Browsing by Issue Date, starting with "1991-09-02"

Now showing 1 - 20 of 91163

STABILITY OF A HEDGEHOG NEMATIC CONFIGURATION IN A SMALL CLOSED CYLINDRICAL CAVITY
(1991-09-02)
CHEN, SH
;
LIANG, BJ
;
交大名義發表
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光電工程學系
;
National Chiao Tung University
This letter presents a study on the stability of molecular configurations in a small closed nematic liquid-crystal cell. A volume point defect exists at the center of the cell with the molecules anchored perpendicularly to the cavity wall. We show that the transformation of a radial hedgehog to a hyperbolic one should occur when the ratio of splay-to-bend elastic constants becomes larger than a certain value that depends on the cell geometry.
BOLOMETRIC YBA2CU3O7-X INFRARED DETECTOR
(1991-09-12)
TSENG, TY
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CHANG, CY
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HAUNG, CJ
;
CHEN, MC
;
電子工程學系及電子研究所
Results of the measurement of optical detection in YBa2Cu3O7-x superconducting epitaxial films at a wavelength of 0.94-mu-m are presented. These films show bolometric responses at temperatures in the resistive transition regions which are strongly dependent on the bias current. For 0.94-mu-m radiation, electronically chopped at 20 Hz, measurement of a meander bridge yields a bolometric responsivity of approximately 6.1 V/W.
FINDING THE MOST VITAL EDGE WITH RESPECT TO MINIMUM SPANNING TREE IN WEIGHTED GRAPHS
(1991-09-13)
HSU, LH
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JAN, RH
;
LEE, YC
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HUNG, CN
;
CHERN, MS
EFFECT OF POLYCARBONATE MOLECULAR-WEIGHT ON PRECRACK HYSTERESIS ENERGY IN DETERMINING ITS DUCTILE-BRITTLE TRANSITION
(1991-09-20)
CHANG, FC
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HSU, HC
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交大名義發表
;
應用化學系
;
National Chiao Tung University
The distinctive ductile-brittle transition behavior of pseudoductile polymeric materials such as polycarbonate (PC) has been discovered to be closely related to the precrack hysteresis loss energy. The higher molecular weight (MW) PC with higher ductility also results in higher precrack hysteresis energy and therefore greater precrack plastic volume under condition of constant loads. If the precrack plastic volume exceeds a critical value, crack initiation thereafter will propagate within the domain of the plastic zone and results in ductile fracture. The deformation displacement is closely related to the precrack plastic volume, and the critical displacement actually determines the critical plastic volume. The higher molecular weight polycarbonate with higher entanglement density is able to withstand earlier crack initiation more effectively. Toughening plastics, such as rubber modification, is simply the result of delaying or retarding the crack initiation and allows the precrack plastic zone to grow over its critical value. A model of crack criterion based on precrack plastic zone is proposed to interpret the ductile-brittle transition phenomenon.
PARAMETRIC NONLINEAR INTEGER PROGRAMMING - THE RIGHT-HAND SIDE CASE
(1991-09-25)
CHERN, MS
;
JAN, RH
;
CHERN, RJ
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資訊工程學系
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Department of Computer Science
In this paper, we present algorithms for solving families of nonlinear integer programming problems in which the problems are related by having identical objective coefficients and constraint matrix coefficients. We consider two types of right-hand sides which have the forms b(l) and b(i) + theta-i(d)i where {b(l)}l = 1,...,L is a given set of vectors, b(i) + theta-i(d)i is a parametric function and the parameter theta-i varies from zero to one. The approach consists primarily of solving the most relaxed problem using branch and search method and then finding the optimal solutions of the proposed parametric programming problems. The application of this methodology to a parametric chance-constrained problem is illustrated with applications in system reliability optimization problems.
AN OPTICAL SIGNAL GENERATOR BASED ON A TRIANGULARLY PHASE-MODULATED INTERFEROMETER
(1991-10-01)
CHIEN, PY
;
PAN, CL
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光電工程學系
;
電信研究中心
;
Department of Photonics
We demonstrated a novel optical signal generator by applying a triangular phase-modulation waveform to a laser diode interferometer. Frequency-multiplied (up to eight hundred times of the modulation signal) output in the format of an optical signal could be generated. By changing the amplitude of the triangular waveform, we can tune the frequency of the optical signal. This system can thus be considered a voltage-controlled oscillator (VCO) with an optical output signal.
THE INFLUENCE OF MODAL CHOICE ON ENERGY-CONSERVATION STRATEGIES IN TRANSPORT - APPLICATION OF A LOGIT MODEL
(1991-10-01)
TZENG, GH
;
CHEN, JJ
;
LAN, CJ
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This paper emphasizes the evaluation of energy conservation strategies that are considered to be sensitive to modal choice by employing a disaggregate logit model. Five hundred households in Taipei city were selected and interviewed on weekdays between 26 December 1986 and 15 January 1987 by using a stratified random sampling process. By computing elasticities of the logit model, three kinds of energy conservation strategies - taxi-fares, exclusive bus lanes and gasoline price - were selected for sensitivity analysis. The results show that a passenger's modal choice and energy consumption in transport are not affected greatly by the three selected energy conservation strategies in the short term. Therefore it is recommended that other strategies are used, such as reducing trip generation, shortening trip length, improving fuel efficiency and increasing vehicle occupancy to reduce energy consumption in transport.
EXTENSION OF LINEAR QUADRATIC OPTIMAL-CONTROL THEORY FOR MIXED BACKGROUNDS
(1991-10-01)
LEE, BK
;
CHEN, BS
;
LIN, YP
;
電子工程學系及電子研究所
;
電控工程研究所
The problem of finding an optimal controller, while both deterministic and stochastic signals are present in the feedback system, is addressed. A general framework is developed to solve the above problem and to unify conventional frequency domain LQ and LQG optimal control theories. Both the system transient and steady-state behaviours are considered and the exact tracking of the arbitrary reference signal is guaranteed. The decomposition of a mixed signal into the deterministic and stochastic parts gives a chance to investigate the effect of the weighting factors, which were specified in the cost function, on the compromise between transient and steady-state system performance. The solution, which characterizes the structure of the optimal controller, results in a set of independent diophantine equations, instead of a set of coupled ones. Moreover, the number of equations can be reduced under weak conditions. Finally, both transient command tracking and steady-state noise rejection capabilities can be optimized simultaneously by using a two-parameter control scheme.
COMBINED CONDUCTION AND RADIATION IN ABSORBING, EMITTING AND ANISOTROPICALLY-SCATTERING, CONCENTRIC, SPHERICAL MEDIA
(1991-10-01)
CHU, HS
;
WENG, LC
;
TSENG, CJ
;
交大名義發表
;
機械工程學系
The steady energy transfer by simultaneous conduction and radiation in an absorbing, emitting and anisotropically-scattering medium has been studied theoretically. The medium is confined between two concentric, gray, diffuse and/or specular spherical surfaces which are isothermal but at different temperatures. The radiative transfer equation is solved by using the P3-approximation method which results in four coupled ordinary differential equations (ODEs). The set of the four ODEs and energy equation is solved as a two-point boundary-value problem. The effects of the ratio of the conduction-to-radiation parameter, single-scattering albedo, the scattering phase function, and boundary reflectivities on the temperatures and heat-flux distributions in the medium are examined in detail.
A STUDY OF THE FEATURELESS ZONE IN RAPIDLY-SOLIDIFIED GAS-ATOMIZED ALUMINUM-ALLOY POWDER
(1991-10-01)
TU, GC
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CHEN, IT
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CHUNG, MS
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交大名義發表
;
材料科學與工程學系
OPTIMAL-DESIGN PARAMETERS IN CAPACITY ASSIGNMENT FOR A BROAD-BAND NETWORK
(1991-10-01)
CHANG, CJ
;
CHU, YJ
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傳播研究所
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電信研究中心
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Institute of Communication Studies
A capacity assignment strategy for a broadband network is proposed and studied in this paper. This broadband network has a large channel capacity in its elements. It usually has two kinds of customers: one is queueable narrowband (NB), and the other is blockable wideband (WB) which needs real-time delivery. Besides the characteristics of these two types of traffic, since the improvement in the blocking probability of WB is more significant than that in the mean waiting time of NB, the capacity assignment strategy favours the WB traffic by providing bit-rate compression, reserving some channels for WB customers with non pre-emption by NB customers, and permitting NB customers to use free WB channels only when the NB queue exceeds a certain length. An analytic model is developed and the solutions are presented. The results show that, via proper choice of design parameters, the proposed strategy can have superior performance.
RESIDUE ARITHMETIC VLSI ARRAY ARCHITECTURE FOR MANIPULATOR PSEUDO-INVERSE JACOBIAN COMPUTATION - REPLY
(1991-10-01)
CHANG, PP
;
LEE, CSG
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電信工程研究所
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Institute of Communications Engineering
FAST ALGORITHM FOR VQ CODEBOOK DESIGN
(1991-10-01)
CHEN, SH
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HSIEH, WM
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交大名義發表
;
電信工程研究所
;
National Chiao Tung University
The paper presents a fast codebook training algorithm for vector quantisation. It uses an elimination rule, based on triangular inequality criteria, as well as the partial distortion elimination method, to relieve the computational burden of a conventional codebook training algorithm, including a binary codeword splitting algorithm for the initial codebook and the LBG recursive algorithm. Over 95% savings in both multiplication and addition operations were achieved in the simulation of a VQ codebook training of a 'Lena' image using 16-dimensional vectors.
EXTENSION OF LINEAR QUADRATIC OPTIMAL-CONTROL THEORY FOR MIXED BACKGROUNDS
(1991-10-01)
LEE, BK
;
CHEN, BS
;
LIN, YP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The problem of finding an optimal controller, while both deterministic and stochastic signals are present in the feedback system, is addressed. A general framework is developed to solve the above problem and to unify conventional frequency domain LQ and LQG optimal control theories. Both the system transient and steady-state behaviours are considered and the exact tracking of the arbitrary reference signal is guaranteed. The decomposition of a mixed signal into the deterministic and stochastic parts gives a chance to investigate the effect of the weighting factors, which were specified in the cost function, on the compromise between transient and steady-state system performance. The solution, which characterizes the structure of the optimal controller, results in a set of independent diophantine equations, instead of a set of coupled ones. Moreover, the number of equations can be reduced under weak conditions. Finally, both transient command tracking and steady-state noise rejection capabilities can be optimized simultaneously by using a two-parameter control scheme.
ENHANCEMENT OF IMAGE QUALITY FOR LOW BIT RATE VIDEO CODING
(1991-10-01)
NGAN, KN
;
LIN, DW
;
LIOU, ML
;
交大名義發表
;
National Chiao Tung University
CCITT Recommendation H.261 on coding for visual telephony is applicable to bit rates of p X 64 kbits/s, where p = 1,2,..., 30. It generally performs well over the intended bit rates. However, at the very low rates of 64 and 128 kbits/s, it suffers from visual degradation due to coarse quantization. In this paper, we studied the various approaches or combinations of them to improve the image quality. Methods studied include reducing the quantizer step size, randomized scanning of the macroblocks, and/or nonuniform quantization of the transform coefficients.
CHARGE-COUPLED DEVICE POLARIMETRY AND ITS MEASUREMENT OF THE STOKES VECTOR OF LIGHT TRANSMITTED BY A POLYMER PLATE
(1991-10-01)
CHAO, YF
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HSIEH, WF
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交大名義發表
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光電工程學系
;
National Chiao Tung University
The Stokes vector of light transmitted by a polycarbonate plate is studied by a modified charge-coupled device polarimeter. A sheet polarizer is measured for comparison.
ADMITTANCE SPECTROSCOPY AND TRAPPING PHENOMENA OF ZNO BASED VARISTORS
(1991-10-01)
CHIOU, BS
;
CHUNG, MC
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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
Electrical properties of ZnO varistors are investigated through admittance spectroscopy. The observed ac admittance dispersion is caused by the existence of two deep bulk trap levels, which are 0.31 eV and 0.245 eV, respectively, below the conduction band. The 0.31 eV level is associated with the oxygen vacancy while the origin of the 0.245 eV level is not yet clear. An equivalent circuit model for ZnO varistors is proposed that is based on the existence of deep bulk traps.
CHARACTERIZATION OF THE SHIELDING EFFECTS ON THE FREQUENCY-DEPENDENT EFFECTIVE DIELECTRIC-CONSTANT OF A WAVE-GUIDE-SHIELDED MICROSTRIP USING THE FINITE-DIFFERENCE TIME-DOMAIN METHOD
(1991-10-01)
WU, LK
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CHANG, YC
;
交大名義發表
;
傳播研究所
;
National Chiao Tung University
The dispersion behavior of waveguide-shielded microstrip line is investigated using the finite-difference time-domain method. The result is a frequency-dependent effective dielectric constant. Structures having centered strip are examined to determine the effects of a top cover alone and the effects of two symmetrically placed sidewalls. Structures with off-centered strip are used to investigate the effects of a single sidewall alone and the combined effects of a single sidewall plus the top wall. Differences between the effects of a single sidewall alone and those of the two symmetrically placed sidewalls are identified. In addition, new results on the combined effects of the top wall plus one sidewall, which are important when considering the placement of the outermost elements of a packaged circuit, are also discussed.
A FULL-WAVE MIXED POTENTIAL MODE-MATCHING METHOD FOR THE ANALYSIS OF PLANAR OR QUASI-PLANAR TRANSMISSION-LINES
(1991-10-01)
TZUANG, CKC
;
TSENG, JD
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傳播研究所
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友訊交大聯合研發中心
;
Institute of Communication Studies
A newly proposed and tested full-wave mixed potential mode-matching method is presented for the analysis of planar and/or quasi-planar transmission lines. The transmission lines under investigation consist of layered (stratified) and nonlayered dielectric substrates and metal strips of finite thickness. The y-directed hybrid TE and TM Hertzian potentials, perpendicular to the interfaces between each layered regions, are employed in the layered regions. The nonlayered regions, which consist of dielectric step discontinuities that destroy the layered configuration in the horizontal plane, utilize the x-directed hybrid TE and TM Hertzian potentials parallel to the horizontal plane. As a direct result, the full-wave formulation of the transmission line problem becomes systematic and easy to handle. Extensive analyses of a particular case study show that the relative convergence criterion needs to be satisfied to obtain accurate electromagnetic field solutions. The theoretical results obtained here are in very good agreement with the published data for various transmission line structures, which are the special limiting cases of the particular case study. The applications of the new formulation to the proximity effects of microstrip and Microslab1 lines are also illustrated by examples.
PHASE-TRANSFORMATION IN AN FE-10.1AL-28.6MN-O.46C ALLOY
(1991-10-01)
WU, CC
;
CHOU, JS
;
LIU, TF
;
機械工程學系
;
材料科學與工程學系
The microstructure of an (alpha + gamma) duplex Fe-10.1A1-28.6Mn-0.46C alloy has been investigated by means of optical microscopy and transmission electron microscopy (TEM). In the as-quenched condition, extremely fine D0(3) particles could be observed within the ferrite phase. During the early stage of isothermal aging at 550-degrees-C, the D0(3) particles grew rapidly, especially the D0(3) particles in the vicinity of the alpha/gamma grain boundary. After prolonged aging at 550-degrees-C, coarse K-phase (Fe, Mn)3AlC precipitates began to appear at the regions contiguous to the D0(3) particles, and beta-Mn precipitates occurred on the alpha/gamma and alpha/alpha grain boundaries. Subsequently, the grain boundary beta-Mn precipitates grew into the adjacent austenite grains accompanied by a gamma --> alpha + beta-Mn transition. When the alloy was aged at 650-degrees-C for short times, coarse K-phase precipitates were formed on the alpha/gamma grain boundary. With increasing the aging time, the alpha/gamma grain boundary migrated into the adjacent austenite grain, owing to the heterogeneous precipitation of the Mn-enriched K phase on the grain boundary. However, the alpha/gamma grain boundary migrated into the adjacent ferrite grain, even though coarse K-phase precipitates were also formed on the alpha/gamma grain boundary in the specimen aged at 750-degrees-C.