Browsing by Issue Date, starting with "2006-10-27"

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Effects of cathode humidification on the gas-liquid interface location in a PEM fuel cell
(2006-10-27)
Lee, Chun-I
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
This study investigates the location of the gas-liquid interface under various humidity conditions in the cathode gas diffusion layer and the conventional flow field of a polymer electrolyte membrane fuel cell (PEMFC), using commercial computational fluid dynamics (CFDRC) analysis, based on a three-dimensional steady state isothermal model. The effects of the formation of liquid water on the transport of reactant gas are considered in the model. The simulation results indicate that the gas-liquid interface approaches the gas flow channel inlet and the cell performance declines gradually as liquid water obstructs the pores in the porous media as the relative humidity of the cathode is increased. Additionally, the oxygen fraction, the water fraction and the liquid water saturation field along the flow channel are presented. (c) 2006 Elsevier B.V. All rights reserved.
Effect of inlet flow maldistribution on the thermal and electrical performance of a molten carbonate fuel cell unit
(2006-10-27)
Liu, Syu-Fang
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Chu, Hsin-Sen
;
Yuan, Ping
;
機械工程學系
;
Department of Mechanical Engineering
This study investigates the temperature and current density distributions in a molten carbonate fuel cell unit when the inlet flows of the anode gas and the cathode gas are mal-distributed in eight patterns. The two-dimensional simultaneous partial differential equations of mass, energy and electrochemistry are solved numerically. The results indicate that the maldistribution of anode and cathode gases dominates the current density field and the cell temperature field, respectively. Moreover, the non-uniform inlet flow slightly affects the mean temperature and mean current density, but worsens the distribution of temperature and current density for most maldistribution patterns. According to the results, the variations of the cell temperature in Pattern G and the current density in Pattern D are 12% and 37% greater than those in the uniform pattern when the deviation of the non-uniform profile is 0.25. Consequently, the effect of non-uniform inlet flow on the temperature and current density distribution on the cell plane is evident, and cannot be neglected. (c) 2006 Elsevier B.V. All rights reserved.
Transient behavior of a PEMFC
(2006-10-27)
Chang, Shih-Ming
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Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
The transient behavior of a proton exchange membrane fuel cell (PEMFC) with porosity is investigated in this study using a two-phase, half-cell model. The thin film agglomerate approach is used to model the catalyst layer. Both vapor transport and liquid water transport in the PEMFC are examined in this study. Proton transport is much faster than the gaseous and liquid water transport. The ionic potential reaches a steady state level in similar to 10(-1) s but liquid water transport takes similar to 10 s. The variation of the ionic potential loss reaches a critical value, decreasing to a steady state, and is not monotonic. The gas diffusion layer (GDL) and the catalyst layer (CL) porosity, which can affect cell performance, have been carefully investigated. The current density rises rapidly within 10(-2) S, then remaining constant. After I s, this is affected by the cell voltage, GDL porosity, and CL porosity, and if the GDL porosity is below 0.4, the current density drops. For the gas diffusion layer porosity, the current density increases between epsilon(GDL) = 0.2 and epsilon(GDL) = 0.5, with increased GDL porosity. For the catalyst layer porosity, the optimum value appears between epsilon(CL) = 0.06 and epsilon(CL) = 0.1 (c) 2006 Elsevier B.V. All rights reserved.
Growth behaviour of Ge nano-islands on the nanosized Si{111} facets bordering on two {100} planes
(2006-10-28)
Ferng, Shyh-Shin
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Yang, Tsung-Hsi
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Luo, Guangli
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Yang, Kai-Ming
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Hsieh, Ming-Feng
Si( 100) substrates were used to fabricate various nanosized {111} facets between the ( 100) planes using photolithography and anisotropic wet chemical etching. Following simultaneous Ge chemical vapour deposition on the neighbouring ( 100) and {111} facets, the Ge nano-island formation and distribution was observed on both the ( 100) terraces and the {111} side walls using a dynamical atomic force microscope. The nano-island formation on the nanosized {111} strip facets was found to be strongly suppressed upon reducing the strip width due primarily to the interaction of adatoms on the neighbouring facets. Specifically, the difference in the effective chemical potential of Ge adatoms on the two neighbouring facets leads to the depletion of nano-islands on the {111} strip with width < 500 nm under the growth condition used in this study.
Experimental and theoretical investigation of rate coefficients of the reaction S(P-3)+OCS in the temperature range of 298-985 K
(2006-10-28)
Lu, Chih-Wei
;
Wu, Yu-Jong
;
Lee, Yuan-Pern
;
Zhu, R. S.
;
Lin, M. C.
The reaction S(P-3)+OCS in Ar was investigated over the pressure range of 50-710 Torr and the temperature range of 298-985 K with the laser photolysis technique. S atoms were generated by photolysis of OCS with light at 248 nm from a KrF excimer laser; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged SO2. At pressures less than 250 Torr, our measurements give k(298 K)=(2.7 +/- 0.5)x10(-15) cm(3) molecule(-1) s(-1), in satisfactory agreement with a previous report by Klemm and Davis [J. Phys. Chem. 78, 1137 (1974)]. New data determined for 407-985 K connect rate coefficients reported previously for T >= 860 and T <= 478 K and show a non-Arrhenius behavior. Combining our results with data reported at high temperatures, we derived an expression k(T)=(6.1 +/- 0.3)x10(-18) T-1.97 +/- 0.24 exp[-(1560 +/- 170)/T] cm(3) molecule(-1) s(-1) for 298 <= T/K <= 1680. At 298 K and P >= 500 Torr, the reaction rate was enhanced. Theoretical calculations at the G2M(CC2) level, using geometries optimized with the B3LYP/6-311+G(3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) calculations agree satisfactorily with experimental observations. According to our calculations, the singlet channel involving formation of SSCO followed by direct dissociation into S-2(a (1)Delta(g))+CO dominates below 2000 K; SSCO is formed via intersystem crossing from the triplet surface. At low temperature and under high pressure the stabilization of OCS2, formed via isomerization of SSCO, becomes important; its formation and further reaction with S atoms partially account for the observed increase in the rate coefficient under such conditions. (c) 2006 American Institute of Physics.
Pulse retrieval from interferometric autocorrelation measurement by use of the population-split genetic algorithm
(2006-10-30)
Chen, Ching-Wei
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Huang, Jung Y.
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Pan, Ci-Ling
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光電工程學系
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Department of Photonics
The population-split genetic algorithm ( PSGA) was successfully applied to retrieve femtosecond optical fields from interferometric autocorrelation traces. PSGA strikes a balance between diversity and the size of population in the genetic algorithm. As a result, PSGA is less likely prematurely converging to sub-optimal solutions. Theoretical and experimental studies indicate that the PSGA can yield more accurate results in shorter time compared with conventional genetic algorithm and the iterative method. (c) 2006 Optical Society of America.
Monolithic red-green-blue laser light source based on cascaded wavelength conversion in periodically poled stoichiometric lithium tantalate
(2006-10-30)
Gao, Z. D.
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Zhu, S. N.
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Tu, Shih-Yu
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Kung, A. H.
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光電工程學系
A compact, pulsed, red, green, and blue laser source based on cascaded quasi-phase-matched wavelength conversion in two periodic superlattices set in tandem in a single stoichiometric LiTaO3 crystal and pumped by a laser source at 532 nm is reported. The white light equivalent flux obtained was 80 lm per 1 W input with a green to white light power conversion efficiency of > 30%. Unity power conversion is feasible in this monolithic approach. (c) 2006 American Institute of Physics.
Generation properties of coherent infrared radiation in the optical absorption region of GaSe crystal
(2006-10-30)
Chen, Ching-Wei
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Hsu, Yu-Kuei
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Huang, Jung Y.
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Chang, Chen-Shiung
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Zhang, Jing-Yuan
We report a study of the effect of optical absorption on generation of coherent infrared radiation from mid-IR to THz region from GaSe crystal. The infrared-active modes of epsilon-GaSe crystal at 236 cm(-1) and 214 cm(-1) were found to be responsible for the observed optical dispersion and infrared absorption edge. Based upon phase matching characteristics of GaSe for difference-frequency generation (DFG), new Sellmeier equations of GaSe were proposed. The output THz power variation with wavelength can be properly explained with a decrease of parametric gain and the spectral profile of absorption coefficient of GaSe. The adverse effect of infrared absorption on (DFG) process can partially be compensated by doping GaSe crystal with erbium ions. (c) 2006 Optical Society of America.
New simple constructions of distance-increasing mappings from binary vectors to permutations
(2006-10-31)
Lin, Jyh-Shyan
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Chang, Jen-Chun
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Chen, Rong-Jaye
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資訊工程學系
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Department of Computer Science
Distance-increasing mappings (DIMs) are mappings from the set of binary vectors of a fixed length to the set of permutations of the same length that increase Hamming distances except when that is obviously not possible. In this paper, we propose new non-recursive constructions of DIMs which are based on simple compositions of permutations. In comparison with Chang's constructions, our new constructions do not need any table-lookup operations, and usually have better distance expansion distributions when the length is odd. (c) 2006 Elsevier B.V. All rights reserved.
The parametric study of carbon nanotips grown by MWPECVD with controllable sharpness using various metallic catalysts
(2006-11-01)
Chen, Chien-Chung
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Chen, Yi-Hui
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Chen, Chia-Fu
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材料科學與工程學系
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Department of Materials Science and Engineering
A parametric study for growing vertically aligned carbon nanotips utilizing microwave plasma enhanced chemical vapor deposition was presented. The effects of process parameters including process time, microwave power and applying bias were discussed. The height of nanotips was affected by the microwave power and process time. The growth of rod-shape or tip-shape structure depends on the microwave power. The high microwave power is favorable for growing rod-shape structure which results from the faster diffusion of carbon atoms in the metallic catalysts under high temperature. The sharpness of carbon nanotips seem possibly to be controlled by varying bias voltage. These carbon nanotips exhibit the characters of high number density and well vertical alignment. Furthermore, we demonstrated that the growth of carbon nanotips by different metallic catalysts, such as Au, Pt, Ag and Si, could be chosen for applying in various regions. (c) 2006 Elsevier B.V. All rights reserved.
An optimum algorithm for compacting error traces for efficient design error debugging
(2006-11-01)
Yen, Chia-Chih
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Jou, Jing-Yang
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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
Diagnosing counterexamples with error traces has acted as one of the most critical steps in functional verification. Unfortunately, error traces are normally very lengthy such that designers need to spend considerable effort to understand them. To alleviate the designers' burden for debugging, we present a SAT-based algorithm for reducing the lengths of error traces. The algorithm performs the paradigm of the binary search algorithm to halve the search space recursively. Furthermore, it applies a novel theorem to guarantee gaining the shortest lengths for the error traces. Based on the optimum algorithm, we develop two robust heuristics to handle real designs. Experimental results demonstrate that our approaches greatly surpass previous work and, indeed, have promising solutions.
Organic light-emitting devices based on a highly robust osmium(II) complex
(2006-11-01)
Liu, Tswen-Hsin
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Chen, Chin H.
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光電工程學系
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Department of Photonics
An osmium(II) complex, Os(fptz)(2)(PPh2Me)(2) [fptz=3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, PPh2Me=methyl-diphenyl-phosphan], when doped in a 4,4(')-N,N-'-dicarbazolebiphenyl host as a phosphorescent red emitter in organic light-emitting devices, has the unusual property of resisting concentration quenching and sustaining its external quantum efficiency (EQE) (8%-9%) over a wide range of doping concentration (20%-40%). Single-crystal x-ray diffraction evidence is presented that the difference in doping behaviors can be linked to the octahedral configuration of Os(fptz)(2)(PPh2Me)(2), which could prevent the undesirable molecular aggregation from occurring at high concentration, thus delaying the onset of quenching. Accordingly, the high doping concentration of Os(fptz)(2)(PPh2Me)(2) leads to a significant suppression of luminescence quenching at high brightness/current and achieves a "flat" EQE versus brightness response owing to the increase in the emission sites in the emission layer. (c) 2006 American Institute of Physics.
An investigation of heat transfer of a reciprocating piston
(2006-11-01)
Fu, Wu-Shung
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Lian, Sin-Hong
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Hao, Liao-Ying
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機械工程學系
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Department of Mechanical Engineering
A numerical simulation of a reciprocating piston cooled by fluid is performed to investigate effects of frequency, amplitude and Reynolds number on heat transfer rate of the piston. For facilitating the analyses, the model of the reciprocating piston is replaced by a "Pi" shape cooling channel. This subject belongs to a kind of moving boundary problems, and the Finite Element Method and arbitrary Lagragian-Eulerian Kinematics description method are then utilized. The heat transfer mechanisms affected by the main parameters of frequency, amplitude and Reynolds number are discussed in detail. The results show that the heat transfer mechanisms influenced by the frequency are more remarkable than those influenced by the amplitude and Reynolds number. Besides, the larger the above three parameters are, the apparent enhancements of heat transfer are usually obtained. (c) 2006 Elsevier Ltd. All rights reserved.
The safe operating area of GaAs-based heterojunction bipolar transistors
(2006-11-01)
Lee, Chien-Ping
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Chati, Frank H. E.
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Ma, Wenlong
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Wang, Nanlei Larry
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電子工程學系及電子研究所
The safe operating area (SOA) of GaAs-based heterojunction bipolar transistors has been studied considering both the self-heating effect and the breakdown effect. The Kirk effect induced breakdown (KIB) was considered to account for the decrease of the breakdown voltage at high currents. With reasonable emitter ballastors, the RIB effect was shown to be the major cause for device failure at high currents, while the thermal effect controls the low current failure. The effect of emitter resistance and base resistance on device stability was also studied. While the emitter resistance always improves the device stability by expanding the SOAs, the base resistance degrades SOAs when the KIB dominates the failure mechanism. The effect of the base resistance on SOAs was explained by its control on the flow of the avalanche current. Since the KIB effect depends on the collector structure, it was shown that a noniuniformly doped collector can effectively improve the SOAs.
IEEE standard 1500 compatible interconnect diagnosis for delay and crosstalk faults
(2006-11-01)
Li, Katherine Shu-Min
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Su, Chauchin
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Chang, Yao-Wen
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Lee, Chung-Len
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Chen, Jwu E.
An interconnect diagnosis scheme based on the oscillation ring (OR) test methodology for systems-on-chip (SOC) design with heterogeneous cores is proposed. In addition to traditional stuck-at and open faults, the OR test can also detect and diagnose important interconnect faults such as delay faults and crosstalk glitches. The large number of test rings in the SOC design, however, significantly complicates the interconnect diagnosis problem. In this paper, the diagnosability of an interconnect structure is first analyzed then a fast diagnosability checking algorithm and an efficient diagnosis ring generation algorithm are proposed. It is shown in this paper that the generation algorithm achieves the maximum diagnosability for any interconnect. Two optimization techniques are also proposed, an adaptive and a concurrent diagnosis method, to improve the efficiency and effectiveness of interconnect diagnosis. Experiments on the MCNC benchmark circuits show the effectiveness of the proposed diagnosis algorithms. In all experiments, the method achieves 100% fault detection coverage and the optimal interconnect diagnosis resolution.
Syntheses and specific interactions of poly(epsilon-caprolactone)-block-poly(vinyl phenol) copolymers obtained via a combination of ring-opening and atom-transfer radical polymerizations
(2006-11-01)
Kuo, Shiao-Wei
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Huang, Chih-Feng
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Lu, Chu-Hua
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Lin, Ho-May
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Jeong, Kwang-Un
A series of PCL-b-PVPh diblock copolymers were prepared through combinations of ring-opening and atom-transfer radical polymerizations of c-caprolactone and 4-acetoxystyrene, and subsequent selective hydrolysis of the acetyl protective group. This PCL-b-PVPh diblock copolymer shows a single glass transition temperature over the entire composition range, indicating that this copolymer is able to form a miscible amorphous phase due to the formation of intermolecular hydrogen bonding between the hydroxyl of PVPh and the carbonyl of PCL. In addition, DSC analyses also indicated that the PCL-b-PVPh diblock copolymers have higher glass transition temperatures than their corresponding PCL/PVPh blends. FT-IR was used to study the hydrogen-bonding interaction between the PVPh hydroxyl group and the PCL carbonyl group at various compositions.
Elastic constants identification of composite materials using single angle-ply laminate
(2006-11-01)
Chen, C. M.
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Kam, T. Y.
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機械工程學系
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Department of Mechanical Engineering
A method is presented for identification of elastic constants for composite materials using three measured strains of a single angle-ply laminate subjected to tensile testing. In the proposed method, the trial material constants of the angle-ply laminate are used to predict the corresponding strains in the laminate. An error function is established to measure the difference between the experimental and theoretical predictions of the strains. The identification of material constants is then formulated as a constrained minimization problem in which the material constants are determined to make the error function a global minimum. The accuracy and capability of the proposed method are demonstrated by means of a number of examples of the identification of material constants of angle-ply laminates with different lay-ups. Experimental data obtained from static tensile tests of several angle-ply laminates are used to identify the material constants of the laminates. The excellent results obtained in the experimental investigation have validated the applicability of the proposed method.
Self-substrate-triggered technique to enhance turn-on uniformity of multi-finger ESD protection devices
(2006-11-01)
Ker, Ming-Dou
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Chen, Jia-Huei
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電機學院
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College of Electrical and Computer Engineering
A novel self-substrate-triggered technique for on-chip ESD protection design is proposed to solve the non-uniform turn-on phenomenon of multi-finger gate-grounded nMOS (GGnMOS). The center-finger nMOS transistors in the multi-finger GGnMOS structure are always turned on first under ESD stress, so its source terminal is connected to the base (substrate) terminals of the other parasitic lateral n-p-n bipolar transistors (BJTs in the GGnMOS structure) to form the self-substrate-triggered design. With the proposed self-substrate-triggered technique, the first turned-on center-finger nMOS transistors are used to trigger on the others. Therefore, all fingers of GGnMOS can be triggered on simultaneously to discharge ESD current. From the experimental results verified in a 0.13-mu m CMOS process with the thin gate oxide of 25 A, the turn-on uniformity and ESD robustness of the GGnMOS can be greatly improved without increasing extra layout area through the proposed self-substrate-triggered technique.
Self-organization of microlens arrays caused by the spin-coating-assisted hydrophobic effect
(2006-11-01)
Chen, Fang-Chung
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Huang, Wen-Kuei
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Ko, Chu-Jung
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光電工程學系
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顯示科技研究所
A simple, low-cost, low-temperature, and shape-controllable approach has been demonstrated to fabricate polymer microlens arrays (MLAs). By using microcontact printing of the self-assembled monolayers and then spin coating, the microlenses were able to organize themselves on the patterned glass substrate. High-quality MLAs made of NOA65 prepolymer with lens-diameters of 50, 75, and 100 pm have been fabricated by this method. Lens shapes can be controlled by changing the spin rates of the prepolymer coating. Optical measurements have revealed an excellent light-collecting capability from the fabricated MLAs. It is anticipated that the technique will be ideally suited to low-cost and high-volume production.
A tight bound on remote reference time complexity of mutual exclusion in the read-modify-write model
(2006-11-01)
Chen, Sheng-Hsiung
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Huang, Ting-Lu
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資訊工程學系
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Department of Computer Science
In distributed shared memory multiprocessors, remote memory references generate processor-to-memory traffic, which may result in a bottleneck. It is therefore important to design algorithms that minimize the number of remote memory references. We establish a lower bound of three on remote reference time complexity for mutual exclusion algorithms in a model where processes communicate by means of a general read-modify-write primitive that accesses at most one shared variable in one instruction. Since the general read-modify-write primitive is a generalization of a variety of atomic primitives that have been implemented in multiprocessor systems, our lower bound holds for all mutual exclusion algorithms that use such primitives. Furthermore, this lower bound is shown to be tight by presenting an algorithm with the matching upper bound. (C) 2006 Elsevier Inc. All rights reserved.