15654508
Gravitational force distribution in fractal structures
We study the (Newtonian) gravitational force distribution arising from a fractal set of sources. We show that, in the case of real structures in finite samples, an important role is played by morphological properties and finite-size effects. For dimensions smaller than d − 1 (being d the space dimension) the convergence of the net gravitational force is assured by the fast decaying of the density, while for fractal dimension D > d − 1 the morphological properties of the structure determine the eventual convergence of the force as a function of distance. We clarify the role played by the cut-offs of the distribution. Some cosmological implications are discussed.
31106687
Gravitational dynamics of an infinite shuffled lattice of particles.
We study, using numerical simulations, the dynamical evolution of self-gravitating point particles in static Euclidean space, starting from a simple class of infinite "shuffled lattice" initial conditions. These are obtained by applying independently to each particle on an infinite perfect lattice a small random displacement, and are characterized by a power spectrum (structure factor) of density fluctuations which is quadratic in the wave number k, at small k. For a specified form of the probability distribution function of the "shuffling" applied to each particle, and zero initial velocities, these initial configurations are characterized by a single relevant parameter: the variance delta(2) of the "shuffling" normalized in units of the lattice spacing l. The clustering, which develops in time starting from scales around l, is qualitatively very similar to that seen in cosmological simulations, which begin from lattices with applied correlated displacements and incorporate an expanding spatial background. From very soon after the formation of the first nonlinear structures, a spatiotemporal scaling relation describes well the evolution of the two-point correlations. At larger times the dynamics of these correlations converges to what is termed "self-similar" evolution in cosmology, in which the time dependence in the scaling relation is specified entirely by that of the linearized fluid theory. Comparing simulations with different delta, different resolution, but identical large scale fluctuations, we are able to identify and study features of the dynamics of the system in the transient phase leading to this behavior. In this phase, the discrete nature of the system explicitly plays an essential role.
33621420
Point processes and stochastic displacement fields.
The effect of a stochastic displacement field on a statistically independent point process is analyzed. Stochastic displacement fields can be divided into two large classes: spatially correlated and uncorrelated. For both cases exact transformation equations for the two-point correlation function and the power spectrum of the point process are found, and a detailed study of them with important paradigmatic examples is done. The results are general and in any dimension. Particular attention is devoted to the kind of large-scale correlations that can be introduced by the displacement field and to the realizability of arbitrary "superhomogeneous" point processes.
15688477
Scaling and fluctuations in galaxy distribution: two tests to probe large scale structures
We present a brief introduction to the statistical properties of systems with large fluctuations. We point out that for such systems the relevant statistical quantities are scaling exponents and the nature of fluctuations is completely different from the one belonging to system with small fluctuations. We then propose two test to be performed on galaxy counts data as a function of apparent magnitude, which may clarify in a direct way the nature of the large scale galaxy clustering
119390803
Statistical Physics for Cosmic Structures
The 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.
14013791
Initial Conditions, Discreteness and Non-Linear Structure Formation in Cosmology
In this lecture we address three different but related aspects of the initial continuous fluctuation field in standard cosmological models. Firstly we discuss the properties of the so-called Harrison-Zeldovich like spectra. This power spectrum is a fundamental feature of all current standard cosmological models. In a simple classification of all stationary stochastic processes into three categories, we highlight with the name “super- homogeneous” the properties of the class to which models like this, with P(0) = 0, belong. In statistical physics language they are well described as glass-like. Secondly, the initial continuous density field with such small amplitude correlated Gaussian fluctuations must be discretised in order to set up the initial particle distribution used in gravitational N-body simulations. We discuss the main issues related to the effects of discretisation, particularly concerning the effect of particle induced fluctuations on the statistical properties of the initial conditions and on the dynamical evolution of gravitational clustering.
110623274
Fast readout logic interfacing a 256-pixel matrix of a dual-layer 3D device
A prototype of a 3D ASIC built up of a fast readout architecture, with sparsification capabilities, which interfaces with a matrix of a 256-pixel sensor, was recently submitted. The chosen technology is CMOS Chartered 130 nm as it is compatible with the Tezzaron facility to interconnect face-to-face two silicon wafers allowing for a vertical integration structure by means of through-silicon-vias. Particularly, the readout logic uses one layer that will be stacked on a sensor layer at the end of the fabrication process.
12001348
Design and construction of an end-ladder prototype board with a 2-D HW compressor
This paper explains the design and the construction of the prototype of an end-ladder card for the silicon drift detector of a high-energy physics experiment at CERN. The end-ladder performs data reduction, compression, and packing for a data acquisition chain. In particular, the end-ladder card includes a chip whose main function is to execute these tasks. Besides the chip's functions, the end-ladder card interfaces with the front-end electronics and processes and transmits the data set received from the front end through an optical channel to the counting room. The paper also describes this chip and the ongoing tests on its production. In addition, the paper shows details of the end-ladder prototype card's design and of the relative tests that are going to be carried out in the near future.
109308730
Heavy-Ions induced SEE effects measurements for the STRURED ASIC
With the aim of developing a radiation-tolerant circuit, a digital test microelectronic device has been designed and fabricated by using a standard-cell library of a 130-nm CMOS technology, including three different architectures to correct circuit malfunctions induced by the occurrence of Single-Event Effects (SEEʼs). SEEʼs are one of the main reasons of failures affecting electronic circuits operating in harsh radiation environments, such as in experiments performed at High Energy Physics (HEP) colliders or in apparatus to be operated in Space. On the same digital circuit specifically designed, three redundant architectures added to a basic scheme have been implemented in order to evaluate their effectiveness to prevent SEE. This may give an indication on their usage in future digital circuits specifically designed for the above mentioned applications. We present the results of SEE cross section measurements performed on a test digital device exposed to a high energy heavy ion beam at the SIRAD irradiation facility of the INFN National Laboratories of Legnaro (Padova Italy).
111132370
Recent developments in 130 nm CMOS monolithic active pixel detectors
We developed monolithic active pixel detectors, by exploiting the triple well option available in a deep-submicron CMOS process. The novel features are the full analog signal processing and digital functionality implemented at the pixel level. The charge collecting element is realized using the deep N-well (DNW), the full in-pixel signal processing chain includes charge preamplifier, shaper, discriminator and latch. We report on the characterization of the two prototype chips, the first (APSEL0) containing single-channel sensors, with different collecting electrode area, and the latter (APSEL1) with several single pixel structures with improved noise figure implementing also an 8 × 8 matrix of 50 × 50 μm 2 pixel area. So far, the pixel matrix has a simple row by row readout, successfully tested with clock frequency up to 30 MHz. The response of the sensors to infra-red laser, β -rays and soft X-rays (from radioactive sources, 90 Sr and 55 Fe respectively) will be presented. The results achieved so far demonstrate the viability of the technology and suggest new design improvements implemented in the next prototype chips submission (APSEL2).
122993753
Recent results and perspectives of the NEMO project
Abstract The latest results and the activities towards the realization of a km 3 Cherenkov neutrino detector carried out by the NEMO Collaboration are described. The realization of a Phase-1 project has validated all relevant technologies proposed for the realization of the km 3 detector on a test site at 2000 m depth. The realization of a new infrastructure on the candidate Capo Passero site (for Phase-2 project) will provide the possibility to test detector components at 3500 m depth.