211,420 research outputs found
Phase transition in a sexual age-structured model of learning foreign languages
The understanding of language competition helps us to predict extinction and
survival of languages spoken by minorities. A simple agent-based model of a
sexual population, based on the Penna model, is built in order to find out
under which circumstances one language dominates other ones. This model
considers that only young people learn foreign languages. The simulations show
a first order phase transition where the ratio between the number of speakers
of different languages is the order parameter and the mutation rate is the
control one.Comment: preliminary version, to be submitted to Int. J. Mod. Phys.
Shape of the 4.438 MeV gamma-ray line of ^12C from proton and alpha-particle induced reactions on ^12C and ^16O
We calculated in detail the angular distribution of gamma-rays and the
resulting shape of the gamma-ray line produced by the nuclear deexcitation of
the 4.439 MeV state of ^12C following proton and alpha-particle interactions
with ^12C and ^16O in the energy range from threshold to 100 MeV per nucleon,
making use of available experimental data. In the proton energy range from 8.6
to 20 MeV, the extensive data set of a recent accelerator experiment on
gamma-ray line shapes and angular distributions was used to deduce
parameterizations for the gamma-ray emission of the 2^+, 4.439 MeV state of
^12C following inelastic proton scattering off ^12C and proton induced
spallation of ^16O. At higher proton energies and for alpha-particle induced
reactions, optical model calculations were the main source to obtain the needed
reaction parameters for the calculation of gamma-ray line shapes and angular
distributions. Line shapes are predicted for various interaction scenarios of
accelerated protons and alpha-particles in solar flares.Comment: REVTeX, 9 pages, 8 figures, 4 tables, to be published by Phys. Rev.
A 12 ÎŒm ISOCAM survey of the ESO-Sculptor field
We present a detailed reduction of a mid-infrared 12 ÎŒm (LW10 filter) ISOCAM open time observation performed on the ESOSculptor
Survey field (Arnouts et al. 1997, A&AS, 124, 163). A complete catalogue of 142 sources (120 galaxies and 22 stars),
detected with high significance (equivalent to 5Ï), is presented above an integrated flux density of 0.24 mJy. Star/galaxy separation
is performed by a detailed study of colour-colour diagrams. The catalogue is complete to 1 mJy and, below this flux density, the
incompleteness is corrected using two independent methods. The first method uses stars and the second uses optical counterparts of
the ISOCAM galaxies; these methods yield consistent results. We also apply an empirical flux density calibration using stars in the
field. For each star, the 12 ÎŒm flux density is derived by fitting optical colours from a multi-band Ï^2 to stellar templates (BaSel-2.0)
and using empirical optical-IR colour-colour relations. This article is a companion analysis to our 2007 paper (Rocca-Volmerange
et al. 2007, A&A, 475, 801) where the 12 ÎŒm faint galaxy counts are presented and analysed per galaxy type with the evolutionary
code PĂGASE.3
Medical education on fitness to drive : a survey of all UK medical schools
Aim: To identify the extent to which medical aspects of fitness to drive (FTD) are taught within UK medical schools.
Methods: A survey of all 32 UK medical schools. In-depth interviews with a range of staff at two medical schools; telephone survey of 30 schools.
Results: Two thirds of schools reported specific teaching on medical aspects of FTD but few covered it in any depth or in relation to specific medical conditions. Only one school taught FTD in relation to elderly medicine. FTD was an examination topic at only 12 schools.
Conclusion: Teaching on FTD is inconsistent across UK medical schools. Many new doctors will graduate with limited knowledge of medical aspects of FTD
Dissociation of vortex stacks into fractional-flux vortices
We discuss the zero field superconducting phase transition in a finite system
of magnetically coupled superconducting layers. Transverse screening is
modified by the presence of other layers resulting in topological excitations
with fractional flux. Vortex stacks trapping a full flux and present at any
finite temperature undergo an evaporation transition which corresponds to the
depairing of fractional-flux vortices in individual layers. We propose an
experiment with a bi-layer system allowing us to identify the dissociation of
bound vortex molecules.Comment: 4 pages, 1 figure; revised version, to appear in Phys. Rev. Let
The 12 ÎŒm ISO-ESO-Sculptor and 24 ÎŒm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(â„10^(12) L_â) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 ÎŒm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 ÎŒm. Then we analyse the 12 ÎŒm (ISO-ESS) and the 24 ÎŒm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the ânormalâ scenarios in our evolutionary code PĂGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 ÎŒm and 24 ÎŒm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 ÎŒm and 24 ÎŒm counts and based on observed 12 ÎŒm and 25 ÎŒm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PĂGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 ÎŒm, 15 ÎŒm (ISO), and 24 ÎŒm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
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