8463215
Quasistationary states and the range of pair interactions.
"Quasistationary" states are approximately time independent out of equilibrium states which have been observed in a variety of systems of particles interacting by long-range interactions. We investigate here the conditions of their occurrence for a generic pair interaction V(r→∞)~1/r(γ) with γ>0, in d>1 dimensions. We generalize analytic calculations known for gravity in d=3 to determine the scaling parametric dependences of their relaxation rates due to two-body collisions, and report extensive numerical simulations testing their validity. Our results lead to the conclusion that, for γ<d-1, the existence of quasistationary states is ensured by the large distance behavior of the interaction alone, while for γ>d-1 it is conditioned on the short distance properties of the interaction, requiring the presence of a sufficiently large soft core in the interaction potential.
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.
14466810
Basic properties of galaxy clustering in the light of recent results from the Sloan Digital Sky Survey
We discuss some of the basic implications of recent results on galaxy correlations published by the SDSS collaboration. In particular we focus on the evidence which has been recently presented for the scale and nature of the transition to homogeneity in the galaxy distribution, and results which describe the dependence of clustering on luminosity. The two questions are in fact strictly entangled, as the stability of the measure of the amplitude of the correlation function depends on the scale at which the mean density becomes well defined. We note that the recent results which indicate the convergence to well defined homogeneity in a volume equivalent to that of a sphere of radius 70 Mpc/h, place in doubt previous detections of luminosity bias from measures of the amplitude of the correlation function. We emphasize that the way to resolve these issues is to first use, in volume limited samples corresponding to different ranges of luminosity, the unnormalized two point statistics to establish the scale (and value) at which the mean density becomes well defined. We note also that the recent SDSS results for these statistics are in good agreement with those obtained by us through analyses of many previous samples, confirming in particular that the galaxy distribution is well described by a fractal dimension D 2 up to a scale of at least 20 Mpc/h. We discuss critically the agreement of this new data with current theoretical models.
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.
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
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.
108906869
Development of a triple well CMOS MAPS device with in-pixel signal processing and sparsified readout capabilities
Abstract The SLIM5 collaboration has designed, fabricated and tested several prototypes of CMOS Monolithic Active Pixel Sensors (MAPS). The key feature of these devices, with respect to traditional MAPS is to include, at the pixel level, charge amplification and shaping and a first sparsification structure that interfaces with on-chip digital readout circuits. Via the 3-well option of the applied 0.13 μ m ST-Microelectronics CMOS technology each pixel includes a charge preamplifier, a shaper, a discriminator, an output latch, while retaining a fill factor of the sensitive area close to 90%. The last device of the family was submitted on Q4 2006 and the tests are ongoing. On this sensor, an on-chip, off-pixel digital readout block (streamout data sparsification) was added to implement, to control and to readout a test matrix built up of 4 × 4 pixels. It is aimed at proposing solutions that will overcome the readout speed limit of future large-matrix MAPS chips.
72023452
Preliminary timing measurements on a data acquisition chain for a SiPM-based detector for prostate imaging
Prostate cancer (PC) is one of the most common diseases in western countries and a leading cause of cancer death. A variety of treatment options are available but a precise disease characterization is needed: evaluation of cancer location, size, and extent and an indication of tumor aggressiveness. The current standard for diagnosing PC is transrectal ultrasound guided sextant biopsy. A novel multidisciplinary approach is required. Imaging may play a key role provided that dedicated prostate imagers and procedures are available: considerable improvements have been achieved in diagnosis with the Magnetic Resonance Imaging (MRI) and nuclear medicine (Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT)) techniques. Nevertheless, due to sub-optimal prostate imaging geometries with these generic large instruments preventing separation of the signal from surrounding organs, the sensitivity, spatial resolution and lesion contrast detected are lower compared to what can be potentially achievable with optimized dedicated prostate imagers and procedures. Fully exploiting the Time Of Flight (TOF) capability would allow not only to increase the Signal-to-Noise ratio (SNR) / Noise Equivalent Count Rate (NECR) but also to get rid of the huge background coming from neighboring organs i.e. the bladder. Recently a new research project was initiated by a large INFN collaboration, and a “TOF-PET and MRI for prostate cancer diagnosis and follow up experiment” (TOPEM) was financed as a 3-year experiment by the Italian “INFN Commissione Scientifica Nazionale V” with the goal of designing, building and testing in phantom tests an endorectal PET-TOF probe compatible with MRI.
123504344
Status of NEMO
Abstract The activities towards the realization of a km 3 Cherenkov neutrino detector carried out by the NEMO Collaboration are described. Long-term exploration of a 3500 m deep-sea site close to the Sicilian coast has shown that it is optimal for the installation of the detector. The realization of a Phase-1 project, which is under way, will validate the proposed technologies 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 site (Phase-2 project) will provide the possibility to test detector components at 3500 m depth.
110682003
High efficiency readout circuits for large matrices of pixels
Abstract In future collider experiments the increasing luminosity and center of mass energy are rising challenges in the research field of tracking systems where it is crucial to have very fast sensors with efficient readout in order to sustain the high particle flux. In this context we propose a high-efficiency digital readout architecture for large binary pixel matrices that is meant to cope with high hit-rates, up to 100 MHz/cm 2 , foreseen in the innermost tracker layer of the new generation particle accelerators. We modelled and designed several readout circuits to be integrated in the periphery of hybrid detectors. In this work we focus on a particular solution, to be interconnected to a 200 × 256 ‐ pixel matrix covering an area of 1.3 cm 2 . The hits are latched at pixel level, and the matrix provides a digital interface to the peripheral digital readout. The architecture is highly paralleled in order to reduce the pixels dead time introduced by readout which can be operated in data-push or triggered mode. In addition, a cluster compression algorithm, exploiting also the time sorted hit extraction, has been developed to reduce the output bandwidth. The architecture has been modelled in a hardware description language, to be synthesized in a net-list of foundry standard-cells. A Monte Carlo hit generator has been attached to simulations to evaluate the readout efficiency, both in data-push and triggered working mode. Simulation results will be presented, pointing out beside the efficiency results, the benefits introduced by the compression algorithm.
119249031
Measurement of the atmospheric muon flux with the NEMO Phase-1 detector
Abstract The NEMO Collaboration installed and operated an underwater detector including prototypes of the critical elements of a possible underwater km 3 neutrino telescope: a four-floor tower (called Mini-Tower) and a Junction Box. The detector was developed to test some of the main systems of the km 3 detector, including the data transmission, the power distribution, the timing calibration and the acoustic positioning systems as well as to verify the capabilities of a single tridimensional detection structure to reconstruct muon tracks. We present results of the analysis of the data collected with the NEMO Mini-Tower. The position of photomultiplier tubes (PMTs) is determined through the acoustic position system. Signals detected with PMTs are used to reconstruct the tracks of atmospheric muons. The angular distribution of atmospheric muons was measured and results compared to Monte Carlo simulations.