229 research outputs found
Relazioni intergenerazionali nonni-nipoti: differenze culturali a confronto
No full textNegli ultimi anni la questione dei rapporti intergenerazionali sta emergendo con maggiore forza dal momento che, con l’invecchiamento progressivo della popolazione, sempre più nonni e bisnonni sono presenti nella vita dei nipoti (Uhlenberg, 2005). Rispetto al passato, dunque, la struttura familiare si sta verticalizzando. Ma in che modo il cambiamento della struttura familiare ha modificato la relazione tra nonni e nipoti
On the origin of Sérsic profiles of galaxies and Einasto profiles of dark-matter halos
No full textThe surface-brightness profiles of galaxies I(R) and the density profiles of dark-matter halos ρ(r) are well represented by the same analytic function, named after either Sérsic, I ~ e-(R/R∗)1/m, or Einasto, ρ ~ e-(r/r∗)α, where R∗ and r∗ are characteristic radii. Systems with high Sérsic index m (or low Einasto index α) have steep central profiles and shallow outer profiles, while systems with low m (or high α) have shallow central profiles and steep profiles in the outskirts. We present the results of idealized numerical experiments which suggest that the origin of these profiles can be traced back to the initial density fluctuation field: high-α (low-m) systems form in smooth regions via few mergers, while low-α (high-m) systems form in clumpy regions via several mergers
4H- and 6H-SiC Rutherford backscattering-channeling spectrometry: polytype finger printing
No full textBNPmix: An R Package for Bayesian Nonparametric Modeling via Pitman-Yor Mixtures
No full textBNPmix is an R package for Bayesian nonparametric multivariate density estimation, clustering, and regression, using Pitman-Yor mixture models, a flexible and robust generalization of the popular class of Dirichlet process mixture models. A variety of model specifications and state-of-the-art posterior samplers are implemented. In order to achieve computational efficiency, all sampling methods are written in C++ and seamless integrated into R by means of the Rcpp and RcppArmadillo packages. BNPmix exploits the ggplot2 capabilities and implements a series of generic functions to plot and print summaries of posterior densities and induced clustering of the data
Radially anisotropic systems with forces: equilibrium states
No full textWe continue the study of collisionless systems governed by additive r-α interparticle forces by focusing on the influence of the force exponent α on radial orbital anisotropy. In this preparatory work, we construct the radially anisotropic Osipkov-Merritt phase-space distribution functions for self-consistent spherical Hernquist models with r-α forces and 1 ≤ α < 3. The resulting systems are isotropic at the centre and increasingly dominated by radial orbits at radii larger than the anisotropy radius ra. For radially anisotropic models we determine the minimum value of the anisotropy radius rac as a function of α for phase-space consistency (such that the phase-space distribution function is nowhere negative for ra ≥ rac). We find that rac decreases for decreasing α, and that the amount of kinetic energy that can be stored in the radial direction relative to that stored in the tangential directions for marginally consistent models increases for decreasing α. In particular, we find that isotropic systems are consistent in the explored range of α. By means of direct N-body simulations, we finally verify that the isotropic systems are also stabl
Analysis of the hole transport through valence band states in heavy Al doped 4H-SiC by ion implantation
No full textGaussian Random Field Power Spectrum and the Sérsic Law
No full textThe surface-brightness profiles of galaxies are well described by the Sérsic law: systems with high Sérsic index m have steep central profiles and shallow outer profiles, while systems with low m have shallow central profiles and steep outer profiles. R. Cen has conjectured that these profiles arise naturally in the standard cosmological model with initial density fluctuations represented by a Gaussian random field (GRF). We explore and confirm this hypothesis with N-body simulations of dissipationless collapses in which the initial conditions are generated from GRFs with different power spectra. The numerical results show that GRFs with more power on small scales lead to systems with higher m. In our purely dissipationless simulations, the Sérsic index is in the range 2 ≤ m ≤ 6.5. It follows that systems with Sérsic index as low as m = 2 can be produced by coherent dissipationless collapse, while high-m systems can be obtained if the assembly history is characterized by several mergers. As expected, dissipative processes appear to be required to obtain exponential profiles (m = 1)
Radially anisotropic systems with r-α forces - II: radial-orbit instability
No full textWe continue to investigate the dynamics of collisionless systems of particles interacting via additive r-α interparticle forces. Here we focus on the dependence of the radial-orbit instability on the force exponent α. By means of direct N-body simulations, we study the stability of equilibrium radially anisotropic Osipkov-Merritt spherical models with Hernquist density profile and with 1 ≤ α 0.3, so they are never flatter than an E7 system
Dry mergers and the size evolution of early-type galaxies
No full textDry (i.e. dissipationless) merging has been proposed as the main driver of the observed size evolution of early-type galaxies (ETGs). The actual role of this mechanism is questioned by the tightness of the local stellar mass-size relation of ETGs. Combining this observed scaling law with simple merging models, which should bracket cosmologically motivated merging histories, we draw the following conclusions: 1) local massive ETGs can have assembled at most ~45% of their stellar mass via dry mergers; 2) extreme fine tuning is required for this to be the case
Conventional thermal annealing for a more efficient p-type doping of Al+ implanted 4H-SiC
No full textThe p-type doping of high purity semi-insulating 4H polytype silicon carbide (HPSI 4H-SiC) by aluminum ion (Al+) implantation has been studied in the range of 1 × 1019 to 8 × 10 20/cm3 (0.39 μm implanted thickness) and a conventional thermal annealing of 1950 °C/5 min. Implanted 4H-SiC layers of p-type conductivity and sheet resistance in the range of 1.6 × 104 to 8.9 ×102 Ω□, corresponding to a resistivity in the range of 4.7 × 10-1 to 2.7 × 10-2 Ω cm have been obtained. Hall carrier density and mobility data in the temperature range of 140-720 K feature the transition from a valence band to an intraband conduction for increasing implanted Al ion concentration from 1 × 10 19/cm3 to 4 × 1020/cm3. A 73% electrical activation, 31% compensation and 146 meV ionization level have been obtained using a best-fit solution of the neutrality equation to Hall carrier data for the lowest concentration.</p
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