Browsing by Issue Date, starting with "1996-04-20"

Now showing 1 - 20 of 85504

Influence of an external electric field on high-T-c superconductivity
(1996-04-20)
Lee, WD
;
Chen, JL
;
Yang, TJ
;
Chiou, BS
;
電子物理學系
The surface superconductivity induced by applying an electric field perpendicular to the surface of a high-T-c superconductor covered by an insulator and a gate electrode is studied theoretically. Taking the idea into account that the change of the surface carrier density confined in a thin screening layer modulates the transport properties of superconductors, we develop a simple method based on the Chen and Yang model to study the T-c shift dependence on the applied voltage in the frameworks of a Thomas-Fermi approximation and BCS theory. In such a case a novel boundary condition is introduced to modify the G-L equations. Solving the modified one, the T-c shift derived by the present model is similar in qualitative behavior to the Shapiro result, but much simpler in form. In addition, it is shown to be proportional to the applied field (the square of applied field) for thin film (thick film) for a given material. Based on our simple results, the critical current density J(c) and nucleation field H-c3 as functions of the applied voltage are easily derived.
Analysis of capacitance-voltage characteristics for two-dimensional multi-conductor in liquid crystal displays
(1996-04-22)
Lin, KW
;
Shieh, HPD
;
Su, FCD
;
光電工程學系
;
Department of Photonics
The capacitance voltage characteristics for the two-dimensional multi-conductor in liquid crystal displays (LCDs) are numerically derived by the method of successive over relaxation (SOR). The nonlinear and anisotropic properties of dielectric constant in the LC cell depend on the orientation of LC molecules under the influence of inhomogeneous electric field. An LC continuum theory implemented by tensor takes elastic anisotropy and inhomogeneous electric field into consideration to calculate the two-dimensional molecule orientations and potential distribution in LCDs. The dependence of capacitance on applied voltages and the geometric of LC cell is quantitatively described, Nonlinear capacitance results in capacitive coupling which causes flicker and adversely degrades image retention in LCD. (C) 1996 American Institute of Physics.
Drawing of microshear deformation zones in glassy polymers: Poly(phenylene oxide) (PPO)
(1996-04-30)
Yang, ACM
;
Wang, RC
;
Kunz, MS
;
Yang, IC
;
電子物理學系
The topography of the microscopic shear deformation zones (SDZ) in the glassy polymer PPO was studied by using atomic force microscopy (AFM) and was used to analyze the growth and breakdown of the SDZ. It was found that the local stress and strain are almost constant within the deformation zones but higher than those in the elastic regions. The maximum strain rate during stretching was found to always locate near the SDZ boundaries, indicating that most drawing took place there. With both the local stress and strain obtained for every point within the SDZ, it is possible to construct a full stress-strain curve for the drawing of the tiny local deformation zones. The stress-strain curve clearly demonstrates a yield point in the beginning of microyielding where the tensile modulus was found to be much lower than that in the elastic regime. Some strain hardening, however, took place at larger deformation. Moreover, we found that for each microscopic region participated in the microdrawing the local strain rate increased with local strain until a critical strain around 0.65 was reached, after which the strain rate decreased with strain. This critical strain may be related to the chain entanglement network structure because it shifted to 0.75 when PS diluents were blended into PPO, indicating that strain hardening was delayed by the increase of chain entanglement mesh size. (C) 1996 John Wiley & Sons, Inc.
A new method for texture analysis using morphological gradient texture histograms
(1996-05-01)
Lee, JH
;
Hsueh, YC
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
A new method using Morphological Gradients, which measures the degree of roughness of image surface, is proposed for texture analysis. In this method, the local texture feature for a given pixel is characterized by its corresponding morphological gradient, and the global texture aspect of an image, denoted the Morphological Gradient Texture Histogram (MGTH), is used as a distinguishing feature for texture analysis and classification. To evaluate the performance of the proposed method, supervised texture classification and rotated texture classification are applied. Experimental results reveal high accuracy classification rates and show that the proposed method is a good tool for texture analysis.
PACCI: A high performance MAC protocol for client-server-based gigabit LANs and MANs
(1996-05-01)
Yuang, MC
;
Liu, JC
;
交大名義發表
;
National Chiao Tung University
Using hypermedia in computer-aided instruction
(1996-05-01)
Chen, LS
;
Liu, PW
;
Chang, KY
;
Chen, JP
;
Chen, SC
Observations of Guinier-Preston zones in an As-deposited Al-1wt.%Si-0.5wt.%Cu thin film
(1996-05-01)
Tung, CH
;
Chiu, RL
;
Chang, PH
;
材料科學與工程學系
;
電子工程學系及電子研究所
A simple laboratory procedure for packaging and testing part-fabricated gas microsensors
(1996-05-01)
Chao, S
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
;
Department of Electrophysics
Simple schemes for gas microsensor packaging and testing are presented. The packaging procedures are developed for mostly hand operations without reliance on sophisticated equipment. Special flow-cell features and compact design enable easy configuration for testing in gas streams by flow-injection. Automation improves the efficiency of the sampling of gas microsensors and hence provides a higher compilation rate for the test data.
5 mm high-power-density dual-delta-doped power HEMT's for 3 V L-band applications
(1996-05-01)
Lai, YL
;
Chang, EY
;
Chang, CY
;
Chen, TK
;
Liu, TH
A high-power-density dual-delta-doped AlGaAs/InGaAs/GaAs high electron mobility transistor (HEMT) for personal communication applications has been developed. A 5.0 mm gate-width device operating at a drain bias of 3.0 V gave an output power over 1 W, The 1 mu m gate-length HEMT exhibited a current density of 425 mA/mm at V-gs = 0.5 V, The maximum transconductance of the device was 270 mS/mm, The effective knee voltage was as low as 0.3 V, At the class AB operation, the HEMT demonstrated an output power density of 200 mW/mm, 64% power-added efficiency and 18.2 dB linear gain at 900 MHz, This is the highest power density of a dual-delta-doped AlGaAs/InGaAs/GaAs HEMT reported to date for low voltage (3 V) wireless applications.
A novel two-step etching process for reducing plasma-induced oxide damage
(1996-05-01)
You, KF
;
Wu, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
During plasma etching, a large amount of charging current due to plasma can flow through the gate oxide near the endpoint, resulting in the degradation of thin gate oxide. In this paper, a two-step etching process using reactive ion etching (RIE) following wet etching is proposed to reduce the gate oxide charging current. The characteristics of the proposed process for gate oxide protection are characterized by time-dependent dielectric breakdown (TDDB), high-frequency capacitance-voltage (HFCV), and quasistatic capacitance-voltage (QSCV) measurements. From measurement results, it is shown that degradation of the gate oxide is dramatically eliminated by the proposed two-step etching method as compared with that using pure RIE. Therefore, the proposed two-step etching process can replace the pure dry etching process to reduce the plasma-induced gate oxide damage.
Numerical simulation of transitional aiding mixed convective air flow in a bottom heated inclined rectangular duct
(1996-05-01)
Huang, CC
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Buoyancy induced transient transitional flow structures and the associated heat transfer in mixed convective aiding flow of air in a bottom heated inclined rectangular duct were numerically investigated. The three-dimensional unsteady Navier-Stokes and energy equations were discretized by higher order finite-difference approximations and directly solved by the projection method. Computations were carried out for the Reynolds number ranging from 100 to 500, aspect ratio of the duct from 2 to 4, duct inclination from 0 degrees to 60 degrees C and buoyancy-to-inertia ratio high enough to cause flow transition. Attention was particularly paid to delineate the effects of the duct inclination on the flow transition and the associated temporal and spatial how structures. It is of interest to note from the predictions that increasing the inclined angle measured from horizontal does not always stabilize the flow. In fact, the flow stability is highly dependent on all the governing parameters and is intimately related to the structural changes in the buoyancy induced longitudinal vortices.
Adaptive fuzzy power control for CDMA mobile radio systems
(1996-05-01)
Chang, PR
;
Wang, BC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
This paper introduces a new application of fuzzy-logic control (FLC) theory to the power control in a direct-sequence, code-division multiple-access (DS/CDMA) cellular system over the mobile fading radio channels. Power control is essential in DS/CDMA to compensate for the differing received powers due to both the slowly varying long-term and fast varying short-term fading processes and co-channel interference. The conventional feedback power control algorithms allow the base station to send a power command to either raise or lower each user transmitting signal power level by a fixed power step and then keep the received powers almost equal. The fixed-step approach is actually an integral control whose power increment is determined according to the bang-bang-like control policy. However, this control scheme suffers from poor system stability, large overshoot, and long rise time. To tackle this difficulty, a fuzzy proportional-plus-integral (PI) control, whose input variables are the received power error and error change, is introduced to determine each user's transmitting power in order to maintain simultaneously all users' signal power received at the base station nearly equal and to achieve better system stability and control performance. The derivation of the fuzzy PI control has been carried out by analyzing both the closed-loop steady state behavior and transient response of the system with a priori knowledge of the dynamics of the CDMA mobile fading channels. In fuzzy control, linguistic descriptions of actions in controlling a process are represented as fuzzy rules. This fuzzy-rule base is used by an inference mechanism in conjunction with some knowledge of the states of process in order to determine control actions. These control actions would lead to the fast rise time, minimum overshoot, and small root-mean-squared (rms) tracking error. Furthermore, the additional advantages of fuzzy PI control over conventional control theories are increased robustness despite interference and the ability to handle the time-delay process without system degradation since there is usually a latency between each user and base station. Simulation results show that the fuzzy PI power control provides much smaller rms tracking error and better traffic capacity performance compared with the fixed-step control, especially in poor co-channel interference conditions.
Trends in outbound tourism from Taiwan
(1996-05-01)
Huang, CT
;
Yung, CY
;
Huang, JH
;
管理科學系
;
Department of Management Science
In 1979, Taiwan's government relaxed its bait on overseas travel, and permitted residents to travel to mainland China to visit relatives in 1987. In 1994, 4.74 million people travelled abroad, about 22% of Taiwan's total population. Thus has Taiwan become one of the world's most prominent tourist-exporting countries. In this article, we review government outbound tourism policies, analyze the market structure and the characteristics of travellers, discuss problems and propose solutions to improve the nation's outbound-tourism standing, and look at the future of Taiwan's outbound travel.
The synthesis and characterization of phosphorus-doped diamond films using trimethyl-phosphite as a doping source
(1996-05-01)
Chen, CF
;
Lo, SF
;
Chen, SH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Producing impurity-doped diamond films is a critical task for modern electronic applications. In this study, the effects of phosphorus in the gas phase on the morphological features of polycrystalline diamond films were investigated. The diamond films were prepared on n-type Si(100) substrates by the microwave plasma chemical vapour deposition. A trimethyl-phosphite vapour was introduced to the CH4-CO2 gas mixture as a dopant source. Surface morphology changed from well-defined facets to ball-like features by increasing the dopant concentration in the gas phase. Phosphorus-doped diamond films of good quality and well defined facets could be obtained by reducing the carbon concentration of reactant gases. This reduction could be achieved by decreasing the CH4 flow rates during the deposition process. An increase in the the dopant source caused the growth rate to become lower, the nucleation density to reduce drastically, and the relative intensity of XRD characteristic (110) peak to increase significantly.
Design techniques for VHF/UHF high-Q tunable bandpass filters using simple CMOS inverter-based transresistance amplifiers
(1996-05-01)
Lu, PH
;
Wu, CY
;
Tsai, MK
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, CMOS inverter-based wideband transresistance R(m) amplifiers are proposed and analyzed. Using the R(m) amplifiers, tunable VHF/UHF R(m)-C bandpass biquadratic filters can be designed. In these filters, the center frequency f(o) can be post-tuned by adjusting the control voltages of the R(m) amplifiers. The pseudodifferential configuration uses the extra inversely connected and self-shorted inverters for Q enhancement. Experimental results have shown that the center frequency f(o) of the single-ended-output R(m)-C bandpass biquad is 386 MHz (258 MHz) and Q = 1.195 (Q = 1.012) for +/-2.5 V (+/-1.5 V) supply voltage. The power consumption is 24.83 mW (3.42 mW), and the dynamic range is 61 dB (55.5 dB). For pseudodifferential-output high-Q configuration, the measured quality factor Q can be as high as 360 with f, = 222.7 MHz. When Q = 94, the power consumption is 56.2 mW and the measured dynamic range is 57.8 dB for +/-2.5 V supply voltage.
Reinforcement learning for an ART-based fuzzy adaptive learning control network
(1996-05-01)
Lin, CJ
;
Lin, CT
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
This paper proposes a reinforcement fuzzy adaptive learning control network (RFALCON) for solving various reinforcement learning problems, The proposed RFALCON is constructed by integrating two fuzzy adaptive learning control networks (FALCON's), each of which is a connectionist model with a feedforward multilayer network developed for the realization of a fuzzy controller, One FALCON performs as a critic network (fuzzy predictor), and the other as an action network (fuzzy controller), Using the temporal difference 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 performs a stochastic exploratory algorithm to adapt itself according to the internal reinforcement signal, An ART-based reinforcement structure/parameter-learning algorithm is developed for constructing the RFALCON dynamically, During the learning process, both structure learning and parameter learning are performed simultaneously in the two FALCON's, The proposed RFALCON can construct a fuzzy control system dynamically and automatically through a reward/penalty signal (i.e., a ''good'' or ''bad'' signal), It is best applied to the learning environment, where obtaining exact training data is expensive, The proposed RFALCON has two important features, First, it reduces the combinatorial demands placed by the standard methods for adaptive Linearization of a system, Second, the RFALCON is a highly autonomous system, Initially, there are no hidden nodes (i.e., no membership functions or Fuzzy rules), They are created and begin to grow as learning proceeds, The RFALCON can also dynamically partition the input-output spaces, tune activation (membership) functions, and find proper network connection types (fuzzy rules), Computer simulations have been conducted to illustrate the performance and applicability of the proposed learning scheme.
A new method for texture analysis using morphological gradient texture histograms
(1996-05-01)
Lee, JH
;
Hsueh, YC
;
資訊工程學系
;
Department of Computer Science
A new method using Morphological Gradients, which measures the degree of roughness of image surface, is proposed for texture analysis. In this method, the local texture feature for a given pixel is characterized by its corresponding morphological gradient, and the global texture aspect of an image, denoted the Morphological Gradient Texture Histogram (MGTH), is used as a distinguishing feature for texture analysis and classification. To evaluate the performance of the proposed method, supervised texture classification and rotated texture classification are applied. Experimental results reveal high accuracy classification rates and show that the proposed method is a good tool for texture analysis.
Experimental study of unstable mixed convection of air in a bottom heated horizontal rectangular duct
(1996-05-01)
Lin, WL
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
An experiment was carried out to investigate the buoyancy induced spatial and temporal flow transition and the associated heat transfer processes in a mixed convective air flow through a bottom heated horizontal rectangular duct, by measuring the local heat transfer coefficient, spanwise temperature distributions, air temperature variation with time at selected locations and by visualizing the cross plane secondary flow for the Reynolds numbers ranging from 9 to 186 and the Grashof numbers up to 5 x 10(6). The results indicated that the heat transfer enhancement is due to the formation and development of a buoyancy driven secondary vortex flow. The onset of thermal instability was found to move upstream for a higher Grashof number and to be delayed for a larger Reynolds number. At increasing Grashof numbers the measured spanwise time-averaged fluid temperature distributions and the corresponding instantaneous flow visualizations clearly show the formation of secondary vortex flow and the changes in the flow structures. At slightly supercritical Grashof numbers, the secondary flow is in the form of two pairs of longitudinal rolls with the vortex flow ascending along the side walls. For higher Grashof numbers the vortex rolls rotate in opposite directions, with the secondary flow descending near the side walls. At even higher Grashof numbers, merging of the vortices takes place and only one pair of vortex rolls exist. Furthermore, raising the Grashof. number or lowering the Reynolds number causes the flow to change from a laminar time periodic to a transitional quasiperiodic and even to a chaotic turbulent state. Based on the present data, a regime map delineating the temporal state of the flow and a correlating equation for the Hopf bifurcation were proposed.
A fully distributed power control algorithm for cellular mobile systems
(1996-05-01)
Lee, TH
;
Lin, JC
;
電信工程研究所
;
Institute of Communications Engineering
Several distributed power control algorithms that can achieve carrier-to-interference ratio (CIR) balancing with probability one have been proposed recently for cellular mobile systems [5]-[8], In these algorithms, only local information is used to adjust transmitting power, However, a normalization procedure is required in each iteration to determine transmitting power and, thus, these algorithms are not fully distributed, In this paper, we present a distributed power control algorithm which does not need the normalization procedure, We show that the proposed algorithm can achieve CIR balancing with probability one, Moreover, numerical results reveal our proposed scheme performs better than the algorithm presented in [7], which has the best performance among the distributed power control algorithms studied in [5]-[8], The excellent performance and the fully distributed property make our proposed algorithm a good choice for cellular mobile systems.
Comparison of the diffusion barrier properties of chemical-vapor-deposited TaN and sputtered TaN between Cu and Si
(1996-05-01)
Tsai, MH
;
Sun, SC
;
Tsai, CE
;
Chuang, SH
;
Chiu, HT
This work investigated the barrier properties of metalorganic chemical-vapor-deposited (CVD) tantalum nitride (TaN) and physical-vapor-deposited (PVD) TaN between Cu and Si. The CVD TaN film had a preferred orientation (200) with a grain size of around 60 nm, while the PVD TaN had a (111) preferred orientation with a grain size of around 20 nm, as determined by transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses. Degradation study of the Cu/TaN/Si contact system was also performed by sheet resistance measurement, scanning electron microscopy (SEM), XRD, secondary ion mass spectroscopy (SIMS), and shallow junction diodes. These results indicated that the PVD TaN film can act as a better diffusion barrier than the CVD TaN film. The higher thermal stability of PVD TaN than CVD TaN can be accounted by their difference in microstructures. The failure mechanisms of both CVD TaN and PVD TaN films as diffusion barriers between Cu and Si were also discussed. (C) 1996 American Institute of Physics.