Browsing by Issue Date, starting with "2005-02-10"

Now showing 1 - 20 of 67167

New dopant and host materials for blue-light-emitting phosphorescent organic electroluminescent devices
(2005-02-10)
Yeh, SJ
;
Wu, MF
;
Chen, CT
;
Song, YH
;
Chi, Y
Efficient organic light-emitting diodes (OLEDs) incorporating Ir-III bis(4,6-difluorophenylpyridinato)3-(trifluoromethyl)-5-(pyridin-2-yl)-1,2,4-triazolate (FIrtaz) and Ir-III bis(4,6-difluorophenylpyridinato)-5- (pyridin-2-yl)-1H-tetrazolate (FIrN4) demonstrate higher-purity blue-light emission than the long-known Ir-III bis(4,6-difluorophenylpyridinato)-picolate (FIrpic) phosphorophore. New host materials with higher glass-transition temperatures were also found to enhance the OLED performance.
分波多工網路中之光功率監測裝置
(2005-02-11)
祁甡
;
李健仲
;
葉建宏
本案關於一種分波多工網路中之光功率監測裝置，尤指一種藉掃描摻鉺光纖放大器不同的增益頻譜方式而應用於分波多工網路中之光功率監測裝置。本案可藉注入一個飽和頻來對此光放大器作到增益箝制的要求。本案分波多工網路中之光功率監測裝置使用的元件取得方便且價格便宜，對於WDM光通訊系統的頻率及功率的監測具有極大的價值，亦可大幅提高對光纖網路系統波頻監測之解析度。
以邊界聲源表示法為基礎之空間音效混成方法
(2005-02-11)
白明憲
;
歐昆應
一種以邊界聲源表示法為基礎之空間音效混成方法；主要係將密閉空間聲場等效成一個主要聲源以及均勻分布在聲場邊界上的虛擬次要聲源。虛擬次要聲源即是用來模擬聲場的反射以及混響的現象，最後根據這個假設所推導數學模式將符合波動方程式(wave equation)。由這個關係式，利用最小平方法(least-square procedure)來求解反矩陣以得到每個虛擬聲源的強度。所算出來的一組虛擬聲源強度即代表一個特定的聲場所產生的混響效果。在模擬的過程中亦可以設定其聲場的幾何大小，以及與頻率相關的邊界條件如聲場邊界的吸音律。
Synthesis of alpha-galactosyl ceramide and the related glycolipids for evaluation of their activities on mouse splenocytes
(2005-02-14)
Fan, GT
;
Pan, YS
;
Lu, KC
;
Cheng, YP
;
Lin, WC
Phytosphingosine and its short-chain analog were efficiently synthesized with 19% overall yield in 10 steps, respectively, starting from an inexpensive D-lyxose. Galactosyl donors of sulfide and phosphite types bearing benzoyl protecting groups of 4- and 6OH underwent glycosylation in excellent alpha-anomeric selectivity. A variety of alpha-galactosyl, fucosyl and glucosyl ceramides and serine-type lipids were prepared, and their activities involved in the proliferation of mouse splenocytes and the expression of cytokines were elucidated. Besides alpha-galactosyl ceramides, a galactosyl serine-type lipid also exhibited substantial effect on the expression of cytokines IFN-gamma and IL-4. (C) 2004 Elsevier Ltd. All rights reserved.
Preparation and characterization of poly seudorotaxanes based on adamantane-modified polybenzoxazines and beta-cyclodextrin
(2005-02-14)
Su, YC
;
Chen, WC
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
P-Cyclodextrin (P-CD) forms inclusion complexes (ICs) with adamantane-modified benzoxazines (2 benzoxazine and 3 benzoxazine). These benzoxazines can readily penetrate into the CD's hydrophobic cavity, causing turbidity of their solutions, from which fine crystalline powders are obtained. We characterized these complexes by powder X-ray diffraction, C-13 and C-13 CP/MAS NMR spectroscopies, DSC, and TGA. The X-ray diffraction and solid-state C-13 CP/MAS NMR spectroscopy indicate that the IC domains of the polypseudorotaxanes maintain their channel-type structures after the ring-opening curing reactions have occurred. Furthermore, DSC measurements indicate that complexing the adamantane-modified benzoxazine units with beta-CDs result in stiffer main chains and, thus, higher glass transition temperature. TGA also indicates that the inclusion complexes have enhanced its thermal stability. (C) 2004 Published by Elsevier Ltd.
A new strategy for the one-step synthesis of block copolymers through simultaneous free radical and ring opening polymerizations using a dual-functional initiator
(2005-02-14)
Huang, CF
;
Kuo, SW
;
Lee, HF
;
Chang, FC
;
應用化學系
Block copolymers are fascinating and complex materials that have been used in a range of diverse scientific and technological capacities. We demonstrate that a single one-step approach based on dual simultaneous polymerizations is a viable technique for the synthesis of a wide range of block copolymers by combining two dissimilar polymerization systems and using a dual-functional initiator. The main advantage of this methodology is that a simple, one-step, and simultaneous polymerization occurs in the bulk, which makes this process very attractive from both industrial and academic points of view. We plan to study the reaction kinetics and evaluate how well the ring opening catalyst [in this case, Sn(oct)(2)] works under reverse ATRP conditions. (C) 2004 Elsevier Ltd. All rights reserved.
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
;
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.