862 research outputs found
Remarkable symmetries in the Milky Way disk's magnetic field
Using a new, expanded compilation of extragalactic source Faraday rotation
measures (RM) we investigate the broad underlying magnetic structure of the
Galactic disk at latitudes over all longitudes ,
where our total number of RM's in this low-latitude range of the Galactic sky
is comparable to those in the combined Canadian Galactic Plane Survey(CGPS) at
and the Southern Galactic Plane (SGPS)
survey. We report newly revealed, remarkably coherent patterns of RM at
from to and RM()
features of unprecedented clarity that replicate in with opposite sign on
opposite sides of the Galactic center. They confirm a highly patterned
bisymmetric field structure toward the inner disc, an axisymmetic pattern
toward the outer disc, and a very close coupling between the CGPS/SGPS RM's at
("mid-plane") and our new RM's up to ("near-plane").
Our analysis also shows the approximate -height -- the vertical height of
the coherent component of the disc field above the Galactic disc's mid-plane --
to be kpc out to kpc from the Sun. This identifies the
approximate height of the transition layer to the halo field structure. We find
no RM sign change across the plane within in any
longitude range. The prevailing {\it disc} field pattern, and its striking
degree of large scale ordering confirm that our side of the Milky Way has a
very organized underlying magnetic structure, for which the inward spiral pitch
angle is at all up to in
the inner semicircle of Galactic longitudes. It decreases to
toward the anticentre.Comment: 7 pages, 5 figures, Version 3. Accepted 2011 for publication in
Publications of the Astronomical Society of Australia(PASA
A summary of observational records on periodicities above the rotational period in the Jovian magnetosphere
The Jovian magnetosphere is a very dynamic system. The plasma mass-loading from the moon Io and the fast planetary rotation lead to regular release of mass from the Jovian magnetosphere and to a change of the magnetic topology. These regular variations, most commonly on several (2.5–4) days scale, were derived from various data sets obtained by different spacecraft missions and instruments ranging from auroral images to in situ measurements of magnetospheric particles. Specifically, ion measurements from the Galileo spacecraft represent the periodicities, very distinctively, namely the periodic thinning of the plasma sheet and subsequent dipolarization, and explosive mass release occurring mainly during the transition between these two phases. We present a review of these periodicities, particularly concentrating on those observed in energetic particle data. The most distinct periodicities are observed for ions of sulfur and oxygen. The periodic topological change of the Jovian magnetosphere, the associated mass-release process and auroral signatures can be interpreted as a global magnetospheric instability with analogies to the two step concept of terrestrial substorms. Different views on the triggering mechanism of this magnetospheric instability are discussed
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False color viewing device
This invention consists of a viewing device for observing objects in near-infrared false-color comprising a pair of goggles with one or more filters in the apertures, and pads that engage the face for blocking stray light from the sides so that all light reaching, the user`s eyes come through the filters. The filters attenuate most visible light and pass near-infrared (having wavelengths longer than approximately 700 nm) and a small amount of blue-green and blue-violet (having wavelengths in the 500 to 520 nm and shorter than 435 nm, respectively). The goggles are useful for looking at vegetation to identify different species and for determining the health of the vegetation, and to detect some forms of camouflage
Row Spacing and Productivity of Russian Wild Rye Pastures in Semiarid Environments
To sustain forage yields in dry years in semiarid climates, row spacings \u3e59cm have been recommended for Russian wild rye [Psathyrostachys juncea (Fisch.) Nevski] (Lawrence & Heinrichs, 1968). However, wide row spacings promote weed invasion, soil erosion, and elevated plant crowns resulting in a rough, washboard ground surface (Kilcher, 1961). Jefferson and Kielly (1998) suggested a 30-cm row spacing for optimum sustainable forage yields in Russian wild rye in the semiarid prairie region of Canada. This study aimed to evaluate the relationship between row spacing and productivity of Russian wild rye at two semiarid sites near Mandan, in the northern Great Plains region of the USA (46º 48\u27 N latitude, 100º 55\u27 W longitude)
Fossil AGN jets as ultra high energy particle accelerators
Remnants of AGN jets and their surrounding cocoons leave colossal
magnetohydrodynamic (MHD) fossil structures storing total energies ~10^{60}
erg. The original active galacic nucleus (AGN) may be dead but the fossil will
retain its stable configuration resembling the reversed-field pinch (RFP)
encountered in laboratory MHD experiments.
In an RFP the longitudinal magnetic field changes direction at a critical
distance from the axis, leading to magnetic re-connection there, and to slow
decay of the large-scale RFP field. We show that this field decay induces
large-scale electric fields which can accelerate cosmic rays with an E^{-2}
power-law up to ultra-high energies with a cut-off depending on the fossil
parameters. The cut-off is expected to be rigidity dependent, implying the
observed composition would change from light to heavy close to the cut-off if
one or two nearby AGN fossils dominate. Given that several percent of the
universe's volume may house such slowly decaying structures, these fossils may
even re-energize ultra-high energy cosmic rays from distant/old sources,
offsetting the ``GZK-losses'' due to interactions with photons of the cosmic
microwave background radiation and giving evidence of otherwise undetectable
fossils. In this case the composition would remain light to the highest
energies if distant sources or fossils dominated, but otherwise would be mixed.
It is hoped the new generation of cosmic ray experiments such as the Pierre
Auger Observatory and ultra-high energy neutrino telescopes such as ANITA and
lunar Cherenkov experiments will clarify this.Comment: 11 pages, 6 figures, additional references and explanations. Accepted
for publication in MNRA
Generation of helical magnetic fields from inflation
The generation of helical magnetic fields during single field inflation due
to an axial coupling of the electromagnetic field to the inflaton is discussed.
We find that such a coupling always leads to a blue spectrum of magnetic fields
during slow roll inflation. Though the helical magnetic fields further evolve
during the inverse cascade in the radiation era after inflation, we conclude
that the magnetic fields generated by such an axial coupling can not lead to
observed field strength on cosmologically relevant scales.Comment: 4 pages, 1 figure; Contribution to the proceedings of the
International Conference on Gravitation and Cosmology (ICGC), Goa, India,
December, 201
MgII absorption systems with W_0 > 0.1 \AA for a radio selected sample of 77 QSOs and their associated magnetic fields at high redshifts
We present a catalogue of MgII absorption systems obtained from high
resolution UVES/VLT data of 77 QSOs in the redshift range 0.6 < z < 2.0, and
down to an equivalent width W_0 > 0.1 \AA. The statistical properties of our
sample are found to be in agreement with those from previous work in the
literature. However, we point out that the previously observed increase with
redshift of dN/dz for weak absorbers, pertains exclusively to very weak
absorbers with W_0 < 0.1 \AA. Instead, dN/dz for absorbers with W_0 in the
range 0.1-0.3 \AA actually decreases with redshift, similarly to the case of
strong absorbers. We then use this catalogue to extend our earlier analysis of
the links between the Faraday Rotation Measure of the quasars and the presence
of intervening MgII absorbing systems in their spectra. In contrast to the case
with strong MgII absorption systems W_0 > 0.3 \AA, the weaker systems do not
contribute significantly to the observed Rotation Measure of the background
quasars. This is possibly due to the higher impact parameters of the weak
systems compared to strong ones, suggesting that the high column density
magnetized material that is responsible for the Faraday Rotation is located
within about 50 kpc of the galaxies. Finally, we show that this result also
rules out the possibility that some unexpected secondary correlation between
the quasar redshift and its intrinsic Rotation Measure is responsible for the
association of high Rotation Measure and strong intervening MgII absorption
that we have presented elsewhere, since this would have produced an equal
effect for the weak absorption line systems, which exhibit a very similar
distribution of quasar redshifts.Comment: Accepted for publication in ApJ. 12 pages, 8 figure
A Magnetized Local Supercluster and the Origin of the Highest Energy Cosmic Rays
A sufficiently magnetized Local Supercluster can explain the spectrum and
angular distribution of ultra-high energy cosmic rays. We show that the
spectrum of extragalactic cosmic rays with energies below eV may
be due to the diffusive propagation in the Local Supercluster with fields of
Gauss. Above eV, cosmic rays propagate
in an almost rectilinear way which is evidenced by the change in shape of the
spectrum at the highest energies. The fit to the spectrum requires that at
least one source be located relatively nearby at Mpc away from the
Milky Way. We discuss the origin of magnetic fields in the Local Supercluster
and the observable predictions of this model.Comment: 11 pages, 2 figures, submitted to PR
Magnetohydrodynamics and Plasma Cosmology
We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous magnetized
fluid of finite conductivity and discuss instability criteria. In addition, we
explore the excitation of cosmological perturbations in anisotropic spacetimes,
in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m)
and fast-magnetosonic modes, propagating normal to the magnetic field, can be
excited, resulting in several implications of cosmological significance.Comment: 9 pages, RevTeX, To appear in the Proceedings of the Peyresq X
Meeting, IJTP Conference Serie
Heating Hot Atmospheres with Active Galactic Nuclei
High resolution X-ray spectroscopy of the hot gas in galaxy clusters has
shown that the gas is not cooling to low temperatures at the predicted rates of
hundreds to thousands of solar masses per year. X-ray images have revealed
giant cavities and shock fronts in the hot gas that provide a direct and
relatively reliable means of measuring the energy injected into hot atmospheres
by active galactic nuclei (AGN). Average radio jet powers are near those
required to offset radiative losses and to suppress cooling in isolated giant
elliptical galaxies, and in larger systems up to the richest galaxy clusters.
This coincidence suggests that heating and cooling are coupled by feedback,
which suppresses star formation and the growth of luminous galaxies. How jet
energy is converted to heat and the degree to which other heating mechanisms
are contributing, eg. thermal conduction, are not well understood. Outburst
energies require substantial late growth of supermassive black holes. Unless
all of the approximately 10E62 erg required to suppress star formation is
deposited in the cooling regions of clusters, AGN outbursts must alter
large-scale properties of the intracluster medium.Comment: 60 pages, 12 figures, to appear in 1997 Annual Reviews of Astronomy
and Astrophysics. This version supersedes the April 2007 version in Reviews
in Advance (references and minor corrections were added), and is similar to
the one scheduled to appear in Volume 45 of ARA
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