Browsing by Issue Date, starting with "2001-11-15"

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Reschedulable-Group-SCAN scheme for mixed real-time/non-real-time disk scheduling in a multimedia system
(2001-11-15)
Chang, HP
;
Chang, RI
;
Shih, WK
;
Chang, RC
;
資訊工程學系
Real-time disk scheduling is important for time-critical multimedia applications. Previous approaches, such as SCAN-earliest deadline first (EDF) or DM-SCAN, applied the SCAN scheme to reschedule service sequence of input tasks to reduce tasks' service time. However, they required the input to be in EDF order. In DM-SCAN, a deadline modification scheme was employed to obtain a pseudo-EDF sequence from non-EDF ordered input tasks. Because the modified deadlines were smaller than the original ones, number of tasks that could be rescheduled is decreased and thus data throughput is reduced. In this paper, we propose Reschedulable-Group-SCAN (RG-SCAN), a new real-time disk scheduling algorithm using the concept of Reschedulable-Group (R-Group). Differing from previous approaches, RG-SCAN has no limitation on the input task's sequence. In addition, by exploiting the service time's reduction after rescheduling in each R-Group, RG-SCAN has been extended to serve mixed real-time and non-real-time workloads. As shown in experimental results. our approach can support more tasks than DM-SCAN, both real-time and non-real-time. Additionally, our approach can provide larger data throughput and offer better response time to non-real-time tasks. For example, given 30 random-generated real-time tasks, the number of non-real-time tasks that can be supported by RG-SCAN is 1.3 times that supported by DM-SCAN. In addition, our data throughput is 1.1 times DM-SCAN's. (C) 2001 Elsevier Science Inc. All rights reserved.
Two interacting electrons in a vertical quantum dot with magnetic fields
(2001-11-15)
Lin, JT
;
Jiang, TF
;
物理研究所
;
Institute of Physics
We present a numerical exact calculation for the energy spectra of two electrons in a finite height cylindrical quantum dot in details by a coupled-channel method. The electron correlation energy for various geometry of quantum dots, with and without applied magnetic fields, for singlet and triplet states a-re investigated. The magnitude of magnetic field for transition of the spin-singlet ground state and the spin-triplet excited state is compared with experimental result. The study shows significant contributions due to the spreading of electron density distribution along the vertical direction. In contrast to the planar circular disk model, the study will be useful for some realistic quantum dots.
Bianchi type-I space and the stability of the inflationary Friedmann-Robertson-Walker solution
(2001-11-15)
Kao, WF
;
物理研究所
;
Institute of Physics
A stability analysis of the Bianchi type-I universe in pure gravity theory is studied in detail, We first derive the nonredundant field equation of the system by introducing the generalized Bianchi type-I metric. This nonredundant equation reduces to the Friedmann equation in the isotropic limit. It is shown further that any unstable mode of the isotropic perturbation with respect to a de Sitter background is also unstable with respect to anisotropic perturbations. The implications of the choice of physical theories are discussed in detail in this paper.
Synthesis and characterization of new hyperbranched poly(aryl ether oxadiazole)s
(2001-11-15)
Wu, FI
;
Shu, CF
;
應用化學系
;
Department of Applied Chemistry
A new AB(2) monomer was synthesized for use in the preparation of a hyperbranched poly(aryl ether oxadiazole) with terminal phenol functionality. The AB2 monomer contains two phenolic groups and a single aryl fluoride group that is activated toward nucleophilic displacement by the attached oxadiazole ring. The nucleophilic substitution of the fluoride with the phenolate groups led to the formation of an ether linkage. Subsequently, a hyperbranched poly(aryl ether oxadiazole) having approximately a 44% degree of branching, as determined by a combination of model compound studies and H-1 NMR, was obtained. The terminal phenolic groups underwent facile functionalization, furnishing hyperbranched polymers with a variety of functional chain ends. The nature of the chain-end groups had a significant influence on the physical properties of the polymers, such as the glass-transition temperature and their solubility. (C) 2001 John Wiley & Sons, Inc.
Computer simulation of electron energy levels for different shape InAs/GaAs semiconductor quantum dots
(2001-11-15)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
電子工程學系及電子研究所
A computational technique for the energy levels calculation of an electron confined by a 3D InAs quantum dot (QD) embedded in GaAs semiconductor matrix is presented. Based on the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, a finite height hard-wall 3D confinement potential, and the Ben Daniel-Duke boundary conditions, the problem is formulated and solved for the disk, ellipsoid, and conical-shaped InAs/GaAs QDs. To calculate the ground state and first excited state energy levels, the nonlinear 3D Schrodinger is solved with a developed nonlinear iterative algorithm to obtain the final self-consistent solutions. In the iteration loops, the Schrodinger equation is discretized with a nonuniform mesh finite difference method, and the corresponding matrix eigenvalue problem is solved with the balanced and shifted QR method. The proposed computational method has a monotonically convergent property for all simulation cases. The computed results show that for different quantum dot shapes, the parabolic band approximation is applicable only for relatively large dot volume. For the first excited states the non-parabolicity effect also has been found to be stronger than it at ground state. The QD model and numerical method presented here provide a novel way to calculate the energy levels of QD and it is also useful to clarify principal dependencies of QD energy states on material band parameter and QDs size for various QD shapes. (C) 2001 Elsevier Science B.V. All rights reserved.
Bound states of L- or T-shaped quantum wires in inhomogeneous magnetic fields
(2001-11-15)
Lin, YK
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The bound-state energies of L- or T-shaped quantum wires in inhomogeous magnetic fields are found to depend strongly on the asymmetric parameter alpha = W-2/W-1, i.e, the ratio of the arm widths. Two effects of magnetic field on bound-state energies of the electron are obtained. One is the depletion effect, which purges the electron out of the OQD system. The other is to create an effective potential due to quantized Landau levels of the magnetic field. The bound-state energies of the electron in L- or T-shaped quantum wires are found to depend quadratically (linearly) on the magnetic field in the weak- (strong-) field region and are independent of the direction of the magnetic field. A simple model is proposed to explain the behavior of the magnetic dependence of the bound-state energy in both weak- and strong-magnetic field regions.
Eigenvalue problems for one-dimensional discrete Schrodinger operators with symmetric boundary conditions
(2001-11-19)
Juang, J
;
Lin, WW
;
Shieh, SF
;
應用數學系
;
Department of Applied Mathematics
In this paper, we investigate the one-dimensional discrete Schrodinger equation with general, symmetric boundary conditions. Our results primarily concern the number of energy states lying in the wells.
Ab initio study of the structural and optical properties of orthorhombic ternary nitride crystals
(2001-11-19)
Huang, JY
;
Tang, LC
;
Lee, MH
;
光電工程學系
;
Department of Photonics
The structural, optical and mechanical properties of orthorhombic ternary nitride crystals have been analysed theoretically with first-principles calculation. Our results indicate that these nitrides possess fairly large optical bandgap (4-6 eV), second-order nonlinear optical susceptibility (13-18 pm V-1), and bulk modulus 170-370 GPa. Therefore these materials could be useful for optical and protective coating applications. Our analysis with the band-by-band and atomic species projection techniques not only yields useful information about material properties, but also provides deep insight into the fundamental understanding of the mechanical and optical properties of orthorhombic ternary nitrides.
Simultaneous mode locking in a diode-pumped passively Q-switched Nd : YVO4 laser with a GaAs saturable absorber
(2001-11-20)
Chen, YF
;
Huang, KF
;
Tsai, SW
;
Lan, YP
;
Wang, SC
Simultaneous mode locking and Q switching is accomplished in a diode-pumped Nd:YVO4/GaAs laser. The average output power is similar to2.0 W at 10.6-W absorbed pump power, and the repetition rate of the Q-switched pulse is similar to 120 kHz. The mode-lo eked pulse inside the Q-switched pulse has a repetition rate of similar to 148 MHz, and its average duration is estimated to be similar to 100 ps. (C) 2001 Optical Society of America.
Observations of segregation of Al in AlGaN alloys
(2001-11-23)
Chang, L
;
Lai, SK
;
Chen, FR
;
Kai, JJ
;
材料科學與工程學系
Transmission electron microscopy has been used to characterize Al segregation in Al0.1Ga0.9N and Al0.3Ga0.7N alloys grown by metal organic chemical vapor deposition on 6H-SiC. It has been found that an interlayer of AlGaN alloy with much higher Al content was formed at first, followed by normal growth of nominal composition of AlGaN alloy. In Al0.1Ga0.9N and Al0.3Ga0.7N films. dislocation lines were also found to have more Al segregated than those regions free of dislocations in the matrix. Furthermore, it shows that more Al atoms segregate to an edge dislocation than to a screw one.
The real inventor of the monitor concept: A short note to correct the SP&E paper entitled 'An enhanced thread synchronization mechanism for Java'
(2001-11-25)
Chiao, HT
;
Yuan, SM
;
資訊工程學系
;
Department of Computer Science
Efficient green organic light-emitting diodes with stericly hindered coumarin dopants
(2001-11-26)
Chen, CH
;
Tang, CW
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We have discovered two stericly hindered green coumarin derivatives which showed significantly better thermal stability and overall electroluminescence (EL) performance than those of the corresponding 3-(2-benzothiazolyl)-7-(diethylamino)-2H-1-benzopyran-2-one (C-6) and 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl- 2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano[6,7, 8-ij] quinolizin-11-one (C-545T). The strategic incorporation of bulky spacer t-butyl groups in these dopants considerably delays the onset of concentration quenching. In particular, 10-[2(5,7-di-t-butyl)benzothiazolyl]-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo-[l]pyrano[6,7,8-ij]quinolizin-11-one (C-545TB) with its superb thermal stability (T-g=142 degreesC; T-d=327 degreesC), high luminance efficiency (similar to 13 cd/A), good Commission Interationale d'Eclairage (CIE) coordinates (x=0.30; y=0.64) and a nearly flat EL efficiency dependence on drive current stands out as one of the best choice of green dopants for use in the passive-matrix organic light-emitting diode displays. (C) 2001 American Institute of Physics.
Simultaneous observation of second-harmonic emission and three-photon excited photoluminescence from hybrid vapor phase epitaxy-grown GaN film
(2001-12-01)
Lee, CK
;
Kao, FJ
;
Wang, SC
;
Pan, CL
;
光電工程學系
Nonlinear optical properties of the undoped hybrid vapor phase epitaxy-grown (GaTN film sample) were investigated and analyzed using a tunable femtosecond laser as an excitation source. As the laser wavelength was tuned from 762-796 nm, the sample emitted signals corresponding to the second-harmonic wavelength from 381-398 nm with a quadratic power dependence. A strong three-photon-process-related signal at 367 nm with cubic power dependence was simultaneously observed for the first time.
Preparation and crystallization behavior of syndiotactic polystyrene-clay nanocomposites
(2001-12-01)
Tseng, CR
;
Wu, JY
;
Lee, HY
;
Chang, FC
;
應用化學系
Syndiotactic polystyrene/modified-clay nanocomposites have been prepared by solution blending by mixing pure s-PS and organophilic clay with adsorbed cetyl pyridium chloride (CPC) in dichlorobenzene. The dispersability of the clay in syndiotactic polystyrene/modified-clay nanocomposites was studied using X-ray and transmission electron microscopy. The clay is well dispersed into the s-PS matrix using solution blending with scale in 1-2 nm or in a few tenths similar to 100 nm depending on surfactant treatment. The CPC is partially compatible with s-PS and allows syndiotactic polystyrene chains intercalating into clay layers. The crystallization behavior of alpha- and beta -crystals for syndiotactic polystyrene nanocomposite has been thoroughly examined using the Fourier transform infrared and differential scanning calorimetry. Our results further demonstrate that the presence of the clay plays a vital role in facilitating the formation on the thermodynamically more favorable beta form crystal when the s-PS is melt- or cold-crystallized. (C) 2001 Elsevier Science Ltd. All rights reserved.
Synthesis and physical properties of linear and branch phenoxies
(2001-12-01)
Chen, JR
;
Li, YS
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
Linear and branch phenoxies have been synthesized by reacting difunctional epoxy and diphenol or triphenol monomer, using phosphonium salt as the catalyst. The reaction kinetics is analyzed by the ASTM E 698 method, which is suitable for a first order reaction system. The bulky structure of the bisphenol Z moiety retards the reaction; therefore, the reaction temperature required is higher- at 200 degreesC, compared to 190 degreesC for the bisphenol A based system. The introduction of a branch structure increases both molecular weight and the polydispersity of the phenoxy. A slightly branched structure tends to increase the distance between the polymer chains and results in a lower shear viscosity for easier processing. A higher branch results in light crosslinking and decreases the mobility of the polymer. The branch structure has a negligible effect on its glass transition temperature because the average distance between branches is substantially longer than the critical mainchain length for T-1's Brownian motion. The 100/1 (bisphenol/ trisphenol) system has the lowest viscosity, but its mechanical properties and the gas permeation properties are poorer than those of the others. The bisphenol Z based phenoxy shows superior mechanical properties, higher T-g, lower coefficient of thermal expansion, and lower gas permeation properties than the corresponding bisphenol A based phenoxy because of the steric hindrance structure of the bisphenol Z moiety.
Design on the low-capacitance bond pad for high-frequency I/O circuits in CMOS technology
(2001-12-01)
Ker, MD
;
Jiang, HC
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Chang, CY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new structure design of bond pad is proposed to reduce its parasitic capacitance in general CMOS processes without extra process modification. The proposed bond pad is constructed by connecting multilayer metals and inserting additional diffusion layers into the substrate below the metal layers. The metal layers except top metal layer are designed with special patterns, which have smaller area than that in the traditional bond pad. Both the additional diffusion layers and patterned metal layers are used to reduce the parasitic capacitance of bond pad. An experimental test chip has been designed and fabricated to investigate the reduction of parasitic capacitance of the bond pad. The bonding reliability tests on the fabricated bond pad, including the ball-shear and wire-pull tests, are also used to verify the bonding adhesion. The experimental results show that the proposed low-capacitance bond pad has a capacitance less than 50% of that in the traditional bond pad. The new proposed bond pads can also keep the same good bonding reliability as that of a traditional bond pad.
The effects of low-pressure rapid thermal post-annealing on the properties of (Ba,Sr)TiO3 thin films deposited by liquid source misted chemical deposition
(2001-12-01)
Yang, MJ
;
Chien, CH
;
Leu, CC
;
Zhang, RJ
;
Wu, SC
The technique of low-pressure post-annealing process with additional second-step annealing for preparation of the Ba0.7Sr0.3TiO3 thin films deposited by liquid source misted chemical deposition (LSMCD) has been proposed. With employing this annealing procedure, the leakage current density can be significantly eliminated by approximately one order of magnitude at 2 V. In particular, process temperature can be reduced from 650 degreesC to 600 degreesC without suffering deteriorated crystallinity issue, which is identified by both C-V measurement and X-ray diffraction spectrum. The extracted dielectric constant is 310 with extreamly low loss tangent of 0.005. The spectrum of atomic force microscopy (AFM) shows that this low-pressure process results in smoother surface topography. Moreover, thermal desorption spectrums assure that less residual organics and contaminations were left after low pressure post-annealing. This may be one of the reasons for lowering crystallization temperature and the improved electrical properties.
Effects of yttrium codoping on photoluminescence of erbium-doped TiO2 films
(2001-12-01)
Ting, CC
;
Chen, SY
;
Hsieh, WF
;
Lee, HY
;
材料科學與工程學系
Er3+-Y3+ codoped TiO2 films were prepared on a fused silica substrate by the sol-gel process. The effect of Y3+ codoping on the similar to1.54 mum photoluminescence (PL) properties of Er3+-doped TiO2 films are investigated. Enhancement of PL properties due to Y3+ codoping by a factor of 10 for intensity and of 1.5 for the full width at half maximum in comparison with the Er3+-Al3+ codoped SiO2 system has been observed in the film annealed at Er3+:Y3+:Ti4+=5:30(similar to 50):100. Extended x-ray absorption fine structure measurements show that the local chemical environment of Er3+ ions in the Er3+-Y3+ codoped TiO2 films is similar to that in Er2O3. The average spatial distance between Er3+ ions is enlarged due to the partial substitution of Y3+ for Er3+ ions in the Er2O3-like local structure. It is believed that the more intense PL emission of the Er3+-Y3+ codoped TiO2 films can be attributed to the better dispersion and distorted local structure of Er3+ ions in the TiO2 host matrix by yttrium codoping. (C) 2001 American Institute of Physics.
Unsupervised texture segmentation by determining the interior of texture regions based on wavelet transform
(2001-12-01)
Lee, KL
;
Chen, LH
;
資訊工程學系
;
Department of Computer Science
Traditional approaches for texture segmentation via wavelet transform usually adopt textural features to achieve segmentation purposes. However, for a natural image, the characteristics of the pixels in a texture region are not similar everywhere from a global viewpoint, and over-segmentation often occurs. To deal with this issue, an unsupervised texture segmentation method based on determining the interior of texture regions is proposed. The key idea of the proposed method is that if the pixels of the input image can be classified into interior pixels (pixels within a texture region) and boundary ones, then the segmentation can be achieved by applying region growing on the interior pixels and reclassifying boundary pixels. Based on the fact that each pixel P within a texture region will have similar characteristics with its neighbors, after applying wavelet transform, pixel P will have similar response with its neighbors in each transformed subimage. Thus, by applying a multilevel thresholding technique to segment each subimage into several regions, pixel P and its neighbors will be assigned to the same region in most subimages. Based on these segmented results, an interior pixels finding algorithm is then provided to find all interior pixels of textural regions. The algorithm considers a pixel which is in the same region as its neighbors in most subimages as an interior pixel. The effectiveness of this method is proved by successfully segmenting natural texture images and comparing with other methods.
Composition and retrieval of visual information for video databases
(2001-12-01)
Cheng, PJ
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
This paper presents a new visual aggregation model for representing visual information about moving objects in video data. Based on available automatic scene segmentation and object tracking algorithms, the proposed model provides eight operations to calculate object motions at various levels of semantic granularity. It represents trajectory, color and dimensions of a single moving object and the directional and topological relations among multiple objects over a time interval. Each representation of a motion can be normalized to improve computational cost and storage utilization. To facilitate query processing, there are two optimal approximate matching algorithms designed to match time-series visual features of moving objects. Experimental results indicate that the proposed algorithms outperform the conventional subsequence matching methods substantially in the similarity between the two trajectories. Finally, the visual aggregation model is integrated into a relational database system and a prototype content-based video retrieval system has been implemented as well. (C) 2001 Academic Press.