Thin Current Sheets (TCS) are regularly formed prior to substorm breakup, even in the near-Earth plasma sheet, as close as the geostationary orbit. A self-consistent kinetic theory describing the response of the plasma sheet to an electromagnetic perturbation is given. This perturbation corresponds to an external forcing, for instance caused by the solar wind (not an internal instability). The equilibrium of the configuration of this TCS in the presence of a time varying perturbation is shown to produce a strong parallel thermal anisotropy (TT) of energetic electrons and ions (E>50keV) as well as an enhanced diamagnetic current carried by low energy ions (E<50keV). Both currents tend to enhance the confinement of this current sheet near the magnetic equator. These results are compared with data gathered by GEOS-2 at the geostationary orbit, where the magnetic signatures of TCS, and parallel anisotropics are regularly observed prior to breakup. By ensuring quasi-neutrality everywhere we find, when low frequency electromagnetic perturbations are applied, that although the magnetic field line remains an equipotential to the lowest order in Te/Ti, a field-aligned potential drop exists to the next order in (Te/Ti). Thus the development of a TCS implies the formation of a field-aligned potential drop ( few hundred volts) to ensure the quasi-neutrality everywhere. For an earthward directed pressure gradient, a field-aligned electric field, directed towards the ionosphere, is obtained, on the western edge of the perturbation (i.e. western edge of the current sheet). Thus field aligned beams of electrons are expected to flow towards the equatorial region on the western edge of the current sheet. We study the stability of these electron beams and show that they are unstable to “High Frequency” (HF) waves. These “HF” waves are regularly observed at frequencies of the order of the proton gyrofrequency (fH+) just before, or at breakup. The amplitude of these HF waves is so large that they can produce a strong pitch-angle diffusion of energetic ions and a spatial diffusion that leads to a reduction of the diamagnetic current. The signature of a fast ion diffusion is indeed regularly observed during the early breakup; it coincides with the sudden development of large amplitude transient fluctuations, ballooning modes, observed at much lower frequencies (fH+). These results suggest that the HF waves, generated by field-aligned electron beams, provide the dissipation which is necessary to destabilize low frequency (ballooning) modes. 相似文献
Imaging X-ray observations of the Fornax cluster of galaxies centered on NGC 1399 and NGC 1404 are presented. NGC 1399 and NGC 1404, which are separated by about 10 arc minutes, are found to have an unusually high ratio of x-ray to optical flux. We consider the possibility that the x-radiation is produced by hot gas in the cores of the galaxies. Weak X-ray emission is also detected from a point almost exactly mid-way between NGC 1399 and NGC 1404. The combined emission from the galaxies is insufficient by over an order of magnitude to account for the the low-energy X-ray emission detected from this region by the HEAO-l satellite. It is suggested that the bulk of the HEAO-1 source is diffuse gas associated with the cluster as a whole, rather than individual galaxies. 相似文献
The possibilities of using spectrographic observations of microwave radio emission as a solar flare plasma diagnostic are discussed. The spectral fine structure of the emission is interpreted in the context of plasma emission mechanisms. The balance equations for particles and plasma turbulence together with the transfer equations for electromagnetic waves in a plasma are solved for a model containing a diverging magnetic loop. As a result of the analysis of the blip-type spectral feature, the structure of energy release region and the unperturbed plasma concentration in the preflare loop are evaluated. The number of accelerated electrons and the intensity of the plasma turbulence in the source region are estimated using the properties of the weak continuum emission following the blip. Based on the degree of circular polarization of both the narrow band and the continuum emission, estimates for the external magnetic field strength and the angular width of the radiating plasma turbulence have been obtained. 相似文献
The aim of the analysis is to determine and to compare the specific mass of nuclear and solar power plants for application in space depending on technological data as well as on data subject to the mission.On the basis of the known theory of Ruppe and Blumenberg[1–3], nuclear power plants with turboelectric generators as well as solar-thermal power plants with parabolic or spheric mirrors are being analysed. The following thermodynamic processes are applied: the Rankine process, the Brayton process and—as an ideal comparative process—the Carnot process. An important parameter of the analysis for nuclear power plants is the net electric power, for the solar-thermal power plant the distance to the sun is of importance. 相似文献
Intensities and profiles of ion emission lines between 1170 A and 1700 A from an active region on the Sun are measured from spectra obtained with the Naval Research Laboratory's High Resolution Telescope and Spectrograph - HRTS. The measurements provide simultaneous determination of line intensities, wavelength shifts and Doppler widths at 50 separate positions in the active region, with spatial resolution of 1 arc second and spectral resolution 0.07 A. Fine structure variation of intensities and gas flow velocities in the temperature range 20,000–200,000 K are determined. The density sensitive line pair I(1486 N IV)/I(1548 C IV) has been used to measure electron pressures. Derived emission measures imply filling factors of 0.05–0.1 to balance the divergence of conductive flux width radiative losses above 60,000 K. 相似文献
The dynamics of a wind turbine driven induction machine and the power system to which it is connected in a dispersed mode are described. The sources of disturbances are identified as ramp and low frequency cyclic turbine torque variations as a consequence of sharp fronted wind gusts and tower shadow, rotor unbalance, etc. Studies have been performed for two levels of wind energy penetration in a single area power system and in a multiarea interconnected power system. Results show that substantial wind energy penetration levels can be handled in a multiarea power system. 相似文献
The EURECA platform offers unique characteristics for microgravity research: a very low level micro-gravity spectrum and a long operation time for recoverable experiments.
Five core facilities on board will perform an impressive number of experiments. The main purpose of the Solution Growth Facility (SGF) is growing crystals at low temperatures by using the double diffusion technique in three compartment reactors. The micro-gravity eliminates the convection in the liquid, while Marangoni convection is avoided by the absence of free surfaces. The thermal gradient in the buffer zone is better than 0.01°C/cm. Turbulence is eliminated by control of the valve rate and by a pressure compensation system. All surfaces are coated with Halar. The diffusion rate can be controlled by the use of filters. The SGF contains three independently controlled reactors.
A forth reactor contains an experiment aiming at measuring the Soret coefficient of twenty binary organic mixtures and aqueous electrolyte solutions. 相似文献