Observations and modelling of soil slip-debris flow initiation processes in pyroclastic deposits: the Sarno 1998 event

International audiencePyroclastic soils mantling a wide area of the Campanian Apennines are subjected to recurrent instability phenomena. This study analyses the 5 and 6 May 1998 event which affected the Pizzo d'Alvano (Campania, southern Italy). More than 400 slides affecting shallow pyroclastic deposits were triggered by intense and prolonged but not extreme rainfall. Landslides affected the pyroclastic deposits that cover the steep calcareous ridges and are soil slip-debris flows and rapid mudflows. About 30 main channels were deeply scoured by flows which reached the alluvial fans depositing up to 400 000 m3 of material in the piedmont areas. About 75% of the landslides are associated with morphological discontinuities such as limestone cliffs and roads. The sliding surface is located within the pyroclastic cover, generally at the base of a pumice layer. Geotechnical characterisation of pyroclastic deposits has been accomplished by laboratory and in situ tests. Numerical modelling of seepage processes and stability analyses have been run on four simplified models representing different settings observed at the source areas. Seepage modelling showed the formation of pore pressure pulses in pumice layers and the localised increase of pore pressure in correspondence of stratigraphic discontinuities as response to the rainfall event registered between 28 April and 5 May. Numerical modelling provided pore pressure values for stability analyses and pointed out critical conditions where stratigraphic or morphological discontinuities occur. This study excludes the need of a groundwater flow from the underlying bedrock toward the pyroclastic cover for instabilities to occur

Soil slips and debris flows on terraced slopes

International audienceTerraces cover large areas along the flanks of many alpine and prealpine valleys. Soil slips and soil slips-debris flows are recurrent phenomena along terraced slopes. These landslides cause damages to people, settlements and cultivations. This study investigates the processes related to the triggering of soil slip-debris flows in these settings, analysing those occurred in Valtellina (Central Alps, Italy) on November 2000 after heavy prolonged rainfalls. 260 landslides have been recognised, mostly along the northern valley flank. About 200 soil slips and slumps occurred in terraced areas and a third of them evolved into debris flows. Field work allowed to recognise the settings at soil slip-debris flow source areas. Landslides affected up to 2.5 m of glacial, fluvioglacial and anthropically reworked deposits overlying metamorphic basement. Laboratory and in situ tests allowed to characterise the geotechnical and hydraulic properties of the terrains involved in the initial failure. Several stratigraphic and hydrogeologic factors have been individuated as significant in determining instabilities on terraced slopes. They are the vertical changes of physical soil properties, the presence of buried hollows where groundwater convergence occurs, the rising up of perched groundwater tables, the overflow and lateral infiltration from superficial drainage network, the runoff concentration by means of pathways and the insufficient drainage of retaining walls

Esperienze progettuali di edifici per attività natatorie

Alla città di Milano manca un centro natatorio di spicco atto ad ospitare eventi sportivi di caratura internazionale. L’articolo affronta il tema della progettazione di edifici per attività natatorie proponendo l’inquadramento di possibili soluzioni progettuali attraverso degli studi eseguiti nell’ambito del corso “Building Technology Studio” al Politecnico di Milano. I progetti sono contestualizzati nell’ambito di un quartiere originariamente pensato per il rapporto con l’acqua, ovvero Porto di Mare, sito alla periferia sud-est di Milano

Particle Acceleration in Turbulence and Weakly Stochastic Reconnection

Fast particles are accelerated in astrophysical environments by a variety of processes. Acceleration in reconnection sites has attracted the attention of researchers recently. In this letter we analyze the energy distribution evolution of test particles injected in three dimensional (3D) magnetohydrodynamic (MHD) simulations of different magnetic reconnection configurations. When considering a single Sweet-Parker topology, the particles accelerate predominantly through a first-order Fermi process, as predicted in previous work (de Gouveia Dal Pino & Lazarian, 2005) and demonstrated numerically in Kowal, de Gouveia Dal Pino & Lazarian (2011). When turbulence is included within the current sheet, the acceleration rate, which depends on the reconnection rate, is highly enhanced. This is because reconnection in the presence of turbulence becomes fast and independent of resistivity (Lazarian & Vishniac, 1999; Kowal et al., 2009) and allows the formation of a thick volume filled with multiple simultaneously reconnecting magnetic fluxes. Charged particles trapped within this volume suffer several head-on scatterings with the contracting magnetic fluctuations, which significantly increase the acceleration rate and results in a first-order Fermi process. For comparison, we also tested acceleration in MHD turbulence, where particles suffer collisions with approaching and receding magnetic irregularities, resulting in a reduced acceleration rate. We argue that the dominant acceleration mechanism approaches a second order Fermi process in this case.Comment: 6 pages, 1 figur

What sets the magnetic field strength and cycle period in solar-type stars?

Two fundamental properties of stellar magnetic fields have been determined by observations for solar-like stars with different Rossby numbers (Ro), namely, the magnetic field strength and the magnetic cycle period. The field strength exhibits two regimes: 1) for fast rotation it is independent of Ro, 2) for slow rotation it decays with Ro following a power law. For the magnetic cycle period two regimes of activity, the active and inactive branches, also have been identified. For both of them, the longer the rotation period, the longer the activity cycle. Using global dynamo simulations of solar like stars with Rossby numbers between ~0.4 and ~2, this paper explores the relevance of rotational shear layers in determining these observational properties. Our results, consistent with non-linear alpha^2-Omega dynamos, show that the total magnetic field strength is independent of the rotation period. Yet at surface levels, the origin of the magnetic field is determined by Ro. While for Ro<1 it is generated in the convection zone, for Ro>1 strong toroidal fields are generated at the tachocline and rapidly emerge towards the surface. In agreement with the observations, the magnetic cycle period increases with the rotational period. However, a bifurcation is observed for Ro~1, separating a regime where oscillatory dynamos operate mainly in the convection zone, from the regime where the tachocline has a predominant role. In the latter the cycles are believed to result from the periodic energy exchange between the dynamo and the magneto-shear instabilities developing in the tachocline and the radiative interior.Comment: 43 pages, 14 figures, accepted for publication in The Astrophysical Journa

Spatial interactions in agent-based modeling

Agent Based Modeling (ABM) has become a widespread approach to model complex interactions. In this chapter after briefly summarizing some features of ABM the different approaches in modeling spatial interactions are discussed. It is stressed that agents can interact either indirectly through a shared environment and/or directly with each other. In such an approach, higher-order variables such as commodity prices, population dynamics or even institutions, are not exogenously specified but instead are seen as the results of interactions. It is highlighted in the chapter that the understanding of patterns emerging from such spatial interaction between agents is a key problem as much as their description through analytical or simulation means. The chapter reviews different approaches for modeling agents' behavior, taking into account either explicit spatial (lattice based) structures or networks. Some emphasis is placed on recent ABM as applied to the description of the dynamics of the geographical distribution of economic activities, - out of equilibrium. The Eurace@Unibi Model, an agent-based macroeconomic model with spatial structure, is used to illustrate the potential of such an approach for spatial policy analysis.Comment: 26 pages, 5 figures, 105 references; a chapter prepared for the book "Complexity and Geographical Economics - Topics and Tools", P. Commendatore, S.S. Kayam and I. Kubin, Eds. (Springer, in press, 2014

Strategy revision opportunities and collusion

This paper studies whether and how strategy revision opportunities affect levels of collusion in indefinitely repeated two-player games. Consistent with standard theory, we find that such opportunities do not affect strategy choices, or collusion levels, if the game is of strategic substitutes. In games of strategic complements, by contrast, revision opportunities lead to more collusion. We discuss alternative explanations for this result