206 research outputs found
Casimir Invariants from Quasi-Hopf (Super)algebras
We show how to construct, starting from a quasi-Hopf (super)algebra, central
elements or Casimir invariants. We show that these central elements are
invariant under quasi-Hopf twistings. As a consequence, the elliptic quantum
(super)groups, which arise from twisting the normal quantum (super)groups, have
the same Casimir invariants as the corresponding quantum (super)groups.Comment: 24 pages, Latex fil
Influence of major mergers on the radio emission of elliptical galaxies
We investigate the influence of major mergers on the radio emission of
elliptical galaxies. We use a complete sample of close pairs, which contains
475 merging and 1828 non-merging paired elliptical galaxies of M_r<-21.5
selected from the Sloan Digital Sky Survey. In addition, a control sample of
2000 isolated field galaxies is used for comparison. We cross-identify the
optical galaxies with the radio surveys of FIRST and NVSS. We find that the
radio fraction of merging paired galaxies is about 6%, which is slightly higher
than the 5% obtained for non-merging paired galaxies, although these values are
consistent with each other owing to the large uncertainty caused by the limited
sample. The radio fraction is twice as that of isolated galaxies, which is less
than 3%. Radio emission of elliptical galaxies is only slightly affected by
major mergers, but predominantly depends on their optical luminosities.
Therefore, merging is not important in triggering the radio emission of
elliptical galaxies.Comment: 5 pages, 5 figures, 1 table, accepted for publication in A&A, minor
change
Turing instabilities in a mathematical model for signaling networks
GTPase molecules are important regulators in cells that continuously run
through an activation/deactivation and membrane-attachment/membrane-detachment
cycle. Activated GTPase is able to localize in parts of the membranes and to
induce cell polarity. As feedback loops contribute to the GTPase cycle and as
the coupling between membrane-bound and cytoplasmic processes introduces
different diffusion coefficients a Turing mechanism is a natural candidate for
this symmetry breaking. We formulate a mathematical model that couples a
reaction-diffusion system in the inner volume to a reaction-diffusion system on
the membrane via a flux condition and an attachment/detachment law at the
membrane. We present a reduction to a simpler non-local reaction-diffusion
model and perform a stability analysis and numerical simulations for this
reduction. Our model in principle does support Turing instabilities but only if
the lateral diffusion of inactivated GTPase is much faster than the diffusion
of activated GTPase.Comment: 23 pages, 5 figures; The final publication is available at
http://www.springerlink.com http://dx.doi.org/10.1007/s00285-011-0495-
3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum
Measurement of the coronal magnetic field is a crucial ingredient in
understanding the nature of solar coronal phenomena at all scales. We employed
STEREO/COR1 data obtained during a deep minimum of solar activity in February
2008 (Carrington rotation CR 2066) to retrieve and analyze the
three-dimensional (3D) coronal electron density in the range of heights from
1.5 to 4 Rsun using a tomography method. With this, we qualitatively deduced
structures of the coronal magnetic field. The 3D electron density analysis is
complemented by the 3D STEREO/EUVI emissivity in the 195 A band obtained by
tomography for the same CR. A global 3D MHD model of the solar corona was used
to relate the reconstructed 3D density and emissivity to open/closed magnetic
field structures. We show that the density maximum locations can serve as an
indicator of current sheet position, while the locations of the density
gradient maximum can be a reliable indicator of coronal hole boundaries. We
find that the magnetic field configuration during CR 2066 has a tendency to
become radially open at heliocentric distances greater than 2.5 Rsun. We also
find that the potential field model with a fixed source surface (PFSS) is
inconsistent with the boundaries between the regions with open and closed
magnetic field structures. This indicates that the assumption of the potential
nature of the coronal global magnetic field is not satisfied even during the
deep solar minimum. Results of our 3D density reconstruction will help to
constrain solar coronal field models and test the accuracy of the magnetic
field approximations for coronal modeling.Comment: Published in "Solar Physics
On the dynamical generation of the Maxwell term and scale invariance
Gauge theories with no Maxwell term are investigated in various setups. The
dynamical generation of the Maxwell term is correlated to the scale invariance
properties of the system. This is discussed mainly in the cases where the gauge
coupling carries dimensions. The term is generated when the theory contains a
scale explicitly, when it is asymptotically free and in particular also when
the scale invariance is spontaneously broken. The terms are not generated when
the scale invariance is maintained. Examples studied include the large
limit of the model in dimensions, a 3D gauged
vector model and its supersymmetric extension. In the latter case the
generation of the Maxwell term at a fixed point is explored. The phase
structure of the case is investigated in the presence of a Chern-Simons
term as well. In the supersymmetric model the emergence of the Maxwell
term is accompanied by the dynamical generation of the Chern-Simons term and
its multiplet and dynamical breaking of the parity symmetry. In some of the
phases long range forces emerge which may result in logarithmic confinement.
These include a dilaton exchange which plays a role also in the case when the
theory has no gauge symmetry. Gauged Lagrangian realizations of the 2D coset
models do not lead to emergent Maxwell terms. We discuss a case where the gauge
symmetry is anomalous.Comment: 38 pages, 4 figures; v2 slightly improved, typos fixed, references
added, published versio
Microvariability in the optical polarization of 3C279
We present results of a microvariability polarization study in the violently
variable quasar 3C279. We have resolved the polarization curves in the V band
for this object down to timescales of minutes. We found two main components in
the evolution of the degree of linear polarization, one consisting of a flicker
with timescales of several tens of minutes and other component with far more
significant variations on timescales of a few days. The linear polarization
descended from % down to % in three nights. The polarization
angle underwent a sudden change of more that 10 degrees in a few hours, perhaps
indicating the injection of a new shock in the jet. The amplitude of the
intranight flickering in the degree of polarization is at the level of %. These are probably the best sampled polarization data ever obtained for
this object. We also performed IR observations and we provide a follow-up of
the evolution of this source at such energies after the main polarization
outburst.Comment: 10 pages, 9 figures, accepted for publication in A&
Radio-Excess IRAS Galaxies: PMN/FSC Sample Selection
A sample of 178 extragalactic objects is defined by correlating the 60 micron
IRAS FSC with the 5 GHz PMN catalog. Of these, 98 objects lie above the
radio/far-infrared relation for radio-quiet objects. These radio-excess
galaxies and quasars have a uniform distribution of radio excesses and appear
to be a new population of active galaxies not present in previous
radio/far-infrared samples. The radio-excess objects extend over the full range
of far-infrared luminosities seen in extragalactic objects. Objects with small
radio excesses are more likely to have far-infrared colors similar to
starbursts, while objects with large radio excesses have far-infrared colors
typical of pure AGN. Some of the most far-infrared luminous radio-excess
objects have the highest far-infrared optical depths. These are good candidates
to search for hidden broad line regions in polarized light or via near-infrared
spectroscopy. Some low far-infrared luminosity radio-excess objects appear to
derive a dominant fraction of their far-infrared emission from star formation,
despite the dominance of the AGN at radio wavelengths. Many of the radio-excess
objects have sizes likely to be smaller than the optical host, but show
optically thin radio emission. We draw parallels between these objects and high
radio luminosity Compact Steep-Spectrum (CSS) and GigaHertz Peaked-Spectrum
(GPS) objects. Radio sources with these characteristics may be young AGN in
which the radio activity has begun only recently. Alternatively, high central
densities in the host galaxies may be confining the radio sources to compact
sizes. We discuss future observations required to distinguish between these
possibilities and determine the nature of radio-excess objects.Comment: Submitted to AJ. 44 pages, 11 figures. A version of the paper with
higher quality figures is available from
http://www.mso.anu.edu.au/~cdrake/PMNFSC/paperI
Can long-term periodic variability and jet helicity in 3C 120 be explained by jet precession?
Optical variability of 3C 120 is discussed in the framework of jet
precession. Specifically, we assume that the observed long-term periodic
variability is produced by the emission from an underlying jet with a
time-dependent boosting factor driven by precession. The differences in the
apparent velocities of the different superluminal components in the
milliarcsecond jet can also be explained by the precession model as being
related to changes in the viewing angle. The evolution of the jet components
has been used to determine the parameters of the precession model, which also
reproduce the helical structure seen at large scales. Among the possible
mechanisms that could produce jet precession, we consider that 3C 120 harbours
a super-massive black hole binary system in its nuclear region and that torques
induced by misalignment between the accretion disc and the orbital plane of the
secondary black hole are responsible for this precession; we estimated upper
and lower limits for the black holes masses and their mean separation.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Signatures of the slow solar wind streams from active regions in the inner corona
Some of local sources of the slow solar wind can be associated with
spectroscopically detected plasma outflows at edges of active regions
accompanied with specific signatures in the inner corona. The EUV telescopes
(e.g. SPIRIT/CORONAS-F, TESIS/CORONAS-Photon and SWAP/PROBA2) sometimes
observed extended ray-like structures seen at the limb above active regions in
1MK iron emission lines and described as "coronal rays". To verify the
relationship between coronal rays and plasma outflows, we analyze an isolated
active region (AR) adjacent to small coronal hole (CH) observed by different
EUV instruments in the end of July - beginning of August 2009. On August 1 EIS
revealed in the AR two compact outflows with the Doppler velocities V =10-30
km/s accompanied with fan loops diverging from their regions. At the limb the
ARCH interface region produced coronal rays observed by EUVI/STEREO-A on July
31 as well as by TESIS on August 7. The rays were co-aligned with open magnetic
field lines expanded to the streamer stalks. Using the DEM analysis, it was
found that the fan loops diverged from the outflow regions had the dominant
temperature of ~1 MK, which is similar to that of the outgoing plasma streams.
Parameters of the solar wind measured by STEREO-B, ACE, WIND, STEREO-A were
conformed with identification of the ARCH as a source region at the
Wang-Sheeley-Arge map of derived coronal holes for CR 2086. The results of the
study support the suggestion that coronal rays can represent signatures of
outflows from ARs propagating in the inner corona along open field lines into
the heliosphere.Comment: Accepted for publication in Solar Physics; 31 Pages; 13 Figure
Radio Frequency Spectra of 388 Bright 74 MHz Sources
As a service to the community, we have compiled radio frequency spectra from
the literature for all sources within the VLA Low Frequency Sky Survey (VLSS)
that are brighter than 15 Jy at 74 MHz. Over 160 references were used to
maximize the amount of spectral data used in the compilation of the spectra,
while also taking care to determine the corrections needed to put the flux
densities from all reference on the same absolute flux density scale. With the
new VLSS data, we are able to vastly improve upon previous efforts to compile
spectra of bright radio sources to frequencies below 100 MHz because (1) the
VLSS flux densities are more reliable than those from some previous low
frequency surveys and (2) the VLSS covers a much larger area of the sky
(declination >-30 deg.) than many other low frequency surveys (e.g., the 8C
survey). In this paper, we discuss how the spectra were constructed and how
parameters quantifying the shapes of the spectra were derived. Both the spectra
and the shape parameters are made available here to assist in the calibration
of observations made with current and future low frequency radio facilities.Comment: Accepted to ApJ
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