Browsing by Issue Date, starting with "1991-01-15"

Now showing 1 - 20 of 91366

IMPROVED ALGAAS/GAAS DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES USING 2-DIMENSIONAL SOURCE ELECTRONS
(1991-01-15)
WU, JS
;
LEE, CP
;
CHANG, CY
;
CHANG, KH
;
LIU, DG
We report the enhancement of peak-to-valley current ratios (PVCRs) of double-barrier resonant tunneling structures (DBRTSs) based on the AlGaAs/GaAs material system. The PVCRs as high as 25.4 and 18 have been obtained at 77 K for superlattice and alloy barrier structures with 0.2-mu-m undoped electrodes, respectively. These are the largest PVCRs to date for AlGaAs/GaAs DBRTSs. The large band bending across the undoped electrodes causes size quantization of the accumulation layer, resulting in better resonant tunneling characteristics.
訪管管
(1991-01-15)
管管
訪管管
(1991-01-15)
管管
訪管管
(1991-01-15)
管管
訪管管
(1991-01-15)
管管
自殺美學之研究
(1991-01-29)
管管
CONCATENATED SOLITON FIBER LINK
(1991-01-31)
CHI, S
;
LIN, MC
;
光電工程學系
;
電信研究中心
;
Department of Photonics
An easy and practical 'soliton fibre' link by concatenating uniform fibre sections is proposed. An ultrahigh bit rate loss-limited fibre communication system can be achieved.
IMPROVING PERFORMANCE OF MULTIDESTINATION ARQ SCHEMES UNDER HIGH ERROR RATE CONDITIONS
(1991-01-31)
LEE, TH
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
;
Institute of Communications Engineering
The throughput efficiencies of a class of continuous multi-destination ARQ schemes are evaluated. The operation of the proposed schemes is simpler than that of the schemes studied previously. Numerical results also show that the optimal proposed scheme offers a better throughput performance than the optimal one investigated previously.
TRACKING A MANEUVERING TARGET WITH CORRELATED MEASUREMENT NOISES BY MANEUVER DETECTION METHOD
(1991-01-31)
GUU, JA
;
WEI, CH
;
交大名義發表
;
電控工程研究所
;
National Chiao Tung University
The tracking problem for a manoeuvring target with correlated measurement noises is considered in this letter. A modified manoeuvre detection method with the decorrelation process is employed for tracking the manoeuvring target. From computer simulation, it can be seen that the system performance can be improved significantly if the effect of noise-correlation is considered.
CHARACTERIZATION OF IMPROVED ALGAAS/GAAS RESONANT TUNNELING HETEROSTRUCTURE BIPOLAR-TRANSISTORS
(1991-02-01)
WU, JS
;
CHANG, CY
;
LEE, CP
;
CHANG, KH
;
LIU, DG
We report on the fabrication of AlGaAs/GaAs resonant tunneling heterostructure bipolar transistors (RTHBT's). The devices exhibit a current peak in the transfer characteristics, with peak-to-valley current ratios of 1.7 and 9 at 300 K and 77 K, respectively. The common-emitter small signal current gains at 300 K and 77 K reach 40 and 28, respectively. They are the best results to date for AlGaAs/GaAs resonant tunneling transistors. Because the double barriers are placed in the emitter and far from the emitter-base interface, and the heterostructure emitter suppresses the hole injection from the base to the emitter, the occurrence of the negative differential resistance (NDR) in the device characteristics is governed by the emitter current but not by the base current. The operation mechanism of the NDR behavior in the common-emitter output characteristics is discussed.
HYDROGENATED AMORPHOUS SI/SIC SUPERLATTICE PHOTOTRANSISTORS
(1991-02-01)
WU, MT
;
FANG, YK
;
HONG, JW
;
CHANG, CY
;
電控工程研究所
In order to improve the performance of the a-Si:H phototransistor (PT) and the a-Si:H/a-SiC:H heterojunction phototransistor (HPT), the a-Si:H/a-SiC:H superlattice (SL) was used for the collector regions of these two devices individually. The resulting superlattice phototransistor (SLPT) and superlatice heterojunction phototransistor (SHPT) were successfully fabricated. Due to the avalanche multiplication in the interpolated a-Si:H/a-SiC:H SL region, the optoelectronic characteristics of the SLPT and the SHPT are considerably better than those of PT and HPT. The SLPT has high photocurrent response and an optical gain as high as 287, when V(CE) = 14 V, I(c) = 0.74 mA, and P(in) (incident power) = 5-mu-W emitted from He-Ne laser. This is the highest optical gain obtainable for various amorphous phototransistors yet reported. The typical shapes of the photo I-V curves for SHPT are much like those of the crystalline-Si (c-Si) phototransistor. This indicates the SHPT is suitable for analog circuits in optoelectronic applications. The SHPT has a maximum optical gain of 78, when V(CE) = 30 V, I(c) = 0.208 mA, and P(in) = 5-mu-W. The response time for SHPT and SLPT are repectively 4.1 +/- 0.1-mu-s and 6.2 +/- 0.1-mu-s at a load resistance R(L) = 1 k-omega.
EXACT SOLUTION IN A SCALE INVARIANT MODEL WITH VANISHING COSMOLOGICAL CONSTANT
(1991-02-01)
KAO, WF
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
;
Department of Electrophysics
We analyze a special scale invariant effective theory with vanishing cosmological constant. We show that, in this theory, the spatial-independence of the inflation is implied by the equation of motion incorporated with the Robertson-Walker metric. Furthermore, we find that this theory can be solved exactly for k = O Robertson-Walker spaces. We also find almost exact solution in k not-equal 0 spaces.
FIBEROPTIC GYROSCOPES BASED ON POLARIZATION SCRAMBLING
(1991-02-01)
CHIEN, PY
;
PAN, CL
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
A novel fiber-optic gyroscope with a single-mode diode laser as the light source and two polarization scramblers as time-varying depolarizers is demonstrated. This arrangement reduces the nonreciprocal phase noise induced by the cross coupling between polarization modes in single-mode fibers. The experimental results show that a phase-noise reduction factor of 18 can be achieved.
DETERMINATION OF ROBOT LOCATIONS BY COMMON OBJECT SHAPES
(1991-02-01)
CHEN, SY
;
TSAI, WH
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
A new approach to the determination of robot locations by common object shapes is proposed. Any object that has a polygon-shaped top and a lateral surface perpendicular to the top can be used for robot location in the approach, as long as the top shape is known in advance. Such objects are seen frequently both in indoor and outdoor environments. In addition, the solution provided by the approach can be computed analytically. These merits make the proposed approach more practical for general applications than other approaches using specially designed marks or requiring iterative computation. From a monocular image of an object, image processing and numerical analysis techniques are applied to extract the projection characteristics of the polygon corners on the object top surface, from which the position and the orientation parameters of a camera-mounted robot can be determined. Experimental results with location errors less than 5% prove the feasibility of the proposed approach. Error analysis that is useful for choosing better viewing angles to get more accurate location results is also included.
NONPERTURBATIVE METHODS FOR THE STUDY OF MULTIPHOTON DYNAMICS IN INTENSE PERIODIC AND MULTICOLOR LASER FIELDS
(1991-02-01)
CHU, SI
;
JIANG, TF
;
電子物理學系
;
Department of Electrophysics
We present a brief account of some recently developed generalized Floquet methods (both time-dependent and time-independent) for the nonperturbative treatment of the time-development of wavefunctions or the density matrix operator of quantum systems driven by intense periodic or multi-color (multi-frequency) laser fields. Both the Schrodinger and Liouville equations are considered. We also explore the feasibility of the fast Fourier transformation (FFT) propagation method for the study of Rydberg atom dynamics. We then present a FFT case study of the time propagation of the wavefunction and coarse-grained Wigner density distribution for the problem of microwave-driven multiphoton excitation and ionization of Rydberg hydrogen atoms.
NEGATIVE-PARITY STATES OF N=88 ISOTONES IN THE SDF BOSON PLUS A FERMION PAIR MODEL
(1991-02-01)
CHUU, DS
;
HSIEH, ST
;
YEN, MMK
;
電子物理學系
;
Department of Electrophysics
The energy levels of negative parity states of N = 88 isotones: Yb-158, Er-156 and Dy-154 are studied in terms of the SDF interacting boson approximation (IBA) model with one s- or d-boson being able to break and form a fermion pair. The fermion pair is allowed to occupy the iota-13/2 single particle orbit. It is found that the energy levels of the negative parity bands of these nuclei can be reproduced satisfactorily. The backbends of the moment of inertia can be also reasonably described.
DIFFUSION FLAME STABILIZATION AND EXTINCTION UNDER NATURALLY CONVECTIVE FLOWS
(1991-02-01)
CHEN, CH
;
HOU, WH
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
The stabilization and extinction phenomena for a two-dimensional diffusion flame around the leading edge of an upright solid fuel under naturally convective environments are studied theoretically. The governing system consists of two-dimensional Navier-Stokes' momentum (including a body force term), energy, species, and continuity equations, together with a finite-rate chemical kinetics described by a second-order Arrhenius-type rate equation. The burning rate of fuel is expressed by an Arrhenius-type pyrolysis law. The nondimensional model is solved numerically. Two parametric studies, based on changing gravity level and ambient oxygen index, respectively, are investigated. Under the variation of gravity, both Damkohler number and preexponential factor for fuel pyrolysis are changed. Two quenching limits are identified separately at a very low and a high gravity level. The envelope flame exists when gravity is less than 1.95 g. As gravity is increased, there appears a transition to open-tip flame, stabilized on the side of fuel plate. A similar trend is found when ambient oxygen index is decreased from the higher value of the lower one but only with a quenching limit that is blowoff. The detailed flame structures for envelope and open-tip flames are illustrated graphically.
FOLD PRINCIPAL AXIS - A NEW TOOL FOR DEFINING THE ORIENTATIONS OF ROTATIONALLY SYMMETRICAL SHAPES
(1991-02-01)
CHOU, SL
;
LIN, JC
;
TSAI, WH
;
資訊工程學系
;
Department of Computer Science
A new type of principal axis, namely, fold principal axis, is introduced in this paper, which can be used to define the orientations of rotationally symmetric shapes. A given shape is first transformed into a new shape on which the well-defined traditional principal axis is detected. The traditional principal axis is then transformed back to obtain the proposed fold principal axes of the given shape. The properties of such axes, including the uniqueness, existence, and invariance under rotation, translation, and scaling, are investigated. Some illustrative examples are also given.
SYNTHESIS AND MESOMORPHIC BEHAVIOR OF POLY(METHYLSILOXANE)S CONTAINING TRANS-CYCLOHEXANE-BASED MESOGENIC SIDE GROUPS
(1991-02-01)
HSU, CS
;
LU, YH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
The synthesis and characterization of poly(methylsiloxane)s containing either trans-4-methylcyclohexyl 4-alkenyloxybenzoate or trans-4-methylcyclohexyl 4'-alkenyloxybiphenyl-4-carboxylate mesogenic side groups are presented. All polymers except two which contain either trans-4-methylcyclohexyl 4-allyloxybenzoate or transmethylcyclohexyl 4-(5-hexene-1-yloxy)benzoate side groups, display liquid crystalline phases. The dependence of phase trasition temperature on the spacer length and the mesogenic core length as well as the thermal stalility of the prepared liquid crystalline polymers (LCPs) are described.
ON THE NUMBER OF POSITIVE SOLUTIONS FOR NONLINEAR ELLIPTIC-EQUATIONS WHEN A PARAMETER IS LARGE
(1991-02-01)
LIN, SS
;
交大名義發表
;
應用數學系
;
National Chiao Tung University
;
Department of Applied Mathematics