10 research outputs found
SCIENTIFIC AND METHODICAL BASIS OF ORGANIZATION AND TEACHING OF DRAWING LESSONS IN GENERAL SECONDARY SCHOOLS
It was shown that at different stages of drawing training not only the application of knowledge to new conditions, but also the solution of the initial state of the graphic material with a high degree of replacement is an important condition for the development of graphic thinking
Modeling the magnetic field in the galactic disk using new rotation measure observations from the Very Large Array
We have determined 194 Faraday rotation measures (RMs) of polarized extragalactic radio sources using
new, multi-channel polarization observations at frequencies around 1.4 GHz from the Very Large Array (VLA) in the Galactic plane at 17◦ ≤ l ≤ 63◦ and 205◦ ≤ l ≤ 253◦. This catalog fills in gaps in the RM coverage of the
Galactic plane between the Canadian Galactic Plane Survey and Southern Galactic Plane Survey. Using this
catalog we have tested the validity of recently-proposed axisymmetric and bisymmetric models of the largescale
(or regular) Galactic magnetic field, and found that of the existing models we tested, an axisymmetric
spiral model with reversals occurring in rings (as opposed to along spiral arms) best matched our observations.
Building on this, we have performed our own modeling, using RMs from both extragalactic sources and pulsars.
By developing independent models for the magnetic field in the outer and inner Galaxy, we conclude that in the
inner Galaxy, the magnetic field closely follows the spiral arms, while in the outer Galaxy, the field is consistent
with being purely azimuthal. Furthermore, the models contain no reversals in the outer Galaxy, and together
seem to suggest the existence of a single reversed region that spirals out from the Galactic cente
Current status of turbulent dynamo theory: From large-scale to small-scale dynamos
Several recent advances in turbulent dynamo theory are reviewed. High
resolution simulations of small-scale and large-scale dynamo action in periodic
domains are compared with each other and contrasted with similar results at low
magnetic Prandtl numbers. It is argued that all the different cases show
similarities at intermediate length scales. On the other hand, in the presence
of helicity of the turbulence, power develops on large scales, which is not
present in non-helical small-scale turbulent dynamos. At small length scales,
differences occur in connection with the dissipation cutoff scales associated
with the respective value of the magnetic Prandtl number. These differences are
found to be independent of whether or not there is large-scale dynamo action.
However, large-scale dynamos in homogeneous systems are shown to suffer from
resistive slow-down even at intermediate length scales. The results from
simulations are connected to mean field theory and its applications. Recent
work on helicity fluxes to alleviate large-scale dynamo quenching, shear
dynamos, nonlocal effects and magnetic structures from strong density
stratification are highlighted. Several insights which arise from analytic
considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue
"Magnetism in the Universe" (ed. A. Balogh
Evolution of galactic magnetic fields
We study the cosmic evolution of the magnetic fields of a large sample of spiral galaxies in a cosmologically representative volume by employing a semi-analytic galaxy formation model and numerical dynamo solver in tandem. We start by deriving time- and radius-dependent galaxy properties using the GALFORM galaxy formation model, which are then fed into the non-linear mean-field dynamo equations. These are solved to give the large-scale (mean) field as a function of time and galactocentric radius for a thin disc, assuming axial symmetry. A simple prescription for the evolution of the small-scale (random) magnetic field component is also adopted. We find that, while most massive galaxies are predicted to have large-scale magnetic fields at redshift z = 0, a significant fraction of them is expected to contain negligible large-scale field. Our model indicates that, for most of the galaxies containing large-scale magnetic fields today, the mean-field dynamo becomes active at z < 3. Moreover, the typical magnetic field strength at any given galactic stellar mass is predicted to decline with time up until the present epoch, in agreement with our earlier results. We compute the radial profiles of pitch angle, and find broad agreement with observational data for nearby galaxies
Magnetic Fields in the Milky Way Halo
Contains fulltext :
141167.pdf (preprint version ) (Open Access
Between peace and hostility: Trebizond and the Pontic Turkish periphery in the Fourteenth century
Plasma Diagnostics of the Interstellar Medium with Radio Astronomy
Contains fulltext :
119335.pdf (preprint version ) (Open Access