Micro-topographic change on calcarenites,grand Cayman Island,West Indies     

T. Spencer 《地球表面变化过程与地形》1981,6(1):85-94

Changes in micro-topography, as a result of varying erosion rates, have been monitored on a calcarenite ridge on Grand Cayman Island, West Indies, using a traversing model of the micro-erosion meter. Erosion takes place through the solution of a calcitic cement and ‘solutional disintegration’ results in a rapid change of micro-relief. Where a protective crust is present, surface lowering is slower and also more uniform; thus the original relative relief is maintained.  相似文献   

Incursion of the Pacific Ocean Water into the Indian Ocean     

G S Sharma  A D Gouveia  Shubha Satyendranath 《Journal of Earth System Science》1978,87(3):29-45

Using the data collected during the International Indian Ocean Expedition, maps showing the distribution of depth, acceleration potential, salinity and oxyty were prepared for the northeast monsoon for the four potential thermosteric anomaly surfaces: 160, 120, 80 and 60 cl/t. Zonal components of current along 84°E were computed from the geopotential dynamic heights. From such an analysis, it became clear that low-salinity water from the Pacific intrudes into the western Indian Ocean through the Banda and Timor seas in the upper layers above 100 cl/t surface, while the North Indian Ocean Water penetrates towards the Eastern Archipelago below 100 cl/t surface. The South Equatorial Countercurrent and the Tropical Countercurrent are well depicted on the vertical section of zonal components as well as on the distribution of acceleration potential.  相似文献   

Numerical simulation of ground acceleration spectra and accelerograms for engineering application     

S. J. Gibowicz  J. Pajchel  Z. Droste  J. Hordejuk 《Pure and Applied Geophysics》1980,119(2):380-391

A numerical approach to the earthquake ground motion analysis is proposed for regions where no accelerograms are available. Using Haskell matrix techniques, the response spectra of a layered substratum for SV waves were calculated and then multiplied by the spectra corresponding to Brune's type pulses. The ground acceleration spectra were obtained for different angles of pulse incidence at the substratum base. The spectrum shape depends upon the substratum response and the pulse shape, while its level was related to the maximum ground acceleration corresponding to the expected maximum intensity. Transformation of the ground spectra into the time domain produced numerical accelerograms for horizontal and vertical components and for different angles of pulse incidence. Finally, a standard statistical procedure was applied to obtain the design response spectra used in engineering applications.  相似文献   

Ulysses的观测与太阳风加速机理初议   总被引：2，自引：0，他引：2       下载免费PDF全文

卢先和 《地球物理学报》1998,41(4):437-446

Ulysses 是迄今为止第一次沿独特的日球纬度方向考察日球高纬度空间区域的飞船。本文描述了 Ulysses 飞船的部分主要观测结果,并进行了分析,在 Ulysses 飞船穿越太阳南,北极之前,科学家们提出了各种不同的太阳风速度、磁场等参量的纬向变化模型。分析表明,这些模型都不能解释 Ulysses 飞船的观测结果。Ulysses 飞船的观测对经典的太阳风理论提出了挑战,太阳风的加热与加速是一个远没有被解决的问题。观测与分析表明,经典热传导不可能驱动高速流,太阳风的加速伴随着加热的发生,而加热率大小可能与离子的回旋频率有关;太阳风的热源可能不是单一的形式,而且不同形式的热源对太阳的加热贡献大小与日球径向距离有关。本文讨论并分析了几种可能的太阳风加热与加速机制。  相似文献   

Electrostatic Potentials in Supernova Remnant Shocks     

Matthew G. Baring  Errol J. Summerlin 《Astrophysics and Space Science》2007,307(1-3):165-168

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   

The Origin and Acceleration of ~3He and Heavy Ions in the 2000 July 14 Event     

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   

Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration     

G. Brunetti  A. Lazarian 《Monthly notices of the Royal Astronomical Society》2007,378(1):245-275

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Particle distributions and X-ray spectra in single or multiple solar current sheets     

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   

Diffusive synchrotron radiation from pulsar wind nebulae     

G. D. Fleishman  M. F. Bietenholz 《Monthly notices of the Royal Astronomical Society》2007,376(2):625-633

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Simulating Poynting Flux Acceleration in the Laboratory with Colliding Laser Pulses     

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