Browsing by Author "Hsu, YH"

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Fast IMDCT and MDCT algorithms - A matrix approach
(2003-01-01)
Cheng, MH
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Hsu, YH
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電控工程研究所
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Institute of Electrical and Control Engineering
This paper presents a systematic investigation of the modified discrete cosine transform/inverse modified discrete cosine transform (MDCT/IMDCT) algorithm using a matrix representation. This approach results in new understanding of the MDCT/IMDCT, enables,the development of new algorithms, and makes clear the connection between the algorithms. We represent in a matrix form the IMDCT as the product of the type-IV DCT with simple scaling, sign-changing, and permutation operations such that fast algorithms for the type-IV DCT can be simply modified for the IMDCT, and vice versa. Then, the simple symmetry and inversion properties of the type-IV DCT are used to develop new algorithms and establish the connection between existing fast IMDCT algorithms. This approach also enables us to show that MDCT and IMDCT share common core operation and present an efficient architecture for implementing both the MDCT and the IMDCT in one hardware.
Memory effect on energy losses of charged particles moving parallel to solid surface
(2006-02-01)
Kwei, CM
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Tu, YH
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Hsu, YH
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Tung, CJ
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電子工程學系及電子研究所
Theoretical derivations were made for the induced potential and the stopping power of a charged particle moving close and parallel to the surface of a solid. It was illustrated that the induced potential produced by the interaction of particle and solid depended not only on the velocity but also on the previous velocity of the particle before its last inelastic interaction. Another words, the particle kept a memory on its previous velocity, v(0), in determining the stopping power for the particle of velocity v. Based on the dielectric response theory, formulas were derived for the induced potential and the stopping power with memory effect. An extended Drude dielectric function with spatial dispersion was used in the application of these formulas for a proton moving parallel to Si surface. It was found that the induced potential with memory effect lay between induced potentials without memory effect for constant velocities v(0) and v. The memory effect was manifest as the proton changes its velocity in the previous inelastic interaction. This memory effect also reduced the stopping power of the proton. The formulas derived in the present work can be applied to any solid surface and charged particle moving with arbitrary parallel trajectory either inside or outside the solid. (c) 2005 Elsevier B.V. All rights reserved.
Memory effect on the inelastic interaction of electrons moving parallel to a solid surface
(2006-02-01)
Kwei, CM
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Hsu, YH
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Tu, YH
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Tung, CJ
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電子工程學系及電子研究所
It is generally assumed that two successive inelastic interactions between an electron and a solid are independent of each other. In other words, the electron has no memory of its previous interaction. However, the previous interaction of the electron generates a potential that should influence its succeeding inelastic interaction. The aim of this work is to establish a model to account for the memory effect of an electron between two successive inelastic interactions. On the basis of the dielectric response theory, formulae for differential inverse inelastic mean free paths (DIIMFPs) and inelastic mean free paths (IMFPs) considering the memory effect were derived for electrons moving parallel to a solid surface by solving the Poisson equation and applying suitable boundary conditions. These mean free paths were then calculated with the extended Drude dielectric function for a Cu surface. It was found that the DIIMFP and the IMFP with the memory effect for electron energy E lay between the corresponding values without the memory effect for electron energy E and previous energy Eo. The memory effect increased with increasing electron energy loss, E-0 - E-1 in the previous inelastic interaction. Copyright (c) 2005 John Wiley & Sons, Ltd.