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Interaction between a two-dimensional pancake vortex and a circular nonsuperconducting defect
(1996-07-01)
Chen, JL
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The interaction energy U-int(r) between a two-dimensional (2D) pancake vortex and a circular dielectric defect with radius a in a superconducting thin film is calculated in the London Limit kappa much greater than 1. We obtain a general expression formula of U-int(r) for all range r > a. Our theory predicts that U-int(r) proportional to ln(1-a(2)/r(2)) at a short distance, which is in the same form as the 3D bulk superconductor, But U-int(r) decreases with r(-4) at a long distance, unlike decreases exponentially in the 3D bulk one.
Magnetic force acting on a magnetic dipole over a superconducting thin film
(1996-12-01)
Wei, JC
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Chen, JL
;
Horng, L
;
Yang, TJ
;
電子物理學系
The magnetostatic interaction energy and corresponding magnetic force acting on a magnetic point dipole placed above a type-II thin superconducting film in the mixed state with a single vortex are calculated using electromagnetics coupled with the London theory of superconductivity. If a vortex is trapped by a circular defect of radius b much less than Lambda, the magnetic forces, caused by the vortex, differ from the results of free from defect pinning by the factor (1 - b/Lambda), where Lambda is the effective penetration depth. The possibility of formation of the vortex in the thin film only in the field of the magnetic point dipole is investigated. The critical position of the dipole for creating the first vortex under the electromagnetic pinning of a circular defect and that position in the absence of defect pinning are obtained for comparison. In particular, in the limit of a/Lambda much greater than 1, where a is the separation between the dipole and the thin film, the only difference between two results is in the cutoff length, i.e., in the case of a circular defect the only difference in the critical position calculation is the cutoff at radius b rather than at coherence length xi. The pinning force of a single vortex by a circular defect is also calculated. Further, we investigate the conditions of the vortex creation for various cases (including the first, second, and third vortices) for a free of pinning center in the examining region. It is found that the creation of a new single vortex in the thin film causes an abrupt change in vertical levitation force: the force changed discontinuously.
Transesterification and cyclization of polycarbonate-epoxy blends cured with anhydride
(1996-08-01)
Li, MS
;
Su, YF
;
Ma, CCM
;
Chen, JL
;
Lu, MS
Infrared spectra have been investigated to study the curing mechanisms of polycarbonate-epoxy blends using anhydride as a hardener catalysed by tertiary amine. Due to a significant difference in the reaction, curing reactions of the system can be considered as two sequential stages: (1) an anionic alternating copolymerization of cyclic anhydride and epoxy resin, and (2) a homopolymerization of oxirane initiated by a quaternary ammonium salt zwitter ion. The transesterification/cyclization of carbonate groups proceeds in the later stage if the oxirane is still available. Degrees of transesterification/cyclization and homopolymerization are higher when a higher epoxy/anhydride ratio is used. This study positively confirms the mechanism of transesterification/cyclization proceeding through a zwitter ion. The zwitter ion is formed from epoxide and tertiary amine, which attacks the carbonate group. Copyright (C) 1996 Elsevier Science Ltd.
The interaction between a single vortex and a columnar defect in the superconducting multilayers
(1996-10-01)
Chen, JL
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The interaction energy per unit length U-int(r) between a single vortex and a columnar defect with radius a in the superconducting multilayers is calculated with the help of London theory. We assume that these superconducting layers are coupled by the magnetic field and the interlayer Josephson coupling can be neglected. We obtain a general expression of U-int(r) for any t, where t is half of the spacing between the layers. For t --> infinity, our theory can be reduced to the result of a thin film. But when r becomes smaller, U-int(r) would tend to exhibit the behavior of 3D superconducting bulk.
The kinetics, thermal and mechanical properties of epoxy-polycarbonate blends cured with aromatic amine
(1998-04-01)
Lu, MS
;
Chen, JL
;
Li, YS
;
Chang, FC
;
Li, MS
PC-DER331 blends are transparent and homogeneous due to the transesterification taking place during hot melting process. This transesterification reaction does not occur or occurs insignificantly during the preparation of PC-DER332 blends. PC is separated from the PC-DER332 melt mixture by slow cooling to room temperature but the mixture remains a single phase by quenching with an ice bath. Two systems of PC-epoxy blends, PC-DER331 blends and PCDER332 blends are cured by the m-phenylene diamine (MPDA) in a stoichiometric ratio. Curing kinetics have been carried out by differential scanning calorimeter (DSC). The presence of PC accelerates the curing reaction. Infrared spectroscopy (IR) indicates the occurrence of transesterification in the PC-DER331/MPDA blends during curing. The flexural modulus increases with the increase of the PC content while the notched Izod impact strength decreases with the increase of the PC content for all the blending systems. The fracture surfaces of the PC-DER331/MPDA blends are smooth, an indication of a homogeneous morphology. The fracture surfaces of the PC-DER332/MPDA blends are rough, an indication of a heterogeneous morphology.
An inheritance flow model for class hierarchy analysis
(1998-06-30)
Chen, JL
;
Wang, FJ
;
資訊工程學系
;
Department of Computer Science
This paper presents an inheritance flow model, which represents the inheritance relationships among classes as a flow graph. A flow operation is associated with each attribute and method in a class to denote the defined (redefined) or inherited member. An inherited member can be deemed as being handled by a sequence of how operations along a path in the flow graph. This model provides several analyses in a class hierarchy, such as implicit inherited member and polymorphic method invocation. These analyses may be applied in various fields of software engineering, such as static analysis, maintenance, and complexity measurement. (C) 1998 Elsevier Science B.V. All rights reserved.
An efficient algorithm for form structure extraction using strip projection
(1998-09-01)
Chen, JL
;
Lee, HJ
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資訊工程學系
;
Department of Computer Science
This paper presents an efficient strip-projection-based approach to extracting form structures from form documents for office automation. To locate the data, we have to extract and interpret the form structure. In this paper, a strip projection method is presented for extracting the form structure. We first segment input form images into uniform vertical and horizontal strips. Since most form lines are vertical or horizontal, we project the image of each vertical strip horizontally and that of each horizontal strip vertically. The peak positions in these projection profiles denote possible locations of lines in form images. We then extract the lines starting with the possible line positions in the source image. After all lines have been extracted, redundant lines are removed using a line-verification algorithm and broken lines are linked using a line-merging algorithm. Experimental results show that the proposed method can extract form structures from A4-sized documents in about 3 seconds which is very efficient, compared with the methods based on Hough transformation and run-based line-detection algorithms. (C) 1998 Pattern Recognition Society. Published by Elsevier Science Ltd. All rights reserved.
Chinese handwritten character segmentation in form documents
(1999)
Chen, JL
;
Wu, CH
;
Lee, HJ
;
資訊工程學系
;
Department of Computer Science
This paper presents a projection based method for segmenting handwritten Chinese characters in form documents with known structures. In the preprocessing phase, a noise removal method is proposed that preserves stroke connections and character edge points. In the character segmentation phase, the projection profile analysis method is used to segment a text line image into projection blocks. In addition, projection blocks are classified into one of four types: mark, half-word, single-word, and two-word. Large blocks are then split and small blocks are merged. In addition, an OCR system is adopted to eliminate errors resulting from the inappropriate merging of Chinese numerical characters with other characters. As for 1319 Chinese characters are tested during our experiments, the correct segmentation rates of 92.34% and 91.76% are obtained with and without the OCR module.
Transesterification in homogeneous poly(epsilon-caprolactone)-epoxy blends
(1999-01-03)
Chen, JL
;
Huang, HM
;
Li, MS
;
Chang, FC
;
應用化學系
Transesterification has been investigated in poly(epsilon-caprolactone) (PCL)-epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol-il (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring-opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA-3,3'-dimethylmethylene-di(cyclohexylamine)-PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T-g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. (C) 1999 John Wiley & Sons, Inc.
Phase separation process in poly(epsilon-caprolactone)-epoxy blends
(1999-08-10)
Chen, JL
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Phase separation process in poly(epsilon-caprolactone)-epoxy blends (PCL-epoxy) cured by 4,4'-diaminodiphenyl sulfone (DDS) was investigated by OM and SEM. The blend compositions higher than the critical point exhibit macrophase separation by the spinodal decomposition (SD) mechanism of the epoxy and results in the epoxy particles being dispersed in the matrix. These epoxy particles grow larger gradually and connect to each other to give macrophase epoxy domains with irregular shape. After that, two more stages of microphase separations bake place via a nucleation and growth (NG) mechanism and result in smaller epoxy particles being dispersed in the matrix. Blend compositions lower than the critical point exhibit the SD or NG mechanisms of PCL, but the microphase separation is observed only within the epoxy matrix. These phase separation mechanisms can be illustrated successfully by the phase diagram constructed by the spinodal and binodal curves. Hydrogen bonding between protons from the epoxy with carbonyls from PCL has been investigated by FTIR. The mixing free energy reduction by the hydrogen bonding can contribute to the LCST behavior rather than the UCST behavior predicted by the Flory-Huggins equation based on only nonpolar interactions.

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