86,666 research outputs found
La valutazione comparativa dei candidati
No full textUna indagine degli atteggiamenti espressi dai selettori alle primarie del PD del dicembre 2013, con particolare riguardo ai giudizi espressi sui tre candidati (Renzi, Cuperlo, Civati)
Velocity and stresses of partially-reflected water waves in the presence of opposing wind
No full textIt is known that long waves (or swell) ruffled by an opposing wind tends to be dissipated, while shorter waves develop on top of them and travel in the wind direction. However, the long waves are mostly considered progressive and the effect of reflection is neglected. We present an experiment study of mechanically generated regular waves in partially-reflective conditions and observed how they interact with wind an opposing. We look at how different reflection conditions and spatial variability affect the water flow and the stresses within it. By breaking down the signal through a triple decomposition, we analyse the velocity components and compare the wave-induced Reynolds stresses with a theoretical model which takes into account partial reflection conditions (Addona et al., 2018). This model helps us understand the spatial variability of the wave-induced stresses and avoid misinterpretations of the experimental results, proving the role the key role of reflection. A quadrant analysis of the fluctuating velocities is performed to study the direction of momentum transfer, which always seems to be from the interface to the water below. The work provides novel experimental data of the flow field of partially-reflected water waves in the presence of wind
Velocity and density measurements in forced fountains with negative buoyancy
No full textIn fluid mechanics, fountains take place when a source fluid is driven by its own momentum into a surrounding ambient fluid, and it is counterbalanced by buoyancy. These phenomena are largely encountered in nature and human activities. Despite the numerous studies on the subject, few experimental data are available about the internal structure of turbulent fountains. Here, we present a set of laboratory experiments with the aim to (i) get direct velocity and density measurements of fountains in a controlled environment and (ii) obtain insights about the basic physics of the phenomenon. The results concern the characteristics of the mean and turbulent flow: we report the analysis of the turbulent kinetic energy, the velocity skewness, and the Reynolds stresses, including a quadrant analysis of the fluctuating velocities. For some tests, the correlation between density and vertical velocity is investigated for both mean and fluctuating values. We have quantified the momentum transport, which is mainly out-downward at the nozzle axis with peaks at the mean rise height, where also maximum levels of the buoyancy and mass fluxes are present. The ability of acoustic Doppler current profilers to identify the rise height of the fountain and to measure the velocity field is also discussed
Temporary clogging effects induced by a sustainable anti-icing hydrogel on the hydraulic conductivity and inertia coefficient of open-graded asphalt pavements
No full textOpen-graded asphalt pavements require special winter maintenance procedures to ensure the effectiveness of anti-icing and deicing measures. A recently developed solution for this type of pavement is represented by an environmental friendly thickened bio-based salt hydrogel, which consists of a thermo-sensitive sodium chloride (NaCl) brine admixed with a gellant agent (seaweed fibers) having the ability to form a gel-like structure when hot-sprayed on a cold surface. This thin salt layer results in a long-lasting residual efficacy of the winter maintenance product and in a reduction of salt consumption, but affects the drainage capacity of the pavement. These transient clogging effects were evaluated on laboratory-made specimens through the measurement of their vertical hydraulic conductivity variations before and after the hydrogel application, using a 1-D air permeameter and a constant head water permeameter. The analyses, based on Darcy–Forchheimer model and Darcy model for lower Reynold numbers, revealed a significant short-term reduction of the hydraulic conductivity, that, anyway, tends to be almost totally restored once the critical weather event is over (after about 6 h)
Advancement in measuring the hydraulic conductivity of porous asphalt pavements
No full textThe measurement of the in situ hydraulic conductivity of porous asphalt pavements, K, is a matter of practical interest; however, there are cases where current techniques are difficult to use. Several methods are documented in literature, mainly based on permeameters with water as fluid. Using water has its advantages, as it is straightforwardly related to the drainage problem during rain storms, but it also involves some major issues, especially on field studies. For instance, the time necessary to reach the steady state is too long and the necessary amount of water could not be available. In addition, non-repeatability and hysteresis phenomena can occur, also due to air bubbles confined in the porous matrix. In the present paper, we describe a novel test method for measuring K using air at low pressure as fluid. The proposed permeameter was first tested in the laboratory, in order to (i) validate the theoretical relationships between KHjavax.xml.bind.JAXBElement@3885566fO and Kair, and (ii) define a model to evaluate an equivalent length scale for asphalt pavements, Leq, as a function of the thickness of the porous layer (this is useful when one-dimensional formulations are adopted in the case of three-dimensional plates or in situ measurements). Finally, the protocol and methodology were validated on two sites in Italy (Monza, Milan, and Poviglio, Reggio Emilia) where Kair was measured by the air field permeameter, and compared with KHjavax.xml.bind.JAXBElement@3d4458c9O, measured by a standard falling head permeameter. The technique allows the determination of the hydraulic conductivity on the basis of the ratio between pressure difference and flow rate, and of Leq
AIR-WATER INTERACTION OF PADDLE WAVES UNDER WIND FORCING
No full textThe air-water interaction has been long studied in ocean physics, due to its importance to natural hazard and impact on human activities. Several studies in the literature provided advancements for a better comprehension of gases, mass and momentum exchanges at the interface. However, the subject is wide and many aspects are still unsolved, especially it is quite hard to extract data from the air and water boundary layer. A non-intrusive useful method to acquire data at the air-water interface is Particle Image Velocimetry (PIV), which can extrapolate a huge amount of information in water. We perform an experimental study of regular waves generated by paddles propagating under the action of the wind. We discuss the importance of sea surface boundary layer under waves and winds based on laboratory experiments and scale analysis
Phase-resolved analysis of velocity field structure and vorticity dynamics under colinear swell and wind-waves
No full textThe objective of this study is to analyze the turbulence field generated by the interaction between mechanical waves and colinear wind-waves in the liquid domain just below the free surface. Detailed three-dimensional velocity measurements close to the surface are decomposed into mean, swell, wind-waves, and turbulence contributions. In this work, we treat wind-waves as macroscale turbulence with a pseudo-random velocity field. Advanced data analysis yields phase-resolved and vertical examinations of wind-waves and turbulence stresses, kinetic energy, and vorticity. The results indicate that near the surface, the spanwise energy dominates both the wind-wave and the turbulence kinetic energy. The wind-waves and turbulence stress tensors exhibit a large anisotropy when swell waves are present, as a consequence of the interaction between swell and wind-waves. Furthermore, we present the spatio-temporal distribution of vorticity, and we elucidate the non-trivial interaction between vorticity and the flow field. This interaction results in body forces that contribute to the local variation in inertia, as described by the Navier–Stokes equation. It is observed that in all combinations, a body force acts, on average, downward, modifying the gradient pressure in the vertical direction
Mappa storica. Archivi fonti immagini. Le radici al plurale di Intesa Sanpaolo
No full textL’Archivio storico di Intesa Sanpaolo, ricercando il canale più efficace per veicolare
le informazioni sulla storia e sui patrimoni documentari delle banche
preesistenti, ha ideato il progetto Mappa storica. Archivi, fonti, immagini
che, in due anni di attenta e scrupolosa ricerca, ha ricostruito questo articolato
e plurisecolare processo attraverso la creazione di una mappa storica,
strutturata secondo un vero e proprio albero genealogico del Gruppo.
Per ciascuno degli istituti bancari censiti (circa 300) è stato redatto un breve profilo storico
utilizzando sia fonti a stampa che archivistiche, allo scopo di inserire dati
essenziali in sintesi e suggerire le coordinate per ulteriori approfondimenti
- …
