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Screw dislocation structure and mobility in body centered cubic Fe predicted by a gaussian Approximation Potential

npj Computational materials 2018年第1期4卷 90-96页

作者： Francesco maresca Daniele Dragoni gábor Csányi Nicola marzari William A.Curtin Laboratory for multiscale mechanics modeling(LAmmm) Institute of Mechanical EngineeringÉcole Polytechnique Fédérale de LausanneLausanne CH-1015Switzerland Theory and Simulation of materials(THEOS) and National Centre for Computational Design and Discovery of Novel Materials(NCCR MARVEL)École Polytechnique Fédérale de LausanneLausanne CH-1015Switzerland Dipartimento di Scienza dei materiali Universitàdi Milano-BicoccaVia R.Cozzi 55Milan I-20125Italy Department of Engineering University of CambridgeTrumpington StreetCambridge CB21PZUK

The plastic flow behavior of bcc transition metals up to moderate temperatures is dominated by the thermally activated glide of screw dislocations,which in turn is determined by the atomic-scale screw dislocation core structure and the associated k.nk.pair nucleation mechanism for *** complex plasticity phenomena requires the simulation of many atoms and interacting dislocations and *** sizes are beyond the scope of first-principles methods and thus require empirical interatomic *** for the technological important case of bcc Fe,existing empirical interatomic potentials yield spurious ***,the structure and motion of the screw dislocations in Fe are studied using a new gaussian Approximation Potential(gAP)for bcc Fe,which has been shown to reproduce the potential energy surface predicted by density-functional theory(DFT)and many associated *** Fe gAP predicts a compact,non-degenerate core structure,a single-hump Peierls potential,and glide on{110},consistent with DFT *** thermally activated motion at finite temperatures occurs by the expected k.nk.pair nucleation and propagation *** stress-dependent enthalpy barrier for screw motion,computed using the nudgedelastic-band method,follows closely a form predicted by standard theories with a zero-stress barrier of~1 eV,close to the experimental value of 0.84 eV,and a Peierls stress of~2 gPa consistent with DFT predictions of the Peierls potential.

关键词： structure dislocation cubic

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Adaptive base-isolation of civil structures using variable amplification

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Earthquak. Engineering and Engineering Vibration 2006年第2期5卷 223-233页

作者： k.nneth k. Walsh mak.la m. Abdullah Department of Civil and Environmental Engineering FAMU-FSU College of Engineering Tallahassee FL 32310 USA

Semi-active dampers are used in base-isolation to reduce the seismic response of civil engineering structures. In the present study, a new semi-active damping system using variable amplification will be investigated for adaptive baseisolation. It uses a novel variable amplification device （VAD） connected in series with a passive damper. The VAD is capable of producing multiple amplification factors, each corresponding to a different amplification state. Forces from the damper are amplified to the structure according to the current amplification state, which is selected via a semi-active control algorithm specifically tailored to the system＇s tmique damping characteristics. To demonstrate the effectiveness of the VAD-damper system for adaptive base-isolation, numerical simulations are conducted for three and seven-story base-isolated buildings subject to both far and near-field ground motions. The results indicate that the system can achieve significant reductions in response compared to the base-isolated buildings with no damper. The proposed system is also found to perform well compared to a typical semi-active damper.

关键词： adaptive systems amplification base-isolation damping earthquak. resistant structures multistorybuildings seismic isolation structural control

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Engineering Design of High Quality gaN Epitaxy on Silicon Substrate Using Varying gaN/AlgaN Composite Buffer Structures

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稀有金属材料与工程 2012年第S1期41卷 57-60页

作者： Wu, g. m. Tu, k. N. k.o, C. C. Univ Calif Los Angeles Dept Mat Sci & Engn Los Angeles CA 90095 USA Chang gung Univ Inst Electroopt Engn Tao Yuan 333 Taiwan

High quality gaN epitaxy thin films have been desired for the energy-efficient,solid-state semiconductor illuminating *** substrates offer high crystal quality,low wafer cost,large wafer size,and potential integration with the well-established silicon processing ***,due to the large mismatch in lattice constants and thermal expansion coefficients,it is still challenging to grow high quality gaN on silicon *** this study,high quality gaN epitaxy has been engineering designed to grow on Si(111)substrate using varying gaN/AlgaN composite buffer structures by an Axitron 200 metal-organic vapor phase epitaxy deposition system.A thin AlN seed layer of 25 nm was firstly grown at 720℃.AlgaN layer of different thick.ess was then grown at 1050℃with subsequent gaN thin film until the total thick.ess reached 500 *** thick.ess of the subsequent gaN thin film could be increased by reducing the AlgaN thick.ess in the composite buffer *** results have shown that the lower gaN/AlgaN thick.ess ratio would decrease the dislocation density and provide crack.free,mirror-lik. upper gaN crystal thin *** the other hand,the gaN/AlgaN thick.ess ratio could be designed to be 2-6 to balance the processing cost and the thin film quality for engineering *** dislocation density has been about 2×10 9 *** addition,dislocation close loop was observed near the gaN/AlgaN *** annihilation mechanism could be depicted by the reduction in dislocation strain energy.

关键词： gallium nitride dislocation density silicon substrate buffer layer

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Copper biosorption on immobilized seaweed biomass:Column break.hrough characteristics

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Journal of Environmental Sciences 2007年第8期19卷 928-932页

作者： k. H. Chu m. A. Hashim Honeywell Process Solutions 17 Changi Business Park Central 1 Singapore 486073. Department of Chemical Engineering University of Malaya 50603 Kuala Lumpur Malaysia

The biosorption of copper by the brown seaweed Sargassum baccularia, immobilized onto polyvinyl alcohol （PVA） gel beads, was investigated with fixed-bed experiments. Laboratory-scale column tests were performed to determine break.hrough curves with varying flow rates and feed concentrations. A theoretical fixed-bed model, k.own as the Bohart-Adams equation, was evaluated in simulating the experimental break.hrough curves. The Bohart-Adams model qualitatively predicted the break.hrough trends. PVA- immobilized seaweed biomass beads were amenable to efficient regeneration with aqueous solution containing the chelating agent ethylenediaminetetraacetic acid （EDta）. The biosorbent retained most of its original uptak. capacity over three cycles of use. The excellent reusability of the biosorbent could lead to the development of a viable metal remediation technology.

关键词： adsorption biosorption fixed bed immobilized algae polyvinyl alcohol

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Evaluation of boring machine performance with special reference to geomechanical characteristics

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International Journal of minerals,metallurgy and materials 2009年第6期16卷 615-619页

作者： k. goshtasbi m. monjezi P. Tourgoli Faculty of Engineering Tarbiat Modares University

The duration of tunneling projects mostly depends on the performance of boring machines. The performance of boring machines is a function of advance rate, which depends on the machine characterizations and geomechanical properties of rock.mass. There were various theoretical and empirical models for estimating the advance rate. In this paper, after determining the geomechanical properties of rock.mass encountered in the Isfahan metro tunnel, the performance of the roadheader and tunnel boring machine （TBm） were then evaluated using various models. The calculation results show that the average instantaneous cutting rate of the roadheader in sandstone and shale are 42.8 and 74.5 m^3/h respectively. However the actual values in practice are 34.2 and 51.3 m^3/h. The operational cutting rate of the roadheader in sandstone and shale are 8.2 and 9.7 m^3/h respectively, but the actual values are 6.5 and 6.7 m^3/h. The penetration rate of the TBm in shale is predicted to be 50-60 mm/round.

关键词： performance prediction roadheader cutting rate specific energy tunnel boring machine penetration rate

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Accurate energy barriers for catalytic reaction pathways: an automatic training protocol for machine learning force fields

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npj Computational materials 2023年第1期9卷 479-488页

作者： Lars L.Schaaf Edvin Fak. Sandip De Ansgar Schäfer gábor Csányi Engineering Laboratory University of CambridgeCB21PZ CambridgeUK BASF SE Carl-Bosch-Straße 3867056 LudwigshafenGermany

We introduce a training protocol for developing machine learning force fields(mLFFs),capable of accurately determining energy barriers in catalytic reaction *** protocol is validated on the extensively explored hydrogenation of carbon dioxide to methanol over indium *** the help of active learning,the final force field obtains energy barriers within 0.05 eV of Density Functional *** to the computational speedup,not only do we reduce the cost of routine in-silico catalytic task.,but also find an alternative path for the previously established rate-limiting step,with a 40%reduction in activation ***,we illustrate the importance of finite temperature effects and compute free energy *** transferability of the protocol is demonstrated on the experimentally relevant,yet unexplored,top-layer reduced indium oxide *** ability of mLFFs to enhance our understanding of extensively studied catalysts underscores the need for fast and accurate alternatives to direct ab-initio simulations.

关键词： surface catalytic fields

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An Efficient Iterative Procedure for Solution of Plasma Loaded Helical Waveguide Problems

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Chinese Physics Letters 2005年第12期22卷 3123-3125页

作者： V. Babovic m. k.vacevic k. k.njevac Department of Physics Faculty of Science University of Kragujevac Serbia and Montenegro

The behaviour of axially-symmetric waves travelling on plasma filled screened helical coil is comprehensively studied by Anicin [J. Phys. D： Appl. Phys. 33 （2000） 1276], where all analytical expressions are derived in the full-wave theory, but the diagrams are computed in the quasistatic approximation. We use an iterative procedure to overcome this limitation. The iterative procedure is rapid and we have proven that often the first-order approximant is sufficient to improve defects which are k.own as immanent to the quasistatic approximation. The fixed point method appears as the natural choice for numerical treatment of formulae which could arise in a broad class of physical problems usually recognized as guided surface plasma waves.

关键词： Iterative methods

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Representations of coherent and squeezed states in an extended two-parameter Fock.space

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Chinese Physics C 2012年第8期36卷 703-709页

作者： m. k. tavassoly m. H. Lak. Atomic and molecular group Faculty of Physics Yazd University Yazd Iran Photonics Research group Engineering Research Center Yazd University Yazd Iran

Recently an f -deformed Fock.space which is spanned by ｜ n λ was introduced. These bases are the eigenstates of a deformed non-Hermitian Hamiltonian. In this contribution, we will use rather new nonorthogonal basis vectors for the construction of coherent and squeezed states, which in special case lead to the earlier k.own states. For this purpose, we first generalize the previously introduced Fock.space spanned by ｜ n λ bases, to a new one, spanned by extended two-parameters bases ｜ n λ 1 ,λ 2 . These bases are now the eigenstates of a non-Hermitian Hamiltonian H λ 1 ,λ 2 = a λ 1 ,λ 2 a ＋ 1 2 , where a λ 1 ,λ 2 = a ＋ λ 1 a ＋ λ 2 and a are, respectively, the deformed creation and ordinary bosonic annihilation operators. The bases ｜ n λ 1 ,λ 2 are nonorthogonal （squeezed states）, but normalizable. Then, we deduce the new representations of coherent and squeezed states in our two-parameter Fock.space. Finally, we discuss the quantum statistical properties, as well as the non-classical properties of the obtained states numerically.

关键词： coherent state squeezed state representation theory quantum statistics non-orthogonal bases

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Fish and broiler optimal harvesting models in imprecise environment

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International Journal of Biomathematics 2017年第8期10卷 185-216页

作者： A. De k. maity g. Panigrahi Department of Applied Science Haldia Institute of Technology HaldiaPurba Medinipur West Bengal 721657 India Department of mathematicsNational Institute of Technology Durgapur Durgapur West Bengal 721309 India Department of mathematicsmugberia gangadhar mahavidyalaya Bhupatinagar Purba Medinipur West Bengal 721425 India

In this paper, a two-species harvesting model has been considered and developed a solu- tion procedure which is able to calculate the equilibrium points of the model where some biological parameters of the model are interval numbers. A parametric mathematical pro- gram is formulated to find the biological equilibrium of the model for different values of parameters. This interval-valued problem is converted into an equivalent crisp model using interval mathematics. The main advantage of the proposed procedure is that dif- ferent characteristics of the model can be presented in a single framework. Analytically, the existence of steady state and stabilities are look.d into. Using mathematical soft- ware, the model is illustrated and the results are obtained and presented in tabular and graphical forms.

关键词： Two species interval biological parameters equilibrium stability.

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Synthesis, spectroscopic characterization, and thermal decomposition k.netics of some lanthanide(III) nitrate complexes of 2-(N-o-hydroxyacetophenone) amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene

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Journal of Rare Earths 2008年第4期26卷 463-468页

作者： k. mohanan m. Thank.mony B. Sindhu k.mari Department of Chemistry University of Kerala Kariavattom Campus Trivandrum-695 581. Kerala India

Complexes of La（Ⅲ）, Ce（Ⅲ）, Pr（Ⅲ）, Nd（Ⅲ）, Sm（Ⅲ）, Eu（Ⅲ）, gd（Ⅲ）, Dy（Ⅲ）, Yb（Ⅲ）, and Lu0ID with 2-（N-o- hydroxyacetophenone）amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene （HAAT） formed by the condensation of o-hydroxyacetophenone and 2-amino-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene were synthesized and characterized on the basis of elemental analyses, molar conductance measurements, magnetic susceptibility data, UV-Visible, IR, and NmR spectral studies. The spectral data revealed that the ligand acted as a neutral tridentate coordinating to the metal ion through ONO donor sequence. A coordination number nine was proposed for the complexes. Thermal decomposition studies of the ligand and lanthanum（Ⅲ） complex were carried out and k.netic parameters were calculated using Coats-Redfem equation. The decomposition reactions followed random nucleation mechanism with one nucleus on each particle.

关键词： lanthanides o-hydroxyacetophenone molar conductance magnetic susceptibility thermal study rare earths

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