812 research outputs found
The extended structure of the remote cluster B514 in M31. Detection of extra-tidal stars
We present a study of the density profile of the remote M31 globular cluster
B514, obtained from HST/ACS observations. Coupling the analysis of the
distribution of the integrated light with star counts we can reliably follow
the profile of the cluster out to r~35", corresponding to ~130pc. The profile
is well fitted, out to ~15 core radii, by a King Model having C=1.65. With an
estimated core radius r_c=0.38", this corresponds to a tidal radius of r_t~17"
(~65pc). We find that both the light and the star counts profiles show a
departure from the best fit King model for r>~8" - as a surface brightness
excess at large radii, and the star counts profile shows a clear break in
correspondence of the estimated tidal radius. Both features are interpreted as
the signature of the presence of extratidal stars around the cluster. We also
show that B514 has a half-light radius significantly larger than ordinary
globular clusters of the same luminosity. In the M_V vs. log r_h plane, B514
lies in a region inhabited by peculiar clusters, like Omega Cen, G1, NGC2419
and others, as well as by the nuclei of dwarf elliptical galaxies.Comment: 9 pages, 6 figures. Accepted for publication in Astronomy &
Astrophysic
Correlations of Globular Cluster Properties: Their Interpretations and Uses
Correlations among the independently measured physical properties of globular
clusters (GCs) can provide powerful tests for theoretical models and new
insights into their dynamics, formation, and evolution. We review briefly some
of the previous work, and present preliminary results from a comparative study
of GC correlations in the Local Group galaxies. The results so far indicate
that these diverse GC systems follow the same fundamental correlations,
suggesting a commonality of formative and evolutionary processes which produce
them.Comment: An invited review, to appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, S.G. Djorgovski, and M. Riello, ASPCS,
in press (2003). Latex file, 8 pages, 5 eps figures, style files include
Transport on a Lattice with Dynamical Defects
Many transport processes in nature take place on substrates, often considered
as unidimensional lanes. These unidimensional substrates are typically
non-static: affected by a fluctuating environment, they can undergo
conformational changes. This is particularly true in biological cells, where
the state of the substrate is often coupled to the active motion of
macromolecular complexes, such as motor proteins on microtubules or ribosomes
on mRNAs, causing new interesting phenomena. Inspired by biological processes
such as protein synthesis by ribosomes and motor protein transport, we
introduce the concept of localized dynamical sites coupled to a driven lattice
gas dynamics. We investigate the phenomenology of transport in the presence of
dynamical defects and find a novel regime characterized by an intermittent
current and subject to severe finite-size effects. Our results demonstrate the
impact of the regulatory role of the dynamical defects in transport, not only
in biology but also in more general contexts
Seeing deconvolution of globular clusters in M31
Seeing deconvolution of surface-brightness profiles using the regularized multi-Gaussian method is potentially a powerful method for extraction of morphological information from digital images. Here we illustrate this method by applying it to CCD images of six globular clusters in M31. We demonstrate that it is possible to make some judgments about the dynamical structure of M31 globulars, using good-seeing, deconvolved CCD images obtained from the ground; for example, whether they have post-core-collapse morphology or not. The effective resolution limit of the method is about 0.1-0.3 arcsec, for the CCD images obtained in FWHM ≃ 1 arcsec seeing, and sampling of 0.3 arcsec/pixel. We also demonstrate the robustness of the method, i.e., its insensivity to the exact choices of the functional representation of the point-spread function, details of the deconvolution technique, etc. The situation is equivalent in terms of angular resolution and sampling to observing globular clusters in the Virgo Cluster (e.g., around M87) with the Hubble Space Telescope, and the methods demonstrated here may be applied to HST data in the future. Dynamical structure of globular clusters, e.g., propensity for the post-core-collapse morphology as a function of position in the host galaxy, reflects the global dynamical evolution of a globular cluster system, as was already demonstrated for our galaxy. Similar studies of large samples of globulars in M31 and other Local Group galaxies from the ground, and out to Virgo with the HST, can provide valuable insights about the mass distribution in galaxies, and the formation and evolution of their globular cluster systems. This pilot study is a step in this direction
Phase Coexistence in Driven One Dimensional Transport
We study a one-dimensional totally asymmetric exclusion process with random
particle attachments and detachments in the bulk. The resulting dynamics leads
to unexpected stationary regimes for large but finite systems. Such regimes are
characterized by a phase coexistence of low and high density regions separated
by domain walls. We use a mean-field approach to interpret the numerical
results obtained by Monte-Carlo simulations and we predict the phase diagram of
this non-conserved dynamics in the thermodynamic limit.Comment: 4 pages, 3 figures. Accepted for publication on Phys. Rev. Let
Mixed population of competing TASEPs with a shared reservoir of particles
We introduce a mean-field theoretical framework to describe multiple totally
asymmetric simple exclusion processes (TASEPs) with different lattice lengths,
entry and exit rates, competing for a finite reservoir of particles. We present
relations for the partitioning of particles between the reservoir and the
lattices: these relations allow us to show that competition for particles can
have non-trivial effects on the phase behavior of individual lattices. For a
system with non-identical lattices, we find that when a subset of lattices
undergoes a phase transition from low to high density, the entire set of
lattice currents becomes independent of total particle number. We generalize
our approach to systems with a continuous distribution of lattice parameters,
for which we demonstrate that measurements of the current carried by a single
lattice type can be used to extract the entire distribution of lattice
parameters. Our approach applies to populations of TASEPs with any distribution
of lattice parameters, and could easily be extended beyond the mean-field case.Comment: 12 pages, 8 figure
L’ectopia tiroidea: problemi di diagnosi e terapia
Gli Autori analizzando la casistica di tireopatie operate in circa un ventennio (2.670) riportano i casi di ectopia tiroidea (22) giunti alla loro osservazione, discutendone le caratteristiche cliniche nonché l’approccio diagnostico e terapeutico. Talora asintomatica, talora emersa clinicamente solo a seguito di tiroidectomia, l’ectopia tiroidea può creare problemi sia di funzione sia, più frequentemente, locali da compressione che richiedono il trattamento chirurgico, sempre indicato a loro parere anche in forme asintomatiche. Seppur rara, infatti, non può essere trascurata l’ipotesi della degenerazione neoplastica, intercorsa in due casi nella loro esperienza
StarFinder: an IDL GUI based code to analyze crowded fields with isoplanatic correcting PSF fitting
StarFinder is a new code for the deep analysis of stellar fields, designed
for well-sampled images with high and low Strehl ratio. It is organized in the
form of a self-contained IDL widget-based application, with a 'user-friendly'
graphic interface. We give here a general description of the code along with
some applications to real data with space-invariant Point Spread Function
(PSF). We present also some methods to handle anisoplanatic effects in
wide-field Adaptive Optics (AO)observations.Comment: 9 pages, to to be published on "Proceeedings of Adaptive Optical
Systems Technology",Proc.of SPIE,Vol.4007,2000. In pres
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