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

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

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

Dynamic correlation functions and Boltzmann Langevin approach for driven one dimensional lattice gas

We study the dynamics of the totally asymmetric exclusion process with open boundaries by phenomenological theories complemented by extensive Monte-Carlo simulations. Upon combining domain wall theory with a kinetic approach known as Boltzmann-Langevin theory we are able to give a complete qualitative picture of the dynamics in the low and high density regime and at the corresponding phase boundary. At the coexistence line between high and low density phases we observe a time scale separation between local density fluctuations and collective domain wall motion, which are well accounted for by the Boltzmann-Langevin and domain wall theory, respectively. We present Monte-Carlo data for the correlation functions and power spectra in the full parameter range of the model.Comment: 10 pages, 9 figure