Browsing by Issue Date, starting with "2001-09-15"

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棠梨弟弟
(2001-09-15)
管管
Decay rate and renormalized frequency shift of a quantum wire Wannier exciton in a planar microcavity
(2001-09-15)
Chen, YN
;
Chuu, DS
;
Brandes, T
;
Kramer, B
;
電子物理學系
Super-radiant decay rate and frequency shift of a Wannier exciton in a one-dimensional quantum wire are studied. It is shown that the dark-mode exciton can be examined experimentally when the quantum wire is embedded in a planar microcavity. It is also found that the decay rate is greatly enhanced as the cavity length L-c is equal to the multiple wavelength of the emitted photon. Similar to its decay-rate counterpart, the frequency shift also shows discontinuities at resonant modes.
Comment on "Dephasing of conduction electrons due to zero-point fluctuation"
(2001-09-15)
Wu, GY
;
Lin, JJ
;
物理研究所
;
Institute of Physics
It is recently proposed by Wang et al. [Phys, Rev. B 61 R5090 (2000)] that dephasing of conduction electrons due to zero-point fluctuation of electromagnetic field in a vacuum can well account for the measured saturation of electron dephasing time at T-->0 in various materials. We point out that this calculation is numerically incorrect. while we also provide arguments showing that zero-point fluctuation of electromagnetic field does not cause any dephasing within this theory of Wang et al.
Defect Auger exciton dissociation and impact ionization in conjugated polymers
(2001-09-15)
Chen, CH
;
Meng, HF
;
物理研究所
;
Institute of Physics
We study theoretically the exciton dissociation and carrier generation in conjugated polymers via defect Auger process, in which the electron (hole) of the exciton drops into the deep defect level while the energy is released to the hole (electron) through Coulomb scattering. Contrary to the usual Auger process among free carriers at high densities, defect Auger process for excitons takes place independent of the exciton density, and is identified as the dominant mechanism of photocarrier generation for excitation below the band gap. The dissociation probability for each passage through the defect is found to be close to one for excitons with thermal velocity, consistent with the picture that exciton decay in oxidized polymers is controlled by diffusion on a chain with quenching centers. We also study the reverse process, i.e., defect impact ionization, in which excitons or free electron hole pairs are created via the impact of hot holes (electrons) on electrons (holes) in the defect level. Excitons are found to be produced predominantly for driving electric field in a window around 10(5) V/cm along the chain. Light emission under unipolar carrier injection is predicted.
棠梨弟弟
(2001-09-15)
管管
棠梨弟弟
(2001-09-15)
管管
Ferroelectric characteristics of oriented Pb(Zr1-xTix)O-3 films
(2001-09-15)
Chen, SY
;
Sun, CL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Pb1.2Zr1-xTix)O-3 (PZT) films with a variety of compositions were prepared by spin coating on Pt/Ti/SiO2/Si substrate with sol-gel processing. The roles of composition (phase) and orientation in ferroelectric properties of PZT films have been determined. The Zr-rich PZT films with (111)-oriented PZT films have a higher remanent polarization but also show a higher fatigue rate as compared to (100)-oriented films in both Zr-rich(65/35) and Ti-rich(35/65) PZT compositions. The lower fatigue rate of (100)-oriented film can be attributed to its easier reversible domain-wall motions compared to (111)-oriented PZT films due to the absence of internal field stress and less dependence on electrical field. A mode based on domain-wall contribution instead of film-electrode interface is favored to elucidate the role of orientation in fatigue characteristics of PZT films. (C) 2001 American Institute of Physics.
棠梨弟弟
(2001-09-15)
管管
Whittaker function approach to determine the impurity energy levels of coated quantum dots
(2001-09-15)
Lin, MC
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The electronic structure of a hydrogenic impurity atom located at the center of a multilayer coated quantum dot (CQD) is investigated. The electronic eigenstates of the CQD system are expressed in terms of the geometry and the material parameters by solving the Schrodinger equations analytically. Image potential effects are ignored and the effective mass approximation is employed. The ground state energy is found to be strongly influenced by the shell thickness and confined potential. In contrast to previous work, our eigenfunctions are expressed in terms of the Whittaker functions in any region, no matter where the energy levels are, i.e., whether they are higher or lower than the potential barriers. Our approach is simpler and has general significance, e.g., the bound state eigenenergies of any n-layered quantum dot can be easily determined by directly solving just "one"(2n-2)-rank secular determinant equation instead of solving 2(n) equations. One can also easily and quickly determine whether a system has bound states by using the Whittaker function approach. (C) 2001 American Institute of Physics.
Improvement of machining accuracy by fuzzy logic at corner parts for wire-EDM
(2001-09-16)
Lin, CT
;
Chung, IF
;
Huang, SY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Wire electrical discharge machining (wire-EDM) has always occupied an important position in some production fields, due to its capability of machining hard materials and intricate shapes. However, the machining accuracy, especially at corner parts, may be destroyed because of some phenomena such as wire deflection and vibration, etc. The purpose of this paper is to develop a control strategy based on fuzzy logic so that the machining accuracy at corner parts for wire-EDM can be improved. The fuzzy rules based on the wire-EDM's physical characteristics, experimental data, and operator's experience are constructed, so that the reduced percentage of sparking force can be determined by a multi-variables fuzzy logic controller. The objective of the total control is to improve the machining accuracy at corner parts, but still keep the cutting feedrate at fair values. As a result of experiments, machining errors of corner parts, especially in rough-cutting, can be reduced to less than 50% of those in normal machining, while the machining process time increases not more than 10% of the normal value. (C) 2001 Elsevier Science B.V. All rights reserved.
An algorithm for generalized fuzzy binary linear programming problems
(2001-09-16)
Yu, CS
;
Li, HL
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Fuzzy binary linear programming (FBLP) problems are very essential in many fields such as assignment and assembly line balancing problems in operational research, multiple projects, locations, and candidates selection cases in management science, as well as representing and reasoning with prepositional knowledge in artificial intelligence. Although FBLP problems play a significant role in human decision environment, not very much research has focused on FBLP problems. This work first proposes a simple means of expressing a triangular fuzzy number as a linear function with an absolute term. A method of linearizing absolute terms is also presented. The developed goal programming (GP) model weighted by decision-makers' (DMs) preference aims to optimize the expected objective function and minimize the sum of possible membership functions' deviations. After presented a novel way of linearizing product terms, the solution algorithm is proposed to generate a crisp trade-off promising solution that is also an optimal solution in a certain sense. Three examples, equipment purchasing choice, investment project selection, and assigning clients to project leaders, illustrate that the proposed algorithm can effectively solve generalized FBLP problems. (C) 2001 Elsevier Science B.V. All rights reserved.
Activated diffusion brazed repair for IN738 hot section components of gas turbines
(2001-09-24)
Su, CY
;
Lih, WC
;
Chou, CP
;
Tsai, HC
;
機械工程學系
The wide-clearance activated diffusion brazing (ADB) techniques with various brazing alloys, namely DF4B and Nicrobraz 150 were applied to restore worn areas of IN738 components. In this study, the microstructure of an ADB joint and the results of thermal cyclic tests as well as tensile tests within the temperature range of from 25 to 980 degreesC were investigated and discussed. The results of the tensile tests showed that ADB specimens brazed by 40 wt.% DF4B at 1190 degreesC exhibited 85% tensile strength of the IN738 base materials at room temperature and retained the same strength as that of the base material at 980 degreesC. However, the ductility of the ADB specimens with both brazing alloys was reduced. The results of cyclic-oxidation tests showed that ADB specimens with Nicrobraz 150 as the brazing alloy decayed after 150 cycles. However, the ADB specimens with DF4B had no obvious weight change until 205 cycles. (C) 2001 Elsevier Science B.V. All rights reserved.
Effect of side chain alkyl length on the electroluminescence characteristics of carbazole-based light emitting polymers
(2001-09-28)
Chao, CS
;
Whang, WT
;
Hung, CH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Three carbazole-based copolymers with different long side chains were synthesized using the Wittig reaction. These three copolymers and model compound were characterized by nuclear magnetic resonance (NMR) spectroscopy to determine the cis/trans ratio. The cis/ trans ratios decrease with the side chain length due to the variation in the degree of steric hindrance in the Wittig reaction. They affect the electroluminescence (EL) characteristics of the carbazole-based light emitting polymers. As the length of the side chain increases the wavelength of the emitted light increases proportionally whereas a decrease in the threshold voltages, 5.2, 4.8, 2.5 V was observed. However, EL intensity at same applied voltage creases with the length of the side chain. The energy levels of these three copolymers were also investigated to account for the phenomenon.
Additive multiplicative increasing functions on nonnegative square matrices and multidigraphs
(2001-09-28)
Chang, CH
;
Chuang, YC
;
Hsu, LH
;
資訊工程學系
;
Department of Computer Science
It is known that if f is a multiplicative increasing function on N, then either f(n) = 0 for all n is an element of N or f (n) = n(alpha) for some alpha greater than or equal to 0. It is very natural to ask if there are similar results in other algebraic systems. In this paper, we first study the multiplicative increasing functions. over nonnegative square matrices with respect to tensor product and then restrict our result to multidigraphs and loopless multidigraphs. (C) 2001 Elsevier Science B.V. All rights reserved.
那是一種現代味的唐詩或離騷
(2001-09-30)
管管
那是一種現代味的唐詩或離騷
(2001-09-30)
管管
那是一種現代味的唐詩或離騷
(2001-09-30)
管管
An automatic macro program for radio frequency MOSFET characteristics analysis
(2001-10-01)
Su, CY
;
Chang, SJ
;
Chen, LP
;
Ho, YP
;
Huang, GW
The parameter extraction language (PEL) in Agilent IC-CAP software is used to develop an automatic macro program for the analysis of the characteristics of RF MOSFETs. By using this powerful macro program, the time spent on the measurement of the MOSFET characteristics and the related analysis is effectively reduced. This macro program permits a fast and accurate method to obtain the DC and RF characteristics of MOSFETs with different device geometries and operating conditions. It is also suitable for high volume measurements and analyses of MOSFET, and provides a solid jou 71 dation for RF circuit design.
Sensitivity of the photo-crosslinkable polyimide for liquid crystal alignment
(2001-10-01)
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
Two methods were developed for enhancing the photosensitivity of the cinnamates-contained polyimide (PICA), One is to increase the content of cinnamate side chain in PICA main chain and another is to blend some photosensitizer into PICA films. Our experimental results show that increasing the rate of photo-dimerization decreases the alignment ability of the PICA films. Using the molecular simulation method, we successfully describe the photoalignment mechanism of the PICA films. It is also found that photo-induced LC alignment ability of the PICA film could be enhanced through choosing a proper coating solvent.
Internet heavy use and addiction among Taiwanese college students: An online interview study
(2001-10-01)
Chou, C
;
教育研究所
;
Institute of Education
This paper presents empirical qualitative results of Internet heavy-use and addiction among some college students in Taiwan. It offers in-depth, online interviews of student-subjects in order to facilitate an interdisciplinary understanding of Internet heavy use, addiction and its potential impacts. A total of 83 subjects were interviewed, both as individuals and in chat-room groups. The analysis of qualitative data presented in six major themes: (1) Internet use and reasons; (2) Internet features; (3) the Internet as replacement for other media; (4) impact of Internet overuse; (5) controlling Internet use; and (6) coping with Internet withdrawal. Discussions, explanations, along with examples and quotes from subjects, are provided in each section. Implications for student affairs administrators and further research directions are also addressed.