Study of domain structure and magnetization reversal after thermal treatments in Fe40Co38Mo4B18 microwires

We have studied the effect of thermal treatment on the magnetic domain structure and magnetic reversal process of amorphous and nanocrystalline Fe₄₀Co₃₈Mo₄B₁₈ microwires. The domain structure and the magnetization reversal of amorphous FeCoMoB microwires reflect the complex stress distribution introduced by the glass coating. Hence, the thickness of radial domain structure decreases with temperature and the temperature dependence of the switching field presents a discontinuous behavior. After nanocrystallization, the domain structure of FeCoMoB microwire is almost constant within the temperature range 10-400 K and the switching field decreases almost linearly with temperature mostly because of the decrease of saturation magnetization.     

Dynamics of the infinitely-thin kink

We consider the dynamics of the domain-wall kink soliton, in particular we study the zero mode of translation. In the infinitely-thin kink limit, we show that the zero mode is almost completely frozen out, the only remnant being a dynamically constrained four-dimensional mode of a single but arbitrary frequency. In relation to this result, we show that the usual mode expansion for dealing with zero modes - implicit collective coordinates - is not in fact a completely general expansion, and that one must use instead a traditional generalised Fourier analysis.     

Simulating bistable biochemical systems by means of reactive multiparticle collision dynamics

Based on a reactive multiple particle collision method, we construct a mesoscopic dynamics model to simulate chemical system. The validity of the reactive multiple particle collision method under various conditions in a double-feedback bi-stable chemical system is studied. Then, we extend it to simulate diffusion-limited reactions with fast reaction rate in cellular environment. Using the improved method, we observe bi-stable behavior with randomly distributed reactants and spatial domain separation of opposite phases. The particle-based mesoscopic method is computationally efficient, although hydrodynamic interactions and fluctuation are both properly accounted for. Stochastic effects shown to play dominant roles in biochemical dynamics are also considered. The improved method could be used to explore a variety of reactions with disparate scale of reaction rates.     

平行六边形区域上的快速离散傅立叶变换

In this paper, we propose a fast algorithm for computing the DGFT (Discrete Generalized Fourier Transforms) on hexagon domains [6], based on the geometric properties of the domain. Our fast algorithm (FDGFT) reduces the computation complexity of DGFT from O(N4) to O(N2 log N). In particulary, for N =2^P23^P34^P45^P56^P6, the floating point computation working amount equals to(17/2P2 16p3 135/8p4 2424/25p5 201/2P6)3N^2. Numerical examples are given to access our analysis.     

Probabilistically induced domain decomposition methods for elliptic boundary-value problems

Monte Carlo as well as quasi-Monte Carlo methods are used to generate only few interfacial values in two-dimensional domains where boundary-value elliptic problems are formulated. This allows for a domain decomposition of the domain. A continuous approximation of the solution is obtained interpolating on such interfaces, and then used as boundary data to split the original problem into fully decoupled subproblems. The numerical treatment can then be continued, implementing any deterministic algorithm on each subdomain. Both, Monte Carlo (or quasi-Monte Carlo) simulations and the domain decomposition strategy allow for exploiting parallel architectures. Scalability and natural fault tolerance are peculiarities of the present algorithm. Examples concern Helmholtz and Poisson equations, whose probabilistic treatment presents additional complications with respect to the case of homogeneous elliptic problems without any potential term and source.     

一种可用于分析任意介电常数张量的各向异性波导导模的二维时域有限差分模型

为分析具有任意介电常数张量的各向异性波导的导模，本文通过把简化的二维时域有限差分（２－ＤＦＤＴＤ）法扩展至任意各向异性介质，提出了一种以Ｄ、Ｅ和Ｈ场为基础的统一的简化２－ＤＦＤＴＤ模型．利用该模型，研究了简化的复数２－ＤＦＤＴＤ方法与实变数２－ＤＦＤＴＤ方法之间的关系．文中还讨论了复变数方法和实变数方法的激励技术．     

高维抛物方程迎风区域分裂差分方法

结合迎风方法和区域分裂思想,采用一阶迎风、二阶修正迎风法逼近高维抛物方程的对流项.内边界处和子区域分别对应区域分裂显隐格式;并运用极值原理和嵌入定理给出了收敛性分析,最后给出数值试验,说明其实际意义.     

Preconditioning the Poincaré-Steklov operator by using Green's function

This paper is concerned with the Poincaré-Steklov operator that is widely used in domain decomposition methods. It is proved that the inverse of the Poincaré-Steklov operator can be expressed explicitly by an integral operator with a kernel being the Green's function restricted to the interface. As an application, for the discrete Poincaré-Steklov operator with respect to either a line (edge) or a star-shaped web associated with a single vertex point, a preconditioner can be constructed by first imbedding the line as the diameter of a disk, or the web as a union of radii of a disk, and then using the Green's function on the disk. The proposed technique can be effectively used in conjunction with various existing domain decomposition techniques, especially with the methods based on vertex spaces (from multi-subdomain decomposition). Some numerical results are reported.

     

A comparison of some domain decomposition and ILU preconditioned iterative methods for nonsymmetric elliptic problems

In recent years, competitive domain-decomposed preconditioned iterative techniques of Krylov-Schwarz type have been developed for nonsymmetric linear elliptic systems. Such systems arise when convection-diffusion-reaction problems from computational fluid dynamics or heat and mass transfer are linearized for iterative solution. Through domain decomposition, a large problem is divided into many smaller problems whose requirements for coordination can be controlled to allow effective solution on parallel machines. A central question is how to choose these small problems and how to arrange the order of their solution. Different specifications of decomposition and solution order lead to a plethora of algorithms possessing complementary advantages and disadvantages. In this report we compare several methods, including the additive Schwarz algorithm, the classical multiplicative Schwarz algorithm, an accelerated multiplicative Schwarz algorithm, the tile algorithm, the CGK algorithm, the CSPD algorithm, and also the popular global ILU-family of preconditioners, on some nonsymmetric or indefinite elliptic model problems discretized by finite difference methods. The preconditioned problems are solved by the unrestarted GMRES method. A version of the accelerated multiplicative Schwarz method is a consistently good performer.