535 research outputs found
Exploring the vs relation with flux transport dynamo models of solar-like stars
Aims: To understand stellar magnetism and to test the validity of the
Babcock-Leighton flux transport mean field dynamo models with stellar activity
observations Methods: 2-D mean field dynamo models at various rotation rates
are computed with the STELEM code to study the sensitivity of the activity
cycle period and butterfly diagram to parameter changes and are compared to
observational data. The novelty is that these 2-D mean field dynamo models
incorporate scaling laws deduced from 3-D hydrodynamical simulations for the
influence of rotation rate on the amplitude and profile of the meridional
circulation. These models make also use of observational scaling laws for the
variation of differential rotation with rotation rate. Results: We find that
Babcock-Leighton flux transport dynamo models are able to reproduce the change
in topology of the magnetic field (i.e. toward being more toroidal with
increasing rotation rate) but seem to have difficulty reproducing the cycle
period vs activity period correlation observed in solar-like stars if a
monolithic single cell meridional flow is assumed. It may however be possible
to recover the vs relation with more complex meridional
flows, if the profile changes in a particular assumed manner with rotation
rate. Conclusions: The Babcock-Leighton flux transport dynamo model based on
single cell meridional circulation does not reproduce the vs
relation unless the amplitude of the meridional circulation is
assumed to increase with rotation rate which seems to be in contradiction with
recent results obtained with 3-D global simulations.Comment: 12 pages, 8 figures, accepted for publication by A&A 1: AIM,
CEA/DSM-CNRS-Univ. Paris 7, IRFU/SAp, France, 2: D.A.M.T.P., Centre for
Mathematical Sciences, Univ. of Cambridge, UK, 3: JILA and Department of
Astrophysical and Planetary Sciences, Univ. of Colorado, US
MUSCLE : automated multi-objective evolutionary optimization of targeted LC-MS/MS analysis:Automated multi-objective evolutionary optimization of targeted LC-MS/MS analysis
Summary: Developing liquid chromatography tandem mass spectrometry (LC-MS/MS) analyses of (bio)chemicals is both time consuming and challenging, largely because of the large number of LC and MS instrument parameters that need to be optimized. This bottleneck significantly impedes our ability to establish new (bio)analytical methods in fields such as pharmacology, metabolomics and pesticide research. We report the development of a multi-platform, user-friendly software tool MUSCLE (multi-platform unbiased optimization of spectrometry via closed-loop experimentation) for the robust and fully automated multi-objective optimization of targeted LC-MS/MS analysis. MUSCLE shortened the analysis times and increased the analytical sensitivities of targeted metabolite analysis, which was demonstrated on two different manufacturer’s LC-MS/MS instruments. Availability and implementation: Available at http://www.muscleproject.org. Contact: [email protected] Supplementary information: Supplementary data are available at Bioinformatics online
Tooth serration morphologies in the genus Machimosaurus (Crocodylomorpha, Thalattosuchia) from the Late Jurassic of Europe
© 2014 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. The attached file is the published version of the article
Impact hydrologique des toitures végétalisées sur le ruissellement urbain à l’échelle du bassin versant – Études de cas dans le département des Hauts-de-Seine (France)
Time-resolved nuclear spin-dependent small-angle neutron scattering from polarised proton domains in deuterated solutions
Abstract.: We have investigated the process of dynamic proton polarisation by means of time-resolved polarised small-angle neutron scattering (SANS) on frozen solutions of EHBA-CrV molecules in glycerol-water mixtures as a function of the concentration of EHBA-CrV and for different degrees of deuteration of the solvent. In the EHBA-CrV complex, the spins of the 20 protons which surround the paramagnetic CrV can be oriented using the method of dynamic nuclear polarisation (DNP), thereby offering the possibility to create locally a nuclear spin-dependent contrast for SANS. The time constants which describe the build-up of polarisation around the paramagnetic centre and the subsequent diffusion of polarisation in the solvent were determined by analysing the temporal evolution of the nuclear polarisation, which in turn was obtained by fitting a core-shell model to the time-dependent SANS curves. The results on the spin dynamics obtained using the scattering function of a core-shell could be independently confirmed by evaluating the integrated SANS intensity. A thermodynamic one-centre model is presented which is able to reproduce the observed dependence of the proton polarisation times on the proton concentration of the solven
Collimated dual species oven source and its characterisation via spatially resolved fluorescence spectroscopy
We describe the design, construction and characterisation of a collimated, dual-species oven source for generating intense beams of lithium and caesium in UHV environments. Our design produces full beam overlap for the two species. Using an aligned microtube array the FWHM of the output beam is restricted to ~ 75 milliradians, with an estimated axial brightness of 3.6x10[superscript]14 atoms s[superscript]-1 sr[superscript]-1 for Li and 7.4x10[superscript]15 atoms s[superscript]-1 sr[superscript]-1 for Cs. We measure the properties of the output beam using a spatially-resolved fluorescence technique, which allows for the extraction of additional information not accessible without spatial resolution
Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold
From a set of stellar spectropolarimetric observations, we report the
detection of surface magnetic fields in a sample of four solar-type stars,
namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the
observed variability of polarimetric signal is controlled by stellar rotation,
we establish the rotation periods of our targets, with values ranging from 8.8
d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental
parameters of the selected objects are very close to the Sun's, making this
sample a practical basis to investigate the specific impact of rotation on
magnetic properties of Sun-like stars.
We reconstruct the large-scale magnetic geometry of the targets as a
low-order (l<10) spherical harmonics expansion of the surface magnetic field.
From the set of magnetic maps, we draw two main conclusions. (a) The magnetic
energy of the large-scale field increases with rotation rate. The increase of
chromospheric emission with the mean magnetic field is flatter than observed in
the Sun. Since the chromospheric flux is also sensitive to magnetic elements
smaller than those contributing to the polarimetric signal, this observation
suggests that a larger fraction of the surface magnetic energy is stored in
large scales as rotation increases. (b) Whereas the magnetic field is mostly
poloidal for low rotation rates, more rapid rotators host a large-scale
toroidal component in their surface field. From our observations, we infer that
a rotation period lower than ~12 days is necessary for the toroidal magnetic
energy to dominate over the poloidal component.Comment: MNRAS (in press
The impact of a fossil magnetic field on dipolar mixed-mode frequencies in sub- and red-giant stars
Stars more massive than M are known to develop a
convective core during the main-sequence: the dynamo process triggered by this
convection could be the origin of a strong magnetic field inside the core of
the star, trapped when it becomes stably stratified and for the rest of its
evolution. The presence of highly magnetized white dwarfs strengthens the
hypothesis of buried fossil magnetic fields inside the core of evolved low-mass
stars. If such a fossil field exists, it should affect the mixed modes of red
giants as they are sensitive to processes affecting the deepest layers of these
stars. The impact of a magnetic field on dipolar oscillations modes was one of
Pr. Michael J. Thompson's research topics during the 90s when preparing the
helioseismic SoHO space mission. As the detection of gravity modes in the Sun
is still controversial, the investigation of the solar oscillation modes did
not provide any hint of the existence of a magnetic field in the solar
radiative core. Today we have access to the core of evolved stars thanks to the
asteroseismic observation of mixed modes from CoRoT, Kepler, K2 and TESS
missions. The idea of applying and generalizing the work done for the Sun came
from discussions with Pr. Michael Thompson in early 2018 before we loss him.
Following the path we drew together, we theoretically investigate the effect of
a stable axisymmetric mixed poloidal and toroidal magnetic field, aligned with
the rotation axis of the star, on the mixed modes frequencies of a typical
evolved low-mass star. This enables us to estimate the magnetic perturbations
to the eigenfrequencies of mixed dipolar modes, depending on the magnetic field
strength and the evolutionary state of the star. We conclude that strong
magnetic fields of 1MG should perturbe the mixed-mode frequency pattern
enough for its effects to be detectable inside current asteroseismic data.Comment: Conference proceeding, in press, 7 pages, 3 figure
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