正三角形晶格金属柱光子带隙结构

采用有限差分法分析了正三角形晶格金属柱光子带隙(PBG)结构中TE模式的色散特性,导出了全局带隙分布图, 探讨了一套系统的设计指定本征频率PBG结构的方法。结果表明,金属柱半径与晶格常数的比值越小,越有利于PBG谐振腔的圆波导耦合输出。说明了类比圆柱波导设计回旋管的可能性。     

Critical currents in quasiperiodic pinning arrays: chains and Penrose lattices

We study the critical depinning current Jc versus the applied magnetic flux Phi, for quasiperiodic (QP) chains and 2D arrays of pinning centers placed on the nodes of a fivefold Penrose lattice. In QP chains, the peaks in Jc(Phi) are determined by a sequence of harmonics of the long and short segments of the chain. The critical current Jc(Phi) has a remarkable self-similarity. In 2D QP pinning arrays, we predict analytically and numerically the main features of Jc(Phi), and demonstrate that the Penrose lattice of pinning sites provides an enormous enhancement of Jc(Phi), even compared to triangular and random pinning site arrays. This huge increase in Jc(Phi) could be useful for applications.     

PARTICULAR SOLITONS IN NONLINEAR LATTICE

One soliton of particle velocity and its amplitude (maximum particle velocity of one soliton) in Toda lattice is given analytically. It has also been known numerically that the maximum particle velocity (when the collision of two solitons reaches their maximum, we define V_n at this time as its maximum particle velocity) during the collision of two solitons moving in the same direction is equal to the difference between the amplitudes of two solitons if the difference is large enough; however, the maximum particle velocity is equal to the adding up of the amplitudes of two solitons moving in the opposite directions. The relationship between the maximum value of e^-(r_n)-1 and their initial amplitude of e^-(r_n)-1 is also given analytically in Toda lattice if the amplitudes of the two solitons are the same and their moving directions are opposite. Compared with the Boussinesq equation, there are differences between the Toda lattice equation and the Boussinesq equation for solitons during the collision.     

Dynamics of bloggers’ communities: Bipartite networks from empirical data and agent-based modeling

We present an analysis of the empirical data and the agent-based modeling of the emotional behavior of users on the Web portals where the user interaction is mediated by posted comments, like Blogs and Diggs. We consider the dataset of discussion-driven popular Diggs, in which all comments are screened by machine-learning emotion detection in the text, to determine positive and negative valence (attractiveness and aversiveness) of each comment. By mapping the data onto a suitable bipartite network, we perform an analysis of the network topology and the related time-series of the emotional comments. The agent-based model is then introduced to simulate the dynamics and to capture the emergence of the emotional behaviors and communities. The agents are linked to posts on a bipartite network, whose structure evolves through their actions on the posts. The emotional states (arousal and valence) of each agent fluctuate in time, subject to the current contents of the posts to which the agent is exposed. By an agent’s action on a post its current emotions are transferred to the post. The model rules and the key parameters are inferred from the considered empirical data to ensure their realistic values and mutual consistency. The model assumes that the emotional arousal over posts drives the agent’s action. The simulations are preformed for the case of constant flux of agents and the results are analyzed in full analogy with the empirical data. The main conclusions are that the emotion-driven dynamics leads to long-range temporal correlations and emergent networks with community structure, that are comparable with the ones in the empirical system of popular posts. In view of pure emotion-driven agents actions, this type of comparisons provide a quantitative measure for the role of emotions in the dynamics on real blogs. Furthermore, the model reveals the underlying mechanisms which relate the post popularity with the emotion dynamics and the prevalence of negative emotions (critique). We also demonstrate how the community structure is tuned by varying a relevant parameter in the model. All data used in these works are fully anonymized.     

Magnetic properties of nonmagnetic metals with randomly distributed paramagnetic impurities

A generalized mean field theory for disordered systems with the RKKY interaction is constructed on the basis of calculation and analysis of distribution functions for random magnetic fields produced by magnetic moments with an irregularly spatial distribution. These distribution functions are determined by two methods: (i) analytically and (ii) numerically by statistical processing of the results of calculation of random fields in a model system. For metals diluted by magnetic impurities, it is shown that the ground state of the system becomes magnetically ordered when the impurity concentration exceeds a certain critical value depending on the type of crystal lattice of the metal and the sample shape. The magnetic phase diagram of the system is determined and the temperature dependence of its magnetic susceptibility, the concentration dependence of the Curie temperature, and the temperature and concentration dependences of the magnetization and magnetic part of the heat capacity of the system are established.     

Correlation effects on frequency dependent conductivity: Application to superionic conductors

The Scher-Lax model for the calculation of a.c. conductivity is modified to allow for temporal and spatial correlations. If, due to, say, lattice relaxation effects, a charge is most likely to continue to move in the same direction (caterpillar mechanism), then the real part of the conductivity will saturate, at large frequencies, below the d.c. level. The reverse will be true if a bounce-back mechanism dominates. These two cases of correlation can be related to the behavior of the superionic conductors AgI and Na β-alumina, respectively. The degree of disorder in the hopping sites determines the distribution of ionic transition rates which in turn governs the details of the conductivity curve. The frequency dependent conductivity due to the motion of an ionic cluster (dimer) is also analyzed.     

利用干涉光刻技术制备LED表面微纳结构

为了制备大面积周期性微纳米结构以提高LED的发光效率,建立了劳厄德(Lloyd)干涉光刻系统。简单分析了该干涉光刻系统的工作原理,并介绍了利用干涉曝光工艺制备一维光栅、二维点阵、孔阵列等纳米结构图形的具体实验过程。最后对纳米图形进行结构转移,制备出了金属纳米结构。实验结果表明:利用劳厄德干涉光刻系统,可以在20 mm×20 mm大小的ITO衬底上稳定制备出周期为450 nm的均匀光栅或二维点阵列图形结构,它们的占空比也是可以调节变化的。     

Molecular-dynamics simulations with explicit hydrodynamics II: On the collision of polymers with molecular obstacles

We present a study of the dynamics of single polymers colliding with molecular obstacles using Molecular-dynamics simulations. In concert with these simulations we present a generalized polymer-obstacle collision model which is applicable to a number of collision scenarios. The work focusses on three specific problems: i) a polymer driven by an external force colliding with a fixed microscopic post; ii) a polymer driven by a (plug-like) fluid flow colliding with a fixed microscopic post; and iii) a polymer driven by an external force colliding with a free polymer. In all three cases, we present a study of the length-dependent dynamics of the polymers involved. The simulation results are compared with calculations based on our generalized collision model. The generalized model yields analytical results in the first two instances (cases i) and ii)), while in the polymer-polymer collision example (case iii)) we obtain a series solution for the system dynamics. For the case of a polymer-polymer collision we find that a distinct V-shaped state exists as seen in experimental systems, though normally associated with collisions with multiple polymers. We suggest that this V-shaped state occurs due to an effective hydrodynamic counter flow generated by a net translational motion of the two-chain system.     

Self-organization in two- and three-dimensional adsorbates with attractive lateral interactions

Self-consistent lattice gas models for the dynamics of monolayer and multilayer adsorbates with attractive lateral interactions are investigated. The existence of spinodal regions with uphill diffusion is shown. For monolayer growth, periodic stationary distributions of adsorbate density are found analytically. Generalized kinetic BET-model for multilayer growth is studied numerically. A possibility for surface transformation into self-organized arrays of quantum dot-like structures is shown.     

Relativistic lattice gas hydrodynamics

Non-relativistic cellular automata can model non-relativistic hydrodynamical flows. In this article we show that if the hopping occurs on a space-time lattice which is generated by discrete subgroups of the Poincaré group and if the collision rules embody the relativistic conservation laws, we can modelrelativistic flows. The simplest version of the relativistic model is formally isomorphic with the non-relativistic Hardy, de Pazzis and Pomeau (HPP) lattice model, provided we reinterpret the various quantities that appear there. This observation explains the non-Galilean invariant results of HPP.     

TheO(3) non-linear σ-model on a 2 dimensional random lattice

TheO(3) σ-model on a 2-dimensional random lattice is studied numerically. The comparison of the continuum behaviors of the model on both random and regular lattices is carried out. It is shown that both lattices have the same continuum limit of the model, and the random lattice seems not to have the advantage of the wider scaling window compared to the same sized regular square lattice.     

直管道中绕平板平面流动的格子气仿真

本文首先根据U.Frisch等人所提出的格子气FHPⅡ模型的要点,建立了该模型的完备的微观动力学(碰撞规则)。在此基础上,对一种CVD问题的简单模型进行了格子气仿真。文中介绍了边界条件和初条件的处理,以及在微机上实现仿真的分段算法。     

Discrete Green's Function for Lattice Random Walk

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Discrete Green's Function for Lattice Random Walk

A lattice random walk model based on particles scattering on discrete lattice of homogenous space is introduced. The discrete Green's function (DFG) for two-dimensional and three-dimensional lattice random walk of photon is found and proved by mathematical induction. The convolution theorem of photon lattice random walk is presented. They can be used with the method of images to calculate the photon density distribution in semi-infinite and finite slab homogenous turbid media such as tissue.     

Dark soliton interaction of spinor Bose-Einstein condensates in an optical lattice

We study the magnetic soliton dynamics of spinor Bose-Einstein condensates in an optical lattice which results in an effective Hamiltonian of anisotropic pseudospin chain. An equation of nonlinear Schrödinger type is derived and exact magnetic soliton solutions are obtained analytically by means of Hirota method. Our results show that the critical external field is needed for creating the magnetic soliton in spinor Bose-Einstein condensates. The soliton size, velocity and shape frequency can be controlled in practical experiment by adjusting the magnetic field. Moreover, the elastic collision of two solitons is investigated in detail.     

光子晶体微波加速结构的计算与设计

用有限差分法计算了由金属棒分别按方形和三角形晶格分布的二维光子晶体的色散曲线, 得出了带隙图．计算结果表明: 对于三角形晶格, 当金属棒半径和棒间距比值小于0.2时, 由该种光子晶体构成的微波加速结构可约束主模、抑制高次模; 用Microwave Studio软件模拟计算了三角形晶格分布的二维光子晶体加速结构, 研究了新加速结构的RF参数与结构尺寸的关系, 优化出一组RF频率为9.37GHz时此种加速腔的结构尺寸, 计算还表明该种新加速结构具有较高的分路阻抗和品质因数.     

Magnons interaction of spinor Bose-Einstein condensates in an optical lattice

We study the interaction of magnons in dipolar spinor Bose-Einstein condensates in an optical lattice. By means of Holstein-Primakoff and Fourier transformations the energy spectra of the ground and the excited states is obtained analytically. Our results show that the collision of magnons is elastic which is expressed by the conservation of wave numbers in the process of collision. At last, we found that the interaction of magnons is attractive which tends to self-localization to form spin waves, i.e., a cluster of a macroscopic number of coherent magnons. Because of the attraction, the instability of spin wave brings about the existence of solitary wave.