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1.
J. J. Quenby T. J Sumner S. D. Sidher S. Immler 《Astrophysics and Space Science》1994,216(1-2):213-217
The shadowing effects of the molecular clouds in the nearby interstellar medium on the soft x-ray background has been investigated, using ROSAT WFC data in conjunction with previous rocket B and C band surveys. Shadowing over a 5° extent occurs only for a few percent of the sky, but the mixed model of the ISM is supported.Detailed modelling of the Draco shadowing region shows little evidence for a multi-temperature, hot ISM component. 相似文献
2.
Energetic particle (0.1 to 100 MeV protons) acceleration is studied by using high resolution interplanetary magnetic field and plasma measurements at 1 AU (HEOS-2) and at 5 AU (Pioneer 10). Energy changes of a particle population are followed by computing test particle trajectories and the energy changes through the particle interaction with the time varying magnetic field. The results show that considerable particle acceleration takes place throughout the interplanetary medium, both in the corotating interaction regions (CIR) (5 AU), and in quiet regions (1 AU). Although shocks may contribute to acceleration we suggest statistical acceleration within the CIRs is sufficient to explain most energetic particle observations (e.g., McDonaldet al., 1975; Barnes and Simpson, 1976).The first and second order statistical acceleration coefficients which include transit time damping and Alfvén resonance interactions, are found to be well represented byD
T
8.5×10–6
T
0.5 MeV s–1 andD
TT
4×10–6
T
1.5 MeV2 s–1 at 5 AU.By comparison, Fisk's estimates (1976), based on quasi-linear theory for transit-time damping, gaveD
TT
5×10–7
T MeV2 s–1 at 1 AU. 相似文献
3.
Eleven large directional discontinuities in the solar wind, simultaneously observed by Explorers 33, 35 and Heos 1 in the period Dec. 1968 to Jan. 1969, have been studied by the triangulation method. Testing the discontinuity normals deduced from the wind speed and timing parameters against those given by the magnetometer observations on different models suggests that 8 were tangential, 2 were rotational while 1 could not be identified. 3 small tangential discontinuities arriving within a period 35 min were also studied and as a result it is suggested that the solar wind remained stratified in separation planes over a distance 0.01 AU during that time. The implication of these results is briefly discussed. 相似文献
4.
T. L. Lim J. J. Quenby M. K. Reuss E. Keppler H. Kunow B. Heber R. J. Forsyth 《Annales Geophysicae》1996,14(4):400-410
During November 1992, a series of forward and reverse shocks passed the ULYSSES spacecraft. Spectral and anisotropy measurements are reported for protons and alpha particles between 0.28 and 6 MeV observed by the Energetic Particle Composition Experiment, data recorded by the Magnetometer Experiment and the high-energy (2.7-300 MeV) proton data from the Kiel Electron Telescope. An analysis of energetic particle, plasma and magnetometer data from ULYSSES has allowed a unique study of the corresponding arrival of fare particles, particles within a corotating interaction region and particles transported with a coronal mass ejection. We present an analysis of these data in terms of possible diffusive shock acceleration but conclude that this is likely to be incompatible with the short transit time of the particles. Shock drift acceleration of particles with energies 0.3 MeV/nucleon or solar acceleration followed by particle trapping behind the shock front are alternative possibilities. 相似文献
5.
The propagation time for solar protons observed during the events of January 24, February 25 and March 17, 1969 are compared with those estimated from numerical solutions of the Fokker-Planck transport equation, using values of the diffusion coefficient of the form K
r
= K
0
r
b
where r is radial distance from the Sun, K
0 is obtained from the plasma-field parameters near the Earth and b varies from - 3 to + 1. K
0 is derived either by assuming that all the magnetic fluctuation power is in small amplitude transverse waves or alternatively in discontinuous changes in ¦B¦ along the flux tube of propagation. In the first case it is found that the K
0 values calculated require either b -3, implying a very rapid wave growth with r, or the Fokker-Planck equation reduces to the situation of purely convective transport which is at variance with the experimental observations. More reasonable results are found in the second case although even here K
0 is probably underestimated. Alternative ways of deducing K
0 empirically from particle anisotropy measurements are put forward and these seem to favour the discontinuity model. 相似文献
6.
Solar Physics - Quiet-time anisotropy data have been obtained by the HEOS-1 spacecraft between December 1968 and April 1970 using an 8-sector analysis of a ?erenkov telescope which has a... 相似文献
7.
Numerical solutions of the Fokker-Planck equation governing the transport of solar protons are obtained using the Crank-Nicholson technique with the diffusion coefficient represented by Kr=K0rb where r is radial distance from the Sun and b can take on positive or negative values. As b ranges from +1 to ?3, the time to the observation of peak flux decreases by a factor of 5 for 1 MeV protons when where V is the solar wind speed. The time to peak flux is found to be very insensitive to assumptions concerning the solar and outer scattering boundary conditions and the presence of exponential time decay in the flux does not depend on the existence of an outer boundary. At , 1 MeV particles come from the Sun by an almost entirely convective process and suffer large adiabatic deceleration at b?0 but for b=+1, large Fermi acceleration is possible at all reasonable values. Implications of this result for the calculation and measurement of particle diffusion coefficients is discussed. At , the pure diffusion approximation to transport overestimates by a factor 2 or more the time to peak flux but as b becomes more negative, the additional effects of convection and energy loss become less important. 相似文献
8.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献
9.
A new method for solving the transport equation and boundary condition describing diffusive shock acceleration for interplanetary corotating interaction regions is provided. It involves inverting a quindiagonal matrix. Application of this method to realistic parameters indicates that the parallel diffusion coefficient magnitude is critical in determining whether observed particle distribution functions are exponential or power law. 相似文献
10.
Crank-Nicholson solutions are obtained to the time-dependent Fokker-Planck equation for propagation in the interplanetary medium following a point in time injection of energetic solar particles and including the acceleration terms $$\frac{\partial }{{\partial T}}\left( {D_{TT} \frac{{\partial U}}{{\partial T}}} \right) - \frac{\partial }{{\partial T}}\left( {\frac{{D_{TT} U}}{{2T}}} \right)$$ . The diffusion coefficient in kinetic energyD TT is allowed to be either independent of radial distance,R(AU), or follow the lawD TT=D0T2R 0 2 /(A2+R2) in either case with the 1 AU value ofD TT at 10 MeV ranging between 10?4 (MeV)2 s?1 and zero. The spatial diffusion mean free path at the Earth's orbit is fixed at λ‖ AU at 10 MeV according to numerical estimates made by Moussas and Quenby. However, a variety ofR dependences are allowed. Reasonable agreement with experimental data out to 4 AU is obtained with the above values ofD TT and the spatial diffusion coefficientK r=K0R?2 forR«1 andK r=K0R0.4 forR»1 AU. It is only in the decay phases of prompt events as seen at 2–4 AU that significant differences in the temporal behaviour of the events can be distinguished, depending on the value ofD TT chosen within the above range. Experimental determination of the decay constant is difficult. 相似文献