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71.
It is widely accepted that diffusive shock acceleration is an important process in the heliosphere, in particular in producing
the energetic particles associated with interplanetary shocks driven by coronal mass ejections. In its simplest formulation
shock acceleration is expected to accelerate ions with higher mass to charge ratios less efficiently than those with lower
mass to charge. Thus it is anticipated that the Fe/O ratio in shock-accelerated ion populations will decrease with increasing
energy above some energy. We examine the circumstances of five interplanetary shocks that have been reported to have associated
populations in which Fe/O increases with increasing energy. In each event, the situation is complex, with particle contributions
from other sources in addition to the shock. Furthermore, we show that the Fe/O ratio in shock-accelerated ions can decrease
even when the shock is traveling through an Fe-rich ambient ion population. Thus, although shock acceleration of an Fe-rich
suprathermal population has been proposed to explain large Fe-rich solar particle events, we find no support for this proposal
in these observations. 相似文献
72.
Aya Bamba Hiroya Yamaguchi Katsuji Koyama Junko S. Hiraga Steve Holt John P. Hughes Hideaki Katagiri Jun Kataoka Satoru Katsuda Shunji Kitamoto Motohide Kokubun Hironori Matsumoto Emi Miyata Koji Mori Hiroshi Nakajima Masanobu Ozaki Rob Petre Akiko Sekiguchi Tadayuki Takahashi Takaaki Tanaka Yukikatsu Terada Hiroshi Tomida Yohko Tsuboi Masahiro Tsujimoto Hiroshi Tsunemi Yasunobu Uchiyama Masaru Ueno Shin Watanabe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):411-415
SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region. 相似文献
73.
E.G. Berezhko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):429-441
We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ∼1017 eV. 相似文献
74.
R. C. Wiens D. S. Burnett C. M. Hohenberg A. Meshik V. Heber A. Grimberg R. Wieler D. B. Reisenfeld 《Space Science Reviews》2007,130(1-4):161-171
The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition,
particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the
solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal
hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing
due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives
will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different
solar-wind regimes, and 15N/14N and 18O/17O/16O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind
and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation
between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere
and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed
system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which
in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped
in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being
measured. 相似文献
75.
加强高校统一战线工作,是新时期需要认真探索与实践的一个重要课题。高校统一战线工作的基础一是思想认识的提高,二是组织制度的落实。积极发挥民主党派和无党派人士尽其所能、建言献策的作用,是高校统战工作的重点和切入点。要紧紧围绕学校的根本任务,在实践中积极探索、寻找统战工作与学校中心工作的最佳结合点;要坚持党委对统战工作的领导,牢牢把握走中国特色社会主义道路、构建和谐社会这一统一战线的政治方向。 相似文献
76.
F. Bocchino R. Bandiera Y. Gallant 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):407-410
The investigation of the general properties of non-thermal (NT) X-ray shell supernova remnants (SNRs), of which SN 1006 is the prototype, is important to understand how electrons are accelerated in SNR shocks and what is the origin of cosmic rays. Using the XMM-Newton satellite, we are carrying on a survey of putative non-thermal SNR candidates previously unknown or little studied in the X-ray band, in order to investigate the different manifestations of NT emission in SNR shells. The SNRs we have selected are likely to expand in a low density medium, and therefore to have a low thermal X-ray emission, that usually outshines the non-thermal one. We report here preliminary results obtained on the SNR shell DA 530. 相似文献
77.
Hardi Peter 《Space Science Reviews》1998,85(1-2):253-260
Ionization-diffusion mechanisms to understand the first ionization potential (FIP) fractionation as observed in the solar
corona and the solar wind are reviewed. The enrichment of the low-FIP elements (<10 eV) compared to the high-FIP elements,
seen in e.g. slow and fast wind or polar plumes, is explained. The behaviour of the heavy noble gases becomes understandable.
The absolute fractionation, i.e. in relation to hydrogen, can be calculated and fits well to the measurements. The theoretical
velocity-dependence of the fractionation will with used to determine the velocities of the solar wind in the chromosphere.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
78.
We present our measurements of the deuterium to hydrogen ratio (D/H) in QSO absorption systems, which give D/H = 3.40 ± 0.25 × 10-5 based on analysis of four independent systems. We discuss the properties of two systems which provide the strongest constraints on D/H. We outline the systematic effects involved in measurements of D/H and introduce a sophisticated method of analysis which properly accounts for these effects. 相似文献
79.
The relation between the lithium abundance observed in Population II stars and the primordial abundance, is still an open question (see Cayrel and Duncan, this meeting). A few recent results are discussed. HIPPARCOS data show that the standard model of stellar evolution can explain the 6Li detection in HD 84937, suggesting a negligible depletion of 7Li. A slope in the Li/Teff relation for Pop II dwarfs and a spread of their Li abundance have been advocated, and both used as arguments in favor of Li depletion. The slope is not confirmed when two other independent temperature scales are used. The Li scatter around the plateau is hardly larger than the scatter predicted from determination errors. Hints from a scatter of Li in subgiants of the globular cluster M92 are not completely conclusive. The determination of more accurate Li abundances in the Pop II stars is an urgent but difficult task, requiring better model atmosphere (better convection treatment) and the help of observational data about Pop II stars (such as long base interferometry). 相似文献
80.
H.J. Völk E.G. Berezhko L.T. Ksenofontov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):473-476
For the case of Tycho’s supernova remnant (SNR), we present the relation between the blast wave and contact discontinuity radii calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is very close to the shock radius. Therefore a consistent explanation of these observations can be given in terms of efficient CR acceleration which makes the medium more compressible. 相似文献