Browsing by Author "Kao, LY"

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Anomalous temperature and disorder dependence of the electron-phonon scattering time in impure metals
(2003-05-01)
Lin, JJ
;
Zhong, YL
;
Kao, LY
;
Meikap, AK
;
物理研究所
We have measured the electron-phonon scattering time, tau(ep), in disordered metals at liquid-helium temperatures, using weak-localization method. The temperature and disorder dependence of tau(ep), is determined for AgPd and AuPd thick films, and V100-xAlx alloys. In all three cases, we find an anomalous temperature and disorder dependence of tau(ep)(-1) proportional to T(2)l where l is the electron elastic mean free path. This temperature and disorder behavior cannot be explained in terms of current theoretical concepts for the electron-phonon interaction in impure conductors. Current theory predicts a form of either tau(ep)(-1) proportional to T(4)l or tau(ep)(-1) proportional to T(2)l(-1) in the dirty limit, depending on the nature of the defects. (C) 2003 Elsevier Science B.V. All rights reserved.
Effect of microstructure on the electron-phonon interaction in the disordered metals Pd60Ag40
(2002-10-01)
Zhong, YL
;
Lin, JJ
;
Kao, LY
;
物理研究所
;
Institute of Physics
Using the weak-localization method, we have measured the electron-phonon scattering times tau(ep) in Pd60Ag40 thick films prepared by dc- and rf-sputtering deposition techniques. In both series of samples, we find an anomalous 1/tau(ep)proportional toT(2)l temperature and disorder dependence, where l is the electron elastic mean free path. This anomalous behavior cannot be explained in terms of the current concepts for the electron-phonon interaction in impure conductors. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the dc- than rf-sputtered films, suggesting that the electron-phonon interaction is not only sensitive to the total level of disorder, but is also sensitive to the microscopic quality of the disorder.
Optimization and quality measurement for the layer 2 compression scheme of MPEG audio coding
(1997)
Hsu, CH
;
Wu, IC
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Kao, LY
;
Ueng, JF
;
資訊工程學系
The layer 2 compression scheme of MPEG audio coding is a very common audio coding standard for CD quality audio (music). However, its encoding process requires a large amount of computations fn this paper, we propose some optimization techniques to make the encoding program much faster while allowing to impair the audio qualify a little. In order to measure how much qualify loss, we define criteria to quantify the quality toss rate of an encoded audio stream. From the definition, we can say that the encoder encoding streams with a quality toss rate equivalently wastes a number of bits, if the encoder that completely conforms to the layer 2 standard can save the same number of bib while keeping the same quality loss rate. In our experiments, we optimize the layer 2 compression programs such that audio streams can be encoded real time on Pentium Pro 180 with only 0.0003% quality loss and equivalently 1.5% bits wasted and on Pentium 180 with only 0.0009% quality loss and equivalently 4% bits wasted.
Saturation of electron dephasing in three-dimensional polycrystalline disordered metals
(2001-02-05)
Lin, JJ
;
Kao, LY
;
物理研究所
;
Institute of Physics
We have systematically investigated the low-temperature electron dephasing times tau (phi) in more than 40 three-dimensional polycrystalline impure metals with distinct material characteristics. In all cases, a saturation of the dephasing time is observed below about a (few) degree(s) Kelvin, depending on samples. The value of the saturated dephasing time tau (0) [= tau (phi)(T --> 0 K)] falls basically in the range 0.005 to 0.5 ns for all samples. Particularly, we find that so scales with the electron diffusion constant D as tau (0) similar to D-alpha, with alpha close to or slightly larger than 1, for over two decades of D from about 0.1 to 10 cm(2) s(-1). Our observation implies an essentially constant saturated dephasing length of rootD tau (0) similar to 1000 Angstrom in three-dimensional polycrystalline disordered metals. A complete theoretical explanation is not yet available.
The design and performance analysis for the multimedia function unit of the NSC-98 CPU
(1997)
Ueng, JF
;
Wu, IC
;
Kuo, YH
;
Kao, LY
;
Chen, CL
Leveraging Taiwan's hardware technologies, National Science Council in Taiwan proposed a project to design an advanced CPU, called NSC-98, compatible to the Intel MMX architecture. This paper discusses the design of multimedia extension, called MFU (Multimedia Function Unit), in this CPU. The MFU has the following two special features. (1) Support three more instructions for permutation operations, parallel distance operations, and parallel average operations; (2) implement two MFU subunits: one without the parallel multiplier and the other without the parallel shifter and converter (for permutation). This paper also does performance analysis by estimating the performances of the MFU with and without these features on some chosen multimedia benchmarks. These performance analysis results can justify our MFU design.