1,722,162 research outputs found
L'utilizzo del materiale strutturato per favorire l'apprendimento logico-matematico negli allievi con ritardo mentale
No full textIl contributo presenta i risultati di una ricerca condotta congiuntamente da due ricecatori che hanno effettuato delle osservazioni partecipanti in alcune classi di scuola primaria italiane e scozzesi. L'obiettivo è stato quello di studiare in che maniera i sussidi didattici utilizzati per l'insegnamento dell'artmetica possano essere di aiuto ai bambini con lieve e moderato ritardo mentale. Dettori ha effettuato l'osservazione in scuole italiane frequentate da allievi con disabilità e Moscardini in scuole speciali scozzesi, le considerazioni di entranbi propongono delle riflessioni sull'efficacia del materiale strutturato per l'insegnamento della matematica ad allievi con ritardo mentale medio e moderato
Collisional versus Collisionless Matter: a One-dimensional Analysis of Gravitational Clustering
No full textWe present the results of a series of one-dimensional N-body and hydrodynamical simulations which have been used for testing the different clustering properties of baryonic and dark matter in an expanding background. The numerical code is based on the piecewise parabolic method. Initial Gaussian random density perturbations with a power-law spectrum P(k)proportional to k(n) are assumed. We analyse the distribution of density fluctuations and thermodynamical quantities for different spectral indices n and discuss the statistical properties of clustering in the corresponding simulations. At large scales the final distribution of the two components is very similar while at small scales the
dark matter presents a lumpiness which is not found in the baryonic matter. The amplitude of density fluctuations in each component depends on the spectral index n but that of the baryonic matter is always larger than the one in the dark component. This result is also confirmed by the behaviour of the bias factor, defined as the ratio between the rms of baryonic and dark matter fluctuations at different scales, which is larger than unity in all the models we have considered. The final temperatures depend on the initial spectral index: the highest values (10(8) K) are obtained for n = -1, and are in proximity to high-density regions. In the other models, the typical post-shock temperatures are smaller (10(5)-10(7) K)
One-Dimensional Hydrodynamical Simulations of Gravitational Clustering in an Expanding Background
No full textThe authors present the results of a series of one-dimensional N-body and hydrodynamical simulations which have been used for testing the different clustering properties of baryonic and dark matter in an expanding background. Initial Gaussian random density perturbations with a power-law spectrum are assumed. They analyse the distribution of density fluctuations and thermodynamical quantities for different spectral indices and discuss the statistical properties of clustering in the corresponding simulations
A Cosmological Hydrodynamic code based on the Piecewise Parabolic Method
No full textWe present a hydrodynamical code for cosmological simulations which uses the piecewise parabolic method (PPM) to follow the dynamics of the gas component and an N-body particle-mesh algorithm for the evolution of the collisionless component. The gravitational interaction between the two components is regulated by the Poisson equation, which is solved by a standard fast Fourier transform (FFT) procedure. In order to simulate cosmological flows, we have introduced several modifications to the original PPM scheme, which we describe in detail. Various tests of the code are presented, including adiabatic expansion, single and multiple pancake formation, and three-dimensional cosmological simulations with initial conditions based on the cold dark matter scenario
Constraining the Cosmological Baryon Density with X--ray clusters
No full textWe study the properties of X-ray galaxy clusters in four cold dark matter models with different baryon fractions Omega_BM, ranging from 5 to 20 per cent. By using an original three-dimensional hydrodynamic code based on the piecewise parabolic method, we run simulations on a box with a size of 64h^-1 Mpc and we identify the clusters by selecting the peaks in the X-ray luminosity field. We analyse these mock catalogues by computing the mass function, the luminosity function, the temperature distribution and the luminosity-temperature relation. By comparing the predictions of the different models to a series of recent observational results, we find that only the models with low baryonic content agree with the data, while models with larger baryon fraction are well outside the 1sigma error bars. In particular, the analysis of the luminosity functions, both bolometric and in the energy band [0.5-2] keV, requires Omega_BM<~0.05 when we fix the values h=0.5 and n=0.8 for the Hubble parameter and the primordial spectral index, respectively. Moreover we find that, independently of the cosmological scenario, all the considered quantities have very little redshift evolution, particularly between z=0.5 and 0
A Parallel Cosmological Hydrodynamic Code Based on the Piecewise Parabolic Method
No full textWe present the parallel implementation of a hydrodynamical code for cosmological simulations which uses the Piecewise Parabolic Method (PPM) to follow the dynamics of the gas component and a Particle-Mesh N-body algorithm for the evolution of the collisionless component. The parallel code is written by using the CRAFT programming model and all the numerical tests and simulations are performed on the Cray T3D supercomputer at CINECA. We describe the time performance of the code, its scalability and the load balancing and we show some results obtained in typical cosmological simulations
The Sunyaev–Zel'dovich effects from a cosmological hydrodynamical simulation: large-scale properties and correlation with the soft X-ray signal
No full textModeling the co-evolution of supermassive black holes and galaxies: I. Black hole scaling relations and the Active Galactive Nuclei luminosity function
No full textWe model the cosmological co-evolution of galaxies and their central supermassive black holes (BHs) within a semi-analytical framework developed on the outputs of the Millennium Simulation. This model, described in detail by Croton et al. and De Lucia and Blaizot, introduces a `radio mode' feedback from active galactic nuclei (AGN) at the centre of X-ray emitting atmospheres in galaxy groups and clusters. Thanks to this mechanism, the model can simultaneously explain: (i) the low observed mass dropout rate in cooling flows; (ii) the exponential cut-off in the bright end of the galaxy luminosity function and (iii) the bulge-dominated morphologies and old stellar ages of the most massive galaxies in clusters. This paper is the first of a series in which we investigate how well this model can also reproduce the physical properties of BHs and AGN. Here we analyse the scaling relations, the fundamental plane and the mass function of BHs, and compare them with the most recent observational data. Moreover, we extend the semi-analytic model to follow the evolution of the BH mass accretion and its conversion into radiation, and compare the derived AGN bolometric luminosity function with the observed one. While we find for the most part a very good agreement between predicted and observed BH properties, the semi-analytic model underestimates the number density of luminous AGN at high redshifts, independently of the adopted Eddington factor and accretion efficiency. However, an agreement with the observations is possible within the framework of our model, provided it is assumed that the cold gas fraction accreted by BHs at high redshifts is larger than at low redshifts
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