8,909 research outputs found
Fermionic Atoms in Optical Superlattices
Fermionic atoms in an optical superlattice can realize a very peculiar
Anderson lattice model in which impurities interact with each other through a
discretized set of delocalized levels. We investigate the interplay between
Kondo effect and magnetism under these finite-size features. We find that Kondo
effect can dominate over magnetism depending on the parity of the number of
particles per discretized set. We show how Kondo-induced resonances of
measurable size can be observed through the atomic interference pattern
Flavoring the gravity dual of N=1 Yang-Mills with probes
We study two related problems in the context of a supergravity dual to N=1
SYM. One of the problems is finding kappa symmetric D5-brane probes in this
particular background. The other is the use of these probes to add flavors to
the gauge theory. We find a rich and mathematically appealing structure of the
supersymmetric embeddings of a D5-brane probe in this background. Besides, we
compute the mass spectrum of the low energy excitations of N=1 SQCD (mesons)
and match our results with some field theory aspects known from the study of
supersymmetric gauge theories with a small number of flavors.Comment: 55 pages, 7 figures, LaTeX; v2: typos corrected, references added;
v3: typos correcte
On the gravitational content of molecular clouds and their cores
(Abridged) The gravitational term for clouds and cores entering in the virial
theorem is usually assumed to be equal to the gravitational energy, since the
contribution to the gravitational force from the mass distribution outside the
volume of integration is assumed to be negligible. Such approximation may not
be valid in the presence of an important external net potential. In the present
work we analyze the effect of an external gravitational field on the
gravitational budget of a density structure. Our cases under analysis are (a) a
giant molecular cloud (GMC) with different aspect ratios embedded within a
galactic net potential, and (b) a molecular cloud core embedded within the
gravitational potential of its parent molecular cloud. We find that for
roundish GMCs, the tidal tearing due to the shear in the plane of the galaxy is
compensated by the tidal compression in the z direction. The influence of the
external effective potential on the total gravitational budget of these clouds
is relatively small, although not necessarily negligible. However, for more
filamentary GMCs, the external effective potential can be dominant and can even
overwhelm self-gravity, regardless of whether its main effect on the cloud is
to disrupt it or compress it. This may explain the presence of some GMCs with
few or no signs of massive star formation, such as the Taurus or the
Maddalena's clouds. In the case of dense cores embedded in their parent
molecular cloud, we found that the gravitational content due to the external
field may be more important than the gravitational energy of the cores
themselves. This effect works in the same direction as the gravitational
energy, i.e., favoring the collapse of cores. We speculate on the implications
of these results for star formation models.Comment: Accepted for publication in MNRA
Physical properties of the gamma-ray binary LS 5039 through low and high frequency radio observations
We have studied in detail the 0.15-15 GHz radio spectrum of the gamma-ray
binary LS 5039 to look for a possible turnover and absorption mechanisms at low
frequencies, and to constrain the physical properties of its emission. We have
analysed two archival VLA monitorings, all the available archival GMRT data and
a coordinated quasi-simultaneous observational campaign conducted in 2013 with
GMRT and WSRT. The data show that the radio emission of LS 5039 is persistent
on day, week and year timescales, with a variability at all
frequencies, and no signature of orbital modulation. The obtained spectra
reveal a power-law shape with a curvature below 5 GHz and a turnover at
GHz, which can be reproduced by a one-zone model with synchrotron
self-absorption plus Razin effect. We obtain a coherent picture for a size of
the emitting region of , setting a magnetic field of
, an electron density of and a mass-loss rate of . These values imply a significant mixing of the stellar wind with the
relativistic plasma outflow from the compact companion. At particular epochs
the Razin effect is negligible, implying changes in the injection and the
electron density or magnetic field. The Razin effect is reported for first time
in a gamma-ray binary, giving further support to the young non-accreting pulsar
scenario.Comment: 16 pages, 9 figures, accepted for publication in MNRA
A Discussion on Massive Gravitons and Propagating Torsion in Arbitrary Dimensions
In this paper, we reassess a particular -type gravity action in D
dimensions, recently studied by Nakasone and Oda, taking now torsion effects
into account. Considering that the vielbein and the spin connection carry
independent propagating degrees of freedom, we conclude that ghosts and
tachyons are absent only if torsion is non-propagating, and we also conclude
that there is no room for massive gravitons. To include these excitations, we
understand how to enlarge Nakasone-Oda's model by means of explicit torsion
terms in the action and we discuss the unitarity of the enlarged model for
arbitrary dimensions.Comment: 11 page
Deep radio images of the HEGRA and Whipple TeV sources in the Cygnus OB2 region
Context. The modern generation of Cherenkov telescopes has revealed a new
population of gamma-ray sources in the Galaxy. Some of them have been
identified with previously known X-ray binary systems while other remain
without clear counterparts a lower energies. Our initial goal here was
reporting on extensive radio observations of the first extended and yet
unidentified source, namely TeV J2032+4130. This object was originally detected
by the HEGRA telescope in the direction of the Cygnus OB2 region and its nature
has been a matter of debate during the latest years.
Aims. We aim to pursue our radio exploration of the TeV J2032+4130 position
that we initiated in a previous paper but taking now into account the latest
results from new Whipple and MILAGRO TeV telescopes.
Methods. Our investigation is mostly based on interferometric radio
observations with the Giant Metre Wave Radio Telescope (GMRT) close to Pune
(India) and the Very Large Array (VLA) in New Mexico (USA). We also conducted
near infrared observations with the 3.5 m telescope and the OMEGA2000 camera at
the Centro Astronomico Hispano Aleman (CAHA) in Almeria (Spain).
Results. We present deep radio maps centered on the TeV J2032+4130 position
at different wavelengths. In particular, our 49 and 20 cm maps cover a field of
view larger than half a degree that fully includes the Whipple position and the
peak of MILAGRO emission. Our most important result here is a catalogue of 153
radio sources detected at 49 cm within the GMRT antennae primary beam with a
full width half maximum (FWHM) of 43 arc-minute. Moreover, our
multi-configuration VLA images reveal the non-thermal extended emission
previously reported by us with improved angular resolution.Comment: 10 pages, 8 figures, 1 online catalogue. Accepted for publication in
Astronomy & Astrophysic
Investigating the mechanisms of the heat shock response impairment in Huntington’s disease mouse models
Huntington’s disease (HD) is a neurodegenerative disease caused by the expansion of a CAG repeat within exon 1 of the huntingtin (HTT) gene. This produces a mutant HTT protein with an abnormally long polyglutamine stretch, which is prone to misfold and form aggregates, as detected in HD patients and mouse models, and which have aberrant interactions with members of key cellular pathways that become disrupted. The heat shock response is a cytoprotective mechanism that aims to prevent and reduce aggregation and maintain proteome integrity. It is regulated by heat shock factor 1 (HSF1) which, under stress conditions, activates the transcription of the heat shock genes. In this thesis, a comprehensive analysis of the heat shock response has been described for HD mouse models R6/2 and zQ175, after in vivo pharmacological induction with the compound NVP-HSP990. The expression of Hsf1 and nine heat shock genes was measured from mouse tissue lysates by a QuantiGene multiplex assay, developed and validated for this purpose. Evidence of an impairment of the heat shock response was found in brain hemispheres, tibialis anterior and striatum of both models, with less consistent evidence in the cortex. As a potential cause of this dysregulation, HSF1 levels were analysed in brain and muscle, however, a decrease in HSF1 was not detected in either tissue. SIRT1 can deacetylate HSF1 and maintain it in a competent state, bound to heat shock gene promoters. SIRT1 levels decline with disease progression in HD mouse models, therefore, whether a decreased SIRT1 activity could be responsible for the impaired heat shock response was investigated. The analysis of the heat shock gene expression with QuantiGene revealed that Sirt1 overexpression on R6/2 mice did not significantly improve the heat shock response impairment in brain or tibialis anterior
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