548 research outputs found
Hamiltonian model of capture into mean motion resonance
Mean motion resonances are a common feature of both our own Solar System and
of extrasolar planetary systems. Bodies can be trapped in resonance when their
orbital semi-major axes change, for instance when they migrate through a
protoplanetary disc. We use a Hamiltonian model to thoroughly investigate the
capture behaviour for first and second order resonances. Using this method, all
resonances of the same order can be described by one equation, with
applications to specific resonances by appropriate scaling. We focus on the
limit where one body is a massless test particle and the other a massive
planet. We quantify how the the probability of capture into a resonance depends
on the relative migration rate of the planet and particle, and the particle's
eccentricity. Resonant capture fails for high migration rates, and has
decreasing probability for higher eccentricities, although for certain
migration rates, capture probability peaks at a finite eccentricity. We also
calculate libration amplitudes and the offset of the libration centres for
captured particles, and the change in eccentricity if capture does not occur.
Libration amplitudes are higher for larger initial eccentricity. The model
allows for a complete description of a particle's behaviour as it successively
encounters several resonances. The model is applicable to many scenarios,
including (i) Planet migration through gas discs trapping other planets or
planetesimals in resonances; (ii) Planet migration through a debris disc; (iii)
Dust migration through PR drag. Full details can be found in
\cite{2010submitted}. (Abridged)Comment: 4 pages, Proceedings of IAUS276 "The Astrophysics of Planetary
Systems: Formation, Structure, and Dynamical Evolution
Socialization of the elderly in outdoor health circuits
En los parques biosaludables, originalmente concebidos para la población madura y anciana, se encuentran usuarios de diferentes edades y con distintas formas de entender la actividad física. El presente trabajo intenta examinar las relaciones de las personas mayores con el resto de usuarios para determinar en qué medida dichos parques pueden cumplir alguna función social más allá del fomento de hábitos saludables. Para ello se ha llevado a cabo una serie de observaciones, participantes y no participantes, en tres parques de la ciudad de Granada, donde se ha visto que, si bien existe una proporción minoritaria pero importante de usuarios jóvenes (aproximadamente un tercio del total), estos tienden a evitar una interacción que parte de los usuarios de mayor edad buscan expresamente
PVS: a web server for protein sequence variability analysis tuned to facilitate conserved epitope discovery
We have developed PVS (Protein Variability Server), a web-based tool that uses several variability metrics to compute the absolute site variability in multiple protein-sequence alignments (MSAs). The variability is then assigned to a user-selected reference sequence consisting of either the first sequence in the alignment or a consensus sequence. Subsequently, PVS performs tasks that are relevant for structure-function studies, such as plotting and visualizing the variability in a relevant 3D-structure. Neatly, PVS also implements some other tasks that are thought to facilitate the design of epitope discovery-driven vaccines against pathogens where sequence variability largely contributes to immune evasion. Thus, PVS can return the conserved fragments in the MSA—as defined by a user-provided variability threshold—and locate them in a relevant 3D-structure. Furthermore, PVS can return a variability-masked sequence, which can be directly submitted to the RANKPEP server for the prediction of conserved T-cell epitopes. PVS is freely available at: http://imed.med.ucm.es/PVS/
Burnout, resiliencia y optimismo en el hockey sobre hierba femenino
os estudios acerca de las relaciones entre burnout, resiliencia y optimismo en el deporte son escasos. Se hace más difícil aún hallar lite- ratura que profundice en estos conceptos en deportes de equipo. Es objeto de este estudio conocer la prevalencia y relación entre la sintomatología del burnout, la resiliencia y el optimismo en jugadoras de hockey sobre hier- ba. Así como su relación con variables como la edad y la dedicación de la práctica deportiva. Fueron evaluadas 130 deportistas (edad de 13 a 19; M = 18,5; DT = 4,3). Los resultados evidencian que un 4,6% de las deportistas puntúan burnout, centrándose el mayor porcentaje dentro de un nivel de sintomatología moderada que alcanza el 42,9%. Asimismo encontramos, una resiliencia elevada en el 8,5% de los participantes en el estudio, encon- trándose en su mayoría dentro de un perl de resiliencia moderada (57,7%). Por su parte, el optimismo alcanza un 66,2% en el nivel moderado y alto. En el caso de la sintomatología de burnout se encontraron diferencias es- tadísticamente signicativas en función de la edad y la dedicación de la práctica deportiva. Resiliencia y optimismo diferían también en función de esta última. Finalmente, encontramos diferencias entre las deportistas que presentan síntomas de burnout en relación con la resiliencia y el opti- mismo, resultando que aquellas que presentan síntomas poseen una menor resiliencia y optimismo. Estos resultados muestran indicadores psicológicos que permiten ser evaluados por un psicólogo deportivo para su detección temprana e intervención en atletas de distintos niveles y dedicación.
New insights from zinc and copper isotopic compositions of atmospheric particulate matter from two major European cities
This study reports spatial and temporal variability of Zn and Cu isotopes in atmospheric particulate matter (PM) collected in two major European cities with contrasting atmospheric pollution, Barcelona and London. We demonstrate that non-traditional stable isotopes identify source contributions of Zn and Cu and can play a major role in future air quality studies. In Barcelona, fine PM were collected at street level at sites with variable traffic density. The isotopic signatures ranged between −0.13±0.09 and −0.55±0.09‰ for d66ZnIRMM and between +0.04±0.20 and +0.33±0.15‰ for d65CuAE633. Copper isotope signatures similar to Cu sulphides and Cu/Sb ratios within the range typically found in brake wear suggest that non-exhaust emissions from vehicles are dominant. Negative Zn isotopic signatures characteristic for gaseous emissions from smelting and combustion and large enrichments of Zn and Cd suggest contribution from metallurgical industries. In London, coarse PM collected on the top of a building over 18 months display isotope signatures ranging between +0.03±0.04 and +0.49±0.02‰ for d66ZnIRMM and between +0.37±0.17 and +0.97±0.21‰ for d65CuAE633. Heavy Cu isotope signatures (up to +0.97±0.21‰) and higher enrichments and Cu/Sb ratios during winter time suggest important contribution from fossil fuel combustion. The positive d66ZnIRMM signatures are in good agreement with signatures characteristic for ore concentrates used for the production of tires and galvanised materials, suggesting non-exhaust emissions from vehicles as the main source of Zn
Investigating the flyby scenario for the HD 141569 system
HD 141569, a triple star system, has been intensively observed and studied
for its massive debris disk. It was rather regarded as a gravitationally bound
triple system but recent measurements of the HD 141569A radial velocity seem to
invalidate this hypothesis. The flyby scenario has therefore to be investigated
to test its compatibility with the observations. We present a study of the
flyby scenario for the HD141569 system, by considering 3 variants: a sole
flyby, a flyby associated with one planet and a flyby with two planets. We use
analytical calculations and perform N-body numerical simulations of the flyby
encounter. The binary orbit is found to be almost fixed by the observational
constraint on a edge-on plane with respect to the observers. If the binary has
had an influence on the disk structure, it should have a passing time at the
periapsis between 5000 and 8000 years ago and a distance at periapsis between
600 and 900 AU. The best scenario for reproducing the disk morphology is a
flyby with only 1 planet. For a 2 Mj (resp. 8 Mj) planet, its eccentricity must
be around 0.2 (resp. below 0.1). In the two cases, its apoapsis is about 130
AU. Although the global disk shape is reasonably well reproduced, some features
cannot be explain by the present model and the likehood of the flyby event
remains an issue. Dynamically speaking, HD 141569 is still a puzzling system
Characterization of the chemical structure of vinyl ester resin in a climate chamber under different conditions of degradation
Due to the good strength and similar toughness of epoxy resins, vinyl ester resins are widely used as thermoset adhesives in structural adhesive joints and as composites for different industrial applications. However, vinyl ester adhesives are difficult to cure completely under environmental conditions, even after long periods of time because of gel formation slows the necessary diffusion of the catalyst across the polymer network. Several studies have used weathering chambers to investigate the degradation mechanisms of vinyl ester adhesives. However, a review of the scientific literature revealed both a wide variety of aging processes and several ambiguities between the recorded experimental results. In this work, post-cured vinyl ester resins at different aging cycles were aged under high temperature and relative humidity, and the changes in their structure, mechanical and adhesion properties were studied. Chemical and structural changes were observed in the vinyl ester resins after aging in a climatic chamber
Epidemics in Networks of Spatially Correlated Three-dimensional Root Branching Structures
Using digitized images of the three-dimensional, branching structures for
root systems of bean seedlings, together with analytical and numerical methods
that map a common 'SIR' epidemiological model onto the bond percolation
problem, we show how the spatially-correlated branching structures of plant
roots affect transmission efficiencies, and hence the invasion criterion, for a
soil-borne pathogen as it spreads through ensembles of morphologically complex
hosts. We conclude that the inherent heterogeneities in transmissibilities
arising from correlations in the degrees of overlap between neighbouring
plants, render a population of root systems less susceptible to epidemic
invasion than a corresponding homogeneous system. Several components of
morphological complexity are analysed that contribute to disorder and
heterogeneities in transmissibility of infection. Anisotropy in root shape is
shown to increase resilience to epidemic invasion, while increasing the degree
of branching enhances the spread of epidemics in the population of roots. Some
extension of the methods for other epidemiological systems are discussed.Comment: 21 pages, 8 figure
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