Browsing by Issue Date, starting with "2002-05-06"

Now showing 1 - 20 of 74684

Photoluminescence and photoluminescence excitation studies of as-grown and P-implanted GaN: On the nature of yellow luminescence
(2002-05-06)
Huang, HY
;
Chuang, CH
;
Shu, CK
;
Pan, YC
;
Lee, WH
We have studied optical and electronic properties of isoelectronic P-implanted GaN films grown by metalorganic chemical vapor phase epitaxy. After rapid thermal annealing, a strong emission band around 430 nm was observed, which is attributed to the recombination of exciton bound to isoelectronic P-hole traps. From the Arrhenius plot, the hole binding energy of similar to180 meV and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, the implantation process likely introduced N(I) and P-related defects. By using photoluminescence excitation technique, we found that the P-implantation-induced localized states not only increase the yellow luminescence but also suppress the transitions from the free carriers to deep levels. (C) 2002 American Institute of Physics.
The effect of pulsed GTA welding on the residual stress of a stainless steel weldment
(2002-05-10)
Tseng, KH
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
The objective of this study was to investigate the effect of pulsed GTA welding parameters on the residual stress of the weldment. Autogenous gas tungsten arc welding was applied on SUS 304 and SUS 3 10 stainless steels to produce a bead-on-plate weld. The residual stress was determined by using the hole-drilling strain-gage method of ASTM standard E837. The experimental results show that a greater pulse frequency, a larger pulse spacing, a greater amplitude ratio, and a greater duration ratio can reduce the magnitude of the residual stress in the austenitic stainless steel weldment. The residual stress of the 3 10 stainless steel weldment is greater than that of the 304 stainless steel weldment under the same welding conditions because of its lower thermal conductivity and thermal diffusivity. The experimental results also showed that pulsed current welding has a smaller range of the tensile residual stress zone as compared to that of constant current welding because of its lesser amount of heat input. (C) 2002 Elsevier Science B.V All rights reserved.
Recent experimental studies of electron dephasing in metal and semiconductor mesoscopic structures
(2002-05-13)
Lin, JJ
;
Bird, JP
;
物理研究所
;
Institute of Physics
In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (tau(phi)) in metal and semiconductor mesoscopic structures. A major focus of this review is on the use of weak localization, and other quantum-interference-related phenomena, to determine the value of tau(phi) in systems of different dimensionality and with different levels of disorder. Significant attention is devoted to a discussion of three-dimensional metal films, in which dephasing is found to predominantly arise from the influence of electron-phonon (e-ph) scattering. Both the temperature and electron mean free path dependences of tau(phi) that result from this scattering mechanism are found to be sensitive to the microscopic quality and degree of disorder in the sample. The results of these studies are compared with the predictions of recent theories for the e-ph interaction. We conclude that, in spite of progress in the theory for this scattering mechanism, our understanding of the e-ph interaction remains incomplete. We also discuss the origins of decoherence in low-diffusivity metal films, close to the metal-insulator transition. in which evidence for a crossover of the inelastic scattering, from e-ph to 'critical' electron-electron (e-e) scattering, is observed. Electron-electron scattering is also found to be the dominant source of dephasing in experimental studies of semiconductor quantum wires, in which the effects of both large- and small-energy-transfer scattering must be taken into account. The latter. Nyquist, mechanism is the stronger effect at a few kelvins, and may be viewed as arising from fluctuations in the electromagnetic back-ground, generated by the thermal motion of electrons. At higher temperatures, however, a crossover to inelastic e-e scattering typically occurs and evidence for this large-energy-transfer process has been found at temperatures as high as 30 K. Electron-electron interactions are also thought to play an important role in dephasing in ballistic quantum dots, and the results of recent experiments in this area are reviewed. A common feature of experiments, in both dirty metals and ballistic and quasi-ballistic semiconductors, is found to be the observation of an unexpected 'saturation' of the dephasing time at temperatures below a kelvin or so. The possible origins of this saturation are discussed, with an emphasis on recent experimental investigations of this effect.
Ultrashort bragg soliton in a fiber bragg grating
(2002-05-15)
Chi, S
;
Luo, B
;
Tseng, HY
;
光電工程學系
;
Department of Photonics
The propagation of a nonlinear ultrashort pulse in a photonic bandgap structure is investigated by using the finite-difference time-domain method. The simulation results show that an ultrashort pulse near the bandgap edge can propagate through a nonlinear fiber Bragg grating, even if the broadband spectrum of this ultrashort pulse overlaps the whole forbidden band of the grating. It is also shown that the time delay of such an ultrashort solitary wave is proportional to its detuning wavelength from the exact Bragg resonance. (C) 2002 Published by Elsevier Science B.V.
Evidence and quantification of the correlation between radar backscatter and ocean colour supported by simultaneously acquired in situ sea truth
(2002-05-15)
Lin, II
;
Wen, LS
;
Liu, KK
;
Tsai, WT
;
Liu, AK
[1] Near simultaneously (within 2 hours) acquired ERS-2 Synthetic Aperture Radar (SAR) and Sea-viewing Wide Field-of-view Scanner (SeaWiFS) data over an upwelling region shows remarkable similarity in feature's location, scale, and boundary. Under uniform wind and sea states, reduction of Normalised Radar Cross Section (NRCS) from SAR is found highly correlated with the increase of SeaWiFS Chlorophyll-a (Chl-a) concentration. Typically, 1 mg/m3 of chlorophyll-a is correspondent with a 5 dB reduction of NRCS. This relationship is supported by simultaneously collected in situ sea truth measurements. This work provides a direct evidence and exceptional quantification of the relationship between radar backscatter and ocean colour that has long been speculated.
Tuning of PID controllers for unstable processes based on gain and phase margin specifications: a fuzzy neural approach
(2002-05-16)
Lee, CH
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper presents a PID tuning method for unstable processes using an adaptive-network-based-fuzzy-inference system (ANFIS) for given gain and phase margin (GPNI) specifications. PID tuning methods are widely used to control stable processes. However, PID controller for unstable processes is less common. In this paper. the PID controller parameters can be deter-mined by the ANFIS. Because the definitions of gain and phase margin equations are complex, an analytical tuning method for achieving specified the gain and phase margins is not yet available. In this paper, the ANFIS is adopted to identify, the relationship between the gain-phase margin specifications and the PID controller parameters, Then, it is used to automatically tune the PID controller parameters for different gain and phase margin specifications so that neither numerical methods nor graphical methods need be used. A simple method is also developed to estimate the stabilizing region of PID controller parameters and valid region for gain-phase margin. Even for unreasonable specifications, out of the valid region, the ANFIS can still find suitable PID controller to guarantee the stability, of the closed-loop system. Simulation results show that the ANFIS can achieve the specified values efficiently. (C) 2002 Elsevier Science B.V. All rights reserved.
詩四首
(2002-05-16)
管管
A silicon nanowire with a Coulomb blockade effect at room temperature
(2002-05-17)
Hu, SF
;
Wong, WZ
;
Liu, SS
;
Wu, YC
;
Sung, CL
An extremely narrow and thin silicon wire has been fabricated on a silicon-on-insulator wafer (see Figure). The room-temperature Coulomb blockade effects as well as the influence of a capacitively coupled gate on the transport properties of this conducting silicon quantum wire are studied. The results obtained are encouraging for the application of such wires in single-electron transistors.
Enhanced ferroelectric properties of Pb(Zr0.53Ti0.47)O-3 thin films on SrRuO3/Ru/SiO2/Si substrates
(2002-05-20)
Wang, YK
;
Tseng, TY
;
Lin, P
;
材料科學與工程學系
;
電子工程學系及電子研究所
Highly (110)-oriented Pb(Zr0.53Ti0.47)O-3 (PZT) films were deposited on SrRuO3 (SRO)/Ru/SiO2/Si substrates using a sol-gel method, in which SrRuO3 films were deposited at various substrate temperatures. The crystallinity of the PZT films was improved after the annealing process. The leakage current, dielectric constant, and polarization versus electric-field characteristics of PZT films were strongly dependent on the annealing and deposition temperatures of the SRO films. The 650 degreesC annealed PZT film grown on SRO has a leakage current of 9x10(-7) A/cm(2) at an applied field of 500 kV/cm, dielectric constant of 1306, remanent polarization (P-r) of 40.1 muC/cm(2) and coercive field (E-c) of 78.5 kV/cm at an applied voltage of 5 V. The PZT films indicated fatigue-free characteristics up to similar to1.0x10(12) switching cycles under 5 V bipolar pulse. (C) 2002 American Institute of Physics.
Low-etch-pit-density GaN substrates by regrowth on free-standing GaN films
(2002-05-20)
Tsai, CC
;
Chang, CS
;
Chen, TY
;
光電工程學系
;
Department of Photonics
In this study, GaN substrates with low-density etch pits were obtained by regrowth on free-standing GaN films (two steps) by hydride vapor-phase epitaxy (HVPE). The etch-pit density was lower than 4x10(4) cm(-2) by atomic-force microscopy. The density is significantly lower than that of the HVPE-grown (one-step) GaN films (HVPE GaN), using sapphire as a substrate. The optical and electrical properties of the two-step HVPE-grown GaN substrates are superior to those of HVPE GaN. Temperature-dependent photoluminescence measurements reveal that thermal quenching behavior of the 2.9 eV band is possibly attributed to a shallow acceptor level at about 118+/-5 meV above the valence band. (C) 2002 American Institute of Physics.
Dynamics of twisted nematic liquid crystal pi-cells
(2002-05-20)
Chen, SH
;
Yang, CL
;
光電工程學系
;
Department of Photonics
A twisted nematic liquid crystal pi-cell with fast optical response time of 2.2 ms was prepared. We investigated the dynamics of this cell and observed the back-flow-induced optical overshoot phenomena both in homeotropic-to-planar state transition and planar-to-homeotropic state transition. We analyzed the behavior of the director and found that there is a tip-over phenomenon when the field is removed from relatively high voltage (>6 V). More important, the fluid flow effect results in the reverse twist both in the rising process and the decay process. Consequently, the reverse twist increases and decreases the effective phase retardation on the optical rising and decay process, respectively, and thus speeds up the optical response in both stages. (C) 2002 American Institute of Physics.
LTCC-MLC chip-type balun realised by LC resonance method
(2002-05-23)
Tang, CW
;
Chang, CY
;
電信工程研究所
;
Institute of Communications Engineering
A multilayer ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A multilayer structure to realise the low temperature co-fired ceramic (LTCC) balun is proposed. This type of balun comprises an embedded capacitor and meandered or spiral coupled lines. The use of an LC resonator can shrink the length of a coupled transmission line and can be designed very easily to have various balanced output port impedances. Excellent performance of phase and amplitude balance may be achieved by the proposed method. Measured results of the LTCC-multilayer ceramic (MLC) balun match well with the computer simulation.
Reliability evaluation for airline network design in response to fluctuation in passenger demand
(2002-06-01)
Hsu, CI
;
Wen, YH
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This study develops a reliability evaluation method for airline network design. Reliability evaluation in the airline network design phase is considered herein as a post-design task. A series of models for determining flight frequencies on individual routes, evaluating reliability under normal/abnormal demand fluctuations, and providing a priori adjustment of flight frequencies are presented. A case study demonstrating the feasibility of applying the proposed models is provided. Study results not only suggest a post evaluation and adjustment method for airline network design in response to future uncertain fluctuation in passenger demand, but also provide ways to improve flexibility in airline flight frequency decision-making. (C) 2002 Elsevier Science Ltd. All rights reserved.
Fully process-compatible layout design on bond pad to improve wire bond reliability in CMOS ICs
(2002-06-01)
Ker, MD
;
Peng, JJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
During manufacture of wire bonding in packaged IC products, the breaking of bond wires and the peeling of bond pads occur frequently. The result is open-circuit failure in IC products. There were several prior methods reported to overcome these problems by using additional process flows or special materials. In this paper, a layout method is proposed to improve the bond wire reliability in general CMOS processes. By changing the layout patterns of bond pads, the reliability of bond wires on bond pads can be improved. A set of different layout patterns of bond pads has been drawn and fabricated in a 0.6-mum single-poly triple-metal CMOS process for investigation by the bond wire reliability tests, the ball shear test and the wire pull test. By implementing effective layout patterns on bond pads in packaged IC products, not only the bond wire reliability can be improved, but also the bond pad capacitance can be reduced for high frequency application. The proposed layout method for bond pad design is fully process-compatible to general CMOS processes.
An optimization model for assessing flight technical delay
(2002-06-01)
Wong, JT
;
Li, SL
;
Gillingwater, D
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This paper identifies the causes as well as the practical measurement of aircraft flight delays. The performance of air traffic management is measured by examining technical delays and scheduled timetable delays, which are derived from a mathematical programming model. To validate the optimization model, flight delays are simulated under various service rules. The outcome of the simulation runs shows that the average delay for each aircraft estimated from the optimization model is marginally higher than that from the simulation run under the "first come first serve" rule. However, under the "arrival flight first" rule, the optimization model's results are either higher or lower than those of the simulation model. Nonetheless, both sets of simulated delays are strongly correlated with those of the optimization model. Results from regression analyses show that the optimization model has the capacity to predict flight technical delays.
Multicriteria analysis of environmental quality in Taipei: public preferences and improvement strategies
(2002-06-01)
Tzeng, GH
;
Tsaur, SH
;
Laiw, YD
;
Opricovic, S
;
運輸與物流管理系註：原交通所+運管所
The public preferences for environmental quality should be a primary consideration of planners and decision-makers in environmental systems planning. In the first stage of multicriteria analysis, a multi-attribute evaluation model for determining public preferences is formulated. The environmental indices are defined for a comparison of environmental quality in different metropolitan districts. The public preferences of the environmental quality in Taipei are obtained using the weighted average rating method. The results indicate air quality and noise pollution as main public concern. In the second stage of multicriteria analysis, strategies are proposed to improve the air quality, and criteria are established. The experts evaluated all alternative strategies according to the criteria. The alternatives are ranked applying the compromise ranking method. (C) 2002 Published by Elsevier Science Ltd.
The structural Birnbaum importance of consecutive-k systems
(2002-06-01)
Chang, HW
;
Chen, RJ
;
Hwang, FK
;
應用數學系
;
資訊工程學系
This paper is concerned with three types of structural Birnbaum importance of components in a consecutive-k system. We accomplish the following three tasks: (i) Survey existing results, including pointing out results claimed but proofs are incomplete. (ii) Give some new results and useful lemmas. (iii) Observe what are still provable and what are not with the help of extensive computing.
Abundance of mosaic patterns for CNN with spatially variant templates
(2002-06-01)
Hsu, CH
;
Yang, TH
;
應用數學系
;
Department of Applied Mathematics
This work investigates the complexity of one-dimensional cellular neural network mosaic patterns with spatially variant templates on finite and infinite lattices. Various boundary conditions are considered for finite lattices and the exact number of mosaic patterns is computed precisely. The entropy of mosaic patterns with periodic templates can also be calculated for infinite lattices. Furthermore, we show the abundance of mosaic patterns with respect to template periods and, which differ greatly from cases with spatially invariant templates.
The key dimensions of criteria for the evaluation FNA selection of ISPS: An exploratory study
(2002-06-01)
Shee, DY
;
Tzeng, GH
;
交大名義發表
;
National Chiao Tung University
The progressive advancements in information technology (IT) coupled with the global expansion of communication infrastructure has enabled firms to create and sustain large scale strategic advantages, with the result of an ever-increasing demand from firms for new types of information services (IS) to facilitate and coordinate their daily operations. Hence, the aim of this research is to explore the underlying dimensions of criteria for the evaluation and selection of information service providers (ISPs). By undertaking a review of the literature, we first analyze the dynamics of ISPs to define their present day role before going on to develop a questionnaire for the field survey. Based on the data collected from 57 firms, two distinct procedures are adopted to carry out the exploratory factor analyses in order to derive the preliminary factor solutions. Followed by a process of post-analysis validation, these empirically derived factor solutions are reviewed and refined in accordance with domain experts' opinions, and as a result, the final factor solution is obtained. It is hoped that through the utilization of mechanical factor analyses and subsequent manual validation, it will be possible to achieve both "parsimony" and "inclusiveness" of the final factor solution. This study results that there are seven dimensions of criteria which are critical to the evaluation and selection of ISPs: (1) performance of information systems; (2) awareness of and response to customer requirements; (3) ISP's market capability; (4) performance of networking; (5) ISP's credibility and fame; (6) provision of customized professional services; and (7) innovative R&D into technology.
Heuristic algorithms for packing of multiple-group multicasting
(2002-06-01)
Wang, CF
;
Liang, CT
;
Jan, RH
;
資訊工程學系
;
Department of Computer Science
Multicast communication is an efficient routing method for multimedia data distribution, since it can save network bandwidth during the communication session. Thus, the multicast routing problems have received much attention from many researchers. In this paper, we consider a multicast routing problem with multiple multicast sessions under a capacity limited constraint. This problem is formulated as a tree packing problem. We propose two heuristic algorithms, Steiner-tree-based heuristic (STH) algorithm and cut-set-based heuristic (CSH) algorithm, for solving this problem. The simulation results show that the STH algorithm can find a better approximate solution in a shorter computation time compared to CSH. In addition, if the available bandwidth for the service is just enough, the STH and CSH algorithms may fail to find a solution even if the solution exists. The simulation results also indicate that CSH has a higher probability than STH to find a solution. Thus, it is suggested that one can apply the STH algorithm first to solve the tree packing problem. In case STH fails, CSH algorithm will be used instead.