5,558 research outputs found
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 attivitĂ natatorie
Alla cittĂ di Milano manca un centro natatorio di spicco atto ad ospitare eventi sportivi di caratura internazionale. Lâarticolo affronta il tema della progettazione di edifici per attivitĂ natatorie proponendo lâinquadramento di possibili soluzioni progettuali attraverso degli studi eseguiti nellâambito del corso âBuilding Technology Studioâ al Politecnico di Milano. I progetti sono contestualizzati nellâambito di un quartiere originariamente pensato per il rapporto con lâacqua, 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
P 386 Human cytomegalovirus plays a role in inhibition of host-cell protein synthesis in a receptor-independent manner
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
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