1,946 research outputs found
Superposed epoch study of ICME sub-structures near Earth and their effects on galactic cosmic rays
Interplanetary coronal mass ejections (ICMEs) are the interplanetary
manifestations of solar eruptions. The overtaken solar wind forms a sheath of
compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of
ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs
pass near Earth, ground observations indicate that the flux of galactic cosmic
rays (GCRs) decreases. The main aims of this paper are to find: common plasma
and magnetic properties of different ICME sub-structures, and which ICME
properties affect the flux of GCRs near Earth. We use a superposed epoch method
applied to a large set of ICMEs observed \insitu\ by the spacecraft ACE,
between 1998 and 2006. We also apply a superposed epoch analysis on GCRs time
series observed with the McMurdo neutron monitors. We find that slow MCs at 1
AU have on average more massive sheaths. We conclude that it is because they
are more effectively slowed down by drag during their travel from the Sun. Slow
MCs also have a more symmetric magnetic field and sheaths expanding similarly
as their following MC, while in contrast, fast MCs have an asymmetric magnetic
profile and a compressing sheath in compression. In all types of MCs, we find
that the proton density and the temperature, as well as the magnetic
fluctuations can diffuse within the front of the MC due to 3D reconnection.
Finally, we derive a quantitative model which describes the decrease of cosmic
rays as a function of the amount of magnetic fluctuations and field strength.
The obtained typical profiles of sheath/MC/GCR properties corresponding to
slow, mid, and fast ICMEs, can be used for forecasting/modelling these events,
and to better understand the transport of energetic particles in ICMEs. They
are also useful for improving future operative space weather activities.Comment: 13 pages, 6 figures, paper accepted in A&
Interaction-induced chaos in a two-electron quantum-dot system
A quasi-one-dimensional quantum dot containing two interacting electrons is
analyzed in search of signatures of chaos. The two-electron energy spectrum is
obtained by diagonalization of the Hamiltonian including the exact Coulomb
interaction. We find that the level-spacing fluctuations follow closely a
Wigner-Dyson distribution, which indicates the emergence of quantum signatures
of chaos due to the Coulomb interaction in an otherwise non-chaotic system. In
general, the Poincar\'e maps of a classical analog of this quantum mechanical
problem can exhibit a mixed classical dynamics. However, for the range of
energies involved in the present system, the dynamics is strongly chaotic,
aside from small regular regions. The system we study models a realistic
semiconductor nanostructure, with electronic parameters typical of gallium
arsenide.Comment: 4 pages, 3ps figure
Cosmological simulations using a static scalar-tensor theory
We present CDM -body cosmological simulations in the framework of
a static general scalar-tensor theory of gravity. Due to the influence of the
non-minimally coupled scalar field, the gravitational potential is modified by
a Yukawa type term, yielding a new structure formation dynamics. We present
some preliminary results and, in particular, we compute the density and
velocity profiles of the most massive group.Comment: 4 pages, 6 figures, to appear in Journal of Physics: Conference
Series: VII Mexican School on Gravitation and Mathematical Physics. 26
November to 1 December 2006, Playa del Carmen, Quintana Roo, Mexic
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