6,295 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
Why evolutionary psychology should abandon modularity
A debate surrounding modularity—the notion that the mind may be exclusively composed of distinct systems or modules—has held philosophers and psychologists captive for nearly 40 years. Concern about this thesis—which has come to be known as the massive modularity debate—serves as the primary grounds for skepticism of evolutionary psychology’s claims about the mind. In this article we argue that the entirety of this debate, and the very notion of massive modularity itself, is ill-posed and confused. In particular, it is based on a confusion about the level of analysis (or reduction) at which one is approaching the mind. Here we provide a framework for clarifying at what level of analysis one is approaching the mind and explain how a systemic failure to distinguish between different levels of analysis has led to profound misunderstandings of not only evolutionary psychology but also of the entire cognitivist enterprise of approaching the mind at the level of the mechanism. We furthermore suggest that confusions between different levels of analysis are endemic throughout the psychological sciences—extending well beyond issues of modularity and evolutionary psychology. Therefore, researchers in all areas should take preventive measures to avoid this confusion in the future
Polariton laser using single micropillar GaAs-GaAlAs semiconductor cavities
Polariton lasing is demonstrated on the zero dimensional states of single
GaAs/GaAlAs micropillar cavities. Under non resonant excitation, the measured
polariton ground state occupancy is found to be as large as . Changing
the spatial excitation conditions, competition between several polariton lasing
modes is observed, ruling out Bose-Einstein condensation. When the polariton
state occupancy increases, the emission blueshift is the signature of
self-interaction within the half-light half-matter polariton lasing mode.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Letter
VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit
HR8799 is orbited by at least four giant planets, making it a prime target
for the recently commissioned Spectro-Polarimetric High-contrast Exoplanet
REsearch (VLT/SPHERE). As such, it was observed on five consecutive nights
during the SPHERE science verification in December 2014. We aim to take full
advantage of the SPHERE capabilities to derive accurate astrometric
measurements based on H-band images acquired with the Infra-Red Dual-band
Imaging and Spectroscopy (IRDIS) subsystem, and to explore the ultimate
astrometric performance of SPHERE in this observing mode. We also aim to
present a detailed analysis of the orbital parameters for the four planets. We
report the astrometric positions for epoch 2014.93 with an accuracy down to 2.0
mas, mainly limited by the astrometric calibration of IRDIS. For each planet,
we derive the posterior probability density functions for the six Keplerian
elements and identify sets of highly probable orbits. For planet d, there is
clear evidence for nonzero eccentricity (), without completely
excluding solutions with smaller eccentricities. The three other planets are
consistent with circular orbits, although their probability distributions
spread beyond , and show a peak at for planet e. The
four planets have consistent inclinations of about with respect to the
sky plane, but the confidence intervals for the longitude of ascending node are
disjoint for planets b and c, and we find tentative evidence for
non-coplanarity between planets b and c at the level.Comment: 23 pages, 14 figure
An earth pole-sitter using hybrid propulsion
In this paper we investigate optimal pole-sitter orbits using hybrid solar sail and solar electric propulsion (SEP). A pole-sitter is a spacecraft that is constantly above one of the Earth's poles, by means of a continuous thrust. Optimal orbits, that minimize propellant mass consumption, are found both through a shape-based approach, and solving an optimal control problem, using a direct method based on pseudo-spectral techniques. Both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows consistent savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions (more than 8 years), a hybrid spacecraft, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft
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