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21.
The calculation of particle trajectories in the Earth's magnetic field has been a subject of interest since the time of Störmer. The fundamental problem is that the trajectory-tracing process involves using mathematical equations that have `no solution in closed form'. This difficulty has forced researchers to use the `brute force' technique of numerical integration of many individual trajectories to ascertain the behavior of trajectory families or groups. As the power of computers has improved over the decades, the numerical integration procedure has grown more tractable and while the problem is still formidable, thousands of trajectories can be computed without the expenditure of excessive resources. As particle trajectories are computed and the characteristics analyzed we can determine the cutoff rigidity of a specific location and viewing direction and direction and deduce the direction in space of various cosmic ray anisotropies. Unfortunately, cutoff rigidities are not simple parameters due to the chaotic behavior of the cosmic-ray trajectories in the cosmic ray penumbral region. As the computational problem becomes more manageable, there is still the issue of the accuracy of the magnetic field models. Over the decades, magnetic field models of increasing complexity have been developed and utilized. The accuracy of trajectory calculations employing contemporary magnetic field models is sufficient that cosmic ray experiments can be designed on the basis of trajectory calculations. However, the Earth's magnetosphere is dynamic and the most widely used magnetospheric models currently available are static. This means that the greatest uncertainly in the application of charged particle trajectories occurs at low energies. 相似文献
22.
H. Krüger H. Moraal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
This paper is a follow-on of that of Krüger et al. [Krüger, H., Moraal, H., Bieber, J.W., Clem, J.M., Evenson, P.A., Pyle, K.R., Duldig, M.L., Humble, J.E. A calibration neutron monitor: energy response and instrumental temperature sensitivity. J. Geophys. Res. 113, A08101, doi:10.1029/2008JA013229, 2008], that describes the characteristics of a pair of calibration neutron monitors that were developed to intercalibrate the count rates of the world’s neutron monitors against each other. Such an intercalibration will allow the calculation of energy (rigidity) spectra, which will enhance the quality of the neutron monitor data. Krüger et al. (2008) investigated the energy and temperature response of the calibrators. This paper studies the statistical accuracy of the calibration procedure, its repeatability, and the sensitivity to its environment. The paper concludes with a calibration procedure that can minimise the uncertainties caused by these five effects, or at least correct for them. 相似文献
23.
It is well established that the prolonged and thorough mixing of numerous nucleosynthetic components that constitutes the
matter in the solar nebula resulted in an essential isotopic homogeneity of the solar system material. This may or may not
be true for the short-lived radionuclides which were injected into or formed within the solar nebula just prior to or during
solar system formation. Distinguishing between their heterogeneous or homogeneous distribution is important because the short-
lived radionuclides are now widely used for the relative chronology of various objects and processes in the early solar system
and as constraints for models of nucleosynthesis. The recent studies of the 53Mn-53Cr isotope system (half life of 53Mn is 3.7 Ma) in various solar system objects have shown that the relative abundance of radiogenic 53Cr is consistent with essentially homogeneous distribution of 53Mn in the asteroid belt. Thus, the relative 53Mn-53Cr chronometer can be directly used for dating samples which originated in the asteroid belt. Importantly, however, all meteorite
groups studied so far indicate a clear excess of 53Cr as compared to Earth and to a lunar sample, which exhibits also a terrestrial 53Cr/52Cr ratio. The results from the Martian (SNC) meteorites show that their 53Cr excesses are less than half of those found in the asteroid belt bodies. Thus, the characteristic 53Cr/52Cr ratio of Mars is intermediate between that of the Earth-Moon system and those of the other meteorites. If these 53Cr variations are viewed as a function of the heliocentric distance, the radial dependence of the relative abundances of radiogenic
53Cr is indicated. This observed gradient can be explained by either an early, volatility controlled, Mn/Cr fractionation within
the nebula or by an initial radial heterogeneous distribution of 53Mn. Although model calculations of the Mn/Cr ratios in the bulk terrestrial planets seem to be inconsistent with the volatility
driven scenario, the precision of these calculations is inadequate for eliminating this possibility. In contrast, recent studies
of the 53Mn-53Cr system in the enstatite chondrites indicate that, while their bulk Mn/Cr ratios are essentially the same as in ordinary
chondrites, the 53Cr excess in bulk enstatite chondrites is three times lower than that in the bulk ordinary chondrites. This difference cannot
be explained by a Mn/Cr fractionation and, thus, strongly suggests that a radial heterogeneous distribution of 53Mn must have existed in at least the early inner solar system. Using the observed gradient and the 53Cr/52Cr ratio of the bulk enstatite chondrites, their parent body(ies) formed at ∼1.4 AU or somewhat closer to the Sun.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
24.
A. Raviart R. Ducros P. Ferrando C. Rastoin B. Heber H. Kunow R. Müller-Mellin H. Sierks G. Wibberenz C. Paizis 《Space Science Reviews》1995,72(1-2):409-414
We describe for the first time the analysis of high energy electrons (above 240 MeV) from the COSPIN/KET experiment onboard Ulysses. The electron time profiles in four energy windows are presented from Oct. 90 to the end of March 94, up to a maximum heliographic latitude of 57 °S. The recovery rates we derived for the electrons are compared to the recovery rates of positively charged particles with the same rigidity. 相似文献
25.
As Viking Landers did not measure rock compositions, Pathfinder (PF) data are the first in this respect. This review gives no proof yet whether the PF rocks are igneous or sedimentary, but for petrogenetic reasons they could be igneous. We suggest a model in which Mars is covered by about 50% basaltic and 50% andesitic igneous rocks. The soils are a mixture of the two with addition of Mg-sulfate and -chloride plus iron compounds possibly derived from the hematite deposits. 相似文献
26.
C. Paizis A. Raviart B. Heber B. Falconi Ph. Ferrando H. Kunow R. Müller-mellin 《Space Science Reviews》2001,97(1-4):349-354
Previous work on the latitudinal gradient and on the amplitude of the recurrent cosmic ray decreases, has shown that their
magnitude does not decrease monotonically with the particle rigidity, but it presents a broad maximun around 1–2 GV. We have
extended this analysis to study the behaviour of cosmic-ray particles during the modulation steps in the rising part of the
solar activity of the present Solar cycle. We found that the ‘depth’ of the modulation step decreases monotonically with increasing
rigidity and that the least energetic particles are the last to reach their minimum intensity value. We also considered in
this analysis electrons of equal rigidity to study the influence of the charge sign on the particle behaviour during the modulation
steps.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
27.
Her X-1 has been observed with EXOSAT for one 35d cycle between March 1 and April 5, 1984 at about 4 day intervals. During three observations, absorption dips were encountered showing fluctuations with time scales in the several hundred seconds range. The data are interpreted with a model where random superposition of absorbing blobs or inhomogeneous structures within the accretion disk, in the line of sight, cause these intensity variations. The calculations give a measure of the extent of the disk both in vertical and radial directions. 相似文献
28.
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30.
Jürgen Blumenberg 《Acta Astronautica》1981,8(8):839-854
In this paper it is shown how a nuclear power system with turboelectric conversion is being optimised for application in space and how data subject to the mission and technological data enter into such an analysis. Thereafter it follows a comparison with nuclear power systems with magnetofluiddynamic and thermionic converters. 相似文献