2,755 research outputs found
Barclay & Crousse. Segnali di vita tra i due deserti. Barclay & Crousse. Señales de vida entre dos desiertos
No full textLa costa desertica peruviana: una lunghissima linea sul Pacifico che si estende da nord a sud per circa 2400 km, scandita da un sistema regolare di oasi trasversali. Ogni traccia della presenza dell’uomo è spesso occultata da questa natura estrema. Anche le rovine precolombiane, che di rado si incontrano ai margini delle oasi, appaiono come tracce astratte di una natura geometrizzata.
La condizione geografica dell’intero Perù è tale da replicare, sia alla grande sia alla piccola scala, analoghe condizioni insediative. Ogni sua porzione si distingue nettamente dal paesaggio desertico a cui si contrappone, che sia l’immensa distesa oceanica, l’impervio altopiano andino o l’impenetrabile foresta pluviale. Tutti gli insediamenti umani, città o edifici, si configurano spesso come strategiche isole di confine tra due frammenti di deserto.
In questa radicale condizione si inserisce il lavoro che Sandra Barclay e Jean Pierre Crousse sviluppano dalla fine degli anni ’90 fino ad oggi raccontato dal libro di Cacciatore e Foti. Dieci case, progettate e costruite sulla costa pacifica, esprimono chiaramente le straordinarie potenzialità architettoniche insite in questo contesto
Capacitance study of thin film SnO2:F/p-type a-Si:H heterojunctions
No full textWe characterized SnO2:F/p-type a-Si:H heterojunctions by current-voltage (I-V) and capacitance-voltage (C-V) measurements at
room temperature to determine the junction parameters. Samples with circular geometry and different diameters were
characterized. The current scales with the junction area, and the current density J as a function of the voltage V is a slightly
asymmetric curve with a super-linear behaviour (cubic law) for high voltages. Using a transmission line model valid for devices
with circular geometry, we studied the effects of the SnO2:F resistivity on the measured capacitance when the SnO2:F layer
works as an electrical contact. The measured C-V curve allows us to determine junction parameters as doping of p-type a-Si:H,
built-in potential and depletion width for the heterojunction with the smallest diameters, demonstrating that for these samples the
TCO effects can be neglected. We compared theoretical and measured data to explain qualitatively the transport mechanism in
this heterojunction
Un progetto per Bologna: l'area Staveco da cittadella militare a Campus Universitario. Ateliermap
No full textOn the estimation of von mises equivalent stress in random vibration analysis
No full textLinear random vibration analysis aims to the probabilistic characterization of response functions; classical procedures are targeted to the time histories of output kinematic variables, such as displacement, velocity and acceleration, and to parameters which are linearly related to them, such as internal forces, deformations, stress components ecc. Much less attention has been devoted, by researcher and developers, to the case of response variables which are non-linearly dependent of the lagrangian coordinates or their derivatives; the most typical among these is the Von Mises equivalent stress, whose square value is quadratic in the components of the stress tensor, and thus in the lagrangian coordinates. The topic is of relevance especially for the structural safety of industrial equipment and systems, which is usually based on local stress integrity assessment. In the paper an innovative analytical procedure to deal with the probabilistic characterization of the VM stress is proposed as an extension of the classical approach adopted for linear output parameters. To this aim the matrix of the quadratic form delivering is decomposed into the sum of suitable factors; each of them deserves the same treatment as for linear parameters. The various features related to the numerical implementation of the procedure for stationary or non-stationary (evolutionary) random excitation are discussed, with reference to both the application via direct frequency domain treatment and to the modal superposition approach; an example is finally shown and commented
3D-electrical resistivity tomography monitoring of salt transport in homogeneous and layered soil samples
No full textMonitoring transport of dissolved substances in soil deposits is particularly relevant where safety is concerned, as in the case of geo-environmental barriers. Geophysical methods are very appealing, since they cover a wide domain, localising possible preferential flow paths and providing reliable links between geophysical quantities and hydrological variables. This paper describes a 3D laboratory application of Electrical Resistivity Tomography (ERT) used to monitor solute transport processes. Dissolution and transport tests on both homogeneous and heterogeneous samples were conducted in an instrumented oedometer cell. ERT was used to create maps of electrical conductivity of the monitored domain at different time intervals and to estimate concentration variations within the interstitial fluid. Comparisons with finite element simulations of the transport processes were performed to check the consistency of the results. Tests confirmed that the technique can monitor salt transport, infer the hydro-chemical behaviour of heterogeneous geomaterials and evaluate the performances of clay barrier
Impact behavior of structural elements in concrete reinforced with PET grids
No full textRecycling of waste materials is one of the most important problems in the future to be solved in all possible ways. Polyethylene terephthalate (PET), for example, is a waste material that could be reused as concrete reinforcement.
In the present article the results of impact tests performed on reinforced concrete specimens with fibers made from waste PET bottles are reported. The fibers have been obtained by simply cutting the bottles and have been utilized as discrete long reinforcement of specimens in concrete in substitution of steel bars. A test set-up and slab specimens have been designed and manufactured for the impact tests.
The tests provided interesting results regarding the impact strength of PET reinforced concrete, suggesting a possible use of this material, in particular for those cases frequently subjected to shocks and impact forces, such as road and, especially, airport pavements, wharfs, etc. The reinforcement with PET has the advantage to be less corrosive and less expensive than reinforcement consisting of steel wire nets and carbon or glass nets
Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography
No full textIn situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi
An enhanced unified model for the self-damping of stranded cables under aeolian vibrations
No full textCarrier transport mechanism in the SnO2:F/p-type a-Si:H heterojunction
No full textWe characterize SnO2:F/p-type a-Si:H/Mo structures by current-voltage (I-V) and capacitance-voltage (C-V) measurements at different temperatures to determine the transport mechanism in the SnO2:F/p-type a-Si:H heterojunction. The experimental I-V curves of these structures, almost symmetric
around the origin, are ohmic for |V| 0.1 V. The structure can be modeled as two diodes back to back connected so that the main current transport mechanisms are due to the reverse current of the diodes. To explain the measured C-V curves, the capacitance of the heterostructure is modeled as the series connection of the depletion capacitances of the two back to back connected SnO2:F/p-type a-Si:H and Mo/p-type a-Si:H junctions. We simulated the reverse I-V curves of the SnO2:F/p-type a-Si:H heterojunction at different
temperatures by using the simulation software SCAPS 2.9.03. In the model the main transport mechanism is generation of holes enhanced by tunneling by acceptor-type interface defects with a trap energy of 0.4 eV above the valence bandedge of the p-type a-Si:H layer and with a density of
4.0 10^13 cm^-2. By using I-V simulations and the proposed C-V model the built-in potential (Vbi) of the SnO2:F/p-type a-Si:H (0.16 V) and p-type a-Si:H/Mo (0.14 V) heterojunctions are extracted and a band diagram of the characterized structure is proposed
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