共查询到20条相似文献,搜索用时 10 毫秒
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Using first-principles calculations, we study the structural, mechanical and electronic properties of the layered silica nanostructures built on base of silica bilayers consisting of four- and six-membered Si–O ring (4 MR and 6 MR) units. These silica nanostructures have high stability and good flexibility comparable to graphene and can serve as a promising precursor for the fabrication of well-ordered silica nanotubes. The porous structure and wide band gap of the silica nanomaterials may find applications in gas separation, slow-release microcapsules, and catalyst supports. 相似文献
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We describe a numerical scheme of combining Monte Carlo procedure and quantum scattering theory to simulate electron transport processes through nanostructures. The transport of electrons through a nanostructure is a highly nontrivial nonequilibrium process in which we should consider the interplay of (i) complicated many-body quantum states in nanostructure, (ii) thermal relaxation processes keeping the leads (electron reservoirs) in local equilibrium, (iii) the coupling between the leads and the nanostructure, and (iv) the bias causing nonequilibrium, current, and evolution of quantum states in the nanostructure. Considering the quantum coherence within the nanostructure, we include the degrees of freedom of the nanostructure and a single tunneling electron and solve the Schrödinger equation for the many-body states to obtain the scattering matrix in the Fock space from which both the transmission of the electron and the variation of the states in nanostructure can be full quantum-mechanically calculated. The transport is investigated by the Monte Carlo simulation of successive scattering events of single electrons which are sampled with the Metropolis scheme governed by the scattering probabilities, the thermal statistics in the leads, and the applied bias. By this way from a given initial nanostructure state we can calculate the time evolutions of the current and the internal state. As examples we investigate the transmission of electrons through a two-level system. It is shown that the proposed method can properly deal with the inelastic effects in transport processes. 相似文献
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Philipp Wopperer Umberto De Giovannini Angel Rubio 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(3):51
We derive and extend the time-dependent surface-flux method introduced in [L. Tao, A. Scrinzi, New J. Phys. 14, 013021 (2012)] within a time-dependent density-functional theory (TDDFT) formalism and use it to calculate photoelectron spectra and angular distributions of atoms and molecules when excited by laser pulses. We present other, existing computational TDDFT methods that are suitable for the calculation of electron emission in compact spatial regions, and compare their results. We illustrate the performance of the new method by simulating strong-field ionization of C60 fullerene and discuss final state effects in the orbital reconstruction of planar organic molecules. 相似文献
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Hildebrand M 《Chaos (Woodbury, N.Y.)》2002,12(1):144-156
Nanoscale patterns can form in reactive adsorbates on catalytic surfaces as a result of attractive lateral interactions. These structures can be described within a mesoscopic theory that is derived by coarse graining the microscopic master equation thus providing a link between microscopic lattice models and reaction-diffusion equations. Such mesoscopic models allow to systematically investigate mechanisms responsible for the formation of nanoscale nonequilibrium patterns in reactive condensed matter. We have found that stationary and traveling nanostructures may result from the interplay of the attractive lateral interactions and nonequilibrium reactions. Besides reviewing these results, a detailed investigation of a single reactive adsorbate in the presence of attractive lateral interactions and global coupling through the gas phase is presented. Finally, it is outlined how a mesoscopic theory should be constructed for a particular scanning tunneling microscopy experiment [the oxidation of hydrogen on a Pt(111) surface] in order to overcome the failure of a corresponding reaction-diffusion model to quantitatively reproduce the experiments. (c) 2002 American Institute of Physics. 相似文献
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Crystalline multilayer systems with structure ABABA... offer the possibility of combining functional properties of two distinctly different materials, and of exploiting the interfaces to couple functionality of one component to the other. The multilayer environment permits the amplification of interface properties as would be important for device applications. The manipulation of ferroelectric, ferromagnetic, and/or ferroelastic properties in so-called ferroic materials through growth of thin films, multilayers, and graded composition structures has received considerable experimental and theoretical attention in recent years. We survey the current status of atomic-scale modeling of multilayer systems which could exhibit ferroic behavior; i.e., spontaneous order below a critical temperature and hysteresis in stimulus-response behavior. The roles of interfacial strain, chemical variability at the interface, and film thickness are explored, taking as a primary example the classic BaTiO3?∣∣Fe3O4 ferroelectric∣∣ferrimagnetic interactions. First principles band structure calculations are used to determine relaxed interface structures and residual stresses, as well as the underlying electronic distributions. Embedded cluster methods are then used to extract local chemical bonding characteristics and hyperfine properties. 相似文献
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闪光X射线源是获得高凝聚态物质内部物理图像的重要手段,阳极杆箍缩二极管(RPD)作为其重要组成部分之一,直接影响闪光X射线源照相质量。研究RPD物理特性对二极管物理结构优化设计及实验调试具有重要意义。分析了RPD空间电荷限制、弱箍缩和磁绝缘阶段物理模型。基于PIC模拟技术,编写了计算程序,研究了RPD不同阶段的电子电流、离子电流及电子束箍缩物理特性。通过理论分析,获得了特定几何结构RPD物理模型修正系数及各个阶段离子电流与电子电流比,验证了粒子模拟代码的有效性。模拟结果表明:空间电荷限制阶段,粒子模拟结果与双极性流计算结果一致;在弱箍缩和磁绝缘阶段,粒子模拟得到的总电流与磁绝缘模型计算结果一致,且与文献给出的经验拟合表达式计算结果一致;磁绝缘阶段离子电流与电子电流之比与电压和二极管几何结构相关,给出了离子电子电流比增大系数η与电压和阴阳极半径比的关系,该系数受电子、离子在不同结构二极管渡越时间的影响,随电压和阴阳极半径比增加而逼近恒定值。 相似文献
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The electron avalanche and laser excitation processes in high-pressure discharges at microwave frequencies are investigated. In our model, the applied electromagnetic field is treated classically and assumed to be monochromatic. The Boltzmann equation for the electron velocity distribution function under the influence of an alternating electric field is numerically solved for a typical XeCl laser gas mixture. All relevant elastic, inelastic and electron-electron collisions are included in solving the Boltzmann equation. The theoretical modeling of microwwave-pumped high-pressure gas lasers are developed based on the first law of thermodynamics in order to determineE
rms/n (root-mean-square field strength/total number density of gas molecules) which is required by the Boltzmann equation to calculate the electron kinetics rates and microwave-power absorption by the plasma. A sample calculation of the microwave-pumped XeCl laser is presented, and a fair agreement between theory and experiment is seen.Paper partially presented at the 10th Int. Conf. on Lasers and Applications, Lake Tahoe, Nevada, USA (1987) 相似文献
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In this mini-review we summarize the progress of Lattice Boltzmann (LB) modeling and simulating compressible flows in our group in recent years. Main contents include (i) Single-Relaxation-Time (SRT) LB model supplemented by additional viscosity, (ii) Multiple-Relaxation-Time (MRT) LB model, and (iii) LB study on hydrodynamic instabilities. The former two belong to improvements of physical modeling and the third belongs to simulation or application. The SRT-LB model supplemented by additional viscosity keeps the original framework of Lattice Bhatnagar-Gross-Krook (LBGK). So, it is easier and more convenient for previous SRT-LB users. The MRT-LB is a completely new framework for physical modeling. It significantly extends the range of LB applications. The cost is longer computational time. The developed SRT-LB and MRT-LB are complementary from the sides of convenience and applicability. 相似文献
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K. Makoshi N. Shima Y. Otsuka 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):656
A simple expression of the electric conductance through a nanostructure connected to two electrodes is obtained by using the phase-shift analysis. The Green function theory applicable to the nonequilibrium system is employed to formulate the electric conductance. The 0 bias limit, i.e., the linear response approximation is taken. The relation between Green functions and phase-shifts is obtained by extending the method applied to the single impurity problem in the metal. It is shown that a channel does not contribute to the conductance if its phase-shift is an integer multiple of π. Also shown is the importance of the effect due to multiple orbitals in nanostructures. Some concrete examples leading to simpler forms are given. 相似文献
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Magnetization orientation of a nanoscale ferromagnet can be manipulated by an electric current via spin-transfer torque(STT) effect,which holds great promise in the applications of non-volatile magnetic random access memory(MRAM) and spintorque oscillators.We review the fundamental mechanism and experimental progress of the STT effect.Then,different formula of STT torque has been classified,which can be added to the conventional Landau-Lifshitz-Gilbert equation.After that,we show some simulation results that mainly concern the STT-driven vortex dynamics,magnetization oscillations excited by a perpendicular polarizer,and the detail dynamics by in-plane and out-of-plane dual spin polarizers. 相似文献
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I. Yu. Gotlib A. K. Ivanov-Schitz I. V. Murin A. V. Petrov R. M. Zakalyukin 《Physics of the Solid State》2011,53(11):2375-2384
Nanostructures formed upon filling single-walled carbon nanotubes of different diameters (ranging from 11.5 to 17.6 ?) with
silver bromide have been investigated using the molecular dynamics method. The results of molecular dynamics computer simulation
have demonstrated that, in such tubes, AgBr nanotubes in the form of rolled-up two-dimensional crystalline networks (including
structures both with a trigonal coordination and with a tetragonal coordination of ions) can be produced as well as fragments
of the NaCltype structure, which is typical of bulk AgBr crystals. In the initial stage of their filling, the carbon nanotubes
in the silver bromide melt are deformed, on average, to a greater extent than those in a similar system with AgI. After taking
out from the melt, the degree of deformation of the nanotubes decreases and, in the majority of cases, AgBr nanotubular structures
based on a hexagonal network are formed inside them. 相似文献
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Sanjay Kumar Behura Pramila Mahala Abhijit Ray Indrajit Mukhopadhyay Omkar Jani 《Applied Physics A: Materials Science & Processing》2013,111(4):1159-1163
Using the fundamental models for voltage and current, we report on the photovoltaic behavior of graphene-on-semiconductor-based devices. The graphene-n-Si and graphene-n-GaAs systems are studied for open-circuit voltage (V OC) and short-circuit current density (J SC) under low- and high-level injection conditions. The effects of semiconductor doping density and surface recombination velocity on the V OC of both systems are investigated. The V OC for graphene-n-Si under low- and high-level injection conditions are found to be 0.353 V and 0.451 V, respectively, whereas the V OC for graphene-n-GaAs under low- and high-level injection conditions are 0.441 V and 0.471 V, respectively. The J SC for graphene-n-Si under low- and high-level injection conditions are calculated as 3 mAcm?2 and 4.78 mAcm?2, respectively, whereas the J SC for graphene-n-GaAs under low- and high-level injection conditions are 5.2 mAcm?2 and 6.68 mAcm?2, respectively. These results are in good agreement with the reported experimental work. 相似文献
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A. Fukuyama 《辐射效应与固体损伤》2017,172(9-10):747-749
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Theoretical modeling and characteristic analysis of moving-train induced ground vibrations 总被引:2,自引:0,他引:2
An integrated train-track-subsoil dynamic interaction model of moving-train induced ground vibration is developed on the basis of vehicle dynamics, track dynamics and the Green's functions of subsoil. The model takes account of the vibrations of vehicle components, the quasi-static axle loads and the dynamic excitations between the wheels and track. The analyzed results from an example show that the ground vibration characteristics have a close relationship with train speed and soil properties; the dynamic responses excited by wheel-track irregularity have big influence on the high frequency components of ground vibration; with the increase of distance to the track, the ground acceleration has the tendency of decrease, and the relevance of acceleration curves and train excitation becomes less obvious; the intersections of moving load speed-lines and subsoil dispersion curves are some resonance frequencies that cause the amplification of ground vibrations; there exists a critical speed for moving train that is close to the minimum velocity of the Rayleigh's wave in the subsoil. 相似文献