Browsing by Issue Date, starting with "2009-07-10"

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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.
Characterization of phase modulated non-return-to-zero (PM-NRZ) format for DWDM long reach PONs
(2009-07-15)
Chow, C. W.
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Yeh, C. H.
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光電工程學系
;
Department of Photonics
A technique which has been shown to be effective to mitigate the Rayleigh backscattering (IB) noise and potentially suited for use in the carrier distributed passive optical networks (PONs), uses a phase modulator (PM) at the reflective optical networking unit (RONU) to reshape the spectrum of the upstream non-return-to-zero (NRZ) signal, named PM-NRZ. Since the PM-NRZ signal has a much wider spectrum than the conventional NRZ signal, it would be very interesting to know its performance when applied to the multiple channels, or dense wavelength division multiplexed (DWDM) environment. Here, we, for the first time, show how close the neighboring channels can be located in the network by means of numerical simulations. We also provide solutions to reduce the crosstalk produced by neighboring PM-NRZ channels. Since in the WDM-PON system the distances between different ONUs and the head-end office vary, we also analyze the network performance when the powers of adjacent PM-NRZ signals change, (C) 2009 Elsevier B.V. All rights reserved,
Photonic Crystal Slab Waveguides Based on Antiresonant Reflecting Optical Waveguide Structures
(2009-07-15)
Yang, Yu-Lin
;
Hsu, Shih-Hsin
;
Lu, Ming-Feng
;
Huang, Yang-Tung
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生物科技學系
A novel two-dimensional photonic crystal slab waveguide based on an antiresonant reflecting optical waveguide (ARROW) structure is proposed and designed. Lightwaves propagating in this waveguide are confined by antiresonance reflection vertically and the photonic band gap laterally. In order to obtain the characteristics of the ARROW-based photonic crystal waveguides, the three-dimensional finite-difference time-domain simulations are performed. With a lateral adiabatic taper, a coupling efficiency of 80.3% from a single-mode fiber to the ARROW-based photonic crystal waveguide of a single-line defect is obtained. In addition, propagation losses less than 10 dB/mm and bend losses of 0.23 and 0.39 dB/bend for the designed 60 degrees and 120 degrees bends are achieved at an operating wavelength of 1.55 mu m.
Analysis of well residual drawdown after a constant-head test
(2009-07-15)
Yeh, Hund-Der
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Wang, Chih-Tse
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環境工程研究所
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Institute of Environmental Engineering
A recovery test measures the residual drawdown after an aquifer pumping test has ended and analyzes the recovery data to determine hydrogeological parameters such as transmissivity and storage coefficient. To our knowledge, the solution for the distribution of residual drawdown following a constant-head test has never been presented. In this paper, we first develop a mathematical model that describes the residual drawdown taking into consideration the wellbore-storage effect and the drawdown distribution occurring at the end of a previous constant-head test. Then, the Laplace-domain solution of the model is developed using the Laplace transforms and its time-domain solution is obtained using the Stehfest algorithm. Numerical results show that the distribution of residual drawdown depends on the boundary condition related to the well drawdown and the initial condition related to the aquifer drawdown. The well residual drawdown (i.e., the residual drawdown at wellbore) during the early recovery period will be over-estimated by the approximate residual drawdown solution based on the Theis-type solution and superposition principle due to the neglect of wellbore storage. For a large recovery time, the effect of wellbore storage is negligible and the approximate residual drawdown solution is therefore applicable. (C) 2009 Elsevier B.V. All rights reserved.
Degradation of carbofuran-contaminated water by the Fenton process
(2009-07-15)
Ma, Ying-Shih
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Kumar, Mathava
;
Lin, Jih-Gaw
;
環境工程研究所
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Institute of Environmental Engineering
In this study, the Fenton process was applied for the degradation of carbofuran from aqueous system. Batch experiments were conducted at two different carbofuran concentrations i.e., 10 and 50 mg/L, and at pH 3. Batch experiments at each carbofuran concentration were designed by central composite design (CCD) with two independent variables i.e. Fe(2+) and H(2)O(2). Experimental results indicate that more than 90% of carbofuran removal was observed within 5 mins of Fenton reaction at 5 mg/L of Fe(2+) concentration and 100 mg/L of H(2)O(2) concentration. Increases in Fe(2+) and/or H(2)O(2) concentrations beyond 5 and 100 mg/L, respectively produced 100% carbofuran removal. Based on the experimental observations, the optimal Fe(2+) and H(2)O(2) dosages required for 10 mg/L of aqueous carbofuran removal were estimated as 7.4 and 143 mg/L, respectively. During this study, three carbofuran intermediates such as 7-benzofuranol,2,3,-dihydro-2,2-dimethyl, 7-hydroxy-2,2-dimethyl-benzofuran-3-one and 1,4-Benzene-di- carboxaldehyde were identified using GC/MS analyses.
Global consensus for discrete-time competitive systems
(2009-07-15)
Shih, Chih-Wen
;
Tseng, Jui-Pin
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應用數學系
;
Department of Applied Mathematics
Grossberg established a remarkable convergence theorem for a class of competitive systems without knowing and using Lyapunov function for the systems. We present the parallel investigations for the discrete-time version of the Grossberg's model. Through developing an extended component-competing analysis for the coupled system, without knowing a Lyapunov function and applying the LaSalle's invariance principle, the global pattern formation or the so-called global consensus for the system can be achieved. A numerical simulation is performed to illustrate the present theory. (C) 2008 Elsevier Ltd. All rights reserved.
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.
Size dependence in tunneling spectra of PbSe quantum-dot arrays
(2009-07-15)
Ou, Y. C.
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Cheng, S. F.
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Jian, W. B.
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電子物理學系
;
物理研究所
Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic, and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. Developments of cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, the dependence of tunneling spectra on the sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored.
Photonic vector signal generation at microwave/millimeter-wave bands employing an optical frequency quadrupling scheme
(2009-07-15)
Lin, Chun-Ting
;
Shih, Po-Tsung
;
Jiang, Wen-Jr
;
Wong, Er-Zih
;
Chen, Jason Jyehong
To the best of our knowledge, a novel photonic architecture to generate vector signals at microwave/millimeter-wave bands employing an optical frequency quadrupling technique based on an external dual-parallel modulator is proposed for the first time. A 312.5 MSym/s quadruple phase-shift keying signal at 25 GHz is experimentally demonstrated using properly precoding driving signal at 6.25 GHz, and optical power penalty is negligible following 50 km single-mode fiber transmission. (C) 2009 Optical Society of America