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91.
Recent advances in the understanding of the properties of supernova remnant shocks have been precipitated by theChandra and XMM X-ray Observatories, and the HESS Atmospheric Čerenkov Telescope in the TeV band. A critical problem for this field
is the understanding of the relative degree of dissipative heating/energization of electrons and ions in the shock layer.
This impacts the interpretation of X-ray observations, and moreover influences the efficiency of injection into the acceleration
process, which in turn feeds back into the thermal shock layer energetics and dynamics. This paper outlines the first stages
of our exploration of the role of charge separation potentials in non-relativistic electron-ion shocks where the inertial
gyro-scales are widely disparate, using results from a Monte Carlo simulation. Charge density spatial profiles were obtained
in the linear regime, sampling the inertial scales for both ions and electrons, for different magnetic field obliquities.
These were readily integrated to acquire electric field profiles in the absence of self-consistent, spatial readjustments
between the electrons and the ions. It was found that while diffusion plays little role in modulating the linear field structure
in highly oblique and perpendicular shocks, in quasi-parallel shocks, where charge separations induced by gyrations are small,
and shock-layer electric fields are predominantly generated on diffusive scales. 相似文献
92.
Gui-Ping Wu Guang-Li Huang Yu-Hua Tang Yu Dai Department of Physics Southeast University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2007,7(1):141-147
1INTRODUCTIONEnrichment of3He and heavy ions(i.e.,Ne,Mg,Si and Fe),characteristic of impulsive?ares,have beenstudied for more than three decades.It is found that they are generally associated with nonthermal energeticelectron-rich events(Reames et al.1988;Reames1999and references therein;Ho et al.2001;Wang et al.2006)and are related to the peculiar ratio of charge to mass(Mazur et al.1996;Reames1999).Althoughthe abundance of3He ions is not correlated with the abundance of heavy ions,s… 相似文献
93.
Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data. 相似文献
94.
95.
C. Gontikakis A. Anastasiadis C. Efthymiopoulos 《Monthly notices of the Royal Astronomical Society》2007,378(3):1019-1030
The acceleration of charged particles in a site of magnetic reconnection is analysed by detailed numerical simulations. Single or multiple encounters of the particles with Harris-type reconnecting current sheets (RCSs) are modelled as an overall stochastic process taking place within an active region. RCS physical parameters are selected in a parameter space relevant to solar flares. Initially, the charged particles form a thermal (Maxwellian) distribution corresponding to coronal temperature ≃2 × 106 K . Our main goal is to investigate how the acceleration process changes the shape of the particles' kinetic energy distribution. The evolution of the kinetic energy distribution, calculated numerically after one encounter of the particles with a single RCS, is found to be in good agreement with our previously published analytical formulae. In the case of consecutive encounters, we find that the kinetic distribution tends to converge to a practically invariant form after a relatively small number of encounters. We construct a discrete stochastic process that reproduces the numerical distributions and we provide a theoretical interpretation of the asymptotic convergence of the energy distribution. We finally compute the theoretical X-ray spectra that would be emitted by the simulated particles in a thick target model of radiation. 相似文献
96.
97.
Edison Liang 《Astrophysics and Space Science》2007,307(1-3):309-313
We review recent PIC simulation results which show that double-sided irradiation of a thin over-dense plasma slab with ultra-intense
laser pulses from both sides can lead to sustained comoving Poynting flux acceleration of electrons to energies much higher
than the conventional ponderomotive limit. The result is a robust power-law electron momentum spectrum similar to astrophysical
sources. We discuss future ultra-intense laser experiments that may be used to simulate astrophysical particle acceleration. 相似文献
98.
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99.
首先论述了航空矢量重力测量中科里奥利加速度的计算模型,给出了科里奥利加速度改正对水平、垂直速度要求的分析模型。数值表明,在低纬地区欲达到1mGal的科里奥利加速度的精度,要求速度的精度为5cm/s左右;依据实测数据,目前GPS测得的载体速度精度为0.3mm/s,完全能够满足航空矢量重力测量对科里奥利加速度改正的要求。 相似文献
100.
Ruchi Mishra 《Planetary and Space Science》2006,54(2):188-199
Dispersion relation, resonant energy transferred, growth rate and marginal instability criteria for the electrostatic ion-cyclotron wave with general loss-cone distribution in low-β anisotropic, homogeneous plasma in the auroral acceleration region are discussed by investigating the trajectories of the charged particles. Effects of the parallel electric field, ion beam velocity, steepness of the loss-cone distribution and temperature anisotropy on resonant energy transferred and growth rate of the instability are discussed. It is found that the effect of the parallel electric field is to stabilize the wave and enhance the transverse acceleration of ions whereas the effect of steepness of loss-cone, ion beam velocity and the temperature anisotropy is to enhance the growth rate and decrease the transverse acceleration of ions. The steepness of the loss-cone also introduces a peak in the growth rate which shifts towards the lower side of the perpendicular wave number with the increasing steepness of the loss-cone. 相似文献