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排序方式: 共有86条查询结果,搜索用时 15 毫秒
41.
PhysicalbackgroundonestimatingbvalueWEIQIONGHUANG(黄玮琼)WENXIANGLI(李文香)InstituteofGeophysics,StateSeismologicalBureau,Beijin... 相似文献
42.
Two Earth-directed coronal mass ejections (CMEs), which were most effective in energetic (1–50 MeV) particle acceleration during the first 18 months since the Solar and Heliospheric Observatory (SOHO) launch, occurred on April 7 and May 12, 1997. In the analysis of these events we have deconvoluted the injection spectrum of energetic protons by using the method described by Anttila et al. In order to apply the method developed earlier for data of a rotating satellite (Geostationary Operational Environmental Satellites, GOES), we first had to develop a method to calculate the omnidirectional energetic particle intensities from the observations of Energetic and Relativistic Nuclei and Electrons (ERNE), which is an energetic particle detector onboard the three-axis stabilized SOHO spacecraft. The omnidirectional intensities are calculated by fitting an exponential pitch angle distribution from directional information of energetic protons observed by ERNE. The results of the analysis show that, compared to a much faster and more intensive CMEs observed during the previous solar maximum, the acceleration efficiency decreases fast when the shock propagates outward from the Sun. The particles injected at distances <0.5 AU from the Sun dominate the particle flux during the whole period, when the shock propagates to the site of the spacecraft. The main portion of particles injected by the shock during its propagation further outward from the Sun are trapped around the shock, and are seen as an intensity increase at the time of the shock passage. 相似文献
43.
Paul J. Kellogg 《Planetary and Space Science》2003,51(11):681-691
Progress in understanding the Langmuir waves which accompany collisionless shocks everywhere in the solar system is briefly reviewed, with some emphasis on the discovery papers, and with discussion and illustrative examples of the most recent progress. 相似文献
44.
L. S. Farenzena P. Iza R. Martinez F. A. Fernandez-Lima E. Seperuelo Duarte G. S. Faraudo C. R. Ponciano M. G. P. Homem A. Naves de Brito K. Wien E. F. da Silveira 《Earth, Moon, and Planets》2005,97(3-4):311-329
Experimental results on fast ion collision with icy surfaces having astrophysical interest are presented. 252Cf fission fragments projectiles were used to induce ejection of ionized material from H2O, CO2, CO, NH3, N2, O2 and Ar ices; the secondary ions were identified by time-of-flight mass spectrometry. It is observed that all the bombarded frozen gas targets emit cluster ions which have the structure XnR±, where X is the neutral ice molecule and R± is either an atomic or a molecular ion. The shape of the positive or negative ion mass spectra is characterized by a decreasing yield as the emitted ion mass increases and is generally described by the sum of two exponential functions. The positive ion water ice spectrum is dominated by the series (H2O)nH3O+ and the negative ion spectrum by the series (H2O)nOH− and (H2O)nO−. The positive ion CO2 ice spectrum is characterized by R+ = C+, O+, CO+, O2+ or CO2+ and the negative one by R− = CO3−. The dominant series for ammonia ice correspond to R+ = NH4+ and to R− = NH2−. The oxygen series are better described by (O3)nOm+ secondary ions where m = 1, 2 or 3. Two positive ion series exist for N2 ice: (N2)nN2+ and (N2)nN+. For argon positive secondary ions, only the (Ar)nAr+ series was observed. Most of the detected molecular ions were formed by one-step reactions. Ice temperature was varied from ∼20 K to complete sublimation. 相似文献
45.
Relativistic shocks provide an efficient method for high-energy particle acceleration in many astrophysical sources. Multiple
shock systems are even more effective and of importance, for example, in the internal shock model of gamma-ray bursts. We
investigate the reacceleration of pre-existing energetic particles at such relativistic internal shocks by the first order
Fermi process of pitch angle scattering. We use a well established eigenfunction method to calculate the resulting spectra
for infinitely thin shocks. Implications for GRBs and relativistic jets are discussed.
Paul Dempsey would like to thank IRCSET for their financial support. 相似文献
46.
Skorov Yuri V. Keller Horst U. Jorda Laurent Davidsson Bjørn J. R. 《Earth, Moon, and Planets》2002,90(1-4):293-303
In this work, we continue revising the theoretical basis ofnumerical models describing the transport of matter andenergy inside
a porous dust-ice mixture at low temperature. Amodel of a light-absorbing near-surface layer of a comet nucleus isinvestigated.
Gas transport is considered simultaneously with thesolution of the general heat transfer equation. Thequasi-stationary temperature
distribution and the H2O massflux and sublimation rate are computed for a nucleus model ofcomet 19P/Borrelly at the Deep Space 1 (DS1) encounter.
Theenergy is deposited in a layer of about 20 particle radii: Thiscorresponds to a solid-state greenhouse effect. The surfacetemperature
of the layer-absorbing model as well as the gasproduction rate are significantly smaller than the ones in thesurface-absorbing
model. An active fraction of 40–50% would berequired to explain the observed water production rate ofP/Borrelly with our layer-absorption
model at the time of the DS1encounter. 相似文献
47.
B.T. Tsurutani X.-Y. Zhou V.M. Vasyliunas G. Haerendel J.K. Arballo G.S. Lakhina 《Surveys in Geophysics》2001,22(2):101-130
Dayside near-polar auroral brightenings occur when interplanetary shocks impinge upon the Earth's magnetosphere. The aurora first brightens near local noon and then propagates toward dawn and dusk along the auroral oval. The propagation speed of this wave of auroral light is 10 km s-1 in the ionosphere. This speed is comparable to the solar wind speed along the outer magnetosphere. The fundamental shock-magnetospheric interaction occurs at the magnetopause and its boundary layer. Several physical mechanisms transferring energy from the solar wind directly to the magnetosphere and from the magnetosphere to the ionosphere are reviewed. The same physical processes can occur at other solar system magnetospheres. We use the Haerendel (1994) formulation to estimate the acceleration of energetic electrons to 50 keV in the Jovian magnetosphere/ionosphere. Auroral brightenings by shocks could be used as technique to discover planets in other stellar systems. 相似文献
48.
49.
Sandip Kumar Chakrabarti 《Astrophysics and Space Science》2005,297(1-4):131-142
Black holes are the most compact objects in the universe. Therefore, matter accreting onto them is likely to radiate photons
of energy comparable to very high gravitational potential energy. We discuss the nature of the emitted radiation in X-rays
and gamma-rays from black hole candidates. We present theoretical solutions, which comprise both Keplerian and sub-Keplerian
components and suggest that shocks in accretion and outflows may play a major role in producing these spectra. 相似文献
50.
D. E. Innes 《Astrophysics and Space Science》1994,216(1-2):311-316
This paper presents models of optical emission line features that characterise catastrophic cooling in radiative shocks. The computations are based on a 1-D magnetohydrodynamic model. Runaway cooling results in the formation of secondary shocks which travel through the previously shocked cooling layer. Several filaments of emission with specific properties and spectral signatures are produced. 相似文献