Browsing by Issue Date, starting with "1999-07-15"

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Use of two-step split-operator approach for 2D shallow water flow computation
(1999-07-15)
Lien, HC
;
Hsieh, TY
;
Yang, JC
;
土木工程學系
;
Department of Civil Engineering
The objective of this paper is to present a methodology of using a two-step split-operator approach for solving the shallow water flow equations in terms of an orthogonal curvilinear co-ordinate system. This approach is in fact one kind of the so-called fractional step method that has been popularly used for computations of dynamic flow. By following that the momentum equations are decomposed into two portions, the computation procedure involves two steps. The first step (dispersion step) is to compute the provisional velocity in the momentum equation without the pressure gradient. The second step (propagation step) is to correct the provisional velocity by considering a divergence-free velocity field, including the effect of the pressure gradient. This newly proposed method, other than the conventional split-operator methods, such as the projection method, considers the effects of pressure gradient and bed friction in the second step. The advantage of this treatment is that it increases flexibility, efficiency and applicability of numerical simulation for various hydraulic problems. Four cases, including back-water flow, reverse flow, circular basin flow and unsteady flow, have been demonstrated to show the accuracy and practical application of the method. Copyright (C) 1999 John Wiley & Sons, Ltd.
Characterization of Si1-x-yGexCy films grown by C+ implantation and subsequent pulsed laser annealing
(1999-07-15)
Luo, JS
;
Lin, WT
;
Chang, CY
;
Shih, PS
;
Pan, FM
Epitaxial Si1-x-yGexCy films have been grown by C+ implantation into Si0.76Ge0.24 films with a dose of 1.0 x 10(16)/cm(2) and subsequent pulsed KrF laser annealing at an energy density of 0.3-1.6 J/cm(2). Upon laser annealing Ce segregation to the film surface and diffusion to the underlying Si appeared at energy densities above 0.8 J/cm(2) and 1.4 J/cm(2), respectively while the depth profiles of C remained nearly unchanged as in the as-implanted Si1-x-yGeyCy film. Concurrently, no SiC and twin were observed. The amount of C incorporated into substitutional sites initially increased with the energy density in the range of 0.3-1.0 J/cm(2), and then saturated at an energy density of 1.0-1.6 J/cm(2). For the Si1-x-yGexCy films grown at 1.0 J/cm(2) for 5 and 20 pulses SiC was formed with its amount increasing with the pulse number because of C segregation to the film surface and the original amorphous/crystal interface where the EOR defects were present. For the Si1-x-yGexCy films grown at energy densities below 1.0 J/cm(2) the reduction of tensile stress mainly resulted from the effect of substitutional carbon incorporation. (C) 1999 Elsevier Science S.A. All rights reserved.
Electrical properties of multiple high-dose Si implantation in p-GaN
(1999-07-15)
Lai, WC
;
Yokoyama, M
;
Tsai, CC
;
Chang, CS
;
Guo, JD
This work performs Si ion implantation the electrical conductive type of the p-GaN film from p-type to n-type. Multiple implantation method is also used to form a uniform Si implanted region in the p-type GaN epitaxial layer. Implant energies for the multiple implantation are 40, 100, and 200 KeV. The implant dose is 5 x 10(15) cm(-2) for each implant energy. After implantation, the samples are annealed in a N-2 ambient for different annealing temperatures and annealing times. The activation efficiency reaches as high as 20% when annealing the sample at 1000 degrees C. The carrier activation energy is about 720 meV. The low activation energy indicates that the hopping process mechanism is the dominant mechanism for the activation of the Si implantation in p-GaN. Moreover, the rectifying I-V characteristic of the p-n GaN diode is also examined.
Coherent quantum transport in narrow constrictions in the presence of a finite-range longitudinally polarized time-dependent field
(1999-07-15)
Tang, CS
;
Chu, CS
;
電子物理學系
;
Department of Electrophysics
We have studied the quantum transport in a narrow constriction acted upon by a finite-range longitudinally polarized time-dependent electric field. The electric field induces coherent inelastic scatterings that involve both intrasubband and intersideband transitions. Subsequently, the dc conductance G is found to exhibit suppressed features. These features are recognized as the quasi-bound-state (QBS) features that are associated with electrons making transitions to the vicinity of a subband bottom, of which the density of states is singular. Having valleylike instead of diplike structures, these QBS features are different from the G characteristics for constrictions acted upon by a finite-range time-modulated potential. In addition, the subband bottoms in the time-dependent electric-field region are shifted upward by an energy proportional to the square of the electric field and inversely proportional to the square of the frequency. This effective potential barrier is originated from the square of the vector potential, and it leads to the interesting field-sensitive QBS features. An experimental setup is proposed for the observation of these features. [S0163-1829(99)01827-5].
Characteristics of transmission of electrons in a bent quantum waveguide with inhomogeneous magnetic fields
(1999-07-15)
Gu, BY
;
Lin, YK
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
We present numerical studies of the transmission properties in an L-shaped quantum waveguide (LQW) subject to an inhomogeneous magnetic field perpendicular to the LQW plane. The magnetic field remains zero at the corner region, thus, a magnetically defined cavity is formed in this LQW. We find that transmission characteristics of electrons in the LQW depend strongly on geometric parameters and magnetic configurations. Sharp peaks with unity amplitude and deep dips are observed in transmission as a function of the Fermi energy of the incident electron at some high fields. The mode-mode coupling between the wires and the cavity and multiple reflection of electrons in the cavity lead to the appearance of these structures in transmission spectrum. We also study the variation of transmission with magnetic field for different magnetic confinement configurations when fixing incident electron energy. In the magnetic depletion process of the propagating modes in wires, the transmission exhibits various patterns, such as stepped drop, wide valley, deep dips, large oscillations, or without any structure, sensitively dependent on incident electron energy and magnetic confinement configurations. It is expected that one can flexibly modify transmission spectrum of the LQW by applying an inhomogeneous magnetic field to match practical requirements. (C) 1999 American Institute of Physics. [S0021-8979(99)05714-X].
給孩子讀詩,他就活得如詩
(1999-07-17)
管管
High purity nano-crystalline carbon nitride films prepared at ambient temperature by ion beam sputtering
(1999-07-18)
Lu, TR
;
Kuo, CT
;
Yang, JR
;
Chen, LC
;
Chen, KH
High purity nano-crystalline carbon nitride films have been successfully deposited by ion beam sputtering. A novel biomolecular C-N compound, 6-aminopurine, of which the characteristic features include covalent C-N bonding, high N/C ratio and a six-membered ring structure similar to that in the hypothetical C3N4 crystal, has been employed as the target material. The films can be deposited onto a variety of substrate, such as copper, silver, stainless steel, nickel and silicon wafer at ambient temperature. SAM examination indicates a high nitrogen-to-carbon ratio at about 0.51. XPS, IR and Raman studies reveal that the chemical bonding structures consist mainly of sp(3)-hybridized carbon as well as sp(2)-hybridized nitrogen and carbon. Both TEM and SAM mapping investigations indicate that the film contains a very dense and homogenous distribution of nanocrystalline grains. However, the structures of these crystals are yet to be determined since their TEM diffraction patterns only matched partially with the calculated pattern for beta-C3N4. (C) 1999 Elsevier Science S.A. All rights reserved.
Mixing macro and micro flowtime estimation model: wafer fab example
(1999-07-20)
Tseng, TY
;
Ho, TF
;
Li, RK
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
Accurately predicting the order flowtime for a wafer fab is a critical task. Previous investigations involving flowtime estimation of the regression approach have extensively applied the macro flowtime estimation concept. The 'macro' flowtime estimation concept constructs only one aggregate model to estimate the flowtime as a whole. In contrast, the 'micro' flowtime estimation approach constructs an individual regression model for each stage of operation to estimate its individual flowtime. The cumulative order estimated flowtime is then the sum of the individual estimated operation flowtime. Each approach has its own merits and limitations. Therefore, in this study we examine the feasibility of mixing the macro and micro flowtime estimation models. Comparing the proposed model with a variety of macro and micro models reveals that the mixed macro and micro flowtime estimation model can achieve a balance between flowtime estimation error and model complexity.
Ultrashort pulse generation from mode-locked erbium-doped fibre ring lasers
(1999-07-20)
Chang, CW
;
Chi, S
;
光電工程學系
;
Department of Photonics
A theoretical model of a passively mode-locked erbium-doped fibre ring laser using nonlinear polarization rotation is developed. Numerical simulations are used to study mode-locking and pulse dynamics in a typical ring configuration. The simulations show that stable operation can exist in both isotropic and birefringent fibres, and stable pulses with a FWHM as short as 45 fs can be generated. It is found that there is an optimal regime of ellipticity such that the stable mode-locking can be obtained. In addition, the condition for high birefringence approximation is also found.
Scanning leaky-wave antenna integrated with self-oscillating doubler
(1999-07-20)
Wang, CJ
;
Jou, CF
;
Wu, JJ
;
傳播研究所
;
Institute of Communication Studies
A new method which can enhance the scanning angle and elevate the operating frequency for active scanning leaky-wave antennas is proposed in this paper. We know that the characteristics and performance of scanning leaky-wave antennas are strongly dependent on the variation of the operating frequency within the leaky-mode region. The self-oscillating doubler without external oscillator sources provides double-frequency variation at the second-harmonic frequency instead of one-frequency variation at the fundamental frequency. Therefore, the antenna scanning range can be enhanced and the operating frequency can be elevated. The measured scanning angle of this antenna is 13 degrees which agrees well with the predicted 13.7 degrees and the data show that the frequency-scanning ability of the leaky-wave antenna using a self-oscillating doubler increases as predicted. This self-oscillating doubler design is very simple, and it not only can improve the scanning capability of the active leaky-wave antenna, but it is also very suitable for millimeter-wave active antenna design. (C) 1999 John Wiley & Sons, Inc.
Characteristics of SiC-based thin-film LED fabricated using plasma-enhanced CVD system with stainless steel mesh
(1999-07-22)
Chen, YA
;
Hsu, ML
;
Laih, LH
;
Hong, JW
;
Chang, CY
A conventional plasma-enhanced chemical vapour deposition (PECVD) system with a stainless steel mesh attached to a cathode was used to fabricate an SiC-based thin-mm light-emitting diode (TFLED) at a low temperature (similar to 180 degrees C). The obtained TFLED had a brightness (B) of 1060cd/m(2) at an injection current density (J) of 600mA/cm(2) and a threshold voltage (V-th) of 12.6V, which were much better than those of 330cd/m(2) and 18.5V for an amorphous SiC-based TFLED fabricated by the same PECVD system without a stainless steel mesh.
Anisotropic peak effect due to structural phase transition in the vortex lattice
(1999-07-26)
Rosenstein, B
;
Knigavko, A
;
電子物理學系
;
Department of Electrophysics
It is shown that the recently observed new peak effect in YBCO could be explained by the softening of the vortex lattice due to a structural phase transition in the vortex lattice. At this transition square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with the softening of shear modes (elastic modulus c(66) vanishes) at melting, in this case the relevant mode is "squash" mode(c(11) + c(22) - 2c(12) vanishes).
Circular chromatic numbers of Mycielski's graphs
(1999-07-28)
Chang, GJ
;
Huang, LL
;
Zhu, XD
;
應用數學系
;
Department of Applied Mathematics
In a search for triangle-free graphs with arbitrarily large chromatic numbers, Mycielski developed a graph transformation that transforms a graph G into a new graph mu(G), we now call the Mycielskian of G, which has the same clique number as G and whose chromatic number equals chi(G) + 1. Let mu(n)(G) = mu(mu(n-1)(G)) for n greater than or equal to 2. This paper investigates the circular chromatic numbers of Mycielski's graphs. In particular, the following results are proved in this paper: (1) for any graph G of chromatic number n, chi(c)(mu(n-1)(G)) less than or equal to chi(mu(n-1)(G)) - 1/2; (2) if a graph G satisfies chi(c)(G) less than or equal to chi(G) - 1/d with d = 2 or 3, then chi(c)(mu(2)(G)) less than or equal to chi(mu(2)(G)) - 1/d; (3) for any graph G of chromatic number 3, chi(c)(mu(G)) = chi(mu(G)) = 4; (4) chi(c)(mu(K-n)) = chi(mu(K-n)) = n + 1 for n greater than or equal to 3 and chi(c)(mu(2)(K-n)) = chi(mu(2)(K-n)) = n + 2 for n greater than or equal to 4. (C) 1999 Elsevier Science B.V. All rights reserved.
把孩子的笑聲加點兒蜜醃起來
(1999-07-31)
管管
Quantum transport in a double-barrier structure in the presence of a finite-range time-modulated potential
(1999-08-01)
Chu, CS
;
Liang, HC
;
電子物理學系
;
Department of Electrophysics
We have studied the quantum transport phenomena in a double-barrier structure acted upon by a finite-range time-modulated potential. Inter-side-band mhw transitions are made possible by the finiteness in the range of the oscillating field. For the case when the barrier width is small, such that the resonance state in between the barriers is too broadened, the de conductance G exhibits peaks or dip structures when the chemical potential mu is at mhw above the band bottom. For the case when the barrier width is large, such that the resonance state in between the barriers is well defined, the above feature is masked by resonant tunneling processes when mu is at energies mhw away from the resonant energy E-b. In both cases, the dips or peaks in G are due to the temporary trapping of the transmitting electrons by the quasi-bound states. Furthermore, for the latter case, we also obtain the quenching of the resonant transmission found by Wagner, but with a small quantitative modification. Our calculation is nonperturbative which is valid for arbitrary potential strength and frequency. The form of the time-modulated potential is expected to be realized in a gate-induced potential configuration.
Temperature control with a neural fuzzy inference network
(1999-08-01)
Lin, CT
;
Juang, CF
;
Li, CP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Although multilayered backpropagation neural networks (BPNN's) have demonstrated high potential in the nonconventional branch of adaptive control, their long training time usually discourages their applications in industry. Moreover, when they are trained on line to adapt to plant variations, the over-tuned phenomenon usually occurs. To overcome the weakness of the BPNN, in this paper we propose a neural fuzzy inference network (NFIN) suitable for adaptive control of practical plant systems in general and for adaptive temperature control of a water bath system in particular. The NFIN is inherently a modified Takagi-Sugeno-Kang (TSK)-type fuzzy rule-based model possessing a neural network's learning ability. In contrast to the general adaptive neural fuzzy networks, where the rules should be decided in advance before parameter learning is performed, there are no rules initially in the NFIN. The rules in the NFIN are created and adapted as on-line learning proceeds via simultaneous structure and parameter identification. The NFIN has been applied to a practical water bath temperature-control system. As compared to the BPNN under the same training procedure, the simulated results show that not only can the NFIN greatly reduce the training time and avoid the over-tuned phenomenon, but the NFIN also has perfect regulation ability. The performance of the NFIN is also compared to that of the traditional PID controller and; fuzzy logic controller (FLC) on the water bath temperature-control system. The three control schemes are compared through experimental studies with respect to set-points regulation, ramp-points tracking, and the influence of unknown impulse noise and large parameter variation in the temperature-control system. It is found that the proposed NFIN control scheme has the best control performance of the three control schemes.
Determination of stability constants of metal complexes by capillary electrophoresis
(1999-08-01)
Chang, CE
;
Chen, CY
;
Chen, HY
;
生物科技學系
;
Department of Biological Science and Technology
The stability constants of several divalent first row transition and trivalent lanthanide metal complexes were determined by capillary electrophoresis (CE) methods. Four different approaches, i.e. direct formation, ligand exchange, metal exchange and metal-ligand double exchange were developed. To verify if these CE methods are indeed applicable, the stability constant of CuHEDTA was re-determined to be 17.47 +/- 0.20 (consistent with the published 17.50) using the CuEDTA and ZnHEDTA metal-ligand double exchange approach. The stability constants of lanthanide (Ce3+ and Eu3+) and transition metal (Ni2+ and Zn2+) complexes of an aminopolycarboxylate ligand, DO2A (1,7-dicarboxymethyl-1,4,7, 10-tetraazacyclododecane) were measured under the direct complex formation condition. The stability constant of the NiDO2A complex was determined by the ligand exchange method using 1,4,8,11-tetraazaundecane (2,3,2-tet) as the competing ligand. The stability constant of CuDO2A complex was determined by the metal exchange method using Zn2+ ion as the competing metal ion, and complex formation competitions of Ni2+ and Cu2+ between DO2A and 2,3,2-tet were studied by the metal-ligand double exchange method. Effects of experimental conditions and the advantages and limitations of these CE methods are discussed.
【陽明人在四方】洪老師-我的另一半
(國立陽明大學牙醫校友會, 1999-08)
陳彥廷
【陽明人在四方】英倫紀行
(國立陽明大學牙醫校友會, 1999-08)
孔憲蘭
New distributed arithmetic algorithm and its application to IDCT
(1999-08-01)
Chang, TS
;
Chen, C
;
Jen, CW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Distributed arithmetic (DA) has been widely used to implement inner product computations with a fixed input. Conventional ROM-based DA suffers from large ROM requirements. A new DA algorithm is proposed that expands the fixed input instead of the variable input into bit level as in ROM-based DA. Thus the new DA algorithm can take advantage of shared partial sum-of-products and sparse nonzero bits in the fixed input to reduce the number of computations. Unlike ROM-based DA that stores the precomputed results the new DA algorithm uses a predefined structure to compute results. When applied to a 1-D eight-point DCT system the new DA algorithm only needs 30% of hardware area and has faster speed as compared with ROM-based DA. To illustrate the efficiency of the proposed algorithm a 2-D IDCT chip was implemented using 0.8 mu m SPDM CMOS technology. The chip with size 4575 x 5525 mu m can deliver a processing rate of 50 Mpixels per second.