Do nuclear collisions create a locally equilibrated quark–gluon plasma?

DOE PAGES

Romatschke, P.

2017-01-10

Experimental results on azimuthal correlations in high energy nuclear collisions (nucleus–nucleus, proton–nucleus, and proton–proton) seem to be well described by viscous hydrodynamics. It is often argued that this agreement implies either local thermal equilibrium or at least local isotropy. In this note, I present arguments why this is not the case. Neither local near-equilibrium nor near-isotropy are required in order for hydrodynamics to offer a successful and accurate description of experimental results. However, I predict the breakdown of hydrodynamics at momenta of order seven times the temperature, corresponding to a smallest possible QCD liquid drop size of 0.15 fm.

Generalized migration in frequency-wavenumber domain (MGF-K) in anisotropic media

NASA Astrophysics Data System (ADS)

Kostecki, Andrzej; Półchłopek, Anna

2013-06-01

In this paper, the background of MGF-K migration in dual domain (wavenumber-frequency K-F and space-time) in anisotropic media is presented. Algorithms for poststack (zero-offset) and prestack migration are based on downward extrapolation of acoustic wavefield by shift-phase with correction filter for lateral variability of medium's parameters. In anisotropic media, the vertical wavenumber was determined from full elastic wavefield equations for two dimensional (2D) tilted transverse isotropy (TTI) model. The method was tested on a synthetic wavefield for TTI anticlinal model (zero-offset section) and on strongly inhomogeneous vertical transverse isotropy (VTI) Marmousi model. In both cases, the proper imaging of assumed media was obtained.

Testing statistical isotropy in cosmic microwave background polarization maps

NASA Astrophysics Data System (ADS)

Rath, Pranati K.; Samal, Pramoda Kumar; Panda, Srikanta; Mishra, Debesh D.; Aluri, Pavan K.

2018-04-01

We apply our symmetry based Power tensor technique to test conformity of PLANCK Polarization maps with statistical isotropy. On a wide range of angular scales (l = 40 - 150), our preliminary analysis detects many statistically anisotropic multipoles in foreground cleaned full sky PLANCK polarization maps viz., COMMANDER and NILC. We also study the effect of residual foregrounds that may still be present in the Galactic plane using both common UPB77 polarization mask, as well as the individual component separation method specific polarization masks. However, some of the statistically anisotropic modes still persist, albeit significantly in NILC map. We further probed the data for any coherent alignments across multipoles in several bins from the chosen multipole range.

Cosmic Ray Proton Anisotropies Measured at Voyager 1 in the Local Interstellar Medium

NASA Astrophysics Data System (ADS)

Decker, R. B.; Krimigis, S. M.; Hill, M. E.; Roelof, E. C.

2016-12-01

Voyager 1 entered the local interstellar medium in August of 2012 at helioradius 121.6 AU and heliolatitude N35°, and is now about 15 AU (≈12% the sun-heliopause distance at Voyager 1) upstream of the heliopause nose. Intensities of low-energy ions and electrons and of anomalous cosmic rays, all of which were routinely measured in the heliosheath, remain at background levels through July 2016. Galactic cosmic ray protons >211 MeV continue to show departures from isotropy, with broad (0.3-0.8 year) episodes of steady intensity depletions of ions gyrating nearly perpendicular to the magnetic field. Percentage intensity decreases during these depletions, relative to intensities of cosmic rays propagating along the field, peak at -7% on 2013.35, -3% on 2014.50, and -10% on 2016.00. In the last case, the peak anisotropy was preceded by an intensity decline lasting at least 9 months. The 2016.00 peak (-10%) anisotropy of was followed by a recovery back toward isotropy. But this recovery was interrupted in mid-April 2016, when the anisotropy had reached -2%, at which time the anisotropy began to again increase and continued to do so through at least July 2016, when the anisotropy reached -3%. We note that during its 4-year propagation through the local interstellar medium, Voyager 1 has encountered mainly anisotropic cosmic ray distributions. The longest period of isotropy occurred during a 4-month period in the latter half of 2014. Gurnett et al. [Ap. J., 809, 2015; Fall 2016 AGU (this meeting)] suggested that the broad periods when cosmic ray intensities evolve away from isotropy are precursor signatures produced by weak magnetic disturbances driven by solar activity. These disturbances propagate through the interstellar medium where they produce the bursts of electron plasma oscillations and peak cosmic ray anisotropies that are measured at Voyager 1 just before the disturbances cross the spacecraft.

Rigorous embedding of cell dynamics simulations in the Cahn-Hilliard-Cook framework: Imposing stability and isotropy

NASA Astrophysics Data System (ADS)

Sevink, G. J. A.

2015-05-01

We have rigorously analyzed the stability of the efficient cell dynamics simulations (CDS) method by making use of the special properties of the local averaging operator <<*>>-* in matrix form. Besides resolving a theoretical issue that has puzzled many over the past three decades, this analysis has considerable practical value: It relates CDS directly to finite-difference approximations of the Cahn-Hilliard-Cook equations and provides a straightforward recipe for replacing the original two- or three-dimensional (2D or 3D) averaging operators in CDS by an equivalent (in terms of stability) discrete Laplacian with superior isotropy and scaling behavior. As such, we open up a route to suppress the unphysical reflection of the computational grid in CDS results (grid artifacts). We found that proper rescaling of discrete Laplacians, needed to employ them in CDS, is equivalent to introducing a well-chosen time step in CDS. In turn, our analysis provides stability conditions for phase-field simulations based on the Cahn-Hilliard-Cook equations. Subsequently, we have quantitatively compared the isotropy and scaling behavior of several discrete 2D or 3D Laplacians, thereby extending the significance of this work to general field-based methodology. We found that all considered discrete Laplacians have equivalent scaling behavior along the Cartesian directions. In addition, and somewhat surprisingly, known "isotropic" discrete Laplacians, i.e., isotropic up to fourth order in |k | , become quite anisotropic for larger wave vectors, whereas "less isotropic" discrete Laplacians (second order) are only slightly anisotropic on the whole |k | range. We identified a hard limit to the accuracy with which the discrete Laplacian can emulate the two important properties of the optimal (continuum) Laplacian, as an improvement of the isotropy, by introducing additional points to the stencil, will negatively affect the scaling behavior. Within this limitation, the discrete compact Laplacians in the D n Q m class known from lattice hydrodynamics, D 2 Q 9 in 2D and D 3 Q 19 in 3D, are found to be optimal in terms of isotropy. However, by being only slightly anisotropic on the whole range and enabling larger time steps, the discrete Laplacians that relate to the local averaging operator of Oono and Puri (2D) and Shinozaki and Oono (3D) as well as the less familiar 3D discrete B v V Laplacian developed for dynamic density functional theory are valid alternatives.

Aether drift and the isotropy of the universe: a measurement of anisotropies in the primordial black-body radiation

NASA Technical Reports Server (NTRS)

Muller, R. A.

1979-01-01

This experiment detected and mapped large-angular-scale anisotropies in the 3 K primordial black-body radiation with a sensitivity of 2x.0001k and an angular resolution of about 10 degs. It measured the motion of the Earth with respect to the distant matter of the Universe (Aether Drift), and probed the homogeneity and isotropy of the Universe (the Cosmological Principle). The experiment used two Dicke radiometers, one at 33 GHz to detect the cosmic anisotropy, and one at 54 GHz to detect anisotropies in the residual oxygen above the detectors. The system was installed in the NASA-Ames Earth Survey Aircraft (U-2), and operated successfully in a series of flights.

Isotropy equilibrium of the double woven fabric with cotton face and wool reverse fibrous compositions

NASA Astrophysics Data System (ADS)

Rahnev, I.; Rimini, G.

2017-10-01

The equilibrium of the masses and the mechanical properties between the warp and the weft is a determining factor for the quality of the woven fabrics. When the fabric has a multi-layered structure and is designed for protective clothing, the uniform distribution of the elastical resistance acquires a paramount importance for the consumer properties. Isotropy in the sense of absolute equalising of the properties between the base and the weft evaluates the achieved optimum cohesion between the weaving threads and directs the weaving cycle settings. The possible variation of the ratio between the elastic modules of the warp and the weft, depending on the weft spacing and the warp tension, is the basic idea of this article.

Discrete exterior calculus approach for discretizing Maxwell's equations on face-centered cubic grids for FDTD

NASA Astrophysics Data System (ADS)

Salmasi, Mahbod; Potter, Michael

2018-07-01

Maxwell's equations are discretized on a Face-Centered Cubic (FCC) lattice instead of a simple cubic as an alternative to the standard Yee method for improvements in numerical dispersion characteristics and grid isotropy of the method. Explicit update equations and numerical dispersion expressions, and the stability criteria are derived. Also, several tools available to the standard Yee method such as PEC/PMC boundary conditions, absorbing boundary conditions, and scattered field formulation are extended to this method as well. A comparison between the FCC and the Yee formulations is made, showing that the FCC method exhibits better dispersion compared to its Yee counterpart. Simulations are provided to demonstrate both the accuracy and grid isotropy improvement of the method.

A test of the one-way isotropy of the speed of light from the T2L2 space experiment

NASA Astrophysics Data System (ADS)

Belli, A.; Exertier, P.; Samain, E.

2017-12-01

The Time Transfer by Laser Link (T2L2) space experiment that is currently flying on-board Jason-2 (1335 km of altitude) provides an opportunity to make a test of the isotropy of the speed of light using one-way propagation on a non-laboratory scale. Following the general framework given by te{Mansouri1977}, which permits violations of Einstein special relativity, we study the problem of deducing the isotropy of the speed between two clocks as the orientation path varies relative to an inertial reference frame. The short term stability of the T2L2 ground-to-space time transfer has been established at 5-6 ps at 60 seconds between a hydrogen maser and the on-board oscillator on use for the Jason-2 satellite. Nevertheless, during the satellite pass above a laser ranging station (of around 1000 seconds), the stability of the space oscillator is decreasing in τ^{3/2} that clearly impacts the expected performance of the present test. We thus give insights into certain modelling issues and processes, including time transfer problems which have a bearing on the global error budget. Our goal is to achieve an accuracy of {δc}/{c} ≈ 2-3.10^{-9} locally with a scope for improvement by cumulating numerous passes over the same laser ranging station.

Invariant Theory for Dispersed Transverse Isotropy: An Efficient Means for Modeling Fiber Splay

NASA Technical Reports Server (NTRS)

Freed, alan D.; Einstein, Daniel R.; Vesely, Ivan

2004-01-01

Most soft tissues possess an oriented architecture of collagen fiber bundles, conferring both anisotropy and nonlinearity to their elastic behavior. Transverse isotropy has often been assumed for a subset of these tissues that have a single macroscopically-identifiable preferred fiber direction. Micro-structural studies, however, suggest that, in some tissues, collagen fibers are approximately normally distributed about a mean preferred fiber direction. Structural constitutive equations that account for this dispersion of fibers have been shown to capture the mechanical complexity of these tissues quite well. Such descriptions, however, are computationally cumbersome for two-dimensional (2D) fiber distributions, let alone for fully three-dimensional (3D) fiber populations. In this paper, we develop a new constitutive law for such tissues, based on a novel invariant theory for dispersed transverse isotropy. The invariant theory is based on a novel closed-form splay invariant that can easily handle 3D fiber populations, and that only requires a single parameter in the 2D case. The model is polyconvex and fits biaxial data for aortic valve tissue as accurately as the standard structural model. Modification of the fiber stress-strain law requires no re-formulation of the constitutive tangent matrix, making the model flexible for different types of soft tissues. Most importantly, the model is computationally expedient in a finite-element analysis.

Aether drift and the isotropy of the universe

NASA Technical Reports Server (NTRS)

Muller, R. A.

1976-01-01

An experiment is proposed which will detect and map the large-angular-scale anisotropies in the 3 deg K primordial black-body radiation with a sensitivity of .0002 deg K and an angular resolution of about 10 deg . It will detect the motion of the earth with respect to the distant matter of the Universe ("Aether Drift"), and will probe the homogeneity and isotropy of the Universe (the "Cosmological Principle"). The experiment will use two Dicke radiometers, one at 33 GHz to detect the cosmic anisotropy, and one at 54 GHz to detect anisotropies in the residual oxygen above the detectors. An upper hatch for the NASA-AMES Earth Survey Aircraft (U-2) is being modified to accept the dual-radiometer system. A few hours of observation should be sufficient to detect an anisotropy.

Estimating three-demensional energy transfer in isotropic turbulence

NASA Technical Reports Server (NTRS)

Li, K. S.; Helland, K. N.; Rosenblatt, M.

1980-01-01

To obtain an estimate of the spectral transfer function that indicates the rate of decay of energy, an x-wire probe was set at a fixed position, and two single wire probes were set at a number of locations in the same plane perpendicular to the mean flow in the wind tunnel. The locations of the single wire probes are determined by pseudo-random numbers (Monte Carlo). Second order spectra and cross spectra are estimated. The assumption of isotropy relative to second order spectra is examined. Third order spectra are also estimated corresponding to the positions specified. A Monte Carlo Fourier transformation of the downstream bispectra corresponding to integration across the plane perpendicular to the flow is carried out assuming isotropy. Further integration is carried out over spherical energy shells.

Renormalization group analysis of the Reynolds stress transport equation

NASA Technical Reports Server (NTRS)

Rubinstein, R.; Barton, J. M.

1992-01-01

The pressure velocity correlation and return to isotropy term in the Reynolds stress transport equation are analyzed using the Yakhot-Orszag renormalization group. The perturbation series for the relevant correlations, evaluated to lowest order in the epsilon-expansion of the Yakhot-Orszag theory, are infinite series in tensor product powers of the mean velocity gradient and its transpose. Formal lowest order Pade approximations to the sums of these series produce a fast pressure strain model of the form proposed by Launder, Reece, and Rodi, and a return to isotropy model of the form proposed by Rotta. In both cases, the model constant are computed theoretically. The predicted Reynolds stress ratios in simple shear flows are evaluated and compared with experimental data. The possibility is discussed of driving higher order nonlinear models by approximating the sums more accurately.

Isotropy of Angular Frequencies and Weak Chimeras with Broken Symmetry

NASA Astrophysics Data System (ADS)

Bick, Christian

2017-04-01

The notion of a weak chimeras provides a tractable definition for chimera states in networks of finitely many phase oscillators. Here, we generalize the definition of a weak chimera to a more general class of equivariant dynamical systems by characterizing solutions in terms of the isotropy of their angular frequency vector—for coupled phase oscillators the angular frequency vector is given by the average of the vector field along a trajectory. Symmetries of solutions automatically imply angular frequency synchronization. We show that the presence of such symmetries is not necessary by giving a result for the existence of weak chimeras without instantaneous or setwise symmetries for coupled phase oscillators. Moreover, we construct a coupling function that gives rise to chaotic weak chimeras without symmetry in weakly coupled populations of phase oscillators with generalized coupling.

Seismic Imaging of VTI, HTI and TTI based on Adjoint Methods

NASA Astrophysics Data System (ADS)

Rusmanugroho, H.; Tromp, J.

2014-12-01

Recent studies show that isotropic seismic imaging based on adjoint method reduces low-frequency artifact caused by diving waves, which commonly occur in two-wave wave-equation migration, such as Reverse Time Migration (RTM). Here, we derive new expressions of sensitivity kernels for Vertical Transverse Isotropy (VTI) using the Thomsen parameters (ɛ, δ, γ) plus the P-, and S-wave speeds (α, β) as well as via the Chen & Tromp (GJI 2005) parameters (A, C, N, L, F). For Horizontal Transverse Isotropy (HTI), these parameters depend on an azimuthal angle φ, where the tilt angle θ is equivalent to 90°, and for Tilted Transverse Isotropy (TTI), these parameters depend on both the azimuth and tilt angles. We calculate sensitivity kernels for each of these two approaches. Individual kernels ("images") are numerically constructed based on the interaction between the regular and adjoint wavefields in smoothed models which are in practice estimated through Full-Waveform Inversion (FWI). The final image is obtained as a result of summing all shots, which are well distributed to sample the target model properly. The impedance kernel, which is a sum of sensitivity kernels of density and the Thomsen or Chen & Tromp parameters, looks crisp and promising for seismic imaging. The other kernels suffer from low-frequency artifacts, similar to traditional seismic imaging conditions. However, all sensitivity kernels are important for estimating the gradient of the misfit function, which, in combination with a standard gradient-based inversion algorithm, is used to minimize the objective function in FWI.

CTE homogeneity, isotropy and reproducibility in large parts made of sintered SiC

NASA Astrophysics Data System (ADS)

Bougoin, Michel; Castel, Didier; Levallois, Franck

2017-11-01

For Herschel SiC primary mirror purpose, a new approach of comparative CTE measurement has been developed; it is based on the well known bimetallic effect ("biceramic" in this case) and also optical measurements. This method offers a good CTE comparison capability in the range of 170-420K (extensible to 5-420K) depending of the thermal test facilities performance, with a resolution of only 0.001 μm/m.K. The Herschel primary mirror is made of 12 SiC segments which are brazed together. The CTE of each segment has been compared with the one of a witness sample and no visible change, higher than the measurement accuracy, has been observed. Furthermore, a lot of samples have been cut out from a spare segment, from different places and also from all X, Y and Z direction of the reference frame. No deviation was seen in all of these tests, thus demonstrating the very good homogeneity, reproducibility and isotropy of the Boostec® SiC material. Some recent literature about SiC material measurements at cryogenic temperature shows a better behaviour of Boostec® SiC material in comparison with other kind of SiC which are also candidate for space optics, in particular for isotropy purpose. After a review of the available literature, this paper describes the comparative CTE measurement method and details the results obtained during the measurement campaigns related to Herschel project.

Aether Drift and the isotropy of the universe: A measurement of anisotropes in the primordial black-body radiation

NASA Technical Reports Server (NTRS)

Smoot, G. F.

1981-01-01

Large-angular-scale anisotropies in the 3 K primordial black-body radiation were detected and mapped with a sensitivity of 2 x to the minus 4 power K and an angular resolution of about 10 deg. The motion of the Earth with respect to the distant matter of the Universe ("Aether Drift") was measured and the homogeneity and isotropy of the Universe (the "Cosmological Principle") was probed. The experiment uses two Dicke radiometers, one at 33 GHz to detect the cosmic anisotropy, and one at 54 GHz to detect anisotropies in the residual oxygen above the detectors. The system was installed in the NASA-Ames Earth survey aircraft (U-2), and operated successfully in a series of flights in both the Northern and Southern Hemispheres. Data taking and analysis to measure the anisotropy were successful.

Tensor Minkowski Functionals for random fields on the sphere

NASA Astrophysics Data System (ADS)

Chingangbam, Pravabati; Yogendran, K. P.; Joby, P. K.; Ganesan, Vidhya; Appleby, Stephen; Park, Changbom

2017-12-01

We generalize the translation invariant tensor-valued Minkowski Functionals which are defined on two-dimensional flat space to the unit sphere. We apply them to level sets of random fields. The contours enclosing boundaries of level sets of random fields give a spatial distribution of random smooth closed curves. We outline a method to compute the tensor-valued Minkowski Functionals numerically for any random field on the sphere. Then we obtain analytic expressions for the ensemble expectation values of the matrix elements for isotropic Gaussian and Rayleigh fields. The results hold on flat as well as any curved space with affine connection. We elucidate the way in which the matrix elements encode information about the Gaussian nature and statistical isotropy (or departure from isotropy) of the field. Finally, we apply the method to maps of the Galactic foreground emissions from the 2015 PLANCK data and demonstrate their high level of statistical anisotropy and departure from Gaussianity.

Grain Refinement of Freeform Fabricated Ti-6Al-4V Alloy Using Beam/Arc Modulation

NASA Technical Reports Server (NTRS)

Mitzner, Scott; Liu, Stephen; Domack, Marcia S.; Hafley, Robert A.

2012-01-01

Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti-6Al-4V alloy, promoting increased strength and enhanced isotropy compared with coarser grained material. Large beta-grains can lead to a segregated microstructure, in regard to both alpha-phase morphology and alpha-lath orientation. Beam modulation, which has been used in conventional fusion welding to promote grain refinement, is explored in this study for use in additive manufacturing processes including electron beam freeform fabrication (EBF(sup 3)) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure. The dynamic molten pool size induced by beam modulation causes rapid heat flow variance and results in a more competitive grain growth environment, reducing grain size. Consequently, improved isotropy and strength can be achieved with relatively small adjustments to deposition parameters.

Photonic band gap in isotropic hyperuniform disordered solids with low dielectric contrast.

PubMed

Man, Weining; Florescu, Marian; Matsuyama, Kazue; Yadak, Polin; Nahal, Geev; Hashemizad, Seyed; Williamson, Eric; Steinhardt, Paul; Torquato, Salvatore; Chaikin, Paul

2013-08-26

We report the first experimental demonstration of a TE-polarization photonic band gap (PBG) in a 2D isotropic hyperuniform disordered solid (HUDS) made of dielectric media with a dielectric index contrast of 1.6:1, very low for PBG formation. The solid is composed of a connected network of dielectric walls enclosing air-filled cells. Direct comparison with photonic crystals and quasicrystals permitted us to investigate band-gap properties as a function of increasing rotational isotropy. We present results from numerical simulations proving that the PBG observed experimentally for HUDS at low index contrast has zero density of states. The PBG is associated with the energy difference between complementary resonant modes above and below the gap, with the field predominantly concentrated in the air or in the dielectric. The intrinsic isotropy of HUDS may offer unprecedented flexibilities and freedom in applications (i. e. defect architecture design) not limited by crystalline symmetries.

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

Fang, Ke; Linden, Tim, E-mail: kefang@umd.edu, E-mail: linden.70@osu.edu

Radio observations at multiple frequencies have detected a significant isotropic emission component between 22 MHz and 10 GHz, commonly termed the ARCADE-2 Excess. The origin of this radio emission is unknown, as the intensity, spectrum and isotropy of the signal are difficult to model with either traditional astrophysical mechanisms or novel physics such as dark matter annihilation. We posit a new model capable of explaining the key components of the excess radio emission. Specifically, we show that the re-acceleration of non-thermal electrons via turbulence in merging galaxy clusters are capable of explaining the intensity, spectrum, and isotropy of the ARCADE-2more » data. We examine the parameter spaces of cluster re-acceleration, magnetic field, and merger rate, finding that the radio excess can be reproduced assuming reasonable assumptions for each. Finally, we point out that future observations will definitively confirm or rule-out the contribution of cluster mergers to the isotropic radio background.« less

Positivity-preserving numerical schemes for multidimensional advection

NASA Technical Reports Server (NTRS)

Leonard, B. P.; Macvean, M. K.; Lock, A. P.

1993-01-01

This report describes the construction of an explicit, single time-step, conservative, finite-volume method for multidimensional advective flow, based on a uniformly third-order polynomial interpolation algorithm (UTOPIA). Particular attention is paid to the problem of flow-to-grid angle-dependent, anisotropic distortion typical of one-dimensional schemes used component-wise. The third-order multidimensional scheme automatically includes certain cross-difference terms that guarantee good isotropy (and stability). However, above first-order, polynomial-based advection schemes do not preserve positivity (the multidimensional analogue of monotonicity). For this reason, a multidimensional generalization of the first author's universal flux-limiter is sought. This is a very challenging problem. A simple flux-limiter can be found; but this introduces strong anisotropic distortion. A more sophisticated technique, limiting part of the flux and then restoring the isotropy-maintaining cross-terms afterwards, gives more satisfactory results. Test cases are confined to two dimensions; three-dimensional extensions are briefly discussed.

Eigenvalues of Random Matrices with Isotropic Gaussian Noise and the Design of Diffusion Tensor Imaging Experiments.

PubMed

Gasbarra, Dario; Pajevic, Sinisa; Basser, Peter J

2017-01-01

Tensor-valued and matrix-valued measurements of different physical properties are increasingly available in material sciences and medical imaging applications. The eigenvalues and eigenvectors of such multivariate data provide novel and unique information, but at the cost of requiring a more complex statistical analysis. In this work we derive the distributions of eigenvalues and eigenvectors in the special but important case of m×m symmetric random matrices, D , observed with isotropic matrix-variate Gaussian noise. The properties of these distributions depend strongly on the symmetries of the mean tensor/matrix, D̄ . When D̄ has repeated eigenvalues, the eigenvalues of D are not asymptotically Gaussian, and repulsion is observed between the eigenvalues corresponding to the same D̄ eigenspaces. We apply these results to diffusion tensor imaging (DTI), with m = 3, addressing an important problem of detecting the symmetries of the diffusion tensor, and seeking an experimental design that could potentially yield an isotropic Gaussian distribution. In the 3-dimensional case, when the mean tensor is spherically symmetric and the noise is Gaussian and isotropic, the asymptotic distribution of the first three eigenvalue central moment statistics is simple and can be used to test for isotropy. In order to apply such tests, we use quadrature rules of order t ≥ 4 with constant weights on the unit sphere to design a DTI-experiment with the property that isotropy of the underlying true tensor implies isotropy of the Fisher information. We also explain the potential implications of the methods using simulated DTI data with a Rician noise model.

The Role of Texture, Cracks, and Fractures in Highly Anisotropic Shales

NASA Astrophysics Data System (ADS)

Baird, Alan F.; Kendall, J. Michael; Fisher, Quentin J.; Budge, Jessica

2017-12-01

Organic shales generally have low permeability unless fractures are present. However, how gas, oil, and water flows into these fractures remains enigmatic. The alignment of clay minerals and the alignment of fractures and cracks are effective means to produce seismic anisotropy. Thus, the detection and characterization of this anisotropy can be used to infer details about lithology, rock fabric, and fracture and crack properties within the subsurface. We present a study characterizing anisotropy using S wave splitting from microseismic sources in a highly anisotropic shale. We observe very strong anisotropy (up to 30%) with predominantly VTI (vertical transverse isotropy) symmetry, but with evidence of an HTI (horizontal transverse isotropy) overprint due to a NE striking vertical fracture set parallel to the maximum horizontal compressive stress. We observe clear evidence of a shear wave triplication due to anisotropy, which to our knowledge is one of only a very few observations of such triplications in field-scale data. We use modal proportions of minerals derived from X-ray fluorescence data combined with realistic textures to estimate the contribution of intrinsic anisotropy as well as possible contributions of horizontally aligned cracks. We find that aligned clays can explain much of the observed anisotropy and that any cracks contributing to the vertical transverse isotropy (VTI) must have a low ratio of normal to tangential compliance (ZN/ZT), typical of isolated cracks with low hydraulic connectivity. Subhorizontal cracks have also been observed in the reservoir, and we propose that their reactivation during hydraulic fracturing may be an important mechanism to facilitate gas flow.

Planar isotropy of passive scalar turbulent mixing with a mean perpendicular gradient.

PubMed

Danaila, L; Dusek, J; Le Gal, P; Anselmet, F; Brun, C; Pumir, A

1999-08-01

A recently proposed evolution equation [Vaienti et al., Physica D 85, 405 (1994)] for the probability density functions (PDF's) of turbulent passive scalar increments obtained under the assumptions of fully three-dimensional homogeneity and isotropy is submitted to validation using direct numerical simulation (DNS) results of the mixing of a passive scalar with a nonzero mean gradient by a homogeneous and isotropic turbulent velocity field. It is shown that this approach leads to a quantitatively correct balance between the different terms of the equation, in a plane perpendicular to the mean gradient, at small scales and at large Péclet number. A weaker assumption of homogeneity and isotropy restricted to the plane normal to the mean gradient is then considered to derive an equation describing the evolution of the PDF's as a function of the spatial scale and the scalar increments. A very good agreement between the theory and the DNS data is obtained at all scales. As a particular case of the theory, we derive a generalized form for the well-known Yaglom equation (the isotropic relation between the second-order moments for temperature increments and the third-order velocity-temperature mixed moments). This approach allows us to determine quantitatively how the integral scale properties influence the properties of mixing throughout the whole range of scales. In the simple configuration considered here, the PDF's of the scalar increments perpendicular to the mean gradient can be theoretically described once the sources of inhomogeneity and anisotropy at large scales are correctly taken into account.

Nonhyperbolic reflection moveout for horizontal transverse isotropy

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

Al-Dajani, A.F.; Tsvankin, I.

1998-09-01

The transversely isotropic model with a horizontal axis of symmetry (HTI) has been used extensively in studies of shear-wave splitting to describe fractured formations with a single system of parallel vertical penny-shaped cracks. Here, the authors present an analytic description of long-spread reflection moveout in horizontally layered HTI media with arbitrary strength of anisotropy. To account for nonhyperbolic moveout, the authors have derived an exact expression for the azimuthally dependent quartic term of the Taylor series traveltime expansion valid for any pure mode in an HTI layer. The quartic moveout coefficient and the NMO velocity are then substituted into themore » nonhyperbolic moveout equation of Tsvankin and Thomsen, originally designed for vertical transverse isotropy (VTI). In multilayered HTI media, the NMO velocity and the quartic moveout coefficient reflect the influence of layering as well as azimuthal anisotropy. The authors show that the conventional Dix equation for NMO velocity remains entirely valid for any azimuth in HTI media if the group-velocity vectors (rays) for data in a common-midpoint (CMP) gather do not deviate from the vertical incidence plane. Although this condition is not exactly satisfied in the presence of azimuthal velocity variations, rms averaging of the interval NMO velocities represents a good approximation for models with moderate azimuthal anisotropy. Furthermore, the quartic moveout coefficient for multilayered HTI media can also be calculated with acceptable accuracy using the known averaging equations for vertical transverse isotropy. This allows one to extend the nonhyperbolic moveout equation to horizontally stratified media composed of any combination of isotropic, VTI, and HTI layers.« less

Eigenvalues of Random Matrices with Isotropic Gaussian Noise and the Design of Diffusion Tensor Imaging Experiments*

PubMed Central

Gasbarra, Dario; Pajevic, Sinisa; Basser, Peter J.

2017-01-01

Tensor-valued and matrix-valued measurements of different physical properties are increasingly available in material sciences and medical imaging applications. The eigenvalues and eigenvectors of such multivariate data provide novel and unique information, but at the cost of requiring a more complex statistical analysis. In this work we derive the distributions of eigenvalues and eigenvectors in the special but important case of m×m symmetric random matrices, D, observed with isotropic matrix-variate Gaussian noise. The properties of these distributions depend strongly on the symmetries of the mean tensor/matrix, D̄. When D̄ has repeated eigenvalues, the eigenvalues of D are not asymptotically Gaussian, and repulsion is observed between the eigenvalues corresponding to the same D̄ eigenspaces. We apply these results to diffusion tensor imaging (DTI), with m = 3, addressing an important problem of detecting the symmetries of the diffusion tensor, and seeking an experimental design that could potentially yield an isotropic Gaussian distribution. In the 3-dimensional case, when the mean tensor is spherically symmetric and the noise is Gaussian and isotropic, the asymptotic distribution of the first three eigenvalue central moment statistics is simple and can be used to test for isotropy. In order to apply such tests, we use quadrature rules of order t ≥ 4 with constant weights on the unit sphere to design a DTI-experiment with the property that isotropy of the underlying true tensor implies isotropy of the Fisher information. We also explain the potential implications of the methods using simulated DTI data with a Rician noise model. PMID:28989561

Probing cosmic anisotropy with gravitational waves as standard sirens

NASA Astrophysics Data System (ADS)

Cai, Rong-Gen; Liu, Tong-Bo; Liu, Xue-Wen; Wang, Shao-Jiang; Yang, Tao

2018-05-01

The gravitational wave (GW) as a standard siren directly determines the luminosity distance from the gravitational waveform without reference to the specific cosmological model, of which the redshift can be obtained separately by means of the electromagnetic counterpart like GW events from binary neutron stars and massive black hole binaries (MBHBs). To see to what extent the standard siren can reproduce the presumed dipole anisotropy written in the simulated data of standard siren events from typical configurations of GW detectors, we find that (1) for the Laser Interferometer Space Antenna with different MBHB models during five-year observations, the cosmic isotropy can be ruled out at 3 σ confidence level (C.L.) and the dipole direction can be constrained roughly around 20% at 2 σ C.L., as long as the dipole amplitude is larger than 0.04, 0.06 and 0.03 for MBHB models Q3d, pop III and Q3nod with increasing constraining ability, respectively; (2) for the Einstein telescope with no less than 200 standard siren events, the cosmic isotropy can be ruled out at 3 σ C.L. if the dipole amplitude is larger than 0.06, and the dipole direction can be constrained within 20% at 3 σ C.L. if the dipole amplitude is near 0.1; (3) for the Deci-Hertz Interferometer Gravitational wave Observatory with no less than 100 standard siren events, the cosmic isotropy can be ruled out at 3 σ C.L. for dipole amplitude larger than 0.03, and the dipole direction can even be constrained within 10% at 3 σ C.L. if the dipole amplitude is larger than 0.07. Our work manifests the promising perspective of the constraint ability on the cosmic anisotropy from the standard siren approach.

Isotropy Constraints on Powerful Sources of Ultrahigh-energy Cosmic Rays at 1019 eV

NASA Astrophysics Data System (ADS)

Takami, Hajime; Murase, Kohta; Dermer, Charles D.

2016-01-01

Anisotropy in the arrival direction distribution of ultrahigh-energy cosmic rays (UHECRs) produced by powerful sources is numerically evaluated. We show that nondetection of significant anisotropy at ≈ {10}19 eV at present and in future experiments imposes general upper limits on UHECR proton luminosity of steady sources as a function of source redshifts. The upper limits constrain the existence of typical steady {10}19 eV UHECR sources in the local universe and limit their local density to ≳ {10}-3 Mpc {}-3, assuming average intergalactic magnetic fields less than {10}-9 G. This isotropy, being stronger than that measured at the highest energies, may indicate the transient generation of UHECRs. Our calculations are applied for extreme high-frequency-peaked BL Lacertae objects 1ES 0229+200, 1ES 1101-232, and 1ES 0347-121, to test the UHECR-induced cascade model, in which beamed UHECR protons generate TeV radiation in transit from sources. While the magnetic-field structure surrounding the sources affects the required absolute cosmic-ray luminosity of the blazars, the magnetic-field structure surrounding the Milky Way directly affects the observed anisotropy. If these magnetic fields are weak enough, significant UHECR anisotropy from these blazars is detectable by the Pierre Auger Observatory unless the maximum energy of UHECR protons is below 1019 eV. Furthermore, if these are the sources of UHECRs above 1019 eV, a local magnetic structure surrounding the Milky Way is needed to explain the observed isotropy at ˜ {10}19 eV, which may be incompatible with large magnetic structures around all galaxies for the UHECR-induced cascade model to work with reasonable jet powers.

A 14 h-3 Gpc3 study of cosmic homogeneity using BOSS DR12 quasar sample

NASA Astrophysics Data System (ADS)

Laurent, Pierre; Le Goff, Jean-Marc; Burtin, Etienne; Hamilton, Jean-Christophe; Hogg, David W.; Myers, Adam; Ntelis, Pierros; Pâris, Isabelle; Rich, James; Aubourg, Eric; Bautista, Julian; Delubac, Timothée; du Mas des Bourboux, Hélion; Eftekharzadeh, Sarah; Palanque Delabrouille, Nathalie; Petitjean, Patrick; Rossi, Graziano; Schneider, Donald P.; Yeche, Christophe

2016-11-01

The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey in the redshift range 2.2 < z < 2.8. We measure the count-in-sphere, N(< r), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, D2(r). For a homogeneous distribution N(< r) propto r3 and D2(r) = 3. Due to the uncertainty on tracer density evolution, 3D surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ``spatial isotropy". Our data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any FLRW fiducial cosmology, resulting in 3 - langleD2rangle < 1.7 × 10-3 (2 σ) over the range 250 < r < 1200 h-1 Mpc for the quasar distribution. If we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. Then, combining with the Copernican principle, we finally get homogeneity of the matter distribution on large scales. Alternatively, using a flat ΛCDM fiducial cosmology with CMB-derived parameters, and measuring the quasar bias relative to this ΛCDM model, our data provide a consistency check of the model, in terms of how homogeneous the Universe is on different scales. D2(r) is found to be compatible with our ΛCDM model on the whole 10 < r < 1200 h-1 Mpc range. For the matter distribution we obtain 3 - langleD2rangle < 5 × 10-5 (2 σ) over the range 250 < r < 1200 h-1 Mpc, consistent with homogeneity on large scales.

Recent Measurement of Energetic Particles from Voyagers 1 and 2

NASA Astrophysics Data System (ADS)

Decker, R. B.; Krimigis, S. M.; Hill, M. E.; Roelof, E. C.

2017-12-01

We review recent measurements of energetic particles made at Voyager 2 (at 116 AU, S32 deg) in the heliosheath and at Voyager 1 (at 140 AU, N35 deg) in the local interstellar medium. Voyager 2 is 31 AU beyond its termination shock crossing (84.4 AU in August 2007), showing that the heliosheath at Voyager 2 is at least 3-4 AU thicker than that traversed by Voyager 1. In the 2017 data at Voyager 2, intensities of heliosheath ions >30 keV and electrons >20 keV have levelled off, with the ions reaching values comparable to those in 2011, following a four-year step-like recovery from minima reached in early 2013. In addition, during 2014-17, variations of the lowest energy ion intensities with scales of order several months or less tend to correlate with similar variations in the solar wind density. This similarity of relatively short-term temporal variations between the thermal and suprathermal ions was not seen in the earlier heliosheath data from Voyager 2. Voyager 1 is now about 18 AU upstream of the heliopause nose. Intensities of low-energy ions and electrons and of anomalous cosmic rays, all of which were routinely measured in the heliosheath, remain at background levels at Voyager 1 through July 2017. Angular distributions of galactic cosmic ray protons >211 MeV continue to depart from isotropy, being characterized instead by broad (0.3-0.8 year) episodes of steady intensity depletions of protons gyrating nearly perpendicular to the magnetic field. Although data in the first half of 2017 continue to show departures from isotropy, the anisotropy amplitudes are generally small, comparable to periods of quasi-isotropy measured during six-month periods in 2013-14 and in 2014-15.

Inflationary tensor fossils in large-scale structure

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

Dimastrogiovanni, Emanuela; Fasiello, Matteo; Jeong, Donghui

Inflation models make specific predictions for a tensor-scalar-scalar three-point correlation, or bispectrum, between one gravitational-wave (tensor) mode and two density-perturbation (scalar) modes. This tensor-scalar-scalar correlation leads to a local power quadrupole, an apparent departure from statistical isotropy in our Universe, as well as characteristic four-point correlations in the current mass distribution in the Universe. So far, the predictions for these observables have been worked out only for single-clock models in which certain consistency conditions between the tensor-scalar-scalar correlation and tensor and scalar power spectra are satisfied. Here we review the requirements on inflation models for these consistency conditions to bemore » satisfied. We then consider several examples of inflation models, such as non-attractor and solid-inflation models, in which these conditions are put to the test. In solid inflation the simplest consistency conditions are already violated whilst in the non-attractor model we find that, contrary to the standard scenario, the tensor-scalar-scalar correlator probes directly relevant model-dependent information. We work out the predictions for observables in these models. For non-attractor inflation we find an apparent local quadrupolar departure from statistical isotropy in large-scale structure but that this power quadrupole decreases very rapidly at smaller scales. The consistency of the CMB quadrupole with statistical isotropy then constrains the distance scale that corresponds to the transition from the non-attractor to attractor phase of inflation to be larger than the currently observable horizon. Solid inflation predicts clustering fossils signatures in the current galaxy distribution that may be large enough to be detectable with forthcoming, and possibly even current, galaxy surveys.« less

Gravity field error analysis for pendulum formations by a semi-analytical approach

NASA Astrophysics Data System (ADS)

Li, Huishu; Reubelt, Tilo; Antoni, Markus; Sneeuw, Nico

2017-03-01

Many geoscience disciplines push for ever higher requirements on accuracy, homogeneity and time- and space-resolution of the Earth's gravity field. Apart from better instruments or new observables, alternative satellite formations could improve the signal and error structure compared to Grace. One possibility to increase the sensitivity and isotropy by adding cross-track information is a pair of satellites flying in a pendulum formation. This formation contains two satellites which have different ascending nodes and arguments of latitude, but have the same orbital height and inclination. In this study, the semi-analytical approach for efficient pre-mission error assessment is presented, and the transfer coefficients of range, range-rate and range-acceleration gravitational perturbations are derived analytically for the pendulum formation considering a set of opening angles. The new challenge is the time variations of the opening angle and the range, leading to temporally variable transfer coefficients. This is solved by Fourier expansion of the sine/cosine of the opening angle and the central angle. The transfer coefficients are further applied to assess the error patterns which are caused by different orbital parameters. The simulation results indicate that a significant improvement in accuracy and isotropy is obtained for small and medium initial opening angles of single polar pendulums, compared to Grace. The optimal initial opening angles are 45° and 15° for accuracy and isotropy, respectively. For a Bender configuration, which is constituted by a polar Grace and an inclined pendulum in this paper, the behaviour of results is dependent on the inclination (prograde vs. retrograde) and on the relative baseline orientation (left or right leading). The simulation for a sun-synchronous orbit shows better results for the left leading case.

Advanced morphological analysis of patterns of thin anodic porous alumina

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

Toccafondi, C.; Istituto Italiano di Tecnologia, Department of Nanostructures, Via Morego 30, Genova I 16163; Stępniowski, W.J.

2014-08-15

Different conditions of fabrication of thin anodic porous alumina on glass substrates have been explored, obtaining two sets of samples with varying pore density and porosity, respectively. The patterns of pores have been imaged by high resolution scanning electron microscopy and analyzed by innovative methods. The regularity ratio has been extracted from radial profiles of the fast Fourier transforms of the images. Additionally, the Minkowski measures have been calculated. It was first observed that the regularity ratio averaged across all directions is properly corrected by the coefficient previously determined in the literature. Furthermore, the angularly averaged regularity ratio for themore » thin porous alumina made during short single-step anodizations is lower than that of hexagonal patterns of pores as for thick porous alumina from aluminum electropolishing and two-step anodization. Therefore, the regularity ratio represents a reliable measure of pattern order. At the same time, the lower angular spread of the regularity ratio shows that disordered porous alumina is more isotropic. Within each set, when changing either pore density or porosity, both regularity and isotropy remain rather constant, showing consistent fabrication quality of the experimental patterns. Minor deviations are tentatively discussed with the aid of the Minkowski measures, and the slight decrease in both regularity and isotropy for the final data-points of the porosity set is ascribed to excess pore opening and consequent pore merging. - Highlights: • Thin porous alumina is partly self-ordered and pattern analysis is required. • Regularity ratio is often misused: we fix the averaging and consider its spread. • We also apply the mathematical tool of Minkowski measures, new in this field. • Regularity ratio shows pattern isotropy and Minkowski helps in assessment. • General agreement with perfect artificial patterns confirms the good manufacturing.« less

Effect of coulomb spline on rotor dynamic response

NASA Technical Reports Server (NTRS)

Nataraj, C.; Nelson, H. D.; Arakere, N.

1985-01-01

A rigid rotor system coupled by a coulomb spline is modelled and analyzed by approximate analytical and numerical analytical methods. Expressions are derived for the variables of the resulting limit cycle and are shown to be quite accurate for a small departure from isotropy.

Transparency through Structural Disorder: A New Concept for Innovative Transparent Ceramics

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

Al Saghir, Kholoud; Chenu, Sébastien; Veron, Emmanuel

2015-01-27

Transparent polycrystalline ceramics present signi fi cant eco- nomical and functional advantages over single crystal materials for optical, communication, and laser technologies. To date, transparency in these ceramics is ensured either by an optical isotropy (i.e., cubic symmetry) or a nanometric crystallite size, and the main challenge remains to eliminate porosity through complex high pressure - high temperature synthesis. Here we introduce a new concept to achieve ultimate transparency reaching the theoretical limit. We use a controlled degree of chemical disorder in the structure to obtain optical isotropy at the micrometer length scale. This approach can be applied in themore » case of anisotropic structures and micrometer scale crystal size ceramics. We thus report Sr 1+ x /2 Al 2+ x Si 2 - x O 8 (0 < x ≤ 0.4) readily scalable polycrystalline ceramics elaborated by full and congruent crystallization from glass. These materials reach 90% transmittance. This innovative method should drive the development of new highly transparent materials with technologically relevant applications.« less

Dynamics of anisotropies close to a cosmological bounce in quantum gravity

NASA Astrophysics Data System (ADS)

de Cesare, Marco; Oriti, Daniele; Pithis, Andreas G. A.; Sakellariadou, Mairi

2018-01-01

We study the dynamics of perturbations representing deviations from perfect isotropy in the context of the emergent cosmology obtained from the group field theory formalism for quantum gravity. Working in the mean field approximation of the group field theory formulation of the Lorentzian EPRL model, we derive the equations of motion for such perturbations to first order. We then study these equations around a specific simple isotropic background, characterised by the fundamental representation of SU(2) , and in the regime of the effective cosmological dynamics corresponding to the bouncing region replacing the classical singularity, well approximated by the free GFT dynamics. In this particular example, we identify a region in the parameter space of the model such that perturbations can be large at the bounce but become negligible away from it, i.e. when the background enters the non-linear regime. We also study the departures from perfect isotropy by introducing specific quantities, such as the surface-area-to-volume ratio and the effective volume per quantum, which make them quantitative.

Using VISAR to assess the M-band isotropy in hohlraums

DOE PAGES

Lanier, Nicholas Edward; Kline, John L.; Morton, John

2016-09-27

In laser based radiation flow experiments, drive variability can often overwhelm the physics sensitivity that one seeks to quantify. Hohlraums can help by providing a more symmetrized, Planckian-like source. However, at higher temperatures, the hohlraum’s actual emission can deviate significantly from a truly blackbody, Lambertian source. At the National Ignition Facility (NIF), Dante provides the best quantification of hohlraum output. Unfortunately, limited diagnostic access coupled with NIF’s natural symmetry does not allow for Dante measurements at more than two angles. As part of the CEPHEUS campaign on NIF, proof-of-principle experiments to better quantify the gold M-band isotropy were conducted. Thesemore » experiments positioned beryllium/aluminum mirrors at differing angles, offset from the hohlraum. Filtering removes the thermal emission of the hohlraum and the remaining M-band radiation is preferentially absorbed in the aluminum layer. The subsequent hydrodynamic motion is measured via VISAR. Although indirect, this M-band measurement can be made at any angle.« less

Unified field theories, the early big bang, and the microwave background paradox

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1979-01-01

It is suggested that a superunified field theory incorporating gravity and possessing asymptotic freedom could provide a solution to the paradox of the isotropy of the universal 3K background radiation. Thermal equilibrium could be established in this context through interactions occurring in a temporally indefinite preplanckian era.

On measurement of the isotropy of the speed of light

DOE PAGES

Wojtsekhowski, B.

2014-10-22

Three experimental concepts investigating possible anisotropy of the speed of light are presented. They are based on i) beam deflection in a 180° magnetic arc, ii) narrow resonance production in an electron-positron collider, and iii) the ratio of magnetic moments of an electron and a positron moving in opposite directions.

The Higgs boson and cosmology

PubMed Central

Shaposhnikov, Mikhail

2015-01-01

I will discuss how the Higgs field of the Standard Model may have played an important role in cosmology, leading to the homogeneity, isotropy and flatness of the Universe; producing the quantum fluctuations that seed structure formation; triggering the radiation-dominated era of the hot Big Bang; and contributing to the processes of baryogenesis and dark matter production.

The Higgs boson and cosmology.

PubMed

Shaposhnikov, Mikhail

2015-01-13

I will discuss how the Higgs field of the Standard Model may have played an important role in cosmology, leading to the homogeneity, isotropy and flatness of the Universe; producing the quantum fluctuations that seed structure formation; triggering the radiation-dominated era of the hot Big Bang; and contributing to the processes of baryogenesis and dark matter production.

The Third BATSE Gamma-Ray Burst Catalog

NASA Technical Reports Server (NTRS)

Meegan, Charles A.; Pendleton, Geoffrey N.; Briggs, Michael S.; Kouveliotou, Chryssa; Koshut, Thomas M.; Lestrade, John Patrick; Paciesas, William S.; McCollough, Michael L.; Brainerd, Jerome J.; Horack, John M.;

Isotropic band gaps and freeform waveguides observed in hyperuniform disordered photonic solids

PubMed Central

Man, Weining; Florescu, Marian; Williamson, Eric Paul; He, Yingquan; Hashemizad, Seyed Reza; Leung, Brian Y. C.; Liner, Devin Robert; Torquato, Salvatore; Chaikin, Paul M.; Steinhardt, Paul J.

2013-01-01

Recently, disordered photonic media and random textured surfaces have attracted increasing attention as strong light diffusers with broadband and wide-angle properties. We report the experimental realization of an isotropic complete photonic band gap (PBG) in a 2D disordered dielectric structure. This structure is designed by a constrained optimization method, which combines advantages of both isotropy due to disorder and controlled scattering properties due to low-density fluctuations (hyperuniformity) and uniform local topology. Our experiments use a modular design composed of Al2O3 walls and cylinders arranged in a hyperuniform disordered network. We observe a complete PBG in the microwave region, in good agreement with theoretical simulations, and show that the intrinsic isotropy of this unique class of PBG materials enables remarkable design freedom, including the realization of waveguides with arbitrary bending angles impossible in photonic crystals. This experimental verification of a complete PBG and realization of functional defects in this unique class of materials demonstrate their potential as building blocks for precise manipulation of photons in planar optical microcircuits and has implications for disordered acoustic and electronic band gap materials. PMID:24043795

A continuum mechanics constitutive framework for transverse isotropic soft tissues

NASA Astrophysics Data System (ADS)

Garcia-Gonzalez, D.; Jérusalem, A.; Garzon-Hernandez, S.; Zaera, R.; Arias, A.

2018-03-01

In this work, a continuum constitutive framework for the mechanical modelling of soft tissues that incorporates strain rate and temperature dependencies as well as the transverse isotropy arising from fibres embedded into a soft matrix is developed. The constitutive formulation is based on a Helmholtz free energy function decoupled into the contribution of a viscous-hyperelastic matrix and the contribution of fibres introducing dispersion dependent transverse isotropy. The proposed framework considers finite deformation kinematics, is thermodynamically consistent and allows for the particularisation of the energy potentials and flow equations of each constitutive branch. In this regard, the approach developed herein provides the basis on which specific constitutive models can be potentially formulated for a wide variety of soft tissues. To illustrate this versatility, the constitutive framework is particularised here for animal and human white matter and skin, for which constitutive models are provided. In both cases, different energy functions are considered: Neo-Hookean, Gent and Ogden. Finally, the ability of the approach at capturing the experimental behaviour of the two soft tissues is confirmed.

Polarization-insensitive optical gain characteristics of highly stacked InAs/GaAs quantum dots

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

Kita, Takashi; Suwa, Masaya; Kaizu, Toshiyuki

2014-06-21

The polarized optical gain characteristics of highly stacked InAs/GaAs quantum dots (QDs) with a thin spacer layer fabricated on an n{sup +}-GaAs (001) substrate were studied in the sub-threshold gain region. Using a 4.0-nm-thick spacer layer, we realized an electronically coupled QD superlattice structure along the stacking direction, which enabled the enhancement of the optical gain of the [001] transverse-magnetic (TM) polarization component. We systematically studied the polarized electroluminescence properties of laser devices containing 30 and 40 stacked InAs/GaAs QDs. The net modal gain was analyzed using the Hakki-Paoli method. Owing to the in-plane shape anisotropy of QDs, the polarizationmore » sensitivity of the gain depends on the waveguide direction. The gain showing polarization isotropy between the TM and transverse-electric polarization components is high for the [110] waveguide structure, which occurs for higher amounts of stacked QDs. Conversely, the isotropy of the [−110] waveguide is easily achieved even if the stacking is relatively low, although the gain is small.« less

Force-chain evolution in a two-dimensional granular packing compacted by vertical tappings

NASA Astrophysics Data System (ADS)

Iikawa, Naoki; Bandi, M. M.; Katsuragi, Hiroaki

2018-03-01

We experimentally study the statistics of force-chain evolution in a vertically-tapped two-dimensional granular packing by using photoelastic disks. In this experiment, the tapped granular packing is gradually compacted. During the compaction, the isotropy of grain configurations is quantified by measuring the deviator anisotropy derived from fabric tensor, and then the evolution of force-chain structure is quantified by measuring the interparticle forces and force-chain orientational order parameter. As packing fraction increases, the interparticle force increases and finally saturates to an asymptotic value. Moreover, the grain configurations and force-chain structures become isotropically random as the tapping-induced compaction proceeds. In contrast, the total length of force chains remains unchanged. From the correlations of those parameters, we find two relations: (i) a positive correlation between the isotropy of grain configurations and the disordering of force-chain orientations, and (ii) a negative correlation between the increasing of interparticle forces and the disordering of force-chain orientations. These relations are universally held regardless of the mode of particle motions with or without convection.

Relative Critical Points

NASA Astrophysics Data System (ADS)

Lewis, Debra

2013-05-01

Relative equilibria of Lagrangian and Hamiltonian systems with symmetry are critical points of appropriate scalar functions parametrized by the Lie algebra (or its dual) of the symmetry group. Setting aside the structures - symplectic, Poisson, or variational - generating dynamical systems from such functions highlights the common features of their construction and analysis, and supports the construction of analogous functions in non-Hamiltonian settings. If the symmetry group is nonabelian, the functions are invariant only with respect to the isotropy subgroup of the given parameter value. Replacing the parametrized family of functions with a single function on the product manifold and extending the action using the (co)adjoint action on the algebra or its dual yields a fully invariant function. An invariant map can be used to reverse the usual perspective: rather than selecting a parametrized family of functions and finding their critical points, conditions under which functions will be critical on specific orbits, typically distinguished by isotropy class, can be derived. This strategy is illustrated using several well-known mechanical systems - the Lagrange top, the double spherical pendulum, the free rigid body, and the Riemann ellipsoids - and generalizations of these systems.

Waveform Tomography of Two-Dimensional Three-Component Seismic Data for HTI Anisotropic Media

NASA Astrophysics Data System (ADS)

Gao, Fengxia; Wang, Yanghua; Wang, Yun

2018-06-01

Reservoirs with vertically aligned fractures can be represented equivalently by horizontal transverse isotropy (HTI) media. But inverting for the anisotropic parameters of HTI media is a challenging inverse problem, because of difficulties inherent in a multiple parameter inversion. In this paper, when we invert for the anisotropic parameters, we consider for the first time the azimuthal rotation of a two-dimensional seismic survey line from the symmetry of HTI. The established wave equations for the HTI media with azimuthal rotation consist of nine elastic coefficients, expressed in terms of five modified Thomsen parameters. The latter are parallel to the Thomsen parameters for describing velocity characteristics of weak vertical transverse isotropy media. We analyze the sensitivity differences of the five modified Thomsen parameters from their radiation patterns, and attempt to balance the magnitude and sensitivity differences between the parameters through normalization and tuning factors which help to update the model parameters properly. We demonstrate an effective inversion strategy by inverting velocity parameters in the first stage and updates the five modified Thomsen parameters simultaneously in the second stage, for generating reliably reconstructed models.

A 14 h {sup −3} Gpc{sup 3} study of cosmic homogeneity using BOSS DR12 quasar sample

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

Laurent, Pierre; Goff, Jean-Marc Le; Burtin, Etienne

2016-11-01

The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey in the redshift range 2.2 < z < 2.8. We measure the count-in-sphere, N (< r ), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, D {sub 2}( r ). For a homogeneous distribution N (< r ) ∝ r {sup 3} and D {sub 2}( r ) = 3. Due to the uncertainty on tracer density evolution, 3D surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ''spatial isotropy'. Ourmore » data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any FLRW fiducial cosmology, resulting in 3 − ( D {sub 2}) < 1.7 × 10{sup −3} (2 σ) over the range 250 < r < 1200 h {sup −1} Mpc for the quasar distribution. If we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. Then, combining with the Copernican principle, we finally get homogeneity of the matter distribution on large scales. Alternatively, using a flat ΛCDM fiducial cosmology with CMB-derived parameters, and measuring the quasar bias relative to this ΛCDM model, our data provide a consistency check of the model, in terms of how homogeneous the Universe is on different scales. D {sub 2}( r ) is found to be compatible with our ΛCDM model on the whole 10 < r < 1200 h {sup −1} Mpc range. For the matter distribution we obtain 3 − ( D {sub 2}) < 5 × 10{sup −5} (2 σ) over the range 250 < r < 1200 h {sup −1} Mpc, consistent with homogeneity on large scales.« less

On the isotropy assumption and the applicability of the gasdynamical equations for collapsing systems.

NASA Astrophysics Data System (ADS)

Hensler, G.; Spurzem, R.; Burkert, A.; Trassl, E.

1995-11-01

Rotating, isothermal collapsing protostellar and protogalactic gas systems are always being treated by use of the isotropic gasdynamical (Euler) equations; while it is standard textbook knowledge that diffusive and viscous effects can be neglected in most astrophysical plasmas with large Reynolds numbers, or in other words non-diagonal elements of the stress-energy tensor (second-order moments of the velocity distribution function) and higher order moments vanish, it is not that clear that the isotropy assumption is correct, i.e. the equality of the diagonal second-order moments. Therefore we address in this paper the question whether a collapsing gas cloud remains always strictly isotropic. Analytically the velocity field of an isothermal collapsing rotating gas cloud is computed and it is shown that strict isotropy can be realized in the static case only. This means that although collisional timescales in the gas might be very short, the collapsing system has to develop an inherent small anisotropy; the trajectory of the system in phase space is initially leading away from the isotropic path, staying continuously apart from it for a small distance. We discuss this phenomenon quantitatively by using moment equations of the Boltzmann equation and examine its consequences. It turns out that the deviation from anisotropy in most cases keeps small enough to allow for a global isotropic treatment which is consistent with expectation; applying our results to systems like cloud fluids or stellar systems, however, yields complementary results. Additionally we prove in this paper the performance of the conditions for the applicability of the gasdynamical description in a handy form and show that these conditions are usually fulfilled. We find that for a slightly Jeans unstable system in pressure equilibrium the ratio of the microscopic collision time to free-fall time has to be of order unity or smaller as has to be the Knudsen number in order to ensure the validity of gasdynamic equations.

Energy-latitude dispersion patterns near the isotropy boundaries of energetic protons

NASA Astrophysics Data System (ADS)

Sergeev, V. A.; Chernyaeva, S. A.; Apatenkov, S. V.; Ganushkina, N. Y.; Dubyagin, S. V.

2015-08-01

Non-adiabatic motion of plasma sheet protons causes pitch-angle scattering and isotropic precipitation to the ionosphere, which forms the proton auroral oval. This mechanism related to current sheet scattering (CSS) provides a specific energy-latitude dispersion pattern near the equatorward boundary of proton isotropic precipitation (isotropy boundary, IB), with precipitation sharply decreasing at higher (lower) latitude for protons with lower (higher) energy. However, this boundary maps to the inner magnetosphere, where wave-induced scattering may provide different dispersion patterns as recently demonstrated by Liang et al. (2014). Motivated by the potential usage of the IBs for the magnetotail monitoring as well as by the need to better understand the mechanisms forming the proton IB, we investigate statistically the details of particle flux patterns near the proton IB using NOAA-POES polar spacecraft observations made during September 2009. By comparing precipitated-to-trapped flux ratio (J0/J90) at >30 and >80 keV proton energies, we found a relatively small number of simple CSS-type dispersion events (only 31 %). The clear reversed (wave-induced) dispersion patterns were very rare (5 %). The most frequent pattern had nearly coinciding IBs at two energies (63 %). The structured precipitation with multiple IBs was very frequent (60 %), that is, with two or more significant J0/J90 dropouts. The average latitudinal width of multiple IB structures was about 1°. Investigation of dozens of paired auroral zone crossings of POES satellites showed that the IB pattern is stable on a timescale of less than 2 min (a few proton bounce periods) but can evolve on a longer (several minutes) scale, suggesting temporal changes in some mesoscale structures in the equatorial magnetosphere. We discuss the possible role of CSS-related and wave-induced mechanisms and their possible coupling to interpret the emerging complicated patterns of proton isotropy boundaries.

On the Universality of the Kolmogorov Constant in Numerical Simulations of Turbulence

NASA Technical Reports Server (NTRS)

Yeung, P. K.; Zhou, Ye

1997-01-01

Motivated by a recent survey of experimental data, we examine data on the Kolmogorov spectrum constant in numerical simulations of isotropic turbulence, using results both from previous studies and from new direct numerical simulations over a range of Reynolds numbers (up to 240 on the Taylor scale) at grid resolutions up to 512(exp 3). It is noted that in addition to k(exp -5/3) scaling, identification of a true inertial range requires spectral isotropy in the same wavenumber range. We found that a plateau in the compensated three-dimensional energy spectrum at k(eta) approx. = 0.1 - -0.2, commonly used to infer the Kolmogorov constant from the compensated three-dimensional energy spectrum, actually does not represent proper inertial range behavior. Rather, a proper, if still approximate, inertial range emerges at k(eta) approx. = 0.02 - 0.05 when R(sub lambda) increases beyond 140. The new simulations indicate proportionality constants C(sub 1) and C in the one- and three-dimensional energy spectra respectively about 0.60 and 1.62. If the turbulence were perfectly isotropic then use of isotropy relations in wavenumber space (C(sub 1) = 18/55 C) would imply that C(sub 1) approx. = 0.53 for C = 1.62, in excellent agreement with experiments. However the one- and three-dimensional estimates are not fully consistent, because of departures (due to numerical and statistical limitations) from isotropy of the computed spectra at low wavenumbers. The inertial scaling of structure functions in physical space is briefly addressed. Since DNS is still restricted to moderate Reynolds numbers, an accurate evaluation of the Kolmogorov constant is very difficult. We focus on providing new insights on the interpretation of Kolmogorov 1941 similarity in the DNS literature and do not consider issues pertaining to the refined similarity hypotheses of Kolmogorov (K62).

Theory of thermoelasticity

NASA Technical Reports Server (NTRS)

Iesan, D.

1980-01-01

The development of the theory of thermoelasticity, which examines the interactions between the deformation of elastic media and the thermal field, is traced and the fundamental problems of the theory are presented. Results of recent studies on the subject are presented. Emphasis is primarily on media with generalized anisotropy, or isotropy media. Thermomechanical problems and mathematical formulations and resolutions are included.

On the Experimental Determination of the One-Way Speed of Light

ERIC Educational Resources Information Center

Perez, Israel

2011-01-01

In this paper the question of the isotropy of the one-way speed of light is addressed from an experimental perspective. In particular, we analyse two experimental methods commonly used in its determination. The analysis is aimed at clarifying the view that the one-way speed of light cannot be determined by techniques in which physical entities…

PLUTONIUM-ZIRCONIUM ALLOYS

DOEpatents

Schonfeld, F.W.; Waber, J.T.

1960-08-30

A series of nuclear reactor fuel alloys consisting of from about 5 to about 50 at.% zirconium (or higher zirconium alloys such as Zircaloy), balance plutonium, and having the structural composition of a plutonium are described. Zirconium is a satisfactory diluent because it alloys readily with plutonium and has desirable nuclear properties. Additional advantages are corrosion resistance, excellent fabrication propenties, an isotropie structure, and initial softness.

A direct correlation of x-ray diffraction orientation distributions to the in-plane stiffness of semi-crystalline organic semiconducting films

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

Zhao, Bingxiao; Awartani, Omar; O'Connor, Brendan

2016-05-02

Large charge mobilities of semi-crystalline organic semiconducting films could be obtained by mechanically aligning the material phases of the film with the loading axis. A key element is to utilize the inherent stiffness of the material for optimal or desired alignment. However, experimentally determining the moduli of semi-crystalline organic thin films for different loading directions is difficult, if not impossible, due to film thickness and material anisotropy. In this paper, we address these challenges by presenting an approach based on combining a composite mechanics stiffness orientation formulation with a Gaussian statistical distribution to directly estimate the in-plane stiffness (transverse isotropy)more » of aligned semi-crystalline polymer films based on crystalline orientation distributions obtained by X-ray diffraction experimentally at different applied strains. Our predicted results indicate that the in-plane stiffness of an annealing film was initially isotropic, and then it evolved to transverse isotropy with increasing mechanical strains. This study underscores the significance of accounting for the crystalline orientation distributions of the film to obtain an accurate understanding and prediction of the elastic anisotropy of semi-crystalline polymer films.« less

Modeling of short fiber reinforced injection moulded composite

NASA Astrophysics Data System (ADS)

Kulkarni, A.; Aswini, N.; Dandekar, C. R.; Makhe, S.

2012-09-01

A micromechanics based finite element model (FEM) is developed to facilitate the design of a new production quality fiber reinforced plastic injection molded part. The composite part under study is composed of a polyetheretherketone (PEEK) matrix reinforced with 30% by volume fraction of short carbon fibers. The constitutive material models are obtained by using micromechanics based homogenization theories. The analysis is carried out by successfully coupling two commercial codes, Moldflow and ANSYS. Moldflow software is used to predict the fiber orientation by considering the flow kinetics and molding parameters. Material models are inputted into the commercial software ANSYS as per the predicted fiber orientation and the structural analysis is carried out. Thus in the present approach a coupling between two commercial codes namely Moldflow and ANSYS has been established to enable the analysis of the short fiber reinforced injection moulded composite parts. The load-deflection curve is obtained based on three constitutive material model namely an isotropy, transversely isotropy and orthotropy. Average values of the predicted quantities are compared to experimental results, obtaining a good correlation. In this manner, the coupled Moldflow-ANSYS model successfully predicts the load deflection curve of a composite injection molded part.

Scalewise invariant analysis of the anisotropic Reynolds stress tensor for atmospheric surface layer and canopy sublayer turbulent flows

NASA Astrophysics Data System (ADS)

Brugger, Peter; Katul, Gabriel G.; De Roo, Frederik; Kröniger, Konstantin; Rotenberg, Eyal; Rohatyn, Shani; Mauder, Matthias

2018-05-01

Anisotropy in the turbulent stress tensor, which forms the basis of invariant analysis, is conducted using velocity time series measurements collected in the canopy sublayer (CSL) and the atmospheric surface layer (ASL). The goal is to assess how thermal stratification and surface roughness conditions simultaneously distort the scalewise relaxation towards isotropic state from large to small scales when referenced to homogeneous turbulence. To achieve this goal, conventional invariant analysis is extended to allow scalewise information about relaxation to isotropy in physical (instead of Fourier) space to be incorporated. The proposed analysis shows that the CSL is more isotropic than its ASL counterpart at large, intermediate, and small (or inertial) scales irrespective of the thermal stratification. Moreover, the small (or inertial) scale anisotropy is more prevalent in the ASL when compared to the CSL, a finding that cannot be fully explained by the intensity of the mean velocity gradient acting on all scales. Implications to the validity of scalewise Rotta and Lumley models for return to isotropy as well as advantages to using barycentric instead of anisotropy invariant maps for such scalewise analysis are discussed.

The effect of gradational velocities and anisotropy on fault-zone trapped waves

NASA Astrophysics Data System (ADS)

Gulley, A. K.; Eccles, J. D.; Kaipio, J. P.; Malin, P. E.

2017-08-01

Synthetic fault-zone trapped wave (FZTW) dispersion curves and amplitude responses for FL (Love) and FR (Rayleigh) type phases are analysed in transversely isotropic 1-D elastic models. We explore the effects of velocity gradients, anisotropy, source location and mechanism. These experiments suggest: (i) A smooth exponentially decaying velocity model produces a significantly different dispersion curve to that of a three-layer model, with the main difference being that Airy phases are not produced. (ii) The FZTW dispersion and amplitude information of a waveguide with transverse-isotropy depends mostly on the Shear wave velocities in the direction parallel with the fault, particularly if the fault zone to country-rock velocity contrast is small. In this low velocity contrast situation, fully isotropic approximations to a transversely isotropic velocity model can be made. (iii) Fault-aligned fractures and/or bedding in the fault zone that cause transverse-isotropy enhance the amplitude and wave-train length of the FR type FZTW. (iv) Moving the source and/or receiver away from the fault zone removes the higher frequencies first, similar to attenuation. (v) In most physically realistic cases, the radial component of the FR type FZTW is significantly smaller in amplitude than the transverse.

Isotropy of the early universe from CMB anisotropies

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

Donoghue, Evan P.; University of Notre Dame, Notre Dame, Indiana 46556; Donoghue, John F.

The acoustic peak in the cosmic microwave background power spectrum is sensitive to causal processes and cosmological parameters in the early universe up to the time of last scattering. We provide limits on correlated spatial variations of the peak height and peak position and interpret these as constraints on the spatial variation of the cosmological parameters (baryon density, cold dark matter density, and cosmological constant as well as the amplitude and tilt of the original fluctuations). We utilize recent work of Hansen, Banday, and Gorski who have studied the spatial isotropy of the power spectrum as measured by WMAP bymore » performing the power spectrum analysis on smaller patches of the sky. We find that there is no statistically significant correlated asymmetry of the peak. Hansen, Banday, and Gorski have also provided preliminary indications of a preferred direction in the lower angular momentum range (l{approx}2-40) and we show how possible explanations of this asymmetry are severely constrained by the data on the acoustic peak. Finally we show a possible non-Gaussian feature in the data, associated with a difference in the northern and southern galactic hemispheres.« less

Testing the cosmological principle of isotropy: local power-spectrum estimates of the WMAP data

NASA Astrophysics Data System (ADS)

Hansen, F. K.; Banday, A. J.; Górski, K. M.

2004-11-01

We apply the Gabor transform methodology proposed by Hansen et al. to the WMAP data in order to test the statistical properties of the cosmic microwave background (CMB) fluctuation field and specifically to evaluate the fundamental assumption of cosmological isotropy. In particular, we apply the transform with several apodization scales, thus allowing the determination of the positional dependence of the angular power spectrum with either high spatial localization or high angular resolution (i.e. narrow bins in multipole space). Practically, this implies that we estimate the angular power spectrum locally in discs of various sizes positioned in different directions: small discs allow the greatest sensitivity to positional dependence, whereas larger discs allow greater sensitivity to variations over different angular scales. In addition, we determine whether the spatial position of a few outliers in the angular power spectrum could suggest the presence of residual foregrounds or systematic effects. For multipoles close to the first peak, the most deviant local estimates from the best-fitting WMAP model are associated with a few particular areas close to the Galactic plane. Such deviations also include the `dent' in the spectrum just shortward of the first peak which was remarked upon by the WMAP team. Estimating the angular power spectrum excluding these areas gives a slightly higher first Doppler peak amplitude. Finally, we probe the isotropy of the largest angular scales by estimating the power spectrum on hemispheres and reconfirm strong indications of a north-south asymmetry previously reported by other authors. Indeed, there is a remarkable lack of power in a region associated with the North ecliptic Pole. With the greater fidelity in l-space allowed by this larger sky coverage, we find tentative evidence for residual foregrounds in the range l= 2-4, which could be associated with the low measured quadrupole amplitudes and other anomalies on these angular scales (e.g. planarity and alignment). However, over the range l= 5-40 the observed asymmetry is much harder to explain in terms of residual foregrounds and known systematic effects. By reorienting the coordinate axes, we partition the sky into different hemispheres and search for the reference frame which maximizes the asymmetric distribution of power. The North Pole for this coordinate frame is found to intersect the sphere at (80°, 57°) in Galactic colatitude and longitude over almost the entire multipole range l= 5-40. Furthermore, the strong negative outlier at l= 21 and the strong positive outlier at l= 39, as determined from the global power spectrum by the WMAP team, are found to be associated with the Northern and Southern hemispheres, respectively (in this frame of maximum asymmetry). Thus, these two outliers follow the general tendency of the multipoles l= 5-40 to be of systematically lower amplitude in the north and higher in the south. Such asymmetric distributions of power on the sky provide a serious test for the cosmological principle of isotropy.

Kinematical Test Theories for Special Relativity

NASA Astrophysics Data System (ADS)

Lämmerzahl, Claus; Braxmaier, Claus; Dittus, Hansjörg; Müller, Holger; Peters, Achim; Schiller, Stephan

A comparison of certain kinematical test theories for Special Relativity including the Robertson and Mansouri-Sext test theories is presented and the accuracy of the experimental results testing Special Relativity are expressed in terms of the parameters appearing in these test theories. The theoretical results are applied to the most precise experimental results obtained recently for the isotropy of light propagation and the constancy of the speed of light.

Bidirectional reflectance distribution function measurements and analysis of retroreflective materials.

PubMed

Belcour, Laurent; Pacanowski, Romain; Delahaie, Marion; Laville-Geay, Aude; Eupherte, Laure

2014-12-01

We compare the performance of various analytical retroreflecting bidirectional reflectance distribution function (BRDF) models to assess how they reproduce accurately measured data of retroreflecting materials. We introduce a new parametrization, the back vector parametrization, to analyze retroreflecting data, and we show that this parametrization better preserves the isotropy of data. Furthermore, we update existing BRDF models to improve the representation of retroreflective data.

Momentum distributions of isotopes produced by fragmentation of relativistic C-12 and O-16 projectiles

NASA Technical Reports Server (NTRS)

Greiner, D. E.; Lindstrom, P. J.; Heckman, H. H.; Cork, B.; Bieser, F. S.

1975-01-01

The fragment momentum distributions in the projectile rest frame are, typically, Gaussian shaped, narrow, consistent with isotropy, depend on fragment and projectile, and have no significant correlation with target mass or beam energy. The nuclear temperature is inferred from the momentum distributions of the fragments and is approximately equal to the projectile nuclear binding energy, indicative of small energy transfer between target and fragment.

How the Laser Helped to Improve the Test of Special Theory of Relativity?

ERIC Educational Resources Information Center

Singh, Satya Pal

2013-01-01

In this paper of I have reviewed the test done for validating the special theory of relativity using masers and lasers in last one century. Michelson-Morley did the first experimental verification for the isotropy of space for the propagation of light in 1887. It has an accuracy of 1/100th of a fringe shift. The predicted fringe shift on the basis…

Arrival directions of cosmic rays of E .4 EeV

NASA Technical Reports Server (NTRS)

Baltrusaitis, R. M.; Cady, R.; Cassiday, G. I.; Cooper, R.; Elbert, J. W.; Gerhardy, P. R.; Ko, S.; Loh, E. C.; Mizumoto, Y.; Salamon, M. H.

1985-01-01

The anisotropy of cosmic rays observed by the Utah Fly's Eye detector has been studied. Emphasis has been placed on examining distributions of events in galactic coordinates. No statistically significant departure from isotropy has been observed for energies greater than 0.4 EeV (1 EeV = 10 to the 18th power eV). Results of the standard harmonic analysis in right ascension are also presented.

On the Weyl curvature hypothesis

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

Stoica, Ovidiu Cristinel, E-mail: holotronix@gmail.com

2013-11-15

The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity. In previous papers it has been proposed an equivalent form of Einstein’s equation, which extends it and remains valid at an important class of singularities (including in particular the Schwarzschild, FLRW, and isotropic singularities). Here it is shown that if the Big-Bang singularity is from this class, it also satisfies the Weyl curvature hypothesis. As an application, we study a very general example of cosmologicalmore » models, which generalizes the FLRW model by dropping the isotropy and homogeneity constraints. This model also generalizes isotropic singularities, and a class of singularities occurring in Bianchi cosmologies. We show that the Big-Bang singularity of this model is of the type under consideration, and satisfies therefore the Weyl curvature hypothesis. -- Highlights: •The singularities we introduce are described by finite geometric/physical objects. •Our singularities have smooth Riemann and Weyl curvatures. •We show they satisfy Penrose’s Weyl curvature hypothesis (Weyl=0 at singularities). •Examples: FLRW, isotropic singularities, an extension of Schwarzschild’s metric. •Example: a large class of singularities which may be anisotropic and inhomogeneous.« less

Real-time detection of dielectric anisotropy or isotropy in unconventional oil-gas reservoir rocks supported by the oblique-incidence reflectivity difference technique

NASA Astrophysics Data System (ADS)

Zhan, Honglei; Wang, Jin; Zhao, Kun; Lű, Huibin; Jin, Kuijuan; He, Liping; Yang, Guozhen; Xiao, Lizhi

2016-12-01

Current geological extraction theory and techniques are very limited to adequately characterize the unconventional oil-gas reservoirs because of the considerable complexity of the geological structures. Optical measurement has the advantages of non-interference with the earth magnetic fields, and is often useful in detecting various physical properties. One key parameter that can be detected using optical methods is the dielectric permittivity, which reflects the mineral and organic properties. Here we reported an oblique-incidence reflectivity difference (OIRD) technique that is sensitive to the dielectric and surface properties and can be applied to characterization of reservoir rocks, such as shale and sandstone core samples extracted from subsurface. The layered distribution of the dielectric properties in shales and the uniform distribution in sandstones are clearly identified using the OIRD signals. In shales, the micro-cracks and particle orientation result in directional changes of the dielectric and surface properties, and thus, the isotropy and anisotropy of the rock can be characterized by OIRD. As the dielectric and surface properties are closely related to the hydrocarbon-bearing features in oil-gas reservoirs, we believe that the precise measurement carried with OIRD can help in improving the recovery efficiency in well-drilling process.

Real-time detection of dielectric anisotropy or isotropy in unconventional oil-gas reservoir rocks supported by the oblique-incidence reflectivity difference technique

PubMed Central

Zhan, Honglei; Wang, Jin; Zhao, Kun; Lű, Huibin; Jin, Kuijuan; He, Liping; Yang, Guozhen; Xiao, Lizhi

2016-01-01

Current geological extraction theory and techniques are very limited to adequately characterize the unconventional oil-gas reservoirs because of the considerable complexity of the geological structures. Optical measurement has the advantages of non-interference with the earth magnetic fields, and is often useful in detecting various physical properties. One key parameter that can be detected using optical methods is the dielectric permittivity, which reflects the mineral and organic properties. Here we reported an oblique-incidence reflectivity difference (OIRD) technique that is sensitive to the dielectric and surface properties and can be applied to characterization of reservoir rocks, such as shale and sandstone core samples extracted from subsurface. The layered distribution of the dielectric properties in shales and the uniform distribution in sandstones are clearly identified using the OIRD signals. In shales, the micro-cracks and particle orientation result in directional changes of the dielectric and surface properties, and thus, the isotropy and anisotropy of the rock can be characterized by OIRD. As the dielectric and surface properties are closely related to the hydrocarbon-bearing features in oil-gas reservoirs, we believe that the precise measurement carried with OIRD can help in improving the recovery efficiency in well-drilling process. PMID:27976746

Doubly negative isotropic elastic metamaterial for sub-wavelength focusing: Design and realization

NASA Astrophysics Data System (ADS)

Oh, Joo Hwan; Seung, Hong Min; Kim, Yoon Young

2017-12-01

In spite of much progress in elastic metamaterials, tuning the effective density and stiffness to desired values ranging from negatives to large positives is still difficult. In particular, simultaneous realization of double negativity and isotropy, critical in sub-wavelength focusing, is very challenging since anisotropy is usually unavoidable in resonance-based metamaterials. The main difficulty is that there is no established systematic design method for simultaneous achieving of double negativity and isotropy. Thus, we propose a unique elastic metamaterial unit cell with which simultaneous realization can be achieved by an explicit step-by-step approach. The unit cell of the proposed metamaterial can be accurately modeled as an equivalent mass-spring system so that the effective properties can be easily controlled with the design parameters. The actual realization was carried out by acquiring the desired properties in sequential steps which is in detail. The specific application for this study is on sub-wavelength focusing, which will be demonstrated by waves from a single point source focused on a region smaller than half the wavelength. Actual experiments were performed on an aluminum plate where the designed metamaterial flat lens was imbedded. The results acquired through simulations and experiments suggest potential applications of the proposed metamaterial and the systematic design approach in advanced acoustic surgery or non-destructive testing.

Estimating statistical isotropy violation in CMB due to non-circular beam and complex scan in minutes

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

Pant, Nidhi; Das, Santanu; Mitra, Sanjit

Mild, unavoidable deviations from circular-symmetry of instrumental beams along with scan strategy can give rise to measurable Statistical Isotropy (SI) violation in Cosmic Microwave Background (CMB) experiments. If not accounted properly, this spurious signal can complicate the extraction of other SI violation signals (if any) in the data. However, estimation of this effect through exact numerical simulation is computationally intensive and time consuming. A generalized analytical formalism not only provides a quick way of estimating this signal, but also gives a detailed understanding connecting the leading beam anisotropy components to a measurable BipoSH characterisation of SI violation. In this paper,more » we provide an approximate generic analytical method for estimating the SI violation generated due to a non-circular (NC) beam and arbitrary scan strategy, in terms of the Bipolar Spherical Harmonic (BipoSH) spectra. Our analytical method can predict almost all the features introduced by a NC beam in a complex scan and thus reduces the need for extensive numerical simulation worth tens of thousands of CPU hours into minutes long calculations. As an illustrative example, we use WMAP beams and scanning strategy to demonstrate the easability, usability and efficiency of our method. We test all our analytical results against that from exact numerical simulations.« less

Enhancing the isotropy of lateral resolution in coherent structured illumination microscopy

PubMed Central

Park, Joo Hyun; Lee, Jae Yong; Lee, Eun Seong

2014-01-01

We present a method to improve the isotropy of spatial resolution in a structured illumination microscopy (SIM) implemented for imaging non-fluorescent samples. To alleviate the problem of anisotropic resolution involved with the previous scheme of coherent SIM that employs the two orthogonal standing-wave illumination, referred to as the orthogonal SIM, we introduce a hexagonal-lattice illumination that incorporates three standing-wave fields simultaneously superimposed at the orientations equally divided in the lateral plane. A theoretical formulation is worked out rigorously for the coherent image formation with such a simultaneous multiple-beam illumination and an explicit Fourier-domain framework is derived for reconstructing an image with enhanced resolution. Using a computer-synthesized resolution target as a 2D coherent sample, we perform numerical simulations to examine the imaging characteristics of our three-angle SIM compared with the orthogonal SIM. The investigation on the 2D resolving power with the various test patterns of different periods and orientations reveal that the orientation-dependent undulation of lateral resolution can be reduced from 27% to 8% by using the three-angle SIM while the best resolution (0.54 times the resolution limit of conventional coherent imaging) in the directions of structured illumination is slightly deteriorated by 4.6% from that of the orthogonal SIM. PMID:24940548

Daily quality assurance software for a satellite radiometer system

NASA Technical Reports Server (NTRS)

Keegstra, P. B.; Smoot, G. F.; Bennett, C. L.; Aymon, J.; Backus, C.; Deamici, G.; Hinshaw, G.; Jackson, P. D.; Kogut, A.; Lineweaver, C.

1992-01-01

Six Differential Microwave Radiometers (DMR) on COBE (Cosmic Background Explorer) measure the large-angular-scale isotropy of the cosmic microwave background (CMB) at 31.5, 53, and 90 GHz. Quality assurance software analyzes the daily telemetry from the spacecraft to ensure that the instrument is operating correctly and that the data are not corrupted. Quality assurance for DMR poses challenging requirements. The data are differential, so a single bad point can affect a large region of the sky, yet the CMB isotropy requires lengthy integration times (greater than 1 year) to limit potential CMB anisotropies. Celestial sources (with the exception of the moon) are not, in general, visible in the raw differential data. A 'quicklook' software system was developed that, in addition to basic plotting and limit-checking, implements a collection of data tests as well as long-term trending. Some of the key capabilities include the following: (1) stability analysis showing how well the data RMS averages down with increased data; (2) a Fourier analysis and autocorrelation routine to plot the power spectrum and confirm the presence of the 3 mK 'cosmic' dipole signal; (3) binning of the data against basic spacecraft quantities such as orbit angle; (4) long-term trending; and (5) dipole fits to confirm the spacecraft attitude azimuth angle.

Field-based optimal-design of an electric motor: a new sensitivity formulation

NASA Astrophysics Data System (ADS)

Barba, Paolo Di; Mognaschi, Maria Evelina; Lowther, David Alister; Wiak, Sławomir

2017-12-01

In this paper, a new approach to robust optimal design is proposed. The idea is to consider the sensitivity by means of two auxiliary criteria A and D, related to the magnitude and isotropy of the sensitivity, respectively. The optimal design of a switched-reluctance motor is considered as a case study: since the case study exhibits two design criteria, the relevant Pareto front is approximated by means of evolutionary computing.

On six-dimensional pseudo-Riemannian almost g.o. spaces

NASA Astrophysics Data System (ADS)

Dušek, Zdeněk; Kowalski, Oldřich

2007-09-01

We modify the "Kaplan example" (a six-dimensional nilpotent Lie group which is a Riemannian g.o. space) and we obtain two pseudo-Riemannian homogeneous spaces with noncompact isotropy group. These examples have the property that all geodesics are homogeneous up to a set of measure zero. We also show that the (incomplete) geodesic graphs are strongly discontinuous at the boundary, i.e., the limits along certain curves are always infinite.

Quasi-hamiltonian quotients as disjoint unions of symplectic manifolds

NASA Astrophysics Data System (ADS)

Schaffhauser, Florent

2007-08-01

The main result of this paper is Theorem 2.12 which says that the quotient μ-1({1})/U associated to a quasi-hamiltonian space (M, ω, μ: M → U) has a symplectic structure even when 1 is not a regular value of the momentum map μ. Namely, it is a disjoint union of symplectic manifolds of possibly different dimensions, which generalizes the result of Alekseev, Malkin and Meinrenken in [AMM98]. We illustrate this theorem with the example of representation spaces of surface groups. As an intermediary step, we give a new class of examples of quasi-hamiltonian spaces: the isotropy submanifold MK whose points are the points of M with isotropy group K ⊂ U. The notion of quasi-hamiltonian space was introduced by Alekseev, Malkin and Meinrenken in their paper [AMM98]. The main motivation for it was the existence, under some regularity assumptions, of a symplectic structure on the associated quasi-hamiltonian quotient. Throughout their paper, the analogy with usual hamiltonian spaces is often used as a guiding principle, replacing Lie-algebra-valued momentum maps with Lie-group-valued momentum maps. In the hamiltonian setting, when the usual regularity assumptions on the group action or the momentum map are dropped, Lerman and Sjamaar showed in [LS91] that the quotient associated to a hamiltonian space carries a stratified symplectic structure. In particular, this quotient space is a disjoint union of symplectic manifolds. In this paper, we prove an analogous result for quasi-hamiltonian quotients. More precisely, we show that for any quasi-hamiltonian space (M, ω, μ: M → U), the associated quotient M//U := μ-1({1})/U is a disjoint union of symplectic manifolds (Theorem 2.12): [ mu^{-1}(\\{1\\})/U = bigsqcup_{jin J} (mu^{-1}(\\{1\\})\\cap M_{K_j})/L_{K_j} . ] Here Kj denotes a closed subgroup of U and MKj denotes the isotropy submanifold of type Kj: MKj = {x ∈ M | Ux = Kj}. Finally, LKj is the quotient group LKj = { N}(Kj)/K_j, where { N}(Kj) is the normalizer of Kj in U. As an intermediary step in our study, we show that MKj is a quasi-hamiltonian space when endowed with the (free) action of LKj.

A model for proton-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Walker, G. H.; Outlaw, R. A.; Stock, L. V.

1982-01-01

A simple model for proton radiation damage in GaAs heteroface solar cells is developed. The model includes the effects of spatial nonuniformity of low energy proton damage. Agreement between the model and experimental proton damage data for GaAs heteroface solar cells is satisfactory. An extension of the model to include angular isotropy, as is appropriate for protons in space, is shown to result in significantly less cell damage than for normal proton incidence.

Turbulence simulation mechanization for Space Shuttle Orbiter dynamics and control studies

NASA Technical Reports Server (NTRS)

Tatom, F. B.; King, R. L.

1977-01-01

The current version of the NASA turbulent simulation model in the form of a digital computer program, TBMOD, is described. The logic of the program is discussed and all inputs and outputs are defined. An alternate method of shear simulation suitable for incorporation into the model is presented. The simulation is based on a von Karman spectrum and the assumption of isotropy. The resulting spectral density functions for the shear model are included.

Derivation of revised formulae for eddy viscous forces used in the ocean general circulation model

NASA Technical Reports Server (NTRS)

Chou, Ru Ling

1988-01-01

Presented is a re-derivation of the eddy viscous dissipation tensor commonly used in present oceanographic general circulation models. When isotropy is imposed, the currently-used form of the tensor fails to return to the laplacian operator. In this paper, the source of this error is identified in a consistent derivation of the tensor in both rectangular and earth spherical coordinates, and the correct form of the eddy viscous tensor is presented.

Three demonstrations of degeneracy lifting

NASA Astrophysics Data System (ADS)

Morrison, Andrew

2005-09-01

Two normal modes of vibration of a single object having exactly the same frequency are said to be degenerate modes. Certain simple systems, such as a circular membrane, have predictable degenerate modes. A lack of isotropy in the material or a geometric asymmetry can separate the frequencies and lift the degeneracy. Demonstration of this effect is easily accomplished in the classroom. Three methods of showing the effect are presented using a handbell, a short metal rod, and a coffee mug.

Granular material flow in two-dimensional hoppers

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

Brennen, C.; Pearce, J.C.

To aid in improving the transport of granular media for industrial purposes, the California Institute of Technology presents a comparison of experimental data with analytical results for the flow of dry granular media (such as coal) through a two-dimensional or wedge-shaped hopper. The analytical solution, which is based on the constitutive postulates (suggested by A.W. Jenike and R.T. Shield) of intergrain Coulomb friction and isotropy, produces results that are in good agreement with the experimental measurements.

Nonzero Ideal Gas Contribution to the Surface Tension of Water.

PubMed

Sega, Marcello; Fábián, Balázs; Jedlovszky, Pál

2017-06-15

Surface tension, the tendency of fluid interfaces to behave elastically and minimize their surface, is routinely calculated as the difference between the lateral and normal components of the pressure or, invoking isotropy in momentum space, of the virial tensor. Here we show that the anisotropy of the kinetic energy tensor close to a liquid-vapor interface can be responsible for a large part of its surface tension (about 15% for water, independent from temperature).

Gravitomagnetic Instabilities in Anisotropically Expanding Fluids

NASA Astrophysics Data System (ADS)

Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos, Demetrios B.; Vlahos, Loukas

Gravitational instabilities in a magnetized Friedman-Robertson-Walker (FRW) universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became evident that the external magnetic field disfavors the perturbations' growth, suppressing the corresponding rate by an amount proportional to its strength. However, the spatial isotropy of the FRW universe is not compatible with the presence of large-scale magnetic fields. Therefore, in this paper we use the general-relativistic version of the (linearized) perturbed magnetohydrodynamic equations with and without resistivity, to discuss a generalized Jeans criterion and the potential formation of density condensations within a class of homogeneous and anisotropically expanding, self-gravitating, magnetized fluids in curved space-time. We find that, for a wide variety of anisotropic cosmological models, gravitomagnetic instabilities can lead to subhorizontal, magnetized condensations. In the nonresistive case, the power spectrum of the unstable cosmological perturbations suggests that most of the power is concentrated on large scales (small k), very close to the horizon. On the other hand, in a resistive medium, the critical wave-numbers so obtained, exhibit a delicate dependence on resistivity, resulting in the reduction of the corresponding Jeans lengths to smaller scales (well bellow the horizon) than the nonresistive ones, while increasing the range of cosmological models which admit such an instability.

Statistical isotropy violation in WMAP CMB maps resulting from non-circular beams

NASA Astrophysics Data System (ADS)

Das, Santanu; Mitra, Sanjit; Rotti, Aditya; Pant, Nidhi; Souradeep, Tarun

2016-06-01

Statistical isotropy (SI) of cosmic microwave background (CMB) fluctuations is a key observational test to validate the cosmological principle underlying the standard model of cosmology. While a detection of SI violation would have immense cosmological ramification, it is important to recognise their possible origin in systematic effects of observations. The WMAP seven year (WMAP-7) release claimed significant deviation from SI in the bipolar spherical harmonic (BipoSH) coefficients and . Here we present the first explicit reproduction of the measurements reported in WMAP-7, confirming that beam systematics alone can completely account for the measured SI violation. The possibility of such a systematic origin was alluded to in WMAP-7 paper itself and other authors but not as explicitly so as to account for it accurately. We simulate CMB maps using the actual WMAP non-circular beams and scanning strategy. Our estimated BipoSH spectra from these maps match the WMAP-7 results very well. It is also evident that only a very careful and adequately detailed modelling, as carried out here, can conclusively establish that the entire signal arises from non-circular beam effect. This is important since cosmic SI violation signals are expected to be subtle and dismissing a large SI violation signal as observational artefact based on simplistic plausibility arguments run the serious risk of "throwing the baby out with the bathwater".

Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory

NASA Astrophysics Data System (ADS)

Aab, A.; Abreu, P.; Aglietta, M.; Samarai, I. Al; Albuquerque, I. F. M.; Allekotte, I.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Anastasi, G. A.; Anchordoqui, L.; Andrada, B.; Andringa, S.; Aramo, C.; Arqueros, F.; Arsene, N.; Asorey, H.; Assis, P.; Aublin, J.; Avila, G.; Badescu, A. M.; Balaceanu, A.; Barreira Luz, R. J.; Baus, C.; Beatty, J. J.; Becker, K. H.; Bellido, J. A.; Berat, C.; Bertaina, M. E.; Bertou, X.; Biermann, P. L.; Billoir, P.; Biteau, J.; Blaess, S. G.; Blanco, A.; Blazek, J.; Bleve, C.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Borodai, N.; Botti, A. M.; Brack, J.; Brancus, I.; Bretz, T.; Bridgeman, A.; Briechle, F. L.; Buchholz, P.; Bueno, A.; Buitink, S.; Buscemi, M.; Caballero-Mora, K. S.; Caccianiga, L.; Cancio, A.; Canfora, F.; Caramete, L.; Caruso, R.; Castellina, A.; Cataldi, G.; Cazon, L.; Chavez, A. G.; Chinellato, J. A.; Chudoba, J.; Clay, R. W.; Colalillo, R.; Coleman, A.; Collica, L.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cooper, M. J.; Coutu, S.; Covault, C. E.; Cronin, J.; D'Amico, S.; Daniel, B.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; de Jong, S. J.; De Mauro, G.; de Mello Neto, J. R. T.; De Mitri, I.; de Oliveira, J.; de Souza, V.; Debatin, J.; Deligny, O.; Di Giulio, C.; Di Matteo, A.; Díaz Castro, M. L.; Diogo, F.; Dobrigkeit, C.; D'Olivo, J. C.; dos Anjos, R. C.; Dova, M. T.; Dundovic, A.; Ebr, J.; Engel, R.; Erdmann, M.; Erfani, M.; Escobar, C. O.; Espadanal, J.; Etchegoyen, A.; Falcke, H.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Fick, B.; Figueira, J. M.; Filipčič, A.; Fratu, O.; Freire, M. M.; Fujii, T.; Fuster, A.; Gaior, R.; García, B.; Garcia-Pinto, D.; Gaté, F.; Gemmeke, H.; Gherghel-Lascu, A.; Ghia, P. L.; Giaccari, U.; Giammarchi, M.; Giller, M.; Głas, D.; Glaser, C.; Golup, G.; Gómez Berisso, M.; Gómez Vitale, P. F.; González, N.; Gorgi, A.; Gorham, P.; Gouffon, P.; Grillo, A. F.; Grubb, T. D.; Guarino, F.; Guedes, G. P.; Hampel, M. R.; Hansen, P.; Harari, D.; Harrison, T. A.; Harton, J. L.; Hasankiadeh, Q.; Haungs, A.; Hebbeker, T.; Heck, D.; Heimann, P.; Herve, A. E.; Hill, G. C.; Hojvat, C.; Holt, E.; Homola, P.; Hörandel, J. R.; Horvath, P.; Hrabovský, M.; Huege, T.; Hulsman, J.; Insolia, A.; Isar, P. G.; Jandt, I.; Jansen, S.; Johnsen, J. A.; Josebachuili, M.; Kääpä, A.; Kambeitz, O.; Kampert, K. H.; Katkov, I.; Keilhauer, B.; Kemp, E.; Kemp, J.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Krause, R.; Krohm, N.; Kuempel, D.; Kukec Mezek, G.; Kunka, N.; Kuotb Awad, A.; LaHurd, D.; Lauscher, M.; Legumina, R.; Leigui de Oliveira, M. A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; Lopes, L.; López, R.; López Casado, A.; Luce, Q.; Lucero, A.; Malacari, M.; Mallamaci, M.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Mariş, I. C.; Marsella, G.; Martello, D.; Martinez, H.; Martínez Bravo, O.; Masías Meza, J. J.; Mathes, H. J.; Mathys, S.; Matthews, J.; Matthews, J. A. J.; Matthiae, G.; Mayotte, E.; Mazur, P. O.; Medina, C.; Medina-Tanco, G.; Melo, D.; Menshikov, A.; Messina, S.; Micheletti, M. I.; Middendorf, L.; Minaya, I. A.; Miramonti, L.; Mitrica, B.; Mockler, D.; Mollerach, S.; Montanet, F.; Morello, C.; Mostafá, M.; Müller, A. L.; Müller, G.; Muller, M. A.; Müller, S.; Mussa, R.; Naranjo, I.; Nellen, L.; Nguyen, P. H.; Niculescu-Oglinzanu, M.; Niechciol, M.; Niemietz, L.; Niggemann, T.; Nitz, D.; Nosek, D.; Novotny, V.; Nožka, H.; Núñez, L. A.; Ochilo, L.; Oikonomou, F.; Olinto, A.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Papenbreer, P.; Parente, G.; Parra, A.; Paul, T.; Pech, M.; Pedreira, F.; Pȩkala, J.; Pelayo, R.; Peña-Rodriguez, J.; Pereira, L. A. S.; Perlín, M.; Perrone, L.; Peters, C.; Petrera, S.; Phuntsok, J.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Plum, M.; Porowski, C.; Prado, R. R.; Privitera, P.; Prouza, M.; Quel, E. J.; Querchfeld, S.; Quinn, S.; Ramos-Pollan, R.; Rautenberg, J.; Ravignani, D.; Revenu, B.; Ridky, J.; Risse, M.; Ristori, P.; Rizi, V.; Rodrigues de Carvalho, W.; Rodriguez Fernandez, G.; Rodriguez Rojo, J.; Rogozin, D.; Roncoroni, M. J.; Roth, M.; Roulet, E.; Rovero, A. C.; Ruehl, P.; Saffi, S. J.; Saftoiu, A.; Salazar, H.; Saleh, A.; Salesa Greus, F.; Salina, G.; Sánchez, F.; Sanchez-Lucas, P.; Santos, E. M.; Santos, E.; Sarazin, F.; Sarmento, R.; Sarmiento, C. A.; Sato, R.; Schauer, M.; Scherini, V.; Schieler, H.; Schimp, M.; Schmidt, D.; Scholten, O.; Schovánek, P.; Schröder, F. G.; Schulz, A.; Schulz, J.; Schumacher, J.; Sciutto, S. J.; Segreto, A.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sigl, G.; Silli, G.; Sima, O.; Śmiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sonntag, S.; Sorokin, J.; Squartini, R.; Stanca, D.; Stanič, S.; Stasielak, J.; Stassi, P.; Strafella, F.; Suarez, F.; Suarez Durán, M.; Sudholz, T.; Suomijärvi, T.; Supanitsky, A. D.; Swain, J.; Szadkowski, Z.; Taboada, A.; Taborda, O. A.; Tapia, A.; Theodoro, V. M.; Timmermans, C.; Todero Peixoto, C. J.; Tomankova, L.; Tomé, B.; Torralba Elipe, G.; Torri, M.; Travnicek, P.; Trini, M.; Ulrich, R.; Unger, M.; Urban, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van Aar, G.; van Bodegom, P.; van den Berg, A. M.; van Vliet, A.; Varela, E.; Vargas Cárdenas, B.; Varner, G.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Vergara Quispe, I. D.; Verzi, V.; Vicha, J.; Villaseñor, L.; Vorobiov, S.; Wahlberg, H.; Wainberg, O.; Walz, D.; Watson, A. A.; Weber, M.; Weindl, A.; Wiencke, L.; Wilczyński, H.; Winchen, T.; Wittkowski, D.; Wundheiler, B.; Yang, L.; Yelos, D.; Yushkov, A.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zepeda, A.; Zimmermann, B.; Ziolkowski, M.; Zong, Z.; Zuccarello, F.

2017-06-01

We report a multi-resolution search for anisotropies in the arrival directions of cosmic rays detected at the Pierre Auger Observatory with local zenith angles up to 80o and energies in excess of 4 EeV (4 × 1018 eV). This search is conducted by measuring the angular power spectrum and performing a needlet wavelet analysis in two independent energy ranges. Both analyses are complementary since the angular power spectrum achieves a better performance in identifying large-scale patterns while the needlet wavelet analysis, considering the parameters used in this work, presents a higher efficiency in detecting smaller-scale anisotropies, potentially providing directional information on any observed anisotropies. No deviation from isotropy is observed on any angular scale in the energy range between 4 and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured; while no other deviation from isotropy is observed for moments beyond the dipole one. The corresponding p-values obtained after accounting for searches blindly performed at several angular scales, are 1.3 × 10-5 in the case of the angular power spectrum, and 2.5 × 10-3 in the case of the needlet analysis. While these results are consistent with previous reports making use of the same data set, they provide extensions of the previous works through the thorough scans of the angular scales.

Large-angle correlations in the cosmic microwave background

NASA Astrophysics Data System (ADS)

Efstathiou, George; Ma, Yin-Zhe; Hanson, Duncan

2010-10-01

It has been argued recently by Copi et al. 2009 that the lack of large angular correlations of the CMB temperature field provides strong evidence against the standard, statistically isotropic, inflationary Lambda cold dark matter (ΛCDM) cosmology. We compare various estimators of the temperature correlation function showing how they depend on assumptions of statistical isotropy and how they perform on the Wilkinson Microwave Anisotropy Probe (WMAP) 5-yr Internal Linear Combination (ILC) maps with and without a sky cut. We show that the low multipole harmonics that determine the large-scale features of the temperature correlation function can be reconstructed accurately from the data that lie outside the sky cuts. The reconstructions are only weakly dependent on the assumed statistical properties of the temperature field. The temperature correlation functions computed from these reconstructions are in good agreement with those computed from the ILC map over the whole sky. We conclude that the large-scale angular correlation function for our realization of the sky is well determined. A Bayesian analysis of the large-scale correlations is presented, which shows that the data cannot exclude the standard ΛCDM model. We discuss the differences between our results and those of Copi et al. Either there exists a violation of statistical isotropy as claimed by Copi et al., or these authors have overestimated the significance of the discrepancy because of a posteriori choices of estimator, statistic and sky cut.

Effects of the symmetry axis orientation of a TI overburden on seismic images

NASA Astrophysics Data System (ADS)

Chang, Chih-Hsiung; Chang, Young-Fo; Tseng, Cheng-Wei

2017-07-01

In active tectonic regions, the primary formations are often tilted and subjected to the processes of folding and/or faulting. Dipping formations may be categorised as tilted transverse isotropy (TTI). While carrying out hydrocarbon exploration in areas of orogenic structures, mispositioning and defocusing effects in apparent reflections are often caused by the tilted transverse isotropy of the overburden. In this study, scaled physical modelling was carried out to demonstrate the behaviours of seismic wave propagation and imaging problems incurred by transverse isotropic (TI) overburdens that possess different orientations of the symmetry axis. To facilitate our objectives, zero-offset reflections were acquired from four stratum-fault models to image the same structures that were overlain by a TI (phenolite) slab. The symmetry axis of the TI slab was vertical, tilted or horizontal. In response to the symmetry axis orientations, spatial shifts and asymmetrical diffraction patterns in apparent reflections were observed in the acquired profiles. Given the different orientations of the symmetry axis, numerical manipulations showed that the imaged events could be well described by theoretical ray paths computed by the trial-and-error ray method and Fermat's principle (TERF) method. In addition, outputs of image restoration show that the imaging problems, i.e. spatial shift in the apparent reflections, can be properly handled by the ray-based anisotropic 2D Kirchhoff time migration (RAKTM) method.

A method to calculate synthetic waveforms in stratified VTI media

NASA Astrophysics Data System (ADS)

Wang, W.; Wen, L.

2012-12-01

Transverse isotropy with a vertical axis of symmetry (VTI) may be an important material property in the Earth's interior. In this presentation, we develop a method to calculate synthetic seismograms for wave propagation in stratified VTI media. Our method is based on the generalized reflection and transmission method (GRTM) (Luco & Apsel 1983). We extend it to transversely isotropic VTI media. GRTM has the advantage of remaining stable in high frequency calculations compared to the Haskell Matrix method (Haskell 1964), which explicitly excludes the exponential growth terms in the propagation matrix and is limited to low frequency computation. In the implementation, we also improve GRTM in two aspects. 1) We apply the Shanks transformation (Bender & Orszag 1999) to improve the convergence rate of convergence. This improvement is especially important when the depths of source and receiver are close. 2) We adopt a self-adaptive Simpson integration method (Chen & Zhang 2001) in the discrete wavenumber integration so that the integration can still be efficiently carried out at large epicentral distances. Because the calculation is independent in each frequency, the program can also be effectively implemented in parallel computing. Our method provides a powerful tool to synthesize broadband seismograms of VIT media at a large epicenter distance range. We will present examples of using the method to study possible transverse isotropy in the upper mantle and the lowermost mantle.

Lorentz Invariance:. Present Experimental Status

NASA Astrophysics Data System (ADS)

Lämmerzahl, Claus

2006-02-01

Being one of the pillars of modern physics, Lorentz invariance has to be tested as precisely as possible. We review the present status of laboratory tests of Lorentz invariance. This includes the tests of properties of light propagation which are covered by the famous Michelson-Morley, Kennedy-Thorndike, and Ives-Stilwell experiments, as well as tests on dynamical properties of matter as, e.g., tests exploring the maximum velocity of massive particles or tests of the isotropy of quantum particles in Hughes-Drever experiments.

Testing the Foundations of Relativity Using Cryogenic Optical Resonators

NASA Astrophysics Data System (ADS)

Müller, H.; Braxmaier, C.; Herrmann, S.; Pradl, O.; Lämmerzahl, C.; Mlynek, J.; Schiller, S.; Peters, A.

We present a new generation of experiments using cryogenic optical resonators(COREs) to test the foundations of relativity. The experiments test the isotropy of the speed of light (Michelson-Morley experiment), the independece of the speed of light from the velocity of the laboratory (Kennedy-Thorndike experiments), and the gravitational redshift for clocks based on an electronic transition. Compared with the best previous results, our tests have already yielded improvements up to a factor of three. Future versions promise significant improvements.

Is the great attractor really a great wall

NASA Technical Reports Server (NTRS)

Stebbins, Albert; Turner, Michael S.

1988-01-01

Some of the cosmological consequences are discussed of a late time phase transition which produces light domain walls. The observed peculiar velocity field of the Universe and the observed isotropy of the microwave background radiation severely constrain the wall surface density in such a scenario. The most interesting consequence of such a phase transition is the possibility that the local, coherent streaming motion reported by the Seven Samurai could be explained by the repulsive effect of a relic domain wall with the Hubble volume (the Great Wall).

Matched metal die compression molded structural random fiber sheet molding compound flywheel

DOEpatents

Kulkarni, Satish V.; Christensen, Richard M.; Toland, Richard H.

1985-01-01

A flywheel (10) is described that is useful for energy storage in a hybrid vehicle automotive power system or in some stationary applications. The flywheel (10) has a body of essentially planar isotropic high strength structural random fiber sheet molding compound (SMC-R). The flywheel (10) may be economically produced by a matched metal die compression molding process. The flywheel (10) makes energy intensive efficient use of a fiber/resin composite while having a shape designed by theory assuming planar isotropy.

Matched metal die compression molded structural random fiber sheet molding compound flywheel. [Patent application

DOEpatents

Kulkarni, S.V.; Christensen, R.M.; Toland, R.H.

1980-09-24

A flywheel is described that is useful for energy storage in a hybrid vehicle automotive power system or in some stationary applications. The flywheel has a body of essentially planar isotropic high strength structural random fiber sheet molding compound (SMC-R). The flywheel may be economically produced by a matched metal die compression molding process. The flywheel makes energy intensive efficient use of a fiber/resin composite while having a shape designed by theory assuming planar isotropy.

How does tissue preparation affect skeletal muscle transverse isotropy?

PubMed Central

Wheatley, Benjamin B.; Odegard, Gregory M.; Kaufman, Kenton R.; Haut Donahue, Tammy L.

2016-01-01

The passive tensile properties of skeletal muscle play a key role in its physiological function. Previous research has identified conflicting reports of muscle transverse isotropy, with some data suggesting the longitudinal direction is stiffest, while others show the transverse direction is stiffest. Accurate constitutive models of skeletal muscle must be employed to provide correct recommendations for and observations of clinical methods. The goal of this work was to identify transversely isotropic tensile muscle properties as a function of post mortem handling. Six pairs of tibialis anterior muscles were harvested from Giant Flemish rabbits and split into two groups: fresh testing (within four hours post mortem), and non-fresh testing (subject to delayed testing and a freeze/thaw cycle). Longitudinal and transverse samples were removed from each muscle and tested to identify tensile modulus and relaxation behavior. Longitudinal non-fresh samples exhibited a higher initial modulus value and faster relaxation than longitudinal fresh, transverse fresh, and transverse rigor samples (p<0.05), while longitudinal fresh samples were less stiff at lower strain levels than longitudinal non-fresh, transverse fresh, and transverse non-fresh samples (p<0.05), but exhibited more nonlinear behavior. While fresh skeletal muscle exhibits a higher transverse modulus than longitudinal modulus, discrepancies in previously published data may be the result of a number of differences in experimental protocol. Constitutive modeling of fresh muscle should reflect these data by identifying the material as truly transversely isotropic and not as an isotropic matrix reinforced with fibers. PMID:27425557

Bounds on strong field magneto-transport in three-dimensional composites

NASA Astrophysics Data System (ADS)

Briane, Marc; Milton, Graeme W.

2011-10-01

This paper deals with bounds satisfied by the effective non-symmetric conductivity of three-dimensional composites in the presence of a strong magnetic field. On the one hand, it is shown that for general composites the antisymmetric part of the effective conductivity cannot be bounded solely in terms of the antisymmetric part of the local conductivity, contrary to the columnar case studied by Briane and Milton [SIAM J. Appl. Math. 70(8), 3272-3286 (2010), 10.1137/100798090]. Thus a suitable rank-two laminate, the conductivity of which has a bounded antisymmetric part together with a high-contrast symmetric part, may generate an arbitrarily large antisymmetric part of the effective conductivity. On the other hand, bounds are provided which show that the antisymmetric part of the effective conductivity must go to zero if the upper bound on the antisymmetric part of the local conductivity goes to zero, and the symmetric part of the local conductivity remains bounded below and above. Elementary bounds on the effective moduli are derived assuming the local conductivity and the effective conductivity have transverse isotropy in the plane orthogonal to the magnetic field. New Hashin-Shtrikman type bounds for two-phase three-dimensional composites with a non-symmetric conductivity are provided under geometric isotropy of the microstructure. The derivation of the bounds is based on a particular variational principle symmetrizing the problem, and the use of Y-tensors involving the averages of the fields in each phase.

Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory

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

Aab, A.; Abreu, P.; Andringa, S.

2017-06-01

We report a multi-resolution search for anisotropies in the arrival directions of cosmic rays detected at the Pierre Auger Observatory with local zenith angles up to 80{sup o} and energies in excess of 4 EeV (4 × 10{sup 18} eV). This search is conducted by measuring the angular power spectrum and performing a needlet wavelet analysis in two independent energy ranges. Both analyses are complementary since the angular power spectrum achieves a better performance in identifying large-scale patterns while the needlet wavelet analysis, considering the parameters used in this work, presents a higher efficiency in detecting smaller-scale anisotropies, potentially providingmore » directional information on any observed anisotropies. No deviation from isotropy is observed on any angular scale in the energy range between 4 and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured; while no other deviation from isotropy is observed for moments beyond the dipole one. The corresponding p -values obtained after accounting for searches blindly performed at several angular scales, are 1.3 × 10{sup −5} in the case of the angular power spectrum, and 2.5 × 10{sup −3} in the case of the needlet analysis. While these results are consistent with previous reports making use of the same data set, they provide extensions of the previous works through the thorough scans of the angular scales.« less

Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory

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

Aab, A.; Abreu, P.; Aglietta, M.

We report a multi-resolution search for anisotropies in the arrival directions of cosmic rays detected at the Pierre Auger Observatory with local zenith angles up to 80(o) and energies in excess of 4 EeV (4 × 10 18 eV). This search is conducted by measuring the angular power spectrum and performing a needlet wavelet analysis in two independent energy ranges. Both analyses are complementary since the angular power spectrum achieves a better performance in identifying large-scale patterns while the needlet wavelet analysis, considering the parameters used in this work, presents a higher efficiency in detecting smaller-scale anisotropies, potentially providing directional information onmore » any observed anisotropies. No deviation from isotropy is observed on any angular scale in the energy range between 4 and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured, while no other deviation from isotropy is observed for moments beyond the dipole one. The corresponding p-values obtained after accounting for searches blindly performed at several angular scales, are 1.3 × 10 -5 in the case of the angular power spectrum, and 2.5 × 10 -3 in the case of the needlet analysis. While these results are consistent with previous reports making use of the same data set, they provide extensions of the previous works through the thorough scans of the angular scales.« less

A critical comparison of second order closures with direct numerical simulation of homogeneous turbulence

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Lumley, John L.

1991-01-01

Recently, several second order closure models have been proposed for closing the second moment equations, in which the velocity-pressure gradient (and scalar-pressure gradient) tensor and the dissipation rate tensor are two of the most important terms. In the literature, these correlation tensors are usually decomposed into a so called rapid term and a return-to-isotropy term. Models of these terms have been used in global flow calculations together with other modeled terms. However, their individual behavior in different flows have not been fully examined because they are un-measurable in the laboratory. Recently, the development of direct numerical simulation (DNS) of turbulence has given us the opportunity to do this kind of study. With the direct numerical simulation, we may use the solution to exactly calculate the values of these correlation terms and then directly compare them with the values from their modeled formulations (models). Here, we make direct comparisons of five representative rapid models and eight return-to-isotropy models using the DNS data of forty five homogeneous flows which were done by Rogers et al. (1986) and Lee et al. (1985). The purpose of these direct comparisons is to explore the performance of these models in different flows and identify the ones which give the best performance. The modeling procedure, model constraints, and the various evaluated models are described. The detailed results of the direct comparisons are discussed, and a few concluding remarks on turbulence models are given.

Field characterization of elastic properties across a fault zone reactivated by fluid injection

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

Jeanne, Pierre; Guglielmi, Yves; Rutqvist, Jonny

In this paper, we studied the elastic properties of a fault zone intersecting the Opalinus Clay formation at 300 m depth in the Mont Terri Underground Research Laboratory (Switzerland). Four controlled water injection experiments were performed in borehole straddle intervals set at successive locations across the fault zone. A three-component displacement sensor, which allowed capturing the borehole wall movements during injection, was used to estimate the elastic properties of representative locations across the fault zone, from the host rock to the damage zone to the fault core. Young's moduli were estimated by both an analytical approach and numerical finite differencemore » modeling. Results show a decrease in Young's modulus from the host rock to the damage zone by a factor of 5 and from the damage zone to the fault core by a factor of 2. In the host rock, our results are in reasonable agreement with laboratory data showing a strong elastic anisotropy characterized by the direction of the plane of isotropy parallel to the laminar structure of the shale formation. In the fault zone, strong rotations of the direction of anisotropy can be observed. Finally, the plane of isotropy can be oriented either parallel to bedding (when few discontinuities are present), parallel to the direction of the main fracture family intersecting the zone, and possibly oriented parallel or perpendicular to the fractures critically oriented for shear reactivation (when repeated past rupture along this plane has created a zone).« less

Renormalization group methods for the Reynolds stress transport equations

NASA Technical Reports Server (NTRS)

Rubinstein, R.

1992-01-01

The Yakhot-Orszag renormalization group is used to analyze the pressure gradient-velocity correlation and return to isotropy terms in the Reynolds stress transport equations. The perturbation series for the relevant correlations, evaluated to lowest order in the epsilon-expansion of the Yakhot-Orszag theory, are infinite series in tensor product powers of the mean velocity gradient and its transpose. Formal lowest order Pade approximations to the sums of these series produce a rapid pressure strain model of the form proposed by Launder, Reece, and Rodi, and a return to isotropy model of the form proposed by Rotta. In both cases, the model constants are computed theoretically. The predicted Reynolds stress ratios in simple shear flows are evaluated and compared with experimental data. The possibility is discussed of deriving higher order nonlinear models by approximating the sums more accurately. The Yakhot-Orszag renormalization group provides a systematic procedure for deriving turbulence models. Typical applications have included theoretical derivation of the universal constants of isotropic turbulence theory, such as the Kolmogorov constant, and derivation of two equation models, again with theoretically computed constants and low Reynolds number forms of the equations. Recent work has applied this formalism to Reynolds stress modeling, previously in the form of a nonlinear eddy viscosity representation of the Reynolds stresses, which can be used to model the simplest normal stress effects. The present work attempts to apply the Yakhot-Orszag formalism to Reynolds stress transport modeling.

Approaching isotropy in the vortex system of SmFeAs(O,F) at extreme magnetic fields

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

Moll, Philip J.W.; Zhidadlo, Nikolai D.; Karpinski, J.

2014-01-07

The role of anisotropy in the iron-pnictides is one of the key questions in understanding their high-temperature superconductivity. The inherent layeredness of these systems, consisting of FeAs layers separated by various layers, gives rise to an upper critical field anisotropy γ(T c) ~ 3 in the “122” system (i.e. (Ba,K)Fe 2As 2) and up to 6-8 in the “1111” system (i.e. SmFeAs(O,F)). In the “122” compounds, this anisotropy is known to decrease upon cooling, converging to almost isotropic superconductivity at lowest temperatures[1]. This can be understood through a particular temperature dependence of the inter- and intra-band scattering. The “1111” classmore » is naturally more anisotropic due to the thicker SmO blocking layer, and the much higher upper critical fields (H c2, HIIab(0)>>100T) cannot be reached at low temperature. Despite this challenging field requirement, the aim of this project is to discern whether this emergent isotropy in the “122” materials is a property of all FeAs classes. Focused Ion Beam (FIB) micromachined samples have in the past proven to be particularly well suited for pulsed magnetic fields[2]. Employing the micrometer precision of the FIB, we fabricated three individual samples on a 2x2 mm chip and thus maximized the acquired transport data per pulse.« less

Field characterization of elastic properties across a fault zone reactivated by fluid injection

DOE PAGES

Jeanne, Pierre; Guglielmi, Yves; Rutqvist, Jonny; ...

2017-08-12

In this paper, we studied the elastic properties of a fault zone intersecting the Opalinus Clay formation at 300 m depth in the Mont Terri Underground Research Laboratory (Switzerland). Four controlled water injection experiments were performed in borehole straddle intervals set at successive locations across the fault zone. A three-component displacement sensor, which allowed capturing the borehole wall movements during injection, was used to estimate the elastic properties of representative locations across the fault zone, from the host rock to the damage zone to the fault core. Young's moduli were estimated by both an analytical approach and numerical finite differencemore » modeling. Results show a decrease in Young's modulus from the host rock to the damage zone by a factor of 5 and from the damage zone to the fault core by a factor of 2. In the host rock, our results are in reasonable agreement with laboratory data showing a strong elastic anisotropy characterized by the direction of the plane of isotropy parallel to the laminar structure of the shale formation. In the fault zone, strong rotations of the direction of anisotropy can be observed. Finally, the plane of isotropy can be oriented either parallel to bedding (when few discontinuities are present), parallel to the direction of the main fracture family intersecting the zone, and possibly oriented parallel or perpendicular to the fractures critically oriented for shear reactivation (when repeated past rupture along this plane has created a zone).« less

Anisotropy of electromagnetically induced left-handedness in atomic three-level media based upon bianisotropic polarizabilities and tensor character

NASA Astrophysics Data System (ADS)

Krowne, Clifford M.

2008-05-01

A three-level atomic system, configured as either a gaseous medium or a solid state material, with a driving field establishing a Rabi frequency of control, is tested by a probe field. The medium has bianisotropic microscopic polarizability and magnetizability, from which the permittivity and permeability tensors are derived. Non-isotropy and polarization dependence for left-handedness (negative index of refraction) is demonstrated through examination of tensor components in the detuning frequency spectrum. These results have important implications for use in optical or electronic devices.

Investigation of 2-Dimensional Isotropy of Under-Ice Roughness in the Beaufort Gyre and Implications for Mixed Layer Ocean Turbulence

DTIC Science & Technology

2008-03-01

this roughness is important for numerical modeling and prediction of the Arctic air-ice-ocean system, which will play a significant role as the US Navy...is important for numerical modeling and prediction of the Arctic air-ice-ocean system, which will play a significant role as the US Navy increases... Model 1 is based on a sequence of plane parallel layers each with a constant gradient whereas Model 2 is based on a series of flat layers of

On the distinction between large deformation and large distortion for anisotropic materials

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

BRANNON,REBECCA M.

2000-02-24

A motion involves large distortion if the ratios of principal stretches differ significantly from unity. A motion involves large deformation if the deformation gradient tensor is significantly different from the identity. Unfortunately, rigid rotation fits the definition of large deformation, and models that claim to be valid for large deformation are often inadequate for large distortion. An exact solution for the stress in an idealized fiber-reinforced composite is used to show that conventional large deformation representations for transverse isotropy give errant results. Possible alternative approaches are discussed.

Pump Spectral Bandwidth, Birefringence, and Entanglement in Type-II Parametric Down Conversion

DOE PAGES

Erenso, Daniel

2009-01-01

The twin photons produced by a type-II spontaneous parametric down conversion are well know as a potential source of photons for quantum teleportation due to the strong entanglement in polarization. This strong entanglement in polarization, however, depends on the spectral composition of the pump photon and the nature of optical isotropy of the crystal. By exact numerical calculation of the concurrence, we have shown that how pump photons spectral width and the birefringence nature of the crystal directly affect the degree of polarization entanglement of the twin photons.

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

Zentgraf, Florian; Baum, Elias; Dreizler, Andreas

Planar particle image velocimetry (PIV) and tomographic PIV (TPIV) measurements are utilized to analyze turbulent statistical theory quantities and the instantaneous turbulence within a single-cylinder optical engine. Measurements are performed during the intake and mid-compression stroke at 800 and 1500 RPM. TPIV facilitates the evaluation of spatially resolved Reynolds stress tensor (RST) distributions, anisotropic Reynolds stress invariants, and instantaneous turbulent vortical structures. The RST analysis describes distributions of individual velocity fluctuation components that arise from unsteady turbulent flow behavior as well as cycle-to-cycle variability (CCV). A conditional analysis, for which instantaneous PIV images are sampled by their tumble center location,more » reveals that CCV and turbulence have similar contributions to RST distributions at the mean tumble center, but turbulence is dominant in regions peripheral to the tumble center. Analysis of the anisotropic Reynolds stress invariants reveals the spatial distribution of axisymmetric expansion, axisymmetric contraction, and 3D isotropy within the cylinder. Findings indicate that the mid-compression flow exhibits a higher tendency toward 3D isotropy than the intake flow. A novel post-processing algorithm is utilized to classify the geometry of instantaneous turbulent vortical structures and evaluate their frequency of occurrence within the cylinder. Findings are coupled with statistical theory quantities to provide a comprehensive understanding of the distribution of turbulent velocity components, the distribution of anisotropic states of turbulence, and compare the turbulent vortical flow distribution that is theoretically expected to what is experimentally observed. The analyses reveal requisites of important turbulent flow quantities and discern their sensitivity to the local flow topography and engine operation.« less

Matrix exponential-based closures for the turbulent subgrid-scale stress tensor.

PubMed

Li, Yi; Chevillard, Laurent; Eyink, Gregory; Meneveau, Charles

2009-01-01

Two approaches for closing the turbulence subgrid-scale stress tensor in terms of matrix exponentials are introduced and compared. The first approach is based on a formal solution of the stress transport equation in which the production terms can be integrated exactly in terms of matrix exponentials. This formal solution of the subgrid-scale stress transport equation is shown to be useful to explore special cases, such as the response to constant velocity gradient, but neglecting pressure-strain correlations and diffusion effects. The second approach is based on an Eulerian-Lagrangian change of variables, combined with the assumption of isotropy for the conditionally averaged Lagrangian velocity gradient tensor and with the recent fluid deformation approximation. It is shown that both approaches lead to the same basic closure in which the stress tensor is expressed as the matrix exponential of the resolved velocity gradient tensor multiplied by its transpose. Short-time expansions of the matrix exponentials are shown to provide an eddy-viscosity term and particular quadratic terms, and thus allow a reinterpretation of traditional eddy-viscosity and nonlinear stress closures. The basic feasibility of the matrix-exponential closure is illustrated by implementing it successfully in large eddy simulation of forced isotropic turbulence. The matrix-exponential closure employs the drastic approximation of entirely omitting the pressure-strain correlation and other nonlinear scrambling terms. But unlike eddy-viscosity closures, the matrix exponential approach provides a simple and local closure that can be derived directly from the stress transport equation with the production term, and using physically motivated assumptions about Lagrangian decorrelation and upstream isotropy.

Minkowski Tensors in Two Dimensions: Probing the Morphology and Isotropy of the Matter and Galaxy Density Fields

NASA Astrophysics Data System (ADS)

Appleby, Stephen; Chingangbam, Pravabati; Park, Changbom; Hong, Sungwook E.; Kim, Juhan; Ganesan, Vidhya

2018-05-01

We apply the Minkowski tensor statistics to two-dimensional slices of the three-dimensional matter density field. The Minkowski tensors are a set of functions that are sensitive to directionally dependent signals in the data and, furthermore, can be used to quantify the mean shape of density fields. We begin by reviewing the definition of Minkowski tensors and introducing a method of calculating them from a discretely sampled field. Focusing on the statistic {W}21,1—a 2 × 2 matrix—we calculate its value for both the entire excursion set and individual connected regions and holes within the set. To study the morphology of structures within the excursion set, we calculate the eigenvalues λ 1, λ 2 for the matrix {W}21,1 of each distinct connected region and hole and measure their mean shape using the ratio β \\equiv < {λ }2/{λ }1> . We compare both {W}21,1 and β for a Gaussian field and a smoothed density field generated from the latest Horizon Run 4 cosmological simulation to study the effect of gravitational collapse on these functions. The global statistic {W}21,1 is essentially independent of gravitational collapse, as the process maintains statistical isotropy. However, β is modified significantly, with overdensities becoming relatively more circular compared to underdensities at low redshifts. When applying the statistics to a redshift-space distorted density field, the matrix {W}21,1 is no longer proportional to the identity matrix, and measurements of its diagonal elements can be used to probe the large-scale velocity field.

Hypersurface Homogeneous Cosmological Model in Modified Theory of Gravitation

NASA Astrophysics Data System (ADS)

Katore, S. D.; Hatkar, S. P.; Baxi, R. J.

2016-12-01

We study a hypersurface homogeneous space-time in the framework of the f (R, T) theory of gravitation in the presence of a perfect fluid. Exact solutions of field equations are obtained for exponential and power law volumetric expansions. We also solve the field equations by assuming the proportionality relation between the shear scalar (σ ) and the expansion scalar (θ ). It is observed that in the exponential model, the universe approaches isotropy at large time (late universe). The investigated model is notably accelerating and expanding. The physical and geometrical properties of the investigated model are also discussed.

Thermal imitators with single directional invisibility

NASA Astrophysics Data System (ADS)

Wang, Ruizhe; Xu, Liujun; Huang, Jiping

2017-12-01

Thermal metamaterials have been intensively studied during the past years to achieve the long-standing dream of invisibility, illusion, and other inconceivable thermal phenomena. However, many thermal metamaterials can only exhibit omnidirectional thermal response, which take on the distinct feature of geometrical isotropy. In this work, we theoretically design and experimentally fabricate a pair of thermal imitators by applying geometrical anisotropy provided by elliptical/ellipsoidal particles and layered structures. This pair of thermal imitators possesses thermal invisibility in one direction, while having thermal opacity in other directions. This work may open a gate in designing direction-dependent thermal metamaterials.

Isotropic quantum walks on lattices and the Weyl equation

NASA Astrophysics Data System (ADS)

D'Ariano, Giacomo Mauro; Erba, Marco; Perinotti, Paolo

2017-12-01

We present a thorough classification of the isotropic quantum walks on lattices of dimension d =1 ,2 ,3 with a coin system of dimension s =2 . For d =3 there exist two isotropic walks, namely, the Weyl quantum walks presented in the work of D'Ariano and Perinotti [G. M. D'Ariano and P. Perinotti, Phys. Rev. A 90, 062106 (2014), 10.1103/PhysRevA.90.062106], resulting in the derivation of the Weyl equation from informational principles. The present analysis, via a crucial use of isotropy, is significantly shorter and avoids a superfluous technical assumption, making the result completely general.

Homogenous isotropic invisible cloak based on geometrical optics.

PubMed

Sun, Jingbo; Zhou, Ji; Kang, Lei

2008-10-27

Invisible cloak derived from the coordinate transformation requires its constitutive material to be anisotropic. In this work, we present a cloak of graded-index isotropic material based on the geometrical optics theory. The cloak is realized by concentric multilayered structure with designed refractive index to achieve the low-scattering and smooth power-flow. Full-wave simulations on such a design of a cylindrical cloak are performed to demonstrate the cloaking ability to incident wave of any polarization. Using normal nature material with isotropy and low absorption, the cloak shows light on a practical path to stealth technology, especially that in the optical range.

Statistical turbulence theory and turbulence phenomenology

NASA Technical Reports Server (NTRS)

Herring, J. R.

1973-01-01

The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion about randomness. Two concepts are involved: (1) a modeling of the turbulence as nearly multipoint Gaussian, and (2) a simultaneous introduction of a generalized eddy viscosity operator.

Is QSO 1146 + 111B,C due to lensing by a cosmic string?

NASA Technical Reports Server (NTRS)

Gott, J. R., III

1986-01-01

A newly discovered lens candidate, QSO 1146 + 111B,C, is discussed which appears to consist of two images of equal brightness of a quasar at redshift 1.01 separated by 2.6 arcmin. If this is produced by a cosmic string, its mass per unit length is about 4.0 x 10 to the 23rd g/cm or more. This value is large enough to be interesting for string-assisted galaxy formation and near the upper limits implied by the isotropy of the cosmic microwave background and constraints on gravitational radiation.

Syntactic Metals: A Survey of Current Technology

NASA Technical Reports Server (NTRS)

Erikson, Ray

2003-01-01

Syntactic metals are a relatively new development in materials science. Several approaches to synthesizing these materials have been tried, and the handful of researchers in this field are beginning to make progress in defining useful compositions and processes. Syntactic metals can provide materials with dramatically improved specific strength and stiffness over their parent alloys, while retaining the isotropy that makes ordinary metals preferable to fiber-reinforced laminated composites in many applications. This paper reviews syntactic material concepts in general, the current state of the art (including the author's own work in syntactic aluminum), and the direction of future developments.

Laboratory Approach to the Study of Elastic Anisotropy on Rock Samples

NASA Astrophysics Data System (ADS)

Pros, Z.; Lokajíček, T.; Klíma, K.

The experimental approach (hardware and software) to the study of the elastic an isotropy of rocks on spherical samples under hydrostatic pressure up to 400 MPa is discussed. A substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media. The innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude. Several options and results obtained with the innovated laboratory equipment are presented.

Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients. [for cosmic ray propagation in interstellar and interplanetary space

NASA Technical Reports Server (NTRS)

Goldstein, M. L.

1977-01-01

In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.

Clock synchronization by accelerated observers - Metric construction for arbitrary congruences of world lines

NASA Technical Reports Server (NTRS)

Henriksen, R. N.; Nelson, L. A.

1985-01-01

Clock synchronization in an arbitrarily accelerated observer congruence is considered. A general solution is obtained that maintains the isotropy and coordinate independence of the one-way speed of light. Attention is also given to various particular cases including, rotating disk congruence or ring congruence. An explicit, congruence-based spacetime metric is constructed according to Einstein's clock synchronization procedure and the equation for the geodesics of the space-time was derived using Hamilton-Jacobi method. The application of interferometric techniques (absolute phase radio interferometry, VLBI) to the detection of the 'global Sagnac effect' is also discussed.

Global universe anisotropy probed by the alignment of structures in the cosmic microwave background.

PubMed

Wiaux, Y; Vielva, P; Martínez-González, E; Vandergheynst, P

2006-04-21

We question the global universe isotropy by probing the alignment of local structures in the cosmic microwave background (CMB) radiation. The original method proposed relies on a steerable wavelet decomposition of the CMB signal on the sphere. The analysis of the first-year Wilkinson Microwave Anisotropy Probe data identifies a mean preferred plane with a normal direction close to the CMB dipole axis, and a mean preferred direction in this plane, very close to the ecliptic poles axis. Previous statistical anisotropy results are thereby synthesized, but further analyses are still required to establish their origin.

Turbulence feature modifications from high to low wind conditions: results from the CCT observations at Ny-Ålesund, Svalbard.

NASA Astrophysics Data System (ADS)

Schiavon, Mario; Mazzola, Mauro; Tampieri, Francesco; Pietro Viola, Angelo; Choi, Taejin

2017-04-01

The turbulence features in the quasi neutral surface layer are investigated as the intensity of the wind decreases, i.e. as the forcing due to the shear decreases. In this aim, a 5-year (2012-2016) set of observations of meteorological and micro-meteorological parameters acquired on the Climate Change Tower (CCT) in Ny-Ålesund, Svalbard Islands, is used. The 34-m high tower, operated by the Italian National Council of Research (CNR) is equipped with four slow response wind and temperature probes and three fast response sonic anemometers and is located on heterogeneous terrain. One of the fast sensors was installed by KOPRI since 2012. The observations are averaged over 10 and 30 minutes intervals. The analysis addresses the share of the mean turbulent kinetic energy (TKE) among the along-wind, cross-wind and vertical velocity variances (respectively < u2 >, < v2 >, < w2 >), with attention to the parameterizations of the boundary layer commonly used in NWP models: the classical Mellor-Yamada (1982) scheme with the return-to-isotropy term by Rotta(1951) and its modifications, and the recent approach by Zilitinkevich and coworkers (2013). The results show that the share of TKE among the vertical < w2 > and the total horizontal variance < u2 > + < v2 > is weakly dependent on the wind velocity while the share of the total horizontal variance between the along-wind and cross-wind components depends on wind speed. At high velocity (and large wind shear) a clear anisotropy , with < u2 >≈ 2 < v2 >, is observed, quite consistent with literature (Tampieri, 2017, pag. 69). As the velocity decreases, the ratio < u2 > /(< u2 > + < v2 >) displays a wide flat distribution between 0.2 and 0.8 with median values corresponding approximately to horizontal isotropy: < u2 >≈< v2 >. These features can be parameterized using suitable coefficients, function of the wind intensity in the equations for the TKE share, capturing the average behaviour of the flow. A further investigation based on estimates of the relative importance of the high frequency and low frequency spectral distribution of TKE suggests that the presence of slow motions (like meandering) affects the tendency to isotropy; in absence of such effects, the horizontal turbulence is anisotropic both in high and in relatively low wind conditions. Some comparison with the results from other data sets is outlined, to give a preliminary answer to the possible generalization of such features. Mellor, Yamada. Rev. G. Space Phys. 20, 851 (1982) Rotta. Z. Phys. 129, 547 (1951) Tampieri. Turbulence and Dispersion in the PBL. Springer (2017) Zilitinkevich et al. Bound.-Layer Meteorol. 146, 341 (2013)

Planck 2015 results. XVI. Isotropy and statistics of the CMB

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Akrami, Y.; Aluri, P. K.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Casaponsa, B.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Contreras, D.; Couchot, F.; Coulais, A.; Crill, B. P.; Cruz, M.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Fantaye, Y.; Fergusson, J.; Fernandez-Cobos, R.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Frolov, A.; Galeotta, S.; Galli, S.; Ganga, K.; Gauthier, C.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huang, Z.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kim, J.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; Liu, H.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marinucci, D.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mikkelsen, K.; Mitra, S.; Miville-Deschênes, M.-A.; Molinari, D.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Pant, N.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Rotti, A.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Souradeep, T.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Trombetti, T.; Tucci, M.; Tuovinen, J.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Yvon, D.; Zacchei, A.; Zibin, J. P.; Zonca, A.

2016-09-01

We test the statistical isotropy and Gaussianity of the cosmic microwave background (CMB) anisotropies using observations made by the Planck satellite. Our results are based mainly on the full Planck mission for temperature, but also include some polarization measurements. In particular, we consider the CMB anisotropy maps derived from the multi-frequency Planck data by several component-separation methods. For the temperature anisotropies, we find excellent agreement between results based on these sky maps over both a very large fraction of the sky and a broad range of angular scales, establishing that potential foreground residuals do not affect our studies. Tests of skewness, kurtosis, multi-normality, N-point functions, and Minkowski functionals indicate consistency with Gaussianity, while a power deficit at large angular scales is manifested in several ways, for example low map variance. The results of a peak statistics analysis are consistent with the expectations of a Gaussian random field. The "Cold Spot" is detected with several methods, including map kurtosis, peak statistics, and mean temperature profile. We thoroughly probe the large-scale dipolar power asymmetry, detecting it with several independent tests, and address the subject of a posteriori correction. Tests of directionality suggest the presence of angular clustering from large to small scales, but at a significance that is dependent on the details of the approach. We perform the first examination of polarization data, finding the morphology of stacked peaks to be consistent with the expectations of statistically isotropic simulations. Where they overlap, these results are consistent with the Planck 2013 analysis based on the nominal mission data and provide our most thorough view of the statistics of the CMB fluctuations to date.

Structural and elastic properties of La{sub 2}Mg{sub 17} from first-principles calculations

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

Luo, Tao-Peng; Ma, Li; Pan, Rong-Kai

2013-10-15

Structural and elastic properties of La{sub 2}Mg{sub 17} with layer structure have been investigated within framework of the density functional theory. Different from the general layer-structured materials, the obtained c/a is less than unity. The calculated elastic constants C{sub 33} is larger than C{sub 11}, being novel in comparison with other alloys with layer structure. The calculated bulk, shear and Young’s modulus of La{sub 2}Mg{sub 17} are higher than other Mg–La alloys with higher La content, implying the stronger covalent bonding. Moreover, the elastic isotropies of La{sub 2}Mg{sub 17} are more excellent. The electronic structure within basal plane is highlymore » symmetric, and the electronic interaction within basal plane is slightly weaker than one between basal planes, which reveal the underlying mechanism for the structural and elastic properties of La{sub 2}Mg{sub 17}. - Graphical abstract: The crystal structure (a) and the atomic positions for (b) (0 0 0 2), (c) (0 0 0 4) and (d) (1 2{sup ¯} 1 0) plane of La{sub 2}Mg{sub 17}. Display Omitted - Highlights: • The c/a of La{sub 2}Mg{sub 17} is anomalously less than unity. • It is novel that for La{sub 2}Mg{sub 17} the elastic constants C{sub 33} is larger than C{sub 11}. • The elastic modulus of La{sub 2}Mg{sub 17} is higher than other Mg–La alloys. • The elastic isotropy of La{sub 2}Mg{sub 17} is excellent. • The electronic structure within basal plane is highly symmetric.« less

Anisotropy in the Australasian upper mantle from Love and Rayleigh waveform inversion

NASA Astrophysics Data System (ADS)

Debayle, Eric; Kennett, B. L. N.

2000-12-01

Records of both Rayleigh and Love waves have been analyzed to determine the pattern of anisotropy in the Australasian region. The approach is based on a two-stage inversion. Starting from a smooth PREM model with transverse isotropy about a vertical symmetry axis, the first step is an inversion of the waveforms of surface waves to produce path specific one-dimensional (1-D) upper mantle models. Under the assumption that the 1-D models represent averages along the paths, the results from 1584 Love and Rayleigh wave seismograms are combined in a tomographic inversion to provide a representation of three-dimensional structure for wavespeed heterogeneities and anisotropy. Polarization anisotropy with SH faster than SV is retrieved in the upper 200-250 km of the mantle for most of Precambrian Australia. In this depth interval, significant lateral variations in the level of polarization anisotropy are present. Locally, the anisotropy can be large, reaching an extreme value of 9% that is difficult to reconcile with current mineralogical models. However, the discrepancy may be explained in part by the presence of strong lateral heterogeneities along the path, or by effects introduced by the simplifying assumption of transverse isotropy for each path. The consistency between the location of polarization and azimuthal anisotropy in depth suggests that both observations share a common origin. The observation of polarization anisotropy down to at least 200 km supports a two-layered anisotropic model as constrained by the azimuthal anisotropy of SV waves. In the upper layer, 150 km thick, anisotropy would be related to past deformation frozen in the lithosphere while in the lower layer, anisotropy would reflect present day deformation due to plate motion.

Measurements of mechanical anisotropy in brain tissue and implications for transversely isotropic material models of white matter

PubMed Central

Feng, Yuan; Okamoto, Ruth J.; Namani, Ravi; Genin, Guy M.; Bayly, Philip V.

2013-01-01

White matter in the brain is structurally anisotropic, consisting largely of bundles of aligned, myelin-sheathed axonal fibers. White matter is believed to be mechanically anisotropic as well. Specifically, transverse isotropy is expected locally, with the plane of isotropy normal to the local mean fiber direction. Suitable material models involve strain energy density functions that depend on the I4 and I5 pseudo-invariants of the Cauchy–Green strain tensor to account for the effects of relatively stiff fibers. The pseudo-invariant I4 is the square of the stretch ratio in the fiber direction; I5 contains contributions of shear strain in planes parallel to the fiber axis. Most, if not all, published models of white matter depend on I4 but not on I5. Here, we explore the small strain limits of these models in the context of experimental measurements that probe these dependencies. Models in which strain energy depends on I4 but not I5 can capture differences in Young’s (tensile) moduli, but will not exhibit differences in shear moduli for loading parallel and normal to the mean direction of axons. We show experimentally, using a combination of shear and asymmetric indentation tests, that white matter does exhibit such differences in both tensile and shear moduli. Indentation tests were interpreted through inverse fitting of finite element models in the limit of small strains. Results highlight that: (1) hyperelastic models of transversely isotropic tissues such as white matter should include contributions of both the I4 and I5 strain pseudo-invariants; and (2) behavior in the small strain regime can usefully guide the choice and initial parameterization of more general material models of white matter. PMID:23680651

Elastic Characterization of Transversely Isotropic Soft Materials by Dynamic Shear and Asymmetric Indentation

PubMed Central

Namani, R.; Feng, Y.; Okamoto, R. J.; Jesuraj, N.; Sakiyama-Elbert, S. E.; Genin, G. M.; Bayly, P. V.

2012-01-01

The mechanical characterization of soft anisotropic materials is a fundamental challenge because of difficulties in applying mechanical loads to soft matter and the need to combine information from multiple tests. A method to characterize the linear elastic properties of transversely isotropic soft materials is proposed, based on the combination of dynamic shear testing (DST) and asymmetric indentation. The procedure was demonstrated by characterizing a nearly incompressible transversely isotropic soft material. A soft gel with controlled anisotropy was obtained by polymerizing a mixture of fibrinogen and thrombin solutions in a high field magnet (B = 11.7 T); fibrils in the resulting gel were predominantly aligned parallel to the magnetic field. Aligned fibrin gels were subject to dynamic (20–40 Hz) shear deformation in two orthogonal directions. The shear storage modulus was 1.08 ± 0. 42 kPa (mean ± std. dev.) for shear in a plane parallel to the dominant fiber direction, and 0.58 ± 0.21 kPa for shear in the plane of isotropy. Gels were indented by a rectangular tip of a large aspect ratio, aligned either parallel or perpendicular to the normal to the plane of transverse isotropy. Aligned fibrin gels appeared stiffer when indented with the long axis of a rectangular tip perpendicular to the dominant fiber direction. Three-dimensional numerical simulations of asymmetric indentation were used to determine the relationship between direction-dependent differences in indentation stiffness and material parameters. This approach enables the estimation of a complete set of parameters for an incompressible, transversely isotropic, linear elastic material. PMID:22757501

Planck 2015 results: XVI. Isotropy and statistics of the CMB

DOE PAGES

Ade, P. A. R.; Aghanim, N.; Akrami, Y.; ...

2016-09-20

In this paper, we test the statistical isotropy and Gaussianity of the cosmic microwave background (CMB) anisotropies using observations made by the Planck satellite. Our results are based mainly on the full Planck mission for temperature, but also include some polarization measurements. In particular, we consider the CMB anisotropy maps derived from the multi-frequency Planck data by several component-separation methods. For the temperature anisotropies, we find excellent agreement between results based on these sky maps over both a very large fraction of the sky and a broad range of angular scales, establishing that potential foreground residuals do not affect ourmore » studies. Tests of skewness, kurtosis, multi-normality, N-point functions, and Minkowski functionals indicate consistency with Gaussianity, while a power deficit at large angular scales is manifested in several ways, for example low map variance. The results of a peak statistics analysis are consistent with the expectations of a Gaussian random field. The “Cold Spot” is detected with several methods, including map kurtosis, peak statistics, and mean temperature profile. We thoroughly probe the large-scale dipolar power asymmetry, detecting it with several independent tests, and address the subject of a posteriori correction. Tests of directionality suggest the presence of angular clustering from large to small scales, but at a significance that is dependent on the details of the approach. We perform the first examination of polarization data, finding the morphology of stacked peaks to be consistent with the expectations of statistically isotropic simulations. Finally, where they overlap, these results are consistent with the Planck 2013 analysis based on the nominal mission data and provide our most thorough view of the statistics of the CMB fluctuations to date.« less

Finite difference modelling of dipole acoustic logs in a poroelastic formation with anisotropic permeability

NASA Astrophysics Data System (ADS)

He, Xiao; Hu, Hengshan; Wang, Xiuming

2013-01-01

Sedimentary rocks can exhibit strong permeability anisotropy due to layering, pre-stresses and the presence of aligned microcracks or fractures. In this paper, we develop a modified cylindrical finite-difference algorithm to simulate the borehole acoustic wavefield in a saturated poroelastic medium with transverse isotropy of permeability and tortuosity. A linear interpolation process is proposed to guarantee the leapfrog finite difference scheme for the generalized dynamic equations and Darcy's law for anisotropic porous media. First, the modified algorithm is validated by comparison against the analytical solution when the borehole axis is parallel to the symmetry axis of the formation. The same algorithm is then used to numerically model the dipole acoustic log in a borehole with its axis being arbitrarily deviated from the symmetry axis of transverse isotropy. The simulation results show that the amplitudes of flexural modes vary with the dipole orientation because the permeability tensor of the formation is dependent on the wellbore azimuth. It is revealed that the attenuation of the flexural wave increases approximately linearly with the radial permeability component in the direction of the transmitting dipole. Particularly, when the borehole axis is perpendicular to the symmetry axis of the formation, it is possible to estimate the anisotropy of permeability by evaluating attenuation of the flexural wave using a cross-dipole sonic logging tool according to the results of sensitivity analyses. Finally, the dipole sonic logs in a deviated borehole surrounded by a stratified porous formation are modelled using the proposed finite difference code. Numerical results show that the arrivals and amplitudes of transmitted flexural modes near the layer interface are sensitive to the wellbore inclination.

PIV measurement of high-Reynolds-number homogeneous and isotropic turbulence in an enclosed flow apparatus with fan agitation

NASA Astrophysics Data System (ADS)

Dou, Zhongwang; Pecenak, Zachary K.; Cao, Lujie; Woodward, Scott H.; Liang, Zach; Meng, Hui

2016-03-01

Enclosed flow apparatuses with negligible mean flow are emerging as alternatives to wind tunnels for laboratory studies of homogeneous and isotropic turbulence (HIT) with or without aerosol particles, especially in experimental validation of Direct Numerical Simulation (DNS). It is desired that these flow apparatuses generate HIT at high Taylor-microscale Reynolds numbers ({{R}λ} ) and enable accurate measurement of turbulence parameters including kinetic energy dissipation rate and thereby {{R}λ} . We have designed an enclosed, fan-driven, highly symmetric truncated-icosahedron ‘soccer ball’ airflow apparatus that enables particle imaging velocimetry (PIV) and other whole-field flow measurement techniques. To minimize gravity effect on inertial particles and improve isotropy, we chose fans instead of synthetic jets as flow actuators. We developed explicit relations between {{R}λ} and physical as well as operational parameters of enclosed HIT chambers. To experimentally characterize turbulence in this near-zero-mean flow chamber, we devised a new two-scale PIV approach utilizing two independent PIV systems to obtain both high resolution and large field of view. Velocity measurement results show that turbulence in the apparatus achieved high homogeneity and isotropy in a large central region (48 mm diameter) of the chamber. From PIV-measured velocity fields, we obtained turbulence dissipation rates and thereby {{R}λ} by using the second-order velocity structure function. A maximum {{R}λ} of 384 was achieved. Furthermore, experiments confirmed that the root mean square (RMS) velocity increases linearly with fan speed, and {{R}λ} increases with the square root of fan speed. Characterizing turbulence in such apparatus paves the way for further investigation of particle dynamics in particle-laden homogeneous and isotropic turbulence.

Absence of Disorder-Driven Metal-Insulator Transitions in Simple Holographic Models

NASA Astrophysics Data System (ADS)

Grozdanov, Sašo; Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad

2015-11-01

We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to the Einstein-Maxwell theory in an asymptotically four-dimensional anti-de Sitter space spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions including emergent isotropy. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond nonperturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

Point force and point electric charge applied to the boundary of three-dimensional anisotropic piezoelectric solid

DOE PAGES

Borovikov, V. A.; Kalinin, S. V.; Khavin, Yu.; ...

2015-08-19

We derive the Green's functions for a three-dimensional semi-infinite fully anisotropic piezoelectric material using the plane wave theory method. The solution gives the complete set of electromechanical fields due to an arbitrarily oriented point force and a point electric charge applied to the boundary of the half-space. Moreover, the solution constitutes generalization of Boussinesq's and Cerruti's problems of elastic isotropy for the anisotropic piezoelectric materials. On the example of piezoceramics PZT-6B, the present results are compared with the previously obtained solution for the special case of transversely isotropic piezoelectric solid subjected to the same boundary condition.

Thick strings, the liquid crystal blue phase, and cosmological large-scale structure

NASA Technical Reports Server (NTRS)

Luo, Xiaochun; Schramm, David N.

1992-01-01

A phenomenological model based on the liquid crystal blue phase is proposed as a model for a late-time cosmological phase transition. Topological defects, in particular thick strings and/or domain walls, are presented as seeds for structure formation. It is shown that the observed large-scale structure, including quasi-periodic wall structure, can be well fitted in the model without violating the microwave background isotropy bound or the limits from induced gravitational waves and the millisecond pulsar timing. Furthermore, such late-time transitions can produce objects such as quasars at high redshifts. The model appears to work with either cold or hot dark matter.

Turbulence: The chief outstanding difficulty of our subject

NASA Technical Reports Server (NTRS)

Bradshaw, Peter

1992-01-01

A review of interesting current topics in turbulence research is decorated with examples of popular fallacies about the behavior of turbulence. Topics include the status of the Law of the Wall, especially in compressible flow; analogies between the effects of Reynolds numbers, pressure gradient, unsteadiness and roughness change; the status of Kolmogorov's universal equilibrium theory and local isotropy of the small eddies; turbulence modelling, with reference to universality, pressure-strain modelling and the dissipation equation; and chaos. Fallacies include the mixing-length concept; the effect of pressure gradient on Reynolds shear stress; the separability of time and space derivatives; models of the dissipation equation; and chaos.

Special Course on Modern Theoretical and Experimental Approaches to Turbulent Flow Structure and its Modelling

DTIC Science & Technology

1987-08-01

be found using the general soluticn to the Poissca equation; at any instant in time, this solution is ui(x) = - f G(x,x’)ei,w,,& (x’)d~x’ (1.9.6) where...any instant of time is 1(X) = •j(kI)e-ik’’x (3.3.2a) k’ I where k = (kl,k 2 , k3 ) is the three-dimensional wavenumber vector, and k "x = kzn. Since the...strain rate. And algebraic models predict instant restoration of isotropy after the removal of an applied mean strain-rate. Hence, if one wants to have

Limits on Anisotropy in the Nanohertz Stochastic Gravitational Wave Background.

PubMed

Taylor, S R; Mingarelli, C M F; Gair, J R; Sesana, A; Theureau, G; Babak, S; Bassa, C G; Brem, P; Burgay, M; Caballero, R N; Champion, D J; Cognard, I; Desvignes, G; Guillemot, L; Hessels, J W T; Janssen, G H; Karuppusamy, R; Kramer, M; Lassus, A; Lazarus, P; Lentati, L; Liu, K; Osłowski, S; Perrodin, D; Petiteau, A; Possenti, A; Purver, M B; Rosado, P A; Sanidas, S A; Smits, R; Stappers, B; Tiburzi, C; van Haasteren, R; Vecchio, A; Verbiest, J P W

2015-07-24

The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational wave background (GWB) from this population is anisotropic, rendering existing analyses suboptimal. We present the first constraints on the angular distribution of a nanohertz stochastic GWB from circular, inspiral-driven SMBHBs using the 2015 European Pulsar Timing Array data. Our analysis of the GWB in the ~2-90 nHz band shows consistency with isotropy, with the strain amplitude in l>0 spherical harmonic multipoles ≲40% of the monopole value. We expect that these more general techniques will become standard tools to probe the angular distribution of source populations.

Observation of Air Shower in Uijeongbu Area using the COREA Prototype Detector System

NASA Astrophysics Data System (ADS)

Cho, Wooram; Shin, Jae-ik; Kwon, Youngjoon; Yang, Jongmann; Nam, Shinwoo; Park, Il H.; Cheon, ByungGu; Kim, Hang Bae; Bhang, Hyoung Chan; Park, Cheolyoung; Kim, Gyhyuk; Choi, Wooseok; Hwang, MyungJin; Shin, Gwangsik

2018-06-01

We report the study of high energy cosmic rays in Uijeongbu area using a cosmic-ray detector array system. The array consists of three detector stations, each of which contains a set of three scintillators and PMTs, a GPS antenna along with data acquisition system. To identify air shower signals originating from a single cosmic ray, time coincidence information is used. We devised a method for estimating the energy range of air shower data detected by an array of only three detectors, using air shower simulation and citing already known energy spectrum. Also, Fast Fourier Transform(FFT) was applied to study isotropy.

Characteristics of turbulence in boundary layer with zero pressure gradient

NASA Technical Reports Server (NTRS)

Klebanoff, P S

1955-01-01

The results of an experimental investigation of a turbulent boundary layer with zero pressure gradient are presented. Measurements with the hot-wire anemometer were made of turbulent energy and turbulent shear stress, probability density and flattening factor of u-fluctuation (fluctuation in x-direction), spectra of turbulent energy and shear stress, and turbulent dissipation. The importance of the region near the wall and the inadequacy of the concept of local isotropy are demonstrated. Attention is given to the energy balance and the intermittent character of the outer region of the boundary layer. Also several interesting features of the spectral distribution of the turbulent motions are discussed.

Limits on Anisotropy in the Nanohertz Stochastic Gravitational Wave Background

NASA Astrophysics Data System (ADS)

Taylor, S. R.; Mingarelli, C. M. F.; Gair, J. R.; Sesana, A.; Theureau, G.; Babak, S.; Bassa, C. G.; Brem, P.; Burgay, M.; Caballero, R. N.; Champion, D. J.; Cognard, I.; Desvignes, G.; Guillemot, L.; Hessels, J. W. T.; Janssen, G. H.; Karuppusamy, R.; Kramer, M.; Lassus, A.; Lazarus, P.; Lentati, L.; Liu, K.; Osłowski, S.; Perrodin, D.; Petiteau, A.; Possenti, A.; Purver, M. B.; Rosado, P. A.; Sanidas, S. A.; Smits, R.; Stappers, B.; Tiburzi, C.; van Haasteren, R.; Vecchio, A.; Verbiest, J. P. W.; EPTA Collaboration

2015-07-01

The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational wave background (GWB) from this population is anisotropic, rendering existing analyses suboptimal. We present the first constraints on the angular distribution of a nanohertz stochastic GWB from circular, inspiral-driven SMBHBs using the 2015 European Pulsar Timing Array data. Our analysis of the GWB in the ˜2 - 90 nHz band shows consistency with isotropy, with the strain amplitude in l >0 spherical harmonic multipoles ≲40 % of the monopole value. We expect that these more general techniques will become standard tools to probe the angular distribution of source populations.

Mechanical suitability of glycerol-preserved human dura mater for construction of prosthetic cardiac valves.

PubMed

McGarvey, K A; Lee, J M; Boughner, D R

1984-03-01

We have examined the tensile viscoelastic properties of fresh and glycerol-preserved human dura mater, and correlated the results with structural information from the scanning electron microscope. The interwoven laminar structure of dura produces rather high flexural stiffness, while the crossed-fibrillar laminae produce planar mechanical isotropy. Glycerol storage shifts the stress-strain curve to lower strain, reduces stress relaxation and creep, and lowers the ultimate tensile strength and strain at fracture. These changes may be due to glyceraldehyde crosslinking, or to increased interfibrillar friction. The latter hypothesis suggests that glycerol storage may reduce the fatigue lifetime of the tissue.

Electrical and magnetic properties of nano-sized magnesium ferrite

NASA Astrophysics Data System (ADS)

T, Smitha; X, Sheena; J, Binu P.; Mohammed, E. M.

2015-02-01

Nano-sized magnesium ferrite was synthesized using sol-gel techniques. Structural characterization was done using X-ray diffractometer and Fourier Transform Infrared Spectrometer. Vibration Sample Magnetometer was used to record the magnetic measurements. XRD analysis reveals the prepared sample is single phasic without any impurity. Particle size calculation shows the average crystallite size of the sample is 19nm. FTIR analysis confirmed spinel structure of the prepared samples. Magnetic measurement study shows that the sample is ferromagnetic with high degree of isotropy. Hysterisis loop was traced at temperatures 100K and 300K. DC electrical resistivity measurements show semiconducting nature of the sample.

Ground-water flow in the Prairie du Chien-Jordan aquifer related to contamination by coal-tar derivatives, St. Louis Park, Minnesota

USGS Publications Warehouse

Stark, J.R.; Hult, M.F.

1985-01-01

Simulation of a proposed gradient-control plan, in which lateral homogeneity and isotropy of individual hydro geologic units was assumed, indicates that the actions would be effective in limiting expansion of the contaminated volume in the Prairie du Chien-Jordan aquifer. The plan includes the control of withdrawal from five wells. The simulations also show, however, that modelcalculated potentiometric surfaces are sensitive to changes in withdrawal rates at wells not intended to be under the control of the plan. Management of discharge from these wells also will be important to overall effectiveness of the remedial-action plan.

A second catalog of gamma ray bursts: 1978 - 1980 localizations from the interplanetary network

NASA Technical Reports Server (NTRS)

Atteia, J. L.; Barat, C.; Hurley, K.; Niel, M.; Vedrenne, G.; Evans, W. D.; Fenimore, E. E.; Klebesadel, R. W.; Laros, J. G.; Cline, T. L.

1985-01-01

Eighty-two gamma ray bursts were detected between 1978 September 14 and 1980 February 13 by the experiments of the interplanetary network (Prognoz 7, Venera 11 and 12 SIGNE experiments, Pioneer Venus Orbiter, International Sun-Earth Explorer 3, Helios 2, and Vela). Sixty-five of these events have been localized to annuli or error boxes by the method of arrival time analysis. The distribution of sources is consistent with isotropy, and there is no statistically convincing evidence for the detection of more than one burst from any source position. The localizations are compared with those of two previous catalogs.

3D tracking of laparoscopic instruments using statistical and geometric modeling.

PubMed

Wolf, Rémi; Duchateau, Josselin; Cinquin, Philippe; Voros, Sandrine

2011-01-01

During a laparoscopic surgery, the endoscope can be manipulated by an assistant or a robot. Several teams have worked on the tracking of surgical instruments, based on methods ranging from the development of specific devices to image processing methods. We propose to exploit the instruments' insertion points, which are fixed on the patients abdominal cavity, as a geometric constraint for the localization of the instruments. A simple geometric model of a laparoscopic instrument is described, as well as a parametrization that exploits a spherical geometric grid, which offers attracting homogeneity and isotropy properties. The general architecture of our proposed approach is based on the probabilistic Condensation algorithm.

Propagation of cosmic rays in the galaxy

NASA Technical Reports Server (NTRS)

Daniel, R. R.; Stephens, S. A.

1974-01-01

The characteristics of a model for analyzing the propagation of cosmic rays are discussed. The requirements for analyzing the relevant observational data on cosmic rays are defines as: (1) the chemical and isotopic composition of cosmic rays as a function of energy, (2) the flux and energy spectrum of the individual nucleonic components, (3) the flux and energy spectrum of the electronic component, (4) the cosmic ray prehistory, and (5) the degree of isotropy in their arrival directions as a function of energy. It is stated that the model which has been able to bring to pass the greatest measure of success is the galactic confinement model.

TOPOGRAPHY, STRESSES, AND STABILITY AT YUCCA MOUNTAIN, NEVADA.

USGS Publications Warehouse

Wolfs, Henri; Savage, William Z.

1985-01-01

Plane-strain solutions are used to analyze the influence of topography on the state of stress at Yucca Mountain, Nye County, Nevada. The results are in good agreement with the measured stress components obtained in drill holes by the hydraulic-fracturing technique, particularly those measured directly beneath the crest of the ridge, and indicate that these stresses are gravitationally induced. A separate analysis takes advantage of the fact that a well-developed set of vertical faults and fractures, subparallel to the ridge trend, imparts a vertical transverse isotropy to the rock and that, as a consequence of gravitational loading, unequal horizontal stresses are induced in directions perpendicular and parallel to the anisotropy.

Test of spatial isotropy using a cryogenic torsion pendulum

NASA Technical Reports Server (NTRS)

Phillips, Peter R.

1987-01-01

Motion of the earth through the cosmic neutrino background, or through certain kinds of vacuum states, produces a term of the form g(sigma) x v in the energy of an electron. To search for such a term, a cryogenic torsion pendulum carrying a transversely polarized magnet was used. Superconducting shields reduced magnetic torques. A sigma x v term would produce a sinusoidal oscillation of the pendulum with a period of one sidereal day. Such an oscillation was not detected, and a new limit of 8.5 x 10 to the -18th eV has been set for the splitting of the spin states of an electron at rest on the earth.

Ground State Structure Search of Fluoroperovskites through Lattice Instability

NASA Astrophysics Data System (ADS)

Mei, W. N.; Hatch, D. M.; Stokes, H. T.; Boyer, L. L.

2002-03-01

Many Fluoroperovskite are capable of a ferroelectric transition from a cubic to a tetragonal and even lower-symmetry structures. In this work, we studied systematically the structural phase transitions of several fluoroperovskites ABF3 where A= Na, K and B= Ca, Sr. Combining the Self-Consistent Atom Deformation (SCAD) -- a density-functional method using localized densities -- and the frozen-phonon method which utilizes the isotropy subgroup operations, we calculate the phonon energies and find instabilities which lower the symmetry of the crystal. Following this scheme, we work down to lower symmetry structures until we no longer find instabilities. The final results are used to compare with those obtained from molecular dynamics based on Gordon-Kim potentials.

Consistent forcing scheme in the cascaded lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Fei, Linlin; Luo, Kai Hong

2017-11-01

In this paper, we give an alternative derivation for the cascaded lattice Boltzmann method (CLBM) within a general multiple-relaxation-time (MRT) framework by introducing a shift matrix. When the shift matrix is a unit matrix, the CLBM degrades into an MRT LBM. Based on this, a consistent forcing scheme is developed for the CLBM. The consistency of the nonslip rule, the second-order convergence rate in space, and the property of isotropy for the consistent forcing scheme is demonstrated through numerical simulations of several canonical problems. Several existing forcing schemes previously used in the CLBM are also examined. The study clarifies the relation between MRT LBM and CLBM under a general framework.

Hypergeometric Equation in Modeling Relativistic Isotropic Sphere

NASA Astrophysics Data System (ADS)

Thirukkanesh, S.; Ragel, F. C.

2014-04-01

We study the Einstein system of equations in static spherically symmetric spacetimes. We obtained classes of exact solutions to the Einstein system by transforming the condition for pressure isotropy to a hypergeometric equation choosing a rational form for one of the gravitational potentials. The solutions are given in simple form that is a desirable requisite to study the behavior of relativistic compact objects in detail. A physical analysis indicate that our models satisfy all the fundamental requirements of realistic star and match smoothly with the exterior Schwarzschild metric. The derived masses and densities are consistent with the previously reported experimental and theoretical studies describing strange stars. The models satisfy the standard energy conditions required by normal matter.

Studying the kinetics of magnetization in high Tc superconductors

NASA Technical Reports Server (NTRS)

Turchinskaya, Marina

1993-01-01

The first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density and polytwin block and twin boundary orientation are reported. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increased with increasing twin density. An isotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

Analysis of borehole expansion and gallery tests in anisotropic rock masses

USGS Publications Warehouse

Amadei, B.; Savage, W.Z.

1991-01-01

Closed-form solutions are used to show how rock anisotropy affects the variation of the modulus of deformation around the walls of a hole in which expansion tests are conducted. These tests include dilatometer and NX-jack tests in boreholes and gallery tests in tunnels. The effects of rock anisotropy on the modulus of deformation are shown for transversely isotropic and regularly jointed rock masses with planes of transverse isotropy or joint planes parallel or normal to the hole longitudinal axis for plane strain or plane stress condition. The closed-form solutions can also be used when determining the elastic properties of anisotropic rock masses (intact or regularly jointed) in situ. ?? 1991.

Numerical experiments in homogeneous turbulence

NASA Technical Reports Server (NTRS)

Rogallo, R. S.

1981-01-01

The direct simulation methods developed by Orszag and Patternson (1972) for isotropic turbulence were extended to homogeneous turbulence in an incompressible fluid subjected to uniform deformation or rotation. The results of simulations for irrotational strain (plane and axisymmetric), shear, rotation, and relaxation toward isotropy following axisymmetric strain are compared with linear theory and experimental data. Emphasis is placed on the shear flow because of its importance and because of the availability of accurate and detailed experimental data. The computed results are used to assess the accuracy of two popular models used in the closure of the Reynolds-stress equations. Data from a variety of the computed fields and the details of the numerical methods used in the simulation are also presented.

The origin of the diffuse background gamma radiation

NASA Technical Reports Server (NTRS)

Stecker, F. W.; Puget, J. L.

1974-01-01

Recent observations provided evidence for diffuse background gamma radiation extending to energies beyond 100 MeV, and evidence of isotropy and implied cosmological origin. Significant features in the spectrum of this background radiation were observed which provide evidence for its origin in nuclear processes in the early stages of big-bang cosmology, and connect these processes with the galaxy formation theory. A test of the theory is in future observations of the background radiation in the 100 MeK to 100 GeV energy range which are made with large orbiting spark-chamber satellite detectors. The theoretical interpretations of present data, their connection with baryon-symmetric cosmology and galaxy formation theory, and the need for future observations are discussed.

General quadrupolar statistical anisotropy: Planck limits

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

Ramazanov, S.; Rubtsov, G.; Thorsrud, M.

2017-03-01

Several early Universe scenarios predict a direction-dependent spectrum of primordial curvature perturbations. This translates into the violation of the statistical isotropy of cosmic microwave background radiation. Previous searches for statistical anisotropy mainly focussed on a quadrupolar direction-dependence characterised by a single multipole vector and an overall amplitude g {sub *}. Generically, however, the quadrupole has a more complicated geometry described by two multipole vectors and g {sub *}. This is the subject of the present work. In particular, we limit the amplitude g {sub *} for different shapes of the quadrupole by making use of Planck 2015 maps. We alsomore » constrain certain inflationary scenarios which predict this kind of more general quadrupolar statistical anisotropy.« less

Empirical Constraints on Proton and Electron Heating in the Fast Solar Wind

NASA Technical Reports Server (NTRS)

Cranmer, Steven R.; Matthaeus, William H.; Breech, Benjamin A.; Kasper, Justin C.

2009-01-01

This paper presents analyses of measured proton and electron temperatures in the high-speed solar wind that are used to calculate the separate rates of heat deposition for protons and electrons. It was found that the protons receive about 60% of the total plasma heating in the inner heliosphere, and that this fraction increases to approximately 80% by the orbit of Jupiter. The empirically derived partitioning of heat between protons and electrons is in rough agreement with theoretical predictions from a model of linear Vlasov wave damping. For a modeled power spectrum consisting only of Alfvenic fluctuations, the best agreement was found for a distribution of wavenumber vectors that evolves toward isotropy as distance increases.

Search for point-like sources of cosmic rays with energies above 1018.5 eV in the HiRes-I monocular data set

NASA Astrophysics Data System (ADS)

High-Resolution Fly'S Eye Collaboration; Abbai, R. U.; Abu-Zayyad, T.; Amann, J. F.; Archbold, G.; Belov, K.; Belz, J. W.; Benzvi, S.; Bergman, D. R.; Blake, S. A.; Cao, Z.; Connolly, B. M.; Deng, W.; Fedorova, Y.; Findlay, J.; Finley, C. B.; Gray, R. C.; Hanlon, W. F.; Hoffman, C. M.; Holzscheiter, M. H.; Hughes, G. A.; Hüntemeyer, P.; Jones, B. F.; Jui, C. C. H.; Kim, K.; Kirn, M. A.; Loh, E. C.; Maestas, M. M.; Manago, N.; Marek, L. J.; Martens, K.; Matthews, J. A. J.; Matthews, J. N.; Moore, S. A.; O'Neill, A.; Painter, C. A.; Perera, L.; Reil, K.; Riehle, R.; Rodriguez, D.; Roberts, M. D.; Sasaki, M.; Schnetzer, S. R.; Scott, L. M.; Sinnis, G.; Smith, J. D.; Sokolsky, P.; Song, C.; Springer, R. W.; Stokes, B. T.; Thomas, J. R.; Thomas, S. B.; Thomson, G. B.; Tupa, D.; Westerhoff, S.; Wiencke, L. R.; Zech, A.; Zhang, X.

2007-07-01

We report the results of a search for point-like deviations from isotropy in the arrival directions of ultra-high energy cosmic rays in the northern hemisphere. In the monocular data set collected by the High-Resolution Fly’s Eye, consisting of 1525 events with energy exceeding 1018.5 eV, we find no evidence for point-like excesses. We place a 90% c.l. upper limit of 0.8 hadronic cosmic rays/km2 yr on the flux from such sources for the northern hemisphere and place tighter limits as a function of position in the sky.

1/f2 Characteristics and Isotropy in the Fourier Power Spectra of Visual Art, Cartoons, Comics, Mangas, and Different Categories of Photographs

PubMed Central

Koch, Michael; Denzler, Joachim; Redies, Christoph

2010-01-01

Art images and natural scenes have in common that their radially averaged (1D) Fourier spectral power falls according to a power-law with increasing spatial frequency (1/f2 characteristics), which implies that the power spectra have scale-invariant properties. In the present study, we show that other categories of man-made images, cartoons and graphic novels (comics and mangas), have similar properties. Further on, we extend our investigations to 2D power spectra. In order to determine whether the Fourier power spectra of man-made images differed from those of other categories of images (photographs of natural scenes, objects, faces and plants and scientific illustrations), we analyzed their 2D power spectra by principal component analysis. Results indicated that the first fifteen principal components allowed a partial separation of the different image categories. The differences between the image categories were studied in more detail by analyzing whether the mean power and the slope of the power gradients from low to high spatial frequencies varied across orientations in the power spectra. Mean power was generally higher in cardinal orientations both in real-world photographs and artworks, with no systematic difference between the two types of images. However, the slope of the power gradients showed a lower degree of mean variability across spectral orientations (i.e., more isotropy) in art images, cartoons and graphic novels than in photographs of comparable subject matters. Taken together, these results indicate that art images, cartoons and graphic novels possess relatively uniform 1/f2 characteristics across all orientations. In conclusion, the man-made stimuli studied, which were presumably produced to evoke pleasant and/or enjoyable visual perception in human observers, form a subset of all images and share statistical properties in their Fourier power spectra. Whether these properties are necessary or sufficient to induce aesthetic perception remains to be investigated. PMID:20808863

1/f 2 Characteristics and isotropy in the fourier power spectra of visual art, cartoons, comics, mangas, and different categories of photographs.

PubMed

Koch, Michael; Denzler, Joachim; Redies, Christoph

2010-08-19

Art images and natural scenes have in common that their radially averaged (1D) Fourier spectral power falls according to a power-law with increasing spatial frequency (1/f(2) characteristics), which implies that the power spectra have scale-invariant properties. In the present study, we show that other categories of man-made images, cartoons and graphic novels (comics and mangas), have similar properties. Further on, we extend our investigations to 2D power spectra. In order to determine whether the Fourier power spectra of man-made images differed from those of other categories of images (photographs of natural scenes, objects, faces and plants and scientific illustrations), we analyzed their 2D power spectra by principal component analysis. Results indicated that the first fifteen principal components allowed a partial separation of the different image categories. The differences between the image categories were studied in more detail by analyzing whether the mean power and the slope of the power gradients from low to high spatial frequencies varied across orientations in the power spectra. Mean power was generally higher in cardinal orientations both in real-world photographs and artworks, with no systematic difference between the two types of images. However, the slope of the power gradients showed a lower degree of mean variability across spectral orientations (i.e., more isotropy) in art images, cartoons and graphic novels than in photographs of comparable subject matters. Taken together, these results indicate that art images, cartoons and graphic novels possess relatively uniform 1/f(2) characteristics across all orientations. In conclusion, the man-made stimuli studied, which were presumably produced to evoke pleasant and/or enjoyable visual perception in human observers, form a subset of all images and share statistical properties in their Fourier power spectra. Whether these properties are necessary or sufficient to induce aesthetic perception remains to be investigated.

The relationship between diffuse auroral and plasma sheet electron distributions near local midnight

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

Schumaker, T.L.; Gussenhoven, M.S.; Hardy, D.A.

1989-08-01

A study of the relationship between diffuse auroral and plasma sheet electron distributions in the energy range from 50 eV to 20 keV in the midnight region was conducted using data from the P78-1 and SCATHA satellites. From 1 1/2 years of data, 14 events were found where the polar-orbiting P78-1 satellite and the near-geosynchronous SCATHA satellite were approximately on the same magnetic field line simultaneously, with SCATHA in the plasma sheet and P78-1 in the diffuse auroral region. For all cases the spectra from the two satellites are in good quantitative agreement. For 13 of the 14 events themore » pitch angle distribution measured at P78-1 was isotropic for angles mapping into the loss cone at the SCATHA orbit. For one event the P78-1 electron flux decreased with pitch angle toward the field line direction. At SCATHA the distributions outside the loss cone were most commonly butterfly or pancake, although distributions peaked toward the field line were sometimes observed at energies below 1 keV. Electron distributions, as measured where there is isotropy within the loss cone but anisotropy outside the loss cone, are inconsistent with current theories for the scattering of cone for the distribution measured at SCATHA, the electron precipitation lifetimes were calculated for the 14 events. Because the distributions are anisotropic at pitch angles away from the loss cone, the calculated lifetimes significantly exceed the lifetimes in the limit when the flu is isotropic at all pitch angles. The computed precipitation lifetimes are found to be weakly dependent on magnetic activity. The average lifetimes exceed those for the case of isotropy at all pitch angles by a factor between 2 and 3 for {ital Kp}{le}2 and approximately 1.5 for {ital Kp}{gt}2. {copyright} American Geophysical Union 1989« less

Electrically Anisotropic 35 Ma Pacific Lithosphere

NASA Astrophysics Data System (ADS)

Chesley, C. J.; Key, K.; Constable, S.; Behrens, J.; MacGregor, L.

2017-12-01

Geophysical studies of anisotropy in the oceanic lithosphere and asthenosphere can yield crucial insights into the processes of plate formation and evolution as the plate cools and thickens. While most previous studies have employed seismic methods to investigate anisotropy, here we examine the electrical conductivity anisotropy as constrained by controlled-source electromagnetic (CSEM) data collected during the Anisotropy and Physics of the Pacific Lithosphere Experiment (APPLE). Unlike passive magnetotelluric data, which are not particularly sensitive to the resistive part of the lithosphere or its anisotropy, CSEM data are highly sensitive to anisotropy in both the resistive crust and uppermost mantle. The APPLE data include a 30 km radius circular deep-tow of a Horizontal Electric Dipole (HED) transmitter around orthogonal pairs of HED receivers. The circular tow was optimized to measure azimuthal anisotropy, while radially oriented data at ranges from 14 to 70 km provided constraints on depth dependence of bulk conductivity. We inverted these data with a nonlinear anisotropic inversion that allows for laterally transverse isotropy, with the vertical plane of isotropy aligned orthogonal to the paleo-spreading direction. Our best model shows at least an order of magnitude resistivity difference between the paleo-spreading and paleo-ridge strike directions in both the crust and upper mantle. In the crust, conductivity is higher in the paleo-ridge and vertical directions. The opposite is true in the upper mantle, where conductivity is ten times higher in the paleo-spreading direction. Since the study area is centered on 35 Ma lithosphere, it is unlikely that melt plays a role in the observed anisotropy. Instead we propose that the crustal anisotropy is due to conductive clay minerals in normal faults promoted by hydration during paleo-extension close to the mid-ocean ridge. The upper mantle anisotropy potentially results from a crystal preferred orientation of olivine induced by shear deformation. These findings offer clues about the processes associated with oceanic spreading and may be of import to ophiolite studies.

Global-scale Joint Body and Surface Wave Tomography with Vertical Transverse Isotropy for Seismic Monitoring Applications

NASA Astrophysics Data System (ADS)

Simmons, Nathan; Myers, Steve

2017-04-01

We continue to develop more advanced models of Earth's global seismic structure with specific focus on improving predictive capabilities for future seismic events. Our most recent version of the model combines high-quality P and S wave body wave travel times and surface-wave group and phase velocities into a joint (simultaneous) inversion process to tomographically image Earth's crust and mantle. The new model adds anisotropy (known as vertical transverse isotropy) to the model, which is necessitated by the addition of surface waves to the tomographic data set. Like previous versions of the model the new model consists of 59 surfaces and 1.6 million model nodes from the surface to the core-mantle boundary, overlaying a 1-D outer and inner core model. The model architecture is aspherical and we directly incorporate Earth's expected hydrostatic shape (ellipticity and mantle stretching). We also explicitly honor surface undulations including the Moho, several internal crustal units, and the upper mantle transition zone undulations as predicated by previous studies. The explicit Earth model design allows for accurate travel time computation using our unique 3-D ray tracing algorithms, capable of 3-D ray tracing more than 20 distinct seismic phases including crustal, regional, teleseismic, and core phases. Thus, we can now incorporate certain secondary (and sometimes exotic) phases into source location determination and other analyses. New work on model uncertainty quantification assesses the error covariance of the model, which when completed will enable calculation of path-specific estimates of uncertainty for travel times computed using our previous model (LLNL-G3D-JPS) which is available to the monitoring and broader research community and we encourage external evaluation and validation. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Experimental criteria for the determination of fractal parameters of premixed turbulent flames

NASA Astrophysics Data System (ADS)

Shepherd, I. G.; Cheng, Robert K.; Talbot, L.

1992-10-01

The influence of spatial resolution, digitization noise, the number of records used for averaging, and the method of analysis on the determination of the fractal parameters of a high Damköhler number, methane/air, premixed, turbulent stagnation-point flame are investigated in this paper. The flow exit velocity was 5 m/s and the turbulent Reynolds number was 70 based on a integral scale of 3 mm and a turbulent intensity of 7%. The light source was a copper vapor laser which delivered 20 nsecs, 5 mJ pulses at 4 kHz and the tomographic cross-sections of the flame were recorded by a high speed movie camera. The spatial resolution of the images is 155 × 121 μm/pixel with a field of view of 50 × 65 mm. The stepping caliper technique for obtaining the fractal parameters is found to give the clearest indication of the cutoffs and the effects of noise. It is necessary to ensemble average the results from more than 25 statistically independent images to reduce sufficiently the scatter in the fractal parameters. The effects of reduced spatial resolution on fractal plots are estimated by artificial degradation of the resolution of the digitized flame boundaries. The effect of pixel resolution, an apparent increase in flame length below the inner scale rolloff, appears in the fractal plots when the measurent scale is less than approximately twice the pixel resolution. Although a clearer determination of fractal parameters is obtained by local averaging of the flame boundaries which removes digitization noise, at low spatial resolution this technique can reduce the fractal dimension. The degree of fractal isotropy of the flame surface can have a significant effect on the estimation of the flame surface area and hence burning rate from two-dimensional images. To estimate this isotropy a determination of the outer cutoff is required and three-dimensional measurements are probably also necessary.

Interplay of Coulomb interactions and disorder in three-dimensional quadratic band crossings without time-reversal symmetry and with unequal masses for conduction and valence bands

NASA Astrophysics Data System (ADS)

Mandal, Ipsita; Nandkishore, Rahul M.

2018-03-01

Coulomb interactions famously drive three-dimensional quadratic band crossing semimetals into a non-Fermi liquid phase of matter. In a previous work [Nandkishore and Parameswaran, Phys. Rev. B 95, 205106 (2017), 10.1103/PhysRevB.95.205106], the effect of disorder on this non-Fermi liquid phase was investigated, assuming that the band structure was isotropic, assuming that the conduction and valence bands had the same band mass, and assuming that the disorder preserved exact time-reversal symmetry and statistical isotropy. It was shown that the non-Fermi liquid fixed point is unstable to disorder and that a runaway flow to strong disorder occurs. In this paper, we extend that analysis by relaxing the assumption of time-reversal symmetry and allowing the electron and hole masses to differ (but continuing to assume isotropy of the low energy band structure). We first incorporate time-reversal symmetry breaking disorder and demonstrate that there do not appear any new fixed points. Moreover, while the system continues to flow to strong disorder, time-reversal-symmetry-breaking disorder grows asymptotically more slowly than time-reversal-symmetry-preserving disorder, which we therefore expect should dominate the strong-coupling phase. We then allow for unequal electron and hole masses. We show that whereas asymmetry in the two masses is irrelevant in the clean system, it is relevant in the presence of disorder, such that the `effective masses' of the conduction and valence bands should become sharply distinct in the low-energy limit. We calculate the RG flow equations for the disordered interacting system with unequal band masses and demonstrate that the problem exhibits a runaway flow to strong disorder. Along the runaway flow, time-reversal-symmetry-preserving disorder grows asymptotically more rapidly than both time-reversal-symmetry-breaking disorder and the Coulomb interaction.

A three-dimensional `Kaiser damage-memory' effect through true-triaxial loading

NASA Astrophysics Data System (ADS)

Meredith, P. G.; Browning, J.; Harland, S. R.; Healy, D.; Stuart, C.; Mitchell, T. M.

2017-12-01

Microcrack damage leading to failure in rocks evolves in response to differential loading. The vast majority of experimental studies investigate damage evolution, the `Kaiser damage-memory' effect, and rock failure using conventional triaxial stress states (σ1 > σ2 = σ3). Such stress states develop a crack population that displays cylindrical transverse isotropy. However, in nature the stress state is in general truly triaxial (σ1 > σ2 > σ3) and experiments that utilise such loading conditions can generate crack populations that display planar transverse isotropy which in turn influences properties such as permeability and strength. We investigate the evolution of crack damage under both conventional and true triaxial stress conditions using results from measurements made on cubic samples of sandstone deformed in three orthogonal directions with independently controlled stress paths. We have measured, simultaneously with stress and strain, the changes in ultrasonic compressional and shear wave velocities in the three principal directions, together with the bulk acoustic emission (AE) output. Changes in acoustic wave velocities are associated with both elastic closure and opening of pre-existing cracks, and the inelastic formation of new cracks. By contrast, AE is only associated with the inelastic growth of new crack damage and as such, we use the onset of AE to determine the initiation of new crack damage. By mapping these damage onsets under both conventional triaxial and true triaxial sequential cyclic loading, we have shown that `damage envelopes' evolve dynamically and can be pushed closer to the failure envelope. Whether a stress state has been `visited' before is key to determining and understanding damage states. Crack damage populations can be generated with multiple orientations depending on the arrangement of loading directions and hence principal stress directions. The sequential cyclic loading tests show that further damage in any one population commences only when the previous maximum differential stress `seen' by that population is exceeded. Understanding anisotropic damage is important for applying the results of true-triaxial tests and hence better replicating natural fractured systems.

Linearized Israel matching conditions for cosmological perturbations in a moving brane background

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

Bucher, Martin; DAMTP, University of Cambridge, Cambridge CB3 0WA; Carvalho, Carla

2005-04-15

In the Randall-Sundrum cosmological models, a (3+1)-dimensional brane subject to a Z{sub 2} orbifold symmetry is embedded in a (4+1)-dimensional bulk spacetime empty except for a negative cosmological constant. The unperturbed braneworld cosmological solutions, subject to homogeneity and isotropy in the three transverse spatial dimensions, are most simply presented by means of a moving brane description. Owing to a generalization of Birkhoff's theorem, as long as there are no perturbations violating the three-dimensional spatial homogeneity and isotropy, the bulk spacetime remains stationary and trivial. For the spatially flat case, the bulk spacetime is described by one of three bulk solutions:more » a pure AdS{sup 5} solution, an AdS{sup 5}-Schwarzschild black hole solution, or an AdS{sup 5}-Schwarzschild naked singularity solution. The brane moves on the boundary of one of these simple bulk spacetimes, its trajectory determined by the evolution of the stress-energy localized on the brane. We derive here the form of the Israel matching conditions for the linearized cosmological perturbations in this moving brane picture. These Israel matching conditions must be satisfied in any gauge. However, they are not sufficient to determine how to describe in a specific gauge the reflection of the bulk gravitational waves off the brane boundary. In this paper we adopt a fully covariant Lorentz gauge condition in the bulk and find the supplementary gauge conditions that must be imposed on the boundary to ensure that the reflected waves do not violate the Lorentz gauge condition. Compared to the form obtained from Gaussian normal coordinates, the form of the Israel matching conditions obtained here is more complex. However, the propagation of the bulk gravitons is simpler because the coordinates used for the background exploit fully the symmetry of the bulk background solution.« less

Large-area measurements of CIB power spectra with Planck HFI maps

NASA Astrophysics Data System (ADS)

Mak, D. S. Y.; Challinor, A.; Efstathiou, G.; Lagache, G.

We present new measurements of the power spectra of the cosmic infrared background (CIB) anisotropies using the Planck 2015 full-mission HFI data at 353, 545, and 857 GHz over 20 000 square degrees. Unlike previous Planck measurements of the CIB power spectra, we do not rely on external HI data to remove Galactic dust emission from the Planck maps. Instead, we model the Galactic emission at the level of the power spectra, using templates constructed directly from the Planck data by exploiting the statistical isotropy of all extragalactic emission components. This allows us to work at the full resolution of Planck over large sky areas. We construct a likelihood based on the measured spectra (for multipoles 50 <= l <= 2500) using analytic covariance matrices that account for masking and the realistic instrumental noise properties. The results of an MCMC exploration of this likelihood are presented, based on simple parameterised models of the CIB power that arises from clustering of infrared galaxies. We explore simultaneously the parameters describing the clustered power, the Poisson power levels, and the amplitudes of the Galactic power spectrum templates across the six frequency (cross-)spectra. The best-fit model provides a good fit to all spectra. As an example, Fig. 1 compares the measured auto spectra at 353, 545, and 857 GHz over 40% of the sky to the power in the best-fit model. We find that the power in the CIB anisotropies from galaxy clustering is roughly equal to the Poisson power at multipoles l =2000 (the clustered power dominates on larger scales), and that our dust-cleaned CIB spectra are in good agreement with previous Planck and Herschel measurements. A key feature of our analysis is that it allows one to make many internal consistency tests. We show that our results are stable to data selection and choice of survey area, demonstrating both our ability to remove Galactic dust power to high accuracy and the statistical isotropy of the CIB signal.

Spherocylindrical microplane constitutive model for shale and other anisotropic rocks

NASA Astrophysics Data System (ADS)

Li, Cunbao; Caner, Ferhun C.; Chau, Viet T.; Bažant, Zdeněk P.

2017-06-01

Constitutive equations for inelastic behavior of anisotropic materials have been a challenge for decades. Presented is a new spherocylindrical microplane constitutive model that meets this challenge for the inelastic fracturing behavior of orthotropic materials, and particularly the shale, which is transversely isotropic and is important for hydraulic fracturing (aka fracking) as well as many geotechnical structures. The basic idea is to couple a cylindrical microplane system to the classical spherical microplane system. Each system is subjected to the same strain tensor while their stress tensors are superposed. The spherical phase is similar to the previous microplane models for concrete and isotropic rock. The integration of stresses over spherical microplanes of all spatial orientations relies on the previously developed optimal Gaussian integration over a spherical surface. The cylindrical phase, which is what creates the transverse isotropy, involves only microplanes that are normal to plane of isotropy, or the bedding layers, and enhance the stiffness and strength in that plane. Unlike all the microplane models except the spectral one, the present one can reproduce all the five independent elastic constants of transversely isotropic shales. Vice versa, from these constants, one can easily calculate all the microplane elastic moduli, which are all positive if the elastic in-to-out-of plane moduli ratio is not too big (usually less than 3.75, which applies to all shales). Oriented micro-crack openings, frictional micro-slips and bedding plane behavior can be modeled more intuitively than with the spectral approach. Data fitting shows that the microplane resistance depends on the angle with the bedding layers non-monotonically, and compressive resistance reaches a minimum at 60°. A robust algorithm for explicit step-by-step structural analysis is formulated. Like all microplane models, there are many material parameters, but they can be identified sequentially. Finally, comparisons with extensive test data for shale validate the model.

Rotation Dynamics Do Not Determine the Unexpected Isotropy of Methyl Radical EPR Spectra.

PubMed

Benetis, Nikolas P; Dmitriev, Yurij; Mocci, Francesca; Laaksonen, Aatto

2015-09-03

A simple first-principles electronic structure computation, further qc (quantum chemistry) computation, of the methyl radical gives three equal hf (hyperfine) couplings for the three protons with the unpaired electron. The corresponding dipolar tensors were notably rhombic and had different orientations and regular magnitude components, as they should, but what the overall A-tensor was seen by the electron spin is a different story! The final g = (2.002993, 2.002993, 2.002231) tensor and the hf coupling results obtained in vacuum, at the B3LYP/EPRIII level of theory clearly indicate that in particular the above A = (-65.19, -65.19, 62.54) MHz tensor was axial to a first approximation without considering any rotational dynamics for the CH3. This approximation was not applicable, however, for the trifluoromethyl CF3 radical, a heavier and nonplanar rotor with very anisotropic hf coupling, used here for comparison. Finally, a derivation is presented explaining why there is actually no need for the CH3 radicals to consider additional rotational dynamics in order for the electron to obtain an axially symmetric hf (hyperfine) tensor by considering the simultaneous dipolar couplings of the three protons. An additional consequence is an almost isotropic A-tensor for the electron spin of the CH3 radical. To the best of our knowledge, this point has not been discussed in the literature before. The unexpected isotropy of the EPR parameters of CH3 was solely attributed to the rotational dynamics and was not clearly separated from the overall symmetry of the species. The present theoretical results allowed a first explanation of the "forbidden" satellite lines in the CH3 EPR spectrum. The satellites are a fingerprint of the radical rotation, helping thus in distinguishing the CH3 reorientation from quantum rotation at very low temperatures.

Eternal inflation, bubble collisions, and the persistence of memory

NASA Astrophysics Data System (ADS)

Garriga, Jaume; Guth, Alan H.; Vilenkin, Alexander

2007-12-01

A “bubble universe” nucleating in an eternally inflating false vacuum will experience, in the course of its expansion, collisions with an infinite number of other bubbles. In an idealized model, we calculate the rate of collisions around an observer inside a given reference bubble. We show that the collision rate violates both the homogeneity and the isotropy of the bubble universe. Each bubble has a center which can be related to “the beginning of inflation” in the parent false vacuum, and any observer not at the center will see an anisotropic bubble collision rate that peaks in the outward direction. Surprisingly, this memory of the onset of inflation persists no matter how much time elapses before the nucleation of the reference bubble.

On the anisotropic satellite distribution around Milky-way-like galaxies in cosmological simulations.

NASA Astrophysics Data System (ADS)

Kihm, Seoneui; Seo, Seongu; Yoon, Suk-jin

2018-01-01

The presence of "anisotropic satellite distribution (ASD)" around massive galaxies is often taken as evidence against the ΛCDM cosmology. To address whether such anisotropy can be reconciled with the standard cosmology, we examine the spatial distributions of satellites around central galaxies in the hydrodynamic cosmological simulation, Illustris. In an attempt to understand the ASD of our Galaxy, we limit our analysis to the systems consisting of a MW-sized host and at least 11 satellites. We find that ASDs are rather a common feature in the simulation and that ASD systems tend to possess a larger fraction of recently accreted satellites than isotropy systems. We discuss a possible link of ASD formation to the surrounding environment in the ΛCDM setting.

Mass Function of Galaxy Clusters in Relativistic Inhomogeneous Cosmology

NASA Astrophysics Data System (ADS)

Ostrowski, Jan J.; Buchert, Thomas; Roukema, Boudewijn F.

The current cosmological model (ΛCDM) with the underlying FLRW metric relies on the assumption of local isotropy, hence homogeneity of the Universe. Difficulties arise when one attempts to justify this model as an average description of the Universe from first principles of general relativity, since in general, the Einstein tensor built from the averaged metric is not equal to the averaged stress-energy tensor. In this context, the discrepancy between these quantities is called "cosmological backreaction" and has been the subject of scientific debate among cosmologists and relativists for more than 20 years. Here we present one of the methods to tackle this problem, i.e. averaging the scalar parts of the Einstein equations, together with its application, the cosmological mass function of galaxy clusters.

A succinct method to generate multi-type HCV beams with a spatial spiral varying retardation-plate

NASA Astrophysics Data System (ADS)

Qi, Junli; Zhang, Hui; Pan, Baoguo; Deng, Haifei; Yang, Jinhong; Shi, Bo; Wang, Hui; Du, Ang; Wang, Weihua; Li, Xiujian

2018-03-01

A simple novel and practical scheme is presented to generate high-power cylindrical vector (HCV) beams with a 36-segment spiral varying retardation-plate sandwiched between two quarter-wave plates (QWPs). Four kinds of HCV beams, such as radially polarized beam and azimuthally polarized beam, are formed by simply rotating two QWPs. A segmented spiral varying phase-plate with isotropy is used to modulate spatial phase distribution to generate in-phase HCV beams. The intensity distributions and polarizing properties of HCV beams are investigated and analyzed in detail. It is demonstrated experimentally that the system can effectively generate multi-type HCV beams with high purity up to 99%, and it can be manufactured as cylindrical vector beam converter commercially.

Gravitational collapse of dark matter interacting with dark energy: Black hole formation

NASA Astrophysics Data System (ADS)

Shah, Hasrat Hussain; Iqbal, Quaid

In this work, we study the gravitational collapsing process of a spherically symmetric star constitute of Dark Matter (DM), ρM, and Dark Energy (DE) ρ. In this model, we use anisotropic pressure with Equation of State (EoS) pt = λρ and pr = lρ, (l + 2λ < -1). It reveals that gravitational collapse of DM and DE with interaction leads to the formation of the black hole. When l + 2λ < -3 (phantoms), dust and phantoms could be ejected from the death of white hole. This emitted matter again undergoes to collapsing process and becomes the black hole. This study gives the generalization for isotropy of pressure in the fluid to anisotropy when there will be interaction between DM and DE.

Geodesic-light-cone coordinates and the Bianchi I spacetime

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

Fleury, Pierre; Nugier, Fabien; Fanizza, Giuseppe, E-mail: pierre.fleury@uct.ac.za, E-mail: fnugier@ntu.edu.tw, E-mail: giuseppe.fanizza@ba.infn.it

The geodesic-light-cone (GLC) coordinates are a useful tool to analyse light propagation and observations in cosmological models. In this article, we propose a detailed, pedagogical, and rigorous introduction to this coordinate system, explore its gauge degrees of freedom, and emphasize its interest when geometric optics is at stake. We then apply the GLC formalism to the homogeneous and anisotropic Bianchi I cosmology. More than a simple illustration, this application (i) allows us to show that the Weinberg conjecture according to which gravitational lensing does not affect the proper area of constant-redshift surfaces is significantly violated in a globally anisotropic universe;more » and (ii) offers a glimpse into new ways to constrain cosmic isotropy from the Hubble diagram.« less

On measurement of the isotropy of the maximum attainable speed

NASA Astrophysics Data System (ADS)

Wojtsekhowski, Bogdan

2015-04-01

A proposal for a precision experiment to investigate possible anisotropy of the maximum attainable speed (MAS) will be presented. It is based on an electron/positron beam with a large Lorentz factor and a 180-degree magnetic arc. The ratio of the momenta at the two ends of the magnetic arc will be used to form an observable which is sensitive to the MAS variation and immune to most of the instabilities of the apparatus. The search will use the sidereal periodicity of a potential signal. The uncertainty of momenta measurement could be greatly reduced by means of the electron and positron beams simultaneously rotating in the same magnetic system. The projected sensitivity of the measurement and the implications will be discussed.

Anisotropy in the lowermost mantle beneath the Indian Ocean Geoid Low from ScS splitting measurements

NASA Astrophysics Data System (ADS)

Padma Rao, B.; Ravi Kumar, M.; Singh, Arun

2017-02-01

The Indian Ocean Geoid Low (IOGL) to the south of Indian subcontinent is the world's largest geoid anomaly. In this study, we investigate the seismic anisotropy of the lowermost mantle beneath the IOGL by analyzing splitting of high-quality ScS phases corrected for source and receiver side upper mantle anisotropy. Results reveal significant anisotropy (˜1.01%) in the D'' layer. The observed fast axis polarization azimuths in the ray coordinate system indicate a TTI (transverse isotropy with a tilted axis of symmetry) style of anisotropy. Lattice Preferred Orientation (LPO) deformation of the palaeo-subducted slabs experiencing high shear strain is a plausible explanation for the observed anisotropy beneath the IOGL.

Flavor instabilities in the neutrino line model

NASA Astrophysics Data System (ADS)

Duan, Huaiyu; Shalgar, Shashank

2015-07-01

A dense neutrino medium can experience collective flavor oscillations through nonlinear neutrino-neutrino refraction. To make this multi-dimensional flavor transport problem more tractable, all existing studies have assumed certain symmetries (e.g., the spatial homogeneity and directional isotropy in the early universe) to reduce the dimensionality of the problem. In this work we show that, if both the directional and spatial symmetries are not enforced in the neutrino line model, collective oscillations can develop in the physical regimes where the symmetry-preserving oscillation modes are stable. Our results suggest that collective neutrino oscillations in real astrophysical environments (such as core-collapse supernovae and black-hole accretion discs) can be qualitatively different from the predictions based on existing models in which spatial and directional symmetries are artificially imposed.

Exact law for homogeneous compressible Hall magnetohydrodynamics turbulence

NASA Astrophysics Data System (ADS)

Andrés, N.; Galtier, S.; Sahraoui, F.

2018-01-01

We derive an exact law for three-dimensional (3D) homogeneous compressible isothermal Hall magnetohydrodynamic turbulence, without the assumption of isotropy. The Hall current is shown to introduce new flux and source terms that act at the small scales (comparable or smaller than the ion skin depth) to significantly impact the turbulence dynamics. The law provides an accurate means to estimate the energy cascade rate over a broad range of scales covering the magnetohydrodynamic inertial range and the sub-ion dispersive range in 3D numerical simulations and in in situ spacecraft observations of compressible turbulence. This work is particularly relevant to astrophysical flows in which small-scale density fluctuations cannot be ignored such as the solar wind, planetary magnetospheres, and the interstellar medium.

Classes of exact Einstein Maxwell solutions

NASA Astrophysics Data System (ADS)

Komathiraj, K.; Maharaj, S. D.

2007-12-01

We find new classes of exact solutions to the Einstein Maxwell system of equations for a charged sphere with a particular choice of the electric field intensity and one of the gravitational potentials. The condition of pressure isotropy is reduced to a linear, second order differential equation which can be solved in general. Consequently we can find exact solutions to the Einstein Maxwell field equations corresponding to a static spherically symmetric gravitational potential in terms of hypergeometric functions. It is possible to find exact solutions which can be written explicitly in terms of elementary functions, namely polynomials and product of polynomials and algebraic functions. Uncharged solutions are regainable with our choice of electric field intensity; in particular we generate the Einstein universe for particular parameter values.

Signal Attenuation Curve for Different Surface Detector Arrays

NASA Astrophysics Data System (ADS)

Vicha, J.; Travnicek, P.; Nosek, D.; Ebr, J.

2014-06-01

Modern cosmic ray experiments consisting of large array of particle detectors measure the signals of electromagnetic or muon components or their combination. The correction for an amount of atmosphere passed is applied to the surface detector signal before its conversion to the shower energy. Either Monte Carlo based approach assuming certain composition of primaries or indirect estimation using real data and assuming isotropy of arrival directions can be used. Toy surface arrays of different sensitivities to electromagnetic and muon components are assumed in MC simulations to study effects imposed on attenuation curves for varying composition or possible high energy anisotropy. The possible sensitivity of the attenuation curve to the mass composition is also tested for different array types focusing on a future apparatus that can separate muon and electromagnetic component signals.

Flavor instabilities in the neutrino line model

DOE PAGES

Duan, Huaiyu; Shalgar, Shashank

2015-05-27

A dense neutrino medium can experience collective flavor oscillations through nonlinear neutrino-neutrino refraction. To make this multi-dimensional flavor transport problem more tractable, all existing studies have assumed certain symmetries (e.g., the spatial homogeneity and directional isotropy in the early universe) to reduce the dimensionality of the problem. In this article we show that, if both the directional and spatial symmetries are not enforced in the neutrino line model, collective oscillations can develop in the physical regimes where the symmetry-preserving oscillation modes are stable. Our results suggest that collective neutrino oscillations in real astrophysical environments (such as core-collapse supernovae and black-holemore » accretion discs) can be qualitatively different from the predictions based on existing models in which spatial and directional symmetries are artificially imposed.« less

Detection, localization and classification of multiple dipole-like magnetic sources using magnetic gradient tensor data

NASA Astrophysics Data System (ADS)

Gang, Yin; Yingtang, Zhang; Hongbo, Fan; Zhining, Li; Guoquan, Ren

2016-05-01

We have developed a method for automatic detection, localization and classification (DLC) of multiple dipole sources using magnetic gradient tensor data. First, we define modified tilt angles to estimate the approximate horizontal locations of the multiple dipole-like magnetic sources simultaneously and detect the number of magnetic sources using a fixed threshold. Secondly, based on the isotropy of the normalized source strength (NSS) response of a dipole, we obtain accurate horizontal locations of the dipoles. Then the vertical locations are calculated using magnitude magnetic transforms of magnetic gradient tensor data. Finally, we invert for the magnetic moments of the sources using the measured magnetic gradient tensor data and forward model. Synthetic and field data sets demonstrate effectiveness and practicality of the proposed method.

Improvements in the order, isotropy and electron density of glypican-1 crystals by controlled dehydration.

PubMed

Awad, Wael; Svensson Birkedal, Gabriel; Thunnissen, Marjolein M G M; Mani, Katrin; Logan, Derek T

2013-12-01

The use of controlled dehydration for improvement of protein crystal diffraction quality is increasing in popularity, although there are still relatively few documented examples of success. A study has been carried out to establish whether controlled dehydration could be used to improve the anisotropy of crystals of the core protein of the human proteoglycan glypican-1. Crystals were subjected to controlled dehydration using the HC1 device. The optimal protocol for dehydration was developed by careful investigation of the following parameters: dehydration rate, final relative humidity and total incubation time Tinc. Of these, the most important was shown to be Tinc. After dehydration using the optimal protocol the crystals showed significantly reduced anisotropy and improved electron density, allowing the building of previously disordered parts of the structure.

Non-naturally reductive Einstein metrics on exceptional Lie groups

NASA Astrophysics Data System (ADS)

Chrysikos, Ioannis; Sakane, Yusuke

2017-06-01

Given an exceptional compact simple Lie group G we describe new left-invariant Einstein metrics which are not naturally reductive. In particular, we consider fibrations of G over flag manifolds with a certain kind of isotropy representation and we construct the Einstein equation with respect to the induced left-invariant metrics. Then we apply a technique based on Gröbner bases and classify the real solutions of the associated algebraic systems. For the Lie group G2 we obtain the first known example of a left-invariant Einstein metric, which is not naturally reductive. Moreover, for the Lie groups E7 and E8, we conclude that there exist non-isometric non-naturally reductive Einstein metrics, which are Ad(K) -invariant by different Lie subgroups K.

Key product development based on cyclo olefin polymer for LCD-TV

NASA Astrophysics Data System (ADS)

Konishi, Yuichiro; Kobayashi, Masahi; Arakawa, Kouhei

2006-09-01

Cyclo Olefin Polymer (COP), which was developed by Zeon Corporation, is well known and used as an optical plastic in optical markets, having unique properties such as high light transmission, low water absorption, low birefringence etc. Optes Inc, who is ZEON CORPORATION's affiliate optical parts manufacturer, has succeeded in the development of high performance optical base films. These are used for retardation and polarizing films in LCD's (Liquid Crystal Displays), made from Cyclo Olefin Polymer with own film extrusion technologies. The Optical base film developed by Optes Inc has superior properties compared with those of existing products such as polycarbonate (PC), polyethylene terephthalate (PET) and Triacetate Cellulose (TAC) base in terms of low birefringence, high optical isotropy and high dimensional stability under high humidity and temperature conditions.

Point-to-point migration functions and gravity model renormalization: approaches to aggregation in spatial interaction modeling.

PubMed

Slater, P B

1985-08-01

Two distinct approaches to assessing the effect of geographic scale on spatial interactions are modeled. In the first, the question of whether a distance deterrence function, which explains interactions for one system of zones, can also succeed on a more aggregate scale, is examined. Only the two-parameter function for which it is found that distances between macrozones are weighted averaged of distances between component zones is satisfactory in this regard. Estimation of continuous (point-to-point) functions--in the form of quadrivariate cubic polynomials--for US interstate migration streams, is then undertaken. Upon numerical integration, these higher order surfaces yield predictions of interzonal and intrazonal movements at any scale of interest. Test of spatial stationarity, isotropy, and symmetry of interstate migration are conducted in this framework.

Exact models for isotropic matter

NASA Astrophysics Data System (ADS)

Thirukkanesh, S.; Maharaj, S. D.

2006-04-01

We study the Einstein-Maxwell system of equations in spherically symmetric gravitational fields for static interior spacetimes. The condition for pressure isotropy is reduced to a recurrence equation with variable, rational coefficients. We demonstrate that this difference equation can be solved in general using mathematical induction. Consequently, we can find an explicit exact solution to the Einstein-Maxwell field equations. The metric functions, energy density, pressure and the electric field intensity can be found explicitly. Our result contains models found previously, including the neutron star model of Durgapal and Bannerji. By placing restrictions on parameters arising in the general series, we show that the series terminate and there exist two linearly independent solutions. Consequently, it is possible to find exact solutions in terms of elementary functions, namely polynomials and algebraic functions.

The origin of the diffuse background gamma-radiation

NASA Technical Reports Server (NTRS)

Stecker, F. W.; Puget, J. L.

1974-01-01

Recent observations have now provided evidence for diffuse background gamma radiation extending to energies beyond 100 MeV. There is some evidence of isotropy and implied cosmological origin. Significant features in the spectrum of this background radiation have been observed which provide evidence for its origin in nuclear processes in the early stages of the big-band cosmology and tie in these processes with galaxy fromation theory. A crucial test of the theory may lie in future observations of the background radiation in the 100 MeV to 100 GeV energy range which may be made with large orbiting spark-chamber satellite detectors. A discussion of the theoretical interpretations of present data, their connection with baryon symmetric cosmology and galaxy formation theory, and the need for future observations are given.

Cosmic microwave background power asymmetry from non-Gaussian modulation.

PubMed

Schmidt, Fabian; Hui, Lam

2013-01-04

Non-Gaussianity in the inflationary perturbations can couple observable scales to modes of much longer wavelength (even superhorizon), leaving as a signature a large-angle modulation of the observed cosmic microwave background power spectrum. This provides an alternative origin for a power asymmetry that is otherwise often ascribed to a breaking of statistical isotropy. The non-Gaussian modulation effect can be significant even for typical ~10(-5) perturbations while respecting current constraints on non-Gaussianity if the squeezed limit of the bispectrum is sufficiently infrared divergent. Just such a strongly infrared-divergent bispectrum has been claimed for inflation models with a non-Bunch-Davies initial state, for instance. Upper limits on the observed cosmic microwave background power asymmetry place stringent constraints on the duration of inflation in such models.

Experimental Study of Vane Heat Transfer and Aerodynamics at Elevated Levels of Turbulence

NASA Technical Reports Server (NTRS)

Ames, Forrest E.

1994-01-01

A four vane subsonic cascade was used to investigate how free stream turbulence influences pressure surface heat transfer. A simulated combustor turbulence generator was built to generate high level (13 percent) large scale (Lu approximately 44 percent inlet span) turbulence. The mock combustor was also moved upstream to generate a moderate level (8.3 percent) of turbulence for comparison to smaller scale grid generated turbulence (7.8 percent). The high level combustor turbulence caused an average pressure surface heat transfer augmentation of 56 percent above the low turbulence baseline. The smaller scale grid turbulence produced the next greatest effect on heat transfer and demonstrated the importance of scale on heat transfer augmentation. In general, the heat transfer scaling parameter U(sub infinity) TU(sub infinity) LU(sub infinity)(exp -1/3) was found to hold for the turbulence. Heat transfer augmentation was also found to scale approximately on Re(sub ex)(exp 1/3) at constant turbulence conditions. Some evidence of turbulence intensification in terms of elevated dissipation rates was found along the pressure surface outside the boundary layer. However, based on the level of dissipation and the resulting heat transfer augmentation, the amplification of turbulence has only a moderate effect on pressure surface heat transfer. The flow field turbulence does drive turbulent production within the boundary layer which in turn causes the high levels of heat transfer augmentation. Unlike heat transfer, the flow field straining was found to have a significant effect on turbulence isotropy. On examination of the one dimensional spectra for u' and v', the effect to isotropy was largely limited to lower wavenumber spectra. The higher wavenumber spectra showed little or no change. The high level large scale turbulence was found to have a strong influence on wake development. The free stream turbulence significantly enhanced mixing resulting in broader and shallower wakes than the baseline case. High levels of flow field turbulence were found to correlate with a significant increase in total pressure loss in the core of the flow. Documenting the wake growth and characteristics provides boundary conditions for the downstream rotor.

Full waveform seismic AVAZ signatures of anisotropic shales by integrated rock physics and the reflectivity method

NASA Astrophysics Data System (ADS)

Liu, Xiwu; Guo, Zhiqi; Han, Xu

2018-06-01

A set of parallel vertical fractures embedded in a vertically transverse isotropy (VTI) background leads to orthorhombic anisotropy and corresponding azimuthal seismic responses. We conducted seismic modeling of full waveform amplitude variations versus azimuth (AVAZ) responses of anisotropic shale by integrating a rock physics model and a reflectivity method. The results indicate that the azimuthal variation of P-wave velocity tends to be more complicated for orthorhombic medium compared to the horizontally transverse isotropy (HTI) case, especially at high polar angles. Correspondingly, for the HTI layer in the theoretical model, the short axis of the azimuthal PP amplitudes at the top interface is parallel to the fracture strike, while the long axis at the bottom reflection directs the fracture strike. In contrast, the orthorhombic layer in the theoretical model shows distinct AVAZ responses in terms of PP reflections. Nevertheless, the azimuthal signatures of the R- and T-components of the mode-converted PS reflections show similar AVAZ features for the HTI and orthorhombic layers, which may imply that the PS responses are dominated by fractures. For the application to real data, a seismic-well tie based on upscaled data and a reflectivity method illustrate good agreement between the reference layers and the corresponding reflected events. Finally, the full waveform seismic AVAZ responses of the Longmaxi shale formation are computed for the cases of HTI and orthorhombic anisotropy for comparison. For the two cases, the azimuthal features represent differences mainly in amplitudes, while slightly in the phases of the reflected waveforms. Azimuth variations in the PP reflections from the reference layers show distinct behaviors for the HTI and orthorhombic cases, while the mode-converted PS reflections in terms of the R- and T-components show little differences in azimuthal features. It may suggest that the behaviors of the PS waves are dominated by vertically aligned fractures. This work provides further insight into the azimuthal seismic response of orthorhombic shales. The proposed method may help to improve the seismic-well tie, seismic interpretation, and inversion results using an azimuth anisotropy dataset.

The distinct character of anisotropy and intermittency in inertial and kinetic range solar wind plasma turbulence

NASA Astrophysics Data System (ADS)

Kiyani, Khurom; Chapman, Sandra; Osman, Kareem; Sahraoui, Fouad; Hnat, Bogdan

2014-05-01

The anisotropic nature of the scaling properties of solar wind magnetic turbulence fluctuations is investigated scale by scale using high cadence in situ magnetic field measurements from the Cluster, ACE and STEREO spacecraft missions in both fast and slow quiet solar wind conditions. The data span five decades in scales from the inertial range to the electron Larmor radius. We find a clear transition in scaling behaviour between the inertial and kinetic range of scales, which provides a direct, quantitative constraint on the physical processes that mediate the cascade of energy through these scales. In the inertial (magnetohydrodynamic) range the statistical nature of turbulent fluctuations are known to be anisotropic, both in the vector components of the magnetic field fluctuations (variance anisotropy) and in the spatial scales of these fluctuations (wavevector or k-anisotropy). We show for the first time that, when measuring parallel to the local magnetic field direction, the full statistical signature of the magnetic and Elsasser field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multi-exponent statistics observed when the local magnetic field is perpendicular to the flow direction. These observations suggest the weakness, or absence, of a parallel magnetofluid turbulence energy cascade. In contrast to the inertial range, there is a successive increase toward isotropy between parallel and transverse power at scales below the ion Larmor radius, with isotropy being achieved at the electron Larmor radius. Computing higher-order statistics, we show that the full statistical signature of both parallel, and perpendicular fluctuations at scales below the ion Larmor radius are that of an isotropic globally scale-invariant non-Gaussian process. Lastly, we perform a survey of multiple intervals of quiet solar wind sampled under different plasma conditions (fast, slow wind; plasma beta etc.) and find that the above results on the scaling transition between inertial and kinetic range scales are qualitatively robust, and that quantitatively, there is a spread in the values of the scaling exponents.

Dynamics of the universe and spontaneous symmetry breaking

NASA Technical Reports Server (NTRS)

Kazanas, D.

1980-01-01

It is shown that the presence of a phase transition early in the history of the universe, associated with spontaneous symmetry breaking (believed to take place at very high temperatures at which the various fundamental interactions unify), significantly modifies its dynamics and evolution. This is due to the energy 'pumping' during the phase transition from the vacuum to the substance, rather than the gravitating effects of the vacuum. The expansion law of the universe then differs substantially from the relation considered so far for the very early time expansion. In particular it is shown that under certain conditions this expansion law is exponential. It is further argued that under reasonable assumptions for the mass of the associated Higgs boson this expansion stage could last long enough to potentially account for the observed isotropy of the universe.

Extension of relativistic dissipative hydrodynamics to third order

NASA Astrophysics Data System (ADS)

El, Andrej; Xu, Zhe; Greiner, Carsten

2010-04-01

Following the procedure introduced by Israel and Stewart, we expand the entropy current up to the third order in the shear stress tensor παβ and derive a novel third-order evolution equation for παβ. This equation is solved for the one-dimensional Bjorken boost-invariant expansion. The scaling solutions for various values of the shear viscosity to the entropy density ratio η/s are shown to be in very good agreement with those obtained from kinetic transport calculations. For the pressure isotropy starting with 1 at τ0=0.4 fm/c, the third-order corrections to Israel-Stewart theory are approximately 10% for η/s=0.2 and more than a factor of 2 for η/s=3. We also estimate all higher-order corrections to Israel-Stewart theory and demonstrate their importance in describing highly viscous matters.

Adaptive lenticular microlens array based on voltage-induced waves at the surface of polyvinyl chloride/dibutyl phthalate gels.

PubMed

Xu, Miao; Jin, Boya; He, Rui; Ren, Hongwen

2016-04-18

We report a new approach to preparing a lenticular microlens array (LMA) using polyvinyl chloride (PVC)/dibutyl phthalate (DBP) gels. The PVD/DBP gels coated on a glass substrate form a membrane. With the aid of electrostatic repulsive force, the surface of the membrane can be reconfigured with sinusoidal waves by a DC voltage. The membrane with wavy surface functions as a LMA. By switching over the anode and cathode, the convex shape of each lenticular microlens in the array can be converted to the concave shape. Therefore, the LMA can present a large dynamic range. The response time is relatively fast and the driving voltage is low. With the advantages of compact structure, optical isotropy, and good mechanical stability, our LMA has potential applications in imaging, information processing, biometrics, and displays.

Large-scale Distribution of Arrival Directions of Cosmic Rays Detected Above 1018 eV at the Pierre Auger Observatory

NASA Astrophysics Data System (ADS)

Pierre Auger Collaboration; Abreu, P.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Albuquerque, I. F. M.; Allard, D.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Alves Batista, R.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Antiči'c, T.; Aramo, C.; Arganda, E.; Arqueros, F.; Asorey, H.; Assis, P.; Aublin, J.; Ave, M.; Avenier, M.; Avila, G.; Badescu, A. M.; Balzer, M.; Barber, K. B.; Barbosa, A. F.; Bardenet, R.; Barroso, S. L. C.; Baughman, B.; Bäuml, J.; Baus, C.; Beatty, J. J.; Becker, K. H.; Bellétoile, A.; Bellido, J. A.; BenZvi, S.; Berat, C.; Bertou, X.; Biermann, P. L.; Billoir, P.; Blanco, F.; Blanco, M.; Bleve, C.; Blümer, H.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Bonino, R.; Borodai, N.; Brack, J.; Brancus, I.; Brogueira, P.; Brown, W. C.; Bruijn, R.; Buchholz, P.; Bueno, A.; Buroker, L.; Burton, R. E.; Caballero-Mora, K. S.; Caccianiga, B.; Caramete, L.; Caruso, R.; Castellina, A.; Catalano, O.; Cataldi, G.; Cazon, L.; Cester, R.; Chauvin, J.; Cheng, S. H.; Chiavassa, A.; Chinellato, J. A.; Chirinos Diaz, J.; Chudoba, J.; Cilmo, M.; Clay, R. W.; Cocciolo, G.; Collica, L.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cook, H.; Cooper, M. J.; Coppens, J.; Cordier, A.; Coutu, S.; Covault, C. E.; Creusot, A.; Criss, A.; Cronin, J.; Curutiu, A.; Dagoret-Campagne, S.; Dallier, R.; Daniel, B.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; De Domenico, M.; De Donato, C.; de Jong, S. J.; De La Vega, G.; de Mello Junior, W. J. M.; de Mello Neto, J. R. T.; De Mitri, I.; de Souza, V.; de Vries, K. D.; del Peral, L.; del Río, M.; Deligny, O.; Dembinski, H.; Dhital, N.; Di Giulio, C.; Díaz Castro, M. L.; Diep, P. N.; Diogo, F.; Dobrigkeit, C.; Docters, W.; D'Olivo, J. C.; Dong, P. N.; Dorofeev, A.; dos Anjos, J. C.; Dova, M. T.; D'Urso, D.; Dutan, I.; Ebr, J.; Engel, R.; Erdmann, M.; Escobar, C. O.; Espadanal, J.; Etchegoyen, A.; Facal San Luis, P.; Falcke, H.; Fang, K.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Ferguson, A. P.; Fick, B.; Figueira, J. M.; Filevich, A.; Filipčič, A.; Fliescher, S.; Fracchiolla, C. E.; Fraenkel, E. D.; Fratu, O.; Fröhlich, U.; Fuchs, B.; Gaior, R.; Gamarra, R. F.; Gambetta, S.; García, B.; Garcia Roca, S. T.; Garcia-Gamez, D.; Garcia-Pinto, D.; Garilli, G.; Gascon Bravo, A.; Gemmeke, H.; Ghia, P. L.; Giller, M.; Gitto, J.; Glass, H.; Gold, M. S.; Golup, G.; Gomez Albarracin, F.; Gómez Berisso, M.; Gómez Vitale, P. F.; Gonçalves, P.; Gonzalez, J. G.; Gookin, B.; Gorgi, A.; Gouffon, P.; Grashorn, E.; Grebe, S.; Griffith, N.; Grillo, A. F.; Guardincerri, Y.; Guarino, F.; Guedes, G. P.; Hansen, P.; Harari, D.; Harrison, T. A.; Harton, J. L.; Haungs, A.; Hebbeker, T.; Heck, D.; Herve, A. E.; Hill, G. C.; Hojvat, C.; Hollon, N.; Holmes, V. C.; Homola, P.; Hörandel, J. R.; Horvath, P.; Hrabovský, M.; Huber, D.; Huege, T.; Insolia, A.; Ionita, F.; Italiano, A.; Jansen, S.; Jarne, C.; Jiraskova, S.; Josebachuili, M.; Kadija, K.; Kampert, K. H.; Karhan, P.; Kasper, P.; Katkov, I.; Kégl, B.; Keilhauer, B.; Keivani, A.; Kelley, J. L.; Kemp, E.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Knapp, J.; Koang, D.-H.; Kotera, K.; Krohm, N.; Krömer, O.; Kruppke-Hansen, D.; Kuempel, D.; Kulbartz, J. K.; Kunka, N.; La Rosa, G.; Lachaud, C.; LaHurd, D.; Latronico, L.; Lauer, R.; Lautridou, P.; Le Coz, S.; Leão, M. S. A. B.; Lebrun, D.; Lebrun, P.; Leigui de Oliveira, M. A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; López, R.; Lopez Agüera, A.; Louedec, K.; Lozano Bahilo, J.; Lu, L.; Lucero, A.; Ludwig, M.; Lyberis, H.; Maccarone, M. C.; Macolino, C.; Maldera, S.; Maller, J.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Marin, J.; Marin, V.; Maris, I. C.; Marquez Falcon, H. R.; Marsella, G.; Martello, D.; Martin, L.; Martinez, H.; Martínez Bravo, O.; Martraire, D.; Masías Meza, J. J.; Mathes, H. J.; Matthews, J.; Matthews, J. A. J.; Matthiae, G.; Maurel, D.; Maurizio, D.; Mazur, P. O.; Medina-Tanco, G.; Melissas, M.; Melo, D.; Menichetti, E.; Menshikov, A.; Mertsch, P.; Messina, S.; Meurer, C.; Meyhandan, R.; Mi'canovi'c, S.; Micheletti, M. I.; Minaya, I. A.; Miramonti, L.; Molina-Bueno, L.; Mollerach, S.; Monasor, M.; Monnier Ragaigne, D.; Montanet, F.; Morales, B.; Morello, C.; Moreno, E.; Moreno, J. C.; Mostafá, M.; Moura, C. A.; Muller, M. A.; Müller, G.; Münchmeyer, M.; Mussa, R.; Navarra, G.; Navarro, J. L.; Navas, S.; Necesal, P.; Nellen, L.; Nelles, A.; Neuser, J.; Nhung, P. T.; Niechciol, M.; Niemietz, L.; Nierstenhoefer, N.; Nitz, D.; Nosek, D.; Nožka, L.; Oehlschläger, J.; Olinto, A.; Ortiz, M.; Pacheco, N.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Palmieri, N.; Parente, G.; Parizot, E.; Parra, A.; Pastor, S.; Paul, T.; Pech, M.; Peķala, J.; Pelayo, R.; Pepe, I. M.; Perrone, L.; Pesce, R.; Petermann, E.; Petrera, S.; Petrolini, A.; Petrov, Y.; Pfendner, C.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Plum, M.; Ponce, V. H.; Pontz, M.; Porcelli, A.; Privitera, P.; Prouza, M.; Quel, E. J.; Querchfeld, S.; Rautenberg, J.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Riggi, S.; Risse, M.; Ristori, P.; Rivera, H.; Rizi, V.; Roberts, J.; Rodrigues de Carvalho, W.; Rodriguez, G.; Rodriguez Cabo, I.; Rodriguez Martino, J.; Rodriguez Rojo, J.; Rodríguez-Frías, M. D.; Ros, G.; Rosado, J.; Rossler, T.; Roth, M.; Rouillé-d'Orfeuil, B.; Roulet, E.; Rovero, A. C.; Rühle, C.; Saftoiu, A.; Salamida, F.; Salazar, H.; Salesa Greus, F.; Salina, G.; Sánchez, F.; Santo, C. E.; Santos, E.; Santos, E. M.; Sarazin, F.; Sarkar, B.; Sarkar, S.; Sato, R.; Scharf, N.; Scherini, V.; Schieler, H.; Schiffer, P.; Schmidt, A.; Scholten, O.; Schoorlemmer, H.; Schovancova, J.; Schovánek, P.; Schröder, F.; Schuster, D.; Sciutto, S. J.; Scuderi, M.; Segreto, A.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sidelnik, I.; Sigl, G.; Silva Lopez, H. H.; Sima, O.; 'Smiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sorokin, J.; Spinka, H.; Squartini, R.; Srivastava, Y. N.; Stanic, S.; Stapleton, J.; Stasielak, J.; Stephan, M.; Stutz, A.; Suarez, F.; Suomijärvi, T.; Supanitsky, A. D.; Šuša, T.; Sutherland, M. S.; Swain, J.; Szadkowski, Z.; Szuba, M.; Tapia, A.; Tartare, M.; Taşcău, O.; Tcaciuc, R.; Thao, N. T.; Thomas, D.; Tiffenberg, J.; Timmermans, C.; Tkaczyk, W.; Todero Peixoto, C. J.; Toma, G.; Tomankova, L.; Tomé, B.; Tonachini, A.; Torralba Elipe, G.; Travnicek, P.; Tridapalli, D. B.; Tristram, G.; Trovato, E.; Tueros, M.; Ulrich, R.; Unger, M.; Urban, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van Aar, G.; van den Berg, A. M.; van Velzen, S.; van Vliet, A.; Varela, E.; Vargas Cárdenas, B.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Verzi, V.; Vicha, J.; Videla, M.; Villaseñor, L.; Wahlberg, H.; Wahrlich, P.; Wainberg, O.; Walz, D.; Watson, A. A.; Weber, M.; Weidenhaupt, K.; Weindl, A.; Werner, F.; Westerhoff, S.; Whelan, B. J.; Widom, A.; Wieczorek, G.; Wiencke, L.; Wilczyńska, B.; Wilczyński, H.; Will, M.; Williams, C.; Winchen, T.; Wommer, M.; Wundheiler, B.; Yamamoto, T.; Yapici, T.; Younk, P.; Yuan, G.; Yushkov, A.; Zamorano Garcia, B.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zaw, I.; Zepeda, A.; Zhou, J.; Zhu, Y.; Zimbres Silva, M.; Ziolkowski, M.

2012-12-01

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 1018 eV at the Pierre Auger Observatory is presented. This search is performed as a function of both declination and right ascension in several energy ranges above 1018 eV, and reported in terms of dipolar and quadrupolar coefficients. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Assuming that any cosmic-ray anisotropy is dominated by dipole and quadrupole moments in this energy range, upper limits on their amplitudes are derived. These upper limits allow us to test the origin of cosmic rays above 1018 eV from stationary Galactic sources densely distributed in the Galactic disk and predominantly emitting light particles in all directions.

Closing in on the large-scale CMB power asymmetry

NASA Astrophysics Data System (ADS)

Contreras, D.; Hutchinson, J.; Moss, A.; Scott, D.; Zibin, J. P.

2018-03-01

Measurements of the cosmic microwave background (CMB) temperature anisotropies have revealed a dipolar asymmetry in power at the largest scales, in apparent contradiction with the statistical isotropy of standard cosmological models. The significance of the effect is not very high, and is dependent on a posteriori choices. Nevertheless, a number of models have been proposed that produce a scale-dependent asymmetry. We confront several such models for a physical, position-space modulation with CMB temperature observations. We find that, while some models that maintain the standard isotropic power spectrum are allowed, others, such as those with modulated tensor or uncorrelated isocurvature modes, can be ruled out on the basis of the overproduction of isotropic power. This remains the case even when an extra isocurvature mode fully anticorrelated with the adiabatic perturbations is added to suppress power on large scales.

The continuum spectral characteristics of gamma-ray bursts observed by BATSE

NASA Technical Reports Server (NTRS)

Pendleton, Geoffrey N.; Paciesas, William S.; Briggs, Michael S.; Mallozzi, Robert S.; Koshut, Tom M.; Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.; Harmon, Alan B.; Kouveliotou, Chryssa

1994-01-01

Distributions of the continuum spectral characteristics of 260 bursts in the first Burst And Transient Source Experiement (BATSE) catalog are presented. The data are derived from flux calculated from BATSE Large Area Detector (LAD) four-channel discriminator data. The data are converted from counts to protons using a direct spectral inversion technique to remove the effects of atmospheric scattering and the energy dependence of the detector angular response. Although there are intriguing clusters of bursts in the spectral hardness ratio distributions, no evidence for the presence of distinct burst classes based in spectral hardness ratios alone is found. All subsets of bursts selected for their spectral characteristics in this analysis exhibit spatial distributions consistent with isotropy. The spectral diversity of the burst population appears to be caused largely by the highly variable nature of the burst production mechanisms themselves.

Sustainably powering wearable electronics solely by biomechanical energy

PubMed Central

Wang, Jie; Li, Shengming; Yi, Fang; Zi, Yunlong; Lin, Jun; Wang, Xiaofeng; Xu, Youlong; Wang, Zhong Lin

2016-01-01

Harvesting biomechanical energy is an important route for providing electricity to sustainably drive wearable electronics, which currently still use batteries and therefore need to be charged or replaced/disposed frequently. Here we report an approach that can continuously power wearable electronics only by human motion, realized through a triboelectric nanogenerator (TENG) with optimized materials and structural design. Fabricated by elastomeric materials and a helix inner electrode sticking on a tube with the dielectric layer and outer electrode, the TENG has desirable features including flexibility, stretchability, isotropy, weavability, water-resistance and a high surface charge density of 250 μC m−2. With only the energy extracted from walking or jogging by the TENG that is built in outsoles, wearable electronics such as an electronic watch and fitness tracker can be immediately and continuously powered. PMID:27677971

Anisotropic shrinkage of insect air sacs revealed in vivo by X-ray microtomography

NASA Astrophysics Data System (ADS)

Xu, Liang; Chen, Rongchang; Du, Guohao; Yang, Yiming; Wang, Feixiang; Deng, Biao; Xie, Honglan; Xiao, Tiqiao

2016-09-01

Air sacs are thought to be the bellows for insect respiration. However, their exact mechanism of action as a bellows remains unclear. A direct way to investigate this problem is in vivo observation of the changes in their three-dimensional structures. Therefore, four-dimensional X-ray phase contrast microtomography is employed to solve this puzzle. Quantitative analysis of three-dimensional image series reveals that the compression of the air sac during respiration in bell crickets exhibits obvious anisotropic characteristics both longitudinally and transversely. Volumetric changes of the tracheal trunks in the prothorax further strengthen the evidence of this finding. As a result, we conclude that the shrinkage and expansion of the insect air sac is anisotropic, contrary to the hypothesis of isotropy, thereby providing new knowledge for further research on the insect respiratory system.

On the mathematical modeling of the Reynolds stress's equations

NASA Technical Reports Server (NTRS)

Lin, Avi

1990-01-01

By considering the Reynolds stress equations as a possible descriptor of complex turbulent fields, pressure-velocity interaction and turbulence dissipation are studied as two of the main physical contributions to Reynolds stress balancing in turbulent flow fields. It is proven that the pressure interaction term contains turbulence generation elements. However, the usual 'return to isotropy' element appears more weakly than in the standard models. In addition, convection-like elements are discovered mathematically, but there is no mathematical evidence that the pressure fluctuations contribute to the turbulent transport mechanism. Calculations of some simple one-dimensional fields indicate that this extra convection, rather than the turbulent transport, is needed mathematically. Similarly, an expression for the turbulence dissipation is developed. The end result is a dynamic equation for the dissipation tensor which is based on the tensorial length scales.

Finite Element Estimation of Meteorite Structural Properties

NASA Technical Reports Server (NTRS)

Hart, Kenneth Arthur

2015-01-01

The goal of the project titled Asteroid Threat Assessment at NASA Ames Research Center is to develop risk assessment tools. The expertise in atmospheric entry in the Entry Systems and Technology Division is being used to describe the complex physics of meteor breakup in the atmosphere. The breakup of a meteor is dependent on its structural properties, including homogeneity of the material. The present work describes an 11-week effort in which a literature survey was carried for structural properties of meteoritic material. In addition, the effect of scale on homogeneity isotropy was studied using a Monte Carlo approach in Nastran. The properties were then in a static structural response simulation of an irregularly-shape meteor (138-scale version of Asteroid Itokawa). Finally, an early plan was developed for doctoral research work at Georgia Tech. in the structural failure fragmentation of meteors.

Cosmological structure formation

NASA Technical Reports Server (NTRS)

Schramm, David N.

1991-01-01

A summary of the current forefront problem of physical cosmology, the formation of structures (galaxies, clusters, great walls, etc.) in the universe is presented. Solutions require two key ingredients: (1) matter; and (2) seeds. Regarding the matter, it now seems clear that both baryonic and non-baryonic matter are required. Whether the non-baryonic matter is hot or cold depends on the choice of seeds. Regarding the seeds, both density fluctuations and topological defects are discussed. The combination of isotropy of the microwave background and the recent observations indicating more power on large scales have severly constrained, if not eliminated, Gaussian fluctuations with equal power on all scales, regardless of the eventual resolution of both the matter and seed questions. It is important to note that all current structure formation ideas require new physics beyond SU(3) x SU(2) x U(1).

Numerical and experimental investigation of turbine blade film cooling

NASA Astrophysics Data System (ADS)

Berkache, Amar; Dizene, Rabah

2017-12-01

The blades in a gas turbine engine are exposed to extreme temperature levels that exceed the melting temperature of the material. Therefore, efficient cooling is a requirement for high performance of the gas turbine engine. The present study investigates film cooling by means of 3D numerical simulations using a commercial code: Fluent. Three numerical models, namely k-ɛ, RSM and SST turbulence models; are applied and then prediction results are compared to experimental measurements conducted by PIV technique. The experimental model realized in the ENSEMA laboratory uses a flat plate with several rows of staggered holes. The performance of the injected flow into the mainstream is analyzed. The comparison shows that the RANS closure models improve the over-predictions of center-line film cooling velocities that is caused by the limitations of the RANS method due to its isotropy eddy diffusivity.

Visualization of anisotropic-isotropic phase transformation dynamics in battery electrode particles

DOE PAGES

Wang, Jiajun; Karen Chen-Wiegart, Yu-chen; Eng, Christopher; ...

2016-08-12

Anisotropy, or alternatively, isotropy of phase transformations extensively exist in a number of solid-state materials, with performance depending on the three-dimensional transformation features. Fundamental insights into internal chemical phase evolution allow manipulating materials with desired functionalities, and can be developed via real-time multi-dimensional imaging methods. In this paper, we report a five-dimensional imaging method to track phase transformation as a function of charging time in individual lithium iron phosphate battery cathode particles during delithiation. The electrochemically driven phase transformation is initially anisotropic with a preferred boundary migration direction, but becomes isotropic as delithiation proceeds further. We also observe the expectedmore » two-phase coexistence throughout the entire charging process. Finally, we expect this five-dimensional imaging method to be broadly applicable to problems in energy, materials, environmental and life sciences.« less

Extending the ΛCDM model through shear-free anisotropies

NASA Astrophysics Data System (ADS)

Pereira, Thiago S.; Pabon, Davincy T.

2016-07-01

If the spacetime metric has anisotropic spatial curvature, one can still expand the universe as if it were isotropic, provided that the energy-momentum tensor satisfies a certain constraint. This leads to the so-called shear-free (SF) metrics, which have the interesting property of violating the cosmological principle while still preserving the isotropy of the cosmic microwave background (CMB) radiation. In this work, we show that SF cosmologies correspond to an attractor solution in the space of models with anisotropic spatial curvature. Through a rigorous definition of linear perturbation theory in these spacetimes, we show that SF models represent a viable alternative to explain the large-scale evolution of the universe, leading, in particular to a kinematically equivalent Sachs-Wolfe (SW) effect. Alternatively, we discuss some specific signatures that SF models would imprint on the temperature spectrum of CMB.

A thermoelastic transversely isotropic thick walled cylinder/disk application: An analytical solution and study

NASA Technical Reports Server (NTRS)

Arnold, S. M.

1989-01-01

A continuum theory is utilized to represent the thermoelastic behavior of a thick walled composite cylinder that can be idealized as transversely isotropic. A multiaxial statement of the constitutive theory employed is presented, as well as the out of the plane of isotropy, plane stress, and plane strain reductions. The derived analytical solution presented is valid for a cylindrical tube or thin disk with a concentric hole, subjected to internal and/or external pressure and a general radial temperature distribution. A specific problem examined is that of a thick walled cylinder subjected to an internal and external pressure loading and a linear radial temperature distribution. The results are expressed in nondimensional form and the effects on the response behavior are examined for various material properties, fiber orientation and types of loadings.

Why galactic gamma-ray bursts might depend on environment: Blast waves around neutron stars

NASA Technical Reports Server (NTRS)

Rees, Martin J.; Meszaros, Peter; Begelman, Mitchell C.

1994-01-01

Although galactic models for gamma-ray bursts are hard to reconcile with the isotropy data, the issue is still sufficiently open that both options should be explored. The most likely 'triggers' for bursts in our Galaxy would be violent disturbances in the magnetospheres of neutron stars. Any event of this kind is likely to expel magnetic flux and plasma at relativistic speed. Such ejecta would be braked by the interstellar medium (ISM), and a gamma-ray flash may result from this interaction. The radiative efficiency, of this mechanism would depend on the density of the circumstellar ISM. Therefore, even if neutron stars were uniformly distributed in space (at least within 1-2 kpc of the Sun), the observed locations of bursts would correlate with regions of above-average ISM density.

Leith diffusion model for homogeneous anisotropic turbulence

DOE PAGES

Rubinstein, Robert; Clark, Timothy T.; Kurien, Susan

2017-06-01

Here, a proposal for a spectral closure model for homogeneous anisotropic turbulence. The systematic development begins by closing the third-order correlation describing nonlinear interactions by an anisotropic generalization of the Leith diffusion model for isotropic turbulence. The correlation tensor is then decomposed into a tensorially isotropic part, or directional anisotropy, and a trace-free remainder, or polarization anisotropy. The directional and polarization components are then decomposed using irreducible representations of the SO(3) symmetry group. Under the ansatz that the decomposition is truncated at quadratic order, evolution equations are derived for the directional and polarization pieces of the correlation tensor. Here, numericalmore » simulation of the model equations for a freely decaying anisotropic flow illustrate the non-trivial effects of spectral dependencies on the different return-to-isotropy rates of the directional and polarization contributions.« less

Diffuse radiation

NASA Technical Reports Server (NTRS)

1981-01-01

A diffuse celestial radiation which is isotropic at least on a course scale were measured from the soft X-ray region to about 150 MeV, at which energy the intensity falls below that of the galactic emission for most galactic latitudes. The spectral shape, the intensity, and the established degree of isotropy of this diffuse radiation already place severe constraints on the possible explanations for this radiation. Among the extragalactic theories, the more promising explanations of the isotropic diffuse emission appear to be radiation from exceptional galaxies from matter antimatter annihilation at the boundaries of superclusters of galaxies of matter and antimatter in baryon symmetric big bang models. Other possible sources for extragalactic diffuse gamma radiation are discussed and include normal galaxies, clusters of galaxies, primordial cosmic rays interacting with intergalactic matter, primordial black holes, and cosmic ray leakage from galaxies.

Roughness encoding in human and biomimetic artificial touch: spatiotemporal frequency modulation and structural anisotropy of fingerprints.

PubMed

Oddo, Calogero Maria; Beccai, Lucia; Wessberg, Johan; Wasling, Helena Backlund; Mattioli, Fabio; Carrozza, Maria Chiara

2011-01-01

The influence of fingerprints and their curvature in tactile sensing performance is investigated by comparative analysis of different design parameters in a biomimetic artificial fingertip, having straight or curved fingerprints. The strength in the encoding of the principal spatial period of ridged tactile stimuli (gratings) is evaluated by indenting and sliding the surfaces at controlled normal contact force and tangential sliding velocity, as a function of fingertip rotation along the indentation axis. Curved fingerprints guaranteed higher directional isotropy than straight fingerprints in the encoding of the principal frequency resulting from the ratio between the sliding velocity and the spatial periodicity of the grating. In parallel, human microneurography experiments were performed and a selection of results is included in this work in order to support the significance of the biorobotic study with the artificial tactile system.

Perspective - Systematic study of Reynolds stress closure models in the computations of plane channel flows

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Sarkar, S.

1993-01-01

The roles of pressure-strain and turbulent diffusion models in the numerical calculation of turbulent plane channel flows with second-moment closure models are investigated. Three turbulent diffusion and five pressure-strain models are utilized in the computations. The main characteristics of the mean flow and the turbulent fields are compared against experimental data. All the features of the mean flow are correctly predicted by all but one of the Reynolds stress closure models. The Reynolds stress anisotropies in the log layer are predicted to varying degrees of accuracy (good to fair) by the models. None of the models could predict correctly the extent of relaxation towards isotropy in the wake region near the center of the channel. Results from the directional numerical simulation are used to further clarify this behavior of the models.

Systematic study of Reynolds stress closure models in the computations of plane channel flows

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Sarkar, S.

1992-01-01

The roles of pressure-strain and turbulent diffusion models in the numerical calculation of turbulent plane channel flows with second-moment closure models are investigated. Three turbulent diffusion and five pressure-strain models are utilized in the computations. The main characteristics of the mean flow and the turbulent fields are compared against experimental data. All the features of the mean flow are correctly predicted by all but one of the Reynolds stress closure models. The Reynolds stress anisotropies in the log layer are predicted to varying degrees of accuracy (good to fair) by the models. None of the models could predict correctly the extent of relaxation towards isotropy in the wake region near the center of the channel. Results from the directional numerical simulation are used to further clarify this behavior of the models.

Interpreting angular momentum transfer between electromagnetic multipoles using vector spherical harmonics.

PubMed

Grinter, Roger; Jones, Garth A

2018-02-01

The transfer of angular momentum between a quadrupole emitter and a dipole acceptor is investigated theoretically. Vector spherical harmonics are used to describe the angular part of the field of the mediating photon. Analytical results are presented for predicting angular momentum transfer between the emitter and absorber within a quantum electrodynamical framework. We interpret the allowability of such a process, which appears to violate conservation of angular momentum, in terms of the breakdown of the isotropy of space at the point of photon absorption (detection). That is, collapse of the wavefunction results in loss of all angular momentum information. This is consistent with Noether's Theorem and demystifies some common misconceptions about the nature of the photon. The results have implications for interpreting the detection of photons from multipole sources and offers insight into limits on information that can be extracted from quantum measurements in photonic systems.

A viscoplastic constitutive theory for metal matrix composites at high temperature

NASA Technical Reports Server (NTRS)

Robinson, David N.; Duffy, Stephen F.; Ellis, John R.

1988-01-01

A viscoplastic constitutive theory is presented for representing the high temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is assumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity.

A viscoplastic constitutive theory for metal matrix composites at high temperature

NASA Technical Reports Server (NTRS)

Robinson, D. N.; Duffy, S. F.; Ellis, J. R.

1986-01-01

A viscoplastic constitutive theory is presented for representing the high-temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is assumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient in this work is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin-walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity.

A viscoplastic constitutive theory for metal matrix composites at high temperature

NASA Technical Reports Server (NTRS)

Robinson, D. N.; Ellis, J. R.; Duffy, S. F.

1987-01-01

A viscoplastic theory is presented for representing the high-temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is presumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient in this work is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin-walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity.

Generalized self-adjustment method for statistical mechanics of composite materials

NASA Astrophysics Data System (ADS)

Pan'kov, A. A.

1997-03-01

A new method is developed for the statistical mechanics of composite materials — the generalized selfadjustment method — which makes it possible to reduce the problem of predicting effective elastic properties of composites with random structures to the solution of two simpler "averaged" problems of an inclusion with transitional layers in a medium with the desired effective elastic properties. The inhomogeneous elastic properties and dimensions of the transitional layers take into account both the "approximate" order of mutual positioning, and also the variation in the dimensions and elastics properties of inclusions through appropriate special averaged indicator functions of the random structure of the composite. A numerical calculation of averaged indicator functions and effective elastic characteristics is performed by the generalized self-adjustment method for a unidirectional fiberglass on the basis of various models of actual random structures in the plane of isotropy.

A Molecular Dynamics Simulation of the Turbulent Couette Minimal Flow Unit

NASA Astrophysics Data System (ADS)

Smith, Edward

2016-11-01

What happens to turbulent motions below the Kolmogorov length scale? In order to explore this question, a 300 million molecule Molecular Dynamics (MD) simulation is presented for the minimal Couette channel in which turbulence can be sustained. The regeneration cycle and turbulent statistics show excellent agreement to continuum based computational fluid dynamics (CFD) at Re=400. As MD requires only Newton's laws and a form of inter-molecular potential, it captures a much greater range of phenomena without requiring the assumptions of Newton's law of viscosity, thermodynamic equilibrium, fluid isotropy or the limitation of grid resolution. The fundamental nature of MD means it is uniquely placed to explore the nature of turbulent transport. A number of unique insights from MD are presented, including energy budgets, sub-grid turbulent energy spectra, probability density functions, Lagrangian statistics and fluid wall interactions. EPSRC Post Doctoral Prize Fellowship.

Why plants make puzzle cells, and how their shape emerges.

PubMed

Sapala, Aleksandra; Runions, Adam; Routier-Kierzkowska, Anne-Lise; Das Gupta, Mainak; Hong, Lilan; Hofhuis, Hugo; Verger, Stéphane; Mosca, Gabriella; Li, Chun-Biu; Hay, Angela; Hamant, Olivier; Roeder, Adrienne Hk; Tsiantis, Miltos; Prusinkiewicz, Przemyslaw; Smith, Richard S

2018-02-27

The shape and function of plant cells are often highly interdependent. The puzzle-shaped cells that appear in the epidermis of many plants are a striking example of a complex cell shape, however their functional benefit has remained elusive. We propose that these intricate forms provide an effective strategy to reduce mechanical stress in the cell wall of the epidermis. When tissue-level growth is isotropic, we hypothesize that lobes emerge at the cellular level to prevent formation of large isodiametric cells that would bulge under the stress produced by turgor pressure. Data from various plant organs and species support the relationship between lobes and growth isotropy, which we test with mutants where growth direction is perturbed. Using simulation models we show that a mechanism actively regulating cellular stress plausibly reproduces the development of epidermal cell shape. Together, our results suggest that mechanical stress is a key driver of cell-shape morphogenesis. © 2018, Sapala et al.

Large scale distribution of ultra high energy cosmic rays detected at the Pierre Auger Observatory with zenith angles up to 80°

DOE PAGES

Aab, Alexander

2015-03-30

In this study, we present the results of an analysis of the large angular scale distribution of the arrival directions of cosmic rays with energy above 4 EeV detected at the Pierre Auger Observatory including for the first time events with zenith angle between 60° and 80°. We perform two Rayleigh analyses, one in the right ascension and one in the azimuth angle distributions, that are sensitive to modulations in right ascension and declination, respectively. The largest departure from isotropy appears in themore » $$E\\gt 8$$ EeV energy bin, with an amplitude for the first harmonic in right ascension $$r_{1}^{\\alpha }=(4.4\\pm 1.0)\\times {{10}^{-2}}$$, that has a chance probability $$P(\\geqslant r_{1}^{\\alpha })=6.4\\times {{10}^{-5}}$$, reinforcing the hint previously reported with vertical events alone.« less

COBE's search for structure in the Big Bang

NASA Technical Reports Server (NTRS)

Soffen, Gerald (Editor); Guerny, Gene (Editor); Keating, Thomas (Editor); Moe, Karen (Editor); Sullivan, Walter (Editor); Truszkowski, Walt (Editor)

1989-01-01

The launch of Cosmic Background Explorer (COBE) and the definition of Earth Observing System (EOS) are two of the major events at NASA-Goddard. The three experiments contained in COBE (Differential Microwave Radiometer (DMR), Far Infrared Absolute Spectrophotometer (FIRAS), and Diffuse Infrared Background Experiment (DIRBE)) are very important in measuring the big bang. DMR measures the isotropy of the cosmic background (direction of the radiation). FIRAS looks at the spectrum over the whole sky, searching for deviations, and DIRBE operates in the infrared part of the spectrum gathering evidence of the earliest galaxy formation. By special techniques, the radiation coming from the solar system will be distinguished from that of extragalactic origin. Unique graphics will be used to represent the temperature of the emitting material. A cosmic event will be modeled of such importance that it will affect cosmological theory for generations to come. EOS will monitor changes in the Earth's geophysics during a whole solar color cycle.

A multi-detector neutron spectrometer with nearly isotropic response for environmental and workplace monitoring

NASA Astrophysics Data System (ADS)

Gómez-Ros, J. M.; Bedogni, R.; Moraleda, M.; Delgado, A.; Romero, A.; Esposito, A.

2010-01-01

This communication describes an improved design for a neutron spectrometer consisting of 6Li thermoluminescent dosemeters located at selected positions within a single moderating polyethylene sphere. The spatial arrangement of the dosemeters has been designed using the MCNPX Monte Carlo code to calculate the response matrix for 56 log-equidistant energies from 10 -9 to 100 MeV, looking for a configuration that permits to obtain a nearly isotropic response for neutrons in the energy range from thermal to 20 MeV. The feasibility of the proposed spectrometer and the isotropy of its response have been evaluated by simulating exposures to different reference and workplace neutron fields. The FRUIT code has been used for unfolding purposes. The results of the simulations as well as the experimental tests confirm the suitability of the prototype for environmental and workplace monitoring applications.

Introduction to Big Bang nucleosynthesis - Open and closed models, anisotropies

NASA Astrophysics Data System (ADS)

Tayler, R. J.

1982-10-01

A variety of observations suggest that the universe had a hot dense origin and that the pregalactic composition of the universe was determined by nuclear reactions that occurred in the first few minutes. There is no unique hot Big Bang theory, but the simplest version produces a primeval chemical composition that is in good qualitative agreement with the abundances deduced from observation. Whether or not any Big Bang theory will provide quantitative agreement with observations depends on a variety of factors in elementary particle physics (number and masses of stable or long-lived particles, half-life of neutron, structure of grand unified theories) and from observational astronomy (present mean baryon density of the universe, the Hubble constant and deceleration parameter). The influence of these factors on the abundances is discussed, as is the effect of departures from homogeneity and isotropy in the early universe.

Constraints on the Origin of Cosmic Rays above 1018 eV from Large-scale Anisotropy Searches in Data of the Pierre Auger Observatory

NASA Astrophysics Data System (ADS)

Pierre Auger Collaboration; Abreu, P.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Albuquerque, I. F. M.; Allard, D.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Alves Batista, R.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Antiči'c, T.; Aramo, C.; Arganda, E.; Arqueros, F.; Asorey, H.; Assis, P.; Aublin, J.; Ave, M.; Avenier, M.; Avila, G.; Badescu, A. M.; Balzer, M.; Barber, K. B.; Barbosa, A. F.; Bardenet, R.; Barroso, S. L. C.; Baughman, B.; Bäuml, J.; Baus, C.; Beatty, J. J.; Becker, K. H.; Bellétoile, A.; Bellido, J. A.; BenZvi, S.; Berat, C.; Bertou, X.; Biermann, P. L.; Billoir, P.; Blanco, F.; Blanco, M.; Bleve, C.; Blümer, H.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Bonino, R.; Borodai, N.; Brack, J.; Brancus, I.; Brogueira, P.; Brown, W. C.; Bruijn, R.; Buchholz, P.; Bueno, A.; Buroker, L.; Burton, R. E.; Caballero-Mora, K. S.; Caccianiga, B.; Caramete, L.; Caruso, R.; Castellina, A.; Catalano, O.; Cataldi, G.; Cazon, L.; Cester, R.; Chauvin, J.; Cheng, S. H.; Chiavassa, A.; Chinellato, J. A.; Chirinos Diaz, J.; Chudoba, J.; Cilmo, M.; Clay, R. W.; Cocciolo, G.; Collica, L.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cook, H.; Cooper, M. J.; Coppens, J.; Cordier, A.; Coutu, S.; Covault, C. E.; Creusot, A.; Criss, A.; Cronin, J.; Curutiu, A.; Dagoret-Campagne, S.; Dallier, R.; Daniel, B.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; De Domenico, M.; De Donato, C.; de Jong, S. J.; De La Vega, G.; de Mello Junior, W. J. M.; de Mello Neto, J. R. T.; De Mitri, I.; de Souza, V.; de Vries, K. D.; del Peral, L.; del Río, M.; Deligny, O.; Dembinski, H.; Dhital, N.; Di Giulio, C.; Díaz Castro, M. L.; Diep, P. N.; Diogo, F.; Dobrigkeit, C.; Docters, W.; D'Olivo, J. C.; Dong, P. N.; Dorofeev, A.; dos Anjos, J. C.; Dova, M. T.; D'Urso, D.; Dutan, I.; Ebr, J.; Engel, R.; Erdmann, M.; Escobar, C. O.; Espadanal, J.; Etchegoyen, A.; Facal San Luis, P.; Falcke, H.; Fang, K.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Ferguson, A. P.; Fick, B.; Figueira, J. M.; Filevich, A.; Filipčič, A.; Fliescher, S.; Fracchiolla, C. E.; Fraenkel, E. D.; Fratu, O.; Fröhlich, U.; Fuchs, B.; Gaior, R.; Gamarra, R. F.; Gambetta, S.; García, B.; Garcia Roca, S. T.; Garcia-Gamez, D.; Garcia-Pinto, D.; Garilli, G.; Gascon Bravo, A.; Gemmeke, H.; Ghia, P. L.; Giller, M.; Gitto, J.; Glass, H.; Gold, M. S.; Golup, G.; Gomez Albarracin, F.; Gómez Berisso, M.; Gómez Vitale, P. F.; Gonçalves, P.; Gonzalez, J. G.; Gookin, B.; Gorgi, A.; Gouffon, P.; Grashorn, E.; Grebe, S.; Griffith, N.; Grillo, A. F.; Guardincerri, Y.; Guarino, F.; Guedes, G. P.; Hansen, P.; Harari, D.; Harrison, T. A.; Harton, J. L.; Haungs, A.; Hebbeker, T.; Heck, D.; Herve, A. E.; Hill, G. C.; Hojvat, C.; Hollon, N.; Holmes, V. C.; Homola, P.; Hörandel, J. R.; Horvath, P.; Hrabovský, M.; Huber, D.; Huege, T.; Insolia, A.; Ionita, F.; Italiano, A.; Jansen, S.; Jarne, C.; Jiraskova, S.; Josebachuili, M.; Kadija, K.; Kampert, K. H.; Karhan, P.; Kasper, P.; Katkov, I.; Kégl, B.; Keilhauer, B.; Keivani, A.; Kelley, J. L.; Kemp, E.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Knapp, J.; Koang, D.-H.; Kotera, K.; Krohm, N.; Krömer, O.; Kruppke-Hansen, D.; Kuempel, D.; Kulbartz, J. K.; Kunka, N.; La Rosa, G.; Lachaud, C.; LaHurd, D.; Latronico, L.; Lauer, R.; Lautridou, P.; Le Coz, S.; Leão, M. S. A. B.; Lebrun, D.; Lebrun, P.; Leigui de Oliveira, M. A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; López, R.; Lopez Agüera, A.; Louedec, K.; Lozano Bahilo, J.; Lu, L.; Lucero, A.; Ludwig, M.; Lyberis, H.; Maccarone, M. C.; Macolino, C.; Maldera, S.; Maller, J.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Marin, J.; Marin, V.; Maris, I. C.; Marquez Falcon, H. R.; Marsella, G.; Martello, D.; Martin, L.; Martinez, H.; Martínez Bravo, O.; Martraire, D.; Masías Meza, J. J.; Mathes, H. J.; Matthews, J.; Matthews, J. A. J.; Matthiae, G.; Maurel, D.; Maurizio, D.; Mazur, P. O.; Medina-Tanco, G.; Melissas, M.; Melo, D.; Menichetti, E.; Menshikov, A.; Mertsch, P.; Messina, S.; Meurer, C.; Meyhandan, R.; Mi'canovi'c, S.; Micheletti, M. I.; Minaya, I. A.; Miramonti, L.; Molina-Bueno, L.; Mollerach, S.; Monasor, M.; Monnier Ragaigne, D.; Montanet, F.; Morales, B.; Morello, C.; Moreno, E.; Moreno, J. C.; Mostafá, M.; Moura, C. A.; Muller, M. A.; Müller, G.; Münchmeyer, M.; Mussa, R.; Navarra, G.; Navarro, J. L.; Navas, S.; Necesal, P.; Nellen, L.; Nelles, A.; Neuser, J.; Nhung, P. T.; Niechciol, M.; Niemietz, L.; Nierstenhoefer, N.; Nitz, D.; Nosek, D.; Nožka, L.; Oehlschläger, J.; Olinto, A.; Ortiz, M.; Pacheco, N.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Palmieri, N.; Parente, G.; Parizot, E.; Parra, A.; Pastor, S.; Paul, T.; Pech, M.; Peķala, J.; Pelayo, R.; Pepe, I. M.; Perrone, L.; Pesce, R.; Petermann, E.; Petrera, S.; Petrolini, A.; Petrov, Y.; Pfendner, C.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Plum, M.; Ponce, V. H.; Pontz, M.; Porcelli, A.; Privitera, P.; Prouza, M.; Quel, E. J.; Querchfeld, S.; Rautenberg, J.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Riggi, S.; Risse, M.; Ristori, P.; Rivera, H.; Rizi, V.; Roberts, J.; Rodrigues de Carvalho, W.; Rodriguez, G.; Rodriguez Cabo, I.; Rodriguez Martino, J.; Rodriguez Rojo, J.; Rodríguez-Frías, M. D.; Ros, G.; Rosado, J.; Rossler, T.; Roth, M.; Rouillé-d'Orfeuil, B.; Roulet, E.; Rovero, A. C.; Rühle, C.; Saftoiu, A.; Salamida, F.; Salazar, H.; Salesa Greus, F.; Salina, G.; Sánchez, F.; Santo, C. E.; Santos, E.; Santos, E. M.; Sarazin, F.; Sarkar, B.; Sarkar, S.; Sato, R.; Scharf, N.; Scherini, V.; Schieler, H.; Schiffer, P.; Schmidt, A.; Scholten, O.; Schoorlemmer, H.; Schovancova, J.; Schovánek, P.; Schröder, F.; Schuster, D.; Sciutto, S. J.; Scuderi, M.; Segreto, A.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sidelnik, I.; Sigl, G.; Silva Lopez, H. H.; Sima, O.; 'Smiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sorokin, J.; Spinka, H.; Squartini, R.; Srivastava, Y. N.; Stanic, S.; Stapleton, J.; Stasielak, J.; Stephan, M.; Stutz, A.; Suarez, F.; Suomijärvi, T.; Supanitsky, A. D.; Šuša, T.; Sutherland, M. S.; Swain, J.; Szadkowski, Z.; Szuba, M.; Tapia, A.; Tartare, M.; Taşcău, O.; Tcaciuc, R.; Thao, N. T.; Thomas, D.; Tiffenberg, J.; Timmermans, C.; Tkaczyk, W.; Todero Peixoto, C. J.; Toma, G.; Tomankova, L.; Tomé, B.; Tonachini, A.; Torralba Elipe, G.; Travnicek, P.; Tridapalli, D. B.; Tristram, G.; Trovato, E.; Tueros, M.; Ulrich, R.; Unger, M.; Urban, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van Aar, G.; van den Berg, A. M.; van Velzen, S.; van Vliet, A.; Varela, E.; Vargas Cárdenas, B.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Verzi, V.; Vicha, J.; Videla, M.; Villaseñor, L.; Wahlberg, H.; Wahrlich, P.; Wainberg, O.; Walz, D.; Watson, A. A.; Weber, M.; Weidenhaupt, K.; Weindl, A.; Werner, F.; Westerhoff, S.; Whelan, B. J.; Widom, A.; Wieczorek, G.; Wiencke, L.; Wilczyńska, B.; Wilczyński, H.; Will, M.; Williams, C.; Winchen, T.; Wommer, M.; Wundheiler, B.; Yamamoto, T.; Yapici, T.; Younk, P.; Yuan, G.; Yushkov, A.; Zamorano Garcia, B.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zaw, I.; Zepeda, A.; Zhou, J.; Zhu, Y.; Zimbres Silva, M.; Ziolkowski, M.

2013-01-01

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 1018 eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 1018 eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.

Adaptive microlens array based on electrically charged polyvinyl chloride/dibutyl phthalate gel

NASA Astrophysics Data System (ADS)

Xu, Miao; Ren, Hongwen

2016-09-01

We prepared an adaptive microlens array (MLA) using a polyvinyl chloride/dibutyl phthalate gel and an indium-tin-oxide (ITO) glass substrate. The gel forms a membrane on the glass substrate and the ITO electrode has a ring array pattern. When the membrane is electrically charged by a DC voltage, the surface of the membrane above each circular electrode in the ring array can be deformed with a convex shape. As a result, the membrane functions as an MLA. By applying a voltage from 20 to ˜65 V to the electrode, the focal length of each microlens can be tuned from 300 to ˜160 μm. The dynamic response time can by reduced largely by changing the polarity of the DC voltage. Due to the advantages of optical isotropy, compact structure, and good stability, our MLA has potential applications in imaging, biometrics, and electronic displays.

A new fifth parameter for transverse isotropy III: reflection and transmission coefficients

NASA Astrophysics Data System (ADS)

Kawakatsu, Hitoshi

2018-04-01

The effect of the newly defined fifth parameter, ηκ, of transverse anisotropy to the reflection and transmission coefficients, especially for P-to-S and S-to-P conversion coefficients, is examined. While ηκ systematically affects the P-to-S and S-to-P conversions, in the incidence angle range of the practical interest of receiver function studies, the effect may be asymmetric in a sense that P-wave receiver function is affected more than S-receiver function in terms of amplitude. This asymmetry may help resolving ηκ via extensive receiver function analysis. It is also found that P-wave anisotropy significantly influences P-to-S and S-to-P conversion coefficients that complicates the interpretation of receiver functions, because, for isotropic media, we typically attribute the primary receiver function signals to S-wave velocity changes but not to P-wave changes.

Electrodynamics and Spacetime Geometry: Foundations

NASA Astrophysics Data System (ADS)

Cabral, Francisco; Lobo, Francisco S. N.

2017-02-01

We explore the intimate connection between spacetime geometry and electrodynamics. This link is already implicit in the constitutive relations between the field strengths and excitations, which are an essential part of the axiomatic structure of electromagnetism, clearly formulated via integration theory and differential forms. We review the foundations of classical electromagnetism based on charge and magnetic flux conservation, the Lorentz force and the constitutive relations. These relations introduce the conformal part of the metric and allow the study of electrodynamics for specific spacetime geometries. At the foundational level, we discuss the possibility of generalizing the vacuum constitutive relations, by relaxing the fixed conditions of homogeneity and isotropy, and by assuming that the symmetry properties of the electro-vacuum follow the spacetime isometries. The implications of this extension are briefly discussed in the context of the intimate connection between electromagnetism and the geometry (and causal structure) of spacetime.

The continuum spectral characteristics of gamma ray bursts observed by BATSE

NASA Technical Reports Server (NTRS)

Pendleton, Geoffrey N.; Paciesas, William S.; Briggs, Michael S.; Mallozzi, Robert S.; Koshut, Tom M.; Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.; Harmon, Alan B.; Kouveliotou, Chryssa

1994-01-01

Distributions of the continuum spectral characteristics of 260 bursts in the first Burst and Transient Source Experiment (BATSE) catalog are presented. The data are derived from flux ratios calculated from the BATSE Large Area Detector (LAD) four channel discriminator data. The data are converted from counts to photons using a direct spectral inversion technique to remove the effects of atmospheric scattering and the energy dependence of the detector angular response. Although there are intriguing clusterings of bursts in the spectral hardness ratio distributions, no evidence for the presence of distinct burst classes based on spectral hardness ratios alone is found. All subsets of bursts selected for their spectral characteristics in this analysis exhibit spatial distributions consistent with isotropy. The spectral diversity of the burst population appears to be caused largely by the highly variable nature of the burst production mechanisms themselves.

Quantum chaos and breaking of all anti-unitary symmetries in Rydberg excitons.

PubMed

Aßmann, Marc; Thewes, Johannes; Fröhlich, Dietmar; Bayer, Manfred

2016-07-01

Symmetries are the underlying principles of fundamental interactions in nature. Chaos in a quantum system may emerge from breaking these symmetries. Compared to vacuum, crystals are attractive for studying quantum chaos, as they not only break spatial isotropy, but also lead to novel quasiparticles with modified interactions. Here we study yellow Rydberg excitons in cuprous oxide which couple strongly to the vacuum light field and interact significantly with crystal phonons, leading to inversion symmetry breaking. In a magnetic field, time-reversal symmetry is also broken and the exciton states show a complex splitting pattern, resulting in quadratic level repulsion for small splittings. In contrast to atomic chaotic systems in a magnetic field, which show only a linear level repulsion, this is a signature of a system where all anti-unitary symmetries are broken simultaneously. This behaviour can otherwise be found only for the electro-weak interaction or engineered billiards.

Suprathermal Ion Populations in ICF Plasmas - Implications for Diagnostics and Ignition

NASA Astrophysics Data System (ADS)

Knapp, Patrick; Schmit, Paul; Sinars, Daniel

2013-10-01

We report on investigations into the effects of suprathermal ion populations on neutron production in Inertial Confinement and Magneto-Inertial Fusion plasmas. In a recent article we showed that a suprathermal population taking the form of a power-law in energy will significantly modify the shape and width of the neutron spectrum and can dramatically increase the fusion reactivity compared to the Maxwellian case. Specific diagnostic signatures are discussed in detail. We build on this work to include the effect of an applied magnetic field on the neutron spectra, isotropy and production rate. Finally, the impact that these modifications have on the ability to reach high fusion yields and ignition is discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration.

Why plants make puzzle cells, and how their shape emerges

PubMed Central

Routier-Kierzkowska, Anne-Lise; Das Gupta, Mainak; Hong, Lilan; Hofhuis, Hugo; Verger, Stéphane; Mosca, Gabriella; Li, Chun-Biu; Hay, Angela; Hamant, Olivier; Roeder, Adrienne HK; Tsiantis, Miltos; Prusinkiewicz, Przemyslaw

2018-01-01

The shape and function of plant cells are often highly interdependent. The puzzle-shaped cells that appear in the epidermis of many plants are a striking example of a complex cell shape, however their functional benefit has remained elusive. We propose that these intricate forms provide an effective strategy to reduce mechanical stress in the cell wall of the epidermis. When tissue-level growth is isotropic, we hypothesize that lobes emerge at the cellular level to prevent formation of large isodiametric cells that would bulge under the stress produced by turgor pressure. Data from various plant organs and species support the relationship between lobes and growth isotropy, which we test with mutants where growth direction is perturbed. Using simulation models we show that a mechanism actively regulating cellular stress plausibly reproduces the development of epidermal cell shape. Together, our results suggest that mechanical stress is a key driver of cell-shape morphogenesis. PMID:29482719

Spectrum of perturbations in anisotropic inflationary universe with vector hair

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

Himmetoglu, Burak, E-mail: burak@physics.umn.edu

2010-03-01

We study both the background evolution and cosmological perturbations of anisotropic inflationary models supported by coupled scalar and vector fields. The models we study preserve the U(1) gauge symmetry associated with the vector field, and therefore do not possess instabilities associated with longitudinal modes (which instead plague some recently proposed models of vector inflation and curvaton). We first intoduce a model in which the background anisotropy slowly decreases during inflation; we then confirm the stability of the background solution by studying the quadratic action for all the perturbations of the model. We then compute the spectrum of the h{sub ×}more » gravitational wave polarization. The spectrum we find breaks statistical isotropy at the largest scales and reduces to the standard nearly scale invariant form at small scales. We finally discuss the possible relevance of our results to the large scale CMB anomalies.« less

Comparison of the plasma pressure distributions over the equatorial plane and at low altitudes under magnetically quiet conditions

NASA Astrophysics Data System (ADS)

Antonova, E. E.; Vorobjev, V. G.; Kirpichev, I. P.; Yagodkina, O. I.

2014-05-01

The distribution of plasma pressure over the equatorial plane is compared with the plasma pressure and the position of the electron precipitation boundaries at low altitudes under the conditions of low geomagnetic activity. The pressure at the equatorial plane is determined using data of the THEMIS international five-satellite mission; the pressure at low altitudes, using data of the DMSP satellites. Plasma pressure isotropy and the validity of the condition of the magnetostatic equilibrium at a low level of geomagnetic activity are taken into account. Plasma pressure in such a case is constant along the magnetic field line and can be considered a "natural tracer" of the field line. It is shown that the plasma ring surrounding the Earth at geocentric distances of ˜6 to ˜10-12 R E is the main source of the precipitations in the auroral oval.

Dynamic Jahn-Teller effect: Calculation of fine structure spectrum, isotope shift and Zeeman behavior at deep center Ni2+ in CdS

NASA Astrophysics Data System (ADS)

Schoepp, Juergen

The internal transition of the deep center Ni2+ in II to IV semiconductor cadmium sulfide is examined with reference to crystal field theory. An algorithm was developed for calculation, in a basis fitted to trigonal symmetry, of fine structure operator matrix which is made of the sum of operators from spin trajectory coupling, trigonal field and electron phonon coupling. The dependence of energy level on the mass was calculated in order to examine the isotropy effect at Ni2+ transition. The mass dependence of phonon energy was estimated in an atomic cluster by using a valence force model from Keating for elastic energy. The Zeeman behavior of Ni2+ transition was examined for magnetic fields; the Zeeman operator was added to the fine structure operator and the resulting matrix was diagonalized. It is noticed that calculations are quantitatively and qualitatively in agreement with experiments.

The origin of density fluctuations in the 'new inflationary universe'

NASA Technical Reports Server (NTRS)

Turner, M. S.

1983-01-01

Cosmological mysteries which are not explained by the Big Bang hypothesis but may be approached by a revamped inflationary universe model are discussed. Attention is focused on the isotropy, the large-scale homogeneity, small-scale inhomogeneity, the oldness/flatness of the universe, and the baryon asymmetry. The universe is assumed to start in the lowest energy state, be initially dominated by false vacuum energy, enter a de Sitter phase, and then cross a barrier which is followed by the formation of fluctuation regions that lead to structure. The scalar fields (perturbation regions) experience quantum fluctuations which produce spontaneous symmetry breaking on a large scale. The scalar field value would need to be much greater than the expansion rate during the de Sitter epoch. A supersymmetric (flat) potential which satisfies the requirement, yields fluctuations of the right magnitude, and allows inflation to occur is described.

Photonic mesophases from cut rod rotators

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

Stelson, Angela C.; Liddell Watson, Chekesha M., E-mail: cml66@cornell.edu; Avendano, Carlos

2016-01-14

The photonic band properties of random rotator mesophases are calculated using supercell methods applied to cut rods on a hexagonal lattice. Inspired by the thermodynamic mesophase for anisotropic building blocks, we vary the shape factor of cut fraction for the randomly oriented basis. We find large, stable bandgaps with high gap isotropy in the inverted and direct structures as a function of cut fraction, dielectric contrast, and filling fraction. Bandgap sizes up to 34.5% are maximized at high dielectric contrast for rods separated in a matrix. The bandgaps open at dielectric contrasts as low as 2.0 for the transverse magneticmore » polarization and 2.25 for the transverse electric polarization. Additionally, the type of scattering that promotes the bandgap is correlated with the effect of disorder on bandgap size. Slow light properties are investigated in waveguide geometry and slowdown factors up to 5 × 10{sup 4} are found.« less

Smoothing Spline ANOVA Decomposition of Arbitrary Splines: An Application to Eye Movements in Reading

PubMed Central

Matuschek, Hannes; Kliegl, Reinhold; Holschneider, Matthias

2015-01-01

The Smoothing Spline ANOVA (SS-ANOVA) requires a specialized construction of basis and penalty terms in order to incorporate prior knowledge about the data to be fitted. Typically, one resorts to the most general approach using tensor product splines. This implies severe constraints on the correlation structure, i.e. the assumption of isotropy of smoothness can not be incorporated in general. This may increase the variance of the spline fit, especially if only a relatively small set of observations are given. In this article, we propose an alternative method that allows to incorporate prior knowledge without the need to construct specialized bases and penalties, allowing the researcher to choose the spline basis and penalty according to the prior knowledge of the observations rather than choosing them according to the analysis to be done. The two approaches are compared with an artificial example and with analyses of fixation durations during reading. PMID:25816246

Second order modeling of boundary-free turbulent shear flows

NASA Technical Reports Server (NTRS)

Shih, T.-H.; Chen, Y.-Y.; Lumley, J. L.

1991-01-01

A set of realizable second order models for boundary-free turbulent flows is presented. The constraints on second order models based on the realizability principle are re-examined. The rapid terms in the pressure correlations for both the Reynolds stress and the passive scalar flux equations are constructed to exactly satisfy the joint realizability. All other model terms (return-to-isotropy, third moments, and terms in the dissipation equations) already satisfy realizability. To correct the spreading rate of the axisymmetric jet, an extra term is added to the dissipation equation which accounts for the effect of mean vortex stretching on dissipation. The test flows used in this study are the mixing shear layer, plane jet, axisymmetric jet, and plane wake. The numerical solutions show that the unified model equations predict all these flows reasonably. It is expected that these models would be suitable for more complex and critical flows.

Riemannian geometry of Hamiltonian chaos: hints for a general theory.

PubMed

Cerruti-Sola, Monica; Ciraolo, Guido; Franzosi, Roberto; Pettini, Marco

2008-10-01

We aim at assessing the validity limits of some simplifying hypotheses that, within a Riemmannian geometric framework, have provided an explanation of the origin of Hamiltonian chaos and have made it possible to develop a method of analytically computing the largest Lyapunov exponent of Hamiltonian systems with many degrees of freedom. Therefore, a numerical hypotheses testing has been performed for the Fermi-Pasta-Ulam beta model and for a chain of coupled rotators. These models, for which analytic computations of the largest Lyapunov exponents have been carried out in the mentioned Riemannian geometric framework, appear as paradigmatic examples to unveil the reason why the main hypothesis of quasi-isotropy of the mechanical manifolds sometimes breaks down. The breakdown is expected whenever the topology of the mechanical manifolds is nontrivial. This is an important step forward in view of developing a geometric theory of Hamiltonian chaos of general validity.

Observations of the diffuse near-UV radiation field

NASA Technical Reports Server (NTRS)

Murthy, J.; Henry, R. C.; Feldman, P. D.; Tennyson, P. D.

1990-01-01

The diffuse radiation field from 1650-3100 A has been observed by spectrometer aboard the Space Shuttle, and the contributions of the zodiacal light an the diffuse cosmic background to the signal have been derived. Colors ranging from 0.65 to 1.2 are found for the zodiacal light with an almost linear increase in the color with ecliptic latitude. This rise in color is due to UV brightness remaining almost constant while the visible brightnesses drop by almost a factor of two. This is interpreted as evidence that the grains responsible for the UV scattering have much more uniform distribution with distance from the ecliptic plane than do those grains responsible for the visible scattering. Intensities for the cosmic diffuse background ranging from 300 units to 900 units are found which are not consistent with either a correlation with N(H I) or with spatial isotropy.

Band gaps in periodically magnetized homogeneous anisotropic media

NASA Astrophysics Data System (ADS)

Merzlikin, A. M.; Levy, M.; Vinogradov, A. P.; Wu, Z.; Jalali, A. A.

2010-11-01

In [A. M. Merzlikin, A. P. Vinogradov, A. V. Dorofeenko, M. Inoue, M. Levy, A. B. Granovsky, Physica B 394 (2007) 277] it is shown that in anisotropic magnetophotonic crystal made of anisotropic dielectric layers and isotropic magneto-optical layers the magnetization leads to formation of additional band gaps (BG) inside the Brillouin zones. Due to the weakness of the magneto-optical effects the width of these BG is much smaller than that of usual BG forming on the boundaries of Brillouin zones. In the present communication we show that though the anisotropy suppresses magneto-optical effects. An anisotropic magnetophotonic crystal made of anisotropic dielectric layers and anisotropic magneto-optical; the width of additional BG may be much greater than the width of the usual Brillouin BG. Anisotropy tends to suppress Brillouin zone boundary band gap formation because the anisotropy suppresses magneto-optical properties, while degenerate band gap formation occurs around points of effective isotropy and is not suppressed.

Electron precipitation in the post midnight sector of the auroral zones. [on the Explorer 40 satellite

NASA Technical Reports Server (NTRS)

Frank, L. A.; Saflekos, N. A.; Ackerson, K. L.

1975-01-01

Comprehensive measurements of the angular distributions and energy spectra of electron intensities with electrostatic analyzer arrays on board the low-altitude satellite Injun 5 are reported. These are for the post-midnight sector of the auroral zones during the high-intensity events accompanying magnetic substorms. Precipitation features on closed terrestrial field lines well equatorward of the trapping boundary for energetic electrons with E greater than 45 keV were examined. No evidences of maxima in the differential energy spectra or of strongly field-aligned currents which are indicative of quasi-static electric fields aligned parallel to the geomagnetic field were found. Precipitation of low-energy electron intensities fluctuated on time scales greater than 2 seconds as viewed at the satellite position. This precipitation was characterized by isotropy for all pitch angles outside the atmospheric backscatter cone.

Noise focusing in neuronal tissues: Symmetry breaking and localization in excitable networks with quenched disorder

NASA Astrophysics Data System (ADS)

Orlandi, Javier G.; Casademunt, Jaume

2017-05-01

We introduce a coarse-grained stochastic model for the spontaneous activity of neuronal cultures to explain the phenomenon of noise focusing, which entails localization of the noise activity in excitable networks with metric correlations. The system is modeled as a continuum excitable medium with a state-dependent spatial coupling that accounts for the dynamics of synaptic connections. The most salient feature is the emergence at the mesoscale of a vector field V (r ) , which acts as an advective carrier of the noise. This entails an explicit symmetry breaking of isotropy and homogeneity that stems from the amplification of the quenched fluctuations of the network by the activity avalanches, concomitant with the excitable dynamics. We discuss the microscopic interpretation of V (r ) and propose an explicit construction of it. The coarse-grained model shows excellent agreement with simulations at the network level. The generic nature of the observed phenomena is discussed.

Kinematics of velocity and vorticity correlations in turbulent flow

NASA Technical Reports Server (NTRS)

Bernard, P. S.

1983-01-01

The kinematic problem of calculating second-order velocity moments from given values of the vorticity covariance is examined. Integral representation formulas for second-order velocity moments in terms of the two-point vorticity correlation tensor are derived. The special relationships existing between velocity moments in isotropic turbulence are expressed in terms of the integral formulas yielding several kinematic constraints on the two-point vorticity correlation tensor in isotropic turbulence. Numerical evaluation of these constraints suggests that a Gaussian curve may be the only form of the longitudinal velocity correlation coefficient which is consistent with the requirement of isotropy. It is shown that if this is the case, then a family of exact solutions to the decay of isotropic turbulence may be obtained which contains Batchelor's final period solution as a special case. In addition, the computed results suggest a method of approximating the integral representation formulas in general turbulent shear flows.

Application and testing of additive manufacturing for mirrors and precision structures

NASA Astrophysics Data System (ADS)

Sweeney, Michael; Acreman, Martyn; Vettese, Tom; Myatt, Ray; Thompson, Mike

2015-09-01

Additive Manufacturing (aka AM, and 3-D printing) is widely touted in the media as the foundation for the next industrial revolution. Beneath the hype, AM does indeed offer profound advantages in lead-time, dramatically reduced consumption of expensive raw materials, while enabling new and innovative design forms that cannot be produced by other means. General Dynamics and their industry partners have begun to embrace this technology for mirrors and precision structures used in the aerospace, defense, and precision optical instrumentation industries. Aggressively lightweighted, open and closed back test mirror designs, 75-150 mm in size, were first produced by AM from several different materials. Subsequent optical finishing and test experiments have exceeded expectations for density, surface finish, dimensional stability and isotropy of thermal expansion on the optical scale of measurement. Materials currently under examination include aluminum, titanium, beryllium, aluminum beryllium, Inconel 625, stainless steel/bronze, and PEKK polymer.

Roughness Encoding in Human and Biomimetic Artificial Touch: Spatiotemporal Frequency Modulation and Structural Anisotropy of Fingerprints

PubMed Central

Oddo, Calogero Maria; Beccai, Lucia; Wessberg, Johan; Wasling, Helena Backlund; Mattioli, Fabio; Carrozza, Maria Chiara

2011-01-01

The influence of fingerprints and their curvature in tactile sensing performance is investigated by comparative analysis of different design parameters in a biomimetic artificial fingertip, having straight or curved fingerprints. The strength in the encoding of the principal spatial period of ridged tactile stimuli (gratings) is evaluated by indenting and sliding the surfaces at controlled normal contact force and tangential sliding velocity, as a function of fingertip rotation along the indentation axis. Curved fingerprints guaranteed higher directional isotropy than straight fingerprints in the encoding of the principal frequency resulting from the ratio between the sliding velocity and the spatial periodicity of the grating. In parallel, human microneurography experiments were performed and a selection of results is included in this work in order to support the significance of the biorobotic study with the artificial tactile system. PMID:22163915

Lattice Boltzmann Equation On a 2D Rectangular Grid

NASA Technical Reports Server (NTRS)

Bouzidi, MHamed; DHumieres, Dominique; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)

2002-01-01

We construct a multi-relaxation lattice Boltzmann model on a two-dimensional rectangular grid. The model is partly inspired by a previous work of Koelman to construct a lattice BGK model on a two-dimensional rectangular grid. The linearized dispersion equation is analyzed to obtain the constraints on the isotropy of the transport coefficients and Galilean invariance for various wave propagations in the model. The linear stability of the model is also studied. The model is numerically tested for three cases: (a) a vortex moving with a constant velocity on a mesh periodic boundary conditions; (b) Poiseuille flow with an arbitrasy inclined angle with respect to the lattice orientation: and (c) a cylinder &symmetrically placed in a channel. The numerical results of these tests are compared with either analytic solutions or the results obtained by other methods. Satisfactory results are obtained for the numerical simulations.

Extension of relativistic dissipative hydrodynamics to third order

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

El, Andrej; Xu Zhe; Greiner, Carsten

2010-04-15

Following the procedure introduced by Israel and Stewart, we expand the entropy current up to the third order in the shear stress tensor pi{sup a}lpha{sup b}eta and derive a novel third-order evolution equation for pi{sup a}lpha{sup b}eta. This equation is solved for the one-dimensional Bjorken boost-invariant expansion. The scaling solutions for various values of the shear viscosity to the entropy density ratio eta/s are shown to be in very good agreement with those obtained from kinetic transport calculations. For the pressure isotropy starting with 1 at tau{sub 0}=0.4 fm/c, the third-order corrections to Israel-Stewart theory are approximately 10% for eta/s=0.2more » and more than a factor of 2 for eta/s=3. We also estimate all higher-order corrections to Israel-Stewart theory and demonstrate their importance in describing highly viscous matters.« less

Decay and growth laws in homogeneous shear turbulence

NASA Astrophysics Data System (ADS)

Briard, Antoine; Gomez, Thomas; Mons, Vincent; Sagaut, Pierre

2016-07-01

Homogeneous anisotropic turbulence has been widely studied in the past decades, both numerically and experimentally. Shear flows have received a particular attention because of the numerous physical phenomena they exhibit. In the present paper, both the decay and growth of anisotropy in homogeneous shear flows at high Reynolds numbers are revisited thanks to a recent eddy-damped quasi-normal Markovian closure adapted to homogeneous anisotropic turbulence. The emphasis is put on several aspects: an asymptotic model for the slow part of the pressure-strain tensor is derived for the return to isotropy process when mean velocity gradients are released. Then, a general decay law for purely anisotropic quantities in Batchelor turbulence is proposed. At last, a discussion is proposed to explain the scattering of global quantities obtained in DNS and experiments in sustained shear flows: the emphasis is put on the exponential growth rate of the kinetic energy and on the shear parameter.

Piezoceramic Actuator Placement for Acoustic Control of Panels

NASA Technical Reports Server (NTRS)

Bevan, Jeffrey S.; Turner, Travis L. (Technical Monitor)

2001-01-01

Optimum placement of multiple traditional piezoceramic actuators is determined for active structural acoustic control of flat panels. The structural acoustic response is determined using acoustic radiation filters and structural surface vibration characteristics. Linear Quadratic Regulator (LQR) control is utilized to determine the optimum state feedback gain for active structural acoustic control. The optimum actuator location is determined by minimizing the structural acoustic radiated noise using a modified genetic algorithm. Experimental tests are conducted and compared to analytical results. Anisotropic piezoceramic actuators exhibits enhanced performance when compared to traditional isotropic piezoceramic actuators. As a result of the inherent isotropy, these advanced actuators develop strain along the principal material axis. The orientation of anisotropic actuators is investigated on the effect of structural vibration and acoustic control of curved and flat panels. A fully coupled shallow shell finite element formulation is developed to include anisotropic piezoceramic actuators for shell structures.

Piezoceramic Actuator Placement for Acoustic Control of Panels

NASA Technical Reports Server (NTRS)

Bevan, Jeffrey S.

2000-01-01

Optimum placement of multiple traditional piezoceramic actuators is determined for active structural acoustic control of flat panels. The structural acoustic response is determined using acoustic radiation filters and structural surface vibration characteristics. Linear Quadratic Regulator (LQR) control is utilized to determine the optimum state feedback gain for active structural acoustic control. The optimum actuator location is determined by minimizing the structural acoustic radiated noise using a modified genetic algorithm. Experimental tests are conducted and compared to analytical results. Anisotropic piezoceramic actuators exhibit enhanced performance when compared to traditional isotropic piezoceramic actuators. As a result of the inherent isotropy, these advanced actuators develop strain along the principal material axis. The orientation of anisotropic actuators is investigated on the effect of structural vibration and acoustic control of curved and flat panels. A fully coupled shallow shell finite element formulation is developed to include anisotropic piezoceramic actuators for shell structures.

Recent results concerning the stability of viscoelastic shear deformable plates under compressive edge loading

NASA Technical Reports Server (NTRS)

Librescu, L.; Chandiramani, N. K.

1989-01-01

Some recent results obtained by the authors are summarized concerning the stability of transversely isotropic flat panels whose materials exhibit a viscoelastic behavior and whose edges are subjected to in-plane biaxial compressive loads. Two transversely isotropic type materials, largely used in advanced technology, are considered: (1) the pyrolytic-graphite type, used in the thermal protection of aerospace vehicles, and (2) the type corresponding to unidirectional fiber-reinforced composites. In the former case, the planes of isotropy are parallel at each point to the midplane of the plate. In the latter case, they are normal to the fiber directions. The micromechanical relations developed by Aboudi (1984, 1986, 1987) are considered in conjunction with the correspondence principle of linear viscoelastic theory in order to predict the macroscopic viscoelastic properties of a material composed of uniaxial elastic fibers embedded in a linear viscoelastic matrix.

BATSE analysis techniques for probing the GRB spatial and luminosity distributions

NASA Technical Reports Server (NTRS)

Hakkila, Jon; Meegan, Charles A.

1992-01-01

The Burst And Transient Source Experiment (BATSE) has measured homogeneity and isotropy parameters from an increasingly large sample of observed gamma-ray bursts (GRBs), while also maintaining a summary of the way in which the sky has been sampled. Measurement of both of these are necessary for any study of the BATSE data statistically, as they take into account the most serious observational selection effects known in the study of GRBs: beam-smearing and inhomogeneous, anisotropic sky sampling. Knowledge of these effects is important to analysis of GRB angular and intensity distributions. In addition to determining that the bursts are local, it is hoped that analysis of such distributions will allow boundaries to be placed on the true GRB spatial distribution and luminosity function. The technique for studying GRB spatial and luminosity distributions is direct. Results of BATSE analyses are compared to Monte Carlo models parameterized by a variety of spatial and luminosity characteristics.

A comparison of three algebraic stress closures for combustor flow calculations

NASA Technical Reports Server (NTRS)

Nikjooy, M.; So, R. M. C.; Hwang, B. C.

1985-01-01

A comparison is made of the performance of two locally nonequilibrium and one equilibrium algebraic stress closures in calculating combustor flows. Effects of four different pressure-strain models on these closure models are also analyzed. The results show that the pressure-strain models have a much greater influence on the calculated mean velocity and turbulence field than the algebraic stress closures, and that the best mean strain model for the pressure-strain terms is that proposed by Launder, Reece and Rodi (1975). However, the equilibrium algebraic stress closure with the Rotta return-to-isotropy model (1951) for the pressure-strain terms gives as good a correlation with measurements as when the Launder et al. mean strain model is included in the pressure-strain model. Finally, comparison of the calculations with the standard k-epsilon closure results show that the algebraic stress closures are better suited for simple turbulent flow calculations.

The influence of anisotropy on the core structure of Shockley partial dislocations within FCC materials

NASA Astrophysics Data System (ADS)

Szajewski, B. A.; Hunter, A.; Luscher, D. J.; Beyerlein, I. J.

2018-01-01

Both theoretical and numerical models of dislocations often necessitate the assumption of elastic isotropy to retain analytical tractability in addition to reducing computational load. As dislocation based models evolve towards physically realistic material descriptions, the assumption of elastic isotropy becomes increasingly worthy of examination. We present an analytical dislocation model for calculating the full dissociated core structure of dislocations within anisotropic face centered cubic (FCC) crystals as a function of the degree of material elastic anisotropy, two misfit energy densities on the γ-surface ({γ }{{isf}}, {γ }{{usf}}) and the remaining elastic constants. Our solution is independent of any additional features of the γ-surface. Towards this pursuit, we first demonstrate that the dependence of the anisotropic elasticity tensor on the orientation of the dislocation line within the FCC crystalline lattice is small and may be reasonably neglected for typical materials. With this approximation, explicit analytic solutions for the anisotropic elasticity tensor {B} for both nominally edge and screw dislocations within an FCC crystalline lattice are devised, and employed towards defining a set of effective isotropic elastic constants which reproduce fully anisotropic results, however do not retain the bulk modulus. Conversely, Hill averaged elastic constants which both retain the bulk modulus and reasonably approximate the dislocation core structure are employed within subsequent numerical calculations. We examine a wide range of materials within this study, and the features of each partial dislocation core are sufficiently localized that application of discrete linear elasticity accurately describes the separation of each partial dislocation core. In addition, the local features (the partial dislocation core distribution) are well described by a Peierls-Nabarro dislocation model. We develop a model for the displacement profile which depends upon two disparate dislocation length scales which describe the core structure; (i) the equilibrium stacking fault width between two Shockley partial dislocations, R eq and (ii) the maximum slip gradient, χ, of each Shockley partial dislocation. We demonstrate excellent agreement between our own analytic predictions, numerical calculations, and R eq computed directly by both ab-initio and molecular statics methods found elsewhere within the literature. The results suggest that understanding of various plastic mechanisms, e.g., cross-slip and nucleation may be augmented with the inclusion of elastic anisotropy.

Concurrent Spectral and Separation-space Views of Small-scale Anisotropy in Rotating Turbulence

NASA Astrophysics Data System (ADS)

Vallefuoco, D.; Godeferd, F. S.; Naso, A.

2017-12-01

Rotating turbulence is central in astrophysical, geophysical and industrial flows. A background rotation about a fixed axis introduces significant anisotropy in the turbulent dynamics through both linear and nonlinear mechanisms. The flow regime can be characterized by two independent non-dimensional parameters, e.g. the Reynolds and Rossby numbers or, equivalently, the ratio of the integral scale to the Kolmogorov scale L/η, and the ratio rZ/L, where rZ=√(ɛ/Ω3) is the Zeman scale, ɛ is the mean dissipation and Ω is the rotation rate. rZ is the scale at which the inertial timescale equals the rotation timescale. According to classical dimensional arguments (Zeman 1994), if the Reynolds number is large, scales much larger than rZ are mainly affected by rotation while scales much smaller than rZare dominated by the nonlinear dynamics and are expected to recover isotropy. In this work, we characterize incompressible rotating turbulence scale- and direction-dependent anisotropy through high Reynolds number pseudo-spectral forced DNS. We first focus on energy direction-dependent spectra in Fourier space: we show that a high anisotropy small wavenumber range and a low anisotropy large wavenumber range arise. Importantly, anisotropy arises even at scales much smaller than rZ and no small-scale isotropy is observed in our DNS, in contrast with previous numerical results (Delache et al. 2014, Mininni et al. 2012) but in agreement with experiments (Lamriben et al. 2011). Then, we estimate the value of the threshold wavenumber kT between these two anisotropic ranges for a large number of runs, and show that it corresponds to the scale at which dissipative effects are of the same order as those of rotation. Therefore, in the asymptotic inviscid limit, kT tends to infinity and only the low-wavenumber anisotropic range should persist. In this range anisotropy decreases with wavenumber, which is consistent with the classical Zeman argument. In addition, anisotropy at scales much smaller than rZ can be detected in physical space too, in particular for the third-order two-point vector moment F=<δu2 δu>, where δu is the velocity increment. We find the expected inertial trends for F (Galtier 2009) at scales sufficiently larger than the dissipative scale, while smaller scales exhibit qualitatively opposite anisotropic features.

Comparing crack damage evolution in rocks deformed under conventional and true triaxial loading

NASA Astrophysics Data System (ADS)

Browning, J.; Meredith, P. G.; Stuart, C.; Healy, D.; Harland, S. R.; Mitchell, T. M.

2017-12-01

The vast majority of experimental studies investigate damage evolution using conventional triaxial stress states (σ1 > σ2 = σ3, CTA), whereas in nature the stress state is generally truly triaxial (σ1 > σ2 > σ3, TTA). We present a comparative study of crack damage evolution during CTA vs. TTA stress conditions using results from measurements made on cubic samples of sandstone deformed in three orthogonal directions with independently controlled stress paths. We have measured, simultaneously with stress and strain, changes in wave velocities in the three principal directions, together with acoustic emission (AE) output. Changes in wave velocities are associated with both elastic closure and opening of pre-existing cracks, and the inelastic formation of new cracks. By contrast, AE is associated only with the inelastic growth of new crack damage. The onset of new damage is shown to be a function of differential stress regardless of the magnitude of mean stress. Hence, we show that damage can form due to a decrease in the minimum principal stress, which reduces mean stress but increases the differential stress. We find an approximately fivefold decrease in the number of AE events in the TTA case in comparison to the CTA case. In essence, we create two end-member crack distributions; one displaying cylindrical transverse isotropy and the other planar transverse isotropy. Taken together, the AE data, the velocities and the crack densities indicate that the intermediate principal stress plays a key role in suppressing the total amount of crack growth and concentrating it in planes sub-parallel to the minimum stress. However, the size of individual cracks remains constant. Hence, the differential stress at which rocks fail (i.e. strength) will be significantly higher under TTA stress (where σ2 > σ3) than under CTA stress (where σ2 = σ3). Cyclic loading tests show that while individual stress states are important, the stress path by which these stress states are reached is equally important. Whether the stress state has been `visited' before is key to determining and understanding damage states. Further damage commences only when the previous maximum differential stress is exceeded, regardless of whether this is achieved by increasing the maximum principal stress or by decreasing the minimum principal stress.

CytoSpectre: a tool for spectral analysis of oriented structures on cellular and subcellular levels.

PubMed

Kartasalo, Kimmo; Pölönen, Risto-Pekka; Ojala, Marisa; Rasku, Jyrki; Lekkala, Jukka; Aalto-Setälä, Katriina; Kallio, Pasi

2015-10-26

Orientation and the degree of isotropy are important in many biological systems such as the sarcomeres of cardiomyocytes and other fibrillar structures of the cytoskeleton. Image based analysis of such structures is often limited to qualitative evaluation by human experts, hampering the throughput, repeatability and reliability of the analyses. Software tools are not readily available for this purpose and the existing methods typically rely at least partly on manual operation. We developed CytoSpectre, an automated tool based on spectral analysis, allowing the quantification of orientation and also size distributions of structures in microscopy images. CytoSpectre utilizes the Fourier transform to estimate the power spectrum of an image and based on the spectrum, computes parameter values describing, among others, the mean orientation, isotropy and size of target structures. The analysis can be further tuned to focus on targets of particular size at cellular or subcellular scales. The software can be operated via a graphical user interface without any programming expertise. We analyzed the performance of CytoSpectre by extensive simulations using artificial images, by benchmarking against FibrilTool and by comparisons with manual measurements performed for real images by a panel of human experts. The software was found to be tolerant against noise and blurring and superior to FibrilTool when analyzing realistic targets with degraded image quality. The analysis of real images indicated general good agreement between computational and manual results while also revealing notable expert-to-expert variation. Moreover, the experiment showed that CytoSpectre can handle images obtained of different cell types using different microscopy techniques. Finally, we studied the effect of mechanical stretching on cardiomyocytes to demonstrate the software in an actual experiment and observed changes in cellular orientation in response to stretching. CytoSpectre, a versatile, easy-to-use software tool for spectral analysis of microscopy images was developed. The tool is compatible with most 2D images and can be used to analyze targets at different scales. We expect the tool to be useful in diverse applications dealing with structures whose orientation and size distributions are of interest. While designed for the biological field, the software could also be useful in non-biological applications.

Extraction of effective solid-liquid interfacial free energies for full 3D solid crystallites from equilibrium MD simulations

DOE PAGES

Zepeda-Ruiz, L. A.; Sadigh, B.; Chernov, A. A.; ...

2017-11-21

Molecular dynamics simulations of an embedded atom copper system in the NPH ensemble are used to study the e ective solid-liquid interfacial free energy of quasispherical solid crystals within a liquid. This is within the larger context of MD simulations of this system undergoing solidi cation, where single individually-prepared crystallites of di erent sizes grow until they reach a thermodynamically stable nal state. The resulting equilibrium shapes possess the full structural details expected for solids with weakly anisotropic surface free energies (in these cases, ~5 % radial attening and rounded [111] octahedral faces). The simplifying assumption of sphericity and perfectmore » isotropy leads to an e ective interfacial free energy as appearing in the Gibbs-Thomson equation, which we determine to be ~179 erg/cm 2, roughly independent of crystal size for radii in the 50 - 250 A range. This quantity may be used in atomistically-informed models of solidi cation kinetics for this system.« less

Systemic characterization and evaluation of particle packings as initial sets for discrete element simulations

NASA Astrophysics Data System (ADS)

Morfa, Carlos Recarey; Cortés, Lucía Argüelles; Farias, Márcio Muniz de; Morales, Irvin Pablo Pérez; Valera, Roberto Roselló; Oñate, Eugenio

2018-07-01

A methodology that comprises several characterization properties for particle packings is proposed in this paper. The methodology takes into account factors such as dimension and shape of particles, space occupation, homogeneity, connectivity and isotropy, among others. This classification and integration of several properties allows to carry out a characterization process to systemically evaluate the particle packings in order to guarantee the quality of the initial meshes in discrete element simulations, in both the micro- and the macroscales. Several new properties were created, and improvements in existing ones are presented. Properties from other disciplines were adapted to be used in the evaluation of particle systems. The methodology allows to easily characterize media at the level of the microscale (continuous geometries—steels, rocks microstructures, etc., and discrete geometries) and the macroscale. A global, systemic and integral system for characterizing and evaluating particle sets, based on fuzzy logic, is presented. Such system allows researchers to have a unique evaluation criterion based on the aim of their research. Examples of applications are shown.

Majority of Solar Wind Intervals Support Ion-Driven Instabilities

NASA Astrophysics Data System (ADS)

Klein, K. G.; Alterman, B. L.; Stevens, M. L.; Vech, D.; Kasper, J. C.

2018-05-01

We perform a statistical assessment of solar wind stability at 1 AU against ion sources of free energy using Nyquist's instability criterion. In contrast to typically employed threshold models which consider a single free-energy source, this method includes the effects of proton and He2 + temperature anisotropy with respect to the background magnetic field as well as relative drifts between the proton core, proton beam, and He2 + components on stability. Of 309 randomly selected spectra from the Wind spacecraft, 53.7% are unstable when the ion components are modeled as drifting bi-Maxwellians; only 4.5% of the spectra are unstable to long-wavelength instabilities. A majority of the instabilities occur for spectra where a proton beam is resolved. Nearly all observed instabilities have growth rates γ slower than instrumental and ion-kinetic-scale timescales. Unstable spectra are associated with relatively large He2 + drift speeds and/or a departure of the core proton temperature from isotropy; other parametric dependencies of unstable spectra are also identified.

Pseudonegative thermal expansion and the state of water in graphene oxide layered assemblies.

PubMed

Zhu, Jian; Andres, Christine M; Xu, Jiadi; Ramamoorthy, Ayyalusamy; Tsotsis, Thomas; Kotov, Nicholas A

2012-09-25

Unraveling the complex interplay between thermal properties and hydration is a part of understanding the fundamental properties of many soft materials and very essential for many applications. Here we show that graphene oxide (GO) demonstrates a highly negative thermal expansion (NTE) coefficient owing to unique thermohydration processes related with fast transport of water between the GO sheets, the amphiphilic nature of nanochannels, and close-to-zero intrinsic thermal expansion of GO. The humidity-dependent NTE of GO layered assemblies, or "pseudonegative thermal expansion" (PNTE), differs from that of other hygroscopic materials due to its relatively fast and highly reversible expansion/contraction cycles and occurrence at low humidity levels while bearing similarities to classic NTE. Thermal expansion of polyvinyl alcohol/GO composites is easily tunable with additional intricacy of thermohydration effects. PNTE combined with isotropy, nontoxicity, and mechanical robustness is an asset for applications of actuators, sensors, MEMS devices, and memory materials and crucial for developing methods of thermal/photopatterning of GO devices.

Wavelet analysis methods for radiography of multidimensional growth of planar mixing layers

DOE PAGES

Merritt, Elizabeth Catherine; Doss, Forrest William

2016-07-06

The counter-propagating shear campaign is examining instability growth and its transition to turbulence in the high-energy-density physics regime using a laser-driven counter-propagating flow platform. In these experiments, we observe consistent complex break-up of and structure growth in a tracer layer placed at the shear flow interface during the instability growth phase. We present a wavelet-transform based analysis technique capable of characterizing the scale- and directionality-resolved average intensity perturbations in static radiographs of the experiment. This technique uses the complete spatial information available in each radiograph to describe the structure evolution. We designed this analysis technique to generate a two-dimensional powermore » spectrum for each radiograph from which we can recover information about structure widths, amplitudes, and orientations. Lastly, the evolution of the distribution of power in the spectra for an experimental series is a potential metric for quantifying the structure size evolution as well as a system’s evolution towards isotropy.« less

BEASTS OF THE SOUTHERN WILD: DISCOVERY OF NINE ULTRA FAINT SATELLITES IN THE VICINITY OF THE MAGELLANIC CLOUDS

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

Koposov, Sergey E.; Belokurov, Vasily; Torrealba, Gabriel

2015-06-01

We have used the publicly released Dark Energy Survey (DES) data to hunt for new satellites of the Milky Way (MW) in the southern hemisphere. Our search yielded a large number of promising candidates. In this paper, we announce the discovery of nine new unambiguous ultra-faint objects, whose authenticity can be established with the DES data alone. Based on the morphological properties, three of the new satellites are dwarf galaxies, one of which is located at the very outskirts of the MW, at a distance of 380 kpc. The remaining six objects have sizes and luminosities comparable to the Seguemore » 1 satellite and cannot be classified straightforwardly without follow-up spectroscopic observations. The satellites we have discovered cluster around the LMC and the SMC. We show that such spatial distribution is unlikely under the assumption of isotropy, and, therefore, conclude that at least some of the new satellites must have been associated with the Magellanic Clouds in the past.« less

Anisotropic string cosmological model in Brans–Dicke theory of gravitation with time-dependent deceleration parameter

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

Maurya, D. Ch., E-mail: dcmaurya563@gmail.com; Zia, R., E-mail: rashidzya@gmail.com; Pradhan, A., E-mail: pradhan.anirudh@gmail.com

We discuss a spatially homogeneous and anisotropic string cosmological models in the Brans–Dicke theory of gravitation. For a spatially homogeneous metric, it is assumed that the expansion scalar θ is proportional to the shear scalar σ. This condition leads to A = kB{sup m}, where k and m are constants. With these assumptions and also assuming a variable scale factor a = a(t), we find solutions of the Brans–Dicke field equations. Various phenomena like the Big Bang, expanding universe, and shift from anisotropy to isotropy are observed in the model. It can also be seen that in early stage ofmore » the evolution of the universe, strings dominate over particles, whereas the universe is dominated by massive strings at the late time. Some physical and geometrical behaviors of the models are also discussed and observed to be in good agreement with the recent observations of SNe la supernovae.« less

Cosmic ray sources, acceleration and propagation

NASA Technical Reports Server (NTRS)

Ptuskin, V. S.

1986-01-01

A review is given of selected papers on the theory of cosmic ray (CR) propagation and acceleration. The high isotropy and a comparatively large age of galactic CR are explained by the effective interaction of relativistic particles with random and regular electromagnetic fields in interstellar medium. The kinetic theory of CR propagation in the Galaxy is formulated similarly to the elaborate theory of CR propagation in heliosphere. The substantial difference between these theories is explained by the necessity to take into account in some cases the collective effects due to a rather high density of relativisitc particles. In particular, the kinetic CR stream instability and the hydrodynamic Parker instability is studied. The interaction of relativistic particles with an ensemble of given weak random magnetic fields is calculated by perturbation theory. The theory of CR transfer is considered to be basically completed for this case. The main problem consists in poor information about the structure of the regular and the random galactic magnetic fields. An account is given of CR transfer in a turbulent medium.

Litmus Test for Cosmic Hemispherical Asymmetry in the Cosmic Microwave Background B -Mode Polarization

NASA Astrophysics Data System (ADS)

Mukherjee, Suvodip; Souradeep, Tarun

2016-06-01

Recent measurements of the temperature field of the cosmic microwave background (CMB) provide tantalizing evidence for violation of statistical isotropy (SI) that constitutes a fundamental tenet of contemporary cosmology. CMB space based missions, WMAP, and Planck have observed a 7% departure in the SI temperature field at large angular scales. However, due to higher cosmic variance at low multipoles, the significance of this measurement is not expected to improve from any future CMB temperature measurements. We demonstrate that weak lensing of the CMB due to scalar perturbations produces a corresponding SI violation in B modes of CMB polarization at smaller angular scales. The measurability of this phenomenon depends upon the scales (l range) over which power asymmetry is present. Power asymmetry, which is restricted only to l <64 in the temperature field, cannot lead to any significant observable effect from this new window. However, this effect can put an independent bound on the spatial range of scales of hemispherical asymmetry present in the scalar sector.

Structure Function Scaling Exponent and Intermittency in the Wake of a Wind Turbine Array

NASA Astrophysics Data System (ADS)

Aseyev, Aleksandr; Ali, Naseem; Cal, Raul

2015-11-01

Hot-wire measurements obtained in a 3 × 3 wind turbine array boundary layer are utilized to analyze high order structure functions, intermittency effects as well as the probability density functions of velocity increments at different scales within the energy cascade. The intermittency exponent is found to be greater in the far wake region in comparison to the near wake. At hub height, the intermittency exponent is found to be null. ESS scaling exponents of the second, fourth, and fifth order structure functions remain relatively constant as a function of height in the far-wake whereas in the near-wake these highly affected by the passage of the rotor thus showing a dependence on physical location. When comparing with proposed models, these generally over predict the structure functions in the far wake region. The pdf distributions in the far wake region display wider tails compared to the near wake region, and constant skewness hypothesis based on the local isotropy is verified in the wake. CBET-1034581.

Systemic characterization and evaluation of particle packings as initial sets for discrete element simulations

NASA Astrophysics Data System (ADS)

Morfa, Carlos Recarey; Cortés, Lucía Argüelles; Farias, Márcio Muniz de; Morales, Irvin Pablo Pérez; Valera, Roberto Roselló; Oñate, Eugenio

2017-10-01

A methodology that comprises several characterization properties for particle packings is proposed in this paper. The methodology takes into account factors such as dimension and shape of particles, space occupation, homogeneity, connectivity and isotropy, among others. This classification and integration of several properties allows to carry out a characterization process to systemically evaluate the particle packings in order to guarantee the quality of the initial meshes in discrete element simulations, in both the micro- and the macroscales. Several new properties were created, and improvements in existing ones are presented. Properties from other disciplines were adapted to be used in the evaluation of particle systems. The methodology allows to easily characterize media at the level of the microscale (continuous geometries—steels, rocks microstructures, etc., and discrete geometries) and the macroscale. A global, systemic and integral system for characterizing and evaluating particle sets, based on fuzzy logic, is presented. Such system allows researchers to have a unique evaluation criterion based on the aim of their research. Examples of applications are shown.

Extraction of effective solid-liquid interfacial free energies for full 3D solid crystallites from equilibrium MD simulations

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

Zepeda-Ruiz, L. A.; Sadigh, B.; Chernov, A. A.

Molecular dynamics simulations of an embedded atom copper system in the NPH ensemble are used to study the e ective solid-liquid interfacial free energy of quasispherical solid crystals within a liquid. This is within the larger context of MD simulations of this system undergoing solidi cation, where single individually-prepared crystallites of di erent sizes grow until they reach a thermodynamically stable nal state. The resulting equilibrium shapes possess the full structural details expected for solids with weakly anisotropic surface free energies (in these cases, ~5 % radial attening and rounded [111] octahedral faces). The simplifying assumption of sphericity and perfectmore » isotropy leads to an e ective interfacial free energy as appearing in the Gibbs-Thomson equation, which we determine to be ~179 erg/cm 2, roughly independent of crystal size for radii in the 50 - 250 A range. This quantity may be used in atomistically-informed models of solidi cation kinetics for this system.« less

Over-Aging Effect on Fracture Toughness of Beryllium Copper Alloy C17200

NASA Astrophysics Data System (ADS)

Jen, Kei-Peng; Xu, Liqun; Hylinski, Steven; Gildersleeve, Nate

2008-10-01

This study experimentally increased the fracture toughness of Beryllium Copper (CuBe) UNS C17200 alloy using three different age hardening processes. At the same time, the micro- and macro-fracture behavior of this alloy were comprehensively studied. ASTM E399 fracture toughness, tensile, and Charpy impact tests were conducted for all three heat-treated rods. The fracture surfaces were examined under both an optical microscope and a scanning electron microscope to investigate the failure mechanisms. Multiple test orientations were considered to explore isotropy. Increasing the temperature and duration at which age hardening was performed increased fracture toughness while decreasing ultimate tensile strength. The maximum fracture toughness was reached on the most overaged specimen, while retaining a serviceable tensile strength. The specimen test data allowed a relationship to be established among Charpy impact toughness, fracture toughness, and yield strength. Analysis of fracture behavior revealed an interesting relationship between fracture toughness and pre-cracking fatigue propagation rate.

Improvements in the order, isotropy and electron density of glypican-1 crystals by controlled dehydration

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

Awad, Wael; Cairo University, Cairo; Svensson Birkedal, Gabriel

The anisotropy of crystals of glypican-1 was significantly reduced by controlled dehydration using the HC1 device, allowing the building of previously disordered parts of the structure. The use of controlled dehydration for improvement of protein crystal diffraction quality is increasing in popularity, although there are still relatively few documented examples of success. A study has been carried out to establish whether controlled dehydration could be used to improve the anisotropy of crystals of the core protein of the human proteoglycan glypican-1. Crystals were subjected to controlled dehydration using the HC1 device. The optimal protocol for dehydration was developed by carefulmore » investigation of the following parameters: dehydration rate, final relative humidity and total incubation time T{sub inc}. Of these, the most important was shown to be T{sub inc}. After dehydration using the optimal protocol the crystals showed significantly reduced anisotropy and improved electron density, allowing the building of previously disordered parts of the structure.« less

Global Simulation of Proton Precipitation Due to Field Line Curvature During Substorms

NASA Technical Reports Server (NTRS)

Gilson, M. L.; Raeder, J.; Donovan, E.; Ge, Y. S.; Kepko, L.

2012-01-01

The low latitude boundary of the proton aurora (known as the Isotropy Boundary or IB) marks an important boundary between empty and full downgoing loss cones. There is significant evidence that the IB maps to a region in the magnetosphere where the ion gyroradius becomes comparable to the local field line curvature. However, the location of the IB in the magnetosphere remains in question. In this paper, we show simulated proton precipitation derived from the Field Line Curvature (FLC) model of proton scattering and a global magnetohydrodynamic simulation during two substorms. The simulated proton precipitation drifts equatorward during the growth phase, intensifies at onset and reproduces the azimuthal splitting published in previous studies. In the simulation, the pre-onset IB maps to 7-8 RE for the substorms presented and the azimuthal splitting is caused by the development of the substorm current wedge. The simulation also demonstrates that the central plasma sheet temperature can significantly influence when and where the azimuthal splitting takes place.

On Stellar Flash Echoes from Circular Rings

NASA Astrophysics Data System (ADS)

Nemiroff, Robert; Mukherjee, Oindabi

2018-01-01

A flash -- or any episode of variability -- that occurs in the vicinity of a circular ring might be seen several times later, simultaneously, as echoes on the ring. Effective images of the flash are created and annihilated in pairs, with as many as four flash images visible concurrently. Videos detailing sequences of image pair creation, tandem motion, and subsequent image annihilation are shown, given simple opacity and scattering assumptions. It is proven that, surprisingly, images from a second pair creation event always annihilate with images from the first. Caustic surfaces between flash locations yielding two and four images are computed. Although such ring echos surely occur, their practical detection might be difficult as it could require dedicated observing programs involving sensitive photometry of extended objects. Potential flash sources include planetary and interstellar gas and dust rings near and around variable stars, flare stars, novae, supernovae, and GRBs. Potentially recoverable information includes size, distance, temporal history, and angular isotropy of both the ring and flash.

Slab photonic crystals with dimer colloid bases

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

Riley, Erin K.; Liddell Watson, Chekesha M., E-mail: cliddell@ccmr.cornell.edu

2014-06-14

The photonic band gap properties for centered rectangular monolayers of asymmetric dimers are reported. Colloids in suspension have been organized into the phase under confinement. The theoretical model is inspired by the range of asymmetric dimers synthesized via seeded emulsion polymerization and explores, in particular, the band structures as a function of degree of lobe symmetry and degree of lobe fusion. These parameters are varied incrementally from spheres to lobe-tangent dimers over morphologies yielding physically realizable particles. The work addresses the relative scarcity of theoretical studies on photonic crystal slabs with vertical variation that is consistent with colloidal self-assembly. Odd,more » even and polarization independent gaps in the guided modes are determined for direct slab structures. A wide range of lobe symmetry and degree of lobe fusion combinations having Brillouin zones with moderate to high isotropy support gaps between odd mode band indices 3-4 and even mode band indices 1-2 and 2-3.« less

Some factors influencing radiation of sound from flow interaction with edges of finite surfaces

NASA Technical Reports Server (NTRS)

Hayden, R. E.; Fox, H. L.; Chanaud, R. C.

1976-01-01

Edges of surfaces which are exposed to unsteady flow cause both strictly acoustic effects and hydrodynamic effects, in the form of generation of new hydrodynamic sources in the immediate vicinity of the edge. An analytical model is presented which develops the explicit sound-generation role of the velocity and Mach number of the eddy convection past the edge, and the importance of relative scale lengths of the turbulence, as well as the relative intensity of pressure fluctuations. The Mach number (velocity) effects show that the important paramater is the convection Mach number of the eddies. The effects of turbulence scale lengths, isotropy, and spatial density (separation) are shown to be important in determining the level and spectrum of edge sound radiated for the edge dipole mechanism. Experimental data is presented which provides support for the dipole edge noise model in terms of Mach number (velocity) scaling, parametric dependence on flow field parameter, directivity, and edge diffraction effects.

Indentation theory on a half-space of transversely isotropic multi-ferroic composite medium: sliding friction effect

NASA Astrophysics Data System (ADS)

Wu, F.; Wu, T.-H.; Li, X.-Y.

2018-03-01

This article aims to present a systematic indentation theory on a half-space of multi-ferroic composite medium with transverse isotropy. The effect of sliding friction between the indenter and substrate is taken into account. The cylindrical flat-ended indenter is assumed to be electrically/magnetically conducting or insulating, which leads to four sets of mixed boundary-value problems. The indentation forces in the normal and tangential directions are related to the Coulomb friction law. For each case, the integral equations governing the contact behavior are developed by means of the generalized method of potential theory, and the corresponding coupling field is obtained in terms of elementary functions. The effect of sliding on the contact behavior is investigated. Finite element method (FEM) in the context of magneto-electro-elasticity is developed to discuss the validity of the analytical solutions. The obtained analytical solutions may serve as benchmarks to various simplified analyses and numerical codes and as a guide for future experimental studies.

Constructing exact perturbations of the standard cosmological models

NASA Astrophysics Data System (ADS)

Sopuerta, Carlos F.

1999-11-01

In this paper we show a procedure to construct cosmological models which, according to a covariant criterion, can be seen as exact (nonlinear) perturbations of the standard Friedmann-Lemaı⁁tre-Robertson-Walker (FLRW) cosmological models. The special properties of this procedure will allow us to select some of the characteristics of the models and also to study in depth their main geometrical and physical features. In particular, the models are conformally stationary, which means that they are compatible with the existence of isotropic radiation, and the observers that would measure this isotropy are rotating. Moreover, these models have two arbitrary functions (one of them is a complex function) which control their main properties, and in general they do not have any isometry. We study two examples, focusing on the case when the underlying FLRW models are flat dust models. In these examples we compare our results with those of the linearized theory of perturbations about a FLRW background.

Buchdahl-Vaidya-Tikekar model for stellar interior in pure Lovelock gravity

NASA Astrophysics Data System (ADS)

Molina, Alfred; Dadhich, Naresh; Khugaev, Avas

2017-07-01

In the paper (Khugaev et al. in Phys Rev D94:064065. arXiv: 1603.07118, 2016), we have shown that for perfect fluid spheres the pressure isotropy equation for Buchdahl-Vaidya-Tikekar metric ansatz continues to have the same Gauss form in higher dimensions, and hence higher dimensional solutions could be obtained by redefining the space geometry characterizing Vaidya-Tikekar parameter K. In this paper we extend this analysis to pure Lovelock gravity; i.e. a (2N+2)-dimensional solution with a given K_{2N+2} can be taken over to higher n-dimensional pure Lovelock solution with K_n=(K_{2N+2}-n+2N+2)/(n-2N-1) where N is degree of Lovelock action. This ansatz includes the uniform density Schwarzshild and the Finch-Skea models, and it is interesting that the two define the two ends of compactness, the former being the densest and while the latter rarest. All other models with this ansatz lie in between these two limiting distributions.

Seismic anisotropy in gas-hydrate- and gas-bearing sediments on the Blake Ridge, from a walkaway vertical seismic profile

USGS Publications Warehouse

Pecher, I.A.; Holbrook, W.S.; Sen, M.K.; Lizarralde, D.; Wood, W.T.; Hutchinson, D.R.; Dillon, William P.; Hoskins, H.; Stephen, R.A.

2003-01-01

We present results from an analysis of anisotropy in marine sediments using walkaway vertical seismic profiles from the Blake Ridge, offshore South Carolina. We encountered transverse isotropy (TI) with a vertical symmetry axis in a gas-hydrate-bearing unit of clay and claystone with Thomsen parameters ?? = 0.05 ?? 0.02 and ?? = 0.04 ?? 0.06. TI increased to ?? = 0.16 ?? 0.04 and ?? = 0.19 ?? 0.12 in the underlying gas zone. Rock physics modeling suggests that the observed TI is caused by a partial alignment of clay particles rather than high-velocity gas-hydrate veins. Similarly, the increase of TI in the gas zone is not caused by thin low-velocity gas layers but rather, we speculate, by the sharp contrast between seismic properties of an anisotropic sediment frame and elongated gas-bearing pore voids. Our results underscore the significance of anisotropy for integrating near-vertical and wide-angle seismic data.

Applications of Bayesian Statistics to Problems in Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Meegan, Charles A.

1997-01-01

This presentation will describe two applications of Bayesian statistics to Gamma Ray Bursts (GRBS). The first attempts to quantify the evidence for a cosmological versus galactic origin of GRBs using only the observations of the dipole and quadrupole moments of the angular distribution of bursts. The cosmological hypothesis predicts isotropy, while the galactic hypothesis is assumed to produce a uniform probability distribution over positive values for these moments. The observed isotropic distribution indicates that the Bayes factor for the cosmological hypothesis over the galactic hypothesis is about 300. Another application of Bayesian statistics is in the estimation of chance associations of optical counterparts with galaxies. The Bayesian approach is preferred to frequentist techniques here because the Bayesian approach easily accounts for galaxy mass distributions and because one can incorporate three disjoint hypotheses: (1) bursts come from galactic centers, (2) bursts come from galaxies in proportion to luminosity, and (3) bursts do not come from external galaxies. This technique was used in the analysis of the optical counterpart to GRB970228.

The Hubble IR cutoff in holographic ellipsoidal cosmologies

NASA Astrophysics Data System (ADS)

Cataldo, Mauricio; Cruz, Norman

2018-01-01

It is well known that for spatially flat FRW cosmologies, the holographic dark energy disfavors the Hubble parameter as a candidate for the IR cutoff. For overcoming this problem, we explore the use of this cutoff in holographic ellipsoidal cosmological models, and derive the general ellipsoidal metric induced by a such holographic energy density. Despite the drawbacks that this cutoff presents in homogeneous and isotropic universes, based on this general metric, we developed a suitable ellipsoidal holographic cosmological model, filled with a dark matter and a dark energy components. At late time stages, the cosmic evolution is dominated by a holographic anisotropic dark energy with barotropic equations of state. The cosmologies expand in all directions in accelerated manner. Since the ellipsoidal cosmologies given here are not asymptotically FRW, the deviation from homogeneity and isotropy of the universe on large cosmological scales remains constant during all cosmic evolution. This feature allows the studied holographic ellipsoidal cosmologies to be ruled by an equation of state ω =p/ρ , whose range belongs to quintessence or even phantom matter.

Anisotropic elastic moduli reconstruction in transversely isotropic model using MRE

NASA Astrophysics Data System (ADS)

Song, Jiah; In Kwon, Oh; Seo, Jin Keun

2012-11-01

Magnetic resonance elastography (MRE) is an elastic tissue property imaging modality in which the phase-contrast based MRI imaging technique is used to measure internal displacement induced by a harmonically oscillating mechanical vibration. MRE has made rapid technological progress in the past decade and has now reached the stage of clinical use. Most of the research outcomes are based on the assumption of isotropy. Since soft tissues like skeletal muscles show anisotropic behavior, the MRE technique should be extended to anisotropic elastic property imaging. This paper considers reconstruction in a transversely isotropic model, which is the simplest case of anisotropy, and develops a new non-iterative reconstruction method for visualizing the elastic moduli distribution. This new method is based on an explicit representation formula using the Newtonian potential of measured displacement. Hence, the proposed method does not require iterations since it directly recovers the anisotropic elastic moduli. We perform numerical simulations in order to demonstrate the feasibility of the proposed method in recovering a two-dimensional anisotropic tensor.

Auxetic hexachiral structures with wavy ligaments for large elasto-plastic deformation

NASA Astrophysics Data System (ADS)

Zhu, Yilin; Wang, Zhen-Pei; Hien Poh, Leong

2018-05-01

The hexachiral structure is in-plane isotropic in small deformation. When subjected to large elasto-plastic deformation, however, the hexachiral structure tends to lose its auxeticity and/or isotropy—properties which are desirable in many potential applications. The objective of this study is to improve these two mechanical properties, without significantly compromising the effective yield stress, in the regime with significant material and geometrical nonlinearity effects. It is found that the deformation mechanisms underlying the auxeticity and isotropy properties of a hexachiral structure are largely influenced by the extent of rotation of the central ring in a unit cell. To facilitate the development of this deformation mechanism, an improved design with wavy ligaments is proposed. The improved performance of the proposed hexachiral structure is demonstrated. An initial study on possible applications as a protective material is next carried out, where the improved hexachiral design is shown to exhibit higher specific energy absorption capacity compared to the original design, as well as standard honeycomb structures.

Wavelet analysis methods for radiography of multidimensional growth of planar mixing layers

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

Merritt, E. C., E-mail: emerritt@lanl.gov; Doss, F. W.

2016-07-15

The counter-propagating shear campaign is examining instability growth and its transition to turbulence in the high-energy-density physics regime using a laser-driven counter-propagating flow platform. In these experiments, we observe consistent complex break-up of and structure growth in a tracer layer placed at the shear flow interface during the instability growth phase. We present a wavelet-transform based analysis technique capable of characterizing the scale- and directionality-resolved average intensity perturbations in static radiographs of the experiment. This technique uses the complete spatial information available in each radiograph to describe the structure evolution. We designed this analysis technique to generate a two-dimensional powermore » spectrum for each radiograph from which we can recover information about structure widths, amplitudes, and orientations. The evolution of the distribution of power in the spectra for an experimental series is a potential metric for quantifying the structure size evolution as well as a system’s evolution towards isotropy.« less

Direct measurement of the Einstein relation in a macroscopic, non-equilibrium system of chaotic surface waves

NASA Astrophysics Data System (ADS)

Welch, Kyle; Liebman-Pelaez, Alexander; Corwin, Eric

Equilibrium statistical mechanics is traditionally limited to thermal systems. Can it be applied to athermal, non-equilibrium systems that nonetheless satisfy the basic criteria of steady-state chaos and isotropy? We answer this question using a macroscopic system of chaotic surface waves which is, by all measures, non-equilibrium. The waves are generated in a dish of water that is vertically oscillated above a critical amplitude. We have constructed a rheometer that actively measures the drag imparted by the waves on a buoyant particle, a quantity entirely divorced in origin from the drag imparted by the fluid in which the particle floats. We also perform a separate, passive measurement, extracting a diffusion constant and effective temperature. Having directly measured all three properties (temperature, diffusion constant, and drag coefficient) we go on to show that our macroscopic, non-equilibrium case is wholly consistent with the Einstein relation, a classic result for equilibrium thermal systems.

Litmus Test for Cosmic Hemispherical Asymmetry in the Cosmic Microwave Background B-Mode Polarization.

PubMed

Mukherjee, Suvodip; Souradeep, Tarun

2016-06-03

Recent measurements of the temperature field of the cosmic microwave background (CMB) provide tantalizing evidence for violation of statistical isotropy (SI) that constitutes a fundamental tenet of contemporary cosmology. CMB space based missions, WMAP, and Planck have observed a 7% departure in the SI temperature field at large angular scales. However, due to higher cosmic variance at low multipoles, the significance of this measurement is not expected to improve from any future CMB temperature measurements. We demonstrate that weak lensing of the CMB due to scalar perturbations produces a corresponding SI violation in B modes of CMB polarization at smaller angular scales. The measurability of this phenomenon depends upon the scales (l range) over which power asymmetry is present. Power asymmetry, which is restricted only to l<64 in the temperature field, cannot lead to any significant observable effect from this new window. However, this effect can put an independent bound on the spatial range of scales of hemispherical asymmetry present in the scalar sector.

Analytical study of mode degeneracy in non-Hermitian photonic crystals with TM-like polarization

NASA Astrophysics Data System (ADS)

Yin, Xuefan; Liang, Yong; Ni, Liangfu; Wang, Zhixin; Peng, Chao; Li, Zhengbin

2017-08-01

We present a study of the mode degeneracy in non-Hermitian photonic crystals (PC) with TM-like polarization and C4 v symmetry from the perspective of the coupled-wave theory (CWT). The CWT framework is extended to include TE-TM coupling terms which are critical for modeling the accidental triple degeneracy within non-Hermitian PC systems. We derive the analytical form of the wave function and the condition of Dirac-like-cone dispersion when radiation loss is relatively small. We find that, similar to a real Dirac cone, the Dirac-like cone in non-Hermitian PCs possesses good linearity and isotropy, even with a ring of exceptional points (EPs) inevitably existing in the vicinity of the second-order Γ point. However, the Berry phase remains zero at the Γ point, indicating the cone does not obey the Dirac equation and is only a Dirac-like cone. The topological modal interchange phenomenon and nonzero Berry phase of the EPs are also discussed.

Influence of Two-Photon Absorption Anisotropy on Terahertz Emission Through Optical Rectification in Zinc-Blende Crystals

NASA Astrophysics Data System (ADS)

Sanjuan, Federico; Gaborit, Gwenaël; Coutaz, Jean-Louis

2018-04-01

We report for the first time on the observation of an angular anisotropy of the THz signal generated by optical rectification in a < 111 > ZnTe crystal. This cubic (zinc-blende) crystal in the < 111 > orientation exhibits both transverse isotropy for optical effects involving the linear χ (1) and nonlinear χ (2) susceptibilities. Thus, the observed anisotropy can only be related to χ (3) effect, namely two-photon absorption, which leads to the photo-generation of free carriers that absorb the generated THz signal. Two-photon absorption in zinc-blende crystals is known to be due to a spin-orbit interaction between the valence and higher-conduction bands. We perform a couple of measurements that confirm our hypothesis, as well as we fit the recorded data with a simple model. This two-photon absorption effect makes difficult an efficient generation, through optical rectification in < 111 > zinc-blende crystals, of THz beams of any given polarization state by only monitoring the laser pump polarization.

Structural characterization and numerical simulations of flow properties of standard and reservoir carbonate rocks using micro-tomography

NASA Astrophysics Data System (ADS)

Islam, Amina; Chevalier, Sylvie; Sassi, Mohamed

2018-04-01

With advances in imaging techniques and computational power, Digital Rock Physics (DRP) is becoming an increasingly popular tool to characterize reservoir samples and determine their internal structure and flow properties. In this work, we present the details for imaging, segmentation, as well as numerical simulation of single-phase flow through a standard homogenous Silurian dolomite core plug sample as well as a heterogeneous sample from a carbonate reservoir. We develop a procedure that integrates experimental results into the segmentation step to calibrate the porosity. We also look into using two different numerical tools for the simulation; namely Avizo Fire Xlab Hydro that solves the Stokes' equations via the finite volume method and Palabos that solves the same equations using the Lattice Boltzmann Method. Representative Elementary Volume (REV) and isotropy studies are conducted on the two samples and we show how DRP can be a useful tool to characterize rock properties that are time consuming and costly to obtain experimentally.

Majority of Solar Wind Intervals Support Ion-Driven Instabilities.

PubMed

Klein, K G; Alterman, B L; Stevens, M L; Vech, D; Kasper, J C

2018-05-18

We perform a statistical assessment of solar wind stability at 1 AU against ion sources of free energy using Nyquist's instability criterion. In contrast to typically employed threshold models which consider a single free-energy source, this method includes the effects of proton and He^{2+} temperature anisotropy with respect to the background magnetic field as well as relative drifts between the proton core, proton beam, and He^{2+} components on stability. Of 309 randomly selected spectra from the Wind spacecraft, 53.7% are unstable when the ion components are modeled as drifting bi-Maxwellians; only 4.5% of the spectra are unstable to long-wavelength instabilities. A majority of the instabilities occur for spectra where a proton beam is resolved. Nearly all observed instabilities have growth rates γ slower than instrumental and ion-kinetic-scale timescales. Unstable spectra are associated with relatively large He^{2+} drift speeds and/or a departure of the core proton temperature from isotropy; other parametric dependencies of unstable spectra are also identified.

Parity-violating CMB correlators with non-decaying statistical anisotropy

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

Bartolo, Nicola; Matarrese, Sabino; Shiraishi, Maresuke

2015-07-01

We examine the effect induced on cosmological correlators by the simultaneous breaking of parity and of statistical isotropy. As an example of this, we compute the scalar-scalar, scalar-tensor, tensor-tensor and scalar-scalar-scalar cosmological correlators in presence of the coupling L = f(φ) ( − 1/4 F{sup 2} + γ/4 F ∼F ) between the inflaton φ and a vector field with vacuum expectation value  A. For a suitably chosen function f, the energy in the vector field ρ{sub A} does not decay during inflation. This results in nearly scale-invariant signatures of broken statistical isotropy and parity. Specifically, we find that the scalar-scalar correlator of primordial curvature perturbations includes a quadrupolar anisotropy, P{submore » ζ}(k) = P(k)[1+g{sub *}( k-circumflex ⋅Â){sup 2}], and a (angle-averaged) scalar bispectrum that is a linear combination of the first 3 Legendre polynomials, B{sub ζ}(k{sub 1}, k{sub 2}, k{sub 3}) = ∑{sub L} c{sub L} P{sub L} ( k-circumflex {sub 1} ⋅  k-circumflex {sub 2}) P(k{sub 1}) P(k{sub 2}) + 2 perms , with c{sub 0}:c{sub 1}:c{sub 2}=2-3:1 (c{sub 1}≠0 is a consequence of parity violation, corresponding to the constant 0γ ≠ ). The latter is one of the main results of this paper, which provides for the first time a clear example of an inflationary model where a non-negligible c{sub 1} contribution to the bispectrum is generated. The scalar-tensor and tensor-tensor correlators induce characteristic signatures in the Cosmic Microwave Background temperature anisotropies (T) and polarization (E/B modes); namely, non-diagonal contributions to (a{sub ℓ1m1}a{sup *}{sub ℓ2m2}), with |ℓ{sub 1} − ℓ{sub 2}| = 1 in TT, TE, EE and BB, and |ℓ{sub 1} − ℓ{sub 2}| = 2 in TB and EB. The latest CMB bounds on the scalar observables (g{sub *}, c{sub 0}, c{sub 1} and c{sub 2}), translate into the upper limit ρ{sub A} / ρ{sub φ} ∼< 10{sup −9} at 0γ=. We find that the upper limit on the vector energy density becomes much more stringent as γ grows.« less

Interactions of Dust Grains with Coronal Mass Ejections and Solar Cycle Variations of the F-Coronal Brightness

NASA Technical Reports Server (NTRS)

Ragot, B. R.; Kahler, S. W.

2003-01-01

The density of interplanetary dust increases sunward to reach its maximum in the F corona, where its scattered white-light emission dominates that of the electron K corona above about 3 Solar Radius. The dust will interact with both the particles and fields of antisunward propagating coronal mass ejections (CMEs). To understand the effects of the CME/dust interactions we consider the dominant forces, with and without CMEs. acting on the dust in the 3-5 Solar Radius region. Dust grain orbits are then computed to compare the drift rates from 5 to 3 Solar Radius. for periods of minimum and maximum solar activity, where a simple CME model is adopted to distinguish between the two periods. The ion-drag force, even in the quiet solar wind, reduces the drift time by a significant factor from its value estimated with the Poynting-Robertson drag force alone. The ion-drag effects of CMEs result in even shorter drift times of the large (greater than or approx. 3 microns) dust grains. hence faster depletion rates and lower dust-pain densities, at solar maxima. If dominated by thermal emission, the near-infrared brightness will thus display solar cycle variations close to the dust plane of symmetry. While trapping the smallest of the grains, the CME magnetic fields also scatter the grains of intermediate size (0.1-3 microns) in latitude. If light scattering by small grains close to the Sun dominates the optical brightness. the scattering by the CME magnetic fields will result in a solar cycle variation of the optical brightness distribution not exceeding 100% at high latitudes, with a higher isotropy reached at solar maxima. A good degree of latitudinal isotropy is already reached at low solar activity since the magnetic fields of the quiet solar wind so close to the Sun are able to scatter the small (less than or approx. 3 microns) grains up to the polar regions in only a few days or less, producing strong perturbations of their trajectories in less than half their orbital periods. Finally, we consider possible observable consequences of individual CME/dust interactions. We show that the dust grains very likely have no observable effect on the dynamics of CMEs. The effect of an individual CME on the dust grains, however, might serve as a forecasting tool for the directions and amplitudes of the magnetic fields within the CME.

Thermal conductivity and phonon transport properties of silicon using perturbation theory and the environment-dependent interatomic potential

NASA Astrophysics Data System (ADS)

Pascual-Gutiérrez, José A.; Murthy, Jayathi Y.; Viskanta, Raymond

2009-09-01

Silicon thermal conductivities are obtained from the solution of the linearized phonon Boltzmann transport equation without the use of any parameter-fitting. Perturbation theory is used to compute the strength of three-phonon and isotope scattering mechanisms. Matrix elements based on Fermi's golden rule are computed exactly without assuming either average or mode-dependent Grüeisen parameters, and with no underlying assumptions of crystal isotropy. The environment-dependent interatomic potential is employed to describe the interatomic force constants and the perturbing Hamiltonians. A detailed methodology to accurately find three-phonon processes satisfying energy- and momentum-conservation rules is also described. Bulk silicon thermal conductivity values are computed across a range of temperatures and shown to match experimental data very well. It is found that about two-thirds of the heat transport in bulk silicon may be attributed to transverse acoustic modes. Effective relaxation times and mean free paths are computed in order to provide a more complete picture of the detailed transport mechanisms and for use with carrier transport models based on the Boltzmann transport equation.

Lensing as a probe of early universe: from CMB to galaxies

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

Hassani, Farbod; Baghram, Shant; Firouzjahi, Hassan, E-mail: farbod@physics.sharif.edu, E-mail: baghram@sharif.edu, E-mail: firouz@ipm.ir

The Cosmic Microwave Background (CMB) radiation lensing is a promising tool to study the physics of early universe. In this work we probe the imprints of deviations from isotropy and scale invariance of primordial curvature perturbation power spectrum on CMB lensing potential and convergence. Specifically, we consider a scale-dependent hemispherical asymmetry in primordial power spectrum. We show that the CMB lensing potential and convergence and also the cross-correlation of the CMB lensing and late time galaxy convergence can probe the amplitude and the scale dependence of the dipole modulation. As another example, we consider a primordial power spectrum with localmore » feature. We show that the CMB lensing and the cross-correlation of the CMB lensing and galaxy lensing can probe the amplitude and the shape of the local feature. We show that the cross correlation of CMB lensing convergence and galaxy lensing is capable to probe the effects of local features in power spectrum on smaller scales than the CMB lensing. Finally we showed that the current data can constrain the amplitude and moment dependence of dipole asymmetry.« less

How Isotropic is the Universe?

PubMed

Saadeh, Daniela; Feeney, Stephen M; Pontzen, Andrew; Peiris, Hiranya V; McEwen, Jason D

2016-09-23

A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of (σ_{V}/H)_{0}<4.7×10^{-11} (95% C.L.), which is an order of magnitude tighter than previous Planck results that used cosmic microwave background temperature only. We also place upper limits on other modes of anisotropic expansion, with the weakest limit arising from the regular tensor mode, (σ_{T,reg}/H)_{0}<1.0×10^{-6} (95% C.L.). Including all degrees of freedom simultaneously for the first time, anisotropic expansion of the Universe is strongly disfavored, with odds of 121 000:1 against.

Modelling welded material for ultrasonic testing using MINA: Theory and applications

NASA Astrophysics Data System (ADS)

Moysan, J.; Corneloup, G.; Chassignole, B.; Gueudré, C.; Ploix, M. A.

2012-05-01

Austenitic steel multi-pass welds exhibit a heterogeneous and anisotropic structure that causes difficulties in the ultrasonic testing. Increasing the material knowledge is a long term research field for LCND laboratory and EDF Les Renardières in France. A specific model has been developed: the MINA model (Modelling an Isotropy from Notebook of Arc welding). Welded material is described in 2D for flat position arc welding with shielded electrode (SMAW) at a functional scale for UT modeling. The grain growth is the result of three physical phenomena: epitaxial growth, influence of temperature gradient, and competition between the grains. The model uses phenomenological rules to combine these three phenomena. A limited number of parameters is used to make the modelling possible from the information written down in a notebook of arc welding. We present all these principles with 10 years' hindsight. To illustrate the model's use, we present conclusions obtained with two recent applications. In conclusion we give also insights on other research topics around this model : inverse problem using a F.E.M. code simulating the ultrasonic propagation, in position welding, 3D prospects, GTAW.

Stability of Poisson Equilibria and Hamiltonian Relative Equilibria by Energy Methods

NASA Astrophysics Data System (ADS)

Patrick, George W.; Roberts, Mark; Wulff, Claudia

2004-12-01

We develop a general stability theory for equilibrium points of Poisson dynamical systems and relative equilibria of Hamiltonian systems with symmetries, including several generalisations of the Energy-Casimir and Energy-Momentum Methods. Using a topological generalisation of Lyapunov’s result that an extremal critical point of a conserved quantity is stable, we show that a Poisson equilibrium is stable if it is an isolated point in the intersection of a level set of a conserved function with a subset of the phase space that is related to the topology of the symplectic leaf space at that point. This criterion is applied to generalise the energy-momentum method to Hamiltonian systems which are invariant under non-compact symmetry groups for which the coadjoint orbit space is not Hausdorff. We also show that a G-stable relative equilibrium satisfies the stronger condition of being A-stable, where A is a specific group-theoretically defined subset of G which contains the momentum isotropy subgroup of the relative equilibrium. The results are illustrated by an application to the stability of a rigid body in an ideal irrotational fluid.

Probability distribution for the Gaussian curvature of the zero level surface of a random function

NASA Astrophysics Data System (ADS)

Hannay, J. H.

2018-04-01

A rather natural construction for a smooth random surface in space is the level surface of value zero, or ‘nodal’ surface f(x,y,z)  =  0, of a (real) random function f; the interface between positive and negative regions of the function. A physically significant local attribute at a point of a curved surface is its Gaussian curvature (the product of its principal curvatures) because, when integrated over the surface it gives the Euler characteristic. Here the probability distribution for the Gaussian curvature at a random point on the nodal surface f  =  0 is calculated for a statistically homogeneous (‘stationary’) and isotropic zero mean Gaussian random function f. Capitalizing on the isotropy, a ‘fixer’ device for axes supplies the probability distribution directly as a multiple integral. Its evaluation yields an explicit algebraic function with a simple average. Indeed, this average Gaussian curvature has long been known. For a non-zero level surface instead of the nodal one, the probability distribution is not fully tractable, but is supplied as an integral expression.

Quantitative analysis of the polarization characteristics of atherosclerotic plaques

NASA Astrophysics Data System (ADS)

Gubarkova, Ekaterina V.; Kirillin, Michail Y.; Dudenkova, Varvara V.; Kiseleva, Elena B.; Moiseev, Alexander A.; Gelikonov, Grigory V.; Timofeeva, Lidia B.; Fiks, Ilya I.; Feldchtein, Felix I.; Gladkova, Natalia D.

2016-04-01

In this study we demonstrate the capability of cross-polarization optical coherence tomography (CP OCT) to assess collagen and elastin fibers condition in atherosclerotic plaques basing on ratio of the OCT signal levels in cross- and co- polarizations. We consider the depolarization factor (DF) and the effective birefringence (Δn) as quantitative characteristics of CP OCT images. We revealed that calculation of both DF and Δn in the region of interest (fibrous cap) yields a statistically significant difference between stable and unstable plaques (0.46+/-0.21 vs 0.09+/-0.04 for IDF; (4.7+/-1.0)•10-4 vs (2.5+/-0.7)•10-4 for Δn p<0.05). In parallel with CP OCT we used the nonlinear microscopy for analysis of thin cross-section of atherosclerotic plaque, revealing the different average isotropy index of collagen and elastin fibers for stable and unstable plaques (0.30 +/- 0.10 vs 0.70 +/- 0.08; p<0.001). The proposed approach for quantitative assessment of CP OCT images allows cross-scattering and birefringence characterization of stable and unstable atherosclerotic plaques.

Small-scale anisotropy induced by spectral forcing and by rotation in non-helical and helical turbulence

NASA Astrophysics Data System (ADS)

Vallefuoco, Donato; Naso, Aurore; Godeferd, Fabien S.

2018-02-01

We study the effect of large-scale spectral forcing on the scale-dependent anisotropy of the velocity field in direct numerical simulations of homogeneous turbulence. ABC-type forcing and helical or non-helical Euler-type forcing are considered. We propose a scale-dependent characterisation of anisotropy based on a modal decomposition of the two-point velocity tensor spectrum. This produces direction-dependent spectra of energy, helicity and polarisation. We examine the conditions that allow anisotropy to develop in the small scales due to forcing and we show that the theoretically expected isotropy is not exactly obtained, even in the smallest scales, for ABC and helical Euler forcings. When adding rotation, the anisotropy level in ABC-forced simulations is similar to that of lower Rossby number Euler-forced runs. Moreover, even at low rotation rate, the natural anisotropy induced by the Coriolis force is visible at all scales, and two distinct wavenumber ranges appear from our fine-grained characterisation, not separated by the Zeman scale but by a scale where rotation and dissipation are balanced.

An efficient method for removing point sources from full-sky radio interferometric maps

NASA Astrophysics Data System (ADS)

Berger, Philippe; Oppermann, Niels; Pen, Ue-Li; Shaw, J. Richard

2017-12-01

A new generation of wide-field radio interferometers designed for 21-cm surveys is being built as drift scan instruments allowing them to observe large fractions of the sky. With large numbers of antennas and frequency channels, the enormous instantaneous data rates of these telescopes require novel, efficient, data management and analysis techniques. The m-mode formalism exploits the periodicity of such data with the sidereal day, combined with the assumption of statistical isotropy of the sky, to achieve large computational savings and render optimal analysis methods computationally tractable. We present an extension to that work that allows us to adopt a more realistic sky model and treat objects such as bright point sources. We develop a linear procedure for deconvolving maps, using a Wiener filter reconstruction technique, which simultaneously allows filtering of these unwanted components. We construct an algorithm, based on the Sherman-Morrison-Woodbury formula, to efficiently invert the data covariance matrix, as required for any optimal signal-to-noise ratio weighting. The performance of our algorithm is demonstrated using simulations of a cylindrical transit telescope.

Criticality and phase diagram of quantum long-range O(N ) models

NASA Astrophysics Data System (ADS)

Defenu, Nicolò; Trombettoni, Andrea; Ruffo, Stefano

2017-09-01

Several recent experiments in atomic, molecular, and optical systems motivated a huge interest in the study of quantum long-range systems. Our goal in this paper is to present a general description of their critical behavior and phases, devising a treatment valid in d dimensions, with an exponent d +σ for the power-law decay of the couplings in the presence of an O(N ) symmetry. By introducing a convenient ansatz for the effective action, we determine the phase diagram for the N -component quantum rotor model with long-range interactions, with N =1 corresponding to the Ising model. The phase diagram in the σ -d plane shows a nontrivial dependence on σ . As a consequence of the fact that the model is quantum, the correlation functions are anisotropic in the spatial and time coordinates for σ smaller than a critical value, and in this region the isotropy is not restored even at criticality. Results for the correlation length exponent ν , the dynamical critical exponent z , and a comparison with numerical findings for them are presented.

The projected gravitational potential of the galaxy cluster MACS J1206 derived from galaxy kinematics

NASA Astrophysics Data System (ADS)

Stock, Dennis; Meyer, Sven; Sarli, Eleonora; Bartelmann, Matthias; Balestra, Italo; Grillo, Claudio; Koekemoer, Anton; Mercurio, Amata; Nonino, Mario; Rosati, Piero

2015-12-01

We reconstruct the radial profile of the projected gravitational potential of the galaxy cluster MACS J1206 from 592 spectroscopic measurements of velocities of cluster members. To accomplish this, we use a method we have developed recently based on the Richardson-Lucy deprojection algorithm and an inversion of the spherically-symmetric Jeans equation. We find that, within the uncertainties, our reconstruction agrees very well with a potential reconstruction from weak and strong gravitational lensing as well as with a potential obtained from X-ray measurements. In addition, our reconstruction is in good agreement with several common analytic profiles of the lensing potential. Varying the anisotropy parameter in the Jeans equation, we find that isotropy parameters, which are either small, β ≲ 0.2, or decrease with radius, yield potential profiles that strongly disagree with that obtained from gravitational lensing. We achieve the best agreement between our potential profile and the profile from gravitational lensing if the anisotropy parameter rises steeply to β ≈ 0.6 within ≈ 0.5 Mpc and stays constant further out.

Optics of short-pitch deformed-helix ferroelectric liquid crystals: Symmetries, exceptional points, and polarization-resolved angular patterns

NASA Astrophysics Data System (ADS)

Kiselev, Alexei D.; Chigrinov, Vladimir G.

2014-10-01

In order to explore electric-field-induced transformations of polarization singularities in the polarization-resolved angular (conoscopic) patterns emerging after deformed-helix ferroelectric liquid crystal (DHFLC) cells with subwavelength helix pitch, we combine the transfer matrix formalism with the results for the effective dielectric tensor of biaxial FLCs evaluated using an improved technique of averaging over distorted helical structures. Within the framework of the transfer matrix method, we deduce a number of symmetry relations and show that the symmetry axis of L lines (curves of linear polarization) is directed along the major in-plane optical axis which rotates under the action of the electric field. When the angle between this axis and the polarization plane of incident linearly polarized light is above its critical value, the C points (points of circular polarization) appear in the form of symmetrically arranged chains of densely packed star-monstar pairs. We also emphasize the role of phase singularities of a different kind and discuss the enhanced electro-optic response of DHFLCs near the exceptional point where the condition of zero-field isotropy is fulfilled.

Morphological and mechanical properties of blades of Saccharina latissima

NASA Astrophysics Data System (ADS)

Vettori, Davide; Nikora, Vladimir

2017-09-01

Interactions between water flow and aquatic vegetation strongly depend on morphological and biomechanical characteristics of vegetation. Although any physical or numerical model that aims to replicate flow-vegetation interactions requires these characteristics, information on morphology and mechanics of vegetation living in coastal waters remains insufficient. The present study investigates the mechanical properties of blades of Saccharina latissima, a seaweed species spread along the shores of the UK and North East Atlantic. More than 50 seaweed samples with lengths spanning from 150 mm to 650 mm were collected from Loch Fyne (Scotland) and tested. Seaweed blades had a natural 'stretched droplet' shape with bullations in the central fascia and ruffled edges in the area close to the stipe. Their morphological features showed high variability for samples longer than 400 mm. The blades were almost neutrally buoyant, their material was found to be very flexible and ductile, being stiffer in longer blades. The laboratory tests showed that estimates of tensile Young's modulus appeared to be similar to bending Young's modulus suggesting a reasonable degree of isotropy in studied seaweed tissues.

Hedonic approaches based on spatial econometrics and spatial statistics: application to evaluation of project benefits

NASA Astrophysics Data System (ADS)

Tsutsumi, Morito; Seya, Hajime

2009-12-01

This study discusses the theoretical foundation of the application of spatial hedonic approaches—the hedonic approach employing spatial econometrics or/and spatial statistics—to benefits evaluation. The study highlights the limitations of the spatial econometrics approach since it uses a spatial weight matrix that is not employed by the spatial statistics approach. Further, the study presents empirical analyses by applying the Spatial Autoregressive Error Model (SAEM), which is based on the spatial econometrics approach, and the Spatial Process Model (SPM), which is based on the spatial statistics approach. SPMs are conducted based on both isotropy and anisotropy and applied to different mesh sizes. The empirical analysis reveals that the estimated benefits are quite different, especially between isotropic and anisotropic SPM and between isotropic SPM and SAEM; the estimated benefits are similar for SAEM and anisotropic SPM. The study demonstrates that the mesh size does not affect the estimated amount of benefits. Finally, the study provides a confidence interval for the estimated benefits and raises an issue with regard to benefit evaluation.

Crystallographic Lattice Boltzmann Method

PubMed Central

Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh

2016-01-01

Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows. PMID:27251098

Tensorial analysis of Eshelby stresses in 3D supercooled liquids

NASA Astrophysics Data System (ADS)

Lemaître, Anaël

2015-10-01

It was recently proposed that the local rearrangements governing relaxation in supercooled liquids impress on the liquid medium long-ranged (Eshelby) stress fluctuations that accumulate over time. From this viewpoint, events must be characterized by elastic dipoles, which are second order tensors, and Eshelby fields are expected to show up in stress and stress increment correlations, which are fourth order tensor fields. We construct here an analytical framework that permits analyzing such tensorial correlations in isotropic media in view of accessing Eshelby fields. Two spherical bases are introduced, which correspond to Cartesian and spherical coordinates for tensors. We show how they can be used to decompose stress correlations and thus test such properties as isotropy and power-law scalings. Eshelby fields and the predicted stress correlations in an infinite medium are shown to belong to an algebra that can conveniently be described using the spherical tensor bases. Using this formalism, we demonstrate that the inherent stress field of 3D supercooled liquids is power law correlated and carries the signature of Eshelby fields, thus supporting the idea that relaxation events give rise to Eshelby stresses that accumulate over time.

Upper Mantle Dynamics of Bangladesh by Splitting Analyzes of Core Refracted SKS and SKKS Waves

NASA Astrophysics Data System (ADS)

Tiwari, A. K.; Bhushan, K.; Eken, T.; Singh, A.

2017-12-01

New shear wave splitting measurements are obtained from hitherto less studied Bengal Basin using core refracted SKS and SKKS phases. Splitting parameters, time delays (δt) and fast polarization directions (Φ) were estimated through analysis of 64 high-quality waveforms (≥ 2.5 signal to noise ratio) from 29 earthquakes with magnitude ≥5.5 recorded at eight seismic stations deployed over Bangladesh. We found no evidence of splitting which indicates azimuthal isotropy beneath the region. Null measurements can be explained by near vertical axis of anisotropy or by the presence of multiple anisotropic layers with different fast polarization directions, where combined effect results in null. We consider that the presence of partial melts within the upper mantle due to Kerguelen mantle plume activities may be the potential geodynamic cause for observed null measurements. It locally perturbed mantle convection flow beneath the region and reoriented the lattice preferred orientation of the upper mantle mineral mainly olivine as this disabled the core refracted SKS and SKKS phases to scan the anisotropic characteristics of the region, and hence null measurements are obtained.

Anisotropy of the cosmic blackbody radiation.

PubMed

Wilkinson, D T

1986-06-20

The universe is filled with thermal radiation having a current temperature of 2.75 K. Originating in the very early universe, this radiation furnishes strong evidence that the Big Bang cosmology best describes our expanding universe from an incredibly hot, compacted early stage until now. The model can be used to extrapolate our physics backward in time to predict events whose effects might be observable in the 2.75 K radiation today. The spectrum and isotropy are being studied with sophisticated microwave radiometers on the ground, in balloons, and in satellites. The results are as predicted by the simple theory: the spectrum is that of a blackbody (to a few percent) and the radiation is isotropic (to 0.01 percent) except for a local effect due to our motion through the radiation. However, a problem is emerging. Primordial fluctuations in the mass density, which later became the great clusters of galaxies that we see today, should have left an imprint on the 2.75 K radiation-bumpiness on the sky at angular scales of about 10 arc minutes. They have not yet been seen.

Improved Limits on Gamma-Ray Burst Repetition from BATSE

NASA Technical Reports Server (NTRS)

Tegmark, Max; Hartmann, Dieter H.; Briggs, Michael S.; Hakkila, Jon; Meegan, Charles A.

1996-01-01

We tighten previous upper limits on gamma-ray burst repetition by analyzing the angular power spectrum of the BATSE 3B catalog of 1122 bursts. At 95% confidence, we find that no more than 2% of all observed bursts can be labeled as repeaters, even if no sources are observed to repeat more than once. If a fraction f of all observed bursts can be labeled as repeaters that are observed to burst upsilon times each, then all models with (upsilon - 1)f greater than or equal to 0.05 are ruled out at 99% confidence, as compared to the best previous 99% limit (upsilon - 1)f greater than or equal to 0.27. At 95% confidence, our new limit is (upsilon - 1)f greater than or equal to 0.02. Thus, even a cluster of six events from a single source would have caused excess power above that present in the 3B catalog. We conclude that the current BATSE data are consistent with no repetition of classical gamma-ray bursts and that any repeater model is severely constrained by the near-perfect isotropy of their angular distribution.

Improved Limits on Gamma-Ray Burst Repetition from BATSE

NASA Technical Reports Server (NTRS)

Tegmark, Max; Hartmann, Dieter H.; Briggs, Michael S.; Meegan, Charles A.; Hakkila, Jon

1996-01-01

We tighten previous upper limits on gamma-ray burst repetition by analyzing the angular power spectrum of the BATSE 3B catalog of 1122 bursts. At 95% confidence, we find that no more than 2% of all observed bursts can be labeled as repeaters, even if no sources are observed to repeat more than once. If a fraction f of all observed bursts can be labeled as repeaters that are observed to burst nu times each, then all models with (nu - 1)f greater than or equal to 0.05 are ruled out at 99% confidence, as compared to the best previous 99% limit (nu - 1)f greater than or equal to 0.27. At 95% confidence, our new limit is (nu - 1)f greater than or equal to 0.02. Thus, even a cluster of six events from a single source would have caused excess power above that present in the 3B catalog. We conclude that the current BATSE data are consistent with no repetition of classical gamma-ray bursts and that any repeater model is severely constrained by the near-perfect isotropy of their angular dis- tribution.

Unconditionally stable finite-difference time-domain methods for modeling the Sagnac effect

NASA Astrophysics Data System (ADS)

Novitski, Roman; Scheuer, Jacob; Steinberg, Ben Z.

2013-02-01

We present two unconditionally stable finite-difference time-domain (FDTD) methods for modeling the Sagnac effect in rotating optical microsensors. The methods are based on the implicit Crank-Nicolson scheme, adapted to hold in the rotating system reference frame—the rotating Crank-Nicolson (RCN) methods. The first method (RCN-2) is second order accurate in space whereas the second method (RCN-4) is fourth order accurate. Both methods are second order accurate in time. We show that the RCN-4 scheme is more accurate and has better dispersion isotropy. The numerical results show good correspondence with the expression for the classical Sagnac resonant frequency splitting when using group refractive indices of the resonant modes of a microresonator. Also we show that the numerical results are consistent with the perturbation theory for the rotating degenerate microcavities. We apply our method to simulate the effect of rotation on an entire Coupled Resonator Optical Waveguide (CROW) consisting of a set of coupled microresonators. Preliminary results validate the formation of a rotation-induced gap at the center of a transfer function of a CROW.

A quest for 2D lattice materials for actuation

NASA Astrophysics Data System (ADS)

Pronk, T. N.; Ayas, C.; Tekõglu, C.

2017-08-01

In the last two decades, most of the studies in shape morphing technology have focused on the Kagome lattice materials, which have superior properties such as in-plane isotropy, high specific stiffness and strength, and low energy requirement for actuation of its members. The Kagome lattice is a member of the family of semi-regular tessellations of the plane. Two fundamental questions naturally arise: i-) What makes a lattice material suitable for actuation? ii-) Are there other tessellations more effective than the Kagome lattice for actuation? The present paper tackles both questions, and provides a clear answer to the first one by comparing an alternative lattice material, the hexagonal cupola, with the Kagome lattice in terms of mechanical/actuation properties. The second question remains open, but, hopefully easier to challenge owing to a newly-discovered criterion: for an n-dimensional (n = 2 , 3) in-plane isotropic lattice material to be suitable for actuation, its pin-jointed equivalent must obey the generalised Maxwell's rule, and must possess M = 3(n - 1) non strain-producing finite kinematic mechanisms.

The Clock Mission Optis

NASA Astrophysics Data System (ADS)

Dittus, Hansjörg; Lämmerzahl, Claus

Clocks are an almost universal tool for exploring the fundamental structure of theories related to relativity. For future clock experiments, it is important for them to be performed in space. One mission which has the capability to perform and improve all relativity tests based on clocks by several orders of magnitude is OPTIS. These tests consist of (i) tests of the isotropy of light propagation (from which information about the matter sector which the optical resonators are made of can also be drawn), (ii) tests of the constancy of the speed of light, (iii) tests of the universality of the gravitational redshift by comparing clocks based on light propagation, like light clocks and various atomic clocks, (iv) time dilation based on the Doppler effect, (v) measuring the absolute gravitational redshift, (vi) measuring the perihelion advance of the satellite's orbit by using very precise tracking techniques, (vii) measuring the Lense-Thirring effect, and (viii) testing Newton's gravitational potential law on the scale of Earth-bound satellites. The corresponding tests are not only important for fundamental physics but also indispensable for practical purposes like navigation, Earth sciences, metrology, etc.

Upper mantle dynamics of Bangladesh by splitting analysis of core-mantle refracted SKS, PKS, and SKKS phases

NASA Astrophysics Data System (ADS)

Tiwari, Ashwani Kant; Bhushan, Kirti; Eken, Tuna; Singh, Arun

2018-06-01

New shear wave splitting measurements are obtained from the Bengal Basin using core-mantle refracted SKS, PKS, and SKKS phases. The splitting parameters, namely time delays (δ t) and fast polarization directions (ϕ), were estimated through analysis of 54 high-quality waveforms (⩾ 2.5 signal to noise ratio) from 30 earthquakes with magnitude ⩾ 5.5 recorded at ten seismic stations deployed over Bangladesh. No evidence of splitting was found, which indicates azimuthal isotropy beneath the region. These null measurements can be explained by either vertically dipping anisotropic fast axes or by the presence of multiple horizontal anisotropic layers with different fast polarization directions, where the combined effect results in a null characterization. The anisotropic fabric preserved from rifting episodes of Antarctica and India, subduction-related dynamics of the Indo-Burmese convergence zone, and northward movement of the Indian plate creating shear at the base of the lithosphere can explain the observed null measurements. The combined effect of all these most likely results in a strong vertical anisotropic heterogeneity, creating the observed null results.

Left-invariant Einstein metrics on S3 ×S3

NASA Astrophysics Data System (ADS)

Belgun, Florin; Cortés, Vicente; Haupt, Alexander S.; Lindemann, David

2018-06-01

The classification of homogeneous compact Einstein manifolds in dimension six is an open problem. We consider the remaining open case, namely left-invariant Einstein metrics g on G = SU(2) × SU(2) =S3 ×S3. Einstein metrics are critical points of the total scalar curvature functional for fixed volume. The scalar curvature S of a left-invariant metric g is constant and can be expressed as a rational function in the parameters determining the metric. The critical points of S, subject to the volume constraint, are given by the zero locus of a system of polynomials in the parameters. In general, however, the determination of the zero locus is apparently out of reach. Instead, we consider the case where the isotropy group K of g in the group of motions is non-trivial. When K ≇Z2 we prove that the Einstein metrics on G are given by (up to homothety) either the standard metric or the nearly Kähler metric, based on representation-theoretic arguments and computer algebra. For the remaining case K ≅Z2 we present partial results.

Testing the cosmic anisotropy with supernovae data: Hemisphere comparison and dipole fitting

NASA Astrophysics Data System (ADS)

Deng, Hua-Kai; Wei, Hao

2018-06-01

The cosmological principle is one of the cornerstones in modern cosmology. It assumes that the universe is homogeneous and isotropic on cosmic scales. Both the homogeneity and the isotropy of the universe should be tested carefully. In the present work, we are interested in probing the possible preferred direction in the distribution of type Ia supernovae (SNIa). To our best knowledge, two main methods have been used in almost all of the relevant works in the literature, namely the hemisphere comparison (HC) method and the dipole fitting (DF) method. However, the results from these two methods are not always approximately coincident with each other. In this work, we test the cosmic anisotropy by using these two methods with the joint light-curve analysis (JLA) and simulated SNIa data sets. In many cases, both methods work well, and their results are consistent with each other. However, in the cases with two (or even more) preferred directions, the DF method fails while the HC method still works well. This might shed new light on our understanding of these two methods.

Linking high-energy cosmic particles by black-hole jets embedded in large-scale structures

NASA Astrophysics Data System (ADS)

Fang, Ke; Murase, Kohta

2018-04-01

The origin of ultrahigh-energy cosmic rays (UHECRs) is a half-century-old enigma1. The mystery has been deepened by an intriguing coincidence: over ten orders of magnitude in energy, the energy generation rates of UHECRs, PeV neutrinos and isotropic sub-TeV γ-rays are comparable, which hints at a grand unified picture2. Here we report that powerful black hole jets in aggregates of galaxies can supply the common origin for all of these phenomena. Once accelerated by a jet, low-energy cosmic rays confined in the radio lobe are adiabatically cooled; higher-energy cosmic rays leaving the source interact with the magnetized cluster environment and produce neutrinos and γ-rays; the highest-energy particles escape from the host cluster and contribute to the observed cosmic rays above 100 PeV. The model is consistent with the spectrum, composition and isotropy of the observed UHECRs, and also explains the IceCube neutrinos and the non-blazar component of the Fermi γ-ray background, assuming a reasonable energy output from black hole jets in clusters.

Importance of the Correlation between Width and Length in the Shape Analysis of Nanorods: Use of a 2D Size Plot To Probe Such a Correlation.

PubMed

Zhao, Zhihua; Zheng, Zhiqin; Roux, Clément; Delmas, Céline; Marty, Jean-Daniel; Kahn, Myrtil L; Mingotaud, Christophe

2016-08-22

Analysis of nanoparticle size through a simple 2D plot is proposed in order to extract the correlation between length and width in a collection or a mixture of anisotropic particles. Compared to the usual statistics on the length associated with a second and independent statistical analysis of the width, this simple plot easily points out the various types of nanoparticles and their (an)isotropy. For each class of nano-objects, the relationship between width and length (i.e., the strong or weak correlations between these two parameters) may suggest information concerning the nucleation/growth processes. It allows one to follow the effect on the shape and size distribution of physical or chemical processes such as simple ripening. Various electron microscopy pictures from the literature or from the authors' own syntheses are used as examples to demonstrate the efficiency and simplicity of the proposed 2D plot combined with a multivariate analysis. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Discovery of Coherent Pulsations from the Ultraluminous X-Ray Source NGC 7793 P13

NASA Technical Reports Server (NTRS)

Furst, F.; Walton, D. J.; Harrison, F. A.; Stern, D.; Barret, D.; Brightman, M.; Fabian, A. C.; Grefenstette, B.; Madsen, K. K.; Middleton, M. J.;

Vapor Phase Synthesis of Organometal Halide Perovskite Nanowires for Tunable Room-Temperature Nanolasers.

PubMed

Xing, Jun; Liu, Xin Feng; Zhang, Qing; Ha, Son Tung; Yuan, Yan Wen; Shen, Chao; Sum, Tze Chien; Xiong, Qihua

2015-07-08

Semiconductor nanowires have received considerable attention in the past decade driven by both unprecedented physics derived from the quantum size effect and strong isotropy and advanced applications as potential building blocks for nanoscale electronics and optoelectronic devices. Recently, organic-inorganic hybrid perovskites have been shown to exhibit high optical absorption coefficient, optimal direct band gap, and long electron/hole diffusion lengths, leading to high-performance photovoltaic devices. Herein, we present the vapor phase synthesis free-standing CH3NH3PbI3, CH3NH3PbBr3, and CH3NH3PbIxCl3(-x) perovskite nanowires with high crystallinity. These rectangular cross-sectional perovskite nanowires have good optical properties and long electron hole diffusion length, which ensure adequate gain and efficient optical feedback. Indeed, we have demonstrated optical-pumped room-temperature CH3NH3PbI3 nanowire lasers with near-infrared wavelength of 777 nm, low threshold of 11 μJ/cm(2), and a quality factor as high as 405. Our research advocates the promise of optoelectronic devices based on organic-inorganic perovskite nanowires.

Hyperuniform Disordered photonic bandgap materials, from 2D to 3D, and their applications

NASA Astrophysics Data System (ADS)

Man, Weining; Florescu, Marian; Sahba, Shervin; Sellers, Steven

Recently, hyperuniform disordered systems attracted increasing attention due to their unique physical properties and the potential possibilities of self-assembling them. We had introduced a class of 2D hyperuniform disordered (HUD) photonic bandgap (PBG) materials enabled by a novel constrained optimization method for engineering the material's isotropic photonic bandgap. The intrinsic isotropy in these disordered structures is an inherent advantage associated with the lack of crystalline order, offering unprecedented freedom for functional defect design impossible to achieve in photonic crystals. Beyond our previous experimental work using macroscopic samples with microwave radiation, we demonstrated functional devices based on submicron-scale planar hyperuniform disordered PBG structures further highlight their ability to serve as highly compact, flexible and energy-efficient platforms for photonic integrated circuits. We further extended the design, fabrication, and characterization of the disordered photonic system into 3D. We also identify local self-uniformity as a novel measure of a disordered network's internal structural similarity, which we found crucial for photonic band gap formation. National Science Foundations award DMR-1308084.

Finite Element Aircraft Simulation of Turbulence

NASA Technical Reports Server (NTRS)

McFarland, R. E.

1997-01-01

A turbulence model has been developed for realtime aircraft simulation that accommodates stochastic turbulence and distributed discrete gusts as a function of the terrain. This model is applicable to conventional aircraft, V/STOL aircraft, and disc rotor model helicopter simulations. Vehicle angular activity in response to turbulence is computed from geometrical and temporal relationships rather than by using the conventional continuum approximations that assume uniform gust immersion and low frequency responses. By using techniques similar to those recently developed for blade-element rotor models, the angular-rate filters of conventional turbulence models are not required. The model produces rotational rates as well as air mass translational velocities in response to both stochastic and deterministic disturbances, where the discrete gusts and turbulence magnitudes may be correlated with significant terrain features or ship models. Assuming isotropy, a two-dimensional vertical turbulence field is created. A novel Gaussian interpolation technique is used to distribute vertical turbulence on the wing span or lateral rotor disc, and this distribution is used to compute roll responses. Air mass velocities are applied at significant centers of pressure in the computation of the aircraft's pitch and roll responses.

Ensemble solute transport in two-dimensional operator-scaling random fields

NASA Astrophysics Data System (ADS)

Monnig, Nathan D.; Benson, David A.; Meerschaert, Mark M.

2008-02-01

Motivated by field measurements of aquifer hydraulic conductivity (K), recent techniques were developed to construct anisotropic fractal random fields in which the scaling, or self-similarity parameter, varies with direction and is defined by a matrix. Ensemble numerical results are analyzed for solute transport through these two-dimensional "operator-scaling" fractional Brownian motion ln(K) fields. Both the longitudinal and transverse Hurst coefficients, as well as the "radius of isotropy" are important to both plume growth rates and the timing and duration of breakthrough. It is possible to create operator-scaling fractional Brownian motion fields that have more "continuity" or stratification in the direction of transport. The effects on a conservative solute plume are continually faster-than-Fickian growth rates, highly non-Gaussian shapes, and a heavier tail early in the breakthrough curve. Contrary to some analytic stochastic theories for monofractal K fields, the plume growth rates never exceed A. Mercado's (1967) purely stratified aquifer growth rate of plume apparent dispersivity proportional to mean distance. Apparent superstratified growth must be the result of other demonstrable factors, such as initial plume size.

On Geomagnetism and Paleomagnetism I

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

2000-01-01

A partial description of Earth's broad scale, core-source magnetic field has been developed and tested three ways. The description features an expected, or mean, spatial magnetic power spectrum that is approximately inversely proportional to horizontal wavenumber atop Earth's core. This multipole spectrum describes a magnetic energy range; it is not steep enough for Gubbins' magnetic dissipation range. Temporal variations of core multipole powers about mean values are to be expected and are described statistically, via trial probability distribution functions, instead of deterministically, via trial solution of closed transport equations. The distributions considered here are closed and neither require nor prohibit magnetic isotropy. The description is therefore applicable to, and tested against, both dipole and low degree non-dipole fields. In Part 1, a physical basis for an expectation spectrum is developed and checked. The description is then combined with main field models of twentieth century satellite and surface geomagnetic field measurements to make testable predictions of the radius of Earth's core. The predicted core radius is 0.7% above the 3480 km seismological value. Partial descriptions of other planetary dipole fields are noted.

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

Li, Xiao-Dong; Park, Changbom; Forero-Romero, J. E.

We propose a method based on the redshift dependence of the Alcock-Paczynski (AP) test to measure the expansion history of the universe. It uses the isotropy of the galaxy density gradient field to constrain cosmological parameters. If the density parameter Ω {sub m} or the dark energy equation of state w are incorrectly chosen, the gradient field appears to be anisotropic with the degree of anisotropy varying with redshift. We use this effect to constrain the cosmological parameters governing the expansion history of the universe. Although redshift-space distortions (RSD) induced by galaxy peculiar velocities also produce anisotropies in the gradientmore » field, these effects are close to uniform in magnitude over a large range of redshift. This makes the redshift variation of the gradient field anisotropy relatively insensitive to the RSD. By testing the method on mock surveys drawn from the Horizon Run 3 cosmological N-body simulations, we demonstrate that the cosmological parameters can be estimated without bias. Our method is complementary to the baryon acoustic oscillation or topology methods as it depends on D{sub AH} , the product of the angular diameter distance and the Hubble parameter.« less

Anisotropy of the cosmic blackbody radiation

NASA Technical Reports Server (NTRS)

Wilkinson, D. T.

1986-01-01

The universe is filled with thermal radiation having a current temperature of 2.75 K. Originating in the very early universe, this radiation furnishes strong evidence that the Big Bang cosmology best describes our expanding universe from an incredibly hot, compacted early stage until now. The model can be used to extrapolate our physics backward in time to predict events whose effects might be observable in the 2.75 K radiation today. The spectrum and isotropy are being studied with sophisticated microwave radiometers on the ground, in balloons, and in satellites. The results are as predicted by the simple theory: the spectrum is that of a blackbody (to a few percent) and the radiation is isotropic (to 0.01 percent) except for a local effect due to our motion through the radiation. However, a problem is emerging. Primordial fluctuations in the mass density, which later became the great clusters of galaxies that we see today, should have left an imprint on the 2.75 K radiation - bumpiness on the sky at angular scales of about 10 arc minutes. They have not been seen.

Scattering of an electromagnetic light wave from a quasi-homogeneous medium with semisoft boundary

NASA Astrophysics Data System (ADS)

Zhou, Jianyang; Zhao, Daomu

2016-08-01

Based on the first-order Born approximation, the scattering of an electromagnetic plane wave from a relatively more realistic random medium, a quasi-homogeneous medium with semisoft boundary, has been investigated. The analytic expressions for the spectral density, the spectral degree of coherence and the spectral degree of polarization have been derived, and the effects of the characteristics of the medium and the polarization of the incident light wave on the far-zone scattered field are determined. The numerical simulations indicate that, with the increasing of the edge softness M of the medium, the spectral density presents a pattern with interference fringes, and the number, position and width of interference fringes can be modified by the parameter. It is also found that there is an obvious value saltation in the coherence profile. Besides, unlike the intensity and the coherence are significantly affected by the properties of the medium, the polarization of the scattered field is irrelevant to them due to the quasi-homogeneity and isotropy of the medium, and it is only connected with the polarization of the incident light.

Spectra and angular distributions of atmospheric gamma rays from 0.3 to 10 MeV at lambda = 40 deg

NASA Technical Reports Server (NTRS)

Ling, J. C.; Gruber, D. E.

1977-01-01

Measurements of the spectral and angular distributions of atmospheric gamma sq cm rays in the energy range 0.3-10 MeV over Palestine, Texas, at residual depths of 2.5 and 70 g/sq cm are reported. In confirmation of the general features of a model prediction, the measurements show at 2.5 g/sq cm upward moving fluxes greater than the downward moving fluxes, the effect increasing with energy, and approximate isotropy at 70 g/sq cm. Numerous characteristic gamma-ray lines were observed, most prominently at 0.511, 1.6, 2.3, 4.4, and 6.1 MeV. Their intensities were also compared with model predictions. Observations were made with an actively shielded scintillator counter with two detectors, one of aperture 50 deg FWHM and the other of 120 deg FWHM. Above 1 MeV, contributions to the counting rate from photons penetrating the shield annulus and from neutron interactions were large; they were studied by means of a Monte Carlo code and are extensively discussed.

The OPTIS satellite-improved tests of Special and General Relativity

NASA Astrophysics Data System (ADS)

Scheithauer, Silvia; Laemmerzahl, Claus; Dittus, Hansjoerg; Schiller, Stephan; Peters, Achim

2005-06-01

The OPTIS satellite mission is an international collaboration initiated by three German University institutes aiming at improving tests regarding the foundations of Special and General Relativity. The mission idea - which has already passed the state of the initial feasibility study - is to contribute to the most challenging project of physics in this century - the search for a Theory of Quantum Gravity. This theory should resolve the incompatibilities between the quantum theory and Einstein's General Relativity. All approaches for a Quantum Gravity Theory predict small deviations from Special and General Relativity. If such deviations could be found (e.g. an anisotropy of the speed of light, violations of the universality of gravitational red shift or of the universality of free fall) the way to a new understanding of the time and space structure of the universe would be open. Therefore the goal of the OPTIS satellite mission is an accuracy improvement of tests regarding the foundations of Special and General Relativity by up to three orders of magnitude. For that purpose several experiments will be carried out on board the OPTIS satellite testing (i) the isotropy of the speed of light, (ii) the independence of the speed of light from the velocity of the laboratory system, (iii) the universality of the gravitational redshift, (iv) the absolute gravitational redshift and (v) the special relativistic time-dilation. Furthermore, orbit analyses will be done in order to measure (vi) the Lense-Thirring effect and (vii) perigee advance as well as to test (viii) the Newtonian View the MathML source gravitational potential. The benefit from bringing these experiments into space is the nearly disturbance free environment allowing precise measurements and large measurement times. The OPTIS mission will use already available key technologies like optical cavities, highly stabilised lasers, atomic clocks, frequency combs, capacitive gravitational reference sensors, drag-free control, laser tracking and laser linking systems. For most of the proposed tests the measurements are done by comparing the rates of different clocks. For the test of the isotropy of the velocity of light (Michelson-Morley experiment) the frequencies of resonators ("light clocks") pointing in different directions are compared. Concerning the constancy of the speed of light (Kennedy-Thorndike experiment) a resonator and atomic clocks under varying velocities are compared. For tests of the time dilation the rates of clocks in different states of motion and for testing the universality of the gravitational redshift clocks at different positions in the gravitational field are compared. This paper will give an overview about the OPTIS satellite mission, including the science goals, science requirements, key technologies, measurement principles and devices.

D" anisotropy and slip systems in post-perovskite

NASA Astrophysics Data System (ADS)

Nowacki, Andy; Wookey, James; Kendall, J.-Michael

2010-05-01

The lowermost few hundred kilometres of the Earth's mantle-known as D″-form the boundary between it and the core below, control the Earth's convective system, and are the site of probable large thermochemical heterogeneity. Seismic observations of D″ show a large (~2%) increase in S-wave velocity and significant seismic anisotropy (the variation of wave speed with direction) are present in many parts of the region. On the basis of continuous regions of fast shear velocity (V S) anomalies in global models, it is also proposed as the resting place of subducted slabs, notably the Farallon beneath North America. The MgSiO3-post-perovskite mineral phase is the most compelling explanation for observations of anisotropy, though an outstanding question is how post-perovskite and other mineral phases may deform to produce this: different mechanisms are possible. With knowledge either of mantle flow or which slip system is responsible for causing deformation, we can determine the other with the seismic anisotropy which is created. We investigate the dynamics at the CMB beneath North America using differential shear wave splitting in S and ScS phases from earthquakes of magnitude MW > 5.5 in South and Central America, Hawaii the Mid-Atlantic Ridge and East Pacific Rise. They are detected on ~500 stations in North America, giving ~700 measurements of anisotropy in D″. We achieve this by correcting for anisotropy in the upper mantle (UM) beneath both the source and receiver. The measurements cover three regions beneath western USA, the Yucatan peninsula and Florida. In each case, two different, crossing ray paths are used, so that the style of anisotropy can be constrained-only one azimuth cannot distinguish differing cases. Our results showing ~1% anisotropy dependent on azimuth are not consistent with transverse isotropy with a vertical symmetry axis (VTI) anywhere. The same but with a tilted axis is possible (TTI) and would be consistent with inclusions of seismically-distinct material such as melt. TTI planes of isotropy dip south beneath Florida, southwest beneath western USA and southeast beneath Yucatan. However we test other slip systems in MgO, pv and ppv to determine if deformation in these phases can account for the observed anisotropy. The systems [100](010) and [¯110](110) in ppv are consistent everywhere; pv is not beneath Yucatan. If we assume a general downwelling and displacement of mantle material in the seismically fast D″, corresponding to the impingement of slab material, slip along [100](010) seems more likely. With a new breed of detailed mantle deformation models, or experimental evidence of which slip system dominates, seismic anisotropy may be used to map deformation in D″ and provide greater insight into Earth's convecting interior.

Seismic anisotropy from walk-around VSP data in the Kumano basin south of Kii Peninsula (IODP Site C0009A)

NASA Astrophysics Data System (ADS)

Tsuji, T.; Hino, R.; Sanada, Y.; Park, J.; No, T.; Araki, E.; Kinoshita, M.; Bangs, N. L.; von Huene, R.; Moore, G. F.

2010-12-01

We estimated seismic anisotropy from the walk-around Vertical Seismic Profiling (VSP) data in Site C0009A obtained during Integrated Ocean Drilling Program (IODP) Expedition 319. It is generally agreed that seismic anisotropy within sediments is related to the cracks. For vertical cracks (Horizontal Transverse Isotropy; HTI), the fast velocity direction coincides with the direction of crack alignment, while the degree of velocity difference provides information about crack density (Crampin, 1985). If cracks are produced by a regional tectonic stress field, seismic anisotropy can be used to estimate stress orientation and magnitude. In unconsolidated sequence, furthermore, the stress-induced anisotropy can be observed due to increasing contact between grains (Johnson et al., 1998). In this case (increasing grain-contact), the fast velocity direction from walk-around VSP experiment is also consistent with the principal horizontal stress direction. Site C0009A is located in the Kumano basin where ~1350m unconsolidated Kumano basin sediment overlies the accretionary prism. During VSP operations, we obtained walk-away, walk-around, and zero-offset VSP data (Saffer et al., 2009). We used mainly walk-around VSP data to study seismic anisotropy. In the walk-around VSP experiments, R/V Kairei deployed 4 air-gun strings (128 L total volume) and generated 275 shots. The shooting interval was 30s and the distance from the borehole was a constant 3.5 km. We deployed the Vertical Seismic Imager (VSI) wireline tool into the borehole between 2989 and 3218m below the sea surface (935-1164m below seafloor). This interval corresponds to the bottom of the Kumano basin sediment section. From the walk-around VSP data, we obtained the following anisotropic parameters: (1) P-wave velocity anisotropy derived from azimuthal velocity analysis (Grechka and Tsvankin, 1998), (2) P-wave amplitude variation with azimuth (AVAZ), and (3) S-wave amplitude variation with azimuth associated with S-wave splitting (Haacke et al., 2009). We observed the S-wave splitting both from the upgoing and downgoing converted S-waves. These analyses demonstrate that the P-wave velocity anisotropy within the Kumano basin sediment (above the VSI tool) is ~5 %. The fast velocity direction and strong amplitude direction are aligned with the convergence vector of the Philippine Sea plate. The fast velocity as well as strong amplitude is clearly observed for at 180 degree from the convergence vector. Therefore the dip of the Kumano basin sequence (Tilted Transverse Isotropy; TTI) should have only a subtle effect on our results. These results indicate that the maximum horizontal stress orientation is the subduction direction at Site C0009C. This observation is consistent with the principal stress orientation estimated from borehole breakout at same borehole (Kinoshita et al., 2008).

Verification of fractional quasilinear renormalization theory using drift-wave turbulence simulations

NASA Astrophysics Data System (ADS)

Newman, D. E.; Sanchez, R.; Carreras, B. A.; van Milligen, B. Ph.

2005-10-01

A very recent renormalization scheme for turbulent transport has been formulated in terms fractional differential operators [1]. In this contribution, we test it against numerous tracer particle transport experiments carried out in simulations of drift-wave turbulence in slab geometry [2]. The simplified geometry allows that simulations be carried out for a sufficiently large number of decorrelation times so that the long-term dynamics captured by these operators can be made apparent. By changing the relative dominance of the polarization and ExB nolinearities artificially, we tune at will the degree of homogeneity and isotropy of the system. Additionally, externally-driven sheared flows can also be considered. This wide spectrum of options creates a superb environment to test the strengths and weaknesses of the fractional renormalization formalism. With it, the potential for application to more realistic geometries such as those in state-of-the-art tokamak turbulence codes will be assessed.References[1] R. S'anchez, B.A. Carreras, D.E. Newman, V. Lynch and B.Ph. van Milligen, submitted (2005) [2] D.E. Newman, P.W. Terry, P.H. Diamond and Y. Liang, Phys. Fluids B 5, 1140 (1993)

Cosmic gamma-ray bursts from BATSE - Another great debate

NASA Technical Reports Server (NTRS)

Hartmann, Dieter H.; The, Lih-Sin; Clayton, Donald D.; Schnepf, Neil G.; Linder, Eric V.

1992-01-01

The BATSE detectors aboard Compton Observatory record about one cosmic gamma-ray burst (GRB) per day. Preliminary data analysis shows a highly isotropic sky map and a nonuniform brightness distribution. Anisotropies expected from a Galactic neutron star population, the most frequently considered source model, did not emerge from the data. Taken at face value, the data seem to suggest a heliocentric solution of the GRB puzzle. The observed isotropy can be achieved if sources are either very near or extragalactic. Pop I neutron stars in the disk do not simultaneously fit sky and brightness distributions. A possibility are sources in an extended Galactic halo with scale length large enough to avoid strong anisotropies due to the solar offset from the Galactic center. If GRBs are located in an extended halo we ask whether the neutron star paradigm can survive. We show that the recently discovered high velocity radio pulsars may provide a natural source population for GRBs. If these pulsars formed in the halo, as suggested by the radio data, the possibility arises that GRBs and high velocity pulsars are two related phenomena that provide observational evidence of the dark Galactic corona. We also discuss cosmological redshift constraints that follow from the observed brightness distribution.

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

Oleinikov, A. I., E-mail: a.i.oleinikov@mail.ru; Bormotin, K. S., E-mail: cvmi@knastu.ru

It is shown that inverse problems of steady-state creep bending of plates in both the geometrically linear and nonlinear formulations can be represented in a variational formulation. Steady-state values of the obtained functionals corresponding to the solutions of the problems of inelastic deformation and springback are determined by applying a finite element procedure to the functionals. Optimal laws of creep deformation are formulated using the criterion of minimizing damage in the functionals of the inverse problems. The formulated problems are reduced to the problems solved by the finite element method using MSC.Marc software. Currently, forming of light metals poses tremendousmore » challenges due to their low ductility at room temperature and their unusual deformation characteristics at hot-cold work: strong asymmetry between tensile and compressive behavior, and a very pronounced anisotropy. We used the constitutive models of steady-state creep of initially transverse isotropy structural materials the kind of the stress state has influence. The paper gives basics of the developed computer-aided system of design, modeling, and electronic simulation targeting the processes of manufacture of wing integral panels. The modeling results can be used to calculate the die tooling, determine the panel processibility, and control panel rejection in the course of forming.« less

Droplet sliding on inclined superhydrophobic surfaces: the effect of anisotropic contact line

NASA Astrophysics Data System (ADS)

Jiang, Youhua; Cao, Lile; Guo, Zongqi; Choi, Chang-Hwan

2017-11-01

Although the effects of solid structures on droplet retention on superhydrophobic surfaces have been studied extensively, the investigation has been restricted to the sessile droplets on horizontal surfaces where the contact line motions are axisymmetric or isotropic (either advancing or receding). In the droplet retention on inclined surfaces, the contact line motions are asymmetric or anisotropic; the advancing and receding motions coexist. In this study, we investigate the correlation between the droplet boundary pinning and the surface morphology on inclined superhydrophobic surfaces. The evolution of the droplet contact angle and width show contrary behaviors between pillar- and pore-structured surfaces due to the distinctive microscopic contact line motions. Therefore, the visualizations of the contact line motions at different locations of the boundary on inclined superhydrophobic surfaces are performed and the averaged contact line density of the boundary is quantified. The result shows that the droplet retentive force monotonously increase with the increase in contact line density, regardless of the surface morphological types, dimensions, or the direction of contact line motion (advancing, receding, or both). The result indicates that the droplet retentive force on superhydrophobic surfaces is mainly determined by the contact line density, regardless of the isotropy of the contact line.

Pipette aspiration applied to the characterization of nonhomogeneous, transversely isotropic materials used for vocal fold modeling.

PubMed

Weiß, S; Thomson, S L; Lerch, R; Döllinger, M; Sutor, A

2013-01-01

The etiology and treatment of voice disorders are still not completely understood. Since the vibratory characteristics of vocal folds are strongly influenced by both anatomy and mechanical material properties, measurement methods to analyze the material behavior of vocal fold tissue are required. Due to the limited life time of real tissue in the laboratory, synthetic models are often used to study vocal fold vibrations. In this paper we focus on two topics related to synthetic and real vocal fold materials. First, because certain tissues within the human vocal folds are transversely isotropic, a fabrication process for introducing this characteristic in commonly used vocal fold modeling materials is presented. Second, the pipette aspiration technique is applied to the characterization of these materials. By measuring the displacement profiles of stretched specimens that exhibit varying degrees of transverse isotropy, it is shown that local anisotropy can be quantified using a parameter describing the deviation from an axisymmetric profile. The potential for this technique to characterize homogeneous, anisotropic materials, including soft biological tissues such as those found in the human vocal folds, is supplemented by a computational study. Copyright © 2012 Elsevier Ltd. All rights reserved.

Satellite test of the isotropy of the one-way spe ed of light using ExTRAS

NASA Technical Reports Server (NTRS)

Wolf, Peter

1995-01-01

A test of the second postulate of special relativity, the universality of the speed of light, using the ExTRAS (Experiment on Timing Ranging and Atmospheric Sounding) payload to be flown on board a Russian Meteor-3M satellite (launch date January 1997) is proposed. The propagation time of a light signal transmitted from one point to another without reflection would be measured directly by comparing the phases of two hydrogen maser clocks, one on board and one on the ground, using laser or microwave time transfer systems. An estimated uncertainty budget of the proposed measurements is given, resulting in an expected sensitivity of the experiment of delta c/c is less than 8xl0(exp -10) which would be an improvement by a factor of approximately 430 over previous direct measurements and by a factor of approximately 4 over the best indirect measurement. The proposed test would require no equipment additional to what is already planned and so is of inherently low-cost. It could be carried out by anyone having access to a laser or microwave ground station and a hydrogen maser.

Studies of the micromorphology of sputtered TiN thin films by autocorrelation techniques

NASA Astrophysics Data System (ADS)

Smagoń, Kamil; Stach, Sebastian; Ţălu, Ştefan; Arman, Ali; Achour, Amine; Luna, Carlos; Ghobadi, Nader; Mardani, Mohsen; Hafezi, Fatemeh; Ahmadpourian, Azin; Ganji, Mohsen; Grayeli Korpi, Alireza

2017-12-01

Autocorrelation techniques are crucial tools for the study of the micromorphology of surfaces: They provide the description of anisotropic properties and the identification of repeated patterns on the surface, facilitating the comparison of samples. In the present investigation, some fundamental concepts of these techniques including the autocorrelation function and autocorrelation length have been reviewed and applied in the study of titanium nitride thin films by atomic force microscopy (AFM). The studied samples were grown on glass substrates by reactive magnetron sputtering at different substrate temperatures (from 25 {}°C to 400 {}°C , and their micromorphology was studied by AFM. The obtained AFM data were analyzed using MountainsMap Premium software obtaining the correlation function, the structure of isotropy and the spatial parameters according to ISO 25178 and EUR 15178N. These studies indicated that the substrate temperature during the deposition process is an important parameter to modify the micromorphology of sputtered TiN thin films and to find optimized surface properties. For instance, the autocorrelation length exhibited a maximum value for the sample prepared at a substrate temperature of 300 {}°C , and the sample obtained at 400 {}°C presented a maximum angle of the direction of the surface structure.

Monolithic Cylindrical Fused Silica Resonators with High Q Factors

PubMed Central

Pan, Yao; Wang, Dongya; Wang, Yanyan; Liu, Jianping; Wu, Suyong; Qu, Tianliang; Yang, Kaiyong; Luo, Hui

2016-01-01

The cylindrical resonator gyroscope (CRG) is a typical Coriolis vibratory gyroscope whose performance is determined by the Q factor and frequency mismatch of the cylindrical resonator. Enhancing the Q factor is crucial for improving the rate sensitivity and noise performance of the CRG. In this paper, for the first time, a monolithic cylindrical fused silica resonator with a Q factor approaching 8 × 105 (ring-down time over 1 min) is reported. The resonator is made of fused silica with low internal friction and high isotropy, with a diameter of 25 mm and a center frequency of 3974.35 Hz. The structure of the resonator is first briefly introduced, and then the experimental non-contact characterization method is presented. In addition, the post-fabrication experimental procedure of Q factor improvement, including chemical and thermal treatment, is demonstrated. The Q factor improvement by both treatments is compared and the primary loss mechanism is analyzed. To the best of our knowledge, the work presented in this paper represents the highest reported Q factor for a cylindrical resonator. The proposed monolithic cylindrical fused silica resonator may enable high performance inertial sensing with standard manufacturing process and simple post-fabrication treatment. PMID:27483263

Propelled microprobes in turbulence

NASA Astrophysics Data System (ADS)

Calzavarini, E.; Huang, Y. X.; Schmitt, F. G.; Wang, L. P.

2018-05-01

The temporal statistics of incompressible fluid velocity and passive scalar fields in developed turbulent conditions is investigated by means of direct numerical simulations along the trajectories of self-propelled pointlike probes drifting in a flow. Such probes are characterized by a propulsion velocity which is fixed in intensity and direction; however, like vessels in a flow they are continuously deviated on their intended course as the result of local sweeping of the fluid flow. The recorded time series by these moving probes represent the simplest realization of transect measurements in a fluid flow environment. We investigate the nontrivial combination of Lagrangian and Eulerian statistical properties displayed by the transect time series. We show that, as a result of the homogeneity and isotropy of the flow, the single-point acceleration statistics of the probes follows a predictable trend at varying the propulsion speed, a feature that is also present in the scalar time-derivative fluctuations. Further, by focusing on two-time statistics we characterize how the Lagrangian-to-Eulerian transition occurs at increasing the propulsion velocity. The analysis of intermittency of temporal increments highlights in a striking way the opposite trends displayed by the fluid velocity and passive scalars.

Comparison between S. T. radar and in situ balloon measurements

NASA Technical Reports Server (NTRS)

Dalaudier, F.; Barat, J.; Bertin, F.; Brun, E.; Crochet, M.; Cuq, F.

1986-01-01

A campaign for simultaneous in situ and remote observation of both troposphere and stratosphere took place near Aire-sur-l'Adour (in southeastern France) on May 4, 1984. The aim of this campaign was a better understanding of the physics of radar echoes. The backscattered signal obtained with a stratosphere-troposphere radar both at the vertical and 15 deg. off vertical is compared with the velocity and temperature measurements made in the same region (about 10 km north of the radar site) by balloon-borne ionic anenometers and temperature sensors. In situ measurements clearly indicate that the temperature fluctuations are not always consistent with the standard turbulent theory. Nevertheless, the assumptions generally made (isotropy and turbulent field in k) and the classical formulation so derived for radar reflectivity are able to reproduce the shape of the radar return power profiles in oblique directions. Another significant result is the confirmation of the role played by the atmospheric stratification in the vertical echo power. It is important to develop these simultaneous in situ and remote experiments for a better description of the dynamical and thermal structure of the atmosphere and for a better understanding of the mechanisms governing clear-air radar reflectivity.

Micro-CT based finite element models for elastic properties of glass-ceramic scaffolds.

PubMed

Tagliabue, Stefano; Rossi, Erica; Baino, Francesco; Vitale-Brovarone, Chiara; Gastaldi, Dario; Vena, Pasquale

2017-01-01

In this study, the mechanical properties of porous glass-ceramic scaffolds are investigated by means of three-dimensional finite element models based on micro-computed tomography (micro-CT) scan data. In particular, the quantitative relationship between the morpho-architectural features of the obtained scaffolds, such as macroscopic porosity and strut thickness, and elastic properties, is sought. The macroscopic elastic properties of the scaffolds have been obtained through numerical homogenization approaches using the mechanical characteristics of the solid walls of the scaffolds (assessed through nanoindentation) as input parameters for the numerical simulations. Anisotropic mechanical properties of the produced scaffolds have also been investigated by defining a suitable anisotropy index. A comparison with morphological data obtained through the micro-CT scans is also presented. The proposed study shows that the produced glass-ceramic scaffolds exhibited a macroscopic porosity ranging between 29% and 97% which corresponds to an average stiffness ranging between 42.4GPa and 36MPa. A quantitative estimation of the isotropy of the macroscopic elastic properties has been performed showing that the samples with higher solid fractions were those closest to an isotropic material. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dragging force on galaxies due to streaming dark matter

NASA Technical Reports Server (NTRS)

Hara, Tetsuya; Miyoshi, Shigeru

1990-01-01

It has been reported that galaxies in large regions (approx. 10(exp 2) Mpc), including some clusters of galaxies, may be streaming coherently with velocities up to 600 km/sec or more with respect to the rest frame determined by the microwave background radiation. On the other hand, it is suggested that the dominant mass component of the universe is dark matter. Because we can only speculate the motion of dark matter from the galaxy motions, much attention should be paid to the correlation of velocities between the observed galaxies and cold dark matter. So the authors investigated whether such coherent large-scale streaming velocities are due to dark matter or only to baryonic objects which may be formed by piling up of gases due to some explosive events. It seems that, although each galaxy will not follow the motion of dark matter, clusters of galaxies may represent the velocity field of dark matter. The origin of the velocity field of dark matter would be due to the initial adiabatic perturbations and, in fact, the observed peculiar velocities of clusters are within the allowed region constrained from the isotropy of the microwave background radiation.

Microelectromechanically tunable multiband metamaterial with preserved isotropy

NASA Astrophysics Data System (ADS)

Pitchappa, Prakash; Ho, Chong Pei; Qian, You; Dhakar, Lokesh; Singh, Navab; Lee, Chengkuo

2015-06-01

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-of-plane movable cantilevers preserves the symmetry at different configurations of the metamaterial. The metamaterial is shown to provide polarization independent response for both electrical inductive-capacitive (eLC) resonance and dipolar resonance at all states of actuation. The proposed metamaterial has a switching range of 0.16 THz and 0.37 THz and a transmission intensity change of more than 0.2 and 0.7 for the eLC and dipolar resonances, respectively for both TE and TM modes. Further optimization of the metal layer thickness, provides an improvement of up to 80% modulation at 0.57 THz. The simultaneously tunable dual band isotropic metamaterial will enable the realization of high performance electro-optic devices that would facilitate numerous terahertz applications such as compressive terahertz imaging, miniaturized terahertz spectroscopy and next generation high speed wireless communication possible in the near future.

Azimuthally Anisotropic Global Adjoint Tomography

NASA Astrophysics Data System (ADS)

Bozdag, E.; Orsvuran, R.; Lefebvre, M. P.; Lei, W.; Peter, D. B.; Ruan, Y.; Smith, J. A.; Komatitsch, D.; Tromp, J.

2017-12-01

Earth's upper mantle shows significant evidence of anisotropy as a result of its composition and deformation. After the first-generation global adjoint tomography model, GLAD-M15 (Bozdag et al. 2016), which has transverse isotropy confined to upper mantle, we continue our iterations including surface-wave azimuthal anisotropy with an emphasis on the upper mantle. We are focusing on four elastic parameters that surface waves are known to be most sensitive to, namely, vertically and horizontally polarized shear waves and the density-normalised anisotropic parameters Gc' & Gs'. As part of the current anisotropic inversions, which will lead to our "second-generation" global adjoint tomography model, we have started exploring new misfits based on a double-difference approach (Yuan et al. 2016). We define our misfit function in terms of double-difference multitaper measurements, where each waveform is normalized by its number of pairs in the period ranges 45-100 s & 90-250 s. New measurements result in better balanced gradients while extracting more information underneath clusters of stations, such as USArray. Our initial results reveals multi-scale anisotorpic signals depending on ray (kernel) coverage close to continental-scale resolution in areas with dense coverage, consistent with previous studies.

Higher order moments, structure functions and spectral ratios in near- and far-wakes of a wind turbine array

NASA Astrophysics Data System (ADS)

Ali, Naseem; Aseyev, A.; McCraney, J.; Vuppuluri, V.; Abbass, O.; Al Jubaree, T.; Melius, M.; Cal, R. B.

2014-11-01

Hot-wire measurements obtained in a 3 × 3 wind turbine array boundary layer are utilized to analyze higher order statistics which include skewness, kurtosis as well as the ratios of structure functions and spectra. The ratios consist of wall-normal to streamwise components for both quantities. The aim is to understand the degree of anisotropy in the flow for the near- and far-wakes of the flow field where profiles at one diameter and five diameters are considered, respectively. The skewness at top tip for both wakes show a negative skewness while below the turbine canopy, this terms are positive. The kurtosis shows a Gaussian behavior in the near-wake immediately at hub-height. In addition, the effect due to the passage of the rotor in tandem with the shear layer at the top tip renders relatively high differences in the fourth order moment. The second order structure function and spectral ratios are found to exhibit anisotropic behavior at the top and bottom-tips for the large scales. Mixed structure functions and co-spectra are also considered in the context of isotropy.

Inferring the three-dimensional distribution of dust in the Galaxy with a non-parametric method . Preparing for Gaia

NASA Astrophysics Data System (ADS)

Rezaei Kh., S.; Bailer-Jones, C. A. L.; Hanson, R. J.; Fouesneau, M.

2017-02-01

We present a non-parametric model for inferring the three-dimensional (3D) distribution of dust density in the Milky Way. Our approach uses the extinction measured towards stars at different locations in the Galaxy at approximately known distances. Each extinction measurement is proportional to the integrated dust density along its line of sight (LoS). Making simple assumptions about the spatial correlation of the dust density, we can infer the most probable 3D distribution of dust across the entire observed region, including along sight lines which were not observed. This is possible because our model employs a Gaussian process to connect all LoS. We demonstrate the capability of our model to capture detailed dust density variations using mock data and simulated data from the Gaia Universe Model Snapshot. We then apply our method to a sample of giant stars observed by APOGEE and Kepler to construct a 3D dust map over a small region of the Galaxy. Owing to our smoothness constraint and its isotropy, we provide one of the first maps which does not show the "fingers of God" effect.

All-Particle Cosmic Ray Energy Spectrum Measured with 26 Icetop Stations

NASA Technical Reports Server (NTRS)

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Andeen, K.; Auffenberg, J.;

The inverse problems of wing panel manufacture processes

NASA Astrophysics Data System (ADS)

Oleinikov, A. I.; Bormotin, K. S.

2013-12-01

It is shown that inverse problems of steady-state creep bending of plates in both the geometrically linear and nonlinear formulations can be represented in a variational formulation. Steady-state values of the obtained functionals corresponding to the solutions of the problems of inelastic deformation and springback are determined by applying a finite element procedure to the functionals. Optimal laws of creep deformation are formulated using the criterion of minimizing damage in the functionals of the inverse problems. The formulated problems are reduced to the problems solved by the finite element method using MSC.Marc software. Currently, forming of light metals poses tremendous challenges due to their low ductility at room temperature and their unusual deformation characteristics at hot-cold work: strong asymmetry between tensile and compressive behavior, and a very pronounced anisotropy. We used the constitutive models of steady-state creep of initially transverse isotropy structural materials the kind of the stress state has influence. The paper gives basics of the developed computer-aided system of design, modeling, and electronic simulation targeting the processes of manufacture of wing integral panels. The modeling results can be used to calculate the die tooling, determine the panel processibility, and control panel rejection in the course of forming.

Optical isotropy and iridescence in a smectic 'blue phase'.

PubMed

Yamamoto, Jun; Nishiyama, Isa; Inoue, Miyoshi; Yokoyama, Hiroshi

2005-09-22

When liquid crystal molecules are chiral, the twisted structure competes with spatially uniform liquid crystalline orders, resulting in a variety of modulated liquid crystal phases, such as the cholesteric blue phase, twist grain boundary and smectic blue phases. Here we report a liquid crystal smectic blue phase (SmBP(iso)), formed from a two-component mixture containing a chiral monomer and a 'twin' containing two repeat units of the first molecule connected by a linear hydrocarbon spacer. The phase exhibits the simultaneous presence of finite local-order parameters of helices and smectic layers, without any discontinuity on a mesoscopic length scale. The anomalous softening of elasticity due to a strong reduction in entropy caused by mixing the monomer and the twin permits the seamless coexistence of these two competing liquid crystal orders. The new phase spontaneously exhibits an optically isotropic but uniformly iridescent colour and automatically acquires spherical symmetry, so that the associated photonic band gap maintains the same symmetry despite the local liquid crystalline order. We expect a range of unusual optical transmission properties based on this three-dimensional isotropic structure, and complete tunability due to the intrinsic softness and responsiveness of the liquid crystalline order against external fields.

Discrete breathers in a two-dimensional hexagonal Fermi Pasta Ulam lattice

NASA Astrophysics Data System (ADS)

Butt, Imran A.; Wattis, Jonathan A. D.

2007-02-01

We consider a two-dimensional Fermi-Pasta-Ulam (FPU) lattice with hexagonal symmetry. Using asymptotic methods based on small amplitude ansatz, at third order we obtain a reduction to a cubic nonlinear Schrödinger equation (NLS) for the breather envelope. However, this does not support stable soliton solutions, so we pursue a higher order analysis yielding a generalized NLS, which includes known stabilizing terms. We present numerical results which suggest that long-lived stationary and moving breathers are supported by the lattice. We find breather solutions which move in an arbitrary direction, an ellipticity criterion for the wavenumbers of the carrier wave, asymptotic estimates for the breather energy, and a minimum threshold energy below which breathers cannot be found. This energy threshold is maximized for stationary breathers and becomes vanishingly small near the boundary of the elliptic domain where breathers attain a maximum speed. Several of the results obtained are similar to those obtained for the square FPU lattice (Butt and Wattis 2006 J. Phys. A: Math. Gen. 39 4955), though we find that the square and hexagonal lattices exhibit different properties in regard to the generation of harmonics, and the isotropy of the generalized NLS equation.

Effective Simulation Strategy of Multiscale Flows using a Lattice Boltzmann model with a Stretched Lattice

NASA Astrophysics Data System (ADS)

Yahia, Eman; Premnath, Kannan

2017-11-01

Resolving multiscale flow physics (e.g. for boundary layer or mixing layer flows) effectively generally requires the use of different grid resolutions in different coordinate directions. Here, we present a new formulation of a multiple relaxation time (MRT)-lattice Boltzmann (LB) model for anisotropic meshes. It is based on a simpler and more stable non-orthogonal moment basis while the use of MRT introduces additional flexibility, and the model maintains a stream-collide procedure; its second order moment equilibria are augmented with additional velocity gradient terms dependent on grid aspect ratio that fully restores the required isotropy of the transport coefficients of the normal and shear stresses. Furthermore, by introducing additional cubic velocity corrections, it maintains Galilean invariance. The consistency of this stretched lattice based LB scheme with the Navier-Stokes equations is shown via a Chapman-Enskog expansion. Numerical study for a variety of benchmark flow problems demonstrate its ability for accurate and effective simulations at relatively high Reynolds numbers. The MRT-LB scheme is also shown to be more stable compared to prior LB models for rectangular grids, even for grid aspect ratios as small as 0.1 and for Reynolds numbers of 10000.

Deployable structures using bistable reeled composites

NASA Astrophysics Data System (ADS)

Daton-Lovett, Andrew J.; Compton-Bishop, Quentin M.; Curry, Richard G.

2000-06-01

This paper describes an innovative, patented use of composite materials developed by RolaTube Technology Ltd. to make smart deployable structures. Bi-stable reeled composites (BRCs) can alternate between two stable forms; that of a strong, rigid structure and that of a compact coil of flat-wound material. Bi-stability arises as a result of the manipulation of Poisson's ratio and isotropy in the various layers of the material. BRCs are made of fiber- reinforced composite materials, most often with a thermoplastic matrix. A range of fibers and polymer matrices can be used according to the requirements of the operating environment. Samples of a BRC structure were constructed using layers of unidirectional, fiber-reinforced thermoplastic sheet with the layers at different angles. The whole assembly was then consolidated under conditions of elevated temperature and pressure. The properties of the BRC are described and the result of a series of experiments performed on the sample to determine the tensile strength of the BRC structure are reported. A full analysis using finite element methods is being undertaken in collaboration with the University of Cambridge, England. The first commercial use has been to fabricate boom and drive mechanisms for the remote inspection of industrial plant.

On the Linearly-Balanced Kinetic Energy Spectrum

NASA Technical Reports Server (NTRS)

Lu, Huei,-Iin; Robertson, F. R.

1999-01-01

It is well known that the earth's atmospheric motion can generally be characterized by the two dimensional quasi-geostrophic approximation, in which the constraints on global integrals of kinetic energy, entrophy and potential vorticity play very important roles in redistributing the wave energy among different scales of motion. Assuming the hypothesis of Kolmogrov's local isotropy, derived a -3 power law of the equilibrium two-dimensional kinetic energy spectrum that entails constant vorticity and zero energy flows from the energy-containing wave number up to the viscous cutoff. In his three dimensional quasi-geostrophic theory, showed that the spectrum function of the vertical scale turbulence - expressible in terms of the available potential energy - possesses the same power law as the two dimensional kinetic energy spectrum. As the slope of kinetic energy spectrum in the inertial range is theoretically related to the predictability of the synoptic scales (Lorenz, 1969), many general circulation models includes a horizontal diffusion to provide reasonable kinetic energy spectra, although the actual power law exhibited in the atmospheric general circulation is controversial. Note that in either the atmospheric modeling or the observational analyses, the proper choice of wave number Index to represent the turbulence scale Is the degree of the Legendre polynomial.

Measurement of the Turbulence Kinetic Energy Budget of a Turbulent Planar Wake Flow in Pressure Gradients

NASA Technical Reports Server (NTRS)

Liu, Xiao-Feng; Thomas, Flint O.; Nelson, Robert C.

2001-01-01

Turbulence kinetic energy (TKE) is a very important quantity for turbulence modeling and the budget of this quantity in its transport equation can provide insight into the flow physics. Turbulence kinetic energy budget measurements were conducted for a symmetric turbulent wake flow subjected to constant zero, favorable and adverse pressure gradients in year-three of research effort. The purpose of this study is to clarify the flow physics issues underlying the demonstrated influence of pressure gradient on wake development and provide experimental support for turbulence modeling. To ensure the reliability of these notoriously difficult measurements, the experimental procedure was carefully designed on the basis of an uncertainty analysis. Four different approaches, based on an isotropic turbulence assumption, a locally axisymmetric homogeneous turbulence assumption, a semi-isotropy assumption and a forced balance of the TKE equation, were applied for the estimate of the dissipation term. The pressure transport term is obtained from a forced balance of the turbulence kinetic energy equation. This report will present the results of the turbulence kinetic energy budget measurement and discuss their implication on the development of strained turbulent wakes.

Nepem-211 ion exchange conductive membrane immobilized tris(2,2´-bipyridyl) ruthenium(II) electrogenerated chemiluminescence flow sensor for high-performance liquid chromatography and its application.

PubMed

Li, Yongbo; Zhang, Zhujun

2013-01-01

We developed a sensitive and robust electrogenerated chemiluminescence (ECL) flow sensor based on Ru(bpy)3(2+) immobilized with a Nepem-211 perfluorinated ion exchange conductance membrane, which has robustness and stability under a wide range of chemical and physical conditions, good electrical conductivity, isotropy and a high exchange capacity for immobilization of Ru(bpy)3(2+). The flow sensor has been used as a post-column detector in high-performance liquid chromatography for determination of erythromycin and clarithromycin in honey and pork, and tricyclic antidepressant drugs in human urine. Under optimal conditions, the linear ranges were 0.03-26 ng/μL and 0.01-1 ng/μL for macrolides and tricyclic antidepressant drugs, respectively. The detection limits were 0.02, 0.01, 0.01, 0.06 and 0.003 ng/μL for erythromycin, clarithromycin, doxepin, amitriptyline and clomipramine, respectively. There is no post-column reagent addition. In addition to the conservation expensive reagents, the experimental setup was simplified. The flow sensor was used for 2 years with high sensitivity and stability. Copyright © 2013 John Wiley & Sons, Ltd.

Toucan and hornbill beaks: a comparative study.

PubMed

Seki, Yasuaki; Bodde, Sara G; Meyers, Marc A

2010-02-01

The structure and mechanical behavior of Toco Toucan (Ramphastos toco) and Wreathed Hornbill (Rhyticeros undulatus) beaks were compared. The beak of both species is a sandwich-structured composite, having an exterior, or rhamphotheca, consisting of multiple layers of keratin scales and a core composed of a fibrous network of bony closed-cell foam. The rhamphotheca is an arrangement of approximately 50microm diameter, overlapping, keratin tiles. The hornbill rhamphotheca exhibits a surface morphology on the ridged casque that is distinguishable from that observed on the bill proper. Intermediate filaments in the keratin matrix were observed by transmission electron microscopy. The Young's modulus measurements of toucan rhamphotheca indicate isotropy in longitudinal and transverse directions, whereas those of hornbill rhamphotheca may suggest anisotropy. The compressive response of beak foam is governed by brittle crushing behavior. The crushing strength of hornbill foam is six times higher than that of toucan foam. Micro- and nanoindentation hardness values were measured for rhamphotheca and foam trabeculae of toucan and hornbill specimens. The sandwich design of beaks was analyzed using the Karam-Gibson and Dawson-Gibson models. The presence of a cellular core increases the bending resistance (Brazier moment) by a factor of 3-6 while decreasing the compressive strength by only 50%.

Symmetry classes of the anisotropy tensors of quasielastic materials and a generalized Kelvin approach

NASA Astrophysics Data System (ADS)

Ostrosablin, N. I.

2017-05-01

The anisotropy matrices (tensors) of quasielastic (Cauchy-elastic) materials were obtained for all classes of crystallographic symmetries in explicit form. The fourth-rank anisotropy tensors of such materials do not have the main symmetry, in which case the anisotropy matrix is not symmetric. As a result of introducing various bases in the space of symmetric stress and strain tensors, the linear relationship between stresses and strains is represented in invariant form similar to the form in which generalized Hooke's law is written for the case of anisotropic hyperelastic materials and contains six positive Kelvin eigen moduli. It is shown that the introduction of modified rotation-induced deformation in the strain space can cause a transition to the symmetric anisotropy matrix observed in the case of hyperelasticity. For the case of transverse isotropy, there are examples of determination of the Kelvin eigen moduli and eigen bases and the rotation matrix in the strain space. It is shown that there is a possibility of existence of quasielastic media with a skew-symmetric anisotropy matrix with no symmetric part. Some techniques for the experimental testing of the quasielasticity model are proposed.

On the spatial distribution of small heavy particles in homogeneous shear turbulence

NASA Astrophysics Data System (ADS)

Nicolai, C.; Jacob, B.; Piva, R.

2013-08-01

We report on a novel experiment aimed at investigating the effects induced by a large-scale velocity gradient on the turbulent transport of small heavy particles. To this purpose, a homogeneous shear flow at Reλ = 540 and shear parameter S* = 4.5 is set-up and laden with glass spheres whose size d is comparable with the Kolmogorov lengthscale η of the flow (d/η ≈ 1). The particle Stokes number is approximately 0.3. The analysis of the instantaneous particle fields by means of Voronoï diagrams confirms the occurrence of intense turbulent clustering at small scales, as observed in homogeneous isotropic flows. It also indicates that the anisotropy of the velocity fluctuations induces a preferential orientation of the particle clusters. In order to characterize the fine-scale features of the dispersed phase, spatial correlations of the particle field are employed in conjunction with statistical tools recently developed for anisotropic turbulence. The scale-by-scale analysis of the particle field clarifies that isotropy of the particle distribution is tendentially recovered at small separations, even though the signatures of the mean shear persist down to smaller scales as compared to the fluid velocity field.

Anomalous transparency in photonic crystals and its application to point-by-point grating inscription in photonic crystal fibers.

PubMed

Baghdasaryan, Tigran; Geernaert, Thomas; Chah, Karima; Caucheteur, Christophe; Schuster, Kay; Kobelke, Jens; Thienpont, Hugo; Berghmans, Francis

2018-04-03

It is common belief that photonic crystals behave similarly to isotropic and transparent media only when their feature sizes are much smaller than the wavelength of light. Here, we counter that belief and we report on photonic crystals that are transparent for anomalously high normalized frequencies up to 0.9, where the crystal's feature sizes are comparable with the free space wavelength. Using traditional photonic band theory, we demonstrate that the isofrequency curves can be circular in the region above the first stop band for triangular lattice photonic crystals. In addition, by simulating how efficiently a tightly focused Gaussian beam propagates through the photonic crystal slab, we judge on the photonic crystal's transparency rather than on isotropy only. Using this approach, we identified a wide range of photonic crystal parameters that provide anomalous transparency. Our findings indicate the possibility to scale up the features of photonic crystals and to extend their operational wavelength range for applications including optical cloaking and graded index guiding. We applied our result in the domain of femtosecond laser micromachining, by demonstrating what we believe to be the first point-by-point grating inscribed in a multi-ring photonic crystal fiber.

Simulation of nanopowder compaction in terms of granular dynamics

NASA Astrophysics Data System (ADS)

Boltachev, G. Sh.; Volkov, N. B.

2011-07-01

The uniaxial compaction of nanopowders is simulated using the granular dynamics in the 2D geometry. The initial arrangement of particles is represented by (i) a layer of particles executing Brownian motion (isotropic structures) and (ii) particles falling in the gravity field (anisotropic structures). The influence of size effects and the size of a model cell on the properties of the structures are studied. The compaction of the model cell is simulated with regard to Hertz elastic forces between particles, Cattaneo-Mindlin-Deresiewicz shear friction forces, and van der Waals-Hamaker dispersion forces of attraction. Computation is performed for monodisperse powders with particle sizes ranging from 10 to 400 nm and for "cohesionless" powder, in which attractive forces are absent. It is shown that taking into account dispersion forces makes it possible to simulate the size effect in the nanopowder compaction: the compressibility of the nanopowder drops as the particles get finer. The mean coordination number and the axial and lateral pressures in the powder systems are found, and the effect of the density and isotropy of the initial structure on the compressibility is analyzed. The applicability of well-known Rumpf's formula for the size effect is discussed.

The Angular Power Spectrum of BATSE 3B Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Tegmark, Max; Hartmann, Dieter H.; Briggs, Michael S.; Meegan, Charles A.

1996-01-01

We compute the angular power spectrum C(sub l) from the BATSE 3B catalog of 1122 gamma-ray bursts and find no evidence for clustering on any scale. These constraints bridge the entire range from small scales (which probe source clustering and burst repetition) to the largest scales (which constrain possible anisotropics from the Galactic halo or from nearby cosmological large-scale structures). We develop an analysis technique that takes the angular position errors into account. For specific clustering or repetition models, strong upper limits can be obtained down to scales l approx. equal to 30, corresponding to a couple of degrees on the sky. The minimum-variance burst weighting that we employ is visualized graphically as an all-sky map in which each burst is smeared out by an amount corresponding to its position uncertainty. We also present separate bandpass-filtered sky maps for the quadrupole term and for the multipole ranges l = 3-10 and l = 11-30, so that the fluctuations on different angular scales can be inspected separately for visual features such as localized 'hot spots' or structures aligned with the Galactic plane. These filtered maps reveal no apparent deviations from isotropy.

Preliminary results from the COBE differential microwave radiometers - Large angular scale isotropy of the cosmic microwave background

NASA Technical Reports Server (NTRS)

Smoot, G. F.; Aymon, J.; Bennett, C. L.; Kogut, A.; Backus, C.

1991-01-01

Preliminary but precise micowave maps are presented of the sky, and thus of the early universe, derived as the first results from the Differential Microwave Radiometers experiment aboard COBE. The dipole anisotropy attributed to the motion of the solar system with respect to the CMB reference frame shows strongly in all six sky maps and is consistent with a Doppler-shifted thermal spectrum. The best-fitted dipole has amplitude 3.3 + or - 0.2 mK in the direction (alpha, delta) = 11.2 h + or - 0.2 h, -7 deg + or - 2 deg (J2000) or (l,b) = 265 deg + or - 2 deg, 48 deg + or - 2 deg. There is no clear evidence in the maps for any other large angular-scale feature. Limits on Delta T/T0 of 3 x 10 to the -5th (T0 = 2.735 K), 4 x 10 to the -5th, and 4 x 10 to the -5th are found for the rms quadrupole amplitude, monochromatic fluctuations, and Gaussian fluctuations, respectively. These measurements place the most severe constraints to date on many potential physical processes in the early universe.

On modelling the pressure-strain correlations in wall bounded flows

NASA Technical Reports Server (NTRS)

Peltier, L. J.; Biringen, S.

1990-01-01

Turbulence models for the pressure-strain term of the Reynolds-stress equations in the vicinity of a moving wall are evaluated for a high Reynolds number flow using decaying grid turbulence as a model problem. The data of Thomas and Hancock are used as a base for evaluating the different turbulence models. In particular, the Rotta model for return-to-isotropy is evaluated both in its inclusion into the Reynolds-stress equation model and in comparison to a nonlinear model advanced by Sarkar and Speziale. Further, models for the wall correction to the transfer term advanced by Launder et al., Shir, and Shih and Lumley are compared. Initial data using the decaying grid turbulence experiment as a base suggests that the coefficients proposed for these models are high perhaps by as much as an order of magnitude. The Shih and Lumley model which satisfies realizability constraints, in particular, seems to hold promise in adequately modeling the Reynolds stress components of this flow. Extensions of this work are to include testing the homogeneous transfer model by Shih and Lumley and the testing of the wall transfer models using their proposed coefficients and the coefficients chosen from this work in a flow with mean shear component.

Discrete Space-Time: History and Recent Developments

NASA Astrophysics Data System (ADS)

Crouse, David

2017-01-01

Discussed in this work is the long history and debate of whether space and time are discrete or continuous. Starting from Zeno of Elea and progressing to Heisenberg and others, the issues with discrete space are discussed, including: Lorentz contraction (time dilation) of the ostensibly smallest spatial (temporal) interval, maintaining isotropy, violations of causality, and conservation of energy and momentum. It is shown that there are solutions to all these issues, such that discrete space is a viable model, yet the solution require strict non-absolute space (i.e., Mach's principle) and a re-analysis of the concept of measurement and the foundations of special relativity. In developing these solutions, the long forgotten but important debate between Albert Einstein and Henri Bergson concerning time will be discussed. Also discussed is the resolution to the Weyl tile argument against discrete space; however, the solution involves a modified version of the typical distance formula. One example effect of discrete space is then discussed, namely how it necessarily imposes order upon Wheeler's quantum foam, changing the foam into a gravity crystal and yielding crystalline properties of bandgaps, Brilluoin zones and negative inertial mass for astronomical bodies.

[Glossary of terms used by radiologists in image processing].

PubMed

Rolland, Y; Collorec, R; Bruno, A; Ramée, A; Morcet, N; Haigron, P

1995-01-01

We give the definition of 166 words used in image processing. Adaptivity, aliazing, analog-digital converter, analysis, approximation, arc, artifact, artificial intelligence, attribute, autocorrelation, bandwidth, boundary, brightness, calibration, class, classification, classify, centre, cluster, coding, color, compression, contrast, connectivity, convolution, correlation, data base, decision, decomposition, deconvolution, deduction, descriptor, detection, digitization, dilation, discontinuity, discretization, discrimination, disparity, display, distance, distorsion, distribution dynamic, edge, energy, enhancement, entropy, erosion, estimation, event, extrapolation, feature, file, filter, filter floaters, fitting, Fourier transform, frequency, fusion, fuzzy, Gaussian, gradient, graph, gray level, group, growing, histogram, Hough transform, Houndsfield, image, impulse response, inertia, intensity, interpolation, interpretation, invariance, isotropy, iterative, JPEG, knowledge base, label, laplacian, learning, least squares, likelihood, matching, Markov field, mask, matching, mathematical morphology, merge (to), MIP, median, minimization, model, moiré, moment, MPEG, neural network, neuron, node, noise, norm, normal, operator, optical system, optimization, orthogonal, parametric, pattern recognition, periodicity, photometry, pixel, polygon, polynomial, prediction, pulsation, pyramidal, quantization, raster, reconstruction, recursive, region, rendering, representation space, resolution, restoration, robustness, ROC, thinning, transform, sampling, saturation, scene analysis, segmentation, separable function, sequential, smoothing, spline, split (to), shape, threshold, tree, signal, speckle, spectrum, spline, stationarity, statistical, stochastic, structuring element, support, syntaxic, synthesis, texture, truncation, variance, vision, voxel, windowing.

Deformation in D″ Beneath North America From Anisotropy

NASA Astrophysics Data System (ADS)

Nowacki, A. J.; Wookey, J.; Kendall, J. M.

2009-12-01

The lowermost few hundred kilometres of the Earth's mantle—known as D″—form the boundary between it and the core below, control the Earth's convective system, and are the site of probable large thermochemical heterogeneity. Seismic observations of D″ show a strong heterogeneity in seismic wave velocity and significant seismic anisotropy (the variation of wave speed with direction) are present in many parts of the region. On the basis of continuous regions of fast shear velocity (VS) anomalies in global models, it is also proposed as the resting place of subducted slabs, notably the Farallon beneath North America. A phase change of MgSiO3-perovskite (pv) to a post-perovskite (ppv) structure at near-core-mantle boundary (CMB) conditions is a compelling mechanism to explain the seismic features of D″. An outstanding question is how this and other mineral phases may deform to produce anisotropy, with different mechanisms possible. With knowledge either of mantle flow or which slip system is responsible for causing deformation, we can potentially determine the other with observations of the resulting seismic anisotropy. We investigate the dynamics at the CMB beneath North America using differential shear wave splitting in S and ScS phases from earthquakes of magnitude MW>5.5 in South and Central America, Hawaii the Mid-Atlantic Ridge and East Pacific Rise. They are detected on ~500 stations in North America, giving ~700 measurements of anisotropy in D″. We achieve this by correcting for anisotropy in the upper mantle (UM) beneath both the source and receiver. The measurements cover three regions beneath western USA, the Yucatan peninsula and Florida. In each case, two different, crossing ray paths are used, so that the style of anisotropy can be constrained—a single azimuth cannot distinguish differing cases. Our results showing ~1% anisotropy dependent on azimuth are not consistent with transverse isotropy with a vertical symmetry axis (VTI) anywhere. The same but with a tilted axis is possible (TTI) and would be consistent with inclusions of seismically-distinct material such as melt. TTI planes of isotropy dip south beneath Florida, southwest beneath western USA and southeast beneath Yucatan. However we test other slip systems in MgO, pv and ppv to determine if deformation in these phases can account for the observed anisotropy. The systems [100](010) and [1̅10](110) in ppv are consistent everywhere; pv is not beneath Yucatan. If we assume a general downwelling and displacement of mantle material in the seismically fast D″, corresponding to the impingement of slab material, slip along [100](010) seems more likely, with the possibility that slip along (110) as a transformation texture also occurs in the seismically fastest regions (Walte et al, GRL, 2009). With a new breed of detailed mantle deformation models, or experimental evidence of which system dominates, seismic anisotropy may be used to map deformation in D″ and provide greater insight into Earth's convecting interior.

Correlation analysis of symmetry breaking in the surface nanostructure ordering: case study of the ventral scale of the snake Morelia viridis

NASA Astrophysics Data System (ADS)

Kovalev, A.; Filippov, A.; Gorb, S. N.

2016-03-01

In contrast to the majority of inorganic or artificial materials, there is no ideal long-range ordering of structures on the surface in biological systems. Local symmetry of the ordering on biological surfaces is also often broken. In the present paper, the particular symmetry violation was analyzed for dimple-like nano-pattern on the belly scales of the skin of the pythonid snake Morelia viridis using correlation analysis and statistics of the distances between individual nanostructures. The results of the analysis performed on M. viridis were compared with a well-studied nano-nipple pattern on the eye of the sphingid moth Manduca sexta, used as a reference. The analysis revealed non-random, but very specific symmetry violation. In the case of the moth eye, the nano-nipple arrangement forms a set of domains, while in the case of the snake skin, the nano-dimples arrangement resembles an ordering of particles (molecules) in amorphous (glass) state. The function of the nano-dimples arrangement may be to provide both friction and strength isotropy of the skin. A simple model is suggested, which provides the results almost perfectly coinciding with the experimental ones. Possible mechanisms of the appearance of the above nano-formations are discussed.

OPTIS - A satellite test of Special and General Relativity

NASA Astrophysics Data System (ADS)

Dittus, H.; Lämmerzahl, C.; Peters, A.; Schiller, S.

OPTIS has been proposed as a small satellite platform in a high elliptical orbit (apogee 40,000 km, perigee 10,000 km) and is designed for high precision tests of foundations of Special and General Relativity. The experimental set-up consists of two ultrastable Nd:YAG lasers, two crossed optical resonators (monolithic cavities), an atomic clock, and an optical comb generator. OPTIS enables (1) a Michelson- Morley experiment to test the isotropy of light propagation (constancy of light speed, dc/c) with an accuracy of 1 part in 101 8 , (2) a Kennedey-Thorndike experiment to measure the independence of the light speed from the velocity of the laboratory in the order of 1 part in 101 6 , and (3) a test of the gravitational red shift by comparing the atomic clock and an optical clock on a precision level of 1 part in 104 . To avoid any influence from atmospheric drag, solar radiation, or earth albedo, the satellite needs drag free control, to depress the residual acceleration down to 10-14 m/s 2 in the frequency range between 100 to 1,000 Hz, and thermal control to stabilize the cavity temperature variation, dT/T, to 1 part in 107 during 100 s and to 1 part in 105 during 1 orbit.

Intrinsic Decomposition of The Stretch Tensor for Fibrous Media

NASA Astrophysics Data System (ADS)

Kellermann, David C.

2010-05-01

This paper presents a novel mechanism for the description of fibre reorientation based on the decomposition of the stretch tensor according to a given material's intrinsic constitutive properties. This approach avoids the necessity for fibre directors, structural tensors or specialised model such as the ideal fibre reinforced model, which are commonly applied to the analysis of fibre kinematics in the finite deformation of fibrous media for biomechanical problems. The proposed approach uses Intrinsic-Field Tensors (IFTs) that build upon the linear orthotropic theory presented in a previous paper entitled Strongly orthotropic continuum mechanics and finite element treatment. The intrinsic decomposition of the stretch tensor therein provides superior capacity to represent the intermediary kinematics driven by finite orthotropic ratios, where the benefits are predominantly expressed in cases of large deformation as is typical in the biomechanical studies. Satisfaction of requirements such as Material Frame-Indifference (MFI) and Euclidean objectivity are demonstrated here—these factors being necessary for the proposed IFTs to be valid tensorial quantities. The resultant tensors, initially for the simplest case of linear elasticity, are able to describe the same fibre reorientation as would the contemporary approaches such as with use of structural tensors and the like, while additionally being capable of showing results intermediary to classical isotropy and the infinitely orthotropic representations. This intermediary case is previously unreported.

A review of terrestrial, aerial and aquatic keratins: the structure and mechanical properties of pangolin scales, feather shafts and baleen plates.

PubMed

Wang, Bin; Sullivan, Tarah N

2017-12-01

Keratinous materials, omnipresent as the hard and durable epidermal appendages of animals, are among the toughest biological materials. They exhibit diverse morphologies and structures that serve a variety of amazing and inspiring mechanical functions. In this work, we provide a review of representative terrestrial, aerial and aquatic keratinous materials, pangolin scales, feather shafts and baleen plates, and correlate their hierarchical structures to respective functions of dermal armor, flight material and undersea filter. The overlapping pattern of pangolin scales provides effective body coverage, and the solid scales show transverse isotropy and strain-rate sensitivity, both important for armor function. The feather shaft displays a distinct shape factor, hierarchical fibrous structure within the cortex, and a solid shell-over-foam design, which enables synergistic stiffening and toughening with exceptional lightness to fulfill flight. Baleen plates exhibit a sandwich-tubular structure that features anisotropic flexural properties to sustain forces from water flow and remarkable fracture toughness that ensures reliable undersea functioning. The latest findings regarding the structural design principles and mechanical properties are presented in order to advance current understanding of keratinous materials and to stimulate the development of new bioinspired materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

Kinetic Simulations of Dense Plasma Focus Breakdown

NASA Astrophysics Data System (ADS)

Schmidt, A.; Higginson, D. P.; Jiang, S.; Link, A.; Povilus, A.; Sears, J.; Bennett, N.; Rose, D. V.; Welch, D. R.

2015-11-01

A dense plasma focus (DPF) device is a type of plasma gun that drives current through a set of coaxial electrodes to assemble gas inside the device and then implode that gas on axis to form a Z-pinch. This implosion drives hydrodynamic and kinetic instabilities that generate strong electric fields, which produces a short intense pulse of x-rays, high-energy (>100 keV) electrons and ions, and (in deuterium gas) neutrons. A strong factor in pinch performance is the initial breakdown and ionization of the gas along the insulator surface separating the two electrodes. The smoothness and isotropy of this ionized sheath are imprinted on the current sheath that travels along the electrodes, thus making it an important portion of the DPF to both understand and optimize. Here we use kinetic simulations in the Particle-in-cell code LSP to model the breakdown. Simulations are initiated with neutral gas and the breakdown modeled self-consistently as driven by a charged capacitor system. We also investigate novel geometries for the insulator and electrodes to attempt to control the electric field profile. The initial ionization fraction of gas is explored computationally to gauge possible advantages of pre-ionization which could be created experimentally via lasers or a glow-discharge. Prepared by LLNL under Contract DE-AC52-07NA27344.

Automatic extraction of tree crowns from aerial imagery in urban environment

NASA Astrophysics Data System (ADS)

Liu, Jiahang; Li, Deren; Qin, Xunwen; Yang, Jianfeng

2006-10-01

Traditionally, field-based investigation is the main method to investigate greenbelt in urban environment, which is costly and low updating frequency. In higher resolution image, the imagery structure and texture of tree canopy has great similarity in statistics despite the great difference in configurations of tree canopy, and their surface structures and textures of tree crown are very different from the other types. In this paper, we present an automatic method to detect tree crowns using high resolution image in urban environment without any apriori knowledge. Our method catches unique structure and texture of tree crown surface, use variance and mathematical expectation of defined image window to position the candidate canopy blocks coarsely, then analysis their inner structure and texture to refine these candidate blocks. The possible spans of all the feature parameters used in our method automatically generate from the small number of samples, and HOLE and its distribution as an important characteristics are introduced into refining processing. Also the isotropy of candidate image block and holes' distribution is integrated in our method. After introduction the theory of our method, aerial imageries were used ( with a resolution about 0.3m ) to test our method, and the results indicate that our method is an effective approach to automatically detect tree crown in urban environment.

A multiphase three-dimensional multi-relaxation time (MRT) lattice Boltzmann model with surface tension adjustment

NASA Astrophysics Data System (ADS)

Ammar, Sami; Pernaudat, Guillaume; Trépanier, Jean-Yves

2017-08-01

The interdependence of surface tension and density ratio is a weakness of pseudo-potential based lattice Boltzmann models (LB). In this paper, we propose a 3D multi-relaxation time (MRT) model for multiphase flows at large density ratios. The proposed model is capable of adjusting the surface tension independently of the density ratio. We also present the 3D macroscopic equations recovered by the proposed forcing scheme. A high order of isotropy for the interaction force is used to reduce the amplitude of spurious currents. The proposed 3D-MRT model is validated by verifying Laplace's law and by analyzing its thermodynamic consistency and the oscillation period of a deformed droplet. The model is then applied to the simulation of the impact of a droplet on a dry surface. Impact dynamics are determined and the maximum spread factor calculated for different Reynolds and Weber numbers. The numerical results are in agreement with data published in the literature. The influence of surface wettability on the spread factor is also investigated. Finally, our 3D-MRT model is applied to the simulation of the impact of a droplet on a wet surface. The propagation of transverse waves is observed on the liquid surface.

The sunstone and polarised skylight: ancient Viking navigational tools?

NASA Astrophysics Data System (ADS)

Ropars, Guy; Lakshminarayanan, Vasudevan; Le Floch, Albert

2014-10-01

Although the polarisation of the light was discovered at the beginning of the nineteenth century, the Vikings could have used the polarised light around the tenth century in their navigation to America, using a 'sunstone' evoked in the Icelandic Sagas. Indeed, the birefringence of the Iceland spar (calcite), a common crystal in Scandinavia, permits a simple observation of the axis of polarisation of the skylight at the zenith. From this, it is possible to guess the azimuth of a hidden Sun below the horizon, for instance. The high sensitivity of the differential method provided by the ordinary and extraordinary beams of calcite at its so-called isotropy point is about two orders higher than that of the best dichroic polariser and permits to reach an accuracy of ±1° for the Sun azimuth (at sunrise and sunset). Unfortunately, due to the relative fragility of calcite, only the so-called Alderney crystal was discovered on board a 16th ancient ship. Curiously, beyond its use as a sunstone by the Vikings, during these last millennia calcite has led to the discovery of the polarisation of the light itself by Malus and is currently being used to detect the atmospheres of exoplanets. Moreover, the differential method for the light polarisation detection is widely used in the animal world.

Three Dimensional Cross-Sectional Properties From Bone Densitometry

NASA Technical Reports Server (NTRS)

Cleek, Tammy M.; Whalen, Robert T.; Dalton, Bonnie P. (Technical Monitor)

2001-01-01

Bone densitometry has previously been used to obtain cross-sectional properties of bone in a single scan plane. Using three non-coplanar scans, we have extended the method to obtain the principal area Moments of inertia and orientations of the principal axes at each cross-section along the length of the scan. Various 5 aluminum phantoms were used to examine scanner characteristics to develop the highest accuracy possible for in vitro non-invasive analysis of mass distribution. Factors considered included X-ray photon energy, initial scan orientation, the included angle of the 3 scans, and Imin/Imax ratios. Principal moments of inertia were accurate to within 3.1% and principal angles were within 1 deg. of the expected value for phantoms scanned with included angles of 60 deg. and 90 deg. at the higher X-ray photon energy. Low standard deviations in error also 10 indicate high precision of calculated measurements with these included angles. Accuracy and precision decreased slightly when the included angle was reduced to 30 deg. The method was then successfully applied to a pair of excised cadaveric tibiae. The accuracy and insensitivity of the algorithms to cross-sectional shape and changing isotropy (Imin/Imax) values when various included angles are used make this technique viable for future in vivo studies.

PIV study of flow through porous structure using refractive index matching

NASA Astrophysics Data System (ADS)

Häfeli, Richard; Altheimer, Marco; Butscher, Denis; Rudolf von Rohr, Philipp

2014-05-01

An aqueous solution of sodium iodide and zinc iodide is proposed as a fluid that matches the refractive index of a solid manufactured by rapid prototyping. This enabled optical measurements in single-phase flow through porous structures. Experiments were also done with an organic index-matching fluid (anisole) in porous structures of different dimensions. To compare experiments with different viscosities and dimensions, we employed Reynolds similarity to deduce the scaling laws. One of the target quantities of our investigation was the dissipation rate of turbulent kinetic energy. Different models for the dissipation rate estimation were evaluated by comparing isotropy ratios. As in many other studies also, our experiments were not capable of resolving the velocity field down to the Kolmogorov length scale, and therefore, the dissipation rate has to be considered as underestimated. This is visible in experiments of different relative resolutions. However, being near the Kolmogorov scale allows estimating a reproducible, yet underestimated spatial distribution of dissipation rate inside the porous structure. Based on these results, the model was used to estimate the turbulent diffusivity. Comparing it to the dispersion coefficient obtained in the same porous structure, we conclude that even at the turbulent diffusivity makes up only a small part of mass transfer in axial direction. The main part is therefore attributed to Taylor dispersion.

Bone material elasticity in a murine model of osteogenesis imperfecta.

PubMed

Mehta, S S; Antich, P P; Landis, W J

1999-01-01

To investigate the source of bone brittleness in the disease osteogenesis imperfecta (OI), biomechanical properties have been measured in the femurs from a homozygous (oim/oim) mutant mouse model of OI, its heterozygous littermates, and wild-type animals. The novel technique of ultrasound critical-angle reflectometry (UCR) was used to determine bone material elasticity matrix from measurements of the pressure and shear wave velocity at different orientations about selected points of the bone specimens. This nondestructive method is the only available means for obtaining measurements of this nature from a single surface. The ultrasound pressure wave velocity showed an increased isotropy in the homozygous compared to the wild-type specimens. This was reflected in a significant decrease in the principal elastic modulus measured along the length of the oim/oim bones (E33) while the modulus along the width (E11) did not change significantly, compared to wild-type specimens. The Poisson's ratio, v12, also had a significantly increased value in oim/oim bones. Measurements of these parameters in heterozygous animals generally fell between those from homozygous and control mice. The differences in the elasticity components in oim/oim bones indicate an altered stress distribution and a modified elastic response to loads, compared to normal bone.

Turbulence Measurements of Rectangular Nozzles with Bevel

NASA Technical Reports Server (NTRS)

Bridges, James; Wernet, Mark P.

2015-01-01

This paper covers particle image velocimetry measurements of a family of rectangular nozzles with aspect ratios 2, 4, and 8, in the high subsonic flow regime. Far-field acoustic results, presented previously, showed that increasing aspect ratios increased the high frequency noise, especially directed in the polar plane containing the minor axis of the nozzle. The measurements presented here have important implications in the modeling of turbulent sources for acoustic analogy theories. While the nonaxisymmetric mean flow from the rectangular nozzles can be studied reliably using computational solutions, the nonaxisymmetry of the turbulent fluctuations, particularly at the level of velocity components, cannot; only measurements such as these can determine the impact of nozzle geometry on acoustic source anisotropy. Additional nozzles were constructed that extended the wide lip on one side of these nozzles to form beveled nozzles. The paper first documents the velocity fields, mean and variance, from the round, rectangular, and beveled rectangular nozzles at high subsonic speeds. A second section introduces measures of the isotropy of the turbulence, such as component ratios and lengthscales, first by showing them for a round jet and then for the rectangular nozzles. From these measures the source models of acoustic analogy codes can be judged or modified to account for these anisotropies.

X-Ray Diffraction Studies of 145 MeV proton-irradiated AlBeMet 162

DOE PAGES

Elbakhshwan, Mohamed; McDonald, Kirk T.; Ghose, Sanjit; ...

2016-08-03

AlBeMet 162 (Materion Co., formerly Brush Wellman) has been irradiated with 145 MeV protons up to 1.2x10 20 cm -2 fluence, with irradiation temperatures in the range of 100-220oC. Macroscopic postirradiation evaluation on the evolution of mechanical and thermal properties was integrated with a comprehensive X-ray- diffraction study using high-energy monochromatic and polychromatic X-ray beams, which offered a microscopic view of the irradiation damage effects on AlBeMet. The study confirmed the stability of the metal-matrix composite, its resistance to proton damage, and the continuing separation of the two distinct phases, fcc aluminum and hcp beryllium, following irradiation. Furthermore, based onmore » the absence of inter-planar distance change during proton irradiation, it was confirmed that the stacking faults and clusters on the Al (111) planes are stable, and thus can migrate from the cascade region and be absorbed at various sinks. XRD analysis of the unirradiated AlBeMet 162 showed clear change in the texture of the fcc phase with orientation especially in the Al (111) reflection which exhibits a “non-perfect” six-fold symmetry, implying lack of isotropy in the composite.« less

Simulations of material mixing in laser-driven reshock experiments

NASA Astrophysics Data System (ADS)

Haines, Brian M.; Grinstein, Fernando F.; Welser-Sherrill, Leslie; Fincke, James R.

2013-02-01

We perform simulations of a laser-driven reshock experiment [Welser-Sherrill et al., High Energy Density Phys. (unpublished)] in the strong-shock high energy-density regime to better understand material mixing driven by the Richtmyer-Meshkov instability. Validation of the simulations is based on direct comparison of simulation and radiographic data. Simulations are also compared with published direct numerical simulation and the theory of homogeneous isotropic turbulence. Despite the fact that the flow is neither homogeneous, isotropic nor fully turbulent, there are local regions in which the flow demonstrates characteristics of homogeneous isotropic turbulence. We identify and isolate these regions by the presence of high levels of turbulent kinetic energy (TKE) and vorticity. After reshock, our analysis shows characteristics consistent with those of incompressible isotropic turbulence. Self-similarity and effective Reynolds number assessments suggest that the results are reasonably converged at the finest resolution. Our results show that in shock-driven transitional flows, turbulent features such as self-similarity and isotropy only fully develop once de-correlation, characteristic vorticity distributions, and integrated TKE, have decayed significantly. Finally, we use three-dimensional simulation results to test the performance of two-dimensional Reynolds-averaged Navier-Stokes simulations. In this context, we also test a presumed probability density function turbulent mixing model extensively used in combustion applications.

An approach to the development of numerical algorithms for first order linear hyperbolic systems in multiple space dimensions: The constant coefficient case

NASA Technical Reports Server (NTRS)

Goodrich, John W.

1995-01-01

Two methods for developing high order single step explicit algorithms on symmetric stencils with data on only one time level are presented. Examples are given for the convection and linearized Euler equations with up to the eighth order accuracy in both space and time in one space dimension, and up to the sixth in two space dimensions. The method of characteristics is generalized to nondiagonalizable hyperbolic systems by using exact local polynominal solutions of the system, and the resulting exact propagator methods automatically incorporate the correct multidimensional wave propagation dynamics. Multivariate Taylor or Cauchy-Kowaleskaya expansions are also used to develop algorithms. Both of these methods can be applied to obtain algorithms of arbitrarily high order for hyperbolic systems in multiple space dimensions. Cross derivatives are included in the local approximations used to develop the algorithms in this paper in order to obtain high order accuracy, and improved isotropy and stability. Efficiency in meeting global error bounds is an important criterion for evaluating algorithms, and the higher order algorithms are shown to be up to several orders of magnitude more efficient even though they are more complex. Stable high order boundary conditions for the linearized Euler equations are developed in one space dimension, and demonstrated in two space dimensions.

Numerical Study of Rotating Turbulence with External Forcing

NASA Technical Reports Server (NTRS)

Yeung, P. K.; Zhou, Ye

1998-01-01

Direct numerical simulation at 256(exp 3) resolution have been carried out to study the response of isotropic turbulence to the concurrent effects of solid-body rotation and numerical forcing at the large scales. Because energy transfer to the smaller scales is weakened by rotation, energy input from forcing gradually builds up at the large scales, causing the overall kinetic energy to increase. At intermediate wavenumbers the energy spectrum undergoes a transition from a limited k(exp -5/3) inertial range to k(exp -2) scaling recently predicted in the literature. Although the Reynolds stress tensor remains approximately isotropic and three-components, evidence for anisotropy and quasi- two-dimensionality in length scales and spectra in different velocity components and directions is strong. The small scales are found to deviate from local isotropy, primarily as a result of anisotropic transfer to the high wavenumbers. To understand the spectral dynamics of this flow we study the detailed behavior of nonlinear triadic interactions in wavenumber space. Spectral transfer in the velocity component parallel to the axis of rotation is qualitatively similar to that in non-rotating turbulence; however the perpendicular component is characterized by a greatly suppressed energy cascade at high wavenumber and a local reverse transfer at the largest scales. The broader implications of this work are briefly addressed.

Characteristics of low reynolds number shear-free turbulence at an impermeable base.

PubMed

Wan Mohtar, W H M; ElShafie, A

2014-01-01

Shear-free turbulence generated from an oscillating grid in a water tank impinging on an impermeable surface at varying Reynolds number 74 ≤ Re(l) ≤ 570 was studied experimentally, where the Reynolds number is defined based on the root-mean-square (r.m.s) horizontal velocity and the integral length scale. A particular focus was paid to the turbulence characteristics for low Re(l) < 150 to investigate the minimum limit of Re l obeying the profiles of rapid distortion theory. The measurements taken at near base included the r.m.s turbulent velocities, evolution of isotropy, integral length scales, and energy spectra. Statistical analysis of the velocity data showed that the anisotropic turbulence structure follows the theory for flows with Re(l) ≥ 117. At low Re(l) < 117, however, the turbulence profile deviated from the prediction where no amplification of horizontal velocity components was observed and the vertical velocity components were seen to be constant towards the tank base. Both velocity components sharply decreased towards zero at a distance of ≈ 1/3 of the integral length scale above the base due to viscous damping. The lower limit where Re(l) obeys the standard profile was found to be within the range 114 ≤ Re(l) ≤ 116.

A study of process parameters on workpiece anisotropy in the laser engineered net shaping (LENSTM) process

NASA Astrophysics Data System (ADS)

Chandra, Shubham; Rao, Balkrishna C.

2017-06-01

The process of laser engineered net shaping (LENSTM) is an additive manufacturing technique that employs the coaxial flow of metallic powders with a high-power laser to form a melt pool and the subsequent deposition of the specimen on a substrate. Although research done over the past decade on the LENSTM processing of alloys of steel, titanium, nickel and other metallic materials typically reports superior mechanical properties in as-deposited specimens, when compared to the bulk material, there is anisotropy in the mechanical properties of the melt deposit. The current study involves the development of a numerical model of the LENSTM process, using the principles of computational fluid dynamics (CFD), and the subsequent prediction of the volume fraction of equiaxed grains to predict process parameters required for the deposition of workpieces with isotropy in their properties. The numerical simulation is carried out on ANSYS-Fluent, whose data on thermal gradient are used to determine the volume fraction of the equiaxed grains present in the deposited specimen. This study has been validated against earlier efforts on the experimental studies of LENSTM for alloys of nickel. Besides being applicable to the wider family of metals and alloys, the results of this study will also facilitate effective process design to improve both product quality and productivity.

Multiscale analysis of the CMB temperature derivatives

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

Marcos-Caballero, A.; Martínez-González, E.; Vielva, P., E-mail: marcos@ifca.unican.es, E-mail: martinez@ifca.unican.es, E-mail: vielva@ifca.unican.es

2017-02-01

We study the Planck CMB temperature at different scales through its derivatives up to second order, which allows one to characterize the local shape and isotropy of the field. The problem of having an incomplete sky in the calculation and statistical characterization of the derivatives is addressed in the paper. The analysis confirms the existence of a low variance in the CMB at large scales, which is also noticeable in the derivatives. Moreover, deviations from the standard model in the gradient, curvature and the eccentricity tensor are studied in terms of extreme values on the data. As it is expected,more » the Cold Spot is detected as one of the most prominent peaks in terms of curvature, but additionally, when the information of the temperature and its Laplacian are combined, another feature with similar probability at the scale of 10{sup o} is also observed. However, the p -value of these two deviations increase above the 6% when they are referred to the variance calculated from the theoretical fiducial model, indicating that these deviations can be associated to the low variance anomaly. Finally, an estimator of the directional anisotropy for spinorial quantities is introduced, which is applied to the spinors derived from the field derivatives. An anisotropic direction whose probability is <1% is detected in the eccentricity tensor.« less

Constraints on Average Radial Anisotropy in the Lower Mantle

NASA Astrophysics Data System (ADS)

Trampert, J.; De Wit, R. W. L.; Kaeufl, P.; Valentine, A. P.

2014-12-01

Quantifying uncertainties in seismological models is challenging, yet ideally quality assessment is an integral part of the inverse method. We invert centre frequencies for spheroidal and toroidal modes for three parameters of average radial anisotropy, density and P- and S-wave velocities in the lower mantle. We adopt a Bayesian machine learning approach to extract the information on the earth model that is available in the normal mode data. The method is flexible and allows us to infer probability density functions (pdfs), which provide a quantitative description of our knowledge of the individual earth model parameters. The parameters describing shear- and P-wave anisotropy show little deviations from isotropy, but the intermediate parameter η carries robust information on negative anisotropy of ~1% below 1900 km depth. The mass density in the deep mantle (below 1900 km) shows clear positive deviations from existing models. Other parameters (P- and shear-wave velocities) are close to PREM. Our results require that the average mantle is about 150K colder than commonly assumed adiabats and consist of a mixture of about 60% perovskite and 40% ferropericlase containing 10-15% iron. The anisotropy favours a specific orientation of the two minerals. This observation has important consequences for the nature of mantle flow.

Response of turbulence subjected to a straining-relaxation-destraining cycle

NASA Astrophysics Data System (ADS)

Chen, Jun; Meneveau, Charles; Katz, Joseph

2004-11-01

The response of turbulence subjected to planar straining and de-straining is studied experimentally, and the impact of the applied distortions on the energy transfer across different length scales is quantified. The data are obtained using Planar Particle Image Velocimetry (PIV) in a water tank, in which high Reynolds number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining mean flows are produced by pushing and pulling a rectangular piston towards, and away from, the bottom wall of the tank. The data are processed to yield the time evolution of Reynolds stresses, anisotropy tensors, turbulence kinetic energy production, and mean subgrid dissipation rate at various scales. During straining, the production rises rapidly. After the relaxation period the small-scale SGS stresses recover isotropy, but the Reynolds stresses at large scales still display significant anisotropy. When destraining is applied, a strong negative production (back-scattering) is observed, by which turbulence fluctuations return kinetic energy to the mean flow. Reversed energy transfer is also revealed in the vorticity fluctuations history. The experiment allows to disentangle in detail the causes for this global backscatter phenomenon in terms of non-equilibrium conditions of the Reynolds stresses, and to follow the trends as function of scale.

Anisotropic Bispectrum of Curvature Perturbations from Primordial Non-Abelian Vector Fields

NASA Astrophysics Data System (ADS)

Bartolo, Nicola; Dimastrogiovanni, Emanuela; Matarrese, Sabino; Riotto, Antonio

2009-10-01

We consider a primordial SU(2) vector multiplet during inflation in models where quantum fluctuations of vector fields are involved in producing the curvature perturbation. Recently, a lot of attention has been paid to models populated by vector fields, given the interesting possibility of generating some level of statistical anisotropy in the cosmological perturbations. The scenario we propose is strongly motivated by the fact that, for non-Abelian gauge fields, self-interactions are responsible for generating extra terms in the cosmological correlation functions, which are naturally absent in the Abelian case. We compute these extra contributions to the bispectrum of the curvature perturbation, using the δN formula and the Schwinger-Keldysh formalism. The primordial violation of rotational invariance (due to the introduction of the SU(2) gauge multiplet) leaves its imprint on the correlation functions introducing, as expected, some degree of statistical anisotropy in our results. We calculate the non-Gaussianity parameter fNL, proving that the new contributions derived from gauge bosons self-interactions can be important, and in some cases the dominat ones. We study the shape of the bispectrum and we find that it turns out to peak in the local configuration, with an amplitude that is modulated by the preferred directions that break statistical isotropy.

The extracellular matrix remodeled

PubMed Central

Kirmse, Robert; Otto, Hannes

2012-01-01

Membrane Type-1 Matrix Metalloproteinase (MT1-MMP, MMP-14) is regarded as the prototype of a membrane- tethered protease. It drives fundamental biological processes ranging from embryogenesis to cancer metastasis. The proteolytic cleavage of proteins by MT1-MMP can rapidly alter the biophysical properties of a cell’s microenvironment. Cell’s must thus be able to sense and react to these alterations and transduce these effectively in biochemical signals and cell responses. Although many cells react as acutely to such physical stimuli as they do to chemical ones, the regulatory effects of these have been less extensively explored. In order to investigate a possible interdependency of proteolytic matrix cleavage by MT1-MMP and the generation and sensing of force by cells, a model system was established which exploits the properties of a matrix array of parallel collagen-I fibers. The resulting an-isotropy of the matrix with high tensile strength along the fibers and high mobility perpendicular to it allows the convenient detection of bundling and cleavage of the collagen fibers, as well as spreading and durotaxis of the cells. In summary, we have demonstrated that cell adhesion, force generation, and force sensing are vital for the regulation of MT1-MMP for efficient cleavage of collagen-I. PMID:22482015

Characteristics of Low Reynolds Number Shear-Free Turbulence at an Impermeable Base

PubMed Central

Wan Mohtar, W. H. M.; ElShafie, A.

2014-01-01

Shear-free turbulence generated from an oscillating grid in a water tank impinging on an impermeable surface at varying Reynolds number 74 ≤ Re l ≤ 570 was studied experimentally, where the Reynolds number is defined based on the root-mean-square (r.m.s) horizontal velocity and the integral length scale. A particular focus was paid to the turbulence characteristics for low Re l < 150 to investigate the minimum limit of Re l obeying the profiles of rapid distortion theory. The measurements taken at near base included the r.m.s turbulent velocities, evolution of isotropy, integral length scales, and energy spectra. Statistical analysis of the velocity data showed that the anisotropic turbulence structure follows the theory for flows with Re l ≥ 117. At low Re l < 117, however, the turbulence profile deviated from the prediction where no amplification of horizontal velocity components was observed and the vertical velocity components were seen to be constant towards the tank base. Both velocity components sharply decreased towards zero at a distance of ≈1/3 of the integral length scale above the base due to viscous damping. The lower limit where Re l obeys the standard profile was found to be within the range 114 ≤ Re l ≤ 116. PMID:25250384

A direct-drive exploding-pusher implosion as the first step in development of a monoenergetic charged-particle backlighting platforn at the National Ignition Facility

DOE PAGES

Rosenberg, M. J.; Zylstra, A. B.; Seguin, F. H.; ...

2016-01-18

A thin-glass-shell, D 3He-filled exploding-pusher inertial confinement fusion implosion at the National Ignition Facility (NIF) has been demonstrated as a proton source that serves as a promising first step toward development of a monoenergetic proton, alpha, and triton backlighting platform at the NIF. Among the key measurements, the D3He-proton emission on this experiment (shot N121128) has been well-characterized spectrally, temporally, and in terms of emission isotropy, revealing a highly monoenergetic (ΔE/E~4%) and isotropic source (~3% proton fluence variation and ~0.5% proton energy variation). On a similar shot (N130129, with D 2 fill), the DD-proton spectrum has been obtained as well,more » illustrating that monoenergetic protons of multiple energies may be utilized in a single experiment. In conclusion, these results, and experiments on OMEGA, point toward future steps in the development of a precision, monoenergetic proton, alpha, and triton source that can readily be implemented at the NIF for backlighting a broad range of high energy density physics (HEDP) experiments in which fields and flows are manifest, and also utilized for studies of stopping power in warm dense matter and in classical plasmas.« less

Anomalies in the GRBs' distribution

NASA Astrophysics Data System (ADS)

Bagoly, Zsolt; Horvath, Istvan; Hakkila, Jon; Toth, Viktor

2015-08-01

Gamma-ray bursts (GRBs) are the most luminous objects known: they outshine their host galaxies making them ideal candidates for probing large-scale structure. Earlier, the angular distribution of different GRBs (long, intermediate and short) has been studied in detail with different methods and it has been found that the short and intermediate groups showed deviation from the full randomness at different levels (e.g. Vavrek, R., et al. 2008). However these result based only angular measurements of the BATSE experiment, without any spatial distance indicator involved.Currently we have more than 361 GRBs with measured precise position, optical afterglow and redshift, mainly due to the observations of the Swift mission. This sample is getting large enough that it its homogeneous and isotropic distribution a large scale can be checked. We have recently (Horvath, I. et al., 2014) identified a large clustering of gamma-ray bursts at redshift z ~ 2 in the general direction of the constellations of Hercules and Corona Borealis. This angular excess cannot be entirely attributed to known selection biases, making its existence due to chance unlikely. The scale on which the clustering occurs is disturbingly large, about 2-3 Gpc: the underlying distribution of matter suggested by this cluster is big enough to question standard assumptions about Universal homogeneity and isotropy.

Fluid identification based on P-wave anisotropy dispersion gradient inversion for fractured reservoirs

NASA Astrophysics Data System (ADS)

Zhang, J. W.; Huang, H. D.; Zhu, B. H.; Liao, W.

2017-10-01

Fluid identification in fractured reservoirs is a challenging issue and has drawn increasing attentions. As aligned fractures in subsurface formations can induce anisotropy, we must choose parameters independent with azimuths to characterize fractures and fluid effects such as anisotropy parameters for fractured reservoirs. Anisotropy is often frequency dependent due to wave-induced fluid flow between pores and fractures. This property is conducive for identifying fluid type using azimuthal seismic data in fractured reservoirs. Through the numerical simulation based on Chapman model, we choose the P-wave anisotropy parameter dispersion gradient (PADG) as the new fluid factor. PADG is dependent both on average fracture radius and fluid type but independent on azimuths. When the aligned fractures in the reservoir are meter-scaled, gas-bearing layer could be accurately identified using PADG attribute. The reflection coefficient formula for horizontal transverse isotropy media by Rüger is reformulated and simplified according to frequency and the target function for inverting PADG based on frequency-dependent amplitude versus azimuth is derived. A spectral decomposition method combining Orthogonal Matching Pursuit and Wigner-Ville distribution is used to prepare the frequency-division data. Through application to synthetic data and real seismic data, the results suggest that the method is useful for gas identification in reservoirs with meter-scaled fractures using high-qualified seismic data.

Spectral Short-circuiting and Wake Production within the Canopy Trunk Space of an Alpine Hardwood Forest

NASA Astrophysics Data System (ADS)

Cava, Daniela; Katul, Gabriel G.

2008-03-01

Using synchronous multi-level high frequency velocity measurements, the turbulence spectra within the trunk space of an alpine hardwood forest were analysed. The spectral short-circuiting of the energy cascade for each velocity component was well reproduced by a simplified spectral model that retained return-to-isotropy and component-wise work done by turbulence against the drag and wake production. However, the use of an anisotropic drag coefficient was necessary to reproduce these measured component-wise spectra. The degree of anisotropy in the vertical drag was shown to vary with the element Reynolds number. The wake production frequency in the measured spectra was shown to be consistent with the vortex shedding frequency at constant Strouhal number given by f vs = 0.21 ū/d, where d can be related to the stem diameter at breast height ( dbh) and ū is the local mean velocity. The energetic scales, determined from the inflection point instability at the canopy atmosphere interface, appear to persist into the trunk space when {C_{du} a_{cr} h_c /β ≫ 1}, where C du is the longitudinal drag coefficient, a cr is the crown-layer leaf area density, h c is the canopy height, and β is the dimensionless momentum absorption at the canopy top.

Traveltime inversion and error analysis for layered anisotropy

NASA Astrophysics Data System (ADS)

Jiang, Fan; Zhou, Hua-wei

2011-02-01

While tilted transverse isotropy (TTI) is a good approximation of the velocity structure for many dipping and fractured strata, it is still challenging to estimate anisotropic depth models even when the tilted angle is known. With the assumption of weak anisotropy, we present a TTI traveltime inversion approach for models consisting of several thickness-varying layers where the anisotropic parameters are constant for each layer. For each model layer the inversion variables consist of the anisotropic parameters ɛ and δ, the tilted angle φ of its symmetry axis, layer velocity along the symmetry axis, and thickness variation of the layer. Using this method and synthetic data, we evaluate the effects of errors in some of the model parameters on the inverted values of the other parameters in crosswell and Vertical Seismic Profile (VSP) acquisition geometry. The analyses show that the errors in the layer symmetry axes sensitively affect the inverted values of other parameters, especially δ. However, the impact of errors in δ on the inversion of other parameters is much less than the impact on δ from the errors in other parameters. Hence, a practical strategy is first to invert for the most error-tolerant parameter layer velocity, then progressively invert for ɛ in crosswell geometry or δ in VSP geometry.

New insights into the North Taranaki Basin from New Zealand's first broadband 3D survey

NASA Astrophysics Data System (ADS)

Uzcategui, Marjosbet; Francis, Malcolm; Kong, Wai Tin Vincent; Patenall, Richard; Fell, Dominic; Paxton, Andrea; Allen, Tristan

2016-06-01

The Taranaki Basin is the only hydrocarbon producing basin in New Zealand. The North Taranaki Basin has widespread two-dimensional (2D) seismic coverage and numerous wells that have not encountered commercial accumulations. This is attributed to the structural complexity in the central graben and the absence of necessary information to help understand the basin's evolution. An active petroleum system has been confirmed by hydrocarbon shows and non-commercial oil and gas discoveries (Karewa-1 and Kora-1). A broadband long offset three-dimensional (3D) seismic survey was acquired and processed by Schlumberger in 2013 to evaluate the hydrocarbon potential of the North Taranaki Basin. Innovative acquisition techniques were combined with advanced processing and imaging methods. Raypath distortions and depth uncertainty were significantly reduced by processing through tilted transverse isotropy (TTI) anisotropic Kirchhoff prestack depth migration with a geologically constrained velocity model. The survey provided the necessary information to understand the petroleum system and provide evidence for material hydrocarbon accumulations. In this investigation, we assessed the hydrocarbon potential of the North Taranaki Basin using the newly acquired data. 3D seismic interpretation and amplitude-versus-offset (AVO) analysis support the renewed potential of the basin and demonstrate effectiveness of these technologies that together can achieve encouraging results for hydrocarbon exploration.

A direct-drive exploding-pusher implosion as the first step in development of a monoenergetic charged-particle backlighting platforn at the National Ignition Facility

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

Rosenberg, M. J.; Zylstra, A. B.; Seguin, F. H.

A thin-glass-shell, D 3He-filled exploding-pusher inertial confinement fusion implosion at the National Ignition Facility (NIF) has been demonstrated as a proton source that serves as a promising first step toward development of a monoenergetic proton, alpha, and triton backlighting platform at the NIF. Among the key measurements, the D3He-proton emission on this experiment (shot N121128) has been well-characterized spectrally, temporally, and in terms of emission isotropy, revealing a highly monoenergetic (ΔE/E~4%) and isotropic source (~3% proton fluence variation and ~0.5% proton energy variation). On a similar shot (N130129, with D 2 fill), the DD-proton spectrum has been obtained as well,more » illustrating that monoenergetic protons of multiple energies may be utilized in a single experiment. In conclusion, these results, and experiments on OMEGA, point toward future steps in the development of a precision, monoenergetic proton, alpha, and triton source that can readily be implemented at the NIF for backlighting a broad range of high energy density physics (HEDP) experiments in which fields and flows are manifest, and also utilized for studies of stopping power in warm dense matter and in classical plasmas.« less

Effect of a growth hormone treatment on bone orthotropic elasticity in dwarf rats

NASA Technical Reports Server (NTRS)

Kohles, S. S.; Martinez, D. A.; Bowers, J. R.; Vailas, A. C.; Vanderby, R. Jr

1997-01-01

A refinement of the current ultrasonic elasticity technique was used to measure the orthotropic elastic properties of rat cortical bone as well as to quantify changes in elastic properties, density, and porosity of the dwarf rat cortex after a treatment with recombinant human growth hormone (rhGH). The ultrasonic elasticity technique was refined via optimized signal management of high-frequency wave propagation through cubic cortical specimens. Twenty dwarf rats (37 days old) were randomly assigned to two groups (10 rats each). The dwarf rat model (5-10% of normal GH) was given subcutaneous injections of either rhGH or saline over a 14-day treatment period. Density was measured using Archimedes technique. Porosity and other microstructural characteristics were also explored via scanning electron microscopy and image analysis. Statistical tests verified significant decreases in cortical orthotropic Young's (-26.7%) and shear (-16.7%) moduli and density (-2.42%) concomitant with an increase in porosity (+125%) after rhGH treatments to the dwarf model (p < 0.05). A change in material symmetry from orthotropy toward planar isotropy within the radial-circumferential plane after GH treatments was also noted. These results demonstrate some alteration in bone properties at this time interval. Structural implications of these changes throughout physiological loading regimens should be explored.

Trabecular architecture of the manual elements reflects locomotor patterns in primates.

PubMed

Matarazzo, Stacey A

2015-01-01

The morphology of trabecular bone has proven sensitive to loading patterns in the long bones and metacarpal heads of primates. It is expected that we should also see differences in the manual digits of primates that practice different methods of locomotion. Primate proximal and middle phalanges are load-bearing elements that are held in different postures and experience different mechanical strains during suspension, quadrupedalism, and knuckle walking. Micro CT scans of the middle phalanx, proximal phalanx and the metacarpal head of the third ray were used to examine the pattern of trabecular orientation in Pan, Gorilla, Pongo, Hylobates and Macaca. Several zones, i.e., the proximal ends of both phalanges and the metacarpal heads, were capable of distinguishing between knuckle-walking, quadrupedal, and suspensory primates. Orientation and shape seem to be the primary distinguishing factors but differences in bone volume, isotropy index, and degree of anisotropy were seen across included taxa. Suspensory primates show primarily proximodistal alignment in all zones, and quadrupeds more palmar-dorsal orientation in several zones. Knuckle walkers are characterized by having proximodistal alignment in the proximal ends of the phalanges and a palmar-dorsal alignment in the distal ends and metacarpal heads. These structural differences may be used to infer locmotor propensities of extinct primate taxa.

Structured light generation by magnetic metamaterial half-wave plates at visible wavelength

NASA Astrophysics Data System (ADS)

Zeng, Jinwei; Luk, Ting S.; Gao, Jie; Yang, Xiaodong

2017-12-01

Metamaterial or metasurface unit cells functioning as half-wave plates play an essential role for realizing ideal Pancharatnam-Berry phase optical elements capable of tailoring light phase and polarization as desired. Complex light beam manipulation through these metamaterials or metasurfaces unveils new dimensions of light-matter interactions for many advances in diffraction engineering, beam shaping, structuring light, and holography. However, the realization of metamaterial or metasurface half-wave plates in visible spectrum range is still challenging mainly due to its specific requirements of strong phase anisotropy with amplitude isotropy in subwavelength scale. Here, we propose magnetic metamaterial structures which can simultaneously exploit the electric field and magnetic field of light for achieving the nanoscale half-wave plates at visible wavelength. We design and demonstrate the magnetic metamaterial half-wave plates in linear grating patterns with high polarization conversion purity in a deep subwavelength thickness. Then, we characterize the equivalent magnetic metamaterial half-wave plates in cylindrical coordinate as concentric-ring grating patterns, which act like an azimuthal half-wave plate and accordingly exhibit spatially inhomogeneous polarization and phase manipulations including spin-to-orbital angular momentum conversion and vector beam generation. Our results show potentials for realizing on-chip beam converters, compact holograms, and many other metamaterial devices for structured light beam generation, polarization control, and wavefront manipulation.

Target Soil Impact Verification: Experimental Testing and Kayenta Constitutive Modeling.

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

Broome, Scott Thomas; Flint, Gregory Mark; Dewers, Thomas

2015-11-01

This report details experimental testing and constitutive modeling of sandy soil deformation under quasi - static conditions. This is driven by the need to understand constitutive response of soil to target/component behavior upon impact . An experimental and constitutive modeling program was followed to determine elastic - plastic properties and a compressional failure envelope of dry soil . One hydrostatic, one unconfined compressive stress (UCS), nine axisymmetric compression (ACS) , and one uniaxial strain (US) test were conducted at room temperature . Elastic moduli, assuming isotropy, are determined from unload/reload loops and final unloading for all tests pre - failuremore » and increase monotonically with mean stress. Very little modulus degradation was discernable from elastic results even when exposed to mean stresses above 200 MPa . The failure envelope and initial yield surface were determined from peak stresses and observed onset of plastic yielding from all test results. Soil elasto - plastic behavior is described using the Brannon et al. (2009) Kayenta constitutive model. As a validation exercise, the ACS - parameterized Kayenta model is used to predict response of the soil material under uniaxial strain loading. The resulting parameterized and validated Kayenta model is of high quality and suitable for modeling sandy soil deformation under a range of conditions, including that for impact prediction.« less

Orthogonal Invariant Sets of the Diffusion Tensor and the Development of a Curvilinear Set Suitable for Low-Anisotropy Tissues

PubMed Central

Damion, Robin A.; Radjenovic, Aleksandra; Ingham, Eileen; Jin, Zhongmin; Ries, Michael E.

2013-01-01

We develop a curvilinear invariant set of the diffusion tensor which may be applied to Diffusion Tensor Imaging measurements on tissues and porous media. This new set is an alternative to the more common invariants such as fractional anisotropy and the diffusion mode. The alternative invariant set possesses a different structure to the other known invariant sets; the second and third members of the curvilinear set measure the degree of orthotropy and oblateness/prolateness, respectively. The proposed advantage of these invariants is that they may work well in situations of low diffusion anisotropy and isotropy, as is often observed in tissues such as cartilage. We also explore the other orthogonal invariant sets in terms of their geometry in relation to eigenvalue space; a cylindrical set, a spherical set (including fractional anisotropy and the mode), and a log-Euclidean set. These three sets have a common structure. The first invariant measures the magnitude of the diffusion, the second and third invariants capture aspects of the anisotropy; the magnitude of the anisotropy and the shape of the diffusion ellipsoid (the manner in which the anisotropy is realised). We also show a simple method to prove the orthogonality of the invariants within a set. PMID:24244366

The Application of Coherent Local Time for Optical Time Transfer and the Quantification of Systematic Errors in Satellite Laser Ranging

NASA Astrophysics Data System (ADS)

Schreiber, K. Ulrich; Kodet, Jan

2018-02-01

Highly precise time and stable reference frequencies are fundamental requirements for space geodesy. Satellite laser ranging (SLR) is one of these techniques, which differs from all other applications like Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and finally Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) by the fact that it is an optical two-way measurement technique. That means that there is no need for a clock synchronization process between both ends of the distance covered by the measurement technique. Under the assumption of isotropy for the speed of light, SLR establishes the only practical realization of the Einstein Synchronization process so far. Therefore it is a powerful time transfer technique. However, in order to transfer time between two remote clocks, it is also necessary to tightly control all possible signal delays in the ranging process. This paper discusses the role of time and frequency in SLR as well as the error sources before it address the transfer of time between ground and space. The need of an improved signal delay control led to a major redesign of the local time and frequency distribution at the Geodetic Observatory Wettzell. Closure measurements can now be used to identify and remove systematic errors in SLR measurements.

Variable Anisotropic Brain Electrical Conductivities in Epileptogenic Foci

PubMed Central

Mandelkern, M.; Bui, D.; Salamon, N.; Vinters, H. V.; Mathern, G. W.

2010-01-01

Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (±SD) electrical conductivities were 0.10 ± 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients. PMID:20440549

Seismic Anisotropy from Surface Refraction Measurements

NASA Astrophysics Data System (ADS)

Vilhelm, J.; Hrdá, J.; Klíma, K.; Lokajícek, T.; Pros, Z.

2003-04-01

The contribution deals with the methods of determining P and S wave velocities in the shallow refraction seismics. The comparison of a P-wave anisotropy from samples and field surface measurement is performed. The laboratory measurement of the P-wave velocity is realized as omni directional ultrasound measurement on oriented spherical samples (diameter 5 cm) under a hydrostatic pressure up to 400 MPa. The field measurement is based on the processing of at least one pair of reversed time-distance curves of refracted waves. Different velocity calculation techniques are involved including tomographic approach from the surface. It is shown that field seismic measurement can reflect internal rock fabric (lineation, mineral anisotropy) as well as effects connected with the fracturing and weathering. The elastic constants derived from laboratory measurements exhibit transversal isotropy. For the estimation of anisotropy influence we perform ray-tracing by the software package ANRAY (Consortium Seismic Waves in Complex 3-D Structures). The use of P and S wave anisotropy measurement to determine hard rock hydro-geological collector (water resource) is presented. In a relatively homogeneous lutaceous sedimentary medium we identified a transversally isotropic layer which exhibits increased value of permeability (transmisivity). The seismic measurement is realized by three component geophones with both vertical and shear seismic sources. VLF and resistivity profiling accompany the filed survey.

Pattern recognition of the targets with help of polarization properties of the signal

NASA Astrophysics Data System (ADS)

Ponomaryov, Volodymyr I.; de Rivera, Luis N.; Castellanos, Aldo B.; Popov, Anatoly V.

1999-10-01

We proposed to use the possibility of recognition of the targets on background of the scattering from the surface, weather objects with the help of polarimetric 3-cm radar. It has been investigated such polarization characteristics: the amplitudes of the polarization matrix elements; an anisotropy coefficient; depolarization coefficient; asymmetry coefficient; the energy section was less than 1 dB at ranges up to 15 km and less than 1.5 dB at ranges up to 100 km. During the experiments urban objects and 6 various ships of small displacement having the closest values of the backscattering cross-section were used. The analysis has shown: the factor of the polarization selection for anisotropy objects and weather objects had the values about 0.02-0.08 Isotropy had the values of polarimetric correlation factor for hydrometers about 0.7-0.8, for earth surface about 0.8-0.9, for sea surface - from 0.33 to 0.7. The results of the work of recognition algorithm of a class 'concrete objects', and 'metal objects' are submitted as example in the paper. The result of experiments have shown that the probability of correct recognition of the identified objects was in the limits from 0.93 to 0.97.

Free-surface turbulent wake of a surface-piercing slender body at various Froude numbers

NASA Astrophysics Data System (ADS)

Seo, Jeonghwa; Samad, Abdus; Rhee, Shin Hyung

2016-11-01

Free-surface effects on the near-wake around a surface-piercing slender body were investigated through flow field and wave elevation measurements. The near-wake flow field was measured by a towed underwater stereoscopic particle image velocimetry (SPIV) system. The measured flow field was analyzed to obtain coherent turbulence structures by using the Reynolds and proper orthogonal decomposition methods. Three different Froude numbers (Fr) - 0.126, 0.282, and 0.400 - were selected to represent mild, intermediate, and violent free-surface motions. At Fr = 0.126, the wave was hardly visible, although the turbulence strength and isotropy increased near the free-surface. At Fr = 0.282, though it was steady and smooth, wave-induced separation was clearly observed near the juncture of the free-surface and model trailing edge. At Fr = 0.400, wave breaking and the resulting bubbly free-surface were developed with an expanded wave-induced separation region. The wave-induced separation stimulated momentum transfer and turbulence dissipation, resulting in a significant change in the frequency of dominant free-surface motion in the downstream. This research was supported by the IT R&D program of MOTIE/KEIT (Grant No. 100660329) and the National Research Foundation of Korea, Grant funded by the Korean government (Grant No. 2013R1A1A2012597).

Teleparallelism as a universal connection on null hypersurfaces in general relativity

NASA Technical Reports Server (NTRS)

Mazur, P. O.; Sokolowski, L. M.

1986-01-01

It is shown that a close relationship between the inner geometry of a null hypersurface N3 and the Newman-Penrose (NP) (1962, 1963) spin coefficient formalism exists. Projecting the null complex NP tetrad onto N3, two triads of basis vectors in N3 are obtained. The inner geometry of N3 is based on the assumption that these vectors are parallelly transported along the surface; this gives rise to the teleparallel connection as a metric nonsymmetric affine connection. The gauge freedom for the choice of the basis triads is given by the isotropy subgroup of the local Lorentz group leaving invariant the direction of the null generators of N3, and teleparallelism is determined by the equivalence class of the basis triads with respect to the global gauge group. Nine of the twelve NP coefficients are identified as the triad components of the torsion and the second fundamental form of N3. The resulting generalized Gauss-Codazzi equations are identical to nine of the NP equations, i.e., to the half of the Ricci identities. This result gives a geometrical meaning to the entire formalism. Finally a general proof of Penrose's theorem that the shear of the null generators of N3 is the only initial null datum for a gravitational field on N3 is presented.

Setting Directions: Anisotropy in Hierarchically Organized Porous Silica

PubMed Central

2017-01-01

Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of sol–gel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the material’s macroporosity is also reflected in its mechanical properties; i.e., the Young’s modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy. PMID:28989232

State relations for a two-phase mixture of reacting explosives and applications

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

Kubota, Shiro; Saburi, Tei; Ogata, Yuji

2007-10-15

To assess the assumptions behind the two phase mixture rule for reacting explosives, the shock-to-detonation transition process was calculated for high explosives using a finite difference method. An ignition and growth model and the Jones-Wilkins-Lee (JWL) equations of state were employed. The simple mixture rule assumes that the reacting explosive is a simple mixture of the reactant and product components. Four different assumptions, such as that of thermal equilibrium and isotropy, were adopted to calculate the pressure. The main purpose of this paper is to present the answer to the question of why the numerical results of shock-initiation are insensitivemore » to the assumptions adopted. The equations of state for reactants and products were assessed by considering plots of the specific internal energy E and specific volume V. If the slopes of the constant-pressure lines for both components in the E-V plane are almost the same, it is demonstrated that the numerical results are insensitive to the assumptions adopted. We have found that the relation for the specific volumes of the two components can be approximately expressed by a single curve of the specific volume of the reactant vs that of the products. We discuss this relationship in terms of the results of the numerical simulation. (author)« less

Seismic anisotropy of the crust: electron-backscatter diffraction measurements from the Basin and Range

NASA Astrophysics Data System (ADS)

Erdman, Monica E.; Hacker, Bradley R.; Zandt, George; Seward, Gareth

2013-11-01

Crystal preferred orientations were measured in a suite of rocks from three locations in the Basin and Range using electron-backscatter diffraction. Anisotropic velocities were calculated for all rocks using single-crystal stiffnesses, the Christoffel equation and Voigt-Reuss-Hill averaging. Anisotropic velocities were calculated for all three crustal sections using these values combined with rock proportions as exposed in the field. One suite of rocks previously measured in the laboratory was used as a benchmark to evaluate the accuracy of the calculated velocities. Differences in the seismic anisotropy of the Funeral Mountains, Ruby Mountains and East Humboldt Range sections arise because of differences in mineralogy and strain, with the calc-silicate dominated Ruby Mountains section having higher P-wave speeds and VP/VS ratios because of the reduced quartz content. In all cases, the velocities show either transverse isotropy or nearly so, with a unique slow axis normal to the foliation. Velocity anisotropy can thus be used to infer the flow plane, but not the flow direction in typical crustal rocks. Areas with a subhorizontal foliation have minimal shear wave splitting for vertically propagating waves and are thus good places to measure mantle anisotropy using SKS-splitting.

Statistical anisotropy in free turbulence for mixing layers at high Reynolds numbers

NASA Astrophysics Data System (ADS)

Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.; Luke, Theodore E.

1996-08-01

A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after propagating through free turbulent mixing layers. Shearing interferometers provide a two-dimensional flow visualization that is nonintrusive. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Experiments were performed on an unbounded, plane shear mixing layer of helium and nitrogen gas at fixed velocities and high Reynolds numbers for six locations in the flow development. Statistical autocorrelation functions and structure functions were computed on the reconstructed phase maps. The autocorrelation function results indicated that the turbulence-induced phase fluctuations were not wide-sense stationary. The structure functions exhibited statistical homogeneity, indicating that the phase fluctuations were stationary in first increments. However, the turbulence-corrupted phase was not isotropic. A five-thirds power law is shown to fit orthogonal slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence. Strehl ratios were computed from the phase structure functions and compared with classical estimates that assume isotropy. The isotropic models are shown to overestimate the optical degradation by nearly 3 orders of magnitude compared with the structure function calculations.

Comparison of measured and computed Strehl ratios for light propagated through a channel flow of a He N 2 mixing layer at high Reynolds numbers

NASA Astrophysics Data System (ADS)

Gardner, Patrick J.; Roggemann, Michael C.; Welsh, Byron M.; Bowersox, Rodney D.; Luke, Theodore E.

1997-04-01

A lateral shearing interferometer was used to measure the slope of perturbed wave fronts after they propagated through a He N 2 mixing layer in a rectangular channel. Slope measurements were used to reconstruct the phase of the turbulence-corrupted wave front. The random phase fluctuations induced by the mixing layer were captured in a large ensemble of wave-front measurements. Phase structure functions, computed from the reconstructed phase surfaces, were stationary in first increments. A five-thirds power law is shown to fit streamwise and cross-stream slices of the structure function, analogous to the Kolmogorov model for isotropic turbulence, which describes the structure function with a single parameter. Strehl ratios were computed from the phase structure functions and compared with a measured experiment obtained from simultaneous point-spread function measurements. Two additional Strehl ratios were calculated by using classical estimates that assume statistical isotropy throughout the flow. The isotropic models are a reasonable estimate of the optical degradation only within a few centimeters of the initial mixing, where the Reynolds number is low. At higher Reynolds numbers, Strehl ratios calculated from the structure functions match the experiment much better than Strehl ratio calculations that assume isotropic flow.

A robust, efficient equidistribution 2D grid generation method

NASA Astrophysics Data System (ADS)

Chacon, Luis; Delzanno, Gian Luca; Finn, John; Chung, Jeojin; Lapenta, Giovanni

2007-11-01

We present a new cell-area equidistribution method for two- dimensional grid adaptation [1]. The method is able to satisfy the equidistribution constraint to arbitrary precision while optimizing desired grid properties (such as isotropy and smoothness). The method is based on the minimization of the grid smoothness integral, constrained to producing a given positive-definite cell volume distribution. The procedure gives rise to a single, non-linear scalar equation with no free-parameters. We solve this equation numerically with the Newton-Krylov technique. The ellipticity property of the linearized scalar equation allows multigrid preconditioning techniques to be effectively used. We demonstrate a solution exists and is unique. Therefore, once the solution is found, the adapted grid cannot be folded due to the positivity of the constraint on the cell volumes. We present several challenging tests to show that our new method produces optimal grids in which the constraint is satisfied numerically to arbitrary precision. We also compare the new method to the deformation method [2] and show that our new method produces better quality grids. [1] G.L. Delzanno, L. Chac'on, J.M. Finn, Y. Chung, G. Lapenta, A new, robust equidistribution method for two-dimensional grid generation, in preparation. [2] G. Liao and D. Anderson, A new approach to grid generation, Appl. Anal. 44, 285--297 (1992).

All-particle cosmic ray energy spectrum measured with 26 IceTop stations

NASA Astrophysics Data System (ADS)

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Baum, V.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Bell, M.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Brown, A. M.; Buitink, S.; Caballero-Mora, K. S.; Carson, M.; Casier, M.; Chirkin, D.; Christy, B.; Clevermann, F.; Cohen, S.; Cowen, D. F.; Cruz Silva, A. H.; D'Agostino, M. V.; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; Degner, T.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; DeYoung, T.; Díaz-Vélez, J. C.; Dreyer, J.; Dumm, J. P.; Dunkman, M.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Góra, D.; Grant, D.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Heereman, D.; Heimann, P.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, B.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Kappes, A.; Karg, T.; Karle, A.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Klepser, S.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krasberg, M.; Kroll, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Laihem, K.; Landsman, H.; Larson, M. J.; Lauer, R.; Lünemann, J.; Madsen, J.; Maruyama, R.; Mase, K.; Matis, H. S.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nowicki, S. C.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Panknin, S.; Paul, L.; Pérez de los Heros, C.; Pieloth, D.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Riedel, B.; Rodrigues, J. P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Scheel, M.; Schmidt, T.; Schöneberg, S.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Smith, M. W. E.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Stüer, M.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Tosi, D.; van Eijndhoven, N.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Wasserman, R.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Zoll, M.

2013-04-01

We report on a measurement of the cosmic ray energy spectrum with the IceTop air shower array, the surface component of the IceCube Neutrino Observatory at the South Pole. The data used in this analysis were taken between June and October, 2007, with 26 surface stations operational at that time, corresponding to about one third of the final array. The fiducial area used in this analysis was 0.122 km2. The analysis investigated the energy spectrum from 1 to 100 PeV measured for three different zenith angle ranges between 0° and 46°. Because of the isotropy of cosmic rays in this energy range the spectra from all zenith angle intervals have to agree. The cosmic-ray energy spectrum was determined under different assumptions on the primary mass composition. Good agreement of spectra in the three zenith angle ranges was found for the assumption of pure proton and a simple two-component model. For zenith angles θ < 30°, where the mass dependence is smallest, the knee in the cosmic ray energy spectrum was observed at about 4 PeV, with a spectral index above the knee of about -3.1. Moreover, an indication of a flattening of the spectrum above 22 PeV was observed.

Wormholes with fluid sources: A no-go theorem and new examples

NASA Astrophysics Data System (ADS)

Bronnikov, K. A.; Baleevskikh, K. A.; Skvortsova, M. V.

2017-12-01

For static, spherically symmetric space-times in general relativity (GR), a no-go theorem is proved: it excludes the existence of wormholes with flat and/or anti-de Sitter asymptotic regions on both sides of the throat if the source matter is isotropic, i.e., the radial and tangential pressures coincide. It explains why in all previous attempts to build such solutions it was necessary to introduce boundaries with thin shells that manifestly violate the isotropy of matter. Under a simple assumption on the behavior of the spherical radius r (x ), we obtain a number of examples of wormholes with isotropic matter and one or both de Sitter asymptotic regions, allowed by the no-go theorem. We also obtain twice asymptotically flat wormholes with anisotropic matter, both symmetric and asymmetric with respect to the throat, under the assumption that the scalar curvature is zero. These solutions may be on equal grounds interpreted as those of GR with a traceless stress-energy tensor and as vacuum solutions in a brane world. For such wormholes, the traversability conditions and gravitational lensing properties are briefly discussed. As a byproduct, we obtain twice asymptotically flat regular black hole solutions with up to four Killing horizons. As another byproduct, we point out intersection points in families of integral curves for the function A (x )=gt t, parametrized by its values on the throat.

Seismic anisotropy and mantle flow below subducting slabs

NASA Astrophysics Data System (ADS)

Walpole, Jack; Wookey, James; Kendall, J.-Michael; Masters, T.-Guy

2017-05-01

Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ∼ 40 , 000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth < 50 km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.

Numerical and experimental analyses of out-of-plane deformation of triaxial woven fabric

NASA Astrophysics Data System (ADS)

Zhou, Hongtao; Xiao, Xueliang; Qian, Kun; Zhang, Kun; Zhang, Diantang

2018-05-01

With three sets of yarns interwoven in plane for angle-interlock structure, triaxial woven fabric (TWF) is a unique and perfect construction material for products subjected to multi-directional loads, as compared to classic fabrics of orthogonal structure. Finite-element analysis (FEA) and experimental methods are applied to study the out-of-plane deformation (OPD) behaviors of TWF and plain woven fabric (PWF). Among this, the yarn cross section, path and woven structure are obtained using optical microscopy, the related parameters are input to finite element model (FEM) for simulating the OPD behavior. This paper presents a detailed analysis on out-of-plane deformation behavior of TWF and PWF by the finite element method and experiment. In consideration of the comparability, TWF and PWF are designed and prepared with the same yarns and areal density (g/m2). The deformation profile, maximum stress and maximum deflection of TWF and PWF are obtained by FEA and experiment. It has been found that the maximum deflection and maximum stress of TWF is smaller than that of PWF under the same uniform negative pressure, both FEA and experiment. Furthermore, the stress distribution of TWF is more evenly than that of PWF, indicating that TWF exhibited superior isotropy in comparison with PWF for one more directional set of yarns in undertaking the OPD.

Dynamical behavior of the Tolman metrics in f (R ,T ) gravity

NASA Astrophysics Data System (ADS)

Hansraj, Sudan; Banerjee, Ayan

2018-05-01

We analyze the behavior of well-known stellar models within the context of f (R ,T ) modified theory of gravity, in which the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R and the trace of the energy-momentum tensor T , namely f (R ,T )=R +2 χ T for some constant χ . The equation of pressure isotropy in this theory is identical to that of the standard Einstein theory therefore all known metric potentials solving Einstein's equations are valid here. However, the pressure and energy density profiles are markedly different due to the presence of the term 2 χ T . The exact solutions to the corresponding static spherically symmetric field equations with a perfect fluid source are the well known Tolman solutions [Phys. Rev. 55, 364 (1939), 10.1103/PhysRev.55.364] in general relativity. To support the theoretical results, graphical representation are employed to investigate the physical viability of compact stars. Specifically we study the density and pressure profiles, the sound speed behavior as well as the energy conditions and mass behavior where appropriate. It is found that in some cases the f (R ,T ) model displays more pleasing behavior than its Einstein counterpart while in other cases the behavior is similar. In no case does the 2 χ T addition negatively impact the model's behavior.

The Camassa-Holm equation as an incompressible Euler equation: A geometric point of view

NASA Astrophysics Data System (ADS)

Gallouët, Thomas; Vialard, François-Xavier

2018-04-01

The group of diffeomorphisms of a compact manifold endowed with the L2 metric acting on the space of probability densities gives a unifying framework for the incompressible Euler equation and the theory of optimal mass transport. Recently, several authors have extended optimal transport to the space of positive Radon measures where the Wasserstein-Fisher-Rao distance is a natural extension of the classical L2-Wasserstein distance. In this paper, we show a similar relation between this unbalanced optimal transport problem and the Hdiv right-invariant metric on the group of diffeomorphisms, which corresponds to the Camassa-Holm (CH) equation in one dimension. Geometrically, we present an isometric embedding of the group of diffeomorphisms endowed with this right-invariant metric in the automorphisms group of the fiber bundle of half densities endowed with an L2 type of cone metric. This leads to a new formulation of the (generalized) CH equation as a geodesic equation on an isotropy subgroup of this automorphisms group; On S1, solutions to the standard CH thus give radially 1-homogeneous solutions of the incompressible Euler equation on R2 which preserves a radial density that has a singularity at 0. An other application consists in proving that smooth solutions of the Euler-Arnold equation for the Hdiv right-invariant metric are length minimizing geodesics for sufficiently short times.

Main reinforcement effects of precipitation phase Mg2Cu3Si, Mg2Si and MgCu2 on Mg-Cu-Si alloys by ab initio investigation

NASA Astrophysics Data System (ADS)

Shi, Xue-Feng; Wang, Hai-Chen; Tang, Ping-Ying; Tang, Bi-Yu

2017-09-01

To predict and compare the main reinforcement effects of the key precipitation phases Mg2Cu3Si, Mg2Si and MgCu2 in Mg-Cu-Si alloy, the structural, mechanical and electronic properties of these phases have been studied by ab initio calculations. The lowest formation enthalpy and cohesive energy indicate that Mg2Cu3Si has the strongest alloying ability and structural stability. The mechanical modulus indicates that Mg2Cu3Si has the strongest resistance to reversible shear/volume distortion and has maximum hardness. The characterization of brittle (ductile) behavior manifests that MgCu2 has favorable ductility. Meanwhile the evaluation of elastic anisotropy indicates that Mg2Si possesses elastic isotropy. Debye temperature prediction shows that Mg2Si and Mg2Cu3Si have better thermal stability. To achieve an unbiased interpretation on the phase stability and mechanical behavior of these precipitation phases, the density of states and differential charge densities are also analyzed. The current study deepens the comprehensive understanding of main reinforcement effects of these precipitation phases on Mg-Cu-Si alloys, and also benefits to optimize the overall performances of Mg-Cu-Si alloy from the hardness, ductility and thermal stability by controlling these second precipitation phases during the heat treatment process.

The diagnostics of ultra-short pulse laser-produced plasma

NASA Astrophysics Data System (ADS)

Roth, Markus

2011-09-01

Since the invention of the laser, coherent light has been used to break down solid or gaseous material and transform it into a plasma. Over the last three decades two things have changed. Due to multiple advancements and design of high power lasers it is now possible to increase the electric and magnetic field strength that pushed the electron motion towards the regime of relativistic plasma physics. Moreover, due to the short pulse duration of the driving laser the underlying physics has become so transient that concepts like thermal equilibrium (even a local one) or spatial isotropy start to fail. Consequently short pulse laser-driven plasmas have become a rich source of new phenomena that we are just about beginning to explore. Such phenomena, like particle acceleration, nuclear laser-induced reactions, the generation of coherent secondary radiation ranging from THz to high harmonics and the production of attosecond pulses have excited an enormous interest in the study of short pulse laser plasmas. The diagnostics of such ultra-short pulse laser plasmas is a challenging task that involves many and different techniques compared to conventional laser-produced plasmas. While this review cannot cover the entire field of diagnostics that has been developed over the last years, we will try to give a summarizing description of the most important techniques that are currently being used.

Effects of tissue conductivity and electrode area on internal electric fields in a numerical human model for ELF contact current exposures

NASA Astrophysics Data System (ADS)

Tarao, H.; Kuisti, H.; Korpinen, L.; Hayashi, N.; Isaka, K.

2012-05-01

Contact currents flow through the human body when a conducting object with different potential is touched. There are limited reports on numerical dosimetry for contact current exposure compared with electromagnetic field exposures. In this study, using an anatomical human adult male model, we performed numerical calculation of internal electric fields resulting from 60 Hz contact current flowing from the left hand to the left foot as a basis case. Next, we performed a variety of similar calculations with varying tissue conductivity and contact area, and compared the results with the basis case. We found that very low conductivity of skin and a small electrode size enhanced the internal fields in the muscle, subcutaneous fat and skin close to the contact region. The 99th percentile value of the fields in a particular tissue type did not reliably account for these fields near the electrode. In the arm and leg, the internal fields for the muscle anisotropy were identical to those in the isotropy case using a conductivity value longitudinal to the muscle fibre. Furthermore, the internal fields in the tissues abreast of the joints such as the wrist and the elbow, including low conductivity tissues, as well as the electrode contact region, exceeded the ICNIRP basic restriction for the general public with contact current as the reference level value.

Analysis of Lagrangian stretching in turbulent channel flow using a database task-parallel particle tracking approach

NASA Astrophysics Data System (ADS)

Meneveau, Charles; Johnson, Perry; Hamilton, Stephen; Burns, Randal

2016-11-01

An intrinsic property of turbulent flows is the exponential deformation of fluid elements along Lagrangian paths. The production of enstrophy by vorticity stretching follows from a similar mechanism in the Lagrangian view, though the alignment statistics differ and viscosity prevents unbounded growth. In this paper, the stretching properties of fluid elements and vorticity along Lagrangian paths are studied in a channel flow at Reτ = 1000 and compared with prior, known results from isotropic turbulence. To track Lagrangian paths in a public database containing Direct Numerical Simulation (DNS) results, the task-parallel approach previously employed in the isotropic database is extended to the case of flow in a bounded domain. It is shown that above 100 viscous units from the wall, stretching statistics are equal to their isotropic values, in support of the local isotropy hypothesis. Normalized by dissipation rate, the stretching in the buffer layer and below is less efficient due to less favorable alignment statistics. The Cramér function characterizing cumulative Lagrangian stretching statistics shows that overall the channel flow has about half of the stretching per unit dissipation compared with isotropic turbulence. Supported by a National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1232825, and by National Science Foundation Grants CBET-1507469, ACI-1261715, OCI-1244820 and by JHU IDIES.

Research on the forward modeling of controlled-source audio-frequency magnetotellurics in three-dimensional axial anisotropic media

NASA Astrophysics Data System (ADS)

Wang, Kunpeng; Tan, Handong

2017-11-01

Controlled-source audio-frequency magnetotellurics (CSAMT) has developed rapidly in recent years and are widely used in the area of mineral and oil resource exploration as well as other fields. The current theory, numerical simulation, and inversion research are based on the assumption that the underground media have resistivity isotropy. However a large number of rock and mineral physical property tests show the resistivity of underground media is generally anisotropic. With the increasing application of CSAMT, the demand for probe accuracy of practical exploration to complex targets continues to increase. The question of how to evaluate the influence of anisotropic resistivity to CSAMT response is becoming important. To meet the demand for CSAMT response research of resistivity anisotropic media, this paper examines the CSAMT electric equations, derives and realizes a three-dimensional (3D) staggered-grid finite difference numerical simulation method of CSAMT resistivity axial anisotropy. Through building a two-dimensional (2D) resistivity anisotropy geoelectric model, we validate the 3D computation result by comparing it to the result of controlled-source electromagnetic method (CSEM) resistivity anisotropy 2D finite element program. Through simulating a 3D resistivity axial anisotropy geoelectric model, we compare and analyze the responses of equatorial configuration, axial configuration, two oblique sources and tensor source. The research shows that the tensor source is suitable for CSAMT to recognize the anisotropic effect of underground structure.

Exploring the effect of anisotropy on body-wave tomography models: Rollback and subduction of the Alboran slab

NASA Astrophysics Data System (ADS)

Lee, H.; Bezada, M.

2017-12-01

Teleseismic P-wave tomography models often show low-velocity anomalies behind subducted slabs (i.e. opposite the direction of subduction). One such anomaly, behind the Alboran slab in the westernmost Mediterranean, requires partial melt in the mantle if taken at face-value. However, mantle anisotropy can cause low-velocity anomalies in tomographic models that assume isotropy. In fact, results from SKS splitting suggest rollback-induced anisotropy within the low-velocity region, and we investigate if this anisotropy can explain the sub-slab anomaly. We include anisotropy as an a priori constraint on the inversion and test different magnitudes, azimuths, and dips within the low-velocity region. We find that a range of anisotropic models can fit the travel time data as well as the isotropic models while significantly reducing or eliminating the low-velocity anomaly behind the slab. We conclude that this alternative interpretation (delays are caused by anisotropic structure) is as consistent with the travel time data as an isotropic low-velocity anomaly, and more consistent with SKS splitting observations and the known history of rollback. In addition, we find that models that include anisotropy with steeply dipping fast axes, meant to simulate the effect of downgoing entrained mantle, provide a poorer fit to the travel times than all the other models. This suggests that the slab may no longer be actively subducting.

Transverse isotropic modeling of the ballistic response of glass reinforced plastic composites

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

Taylor, P.A.

1997-12-31

The use of glass reinforced plastic (GRP) composites is gaining significant attention in the DoD community for use in armor applications. These materials typically possess a laminate structure consisting of up to 100 plies, each of which is constructed of a glass woven roving fabric that reinforces a plastic matrix material. Current DoD attention is focused on a high strength, S-2 glass cross-weave (0/90) fabric reinforcing a polyester matrix material that forms each ply of laminate structure consisting anywhere from 20 to 70 plies. The resulting structure displays a material anisotropy that is, to a reasonable approximation, transversely isotropic. Whenmore » subjected to impact and penetration from a metal fragment projectile, the GRP displays damage and failure in an anisotropic manner due to various mechanisms such as matrix cracking, fiber fracture and pull-out, and fiber-matrix debonding. In this presentation, the author will describe the modeling effort to simulate the ballistic response of the GRP material described above using the transversely isotropic (TI) constitutive model which has been implemented in the shock physics code, CTH. The results of this effort suggest that the model is able to describe the delamination behavior of the material but has some difficulty capturing the in-plane (i.e., transverse) response of the laminate due to its cross-weave fabric reinforcement pattern which causes a departure from transverse isotropy.« less

Gravity Field Recovery from the Cartwheel Formation by the Semi-analytical Approach

NASA Astrophysics Data System (ADS)

Li, Huishu; Reubelt, Tilo; Antoni, Markus; Sneeuw, Nico; Zhong, Min; Zhou, Zebing

2016-04-01

Past and current gravimetric satellite missions have contributed drastically to our knowledge of the Earth's gravity field. Nevertheless, several geoscience disciplines push for even higher requirements on accuracy, homogeneity and time- and space-resolution of the Earth's gravity field. Apart from better instruments or new observables, alternative satellite formations could improve the signal and error structure. With respect to other methods, one significant advantage of the semi-analytical approach is its effective pre-mission error assessment for gravity field missions. The semi-analytical approach builds a linear analytical relationship between the Fourier spectrum of the observables and the spherical harmonic spectrum of the gravity field. The spectral link between observables and gravity field parameters is given by the transfer coefficients, which constitutes the observation model. In connection with a stochastic model, it can be used for pre-mission error assessment of gravity field mission. The cartwheel formation is formed by two satellites on elliptic orbits in the same plane. The time dependent ranging will be considered in the transfer coefficients via convolution including the series expansion of the eccentricity functions. The transfer coefficients are applied to assess the error patterns, which are caused by different orientation of the cartwheel for range-rate and range acceleration. This work will present the isotropy and magnitude of the formal errors of the gravity field coefficients, for different orientations of the cartwheel.

Elastic Properties and Enhanced Piezoelectric Response at Morphotropic Phase Boundaries

PubMed Central

Cordero, Francesco

2015-01-01

The search for improved piezoelectric materials is based on the morphotropic phase boundaries (MPB) between ferroelectric phases with different crystal symmetry and available directions for the spontaneous polarization. Such regions of the composition x−T phase diagrams provide the conditions for minimal anisotropy with respect to the direction of the polarization, so that the polarization can easily rotate maintaining a substantial magnitude, while the near verticality of the TMPBx boundary extends the temperature range of the resulting enhanced piezoelectricity. Another consequence of the quasi-isotropy of the free energy is a reduction of the domain walls energies, with consequent formation of domain structures down to nanoscale. Disentangling the extrinsic and intrinsic contributions to the piezoelectricity in such conditions requires a high level of sophistication from the techniques and analyses for studying the structural, ferroelectric and dielectric properties. The elastic characterization is extremely useful in clarifying the phenomenology and mechanisms related to ferroelectric MPBs. The relationship between dielectric, elastic and piezoelectric responses is introduced in terms of relaxation of defects with electric dipole and elastic quadrupole, and extended to the response near phase transitions in the framework of the Landau theory. An account is provided of the anelastic experiments, from torsional pendulum to Brillouin scattering, that provided new important information on ferroelectric MPBs, including PZT, PMN-PT, NBT-BT, BCTZ, and KNN-based systems. PMID:28793707

Scale interactions of turbulence subjected to a straining relaxation destraining cycle

NASA Astrophysics Data System (ADS)

Chen, Jun; Meneveau, Charles; Katz, Joseph

2006-09-01

The response of turbulence subjected to planar straining and de-straining is studied experimentally, and the impact of the applied distortions on the energy transfer across different length scales is quantified. The data are obtained using planar particle image velocimetry (PIV) in a water tank, in which high-Reynolds-number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining mean flows are produced by pushing and pulling a rectangular piston towards, and away from, the bottom wall of the tank. The data are processed to yield the time evolution of Reynolds stresses, anisotropy tensors, turbulence kinetic energy production, and mean subgrid-scale (SGS) dissipation rate at various scales. During straining, the production rises rapidly. After the relaxation period the small-scale SGS stresses recover isotropy, but the Reynolds stresses still display significant anisotropy. Thus when destraining is applied, a strong negative production (mean backscatter) occurs, i.e. the turbulence returns kinetic energy to the mean flow. The SGS dissipation displays similar behaviour at large filter scales, but the mean backscatter gradually disappears with decreasing filter scales. Energy spectra are compared to predictions of rapid distortion theory (RDT). Good agreement is found for the initial response but, as expected for the time-scale ratios of the experiment, turbulence relaxation causes discrepancies between measurements and RDT at later times.

Einstein’s sigh: hidden symmetry in Einstein’s derivation of the Lorentz transformation

NASA Astrophysics Data System (ADS)

Chao, Sheng D.

2017-03-01

‘Das hätte ich einfacher sagen können (I could have said that more simply).’ was Einstein’s sigh when he had a chance to remark on his own derivation of the Lorentz transformation (LT) in the 1905 seminal paper. In fact, in a popular science exposition of the theory of relativity Einstein did provide such a simple derivation of the LT. It is a curious historical fact that the latter derivation was presented in 1916, while Einstein’s remark was made in 1943. Was the 1916 derivation simple enough to relieve his sigh? Had he expected an even simpler derivation beyond his thoughts? In this paper, Einstein’s simple derivation of the LT is revisited and analysed. We show that the LT can be obtained from a symmetry principle hidden in Einstein’s logical reasoning. First, the relativity principle can be restated as a mirror principle based on the space-time exchange-inversion operation. Second, the assumed constancy of the speed of light (Einstein’s second postulate) can be derived by using the velocity reciprocity property, which is a deductive result of the space-time homogeneity and the space isotropy. Therefore, Einstein could have presented his derivation of the LT more simply, thus turning Einstein’s sigh of regret into a sigh of relief.

Diverse anisotropy of phonon transport in two-dimensional group IV-VI compounds: A comparative study

NASA Astrophysics Data System (ADS)

Qin, Guangzhao; Qin, Zhenzhen; Fang, Wu-Zhang; Zhang, Li-Chuan; Yue, Sheng-Ying; Yan, Qing-Bo; Hu, Ming; Su, Gang

2016-05-01

New classes of two-dimensional (2D) materials beyond graphene, including layered and non-layered, and their heterostructures, are currently attracting increasing interest due to their promising applications in nanoelectronics, optoelectronics and clean energy, where thermal transport is a fundamental physical parameter. In this paper, we systematically investigated the phonon transport properties of the 2D orthorhombic group IV-VI compounds of GeS, GeSe, SnS and SnSe by solving the Boltzmann transport equation (BTE) based on first-principles calculations. Despite their similar puckered (hinge-like) structure along the armchair direction as phosphorene, the four monolayer compounds possess diverse anisotropic properties in many aspects, such as phonon group velocity, Young's modulus and lattice thermal conductivity (κ), etc. Especially, the κ along the zigzag and armchair directions of monolayer GeS shows the strongest anisotropy while monolayer SnS and SnSe show almost isotropy in phonon transport. The origin of the diverse anisotropy is fully studied and the underlying mechanism is discussed in details. With limited size, the κ could be effectively lowered, and the anisotropy could be effectively modulated by nanostructuring, which would extend the applications to nanoscale thermoelectrics and thermal management. Our study offers fundamental understanding of the anisotropic phonon transport properties of 2D materials, and would be of significance for further study, modulation and applications in emerging technologies.

Strain localization and elastic-plastic coupling during deformation of porous sandstone

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

Dewers, Thomas A.; Issen, Kathleen A.; Holcomb, David J.

Results of axisymmetric compression tests on weak, porous Castlegate Sandstone (Cretaceous, Utah, USA), covering a range of dilational and compactional behaviors, are examined for localization behavior. Assuming isotropy, bulk and shear moduli evolve as increasing functions of mean stress and Mises equivalent shear stress respectively, and as decreasing functions of work-conjugate plastic strains. Acoustic emissions events located during testing show onset of localization and permit calculation of observed shear and low-angle compaction localization zones, or bands, as localization commences. Total strain measured experimentally partitions into: A) elastic strain with constant moduli, B) elastic strain due to stress dependence of moduli,more » C) elastic strain due to moduli degradation with increasing plastic strain, and D) plastic strain. The third term is the elastic-plastic coupling strain, and though often ignored, contributes significantly to pre-failure total strain for brittle and transitional tests. Constitutive parameters and localization predictions derived from experiments are compared to theoretical predictions. In the brittle regime, predictions of band angles (angle between band normal and maximum compression) demonstrate good agreement with observed shear band angles. Compaction localization was observed in the transitional regime in between shear localization and spatially pervasive compaction, over a small range of mean stresses. In contrast with predictions however, detailed acoustic emissions analyses in this regime show low angle, compaction-dominated but shear-enhanced, localization.« less

Seismic moment tensor for anisotropic media: implication for Non-double-couple earthquakes

NASA Astrophysics Data System (ADS)

Cai, X.; Chen, X.; Chen, Y.; Cai, M.

2008-12-01

It is often found that the inversion results of seismic moment tensor from real seismic recorded data show the trace of seismic moment tensor M is not zero, a phenomenon called non-double-couple earthquake sources mechanism. Recently we have derived the analytical expressions of M in transversely isotropic media with the titled axis of symmetry and the results shows even only pure shear-motion of fault can lead to the implosive components determined by several combined anisotropic elastic constants. Many non-double-couple earthquakes from observations often appear in volcanic and geothermal areas (Julian, 1998), where there exist a mount of stress-aligned fluid-saturated parallel vertical micro-cracks identical to transversely isotropic media (Crampin, 2008), this stress-aligned crack will modify the seismic moment tensor. In another word, non-double-couple earthquakes don't mean to have a seismic failure movement perpendicular to the fault plane, while traditional research of seismic moment tensor focus on the case of isotropy, which cannot provide correct interpretation of seismic source mechanism. Reference: Julian, B.R., Miller, A.D. and Foulger, G.R., 1998. Non-double-couple earthquakes,1. Theory, Rev. Geophys., 36, 525¨C549. Crampin,S., Peacock,S., 2008, A review of the current understanding of seismic shear-wave splitting in the Earth's crust and common fallacies in interpretation, wave motion, 45,675-722

Acceleration of runaway electrons in solar flares

NASA Technical Reports Server (NTRS)

Moghaddam-Taaheri, E.; Goertz, C. K.

1990-01-01

The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2.

Method of producing exfoliated graphite composite compositions for fuel cell flow field plates

DOEpatents

Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng; Jang, Bor Z

2014-04-08

A method of producing an electrically conductive composite composition, which is particularly useful for fuel cell bipolar plate applications. The method comprises: (a) providing a supply of expandable graphite powder; (b) providing a supply of a non-expandable powder component comprising a binder or matrix material; (c) blending the expandable graphite with the non-expandable powder component to form a powder mixture wherein the non-expandable powder component is in the amount of between 3% and 60% by weight based on the total weight of the powder mixture; (d) exposing the powder mixture to a temperature sufficient for exfoliating the expandable graphite to obtain a compressible mixture comprising expanded graphite worms and the non-expandable component; (e) compressing the compressible mixture at a pressure within the range of from about 5 psi to about 50,000 psi in predetermined directions into predetermined forms of cohered graphite composite compact; and (f) treating the so-formed cohered graphite composite to activate the binder or matrix material thereby promoting adhesion within the compact to produce the desired composite composition. Preferably, the non-expandable powder component further comprises an isotropy-promoting agent such as non-expandable graphite particles. Further preferably, step (e) comprises compressing the mixture in at least two directions. The method leads to composite plates with exceptionally high thickness-direction electrical conductivity.

Fluid-structure interaction in abdominal aortic aneurysms: Structural and geometrical considerations

NASA Astrophysics Data System (ADS)

Mesri, Yaser; Niazmand, Hamid; Deyranlou, Amin; Sadeghi, Mahmood Reza

2015-08-01

Rupture of the abdominal aortic aneurysm (AAA) is the result of the relatively complex interaction of blood hemodynamics and material behavior of arterial walls. In the present study, the cumulative effects of physiological parameters such as the directional growth, arterial wall properties (isotropy and anisotropy), iliac bifurcation and arterial wall thickness on prediction of wall stress in fully coupled fluid-structure interaction (FSI) analysis of five idealized AAA models have been investigated. In particular, the numerical model considers the heterogeneity of arterial wall and the iliac bifurcation, which allows the study of the geometric asymmetry due to the growth of the aneurysm into different directions. Results demonstrate that the blood pulsatile nature is responsible for emerging a time-dependent recirculation zone inside the aneurysm, which directly affects the stress distribution in aneurismal wall. Therefore, aneurysm deviation from the arterial axis, especially, in the lateral direction increases the wall stress in a relatively nonlinear fashion. Among the models analyzed in this investigation, the anisotropic material model that considers the wall thickness variations, greatly affects the wall stress values, while the stress distributions are less affected as compared to the uniform wall thickness models. In this regard, it is confirmed that wall stress predictions are more influenced by the appropriate structural model than the geometrical considerations such as the level of asymmetry and its curvature, growth direction and its extent.

Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets

NASA Astrophysics Data System (ADS)

Pouransari, Z.; Biferale, L.; Johansson, A. V.

2015-02-01

The concept of local isotropy in a chemically reacting turbulent wall-jet flow is addressed using direct numerical simulation (DNS) data. Different DNS databases with isothermal and exothermic reactions are examined. The chemical reaction and heat release effects on the turbulent velocity, passive scalar, and reactive species fields are studied using their probability density functions (PDFs) and higher order moments for velocities and scalar fields, as well as their gradients. With the aid of the anisotropy invariant maps for the Reynolds stress tensor, the heat release effects on the anisotropy level at different wall-normal locations are evaluated and found to be most accentuated in the near-wall region. It is observed that the small-scale anisotropies are persistent both in the near-wall region and inside the jet flame. Two exothermic cases with different Damköhler numbers are examined and the comparison revealed that the Damköhler number effects are most dominant in the near-wall region, where the wall cooling effects are influential. In addition, with the aid of PDFs conditioned on the mixture fraction, the significance of the reactive scalar characteristics in the reaction zone is illustrated. We argue that the combined effects of strong intermittency and strong persistency of anisotropy at the small scales in the entire domain can affect mixing and ultimately the combustion characteristics of the reacting flow.

Turbulence generation through intense kinetic energy sources

NASA Astrophysics Data System (ADS)

Maqui, Agustin F.; Donzis, Diego A.

2016-06-01

Direct numerical simulations (DNS) are used to systematically study the development and establishment of turbulence when the flow is initialized with concentrated regions of intense kinetic energy. This resembles both active and passive grids which have been extensively used to generate and study turbulence in laboratories at different Reynolds numbers and with different characteristics, such as the degree of isotropy and homogeneity. A large DNS database was generated covering a wide range of initial conditions with a focus on perturbations with some directional preference, a condition found in active jet grids and passive grids passed through a contraction as well as a new type of active grid inspired by the experimental use of lasers to photo-excite the molecules that comprise the fluid. The DNS database is used to assert under what conditions the flow becomes turbulent and if so, the time required for this to occur. We identify a natural time scale of the problem which indicates the onset of turbulence and a single Reynolds number based exclusively on initial conditions which controls the evolution of the flow. It is found that a minimum Reynolds number is needed for the flow to evolve towards fully developed turbulence. An extensive analysis of single and two point statistics, velocity as well as spectral dynamics and anisotropy measures is presented to characterize the evolution of the flow towards realistic turbulence.

POWER ASYMMETRY IN COSMIC MICROWAVE BACKGROUND FLUCTUATIONS FROM FULL SKY TO SUB-DEGREE SCALES: IS THE UNIVERSE ISOTROPIC?

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

Hansen, F. K.; Eriksen, H. K.; Lilje, P. B.

We repeat and extend the analysis of Eriksen et al. and Hansen et al., testing the isotropy of the cosmic microwave background fluctuations. We find that the hemispherical power asymmetry previously reported for the largest scales l = 2-40 extends to much smaller scales. In fact, for the full multipole range l = 2-600, significantly more power is found in the hemisphere centered at (theta = 107{sup 0} +- 10{sup 0}, phi = 226{sup 0} +- 10{sup 0}) in galactic co-latitude and longitude than in the opposite hemisphere, consistent with the previously detected direction of asymmetry for l = 2-40.more » We adopt a model selection test where the direction and amplitude of asymmetry, as well as the multipole range, are free parameters. A model with an asymmetric distribution of power for l = 2-600 is found to be preferred over the isotropic model at the 0.4% significance level, taking into account the additional parameters required to describe it. A similar direction of asymmetry is found independently in all six subranges of 100 multipoles between l = 2-600. None of our 9800 isotropic simulated maps show a similarly consistent direction of asymmetry over such a large multipole range. No known systematic effects or foregrounds are found to be able to explain the asymmetry.« less

Characteristics of the turbulence in the flow at a tidal stream power site.

PubMed

Milne, I A; Sharma, R N; Flay, R G J; Bickerton, S

2013-02-28

This paper analyses a set of velocity time histories which were obtained at a fixed point in the bottom boundary layer of a tidal stream, 5 m from the seabed, and where the mean flow reached 2.5 m s(-1). Considering two complete tidal cycles near spring tide, the streamwise turbulence intensity during non-slack flow was found to be approximately 12-13%, varying slightly between flood and ebb tides. The ratio of the streamwise turbulence intensity to that of the transverse and vertical intensities is typically 1 : 0.75 : 0.56, respectively. Velocity autospectra computed near maximum flood tidal flow conditions exhibit an f(-2/3) inertial subrange and conform reasonably well to atmospheric turbulence spectral models. Local isotropy is observed between the streamwise and transverse spectra at reduced frequencies of f>0.5. The streamwise integral time scales and length scales of turbulence at maximum flow are approximately 6 s and 11-14 m, respectively, and exhibit a relatively large degree of scatter. They are also typically much greater in magnitude than the transverse and vertical components. The findings are intended to increase the levels of confidence within the tidal energy industry of the characteristics of the higher frequency components of the onset flow, and subsequently lead to more realistic performance and loading predictions.

Cross-sectional structural parameters from densitometry

NASA Technical Reports Server (NTRS)

Cleek, Tammy M.; Whalen, Robert T.

2002-01-01

Bone densitometry has previously been used to obtain cross-sectional properties of bone from a single X-ray projection across the bone width. Using three unique projections, we have extended the method to obtain the principal area moments of inertia and orientations of the principal axes at each scan cross-section along the length of the scan. Various aluminum phantoms were used to examine scanner characteristics to develop the highest accuracy possible for in vitro non-invasive analysis of cross-sectional properties. Factors considered included X-ray photon energy, initial scan orientation, the angle spanned by the three scans (included angle), and I(min)/I(max) ratios. Principal moments of inertia were accurate to within +/-3.1% and principal angles were within +/-1 degrees of the expected value for phantoms scanned with included angles of 60 degrees and 90 degrees at the higher X-ray photon energy (140 kVp). Low standard deviations in the error (0.68-1.84%) also indicate high precision of calculated measurements with these included angles. Accuracy and precision decreased slightly when the included angle was reduced to 30 degrees. The method was then successfully applied to a pair of excised cadaveric tibiae. The accuracy and insensitivity of the algorithms to cross-sectional shape and changing isotropy (I(min)/I(max)) values when various included angles are used make this technique viable for future in vivo studies.

Foundations of quantum gravity: The role of principles grounded in empirical reality

NASA Astrophysics Data System (ADS)

Holman, Marc

2014-05-01

When attempting to assess the strengths and weaknesses of various principles in their potential role of guiding the formulation of a theory of quantum gravity, it is crucial to distinguish between principles which are strongly supported by empirical data - either directly or indirectly - and principles which instead (merely) rely heavily on theoretical arguments for their justification. Principles in the latter category are not necessarily invalid, but their a priori foundational significance should be regarded with due caution. These remarks are illustrated in terms of the current standard models of cosmology and particle physics, as well as their respective underlying theories, i.e., essentially general relativity and quantum (field) theory. For instance, it is clear that both standard models are severely constrained by symmetry principles: an effective homogeneity and isotropy of the known universe on the largest scales in the case of cosmology and an underlying exact gauge symmetry of nuclear and electromagnetic interactions in the case of particle physics. However, in sharp contrast to the cosmological situation, where the relevant symmetry structure is more or less established directly on observational grounds, all known, nontrivial arguments for the "gauge principle" are purely theoretical (and far less conclusive than usually advocated). Similar remarks apply to the larger theoretical structures represented by general relativity and quantum (field) theory, where - actual or potential - empirical principles, such as the (Einstein) equivalence principle or EPR-type nonlocality, should be clearly differentiated from theoretical ones, such as general covariance or renormalizability. It is argued that if history is to be of any guidance, the best chance to obtain the key structural features of a putative quantum gravity theory is by deducing them, in some form, from the appropriate empirical principles (analogous to the manner in which, say, the idea that gravitation is a curved spacetime phenomenon is arguably implied by the equivalence principle). Theoretical principles may still be useful however in formulating a concrete theory (analogous to the manner in which, say, a suitable form of general covariance can still act as a sieve for separating theories of gravity from one another). It is subsequently argued that the appropriate empirical principles for deducing the key structural features of quantum gravity should at least include (i) quantum nonlocality, (ii) irreducible indeterminacy (or, essentially equivalently, given (i), relativistic causality), (iii) the thermodynamic arrow of time, (iv) homogeneity and isotropy of the observable universe on the largest scales. In each case, it is explained - when appropriate - how the principle in question could be implemented mathematically in a theory of quantum gravity, why it is considered to be of fundamental significance and also why contemporary accounts of it are insufficient. For instance, the high degree of uniformity observed in the Cosmic Microwave Background is usually regarded as theoretically problematic because of the existence of particle horizons, whereas the currently popular attempts to resolve this situation in terms of inflationary models are, for a number of reasons, less than satisfactory. However, rather than trying to account for the required empirical features dynamically, an arguably much more fruitful approach consists in attempting to account for these features directly, in the form of a lawlike initial condition within a theory of quantum gravity.

Is 2-D turbulence relevant in the atmosphere?

NASA Astrophysics Data System (ADS)

Lovejoy, Shaun; Schertzer, Daniel

2010-05-01

Starting with (Taylor, 1935), the paradigm of isotropic (and scaling!) turbulence was developed initially for laboratory applications, but following (Kolmogorov, 1941), three dimensional isotropic turbulence was progressively applied to the atmosphere. Since the atmosphere is strongly stratified, a single wide scale range model which is both isotropic and scaling is not possible so that theorists had to immediately choose between the two symmetries: isotropy or scale invariance. Following the development of models of two dimensional isotropic turbulence ((Fjortoft, 1953), but especially (Kraichnan, 1967) and (Charney, 1971)), the mainstream choice was to first make the convenient assumption of isotropy and to drop wide range scale invariance. Starting at the end of the 1970's this "isotropy primary" (IP) paradigm has lead to a series of increasingly complex isotropic 2D/isotropic 3D models of atmospheric dynamics which continue to dominate the theoretical landscape. Justifications for IP approaches have focused almost exclusively on the horizontal statistics of the horizontal wind in both numerical models and analyses and from aircraft campaigns, especially the highly cited GASP (Nastrom and Gage, 1983), (Gage and Nastrom, 1986; Nastrom and Gage, 1985) and MOZAIC (Cho and Lindborg, 2001) experiments. Since understanding the anisotropy clearly requires comparisons between horizontal and vertical statistics/structures this focus has been unfortunate. Over the same thirty year period that 2D/3D isotropic models were being elaborated, evidence slowly accumulated in favour of the opposite theoretical choice: to drop the isotropy assumption but to retain wide range scaling. The models in the alternative paradigm are scaling but strongly anisotropic with vertical sections of structures becoming increasingly stratified at larger and larger scales albeit in a power law manner; we collectively refer to these as "SP" for "scaling primary" approaches. Early authors explicitly using SP models to explain their observations include ((Van Zandt, 1982), (Schertzer and Lovejoy, 1985), (Schertzer and Lovejoy, 1987), (Fritts et al., 1988), (Tsuda et al., 1989), (Dewan, 1997; Lazarev et al., 1994), (Gardner et al., 1993), (Hostetler and Gardner, 1994). In addition, many experiments found non-standard vertical scaling exponents thus implicitly supporting the SP position. Today, state-of-the-art lidar vertical sections of passive scalars (Lilley et al., 2004) or satellite vertical radar sections of clouds give direct evidence for the corresponding scaling (power law) stratification of structures. State-of-the-art drop sondes have even been used to show that the IP standard bearer - 3D isotropic Kolmogorov turbulence - apparently doesn't exist in the atmosphere at any scale at least down to 5 m in scale or at any altitude level within the troposphere (Lovejoy et al., 2007). At the same time, massive quantities of high quality satellite data have directly demonstrated the wide range horizontal scaling of the atmospheric forcing (long and short wave radiances; see e.g. (Lovejoy et al., 2009a)) and numerical atmospheric models and reanalyses have been shown to display nearly perfect (scaling) cascade structures over their entire available horizontal ranges (Stolle et al., 2009). This shows also that the source/sink free "inertial ranges" used in IP models are at best academic idealizations. The IP/SP opposition is arguably a main contributor to today's lack of scientific consensus about the scale by scale statistical structure of both the atmosphere and of atmospheric models and reanalyses. In order to resolve the deadlock, either the IP camp must show how the findings of wide range vertical and horizontal scaling can be adequately explained through a hierarchy of isotropic models, or the SP camp must explain the key aircraft and numerical model results cited against them as evidence of two (or more) isotropic regimes. In this talk we review the debate and argue that now exactly such a reinterpretation of the aircraft data has been found (Lovejoy et al., 2009b). We argue that the debate has now been decisively resolved in favour of the SP approaches so that neither 2-D isotropic nor 3D isotropic turbulence - are relevant in the atmosphere. References: J.G. Charney, Geostrophic Turbulence, J. Atmos. Sci 28(1971), p. 1087. J. Cho and E. Lindborg, Horizontal velocity structure functions in the upper troposphere and lower stratosphere i: Observations, J. Geophys. Res. 106(2001), pp. 10223-10232. E. Dewan, Saturated-cascade similtude theory of gravity wave sepctra, J. Geophys. Res. 102(1997), pp. 29799-29817. R. Fjortoft, On the changes in the spectral distribution of kinetic energy in two dimensional, nondivergent flow, Tellus 7(1953), pp. 168-176. D. Fritts, T. Tsuda, T. Sato, S. Fukao and S. Kato, Observational evidence of a saturated gravity wave spectrum in the troposphere and lower stratosphere, Journal of the Atmospheric Sciences 45(1988), p. 1741. K.S. Gage and G.D. Nastrom, Theoretical Interpretation of atmospheric wavenumber spectra of wind and temperature observed by commercial aircraft during GASP, J. of the Atmos. Sci. 43(1986), pp. 729-740. C.S. Gardner, C.A. Hostetler and S.J. Franke, Gravity Wave models for the horizontal wave number spectra of atmospheric velocity and density flucutations, J. Geophys. Res. 98(1993), pp. 1035-1049. C.A. Hostetler and C.S. Gardner, Observations of horizontal and vertical wave number spectra of gravity wave motions in the stratosphere and mesosphere ove rthe mid-Pacific, J. Geophys. Res. 99(1994), pp. 1283-1302. A.N. Kolmogorov, Local structure of turbulence in an incompressible liquid for very large Reynolds numbers. (English translation: Proc. Roy. Soc. A434, 9-17, 1991), Proc. Acad. Sci. URSS., Geochem. Sect. 30(1941), pp. 299-303. R.H. Kraichnan, Inertial ranges in two-dimensional turbulence, Physics of Fluids 10(1967), pp. 1417-1423. A. Lazarev, D. Schertzer, S. Lovejoy and Y. Chigirinskaya, Unified multifractal atmospheric dynamics tested in the tropics: part II, vertical scaling and Generalized Scale Invariance, Nonlinear Processes in Geophysics 1(1994), pp. 115-123. M. Lilley, S. Lovejoy, K. Strawbridge and D. Schertzer, 23/9 dimensional anisotropic scaling of passive admixtures using lidar aerosol data, Phys. Rev. E 70(2004), pp. 036307-036301-036307. S. Lovejoy et al., Atmospheric complexity or scale by scale simplicity? , Geophys. Resear. Lett. 36(2009a), pp. L01801, doi:01810.01029/02008GL035863. S. Lovejoy, A.F. Tuck, S.J. Hovde and D. Schertzer, Is isotropic turbulence relevant in the atmosphere?, Geophys. Res. Lett. L14802, doi:10.1029/2007GL029359.(2007). S. Lovejoy, A.F. Tuck, D. Schertzer and S.J. Hovde, Reinterpreting aircraft measurements in anisotropic scaling turbulence, Atmos. Chem. Phys. Discuss., 9(2009b), pp. 3871-3920. G.D. Nastrom and K.S. Gage, A first look at wave number spectra from GASP data, Tellus 35(1983), p. 383. G.D. Nastrom and K.S. Gage, A climatology of atmospheric wavenumber spectra of wind and temperature by commercial aircraft, J. Atmos. Sci. 42(1985), pp. 950-960. D. Schertzer and S. Lovejoy, The dimension and intermittency of atmospheric dynamics. In: B. Launder, Editor, Turbulent Shear Flow 4, Springer-Verlag (1985), pp. 7-33. D. Schertzer and S. Lovejoy, Physical modeling and Analysis of Rain and Clouds by Anisotropic Scaling of Multiplicative Processes, Journal of Geophysical Research 92(1987), pp. 9693-9714. J. Stolle, S. Lovejoy and D. Schertzer, The stochastic cascade structure of deterministic numerical models of the atmosphere, Nonlin. Proc. in Geophys. 16(2009), pp. 1-15. G.I. Taylor, Statistical theory of turbulence, Proc. Roy. Soc. I-IV, A151(1935), pp. 421-478. T. Tsuda et al., MST radar observations of a saturated gravity wave spectrum, Journal of the Atmospheric Sciences 46(1989), p. 2440. T.E. Van Zandt, A universal spectrum of buoyancy waves in the atmosphere, Geophysical Research Letter 9(1982), pp. 575-578.

Standard rulers, candles, and clocks from the low-redshift universe.

PubMed

Heavens, Alan; Jimenez, Raul; Verde, Licia

2014-12-12

We measure the length of the baryon acoustic oscillation (BAO) feature, and the expansion rate of the recent Universe, from low-redshift data only, almost model independently. We make only the following minimal assumptions: homogeneity and isotropy, a metric theory of gravity, a smooth expansion history, and the existence of standard candles (supernovæ) and a standard BAO ruler. The rest is determined by the data, which are compilations of recent BAO and type IA supernova results. Making only these assumptions, we find for the first time that the standard ruler has a length of 103.9±2.3h⁻¹ Mpc. The value is a measurement, in contrast to the model-dependent theoretical prediction determined with model parameters set by Planck data (99.3±2.1h⁻¹ Mpc). The latter assumes the cold dark matter model with a cosmological constant, and that the ruler is the sound horizon at radiation drag. Adding passive galaxies as standard clocks or a local Hubble constant measurement allows the absolute BAO scale to be determined (142.8±3.7 Mpc), and in the former case the additional information makes the BAO length determination more precise (101.9±1.9h⁻¹ Mpc). The inverse curvature radius of the Universe is weakly constrained and consistent with zero, independently of the gravity model, provided it is metric. We find the effective number of relativistic species to be N(eff)=3.53±0.32, independent of late-time dark energy or gravity physics.

Development of a Low-Reynolds Number, Nonlinear kappa-epsilon Model for the Reduced Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Boger, David A.; Govindan, T. R.; McDonald, Henry

1997-01-01

Previous work at NASA LeRC has shown that flow distortions in aircraft engine inlet ducts can be significantly reduced by mounting vortex generators, or small wing sections, on the inside surface of the engine inlet. The placement of the vortex generators is an important factor in obtaining the optimal effect over a wide operating envelope. In this regard, the only alternative to a long and expensive test program which would search out this optimal configuration is a good prediction procedure which could narrow the field of search. Such a procedure has been developed in collaboration with NASA LeRC, and results obtained by NASA personnel indicate that it shows considerable promise for predicting the viscous turbulent flow in engine inlet ducts in the presence of vortex generators. The prediction tool is a computer code which numerically solves the reduced Navier-Stokes equations and so is commonly referred to as RNS3D. Obvious deficiencies in RNS3D have been addressed in previous work. Primarily, it is known that the predictions of the mean velocity field of a turbulent boundary layer flow approaching separation are not in good agreement with data. It was suggested that the use of an algebraic mixing-length turbulence model in RNS3D is at least partly to blame for this. Additionally, the current turbulence model includes an assumption of isotropy which will ultimately fail to capture turbulence-driven secondary flow known to exist in noncircular ducts.

Hidden in the background: a local approach to CMB anomalies

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

Sánchez, Juan C. Bueno, E-mail: juan.c.bueno@correounivalle.edu.co

2016-09-01

We investigate a framework aiming to provide a common origin for the large-angle anomalies detected in the Cosmic Microwave Background (CMB), which are hypothesized as the result of the statistical inhomogeneity developed by different isocurvature fields of mass m ∼ H present during inflation. The inhomogeneity arises as the combined effect of ( i ) the initial conditions for isocurvature fields (obtained after a fast-roll stage finishing many e -foldings before cosmological scales exit the horizon), ( ii ) their inflationary fluctuations and ( iii ) their coupling to other degrees of freedom. Our case of interest is when thesemore » fields (interpreted as the precursors of large-angle anomalies) leave an observable imprint only in isolated patches of the Universe. When the latter intersect the last scattering surface, such imprints arise in the CMB. Nevertheless, due to their statistically inhomogeneous nature, these imprints are difficult to detect, for they become hidden in the background similarly to the Cold Spot. We then compute the probability that a single isocurvature field becomes inhomogeneous at the end of inflation and find that, if the appropriate conditions are given (which depend exclusively on the preexisting fast-roll stage), this probability is at the percent level. Finally, we discuss several mechanisms (including the curvaton and the inhomogeneous reheating) to investigate whether an initial statistically inhomogeneous isocurvature field fluctuation might give rise to some of the observed anomalies. In particular, we focus on the Cold Spot, the power deficit at low multipoles and the breaking of statistical isotropy.« less

Interpretation of the Electron Paramagnetic Resonance Spectra of Copper(II)-Tyrosine Complex

NASA Astrophysics Data System (ADS)

Xu, Xiao-Hui; Kuang, Min-Quan

2017-12-01

The electron paramagnetic resonance (EPR) spectra of [Cu(l-tyrosine)2]n (CuA) were interpreted based on the fourth-order perturbation treatments where the contributions due to the local distortion, ligand orbit and spin-orbit coupling were included. The calculated band transitions d_{x^2} - y^2 to dxy (≈16412 cm-1) and d_{z^2} (≈14845 cm-1) agree well with the band analysis results (d_{x^2} - y^2 \\to d_{xy} ≈16410 and d_{x^2} - y^2 \\to d_{z^2} ≈14850 cm-1). The unresolved separations d_{x^2} - y^2 \\to d_{xz} and d_{x^2} - y^2 \\to d_{yz} in the absorption spectra were evaluated as 26283 and 26262 cm-1, respectively. For CuA, copper chromophores in 1,3-diaminorpropane isophtalate copper(II) complex (CuB) and N-methyl-1,2-diaminoetaane-bis copper(II) polymer (CuC), the transition d_{x^2} - y^2 \\to d_{xy} (=E1≈10Dq) suffered an increase with a decrease in R̅L which was evaluated as the mean value of the copper-ligand bond lengths. The correlations between the tetragonal elongation ratio ρ (=(Rz-R̅L)/R̅L) (or the ratio G=(gz-ge)/((gx+gy)/2-ge)) and the g isotropy gav (=(gx+gy+gz)/3) (or the covalency factor N) for CuA, CuB and CuC were acquired and all the results were discussed.

Test of the FLRW Metric and Curvature with Strong Lens Time Delays

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

Liao, Kai; Li, Zhengxiang; Wang, Guo-Jian

We present a new model-independent strategy for testing the Friedmann–Lemaître–Robertson–Walker (FLRW) metric and constraining cosmic curvature, based on future time-delay measurements of strongly lensed quasar-elliptical galaxy systems from the Large Synoptic Survey Telescope and supernova observations from the Dark Energy Survey. The test only relies on geometric optics. It is independent of the energy contents of the universe and the validity of the Einstein equation on cosmological scales. The study comprises two levels: testing the FLRW metric through the distance sum rule (DSR) and determining/constraining cosmic curvature. We propose an effective and efficient (redshift) evolution model for performing the formermore » test, which allows us to concretely specify the violation criterion for the FLRW DSR. If the FLRW metric is consistent with the observations, then on the second level the cosmic curvature parameter will be constrained to ∼0.057 or ∼0.041 (1 σ ), depending on the availability of high-redshift supernovae, which is much more stringent than current model-independent techniques. We also show that the bias in the time-delay method might be well controlled, leading to robust results. The proposed method is a new independent tool for both testing the fundamental assumptions of homogeneity and isotropy in cosmology and for determining cosmic curvature. It is complementary to cosmic microwave background plus baryon acoustic oscillation analyses, which normally assume a cosmological model with dark energy domination in the late-time universe.« less

Hyperuniform disordered photonic bandgap materials, from microwave to infrared wavelength regime

NASA Astrophysics Data System (ADS)

Man, Weining

Recently, we have introduced a new class of hyperuniform disordered (HUD) photonic bandgap (PBG) materials enabled by a novel constrained optimization method for engineering the material's Fourier transform to be continuous, isotropic and stealthy. Their structure factor S (k) is equal to zero for small kand exhibits a broad ring of maximum values around a characteristic wave-length range. Experimentally, an isotropic complete PBG (at all angles and for all polarizations) in an alumina-based HUD structure and single-polarized PBGs for plastic-based HUD structure have been demonstrated. Using measured and simulated transmission and phase delay information through these HUD structures, we also unfolded their band structures and reconstructed the effective dispersion relations of propagating electromagnetic modes in them. The intrinsic isotropy in these disordered structures is an inherent advantage associated with the lack of crystalline order, offering unprecedented freedom for functional defect design impossible to achieve in photonic crystals. In the microwave regime, we have shown the creation of freeform waveguides, which can channel photons robustly along arbitrarily curved paths and around sharp bends, and be decorated with defects to produce sharply resonant structures useful for filtering and frequency splitting. Recent simulation and experimental results for waveguides and modulators based on submicron-scale planar hyperuniform disordered PBG structures further highlight their ability to serve as highly compact, flexible and energy-efficient platforms for photonic integrated circuits. NSF DMR-1308084, EPSRC (UK) DTG Grant KD5050, EPSRC (UK) Strategic Equipment Grant EP/M008576/1, NSF SBIR-1345168, NSF MRI-1040444.

Mesoscale properties of clay aggregates from potential of mean force representation of interactions between nanoplatelets

NASA Astrophysics Data System (ADS)

Ebrahimi, Davoud; Whittle, Andrew J.; Pellenq, Roland J.-M.

2014-04-01

Face-to-face and edge-to-edge free energy interactions of Wyoming Na-montmorillonite platelets were studied by calculating potential of mean force along their center to center reaction coordinate using explicit solvent (i.e., water) molecular dynamics and free energy perturbation methods. Using a series of configurations, the Gay-Berne potential was parametrized and used to examine the meso-scale aggregation and properties of platelets that are initially random oriented under isothermal-isobaric conditions. Aggregates of clay were defined by geometrical analysis of face-to-face proximity of platelets with size distribution described by a log-normal function. The isotropy of the microstructure was assessed by computing a scalar order parameter. The number of platelets per aggregate and anisotropy of the microstructure both increases with platelet plan area. The system becomes more ordered and aggregate size increases with increasing pressure until maximum ordered state at confining pressure of 50 atm. Further increase of pressure slides platelets relative to each other leading to smaller aggregate size. The results show aggregate size of (3-8) platelets for sodium-smectite in agreement with experiments (3-10). The geometrical arrangement of aggregates affects mechanical properties of the system. The elastic properties of the meso-scale aggregate assembly are reported and compared with nanoindentation experiments. It is found that the elastic properties at this scale are close to the cubic systems. The elastic stiffness and anisotropy of the assembly increases with the size of the platelets and the level of external pressure.

Seismic anisotropy and its relation with crust structure and stress field in the Reggio Emilia Region (Northern Italy)

NASA Astrophysics Data System (ADS)

Margheriti, L.; Ferulano, M. F.; Di Bona, M.

2006-11-01

Shear wave splitting is measured at 14 seismic stations in the Reggio Emilia region above local background seismicity and two sequences of seismic events. The good quality of the waveforms together with the favourable distribution of earthquake foci allows us to place strong constraints on the geometry and the depth of the anisotropic volume. It is about 60 km2 wide and located between 6 and 11 km depth, inside Mesozoic age carbonate rocks. The splitting results suggest also the presence of a shallower anisotropic layer about 1 km thick and few km wide in the Pliocene-Quaternary alluvium above the Mesozoic layer. The fast polarization directions (N30°E) are approximately parallel to the maximum horizontal stress (σ1 is SSW-NNE) in the region and also parallel to the strike of the main structural features in the Reggio Emilia area. The size of the delay times suggests about 4.5 per cent shear wave velocity anisotropy. These parameters agree with an interpretation of seismic anisotropy in terms of the extensive-dilatancy anisotropy model which considers the rock volume to be pervaded by fluid-saturated microcracks aligned by the active stress field. We cannot completely rule out the contribution of aligned macroscopic fractures as the cause of the shear wave anisotropy even if the parallel shear wave polarizations we found are diagnostic of transverse isotropy with a horizontal axis of symmetry. This symmetry is commonly explained by parallel stress-aligned microcracks.

Scale disparity and spectral transfer in anisotropic numerical turbulence

NASA Technical Reports Server (NTRS)

Zhou, YE; Yeung, P. K.; Brasseur, James G.

1994-01-01

To study the effect of cancellations within long-range interactions on local isotropy at the small scales, we calculate explicitly the degree of cancellation in distant interactions in the simulations of Yeung & Brasseur and Yeung, Brasseur & Wang using the single scale disparity parameter 's' developed by Zhou. In the simulations, initially isotropic simulated turbulence was subjected to coherent anisotropic forcing at the large scales and the smallest scales were found to become anisotropic as a consequence of direct large-small scale couplings. We find that the marginally distant interactions in the simulation do not cancel out under summation and that the development of small-scale anisotropy is indeed a direct consequence of the distant triadic group, as argued by Yeung, et. al. A reduction of anisotropy at later times occurs as a result of the isotropizing influences of more local energy-cascading triadic interactions. Nevertheless, the local-to-nonlocal triadic group persists as an isotropizing influence at later times. We find that, whereas long-range interactions, in general, contribute little to net energy transfer into or out of a high wavenumber shell k, the anisotropic transfer of component energy within the shell increases with increasing scale separations. These results are consistent with results by Zhou, and Brasseur & Wei, and suggest that the anisotropizing influences of long range interactions should persist to higher Reynolds numbers. The residual effect of the forced distant group in this low-Reynolds number simulation is found to be forward cascading, on average.

Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA

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

Manuel, M. J.-E.; Zylstra, A. B.; Rinderknecht, H. G.

2012-06-15

A monoenergetic proton source has been characterized and a modeling tool developed for proton radiography experiments at the OMEGA [T. R. Boehly et al., Opt. Comm. 133, 495 (1997)] laser facility. Multiple diagnostics were fielded to measure global isotropy levels in proton fluence and images of the proton source itself provided information on local uniformity relevant to proton radiography experiments. Global fluence uniformity was assessed by multiple yield diagnostics and deviations were calculated to be {approx}16% and {approx}26% of the mean for DD and D{sup 3}He fusion protons, respectively. From individual fluence images, it was found that the angular frequenciesmore » of Greater-Than-Or-Equivalent-To 50 rad{sup -1} contributed less than a few percent to local nonuniformity levels. A model was constructed using the Geant4 [S. Agostinelli et al., Nuc. Inst. Meth. A 506, 250 (2003)] framework to simulate proton radiography experiments. The simulation implements realistic source parameters and various target geometries. The model was benchmarked with the radiographs of cold-matter targets to within experimental accuracy. To validate the use of this code, the cold-matter approximation for the scattering of fusion protons in plasma is discussed using a typical laser-foil experiment as an example case. It is shown that an analytic cold-matter approximation is accurate to within Less-Than-Or-Equivalent-To 10% of the analytic plasma model in the example scenario.« less

Seismic fault zone trapped noise

NASA Astrophysics Data System (ADS)

Hillers, G.; Campillo, M.; Ben-Zion, Y.; Roux, P.

2014-07-01

Systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics. Here we construct trapped waves from the scattered seismic wavefield recorded by a fault zone array. The frequency-dependent interaction between the ambient wavefield and the fault zone environment is studied using properties of the noise correlation field. A critical frequency fc ≈ 0.5 Hz defines a threshold above which the in-fault scattered wavefield has increased isotropy and coherency compared to the ambient noise. The increased randomization of in-fault propagation directions produces a wavefield that is trapped in a waveguide/cavity-like structure associated with the low-velocity damage zone. Dense spatial sampling allows the resolution of a near-field focal spot, which emerges from the superposition of a collapsing, time reversed wavefront. The shape of the focal spot depends on local medium properties, and a focal spot-based fault normal distribution of wave speeds indicates a ˜50% velocity reduction consistent with estimates from a far-field travel time inversion. The arrival time pattern of a synthetic correlation field can be tuned to match properties of an observed pattern, providing a noise-based imaging tool that can complement analyses of trapped ballistic waves. The results can have wide applicability for investigating the internal properties of fault damage zones, because mechanisms controlling the emergence of trapped noise have less limitations compared to trapped ballistic waves.

Kinetic Features Observed in the Solar Wind Electron Distributions

NASA Astrophysics Data System (ADS)

Pierrard, V.; Lazar, M.; Poedts, S.

2016-12-01

More than 120 000 of velocity distributions measured by Helios, Cluster and Ulysses in the ecliptic have been analyzed within an extended range of heliocentric distances from 0.3 to over 4 AU. The velocity distribution of electrons reveal a dual structure with a thermal (Maxwellian) core and a suprathermal (Kappa) halo. A detailed observational analysis of these two components provides estimations of their temperatures and temperature anisotropies, and we decode any potential interdependence that their properties may indicate. The core temperature is found to decrease with the radial distance, while the halo temperature slightly increases, clarifying an apparent contradiction in previous observational analysis and providing valuable clues about the temperature of the Kappa-distributed populations. For low values of the power-index kappa, these two components manifest a clear tendency to deviate from isotropy in the same direction, that seems to confirm the existence of mechanisms with similar effects on both components, e.g., the solar wind expansion, or the particle heating by the fluctuations. However, the existence of plasma states with anti-correlated anisotropies of the core and halo populations and the increase of their number for high values of the power-index kappa suggest a dynamic interplay of these components, mediated most probably by the anisotropy-driven instabilities. Estimating the temperature of the solar wind particles and their anisotropies is particularly important for understanding the origin of these deviations from thermal equilibrium as well as their effects.

Modeling near wall effects in second moment closures by elliptic relaxation

NASA Technical Reports Server (NTRS)

Laurence, D.; Durbin, P.

1994-01-01

The elliptic relaxation model of Durbin (1993) for modeling near-wall turbulence using second moment closures (SMC) is compared to DNS data for a channel flow at Re(sub t) = 395. The agreement for second order statistics and even the terms in their balance equation is quite satisfactory, confirming that very little viscous effects (via Kolmogoroff scales) need to be added to the high Reynolds versions of SMC for near-wall-turbulence. The essential near-wall feature is thus the kinematic blocking effect that a solid wall exerts on the turbulence through the fluctuating pressure, which is best modeled by an elliptic operator. Above the transition layer, the effect of the original elliptic operator decays rapidly, and it is suggested that the log-layer is better reproduced by adding a non-homogeneous reduction of the return to isotropy, the gradient of the turbulent length scale being used as a measure of the inhomogeneity of the log-layer. The elliptic operator was quite easily applied to the non-linear Craft & Launder pressure-strain model yielding an improved distinction between the spanwise and wall normal stresses, although at higher Reynolds number (Re) and away from the wall, the streamwise component is severely underpredicted, as well as the transition in the mean velocity from the log to the wake profiles. In this area a significant change of behavior was observed in the DNS pressure-strain term, entirely ignored in the models.

Analytical one-dimensional model for laser-induced ultrasound in planar optically absorbing layer.

PubMed

Svanström, Erika; Linder, Tomas; Löfqvist, Torbjörn

2014-03-01

Ultrasound generated by means of laser-based photoacoustic principles are in common use today and applications can be found both in biomedical diagnostics, non-destructive testing and materials characterisation. For certain measurement applications it could be beneficial to shape the generated ultrasound regarding spectral properties and temporal profile. To address this, we studied the generation and propagation of laser-induced ultrasound in a planar, layered structure. We derived an analytical expression for the induced pressure wave, including different physical and optical properties of each layer. A Laplace transform approach was employed in analytically solving the resulting set of photoacoustic wave equations. The results correspond to simulations and were compared to experimental results. To enable the comparison between recorded voltage from the experiments and the calculated pressure we employed a system identification procedure based on physical properties of the ultrasonic transducer to convert the calculated acoustic pressure to voltages. We found reasonable agreement between experimentally obtained voltages and the voltages determined from the calculated acoustic pressure, for the samples studied. The system identification procedure was found to be unstable, however, possibly from violations of material isotropy assumptions by film adhesives and coatings in the experiment. The presented analytical model can serve as a basis when addressing the inverse problem of shaping an acoustic pulse from absorption of a laser pulse in a planar layered structure of elastic materials. Copyright © 2013 Elsevier B.V. All rights reserved.

The influence of jet-grid turbulence on heat transfer from the stagnation region of a cylinder in crossflow

NASA Technical Reports Server (NTRS)

Obrien, J. E.; Vanfossen, G. J., Jr.

1985-01-01

The effect of high-intensity turbulence on heat transfer from the stagnation region of a circular cylinder in crossflow was studied. The work was motivated by the desire to be able to more fully understand and predict the heat transfer to the leading edge of a turbine airfoil. In order to achieve high levels of turbulence with a reasonable degree of isotropy and homogeneity, a jet-injection turbulence grid was used. The jet grid provided turbulence intensities of 10 to 12 percent, measured at the test cylinder location, for downstream blowing with the blowing rate adjusted to an optimal value for flow uniformity. Heat transfer augmentation above the zeroturbulence case ranged from 37 to 53 percent for the test cylinder behind the jet grid for a cylinder Reynolds number range of 48,000 to 180,000, respectively. The level of heat transfer augmentation was found to be fairly uniform with respect to circumferential distance from the stagnation line. Stagnation point heat transfer results (expressed in terms of the Frossling number) were found to be somewhat low with respect to previous studies, when compared on the basis of equal values of the parameter Tu Re(1/2), indicating an additional Reynolds number effect as observed by previous investigators. Consequently, for a specified value of Tu Re(1/2), data obtained with a relatively high turbulence intensity will have a lower value of the Frossling number.

Quantum cellular automata and free quantum field theory

NASA Astrophysics Data System (ADS)

D'Ariano, Giacomo Mauro; Perinotti, Paolo

2017-02-01

In a series of recent papers [1-4] it has been shown how free quantum field theory can be derived without using mechanical primitives (including space-time, special relativity, quantization rules, etc.), but only considering the easiest quantum algorithm encompassing a countable set of quantum systems whose network of interactions satisfies the simple principles of unitarity, homogeneity, locality, and isotropy. This has opened the route to extending the axiomatic information-theoretic derivation of the quantum theory of abstract systems [5, 6] to include quantum field theory. The inherent discrete nature of the informational axiomatization leads to an extension of quantum field theory to a quantum cellular automata theory, where the usual field theory is recovered in a regime where the discrete structure of the automata cannot be probed. A simple heuristic argument sets the scale of discreteness to the Planck scale, and the customary physical regime where discreteness is not visible is the relativistic one of small wavevectors. In this paper we provide a thorough derivation from principles that in the most general case the graph of the quantum cellular automaton is the Cayley graph of a finitely presented group, and showing how for the case corresponding to Euclidean emergent space (where the group resorts to an Abelian one) the automata leads to Weyl, Dirac and Maxwell field dynamics in the relativistic limit. We conclude with some perspectives towards the more general scenario of non-linear automata for interacting quantum field theory.

Cosmic voids detection without density measurements

NASA Astrophysics Data System (ADS)

Elyiv, Andrii; Marulli, Federico; Pollina, Giorgia; Baldi, Marco; Branchini, Enzo; Cimatti, Andrea; Moscardini, Lauro

2015-03-01

Cosmic voids are effective cosmological probes to discriminate among competing world models. Their identification is generally based on density or geometry criteria that, because of their very nature, are prone to shot noise. We propose two void finders that are based on dynamical criterion to select voids in Lagrangian coordinates and minimize the impact of sparse sampling. The first approach exploits the Zel'dovich approximation to trace back in time the orbits of galaxies located in voids and their surroundings; the second uses the observed galaxy-galaxy correlation function to relax the objects' spatial distribution to homogeneity and isotropy. In both cases voids are defined as regions of the negative velocity divergence, which can be regarded as sinks of the back-in-time streamlines of the mass tracers. To assess the performance of our methods we used a dark matter halo mock catalogue CODECS, and compared the results with those obtained with the ZOBOV void finder. We find that the void divergence profiles are less scattered than the density ones and, therefore, their stacking constitutes a more accurate cosmological probe. The significance of the divergence signal in the central part of voids obtained from both our finders is 60 per cent higher than for overdensity profiles in the ZOBOV case. The ellipticity of the stacked void measured in the divergence field is closer to unity, as expected, than what is found when using halo positions. Therefore, our void finders are complementary to the existing methods, which should contribute to improve the accuracy of void-based cosmological tests.

Dimensional isotropy of 6H and 3C SiC under neutron irradiation

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

Snead, Lance L.; Katoh, Yutai; Koyanagi, Takaaki

2016-01-16

This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 10 23 to 2 × 10 26 n/m 2 (E > 0.1 MeV), or about 0.02–20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstratedmore » equivalent swelling behavior. Moreover the 6H–SiC expanded isotropically. The magnitude of the swelling followed a ~0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ~7.8% volume expansion in SiC was observed prior to amorphization. Above ~0.9 × 10 25 n/m 2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm 3. As a result, the as-amorphized density was the same at the 2 × 10 25 and 2 × 10 26 n/m 2 (E > 0.1 MeV) dose levels.« less

Treatment of temporal aliasing effects in the context of next generation satellite gravimetry missions

NASA Astrophysics Data System (ADS)

Daras, Ilias; Pail, Roland

2017-09-01

Temporal aliasing effects have a large impact on the gravity field accuracy of current gravimetry missions and are also expected to dominate the error budget of Next Generation Gravimetry Missions (NGGMs). This paper focuses on aspects concerning their treatment in the context of Low-Low Satellite-to-Satellite Tracking NGGMs. Closed-loop full-scale simulations are performed for a two-pair Bender-type Satellite Formation Flight (SFF), by taking into account error models of new generation instrument technology. The enhanced spatial sampling and error isotropy enable a further reduction of temporal aliasing errors from the processing perspective. A parameterization technique is adopted where the functional model is augmented by low-resolution gravity field solutions coestimated at short time intervals, while the remaining higher-resolution gravity field solution is estimated at a longer time interval. Fine-tuning the parameterization choices leads to significant reduction of the temporal aliasing effects. The investigations reveal that the parameterization technique in case of a Bender-type SFF can successfully mitigate aliasing effects caused by undersampling of high-frequency atmospheric and oceanic signals, since their most significant variations can be captured by daily coestimated solutions. This amounts to a "self-dealiasing" method that differs significantly from the classical dealiasing approach used nowadays for Gravity Recovery and Climate Experiment processing, enabling NGGMs to retrieve the complete spectrum of Earth's nontidal geophysical processes, including, for the first time, high-frequency atmospheric and oceanic variations.

The local structure and EPR parameter of compressed tetrahedral CuIIX4 components in proteins, liquid precursors and nanomaterials

NASA Astrophysics Data System (ADS)

Kuang, Min-Quan; Yuan, Hong-Kuan; Chen, Hong; Wang, Li-Dan; Duan, Shu-Kai

2017-11-01

The local structures and EPR parameters of flatten CuIIX4 (X = N, O, S, Se, Cl and Br) compositions in proteins, liquid precursors and nanocrystals are analyzed and computed based on the cluster approach and perturbation method. The g and A components of copper(II) under D2d symmetry are well explained in terms of a global parameter β characterizing the local angular distortion away from the ideal Td tetrahedron where β0 ≈ 109.4712°. The calculated isotropy and anisotropy of g factors (gav and Δg) are found suffering an increase with the enlargement of the obtained βcal, which is consistent with the increasing trends of both experimental Δg and gav. The variation trend of gav can also be interpreted by the decreasing covalence of the studied system (or the increasing covalency factor ρ). On the other hand, the hyperfine structure constant A‖ decreases with increasing βcal. The obtained cubic crystal field parameter Dq and the core polarization constant κ experience the dropping and growing tendencies, respectively, with the enlarging copper-ligand bond length R. The above correlations are appropriate for all the studied CuIIX4 complexes and thus this work would be helpful to establish the complete physical scheme for uniform analysis on spectroscopic and magnetic behaviours of MX4 (M = transition metal and X = halides and pseudohalides) compounds.

Free Quantum Field Theory from Quantum Cellular Automata

NASA Astrophysics Data System (ADS)

Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Tosini, Alessandro

2015-10-01

After leading to a new axiomatic derivation of quantum theory (see D'Ariano et al. in Found Phys, 2015), the new informational paradigm is entering the domain of quantum field theory, suggesting a quantum automata framework that can be regarded as an extension of quantum field theory to including an hypothetical Planck scale, and with the usual quantum field theory recovered in the relativistic limit of small wave-vectors. Being derived from simple principles (linearity, unitarity, locality, homogeneity, isotropy, and minimality of dimension), the automata theory is quantum ab-initio, and does not assume Lorentz covariance and mechanical notions. Being discrete it can describe localized states and measurements (unmanageable by quantum field theory), solving all the issues plaguing field theory originated from the continuum. These features make the theory an ideal framework for quantum gravity, with relativistic covariance and space-time emergent solely from the interactions, and not assumed a priori. The paper presents a synthetic derivation of the automata theory, showing how the principles lead to a description in terms of a quantum automaton over a Cayley graph of a group. Restricting to Abelian groups we show how the automata recover the Weyl, Dirac and Maxwell dynamics in the relativistic limit. We conclude with some new routes about the more general scenario of non-Abelian Cayley graphs. The phenomenology arising from the automata theory in the ultra-relativistic domain and the analysis of corresponding distorted Lorentz covariance is reviewed in Bisio et al. (Found Phys 2015, in this same issue).

Conical Fourier shell correlation applied to electron tomograms.

PubMed

Diebolder, C A; Faas, F G A; Koster, A J; Koning, R I

2015-05-01

The resolution of electron tomograms is anisotropic due to geometrical constraints during data collection, such as the limited tilt range and single axis tilt series acquisition. Acquisition of dual axis tilt series can decrease these effects. However, in cryo-electron tomography, to limit the electron radiation damage that occurs during imaging, the total dose should not increase and must be fractionated over the two tilt series. Here we set out to determine whether it is beneficial fractionate electron dose for recording dual axis cryo electron tilt series or whether it is better to perform single axis acquisition. To assess the quality of tomographic reconstructions in different directions here we introduce conical Fourier shell correlation (cFSCe/o). Employing cFSCe/o, we compared the resolution isotropy of single-axis and dual-axis (cryo-)electron tomograms using even/odd split data sets. We show that the resolution of dual-axis simulated and cryo-electron tomograms in the plane orthogonal to the electron beam becomes more isotropic compared to single-axis tomograms and high resolution peaks along the tilt axis disappear. cFSCe/o also allowed us to compare different methods for the alignment of dual-axis tomograms. We show that different tomographic reconstruction programs produce different anisotropic resolution in dual axis tomograms. We anticipate that cFSCe/o can also be useful for comparisons of acquisition and reconstruction parameters, and different hardware implementations. Copyright © 2015 Elsevier Inc. All rights reserved.

Characterization of nuclear graphite elastic properties using laser ultrasonic methods

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

Zeng, Fan W; Han, Karen; Olasov, Lauren R

2015-01-01

Laser ultrasonic methods have been used to characterize the elastic behaviors of commercially-available and legacy nuclear graphites. Since ultrasonic techniques are sensitive to various aspects of graphite microstructure including preferred grain orientation, microcrack orientation and porosity, laser ultrasonics is a candidate technique for monitoring graphite degradation and structural integrity in environments expected in high-temperature, gas-cooled nuclear reactors. Aspects of materials texture can be assessed by studying ultrasonic wavespeeds as a function of propagation direction and polarization. Shear wave birefringence measurements, in particular, can be used to evaluate elastic anisotropy. In this work, laser ultrasonic measurements of graphite moduli have beenmore » made to provide insight into the relationship between the microstructures and the macroscopic stiffnesses of these materials. In particular, laser ultrasonic measurements have been made using laser line sources to produce shear waves with specific polarizations. By varying the line orientation relative to the sample, shear wave birefringence measurements have been recorded. Results from shear wave birefringence measurements show that an isostatically molded graphite, such as PCIB, behaves isotropically, while an extruded graphite, such as H-451, displays significant ultrasonic texture. Graphites have complicated microstructures that depend on the manufacturing processes used, and ultrasonic texture in these materials could originate from grain orientation and preferred microcrack alignment. Effects on material isotropy due to service related microstructural changes are possible and the ultimate aim of this work is to determine the degree to which these changes can be assessed nondestructively using laser ultrasonics measurements« less

Effect of texture dispersion on the effective biaxial modulus of fiber-textured hexagonal, tetragonal, and orthorhombic films

NASA Astrophysics Data System (ADS)

Wu, Huaping; Wu, Linzhi; Du, Shanyi

2008-04-01

The effective biaxial modulus (Meff) of fiber-textured hexagonal, tetragonal, and orthorhombic films is estimated by using the Voigt-Reuss-Hill and Vook-Witt grain-interaction models. The orientation distribution function with Gaussian distributions of the two Euler angles θ and ϕ is adopted to analyze the effect of texture dispersion degree on Meff. Numerical results that are based on ZnO, BaTiO3, and yttrium barium copper oxide (YBCO) materials show that the Vook-Witt average of Meff is identical to the Voigt-Reuss-Hill average of Meff for the (001) plane of ideally fiber-textured hexagonal and tetragonal films. The ϕ distribution has no influence on Meff of the (hkl)-fiber-textured hexagonal film at any θ distribution in terms of the isotropy in the plane perpendicular to the [001] direction. Comparably, tetragonal and orthorhombic films represent considerable actions of ϕ dispersion on Meff, and the effect of ϕ dispersion on Meff of a (001)-fiber-textured YBCO film is smaller than that for a (001)-fiber-textured BaTiO3 film since the shear anisotropic factor in the (001) shear plane of a YBCO film more closely approaches 1. Enhanced θ and ϕ distributions destroy the perfect fiber textures, and as a result, the films exhibit an evolution from ideal (hkl) fiber textures to random textures with varying full widths at half maximums of θ and ϕ.

Modeling near wall effects in second moment closures by elliptic relaxation

NASA Astrophysics Data System (ADS)

Laurence, D.; Durbin, P.

1994-12-01

The elliptic relaxation model of Durbin (1993) for modeling near-wall turbulence using second moment closures (SMC) is compared to DNS data for a channel flow at Re(sub t) = 395. The agreement for second order statistics and even the terms in their balance equation is quite satisfactory, confirming that very little viscous effects (via Kolmogoroff scales) need to be added to the high Reynolds versions of SMC for near-wall-turbulence. The essential near-wall feature is thus the kinematic blocking effect that a solid wall exerts on the turbulence through the fluctuating pressure, which is best modeled by an elliptic operator. Above the transition layer, the effect of the original elliptic operator decays rapidly, and it is suggested that the log-layer is better reproduced by adding a non-homogeneous reduction of the return to isotropy, the gradient of the turbulent length scale being used as a measure of the inhomogeneity of the log-layer. The elliptic operator was quite easily applied to the non-linear Craft & Launder pressure-strain model yielding an improved distinction between the spanwise and wall normal stresses, although at higher Reynolds number (Re) and away from the wall, the streamwise component is severely underpredicted, as well as the transition in the mean velocity from the log to the wake profiles. In this area a significant change of behavior was observed in the DNS pressure-strain term, entirely ignored in the models.

Improved detection of soma location and morphology in fluorescence microscopy images of neurons.

PubMed

Kayasandik, Cihan Bilge; Labate, Demetrio

2016-12-01

Automated detection and segmentation of somas in fluorescent images of neurons is a major goal in quantitative studies of neuronal networks, including applications of high-content-screenings where it is required to quantify multiple morphological properties of neurons. Despite recent advances in image processing targeted to neurobiological applications, existing algorithms of soma detection are often unreliable, especially when processing fluorescence image stacks of neuronal cultures. In this paper, we introduce an innovative algorithm for the detection and extraction of somas in fluorescent images of networks of cultured neurons where somas and other structures exist in the same fluorescent channel. Our method relies on a new geometrical descriptor called Directional Ratio and a collection of multiscale orientable filters to quantify the level of local isotropy in an image. To optimize the application of this approach, we introduce a new construction of multiscale anisotropic filters that is implemented by separable convolution. Extensive numerical experiments using 2D and 3D confocal images show that our automated algorithm reliably detects somas, accurately segments them, and separates contiguous ones. We include a detailed comparison with state-of-the-art existing methods to demonstrate that our algorithm is extremely competitive in terms of accuracy, reliability and computational efficiency. Our algorithm will facilitate the development of automated platforms for high content neuron image processing. A Matlab code is released open-source and freely available to the scientific community. Copyright © 2016 Elsevier B.V. All rights reserved.

Evaluation of machine learning algorithms for prediction of regions of high Reynolds averaged Navier Stokes uncertainty

DOE PAGES

Ling, Julia; Templeton, Jeremy Alan

2015-08-04

Reynolds Averaged Navier Stokes (RANS) models are widely used in industry to predict fluid flows, despite their acknowledged deficiencies. Not only do RANS models often produce inaccurate flow predictions, but there are very limited diagnostics available to assess RANS accuracy for a given flow configuration. If experimental or higher fidelity simulation results are not available for RANS validation, there is no reliable method to evaluate RANS accuracy. This paper explores the potential of utilizing machine learning algorithms to identify regions of high RANS uncertainty. Three different machine learning algorithms were evaluated: support vector machines, Adaboost decision trees, and random forests.more » The algorithms were trained on a database of canonical flow configurations for which validated direct numerical simulation or large eddy simulation results were available, and were used to classify RANS results on a point-by-point basis as having either high or low uncertainty, based on the breakdown of specific RANS modeling assumptions. Classifiers were developed for three different basic RANS eddy viscosity model assumptions: the isotropy of the eddy viscosity, the linearity of the Boussinesq hypothesis, and the non-negativity of the eddy viscosity. It is shown that these classifiers are able to generalize to flows substantially different from those on which they were trained. As a result, feature selection techniques, model evaluation, and extrapolation detection are discussed in the context of turbulence modeling applications.« less

An investigation of small scales of turbulence in a boundary layer at high Reynolds numbers

NASA Technical Reports Server (NTRS)

Wallace, James M.; Ong, L.; Balint, J.-L.

1993-01-01

The assumption that turbulence at large wave-numbers is isotropic and has universal spectral characteristics which are independent of the flow geometry, at least for high Reynolds numbers, has been a cornerstone of closure theories as well as of the most promising recent development in the effort to predict turbulent flows, viz. large eddy simulations. This hypothesis was first advanced by Kolmogorov based on the supposition that turbulent kinetic energy cascades down the scales (up the wave-numbers) of turbulence and that, if the number of these cascade steps is sufficiently large (i.e. the wave-number range is large), then the effects of anisotropies at the large scales are lost in the energy transfer process. Experimental attempts were repeatedly made to verify this fundamental assumption. However, Van Atta has recently suggested that an examination of the scalar and velocity gradient fields is necessary to definitively verify this hypothesis or prove it to be unfounded. Of course, this must be carried out in a flow with a sufficiently high Reynolds number to provide the necessary separation of scales in order unambiguously to provide the possibility of local isotropy at large wave-numbers. An opportunity to use our 12-sensor hot-wire probe to address this issue directly was made available at the 80'x120' wind tunnel at the NASA Ames Research Center, which is normally used for full-scale aircraft tests. An initial report on this high Reynolds number experiment and progress toward its evaluation is presented.

An analytically iterative method for solving problems of cosmic-ray modulation

NASA Astrophysics Data System (ADS)

Kolesnyk, Yuriy L.; Bobik, Pavol; Shakhov, Boris A.; Putis, Marian

2017-09-01

The development of an analytically iterative method for solving steady-state as well as unsteady-state problems of cosmic-ray (CR) modulation is proposed. Iterations for obtaining the solutions are constructed for the spherically symmetric form of the CR propagation equation. The main solution of the considered problem consists of the zero-order solution that is obtained during the initial iteration and amendments that may be obtained by subsequent iterations. The finding of the zero-order solution is based on the CR isotropy during propagation in the space, whereas the anisotropy is taken into account when finding the next amendments. To begin with, the method is applied to solve the problem of CR modulation where the diffusion coefficient κ and the solar wind speed u are constants with an Local Interstellar Spectra (LIS) spectrum. The solution obtained with two iterations was compared with an analytical solution and with numerical solutions. Finally, solutions that have only one iteration for two problems of CR modulation with u = constant and the same form of LIS spectrum were obtained and tested against numerical solutions. For the first problem, κ is proportional to the momentum of the particle p, so it has the form κ = k0η, where η =p/m_0c. For the second problem, the diffusion coefficient is given in the form κ = k0βη, where β =v/c is the particle speed relative to the speed of light. There was a good matching of the obtained solutions with the numerical solutions as well as with the analytical solution for the problem where κ = constant.

Rheological characterization of schizophyllan aqueous solutions after denaturation-renaturation treatment.

PubMed

Fang, Yapeng; Takahashi, Rheo; Nishinari, Katsuyoshi

2004-07-01

Schizophyllan (SPG) with a molecular weight of 2.6x10(6), designated SPG-1, is denatured and then renatured at a concentration of 1.8 wt % by alkalization-neutralization. The prepared denatured-renatured samples (DRSPG-1) are diluted to various concentrations and equilibrated for 10 days before rheological and intrinsic viscosity measurements. When concentration (C(p)) is above 0.75 wt %, DRSPG-1 aqueous systems have weak gel-type rheological properties. However, for 0.28 wt %