30,899 research outputs found
Resource Letter: Gravitational Lensing
This Resource Letter provides a guide to a selection of the literature on
gravitational lensing and its applications. Journal articles, books, popular
articles, and websites are cited for the following topics: foundations of
gravitational lensing, foundations of cosmology, history of gravitational
lensing, strong lensing, weak lensing, and microlensing.Comment: Resource Letter, 2012, in press
(http://ajp.dickinson.edu/Readers/resLetters.html); 21 pages, no figures;
diigo version available at
http://groups.diigo.com/group/gravitational-lensin
Luminous Satellites II: Spatial Distribution, Luminosity Function and Cosmic Evolution
We infer the normalization and the radial and angular distributions of the
number density of satellites of massive galaxies
() between redshifts 0.1 and 0.8 as a function
of host stellar mass, redshift, morphology and satellite luminosity. Exploiting
the depth and resolution of the COSMOS HST images, we detect satellites up to
eight magnitudes fainter than the host galaxies and as close as 0.3 (1.4)
arcseconds (kpc). Describing the number density profile of satellite galaxies
to be a projected power law such that P(R)\propto R^{\rpower}, we find
\rpower=-1.1\pm 0.3. We find no dependency of \rpower on host stellar mass,
redshift, morphology or satellite luminosity. Satellites of early-type hosts
have angular distributions that are more flattened than the host light profile
and are aligned with its major axis. No significant average alignment is
detected for satellites of late-type hosts. The number of satellites within a
fixed magnitude contrast from a host galaxy is dependent on its stellar mass,
with more massive galaxies hosting significantly more satellites. Furthermore,
high-mass late-type hosts have significantly fewer satellites than early-type
galaxies of the same stellar mass, likely a result of environmental
differences. No significant evolution in the number of satellites per host is
detected. The cumulative luminosity function of satellites is qualitatively in
good agreement with that predicted using subhalo abundance matching techniques.
However, there are significant residual discrepancies in the absolute
normalization, suggesting that properties other than the host galaxy luminosity
or stellar mass determine the number of satellites.Comment: 23 pages, 12 figures, Accepted for publication in the Astrophysical
Journa
Collisional modelling of the debris disc around HIP 17439
We present an analysis of the debris disc around the nearby K2 V star HIP
17439. In the context of the Herschel DUNES key programme the disc was observed
and spatially resolved in the far-IR with the Herschel PACS and SPIRE
instruments. In a first model, Ertel et al. (2014) assumed the size and radial
distribution of the circumstellar dust to be independent power laws. There, by
exploring a very broad range of possible model parameters several scenarios
capable of explaining the observations were suggested. In this paper, we
perform a follow-up in-depth collisional modelling of these scenarios trying to
further distinguish between them. In our models we consider collisions, direct
radiation pressure, and drag forces, i.e. the actual physical processes
operating in debris discs. We find that all scenarios discussed in Ertel et al.
are physically sensible and can reproduce the observed SED along with the PACS
surface brightness profiles reasonably well. In one model, the dust is produced
beyond 120au in a narrow planetesimal belt and is transported inwards by
Poynting-Robertson and stellar wind drag. A good agreement with the observed
radial profiles would require stellar winds by about an order of magnitude
stronger than the solar value, which is not supported, although not ruled out,
by observations. Another model consists of two spatially separated planetesimal
belts, a warm inner and a cold outer one. This scenario would probably imply
the presence of planets clearing the gap between the two components. Finally,
we show qualitatively that the observations can be explained by assuming the
dust is produced in a single, but broad planetesimal disc with a surface
density of solids rising outwards, as expected for an extended disc that
experiences a natural inside-out collisional depletion. Prospects of
discriminating between the competing scenarios by future observations are
discussed.Comment: Astronomy and Astrophysics (accepted for publication). 11 pages, 8
figure
A Dynamical Analysis of the Proposed Circumbinary HW Virginis Planetary System
In 2009, the discovery of two planets orbiting the evolved binary star system
HW Virginis was announced, based on systematic variations in the timing of
eclipses between the two stars. The planets invoked in that work were
significantly more massive than Jupiter, and moved on orbits that were mutually
crossing - an architecture which suggests that mutual encounters and strong
gravitational interactions are almost guaranteed. In this work, we perform a
highly detailed analysis of the proposed HW Vir planetary system. First, we
consider the dynamical stability of the system as proposed in the discovery
work. Through a mapping process involving 91,125 individual simulations, we
find that the system is so unstable that the planets proposed simply cannot
exist, due to mean lifetimes of less than a thousand years across the whole
parameter space. We then present a detailed re-analysis of the observational
data on HW Vir, deriving a new orbital solution that provides a very good fit
to the observational data. Our new analysis yields a system with planets more
widely spaced, and of lower mass, than that proposed in the discovery work, and
yields a significantly greater (and more realistic) estimate of the uncertainty
in the orbit of the outermost body. Despite this, a detailed dynamical analysis
of this new solution similarly reveals that it also requires the planets to
move on orbits that are simply not dynamically feasible. Our results imply that
some mechanism other than the influence of planetary companions must be the
principal cause of the observed eclipse timing variations for HW Vir. If the
sys- tem does host exoplanets, they must move on orbits differing greatly from
those previously proposed. Our results illustrate the critical importance of
performing dynamical analyses as a part of the discovery process for
multiple-planet exoplanetary systems.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
A Linked Data Approach to Sharing Workflows and Workflow Results
A bioinformatics analysis pipeline is often highly elaborate, due to the inherent complexity of biological systems and the variety and size of datasets. A digital equivalent of the âMaterials and Methodsâ section in wet laboratory publications would be highly beneficial to bioinformatics, for evaluating evidence and examining data across related experiments, while introducing the potential to find associated resources and integrate them as data and services. We present initial steps towards preserving bioinformatics âmaterials and methodsâ by exploiting the workflow paradigm for capturing the design of a data analysis pipeline, and RDF to link the workflow, its component services, run-time provenance, and a personalized biological interpretation of the results. An example shows the reproduction of the unique graph of an analysis procedure, its results, provenance, and personal interpretation of a text mining experiment. It links data from Taverna, myExperiment.org, BioCatalogue.org, and ConceptWiki.org. The approach is relatively âlight-weightâ and unobtrusive to bioinformatics users
Mechanisms of Individual Differences in Impulsive and Risky Choice in Rats
Citation: Kirkpatrick, K., Marshall, A. T., & Smith, A. P. (2015). Mechanisms of Individual Differences in Impulsive and Risky Choice in Rats. Comparative Cognition & Behavior Reviews, 10. Retrieved from http://comparative-cognition-and-behavior-reviews.org/2015/vol10_kirkpatrick_marshall_smith/Mechanisms of Individual Differences in Impulsive and Risky Choice in Rats Kimberly Kirkpatrick Department of Psychological Sciences, Kansas State University Andrew T. Marshall Department of Psychological Sciences, Kansas State University Aaron P
Short gamma-ray bursts within 200 Mpc
We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14âyr of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance âČ100 Mpc and four plausible candidates in the range 100âMpc âČ DââČ 200âMpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses (â âČ10â3Mââ ) of lanthanide-poor ejecta or unfavorable orientations (Ξ_(obs) âł 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is 1.3^(+1.7)_(â0.8) yrâ»Âč (68 perâcent confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of âČ2.0 yrâ»Âč (90 perâcent confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi
Experimental tests of hidden variable theories from dBB to Stochastic Electrodynamics
In this paper we present some of our experimental results on testing hidden
variable theories, which range from Bell inequalities measurements to a
conclusive test of stochastic electrodynamics
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