Browsing by Issue Date, starting with "1992-10-03"

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FATIGUE RELIABILITY OF STRUCTURES BASED ON PROBABILITY AND POSSIBILITY MEASURES
(1992-10-03)
LIU, TS
;
HUANG, GR
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
The randomness of fatigue life prediction has been commonly recognized, but recently researchers have begun to recognize the fuzziness of fatigue failure descriptions resulting from the lack of distinct definitions and precise information. In this paper, both probability- and possibility-based reliabilities of components subjected to fatigue loading are investigated. In the probability-based reliability, the material properties and the amplitude of a loading history are assumed to be random. In the possibility-based method, the fuzzy linear regression method is employed to account for the fuzziness. This work employs S-functions to define fuzzy limit state functions. Failure probabilities are calculated in terms of probability distributions of fuzzy damage and fuzzy limit state functions. Both probability- and possibility-based reliabilities of a portal frame are examined. Accordingly, the reliability of systems in the presence of fuzziness is calculated and compared to the results obtained from the probability-based method.
EFFECT OF SIDE-CHAIN LENGTH ON RECTIFICATION AND PHOTOVOLTAIC CHARACTERISTICS OF POLY(3-ALKYLTHIOPHENE) SCHOTTKY BARRIERS
(1992-10-15)
FANG, Y
;
CHEN, SA
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CHU, ML
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光電工程學系
;
Department of Photonics
Schottky diodes of aluminium/poly(3-alkylthiophene) (P3AT)/indium-tin oxide (ITO) with large area (0.15-0.5 cm2) are prepared using the proposed new casting technique. The P3ATs investigated involve poly(3-butylthiophene) (P3BT), poly(3-octylthiophene) (P3OT) and poly(3-dodecylthiophene) (P3DDT), which are prepared using the chemical method. The diodes, in which P3AT behaves as a p-type semiconductor, exhibit a moderate rectifying behaviour and low leakage current. Photovoltaic measurements show a power conversion efficiency of about 10(-2)-10(-3)% at a light intensity of 0.5-5 mW/cm2, which decreases with increasing light intensity. The longer alkyl side-chain length of P3ATs can cause a lower rectifying effect, barrier height, depletion region width and photovoltaic conversion efficiency.
盜印四版
(1992-10-15)
管管
盜印四版
(1992-10-15)
管管
EFFECT OF DYE CONCENTRATION ON PICOSECOND AND FEMTOSECOND CW PASSIVELY MODE-LOCKED TI-SAPPHIRE DDI LASERS
(1992-10-15)
PAN, CL
;
HWANG, CD
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KUO, JC
;
SHIEH, JM
;
WU, KH
The role of the saturable absorber dye DDI in the cw passively mode-locked Ti:sapphire/DDI laser both with and without compensation prisms is investigated. This laser self-starts when the concentration of the dye is greater than almost-equal-to 2 X 10(-4) M for both picosecond and femtosecond pulses. With the prism pair, the laser generates Gaussian pulses 150 fs in duration. The corresponding spectrum is sech2 in shape with a FWHM of 8 nm. These parameters are independent of the DDI concentration. Without the prism pair, the laser generates picosecond pulses with the FWHM decreasing from 8 to 3 ps as the dye concentration is increased from 2.5 x 10(-4) to 1 X 10(-3) M. Concurrently the pulse shape changes from a Lorentzian to a nearly symmetric two-sided exponential shape. The picosecond spectra for different dye concentrations are also presented.
盜印四版
(1992-10-15)
管管
盜印四版
(1992-10-15)
管管
CHEMORHEOLOGY ON SIMULTANEOUS IPN FORMATION OF EPOXY-RESIN AND UNSATURATED POLYESTER
(1992-10-15)
LIN, MS
;
CHANG, RJ
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交大名義發表
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應用化學系
;
National Chiao Tung University
Study of the simultaneous interpenetrating polymer network (IPN) between diglycidyl ether of bisphenol-A (DGEBA) and unsaturated polyester (UP) was carried out at ambient temperature. Fourier transform infrared (FTIR) spectroscopy was employed to investigate the intermolecular H-bonding and functional group changes. Viscosity changes due to H-bonding and crosslinking were examined with a Brookfield viscometer. Gelation time was measured by a Techne gelation timer. Complexation between Co (II) (the promoter for UP cure) and diamine (the curing agent for DGEBA) was detected with UV-visible spectrometer. Experimental evidence revealed that intermolecular interactions were observed in systems such as DGEBA/UP, DGEBA/diamine, UP/diamine, Co (II) /diamine, DGEBA/uncured UP, and UP/uncured DGEBA. All such interactions had measurable effects on the curing behaviors for both networks, as were indicated by the viscosity changes and gelation time. The IPNs thus obtained were further characterized with rheometric dynamic spectroscopy (RDS) and differential scaning calorimetry (DSC). Partial compatibility between UP and DGEBA networks was evidenced from a main damping peak with a shoulder near glass transition temperature (T(g)) for lower UP content; while at higher UP content, only a main damping peak near T(g) was observed. DSC revealed a broad glass transition for all IPNs. The resultant IPN materials were all transparent.
TWINNED STRUCTURE OF M(6)C CARBIDE IN AN FE-MN-AL-MO-C ALLOY
(1992-11-01)
PENG, SW
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CHOU, CP
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
OFF-LINE RECOGNITION OF HANDWRITTEN CHINESE CHARACTERS BY ONLINE MODEL-GUIDED MATCHING
(1992-11-01)
HSIEH, CC
;
LEE, HJ
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資訊工程學系
;
Department of Computer Science
A model-guided structural matching method for recognizing handwritten off-line Chinese characters is presented. According to the stroke writing sequence, each character is described by an on-line model, which is a one-dimensional (1D) string consisting of a stroke sequence interleaved with relationships between two consecutive strokes. After an unknown input is thinned and line approximated, all possible strokes are extracted. A tree is created to represent all possible combinations of the extracted strokes which have the same stroke sequence as the one defined in the model. In the recognition process, we match the strokes with those defined in the on-line model. The matching process is formulated as a tree searching algorithm guided by the relationships in the model. The modelled character is taken to be a candidate if there is a feasible path which satisfies the relationships defined in the on-line model and the number of missing strokes in the input is less than a given threshold. The input is recognized as the character with the greatest number of matched strokes among all candidates. Experimental results on 300 frequently used characters in a database called CCL/HCCR1, which contains 5401 Chinese characters and about 250 variations for each one, show that the recognition rate is over 90%.
ANOMALOUS PR ORDERING IN THE NEW TLBA2PRCU2O7-DELTA COMPOUND
(1992-11-01)
LAI, CC
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CHIOU, BS
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CHEN, YY
;
HO, JC
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KU, HC
Magnetic measurements on the new tetragonal Tl(1212) compound TlBa2PrCu2O7-delta (a = 3.910 angstrom and c = 12.53 angstrom) reveal an anomalously high antiferromagnetic Neel temperature T(N) congruent-to 8 K. This transition temperature is higher than T(N) = 2.2 K for isostructural TlBa2GdCu2O7-delta. Corroborative evidence comes from calorimetric studies, in which a magnetic entropy was obtained DELTAS congruent-to 0.5 Rln 2 between 2 and 10 K, as well as a sizeable linear term in specific heat comparable to those found in heavy-fermion systems. Through structural consideration, these observations can not only be correlated to the almost identical but still puzzling features of PrBa2Cu3O7-y, but also remove some ambiguity in the interpretation of earlier results.
BIREFRINGENCE-INDUCED SPECTRAL FEATURES IN CONTINUOUS-WAVE AND PASSIVELY MODE-LOCKED TI-SAPPHIRE LASERS
(1992-11-01)
PAN, CL
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HWANG, CD
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KUO, JC
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SHIEH, JM
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WU, KH
We show that the transient spectrum of a continuous-wave Ti:sapphire laser during the initial stage of the buildup, which exhibits multiple clusters (of longitudinal modes), is due to the spectral windowing effect of the Brewster-angle-cut Ti:sapphire crystal, which acts as a birefringent filter in the laser cavity. This effect is also responsible for certain spectral features of a passively mode-locked Ti:sapphire/DDI laser.
ALUMINA-CHROMIUM CARBIDE COMPOSITE THROUGH AN INTERNAL SYNTHESIS METHODS
(1992-11-01)
CHUANG, SC
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KUO, CT
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LEE, CS
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HO, CT
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LI, AK
In situ formation of chromium carbide parlicles, through a solid state reaction between Cr2O3 and SiC, for strengthening Al2O3 has been studied. Three kinds of chromium compound, Cr3Si, Cr3C2 and Cr7C3 and mullite were formed in the alumina matrix. The reaction behaviour during hot pressing depends on heating parameters such as temperature and atmosphere. In a vacuum environment, the Cr3Si particles formed first and was the dominant dispersed phase below 1550-degrees-C, while the Cr7C3 phase was only dominant above 1600-degrees-C. The Cr3C2 phase emerged briefly then diminished at temperature greater-than-or-equal-to 1500-degrees-C. In an argon environment, however, the Cr3C2 phase was the main product component at temperatures ranging from 1450-1550-degrees-C. The mullite phase formed concurrently through the diffusion Of SiO2 phase into the A12O3 matrix, which is a by-product from the reaction between Cr2O3 and SiC. Incorporating chromium carbide or silicide particles into the Al2O3 matrix induces a strengthening effect. However, only when the content of dispersed phases is low and is mainly of Cr3C2 particles, is the strengthening effect significant. For instance, the composite, containing 5 vol % chromium carbide and hot-pressed at 1500-degrees-C in argon, gives a flexural strength and fracture toughness up to 600 M Pa and 6.1 MPa m1/2, respectively.
ACTIVE CONTROL OF AN ASYMMETRICAL RIGID ROTOR SUPPORTED BY MAGNETIC BEARINGS
(1992-11-01)
FAN, YH
;
CHEN, ST
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LEE, AC
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交大名義發表
;
機械工程學系
Vibration control of a horizontal rotor with an asymmetrical moment of inertia is investigated. A linear optimal control system is developed to stabilize and control the rotor system by using the mathematical model of a rotor system expressed in the rotating coordinates. An approximated dynamical equation of a long rotor system is derived and used to obtain the compensator in analytical form (which saves much computational effort in control design), and is particularly useful in hardware implementation. Simulation results show the efficiency of the proposed strategy. The influences of weighting matrices and the effects of the asymmetrical moment of inertia on system performance for different controllers are also assessed.
SYNCHRONIZATION OF ELECTRICAL AND OPTICAL SIGNALS BY USING AN OPTOELECTRONIC TIMING DISCRIMINATOR IN A PHASE-LOCK LOOP
(1992-11-01)
PAN, CL
;
WU, HH
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
A GaAs:Cr photoconductive switch is employed as an optoelectronic timing discriminator or phase detector in the phase-lock loop. Timing information is derived from the temporally sloped output of the switch, which is the cross-correlation function of the electrical signal and the photoconductive response induced by the laser pulse train. Optoelectronic synchronization of microwave signals up to 12 GHz in a laser-diode-based system has been demonstrated. The long-term relative timing jitter between the electrical and optical signals is estimated from the error signal in the PLL to be less than 500 fs. This technique can also be used to synchronize lasers.
TRANSIENT ANALYSIS OF AN ASYMMETRIC ROTOR-BEARING SYSTEM DURING ACCELERATION
(1992-11-01)
LEE, AC
;
KANG, Y
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TSAI, KL
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HSIAO, KM
;
交大名義發表
This paper deals with the transient vibration of asymmetric rotor systems during acceleration passing through several critical speeds at which synchronous or super-harmonic resonance occurs. The dynamic equations of the rotor-bearing system are formulated by the finite element model and the resulting dynamic equations are time-varying due to the effects of acceleration and asymmetry. In the formulation, a Timoshenko beam element is employed to simulate the rotating shaft and Eulerian angles are used to describe the orientations of the shaft element and disk. The numerical integration scheme for transient analysis is generated from the finite element model. Numerical examples are presented to illustrate (1) the effects of acceleration on peak amplitude and speed at which the peak occurs as the system passes through critical speeds, (2) the optimal acceleration process, which can be obtained by minimizing the peak response and the period of acceleration, (3) the speed regions where the transient instability exists.
QUANTUM-WELL GEOMETRICAL EFFECTS ON 2-DIMENSIONAL ELECTRON-MOBILITY
(1992-11-01)
WANG, TH
;
HSIEH, TH
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CHEN, YT
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交大名義發表
;
電控工程研究所
A Monte Carlo analysis to study the quantization effects on the low-field electron mobility in various AlGaAs/GaAs/AlGaAs quantum well structures has been performed. The influence of the electron envelop wave-function and the subband structure on the two-dimensional electron scattering rates was evaluated. Our results showed that a maximum two-dimensional electron mobility can be achieved in a quantum well structure where the energy difference between the first subband and the second subband is about two times the polar optical phonon energy.
MODELING HOT-ELECTRON GATE CURRENT IN SI MOSFETS USING A COUPLED DRIFT-DIFFUSION AND MONTE-CARLO METHOD
(1992-11-01)
HUANG, CM
;
WANG, TH
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CHEN, CN
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CHANG, MC
;
FU, J
A coupled two-dimensional drift-diffusion and Monte Carlo analysis is developed to study the hot-electron-caused gate leakage current in Si n-MOSFET's. The electron energy distribution in a device is evaluated directly from a Monte Carlo model at low and intermediate electron energies. In the portion of high electron energy where the distribution function cannot be resolved by the Monte Carlo method due to limited computational resources, an extrapolation technique is adopted with an assumption of a Boltzmann tail distribution. This assumption is based on the simulation result that although the distribution function at a high electric field shows a markedly non-Maxwellian feature globally, it has approximately an exponential decay in an energy region much above average electron energy. A particular averaging method is employed to extract the effective electron temperature in the extrapolation. Our result shows that the electron temperature obtained in this approach is about three times lower than that derived from average electron energy by means of [E] = 3/2 kT(e) in the high-field domain of a device. Channel hot electron injection into a gate via quantum tunneling and thermionic emission is simulated. Electron scattering in gate oxide is also taken into account. The calculated values of gate current are in good agreement with experimental results. In the simulation, the most serious hot electron injection occurs about 200-300 angstrom behind the peak of average electron energy due to a delayed heating effect.
THROUGHPUT PERFORMANCE OF A CLASS OF CONTINUOUS ARQ STRATEGIES FOR BURST-ERROR CHANNELS
(1992-11-01)
LEE, TH
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電信工程研究所
;
電信研究中心
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Institute of Communications Engineering
;
Center for Telecommunications Research
This paper studies the throughput performance of a class of continuous automatic repeat request (ARQ) strategies for burst-error channels modeled by two-state Markov chains. The operation of the investigated ARQ strategies can be described as follows. A chunk of m or fewer copies of each data block is transmitted contiguously to the receiver. Whenever a repeat request is received, the transmitter goes back to and retransmits that data block and all successive ones. However, the maximal number of copies transmitted is equal to n in each retransmission. It is proved that the optimal repetition sequence which maximizes the throughput efficiency among a more general set of ARQ schemes falls in the class of investigated strategies. Numerical results reveal that throughput efficiency is very likely to be maximized at m = n.
A NEW APPROACH TO INEXACT REASONING FOR RULE-BASED SYSTEMS
(1992-11-01)
CHEN, SM
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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 algorithm for dealing with inexact reasoning problems, where the certainty factors of the rules and the truth values of the conditions appearing in the rules are represented by linguistic terms. The algorithm performs inexact reasoning via repeatedly transforming an augmented linguistic truth state vector T by an augmented linguistic rule matrix F. Given the linguistic truth values of some conditions, the algorithm can perform inexact reasoning to evaluate the linguistic truth values of other conditions automatically.