Browsing by Issue Date, starting with "2009-01-13"

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Identification of Essential Residues of Human alpha-L-Fucosidase and Tests of Its Mechanism
(2009-01-13)
Liu, Sheng-Wen
;
Chen, Chao-Sheng
;
Chang, Shih-Shen
;
Mong, Kwok-Kong Tony
;
Lin, Chun-Hung
Fucosylated glycoconjugates have critical roles in biological processes, but a limited availability Of alpha-L-fucosidase has hampered research on this human enzyme (h-Fuc) at a molecular level. After overexpressing h-Fuc in Escherichia coli as an active form, we investigated the catalytic function of this recombinant enzyme. Based on sequence alignment and structural analysis of close homologues of h-Fuc, nine residues of glutamate and aspartate in h-Fuc were selected for mutagenic tests to determine the essential residues. Among the mutants, D225N, E289Q, and E289G lost catalytic activity significantly; their k(cat) values are 1/5700, 1/430, and 1/340, respectively, of that of the wild-type enzyme. The Bronsted plot for k(cat)/K(m) for the E289G mutant is linear with beta(1g) = -0.93, but that for k(cat) is biphasic, with beta(1g) for poor substrates being -0.88 and for activated substrates being -0.11. The small magnitude of Pig for the activated substrates may indicate that the rate-limiting step of the reaction is defucosylation, whereas the large magnitude of the latter Pig value for the poor substrates indicates that the rate-limiting step of the reaction becomes fucosylation. The kinetic outcomes support an argument that ASp(225) functions as a nucleophile and Glu(289) as a general acid/base catalyst. As further evidence, azide significantly reactivated D225G and E289G, and (1)H NMR spectral analysis confirmed the formation of beta-fucosyl azide and alpha-fucosyl azide in the azide rescues of D225G and E289G catalyses, respectively. As direct evidence to prove the function of Glu(289), an accumulation of fucosyl-enzyme intermediate was detected directly through ESI/MS analysis.
Effects of nanomorphological changes on the performance of solar cells with blends of poly[9,9 '-dioctyl-fluorene-co-bithiophene] and a soluble fullerene
(2009-01-14)
Huang, Jen-Hsien
;
Ho, Zhong-Yo
;
Kekuda, Dhananjay
;
Chang, Yung
;
Chu, Chih-Wei
Controlled nanophase segregation within the blended films of a conjugated polymer and a soluble fullerene has enabled us to form a continuous transfer pathway for the carriers, thereby increasing the photocurrent generation for polymer photovoltaic devices. Here, we study the effects of nanomorphological changes on the performance of polymer solar cells using blended films of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Different weight ratios of the F8T2 and PCBM blends in various solvents were studied at different annealing temperatures. The morphology of the films seems to be a strong function of the processing conditions. The power conversion efficiency (PCE) of the photovoltaic devices has improved significantly from 0.34% to 2.14% under air mass 1.5 simulated solar illumination (100 mW cm(-2)), which could be attributed to the nanomorphological changes in the films.
Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO3 thin films
(2009-01-14)
Lin, T. H.
;
Shih, H. C.
;
Hsieh, C. C.
;
Luo, C. W.
;
Lin, J-Y
We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO3 (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO3(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho3+ moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c- axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.
Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO(3) thin films
(2009-01-14)
Lin, T. H.
;
Shih, H. C.
;
Hsieh, C. C.
;
Luo, C. W.
;
Lin, J-Y
We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO(3) (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO(3)(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho(3+) moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c- axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.
Free carrier dynamics of InN nanorods investigated by time-resolved terahertz spectroscopy
(2009-01-15)
Ahn, H.
;
Chuang, C. -H.
;
Ku, Y. -P.
;
Pan, C. -L.
;
光電工程學系
Ultrafast time-resolved terahertz spectroscopy is employed to investigate the carrier dynamics of indium nitride (InN) nanorod arrays and an epitaxial film. Transient differential transmission of terahertz wave shows that hot carrier cooling and defect-related nonradiative recombination are the common carrier relaxation processes for InN film and nanorods. However, the electrons confined in the narrow structure of nanorods are significantly affected by the carrier diffusion process near the surface, which causes the abnormally long relaxation time for nanorods.
Damage of light-emitting diodes induced by high reverse-bias stress
(2009-01-15)
Chen, N. C.
;
Wang, Y. N.
;
Wang, Y. S.
;
Lien, W. C.
;
Chen, Y. C.
The ability of a nitride light-emitting diode (LED) to withstand electrostatic discharge (ESD) is important because of the insulating property of the sapphire substrate. Therefore, damage caused by ESD to a nitride LED is a valuable subject. However, damage is caused by ESD in a very short period, so monitoring its evolution is very difficult. Accordingly, ESD experiments are performed and the effects of a high reverse Current (HRC) on devices are investigated. Damage caused by ESD and HRC and their other effects on devices are compared. Four distinct effects of the ESD on devices are illustrated. (c) 2008 Elsevier B.V. All rights reserved.
Spatial complexity in multi-layer cellular neural networks
(2009-01-15)
Ban, Jung-Chao
;
Chang, Chih-Hung
;
Lin, Song-Sun
;
Lin, Yin-Heng
;
應用數學系
This study investigates the complexity of the global set of output patterns for one-dimensional multi-layer cellular neural networks with input. Applying labeling to the output space produces a sofic shift space. Two invariants, namely spatial entropy and dynamical zeta function, can be exactly computed by studying the induced sofic shift space. This study gives sofic shift a realization through a realistic model. Furthermore, a new phenomenon, the broken of symmetry of entropy, is discovered in multi-layer cellular neural networks with input. (C) 2008 Elsevier Inc. All rights reserved.
Growth mode and novel structure of ultra-thin KCl layers on the Si(100)-2 x 1 surface
(2009-01-15)
Tsay, S-F.
;
Chung, J. Y.
;
Hsieh, M-F.
;
Ferng, S-S.
;
Lou, C-T.
This study investigates ultra-thin potassium chloride (KCl) films on the Si(1 0 0)-2 x 1 surfaces at near room temperature. The atomic structure and growth mode of this ionic solid film on the covalent bonded semiconductor surface is examined by synchrotron radiation core level photoemission, scanning tunneling microscopy and ab initio calculations. The Si 2p, K 3p and Cl 2p core level spectra together indicate that adsorbed KCl molecules at submonolayer coverage partially dissociate and that KCl overlayers; above one monolayer (ML) have similar features in the valance band density of states as those of the bulk KCl crystal. STM results reveal a novel c(4 x 4) structure at 1 ML coverage. Ab initio calculations show that a model that comprises a periodic pyramidal geometry is consistent with experimental results. (C) 2009 Elsevier B.V. All rights reserved.
MULTIPLEXING METHOD AND APPARATUS THEREOF FOR DATA SWITCHING
(2009-01-15)
Wang, Chung-Hsuan
;
Lee, Shuenn-Gi
A multiplexing method for data switching is disclosed. In the method, a continuous data is received, and the continuous data includes a plurality of super frames, and each super frame includes a plurality of frames. These super frames are divided into a set of even super frames and a set of odd super frames. The frames included in the set of odd super frames are sorted by corresponding required bit error rate of each frame decreasingly or increasingly. The frames included in the set of even super frames are sorted by the required bit error rate of each frame increasingly or decreasingly. An encoder is used to encode these sorted super frames.
Design and Characterization of Novel Porphyrins with Oligo(phenylethylnyl) Links of Varied Length for Dye-Sensitized Solar Cells: Synthesis and Optical, Electrochemical, and Photovoltaic Investigation
(2009-01-15)
Lin, Ching-Yao
;
Lo, Chen-Fu
;
Luo, Liyang
;
Lu, Hsueh-Pei
;
Hung, Chen-Shiung
Novel zinc porphyrins with 1-4 pi-conjugated phenylethyinyl (PE) units (labeled PE1-PE4) as a link of controlled length were synthesized for fundamental tests and applications as a dye-serisitized solar cell (DSSC). The UV-visible spectra of the solution samples show clear absorption patterns of the PE groups in a region 300-400 nm, consistent with results calculated with density-functional theory. Cyclic voltammograms of PE1-PE4 in tetrahydrofuran show similar electrochemical potentials for each compound. Ferntosecond fluorescence up-conversion of solution samples and of porphyrin-sensitized TiO(2) films was measured with excitation at 420 or 430 nm and emission at 460, 470, 620, and 680 nm. When these porphyrins were fabricated into DSSC devices, the efficiency of power conversion of these devices decreased systematically with increasing length of the link: 2.5 +/- 0.2% (PE1), 2.0 +/- 0.1% (PE2), 0.78 +/- 0.09% (PE3), 0.25 +/- 0.02% (PE4). This great photovoltaic degradation from PE1 to PE4 is not interpretable according to the rate of electron injection independent of length; other factors, including electron transfer from the semiconductor back to the porphyrin cation or the electrolyte, must be considered to account for the observed dependence of photovoltaic performance on length.
Calibration and on-line data selection of multiple optical flow sensors for odometry applications
(2009-01-15)
Hu, Jwu-Sheng
;
Chang, Yung-Jung
;
Hsu, Yu-Lun
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This work proposes a calibration method and a computational algorithm to integrate the data of multiple optical flow sensors for two-dimensional trajectory measurements. Optical flow sensors offer a different kind of odometer as compared to the wheel encoder. Using multiple sensors can reduce the effect of measurement uncertainties. Since all sensors are mounted on a rigid body, their measurement data must obey a certain relation. which is utilized in this work. Additionally, mathematical formulae are developed to realize the computation. Analytical results show that the calibration procedure can be cast as an optimization problem given measurement data. Furthermore, the rigid-body relation is formulated as a null-space constraint using the calibrated parameters. Unreliable sensor measurements can be removed during operation by accessing the error distance to the null space. Experimental results are presented to support the proposed methods. (C) 2008 Elsevier B.V. All rights reserved.
Structure of high power edge emission laser diode
(2009-01-15)
Lu, Tien-Chang
;
Chen, Chyong-Hua
A structure of high power edge emission laser diode that has plural mode extension sublayers with a chirp periodic distribution is provided. The Near Field Pattern (NFP) is an L shape, and the high intensity portion is nicely overlapped with the multi quantum wells. Furthermore, the low intensity portion will extend to the n-type cladding as it can as possible. Accordingly, the optical power density on the mirror surface of the high power edge emission laser diode is lower down and the vertical divergence angle is decreased, so as to prolong its lifetime.
Electromigration in Sn-Cu intermetallic compounds
(2009-01-15)
Wei, C. C.
;
Chen, C. F.
;
Liu, P. C.
;
Chen, Chih
;
材料科學與工程學系
As the shrinking in bump size continues, the effect of intermetallic compounds (IMCs) on electromigration becomes more pronounced. Electromigration in Sn-Cu intermetallic compounds was examined using edge displacement method. It was found that Cu(6)Sn(5) compounds are more susceptible to electromigration than Cu(3)Sn compounds. The lower solidus temperature and higher resistivity of the Cu(6)Sn(5) IMCs are responsible for its higher electromigration rate. Length-dependent electromigration behavior was found in the stripes of various lengths and the critical length was determined to be between 5 and 10 mu m at 225 degrees C, which corresponded to a critical product between 2.5 and 5 A/cm. Furthermore, the Sn-Cu compounds were proven to have better electromigration resistance than eutectic SnAgCu solder.
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
;
Mebel, A. M.
;
Hayashi, M.
;
Chang, H. C.
;
Lin, S. H.
Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV(0) and NV(-)) have been performed employing various theoretical methods and basis Sets and using finite model NC(n)H(m) clusters. Unpaired electrons in the ground doublet state of NV(0) and triplet state of NV(-) are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV(-) are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV(0) we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009
Spatial complexity in multi-layer cellular neural networks
(2009-01-15)
Ban, Jung-Chao
;
Chang, Chih-Hung
;
Lin, Song-Sun
;
Lin, Yin-Heng
;
應用數學系
This study investigates the complexity of the global set of output patterns for one-dimensional multi-layer cellular neural networks with input. Applying labeling to the output space produces a sofic shift space. Two invariants, namely spatial entropy and dynamical zeta function, can be exactly computed by studying the induced sofic shift space. This study gives sofic shift a realization through a realistic model. Furthermore, a new phenomenon, the broken of symmetry of entropy, is discovered in multi-layer cellular neural networks with input. (C) 2008 Elsevier Inc. All rights reserved.
Growth mode and novel structure of ultra-thin KCl layers on the Si(100)-2 x 1 surface
(2009-01-15)
Tsay, S-F.
;
Chung, J. Y.
;
Hsieh, M-F.
;
Ferng, S-S.
;
Lou, C-T.
This study investigates ultra-thin potassium chloride (KCl) films on the Si(1 0 0)-2 x 1 surfaces at near room temperature. The atomic structure and growth mode of this ionic solid film on the covalent bonded semiconductor surface is examined by synchrotron radiation core level photoemission, scanning tunneling microscopy and ab initio calculations. The Si 2p, K 3p and Cl 2p core level spectra together indicate that adsorbed KCl molecules at submonolayer coverage partially dissociate and that KCl overlayers; above one monolayer (ML) have similar features in the valance band density of states as those of the bulk KCl crystal. STM results reveal a novel c(4 x 4) structure at 1 ML coverage. Ab initio calculations show that a model that comprises a periodic pyramidal geometry is consistent with experimental results. (C) 2009 Elsevier B.V. All rights reserved.
Calibration and on-line data selection of multiple optical flow sensors for odometry applications
(2009-01-15)
Hu, Jwu-Sheng
;
Chang, Yung-Jung
;
Hsu, Yu-Lun
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This work proposes a calibration method and a computational algorithm to integrate the data of multiple optical flow sensors for two-dimensional trajectory measurements. Optical flow sensors offer a different kind of odometer as compared to the wheel encoder. Using multiple sensors can reduce the effect of measurement uncertainties. Since all sensors are mounted on a rigid body, their measurement data must obey a certain relation. which is utilized in this work. Additionally, mathematical formulae are developed to realize the computation. Analytical results show that the calibration procedure can be cast as an optimization problem given measurement data. Furthermore, the rigid-body relation is formulated as a null-space constraint using the calibrated parameters. Unreliable sensor measurements can be removed during operation by accessing the error distance to the null space. Experimental results are presented to support the proposed methods. (C) 2008 Elsevier B.V. All rights reserved.
Power factor correction method and device
(2009-01-15)
Chen, Hung-Chi
A power factor correction method and the controller thereof, applied to a boost-type converter, are provided. First, the power factor correction method uses the input and output voltages to generate a reference switching signal. Next, a voltage control circuit uses the difference between the output voltage and a voltage command to get a duty phase. Then, the switching control signal is determined by shifting the phase of the reference switching signal according to the duty phase. Finally, a comparator compares the switching control signal with a triangle waveform signal to determine the switching signal. A power factor controller, which utilizes this method, uses only a single voltage control circuit to get the switching signal to regulate the output voltage and shape the current waveform without sensing current and a current control circuit, so that the complexity of the invented control circuit for the power factor correction is reduced dramatically.
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
;
Mebel, A. M.
;
Hayashi, M.
;
Chang, H. C.
;
Lin, S. H.
Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV0 and NV-) have been performed employing various theoretical methods and basis Sets and using finite model NCnHm clusters. Unpaired electrons in the ground doublet state of NV0 and triplet state of NV- are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV- are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV0 we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009
適用於資料切換多工之方法及裝置
(2009-01-16)
王忠炫
;
李順吉
一種適用於資料切換的多工方法,包括輸入一連續資料,其中此資料包括多個超級訊框,且每一個超級訊框包含多個框架。區分這些超級訊框成多個奇數部份及多個偶數部份之超級訊框。重新排列每一個奇數部份之超級訊框所包含之多個框架,其排列方式為依據其包含之這些框架所需求的位元錯誤率(BER)由大到小或由小到大排列。重新排列每一個偶數部份之超級訊框所包含之多個框架,其排列方式為依據其包含之框架所需求的位元錯誤率由小到大或由大到小排列。以及使用一編碼器對重新排列過後的超級訊框進行編碼。