21,135 research outputs found
A fuzzy approach for competency characterisation based on a work situation analysis.
International audienceThe purpose of this work is to give a decision support to meet requirements in competencies management. We assume that the building, the development, and the use of each competency need the concurrence of different kinds of interactions in the real work situation. The competency characteristics can be evaluated by an expert within an analysis of work situation, to get an interpretation of these interactions. In this sense, we propose a qualitative method of competency characterisation based on a formal representation of the situation. The aim of this paper is not to give all mathematical details of a fuzzy approach but rather to present how qualitative knowledge about the situation can be used to characterise associated competency
Gravitational waves from resolvable massive black hole binary systems and observations with Pulsar Timing Arrays
Massive black holes are key components of the assembly and evolution of
cosmic structures and a number of surveys are currently on-going or planned to
probe the demographics of these objects and to gain insight into the relevant
physical processes. Pulsar Timing Arrays (PTAs) currently provide the only
means to observe gravitational radiation from massive black hole binary systems
with masses >10^7 solar masses. The whole cosmic population produces a
stochastic background that could be detectable with upcoming Pulsar Timing
Arrays. Sources sufficiently close and/or massive generate gravitational
radiation that significantly exceeds the level of the background and could be
individually resolved. We consider a wide range of massive black hole binary
assembly scenarios, we investigate the distribution of the main physical
parameters of the sources, such as masses and redshift, and explore the
consequences for Pulsar Timing Arrays observations. Depending on the specific
massive black hole population model, we estimate that on average at least one
resolvable source produces timing residuals in the range ~5-50 ns. Pulsar
Timing Arrays, and in particular the future Square Kilometre Array (SKA), can
plausibly detect these unique systems, although the events are likely to be
rare. These observations would naturally complement on the high-mass end of the
massive black hole distribution function future surveys carried out by the
Laser Interferometer Space Antenna (LISA)Comment: 12 pages, 10 figures, accepted for publication in MNRAS. Results
revised (differences within a factor of two) after a bug in the code for
generating the timing residuals has been fixe
Close Galaxy Pairs at z = 3: A Challenge to UV Luminosity Abundance Matching
We use a sample of z~3 Lyman Break Galaxies (LBGs) to examine close pair
clustering statistics in comparison to LCDM-based models of structure
formation. Samples are selected by matching the LBG number density and by
matching the observed LBG 3-D correlation function of LBGs over the two-halo
term region. We show that UV-luminosity abundance matching cannot reproduce the
observed data, but if subhalos are chosen to reproduce the observed clustering
of LBGs we are able to reproduce the observed LBG pair fraction, (Nc), defined
as the average number of companions per galaxy. This model suggests an over
abundance of LBGs by a factor of ~5 over those observed, suggesting that only 1
in 5 halos above a fixed mass hosts a galaxy with LBG-like UV luminosity
detectable via LBG selection techniques. We find a total observable close pair
fraction of 23 \pm 0.6% (17.7 \pm 0.5%) using a prototypical cylinder radius in
our overdense fiducial model and 8.3 \pm 0.5% (5.6 \pm 0.2%) in an abundance
matched model (impurity corrected). For the matched spectroscopic slit
analysis, we find Ncs = 5.1\pm0.2% (1.68\pm0.02%), the average number of
companions observed serendipitously in our for fiducial slits (abundance
matched), whereas the observed fraction of serendipitous spectroscopic close
pairs is 4.7\pm1.5 per cent using the full LBG sample and 7.1\pm2.3% for a
subsample with higher signal-to-noise ratio. We show that the standard method
of halo assignment fails to reproduce the break in the LBG close pair behavior
at small scale. To reconcile these discrepancies we suggest that a plausible
fraction of LBGs in close pairs with lower mass than our sample experience
interaction-induced enhanced star formation that boosts their luminosity
sufficiently to be detected in observational sample but are not included in the
abundance matched simulation sample.Comment: 18 pages, 12 figures, 1 table, published in MNRA
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