Anisotropic electron spin lifetime in( In , Ga ) As ∕ Ga As
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Anisotropic electron spin lifetimes in strained undoped $(\mathrm{In},\mathrm{Ga})\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ (110) quantum wells of different widths and heights are investigated by time-resolved Faraday rotation and time-resolved transmission and are compared to the (001) orientation. From the suppression of spin precession as a function of transverse magnetic fields, the ratio of in-plane to out-of-plane spin lifetimes is calculated. While the ratio increases with In concentration in agreement with theory, an unprecedented high anisotropy of 480 is observed for the broadest quantum well at the low In concentration, when expressed in terms of spin relaxation times.Cite
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ABSTRACT An account is given of the use of the square array technique in investigating the surface effects of rotational anisotropy when the axes of anisotropy are inclined to the surface. It is shown that, as with other arrays, two anisotropy parameters and n can be derived by varying the array orientation. On the basis of these considerations, the effects of such anisotropy on the values of the mean apparent resistivity and azimuthal inhomogeneity ratio normally obtained in square array measurements is reviewed. Particular attention is paid to the variation of resistivity with orientation and it is noted that, in areas of moderate anisotropy, this variation is lower for the square than for the Schlumberger array. In addition to this advantage, the azimuthal inhomogeneity ratio obtained from square array measurements may be used to indicate the severity of anisotropy in an area and two field examples of this use are given. Where anisotropy is severe, gross variations of apparent resistivity with orientation are obtained with either square or collinear arrays. In these circumstances, the use of crossed measurements is considered and the particular stability of the crossed square array demonstrated.
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The structural anisotropy of open-cell foam leads to the anisotropy of effective thermal conductivity (ETC). To quantitatively analyze the effect of structural anisotropy on the anisotropy of ETC, a new predicting model for the ETC of anisotropic open-cell foam was proposed based on an anisotropy tetrakaidecahedron cell (ATC). Feret diameters in three orthogonal directions obtained by morphological analysis of real foam structures were used to characterize the anisotropy of ATC. To validate our proposed anisotropic model, the ETCs of real foam structures in three orthogonal directions predicted by it were compared with the numerical results, for which the structures of numerical models are reconstructed by X-ray computed tomography (X-CT). Using the present anisotropic model, the influences of the thermal conductivity ratio (TCR) and porosity of the foams on the anisotropic ratios of ETCs are also investigated. Results show that there is good consistency between the ETCs obtained by the anisotropic model and the numerical method. The maximum relative errors between them are 2.84% and 13.57% when TCRs are 10 and 100, respectively. The present anisotropic model can not only predict the ETCs in different orthogonal directions but also quantitatively predict the anisotropy of ETC. The anisotropies of the ETCs decrease with porosity because the proportion of the foam skeleton decreases. However, the anisotropies of ETCs increase with TCR, and there exist asymptotic values in anisotropic ratios of ETCs as TCR approaches infinity and they are equal to the relative Feret diameters in different orthogonal directions.
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Decisions on positioning of monitoring wells in the vicinity of hazardous waste sites can be significantly affected by knowledge of the natural anisotropic hydraulic conductivity. That the vertical permeability is usually less than the horizontal permeability is well known: however, the anisotrophy in the horizontal plane may influence the choice of positions for those monitoring wells that are downgradient from the waste-management area. Very little information on the horizontal anisotropy is available. Furthermore, field measurements to estimate the horizontal anisotropy are expensive because at least three interacting wells are necessary, with more than three being preferred. The Kozeny equation suggests that directional anisotropy of the electrical conductivity of a porous media should correlate closely with the anisotropy of the permeability [S. J. Pirson, Geological Well Log Analysis (Gulk Publ. Co., 1981), p. 135]. A close relationship should also exist between the acoustic anisotropy and the anisotropy of the permeability. Recent advances in techniques for measuring acoustic velocities in a borehole make it feasible to obtain estimates of the anisotropy of the permeability from observations of the anistropy of the seismic velocities. [Work supported by EPA.]
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This chapter contains sections titled: Introduction Anisotropy in Cubic Crystals Anisotropy in Hexagonal Crystals Physical Origin of Crystal Anisotropy Anisotropy Measurement Anisotropy Measurement (from Magnetization Curves) Anisotropy Constants Polycrystalline Materials Anisotropy in Antiferromagnetics Shape Anisotropy Mixed Anisotropies Problems
Magnetocrystalline anisotropy
Crystal (programming language)
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Crystal (programming language)
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The tri-axial (or multi-component) induction log is used to measure not only the resistivity anisotropy of an anisotropic formation but also the relative dip of the tool with respect to the formation. When the tri-axial induction log is run at multiple frequencies, multi-frequency focusing can be applied to the measurements. The apparent dip and the apparent anisotropy are algebraically deflned from the frequency-focused tri-axial induction measurements. The apparent dip gives the true dip in thinly bedded formations, but a smaller dip than the true dip in a thick anisotropic bed when the anisotropy is small (the anisotropy efiect). The apparent anisotropy gives the true anisotropy in thick anisotropic formations but is afiected by the shoulder bed anisotropy when the formation is not thick (the shoulder bed efiect).
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Intensity
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Abstract Seismic anisotropy usually arises from different mechanisms, which include lattice or crystallographic preferred orientation (LPO, CPO), alignment of cracks with or without fluid inclusions, fine layering, or partial melting. This makes the interpretation of anisotropy in terms of “intrinsic” (produced by LPO, CPO) versus “extrinsic” (produced by other mechanisms) properties difficult and nonunique. The radial anisotropy in the one‐dimensional, global spherically symmetric reference Earth is usually claimed to be intrinsic. Here we explore whether the radial anisotropy in one‐dimensional reference Earth models including preliminary reference Earth model (PREM) and the constrained reference Earth model ACY400 contains extrinsic anisotropy, especially in relation to fine layering. We conclude that as well as intrinsic anisotropy, extrinsic anisotropy introduced by finely layered models, can be considered to explain the lithospheric anisotropy in PREM, but cannot explain alone its asthenospheric anisotropy. We also find that radial anisotropy in model ACY400 is mainly intrinsic due to its petrological constraints.
Layering
Magnetocrystalline anisotropy
Seismic anisotropy
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