16,013 research outputs found
Functorial properties of Putnam's homology theory for Smale spaces
We investigate functorial properties of Putnam's homology theory for Smale
spaces. Our analysis shows that the addition of a conjugacy condition is
necessary to ensure functoriality. Several examples are discussed that
elucidate the need for our additional hypotheses. Our second main result is a
natural generalization of Putnam's Pullback Lemma from shifts of finite type to
non-wandering Smale spaces.Comment: Updated to agree with published versio
Description of nuclear systems with a self-consistent configuration-mixing approach. I: Theory, algorithm, and application to the C test nucleus
Although self-consistent multi-configuration methods have been used for
decades to address the description of atomic and molecular many-body systems,
only a few trials have been made in the context of nuclear structure. This work
aims at the development of such an approach to describe in a unified way
various types of correlations in nuclei, in a self-consistent manner where the
mean-field is improved as correlations are introduced. The goal is to reconcile
the usually set apart Shell-Model and Self-Consistent Mean-Field methods. This
approach is referred as "variational multiparticle-multihole configuration
mixing method". It is based on a double variational principle which yields a
set of two coupled equations that determine at the same time the expansion
coefficients of the many-body wave function and the single particle states. The
formalism is derived and discussed in a general context, starting from a
three-body Hamiltonian. Links to existing many-body techniques such as the
formalism of Green's functions are established. First applications are done
using the two-body D1S Gogny effective force. The numerical procedure is tested
on the C nucleus in order to study the convergence features of the
algorithm in different contexts. Ground state properties as well as
single-particle quantities are analyzed, and the description of the first
state is examined. This study allows to validate our numerical algorithm and
leads to encouraging results. In order to test the method further, we will
realize in the second article of this series, a systematic description of more
nuclei and observables obtained by applying the newly-developed numerical
procedure with the same Gogny force. As raised in the present work,
applications of the variational multiparticle-multihole configuration mixing
method will however ultimately require the use of an extended and more
constrained Gogny force.Comment: 22 pages, 18 figures, accepted for publication in Phys. Rev. C. v2:
minor corrections and references adde
The Galactic bulge as seen in optical surveys
The bulge is a region of the Galaxy of tremendous interest for understanding
galaxy formation. However measuring photometry and kinematics in it raises
several inherent issues, such as severe crowding and high extinction in the
visible. Using the Besancon Galaxy model and a 3D extinction map, we estimate
the stellar density as a function of longitude, latitude and apparent magnitude
and we deduce the possibility of reaching and measuring bulge stars with Gaia.
We also present an ongoing analysis of the bulge using the Canada-France-Hawaii
Telescope.Comment: In SF2A-2008: Proceedings of the Annual meeting of the French Society
of Astronomy and Astrophysic
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Remote detection and location of explosive volcanism in Alaska with the EarthScope Transportable Array
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Application of frequency map analysis to the ALS
Frequency map analysis is a numerical method based on Fourier techniques which provides a clear representation of the global dynamics of many multi-dimensional systems, and which is particularly useful for systems of 3 degrees of freedom and more. The frequency dependence with time also allows refined estimates of the diffusion of the orbits. Here are presented the theoretical foundation of the method, and some applications to the Advanced Light Source, demonstrating how frequency map analysis can be used to understand the limits of the dynamic aperture under various lattice conditions and predict more favorable working points
SlicerAstro: a 3-D interactive visual analytics tool for HI data
SKA precursors are capable of detecting hundreds of galaxies in HI in a
single 12 hours pointing. In deeper surveys one will probe more easily faint HI
structures, typically located in the vicinity of galaxies, such as tails,
filaments, and extraplanar gas. The importance of interactive visualization has
proven to be fundamental for the exploration of such data as it helps users to
receive immediate feedback when manipulating the data. We have developed
SlicerAstro, a 3-D interactive viewer with new analysis capabilities, based on
traditional 2-D input/output hardware. These capabilities enhance the data
inspection, allowing faster analysis of complex sources than with traditional
tools. SlicerAstro is an open-source extension of 3DSlicer, a multi-platform
open source software package for visualization and medical image processing.
We demonstrate the capabilities of the current stable binary release of
SlicerAstro, which offers the following features: i) handling of FITS files and
astronomical coordinate systems; ii) coupled 2-D/3-D visualization; iii)
interactive filtering; iv) interactive 3-D masking; v) and interactive 3-D
modeling. In addition, SlicerAstro has been designed with a strong, stable and
modular C++ core, and its classes are also accessible via Python scripting,
allowing great flexibility for user-customized visualization and analysis
tasks.Comment: 18 pages, 11 figures, Accepted by Astronomy and Computing.
SlicerAstro link: https://github.com/Punzo/SlicerAstro/wiki#get-slicerastr
Ultra- and Hyper-compact HII regions at 20 GHz
We present radio and infrared observations of 4 hyper-compact HII regions and
4 ultra-compact HII regions in the southern Galactic plane. These objects were
selected from a blind survey for UCHII regions using data from two new radio
surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and
the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our
knowledge, this is the first blind radio survey for hyper- and ultra-compact
HII regions.
We have followed up these sources with the Australia Telescope Compact Array
to obtain H70-alpha recombination line measurements, higher resolution images
at 20 GHz and flux density measurements at 30, 40 and 95 GHz. From this we have
determined sizes and recombination line temperatures as well as modeling the
spectral energy distributions to determine emission measures. We have
classified the sources as hyper-compact or ultra-compact on the basis of their
physical parameters, in comparison with benchmark parameters from the
literature.
Several of these bright, compact sources are potential calibrators for the
Low Frequency Instrument (30-70 GHz) and the 100-GHz channel of the High
Frequency Instrument of the Planck satellite mission. They may also be useful
as calibrators for the Australia Telescope Compact Array, which lacks good
non-variable primary flux calibrators at higher frequencies and in the Galactic
plane region. Our spectral energy distributions allow the flux densities within
the Planck bands to be determined, although our high frequency observations
show that several sources have excess emission at 95 GHz (3 mm) that can not be
explained by current models.Comment: 13 pages, 7 figures, accepted for publication in MNRA
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