Manabu Takahashi

Theoretical Evaluation of the Transient Response of Constant Head and Constant Flow-Rate Permeability Tests

A theoretical analysis is presented that compares the response characteristics of the constant head and the constant flow-rate (flow pump) laboratory techniques for quantifying the hydraulic properties of geologic materials having permeabilities less than 10−10 m/s. Rigorous analytical solutions that describe the transient distributions of hydraulic gradient within a specimen are developed, and equations are derived for each method. Expressions simulating the inflow and outflow rates across the specimen boundaries during a constant-head permeability test are also presented. These solutions illustrate the advantages and disadvantages of each method, including insights into measurement accuracy and the validity of using Darcys law under certain conditions. The resulting observations offer practical considerations in the selection of an appropriate laboratory test method for the reliable measurement of permeability in low-permeability geologic materials.

ELECTRONIC STRUCTURE OF C60 SIMPLE CUBIC PHASE BY FULL-POTENTIAL MIXED-BASIS BAND CALCULATION

An electronic structure calculation with full-potential and all-electron ab initio formalism is performed for hypothetical low-temperature simple cubic phases ( and space groups) of C60 molecular crystal, in which every molecule is orientationally freezed. The degeneracies at special k-points, the magnitudes of energy gaps, and the widths of bands have been found to be sensitive to the orientation of the fullerenes in the crystal. Our result suggests that the structure with space group with –22° rotation around [111] directions, which David et al. proposed, is more stable compared to the structure with space group with the same rotation angle.

Site preference of ternary additions in Ni{sub 3}Al

The site preference of a large number of alloying elements in Ni 3 AI (γ′) was studied in a systematic way by using electronic structure calculations based on the local density approximation. Alloying elements in this intermetallic may occupy exclusively the Ni or Al sublattices, or may exhibit no particular site preference. By performing the calculations both for spin-polarized and non-spin-polarized cases, it was found that magnetism strongly affects the computed site substitution behavior of Mn, Fe, and Co in Ni 3 Al. In the case of Fe, for example, a preference for the Ni sublattice is computed when magnetic effects are ignored, but when magnetic effects are accounted for it is found that Fe has no significant site preference, in much better agreement with a large number of experimental determinations. Some trends regarding the site preference across the periodic table are shown and discussed.

Ab initiocalculation of magnetic resonant x-ray scattering spectra in NiO

We investigate the magnetic resonant x-ray scattering spectra around the K edge of Ni in antiferromagnetic NiO using an ab initio band-structure calculation based on the density-functional theory. By taking account of orbital polarization through the spin-orbit interaction, we reproduce well the spectra obtained experimentally, thus demonstrating the usefulness of the ab initio calculation. It is shown that the main-edge peak, which mainly comes from the dipolar (Is→4p) transition, is a direct reflection of the orbital polarization of the 4p states. It is clarified that the 4p orbital polarization is mainly induced from the spin polarization on the 4p states by the spin-orbit interaction. The 3d orbital polarization at neighboring Ni sites gives rise to only a minor contribution to the 4p orbital polarization through a p-d mixing. It is also shown that the pre-edge peak, which mainly originates from the quadrupolar (1s→3d) transition, is a direct reflection of the orbital polarization of the unoccupied 3d states. It shows a Fano-type antiresonant dip due to interference with the nonresonant contribution, in agreement with the experimental result.

Resonant x-ray scattering from chiral materials:α-quartz andα-berlinite

We study the resonant x-ray scattering at Si and Al K-edges from chiral materials,

Ab initiostudy of2pcore-level x-ray photoemission spectra in ferromagnetic transition metals

alpha

Laboratory Measurement of Low-Permeability Rocks With a New Flow Pump System

-quartz and

Hyperfine fields and electronic structures in FeCo and FeNi multilayer systems

alpha

Ab Initio Study of L-edge X-ray Resonant Scattering from Chromium in Spin Density Wave State

-berlinite. We derive the general form of the scattering matrix for the dipole transition by summing up the local scattering matrices which satisfy the symmetry requirement. The oscillation term is obtained in the spectral intensity as a function of azimuthal angle with an expression of possible phase shift. We evaluate the parameters undetermined by the symmetry argument alone on the basis of underlying electronic structures given by the bond-orbital model. The spectra are calculated on forbidden spots

RESONANT X-RAY SCATTERING IN YTiO3 AND YVO3

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