Browsing by Issue Date, starting with "2000-03-30"

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Apodised fibre Bragg gratings fabricated with uniform phase mask using low cost apparatus
(2000-03-30)
Yang, CC
;
Lai, YC
;
光電工程學系
;
Department of Photonics
New exposure schemes for fabricating apodised fibre Bragg gratings using a uniform phase mask are described. A sidelobe suppression level as high as 20dB in the lower wavelength region has been successfully achieved. The schemes allow the writing of truly apodised fibre Bragg gratings using low cost and simple apparatus.
Pseudo-Hamiltonian-connected graphs
(2000-03-30)
Chang, GJ
;
Zhu, XD
;
應用數學系
;
Department of Applied Mathematics
Given a graph G and a positive integer k, denote by G[k] the graph obtained from G by replacing each vertex of G with an independent set of size k. A graph G is called pseudo-k Hamiltonian-connected if G[k] is Hamiltonian-connected, i.e., every two distinct vertices of G[k] are connected by a Hamiltonian path. A graph G is called pseudo Hamiltonian-connected if it is pseudo-k Hamiltonian-connected for some positive integer k. This paper proves that a graph G is pseudo-Hamiltonian-connected if and only if for every non-empty proper subset X of V(G), N(X) > X. The proof of the characterization also provides a polynomial-time algorithm that decides whether or not a given graph is pseudo-Hamiltonian-connected. The characterization of pseudo-Hamiltonian-connected graphs also answers a question of Richard Nowakowski, which motivated this paper. (C) 2000 Elsevier Science B.V. All rights reserved.
Beam-switchable scanning leaky-wave antenna
(2000-03-30)
Wang, CJ
;
Shih, YC
;
Jou, CF
;
傳播研究所
;
Institute of Communication Studies
A beam-switchable scanning leaky-wave antenna (LWA) has been developed. This LWA with a two-terminal feeding microstrip, line structure is integrated with a single port double throw (SPDT) snitch as a control circuit. In dual-beam mode, the scanning angle is steered over a range of 36-64 degrees for the right-hand beam and 144 -116 degrees for the left-hand beam. In one-beam made, the scanning angle is measured over 20 degrees for the right-hand beam. The measured result shows that we can change from the, one-beam mode to the dual-beam mode electronically by controlling the on/off status of an SPDT switch, in contrast to the case For traditional leaky wave antennas.
iGSM: VolP service for mobile networks
(2000-04-01)
Rao, HCH
;
Lin, YB
;
Cho, SL
;
資訊工程學系
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Department of Computer Science
This article proposes iGSM: a voice-over-IF value-added service for mobile network. The iGSM service provides user mobility to subscribers, which allows them to use either GSM handsets or H.323 terminals (IP phones or PCs) to access telecommunications services. We describe how the iGSM registration, deregistration, and call delivery procedures can be implemented without modifying the GSM network. We study how the tromboning effect in the standard GSM system can be avoided when accessing the IP network. Then we investigate the misrouting problem caused by user mobility.
Crystallization kinetics of poly(trimethylene terephthalate)
(2000-04-01)
Huang, JM
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) have been investigated using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Enthalpy data of exotherm from isothermal crystallization were analyzed using the Avrami theory. The average value of the Avrami exponent, n, is about 2.8. From the melt, PTT crystallizes according to a spherulite morphology. The spherulite growth rate and the overall crystallization rate depend on crystallization temperature. The increase in the spherulitic radius was examined by polarized light microscopy. Using values of transport parameters common to many polymers (U* = 1500 cal/mol, T-infinity = T-g - 30 degrees C) together with experimentally determined values of T-m(0) (248 degrees C) and T-g (44 degrees C), the nucleation parameter, k(g), for PTT was determined. On the basis of secondary nucleation analyses, a transition between regimes III and II was found in the vicinity of 194 degrees C (Delta T congruent to 54 K). The ratio of k(g) of these two regimes is 2.1, which is very close to 2.0 as predicted by the Lauritzen-Hoffman theory. The lateral surface-free energy, sigma = 10.89 erg/cm(2) and the fold surface-free energy, sigma(e) = 56.64 erg/cm(2) were determined. The latter leads to a work of chain-folding, q = 4.80 kcal/mol folds, which is comparable to PET and PET previously reported. (C) 2000 John Wiley & Sons, Inc.
Electrostatic dissipation and flexibility of poly(oxyalkylene)amine segmented epoxy derivatives
(2000-04-01)
Lin, JJ
;
Tseng, FP
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A family of hydrophilic and flexible epoxy polymers was prepared from the reaction of poly(oxyalkylene)amines and diglycidyl ether of bisphenol-A (DGEBA) at 1:1 molar ratio of N-H to epoxide. The use of a high molecular weight (M-W = 1000-6000) poly(oxyethylene-oxypropylene)amine and a low M-W amine as curing agents provided epoxy materials with good properties in toughness and hydrophilicity. The hydrophilicity, probed by surface resistivity of these cured materials, was found to be affected by the nature and weight content of poly(oxyethylene) segment in the polymer backbone, and also by the degree of crystallinity. Specifically, in the presence of a water-soluble poly(oxyethylene-oxypropylene)diamine of M-W 2000 the cured epoxies can reach surface resistivity as low as 10(8.6-9.6) Omega/square. In comparison, the water-insoluble poly(oxypropylene) diamine of M-W 2000 afforded a higher surface resistivity of 10(10.5) Omega/square because of the difference in hydrophilicity between oxyethylene and oxypropylene functionalities. Poly(oxypropylene)diamine of M-W 230 as the sole curing agent generated an epoxy with even higher surface resistivity of 10(13) Omega/square due to a highly crosslinking structure. With proper selection of mixed poly(oxyethylene-oxypropylene)diamine (25 wt%) and 2-aminoethanol (9 wt%), the DGEBA cured polymer had an appropriate surface resistivity of 10(9.8) Omega/square for antistatics. Moreover, this material was extremely ductile in appearance and showed over 500% elongation at break during mechanical tests. The high flexibility is rationalized by the balanced chemical structure of poly(oxyalkylene) segments and bisphenol-A distributed in a slightly crosslinked system. (C) 2000 Society of Chemical Industry.
Design on the low-leakage diode string for using in the power-rail ESD clamp circuits in a 0.35-mu m silicide CMOS process
(2000-04-01)
Ker, MD
;
Lo, WY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new design on the diode string with very tow leakage current is proposed for using in the ESD clamp circuits across the power rails. By adding an NMOS-controlled lateral SCR (NCLSCR) device into the stacked diode string, the Leakage current of this new diode string with six stacked diodes at 5-V (3.3-V) forward bias can be reduced to only 2.1 (1.07) nA at a temperature of 125 degrees C in a 0.35-mu m silicide CMOS process, whereas the previous designs have a leakage current in the order of mA, The total blocking voltage of this new design with NCLSCR can be linearly adjusted by changing the number of the stacked diodes in the diode string without causing latch-up danger across the power rails. From the experimental results, the human-body-model ESD level of the ESD clamp circuit with the proposed low-leakage diode string is greater than 8 kV in a 0.35-mu m silicide CMOS process by using neither the ESD-implantation nor the silicide-blocking process modifications.
Resin transfer molding (RTM) process of a high performance epoxy resin. I: Kinetic studies of cure reaction
(2000-04-01)
Lee, CL
;
Ho, JC
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Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The cure kinetics of a high performance PR500 epoxy resin in the temperature range of 160-197 degrees C for the resin transfer molding (RTM) process have been investigated. The thermal analysis of the curing kinetics of PR500 resin was carried out by differential scanning calorimetry (DSC), with the ultimate heat of reaction measured in the dynamic mode and the rate of cure reaction and the degree of cure being determined under isothermal conditions. A modified Kamal's kinetic model was adapted to describe the autocatalytic and diffusion-controlled curing behavior of the resin. A reasonable agreement between the experimental data and the kinetic model has been obtained over the whole processing temperature range, including the mold filling and the final curing stages of the RTM process.
W ohmic contact for highly doped n-type GaN films
(2000-04-01)
Lin, CF
;
Cheng, HC
;
Chi, GC
;
電子工程學系及電子研究所
;
奈米中心
Ohmic contacts with low resistance and low barrier height were fabricated on n-type GaN films using W metallization. The n-type GaN films were grown by low pressure metalorganic chemical vapor deposition (LPMOCVD) with Si as the dopant. Ohmic characteristics were studied for GaN films with Si carrier concentration varying from 1.4 x 10(17) to 1.8 x 10(19) cm(-3). The specific contact resistivity were reduced with increasing Si-doping concentration on as-deposited W/GaN films, and the lowest value was 3.6 x 10(-4) Ohm cm(2) on n-type GaN with a concentration of 1.8 x 10(19) cm(-3). After rapid thermal annealing (RTA) treatment on W/GaN films at 1000 degrees C for 30 s, the specific contact resistivity were reduced to 1 x 10(-4) Ohm cm(2). The W metal on n-type GaN films, show that good thermal stability varied the annealing temperatures. The barrier height of as-deposited W metal on GaN is calculated to be 0.058 eV. (C) 2000 Elsevier Science Ltd. All rights reserved.
Emission current influence of gated structure and diamond emitter morphologies in triode-type field emission arrays
(2000-04-01)
Chen, CF
;
Hsieh, HC
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材料科學與工程學系
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Department of Materials Science and Engineering
Field emission display is evolving as a promising technique for the future generation of flat panel displays. Characteristics affecting the power of field emitter arrays include the shape and work function of emission materials, distance between tip and gate, and the environmental vacuum condition. In this work, we present a novel scheme that involves a new fabrication process of gate structure metal-insulator-semiconductor (MIS) diode using IC technology. Deposition of the diamond film in this MIS diode forms a column-like diamond with gated field emission arrays (FEAs). This process is completed using a bias-assisted microwave plasma chemical vapor deposition system. Our results indicate that the threshold voltage of column-like diamond FEAs is about 10 V, and the field emission current density is about 139 mA cm(-2) (at V-gc = 20 V). The diamond field emitter array devices with the new gate structure and tip morphology significantly influence the electron field emission characteristics. (C) 2000 Elsevier Science S.A. All rights reserved.
Genetic reinforcement learning through symbiotic evolution for fuzzy controller design
(2000-04-01)
Juang, CF
;
Lin, JY
;
Lin, CT
;
電控工程研究所
;
Institute of Electrical and Control Engineering
An efficient genetic reinforcement learning algorithm for designing fuzzy controllers is proposed in this paper. The genetic algorithm (GA) adopted in this paper is based upon symbiotic evolution which, when applied to fuzzy controller design, complements the local mapping property of a fuzzy rule. Using this Symbiotic-Evolution-based Fuzzy Controller (SEFC) design method, the number of control trials, as well as consumed CPU time, are considerably reduced when compared to traditional GA-based fuzzy controller design methods and other types of genetic reinforcement learning schemes. Moreover, unlike traditional fuzzy controllers, which partition the input space into a grid, SEFC partitions the input space in a flexible way, thus creating fewer fuzzy rules. In SEFC, different types of fuzzy rules whose consequent parts are singletons, fuzzy sets, or linear equations (TSK-type fuzzy rules) are allowed. Further, the free parameters (e.g., centers and widths of membership functions) and fuzzy rules are all tuned automatically. For the TSK-type fuzzy rule especially, which put the proposed learning algorithm in use, only the significant input variables are selected to participate in the consequent of a rule. The proposed SEFC design method has been applied to different simulated control problems, including the cart-pole balancing system, a magnetic levitation system, and a water bath temperature control system. The proposed SEFC has been verified to be efficient and superior from these control problems, and from comparisons with some traditional GA-based fuzzy systems.
Deposition of heteroepitaxial diamond on 6H-SiC single crystal by bias-enhanced microwave plasma chemical vapor deposition
(2000-04-01)
Chang, L
;
Yan, JE
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Chen, FR
;
Kai, JJ
;
材料科學與工程學系
Deposition of heteroepitaxial diamond on substrates of 6H-SiC single crystal by a d.c. voltage biased-enhanced microwave plasma chemical vapor deposition method has been attempted. Various concentrations of methane (CH4) up to 10% in hydrogen (H-2) was used to evaluate its effect on epitaxy. Characterization of cross-sectional transmission electron microscopy with electron energy loss spectroscopy shows that an interlayer can form between diamond 6H-SiC, depending on the CH4 concentration. With low CH4 concentration, diamond was directly nucleated on 6H-SiC with an orientation relationship of diamond {111}//6H-SiC {0001} and diamond [110]//6H-SiC [11 (2) over bar 0]. (C) 2000 Elsevier Science S.A. All rights reserved.
Optimal fuzzy controller design: Local concept approach
(2000-04-01)
Wu, SJ
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Lin, CT
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, we present a global optimal and stable fuzzy controller design method for both continuous- and discrete-time fuzzy systems under both finite and infinite horizons. First, a sufficient condition is proposed which indicates that the global optimal effect can be achieved by the fuzzily combined local optimal controllers. Based on this sufficient condition, we derive a local concept approach to designing the optimal fuzzy controller by applying traditional linear optimal control theory, The stability of the entire closed-loop continuous fuzzy system can be ensured by the designed optimal fuzzy controller. The optimal feedback continuous fuzzy system can not only be guaranteed to be exponentially stable, but also be stabilized to any desired degree. Also, the total energy of system output is absolutely finite. Moreover, the resultant feedback continuous fuzzy system possesses an infinite gain margin; that is, its stability is guaranteed no matter how large the feedback gain becomes, Two examples are given to illustrate the proposed optimal fuzzy controller design approach and to demonstrate the proved stability properties.
Effective induction, purification and characterization of Trichoderma koningii G-39 beta-xylosidase with high transferase activity
(2000-04-01)
Li, YK
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Yao, HJ
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Cho, YT
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應用化學系
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Department of Applied Chemistry
A beta-xylosidase was induced and purified from the culture filtrate of Trichoderma koningii G-39, grown in a medium containing 1% oat spelts xylan and 0.1% xylose, The presence of xylose unequivocally enhanced the induction of beta-xylosidase. The purified enzyme, which exhibited a significant alpha-arabinosidase activity, was obtained with high yield simply via ethanol precipitation and a single anion-exchange chromatography and was characterized as a monomeric glycoprotein with an estimated molecular mass of 104 kDa and a pl of 4.6. The K-m values towards P-nitrophenyl beta-D-xylopyranoside and p-nitrophenyl alpha-L-arabinopyranoside are 0.04 and 7.5 mM, respectively. It is stable at pH 2.5-7.4, 37 degrees C. The pH and temperature optima are in the range of 3.5-4.0 and 55-60 degrees C, respectively. Contrary to most beta-xylosidases from other sources, Hg2+ (up to 25 mM) has no effect on enzyme activity. Xylose was shown to inhibit the purified enzyme with a moderate Ki value of 5 mM, The enzyme exhibited transxylosylation activity and was characterized as a 'retaining' enzyme, catalysing the hydrolysis of substrate with the retention of anomeric configuration.
A semantic differential study of designers' and users' product form perception
(2000-04-01)
Hsu, SH
;
Chuang, MC
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Chang, CC
;
應用藝術研究所
;
工業工程與管理學系
This study investigated the differences in the product form perception of designers and users. The semantic differential (SD) method was employed to examine the relationship between the subjects' evaluation of telephone samples and form design elements. The authors used 14 image-word pairs for the evaluation of telephone design. The format for a measurement scale was constructed by a projection method in order to extract design attributes for an SD test. Twenty-four real telephone samples were presented to 40 subjects (20 designers and 20 users) for subjective evaluation. Multivariate analyses were performed to analyze the subject's perceptions and to build conceptual models for telephone design. The result revealed that many differences exist between designers' and users' perceptions of the same real objects and their interpretations of the same image-words. Users are not clear regarding the meaning of the image-words. Moreover, they are very concerned about whether a telephone looks new. Designers tend to value telephone samples with an elegant style while users prefer modern and sleek designs. The conceptual models of the two subject groups are made up of different components. Creative, mature, delicate design images play a greater role in affecting the designers' preference while the users' preference is affected mainly by images of delicacy. The implications of differences in preference and the relationship between image-word and actual design elements for the two subject groups are discussed. Relevance to industry It is the users' needs and preferences, not those of the designers, that should be taken into consideration during the product design process. Due to the fact that many differences exist between designers and users, it is a challenge for designers to transfer the consumer's needs into technical and design specifications. Quantitative data on the relationship between design elements and user evaluations is useful to product designers and managers in formulating design strategies. (C) 2000 Elsevier Science B.V. All rights reserved.
GA-based fuzzy reinforcement learning for control of a magnetic bearing system
(2000-04-01)
Lin, CT
;
Jou, CP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper proposes a TD (temporal difference) and GA (genetic algorithm)-based reinforcement (TDGAR) learning method and applies it to the control of a real magnetic bearing system. The TDGAR learning scheme is a new hybrid GA, which integrates the TD prediction method and the GA to perform the reinforcement learning task, The TDGAR learning system is composed of two integrated feedforward networks. One neural network acts as a critic network to guide the learning of the other network (the action network) which determines the outputs (actions) of the TDGAR learning system, The action network can be a normal neural network or a neural fuzzy network, Using the TD prediction method, the critic network can predict the external reinforcement signal and provide a more informative internal reinforcement signal to the action network. The action network uses the GA to adapt itself according to the internal reinforcement signal, The key concept of the TDGAR learning scheme is to formulate the internal reinforcement signal as the fitness function for the GA such that the GA can evaluate the candidate solutions (chromosomes) regularly, even during periods without external feedback from the environment. This enables the GA to proceed to new generations regularly without waiting for the arrival of the external reinforcement signal. This can usually accelerate the GA learning since a reinforcement signal may only be available at a time long after a sequence of actions has occurred in the reinforcement learning problem, The proposed TDGAR learning system has been used to control an active magnetic bearing (AMB) system in practice. A systematic design procedure is developed to achieve successful integration of all the subsystems including magnetic suspension, mechanical structure, and controller training. The results show that the TDGAR learning scheme can successfully find a neural controller or a neural fuzzy controller for a self-designed magnetic bearing system.
A robust training algorithm for adverse speech recognition
(2000-04-01)
Hong, WT
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Chen, SH
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電信工程研究所
;
Institute of Communications Engineering
In this paper, anew robust training algorithm is proposed for the generation of a set of bias-removed, noise-suppressed reference speech HMM models in adverse environment suffering from both channel bias and additive noise. Its main idea is to incorporate a signal bias-compensation operation and a PMC noise-compensation operation into its iterative training process. This makes the resulting speech HMM models more suitable to the given robust speech recognition method using the same signal bias-compensation and PMC noise-compensation operations in the recognition process. Experimental results showed that the speech HMM models it generated outperformed both the clean-speech HMM models and those generated by the conventional k-means algorithm for two adverse Mandarin speech recognition tasks. So it is a promising robust training algorithm. (C) 2000 Elsevier Science B.V. All rights reserved.
A simple processor core design for DCT/IDCT
(2000-04-01)
Chang, TS
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Kung, CS
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Jen, CW
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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
This paper presents a cost effective processor core design that features the simplest hardware and is suitable for discrete cosine transform/indiscrete cosine transform (DCT/IDCT) operations in H.263 and digital camera. This design combines the techniques of fast direct two dimensional DCT algorithm, the bit-level adder-based distributed arithmetic, and common subexpression sharing;to reduce the hardware cost and enhance the computing speed. The resulting architecture is very simple and regular such that it can be easily scaled for higher throughput rate requirements. The DCT design has been implemented by 0.6 mu m SPDM CMOS technology and only costs 1493 gate count, or 0.78 mm(2), The proposed design can meet real-time DCT/IDCT requirements of H.263 codec system for QCIF image frame size at 10 frames/s with 4:2:0 color format. Moreover, the proposed design still possesses additional computing power for other operations when operating at 33 Mhz.
Chan-Paton soliton gauge states of the compactified open string
(2000-04-01)
Lee, JC
;
電子物理學系
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Department of Electrophysics
Mle study the mechanism of the enhanced gauge symmetry of the bosonic open string compactified on a torus by analyzing the zero-norm soliton (non-zero winding of the Wilson line) gauge states in the spectrum. Unlike the closed string case, we find that the soliton gauge state exists only at massive levels. These soliton gauge states correspond to the existence of enhanced massive gauge symmetries with transformation parameters containing both Einstein and Yang-Mills indices. In the T-dual picture, these symmetries exist only at some discrete values of compactified radii when N D-branes are coincident.
Coulomb tunneling anomaly in disordered copper-germanium alloys
(2000-04-01)
Hsu, SY
;
Wang, IC
;
Liao, JT
;
電子物理學系
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Department of Electrophysics
We have performed electronic tunneling density of states and resistivity measurements in three-dimensional CuxGe100-x films spanning the weakly and strongly localized regimes. We found that the Coulomb anomaly in tunneling density of states in the strongly disordered regime is very profound and grows in strength with resistivity. However, when the system becomes less disorderly and approaches the weakly disordered regime, this anomaly weakens rapidly. The data suggest that the disorder enhanced electron-electron interaction effects can drive the crossover from weak: disorder to strong disorder in CuGe alloy system. (C) 2000 Elsevier Science B.V. All rights reserved.