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811.
E.L. Afraimovich E.I. AstafyevaV.V. Demyanov I.F. Gamayunov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Degradation of transionospheric radio signals and operation failures during ionospheric disturbances constitute a crucial factor of space weather influence on radio engineering satellite systems performance. We found that during the main phase of strong magnetic storms in 2000–2003 when the auroral oval expands into mid-latitudes, its southern boundary develops a region with intense small-scale electron density irregularities. Such irregularities may cause strong amplitude scintillations of GPS signals at both GPS operating frequencies. The another consequence of it was significant random GPS signal phase fluctuations, breaking-down of signal tracking, and sharp increasing of GPS positioning errors as a result. 相似文献
812.
Based on the archive OMNI data for the period 1976–2000 an analysis has been made of 798 geomagnetic storms with D
st
< −50 nT and their interplanetary sources-large-scale types of the solar wind: CIR (145 magnetic storms), Sheath (96), magnetic
clouds MC (62), and Ejecta (161). The remaining 334 magnetic storms have no well-defined sources. For the analysis, we applied
the double method of superposed epoch analysis in which the instants of the magnetic storm beginning and minimum of D
st
index are taken as reference times. The well-known fact that, independent of the interplanetary source type, the magnetic
storm begins in 1–2 h after a southward turn of the IMF (B
z
< 0) and both the end of the main phase of a storm and the beginning of its recovery phase are observed in 1–2 h after disappearance
of the southward component of the IMF is confirmed. Also confirmed is the result obtained previously that the most efficient
generation of magnetic storms is observed for Sheath before MC. On the average parameters B
z
and E
y
slightly vary between the beginning and end of the main phase of storms (minimum of D
st
and D
st
* indices), while D
st
and D
st
* indices decrease monotonically proportionally to integral of B
z
and E
y
over time. Such a behavior of the indices indicates that the used double method of superposed epoch analysis can be successfully
applied in order to study dynamics of the parameters on the main phase of magnetic storms having different duration. 相似文献
813.
Gates David F. Haislmaier Robert J. Hill Lemmuel L. 《IEEE transactions on aerospace and electronic systems》1967,(2):303-308
A Doppler radar tracking system has been used successfully to measure impact drag coefficients for several water-entry configurations. Hemisphere-cylinder and cone-cylinder models were launched vertically into a tank of water at velocities between 100 and 200 feet per second. These launchings were evaluation tests for a system to be used in a new facility at the Naval Ordnance Laboratory?the Hydroballistics Tank. Planned launchings in that facility will be at velocities up to 3000 feet per second. Knowledge of the drag coefficient profile (CD versus depth of penetration) is important in the design of high-velocity water-entry weapons. 相似文献
814.
V. A. Gladyshev A. Yu. Shchekotov N. V. Yagova J. -J. Berthelier M. Parrot O. S. Akent’eva L. N. Baranskii E. N. Fedorov T. M. Mulyarchik O. A. Molchanov 《Cosmic Research》2012,50(2):103-115
Variations in concentration of ions H+, He+, and O+ are studied at a height of about 700 km using the data of continuous observations onboard the DEMETER satellite at the decline and in the minimum of solar activity from 2004 to 2008. Latitudinal distributions, seasonal behavior,
and irregular variations in ion concentrations and their dependence on solar and geomagnetic activity are considered. Within
this altitude range, for the first time an analysis is performed of the dataset of many-year continuous observations in both
hemispheres from the equatorial to subauroral latitudes. This made it possible to describe the seasonal and irregular variations
of the concentrations of main ion species with better time and spatial resolution than in the available empirical models.
The dependence of concentrations of three types of ions on solar and geomagnetic activity is studied at time scales from several
days to several years, and it is shown that the anti-phase change in concentrations of O+ and light ions known from publications is partly a result of mutual dependence of solar and geomagnetic activity and is observed
only at time scales beginning from several months. At time scales from several days to several weeks, variations in the concentration
of O+ and light ions are governed mainly by solar and geomagnetic activity, respectively. 相似文献
815.
Herein, some critical aspects related to the acquisition of the future Galileo signals are discussed. In particular, the Alternative Binary Offset Carrier (AItBOC) modulation that will be used by the Galileo satellites to broadcast navigation signals on the E5 band is considered, addressing acquisition issues only partially analyzed in previous works. The implementation of an acquisition section for the AltBOC signals is not straightforward, since several different receiver architectures can be used and remarkable differences are required with respect to the conventional signal processing used in GPS receivers. The main problems that must be handled (risk of false lock, resolution of the search space, and computational burden) are outlined in the following. An innovative technique, called multiresolution acquisition and tailored to the AltBOC signals, is then proposed as an effective solution to previous problems. As demonstrated by means of simulations, this novel strategy can be successfully used in coherent dual-band AltBOC receiver architectures with a feasible implementation complexity and it leads to remarkable advantages in terms of acquisition time. 相似文献
816.
O. B. Barysheva 《Russian Aeronautics (Iz VUZ)》2007,50(4):374-379
The behavior of generalized diffusion coefficients and diffusion flows of individual substances in the multicomponent gas mixture is investigated. The combustion products of liquid rocket propellants being used are considered. 相似文献
817.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):195-205
Solar energetic particles (SEPs) provide a sample of the Sun from which solar composition may be determined. Using high-resolution
measurements from the Solar Isotope Spectrometer (SIS) onboard NASA’s Advanced Composition Explorer (ACE) spacecraft, we have
studied the isotopic composition of SEPs at energies ≥20 MeV/nucleon in large SEP events. We present SEP isotope measurements
of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in 49 large events from late 1997 to the present. The isotopic composition
is highly variable from one SEP event to another due to variations in seed particle composition or due to mass fractionation
that occurs during the acceleration and/or transport of these particles. We show that various isotopic and elemental enhancements
are correlated with each other, discuss the empirical corrections used to account for the compositional variability, and obtain
estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with solar wind
and other solar system abundances and find generally good agreement. 相似文献
818.
In this paper, the existing techniques of electrochemical dimensional machining are considered. The use of an additional current-conducting template makes it possible to improve the accuracy of materials separation with the aid of the electric field superimposed. 相似文献
819.
A technique for calculating the geometrically and physically nonlinear stress strain state of nonshallow shells of revolution under the nonaxisymmetric wind-like loading is proposed. The calculation results for a semispherical shell with the central hole and rigidly fixed edges depending on the loading nonaxisymmetry, material characteristics and thickness are presented. We demonstrate not only quantitative but also qualitative influence of taking into account the factor of joint nonlinearity on the process of shell deformation. 相似文献
820.
A. V. Sedel’nikov 《Russian Aeronautics (Iz VUZ)》2007,50(3):322-325
Making use of the Weierstrass-Mandelbrot fractal function, some problems connected with the adequate assessment of microaccelerations aboard a spacecraft are considered. The ranges of values for the function parameters that make it possible to simulate the quasi-static component of microaccelerations are also determined. 相似文献