Browsing by Issue Date, starting with "2002-10-01"

Now showing 1 - 20 of 74409

Novel electro-optic sampling system with an optoelectronic phase-locked phase shifter as a delay-time controller
(2002-10-01)
Lin, GR
;
Chang, YC
;
光電工程學系
;
Department of Photonics
An inherently delay-time-tunable pulsed laser diode controlled by a voltage-adjusted optoelectronic phase shifter is employed to realize a novel electro-optic sampling system without use of a conventional opto-mechanic delay line. The maximum scanning speed, time, responsivity. and resolution of the optoelectronic delay line are 100 points/s, 3.6ns (1.8 periods), 0.54ns/V, and 0.2ps. respectively. The waveform-sampling of a sinusoidal signal at 500MHz and an electrical pulse with 91.5-ps full-width at half-maximum generated from a microwave oscillator and comb generator. respectively, are reported with measurement error of less than 5%.
Adaptive order tracking technique using recursive least-square algorithm
(2002-10-01)
Bai, MSR
;
Jeng, J
;
Chen, CY
;
機械工程學系
;
Department of Mechanical Engineering
Order tracking technique is one of the important tools for diagnosis of rotating machinery Conventional methods of order tracking are primarily based on Fourier analysis with reference to shaft speed. Resampling is generally required in the fast Fourier transform (FFT)-based methods to compromise between time and frequency resolution for varying shaft speeds. Conventional methods suffer from a number of shortcomings. In particular smearing problems arise when closely spaced orders or crossing orders are present. Conventional methods also are ineffective for the applications involving multiple independent shaft speeds. This paper presents an adaptive order tracking technique based on the Recursive Least-Squares (RLS) algorithm to overcome the problems encountered in conventional methods. In the proposed method, the problem is treated as the tracking of frequency-varying bandpass signals. Order amplitudes can be calculated with high resolution by using the proposed method in real-time fashion. The RLS order tracking technique is applicable whether it is a single-axle or multi-axle system.
Low-power adaptive pseudo noise code acquisition for spread-spectrum systems
(2002-10-01)
Wu, ML
;
Wen, KA
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A novel pseudo noise code acquisition combined with the newly proposed adaptive sampling rate and threshold control (ASTC) algorithm is derived for low-power spread-spectrum systems with complementary metal-oxide-semiconductor implementations. Low-power performance can be achieved by reducing the sampling rate of the proposed system while maintaining the system performance. The sampling rate is dynamically updated due to the change of the channel noise level. Under the assumptions that the channel is additive white Gaussian noise slow-fading channel, up to 74.3% reduction in power consumption compared to the conventional fixed-sampling rate and fixed-threshold architecture is demonstrated with insignificant increase of system complexity. The proposed architecture can be applied to the design of low-power and controllable-performance spread-spectrum communication systems.
Trimethylchlorosilane treatment of ultralow dielectric constant material after photoresist removal processing
(2002-10-01)
Chang, TC
;
Mor, YS
;
Liu, PT
;
Tsai, TM
;
Chen, CW
The dielectric properties of organic-porous silica films deteriorate after photoresist removal processing. O-2 plasma ashing has been commonly used to remove photoresist. Nevertheless, the O-2 plasma will destroy the functional groups and induce moisture uptake in porous silica films. In this study, trimethylchlorosilane (TMCS) is used to repair the damage to porous silica caused by the O-2 plasma ashing process. The leakage current and dielectric constant will decrease significantly after the TMCS treatment is applied to damaged porous silica. These experimental results show that the TMCS treatment is a promising technique to repair the damage to porous silica during photoresist removal processing. (C) 2002 The Electrochemical Society.
Effect of microstructure on the electron-phonon interaction in the disordered metals Pd60Ag40
(2002-10-01)
Zhong, YL
;
Lin, JJ
;
Kao, LY
;
物理研究所
;
Institute of Physics
Using the weak-localization method, we have measured the electron-phonon scattering times tau(ep) in Pd60Ag40 thick films prepared by dc- and rf-sputtering deposition techniques. In both series of samples, we find an anomalous 1/tau(ep)proportional toT(2)l temperature and disorder dependence, where l is the electron elastic mean free path. This anomalous behavior cannot be explained in terms of the current concepts for the electron-phonon interaction in impure conductors. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the dc- than rf-sputtered films, suggesting that the electron-phonon interaction is not only sensitive to the total level of disorder, but is also sensitive to the microscopic quality of the disorder.
Generating learning sequences for decision makers through data mining and competence set expansion
(2002-10-01)
Hu, YC
;
Chen, RS
;
Tzeng, GH
;
科技管理研究所
;
資訊管理與財務金融系註：原資管所+財金所
For each decision problem, there is a competence set, proposed by Yu, consisting of ideas, knowledge, information, and skills required for solving the problem. Thus, it is reasonable that we view a set of useful patterns discovered from a relational database by data mining techniques as a needed competence set for solving one problem. Significantly, when decision makers have not acquired the competence set, they may lack confidence in making decisions. In order to effectively acquire a needed competence set to cope with the corresponding problem, it is necessary to find appropriate learning sequences of acquiring those useful patterns, the so-called competence set expansion. This paper thus proposes an effective method consisting of two phases to generate learning sequences. The first phase finds a competence set consisting of useful patterns by using a proposed data mining technique. The other phase expands that competence set with minimum learning cost by the minimum spanning table method proposed by Feng and Yu. From a numerical example, we can see that it is possible to help decision makers to solve the decision problems by use of the data mining technique and the competence set expansion, enabling them to make better decisions.
QoS-guaranteed fuzzy transmission controller for dynamic TDMA protocol in multimedia communication systems
(2002-10-01)
Ren, FC
;
Chang, CJ
;
Cheng, RG
;
電信工程研究所
;
Institute of Communications Engineering
The paper proposes a QoS-guaranteed fuzzy transmission controller (FTC) for the dynamic TDMA protocol in multimedia communication systems. The dynamic TDMA protocol adopts a mini-slot technique for reducing contention cost, and the mini-slots are further partitioned into multiple MAC regions that users can access with their respective quality-of-service (QoS) requirements. The FTC mainly contains a Sugeno self-tuning fuzzy MAC threshold controller and a fuzzy access controller. The former applies a position-gradient-type reasoning method to properly determine the MAC regions; the latter employs max-min inference fuzzy logic to determine the access probabilities of users for enhancing dynamic TDMA efficiency under the QoS constraint. Simulation results show that the dynamic TDMA protocol with FTC can always guarantee the QoS requirement of real-time packet loss probability, regardless of the non-real-time traffic loads. Furthermore, it achieves higher system utilisation and less non-real-time packet delay compared to previously proposed PRMA, IPRMA and FRMA protocols.
On the applicability of the longest-match rule in lexical analysis
(2002-10-01)
Yang, W
;
Tsay, CW
;
Chan, JT
;
資訊工程學系
;
Department of Computer Science
The lexical analyzer of a compiler usually adopts the longest-match rule to resolve ambiguities when deciding the next token in the input stream. However, that rule may not be applicable in all situations. Because the longest-match rule is widely used, a language designer or a compiler implementor frequently overlooks the subtle implications of the rule. The consequence is either a flawed language design or a deficient implementation. We propose a method that automatically checks the applicability of the longest-match rule and identifies precisely the situations in which that rule is not applicable. The method is useful to both language designers and compiler implementors. In particular, the method is indispensable to automatic generators of language translation systems since, without the method, the generated lexical analyzers can only blindly apply the longest-match rule and this results in erroneous behaviors. The crux of the method consists of two algorithms: one is to compute the regular set of the sequences of tokens produced by a nondeterministic Mealy automaton when the automaton processes elements of an input regular set. The other is to determine whether a regular set and a context-free language have nontrivial intersection with a set of equations. (C) 2002 Elsevier Science Ltd. All rights reserved.
Secret image sharing
(2002-10-01)
Thien, CC
;
Lin, JC
;
資訊工程學系
;
Department of Computer Science
Molecular alignment and field-induced reorientation in a twisted nematic liquid crystal pi-cell
(2002-10-01)
Shih, WT
;
Huang, JY
;
光電工程學系
;
Department of Photonics
A twisted nematic pi-cell has been studied by optical transmission measurement, polarized Fourier-transform infrared (pFTIR) absorption spectroscopy, and Raman spectroscopy. Our pFTIR results suggest that the LC molecules undergo a restricted rotation about the molecular long axis. The rise and decay times of the optical response were found to be 6 ms and 1.6 ms, respectively. The switching dynamics of the twisted pi-cell was also studied using time-resolved Raman spectroscopy. A normal mode associated with the C-H out-of-plane wag on the LC core was found to be enhanced after the electric field was switched off. Our data show that LC molecules in the twisted pi-cell do not rotate like a rigid molecule during the field-induced reorientation process. The methods employed in this study have yielded valuable information about LC alignment and field-induced reorientation with respect to functional group specificity.
New applications of an old theory - The Rouse theory - in polymer dynamics and viscoelasticity
(2002-10-01)
Lin, YH
;
應用化學系
;
Department of Applied Chemistry
As recently shown by a close agreement between the calculated and measured viscoelastic spectra of a binary blend solution over a wide frequency range, the quantitative validity of the Rouse theory is discussed, pointing out why the traditional way of testing by a single parameter - the viscosity - is misleading. A "bird's-eye" view of the Rouse theory in relation to various aspects of polymer dynamics and viscoelasticity is shown. This represents a fresh way of looking at some of interrelations between fundamental problems in chain dynamics. This paper illustrates the application potential of the Rouse theory by reviewing the research schemes that make use of the well-tested theory to elucidate two fundamental problems : (1) onset of entanglement and (2) the motions associated with a single Rouse segment. It is shown that through careful designs of research, analyses in terms of the Rouse theory can provide vitally important and informing results.
Selective growth and photoluminescence studies of InAs self-organized quantum dot arrays on patterned GaAs(001) substrates
(2002-10-01)
Sun, KW
;
Wu, JC
;
Lee, BC
;
Lee, CP
;
電子工程學系及電子研究所
In this paper, we present experimental results oil the selective growth of InAs self-organized quantum dots on patterned substrates using electron-beam lithography and molecular beam epitaxy. Higher dot densities were found on the patterned substrate with a particular pattern orientation compared to the densities of dots grown on the non-patterned area. Good quality of the quantum dot arrays and long-range ordering was also achieved. We have also studied the luminescence spectra of these quantum dots. Dots grown on patterned substrates do indeed show different luminescence characteristics compared to dots on non-patterned surfaces. (Some figures in this article are in colour only in the electronic version).
Critical spacing between emitter and base in InGaP heterojunction bipolar transistors (HBTs)
(2002-10-01)
Huang, CE
;
Lee, CP
;
Liang, HC
;
Huang, RT
;
電子工程學系及電子研究所
In this paper, the influence of the spacing between the emitter and the base on the performance of InGaP heterojunction bipolar transistors (HBT) was experimentally studied. We found that the emitter to base spacing can be reduced to as small as 0.6 mum without causing a significant drop in the current gain. The reduction in emitter-to-base spacing, however, leads to improvement in high-frequency performance and device phase noise. For optimal dc, RF, and low-frequency noise performances, we have determined that a critical spacing of 0.6similar to0.8 mum between the emitter and the base of an InGaP HBT is required.
Molecular techniques to identify freshwater eels: RFLP analyses of PCR-amplified DNA fragments and allele-specific PCR from mitochondrial DNA
(2002-10-01)
Lin, YS
;
Poh, YP
;
Lin, SM
;
Tzeng, CS
;
生物科技學系
Because of morphological ambiguity, traditional classification of freshwater eel elvers (of the genus Anguilla) has always been difficult and unreliable. This study analyzes 2 mitochondrial genes viz., cytochrome b and 12S ribosomal RNA (rRNA) genes from previous studies, to establish molecular standards for eel identification. Prediction of restriction fragment length polymorphism (RFLP) indicated that a combination of 3 enzyme results for cytochrome b revealed good resolution power. We also selected 39 specific nucleotide sites of the 2 genes at which the site is unique for individual species: thus these can potentially be used for identification by polymerase chain reaction (PCR). To verify the accuracy of our predictions, we examined 58 specimens from 4 species by DpnII and HaeIII digestions and by PCR amplification using species-specific primers. Consistent with the putative mutation rates, more than 95% and 99% of the specimens could be successfully identified by the RFLP and PCR methods, respectively. The molecular techniques developed here can be helpful in eel aquaculture and ecological studies.
Significant glass-transition-temperature increase through hydrogen-bonded copolymers
(2002-10-01)
Kuo, SW
;
Xu, HY
;
Huang, CF
;
Chang, FC
;
應用化學系
The role of hydrogen bonding in promoting intermolecular cohesion and higher glass-transition temperatures of polymer is a subject of longstanding interest. A series of poly(vinylphenol-co-vinylpyrrolidone) copolymers were prepared by the free-radical copolymerization of acetoxystyrene and vinylpyrrolidone; this was followed by the selective removal of the acetyl protective group, with corresponding and significant glass-transition-temperature increases after this procedure. The incorporation of acetoxystyrene into poly(vinylpyrrolidone) resulted in lower glass-transition temperatures because of the reduced dipole interactions in its homopolymers. However, the deacetylation of acetoxystyrene to transform the poly(vinylphenol-co-vinylpyrrolidone) copolymer enhanced the higher glass-transition temperature because of the strong hydrogen bonding in the copolymer chain. The thermal properties and hydrogen bonding of these two copolymers were investigated with differential scanning calorimetry and Fourier transform infrared spectroscopy, and good correlations between the thermal behaviors and IR results were observed. (C) 2002 Wiley Periodicals, Inc.
Controlling steps during early stages of the aligned growth of carbon nanotubes using microwave plasma enhanced chemical vapor deposition
(2002-10-01)
Chen, LC
;
Wen, CY
;
Liang, CH
;
Hong, WK
;
Chen, KJ
Vertically aligned carbon nanotubes (CNTs) with controllable length and diameter fabricated by microwave plasma enhanced chemical vapor deposition (MPECVD) are of continuing interest for various applications. This paper describes the role of process gas composition as well as the pre-coating catalytic layer characteristics. It is observed that nucleation of CNTs was significantly enhanced by adding nitrogen in the MPECVD process, which also promoted formation of bamboo-like structures. The very first key step toward growth of aligned CNTs was the formation of high-density fine carbon onion encapsulated metal (COEM) particles under a hydrogen plasma. Direct microscopic investigation of their structural evolution during the very early stages revealed that elongation, necking, and splitting of the COEM particles occurred accompanying the growth of CNTs, such that one of the split portions rode on the top of the growing tube while the remaining one resided on the root. Our results suggest that CNTs grow via the "tip-growth" as well as "root-growth" mechanisms.
A quality assurance approach for land subsidence interpolation
(2002-10-01)
Peng, MH
;
Shih, TY
;
土木工程學系
;
Department of Civil Engineering
Land subsidence in southwest Taiwan is mainly caused by ground-water withdrawal and a monitoring network of benchmarks has been established to observe this subsidence. Using results from differential leveling, the magnitudes of land subsidence from 1992 to 7994 were calculated for 50 benchmarks. The calculated maximum magnitude of land subsidence is 15.4 centimeters between these two years. Spatial interpolation is frequently required to provide information for assessing the distribution and extent of subsidence. In this study, geostatistics were applied to describe and characterize the spatial structure of sample data. Thus, an implementation procedure was proposed for the quality assessment of interpolation. The procedure includes geostatistical analysis, outlier detection, and comparison of different estimation techniques. The results,chow that the approach proposed in this study is effective to ensure the quality of interpolation.
Optimal ranging algorithms for medium access control in hybrid fiber coax networks
(2002-10-01)
Lin, FYS
;
Yin, WM
;
Lin, YD
;
Lin, CH
;
資訊工程學系
The ranging algorithm allows active stations to measure their distances to the headend for synchronization purpose in Hybrid Fiber Coax (HFC) networks. A practicable mechanism to resolve contention among numerous stations is to randomly delay the transmission of their control messages. Since shorter contention cycle time increases slot throughput, this study develops three mechanisms, fixed random delay, variable random delay, and optimal random delay, to minimize the contention cycle time. Simulation demonstrates that the optimal random delay effectively minimizes the contention cycle time and approaches the theoretical optimum throughput of 0.18 from pure ALOHA. Furthermore, over-estimation reduces the impact on contention cycle time more than under-estimation through sensitivity analysis, and both phenomenon damage slot throughput. Two estimation schemes, maximum likelihood and average likelihood, are thereby presented to estimate the number of active stations for each contention resolution round. Simulation proofs that the proposed estimation schemes are effective even when the estimated number of active stations in initial contention round is inaccurate.
Phase gratings in pretilted homeotropic cholesteric liquid crystal films
(2002-10-01)
Wu, JJ
;
Chen, FC
;
Wu, YS
;
Chen, SH
;
光電工程學系
We studied the fingerprint texture of homeotropic cholesteric liquid crystal (CLC) films. Parallel (360) and antiparallel (180) alignment treatments were adopted for these films such that the molecules at the boundaries had an approximately I pretilt angle to the substrate normal. The experimental results showed that the homeotropic film may be more suitable than the planar-parallel film for use in an electrically controlled phase grating.
An automorphic approach to verification pattern generation for SoC design verification using port-order fault model
(2002-10-01)
Wang, CY
;
Tung, SW
;
Jou, JY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Embedded cores are being increasingly used in the design of large system-on-a-chip (SoC). Because of the high complexity of SoC, the design verification is a challenge for system integrators. To reduce the verification complexity, the port-order fault (POF) model was proposed. It has been used for verifying core-based designs and the corresponding verification pattern generation has been developed. Here, the authors present an automorphic technique to improve the efficiency of the automatic verification pattern generation (AVPG) for SoC design verification based on the POF model. On average, the size of pattern sets obtained on the ISCAS-85 and MCNC benchmarks are 45 % smaller and the run time decreases 16 % as compared with the previous results of AVPG.