1,721,219 research outputs found
The two-dimensional stochastic heat equation: renormalizing a multiplicative noise
No full textWe study, in two space dimensions,the heat equation with a random potential that is a white noise in space and time. We introduce a regularization of the noise and prove that, by a suitable renormalization of the coupling coefficient, the covariance has a non-trivial limit when the regularization is removed. The limit is described in terms of a two-body Schrodinger operator with singular interaction
THE STOCHASTIC HEAT-EQUATION - FEYNMAN-KAC FORMULA AND INTERMITTENCE
No full textWe study, in one space dimension, the heat equation with a random potential that is a white noise in space and time. This equation is a linearized model for the evolution of a scalar field in a space-time-dependent random medium. It has also been related to the distribution of two-dimensional directed polymers in a random environment, to the KPZ model of growing interfaces, and to the Burgers equation with conservative noise. We show how the solution can be expressed via a generalized Feynman-Kac formula. We then investigate the statistical properties: the two-point correlation function is explicitly computed and the intermittence of the solution is proven. This analysis is carried out showing how the statistical moments can be expressed through local times of independent Brownian motions
“Analisi economica della criminalità e bilancio della sicurezza in Italia” Nota n. 4, Ministero dell’Economia e delle Finanze, Commissione Tecnica per la Spesa Pubblica
No full text
Small noise asymptotic of the Gallavotti-Cohen functional for diffusion processes
No full textWe analyze the Gallavotti-Cohen functional, defined as the empirical power dissipated by the non conservative part of the drift, fora diffusion process in R-n. In particular we prove a large deviation principle in the limit in which the noise vanishes and the time interval diverges. The corresponding rate functional, which satisfies the fluctuation theorem, is expressed in terms of a variational problem on the classical Freidlin-Wentzell functional. As shown in an example, the rate functional can be not strictly convex
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Strong asymmetric limit of the quasi-potential of the boundary driven weakly asymmetric exclusion process
No full textWe consider the weakly asymmetric exclusion process on a bounded
interval with particles reservoirs at the endpoints. The hydrodynamic limit for the empirical
density, obtained in the diffusive scaling, is given by the viscous Burgers equation
with Dirichlet boundary conditions. In the case in which the bulk asymmetry is in the
same direction as the drift due to the boundary reservoirs, we prove that the quasipotential
can be expressed in terms of the solution to a one-dimensional boundary value
problem which has been introduced by Enaud and Derrida [16].We consider the strong
asymmetric limit of the quasi-potential and recover the functional derived by Derrida,
Lebowitz, and Speer [15] for the asymmetric exclusion proces
A parametric VLSI architecture for video motion estimation
No full textThis paper presents a VLSI macro-cell for the implementation of full-search (FS) motion estimation that is a key issue of various video processing and compression standards such as MPEG and H.263. Beyond the usual algorithm, advanced-prediction and static-priority options are supported to improve the SNR/bit-rate efficiency. The architecture is fully parametric in terms of block size and maximum search area size and the latter is also dynamically programmable. Based on a hardware multiplexing strategy and a saturation mechanism, the architecture features high throughput/area efficiency and reduced hardware complexity with respect to conventional FS systolic arrays. Two ASICs were implemented on a 0.25 mum CMOS technology. The high-speed one features a 5.4 mm(2) core size and processes up to 4CIF format at 105 MHz. The smaller one features a 2 mm(2) core size and processes QCIF and CIF formats at 18 and 72 MHz, respectively. Exploiting the search area size programmability, these two formats can be processed with an average power consumption of 16 and 65 mW, respectively, which is of paramount interest for wireless applications. (C) 2001 Elsevier Science B.V. All rights reserved
Residual stresses influence on the fatigue strength of structural components
Full text linkSeveral production processes, both conventional and innovative, may result in residual stresses arising in critical areas of a component. The main issues include high distortion, reduced fatigue life, fracturing or delamination. In this context, standard fatigue design codes traditionally consider residual stresses through conservative assumptions, leading to either sub-optimal design or unexpected failures. Recently, innovative computational techniques have been developed to address residual stresses in a more comprehensive way. As a result, a more effective material utilisation and a more accurate fatigue life assessment can be achieved. The present work examines the influence of residual stresses on the fatigue endurance of S355JR structural steel components. Both welded and notched components were analysed, carrying out numerical and experimental analyses. In the case of welded components, residual stresses resulting from the welding process were numerically evaluated by means of an uncoupled thermal-structural simulation, while for notched specimens a preload causing limited yielding was used to induce a local residual stress field comparable to that obtained for welded specimens nearby the critical locations. Even if he work is still in progress, tests carried out with different specimens under different loading conditions allowed to understand the effect of residual stresses on the fatigue life
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