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261.
Yu.K. Chasovitin V.B. Shushkova T.N. Sykilinda P.F. Denisenko V.V. Sotsky N.E. Shejdakov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(7):21-24
Our empirical model of electron density (ne) for quiet and weakly disturbed geomagnetic conditions (Kp not greater 4) takes account of comparative analysis of existing models and of experimental data obtained by rockets and incoherent scatter radar. The model describes the ne distribution in the 80 to 200 km height range at low and middle latitudes, and to some extent, in the subauroral region. It is presented in analytical form thus allowing one to calculate electron density profiles for any time. The electron density distribution at 140 km depends on the season (day of the year) and on the solar zenith angle. Profile variations during the day are for one season shown. Different from other models, ours specifies the variations during sunrise and sunset and reflects the particular profile shape at night admitting the occurrence of an intermediate layer. 相似文献
262.
J. Heise J.A.M. Bleeker A.C. Brinkman E. Gronenschild F. Paerels M. Grewing C. Wulf-Mathies K. Beuerman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(3):61-64
EXOSAT has observed 19 hot white dwarfs with alleged strong soft X-ray emission. Positive detection of a large fraction of this sample was obtained, among these practically all hot DA dwarfs. High-resolution spectral data, acquired with the 500 1/mm grating spectrometer, indicates no traces of He in the atmosphere of HZ43, i.e. n(He)/n(H) ? 10?5 at a photospheric temperature of 60000 K (log g = 8). In contrast, the hot DA1 dwarf Feige 24 shows the presence of an appreciable He-abundance (n(He)/n(H) ? 10?3); however no simple homogeneously mixed H/He atmosphere can explain the observed spectral shape. 相似文献
263.
As we resolve ever smaller structures in the solar atmosphere, it has become clear that magnetism is an important component of those small structures. Small-scale magnetism holds the key to many poorly understood facets of solar magnetism on all scales, such as the existence of a local dynamo, chromospheric heating, and flux emergence, to name a few. Here, we review our knowledge of small-scale photospheric fields, with particular emphasis on quiet-sun field, and discuss the implications of several results obtained recently using new instruments, as well as future prospects in this field of research. 相似文献
264.
L.L. Lazutin A.A. Khrushchinsky T.V. Kozelova A.O. Melnikov Ya. Sakharov G. Kremser W.K. Riedler K.M. Torkar K. Glassmeier J.-P. Treilhou A. Pedersen G. Gustafsson R. Pellinen J. Kangas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):171-174
For investigations of the isolated magnetospheric substorm the ground-based and satellite geophysical data are discussed. The active phase of the substorm has two parts: an active-convective phase and a classical active phase. The analysed data show that the breakup of the substorm takes place at closed and not very much stretched magnetic field lines. 相似文献
265.
K Eguchi-Kasai M Murakami H Itsukaichi K Fukutsu F Yatagai T Kanai H Ohara K Sato 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(4):543-549
It has been suggested that it is not simple double-strand breaks (dsb) but the non-reparable breaks which correlate well with the high biological effectiveness of high LET radiations for cell killing (Kelland et al., 1988; Radford, 1986). We have compared the effects of charged particles on cell death in 3 pairs of cell lines which are normal or defective in the repair of DNA dsbs. For the cell lines SL3-147, M10, and SX10 which are deficient in DNA dsb repair, RBE values were close to unity for cell killing induced by charged particles with linear energy transfer (LET) up to 200 keV/micrometer and were even smaller than unity for the LET region greater than 300 keV/micrometer. The inactivation cross section (ICS) increased with LET for all 3 pairs. The ICS of dsb repair deficient mutants was always larger than that of their parents for all the LET ranges, but with increasing LET the difference in ICS between the mutant and its parent became smaller. Since a small difference in ICS remained at LET of about 300 keV/micrometer, dsb repair may still take place at this high LET, even if its role is apparently small. These results suggest that the DNA repair system does not play a major role in protection against the attack of high LET radiations and that a main muse of cell death is non-reparable dsb which are produced at a higher yield compared with low LET radiations. No correlation was observed between DNA content or nuclear area and ICS. 相似文献
266.
A method of modeling the total electron content (TEC) based on the semi-empirical ionospheric model developed in Irkutsk State
University is suggested. Comparison with the Klobuchar model has shown that the proposed method provides a more accurate presentation
of TEC. A conclusion is drawn that the use of this method for compensation of the ionospheric error in single-frequency navigation
receivers would lead to a substantial increase in the accuracy of their positioning. 相似文献
267.
J Tweed J W Wilson R K Tripathi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1311-1318
Ion beam transport theory allows testing of material transmission properties in the laboratory environment generated by particle accelerators. This is a necessary step in materials development and evaluation for space use. The approximations used in solving the Boltzmann transport equation for the space setting are often not sufficient for laboratory work and those issues are the main emphasis of the present work. In consequence, an analytic solution of the linear Boltzmann equation is pursued in the form of a Green's function allowing flexibility in application to a broad range of boundary value problems. It has been established that simple solutions can be found for high charge and energy (HZE) ions by ignoring nuclear energy downshifts and dispersion. Such solutions were found to be supported by experimental evidence with HZE ion beams when multiple scattering was added. Lacking from the prior solutions were range and energy straggling and energy downshift with dispersion associated with nuclear events. Recently, we have found global solutions including these effects providing a broader class of HZE ion solutions. 相似文献
268.
269.
A.I. Efimov V.K. Rudash L.N. Samoznaev M.K. Bird I.V. Chashei D. Plettemeier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Frequency fluctuations of the Galileo S-band radio signal were recorded nearly continuously during the spacecraft’s solar conjunction from December 1996 to February 1997. A strong propagating disturbance, most probably associated with a coronal mass ejection (CME), was detected on 7 February when the radio ray path proximate point was on the west solar limb at about 54 solar radii from the Sun. The CME passage through the line of sight is characterized by a significant increase in the fluctuation intensity of the recorded frequency and by an increase in the plasma speed from about 234 km s−1 up to about 755 km s−1. These velocity estimates are obtained from a correlation analysis of frequency fluctuations recorded simultaneously at two widely-separated ground stations. The density turbulence power spectrum is found to steepen behind the CME front. The Galileo radio-sounding data are compared with SOHO/LASCO observations of the CME in the corona and with WIND spacecraft data near the Earth’s orbit. 相似文献
270.
This work extends the so-called simple adaptive control approach to direct model reference adaptive control of multi-input multi-output systems to include loss of control effectiveness failures. It is proven that all signals are bounded for loss of control effectiveness failures during a bounded input disturbance. A state space approach is introduced for computing the feedforward compensator that is required by the stability result. The adaptive algorithm is applied to a three input model of the linearized lateral dynamics of the F/A-18 aircraft. Simulation results are obtained with single, double, and triple control effectiveness failures of 88% during the occurrence of a lateral gust. These results show that the adaptive controller exhibits improved model following as compared with a fixed gain eigenstructure assignment controller. 相似文献