Browsing by Issue Date, starting with "2007-09-26"

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Computational study of molecular properties of aggregates of C-60 and (16,0) zigzag nanotube
(2007-09-26)
Witek, Henryk A.
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Trzaskowski, Bartosz
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Malolepza, Edyta
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Morokuma, Keiji
;
Adamowicz, Ludwik
Molecular properties for two aggregates of C-60 and a (16, 0) zigzag nanotube: (a) C-60 encapsulated in the nanotube, (b) C-60 attached to the outer wall of the nanotube, are studied using the self-consistent charge density-functional tight-binding method with additional dispersion correction. The binding energy for the encapsulated fullerene is -108.3 kcal/mol and for the attached fullerene, only -20.3 kcal/mol. The harmonic vibrational frequencies of the aggregates are found to be almost identical to those obtained for the non-interacting system. Very small extent of the changes upon interaction may pose a challenge to study the aggregated structures using experimental spectroscopic methods. (C) 2007 Elsevier B.V. All rights reserved.
Formation of a precursor layer in self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy
(2007-09-26)
Yang, C. S.
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Wang, J. S.
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Lai, Y. J.
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Luo, C. W.
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Chen, D. S.
The growth mode of CdTe quantum dots ( QDs) grown on highly lattice-mismatched ZnSe buffer was investigated. CdTe QDs ( 0.6 to 5.0 mono-layers ( MLs)) were deposited on the Se-stabilized ZnSe buffer layers using an alternating supply of Cd and Te atomic sources. Cross-sectional transmission electron microscopy and photoluminescence ( PL) measurements revealed the existence of a CdSe-like two-dimensional precursor layer ( PCL). The prominent difference in the temperature-dependent PL peak shift was associated with the emissions from the respective CdSe PCL and CdTe QDs. In addition, the PL excitation measurement demonstrated the existence of the first QD excited excitonic state.
Auditory cortical receptive fields: Stable entities with plastic abilities
(2007-09-26)
Elhilali, Mounya
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Fritz, Jonathan B.
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Chi, Tai-Shih
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Shamma, Shihab A.
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電信工程研究所
To form a reliable, consistent, and accurate representation of the acoustic scene, a reasonable conjecture is that cortical neurons maintain stable receptive fields after an early period of developmental plasticity. However, recent studies suggest that cortical neurons can be modified throughout adulthood and may change their response properties quite rapidly to reflect changing behavioral salience of certain sensory features. Because claims of adaptive receptive field plasticity could be confounded by intrinsic, labile properties of receptive fields themselves, we sought to gauge spontaneous changes in the responses of auditory cortical neurons. In the present study, we examined changes in a series of spectrotemporal receptive fields (STRFs) gathered from single neurons in successive recordings obtained over time scales of 30-120 min in primary auditory cortex (A1) in the quiescent, awake ferret. We used a global analysis of STRF shape based on a large database of A1 receptive fields. By clustering this STRF space in a data-driven manner, STRF sequences could be classified as stable or labile. We found that > 73% of A1 neurons exhibited stable receptive field attributes over these time scales. In addition, we found that the extent of intrinsic variation in STRFs during the quiescent state was insignificant compared with behaviorally induced STRF changes observed during performance of spectral auditory tasks. Our results confirm that task-related changes induced by attentional focus on specific acoustic features were indeed confined to behaviorally salient acoustic cues and could be convincingly attributed to learning-induced plasticity when compared with "spontaneous" receptive field variability.
Effects of temperature on the location of the gas-liquid interface in a PEM fuel cell
(2007-09-27)
Lee, Chun-I
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Chu, Hsin-Sen
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機械工程學系
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Department of Mechanical Engineering
The objective of this study is to investigate the location of the gas-liquid interface at various temperatures in a polymer electrolyte membrane fuel cell under non-isothermal conditions. A mathematical model, coupled with the electrochemical process, two-phase flows, species transfer, and heat transfer is employed. A finite volume-based CFD approach is applied to investigate the species transport behavior in a fuel cell. The effects of two model parameters, namely cell temperature (T-cell) and humidification temperature (T-h), on the gas-liquid interface and cell performance are presented. Simulation results indicate that variations of these two parameters influence the location of the gas-liquid interface, the cell performance, and the distribution of liquid water saturation. At lower cell temperatures, the gas-liquid interface moves toward the inlet port of the channel when the humidification temperature is greater than the cell temperature. Therefore, the cell performance decreases as the liquid water clogs the passage for the transport of oxygen. Furthermore, these two factors are closely related to the membrane temperature distribution. Obvious variations in magnitude are seen at a cell temperature of 323 K and a humidification temperature of 343 K. (C) 2007 Elsevier B.V. All rights reserved.
Photodissociation of 1,3,5-triazine: An ab initio and RRKM study
(2007-09-27)
Dyakov, Y. A.
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Mebel, A. M.
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Lin, S. H.
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Lee, Y. T.
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Ni, C.-K.
The ab initio/Rice-Ramsperger-Kassel-Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of 1,3,5-triazine at different wavelengths of the absorbed photon. Reaction pathways leading to various decomposition products have been mapped out at the G3(MP2,CC)//B3LYP level, and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for the dissociation products have been calculated using the steady-state approach. The results show that, after being excited by 275, 248, or 193 nm photons, the triazine molecule isomerizes to an opened-ring structure on the first singlet excited-state potential energy surface (PES), which is followed by relaxation into the ground electronic state via internal conversion. On the contrary, excitation by 285 and 295 nm photons cannot initiate the ring-opening reaction on the excited-state PES, and the molecule relaxes into the energized ring isomer in the ground electronic state. The dissociation reaction starting from the ring isomer is calculated to have branching ratios of various reaction channels significantly different from those for the reaction initiating from the opened-ring structure. The existence of two distinct mechanisms of 1,3,5-triazine photodissociation can explain the inconsistency in the translational energy distributions of HCN moieties at different wavelengths observed experimentally.
System and method for visualizing sound source energy distribution
(2007-09-27)
Bai, Mingsian R.
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Lin, Jia-Hong
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Ning, Yu-Wei
The present invention discloses a system for visualizing sound source energy distribution and a method thereof, wherein a propagation matrix and a window matrix are obtained firstly; next, an inverse operation of the propagation matrix is performed; next, a multiplication operation of the result of the inverse operation and the window matrix is performed; next, the result of the multiplication operation is transformed from the time domain to the frequency domain; thus, a sound source energy distribution reconstructor is established; then, an array of microphones is used to receive the sound source signals; next, a multi-channel capture device transforms the received sound source signals into digital sound source signals; lastly, a convolution operation is performed on the digital sound source signals and the sound source energy distribution reconstructor to obtain a visualized sound source energy distribution. Therefore, the present invention can provide the energy distributions of nearfield/farfield stable-state/unstable-state sound sources.
Thermodynamical study of the thermoelectric effect for magnesium silicide
(2007-09-27)
Zhu, Z. H.
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Zhu, Chaoyuan
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應用化學系分子科學碩博班
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Institute of Molecular science
The thermoelectric effect of magnesium silicide is studied by using it thermodynamical method in the presence of an electric field. The thermoelectric potential is evaluated from the partial derivative of free energy with respect to charge in which the free energy is calculated at the B3LYP/6-31G(d,p) level of density functional theory. This free energy is also utilized to determine the average dipole moment from which the polarizability, alpha; molar polarization, Psi; and dielectric constant can be computed. The present calculation for the dielectric constant (similar to 24-20) is in very good agreement with the experimental value (20). This accurate dielectric constant can be used to derive the relation of the thermoelectric potential with respect to temperature, from which the thermoelectric power or the Seebeck coefficients are calculated. The present result shows good agreement with experiment measurement for the Seebeck coefficients. In comparison, that calculation from the energy band structure theory is far off from the experimental values.
Photodissociation dynamics of phenol
(2007-09-27)
Tseng, Chien-Ming
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Lee, Yuan T.
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Lin, Ming-Fu
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Ni, Chi-Kung
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Liu, Suet-Yi
The photodissociation of phenol at 193 and 248 nm was studied using multimass ion-imaging techniques and step-scan time-resolved Fourier-transform spectroscopy. The major dissociation channels at 193 nm include cleavage of the OH bond, elimination of CO, and elimination of H2O. Only the former two channels are observed at 248 nm. The translational energy distribution shows that H-atom elimination occurs in both the electronically excited and ground states, but elimination of CO or HO occurs in the electronic ground state. Rotationally resolved emission spectra of CO (1 <= v <= 4) in the spectral region of 1860-2330 cm(-1) were detected upon photolysis at 193 nm. After a correction for rotational quenching, CO (v 4) shows a nascent rotational temperature of similar to 4600 K. The observed vibrational distribution of (v = 1)1(v 2)/(v = 3)/(v = 4) = 64.3/22.2/9.1/4.4 corresponds to a vibrational temperature of 3350 +/- 20 K. An average rotational energy of 6.9 +/- 0.7 kcal mol(-1) and vibrational energy of 3.8 +/- 0.7 kcal mol(-1) are observed for the CO product. The dissociation channels, translational energy distributions of the photofragment, and vibrational and rotational energies of product CO are consistent with potential energy surfaces from quantum chemical calculations and the branching ratios from an RRKM calculation.
Experimental and theoretical investigation of high-power laser ionization and dissociation of methane
(2007-09-27)
Sharifi, A.
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Kong, F.
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Chin, S. L.
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Mineo, H.
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Dyakov, Y.
The main purpose of this paper is to report the high-power laser ionization-dissociation of CH4 at various femtosecond (fs) laser intensities (from 1 x 10 14 W/cm(2) to 2 x 1015 W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH4+ and CH4++. Outside the influence of the A intense laser, we propose to calculate the mass spectra due to the decomposition of CH4+ and CH4++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.
Theoretical investigation of carrier envelope phase dependence of all-optical poling with the third- and higher-order nonlinear processes
(2007-09-27)
Taneichi, Takashi
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Kobayashi, Takayoshi
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電子物理學系
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Department of Electrophysics
Dependence of efficiency in all-optical poling with nonlinear processes, up to eighth order, is considered. The explicit form of the nonlinear susceptibility that is responsible for the poling is derived, which shows both CEP and phase mismatch dependence. On the basis of an analysis of pulse propagation in a nonlinear material, it is shown that one can identify the order of nonlinearity that is relevant to the poling process, relying on current technology of CEP stabilization and thin-film growth.
Groundwater contaminant source identification by a hybrid heuristic approach
(2007-09-29)
Yeh, Hund-Der
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Chang, Tung-Hua
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Lin, Yu-Chung
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環境工程研究所
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Institute of Environmental Engineering
This study proposes an approach, SATS-GWT, that combines simulated annealing (SA), tabu search (TS), and the three-dimensional groundwater flow and solute transport model (MODFLOW-GWT). Our approach is used to estimate the source information: source location, release concentration, and release period. The sampling concentrations at monitoring points are simulated by the MODFLOW-GWT with an assumed release concentration and release period at a known source location. In the source estimation process, the source location is selected by TS within the suspected source area, and the trials for release concentrations and release periods are generated by SA. The MODFLOW-GWT is employed to compute the simulated concentrations at the monitoring points with the trial solution. The above mentioned procedures are repeated until the stopping criterion regarding the differences of objective function value (OFV) is met. The last trial source information which yields the best OFV is the final solution. Six studies on the homogeneous site, two studies on the heterogeneous site, and one study on the transient flow problem are conducted in this study. A suggestion regarding the optimal number of monitoring points and the condition for estimating the source information is given on the basis of the studies for homogeneous and heterogeneous aquifers. All results indicate that the proposed SATS-GWT can give good estimations, even when the sampling concentrations contain measurement errors.
頂級旅遊看城市：台北
(2007-09-30)
蘇芳儀
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Department of Communication and Technology
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傳播與科技學系
【記者蘇芳儀／專題報導】受CNBC青睞的台北，除了擁有頂級消費環境之外，更應發展自己多元的特色。
The effects of hydrogen plasma pretreatment on the formation of vertically aligned carbon nanotubes
(2007-09-30)
Wang, Wen-Pin
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Juang, Jenh-Yih
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Lai, Yi-Shao
The effects of H-2 plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H-2 and CH4 with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands (I-D/I-G) is decreased with increasing gas flow rate. TEM results suggest H-2 plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and. thus. is playing a crucial role in modifying the obtained CNTs structures. (c) 2007 Elsevier B.V. All rights reserved.
由「超級星光大道」看台灣近代社會現象
(2007-09-30)
李怡萱
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Department of Communication and Technology
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傳播與科技學系
【記者李怡萱／新竹報導】最近台灣吹起一股歌唱競賽風，不可否認的，一方面當然也是因為製作單位的炒作，例如營造成員間的感情或誹聞；另方面，我們也必須承認，我們從他們的歌聲中聽到了年輕人對歌唱單純的熱愛與其等待，其中所反應的社會現象，值得我們細細探討。
異樣眼光‧台北映象
(2007-09-30)
盧沛樺
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Department of Communication and Technology
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傳播與科技學系
當101成為大台北的代名詞，「一個台灣，兩個世界」的現象並不會就此消失。
《色．戒》—奠基於情慾的愛情圈套
(2007-09-30)
賴奕如
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Department of Communication and Technology
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傳播與科技學系
即便出了戲院，仍舊沈浸在不能自己的悲傷當中，李安成功的將張愛玲筆下的歷史，用深刻強烈的「色」、隱晦卻敏感的「戒」，將你帶入那段令人惆悵的愛情悲劇當中…
《沉睡的青春》今天的你是誰？
(2007-09-30)
姜建亨
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Department of Communication and Technology
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傳播與科技學系
【記者姜建亨／專題報導】整部看似以愛情貫穿的片，結局卻耐人尋味、讓人深省。今天的你是誰？是從別人那邊喚起最深處的自己？抑或是逃避讓自己陷入幻想中的另一個人格...
《父女7日變》我愛你們
(2007-09-30)
鄧詠兒
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Department of Communication and Technology
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傳播與科技學系
這是一個現代社會很普遍的親子問題，父女的關係日久變差，現代父母為了讓孩子能有更好的生活品質而拼命工作，都疏忽了對孩子的關懷，父母單方面給予孩子金錢，就是對孩子好嗎？我是想借這個故事，去探討現代社會的親子關係。
《看上去很美　小紅花》幼兒園裡的暴力寓言
(2007-09-30)
黃夙蓮
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Department of Communication and Technology
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傳播與科技學系
【記者黃夙蓮／專題報導】幼兒園的壓迫統治下，反抗是錯誤嗎？
全身酸、麻、痛，竟是使用電腦姿勢不良造成的?
(2007-09-30)
汪承漢
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Department of Communication and Technology
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傳播與科技學系
【汪承漢/新竹報導】在學生住宿率達九成的交通大學，學生在宿舍裡的活動，除了讀書、睡覺的時間以外，電腦似乎是打發時間的最佳良伴，不論是玩遊戲、上網、看影片、寫作業，在交大宿舍的生活，沒有電腦幾乎是萬萬不能的。