Ligament break-up simulation through pseudo-potential Lattice Boltzmann Method

The Plateau-Rayleigh instability causes the fragmentation of a liquid ligament into smaller droplets. In this study a numerical study of this phenomenon based on a single relaxation time (SRT) pseudo-potential lattice Boltzmann method (LBM) is proposed. If systematically analysed, this test case allows to design appropriate parameters sets to deal with engineering applications involving the hydrodynamics of a jet. Grid convergence simulations are performed in the limit where the interface thickness is asymptotically smaller than the characteristic size of the ligament. These simulations show a neat asymptotic behaviour, possibly related to the convergence of LBM diffuse-interface physics to sharp interface hydrodynamics

Hydrodynamic behavior of the Pseudo-Potential lattice Boltzmann method for interfacial flows

The lattice Boltzmann method (LBM) is routinely employed in the simulation of complex multiphase flows comprising bulk phases separated by non-ideal interfaces. LBM is intrinsically mesoscale with an hydro-dynamic equivalence popularly set by the Chapman-Enskog analysis, requiring that fields slowly vary in space and time. The latter assumptions become questionable close to interfaces, where the method is also known to be affected by spurious non hydrodynamical contributions. This calls for quantitative hydrodynamical checks. In this paper we analyze the hydrodynamic behaviour of LBM pseudo-potential models for the problem of break-up of a liquid ligament triggered by the Plateau-Rayleigh instability. Simulations are performed at fixed interface thickness, while increasing the ligament radius, i.e. in the "sharp interface" limit. Influence of different LBM collision operators is also assessed. We find that different distributions of spurious currents along the interface may change the outcome of the pseudo-potential model simulations quite sensibly, which suggests that a proper fine-tuning of pseudo-potential models in time-dependent problems is needed before the utilization in concrete applications. Taken all together, we argue that the results of the proposed study provide a valuable insight for engineering pseudo-potential model applications involving the hydrodynamics of liquid jets

Chapter “Rievocare certe nobili opere dei nostri maggiori”: the Istituto per il Medio ed Estremo Oriente (IsMEO) and the “Myth” of Italian Travellers to the East

This study aims to investigate the development of a shared sense of identity and community that occurred in Italy from its unification until the end of the colonial empire, and its traces in the republican period. This nation-building process will be examined by analysing Italy’s relationship with the early modern age of the Peninsula and its pre-unification travellers to the East. We will see how the production and dissemination of an Italian national consciousness and sentiment was based largely on the construction of a “mythical past” through exhibitions, collections, printed works, magazines and institutes dedicated to magnifying the “exploits” of travellers and explorers in the East, from Marco Polo to Giuseppe Tucci

Lattice Boltzmann models for non-ideal fluids with arrested phase-separation

The effects of mid-range repulsion in Lattice Boltzmann models on the coalescence/breakup behaviour of single-component, non-ideal fluids are investigated. It is found that mid-range repulsive interactions allow the formation of spray-like, multi-droplet configurations, with droplet size directly related to the strength of the repulsive interaction. The simulations show that just a tiny ten-percent of mid-range repulsive pseudo-energy can boost the surface/volume ratio of the phase- separated fluid by nearly two orders of magnitude. Drawing upon a formal analogy with magnetic Ising systems, a pseudo-potential energy is defined, which is found to behave like a quasi-conserved quantity for most of the time-evolution. This offers a useful quantitative indicator of the stability of the various configurations, thus helping the task of their interpretation and classification. The present approach appears to be a promising tool for the computational modelling of complex flow phenomena, such as atomization, spray formation and micro-emulsions, break-up phenomena and possibly glassy-like systems as well.Comment: 12 pages, 9 figure

Low pH, high salinity: too much for Microbial Fuel Cells?

Twelve single chambered, air-cathode Tubular Microbial Fuel Cells (TMFCs) have been filled up with fruit and vegetable residues. The anodes were realized by means of a carbon fiber brush, while the cathodes were realized through a graphite-based porous ceramic disk with Nafion membranes (117 Dupont). The performances in terms of polarization curves and power production were assessed according to different operating conditions: percentage of solid substrate water dilution, adoption of freshwater and a 35mg/L NaCl water solution and, finally, the effect of an initial potentiostatic growth. All TMFCs operated at low pH (pH$=3.0 \pm 0.5$), as no pH amendment was carried out. Despite the harsh environmental conditions, our TMFCs showed a Power Density (PD) ranging from 20 to 55~mW/m$^2 \cdot$kg$_{\text{waste}}$ and a maximum CD of 20~mA/m$^2 \cdot$kg$_{\text{waste}}$, referred to the cathodic surface. COD removal after a $28-$day period was about $45 \%$. The remarkably low pH values as well as the fouling of Nafion membrane very likely limited TMFC performances. However, a scale-up estimation of our reactors provides interesting values in terms of power production, compared to actual anaerobic digestion plants. These results encourage further studies to characterize the graphite-based porous ceramic cathodes and to optimize the global TMFC performances, as they may provide a valid and sustainable alternative to anaerobic digestion technologies.Comment: 13 pages, 10 Figure

Lattice Boltzmann Models with Mid-Range Interactions \ud \ud

An extension of the standard Shan-Chen model for non ideal-fluids, catering for mid-range, soft-core and hard-core repulsion, is investigated. It is shown that the inclusion of such mid-range interactions does not yield any visible enhancement of the density jump across the dense and light phases. Such an enhancement can however be obtained by tuning the exponents of the effective interaction. The results also indicate that the inclusion of soft-core repulsion can prevent the coalescence of neighborhood bubbles, thereby opening the possibility of tailoring the size of multi-droplet configurations, such as sprays and related phase-separating fluids. \ud \u

Classificazione di una collezione di pigmenti del primo Novecento

Viene descritta la campagna di indagini scientifiche eseguite su una collezione di pigmenti di primo Novecento appartenuta a famosi restauratori fiorentini. La finalità della ricerca è l’integrazione di dati storici, chimici e fisici per caratterizzare i singoli pigmenti inseriti in un archivio informatico da implementare periodicamente al fine di ottenere un insieme di dati conoscitivi sui materiali impiegati sia dagli artisti che dai restauratori tra 1850 e 1950. A systematic campaign of scientific analyses on a early XXth century pigments’s collection belonged to famous florentine restorers is carried out, in order to obtain chemical, physical and historical classification of each material. The aim of research is to characterize all pigments in a database periodically uploaded and integrated with new analytical data, by supplying references on the products commercialized between 1850 and 1950, that were largely used for conservation treatments

Modern Lattice Boltzmann methods for multiphase micro-flows

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.During the last decade, the Lattice Boltzmann (LB) method has captured an increasing attention as an efficient tool for the numerical simulation of complex fluids, particularly multi-phase and multi-component flows. In this paper, we revisit the basic features of two modern variants of lattice Boltzmann models for non-ideal fluids, which offer promising perspectives for the numerical simulation of complex micro- flows.This study is funded from the European Project INFLUS, NMP3-CT-2006-031980

Il Mausoleo dei Plautii a Tivoli: la diagnostica per la conservazione del travertino

Il Mausoleo dei Plautii, del I secolo d.C., rappresenta un elemento monumentale del più ampio complesso di Ponte Lucano, il simbolo della salita verso Tivoli, che da sempre ha attratto l’interesse degli artisti e dei conoscitori d’arte che in pochi passi raggiungevano l’affascinante sito di Villa Adriana, patrimonio Mondiale dell’Umanità. Oggi il Mausoleo, oltre a trovarsi in una situazione di totale incuria, risulta inserito in un contesto ambientale piuttosto critico, a ridosso cioè del fiume Aniene, e quindi continuamente soggetto ad esondazioni che si estendono fino ad invadere il monumento funerario dove le acque ristagnano anche per la presenza di un muro in cemento di recente costruzione. Al fine di valutare lo stato di conservazione del travertino, materiale costitutivo del sepolcro, e fornire un elemento utile per programmare eventuali interventi di tutela e difesa di questo importante monumento, sono state effettuate alcune indagini diagnostiche tramite prelievi in situ sul Mausoleo e su materiali di cava. Le indagini diagnostiche hanno previsto: esami chimico-mineralogici tramite microscopio polarizzatore, mediante FTIR, μ-FTIR e XRD; analisi morfologica, tramite SEM, di alcune forme di alterazione biologica; test microanalitici per localizzare particolari elementi presenti nel travertino; analisi spettrometrica nel visibile dei sali solubili; prove di imbibizione e di evaporazione