplate seismicity of the Indian Ocean on the whole.

  5. Elevated temperature differentially affects virulence, VirB protein accumulation, and T-pilus formation in different Agrobacterium tumefaciens and Agrobacterium vitis strains.

    PubMed

    Baron, C; Domke, N; Beinhofer, M; Hapfelmeier, S

    2001-12-01

    That gene transfer to plant cells is a temperature-sensitive process has been known for more than 50 years. Previous work indicated that this sensitivity results from the inability to assemble a functional T pilus required for T-DNA and protein transfer to recipient cells. The studies reported here extend these observations and more clearly define the molecular basis of this assembly and transfer defect. T-pilus assembly and virulence protein accumulation were monitored in Agrobacterium tumefaciens strain C58 at different temperatures ranging from 20 degrees C to growth-inhibitory 37 degrees C. Incubation at 28 degrees C but not at 26 degrees C strongly inhibited extracellular assembly of the major T-pilus component VirB2 as well as of pilus-associated protein VirB5, and the highest amounts of T pili were detected at 20 degrees C. Analysis of temperature effects on the cell-bound virulence machinery revealed three classes of virulence proteins. Whereas class I proteins (VirB2, VirB7, VirB9, and VirB10) were readily detected at 28 degrees C, class II proteins (VirB1, VirB4, VirB5, VirB6, VirB8, VirB11, VirD2, and VirE2) were only detected after cell growth below 26 degrees C. Significant levels of class III proteins (VirB3 and VirD4) were only detected at 20 degrees C and not at higher temperatures. Shift of virulence-induced agrobacteria from 20 to 28 or 37 degrees C had no immediate effect on cell-bound T pili or on stability of most virulence proteins. However, the temperature shift caused a rapid decrease in the amount of cell-bound VirB3 and VirD4, and VirB4 and VirB11 levels decreased next. To assess whether destabilization of virulence proteins constitutes a general phenomenon, levels of virulence proteins and of extracellular T pili were monitored in different A. tumefaciens and Agrobacterium vitis strains grown at 20 and 28 degrees C. Levels of many virulence proteins were strongly reduced at 28 degrees C compared to 20 degrees C, and T-pilus assembly did

  6. Accumulate repeat accumulate codes

    NASA Technical Reports Server (NTRS)

    Abbasfar, Aliazam; Divsalar, Dariush; Yao, Kung

    2004-01-01

    In this paper we propose an innovative channel coding scheme called 'Accumulate Repeat Accumulate codes' (ARA). This class of codes can be viewed as serial turbo-like codes, or as a subclass of Low Density Parity Check (LDPC) codes, thus belief propagation can be used for iterative decoding of ARA codes on a graph. The structure of encoder for this class can be viewed as precoded Repeat Accumulate (RA) code or as precoded Irregular Repeat Accumulate (IRA) code, where simply an accumulator is chosen as a precoder. Thus ARA codes have simple, and very fast encoder structure when they representing LDPC codes. Based on density evolution for LDPC codes through some examples for ARA codes, we show that for maximum variable node degree 5 a minimum bit SNR as low as 0.08 dB from channel capacity for rate 1/2 can be achieved as the block size goes to infinity. Thus based on fixed low maximum variable node degree, its threshold outperforms not only the RA and IRA codes but also the best known LDPC codes with the dame maximum node degree. Furthermore by puncturing the accumulators any desired high rate codes close to code rate 1 can be obtained with thresholds that stay close to the channel capacity thresholds uniformly. Iterative decoding simulation results are provided. The ARA codes also have projected graph or protograph representation that allows for high speed decoder implementation.

  7. The importance of shear heating for shear localization during tectonic nappe displacement

    NASA Astrophysics Data System (ADS)

    Kiss, Dániel; Duretz, Thibault; Podladchikov, Yuri; Schmalholz, Stefan M.

    2016-04-01

    Localization of deformation plays a major role during tectonic processes at all scale, from the formation of deformation bands within single grains up to crustal and lithospheric scale shear zones. The role of shear localization is particularly important for the formation and displacement of tectonic nappes during orogeny. It has been shown that a simple one-dimensional (1D) thermo-mechanical shear zone model, which considers a power-law flow law and temperature dependent viscosity, can to the first-order explain thrust-sheet and fold nappe formation. This 1D model could successfully reproduce the overall shear strain distribution across natural nappes and shear zones, but underestimated systematically the shear strain at the base of the nappe and shear zone. This underestimation indicates that certain processes have been ignored in the analysis. We present therefore a new 1D thermo-mechanical model which also considers shear heating and the related thermal softening of temperature-dependent viscosity to quantify the impact of shear heating on strain localization during nappe displacement. We perform a dimensional analysis of the equations which describe the 1D shear zone model to determine the dimensionless parameters which control the deformation. Three deformation modes controlled by dimensionless parameters will be distinguished: (1) shear deformation for which shear heating is negligible, (2) shear deformation for which shear heating is moderate and displacement velocities stay in the range of plate velocities, (3) shear deformation for which shear heating is significant and velocities and temperatures increase continuously (thermal runaway). The 1D shear zone model is applied to the Helvetic nappe system in general and the Morcles, Doldenhorn and Wildhorn nappes in particular. For the geological and microstructural data available for the Helvetic nappe system we determine whether shear heating was important during nappe formation or not. The 1D results are

  8. Shear modulus estimation with vibrating needle stimulation.

    PubMed

    Orescanin, Marko; Insana, Michael

    2010-06-01

    An ultrasonic shear wave imaging technique is being developed for estimating the complex shear modulus of biphasic hydropolymers including soft biological tissues. A needle placed in the medium is vibrated along its axis to generate harmonic shear waves. Doppler pulses synchronously track particle motion to estimate shear wave propagation speed. Velocity estimation is improved by implementing a k-lag phase estimator. Fitting shear-wave speed estimates to the predicted dispersion relation curves obtained from two rheological models, we estimate the elastic and viscous components of the complex shear modulus. The dispersion equation estimated using the standard linear solid-body (Zener) model is compared with that from the Kelvin-Voigt model to estimate moduli in gelatin gels in the 50 to 450 Hz shear wave frequency bandwidth. Both models give comparable estimates that agree with independent shear rheometer measurements obtained at lower strain rates. PMID:20529711

  9. Dynamic shear deformation in high purity Fe

    SciTech Connect

    Cerreta, Ellen K; Bingert, John F; Trujillo, Carl P; Lopez, Mike F; Gray, George T

    2009-01-01

    The forced shear test specimen, first developed by Meyer et al. [Meyer L. et al., Critical Adiabatic Shear Strength of Low Alloyed Steel Under Compressive Loading, Metallurgical Applications of Shock Wave and High Strain Rate Phenomena (Marcel Decker, 1986), 657; Hartmann K. et al., Metallurgical Effects on Impact Loaded Materials, Shock Waves and High Strain rate Phenomena in Metals (Plenum, 1981), 325-337.], has been utilized in a number of studies. While the geometry of this specimen does not allow for the microstructure to exactly define the location of shear band formation and the overall mechanical response of a specimen is highly sensitive to the geometry utilized, the forced shear specimen is useful for characterizing the influence of parameters such as strain rate, temperature, strain, and load on the microstructural evolution within a shear band. Additionally, many studies have utilized this geometry to advance the understanding of shear band development. In this study, by varying the geometry, specifically the ratio of the inner hole to the outer hat diameter, the dynamic shear localization response of high purity Fe was examined. Post mortem characterization was performed to quantify the width of the localizations and examine the microstructural and textural evolution of shear deformation in a bcc metal. Increased instability in mechanical response is strongly linked with development of enhanced intergranular misorientations, high angle boundaries, and classical shear textures characterized through orientation distribution functions.

  10. Zipper and freeway shear zone junctions

    NASA Astrophysics Data System (ADS)

    Passchier, Cees; Platt, John

    2016-04-01

    Ductile shear zones are usually presented as isolated planar high-strain domains in a less deformed wall rock, characterised by shear sense indicators such as characteristic deflected foliation traces. Many shear zones, however, form branched systems and if movement on such branches is contemporaneous, the resulting geometry can be complicated and lead to unusual fabric geometries in the wall rock. For Y-shaped shear zone junctions with three simultaneously operating branches, and with slip directions at a high angle to the branch line, eight basic types of shear zone triple junctions are possible, divided into three groups. The simplest type, called freeway junctions, have similar shear sense on all three branches. If shear sense is different on the three branches, this can lead to space problems. Some of these junctions have shear zone branches that join to form a single branch, named zipper junctions, or a single shear zone which splits to form two, known as wedge junctions. Closing zipper junctions are most unusual, since they form a non-active high-strain zone with opposite deflection of foliations. Shear zipper and shear wedge junctions have two shear zones with similar shear sense, and one with the opposite sense. All categories of shear zone junctions show characteristic flow patterns in the shear zone and its wall rock. Shear zone junctions with slip directions normal to the branch line can easily be studied, since ideal sections of shear sense indicators lie in the plane normal to the shear zone branches and the branch line. Expanding the model to allow slip oblique and parallel to the branch line in a full 3D setting gives rise to a large number of geometries in three main groups. Slip directions can be parallel on all branches but oblique to the branch line: two slip directions can be parallel and a third oblique, or all three branches can have slip in different directions. Such more complex shear zone junctions cannot be studied to advantage in a

  11. Time series analysis of strain accumulation along the Haiyuan fault (Gansu, China) over the 1993-2009 period, from ERS and ENVISAT InSAR data

    NASA Astrophysics Data System (ADS)

    Jolivet, Romain; Lasserre, Cecile; Doin, Marie-Pierre; Guillaso, Stéphane; Cavalié, Olivier; Peltzer, Gilles; Sun, Jianbao; Rong, Dailu; Shen, Zheng-Kang; Xu, Xiwei

    2010-05-01

    We use SAR interferometry to measure the strain accumulation along the left-lateral Haiyuan fault system (HFS), that marks the north-eastern boundary of the tibetan plateau. The last major earthquakes that occured along the HFS are the M~8 1920 Haiyuan earthquake (strike-slip mechanism) and the Ml=8-8.3 1927 Gulang earthquake that ruptured a thrust fault system. No large earthquake is reported on the central section of the HFS, the "Tianzhu seismic gap", since ~1000 years. We first analyze the complete ENVISAT SAR data archive along 4 descending and 2 ascending tracks for the 2003-2009 period and construct an InSAR-based mean Line-Of-Sight (LOS) velocity map around the HFS from the eastern end of the Qilian shan (102° E), to the west, to the Liupan shan (106° E), to the east. Data are processed using a small baseline chain type. For each track, all radar images are coregistrated to a single master and interferograms are produced using a local adaptative range filtering. Residual orbital and atmospheric delays are jointly inverted and corrected for each unwrapped interferogram. Atmospheric corrections are validated using the ERA40 global atmospheric model (ECMWF). The interferograms series on each track are then inverted to obtain the increments of LOS radar delays between acquisition dates, adapting the Lopez-Quiroz et al. 2009 time series analysis. The obtained LOS mean velocity maps show a dominant left-lateral motion across the fault with along-strike variations: some fault sections are locked at shallow depth while others are creeping and local vertical movements are observed (subsidence in the "Jingtai" pull-apart basin). For various fault slip rates imposed below 20 km (4-10 mm/yr), we model the shallow velocity by inverting the mean LOS velocity maps for both strike-slip and dip-slip motion on vertical, 5km x 2.5km discretized patches, using a least-square method with an appropriate degree of smoothing. The fault geometry follows the surface trace of the

  12. Lateral shear interferometry with holo shear lens

    NASA Astrophysics Data System (ADS)

    Joenathan, C.; Mohanty, R. K.; Sirohi, R. S.

    1984-12-01

    A simple method for obtaining lateral shear using holo shear lenses (HSL) has been discussed. This simple device which produces lateral shears in the orthogonal directions has been used for lens testing. The holo shear lens is placed at or near the focus of the lens to be tested. It has also been shown that HSL can be used in speckle shear interferometry as it performs both the functions of shearing and imaging.

  13. Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone: The case of the right-lateral Karakorum fault

    NASA Astrophysics Data System (ADS)

    Boutonnet, Emmanuelle; Leloup, P. H.; Arnaud, N.; Paquette, J.-L.; Davis, W. J.; Hattori, K.

    2012-08-01

    New structural observations coupled with 15 U/Pb and 24 Ar/Ar new ages from the Karakorum shear zone (KSZ) constrain the timing and slip rate of the right-lateral Karakorum fault zone (KFZ), one of the great continental Asian strike-slip faults. In the Tangtse-Darbuk area, the Tangtse (SW) and Muglib (NE) mylonitic strands of the KSZ frame the less deformed Pangong Range. Inherited U/Pb ages show that granitic protoliths are mostly from the Karakorum and Ladakh batoliths, with a major Miocene melting event lasting from ≥21.5 to 13.5 Ma. Some of the Miocene granitic bodies show structural evidence for intrusion synkinematic to the KSZ. The oldest of these granitoids is 18.8 ± 0.4 Ma old, implying that deformation started prior to ˜19 Ma. Microstructural data show that right-lateral deformation pursued during cooling. Ar/Ar data show that ductile deformation stopped earlier in the Tangtse (˜11 Ma) than in the Muglib strand (˜7 Ma). Deformation ended at ˜11 Ma in the Tangtse strand while it is still active in the Muglib strand, suggesting a progressive localization of deformation. When merged with published observations along the KFZ, these data suggest that the KFZ nucleated in the North Ayilari range at least ˜22 Ma ago. The long-term fault rate is 0.84 to 1.3 cm/yr, considering a total offset of 200 to 240 km. The KSZ collected magma produced within the shear zone and/or deeper in crust for which the producing mechanism stays unclear but was not the lower crustal channel flow.

  14. Folds with vergence opposite to the sense of shear

    NASA Astrophysics Data System (ADS)

    Krabbendam, M.; Leslie, A. G.

    1996-06-01

    Near-similar folds with persistent NW-vergence occur in the southeast Highlands of Scotland and are interpreted to have formed in a regime of SE-directed non-coaxial shear. The sense of shear is corroborated by independent kinematic indicators. The folds are formed by a mechanism in which strongly partitioned shear produced an alternation of high strain zones, forming long limbs, and low strain zones, forming short limbs. Progressive strain results in the rotation and attenuation of strain markers in the long limbs and in the consumption of low strain zones. High strain may ultimately lead to the disappearance of the short limbs.

  15. Time series and MinTS analysis of strain accumulation along the Haiyuan fault (Gansu, China) over the 2003-2010 period, from ENVISAT InSAR data

    NASA Astrophysics Data System (ADS)

    Jolivet, R.; Lasserre, C.; Lin, N.; Simons, M.; Doin, M.; Hetland, E. A.; Muse, P.; Peltzer, G.; Jianbao, S.; Dailu, R.

    2010-12-01

    We use SAR interferometry to measure the strain accumulation along the left-lateral Haiyuan fault system (hereafter HFS), that marks the north-eastern boundary of the tibetan plateau. The last major earthquakes that occured along the HFS are the M~8 1920 Haiyuan earthquake (strike-slip mechanism) and the Ml=8-8.3 1927 Gulang earthquake that ruptured a thrust fault system. There has been no known large earthquake on the central section of the HFS, the “Tianzhu seismic gap”, in the last ~1000 years. We first analyze the complete ENVISAT SAR data archive along three descending and two ascending tracks for the 2003-2009 period and construct an InSAR-based mean line-of-sight (LOS) velocity map around the HFS from the eastern end of the Qilian Shan (102° E), to the west, to the Liupan Shan (106° E), to the east. We empirically correct our interferograms for propagation delays associated with changes on the stratified atmospheric structure. We then estimate the mean LOS velocity for each track using a time series analysis which reveals the existence of a 40 km long creeping segment located at the western end of the 1920 rupture. Extending from the Jingtai pull-apart basin, which shows a 2-3 mm/yr subsidence rate, to the Mao Mao Shan, the creep rate is estimated to reach 8 mm/yr locally and is higher than the long term loading rate of the Haiyuan fault, estimated geodetically at 5±1 mm/yr. The surface extension of the creeping segment is colocated with strong micro- and moderate seismic activity. We also explore the possibility of transient creep during the 2003-2010 time period, using a SBAS style, smoothed, time series analysis and the Multiscale Interferometric Time Series method (MinTS, CalTech, see Hetland et al. 2010 AGU abstract). While classic time series methods are based on a pixel-by-pixel approach and do not consider spatial data covariances, due to residual atmospheric noise, the wavelet decomposition of each interferograms and the time inversion in the

  16. Multidirectional direct simple shear apparatus

    SciTech Connect

    DeGroot, D.J.; Germaine, J.T.; Ladd, C.C.

    1993-09-01

    The paper describes a new simple shear testing device, the multidirectional direct simple shear (MDSS) apparatus, for testing soil specimens under conditions that simulate, at the element level, the state of stress acting within the foundation soil of an offshore Arctic gravity structure. The MDSS uses a circular specimen that is consolidated under both a vertical effective stress ({sigma}{sub vc}{prime}) and a horizontal shear stress ({tau}{sub 1}). The specimen is subsequently sheared undrained by applying a second independent horizontal shear stress ({tau}{sub 2}) at an angle {theta} relative to the horizontal consolidation shear stress {tau}{sub 1}. Evaluation of the MDSS first compares conventional K{sub D}-consolidated undrained direct simple shear (CK{sub 0}UDSS) test data ({tau}{sub 1} = 0) on normally consolidated Boston blue clay (BBC) with results obtained in the Geonor DSS device. The MDSS gives lower secant Young`s modulus values and on average 8% lower strengths, but produces remarkably less scatter in the test results than the Geonor DSS. Kinematic proof tests with an elastic material (rubber) confirm that the setup procedure, application of forces, and strain measurement systems in the MDSS work properly and produce repeatable results. Results from a MDSS test program on BBC wherein specimens were first normally consolidated with {sigma}{sub vc}{prime} and {tau}{sub 1} = 0.2{sigma}{sub vc}{prime} and then sheared undrained at {theta} varing in 30{degree} increments from zero (shear in same direction) to 150{degree} show dramatic differences in the response of the soil as a function of {theta}. The peak undrained strength varies almost twofold from 0 = 0 to 120{degree}, while the deformation behavior varies from very brittle at low {theta} angles to becoming ductile at higher angles. 11 refs., 15 figs.

  17. Shear rates measurements in natural shear zones using quartz piezometers.

    NASA Astrophysics Data System (ADS)

    Boutonnet, Emmanuelle; Hervé Leloup, Philippe

    2010-05-01

    Whether deformation within the deep continental crust is fundamentally concentrated in narrow shear zones or distributed in wide zones stays a major controversy of the earth sciences. This is in part because direct measurements of ductile strain or strain rate are difficult, especially when deformation is intense as it is the case in ductile shear zones. Paleo-shear stress can be evaluated by using paleo-piezometers that link shear stress to the size of recrystallized minerals. Such piezometers are calibrated by microphysical models or experimental studies. Indirect measurements of strain rate in natural rocks can be achieved using shear stress, an estimation of the temperature of deformation, and assuming a flow law. However, such estimates have rarely been validated by independent constraints. By comparing shear rates calculated from paleopiezometry, and measured in situ in the same outcrop we determined the more appropriate paleopiezometer and power flow law in order to generalize the method to other outcrops. Within the Ailao - Red River shear zone (ASSR, SE Asia) paleo strain rates during the Miocene left-lateral shear are estimated between 1*10-13 s-1 and 2*10-13 s-1 from tectonic considerations. At site C1, by combining dating of syntectonic dykes and measurements of their deformation, the strain rate is calculated between 3 and 4*10-14 s-1 between 29 to 22 Ma, (Sassier et al., JGR, 2009). Quartz ribbons of sample YY33 from the same outcrop show continuous dynamic recrystallisation (DRX) mechanisms, characterized by subgrain rotation nucleation, and growth by grain boundary migration (Shimitzu et al. JSG, 2008). This dislocation creep regime is compatible with the microphysical models of Twiss (Pure Ammp. Geoph., 1977) and Shimitzu (JSG, 2008) and the experimental piezometer of Stipp and Tullis (GRL, 2003). The measured quartz grain size range between 10 and 960 μm, while the mean recrystallized grain size is 112.2 ± 1.5μm. The associated paleostress is

  18. Evidence for lower crustal ductile strain localization in southern New York

    USGS Publications Warehouse

    Zoback, M.D.; Prescott, W.H.; Krueger, S.W.

    1985-01-01

    Historic triangulation data have been analysed to determine whether intraplate seismicity is associated with ongoing ductile deformation in the lower crust. The model we have attempted to test is basically analogous to strain accumulation and release along plate-boundary strike-slip faults like the San Andreas Fault in California. That is, beneath an elastic-seismogenic upper crust ???20 km thick, strain is preferentially localized within ductile shear zones in the lower crust due to broad-scale plate driving forces. The localized lower-crustal ductile strain causes stress and strain to accumulate elastically in the brittle crust which is eventually released in crustal earthquakes. At greater depths, this localized shear deformation probably develops into pervasive ductile flow. Numerous geodetic measurements along the San Andreas Fault confirm that earthquakes in the brittle upper crust are produced by the release of elastic strain that results from ongoing ductile shear or slip in the lower crust1,2. We have found evidence of high rates of crustal deformation in southern New York which suggest that localized ductile shear is occurring in the lower crust. ?? 1985 Nature Publishing Group.

  19. 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

  20. Haptic Edge Detection Through Shear.

    PubMed

    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

  1. Shear banding in titanium with controlled elongations at 10/sup 6//sec

    SciTech Connect

    Staudhammer, K.P.; Gray, A.J.

    1989-01-01

    Adiabatic shear bands were obtained in titanium with controlled strains to 10.8%. Two types of shear bands were observed and characterized. In general the quantity and shear band width increased with increasing elongation. At elongations below /approximately/5% the shear bands were typically characteristic of shear bands observed at lower strain rates. Above 5% elongations many of the shear bands contained a boundary regime adjacent to the shear band and increased in width with increasing total elongation. This effect was attributed to the strain heat. 14 refs., 9 figs.

  2. 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.

  3. Effect of finite strain on clast-based vorticity gauges

    NASA Astrophysics Data System (ADS)

    Stahr, Donald W., III; Law, Richard D.

    2011-07-01

    Clast-based vorticity gauges utilize orientations of grains assumed to have behaved as isolated rigid particles suspended in a flowing viscous matrix. A fundamental assumption behind use of the method is that sufficient strain has accumulated for high aspect ratio grains to rotate into positions approaching their stable sink orientation, and that clasts below a critical aspect ratio may be observed in any orientation relative to the flow plane. We constructed a numerical model to explore the effect of variable finite strain on development of the orientation distribution of a large population of rigid clasts embedded in a viscous medium for end-member pure and simple shear and for several distinct general shear flows. Our model predicts the technique will tend to produce vorticity overestimates for lower vorticity flows for a wide range of finite strain. The model also indicates that clast populations in moderate to high vortical flows tend to develop shape preferred orientations that closely resemble those expected for flows of lower vorticity. We conclude that clast-based methods are not effective for extracting detailed kinematic information from a mylonite deformed in a flow with arbitrary boundary conditions. In fact, it appears that most general shear flows continued long enough to develop moderate-high finite strains will tend to produce a clast orientation distribution that will yield a visual estimate of the critical aspect ratio that suggests approximately equal contributions of pure and simple shear components.

  4. Temporal oscillations of the shear stress and scattered light in a shear-banding--shear-thickening micellar solution.

    PubMed

    Azzouzi, H; Decruppe, J P; Lerouge, S; Greffier, O

    2005-08-01

    The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.

  5. Temporal oscillations of the shear stress and scattered light in a shear-banding-shear-thickening micellar solution

    NASA Astrophysics Data System (ADS)

    Azzouzi, H.; Decruppe, J. P.; Lerouge, S.; Greffier, O.

    2005-08-01

    The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.

  6. Novel shear mechanism in nanolayered composites

    SciTech Connect

    Mara, Nathan; Bhattacharyya, Dhriti; Hirth, John P; Dickerson, Patricia O; Misra, Amit

    2009-01-01

    Recent studies have shown that two-phase nanocomposite materials with semicoherent interfaces exhibit enhanced strength, deformability, and radiation damage resistance. The remarkable behavior exhibited by these materials has been attributed to the atomistic structure of the bi-metal interface that results in interfaces with low shear strength and hence, strong barriers for slip transmission due to dislocation core spreading along the weak interfaces. In this work, the low interfacial shear strength of Cu/Nb nanoscale multilayers dictates a new mechanism for shear banding and strain softening during micropillar compression. Previous work investigating shear band formation in nanocrystalline materials has shown a connection between insufficient strain hardening and the onset of shear banding in Fe and Fe-10% Cu, but has also shown that hardening does not necessarily offset shear banding in Pd nanomaterials. Therefore, the mechanisms behind shear localization in nanocrystalline materials are not completely understood. Our findings, supported by molecular dynamics simulations, provide insight on the design of nanocomposites with tailored interface structures and geometry to obtain a combination of high strength and deformability. High strength is derived from the ability of the interfaces to trap dislocations through relative ease of interfacial shear, while deformability can be maximized by controlling the effects of loading geometry on shear band formation.

  7. Accumulate-Repeat-Accumulate-Accumulate-Codes

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Dolinar, Sam; Thorpe, Jeremy

    2004-01-01

    Inspired by recently proposed Accumulate-Repeat-Accumulate (ARA) codes [15], in this paper we propose a channel coding scheme called Accumulate-Repeat-Accumulate-Accumulate (ARAA) codes. These codes can be seen as serial turbo-like codes or as a subclass of Low Density Parity Check (LDPC) codes, and they have a projected graph or protograph representation; this allows for a high-speed iterative decoder implementation using belief propagation. An ARAA code can be viewed as a precoded Repeat-and-Accumulate (RA) code with puncturing in concatenation with another accumulator, where simply an accumulator is chosen as the precoder; thus ARAA codes have a very fast encoder structure. Using density evolution on their associated protographs, we find examples of rate-lJ2 ARAA codes with maximum variable node degree 4 for which a minimum bit-SNR as low as 0.21 dB from the channel capacity limit can be achieved as the block size goes to infinity. Such a low threshold cannot be achieved by RA or Irregular RA (IRA) or unstructured irregular LDPC codes with the same constraint on the maximum variable node degree. Furthermore by puncturing the accumulators we can construct families of higher rate ARAA codes with thresholds that stay close to their respective channel capacity thresholds uniformly. Iterative decoding simulation results show comparable performance with the best-known LDPC codes but with very low error floor even at moderate block sizes.

  8. Growth and (137)Cs uptake and accumulation among 56 Japanese cultivars of Brassica rapa, Brassica juncea and Brassica napus grown in a contaminated field in Fukushima: Effect of inoculation with a Bacillus pumilus strain.

    PubMed

    Djedidi, Salem; Kojima, Katsuhiro; Ohkama-Ohtsu, Naoko; Bellingrath-Kimura, Sonoko Dorothea; Yokoyama, Tadashi

    2016-06-01

    Fifty six local Japanese cultivars of Brassica rapa (40 cultivars), Brassica juncea (10 cultivars) and Brassica napus (6 cultivars) were assessed for variability in growth and (137)Cs uptake and accumulation in association with a Bacillus pumilus strain. Field trial was conducted at a contaminated farmland in Nihonmatsu city, in Fukushima prefecture. Inoculation resulted in different responses of the cultivars in terms of growth and radiocesium uptake and accumulation. B. pumilus induced a significant increase in shoot dry weight in 12 cultivars that reached up to 40% in one B. rapa and three B. juncea cultivars. Differences in radiocesium uptake were observed between the cultivars of each Brassica species. Generally, inoculation resulted in a significant increase in (137)Cs uptake in 22 cultivars, while in seven cultivars it was significantly decreased. Regardless of plant cultivar and bacterial inoculation, the transfer of (137)Cs to the plant shoots (TF) varied by a factor of up to 5 and it ranged from to 0.011 to 0.054. Five inoculated cultivars, showed enhanced shoot dry weights and decreased (137)Cs accumulations, among which two B. rapa cultivars named Bitamina and Nozawana had a significantly decreased (137)Cs accumulation in their shoots. Such cultivars could be utilized to minimize the entry of radiocesium into the food chain; however, verifying the consistency of their radiocesium accumulation in other soils is strongly required. Moreover, the variations in growth and radiocesium accumulation, as influenced by Bacillus inoculation, could help selecting well grown inoculated Brassica cultivars with low radiocesium accumulation in their shoots.

  9. Growth and (137)Cs uptake and accumulation among 56 Japanese cultivars of Brassica rapa, Brassica juncea and Brassica napus grown in a contaminated field in Fukushima: Effect of inoculation with a Bacillus pumilus strain.

    PubMed

    Djedidi, Salem; Kojima, Katsuhiro; Ohkama-Ohtsu, Naoko; Bellingrath-Kimura, Sonoko Dorothea; Yokoyama, Tadashi

    2016-06-01

    Fifty six local Japanese cultivars of Brassica rapa (40 cultivars), Brassica juncea (10 cultivars) and Brassica napus (6 cultivars) were assessed for variability in growth and (137)Cs uptake and accumulation in association with a Bacillus pumilus strain. Field trial was conducted at a contaminated farmland in Nihonmatsu city, in Fukushima prefecture. Inoculation resulted in different responses of the cultivars in terms of growth and radiocesium uptake and accumulation. B. pumilus induced a significant increase in shoot dry weight in 12 cultivars that reached up to 40% in one B. rapa and three B. juncea cultivars. Differences in radiocesium uptake were observed between the cultivars of each Brassica species. Generally, inoculation resulted in a significant increase in (137)Cs uptake in 22 cultivars, while in seven cultivars it was significantly decreased. Regardless of plant cultivar and bacterial inoculation, the transfer of (137)Cs to the plant shoots (TF) varied by a factor of up to 5 and it ranged from to 0.011 to 0.054. Five inoculated cultivars, showed enhanced shoot dry weights and decreased (137)Cs accumulations, among which two B. rapa cultivars named Bitamina and Nozawana had a significantly decreased (137)Cs accumulation in their shoots. Such cultivars could be utilized to minimize the entry of radiocesium into the food chain; however, verifying the consistency of their radiocesium accumulation in other soils is strongly required. Moreover, the variations in growth and radiocesium accumulation, as influenced by Bacillus inoculation, could help selecting well grown inoculated Brassica cultivars with low radiocesium accumulation in their shoots. PMID:26986237

  10. Small scale shear zone in calcite: AMS and microstructure

    NASA Astrophysics Data System (ADS)

    Roxerová, Zuzana; Machek, Matěj; Kusbach, Vladimír; Racek, Martin; Silva, Pedro F.

    2016-04-01

    Two structural profiles across thin shear zone in calcite from quarry in Estremoz (Portugal) were studied to find a relationship between AMS and strain in natural rocks. The mesoscopic fabric is characterized by the change from the subhorizontal coarse-grained foliation towards the ~2cm-wide shear zone center with subvertical fine-grained foliation. In microstructure, the shear zone records dynamic recrystallization of calcite aggregate which resulted in development of porphyroclastic microstructure with increasing proportion of fine-grained recrystallized matrix towards the shear zone center. Two distinct crystallographic preferred orientations of calcite were recorded. One related with porphyroclasts, characterized by subvertical orientation of calcite axes and another associated with recrystallized matrix showing subhorizontal calcite axes orientation. The magnetic susceptibility ranges from -8e-6SI to 9e-6SI, with the average -4e-6SI. The majority of the rock mass is diamagnetic, corresponding well with the thermomagnetic curves, with local paramagnetic accumulations in form of thin bands. The AMS of the both profiles exhibits stable subvertical foliation bearing vertical lineation which is locally alternated by the medium-angle foliation. We interpret the AMS fabric pattern which is perpendicular to the mineral one as a type of inverse AMS fabric, due to high iron content in major part of calcite grains The magnetic and microstructural description of the shear zone is accompanied by numerical modeling of AMS based on CPO and different proportion of porphyroclasts, matrix and mica for purposes of deciphering the influence of present microstructural features on AMS.

  11. Accumulate-Repeat-Accumulate-Accumulate Codes

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Dolinar, Samuel; Thorpe, Jeremy

    2007-01-01

    Accumulate-repeat-accumulate-accumulate (ARAA) codes have been proposed, inspired by the recently proposed accumulate-repeat-accumulate (ARA) codes. These are error-correcting codes suitable for use in a variety of wireless data-communication systems that include noisy channels. ARAA codes can be regarded as serial turbolike codes or as a subclass of low-density parity-check (LDPC) codes, and, like ARA codes they have projected graph or protograph representations; these characteristics make it possible to design high-speed iterative decoders that utilize belief-propagation algorithms. The objective in proposing ARAA codes as a subclass of ARA codes was to enhance the error-floor performance of ARA codes while maintaining simple encoding structures and low maximum variable node degree.

  12. Microbial uptake and accumulation of (/sup 14/C Carbofuran) 1,3-dihydro-2,2-dimethyl-7 benzofuranylmethyl carbamate in twenty fungal strains isolated by miniecosystem studies

    SciTech Connect

    Arunachalam, K.D.; Lakshmanan, M.

    1988-07-01

    Studies have amply demonstrated that members of the microbial world vary widely in their response to pesticides and that several factors may influence the toxicity of pesticides. Similarly, the microbial tolerance of pesticides may be affected by growth conditions, physiological conditions of cells and various stress factors which might exist in natural population. The pesticides are incorporated into microorganisms by an active or passive accumulation mechanism. Most observations of pesticide accumulation within the cells were recorded with chlorinated hydrocarbons. It was found that not only live bacterial cells, but autoclaved cells also, show a similar uptake of pesticides. Since aquatic microorganisms and plankton in freshwater and marine environments are an important nutrient source for a broad spectrum of aquatic filter-feeding organisms, their accumulation of pesticides can constitute a hazardous link in the food chain to fish and higher vertebrates.

  13. Shear Relaxations of Confined Liquids.

    NASA Astrophysics Data System (ADS)

    Carson, George Amos, Jr.

    Ultrathin (<40 A) films of octamethylcyclotetrasiloxane (OMCTS), hexadecane, and dodecane were subjected to linear and non-linear oscillatory shear between flat plates. Shearing frequencies of 0.1 to 800 s^{-1} were applied at pressures from zero to 0.8 MPa using a surface rheometer only recently developed. In most cases the plates were atomically smooth mica surfaces; the role of surface interactions was examined by replacing these with alkyl chain monolayers. OMCTS and hexadecane were examined at a temperature about 5 Celsius degrees above their melting points and tended to solidify. Newtonian plateaus having enormous viscosities were observed at low shear rates. The onset of shear thinning implied relaxation times of about 0.1 s in the linear structure of the confined liquids. Large activation volumes (~80 nm ^3) suggested that shear involved large-scale collective motion. Dodecane was studied at a much higher temperature relative to its melting point and showed no signs of impending solidification though it exhibited well-defined regions of Newtonian response and power law shear thinning. When treated with molecular sieves before use, dodecane had relaxation times which were short (0.02 s) compared to hexadecane, but still exhibited large-scale collective motion. When treated with silica gel, an unexplained long -time relaxation (10 s) was seen in the Newtonian viscosity of dodecane. The relaxation time of the linear structure, 0.005 s was very small, and the storage modulus was unresolvable. The small activation volume (7nm^3) indicated a much lower level of collective motion. The activation volume remained small when dodecane was confined between tightly bound, low energy, alkyl monolayers. At low strains the storage and loss moduli became very large (>10^4 Pa), probably due to interactions with flaws in the monolayers. Dramatic signs of wall slip were observed at large strains even at low pressures.

  14. 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

    Kelemen and Hirth (Fall 2004 AGU) presented a model for periodic, viscous shear heating instabilities along pre-existing, fine grained shear zones. This provides an attractive alternative to dehydration embrittlement for explaining intermediate-depth earthquakes, especially those in a narrow thermal window within the mantle section of subducting oceanic plates (Hacker et al JGR03). Ductile shear zones with widths of cm to m are common in shallow mantle massifs and peridotite along oceanic fracture zones. Pseudotachylites in a mantle shear zone show that shear heating temperatures exceeded the mantle solidus (Obata & Karato Tectonophys95). Olivine grain growth in shear zones is pinned by closely spaced pyroxenes; thus, once formed, these features do not `heal' on geological time scales in the absence of melt or fluid (Warren & Hirth EPSL05). Grain-size sensitive creep will be localized within these shear zones, in preference to host rocks with olivine grain size from 1 to 10 mm. Inspired by the work of Whitehead & Gans (GJRAS74), we proposed that such pre-existing shear zones might undergo repeated shear heating instabilities. This is not a new concept; what is new is that viscous deformation is limited to a narrow shear zone, because grain boundary sliding, sensitive to both stress and grain size, may accommodate creep even at high stress and high temperature. These new ideas yield a new result: simple models for a periodic shear heating instability. Last year, we presented a 1D numerical model using olivine flow laws, assuming that viscous deformation remains localized in shear zones, surrounded by host rocks undergoing elastic deformation. Stress evolves due to elastic strain and drives viscous deformation in a shear zone of specified width. Shear heating and thermal diffusion control T. A maximum of 1400 C (substantial melting of peridotite ) was imposed. Grain size evolves due to recrystallization and diffusion. For strain rates of E-13 to E-14 per sec and

  15. Development of a deep-crustal shear zone in response to syntectonic intrusion of mafic magma into the lower crust, Ivrea-Verbano zone, Italy

    USGS Publications Warehouse

    Snoke, A.W.; Kalakay, T.J.; Quick, J.E.; Sinigoi, S.

    1999-01-01

    A 1 to 1.5 km-thick, high-temperature shear zone is localized in wall rocks subparallel to the eastern intrusive contact of the Permian Mafic Complex of the Ivrea-Verbano zone (IVZ), Italy. The shear zone is characterized by concentrated ductile deformation manifested by a penetrative foliation subparallel to the intrusive contact and a northeast-plunging sillimanite lineation. Evidence of noncoaxial strain and transposition is widespread in the shear zone including such features as rootless isoclinal folds, dismemberment of competent layers, and scattered kinematic indicators. The metasedimentary rocks in the shear zone are migmatitic, and the accumulation of leucosome is variable within the shear zone. Near the intrusive contact with the Mafic Complex leucosome forms ~20 vol% of the wall rock, whereas leucosome concentrations may locally reach ~60 vol% of the wall rock near the outer limits of the shear zone. This variation in vol% leucosome suggests melt/magma migration from the inferred site of anatexis along the intrusive contact to lower-strain regions within and near the margins of the shear zone. The leucosome accumulations chiefly occur as layer-parallel concentrations, but are also folded and boudined, and locally are associated with tension gashes and fracture arrays. Networks of granitic dikes and small plutons in the eastern IVZ suggest that some magmas migrated out of the high-temperature shear zone. Some magma apparently migrated laterally along the strike of the shear zone and concentrated in areas of lower strain where the intrusive contact takes a major westward bend. The high-temperature shear zone is interpreted as a 'stretching fault' (or stretching shear zone) after Means [W.D. Means, Stretching faults, Geology 17 (1989) 893-896], whereupon the metasedimentary wall rocks and associated leucosome deformed synchronously with the multistage emplacement and deformation flow of the Mafic Complex. The recognition of a high-temperature shear zone

  16. Suppressor Mutations in the Study of Photosystem I Biogenesis: sll0088 Is a Previously Unidentified Gene Involved in Reaction Center Accumulation in Synechocystis sp. Strain PCC 6803

    PubMed Central

    Yu, Jianping; Shen, Gaozhong; Wang, Tao; Bryant, Donald A.; Golbeck, John H.; McIntosh, Lee

    2003-01-01

    In previous work, some members of our group isolated mutant strains of Synechocystis sp. strain PCC 6803 in which point mutations had been inserted into the psaC gene to alter the cysteine residues to the FA and FB iron-sulfur clusters in the PsaC subunit of photosystem I (J. P. Yu, I. R. Vassiliev, Y. S. Jung, J. H. Golbeck, and L. McIntosh, J. Biol. Chem. 272:8032-8039, 1997). These mutant strains did not grow photoautotrophically due to suppressed levels of chlorophyll a and photosystem I. In the results described here, we show that suppressor mutations produced strains that are capable of photoautotrophic growth at moderate light intensity (20 μmol m−2 s−1). Two separate suppressor strains of C14SPsaC, termed C14SPsaC-R62 and C14SPsaC-R18, were studied and found to have mutations in a previously uncharacterized open reading frame of the Synechocystis sp. strain PCC 6803 genome named sll0088. C14SPsaC-R62 was found to substitute Pro for Arg at residue 161 as the result of a G482→C change in sll0088, and C14SPsaC-R18 was found to have a three-amino-acid insertion of Gly-Tyr-Phe following Cys231 as the result of a TGGTTATTT duplication at T690 in sll0088. These suppressor strains showed near-wild-type levels of chlorophyll a and photosystem I, yet the serine oxygen ligand to FB was retained as shown by the retention of the S ≥ 3/2 spin state of the [4Fe-4S] cluster. The inactivation of sll0088 by insertion of a kanamycin resistance cartridge in the primary C14SPsaC mutant produced an engineered suppressor strain capable of photoautotrophic growth. There was no difference in psaC gene expression or in the amount of PsaC protein assembled in thylakoids between the wild type and an sll0088 deletion mutant. The sll0088 gene encodes a protein predicted to be a transcriptional regulator with sequence similarities to transcription factors in other prokaryotic and eukaryotic organisms, including Arabidopsis thaliana. The protein contains a typical helix

  17. Cultivar-Dependent Transcript Accumulation in Wheat Roots Colonized by Pseudomonas fluorescens Q8r1-96 Wild Type and Mutant Strains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In Triticum aestivum L. (wheat), the root-colonizing bacterium Pseudomonas fluorescens strain Q8r1-96 produces the antifungal metabolite 2,4-diacetylphloroglucinol (DAPG), suppresses damage caused by soilborne root pathogens, and modulates multiple stress or defense pathways in wheat roots. To test...

  18. Stress and strain relaxation in magnesium AZ31 rolled plate: In-situ neutron measurement and elastic viscoplastic polycrystal modeling

    DOE PAGES

    Wang, Huamiao; Clausen, Bjorn; Capolungo, Laurent; Beyerlein, Irene Jane; Wang, Jian; Tome, Carlos N.

    2015-07-16

    Continuous mechanical tests with strain holds (stress relaxation) and with stress holds (strain relaxation) are performed simultaneously with in-situ neutron measurements to analyze the mechanisms of stress and strain relaxation in Mg AZ31 rolled plate. A dislocation activity based constitutive model, accounting for internal stress statistical distributions, is proposed and implemented into an elastic viscoplastic self-consistent (EVPSC) framework to simultaneously describe both stress and strain relaxation. The model captures the experimental data in terms of macroscopic stress strain curves, evolution of stress and strain during holding, as well as evolution of the internal elastic strains. Model results indicate that themore » magnitude of the stress relaxed during strain holding is dependent on both, the magnitude of the flow stress and the spread of the resolved shear stress distribution. The magnitude of strain accumulated during stress holding is, on the other hand, dependent on the magnitude of the hardening rate and on the spread of the resolved shear stress distribution. Furthermore, the internal elastic strains are directly correlated with the stress state, and hence the stress relaxation during strain holds has a greater influence on the lattice strains than strain relaxation during stress holds.« less

  19. Versatility of Biofilm Matrix Molecules in Staphylococcus epidermidis Clinical Isolates and Importance of Polysaccharide Intercellular Adhesin Expression during High Shear Stress

    PubMed Central

    Schaeffer, Carolyn R.; Hoang, Tra-My N.; Sudbeck, Craig M.; Alawi, Malik; Tolo, Isaiah E.; Robinson, D. Ashley; Horswill, Alexander R.; Rohde, Holger

    2016-01-01

    ABSTRACT Staphylococcus epidermidis is a leading cause of hospital-associated infections, including those of intravascular catheters, cerebrospinal fluid shunts, and orthopedic implants. Multiple biofilm matrix molecules with heterogeneous characteristics have been identified, including proteinaceous, polysaccharide, and nucleic acid factors. Two of the best-studied components in S. epidermidis include accumulation-associated protein (Aap) and polysaccharide intercellular adhesin (PIA), produced by the enzymatic products of the icaADBC operon. Biofilm composition varies by strain as well as environmental conditions, and strains producing PIA-mediated biofilms are more robust. Clinically, biofilm-mediated infections occur in a variety of anatomical sites with diverse physiological properties. To test the hypothesis that matrix composition exhibits niche specificity, biofilm-related genetic and physical properties were compared between S. epidermidis strains isolated from high-shear and low-shear environments. Among a collection of 105 clinical strains, significantly more isolates from high-shear environments carried the icaADBC operon than did those from low-shear settings (43.9% versus 22.9%, P < 0.05), while there was no significant difference in the presence of aap (77.2% versus 75.0%, P > 0.05). Additionally, a significantly greater number of high-shear isolates were capable of forming biofilm in vitro in a microtiter assay (82.5% versus 45.8%, P < 0.0001). However, even among high-shear clinical isolates, less than half contained the icaADBC locus; therefore, we selected for ica-negative variants with increased attachment to abiotic surfaces to examine PIA-independent biofilm mechanisms. Sequencing of selected variants identified substitutions capable of enhancing biofilm formation in multiple genes, further highlighting the heterogeneity of S. epidermidis biofilm molecules and mechanisms. IMPORTANCE Staphylococcus epidermidis is a leading cause of

  20. 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

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

    SciTech Connect

    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 in 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.

  2. Characterization of plant-growth-promoting effects and concurrent promotion of heavy metal accumulation in the tissues of the plants grown in the polluted soil by Burkholderia strain LD-11.

    PubMed

    Huang, Gui-Hai; Tian, Hui-Hui; Liu, Hai-Ying; Fan, Xian-Wei; Liang, Yu; Li, You-Zhi

    2013-01-01

    Plant-growth-promoting (PGP) bacteria especially with the resistance to multiple heavy metals are helpful to phytoremediation. Further development of PGP bacteria is very necessary because of the extreme diversity of plants, soils, and heavy metal pollution. A Burkholderia sp. strain, numbered LD-11, was isolated, which showed resistances to multiple heavy metals and antibiotics. It can produce indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase and siderophores. Inoculation with the LD-11 improved germination of seeds of the investigated vegetable plants in the presence of Cu, promoted elongation of roots and hypocotyledonary axes, enhanced the dry weights of the plants grown in the soils polluted with Cu and/or Pb, and increased activity of the soil urease and the rhizobacteria diversity. Inoculation with the LD-11 significantly enhanced Cu and/or Pb accumulation especially in the roots of the plants grown in the polluted soils. Notably, LD-11 could produce siderophores in the presence of Cu. Conclusively, the PGP effects and concurrent heavy metal accumulation in the plant tissues results from combined effects of the above-mentioned multiple factors. Cu is an important element that represses production of the siderophore by the bacteria. Phytoremediation by synergistic use of the investigated plants and the bacterial strain LD-11 is a phytoextraction process. PMID:23819291

  3. Characterization of plant-growth-promoting effects and concurrent promotion of heavy metal accumulation in the tissues of the plants grown in the polluted soil by Burkholderia strain LD-11.

    PubMed

    Huang, Gui-Hai; Tian, Hui-Hui; Liu, Hai-Ying; Fan, Xian-Wei; Liang, Yu; Li, You-Zhi

    2013-01-01

    Plant-growth-promoting (PGP) bacteria especially with the resistance to multiple heavy metals are helpful to phytoremediation. Further development of PGP bacteria is very necessary because of the extreme diversity of plants, soils, and heavy metal pollution. A Burkholderia sp. strain, numbered LD-11, was isolated, which showed resistances to multiple heavy metals and antibiotics. It can produce indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase and siderophores. Inoculation with the LD-11 improved germination of seeds of the investigated vegetable plants in the presence of Cu, promoted elongation of roots and hypocotyledonary axes, enhanced the dry weights of the plants grown in the soils polluted with Cu and/or Pb, and increased activity of the soil urease and the rhizobacteria diversity. Inoculation with the LD-11 significantly enhanced Cu and/or Pb accumulation especially in the roots of the plants grown in the polluted soils. Notably, LD-11 could produce siderophores in the presence of Cu. Conclusively, the PGP effects and concurrent heavy metal accumulation in the plant tissues results from combined effects of the above-mentioned multiple factors. Cu is an important element that represses production of the siderophore by the bacteria. Phytoremediation by synergistic use of the investigated plants and the bacterial strain LD-11 is a phytoextraction process.

  4. Two-axis direct fluid shear stress sensor

    NASA Technical Reports Server (NTRS)

    Bajikar, Sateesh (Inventor); Scott, Michael A. (Inventor); Adcock, Edward E. (Inventor)

    2011-01-01

    A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.

  5. Three dimensional fabric evolution of sheared sand

    SciTech Connect

    Hasan, Alsidqi; Alshibli, Khalid

    2012-10-24

    Granular particles undergo translation and rolling when they are sheared. This paper presents a three-dimensional (3D) experimental assessment of fabric evolution of sheared sand at the particle level. F-75 Ottawa sand specimen was tested under an axisymmetric triaxial loading condition. It measured 9.5 mm in diameter and 20 mm in height. The quantitative evaluation was conducted by analyzing 3D high-resolution x-ray synchrotron micro-tomography images of the specimen at eight axial strain levels. The analyses included visualization of particle translation and rotation, and quantification of fabric orientation as shearing continued. Representative individual particles were successfully tracked and visualized to assess the mode of interaction between them. This paper discusses fabric evolution and compares the evolution of particles within and outside the shear band as shearing continues. Changes in particle orientation distributions are presented using fabric histograms and fabric tensor.

  6. Switches in the mode of transmission select for or against a poorly aphid-transmissible strain of potato virus Y with reduced helper component and virus accumulation.

    PubMed

    Legavre, T; Maia, I G; Casse-Delbart, F; Bernardi, F; Robaglia, C

    1996-07-01

    A poorly aphid-transmissible potato virus Y (PVY-PAT) variant emerged after several cycles of mechanical transmission of an initially aphid-transmissible (AT) isolate. Sequence analysis of the N-terminal region of the helper component-proteinase (HC-Pro) gene revealed a Lys to Glu change at a position previously found to abolish the HC-Pro aphid transmission activity in several potyviruses. Two cycles of aphid transmission allowed the virus population to evolve towards an AT form (PVY-ATnew) where a Glu to Lys change was observed. PVY-PAT produced lower amounts of coat protein and the accumulation of its HC-Pro in infected plants decreased from 7 to 28 days post-inoculation, as compared to PVY-ATnew. RT-PCR and restriction analysis showed that the two virus populations co-existed in the PVY-AT isolate and that the AT form was counter-selected during mechanical transmission. These observations suggest that the Lys to Glu substitution leads to decreased stability of HC-Pro resulting in poor transmissions by aphids, and further strengthen the idea that HC-Pro is involved in the accumulation of potyvirus in infected plants.

  7. Shear bands in a bulk metallic glass after large plastic deformation

    SciTech Connect

    Qu, D.D.; Wang, Y.B.; Liao, X.Z.; Shen, J.

    2012-10-23

    A transmission electron microscopy investigation is conducted to trace shear bands in a Zr{sub 53}Cu{sub 18.7}Ni{sub 12}Al{sub 16.3} bulk metallic glass after experiencing 4% plastic deformation. Shear band initiation, secondary shear band interactions, mature shear band broadening and the interactions of shear bands with shear-induced nanocrystals are captured. Results suggest that the plasticity of the bulk metallic glass is enhanced by complex shear bands and their interactions which accommodate large plastic strain and prevent catastrophic shear band propagation.

  8. The contribution of remotely triggered displacement events to the long-term strain accumulation along the Atacama Fault System, N-Chile

    NASA Astrophysics Data System (ADS)

    Victor, P.; Schurr, B.; Sobiesiak, M.; Ewiak, O.; Oncken, O.

    2012-12-01

    The Atacama Fault System (AFS) in N-Chile is an active trench-parallel fault system, located above approximately the down-dip end of coupling of the north Chilean subduction zone. The average long-term displacement rate for the last 100 000 - 10 000 years ranges between 0.2 and 0.3 mm/yr as determined by various methods and authors. The mode of displacement accumulation through time for this type of fault is not well understood. Surface ruptures along individual segments of the main fault scarp unambiguously reveal that the AFS has seismically ruptured several times during its past, but recurrence intervals are at least one order of magnitude longer than the megathrust earthquake cycle of the underlying subduction interface. Nevertheless these trench parallel fault systems bear a potential of unexpected large seismic ruptures as demonstrated by prominent examples like the Kobe Earthquak in 1995 and Denali Earthquake in 2002. The aim of this study is to quantify the relative proportion of aseismic and seismic slip through time and to investigate the impact of subduction zone earthquakes on the slip behavior of the AFS. Since 2008 we continuously monitor four active fault segments of the AFS with an array of 11 creepmeter stations, two of them co-located with Broadband seismometers. The displacement across the fault is continuously monitored with 2 samples/min with a resolution of 1μm. The displacement time series reveals that no continuous creep can be detected for 10 of the 11 stations. Instead we observe sudden displacement events correlated in time with far field megathrust earthquakes or local earthquakes on the plate interface or in the overriding crust. The most prominent event recorded on the creepmeters was the Mw=8.8 Maule earthquake in 2010 located 1500km to 1800km away from the creepmeter array. All of the stations showed a triggered sudden displacement event 6-8 min after the main shock. Correlation with seismological data from a nearby IPOC station

  9. Disentangling the role of structure and friction in shear jamming

    NASA Astrophysics Data System (ADS)

    Vinutha, H. A.; Sastry, Srikanth

    2016-06-01

    Amorphous sphere packings have been intensely investigated to understand mechanical and flow behaviour of dense granular matter and to explore universal aspects of the jamming transition, from fluid to structurally arrested states. Considerable recent research has focused on anisotropic packings of frictional grains generated by shear deformation leading to shear jamming, occurring below the jamming density for isotropic packings of frictionless grains. Here, with the aim of disentangling the role of shear-deformation-induced structures and friction in generating shear jamming, we computationally study sheared assemblies of frictionless spheres, over a wide range of densities. We demonstrate that shear deformation alone leads to the emergence of geometric features characteristic of jammed packings, with the increase of shear strain. We also show that such emergent geometry, together with friction, leads to mechanically stable, shear-jammed, packings above a threshold density that lies well below the isotropic jamming point.

  10. Nonlocal Shear Stress for Homogeneous Fluids

    NASA Astrophysics Data System (ADS)

    Todd, B. D.; Hansen, J. S.; Daivis, Peter J.

    2008-05-01

    It has been suggested that for fluids in which the rate of strain varies appreciably over length scales of the order of the intermolecular interaction range, the viscosity must be treated as a nonlocal property of the fluid. The shear stress can then be postulated to be a convolution of this nonlocal viscosity kernel with the strain rate over all space. In this Letter, we confirm that this postulate is correct by a combination of analytical and numerical methods for an atomic fluid out of equilibrium. Furthermore, we show that a gradient expansion of the nonlocal constitutive equation gives a reasonable approximation to the shear stress in the small wave vector limit.

  11. Simple shear experiments on magnetized wax-hematite samples

    NASA Astrophysics Data System (ADS)

    Cogné, Jean-Pascal; Canot-Laurent, Sandrine

    1992-08-01

    We present the results of a series of simple shear experiments on hematite-bearing paraffin wax samples. Homogeneous and continuous deformation was obtained up to a shear strain value of γ = 1.4, by deforming the samples in a temperature-controlled bath, and at a constant strain rate of 9 × 10-5 s-1. During deformation, henatite platelets progressively rotate, which has been checked by measuring the anisotropy of magnetic susceptibility (AMS). Pricipal susceptibility directions tend to paralled the corresponding principal strain directions, and AMS instensity increases with increasing strain. This supports the idea that the hematite population develops a preferred orientation by progressive rigid rotation within the paraffin matrix. Before each deformation step, an isothermal remanent magnetization (IRM) was given to the samples, within the λ1λ3 finite strain plane (the plane containing the shear direction, and normal to the shear plane), with various initial angles to the shear direction ranging from 0° to 180°. After each deformation step, the IRM was measured. I showed no deflection towards the λ2 finite strain direction. In contrast, it did show a systematic rotation within the λ1λ3 plane, always in the same sense as the rotation of strain axes (e.g. counterclockwise in sinistral shear). Furthermore, IRM deviation is of the same order of magnitude for each initial direction from 0° to 180°. This contradicts the passive model that has previously been shown to hold for IRM in coaxially deformed samples. Finally, we show that, in the shear strain range of out experiments (γ = 0 to 1.4), the deviation of IRM depends only on the shear value, and not on its initial direction, and that this deviation is equal to the rigid rotation angle of the shear strain tensor.

  12. Stress and strain relaxation in magnesium AZ31 rolled plate: In-situ neutron measurement and elastic viscoplastic polycrystal modeling

    SciTech Connect

    Wang, Huamiao; Clausen, Bjorn; Capolungo, Laurent; Beyerlein, Irene Jane; Wang, Jian; Tome, Carlos N.

    2015-07-16

    Continuous mechanical tests with strain holds (stress relaxation) and with stress holds (strain relaxation) are performed simultaneously with in-situ neutron measurements to analyze the mechanisms of stress and strain relaxation in Mg AZ31 rolled plate. A dislocation activity based constitutive model, accounting for internal stress statistical distributions, is proposed and implemented into an elastic viscoplastic self-consistent (EVPSC) framework to simultaneously describe both stress and strain relaxation. The model captures the experimental data in terms of macroscopic stress strain curves, evolution of stress and strain during holding, as well as evolution of the internal elastic strains. Model results indicate that the magnitude of the stress relaxed during strain holding is dependent on both, the magnitude of the flow stress and the spread of the resolved shear stress distribution. The magnitude of strain accumulated during stress holding is, on the other hand, dependent on the magnitude of the hardening rate and on the spread of the resolved shear stress distribution. Furthermore, the internal elastic strains are directly correlated with the stress state, and hence the stress relaxation during strain holds has a greater influence on the lattice strains than strain relaxation during stress holds.

  13. Reduced shear power spectrum

    SciTech Connect

    Dodelson, Scott; Shapiro, Charles; White, Martin J.; /UC, Berkeley, Astron. Dept. /UC, Berkeley

    2005-08-01

    Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.

  14. Experimental observations of shear band nucleation and propagation in a bulk metallic glass using wedge-like cylindrical indentation

    NASA Astrophysics Data System (ADS)

    Antoniou, Antonia Maki

    2006-12-01

    process zone front and presents an included angle of 78°-80°. The other set of bands evolves at a later stage of loading within the originally formed ones but with consistently higher included angle of around 87°. The band spacing is found to scale with the local average of maximum in-plane shear strain such that the local strain energy is minimized. The measurements shed light on the critical shear strain needed to initiate these bands. The richness of the shear band network establishes a basis for calibration of constitutive models. Experimental in-plane deformation maps show the amount of total strain that builds prior to the initiation of localized deformation. Furthermore, the maps help examine the change imposed on the surrounding strain field by the appearance of shear bands. It was verified that shear bands relax the asymptotic field by changing the order of singularity. Finally, it was seen that the shear bands are not the only accumulation of permanent deformation but that the surrounding material can accrue relatively high level of inelastic deformation (up to 5%). To rationalize these findings, the Johnson cavity expansion model is adapted and modified to account for pressure-dependent yielding conditions. The elasto-plastic boundary from such analysis is used to scale the experimental measurements for all indenter radii, loading level and spatial position beneath the indenter. The continuum finite element simulations have shown that the macroscopic measurements of force-depth indentation curves would predict a lower value of the pressure sensitivity than those observed from the detailed microscopic measurements. Moreover, a transition from pressure insensitive response to progressive pressure sensitivity is observed by decreasing the indenter radius, or in effect by increasing the level of hydrostatic pressure under the indenter. This leads to the belief that the BMG's pressure sensitivity parameter is in itself dependent on the level of the applied

  15. Non-Saccharomyces and Saccharomyces strains co-fermentation increases acetaldehyde accumulation: effect on anthocyanin-derived pigments in Tannat red wines.

    PubMed

    Medina, Karina; Boido, Eduardo; Fariña, Laura; Dellacassa, Eduardo; Carrau, Francisco

    2016-07-01

    During fermentation, Saccharomyces cerevisiae releases into the medium secondary metabolic products, such as acetaldehyde, able to react with anthocyanins, producing more stable derived pigments. However, very limited reports are found about non-Saccharomyces effects on grape fermentation. In this study, six non-Saccharomyces yeast strains, belonging to the genera Metschnikowia and Hanseniaspora, were screened for their effect on red wine colour and wine-making capacity under pure culture conditions and mixed with Saccharomyces. An artificial red grape must was prepared, containing a phenolic extract of Tannat grapes that allows monitoring changes of key phenol parameters during fermentation, but without skin solids in the medium. When fermented in pure cultures, S. cerevisiae produced higher concentrations of acetaldehyde and vitisin B (acetaldehyde reaction-dependent) compared to M. pulcherrima M00/09G, Hanseniaspora guillermondii T06/09G, H. opuntiae T06/01G, H. vineae T02/05F and H. clermontiae (A10/82Fand C10/54F). However, co-fermentation of H. vineae and H. clermontiae with S. cerevisiae resulted in a significantly higher concentration of acetaldehyde compared with the pure S. cerevisiae control. HPLC-DAD-MS analysis confirmed an increased formation of vitisin B in co-fermentation treatments when compared to pure Saccharomyces fermentation, suggesting the key role of acetaldehyde. Copyright © 2016 John Wiley & Sons, Ltd. PMID:26888345

  16. Non-Saccharomyces and Saccharomyces strains co-fermentation increases acetaldehyde accumulation: effect on anthocyanin-derived pigments in Tannat red wines.

    PubMed

    Medina, Karina; Boido, Eduardo; Fariña, Laura; Dellacassa, Eduardo; Carrau, Francisco

    2016-07-01

    During fermentation, Saccharomyces cerevisiae releases into the medium secondary metabolic products, such as acetaldehyde, able to react with anthocyanins, producing more stable derived pigments. However, very limited reports are found about non-Saccharomyces effects on grape fermentation. In this study, six non-Saccharomyces yeast strains, belonging to the genera Metschnikowia and Hanseniaspora, were screened for their effect on red wine colour and wine-making capacity under pure culture conditions and mixed with Saccharomyces. An artificial red grape must was prepared, containing a phenolic extract of Tannat grapes that allows monitoring changes of key phenol parameters during fermentation, but without skin solids in the medium. When fermented in pure cultures, S. cerevisiae produced higher concentrations of acetaldehyde and vitisin B (acetaldehyde reaction-dependent) compared to M. pulcherrima M00/09G, Hanseniaspora guillermondii T06/09G, H. opuntiae T06/01G, H. vineae T02/05F and H. clermontiae (A10/82Fand C10/54F). However, co-fermentation of H. vineae and H. clermontiae with S. cerevisiae resulted in a significantly higher concentration of acetaldehyde compared with the pure S. cerevisiae control. HPLC-DAD-MS analysis confirmed an increased formation of vitisin B in co-fermentation treatments when compared to pure Saccharomyces fermentation, suggesting the key role of acetaldehyde. Copyright © 2016 John Wiley & Sons, Ltd.

  17. Rotatable shear plate interferometer

    DOEpatents

    Duffus, Richard C.

    1988-01-01

    A rotatable shear plate interferometer comprises a transparent shear plate mounted obliquely in a tubular supporting member at 45.degree. with respect to its horizontal center axis. This tubular supporting member is supported rotatably around its center axis and a collimated laser beam is made incident on the shear plate along this center axis such that defocus in different directions can be easily measured.

  18. Time-dependent rheological behavior of natural polysaccharide xanthan gum solutions in interrupted shear and step-incremental/reductional shear flow fields

    NASA Astrophysics Data System (ADS)

    Lee, Ji-Seok; Song, Ki-Won

    2015-11-01

    The objective of the present study is to systematically elucidate the time-dependent rheological behavior of concentrated xanthan gum systems in complicated step-shear flow fields. Using a strain-controlled rheometer (ARES), step-shear flow behaviors of a concentrated xanthan gum model solution have been experimentally investigated in interrupted shear flow fields with a various combination of different shear rates, shearing times and rest times, and step-incremental and step-reductional shear flow fields with various shearing times. The main findings obtained from this study are summarized as follows. (i) In interrupted shear flow fields, the shear stress is sharply increased until reaching the maximum stress at an initial stage of shearing times, and then a stress decay towards a steady state is observed as the shearing time is increased in both start-up shear flow fields. The shear stress is suddenly decreased immediately after the imposed shear 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 shear flow fields is decreased whereas the shearing time exerts a slight influence on this behavior. (iii) In step-incremental shear flow fields, after passing through the maximum stress, structural destruction causes a stress decay behavior towards a steady state as an increase in shearing time in each step shear flow region. The time needed to reach the maximum stress value is shortened as an increase in step-increased shear rate. (iv) In step-reductional shear flow fields, after passing through the minimum stress, structural recovery induces a stress growth behavior towards an equilibrium state as an increase in shearing time in each step shear flow region. The time needed to reach the minimum stress value is lengthened as a decrease in step-decreased shear rate.

  19. Dislocation Modeling and Comparison With GPS Data to Assess Possible Elastic Strain Accumulation in the Central Lesser Antilles: New Constraints From the NSF REU Site in Dominica Between 2001 and 2007

    NASA Astrophysics Data System (ADS)

    Staisch, L.; Styron, R. H.; James, S.; Turner, H. L.; Ashlock, A.; Cavness, C. L.; Collier, X.; Fauria, K.; Feinstein, R.; Murphy, R.; Williams, B.; Mattioli, G. S.; Jansma, P. E.; Cothren, J.

    2007-12-01

    The Caribbean, North and South American plates are converging at a rate of 2 cm/yr in the central region of the Lesser Antilles arc. Here we report high-precision GPS data in concert with forward modeling of a simplified subduction zone geometry to assess strain accumulation for the Lesser Antilles trench. We are able to constrain both vertical and horizontal surface deformation from campaign and continuous GPS observations from 28 geodetic benchmarks located in Guadeloupe, Dominica and Aves Island. Precise station positions were estimated with GIPSY-OASIS II using an absolute point positioning strategy and final, precise orbits, clocks, earth orientation parameters, and x-files. All position estimates were updated to ITRF05 and a revised Caribbean Euler pole was used to place our observations in a CAR-fixed frame. Surface displacements for each site were estimated over 2-7 years. CAR-fixed velocities are projected onto a 500 kilometer transect from the LA trench to Aves Island and compared to calculated displacements for 88 different subduction models. Finite dislocations within an elastic half-space with variable parameters such as angle of the subducting slab, the downdip extent of the locked zone, and percentage of plate interface locking were investigated. Other parameters, such as trench length and slip remained constant. Using a chi-squared, best-fit statistical criterion, the GPS data constrain the subduction interface to a 75 kilometer downdip extent, a 10° dip angle, and near 50% locking. This implies that the subduction zone offshore Dominica is in an interseismic state, thus accumulating strain and causing small westward and upward displacement of the Lesser Antilles relative to the stable Caribbean interior.

  20. An empirical scaling of shear-induced outgassing during magma ascent

    NASA Astrophysics Data System (ADS)

    Namiki, A.

    2012-04-01

    Outgassing, which changes the distribution of volcanic gases in magmas, is one of the most important processes to determine the eruption styles. Shear deformation of ascending bubbly magmas at the vicinity of the volcanic conduit wall has been considered as an efficient mechanism of outgassing. On the other hand, seismological observations of volcanic eruptions reveal the long-period (LP) earthquakes, suggesting the existence of a large void space in the conduit. However both, the quantitative features of shear-induced outgassing and a mechanism to make a large void space, has still remain unknown. Here I perform a series of model experiments simulating the shear deformation of bubbly magma ascending in a volcanic conduit. Syrup foam including CO2 gas as an analogue of bubbly magma is deformed by using a timing belt. When the imposed shear strain is large enough, the height of the foam decreases indicating that outgassing occurs. Experiments also show that shear localization of syrup foam causes outgassing by making large bubbles or a crack-like void space, likely a LP earthquake source. Measured CO2 concentration above the foam increases as an evidence that the gas is came from the inside bubbles. When there is an impermeable layer at the top of the foam, the gas accumulates beneath that layer. There is a critical strain, γ, above which outgassing occurs depending on the Capillary number, Ca, γ > 1 for Ca < 1 and γ > Ca-1 for Ca≥ 1. The thickening rate of the region in which outgassing occurs is described as a function of γ-0.54Ca1.2. Outgassing occurs efficiently at the very beginning of the deformation, suggesting that intermittent magma ascent causes effective outgassing such that the eruption style becomes effusive. This hypothesis is consistent with the fact that cyclic activity has been observed during effusive dome eruptions.

  1. A void coalescence model for combined tension and shear

    NASA Astrophysics Data System (ADS)

    Butcher, C.; Chen, Z. T.

    2009-03-01

    The influence of shear loading on damage development in Gurson-based models has long been neglected resulting in inadequate fracture strain predictions at low triaxiality where shear effects become significant. The plastic limit-load fracture criterion used in advanced Gurson models neglects the influence of shear loading and overestimates the fracture strain and porosity at low triaxiality. In this paper, we extend the recently proposed shear damage model of Xue [1] to provide a stronger physical foundation by removing the simplifying assumptions. Then we directly modify the plastic limit-load fracture criterion by coupling with the extended shear damage model to account for shear weakening and failure of the intervoid ligament in void coalescence. We apply the modified plastic limit-load criterion to predict the necking of sheet tensile specimens and find very good agreement with the available experimental results.

  2. Steady-state creep of bent reinforced metal-composite plates with consideration of their reduced resistance to transverse shear 2. Analysis of calculated results

    NASA Astrophysics Data System (ADS)

    Yankovskii, A. P.

    2014-07-01

    Deformation of annular plates with different structures of helical reinforcement is studied. It is demonstrated that the use of the classical theory for calculating steady-state creep for thick reinforced plates subjected to bending leads to underprediction of the compliance of thin-walled metal-composite structures. It is also shown that there are significant shear strain rates in the binder of such plates, which has to be taken into account and which is mainly responsible for creep strain accumulation. Results calculated by two different models, which take into account the composite structure, are compared.

  3. A comparison of three popular test methods for determining the shear modulus of composite materials

    NASA Technical Reports Server (NTRS)

    Ho, H.; Tsai, M. Y.; Morton, J.; Farley, G. L.

    1993-01-01

    Three popular shear tests - the 10 deg off-axis, the +/- 45 deg tensile and the Iosipescu specimen tested in the modified Wyoming fixture - for shear modulus measurement are evaluated for a graphite-epoxy composite material system. A comparison of the shear stress-strain response for each test method is made using conventional strain gage instrumentation and moire interferometry. The uniformity and purity of the strain fields in the test sections of the specimens are discussed, and the shear responses obtained from each test technique are presented and compared. For accurate measurement of the shear modulus, the 90 deg Iosipescu specimen is recommended.

  4. A comparison of three popular test methods for determining the shear modulus of composite materials

    NASA Technical Reports Server (NTRS)

    Ho, Henjen; Tsai, Ming-Yi; Morton, John; Farley, Gary L.

    1991-01-01

    Three popular shear tests (the 10 degree off-axis, the plus or minus 45 degree tensile, and the Iosipescu specimen tested in the modified Wyoming fixture) for shear modulus measurement are evaluated for a graphite-epoxy composite material system. A comparison of the shear stress-strain response for each test method is made using conventional strain gage instrumentation and moire interferometry. The uniformity and purity of the strain fields in the test sections of the specimens are discussed, and the shear responses obtained from each test technique are presented and compared. For accurate measurement of shear modulus, the 90 degree Iosipescu specimen is recommended.

  5. Nature of stress accommodation in sheared granular material: Insights from 3D numerical modeling

    NASA Astrophysics Data System (ADS)

    Mair, Karen; Hazzard, James F.

    2007-07-01

    Active faults often contain distinct accumulations of granular wear material. During shear, this granular material accommodates stress and strain in a heterogeneous manner that may influence fault stability. We present new work to visualize the nature of contact force distributions during 3D granular shear. Our 3D discrete numerical models consist of granular layers subjected to normal loading and direct shear, where gouge particles are simulated by individual spheres interacting at points of contact according to simple laws. During shear, we observe the transient microscopic processes and resulting macroscopic mechanical behavior that emerge from interactions of thousands of particles. We track particle translations and contact forces to determine the nature of internal stress accommodation with accumulated slip for different initial configurations. We view model outputs using novel 3D visualization techniques. Our results highlight the prevalence of transient directed contact force networks that preferentially transmit enhanced stresses across our granular layers. We demonstrate that particle size distribution (psd) controls the nature of the force networks. Models having a narrow (i.e. relatively uniform) psd exhibit discrete pipe-like force clusters with a dominant and focussed orientation oblique to but in the plane of shear. Wider psd models (e.g. power law size distributions D = 2.6) also show a directed contact force network oblique to shear but enjoy a wider range of orientations and show more out-of-plane linkages perpendicular to shear. Macroscopic friction level, is insensitive to these distinct force network morphologies, however, force network evolution appears to be linked to fluctuations in macroscopic friction. Our results are consistent with predictions, based on recent laboratory observations, that force network morphologies are sensitive to grain characteristics such as particle size distribution of a sheared granular layer. Our numerical

  6. Evolution of Continental Lower Crust Recorded By an Exhumed Deep Crustal Intracontinental Shear Zone

    NASA Astrophysics Data System (ADS)

    Dumond, G.; Mahan, K. H.; Regan, S. P.; Williams, M. L.; Goncalves, P.; Wood, V. R.

    2014-12-01

    Exposures of deep crustal shear zones are fundamental records of strain localization and the temporal evolution of ductile to brittle behavior as these tectonites were exhumed to the surface. We present results from a decade of field-based research on a deeply exhumed (~35 km-paleodepths) strike-slip shear zone in the western Churchill province of the Canadian Shield. The Grease River shear zone is a >400 km-long and 7 km-thick structure that cuts the Athabasca granulite terrane, North America's largest exposure of continental lower crust (>20,000 km2). The shear zone is dominated by granulite- to amphibolite-grade L-S and L>S tectonites characterized by penetrative NE-striking steeply-dipping foliations with gently-plunging to sub-horizontal stretching and intersection lineations. These fabrics are locally overprinted by pseudotachylyte and narrow (<500 m-thick) greenschist-grade zones of cataclasite. Dextral kinematics are defined by deflected foliation trajectories, C' shear bands, and well-developed σ- and δ-type porphyroclasts of Kfs + Pl + Opx + Grt + Hb in felsic to intermediate granulite paragneisses and orthogneisses. Data collected along a well-exposed, nearly 150 km-long segment of the shear zone documents a >100 m.y. episodic record of transpressive to strike-slip intracontinental strain accumulation that coincided with two oppositely convergent orogenies: the east-vergent arc-continent collision of the 1.94-1.90 Ga Taltson orogen and the west-vergent continent-continent collision of the 1.9-1.8 Ga Trans-Hudson orogen. Deformation mechanisms evolved from distributed ductile dynamic recrystallization and grain-size reduction to localized pseudotachylyte development, cataclastic flow, and brittle faulting. Lower crustal behavior during strain localization was dynamic. Melt-weakened mono-cyclic crust was juxtaposed against strong isobarically-cooled poly-cyclic crust along the shear zone at 1.92-1.90 Ga. Brittle-ductile reactivation of the structure

  7. Interseismic strain accumulation measured by GPS in the seismic gap between Constitución and Concepción in Chile

    NASA Astrophysics Data System (ADS)

    Ruegg, J. C.; Rudloff, A.; Vigny, C.; Madariaga, R.; de Chabalier, J. B.; Campos, J.; Kausel, E.; Barrientos, S.; Dimitrov, D.

    2009-06-01

    The Concepción-Constitución area [35-37°S] in South Central Chile is very likely a mature seismic gap, since no large subduction earthquake has occurred there since 1835. Three campaigns of global positioning system (GPS) measurements were carried out in this area in 1996, 1999 and 2002. We observed a network of about 40 sites, including two east-west transects ranging from the coastal area to the Argentina border and one north-south profile along the coast. Our measurements are consistent with the Nazca/South America relative angular velocity (55.9°N, 95.2°W, 0.610°/Ma) discussed by Vigny et al. (2008, this issue) which predicts a convergence of 68 mm/year oriented 79°N at the Chilean trench near 36°S. With respect to stable South America, horizontal velocities decrease from 45 mm/year on the coast to 10 mm/year in the Cordillera. Vertical velocities exhibit a coherent pattern with negative values of about 10 mm/year on the coast and slightly positive or near zero in the Central Valley or the Cordillera. Horizontal velocities have formal uncertainties in the range of 1-3 mm/year and vertical velocities around 3-6 mm/year. Surface deformation in this area of South Central Chile is consistent with a fully coupled elastic loading on the subduction interface at depth. The best fit to our data is obtained with a dip of 16 ± 3°, a locking depth of 55 ± 5 km and a dislocation corresponding to 67 mm/year oriented 78°N. However in the northern area of our network the fit is improved locally by using a lower dip around 13°. Finally a convergence motion of about 68 mm/year represents more than 10 m of displacement accumulated since the last big interplate subduction event in this area over 170 years ago (1835 earthquake described by Darwin). Therefore, in a worst case scenario, the area already has a potential for an earthquake of magnitude as large as 8-8.5, should it happen in the near future.

  8. Buckling and failure characteristics of graphite-polyimide shear panels

    NASA Technical Reports Server (NTRS)

    Shuart, M. J.; Hagaman, J. A.

    1983-01-01

    The buckling and failure characteristics of unstiffened, blade stiffened, and hat stiffened graphite-polyimide shear panels are described. The picture frame shear test is used to obtain shear stress-strain data at room temperature and at 316 deg C. The experimental results are compared with a linear buckling analysis, and the specimen failure modes are described. The effect of the 316 deg C test temperature on panel behavior are discussed.

  9. Hyperuniformity in periodically sheared dilute suspensions

    NASA Astrophysics Data System (ADS)

    Wilken, Sam; Guerra, Rodrigo; Pine, David J.; Chaikin, Paul M.

    Periodically sheared dilute, non-Brownian suspensions explore new configurations through collisions in an otherwise reversible flow. Below a critical strain, the particles remain active until they find a configuration with no collisions and reach an absorbing state. Recent simulations by Hexner and Levine have shown that the configuration of particles in the critically absorbing state is hyperuniform. The particle number fluctuations of hyperuniform systems decrease with counting box size more rapidly than random systems (like the same suspension that is not in a critically absorbing state). We built a compact, lightweight uni-axial shear cell where particle coordinates can be measured while shearing with a confocal microscope. We have identified hyperuniform structures with density fluctuation measurements in colloidal suspensions of up to 40% volume fraction in the critically absorbing state with a strain ramp down protocol and find hyperuniform scaling of the density fluctuations.

  10. Interfacial shear strength in abalone nacre.

    PubMed

    Lin, Albert Yu-Min; Meyers, Marc André

    2009-12-01

    The shear strength of the interface between tiles of aragonite in the nacre of red abalone Haliotis rufescens was investigated through mechanical tensile and shear tests. Dog-bone shaped samples were used to determine the tensile strength of nacre when loaded parallel to the plane of growth; the mean strength was 65 MPa. Shear tests were conducted on a special fixture with a shear gap of 200 microm, approximately 100 microm narrower than the spacing between mesolayers. The shear strength is found to be 36.9+/-15.8 MPa with an average maximum shear strain of 0.3. Assuming the majority of failure occurs through tile pull-out and not through tile fracture, the tensile strength can be converted into a shear strength of 50.9 MPa. Three mechanisms of failure at the tile interfaces are discussed: fracture of mineral bridges, toughening due to friction created through nanoasperities, and toughening due to organic glue. An additional mechanism is fracture through individual tiles.

  11. 49 CFR 178.338-12 - Shear section.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Specifications for Containers for Motor Vehicle Transportation § 178.338-12 Shear section. Unless the valve is... installation of each valve, damage to which could result in loss of liquid or vapor, must incorporate a shear... must yield or break under strain without damage to the valve that would allow the loss of liquid...

  12. Atomic structure of amorphous shear bands in boron carbide.

    PubMed

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

  13. Amorphous silicon under mechanical shear deformations: Shear velocity and temperature effects

    NASA Astrophysics Data System (ADS)

    Kerrache, Ali; Mousseau, Normand; Lewis, Laurent J.

    2011-04-01

    Mechanical shear deformations lead, in some cases, to effects similar to those resulting from ion irradiation. Here we characterize the effects of shear velocity and temperature on amorphous silicon (a-Si) modeled using classical molecular-dynamics simulations based on the empirical environment-dependent interatomic potential (EDIP). With increasing shear velocity at low temperature, we find a systematic increase in the internal strain leading to the rapid appearance of structural defects (fivefold-coordinated atoms). The impacts of externally applied strain can be almost fully compensated by increasing the temperature, allowing the system to respond more rapidly to the deformation. In particular, we find opposite power-law relations between the temperature and the shear velocity and the deformation energy. The spatial distribution of defects is also found to depend strongly on temperature and strain velocity. For low temperature or high shear velocity, defects are concentrated in a few atomic layers near the center of the cell, while with increasing temperature or decreasing shear velocity, they spread slowly throughout the full simulation cell. This complex behavior can be related to the structure of the energy landscape and the existence of a continuous energy-barrier distribution.

  14. Accumulate Repeat Accumulate Coded Modulation

    NASA Technical Reports Server (NTRS)

    Abbasfar, Aliazam; Divsalar, Dariush; Yao, Kung

    2004-01-01

    In this paper we propose an innovative coded modulation scheme called 'Accumulate Repeat Accumulate Coded Modulation' (ARA coded modulation). This class of codes can be viewed as serial turbo-like codes, or as a subclass of Low Density Parity Check (LDPC) codes that are combined with high level modulation. Thus at the decoder belief propagation can be used for iterative decoding of ARA coded modulation on a graph, provided a demapper transforms the received in-phase and quadrature samples to reliability of the bits.

  15. The Role played by Shear Modulus Contrast in Earth Materials on Facilitating Shear Localization in the Lithosphere

    NASA Astrophysics Data System (ADS)

    So, B.-D.; Yuen, D. A.; Regenauer-Lieb, K.; Lee, S.-M.

    2012-04-01

    Viscoplasticity has been considered to be a dominant element in causing the nucleation of shear instability leading to shear localization. Here we propose that a simple contrast in shear moduli may be sufficient for explaining the fast timescale asymmetric shear instability in a bi-material setting. Up to now, no studies have been made on asymmetric shear instability induced by elastic modulus contrast. Thermal-mechanical numerical simulations based on high resolution finite-element methods were performed to understand the effects of shear modulus contrast on inducing asymmetric instabilities. Strain-rate and stress dependent rheology are used with a wide range of activation energy 0-850 kJ/mol for all models. Numerical results with enough shear modulus contrast show the asymmetric shear instability, which is generated around the interface and then propagates across the interface. We also examined the role of activation energy (0-850 kJ/mol) on the geometrical pattern and the initiation time of asymmetric shear localization. The shear modulus contrast has to be close to 2 for triggering asymmetric shear instability and is found to be by far a more important controlling factor in causing shear instability than activation energy of the creep law. Our work suggests that initiation of lithosphere-scale asymmetric instability would be faster than previous considerations. In a view of the stored energy and its release as shear heating, the network between the various contrasts in yield strength and shear moduli controls the developing feature of asymmetric instability . Higher yield strength contrast induces severe deformation and a small temperature increase. It may hold the key for resolving the heat flow paradox question. Our finding stresses that naturally occurring shear modulus contrast have also important impact on many geological problems related to shear zone formation.

  16. Shearing stability of lubricants

    NASA Technical Reports Server (NTRS)

    Shiba, Y.; Gijyutsu, G.

    1984-01-01

    Shearing 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 shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.

  17. Uniaxial Tensile and Simple Shear Behavior of Resistance Spot-Welded Dual-Phase Steel Joints

    NASA Astrophysics Data System (ADS)

    Tao, Hong; Tong, Wei; Hector, Louis G.; Zavattieri, Pablo D.

    2008-08-01

    Small test coupons were machined from single spot welds in a dual-phase steel (DP600) to investigate deformation and failure of weld joints in both tension and shear. Quasi-static ( ifmmodeexpandafterdotelseexpandafter\\.fi{\\upvarepsilon } ˜ 10^{{ - 4}} 1/{text{s}} ) testing was conducted in a miniature tensile stage with a custom image acquisition system. Strain accumulation in each weld was analyzed where fracture occurred, which was typically outside the fusion zone. A few shear test coupons that failed in the fusion zone were found to have the same spheroidal defects noted in previous work, and thus, severely limited weld strength and ductility. A novel strain mapping method based upon digital image correlation was employed to generate two-dimensional deformation maps, from which local stress-strain curves to failure were computed. As an important first step toward incorporation of material models into weld simulations, a preliminary finite element analysis of a tension test successfully reproduced the experimental results with material models for the base, heat-affected, and fusion zone materials generated from prior work.

  18. 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.

  19. TURBULENT SHEAR ACCELERATION

    SciTech Connect

    Ohira, Yutaka

    2013-04-10

    We consider particle acceleration by large-scale incompressible turbulence with a length scale larger than the particle mean free path. We derive an ensemble-averaged transport equation of energetic charged particles from an extended transport equation that contains the shear acceleration. The ensemble-averaged transport equation describes particle acceleration by incompressible turbulence (turbulent shear acceleration). We find that for Kolmogorov turbulence, the turbulent shear acceleration becomes important on small scales. Moreover, using Monte Carlo simulations, we confirm that the ensemble-averaged transport equation describes the turbulent shear acceleration.

  20. 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.

  1. 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

  2. Self-organized criticality of plastic shear bands in rocks

    SciTech Connect

    Poliakov, A.N.B.; Herrmann, H.J.

    1994-09-01

    We show that the shear bands that appear during the pure shear numerical simulations of rocks with a non-associated plastic flow rule form fractal networks. The system drives spontaneously into a state in which the length distribution of shear bands follows a power law (self-organized criticality) with exponent 2.07. The distribution of local gradients in deviatoric strain rate has different scaling exponents for each moment, in particular the geometrical fractal dimension is 1.7. Samples of granodiorite sheared under high confining pressure from the Pyrenees are analyzed and their properties compared with the numerical results.

  3. Void deformation and breakup in shearing silica glass.

    PubMed

    Chen, Yi-Chun; Nomura, Ken-ichi; Kalia, Rajiv K; Nakano, Aiichiro; Vashishta, Priya

    2009-07-17

    We study shear deformation and breakup of voids in silica glass using molecular dynamics simulations. With an increase in the shear strain, two kinds of defects--threefold-coordinated silicon and nonbridging oxygen atoms--appear as spherical voids deform elastically into ellipsoidal shapes. For shear strains epsilon>15%, nanocracks appear on void surfaces and voids deform plastically into a threadlike structure. Nanocracks are nucleated by the migration of threefold-coordinated Si and nonbridging O on -Si-O-Si-O- rings. For epsilon>40%, the threadlike structures break up into several fragments. PMID:19659293

  4. Domino boudinage under layer-parallel simple shear

    NASA Astrophysics Data System (ADS)

    Dabrowski, Marcin; Grasemann, Bernhard

    2014-11-01

    The boudin segments of a torn competent layer experience synthetic rotation in layer-parallel simple shear. As long as the individual segments in a boudin train are constrained by their neighbors, even a highly viscous boudin deforms internally to create the necessary space for rotation. The rotation rate is then much smaller compared to the case of an isolated segment. Hence, a small tilt of boudin segments is not indicative of low strain. The rotation rate at this stage largely depends on the aspect ratio of the boudin segments and the scaled gap width. Once the tilted boudins are no longer constrained by their neighbors, the rotation rate greatly accelerates. In the case of a low viscosity ratio between the boudins and the host, the boudin segments develop complex shapes, which may give an impression of shear-band boudins forming under the opposite shear sense. We furthermore investigate the behavior of boudin trains of finite length. The terminal segments are displaced out of the shear plane, deforming into isoclinal folds, and separate into groups of boudin segments that rotate into the shear direction and eventually lead to an overall chaotic appearance of the structure. Natural examples of domino boudinage from a high shear -strain detachment zone in the Western Cyclades (Greece) show many similarities with the modeled structures suggesting that, under simple shear deformation, the rotation and separation of boudin segments is an indicator for high shear strain.

  5. Strain analysis and strain path modelling in the Loch Tollie gneisses, Gairloch, NW Scotland

    NASA Astrophysics Data System (ADS)

    Odling, N. E.

    A quantitative structural analysis is presented for the Loch Tullie gneisses of the Lewisian complex outcropping at Gairloch. The gneisses and the dykes they contain are folded into a large antiformal structure known as the Tollic Antiform. Quartz aggregates in quartzo-feldspathic gneisses have been used as finite strain markers in eleven specimens across the antiform. Two models, using rotational strain (simple shear) and irrotational strain (pure shear), are used to reconstruct the strain path. Results show that only the rotational strain model satisfies the strain data and the field evidence, and indicates a steeply northeast (75°) dipping shear plane and moderately northwest (55°) plunging shear direction, with a southwest-side-down sense of shear. A strain profile is constructed for the Tollie gneisses using the model and the attitude of gneissose layering. This shows increasing shear strain to the southwest to a maximum gamma value of approximately 8. The strain profile indicates a horizontal dextral displacement of 4.7 km and a vertical displacement of 6.8 km for the Tollie gneisses. The Tollie Antiform thus lies on the northeast margin of a large-scale shear zone, the main zone of deformation of which can be traced southwestwards some 4 km. Such a shear zone presents a major tectonic boundary within the Lewisian of northwest Scotland.

  6. Verification and application of the Iosipescu shear test method

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    Finite element models were used to study the effects of notch angle variations on the stress state within an Iosipescu shear test speciment. These analytical results were also studied to determine the feasibility of using strain gage rosettes and a modified extensometer to measure shear strains in this test specimen. Analytical results indicate that notch angle variations produced only small differences in simulated shear properties. Both strain gage rosettes and the modified extensometer were shown to be feasible shear strain transducers for the test method. The Iosipoescu shear test fixture was redesigned to incorporate several improvements. These improvements include accommodation of a 50 percent larger specimen for easier measurement of shear train, a clamping mechanism to relax strict tolerances on specimen width, and a self contained alignment tool for use during specimen installation. A set of in-plane and interlaminar shear properties were measured for three graphite fabric/epoxy composites of T300/934 composite material. The three weave patterns were Oxford, 5-harness satin, and 8-harness satin.

  7. Heat accumulator

    SciTech Connect

    Bracht, A.

    1981-09-29

    A heat accumulator comprises a thermally-insulated reservoir full of paraffin wax mixture or other flowable or meltable heat storage mass, heat-exchangers immersed in the mass, a heat-trap connected to one of the heat-exchangers, and a heat user connected to the other heat-exchanger. Pumps circulate fluids through the heat-trap and the heat-using means and the respective heat-exchangers, and a stirrer agitates and circulates the mass, and the pumps and the stirrer and electric motors driving these devices are all immersed in the mass.

  8. Strain rate influence on fracture development in experimental ductile multilayers

    NASA Astrophysics Data System (ADS)

    Gomez-Rivas, Enrique; Griera, Albert

    2011-04-01

    The far-field strain rate is a crucial parameter that controls the transition between brittle and ductile deformation. We have used analogue experiments to study the strain rate influence on the development of brittle fractures in a ductile composite material. Plasticine multilayer models were deformed under coaxial boundary conditions at three different strain rates to analyse the transition from non-localised deformation to the development of a brittle fracture network that accommodates part of the deformation. The results show that tension cracks and voids are the first macroscopic structures that nucleate after an early stage of ductile deformation. Coalescence and collapse of these structures lead to the development of brittle shear fractures. The evolution of fracture orientations, lengths and displacements was systematically analysed. The ratio of the accumulated fracture displacement vs. fracture length ( dmax/ L) depends not only on the total deformation, but also on the strain rate at which the system is deformed. The accumulated displacement with respect to fracture length increases with strain rate.

  9. Enhancing Rotational Diffusion Using Oscillatory Shear

    NASA Astrophysics Data System (ADS)

    Leahy, Brian D.; Cheng, Xiang; Ong, Desmond C.; Liddell-Watson, Chekesha; Cohen, Itai

    2013-05-01

    Taylor dispersion—shear-induced enhancement of translational diffusion—is an important phenomenon with applications ranging from pharmacology to geology. Through experiments and simulations, we show that rotational diffusion is also enhanced for anisotropic particles in oscillatory shear. This enhancement arises from variations in the particle’s rotation (Jeffery orbit) and depends on the strain amplitude, rate, and particle aspect ratio in a manner that is distinct from the translational diffusion. This separate tunability of translational and rotational diffusion opens the door to new techniques for controlling positions and orientations of suspended anisotropic colloids.

  10. Compressible homogeneous shear: Simulation and modeling

    NASA Technical Reports Server (NTRS)

    Sarkar, S.; Erlebacher, G.; Hussaini, M. Y.

    1992-01-01

    Compressibility effects were studied on turbulence by direct numerical simulation of homogeneous shear flow. A primary observation is that the growth of the turbulent kinetic energy decreases with increasing turbulent Mach number. The sinks provided by compressible dissipation and the pressure dilatation, along with reduced Reynolds shear stress, are shown to contribute to the reduced growth of kinetic energy. Models are proposed for these dilatational terms and verified by direct comparison with the simulations. The differences between the incompressible and compressible fields are brought out by the examination of spectra, statistical moments, and structure of the rate of strain tensor.

  11. Boundary-Driven Colloidal Crystallization in Simple Shear Flow

    NASA Astrophysics Data System (ADS)

    Shereda, Laura T.; Larson, Ronald G.; Solomon, Michael J.

    2010-11-01

    Using confocal microscopy, we directly observe that simple shear flow induces transient crystallization of colloids by wall-normal propagation of crystallization fronts from each shearing surface. The initial rate of the front propagation was 1.75±0.07 colloidal layers per unit of applied strain. The rate slowed to 0.29±0.04 colloidal layers per unit of applied strain as the two fronts approached each other at the midplane. The retardation of the front propagation is caused by self-concentration of shear strain in the growing bands of the lower-viscosity crystal, an effect that leads to a progressive reduction of the shear rate in the remaining amorphous material. These findings differ significantly from previous hypotheses for flow-induced colloidal crystallization by homogeneous mechanisms.

  12. Numerical modeling of shear band formation in PBX-9501

    SciTech Connect

    Dey, T.N.; Kamm, J.R.

    1998-12-31

    Adiabatic shear bands in explosives may be a source of ignition and lead to detonation. Three possible mechanisms leading to shear banding are (1) thermal softening, (2) mechanical softening due to microcracking, and (3) quasi-granular constitutive response. The latter two mechanisms can lead to shear band formation in PBXs at nominal strains much smaller than those required for the thermal softening mechanism. The authors study formation of shear bands with models including the latter two mechanisms under unconfined compression. Statistical variation of numerical results is similar to that observed in some experiments. However, the commonly used methods of calibrating constitutive models can be misleading because of effects due to shear band formation. One model currently being used for studies of shear band formation and ignition in PBX 9501 was calibrated in this way and may need re-examination.

  13. Attenuated Escherichia coli strains expressing the colonization factor antigen I (CFA/I) and a detoxified heat-labile enterotoxin (LThK63) enhance clearance of ETEC from the lungs of mice and protect mice from intestinal ETEC colonization and LT-induced fluid accumulation.

    PubMed

    Byrd, Wyatt; Boedeker, Edgar C

    2013-03-15

    Although enterotoxigenic Escherichia coli (ETEC) infections are important causes of infantile and traveler's diarrhea there is no licensed vaccine available for those at-risk. Our goal is to develop a safe, live attenuated ETEC vaccine. We used an attenuated E. coli strain (O157:H7, Δ-intimin, Stx1-neg, Stx2-neg) as a vector (ZCR533) to prepare two vaccine strains, one strain expressing colonization factor antigen I (ZCR533-CFA/I) and one strain expressing CFA/I and a detoxified heat-labile enterotoxin (ZCR533-CFA/I+LThK63) to deliver ETEC antigens to mucosal sites in BALB/c mice. Following intranasal and intragastric immunization with the vaccine strains, serum IgG and IgA antibodies were measured to the CFA/I antigen, however, only serum IgG antibodies were detected to the heat-labile enterotoxin. Intranasal administration of the vaccine strains induced respiratory and intestinal antibody responses to the CFA/I and LT antigens, while intragastric administration induced only intestinal antibody responses with no respiratory antibodies detected to the CFA/I and LT antigens. Mice immunized intranasally with the vaccine strains showed enhanced clearance of wild-type (wt) ETEC bacteria from the lungs. Mice immunized intranasally and intragastrically with the vaccine strains were protected from intestinal colonization following oral challenge with ETEC wt bacteria. Mice immunized intragastrically with the ZCR533-CFA/I+LThK63 vaccine strain had less fluid accumulate in their intestine following challenge with ETEC wt bacteria or with purified LT as compared to the sham mice indicating that the immunized mice were protected from LT-induced intestinal fluid accumulation. Thus, mice intragastrically immunized with the ZCR533-CFA/I+LThK63 vaccine strain were able to effectively neutralize the activity of the LT enterotoxin. However, no difference in intestinal fluid accumulation was detected in the mice immunized intranasally with the vaccine strain as compared to the sham

  14. Parametric Dependence of Homogeneous Turbulent Shear Flow on Reynolds Number and Shear Parameter

    NASA Astrophysics Data System (ADS)

    Isaza, Juan; Vaithianathan, T.

    2005-11-01

    The combined role of the Shear Parameter, S^* = S k / ɛ, and the Reynolds number in homogeneous turbulent shear flow is studied using direct numerical simulations (DNS). The parametric investigation involves DNS of 256^3, 512^3 and 1024^3 with a constant shear parameter, S^*, between 1 and 100. Particular attention is given to velocity derivatives (strain and rotation) and higher-order structure functions and their scaling with the two parameters. This study is in line with some recent results reported by Schumacher, [Phys. Fluids 16, 2004]. Due to the high level of shear investigated, a new algorithm that avoids the remeshing step is used. The 20% - 40% loss in kinetic energy and dissipation rate reported by Lee et al. [JFM, 216, 1990] using the Rogallo code is consequently avoided.

  15. 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.

  16. Role of 3D force networks in linking grain scale to macroscale processes in sheared granular debris

    NASA Astrophysics Data System (ADS)

    Mair, K.; Jettestuen, E.; Abe, S.

    2013-12-01

    Active faults, landslides and subglacial tills contain accumulations of granular debris that evolve during sliding. The macroscopic motion in these environments is at least to some extent determined by processes operating in this sheared granular material. A valid question is how the local behavior at the individual granular contacts actually sums up to influence macroscopic sliding. Laboratory experiments and numerical modeling can potentially help elucidate this. Observations of jamming (stick) and unjamming (flow) as well as concentrated shear bands on the scale of 5-10 grains suggest that a simple continuum description may be insufficient to capture important elements of the behavior. We therefore seek a measure of the organization of the granular fabric and the 3D structure of the load bearing skeleton that effectively demonstrates how the individual grain interactions are manifested in the macroscopic sliding behavior we observe. Contact force networks are an expression of this. Here we investigate the structure and variability of the most connected system spanning force networks produced in 3D discrete element models of granular layers under shear. We use percolation measures to identify, characterize, compare and track the evolution of these strongly connected contact force networks. We show that specific topological measures used in describing the networks, such as number of contacts and coordination number, are sensitive to grain size distribution (and likely the grain shape) of the material as well as loading conditions. Hence, faults of different maturity would be expected to accommodate shear in different ways. Distinct changes in the topological characteristics i.e. the geometry of strong force networks with accumulated strain are directly correlated to fluctuations in macroscopic shearing resistance. This suggests that 3D force networks play an important bridging role between individual grain scale processes and macroscopic sliding behavior.

  17. Geometric aspects of shear jamming induced by deformation of frictionless sphere packings

    NASA Astrophysics Data System (ADS)

    Vinutha, H. A.; Sastry, Srikanth

    2016-09-01

    It has recently been demonstrated that shear deformation of frictionless sphere packings leads to structures that will undergo jamming in the presence of friction, at densities well below the isotropic jamming point {φj}≈ 0.64 , and at high enough strains. Here, we show that the geometric features induced by strain are robust with respect to finite size effects, and include the feature of hyperuniformity, previously studied in the context of jamming, and more recently in driven systems. We study the approach to jamming as strain is increased, by evolving frictionless sheared configurations through frictional dynamics, and thereby identify a critical, or jamming, strain for each density, for a chosen value of the coefficient of friction. In the presence of friction above a certain strain value the sheared frictionless packings begin to develop finite stresses, which marks the onset of shear jamming. At a higher strain value, the shear stress reaches a saturation value after rising rapidly above the onset of shear jamming, which permits identification of the shear jamming transition. The onset of shear jamming and shear jamming are found to occur when the coordination number Z reaches values of Z  =  3 and Z  =  4 respectively. By considering percolation probabilities for the contact network, clusters of four coordinated and six coordinated spheres, we show that the percolation of four coordinated spheres corresponds to the onset of shear jamming behaviour, whereas the percolation of six coordinated spheres corresponds to shear jamming, for the chosen friction coefficients. At the onset of shear jamming, the force distribution begins to develop a peak at finite value and the force network is anisotropic and heterogeneous. And at the shear jamming transition, the force distribution has a well defined peak close to < f> and the force network is less anisotropic and homogeneous. We briefly discuss mechanical aspects of the jamming behaviour by

  18. Shear-induced conformation change in α-crystalline nylon6

    SciTech Connect

    Arabnejad, Saeid; Manzhos, Sergei; Shim, V. P. W.; He, Chaobin

    2014-12-01

    A study of shear deformation of α-crystalline nylon6 is undertaken, using dispersion-corrected density functional theory. The shear stress-strain relationship and shear strength for interlayer shear deformation are computed. A conformation change induced by shear is identified along twinning deformation, whereby the conformation of chains, specifically the location of non-H-bonded hydrogen atoms, changes continuously. This paves a way for the modulation of properties of this group of materials by small shear deformation, if the non-H-bonded hydrogens are chemically substituted to form non-equivalent conformations when deformed.

  19. Finite strip analysis of anisotropic laminated composite plates using higher-order shear deformation theory

    NASA Astrophysics Data System (ADS)

    Akhras, G.; Cheung, M. S.; Li, W.

    1994-08-01

    In the present study, a finite strip method for the elastic analysis of anisotropic laminated composite plates is developed according to higher-order shear deformation theory. This theory accounts for the parabolic distribution of the transverse shear strains through the thickness of the plate and for zero transverse shear stresses on the plate surfaces. In comparison with the finite strip method based on first-order shear deformation theory, the present method gives improved results while using approximately the same number of degrees of freedom. It also eliminates the need for shear correction factors in calculating the transverse shear stiffness.

  20. What are the microscopic origins of shear jamming?

    NASA Astrophysics Data System (ADS)

    Behringer, Bob; Wang, Dong; Ren, Jie; Bares, Jonathan; Chakraborty, Bulbul; Kovalcinova, Lenka; Kondic, Lou

    Granular materials can jam by shear: shear strain applied to a stress-free state in a packing fraction range ϕS < ϕ <ϕJ , leads to mechanically stable (jammed) anisotropic states (Bi et al. Nature, 2011). ϕJ is the lowest ϕ for which an isotropic state is jammed, and shear jamming ceases below ϕS. The process of shear jamming involves the formation of strong force networks that are initially highly anistropic `force chains', then become become more isotropic with increasing shear. The mechanisms that lead to shear jamming are also presumably similar to those that lead to Reynolds dilatancy. What microscopic processes can account for shear jamming? Force chains, roughly linear sequences of particles experiencing average or above forces are not stable by themselves. Hence, force chain particles must form additional `non-chain' contacts. Here, we propose micro-scale structures and their response to shear that serve as a basis to understand the formation of stable force networks and shear jamming. We identify these structures in experimental and numerical data, and track their response to shear. Work supported by NSF-DMR1206351, DMS1248071, NASA NNX15AD38G, and the W.M. Keck Foundation.

  1. Angular shear plate

    SciTech Connect

    Ruda, Mitchell C.; Greynolds, Alan W.; Stuhlinger, Tilman W.

    2009-07-14

    One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear 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 shear plate, light passing therethrough can be focused at variable positions.

  2. Fighting wind shear

    NASA Astrophysics Data System (ADS)

    A “coherent and sustained program” of improved radar detection of weather, pilot training, and better communication between pilots and air controllers can greatly reduce the risk of wind shear to airplanes landing or taking off, according to a National Research Council (NRC) committee.Wind shear, characterized by winds rapidly changing direction and speed, has caused several serious accidents in recent years; among the most notable is the July 8, 1982, crash of a Pan American World Airlines jetliner at the New Orleans International Airport, which killed 153 persons. Following the accident, Congress directed the Federal Aviation Administration (FAA) to contract with the NRC to study wind shear.

  3. An evaluation of the Iosipescu specimen for composite materials shear property measurement

    NASA Technical Reports Server (NTRS)

    Morton, J.; Ho, H.; Tsai, M. Y.; Farley, G. L.

    1992-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. A linear finite element model of the specimen is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon strain gage measurements used for the determination of composite shear moduli. Based upon test results from graphite-epoxy laminates, the proximity of the load introduction point to the test section and the material orthotropy greatly influence the individual gage readings, however, shear modulus determination is not significantly affected by the lack of pure shear. Correction factors are needed to allow for the nonuniformity of the strain field and the use of the average shear stress in the shear modulus evaluation. The correction factors are determined for the region occupied by the strain gage rosette. A comparison of the strain gage readings from one surface of a specimen with corresponding data from moire interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to eccentric loading which induced twisting and spurious shear stress-strain curves. The discovery of specimen twisting explains the apparently inconsistent shear property data found in the literature. Recommendations for improving the reliability and accuracy of the shear modulus values are made, and the implications for shear strength measurement discussed.

  4. Depth Dependence of Shear Properties in Articular Cartilage

    NASA Astrophysics Data System (ADS)

    Buckley, Mark; Gleghorn, Jason; Bonassar, Lawrence; Cohen, Itai

    2007-03-01

    Articular cartilage is a highly complex and heterogeneous material in its structure, composition and mechanical behavior. Understanding these spatial variations is a critical step in designing replacement tissue and developing methods to diagnose and treat tissue affected by damage or disease. Existing techniques in particle image velocimetry (PIV) have been used to map the shear properties of complex materials; however, these methods have yet to be applied to understanding shear behavior in cartilage. In this talk, we will show that confocal microscopy in conjunction with PIV techniques can be used to determine the depth dependence of the shear properties of articular cartilage. We will show that the shear modulus of this tissue varies by over an order of magnitude over its depth, with the least stiff region located about 200 microns from the surface. Furthermore, our data indicate that the shear strain profile of articular cartilage is sensitive to both the degree of compression and the total applied shear strain. In particular, we find that cartilage strain stiffens most dramatically in a region 200-500 microns below the surface. Finally, we will describe a physical model that accounts for this behavior by taking into account the local buckling of collagen fibers just below the cartilage surface and present second harmonic generation (SHG) imaging data addressing the collagen orientation before and after shear.

  5. Analysis of serrations and shear bands fractality in UFGs

    NASA Astrophysics Data System (ADS)

    Iliopoulos, Aggelos C.; Nikolaidis, Nikolaos S.; Aifantis, Elias C.

    2015-05-01

    Tsallis nonextensive statistics is employed to characterize serrated flow, as well as multiple shear band formation in ultrafine grain (UFG) size materials. Two such UFG materials, a bi-modal Al-Mg alloy and a Fe-Cu alloy, were chosen. In the first case, at low strain rates serrated flow emerges as recorded in the stress-strain graphs, whereas at high strain rates, extensive shear banding occurs. In the second case, multiple shear banding is the only mechanism for plastic deformation, but serrations in the stress-strain graph are not recorded. The analysis aims at the estimation of Tsallis entropic index qstat (stat denotes stationary state), as well as the estimation of fractal dimension. The results reveal that the distributions of serrations and shear bands do not follow Gaussian statistics as implied by Boltzmann-Gibbs extensive thermodynamics, but are approximated instead by Tsallis q-Gaussian distributions, as suggested by nonextensive thermodynamics. In addition, fractal analysis of multiple shear band images reveals a (multi)fractal and hierarchical profile of the spatial arrangement of shear bands.

  6. Orientation of shear bands for a rigid plastic frictional material in simple shear

    NASA Astrophysics Data System (ADS)

    Papon, A.; Liu, X.; Muhlhaus, H.; Gross, L.

    2012-10-01

    The orientation of shear bands is investigated analytically and numerically for a rigid plastic frictional material in simple shear. The model is based on co-axial flow rule, incompressible deformations and a friction factor which depends on the strain history. Since we are focussing on geological timescales, the influence of elasticity is neglected. Firstly, a linear stability analysis is performed confirming Rice's 1976 assertion [The localization of plastic deformation, in Proceedings of the 14th International Congress on Theoretical and Applied Mechanics, W.T. Koiter, ed., North Holland, Amsterdam, 1976, p.207] that, in the hardening regime, bifurcation is possible at every stage. Orientation of shear bands against the less compressive principal axis lies anywhere between the Roscoe and Coulomb angles, namely between π/4+ψ/2 and π/4 + ϕ/2, where ϕ and ψ are the mobilised angles of friction and dilatancy, respectively (in our study, we assume ψ = 0). The linear stability analysis leaves open the question of which orientation will actually emerge in a boundary value problem that consider all nonlinearities. This question is addressed in a finite element study of simple shear with periodic boundary conditions in the shear direction. Our simulations show temporary inclined shear bands in the hardening regime followed by a persistent horizontal shear band. A sensitivity study with respect to geometric and constitutive parameters indicates that the height of the sample controls the orientation of the inclined shear bands. Finally, we extend our analytical and numerical studies to Cosserat plasticity. It turns out that inclined shear bands are suppressed for large values of the internal length R (narrow bands). The case of a standard continuum is gradually recovered for small R (wide bands).

  7. Deformation textures of AA8011 aluminum alloy sheets severely deformed by accumulative roll bonding

    NASA Astrophysics Data System (ADS)

    Kim, Hyoung Wook; Kang, Suk Bong; Tsuji, Nobuhiro; Amino, Yoritoshi Min

    2005-11-01

    A fully annealed AA8011 aluminum alloy sheet containing a number of large particles (˜5 µm) was severely deformed up to an equivalent strain of 12 by an accumulative roll-bonding (ARB) process. The texture evolution during the ARB process was clarified, along with the microstructure. The ARB-processed aluminum alloy sheets had a different texture distribution through the sheet thickness, due to the high friction between the roll and the material during the ARB process. The shear textures composed of {001} <110> and {111} <110> orientations developed at the sheet surface, while the rolling textures, including Cu {112} <111> and Dillamore {4,4,11} <11,11,8> orientations, developed at the sheet center. The textural change from a shear texture to a rolling texture at the sheet center during the ARB process contributed to an increase in the fraction of high-angle boundaries. Also, a large number of second-phase particles in the AA8011 alloy sheets weakened the texture. Up to the medium strain range (below ɛ=6.4), relatively weak textures developed, due to the inhomogeneous deformation around the second-phase particles; after the strain of 6.4, strong rolling-texture components, such as the Dillamore and Cu orientations, developed. This remarkable textural change can be explained by the reprecipitation of fine particles in grain interiors.

  8. Shear-stress relaxation and ensemble transformation of shear-stress autocorrelation functions.

    PubMed

    Wittmer, J P; Xu, H; Baschnagel, J

    2015-02-01

    We revisit the relation between the shear-stress relaxation modulus G(t), computed at finite shear strain 0<γ≪1, and the shear-stress autocorrelation functions C(t)|(γ) and C(t)|(τ) computed, respectively, at imposed strain γ and mean stress τ. Focusing on permanent isotropic spring networks it is shown theoretically and computationally that in general G(t)=C(t)|(τ)=C(t)|(γ)+G(eq) for t>0 with G(eq) being the static equilibrium shear modulus. G(t) and C(t)|(γ) thus must become different for solids and it is impossible to obtain G(eq) alone from C(t)|(γ) as often assumed. We comment briefly on self-assembled transient networks where G(eq)(f) must vanish for a finite scission-recombination frequency f. We argue that G(t)=C(t)|(τ)=C(t)|(γ) should reveal an intermediate plateau set by the shear modulus G(eq)(f=0) of the quenched network.

  9. Experimental and Computational Investigations of Strain Localization in Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Bharathula, Ashwini

    non-localized contributions at low strains. Moreover, the magnitude of strain bursts was found to decrease with decrease in specimen size. Furthermore, Weibull statistical analysis was performed to investigate the effect of specimen size on yield strength in this metallic glass. It was revealed that the dispersion in strengths increases dramatically with decrease in sample size, attributed to the size distribution of the defects responsible for shear banding. The findings are crucial in designing systems which promote plasticity in metallic glasses by suppressing the shear-band instability and also in direct application of these materials for structural purposes as small components in micro- and nano-scale systems. On the computational front, Molecular Dynamics (MD) simulations have been employed to generate Zr-Cu metallic glass structures. In order to analyze and better understand and visualize the concepts of "free" volume and flow defects in metallic glasses, an electron density model was developed as an upgrade to the traditional hard sphere approaches. Simple tension and shear modes of deformation were simulated using MD in Zr-Cu system, and role of open volume in deformation was studied using the electron density model. In uniaxial tension simulations, effect of temperature and deformation rate is examined, and the process of accumulation of free volume to the point of catastrophic failure is visualized using the Electron Density model. In shear simulations, we find that the as-quenched glass structures undergo homogeneous deformation and do not exhibit any strain localization. However, it is found that by incorporating a cylindrical void in the glass structure as a source of "free" volume, it is possible to induce strain localization. It was found that a critical void diameter of 8A was required to successfully initialize strain localization in this system.

  10. Uncoupling shear and uniaxial elastic moduli of semiflexible biopolymer networks: compression-softening and stretch-stiffening

    PubMed Central

    van Oosten, Anne S. G.; Vahabi, Mahsa; Licup, Albert J.; Sharma, Abhinav; Galie, Peter A.; MacKintosh, Fred C.; Janmey, Paul A.

    2016-01-01

    Gels formed by semiflexible filaments such as most biopolymers exhibit non-linear behavior in their response to shear deformation, e.g., with a pronounced strain stiffening and negative normal stress. These negative normal stresses suggest that networks would collapse axially when subject to shear stress. This coupling of axial and shear deformations can have particularly important consequences for extracellular matrices and collagenous tissues. Although measurements of uniaxial moduli have been made on biopolymer gels, these have not directly been related to the shear response. Here, we report measurements and simulations of axial and shear stresses exerted by a range of hydrogels subjected to simultaneous uniaxial and shear strains. These studies show that, in contrast to volume-conserving linearly elastic hydrogels, the Young’s moduli of networks formed by the biopolymers are not proportional to their shear moduli and both shear and uniaxial moduli are strongly affected by even modest degrees of uniaxial strain. PMID:26758452

  11. A technique for combined dynamic compression-shear test

    NASA Astrophysics Data System (ADS)

    Zhao, P. D.; Lu, F. Y.; Chen, R.; Lin, Y. L.; Li, J. L.; Lu, L.; Sun, G. L.

    2011-03-01

    It is critically important to study the dynamic response of materials under a combined compression-shear loading for developing constitutive laws more accurately and fully. We present a novel technique to achieve the combined compression and shear loadings at high strain rates. The main apparatus consists of a strike bar, an incident bar, and two transmission bars. The close-to-specimen end of the incident bar is wedge-shaped with 90°. In each experiment, there are two identical specimens, respectively, agglutinated between one side of the wedge and one of transmission bars. When a loading impulse travels to specimens along the incident bar, because of the special geometrical shape, the specimen-incident bar interface gets an axial and a transverse velocity. Specimens endure a combined compression-shear loading at high strain rates. The compression stress and strain of the specimens are deduced from signals recorded by strain gages mounted on the bars. The shear stress is measured by two piezoelectric transducers of quartz (Y-cut with rotation angle 17.7°) embedded at the close-to-specimen end of transmission bars; the shear strain is measured with a novel optical technique, which is based on the luminous flux method. An analytic model was proposed and validated by the numerical simulations. The simulation results yield good agreement with the analytic results. The proposed technique was then validated through experiments carried out on lead specimens, by comparing experimental results with that of the split Hopkinson pressure bar experiments.

  12. A comparison of three shear test methods for composite materials

    NASA Technical Reports Server (NTRS)

    Ho, H.; Tsai, M. Y.; Morton, J.; Farley, G. L.

    1991-01-01

    A graphite-epoxy composite material system is used to evaluate the performance of three popular shear tests - the 10-deg off-axis, the +/-45-deg tension, and the Iosipescu specimen tested in the modified Wyoming fixture. A comparison of the shear stress-strain response for each test method is made using a conventional strain gage instrument and moire interferometry. The uniformity and purity of the strain fields in the test sections of the specimens are discussed, and the shear responses obtained from each test are presented and compared. It is shown that the shear stress-strain responses obtained by instrumenting only one face of the 90-deg Iosipescu specimen could give erroneous results. The +/-45-deg tensile and 0-deg Iosipescu specimens were not affected by front-to-back face shear strain variations. Correction factors could be applied to bring all responses together, within the limits of the material uniformity, which was itself documented in the moire fringe patterns.

  13. Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Possible Mechanism for Intermediate Depth Earthquakes and Slow Earthquakes?

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.; Hirth, G.

    2004-12-01

    Localized ductile shear 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 shear zone show that shear heating temperatures can exceed the mantle solidus (e.g., Obata & Karato Tectonophys 95). Simple shear, recrystallization, and grain boundary sliding all decrease the spacing between pyroxenes, so olivine grain growth at lower stress is inhibited; thus, once formed, these shear zones do not "heal" on geological time scales. Reasoning that grain-size sensitive creep will be localized within these shear 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 shear heating instabilities. In this view, as elastic stress increases, the shear zone weakens via shear heating; rapid deformation of the weak shear 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 shear 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 shear zone of specified width. Shear heating and thermal diffusion control temperature evolution in the shear zone and host rocks. A maximum of 1400 C (where substantial melting of peridotite would occur) is imposed. Grain size evolves during dislocation

  14. Direct Shear of Olivine Single Crystals

    NASA Astrophysics Data System (ADS)

    Tielke, Jacob; Zimmerman, Mark; Kohlstedt, David

    2016-04-01

    Knowledge of the strength of individual dislocation slip systems in olivine is fundamental to understanding the flow behavior and the development of lattice-preferred orientation in olivine-rich rocks. The most direct measurements of the strengths of individual slip systems are from triaxial compression experiments on olivine single crystals. However, such experiments only allow for determination of flow laws for two of the four dominate slip systems in olivine. In order to measure the strengths of the (001)[100] and (100)[001] slip systems independently, we performed deformation experiments on single crystals of San Carlos olivine in a direct shear geometry. Experiments were carried out at temperatures of 1000° to 1300°C, a confining pressure of 300 MPa, shear stresses of 60 to 334 MPa, and resultant shear strain rates of 7.4 x 10‑6 to 6.7 x 10‑4 s‑1. At high-temperature (≥1200°C) and low-stress (≤200 MPa) conditions, the strain rate of crystals oriented for direct shear on either the (001)[100] or the (100)[001] slip system follows a power law relationship with stress, whereas at lower temperatures and higher stresses, strain rate depends exponentially on stress. The flow laws derived from the mechanical data in this study are consistent with a transition from the operation of a climb-controlled dislocation mechanism during power-law creep to the operation of a glide-controlled dislocation mechanism during exponential creep. In the climb-controlled regime, crystals oriented for shear on the (001)[100] slip system are weaker than crystals orientated for shear on the (100)[001] slip system. In contrast, in the glide-controlled regime the opposite is observed. Extrapolation of flow laws determined for crystals sheared in orientations favorable for slip on these two slip systems to upper mantle conditions reveals that the (001)[100] slip system is weaker at temperatures and stresses that are typical of the asthenospheric mantle, whereas the (100

  15. Shear wave elastography with a new reliability indicator

    PubMed Central

    Dong, Yi

    2016-01-01

    Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies. PMID:27679731

  16. Shear wave elastography with a new reliability indicator.

    PubMed

    Dietrich, Christoph F; Dong, Yi

    2016-09-01

    Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies. PMID:27679731

  17. Shear wave elastography with a new reliability indicator

    PubMed Central

    Dong, Yi

    2016-01-01

    Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

  18. Shear wave elastography with a new reliability indicator.

    PubMed

    Dietrich, Christoph F; Dong, Yi

    2016-09-01

    Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

  19. A refined nonlinear theory of plates with transverse shear deformation

    NASA Technical Reports Server (NTRS)

    Reddy, J. N.

    1984-01-01

    A higher-order shear deformation theory of plates accounting for the von Karman strains is presented. The theory contains the same dependent unknowns as in the Hencky-Mindlin type first-order shear deformation theory and accounts for parabolic distribution of the transverse shear strains through the thickness of the plate. Exact solutions of simply supported plates are obtained using the linear theory and the results are compared with the exact solutions of three-dimensional elasticity theory, the first order shear deformation theory, and the classical plate theory. The present theory predicts the deflections, stresses, and frequencies more accurately when compared to the first-order theory and the classical plate theory.

  20. A new parallel plate shear cell for in situ real-space measurements of complex fluids under shear flow.

    PubMed

    Wu, Yu Ling; Brand, Joost H J; van Gemert, Josephus L A; Verkerk, Jaap; Wisman, Hans; van Blaaderen, Alfons; Imhof, Arnout

    2007-10-01

    We developed and tested a parallel plate shear cell that can be mounted on top of an inverted microscope to perform confocal real-space measurements on complex fluids under shear. 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 shear rates cover the range of 0.02-10(3) s(-1). This shear cell can apply an oscillatory shear 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 shear with such a large amplitude can be regarded as a continuous shear. We measured the flow profile of a suspension of silica colloids in this shear 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 shear induced crystallization and melting of concentrated suspensions of 1 microm diameter silica colloids.

  1. Analysis of orthotropic plates with nonlinear shear characteristics

    SciTech Connect

    Raouf, R.A.

    1994-12-31

    This paper presents an analytical study of the response of orthotropic plates with nonlinear shear characteristics to transverse loading. The shear stress-shear strain relationship is based on experimental results available in the literature. It is nonlinear and of the polynomial type. The symbolic manipulator Mathematics is used to implement a Rayleigh-Ritz procedure to derive a set of approximate nonlinear algebraic equations of equilibrium for the plate under a uniformly distributed load. The equations of equilibrium show that the nonlinearity introduces a coupling between the in-plane displacements and the transverse displacement. The studied case shows that the nonlinearity has a hardening effect on the transverse displacements but a softening effect on the in-plane displacements. Moreover, the studied case shows that the linear solution underestimates the magnitude of shear stress. The nonlinear solution indicates that the in-plane shear stress predicted by the nonlinear analysis is higher than those predicted by the linear theory.

  2. Shear band in sand with spatially varying density

    NASA Astrophysics Data System (ADS)

    Borja, Ronaldo I.; Song, Xiaoyu; Rechenmacher, Amy L.; Abedi, Sara; Wu, Wei

    2013-01-01

    Bifurcation theory is often used to investigate the inception of a shear band in a homogeneously deforming body. The theory predicts conjugate shear bands that have the same likelihood of triggering. For structures loaded symmetrically the choice of which of the two conjugate shear bands will persist is arbitrary. In this paper we show that spatial density variation could be a determining factor for the selection of the persistent shear band in a symmetrically loaded localizing sand body. We combine experimental imaging on rectangular sand specimens loaded in plane strain compression with mesoscale finite element modeling on symmetrically loaded sand specimens to show that spatial heterogeneity in density does have a profound impact on the persistent shear band.

  3. Free volume under shear

    NASA Astrophysics Data System (ADS)

    Maiti, Moumita; Vinutha, H. A.; Sastry, Srikanth; Heussinger, Claus

    2015-10-01

    Using an athermal quasistatic simulation protocol, we study the distribution of free volumes in sheared hard-particle packings close to, but below, the random-close packing threshold. We show that under shear, and independent of volume fraction, the free volumes develop features similar to close-packed systems — particles self-organize in a manner as to mimick the isotropically jammed state. We compare athermally sheared packings with thermalized packings and show that thermalization leads to an erasure of these structural features. The temporal evolution in particular the opening-up and the closing of free-volume patches is associated with the single-particle dynamics, showing a crossover from ballistic to diffusive behavior.

  4. Free volume under shear.

    PubMed

    Maiti, Moumita; Vinutha, H A; Sastry, Srikanth; Heussinger, Claus

    2015-10-14

    Using an athermal quasistatic simulation protocol, we study the distribution of free volumes in sheared hard-particle packings close to, but below, the random-close packing threshold. We show that under shear, and independent of volume fraction, the free volumes develop features similar to close-packed systems - particles self-organize in a manner as to mimick the isotropically jammed state. We compare athermally sheared packings with thermalized packings and show that thermalization leads to an erasure of these structural features. The temporal evolution in particular the opening-up and the closing of free-volume patches is associated with the single-particle dynamics, showing a crossover from ballistic to diffusive behavior.

  5. Diffusion of Brownian Particles under Oscillatory Shear Flow

    NASA Astrophysics Data System (ADS)

    Takikawa, Yoshinori; Orihara, Hiroshi

    2012-12-01

    Brownian motion has been investigated in oscillatory flows. A number of polystyrene spheres dispersed in water were traced with a confocal scanning laser microscope, and the time dependences of their coordinates were obtained. From the trajectories of the particles observed, mean-square displacements (MSDs) were calculated. We found that although the MSD in the vorticity direction is independent of the amplitude of shear strain, that of MSD in the flow direction increases as the amplitude of shear strain is increased, and that the effective diffusion constant depends on both the amplitude and initial phase of the applied sinusoidal shear strains. All experimental results are in good agreement with the theoretical results derived from the Langevin equation.

  6. Probe Oscillation Shear Elastography (PROSE): A High Frame-Rate Method for Two-Dimensional Ultrasound Shear Wave Elastography.

    PubMed

    Mellema, Daniel C; Song, Pengfei; Kinnick, Randall R; Urban, Matthew W; Greenleaf, James F; Manduca, Armando; Chen, Shigao

    2016-09-01

    Ultrasound shear wave elastography (SWE) utilizes the propagation of induced shear waves to characterize the shear modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate shear 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 Shear Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates shear 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 shear 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 shear waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) shear wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of shear wave motion. The shear 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 shear 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

  7. Probe Oscillation Shear Elastography (PROSE): A High Frame-Rate Method for Two-Dimensional Ultrasound Shear Wave Elastography.

    PubMed

    Mellema, Daniel C; Song, Pengfei; Kinnick, Randall R; Urban, Matthew W; Greenleaf, James F; Manduca, Armando; Chen, Shigao

    2016-09-01

    Ultrasound shear wave elastography (SWE) utilizes the propagation of induced shear waves to characterize the shear modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate shear 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 Shear Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates shear 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 shear 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 shear waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) shear wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of shear wave motion. The shear 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 shear 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

  8. Ultrasonic shear wave couplant

    DOEpatents

    Kupperman, David S.; Lanham, Ronald N.

    1985-01-01

    Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

  9. Ultrasonic shear wave couplant

    DOEpatents

    Kupperman, D.S.; Lanham, R.N.

    1984-04-11

    Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

  10. Shear response and design of RC beams strengthened using CFRP laminates

    NASA Astrophysics Data System (ADS)

    Singh, Shamsher B.

    2013-12-01

    The present investigation addresses the shear strengthening of deficient reinforced concrete (RC) beams using carbon fiber-reinforced polymer (CFRP) sheets. The effect of the pattern and orientation of the strengthening fabric on the shear capacity of the strengthened beams were examined. Three beams with various lay-ups of strengthening fabric, 45°, 0°/90°, and 0°/90°/45° were examined, in addition to an unstrengthened control beam. Principal and shear strains were measured at different locations at the critical sections of the strengthened beams corresponding to each applied shear force. Experimental results showing the advantage of beam strengthened using the various lay-ups of CFRP sheets are discussed. It is concluded that Beam-45°, Beam-0°/90°, and Beam-0°/90°/45° show about 25%, 19%, and 40% increases in shear-load carrying capacity in comparison to the control beam, respectively. Also, there exists a critical value of shear force up to which there is no appreciable shear strain in the CFRP sheets/beam. This shear force marks the ultimate shear resistance of the control beam. However, the strengthened beams exhibited significant strength and stiffness even beyond the critical value of the shear force. A design example for shear strengthening shows that the design equations available in the literature underestimate the actual shear strength of the beams.

  11. Shear wave transmissivity measurement by color Doppler shear wave imaging

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Yamazaki, Mayuko; Kasahara, Toshihiro; Sunaguchi, Naoki; Yuminaka, Yasushi

    2016-07-01

    Shear wave elastography is a useful method for evaluating tissue stiffness. We have proposed a novel shear wave imaging method (color Doppler shear wave imaging: CD SWI), which utilizes a signal processing unit in ultrasound color flow imaging in order to detect the shear wave wavefront in real time. Shear wave velocity is adopted to characterize tissue stiffness; however, it is difficult to measure tissue stiffness with high spatial resolution because of the artifact produced by shear wave diffraction. Spatial average processing in the image reconstruction method also degrades the spatial resolution. In this paper, we propose a novel measurement method for the shear wave transmissivity of a tissue boundary. Shear wave wavefront maps are acquired by changing the displacement amplitude of the shear wave and the transmissivity of the shear wave, which gives the difference in shear wave velocity between two mediums separated by the boundary, is measured from the ratio of two threshold voltages required to form the shear wave wavefronts in the two mediums. From this method, a high-resolution shear wave amplitude imaging method that reconstructs a tissue boundary is proposed.

  12. Development of conjugate shear bands during bulk simple shearing

    NASA Astrophysics Data System (ADS)

    Harris, L. B.; Cobbold, P. R.

    In rocks possessing a strong planar fabric, shear bands of constant shear sense and oriented at an oblique angle to the foliation are considered by many authors to be characteristic of a non-coaxial bulk deformation history, whereas conjugate shear bands are considered to indicate coaxial shortening. However, in two areas where bulk deformation history appears to be non-coaxial (Cap Corse, Corsica and Ile de Groix, Brittany), conjugate shear bands are observed. In order to investigate this problem, experiments were performed by bulk simple shearing using Plasticine as a rock analogue. When slip between layers of the model is permitted, shear bands of normal-fault geometry form with both the same and opposite shear sense as the bulk simple shearing at approximately the same angle with the layering (40°) irrespective of layer orientation in the undeformed state (for initial orientations of 50, 30 and 15°). Shear bands are initially formed within individual layers and may propagate across layer interfaces when further movement along these is inhibited. The existence of conjugate shear bands in Corsica and Ile de Groix is therefore not incompatible with a model of bulk simple shearing for these two regions. In field studies, one should perhaps exercise care in using shear bands to determine the kind of motion or the sense of bulk shearing.

  13. Shear band formation in plastic bonded explosive (PBX)

    SciTech Connect

    Dey, T.N.; Johnson, J.N.

    1997-07-01

    Adiabatic shear bands can be a source of ignition and lead to detonation. At low to moderate deformation rates, 10-1000/s , two other mechanisms can also give rise to shear bands. These mechanisms are: 1) softening caused by microcracking and 2) a constitutive response with a non-associated flow rule as is observed in granular material such as soil. Brittle behavior at small strains and the granular nature of HMX suggest that PBX-9501 constitutive behavior may be similar to sand. A constitutive model for the first of these mechanisms is studied in a series of calculations. This viscoelastic constitutive model for PBX-9501 softens via a statistical crack model. A sand model is used to provide a non-associated flow rule and detailed results will be reported elsewhere. Both models generate shear band formation at 1-2% strain at nominal strain rates at and below 1000/s. Shear band formation is suppressed at higher strain rates. Both mechanisms may accelerate the formation of adiabatic shear bands.

  14. Viscous shear heating instabilities in a 1-D viscoelastic shear zone

    NASA Astrophysics Data System (ADS)

    Homburg, J. M.; Coon, E. T.; Spiegelman, M.; Kelemen, P. B.; Hirth, G.

    2010-12-01

    Viscous shear 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 shear heating (e.g. Braeck and Podladchikov, 2007), most have used thermal anomalies to initiate a shear 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 shear zone and coarse grained host rock to initiate an instability. This choice is supported by observations of numerous fine grained ductile shear 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 shear 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 shear zone, a background grain size of 1 mm, a shear zone grain size of 150 μm, and an initial temperature of 650°C) dramatic

  15. Holographic lateral shear interferometer.

    PubMed

    Malacara, D; Mallick, S

    1976-11-01

    A new type of lateral shear holographic interferometer is described. It can be used to test lenses as well as spherical and aspherical surfaces. A null pattern with straight fringes can be obtained for an aspherical surface, provided one has a prototype that can be used for making the hologram.

  16. Evolution of shear banding flows in metallic glasses characterized by molecular dynamics

    NASA Astrophysics Data System (ADS)

    Yao, Li; Luan, Yingwei

    2016-06-01

    To reveal the evolution of shear banding flows, one-dimensional nanostructure metallic glass composites have been studied with molecular dynamics. The inherent size determines the initial thickness of shear bands, and the subsequent broadening can be restricted to some extent. The vortex-like flows evoke the atomic motion perpendicular to the shear plane, which accelerates the interatomic diffusion. The reduction of local strain rate causes the flow softening for monolithic Cu-Zr glass, but the participation of Cu-atoms in the shear banding flow gradually leads to the shear hardening for the composites.

  17. Progressive Failure Studies of Stiffened Panels Subjected to Shear Loading

    NASA Technical Reports Server (NTRS)

    Ambur, Damodar R.; Jaunky, Navin; Hilburger, Mark W.; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    Experimental and analytical results are presented for progressive failure of stiffened composite panels with and without a notch and subjected to in plane shear loading well into their postbuckling regime. Initial geometric imperfections are included in the finite element models. Ply damage modes such as matrix cracking, fiber-matrix shear, and fiber failure are modeled by degrading the material properties. Experimental results from the test include strain field data from video image correlation in three dimensions in addition to other strain and displacement measurements. Results from nonlinear finite element analyses are compared with experimental data. Good agreement between experimental data and numerical results are observed for the stitched stiffened composite panels studied.

  18. Shear mechanical properties of the spleen: experiment and analytical modelling.

    PubMed

    Nicolle, S; Noguer, L; Palierne, J-F

    2012-05-01

    This paper aims at providing the first shear mechanical properties of spleen tissue. Rheometric tests on porcine splenic tissues were performed in the linear and nonlinear regime, revealing a weak frequency dependence of the dynamic moduli in linear regime and a distinct strain-hardening effect in nonlinear regime. These behaviours are typical of soft tissues such as kidney and liver, with however a less pronounced strain-hardening for the spleen. An analytical model based on power laws is then proposed to describe the general shear viscoelastic behaviour of the spleen. PMID:22498291

  19. The Application of Strain Range Partitioning Method to Torsional Creep-Fatigue Interaction

    NASA Technical Reports Server (NTRS)

    Zamrik, S. Y.

    1975-01-01

    The method of strain range partitioning was applied to a series of torsional fatigue tests conducted on tubular 304 stainless steel specimens at 1200 F. Creep strain was superimposed on cycling strain, and the resulting strain range was partitioned into four components; completely reversed plastic shear strain, plastic shear strain followed by creep strain, creep strain followed by plastic strain and completely reversed creep strain. Each strain component was related to the cyclic life of the material. The damaging effects of the individual strain components were expressed by a linear life fraction rule. The plastic shear strain component showed the least detrimental factor when compared to creep strain reversed by plastic strain. In the latter case, a reduction of torsional fatigue life in the order of magnitude of 1.5 was observed.

  20. Shear of ordinary and elongated granular mixtures

    NASA Astrophysics Data System (ADS)

    Hensley, Alexander; Kern, Matthew; Marschall, Theodore; Teitel, Stephen; Franklin, Scott

    2015-03-01

    We present an experimental and computational study of a mixture of discs and moderate aspect-ratio ellipses under two-dimensional annular planar Couette shear. Experimental particles are cut from acrylic sheet, are essentially incompressible, and constrained in the thin gap between two concentric cylinders. The annular radius of curvature is much larger than the particles, and so the experiment is quasi-2d and allows for arbitrarily large pure-shear strains. Synchronized video cameras and software identify all particles and track them as they move from the field of view of one camera to another. We are particularly interested in the global and local properties as the mixture ratio of discs to ellipses varies. Global quantities include average shear rate and distribution of particle species as functions of height, while locally we investigate the orientation of the ellipses and non-affine events that can be characterized as shear transformational zones or possess a quadrupole signature observed previously in systems of purely circular particles. Discrete Element Method simulations on mixtures of circles and spherocylinders extend the study to the dynamics of the force network and energy dissipated as the system evolves. Supported by NSF CBET #1243571 and PRF #51438-UR10.

  1. Interaction of monopoles, dipoles, and turbulence with a shear flow

    NASA Astrophysics Data System (ADS)

    Marques Rosas Fernandes, V. H.; Kamp, L. P. J.; van Heijst, G. J. F.; Clercx, H. J. H.

    2016-09-01

    Direct numerical simulations have been conducted to examine the evolution of eddies in the presence of large-scale shear flows. The numerical experiments consist of initial-value-problems in which monopolar and dipolar vortices as well as driven turbulence are superposed on a plane Couette or Poiseuille flow in a periodic two-dimensional channel. The evolution of the flow has been examined for different shear rates of the background flow and different widths of the channel. Results found for retro-grade and pro-grade monopolar vortices are consistent with those found in the literature. Boundary layer vorticity, however, can significantly modify the straining and erosion of monopolar vortices normally seen for unbounded domains. Dipolar vortices are shown to be much more robust coherent structures in a large-scale shear flow than monopolar eddies. An analytical model for their trajectories, which are determined by self-advection and advection and rotation by the shear flow, is presented. Turbulent kinetic energy is effectively suppressed by the shearing action of the background flow provided that the shear is linear (Couette flow) and of sufficient strength. Nonlinear shear as present in the Poiseuille flow seems to even increase the turbulence strength especially for high shear rates.

  2. Shear Thinning of Noncolloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Vázquez-Quesada, Adolfo; Tanner, Roger I.; Ellero, Marco

    2016-09-01

    Shear thinning—a reduction in suspension viscosity with increasing shear rates—is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates.

  3. Shear Thinning of Noncolloidal Suspensions.

    PubMed

    Vázquez-Quesada, Adolfo; Tanner, Roger I; Ellero, Marco

    2016-09-01

    Shear thinning-a reduction in suspension viscosity with increasing shear rates-is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates. PMID:27636496

  4. Tensile-shear correlations obtained from shear punch test technique using a modified experimental approach

    NASA Astrophysics Data System (ADS)

    Karthik, V.; Visweswaran, P.; Vijayraghavan, A.; Kasiviswanathan, K. V.; Raj, Baldev

    2009-09-01

    Shear punch testing has been a very useful technique for evaluating mechanical properties of irradiated alloys using a very small volume of material. The load-displacement data is influenced by the compliance of the fixture components. This paper describes a modified experimental approach where the compliances of the punch and die components are eliminated. The analysis of the load-displacement data using the modified setup for various alloys like low carbon steel, SS316, modified 9Cr-1Mo, 2.25Cr-1Mo indicate that the shear yield strength evaluated at 0.2% offset of normalized displacement relates to the tensile YS as per the Von Mises yield relation ( σys = 1.73 τys). A universal correlation of type UTS = mτmax where m is a function of strain hardening exponent, is seen to be obeyed for all the materials in this study. The use of analytical models developed for blanking process are explored for evaluating strain hardening exponent from the load-displacement data. This study is directed towards rationalizing the tensile-shear empirical correlations for a more reliable prediction of tensile properties from shear punch tests.

  5. Direct Numerical Simulation of Surfactant-Stabilized Emulsions Morphology and Shear Viscosity in Starting Shear Flow

    SciTech Connect

    Roar Skartlien; Espen Sollum; Andreas Akselsen; Paul Meakin

    2012-07-01

    A 3D lattice Boltzmann model for two-phase flow with amphiphilic surfactant was used to investigate the evolution of emulsion morphology and shear stress in starting shear flow. The interfacial contributions were analyzed for low and high volume fractions and varying surfactant activity. A transient viscoelastic contribution to the emulsion rheology under constant strain rate conditions was attributed to the interfacial stress. For droplet volume fractions below 0.3 and an average capillary number of about 0.25, highly elliptical droplets formed. Consistent with affine deformation models, gradual elongation of the droplets increased the shear stress at early times and reduced it at later times. Lower interfacial tension with increased surfactant activity counterbalanced the effect of increased interfacial area, and the net shear stress did not change significantly. For higher volume fractions, co-continuous phases with a complex topology were formed. The surfactant decreased the interfacial shear stress due mainly to advection of surfactant to higher curvature areas. Our results are in qualitative agreement with experimental data for polymer blends in terms of transient interfacial stresses and limited enhancement of the emulsion viscosity at larger volume fractions where the phases are co-continuous.

  6. Structure and development of an anastomosing network of ductile shear zones

    NASA Astrophysics Data System (ADS)

    Carreras, Jordi; Czeck, Dyanna M.; Druguet, Elena; Hudleston, Peter J.

    2010-05-01

    A detailed structural analysis of an anastomosing shear zone network in metagabbros from the Archean Rainy Lake zone (Canada) revealed the existence of prevalent dextral and minor sinistral conjugate shear zones with the obtuse angle (>130°) facing the main shortening direction. A typology of shear zone intersections, confluences, and other features shows that all shears formed during a single deformation event, with dextral and sinistral shears being active together or in an alternating fashion. In spite of the difficulty of establishing a complete kinematic sequence, early and late shears can be distinguished. The final angular pattern between dextral and sinistral shears is not an original feature. Dextral and sinistral shears formed at nearly right angles, and the angles progressively opened towards the extension direction as a result of increasing strain. The obtuse angles were achieved by the combined effects of continued shearing on newly forming shears and internal deformation of the lozenge-shaped domains of lesser-deformed rock bounded by the shears. Through time, there was an increasing prevalence of dextral shears over sinistral ones. The studied pattern and sequential analysis indicate that the bulk deformation was noncoaxial with a deformation regime evolving from a pure shear-dominated dextral transpression to a higher vorticity dextral transpression.

  7. Pulsatile Fluid Shear in Bone Remodeling

    NASA Technical Reports Server (NTRS)

    Frangos, John A.

    1997-01-01

    The objective of this investigation was to elucidate the sensitivity to transients in fluid shear stress in bone remodeling. Bone remodeling is clearly a function of the local mechanical environment which includes interstitial fluid flow. Traditionally, load-induced remodeling has been associated with low frequency (1-2 Hz) signals attributed to normal locomotion. McLeod and Rubin, however, demonstrated in vivo remodeling events associated with high frequency (15-30 Hz) loading. Likewise, other in vivo studies demonstrated that slowly applied strains did not trigger remodeling events. We therefore hypothesized that the mechanosensitive pathways which control bone maintenance and remodeling are differentially sensitive to varying rates of applied fluid shear stress.

  8. Spatial periodicity in growth plate shear mechanical properties is disrupted by vitamin D deficiency

    PubMed Central

    Sevenler, Derin; Buckley, Mark R.; Kim, Grace; van der Meulen, Marjolein C.H.; Cohen, Itai; Bonassar, Lawrence J.

    2013-01-01

    The growth plate is a highly organized section of cartilage in the long bones of growing children that is susceptible to mechanical failure as well as structural and functional disruption caused by a dietary deficiency of vitamin D. The shear mechanical properties of the proximal tibial growth plate of rats raised either on normal or vitamin D and calcium deficient diets were measured. A sinusoidal oscillating shear load was applied to small excised growth plate specimens perpendicular to the direction of growth while imaging the deformation in real time with a fast confocal microscope. Local deformations and shear strains were quantified using image correlation. The proliferative zone of the growth plate bores the majority of the shear strain and the resting, hypertrophic and calcification zones deformed less. Surprisingly, we regularly observed discontinuous deformations in the proliferative zone in both groups that resembled cell columns sliding past one another in the direction of growth. These discontinuities manifested as regions of concentrated longitudinal shear strain. Furthermore, these shear strain concentrations were spaced evenly in the proliferative zone and the spacing between them was similar across growth plate regions and across control specimens. In contrast to the healthy controls, the vitamin D deficient growth plate exhibited larger variations in the size and orientation of cellular columns in the proliferative and hypertrophic zones. High strains were observed between columns, much as they were in the controls. However, the regular spacing of shear strain concentrations was not preserved, echoing the observation of decreased structural organization. PMID:23706979

  9. Spatial periodicity in growth plate shear mechanical properties is disrupted by vitamin D deficiency.

    PubMed

    Sevenler, Derin; Buckley, Mark R; Kim, Grace; van der Meulen, Marjolein C H; Cohen, Itai; Bonassar, Lawrence J

    2013-06-21

    The growth plate is a highly organized section of cartilage in the long bones of growing children that is susceptible to mechanical failure as well as structural and functional disruption caused by a dietary deficiency of vitamin D. The shear mechanical properties of the proximal tibial growth plate of rats raised either on normal or vitamin D and calcium deficient diets were measured. A sinusoidal oscillating shear load was applied to small excised growth plate specimens perpendicular to the direction of growth while imaging the deformation in real time with a fast confocal microscope. Local deformations and shear strains were quantified using image correlation. The proliferative zone of the growth plate bores the majority of the shear strain and the resting, hypertrophic and calcification zones deformed less. Surprisingly, we regularly observed discontinuous deformations in the proliferative zone in both groups that resembled cell columns sliding past one another in the direction of growth. These discontinuities manifested as regions of concentrated longitudinal shear strain. Furthermore, these shear strain concentrations were spaced evenly in the proliferative zone and the spacing between them was similar across growth plate regions and across control specimens. In contrast to the healthy controls, the vitamin D deficient growth plate exhibited larger variations in the size and orientation of cellular columns in the proliferative and hypertrophic zones. High strains were observed between columns, much as they were in the controls. However, the regular spacing of shear strain concentrations was not preserved, echoing the observation of decreased structural organization.

  10. Microstructural evolution and rheology of quartz in a mid-crustal shear zone

    NASA Astrophysics Data System (ADS)

    Rahl, Jeffrey M.; Skemer, Philip

    2016-06-01

    We present microstructural and crystallographic preferred orientation (CPO) data on quartz deformed in the middle crust to explore the interaction and feedback between dynamic recrystallization, deformation processes, and CPO evolution. The sample investigated here is a moderately deformed quartz-rich mylonite from the Blue Ridge in Virginia. We have created high-resolution crystallographic orientation maps using electron backscatter diffraction (EBSD) of 51 isolated quartz porphyroclasts with recrystallized grain fractions ranging from 10 to 100%. Recrystallized grains are internally undeformed and display crystallographic orientations dispersed around the orientation of the associated parent porphyroclast. We document a systematic decrease in fabric intensity with recrystallization, suggesting that progressive deformation of the recrystallized domains involves processes that can weaken a pre-existing CPO. Relationships between recrystallization fraction and shear strain suggest that complete microstructural re-equilibration requires strains in excess of γ = 5. Variation in the degree of recrystallization implies that strain was accumulated heterogeneously, and that a steady-state microstructure and rheology were not achieved.

  11. Standing shear waves in anisotropic viscoelastic media

    NASA Astrophysics Data System (ADS)

    Krit, T.; Golubkova, I.; Andreev, V.

    2015-10-01

    We studied standing shear waves in anisotropic resonator represented by a rectangular parallelepiped (layer) fixed without slipping between two wooden plates of finite mass. The viscoelastic layer with edges of 70 mm × 40 mm × 15 mm was made of a rubber-like polymer plastisol with rubber bands inside. The bands were placed vertical between the top and the bottom plate. Mechanical properties of the plastisol itself were carefully measured previously. It was found that plastisol shows a cubic nonlinear behavior, i.e. the stress-strain curve could be represented as: σ = μɛ + βμɛ3, where ɛ stands for shear strain and σ is an applied shear stress. The value of shear modulus μ depends on frequency and was found to be several kilopascals which is common for such soft solids. Nonlinear parameter β is frequency dependent too and varies in range from tenths to unity at 1-100 Hz frequency range, decreasing with frequency growth. Stretching the rubber bands inside the layer leads to change of elastic properties in resonator. Such effect could be noticed due to frequency response of the resonator. The numerical model of the resonator was based on finite elements method (FEM) and performed in MatLab. The resonator was cut in hundreds of right triangular prisms. Each prism was provided with viscoelastic properties of the layer except for the top prisms provided with the wooden plate properties and the prisms at the site of the rubber bands provided with the rubber properties. The boundary conditions on each prism satisfied the requirements that resonator is inseparable and all its boundaries but bottom are free. The bottom boundary was set to move horizontally with constant acceleration amplitude. It was shown numerically that the resonator shows anisotropic behavior expressed in different frequency response to oscillations applied to a bottom boundary in different directions.

  12. Shear-thinning Fluid

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.

  13. Gelation under shear

    SciTech Connect

    Butler, B.D.; Hanley, H.J.M.; Straty, G.C.; Muzny, C.D.

    1995-12-31

    An experimental small angle neutron scattering (SANS) study of dense silica gels, prepared from suspensions of 24 nm colloidal silica particles at several volume fractions {theta} is discussed. Provided that {theta}{approx_lt}0.18, the scattered intensity at small wave vectors q increases as the gelation proceeds, and the structure factor S(q, t {yields} {infinity}) of the gel exhibits apparent power law behavior. Power law behavior is also observed, even for samples with {theta}>0.18, when the gel is formed under an applied shear. Shear also enhances the diffraction maximum corresponding to the inter-particle contact distance of the gel. Difficulties encountered when trying to interpret SANS data from these dense systems are outlined. Results of computer simulations intended to mimic gel formation, including computations of S(q, t), are discussed. Comments on a method to extract a fractal dimension characterizing the gel are included.

  14. Anisotropic shear melting and recrystallization of a two-dimensional complex plasma.

    PubMed

    Nosenko, V; Ivlev, A V; Morfill, G E

    2013-04-01

    A two-dimensional plasma crystal was melted by suddenly applying localized shear stress. A stripe of particles in the crystal was pushed by the radiation pressure force of a laser beam. We found that the response of the plasma crystal to stress and the eventual shear melting depended strongly on the crystal's angular orientation relative to the laser beam. Shear stress and strain rate were measured, from which the spatially resolved shear viscosity was calculated. The latter was shown to have minima in the regions with highest strain rate, thus demonstrating shear thinning. Shear-induced reordering was observed in the steady-state flow, where particles formed strings aligned in the flow direction.

  15. The 3-D strain patterns in Turkey using geodetic velocity fields from the RTK-CORS (TR) network

    NASA Astrophysics Data System (ADS)

    Kutoglu, Hakan Senol; Toker, Mustafa; Mekik, Cetin

    2016-03-01

    This study presents our use of GPS data to obtain and quantify the full continuous strain tensor using a 3-D velocity field in Turkey. In this study, GPS velocities improve the estimation of short-term strain tensor fields for determining the seismic hazard of Turkey. The tensorial analysis presents different aspects of deformation, such as the normal and shear strains, including their directions, the compressional and extensional strains. This analysis is appropriate for the characterizing the state of the current seismic deformation. GPS velocity data from continuous measurements (2009-2012) to estimate deformations were processed using the GAMIT/GLOBK software. Using high-rate GPS data from permanent 146 GNSS stations (RTK-CORS-TR network), the strain distribution was determined and interpolated using a biharmonic spline technique. We show the strain field patterns within axial and plane form at several critical locations, and discuss these results within the context of the seismic and tectonic deformation of Turkey. We conclude that the knowledge of the crustal strain patterns provides important information on the location of the main faults and strain accumulation for the hazard assessment. The results show an agreement between the seismic and tectonic strains confirming that there are active crustal deformations in Turkey.

  16. Spatial variations in Achilles tendon shear wave speed

    PubMed Central

    DeWall, Ryan J.; Slane, Laura C.; Lee, Kenneth S.; Thelen, Darryl G.

    2014-01-01

    Supersonic shear imaging (SSI) is an ultrasound imaging modality that can provide insight into tissue mechanics by measuring shear wave propagation speed, a property that depends on tissue elasticity. SSI has previously been used to characterize the increase in Achilles tendon shear wave speed that occurs with loading, an effect attributable to the strain-stiffening behavior of the tissue. However, little is known about how shear wave speed varies spatially, which is important, given the anatomical variation that occurs between the calcaneus insertion and the gastrocnemius musculotendon junction. The purpose of this study was to investigate spatial variations in shear wave speed along medial and lateral paths of the Achilles tendon for three different ankle postures: resting ankle angle (R, i.e. neutral), plantarflexed (P; R − 15 deg), and dorsiflexed (D; R + 15 deg). We observed significant spatial and posture variations in tendon shear wave speed in ten healthy young adults. Shear wave speeds in the Achilles free tendon averaged 12 ± 1.2 m/s in a resting position, but decreased to 7.2 ± 1.8 m/s with passive plantarflexion. Distal tendon shear wave speeds often reached the maximum tracking limit (16.3 m/s) of the system when the ankle was in the passively dorsiflexed posture (+15 deg from R). At a fixed posture, shear wave speeds decreased significantly from the free tendon to the gastrocnemius musculotendon junction, with slightly higher speeds measured on the medial side than on the lateral side. Shear wave speeds were only weakly correlated with the thickness and depth of the tendon, suggesting that the distal-to-proximal variations may reflect greater compliance in the aponeurosis relative to the free tendon. The results highlight the importance of considering both limb posture and transducer positioning when using SSI for biomechanical and clinical assessments of the Achilles tendon. PMID:24933528

  17. The experimental basis for interpreting particle and magnetic fabrics of sheared till

    USGS Publications Warehouse

    Iverson, N.R.; Hooyer, T.S.; Thomason, J.F.; Graesch, M.; Shumway, J.R.

    2008-01-01

    Particle fabrics of basal tills may allow testing of the bed-deformation model of glacier flow, which requires high bed shear strains (>100). Field studies, however, have not yielded a systematic relationship between shear-strain magnitude and fabric development. To isolate this relationship four basal tills and viscous putty were sheared in a ring-shear device to strains as high as 714. Fabric was characterized within a zone of shear deformation using the long-axis orientations of fine-gravel and sand particles and the anisotropy of magnetic susceptibility (AMS) of small (???5-8 cm3) intact samples. Results indicate that till particles rotate toward the plane of shearing with long-axis orientations that become tightly clustered in the direction of shear (0??78 < S1 < 0??94 for three-dimensional data). These strong, steady-state fabrics are attained at shear strains of 7-30, with no evidence of fabric weakening with further strain, regardless of the specific till or particle-size fraction under consideration. These results do not support the Jeffery model of particle rotation, which correctly describes particle rotation in the viscous putty but not in the tills, owing to fluid-mechanical assumptions of the model that are violated in till. The sensitivity of fabric development to shear-strain magnitude indicates that, for most till units where shear-strain magnitude is poorly known, attributing fabric variations to spatial differences in other variables, such as till thickness or water content, will be inherently speculative. Attributing fabric characteristics to particular basal till facies is uncertain because shear-strain magnitude is unlikely to be closely correlated to till facies. Weak or spatially variable fabrics, in the absence of post-depositional disturbance or major deviations from unidirectional simple shear, indicate that till has not been pervasively sheared to the high strains required by the bed-deformation model. Strong flow-parallel fabrics are a

  18. Spatiotemporal evolution of a fault shear stress patch due to viscoelastic interseismic fault zone rheology

    NASA Astrophysics Data System (ADS)

    Sone, Hiroki; Uchide, Takahiko

    2016-08-01

    We conducted numerical studies to explore how shear stress anomalies on fault planes (shear stress patches) evolve spatiotemporally during the interseismic period under the influence of viscoelastic rheology assigned to fault zones of finite thickness. 2-D viscoelastic models consisting of a fault zone and host rock were sheared to simulate shear stress accumulation along fault zones due to tectonic loading. No fault slip along a distinct fault planes is implied in the model, thus all fault shear motion is accommodated by distributed deformation in the viscoelastic fault zone. Results show that magnitudes of shear stress patches evolve not only temporally, but also spatially, especially when the stress anomaly is created by a geometrical irregularity (asperity) along the interface of an elastic host rock and viscoelastic fault zone. Such shear stress anomalies diffuse spatially so that the spatial dimension of the shear stress patch appears to grow over time. Models with varying fault zone viscoelastic properties and varying fault zone viscosity both show that such spatial diffusion of shear stress is enhanced by increasing the contribution of the viscous behavior. The absolute rate at which shear stress patches grow spatially is generally not influenced by the size of the shear stress patch. Therefore shear stress patches with smaller dimensions will appear to grow quicker, in the relative sense, compared to larger stress patches. These results suggest that the minimum dimensions of shear stress patches that can exist along a fault could be governed by the effective viscosity of the fault zone. Therefore patterns of accumulated shear stress could vary along faults when viscous properties are heterogeneous, for instance due to depth or material heterogeneity, which has implications on how earthquake rupture behavior could vary along faults.

  19. Large-scale ordering of nanoparticles using viscoelastic shear processing

    PubMed Central

    Zhao, Qibin; Finlayson, Chris E.; Snoswell, David R. E.; Haines, Andrew; Schäfer, Christian; Spahn, Peter; Hellmann, Goetz P.; Petukhov, Andrei V.; Herrmann, Lars; Burdet, Pierre; Midgley, Paul A.; Butler, Simon; Mackley, Malcolm; Guo, Qixin; Baumberg, Jeremy J.

    2016-01-01

    Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles. PMID:27255808

  20. Large-scale ordering of nanoparticles using viscoelastic shear processing.

    PubMed

    Zhao, Qibin; Finlayson, Chris E; Snoswell, David R E; Haines, Andrew; Schäfer, Christian; Spahn, Peter; Hellmann, Goetz P; Petukhov, Andrei V; Herrmann, Lars; Burdet, Pierre; Midgley, Paul A; Butler, Simon; Mackley, Malcolm; Guo, Qixin; Baumberg, Jeremy J

    2016-01-01

    Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles. PMID:27255808

  1. Shear-banding Induced Indentation Size Effect in Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Lu, Y. M.; Sun, B. A.; Zhao, L. Z.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.

    2016-06-01

    Shear-banding is commonly regarded as the “plasticity carrier” of metallic glasses (MGs), which usually causes severe strain localization and catastrophic failure if unhindered. However, through the use of the high-throughput dynamic nanoindentation technique, here we reveal that nano-scale shear-banding in different MGs evolves from a “distributed” fashion to a “localized” mode when the resultant plastic flow extends over a critical length scale. Consequently, a pronounced indentation size effect arises from the distributed shear-banding but vanishes when shear-banding becomes localized. Based on the critical length scales obtained for a variety of MGs, we unveil an intrinsic interplay between elasticity and fragility that governs the nanoscale plasticity transition in MGs. Our current findings provide a quantitative insight into the indentation size effect and transition mechanisms of nano-scale plasticity in MGs.

  2. Large-scale ordering of nanoparticles using viscoelastic shear processing.

    PubMed

    Zhao, Qibin; Finlayson, Chris E; Snoswell, David R E; Haines, Andrew; Schäfer, Christian; Spahn, Peter; Hellmann, Goetz P; Petukhov, Andrei V; Herrmann, Lars; Burdet, Pierre; Midgley, Paul A; Butler, Simon; Mackley, Malcolm; Guo, Qixin; Baumberg, Jeremy J

    2016-06-03

    Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.

  3. Shear-banding Induced Indentation Size Effect in Metallic Glasses

    PubMed Central

    Lu, Y. M.; Sun, B. A.; Zhao, L. Z.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.

    2016-01-01

    Shear-banding is commonly regarded as the “plasticity carrier” of metallic glasses (MGs), which usually causes severe strain localization and catastrophic failure if unhindered. However, through the use of the high-throughput dynamic nanoindentation technique, here we reveal that nano-scale shear-banding in different MGs evolves from a “distributed” fashion to a “localized” mode when the resultant plastic flow extends over a critical length scale. Consequently, a pronounced indentation size effect arises from the distributed shear-banding but vanishes when shear-banding becomes localized. Based on the critical length scales obtained for a variety of MGs, we unveil an intrinsic interplay between elasticity and fragility that governs the nanoscale plasticity transition in MGs. Our current findings provide a quantitative insight into the indentation size effect and transition mechanisms of nano-scale plasticity in MGs. PMID:27324835

  4. Large-scale ordering of nanoparticles using viscoelastic shear processing

    NASA Astrophysics Data System (ADS)

    Zhao, Qibin; Finlayson, Chris E.; Snoswell, David R. E.; Haines, Andrew; Schäfer, Christian; Spahn, Peter; Hellmann, Goetz P.; Petukhov, Andrei V.; Herrmann, Lars; Burdet, Pierre; Midgley, Paul A.; Butler, Simon; Mackley, Malcolm; Guo, Qixin; Baumberg, Jeremy J.

    2016-06-01

    Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.

  5. The in-plane shear properties of pultruded materials

    NASA Astrophysics Data System (ADS)

    Cho, Baik-Soon

    1998-12-01

    This thesis presents the details for a new in-plane shear test method applicable to pultruded materials reinforced with continuous strand mat (CSM) and rovings. The loading system and the size of the specimen are different from those currently used in the ASTM D-5379 specification in order to reduce the effect of the inherent heterogeneity of the pultruded materials. Then, the performance of the ASTM D-5379 V-notched beam test fixture and that of the newly developed test fixture at the Georgia Institute of Technology will be discussed. The thesis also presents various predicted techniques for estimating the in-plane shear modulus of pultruded materials from the properties of the constituents. Finally, a third-order polynomial shear stress---shear strain (tau - gamma) equation is proposed for more accurate structural analysis of pultruded materials reinforced with rovings and continuous strand mats.

  6. Dynamic shear behavior of alumina-filled epoxy

    SciTech Connect

    Costin, L.S.

    1982-03-01

    Thin-walled tubular specimens of alumina-filled epoxy were loaded in torsion at a strain rate of approximately 10/sup 3/ s/sup -1/ using a stored-torque Kolsky bar. In addition to measuring the time resolved shear stress and shear strain in the specimen, the axial stress generated by the dilation of the material during shear deformation was also obtained as a function of time. Tests were conducted at room temperature and at -60/sup 0/C. At room temperature, a moderate amount of plastic deformation occurred before failure. Material dilation was associated with the plastic flow. At -60/sup 0/C, there was a marked increase in failure stress over the failure stress at room temperature. However, little or no plastic deformation or dilation occurred before failure.

  7. Material characterization of structural adhesives in the lap shear mode

    NASA Technical Reports Server (NTRS)

    Sancaktar, E.; Schenck, S. C.

    1983-01-01

    A general method for characterizing structual adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semiempirical and theoretical approaches are used. The semiempirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Two different model adhesives are used in the single lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.

  8. In situ observation of shear-driven amorphization in silicon crystals

    NASA Astrophysics Data System (ADS)

    He, Yang; Zhong, Li; Fan, Feifei; Wang, Chongmin; Zhu, Ting; Mao, Scott X.

    2016-10-01

    Amorphous materials are used for both structural and functional applications. An amorphous solid usually forms under driven conditions such as melt quenching, irradiation, shock loading or severe mechanical deformation. Such extreme conditions impose significant challenges on the direct observation of the amorphization process. Various experimental techniques have been used to detect how the amorphous phases form, including synchrotron X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy, but a dynamic, atomistic characterization has remained elusive. Here, by using in situ high-resolution TEM (HRTEM), we show the dynamic amorphization process in silicon nanocrystals during mechanical straining on the atomic scale. We find that shear-driven amorphization occurs in a dominant shear band starting with the diamond-cubic (dc) to diamond-hexagonal (dh) phase transition and then proceeds by dislocation nucleation and accumulation in the newly formed dh-Si phase. This process leads to the formation of an amorphous Si (a-Si) band, embedded with dh-Si nanodomains. The amorphization of dc-Si via an intermediate dh-Si phase is a previously unknown pathway of solid-state amorphization.

  9. Earthquakes initiation and thermal shear instability in the Hindu Kush intermediate depth nest

    NASA Astrophysics Data System (ADS)

    Poli, Piero; Prieto, German; Rivera, Efrain; Ruiz, Sergio

    2016-02-01

    Intermediate depth earthquakes often occur along subducting lithosphere, but despite their ubiquity the physical mechanism responsible for promoting brittle or brittle-like failure is not well constrained. Large concentrations of intermediate depth earthquakes have been found to be related to slab break-off, slab drip, and slab tears. The intermediate depth Hindu Kush nest is one of the most seismically active regions in the world and shows the correlation of a weak region associated with ongoing slab detachment process. Here we study relocated seismicity in the nest to constraint the geometry of the shear zone at the top of the detached slab. The analysis of the rupture process of the Mw 7.5 Afghanistan 2015 earthquake and other several well-recorded events over the past 25 years shows an initially slow, highly dissipative rupture, followed by a dramatic dynamic frictional stress reduction and corresponding large energy radiation. These properties are typical of thermal driven rupture processes. We infer that thermal shear instabilities are a leading mechanism for the generation of intermediated-depth earthquakes especially in presence of weak zone subjected to large strain accumulation, due to ongoing detachment process.

  10. Shear-induced orientation in model polymer-clay nanocomposites

    NASA Astrophysics Data System (ADS)

    Dykes, Laura; Burghardt, Wesley; Krishnamoorti, Ramanan

    2003-03-01

    We report studies of the structural dynamics in model polymer/clay inorganic nanocomposites. Organically modified montmorillonite and fluorohectorite are dispersed in relatively low viscosity PDMS-PDPS copolymer, leading to rheologically complex materials that may be conveniently studied at room temperature. We utilize an annular cone and plate x-ray shear cell, in conjunction with synchrotron x-ray scattering to enable real-time measurements of the average degree and direction of platelet orientation within the flow-gradient (1-2) plane in shear flow. We characterize orientation in steady unidirectional shear flow, upon flow reversal and cessation, and during large-amplitude oscillatory shear. Average platelet orientation increases modestly with increasing shear rate, while the average platelet orientation moves somewhat closer to the flow direction. In all samples studied, orientation does not relax significantly upon cessation of shear. Upon flow reversal, moderately concentrated montmorillonite dispersions exhibit oscillations in anisotropy and orientation angle that scale with shear strain, presumably associated with the tumbling motion of the plate-like clay particles. These oscillations are suppressed at higher particle concentrations.

  11. Measurement of Oblique Impact-generated Shear Waves

    NASA Technical Reports Server (NTRS)

    Dahl, J. M.; Schultz, P. H.

    2001-01-01

    Experimental strain measurements reveal that oblique impacts can generate shear waves with displacements as large as those in the P-wave. Large oblique impacts may thus be more efficient sources of surface disruption than vertical impacts. Additional information is contained in the original extended abstract.

  12. A comparative evaluation of in-plane shear test methods for laminated graphite-epoxy composites

    NASA Technical Reports Server (NTRS)

    Morton, John; Ho, Henjen

    1992-01-01

    The objectives were to evaluate popular shear test methods for various forms of graphite-epoxy composite materials and to determine the shear response of graphite-epoxy composites with various forms of fiber architecture. Numerical and full-field experimental stress analyses were performed on four shear test configurations for unidirectional and bidirectional graphite-epoxy laminates to assess the uniformity and purity of the shear stress (strain) fields produced in the specimen test section and to determine the material in-plane shear modulus and shear response. The test methods were the 10 deg off-axis, the +/- 45 deg tension, the Iosipescu V-notch, and a compact U-notch specimen. Specimens were prepared from AS4/3501-6 graphite-epoxy panels, instrumented with conventional strain gage rosettes and with a cross-line moire grating, and loaded in a convenient testing machine. The shear responses obtained for each test method and the two methods of specimen instrumentation were compared. In a second phase of the program the shear responses obtained from Iosipescu V-notch beam specimens were determined for woven fabric geometries of different weave and fiber architectures. Again the responses of specimens obtained from strain gage rosettes and moire interferometry were compared. Additional experiments were performed on a bidirectional cruciform specimen which was also instrumented with strain gages and a moire grating.

  13. A method for planar biaxial mechanical testing that includes in-plane shear.

    PubMed

    Sacks, M S

    1999-10-01

    A limitation in virtually all planar biaxial studies of soft tissues has been the inability to include the effects of in-plane shear. This is due to the inability of current mechanical testing devices to induce a state of in-plane shear, due to the added cost and complexity. In the current study, a straightforward method is presented for planar biaxial testing that induces a combined state of in-plane shear and normal strains. The method relies on rotation of the test specimen's material axes with respect to the device axes and on rotating carriages to allow the specimen to undergo in-plane shear freely. To demonstrate the method, five glutaraldehyde treated bovine pericardium specimens were prepared with their preferred fiber directions (defining the material axes) oriented at 45 deg to the device axes to induce a maximum shear state. The test protocol included a wide range of biaxial strain states, and the resulting biaxial data re-expressed in material axes coordinate system. The resulting biaxial data was then fit to the following strain energy function W: [equation: see text] where E'ij is the Green's strain tensor in the material axes coordinate system and c and Ai are constants. While W was able to fit the data very well, the constants A5 and A6 were found not to contribute significantly to the fit and were considered unnecessary to model the shear strain response. In conclusion, while not able to control the amount of shear strain independently or induce a state of pure shear, the method presented readily produces a state of simultaneous in-plane shear and normal strains. Further, the method is very general and can be applied to any anisotropic planar tissue that has identifiable material axes.

  14. Consideration of microstructural changes in the study of adiabatic shear bands

    NASA Astrophysics Data System (ADS)

    Batra, Romesh C.

    1994-09-01

    We have analyzed the effect of microstructural changes on the initiation and growth of shear bands. These have been studied by developing an adaptive mesh refinement technique to decipher adiabatic shear bands in two-dimensional problems, formulating a three-dimensional finite-deformation theory for dipolar thermoviscoplastic materials and using it to examine the initiation and growth of shear bands in plane strain thermomechanical deformations of dipolar materials, employing an internal variable theory of Brown, Kim and Anand to study the shear band problem, investigating the possibility of phase transformations during the development of adiabatic shear bands in a steel specimen, ascertaining the speed of propagation of a shear band in a steel tube, assessing the effect of frictional forces between the loading device and the cylinder ends, and, analyzing the development of a shear band in a FCC single crystal. Principal results obtained during these investigations are summarized in the report.

  15. Rheology of talc sheared at high pressure and temperature: a case study for hot subduction zones

    NASA Astrophysics Data System (ADS)

    Misra, Santanu; Boutareaud, Sébastien; Burg, Jean-Pierre

    2014-01-01

    Talc is a common fault-coating mineral occurring in a variety of tectonic settings from the immediate subsurface down to more than 100 km depth along subducting plate interfaces. It is considered to stabilize slip at seismogenic depth. To gain insight into the rheological behavior of talc and related deformation processes along the subduction interface of hot oceanic slabs, we conducted torsion experiments on intact synthetic talc samples at 200-600 °C under 100-300 MPa confining pressure at intermediate strain rates (3 × 10- 4 and 2.45 × 10- 3 s- 1) for bulk shear strains up to 12.6.We also conducted stepping strain rate experiments to investigate rate and temperature dependence on sliding velocity and slide-hold-slide experiments to explore the re-strengthening and frictional healing of the sliding zones. The experimental results reveal 1) post-yield strain hardening followed by brief weakening episodes and then again strain hardening with increasing deformation and 2) a gradual transition of friction evolution from velocity-strengthening to velocity-neutral. Microstructural observations coupled with mechanical data suggest that talc rheology combines localized and distributed deformation, in a state called the brittle-ductile transition, with a predominance of crystal-plastic over cataclastic (brittle to semi-brittle) processes at 600 °C and 300 MPa confining pressure. These data suggest that talc cannot accumulate the tectonic stress necessary for earthquake-generating rupture along the subduction interface. This result concurs with the concept that in weak heterogeneous talc-rich material, strong asperities that can resist the tectonic stress to a greater extent are responsible for the consequential earthquake occurrence.

  16. Hydrolytic weakening and penetrative deformation within a natural shear zone

    NASA Astrophysics Data System (ADS)

    Kronenberg, Andreas K.; Segall, Paul; Wolf, George H.

    Processes of fluid infiltration, hydrolytic weakening, and penetrative deformation within a small ductile shear zone within granitic rocks of the central Sierra Nevada have been investigated using integrated field observations, strain analysis, infrared spectroscopy, and transmission electron microscopy. Several lines of evidence suggest that tensile fracturing accompanied by fluid infiltration preceded the ductile shearing event and that shear strains have localized on a pre-existing sealed fracture. Finite shear strains within an aplite dike and granodiorite host increase sharply from nominally O outside the shear zone to values of 10±2 near its center. Water contents of quartz grains exhibit similar spatial trends to that of strain, rising from 60 and 2000 ppm within the undeformed aplite and granodiorite, respectively, to 4000 and 11,000 ppm within their highly sheared equivalents. Infrared signatures of absorptions measured at room temperature and at 77 K show that most of the intragranular water within quartz and feldspar resides in fluid inclusions. Two distinct populations of fluid inclusions have been observed by optical and electron microscopy; one decorating healed microcracks and the second decorating dislocations. We interpret these relations to record interactions between fluids and processes of brittle failure and ductile flow. Fluid inclusions, forming planar arrays along the traces of healed microcracks, are relatively large (˜0.4-3 μm in diameter) and irregular in shape. A second set of fluid inclusions consists of extremely fine (20-140 nm in diameter), more nearly spherical inclusions which consistently lie along free dislocations and dislocation nodes, and exhibit relationships with dislocations similar to those observed in hydrolytically-weakened synthetic quartz. These observations suggest that water-related defects gained access to grain interiors and dislocation cores by fluid infiltration along open microcracks followed by pipe

  17. A microcomputer-based data acquisition and control system for the direct shear, ring shear, triaxial shear, and consolidation tests

    USGS Publications Warehouse

    Powers, Philip S.

    1983-01-01

    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 type 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 shear tests, ring shear tests, and triaxial shear tests.

  18. Numerical simulation of systems of shear bands in ductile metal with inclusions

    NASA Astrophysics Data System (ADS)

    Plohr, JeeYeon N.; Plohr, Bradley J.

    2016-02-01

    We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation (adiabatic shear bands). This method employs the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. 127-139, 1992] to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31-41, 1996]. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. We use the Preston-Tonks-Wallace viscoplasticity model [J. Appl. Phys., vol. 93, pp. 211-220, 2003], which applies to the high strain-rate regime of an isotropic viscoplastic solid. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.

  19. An Evaluation of the Iosipescu Specimen for Composite Materials Shear Property Measurement. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Ho, Henjen

    1991-01-01

    A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. An experimental investigation using conventional strain gage instrumentation and moire interferometry is performed. A finite element analysis of the Iosipescu shear test for unidirectional and cross-ply composites is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon the strain gage measurements used for the determination of composite shear moduli. From the test results for graphite-epoxy laminates, it is shown that the proximity of the load introduction point to the test section greatly influences the individual gage readings for certain fiber orientations but the effect upon shear modulus measurement is relatively unimportant. A numerical study of the load contact effect shows the sensitivity of some fiber configurations to the specimen/fixture contact mechanism and may account for the variations in the measured shear moduli. A comparison of the strain gage readings from one surface of a specimen with corresponding data from moire interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to eccentric loading which induced twisting and yielded spurious shear stress-strain curves. In the numerical analysis, it is shown that the Iosipescu specimens for different fiber orientations have to be modeled differently in order to closely approximate the true loading conditions. Correction factors are needed to allow for the nonuniformity of the strain field and the use of the average shear stress in the shear modulus evaluation. The correction factors, which are determined for the region occupied by the strain gage rosette, are found to be dependent upon the material orthotropic ratio and the finite element models. Based upon the experimental and numerical results, recommendations for improving the reliability and

  20. Smoothing and roughening of slip surfaces in direct shear experiments

    NASA Astrophysics Data System (ADS)

    Sagy, Amir; Badt, Nir; Hatzor, Yossef H.

    2015-04-01

    , increases as a function of slip amount. The roughness measured after slip can be fitted by a power-law similar to that of the initial tensile surface. In the next series of experiments a similar procedure is applied when the roughness evolution is measured as a function of increasing normal stress for a fixed displacement amount of 10 mm. While samples sheared under a constant normal stress of 5 MPa generated surface smoothing, shearing under normal stress of 7.5 MPa to 15 MPa exhibited surface roughening at the measured range of scales. We find that roughening is correlated with the attained peak shear stress values, stress drop (peak shear stress minus residual shear stress) and with wear accumulation, a novel measurement procedure of which is developed here. Analysis of the sheared samples shows that roughening is generated by sets of dense fractures that significantly damaged the sample in the immediate proximity to large asperities. This roughening is related to penetrative damage during transient wear in rough surfaces.

  1. TUBE SHEARING VALVE

    DOEpatents

    Wilner, L.B.

    1960-05-24

    Explosive operated valves can be used to join two or more containers in fluid flow relationship, one such container being a sealed reservoir. The valve is most simply disposed by mounting it on the reservoir so thst a tube extends from the interior of the reservoir through the valve body, terminating at the bottom of the bore in a closed end; other containers may be similarly connected or may be open connected, as desired. The piston of the valve has a cutting edge at its lower end which shears off the closed tube ends and a recess above the cutting edge to provide a flow channel. Intermixing of the fluid being transferred with the explosion gases is prevented by a copper ring at the top of the piston which is force fitted into the bore at the beginning of the stroke. Although designed to avoid backing up of the piston at pressures up to 10,000 psi in the transferred fluid, proper operation is independent of piston position, once the tube ends were sheared.

  2. Wind shear test

    NASA Astrophysics Data System (ADS)

    Techniques for forecasting and detecting a type of wind shear called microbursts are being tested this month in an operational program at Denver's Stapleton International Airport as part of an effort to reduce hazards to airplanes and passengers.Wind shear, which can be spawned by convective storms, can occur as a microburst. These downbursts of cool air are usually recognizable as a visible rain shaft beneath a thundercloud. Sometimes, however, the rain shaft evaporates before reaching the ground, leaving the downdraft invisible. Although thunderstorms are traditionally avoided by airplane pilots, these invisible downdrafts also harbor hazards in what usually appear to be safe skies. When the downdraft reaches the earth's surface, the downdraft spreads out horizontally, much like a stream of water gushing from a garden hose on a concrete surface, explained John McCarthy, director of the operational program. Airplanes can encounter trouble when the downdraft from the microburst causes sudden shifts in wind direction, which may reduce lift on the wing, an especially dangerous situation during takeoff.

  3. Excited waves in shear layers

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.

    1982-01-01

    The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear 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 shear layer having different velocities and densities. Furthermore, the excitation of a shear 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 shear layer were carried out.

  4. Fluid migration in ductile shear zones

    NASA Astrophysics Data System (ADS)

    Fusseis, Florian; Menegon, Luca

    2014-05-01

    Fluid migration in metamorphic environments depends on a dynamically evolving permeable pore space, which was rarely characterised in detail. The data-base behind our understanding of the 4-dimensional transport properties of metamorphic rocks is therefore fragmentary at best, which leaves conceptual models poorly supported. Generally, it seems established that deformation is a major driver of permeability generation during regional metamorphism, and evidence for metamorphic fluids being channelled in large scale shear zones has been found in all depth segments of the continental crust. When strain localizes in ductile shear zones, the microfabric is modified until a steady state mylonite is formed that supports large deformations. A dynamic porosity that evolves during mylonitisation controls the distinct transport pathways along which fluid interacts with the rock. This dynamic porosity is controlled by a limited number of mechanisms, which are intrinsically linked to the metamorphic evolution of the rock during its deformational overprint. Many mid- and lower-crustal mylonites comprise polyphase mixtures of micron-sized grains that show evidence for deformation by dissolution/precipitation-assisted viscous grain boundary sliding. The establishment of these mineral mixtures is a critical process, where monomineralic layers are dispersed and grain growth is inhibited by the heterogeneous nucleation of secondary mineral phases at triple junctions. Here we show evidence from three different mid- and lower-crustal shear zones indicating that heterogeneous nucleation occurs in creep cavities. Micro- and nanotomographic observations show that creep cavities provide the dominant form of porosity in these ultramylonites. They control a "granular fluid pump" that directs fluid migration and hence mass transport. The granular fluid pump operates on the grain scale driven by viscous grain boundary sliding, and requires only small amounts of fluid. The spatial arrangement of

  5. Numerical simulations of pattern evolution of shear bands during pure shear of geomaterials

    NASA Astrophysics Data System (ADS)

    Chen, Tielin; Liu, Jingjing; Jie, Yuxin; Zhang, Dingli

    2015-07-01

    Numerical simulations with finite element method were carried out and five types of patterns of shear bands and their process of self-organization were obtained. The elasto-plastic theory of constitutive relationship with the non-associated flow rule, vertex-like yielding surfaces and strain softening of strength were adopted to describe the mechanical behavior of geomaterials of rock or soil. The non-symmetrical matrix due to the adoption of the non-associated flow rule was solved with the algorithm of dynamical relaxation of finite element method. The discrete or banded patterns of shear strain in the form of superlattice, parallel strips, super lattice turned parallel strips, rhomboid net and concentric rhomboid loops, were gradually formed as the loading increased. The mechanism of the structural pattern generation and the process of pattern self-organization in geomaterials of rock and soil were a process of mechanical equilibrium of stresses and the allocation of material deformation between the elastic sites and plastic sites. The approach provided a way for researching mechanical origin of shear band pattern.

  6. Inductive shearing of drilling pipe

    DOEpatents

    Ludtka, Gerard M.; Wilgen, John; Kisner, Roger; Mcintyre, Timothy

    2016-04-19

    Induction shearing 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 shear the drillpipe. After shearing the drillpipe, the drillpipe may be sealed to prevent further leakage of well contents.

  7. Rate-dependent undrained shear behavior of saturated clay

    SciTech Connect

    Sheahan, T.C.; Ladd, C.C.; Germaine, J.T.

    1996-02-01

    The paper describes results from 250 K{sub 0} consolidated-undrained triaxial compression tests on resedimented Boston blue clay using a computer-automated triaxial apparatus with lubricated end platens and a midheight pore-pressure measurement device. Specimens were consolidated to four over consolidation ratios (OCR = 1, 2, 4, or 8), and for each OCR, undrained shear was performed using four axial strain rates (0.05%, 0.5%, 5%, and 50%/h). The results show that the undrained strength (s{sub u}) rate sensitivity (percent increase in s{sub u} per log cycle strain rate) across the two fastest strain rates does not vary with OCR and equals about 9%. However, across the three slower rates, increases in OCR cause a consistent decrease in the rate sensitivity that reaches zero at OCR = 8. For high OCR clay, increases in s{sub u} (if they occur) are caused by lower shear-induced pore pressures since the effective stress envelope at the peak strength does not vary with strain rate. For low OCR clay, increases in s{sub u} are caused by both lower shear-induced pore pressures and increases in the mobilized friction angle. A simple technique is proposed for modeling the rate dependent stress-strain curves of over consolidated clay.

  8. True Shear Parallel Plate Viscometer

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin; Kaukler, William

    2010-01-01

    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 shear 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 shear force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of shear stress to shear rate.

  9. Tunable shear thickening in suspensions.

    PubMed

    Lin, Neil Y C; Ness, Christopher; Cates, Michael E; Sun, Jin; Cohen, Itai

    2016-09-27

    Shear thickening, an increase of viscosity with shear rate, is a ubiquitous phenomenon in suspended materials that has implications for broad technological applications. Controlling this thickening behavior remains a major challenge and has led to empirical strategies ranging from altering the particle surfaces and shape to modifying the solvent properties. However, none of these methods allows for tuning of flow properties during shear itself. Here, we demonstrate that by strategic imposition of a high-frequency and low-amplitude shear perturbation orthogonal to the primary shearing flow, we can largely eradicate shear thickening. The orthogonal shear effectively becomes a regulator for controlling thickening in the suspension, allowing the viscosity to be reduced by up to 2 decades on demand. In a separate setup, we show that such effects can be induced by simply agitating the sample transversely to the primary shear direction. Overall, the ability of in situ manipulation of shear thickening paves a route toward creating materials whose mechanical properties can be controlled. PMID:27621472

  10. Study, Development, and Design of Replaceable Shear Yielding Steel Panel Damper

    SciTech Connect

    Murakami, Katsuhide; Keii, Michio

    2008-07-08

    For middle-high rise buildings, vibration controlled structures to reduce the damage of main frames are recently becoming general in Japan. A steel material damper is low price and excellent in the energy absorption efficiency at a large earthquake. Though the exchange of the dampers are necessary when an excessive accumulation of plasticity deformation occurs, a steel material damping system, which received an excessive accumulation of plasticity deformation after a large earthquake, can recover a seismic-proof performance and property value of the building after the replacement. In the paper, shear yielding steel panel dampers installed in the web of a beam connected with high tension bolt joint is introduced. This damper is made of low-yield point steel, and the advantages of this system are low cost, easy-production and easy-replacement. For this steel panel damper, the finite element method (FEM) analysis using the shell element model adjusted to 1/2 of 6.4 m beam span is executed to make the design most effective. Yielding property of the beam installing this damper, shape of the splice plate and the bolt orientation for the connecting are examined in this analysis. As a result, we found that the plastic strain extends uniformly to the entire damping panel when making the splice plate a trapezoidal shape. The basic performance confirmation examination was also done using the real scale examination model besides the FEM analysis, and the performance of the system was confirmed. In addition, design of a high rise building in which the steel shear-yielding panel dampers and oil dampers were adopted without disturbing an architectural plan is also introduced.

  11. Detecting plastic strain distribution by a nonlinear wave mixing method

    NASA Astrophysics Data System (ADS)

    Tang, Guangxin; Liu, Minghe; Jacobs, Laurence J.; Qu, Jianmin

    2013-01-01

    A nonlinear wave mixing method is used to measure the plastic strain distribution in polycrystalline materials. A pair of collinear longitudinal and shear waves is generated. Under the phase matching condition, a resonant shear wave with a difference frequency is generated and propagates towards the shear wave transducer. The amplitude of this resonant shear wave is proportional to the acoustic nonlinearity parameter β, which is known to be related to plastic deformation. By adjusting the two primary waves so that they mix at different locations, the distribution of β can be obtained. This study demonstrates the feasibility of detecting plastic strain distribution in polycrystalline materials by the nonlinear wave mixing technique.

  12. 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

  13. Open boundary molecular dynamics of sheared star-polymer melts.

    PubMed

    Sablić, Jurij; Praprotnik, Matej; Delgado-Buscalioni, Rafael

    2016-02-28

    Open boundary molecular dynamics (OBMD) simulations of a sheared star polymer melt under isothermal conditions are performed to study the rheology and molecular structure of the melt under a fixed normal load. Comparison is made with the standard molecular dynamics (MD) in periodic (closed) boxes at a fixed shear rate (using the SLLOD dynamics). The OBMD system exchanges mass and momentum with adjacent reservoirs (buffers) where the external pressure tensor is imposed. Insertion of molecules in the buffers is made feasible by implementing there a low resolution model (blob-molecules with soft effective interactions) and then using the adaptive resolution scheme (AdResS) to connect with the bulk MD. Straining with increasing shear stress induces melt expansion and a significantly different redistribution of pressure compared with the closed case. In the open sample, the shear viscosity is also a bit lowered but more stable against the viscous heating. At a given Weissenberg number, molecular deformations and material properties (recoverable shear strain and normal stress ratio) are found to be similar in both setups. We also study the modelling effect of normal and tangential friction between monomers implemented in a dissipative particle dynamics (DPD) thermostat. Interestingly, the tangential friction substantially enhances the elastic response of the melt due to a reduction of the kinetic stress viscous contribution. PMID:26820315

  14. A failure criterion for laminates governed by free edge interlaminar shear stress

    NASA Astrophysics Data System (ADS)

    Joo, J. W.; Sun, C. T.

    1992-01-01

    Interlaminar shear stresses in balanced and symmetric laminates with free edges and failure due to these stresses were studied. It was shown that the average interlaminar shear stress near the free edge is linearly related to the mismatch of the extension-shear coupling of the top and bottom sublaminates separated by the interface of interest. A simple failure criterion based on the mismatch of the extension shear coupling was introduced to predict laminate failure stress and strain. The validity of this criterion was verified by experiments using AS4/3501-6 graphite/epoxy composite laminates.

  15. Shear-induced breaking of cages in colloidal glasses: Scattering experiments and mode coupling theory.

    PubMed

    Amann, Christian P; Denisov, Dmitry; Dang, Minh Triet; Struth, Bernd; Schall, Peter; Fuchs, Matthias

    2015-07-21

    We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses. PMID:26203034

  16. Shear-induced breaking of cages in colloidal glasses: Scattering experiments and mode coupling theory

    SciTech Connect

    Amann, Christian P. Fuchs, Matthias; Denisov, Dmitry; Dang, Minh Triet; Schall, Peter; Struth, Bernd

    2015-07-21

    We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses.

  17. Crack initiation observation and local stress analysis in shear fracture tests of ultra-high strength steels

    NASA Astrophysics Data System (ADS)

    Ma, Ninshu; Takada, Kenji; Sugimoto, Nao

    2016-08-01

    To investigate the local strain and stress at the crack initiation position in shear fracture test pieces of ultra-high strength steels, a butterfly shear fracture specimen was employed. The crack initiation position and propagation direction were observed during shear fracture tests by high speed cameras and investigated through analysing the fracture surface by scanning electron microscope. Further, the finite element method was employed and the stress-triaxiality at the crack initiation position was investigated. It can be obtained that the crack initiated at the position where the stress state is close to uniaxial tensile state or plane strain state more than pure shear stress state.

  18. On the persistence of adiabatic shear bands

    NASA Astrophysics Data System (ADS)

    Boakye-Yiadom, S.; Bassim, M. N.; Al-Ameeri, S.

    2012-08-01

    It is generally agreed that the initiation and development of adiabatic shear bands (ASBs) are manifestations of damage in metallic materials subjected to high strain rates and large strains as those due to impact in a Hopkinson Bar system. Models for evolution of these bands have been described in the literature. One question that has not received attention is how persistent these bands are and whether their presence and effect can be reversed or eliminated by using a process of thermal (heat treatment) or thermo-mechanical treatment that would relieve the material from the high strain associated with ASBs and their role as precursors to crack initiation and subsequent failure. Since ASBs are more prevalent and more defined in BCC metals including steels, a study was conducted to investigate the best conditions of generating ASBs in a heat treatable steel, followed by determining the best conditions for heat treatment of specimens already damaged by the presence of ASBs in order to relieve the strains due to ASBs and restore the material to an apparent microstructure without the "scars" due to the previous presence of ASBs. It was found that heat treatment achieves the curing from ASBs. This presentation documents the process undertaken to achieve this objective.

  19. Flexible Micropost Arrays for Shear Stress Measurement

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Palmieri, Frank L.; Hopkins, John W.; Jackson, Allen M.; Connell, John W.; Lin, Yi; Cisotto, Alexxandra A.

    2015-01-01

    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 shear stress in boundary layer airflow would enable a better understanding of how aircraft structure and flight dynamics affect skin friction. Current shear stress measurement techniques suffer from reliability, complexity, and airflow disruption, thereby compromising resultant shear stress data. The state-of-the-art for shear 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 type 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

  20. Evolution of the contact distribution in sheared 2D granular packings

    NASA Astrophysics Data System (ADS)

    Boberski, Jens; Shaebani, M. Reza; Wolf, Dietrich E.

    2013-06-01

    We study the elastic response and the fabric evolution of sheared granular materials by looking at the underlying dynamics at the level of individual contacts. Unilateral interparticle interactions lead to opening and closing of contacts during quasi-static shear deformations, which anisotropically modify the fabric and affect the elastic response of the material. Additionally, the presence of non-affine motions leads to softening of the response. We numerically investigate the evolution of the contact orientation distribution of a two dimensional packing, during isotropic compression and bi-axial shear deformation processes. In the isotropic compression case, the normal overlap distribution can be well fitted by a Gaussian, and broadens with a width which linearly grows with the volumetric strain. This is in contrast to the (volume conserving) pure shear case, where the width remains approximately unaffected by the shear strain.

  1. Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling

    NASA Astrophysics Data System (ADS)

    Le Pourhiet, L.; Huet, B.; Labrousse, L.; Yao, K.; Agard, P.; Jolivet, L.

    2013-04-01

    We have designed a series of fully dynamic numerical simulations aimed at assessing how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented. In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying initial dip of inherited layering in the footwall with regard to the orientation of simple shear applied at the rigid boundary simulating a rigid hanging wall, all scaling and rheological parameter kept constant. It appears that when Mohr-Coulomb plasticity is being used, shear bands are found to localise only when the layering is being stretched. This corresponds to early deformational stages for inital layering dipping in the same direction as the shear is applied, and to later stages for intial layering dipping towards the opposite direction of shear. In all the cases, localisation of the strain after only γ=1 requires plastic yielding to be activated in the strong layer. The second parametric study shows that results are length-scale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. However, decreasing or increasing strain rate is shown to reduce the capacity of the shear zone to localise strain. In the later case, the strain pattern resembles a mylonitic band but the rheology is shown to be effectively linear. Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes extremely penetrative but

  2. Spherulitic nucleation and growth rates in a sheared polypropylene melt

    NASA Astrophysics Data System (ADS)

    De Santis, F.; Scermino, R.; Pantani, R.; Titomanlio, G.

    2014-05-01

    In common polymer processing operations such as injection molding, film blowing, and fiber spinning, the molten polymer is subjected to intense shear and/or elongational flow fields and crystallizes during or after the application of flow. The semicrystalline morphology that develops in the final product is typically very different from what is observed during quiescent crystallization of the same polymer, and the properties change accordingly. The possibility of controlling the final morphology and the resulting mechanical and functional properties of semicrystalline polymers based on the study of polymer melt crystallization stimulated by flow is highly intriguing. This work starts from the experimental evidence that there exists qualitatively three regimes of crystallization under shear: (a) very low shear rates, in which there is no effect on kinetics; (b) higher shear rates, in which orientational effects enhance just the nucleation and growth rates, and spherulitic crystallization is observed; and (c) high shear rates, in which molecular stretching occurs giving rise to a fibrillar morphology development under very fast kinetics. The first two regimes are explored and analyzed by means of experimental protocols developed on purpose. In particular: - spherulitic nucleation and growth rates under continuous shear rates were carefully measured and related to molecular strain - the condition below which crystallization turns out to be essentially quiescent was evidenced.

  3. The Critical Criterion on Runaway Shear Banding in Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Sun, B. A.; Yang, Y.; Wang, W. H.; Liu, C. T.

    2016-02-01

    The plastic flow of metallic glasses (MGs) in bulk is mediated by nanoscale shear bands, which is known to proceed in a stick-slip manner until reaching a transition state causing catastrophic failures. Such a slip-to-failure transition controls the plasticity of MGs and resembles many important phenomena in natural science and engineering, such as friction, lubrication and earthquake, therefore has attracted tremendous research interest over past decades. However, despite the fundamental and practical importance, the physical origin of this slip-to-failure transition is still poorly understood. By tracking the behavior of a single shear band, here we discover that the final fracture of various MGs during compression is triggered as the velocity of the dominant shear band rises to a critical value, the magnitude of which is independent of alloy composition, sample size, strain rate and testing frame stiffness. The critical shear band velocity is rationalized with the continuum theory of liquid instability, physically originating from a shear-induced cavitation process inside the shear band. Our current finding sheds a quantitative insight into deformation and fracture in disordered solids and, more importantly, is useful to the design of plastic/tough MG-based materials and structures.

  4. The Critical Criterion on Runaway Shear Banding in Metallic Glasses

    PubMed Central

    Sun, B. A.; Yang, Y.; Wang, W. H.; Liu, C. T.

    2016-01-01

    The plastic flow of metallic glasses (MGs) in bulk is mediated by nanoscale shear bands, which is known to proceed in a stick-slip manner until reaching a transition state causing catastrophic failures. Such a slip-to-failure transition controls the plasticity of MGs and resembles many important phenomena in natural science and engineering, such as friction, lubrication and earthquake, therefore has attracted tremendous research interest over past decades. However, despite the fundamental and practical importance, the physical origin of this slip-to-failure transition is still poorly understood. By tracking the behavior of a single shear band, here we discover that the final fracture of various MGs during compression is triggered as the velocity of the dominant shear band rises to a critical value, the magnitude of which is independent of alloy composition, sample size, strain rate and testing frame stiffness. The critical shear band velocity is rationalized with the continuum theory of liquid instability, physically originating from a shear-induced cavitation process inside the shear band. Our current finding sheds a quantitative insight into deformation and fracture in disordered solids and, more importantly, is useful to the design of plastic/tough MG-based materials and structures. PMID:26893196

  5. Actuating dielectric elastomers in pure shear deformation by elastomeric conductors

    SciTech Connect

    Wang, Yin; Chen, Baohong; Zhou, Jinxiong; Bai, Yuanyuan; Wang, Hong

    2014-02-10

    Pure shear experiments are commonly used to characterize dielectric elastomer (DE) material properties and to evaluate DE actuator/generator performance. It is increasingly important for many applications to replace conventional carbon grease electrodes with stretchable elastomeric conductors. We formulate a theory for DE with elastomeric conductors, synthesize transparent hydrogel as ionic conductors, and measure actuation of DE in pure shear deformation. Maximum 67% actuation strain is demonstrated. The theory agrees well with our measurement and also correlates well with reported experiments on DE with electronic conductors.

  6. Shear Induced Structural Relaxation in a Supercooled Colloidal Liquid

    NASA Astrophysics Data System (ADS)

    Chen, Dandan; Semwogerere, Denis; Weeks, Eric R.

    2009-11-01

    Amorphous materials include many common products we use everyday, such as window glass, moisturizer, shaving cream and peanut butter. These materials have liquid-like disordered structure, but keep their shapes like a solid. The rheology of dense amorphous materials under large shear strain is not fully understood, partly due to the difficulty of directly viewing the microscopic details of such materials. We use a colloidal suspension to simulate amorphous materials, and study the shear- induced structural relaxation with fast confocal microscopy. We quantify the plastic rearrangements of the particles using standard analysis techniques based on the motion of the particles.

  7. Molecularly base