Theory and Simulation of Reconnection

Reconnection is a major commonality of solar and magnetospheric physics. It was conjectured by Giovanelli in 1946 to explain particle acceleration in solar flares near magnetic neutral points. Since than it has been broadly applied in space physics including magnetospheric physics. In a special way this is due to Harry Petschek, who in 1994 published his ground breaking solution for a 2D magnetized plasma flow in regions containing singularities of vanishing magnetic field. Petschek’s reconnection theory was questioned in endless disputes and arguments, but his work stimulated the further investigation of this phenomenon like no other. However, there are questions left open. We consider two of them – “anomalous” resistivity in collisionless space plasma and the nature of reconnection in three dimensions. The CLUSTER and SOHO missions address these two aspects of reconnection in a complementary way -- the resistivity problem in situ in the magnetosphere and the 3D aspect by remote sensing of the Sun. We demonstrate that the search for answers to both questions leads beyond the applicability of analytical theories and that appropriate numerical approaches are necessary to investigate the essentially nonlinear and nonlocal processes involved. Necessary are both micro-physical, kinetic Vlasov-equation based methods of investigation as well as large scale (MHD) simulations to obtain the geometry and topology of the acting fields and flows.     

Acceleration and Composition of Solar Wind Suprathermal Tails

Observations in the solar wind have revealed important insights into how energetic particles are accelerated in astrophysical plasmas. In circumstances where stochastic acceleration is expected, a suprathermal tail on the distribution function is formed with a common spectral shape: the spectrum is a power law in particle speed with a spectral index of −5. Recent theories for this phenomenon, in which thermodynamic constraints are applied to explain the common spectral shape, are reviewed. As an example of potential extensions of this theoretical work, consideration is given to the acceleration of Anomalous Cosmic Rays in the heliosheath.     

延伸喷管展开ADAMS动力学仿真

利用机械系统动力学仿真分析软件ADAMS进行延伸喷管展开动力学仿真,在已知延伸喷管结构尺寸、各部件质量特性、作动筒内压力及各种展开阻力的条件下,计算了延伸锥展开位移、速度和加速度。并与试验结果比较,两种结果接近。对计算结果分析得知,在保证展开时间满足要求的前提下,适当降低展开速度并尽可能匀速展开,可以减小展开过程中延伸锥与基础喷管之间的撞击力;为了保证展开可靠性,作动筒的展开力应有一定持续时间,尽量避免出现压力峰后压力突降。对固体火箭发动机延伸喷管设计与研究具有重要意义。     

Laboratory investigation of physical mechanisms of auroral charged particle acceleration in the field-aligned current layers

One of the major topics of space weather research is to understand auroral structure and the processes that guide, accelerate, and otherwise control particle precipitation and during substorms. The problem is that it is not clear the structure of the magnetic field-aligned electric fields and how they are supported in the magnetospheric plasma. The objective of this research is to study the physical mechanisms of these phenomena in a laboratory experiment. It should be achieved by simulating the charged particle acceleration due to field-aligned electrical field generation in all totality of the interconnected events: generation of a plasma flow, its evolution in the magnetic field, polarization of plasma, generation of the field-aligned currents, development of instabilities in the plasma and current layers, double layers or anomalous resistance regions appearance, electron acceleration. Parameters of the laboratory simulation and preliminary results of the experiment are discussed.     

激光测振技术的最新进展

激光测振技术在近20年取得了巨大进展。本文以2004年6月在意大利召开的第六届激光测振国际会议的技术内容为基础，重点介绍激光测振技术在计量学方面的进展和在其他领域的应用。     

Particle Acceleration in Mercury’s Magnetosphere

This paper is devoted to the problem of particle acceleration in the closest to the Sun Hermean magnetosphere. We discuss few available observations of energetic particles in Mercury environment made by Mariner-10 in 1974–1975 during Mercury flyby’s and by Helios in 1979 upstream of the Hermean bow shock. Typically ions are non-adiabatic in a very dynamic and compact Mercury magnetosphere, so one may expect that particle acceleration will be very effective. However, it works perfectly for electrons, but for ions the scale of magnetosphere is so small that it allows their acceleration only up to 100 keV. We present comparative analysis of the efficiency of various acceleration mechanisms (inductive acceleration, acceleration by the centrifugal impulse force, stochastic acceleration in a turbulent magnetic fields, wave–particle interactions and bow shock energization) in the magnetospheres of the Earth and Mercury. Finally we discuss several points which need to be addressed in a future Hermean missions.     

Cone model-based SEP event calculations for applications to multipoint observations

The problem of modeling solar energetic particle (SEP) events is important to both space weather research and forecasting, and yet it has seen relatively little progress. Most important SEP events are associated with coronal mass ejections (CMEs) that drive coronal and interplanetary shocks. These shocks can continuously produce accelerated particles from the ambient medium to well beyond 1 AU. This paper describes an effort to model real SEP events using a Center for Integrated Space weather Modeling (CISM) MHD solar wind simulation including a cone model of CMEs to initiate the related shocks. In addition to providing observation-inspired shock geometry and characteristics, this MHD simulation describes the time-dependent observer field line connections to the shock source. As a first approximation, we assume a shock jump-parameterized source strength and spectrum, and that scatter-free transport occurs outside of the shock source, thus emphasizing the role the shock evolution plays in determining the modeled SEP event profile. Three halo CME events on May 12, 1997, November 4, 1997 and December 13, 2006 are used to test the modeling approach. While challenges arise in the identification and characterization of the shocks in the MHD model results, this approach illustrates the importance to SEP event modeling of globally simulating the underlying heliospheric event. The results also suggest the potential utility of such a model for forcasting and for interpretation of separated multipoint measurements such as those expected from the STEREO mission.     

One dimensional blood flow in a planetocentric orbit

All life on earth is accustomed to the presence of gravity. When gravity is altered, biological processes can go awry. It is of great importance to ensure safety during a spaceflight. Long term exposure to microgravity can trigger detrimental physiological responses in the human body. Fluid redistribution coupled with fluid loss is one of the effects. In particular, in microgravity blood volume is shifted towards the thorax and head. Sympathetic nervous system-induced vasoconstriction is needed to maintain arterial pressure, while venoconstriction limits venous pooling of blood prevents further reductions in venous return of blood to the heart. In this paper, we modify an existing one dimensional blood flow model with the inclusion of the hydrostatic pressure gradient that further depends on the gravitational field modified by the oblateness and rotation of the Earth. We find that the velocity of the blood flow V_B is inversely proportional to the blood specific volume d, also proportional to the oblateness harmonic coefficient J₂, the angular velocity of the Earth ω_E, and finally proportional to an arbitrary constant c. For c = −0.39073 and ξ_H = −0.5 mmHg, all orbits result to less blood flow velocities than that calculated on the surface of the Earth. From all considered orbits, elliptical polar orbit of eccentricity e = 0.2 exhibit the largest flow velocity V_B = 1.031 m/s, followed by the orbits of inclination i = 45°and 0°. The Earth’s oblateness and its rotation contribute a 0.7% difference to the blood flow velocity.     

应用于飞机装配的并联机构技术发展综述

并联机构的闭链结构使其具有良好的精度、刚性及动态性能,可满足飞机装配的精度、效率需求,因此,以并联机构为构型主体的自动化装配装备正越来越多地应用于飞机装配中。首先,概述了当前并联机构发展现状及飞机装配体现出的新特点,分析了并联机构应用于飞机装配的优势。其次,从飞机装配零部件加工和飞机零部件装配调姿定位两个方面综述了应用于飞机装配并联机构的国内外发展现状。然后,探讨了并联机构主要的前沿研究问题,从并联机构可重构设计、性能评价及优化设计、精度建模和力/位协同控制等4个方面,详细分析了并联机构应用于飞机装配中的关键技术。最后,对并联机构应用在飞机装配中未来的发展方向和机遇做了展望。     

基于N-dot的涡扇发动机加速控制器设计

针对双转子民用涡扇发动机,进行基于转子加速度的加速控制器设计研究。采用常规的PI控制器结构,针对结构中所需的转子加速度指令,给出了1种满足要求的设计方法,并将PI控制参数的求解过程转化为带约束的非线性优化问题,利用模式搜索算法求解。构建包含稳态控制器和加速控制器的涡扇发动机闭环控制回路,进行加速过程仿真测试。结果表明:所设计的加速控制器满足涡扇发动机加速过程的性能要求,对于工程设计与应用具有一定的参考价值。