1,721,025 research outputs found
Gravitational structure formation, the cosmological problem and statistical physics
No full textModels of structure formation in the universe postulate that matter distributions observed today in galaxy catalogs arise, through a complex non-linear dynamics, by gravitational evolution from a very uniform initial state. Dark matter plays the central role of providing the primordial density seeds which will govern the dynamics of structure formation. We critically examine the role of cosmological dark matter by considering three different and related issues: Basic statistical properties of theoretical initial density fields, several elements of the gravitational many-body dynamics and key correlation features of the observed galaxy distributions are discussed, stressing some useful analogies with known systems in modern statistical physics. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200698.80.-k Cosmology, 05.70.-a Thermodynamics, 02.50.-r Probability theory, stochastic processes, and statistics, 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion ,
Statistical physics for cosmic structures
No full textThe recent observations of galaxy and dark matter clumpy distributions have provided new elements to the understanding of the problem of cosmological structure formation. The strong clumping characterizing galaxy structures seems to be present in the overall mass distribution and its relation to the highly isotropic Cosmic Microwave Background Radiation represents a fundamental problem. The extension of structures, the formation of power-law correlations characterizing the strongly clustered regime and the relation between dark and visible matter are the key problems both from an observational and a theoretical point of view. We discuss recent progresses in the studies of structure formation by using concepts and methods of statistical physics
The problem of cosmological dark matter and statistical physics
No full textAlthough dark matter is supposed to provide with more than 0.9 of the total fraction of the mass-energy in universe, its amount and properties can only be defined a posteriori. In this context, a crucial point concerns the identification of a possible clear feature of dark matter fields which is not arbitrary, i.e. a property which has to be satisfied by dark matter fluctuations under some very general theoretical conditions. We discuss the fact that this property, in standard cosmological models, is represented by super-homogeneity, i.e. a very fine tuned balance between negative and positive correlations of density fluctuations, which must be imprinted both in the anisotropies of the CMBR and in the large scale distribution of galaxies. We review the main aspects of this property, considering examples of super-homogeneous systems well-studied in statistical physics, and discuss its possible observational evidences
Scale Invariance of galaxy clustering
No full textSome years ago we proposed a new approach to the analysis of galaxy and cluster correlations based on the concepts and methods of modern statistical Physics. This led to the surprising result that galaxy correlations are fractal and not homogeneous up to the limits of the available catalogs. The usual statistical methods, which are based on the assumption of homogeneity, are therefore inconsistent for all the length scales probed so far, and a new, more general, conceptual framework is necessary to identify the real physical properties of these structures. In the last few years the 3-d catalogs have been significatively improved and we have extended our methods to the analysis of number counts and angular catalogs. This has led to a complete analysis of all the available data that we present in this review. In particular we discuss the properties of the following catalogs: CfA, Perseus-Pisces, SSRS, IRAS, LEDA, APM-Stromlo, Las Campanas and ESP for galaxies and Abell and ACO for galaxy clusters. The result is that galaxy structures are highly irregular and self-similar: all the available data are consistent with each other and show fractal correlations (with dimension D similar or equal to 2) up to the deepest scales probed so far (1000 h(-1) Mpc) and even more as indicated from the new interpretation of the number counts. The evidence for scale-invariance of galaxy clustering is very strong up to 150 h(-1) Mpc due to the statistical robustness of the data but becomes progressively weaker (statistically) at larger distances due to the limited data. In addition, the luminosity distribution is correlated with the space distribution in a specific way. These facts lead to fascinating conceptual implications about our knowledge of the universe and to a new scenario for the theoretical challenge in this field. (C) 1998 Elsevier Science B.V
STATISTICAL PHYSICS FOR COMPLEX COSMIC STRUCTURES
No full textCosmic structures at large scales represent the earliest and most extended form of matter condensation. In this lecture we review the application of the methods and concepts of modern statistical physics to these structures. This leads to a new perspective in the field which can be tested by the many new data which are appearing in the near future. In particular, galaxy structures show fractal correlation up to the present observational limits. The cosmic microwave background radiation, which should trace the initial conditions from which these structures have emerged through gravitational dynamics, is instead extremely smooth. Understanding the relation between the complex galaxy structures and the smooth microwave background radiation represents an extremely challenging problem in the field of structure formation
Scaling in cosmic structures
No full textThe study of the properties of cosmic structures in the universe is one of the most fascinating subject of the modern cosmology research. Far from being predicted, the large scale structure of the matter distribution is a very recent discovery, which continuosly exhibits new features and issues. We have faced such topic along two directions; from one side we have studied the correlation properties of the cosmic structures, that we have found substantially different from the commonly accepted ones. From the other side, we have studied the statistical properties of the very simplified system, in the attempt to capture the essential ingredients of the formation of the observed strucures
Nuovo insediamento integrato urbano/universitario nella città di Bologna (zona Bertalia-Lazzaretto)
No full textMuseo Nacional del Judaismo Italiano el Holocausto Ferrara
No full textL'Articolo illustra il progetto architettonico selezionato dalla Giuria meritevole di menzione
romArchitettura per la valorizzazione dell'architettura contemporanea nel Lazio. Terza edizione
No full textPremio per un intervento di nuova costruzione. Progetto segnalat
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