Electron-Ion Temperature Equilibration in Collisionless Shocks: The Supernova Remnant-Solar Wind Connection

Collisionless shocks are loosely defined as shocks where the transition between pre-and post-shock states happens on a length scale much shorter than the collisional mean free path. In the absence of collision to enforce thermal equilibrium post-shock, electrons and ions need not have the same temperatures. While the acceleration of electrons for injection into shock acceleration processes to produce cosmic rays has received considerable attention, the related problem of the shock heating of quasi-thermal electrons has been relatively neglected. In this paper we review the state of our knowledge of electron heating in astrophysical shocks, mainly associated with supernova remnants (SNRs), shocks in the solar wind associated with the terrestrial and Saturnian bowshocks, and galaxy cluster shocks. The solar wind and SNR samples indicate that the ratio of electron temperature, (T _e ) to ion temperature (T _p ) declining with increasing shock speed or Alfvén Mach number. We discuss the extent to which such behavior can be understood on the basis of waves generated by cosmic rays in a shock precursor, which then subsequently damp by heating electrons, and speculate that a similar explanation may work for both solar wind and SNR shocks.     

Contemporary Czech space policy and its future prospects

Czechoslovakia was the third nation to have a citizen in space when Vladimir Remek flew in 1978. It was present at the formulation of international space law principles and ran some space-related projects within Intercosmos. The Czech Republic reassumed this tradition after Czechoslovakia was dissolved in 1993. There are no special funds to support space R&D. Hence, participants must compete for R&D resources with companies from other areas of industry. This improves their competitiveness. Czech society is broadly interested in space-related activities. The graduate system structure reflects this. Not only can one study space-related courses at technical universities but international space law is an obligatory part of international public law courses in the Czech Republic. Strong support for space activities is mirrored in the institutional fragmentation of this sphere. Competences in space applications are distributed among some 20 institutions and organizations. This status harms the Czech potential in space activities and R&D. The Czech Republic became a member of ESA in 2008 but Czech companies have not taken advantage of the full potential of membership. Participation in international projects is very important for a small post-communist economy because economic growth is based on convergence towards developed countries, which may dissipate after 2020. Now is the right time to strengthen the primary research that will establish a strong foundation for innovation-based economic growth.     

PTC推出优化人机交互的Pro/Engineer Mankin

数字化人体建模技术--Pro/Engimeer Mankin 近日,PTC公司推出的Pro/Engineer Mankin是一款能够使设计团队在3D产品的设计模型中插入3D数字化人体造模解决方案,用以模拟仿真及实现人机互动.     

Prediction of horizontal gas–solid flows under different gravitational fields

In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.     

Navigation in outdoor environments as an embodied,social, cultural,and situated experience: An empirical study of orienteering

This study investigated novices' “lived experiences” of navigation within the sport of orienteering from an enactive and phenomenological approach. The objective was to qualitatively characterize elements of task-related situations that were meaningful for orienteers. The results showed that the participants continuously made judgments about the reliability of their estimations about whether they were on “the right route” on the course. When the participants judged that they were only approximately on the right route or were unable to locate themselves, elements of the situation other than map and terrain features became meaningful for them. These results demonstrate that, for novice orienteers, navigation activity must extend beyond navigation as a logical, computational way-finding problem to include embodied, social, cultural and situated dimensions.     

The ground-based large-area wide-angle γ-ray and cosmic-ray experiment HiSCORE

The question of the origin of cosmic rays and other questions of astroparticle and particle physics can be addressed with indirect air-shower observations above 10 TeV primary energy. We propose to explore the cosmic ray and γ-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV with the new ground-based large-area wide angle (ΔΩ ∼ 0.85 sterad) air-shower detector HiSCORE (Hundred^∗i Square-km Cosmic ORigin Explorer). The HiSCORE detector is based on non-imaging air-shower Cherenkov light-front sampling using an array of light-collecting stations. A full detector simulation and basic reconstruction algorithms have been used to assess the performance of HiSCORE. First prototype studies for different hardware components of the detector array have been carried out. The resulting sensitivity of HiSCORE to γ-rays will be comparable to CTA at 50 TeV and will extend the sensitive energy range for γ-rays up to the PeV regime. HiSCORE will also be sensitive to charged cosmic rays between 100 TeV and 1 EeV.     

WHISPER, A RESONANCE SOUNDER AND WAVE ANALYSER: PERFORMANCES AND PERSPECTIVES FOR THE CLUSTER MISSION

The WHISPER sounder on the Cluster spacecraft is primarily designed to provide an absolute measurement of the total plasma density within the range 0.2–80 cm^-3. This is achieved by means of a resonance sounding technique which has already proved successful in the regions to be explored. The wave analysis function of the instrument is provided by FFT calculation. Compared with the swept frequency wave analysis of previous sounders, this technique has several new capabilities. In particular, when used for natural wave measurements (which cover here the 2–80 kHz range), it offers a flexible trade-off between time and frequency resolutions. In the basic nominal operational mode, the density is measured every 28 s, the frequency and time resolution for the wave measurements are about 600 Hz and 2.2 s, respectively. Better resolutions can be obtained, especially when the spacecraft telemetry is in burst mode. Special attention has been paid to the coordination of WHISPER operations with the wave instruments, as well as with the low-energy particle counters. When operated from the multi-spacecraft Cluster, the WHISPER instrument is expected to contribute in particular to the study of plasma waves in the electron foreshock and solar wind, to investigations about small-scale structures via density and high-frequency emission signatures, and to the analysis of the non-thermal continuum in the magnetosphere.     

Studies of anomalous potential drops due to ion density inhomogeneities

The dynamic response of a 1-dimensional plasma diode to an applied step voltage is studied during a few electron transit times by numerical simulations when the initial state has an ion density minimum (an ion density cavity). Depending on the cavity depth and the applied voltage the potential drop distributes over the cavity or concentrates in a cathode sheath. The transistion between the two states as well as the cavity potential profiles are predicted by an analytical model. Simulations with periodic cavities as initial state show that the applied voltage can be shared between the cavities. A double layer, steady on the ion time scale, is created by introducing a steady cavity by ion losses.