2,417 research outputs found
Large-scale electronic-structure theory and nanoscale defects formed in cleavage process of silicon
Several methods are constructed for large-scale electronic structure
calculations. Test calculations are carried out with up to 10^7 atoms. As an
application, cleavage process of silicon is investigated by molecular dynamics
simulation with 10-nm-scale systems. As well as the elementary formation
process of the (111)-(2 x 1) surface, we obtain nanoscale defects, that is,
step formation and bending of cleavage path into favorite (experimentally
observed) planes. These results are consistent to experiments. Moreover, the
simulation result predicts an explicit step structure on the cleaved surface,
which shows a bias-dependent STM image.Comment: 4 page 4 figures. A PDF file with better graphics is available at
http://fujimac.t.u-tokyo.ac.jp/lses
Very early responses to colour stimuli detected in prestriate visual cortex by magnetoencephalography (MEG)
Our previous studies with the visual motion and form systems show that visual stimuli belonging to these categories trigger much earlier latency responses from the visual cortex than previously supposed and that the source of the earliest signals can be located in either the prestriate cortex or in both the striate (V1) and prestriate cortex. This is consistent with the known anatomical connections since, in addition to the classical retino-geniculo-striate cortex input to the prestriate visual areas, there are direct anatomical inputs from both the lateral geniculate nucleus and the pulvinar that reach the prestriate visual cortex without passing through striate cortex. In pursuing our studies, we thought it especially interesting to study another cardinal visual attribute, namely colour, to learn whether colour stimuli also provoke very early responses, at less than 50 ms from visual cortex. To address the question, we asked participants to view stimuli that changed in colour and used magneto-encephalography to detect very early responses (< 50 ms) in the occipital visual cortex. Our results show that coloured stimuli also provoke an early cortical response (M30), with an average peak time at 31.7 ms, thus bringing the colour system into line with the visual motion and form systems. We conclude that colour signals reach visual cortex, including prestriate visual cortex, earlier than previously supposed
Linear Algebraic Calculation of Green's function for Large-Scale Electronic Structure Theory
A linear algebraic method named the shifted
conjugate-orthogonal-conjugate-gradient method is introduced for large-scale
electronic structure calculation. The method gives an iterative solver
algorithm of the Green's function and the density matrix without calculating
eigenstates.The problem is reduced to independent linear equations at many
energy points and the calculation is actually carried out only for a single
energy point. The method is robust against the round-off error and the
calculation can reach the machine accuracy. With the observation of residual
vectors, the accuracy can be controlled, microscopically, independently for
each element of the Green's function, and dynamically, at each step in
dynamical simulations. The method is applied to both semiconductor and metal.Comment: 10 pages, 9 figures. To appear in Phys. Rev. B. A PDF file with
better graphics is available at http://fujimac.t.u-tokyo.ac.jp/lses
Material Selection of Z-fibre in Stitched Composites - Experimental and Analytical Comparison Approach
Strain energy release rates are measured and compared for laminated composites stitched with different fibre materials – Carbon, Kevlar and Vectran. DCB test and FE simulation are performed to evaluate the interlaminar toughness. It is proven that Vectran provides the toughest interlaminar reinforcement and is most suitable for Zfibre application
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