PROGETTAZIONE DI PARATIE FILTRANTI A SOSTEGNO DI PENDII INSTABILI

Nella nota, facendo riferimento al caso delle paratie filtranti, sono analizzate tre classi di metodi progettuali semplificati (metodi allo Stato Limite Ultimo, Metodi Ibridi e Metodi negli Spostamenti), con l’intento di fornire uno strumento utile al progettista per dimensionare la struttura e per valutare l’efficacia dell’intervento

The Wonder of Colors and the Principle of Ariadne

The Principle of Ariadne, formulated in 1988 ago by Walter Carnielli and Carlos Di Prisco and later published in 1993, is an infinitary principle that is independent of the Axiom of Choice in ZF, although it can be consistently added to the remaining ZF axioms. The present paper surveys, and motivates, the foundational importance of the Principle of Ariadne and proposes the Ariadne Game, showing that the Principle of Ariadne, corresponds precisely to a winning strategy for the Ariadne Game. Some relations to other alternative. set-theoretical principles are also briefly discussed

Experimental tests on shallow foundations of onshore wind turbine towers

The current effort towards the progressive switch from carbon-based to renewable energy production is leading to a relevant spreading of both on- and off-shore wind turbine towers. Regarding reinforced concrete shallow foundations of onshore wind turbine steel towers, possible reductions of reinforcement may increase their sustainability, speed of erection, and competitiveness. The article presents the results of an experimental program carried out at Politecnico di Milano concerning both cyclic and monotonic loading, simulating extreme wind conditions on 1:15 scaled models of wind turbine steel towers connected by stud bolt adapters to reinforced concrete shallow foundations embedded in a sandy soil. Three couples of foundation specimens were tested with different reinforcement layouts: (a) similar to current praxis, (b) without shear reinforcement, and (c) without shear reinforcement and with 50% of ordinary steel rebars replaced by steel fibers. Additional vertical loads were added to the small-scale models in order to ensure similarity in terms of stresses. The test results allowed to (i) characterize the mechanical behavior of the foundation element considering soil-structure interaction under both service and ultimate load conditions, (ii) assess the foundation failure mode, (iii) highlight the role of each typology of reinforcing bars forming the cage, and (iv) provide hints for the optimization of these latter

Dry granular flows: micromechanical interpretation of impacts on rigid obstacles.

The evaluation of impact forces exerted by flowing granular masses on rigid obstacles is of fundamental importance for the assessment of the associated risk and for the design of protection measures. A number of formulae are available in the literature for the maximum impact force; most of them are based on oversimplifying hypotheses about the behaviour of the granular material. For practical applications, formulations based on either hydrodynamic or elastic body models are often employed. These formulations require the use of empirical correcting factors. In order to better understand the impact mechanics, the authors have recently performed an extensive numerical campaign by using a Discrete Element approach (PFC3D code), where a dry granular mass is represented as a random distribution of rigid spherical particles. A new design formula, combining the hydrodynamic and elastic body theories, has been proposed on the base of the results obtained at the macroscopic scale. The parameters of the formula have been correlated with geometrical factors, namely front inclination and flow height. In this paper, the same DEM model is further used in order to investigate the relationship between the evolution with time of the impact force and the micromechanics of the granular mass. In particular, information about contact forces and particle velocities will be discussed and critically compared with macroscopic results. In order to progressively introduce the complexity of the impact phenomenon, three geometrical conditions are considered: a) vertical front, confined flow; b) vertical front, free surface flow; c) inclined front, free surface flow

Frame dragging and super-energy

We show that the vorticity appearing in stationary vacuum spacetimes is always related to the existence of a flow of super-energy on the plane orthogonal to the vorticity vector. This result, toghether with the previously established link between vorticity and super--energy in radiative (Bondi-Sachs) spacetimes strength further the case for this latter quantity as the cause of frame dragging.Comment: 12 pages Latex. To appear in Phys.Rev. D. Typos correcte

Le api svelano il mistero delle fonti di emissione di particolato inquinante

Si tratta di una ricerca che è durata due anni, ed è stata pubblicata sul numero di luglio 2015 della Rivista scientifica internazionale Plos One. Gli autori: Ilaria Negri, Marco Pellecchia (Koiné - Consulenze Ambientali S.n.c., Parma, Italy), Christian Mavris (Department of Earth Sciences, Natural History Museum, London, United Kingdom), Gennaro Di Prisco, Emilio Caprio (Dipartimento di Agraria, Laboratorio di Entomologia E. Tremblay, Università degli Studi di Napoli Federico II, Portici - Napoli). Nello studio scientifico i ricercatori dimostrano che le api si comportano anche come “campionatori” attivi di particolato atmosferico, i cosiddetti PM (dall’inglese “Particulate Matter”), di cui sono ricche le nostre città come troppo spesso avvertono i dati dell’Agenzia Regionale di Protezione dell’Ambiente (ARPA). Dice che l’Iglesiente (Iglesias, Sardegna) è inquinato, fortemente contaminato da metalli pesanti come il piombo e il bario. E svela poi che la salute di chi ci vive potrebbe essere compromessa, se non lo è già, anche dall’alta concentrazione di ferro, silicio e alluminio. Rivela ancora, con scientifica precisione, da dove provengono le micro particelle di queste impercettibilissime polveri: dalle miniere dell’Iglesiente e dalle industrie di Portovesm

Honey Bees (Apis mellifera, L.) as Active Samplers of Airborne Particulate Matter

© 2015 Negri et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. [CC by 4.0] The attached file is the published version of the article

The spectral element method as an effective tool for solving large scale dynamic soil-structure interaction problems

The spectral element method (SEM) is a powerful numerical technique naturally suited for wave propagation and dynamic soil-structure interaction (DSSI) analyses. A class of SEM has been widely used in the seismological field (local or global seismology) thanks to its capability of providing high accuracy and allowing the implementation of optimized parallel algorithms. We illustrate inthis contribution how the SEM can be effectively used also for the numerical analysis of DSSI problems, with reference to the 3D seismic response of a railway viaduct in Italy. This numerical analysis includes the combined effect of: a) strong lateral variations of soil properties; b) topographic amplification; c) DSSI; d) spatial variation of earthquake ground motion in the structural response. Some hints on the work in progress to effectively handle nonlinear problems with SEM are also given

Dynamics of viscous dissipative gravitational collapse: A full causal approach

The Misner and Sharp approach to the study of gravitational collapse is extended to the viscous dissipative case in, both, the streaming out and the diffusion approximations. The dynamical equation is then coupled to causal transport equations for the heat flux, the shear and the bulk viscosity, in the context of Israel--Stewart theory, without excluding the thermodynamics viscous/heat coupling coefficients. The result is compared with previous works where these later coefficients were neglected and viscosity variables were not assumed to satisfy causal transport equations. Prospective applications of this result to some astrophysical scenarios are discussed.Comment: 22 pages Latex. To appear in Int. J. Mod. Phys. D. Typos correcte