11,717 research outputs found
Old open clusters: UBGVRI photometry of NGC 2506
UBGVRI photometry for the open cluster NGC 2506 is presented. From comparison
of the observed colour-magnitude diagrams with simulations based on stellar
evolutionary models we derive in a self consistent way reddening, distance, and
age of the cluster: E(B-V)=0-0.07, (m-M)o = 12.6, age = 1.5-2.2 Gyr. The
cluster shows a well definite secondary sequence, suggesting that binary
systems constitute about 20 % of the cluster members visible in the
colour-magnitude diagram.Comment: 11 pages, 7 figures, MNRAS latex style, accepte
Latest results from EXO-200
The Enriched Xenon Observatory (EXO) is an experimental program searching for neutrino-less double beta decay in xenon-136. The first stage of this program, EXO-200, has been in operation since early 2011. I present here the latest physics results from the experiment
Distribution of Gaussian Process Arc Lengths
We present the first treatment of the arc length of the Gaussian Process (GP)
with more than a single output dimension. GPs are commonly used for tasks such
as trajectory modelling, where path length is a crucial quantity of interest.
Previously, only paths in one dimension have been considered, with no
theoretical consideration of higher dimensional problems. We fill the gap in
the existing literature by deriving the moments of the arc length for a
stationary GP with multiple output dimensions. A new method is used to derive
the mean of a one-dimensional GP over a finite interval, by considering the
distribution of the arc length integrand. This technique is used to derive an
approximate distribution over the arc length of a vector valued GP in
by moment matching the distribution. Numerical simulations
confirm our theoretical derivations.Comment: 10 pages, 4 figures, Accepted to The 20th International Conference on
Artificial Intelligence and Statistics (AISTATS
Evidence for regulated expression of Telomeric Repeat-containing RNAs (TERRA) in parasitic trypanosomatids
The Telomeric Repeat-containing RNAs (TERRA) participate in the homeostasis of telomeres in higher eukaryotes. Here, we investigated the expression of TERRA in Leishmania spp. and Trypanosoma brucei and found evidences for its expression as a specific RNA class. The trypanosomatid TERRA are heterogeneous in size and partially polyadenylated. The levels of TERRA transcripts appear to be modulated through the life cycle in both trypanosomatids investigated, suggesting that TERRA play a stage-specific role in the life cycle of these early-branching eukaryotes
Chemical abundances and properties of the ionized gas in NGC 1705
We obtained [O III] narrow-band imaging and multi-slit MXU spectroscopy of
the blue compact dwarf (BCD) galaxy NGC 1705 with FORS2@VLT to derive chemical
abundances of PNe and H II regions and, more in general, to characterize the
properties of the ionized gas. The auroral [O III]\lambda4363 line was detected
in all but one of the eleven analyzed regions, allowing for a direct estimate
of their electron temperature. The only object for which the [O III]\lambda4363
line was not detected is a possible low-ionization PN, the only one detected in
our data. For all the other regions, we derived the abundances of Nitrogen,
Oxygen, Neon, Sulfur and Argon out to ~ 1 kpc from the galaxy center. We detect
for the first time in NGC 1705 a negative radial gradient in the oxygen
metallicity of -0.24 \pm 0.08 dex kpc^{-1}. The element abundances are all
consistent with values reported in the literature for other samples of dwarf
irregular and blue compact dwarf galaxies. However, the average (central)
oxygen abundance, 12 + log(O/H)=7.96 \pm 0.04, is ~0.26 dex lower than previous
literature estimates for NGC 1705 based on the [O III]\lambda4363 line. From
classical emission-line diagnostic diagrams, we exclude a major contribution
from shock excitation. On the other hand, the radial behavior of the emission
line ratios is consistent with the progressive dilution of radiation with
increasing distance from the center of NGC 1705. This suggests that the
strongest starburst located within the central 150 pc is responsible for
the ionization of the gas out to at least 1 kpc. The gradual dilution of
the radiation with increasing distance from the center reflects the gradual and
continuous transition from the highly ionized H II regions in the proximity of
the major starburst into the diffuse ionized gas.Comment: Accepted for publication on A
Single-particle and collective excitations in a charged Bose gas at finite temperature
The main focus of this work is on the predictions made by the dielectric
formalism in regard to the relationship between single-particle and collective
excitation spectra in a gas of point-like charged bosons at finite temperature
below the critical region of Bose-Einstein condensation. Illustrative
numerical results at weak coupling () are presented within the Random
Phase Approximation. We show that within this approach the single-particle
spectrum forms a continuum extending from the transverse to the longitudinal
plasma mode frequency and leading to a double-peak structure as increases,
whereas the density fluctuation spectrum consists of a single broadening peak.
We also discuss the momentum distribution and the superfluidity of the gas.Comment: 15 pages, 5 figure
Excised acoustic black holes: the scattering problem in the time domain
The scattering process of a dynamic perturbation impinging on a draining-tub
model of an acoustic black hole is numerically solved in the time domain.
Analogies with real black holes of General Relativity are explored by using
recently developed mathematical tools involving finite elements methods,
excision techniques, and constrained evolution schemes for strongly hyperbolic
systems. In particular it is shown that superradiant scattering of a
quasi-monochromatic wavepacket can produce strong amplification of the signal,
offering the possibility of a significant extraction of rotational energy at
suitable values of the angular frequency of the vortex and of the central
frequency of the wavepacket. The results show that theoretical tools recently
developed for gravitational waves can be brought to fruition in the study of
other problems in which strong anisotropies are present.Comment: 8 pages, 9 figure
Fully Frustrated Cold Atoms
Fully frustrated Josephson Junction arrays (FF-JJA's) exhibit a subtle
compound phase transition in which an Ising transition associated with discrete
broken translational symmetry and a Berezinskii-Kosterlitz-Thouless (BKT)
transition associated with quasi-long-range phase coherence occur nearly
simultaneously. In this Letter we discuss a cold atom realization of the FF-JJA
system. We demonstrate that both orders can be studied by standard
momentum-distribution-function measurements and present numerical results,
based on a successful self-consistent spin-wave approximation, that illustrate
the expected behavior of observables.Comment: 5 pages, 3 figures, submitte
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