Browsing by Issue Date, starting with "1996-02-15"

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Induced Einstein-Kalb-Ramond theory and the black hole
(1996-02-15)
Kao, WF
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Dai, WB
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Wang, SY
;
Chyi, TK
;
Lin, SY
A four-dimensional induced Einstein-Kalb-Ramond theory with a conformally coupled Kalb-Ramond term is discussed. It is argued that the Kalb-Ramond field is difficult to interpret as an axion field from a dynamical point of view, and hence tends to be unstable. One can, however, apply Routh's method to extract an effective action for the axion field. It is found that the Kalb-Ramond hair will turn the event horizon into a naked singularity. Such an exact solution is found and analyzed carefully.
The dynamics of thermal annealing in arsenic-ion-implanted GaAs
(1996-02-15)
Chen, WC
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Lin, GR
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Chang, CS
;
交大名義發表
;
光電工程學系
The effect of thermal annealing on the surfaces of arsenic-ion-implanted GaAs has been investigated by transmission electron microscopy, deep level transient spectroscopy and temperature-dependent resistance measurements. For the annealed films of arsenic-ion-implanted GaAs arsenic precipitates and a band of deep-level defects with the activation energy of around 0.6 eV near the surface are observed. The mean size and concentration of As precipitates in samples implanted at a dosage of 10(16) cm(-2) are about 2-3 nm and 7 x 10(16) cm(-3), respectively. The cross section of the deep level defects near the surface is calculated to be 7 x 10(-14) cm(2). The carrier-transport mechanisms of both as-implanted GaAs and post-annealed GaAs are shown dominantly to be hopping type conduction and active type conduction, respectively.
Weyl invariant black hole
(1996-02-15)
Kao, WF
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Lin, SY
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Chyi, TK
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電子物理學系
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物理研究所
The properties of the Weyl invariant black hole and its implications are studied. The calculation shows that there is no hair, up to a gauge choice, for a Weyl gauge field outside the event horizon of a black hole in the Weyl invariant limit. We also show that a scalar held will remain constant once the scale symmetry is broken spontaneously by the well-known Higgs potential. As a result, classical hair for the Weyl vector meson and scalar measuring field vanishes strictly in the presence of a spontaneously symmetry-breaking potential. Hence the no-hair theorem holds both in the Weyl invariant limit and the symmetry-breaking phase.
Critical current densities of submillimeter single-grain TL-2223 superconducting thin film
(1996-02-15)
Lin, HC
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Juang, JY
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Wu, KH
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Gou, YS
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Uen, TM
Large single-crystalline superconducting grains of Tl2Ba2Ca2Cu3O10+x (Tl-2223) with sizes up to 150 mu m x 150 mu m x 1 mu m are obtained on both MgO(100) and LaAlO3 (100) substrates by a single-target de-sputtering process followed by appropriate postannealing at temperatures around 910 degrees C. Such superconducting grains were isolated and patterned into 10-mu m-wide bridges by reactive ion etching. The etching process was found to only minimally affect the transition temperature, T-c, typically around 110 K, of the films. Although there was evidence that these films were indeed two-dimensional in nature, the critical current densities, J(c), were greater than 10(6) A/cm(2) at temperatures below 90 K. At lower temperatures, e.g., T = 30 K, the J(c) value of these films remains well above 10(6) A/cm(2) even with magnetic fields as large as 7 T applied parallel to the c-axis of the grains. The results are in sharp contrast to the low J(c) values expected from the low-dimensionality nature of this system.
Quantum transport in the presence of a finite-range time-modulated potential
(1996-02-15)
Tang, CS
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Chu, CS
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電子物理學系
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Department of Electrophysics
Quantum transport in a narrow constriction and in the presence of a finite-range time-modulated potential is studied. The potential takes the form V(x,t) = V-0 theta(x)theta(a-x)cos(omega t), with a the range of the potential and x the transmission direction. Intrasubband transitions for the electrons and for arbitrary omega are made possible by the finiteness in the potential range. Our results show that, as the chemical potential mu increases, the dc conductance G exhibits dip structures when mu is at nn omega above the threshold energy of a subband. These structures in G are found in both the small a (a similar to lambda) and the large a (a much greater than lambda) regime. These dips are associated with the formation of quasi-bound-states. Our results can be reduced to the limiting case of a delta-profile oscillating potential when both a much less than lambda and V(0)a much less than 1 are satisfied. The assumed form of the time-modulated potential is expected to be realized in a gate-induced potential configuration.
Counter-current chromatography using supercritical fluid carbon dioxide as mobile phase
(1996-02-16)
Yu, T
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Li, SE
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Chen, YH
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Wang, HP
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應用化學系
Supercritical fluid carbon dioxide was employed in solar eccentric counter-current chromatography (SECCC) to replace the liquid mobile phase in the traditional arrangement. The fundamental difference from the conventional liquid-liquid system is the requirement for high-pressure operation. The experimental set-up is presented to illustrate the necessary modifications that accommodate operation with a supercritical fluid. Studies on the stationary phase retention due to various experimental conditions are discussed. A mixture of acetophenone and benzophenone was chromatographed using mixtures of water and methanol as the stationary solvent system to demonstrate the feasibility of this technique. At present the efficiency of the separation is not satisfactory owing to the phase separator inserted in the system to remove liquid droplets which contributed to considerable peak broadening.
Effect of member initial curvature on a flexible mechanism response
(1996-02-22)
Hsiao, KM
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Yang, RT
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
A co-rotational finite element formulation of slender curved beam element is presented to investigate the effect of member initial curvature on the dynamic behaviour of planar flexible mechanisms. The Euler-Bernoulli hypothesis and the initial curvature are properly considered for the kinematics of curved beam. The nodal co-ordinates, incremental displacements and rotations, velocities, accelerations and the equations of motion of the system are defined in terms of a fixed global co-ordinate system, while the total strains in the beam element are measured in element co-ordinates which are constructed at the current configuration of the beam element. The element equations are constructed first in the element co-ordinate system and then transformed to the global co-ordinate system by using standard procedures. Both the deformation nodal forces and the inertia nodal forces of the beam element are systematically derived by consistent linearization of the non-linear beam theory in the element co-ordinates. An incremental-iterative method based on the Newmark direct integration method and the Newton-Raphson method is employed here for the solution of the non-linear dynamic equilibrium equations. Numerical examples are presented to demonstrate the effectiveness of the proposed element and to investigate the effect of the initial curvature on the dynamic response of the flexible mechanisms. (C) 1996 Academic Press Limited
Designing lower-dimensional regular arrays for algorithms with uniform dependencies
(1996-02-25)
Tsay, JC
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Chang, PY
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交大名義發表
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工學院
;
National Chiao Tung University
In this paper, we will propose a polynomial-time method to design m-dimensional regular arrays for n (n greater than or equal to m + 1) dimensional algorithms with uniform dependencies, regular algorithms. The proposed method has two steps: the first one is to transform an independently partitioned regular algorithm to a new one, which has an identity dependence matrix. We call this step identity transformation, which is an affine one. In the second step, we propose a spacetime mapping in a fixed form to map the new regular algorithm to a lower-dimensional regular array. Thus, an affine spacetime mapping is constructed by combining the identity transformation and the fixed form's spacetime mapping together. With the proposed affine spacetime mapping, the original regular algorithm can be mapped to a lower-dimensional regular array in polynomial time, which depends only on the number of dimensions of the regular algorithm. Meanwhile, the designed regular array is asymptotically optimal in time and space. (C) 1996 Academic Press, Inc.
Co[poly(ethylene terephthalate-p-oxybenzoate)] and its blends with poly(ethylene terephthalate): Transesterification reaction and fractured surface morphology
(1996-02-28)
Ou, CF
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Lin, CC
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材料科學與工程學系
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Department of Materials Science and Engineering
A series of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, viz., P28, P46, P64, and P82, were synthesized. These copolyesters were blended with poly(ethylene terephthalate) (PET) at the level of 10 wt % at 293 degrees C for different times. The results from proton NMR analysis reveal that a significant amount of the transesterification has been detected in the cases of PET/P28, PET/P46, and PET/P64 blends. The blending time necessary before any transesterification reaction could be detected depends on the composition of copolyester, e.g., a time less than 3 min is needed for both PET/P28 and PET/P46 blends, while a longer time of 8-20 min is needed for the PET/P64 blend. It is concluded that the higher the mol ratio of the POB moiety in the copolyester is the longer the blending time needed to initiate the transesterification. The degree of transesterification is also increased as the duration of melt blending is prolonged. Two-phase morphology was observed by scanning electron microscopy (SEM) micrographs in all the blends. It was observed that the more similar the composition between the copolyester and PET in the blends is the better the miscibility or interfacial adhesion between the two phases. Moreover, the miscibility can be markedly improved by the duration of melt blending. (C) 1996 John Wiley & Sons, Inc.
Structural and electrical properties of GaSb, AlGaSb and their heterostructures grown on GaAs by metalorganic chemical vapor deposition
(1996-03-01)
Wang, PY
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Chen, JF
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Chen, WK
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電子物理學系
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Department of Electrophysics
A systematic study of structural and electrical properties of GaSb and AlGaSb grown on GaAs by metalorganic chemical vapor deposition is reported. In general, the results obtained from surface morphologies, X-ray linewidths and Hall properties are consistent with each other and indicate that the optimal growth conditions for GaSb are at 525 degrees C around V/III = 1. A highest hole mobility of 652 cm(2)/V . s at RT (3208 cm(2)/V . s at 77 K) and a lowest concentration of 2.8 x 10(16) cm(-3) (1.2 X 10(15) cm(-3) at 77 K) were obtained for GaSb grown under this optimal condition. Compared to the GaSb growth, a smaller V/III ratio is needed for the AlGaSb growth to protect the surface morphology. When Al was incorporated into GaSb growth, mobility decreased and carrier concentration increased sharply. The AlGaSb grown at 600 degrees C had a background concentration about one order of magnitude lower than the AlGaSb grown at 680 degrees C. Room-temperature current-voltage characteristics of GaSb/AlxGa1-xSb/GaSb show a rectifying feature when Al composition x is higher than 0.3, suggesting a valence-band discontinuity at the AlGaSb/GaSb interface. A leakage current much higher than the value predicted by the thermionic emission theory is observed at 77 K, presumably due to a large number of dislocations generated by the huge lattice mismatch between GaSb and GaAs.
Stability and chaotic motions of a symmetric heavy gyroscope
(1996-03-01)
Ge, ZM
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Chen, HK
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
The nonlinear motion of a symmetric heavy gyro mounted on a vibrating base, particularly its long-term dynamic behavior for a wide range of parameters, is investigated, The system exhibits both regular and chaotic motions. Two typical routes to chaos, namely through period-doubling and intermittency, are found in this study, The method of multiple scales is used to analyze the responses and to determine the stability of the trivial fixed point for the system excited by single harmonic force. The stability of the system excited by multiple harmonic forces has been studied by Lyapunov's direct method. As the system is subjected to external disturbance, the Melnikov method is used to show the existence of chaotic motion. The effect of the number of forcing frequencies on the chaotic regions is also established. The numerical results, in which the existence of chaos is demonstrated, are presented in the form of bifurcation diagrams, phase portraits, Poincare maps, and Lyapunov exponents. The effect of the gyroscope's spinning speed is also studied. It is found that increasing the gyroscope's spin speed is the simplest method to overcome the chaotic motion for this system.
Mechanical properties and 95 degrees C aging characteristics of zircon-reinforced Zn-4Al-3Cu alloy
(1996-03-01)
Li, BJ
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Chao, CG
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交大名義發表
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材料科學與工程學系
;
National Chiao Tung University
A process for preparing zinc alloy castings containing dispersions of zircon particles is described. Composites were prepared by stirring zircon particles in Zn-4Al-3Cu (ZAS) alloy melts and subsequently casting these melts in permanent molds. It was found that additions of zircon resulted in an increase in the sliding wear resistance and in the proportional limit in compression. The aging characteristics of the ZAS alloy have also been investigated by hardness tests, dilatometry technique, and transmission electron microscopy observations. There are two kinds of precipitates that occur during the aging process. The alpha-phase precipitates from the eta phase in the early stage of aging and the copper-rich epsilon-phase precipitates from the eta phase in the later stage of aging. Therefore, there are two peaks in the hardening curve caused by both alpha-phase and epsilon-phase precipitation. The alpha-phase precipitation induces the dimensional shrinkage, and the copper-rich epsilon phase precipitation results in dimensional expansion. Zircon particles existing in ZAS alloy reduce the maximum shrinkage from 353 X 10(-6) for the monolith to 167 x 10(-6) for the composite. Two groups of parallel alpha-phase plates had formed within the eta dendrite during aging at 95 degrees C. The orientation relationship between the alpha phase and matrix was determined as [(1) over bar 101](//[l (1) over bar 0](alphaalpha), (11 (2) over bar 0)(eta)//(111)(alpha).
Active noise cancellation in ducts using internal model-based control algorithms
(1996-03-01)
Hu, JS
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交大名義發表
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電控工程研究所
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National Chiao Tung University
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Institute of Electrical and Control Engineering
A feedback control algorithm based on the internal model principle is proposed to solve the active noise control (ANC) problem in ducts. Because of its infinite open-loop gain at selected frequencies, the controller is able, at the cancellation speaker position, to block noise transmission of these frequencies. In other words, the speaker acts like a totally reflective boundary, Stability analysis of the closed-loop system is performed using the Nyquist criterion, Experimental results confirm the theoretical analysis, showing an average noise level reduction of 30 to 40 dB at the target frequencies.
A potential-based approach for shape matching and recognition
(1996-03-01)
Chuang, JH
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交大名義發表
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資訊工程學系
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National Chiao Tung University
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Department of Computer Science
This paper presents a novel potential-based approach for recognizing the shape of a two-dimensional (2D) region by identifying the best match from a selected group of shape templates. The proposed model assumes that the border of every 2D region is uniformly charged. An initially small shape template placed inside a shape sample will experience the repulsive force and torque arising from the potential field. A better match in the shape between the template and the sample can be obtained if the template translates and reorients itself to reduce the potential while growing in size. The shape template with the largest final size corresponds to the best match and represents the shape of the given sample. The potential and the associated repulsive force and torque between the polygonal contours are analytically tractable, hence resulting in high computational efficiency of the matching process. The proposed approach is intrinsically invariant under translation, rotation and size changes of the shape sample. Moreover, not only can the matching be carried out directly for shape contours at different viewscales, but the contours can also be unconnected, provided that the template is confined within the shape sample throughout the matching process.
Dielectric degradation of Cu/SiO2/Si structure during thermal annealing
(1996-03-01)
Chiou, JC
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Wang, HI
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Chen, MC
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The impact of Cu on the dielectric SiO2 layer was studied using a Cu/SiO2/Si metal oxide semiconductor capacitor and rapid thermal annealing (RTA) treatment. With the RTA treatment, no chemical reaction was observed up to 900 degrees C; however, dielectric degradation occurred following RTA at 300 degrees C for 60 s and became worse with the increase of annealing temperature. The interface-trap density at the SiO2/Si interface also increased from 5 x 10(10) to 5 x 10(13) eV(-1) cm(-2) after 800 degrees C RTA treatment. The RTA anneal introduced a large number of positive Cu ions into the dielectric SiO2 layer. Under bias-temperature stress, Cu ions drift quickly in the SiO2 layer and may drift across the SiO2/Si interface and enter the Si substrate. With the use of 1200 Angstrom thick TiN and TiW barrier layers, respectively, the dielectric strength of the Cu/(barrier)/SiO2/Si structures was able to remain stable up to 500 and 600 degrees C.
肥了秋陽瘦了乳房
(1996-03-01)
管管
A design strategy for short gate length SOI MESFETs
(1996-03-01)
Hou, CS
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Wu, CY
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A design strategy for short gate length, self-aligned Si-SOI MESFETs is proposed, in which the design considerations for the important device parameters of the SOI MESFET are studied by using a 2D numerical simulator. It is shown that the sub-threshold I-ds-V-gs characteristics can be used to determine the thickness of silicon film for a given channel doping level under a specified threshold voltage. Moreover, the 2D effect can be suppressed by reducing the thickness of buried oxide to improve the bottom-gate controllability over the channel charges. Moreover, it is shown the backgate bias is also an important controllable parameter for modulating the characteristics of the SOI MESFET in both sub-threshold and saturation regions. An example for designing a very short gate length (0.1 mu m) SOI MESFET has been carried out to verify this strategy. It is shown that the proposed strategy does provide an effective procedure for designing an Si-SOI MESFET with high performance.
Stress analysis of the rotational object under the condition of transient state
(1996-03-01)
Lu, TC
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Jeng, TH
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交大名義發表
;
National Chiao Tung University
A novel method for extracting the metallurgical channel length of MOSFET's using a single device
(1996-03-01)
Li, HH
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Chu, YL
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Wu, CY
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A new charge-pumping method with de source/drain biases and specified gate waveforms is proposed to extract the metallurgical channel length of MOSFET's by using a single device. Using two charge-pumping currents of a single nMOSFET measured under different V-GL (V-GH for pMOSFET's), the metallurgical channel length can be easily extracted with an accuracy of 0.02 mu m. It is shown that the proposed novel method is self-consistent with the results obtained by the charge-pumping current measured from multidevices under different gate pulse waveforms and bias conditions.
Modeling of a finger-follower cam system with verification in contact forces
(1996-03-01)
Hsu, WY
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Pisano, AP
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交大名義發表
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機械工程學系
;
National Chiao Tung University
A lumped/distributed-parameter dynamic model is developed to investigate the dynamic responses of a finger-follower cam system by considering a hydraulic lash adjuster with an oscillating pivot, and frictional forces between sliding surfaces. The measured force data at low speed are employed to derive an algorithm to determine the dynamic Coulomb friction coefficients at contact points. The contact position between the earn and the follower with moving pivot is determined by a constraint equation method. A hydraulic lash adjuster acting as the pivot of the follower is also modeled with the effects of oil compressibility and oil refill mechanism. Simulated contact forces at three different speeds are shown to have good agreement with experimental data. The separation between the hydraulic lash adjuster and the follower is predicted at a camshaft speed of 2535 rpm, ana experiment indicates at 2520 rpm.