18,399 research outputs found
NICE DSU Technical Support Document 3: Heterogeneity: Subgroups, Meta-Regression, Bias and Bias-Adjustment
A Multi-Membership Catalogue for 1876 Open Clusters using UCAC4 data
The main objective of this work is to determine the cluster members of 1876
open clusters, using positions and proper motions of the astrometric catalogue
UCAC4. For this purpose we apply three different methods, all them based on a
Bayesian approach, but with different formulations: a purely parametric method,
another completely non-parametric algorithm, and a third, recently developed by
Sampedro & Alfaro, using both formulations at different steps of the whole
process. The first and second statistical moments of the members phase-space
subspace, obtained after applying the three methods, are compared for every
cluster. Although, on average, the three methods yield similar results,
specific differences between them, as well as for some particular clusters, are
also present. The comparison with other published catalogues shows good
agreement. We have also estimated for the first time the mean proper motion for
a sample of 18 clusters. The results are organized in a single catalogue formed
by two main files, one with the most relevant information for each cluster,
partially including that in UCAC4, and the other showing the individual
membership probabilities for each star in the cluster area. The final
catalogue, with an interface design that enables an easy interaction with the
user, is available in electronic format at SSG-IAA
(http://ssg.iaa.es/en/content/sampedro-cluster-catalog) website.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 6 table
A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers
We investigate the spin-polarized transport of GaMnAs nanolayers in which a
ferromagnetic order exists below a certain transition temperature. Our
calculation for the self-averaged resistivity takes into account the existence
of an impurity band determining the extended ("metallic" transport) or
localized (hopping by thermal excitation) nature of the states at and near the
Fermi level. Magnetic order and resistivity are inter-related due to the
influence of the spin polarization of the impurity band and the effect of the
Zeeman splitting on the mobility edge. We obtain, for a given range of Mn
concentration and carrier density, a "metallic" behavior in which the transport
by extended carriers dominates at low temperature, and is dominated by the
thermally excited localized carriers near and above the transition temperature.
This gives rise to a conspicuous hump of the resistivity which has been
experimentally observed and brings light onto the relationship between
transport and magnetic properties of this material
Mechanism of magnetostructural transformation in multifunctional MnGaC
MnGaC undergoes a ferromagnetic to antiferromagnetic, volume
discontinuous cubic-cubic phase transition as a function of temperature,
pressure and magnetic field. Through a series of temperature dependent x-ray
absorption fine structure spectroscopy experiments at the Mn K and Ga K edge,
it is shown that the first order magnetic transformation in MnGaC is
entirely due to distortions in Mn sub-lattice and with a very little role for
Mn-C interactions. The distortion in Mn sub-lattice results in long and short
Mn-Mn bonds with the longer Mn-Mn bonds favoring ferromagnetic interactions and
the shorter Mn-Mn bonds favoring antiferromagnetic interactions. At the first
order transition, the shorter Mn-Mn bonds exhibit an abrupt decrease in their
length resulting in an antiferromagnetic ground state and a strained lattice.Comment: Accepted in J. Appl. Phys. Please contact authors for supplementary
informatio
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