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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Shear band velocity and activation volume during shear deformation by acoustic emission in a Zr-based bulk metallic glass

Here, an analysis is presented for the shear band velocity of plastic deformation and activation volume of the shear transformation zone (STZ) in a Zr 60 Cu 30 Al 10 bulk metallic glass (BMG). Compared to the values calculated by the stick-slip model, the values of shear band velocity calculated after optimization by the acoustic emission technique are much larger than those reported previously. Plastic flow in BMGs is found to be described by a power-law correlation between the maximum velocity of the shear band and the strain rates. Combining the free volume theory and the STZ theory, the relationship between the volume change in the STZ and the shear band velocity is derived as $Ω=A$(27–ln$v/l$). The value of A, which is a material dependent constant, is 5.43 × 10 –3 for the current BMG at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Experimental development of low-frequency shear modulus and attenuation measurements in mated rock fractures: Shear mechanics due to asperity contact area changes with normal stress

Reservoir core measurements can help guide seismic monitoring of fluid-induced pressure variations in tight fractured reservoirs including those targeted for supercritical CO 2 injection. We present the first seismic-frequency ‘room-dry’ measurements of fracture specific shear stiffness, using artificially fractured standard granite samples with different degrees of mating, a well-mated tensile fracture from a dolomite reservoir core, as well as simple roughened polymethyl methacrylate (PMMA) surfaces. We have adapted a low-frequency (0.01 to 100 Hz) shear modulus and attenuation apparatus to explore the seismic signature of fractures and understand the mechanics of asperity contacts under a range of normal stress conditions. Our instrument is unique in its ability to measure at low normal stresses (0.5 – 20 MPa), simulating 'open' fractures in shallow or high fluid pressure reservoirs. The accuracy of our instrument is demonstrated by calibration and comparison to ultrasonic measurements and low-frequency direct shear measurements of intact samples from the literature. Pressure sensitive film was used to measure real contact area of the fracture surfaces. The fractured shear modulus for the majority of the samples shows an exponential dependence on real contact area. A simple numerical model, with one bonded circular asperity, predicts this behavior and matches the data for the simple PMMA surfaces. The rock surfaces reach their intact moduli at lower contact area than the model predicts, likely due to more complex geometry. Lastly, we apply our results to a Linear-Slip Interface Model to estimate reflection coefficients and calculate shear wave time delays due to the lower wave velocities through the fractured zone. We find that cross-well surveys could detect even well-mated hard rock fractures assuming the availability of high repeatability acquisition systems.

58 GEOSCIENCES↗
DOE OSTI2013

Size and structure of Chlorella zofingiensis /FeCl 3 flocs in a shear flow: Algae Floc Structure

Flocculation is a promising method to overcome the economic hurdle to separation of algae from its growth medium in large scale operations. But, understanding of the floc structure and the effects of shear on the floc structure are crucial to the large scale implementation of this technique. The floc structure is important because it determines, in large part, the density and settling behavior of the algae. Freshwater algae floc size distributions and fractal dimensions are presented as a function of applied shear rate in a Couette cell using ferric chloride as a flocculant. Comparisons are made with measurements made for a polystyrene microparticle model system taken here as well as reported literature results. The algae floc size distributions are found to be self-preserving with respect to shear rate, consistent with literature data for polystyrene. Moreover, three fractal dimensions are calculated which quantitatively characterize the complexity of the floc structure. Low shear rates result in large, relatively dense packed flocs which elongate and fracture as the shear rate is increased. Our results presented here provide crucial information for economically implementing flocculation as a large scale algae harvesting strategy.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

The effect of shear strain and shear localization on fault healing

The seismic cycle of repeated earthquake failure requires that faults regain frictional strength during the interseismic phase, when the fault is locked or undergoing quasi-static creep. Fault healing plays a central role in determining earthquake stress drop, recurrence interval, elastic radiation frequency and other source parameters. In particular, the longer a fault remains quasi-stationary, the stronger it becomes and the larger the potential stress drop can be for the next event. Here, we address the role of shear strain and strain localization on fault healing and healing rate. We performed slide-hold-slide friction experiments on quartz gouge in the double-direct shear configuration for shear strain up to 25 and hold times from 10 to 1000 s. The results show that both healing and healing rate increase nonlinearly with increasing shear strain. Frictional healing scales with volumetric strain within the laboratory fault zone. Using the volumetric strain upon reshear as a proxy for strain localization, we demonstrate that the capacity of a fault to heal is directly proportional to shear bandwidth and degree of strain localization. The more the deformation is localized, the higher are the healing and healing rate, and thus, the fault strength. Our data provide a framework for understanding variations in fault strength over the seismic cycle and the role of brecciation and strain localization on spatiotemporal variations in fault strength.

58 GEOSCIENCES↗
DOE OSTI2023

Collaborative Research: Effects of the magnetic field shear and flow shear on the kinetic physics and particle acceleration in relativistic magnetic reconnection (Final Report)

Magnetic reconnection is a fundamental plasma process that allows rapid changes of magnetic field topology and the conversion of magnetic energy into plasma kinetic energy. There has been a strong surge of interest in relativistic reconnection over the past few years in plasma astrophysics, but the rich physics of collisionless reconnection and its associated particle acceleration in the relativistic regime remain less studied compared to the non-relativistic counterparts. Magnetic reconnection in a realistic system is often accompanied with the magnetic field shear and shear flows. This setting is more general and likely the more common situation where most reconnection takes place. Within the past few decades, researchers had made significant progress in understanding how magnetic reconnection works under these conditions in the non-relativistic regime. However, how the effect of special relativity, among other effects, influences the dynamics of reconnection in the strongly magnetized astrophysical plasmas under these conditions is largely unknown. Our proposed research is to use fully kinetic simulations to understand kinetic physics and particle acceleration in relativistic magnetic reconnection in more realistic configurations and physical conditions. The primary goal of this project is to identify the fundamental effects caused by special relativity under the presence of field shear and flow shear.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Coupling of dust acoustic and shear mode through velocity shear in a strongly coupled dusty plasma

In the strongly coupled limit, the generalized hydrodynamic model shows that a dusty plasma, acquiring significant rigidity, is able to support a “shear” like mode. It is being demonstrated here that in presence of velocity shear gradient, this shear like mode gets coupled with the dust acoustic mode which is generated by the compressibility effect of the dust fluid due to the finite temperatures of the dust, electron, and ion fluids. In the local analysis, the dispersion relation shows that velocity shear gradient not only couples the two modes but is also responsible for the instabilities of that coupled mode which is confirmed by nonlocal analysis with numerical techniques.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Development of core ion temperature gradients and edge sheared flows in a helicon plasma device investigated by laser induced fluorescence measurements

We report experimental observation of ion heating and subsequent development of a prominent ion temperature gradient in the core of a linear magnetized plasma device, and the controlled shear de-correlation experiment. Simultaneously, we also observe the development of strong sheared flows at the edge of the device. Both the ion temperature and the azimuthal velocity profiles are quite flat at low magnetic fields. As the magnetic field is increased, the core ion temperature increases, producing centrally peaked ion temperature profiles and therefore strong radial gradients in the ion temperature. Similarly, we observe the development of large azimuthal flows at the edge, with increasing magnetic field, leading to strong radially sheared plasma flows. The ion velocities and temperatures are derived from laser induced fluorescence measurements of Doppler resolved velocity distribution functions of argon ions. These features are consistent with the previous observations of simultaneously existing radially separated multiple plasma instabilities that exhibit complex plasma dynamics in a very simple plasma system. The ion temperature gradients in the core and the radially sheared azimuthal velocities at the edge point to mechanisms that can drive the multiple plasma instabilities, that were reported earlier.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

MASKED AREAS IN SHEAR PEAK STATISTICS: A FORWARD MODELING APPROACH

The statistics of shear peaks have been shown to provide valuable cosmological information beyond the power spectrum, and will be an important constraint of models of cosmology in forthcoming astronomical surveys. Surveys include masked areas due to bright stars, bad pixels etc., which must be accounted for in producing constraints on cosmology from shear maps. We advocate a forward-modeling approach, where the impacts of masking and other survey artifacts are accounted for in the theoretical prediction of cosmological parameters, rather than correcting survey data to remove them. We use masks based on the Deep Lens Survey, and explore the impact of up to 37% of the survey area being masked on LSST and DES-scale surveys. By reconstructing maps of aperture mass the masking effect is smoothed out, resulting in up to 14% smaller statistical uncertainties compared to simply reducing the survey area by the masked area. We show that, even in the presence of large survey masks, the bias in cosmological parameter estimation produced in the forward-modeling process is ≈1%, dominated by bias caused by limited simulation volume. We also explore how this potential bias scales with survey area and evaluate how much small survey areas are impacted by the differences in cosmological structure in the data and simulated volumes, due to cosmic variance.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

A road map to cosmological parameter analysis with third-order shear statistics: III. Efficient estimation of third-order shear correlation functions and an application to the KiDS-1000 data

Context. Third-order lensing statistics contain a wealth of cosmological information that is not captured by second-order statistics. However, the computational effort it takes to estimate such statistics in forthcoming stage IV surveys is prohibitively expensive. Aims. We derive and validate an efficient estimation procedure for the three-point correlation function (3PCF) of polar fields such as weak lensing shear. We then use our approach to measure the shear 3PCF and the third-order aperture mass statistics on the KiDS-1000 survey. Methods We constructed an efficient estimator for third-order shear statistics that builds on the multipole decomposition of the 3PCF. We then validated our estimator on mock ellipticity catalogs obtained from N -body simulations. Finally, we applied our estimator to the KiDS-1000 data and presented a measurement of the third-order aperture statistics in a tomographic setup. Results. Our estimator provides a speedup of a factor of ∼100–1000 compared to the state-of-the-art estimation procedures. It is also able to provide accurate measurements for squeezed and folded triangle configurations without additional computational effort. We report a significant detection of tomographic third-order aperture mass statistics in the KiDS-1000 data (S/N = 6.69). Conclusions. Our estimator will make it computationally feasible to measure third-order shear statistics in forthcoming stage IV surveys. Furthermore, it can be used to construct empirical covariance matrices for such statistics.

Astronomy & Astrophysics↗
DOE OSTI2014

Possible contribution of low shear modulus C{sub 44} to the low Young's modulus of Ti-36Nb-5Zr alloy

Despite the importance of single-crystal elastic constants of β-phase titanium alloys in understanding their low Young's modulus—a property crucial for many applications, such data are often difficult to obtain when the alloy composition is close to the instability limit of the β phase, where the presence of α' martensite precludes the fabrication of β-phase single crystal. In the present study, we extracted the single-crystal elastic constants of such a β-phase titanium alloy with low Young's modulus, Ti-36Nb-5Zr (wt. %), from polycrystalline specimens by using an in-situ synchrotron X-ray diffraction technique. It is indicated that the low Young's modulus of the alloy originates from the anomalously low shear modulus C{sub 44} as well as the low shear modulus C′, which is different from a common viewpoint that the Young's modulus of β-phase titanium alloys is dominantly controlled by the C′. This suggests that low C{sub 44} is an important contributor to low Young's modulus for instable β-phase titanium alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Shear-induced lift force on spheres in a viscous linear shear flow at finite volume fractions

Several studies have shown a significant increase in drag on a distribution of solid spherical particles within a fluid with increasing particle volume fraction. As a result, many empirical drag laws accounting for the dependence on the Reynolds number and volume fraction can be found in the literature. This study investigates the possibility of a similar effect of the particle volume fraction on the mean hydrodynamic lift force on randomly distributed spherical particles in a linear shear flow. Particle-resolved direct numerical simulations are performed to evaluate the mean lift force, and the results are compared with the case of an isolated particle in a linear shear flow for the same Reynolds number and shear rate. The mean lift force acting on the particles appears to remain nearly the same as that on an isolated particle. However, due to the influence of neighboring particles, there is a substantial force variation in transverse directions on each individual particle, whose magnitude is comparable to the mean drag force. The distribution of drag force in a linear shear flow is shown to be nearly the same as in a uniform flow at the same volume fraction and Reynolds number. A simple stochastic model based on a Gaussian distribution is presented for the lift force variation, and its performance is compared to the prediction of the deterministic pairwise interaction extended point-particle model.

42 ENGINEERING↗
DOE OSTI2015

First frontier field constraints on the cosmic star formation rate density AT z ~ 10—the impact of lensing shear on completeness of high-redshift galaxy samples

In this work, we search the complete Hubble Frontier Field data set of Abell 2744 and its parallel field for $z\sim 10$ sources to further refine the evolution of the cosmic star formation rate density (SFRD) between $z\sim 8$ and $z\sim 10$. We independently confirm two images of the recently discovered triply imaged $z\sim 9.8$ source by Zitrin et al. and set an upper limit for similar $z\sim 10$ galaxies with red colors of ${J}_{125}-{H}_{160}\gt 1.2$ in the parallel field of Abell 2744. We utilize extensive simulations to derive the effective selection volume of Lyman-break galaxies at $z\sim 10$, both in the lensed cluster field and in the adjacent parallel field. Particular care is taken to include position-dependent lensing shear to accurately account for the expected sizes and morphologies of highly magnified sources. We show that both source blending and shear reduce the completeness at a given observed magnitude in the cluster, particularly near the critical curves. These effects have a significant, but largely overlooked, impact on the detectability of high-redshift sources behind clusters, and substantially reduce the expected number of highly magnified sources. The detections and limits from both pointings result in an SFRD which is consistent within the uncertainties with previous estimates at $z\sim 10$ from blank fields. The combination of these new results with all other estimates is also consistent with a rapidly declining SFRD in the 170 Myr from $z\sim 8$ to $z\sim 10$ as predicted by cosmological simulations and dark-matter halo evolution in ΛCDM. Once biases introduced by magnification-dependent completeness are accounted for, the full six cluster and parallel Frontier Field program will be an extremely powerful new data set to probe the evolution of the galaxy population at $z\gt 8$ before the advent of the James Webb Space Telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Shear Pleasure: The Structure, Formation, and Thermodynamics of Crystallographic Shear Phases

A renaissance of interest in crystallographic shear structures and our recent work in this remarkable class of materials inspired this review. We first summarize the geometrical aspects of shear plane formation and possible transformations in ReO 3 , rutile, and perovskite-based structures. Then we provide a mechanistic overview of crystallographic shear formation, plane ordering, and propagation. Next we describe the energetics of planar defect formation and interaction, equilibria between point and extended defect structures, and thermodynamic stability of shear compounds. Finally, we emphasize the remaining challenges and propose future directions in this exciting area.

Materials Science↗
DOE OSTI2016

Cosmic shear results from the deep lens survey. II. Full cosmological parameter constraints from tomography

We present a tomographic cosmic shear study from the Deep Lens Survey (DLS), which, providing a limiting magnitude r{sub lim}∼27 (5σ), is designed as a precursor Large Synoptic Survey Telescope (LSST) survey with an emphasis on depth. Using five tomographic redshift bins, we study their auto- and cross-correlations to constrain cosmological parameters. We use a luminosity-dependent nonlinear model to account for the astrophysical systematics originating from intrinsic alignments of galaxy shapes. We find that the cosmological leverage of the DLS is among the highest among existing >10 deg{sup 2} cosmic shear surveys. Combining the DLS tomography with the 9 yr results of the Wilkinson Microwave Anisotropy Probe (WMAP9) gives Ω{sub m}=0.293{sub −0.014}{sup +0.012}, σ{sub 8}=0.833{sub −0.018}{sup +0.011}, H{sub 0}=68.6{sub −1.2}{sup +1.4} km s{sup −1} Mpc{sup −1}, and Ω{sub b}=0.0475±0.0012 for ΛCDM, reducing the uncertainties of the WMAP9-only constraints by ∼50%. When we do not assume flatness for ΛCDM, we obtain the curvature constraint Ω{sub k}=−0.010{sub −0.015}{sup +0.013} from the DLS+WMAP9 combination, which, however, is not well constrained when WMAP9 is used alone. The dark energy equation-of-state parameter w is tightly constrained when baryonic acoustic oscillation (BAO) data are added, yielding w=−1.02{sub −0.09}{sup +0.10} with the DLS+WMAP9+BAO joint probe. The addition of supernova constraints further tightens the parameter to w=−1.03±0.03. Our joint constraints are fully consistent with the final Planck results and also with the predictions of a ΛCDM universe.

79 ASTRONOMY AND ASTROPHYSICS↗