444 research outputs found
Formation of Hot Planets by a combination of planet scattering, tidal circularization, and Kozai mechanism
We have investigated the formation of close-in extrasolar giant planets
through a coupling effect of mutual scattering, Kozai mechanism, and tidal
circularization, by orbital integrations. We have carried out orbital
integrations of three planets with Jupiter-mass, directly including the effect
of tidal circularization. We have found that in about 30% runs close-in planets
are formed, which is much higher than suggested by previous studies. We have
found that Kozai mechanism by outer planets is responsible for the formation of
close-in planets. During the three-planet orbital crossing, the Kozai
excitation is repeated and the eccentricity is often increased secularly to
values close enough to unity for tidal circularization to transform the inner
planet to a close-in planet. Since a moderate eccentricity can remain for the
close-in planet, this mechanism may account for the observed close-in planets
with moderate eccentricities and without nearby secondary planets. Since these
planets also remain a broad range of orbital inclinations (even retrograde
ones), the contribution of this process would be clarified by more observations
of Rossiter-McLaughlin effects for transiting planets.Comment: 15 pages, 16 figures, Accepted for publication in Ap
Effect of the Reconnection Electric Field on Electron Distribution Functions in the Diffusion Region of Magnetotail Reconnection
Electron distribution functions in the electron diffusion region during symmetric magnetic reconnection are investigated by means of theory and fully kinetic simulations. Crescentlike striations are formed in distribution functions in the velocity plane perpendicular to the magnetic field. Using an analytical current sheet, we solve the equation of motion for electrons, and derive the shape of a crescent distribution, as a function of the distance from the neutral line, field gradients, and the reconnection electric field. Each crescent is tilted in the velocity plane because of the acceleration by the reconnection electric field, and multiple stripes appear due to multiple meandering bounces. Applying the theory to distribution functions observed in Earth's magnetotail, we deduce the amplitude of the reconnection electric field
High speed rotating disc type generator for high magnetic field
A high magnetic field generator based on a new idea is described in this paper. The principle of the generator is different from those of previously published or tested. The fundamental principle of generating a high magnetic field is that the magnetic flux induced by an electromagnet with an iron core is concentrated by eddy currents on a rotating conductive disc and is compressed to high magnetic flux density on the hole surrounded with four discs. The energy for concentrating a magnetic flux is fed from the kinetic energy of rotating discs. Therefore, the generator is non-destructive and has only a relatively small electric source. The high magnetic field has a long pulse duration
Strong reconnection electric fields in shock-driven turbulence
Turbulent magnetic reconnection in a quasi-parallel shock under parameters relevant to the Earth's bow shock is investigated by means of a two-dimensional particle-in-cell simulation. The addressed aspects include the reconnection electric field, the reconnection rate, and the electron and the ion outflow speeds. In the shock transition region, many current sheets are generated in shock-driven turbulence, and electron-only reconnection and reconnection where both ions and electrons are involved can occur in those current sheets. The electron outflow speed in electron-only reconnection shows a positive correlation with the theoretical speed, which is close to the local electron Alfvén speed, and a strong convection electric field is generated by the large electron outflow. As a result, the reconnection electric field becomes much larger than those in the standard magnetopause or magnetotail reconnection. In shock-driven reconnection that involves ion dynamics, both electron outflows and ion outflows can reach of the order of 10 times the Alfvén speed in the X-line rest frame, leading to a reconnection electric field the same order as that in electron-only reconnection. An electron-only reconnection event observed by the magnetospheric multiscale mission downstream of a quasi-parallel shock is qualitatively similar to those in the simulation and shows that the outflow speed reaches approximately half the local electron Alfvén speed, supporting the simulation prediction
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