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Lili Li - One of the best experts on this subject based on the ideXlab platform.

  • determining the Bravais Lattice using a single electron backscatter diffraction pattern
    Journal of Applied Crystallography, 2015
    Co-Authors: Lili Li
    Abstract:

    The ab initio derivation of the Bravais Lattice from the Kikuchi bands detected from a single electron backscatter diffraction (EBSD) pattern is successfully performed. The as-measured band widths and azimuths always suffer from gnomonic distortions which need to be corrected. A primitive reciprocal cell is first reconstructed by means of the corrected data and the cell parameters are then refined by least-squares analysis of hugely over-determined equations. This allows one to further derive a Niggli reduced cell from the primitive cell. The algorithm presented is not related to any crystal symmetry information and is therefore applicable to all crystal systems. The feasibility of the determination of the Bravais Lattice type and parameters from a single EBSD pattern is demonstrated using a mineral sample without any a priori information about its crystal structure. The novel application developed in the present work opens the way to the determination of the Bravais Lattice of crystalline materials using scanning electron microscopy combined with the EBSD technique.

Tetsuo Mohri - One of the best experts on this subject based on the ideXlab platform.

  • conversion of magnetic freedoms into atomic configurational freedoms within the cluster variation method
    Materials Transactions, 2019
    Co-Authors: Ryo Yamada, Tetsuo Mohri
    Abstract:

    The continuous displacement cluster variation method (CDCVM) has introduced local atomic displacements into the theoretical framework of the cluster variation method (CVM) by viewing an atom displaced from a Bravais Lattice point as a particular atomic species located at the Lattice point. This idea of conversion from a freedom of local displacements into configurational freedom is extended in this paper to magnetic freedoms. Various magnitudes of local magnetic moments are considered, as well as two spin directions, on up-spins and down-spins. The approach is applied to pure Ni and its Curie temperature is explored with the entropy formula of the tetrahedron approximation in the CVM, using the first-nearest-neighbor pair interaction energies extracted from the total energies of various spin configurations, which are estimated from electronic-structure calculations.

  • theoretical investigation of alloy phase equilibria by continuous displacement cluster variation method
    Solid State Phenomena, 2011
    Co-Authors: Tetsuo Mohri
    Abstract:

    Continuous Displacement Cluster Variation Method is employed to study binary phase equilibria on the two dimensional square Lattice with Lennard-Jones type pair potentials. It is confirmed that the transition temperature decreases significantly as compared with the one obtained by conventional Cluster Variation Method. This is ascribed to the distribution of atomic pairs in a wide range of atomic distance, which enables the system to attain the lower free energy. The spatial distribution of atomic species around a Bravais Lattice point is visualized. Although the average position of an atom is centred at the Bravais Lattice point, the maximum pair probability is not necessarily attained for the pairs located at the neighboring Bravais Lattice points. In addition to the real space information, k-space information are calculated in the present study. Among them, the diffuse intensity spectra due to short range ordering and atomic displacement are discussed.

  • theoretical investigation of phase equilibria by the continuous displacement cluster variation method
    International Journal of Materials Research, 2009
    Co-Authors: Tetsuo Mohri
    Abstract:

    Abstract By employing the continuous displacement cluster variation method, order – disorder transition behavior of a two-dimensional square Lattice is investigated. It is demonstrated that the distribution of displaced atoms around a Bravais Lattice point continuously changes with temperature. The additional freedom of atomic displacement contributes to the entropy and thermal Lattice expansion is confirmed. Finally, it is shown that the order – disorder transition temperature decreases as compared with the one by the conventional cluster variation method in which no local atomic displacements are allowed.

  • theoretical study of glass transition based on cluster variation method
    Materials Science Forum, 2007
    Co-Authors: Tetsuo Mohri, Yoshitaka Kobayashi
    Abstract:

    Modeling of Glass transition is attempted based on the Cluster Variation Method. Free energy functional of an L10 ordered phase is employed to describe the first order nature of the transition. Free energy contour surface calculated as a function of temperature and an order parameter which simulates an amount of defects provides a generalized stability diagram in which the ideal glass transition temperature is identified as a critical point. Transition kinetics is investigated by Path Probability Method which is the kinetics version of the CVM to time domain. Continuous cooling behavior is calculated by explicitly incorporating the temperature dependent viscosity term based on VFT (Vogel-Fulcher-Tamman) formula. The glass transition is realized as the freezing of the order parameter due to the enhanced viscosity. The extension of the present theoretical scheme to non-Bravais Lattice is attempted by Continuous Cluster Variation Method.

K. Niizeki - One of the best experts on this subject based on the ideXlab platform.

  • The space groups of orthorhombic approximants to the icosahedral quasiLattice
    Journal of Physics A: General Physics, 1992
    Co-Authors: K. Niizeki
    Abstract:

    The space groups of the orthorhombic approximant Lattices\nto the primitive icosahedral quasiLattice are classified.\nThere exist three Bravais classes: Pmmm, Cmmm and Immm. The\nbasis vectors of the Bravais Lattice of an approximant are\nparallel to two-, three- and/or fivefold axes of the\nquasiLattice. It is found that there exist many\nnon-symmorphic space groups with a common Bravais Lattice\nin addition to symmorphic ones. This is because glides\ncommonly appear.

Howard D Flack - One of the best experts on this subject based on the ideXlab platform.

  • Methods of space-group determination - a supplement dealing with twinned crystals and metric specialization.
    Acta crystallographica. Section C Structural chemistry, 2015
    Co-Authors: Howard D Flack
    Abstract:

    Tables for the determination of space group for single crystals, twinned crystals and crystals with a specialized metric are presented in the form of a spreadsheet for use on a computer. There are 14 tables, one for each of the Bravais-Lattice types. The content of the tables is arranged so that at the intersection of rows, displaying the conditions for reflection, and of columns, displaying the Laue and crystal classes, one finds those space groups compatible with the observed Bravais-Lattice type, the conditions for reflection and the Laue and crystal classes. The tables are intended to be of direct use to an experimentalist working with an unknown structure.

  • Methods of space-group determination – a supplement dealing with twinned crystals and metric specialization
    Acta Crystallographica Section C Structural Chemistry, 2015
    Co-Authors: Howard D Flack
    Abstract:

    Tables for the determination of space group for single crystals, twinned crystals and crystals with a specialized metric are presented in the form of a spreadsheet for use on a computer. There are 14 tables, one for each of the Bravais-Lattice types. The content of the tables is arranged so that at the intersection of rows, displaying the conditions for reflection, and of columns, displaying the Laue and crystal classes, one finds those space groups compatible with the observed Bravais-Lattice type, the conditions for reflection and the Laue and crystal classes. The tables are intended to be of direct use to an experimentalist working with an unknown structure.

Pavel Zemanek - One of the best experts on this subject based on the ideXlab platform.

  • omnidirectional transport in fully reconfigurable two dimensional optical ratchets
    Physical Review Letters, 2017
    Co-Authors: Alejandro V Arzola, Mario Villasantebarahona, Karen Volkesepulveda, Petr Jakl, Pavel Zemanek
    Abstract:

    A fully reconfigurable two-dimensional (2D) rocking ratchet system created with holographic optical micromanipulation is presented. We can generate optical potentials with the geometry of any Bravais Lattice in 2D and introduce a spatial asymmetry with arbitrary orientation. Nontrivial directed transport of Brownian particles along different directions is demonstrated numerically and experimentally, including on axis, perpendicular, and oblique with respect to an unbiased ac driving. The most important aspect to define the current direction is shown to be the asymmetry and not the driving orientation, and yet we show a system in which the asymmetry orientation of each potential well does not coincide with the transport direction, suggesting an additional symmetry breaking as a result of a coupling with the Lattice configuration. Our experimental device, due to its versatility, opens up a new range of possibilities in the study of nonequilibrium dynamics at the microscopic level.