Browsing by Issue Date, starting with "2008-09-29"

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High quality ultraviolet AlGaN/GaN multiple quantum wells with atomic layer deposition grown AlGaN barriers
(2008-09-29)
Li, Zhen-Yu
;
Lo, Ming-Hua
;
Hung, C. T.
;
Chen, Shih-Wei
;
Lu, Tien-Chang
Low dislocation density ultraviolet (UV) AlGaN/GaN multiple quantum well (MQW) structure was grown using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers formed by ALD grown AlN/GaN superlattices. The as-grown sample showed smooth surface morphology with a root-mean-square roughness value of only 0.35 nm, and no surface cracks were found. The dislocation density was estimated to be as low as 3.5 x 10(7) cm(-2). X-ray and transmission electron microscope data showed the MQW had sharp interfaces with good periodicity. The sample had an UV photoluminescence emission at 334 nm (3.71 eV) with a very narrow linewidth of 47 meV at 13 K. The cathodoluminescence image revealed a fairly uniform luminescence pattern at room temperature. The AlGaN/GaN MQW grown by ALD technique should be useful for providing high crystalline quality for fabrication of various optical devices. c 2008 American Institute of Physics.
Dark carrier recombination in organic solar cell
(2008-09-29)
Wang, Ying-Xuan
;
Tseng, Shin-Rong
;
Meng, Hsin-Fei
;
Lee, Kuan-Chen
;
Liu, Chiou-Hua
The carrier recombination in organic solar cells is investigated by numerical modeling to understand the weak dependence of theopen-circuit voltage on the workfunction of the electrodes. In Ohmic contact structures, photocarriers recombine predominantly with dark carriers diffused from the electrode into the semiconductor. Such dark carrier recombination becomes the main limit of power conversion efficiency and open-circuit voltage. For a given semiconductor decreasing the workfunction difference of the electrodes reduces simultaneously the dark carrier recombination and the flat band voltage. The balance between these two opposite factors gives a nearly constant open-circuit voltage. In an ideal bilayer structure there is no dark carrier recombination and the efficiency is demonstrated to be 60% higher than single layer blend. (C) 2008 American Institute of Physics.
Method for fabricating microneedle array and method for fabricating embossing mold of microneedle array
(2008-09-30)
Chiou
;
Jin-Chern
;
Hung
;
Chen-Chun
;
Chang
The present invention discloses a method for fast fabricating microneedle arrays with an embossing process and a method for fabricating an embossing mold of a microneedle array, wherein a master pattern of a high aspect ratio silicon microneedle array is fabricated with a microelectromechanical technology, and the master pattern is used to fabricate an embossing mold; a thermosetting material is filled into the embossing mold; then, baking, pressing and mold-stripping are undertaken; thereby, disposable solid polymer microneedle arrays can be batch-fabricated.
Asymmetries in intrinsic spin-Hall effect in low in-plane magnetic field
(2008-10-01)
Wang, L. Y.
;
Chu, C. S.
;
Mal'shukov, A. G.
;
電子物理學系
;
Department of Electrophysics
Effects of low in-plane magnetic field on bulk spin densities and edge spin accumulations of a diffusive two-dimensional semiconductor stripe are studied. Focusing upon the Dresselhaus-type intrinsic spin-orbit interaction (SOI), we look for the symmetry, or asymmetry, characteristics in two magnetic-field orientations: along and transverse to the stripe. For longitudinal field, the out-of-plane spin density S(z) exhibits odd parity across the stripe and even parity in the magnetic field and is an edge accumulation. For transverse field, the out-of-plane S(z) becomes asymmetric in both spatial and field dependencies and has finite bulk values for finite magnetic fields. Our results support utilizing low in-plane magnetic fields for the probing of the underlying SOI.
Sintering Behavior, Microstructure, and Dielectric Properties of Nano-Ba0.7Sr0.3TiO3 Ceramics
(2008-10-01)
Ying, Kuo-Liang
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nanoscale Ba0.7Sr0.3TiO3 (BST) powders were synthesized by solid-state reaction, chemical dispersion, and mechanical grinding. Capacitor samples based on the nano-BST powders were then prepared; their sintering behaviors at different temperatures, dielectric properties, and correlations to microstructure were investigated accordingly. It was found that specific sintering conditions are essential for achieving high-density (>= 95%) BST samples with a desired microstructure. Dielectric property measurements revealed that the best result was achieved in samples sintered at 1200 degrees C for 6h (dielectric constant = 9700; dielectric loss = 0.04) or at 1300 degrees C for 1 h (dielectric constant = 9800; dielectric loss = 0.075). The BST samples exhibited a lower Curie point (T-C) than conventional BaTiO3 (BTO) and BST systems. The improvement of dielectric properties and phase transition temperature were attributed to the fine grain structure in BST samples.
Results of geodetic and geotechnical monitoring of subsidence for Taiwan High Speed Rail operation
(2008-10-01)
Hwang, Cheinway
;
Hung, Wei-Chia
;
Liu, Chih-Hsi
;
土木工程學系
;
Department of Civil Engineering
Taiwan High Speed Rail (THSR), which began operations in January 2007, passes through an area in Yunlin County where the largest cumulative subsidence measured during 1992-2006 exceeds 100 cm. Leveling benchmarks, GPS pillars and multi-level monitoring wells were deployed in this area to collect detailed subsidence data from October 2003 to 2006. Leveling is carried out on both ground benchmarks and survey bolts attached to THSR columns. Minimum constraint solutions of leveling networks produce estimated heights accurate to a few mm. Special attention is paid to code smoothing, ionospheric, tropospheric and ocean tidal loading (OTL) effects, so that height estimates from GPS are optimal. Leveling and GPS-derived height changes are consistent to 1 cm, and show that from Stations 210 to 240K of TSHR, the subsidence is bowl shaped. Measurements of sediment compaction in specific depth intervals at three monitoring wells indicate that most of the subsidence is caused by sediment compaction at depths from 50 to 300 m. The major compaction occurs in the interval 220-300 m and is attributed to ground water withdrawal. Large angular deflections as determined from subsidence measurements are detected at some columns, but are below the upper bound (1/1,000) of tolerance specified in the safety code. With the current subsidence and sediment compaction, no significantly reduced loading capacity of the columns is expected to occur. For a safe THSR operation, subsidence and sediment-compaction monitoring should be continued, and current ground water withdrawal in Yunlin must be reduced or stopped.
國際多角化與企業績效、企業風險的關聯性及其影響因素之研究
(2008-10-01)
孫梅瑞
;
蕭瑞子
;
Mei-Jui Sun
;
Jui-Tzu Hsiao
;
Institute of Business and Management
本研究針對1996-2000年間台灣上市企業122個國際多角化投資案爲研究對象，探討影響企業績效與風險的各種相關因素，也進一步討論企業績效與風險對國際多角化的影響，並且利用多元迴歸及Logistic迴歸模式逐一驗證各項因素。本研究探討台灣企業從事國際多角化投資是否可提高其企業價值，投資後企業風險是否減少；並以企業國際多角化的程度、國際多角化的類型、企業與投資案特性、被投資國家特性、經濟景氣及產業別等構面來探討國際多角化的績效與風險，並試圖找出企業國際多角化投資的成功因素。此外，本研究探討國際多角化策略與企業經營績效、企業風險間的關聯性，亦即台灣企業進行國際多角化投資後的經營績效與風險，是否會影響企業再次從事國際多角化投資；以瞭解是國際多角化策略影響了企業經營績效與風險，還是經營績效與風險影響了企業的國際多角化投資決策。本研究發現企業從事國際多角化投資確實能提升企業績效，但企業風險也相對提高；企業選擇相關國際多角化，可提高企業績效，但無法分散本業風險，相反的非相關國際多角化則可分散本業風險，但企業績效較差；當台灣企業規模愈大、經營能力愈佳、在中所得國家投資、負債比率愈低、文化距離較高、無形資產愈多、管理者持股比率愈低及新設事業資本支出愈高，則企業從事國際多角化的績效會增加；雖然進行國際多角化投資風險不減反增，但是當台灣企業規模愈小、管理者持股比率愈低、在低所得且低風險國家投資、景氣較差、文化距離較大及負債比率愈低情況下，則企業從事國際多角化的風險會較低。
Formation of Branched ZnO Nanowires from Solvothermal Method and Dye-Sensitized Solar Cells Applications
(2008-10-01)
Cheng, Hsin-Ming
;
Chiu, Wei-Hao
;
Lee, Chia-Hua
;
Tsai, Song-Yeu
;
Hsieh, Wen-Feng
Branched ZnO nanowires have been fabricated on conductive glass substrates via a solvothermal method for dye-sensitized solar cells (DSCs). The 1D branched nanostructures can afford a direct conduction pathway instead of interparticle hops while using nanoparticles. Furthermore, the short-circuit current density and the energy conversion efficiency of the branched ZnO nanowire DSCs are 4.27 mA/cm(2) and 1.51%,which are twice as high as the bare ZnO nanowire ones. The improvement was a consequence of the enlargement of the internal surface area within the photoelectrode and allowed us to achieve higher dye adsorption to significantly enhance the performance of the DSCs.
資深作家近況報導
(2008-10-01)
管管
High Er3+ concentration low refractive index fluorophosphate glass for evanescent wave optical amplifiers
(2008-10-01)
Zhang, Liyan
;
Chen, Nan-Kuang
;
Hu, Lili
;
光電工程學系
;
Department of Photonics
This is about the first reported laser glass with very low no, high Er3+ concentration and no quenching. In this work, a series of high Er3+ concentration (10.6-12.2 x 10(20) ions/cm(3)), low refractive index (n(1550) < 1.47) and relatively high fluorescence lifetime (6.8-12.6 ms) fluorophosphate glasses were made. A cw-pumping evanescent wave optical amplifier experiment was performed with it, and a relative gain of around 2dB at 1550 nm wavelength was achieved while the noise level was almost unchanged. To our knowledge, this is the first successful relative gain in evanescent wave optical amplifiers (EWOA) demonstrated with cw pumping. It is a valuable study of specially designed fluorophosphate glass suitable for EWOA communication experiment. (C) 2008 Elsevier B.V. All rights reserved.
Comparing the level of positive tendency in a life satisfaction evaluation between Chinese and Western people
(2008-10-01)
Lee, Shih-jung
;
Wu, Chia-huei
;
經營管理研究所
;
Institute of Business and Management
We demonstrate that people from Chinese cultural backgrounds have a smaller positive tendency in life evaluation compared to people in typical Western cultures. Participants first described their imagined best and worst life and then rated their current life on scale anchored by those imaginings (Mellor et al. International Journal of Social Research Methodology Theory and Practice, 2, 263-278, 1999), with scores above 50 indicating the strength of positive tendency. We compare responses from 82 Taiwanese students to data from the 22 Australian students in Mellor et al.'s (International Journal of Social Research Methodology Theory and Practice, 2, 263-278, 1999) study. Results of independent t tests support the hypothesis that culturally Chinese subjects have a lower positive tendency (65.32%SM) than Australian participants (76.12%SM) in life satisfaction evaluation.
Information Distribution and the Informative Efficiency
(2008-10-01)
陳立偉
;
Li-Wei Chen
;
Institute of Business and Management
;
經營管理研究所
本研究提供建構股價模型之理論基礎。研究中特別將私人訊息分配之情形納入模型中，並假設投資人之絕對風險厭惡係數爲常數，各自追求預期效用極大，得出市場結清均衡時，均衡價格爲市場訊息按照其精確度與觀察頻率之乘積加權平均。主要發現有：第一，市場訊息分配均等將導致均衡價格取代私人訊息而成爲市場中各種訊息之充分統計量，此時證券市場具有資訊效率，投資人失去蒐集私人訊息之動機。第二，市場訊息分配與資訊觀察值成正比爲市場具有資訊效率之充要條件。然實際上述條件難以成就，投資人仍具有蒐集私人資訊之動機。
Expression and characterization of the biofilm-related and carnosine-hydrolyzing aminoacylhistidine dipeptidase from Vibrio alginolyticus
(2008-10-01)
Wang, Ting-Yi
;
Chen, Yi-Chin
;
Kao, Liang-Wei
;
Chang, Chin-Yuan
;
Wang, Yu-Kuo
The biofilm-related and carnosine-hydrolyzing aminoacylhistidine dipeptidase (pepD) gene from Vibrio alginolyticus was cloned and sequenced. The recombinant PepD protein was produced and biochemically characterized and the putative active-site residues responsible for metal binding and catalysis were identified. The recombinant enzyme, which was identified as a homodimeric dipeptidase in solution, exhibited broad substrate specificity for Xaa-His and His-Xaa dipeptides, with the highest activity for the His-His dipeptide. Sequence and structural homologies suggest that the enzyme is a member of the metal-dependent metallopeptidase family. Indeed, the purified enzyme contains two zinc ions per monomer. Reconstitution of His.Tag-cleaved native apo-PepD with various metal ions indicated that enzymatic activity could be optimally restored when Zn(2+) was replaced with other divalent metal ions, including Mn(2+), Co(2+), Ni(2+), Cu(2+) and Cd(2+), and partially restored when Zn(2+) was replaced with Mg(2+). Structural homology modeling of PepD also revealed a 'catalytic domain' and a 'lid domain' similar to those of the Lactobacillus delbrueckii PepV protein. Mutational analysis of the putative active-site residues supported the involvement of His80, Asp119, Glu150, Asp173 and His461 in metal binding and Asp82 and Glu149 in catalysis. In addition, individual substitution of Glu149 and Glu150 with aspartic acid resulted in the partial retention of enzymatic activity, indicating a functional role for these residues on the catalysis and zinc ions, respectively. These effects may be necessary either for the activation of the catalytic water molecule or for the stabilization of the substrate-enzyme tetrahedral intermediate. Taken together, these results may facilitate the design of PepD inhibitors for application in antimicrobial treatment and antibody-directed enzyme prodrug therapy.
Impacts of SiN deposition parameters on n-channel metal-oxide-semiconductor field-effect-transistors
(2008-10-01)
Lu, Ching-Sen
;
Lin, Horng-Chih
;
Huang, Tiao-Yuan
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Although the incorporation of a SiN capping layer could dramatically enhance device performance, the accompanying hydrogen species contained in the capping layer may aggravate hot-carrier reliability. In order to alleviate this shortcoming, we vary the precursor flow conditions and deposition temperature of SiN film during plasma-enhanced chemical vapor deposition (PECVD) and study their impacts on the device performance and reliability. We found that SiN film with higher nitrogen content depicts larger tensile stress and therefore better mobility. More importantly, the resistance to hot-carrier degradation is also improved by increasing N-2 gas flow rate and deposition temperature because of less hydrogen diffusion from the capping layer. (C) 2008 Elsevier Ltd. All rights reserved.
Low-operating-voltage polymeric transistor with solution-processed low-k polymer/high-k metal-oxide bilayer insulators
(2008-10-01)
Yang, Feng-Yu
;
Chang, Kuo-Jui
;
Hsu, Meei-Yu
;
Liu, Cheng-Chin
;
電子工程學系及電子研究所
We have successfully demonstrated a polymeric semiconductor-based transistor with low-k polymer/high-k metal-oxide (TiO2) bilayer as gate dielectric. The TiO2 layers are readily processable from solution and cured at low temperature, instead of traditionally sputtering or high temperature sintering process, thus may suitable for a low-cost organic field effect transistors (FETs) manufacture. The low-k polymer capped on TiO2 layer could further smooth the TiO2 dielectric surface and suppress the leakage current from grain boundary of TiO2 films. The resulting unpatented P3HT-OFETs could operate with supply voltage less than 10 V and the mobility and threshold voltage were 0.0140 cm(2)/V s and 1.14 V, respectively. The on/off ratio was 1.0 x 10(3). (C) 2008 Elsevier B.V. All rights reserved.
資深作家近況報導
(2008-10-01)
管管
Robust Receiver Design for MIMO Single-Carrier Block Transmission over Time-Varying Dispersive Channels Against Imperfect Channel Knowledge
(2008-10-01)
Lin, Chih-Yuan
;
Wu, Jwo-Yuh
;
Lee, Ta-Sung
;
電信工程研究所
;
Institute of Communications Engineering
We consider MIMO single-carrier block transmission over time-varying multipath channels, under the assumption that the channel parameters are not exactly known but are estimated via the least-squares training technique. While the channel temporal variation is known to negate the tone-by-tone frequency-domain equalization facility, it is otherwise shown that in the time domain the signal signatures can be arranged into groups of orthogonal components, leading to a very natural yet efficient group-by-group symbol recovery scheme. To realize this figure of merit we propose a constrained-optimization based receiver which also takes into account the mitigation of channel mismatch effects caused by time variation and imperfect estimation. The optimization problem is formulated in an equivalent unconstrained generalized-sidelobe-canceller setup. This enables us to directly model the channel mismatch effect into the system equations through the perturbation technique and, in turn, to further exploit the statistical assumptions on channel temporal variation and estimation errors for deriving a dosed-form solution. Within the considered framework the proposed robust equalizer can be combined with the successive interference cancellation mechanism for further performance enhancement. Flop count evaluation and numerical simulation are used to evidence the advantages of the proposed scheme.
應用於低密度奇偶校驗（LDPC）解碼器之集合迴旋比較方法
(2008-10-01)
洪瑞徽
;
洪瑞鴻
;
陳紹基
本發明係揭露一種應用於低密度奇偶校驗解碼器之集合迴旋比較方法,其係應用在一查核節點單元(CNU)或變量節點單元(VNU)中。此種有系統化之方法係先對輸入之所有元素進行初始化以取得一個矩陣;再利用矩陣之對稱性與每列之近似性的特性,依序對所有元素之水平與垂直方向重覆數量最多、水平方向為連續元素者、非連續元素但為對稱之非邊界元素,以及邊界元素與其同列之端迴相鄰元素等原則形成不同類型之集合,以利用每個比較集合之間的高度重疊性,來有效降低基本比較運算量,並適用各種輸入數目,進而提高整體低密度奇偶校驗解碼器之效能。
Green phosphorescent iridium dendrimers containing dendronized benzoimidazole-based ligands for OLEDs
(2008-10-01)
Huang, Wei-Sheng
;
Lin, Jiann T.
;
Lin, Hong-Cheu
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of novel non-conjugated functionalized benzoimidazole-based dendrimers containing peripheral benzyl ether type dendrons have been synthesized and characterized. These compounds undergo cyclometalation with iridium trichloride to form iridium(III) complexes. The emission wavelengths of these dendrimers are in the range from 510 to 530 nm, and the photoluminescence quantum yields (PLQYs) in the range from 0.45 to 0.80. Dendrimers (Gn)(2)Ir(acac) and (Gn)(3)Ir exhibit a reversible one-electron oxidation wave at similar to 0.55 V and similar to 0.37 V (vs. Ag/AgNO3), respectively. With a device configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)/4, 4'-bis(N-carbarzolyl)biphenyl:(G2)(3)Ir 20 wt% dopant/1,3,5-tris(2-N-phenyl-benzoimidazolyl)benzene/LiF/Al has a maximum external quantum efficiency (EQE) of 17.6% and a maximum current efficiency of 61.5 cd/A. (C) 2008 Elsevier B.V. All rights reserved.
Using a strategy based on the concept of convergent evolution to identify residue substitutions responsible for thermal adaptation
(2008-10-01)
Lin, Yeong-Shin
;
生物資訊及系統生物研究所
;
Institude of Bioinformatics and Systems Biology
Factors that are related to thermostability of proteins have been extensively studied in recent years, especially by comparing thermophiles and mesophiles. However, most of them are global characters. It is still not clear how to identify specific residues or fragments which may be more relevant to protein thermostability. Moreover, some of the differences among the thermophiles and mesophiles may be due to phylogenetic differences instead of thermal adaptation. To resolve these problems, I adopted a strategy to identify residue substitutions evolved convergently in thermophiles or mesophiles. These residues may therefore be responsible for thermal adaptation. Four classes of genomes were utilized in this study, including thermophilic archaea, mesophilic archaea, thermophilic bacteria, and mesophilic bacteria. For most clusters of orthologous groups (COGs) with sequences from all of these four classes of genomes, I can identify specific residues or fragments that may potentially be responsible for thermal adaptation. Functional or structural constraints (represented as sequence conservation) were suggested to have higher impact on thermal adaption than secondary structure or solvent accessibility does. I further compared thermophilic archaea and mesophilic bacteria; and found that the most diverged fragments may not necessarily correspond to the thermostability-determining ones. The usual approach to compare thermophiles and mesophiles without considering phylogenetic relationships may roughly identify sequence features contributing to thermostability; however, to specifically identify residue substitutions responsible for thermal adaptation, one should take sequence evolution into consideration.