Browsing by Issue Date, starting with "2005-02-15"

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Stimulated Raman scattering in a potassium titanyl phosphate crystal: simultaneous self-sum frequency mixing and self-frequency doubling
(2005-02-15)
Chen, YF
;
電子物理學系
;
Department of Electrophysics
A potassium titanyl phosphate crystal is used to achieve efficient stimulated Raman scattering conversion with simultaneous self-sum frequency mixing and self-frequency doubling. Inside a diode-pumped Nd:YAG Q-switched laser cavity, 1.03 W of 1129-nm second Stokes average output power and 0.25 W of 548-nm sum-frequency average power are simultaneously generated with a diode input power of 10 W at a pulse repetition rate of 10 kHz. (C) 2005 Optical Society of America.
Polyfluorene containing diphenylquinoline pendants and their applications in organic light emitting diodes
(2005-02-15)
Su, HJ
;
Wu, FI
;
Shu, CF
;
Tung, YL
;
Yun, C
We present a short, efficient synthetic route for the preparation of a novel polyfluorene copolymer (PF-Q) containing two electron-deficient, 2,4-diphenylquinoline groups functionalized at the C-9 positions of alternate fluorene units that form a three-dimensional cardostructure. The presence of the rigid bulky pendent groups leads to a polyfluorene possessing a high glass-transition temperature (207 degreesC) and very good thermal stability (5% weight loss observed at 460 degreesC). A photoluminescence study revealed that the Forster energy transfer from the excited quinoline groups to the polyfluorene backbone is Very efficient; it also demonstrated that, the commonly observed aggregate/excimer formation in polyfluorenes is suppressed very effectively, in this polymer, even after it has been annealed at 150 degreesC for 20 h. A light emitting diode (LED) device prepared with PF-Q as the emitting layer exhibits a stable blue emission with a maximum brightness of 1121 cd/m(2) at 12 V and a maximum external quantum efficiency of 0.80% at 250 cd/m(2). We also used PF-Q, which contains diphenylquinoline units that behave as electron-transporting side chains, as a host. material and doped it with 2.4 wt % of a red-emitting phosphorescent dye, Os(fppz). to realize a red electrolumineseence with CIE color coordinates of (0.66, 0.34). The doped device exhibits a maximum external quantum efficiency of 6.63% (corresponding a luminance efficiency of 8.71 cd/A) at a current density of 47.8 mV/cm(2) together with a maximum brightness of 10457 cd/m(2). (C) 2005 Wiley Periodicals, Inc.
A two-level scheduling method: an effective parallelizing technique for uniform nested loops on a DSP multiprocessor
(2005-02-15)
Lee, YH
;
Chen, C
;
資訊工程學系
;
Department of Computer Science
A digital signal processor (DSP), which is a special-purpose microprocessor, is designed to achieve higher performance on DSP applications. Because most DSP applications contain many nested loops and permit a very high degree of parallelism, the DSP multiprocessor has a suitable architecture to execute these applications. Unfortunately, conventional scheduling methods used on DSP multiprocessors allocate only one operation to each DSP every time unit, even if the DSP includes several function units that can operate in parallel. Obviously they cannot achieve full function unit utilization. Hence, in this paper, we propose a two-level scheduling method (TSM) to overcome this common failing. TSM contains two approaches, which integrates unimodular transformations, loop tiling technique, and conventional methods used on single DSP, Besides introducing algorithm, we also use an analytic module to analyze its preliminary performance. Based on our analyses the TSM can achieve shorter execution time and more scalable speedup results. In addition, the TSM causes less memory access and synchronization overheads, which are usually negligible in the DSP multiprocessor architecture. (C) 2004 Elsevier Inc. All rights reserved.
Growth of zinc oxide thin films on Y2O3/Si substrates by chemical vapor deposition
(2005-02-15)
Lin, Chih-Wei
;
Cheng, Tsan-Yao
;
Chang, Li
;
Juang, Jenh-Yih
;
電子物理學系
Epitaxial ZnO was deposited on Si(1 1 1) substrate by atmospheric pressure metal-organic chemical vapor deposition (MOCVD) at 500 degrees C. A Y2O3 buffer layer in epitaxy with Si substrate has successfully suppressed the Si oxidation before ZnO deposition. The Y2O3 film was grown by pulsed laser deposition (PLD) on Si(1 1 1) substrate at 800 degrees C. Also, ZnO was deposited by PLD for comparison with MOCVD. X-ray diffraction and cross-sectional transmission electron microscopy was used to characterize microstructures of the ZnO films and their interfaces with Y2O3. The result shows ZnO(0 0 0 2) parallel to Y2O3(1 1 1). With the increase of the deposition time, the grain morphology of ZnO thin films evolved from flat structure to columnar structure. Most of the columnar ZnO grains are c-axis oriented perpendicular to the interface. (C) 2004 Elsevier B. V. All rights reserved.
Synthesis of silicon carbide nanostructures via a simplified Yajima process - Reaction at the vapor-liquid interface
(2005-02-23)
Wang, CH
;
Chang, YH
;
Yen, MY
;
Peng, CW
;
Lee, CY
A preceramic polymer route developed in 1975 has been simplified to efficiently generate beta-SiC nanostructures, including cubic cages (see Figure), cubic shells, and nanoparticles. The nanostructures are generated by the reaction of liquid sodium with the vapors of methylchlorosilanes, with the morphology of the resulting nanostructures dependent upon the interactions between the phase-separated solid products generated at the interface of the vapor-liquid/solid reactions.
Fault diagnosis of rotating machinery using an intelligent order tracking system
(2005-02-23)
Bai, MS
;
Huang, JM
;
Hong, MH
;
Su, FC
;
機械工程學系
This research focuses on the development of an intelligent diagnostic system for rotating machinery. The system is composed of a signal processing module and a state inference module. In the signal processing module, the recursive least square (RLS) algorithm and the Kalman filter are exploited to extract the order amplitudes of vibration signals, followed by fault classification using the fuzzy state inference module. The RLS algorithm and Kalman filter provide advantages in order tracking over conventional Fourier-based techniques in that they are insensitive to smearing problems arising from closely spaced orders or crossing orders. On the basis of thus obtained order features, the potential fault types are then deduced with the aid of a state inference engine. Human diagnostic rules are fuzzified for various common faults, including the single fault and double fault situations. This system is implemented on the platform of a floating point digital signal processor, where a photo switch and an accelerometer supply the shaft speed and acceleration signals, respectively. Experiments were carried out for a rotor kit and a practical four-cylinder engine to show the effectiveness of the proposed system in tracking the rotating order with precise inference. (C) 2003 Elsevier Ltd. All rights reserved.
Microwave-absorbing characteristics for the composites of thermal-plastic polyurethane (TPU)-bonded NiZn-ferrites prepared by combustion synthesis method
(2005-02-25)
Peng, CH
;
Hwang, CC
;
Wan, J
;
Tsai, JS
;
Chen, SY
NiZn ferrite with the chemical formula Ni0.5-xZn0.5-xM2xFe2O4 (M = Co, Cu, or Mg, and x = 0 or 0.05) was synthesized by a combustion synthesis method using metal nitrates and urea ((NH2)(2)CO) as reactants. The narrocrystallite of these materials were mixed with a thermal-plastic polyurethane (TPU) elastomer to be converted into a microwave-absorbing composite. The complex relative permittivity (epsilon(r) = epsilon'-jepsilon") and permeability (mu(r)=mu'-jmu") of the absorber were measured in a frequency range of 2-12GHz. The reflection loss (R.L.), matching frequency (f(m)) and matching thickness (d(m)) were calculated using the theory of the absorbing wall. Effects of both the particle size of ferrite and the dopant presented in the ferrite on the electromagnetic properties and microwave-absorbing characteristics were investigated. It was found that nanoparticles around 40 nm exhibit higher reflection loss than both those obtained from micro-sized powders and those with size less than 25 nm. Also, it was shown that the Co-doped, Mg-doped, and Cu-doped NiZn ferrite-TPU composites could be designed to be more negative than -20 dB, in a frequency range of 2-12 GHz, to become promising materials for microwave-absorbing application. These doped ferrite-containing composites have more effective microwave-absorbing characteristics compared to undoped one. (C) 2004 Elsevier B.V. All rights reserved.
Improved performance and stability of organic light-emitting devices with Al-Cu alloy cathode
(2005-02-28)
Chen, IC
;
Hwang, SW
;
Chen, CH
;
應用化學系
;
友訊交大聯合研發中心
We have developed a stable green organic electroluminescent (EL) device by using an Al-Cu alloy as a cathode, which has better performance and reliability than the device with an Al cathode. The device with an Al-Cu alloy cathode achieved an EL efficiency of 3.78 cd/A(2.18 lm/W) at 20 mA/cm(2) and the operating voltage was 5.46 V, while device with Al cathode had an EL efficiency of 3.1 cd/A(1.34 lm/W) and 7.3 V at the same drive condition. The Al-Cu device achieved a 20% decay lifetime (t(80)) of 1234 h at an initial brightness of 756 cd/m(2), which is twice the lifetime of conventional device with the state-of-the-art LiF/Al cathode. (C) 2005 American Institute of Physics.
Composition determination of semiconductor quantum wires by X-ray scattering
(2005-02-28)
Hsu, CH
;
Tang, MT
;
Lee, HY
;
Huang, CM
;
Liang, KS
Self-assembled semiconductor nano-structures, e.g. quantum dots and wires, have recently attracted intensive interests due to their potential applications in optoelectronic industry. Strain field, compositional profile, size, and shape are the key factors determining the physical properties of these nano-structures. However, due to their mesoscopic size, it is a challenge to accurately determine those geometric and chemical parameters. In this work, we present the structural and compositional investigation of GaAs quantum wires grown on InP(0 0 1) substrates by grazing incidence X-ray scattering. In particular, we applied resonant X-ray scattering to determine the compositional distribution within the wires. With properly chosen diffraction peak and X-ray energy range, the profile of energy scan is highly sensitive to the composition of the region with selected lattice constant. As compared to other composition determination methods, which rely on the intensity ratio either between a strong and a weak diffraction or between the same Bragg diffraction collected at different energies, the profile of energy scan is not affected by the significant intensity modulation introduced by inter-wire correlation. Therefore, this method can be applied to systems of various surface morphologies and ordered structures and still provides compositional information with high accuracy and good resolution. (C) 2004 Elsevier B.V. All rights reserved.
Variations of differential capacitance in SrBi2Ta2O9 ferroelectric films induced by photoperturbation
(2005-02-28)
Leu, CC
;
Chien, CH
;
Chen, CY
;
Chang, MN
;
Hsu, FY
In this letter, we demonstrated the impact of illumination on the differential capacitance variation of a strontium bismuth tantalite (SBT) capacitor during scanning capacitance microscopy measurements. It was found that illumination with a stray light of laser in an atomic force microscope could perturb the dC/dV signals of the samples. We attribute this phenomenon to the generation of free carriers by the photon absorptions via defect traps in the SBT thin film. Therefore, this present work suggests that the effect of laser illumination must be carefully taken into consideration whenever a field-sensitive technique is employed to analyze the properties of a ferroelectric material. (C) 2005 American Institute of Physics.
Ward identities and high energy scattering amplitudes in string theory
(2005-02-28)
Chan, CT
;
Ho, PM
;
Lee, JC
;
電子物理學系
;
Department of Electrophysics
High-energy limit alpha' --> infinity, of stringy Ward identities derived from the decoupling of two types of zero-norm states in the old covariant first quantized (OCFQ) spectrum of open bosonic string are used to check the consistency of saddle point calculations of high energy scattering amplitudes of Gross and Mende and Gross and Manes. Some inconsistencies of their saddle point calculations are found even for the string-tree scattering amplitudes of the excited string states. We discuss and calculate the missing terms of the calculation by those authors to recover the stringy Ward identities. In addition, based on the tree-level stringy Ward identities, we give the proof of a general formula, which was proposed previously, of all high energy four-point string-tree amplitudes of arbitrary particles in the string spectrum. In this formula all such scattering amplitudes are expressed in terms of those of tachyons as conjectured by Gross. The formula is extremely simple which manifestly demonstrates the universal high energy behavior of the interactions among all string states. (C) 2004 Elsevier B.V. All rights reserved.
Photochemistry and photodissociation of benzosultine and naphthosultine: electronic relaxation of sultines and kinetics and theoretical studies of fragment o-quinodimethanes
(2005-02-28)
Tang, KC
;
Lee, SJ
;
Chi, SH
;
Lu, KL
;
Chen, WC
Fluorescence decays of benzosultine and naphthosultine excited at 263 nm are detected with time-correlated single-photon counting (TCSPC). Both molecules display biexponential decay with a rapid component (time constants 90 and 350 ps for benzosultine and naphthosultine, respectively) assigned to an electronically excited state S-n at high energy and the slow one (constants 7.5 and 9.0 ns for benzosultine and naphthosultine, respectively) to the S-1 state. Dissociation of both molecules was investigated with nanosecond laser flash photolysis combined with transient absorption to detect the intermediates and products. With excitation at 266 nm, benzosultine yields a transient with absorption maximum at lambda(max) = 370 nm; this transient has a short-lived component with lifetime around 1 mus and a long-lived component. Both components are insensitive to molecular oxygen. The short-lived component is tentatively assigned to the dissociation intermediate and the long-lived to be singlet o-benzoquinodimethane (o-BQDM). Photolysis of naphthosultine yields two transient species with absorption at; lambda(max) = 420 and 520 nm; we assign the former band to triplet-triplet absorption of naphthosultine and the latter to absorption by the product singlet o-naphthoquinodimethane. Optimal geometries, energetics, and vertical transitions of benzosultine, naphthosultine, o-benzoquinodimethane, and o-naphthoquinodimethane are calculated using methods based on density-functional theory (B3LYP/6-311++G**) and time-dependent density-functional theory (TD-DFT). The results of these calculations imply that the ground electronic state of these two o-quinodimethanes (o-QDM) is singlet with a structure of diene form. Their triplet states display a biradical structure. The energy separation between singlet and triplet states of o-benzoquinodimethane is calculated to be ca. 93.6 kJ/mol, but for o-naphthoquinodimethane, it is only ca. 27.8 kJ/mol. (C) 2004 Elsevier B.V. All rights reserved.
High-performance poly-Si TFTs fabricated by implant-to-silicide technique
(2005-03-01)
Lin, CP
;
Mao, YH
;
Tsui, BY
;
電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
High-performance poly-Si thin-film transistors (TFTs) with fully silicided source/drain (FSD) and ultrashort shallow extension (SDE) fabricated by implant-to-silicide (ITS) technique are proposed for the first time. Using the FSD structure, the S/D parasitic resistance can be suppressed effectively. Using the ITS technique, an ultrashort and defect-free SDE can also be formed quickly at about 600 degreesC. Therefore, the FSD poly-Si TFTs exhibits better current-voltage characteristics than those of conventional TFTs. It should be noted that the on/off current ratios of FSD poly-Si TFT (W/L = 1/4,mum) is over 3.3 x 10(7), and the field-effective mobility of that device is about 141.6 (cm(2)/Vs). Moreover, the superior short-channel characteristics of FSD poly-Si TFTs are also observed. It is therefore believed that the proposed FSD poly-Si TFT is a very promising TFT device.
Modeling channel assignment of small-scale cellular networks
(2005-03-01)
Hung, HN
;
Lee, PC
;
Lin, YB
;
Peng, NF
;
統計學研究所
In a cellular telecommunications network, the call blocking, forced termination, and call incompletion probabilities are major output measures of system performance. Most previous analytic studies assumed that the handover traffic to a cell is a fixed-rate Poisson process. Such assumption may cause significant inaccuracy in modeling. This paper shows that the handover traffic to a cell depends on the workloads of the neighboring cells. Based on this observation, we derive the exact equation for the handover force-termination probability when the mobile station (MS) cell residence times are exponentially distributed. Then, we propose an approximate model with general MS cell residence time distributions. The results are compared with a previously proposed model. Our comparison study indicates that the new model can capture the handover behavior much better than the old one for small-scale cellular networks.
Dynamic wavelength allocation in wavelength division multiplexing radio-over-fiber access network
(2005-03-01)
Lin, WP
;
Peng, WR
;
Chi, S
;
光電工程學系
;
Department of Photonics
We demonstrate that dynamic wavelength add-drop multiplexing technology based on a fiber Bragg grating array (FBGA) can be used to improve the efficiency of wavelengths at a burst traffic load for wavelength division multiplexing radio-over-fiber (ROF) access networks. Moreover, we also propose an upstream injection-locked longitudinal mode scheme in a remote node to offer a simple ROF interface. Experimental results demonstrate that these technologies can provide robust and reliable characteristics for large radio terminals.
管管作品五首
(2005-03-01)
管管
管管作品五首
(2005-03-01)
管管
Preferences toward the constructivist Internet-based learning environments among high school students in Taiwan
(2005-03-01)
Chuang, SC
;
Tsai, CC
;
教育研究所
;
師資培育中心
;
Institute of Education
This paper explored students' preferences toward the constructivist Internet-based learning environments. A Constructivist Internet-based Learning Environment Survey (CILES) was developed. The CILES consisted of six scales, including student negotiation, inquiry learning, reflective thinking, relevance, ease of use and challenge. Questionnaire responses gathered from more than 700 high school students in Taiwan suggested that the survey showed adequate reliability in assessing students' preferences. Students showed stronger preferences for the learning environments, which were easy to use or navigate and integrate complex real-life problems with relevant knowledge in a meaningful way. In addition, males and females shared similar preferences toward the Internet-based learning environments. Students having moderate Internet experiences seemed to be more critical to the preferences of the Internet-based learning environments, in which they may have demanded authentic and facilitated Internet-based learning environments, while their inquiry and reflective thinking should be promoted. (C) 2004 Elsevier Ltd. All rights reserved.
A parallel adaptive finite volume method for nanoscale double-gate MOSFETs simulation
(2005-03-01)
Li, YM
;
Yu, SM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We propose in this paper a quantum correction transport model for nanoscale double-gate metal-oxide-semiconductor field effect transistor (MOSFET) device simulation. Based on adaptive finite volume, parallel domain decomposition, monotone iterative, and a posteriori error estimation methods, the model is solved numerically on a PC-based Linux cluster with MPI libraries. Quantum mechanical effect plays an important role in semiconductor nanoscale device simulation. To model this effect. a physical-based quantum correction equation is derived and solved with the hydrodynamic transport model. Numerical calculation of the quantum correction transport model is implemented with the parallel adaptive finite volume method which has recently been proposed by us in deep-submicron semiconductor device simulation. A 20 nm double-gate MOSFET is simulated with the developed quantum transport model and computational technique. Compared with a classical transport model. it is found that this model can account for the quantum mechanical effects of the nanoscale double-gate MOSFET quantitatively. Various biasing conditions have been verified on the simulated device to demonstrate its accuracy. Furthermore. for the same tested problem, the parallel adaptive computation shows very good computational performance in terms of the mesh refinements, the parallel speedup, the load-balancing, and the efficiency. (C) 2004 Elsevier B.V. All rights reserved.
Susceptibilities to amphotericin B and fluconazole of Candida species in TSARY 2002
(2005-03-01)
Yang, YL
;
Li, SY
;
Cheng, HH
;
Lo, HJ
;
生物科技學系
Susceptibilities to amphotericin B and fluconazole of 909 Candida species collected during the Taiwan Surveillance of Antimicrobial Resistance of Yeasts (TSARY) in 2002 were determined by the broth microdilution method. There were 395 (43.5%) Candida albicans, 244 (26.8%) C. tropicalis, 187 (20.6%) C. glabrata, 63 (6.9%) C. parapsilosis, 9 (1%) C. krusei, and 11 (1.2%) others. Among them, 23 (2.5%) isolates were resistant to amphotericin B. They consisted of 10 C. glabrata, 6 C. krusei, 3 C. albicans, 1 C. tropicalis, 1 C. parapsilosis, and 2 others. The resistance rate to amphotericin B has increased compared with that of TSARY 1999 (2.5% versus 0.5%). There were 7 C. krusei, 5 C. albicans, 3 C. glabrata, and 2 others isolates resistant to fluconazole. The resistance rate to fluconazole has decreased from 8.4% in 1999 to 1.9% in 2002. A pattern of coresistance to both amphotericin B and fluconazole was observed. (c) 2005 Elsevier Inc. All rights reserved.