Browsing by Issue Date, starting with "2000-01-31"

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Effect of diatomic islands on step morphological stability of a terrace edge in molecular beam epitaxy (vol 353, pg 174, 1999)
(2000-01-31)
Lin, SP
;
Hwang, CC
;
Chu, HS
;
機械工程學系
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Department of Mechanical Engineering
Mechanistic study of beta-xylosidase from Trichoderma koningii G-39
(2000-02-01)
Li, YK
;
Yao, HJ
;
Pan, IH
;
應用化學系
;
Department of Applied Chemistry
The catalytic mechanism of the beta-xylosidase purified from the culture filtrate of Trichoderma Koningii G-39 was investigated. By NMR spectroscopy, the stereochemistry of the enzyme catalyzing the hydrolysis of 2,4,dinitrophenyl and p-nitrophenyl-beta-D-xylosides was found unequivocally to involve retention of the anomeric configuration, Based on the k(cat) values of a series of arylxylosides with leaving group pK(a)s in the range of 4-10, an extended Bronsted plot was constructed with a slope (beta(Ig)) near zero. Enzymatic hydrolysis of aryl-beta-D-xylosides in acetate buffer (pH 4.0) containing 3 or 5% methanol showed a constant product ratio (methylxyloside/xylose), indicating the presence of a common intermediate, probably the xylosyl-enzyme intermediate. In the presence of DTT, the k(cat) values of p-cyanophenyl-beta-D-xylopyranoside and p-nitrophenyl-beta-xylopyranoside increased greatly. A two-step mechanism involving the formation and breakdown of the xylosyl-enzyme intermediate was therefore proposed. The rate-limiting step is the breakdown of the intermediate. The secondary deuterium kinetic isotope effect (k(H)/k(D)) measured for 2,4-dinitrophenyl-beta-D-xyloside was 1.02+/-0.01, suggesting that the transition state for breakdown of the xylosyl-enzyme intermediate is S(N)2-like.
HTS surface wave resonators
(2000-02-01)
Melkov, GA
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Egorov, YV
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Ivanjuta, OM
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Malyshev, VY
;
Zeng, HK
A novel class of surface wave high-temperature superconductivity (HTS) resonators was investigated. The resonator consists of HTS film and one or two dielectric plates. One of the dielectric plates may be the HTS film substrate. Theoretical analysis of the resonator structure was carried out using the partial region method, with the 20 lowest waves being considered in every region. The resonant frequencies, quality of oscillations, and the field and current distributions were calculated. It was shown that there is a high-density and homogeneous microwave current flowing on the film surfaces. Experimental measurements carried out in the 3-cm wavelength range demonstrate good agreement with simulated data.
Effects of polysilicon gate doping concentration on plasma charging damage in ultrathin gate oxides
(2000-02-01)
Chen, CC
;
Lin, HC
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Chang, CY
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Huang, TY
;
Chien, CH
Effects of poly-gate doping concentration on plasma charging damage in ultrathin gate oxides were investigated. While the charge-to-breakdown (Q(bd)) value under gate injection stress polarity (-V-g) is independent of the doping concentration, eb, under substrate injection stress polarity (+V-g) shows a noticeable improvement with increasing doping concentration. However, our results show that plasma-induced oxide degradation is actually aggravated with increasing poly-gate doping concentration. These seemingly inconsistent observations can be explained by the lowering of plasma charging potential in the case of insufficient poly-gate doping. (C) 1999 The Electrochemical Society. S1099-0062(99)10-079-8. All rights reserved.
Fast VQ encoding by an efficient kick-out condition
(2000-02-01)
Wu, KS
;
Lin, JC
;
資訊工程學系
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Department of Computer Science
A new fast approach to the nearest codeword search using a single kick-out condition is proposed. The nearest codeword found by the proposed approach is identical to the one Found by the full search, although the processing time is much shorter. The principle is to bypass those codewords which satisfy the proposed kick-out condition without the actual (and time-consuming) computation of the distortions from the bypassed codewords to the query vector. Due to the efficiency and simplicity of the proposed condition, a considerable saving of the central processing unit time needed to encode a data set (using a given codebook) can be achieved. Moreover, the memory requirement is low. Comparisons with some recent works are included to show these two benefits.
Two-dimensional beam-scanning linear active leaky-wave antenna array using coupled VCOs
(2000-02-01)
Hu, CC
;
Jou, CF
;
Wu, JJ
;
傳播研究所
;
Institute of Communication Studies
An active phased-array design for electronic two-dimensional beam scanning using a phase-shifterless linear one-dimensional active leaky-wave antenna array is demonstrated. The varactor-tuned voltage-controlled oscillators (VCOs) and coupling network are implemented in this array. Three coupling networks are designed and compared for optimum coupling strength between each VCO element. The measured pattern of a 4 x 1 active leaky-wave antenna array shows that the main beam can be continuously scanned from 68 degrees to 40 degrees in elevation, as the frequency varies from 8.24GHz to 9.15GHz. This is equivalent to over 10% electronic tuning bandwidth. By tuning the free-running frequencies of the end elements, the main beam can be continuously scanned from -26 degrees to +10 degrees from broadside with azimuth symmetry in a conical scan manner.
Optimal multiple stage expansion of competence set
(2000-02-01)
Li, JM
;
Chiang, CI
;
Yu, PL
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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
In this paper, we consider the expansion processes of competence sets which have asymmetric cost functions, intermediate skills, and compound skills; among the skills, cyclic connections are possible. We introduce the concept of the stage expansion process (SEP) of the competence set, and provide mathematical programming methods to find a minimal cost SEP and the ordering of expansion. (C) 2000 Elsevier Science B.V. All rights reserved.
An early vision-based snake model for ultrasound image segmentation
(2000-02-01)
Chen, CM
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Lu, HHS
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Lin, YC
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統計學研究所
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Institute of Statistics
Due to the speckles and the ill-defined edges of the object of interest, the classic image-segmentation techniques are usually ineffective in segmenting ultrasound (US) images. In this paper, we present a new algorithm for segmenting general US images that is composed of two major techniques; namely, the early-vision model and the discrete-snake model, By simulating human early vision, the early-vision model can capture both grey-scale and textural edges while the speckle noise is suppressed. By performing deformation only on the peaks of the distance map, the discrete-snake model promises better noise immunity and more accurate convergence. Moreover, the constraint for most conventional snake models that the initial contour needs to be located very close to the actual boundary has been relaxed substantially. The performance of the proposed snake model has been shown to be comparable to manual delineation and superior to that of the gradient vector flow (GVF) snake model. (C) 2000 World Federation for Ultrasound in Medicine & Biology.
Enhancement of barrier properties in chemical vapor deposited TiN employing multi-stacked Ti/TiN structure
(2000-02-01)
Chang, TC
;
Liu, PT
;
Yang, YL
;
Hu, JC
;
Sze, SM
A novel multi-stacked Ti/TiN structure was proposed to enhance the barrier properties of chemical vapor deposited TiN film. Both the chlorine content and the resistivity of the multi-stacked Ti/TiN films are significantly decreased when compared with a single layer of chemical vapor deposited (CVD) TiN film with the same thickness. Secondary ion mass spectrometry (SIMS) data showed that Ti atom distribution is fairly uniform to fill the grain boundary of TiN film. Therefore, the leakage current resulted from junction spiking was further reduced by the grain boundary effects when employing multi-stacked Ti/TiN as diffusion barrier layer instead of a single layer of TiN film.
Joint wavelet and spatial transformation for digital watermarking
(2000-02-01)
Tsai, MJ
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Yu, KY
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Chen, YZ
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資訊管理與財務金融系註：原資管所+財金所
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Department of Information Management and Finance
A new watermarking scheme which incorporates wavelet and spatial transformation has been del eloped for digital images in this paper. This algorithm utilizes the wavelet multiresolutional structure to construct the image frequency components and the chaotic transformation as two dimensional integer vector generators for spatial transform to select the location during the watermark embedding. To efficiently embed the watermark; within the image without the loss of image quality and provide the robustness for the watermark detection under attacks, a modular based spatial threshold and adjustment scheme of the wavelet coefficients has been developed in this research. Unlike other watermarking schemes which usually rely on significantly large amount of side information for watermark detection, our algorithm need only few key parameters to detect the watermark with meaningful content. Compared with some known approaches of watermarking schemes, this algorithm results in superior robustness and information protection fur beeping watermark intact under image processing attacks like image: compression.
Step-by-step decoding algorithm for Reed-Solomon codes
(2000-02-01)
Chen, TC
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Wei, CH
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Wei, SW
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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 new step-by-step decoding algorithm for decoding Reed-Solomon codes over GF(2(m)) is presented. Based on several properties of the syndrome matrices, the new step-by-step decoding algorithm can directly determine whether every received symbol is an error locator, The detection of error location is based only on the determinant of a v x v syndrome matrix, where v is the number of errors. When an error location is found, its corresponding error value can also be determined by performing a determinant division operation between two syndrome matrices. The new decoding algorithm can significantly reduce computation complexity and improve the decoding speed compared with the conventional step-by-step decoding algorithm.
Synthesis of laterally substituted bistolane liquid crystals
(2000-02-01)
Hsu, CS
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Shyu, KF
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Chuang, YY
;
Wu, ST
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應用化學系
Methods for synthesizing bistolane liquid crystal materials with lateral methyl and ethyl substituents are presented. Some of the bistolanes are nematic at room temperature. These highly conjugated mesogens exhibit wide nematic ranges, small enthalpies of fusion, high birefringence and modest viscosity. Their potential applications for flat panel displays employing light scattering or Bragg reflection and for infrared optically phased arrays are foreseeable.
Barrier layer effect of titanium-tungsten on the electromigration in sputtered copper films on polyimide
(2000-02-01)
Wang, HW
;
Chiou, BS
;
電子物理學系
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電子工程學系及電子研究所
;
Department of Electrophysics
Titanium-tungsten is employed as the diffusion barrier in a Cu/barrier/polyimide/Si system. The electromigration damage (EMD) of Cu with a TiW barrier is investigated utilizing an empirical formula. Two activation energies are obtained suggesting a surface electromigration mechanism at low temperature (140-190 degrees C) and a combined migration mechanism at high temperature (190-230 degrees C). The presence of the TiW barrier layer improves the high temperature electromigration resistance. The effects of the TiW barrier on the microstructure and electrical properties of Cu metallization are discussed.
A CMOS delta-sigma true RMS converter
(2000-02-01)
Wey, WS
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Huang, YC
;
電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Conventionally, monolithic electronics true rms converters are constructed by bipolar circuitry, This paper describes a new architecture based on delta-sigma (Delta Sigma) modulation to realize a low-cost rms converter in CMOS technologies, especially intended for handheld digital multimeters. The signal-to-quantization noise ratio as well as transfer characteristics of this architecture have been deduced to obtain initial design parameters. The use of an indirect charge transfer technique makes the converter gain depend only on an on-chip capacitor ratio, reducing gain drift and offering good gain accuracy, Measured results show that this converter achieves a signal-to-noise ratio of 88 dB and a relative error of +/-0.2% for arbitrary inputs with a signal crest factor up to three. The signal bandwidth exceeds 50 kHz, and the full-scale input range is greater than 0.4 V-rms. Without trimming and calibration, this converter has an absolute gain error less than +/-0.4%. This chip is fabricated in a 0.8-mu m double-poly; double-metal CMOS process and occupies active area of 1 mm(2).
Relaxation of pinned domains in patterned magnetic thin films
(2000-02-01)
Wu, TH
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Wu, JC
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Huang, YW
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Ye, LX
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Chen, BM
We have shown in previous papers that the magnetic domains could be pinned inside the artificially patterned hole arrays under suitable geometry aspect ratio. Nevertheless, we have found that if we reverse the magnetization directions through domain wall motion, the confined domains expand from smaller territory into larger territory for some samples. In addition, the pinned domains maintained the same moment's orientation after the domain expansion. The possible reason for the pinned domains to retain the same moment's orientation maybe those pinning holes that act as high anisotropy defects. Thus, domain wall motion was around the high anisotropy sites and only peeled away the domain in the land area while the enclosed domain of the hole area maintained the same orientation. Moreover, the feasible reason for the expansion domains is the coercive force, which is perpendicular to the side-walls and pinning the domains inside the holes, are relaxed and thus causing the domains growth. This phenomenon is called the relaxation of pinning domains. (C) 2000 Elsevier Science B.V. All rights reserved.
Oxidation of 2-chlorophenol in water by ultrasound/Fenton method
(2000-02-01)
Lin, JG
;
Ma, YS
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環境工程研究所
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Institute of Environmental Engineering
One of the toxic and refractory pollutants formed during the color removal of fertilizer, chemical, and petroleum industrial effluents by chlorine is 2-chlorophenol (2-cp). The objective of this study is to investigate the effect of H2O2 and Fe2+ dosages on the decomposition of 2-cp using a coupled ultrasound/Fe2+/H2O2 process. The extent of 2-cp decomposition and mineralization depends on the dosages of H2O2 and Fe2+. More than 99% of 2-cp was decomposed and 86% of 2-cp was mineralized using the ultrasound/Fe2+/H2O2 process at Fe2+ of 10 mg/L and H2O2 of 500 mg/L. Oxidation-reduction potential (ORP) monitoring is a useful method for determining the decomposition efficiency of the target compound. There was a slight increase in the ORP values with increasing Fe2+ dosages, and an apparent increase with increasing H2O2 dosages was observed. The major intermediate formed during the decomposition of 2-cp was 2-chloro-p-benzoquinone. It was also readily decomposed using the coupled ultrasound/Fe2+/H2O2 process.
Optical chaotic AM demodulation by asymptotic synchronization
(2000-02-01)
Juang, C
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Hwang, TM
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Juang, J
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Lin, WW
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應用數學系
Synchronization between two identical chaotic systems (drive and response) with different initial conditions can be achieved provided that the conditional Lyapunov exponents are all negative. Adding an AM signal to the drive system, the two systems become asymptotically synchronized. The AM signal can be recovered by utilizing the property of the asymptotic synchronization. Chaotic AM noise is present as a direct result of the chaotic AM demodulation. Signal-to-chaotic-AM-noise ratio is calculated as a function of the signal amplitude.
Loss-less pulse intensity repetition-rate multiplication using optical all-pass filtering
(2000-02-01)
Huang, CB
;
Lai, YC
;
光電工程學系
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Department of Photonics
Schemes based on optical all-pass filtering techniques for multiplying the intensity repetition-rate of an optical pulse train are examined. These methods are in principle without energy loss acid the multiplication factor can be any given integer. Practical implementation using cascaded side-coupled ring resonators or multireflection tilters is proposed and analyzed for the first time.
Minimization of the life cycle cost for a multistate system under periodic maintenance
(2000-02-01)
Su, CT
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Chang, CC
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工業工程與管理學系
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Department of Industrial Engineering and Management
Although preventive maintenance policies have received extensive interest, limited attention has been paid to implementing multiple maintenance actions for a multistate system over a finite horizon in continuous time. Therefore, this study closely ex-amines such maintenance actions by viewing a coherent multicomponent system as a multistate system and assuming that the necessary maintenance action and cost which move the current state to an extremely better state depends on the current state. The above problem is also formulated as a periodic maintenance model. In addition, the model's characteristics are elucidated to obtain the optimal cycle time of maintenance actions, thereby minimizing the life cycle cost over a specific finite horizon.
Electrical properties of Ta2O5 thin films deposited on Cu
(2000-02-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrical and dielectric properties of reactively sputtered Ta2O5 thin films with Cu as the top and bottom electrodes forming a simple metal insulator metal (MIM) structure, Cu/Ta2O5/Cu/n-Si, were studied. Ta2O5 films subjected to rapid thermal annealing (RTA) at 800 degrees C for 30 s in N-2 ambient crystallized the film, decreased the leakage current density and resulted in reliable time-dependent dielectric breakdown characteristics. The conduction mechanism at low electric fields (<100 kV/cm) is due to Ohmic conduction; however, the Schottky mechanism becomes predominant at high fields (>100 kV/cm). Present studies demonstrate the use of Cu as a potential electrode material to replace the conventional precious metal electrodes for Ta2O5 storage capacitors. (C) 2000 Elsevier Science S.A. All rights reserved.