Department of Engineering "Enzo Ferrari"

This paper investigates how a p2p television platform can take advantage of the presence of frequent channel viewers to grant them a more satisfying service than to less regular spectators, and how such privileged users can also be protected when unfavorable operating conditions manifest within the overlay. The explored idea is to learn beforehand about the users' interests, monitoring their behavior in the recent past, in order to cluster them in groups that display different habits; then, the video chunk scheduling algorithm of the overlay is altered, with the aim of serving frequent spectators in a privileged manner, providing them with a better viewing experience and a faster access to the selected channel without overly penalizing less habitual customers. An analytical model is developed, to capture the difference in average startup delay that the proposed modifications introduce; several additional performance metrics are numerically determined, in order to thoroughly size up the performance of both groups of viewers. The obtained results show that a clear service differentiation is attained and demonstrate that, if bandwidth resources become scarce, frequent viewers are protected and still enjoy a broadcasting service of superior quality.

This work proposes to combine Peer-to-Peer (P2P) and Dynamic Adaptive Streaming over HTTP (DASH), leveraging the scalability and self-organization properties of the former and the capability of the latter to adapt the rate of the delivered video to varying operating conditions. The devised P2P-DASH architecture is a multi-overlay P2P platform, where every peer implements a decentralized rate control strategy that steers its transitions from one overlay to another, so as to achieve a good viewing quality and also preserve the good functioning of the entire system. At peer's site, the new architecture displays the following salient features: (i) an augmented pool of neighbors, to provide every node with the knowledge of the streaming process within adjacent overlays; (ii) a priority mechanism to speed up the delivery of video chunks to peers that newly enter the system or switch from the current to a new overlay, in order to quickly turn them into active peers; (iii) some alternative rate control algorithms to guarantee, with different degrees, more resources to overlays that deliver higher streaming rates, therefore reducing the misalignment among streaming processes which occur in different overlays, and ultimately improve the viewing quality of the single user. System behavior is extensively investigated through simulation and some clear design guidelines are provided.

Dynamic Adaptive Streaming over HTTP (DASH) is a recently proposed standard that offers different versions of the same media content to adapt the delivery process over the Internet to dynamic bandwidth fluctuations and different user device capabilities. The peer-to-peer (P2P) paradigm for video streaming allows us to leverage the cooperation among peers, guaranteeing the service of video requests with increased scalability and reduced cost. We propose to combine these two approaches in a P2P-DASH architecture, exploiting the potentiality of both. The new platform is made of several swarms and a different DASH representation is streamed within each of them; unlike client-server DASH architectures, where each client autonomously selects which version to download according to current network conditions and to its device resources, we put forth a new rate control strategy implemented at peer site to maintain a good viewing quality to the local user and to simultaneously guarantee the s...

The paper focuses on the development of a framework for high-order compact finite volume discretization of the three-dimensional scalar advection–diffusion equation. In order to deal with irregular domains, a coordinate transformation is applied between a curvilinear, non-orthogonal grid in the physical space and the computational space. Advective fluxes are computed by the fifth-order upwind scheme introduced by Pirozzoli [S. Pirozzoli, Conservative hybrid compact-WENO schemes for shock–turbulence interaction, J. Comp. Phys. 178 (2002) 81] while the Coupled Derivative scheme [M.H. Kobayashi, On a class of Padé finite volume methods, J. Comp. Phys. 156 (1999) 137] is used for the discretization of the diffusive fluxes.Numerical tests include unsteady diffusion over a distorted grid, linear free-surface gravity waves in a irregular domain and the advection of a scalar field. The proposed methodology attains high-order formal accuracy and shows very favorable resolution characteristics for the simulation of problems with a wide range of length scales.

In this paper we attack the problem of devising a finite volume method for computational fluid dynamics and related phenomena which can deal with complex geometries while attaining high-orders of accuracy and spectral convergence at a reasonable computational cost. As a first step towards this end, we propose a control volume finite element method for the solution of the advection–diffusion equation. The numerical method and its implementation are carefully tested in the paper where h- and p-convergence are checked by comparing numerical results against analytical solutions in several relevant test-cases. The numerical efficiency of a selected set of operations implemented is estimated by operation counts, ill-conditioning of coefficient matrices is avoided by using an appropriate distribution of interpolation points and control-volume edges.

Natural convection in inclined channels is a rather common flow configuration: it occurs in solar energy systems, ventilated roofs as well as in many industrial applications and chemical processes. Analytical solutions for laminar, fully-developed natural convection in inclined parallel-plate channels are presented in this paper. The Boussinesq approximation is applied and viscous energy dissipation is neglected. One specific thermal configuration is addressed, where one wall is perfectly insulated and a constant, uniform heat flux is released to the fluid from the other wall. The resulting set of governing equations is non-linear, as the mean velocity is not assigned a priori but determined as part of the solution. Depending on the channel inclination angle and on the imposed heat flux conditions, either no solution, one solution, multiple or infinite solutions exist. Under restrictive assumptions velocity profiles are self-similar with respect to the channel inclination, while the temperature profile is independent of the inclination. The two-dimensional, hydraulically-and thermally-developing natural convection channel flow is simulated numerically for some combinations of channel inclination angle and heating intensity to identify the most physical between the many solutions.

Open-cell metal foams are used in a growing number of applications like lightweight porous structures, enhanced heat transfer devices and compact heat exchangers, catalytic reactors, and even rotors of centrifugal compressors. In many cases, pressure drops and flow rates through the metal foams are predicted using the macroscopic Darcy-Forchheimer equation. Values obtained can be accurate enough for applications, provided the hydraulic properties of the foam are known. The present work is aimed to describe a numerical approach for calculating the hydraulic permeability and the Ergun coefficient of a real sample of metal foam starting from an x-ray tomography of the sample. Fluid dynamic simulations are conducted in the digital sample at the scale of the pores and data obtained are postprocessed to obtain the main hydraulic properties of the porous material.

Convective heat transfer in laminar conditions is studied numerically for a Prandtl number Pr = 0.025, representative of liquid lead-bismuth eutectic (LBE). The geometry investigated is a channel with a periodic series of shallow cavities. Finite-volume simulations are carried out on structured orthogonal curvi-linear grids, for ten values of the Reynolds number based on the hydraulic diameter between Re m = 24.9 and Re m = 2260. Flow separation and reattachment are observed also at very low Reynolds numbers and wall friction is found to be remarkably unequal at the two walls. In almost all cases investigated, heat transfer rates are smaller than the corresponding flat channel values. Low-Prandtl number heat transfer rates, investigated by comparison with Pr = 0.71 results, are large only for uniform wall temperature and very low Re. Influence of flow separation on local heat transfer rates is discussed, together with the effect of different thermal boundary conditions. Dependency of heat transfer performance on the cavity geometry is also considered.

Turbulent forced convection is investigated by Direct Numerical Simulation in a channel with one sinusoidal wavy wall and one flat wall. Fluid flow and heat transfer are periodically fully developed, the simulated Reynolds number of the bulk velocity and the hydraulic diameter is Re = 18, 880 while three Prandtl numbers are considered, i.e. Pr = 0.025, Pr = 0.2, and Pr = 0.71. The fluid flow is characterized by separation, reattachment and a shear layer downstream the wave peak, these are conditions relevant for turbulent heat transfer and passive scalar transport applications. In the range of Péclet numbers investigated, the most important heat transfer mechanism is by mean flow advection. Accordingly, the peak heat transfer region is in the upslope part of the domain. The separation bubble instead acts as a barrier to convection and the heat transfer rate is minimum close to separation. An a priori analysis is performed in order to assess the accuracy of turbulent heat transfer models based on the Generalized Gradient Diffusion Hypothesis.

Turbulent forced convection in a channel with one planar wall and one wall of sinusoidal shape is investigated by Direct Numerical Simulation. The flow is fully developed and the Reynolds number based on the mean bulk velocity and the average hydraulic diameter is Re z 18,900; in this weakly turbulent flow regime three different Prandtl number values are investigated, Pr ¼ 0.025, 0.20, 0.71. The fluid is in contact with the colder channel walls at an equal, uniform temperature. The main statistical quantities, like the root-mean-square of temperature fluctuations and the turbulent heat fluxes, the local heat transfer coefficient and turbulent Prandtl number values are reported. Effects of flow separation and reattachment on the local heat transfer rate and turbulent Prandtl number distribution are also presented and discussed. An a priori analysis of the behavior of the simple gradient diffusion model of turbulent heat fluxes is performed in the low Prandtl number, separated flow conditions of the present work. While the low Prandtl number effect can be accounted for by an appropriate selection of the turbulent Prandtl number value to be provided to the model, deviations form the expected behavior of turbulent heat fluxes are seen to occur in the flow separation region and downstream reattachment.

Per giustificare alcune delle scelte fatte, che verranno spiegate successivamente si rende necessario dare una breve panoramica della monoposto e del tipo di competizione. La monoposto in questione è caratterizzata da: Telaio: è stata scelta una struttura in tralicci di alluminio in ottica riduzione pesi, soluzione adottata per la prima volta nel 2010 proprio dall'Università di Modena. Gruppo ruota: porta mozzi in ergal ricavati dal pieno; cerchi in lega d'alluminio sviluppati dall'OZ per applicazione specifica formula SAE (poco più di 1kg per cerchio); pinze freni AP Racing in alluminio. Motore: sempre in ottica riduzione pesi si utilizzerà per il 2011 un motore Husquvarna da 530cc di cilindrata che garantisce un guadagno in termini di peso di ben 22kg rispetto al gruppo termico del 2010. Peso: la stima di questo dato è di 165/170kg e per dare un'idea del lavoro che c'è dietro questo valore si riporta una rapida statistica: 170kg nel 2011 190 kg nel 2010 259 kg nel 2009

Riassunto Il telerilevamento satellitare ed aereo riveste un ruolo fondamentale nella mappatura termica dei corpi idrici poiché consente il monitoraggio di ampie aree quasi in tempo reale. Le bande utilizzate sono quelle dell'infrarosso termico (TIR) e il valore misurato è quello della temperatura pellicolare dell'acqua, ossia dei primi 100 μm di spessore. In questo ambito il principale fattore limite dei dati telerilevati è la risoluzione spaziale.

Page 1. CAL/VAL ACTIVITIES ON EUROPEAN VOLCANOES TEST SITES IN THE VNIR-SWIR SPECTRAL RANGE. Massimo Musacchio, Maria Fabrizia Buongiorno, Stefania Amici, Stefano Corradini, Alessandro Piscini, Luca Merucci, Valerio Lombardo, Malvina Silvestri, Claudia Spinetti, Laura Colini. Istituto Nazionale di Geofisica e Vulcanologia, Remote Sensing Unit, Rome Italy Page 2.

Abstract Atmospheric modeling with a radiative transfer code is very important when ground or atmospheric physical properties are analysed by means of remote sensing data acquired by imaging spectrometers. In order to describe the local conditions in the low atmospheric layers, radiative transfer codes such as MODTRAN need to be adjusted with local information.

Riassunto In questo contributo è mostrata una procedura software sviluppata per apportare le correzioni atmosferiche e orografiche ad immagini telerilevate nella regione del visibile-vicino infrarosso. I termini di correzione atmosferica sono calcolati, per ogni pixel, utilizzando i modelli di trasferimento radiativo MODTRAN e 6S.

Abstract This paper presents an algorithm to improve the spatial resolution, from 90 m to 30 m, of the thermal mapping of small bodies of water or near coasts obtained from the ASTER satellite sensor. The entire procedure is based only on ASTER images. The first part of the work deals with the physical and mathematical basis on which the algorithm was constructed, the schema of the main steps and the methods of validation of the algorithm.

Waste incineration releases into the environment toxic substances having a teratogenic potential, but little epidemiologic evidence is available on this topic. We aimed at examining the relation between exposure to the emissions from a municipal solid waste incinerator and risk of birth defects in a northern Italy community, using Geographical Information System (GIS) data to estimate exposure and a population-based case-control study design.

Abstract Background: Some epidemiologic studies have suggested an association between electromagnetic field exposure induced by high voltage power lines and childhood leukemia, but null results have also been yielded and the possibility of bias due to unmeasured confounders has been suggested.

Abstract Continuous meteorological examination of the Pre-Alpine zones in Northern Italy (Po Valley) is important for determination of atmospheric water cycles connected with floods and rainfalls. During a special meteorological observing period (MAP-SOP), radiosounding and other measurements were made in the site of Verona (Italy). This paper deals with Zenith Total Delay (ZTD) and Precipitable Water (PW) comparisons obtained by GPS, radiosounding and other meteorological measurements.

Abstract The ASI-SRV (Sistema Rischio Vulcanico) project started at the beginning of the 2007 is funded by the Italian Space Agency (ASI) in the frame of the National Space Plan 2003-2005 under the Earth Observations section for natural risks management.