Browsing by Issue Date, starting with "2001-03-15"

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Effects of thermal annealing on Ni/Ta/n-GaN Schottky diodes
(2001-03-15)
Chen, GL
;
Chang, FC
;
Chung, WC
;
Huang, BR
;
Chen, WH
The thermal effects of Ni/Ta/n-GaN Schottky diodes have been investigated for the first time using current-voltage, X-ray photoemission spectroscopy and Auger electron spectroscopy (AES) methods. Their barrier height is found to increase monotonously with increasing annealing temperature up to 800 degreesC. Preliminary results indicate that when a Th intermediate layer is added into the Ni/GaN diodes, it can prevent the metal-semiconductor interdiffusion and Ni accumulation adjacent to GaN substrate to a large extent so that a more thermally stable device can be obtained.
A new locality-based IP multicasting scheme for mobile hosts
(2001-03-15)
Tseng, CC
;
Chi, KH
;
Huang, TL
;
資訊工程學系
;
Department of Computer Science
Internet protocol multicasting is a mechanism widely used in the Internet to disseminate information. Multicast delivery paths may need to be frequently restructured along with host migrations, at the expense of nontrivial overhead or multicast latency. This paper presents a scheme with short multicast latency, while retaining acceptable overhead in adapting the delivery paths to mobile host locations. We exploit the locality in host movements and keep active the networks that mobile hosts have most recently visited. As long as hosts migrate within these active networks, multicast delivery paths can remain unchanged upon host movements. Performance results show that, compared with the best known proposal, our scheme is promising. (C) 2001 Elsevier Science B.V. All rights reserved.
Heterogeneous and homogeneous catalytic oxidation by supported gamma-FeOOH in a fluidized bed reactor: Kinetic approach
(2001-03-15)
Chou, SS
;
Huang, CP
;
Huang, YH
;
環境工程研究所
;
Institute of Environmental Engineering
Oxidation of benzoic,acid (BA) by H2O2 was performed with a never supported gamma -FeOOH catalyst in a circulating fluidized-bed reactor (CFBR).; This study focused mainly on determining the proportions of homogeneous catalysis and heterogeneous catalysis in this CFBR. Also studied herein was how pH, H2O2 concentration, and BA concentration affect the oxidation of BA. Experimental results indicate that the decomposition rate of H2O2 was proportional to its concentration and that the oxidation rate of BA depended on both H2O2 and BA concentrations. The change in the rate constant of heterogeneous catalysis by pH was described in terms of ionization fractions of surface hydroxyl group. From the mathematical deduction, we-can infer that the reaction rate associated with equivalent toF(III)OH(2)(+) is markedly higher than that with equivalent toF(III)OH. Conclusively, although heterogeneous catalysis contributes primarily to the oxidation of BA at pH 4.4-7.0, the homogeneous catalysis is of increasing importance below pH 4.4 because of the reductive dissolution of gamma -FeOOH.
Comparison of ultrathin CoTiO3 and NiTiO3 high-k gate dielectrics
(2001-03-15)
Pan, TM
;
Lei, TF
;
Chao, TS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
High-k cobalt-titanium oxide (CoTiO3) and nickel-titanium oxide (NiTiO3) were formed by directly oxidizing sputtered Co/Ti and Ni/Ti film. Al/CoTiO3/Si3N4/Si and Al/NiTiO3/Si3N4/Si capacitor structures were fabricated and measured. The effective dielectric constant (k value congruent to 45) with buffer layer for CoTiO3 is larger than that of NiTiO3. In addition, CoTiO3 depicts excellent electrical properties at the same time. This metal oxide thus appears to be a very promising high-k gate dielectric for future ultralarge scale integrated devices. (C) 2001 American Institute of Physics.
Field emission properties of two-layer structured SiCN films
(2001-03-15)
Tarntair, FG
;
Wu, JJ
;
Chen, KH
;
Wen, CY
;
Chen, LC
The electron emission characteristics of two-layer structured silicon carbon nitride (SiCN) films, which were composed of amorphous and nanocrystalline phases, were studied. Rutherford backscattering spectroscopy (RBS) was used to determine the composition of the SiCN film. The ratio (Si;C)/N of the SiCN film was kept at approximately 0.75, which is identical to that of Si3N4 him. High resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to investigate the bonding structures of the SiCN films. In comparison with silicon nitride films, the turn-on Voltage (for an emission current of 0.01 mA/cm(2)) of the SiCN films was rower and the emission current densities of the SiCN significantly enhanced. The promising emission properties of the SiCN film could be due to the unique two-layer structure wherein nanocrystalline SiCN was grown on top of the amorphous interlayer with sp(2) CN bond in the SiCN film. (C) 2001 Elsevier Science B.V. All rights reserved.
Temperature dependence of the penetration depth and effective dielectric constant measured by YBa2Cu3O7-delta microstrip ring resonators
(2001-03-15)
Zeng, HK
;
Juang, JY
;
Lin, JY
;
Wu, KH
;
Uen, TM
YBa2Cu3O7-delta(YBCO) superconducting ring resonators with a YBCO ground plane were successfully fabricated using double-side YBCO films deposited on LaAlO3 (LAO) substrates. The temperature dependent London penetration depth, Delta lambda = lambda (T) - lambda (5 K), was systematically studied by varying the oxygen content of the same resonator structure. For fully oxygenated case (delta = 0.05), the resonator exhibits a quality factor Q > 10(4) at 16 K, and Delta lambda (T) displays a linear behavior over a wide range of temperatures. With increasing delta (e.g. delta = 0.2, 0.4), although Delta lambda is still linear in temperature, the slope changes with increasing oxygen deficiency. The results suggest that, in the underdoped regime, the inelastic scattering of charged carriers may become increasingly prominent. From the effective dielectric constant obtained from the ring resonator the dielectric constant of the LAO substrate was estimated to be epsilon (r) congruent to 25.5 at 5 K and a frequency of about 3.6 GHz. (C) 2001 Elsevier Science B.V. All rights reserved.
ODCHP: a new effective mechanism to maximize parallelism of nested loops with non-uniform dependences
(2001-03-15)
Pean, DL
;
Chen, C
;
資訊工程學系
;
Department of Computer Science
There are many methods for nested loop partitioning. However, most of them perform poorly when partitioning loops with nonuniform dependences. This paper proposes a generalized and optimized loop partitioning mechanism to exploit parallelism from nested loops with non-uniform dependences. Our approach, based on dependence convex theory, will divide the loop into variable size partitions. Furthermore, the proposed algorithm partitions a nested loop by using the copy-renaming and the optimized partitioning techniques to minimize the number of parallel regions of the iteration space. Consequently, it outperforms the previous partitioning mechanisms of nested loops with non-uniform dependences. Many optimization techniques are used to reduce the complexity of the algorithm. Compared with other popular techniques, our scheme shows a dramatic improvement in the preliminary performance results. (C) 2001 Elsevier Science Inc. All rights reserved.
Effect of substrate concentration on bioleaching of metal-contaminated sediment
(2001-03-19)
Chen, SY
;
Lin, JG
;
環境工程研究所
;
Institute of Environmental Engineering
The remediation of metal-contaminated sediment wits studied using the bioleaching process with a mixed culture of sulfur-oxidizing bacteria. The effects of substrate concentration (elemental sulfur) on sediment acidification, sulfur oxidation and metal solubilization from contaminated sediment during the bioleaching process were investigated with free-cell suspensions. Sulfur concentration greater than 0.5% (w/v) was found to be inhibitory to bacterial activity and metal solubilization from sediment. The sulfate production was well described by a substrate inhibition expression and Haldane's equation. In addition, an empirical equation related to sulfur concentration was also used to describe the metal solubilization in the bioleaching process. (C) 2001 Elsevier Science B.V. All rights reserved.
Reactive compatibilization of PP/PBT blends by a mixture of PP-g-MA and epoxy resin
(2001-03-21)
Shieh, YT
;
Liao, TN
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
In this study, dual compatibilizers composed of the commercially available maleic anhydride-grafted polypropylene (PP-MA) and a multifunctional epoxy resin were demonstrated to effectively compatibilize the immiscible and incompatible blends of PP and poly(butylene terephthalate) (PBT). The PP-MA with a low MA content is totally miscible with PP to make the PP phase quasi-functionalized, so that the multifunctional epoxy has the chance to react with PBT and PP-MA simultaneously to form PP-MA-co-epoxy-co-PBT copolymers at the interface. These desired copolymers are able to anchor along the interface and serve as efficient compatibilizers. The compatibilized blends, depending on the quantity of dual compatibilizers employed, exhibit higher viscosity, finer phase domain, and improved mechanical properties. Epoxy does not show compatibilization effects for the PP/PBT blends without the presence of PP-MA in the blends. (C) 2001 John Wiley & Sons, Inc.
Disproving a conjecture on planar visibility graphs
(2001-03-28)
Chen, CY
;
Wu, KP
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應用數學系
;
Department of Applied Mathematics
Two vertices A and B of a simple polygon P are (mutually) visible if AB does not intersect the exterior of P. A graph G is a visibility graph if there exists a simple polygon P such that each vertex of G corresponds to a vertex of P and two vertices of G are joined by an edge if and only if their corresponding vertices in P are visible, No characterization of visibility graphs is available. Abello, Lin and Pisupati conjectured that every hamiltonian maximal planar graph with a 3-clique ordering is a visibility graph. In this paper, we disprove this conjecture. (C) 2001 Elsevier Science B.V. All rights reserved.
Structural identification from ambient vibration measurement using the multivariate AR model
(2001-03-29)
Huang, CS
;
土木工程學系
;
Department of Civil Engineering
A procedure for identifying the dynamic characteristics of a structural system using the multivariate AR (ARV) model is presented in the paper. A least-squares approach to determine the coefficient matrices of the ARV model is proposed, which is a modification of the traditional one. The modification is based on the equivalence between the correlation function matrix for the responses of a linear system subjected to white-noise input and the deterministic free vibration responses of the system. Then, the dynamic characteristics of the system are evaluated directly from the coefficient matrices of the ARV model by adopting the concept behind Ibrahim's system identification technique. The superiority of the proposed procedure over the traditional one is demonstrated through numerical studies on a six-story shear building. Finally, the present identification procedure is applied to identify the dynamic characteristics of a three-span highway bridge from its ambient vibration responses subjected to traffic flow. The validity of the present procedure is confirmed by the excellent agreement between the identified results obtained in the present study and those obtained from an impulse test. (C) 2001 Academic Press.
Origin of size effect on superconductivity in (R-0.8 Pr-0.2)Ba2Cu3O7 studied by soft X-ray absorption spectroscopy
(2001-03-30)
Chen, JM
;
Nachimuthu, P
;
Lin, JY
;
Hong, IP
;
Chang, CF
O K-edge X-ray absorption near-edge structure (XANES) spectroscopy of (R-0.8 Pr-0.2)Ba2Cu3O7 (R = Y, Tm, Dy, Gd, Eu and Sm) has been performed to investigate the dependence of hole distribution on ionic size of the R3+ ions. Near the O Is absorption edge, pre-peaks at similar to 527.8 and similar to 528.5 eV are assigned to transitions into O 2p hole states located in the CuO3 ribbons and CuO2 planes, respectively. As deduced from O K-edge X-ray absorption spectra, the hole concentrations in the CuO2 planes decrease monotonically with increasing ionic size of the rare-earth elements. The present XANES results clearly demonstrate that the suppression of superconductivity in (R1-x Pr-x)Ba2Cu3O7 With ionic radius of the R3+ ions results predominantly from the hole-depletion effect. (C) 2001 Elsevier Science B.V. All rights reserved.
Exact Green function of Aharonov-Bhm billiard system
(2001-03-30)
Chuu, DS
;
Lin, DH
;
電子物理學系
;
Department of Electrophysics
The exact Green functions of the relativistic spherical quantum Aharonov-Bohm billiard systems in two- and three-dimensional spaces are given by the path integral approach. The transcendental equations for determining the energy spectra are discussed.
Discrepancies between different response parameters in batch and continuous algal toxicity tests
(2001-03-30)
Chao, MR
;
Chen, CY
;
環境工程研究所
;
Institute of Environmental Engineering
The test sensitivities and reproducibilities based on different response endpoints (cell density and total cell volume) were compared using both bath and continuous algal toxicity tests. Parameters related to algal cell density are found to be more sensitive and reproducible than total cell volume which bears a direct correlation to algal biomass or dry weight. The magnitude of differences in the median effective concentration values could be upto six folds. The main cause for the above discrepancies is because the cell density and total cell volume are two response endpoints reflecting the degree of inhibition on the binary fission mechanism and overall photosynthesis, respectively. At low toxicant concentrations, the inhibitory effect is primarily on the cell division rather than on the cellular photosynthesis. Thus, more severe toxic effects are expected to be observed based on the cell density than the total cell volume. The results of this study clearly demonstrate that sensitivity and reproducibility can be significantly improved if response parameters are calculated based on the cell density. Traditionally, cell density data are often converted into biomass before assessing the effects of toxicants. This procedure may not be necessary and may reduce the test sensitivity. (C) 2001 Elsevier Science B.V. All rights reserved.
Luminescence intensity reduction in Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy
(2001-04-01)
Shu, CK
;
Chen, HH
;
Lee, WH
;
Pan, YC
;
Huang, HY
Photoluminescence dynamic responses of a heavily Mg-doped GaN grown by metalorganic chemical vapor phase epitaxy have been investigated. As the probe power density increased from 2.5 to 925 W/cm(2), a Mg-related emission band shifted from 2.82 to 3.16 eV revealing characteristics of donor-acceptor pair recombination. The intensity evolution also showed slow decay that suggests the metastable emission behavior. A simple potential barrier model was proposed to occur between the Mg related deep levels and common Mg acceptor level, which impedes electron relaxation and thus slows down the luminescence decay. From the variation of decay time constant with temperature. a barrier energy was deduced to be about 69 meV which is very close to the electrical result of 68 meV.
Numerical and experimental study of internal flow field for a carbon fiber tow pneumatic spreader
(2001-04-01)
Chen, JC
;
Chao, CG
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材料科學與工程學系
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Department of Materials Science and Engineering
In this study, a three-dimensional (3-D) mathematical model of a fiber pneumatic spreader was successfully developed in the physical phenomena of the internal flow field by a far-field treatment at boundary conditions. The 3-D numerical analysis was carried out on incompressible fluid flows in the pneumatic spreader by using finite volume method combined with the k-epsilon turbulence model which solves Reynolds-averaged Naiver-Stokes equations. Characteristics of the flow field in the spreader at different service conditions are investigated by velocity and pressure distributions. Comparisons of numerical results with measured velocity and pressure distributions were made to determine the accuracy of the employed method. A good agreement was found in both qualitative and quantitative analysis. Fibers were spread on 1:1-scale model of the pneumatic spreader at various fiber transporting rates and air flow rates. Photography techniques were simultaneously used to record the procedures of fibers spread. The carbon fiber tow was easily spread out at service conditions. The performance was better than prior studies in one-dimensional orifice formulation. The results revealed details of the fiber spreading processes. Agreement among those results validated the assumptions inherent to the computational calculation and gave confidence to more complex geometries as well as flow fields. In other words, the use of numerical analysis in the internal flow field was useful for the fiber pneumatic spreader design.
Possibilistic programming in production planning of assemble-to-order environments
(2001-04-01)
Hsu, HM
;
Wang, WP
;
工業工程與管理學系
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Department of Industrial Engineering and Management
For the sake of alleviating the influences of demand uncertainty in assemble-to-order (ATO) environments, the strategies of regulating dealers' forecast demands, determining appropriate safety stocks, and deciding the numbers of key machines are usually adopted by manufacturers. In this paper, we propose a possibility linear programming model to manage these production planning problems. The proposed model accomplishes forecasting adjustments, material management, and production activities. Because of price fluctuations, material obsolescence, and the time value of, capital. the ambiguity of cost is considered in the objective function of the model. We substituted the fuzzy objective function with three crisp objectives: minimizing the most possible cost, maximizing the possibility of obtaining lower cost, and minimizing the risk of obtaining higher cost. Zimmermann's fuzzy programming method is then applied for achieving an overall satisfactory compromise solution. Finally, an example is given to illustrate our model. (C) 2001 Elsevier Science B.V. All rights reserved.
Integration of thin film transistor controlled carbon nanotubes for field emission devices
(2001-04-01)
Cheng, HC
;
Hong, WK
;
Tarntair, FG
;
Chen, KJ
;
Lin, JB
A new field emission device composed of carbon nanotubes and a thin film transistor (TFT) has been successfully demonstrated to significantly improve emission stability. Carbon nanotubes are directly integrated in the drain region of the TFT and the emission current from the carbon nanotubes is controlled via the TFT drain current. The fluctuation of the emission current of the TFT-controlled carbon nanotubes can be suppressed to less than 2%, below the fluctuation of uncontrolled carbon nanotubes. The novel field emission device exhibits low-voltage controllability, good emission stability, and structural simplicity, making it promising for application to future field-emission display. (C) 2001 The Electrochemical Society.
A framework for temporal similarity measures of content-based scene retrieval
(2001-04-01)
Shan, MK
;
Lee, SY
;
資訊科學與工程研究所
;
Institute of Computer Science and Engineering
The distinguished features of video retrieval lie in the similarity measures and content-based retrieval. Most research on content-based video retrieval represents the content of video as a set of frames, leaving out the temporal ordering of frames in the shot. In this paper, the similarity measures of video content are investigated. We propose a series of similarity measures based on the similarity of frame sequence which take temporal ordering into consideration. All the algorithms corresponding to the similarity measures are based on the approach of dynamic programming. (C) 2001 Published by Elsevier Science B.V.
Ordered lookup with bypass matching for scalable per-flow classification in layer 4 routers
(2001-04-01)
Lin, YD
;
Wei, HY
;
Wu, KJ
;
資訊工程學系
;
Department of Computer Science
In order to provide different service treatments to individual or aggregated hows, layer 4 routers in Integrated Services networks need to classify packets into different queues. The classification module of layer 4 routers must be fast enough to support gigabit links at a rate of millions of packets per second. In this work, we present a new software method OLBM to lookup multiple fields of a packet, in a dynamically pre-defined order, against the classification database. This algorithm also uses a technique called bypass matching and can classify packets at a rate of well over one million packets per second while scaling to support more than 300k flows. Complexity analysis and experiment measurements are also presented in this study. (C) 2001 Elsevier Science B.V. All rights reserved.