Browsing by Issue Date, starting with "2000-04-15"

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Carrier generation mechanisms for photoconductivity in conjugated polymers
(2000-04-15)
Meng, HF
;
Hong, TM
;
物理研究所
;
Institute of Physics
We study theoretically the origin of photoconductivity in conjugated polymers. The charge carriers are released when excitons dissociate through the deep levels within the semiconductor bandgap caused by either oxidation (carbonyl group) or structure defects. Our results explain the recent observations of the temperature-independent photocurrent in the sweep-out regime and the transient photocurrent at high excitation. The tightly bound exciton versus semiconductor band controversy on the photocarrier generation process is clarified.
Novel sidewall capping for degradation-free damascene trenches of low-permittivity methylsilsesquioxane
(2000-04-15)
Yeh, CF
;
Lee, YC
;
Su, YC
;
Wu, KH
;
Lin, CH
A low-permittivity organic dielectric, methylsilsesquioxane (MSQ), used as an interlevel dielectric is expected to reduce the parasitic capacitance in integrated circuit. However, MSQ film can he easily degraded during resist ashing after the film is etched with the damascene trenches being created. In this work, a novel sidewall capping technology is developed to solve the degradation issue. Prior to resist ashing, a high-quality, low-permittivity oxide him is selectively deposited onto the sidewalls of MSQ trenches using selective liquid-phase deposition. Experimental results demonstrate that the capping oxide can effectively protect the sidewalls of MSQ trenches from ashing-induced degradation.
Efficient terahertz radiation generation from a bulk InAs mirror as an intracavity terahertz radiation emitter
(2000-04-15)
Liu, ZL
;
Ono, S
;
Ohtake, H
;
Sarukura, N
;
Liu, TA
Terahertz (THz) radiation is generated efficiently from a bulk InAs mirror with a shallow incidence angle inside the cavity of a femtosecond, mode-locked Ti:sapphire laser self-started by a strained saturable Bragg reflector A magnetic field is also applied to the InAs mirror to enhance THz radiation.
Competitive adsorption of ferricyanide and ferrocyanide on gamma-Al2O3 surface
(2000-04-15)
Cheng, WP
;
Huang, C
;
Chien, YC
;
環境工程研究所
;
Institute of Environmental Engineering
In the past 3 decades, research has proven the significance of competitive adsorption in the equilibrium of pollutants between solid and liquid phases. However, studies on the competitive adsorption of complex ions are very limited in spite of its important role in transporting pollutants in the natural environment. The objective of this study is to derive the thermodynamic parameters of the competitive adsorption between ferricyanide and ferrocyanide from the modified Langmuir isotherm and the triple-layer model (TLM) to determine the location of adsorption. The effects of pH, temperature, and ion concentration on competitive adsorption onto gamma-Al2O3 were investigated. The results demonstrate that ferrocyanide is more competitive than ferricyanide. By comparing the derived K-app with K-int, we inferred that the adsorption of ferricyanide and ferrocyanide onto gamma-Al2O3 was achieved through outer-sphere complexation. The negative Delta H-3 indicated that the adsorption was exothermic, The positive entropy (Delta S degrees) was caused by the replacement and release of a greater number of smaller surface ions by adsorbed ferricyanide and ferrocyanide ions of larger size. (C) 2000 Academic Press.
Decay rate and renormalized frequency shift of superradiant excitons: Crossover from two-dimensional to three-dimensional crystals
(2000-04-15)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The superradiant decay rate and renormalized frequency shift of Wannier excitons in a semiconductor film of N layers are studied. It is found that both the decay rate and renormalized frequency shift show oscillatory dependence on layer thickness. The crossover from the superradiant exciton to the bulk polariton when varying N from 1 to infinity is also examined.
Water bath temperature control with a neural fuzzy inference network
(2000-04-16)
Lin, CT
;
Juang, CF
;
Li, CP
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Although multilayered backpropagation neural networks (BPNN) have demonstrated high potential in the nonconventional branch of adaptive control, its long training time usually discourages their applications in industry. Moreover, when they are trained on-line to adapt to plant variations, the overtuned phenomenon usually occurs. To overcome the weakness of the BPNN, we propose a neural fuzzy inference network (NFIN) in this paper suitable for adaptive control of practical plant systems in general, and for adaptive temperature control of a water bath system in particular. The NFIN is inherently a modified TSK (Takagi-Sugeno-Kang)-type fuzzy rule-based model possessing neural network's learning ability. In contrast to the general adaptive neural fuzzy networks, where the rules should be decided in advance before parameter learning is performed, there are no rules initially in the NFIN. The rules in the NFIN are created and adapted as on-line learning proceeds via simultaneous structure and parameter identification. The NFIN has been applied to a water bath temperature control system. As compared to the BPNN under the same training procedure, the control results show that not only can the NFIN greatly reduce the training time and avoid the overtuned phenomenon, but the NFIN also has perfect regulation ability. (C) 2000 Elsevier Science B.V. All rights reserved.
Annealing dynamics of nitrogen-implanted GaAs films investigated by current-voltage and deep-level transient spectroscopy
(2000-04-17)
Chen, JF
;
Wang, JS
;
Huang, MM
;
Chen, NC
;
電子物理學系
We present electrical data to show that, after nitrogen implantation, GaAs films become resistive after high-temperature annealing. The activation energies of the resistance are determined to be 0.34, 0.59, and 0.71 eV after annealing at 500, 700, and 950 degrees C, respectively. The increase in the activation energy with increasing annealing temperature can be explained by the results of traps detected in deep-level transient spectroscopy, where two traps at 0.32 and 0.70 eV are observed in the samples after annealing. The intensity of the trap at 0.32 eV is found to reduce by annealing. By comparing to the result of the x-ray diffraction, we suspect that this trap is related to the lattice-expansion defects. The trap at 0.70 eV is observed only in samples annealed at high temperatures. Since this trap contributes to the high-resistive effect, we believe that it is associated with the nitrogen ions. (C) 2000 American Institute of Physics. [S0003-6951(00)04716-1].
Synthesis and characterization of dendritic poly(ether imide)s
(2000-04-18)
Leu, CM
;
Chang, YT
;
Shu, CF
;
Teng, CF
;
Shiea, J
New dendritic poly(ether imide)s were synthesized by the convergent growth approach, using 1-(4-aminophenyl)-1,1-bis(4-hydroxyphenyl)ethane as the building block. The aromatic nucleophilic substitution of the building block with 3-nitro-N-phenylphthalimide led to the first-generation dendron with aminophenyl group at the focal point, which was subsequently reacted with 3-nitrophthalic anhydride to yield the dendritic wedge containing an activated nitro group; The resulting nitro functionality was allowed to react with the building block to give the second-generation dendron, which was then condensed with 3-nitrophthalic anhydride, followed by ring closure to re-form the phthalimide ring and restore a reactive nitro group. Through an aromatic nucleophilic substitution, the dendritic wedges with an activated nitro group were coupled to the polyfunctional core to form the dendritic macromolecules. Structures of the ether-imide dendrimers were fully characterized by use of a combination of techniques including H-1 NMR, C-13 NMR, IR, and mass spectrometry. The glass transition temperature of the dendrimers increased with molecular weight, and the variation was consistent with theoretical calculations. These dendritic poly(ether imide)s are soluble in various organic solvents and had a thermal stability comparable to linear poly(aryl ether imide)s.
Monte Carlo simulation of the motions associated with a single Rouse segment
(2000-04-22)
Lin, YH
;
Luo, ZH
;
應用化學系
;
Department of Applied Chemistry
The validity of the Monte Carlo simulation for studying the dynamics of a Rouse chain with a finite number of beads, N, is established by showing the close agreement between the simulation results and the analytical solutions for the time-correlation function of the end-to-end vector. Then, the Monte Carlo simulation is used to calculate the dynamic functions associated with the bond vector b(t) or direction u(t)=b(t)/(t) of an elastic dumbbell and a Rouse segment in a chain. The effect of chain connectivity on the motions of a single Rouse segment is studied. In particular, it is shown that the dynamic function < P-2[u(0). u(t)]>(2) over a wide dynamic range, which is the main region probed by the depolarized photon-correlation spectroscopy, is basically independent of the values of N greater than or equal to 8 in agreement with the experimental results. Furthermore, the line shape of the depolarized photon-correlation functions of the concentrated solutions (approximate to 60 wt. %) of polystyrene in cyclohexane at the theta point can be fully accounted for by including the effect of chain connectivity regardless of the crudeness of the Rouse segment relative to the chemical structure. From this study, the molecular weight for a Rouse segment of polystyrene in the concentrated solutions is estimated to be 1100, which is slightly larger than the values m=780-900 obtained for polystyrene in the melt state by other methods. (C) 2000 American Institute of Physics. [S0021-9606(00)50316-X].
管管聽荷花說法
(2000-04-22)
常堯
Purification and characterization of neutral sphingomyelinase from Helicobacter pylori
(2000-04-25)
Chan, EC
;
Chang, CC
;
Li, YS
;
Chang, CA
;
Chiou, CC
Phospholipase activities of human gastric bacterium, Helicobacter pylori , are regarded as the pathogenic factors owing to their actions on epithelial eel membranes. In this study, we purified and characterized neutral sphingomyelinase (N-SMase) from the superficial components of H. pylori strains for the first time. N-SMase was purified 2083-fold with an overall recovery of 37%. The purification steps included acid glycine extraction, ammonium sulfate precipitation, CM-Sepharose, Mono-Q, and Sephadex G-75 column chromatography. Approximate molecular mass for the native N-SMase was around 32 kDa. When N-omega-trinitrophenylaminol auryl sphingomyelin (TNPAL-SM) was used as a substrate, the purified enzyme exhibited a K-m of 6.7 mu M and a V-max of 15.6 nmol of TNPAL-sphingosine/h/mg of protein at 37 degrees C in 50 mM phosphate-buffered saline, pH 7.4. N-SMase I-caches optimal activity at pH 7.4 and has a pi of 7.5. The enzyme activity is magnesium dependent and specifically hydrolyzed sphingomyelin and phosphatidylethanolamine. The enzyme also exhibits hemolytic activity on human erythrocytes. According to Western blot analysis, a rabbit antiserum against purified N-SMase from H. pylori cross-reacted with SMase from Bacillus cereus. Sera from individuals with H, pylori infection but not uninfected ones recognizing the purified N-SMase indicated that it was produced in vivo. In enzyme linked immunosorbent assays, the purified N-SMase used as an antigen was as effective as crude protein antigens in detecting human antibodies to H. pylori.
故意花瓣牆
(2000-04-25)
管管
Signal bias removal with orthogonal transform for adverse Mandarin speech recognition
(2000-04-27)
Wang, WJ
;
Chen, SH
;
電信工程研究所
;
Institute of Communications Engineering
A new method for applying orthogonal transforms in signal bias removal (SBR) for adverse Mandarin speech recognition (MSR) is proposed. The orthogonal transform process is performed in a moving window manner to extract features from the input speech. Codewords are then obtained by matching high-order, bias-free features with pre-trained codebooks for bias estimation. The effectiveness of the method has been confirmed by an experiment involving multi-speaker adverse continuous MSR. Significant improvements in the recognition accuracy and computation time were achieved as compared with the conventional SBR method.
An ANOVA test for the equivalency of means under unequal variances
(2000-04-28)
Chen, SY
;
Chen, HJ
;
Ding, CG
;
經營管理研究所
;
Institute of Business and Management
In this paper, we present a two-stage test procedure for testing the hypothesis that the normal means are falling into a practically indifferent zone. Both the level and the power associated with the proposed test are controllable and are completely independent of the unknown variances. Relation to a single-stage procedure is discussed when the two-stage sampling procedure cannot be completely carried through. An example and tables needed for implementation are given. (C) 2000 Elsevier Science B.V. All rights reserved.
Deformation and fracture of Al2O3/Al-Zn-Mg-Cu metal matrix composites at room and elevated temperatures
(2000-04-30)
Wu, YL
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Al2O3/Al-Zn-Mg-Cu metal matrix composites containing 2.22 similar to 3.08 wt.% Mg in the matrix alloys have been fabricated by squeeze casting. The aim of the present study is to investigate the deformation and fracture behavior of the composites at RT (room temperature) and elevated temperature. Optical microscopy, scanning electron microscopy and image analysis were used to examine and to analyze the details of the microstructure and the fracture surface. Tensile tests were utilized to evaluate the mechanical properties from 25 to 400 degrees C. The yield stress (YS) values and UTS values for all the composites were larger than those of monolithic alloys. The UTS values for composites and monolithic alloys increased with increasing Mg content. Elevated temperature tests indicated a good strength retention for the composites; especially, UTS values of the composites showed an improvement of 18% exceeds that of the monolithic alloys from 200 to 300 degrees C. Significant dynamic strain aging occurred for composites; however, recovery and softening remained the dominant process for monolithic alloys in the range 25-300 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved.
Excitation of ''rotation'' collective modes in vortex lattice of clean type II superconductors
(2000-05-01)
Kasatkin, A
;
Rosenstein, B
;
電子物理學系
;
Department of Electrophysics
In superclean limit, the Magnus force on Abrikosov vortices is stronger than friction. Due to this nondissipative force, vortex segments rotate around pinning centers. Waves of such rotations under certain conditions are only weakly damped (not overdamped as is usually the case) and lead to resonances in ac response. Excitation of such waves by applied ac field near the surface is considered. Surface impedance, ac resistivity and magnetic permeability are calculated using elasticity theory of the vortex lattice. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
Feedforward active noise controller design in duets without independent noise source measurements
(2000-05-01)
Hu, JS
;
Lin, JF
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Feedforward control architectures have been widely used in active noise control systems to achieve broad-band noise reductions. The basic principle of the control algorithm requires that the feedforward signal, usually the noise source, be independent from the actuator's output. Failure to meet this requirement implies that the overall system contains an acoustic feedback loop and stability and robustness issues become important. This paper investigates this problem in a one-dimensional sound field (e.g., ducts) using a unidirectional sound wave as the feedforward signal. Controller design based on a distributed parameter model is studied. Several experiments are conducted to illustrate the design procedure as well as verify the effectiveness of broad-band noise reductions.
Design and analysis of traffic control for guaranteed services on the Internet
(2000-05-01)
Wang, PC
;
Chan, CT
;
Chen, YC
;
資訊工程學系
;
Department of Computer Science
Real-time communications services will be one of the most promising applications on the Internet. Real-time traffic usually utilizes a significant amount of resources while traversing through the network. To provide guaranteed service for delay-sensitive real-time applications, both resource reservation and effective traffic control are necessary. The resource reservation protocol (RSVP) was developed to deal with the former problem while various approaches have been proposed to solve the latter one. It is crucial for guaranteed services to maintain satisfactory performance through effective traffic control, which must be implemented in a feasible way and be able to work with RSVP. In this article, we present a flexible and effective traffic-control approach with a resource reservation scheme to accommodate delay-sensitive services on the Internet. We demonstrate that our approach features proven bounded end-to-end queueing delay for delay-sensitive applications and good resilience for resource allocation. In addition, our packet transmission discipline achieves significant improvement in end-to-end delay control.
A direction-based location update scheme with a line-paging strategy for PCS networks
(2000-05-01)
Hwang, HW
;
Chang, MF
;
Tseng, CC
;
資訊工程學系
;
Department of Computer Science
On the problem of location update and terminal paging, many schemes using ring-paging strategies have been proposed, However, sequentially paging the rings surrounding the mobile user's last updated location may cause large paging cost. In this letter, we propose a direction-based location update (DBLU) scheme using a line-paging strategy to reduce the paging cost. A moving direction identification mechanism using only simple computations detects the change of moving direction and updates the mobile's location. The numerical results show that our DBLU scheme achieves good performance when the paging cost is high.
Using NH3 plasma treatment to improve the characteristics of hydrogen silsesquioxane for copper interconnection application
(2000-05-01)
Chang, KM
;
Deng, IC
;
Yeh, SJ
;
Tsai, YP
;
電子工程學系及電子研究所
Hydrogen silsesquioxane, a material with low dielectric constant, can successfully suppress Cu diffusion without using a barrier metal by implementing a NH3 plasma treatment. Lower leakage current and better barrier capability can be achieved by hydrogen silsesquioxane film after NH3 plasma treatment. Having been treated with different plasma exposure rimes. this film can still maintain its original dielectric constant with few changes. The decrease in leakage current with increasing exposure time can be attributed to the following mechanisms: dielectric film becomes denser, dangling bonds are passivated, nitride film is formed on the hydrogen silsesquioxane, and the bulk damage of hydrogen silsesquioxane is annealed out. A thin layer of nitride formed on the dielectric is the cause for having better capability. The thickness of the nitride layer on hydrogen silsesquioxane is about 35 nm, and it can prevent the Cu diffusion/migration into the underlying dielectric. The role of our nitride film is to act as a passive diffusion barrier. (C) 2000 The Electrochemical Society. S0013-4651(99)10-093-4. All rights reserved.