4,924 research outputs found
Predicted multiply-imaged X-ray AGNs in the XXL survey
We estimate the incidence of multiply-imaged AGNs among the optical
counterparts of X-ray selected point-like sources in the XXL field. We also
derive the expected statistical properties of this sample, such as the redshift
distribution of the lensed sources and of the deflectors that lead to the
formation of multiple images, modelling the deflectors using both spherical
(SIS) and ellipsoidal (SIE) singular isothermal mass distributions. We further
assume that the XXL survey sample has the same overall properties as the
smaller XMM-COSMOS sample restricted to the same flux limits and taking into
account the detection probability of the XXL survey. Among the X-ray sources
with a flux in the [0.5-2] keV band larger than 3.0x10 erg cm
s and with optical counterparts brighter than an r-band magnitude of 25,
we expect ~20 multiply-imaged sources. Out of these, ~16 should be detected if
the search is made among the seeing-limited images of the X-ray AGN optical
counterparts and only one of them should be composed of more than two lensed
images. Finally, we study the impact of the cosmological model on the expected
fraction of lensed sources.Comment: 15 pages, 7 figures, 1 table, accepted for publication in MNRA
Superconducting properties of nanocrystalline MgB thin films made by an in situ annealing process
We have studied the structural and superconducting properties of MgB thin
films made by pulsed laser deposition followed by in situ annealing. The
cross-sectional transmission electron microscopy reveals a nanocrystalline
mixture of textured MgO and MgB with very small grain sizes. A
zero-resistance transition temperature () of 34 K and a zero-field
critical current density () of A/cm were obtained.
The irreversibility field was 8 T at low temperatures, although severe
pinning instability was observed. These bulk-like superconducting properties
show that the in situ deposition process can be a viable candidate for MgB
Josephson junction technologies
The Apparent Fractal Conjecture: Scaling Features in Standard Cosmologies
This paper presents an analysis of the smoothness problem in cosmology by
focussing on the ambiguities originated in the simplifying hypotheses aimed at
observationally verifying if the large-scale distribution of galaxies is
homogeneous, and conjecturing that this distribution should follow a fractal
pattern in perturbed standard cosmologies. This is due to a geometrical effect,
appearing when certain types of average densities are calculated along the past
light cone. The paper starts reviewing the argument concerning the possibility
that the galaxy distribution follows such a scaling pattern, and the premises
behind the assumption that the spatial homogeneity of standard cosmology can be
observable. Next, it is argued that to discuss observable homogeneity one needs
to make a clear distinction between local and average relativistic densities,
and showing how the different distance definitions strongly affect them,
leading the various average densities to display asymptotically opposite
behaviours. Then the paper revisits Ribeiro's (1995: astro-ph/9910145) results,
showing that in a fully relativistic treatment some observational average
densities of the flat Friedmann model are not well defined at z ~ 0.1, implying
that at this range average densities behave in a fundamentally different manner
as compared to the linearity of the Hubble law, well valid for z < 1. This
conclusion brings into question the widespread assumption that relativistic
corrections can always be neglected at low z. It is also shown how some key
features of fractal cosmologies can be found in the Friedmann models. In view
of those findings, it is suggested that the so-called contradiction between the
cosmological principle, and the galaxy distribution forming an unlimited
fractal structure, may not exist.Comment: 30 pages, 2 figures, LaTeX. This paper is a follow-up to
gr-qc/9909093. Accepted for publication in "General Relativity and
Gravitation
Molecular dynamics simulation of the fragile glass former ortho-terphenyl: a flexible molecule model
We present a realistic model of the fragile glass former orthoterphenyl and
the results of extensive molecular dynamics simulations in which we
investigated its basic static and dynamic properties. In this model the
internal molecular interactions between the three rigid phenyl rings are
described by a set of force constants, including harmonic and anharmonic terms;
the interactions among different molecules are described by Lennard-Jones
site-site potentials. Self-diffusion properties are discussed in detail
together with the temperature and momentum dependencies of the
self-intermediate scattering function. The simulation data are compared with
existing experimental results and with the main predictions of the Mode
Coupling Theory.Comment: 20 pages and 28 postscript figure
The Transiting System GJ1214: High-Precision Defocused Transit Observations and a Search for Evidence of Transit Timing Variation
Aims: We present 11 high-precision photometric transit observations of the
transiting super-Earth planet GJ1214b. Combining these data with observations
from other authors, we investigate the ephemeris for possible signs of transit
timing variations (TTVs) using a Bayesian approach.
Methods: The observations were obtained using telescope-defocusing
techniques, and achieve a high precision with random errors in the photometry
as low as 1mmag per point. To investigate the possibility of TTVs in the light
curve, we calculate the overall probability of a TTV signal using Bayesian
methods.
Results: The observations are used to determine the photometric parameters
and the physical properties of the GJ1214 system. Our results are in good
agreement with published values. Individual times of mid-transit are measured
with uncertainties as low as 10s, allowing us to reduce the uncertainty in the
orbital period by a factor of two.
Conclusions: A Bayesian analysis reveals that it is highly improbable that
the observed transit times is explained by TTV, when compared with the simpler
alternative of a linear ephemeris.Comment: Submitted to A&
Disorder Effects on Exciton-Polariton Condensates
The impact of a random disorder potential on the dynamical properties of Bose
Einstein condensates is a very wide research field. In microcavities, these
studies are even more crucial than in the condensates of cold atoms, since
random disorder is naturally present in the semiconductor structures. In this
chapter, we consider a stable condensate, defined by a chemical potential,
propagating in a random disorder potential, like a liquid flowing through a
capillary. We analyze the interplay between the kinetic energy, the
localization energy, and the interaction between particles in 1D and 2D
polariton condensates. The finite life time of polaritons is taken into account
as well. In the first part, we remind the results of [G. Malpuech et al. Phys.
Rev. Lett. 98, 206402 (2007).] where we considered the case of a static
condensate. In that case, the condensate forms either a glassy insulating phase
at low polariton density (strong localization), or a superfluid phase above the
percolation threshold. We also show the calculation of the first order spatial
coherence of the condensate versus the condensate density. In the second part,
we consider the case of a propagating non-interacting condensate which is
always localized because of Anderson localization. The localization length is
calculated in the Born approximation. The impact of the finite polariton life
time is taken into account as well. In the last section we consider the case of
a propagating interacting condensate where the three regimes of strong
localization, Anderson localization, and superfluid behavior are accessible.
The localization length is calculated versus the system parameters. The
localization length is strongly modified with respect to the non-interacting
case. It is infinite in the superfluid regime whereas it is strongly reduced if
the fluid flows with a supersonic velocity.Comment: chapter for a book "Exciton Polaritons in Microcavities: New
Frontiers" by Springer (2012), the original publication is available at
http://www.springerlink.co
Structural studies on ceramides as lithiated adducts by low energy collisional-activated dissociation tandem mass spectrometry with electrospray ionization
High-precision photometry by telescope defocussing - VI. WASP-24, WASP-25 and WASP-26
The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013/) under grant agreement nos. 229517 and 268421. This publication was supported by grants NPRP 09-476-1-078 and NPRP X-019-1-006 from Qatar National Research Fund (a member of Qatar Foundation). TCH acknowledges financial support from the Korea Research Council for Fundamental Science and Technology (KRCF) through the Young Research Scientist Fellowship Programme and is supported by the KASI (Korea Astronomy and Space Science Institute) grant 2012-1-410-02/2013-9-400-00. SG, XW and XF acknowledge the support from NSFC under the grant no. 10873031. The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (grant agreement no. 267864). DR, YD, AE, FF (ARC), OW (FNRS research fellow) and J Surdej acknowledge support from the Communauté française de Belgique – Actions de recherche concertées – Académie Wallonie-Europe.We present time series photometric observations of 13 transits in the planetary systems WASP-24, WASP-25 and WASP-26. All three systems have orbital obliquity measurements, WASP-24 and WASP-26 have been observed with Spitzer, and WASP-25 was previously comparatively neglected. Our light curves were obtained using the telescope-defocussing method and have scatters of 0.5–1.2 mmag relative to their best-fitting geometric models. We use these data to measure the physical properties and orbital ephemerides of the systems to high precision, finding that our improved measurements are in good agreement with previous studies. High-resolution Lucky Imaging observations of all three targets show no evidence for faint stars close enough to contaminate our photometry. We confirm the eclipsing nature of the star closest to WASP-24 and present the detection of a detached eclipsing binary within 4.25 arcmin of WASP-26.Publisher PDFPeer reviewe
Post-Optimality Pareto-Robustness Analysis of an Earth-Observation Satellite Mission
In this paper a methodology for post-optimality studies to assess the robustness of the Pareto-optimal solutions, computed with a multi-objective optimization algorithm, is presented. The proposed Pareto-Robust Optimization Approach (PROA) is based on factorial design for sampling the design region in the neighborhood of the Pareto-optimal solutions. It allows for estimating a metric for the Pareto-Robustness and contributes to improving convergence of the known Pareto-front towards the true Pareto-front. Further, the sensitivity of the performance (the objectives of the analysis) to the dispersion of the design variables is analyzed using variance decomposition techniques. The shape of the design space is studied using the response surfaces method without additional computational cost. The proposed approach is applied to three validation test cases and to the design of a satellite Earth-observation mission for disaster monitoring. The results show that PROA can correctly detect Pareto-robust solutions on the Pareto front and that it provides additional Pareto-optimal solutions at the same time, eventually improving the original known Pareto front. Further, PROA shows its potentialities in effectively narrowing the search-space to only one limited portion. In the case of the Earth-observation mission, the study demonstrates the possibility to enable and promote trade-offs amongst the engineering-team members to obtain an effective decision-making process. The solution identified as the most Pareto-robust one can be considered quite uncommon, but still very reasonable due to the assumptions, presenting a satellite in a non sun-synchronous Medium Earth Orbi
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