Browsing by Issue Date, starting with "2007-04-15"

Now showing 1 - 20 of 59849

Electrochemical reaction and performance of proton exchange membrane fuel cells with a novel cathode flow channel shape
(2007-04-15)
Chiang, Mu-Sheng
;
Chu, Hsin-Sen
;
Chen, Cha'o-Kuang
;
Jian, Sheng-Rui
;
機械工程學系
This study focuses on the investigation of the electrochemical reaction along a novel cathode flow channel of PEM fuel cells with various shoulder/channel (S/C) ratios at the outlet port. A three-dimensional mathematical model, considering conservation principles of mass, momentum, species and electric current is employed. Local variations of important model variables such as reactant concentration and local current density are presented by contour plots to elucidate the effects of channel geometry on transport process, catalyst reaction and cell performance. The potential fields of solid and membrane phases are also resolved in the cell domain and the driving force of the electrochemical reactions - the catalyst activation overpotential - is harnessed in modeling. Numerical calculations reveal the influence of the cathode channel configuration on the local distributions of various model variables. The results also show the dependence between optimal channel configuration and cell operating condition. At a medium reaction rate, the reaction sites underneath the shoulder region generate more current than the channel region. Therefore, a convergent channel configuration with a larger S/C ratio at the outlet port develops more current because such a design facilitates the electron transport and enhances local activation overpotential. However, as the cell voltage decreases and the reaction rate increases, such configuration loses its merit gradually as the requirement for a higher reactant concentration is more important and the reaction sites underneath the channel region have a higher reaction rate. Consequently, the divergent channel configuration with a lower S/C ratio of 0.67 perfonns better at a cell voltage of 0.22 V (c) 2007 Elsevier B.V. All rights reserved.
Gel electrophoresis of polyphenol oxidase with instant identification by in situ blotting
(2007-04-15)
Cheng, Tsai-Mu
;
Huang, Pei-Chen
;
Pan, Ju-Pin
;
Lin, Kuan-Yu
;
Mao, Simon J. T.
Polyphenol oxidase (PPO) or tyrosinase is an important and ubiquitous enzyme responsible for browning in plants and melanization in animals. The molecular size of the plant PPO is varied among the species and its activity can be enhanced by a variety of anionic detergents. In the present study, we developed a simple method for the first-step identification of PPO in fruit and vegetable extracts. First, 3 mm chromatographic paper was immersed in 0.5% (w/v) catechol solution as an immobilized PPO substrate. After running the extract with 10% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SIDS-PAGE), one side of the glass plate was removed. The plate was immediately laid on top of the dried catechol-paper. A dark-brown band corresponding to PPO was visualized within I min and was further confirmed by a conventional Western blot using an antibody prepared against mushroom PPO. It also reveals that some vegetation (such as tomato, radish, and oriental melon) with low or no detectable activity in a conventional enzyme assay actually possessed marked levels of PPO activity when assessed by PAGE-blot. We propose that an inhibitor is associated with PPO in some plants; the inhibitor, however, is dissociated during the electrophoresis. Therefore, in addition to identify the molecular form of PPO, the present technique may explore the existence of PPO inhibitor(s) in plants. The detail of the method with respect to its relevance for searching a natural PPO inhibitor is described and discussed. (c) 2006 Elsevier B.V. All rights reserved.
A novel method for fabrication of self-aligned double microlens arrays
(2007-04-15)
Ho, Jeng-Rong
;
Shih, Teng-Kai
;
Cheng, J. W. John
;
Sung, Cheng-Kuo
;
Chen, Chia-Fu
Based on the excimer laser microdrilling and the spin coating scheme, a new fabrication method of polymeric, double microlens arrays on a thin plastic pedestal sheet is proposed in this study. On each through hole on the pedestal sheet, a double microlens pair, consisting of two microlenses with different parabolic surfaces, is sited. The two microlenses of each pair are located respectively on both ends of the through hole and arranged surface to surface and automatically share a common lens principal axis. The fabricated microlens arrays are made of PMMA that are formed on a PMMA pedestal sheet with thickness of 100 mu m. The diameter and height for the microlens on one layer are of 150 mu m and 28 mu m, respectively, and they are correspondingly of 130 mu m and 24 mu m on the other layer. Experimental results demonstrate that the double microlens arrays have a better focusing property than the single-layer mircolens array. Simulation results indicate that, simply by changing the thickness of the pedestal sheet, the present fabricated double microlens arrays can serve the purposes for light collimating and diffusing. Due to its inherent simplicity in fabrication, the present method has high flexibility for making double microlens arrays with different lens configurations and various lens refractive indices. The facts that precise alignment and all processing steps are performed in ambient and at low temperature render the proposed approach a potential low-cost method for fabrication of double microlens arrays. (c) 2006 Elsevier B.V. All rights reserved.
Node-pancyclicity and edge-pancyclicity of hypercube variants
(2007-04-15)
Hu, Ken S.
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Yeoh, Shyun-Shyun
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Chen, Chiuyuan
;
Hsu, Lih-Hsing
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應用數學系
Twisted cubes, crossed cubes, Mobius cubes, and locally twisted cubes are some of the widely studied hypercube variants. The 4-pancyclicity of twisted cubes, crossed cubes, Mobius cubes, locally twisted cubes and the 4-edge-pancyclicity of twisted cubes, crossed cubes, Mobius cubes are proven in [C.P. Chang, J.N. Wang, L.H. Hsu, Topological properties of twisted cube, Inform. Sci. 113 (1999) 147-167; C.P. Chang, T.Y. Sung, L.H. Hsu, Edge congestion and topological properties of crossed cubes, IEEE Trans. Parall. Distr. 11 (1) (2000) 64-80; J. Fan, Hamilton-connectivity and cycle embedding of the Mobius cubes, Inform. Process. Lett. 82 (2002) 113-117; X. Yang, G.M. Megson, D.J. Evans, Locally twisted cubes are 4-pancyclic, Appl. Math. Lett. 17 (2004) 919-925; J. Fan, N. Yu, X. Jia, X. Lin, Embedding of cycles in twisted cubes with edge-pancyclic, Algorithmica, submitted for publication; J. Fan, X. Lin, X. Jia, Node-pancyclic and edge-pancyclic of crossed cubes, Inform. Process. Lett. 93 (2005) 133-138; M. Xu, J.M. Xu, Edge-pancyclicity of Mobius cubes, Inform. Process. Lett. 96 (2005) 136-140], respectively. It should be noted that 4-edge-pancyclicity implies 4-node-pancyclicity which further implies 4-pancyclicity. In this paper, we outline an approach to prove the 4-edge-pancyclicity of some hypercube variants and we prove in particular that Mobius cubes and locally twisted cubes are 4-edge-pancyclic. (c) 2006 Elsevier B.V. All rights reserved.
High-speed GaAs metal gate semiconductor field effect transistor structure grown on a composite Ge/Ge(x)Si(1-x)/Si substrate
(2007-04-15)
Luo, Guang-Li
;
Hsieh, Yen-Chang
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Chang, Edward Yi
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Pilkuhn, M. H.
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Chien, Chao-Hsin
In this study we used a low-pressure metal organic vapor phase epitaxy method to investigate the growth of GaAs metal gate semiconductor field effect transistor (MESFET) structures on a Si substrate. The buffer layer between the Si substrate and the grown GaAs epitaxial layers was a composite Ge/Si(0.05)Ge(0.95)/Si(0.1)Ge(0.9) metamorphic layer. We used transmission electron microscopy to observe the microstructures formed in the grown GaAs/Ge/Si(x)Ge(1-x)/Si material and atomic force microscopy to analyze the surface morphology and the formation of antiphase domains in the GaAs epitaxial layers. The measured Hall electron mobility in the channel layer of a MESFET structure grown on a 6 degrees misoriented Si substrate was 2015 cm(2) V(-1) s(-1) with a carrier concentration of 5.0x10(17) cm(-3). The MESFET device fabricated on this sample exhibited good current-voltage characteristics.
Design and implementation of a sliding-mode controller and a high-gain observer for output tracking of a three-axis pickup
(2007-04-15)
Chao, Paul C. -P.
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Shen, Chien-Yu
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電控工程研究所
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Institute of Electrical and Control Engineering
A novel decoupling actuation scheme applied to a new three-axis four-wire optical pickup is synthesized in this study based on theories of sliding-mode control and high-gain observer. The three-axis pickup owns the capability to move the lens holder in three directions of focusing, tracking and tilting. This capability is required particularly for higher data-density optical disks to annihilate the non-zero lens tilting. To achieve control design, Lagrange's equations are first employed to derive equations of motion for the lens holder. A sliding-mode controller is then designed to perform dynamic decoupling and nonlinearity cancellation with the aims of precision tracking, focusing and no tilting. A full-order high-gain observer is next forged to estimate the velocities of the moving lens holder in order to provide low-noised feedback velocity signals for the designed sliding-mode controller. Simulations are carried out to choose appropriate parameter values of the designed controller and observer. Finally, experiments are conducted to validate the effectiveness of the controller for annihilating lens tilting and the capability of the observer for reducing the effects of digital noises on pickup positionings. (c) 2006 Elsevier B.V. All rights reserved.
Optimal resilient threshold GQ signatures
(2007-04-15)
Cheng-Kang Chu
;
Wen-Guey Tzeng
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資訊工程學系
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Department of Computer Science
GQ signature scheme is widely used in many cryptographic protocols, such as forward-secure signature scheme, identity-based signature scheme, etc. However, there is no threshold version of this important signature scheme in the open literature. We proposed the first threshold GQ signature scheme. The scheme is proved unforgeable and robust against any adaptive adversary by assuming hardness of computing discrete logarithm modulo a safe prime and existence of fully synchronous broadcast channel. Furthermore, with some modifications, our scheme achieves optimal resilience such that the adversary can corrupt up to a half of the players. As an extension of our work, we provided a threshold identity-based signature scheme and a threshold forward-secure signature scheme, which is the threshold version of the most efficient forward-secure signature scheme up to now. (C) 2006 Elsevier Inc. All rights reserved.
High-efficiency blue multilayer polymer light-emitting diode based on poly(9,9-dioctylfluorene)
(2007-04-15)
Tseng, Shin-Rong
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Li, Shiuan-Yi
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Meng, Hsin-Fei
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Yu, Yi-Hsiang
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Yang, Chia-Ming
A highly efficient blue polymer light-emitting diode based exclusively on commercial poly(9,9-dioctylfluorene) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4(')-(N-(4-s-butylphenyl)) diphenylamine)] is demonstrated. High electroluminescent efficiency is achieved by enhancing electron currents and making devices in multilayered structures. CsF/Al is used as the efficient electron injection cathode, and the fabrication process is in the glove box to enhance electron mobility by reducing oxygen adsorption. The multilayer structure is prepared by the liquid buffer layer technique. The maximum efficiency is 2.5 cd/A at deep blue with the corresponding external quantum efficiency of 2%.
A temperature modulation photonic crystal Mach-Zehnder interferometer composed of copper oxide high-temperature superconductor
(2007-04-15)
Pei, Ting-Hang
;
Huang, Yang-Tung
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A tunable Mach-Zehnder interferometer with a two-dimensional photonic crystal structure using copper oxide high-temperature superconductor is proposed. This photonic crystal is composed of rods of which axes are perpendicular to the two-dimensional anisotropic copper oxide plane. By tuning the temperature of the superconductor, the refractive index of the superconductor as well as the photonic band gap can be changed. The photonic band structures of two-dimensional photonic crystals composed of the superconductor are calculated by using the plane-wave expansion method, and interference properties are investigated by using the finite-difference time-domain method. For our designed photonic crystal Mach-Zehnder interferometer, the simulation results show that the light transmission can be modulated from 92.7% to 1.4% with different temperature distributions.
Sintering behaviors and dielectric properties of nanocrystalline barium titanate
(2007-04-15)
Ying, Kuo-Liang
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Hsieh, T.-E.
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材料科學與工程學系
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Department of Materials Science and Engineering
Nanometer-scale barium titanate (BaTiO3) Powders were prepared via a process consisting of chemical dispersion and physical grinding/mixing. Sintering behaviors, microstructures as well as their correlations to dielectric properties of nano-BaTiO3 sintered at the temperatures ranging from 1100 to 1300 degrees C for various time spans were investigated. It was found that specific control on sintering condition is required for the nano-BaTiO3 powders to achieve desired microstructure, crystalline phase and dielectric properties of devices. The BaTiO3 sample sintered at 1100 degrees C for 6 h possesses relatively small grain sizes (about 140 nm), high density (about 95% T.D.) and distinct room-temperature dielectric properties (dielectric constant = 8000; dielectric loss = 5 x 10(-3)). Hence, in addition to the saving of thermal budget, the adoption of nano-scale ceramic powders in conjunction with appropriate sintering process may dramatically improve the dielectric properties of devices. (C) 2007 Elsevier B.V. All rights reserved.
Synthesis and characterization of polyimide-silica nanocomposites using novel fluorine-modified silica nanoparticles
(2007-04-15)
Mo, Te-Cheng
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Wang, Hong-Wen
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Chen, San-Yan
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Dong, Rui-Xuan
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Kuo, Chien-Hung
Polyimide-silica nanocomposites were synthesized with 4,4'-oxydianiline, 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine-modified silica nanoparticles. Fluorinated precursors such as 4",4'"-(hexafluoroisopropylidene)bis(4-phenoxyaniline) (6FBPA) and 4,4'-(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polymide-silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide-silica nanocomposites containing 6FBPA-modified silica exhibited more uniformity than those of the nanocomposites containing BISAF-modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA-modified silica but not BISAF-modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA-modified silica nanoparticles demonstrated an effective way of synthesizing low-dielectric-constant polyimide-silica nanocomposites. (c) 2007 Wiley Periodicals, Inc.
Optical properties of InGaN quantum dots grown by SiN(x) nanomasks
(2007-04-15)
Huang, L. L.
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Chang, H. J.
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Chou, Y. Y.
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Wang, C. H.
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Chen, T. T.
InGaN quantum dots (QDs) deposited on SiN(x) nanomasks have been investigated by atomic force microscopy, photoluminescence (PL), and photoluminescence excitation (PLE) measurements. It was found that the size of QDs can be well controlled by SiN(x) nanomasks, enabling the manipulation of quantum confinement effect. The PL spectra of InGaN QDs contain several fine structures, and the main peaks can be attributed to families of QDs with different sizes. The emission arising from InGaN QDs and GaN buffer layer can be clearly distinguished based on PLE measurement, which can be used to improve the interpretation in the previous reports. Our study indicates that the quantum confined Stark effect due to piezoelectric field plays a very important role in the optical properties of InGaN QDs, which is very useful for the application of optoelectronic devices.(c) 2007 American Institute of Physics.
POPI: predicting immunogenicity of MHC class I binding peptides by mining informative physicochemical properties
(2007-04-15)
Tung, Chun-Wei
;
Ho, Shinn-Ying
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生物科技學系
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生物資訊及系統生物研究所
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Department of Biological Science and Technology
Motivation: Both modeling of antigen-processing pathway including major histocompatibility complex (MHC) binding and immunogenicity prediction of those MHC-binding peptides are essential to develop a computer-aided system of peptide-based vaccine design that is one goal of immunoinformatics. Numerous studies have dealt with modeling the immunogenic pathway but not the intractable problem of immunogenicity prediction due to complex effects of many intrinsic and extrinsic factors. Moderate affinity of the MHC-peptide complex is essential to induce immune responses, but the relationship between the affinity and peptide immunogenicity is too weak to use for predicting immunogenicity. This study focuses on mining informative physicochemical properties from known experimental immunogenicity data to understand immune responses and predict immunogenicity of MHC-binding peptides accurately. Results: This study proposes a computational method to mine a feature set of informative physicochemical properties from MHC class I binding peptides to design a support vector machine (SVM) based system (named POPI) for the prediction of peptide immunogenicity. High performance of POPI arises mainly from an inheritable bi-objective genetic algorithm, which aims to automatically determine the best number m out of 531 physicochemical properties, identify these m properties and tune SVM parameters simultaneously. The dataset consisting of 428 human MHC class I binding peptides belonging to four classes of immunogenicity was established from MHCPEP, a database of MHC-binding peptides (Brusic et al., 1998). POPI, utilizing the m = 23 selected properties, performs well with the accuracy of 64.72% using leave-one-out cross-validation, compared with two sequence alignment-based prediction methods ALIGN (54.91%) and PSI-BLAST (53.23%). POPI is the first computational system for prediction of peptide immunogenicity based on physicochemical properties.
Anticontrol of chaos of the fractional order modified van der Pol systems
(2007-04-15)
Ge, Zheng-Ming
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Zhang, An-Ray
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機械工程學系
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Department of Mechanical Engineering
Anticontrol of chaos of fractional order modified van der Pol systems is studied. Addition of a constant term and addition of k vertical bar x vertical bar sinx term where x is a state of the system are used to anticontrol the system effectively. By applying numerical results, phase portrait, Poincare maps and bifurcation diagrams a variety of the phenomena of the chaotic motion can be presented. Finally, it can be find that chaos under these procedures exists in the fractional order systems of a modified van der Pol system. (c) 2006 Elsevier Inc. All rights reserved.
Upstream power equalization in a gigabit passive optical network
(2007-04-16)
Yeh, Chien-Hung
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Hsu, Dar-Zu
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Chi, Sien
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光電工程學系
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Department of Photonics
We propose a technique for achieving equalized power in upstream traffic in the gigabit passive optical network (G-PON). A simple power equalizer based on a Fabry - Perot laser diode (FP-LD) is proposed and demonstrated experimentally. By the proposed scheme, the different upstream powers can be equalized. As a result, a 20 dB dynamic upstream power range from - 5 to - 25 dBm, having a 1.7 dB maximal power variation, is attained. Moreover, the performance of the proposed configuration is also discussed. (c) 2007 Optical Society of America.
主題式分類的網路購物方法及系統
(2007-04-16)
陳穎平
本發明係有關於一種主題式分類的網路購物方法及系統,使用者透過網路瀏覽器連結到網路購物系統,進入一購物或檢索性質的網站,該網站提供使用者輸入公衆人物、美術、圖書、音樂、電影、戲刻、文藝著作、漫畫、新聞等一個或一個以上之關鍵語,將所輸入之關鍵語與資料庫中比對是否有相關之產品。
低密度高韌性合金材料及其製法
(2007-04-16)
劉增豐
;
李堅瑋
一種低密度高韌性合金材料及其製法,其主要組成為以重量百分比計,大於等於23小於等於33的錳,大於等於8.1小於等於9.8的鋁,大於等於3小於等於7.8的鉻,大於等於0.6小於等於1.2的碳,大於等於0.1小於等於0.24的矽及其餘比例為鐵之合金材料。上所揭示之合金成份之合金材料製作高爾夫球頭時,不須任何熱處理及鍛造、軋延等熱作和冷作塑性加工,即可使高爾夫球頭具有極佳的延伸性、强度、吸震性及抗蝕性等特性,大幅降低目前的生產成本。
Size dependence of tetrahedral bond lengths in CdSe nanocrystals
(2007-04-16)
Wu, Pin-Jiun
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Stetsko, Yuri P.
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Tsuei, Ku-Ding
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Dronyak, Roman
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Liang, Keng S.
The structural characteristics of organically passivated CdSe nanocrystals (NCs) were investigated with x-ray diffraction and extended x-ray absorption fine structure. As the NC size decreases, the axial bond length R-(1) for an atomic tetrahedron extends but the equatorial bond length R-(2) contracts, with a similar tendency of distortion for the lattice parameters of the wurtzite structure. The authors suggest that the observed hexagonal distortion is attributed to the surface stress of the NCs related to the organic passivation effect and the relaxation of atomic positions at the stacking fault interface. (c) 2007 American Institute of Physics.
White light generation under violet-blue excitation from tunable green-to-red emitting Ca2MgSi2O7 : Eu,Mn through energy transfer
(2007-04-16)
Chang, Chun-Kuei
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
Yellowish green-to-orange red emission can be generated by energy transfer from Eu2+ to Mn2+ in the Ca2MgSi2O7 host matrix. Eu2+-doped Ca2MgSi2O7 shows a broad green emission band centering at 528 nm and Mn2+-doped Ca2MgSi2O7 exhibits a red emission at around 602 nm. The authors have demonstrated that the mechanism of energy transfer from Eu2+ to Mn2+ in Ca2MgSi2O7:Eu,Mn phosphor is a resonant type via a dipole-quadrupole mechanism. They have also shown that the white light with varied hue, depending on contents of Mn2+, is generated by combination of predesigned emission wavelength-tunable Ca2MgSi2O7:Eu,Mn phosphors and violet-blue light source. (c) 2007 American Institute of Physics.
Nanogap formation by palladium hydrogenation for surface conduction electron emitters fabrication
(2007-04-16)
Tsai, Chih-Hao
;
Pan, Fu-Ming
;
Chen, Kuan-Jung
;
Wei, Cheng-Yang
;
Liu, Mei
Nanometer-scale gaps in Pd strips are obtained by hydrogen absorption under high pressure treatment. The resulting lattice constant increase due to the Pd phase transformation after hydrogen uptake results in a large compressive stress on the thin Pd films. Under proper geometric arrangement of the Pd electrode within a surface conduction electron (SCE) emitter structure, a single nanogap per SCE device is obtained. A turn-on voltage of 41 V is observed for emitters with a 25 nm gap. (c) 2007 American Institute of Physics.