6,016 research outputs found
Correlated adaptation of agents in a simple market: a statistical physics perspective
We discuss recent work in the study of a simple model for the collective
behaviour of diverse speculative agents in an idealized stockmarket, considered
from the perspective of the statistical physics of many-body systems. The only
information about other agents available to any one is the total trade at time
steps. Evidence is presented for correlated adaptation and phase
transitions/crossovers in the global volatility of the system as a function of
appropriate information scaling dimension. Stochastically controlled
irrationally of individual agents is shown to be globally advantageous. We
describe the derivation of the underlying effective stochastic differential
equations which govern the dynamics, and make an interpretation of the results
from the point of view of the statistical physics of disordered systems.Comment: 15 Pages. 5 figure
Les biomarqueurs dans la maladie de Fabry: relation entre Sphingosine-1 phosphate et Lyso-Gb3
Problématique :
La maladie de Fabry est une maladie métabolique à stockage lysosomal. C'est une maladie héreditaire à transmission récessive qui concerne l'enzyme alpha-Galactosidase A. Le gène de l'alpha-Galactosidase A (GLA) se trouve au niveau du bras long du chromosome X «carté en Xq21.33-Xq22 ». L'enzyme muté ne recouvre plus son rôle catabolisateur et il ne métabolise pas le substrat globotriaosylceramide (Gb3). Par conséquence le Gb3 s'accumule dans tous les tissus. Dans les parois des vaisseaux sanguins le Gb3 s'accumule dans l'endothelium, la tunique interne des vaisseaux sanguins. Ce déficit métabolique se traduit par l'épaississement de la paroi vasculaire, des processus d'infarctus et ischémies du tissu cardiaque, rénal et cérébral. L'implication cardiaque de la maladie de Fabry est décrite chez plus de 78% des patients affectés par la maladie et se manifeste par une hypertrophie cardiaque du ventricule gauche. Toutefois, il n'existe pas de relation étroite entre hypertrophie cardiaque et le Gb3. La sphingosine 1-phosphate à été identifiée dans notre laboratoire et proposée comme facteur de croissance à l'origine du remodelage cardiovasculaire. De plus, la Globotriaosylsphingosine (Lyso-Gb3) à été aussi proposée comme facteur vasoactif chez les patients Fabry.
Objectif :
L'identification d'un biomarqueur pour le diagnostic et le suivi thérapeutique de la maladie de Fabry représente une domaine d'investigation active en recherche scientifique. Le Gb3 plasmatique ou dans les urines, la biopsie rénale ou cardiaque qui est mis en évidence grâce à la microscopie électronique sous forme de corps concentrique lamellaires, constituent les biomarqueurs classiques de la maladie de Fabry. Dernièrement, le Lyso-Gb3 et le Sphingosine-1 phosphate (S1P) ont été proposés comme marqueurs du remodelage cardiovasculaire. Le but de ce travail est de rassembler et de discuter la littérature concernant ces nouveaux marqueurs et, d'étudier une possible interaction entre Lyso-Gb3 et le S1P.
Méthodologie :
Rassembler la littérature scientifique et analyser l'implication de ces marqueurs dans la maladie de Fabry et leur effets cardiovasculaires. De plus, un travail expérimental est effectué. Ce travail consiste en l'identification d'une relation possible entre le Lyso-Gb3 et le S1P.
Résultats :
Avec ce travail on a cherché à actualiser et mettre à jour les notions concernant les biomarqueurs qui prennent place dans cette pathologie et les connaissances qu'on possède à ce jour sur les manifestations cardiovasculaires et neurologiques.La recherche d'un biomarqueur prime par le fait qu'un nombre considerable de patients est sous-diagnostiqués pour la maladie de Fabry et que entre les taux de substrat enzymatique accumulé dans les tissus et l'hypertrophie cardiaque, on peut constater une discordance. Grâce à ce travail expérimental, on a exclue la possibilité d'un effet précurseur du lyso-Gb3 pour le S1P. Nous avons montré que le Lyso-Gb3 est reconnu par les récepteurs du S1P avec des effets commun pour les S1P1-3 et différents pour le S1P2. Les taux du Lyso-Gb3 et du S1P doivent être mesuré chez les patients Fabry et une stratégie thérapeutique doit prendre en compte le rapport S1P/Lyso-Gb3
Atmosphere above a large solar pore
A large solar pore with a granular light bridge was observed on October 15,
2008 with the IBIS spectrometer at the Dunn Solar Telescope and a 69-min long
time series of spectral scans in the lines Ca II 854.2 nm and Fe I 617.3 nm was
obtained. The intensity and Doppler signals in the Ca II line were separated.
This line samples the middle chromosphere in the core and the middle
photosphere in the wings. Although no indication of a penumbra is seen in the
photosphere, an extended filamentary structure, both in intensity and Doppler
signals, is observed in the Ca II line core. An analysis of morphological and
dynamical properties of the structure shows a close similarity to a
superpenumbra of a sunspot with developed penumbra. A special attention is paid
to the light bridge, which is the brightest feature in the pore seen in the Ca
II line centre and shows an enhanced power of chromospheric oscillations at 3-5
mHz. Although the acoustic power flux in the light bridge is five times higher
than in the "quiet" chromosphere, it cannot explain the observed brightness.Comment: 6 pages, 3 figures, accepted in Journal of Physics: Conference Serie
Imaging Spectropolarimetry with IBIS: Evolution of Bright Points in the Quiet Sun
We present the results from first spectropolarimetric observations of the
solar photosphere acquired at the Dunn Solar Telescope with the Interferometric
Bidimensional Spectrometer. Full Stokes profiles were measured in the Fe I
630.15 nm and Fe I 630.25 nm lines with high spatial and spectral resolutions
for 53 minutes, with a Stokes V noise of 0.003 the continuum intensity level.
The dataset allows us to study the evolution of several magnetic features
associated with G-band bright points in the quiet Sun. Here we focus on the
analysis of three distinct processes, namely the coalescence, fragmentation and
cancellation of G-band bright points. Our analysis is based on a SIR inversion
of the Stokes I and V profiles of both Fe I lines. The high spatial resolution
of the G-band images combined with the inversion results helps to interpret the
undergoing physical processes. The appearance (dissolution) of high-contrast
G-band bright points is found to be related to the local increase (decrease) of
the magnetic filling factor, without appreciable changes in the field strength.
The cancellation of opposite-polarity bright points can be the signature of
either magnetic reconnection or the emergence/submergence of magnetic loops.Comment: 4 pages, 5 figures, accepted for publication in ApJ Letter
Super-diffusion versus competitive advection: a simulation
Magnetic element tracking is often used to study the transport and diffusion
of the magnetic field on the solar photosphere. From the analysis of the
displacement spectrum of these tracers, it has been recently agreed that a
regime of super-diffusivity dominates the solar surface. Quite habitually this
result is discussed in the framework of fully developed turbulence. But the
debate whether the super-diffusivity is generated by a turbulent dispersion
process, by the advection due to the convective pattern, or by even another
process, is still open, as is the question about the amount of diffusivity at
the scales relevant to the local dynamo process. To understand how such
peculiar diffusion in the solar atmosphere takes places, we compared the
results from two different data-sets (ground-based and space-borne) and
developed a simulation of passive tracers advection by the deformation of a
Voronoi network. The displacement spectra of the magnetic elements obtained by
the data-sets are consistent in retrieving a super-diffusive regime for the
solar photosphere, but the simulation also shows a super-diffusive displacement
spectrum: its competitive advection process can reproduce the signature of
super-diffusion. Therefore, it is not necessary to hypothesize a totally
developed turbulence regime to explain the motion of the magnetic elements on
the solar surface
Chromospheric heating by acoustic waves compared to radiative cooling
Acoustic and magnetoacoustic waves are among the possible candidate
mechanisms that heat the upper layers of solar atmosphere. A weak chromospheric
plage near a large solar pore NOAA 11005 was observed on October 15, 2008 in
the lines Fe I 617.3 nm and Ca II 853.2 nm with the Interferometric
Bidimemsional Spectrometer (IBIS) attached to the Dunn Solar Telescope.
Analyzing the Ca II observations with spatial and temporal resolutions of 0.4"
and 52 s, the energy deposited by acoustic waves is compared with that released
by radiative losses. The deposited acoustic flux is estimated from power
spectra of Doppler oscillations measured in the Ca II line core. The radiative
losses are calculated using a grid of seven 1D hydrostatic semi-empirical model
atmospheres. The comparison shows that the spatial correlation of maps of
radiative losses and acoustic flux is 72 %. In quiet chromosphere, the
contribution of acoustic energy flux to radiative losses is small, only of
about 15 %. In active areas with photospheric magnetic field strength between
300 G and 1300 G and inclination of 20-60 degrees, the contribution increases
from 23 % (chromospheric network) to 54 % (a plage). However, these values have
to be considered as lower limits and it might be possible that the acoustic
energy flux is the main contributor to the heating of bright chromospheric
network and plages.Comment: 9 pages, 10 figures. Accepted for publication in The Astrophysical
Journa
Effect of shape and thickness of asbestos bundles and fibres on EDS microanalysis: A Monte Carlo simulation
Quantitative microanalysis of tiny asbestos mineral fibres by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDS) still represents a complex analytical issue. This complexity arises from the variable fibre shape and small thickness (< 5 μm) compared with the penetration of the incident electron beam. Here, we present the results of Monte Carlo simulations of chrysotile, crocidolite and amosite fibres (and bundles of fibres) of circular and square section and thicknesses from 0.1 μm to 10 μm, to investigate the effect of shape and thickness on SEM-EDS microanalysis. The influence of shape and thickness on the simulated spectrum was investigated for electron beam energies of 5, 15 and 25 keV, respectively. A strong influence of the asbestos bundles and fibres shape and thickness on the detected EDS X-ray intensity was observed. The X-ray intensity trends as a function of fibre thickness showed a non-linear dependence for all the elements and minerals. In general, the X-ray intensities showed a considerable reduction for thicknesses below about 5 μm at 5 keV, 2 μm at 15 keV, and 5 μm at 25 keV. Correction parameters, k-ratios, for the asbestos fibre thickness effect, are reported
Risk management in solitary agricultural work: new technologies for handling emergency and falls from great heights (SHADE)
Solitary work and agricultural activities are the scenarios of a large number of severe injuries and deaths, also because first aid may be difficult to achieve in isolated locations. This work proposes a technology available on smartphones that allows triggering an emergency call when a fall from height or an unconsciousness state is detected. The results of several tests, which include different detection algorithms and scenarios, are reported in this work. Tests performed with the aid of a dummy have allowed developing a reliable algorithm for the detection of dangerous situations. This system is available as an Android application
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