1,493 research outputs found
Coev-web: a web platform designed to simulate and evaluate coevolving positions along a phylogenetic tree.
BACKGROUND: Available methods to simulate nucleotide or amino acid data typically use Markov models to simulate each position independently. These approaches are not appropriate to assess the performance of combinatorial and probabilistic methods that look for coevolving positions in nucleotide or amino acid sequences.
RESULTS: We have developed a web-based platform that gives a user-friendly access to two phylogenetic-based methods implementing the Coev model: the evaluation of coevolving scores and the simulation of coevolving positions. We have also extended the capabilities of the Coev model to allow for the generalization of the alphabet used in the Markov model, which can now analyse both nucleotide and amino acid data sets. The simulation of coevolving positions is novel and builds upon the developments of the Coev model. It allows user to simulate pairs of dependent nucleotide or amino acid positions.
CONCLUSIONS: The main focus of our paper is the new simulation method we present for coevolving positions. The implementation of this method is embedded within the web platform Coev-web that is freely accessible at http://coev.vital-it.ch/, and was tested in most modern web browsers
Lipome geant parapharynge
Lâespace parapharyngĂ© est une rĂ©gion anatomique complexe. Seulement 0,5% des tumeurs de la tĂȘte et cou se localisent Ă ce niveau. elles sont essentiellement reprĂ©sentĂ©es par les tumeurs nerveuses, salivaires et vasculaires, les lipomes ont Ă©tĂ© exceptionnellement dĂ©crits. Notre observation a un double intĂ©rĂȘt : documenter cette raretĂ© et faire une mise au point sur lâabord chirurgical de cette rĂ©gion.Mots clĂ©s :Lipome, espace parapharyngĂ©, chirurgi
A protosolar nebula origin for the ices agglomerated by Comet 67P/Churyumov-Gerasimenko
The nature of the icy material accreted by comets during their formation in
the outer regions of the protosolar nebula is a major open question in
planetary science. Some scenarios of comet formation predict that these bodies
agglomerated from crystalline ices condensed in the protosolar nebula.
Concurrently, alternative scenarios suggest that comets accreted amorphous ice
originating from the interstellar cloud or from the very distant regions of the
protosolar nebula. On the basis of existing laboratory and modeling data, we
find that the N/CO and Ar/CO ratios measured in the coma of the Jupiter
family comet 67P/Churyumov-Gerasimenko by the ROSINA instrument aboard the
European Space Agency's Rosetta spacecraft match those predicted for gases
trapped in clathrates. If these measurements are representative of the bulk
N/CO and Ar/CO ratios in 67P/Churyumov-Gerasimenko, it implies that the
ices accreted by the comet formed in the nebula and do not originate from the
interstellar medium, supporting the idea that the building blocks of outer
solar system bodies have been formed from clathrates and possibly from pure
crystalline ices. Moreover, because 67P/Churyumov-Gerasimenko is impoverished
in Ar and N, the volatile enrichments observed in Jupiter's atmosphere
cannot be explained solely via the accretion of building blocks with similar
compositions and require an additional delivery source. A potential source may
be the accretion of gas from the nebula that has been progressively enriched in
heavy elements due to photoevaporation.Comment: The Astrophysical Journal Letters, in pres
Reactivity of 3-hydroxy-3-methyl-2-butanone: Photolysis and \OH\ reaction kinetics
International audienceHydroxycarbonyl compounds are important secondary reaction products in the oxidation of Volatile Organic Compounds (VOCs) in the atmosphere. The atmospheric fate of these oxygenated \VOCs\ is however poorly understood, especially the relevance of the photolytic pathway. In this work, a combined investigation of the photolysis and temperature-dependent \OH\ radical reaction of 3-hydroxy-3-methyl-2-butanone (3H3M2B) is presented. A photolysis lifetime of about 4-5 days was estimated with a global quantum yield of 0.10. The \OH\ reaction rate coefficient follows the Arrhenius trend (298-356 K) and could be modelled through the following expression: k3H3M2B(T) = (5.12 ± 0.07) Ă 10â12 exp(â563 ± 119/T) in cm3 moleculeâ1 sâ1. A 3H3M2B atmospheric lifetime of 15 days towards the \OH\ radical was evaluated. Our results showed that the photolysis pathway is the major degradation channel for 3H3M2B. Photolysis products were identified and quantified in the present work with a carbon balance of around 80% enabling a reaction mechanism to be proposed. The present work underlines the need for further studies on the atmospheric chemistry of oxygenated VOCs
Consistently computing the K -> pi long distance weak transition
First we extract the long-distance (LD) weak matrix element from certain data
and give compatible theoretical estimates. We also link this LD scale to the
single-quark-line (SQL) transition scale and then test the latter SQL scale
against the decuplet weak decay amplitude ratio. Finally, we study LD decay.
All of these experimental and theoretical values are in good agreement. We
deduce an average value from eleven experimental determinations compared to the
theoretical SQL values average.Comment: 19 pages, 9 figures minor change to the Conclusions and abstract
sectio
Detection and characterization of Io's atmosphere from high-resolution 4-{\mu}m spectroscopy
We report on high-resolution and spatially-resolved spectra of Io in the 4.0
{\mu}m region, recorded with the VLT/CRIRES instrument in 2008 and 2010, which
provide the first detection of the {\nu}1 + {\nu}3 band of SO2 in Io's
atmosphere. Data are analyzed to constrain the latitudinal, longitudinal, and
diurnal distribution of Io's SO2 atmosphere as well as its characteristic
temperature. equatorial SO2 column densities clearly show longitudinal
asymmetry, but with a maximum of around 1.5e17 cm-2 at central meridian
longitude L = 200-220 and a minimum of around 3e16 cm-2 at L = 285-300, the
longitudinal pattern somewhat differs from earlier inferences from Ly {\alpha}
and thermal IR measurements. Within the accuracy of the measurements, no
evolution of the atmospheric density from mid-2008 to mid-2010 can be
distinguished. The decrease of the SO2 column density towards high latitude is
apparent, and the typical latitudinal extent of the atmosphere found to be (+-)
40{\deg} at half-maximum. The data show moderate diurnal variations of the
equatorial atmosphere, which is evidence for a partially sublimation-supported
atmospheric component. Compared to local noon, factor of 2 lower densities are
observed around 40{\deg} before and 80{\deg} after noon. Best-fit gas
temperatures range from 150 to 220 K, with a weighted mean value of 170 (+-) 20
K, which should represent the column-weighted mean kinetic temperature of Io's
atmosphere. Finally, although the data include clear thermal emission due to
Pillan (in outburst in July 2008) and Loki, no detectable enhancements in the
SO2 atmosphere above these volcanic regions are found, with an upper limit of
4e16 cm-2 at Pillan and 1e17 cm-2 at Loki.Comment: Accepted for publication in Icaru
Analytical theory for the initial mass function: CO clumps and prestellar cores
We derive an analytical theory of the prestellar core initial mass function
based on an extension of the Press-Schechter statistical formalism. With the
same formalism, we also obtain the mass spectrum for the non self-gravitating
clumps produced in supersonic flows. The mass spectrum of the self-gravitating
cores reproduces very well the observed initial mass function and identifies
the different mechanisms responsible for its behaviour. The theory predicts
that the shape of the IMF results from two competing contributions, namely a
power-law at large scales and an exponential cut-off (lognormal form) centered
around the characteristic mass for gravitational collapse. The cut-off exists
already in the case of pure thermal collapse, provided that the underlying
density field has a lognormal distribution. Whereas pure thermal collapse
produces a power-law tail steeper than the Salpeter value, dN/dlog M\propto
M^{-x}, with x=1.35, this latter is recovered exactly for the (3D) value of the
spectral index of the velocity power spectrum, n\simeq 3.8, found in
observations and in numerical simulations of isothermal supersonic turbulence.
Indeed, the theory predicts that x=(n+1)/(2n-4) for self-gravitating structures
and x=2-n'/3 for non self-gravitating structures, where n' is the power
spectrum index of log(rho). We show that, whereas supersonic turbulence
promotes the formation of both massive stars and brown dwarfs, it has an
overall negative impact on star formation, decreasing the star formation
efficiency. This theory provides a novel theoretical foundation to understand
the origin of the IMF and to infer its behaviour in different environments. It
also provides a complementary approach and useful guidance to numerical
simulations exploring star formation, while making testable predictions.Comment: To appear in Ap
Magnetic field structure around cores with very low luminosity objects
Aims. We carried out optical polarimetry of five dense cores, (IRAM 04191, L1521F, L328, L673-7, and L1014) which are found to harbour very low luminosity objects (VeLLOs; Lint âČ 0.1 Lâ). This study was conducted mainly to understand the role played by the magnetic field in the formation of very low and substellar mass range objects.
Methods. Light from the stars, while passing through the dust grains that are aligned with their short axis parallel to an external magnetic field, becomes linearly polarised. The polarisation position angles measured for the stars can provide the plane-of-the sky magnetic field orientation. Because the light in the optical wavelength range is most efficiently polarised by the dust grains typically found at the outer layers of the molecular clouds, optical polarimetry mostly traces the magnetic field orientation of the core envelope.
Results. The polarisation observations of stars projected on IRAM 04191, L328, L673-7, and L1014 were obtained in the R-band and those of L1521F were obtained in the V-band. The angular offsets between the envelope magnetic field direction (inferred from optical polarisation measurements) and the outflow position angles from the VeLLOs in IRAM 04191, L1521F, L328, L673-7, and L1014 are found to be 84°, 53°, 24°, 08°, and 15°, respectively. The mean value of the offsets for all the five clouds is ~ 37°. If we exclude IRAM 04191, the mean value reduces to become ~ 25°. In IRAM 04191, the offset between the projected envelope and the inner magnetic field (inferred from the submillimetre data obtained using SCUBA-POL) is found to be ~ 68°. The inner magnetic field, however, is found to be nearly aligned with the projected position angles of the minor axis, the rotation axis of the cloud, and the outflow from the IRAM 04191-IRS. We discuss a possible explanation for the nearly perpendicular orientation between the envelope and core scale magnetic fields in IRAM 04191. The angular offset between the envelope magnetic field direction and the minor axis of IRAM 04191, L1521F, L673-7, and L1014 are 82°, 60°, 47°, and 55°, respectively. The mean value of the offsets between the envelope magnetic field and the minor axis position angles for the four cores is found to be ~ 60°.
Conclusions. The results obtained from our study on the limited sample of five cores with VeLLOs show that the outflows in three of them tend to nearly align with the envelope magnetic field
Spin-down of neutron stars by neutrino emission
We study the spin-down of a neutron star during its early stages due to the
neutrino emission. The mechanism we consider is the subsequent collisions of
the produced neutrinos with the outer shells of the star. We find that this
mechanism can indeed slow down the star rotation but only in the first tens of
seconds of the core formation, which is when the appropriate conditions of flux
and collision rate are met. We find that this mechanism can extract less than 1
% of the star angular momentum, a result which is much less than previously
estimated by other authors.Comment: 9 pages, 2 eps figures, RevTeX 4-1. The paper was significantly
modified. Now it addresses only the issues of a neutron star spin-down.
Version to be published in Phys. Rev.
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