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861.
The minimal scale of the Alfvénic turbulence transverse to the external magnetic field in the topside auroral ionosphere is investigated using electric field observations of the FAST spacecraft (the resolution 512 s–1). The events in which the power law form of the electric fluctuation spectra with a 2.0–2.5 slope (typical of Alfvénic turbulence) remains unchanged down to acoustic gyroradius ρs or ion gyroradius ρi local values are illustrated for the first time. In this case, the character of spectrum variation does not change at the electron inertial length λe, which is much larger than ρs and ρi for FAST altitudes (apogee ~4000 km). We have tried to explain this experimental fact by consideration of the known scenarios of the appearance of a small transverse scale in an Alfvénic perturbation. It has been noted that the effects of front steepening in an inertial Alfvén wave with a finite amplitude, which propagates at an angle smaller than (me/mi)1/2 with respect to the transverse direction, can result in small transverse scales comparable with acoustic gyroradius appearing in a perturbation. 相似文献
862.
V. Iafolla D.M. Lucchesi S. Nozzoli M. Ravenna F. Santoli I.I. Shapiro E.C. Lorenzini M.L. Cosmo C. Bombardelli J. Ashenberg P.N. Cheimets S. Glashow 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We presents the results of an activity concerning the test of the Einstein Weak Equivalence Principle with an accuracy of about 5 × 10−15. The experiment will be performed in an “Einstein elevator” using a differential accelerometer with a final sensitivity of about 10−14 g⊕/Hz1/2. The differential accelerometer is spun about an horizontal axis at a frequency in the range 0.5–1 Hz in order to modulate, during the free fall, the signal from a possible violation of the Equivalence Principle. In the paper the perturbing effects with the same signature of the possible violation are analyzed and constrained. The experimental results obtained in the laboratory with a first prototype of the differential accelerometer are discussed, comparing this results with those obtained using a new prototype. 相似文献
863.
864.
Results of almost two years (January 1999–October 2000) of continuous observations of auroral kilometric radio emission with the instrument AKR-X onboard the high-apogee satellite of the Earth Interball-1 are presented. The observations were conducted at the growth stage (in 1999) and in the maximum (2000) of solar activity within the 100–1500 kHz frequency band. The results of AKR detection in the vicinity of the maximum of its spectrum at a frequency of 252 kHz are presented. Both similarity (for example, the character of global directivity) and important differences from the AKR emission observed during the solar activity minimum [5] are found. Together with very high sporadicity, strong seasonal changes in the intensity are typical for the emission. It is completely absent in the spring-summer period in the Northern Hemisphere and is strongly suppressed in this period in the Southern Hemisphere. Probable nature of these features of AKR is discussed. 相似文献
865.
D.B. Korovinskiy V.V. Ivanova N.V. Erkaev V.S. Semenov I.B. Ivanov H.K. Biernat M. Zellinger 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A linear MHD instability of the electric current sheet, characterized by a small normal magnetic field component, varying along the sheet, is investigated. The tangential magnetic field component is modeled by a hyperbolic function, describing Harris-like variations of the field across the sheet. For this problem, which is formulated in a 3D domain, the conventional compressible ideal MHD equations are applied. By assuming Fourier harmonics along the electric current, the linearized 3D equations are reduced to 2D ones. A finite difference numerical scheme is applied to examine the time evolution of small initial perturbations of the plasma parameters. This work is an extended numerical study of the so called “double gradient instability”, – a possible candidate for the explanation of flapping oscillations in the magnetotail current sheet, which has been analyzed previously in the framework of a simplified analytical approach for an incompressible plasma. The dispersion curve is obtained for the kink-like mode of the instability. It is shown that this curve demonstrates a quantitative agreement with the previous analytical result. The development of the instability is investigated also for various enhanced values of the normal magnetic field component. It is found that the characteristic values of the growth rate of the instability shows a linear dependence on the square root of the parameter, which scales uniformly the normal component of the magnetic field in the current sheet. 相似文献
866.
As a part of the program of searching for exoplanets, the hypothetical influence of changeable velocity of light (due to parameters of motion of a radiation source) on the results of spectrometric measurements of stars is considered. Accelerations of stars relative to the barycenter of a system star-planet (planets) are taken into account. It is shown that the dependence of velocity of light on the barycentric radial velocity and on the component of barycentric radial acceleration of stars should result in significant increase (up to an order of magnitude) of semimajor axes of the found candidates for exoplanets. Consequently, a correct comparison of the spectral method with other known modern methods of finding exoplanets would allow one to use the results obtained in this paper as a reliable test for inspection of invariance of the velocity of light. 相似文献
867.
In this paper, we perform numerical simulation and experimental determination of the limiting resistance of the spacecraft design elements used when developing anti-meteorite protection of spacecraft as well as protection against space debris. One possible way to increase the efficiency of protective shields and satisfy the requirements of the mass characteristics of the latter is the use of mesh barriers. 相似文献
868.
We analyze the elastoplastic stress-strain state of an axisymmetrical parabolic type shell of revolution at the pole of which the concentrated force is applied. The shell is considered as a momentless one, and the properties of its material are schematized by the tensile diagram with linear hardening. The problem is solved in stresses, the corresponding equations are constructed, and the solution is given. 相似文献
869.
It is suggested that simultaneous monitoring of two flight actuator parameters, with proper analysis, could provide meaningful diagnostic information at very early stages of the developing failure 相似文献
870.
Coronal Mass Ejections (CMEs) are plasma eruptions from the solar atmosphere involving previously closed field regions which
are expelled into the interplanetary medium. Such regions, and the shocks which they may generate, have pronounced effects
on cosmic ray densities both locally and at some distance away. These energetic particle effects can often be used to identify
CMEs in the interplanetary medium, where they are usually called `ejecta'. When both the ejecta and shock effects are present
the resulting cosmic ray event is called a `classical, two-step' Forbush decrease. This paper will summarize the characteristics
of CMEs, their effects on particles and the present understanding of the mechanisms involved which cause the particle effects.
The role of CMEs in long term modulation will also be discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献