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Sample records for accumulated shear strain

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

    NASA Astrophysics Data System (ADS)

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

    2001-10-01

    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 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).

  3. Transient strain accumulation and fault interaction in the Eastern California shear zone

    NASA Astrophysics Data System (ADS)

    Peltzer, Gilles; Crampé, Fréderic; Hensley, Scott; Rosen, Paul

    2001-11-01

    Satellite synthetic aperture radar interferometry reveals transient strain accumulation along the Blackwater Little Lake fault system within the Eastern California shear zone. The surface strain map obtained by averaging eight years (1992 2000) of Earth Resource Satellite (ERS) radar data shows a 120-km-long, 20-km- wide zone of concentrated shear between the southern end of the 1872 Owens Valley earthquake surface break and the northern end of the 1992 Landers earthquake surface break. The observed shear zone is continuous through the Garlock fault, which does not show any evidence of left-lateral slip during the same time period. A dislocation model of the observed shear indicates right-lateral slip at 7 ± 3 mm/yr on a vertical fault below ˜5 km depth, a rate that is two to three times greater than the geologic rates estimated on northwest-trending faults in the eastern Mojave area. This transient slip rate and the absence of resolvable slip on the Garlock fault may be the manifestation of an oscillatory strain pattern between interacting, conjugate fault systems.

  4. Large-magnitude transient strain accumulation on the Blackwater fault, Eastern California shear zone

    NASA Astrophysics Data System (ADS)

    Oskin, Michael; Iriondo, Alex

    2004-04-01

    We investigate the Quaternary slip rate for the Blackwater fault, Eastern California shear zone, through mapping and geochronology of offset volcanic rocks. Basalt flows of the Black Mountains support the presence of faulting at 3.77 ± 0.11 Ma, 1.8 ± 0.1 km of subsequent slip, and a well-constrained long-term slip rate of 0.49 ± 0.04 mm/yr. Total slip diminishes northward, evidenced by a 0.3 1.8 km offset of a 7.23 ± 1.07 Ma dacite flow in the Black Hills and fault termination in the Lava Mountains, 5 km short of the Garlock fault. Slow long-term slip rate together with sparse evidence for Holocene rupture contradict predictions of rapid slip rate from tectonic geodesy. These results support the conclusion that as much as 95% of geodetic strain accumulation across the Blackwater fault, and thus from 1 to 6 mm/yr of geodetic strain measured across the Eastern California shear zone, is a transitory phenomenon. Discrepant geologic and geodetic results may indicate an increased near-term seismic hazard, but merit caution for interpretation of fault slip rates from geodesy alone.

  5. Slip rate of the Calico fault: Implications for anomalous geodetic strain accumulation across the Eastern California shear zone

    NASA Astrophysics Data System (ADS)

    Oskin, M.; Perg, L.; Blumentritt, D.; Mukhopadhyay, S.; Iriondo, A.

    2004-12-01

    Recent earthquake activity and high geodetically derived fault-slip rates across the Eastern California shear zone motivate comparisons with long-term geologic deformation rates to test for transient strain accumulation. We report new geologic slip-rate results from a transect at 34.8° N across the central Mojave Desert where six dextral faults (Helendale, Lenwood, Camp Rock, Calico, Pisgah-Bullion, and Ludlow) accommodate all late Quaternary right-lateral displacement. High-resolution LIDAR topography data have been successfully acquired across all six faults as part of a project to measure a complete budget of long-term geologic fault slip rates. Field investigations of the northern Rodman Mountains conducted with the aid of the new topography data identified several surfaces dextrally offset by the Calico fault. A preliminary slip rate of 1.3±0.3 mm/yr is calculated from an 800± 200 m offset of alluvial fan deposits containing clasts of the ca. 600 ka Pipkin basalt flow. Cosmogenic surface exposure age dating of offset geomorphic surfaces and refined Ar/Ar dating of the basalt flow, in progress, will provide multiple constraints of this fault slip rate. The slip rate of the Calico fault is more than twice that of the Blackwater fault, located on strike with the Calico fault in the northwest Mojave Desert. This discrepancy supports that strain is transferred away from the Calico fault and other adjacent northwest-striking dextral faults onto domino-style rotating blocks bounded by sinistral faults in the Fort Irwin region. A newly identified active thrust fault and fault-related fold bounding the northern Rodman mountains accommodates shortening east of the Calico fault that may be caused by space problems at the intersection of these conjugate fault systems. Overall, slip rate on the Calico fault, together with existing paleoseismic histories on adjacent faults, does not account for more than 5 mm/yr of strain accumulation across the Eastern California shear

  6. 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.

  7. 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

  8. Episodic strain accumulation in southern california.

    PubMed

    Thatcher, W

    1976-11-12

    Reexamination of horizontal geodetic data in the region of recently discovered aseismic uplift has demonstrated that equally unusual horizontal crustal deformation accompanied the development of the uplift. During this time interval compressive strains were oriented roughly normal to the San Andreas fault, suggesting that the uplift produced little shear strain accumulation across this fault. On the other hand, the orientation of the anomalous shear straining is consistent with strain accumulation across northdipping range-front thrusts like the San Fernando fault. Accordingly, the horizontal and vertical crustal deformation disclosed by geodetic observation is interpreted as a short epoch of rapid strain accumulation on these frontal faults. If this interpretation is correct, thrust-type earthquakes will eventually release the accumulated strains, but the geodetic data examined here cannot be used to estimate when these events might occur. However, observation of an unusual sequence of tilts prior to 1971 on a level line lying to the north of the magnitude 6.4 San Fernando earthquake offers some promise for precursor monitoring. The data are adequately explained by a simple model of up-dip aseismic slip propagation toward the 1971 epicentral region. These observations and the simple model that accounts for them suggest a conceptually straightforward monitoring scheme to search for similar uplift and tilt precursors within the uplifted region. Such premonitory effects could be detected by a combination of frequenlty repeated short (30 to 70 km in length) level line measurements, precise gravity traverses, and continuously recording gravimeters sited to the north of the active frontal thrust faults. Once identified, such precursors could be closely followed in space and time, and might then provide effective warnings of impending potentially destructive earth-quakes. PMID:17832524

  9. 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.

  10. Shear-strain contours from moire interferometry

    NASA Technical Reports Server (NTRS)

    Post, D.; Czarnek, R.; Joh, D.

    1985-01-01

    The development of whole-field contour maps of shear strains gamma (xy), derived from displacement fields obtained by moire interferometry with 2400 lines/mm, is described. The use of mechanical differentiation to obtain cross-derivatives of displacements and the use of graphical additive moire to sum the cross-derivatives are explained. Quantitative analysis in the small-strain domain is possible because of the high sensitivity of moire interferometry. The applicability of this technique is shown by the testing of a short epoxy beam under three-point bending.

  11. Strain accumulation along the Laguna Salada fault, Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Savage, J. C.; Lisowski, M.; King, N. E.; Gross, W. K.

    1994-09-01

    Strain accumulation observed over the 1978-1991 interval in a 30 x 100 km aperture trilateration network spanning the Laguna Salada fault is described by the principal strain rates 0.101 +/- 0.012 microstrain/yr N80 deg E +/- 2 deg and -0.021 +/- 0.012 microstrain/yr N 10 deg W +/- 2 deg, extension reckoned coseismic effects of the nearby 1979 Imperial Valley (M = 6.5), 1980 Vistoria (Baja California) (M = 6.4), 1987 Superstition Hills (M = 6.5), and 1987 Elmore Ranch (M = 5.9) earthquakes. The observed strain rates indicate extension at a rate of about 0.08 microstrain/yr perpendicular to the trend (N 35 deg W) of the Salton trough as well as a right-lateral tensor shear strain rate 0.05 microstrain/yr across it. The extension perpendicular to the trough is observed neither farther north near the Salton Sea nor farther south across the Gulf of California. However, Holocene slip on the Laguna Salada fault, about equal parts right-lateral and normal slip, is consistent with the observed strain accumulation. A simple dislocation model intended to explain the observed strain accumulation as a product of slip at depth on the Laguna Salada Fault would require that the fault be listric.

  12. Strain accumulation along the Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Murray, Mark H.; Lisowski, Michael

    2000-11-01

    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.

  13. 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.

  14. 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.

  15. Autocatalytic Decomposition at Shear-Strain Interfaces

    NASA Astrophysics Data System (ADS)

    Kuklja, M. M.; Rashkeev, Sergey N.

    2009-12-01

    Atomic scale mechanisms of the initiation of chemical processes in energetic molecular crystals leading to the decomposition and ultimately to an explosive chain reaction, are far from being completely understood. We investigated the onset of the initiation processes in two energetic crystals—diamino-dinitroethylene (DADNE, C2H4N4O4) and triamino-trinitrobenzene (TATB, C6H6N6O6). We suggest that an autocatalytic decomposition mechanism is likely to take place in DADNE crystal that is built out of corrugated, dashboard-shaped molecular layers, and the level of the induced shear-strain perturbation between the layers strongly depends upon the presence of interstitial NO2 groups. Unlike this, in TATB, which consists of flat, graphite-like molecular layers, an interstitial NO2 group positioned between two layers produces a local molecular orientation disorder and barely affects the C-NO2 decomposition barrier. Split off NO2 groups in the interstitial exhibit a series of exothermic reactions. In DADNE, these reactions start at a lower concentration of interstitial nitro-groups which may be correlated to the higher sensitivity of this material to the initiation as compared to TATB.

  16. 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.

  17. Controlling the shear profile of highly strained granular materials

    NASA Astrophysics Data System (ADS)

    Bares, Jonathan; Behringer, Bob

    2015-11-01

    Bi et al. (Nature 2011) have shown that, if sheared, a granular material can jam even if its packing fraction (ϕ) is lower than the critical isotropic jamming point ϕJ. They have introduced a new critical packing fraction value ϕS such that for ϕS< ϕ<ϕJ the system jams if sheared. Nevertheless, the value of ϕS as a function of the shear profile or the strain necessary to observe jamming remain poorly understood because of the experimental complexity to access high strain without the formation of shear bands. We present a novel 2D periodic shear apparatus made of 21 independent, aligned and mirrored glass rings. Each of ring can be moved independently which permits us to impose any desired shear profile. The circular geometry allows access to any strain value. The forces between grains are measured using reflective photoelasticity. This talk will present this novel apparatus and discuss the effect of the shear profile and shear amplitude on the jamming transition.

  18. 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.

  19. 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

  20. 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

  1. High shear strain of olivine aggregates: rheological and seismic consequences.

    PubMed

    Bystricky, M; Kunze, K; Burlini, L; Burg, J

    2000-11-24

    High-pressure and high-temperature torsion experiments on olivine aggregates in dislocation creep show about 15 to 20% strain weakening before steady-state behavior, characterized by subgrain-rotation recrystallization and a strong lattice preferred orientation. Such weakening may provide a way to focus flow in the upper mantle without a change in deformation mechanism. Flow laws derived from low strain data may not be appropriate for use in modeling high strain regions. In such areas, seismic wave propagation will be anisotropic with an axis of approximate rotational symmetry about the shear direction. In contrast to current thinking, the anisotropy will not indicate the orientation of the shear plane in highly strained, recrystallized olivine-rich rocks. PMID:11090352

  2. 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.

  3. Origin of critical strain amplitude in periodically sheared suspensions

    NASA Astrophysics Data System (ADS)

    Pham, Phong; Butler, Jason E.; Metzger, Bloen

    2016-06-01

    The role of solid-solid contacts on the transition between reversible and irreversible dynamics occurring in periodically sheared suspensions is investigated experimentally by modifying the particle roughness. Smoother particles lead to a larger critical strain amplitude. A geometrical model based on the assumption that colliding particles produce irreversibility is derived. The model, which considers a quasiparticle having a strain- and roughness-dependent effective volume, successfully reproduces the measured values of the critical strain amplitude as functions of the volume fraction and particle roughness.

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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.

  9. Shear Band Formation in Plane Strain Experiments of Sand

    NASA Technical Reports Server (NTRS)

    Alshibli, Khalid A.; Sture, Stein

    2000-01-01

    A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.

  10. Effect of Shear Strain on the High-Pressure Behavior of Nitromethane: Raman Spectroscopy in a Shear Diamond Anvil Cell

    NASA Astrophysics Data System (ADS)

    Hébert, P.; Isambert, A.; Petitet, J. P.; Zerr, A.

    2009-12-01

    The effect of shear strain on the high-pressure behavior of nitromethane has been studied by Raman spectroscopy in a shear diamond anvil cell (SDAC). Two major effects of shear strain have been observed. The first one is a lowering of the pressures at which the different spectral transformations occur. The second effect is observed at 28 GPa. At this pressure, a sudden decomposition of the sample occurs due to the shear deformation. Observation of the sample after decomposition shows the presence of a black residue, which is mainly composed of carbon soot.

  11. Pressure-strain-rate events in homogeneous turbulent shear flow

    NASA Technical Reports Server (NTRS)

    Brasseur, James G.; Lee, Moon J.

    1988-01-01

    A detailed study of the intercomponent energy transfer processes by the pressure-strain-rate in homogeneous turbulent shear flow is presented. Probability density functions (pdf's) and contour plots of the rapid and slow pressure-strain-rate show that the energy transfer processes are extremely peaky, with high-magnitude events dominating low-magnitude fluctuations, as reflected by very high flatness factors of the pressure-strain-rate. A concept of the energy transfer class was applied to investigate details of the direction as well as magnitude of the energy transfer processes. In incompressible flow, six disjoint energy transfer classes exist. Examination of contours in instantaneous fields, pdf's and weighted pdf's of the pressure-strain-rate indicates that in the low magnitude regions all six classes play an important role, but in the high magnitude regions four classes of transfer processes, dominate. The contribution to the average slow pressure-strain-rate from the high magnitude fluctuations is only 50 percent or less. The relative significance of high and low magnitude transfer events is discussed.

  12. Localization of shear strain and shear band formation induced by deformation in semi-solid Al-Cu alloys

    NASA Astrophysics Data System (ADS)

    Nagira, T.; Morita, S.; Yasuda, H.; Gourlay, C. M.; Yoshiya, M.; Sugiyama, A.; Uesugi, K.

    2015-06-01

    In situ observation of deformation in globular Al-Cu samples at a solid fraction of ∼⃒50% and a global shear strain rate of 10-1 s-1 was performed using time-resolved X-ray imaging. The solid particle motion during shear was quantitatively analysed. The force was transmitted though the contacts between solid particles over a long distance parallel to the shear plane (18 mean grain size, d) after only a 1d increment of the Al2O3 push-plate motion. On the other hand, the distance of transmitted force in the perpendicular direction to the shear plane was restricted to approximately 11d even for a high displacement of the Al2O3 push-plate. A relatively high shear strain rate became localized at the shear domain after a small amount of deformation (a 1d increment). The solid fraction decreased in the region of localized shear strain rate. The shear band width, where the shear strain was localized and the solid fraction decreased, remained mostly unchanged over a 4 d increment of Al2O3 push-plate motion.

  13. Exploration of Local Strain Accumulation in Nickel-based Superalloys

    NASA Astrophysics Data System (ADS)

    Carter, Jennifer Lynn Walley

    Deformation in polycrystalline nickel-based superalloys is a complex process dependent on the interaction of dislocations with both the intra-granular γ'' particles and the grain boundaries. An extensive body of work exists on understanding the interaction between dislocations and the γ'' particles, but understanding the interaction between dislocations and grain boundaries has been historically hindered by the experimental techniques. In this work a full field strain mapping technique was developed and utilized to explore surface strain accumulation at grain boundaries of René 104 samples with different microstructures. The full field strain mapping technique utilized Correlated Solutions VIC-2D software for digital image correlation to measure strain accumulation from secondary electron images taken during constant load tests at elevated temperature. This technique indicated that the two different microstructures of René 104, one with microscopically flat grain boundaries and the other with serrated grain boundaries, accumulate strain by different methods. Analysis of discrete offsets in grid lines placed prior to deformation indicate that grain boundary sliding (GBS) is an active deformation mechanism at these temperature and strain rate regimes, and that the development of serrated high angle grain boundaries can decrease the activity of this mechanism by 30%. Slip transmission parameters, which mathematically assess the ease of slip transmission across a grain boundary, were calculated based on grain boundary misorientation and grain boundary trace. These parameters proved unsuccessful at predicting strain localization sites in these materials, indicating that slip transmission is not the only factor dictating strain localization sites. AAA Full field strain maps were used to site-specifically extract grain boundaries of interest to study dislocation interaction and sub-surface grain boundary neighborhood. Representative from each of four types of

  14. 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.

  15. 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

  16. 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.

  17. Controlled high-rate-strain shear bands in inert and reactant porous materials

    NASA Astrophysics Data System (ADS)

    Nesterenko, V. F.

    1998-07-01

    Shear localization is considered as one of the main reasons for initiation of chemical reaction in energetic materials under dynamic loading. However despite of widely 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 strain 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 107s-1. Experimental results are presented for inert materials (granular, fractured ceramics) and for reactant porous mixtures (Nb-Si, Ti-Si, Ti-graphite and Ti-ultrafine diamond).

  18. Axial Shear Strain Imaging for Differentiating Benign and Malignant Breast Masses

    PubMed Central

    Xu, Haiyan; Rao, Min; Varghese, Tomy; Sommer, Amy; Baker, Sara; Hall, Timothy J; Sisney, Gale A; Burnside, Elizabeth S

    2010-01-01

    Axial strain imaging has been utilized for the characterization of breast masses for over a decade; however, another important feature namely the shear strain distribution around breast masses has only recently been used. In this paper, we examine the feasibility of utilizing in-vivo axial-shear strain imaging for differentiating benign from malignant breast masses. Radiofrequency data was acquired using a VFX 13-5 linear array transducer on 41 patients using a Siemens SONOLINE Antares real-time clinical scanner at the University of Wisconsin Breast Cancer Center. Free-hand palpation using deformations of up to 10% was utilized to generate axial strain and axial-shear strain images using a two-dimensional cross-correlation algorithm from the radiofrequency data loops. Axial-shear strain areas normalized to the lesion size, applied strain and lesion strain contrast was utilized as a feature for differentiating benign from malignant masses. The normalized axial-shear strain area feature estimated on 8 patients with malignant tumors and 33 patients with fibroadenomas was utilized to demonstrate its potential for lesion differentiation. Biopsy results were considered the diagnostic standard for comparison. Our results indicate that the normalized axial-shear strain area is significantly larger for malignant tumors when compared to benign masses such as fibroadenomas. Axial-shear strain pixel values greater than a specified threshold, including only those with correlation coefficient values greater than 0.75, were overlaid on the corresponding B-mode image to aid in diagnosis. A scatter plot of the normalized area feature demonstrates the feasibility of developing a linear classifier to differentiate benign from malignant masses. The area under the receiver operator characteristic curve utilizing the normalized axial-shear strain area feature was 0.996, demonstrating the potential of this feature to noninvasively differentiate between benign and malignant breast masses

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

    NASA Astrophysics Data System (ADS)

    Finch, Melanie; Hasalova, Pavlina; Weinberg, Roberto

    2013-04-01

    Ultramylonites are the ultimate product of mylonitisation in ductile shear zones where strain causes almost complete recrystallisation of the rock. They are the weakest rock in a shear zone and accommodate high amounts of strain, usually in a relatively narrow band. However, ultramylonitic shear zones hundreds of metres thick are occasionally reported in the literature, indicating inefficient localisation processes. This work describes the >3.5 km thick El Pichao shear zone of the Sierra de Quilmes, a metamorphic complex of the 470 Ma Famatinian orogeny in the Sierras Pampeanas of Argentina. The core to the El Pichao shear zone is a one kilometre thick band of continuous ultramylonite. Although rare, other shear zones of comparable thickness are reported in the literature and are often related to major orogenic fronts. The width of shear zones is determined by plate velocity and rock strength, with greater widths at high velocities and low rock strength. Shear zones widen when the degree of strain localisation decreases. This can be caused by hardening of the shear zone, weakening of the host rock, or an increase in temperature which decreases the yield stress of the rock. There are several mechanisms that can lead to each outcome but these are difficult to determine in studies of shear zones. El Pichao shear zone overprints granulite facies migmatites in the hanging wall, granites in the ultramylonitic shear zone core, and amphibolite facies Grt-schists in the footwall. Field relationships and mineralogy suggest that the migmatitic hanging wall was at higher temperatures during shearing than the ultramylonitic granitic core. Theoretically this makes the migmatites easier to deform than the granite. Additionally, the migmatite is very heterogenous with a mica-rich mesosome and syn-kinematic Qtz-Kfs rich leucosomes making it the ideal site for strain localisation and partitioning between strong and weak phases. Despite this, ultramylonite is localised to the

  20. Strain accumulation and surface deformation along the San Andreas, California

    NASA Technical Reports Server (NTRS)

    Li, Victor C.

    1986-01-01

    Stressing and rupture of a locked zone adjacent to a creeping fault segment was studied with special reference to strength heterogeneity depthwise and along-strike. The resulting precursory temporal and spatial variations of surface strain rate profiles were compared to geodetic measurements on the San Andreas fault in central California. Crustal deformation in great California earthquake cycles was also studied with special reference to the temporal decay of strain rate observed since the 1957 and 1906 great earthquakes, and comtemporary surface strain rate and velocity profiles at several locations along the San Andreas. The effect of viscoelastic response in the deep aseismic shear zone on the surface deformation behavior was examined. Work was begun on a fundamental reformulation of the crustal deformation problem focusing on the crustal deformation process affected by deep aseismic slip as the slip zone progresses toward an instability and as deep seismic slip continues postseismically, the 3-D nature of the problem due to geometry and material heterogeneity, and the time-dependent source coming from the lithosphere/astenospheric coupling process.

  1. The influence of viscosity on the shear strain remotely induced by focused ultrasound in viscoelastic media.

    PubMed

    Barannik, E A; Girnyk, S A; Tovstiak, V V; Marusenko, A I; Volokhov, V A; Sarvazyan, A P; Emelianov, S Y

    2004-05-01

    Shear wave elasticity imaging (SWEI), an emerging acoustic technology for medical diagnostics, is based on remote generation of shear waves in tissue by radiation force in the focal region of an ultrasonic beam. In this study, the feasibility of Doppler ultrasonic technique to visualize the remotely induced shear waves was demonstrated. The generation of shear displacement in the focal region of a pulsed 1-MHz ultrasound beam with pulse duration of approximately about 2 ms and intensity levels on the order of 145 W/cm2, and consequent propagation of shear wave in tissue-mimicking and muscle tissue in vitro, were measured. The analysis of temporal behavior of shear displacement within the focal plane allowed estimation of shear wave velocities. The velocities were 4 and 7 m/s in hard phantom and tissue containing phantom, respectively. The measured shear displacements on the order of micrometers in gel-based phantoms are in reasonable agreement with theoretical estimates derived from an earlier developed model of shear wave generation by radiation force of focused ultrasound. The study revealed significant dependence of shear strain on the medium viscosity. The complex oscillatory character of shear strain relaxation in viscoelastic phantom and muscle tissue in vitro was observed. PMID:15139649

  2. 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.

  3. 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.

  4. In-vivo Vascular Wall Shear Rate and Circumferential Strain of Renal Disease Patients

    PubMed Central

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

    2012-01-01

    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. PMID:23211936

  5. 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.

  6. 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.

  7. Mechanical characterization of brain tissue in simple shear at dynamic strain rates.

    PubMed

    Rashid, Badar; Destrade, Michel; Gilchrist, Michael D

    2013-12-01

    During severe impact conditions, brain tissue experiences a rapid and complex deformation, which can be seen as a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue in shear at these strains and strain rates is thus of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. However, very few studies in the literature provide this information. In this research, an experimental setup was developed to perform simple shear tests on porcine brain tissue at strain rates ≤120/s. The maximum measured shear stress at strain rates of 30, 60, 90 and 120/s was 1.15±0.25kPa, 1.34±0.19kPa, 2.19±0.225kPa and 2.52±0.27kPa, (mean±SD), respectively at the maximum amount of shear, K=1. Good agreement of experimental, theoretical (Ogden and Mooney-Rivlin models) and numerical shear stresses was achieved (p=0.7866-0.9935). Specimen thickness effects (2.0-10.0mm thick specimens) were also analyzed numerically and we found that there is no significant difference (p=0.9954) in the shear stress magnitudes, indicating a homogeneous deformation of the specimens during simple shear tests. Stress relaxation tests in simple shear were also conducted at different strain magnitudes (10-60% strain) with the average rise time of 14ms. This allowed us to estimate elastic and viscoelastic parameters (initial shear modulus, μ=4942.0Pa, and Prony parameters: g1=0.520, g2=0.3057, τ1=0.0264s, and τ2=0.011s) that can be used in FE software to analyze the non-linear viscoelastic behavior of brain tissue. This study provides new insight into the behavior in finite shear of brain tissue under dynamic impact conditions, which will assist in developing effective brain injury criteria and adopting efficient countermeasures against

  8. 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

  9. Effect of viscoelastic postseismic relaxation on estimates of interseismic crustal strain accumulation at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Hammond, William C.; Kreemer, Corné; Blewitt, Geoffrey; Plag, Hans-Peter

    2010-03-01

    We estimate the long-term crustal strain rate at Yucca Mountain (YM), Nevada from GPS velocities taking into account viscoelastic relaxation following recent earthquakes to remove bias associated with transient deformation. The YM data reveal postseismic relaxation in time series non-linearity and geographic variation of the transient signal. From the data we estimate best-fitting lower crust and upper mantle viscosities of 1019.5 Pa s and 1018.5 Pa s, respectively. Once the relaxation model predictions are subtracted from the data, the long-term shear strain accumulation rate is between 16.3 and 25.1 nanostrains/year (ns/yr) to 99% confidence, a range much larger than the formal uncertainties from GPS measurement. We conclude that 1) a Maxwell viscoelastic model cannot explain all the deformation observed at YM, 2) uncertainty in viscosities dominates uncertainty in YM strain rates, and 3) the effects of large, recent earthquakes must be accounted for in seismic hazard studies using GPS.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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.

  19. Observations of strain accumulation across the san andreas fault near palmdale, california, with a two-color geodimeter.

    PubMed

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

    1982-12-17

    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. PMID:17802470

  20. 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.

  1. Finite strain analysis of metavolcanics and metapyroclastics in gold-bearing shear zone of the Dungash area, Central Eastern Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Kassem, Osama M. K.; Abd El Rahim, Said H.

    2014-11-01

    The Dungash gold mine area is situated in an EW-trending quartz vein along a shear zone in metavolcanic and metasedimentary host rocks in the Eastern Desert of Egypt. These rocks are associated with the major geologic structures, which are attributed to various deformational stages of the Neoproterozoic basement rocks. Field geology, finite strain and microstructural analyses were carried out and the relation-ships between the lithological contacts and major/minor structures have been studied. The R f/ϕ and Fry methods were applied on the metavolcano-sedimentary and metapyroclastic samples from 5 quartz veins samples, 7 metavolcanics samples, 3 metasedimentary samples and 4 metapyroclastic samples in Dungash area. Finite-strain data show that a low to moderate range of deformation of the metavolcano-sedimentary samples and axial ratios in the XZ section range from 1.70 to 4.80 for the R f/ϕ method and from 1.65 to 4.50 for the Fry method. We conclude that finite strain in the deformed rocks is of the same order of magnitude for all units of metavolcano-sedimentary rocks. Furthermore, the contact between principal rock units is sheared in the Dungash area under brittle to semi-ductile deformation conditions. In this case, the accumulated finite strain is associated with the deformation during thrusting to assemble nappe structure. It indicates that the sheared contacts have been formed during the accumulation of finite strain.

  2. A comparison of GPS solutions for strain and SKS fast directions: Implications for modes of shear in the mantle of a plate boundary zone

    NASA Astrophysics Data System (ADS)

    houlie, nicolas; Stern, Tim

    2014-05-01

    We study the strain rate field computed using the GPS GEONET dataset collected during the last decade. We show that we can infer the amount of simple shear accumulated in the mantle by comparing the compression strain orientation with the SKS fast directions. We suggest the mantle beneath the southern part of the south island is under pure shear while to the north the amount of distributed shear is larger. At last, we confirm that, in that context, the strike of New Zealand fault systems make a 60 degree angle with the compression strain rate axis. We compute the strain rate field and the vectors for the principal axis of strain in within New Zealand based on 10 years of data from the Geonet network. A comparison of the principal axis of extension with the fast directions from SKS splitting shows a consistent 20 degree divergence in the northern south Island with the two sets of vectors becoming parallel in central South Island. We firstly interpret these data as confirmation of mantle flow driving crustal kinematics. In addition we suggest the data are consistent with a mode of predominately simple and pure shear in northern and central South Island respectively.

  3. Reduced thoracolumbar fascia shear strain in human chronic low back pain

    PubMed Central

    2011-01-01

    Background The role played by the thoracolumbar fascia in chronic low back pain (LBP) is poorly understood. The thoracolumbar fascia is composed of dense connective tissue layers separated by layers of loose connective tissue that normally allow the dense layers to glide past one another during trunk motion. The goal of this study was to quantify shear plane motion within the thoracolumbar fascia using ultrasound elasticity imaging in human subjects with and without chronic low back pain (LBP). Methods We tested 121 human subjects, 50 without LBP and 71 with LBP of greater than 12 months duration. In each subject, an ultrasound cine-recording was acquired on the right and left sides of the back during passive trunk flexion using a motorized articulated table with the hinge point of the table at L4-5 and the ultrasound probe located longitudinally 2 cm lateral to the midline at the level of the L2-3 interspace. Tissue displacement within the thoracolumbar fascia was calculated using cross correlation techniques and shear strain was derived from this displacement data. Additional measures included standard range of motion and physical performance evaluations as well as ultrasound measurement of perimuscular connective tissue thickness and echogenicity. Results Thoracolumbar fascia shear strain was reduced in the LBP group compared with the No-LBP group (56.4% ± 3.1% vs. 70.2% ± 3.6% respectively, p < .01). There was no evidence that this difference was sex-specific (group by sex interaction p = .09), although overall, males had significantly lower shear strain than females (p = .02). Significant correlations were found in male subjects between thoracolumbar fascia shear strain and the following variables: perimuscular connective tissue thickness (r = -0.45, p <.001), echogenicity (r = -0.28, p < .05), trunk flexion range of motion (r = 0.36, p < .01), trunk extension range of motion (r = 0.41, p < .01), repeated forward bend task duration (r = -0.54, p < .0001) and

  4. Development of a novel bioreactor to apply shear stress and tensile strain simultaneously to cell monolayers

    NASA Astrophysics Data System (ADS)

    Breen, Liam T.; McHugh, Peter E.; McCormack, Brendan A.; Muir, Gordon; Quinlan, Nathan J.; Heraty, Kevin B.; Murphy, Bruce P.

    2006-10-01

    To date many bioreactor experiments have investigated the cellular response to isolated in vitro forces. However, in vivo, wall shear stress (WSS) and tensile hoop strain (THS) coexist. This article describes the techniques used to build and validate a novel vascular tissue bioreactor, which is capable of applying simultaneous wall shear stress and tensile stretch to multiple cellular substrates. The bioreactor design presented here combines a cone and plate rheometer with flexible substrates. Using such a combination, the bioreactor is capable of applying a large range of pulsatile wall shear stress (-30to+30dyn/cm2) and tensile hoop strain (0%-12%). The WSS and THS applied to the cellular substrates were validated and calibrated. In particular, curves were produced that related the desired WSS to the bioreactor control parameters. The bioreactor was shown to be biocompatible and noncytotoxic and suitable for cellular mechanical loading studies in physiological condition, i.e., under simultaneous WSS and THS conditions.

  5. 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.

  6. 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.

  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. Polydimethylsiloxane-fabricated optical fiber sensor capable of measuring both large axial and shear strain

    NASA Astrophysics Data System (ADS)

    Shen, Yu; Wang, Ziyuan; Wen, Huaihai; Zhou, Zhi

    2014-11-01

    Fiber optic sensor (FOS) has received much attention in the field of Structure Health Monitoring (SHM) due to its advantages of low weight, small size, high sensitivity multiplexing ability, free of electromagnetic interference and long durability. However, in harsh environments, structures often undergo large strain where few traditional fiber optic sensors could survive. This paper report a novel material with features of light-transparent, chemically inert, thermally stable material Polydimethylsiloxane(PDMS) fabricated large axial/shearing strain sensor. The sensor was fabricated by directly coupling a conventional signal mode fiber into half cured PDMS material using a translation stage under the inspection of a microscope. Meanwhile, a laser diode and a photo detector were used in the fabrication process to make sure the sensor achieved minimum light loss. An experiment was conducted later to investigate the sensor's transmission characteristic in 1310nm infrared laser relating with the applied axial/shearing strain. The results show that the proposed sensor survived an axial strain of 6 7.79 x 106 μɛ ; a shear of 4 6.49 x 104 μɛ with good linearity and repetition. The experiment indicates that the proposed sensor can potentially be used as strain sensing elements in Structure Health Monitoring systems under earthquake or explosion.

  9. 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.

  10. Isotopic dating of strain fringe increments: duration and rates of deformation in shear zones

    PubMed

    Muller; Aerden; Halliday

    2000-06-23

    The time scales over which deformation in the Earth's crust remains localized in shear zones are poorly known, as are the associated strain rates. We have determined the longevity and rates of deformation using rubidium-strontium (Rb-Sr) microsampling dating of increments of fibrous strain fringes from a Pyrenean shear zone. The fibers grew quasi-continuously through a protracted deformation history between 87 and 50 million years ago, over a period comparable to that of an orogeny. During a short interval between 66 and 62 million years, a rise in strain rate from 1.1 x 10(-15) to 7. 7 x 10(-15) seconds(-1) occurred. This acceleration correlates with an abrupt change in fiber-growth direction and a stress-field inversion from gravitational collapse to renewed horizontal crustal shortening. PMID:10864865

  11. 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

  12. Mineralogically triggered strain localization: inferences from ductile paired shear zones (Tauern Window, Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Duprat-Oualid, Sylvia; Grasemann, Bernhard; Huet, Benjamin; Yamato, Philippe; Habler, Gerlinde

    2016-04-01

    Lithosphere is mainly constituted by polyphase rocks whose mineralogical, structural and textural characteristics control the spatial distribution of strain, and so, its effective mechanical strength. Variations in local mineralogical compositions may lead to drastic changes in the local microstructures and texture leading, by mechanical feedback processes, to strain hardening or weakening. Understanding these small-scale relations between the petrological characteristics, the rheological properties and the development of progressive deformation is thus of fundamental importance for understanding the strength of rocks at large-scale, especially the mechanical behavior of plates boundaries. We acknowledge the importance of brittle precursors for the localization of strain in the viscous deforming part of the crust. In this study, we focus in centimeter-wide paired ductile shear zones shaped nearby along on both sides of ep-grt-qtz veins within a late Variscan metagranodiorite of the "Zentralgneis" in the Tauern Window (Berlinerhütte, Zillertal, Austria). The paired shear zones, underlined by biotite bands, localized at some centimeters away from the veins associated with a metasomatic domain, within the relatively undeformed host rock. According to their spatial orientations, they exhibit different intensities of shearing (from incipient linking of biotites to anastomosing ultra-mylonitic bands) and thus can be explored as successive strain domains of a shear zone developing in space and time. Here, we present a combination of high-resolution petro-chemical section across the paired shear zones with microstructural and textural measurements in order to constrain mineral reactions and deformation processes associated with the development of localized shear zones. Whole rock chemical analyzes combined with continuous mineralogical mapping revealed small chemical variations induced by fluid-rock interactions in the vicinity of the veins. Although macroscopically

  13. 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.

  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. 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

  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. Improved finite strip Mindlin plate bending element using assumed shear strain distributions

    NASA Technical Reports Server (NTRS)

    Chulya, Abhisak; Thompson, Robert L.

    1988-01-01

    A linear finite strip plate element based on Mindlin/Reissner plate theory is developed. The analysis is suitable for both thin and thick plates. In the formulation new transverse shear strains are introduced and assumed constant in each two-code linear strip. The element stiffness matrix is explicitly formulated for efficient computation and computer implementation. Numerical results showing the efficiency and predictive capability of the element for the analysis of plates are presented for different support and loading conditions and a wide range of thicknesses. No sign of shear locking phenomenon was observed with the newly developed element.

  18. Interaponeurosis shear strain modulates behavior of myotendinous junction of the human triceps surae

    PubMed Central

    Kinugasa, Ryuta; Oda, Toshiaki; Komatsu, Toshihiko; Edgerton, V Reggie; Sinha, Shantanu

    2013-01-01

    Muscle fascicles insert into a sheet-like aponeurosis. Adjacent aponeuroses are structurally in contact with each other, and ultimately merge into a common tendon. Consequently, fascicle shortening in planes of tissue layers in adjacent compartments must cause sliding between aponeuroses parallel to the acting forces. In this study, we used velocity-encoded, phase-contrast, and water-saturated spin-lattice relaxation time-weighted imaging to identify and track fascicle and aponeurosis behaviors of human medial gastrocnemius (MG) and soleus (Sol) during 15° dorsiflexion to 30° plantarflexion contractions of the ankle. Interaponeurosis shear strain, which was defined as the relative displacement of the aponeurosis at the fascicle end points (insertion) of the MG and Sol, was an average of 1.35 ± 0.27% (range 1.12 ∼ 1.87%), indicating that the strain is greater in the aponeurosis of MG fascicle insertion than the Sol. The myotendinous junction (MTJ) displacement increased significantly with decreasing interaponeurosis shear strain (P < 0.05). The magnitude of interaponeurosis shear strain had significant correlation with the temporal difference between the time at which the peak aponeurosis displacement of the MG and Sol occurred (P < 0.05). Our model also indicated that theoretical MTJ displacement varies in relation to temporal difference: no temporal difference caused the largest MTJ displacement and presence of temporal differences indicated a reduction in MTJ displacement. Therefore, we concluded that interaponeurosis shear strain is a mechanism enabling individual muscle contraction and thus specific loading of the tendon and joint. PMID:24400149

  19. Interaponeurosis shear strain modulates behavior of myotendinous junction of the human triceps surae.

    PubMed

    Kinugasa, Ryuta; Oda, Toshiaki; Komatsu, Toshihiko; Edgerton, V Reggie; Sinha, Shantanu

    2013-11-01

    Muscle fascicles insert into a sheet-like aponeurosis. Adjacent aponeuroses are structurally in contact with each other, and ultimately merge into a common tendon. Consequently, fascicle shortening in planes of tissue layers in adjacent compartments must cause sliding between aponeuroses parallel to the acting forces. In this study, we used velocity-encoded, phase-contrast, and water-saturated spin-lattice relaxation time-weighted imaging to identify and track fascicle and aponeurosis behaviors of human medial gastrocnemius (MG) and soleus (Sol) during 15° dorsiflexion to 30° plantarflexion contractions of the ankle. Interaponeurosis shear strain, which was defined as the relative displacement of the aponeurosis at the fascicle end points (insertion) of the MG and Sol, was an average of 1.35 ± 0.27% (range 1.12 ∼ 1.87%), indicating that the strain is greater in the aponeurosis of MG fascicle insertion than the Sol. The myotendinous junction (MTJ) displacement increased significantly with decreasing interaponeurosis shear strain (P < 0.05). The magnitude of interaponeurosis shear strain had significant correlation with the temporal difference between the time at which the peak aponeurosis displacement of the MG and Sol occurred (P < 0.05). Our model also indicated that theoretical MTJ displacement varies in relation to temporal difference: no temporal difference caused the largest MTJ displacement and presence of temporal differences indicated a reduction in MTJ displacement. Therefore, we concluded that interaponeurosis shear strain is a mechanism enabling individual muscle contraction and thus specific loading of the tendon and joint. PMID:24400149

  20. 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.

  1. 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.

  2. 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.

  3. Surface shear strains induced by quasi-steady sweeping detonation waves

    NASA Astrophysics Data System (ADS)

    Hull, Lawrence; Briggs, Matthew; Faulkner, James

    2012-03-01

    Sweeping wave experiments create conditions of greater shear than corresponding onedimensional motion experiments, and are of current interest for material damage characterization. Sweeping waves are also important with regards to the spectrum of applications of explosives driving metals. The intensity of the shear developed in a sweeping wave experiment may be monitored using crossed beams of Photon Doppler Velocimetry (PDV). During the time the material is traversing the volume defined by the crossed beams, the interferometer is measuring the velocity of the same mass element (approximately) from two directions. It is known that PDV measures the velocity component that lies along the beam direction, so that with crossed beams, two independent directions are simultaneously measured and therefore the vector velocity (both magnitude and direction) are captured. The vector velocity is readily related to the strain rates on the surface (after removing the rigid rotation rates), and the equations are integrated to obtain the strains.

  4. Strain hardening in startup shear of long-chain branched polymer solutions.

    PubMed

    Liu, Gengxin; Cheng, Shiwang; Lee, Hyojoon; Ma, Hongwei; Xu, Hongde; Chang, Taihyun; Quirk, Roderic P; Wang, Shi-Qing

    2013-08-01

    We show for the first time that entangled polymeric liquids containing long-chain branching can exhibit strain hardening upon startup shear. As the significant long-chain branching impedes chain disentanglement, Gaussian coils between entanglements can deform to reach the finite extensibility limit where the intrachain retraction force exceeds the value expected from the usual conformational entropy loss evaluated based on Gaussian chain statistics. The phenomenon is expected to lead to further theoretical understanding. PMID:23971617

  5. 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

  6. 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.

  7. 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

  8. 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

  9. 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

  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. Strain accumulation and surface deformation along the San Andreas, California

    NASA Technical Reports Server (NTRS)

    Li, Victor C.

    1989-01-01

    The goal of this project remains to be the achievement of a better understanding of the regional and local deformation and crustal straining processes in western North America, particularly the effect of the San Andreas and nearby faults on the spatial and temporal crustal deformation behavior. Construction of theoretical models based on the mechanics of coupled elastic plate/viscoelastic foundation and large scale crack mechanics provide a rational basis for the interpretation of seismic and aseismic anomalies and expedite efforts in forecasting the stability of plate boundary deformations. In the present period, special focus is placed on the 3-D effect of irregular fault locked patches on the ground measured deformation fields. Specifically, use is made of a newly developed 3-D boundary element program to analyze the fault slip and vertical ground motion in the Parkfield area on the San Andreas.

  12. Impact Fragmentation and Crushing of Concrete and Other Solids Due to Kinetic Energy of High Shear Strain Rate

    NASA Astrophysics Data System (ADS)

    Bazant, Zdenek; Kirane, Kedar

    While numerous studies have dealt with dynamic crack propagation, they have not led to a macroscopic continuum model usable in FE analysis. Recent work on such a model is reviewed. The key idea is that comminution under high-rate shear is driven by the release local kinetic (rather than strain) energy of the shear strain rate field in forming finite-size fragments. At strain rates >103/s, this energy exceeds the maximum possible elastic strain energy by orders of magnitude. It is found that the particle size scales as the -2/3 power of the shear strain rate and as the 2/3 power of interface fracture energy, and the released and dissipated kinetic energy as the 2/3 power of the shear strain rate. These results explain the long debated phenomenon of ``dynamic overstress''. In FE simulations, this kinetic energy of strain rate field can be dissipated either by equivalent viscosity or by the work of increased strength limits. In simulating the impact of missiles into concrete walls, both approaches give nearly equivalent results. A dimensionless indicator of the comminution intensity is also 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.

  13. 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.

  14. 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.

  15. Strain accumulation in the Santa Barbara Channel, 1971-1987

    NASA Technical Reports Server (NTRS)

    Larsen, Shawn; King, Nancy; Agnew, Duncan; Hager, Bradford

    1988-01-01

    Geophysical evidence suggests a significant amount of north-south convergence occurs across the Santa Barbara Channel. Tectonic studies indicate a discrepancy between observed fault slip in California and the North American-Pacific plate motion. Newer plate motion models (NUVEL-1) yield a lower rate of convergence. Global Positioning System (GPS) data collected in the Santa Barbara Channel in 1987, when combined with 1971 trilateration measurements, should be sufficient to resolve the present-day convergence rate. In early 1987. from January 3 to 7, GPS data were collected at 14 sites in California and at 5 additional stations throughout North America. The data can be used to estimate the rate of crustal deformation (convergence) ocurring across the Santa Barbara Channel. The GPS baselines were computed with the Bernese 2nd generation software. A comparison was made between baseline lengths obtained with the Burnese and MIT softwares. Baseline changes from 1971 to January, 1987 (GPS-Bernese) across the Santa Barbara Channel were computed. A uniform strain model was calculated from the baseline changes. The present-day rate of convergence across the Santa Barbara Channel was determined to be 8 to 10 mm/yr. This conclusion is obtained from changes in the baseline length measured with a 1971 trilateration survey and a January, 1987, GPS survey. The rapid convergence rate, in addition to the history of large seismic events, suggests this region is a prime target for future geodetic and geophysical studies.

  16. Areal and Shear Strain Coupling of PBO Borehole Strainmeters From Teleseismic Surface Waves

    NASA Astrophysics Data System (ADS)

    Roeloffs, E.; McCausland, W.

    2007-12-01

    In order to compare borehole strainmeter data with tectonic models, we must know the coupling parameters relating elastic deformation of the strainmeter to strain in the surrounding rock. At least two coupling parameters are required: the ratios of instrument areal and shear strain to formation areal and shear strain, respectively. These coupling parameters depend on the relative elastic moduli of the formation, grout, and strainmeter, and typical elastic moduli yield nominal coupling parameters of 1.5 and 3. More accurate coupling parameters must be determined by analyzing each strainmeter's response to a known deformation source after the instrument has been grouted into the borehole. Borehole strainmeters installed by the National Science Foundation-funded Earthscope Plate Boundary Observatory (PBO) consist of four gauges, sampled at 20 Hz, that measure extension along distinct azimuths. Teleseismic Love and Rayleigh waves that produce fractional gauge elongations > 10-7 , such as those from the M8.3 Kuril Islands earthquake of November 15, 2006, can be used to constrain the coupling parameters. A planar Love or Rayleigh wave is expected to have a simple strain field that produces the same waveform on all four gauges of a strainmeter. The two-parameter coupling model is consistent with the variation of surface wave amplitudes as functions of azimuth for the borehole strainmeter data analyzed to date, although most of the PBO strainmeters require that differences in the relative gains of the four gauges be estimated as well. Fits to the data can be improved for some strainmeters by allowing for two distinct shear strain coupling parameters, and/or for a small (<10 degrees) error in the orientation of the strainmeter as measured during installation. However, data from more earthquakes will need to be analyzed before these refinements can be called significant. The Rayleigh wave data provide tight constraints on the ratio of shear to areal coupling. For borehole

  17. Pure shear deformation of square objects, and applications to geological strain analysis

    NASA Astrophysics Data System (ADS)

    Treagus, Susan H.; Lan, Labao

    2000-01-01

    Geological objects that deform differently from the rock matrix, such as pebbles or other clasts, are unlikely to have been originally circular or elliptical in section, and must therefore be expected to deform heterogeneously and change shape irregularly. We investigate this process with finite element models of pure shear deformation of square objects in three orientations, square, skew and diagonal, in a matrix with different viscosity. Modelling shows that 'squares' deform irregularly, with competent objects becoming barrel shaped and 'fish mouthed' (cf. boudins), whereas incompetent objects become bone shaped or elongate lobes. The object aspect ratios (RO) are less different from the bulk strain ratio (RS) than for equivalent circular objects. In contrast, diagonal squares deform almost homogeneously into 'rhombs', with aspect ratios closer to those for circles. Asymmetrically oriented 'skew squares' behave intermediately, developing skew flag and hooked shapes according to competence contrasts, that might be misdiagnosed as shear criteria. All these square objects (and circles in theory), show almost linear strain paths of object versus bulk (R-1), with slope related to viscosity ratio, object shape and orientation. Linear relationships are also found for concavity/convexity shape factors for 'squares'. The results have implications for strain analysis and competence contrasts in rocks.

  18. 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

  19. Accumulated Financial Strain and Women’s Health Over Three Decades

    PubMed Central

    2012-01-01

    Objective. Drawing from cumulative inequality theory, this research examines how accumulated financial strain affects women’s self-rated health in middle and later life. Method. Using data from the National Longitudinal Survey of Mature Women (1967–2003), we employ random-coefficient growth curve models to examine whether recurring financial strain influences women’s health, above and beyond several measures of objective social status. Predicted probabilities of poor health were estimated by the frequency of financial strain. Results. Financial strain is associated with rapid declines in women’s health during middle and later life, especially for those women who reported recurrent strain. Changes in household income and household wealth were also associated with women’s health but did not eliminate the effects due to accumulated financial strain. Discussion. Accumulated financial strain has long-term effects on women’s health during middle and later life. The findings demonstrate the importance of measuring life course exposure to stressors in studies of health trajectories. PMID:22929397

  20. 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.

  1. PII-Regulated Arginine Synthesis Controls Accumulation of Cyanophycin in Synechocystis sp. Strain PCC 6803

    PubMed Central

    Maheswaran, Mani; Ziegler, Karl; Lockau, Wolfgang; Hagemann, Martin; Forchhammer, Karl

    2006-01-01

    Cyanophycin (multi-l-arginyl-poly-l-aspartic acid) is a nitrogen storage polymer found in most cyanobacteria and some heterotrophic bacteria. The cyanobacterium Synechocystis sp. strain PCC 6803 accumulates cyanophycin following a transition from nitrogen-limited to nitrogen-excess conditions. Here we show that the accumulation of cyanophycin depends on the activation of the key enzyme of arginine biosynthesis, N-acetyl-l-glutamate kinase, by signal transduction protein PII. PMID:16547064

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. Geodimeter measurements of slip and strain accumulation along the san andreas fault

    USGS Publications Warehouse

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

    1974-01-01

    The U.S. Geological Survey conducts repeated geodimeter surveys of trilateration networks in central California in order to study the processes of slip and strain accumulation along the San Andreas fault. The precision of distance measurement is described by a standard deviation ?? = (a2 + b2L2) 1 2 where a = 3mm, b = 2 ?? 10-7, and L is the line length. Within the precision of measurement, no anomalous strain episodes preceding earthquakes or even strain discontinuities at the time of earthquakes were detected from repeated measurements of lines near the epicenters of small (magnitude 4.5-5.1) earthquakes. Annual measurements of small (5-km aperture) strain polygons near the San Andreas fault have not proved strain accumulation in a 3-year period. Repeated measurements of longer lines over periods of 8 to 14 years indicate changes that cannot be attributed to fault slip and must represent strain accumulation at the level of a few parts in 107 per year. ?? 1974.

  7. 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

  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. Stability of elastic and viscoelastic plates in a gas flow taking into account shear strains

    NASA Astrophysics Data System (ADS)

    Potapov, V. D.

    2004-09-01

    It is well known that the internal friction in a material can have a considerable destabilizing effect on the stability of non-conservative systems. Apart from the Voigt model, the viscoelastic body model is sometimes utilized to describe material damping. This relates the stability problem for non-conservative elastic systems with that for viscoelastic system. The Bubnov-Galerkin method is usually applied for solving the problems. In this case, the displacement functions are represented by series in terms of natural vibration modes ϕ i( x) of the elastic system. To provide a high degree of accuracy for the solution, one should involve a fairly large number of modes. For a viscoelastic plate, the number of terms to be kept in the expansion of the deflection can be substantially more. One should bear in mind, however, that as the number of modes preserved in the expansion increases, the influence of shear strains and rotational inertia on the behavior of the solution becomes more pronounced. In view of this, it is important to study the stability of non-conservative viscoelastic systems with the shear strain and rotational inertia being taken into account. In the present paper this problem is solved for a viscoelastic plate in a supersonic gas flow.

  10. 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

  11. 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. PMID:26735954

  12. Modeling the influence of tectonic extrusion and volume loss on the geometry, displacement, vorticity, and strain compatibility of ductile shear zones

    NASA Astrophysics Data System (ADS)

    Baird, Graham B.; Hudleston, Peter J.

    2007-10-01

    Oblate strains are often observed in meso-scale ductile shear zones and this is generally taken to indicate narrowing across the shear zone during formation. Volume loss is one mechanism that could produce shear zone narrowing. However, not all shear zones display characteristics consistent with volume loss, and in such cases, the narrowing must be accomplished by the extrusion of material from within the shear zone. To explore the relationship between shear zone geometry, volume loss, and extrusion, shear zones were mathematically modeled. Results demonstrate the important influence of pure shear and volume loss on controlling the geometry, displacement, and vorticity of ductile shear zones. Further, volume loss does not preclude extrusion unless, for a given volume loss, the strain is of a specific geometry. Extrusion is a likely mechanism important in shear zone development, even if volume loss occurs. Extrusion presents strain compatibility problems because, unlike crustal-scale shear zones, meso-scale ductile shear zones do not possess a free surface. If extrusion occurs, bulk strain compatibility can be maintained if shear zones interlink in anastomosing arrays or change in thickness, though not all shear zone systems display such characteristics. Modeling results elucidate the deformation style of shear zone in the northwest Adirondacks in NY and in the Kebnekaise region in northern Sweden.

  13. Interseismic strain accumulation across the Ashkabad fault (NE Iran) from MERIS-corrected ASAR data

    NASA Astrophysics Data System (ADS)

    Walters, R. J.; Elliott, J. R.; Li, Z.; Parsons, B. E.

    2011-12-01

    The right-lateral Ashkabad Fault separates deforming NE Iran from the stable Turkmenistan platform to the north, and also facilitates the north-westwards extrusion of the South Caspian block (along with the left-lateral Shahrud fault zone). The fault represents the northernmost boundary of significant deformation of the Arabia-Eurasia collision in NE Iran. The 1948 M 7.3 Ashkabad earthquake, which killed around 110,000 people and was the deadliest earthquake to hit Europe or the Middle East in the 20th Century, also possibly occurred on this fault. However, the slip rate and therefore the seismic hazard that the Ashkabad fault represents are not well known. GPS data in NE Iran are sparse, and there are no direct geological or quaternary rates for the main strand of the fault. We use Envisat ASAR data acquired between 2003 and 2010 to measure interseismic strain accumulation across the fault, and hence estimate the slip rate across it. Due to the proximity of this region to the Caspian Sea and the presence of highly variable weather systems, we use data from Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument, as well as modelled weather data from the European Centre for Medium-Range Weather Forecasting (ECMWF), to correct interferograms for differences in water vapour and atmospheric pressure. We mitigate the effects of remaining noise by summing the 13 corrected interferograms that cover the fault, effectively creating a 30 year interferogram with improved signal-to-noise ratio, and we empirically correct for orbital errors. Our measurements of rates of displacement are consistent with an interseismic model for the Ashkabad fault where deformation occurs at depth on a narrow shear zone below a layer in which the fault is locked. We invert the data to solve for best fitting model parameters, estimating both the slip rate and the depth to which the fault is locked. Our measurements show that the Ashkabad fault is accumulating strain at a rate of 9 mm

  14. Draft Genome Sequence of the Nitrate- and Phosphate-Accumulating Bacillus sp. Strain MCC0008

    PubMed Central

    DebRoy, Shreya; Bhattacharjee, Amrita; Thakur, Ashoke Ranjan

    2013-01-01

    Here, we report the draft genome sequence of the nitrate- and phosphate-accumulating Bacillus sp. strain MCC0008, isolated from a consortium enriched from municipal sewage in nitrate broth (HiMedia M439). The total size of the genome is 5,609,456 bp, with a G+C content of 35.1%. PMID:23409265

  15. VISUALIZATION OF HIFU-INDUCED LESION BOUNDARIES BY AXIAL-SHEAR STRAIN ELASTOGRAPHY: A FEASIBILITY STUDY

    PubMed Central

    Thittai, Arun K.; Galaz, Belfor; Ophir, Jonathan

    2010-01-01

    In this paper, we report on a study that investigated the feasibility of reliably visualizing high-intensity focused ultrasound (HIFU) lesion boundaries using axial-shear strain elastograms (ASSE). The HIFU-induced lesion cases used in the present work were selected from data acquired in a previous study. The samples consisted of excised canine livers with thermal lesions produced by an MR-compatible HIFU system (GE Medical System, Milwaukee, WI) and were cast in a gelatin block for elastographic experiment. Both single and multiple HIFU-lesion samples were investigated. For each of the single lesion sample, the lesion boundaries were determined independently from the axial strain elastogram (ASE) and ASSE at various iso-intensity contour thresholds (from −2dB to −6dB), and the area of the enclosed lesion was computed. For samples with multiple lesions, the corresponding ASSE was analyzed for identifying any unique axial-shear strain zones of interest. We further performed Finite Element Modeling (FEM) of simple two inclusion cases to verify if the in-vitro ASSE obtained were reasonable. The results show that the estimation of the lesion area using ASSE is less sensitive to iso-intensity threshold selection- making this method more robust compared to ASE-based method. For multiple lesion case, it was shown that ASSE enables high-contrast visualization of a ‘thin’ untreated region in between multiple fully-treated HIFU-lesions. This contrast visualization was also noticed in the FEM predictions. In summary, the results demonstrate that it is feasible to reliably visualize HIFU lesion boundaries using ASSE. PMID:21276656

  16. Accommodation of missing shear strain in the Central Walker Lane, western North America: Constraints from dense GPS measurements

    NASA Astrophysics Data System (ADS)

    Bormann, Jayne M.; Hammond, William C.; Kreemer, Corné; Blewitt, Geoffrey

    2016-04-01

    We present 264 new interseismic GPS velocities from the Mobile Array of GPS for Nevada Transtension (MAGNET) and continuous GPS networks that measure Pacific-North American plate boundary deformation in the Central Walker Lane. Relative to a North America-fixed reference frame, northwestward velocities increase smoothly from ∼4 mm/yr in the Basin and Range province to 12.2 mm/yr in the central Sierra Nevada resulting in a Central Walker Lane deformation budget of ∼8 mm/yr. We use an elastic block model to estimate fault slip and block rotation rates and patterns of deformation from the GPS velocities. Right-lateral shear is distributed throughout the Central Walker Lane with strike-slip rates generally <1.5 mm/yr predicted by the block model, but extension rates are highest near north-striking normal faults found along the Sierra Nevada frontal fault system and in a left-stepping, en-echelon series of asymmetric basins that extend from Walker Lake to Lake Tahoe. Neotectonic studies in the western Central Walker Lane find little evidence of strike-slip or oblique faulting in the asymmetric basins, prompting the suggestion that dextral deformation in this region is accommodated through clockwise block rotations. We test this hypothesis and show that a model relying solely on the combination of clockwise block rotations and normal faulting to accommodate dextral transtensional strain accumulation systematically misfits the GPS data in comparison with our preferred model. This suggests that some component of oblique or partitioned right-lateral fault slip is needed to accommodate shear in the asymmetric basins of the western Central Walker Lane. Present-day clockwise vertical axis rotation rates in the Bodie Hills, Carson Domain, and Mina Deflection are between 1-4°/Myr, lower than published paleomagnetic rotation rates, suggesting that block rotation rates have decreased since the Late to Middle Miocene.

  17. 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.

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

    PubMed

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

    2014-09-01

    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. 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.

  20. 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.

  1. 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

  2. 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

  3. 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

  4. 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.

  5. Determination of the shear buckling load of a large polymer composite I-section using strain and displacement sensors.

    PubMed

    Park, Jin Y; Lee, Jeong Wan

    2012-01-01

    This paper presents a method and procedure of sensing and determining critical shear buckling load and corresponding deformations of a comparably large composite I-section using strain rosettes and displacement sensors. The tested specimen was a pultruded composite beam made of vinyl ester resin, E-glass and carbon fibers. Various coupon tests were performed before the shear buckling test to obtain fundamental material properties of the I-section. In order to sensitively detect shear buckling of the tested I-section, twenty strain rosettes and eight displacement sensors were applied and attached on the web and flange surfaces. An asymmetric four-point bending loading scheme was utilized for the test. The loading scheme resulted a high shear and almost zero moment condition at the center of the web panel. The web shear buckling load was determined after analyzing the obtained test data from strain rosettes and displacement sensors. Finite element analysis was also performed to verify the experimental results and to support the discussed experimental approach. PMID:23443364

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

    PubMed

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

    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

  7. 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

  8. 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

  9. 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

  10. 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

  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. Synthesis and accumulation of aromatic aldehydes in an engineered strain of Escherichia coli.

    PubMed

    Kunjapur, Aditya M; Tarasova, Yekaterina; Prather, Kristala L J

    2014-08-20

    Aromatic aldehydes are useful in numerous applications, especially as flavors, fragrances, and pharmaceutical precursors. However, microbial synthesis of aldehydes is hindered by rapid, endogenous, and redundant conversion of aldehydes to their corresponding alcohols. We report the construction of an Escherichia coli K-12 MG1655 strain with reduced aromatic aldehyde reduction (RARE) that serves as a platform for aromatic aldehyde biosynthesis. Six genes with reported activity on the model substrate benzaldehyde were rationally targeted for deletion: three genes that encode aldo-keto reductases and three genes that encode alcohol dehydrogenases. Upon expression of a recombinant carboxylic acid reductase in the RARE strain and addition of benzoate during growth, benzaldehyde remained in the culture after 24 h, with less than 12% conversion of benzaldehyde to benzyl alcohol. Although individual overexpression results demonstrated that all six genes could contribute to benzaldehyde reduction in vivo, additional experiments featuring subset deletion strains revealed that two of the gene deletions were dispensable under the conditions tested. The engineered strain was next investigated for the production of vanillin from vanillate and succeeded in preventing formation of the byproduct vanillyl alcohol. A pathway for the biosynthesis of vanillin directly from glucose was introduced and resulted in a 55-fold improvement in vanillin titer when using the RARE strain versus the wild-type strain. Finally, synthesis of the chiral pharmaceutical intermediate L-phenylacetylcarbinol (L-PAC) was demonstrated from benzaldehyde and glucose upon expression of a recombinant mutant pyruvate decarboxylase in the RARE strain. Beyond allowing accumulation of aromatic aldehydes as end products in E. coli, the RARE strain expands the classes of chemicals that can be produced microbially via aldehyde intermediates. PMID:25076127

  13. 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

  14. 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.

  15. 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. PMID:26496619

  16. 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

  17. Interaction between selected bacterial strains and Arabidopsis halleri modulates shoot proteome and cadmium and zinc accumulation

    PubMed Central

    Panigati, Monica; Furini, Antonella

    2011-01-01

    The effects of plant–microbe interactions between the hyperaccumulator Arabidopsis halleri and eight bacterial strains, isolated from the rhizosphere of A. halleri plants grown in a cadmium- and zinc-contaminated site, were analysed for shoot metal accumulation, shoot proteome, and the transcription of genes involved in plant metal homeostasis and hyperaccumulation. Cadmium and zinc concentrations were lower in the shoots of plants cultivated in the presence of these metals plus the selected bacterial strains compared with plants grown solely with these metals or, as previously reported, with plants grown with these metals plus the autochthonous rhizosphere-derived microorganisms. The shoot proteome of plants cultivated in the presence of these selected bacterial strains plus metals, showed an increased abundance of photosynthesis- and abiotic stress-related proteins (e.g. subunits of the photosynthetic complexes, Rubisco, superoxide dismutase, and malate dehydrogenase) counteracted by a decreased amount of plant defence-related proteins (e.g. endochitinases, vegetative storage proteins, and β-glucosidase). The transcription of several homeostasis genes was modulated by the microbial communities and by Cd and Zn content in the shoot. Altogether these results highlight the importance of plant-microbe interactions in plant protein expression and metal accumulation and emphasize the possibility of exploiting microbial consortia for increasing or decreasing shoot metal content. PMID:21357773

  18. 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.

  19. 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

  20. Nutrient removal and lipid accumulation properties of newly isolated microalgal strains.

    PubMed

    Han, Lin; Pei, Haiyan; Hu, Wenrong; Han, Fei; Song, Mingming; Zhang, Shuo

    2014-08-01

    In this work, four microalgae including Chlorella sp. SDEC-10, Chlorella ellipsoidea SDEC-11, Scenedesmus bijuga SDEC-12 and Scenedesmus quadricauda SEDC-13 isolated from a local lake have been investigated for the properties of growth, nutrient removal and lipid accumulation in synthetic sewage. Their biomass ranged between 0.4 and 0.5g/L. The total phosphorus removal efficiency of four strains was nearly 100%, but in the case of total nitrogen and ammonium the removal efficiency was relatively low. Their lipid content, ranging from 25.92% to 27.76% and corresponding to the lipid productivity 7.88-18.08mg/L/d, was higher than that obtained in BG-11. Palmitic acid and oleic acid were the predominant compositions found through fatty acids analysis. S. quadricauda SDEC-13 performed best both in nutrient removal and in lipid production among the four strains. PMID:24731916

  1. The impact of nitrogen starvation on the dynamics of triacylglycerol accumulation in nine microalgae strains.

    PubMed

    Breuer, Guido; Lamers, Packo P; Martens, Dirk E; Draaisma, René B; Wijffels, René H

    2012-11-01

    Microalgae-derived lipids are an alternative to vegetable and fossil oils, but lipid content and quality vary among microalgae strains. Selection of a suitable strain for lipid production is therefore of paramount importance. Based on published results for 96 species, nine strains were selected to study their biomass, total fatty acid, and triacylglycerol (TAG) production under nitrogen-sufficient and deficient cultivation conditions. Under nitrogen-deficient conditions, Chlorella vulgaris, Chlorella zofingiensis, Neochloris oleoabundans, and Scenedesmus obliquus, accumulated more than 35% of their dry weight as TAGs. Palmitic and oleic acid were the major fatty acids produced. The main difference between these strains was the amount of biomass that was produced (3.0-7.8-fold increase in dry weight) and the duration that the biomass productivity was retained (2-7 days) after nitrogen depletion. S. obliquus (UTEX 393) and C. zofingiensis (UTEX B32) showed the highest average TAG productivity (322 and 243 mg l(-1)day(-1)). PMID:22995162

  2. 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.

  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. 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

  5. Single Myosin Cross-Bridge Orientation in Cardiac Papillary Muscle Detects Lever-Arm Shear Strain in Transduction

    PubMed Central

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

    2011-01-01

    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. PMID:21819137

  6. 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

  7. Grainsize evolution in ductile shear zones: Implications for strain localization and the strength of the lithosphere

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Behr, W. M.

    2011-04-01

    At high stresses and low temperatures, grainsize reduction by dynamic recrystallization profoundly modifies rock rheology. Strain energy driven grain-boundary migration (ρGBM) is involved both in the nucleation of new grains by the grain-boundary bulging mechanism (BLG), and in the subsequent evolution of the microstructure. Above the Dmin line, which is a line in stress/grainsize space that defines the minimum size of nucleus that can form by BLG, ρGBM dominates the microstructure, and grain growth by surface energy driven grain-boundary migration (γGBM) is inhibited. The recrystallized grainsize is therefore dominated by the nucleation process, possibly controlled by the size of subgrains or dislocation cells within the old grains. This provides a first-order explanation for the experimentally observed grainsize-stress relationship. ρGBM is an important agent of recovery in rocks deformed by dislocation creep, sweeping out dislocations and counteracting work-hardening. We have derived a new flow law (DRX-assisted dislocation creep) based on this process, which exhibits grainsize sensitivity as a result of the role of ρGBM. If grainsize obeys the empirically-determined grainsize-stress relationship, DRX creep has an effective stress exponent of a little over 4, consistent with experimental observations and inferences from naturally deformed rocks. DRX creep may be an important agent in weakening quartz at low temperatures, whereas current flow law data suggest it may not be important in olivine. Rocks deformed and dynamically recrystallized above the Dmin line may switch from climb-assisted dislocation creep to grainsize-sensitive creep (Coble creep, DRX creep, or creep dominated by grain-boundary sliding), resulting in weakening. Lithospheric-scale shear zones are likely to evolve at approximately constant stress; under these conditions weakening results in an increase in strain rate, not a stress drop. The rate of dislocation motion, the dislocation density

  8. 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. PMID:26931336

  9. 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).

  10. 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.

  11. Metabolism of bismuth subsalicylate and intracellular accumulation of bismuth by Fusarium sp. strain BI.

    PubMed

    Dodge, Anthony G; Wackett, Lawrence P

    2005-02-01

    Enrichment cultures were conducted using bismuth subsalicylate as the sole source of carbon and activated sludge as the inoculum. A pure culture was obtained and identified as a Fusarium sp. based on spore morphology and partial sequences of 18S rRNA, translation elongation factor 1-alpha, and beta-tubulin genes. The isolate, named Fusarium sp. strain BI, grew to equivalent densities when using salicylate or bismuth subsalicylate as carbon sources. Bismuth nitrate at concentrations of up to 200 muM did not limit growth of this organism on glucose. The concentration of soluble bismuth in suspensions of bismuth subsalicylate decreased during growth of Fusarium sp. strain BI. Transmission electron microscopy and energy-dispersive spectroscopy revealed that the accumulated bismuth was localized in phosphorus-rich granules distributed in the cytoplasm and vacuoles. Long-chain polyphosphates were extracted from fresh biomass grown on bismuth subsalicylate, and inductively coupled plasma optical emission spectrometry showed that these fractions also contained high concentrations of bismuth. Enzyme activity assays of crude extracts of Fusarium sp. strain BI showed that salicylate hydroxylase and catechol 1,2-dioxygenase were induced during growth on salicylate, indicating that this organism degrades salicylate by conversion of salicylate to catechol, followed by ortho cleavage of the aromatic ring. Catechol 2,3-dioxygenase activity was not detected. Fusarium sp. strain BI grew with several other aromatic acids as carbon sources: benzoate, 3-hydroxybenzoate, 4-hydroxybenzoate, gentisate, d-mandelate, l-phenylalanine, l-tyrosine, phenylacetate, 3-hydroxyphenylacetate, 4-hydroxyphenylacetate, and phenylpropionate. PMID:15691943

  12. Mechanisms of strain accumulation and damage development during creep of prestrained 316 stainless steels

    NASA Astrophysics Data System (ADS)

    Wilshire, B.; Willis, M.

    2004-02-01

    The effects of prestraining at room temperature and at the creep temperature of 848 K, as well as the responses to stress reductions during creep, have been studied for 316 stainless steels varying in composition and initial microstructure. The results are analyzed by contrasting the strengthening effects achieved by introducing high dislocation densities prior to creep exposure with the deleterious effects, which can occur when prestraining causes premature void nucleation at grain boundaries. In addition, by recognizing the differing contributions made by the grain interiors and the grain boundary zones to the overall rates of creep strain accumulation, a consistent explanation is provided for the diverse creep behavior patterns reported for different metals and alloys after various prestraining treatments.

  13. 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.

  14. Pressure Rate of Strain, Pressure Diffusion and Velocity Pressure Gradient Tensor Measurements in a Cavity Shear Layer Flow

    NASA Astrophysics Data System (ADS)

    Liu, Xiaofeng; Katz, Joseph

    2014-11-01

    Pressure related turbulence statistics of a 2D open cavity shear layer flow was investigated experimentally in a water tunnel at a Reynolds number of 40,000. Time-resolved PIV sampled at 4500 fps and a field of view of 25 × 25 mm was used to simultaneously measure the instantaneous velocity, material acceleration and pressure distributions. The pressure was obtained by spatially integrating the measured material acceleration. Results based on 150,000 measurement samples enable direct estimates of components of the pressure-rate-of-strain, pressure diffusion and velocity-pressure-gradient tensors. The pressure and streamwise velocity correlation changes its sign from negative values far upstream from the downstream corner to positive values near the corner due to the strong adverse pressure gradient imposed by the corner. Moreover, once its sign changes, the pressure-velocity correlation preserves its positive value for the streamwise correlations, and negative value for the spanwise correlations, even after the shear layer propagates beyond the adverse pressure gradient region along both the vertical and horizontal corner walls. The pressure diffusion term is of the same order as the production rate. In the shear layer, the streamwise pressure-rate-of-strain term, R11, is mostly negative while the perpendicular term, R22, is positive but with a smaller magnitude, implying turbulent energy redistribution from streamwise to lateral directions. Sponsored by ONR and NSF.

  15. InSAR velocity field across the North Anatolian Fault (eastern Turkey): Implications for the loading and release of interseismic strain accumulation

    NASA Astrophysics Data System (ADS)

    Cakir, Ziyadin; Ergintav, Semih; Akoǧlu, Ahmet M.; ćakmak, Rahşan; Tatar, Orhan; Meghraoui, Mustapha

    2014-10-01

    We use the Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) technique with the European Space Agency's Envisat and ERS SAR data acquired on three neighboring descending tracks (T350, T078, and T307) to map the interseismic strain accumulation along a ~225 km long, NW-SE trending section of the North Anatolian Fault that ruptured during the 1939, 1942, and 1943 earthquakes in eastern Turkey. We derive a line-of-sight velocity map of the region with a high spatial resolution and accuracy which, together with the maps of earthquake surface ruptures, shed light on the style of continental deformation and the relationships between the loading and release of interseismic strain along segmented continental strike-slip faults. In contrast with the geometric complexities at the ground surface that appear to control rupture propagation of the 1939 event, modeling of the high-resolution PS-InSAR velocity field reveals a fairly linear and narrow throughgoing shear zone with an overall 20 ± 3 mm/yr slip rate above an unexpectedly shallow 7 ± 2 km locking depth. Such a shallow locking depth may result from the postseismic effects following recent earthquakes or from a simplified model that assumes a uniform degree of locking with depth on the fault. A narrow throughgoing shear zone supports the thick lithosphere model in which continental strike-slip faults are thought to extend as discrete shear zones through the entire crust. Fault segmentation previously reported from coseismic surface ruptures is thus likely inherited from heterogeneities in the upper crust that either preexist and/or develop during coseismic rupture propagation. The geometrical complexities that apparently persist for long periods may guide the dynamic rupture propagation surviving thousands of earthquake cycles.

  16. 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

  17. 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

  18. Precision estimation and imaging of normal and shear components of the 3D strain tensor in elastography.

    PubMed

    Konofagou, E E; Ophir, J

    2000-06-01

    In elastography we have previously developed a tracking and correction method that estimates the axial and lateral strain components along and perpendicular to the compressor/scanning axis following an externally applied compression. However, the resulting motion is a three-dimensional problem. Therefore, in order to fully describe this motion we need to consider a 3D model and estimate all three principal strain components, i.e. axial, lateral and elevational (out-of-plane), for a full 3D tensor description. Since motion is coupled in all three dimensions, the three motion components have to be decoupled prior to their estimation. In this paper, we describe a method that estimates and corrects motion in three dimensions, which is an extension of the 2D motion tracking and correction method discussed before. In a similar way as in the 2D motion estimation, and by assuming that ultrasonic frames are available in more than one parallel elevational plane, we used methods of interpolation and cross-correlation between elevationally displaced RF echo segments to estimate the elevational displacement and strain. In addition, the axial, lateral and elevational displacements were used to estimate all three shear strain components that, together with the normal strain estimates, fully describe the full 3D normal strain tensor resulting from the uniform compression. Results of this method from three-dimensional finite-element simulations are shown. PMID:10870710

  19. Charts for Determining Preliminary Values of Span-load, Shear, Bending-moment, and Accumulated-torque Distributions of Swept Wings of Various Taper Ratios

    NASA Technical Reports Server (NTRS)

    Wollner, Bertram C

    1948-01-01

    Contains charts for use in determining preliminary values of the spanwise-load, shear, bending-moment, and accumulated-torque distributions of swept wings. The charts are based on strip theory and include four aerodynamic-load distributions, two section-moment distributions, and two inertia-load distributions. The taper ratios considered cover the range from 1.0 to 0 and the results are applicable to any angle of sweep.

  20. Interseismic strain accumulation and the earthquake potential on the southern San Andreas fault system.

    PubMed

    Fialko, Yuri

    2006-06-22

    The San Andreas fault in California is a mature continental transform fault that accommodates a significant fraction of motion between the North American and Pacific plates. The two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857, respectively. The southern section of the fault, however, has not produced a great earthquake in historic times (for at least 250 years). Assuming the average slip rate of a few centimetres per year, typical of the rest of the San Andreas fault, the minimum amount of slip deficit accrued on the southern section is of the order of 7-10 metres, comparable to the maximum co-seismic offset ever documented on the fault. Here I present high-resolution measurements of interseismic deformation across the southern San Andreas fault system using a well-populated catalogue of space-borne synthetic aperture radar data. The data reveal a nearly equal partitioning of deformation between the southern San Andreas and San Jacinto faults, with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces. The observed strain rates confirm that the southern section of the San Andreas fault may be approaching the end of the interseismic phase of the earthquake cycle. PMID:16791192

  1. 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

  2. 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. PMID:25909879

  3. Effect of Shear Strain on the α-ε Phase Transition of Iron: a New Approach in the Rotational Diamond Anvil Cell

    SciTech Connect

    Ma,Y.; Selvi, E.; Levitas, V.; Hashemi, J.

    2006-01-01

    The effect of shear strain on the iron {alpha}-{var_epsilon} phase transformation has been studied using a rotational diamond anvil cell (RDAC). The initial transition is observed to take place at the reduced pressure of 10.8 GPa under pressure and shear operation. Complete phase transformation was observed at 15.4 GPa. The rotation of an anvil causes limited pressure elevation and makes the pressure distribution symmetric in the sample chamber before the phase transition. However, it causes a significant pressure increase at the center of the sample and brings about a large pressure gradient during the phase transformation. The resistance to the phase interface motion is enhanced due to strain hardening during the pressure and shear operations on iron and this further increases the transition pressure. The work of macroscopic shear stress and the work of the pressure and shear stress at the defect tips account for the pressure reduction of the iron phase transition.

  4. 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

  5. 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

  6. DYNAMIC PLANE-STRAIN SHEAR RUPTURE WITH A SLIP-WEAKENING FRICTION LAW CALCULATED BY A BOUNDARY INTEGRAL METHOD.

    USGS Publications Warehouse

    Andrews, D.J.

    1985-01-01

    A numerical boundary integral method, relating slip and traction on a plane in an elastic medium by convolution with a discretized Green function, can be linked to a slip-dependent friction law on the fault plane. Such a method is developed here in two-dimensional plane-strain geometry. Spontaneous plane-strain shear ruptures can make a transition from sub-Rayleigh to near-P propagation velocity. Results from the boundary integral method agree with earlier results from a finite difference method on the location of this transition in parameter space. The methods differ in their prediction of rupture velocity following the transition. The trailing edge of the cohesive zone propagates at the P-wave velocity after the transition in the boundary integral calculations. Refs.

  7. 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.

  8. 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

  9. 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

  10. Scaling of Viscous Shear Zones with Depth Dependent Viscosity and Power Law Stress-strain Rate Dependence

    NASA Astrophysics Data System (ADS)

    Moore, J. D. P.; Parsons, B.

    2014-12-01

    One of the unresolved questions concerning fault deformation is the degree and cause of localisation of shear at depth beneath a fault. Geologic observations of exhumed shear zones indicate that whilst the motion is no longer planar, it can still be localised near the down-dip extension of the fault; however, the degree of localisation 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 localise a shear zone. As we are concerned with long-term structure the model is time-averaged across the earthquake cycle, consisting of an idealised strike-slip fault within a rigid lid over a viscous layer. For a depth dependent viscosity, η = η0 exp (-z/z0), we find a shear zone develops with a half-width δw √z0 for small z0, where lengths are non-dimensionalised by the layer thickness (d km). Including a non-linear stress-strain rate relation (ɛ ˙ ∝ σn) scales δw by 1/√n, comparable to deformation length scales in thin viscous sheet calculations. We find that the primary control on δw is the depth dependence of viscosity arising from the increase in temperature with depth. As this relationship is exponential, scaling relations give a half-width that scales approximately as δw≈T(z=1/2)RdnQβ-----√km,delta_wapprox T(z=1/2){sqrtfrac{Rd}{nQbeta}} km, with T (K), gas constant R (J/mol K), activation energy Q (J/mol), and geotherm β (K/km). Figure illustrates shear zones for a dry olivine composition. For n = 1 the shear zone half-width is δw = 4 km, which reduces to δw = 2.3 km when n = 3; other parameter choices consistent with laboratory-derived rheological properties give δwfrom 2-6 km. The inclusion of shear-stress heating only reduces δw by an additional 5-25%, depending on the initial width of the shear zone; in the case of dry olivine with n = 3 we get δw = 1.8 km. This

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Larsen, Shawn; Reilinger, Robert

    1992-06-01

    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.

  13. 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.

  14. 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.

  15. 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.

  16. Development of shear bands in dynamic plane strain compression of depleted uranium and tungsten blocks. Interim report, 15 November 1994-22 June 1995

    SciTech Connect

    Batra, R.C.; Peng, Z.

    1995-12-31

    The authors study the initiation and growth of shear bands in prismatic bodies of rectangular cross-section made of either depleted uranium or tungsten and deformed in plane strain compression at a nominal strain-rate of 5000/s. It is found that, in the deformed configuration, shear bands in depleted uranium blocks are inclined at approximately 42.5 deg counterclockwise from the horizontal axis, those in tungsten are inclined at nearly l35 deg. When shear bands initiate, the total compressive force required to deform the body drops sharply for the uranium blocks but gradually for the tungsten blocks. After a shear band has developed, dead zones form in both uranium and tungsten blocks; the size of the dead zone in the tungsten block is more than that in the uranium block. When the shear modulus for the tungsten is artificially changed so as to equal that for the uranium, the angle of inclination for the shear bands in tungsten blocks changes to that found for the uranium blocks. This suggests that the value of the shear modulus plays a noticeable role in the development of shear bands.

  17. 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.

  18. 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.

  19. Uniform strain field inside a non-circular inhomogeneity with homogeneously imperfect interface in anisotropic anti-plane shear

    NASA Astrophysics Data System (ADS)

    Dai, Ming; Schiavone, Peter; Gao, Cun-Fa

    2016-06-01

    We re-examine the conclusion established earlier in the literature that in the presence of a homogeneously imperfect interface, the circular inhomogeneity is the only shape of inhomogeneity which can achieve a uniform internal strain field in an isotropic or anisotropic material subjected to anti-plane shear. We show that under certain conditions, it is indeed possible to design such non-circular inhomogeneities despite the limitation of a homogeneously imperfect interface. Our method proceeds by prescribing a uniform strain field inside a non-circular inhomogeneity via perturbations of the uniform strain field inside the analogous circular inhomogeneity and then subsequently identifying the corresponding (non-circular) shape via the use of a conformal mapping whose unknown coefficients are determined from a system of nonlinear equations. We illustrate our results with several examples. We note also that, for a given size of inhomogeneity, the minimum value of the interface parameter required to guarantee the desired uniform internal strain increases as the elastic constants of the inclusion approach those of the matrix. Finally, we discuss in detail the relationship between the curvature of the interface and the displacement jump across the interface in the design of such inhomogeneities.

  20. Supersonic crack growth in a solid of upturn stress?strain relation under anti-plane shear

    NASA Astrophysics Data System (ADS)

    Guo, Gaofeng; Yang, Wei; Huang, Y.

    2003-11-01

    This paper examines, from the prospect of continuum analysis, the possibility for a supersonic crack growth in a solid with an upturn stress-strain relation. The stress has a linear-upturn power-law relation with the strain, resulting in an elastic modulus, and consequently a wave speed, that increase with the strain. Though appearing to be "supersonic", the local wave speed in the crack tip vicinity of the solid with a sufficient upturn stress-strain relation exceeds the crack extension speed. A pre-request for such a supersonic crack growth is the storage of sufficient deformation energy within the solid to nurse the energy flux drawn to the crack tip that extends at an "apparent supersonic" speed. The idea is demonstrated for the simplest case, the anti-plane shear. We examine the steady-state supersonic crack growth in a hyperelastic material. The governing equation is elliptical in the crack tip vicinity but hyperbolic elsewhere. The boundary between two regions is determined with a certain extent. An asymptotic solution is constructed within the super-hardening zone. The solution connects to the hyperbolic radiation strips by weak discontinuity boundaries and to the pre-stressed frontal field by a strong discontinuity boundary.

  1. 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.

  2. Moderate ischemic mitral regurgitation after postero-lateral myocardial infarction in sheep alters left ventricular shear but not normal strain in the infarct and infarct borderzone

    PubMed Central

    Ge, Liang; Wu, Yife; Soleimani, Mehrdad; Khazalpour, Michael; Takaba, Kiyoaki; Tartibi, Mehrzad; Zhang, Zhihong; Acevedo-Bolton, Gabriel; Saloner, David A.; Wallace, Arthur W.; Mishra, Rakesh; Grossi, Eugene A.; Guccione, Julius M.; Ratcliffe, Mark B.

    2016-01-01

    Background Chronic ischemic mitral regurgitation (CIMR: MR) is associated with poor outcome. Left ventricular (LV) strain after postero-lateral myocardial infarction (MI) may drive LV remodeling. Although moderate CIMR has been previously shown to effect LV remodeling, the effect of CIMR on LV strain after postero-lateral MI remains unknown. We tested the hypothesis that moderate CIMR alters LV strain after postero-lateral MI. Methods/Results Postero-lateral MI was created in 10 sheep. Cardiac MRI with tags was performed 2 weeks before and 2, 8 and 16 weeks after MI. LV and right ventricular (RV) volumes were measured and regurgitant volume indexed to body surface area (BSA; RegurgVolume Index) calculated as the difference between LV and RV stroke volumes / BSA. Three-dimensional strain was calculated. Circumferential (Ecc)and longitudinal (Ell) strains were reduced in the infarct proper, MI borderzone (BZ) and remote myocardium 16 weeks after MI. In addition, radial circumferential (Erc) and radial longitudinal (Erl) shear strains were reduced in remote myocardium but increased in the infarct and BZ 16 weeks after MI. Of all strain components, however, only Erc was effected by RegurgVolume Index (p=0.0005). There was no statistically significant effect of RegurgVolume Index on Ecc, Ell, Erl, or circumferential longitudinal shear strain (Ecl). Conclusions Moderate CIMR alters radial circumferential shear strain after postero-lateral MI in the sheep. Further studies are needed to determine the effect of shear strain on myocyte hypertrophy and the effect of mitral repair on myocardial strain. PMID:26857634

  3. Strain localization on different scales and the importance of brittle precursors during deformation in the lower crust (Davenport Shear Zone, Central Australia)

    NASA Astrophysics Data System (ADS)

    Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Camacho, Alfredo; Pennacchioni, Giorgio

    2014-05-01

    High strain rocks in the Musgrave Ranges (Central Australia) provide a rather unique insight into the development of lower crustal shear zones during the 550 Ma Petermann Orogeny, allowing common models for lower crustal deformation to be critically evaluated. The observed structures in the study area are, from south to north: (1) The Mann Fault, which is poorly exposed but evident on airborne geomagnetic maps. This regional scale fault with a component of dextral shear shows a step-over resulting in the formation of a pull-apart basin. (2) The Davenport Shear Zone, accommodating the horizontal extension in a 7 km wide WNW-ESE-trending mylonitic zone developed under subeclogitic, lower crustal conditions. This high strain zone is bounded to the north by a more than 50 km long, continuous, sheared dolerite dyke. North of this dyke, the ~1200 Ma Musgravian fabric is still preserved, only slightly rotated and typically N-S trending. (3) The Woodroffe Thrust, marking the northern boundary of the Musgrave Ranges, brings these lower crustal rocks on top of amphibolite facies units, with a top-to-north sense of movement. Strain in the Davenport Shear Zone is very heterogeneously distributed, with localization and partitioning from the kilometre down to the millimetre scale. Pseudotachylyte is commonly associated with dykes, especially on the boundaries, and is often sheared. The orientation of sheared dykes and localized shear zones is typically at a high angle to either side of the shortening direction, resulting in a variable sense of shear and a major component of flattening, with a nearly horizontal extension direction. Detailed outcrop-scale mapping shows that compositional inhomogeneities, such as quartz veins, are generally not exploited, even when favourably oriented for shear reactivation. Ultramylonitic shear zones are sometimes only a few millimetres wide but extend for several metres and are generally oblique to the background foliation. Pseudotachylyte often

  4. 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

  5. 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

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

    NASA Astrophysics Data System (ADS)

    Niemeijer, A. R.; Boulton, C. J.; Toy, V. G.; Townend, J.; Sutherland, R.

    2014-12-01

    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. The absence of measurable contemporary surface deformation has been interpreted to indicate that the fault slips mostly in quasi-periodic large earthquakes (< Mw 8.0). In order 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 preliminary 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 and 450 °C. Using the shallow geothermal gradient of 63 °C/km determined in phase 1 of DFDP, our highest temperature corresponds to a depth of ~7 km or 10 km using a more moderate geotherm of 45 ºC/km as suggested by Toy et al. (2010). To explore temperature constraints on the limit of the brittle faulting processes, additional experiments at 600 ˚C (or ~10-15 km depth) are planned. Preliminary results on two hanging wall (foliated) cataclasite 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 being more dominant at lower sliding velocities. Moreover, shear stress depends linearly on effective normal stress, indicating that shearing is essentially frictional and no transition to ductile (normal stress independent) flow has been

  7. Strain Accumulation Estimated from Seafloor Crustal Deformation at the Nankai Trough, Japan

    NASA Astrophysics Data System (ADS)

    Tadokoro, K.; Watanabe, T.; Nagai, S.; Ikuta, R.; Okuda, T.; Kenji, Y.; Sakata, T.

    2012-12-01

    Our research has developed an observation system for seafloor crustal deformation composed of the kinematic GPS and acoustic ranging techniques [Tadokoro et al., 2006; Ikuta et al., 2008]. We monitored crustal deformation at the Nankai Trough, Japan, where the Philippine Sea Plate subducts beneath the Amurian Plate. The convergence rate is predicted at 60 mm/y in the N59W direction by the Euler vector of REVEL [Sella et al., 2002]. We installed three monitoring sites (named KMN, KMS, and KME) on the seafloor at depths of about 1920-2030 m. The sites KMN and KMS are installed perpendicular to the trough axis with a spacing of 20 km; the site KME is 50 km from KMN and KMS in the direction parallel to the trough axis. The monitoring was started in 2004, 2005, and 2008 at KMS, KMN, and KME, respectively. The numbers of measurements are 16, 20, and 5 times at KMN, KMS, and KME, respectively. We obtained 3-7 years averaged horizontal site velocities within ITRF2000 adopting a robust estimation method with Tukey's biweight function to the time series of site position measured until the end of 2011. Substituting the synthetic rigid block motions of the Amurian Plate from the velocities within ITRF2000, we obtained the following site velocities with respect to the Amurian Plate [Tadokoro et al., 2012]: KMN 41±4 mm/y, N77±7W KMS 43±5 mm/y, N80±6W KME 42±5 mm/y, N80±7W In contrast, the on-land GPS horizontal velocities along the coast is 23-33 mm/y toward N74-80W. The present observational results show: (1) the velocity vectors are all the same length and direction, which indicates no internal deformation in this region; (2) the back-slip model predicts that the plate interface beneath the region is uniformly locked with coupling ratios of 60-80 %, indicating strain accumulation that will be released during the anticipated mega-thrust Tonankai earthquake; and (3) the directions of site velocities differ from that of convergence vector by 20 degrees, which is affected by

  8. 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

  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. Interseismic Strain Accumulation in the Imperial Valley and Implications for Triggering of Large Earthquakes in Southern California

    NASA Astrophysics Data System (ADS)

    Crowell, B. W.; Bock, Y.; Sandwell, D. T.

    2009-12-01

    From February, 2008 to March, 2009, we performed three rapid-static Global Positioning System (GPS) surveys of 115 geodetic monuments stretching from the United States-Mexico border into the Coachella Valley using the method of instantaneous positioning. The monuments are located in key areas near the Imperial, Superstition Hills, San Jacinto, San Andreas and Brawley Faults with nominal baselines generally less than 10 km. We perform a bicubic spline interpolation on the crustal motion vectors from the campaign measurements and 1005 continuous GPS monuments in western North America and solve for the velocity gradient tensor to look at the maximum shear strain, dilatation and rotation rates in the Imperial Valley. We then compare our computed strain field to that computed using the Southern California Earthquake Center Crustal Motion Map 3.0, which extends through 2003 and includes 840 measurements. We show that there is an interseismic strain transient that corresponds to an increase in the maximum shear strain rate of 0.7 μstrain/yr near Obsidian Buttes since 2003 along a fault referred to as the Obsidian Buttes Fault (OBF). A strong subsidence signal of 27 mm/yr and a left-lateral increase of 10 mm/yr are centered along the OBF. Changes in the dilatation and rotation rates confirm the increase in left-lateral motion, as well as infer a strong increase in spreading rate in the southern Salton Sea. The increase in spreading rate has caused an accelerated slip rate along the southern San Andreas near Durmid Hill as evidenced by continuous GPS, which has the potential for earthquake triggering.

  11. 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.

  12. Grain size reduction of feldspar and pyroxene, phase mixing, and strain localization in lower crustal shear zones (Lofoten, Norway)

    NASA Astrophysics Data System (ADS)

    Menegon, L.; Stunitz, H.; Nasipuri, P.; Svahnberg, H.; Heilbronner, R.

    2011-12-01

    compositional domains are indistinguishable and the degree of phase mixing is higher. Fractured fragments of mesoperthite are not preserved, the grain size of plagioclase, K-feldspar and quartz is further reduced compared to the mylonite (20 μm Vs. 25-30 μm), and the main constituent phases do not show a CPO. Diffusion creep is interpreted to be the dominant deformation mechanism. In summary, shear zone formation is invariably associated with a preliminary stage of cracking and fluid infiltration, which triggers syndeformational metamorphic reactions, strong grain size reduction, and activation of diffusion creep. Initial cracking at the estimated deformation conditions requires high differential stresses (in the absence of high pore pressures), and indicates a high strength of the lower continental crust at the onset of the deformation. A strain-dependent transition from dislocation creep to diffusion creep is not observed, and diffusion creep appears to be the dominant deformation mechanism in all compositional domains from the mylonite to ultramylonite stage.

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

    PubMed

    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

  14. 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

  15. 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

  16. 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.

  17. Estimation of Rate of Strain Magnitude and Average Viscosity in Turbulent Flow of Shear Thinning and Yield Stress Fluids

    NASA Astrophysics Data System (ADS)

    Sawko, Robert; Thompson, Chris P.

    2010-09-01

    This paper presents a series of numerical simulations of non-Newtonian fluids in high Reynolds number flows in circular pipes. The fluids studied in the computations have shear-thinning and yield stress properties. Turbulence is described using the Reynolds-Averaged Navier-Stokes (RANS) equations with the Boussinesq eddy viscosity hypothesis. The evaluation of standard, two-equation models led to some observations regarding the order of magnitude as well as probabilistic information about the rate of strain. We argue that an accurate estimate of the rate of strain tensor is essential in capturing important flow features. It is first recognised that an apparent viscosity comprises two flow dependant components: one originating from rheology and the other from the turbulence model. To establish the relative significance of the terms involved, an order of magnitude analysis has been performed. The main observation supporting further discussion is that in high Reynolds number regimes the magnitudes of fluctuating rates of strain and fluctuating vorticity dominate the magnitudes of their respective averages. Since these quantities are included in the rheological law, the values of viscosity obtained from the fluctuating and mean velocity fields are different. Validation against Direct Numerical Simulation data shows at least an order of magnitude discrepancy in some regions of the flow. Moreover, the predictions of the probabilistic analysis show a favourable agreement with statistics computed from DNS data. A variety of experimental, as well as computational data has been collected. Data come from the latest experiments by Escudier et al. [1], DNS from Rudman et al. [2] and zeroth-order turbulence models of Pinho [3]. The fluid rheologies are described by standard power-law and Herschel-Bulkley models which make them suitable for steady state calculations of shear flows. Suitable regularisations are utilised to secure numerical stability. Two new models have been

  18. 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

  19. 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.

  20. ANS shell elements with improved transverse shear accuracy. [Assumed Natural Coordinate Strain

    NASA Technical Reports Server (NTRS)

    Jensen, Daniel D.; Park, K. C.

    1992-01-01

    A method of forming assumed natural coordinate strain (ANS) plate and shell elements is presented. The ANS method uses equilibrium based constraints and kinematic constraints to eliminate hierarchical degrees of freedom which results in lower order elements with improved stress recovery and displacement convergence. These techniques make it possible to easily implement the element into the standard finite element software structure, and a modified shape function matrix can be used to create consistent nodal loads.

  1. 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

  2. Accumulation of astaxanthin by a new Haematococcus pluvialis strain BM1 from the white sea coastal rocks (Russia).

    PubMed

    Chekanov, Konstantin; Lobakova, Elena; Selyakh, Irina; Semenova, Larisa; Sidorov, Roman; Solovchenko, Alexei

    2014-08-01

    We report on a novel arctic strain BM1 of a carotenogenic chlorophyte from a coastal habitat with harsh environmental conditions (wide variations in solar irradiance, temperature, salinity and nutrient availability) identified as Haematococcus pluvialis Flotow. Increased (25‰) salinity exerted no adverse effect on the growth of the green BM1 cells. Under stressful conditions (high light, nitrogen and phosphorus deprivation), green vegetative cells of H. pluvialis BM1 grown in BG11 medium formed non-motile palmelloid cells and, eventually, hematocysts capable of a massive accumulation of the keto-carotenoid astaxanthin with a high nutraceutical and therapeutic potential. Routinely, astaxanthin was accumulated at the level of 4% of the cell dry weight (DW), reaching, under prolonged stress, 5.5% DW. Astaxanthin was predominantly accumulated in the form of mono- and diesters of fatty acids from C16 and C18 families. The palmelloids and hematocysts were characterized by the formation of red-colored cytoplasmic lipid droplets, increasingly large in size and number. The lipid droplets tended to merge and occupied almost the entire volume of the cell at the advanced stages of stress-induced carotenogenesis. The potential application of the new strain for the production of astaxanthin is discussed in comparison with the H. pluvialis strains currently employed in microalgal biotechnology. PMID:25196836

  3. Accumulation of Astaxanthin by a New Haematococcus pluvialis Strain BM1 from the White Sea Coastal Rocks (Russia)

    PubMed Central

    Chekanov, Konstantin; Lobakova, Elena; Selyakh, Irina; Semenova, Larisa; Sidorov, Roman; Solovchenko, Alexei

    2014-01-01

    We report on a novel arctic strain BM1 of a carotenogenic chlorophyte from a coastal habitat with harsh environmental conditions (wide variations in solar irradiance, temperature, salinity and nutrient availability) identified as Haematococcus pluvialis Flotow. Increased (25‰) salinity exerted no adverse effect on the growth of the green BM1 cells. Under stressful conditions (high light, nitrogen and phosphorus deprivation), green vegetative cells of H. pluvialis BM1 grown in BG11 medium formed non-motile palmelloid cells and, eventually, hematocysts capable of a massive accumulation of the keto-carotenoid astaxanthin with a high nutraceutical and therapeutic potential. Routinely, astaxanthin was accumulated at the level of 4% of the cell dry weight (DW), reaching, under prolonged stress, 5.5% DW. Astaxanthin was predominantly accumulated in the form of mono- and diesters of fatty acids from C16 and C18 families. The palmelloids and hematocysts were characterized by the formation of red-colored cytoplasmic lipid droplets, increasingly large in size and number. The lipid droplets tended to merge and occupied almost the entire volume of the cell at the advanced stages of stress-induced carotenogenesis. The potential application of the new strain for the production of astaxanthin is discussed in comparison with the H. pluvialis strains currently employed in microalgal biotechnology. PMID:25196836

  4. 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.

  5. 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.

  6. 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

  7. 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

    2015-06-01

    The study of a heterogeneous ductile shear zone that developed at ~ 500 °C and 0.2 GPa during post-magmatic cooling of a granodiorite has allowed 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 thermobarometry to mylonites. Differently strained quartz across the shear zone shows a heterogeneous distribution of Ti concentrations ([Ti]) (measured by Secondary Ion Mass Spectrometry, SIMS) ranging between 2 and 45 ppm. Quartz cathodoluminescence (CL) is proven by spectral analysis to be correlated with [Ti], allowing CL images to be 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. Resetting to lower [Ti] occurred locally: (i) in haloes surrounding titanite and biotite inclusions ([Ti] as low as 6 ppm); (ii) along grain boundaries; and (iii) towards the interface of quartz domains with other mineral domains. With increasing strain, quartz underwent progressive grain size 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 (SGR). Dynamic recrystallization by SGR, associated with prism < a > slip, became increasingly dominant over GBM as strain increased towards the shear zone core. Significant resetting of Ti in quartz only occurred in high strain domains (at shear strain γ probably >> 10) in the shear zone core where fine recrystallization amounts to 50-60% by area and coarser cores are strongly sub-structured. These domains are not compositionally homogeneous and still show a range of [Ti] mostly 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 ~ 2 ppm. The pristine

  8. 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

  9. 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.

  10. 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

  11. 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

  12. Distributed Anelastic Strain and its Relationship to Compliant Zones Surrounding Active Faults of the Eastern California Shear Zone

    NASA Astrophysics Data System (ADS)

    Shelef, E.; Oskin, M.; Fialko, Y.

    2006-12-01

    Geologic measurements of distributed anelastic strain (DAS) adjacent to active strike slip faults of the Mojave Desert portion of the Eastern California shear zone quantify the magnitude, mechanism, temporal evolution, and relationship of DAS to fault compliant zones imaged via InSAR. Prefaulting markers (mylonitic lineation, dikes, and faults assumed linear prior to dextral faulting) in crystalline rocks next to the Harper Lake fault and Calico fault indicate that DAS accounts for 6 to 23 percent of total displacement and that this displacement scales with fault slip. We conclude that DAS is a significant, active process that is not restricted to the initial fault propagation stage. We find that the width of the zone of DAS is 400-700 m on each side of the faults studied, irrespective of total fault slip. 60 percent of the displacement due to DAS occurs within 100 m of the Calico fault. A similar zone of more intense deformation occurs adjacent to the Harper Lake fault. These 100m- wide-zones are of the same extent but much less intensely deformed compared to the damage zones surrounding the San Andreas fault. Based on these relationships, we hypothesize that damage feedback progressively focuses DAS into a stable, approximately 100-m-wide-zone where its intensity can increase proportionally to fault slip. Disruption of linear markers supports that DAS in crystalline rocks occurs via slip along secondary faults and small-scale block rotation with block sizes decreasing with proximity to faults. The widths of the geologically documented zones of DAS in the Eastern California shear zone are similar to the approximately 1 km width of compliant zones modeled from InSAR observations of surface deformation due to stress changes caused by nearby earthquakes. This correlation suggests a relationship between damage- reduction of shear modulus and displacement via DAS. Paleomagnetic measurements of prefaulting and syntectonically emplaced volcanic rocks in sedimentary

  13. 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

  14. 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.

  15. 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. PMID:25768445

  16. Shear-accelerated crystallization in a supercooled atomic liquid

    NASA Astrophysics Data System (ADS)

    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 γ˙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.

  17. Earthquake depths and the relation to strain accumulation and stress near strike-slip faults in southern California

    SciTech Connect

    Sanders, C.O. )

    1990-04-10

    Earthquakes in the major fault zones are predominantly deep. Earthquakes in the crustal blocks bounding the fault zones are predominantly shallow. In the San Jacinto fault zone, maximum earthquake depths correlate with surface heat flow. These relations together with focal mechanisms, geodetic strain measurements, and fault zone models are consistent with the following ideas: (1) Interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes. (2) The aseismic slip in a narrow fault zone in the brittle-plastic transition region concentrates strain at the base of the brittle fault zone. (3) Deep earthquakes occur in thelower part of the brittle fault zone due to stick-slip failure of highly stressed patches. (4) Background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding (deep) and stick-slip (shallow) regions of the fault zone. Furthermore, the difference in seismicity between the San Jacinto and southern San Andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases. (5) Shear stress may be less in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks. (6) In the stress field produced by plate motion and slip in the deep fault zone, the upper brittle fault zone is not oriented favorably for shear failure. Lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation.

  18. 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

  19. 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

  20. 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.

    2015-07-01

    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 show a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high- and low-strain microstructures in the shear zone represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. Instead, we propose that the microstructural and mineralogical changes in the shear zone centre arise from a local metasomatic alteration around a brittle precursor. When the weaker fine-grained microstructure is established, the further flow is controlled by transient porosity created at (i) grain boundaries in fine

  1. 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

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

    PubMed

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

    2013-09-01

    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

  3. Acoustic radiation force impulse induced strain elastography and point shear wave elastography for evaluation of thyroid nodules

    PubMed Central

    Huang, Xian; Guo, Le-Hang; Xu, Hui-Xiong; Gong, Xue-Hao; Liu, Bo-Ji; Xu, Jun-Mei; Zhang, Yi-Feng; Li, Xiao-Long; Li, Dan-Dan; Qu, Shen; Fang, Lin

    2015-01-01

    The aim of the study was to evaluate the diagnostic performance of acoustic radiation force impulse (ARFI) induced strain elastography (SE), point shear wave elastography (p-SWE), and their combined use in differentiating thyroid nodules. This retrospective study included 155 thyroid nodules (94 benign and 61 malignant) in 136 patients. Ultrasound, ARFI-induced SE and p-SWE were performed on each nodule. Receiver operating characteristic curve (ROC) analyses were performed to assess the diagnostic efficacy of ARFI-induced SE, p-SWE and their combined use to distinguish benign from malignant thyroid nodules with histological results used as the reference standard. The areas under the ROC for ARFI-induced SE, p-SWE, and their combined use were 0.828, 0.829, and 0.840, respectively (both P > 0.05). The specificity of ARFI-induced SE was higher than that of p-SWE as well as their combined use (both P < 0.05). The combination of the two methods significantly improved the diagnostic sensitivity and NPV compared with either ARFI-induced SE or p-SWE alone (both P < 0.05). For nodules ≤ 10 mm, the combination of the two methods significantly improved the diagnostic sensitivity only. For nodules > 10 mm, there were no significant differences in sensitivity and NPV among the three methods in differentiating thyroid nodules (all P > 0.05). In conclusions, ARFI-induced SE and p-SWE are both valuable tools for detecting malignant thyroid nodules. The combined use of ARFI-induced SE and p-SWE improves the diagnostic sensitivity and NPV significantly whereas ARFI-induced SE alone achieves the highest specificity. PMID:26379890

  4. New Insights into Strain Accumulation and Release in the Central and Northern Walker Lane, Pacific-North American Plate Boundary, California and Nevada, USA

    NASA Astrophysics Data System (ADS)

    Bormann, Jayne M.

    The Walker Lane is a 100 km-wide distributed zone of complex transtensional faulting that flanks the eastern margin of the Sierra Nevada. Up to 25% of the total Pacific-North American relative right-lateral plate boundary deformation is accommodated east of the Sierra Nevada, primarily in the Walker Lane. The results of three studies in the Central and Northern Walker Lane offer new insights into how constantly accumulating plate boundary shear strain is released on faults in the Walker Lane and regional earthquake hazards. This research is based on the collection and analysis of new of geologic and geodetic datasets. Two studies are located in the Central Walker Lane, where plate boundary deformation is accommodated on northwest trending right-lateral faults, east-northeast trending left-lateral faults, and north trending normal faults. In this region, a prominent set of left-stepping, en-echelon, normal fault-bounded basins between Walker Lake and Lake Tahoe fill a gap in Walker Lane strike slip faults. Determining how these basins accommodate shear strain is a primary goal of this research. Paleoseismic and neotectonic observations from the Wassuk Range fault zone in the Walker Lake basin record evidence for at least 3 Holocene surface rupturing earthquakes and Holocene/late Pleistocene vertical slip rates between 0.4-0.7 mm/yr on the normal fault, but record no evidence of right-lateral slip along the rangefront fault. A complementary study presents new GPS velocity data that measures present-day deformation across the Central Walker Lane and infers fault slip and block rotation rates using an elastic block model. The model results show a clear partitioning between distinct zones of strain accommodation characterized by (1) right-lateral translation of blocks on northwest trending faults, (2) left-lateral slip and clockwise block rotations between east and northeast trending faults, and (3) right-lateral oblique normal slip with minor clockwise block rotations

  5. 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.

  6. A joint analysis of GPS and PS-InSAR to infer the fault segmentation and interseismic strain accumulation for the North Tabriz fault, NW Iran

    NASA Astrophysics Data System (ADS)

    Su, Zhe; Hu, Jyr-Ching; Talebian, Morteza; Karimzadeh, Sadra

    2014-05-01

    The accommodation of deformation due to the collision of between Arabian and Eurasian plates dominates in shortening along the Greater and Lesser Caucasus to the north and conjugated strike-slip fault in Turkish and Armenia plateau. Several discontinuous strike-slip faults are distributed all over the NW Iran to the south, which control the lateral motion of micro-blocks. The North Tabriz fault (NTF) in one of them. Furthermore, the area of NW Iran is suggested as a possible southward termination of the 2000-km long North Anatolian Fault into and northward termination of the 600-km long Zagros Main Recent fault. The reason why such a large-scale strike-slip fault system disappears in the NW Iran and the interaction with the other small fault systems is unclear right now. After the 1780 earthquake (M ~7.4), no big earthquake (Mw > 7.0) has occurred along the NTF for almost three centuries. Thus the GPS data and small-baselines PS-InSAR technique are used to study the interseismic strain accumulation and slip deficit distribution along the NTF. We also calculate the maximum and minimum principal strain rates, rotational and dextral shear strain rates across the NTF. Based on the 6 profiles of deformation rate along line of sight (LOS) towards to satellite, we find that the northern and central segment of the NTF is more active than the southern one. In addition, the extensional deformation dominates in the southern segment of the NTF. We also use the Okada's code to inverse the inter-seismic slip on the fault patches. The locking depth of the northern and central segments is ~10 km while the southern one demonstrates a deeper locking depth of ~15-20 km. We estimate recurrence interval is ~1500 years for a big earthquake M > 7.0. If the Gailatu-Siak-Khoy and North Mishu faults are the segments of the NTF, this recurrence interval might be underestimated in terms of our numerical simulation.

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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

  13. Significance of Bacillus subtilis strain SJ-101 as a bioinoculant for concurrent plant growth promotion and nickel accumulation in Brassica juncea.

    PubMed

    Zaidi, Sabina; Usmani, Saima; Singh, Braj Raj; Musarrat, Javed

    2006-08-01

    In this study, a nickel (Ni)-tolerant Bacillus subtilis strain SJ-101 was characterized based on the 16SrDNA homology and phylogenetic analysis. The role of this strain ascertained in facilitating Ni accumulation in the Indian mustard plant (Brassica juncea [L]. Czern and Coss) var. Pusa Bold (DIR-50), to elucidate the potential of Ni phytoremediation in combination with metal-tolerant rhizobacteria. The data revealed that the plants exposed to NiCl2 (1750 mg kg(-1)) in soil bioaugmented with strain SJ-101 have accumulated 0.147% Ni vis-à-vis 0.094% accumulation in dry biomass of the plants grown in uninoculated soil. The strain SJ-101 has also exhibited the capability of producing indole acetic acid (IAA) (55 microg ml(-1)), and solubilizing inorganic phosphate (90 microg ml(-1)) in specific culture media. The pot culture experiments clearly demonstrated the beneficial effects of bioinoculant strain SJ-101 with significant increase (p<0.05) in the plant growth attributes in untreated control soil. Furthermore, the protective effect of the strain SJ-101 against Ni phytotoxicity was evident in plants grown in soil treated with NiCl2 in concentration range of 250-1750 mg kg(-1). Thus, it is suggested that the strain SJ-101 owing to its intrinsic abilities of plant growth promotion, and attenuation of soil Ni by biosorption and bioaccumulation, could be exploited for bacteria-assisted phytoaccumulation of this toxic heavy metal from contaminated sites. PMID:16487570

  14. 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

  15. 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.

  16. 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

  17. Endovascular shear strain elastography for the detection and characterization of the severity of atherosclerotic plaques: in vitro validation and in vivo evaluation.

    PubMed

    Majdouline, Younes; Ohayon, Jacques; Keshavarz-Motamed, Zahra; Roy Cardinal, Marie-Hélène; Garcia, Damien; Allard, Louise; Lerouge, Sophie; Arsenault, Frédéric; Soulez, Gilles; Cloutier, Guy

    2014-05-01

    This work explores the potential of shear strain elastograms to identify vulnerable atherosclerotic plaques. The Lagrangian speckle model estimator (LSME) elasticity imaging method was further developed to estimate shear strain elasticity (SSE). Three polyvinyl alcohol cryogel vessel phantoms were imaged with an intravascular ultrasound (IVUS) scanner. The estimated SSE maps were validated against finite-element results. Atherosclerosis was induced in carotid arteries of eight Sinclair mini-pigs using a combination of surgical techniques, diabetes and a high-fat diet. IVUS images were acquired in vivo in 14 plaques before euthanasia and histology. All plaques were characterized by high magnitudes in SSE maps that correlated with American Heart Association atherosclerosis stage classifications (r = 0.97, p < 0.001): the worse the plaque condition the higher was the absolute value of SSE, i.e. |SSE| (e.g., mean |SSE| was 3.70 ± 0.40% in Type V plaques, whereas it was reduced to 0.11 ± 0.01% in normal walls). This study indicates the feasibility of using SSE to highlight atherosclerotic plaque vulnerability characteristics. PMID:24495438

  18. Applications of probabilistic methods in geotechnical engineering. Part 2. Analysis of documented case histories using a stochastic model for seismically generated pore pressure and shear strain potential

    SciTech Connect

    Kavazanjian, E. Jr.; Chameau, J.L.; Clough, G.W.; Hadk-Hamou, T.

    1983-09-01

    This report presents the basics of a new stochastic model for seismically-generated pore pressure and shear strain potential and illustrates its use for documented case histories. Model parameters are chosen according to available information on the variability of soil properties, and it is applied to sites where liquefaction was observed and where no evidence of liquefaction was observed and where no evidence of liquefaction was observed after major seismic events. Results of the analysis are in substantial agreement with observed field behavior, indicating that this model can be used in a predictive capacity if parameters are chosen correctly. An application of the model to a comprehensive risk analysis of seismically induced initial liquefaction is also briefly described. An example using available seismic information for a hypothetical soil site near San Francisco is presented to illustrate the use of this type of model. Two models are applied to documented case histories to demonstrate their applicability and to illustrate how the probabilistic design parameters are chosen. The probabilistic pore pressure model developed by Chameau (1980) and the probabilistic shear strain model developed by Hadj Hamou (1982) are used herein to analyze the behavior of three sites where liquefaction did and did not occur during earthquakes.

  19. 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

  20. Probing the cross-effect of strains in non-linear elasticity of nearly regular polymer networks by pure shear deformation.

    PubMed

    Katashima, Takuya; Urayama, Kenji; Chung, Ung-il; Sakai, Takamasa

    2015-05-01

    The pure shear deformation of the Tetra-polyethylene glycol gels reveals the presence of an explicit cross-effect of strains in the strain energy density function even for the polymer networks with nearly regular structure including no appreciable amount of structural defect such as trapped entanglement. This result is in contrast to the expectation of the classical Gaussian network model (Neo Hookean model), i.e., the vanishing of the cross effect in regular networks with no trapped entanglement. The results show that (1) the cross effect of strains is not dependent on the network-strand length; (2) the cross effect is not affected by the presence of non-network strands; (3) the cross effect is proportional to the network polymer concentration including both elastically effective and ineffective strands; (4) no cross effect is expected exclusively in zero limit of network concentration in real polymer networks. These features indicate that the real polymer networks with regular network structures have an explicit cross-effect of strains, which originates from some interaction between network strands (other than entanglement effect) such as nematic interaction, topological interaction, and excluded volume interaction. PMID:25956121

  1. 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

  2. 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

  3. Interseismic strain accumulation across the North Tabriz Fault (NW Iran) deduced from InSAR time series

    NASA Astrophysics Data System (ADS)

    Karimzadeh, Sadra; Cakir, Ziyadin; Osmanoğlu, Batuhan; Schmalzle, Gina; Miyajima, Masakatsu; Amiraslanzadeh, Reza; Djamour, Yahya

    2013-05-01

    We present the surface deformation along the North Tabriz Fault (NTF) deduced from Synthetic Aperture Radar Interferometry (InSAR) technique. The NTF, a major right-lateral strike-slip fault within the active Arabia-Eurasia collision zone, is located 40-45 km southwest of the Mw 6.5 and Mw 6.3, August 11, 2012 earthquake sequence that caused heavy damage and more than 300 deaths in Ahar, NW Iran. InSAR time series analysis of 17 ENVISAT radar images acquired between 2004 and 2010 using combination of the permanent scatterers InSAR (PSI) and the small baseline InSAR (SBAS) approach reveals sub-centimeter interseismic strain accumulation across the NTF and rapid subsidence in the Tabriz basin. Elastic dislocation modeling of the mean line-of-sight velocity field estimated from SBAS time series yields an average slip rate of 8.7 ± 2.5 mm/year with a locking depth of 15.8 ± 10.8 km. This rate is consistent with previous geodetic estimates based on recent Global Positioning System measurements, and suggests a recurrence interval of 250-300 years for major earthquakes of Mw 7.0-7.3 on the NTF, much shorter than those estimated from paleoseismic investigations (821 ± 176 years). This in turn implies a high seismic potential on the NTF taking into account the occurrence of the two last earthquakes on the NTF in 1721 and 1780. SAR time series analysis also reveals three regions of rapid subsidence with a maximum rate of 20 mm/year near the Tabriz thermal power plant in the Tabriz basin. Piezometric data from groundwater wells suggest that accelerated subsidence over the last several years may result from fluctuations in the ground water table.

  4. 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, G.; Menegon, L.; Archanjo, C. J.

    2015-10-01

    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 ⟨a⟩ and rhomb ⟨a⟩ slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the transposed 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 crystal plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the polyphase

  5. 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. PMID:25771890

  6. Forearc Sliver Translation, a Lack of Arc-Normal Strain Accumulation, and Interplate Thrust Earthquakes: GPS Geodesy in Western Nicaragua

    NASA Astrophysics Data System (ADS)

    Turner, H. L.; Mattioli, G. S.; Jansma, P. E.; Styron, R. H.

    2007-05-01

    We have been investigating the kinematics of the Nicaraguan forearc using campaign GPS measurements of our geodetic network made over the last seven years (Turner et al., 2007). We currently have interseismic velocities for 18 campaign sites and have installed 10 additional sites in the backarc to investigate the nature of the transition from forearc sliver motion to stable Caribbean Plate motion. Our work focusing on the later issue is presented elsewhere at this meeting (Styron et al., 2007). Corrections for modeled coseismic offsets from the Jan. 13, 2001 Mw7.7 earthquake off the coast of El Salvador have been applied to our campaign site velocities. Some of our time-series are also strongly affected by coseismic and postseismic effects of the Oct. 9, 2004 Mw6.9 earthquake off of the coast of Nicaragua. The geodetic effects of this event are being removed from the affected time-series for interseismic velocity analysis. We have also derived interseismic velocities for five continuous GPS sites in the region. Our GPS results confirm previous predictions of northwest transport of a forearc sliver with an average Northwest velocity of ~15 mm yr-1, but show little evidence for an arc- normal component of strain accumulation associated with locking on the subduction interface. However, the amount of seismicity along this section of the Middle America Trench, including several recent large events such as the 1992 Mw7.6 and 2004 Mw6.9 earthquakes, indicates some amount of locking is present. Several possibilities may account for the apparent contradiction between the GPS results and observed seismicity. The locked zone may be too shallow and too far offshore for the arc-normal component to show up in our network, or the arc-normal signal may be masked by post-seismic effects from the 1992 offshore earthquake. If coupling between the downgoing slab and the overriding plate is weak or limited to a small seismogenic zone, then arc-parallel motion of the forearc sliver may

  7. 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

  8. 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

  9. [The accumulation of proteins with chitinase activity in the culture media of the parent and mutant Serratia marcescens strain grown in the presence of mitomycin C].

    PubMed

    Iusupova, D V; Petukhova, E V; Sokolova, R B; Gabdrakhmanova, L A

    2002-01-01

    The study of the accumulation pattern of extracellular proteins with chitinase activity in the parent Serratia marcescens strain Bú 211 (ATCC 9986) grown in the presence of mitomycin C and its mutant strain with the constitutive synthesis of chitinases grown in the absence of the inducer showed that chitinase activity appeared in the culture liquids of both strains at the end of the exponential phase (4 h of growth) and reached a maximum in the stationary phase (18-20 h of growth). The analysis of the culture liquids (12 h of growth) by denaturing electrophoresis in PAAG followed by the protein renaturation step revealed the presence of four extracellular proteins with chitinase activity and molecular masses of 21, 38, 52, and 58 kDa. PMID:12449629

  10. 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

  11. Coseismic deformations of the 2015 MW 7.8 Gorkha earthquake and interseismic strain accumulation in the Himalayan tectonic belt and Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Wu, Yanqiang; Jiang, Zaisen; Liang, Hongbao; Chang, Liu; Chen, Changyun; Zhu, Shuang; Zhao, Jingyang; Du, Jiliang

    2016-02-01

    The principal strain rate, derived from GPS velocities from the Tibetan Plateau and the India Plate, shows that the Himalayan tectonic belt exhibits compression deformation in a NE-NS-NE direction from the west to the east. The GPS velocity profiles reflect that the distribution of strain accumulation is uneven: there is a 17.1 mm/yr. compressive deformation distributed over 400 km along 85° E longitude, a 20.9-22.2 mm/yr. compressive deformation dispersed across 400-500 km along 79° E longitude, and a 15.3-16.9 mm/yr. compressive deformation spread across 500-600 km along 91° E longitude. The MW 7.8 Gorkha earthquake occurred at the edge of an intense compression deformation zone of about 6.0 × 10- 8/yr. in a north-south direction, and an about 90% compressive strain is absorbed in the 300 km region near the Main Frontal Thrust (MFT). Coseismic displacements, larger than three standard deviations (3SD), are mainly concentrated within 360 km from the epicenter. The nodal plane of the main shock divides the areas where tensile strain release in an exponential attenuation pattern is dominant to the north, and where compressive strain with upward movement is dominant to the south. The results inversed by the SDM program reveal that the maximal slip of the Gorkha earthquake is 5.33 m, and its moment magnitude is MW 7.85, and the largest stress drop is 4.21 Mpa. Slips larger than 0.5 m are mainly distributed in a region approximately 135 km × 105 km, which show that the rupture of the Gorkha earthquake does not reach the surface. Finally, we estimate that the recurrence period of this earthquake is about 166 ± 20 years according to the strain accumulation before the earthquake and the coseismic release feature.

  12. Transient solution for a plane-strain fracture driven by a shear-thinning, power-law fluid

    NASA Astrophysics Data System (ADS)

    Garagash, D. I.

    2006-12-01

    This paper analyses the problem of a fluid-driven fracture propagating in an impermeable, linear elastic rock with finite toughness. The fracture is driven by injection of an incompressible viscous fluid with power-law rheology. The relation between the fracture opening and the internal fluid pressure and the fracture propagation in mobile equilibrium are described by equations of linear elastic fracture mechanics (LEFM), and the flow of fluid inside the fracture is governed by the lubrication theory. It is shown that for shear-thinning fracturing fluids, the fracture propagation regime evolves in time from the toughness- to the viscosity-dominated regime. In the former, dissipation in the viscous fluid flow is negligible compared to the dissipation in extending the fracture in the rock, and in the later, the opposite holds. Corresponding self-similar asymptotic solutions are given by the zero-viscosity and zero-toughness (J. Numer. Anal. Meth. Geomech. 2002; 26:579-604) solutions, respectively. A transient solution in terms of the crack length, the fracture opening, and the net fluid pressure, which describes the fracture evolution from the early-time (toughness-dominated) to the large-time (viscosity-dominated) asymptote is presented and some of the implications for the practical range of parameters are discussed. Copyright

  13. 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

  14. An apparent shear zone trending north-northwest across the Mojave Desert into Owens Valley, eastern California

    SciTech Connect

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

    1990-11-01

    Strain rates measured at four geodetic networks in eastern California situated between northern Owens Valley and Transverse Ranges along a small circle drawn about the Pacific-North America pole of rotation are remarkably consistent. Each exhibits 0.14 {mu}rad/yr simple right-lateral engineering-shear-strain accumulation across the local vertical plane tangent to the small circle. Local faults (e.g., Owens Valley, Garlock, Helendale) traversing these networks are not as closely aligned with the vertical planes of maximum shear-strain accumulation as is the local tangent to the small circle. A fifth network slightly east of the small circle shows no significant strain accumulation. Thus, a shear zone trending N35{degree}W from near the eastern end of the big bend of the San Andreas fault to northern Owens Valley is indicated by these data. This corresponds to the Eastern California shear zone proposed on geological evidence by Dokka and Travis. The shear zone carries {approximately}8 mm/yr of the Pacific-North America relative plate motion from the San Andreas fault north-northwest across the Mojave Desert into Owens Valley and the northern Basin and Range province. The shear zone observed at the surface may be a manifestation of a through-going subcrustal fault.

  15. Influence of Volatile Fatty Acids on Nitrite Accumulation by a Pseudomonas stutzeri Strain Isolated from a Denitrifying Fluidized Bed Reactor

    PubMed Central

    van Rijn, J.; Tal, Y.; Barak, Y.

    1996-01-01

    Intermediate nitrite accumulation during denitrification by Pseudomonas stutzeri isolated from a denitrifying fluidized bed reactor was examined in the presence of different volatile fatty acids. Nitrite accumulated when acetate or propionate served as the carbon and electron source but did not accumulate in the presence of butyrate, valerate, or caproate. Nitrite accumulation in the presence of acetate was caused by differences in the rates of nitrate and nitrite reduction and, in addition, by competition between nitrate and nitrite reduction pathways for electrons. Incubation of the cells with butyrate resulted in a slower nitrate reduction rate and a faster nitrite reduction rate than incubation with acetate. Whereas nitrate inhibited the nitrite reduction rate in the presence of acetate, no such inhibition was found in butyrate-supplemented cells. Cytochromes b and c were found to mediate electron transport during nitrate reduction by the cells. Cytochrome c was reduced via a different pathway when nitrite-reducing cells were incubated with acetate than when they were incubated with butyrate. Furthermore, addition of antimycin A to nitrite-reducing cells resulted in partial inhibition of electron transport to cytochrome c in acetate-supplemented cells but not in butyrate-supplemented cells. On the basis of these findings, we propose that differences in intermediate nitrite accumulation are caused by differences in electron flow to nitrate and nitrite reductases during oxidation of either acetate or butyrate. PMID:16535368

  16. 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

  17. 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.

  18. Synchrotron-FTIR microspectroscopy enables the distinction of lipid accumulation in thraustochytrid strains through analysis of individual live cells.

    PubMed

    Vongsvivut, Jitraporn; Heraud, Philip; Gupta, Adarsha; Thyagarajan, Tamilselvi; Puri, Munish; McNaughton, Don; Barrow, Colin J

    2015-02-01

    The superior characteristics of high photon flux and diffraction-limited spatial resolution achieved by synchrotron-FTIR microspectroscopy allowed molecular characterization of individual live thraustochytrids. Principal component analysis revealed distinct separation of the single live cell spectra into their corresponding strains, comprised of new Australasian thraustochytrids (AMCQS5-5 and S7) and standard cultures (AH-2 and S31). Unsupervised hierarchical cluster analysis (UHCA) indicated close similarities between S7 and AH-7 strains, with AMCQS5-5 being distinctly different. UHCA correlation conformed well to the fatty acid profiles, indicating the type of fatty acids as a critical factor in chemotaxonomic discrimination of these thraustochytrids and also revealing the distinctively high polyunsaturated fatty acid content as key identity of AMCQS5-5. Partial least squares discriminant analysis using cross-validation approach between two replicate datasets was demonstrated to be a powerful classification method leading to models of high robustness and 100% predictive accuracy for strain identification. The results emphasized the exceptional S-FTIR capability to perform real-time in vivo measurement of single live cells directly within their original medium, providing unique information on cell variability among the population of each isolate and evidence of spontaneous lipid peroxidation that could lead to deeper understanding of lipid production and oxidation in thraustochytrids for single-cell oil development. PMID:25594491

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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

  4. Construction of a Vibrio cholerae Vaccine Candidate Strain O395-N1-E1 which Accumulates Cell-associated Cholera Toxin B Subunit

    PubMed Central

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

    2012-01-01

    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 technical problem that might be solved simply by engineering strains of V. cholerae that express cell-associated CTB that would co-purify with the bacterial cell fraction during manufacture of WC vaccine. Here we report that construction of a V. cholerae O1 classical strain, 0395-N1-E1, that has been engineered to accumulate CTB in the periplasmic fraction by disrupting the epsE gene of type II secretion pathway. 0395-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, 0395-N1. Our results suggest that this type of cholera vaccine candidate strain may assist in preparing improved, effective, and inexpensive oral or parenteral cholera vaccine without the need to purify CTB separately. PMID:18582519

  5. [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

  6. 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

  7. Accumulation of docosahexaenoic acid-rich lipid in thraustochytrid Aurantiochytrium sp. strain T66: effects of N and P starvation and O2 limitation.

    PubMed

    Jakobsen, Anita N; Aasen, Inga M; Josefsen, Kjell D; Strøm, Arne R

    2008-08-01

    Aurantiochytrium sp. strain T66 was grown in batch bioreactor cultures in a defined glutamate- and glycerol-containing growth medium. Exponentially growing cells had a lipid content of 13% (w/w) of dry weight. A fattening of cells fed excess glycerol occurred in the post-exponential growth phase, after the medium was depleted of N or P. Lipid accumulation was also initiated by O2 limitation (below 1% of saturation). N starvation per se, or in combination with O2 limitation, gave the highest lipid content, i.e., 54% to 63% (w/w) of dry weight. The corresponding maximum culture density was 90 to 100 g/l dry biomass. The content of docosahexaenoic acid (22:6n-3) in N starved, well-oxygenated cells reached 29% (w/w) of total fatty acids but increased to 36% to 52% in O2-limited cells, depending on the time span of the limitation. O2-limited cells did not accumulate the monounsaturated fatty acids that were normally present. We inferred that the biological explanation is that O2 limitation hindered the O2-dependent desaturase(s) and favored the O2-independent polyunsaturated fatty acid synthase. The highest overall volumetric productivity of docosahexaenoic acid observed was 93 mg/l/h. Additionally, we present a protocol for quantitative lipid extraction, involving heat and protease treatment of freeze-dried thraustochytrids. PMID:18560831

  8. Transtensional Analyses of Fault Patterns and Strain Provinces of the Eastern California Shear Zone-Walker Lane on the Eastern Margin of the Sierra Nevada Microplate, California and Nevada

    NASA Astrophysics Data System (ADS)

    Taylor, T. R.; Dewey, J. F.

    2008-12-01

    Substantial work on the theory of transtensional strain at various scales has shown that transtension produces triaxial non-plane constrictional strains. At the plate boundary scale, fault geometries predicted by transtensional theory better explain observed fault patterns in the transtensional Eastern California shear zone-Walker Lane than 2D plane strain pure or simple shear solutions. Seemingly heterogeneous fault patterns and strain styles within structural provinces along the higher strain corridor adjacent to the eastern Sierra Nevada microplate margin are reconciled by non-plane strain evaluation, and in the context of triaxial, 3D strain partitioning characteristic of transtensional deformation. Among these structural provinces, which include the Honey Lake-Pyramid Lake region, the Lake Tahoe region, the Mono Lake-Long Valley region, Owens Valley, and the Coso region, all are found to be undergoing coaxially dominated transtension, except for the Mono Lake-Long Valley region which has possibly formed by noncoaxially dominated strain, and the northern Honey Lake-Pyramid Lake region, where the Sierra Nevada microplate boundary zone curves west toward the Mendocino triple junction. The local geometry of the transtensional zone boundary and the microplate transport direction determine the dominant type of non-plane strain. Fault orientations predicted by application of transtensional theory to identify instantaneous strain axes are consistent with those observed in each structural province, and comparatively, are not adequately explained by plane strain kinematic models. The orientations and amount of shortening and elongation of the finite strain ellipsoid axes for each province indicate smaller amounts of shortening, elongation and rotation of axes, and overall less ellipticity, in the coaxially dominated strain areas, and greater shortening, elongation, and rotation, and overall greater ellipticity, in the noncoaxially dominated areas. Exceptions are the

  9. 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.

  10. Transverse shear stiffness of laminated anisotropic shells

    NASA Technical Reports Server (NTRS)

    Cohen, G. A.

    1978-01-01

    Equations are derived for the transverse shear stiffness of laminated anisotropic shells. Without making assumptions for thickness distribution for either transverse shear stresses or strains, constitutive equations for the transverse shear deformation theory of anisotropic heterogeneous shells are found. The equations are based on Taylor series expansions about a generic point for stress resultants and couples, identically satisfying plate equilibrium equations. These equations are used to find statically correct expressions for in-surface stresses, transverse shear stresses, and the area density of transverse shear strain energy, in terms of transverse shear stress resultants and redundants. The application of Castigliano's theorem of least work minimizes shear strain energy with respect to the redundants. Examples are presented for several laminated walls. Good agreement is found between the results and those of exact three-dimensional elasticity solutions for the cylindrical bending of a plate.

  11. 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.

  12. 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

  13. 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.

  14. Homogeneous crystal-rich vs. zoned crystal-poor ignimbrites: how much strain accumulates in large magma reservoirs between a new magma recharge and eruption? (Invited)

    NASA Astrophysics Data System (ADS)

    Huber, C.; Bachmann, O.; Dufek, J.; Manga, M.

    2010-12-01

    Silicic volcanic fields often display two different types of deposits: (1) crystal-rich dacitic magmas that display a striking homogeneity at the hand-sample scale and (2 dominantly crystal-poor, rhyolitic magmas that commonly grade into more mafic and more crystal-rich magmas towards the end of the eruption. An well-documented example of this dichotomy is the Central San Juan Volcanic Field (Colorado, USA), where, from the 9 major ignimbrites erupted during the climactic stage (~28.6 to 26.9 Ma), 4 occur as zoned crystal-poor to crystal-rich units and the remaining 5 form crystal-rich homogeneous deposits (make sure you explain what zoned means). In this presentation, we discuss different thermal and mechanical processes that influence the homogeneity of magmas as they evolve in shallow reservoirs. For magma bodies that are able to convect, we discuss the effect of stirring and introduce a new metric for their homogeneity for time-dependent convection. We show that the strain accumulated during 5-10 convective overturns is necessary to homogenize a magma to the hand-sample scale. In contrast, crystal-rich magmas do not experience any/enough stirring as they reach a rigid mush state. For these magmas, we discuss the effect of latent heat buffering as an agent for homogenization of temperature and crystallinity near the solidus. In order to become eruptible again, a crystal mush requires a reactivation event usually, usually attributed to the injection of new, hotter magma. We show that the time required to reactivate a mush, in every relevant case, greatly exceeds the time required to accumulate 5-10 overturns for the part of the mush that is able to convect. This difference in time-scales explains why reactivated mushes are inherently homogenous when they erupt. On the other hand, dominantly crystal-poor magmas do not need to be reactivated. Their homogeneity is governed by the competition between the time between the introduction of heterogeneities (for example

  15. 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.

  16. 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.

  17. Strain on the san andreas fault near palmdale, california: rapid, aseismic change.

    PubMed

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

    1981-01-01

    Frequently repeated strain measurements near Palmdale, California, during the period from 1971 through 1980 indicate that, in addition to a uniform accumulation of right-lateral shear strain (engineering shear, 0.35 microradian per year) across the San Andreas fault, a 1-microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between February and November 1979. Subsequently (November 1979 to March 1980), about half of the contraction was recovered. This sequence of strain changes can be explained in terms of south-southwestward migration of a slip event consisting of the south-southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers. The large strain change in 1979 corresponds to the passage of the slip event beneath the San Andreas fault. PMID:17731244

  18. Seismic slip and down-dip strain rates in wadati-benioff zones.

    PubMed

    Bevis, M

    1988-06-01

    The rate of accumulation of seismic moment in Wadati-Benioff zones is used to estimate strain rates in subducting slabs that are sinking through the asthenosphere. Between depths of 75 and 175 kilometers a typical down-dip strain rate is about 10(-15) per second, which implies that slabs in this depth range typically accumulate strain of order 10(-1). This result is in accord with geometrical arguments that subducted slabs must experience large membrane strains to deform to their observed shapes. Mantle seismicity (repeated catastrophic shear failure) is apparently a primary mechanism by which large membrane strains accumulate in the cold cores of subducting slabs. Slabs are penetratively deformed, and they have low flexural rigidity compared to oceanic plates at the earth's surface. PMID:17815851

  19. 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.

  20. 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

  1. Mechanical properties of graphynes under shearing and bending

    NASA Astrophysics Data System (ADS)

    Yi, Lijun; Zhang, Yingyan; Feng, Xiqiao; Chang, Tienchong; Wang, Ji; Du, Jianke; Zhou, Jianxin

    2016-05-01

    Graphynes are the allotrope of graphene. In this work, extensive molecular dynamics simulations are performed on four different graphynes ( α - , β - , γ - , and 6,6,12-graphynes) to explore their mechanical properties (shear modulus, shear strength, and bending rigidity) under shearing and bending. While the shearing properties are anisotropic, the bending rigidity is almost independent of the chirality of graphynes. We also find that the shear modulus and shear fracture strength of graphynes decrease with increasing temperature. The effect of the percentage of the acetylenic linkages on the shear mechanical properties and bending rigidity is investigated. It is shown that the fracture shear strengths and bending rigidities of the four types of graphynes decrease, while the fracture shear strain increases, with increasing percentages of the acetylenic linkages. Significant wrinkling is observed in graphyne under shear strain. The influence of the temperatures and percentages of the acetylenic linkages on the ratio of amplitude-to-wavelength in the wrinkles are examined.

  2. 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

  3. Improved Correlation of Strain Indices with Cognitive Dysfunction with Inclusion of Adventitial Layer with Carotid Plaque.

    PubMed

    Wang, X; Mitchell, C C; Varghese, T; Jackson, D C; Rocque, B G; Hermann, B P; Dempsey, R J

    2016-05-01

    Plaque instability may lead to chronic embolization, which in turn may contribute to progressive cognitive decline. Accumulated strain tensor indices over a cardiac cycle within a pulsating carotid plaque may be viable biomarkers for the diagnosis of plaque instability. Using plaque-only carotid artery segmentations, we recently demonstrated that impaired cognitive function correlated significantly with maximum axial and lateral strain indices within a localized region of interest in plaque. Inclusion of the adventitial layer focuses our strain or instability measures on the vessel wall-plaque interface hypothesized to be a region with increased shearing forces and measureable instability. A hierarchical block-matching motion tracking algorithm developed in our laboratory was used to estimate accumulated axial, lateral, and shear strain distribution in plaques identified with the plaque-with-adventitia segmentation. Correlations of strain indices to the Repeatable Battery for the Assessment of Neuropsychological Status Total score were performed and compared with previous results. Overall, correlation coefficients (r) and significance (p) values improved for axial, lateral, and shear strain indices. Shear strain indices, however, demonstrated the largest improvement. The Pearson correlation coefficients for maximum shear strain and cognition improved from the previous plaque-only analyses of -0.432 and -0.345 to -0.795 and -0.717 with the plaque-with-adventitia segmentation for the symptomatic group and for all patients combined, respectively. Our results demonstrate the advantage of including adventitia for ultrasound carotid strain imaging providing improved association to parameters assessing cognitive impairment in patients. This supports theories of the importance of the vessel wall plaque interface in the pathophysiology of embolic disease. PMID:26025578

  4. Isogeometric analysis of shear bands

    NASA Astrophysics Data System (ADS)

    Berger-Vergiat, Luc; McAuliffe, Colin; Waisman, Haim

    2014-08-01

    Numerical modeling of shear bands present several challenges, primarily due to strain softening, strong nonlinear multiphysics coupling, and steep solution gradients with fine solution features. In general it is not known a priori where a shear band will form or propagate, thus adaptive refinement is sometimes necessary to increase the resolution near the band. In this work we explore the use of isogeometric analysis for shear band problems by constructing and testing several combinations of NURBS elements for a mixed finite element shear band formulation. Owing to the higher order continuity of the NURBS basis, fine solution features such as shear bands can be resolved accurately and efficiently without adaptive refinement. The results are compared to a mixed element formulation with linear functions for displacement and temperature and Pian-Sumihara shape functions for stress. We find that an element based on high order NURBS functions for displacement, temperature and stress, combined with gauss point sampling of the plastic strain leads to attractive results in terms of rate of convergence, accuracy and cpu time. This element is implemented with a -bar strain projection method and is shown to be nearly locking free.

  5. 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.

  6. Determining brittle extension and shear strain using fault length and displacement systematics: Part II: Data evaluation and test of the theory

    NASA Astrophysics Data System (ADS)

    Twiss, Robert J.; Marrett, Randall

    2010-12-01

    We use the theoretical relations developed in Part I of this work to evaluate the self-consistency of fault-length and fault-displacement data gathered in domains of one and two dimensions from the Yucca Mountain area and from the coalfields in south Yorkshire, U.K. These data sets are not all self-consistent. For the Yucca Mt. area, the theory shows that, the volume over which the sampling of the faults must occur should have a horizontal width no smaller than 2.4 times the horizontal length of the largest fault, and a depth no smaller than 1.6 times the vertical extent of the largest vertical-equivalent-fault. It also shows that the volumetric extension must be ≥95% of the extension of a two-dimensional domain and ≥80% of the extension of a one-dimensional domain. The theory successfully accounts for the observed cumulative extensional strain derived from fault-displacement data from a one-dimensional sampling domain at Yucca Mt., Nevada, U.S.A. Faults up to about four orders of magnitude smaller than the largest fault make a significant contribution to the strain. The most robust calculation of cumulative fractional strain requires the parameters inferred from sampling displacement in a one-dimensional domain. This sampling procedure therefore provides the most reliable results.

  7. Shear instabilities in granular flows

    NASA Astrophysics Data System (ADS)

    Goldfarb, David J.; Glasser, Benjamin J.; Shinbrot, Troy

    2002-01-01

    Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows.

  8. Shear instabilities in granular flows.

    PubMed

    Goldfarb, David J; Glasser, Benjamin J; Shinbrot, Troy

    2002-01-17

    Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows. PMID:11797003

  9. 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.

  10. Accumulation of soluble and wall-bound indolic metabolites in Arabidopsis thaliana leaves infected with virulent or avirulent Pseudomonas syringae pathovar tomato strains

    PubMed Central

    Hagemeier, Jens; Schneider, Bernd; Oldham, Neil J.; Hahlbrock, Klaus

    2001-01-01

    The chemical structures and accumulation kinetics of several major soluble as well as wall-bound, alkali-hydrolyzable compounds induced upon infection of Arabidopsis thaliana leaves with Pseudomonas syringae pathovar tomato were established. All identified accumulating products were structurally related to tryptophan. Most prominent among the soluble substances were tryptophan, β-d-glucopyranosyl indole-3-carboxylic acid, 6-hydroxyindole-3-carboxylic acid 6-O-β-d-glucopyranoside, and the indolic phytoalexin camalexin. The single major accumulating wall component detectable under these conditions was indole-3-carboxylic acid. All of these compounds increased more rapidly, and camalexin as well as indole-3-carboxylic acid reached much higher levels, in the incompatible than in the compatible P. syringae/A. thaliana interaction. The only three prominent phenylpropanoid derivatives present in the soluble extract behaved differently. Two kaempferol glycosides remained largely unaffected, and sinapoyl malate decreased strongly upon bacterial infection with a time course inversely correlated with that of the accumulating tryptophan-related products. The accumulation patterns of both soluble and wall-bound compounds, as well as the disease resistance phenotypes, were essentially the same for infected wild-type and tt4 (no kaempferol glycosides) or fah1 (no sinapoyl malate) mutant plants. Largely different product combinations accumulated in wounded or senescing A. thaliana leaves. It seems unlikely that any one of the infection-induced compounds identified so far has a decisive role in the resistance response to P. syringae. PMID:11136235

  11. 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

  12. Shear-enhanced compaction and strain localization in porous limestone: a study based on X-ray Computed Tomography and Digital Image Correlation

    NASA Astrophysics Data System (ADS)

    Ji, Y.; Baud, P.; Hall, S.; Wong, T.

    2011-12-01

    The brittle-ductile transition in porous sandstones has now been studied extensively. Microstructural studies combining various techniques on samples deformed in the laboratory documented the development of a wide variety on strain localization patterns and failure modes in overall agreement with the field observations in various sandstone formations. In contrast, there is a paucity of mechanical and microstructural laboratory data on the brittle-ductile transition in porous carbonates, particularly for the high porosity end-members. This lack of data is related to various specific difficulties associated with the study of inelastic deformation in high porosity limestones: the interplay between microcracking and crystal plasticity even at room temperature, dissolution of calcite in presence of water, etc... The question of strain localization is in particular hard to tackle as conventional microstructural analyses cannot as in sandstone be guided by acoustic emission statistics. In this context, X-ray Computed Tomography (CT) imaging provides a promising technique to accurately describe the various failure modes associated with the brittle-ductile transition in porous limestone. In this study, we focused on a grainstone from the Majella Mountain, central Italy. Detailed field observations performed in this formation by Tondi et al. (2006) have revealed some complex interplay between deformation/compaction bands and stylolites. Our samples of Majella grainstone had a nominal porosity of 31% and were primarily composed of calcite. A series of hydrostatic and conventional triaxial experiments were performed at room temperature, constant strain rate and at confining pressures ranging from 5 to 50 MPa. Several sets of CT images at resolutions between 4 and 40 microns were acquired before and after deformation. Statistics on the macropores and spatial distribution of microporosity were characterized. Digital Image Correlation (DIC) was performed on images of the intact

  13. Adiabatic shear banding and scaling laws in chip formation with application to cutting of Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Molinari, A.; Soldani, X.; Miguélez, M. H.

    2013-11-01

    The phenomenon of adiabatic shear banding is analyzed theoretically in the context of metal cutting. The mechanisms of material weakening that are accounted for are (i) thermal softening and (ii) material failure related to a critical value of the accumulated plastic strain. Orthogonal cutting is viewed as a unique configuration where adiabatic shear bands can be experimentally produced under well controlled loading conditions by individually tuning the cutting speed, the feed (uncut chip thickness) and the tool geometry. The role of cutting conditions on adiabatic shear banding and chip serration is investigated by combining finite element calculations and analytical modeling. This leads to the characterization and classification of different regimes of shear banding and the determination of scaling laws which involve dimensionless parameters representative of thermal and inertia effects. The analysis gives new insights into the physical aspects of plastic flow instability in chip formation. The originality with respect to classical works on adiabatic shear banding stems from the various facets of cutting conditions that influence shear banding and from the specific role exercised by convective flow on the evolution of shear bands. Shear bands are generated at the tool tip and propagate towards the chip free surface. They grow within the chip formation region while being convected away by chip flow. It is shown that important changes in the mechanism of shear banding take place when the characteristic time of shear band propagation becomes equal to a characteristic convection time. Application to Ti-6Al-4V titanium are considered and theoretical predictions are compared to available experimental data in a wide range of cutting speeds and feeds. The fundamental knowledge developed in this work is thought to be useful not only for the understanding of metal cutting processes but also, by analogy, to similar problems where convective flow is also interfering with

  14. 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.

  15. Haptic Edge Detection Through Shear

    NASA Astrophysics Data System (ADS)

    Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent

    2016-03-01

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

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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. PMID:16132153

  2. 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.

  3. Complete Genome Sequence of Sedimenticola thiotaurini Strain SIP-G1, a Polyphosphate- and Polyhydroxyalkanoate-Accumulating Sulfur-Oxidizing Gammaproteobacterium Isolated from Salt Marsh Sediments

    PubMed Central

    Jones, Daniel S.; Bailey, Jake V.

    2015-01-01

    We report the closed genome sequence of Sedimenticola thiotaurini strain SIP-G1 and an unnamed plasmid obtained through PacBio sequencing with 100% consensus concordance. The genome contained several distinctive features not found in other published Sedimenticola genomes, including a complete nitrogen fixation pathway, a complete ethanolamine degradation pathway, and an alkane-1-monooxygenase. PMID:26089430

  4. 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.

  5. Large amplitude compression and shear wave propagation in an elastomer

    NASA Astrophysics Data System (ADS)

    Gupta, Y. M.; Murri, W. J.; Henley, D.

    1982-04-01

    Experimental techniques have been developed to measure the high strain-rate compression and shear response of Solithane 113. Compression and shear wave profiles have been measured in specimens compressed to 20% (compressive stresses ˜1.2 GPa). The compressive profiles are nearly steady and the compressive stress-strain response is typical of a compliant material. The shear wave profiles are dispersive and show attenuation with propagation. Analyses of these wave profiles will be presented. Shear moduli vary from 0.35 GPa to 0.8 GPa for the compression range examined to date. These values are within a factor of two of the static shear moduli in the glassy state. The data described here have been used to calculate the high strain rate compressive and shear stress-strain curves for Solithane 113.

  6. Regional GPS data confirm high strain accumulation prior to the 2000 June 4 Mw = 7.8 earthquake at southeast Sumatra

    NASA Astrophysics Data System (ADS)

    Michel, G. W.; Becker, M.; Reigber, Ch.; Tibi, R.; Yu, Y. Q.; Zhu, S. Y.

    2001-09-01

    Site velocities derived from repeated measurements in a regional GPS network in Southeast Asia help to constrain the motion of tectonic blocks as well as slip rates along major faults in the area. Using 3-D forward dislocation modelling, the influence of seismic elastic loading and unloading on the measured site motions are approximated. Results suggest that the northwestern Sunda arc is fully coupled seismogenically, whereas its eastern part along Java shows localized deformation. Higher horizontal velocity gradients than expected from the modelling of a fully coupled plate interface west of Manila in the Philippines suggest that deformation may be localized there. Assuming that geodetically derived convergence represents long-term rates, accumulated geodetic moments are compared to those derived using seismic data from 1977 to 2000 (Harvard CMT catalogue). If areas displaying localized deformation are dominated by creep processes, the largest difference between accumulated and seismically released deformation is located where the 2000 June 4 Mw=7.8 Sumatra earthquake occurred.

  7. Chaotic Boundaries of Nematic Polymers in Mixed Shear and Extensional Flows

    NASA Astrophysics Data System (ADS)

    Forest, M. Gregory; Zhou, Ruhai; Wang, Qi

    2004-08-01

    Chaotic orientational dynamics of sheared nematic polymers is documented in laboratory experiments and predicted by Doi-Hess kinetic theory for infinitely thin rods. We address robustness of rheochaos when simple shear is modified by a planar straining flow, and the macromolecules have finite aspect ratio. We predict persistence of sheared chaotic response up to a threshold straining flow strength and minimum aspect ratio, beyond which chaotic behavior is arrested. More intriguing, a straining component can induce chaos from periodic shear responses.

  8. Strain fields for aluminum at different tooling temperatures and extrusion ratios

    SciTech Connect

    Peacock, H.B.; Berghaus, D.G.

    1985-03-01

    Strain distributions throughout the die region are obtained for axisymmetric extrusion of aluminum billets. Results which include the three extensional strains and accumulated shear are produced from an analysis of experimentally obtained laminar flow lines on extruded specimens. Extrusion experiments are performed at average tooling temperatures of 174/sup 0/C and 354/sup 0/C and for extrusion ratios from 1.9 to 12.4. Both tooling temperatures and extrusion ratios affect the magnitude and/or the distribution of plastic strains in extruded aluminum.

  9. Shear Instabilities in Granular Flows

    NASA Astrophysics Data System (ADS)

    Shinbrot, Troy

    2003-03-01

    Unstable waves have long been studied in fluid shear layers. These waves affect transport in the atmosphere and oceans as well as slipstream stability behind ships, planes, and heat transfer devices. Corresponding instabilities in granular flows have not previously been documented, despite the importance of these flows in geophysical and industrial systems. We report here that breaking waves can form at the interface between two streams of identical grains downstream of a splitter plate. These waves appear abruptly in flow down an inclined plane as either shear rate or angle of incline is changed, and we analyze a granular flow model that qualitatively agrees with our experimental data. The waves appear from the model to be a manifestation of a competition between shear and extensional strains in the flowing granular bed, and we propose a dimensionless group to govern the transition between steady and wavy flows.

  10. Shear Mechanics of the TMJ Disc

    PubMed Central

    Juran, C.M.; Dolwick, M.F.; McFetridge, P.S.

    2012-01-01

    The temporomandibular joint (TMJ) is a complex hinge and gliding joint that induces significant shear loads onto the fibrocartilage TMJ disc during jaw motion. The purpose of this study was to assess regional variation in the disc’s shear loading characteristics under physiologically relevant loads and to associate those mechanical findings with common clinical observations of disc fatigue and damage. Porcine TMJ discs were compressed between an axially translating bottom platen and a 2.5-cm-diameter indenter within a hydrated testing chamber. Discs were cyclically sheared at 0.5, 1, or 5 Hz to 1, 3, or 5% shear strain. Within the anterior and intermediate regions of the disc when sheared in the anteroposterior direction, both shear and compressive moduli experienced a significant decrease from instantaneous to steady state, while the posterior region’s compressive modulus decreased approximately 5%, and no significant loss of shear modulus was noted. All regions retained their shear modulus within 0.5% of instantaneous values when shear was applied in the mediolateral direction. The results of the disc’s regional shear mechanics suggest an observable and predictable link with the common clinical observation that the posterior region of the disc is most often the zone in which fatigue occurs, which may lead to disc damage and perforation. PMID:23166043

  11. The Improvement of SAM Accumulation by Integrating the Endogenous Methionine Adenosyltransferase Gene SAM2 in Genome of the Industrial Saccharomyces cerevisiae Strain.

    PubMed

    Zhao, Weijun; Shi, Feng; Hang, Baojian; Huang, Lei; Cai, Jin; Xu, Zhinan

    2016-03-01

    S-Adenosyl-L-methionine (SAM) plays important roles in trans-methylation, trans-sulfuration, and polyamine synthesis in all living cells, and it is also an effective cure for liver disease, depressive syndromes, and osteoarthritis. The increased demands of SAM in pharmaceuticals industry have aroused lots of attempts to improve its production. In this study, a multiple-copy integrative plasmid pYMIKP-SAM2 was introduced into the chromosome of wild-type Saccharomyces cerevisiae strain ZJU001 to construct the recombined strain R1-ZJU001. Further studies showed that the recombinant yeast exhibited higher enzymatic activity of methionine adenosyltransferase and improved its SAM biosynthesis. With a three-phase fed-batch strategy in 15-liter bench-top fermentor, 8.81 g/L SAM was achieved after 52 h cultivation of R1-ZJU001, about 27.1 % increase over its parent strain ZJU001, whereas the SAM content was also improved from 64.6 mg/g DCW to 91.0 mg/g DCW. Our results shall provide insights into the metabolic engineering of SAM pathway in yeast for improved productivity of SAM and subsequent industrial applications. PMID:26728652

  12. 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

  13. 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

  14. 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.

  15. Shear relaxations of confined liquids

    SciTech Connect

    Carson, G.A. Jr.

    1992-01-01

    Ultrathin (<40 [angstrom]) 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[sup [minus]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 Celcius 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 ([approximately]80 nm[sup 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 (7 nm[sup 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[sup 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.

  16. Electrorheological fluid under elongation, compression, and shearing

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Meng, Y.; Mao, H.; Wen, S.

    2002-03-01

    Electrorheological (ER) fluid based on zeolite and silicone oil under elongation, compression, and shearing was investigated at room temperature. Dc electric fields were applied on the ER fluid when elongation and compression were carried out on a self-constructed test system. The shear yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of shearing and perpendicular to the direction of the electric field, was also obtained by a HAAKE RV20 rheometer. The tensile yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of the electric field, was achieved as the peak value in the elongating curve with an elongating yield strain of 0.15-0.20. A shear yield angle of about 15°-18.5° reasonably connected tensile yield stress with shear yield stress, agreeing with the shear yield angle tested well by other researchers. The compressing tests showed that the ER fluid has a high compressive modulus under a small compressive strain lower than 0.1. The compressive stress has an exponential relationship with the compressive strain when it is higher than 0.1, and it is much higher than shear yield stress.

  17. 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

  18. 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

  19. Post-Seismic Strain and Stress Evolution from Continuous GPS Observations

    NASA Astrophysics Data System (ADS)

    Shcherbenko, Gina Nicole

    Strain evolution and stress evolution following the 4 April 2010 M7.2 El Mayor-Cucapah earthquake are modeled using an adaptation of the strain transient detection tool developed by Holt and Shcherbenko 2013. The evolution of stress is calculated from postseismic strains, which are modeled from continuous GPS horizontal displacements. Strain fields are modeled in 2 ways; the total strain field based on total observed cGPS displacements, and the residual strain field, which subtracts a reference field from the total model. The residual shows anomalous strains resulting from the postseismic relaxation of the 2010 event. Anomalous and total strains are modeled in 0.1 year epochs for 2.4 years following the event. Both total and anomalous strains are converted into stress changes over time, assuming elastic incompressible behavior. Following the El Mayor event, the GPS constrained strain evolution shows the following: (1) The Southern San Andreas experiences a reduced rate of right-lateral strike slip strain accumulation between 3 July 2010 and 7 August 2012 (Figure 16a-d). (2) The San Jacinto Fault has normal rate of right-lateral strike-slip strain accumulation during this time. (3) Before the Brawley swarm of 26 August 2012, the state of strain evolves to enable unclamping of a left-lateral fault zone in the Brawley Seismic Zone (Figure 16a-d). (4) Large shear strains accumulate on the Laguna Salada Fault (northernmost segment)/southern Elsinore FZ (Figure 16a-d). We converted the strain changes into Coulomb stress changes on existing faults (both right-lateral and left-lateral). Several regions show increased Coulomb stress changes throughout the postseismic process. Furthermore, the Coulomb stress changes on the faults in the region progressively increase toward failure up to the time of the Brawley swarm.

  20. 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.

  1. Inference of dynamic shear modulus from Lotung downhole data

    SciTech Connect

    Chang, C.Y.; Mok, C.M.; Tang, H.T.

    1996-08-01

    Downhole ground motions recorded at the Lotung Large-Scale Seismic Test (LSST) site were used in this paper to infer in-situ dynamic soil properties. The purposes were (1) to provide field evidence of nonlinear soil behavior during earthquake excitation; and (2) to evaluate the accuracy of dynamic properties obtained from geophysical measurements and laboratory tests. For each horizontal component and event analyzed, representative shear-wave velocity and effective shear strain (defined as 65% of peak strain) between consecutive recording stations were estimated. The representative shear-wave velocities were estimated from fundamental resonant frequencies identifiable from the Fourier spectral ratios. The effective shear strains were estimated by linear ground response deconvolution analyses based on the inferred shear-wave velocity profiles. The inferred reduction in shear modulus with increasing effective shear strain was compared with laboratory test data. The degree of agreement between the inferred shear modulus reduction curves and the laboratory test data varied with different testing programs. The inferred low-strain shear-wave velocity profile agreed with geophysical measurements. These observations not only provide field evidence of nonlinear dynamic soil behavior during earthquakes, but also confirm the reasonableness of data provided by geophysical measurements and laboratory tests.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Study of shear-stiffened elastomers

    NASA Astrophysics Data System (ADS)

    Tian, Tongfei; Li, Weihua; Ding, Jie; Alici, Gursel; Du, Haiping

    2013-06-01

    Shear thickening fluids, which are usually concentrated colloidal suspensions composed of non-aggregating solid particles suspended in fluids, exhibit a marked increase in viscosity beyond a critical shear rate. This increased viscosity is seen as being both 'field-activated', due to the dependence on shearing rate, as well as reversible. Shear thickening fluids have found good applications as protection materials, such as in liquid body armor, vibration absorber or dampers. This research aims to expand the protection material family by developing a novel solid status shear thickening material, called shear-stiffened elastomers. These new shear-stiffened elastomers were fabricated with the mixture of silicone rubber and silicone oil. A total of four SSE samples were fabricated in this study. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel-plate. The effects of silicone oil composition and angular frequency were summarized. When raising the angular frequency in dynamic shear test, the storage modulus of conventional silicone rubber shows a small increasing trend with the frequency. However, if silicone oil is selected to be mixed with silicone rubber, the storage modulus increases dramatically when the frequency and strain are both beyond the critical values.

  9. Experiments on Memory in a Sheared Soft Solid

    NASA Astrophysics Data System (ADS)

    Keim, Nathan; Wieker, Devin; Horowitz, Luke

    2015-11-01

    We consider how a soft 2D jammed material may form memories of past deformation. Our experiments cyclically shear a material made of repulsive particles at an oil-water interface, observing the motion of many particles. Under repeated shearing, the system can evolve toward a ``limit cycle'' in which the same particle rearrangements recur on each cycle of shear; the set of rearrangements is specific to the strain amplitude. We discuss how the material's history-dependence may be viewed as a memory of the strain amplitude, and we report on progress in describing this behavior, including whether memories of multiple strains may coexist.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. Two-dimensional magnetic colloids under shear.

    PubMed

    Mohorič, Tomaž; Dobnikar, Jure; Horbach, Jürgen

    2016-04-01

    Complex rheological properties of soft disordered solids, such as colloidal gels or glasses, inspire a range of novel applications. However, the microscopic mechanisms of their response to mechanical loading are not well understood. Here, we elucidate some aspects of these mechanisms by studying a versatile model system, i.e. two-dimensional superparamagnetic colloids in a precessing magnetic field, whose structure can be tuned from a hexagonal crystal to a disordered gel network by varying the external field opening angle θ. We perform Langevin dynamics simulations subjecting these structures to a constant shear rate and observe three qualitatively different types of material response. In hexagonal crystals (θ = 0°), at a sufficiently low shear rate, plastic flow occurs via successive stress drops at which the stress releases due to the formation of dislocation defects. The gel network at θ = 48°, on the contrary, via bond rearrangement and transient shear banding evolves into a homogeneously stretched network at large strains. The latter structure remains metastable after switching off of the shear. At θ = 50°, the external shear makes the system unstable against phase separation and causes a failure of the network structure leading to the formation of hexagonal close packed clusters interconnected by particle chains. At a microcopic level, our simulations provide insight into some of the mechanisms by which strain localization as well as material failure occur in a simple gel-like network. Furthermore, we demonstrate that new stretched network structures can be generated by the application of shear. PMID:26877059

  1. Crustal strain rate patterns of the western North America Plate boundary

    NASA Astrophysics Data System (ADS)

    Hackl, M.; Malservisi, R.; Furlong, K.; Kirby, E.

    2009-04-01

    The knowledge of the crustal strain rate tensor provides a description of geodynamic processes such as fault strain accumulation. We use interpolation of GPS geodetic measurements to derive the regional strain rate field for selected regions within the western North America plate boundary. We applied the interpolation scheme to data from the Eastern California Shear Zone, the Mendocino triple junction region, and the transition from the Sierra block to the Pacific North West. Our results allow us to define regions of localization of the strain rate at the northern end of the San Andrea Fault system and within the boundary between the Sierra Nevada and Basin and Range. These results help to understand the way in which strain is accommodated in the Sierra/Pacific North West transition. The results will be compared with geologic and tectonic observation of the region.

  2. Sheath fold morphology in simple shear

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Dabrowski, Marcin; Galland, Olivier; Schmid, Daniel W.

    2013-08-01

    Sheath folds are highly non-cylindrical structures often associated with shear zones. We investigate the formation of sheath folds around a weak inclusion acting as a slip surface in simple shear by means of an analytical model. We present results for different slip surface orientations and shapes. Cross-sections perpendicular to the shear direction through the sheath fold display closed contours, so called eye-structures. The aspect ratio of the outermost closed contour is strongly dependent on the initial slip surface configuration. The center of the eye-structure is subject to change in height with respect to the upper edge of the outermost closed contour for different cross-sections perpendicular to the shear direction. This results in a large variability in layer thickness across the sheath fold length, questioning the usefulness of eye-structures as shear sense indicators. The location of the center of the eye structure is largely invariant to the initial configurations of the slip surface as well as to strain. The values of the aspect ratios of the closed contours within the eye-pattern are dependent on the strain and the cross-section location. The ratio (R') of the aspect ratios of the outermost closed contour (Ryz) and the innermost closed contour (Ry'z') shows values above and below 1. R' shows dependence on the slip surface shape and orientation but not on the number of involved contours. Using R' measurements to deduce the bulk strain type may be erroneous.

  3. 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.

  4. How to create mylonitic shear zones in the presence of shear heating

    NASA Astrophysics Data System (ADS)

    Thielmann, Marcel; Rozel, Antoine; Kaus, Boris; Ricard, Yanick

    2013-04-01

    Lithospheric-scale shear zones are commonly defined as regions inhomogeneous and localized deformation. Strain softening has been demonstrated to be necessary for localization in those shear zones, but there is still debate about the physical cause of this softening. Here, we investigate the interplay between two mechanisms that have been suggested to have a significant impact on lithospheric localization: shear heating and grain size reduction. Shear heating has been suggested to play an important role in i) creating deep focus as well as intermediate-depth earthquakes (Ogawa (1987), Kelemen and Hirth (2007)) and ii) creating lithospheric-scale shear zones, thus creating a weak decoupling interface that enables subsequent subduction initiation (Kaus and Podlatchikov (2006), Crameri and Kaus (2010)). As natural shear zones typically have a significantly reduced grain size, it has been put forward that grain size reduction provides the necessary strain softening to localize deformation. As grain size reduces, the dominant deformation mechanism switches from dislocation to diffusion creep, thus requiring less stress to deform the rock. Usually, the equilibrium grain size is thought to follow a piezometric relationship, thus indicating the stress under which a shear zone deformed. Recent work (Austin and Evans (2007), Rozel et al. (2011)) suggests that the equilibrium grain size is not dependent on stress, but rather on the deformational work. In our study, we employ the grain size evolution law of Rozel et al. and use 1D viscoelastic numerical models of simple shear deformation to investigate the influence of both weakening mechanisms and their interaction for a variety of boundary conditions. We find that grain size reduction in pure olivine does not localize very efficiently, as grain size very rapidly reaches a steady state. Even when a fraction of the deformational work is used by grain size reduction processes, shear heating is found to localize very efficiently

  5. Shear strength of municipal solid waste for stability analyses

    NASA Astrophysics Data System (ADS)

    Stark, Timothy D.; Huvaj-Sarihan, Nejan; Li, Guocheng

    2009-06-01

    This paper investigates the shear strength of municipal solid waste (MSW) using the back analysis of failed waste slopes as well as field and laboratory test results. Shear strength of MSW is a function of many factors such as waste type, composition, compaction, daily cover, moisture conditions, age, decomposition, overburden pressure, etc. These factors together with non-standardized sampling methods, insufficient sample size to be representative of in situ conditions, and limited shear displacement or axial strain imposed during the laboratory shear testing have created considerable scatter in reported results. Based on the data presented herein, large shear displacements are required to mobilize the peak shear strength of MSW which can lead to displacement incompatibility between MSW and the underlying material(s) such as geosynthetic interfaces and foundation soils. The data presented herein are used to develop displacement compatible shear strength parameters for MSW. Recommendations are presented for modeling the displacement and stress dependent strength envelope in stability analyses.

  6. Probing the shear-band formation in granular media with sound waves.

    PubMed

    Khidas, Y; Jia, X

    2012-05-01

    We investigate the mechanical responses of dense granular materials, using a direct shear box combined with simultaneous acoustic measurements. Measured shear wave speeds evidence the structural change of the material under shear, from the jammed state to the flowing state. There is a clear acoustic signature when the shear band is formed. Subjected to cyclic shear, both shear stress and wave speed show the strong hysteretic dependence on the shear strain, likely associated with the geometry change in the packing structure. Moreover, the correlation function of configuration-specific multiply scattered waves reveals an intermittent behavior before the failure of material. PMID:23004745

  7. 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.

  8. Shear Strength of Aluminum Oxynitride

    NASA Astrophysics Data System (ADS)

    Dandekar, Dattatraya P.; Vaughan, Brian A. M.; Proud, William G.

    2007-06-01

    Aluminum oxynitride (AlON) is a transparent, polycrystalline cubic spinel. The results of investigations^1-4 on shock response of AlON permit determination of the equation of state, and shear strength retained under shock compression. Whereas the values of the HEL of AlON holds no surprises, the inelastic response of AlON reported in Ref. 1-4 differ significantly and is stress dependent. The results of Ref. 1-2 show that AlON retains a shear strength of 3 to 4 GPa when shocked up to around 20 GPa, but the results of Ref, 3-4 seem to suggest a possible loss of shear strength when shocked to 16 GPa and beyond. Our analysis examines the observed differences in the inelastic response of AlON reported in these four studies . 1. J. U. Cazamias, et. al., in Fundamental Issues and Applications of Shock-Wave and High Strain Rate Phenomena, Eds. Staudhammer, Murr, and Meyers, Elsevier, NY, 173 (2001). 2. B. A. M. Vaughn, et.al., Shock Physics, Cavendish Laboratory, Report SP/1092 (2001) 3. T. Sekine, et.al., J. Appl. Phys. 94, 4803 (2003). 4. T. F. Thornhill, et.al., Shock Compression of Matter-2005, Eds. Furnish, Elert, Russell, White, AIP, NY, 143 (2006).

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Shear-enhanced adhesion of Pseudomonas aeruginosa

    NASA Astrophysics Data System (ADS)

    Lecuyer, Sigolene; Rusconi, Roberto; Shen, Yi; Forsyth, Alison; Stone, Howard

    2010-03-01

    Bacterial adhesion is the first step in the development of surface-associated communities known as biofilms, which are the cause of many problems in medical devices and industrial water systems. However the underlying mechanisms of initial bacterial attachment are not fully understood. We have investigated the effects of hydrodynamics on the probability of adsorption and detachment of Pseudomonas aeruginosa strain PA14 on model surfaces under flow, in straight microfluidic channels, and measured the distribution of bacteria residence time as a function of the shear rate. Our main discovery is a counter-intuitive enhanced adhesion as the shear stress is increased over a wide range of shear rates. In order to identify the origin of this phenomenon, we have performed experiments with several mutant strains. Our results show that shear-enhanced adhesion is not regulated by primary surface organelles, and that this process is not specific to a certain type of surface, but rather appears a general feature of the adhesive behavior of P. aeruginosa. These results suggest that shear-induced adhesion could be a very widespread strategy in nature.

  15. 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.

  16. 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.

  17. Doubly anchored nematic polymer brushes: Shear, field effects, and quasipiezoelectricity

    NASA Astrophysics Data System (ADS)

    Halperin, A.; Williams, D. R. M.

    1994-02-01

    The shear behavior of a doubly anchored brush of liquid-crystalline polymers immersed in a nematic solvent is investigated. In such a brush the grafted polymers bridge two plates. Remarkably, the Franck nematic elasticity in this system can dominate the shear modulus. In the presence of a field the system undergoes a Fréedericksz transition modified by the bridging polymers. In particular: (i) the polymeric elasticity affects the critical field Ec; (ii) the shear modulus vanishes as the field approaches Ec; and (iii) the nematic distortion couples to a shear strain. The system exhibits quasipiezoelectricity, which is nonlinear and is not associated with any inverse effect.

  18. 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.

  19. Characterising fabric, force distributions and porosity evolution in sheared granular media

    NASA Astrophysics Data System (ADS)

    Mair, Karen; Abe, Steffen; Jettestuen, Espen

    2014-05-01

    Active faults, landslides, subglacial tills and poorly or unconsolidated sands essentially contain accumulations of granular debris that evolve under load. Both the macroscopic motions and the bulk fluid flow characteristics that result are determined by the particular grain scale processes operating in this deformed or transformed granular material. A relevant question is how the local behavior at the individual granular contacts actually sums up, and in particular how the load bearing skeleton (an important expression of connected load) and spatial distribution of pore space (and hence fluid pathways) are linked. Here we investigate the spatial distribution of porosity with granular rearrangements (specifically contact force network characteristics) produced in 3D discrete element models of granular layers under shear. We use percolation measures to identify, characterize, compare and track the evolution of 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 of the material as well as loading conditions. In addition we probe the 3D spatial distribution of porosity as a function of increasing strain. Two cases will be considered. The first, a non-fracture regime where configurational changes occur during shear but grain size distribution remains constant. This would be expected for a soil or granular material under relatively low normal loading. Secondly we consider a fragmentation regime where the grain size distributions of the granular material evolve with accumulated strain. This mirrors the scenario for faults or basal shear zones of slides under higher normal stress where comminution is typically a mark of increasing maturity and plays a major role in the poro-perm evolution of the system. We will present the correlated and anti-correlated features appearing in our simulations as well as discussing

  20. 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.

  1. Dynamics of Concentrated Silica Suspension under Oscillatory Shear Studied by SAXS and XPCS

    NASA Astrophysics Data System (ADS)

    Lee, Jonghun; Lin, Xiao-Min; Sandy, Alec; Narayanan, Suresh; X-ray Science Division Team; CenterNanomaterials Team

    2015-03-01

    The viscoelastic properties of complex fluids are often obtained by applying small amplitude oscillatory shear (SAOS). In this regime, their microstructure does not change by shear, and the shear stress linearly responds to the applied strain. However, in the real application, high shear strain or rate is applied, where the viscoelastic properties are affected by the microstructural deformation by this high shear. The rheological behavior of complex fluids under large amplitude oscillatory shear (LAOS) has been widely studied, but there is a lack of studies in microscopic dynamics of complex fluids under LAOS. X-ray scattering is a suitable method to understand microscopic perspective of rheology because of its proper length scales of tens to hundreds nm and time scales of millisecond to thousands second. Here, we studied the dynamics of the concentrated silica nanoparticle suspensions in PEG under different shear strain regimes using small angle x-ray scattering (SAXS) and x-ray photon correlation spectroscopy (XPCS). With strain increasing, these suspensions showed shear thinning and shear thickening behavior, and their microstructural change was observed by SAXS. In oscillatory shear, as the original scattering volume periodically comes back to the original position, we could better study the changes in autocorrelation function by shear and diffusion than steady shear study where correlation decays by transit.

  2. Stress dynamics of a 2D dense granular system near shear jamming

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Dijksman, Joshua; Behringer, Robert

    2013-03-01

    We study the dynamics of pressure and shear stress in a frictional 2D dense granular system using a novel apparatus that can provide fixed-volume shear without generating inhomogeneities. Under increasing shear strain, the system's pressure shows a strong increase with strain, characterized by a ``Reynolds coefficient,'' R =d2 P / dγ2 . R depends only on packing fraction ϕ, and shows a strong increase as ϕ approaches ϕJ from below. In the meantime, the system's shear stress shows a non-monotonic behavior with increasing strain. It first increases with strain as the system is in ``fragile'' states and builds up long force chains along the compression direction. After a certain amount of strain, force chains along the dilation direction starts to build up, and the system transfers into a ``shear-jammed'' state and the shear stress starts to decrease with strain. Under oscillatory shear, both pressure and shear stress show limit-cycle behavior and reach steady states after many cycles. However, the limit cycles of pressure and shear stress are very different: the pressure exhibits a hysteresis-free parabolic curve, while the shear stress exhibits a strongly hysteretic loop. This work is funded by NSF grants: DMR0906908, DMS0835571, NASA grant NNX10AU01G and ARO grant W911NF-11-1-0110.

  3. 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.

  4. 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.

  5. Suppression of turbulence and transport by sheared flow

    SciTech Connect

    Terry, P. W.

    2000-01-01

    The role of stable shear flow in suppressing turbulence and turbulent transport in plasmas and neutral fluids is reviewed. Localized stable flow shear produces transport barriers whose extensive and highly successful utilization in fusion devices has made them the primary experimental technique for reducing and even eliminating the rapid turbulent losses of heat and particles that characterize fusion-grade plasmas. These transport barriers occur in different plasma regions with disparate physical properties and in a range of confining configurations, indicating a physical process of unusual universality. Flow shear suppresses turbulence by speeding up turbulent decorrelation. This is a robust feature of advection whenever the straining rate of stable mean flow shear exceeds the nonlinear decorrelation rate. Shear straining lowers correlation lengths in the direction of shear and reduces turbulent amplitudes. It also disrupts other processes that feed into or result from turbulence, including the linear instability of important collective modes, the transport-producing correlations between advecting fluid and advectants, and large-scale spatially connected avalanchelike transport events. In plasmas, regions of stable flow shear can be externally driven, but most frequently are created spontaneously in critical transitions between different plasma states. Shear suppression occurs in hydrodynamics and represents an extension of rapid-distortion theory to a long-time-scale nonlinear regime in two-dimensional stable shear flow. Examples from hydrodynamics include the emergence of coherent vortices in decaying two-dimensional Navier-Stokes turbulence and the reduction of turbulent transport in the stratosphere. (c) 2000 The American Physical Society.

  6. Shear flexibility for structures

    NASA Technical Reports Server (NTRS)

    Stangeland, Maynard L. (Inventor)

    1976-01-01

    This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.

  7. Shear flexibility for structures

    NASA Technical Reports Server (NTRS)

    Stangeland, Maynard L. (Inventor)

    1977-01-01

    This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.

  8. Progressive Shear Failure in Granular Materials: Linking Force Fluctuations With Acoustic Emissions

    NASA Astrophysics Data System (ADS)

    Michlmayr, G. K.; Cohen, D. O.; Or, D.

    2011-12-01

    Natural hazards associated with rapid mass movements such as shallow landslides, rock falls or debris flows are notoriously difficult to predict even though precursor events associated with small internal failures are known to occur. In this study we focus on grain scale processes preceding the formation of a shear plane in granular materials such as frictional sliding of grain contacts, accommodation of contact networks and fracturing of grain bonds (in cohesive materials) - all of which are discrete micro-mechanical failure events that emit characteristic acoustic emissions that could be used to study internal failure and potentially provide early warning (albeit short). Experiments involving direct shear tests using glass beads and sand were combined with acoustic emission (AE) measurements using piezoelectric sensors with sensitivities to frequencies in the range of 20kHz - 200kHz and accelerometers (0.2kHz - 20kHz) buried within the sheared sample. We obtained good correlations between shear deformation and associated grain-scale mechanical behavior with key characteristics of measured AE (frequency content, signal energy). Fluctuations of shear force occurring during strain controlled deformation are assumed to represent micro-structural rearrangements of the material. We obtained exponential distributions of force fluctuation magnitudes and low frequency AE event statistics. The number of AE events increased with confining stress as well as with particle roughness and were inversely related to grain size. These results were linked with conceptual models of failure accumulation such as the fiber-bundle model. The statistics of AE event occurrence, particularly magnitude-frequency distributions may provide prediction of imminent mechanical collapse. The strong attenuation of acoustic signals within most earth materials present a major challenge to field applications requiring innovative deployment strategies such as the use of acoustic waveguides.

  9. 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.

  10. 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.

  11. 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.

  12. Laboratory study of fabric development in shearing till: The importance of effective pressure and shearing rate

    NASA Astrophysics Data System (ADS)

    Jacobson, William R.; Hooyer, Thomas S.

    2015-12-01

    Herein we present data on the shearing rate (glacier velocity) and effective pressure (difference between the ice-overburden pressure and pore-water pressure) in the development of magnetic fabric (anisotropy of magnetic susceptibility) using a rotary ring-shear device. A Wisconsin-age basal till was used in the experiments and deformed to its critical state at shear strains as high as 93. We also present data from hysteresis and high temperature susceptibility experiments to identify the magnetic carrier in the basal till. Results showed little change in fabric strength when varying the shearing rate in the speed range of 110-860 m year- 1. Moreover, the effective pressure tests also showed an inconsistency in fabric between 30 and 150 kPa; however, a slight strengthening effect was documented. Thus, the k1 magnetic fabric strength is independent of the shearing rate and effective pressure. This suggests that the fabric strength upon these variables cannot be used as a benchmark for estimating shear deformation to the geological record. The k1 fabric strength in this study; however, remained consistent with respect to other till particle fabric methods (e.g., sand and pebble) in which the same conclusion was drawn; all particles align parallel to the direction of shear and plunge mildly up glacier.

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

    PubMed

    Arnal, Bastien; Pernot, Mathieu; Tanter, Mickael

    2011-08-01

    The clinical applicability of high-intensity focused ultrasound (HIFU) for noninvasive therapy is currently hampered by the lack of robust and real-time monitoring of tissue damage during treatment. The goal of this study is to show that the estimation of local tissue elasticity from shear wave imaging (SWI) can lead to a precise mapping of the lesion. HIFU treatment and monitoring were respectively performed using a confocal setup consisting of a 2.5-MHz single element transducer focused at 34 mm on ex vivo samples and an 8-MHz ultrasound diagnostic probe. Ultrasound-based strain imaging was combined with shear wave imaging on the same device. The SWI sequences consisted of 2 successive shear waves induced at different lateral positions. Each wave was created with pushing beams of 100 μs at 3 depths. The shear wave propagation was acquired at 17,000 frames/s, from which the elasticity map was recovered. HIFU sonications were interleaved with fast imaging acquisitions, allowing a duty cycle of more than 90%. Thus, elasticity and strain mapping was achieved every 3 s, leading to real-time monitoring of the treatment. When thermal damage occurs, tissue stiffness was found to increase up to 4-fold and strain imaging showed strong shrinkages that blur the temperature information. We show that strain imaging elastograms are not easy to interpret for accurate lesion characterization, but SWI provides a quantitative mapping of the thermal lesion. Moreover, the concept of shear wave thermometry (SWT) developed in the companion paper allows mapping temperature with the same method. Combined SWT and shear wave imaging can map the lesion stiffening and temperature outside the lesion, which could be used to predict the eventual lesion growth by thermal dose calculation. Finally, SWI is shown to be robust to motion and reliable in vivo on sheep muscle. PMID:21859579

  14. Structural Evidence for Fluid-Assisted Shear Failure within a Ductile Shear Zone

    NASA Astrophysics Data System (ADS)

    Compton, K.; Kirkpatrick, J. D.

    2014-12-01

    Recent observations of seismic slip occurring below the seismogenic zone of large fault zones have emphasized the significance of coeval ductile and brittle processes at high temperatures. We present observations of a shear zone contained within the Saddlebag Lake pendant of the eastern Sierra Nevada, CA, where Triassic and Jurassic metavolcanics and metasediments are highly strained in a high-temperature shear zone. Transposed bedding and cleavage that define a flattening fabric, dextrally rotated porphyroclasts, and a steep, pervasive lineation together suggest an overall transpressive kinematic regime for the ductile deformation. The high-strain rocks exhibit multiple episodes of vein formation, indicating a prolonged migration of hydrothermal fluids throughout the system. Crosscutting relationships and mineral assemblages define discrete sets of differently oriented veins. The veins form by fracture, but many veins are folded and boudinaged, showing synkinematic brittle and ductile deformation. We document foliation-parallel quartz veins that show shear displacement from the geometry of pull-apart structures and offsets of earlier veins. Synkinematic equilibrium mineral assemblages within the host rock and dynamic recrystallization of the quartz veins show they formed at temperatures around 400 to 500°C. The shear fractures have horizontal trace lengths of up to a few meters and displacements range from 2-3 mm to ~3 cm, with 1-5 mm of opening. Assuming the observed offset in the fractures occurred in a single event, these measurements are consistent with stress drops of 1 to 10 MPa. We interpret these observations to show that the veins formed as a result of high pore fluid pressure that caused shear failure at low effective stresses. Because foliated rocks are mechanically anisotropic, the foliation provided planes of weakness for failure with a preferred orientation. Evidence for shear failure occurring within crystal-plastic shear zones at high temperatures

  15. Shear-induced conformation change in α-crystalline nylon6

    NASA Astrophysics Data System (ADS)

    Arabnejad, Saeid; Manzhos, Sergei; He, Chaobin; Shim, V. P. W.

    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.

  16. Predicting km-scale shear zone formation

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Because km-scale shear zones play a first-order role in lithospheric kinematics, accurate conceptual and numerical models of orogenic development require predicting when and where they form. Although a strain-based algorithm in the upper crust for weakening due to faulting appears to succeed (e.g., Koons et al., 2010, doi:10.1029/2009TC002463), a comparable general rule for the viscous crust remains unestablished. Here we consider two aspects of the geological argument for a similar algorithm in the viscous regime, namely (1) whether predicting km-scale shear zone development based on a single parameter (such as strain or shear heating) is reasonable; and (2) whether lithologic variability inherent in most orogenic systems precludes a simple predictive rule. A review of tectonically significant shear zones worldwide and more detailed investigations in the Central Gneiss belt of the Ontario segment of the Grenville Province reveals that most km-scale shear zones occur at lithological boundaries and involve mass transfer, but have fairly little else in common. As examples, the relatively flat-lying Twelve Mile Bay shear zone in the western Central Gneiss belt bounds the Parry Sound domain and is likely the product of both localized anatexis and later retrograde hydration with attendant metamorphism. Moderately dipping shear zones in granitoids of the Grenville Front Tectonic Zone apparently resulted from cooperation among several complementary microstructural processes, such as grain size reduction, enhanced diffusion, and a small degree of metamorphic reaction. Localization into shear zones requires the operation of some spatially restricted processes such as stress concentration, metamorphism/fluid access, textural evolution, and thermal perturbation. All of these could be due in part to strain, but not necessarily linearly related to strain. Stress concentrations, such as those that form at rheological boundaries, may be sufficient to nucleate high strain

  17. Shear Strength Prediction of RC Beams Wrapped with Frp

    NASA Astrophysics Data System (ADS)

    Wang, Suyan; Zhou, Yingwu; Li, Hongnan

    During past decades, substantial studies on the external bonding of fiber reinforced polymer (FRP) strips to deficient reinforced concrete (RC) beams have been carried out for the well-known superior properties of the FRP. Several shear prediction models have been established by using the effective strain of the FRP or introducing an ultimate stress discount coefficient. And the latest design concept is the use of stress distribution factor. In this paper, an equivalent effective strain model of the FRP is presented, which contains the concepts of maximum strain, stress distribution factor and critical shear crack angle influences. To develop a simple and accurate approach for such equivalent effective strain, major influenced factors are investigated and analyzed by the statistical independent hypothetic tests on a database of 128 RC beams wrapped by the FRP. Finally, a simple and rational shear design proposal is given, which is more accurate than the existing models using the above database.

  18. Softening by void nucleation and growth in tension and shear

    NASA Astrophysics Data System (ADS)

    Fleck, N. A.; Hutchinson, J. W.; Tvergaard, V.

    THE EFFECT of void nucleation and growth on overall stress-strain behavior is investigated for solids undergoing plastic straining under axisymmetric and shearing conditions. Contact between the void surface and the nucleating particle is taken into account and is found to be important under shear and under axisymmetric straining when the stress triaxiality is low. The notion of the macroscopic stress drop due to nucleation of a void is defined and computed, both for isolated voids and for voids in periodic arrays. The stress drop for an isolated void in an infinite matrix can be used to predict softening due to void nucleation when the void concentration is dilute. Interaction between voids in shear during nucleation is analysed numerically and softening effects are calculated along with large strain aspects of void deformation during subsequent growth.

  19. 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.

  20. Geodetic Strain Analysis Tool

    NASA Technical Reports Server (NTRS)

    Kedar, Sharon; Baxter, Sean C.; Parker, Jay W.; Webb, Frank H.; Owen, Susan E.; Sibthorpe, Anthony J.; Dong, Danan

    2011-01-01

    A geodetic software analysis tool enables the user to analyze 2D crustal strain from geodetic ground motion, and create models of crustal deformation using a graphical interface. Users can use any geodetic measurements of ground motion and derive the 2D crustal strain interactively. This software also provides a forward-modeling tool that calculates a geodetic velocity and strain field for a given fault model, and lets the user compare the modeled strain field with the strain field obtained from the user s data. Users may change parameters on-the-fly and obtain a real-time recalculation of the resulting strain field. Four data products are computed: maximum shear, dilatation, shear angle, and principal components. The current view and data dependencies are processed first. The remaining data products and views are then computed in a round-robin fashion to anticipate view changes. When an analysis or display parameter is changed, the affected data products and views are invalidated and progressively re-displayed as available. This software is designed to facilitate the derivation of the strain fields from the GPS and strain meter data that sample it to facilitate the understanding of the strengths and weaknesses of the strain field derivation from continuous GPS (CGPS) and other geodetic data from a variety of tectonic settings, to converge on the "best practices" strain derivation strategy for the Solid Earth Science ESDR System (SESES) project given the CGPS station distribution in the western U.S., and to provide SESES users with a scientific and educational tool to explore the strain field on their own with user-defined parameters.

  1. Methods for robust in vivo strain estimation in the carotid artery.

    PubMed

    McCormick, M; Varghese, T; Wang, X; Mitchell, C; Kliewer, M A; Dempsey, R J

    2012-11-21

    A hierarchical block-matching motion tracking algorithm for strain imaging is presented. Displacements are estimated with improved robustness and precision by utilizing a Bayesian regularization algorithm and an unbiased subsample interpolation technique. A modified least-squares strain estimator is proposed to estimate strain images from a noisy displacement input while addressing the motion discontinuity at the wall-lumen boundary. Methods to track deformation over the cardiac cycle incorporate a dynamic frame skip criterion to process data frames with sufficient deformation to produce high signal-to-noise displacement and strain images. Algorithms to accumulate displacement and/or strain on particles in a region of interest over the cardiac cycle are described. New methods to visualize and characterize the deformation measured with the full 2D strain tensor are presented. Initial results from patients imaged prior to carotid endarterectomy suggest that strain imaging detects conditions that are traditionally considered high risk including soft plaque composition, unstable morphology, abnormal hemodynamics and shear of plaque against tethering tissue can be exacerbated by neoangiogenesis. For example, a maximum absolute principal strain exceeding 0.2 is observed near calcified regions adjacent to turbulent flow, protrusion of the plaque into the arterial lumen and regions of low echogenicity associated with soft plaques. Non-invasive carotid strain imaging is therefore a potentially useful tool for detecting unstable carotid plaque. PMID:23079725

  2. 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.

  3. Viscous shear dampers

    SciTech Connect

    Zilahi-Szabo, I.

    1980-10-07

    In a viscous shear damper, the seismic mass is chamfered at all its corners. Thus, the clearances between the seismic mass and its casing are gaps with oppositely widening out sections separated by middle sections of smallest widths.

  4. 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. PMID:25768458

  5. 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

  6. Uncoupling shear and uniaxial elastic moduli of semiflexible biopolymer networks: compression-softening and stretch-stiffening

    NASA Astrophysics Data System (ADS)

    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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. Numerical method for shear bands in ductile metal with inclusions

    SciTech Connect

    Plohr, Jee Yeon N; Plohr, Bradley J

    2010-01-01

    A numerical method for mesoscale simulation of high strain-rate loading of ductile metal containing inclusions is described. Because of small-scale inhomogeneities, such a composite material is prone to localized shear deformation (adiabatic shear bands). The modeling framework is the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. /27-139, 1992], which ensures that the micromechanical response of the material is reflected in the behavior of the composite at the mesoscale. To calculate the effective plastic strain rate when shear bands are present, the analytic and numerical analysis of shear bands by Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31-41, 1996] is adapted and extended.

  12. High-strain-rate deformation and comminution of silicon carbide

    NASA Astrophysics Data System (ADS)

    Shih, C. J.; Nesterenko, V. F.; Meyers, M. A.

    1998-05-01

    Granular flow of comminuted ceramics governs the resistance for penetration of ceramic armor under impact. To understand the mechanism of the granular flow, silicon carbide was subjected to high-strain, high-strain-rate deformation by radial symmetric collapse of a thick-walled cylinder by explosive. The deformation, under compressive stresses, was carried out in two stages: the first stage prefractured the ceramic, while a large deformation was accomplished in the second stage. The total tangential strain (-0.23) was accommodated by both homogeneous deformation (-0.10) and shear localization (-0.13). Three microstructures, produced by different processing methods, were investigated. The microstructural differences affected the microcrack propagation: either intergranular or transgranular fracture was observed, depending on the processing conditions. Nevertheless, the spacing between shear bands and the shear displacement within the shear bands were not significantly affected by the microstructure. Within the shear bands, the phenomenon of comminution occurred, and the thickness of the shear bands increased gradually with the shear strain. A bimodal distribution of fragments developed inside the shear bands. The comminution proceeded through the incorporation of fragments from the shear-band interfaces and the erosion of fragments inside the shear band. Outside the shear bands, an additional comminution mechanism was identified: localized bending generated comminution fronts, which transformed the fractured material into the comminuted material. The observed features of high-strain-rate deformation of comminuted SiC can be used for validation of computer models for penetration process.

  13. A shear localization mechanism for lubricity of amorphous carbon materials

    PubMed Central

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

  14. A shear localization mechanism for lubricity of amorphous carbon materials.

    PubMed

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

  15. A shear localization mechanism for lubricity of amorphous carbon materials

    NASA Astrophysics Data System (ADS)

    Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

    2014-01-01

    Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials.

  16. Anisotropy of force distributions in sheared soft-particle systems

    NASA Astrophysics Data System (ADS)

    Boberski, Jens; Shaebani, M. Reza; Wolf, Dietrich E.

    2014-11-01

    In this numerical study, measurements of the contact forces inside a periodic two-dimensional sheared system of soft frictional particles are reported. The distribution \\text{P}(fn) of normalized normal forces fn=Fn/< Fn > exhibits a gradual broadening with the increase of the pure shear deformation γ, leading to a slower decay for large forces. The process, however, slows down and \\text{P}(fn) approaches an invariant shape at high γ. By introducing the joint probability distribution \\text{P}(fn,α) in sheared configurations, it is shown that for a fixed direction α, the force distribution decays faster than exponentially even in a sheared system. The overall broadening can be attributed to the averaging over different directions in the presence of shear-induced stress anisotropy. The distribution of normalized tangential forces almost preserves its shape for arbitrary applied strain.

  17. Coexistence and transition between shear zones in slow granular flows.

    PubMed

    Moosavi, Robabeh; Shaebani, M Reza; Maleki, Maniya; Török, János; Wolf, Dietrich E; Losert, Wolfgang

    2013-10-01

    We report experiments on slow granular flows in a split-bottom Couette cell that show novel strain localization features. Nontrivial flow profiles have been observed which are shown to be the consequence of simultaneous formation of shear zones in the bulk and at the boundaries. The fluctuating band model based on a minimization principle can be fitted to the experiments over a large variation of morphology and filling height with one single fit parameter, the relative friction coefficient μ(rel) between wall and bulk. The possibility of multiple shear zone formation is controlled by μ(rel). Moreover, we observe that the symmetry of an initial state, with coexisting shear zones at both side walls, breaks spontaneously below a threshold value of the shear velocity. A dynamical transition between two asymmetric flow states happens over a characteristic time scale which depends on the shear strength. PMID:24138274

  18. Shear modulus and dilatancy softening in granular packings above jamming.

    PubMed

    Coulais, C; Seguin, A; Dauchot, O

    2014-11-01

    We investigate experimentally the mechanical response to shear of a monolayer of bidisperse frictional grains across the jamming transition. We inflate an intruder inside the packing and use photoelasticity and tracking techniques to measure the induced shear strain and stresses at the grain scale. We quantify experimentally the constitutive relations for strain amplitudes as low as 10(-3) and for a range of packing fractions within 2% variation around the jamming transition. At the transition strong nonlinear effects set in: both the shear modulus and the dilatancy shear soften at small strain until a critical strain is reached where effective linearity is recovered. The scaling of the critical strain and the associated critical stresses on the distance to jamming are extracted. We check that the constitutive laws, together with mechanical equilibrium, correctly predict to the observed stress and strain profiles. These profiles exhibit a spatial crossover between an effective linear regime close to the inflater and the truly nonlinear regime away from it. The crossover length diverges at the jamming transition. PMID:25415925

  19. A new parallel plate shear cell for in situ real-space measurements of complex fluids under shear flow

    NASA Astrophysics Data System (ADS)

    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 200μm with parallelism better than 1μm. 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 0.02-103s-1. This shear cell can apply an oscillatory shear with adjustable amplitude and frequency. The maximum travel of each plate equals 1cm, 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 1μm diameter silica colloids.

  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. PMID:17979430

  1. Converging shear rheometer

    NASA Astrophysics Data System (ADS)

    Baek, Hyung M.; Mix, Adam W.; Giacomin, A. Jeffrey

    2014-05-01

    For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly converging flow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscous Newtonian fluid between two gently converging plates with no slip boundaries using the equation of motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problem using the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionless velocity, pressure and shear stress. This work deepens our understanding of a drag flow through a gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell model to explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutions to finite element calculations for both Newtonian and corotational Maxwell cases. A worked example for determining the Newtonian viscosity using a converging shear rheometer is also included. With this work, we provide the framework for exploring other constitutive equations or other boundary conditions in future work. Our results can also be used to design the linear bearings used for the parallel sliding plate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that is caused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporated into a SPR.

  2. Conjugate-shear folding: A model for the relationships between foliations, folds and shear zones

    NASA Astrophysics Data System (ADS)

    Aerden, Domingo G. A. M.; Sayab, Mohammad; Bouybaouene, Mohamed L.

    2010-08-01

    Microstructural mapping of whole thin sections cut from two samples of micaschist containing cm-scale folds plus garnet porphyroblasts has provided new insight in the relationships between folding, shearing and foliation development. The garnets exhibit coherent inclusion-trail patterns that place important constraints on the kinematic development of both samples, which are shown to be representative of coaxial versus non-coaxial deformation in rocks containing a pre-existing schistosity. A comparison of crenulations-cleavages geometries in both samples and a review of the geometry of natural and experimental multilayer folds leads to the conclusion that folding involves conjugate shearing at different scales. At microscopic scales, crenulation cleavages nucleate as conjugate-kink or shear instabilities and develop further as a function of the macroscopic partitioning of deformation. In fold-hinge domains, bulk-coaxial deformation results in equal development of conjugate crenulations that progressively coalescence into symmetrical crenulation patterns so that, macroscopically, parallelism is achieved between foliation, fold-axial planes and long axes of strain ellipses. Fold-limb domains represent a system of conjugate-shear zones where single sets of crenulation instabilities with synthetic shearing component preferentially develop producing oblique relationships between the aforementioned elements. Cleavage fanning is inferred as a direct consequence of this conjugate-shear origin of folds. The model implies that crenulation cleavages and S-C fabrics in shear zones form by analogous processes, in both cases involving a component of shearing along foliation planes. The development of conjugate sets of foliation planes surrounding porphyroblasts during early, relatively coaxial stages of deformation explains continued "gyrostatic" behaviour during more advanced non-coaxial stages, as indicated by consistently oriented inclusion trails in the studied samples.

  3. 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.

  4. Nonequilibrium structure of colloidal dumbbells under oscillatory shear

    NASA Astrophysics Data System (ADS)

    Heptner, Nils; Chu, Fangfang; Lu, Yan; Lindner, Peter; Ballauff, Matthias; Dzubiella, Joachim

    2015-11-01

    We investigate the nonequilibrium behavior of dense, plastic-crystalline suspensions of mildly anisotropic colloidal hard dumbbells under the action of an oscillatory shear field by employing Brownian dynamics computer simulations. In particular, we extend previous investigations, where we uncovered nonequilibrium phase transitions, to other aspect ratios and to a larger nonequilibrium parameter space, that is, a wider range of strains and shear frequencies. We compare and discuss selected results in the context of scattering and rheological experiments. Both simulations and experiments demonstrate that the previously found transitions from the plastic crystal phase with increasing shear strain also occur at other aspect ratios. We explore the transition behavior in the strain-frequency phase and summarize it in a nonequilibrium phase diagram. Additionally, the experimental rheology results hint at a slowing down of the colloidal dynamics with higher aspect ratio.

  5. Strain in southern California: Measured uniaxial north-south regional contraction

    USGS Publications Warehouse

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

    1978-01-01

    The plate tectonics model of the Pacific moving northwest relative to North America implies that the regional strain in California should be simple shear across a vertical plane striking N45??W or equivalently equal parts of north-south contraction and east-west extension. Measurements of the strain accumulation at seven separate sites in southern California in the interval 1972 through 1978 indicate a remarkably consistent uniaxial north-south contraction of about 0.3 part per million per year; the expected east-west extension is absent. It is not clear whether the period from 1972 through 1978 is anomalous or whether the secular strain in southern California is indeed a uniaxial north-south contraction.

  6. 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. PMID:26472384

  7. Reynolds Pressure and Relaxation in a Homogeneous Sheared Granular System

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Dijksman, Joshua; Behringer, Robert

    2012-11-01

    We describe experiments on the constitutive behavior of a system composed of a disordered collection of frictional disks. We use a novel shear apparatus that avoids the formation of inhomogeneities known as shear bands. We probe the evolution of shear jammed states, occurring for packing fractions φS <= φ <=φJ , where above φJ there are no stress-free static states, and below φS, all static states are stress-free. Our linearly sheared, fixed φ system exhibits coupling between the shear strain, γ, and the pressure, P, which we characterize by the ``Reynolds pressure,'' and a ``Reynolds coefficient,'' R (φ) = (∂2 P / ∂γ2) / 2 . R depends only on φ, and diverges as R ~(φc - φ)α , where φc ~=φJ , and α ~= - 3 . 3 . Moreover, by using asymmetric strain cycles, we find that the observed constitutive relations are limit cycles that are approached logarithmically slowly under cyclic shear. We characterize the relaxation in terms of the pressure asymmetry at cycle n: ΔP ~= - β ln (n /n0) . β depends only on the shear cycle amplitude, suggesting an activated process where β plays a temperature-like role. This work is supported by NSF grant DMR12-06351, NSF grant 0835742, and ARO grant W911NF-11-1-0110.

  8. Vibration of shear deformable rings: Theory and experiment†

    NASA Astrophysics Data System (ADS)

    Gardner, T. G.; Bert, C. W.

    1985-12-01

    A new first-approximation theory is presented for analysis of the in-plane dynamic behavior of shear deformable ring structures. This theory may be applied to curved beams as well as complete rings. Natural frequencies and associated vibrational modes for a complete ring are investigated experimentally using modern instrumentation and experimental techniques. The natural frequencies predicted by the new theory are compared with the new experimental data as well as some previously reported data and predictions from thin-ring theory, various other shear deformable theories, elasticity theory, and various finite element analyses. The present theory includes a description of transverse shear strain which permits satisfaction of the physical requirements of zero shear stress at the inner-and outer-ring surfaces. Transverse shear strain is an important effect when analyzing thick, homogeneous, material rings and even more significant for rings made of composite materials. This theory is an advancement over Bresse-type, shear-correction theories, which utilize a shear correction factor determined in an ad hoc fashion.

  9. 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.

  10. Metal shearing energy absorber

    NASA Technical Reports Server (NTRS)

    Fay, R. J.; Wittrock, E. P. (Inventor)

    1973-01-01

    A metal shearing energy absorber is described. The absorber is composed of a flat thin strip of metal which is pulled through a slot in a cutter member of a metal, harder than the metal of the strip. The slot's length, in the direction perpendicular to the pull direction, is less than the strip's width so that as the strip is pulled through the slot, its edges are sheared off, thereby absorbing some of the pulling energy. In one embodiment the cutter member is a flat plate of steel, while in another embodiment the cutter member is U-shaped with the slot at its base.

  11. 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.

  12. 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.

  13. Infrared lateral shearing interferometers

    NASA Astrophysics Data System (ADS)

    Kwon, O.

    1980-04-01

    Recently IR interferometry has received much attention for its special capabilities of testing IR materials, diamond-turned metal mirrors, deep aspherics, unpolished rough surface optics, and other unconventional optics. A CW CO2 laser is used as a coherent light source at 10.6 microns, and germanium and zinc selenide optics are used for lenses and beam splitters. A pyroelectric vidicon (PEV) detects the modulated interference pattern through a TV monitor and video recorder-player. This paper presents three methods of IR lateral shear interferometry using (1) a germanium plane-parallel plate, (2) a Ronchi ruling, and (3) a double-grating lateral shear interferometer.

  14. 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.

  15. Two-dimensional shear bands growing dynamically in plates: An investigation of transient deformation fields, temperature fields and shear band toughness

    SciTech Connect

    Rosakis, A.J.

    1995-12-31

    The phenomenon of dynamic initiation and propagation of two-dimensional adiabatic shear bands is experimentally and numerically investigated. Prenotched metal plates are subjected to asymmetric impact load histories (dynamic mode-II loading). Dynamic shear bands emanate from the notch-tip and propagate rapidly in a direction nearly parallel to the direction of impact. Real time temperature histories along a line intersecting and perpendicular to the shear band paths are recorded by means of a high speed infrared detector system. The materials studied are C-300 (a maraging steel), HY-100 steel and Ti-6Al-4V. Experiments show that the peak temperatures inside the propagating shear bands are approaching 90% of the melting point for C-300 and are significantly lower for the titanium alloy (up to 6000C). Additionally, measured distances of shear band propagation indicate stronger resistance to shear banding by HY-100 steel and Ti-6Al-4V. Deformation fields around the propagating shear band are recorded using high speed photography. Shear band speeds are found to strongly depend on impact velocity are as high as 1200 m/s for C-300 steel. Finite element simulations of the experiment are carried out under the context of plane strain, considering finite deformations, inertia, heat conduction, thermal softening, strain hardening and strain-rate hardening. In the simulations, the shear band propagation is assumed to be governed by a critical plastic strain criterion. The results are compared with experimental measurements obtained using the high speed infrared detectors and high speed photography. Finally, the numerical calculations are used to investigate motions of shear band toughness. The shear band driving force is calculated as a function of shear band velocity and compared to the crack driving force versus velocity relations for mode-I, opening cracks in the same material.

  16. Microstructural changes, steady-state deformation and strain localisation during large strain deformation of rocks

    NASA Astrophysics Data System (ADS)

    Barnhoorn, A.

    2012-04-01

    Ductile deformation in the Earth's crust and mantle is often concentrated in narrow shear zones. These shear zones play a fundamental role in the deformation dynamics of the earth's lithosphere during mountain building, subduction and continental break-up. Shear zones exhibit large amounts of strain with an increase in strain from the edge to the center of the shear zone. Those large strains are often accompanied with large changes in microstructure due to processes such as dynamic recrystallization, grain size refinement, development of strong foliations, development of crystallographic preferred orientations, weakening of the rock as well as progressive localisation of the deformation into more and more concentrated zones. The interplay between all those different processes produce the various microstructures that are often studied in natural shear zones to assess the deformation conditions and history of plate tectonic processes. Experimental deformation studies under controlled conditions are used to produce relationships between the different processes active in shear zones (rheology, microstructural changes, and CPO development) in order to make those quantitative inferences on natural shear zones, Here I will present the outcomes from large strain torsion experiments at elevated temperatures and pressures on monophase calcitic rocks showing that very large strains are needed before true steady-state conditions in rocks are attained. Continuous changes in crystallographic preferred orientations and continuous dynamic recrystallization by grain boundary migration and subgrain rotation recrystallization occur up to the largest shear strains achieved in the study (shear strain of 50). Dynamic recrystallization from an undeformed coarse-grained calcite rock types towards a fine-grained ultramylonite is accompanied by a modest (~20%) weakening of the rock. However, this modest weakening never caused strain localisation in the samples. In contrast to the

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Sheared Electroconvective Instability

    NASA Astrophysics Data System (ADS)

    Kwak, Rhokyun; Pham, Van Sang; Lim, Kiang Meng; Han, Jongyoon

    2012-11-01

    Recently, ion concentration polarization (ICP) and related phenomena draw attention from physicists, due to its importance in understanding electrochemical systems. Researchers have been actively studying, but the complexity of this multiscale, multiphysics phenomenon has been limitation for gaining a detailed picture. Here, we consider electroconvective(EC) instability initiated by ICP under pressure-driven flow, a scenario often found in electrochemical desalinations. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of sheared EC: unidirectional vortex structures, its size selection and vortex propagation. Selected by balancing the external pressure gradient and the electric body force, which generates Hagen-Poiseuille(HP) flow and vortical EC, the dimensionless EC thickness scales as (φ2 /UHP)1/3. The pressure-driven flow(or shear) suppresses unfavorably-directed vortices, and simultaneously pushes favorably-directed vortices with constant speed, which is linearly proportional to the total shear of HP flow. This is the first systematic characterization of sheared EC, which has significant implications on the optimization of electrodialysis and other electrochemical systems.

  3. Granular dynamics under shear with deformable boundaries

    NASA Astrophysics Data System (ADS)

    Geller, Drew; Backhaus, Scott; Ecke, Robert

    2015-03-01

    Granular materials under shear develop complex patterns of stress as the result of granular positional rearrangements under an applied load. We consider the simple planar shear of a quasi two-dimensional granular material consisting of bi-dispersed nylon cylinders confined between deformable boundaries. The aspect ratio of the gap width to total system length is 50, and the ratio of particle diameter to gap width is about 10. This system, designed to model a long earthquake fault with long range elastic coupling through the plates, is an interesting model system for understanding effective granular friction because it essentially self tunes to the jamming condition owing to the hardness of the grains relative to that of the boundary material, a ratio of more than 1000 in elastic moduli. We measure the differential strain displacements of the plates, the inhomogeneous stress distribution in the plates, the positions and angular orientations of the individual grains, and the shear force, all as functions of the applied normal stress. There is significant stick-slip motion in this system that we quantify through our quantitative measurements of both the boundary and the grain motion, resulting in a good characterization of this sheared 2D hard sphere system.

  4. Measuring the reduced shear

    SciTech Connect

    Zhang, Jun

    2011-11-01

    Neglecting the second order corrections in weak lensing measurements can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Existing methods which claim to measure the reduced shears are not necessarily accurate to the second order when a point spread function (PSF) is present. We show that the method of Zhang (2008) exactly measures the reduced shears at the second order level in the presence of PSF. A simple theorem is provided for further confirming our calculation, and for judging the accuracy of any shear measurement method at the second order based on its properties at the first order. The method of Zhang (2008) is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the PSF. To reach a sub-percent level accuracy, the CCD pixel size is required to be not larger than 1/3 of the Full Width at Half Maximum (FWHM) of the PSF, regardless of whether the PSF has a power-law or exponential profile at large distances. Using a large ensemble (∼>10{sup 7}) of mock galaxies of unrestricted morphologies, we study the shear recovery accuracy under different noise conditions. We find that contaminations to the shear signals from the noise of background photons can be removed in a well defined way because they are not correlated with the source shapes. The residual shear measurement errors due to background noise are consistent with zero at the sub-percent level even when the amplitude of such noise reaches about 1/10 of the source flux within the half-light radius of the source. This limit can in principle be extended further with a larger galaxy ensemble in our simulations. On the other hand, the source Poisson noise remains to be a cause of systematic errors. For a sub-percent level accuracy, our method requires the amplitude of the source Poisson noise to be less than 1/80 ∼ 1/100 of the source flux within the half-light radius of the source

  5. 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.

  6. Shear degradation in fiber reinforced laminates due to matrix damage

    NASA Astrophysics Data System (ADS)

    Salavatian, Mohammedmahdi

    The objective of this study was to develop and implement a shear modulus degradation model to improve the failure analysis of the fiber reinforced composite structures. Matrix damage, involving transverse and shear cracks, is a common failure mode for composite structures, yet little is known concerning their interaction. To understand the material behavior after matrix failure, the nonlinear response of the composite laminate was studied using pressure vessels made from a [+/-o] bias orientation, which tend to exhibit a matrix dominated failure. The result of this work showed laminate matrix hardening in shear and softening in the transverse direction. A modified Iosipescu coupon was proposed to study the evolution of shear and transverse damage and their mutual effects. The proposed method showed good agreement with tubular results and has advantages of simplified specimen fabrication using standard test fixtures. The proposed method was extended by introducing a novel experimental technique to study the shear degradation model under biaxial loading. Experimental results of the transverse modulus reduction were in good agreement with material degradation models, while the predicted shear modulus reduction was higher than experiment. The discrepancy between available models and observations was due to the presence of a traction between the crack surfaces. Accordingly, a closed form solution was proposed for the shear stress-strain field of a cracked laminate by replacing the cracks with cohesive zones. The constitutive equations of the crack laminate were derived including the effects of internal tractions and transverse stress on the shear modulus. The proposed analytical model was shown to be the most comprehensive model for shear modulus degradation reduction of the fiber reinforced laminates. A numerical implementation of the shear degradation model was done using continuum damage mechanics. Through this work it was shown the common assumption of a linear

  7. Numerical Modeling of Shear Bands and Dynamic Fracture in Metals

    NASA Astrophysics Data System (ADS)

    McAuliffe, Colin James

    Understanding the failure of metals at high strain rate is of utmost importance in the design of a broad range of engineering systems. Numerical methods offer the ability to analyze such complex physics and aid the design of structural systems. The objective of this research will be to develop reliable finite element models for high strain rate failure modelling, incorporating shear bands and fracture. Shear band modelling is explored first, and the subsequent developments are extended to incorporate fracture. Mesh sensitivity, the spurious dependence of failure on the discretization, is a well known hurdle in achieving reliable numerical results for shear bands and fracture, or any other strain softening model. Mesh sensitivity is overcome by regularization, and while details of regularization techniques may differ, all are similar in that a length scale is introduced which serves as a localization limiter. This dissertation contains two main contributions, the first of which presents several developments in shear band modeling. The importance of using a monolithic nonlinear solver in combination with a PDE model accounting for thermal diffusion is demonstrated. In contrast, excluding one or both of these components leads to unreliable numerical results. The Pian-Sumihara stress interpolants are also employed in small and finite deformation and shown to significantly improve the computational cost of shear band modelling. This is partly due to the fact that fewer unknowns than an irreducible discretization result from the same mesh, and more significantly, the fact that convergence of numerical results upon mesh refinement is improved drastically. This means coarser meshes are adequate to resolve shear bands, alleviating some of the computational cost of numerical modelling, which are notoriously significant. Since extremely large deformations are present during shear banding, a mesh to mesh transfer algorithm is presented for the Pian Sumihara element and used as

  8. 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.

  9. Microstructural evolution during strain localization in dolomite aggregates

    NASA Astrophysics Data System (ADS)

    Holyoke, Caleb W.; Kronenberg, Andreas K.; Newman, Julie

    2014-12-01

    Dolomite aggregates deformed by dislocation creep over a wide range of conditions (T = 700-1000 °C, effective pressure of 900 MPa, strain rates of 10-7 - 10-4/s) strain weaken by up to 75% of the peak differential stress. Microstructural study of samples shortened to different finite strains beyond the peak differential stress shows that strain becomes highly localized within shear zones by high-temperature creep processes, with no contribution of brittle cracking. At low strains (8%), dolomite deforms homogeneously by recrystallization-accommodated dislocation creep. At progressively higher sample strains, deformation is localized into narrow shear zones made up of very fine (˜3 μm) recrystallized grains and relict porphyroclasts (20-100 μm). Finely-recrystallized dolomite grains in the shear zones are largely dislocation free and localized shear is facilitated by diffusion creep. In contrast, original dolomite grains and porphyroclasts in shear zones have high dislocation densities and do not deform after shear zone formation. Calculated strain rates in the shear zones are two to three orders of magnitude faster than the imposed bulk strain rate of the samples and these strain rates are consistent with predictions of the diffusion creep flow law for fine-grained dolomite.

  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. 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.

  12. A theoretical model of sheath fold morphology in simple shear

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Dabrowski, Marcin; Galland, Olivier; Schmid, Daniel W.

    2013-04-01

    Sheath folds are highly non-cylindrical structures often associated with shear zones. The geometry of sheath folds, especially cross-sections perpendicular to the stretching direction that display eye-patterns, have been used in the field to deduce kinematic information such as shear sense and bulk strain type. However, how sheath folds form and how they evolve with increasing strain is still a matter of debate. We investigate the formation of sheath folds around a weak inclusion acting as a slip surface in simple shear by means of an analytical model. We systematically vary the slip surface orientation and shape and evaluate the impact on the evolving eye-pattern. In addition we compare our results to existing classifications. Based on field observations it has been suggested that the shear sense of a shear zone can be determined by knowing the position of the center of an eye-pattern and the closing direction of the corresponding sheath fold. In our modeled sheath folds we can observe for a given strain that the center of the eye-structure is subject to change in height with respect to the upper edge of the outermost closed contour for different cross-sections perpendicular to the shear direction. This results in a large variability in layer thickness, questioning the usefulness of sheath folds as shear sense indicators. The location of the center of the eye structure, however, is largely invariant to the initial configurations of the slip surface as well as to strain. It has been suggested that the ratio of the aspect ratio of the innermost and outermost closed contour in eye-patterns could be linked to the bulk strain type based on filed observations. We apply this classification to our modeled sheath folds and we observe that the values of the aspect ratios of the closed contours within the eye-pattern are dependent on the strain and the cross-section location. The ratio (R') of the aspect ratios of the outermost closed contour (Ryz) and the innermost closed

  13. 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

  14. 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.

  15. 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.

  16. CAT LIDAR wind shear studies

    NASA Technical Reports Server (NTRS)

    Goff, R. W.

    1978-01-01

    The studies considered the major meteorological factors producing wind shear, methods to define and classify wind shear in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection and measurement of wind shear, and the tradeoffs involved in sensor performance such as range/velocity resolution, update frequency and data averaging interval.

  17. Rheology linked with phase changes as recorded by development of shear bands in the South Armorican Shear Zone

    NASA Astrophysics Data System (ADS)

    Jeřábek, Petr; Bukovská, Zita

    2015-04-01

    recrystallization along thin shear bands records strain rates of ~10^-14 whereas the recrystallization along thick shear bands records strain rates of ~10^-15. The contemporaneous operation of solution-precipitation creep in shear bands and dislocation creep in quartz along the shear band boundary suggests low viscosity contrast between the mixed phase shear band matrix and pure quartz aggregate implying that the solution-precipitation creep reflect similar stress and strain rate conditions as the dislocation creep in quartz. Stage III of shear band evolution is characterized by interconnection of dispersed muscovite grains and the deformation becomes accommodated by dislocation creep in thin muscovite bands separating the inactive domains of stage II microstructure. References: Holyoke III, C. W., & Kronenberg, A. K. (2010). Accurate differential stress measurement using the molten salt cell and solid salt assemblies in the Griggs apparatus with applications to strength, piezometers and rheology. Tectonophysics, 494(1-2), 17-31. Paterson, M. S., & Luan, F. C. (1990). Quartzite rheology under geological conditions. In R. J. Knipe & E. H. Rutter (Eds.), Deformation Mechanisms, Rheology and Tectonics (pp. 299-307). London: Geological Society Special Publications. Stipp, M., & Tullis, J. (2003). The recrystallized grain size piezometer for quartz. Geophysical Research Letters, 30(21), 1-5.

  18. Raman spectroscopy study of nitromethane in a shear diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Hébert, Philippe; Isambert, Aude; Petitet, Jean-Pierre; Zerr, Andreas

    2010-03-01

    In addition to pressure and temperature effects, shear strain has been proposed to play an important role in the initiation and decomposition mechanisms of energetic materials. To study the effect of shear strain in more detail, a shear diamond anvil cell has been developed. In this paper, we present a Raman spectroscopy study of the effects of shear strain on the high-pressure behaviour of nitromethane (NM). Two major effects are observed in our experiments. The first one is a lowering of the pressures at which the different structural modifications of NM occur. The second one is observed at 28 GPa, where the sample decomposes suddenly just after shear application. Examination of the black residue showed that it is composed of carbon, as indicated by the Raman spectrum.

  19. Finite element analyses for Seismic Shear Wall International Standard Problem

    SciTech Connect

    Park, Y.; Hofmayer, C.; Chokshi, N.

    1997-04-01

    In the seismic design of shear wall structures, e.g., nuclear reactor buildings, a linear FEM analysis is frequently used to quantify the stresses under the design loading condition. The final design decisions, however, are still based on empirical design rules established over decades from accumulated laboratory test data. This paper presents an overview of the state-of-the-art on the application of nonlinear FEM analysis to reinforced concrete (RC) shear wall structures under severe earthquake loadings based on the findings obtained during the Seismic Shear Wall International Standard Problem (SSWISP) Workshop in 1996. Also, BNL`s analysis results of the International Standard Problem (ISP) shear walls under monotonic static, cyclic static and dynamic loading conditions are described.

  20. 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.

  1. 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.

  2. Interseismic Plate coupling and strain partitioning in the Northeastern Caribbean

    NASA Astrophysics Data System (ADS)

    Manaker, D. M.; Calais, E.; Freed, A. M.; Ali, S. T.; Przybylski, P.; Mattioli, G.; Jansma, P.; Prépetit, C.; de Chabalier, J. B.

    2008-09-01

    The northeastern Caribbean provides a natural laboratory to investigate strain partitioning, its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary. Here, we use GPS and earthquake slip vector data to produce a present-day kinematic model that accounts for secular block rotation and elastic strain accumulation, with variable interplate coupling, on active faults. We confirm that the oblique convergence between Caribbean and North America in Hispaniola is partitioned between plate boundary parallel motion on the Septentrional and Enriquillo faults in the overriding plate and plate-boundary normal motion at the plate interface on the Northern Hispaniola Fault. To the east, the Caribbean/North America plate motion is accommodated by oblique slip on the faults bounding the Puerto Rico block to the north (Puerto Rico subduction) and to the south (Muertos thrust), with no evidence for partitioning. The spatial correlation between interplate coupling, strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate, facilitating strike-slip faulting in the overriding plate. The model slip rate deficit, together with the dates of large historical earthquakes, indicates the potential for a large (Mw7.5 or greater) earthquake on the Septentrional fault in the Dominican Republic. Similarly, the Enriquillo fault in Haiti is currently capable of a Mw7.2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today. The model results show that the Puerto Rico/Lesser Antilles subduction thrust is only partially coupled, meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion. This does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes, but whose

  3. 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

  4. Brittle reactivation of ductile shear zones in NW Namibia

    NASA Astrophysics Data System (ADS)

    Salomon, Eric; Koehn, Daniel; Passchier, Cees

    2014-05-01

    Existing structural elements, such as shear zones, are regarded to have a significant influence on the orientation and extent of younger structures. Thus, shear zones are seen as a primary controlling factor on the development of rift zones (e.g. Piqué & Laville, 1996). Indeed, reactivation of such structures is observed in numerous areas. However, information on the amount of offset associated with a reactivation is often lacking. Reactivation of shear zones is also reported of in NW Namibia in relation to the South Atlantic Rifting (Marsh et al., 2001; Stanistreet & Charlesworth, 2001). Here, we present the results of a quantitative study on this reactivation. NW Namibia is characterized by the ~N-S trending Kaoko Belt which developed during the assemblage of Gondwana in the Neo-Proterozoic and incorporates a number of shear zones, e.g. the Purros Shear Zone and Three Palms Shear Zone, which run sub-parallel to the present-day continental margin. The shear zones are partly covered by the extrusives of the Paraná-Etendeka Large Igneous Province (~133 Ma) which extruded shortly before or during the onset of the Atlantic rifting (e.g. Blaich et al., 2011). Combining the analysis of satellite imagery and digital elevation models with extensive field work, we identified numerous faults tracing the old shear zones along which the Etendeka basalts were down-faulted. Listric faults developed along the shear zones and accumulated vertical offsets up to 900 m. The faults developed in areas where the foliation along the shear zones is steepest, indicating that a dip of >65° is necessary for normal reactivation. A basin developed along the section where the shear zone is supposedly widest. Our results contribute to the view that the basement inheritance plays a significant role on rifting processes and that the reactivation of shear zones can accumulate significant amounts of displacement. References: Blaich, O.A. et al. (2011). Journal of Geophysical Research - Solid

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. Deformation measurements of composite multi-span beam shear specimens by Moire interferometry

    NASA Technical Reports Server (NTRS)

    Post, D.; Czarnek, R.; Joh, D.; Wood, J.

    1984-01-01

    Experimental analyses were performed for determination of in plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight ply beams were subjected to 5 point and 3 point flexure. Whole field measurements were recorded at load levels from about 20% to more than 90% of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole field contour maps of shear strains were obtained by a method developed for these tests. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin rich zones in regions of shear tractions; free edge shear strains in quasi-isotropic specimens in regions of normal stresses; and shear stresses associated with cyclic shear compliances of quasi-isotropic plies in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of relaxation; influence of contact stress distribution; specimen failure; effect of specimen overhang; nonlinearity; and qualities of 5 and 3 point flexure tests.

  15. 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.

  16. Factors determining crystal--liquid coexistence under shear.

    PubMed

    Butler, Scott; Harrowell, Peter

    2002-02-28

    The interaction between an imposed shear flow and an order--disorder transition underlies a broad range of phenomena. Under the influence of shear flow, a variety of soft matter is observed to spontaneously form bands characterized by different local order---for example, thermotropic liquid crystals subjected to shear flow exhibit rich phase behaviour. The stability of order under the influence of shear flow is also fundamental to understanding frictional wear and lubrication. Although there exists a well developed theoretical approach to the influence of shear flow on continuous transitions in fluid mixtures, little is known about the underlying principles governing non-equilibrium coexistence between phases of different symmetry. Here we show, using non-equilibrium molecular dynamics simulations of a system of spherical particles, that a stationary coexistence exists between a strained crystal and the shearing liquid, and that this coexistence cannot be accounted for by invoking a non-equilibrium analogue of the chemical potential. Instead of such thermodynamic arguments, we argue that a balancing of the crystal growth rate with the rate of surface erosion by the shearing melt can account for the observed coexistence. PMID:11875564

  17. Mechanical modeling of shear localization in foliated media

    NASA Astrophysics Data System (ADS)

    Le Pourhiet, L.; Huet, B.; Agard, P.

    2009-12-01

    Crustal rocks have generally an anisotropic behavior at scale that largely exceeds the mineral/grain size. In the upper crust, the bedding of the sediments causes this anisotropy. In the middle crust, towards the base of the sismogenic zone, the rocks usually present a penetrative foliation, which also results in an anisotropic behavior. In order to better understand the response of foliated rocks to simple shear, we perform mechanical numerical model. The set up of the model consist of a layered media made of a weak and a strong phase submitted to simple shear. The parameters of the analysis are the initial angle formed by the bedding and the simple shear direction and the relative thickness of the strong and weak layers. Those layers are both isotropic. The anisotropy introduced explicitly through the geometry. In both case, we use visco-elasto-plastic material. The plastic part of the strain is modeled with Mohr Coulomb plasticity and elastic moduli are identical in the weak and strong phase. We neglect the effect of gravity and temperature. The numerical experiments are run until the global shear of the model reach γ=2. However, locally the shear may be of one to two orders of magnitude higher. In general, shear banding occurs when the layering of the sample of the sample forms a 30° angle with the shear direction. Therefore the results of the experiments may be tiled into to end member cases. In the first one, the shear bands form a large (more than 90°) angle to the shear sense. Those experiments show very long phase of passive rotation and stretching of the strong layer during which the average strength of the media decreases slowly. However, once, the angle of 90° is passed, the strength of the media increase again until shear banding occurs resulting in a rapid drop of the strength. In the second end member case, the sample strength tends to increase right away before the occurrence of the first shear band. We finally study the geometry of the sheared

  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. 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.