Browsing by Author "Yang, J. C."

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3D Modeling of Flood Induced Flows and Sediment Concentration in Shihmen Reservoir
(2008)
Wang, K. H.
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Yang, J. C.
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Wu, C. H.
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土木工程學系
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Department of Civil Engineering
Hydrodynamic and sediment transport modeling is important to the analyses of the aggradation and degradation of a river system, the sediment management in a reservoir, and the study of downstream effect on the coastal sediment. This paper presents a development of a three-dimensional hydrodynamic and sediment transport model to investigate the variation of sediment concentration in Shihmen Reservoir in Taiwan under typhoon induced flood events. The fundamental equations that govern fluid flows and sediment concentration are the Reynolds-averaged Navier-Stokes (RANS) equations and sediment transport equation. Model equations are solved by using an implicit, finite-difference scheme in a curvilinear and vertically stretched coordinate system. A case study of Shihmen Reservoir utilizing the present flow and transport model is presented. The upstream flow-rate conditions are obtained from the data recorded during the 2005 Typhoon Haitang. The computed results clearly reflect the three-dimensional feature of the velocity field in the reservoir. The predicted time-varying water surface elevation during the 140-hour flood event agrees well with measured data. For the sediment concentration, only limited measurements in the domain are available. When comparing with the measured data, the present model is capable of providing reasonable predictions on the rising trend of sediment concentration during the period that flow rate increases, however, the model overestimates concentration values at the recession stage when the measurements of sediment concentration are shown in the decreasing trend. Other results showing the time variation of the velocity vectors and sediment concentration at selected vertical layers are presented and discussed.
Conduction control at ferroic domain walls via external stimuli
(2014)
Yang, J. C.
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Yeh, C. H.
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Chen, Y. T.
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Liao, S. C.
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Huang, R.
Intriguing functionalities at nano-sized domain walls have recently spawned a new paradigmfor developing novel nanoelectronics due to versatile characteristics. In this study, we explore a new scenario to modulate the local conduction of ferroic domain walls. Three controlling parameters, i.e., external electrical field, magnetic field and light, are introduced to the 90 degrees domain walls (90 degrees DWs) of BiFeO3. Electrical modulation is realized by electrical transport, where the mobility of 90 degrees DWs can be altered by gating voltage. We further use the ferromagnetic/antiferromagnetic coupling to reveal the inherent magnetism at the DWs. With an established magnetic nature, magneto-transport has been conducted to introduce magnetic controlling parameter, where a giant positive magnetoresistance change can be observed up to 200%. In addition, light modulated conduction, a core factor for multifunctional applications, is successfully demonstrated (current enhancement by a factor of 2 with 11 W white lamp). These results offer new insights to discover the tunability of domain wall nanoelectronics.
Direct observation of ferroelectric polarization-modulated band bending at oxide interfaces
(2012-03-19)
Huang, B. C.
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Chen, Y. T.
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Chiu, Y. P.
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Huang, Y. C.
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Yang, J. C.
This study presents a direct visualization of the influences of ferroelectric polarization on the electronic properties of the Schottky contact at the Nb-SrTiO3/BiFeO3 hetero-interface using scanning tunneling microscopy and spectroscopy (STM/S). The evolution of the local density of states across the Nb-SrTiO3/BiFeO3 interface reveals the interfacial band alignment and the characteristic quantities of the metal/ferroelectric contact. The unique combination of STM and STS in this study delivers an approach to obtain critical information on the interfacial electronic configurations of ferroelectric oxide interfaces and also their variation with ferroelectric polarization switching. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3691615]
Distribution of electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
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Liao, Y. F.
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Tra, V. T.
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Yang, J. C.
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Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti(4+) to Ti(3+) occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO(3) with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Distribution of electronic reconstruction at the n-type LaAlO3/SrTiO3 interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
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Liao, Y. F.
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Tra, V. T.
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Yang, J. C.
;
Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO3/SrTiO3 interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti4+ to Ti3+ occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO3 with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Effect of Stony Debris Flow on Design Discharge for Tung-Pu-Ray Creek
(2004)
Hsieh, T. Y.
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Chang, C. H.
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Pen, S. C.
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Yang, J. C.
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防災與水環境研究中心
The primary objective of this research is to investigate the impact of stony debris flows of Tung-Pu-Ray Creek on its design discharge by using the quasi two-dimensional cell model for inundation simulation. The research is based on the assumption that there is a linear relationship between the actual discharge hydrograph of sediment-laden flows, and the discharge hydrograph of sediment free flows. That is, the ordinates of the discharge hydrograph of sediment-laden flows are n times of water flows. Hence, using the inundation simulation by the quasi two-dimensional cell model, one can define the extent of the impact of stony debris flows of Tung-Pu-Ray Creek on its design discharge through the calibration with the actual flood inundation of the typhoon Toraji of 1990. The simulation indicates that the actual discharge of Tung-Pu-Ray Creek's sediment flows can be determined as 1.4 times of the discharge hydrograph derived from the actual precipitation data. In other words, the weighted impact of the stony debris flows on the design discharge is approximately 0.4 times in the Tung-Pu-Ray Creek case.
Multifunctionalities driven by ferroic domains
(2014-08-14)
Yang, J. C.
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Huang, Y. L.
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He, Q.
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Chu, Y. H.
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材料科學與工程學系
Considerable attention has been paid to ferroic systems in pursuit of advanced applications in past decades. Most recently, the emergence and development of multiferroics, which exhibit the coexistence of different ferroic natures, has offered a new route to create functionalities in the system. In this manuscript, we step from domain engineering to explore a roadmap for discovering intriguing phenomena and multifunctionalities driven by periodic domain patters. As-grown periodic domains, offering exotic order parameters, periodic local perturbations and the capability of tailoring local spin, charge, orbital and lattice degrees of freedom, are introduced as modeling templates for fundamental studies and novel applications. We discuss related significant findings on ferroic domain, nanoscopic domain walls, and conjunct heterostructures based on the well-organized domain patterns, and end with future prospects and challenges in the field. (C) 2014 AIP Publishing LLC.
Orthorhombic BiFeO3
(2012-12-14)
Yang, J. C.
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He, Q.
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Suresha, S. J.
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Kuo, C. Y.
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Peng, C. Y.
A new orthorhombic phase of the multiferroic BiFeO3 has been created via strain engineering by growing it on a NdScO3(110)(o) substrate. The tensile-strained orthorhombic BiFeO3 phase is ferroelectric and antiferromagnetic at room temperature. A combination of nonlinear optical second harmonic generation and piezoresponse force microscopy revealed that the ferroelectric polarization in the orthorhombic phase is along the in-plane < 110 >(pc) directions. In addition, the corresponding rotation of the antiferromagnetic axis in this new phase was observed using x-ray linear dichroism. DOI: 10.1103/PhysRevLett.109.247606
Role of measurement voltage on hysteresis loop shape in Piezoresponse Force Microscopy
(2012-11-05)
Strelcov, E.
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Kim, Y.
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Yang, J. C.
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Chu, Y. H.
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Yu, P.
The dependence of field-on and field-off hysteresis loop shape in Piezoresponse Force Microscopy (PFM) on driving voltage, V-ac, is explored. A nontrivial dependence of hysteresis loop parameters on measurement conditions is observed. The strategies to distinguish between paraelectric and ferroelectric states with small coercive bias and separate reversible hysteretic and non-hysteretic behaviors are suggested. Generally, measurement of loop evolution with V-ac is a necessary step to establish the veracity of PFM hysteresis measurements. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764939]
Single-domain multiferroic BiFeO3 films
(2016-09-01)
Kuo, C. -Y.
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Hu, Z.
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Yang, J. C.
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Liao, S. -C.
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Huang, Y. L.
The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii-Moriya interaction is parallel to the a axis. Furthermore, by fabricating a Co/BiFeO3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3.
Two-Dimensional Nonequilibrium Noncohesive and Cohesive Sediment Transport Model
(2009-05-01)
Hung, M. C.
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Hsieh, T. Y.
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Wu, C. H.
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Yang, J. C.
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土木工程學系
The purpose of this paper is to develop an unsteady 2D depth-averaged model for nonuniform sediment transport in alluvial channels. In this model, the orthogonal curvilinear coordinate system is adopted; the transport mechanisms of cohesive and noncohesive sediment are both embedded; the suspended load and bed load are treated separately. In addition, the processes of hydraulic sorting, armoring, and bed consolidation are also included in the model. The implicit two-step split-operator approach is used to solve the flow governing equations and the coupling approach with iterative method are used to solve the mass-conservation equation of suspended sediment, mass-conservation equation of active-layer sediment, and global mass-conservation equation for bed sediment simultaneously. Three sets of data, including suspension transport, degradation and aggradation cases for noncohesive sediment, and aggradation, degradation, and consolidation cases for cohesive sediment, have been demonstrated to show the rationality and accuracy of the model. Finally, the model is applied to evaluate the desilting efficiency for Ah Gong Diann Reservoir located in Taiwan to show its applicability.
Ultrafast Dynamics of BiFeO(3) Thin Films Studied by Dual-Color Femtosecond Spectroscopy
(2011-01-01)
Chen, L. Y.
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Yang, J. C.
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Shih, H. C.
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Liang, C. W.
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Wu, T. -Y.
The ultrafast dynamics in (100)-oriented BiFeO(3) thin films were studied from 20 K to 300 K by using the dual-color femtosecond pump-probe spectroscopy, which were performed by the 400 nm (3.1 eV) pump pulses above the energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap of 2.67 eV. From the temperature-dependent transient reflectivity changes (Delta R/R), the anomalous changes were clearly observed below 200 K caused by magnons. Thus, the femtosecond pump-probe spectroscopy could unambiguously reveal the magnetization dynamics in BiFeO(3) with strong magnetoelectric coupling.
Ultrafast Dynamics of BiFeO3 Thin Films Studied by Dual-Color Femtosecond Spectroscopy
(2011-01-01)
Chen, L. Y.
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Yang, J. C.
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Shih, H. C.
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Liang, C. W.
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Wu, T. -Y.
The ultrafast dynamics in (100)-oriented BiFeO3 thin films were studied from 20 K to 300 K by using the dual-color femtosecond pump-probe spectroscopy, which were performed by the 400 nm (3.1 eV) pump pulses above the energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap of 2.67 eV. From the temperature-dependent transient reflectivity changes (Delta R/R), the anomalous changes were clearly observed below 200 K caused by magnons. Thus, the femtosecond pump-probe spectroscopy could unambiguously reveal the magnetization dynamics in BiFeO3 with strong magnetoelectric coupling.
Ultrafast photoinduced mechanical strain in epitaxial BiFeO3 thin films
(1970-01-01)
Chen, L. Y.
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Yang, J. C.
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Luo, C. W.
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Laing, C. W.
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Wu, K. H.
We studied ultrafast dynamics and photoinduced mechanical strain of BiFeO3 thin films by dual-color transient reflectivity measurements (Delta R/R). Anisotropic photostriction in BiFeO3 is found to be mainly driven by the optical rectification effect. Results of the photostriction at various thicknesses show that the estimated sound velocity along [110] direction of BiFeO3 is 4.76 km/s. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734512]