Browsing by Issue Date, starting with "1994-05-06"

Now showing 1 - 20 of 88289

PHOTODISSOCIATION OF CBRCL3 AT 248 NM BY TRANSLATIONAL SPECTROSCOPY
(1994-05-06)
LEE, YR
;
TZENG, WB
;
YANG, YJ
;
LIN, YY
;
LIN, SM
The photodissociation of CBrCl3 at 248 nm has been studied by translational spectroscopy. The primary dissociation process is shown to produce exclusively CCl3 and Br with an average translational energy of 20 kcal/mol. From the measured anisotropy parameter beta=-0.4+/-0.2, CBrCl3 undergoes a simple C-Br bond scission after ''citation via an E<--A1 transition polarized perpendicular to this bond. A secondary dissociation process from CCl3 by absorbing an additional photon is also observed at high laser powers.
2-DIMENSIONAL ARSENIC PRECIPITATION BY IN DELTA-DOPING DURING LOW-TEMPERATURE MOLECULAR-BEAM EPITAXY GROWTH OF GAAS OR ALGAAS
(1994-05-09)
CHENG, TM
;
CHANG, CY
;
CHIN, A
;
HUANG, MF
;
HUANG, JH
Low temperature (LT) GaAs delta doped with In and Al have been grown by molecular beam epitaxy and annealed at 600-900-degrees-C for 10 min. As precipitates have been observed to form preferentially on In doping planes while depleting on the Al planes. Similar As precipitates in In-doped LT-Al0.25Ga0.75As are 50% more efficient than that of GaAs. The accumulation or depletion of As precipitates in two-dimensional planes in LT materials using isoelectronic impurities show that the phenomena is not directly related to the electronic properties of dopant impurities and therefore has many device applications.
USE OF RADIUS WEIGHTED MEAN TO CLUSTER 2-CLASS DATA
(1994-05-12)
YANG, CY
;
LIN, JC
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
A new method using the radius weighted mean to cluster two-class data is proposed. Experiments show that the clustering results are good, the computation is fast, and the method is easy to implement. The method can be applied to block truncation coding, codebook generation, and decision tree construction.
LONGITUDINAL-OPTICAL-PHONON EFFECTS ON THE EXCITON BINDING-ENERGY IN A SEMICONDUCTOR QUANTUM-WELL
(1994-05-15)
CHUU, DS
;
WON, WL
;
PEI, JH
;
電子物理學系
;
物理研究所
The longitudinal-optical-phonon effect on the exciton binding energies in a quantum well consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1-xAlxAs are studied. By using the Lee-Low-Pine unitary transformation, the Hamiltonian can be separated into two parts which contain the phonon variables and exciton variables, respectively, providing that the virtual phonon-electron and virtual phonon-hole interactions are neglected. A trial wave function, which is able to reproduce the correct exciton binding energy in a quantum well, is obtained by using a perturbative variational technique. The trial wave function consists of a product of the envelope function in the z direction (perpendicular to the layers) for electron and hole and a purely two-dimensional exciton wave function. The dependence of the ground-state binding energy, which includes the effect of electron-phonon interaction on the well width, is investigated. It is found that the correction due to polaron effects on the exciton binding energy is quite significant for a well width of several hundred angstroms and the effects of either surface phonons or bulk phonons on the binding energy of the heavy-hole exciton is always larger than that of the light-hole exciton. Our results are compared with some previous results, and satisfactory agreements are obtained.
OPTOELECTRONIC PHASE-TRACKING AND WAVE-FORM DISPLAY OF MICROWAVE SIGNALS UP TO 8 GHZ USING GAIN-SWITCHED LASER-DIODES
(1994-05-15)
WU, HH
;
WANG, CL
;
LIN, GR
;
CHANG, CS
;
PAN, CL
We present a new, more versatile scheme for maintaining phase coherence between optical probe pulses and microwave signals under test in a laser-diode-based optoelectronic sampling system. This approach takes advantage of the relative ease of changing the repetition rate of the gain-switched laser diode (GSLD). The microwave signal to be sampled is used as the clock signal for phase-locking of a voltage controlled-oscillator (VCO) which drives the GSLD. Phase-tracking and display of waveforms at frequencies up to 8 GHz have been realized. It is also shown that lower phase noise sidebands for the phase-locked VCO can be realized by locking the higher harmonics of the laser pulse to the microwave clock.
INTERACTIONS BETWEEN AL-1 WT-PERCENT SI THIN-FILM AND W-TI BARRIER LAYER
(1994-05-15)
CHANG, PH
;
CHEN, HM
;
LIU, HY
;
BOHLMAN, JG
;
材料科學與工程學系
The interaction of Al-1 wt% Si with a W-Ti barrier layer in the Al/Ti3W7/SiO2/Si system was studied over the temperature range of 400-500-degrees-C for reaction times up to 300 h. The interaction was found to be diffusion-controlled, and to occur in a layer-by-layer fashion. The first reaction product is always Al12W, which forms at the Al/Ti3W7 interface. With excess W in the system, Al will eventually be completely converted to Al12W, and further interactions result in the formation of an Al4W layer at the Al12W/Ti3W7 interface. The amount of Al4W increases at the expense of Al12W. Ti plays a minor role in the interaction and forms a small amount of Al3Ti precipitates in the Al12W matrix. Decomposition of the Ti3W7 pseudoalloy into W and Ti phases is not significant, and is not detected by X-ray diffraction even after annealing at 500-degrees-C for 300 h. The kinetics of the Al12W formation follows a parabolic reaction law with an activation energy of 2.53 eV. The sheet resistance of the film is insensitive to compound formation as long as a continuous Al film exists in the system. The sheet resistance increases dramatically when Al is consumed to the extent that it is no longer a continuous film. The sheet resistance of the Al12W layer is estimated to be 570 mOMEGA square-1.
ANOMALOUS MOBILITY ENHANCEMENT IN HEAVILY CARBON-DOPED GAAS
(1994-05-15)
CHEN, HD
;
FENG, MS
;
LIN, KC
;
CHEN, PA
;
WU, CC
An anomalous mobility enhancement and metallic-type conductivity were observed in heavily carbon-doped GaAs grown by low-pressure metalorganic chemical vapor deposition. The 77 K mobility was slightly lower than that of 300 K for hole concentration between 1 x 10(18) and 4 x 10(18) cm-3. However, the 77 K mobility was enhanced from p > 4 X 10(18) cm-3, and the 300 K mobility slowly decreased with increasing hole concentration that ranged from 7 X 10(18) to 3 X 10(19) cm -3. As a result, the 77 K mobility was around 50%-60% greater than the 300 K mobility due to the metallic-type conductivity.
POLYURETHANES SYNTHESIZED FROM POLYESTER POLYOLS DERIVED FROM PET WASTE .2. THERMAL-PROPERTIES
(1994-05-16)
LEE, SC
;
SZE, YW
;
LIN, CC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Polyurethanes were synthesized from polyester polyols, derived from PET waste. The PET waste was first depolymerized by glycolysis. The glycolysized products were reacted with adipic acid to yield polyester polyols, and the polyester polyols were then reacted with either MDI or TDI to obtain polyurethanes. In this article, the thermal properties of the polyurethanes obtained are discussed in detail. (C) 1994 John Wiley & Sons, Inc.
黃昏裡的廟之黃昏
(1994-05-22)
管管
MECHANICAL-PROPERTIES OF THE RUBBER-TOUGHENED POLYMER BLENDS OF POLYCARBONATE (PC) AND POLY(ETHYLENE-TEREPHTHALATE) (PET)
(1994-05-23)
LIAO, ZL
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
The intrinsically impact-brittle PC / PET blends can be effectively toughened, in terms of lower ductile brittle transition temperature (DBTT) and reduced notch sensitivity, by incorporating butylacrylate core-shell rubber. The rubber particles are distributed exclusively in the PC phase. Varying the PC melt flow rate (MFR) is more important than varying the PET I.V. to vary the low temperature toughness of the blends. PC with MFR = 3 is essential to produce the toughest PC / PET / rubber blend. The presence of rubber slightly relieves the strain rate sensitivity on yield stress increase. Lower MFR PC in the blend results in smaller activation volume and, therefore, higher strain rate sensitivity, because a greater number of chain segments are involved in the cooperative movement during yielding. Two separate modes, localized and mass shear yielding, work simultaneously in the rubber toughening mechanism. The plane-strain localized shear yielding dominates the toughening mechanism at lower temperatures and brittle failure, while the plane-stress mass shear yielding dominates at higher temperatures and ductile failure. The critical precrack plastic zone volume has been used to interpret the observed phenomenon. (C) 1994 John Wiley & Sons, Inc.
FUZZY SYSTEM RELIABILITY-ANALYSIS USING FUZZY NUMBER ARITHMETIC OPERATIONS
(1994-05-25)
CHEN, SM
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
;
Department of Computer Science
This paper presents a new method to analyze fuzzy system reliability using fuzzy number arithmetic operations, where the reliability of each system component is represented by a triangular fuzzy number. Because the proposed method uses simplified fuzzy arithmetic operations of fuzzy numbers rather than the complicated interval arithmetic operations of fuzzy numbers mentioned by Cheng and Mon in Fuzzy Sets and Systems 56 (1993) 29-35 or the complicated extended algebraic operations of fuzzy numbers mentioned by Singer in Fuzzy Sets and Systems 34 (1990) 145-155, its execution is faster than the ones presented by Cheng and Mon, and Singer.
MEASURING EMISSION CROSS-SECTION PROFILE OF ERBIUM-DOPED FIBER WITH LOW-INPUT POWER
(1994-05-26)
CHEN, CY
;
WEN, S
;
CHI, S
;
光電工程學系
;
電信研究中心
A simple and elegant method is proposed to measure the emission cross-section profile of erbium-doped fibre by using a short piece of erbium-doped fibre with input pump or signal power less than 1mW. Relative error is within 1% over the whole spectrum. The theoretical and experimental results are discussed.
GROWTH OF ZNGA2O4 PHOSPHOR BY RADIO-FREQUENCY MAGNETRON SPUTTERING
(1994-06-01)
HSIEH, IJ
;
FENG, MS
;
KUO, KT
;
LIN, P
;
材料科學與工程學系
ZnGa2O4 films have been prepared by radio frequency (RF) magnetron sputtering at various total pressure, RF power, and substrate temperatures. Microstructure and crystallographic orientation were characterized by x-ray diffraction Surface morphologies were observed by scanning electron microscope. In addition, cathodoluminescence (CL) measurement was employed to observe the emission spectra of ZnGa2O4 films. The influences of various deposition parameters on the properties of grown films were studied. The optimum substrate deposition temperature for luminous characteristics was about 500-degrees-C in this investigation. A blue cathodoluminescent emission peaked at 470 nm was observed. Good luminescent properties were observed in the films which exhibit the standard ZnGa2O4 x-ray diffraction pattern.
VARIABLE FRAME RATE SPEECH CODING USING OPTIMAL INTERPOLATION
(1994-06-01)
CHUNG, CJ
;
CHEN, SH
;
電信工程研究所
;
電信研究中心
;
Institute of Communications Engineering
A VFR LPC vocoder using optimal interpolation is presented in this paper. In the encoder, some representative frames of an utterance are selected for transmission. In the decoder, LPC parameters of all untransmitted frames are restored by optimal interpolation. Simulation results show that this coding scheme outperforms the conventional VFR vocoder using linear interpolation. By incorporating contour quantization of gain and pitch information, a low variable-rate LPC vocoder is realized. An informal listening test shows that very high intelligible reconstructed speech was obtained at an average data rate of 300 bps.
EFFECTIVE ACTIVE DAMPING DESIGN FOR SUPPRESSION OF VIBRATION IN FLEXIBLE SYSTEMS VIA DISLOCATED SENSOR ACTUATOR POSITIONING
(1994-06-01)
CHEN, ST
;
FAN, YH
;
LEE, AC
;
交大名義發表
;
機械工程學系
In this paper we present a new controller design method that effectively suppresses vibration in flexible systems. The method allows integrated determination of sensor/actuator locations and feedback gain via minimization of an energy criterion which represents the integrated total energy stored in the system. This energy criterion is characterized by an effective representation of vibration, determined via an efficient solution of the Lyapunov equation and minimized with a quasi-Newton or recursive quadratic programming algorithm. The application of this method to a simple flexible structure confirms the direct relationship between our optimization criterion and effectiveness of vibration suppression.
A MODIFIED CRITERION FOR OPTIMAL LINEAR TIME-INVARIANT OBSERVER PROBLEMS
(1994-06-01)
HWANG, MS
;
LEE, FC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
A modified criterion for designing a linear time-invariant observer is studied. This criterion is a compromise between errors due to stochastic and modal-type deterministic signals. The advantage of this criterion is in its design potentiality to take care of both transient and steady-state behavior. Theoretical properties such as existence, uniqueness, and stability of the optimal solution can be guaranteed for detectable systems under a weak stabilizability condition, which is satisfied by any reasonably defined problem. Moreover, under the criterion, relationships with other existing methods are also discussed.
AN ALGORITHM FOR COMPUTING THE RELIABILITY OF WEIGHTED-K-OUT-OF-N SYSTEMS
(1994-06-01)
WU, JS
;
CHEN, RJ
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
This paper constructs a new k-out-of-n model, viz, a weighted-k-out-of-n system, and proposes an O(n . k) algorithm for computing its reliability.
A RIPPLE FREE SAMPLED-DATA ROBUST SERVOMECHANISM CONTROLLER USING EXPONENTIAL HOLD
(1994-06-01)
WU, YC
;
YEN, NZ
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In a general command tracking and disturbance rejection problem, it is known that a sampled-data controller using zero-order hold may only guarantee the asymptotic tracking at the sampling instances, but cannot smooth out the ripples between the sampling instances. In this paper, a sampled-data robust servomechanism controller using exponential hold is developed for guaranteeing the asymptotic tracking not only at, but also between, the sampling instances In this development, a so called ''internally-reducible'' condition to characterize a class of robust servomechanism controllers is derived first, then the proposed controller is shown to be contained in this class. Generally speaking, a sampled-data structure using exponential hold can provide more design freedoms so that it tends to simplify the construction of a robust servomechanism controller and facilitate the implementation on digital computers. An example for a dc motor control is presented to illustrate the advantages of this approach.
CONSTRAINED OPTIMIZATION OF ACTIVE NOISE-CONTROL SYSTEMS IN ENCLOSURES
(1994-06-01)
YANG, TC
;
TSENG, CH
;
LING, SF
;
機械工程學系
;
Department of Mechanical Engineering
An effective software design tool is proposed for solving active noise control problems associated with constraints in which the complex strength and location of the secondary source of an active noise control system in an enclosed space are simultaneously optimized. The boundary element method is adopted to evaluate the sound field in enclosures. Furthermore, the boundary used could be of pressure, velocity, or impedance; in addition, the primary source may be at an arbitrary position. An optimizer based on sequential quadratic programming is selected for its accuracy, efficiency, and reliability. Bounds for design variables and proper constraints on the sound field and secondary source can be specified as required. The powerfulness of the proposed tool is demonstrated by optimizing an active control system for an enclosure. For a rectangular cavity, the optimal location of the secondary source is confirmed by observed simulations as always forming a dipole with the primary source situated at off-resonance excitations and subsequently approaching a mirror image position of the primary source at resonance excitations. The optimal location of the controller is found to change with varied upper bounds of the strength of the secondary source. These findings show a discrepancy from those reported in previous researches based on an unconstrained formulation. Sensitivity analysis at the optimum is also included to provide information of practical concern for implementing optimized active noise control systems.
FAST CLOSEST CODEWORD SEARCH ALGORITHM FOR VECTOR QUANTIZATION
(1994-06-01)
LEE, CH
;
CHEN, LH
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
One of the most serious problems for vector quantisation is the high computational complexity of searching for the closest codeword in the codebook design and encoding phases. The authors present a fast algorithm to search for the closest codeword. The proposed algorithm uses two significant features of a vector, mean value and variance, to reject many unlikely codewords and saves a great deal of computation time. Since the proposed algorithm rejects those codewords that are impossible to be the closest codeword, this algorithm introduces no extra distortion than conventional full search method. The results obtained confirm the effectiveness of the proposed algorithm.