Bursty Bulk Flow Driven Turbulence in the Earth’s Plasma Sheet

During the last several years significant progress has been made in understanding MHD turbulence in the Earth’s plasma sheet. Due to the statistically transitory properties of fluctuations, finite size and boundary effects, however, issues of fundamental importance remain unresolved. Here we concentrate on such intrinsic features of plasma sheet turbulence as its origin and dynamical nature. In particular, we investigate bursty bulk flow driven multi-scale transfer of energy towards the dissipation scale, and provide evidence for the presence of non-linear interactions. We show that, in contrast with previous results, Alfvénic fluctuations together with 2D eddy interactions may appear as important constituents of turbulence in the plasma sheet.     

Do we know the cosmic-ray boosters?

The literature on cosmic-ray acceleration tends to favour strong shocks (in supernovae, stellar and galactic winds) over compact boosters. Difficulties are posed by the spectrum which does not reveal the implied upper cutoff (at E = 10^13±1 eV), by the energy-dependent anisotropy at the high-energy end (at E 10¹⁸ eV), the missing hydrogen, the large required boosting efficiency, the high positron abundance at E 10 GeV, detailed studies of supernova shells, and by an inadequacy of the Sedov-Taylor model for supernova explosions. Solar and solar-wind data support single-step or few-step accelerations because of the large observed anisotropies and short time scales.

The importance of spindown in compact binary systems is often underestimated. Several neutron-star binaries have been detected at cosmic γ-ray energies. Cosmic-ray escape from the Galaxy may proceed supersonically through narrow tubes rather than via convective diffusion.     

High resolution spectro-polarimetry with a large balloon-borne solar telescope

The balloon mission “Sunrise” consists of a 1m lightweight solar telescope equipped with a powerful spectro-graph-polarimeter and a multi-channel filtergraph for the visible and the UV. The science goals of Sunrise are focussed on, but not limited to, the investigation of the solar surface magnetism. The key questions include the generation and maintenance of the variable magnetic field, the structure and dynamics of the chromosphere, and the interaction of material flow and magnetic field in sunspots.     

Thin Current Sheets in the Magnetotail Observed by Cluster

The dynamics of the current sheet is one of the most essential elements in magnetotail physics. Particularly, thin current sheets, which we define here as those with a thickness of less than several ion inertia lengths, are known to play an important role in the energy conversion process in the magnetotail. With its capability of multi-point observation, Cluster succeeded to obtain the current density continuously and therefore identify structures of thin current sheets. We discuss characteristics of the thin current sheets by showing their temporal evolution and the spatial structures based on several Cluster observations.     

Radial propagation velocity of energetic particle injections according to measurements onboard the <Emphasis Type="Italic">Cluster</Emphasis> satellites

Injections of energetic electrons with a dispersion over energies were observed during the February 23, 2004 (at about 03:20 UT) substorm onboard the Cluster satellites in the vicinity of perigee near the midnight meridian. The delays in the particle observation caused by the energy dependence of the magnetic drift velocities made it possible to determine the position and time of the beginning of the drift, tracing the trajectories of the leading center of particles back in time in the magnetospheric model. The comparisons of the measurements of four satellites allowed us to determine the radial propagation of the injection front with a velocity of 100–150 km/s at a distance of 7–9 R _E. The comparison with a few previous measurements shows a substantial slowing down of injections as they approached the Earth, and this confirms the prospects of this method for more detailed study of propagation of plasma injection into the inner magnetosphere.     

Investigation of thermosolutally caused convection during -growth of BiSbTe3-mixed crystals at normal and reduced gravity

BiSbTe₃-mixed crystals have been grown at normal and reduced gravity (during the MIR'97-mission) using a -configuration of the TITUS facility. The distribution of the components in the melt, and so the homogeneity of the growing crystal, is strongly influenced by the flow in the melt even in the case of weak convection. The flow configuration in the melt especially in front of the solid-liquid phase boundary can be investigated by means of a segregation analysis of the system components and an additional Pb-dopant. The BiSbTe₃-system is because of its hydro-dynamic properties a typical representative of semiconductor melts (low number, high number) but there are also some special properties relating to the segregationally caused enrichment of the lighter tellurium at the phase boundary and the resulting solutal destabilities. Experimental experiences from segregation analysis have shown that the mass transport in the melt at normal gravity is mainly influenced by convective mixing determined by thermally and solutally caused buoyancy forces. Numerical simulations have been performed for the real experimentally used configurations. These simulations have shown that a strong coupling of thermal and solutal effects exists and have given axial as well as radial segregation profiles being in excellent agreement with the experimental results for the vertical normal gravity grown crystals. For micro gravity conditions a reduction of the flow velocity of more than two orders of magnitude (depending on the micro gravity level and the direction of the residual acceleration) resulting in diffusion controlled component segregation has been predicted.The results of the two micro gravity grown crystals, especially the axial and radial segregation profiles as a sensitive indicator for the flow configuration in front of the phase boundary will be given and discussed in the paper. They will be compared with the results of numerical simulations of the melt flow for the real processing parameters measured during the TITUS growth processes and with experimental as well as numerical results for vertical normal gravity grown reference Samples.     

First Results of the THEMIS Search Coil Magnetometers

We present the first data from the THEMIS Search Coil Magnetometers (SCM), taken between March and June 2007 while the THEMIS constellation apogee moved from the duskside toward the dawnside. Data reduction, especially the SCM calibration method and spurious noise reduction process, is described. The signatures of magnetic fluctuations in key magnetospheric regions such as the bow shock, the magnetopause and the magnetotail during a substorm, are described. We also discuss the role that magnetic fluctuations could play in plasma transport, acceleration and heating.     

固化过程可视化:采用集成的超声传感器监测交联反应过程

在工艺过程中,树脂的反应程度或固化度通常因为其不会导致可见的缺陷,所以常被忽视.然而,未完全固化的产品会对最终的力学性能产生很大的影响,在使用过程中伴随有较大温度变化的情况下尤其如此.