Browsing by Author "CHEN, JL"

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A MODIFIED FINITE-ELEMENT METHOD FOR ANALYSIS OF FINITE PERIODIC STRUCTURES
(1994-08-01)
CHUNG, SJ
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CHEN, JL
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交大名義發表
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傳播研究所
;
National Chiao Tung University
A modified finite element method with new solving algorithm is proposed to analyze electromagnetic problems of finite periodic structures. Dielectric-loaded parallel-plate waveguides with rectangular and triangular dielectric gratings are tackled as an example of the present approach. Numerical results are checked by the self-convergence test and by comparing with those obtained by other methods. Finally, the dependence of the scattering parameters on the frequency, the period number, and the grating height is analyzed and compared.
AN OBJECT-ORIENTED APPROACH TO CONSTRUCTING COMMUNICATION PROTOCOLS
(1995-05-01)
CHEN, JL
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WANG, FJ
;
TING, YC
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交大名義發表
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資訊科學與工程研究所
The development of communication protocols for computer networks and distributed systems is an increasingly complex and cost-sensitive process. This paper presents an object-oriented concurrent (OOC) model for the development of communication protocols. This model consists of three kinds of entities: data entities, which represent the communicated data units, state entities, which describe their behavior, and connection, entities, which are responsible for communication services. The state transitions in a protocol are modeled by using state entities, and a communication service is performed by a group of connection and state entities. A C++ library based on our OOC model is described that contains three class hierarchies, for data, state; and connection entities, respectively In addition, an approach to constructing a protocol using this OOC model and the library is presented. An example in which a T.62 protocol is constructed shows that this approach provides a high level of modeling, concurrency, and reusability.
ANOMALOUS HALL-EFFECT FROM VORTEX MOTION IN HIGH-TC SUPERCONDUCTORS
(1994-08-01)
CHEN, JL
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YANG, TJ
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電子物理學系
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光電工程研究所
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Department of Electrophysics
In this work, the unusual Seebeck effect is taken into consideration in explaining the possible origin of the anomalous Hall effect for high-T(c) superconductors. Combining Maki's theory of transport entropy and Tinkham's theory of resistive transition, we explain why the anomalous Hall effect can be observed in high-T(c) superconductors, but is absent in most conventional superconductors. The behavior of rho(xy) (H, T) in our theory is qualitatively consistent with experiments. In addition, our theory not only predicts that rho(xy) will become positive from rho(xy) < 0 when the temperature is decreased in constant magnetic field, but also predicts that \rho(xy)\ is-proportional-to rho(xx)2 in the region of pho(xy) < 0 and that the negative p(xy) will diminish with increasing defect concentration.
DIAMOND FILM GROWTH ON CEMENTED TUNGSTEN CARBIDES STUDIED BY SEM, AES AND XPS
(1992-11-23)
CHEN, JL
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HUANG, TH
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PAN, FM
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KUO, CT
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CHANG, CS
Diamond films were deposited on cemented WC substrates using a hot filament chemical vapor deposition (CVD) system with a mixture of CH4 and H-2 as the source gases. The effect of the surface pretreatments of scratching the surface and etching to remove the surface Co from the substrate on diamond nucleation and growth was studied. The effect of CH4 Concentration on diamond growth was also examined. Scanning electron microscopy, Auger electron, X-ray photoelectron and energy dispersive spectroscopies were used to examine the film morphology, quality and compositions. The results show that a good diamond-crystal quality can be obtained by reducing the surface Co content in the substrate to below 1%. Co in the surface layer of the substrate inhibits both diamond nucleation and growth. Polishing and etching treatments to scratch the surface and to remove the surface Co of the substrates are essential to maintain the surface roughness in an appropriate range to obtain diamond films with a good quality and adhesion. A change in CH4 Concentration in the source gases from 0.5 to 0.15% can change the preferred orientation of the diamond films fro m the {100} to the {111} plane.
FLUX-FLOW OF ABRIKOSOV VORTICES IN TYPE-II SUPERCONDUCTORS
(1994-07-01)
CHEN, JL
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YANG, TJ
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電子物理學系
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光電工程研究所
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Department of Electrophysics
The theory of flux flow developed by Bardeen and Stephen (BS) is modified and extended to the high-field case. The Clem model and Wigner-Seitz circle-cell approximation for vortices are used in our approach. The distinct boundary of the normal core of a vortex in BS theory is removed and treated naturally. Several interesting results come out as a consequence. The Lorentz force is determined by the normal current rather than the supercurrent. But the supercurrent can sustain the magnetic-field distribution of flux quanta. From energy dissipation considerations, the Lorentz force is equal to viscosity force automatically without assumption as made in BS theory. An expression for the viscosity is also obtained.
SURFACE SUPERCONDUCTIVITY OF SHORT COHERENCE LENGTH SUPERCONDUCTORS
(1994-09-20)
CHEN, JL
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YANG, TJ
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電子物理學系
;
光電工程學系
;
Department of Electrophysics
Based on the theory of Valls et al. for short coherence length superconductors, de Gennes' boundary theory for conventional superconductors with xi(0)>>k(F)(-1) may be modified. We solve the G-L equation exactly under zero magnetic field for various temperatures. The order parameter psi(x) is not depleted but enhanced near the surface. We also obtain some interesting results: T-c will be enhanced by contracting of the thickness of a superconducting film. The nucleation field H-c3(T) proportional to (T-cb-T) near T-cb; and H-c3(T)proportional to(T-c-T)(1/2) near T-c. The critical current in SIS Josephson junctions J(c)(T)proportional to(T-c- T) + root 2 tau(0)(T-0-T) for T
SURFACE SUPERCONDUCTIVITY OF SHORT COHERENCE LENGTH SUPERCONDUCTORS
(1994-09-20)
CHEN, JL
;
YANG, TJ
;
電子物理學系
;
光電工程研究所
;
Department of Electrophysics
Based on the theory of Valls et al. for short coherence length superconductors, de Gennes' boundary theory for conventional superconductors with xi(0)>>k(F)(-1) may be modified. We solve the G-L equation exactly under zero magnetic field for various temperatures. The order parameter psi(x) is not depleted but enhanced near the surface. We also obtain some interesting results: T-c will be enhanced by contracting of the thickness of a superconducting film. The nucleation field H-c3(T) proportional to (T-cb-T) near T-cb; and H-c3(T)proportional to(T-c-T)(1/2) near T-c. The critical current in SIS Josephson junctions J(c)(T)proportional to(T-c- T) + root 2 tau(0)(T-0-T) for T
SURFACE SUPERCONDUCTIVITY OF SHORT COHERENCE LENGTH SUPERCONDUCTORS
(1994-12-01)
YANG, TJW
;
CHEN, JL
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
Based on the microscopic theory of Valls et al for short coherence length superconductors, the surface critical temperature T-cs is assumed to be higher than the bulk critical temperature T-cb and the term of surface energy is added in the Ginzburg-Landau (GL) free energy. A boundary condition is obtained and used to solve the GL equation exactly under zero magnetic field for various temperatures. Two examples are given. The critical temperature Tc will be enhanced by reducing the thickness of a superconducting thin film. The nucleation field H-c3 (T) is proportional to T-cb - T near T-cb; and H-c3 (T) is also proportional to (T-c - T)(1/2) near Tc.
THE HYSTERESIS OF MAGNETIZATION IN THE GENERALIZED CRITICAL-STATE MODEL - LOW-FIELD APPROXIMATION
(1994-05-01)
CHEN, JL
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YANG, TJ
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電子物理學系
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光電工程學系
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Department of Electrophysics
The generalized critical-state model is extended to the low-field case by a new low-field approximation. We calculate the hysteresis loops of magnetization for H(max) < H* and H(max) > H*. We obtain new behaviors of M(H) which are different from the results derived from the Bean and Kim models. Our theory qualitatively agrees with the experimental results for high-T(c) superconductors. Some important macroscopic parameters may be obtained by fitting our theory with the experimental data.