Major construction and initial-phase operation of a second-generation gravitational-wave detector KAGRA has been completed. The entire 3-km detector is installed underground in a mine in order to be isolated from back...
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Layered materials, such as graphite/graphene, boron nitride, transition metal dichalcogenides, represent materials in which reduced size, dimensionality, and symmetry play critical roles in their physical properties. ...
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Layered materials, such as graphite/graphene, boron nitride, transition metal dichalcogenides, represent materials in which reduced size, dimensionality, and symmetry play critical roles in their physical properties. Here, we report on a comprehensive investigation of the phonon properties in the topological insulator Bi2Te3 and Bi2Se3 two-dimensional (2D) crystals, with the combination of Raman spectroscopy, first-principles calculations, and group theory analysis. Low frequency (<30cm−1) interlayer vibrational modes are revealed in few-quintuple-layer (QL) Bi2Te3/Bi2Se3 2D crystals, which are absent in the bulk crystal as a result of different symmetries. The experimentally observed interlayer shear and breathing mode frequencies both show blueshifts, with decreasing thickness in few-QL Bi2Te3 (down to 2QL) and Bi2Se3 (down to 1QL), in agreement with first-principles calculations and a linear chain model, from which the interlayer coupling force constants can be estimated. Besides, an intense ultralow (<12cm−1) frequency peak is observed in 2–4QL Bi2Te3, which is tentatively attributed to a substrate-induced interface mode supported by a linear chain model analysis. The high frequency Raman peaks exhibit frequency shifts and broadening from 3D to 2D as a result of the phonon confinement effect. Our studies shed light on a general understanding of the influence of dimensionality and crystal symmetry on the phonon properties in layered materials.
Shrinking the size of a solid down to nanometer scale is indeed fascinating, which makes all the otherwise constant physical quantities to be tunable such as the Young's modulus, dielectric constant, melting point...
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We investigate and compare a few parallel preconditioning techniques in the iterative solution of large sparse linear systems arising from solid Earth simulation with and without using contact information in the domai...
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We investigate and compare a few parallel preconditioning techniques in the iterative solution of large sparse linear systems arising from solid Earth simulation with and without using contact information in the domai...
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We investigate and compare a few parallel preconditioning techniques in the iterative solution of large sparse linear systems arising from solid Earth simulation with and without using contact information in the domain partitioning process. Previous studies are focused on using static or matrix pattern based incomplete LU (ILU) preconditioners in a localized preconditioner implementation. Our current studies are concerned with preconditioner performance for solving two different cases with and without known contact information. For the cases with contact information, we use localized threshold value based incomplete LU (ILUT) preconditioner to improve efficiency. For the cases without contact information, we use a global sparse approximate inverse preconditioner with a static sparsity pattern to achieve robustness. Numerical results from simulating ground motion on a parallel supercomputer are given to compare the effectiveness of these parallel preconditioning techniques.
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