Browsing by Issue Date, starting with "1997-07-11"

Now showing 1 - 20 of 83604

Face selectivity in the 1,3-dipolar cycloaddition reactions of benzonitrile oxide with 5-substituted adamantane-2-thiones and 2-methyleneadamantanes
(1997-07-11)
Chung, WS
;
Tsai, TL
;
Ho, CC
;
Chiang, MYN
;
leNoble, WJ
The 1,3-dipolar cycloaddition reactions of benzonitrile oxide with 5-substituted adamantane-2-thiones (2-X) and 2-methyleneadamantanes (3-X) produced two geometrically isomeric Delta(2)-1,4,2-oxathiazolines (5-Xs) and two Delta(2)-isoxazolines (6-Xs), respectively. The substituent was varied from fluoro, chloro, bromo, to phenyl. X-ray single-crystal analysis confirmed the configuration of (Z)-5-F. The produce formation bias resulting from the favored attack of nitrile oxide on the zu-face is discussed in terms of transition-state hyperconjugation and frontier molecular orbital theory.
Persistent photoconductivity in n-type GaN
(1997-07-15)
Chen, HM
;
Chen, YF
;
Lee, MC
;
Feng, MS
;
材料科學與工程學系
Results of photoconductivity measurements in undoped n-type and Se-doped GaN epitaxial thin films are presented. Similar to the photoluminescence spectra, the photoconductivity also shows a broad yellow band centered around 2.2 eV. It is found that persistent photoconductivity (PPC) does exist in all the studied thin films. In addition, the PPC effects can be observed for the pumping photon energy down to the yellow band. The results reveal that the origin of the PPC effect and yellow luminescence may arise from the same intrinsic defect. It is shown that the most probable candidate of the intrinsic defect is nitrogen antisite. (C) 1997 American Institute of Physics.
Magnetic force signal of vortex creation in type-II superconducting thin films
(1997-07-15)
Wei, JC
;
Horng, L
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
The possibility of the formation of a vortex in thin film due to the field of magnetic dipole moment when a point dipole is vertically approaching the surface of a thin film is discussed. Calculations are performed for certain discrete values of the critical position of the point dipole for creating the vortex in the thin film and the equilibrium positions of the vortex, both of which depend on the strength of magnetic dipole moment. The creation of a new single vortex in the thin film causes an abrupt change in the vertical force. (C) 1997 Elsevier Science B.V.
Low-frequency plasmons in metallic carbon nanotubes
(1997-07-15)
Lin, MF
;
Chuu, DS
;
Shung, KWK
;
電子物理學系
;
物理研究所
A metallic carbon nanotube could exhibit a low-frequency plasmon, while a semiconducting carbon nanotube or a graphite layer could not. This plasmon is due to the free carders in the linear subbands intersecting at the Fermi level. The low-frequency plasmon, which corresponds to the vanishing transferred angular momentum, belongs to an acoustic plasmon. For a smaller metallic nanotube, it could exist at larger transferred momenta, and its frequency is higher. Such a plasmon behaves as that in a one-dimensional electron gas (EGS). However, it is very different from the pi plasmons in all carbon nanotubes. Intertube Coulomb interactions in a metallic multishell nanotube and a metallic nanotube bundle have been included. They have a strong effect on the low-frequency plasmon. The intertube coupling among coaxial nanotubes markedly modifies the acoustic plasmons in separate metallic nanotubes. When metallic carbon nanotubes are packed in the bundle form, the low-frequency plasmon would change into an optical plasmon, and behave like that in a three-dimensional EGS. Experimental measurements could be used to distinguish metallic and semiconducting carbon nanotubes.
Low-frequency plasmons in metallic carbon nanotubes
(1997-07-15)
Lin, MF
;
Chuu, DS
;
Shung, KWK
;
電子物理學系
;
物理研究所
A metallic carbon nanotube could exhibit a low-frequency plasmon, while a semiconducting carbon nanotube or a graphite layer could not. This plasmon is due to the free carders in the linear subbands intersecting at the Fermi level. The low-frequency plasmon, which corresponds to the vanishing transferred angular momentum, belongs to an acoustic plasmon. For a smaller metallic nanotube, it could exist at larger transferred momenta, and its frequency is higher. Such a plasmon behaves as that in a one-dimensional electron gas (EGS). However, it is very different from the pi plasmons in all carbon nanotubes. Intertube Coulomb interactions in a metallic multishell nanotube and a metallic nanotube bundle have been included. They have a strong effect on the low-frequency plasmon. The intertube coupling among coaxial nanotubes markedly modifies the acoustic plasmons in separate metallic nanotubes. When metallic carbon nanotubes are packed in the bundle form, the low-frequency plasmon would change into an optical plasmon, and behave like that in a three-dimensional EGS. Experimental measurements could be used to distinguish metallic and semiconducting carbon nanotubes.
Magnetic force signal of vortex creation in type-II superconducting thin films
(1997-07-15)
Wei, JC
;
Horng, L
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
The possibility of the formation of a vortex in thin film due to the field of magnetic dipole moment when a point dipole is vertically approaching the surface of a thin film is discussed. Calculations are performed for certain discrete values of the critical position of the point dipole for creating the vortex in the thin film and the equilibrium positions of the vortex, both of which depend on the strength of magnetic dipole moment. The creation of a new single vortex in the thin film causes an abrupt change in the vertical force. (C) 1997 Elsevier Science B.V.
Electro-optical properties of aligned polymer dispersed liquid crystal films
(1997-07-21)
Wu, JJ
;
Wang, CM
;
光電工程學系
;
Department of Photonics
We study the electro-optical properties of polymer dispersed liquid crystal (PDLC) films with various kinds of alignment. These films are transparent in the electric field-on state and opaque in the field-off slate. Experimental data show that the contrast ratio of these aligned films can be higher than that of a usual type PDLC film. The relationship between the field-off state transmittance of such a PDLC film and the polarization of the incident light is discussed. The optical properties of such aligned films can be described by a theory based on Beer's law. (C) 1997 Published by Elsevier Science B.V.
Reactive compatibilization of PET and PPE blends by epoxy couplers
(1997-07-25)
Lo, DW
;
Chiang, CR
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
A commercially available tetrafunctional epoxy monomer was demonstrated to be an effective reactive compatibilizer for blends of poly( ethylene terephthalate) (PET) and polyphenylene ether (PPE). It requires about 10-20% by weight of a conventional reactive compatibilizer to achieve the same level of compatibilization in terms of domain size reduction and mechanical property improvement. This epoxy monomer is able to contact and react with PET and PPE simultaneously during high shear extruder blending to form the desirable PET-epoxy-PPE mixed copolymer. This mixed copolymer contains PET and PPE segments that tend to anchor at the interface to act as an efficient compatibilizer of the PET and PPE blends. (C) 1997 John Wiley & Sons, Inc.
Precrack hysteresis energy in determining polycarbonate ductile-brittle transition .4. Effect of strain rate
(1997-07-25)
Chiou, KC
;
Hsu, HC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Effect of deformation rate on the ductile-brittle transition behavior for polycarbonate (PC) with different molar mass, notch radius, and rubber content has been investigated. PC with higher molar mass, notch radius, or rubber-modification possesses a higher critical strain rate when the ductile-brittle transition occurs. Whether a notched specimen will fail in a ductile mode or a brittle mode is already decided before the onset of the crack initiation. If size of the precrack plastic zone exceeds a critical level prior to onset of crack initiation, the crack extension developed later will propagate within the plastic zone and result in a ductile mode fracture. The precrack elastic storage energy, the input energy subtracting the hysteresis energy, is the main driving force to strain the crack tip for crack initiation. The precrack hysteresis energy (directly related to the precrack plasticity) increases with the decrease of the applied strain rate. Therefore, the strain rate is also closely related to the size of the precrack plastic zone. If the strain rate is lower than the critical strain rate, the specimen is able to grow a precrack plastic zone exceeding the critical plastic zone and results in a ductile mode fracture. (C) 1997 John Wiley & Sons, Inc.
Precrack hysteresis energy in determining polycarbonate ductile-brittle transition .4. Effect of strain rate
(1997-07-25)
Chiou, KC
;
Hsu, HC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Effect of deformation rate on the ductile-brittle transition behavior for polycarbonate (PC) with different molar mass, notch radius, and rubber content has been investigated. PC with higher molar mass, notch radius, or rubber-modification possesses a higher critical strain rate when the ductile-brittle transition occurs. Whether a notched specimen will fail in a ductile mode or a brittle mode is already decided before the onset of the crack initiation. If size of the precrack plastic zone exceeds a critical level prior to onset of crack initiation, the crack extension developed later will propagate within the plastic zone and result in a ductile mode fracture. The precrack elastic storage energy, the input energy subtracting the hysteresis energy, is the main driving force to strain the crack tip for crack initiation. The precrack hysteresis energy (directly related to the precrack plasticity) increases with the decrease of the applied strain rate. Therefore, the strain rate is also closely related to the size of the precrack plastic zone. If the strain rate is lower than the critical strain rate, the specimen is able to grow a precrack plastic zone exceeding the critical plastic zone and results in a ductile mode fracture. (C) 1997 John Wiley & Sons, Inc.
Growth of CdMnS films by pulsed laser evaporation
(1997-07-30)
Chuu, DS
;
Chang, YC
;
Hsieh, CY
;
電子物理學系
;
Department of Electrophysics
High orientation CdMnS thin films were grown on glass substrate by the pulsed laser evaporation (PLE) technique. Pulsed Nd:Yag laser was used as the evaporation source. During the deposition, various pulsed laser powers, substrate temperatures and different ratios of high purity CdS and MnS powder were used. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) were employed to study the crystal structure, surface morphology and the Mn concentration of the as-deposited films. Absorption spectra were used to investigate the band gap of CdMnS films. It was found that the deviation of the band gap of CdMnS films from that of bulk CdS at room temperature depends on the concentration of Mn, The Raman spectra of our samples showed that the mixed mode behavior of transversal (longitudinal) frequency omega(T) (omega(L)) might exist in the CdMnS thin films. (C) 1997 Elsevier Science S.A.
A real-time poling approach for preparing second-order nonlinear optical polymer thin films
(1997-07-30)
Jou, JH
;
Wu, HS
;
Chiou, JF
;
Yang, PK
;
Huang, JY
A new real-time poling approach for preparing second-order nonlinear optical (NLO) polymer thin films is presented. The presented method may be conveniently applied to many polymer thin film systems without going through the complicated conventional synthesis and poling procedures. This method, which is proven in this work to be feasible experimentally, is done by simultaneously co-depositing a NLO active dye, disperse red 1 and two polyamide thin film forming monomers on a gold electrodes pre-patterned glass substrate while concurrently applying an electrical field for poling. A second harmonic generation (SHG) signal is detected from the resultant thin films at a very low poring field ranging from 0.01 to 0.1 MV/cm which increases in intensity as the poling field increases. (C) 1997 Elsevier Science S.A.
A real-time poling approach for preparing second-order nonlinear optical polymer thin films
(1997-07-30)
Jou, JH
;
Wu, HS
;
Chiou, JF
;
Yang, PK
;
Huang, JY
A new real-time poling approach for preparing second-order nonlinear optical (NLO) polymer thin films is presented. The presented method may be conveniently applied to many polymer thin film systems without going through the complicated conventional synthesis and poling procedures. This method, which is proven in this work to be feasible experimentally, is done by simultaneously co-depositing a NLO active dye, disperse red 1 and two polyamide thin film forming monomers on a gold electrodes pre-patterned glass substrate while concurrently applying an electrical field for poling. A second harmonic generation (SHG) signal is detected from the resultant thin films at a very low poring field ranging from 0.01 to 0.1 MV/cm which increases in intensity as the poling field increases. (C) 1997 Elsevier Science S.A.
Growth rate control of fumarase (fumA) gene expression in Escherichia coli
(1997-07-31)
Tseng, CP
;
Yu, CC
;
Hwang, SM
;
交大名義發表
;
National Chiao Tung University
Reactions of phenol sulfotransferase with nucleotides
(1997-07-31)
Yang, YS
;
Lin, ES
;
生物科技學系
;
Department of Biological Science and Technology
Reactions of phenol sulfotransferase with nucleotides
(1997-07-31)
Yang, YS
;
Lin, ES
;
生物科技學系
;
Department of Biological Science and Technology
A multicasting solution for ATM video applications
(1997-08-01)
Tsai, JM
;
Fang, HH
;
Lee, CY
;
交大名義發表
;
電子工程學系及電子研究所
This paper presents a multicasting solution for shared-buffer ATM switch, The cell duplicating function is performed by a one-to-many modified demur circuit, A shared multicast server is used to translate input multicast cells to find destination ports and corresponding routing information, By using link-list based ring structure, the multicast server can provide high speed (5 ns to search entry in 256-entry block in 0.8-mu m CMOS process) and cascadable multicast translating function, In addition, the channel complexity of multipoint-to-multipoint multicast applications can be reduced to N channels per N users. The shared-buffer controller is modified by adding controlling and scheduling functions for multicasting queues to process the multicast feature. Finally with the aid of the quality of service (QoS) management, this proposed solution provides multi-QoS for multicast cells to meet the needs of various video applications.
Thickness dependence of magnetic force acting on a magnetic dipole over a type-II superconducting thin film
(1997-08-01)
Yang, TJ
;
Wei, JC
;
Chen, JL
;
Horng, L
;
電子物理學系
The thickness dependence of the magnetic force acting on a point magnetic dipole over a superconducting thin film in the mixed state with a single vortex line is calculated by London theory. The magnetic force is decomposed into two parts, vertical and lateral components. Both vertical and lateral force components approach to the saturated value with increasing thickness when the thickness is much larger than the London penetration depth. A single vortex created in the thin film by the field of the magnetic dipole is also considered. The thickness dependence of the critical position of the point dipole for creating the first vortex line in the thin film is exploited and derived.
The design of a hybrid filter bank for the psychoacoustic model in ISO/MPEG phases 1,2 audio encoder
(1997-08-01)
Liu, CM
;
Lee, WC
;
資訊工程學系
;
Department of Computer Science
The ISO/MPEG phases 1 and 2 audio compression are receiving a wide range of applications. In the encoding process of MPEG, the psychoacoustic model exploits audio irrelevancy which is the key role to achieve high compression ratio without losing audio quality. However, the Fourier transform (FT) which has been used by the two psychoacoustic models suggested in standard draft requires high computational complexity, and hence leads to high hardware and software cost for real-time applications. This paper presents a new design named the hybrid filter bank to replace the FT. The hybrid filter bank can be integrated with the psychoacoustic models and provides a much lower complexity than the FT. Also, this paper shows that the hybrid filter is more suitable for the stereo coding and hence can provide a better quality for the intensity stereo coding, which is the key technology for the MPEG 1 to achieve near transparent quality lower than 96x2 kbits for two stereo channels.
Objective image quality measure for block-based DCT coding
(1997-08-01)
Liu, CM
;
Lin, JY
;
Wu, KG
;
Wang, CN
;
交大名義發表
The block-based discrete cosine transform (DCT) coding has been widely adopted in image or video compression standards, such as JPEG and MPEG. Such type of coding will produce a noticeable artifact known as the blocking effect at very low bit rate applications. In the literature, there have been various postprocessing methods proposed to reduce the blacking effect. However, there is no suitable objective criterion evaluating the effectiveness of these various methods. This paper presents a new objective measure evaluating the postprocessing methods. The proposed measure also provides an analytical result on the underlying sources of artifacts.