5,953 research outputs found
Detecting synchronization in spatially extended discrete systems by complexity measurements
The synchronization of two stochastically coupled one-dimensional cellular
automata (CA) is analyzed. It is shown that the transition to synchronization
is characterized by a dramatic increase of the statistical complexity of the
patterns generated by the difference automaton. This singular behavior is
verified to be present in several CA rules displaying complex behavior.Comment: 4 pages, 2 figures; you can also visit
http://add.unizar.es/public/100_16613/index.htm
Interactions and star formation activity in Wolf-Rayet galaxies
We present the main results of the PhD Thesis carried out by
L\'opez-S\'anchez (2006), in which a detailed morphological, photometrical and
spectroscopical analysis of a sample of 20 Wolf-Rayet (WR) galaxies was
realized. The main aims are the study of the star formation and O and WR
stellar populations in these galaxies and the role that interactions between
low surface companion objects have in the triggering of the bursts. We analyze
the morphology, stellar populations, physical conditions, chemical abundances
and kinematics of the ionized gas, as well as the star-formation activity of
each system.Comment: 16 pages, 15 figure
Integral Field Spectroscopy of HH 262: The Spectral Atlas
HH 262 is a group of emitting knots displaying an "hour-glass" morphology in
the Halpha and [SII] lines, located 3.5' to the northeast of the young stellar
object L1551-IRS5, in Taurus. We present new results of the kinematics and
physical conditions of HH 262 based on Integral Field Spectroscopy covering a
field of 1.5'x3', which includes all the bright knots in HH 262. These data
show complex kinematics and significant variations in physical conditions over
the mapped region of HH 262 on a spatial scale of <3". A new result derived
from the IFS data is the weakness of the [NII] emission (below detection limit
in most of the mapped region of HH 262), including the brightest central knots.
Our data reinforce the association of HH 262 with the redshifted lobe of the
evolved molecular outflow L1551-IRS5. The interaction of this outflow with a
younger one, powered by L1551 NE, around the position of HH 262 could give rise
to the complex morphology and kinematics of HH 262.Comment: Accepted for publication in MNRA
Coherent spin rotations in open driven double quantum dots
We analyze the charge and spin dynamics in a DC biased double quantum dot
driven by crossed DC and AC magnetic fields. In this configuration, spatial
delocalization due to inter-dot tunnel competes with intra-dot spin rotations
induced by the time dependent magnetic field, giving rise to a complicated time
dependent behavior of the tunnelling current. When the Zeeman splitting has the
same value in both dots and spin flip is negligible, the electrons remain in
the triplet subspace (dark subspace) performing coherent spin rotations and the
current does not flow. This electronic trapping is removed either by finite
spin relaxation or when the Zeeman splitting is different in each quantum dot.
In the first case, our results show that measuring the current will allow to
get information on the spin relaxation time. In the last case, we will show
that applying a resonant bichromatic magnetic field, the electrons become
trapped in a coherent superposition of states and electronic transport is
blocked. Then, manipulating AC magnetic fields, electrons are driven to perform
coherent spin rotations which can be unambiguously detected by direct
measurement of the tunneling current.Comment: 7 pages, 6 figures. Extended published versio
The complex structure of HH 110 as revealed from Integral Field Spectroscopy
HH 110 is a rather peculiar Herbig-Haro object in Orion that originates due
to the deflection of another jet (HH 270) by a dense molecular clump, instead
of being directly ejected from a young stellar object. Here we present new
results on the kinematics and physical conditions of HH 110 based on Integral
Field Spectroscopy. The 3D spectral data cover the whole outflow extent (~4.5
arcmin, ~0.6 pc at a distance of 460 pc) in the spectral range 6500-7000 \AA.
We built emission-line intensity maps of H, [NII] and [SII] and of
their radial velocity channels. Furthermore, we analysed the spatial
distribution of the excitation and electron density from [NII]/H,
[SII]/H, and [SII] 6716/6731 integrated line-ratio maps, as well as
their behaviour as a function of velocity, from line-ratio channel maps. Our
results fully reproduce the morphology and kinematics obtained from previous
imaging and long-slit data. In addition, the IFS data revealed, for the first
time, the complex spatial distribution of the physical conditions (excitation
and density) in the whole jet, and their behaviour as a function of the
kinematics. The results here derived give further support to the more recent
model simulations that involve deflection of a pulsed jet propagating in an
inhomogeneous ambient medium. The IFS data give richer information than that
provided by current model simulations or laboratory jet experiments. Hence,
they could provide valuable clues to constrain the space parameters in future
theoretical works.Comment: 12 pages, 15 figures Accepted in MNRA
Deep Near-Infrared Surface Photometry and Properties of Local Volume Dwarf Irregular Galaxies
We present deep H-band surface photometry and analysis of 40 Local Volume
galaxies, a sample primarily composed of dwarf irregulars in the Cen A group,
obtained using the IRIS2 detector at the 3.9m Anglo-Australian Telescope. We
probe to a surface brightness of ~25 mag arcsec, reaching a 40 times
lower stellar density than the Two Micron All Sky Survey (2MASS). Employing
extremely careful and rigorous cleaning techniques to remove contaminating
sources, we perform surface photometry on 33 detected galaxies deriving the
observed total magnitude, effective surface brightness and best fitting
S\'ersic parameters. We make image quality and surface photometry comparisons
to 2MASS and VISTA Hemispheric Survey (VHS) demonstrating that deep targeted
surveys are still the most reliable means of obtaining accurate surface
photometry. We investigate the B-H colours with respect to mass for Local
Volume galaxies, finding that the colours of dwarf irregulars are significantly
varied, eliminating the possibility of using optical-NIR colour transformations
to facilitate comparison to the more widely available optical data sets. The
structure-luminosity relationships are investigated for our `clean' sample of
dwarf irregulars. We demonstrate that a significant fraction of the Local
Volume dwarf irregular population have underlying structural properties similar
to both Local Volume and Virgo Cluster dwarf ellipticals. Linear regressions to
structure-luminosity relationships for the Local Volume galaxies and Virgo
Cluster dwarf ellipticals show significant differences in both slope and
scatter around the established trend lines, suggesting that environment might
regulate the structural scaling relationships of dwarf galaxies in comparison
to their more isolated counterparts.Comment: 27 pages, 14 figures, 5 table
Radiative two-pion decay of the tau lepton
We consider the bremsstrahlung and model-dependent contributions to the
radiative decay in the context of a
meson dominance model. We focus on several observables related to this decay,
including the branching ratio and the photon and di-pion spectra. Particular
attention is paid to the sensitivity of different observables upon the effects
of model-dependent contributions and of the magnetic dipole moment of the
vector meson. Important numerical differences are found with
respect to results obtained in the framework of chiral perturbation theory.Comment: 14 pages, 8 figures, submitted for publicatio
Deep into the Water Fountains: The case of IRAS 18043-2116
(Abridged) The formation of large-scale (hundreds to few thousands of AU)
bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic
Giant Branch (post-AGB) stars is poorly understood. The shape of these
structures, traced by emission from fast molecular outflows, suggests that the
dynamics at the innermost regions of these CSEs does not depend only on the
energy of the radiation field of the central star. Deep into the Water
Fountains is an observational project based on the results of programs carried
out with three telescope facilities: The Karl G. Jansky Very Large Array
(JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large
Telescope (SINFONI-VLT). Here we report the results of the observations towards
the WF nebula IRAS 180432116: Detection of radio continuum emission in the
frequency range 1.5GHz - 8.0GHz; HO maser spectral features and radio
continuum emission detected at 22GHz, and H ro-vibrational emission lines
detected at the near infrared. The high-velocity HO maser spectral
features, and the shock-excited H emission detected could be produced in
molecular layers which are swept up as a consequence of the propagation of a
jet-driven wind. Using the derived H column density, we estimated a
molecular mass-loss rate of the order of Myr. On the
other hand, if the radio continuum flux detected is generated as a consequence
of the propagation of a thermal radio jet, the mass-loss rate associated to the
outflowing ionized material is of the order of 10Myr.
The presence of a rotating disk could be a plausible explanation for the
mass-loss rates estimated.Comment: 10 pages, 5 figures. Accepted for publication in A&
The role of gas infall in the evolution of disc galaxies
Spiral galaxies are thought to acquire their gas through a protracted infall
phase resulting in the inside-out growth of their associated discs. For field
spirals, this infall occurs in the lower density environments of the cosmic
web. The overall infall rate, as well as the galactocentric radius at which
this infall is incorporated into the star-forming disc, plays a pivotal role in
shaping the characteristics observed today. Indeed, characterising the
functional form of this spatio-temporal infall in-situ is exceedingly
difficult, and one is forced to constrain these forms using the present day
state of galaxies with model or simulation predictions. We present the infall
rates used as input to a grid of chemical evolution models spanning the mass
spectrum of discs observed today. We provide a systematic comparison with
alternate analytical infall schemes in the literature, including a first
comparison with cosmological simulations. Identifying the degeneracies
associated with the adopted infall rate prescriptions in galaxy models is an
important step in the development of a consistent picture of disc galaxy
formation and evolution.Comment: 12 pages, 12 figures, MNRAS, accepte
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