Browsing by Issue Date, starting with "2009-07-08"

Now showing 1 - 20 of 50290

Effects of polydispersity index and molecular weight on crystallization kinetics of syndiotactic polystyrene (sPS)
(2009-07-08)
Chen, Chen-Ming
;
Hsieh, Tsung-Eong
;
Ju, Ming-Yih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Isothermal crystallization kinetics of syndiotactic polystyrene (sPS) is reported in this work with Avrami analytical method. it was found that the spherulite growth rate and overall crystallization rate depend on the crystallization temperatures, average molecular weight ((M) over bar (W)) and polydispersity index (PDI). The experimental results for the melt and cold crystallization processes of sPS revealed that the PDI and (M) over bar (W) exhibit pivotal effects on the crystallization rate, which increases with the decrease of (M) over bar (W) and PDI. (C) 2009 Elsevier B.V. All rights reserved.
Comparative Investigation of Ultrafast Photoinduced Processes in Salicylidene-Aminopyridine in Solution and Solid State
(2009-07-09)
Sliwa, Michel
;
Mouton, Nicolas
;
Ruckebusch, Cyril
;
Aloise, Stephane
;
Poizat, Olivier
Photodynamics and excited-state intramolecular proton transfer (ESIPT) of N-(3,5-ditert-butylsalicylidene)-4-aminopyridine (4P) and N-(3,5-ditert-butylsalicylidene)-2-aminopyridine (2P) are studied by steady-state and transient optical spectroscopy in solution and solid state (microcrystalline powder). These two compounds are representative of anils Classes A and B, respectively. The results confirm that in solution both compounds have a similar dynamic behavior: upon excitation at 390 nm, ESIPT leads to different cis-keto* fluorescent species which relax to the photochromic trans-keto photoproduct within a few tens of picoseconds. Furthermore, for the first time, picosecond data are recorded for the two classes of anils in the solid state: in 2P, two cis-keto* fluorescent excited state species (23 and 250 ps lifetime) are relaxing exclusively to the cis-keto ground state, whereas in 4P, a single cis-keto* fluorescent species is observed which leads to the trans-keto photoproduct in 250 ps via an intermediate metastable species.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO2 Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO2 films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO2 films with S-1 excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO2 film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO2 film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO2 is smaller than that in PEI/TiO2. Our results imply that back electron transfer at the TiO2/dye interface is an important factor to be considered to account for the cell performance of a device.
Ionization and Dissociation Processes of Pyrrolidine in Intense Femtosecond Laser Field
(2009-07-09)
Wang, Qiaoqiao
;
Wu, Di
;
Zhang, Dongdong
;
Jin, Mingxing
;
Liu, Fuchun
Ionization and dissociation mechanisms of pyrrolidine in intense 800 nm laser field (10(13) to 10(14) W/cm(2)) have been experimentally investigated by using a method of molecular beam and time-of-flight mass spectrometer. Singly charged parent ion and numerous fragment ions are observed in the mass spectra, which are investigated as a function of laser intensity and polarization. In order to understand the details of the ionization processes of pyrrolidine in intense femtosecond laser field, we quantitatively calculate the rate constants and ion yields by means of generalized Keldysh-Faisal-Reiss theory, and the excitation probabilities of the excited states are also calculated by using Floquet theory. The results suggest that the ionization might occur partially through the excited states of neutral pyrrolidine. Comparing with linearly polarized (LP) laser field, we observe some enhancement of fragmentation with a circularly polarized (CP) laser field above the saturation threshold intensity which might be explained by the active energies of the pyrrolidine molecular ions are different under CP and LP laser irradiated. To interpret the dissociation patterns of the pyrrolidine ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations.
Spectral and 3-Dimensional Tracking of Single Gold Nanoparticles in Living Cells Studied by Rayleigh Light Scattering Microscopy
(2009-07-09)
Louit, Guillaume
;
Asahi, Tsuyoshi
;
Tanaka, Go
;
Uwada, Takayuki
;
Masuhara, Hiroshi
Using a confocal Rayleigh light scattering microspectroscopy and imaging system, we followed and recorded the scattering spectra of single gold nanoparticles interacting with living mouse fibroblast cells, during the scale of I h. A white light continuum produced by a femtosecond laser was focused on gold nanoparticles with a diameter of 80 nm, while an incubation system ensured viability of the living cells. After reporting spectral characteristics of gold nanoparticles and their target fibroblasts, separately and in combination, tracking sequences of single nanoparticles in contact with a single cell are described. Through the study of three separate and representative cases, transitory as well as plasmon resonance band shifts, which can be linked to biological events, have been observed and are discussed here.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO(2) Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO(2) films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO(2) films with S(1) excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO(2) film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO(2) film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO(2) is smaller than that in PEI/TiO(2). Our results imply that back electron transfer at the TiO(2)/dye interface is an important factor to be considered to account for the cell performance of a device.
Electric Field Effects on Photoluminescence of Polyfluorene Thin Films: Dependence on Excitation Wavelength, Field Strength, and Temperature
(2009-07-09)
Mehata, Mohan Singh
;
Hsu, Chain-Shu
;
Lee, Yuan-Pern
;
Ohta, Nobuhiro
;
應用化學系
Electroabsorption (E-A) and electrophotoluminescence (E-F) spectra of thin films of blue-light-emitting poly(9,9-dioctylfluorene) (PFO) have been measured at temperatures ranging from 25 to 295 K to examine both the optical property and excitation dynamics of these films in the presence of external electric fields of 0-1.2 MV cm(-1). Electric field effects on excitation dynamics depend on not only applied field strength but also excitation wavelength and temperature. For photoexcitation at 344 or 402 nm, E-F spectra observed with low applied fields show only the Stark shift, whereas fluorescence quenching is induced only by strong electric fields. For photoexcitation at a shorter wavelength of 298 nm, on the other hand, field-induced quenching of fluorescence is observed even with a weak electric field at any temperature. The presence of a nonradiative process from highly excited states that is effectively affected by electric fields is suggested.
Image synthesis system for a vehicle and the manufacturing method thereof
(2009-07-09)
CHEN, Yong-Sheng
;
Liu, Yu-Chih
;
Lin, Kai-Ying
The present invention discloses an image synthesis system for a vehicle to provide the driver with a downward-facing image of the car's 360° surrounding view. The system includes: a first camera, which is used to shoot a first image of the periphery of the vehicle; a second camera, which is used to shoot a second image of the periphery of said vehicle, wherein the second image and the first image have an overlap region; an image processing device comprising a defining component and a synthesis component, which is used to synthesize the first image and the second image and output a third image; a display device, which is used to display the third image.
Unraveling Deterministic Mesoscopic Polarization Switching Mechanisms: Spatially Resolved Studies of a Tilt Grain Boundary in Bismuth Ferrite
(2009-07-10)
Rodriguez, Brian J.
;
Choudhury, Samrat
;
Chu, Y. H.
;
Bhattacharyya, Abhishek
;
Jesse, Stephen
The deterministic mesoscopic mechanism of ferroelectric domain nucleation is probed at a single atomically-defined model defect: an artificially fabricated bicrystal grain boundary (GB) in an epitaxial bismuth ferrite film. Switching spectroscopy piezoresponse force microscopy (SS-PFM) is used to map the variation of local hysteresis loops at the GB and in its immediate vicinity. It is found that the the influence of the GB on nucleation results in a slight shift of the negative nucleation bias to larger voltages. The mesoscopic mechanisms of domain nucleation in the bulk and at the GB are studied in detail using phase-field modeling, elucidating the complex mechanisms governed by the interplay between ferroelectric and ferroelastic wall energies, depolarization fields, and interface charge. The combination of phase-field modeling and SS-PFM allows quantitative analysis of the mesoscopic mechanisms for polarization switching, and hence suggests a route for unraveling the mechanisms of polarization switching at a single defect level and ultimately optimizing materials properties through microstructure engineering.
Interfacial Polar-Bonding-Induced Multifunctionality of Nano-Silicon in Mesoporous Silica
(2009-07-10)
Huang, Jung Y.
;
Shieh, Jia M.
;
Kuo, Hao C.
;
Pan, Ci L.
;
光電工程學系
The optoelectronic response of a material governs its suitability for a wide range of applications, from photon detection to photovoltaic conversion. To conquer the material limitations and achieve improved optoelectronic responses, nanotechnology has been employed to arranges subunits with specific size-dependent quantum mechanical properties in a hierarchically organized structure. However, building a functional optoelectronic system from nano-objects remains a formidable challenge. In this paper, the fabrication of a new artificially engineered optoelectronic material by the preferential growth of silicon nanocrystals on the bottom of the pore-channels of mesoporous silica is reported. The nanocrystals form highly stable interface structures bonded on one side; these structure show strong electron-phonon coupling and a ferroelectric-like hysteretic switching property. A new class of multifunctional materials is realized by invoking a concept that employs semiconductor nanocrystals for optical sensing and utilizes interfacial polar layers to facilitate carrier transport and emulate ferroelectric-like switching.
Optimizing system capacity expansion schedules for groundwater supply
(2009-07-10)
Chang, Liang-Cheng
;
Chen, Yu-Wen
;
Yeh, Ming-Sheng
;
土木工程學系
;
Department of Civil Engineering
Groundwater plays a vital role in regional water resources management. In conventional design, a full-scale network system is installed initially to use groundwater resources. However, the system capacity may exceed water demand in the early stages because water demand generally increases with time. Therefore, this work proposes a novel optimal capacity expansion model capable of determining an optimal schedule to expand system capacity according to increasing water demand. The proposed algorithm hybridizes a genetic algorithm (GA) and constrained differential dynamic programming (CDDP). The chromosomes of the GA represent a possible design alternative, a groundwater network with capacity that expands with time. The CDDP algorithm is then used to compute the optimal pumping policy associated with the chromosome. Simulation results indicate that the capacity expansion model saves more total present value cost than conventional designs for the same annual interest rate and water demand. Results of this study demonstrate promise for the proposed model in facilitating a cost-effective groundwater network design with capacity expansion for regional groundwater supply.
A study on using pre-bent steel strips as seismic energy-dissipative devices
(2009-07-10)
Wang, Yen-Po
;
Chien, Chia-Shang Chang
;
土木工程學系
;
Department of Civil Engineering
Buckling is usually conceived as an unstable Structural behavior leading to lateral instability of axially loaded members, if not properly supported. However, a pre-bent strip Would become an excellent seismic energy-dissipative device it it is deformed in a guided direction and ratio, e. Geometrically large lateral deformation of the steel strips in buckling leads to inelastic behavior of the material and dissipates energy as a consequence. The purpose of this study is to propose a new type of seismic damper in the form of braces based on pre-bent steel strips. The nonlinear elastic stiffness of monotonously loaded pre-bent strips in both compression and tension is derived. The energy-dissipative characteristics of the proposed damping device are investigated via component tests under cyclic loads. Experimental results indicate that the force-displacement relationship of pre-bent strips in cyclic loads exhibits mechanical characteristics of displacement-dependent dampers. A series of seismic performance tests has been conducted further to verify the feasibility and effectiveness of using the proposed device as seismic dampers. Encouraging test results have been obtained, suggesting feasibility of the proposed device for earthquake-resistant design. Copyright (C) 2008 John Wiley & Sons, Ltd.
利用磁場控制液晶雙折射之兆赫波可調波長選擇器裝置
(2009-07-11)
趙如蘋
;
潘犀靈
;
陳昭遠
本發明提供一種兆赫波可調之波長選擇器裝置,該裝置包含固定相位延遲器、可調相位延遲器、以及一對線性偏光片來構成一個單元。該固定相位延遲器及可調相位延遲器在基本上均藉由液晶來提供相位延遲,而且利用液晶所具有的雙折射現象可提供足夠大的相位延遲。固定相位延遲器藉由水平定向之液晶盒來提供固定的相位延遲,而可調相位延遲器則藉由垂直定向之液晶盒及一可旋轉之磁鐵來提供可調的相位延遲,其中該可調相位延遲器可根據磁鐵旋轉軸之方向來提供相對於固定相位延遲器之正或負的相位延遲,進而將全部的可調範圍完全用於調整可通過的頻率。此外,本發明亦可串聯多個上述單元而達成足夠窄的帶通頻寬。
Rotationally resolved ultrahigh-resolution laser spectroscopy of the S(2) (1)A(1)<- S(0) (1)A(1) transition of azulene
(2009-07-14)
Semba, Yosuke
;
Yoshida, Kazuto
;
Kasahara, Shunji
;
Ni, Chi-Kung
;
Hsu, Yen-Chu
We have observed rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the 0(0)(0) (a-type) and 0(0)(0)+467 cm(-1) (b-type) bands of the S(2) (1)A(1)<- S(0) (1)A(1) transition of jet-cooled azulene. The observed linewidth is 0.0017 cm(-1), which corresponds to the lifetime of 3.1 ns in the S(2) state. Zeeman splitting of rotational lines is very small so that intersystem crossing to the triplet state is considered to be very slow. Inertial defect is very small and the molecule is considered to be planar in the S(0) and S(2) states (C(2 upsilon) symmetry). Rotational constants of the S(2) state are almost identical to those of the S(0) state, indicating that geometrical structure is similar in both electronic states. In this case, internal conversion (IC) by vibronic coupling is thought to be inactive. Therefore, the main radiationless transition process in the S(2) (1)A(1) state of azulene was identified to be IC to the S(1) (1)B(2) state. However, this S(2)-> S(1) IC is still slower than that of conventional polycyclic aromatic hydrocarbons. We consider it to be due to the shallower potential energy curve in the S(1) (1)B(2) state, which is also responsible for the extraordinarily fast S(1)-> S(0) IC in the isolated azulene molecule. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168394]
Rotationally resolved ultrahigh-resolution laser spectroscopy of the S-2 (1)A(1)<- S-0 (1)A(1) transition of azulene
(2009-07-14)
Semba, Yosuke
;
Yoshida, Kazuto
;
Kasahara, Shunji
;
Ni, Chi-Kung
;
Hsu, Yen-Chu
We have observed rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the 0(0)(0) (a-type) and 0(0)(0)+467 cm(-1) (b-type) bands of the S-2 (1)A(1)<- S-0 (1)A(1) transition of jet-cooled azulene. The observed linewidth is 0.0017 cm(-1), which corresponds to the lifetime of 3.1 ns in the S-2 state. Zeeman splitting of rotational lines is very small so that intersystem crossing to the triplet state is considered to be very slow. Inertial defect is very small and the molecule is considered to be planar in the S-0 and S-2 states (C-2 upsilon symmetry). Rotational constants of the S-2 state are almost identical to those of the S-0 state, indicating that geometrical structure is similar in both electronic states. In this case, internal conversion (IC) by vibronic coupling is thought to be inactive. Therefore, the main radiationless transition process in the S-2 (1)A(1) state of azulene was identified to be IC to the S-1 B-1(2) state. However, this S-2 -> S-1 IC is still slower than that of conventional polycyclic aromatic hydrocarbons. We consider it to be due to the shallower potential energy curve in the S-1 B-1(2) state, which is also responsible for the extraordinarily fast S-1 -> S-0 IC in the isolated azulene molecule. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168394]
Modular units and cuspidal divisor class groups of X(1)(N)
(2009-07-15)
Yang, Yifan
;
應用數學系
;
Department of Applied Mathematics
In this article, we consider the group F(1)(infinity)(N) of modular units on X(1)(N) that have divisors supported on the cusps lying over infinity of X(0)(N), called the infinity-cusps. For each positive integer N, we will give an explicit basis for the group F(1)(infinity)(N). This enables us to compute the group structure of the rational torsion subgroup l(1)(infinity)(N) of the Jacobian J(1)(N) of X(1)(N) generated by the differences of the infinity-cusps. In addition, based on our numerical computation, we make a conjecture on the structure of the p-primary part of l(1)(infinity)(p(n)) for a regular prime p. (C) 2009 Elsevier Inc. All rights reserved.
Traveling wavefronts for time-delayed reaction-diffusion equation: (I) Local nonlinearity
(2009-07-15)
Mei, Ming
;
Lin, Chi-Kun
;
Lin, Chi-Tien
;
So, Joseph W. -H.
;
應用數學系
In this paper, we study a class of time-delayed reaction-diffusion equation with local nonlinearity for the birth rate. For all wave-fronts with the speed c > c(*), where c(*) > 0 is the critical wave speed, we prove that these wavefronts are asymptotically stable, when the initial perturbation around the traveling waves decays exponentially as x -> -infinity, but the initial perturbation can be arbitrarily large in other locations. This essentially improves the stability results obtained by Mei. So. Li and Shen [M. Mei, J.W.-H. So, M.Y. Li, S.S.R Shen, Asymptotic stability of traveling waves for the Nicholson's blowflies equation with diffusion, Proc. Roy. Soc. Edinburgh Sect. A 134 (2004) 579-594] for the speed c > 2 root D(m) (epsilon p - d(m)) with small initial perturbation and by Lin and Mei [C.-K. Lin, M. Mei, On travelling wavefronts of the Nicholson's blowflies equations with diffusion, submitted for publication] for c > c(*) with sufficiently small delay time r approximate to 0. The approach adopted in this paper is the technical weighted energy method used in [M. Mei, J.W.-H. So, M.Y. Li, S.S.R Shen, Asymptotic stability of traveling waves for the Nicholson's blowflies equation with diffusion, Proc. Roy. Soc. Edinburgh Sect. A 134 (2004) 579-594], but inspired by Gourley [S.A. Gourley, Linear stability of travelling fronts in an age-structured reaction-diffusion Population model, Quart. J. Mech. Appl. Math. 58 (2005) 257-268] and based on the property of the critical wavefronts, the weight function is carefully selected and it plays a key role in proving the stability for any c > c(*) and for an arbitrary time-delay r > 0. (C) 2009 Elsevier Inc. All rights reserved.
Incorporating Structural Characteristics for Identification of Protein Methylation Sites
(2009-07-15)
Shien, Dray-Ming
;
Lee, Tzong-Yi
;
Chang, Wen-Chi
;
Hsu, Justin Bo-Kai
;
Horng, Jorng-Tzong
Studies over the last few years have identified protein methylation on histones and other proteins that are involved in the regulation of gene transcription. Several works have developed approaches to identify computationally the potential methylation sites on lysine and arginine. Studies of protein tertiary structure have demonstrated that the sites of protein methylation are preferentially in regions that are easily accessible. However, previous studies have not taken into account the solvent-accessible surface area (ASA) that surrounds the methylation sites. This work presents a method named MASA that combines the support vector machine with the sequence and structural characteristics of proteins to identify methylation sites on lysine, arginine, glutamate, and asparagine. Since most experimental methylation sites are not associated with corresponding protein tertiary structures in the Protein Data Bank, the effective solvent-accessible prediction tools have been adopted to determine the potential ASA values of amino acids in proteins. Evaluation of predictive performance by cross-validation indicates that the ASA values around the methylation sites can improve the accuracy of prediction. Additionally, an independent test reveals that the prediction accuracies for methylated lysine and arginine are 80.8 and 85.0%, respectively. Finally, the proposed method is implemented as an effective system for identifying protein methylation sites. The developed web server is freely available at http:/IMASA.mbc.nctu.edu.tw/. (C) 2009 Wiley Periodicals, Inc. J Comput Chem 30: 1532-1543, 2009
Traveling wavefronts for time-delayed reaction-diffusion equation: (II) Nonlocal nonlinearity
(2009-07-15)
Mei, Ming
;
Lin, Chi-Kun
;
Lin, Chi-Tien
;
So, Joseph W. -H.
;
應用數學系
This is the second part of a series of study oil the stability of traveling wavefronts of reaction-diffusion equations with time delays. In this paper we will consider a nonlocal time-delayed reaction-diffusion equation. When the initial perturbation around the traveling wave decays exponentially as x -> -infinity (but the initial perturbation call be arbitrarily large in other locations), we prove the asymptotic stability of all traveling waves for the reaction-diffusion equation, including even the slower waves whose speed are close to the critical speed. This essentially improves the previous stability results by Mei and So [M. Mei, J.W.-H. So, Stability of strong traveling waves for a nonlocal time-delayed reaction-diffusion equation, Proc. Roy. Soc. Edinburgh Sect. A 138 (2008) 551-568] for the speed c > 2 root D(m)(3 epsilon p-2d(m)) with a small initial perturbation. The approach we use here is the weighted energy method, but the weight function is more tricky to construct due to the property of the critical wavefront, and the difficulty arising from the nonlocal nonlinearity is also overcome. Finally, by using the Crank-Nicholson scheme, we present some numerical results which confirm Our theoretical Study. (C) 2009 Elsevier Inc. All rights reserved.
The geometric effect and programming current reduction in cylindrical-shaped phase change memory
(2009-07-15)
Li, Yiming
;
Hwang, Chih-Hong
;
Li, Tien-Yeh
;
Cheng, Hui-Wen
;
電子工程學系及電子研究所
This study conducts a three-dimensional electro-thermal time-domain simulation for numerical analysis of cylindrical-shaped phase change memories (PCMs). The influence of chalcogenide material, germanium antimony telluride (GeSbTe or GST), structure on PCM operation is explored. GST with vertical structure exhibits promising characteristics. The bottom electrode contact (BEC) is advanced to improve the operation of PCMs, where a 25% reduction of the required programming current is achieved at a cost of 26% reduced resistance ratio. The position of the BEC is then shifted to further improve the performance of PCMs. The required programming current is reduced by a factor of 11, where the resistance ratio is only decreased by 6.9%. However, the PCMs with a larger shift of BEC are sensitive to process variation. To design PCMs with less than 10% programming current variation, PCMs with shifted BEC, where the shifted distance is equal to 1.5 times the BEC's radius, is worth considering. This study quantitatively estimates the structure effect on the phase transition of PCMs and physically provides an insight into the design and technology of PCMs.