945 research outputs found
Slope dynamics and streambed uplift during the Pergalla landslide reactivation in March 2016 and discussion of concurrent causes (Northern Apennines, Italy)
No full textOn March 28, 2016, the toe zone of the apparently dormant Pergalla earthslide-earthflow (Northern Apennines, Italy) had a paroxysmal reactivation. In the course of 2 days, displacements up to almost 8 m severely damaged several houses and roads. At the bottom of the slope, the emersion of rotational sliding surfaces determined the uplift of almost 3 m of the Nure river streambed that was consequently partially dammed. The paper describes the landslide event on the basis of field surveys and analysis of post-event aerial photos, as well as data from geophysical surveys and pre- to post-failure displacement monitoring. It also discusses the possible concurrent causes of the event, including antecedent rainfall, the migration of active streambed channels of Nure river toward the landslide toe in the previous year, and the existence of long-term pre-failure slow movements. It is concluded that these factors, together with the presence of sliding surfaces extending beneath the valley floor, should be primarily considered if a preventive assessment of river damming potential due to streambed uplift should be made for other similar landslides in the Apennines
Sorption properties of dispersed MBH4-MgH2 (M=Na, Li) systems in nano-mesoporous scaffolds
No full textThe sorption properties of MBH4-MgH2 (M=Na, Li) composites dispersed in nano-mesoporous scaffolds are evaluated by manometric, calorimetric and thermal programmed desorption analyses
Knowledge-based bioinformatics for the study of mammalian oocytes
No full textBioinformatics tools have been recently applied to study the differentiation of the mammalian oocyte during folliculogenesis. In this review, we will summarize our knowledge of 1) the use of biological databases for the extraction of relevant information, 2) bioinformatics methods for knowledge extraction and representation, 3) the application of these methods to the study of mammalian oocyte differentiation and 4) state-of the-art prediction approaches for the assessment and estimation of the cell differentiation status
Research advancement on Submerged Floating Tunnels: Recent activity at DICA-Politecnico di Milano
No full textA few topics, selected from the recent research activities performed at DICA on Submerged Floating Tunnels (SFTs), are presented concerning load modelling, design procedures and dynamic interaction with travelling vehicles. The prototype structure at study, a design proposal for the Messina Strait crossing, is composed of two single tubes independently anchored to the seabed. A model for generating seaquake effects taking into account the variability of the seabed ground motion over the length-scale of a few kilometers is described. A semi-analytical procedure is proposed to perform a preliminary design, without using a complete finite element model. The bridge-vehicle dynamic interaction is analyzed, to assess the serviceability conditions under the transit of heavy vehicles and high- and medium-speed trains. The research effort aims to the development of a complete analysis and simulation toolbox for the design of SFTs in medium-to-high seadepth
FE modelling of the Streicker footbridge
No full textThe Streicker footbridge was completed in 2010 at the Princeton University Campus, over the Washington Road. It is about 104 m long and consists of a central main span supported by a steel arch and four lateral approaching legs. The deck is a post-tensioned high-performance concrete girder. Steel columns with “Y” shape support four lateral legs that connect the bridge to the lateral bearings on the ground and the whole system results a slender varying cross section main girder. The original shape in the horizontal plane provides horizontal stability to the footbridge despite the intrinsic slenderness of the steel supporting columns. Vertical stability is provided also by the arch in the central main-span and by the supporting columns under the legs. Cross section width increases from the midpoint of the main span to the connections with the legs and then remains constant up to the ground bearings. This work is focused on the development of a finite element analysis of the footbridge at different levels of refinement from the essential implementation of beam elements to more refined FE solutions for the prestressed concrete deck. The models are identified with respect to the available operational modal parameters. This deck discretization could further allow simulating the motion of a running/walking pedestrian along different trajectories
The Monte Ulmus Unit (SW Sardinia, Italy): stratigraphy of a rheomorphic welded ignimbrite.
No full textMonte Ulmus Ignimbrite (MUI) is a high-grade, rhyolitic, welded, locally rheomorphic, low-aspect-ratio ignimbrite. Three main pyroclastic flow units (in the sense of Smith, 1960), preceded by a basal fall-out deposit (F) have been distinguished, named A, B1 and B2. Each flow unit is constituted by different lithofacies strongly related to the morphology at emplacement. Unit A is a 2 to 32 m thick, reddish to grey, fine grained, high-grade, welded ignimbrite that crops out mainly in Sant’Antioco Island. A basal vitrophyre, 30 cm thick, represents the base of unit A, overlain by a massive glassy lithofacies. These two lithofacies develop independently by paleotopography. In paletopographic lows, the main part of the ignimbrite is characterized by the presence of a rheomorphic facies with thinly spaced sheet joints and decimetric to decametric rheomorphic folds. This rheomorphic portion of unit A develops a secondary vesiculation and a granophyric crystallization style. Units B1 and B2, 5 to 52 m thick, crop out mainly in San Pietro Island and Sulcis area. They are represented by a poorly porphyritic, Quartz- and Sanidine-bearing, high grade deposit in which four different lithofacies have been described. These units are characterized by a high concentration of different, randomly oriented, juvenile pyroclasts and present rheomorphic deformation in correspondence of topographic lows. Vertical variation of textural features along MUI clearly reflect into the observed variation of bulk rock density. On topographic highs, discontinuities in the textural and physical features along the ignimbrite sequence clearly trace the transition between different flow units. On topographic lows and on gently dipping paleovalley slopes, the rheomorphic processes smoothed the discontinuities between the different flow units, locally inducing secondary vesiculation which disturbs the vertical density profile. The occurrence of coarse lithic boulders in the northern sector of San Pietro Island, and the inferred dispersal of the fall deposits at the base of the ignimbrite suggest that the source was possibly located north-northeast of the San Pietro Island
Fluidized bed desulfurization using lime obtained after slow calcination of limestone particles
No full textIn this work we have tested the fluidized bed desulfurization performance of lime particles obtained by
means of a limestone slow calcination pre-treatment technique. This performance was compared to that
of the parent untreated limestone particles. The occurrence of particle fragmentation and attrition during
the fluidized bed operation was also investigated with a specific test protocol for both raw limestone and
pre-treated lime sorbent. Two particle size ranges were tested under typical fluidized bed coal combustion
conditions (T = 850 °C; SO2 = 1800 ppm). The experiments were complemented by porosimetric and
morphological (SEM) analyses of the sorbent. Results showed that limestone pre-treatment was able to
preserve the high mechanical strength of the parent particles as opposed to the fast in situ calcination
typically active in fluidized beds. In addition, a high calcium reactivity and final conversion were
observed for the pre-treated lime particles, leading to a SO2 capture capacity per unit mass of sorbent
much higher than that obtained with the untreated limestone. Simple economic evaluations suggest that
the use of the pre-treated lime in place of limestone can involve significant economies for fluidized bed
coal combustor operators
Ordered mesoporous scaffolds for the confinement of nanosized complex and metal hydrides
No full textRising attention has been recently addressed to the sorption properties of nanosized materials confined into different mesoporous matrices. The reduction to nanometer scale and the control of grain size of hydrides particles could, at least in principle, induce an enhancement of the hydrogen release and uptake through the tuning of thermodynamic and kinetic properties [1]. While grain growth and particle agglomeration can be avoided, ordered scaffolds can also allow to obtain homogeneous size distribution of active phases. Most of the works recently published concern C based porous materials [2], whereas less attention has been addressed to chemically different scaffolds which, in turn, could offer further opportunities in tuning the sorption properties of hydrogen rich phases.
In this study we focus on the properties of nanosized hydrides confined into mesoporous scaffolds. Highly ordered Si-, C-, and transition metal-based mesoporous structures were prepared by sol-gel methods, and then embedded with mixtures of MgH2 and different complex borohydrides, by resorting to wet chemical impregnation and melting infiltration processes.
Structural characterization was performed by X-Ray diffraction (XRD), small angle neutron scattering (SANS) and transmission electron microscopy (TEM), in order to estimate the efficiency of confinement pathways. The thermodynamics and kinetics of the hydrogen absorption and desorption processes, as well as the chemical nature of the released gas, were then investigated by high-pressure differential scanning calorimetric device (HP-DSC), Sievert apparatus (PCT-Pro2000) and mass spectroscopy (MS).
Preliminary results indicate evident improvement in the sorption properties of the nanoconfined hydrides with regard to the corresponding materials in bulk conditions. The decrease of desorption temperatures in the multistep processes were tentatively related to the structural characteristics of the studied systems [3].
[1] M. Fichtner, Nanotechnology, 20, (2009) 204009.
[2] P. Adelhelm, J. Gao, M.H.W. Verkuijlen, C. Rongeat, M. Herrich, P.J.M. van Bentum, O. Gutfleisch, A.P.M. Kentgens, K.P. de Jong, P.E. de Jongh, Chemistry of Materials 22 (2010) 2233-2238.
[3] G. Mulas, R. Campesi, S. Garroni, E. Napolitano, C. Milanese, F. Dolci, E. Pellicer, D. Baró, A. Marini, Journal of Alloys and Compounds (2012) doi:10.1016/j.jallcom.2011.12.04
Collapse of a fluid storage tank in a biogas plant: an investigation on possible causes
No full textThis paper is referred to the collapse of a reinforced concrete (R. C.) wall of a rectangular digester, which was filled by fluid waste (whose density is almost equal to water) and by pressurized biogas above the fluid surface. The overall height of the wall was 6.00 m, its width was 26.00 m and its thickness was 0.35 m. The collapse, which involved a significant portion of the wall around its center, took place three years after commissioning of the plant. At the moment of the collapse, neither earthquakes nor other environmental extreme events were reported in the area. Moreover, the plant seemed to work properly when failure occurred. A simple elastic analysis, in the presence of the standard service loads, revealed that the stress levels (both in concrete and in reinforcing steel) did not exceed the elastic thresholds, as they have been measured on extracted specimens. Consequently, the possible causes of collapse have been investigated by considering several aspects. The analyses led to the conclusion that the structural collapse can be enclosed in the framework of damage accumulation for the reinforcing steel bars
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