Distribution by Scientific Domains
Distribution within Physics and Astronomy

Kinds of Anisotropy

  • diffusion anisotropy
  • fluorescence anisotropy
  • fractional anisotropy
  • high anisotropy
  • in-plane anisotropy
  • magnetic anisotropy
  • material anisotropy
  • mechanical anisotropy
  • mobility anisotropy
  • optical anisotropy
  • perpendicular magnetic anisotropy
  • polarization anisotropy
  • seismic anisotropy
  • shape anisotropy
  • significant anisotropy
  • soil anisotropy
  • strong anisotropy
  • temperature anisotropy
  • uniaxial anisotropy
  • velocity anisotropy

  • Terms modified by Anisotropy

  • anisotropy effects
  • anisotropy field
  • anisotropy measurement
  • anisotropy ratio
  • anisotropy spectroscopy
  • anisotropy value

  • Selected Abstracts

    The influence of parent material on topsoil geochemistry in eastern England

    B. G. Rawlins
    Abstract The topsoil of around 10 000 km2 in eastern England has recently been sampled intensely at 4609 sites to characterize its geochemistry. The parent materials, which include both solid geology and Quaternary sediments, range in age from Permian to Holocene. The distributions of the concentrations of major and trace elements have been characterized geostatistically, and the role of parent material on their spatial structure (anisotropy) and their spatial relationships (coregionalization) have been investigated. Analysis of variance with the sites grouped by major parent material type showed that this classi,cation accounted for 14 to 48 per cent of the variance for the various elements. Global variograms of 13 elements (Al, As, Ca, Cr, Cu, Fe, Mg, Mo, Ni, P, Pb, Ti, and U) have been computed and modelled. Eleven of the variograms seem to comprise two structures, both of which we modelled with spherical functions, one of short range, 3·5 to 9 km, and the other with a range of 15 to 23 km. The models included a nugget variance, which varied from 27 per cent (for As, Fe, and Mg) to 63 per cent (for P) of the total. The long-range structures are related to the separations of the major parent materials. The variograms of several elements showed appreciable anisotropy, most notably that of Mg. Anisotropy is evident at short ranges of less than 5 km. This accords with the geological structure of the beds which dip from west to east so that their outcrops are elongated from north to south. A linear model of coregionalization ,tted to the data emphasized several important geochemical associations, which we interpret. Elements commonly associated with clay minerals (Mg, Al) and the clay size fraction (Ti) are dominated by the long-range structure of the coregionalization, whilst several trace elements (As, Cr, Ni and U) are spatially correlated with Fe over short distances, through adsorption of the former on the surfaces of Fe oxyhydroxides. The topsoil around large urban areas is enriched in lead, but it is not clear whether anthropogenic sources are responsible for this metal's anomalous spatial relationships with other elements. Crown copyright © 2003. Reproduced with the permission of Her Majesty's Stationery Of,ce. Published by John Wiley & Sons, Ltd. [source]

    Arrays of Electroplated Multilayered Co/Cu Nanowires with Controlled Magnetic Anisotropy

    R. Pirota
    The controlled production of arrays of nanowires exhibiting outstanding characteristics is recently attracting much interest owing to their applications in a number of emerging technologies related with multifunctional biosensor applications, controlled optomagnetic response, magnetic storage, magnetotransport, or catalytic performance. While nanolitography methodes require sophisticated experimental facilities, an alternative technique that makes use of much simpler conventional anodization and electrodeposition methods in the fabrication of metallic nanowires arrays is increasingly employed. This method allows the preparation of arrays of highly-ordered nanopores induced by anodisation, and its filling with metallic elements by electrodepositon. [source]

    Cell Migration: Guided Cell Migration on Microtextured Substrates with Variable Local Density and Anisotropy (Adv. Funct.

    A novel microtextured cell substrate with variable local density and anisotropy as a platform for guided cell migration is presented by A. Levchenko, K.-Y. Suh, et al. on page 1579. A simple, scalable, and cost-effective technique, capillary force lithography, is used to fabricate precise microtopographic features on an optically transparent glass coverslip. Live cell motility is found to be extremely sensitive to variation in the local density and anisotropy of rectangular lattices, with cell elongation and speed decreasing on a symmetric lattice. Cells integrate orthogonal contact guidance cues when determining the direction of their orientation and movement. [source]

    Guided Cell Migration on Microtextured Substrates with Variable Local Density and Anisotropy

    Deok-Ho Kim
    Abstract This work reports the design of and experimentation with a topographically patterned cell culture substrate of variable local density and anisotropy as a facile and efficient platform to guide the organization and migration of cells in spatially desirable patterns. Using UV-assisted capillary force lithography, an optically transparent microstructured layer of a UV curable poly(urethane acrylate) resin is fabricated and employed as a cell-culture substrate after coating with fibronectin. With variable local pattern density and anisotropy present in a single cell-culture substrate, the differential polarization of cell morphology and movement in a single experiment is quantitatively characterized. It is found that cell shape and velocity are exquisitely sensitive to variation in the local anisotropy of the two-dimensional rectangular lattice arrays, with cell elongation and speed decreasing on symmetric lattice patterns. It is also found that cells could integrate orthogonal spatial cues when determining the direction of cell orientation and movement. Furthermore, cells preferentially migrate toward the topographically denser areas from sparser ones. Consistent with these results, it is demonstrated that systematic variation of local densities of rectangular lattice arrays enable a planar assembly of cells into a specified location. It is envisioned that lithographically defined substrates of variable local density and anisotropy not only provide a new route to tailoring the cell-material interface but could serve as a template for advanced tissue engineering. [source]

    Spectral-element simulations of global seismic wave propagation,II.

    Three-dimensional models, oceans, rotation, self-gravitation
    Summary We simulate global seismic wave propagation based upon a spectral-element method. We include the full complexity of 3-D Earth models, i.e. lateral variations in compressional-wave velocity, shear-wave velocity and density, a 3-D crustal model, ellipticity, as well as topography and bathymetry. We also include the effects of the oceans, rotation and self-gravitation in the context of the Cowling approximation. For the oceans we introduce a formulation based upon an equivalent load in which the oceans do not need to be meshed explicitly. Some of these effects, which are often considered negligible in global seismology, can in fact play a significant role for certain source,receiver configurations. Anisotropy and attenuation, which were introduced and validated in a previous paper, are also incorporated in this study. The complex phenomena that are taken into account are introduced in such a way that we preserve the main advantages of the spectral-element method, which are an exactly diagonal mass matrix and very high computational efficiency on parallel computers. For self-gravitation and the oceans we benchmark spectral-element synthetic seismograms against normal-mode synthetics for the spherically symmetric reference model PREM. The two methods are in excellent agreement for all body- and surface-wave arrivals with periods greater than about 20 s in the case of self-gravitation and 25 s in the case of the oceans. At long periods the effect of gravity on multiorbit surface waves up to R4 is correctly reproduced. We subsequently present results of simulations for two real earthquakes in fully 3-D Earth models for which the fit to the data is significantly improved compared with classical normal-mode calculations based upon PREM. For example, we show that for trans-Pacific paths the Rayleigh wave can arrive more than a minute earlier than in PREM, and that the Love wave is much shorter in duration. [source]

    A laboratory study of seismic velocity and attenuation anisotropy in near-surface sedimentary rocks

    Angus I. Best
    ABSTRACT The laboratory ultrasonic pulse-echo method was used to collect accurate P- and S-wave velocity (±0.3%) and attenuation (±10%) data at differential pressures of 5,50 MPa on water-saturated core samples of sandstone, limestone and siltstone that were cut parallel and perpendicular to the vertical borehole axis. The results, when expressed in terms of the P- and S-wave velocity and attenuation anisotropy parameters for weakly transversely isotropic media (,, ,, ,Q, ,Q) show complex variations with pressure and lithology. In general, attenuation anisotropy is stronger and more sensitive to pressure changes than velocity anisotropy, regardless of lithology. Anisotropy is greatest (over 20% for velocity, over 70% for attenuation) in rocks with visible clay/organic matter laminations in hand specimens. Pressure sensitivities are attributed to the opening of microcracks with decreasing pressure. Changes in magnitude of velocity and attenuation anisotropy with effective pressure show similar trends, although they can show different signs (positive or negative values of ,, ,Q, ,, ,Q). We conclude that attenuation anisotropy in particular could prove useful to seismic monitoring of reservoir pressure changes if frequency-dependent effects can be quantified and modelled. [source]

    Understanding the Impacts of Anisotropy on the Extent of Drawdown

    GROUND WATER, Issue 4 2010
    Ty P.A. Ferré
    No abstract is available for this article. [source]

    Cover Picture: Anisotropy and Dynamic Ranges in Effective Properties of Sheared Nematic Polymer Nanocomposites (Adv. Funct.

    Abstract Forest and co-workers report on p.,2029 that nematic polymer nanocomposite (NPNC) films can be processed in steady shear flows, which generate complex orientational distributions of the nanorod inclusions. Distribution functions for a benchmark NPNC (11,vol.-% of 1,nm,×,200,nm rods) are computed for a range of shear rates, yielding a bifurcation diagram with steady states at very low (logrolling) and high (flow-aligning) shear rates, and limit cycles (tumbling, wagging, kayaking) at intermediate shear rates. The orientational distributions dictate the effective conductivity tensor of the NPNC film, which is computed for all distribution functions, and extract the maximum principal conductivity enhancement (Emax, averaged in time for periodic distributions) relative to the matrix. The result is a "property bifurcation diagram" for NPNC films, which predicts an optimal shear rate that maximizes Emax. Nematic, or liquid-crystalline, polymer nanocomposites (NPNCs) are composed of large aspect ratio, rod-like or platelet, rigid macromolecules in a matrix or solvent, which itself may be aqueous or polymeric. NPNCs are engineered for high-performance material applications, ranging across mechanical, electrical, piezoelectric, thermal, and barrier properties. The rods or platelets possess enormous property contrasts relative to the solvent, yet the composite properties are strongly affected by the orientational distribution of the nanophase. Nematic polymer film processing flows are shear-dominated, for which orientational distributions are well known to be highly sensitive to shear rate and volume fraction of the nematogens, with unsteady response being the most expected outcome at typical low shear rates and volume fractions. The focus of this article is a determination of the ranges of anisotropy and dynamic fluctuations in effective properties arising from orientational probability distribution functions generated by steady shear of NPNC monodomains. We combine numerical databases for sheared monodomain distributions[1,2] of thin rod or platelet dispersions together with homogenization theory for low-volume-fraction spheroidal inclusions[3] to calculate effective conductivity tensors of steady and oscillatory sheared mesophases. We then extract maximum scalar conductivity enhancement and anisotropy for each type of sheared monodomain (flow-aligned, tumbling, kayaking, and chaotic). [source]

    Correlating Nanomorphology with Charge-Transport Anisotropy in Conjugated-Polymer Thin Films,

    ADVANCED MATERIALS, Issue 29 2009
    Yi-Fang Huang
    Anisotropic mobility in spin-coated MEH-PPV films is due to an interfacial layer of several nanometers at the film-substrate interface with a higher electron density assisted by local chain alignment parallel to the substrate. This layer is formed via spin-coating. The strength of this interface effect is dependent on the solvent used. [source]

    Luminescent Conjugated Polymer Nanowire Y-Junctions with On-Branch Molecular Anisotropy

    ADVANCED MATERIALS, Issue 10-11 2009
    Deirdre O'Carroll
    Polyfluorene nanowire Y-junctions synthesized by solution-assisted template wetting are shown to exhibit strongly polarized light emission from the branches and stems. It is demonstrated that the Y-junctions can be positioned, and branching angles may be adjusted, by micromanipulation. Nanowire junctions of this type could ultimately facilitate the incorporation of conjugated polymer materials into highly integrated electronic and photonic circuits and systems. [source]

    Anisotropy of magnetic susceptibility and petrofabric studies in the Garhwal synform, Outer Lesser Himalaya: Evidence of pop-up klippen

    ISLAND ARC, Issue 3 2009
    Upasana Devrani
    Abstract Geological field, petrographic, and anisotropy of magnetic susceptibility studies help in understanding the evolutionary history of the Garhwal synform that lies in the western Outer Lesser Himalaya. Orientations of the magnetic susceptibility axes reveal large variations at short distances as a result of superimposed deformation, and predominant stress conditions favorable for normal faulting. Rocks forming the outer limbs of the Garhwal Synform are metamorphosed up to the lower greenschist facies. The metamorphic grade increases to chlorite zone in the inner limb and the core is characterized by chlorite,biotite to garnet zones. The different grades of metamorphism are separated by thrusts and the structure is described as a pop-up klippen. [source]

    Lack of Effect of Conduction Direction on Action Potential Durations in Anisotropic Ventricular Strips of Pig Heart

    Anisotropy and Repolarization.Introduction: The influence of activation sequence on the rate of rise of the depolarization phase of action potentials in atrial or ventricular muscles has been well established. However, whether myocardial fiber orientation is important in modulating the repolarization process is unclear. Methods and Results: We examined the influence of activation sequence on the repolarization phase of action potentials in epicardial tissues from the right and left ventricles of domestic pigs. Whereas cells from the right ventricle exhibited direction-dependent differences in action potential duration at 30%, 50%, and 90% of full repolarization (190.6 ± 31.1 msec vs 181.8 ± 32.8 msec, 240.3 ± 23.5 msec vs 236.7 ± 25.4 msec, and 291.3 ± 23.7 msec vs 287.4 ± 25.1 msec for longitudinal and transverse propagation, respectively; P < 0.001), a similar duration of repolarization during both directions of propagation was observed in cells from the left ventricle at 50% and 90% of full repolarization (241.4 ± 39.4 msec and 285.5 ± 39.5 msec vs 240.4 ± 38.9 msec and 284.9 ± 39.6 msec for longitudinal and transverse propagation respectively; P = NS). A slight but significant difference was found at 30% of full repolarization in cells from the left ventricle (190.4 ± 39.0 msec vs 187.0 ± 38.0 msec for longitudinal and transverse propagation, respectively; P < 0.05). In the left ventricle, the duration of repolarization did not change as the distance between the recording site and stimulation site increased. Conclusion: The direction of wavefront propagation with respect to fiber orientation may not play an important role in modulating the duration of repolarization in epicardial cells from the left ventricle. [source]

    Anisotropy in high angular resolution diffusion-weighted MRI ,

    Lawrence R. Frank
    Abstract The diffusion in voxels with multidirectional fibers can be quite complicated and not necessarily well characterized by the standard diffusion tensor model. High angular resolution diffusion-weighted acquisitions have recently been proposed as a method to investigate such voxels, but the reconstruction methods proposed require sophisticated estimation schemes. We present here a simple algorithm for the identification of diffusion anisotropy based upon the variance of the estimated apparent diffusion coefficient (ADC) as a function of measurement direction. The rationale for this method is discussed, and results in normal human subjects acquired with a novel diffusion-weighted stimulated-echo spiral acquisition are presented which distinguish areas of anisotropy that are not apparent in the relative anisotropy maps derived from the standard diffusion tensor model. Magn Reson Med 45:935,939, 2001. Published 2001 Wiley-Liss, Inc. [source]

    Anisotropy of spin relaxation of water protons in cartilage and tendon

    NMR IN BIOMEDICINE, Issue 3 2010
    Konstantin I. Momot
    Abstract Transverse spin relaxation rates of water protons in articular cartilage and tendon depend on the orientation of the tissue relative to the applied static magnetic field. This complicates the interpretation of magnetic resonance images of these tissues. At the same time, relaxation data can provide information about their organisation and microstructure. We present a theoretical analysis of the anisotropy of spin relaxation of water protons observed in fully hydrated cartilage. We demonstrate that the anisotropy of transverse relaxation is due almost entirely to intramolecular dipolar coupling modulated by a specific mode of slow molecular motion: the diffusion of water molecules in the hydration shell of a collagen fibre around the fibre, such that the molecular director remains perpendicular to the fibre. The theoretical anisotropy arising from this mechanism follows the ,magic-angle' dependence observed in magnetic-resonance measurements of cartilage and tendon and is in good agreement with the available experimental results. We discuss the implications of the theoretical findings for MRI of ordered collagenous tissues. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Protein Matrix Elasticity Determined by Fluorescence Anisotropy of Its Tryptophan Residues,

    Christian Zentz
    ABSTRACT Rotational motions of Trp residues embedded within human hemoglobin matrix have been measured by using their steady-state fluorescence anisotropy. The mean square angular displacement ,2 of Trp residues, depending on the temperature, can be expressed by where W is the thermal energy acting on the Trp residues and C the resilient torque constant of the protein matrix. To study the external medium influencing the protein dynamics, comparative experiments were made with protein in aqueous buffer and in the presence of 32% glycerol. The data show that between 5°C and 25°C, external medium acts on the protein matrix elasticity. [source]

    Wet chemical etching behavior of ,-Ga2O3 single crystal

    Shigeo Ohira
    Abstract Wet chemical etching behavior of ,-Ga2O3 single crystal was investigated to evaluate its chemical stability and to explore etchants for ,-Ga2O3 single crystal. Undoped and Sn-doped ,-Ga2O3 single crystals were grown by the floating zone method, and (100)- and (001)-oriented samples were chemical-mechanical-polished to wafers. The samples were wet chemically etched in solutions such as HCl, H2SO4, HNO3, HF, H2O2:H2SO4:H2O=1:4:1, KOH, and NaOH. The samples were chemically stable against both acids and alkalis except HF and NaOH. Aqueous HF solution was found to etch ,-Ga2O3 uniformly at room temperature. The etch rate increased with increasing immersion time and HF content. Anisotropy of etch rate was observed between the (100) and (001) planes. The etch rate of Sn-doped ,-Ga2O3 was lower than that of undoped ,-Ga2O3, and the etch rate decreased with increasing Sn doping content. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Anisotropy of magnetization and magnetoresistance of (Zn,Co)O films grown by pulsed laser deposition

    J. W. Lee
    Abstract We report the anisotropy in magnetic and magneto-transport properties of c - and a -plane Zn1,xCoxO (x = 0.05, 0.1 and 0.15) thin films grown on c - or r -surface sapphire by PLD technique. The magnetization and magnetoresistance (MR) measurements were performed with magnetic fields parallel or perpendicular to the film plane. It was found that both the c - and a -plane films were paramagnetic down to the lowest temperature of 2K. The magnitudes of the magnetization and the positive MR were larger under magnetic fields along a - or b -axis than along c -axis for both the c - or a -plane films. These anisotropic behaviours are interpreted as intrinsic properties originating from Co2+ spins substituting the Zn site in ZnO. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Anisotropy of the ,-point effective mass and mobility in hexagonal InN

    T. Hofmann
    Abstract We determine the anisotropic electron effective mass and mobility parameters in wurtzite InN thin films with free electron concentration N from 1.8 × 1017 cm,3 to 9.5 × 1018 cm,3 using Infrared Magneto-optic Generalized Ellipsometry. The room-temperature measurements were carried out with magnetic fields up to 4.5 T. For the ,-point we estimate m*, = 0.047m0 and m*, = 0.039m0 for polarization perpendicular and parallel to the c -axis, respectively. Scattering by impurities or ionized donors may explain the decrease of mobility for polarization parallel to the c -axis from 1600 cm2/(Vs) to 800 cm2/(Vs) with increase in N , where the perpendicular mobility is further decreased, likely caused by additional grain boundary scattering. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Size, shape and intensity of aggregation of take-all disease during natural epidemics in second wheat crops

    PLANT PATHOLOGY, Issue 1 2007
    M. Gosme
    Point pattern analysis (fitting of the beta-binomial distribution and binary form of power law) was used to describe the spatial pattern of natural take-all epidemics (caused by Gaeumannomyces graminis var. tritici) on a second consecutive crop of winter wheat in plots under different cropping practices that could have an impact on the quantity and spatial distribution of primary inoculum, and on the spread of the disease. The spatial pattern of take-all was aggregated in 48% of the datasets when disease incidence was assessed at the plant level and in 83% when it was assessed at the root level. Clusters of diseased roots were in general less than 1 m in diameter for crown roots and 1,1·5 m for seminal roots; when present, clusters of diseased plants were 2,2·5 m in diameter. Anisotropy of the spatial pattern was detected and could be linked to soil cultivation. Clusters did not increase in size over the cropping season, but increased spatial heterogeneity of the disease level was observed, corresponding to local disease amplification within clusters. The relative influences of autonomous spread and inoculum dispersal on the size and shape of clusters are discussed. [source]

    Anisotropy in the electrical behavior of immiscible polypropylene/nylon/carbon black blends processed slightly below the melting temperature of the nylon

    J. Zoldan
    Carbon black (CB) containing polypropylene/nylon (PP/Ny) blends, processed slightly below the melting temperature (Tm) of the dispersed Ny phase, leads to formation of fibrillar Ny phase and electrically anisotropic systems. CB containing PP/Ny blends were compounded (twin screw extruder) and processed (injection molding) slightly below the Tm of dispersed Ny phase at different blending sequences. To establish structure,property relationships scanning electron microscopy, high resolution scanning electron microscopy, differential scanning calorimeter were used and electrical properties were also studied. Addition of CB to binary PP/Ny blends, processed below the Ny Tm, altered the Ny fibrillation process forming an irregular continuous phase, containing the CB particles, rather than the fibrils formed in the PP/Ny blends. Yet, upon changing the processing sequence, i.e., compounding PP and CB and then adding Ny in the injection molding stage, Ny fibrils were attained, maintaining phase continuity, oriented in the flow direction and CB particles preferentially located on their surfaces. Blends exhibiting a fibrillar Ny network covered by CB particles exhibited electrical anisotropy. The Ny fibrils exhibited an additional higher crystalline melting peak and molecular orientation. The composites are conductive in the Ny fibril direction, while insulating in the perpendicular direction. Once the CB is located within both, the Ny and the PP matrix the electrical behavior is isotropic. POLYM. ENG. SCI., 46:1250,1262, 2006. © 2006 Society of Plastics Engineers [source]

    Anisotropy in optical transmittance and molecular chain orientation of silver- dispersed uniaxially drawn polyimide films

    Sho-ichi Matsuda
    Abstract The anisotropy in optical transmittance in the visible and near-infrared region observed for uniaxially drawn and silver-dispersed polyimide (PI) films was investigated. The films were prepared in a one-step operation that consists of thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films dissolving 5.7,,,20 mol% of silver nitrate. The PAA was converted to PI by heating, and the PI chains were orientated along the drawing direction during curing. Silver nanoparticles were precipitated in the films when they were cured in air and under nitrogen. In particular, silver nanoparticles aggregated along drawing direction and spheroidal nanoparticles (size of longer axis: 10,25,nm, aspect ratio: ca. 1.5) were observed in the films cured in air, and distinct anisotropy in optical transmittance was observed. The maximum optical anisotropy was obtained with a specific holding time at the final curing temperature (320,°C). In addition, the anisotropy can be controlled by polymer chain orientation when films are cured with the optimal holding time. In optimized preparing conditions, anisotropies in transmittance larger than 500,:,1 were obtained at the wavelengths between 700 and 900,nm, and its optical properties were retained after annealing at 150,°C for 1,hr. The PI films thus obtained can be used as thermally stable thin-film polarizers. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Probing Vibrational Anisotropy with Nuclear Resonance Vibrational Spectroscopy,

    ANGEWANDTE CHEMIE, Issue 26 2010
    Sondierung der Lage: Eine resonanzschwingungsspektroskopische Einkristallstudie lieferte detaillierte Informationen zu den In-Plane-Schwingungen eines Nitrosyl-Eisenporphyrinats, [Fe(oep)(NO)] (siehe Bild; oep=Octaethylporphyrin). Der axiale Nitrosyl-Ligand bestimmt die Richtung der In-Plane-Bewegung des Eisenzentrums. [source]

    Ionothermal Synthesis of Extra-Large-Pore Open-Framework Nickel Phosphite 5,H3O,[Ni8(HPO3)9Cl3],1.5,H2O: Magnetic Anisotropy of the Antiferromagnetism,

    ANGEWANDTE CHEMIE, Issue 13 2010
    Hongzhu Xing
    Mikroporöse Magnete: Die Struktur der Titelverbindung (siehe Einschub) weist zweidimensionale Nickel-Sauerstoff/Chlorid-18-Ring-Schichten auf, die entlang der c -Achse gestapelt und durch HPO3 -Einheiten verknüpft sind. Nach Messungen der magnetischen Anisotropie an ausgerichteten Einkristallen (siehe Graph) ist die leichte magnetische Achse senkrecht zur Schichtebene. [source]

    Building anisotropic sampling schemes for the estimation of anisotropic dispersal

    S. Soubeyrand
    Abstract Anisotropy, a structural property of dispersal, is observed in dispersal patterns occurring for a wide range of biological systems. While dispersal models more and more often incorporate anisotropy, the sampling schemes required to collect data for validation usually do not account for the anisotropy of dispersal data. Using a parametric model already published to describe the spatial spread of a plant disease, the wheat yellow rust, we carry out a study aimed at recommending an appropriate sampling scheme for anisotropic data. In a first step, we show with a simulation study that prior knowledge of dispersal anisotropy can be used to improve the sampling scheme. One of the main guidelines to be proposed is the orientation of the sampling grid around the main dispersal directions. In a second step, we propose a sequential sampling procedure (SSP) used to automatically build anisotropic sampling schemes adapted to the actual anisotropy of dispersal. The SSP is applied to simulated and real data. The proposed methodology is expected to be adapted easily to any kind of organisms with wind-borne propagule dispersal because it does not require the inclusion of biological features specific of the considered organism. [source]

    Anisotropy and rotation in homeoidally striated Jacobi ellipsoids

    R. Caimmi
    Abstract In this paper a unified theory of systematically rotating and peculiar motions is developed for homeoidally striated Jacobi ellipsoids, where both real and imaginary rotations are considered. The effect of positive or negative residual motion excess along the equatorial plane is considered to be equivalent either to an additional real or an imaginary rotation, respectively. The principle results consist of (i) the discovery that homeoidally striated Jacobi ellipsoids always admit an adjoint configuration i.e. a classical Jacobi ellipsoid of equal mass and axes; (ii) the establishment of further constraints on the amount of residual velocity anisotropy along the principal axes for triaxial configurations; (iii) the finding that bifurcation points from axisymmetric to triaxial configurations occur as in classical Jacobi ellipsoids, contrary to earlier findings. An interpretation of recent results from numerical simulations on stability is provided in the light of the model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Vp/Vs Anisotropy and Implications for Crustal Composition Identification and Earthquake Prediction

    Qian WANG
    Abstract: The ratio of P- to S-wave velocities (Vp/Vs) is regarded as one of the most diagnostic properties of natural rocks. It has been used as a discriminant of composition for the continental crust and provides valuable constraints on its formation and evolution processes. Furthermore, the spatial and temporal changes in Vp/Vs before and after earthquakes are probably the most promising avenue to understanding the source mechanics and possibly predicting earthquakes. Here we calibrate the variations in Vp/Vs in dry, anisotropic crustal rocks and provide a set of basic information for the interpretation of future seismic data from the Wenchuan earthquake Fault zone Scientific Drilling (WFSD) project and other surveys. Vp/Vs is a constant (,0) for an isotropic rock. However, most of crustal rocks are anisotropic due to lattice-preferred orientations of anisotropic minerals (e.g., mica, amphibole, plagioclase and pyroxene) and cracks as well as thin compositional layering. The Vp/Vs ratio of an anisotropic rock measured along a selected pair of propagation-vibration directions is an apparent value (,ij) that is significantly different from the value for its isotropic counterpart (,0). The usefulness of apparent Vp/Vs ratios as a diagnostic of crustal composition depends largely on rock seismic anisotropy. A 5% of P- and S-wave velocity anisotropy is sufficient to make it impossible to determine the crustal composition using the conventional criteria (Vp/Vs,1.756 for felsic rocks, 1.7561.944 fluid-filled porous/fractured or partially molten rocks) if the information about the wave propagation-polarization directions with respect to the tectonic framework is unknown. However, the variations in Vp/Vs measured from borehole seismic experiments can be readily interpreted according to the orientations of the ray path and the polarization of the shear waves with respect to the present-day principal stress directions (i.e., the orientation of cracks) and the frozen fabric (i.e., foliation and lineation). [source]

    Anisotropy in the Anodic Oxidation of Silicon in KOH Solution.

    CHEMINFORM, Issue 48 2005
    Harold G. G. Philipsen
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Anisotropy in Magnetic and Transport Properties of GdCrSb3.

    CHEMINFORM, Issue 46 2004
    D. D. Jackson
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    White matter changes in extremely preterm infants, a population-based diffusion tensor imaging study

    ACTA PAEDIATRICA, Issue 6 2010
    Béatrice Skiöld
    Abstract Aim:, To investigate cerebral white matter (WM) abnormalities (J Pediatr 2003; 143: 171) and diffuse and excessive high signal intensities (DEHSI), (J Pediatr 1999; 135: 351) in a cohort of extremely preterm infants born in Stockholm during a 3-year period, using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). Methods:, MRI at term-equivalent age was performed in 109 infants and DTI data were acquired in 54 infants. Survival rate in the entire cohort was 67%. Sixteen term-born healthy control infants were scanned for comparison. Results:, No or mild WM abnormalities were seen in 86% of infants and 14% had moderate or severe WM abnormalities. DEHSI were seen in infants with all grades of white matter abnormalities and were present in 56% of infants. In the WM at the level of centrum semiovale, infants with any WM abnormalities or DEHSI had lower Fractional Anisotropy and higher Apparent Diffusion Coefficient compared with control infants. No significant differences in diffusion were seen in infants without DEHSI compared with the controls in this region. Compared with controls, the preterm infants had significantly altered diffusion in the corpus callosum. Conclusion:, Only 14% of the extremely preterm infants had moderate or severe WM abnormalities on MRI. However, the incidence of DEHSI was high. In the DEHSI regions, changes in diffusion parameters were detected, indicating altered WM organization. [source]

    How to Build Molecules with Large Magnetic Anisotropy

    Jordi Cirera Dr.
    Abstract Predicting single-molecule magnets? Magnetic anisotropy, a property that plays a key role in single-molecule magnets (SMMs), has been analyzed by using theoretical methods. Mononuclear complexes and the dependence of the magnetic anisotropy on their geometrical and electronic structure, as well as how such mononuclear complexes must be combined as building blocks to obtain polynuclear complexes with large anisotropy (see figure) are considered. The magnetic anisotropy of mononuclear transition-metal complexes has been studied by means of electronic structure calculations based on density functional theory. The variation of the zero-field splitting (ZFS) parameters has been analyzed for the following characteristic distortions: a tetragonal Jahn,Teller distortion, the Bailar twist, the Berry pseudorotation, and the planarization of tetrahedral complexes. Finally, the coupling of mononuclear building blocks in polynuclear complexes to obtain a large negative magnetic anisotropy necessary to improve their single-molecule-magnet (SMM) behavior has been studied. [source]