Browsing by Issue Date, starting with "2008-04-01"

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Improved shrinkage estimation of squared multiple correlation coefficient and squared cross-validity coefficient
(2008-04-01)
Shieh, Gwowen
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管理科學系
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Department of Management Science
The sample squared multiple correlation coefficient is widely used for describing the usefulness of a multiple linear regression model in many areas of science. In this article, the author considers the problem of estimating the squared multiple correlation coefficient and the squared cross-validity coefficient under the assumption that the response and predictor variables have a joint multinormal distribution. Detailed numerical investigations are conducted to assess the exact bias and mean square error of the proposed modifications of established estimators. Notably, the positive-part Pratt estimator and the synthesis of Browne and positive-part Pratt estimators are recommended in the estimation of squared multiple correlation coefficient and squared cross-validity coefficient, respectively, for their overall advantages of incurring the least amount of statistical discrepancy and computational requirement.
Determining vortex chirality in ferromagnetic ring by lateral nonlocal spin valve
(2008-04-01)
Chen, D. C.
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Yao, Y. D.
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Wu, J. K.
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Yu, C.
;
Lee, S. F.
We demonstrate detecting chirality of vortex state in a magnetic ring by lateral nonlocal spin-valve (NLSV) measurement. A Permalloy (Py) ring, a Py narrow wire, and copper contacts were used as spin injector, detector, and the normal-metal diffusive channel, respectively. By comparing the anisotropic magnetoresistance loop of the individual ring with NLSV loop, the vortex chirality and the related switching field of the ring can be determined. Both onion-to-vortex transition field and vortex chirality were found to alternate in both the same and different current probe arrangements on the magnetic ring. (C) 2008 American Institute of Physics.
Effects of interfacial sulfidization and thermal annealing on the electrical properties of an atomic-layer-deposited Al(2)O(3) gate dielectric on GaAs substrate
(2008-04-01)
Cheng, Chao-Ching
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Chien, Chao-Hsin
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Luo, Guang-Li
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Yang, Chun-Hui
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Chang, Ching-Chih
In this study we investigated the interfacial chemistry occurring between an atomic-layer-deposited Al(2)O(3) high-k film and a GaAs substrate and the impact of sulfidization and thermal annealing on the properties of the resultant capacitor. We observed that sulfide passivation of the Al(2)O(3)/GaAs structure improved the effect of Fermi level pinning on the electrical characteristics, thereby providing a higher oxide capacitance, smaller frequency dispersion, and reduced surface states, as well as decreased interfacial charge trapping and gate leakage currents. Photoemission analysis indicated that the (NH(4))(2)S-treated GaAs improved the quality of the as-deposited Al(2)O(3) thin film and preserved the stoichiometry of the dielectric during subsequent high-temperature annealing. This behavior was closely correlated to the diminution of GaAs native oxides and elemental arsenic defects and their unwanted diffusion. In addition, thermal processing under an O(2) atmosphere, relative to that under N(2), decreased the thickness of the Al(2)O(3) gate dielectric and relieved the gate leakage degradation induced by metallic arsenic; as a result, superior dielectric reliability was attained. We discuss the underlying thermochemical reactions that account for these experimental observations. (C) 2008 American Institute of Physics.
Growth of gamma-In2Se3 films on Si substrates by metal-organic chemical vapor deposition with different temperatures
(2008-04-01)
Huang, Yen-Chin
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Li, Zhen-Yu
;
Uen, Wu-Yih
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Lan, Shan-Ming
;
Chang, K. J.
In2Se3 films were deposited on the p(+)-Si(1 1 1) substrates by metal-organic chemical vapor deposition (MOCVD) for the first time at temperatures higher than 500 degrees C. Trimethyl indium (TMI) and H2Se were used as the source reactants with the flow ratio of [H2Se]/[TMI] being maintained at 6.7. The growth temperature was varied from 350 to 650 degrees C. Powder X-ray diffraction analyses revealed that the In2Se3 film grown is polycrystalline and has a wurtzite structure when the growth temperature is below 450 degrees C. Instead, a rhombohedral structure began to appear when the growth temperature is above 450 degrees C. Besides, SEM observations indicated a surface morphology of columnar structure for all films grown. Optical properties were examined by photoluminescence (PL) measurements. It was found that by conducting the growth at 550 degrees C a strong PL emission at around 2.14 eV was observed at 20 K. The luminescence mechanism was found to be dominated by the free excitons based on the temperature-dependent PL spectra from 20 to 120 K. However, bound exciton emissions were also observed or even became the dominant band when the films were grown at temperatures lower than 500 degrees C. Otherwise, the intensity of the 2.14 eV peak reduced greatly when the growth temperature was higher than 5 50 degrees C. Power-dependent PL measurements with excitation power varying from 0.1 to 100 mW confirm the luminescent mechanism and the material quality of the film grown at 550 degrees C. It is concluded that single-phase gamma-In2Se3 films can be achieved at temperatures lower than 450 degrees C; however, good-quality In2Se3 films with the simultaneous appearance of gamma- and beta-phase structures can be grown at around 550 degrees C. (C) 2007 Elsevier B.V. All rights reserved.
網站購買意願影響因素之探討
(2008-04-01)
林娟娟
;
陳岱昀
;
Judy Chuan-Chuan Lin
;
Tai-Yun Chen
;
Institute of Business and Management
網際網路的普及與行動通訊技術的快速發展，讓消費者隨時隨地皆能透過網路進行購物或瀏覽資訊，而由於網站爲網路消費者與商家接觸的重要介面，因此網站的資訊系統品質、內容及呈現方式，將影響消費者對網站的使用態度。爲留住顧客並提升其對於網站商品的購買意願，掌握網路消費者之喜好及信任態度，是網站經營者所應致力的目標。本研究彙整電子商務之相關文獻，提出以技術面、社會面及個人面三個層面，探討影響消費者網路購物行爲的前置因子，並提出一適用於網路購物之模型，以協助網站經營者掌握其中之關鍵，增加消費者對購物網站商品的購買意願。本研究使用LISREL統計軟體進行驗證性因素分析，以及結構方程模式分析，實證研究的結果顯示，消費者對網站的喜好及信任態度，正向影響消費者的購買意願，而在影響消費意願之前置因素中，又以消費者對網站的系統品質認知爲購買意願的重要影響因素，而消費者與網站互動產生的愉悅感受及網站的熟悉程度等因素亦顯著影響消費者的網站購物意願。此研究結果除了顯示影響消費者對購物網站商品之購買因素外，亦可瞭解消費者對網站之技術面、社會面及個人層面之認知，對於日後網站經營者在建置網站上，提供參考之依據。
Rapid and homogeneous dispersion of pt catalyst particles on multi-walled carbon nanotubes by temperature-controlled microwave polyol method
(2008-04-01)
Chen, Chieng-Ming
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Chen, Mi
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Yu, Hung-Wei
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Lu, Su-Chen
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Chen, Chia-Fu
Fuel cells, particularly direct methanol fuel cells (DMFCs), have great potential as mobile power sources. It has been extensively reported that the DMFC performance strongly depends on the electrode catalyst, and many research groups have focused on the preparation of high efficiency cathode catalysts using all types of metal nanoparticle and support. However, most of these methods are either time-consuming with multiple-steps or there is low loading of the nanocatalyst dispersed on the supports. In this study, platinum nanoparticles of uniform diameter (approximately 4.3 nm) were efficiently dispersed on multi-walled carbon nanotubes (MWCNTs) by the temperature-control led, microwave-assisted polyol method with the addition of sodium dodecyl sulfate (SDS) and [poly(vinyl pyrrolidone)] (PVP). The addition of SDS and PVP in chloroplatinic acid/ethylene glycol (EG) solution can cause the efficient and homogeneous dispersion of the catalyst particles on MWCNTs, enhance the adsorption of platinum particles, and reduce the residue of platinum particles. Moreover, temperature was determined to be the most important factor affecting the reduction of Pt in the process, and large amounts of Pt particles were characterized when the temperature ranged from 140 to 160 degrees C. The results indicate that the optimum temperature ranges from 140 to 160 degrees C, and that the loading amount of Pt/CNTs can reach more than 50 wt % in only 90 s of processing time. The significant improvements in dispersion and loading are due to the ability of SDS, to wrap the PVP-stabilized Pt nanoparticles around the surface of the carbon nanotubes. The characterization analyses were conducted by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and thermal gravinnetric analysis (TGA).
智慧型音訊處理器及其方法
(2008-04-01)
白明憲
;
陳孟君
一種智慧型音訊處理器,包括:一特徵擷取單元接收一音訊訊號,並使用數個音訊描述子對音訊訊號擷取數個特徵値;一資料預處理單元對數個特徵値正規化,以作為智慧型音訊處理系統之分類資訊;以及一分類演算單元依分類資訊將音訊訊號分類成數種不同種類的音樂。
Adaptive two-stage GSC-based PIC detection for time-varying MIMO channels
(2008-04-01)
Lee, Yinman
;
Wu, Wen-Rong
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電信工程研究所
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Institute of Communications Engineering
Adaptive parallel interference cancellation (PIC) has been recently proposed for the signal detection in multiple-input multiple-output (MIMO) systems. However, it suffers from error propagation when operated in time-varying channels. In this letter, an adaptive two-stage PIC with the minimum variance (MV) criterion is proposed to solve the problem. Adaptation with the MV criterion is realized with a decision feedback generalized sidelobe canceller (DFGSC). In the first-stage cancellation, a special structure involving dual DFGSCs is developed. All adaptation operations are implemented with the least-mean-square (LMS) algorithm. Simulations show that the proposed adaptive PIC detection can significantly outperform the conventional adaptive PIC detection in time-varying MIMO channel environments.
Bio-imaging of alpha-bungarotoxin binding to target cell by carboxylated nanodiamond
(2008-04-01)
Chao, Jui-I
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Liu, Kuang-Kai
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Chen, Mei-Fang
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Chen, Po-Yi
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Lee, Tony J. F.
Mixing flow characteristics in a vessel agitated by the screw impeller with a draught tube
(2008-04-01)
Tsui, Yeng-Yung
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Hu, Yu-Chang
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機械工程學系
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Department of Mechanical Engineering
The circulating flow in a vessel induced by rotating impellers has drawn a lot of interests in industries for mixing different fluids. It used to rely on experiments to correlate the performance with system parameters because of the theoretical difficulty to analyze such a complex flow. The recent development of computational methods makes it possible to obtain the entire flow field via solving the Navier-Stokes equations. In this study, a computational procedure, based on multiple frames of reference and unstructured grid methodology, was used to investigate the flow in a vessel stirred by a screw impeller rotating in a draught tube. The performance of the mixer was characterized by circulation number, power number, and nondimensionalized mixing energy. The effects on these dimensionless parameters were examined by varying the settings of tank diameter, shaft diameter, screw pitch, and the clearance between the impeller and the draught tube. Also investigated was the flow system without the draught tube. The flow mechanisms to cause these effects were delineated in detail.
Dam overtopping risk assessment considering inspection program
(2008-04-01)
Kuo, Jan-Tai
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Hsu, Yung-Chia
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Tung, Yeou-Koung
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Yeh, Keh-Chia
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Wu, Jian-De
Safety inspection of large dams in Taiwan is conducted every 5 years. The practice does not take into consideration uncertainty of dam conditions. The goal of this study is to determine the optimal dam inspection interval under the consideration of overtopping risk incorporating uncertainty gate availability. In earlier studies, assessment of overtopping risk only considered the uncertainties in reservoir properties and natural randomness of hydrologic events without giving much thought to the availability of spillway gates. As a result, the overtopping risk could be underestimated. In this study, an innovative concept is proposed to evaluate dam overtopping by taking into account spillway gate availability. The framework consists of three parts: (1) evaluation of conditional overtopping risk for different numbers of malfunctioning spillway gates; (2) evaluation of spillway gate availability; and (3) dam inspection scheduling. Furthermore, considerations are given to overtopping risk, inspection cost, and dam break cost for determining the optimal inspection schedule. The methodology is applied to the Shihmen Reservoir in Taiwan and to evaluate its time-dependent overtopping risk. Results show that overtopping risk considering the availability of the spillway gates is higher than the one without considering the availability of the spillway gates.
Multimode G(m)-C channel selection filter for mobile applications in 1-V supply voltage
(2008-04-01)
Lo, Tien-Yu
;
Hung, Chung-Chih
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電信工程研究所
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Institute of Communications Engineering
A CMOS transconductor for multimode channel selection filter is presented. The transconductor includes a voltage-to-current converter and a current multiplier. Voltage-to-current conversion employs linear region MOS transistors, and the conversion features high linearity over a wide input swing range. The current multiplier which operates in the weak inversion region provides a wide transconductance tuning range without degrading the linearity. A third-order Butter-worth low-pass filter implemented. with the transconductors was designed by TSMC 0.18-mu m CMOS process. The measurement results show that the filter can operate with the cutoff frequency of 135 kHz to 2.2 MHz. The tuning range and the linearity performance would be suitable for the wireless specifications of GSM, Bluetooth, cdma2000, and wide-band CDMA. In the design, the maximum power consumption at the highest cutoff frequency is 2 mW under a 1-V supply voltage.
RF and logic performance improvement of In0.7Ga0.3As/InAs/In0.7Ga0.3As composite-channel HEMT using gate-sinking technology
(2008-04-01)
Kuo, Chien-I
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Hsu, Heng-Tung
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Chang, Edward Yi
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Chang, Chia-Yuan
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Miyamoto, Yasuyuki
Eighty-nanometer-gate In0.7Ga0.3As/InAs/ In0.7Ga0.3As composite-channel high-electron mobility transistors (HEMTs), which are fabricated using platinum buried gate as the Schottky contact metal, were evaluated for RF and logic application. After gate sinking at 250 degrees C for 3 min, the device exhibited a high g(m) value of 1590 mS/mm at V-d = 0.5 V, the current-gain cutoff frequency f(T) was increased from 390 to 494 GHz, and the gate-delay time was decreased from 0.83 to 0.78 ps at supply voltage of 0.6 V. This is the highest f(T) achieved for 80-nm-gate-length HEMT devices. These superior performances are attributed to the reduction of distance between gate and channel and the reduction of parasitic gate capacitances during the gate-sinking process. Moreover, such superior performances were achieved through a very simple and straightforward fabrication process with optimal epistructure of the device.
Preface to the special issue on satellite altimetry over land and coastal zones: Applications and challenges
(2008-04-01)
Hwang, Cheinway
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Benveniste, Jerome
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Dang, Yamin
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Shum, C. K.
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土木工程學系
Low levels of haptoglobin and putative amino acid sequence in Taiwanese Lanyu miniature pigs
(2008-04-01)
Yueh, Sunny C. H.
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Wang, Yao Horng
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Lin, Kuan Yu
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Tseng, Chi Feng
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Chu, Hsien Pin
Porcine haptoglobin (Hp) is an acute phase protein. Its plasma level increases significantly during inflammation and infection. One of the main functions of Hp is to bind free hemoglobin (Hb) and inhibit its oxidative activity. In the present report, we studied the Hp phenotype of Taiwanese Lanyu miniature pigs (TLY minipigs; n=43) and found their Hp structure to be a homodimer (beta-alpha-alpha-beta) similar to human Hp 1-1. Interestingly, Western blot and high performance liquid chromatographic (HPLC) analysis showed that 25% of the TLY minipigs possessed low or no plasma Hp level (<0.05 mg/ml). The Hp cDNA of these TLY minipigs was then cloned, and the translated amino acid sequence was analyzed. No sequences were found to be deficient; they showed a 99.7% identity with domestic pigs (NP_999165). The mean overall Hp level of the TLY minipigs (0.21 +/- 0.25 mg/ml; n=43) determined by enzyme-linked immunosorbent assay (ELISA) was markedly lower than that of domestic pigs (0.78 +/- 0.45 mg/ml; p<0.001), while 25% of the TLY minipigs had an Hp level that was extremely low (<0.05 mg/ml). In addition, the initial recovery rate (first 40 min) in the circulation of infused fluorescein isothiocyanate (FITC)-Hb was significantly higher in the TLY minipigs with extremely low Hp levels than those with high levels. This data suggests that the low concentration of Hp-Hb complex is responsible for the higher recovery rate of Hb in the circulation. TLY minipigs have been used as an experimental model for cardiovascular diseases; whether they can be used as a model for inflammatory diseases, with Hp as a marker, remains a topic of interest. However, since the Hp level varies significantly among individual TLY minipigs, it is necessary to prescreen the Hp levels of the animals to minimize variation in the experimental baseline. The present study may provide a reference value for future use of the TLY minipig as an animal model for inflammation-associated diseases.
A two-matrix system for MALDI MS analysis of serine phosphorylated peptides concentrated by Fe3O4/Al2O3 magnetic nanoparticles
(2008-04-01)
Chen, Cheng-Tai
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Chen, Yu-Chie
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
Bias-enhanced nucleation of oriented diamonds on cone-like Si
(2008-04-01)
Chang, Li
;
Yan, Jhih-Kun
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材料科學與工程學系
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Department of Materials Science and Engineering
Uniform distribution of bias-enhanced nucleation of diamond has been improved on Si substrate of an area of 1 x 1 cm(2) by using a domeshaped Mo counter electrode in a microwave plasma chemical vapor deposition reactor. A nucleation density of 10(9) cm(2) can be reached within a few minutes when the bias voltage of - 100 V is applied on the substrates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that a single-crystalline diamond in a few nanometered size can be deposited on a volcano-shaped cubic SiC which is epitaxially formed on a Si cone. Examination reveals a large fraction of diamond nuclei are oriented along with one side of SiC on each Si cone. The Si cone formed on the Si substrate is due to plasma etching. The diamond nuclei have a shape close to rhombus in TEM. With further growth, secondary nucleation of diamond occurs on top of diamond nuclei and SiC which grows with Si cones. As a result, polycrystalline diamonds are deposited on each Si cone. (C) 2008 Elsevier B.V. All fights reserved.
Metal organic chemical vapor deposition growth of GaN-based light emitting diodes with naturally formed nano pyramids
(2008-04-01)
Chiu, Ching-Hua
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Lee, Chia-En
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Lo, Ming-Hua
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Huang, Hung-Wen
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Lu, Tien-Chang
GaN-based light-emitting diodes (LEDs) with naturally formed nano pyramids roughened surfaces grown by metal organic chemical vapor deposition (MOCVD) were demonstrated. In this study, Mg-treatment, a growth-.interruption step and a surface treatment using biscyclopentadienyl magnesium (CP(2)Mg), was performed to form the nano pyramids on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface. Assisted by the nano pyramids surface roughening process, the light output power of the LEDs reached 11.3 and 9.7 mW with 10 and 5 min Mg-treatment at a driving current of 20 mA. The light outputs were increased by 48 and 27%, respectively, compared with the results from the LED without Mg-treatment.
Study of the performance of stainless steel A-TIG welds
(2008-04-01)
Shyu, S. W.
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Huang, H. Y.
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Tseng, K. H.
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Chou, C. P.
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機械工程學系
The purpose of the present work was to investigate the effect of oxide fluxes on weld morphology, arc voltage, mechanical properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of 5 mm thick austenitic stainless steel plates. A novel variant of the autogenous TIG welding process, oxide powders (Al2O3, Cr2O3, TiO2, SiO2 and CaO) was applied on a type 304 stainless steel through a thin layer of the flux to produce a bead on plate welds. The experimental results indicated that the increase in the penetration is significant with the use of Cr2O3, TiO2, and SiO2. A-TIG welding can increase the weld depth to bead-width ratio, and tends to reduce the angular distortion of the weldment. It was also found that A-TIG welding can increase the retained delta-ferrite content of stainless steel 304 welds and, in consequence, the hot-cracking susceptibility of as-welded is reduced. Physically constricting the plasma column and reducing the anode spot are the possible mechanism for the effect of certain flux on A-TIG penetration.
Effective transmission opportunity allocation scheme for real-time variable bit rate traffic flows with different delay bounds
(2008-04-01)
Lee, T. -H.
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Huang, Y. -W.
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電信工程研究所
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Institute of Communications Engineering
The medium access control of IEEE 802.11e defines a novel coordination function, namely, hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate traffic, packet loss may occur seriously. The authors propose a TXOP allocation scheme to efficiently allocate bandwidth and meet the QoS requirements in terms of both delay bound and packet loss probability. To achieve high bandwidth efficiency, the authors take advantage of not only intra-flow multiplexing gain of traffic flows with large delay bounds, but also inter-flow multiplexing gain of multiple traffic flows with different delay bounds. According to numerical results obtained by computer simulations, the proposed TXOP allocation scheme results in much higher bandwidth efficiency than previous algorithms under the same constraints of delay bounds and packet loss probability.