Browsing by Issue Date, starting with "2000-03-15"

Now showing 1 - 20 of 78481

Solubilization of hydrophilic compounds in 1,1,1,2-tetrafluoroethane with a cationic surfactant
(2000-03-15)
Li, JR
;
Lee, YM
;
Yu, T
;
應用化學系
;
Department of Applied Chemistry
Solubilization of hydrophilic compounds was examined in liquid 1,1,1,2-tetrafluoroethane (R134a) in the presence of the cationic surfactant trioctylmethylammonium chloride (TOMAC). The absorption spectra of methyl orange in the TOMAC-containing R134a solutions were obtained. Significant blue shifts were observed in comparison with the spectrum of methyl orange in aqueous solution. The shifts decreased as the water-to-surfactant ratio, Wb, increased. In addition, spectral measurements confirmed the dissolution of cytochrome c in R134a in the presence of TOMAC. R134a remains as a liquid under mild applied pressure and becomes gas under ambient conditions; it therefore separates from analytes of interest directly without further concentration when used as an extraction solvent. Accordingly, it may be applied to recover valuable hydrophilic substances of low concentration from aqueous solutions.
管管作品六首
(2000-03-15)
管管
Dissipation in a partially coherent flux-driven ring
(2000-03-15)
Liu, MT
;
Chu, CS
;
電子物理學系
;
Department of Electrophysics
We have studied a mesoscopic ring threaded by a magnetic flux that increases linearly with time. The ring is partially coherent such that conduction electrons in the ring will encounter incoherent scatterings. We have treated both the incoherent scatterings and the coherent inelastic processes on the same footing. A S-matrix model, as proposed by Buttiker(1,2) for incoherent scatterings, has been adopted for our situation. This allows us to solve exactly, and analytically, the coherent inelastic processes caused by the time-varying magnetic flux. Our results demonstrate unequivocally that, for the electrons emanating out of incoherent scatterings, the lower the energies of these electrons the greater will be their net contribution to the de component of the induced current. A physical explanation is presented.
管管作品六首
(2000-03-15)
管管
Aging behavior and recovery of polarization in Sr0.8Bi2.4Ta2O9 thin films
(2000-03-15)
Chen, SY
;
Lee, VC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Ferroelectric thin films of bismuth-containing layered perovskite Sr0.8Bi2.4Ta2O9 (SBT) have been prepared by both metalorganic decomposition (designated as MOD-SBT film) and magnetron sputtering (designated as sputtering-SBT film) processes. SBT thin films are well known to exhibit free-fatigue behavior with electrical field cycling. However, it was found that after the SBT films were applied with electrical field display, the polarization reduction with time was observed. The aging rate was related to microstructure, which in turn was dependent on the film processing. The sputtering-SBT films show a slower degradation rate than MOD-SBT films. The suppressed polarization can be near-completely recovered by applying either thermal treatment above 150 degrees C or electric-field cycling. There exists a minimum required thermal energy to restore the polarization. The easy recovery exhibited by SBT films in suppressed polarization reveals that a relatively weak domain pinning may exist between domain wall and electronic defects in SBT. The SBT shows little fatigue behavior during electric field cycling but exhibits an aging phenomenon after applied electric field. (C) 2000 American Institute of Physics. [S0021-8979(00)04906-9].
管管作品六首
(2000-03-15)
管管
管管作品六首
(2000-03-15)
管管
Heuristic fuzzy-neuro network and its application to reactive navigation of a mobile robot
(2000-03-16)
Song, KT
;
Sheen, LH
;
電控工程研究所
;
Institute of Electrical and Control Engineering
A novel pattern recognition approach to reactive navigation of a mobile robot is presented in this paper. A heuristic fuzzy-neuro network is developed for pattern-mapping between quantized ultrasonic sensory data and velocity commands to the robot. The design goal was to enable an autonomous mobile robot to navigate safely and efficiently to a target position in a previously unknown environment. Useful heuristic rules were combined with the fuzzy Kohonen clustering network (FKCN) to build the desired mapping between perception and motion. This method provides much faster response to unexpected events and is less sensitive to sensor misreading than conventional approaches. It allows continuous, fast motion of the mobile robot without any need to stop for obstacles. The effectiveness of the proposed method is demonstrated in a series of practical tests on our experimental mobile robot. (C) 2000 Elsevier Science B.V. All rights reserved.
Tracking a near-field moving target using fuzzy neural networks
(2000-03-16)
Ma, CW
;
Teng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper we explore the problem of tracking a near-field moving target using fuzzy neural networks (FNNs). The moving target radiates narrow band waves that impinge on an array of passive sensors. At a particular time instance, the location of the target is estimated by several judiciously constructed FNN-based angle and distance estimators. When the target is moving, its trajectory can be on-line estimated due to the parallel and real-time computational capability of the FNNs. Computer simulation results illustrate the performance of the FNN-based angle estimator, distance estimator, and the near-field moving target tracker. (C) 2000 Elsevier Science B.V. All rights reserved.
Reduction of epitaxial alignment in n(+)-p poly-Si emitter diode due to gettering of P and As by Ar implantation
(2000-03-16)
Lee, LS
;
Lee, CL
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
It is demonstrated that Ar implantation can retard the epitaxial realignment of poly-Si/Si in an As- or P-doped n(+)-p poly-emitter diode during BF2 implantation. This is believed to be due to the gettering of As, P, and F by bubble-like defects created by the Ar implantation used to reduce the pile-up of these dopants at the poly-Si/Si interface. Consequently, there is less break-up of the interface oxide, resulting in a reduction in epitaxial realignment.
Robot learning schemes that trade motion accuracy for command simplification
(2000-03-16)
Young, KY
;
Lee, JF
;
Jou, HJ
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This study was inspired by the human motor control system in its ability to accommodate a wide variety of motions. By contrast, the biologically inspired robot learning controller usually encounters huge learning space problems in many practical applications. A hypothesis for the superiority of the human motor control system is that it may have simplified the motion command at the expense of motion accuracy. This tradeoff provides an insight into how fast and simple control can be achieved when a robot task does not demand high accuracy. Two motion command simplification schemes are proposed in this paper based on the equilibrium-point hypothesis for human motion control. Investigation into the tradeoff between motion accuracy and command simplification reported in this paper was conducted using robot manipulators to generate signatures. Signature generation involves fast handwriting, and handwriting is a human skill acquired via practice. Because humans learn how to sign their names after they learn how to write, in the second learning process, they somehow learn to trade motion accuracy for motion speed and command simplicity, since signatures are simplified forms of original handwriting. Experiments are reported that demonstrate the effectiveness of the proposed schemes. (C) 2000 Elsevier Science B.V. All rights reserved.
Power PHEMT with compact device layout for low voltage CDMA application
(2000-03-16)
Chang, EY
;
Lee, DH
;
Chen, SH
;
Chang, HC
;
材料科學與工程學系
A high efficiency low voltage operation dual delta-doped AlGaAs/ InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) for low voltage code division multiple access (CDMA) application has been developed. When tested at 2.4V and 1.9GHz under IS-95 CDMA modulation, the 20.16mm PHEMT device was found to have a linear output power of 28dBm with a power added efficiency of 30.2%. The device also has a saturation power of 30.0dBm with a power added efficiency of 61.5%. The high efficiency and linearity of the PHEMT at low bias voltage is attributed to the use of the dual delta-doped PHEMT structure and to the reduction of the size of the device layout. The device is suitable for low voltage CDMA applications.
Temperature dependence of RHEED oscillation in homoepitaxial growth of SrTiO3(100) films on stepped substrates
(2000-03-20)
Lee, JY
;
Juang, JY
;
Wu, KH
;
Uen, TM
;
Gou, YS
Homoepitaxial growth of SrTiO3 (STO) films on STO(100) substrates with unit-cell-high steps manifests itself by a marked change in the intensity oscillations of the specular reflectivity of reflection high-energy electron diffraction (RHEED) oscillations with increasing temperature. Atomic force microscopy (AFM) revealed a high density of growing islands distributed all over the edges and terraces of the pre-existing steps at lower deposition temperatures. In response, the RHEED intensity exhibits an 'overdamped' profile with no oscillation. At higher deposition temperatures (T-s approximate to 500 degrees C), larger (approximate to 40 nn) but fewer islands were observed to form preferentially on the step edges with a gradually recovered RHEED intensity, followed by RHEED oscillations after a few monolayers of coverage. At even higher growth temperatures, immediate periodic oscillations in RHEED intensity were observed. However, the temperature dependence of the oscillation period indicates that it may not be directly related to a layer-by-layer growth mode, as is generally believed. (C) 2000 Elsevier Science B.V. All rights reserved.
On the alpha-labeling number of bipartite graphs
(2000-03-21)
El-Zanati, S
;
Fu, HL
;
Shiue, CL
;
應用數學系
;
Department of Applied Mathematics
In this note we show that the alpha-labeling number of a bipartite graph G is bounded, which proves a conjecture of Snevily. (C) 2000 Elsevier Science B.V. All rights reserved.
On the alpha-labeling number of bipartite graphs
(2000-03-21)
El-Zanati, S
;
Fu, HL
;
Shiue, CL
;
應用數學系
;
Department of Applied Mathematics
In this note we show that the alpha-labeling number of a bipartite graph G is bounded, which proves a conjecture of Snevily. (C) 2000 Elsevier Science B.V. All rights reserved.
Cellular neural networks: Mosaic pattern and spatial chaos
(2000-03-21)
Juang, J
;
Lin, SS
;
應用數學系
;
Department of Applied Mathematics
We consider a cellular neural network (CNN) with a bias term z in the integer lattice Z(2) on the plane R-2. We impose a symmetric coupling between nearest neighbors, and also between next-nearest neighbors. Two parameters, a and epsilon, are used to describe the weights between such interacting cells. We study patterns that can exist as stable equilibria. In particular, the relationship between mosaic patterns and the parameter space (z, a; epsilon) can be completely characterized. This, in turn, addresses the so-called learning problem in CNNs. The complexities of mosaic patterns are also addressed.
Mutation at noncysteine positions eliminates the oxidation/reduction effect on the activity of phenol sulfotransferase.
(2000-03-26)
Yang, YS
;
生物科技學系
;
Department of Biological Science and Technology
Apodised fibre Bragg gratings fabricated with uniform phase mask using low cost apparatus
(2000-03-30)
Yang, CC
;
Lai, YC
;
光電工程學系
;
Department of Photonics
New exposure schemes for fabricating apodised fibre Bragg gratings using a uniform phase mask are described. A sidelobe suppression level as high as 20dB in the lower wavelength region has been successfully achieved. The schemes allow the writing of truly apodised fibre Bragg gratings using low cost and simple apparatus.
Pseudo-Hamiltonian-connected graphs
(2000-03-30)
Chang, GJ
;
Zhu, XD
;
應用數學系
;
Department of Applied Mathematics
Given a graph G and a positive integer k, denote by G[k] the graph obtained from G by replacing each vertex of G with an independent set of size k. A graph G is called pseudo-k Hamiltonian-connected if G[k] is Hamiltonian-connected, i.e., every two distinct vertices of G[k] are connected by a Hamiltonian path. A graph G is called pseudo Hamiltonian-connected if it is pseudo-k Hamiltonian-connected for some positive integer k. This paper proves that a graph G is pseudo-Hamiltonian-connected if and only if for every non-empty proper subset X of V(G), N(X) > X. The proof of the characterization also provides a polynomial-time algorithm that decides whether or not a given graph is pseudo-Hamiltonian-connected. The characterization of pseudo-Hamiltonian-connected graphs also answers a question of Richard Nowakowski, which motivated this paper. (C) 2000 Elsevier Science B.V. All rights reserved.
Beam-switchable scanning leaky-wave antenna
(2000-03-30)
Wang, CJ
;
Shih, YC
;
Jou, CF
;
傳播研究所
;
Institute of Communication Studies
A beam-switchable scanning leaky-wave antenna (LWA) has been developed. This LWA with a two-terminal feeding microstrip, line structure is integrated with a single port double throw (SPDT) snitch as a control circuit. In dual-beam mode, the scanning angle is steered over a range of 36-64 degrees for the right-hand beam and 144 -116 degrees for the left-hand beam. In one-beam made, the scanning angle is measured over 20 degrees for the right-hand beam. The measured result shows that we can change from the, one-beam mode to the dual-beam mode electronically by controlling the on/off status of an SPDT switch, in contrast to the case For traditional leaky wave antennas.