5,511 research outputs found
Spiral Structure in Galaxies : A Density Wave Theory
No full textHow does it happen that billions of stars can cooperate to produce the beautiful spirals that characterize so many galaxies, including ours? This book presents a theory of spiral structure that has been developed over the past three decades under the continuous stimulus of new observational studies. The theory unfolds in a way that can be grasped by any reader with an undergraduate science background who is interested in astronomy, as well as by graduate students and scientists actively involved in astronomy or related subjects who want to see the "backbone" and the physical content of the theory. The foundations of this theoretical framework were laid in the early 1960s, following the pioneering work of B. Lindblad. C. C. Lin had already contributed significantly to the field of fluid mechanics when he turned his attention to spiral structures, and he has focused on the problem ever since. Giuseppe Bertin joined this research effort when he first visited at MIT in 1975, bringing to the project knowledge from his work on elliptical galaxies and plasma astrophysics. Together, Bertin and Lin have contributed to the exciting developments on spiral structure of the last few decades, working closely with many observers and other theorists. In this book they describe the density-wave theory with the goal of making the key concepts and astrophysical implications explicit and accessible. The essence of the solution Bertin and Lin present is that the spirals are wave rather than material phenomena and generally trace intrinsic characteristics of the individual galaxies. The book is in three parts—Physical Concepts, Observational Studies, and Dynamical Mechanisms—with most of the technical details confined to the last part
Bertin (G.) - L'investissement international.
No full textSaint Marc Michèle. Bertin (G.) - L'investissement international.. In: Revue économique, volume 19, n°4, 1968. pp. 726-727
Dynamical properties of a family of collisionless models of elliptical galaxies
No full textN-body simulations of collisionless collapse have offered important clues to the construction of realistic stellar dynamical models of elliptical galaxies. Such simulations confirm and quantify the qualitative expectation that rapid collapse of a self-gravitating collisionless system, initially cool and significantly far from equilibrium, leads to incomplete relaxation, that is to a quasi-equilibrium configuration characterized by isotropic, quasi-Maxwellian distribution of stellar orbits in the inner regions and by radially biased anisotropic pressure in the outer parts. In earlier studies, as illustrated in a number of papers several years ago (see Bertin et al. 1993 and references therein), the attention was largely focused on the successful comparison between the models (constructed under the qualitative clues offered by the N-body simulations mentioned above) and the observations. In this paper we revisit the problem of incomplete violent relaxation, by making a direct comparison between the detailed properties of a family of distribution functions and those of the products of collisionless collapse found in N-body simulations
La centralità del territorio: i nodi del cambiamento
No full textI sistemi sanitari sono interessati da un profondo processo di cambiamento e, ad oggi è difficile individuare l'esito del cambiamento in atto. L'assetto dei sistemi locali dipenderà dalla capacità di attivare di tener conto di: i) la forte disomogeneità delle esperienze e la necessità di sviluppare processi di costruzione di basi semantiche omogenee per poter attivare processi di confronto delle informazioni anche fra le azioni svolte a livello territoriale; ii) le dinamiche di conflitto e concorrenza fra le diverse figure professionali presenti nel territorio e nelle strutture residenziali. L’azione territoriale necessita, infatti, di una legittimazione reciproca fra le professioni e di processi di coordinamento e integrazione delle loro attività; iii) la diversificazione del sistema degli attori e la sperimentazione di pratiche di governance capaci di integrare l’azione elle singole organizzazioni compreseti nel processo di produzione dei servizi; iv) la centralità delle dinamiche e delle opportunità offerte dalla web-society, in grado di modificare i processi e le abitudini di produzione e di utilizzo dei servizi sanitari territoriali
Invecchiamento: orientamenti della Commissione Europea e politiche degli stati membri
No full textEuropean policies on ageing. Author makes a reconstruction of the welfare policies that the
European Commission has promoted and activated to address the problem of an ageing population.
The directives towards which the Commission has pushed the debate of the individual
states can be summarized in: the promotion of active ageing; the review of interventions to
make them sustainable in the face of demographic change; the development of long-term care
policies. These recommendations have contributed to the development of reform processes in
all European states. The forms taken by the services are the combined effect of the history of
the individual welfare systems and show in part different characteristic
Nécrologie. Le chanoine Paul Bertin
No full textC. G. Nécrologie. Le chanoine Paul Bertin. In: Revue du Nord, tome 41, n°162, Avril-juin 1959. p. 240
Nécrologie. Le chanoine Paul Bertin
No full textC. G. Nécrologie. Le chanoine Paul Bertin. In: Revue du Nord, tome 41, n°162, Avril-juin 1959. p. 240
Tides, Rotation Or Anisotropy? Self-consistent Nonspherical Models For Globular Clusters
No full textSpherical models of quasi-relaxed stellar systems provide a successful zeroth-order description of globular clusters. Yet, the great progress made in recent years in the acquisition of detailed information of the structure of these stellar systems calls for a renewed effort on the side of modeling. In particular, more general analytical models would allow to address the long-standing issue of the physical origin of the deviations from spherical symmetry of the globular clusters, that now can be properly measured. In fact, it remains to be established which is the cause of the observed flattening, among external tides, internal rotation, and pressure anisotropy.
In this paper we focus on the first two physical ingredients. We start by briefly describing a recently studied family of triaxial models that incorporate in a self-consistent way the tidal effects of the host galaxy, as a collisionless analogue of the Roche problem (Varri & Bertin ApJ 2009). We then present two new families of axisymmetric models in which the deviations from spherical symmetry are induced by the presence of internal rotation. The first one is an extension of the well-known family of King models to the case of axisymmetric equilibria flattened by solid-body rotation. The second family is characterized by differential rotation, designed to be rigid in the center and to vanish in the outer parts, where the imposed truncation in phase space becomes effective.
For possible application to globular clusters, models of interest should be those, in both families, characterized by low values of the rotation strength parameter and quasi-spherical shape. For general interest in stellar dynamics, we show that, for high values of that parameter, the differentially rotating models may exhibit unexpected morphologies, even with a toroidal core
Cultura della legalità: le basi sociali dei comportamenti illegali
No full textThis paper designs a multidimensional index of well-being for 20 Italian regions, based on a set of 41 indicators organized in an original hierarchical structure, a decision-tree whose four main pillars are Economy, Society, Environment and Health. Our novel approach combines the objective dimension of the evaluation (a comprehensive set of statistical indicators) within a flexible non-additive aggregation model (the Choquet integral) characterized with the preferences of informed Italian stakeholders. Adopting the Choquet integral allows us to overcome the well-known limitations embedded in the linear models, by assigning a weight (capacity) to any coalitions of dimensions, and by allowing a different degree of substitutability within each decision node in the tree. The weights and the parameters for the aggregation are elicited through a computer-based nominal group technique, a method which reduces the occurrences of drastically dissenting valuations and the potential expert-selection bias. Our results show that experts’ perception of synergies and redundancies is quite heterogeneous between levels and nodes in the tree. Moreover, well-being measures are much influenced by the degree of substitutability embedded in the experts’ preferences. Overall, the Italian picture looks more heterogeneous when analysed through the Choquet integral, with respect to a linear model
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