39 research outputs found
On the reconstruction of a magnetosphere of pulsars nearby the light cylinder surface
A mechanism of generation of a toroidal component of large scale magnetic
field, leading to the reconstruction of the pulsar magnetospheres is presented.
In order to understand twisting of magnetic field lines, we investigate
kinematics of a plasma stream rotating in the pulsar magnetosphere. Studying an
exact set of equations describing the behavior of relativistic plasma flows,
the increment of the curvature drift instability is derived, and estimated for
pulsars. It is shown that a new parametric mechanism is very efficient and
can explain rotation energy pumping in the pulsar magnetospheres.Comment: 6 pages, 2 figure
Investigation of Dynamics of Self-Similarly Evolving Magnetic Clouds
Magnetic clouds (MCs) are "magnetized plasma clouds" moving in the solar
wind. MCs transport magnetic flux and helicity away from the Sun. These
structures are not stationary but feature temporal evolution. Commonly,
simplified MC models are considered. The goal of the present study is to
investigate the dynamics of more general, radially expanding MCs. They are
considered as cylindrically symmetric magnetic structures with low plasma
{\beta}. In order to study MC`evolution the self-similar approach method and a
numerical approach are used. It is shown that the forces are balanced in the
considered self-similarly evolving, cylindrically symmetric magnetic
structures. Explicit analytical expressions for magnetic field, plasma
velocity, density and pressure within MCs are derived. These solutions are
characterized by conserved values of magnetic flux and helicity. We also
investigate the dynamics of self-similarly evolving MCs by means of the
numerical code "Graale". In addition, their expansion in a medium with higher
density and higher plasma {\beta} is studied. It is shown that the physical
parameters of the MCs maintain their self-similar character throughout their
evolution. Conclusions. A comparison of the different self-similar and
numerical solutions allows us to conclude that the evolving MCs are quite
adequately described by our self-similar solutions - they retain their
self-similar, coherent nature for quite a long time and over large distances
from the Sun
Composition of Heavy Metals in the Water of the River Lopota and Floating Silt
Like other small rivers in Georgia, the river Lopota, which is one of the most important left tributaries of the river Alazani, is ecologically less studied. Although, phosphorus - potassium fertilizers containing heavy metals from agricultural lands, leaching sediment , composts made of municipal and household waste are systematically leached into the river Lopota, the composition of heavy metals, copper, zinc, iron, lead, nickel, manganese is lower than it is accepted. This fact is promoted by water pH, under which these metals are hydrolyzed and their main mass is accumulated at the bottom, and the rest of it is absorbed in the floating silt. Therefore, they cannot have a negative impact on self-scouring and ecological condition of the river
Magnetic clouds in the solar wind: A numerical assessment study of analytical models
Magnetic clouds (MCs) are "magnetized plasma clouds" moving in the solar
wind. MCs transport magnetic flux and helicity away from the Sun. These
structures are not stationary but feature temporal evolution as they propagate
in the solar wind. Simplified analytical models are frequently used for the
description of MCs, and fit certain observational data well. The goal of the
present study is to investigate numerically the validity of an analytical model
which is widely used for the description of MCs, and to determine under which
conditions this model's implied assumptions cease to be valid. A numerical
approach is applied. Analytical solutions that have been derived in previous
studies are implemented in a \textbf{3-D magnetohydrodynamic} simulation code
as initial conditions. Initially, the analytical model represents the main
observational features of the MCs. However, these characteristics prevail only
if the structure moves with a velocity close to the velocity of the background
flow. In this case an MC's evolution can quite accurately be described using an
analytic, self-similar approach. The dynamics of the magnetic structures which
move with a velocity significantly above or below that of the velocity of the
solar wind is investigated in detail. Besides the standard case in which MCs
only expand and propagate in the solar wind, the case of an MC rotating around
its axis of symmetry is also considered, and the resulting influence on the
MC's dynamics is studied
Coronal mass ejections as expanding force-free structures
We mode Solar coronal mass ejections (CMEs) as expanding force-fee magnetic
structures and find the self-similar dynamics of configurations with spatially
constant \alpha, where {\bf J} =\alpha {\bf B}, in spherical and cylindrical
geometries, expanding spheromaks and expanding Lundquist fields
correspondingly. The field structures remain force-free, under the conventional
non-relativistic assumption that the dynamical effects of the inductive
electric fields can be neglected. While keeping the internal magnetic field
structure of the stationary solutions, expansion leads to complicated internal
velocities and rotation, induced by inductive electric field. The structures
depends only on overall radius R(t) and rate of expansion \dot{R}(t) measured
at a given moment, and thus are applicable to arbitrary expansion laws. In case
of cylindrical Lundquist fields, the flux conservation requires that both axial
and radial expansion proceed with equal rates. In accordance with observations,
the model predicts that the maximum magnetic field is reached before the
spacecraft reaches the geometric center of a CME.Comment: 19 pages, 9 Figures, accepted by Solar Physic
4pi Models of CMEs and ICMEs
Coronal mass ejections (CMEs), which dynamically connect the solar surface to
the far reaches of interplanetary space, represent a major anifestation of
solar activity. They are not only of principal interest but also play a pivotal
role in the context of space weather predictions. The steady improvement of
both numerical methods and computational resources during recent years has
allowed for the creation of increasingly realistic models of interplanetary
CMEs (ICMEs), which can now be compared to high-quality observational data from
various space-bound missions. This review discusses existing models of CMEs,
characterizing them by scientific aim and scope, CME initiation method, and
physical effects included, thereby stressing the importance of fully 3-D
('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication
in Solar Physics (SUN-360 topical issue
Dynamics of rising magnetized cavities and UHECR acceleration in clusters of galaxies
We study the expansion of low density cavities produced by Active Galactic
Nuclei jets in clusters of galaxies. The long term stability of these cavities
requires the presence of linked magnetic fields. We find solutions describing
the self-similar expansion of structures containing large-scale electromagnetic
fields. Unlike the force-free spheromak-like configurations, these solutions
have no surface currents and, thus, are less susceptible to resistive decay.
The cavities are internally confined by external pressure, with zero gradient
at the surface. If the adiabatic index of the plasma within the cavity is
, the expansion ultimately leads to the formation of large-scale
current sheets. The resulting dissipation of the magnetic field can only
partially offset the adiabatic and radiative losses of radio emitting
electrons. We demonstrate that if the formation of large-scale current sheets
is accompanied by explosive reconnection of the magnetic field, the resulting
reconnection layer can accelerate cosmic rays to ultra high energies. We
speculate that the enhanced flux of UHECRs towards Centaurus A originates at
the cavities due to magnetic reconnection.Comment: 9 page