Browsing by Issue Date, starting with "1992-08-15"

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MICROSTRUCTURE DEVELOPMENT AND MECHANICAL-PROPERTIES OF Y2O3-DOPED TETRAGONAL ZRO2 POLYCRYSTALS AND MULLITE COMPOSITES
(1992-08-15)
CHUANG, SC
;
KUO, CT
;
LI, AK
;
機械工程學系
;
Department of Mechanical Engineering
Composites containing Y2O3-doped tetragonal ZrO2 polycrystals (Y-TZP) and mullite were prepared by adding Y-TZP powder to a silicon aluminate sol, which is the precursor of the mullite phase. After filtration and drying, the mixed powder was compacted and sintered at 1500-degrees-C in air for various lengths of time. The mullite particles were uniformly distributed in a Y-TZP matrix; energy-dispersive spectroscopy microanalysis indicated that the chemical composition of these particles ranged from 3Al2O3-2SiO2 to 2Al2O3-SiO2. Incorporating mullite particles in a Y-TZP matrix had two evident effects on the composites: first, the ZrO2 grain size was substantially increased; second, the fracture toughness of the composites showed a 50% increase (from 9 to 13.5 MPa m0.5). This increased toughness was due to the enhanced transformability of the tetragonal ZrO2 (t-ZrO2), which resulted mainly from the enlarged grain size and the increased tetragonality of the t-ZrO2.
CHARACTERIZATION OF ULTRATHIN OXIDE PREPARED BY LOW-TEMPERATURE WAFER LOADING AND NITROGEN PREANNEALING BEFORE OXIDATION
(1992-08-15)
WU, SL
;
LEE, CL
;
LEI, TF
;
LIANG, MS
;
電子工程學系及電子研究所
In this study, we report a high-performance ultrathin oxide (almost-equal-to 80 angstrom) prepared by a low-temperature wafer loading and N2 preannealing before oxidation. This recipe can reduce native oxide thickness and thermal stress compared to the conventional oxidation recipe. The high-resolution transmission electron microscopy reveals that the SiO2/Si interface is atomically flat, and a thin crystalline-like oxide layer about 7 angstrom exists at the interface. Oxides prepared by the proposed recipe show a very high dielectric breakdown field (greater-than-or-equal-to 16 MV/cm) and a very low interface state density (N(it) almost-equal-to 3 X 10(9) eV-1 cm-2 at midgap). The effective barrier height at cathode derived from the slopes of log(J(g)/E2(ox)2 vs 1/E(ox) and t(bd) vs 1/E(ox) plots is about 3.9 eV, instead of 3.2 eV for the control sample. It also shows a better immunity to the charge trapping and interface state generation under high-field stressing, and superior time-dependent dielectric breakdown characteristics.
HYDROGENIC IMPURITY STATES IN QUANTUM DOTS AND QUANTUM WIRES
(1992-08-15)
CHUU, DS
;
HSIAO, CM
;
MEI, WN
;
電子物理學系
;
Department of Electrophysics
The energies of hydrogenic impurity states with an impurity atom located at the center of a quantum dot and on the axis of a quantum-well wire are studied. These two systems are all assumed to have an infinite confining potential. In the case of the quantum dot, the impurity eigenfunctions are expressed in terms of Whittaker functions and Coulomb scattering functions. The calculated ground-state energy of the impurity approaches the correct limit of three-dimensional hydrogen atom as the radius of the quantum dot becomes very large. In the case of the quantum-well wire, analytical solutions can be obtained if we divide the space into a two-dimensional subspace (perpendicular to the axis of the quantum-well wire) and a one-dimensional subspace (parallel to the axis of the quantum-well wire). The calculated ground-state energy of the quantum-well wire approaches the ground-state energy of the shallow-impurity atom located on the surface as the radius of the wire becomes infinite. Variations of the state energies with the radius of the quantum dot and the quantum-well wire are obtained.
PHOTOREFLECTION STUDY ON THE SURFACE ELECTRIC-FIELD OF DELTA-DOPED GAAS GROWN BY MOLECULAR-BEAM EPITAXY
(1992-08-15)
LIU, DG
;
CHANG, KH
;
LEE, CP
;
HSU, TM
;
TIEN, YC
Photoreflectance spectroscopy has been used to study the surface electric-field strength and the surface potential of delta-doped GaAs. Franz-Keldysh oscillations in the reflectance spectra were clearly observed and the oscillation periods were used to calculate the internal electric fields of the delta-doped samples. Based on the measured results and the self-consistent calculation, a surface potential of 0.6 eV is obtained.
RENORMALIZED FREQUENCY-SHIFT OF SUPERRADIANT EXCITONS IN THIN SEMICONDUCTOR-FILMS
(1992-08-17)
LEE, YC
;
CHUU, DS
;
MEI, WN
;
電子物理學系
;
Department of Electrophysics
The radiative frequency shift of an exciton in a thin semiconductor film, like its radiative level width, is shown to be superradiatively enhanced. Unlike the latter, however, a finite frequency shift can only be obtained after proper renormalization for the correlated system. The shift is found to be inversely proportional to the square of the factor k0d and proportional to the film thickness T; k0 = E(qn)/H(BAR)c, E(qn) being the exciton energy gap and d the lattice constant of the semiconductor. Therefore, the coherent frequency shift can be observed experimentally if one varies the thickness, or the exciton energy gap E(qn) by imposing high pressure.
PERFORMANCE ANALYSIS OF A STATISTICAL MULTIPLEXER FOR INTEGRATED SERVICE IN THE CUSTOMER-PREMISE EQUIPMENT
(1992-08-17)
CHANG, CJ
;
WANG, SY
;
電信工程研究所
;
Institute of Communications Engineering
A statistical multiplexer for integrated service in the customer-premise equipment is analyzed. The integrated service is generally assumed to contain both wideband (WB) and narrowband (NB) services. The arrival process for the former is modeled as a discrete birth-death Markov chain and that for the latter is modeled as an independent Poisson. Each customer of WB arrival requires more than one channels (servers) for service, while each customer of NB arrival requires a single channel, and the service times of channels are the same and constant. These two types of customers are assumed to be delayed in a finite waiting room if blocked. Also, a cutoff parameter specifying the maximum number of WB customers that can receive service in one slot is provided for protection of NB. The performance measures include queue length distribution, blocking probability, and mean waiting time. Simulation results are also provided to help verify the validity of the analysis.
SYNTHESIS OF LIQUID-CRYSTALLINE POLYSILOXANES CONTAINING DIPHENYLDIACETYLENE SIDE GROUPS
(1992-08-23)
HSU, CS
;
LU, YH
;
CHEN, YN
;
應用化學系
;
Department of Applied Chemistry
SPECIAL SUBGRAPHS OF WEIGHTED VISIBILITY GRAPHS
(1992-08-24)
HSU, FR
;
LEE, RCT
;
CHANG, RC
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
BINDING-ENERGY SPECTRA OF ABC-EXCITONS OF CDS
(1992-09-01)
DAI, CM
;
CHUU, DS
;
電子物理學系
;
Department of Electrophysics
A novel perturbative variational method was employed to calculate the exciton energy spectra of CdS. The band mixing effects were included by taking into account the detail feature of the valence bands. More extensive charcteristics of the energy spectra of A-, B- and C-excitons were identified. It is found that the binding energy of the ground state of a B-exciton is larger than that of an A-exciton, whilst the binding energy of the 2s state of a B-exciton is slightly lower than that of an A-exciton. Our results are compared with the previous theoretical values using the conventional perturbation method and the available experimental data. Better agreements between our results and the observed values are obtained.
STUDY ON THE INTRINSIC THERMAL-STABILITY OF THIN-FILM SUPERCONDUCTORS DUE TO A POINT HEAT-SOURCE
(1992-09-01)
CHU, HS
;
CHEN, RC
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without Joule heating at all times after the occurrence of a localized release of thermal disturbance. The present work deals with the intrinsic thermal stability of an anisotropic thin-film superconductor under a localized release of thermal energy. A three-dimensional analysis is introduced to consider an instantaneous release of energy in the form of a point source at different locations. Through the transformation of coordinate, an exact solution is obtained by the method of separation of variables. Results from this study indicate that the thermal stability parameter of highly oriented films of superconductors is strongly under the influence of anisotropy. The stability parameter also depends on the location of point source, the amount of disturbance energy, the Biot number, and the aspect ratio in the plane of thin film and normal to it.
OPTOELECTRONIC SYNCHRONIZATION OF DISTRIBUTED MICROWAVE-OSCILLATORS USING SEMICONDUCTOR-LASER DIODES
(1992-09-01)
WU, HH
;
CHANG, CS
;
PAN, CL
;
交大名義發表
;
光電工程學系
We report a laser-diode-based system for optoelectronic synchronization of two distributed microwave oscillators at 10-GHz. The relative phase between the 10-GHz signals can be continuously tuned over a complete cycle by an optical delay line. Phase-locking of the two oscillators with a frequency offset of 10 kHz is also demonstrated. This method can be used to synchronize millimeter-wave oscillators for distributed architectures via fiber-optic links in the future.
RELOCATION PROBLEMS OF MAXIMIZING NEW CAPACITIES UNDER A COMMON DUE DATE
(1992-09-01)
LIN, MT
;
TSENG, SS
;
資訊工程學系
;
Department of Computer Science
Given a set of h buildings to be torn down and rebuilt, each building B(i) demands n(i) units of temporary vacancies for reconstruction (i.e. the reconstruction of B(i) can be started only if there are at least n(i) temporary vacancies available) and returns a(i) units of vacancies when it is rebuilt. The reconstruction time of each building is assumed to be unitary. Under the initial provision of V0 units of vacancies and a specified due date d, SIGMA(Bi is-an-element-of S)a(i), where S is a feasible sequence such that absolute value of S less-than-or-equal-to d, is the objective function to be maximized. We show that the problem is NP-complete. Based on a dominance heuristics, we further propose a branch-and-bound algorithm. Experimental results are included to elucidate the effectiveness of our algorithm. Two further restricted versions are also polynomially solvable.
AN IMPROVED ALGORITHM FOR INEXACT REASONING BASED ON EXTENDED FUZZY PRODUCTION RULES
(1992-09-01)
CHEN, SM
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
;
Department of Computer Science
This paper proposes a new algorithm to deal with inexact reasoning, where extended fuzzy production rules are used for knowledge representation. Given the truth values of some conditions, the algorithm can perform inexact reasoning to evaluate the truth values of other conditions efficiently and automatically. First, the extended fuzzy production rules in a knowledge base are modeled by an augmented fuzzy rule matrix F. Then, based on the transitive closure of the augmented fuzzy rule matrix F, we develop an efficient algorithm for inexact reasoning. The algorithm proposed in this paper is better than the one presented in Chen et al. (1991) because it can handle the case of circular rules and can be executed more efficiently.
THE DISPERSION-RELATIONS OF PLASMONS IN A SIMPLIFIED SYSTEM OF CUO2 LAYERS AND CU-O CHAINS
(1992-09-01)
TSAY, SF
;
WANG, SY
;
YANG, TJW
;
電子物理學系
;
Department of Electrophysics
A simplified model for YBa2Cu3O7 system composed of CuO2 layers and Cu-O chains has been calculated with the long range effect of the all-neighbors Coulombic e-e interactions taken into consideration. Dispersion relations have been worked out and discussed. The most striking consequence from the all-neighbors interaction is that the plasmons have, in the long wavelength limit, in addition to the usual vanishingly small two-dimensional acoustic plasmon energies which result from only nearest neighbor interactions, a non-zero omega(P)* consistent with the bulk plasma frequency of a three dimensional system. The data of an optical reflectance from an EELS experiment has been refitted based on calculated results for plasmon dispersion relations in the YBa2Cu3O7 system.
OPTIMAL VIBRATION CONTROL FOR A FLEXIBLE ROTOR WITH GYROSCOPIC EFFECTS
(1992-09-01)
LEE, AC
;
CHEN, ST
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
Active vibration control of flexible rotor systems with gyroscopic effects is investigated in this paper. Using the finite element formulation for the mathematical model of flexible rotors, a new rotating velocity dependent output-feedback controller, in addition to the optimal independent modal-space control system, is proposed to suppress the vibration level and in consequence, achieve better operating conditions. This new active control loop is added in order to compensate the gyroscopic effects during rotation, especially in the higher-flexibility modes. Furthermore, stability analysis via the Kelvin Tait-Chetaev (KTC) stability theorem for a mechanical system is presented. It demonstrates that if the placement of actuators and sensors are collocated, the fulfillment of optimality and stability for each independently controlled mode is a prerequisite to guaranteeing full-order closed-loop (FOCL) stability. Simulation results are shown in order to confirm that the proposed controller effectively promotes control performance. In addition, the significant impact of the allocation of sensors and actuators on the effectiveness of such a controller is also discussed.
EFFICIENT ALGORITHMS FOR METHOD DISPATCH IN OBJECT-ORIENTED PROGRAMMING SYSTEMS
(1992-09-01)
HUANG, SK
;
CHEN, DJ
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
ON THE PERFORMANCE OF A RATE 8/10 MATCHED SPECTRAL NULL CODE FOR CLASS-4 PARTIAL RESPONSE
(1992-09-01)
THAPAR, H
;
RAE, J
;
SHUNG, C
;
KARABED, R
;
SIEGEL, P
We present the application and performance of a rate 8/10 Matched-Spectral-Null (MSN) trellis code in conjunction with Class-4 partial response (PR4) signalling. The VLSI implementation of an MSN code is described. Results of experiments using synthesized PR4 waveforms are presented and it is shown that the rate 8/10 code can provide about a 3dB advantage relative to the Class-4 partial response maximum likelihood detection (PRML) in the presence of additive white Gaussian noise as well as additive synthesized adjacent track interference.
EFFECT OF POSITION-DEPENDENT TIME CONSTANT ON PHOTOREFRACTIVE 2-WAVE MIXING
(1992-09-01)
DAI, LK
;
GU, C
;
YEH, P
;
光電工程學系
;
Department of Photonics
The effect of a position-dependent time constant on nondegenerate photorefractive two-wave mixing is analyzed. For codirectional two-wave mixing the results indicate that the bandwidth of the two-wave-mixing gain decreases when the medium becomes lossy and that the photorefractive phase shift depends on the loss of the medium. In contradirectional two-wave mixing the total local intensity strongly depends on the coupling even if the medium is lossless. Thus the bandwidth is dependent on the energy coupling.
RETRIEVING THE MOST SIMILAR SYMBOLIC PICTURES FROM PICTORIAL DATABASES
(1992-09-01)
CHANG, CC
;
WU, TC
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
In this article, we suggest an iconic indexing mechanism for spatial similarity retrieval on iconic image databases based upon the spatial relationships among the objects in a picture. The iconic objects we deal with are some kinds of gross panorama of simple objects. We also assume that any one iconic object is not distinguished from any other object of the same kind. For our mechanism, we first transform each iconic picture into a set of ordered triples (O(i), O(j), R(ij)) where O(i) and O(j) are objects and R(ij) is the predefined spatial relationship codes between O(i) and O(j). Then we construct a set of hashing functions for all spatial relationship codes R(ij), separately, associated with all ordered pairs (O(i), O(j)) extracted from the ordered triples (O(i), O(j), R(ij)), Thereafter, an iconic index table can be established according to the constructed hashing functions for all predefined spatial relationship codes. By applying the constructed hashing functions, the most similar pictures in the database satisfying a specified query can be fast determined. We can easily extend our mechanism for handling the case when some new spatial relationship codes are defined later for the considerations of refined spatial similarity retrieval under the maximum-likelihood measure criterion.
CONTACT RESISTIVITY OF SHALLOW JUNCTIONS FORMED BY IMPLANTATION THROUGH PT OR PTSI
(1992-09-01)
TSUI, BY
;
CHEN, MC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The specific contact resistance (rho(c)) of PtSi/p+ and PtSi/n+ contacts formed by ion implantation through Pt or PtSi was studied. A simple process to form self-aligned six-terminal Kelvin structure was developed in order to measure the specific contact resistance. For the PtSi/p+ contact system, a rho(c) lower than 1 x 10(-6) OMEGA-cm2 was achieved by BF2+ implantation at 40 keV to a dose of 5 x 10(15) cm-2. Increase of dose or energy could further decrease the rho(c) to be lower than 5 x 10(-7) OMEGA-cm2. The rho(c) of the PtSi/n+ contact system was lower than that of the PtSi/p+ contact system and a rho(c) of 1 x 10(-7) OMEGA-cm2 was obtained. These results indicate that although the PtSi-contacted junction is formed at temperatures lower than 800-degrees-C, the rho(c) is low enough to satisfy the requirements of submicrometer technology. We suggest that PtSi should be a favorable material to form shallow junctions and contacts simultaneously for future VLSI processes and to satisfy low thermal budget requirement.