Application of the catastrophe theory in studying the magnetic reconnection process

A mathematical model of the magnetic reconnection process in the vicinity of critical points is discussed. The diagram method of the catastrophe theory for studying the process of the transformation of structurally unstable magnetic configurations into structurally stable ones is presented. The results of analytical research are confirmed by numerical calculations.     

A parallel algorithm for global magnetic reconnection studies

A new algorithm is presented for the computation of two-dimensional magnetic reconnection in plasmas. Both resistive magnetohydrodynamic (MHD) and two-fluid models are considered. It has been implemented on several parallel platforms and shows good scalability up to 32 CPUs for reasonable problem sizes. A fixed, non-uniform rectangular mesh is used to resolve the different spatial scales in the reconnection problem. The resistive MHD version uses an implicit/explicit hybrid method, while the two-fluid version uses an alternating-direction implicit (ADI) method with high-order artificial dissipation. The technique has proven useful for comparing several different theories of collisional and collisionless reconnection.     

A test electron model for the study of three dimensional magnetic reconnection effects

Understanding the mechanisms that enable the conversion of the explosive release of magnetic energy into the electron energization that is experimentally observed in space and laboratory plasmas represents a long-standing question in the study of magnetic reconnection.     

Moving grids for magnetic reconnection via Newton–Krylov methods

This paper presents a set of computationally efficient, adaptive grids for magnetic reconnection phenomenon where the current density can develop large gradients in the reconnection region. Four-field extended MagnetoHydroDynamics (MHD) equations with hyperviscosity terms are transformed so that the curvilinear coordinates replace the Cartesian coordinates as the independent variables, and moving grids' velocities are also considered in this transformed system as a part of interpolating the physical solutions from the old grid to the new grid as time advances. The curvilinear coordinates derived from the current density through the Monge–Kantorovich (MK) optimization approach help to reduce the resolution requirements during the computation.     

Two-dimensional full-electromagnetic Vlasov code with conservative scheme and its application to magnetic reconnection

A detailed procedure of full-electromagnetic Vlasov simulation technique is presented. Our new unsplitting conservative scheme exactly satisfies the continuity equation for charge. The implicit Finite Difference Time Domain method is also adopted for computation of electromagnetic fields, which is not restricted by the CFL condition for light. The Geospace Environment Modeling magnetic reconnection challenge problem is adopted as a benchmark test. The characteristics of the present Vlasov code are studied by varying the resolution in configuration space.     

Multi-scale simulations of plasma with iPIC3D

The implicit Particle-in-Cell method for the computer simulation of plasma, and its implementation in a three-dimensional parallel code, called iPIC3D, are presented. The implicit integration in time of the Vlasov–Maxwell system, removes the numerical stability constraints and it enables kinetic plasma simulations at magnetohydrodynamics time scales. Simulations of magnetic reconnection in plasma are presented to show the effectiveness of the algorithm.     

分支点邻域内的奇异路径跟踪

在非冗余机械臂运动学的分支奇异点邻域内，由于出现逆运动学解的分支 现象，用基于零空间的拟弧长法求解路径跟踪问题会遇到困难．为此，本文通过计算分支点 的局部模型，提出从分支点开始向两侧延拓的解曲线计算方法，有效地完成了路径跟踪求解 ，在关节空间获得光滑的运动轨迹．     

Peculiarities of null string motion in the gravitational field of a radially expanding or radially collapsing multistring system

We have found a solution to the Einstein equations for the case of radial expansion or radial collapse of a multistring system having a layered structure. It has been shown that the influence of the gravitational field of such multistring system can lead to stable oscillations of a test null string in the vicinity of a fixed (stationary) point in space, which can be regarded as a spatially localized particle with a nonzero effective rest mass. In this case, the ability of multistring systems to create such particles can be considered as a possible alternative to the Higgs mechanism. It has also been noted that for a gas of null strings, creation of particles with nonzero effective rest mass is possible at early stages of the Universe evolution, where due to high pressures and a domain structure of such a gas, mutual penetration of null strings belonging to neighboring domains was unavoidable and could emerge in mass. At later stages, due to expansion of the Universe, such an opportunity could be lost.     

EAST等离子体击穿计算

关于等离子体放电优化控制问题,由于在托卡马克等离子体放电中,等离子体击穿的条件是获得合适的环电压以及尽可能大的零场区。较好的零场只有通过调节极向场线圈电流才能实现,同时EAST极向场系统采用了一体化的设计,但还没有专门的补偿线圈来控制放电初期有较好的零场,根据要求计算零场区结果应与实际实验结果相符。为解决上述问题,提出调节极向场线圈电流以获得较好的零场区,使等离子体顺利击穿。根据提出的磁通环、磁探针等测量信号,计算出了等离子体击穿的零场区、击穿前后的涡流变化及分布,并利用高速CCD记录等离子体放电的击穿过程来验证结果的准确性,取得了与实验一致的结果,为EAST正常放电提供了很好的参考价值。     

An approach to the calculation of multilayer magnetic shielding using artificial neural network

The electromagnetic interference has many undesired effects to the office equipments and the performance of technological devices. Therefore, electrical devices should have field protection mechanism against magnetic fields. The shielding mechanism prevents external magnetic field emitted from the device to the vicinity area. This work attempts to apply artificial neural network in order to estimate shielded magnetic field for multilayer shielding application. The multilayer magnetic shielding performances of cylindrical shaped ferromagnetic shields under extremely low frequency are investigated. For this purpose, three different ferromagnetic materials in cylindrical shape are chosen for magnetic shielding. The shielding performances of these materials are measured and a selected set of data is used to train and test an artificial neural network. The proposed neural network model achieves an intelligent decision for the shielded magnetic field level based on distance, unshielded magnetic field value, number of shield layer and skin-depth of the shield.     

高精度磁电子罗盘的研制

介绍了磁电子罗盘的设计.利用自己生产的磁电阻传感器研制了新型的磁电子罗盘.信号调理电路采用交流放大技术,有效解决了磁阻传感器失调及漂移的影响.针对干扰因素的特点,采用八位置标定法进行自动标定.对所研制的罗盘进行了室外试验,最大罗差小于0.1°.试验结果表明,该磁电子罗盘具有较高的精度.     

Plasma configurations in Galatheya traps and current sheets

The mathematical models and computation results for plasma confinement in magnetic traps called “Galatheyas” and for the evolution of the neutral current sheet in the vicinity of the magnetic zero line are compared. The computer simulations of plasma, magnetic field, and electric current configurations and their formation are based on solving MHD problems. Models of equilibrium configurations in the Galatheya–Belt trap and the current sheet use different dependences p(Ψ) of the plasma pressure on the magnetic flux function in the boundary problems with the Grad–Shafranov equation. Time-dependent models of the configuration formation in both setups differ by the electric current regime in the conductors producing the magnetic field.     

Fabrication of three-dimensional magnetic microdevices with embedded microcoils for magnetic potential concentration

Novel magnetic microdevices were developed for magnetic field generation and concentration and successfully characterized and tested for magnetic potential focusing which is very important for various MEMS applications such as magnetic particles manipulation. These microdevices have been fabricated using an innovative processing sequence which eliminates many problems associated with other fabrication techniques and provides a platform for adding other subsequent fabrication steps required to integrate the microcoils with other microcomponents. They consist of high aspect ratio planar coils made of electroplated copper embedded in the silicon substrate, with ferromagnetic pillars and backside plates made of a CoNiP ternary alloy. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The manipulation of micromagnetic particles in a static and continuous flow conditions has been demonstrated.     

Customized trapping of magnetic particles

This paper presents an efficient technique for trapping of magnetic particles in confined spatial locations using customized designs of micro-coils (MCs). Large magnetic field gradients of up to 20 T/mm and large magnetic forces in the range of 10⁻⁸ Newton on magnetic particles with diameter of 1 μm have been achieved using MCs with several planar geometrical configurations. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high-flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The system allowed capturing of suspended magnetic particles as far as 1,000 μm from the center of the device. Magnetic particles/cells have been trapped and confined in single and in arrays of deep magnetic potential wells corresponding to the MCs configuration.     

Expanding a distributed deductive database with mobile computing

Mobile computing is a component that will be included in many future computing environments. This paper presents a scheme that will allow the addition of a mobile component to an existing distributed deductive database. This scheme allows for the following features: 1) data replication on the mobile unit, 2) transaction logging to log changes both in the mobile user's database and in the network's database, 3) concurrency control to prevent both copies from updating the same record, and 4) reconnection procedures to update both copies upon reconnection. To facilitate data replication and reconnection updates, we have established Proxy Nodes in the network database to keep track of data of interest to the mobile user.     

PeerCast广播机制与维护算法的研究与改进

在分析PeerCast广播机制和节点维护算法的基础上,增加上游节点向下游节点广播状态信息的函数,改进节点的加入和维护策略,并在局域网内进行实验验证。实验结果表明,改进的广播机制和节点维护算法能够减少节点断线重连的时间,提高断线重连的成功率,降低断线后对YP的访问次数,减轻YP的压力。     

Interaction of a plasma plume induced by a pulsed plasma thruster with an incident flow of rarefied magnetized plasma

A three-dimensional computational model and the results of the calculation for the dynamics of a plasma plume induced by a pulsed plasma thruster (PPT) in a magnetized flow of the ambient plasma are presented. A nonstationary expansion process of a PPT-induced plasma plume is studied in the ionospheric plasma over 100 μs after the start of a 6-microsecond plasma pulse. The parameters of the plasma plume in the PPT outlet section simulate the performance characteristics of a pulsed thruster PPT-4 (Pulsed Plasma Thruster 4 [3]) utilizing solid Teflon propellant. The magnetohydrodynamic (MHD) model of the process is based on the approximation of the ideal magnetic gas dynamics and makes it possible to predict the dynamics of a plasma bunch after the pulse termination during its interaction with the ambient medium and the magnetic field as well as the induced electric fields and currents in the vicinity of the expanding plasma     

复杂网络匹配系数控制算法

针对CAIDA提供的探测数据进行分析,得到互联网AS级宏观拓扑结构的随时间演化情况,在对匹配系数进行深入分析的基础上,提出了一种单调改变网络匹配系数的算法--边重连算法。该算法可以在两个方向上构造具有连续匹配系数的网络集合,选择向同配方向重连则可构建匹配系数渐进增大的连续匹配系数网络,选择向异配方向重连则可构建匹配系数不断减小的连续匹配系数网络,当边重连足够充分时可以得到具有极大匹配系数或极小匹配系数的网络。     

ReALE: A Reconnection Arbitrary-Lagrangian–Eulerian method in cylindrical geometry

This paper deals with the extension to the cylindrical geometry of the recently introduced Reconnection algorithm for Arbitrary-Lagrangian–Eulerian (ReALE) framework. The main elements in standard ALE methods are an explicit Lagrangian phase, a rezoning phase, and a remapping phase. Usually the new mesh provided by the rezone phase is obtained by moving grid nodes without changing connectivity of the underlying mesh. Such rezone strategy has its limitation due to the fixed topology of the mesh. In ReALE we allow connectivity of the mesh to change in rezone phase, which leads to general polygonal mesh and permits to follow Lagrangian features much better than for standard ALE methods. Rezone strategy with reconnection is based on using Voronoi tesselation machinery. In this work we focus on the extension of each phase of ReALE to cylindrical geometry. The Lagrangian, rezone with reconnection and remap phases are revamped to take into account the cylindrical geometry. We demonstrate the efficiency of our ReALE in cylindrical geometry on series of numerical examples.     

The influence of magnetic and chemical ordering on the phase diagram of Cr-Fe-Ni

A thermodynamic dataset for the ternary system Cr-Fe-Ni which has been reported in the literature for the range from medium to high temperatures has been supplemented with datasets from the binary sub-systems at lower temperatures. The magnetic and the chemical ordering transitions which are known from the binary Fe-Ni system were extrapolated into the ternary system Cr-Fe-Ni. The phase diagram of Cr-Fe-Ni alloys at temperatures below 500 °C was predicted. The magnetic contribution to the Gibbs energy of Ni-rich alloys induces a miscibility gap which appears in the binary phase diagram of Fe-Ni as a small triangle-like field ending in a tricritical point. In the ternary system Cr-Fe-Ni the miscibility gap is present as a broad two-phase field in the vicinity of the composition FeNi₃. At lower temperatures this miscibility gap participates in a sequence of changing equilibria when it interferes with the chemically ordered L1₂ phase.