Browsing by Issue Date, starting with "1999-02-15"

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Active impedance control of linear one-dimensional wave equations
(1999-02-15)
Hu, JS
;
Lin, JF
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Active impedance control of linear one-dimensional wave equations is investigated. The proposed control algorithms are based on the concepts of wave propagation and impedance matching. Two control objectives are considered. The first objective is to obtain total reflection, and the second objective is to achieve total absorption (e.g. matched impedance). Both control laws utilize some interesting properties of the wave-type partial differential equation and do not require information about the disturbance and boundary conditions. The resulting controllers, although boundary-independent, contain an infinite number of poles on the imaginary axis and the closed-loop systems are not internally stable. A simple modification is added to the control laws and the stability is analysed. An example of active sound cancellation in ducts with a moving medium is given to demonstrate one of the control algorithms.
Asymptotic stabilization of driftless systems
(1999-02-15)
Liaw, DC
;
Liang, YW
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Issues of asymptotic stabilization of a class of non-linear driftless systems are presented. In addition to the necessary and sufficient condition for the existence of a smooth time-invariant asymptotic stabilizer, sufficient condition for the existence of a quadratic-type Lyapunov function candidate is also proposed herein to alleviate the construction of stabilizing control laws. Following the deduction of the equivalence of the sufficient condition and the determination of the local definiteness of a defined scalar function, the stabilizability checking conditions are then derived in terms of system dynamics and its derivatives at the origin only. These are achieved by taking Taylor's series expansion on system dynamics. The derived conditions are shown to be consistent with those obtained by Brockett. Comparative results of Liaw and Liang are also included. Finally, examples are given to demonstrate the use of the main results.
Evaluation of a modified chitosan biopolymer for coagulation of colloidal particles
(1999-02-15)
Pan, JRS
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Huang, CP
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Chen, SC
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Chung, YC
;
環境工程研究所
Chitosan, a deacetylated derivative of chitin, is a biodegradable cationic polymer. Chitosan can be a potential substitute for aluminum salts and synthetic polyelectrolytes in water treatment because it can: (1) avoid the health effects from residual aluminum (III) and synthetic polymers; (2) produce biodegradable sludge; and (3) reuse the crab shell. Chitosan can be modified with various pretreatments including dissolution in acid solution and various deacetylation conditions to improve its coagulation efficiency. In this study, coagulations of synthetic and real water with the modified chitosan, mixed coagulant of chitosan and PACl at various ratios, and PACl were compared. The efficiency was evaluated by the factors of settling rate, hoc diameter, and residual turbidity. Coagulation with chitosan alone required least dosage. Chitosan coagulants also produced larger flee with higher settling velocity. Satisfactory results were obtained from the mixed coagulant of chitosan/PACl = 4:1. Although low pH decreased the optimal dosage, the flocs produced were smaller with slower settling rate. Increasing the rapid mixing strength improved the coagulation only when the applied dosage was less than the optimum dosage. Studies using other particles such as kaolinite and clay indicate that the properties of particles have a significant effect on the chitosan coagulation efficiency. (C) 1999 Elsevier Science B.V. All rights reserved.
Numerical solution for the second-order wave interaction with porous structures
(1999-02-15)
Hsu, HH
;
Wu, YC
;
土木工程學系
;
Department of Civil Engineering
This study mathematically formulates the fluid field of a water-wave interaction with a porous structure as a two-dimensional, non-linear boundary value problem (bvp) in terms of a generalized velocity potential. The non-linear bvp is reformulated into an infinite set of linear bvps of ascending order by Stokes perturbation technique, with wave steepness as the perturbation parameter. Only the first- and second-order linear bvps are retained in this study. Each linear bvp is transformed into a boundary integral equation. In addition, the boundary element method (BEM) with linear elements is developed and applied to solve the first- and second-order integral equations. The first- and second-order wave profiles, reflection and transmission coefficients, and the amplitude ratio of the second-order components are computed as well. The numerical results correlate well with previous analytical and experimental results. Numerical results demonstrate that the second-order component can be neglected for a deep water-wave and may become significant for an intermediate depth wave. Copyright (C) 1999 John Wiley & Sons, Ltd.
Temperature and para-substituent effects on the face selectivity of 1,3-dipolar cycloaddition reactions of benzonitrile oxides with 5-substituted adamantane-2-thiones, N-benzyladamantyl-2-imines, and 2-methyleneadamantanes
(1999-02-19)
Tsai, TL
;
Chen, WC
;
Yu, CH
;
le Noble, WJ
;
Chung, WS
The 1,3-dipolar cycloaddition reactions of para-substituted benzonitrile oxides (5-Y) with 5-fluoroadamantane-2-thione (2-F) and -2-methyleneadamantane (3-F) as well as with variously 5-substituted-N-benzyladamantyl-2-imines (4-X) were examined. They produce two geometrically isomeric Delta(2)-1,4,2-oxathiazolines (7-F,Y), Delta(2)-isoxazolines (8-F,Y), and Delta(2)-1,2,4-oxadiazolines (11-X,Y), respectively. The face selectivity in the latter reaction was found to be similar to 1:1 regardless of the variations in Ei-substituent and the temperature. For the former two reactions, the para-substituent was varied from electron-withdrawing (Y = F, Cl, Br, CN, or NO2) to -releasing (Y = Me, or OMe). The face selectivity was measured in all cases. The differences ap for the reactions of 2- and 3-F with 5-Y were obtained from linear Hammett plots; they are +0.12 and 0.0, respectively. These low values and information from previous studies imply a concerted one-step mechanism with very little charge distribution differences in the transition states: These effects of temperature on the Z/E product ratios provide us, for the first time, with activation parameter differences between the syn- and anti transition states; their values are discussed. The product bias resulting from the favored attack of nitrile oxide on the zu face is discussed in terms of transition state hyperconjugation based on the experimental results and AM1 calculations.
Involvement of scattered UV light in the generation of photoluminescence in powdered phosphor screens
(1999-02-21)
Fran, YS
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In powdered phosphor screens, a large fraction of incident UV light is reflected from the surface of individual particles, with the remainder penetrating the phosphor surface to generate photoluminescence. The reflected UV photons entering the screen are randomly scattered throughout the particulate structure, resulting in photoluminescence down to, for example, 10 layers deep from the surface. An optimum number of layers within a screen for luminance in reflection and transmission modes can be calculated after determination of the absorption and scattering coefficients per layer in a practical phosphor screen. Good agreement has been obtained between the calculated and experimental results.
The number of maximal independent sets in connected triangle-free graphs
(1999-02-28)
Chang, GJ
;
Jou, MJ
;
應用數學系
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Department of Applied Mathematics
Erdos and Moser raised the problem of determining the largest number of maximal independent sets of a general graph G of order n and those graphs achieving this largest number. This problem was solved by Erdos, and later Moon and Moser. It then was extensively studied for various classes of graphs, including trees, forests, (connected) graphs with at most one cycle, bipartite graphs, connected graphs, k-connected graphs and triangle-free graphs. This paper studies the problem for connected triangle-free graphs. In particular, we prove that every connected triangle-free graph of order n greater than or equal to 22 has at most 5 . 2((n-6)/2) (respectively, 2((n-1)/2)) maximal independent sets if n is even (respectively, odd). Extremal graphs achieving this maximum value are also characterized. (C) 1999 Elsevier Science B.V. All rights reserved.
Distance graphs and T-coloring
(1999-03-01)
Chang, GJ
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Liu, DDF
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Zhu, XD
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應用數學系
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Department of Applied Mathematics
We discuss relationships among T-colorings of graphs and chromatic numbers, fractional chromatic numbers, and circular chromatic numbers of distance graphs. We first prove that for any finite integral set T that contains 0, the asymptotic T-coloring ratio R(T) is equal to the fractional chromatic number of the distance graph G(Z, D), where D = T-{0}. This fact is then used to study the distance graphs with distance sets of the form D-m,D- k = {1, 2, ..., m}- {k}. The chromatic numbers and the fractional chromatic numbers of G(Z, D-m,D- k) are determined for all values of m and k. Furthermore, circular chromatic numbers of G(Z, D-m,D- k) fur some special values of m and k are obtained. (C) 1999 Academic Press.
Anisotropic impurity scattering effects on T-c and H-c2 in YBa2Cu3Ox
(1999-03-01)
Lin, JY
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Chen, SJ
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Chen, SY
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Chang, CF
;
Yang, HD
We have studied the impurity effects on the superconducting transition temperature T-c and the upper critical field H-c2 in electron irradiated YBa2Cu3Oy with in-plane oxygen defects and YBa2(Cu1-xZnx)(3)O-y. It is found that the effects of the same type of defects or impurities on T-c are the same regardless of the oxygen contents of the samples. Furthermore, T-c decreases slower in irradiated YBa2Cu3Oy than in YBa2(Cu1-xZnx)(3)O-y. This may be well explained by the model that the scattering due to in-plane oxygen defects is more anisotropic than that due to Zn impurities. The different behavior of the reduced slopes (dH(c2)/dT)(Tc)/(dH(c2)/dT)(Tc0) these two types of samples can also be understood in this context. [S0163-1829(99)08309-5].
On k-ary spanning trees of tournaments
(1999-03-01)
Lu, XY
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Wang, DW
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Chang, GJ
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Lin, IJ
;
Wong, CK
It is well known that every tournament contains a Hamiltonian path, which can be restated as that every tournament contains a unary spanning tree. The purpose of this article is to study the general problem of whether a tournament contains a k-ary spanning tree. In particular, we prove that, for any fixed positive integer k, there exists a minimum number h(k) such that every tournament of order at least h(k) contains a k-ary spanning tree. The existence of a Hamiltonian path for any tournament is the same as h(1) = 1. We then show that h(2) = 4 and h(3) = 8. The values of h(k) remain unknown for k greater than or equal to 4. (C) 1999 John Wiley & Sons. Inc. J Graph Theory 30: 167-176, 1999.
Finite element analysis and optimization on springback reduction
(1999-03-01)
Chou, IN
;
Hung, CH
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機械工程學系
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Department of Mechanical Engineering
Several springback reduction techniques used in the U-channel bending processes were analyzed with the finite element method, which included are bottoming, pinching die, spanking and movement techniques. The relationship between the amount of springback and the forming parameters in each technique was first established through finite element simulations, and then the optimization analysis was coupled with the finite element analysis to find the optimum forming parameters for each springback reduction technique. (C) 1998 Elsevier Science Ltd. All rights reserved.
Electrical properties of rapid thermal-enhanced low pressure chemical vapor deposited Ta2O5 thin films
(1999-03-01)
Lee, CJ
;
Huang, LT
;
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
Electrical properties of rapid thermal-enhanced low pressure chemical vapor deposited Ta2O5 thin films subjected to an in situ two-step postannealing process were studied. Films treated by rapid thermal annealing in O-2 at 550 degrees C for 90 s followed by plasma O-2 at 550 degrees C for 30 s exhibit a leakage current density of 7.91 x 10(-9) A/cm(2) at an applied electric field of 100 kV/cm and a dielectric constant of similar to 38. The decrease in leakage current density of the annealed Ta2O5 films in comparison to the as-deposited films is attributed mainly to the effective reduction of carbon impurities and oxygen vacancies by the two-step postannealing process. (C) 1999 The Electrochemical Society. S1099-0062(98)08-064-X. All rights reserved.
Fractal extraction from a mixed fBm signal using discrete wavelet transforms
(1999-03-01)
Wu, BF
;
Su, YL
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電控工程研究所
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Institute of Electrical and Control Engineering
Since stationarity, ergodicity and self-similarity for the discrete wavelet transform of fractional Brownian motion (fBm) processes have been shown in previous works, these characteristics could be applied to extract the parameters of two fBm signals from a mixed fBm signal using time-average correlation functions. The goal of this paper is to distinguish the two identical power fBm signals from the mixed signal. In this case, we suppose that the mixed signal is available, but information on the parameters of the two fBm signals is not provided. A method is proposed to find the parameters of these two fBm signals. The smaller parameter can be detected from the fractal dimension of the mixed fBm signal. The parameter of the other fBm is estimated by processing the wavelet coefficients of the mixed fBm signal. Finally, the simulation results showed that this approach works well in increasing the difference between the parameters of the two fBms.
Preparation and properties of tantalum pentoxide (Ta2O5) thin films for ultra large scale integrated circuits (ULSIs) application - A review
(1999-03-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Tantalum pentoxide (Ta2O5) thin films have rapidly evolved into an important field of research/development for both basic and applied science with the promise of creating a new generation of advanced micro devices for electronics applications. This paper provides a broad review of the current status and future trends of Ta2O5 thin films as a high ly promising storage dielectric material for high-density dynamic random access memory applications. Various methods of thin film material processing are briefly reviewed. The physical, electrical and dielectric characteristics of Ta2O5 thin films with specific examples from recent literature and the associated conduction mechanisms are summarized and discussed. Some suggestions to improve the electrical properties of the films are finally included. (C) 1998 Kluwer Academic Publishers.
Nano-carbon nitride synthesis from a bio-molecular target for ion beam sputtering at low temperature
(1999-03-01)
Wu, JJ
;
Lu, TR
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Wu, CT
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Wang, TY
;
Chen, LC
Nano-crystalline carbon nitride has been successfully synthesized at a temperature below 100 degrees C from an adenine(C5N5H5) target sputtered by an Ar ion beam. Because adenine possesses a ring structure similar to the hypothetical beta-C3N4 phase, the use of this bio-molecular compound as the target is believed to reduce the energy barrier of carbon-nitride growth. The effect of Ar ion-sputtering voltage on the film growth and the effect of extra-N-atom incorporation on the carbon-nitride film growth are examined in this study. Only a carbon film is formed with an ion energy of 500 V. For the ion-beam energy above 750 V, carbon nitride films are deposited, and there is some hydrogen incorporation in the films. The N/C composition ratio in the films could reach 1:1 and is independent on the ion beam voltage. The nitrogen is bonded with carbon within the films, as determined by the IR and XPS measurements. However, the films deposited at a higher ion voltage could possess some original functional groups of adenine. A strong and broad peak at a d-spacing of 0.32 nm, comparable to the calculated d-spacing of the beta-C3N4(110), is observed in the XRD spectra of the carbon nitride films. The TEM results indicated that the film contained nano-crystalline grains. Several d values are also in good agreement with those of adenine and the calculated values of beta-C3N4. The C/N ratios of the films are still kept at almost 1:1 with N atoms added during deposition. The XRD spectra and IR spectra of these films are all similar to the film deposited without nitrogen source. (C) 1999 Elsevier Science S.A. All rights reserved.
Transition of carrier distribution from a strained to relaxed state in InGaAs/GaAs quantum well
(1999-03-01)
Wang, PY
;
Chen, JF
;
Wang, JS
;
Chen, NC
;
Chen, YS
This work investigates the transition of carrier distribution from the strained to the relaxed state in In0.2Ga0.8As/GaAs quantum well by measuring capacitance voltage and analyzing x-ray diffraction. According to those results, there is carrier confinement in the In0.2Ga0.8As quantum well with well thickness less than the critical thickness. Increasing the well thickness beyond the critical thickness leads to a significant carrier depletion around the quantum well. Double-crystal x-ray rocking curves reveal that when InGaAs well thickness increases beyond the critical thickness, the interference pattern disappears and relaxation begins to occur from near the bottom InGaAs/GaAs interface while the top interface still remains strained. Results obtained from the critical thickness determined from x-ray diffraction correspond to the transition of carrier distribution, illustrating that the capacitance-voltage measurement is a rather effective means of determining the critical thickness. (C) 1999 American Institute of Physics. [S0021-8979(99)01505-4].
Properties and thermal stability of chemically vapor deposited W-rich WSix thin films
(1999-03-01)
Wang, MT
;
Lin, YC
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Chuang, MS
;
Chun, MC
;
Chen, LJ
The tungsten-rich (Si/W atomic ratio less than 2.0) chemical vapor deposition (CVD)-WSix layer was found to be an efficient diffusion barrier against Cu diffusion. In this study, the properties and thermal stability of the W-rich WSix films chemically vapor deposited at various deposition temperatures, pressures, and SiH4/WF6 reactant gas flow ratios were investigated. With SiH4/WF6 flow rates of 6/2 seem and a total gas pressure of 12 mTorr, the activation energy of the CVD process was determined to be 3.0 kcal/mole, and the film deposited at 250 degrees C has a Si/W atomic ratio of unity. The WSix, films have a low residual stress, low electrical resistivity, and excellent step coverage. For the WSix layers deposited on Si substrates, the residual stress varies from 7 to 9 X 10(8) dynes/cm(2) depending on the deposition temperature. The resistivity of the WSI, films varies from 200 to 340 mu Omega cm; higher deposition temperatures and SiH4/WF6 flow ratios resulted in higher film resistivities. The as-deposited amorphous WSix layer is thermally stable up to 600 degrees C; however, crystallization of the deposited film takes place at 650 degrees C and WSix was transformed into WSi2 phase when the WSix/Si structure was thermally annealed at temperatures above 650 degrees C. (C) 1999 American Vacuum Society. [S0734-211X(99)03602-1].
A distributed fault-tolerant design for multiple-server VOD systems
(1999-03-01)
Shyu, IJ
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Shieh, SP
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資訊工程學系
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Department of Computer Science
Fault tolerance is an important design criterion for reliable and robust video-on-demand systems. Conventional fault-tolerant designs use either a primary backup or an active replication method to provide system fault tolerance. However, these approaches suffer from low utilization of the backup or replication system. In this paper we propose two playback-recovery schemes for distributed video-on-demand systems called the forward playback-recovery scheme and the backward playback-recovery scheme. Unlike conventional fault-tolerant designs, our schemes use existing playback resources to recover faulty playbacks without allocating new resources, significantly reducing recovery overhead. To use the schemes effectively, we developed a distributed algorithm for determining the order and gap information between the playbacks on the distributed video-on-demand servers so that overhead for recovering from a server failure can be minimized. This algorithm achieves N - 1 fault-tolerant resiliency for N-server video-on-demand systems. In addition, three server-recovery policies are also presented to guide surviving servers in applying the proper scheme to recover faulty playbacks, thus reducing overall recovery costs. Simulation results show that the proposed recovery schemes are effective and useful in designing fault-tolerant multiple-server video-on-demand systems.
The market acceptance of electric motorcycles in Taiwan experience through a stated preference analysis
(1999-03-01)
Chiu, YC
;
Tzeng, GH
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運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
The environmental and energy concerns of using motorcycles in urban areas have fostered the rapid development development of electric motorcycles (EMs) in Taiwan in recent years. EMs' zero-emission, low noise level and high energy efficiency features provide the promising potential to alleviate the severe environmental pollution problem caused by the existing gasoline motorcycles. This study summarizes the recent development of the EM. More specifically, this study aims to analyze the potential demand for EMs based on an interview survey using stated preference modeling approaches. Study results show that female motorists are the potential target market for EMs. Developmental and energy-use issues of EMs are also discussed in this study. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Electron paramagnetic resonance and luminescence study of sol-gel derived YAG : Cr powder
(1999-03-01)
Lo, JR
;
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Electron paramagnetic resonance (EPR) and luminescence studies were carried out for the sol-gel-derived YAG:Cr powders subjected to three kinds of heat treatment processes. The results show that powders processed using the two-step heat treatment process with the addition of 20 wt% LiCl and by direct heat treatment at 1500 degrees C exhibit good luminescence properties. The emission spectrum for the powders obtained by the two-step process shows the R-line at 688 nm, whereas the powders directly heat treated at 1500 degrees C display an additional R-line of Al2O3 : Cr at 694 nm: EPR measurements show that the presence or absence of absorption peaks depends on the Cr3+ environment in-the host lattice resulting from the different methods of heat treatment of the powder. The EPR spectra of YAG:Cr3+ phosphors were interpreted to indicate both Cr3+ single ion and Cr3+-Cr3+ pair (with spin three) transitions.