Browsing by Issue Date, starting with "2004-08-19"

Now showing 1 - 20 of 69632

Syntheses, thermal properties, and phase morphologies of novel benzoxazines functionalized with polyhedral oligomeric silsesquioxane (POSS) nanocomposites
(2004-08-19)
Lee, YJ
;
Kuo, SW
;
Su, YC
;
Chen, JK
;
Tu, CW
We have successfully synthesized a novel benzoxazine ring-containing polyhedral oligomeric silsesquioxane (BZ-POSS) monomer by two routes: (1) hydrosilylation of a vinyl-terminated benzoxazine using the hydro-silane functional group of a polyhedral oligomeric silsesquioxane (H-POSS) and (2) reaction of a primary amine-containng POSS (Amine-POSS) with phenol and formaldehyde. The benzoxazine-containing POSS (BZ-POSS) monomer can be copolymerized with other benzoxazine monomers through ring-opening polymerization under conditions similar to that used for polymerizing pure benzoxazines. Thermal properties of these POSS-containing organic/inorganic polybenzoxazine nanocomposites have been improved over the pure polybenzoxazine analyzed by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The BZ-POSS monomer is poorly miscible with the benzoxazine monomer and tends to aggregate and forms its own domains, both before and after polymerization. At a higher BZ-POSS content, gross aggregation occurs and results in a lower than expected improvement in the thermal properties. (C) 2004 Elsevier Ltd. All rights reserved.
Design and analyses of compact bent-tapered waveguides using guided-wave lens sets
(2004-08-20)
Chang, CW
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We propose compact bent-tapered waveguides using guided-wave lens sets, which are constructed by disposing lens-shaped waveguide regions in planar tapered waveguides. Two applications of the abruptly bent tapered waveguide and the Z-bend tapered waveguide demonstrate high transmittances of 91% and 86% with bent and tapered angles of 10degrees. (C) 2004 Wiley Periodicals, Inc.
Polarized backlight based on selective total internal reflection at microgrooves
(2004-08-20)
Chien, KW
;
Shieh, HPD
;
Cornelissen, H
;
光電工程學系
;
Department of Photonics
A polarized backlight for LCD illumination is designed and fabricated in which s-polarized light is extracted owing to selective total internal reflection at microstructures in the anisotropic layer. From the measurement, the contrast ratio in normal viewing direction can be as high as 64. Luminous uniformity of higher than 80% is achieved for polarized backlights. Furthermore, 1.6 gain in efficiency is obtained aiming for high-efficiency LCD illumination. (C) 2004 Optical Society of America.
Effect of Sn dopant on the properties of ZnO nanowires
(2004-08-21)
Li, SY
;
Lin, P
;
Lee, CY
;
Tseng, TY
;
Huang, CJ
Sri doped ZnO (SZO) nanowires were fabricated by a vapour-liquid-solid growth process. The reaction temperature for the formation of the nanowires can be reduced to similar to100degreesC due to Sri doping. The growth direction and morphology of SZO nanowires depend on the amount of Sn, which is attributed to the difference in sizes between Zn and Sri atoms. The ultraviolet emission of SZO nanowires varies from 380 to 396 nm since Sri acts as a doubly ionized donor and introduces deep states in the band gap. In addition, the SZO nanowires exhibit significantly Improved field emission characteristics with a turn-on electric field of 0.05 V mum(-1) under a current density of 0.5 mA cm(-2) in comparison with undoped ZnO nanowires. The work function of the SZO nanowire decreases for higher carrier concentrations and the field enhancement factor increases for smaller diameters. Also, the resistance of the SZO nanowire is decreased for the higher Sri mole fraction. Therefore, it is expected that SZO nanowires can be applied in nano-lasers and flat panel displays in the future.
Instantaneous normal mode analysis of orientational motions in liquid water: Local structural effects
(2004-08-22)
Chang, SL
;
Wu, TM
;
Mou, CY
;
物理研究所
;
Institute of Physics
We have investigated the effects of local structures on the orientational motions in liquid water in terms of the instantaneous normal mode (INM) analysis. The local structures of a molecule in liquid water are characterized by two different kinds of index: the asphericity parameter of its Voronoi polyhedron and the numbers of the H bonds donated and accepted by the molecule. According to the two kinds of index, the molecules in the simulated water are classified into subensembles, for which the rotational contributions to the INM spectrum are calculated. Our results indicate that by increasing the asphericity, the rotational contribution has a shift toward the high-frequency end in the real spectrum and a decrease in the fraction of the imaginary modes. Furthermore, we find that this shift essentially relies on the number of the donated H bonds of a molecule, but has almost nothing to do with that of the accepted H bonds. The local structural effects resulting from the geometry of water molecule are also discussed. (C) 2004 American Institute of Physics.
Resolution of the inversion-rotation controversy of azobenzene in solution via femtosecond fluorescence anisotropy on S1 excitation.
(2004-08-22)
Diau, EWG
;
Chang, CW
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Ionization of 2-halo-1,1-difluoro-1-arylethanes in the presence of nitriles.
(2004-08-22)
Ho, TL
;
Chein, RJ
;
應用化學系
;
Department of Applied Chemistry
Phase behavior in polystyrene-block-poly (ethylene oxide) nanocomposites with colloidal CDS quantum dots upon heating.
(2004-08-22)
Sun, YS
;
Jeng, US
;
Liang, KS
;
Yeh, SW
;
Wei, KH
Applications of semiconductor nanoparticles in electron transfer, energy transfer and metal ion recognition.
(2004-08-22)
Chou, YH
;
Chiu, HT
;
Chen, CY
;
Cheng, CT
;
Chou, PT
Chemical vapor deposition of the hafnium oxynitride for use as HIGH-K materials in microelectronic devices.
(2004-08-22)
Chuang, SH
;
Chou, YH
;
Chiu, HT
;
應用化學系
;
Department of Applied Chemistry
Highly efficient red electrophosphorescent devices based on an iridium complex with trifluoromethyl-substituted pyrimidine ligand
(2004-08-30)
Niu, YH
;
Chen, BQ
;
Liu, S
;
Yip, H
;
Bardecker, J
Highly efficient red-emitting electrophosphorescent devices were fabricated by doping an iridium (Ir) complex containing trifluoromethyl (CF3)-substituted pyrimidine ligand into a conjugated bipolar polyfluorene with triphenylamine and oxadiazole as side chains. The device efficiency can be enhanced through effective exciton confinement using a layer of 1,3,5-tris(N- phenylbenzimidazol-2-yl)benzene on the cathode side and a layer of in situ polymerized tetraphenyldiamine-perfluorocyclobutane on the anode side. For a blend with 5 wt % of the Ir complex, a maximum external quantum efficiency of 7.9 photon/electron % and a maximum brightness of 15800 cd/m(2) are reached with Commission Internationale de L'Eclairage chromaticity coordinates of x=0.65 and y=0.34. (C) 2004 American Institute of Physics.
Interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields
(2004-09-01)
Hawrylak, P
;
Sheng, W
;
Cheng, S
;
電子物理學系
;
Department of Electrophysics
Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and of excitonic quantum Hall droplets at a filling factor nu = 2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons.
Equivalence classes of Vogan diagrams
(2004-09-01)
Chuah, MK
;
Hu, CC
;
應用數學系
;
Department of Applied Mathematics
A Vogan diagram is a Dynkin diagram with an involution, and the vertices fixed by the involution may be painted. They represent real simple Lie algebras, and two diagrams are said to be equivalent if they represent the same Lie algebra. In this article we classify the equivalence classes of all Vogan diagrams. In doing so, we find that the underlying Dynkin diagrams have certain properties in graph painting. We show that this combinatorial property provides an easy classification for most of the simply-laced Dynkin diagrams. (C) 2004 Published by Elsevier Inc.
A simple approach using Bouwer and Rice's method for slug test data analysis
(2004-09-01)
Yang, SY
;
Yeh, HD
;
環境工程研究所
;
Institute of Environmental Engineering
Slug test data obtained from tests performed in an unconfined aquifer are commonly analyzed by graphical or numerical approaches to determine the aquifer parameters. This paper derives three fourth-degree polynomials to represent the relationship between Bouwer and Rice's coefficients and the ratio of the screen length to the radius of the gravel envelope. A numerical approach using the nonlinear least squares and Newton's method is used to determine hydraulic conductivity from the best fit of the slug test data. The method of nonlinear least squares minimizes the sum of the squares of the differences between the predicted and observed water levels inside the well. With the polynomials, the hydraulic conductivity can be obtained by simply solving the nonlinear least squares equation by Newton's method. A computer code, SLUGBR, was developed from the derived polynomials using the proposed numerical approach. The results of analyzing two slug test datasets show that SLUGBR can determine hydraulic conductivity with very good accuracy.
己未年暮春過新公園楓林即事
(2004-09-01)
管管
己未年暮春過新公園楓林即事
(2004-09-01)
管管
Intelligent call admission control for wideband CDMA cellular systems
(2004-09-01)
Shen, S
;
Chang, CJ
;
Huang, CY
;
Bi, Q
;
電子工程學系及電子研究所
In this paper, we propose intelligent call admission control for wideband code-division multiple-access (CDMA) cellular systems to support differentiated quality-of-service (QoS) requirements, guarantee the forced termination probability of handoffs, and maximize the spectrum utilization. The intelligent call admission controller (ICAC) contains a fuzzy call admission processor to make admission decision for a call request by considering QoS measures such as the forced termination (drop call) probability of handoff, the outage probability of all service types, the predicted next-step existing-call interference, the link gain, and the estimated equivalent interference of the call request. The pipeline recurrent neural network (PRNN) is used to accurately predict the next-step existing-call interference, and the fuzzy logic theory is applied to estimate the new/handoff call interference based on knowledge of effective bandwidth method. Simulation results indicate that ICAC achieves system capacity higher than conventional CAC schemes by an amount of more than 10% in both low and high moving speed cases. Moreover, ICAC can cope with the unpredictable statistical fluctuation of wireless multimedia traffic; it always fulfill QoS requirements for all service types and keep the forced termination probability satisfied, while the CAC of multimedia calls (MCAC) and SIR-based CAC with intercell interference prediction (PSIR-CAC) fail to adapt to the variation of traffic conditions.
Time-resolved photoluminescence and capacitance-voltage analysis of the neutral vacancy defect in silicon implanted SiO2 on silicon substrate
(2004-09-01)
Lin, GR
;
Lin, CJ
;
Yu, KC
;
光電工程學系
;
Department of Photonics
The nanosecond photoluminescence (PL) dynamics of neutral oxygen vacancy (NOV) defects at 410-460 nm, and less pronounced nanocrystallite Si precursor (E'(delta)) defects at 520 nm in multi-energy silicon-ion-implanted SiO2 (SiO2:Si+) are investigated. The density of NOV defects in as-implanted SiO2:Si+ of 8x10(16) cm(-3) (or 2.5x10(16) cm(-3) calculated from time-resolved PL) is determined by using capacitance-voltage measurement. After annealing at 1100 degreesC for 3 h, the NOV defects are completely activated with a concentration of 4.8x10(17) cm(-3) and a corresponding absorption cross section of 9x10(-17) cm(2). The time-resolved PL lifetime of NOV defects in SiO2:Si+ is significantly shortened from 26 to 3.6 ns and these defects are fully activated after annealing for 3 h. Longer annealing time greatly attenuates the blue-green PL intensity and eliminates the NOV defects, whereas the PL intensity and concentration of E'(delta) defects with lifetime of 20-50 ns increases by a factor of 2. (C) 2004 American Institute of Physics.
Chaos, chaos control and synchronization of the vibrometer system
(2004-09-01)
Ge, ZM
;
Lin, CC
;
Chen, YS
;
機械工程學系
;
Department of Mechanical Engineering
The dynamic system of the vibrometer is shown to produce regular and chaotic behaviour as the parameters are varied. When the system is non-autonomous, the periodic and chaotic motions are obtained by numerical methods. Many effective methods have been used in chaos synchronization. It has been shown that chaos can be synchronized using special feedback control and that external excitations affect the synchronization.
Formulation of a family of sure-success quantum search algorithms
(2004-09-01)
Hsieh, JY
;
Li, CM
;
Lin, JS
;
Chuu, DS
;
電子物理學系
In this work, we consider a family of sure-success quantum algorithms, which is grouped into even and odd members for solving a generalized Grover search problem. We prove the matching conditions for both groups and give the corresponding formulae for evaluating the iterations or oracle calls required in the search computation. We also present how to adjust the phase angles in the generalized Grover operator to ensure the sure-success if minimal oracle calls axe demanded in the search.