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21.
Jie Jiang Robert H. Cameron Dieter Schmitt Manfred Schüssler 《Space Science Reviews》2013,176(1-4):289-298
To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations. 相似文献
22.
Ontological Modularity and Spatial Diversity 总被引:1,自引:1,他引:0
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Measuring temperatures, mechanical loads and derived quantities precisely and reliably play an important role in spaceflight. With spacecraft becoming increasingly complex, upscaling of present telemetry techniques can become cumbersome. Additionally, there are entirely new sensory requirements, resulting from emerging technologies such as smart structures, active vibration damping and composite material health monitoring. It has been demonstrated in preceding studies that these measurements can be advantageously and efficiently carried out by means of fiber-optic systems. The most prominent fiber-optic strain and temperature sensor is the fiber Bragg grating. Typically, multiple fiber Bragg gratings are used to translate entire temperature and strain fields into an optical wavelength information. For the interrogation of these sensors, a broadband or scanning light source is required. Additional requirements with respect to the light source are high intensity and unpolarized illumination of the gratings. These constraints can be met by a light source that is based on amplified spontaneous emission in a rare-earth-doped fiber. In the presented work, a compact light source, adapted for measurement applications and targeted towards space applications, has been developed. The design of this light source is presented, as well as its implementation. The light source has been designed and tested for selected core aspects of space robustness and the results of these tests are summarized. 相似文献
25.
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
26.
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
27.
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
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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