Department of Mechanical Systems and Infrastructures

Fluidization of pyroclastic solids has long been indicated as one key to explain the enhanced mobility of dense pyroclastic gravity currents and their associated hazard. However there is a lack of characterization of the actual pattern and extent of fluidization establishing in real pyroclastic flows and some authors still raise arguments about the relevance of fluidization to the mobility of dense pyroclastic gravity currents. The present paper addresses the fluidization of pyroclastic granular solids with a specific focus on the analysis of factors that may promote homogeneous fluidization and retard solids de-aeration and consolidation. These factors include fines content, particle polydispersity and the establishment of shear flow.

The influence of fines content and particle polydispersity has been assessed by analyzing the fluidization behaviour of mixtures of pyroclastic solids characterized by different and properly tailored particle size distributions and fines content. Pyroclastic mixtures, extracted from a Neapolitan Yellow Tuff deposit, were nearly homogeneous as to the lithological composition. The experimental campaign has been carried out with a lab-scale segmented fluidization column 120 mm ID. Experiments included quasi-steady fluidization of granular mixtures at variable gas superficial velocity as well as collapse tests from pre-set fluidized states. Results of the collapse tests were independently analyzed by looking at the time-series of the pressure drop across the bed as well as at the bed surface level as a function of time, recorded with a high-speed video camera.

The study has been pursued further to analyze the effect of shear on the fluidization behaviour of pyroclastites. To this end the experimental apparatus has been modified and equipped with a rotating cylinder which could be used to impose a given shear rate to the fluidized bed. Shear rates were comparable to those that are likely to establish in real pyroclastic flows. Quasi-steady fluidization experiments and collapse tests were carried out under either stationary or sheared fluidization conditions.

We compared the fluidization behaviour of mixtures characterized by different fines contents. Moreover we compared the fluidization behaviour recorded under either stationary or sheared flow conditions. Results of experimental tests highlight that both the presence of a fine fraction and the establishment of shear flow significantly influence the fluidization behaviour of pyroclastic mixtures, promoting homogeneous fluidization of the granular mixtures. The range of gas superficial velocities within which bubble-free fluidization occurs is significantly broadened by the presence of fines, by the polydisperse nature of the mixtures and by the establishment of shear. The de-aeration/consolidation times determined by the collapse tests are correspondingly much longer.

Altogether, results of the present study confirm that key features of dense pyroclastic density currents, like the large fines fractional content, the polydisperse nature of the particle size distribution and strongly sheared flow conditions, exert a significant influence on fluidization, promote suppression of bubbling, retard solids de-aeration, enhance the mobility of the solids.

The fast motion of gravity currents of group A granular solids is studied with a focus on the dynamical structure of the frontal zone. The frontal zone of the current is "immobilized" and observed in a xed frame of reference by letting the current flow inside a rotary drum, big enough to make curvature effects negligible. The establishment of a variety of flow regimes, including intermittent avalanching, periodic \plunging breaking" and permanent fluidization of the granular solids in the frontal zone, can be related to flow conditions and to the nature of the granular solids.

Pyroclastic flows are fluidized mixtures of solid particles and gases, which move rapidly subject to gravity. Upflow of gas across the flow is a common feature of a pyroclastic density current. The ascent velocity of the gas across the current may be so large to establish a fluidized state in the granular phase. For this reason, the definition of the fluidodynamic behaviour of pyroclastic granular solids is relevant to fully characterize the pyroclastic flow. Previous studies suggest that the pyroclastic flow motion can be read through the theories that analyze the fluidization phenomena and internal dynamics of the granular systems. The present research reports a theorical and experimental approach to the investigation of the fluidoyinamical behaviour of pyroclastic granular mixtures.
The theorical approach focused on the dynamics of the frontal zone of a dense pyroclastic density current, in particular on the establishment of motion-induced air entrainment and onset of self-fluidization. A simplified theoretical framework is proposed, based on the hypothesis of fully developed turbulent flow and pseudo-homogeneous behaviour of the gas-solid suspension.
The experimental campaign focused on the fluidodynamic characterization of pyroclastic natural mixtures. The pyroclastic material, used for the experimental phase, has different litological and granulometrical characteristic, and is thought to be representative of granular phase of real pyroclastic currents. The experimental campaign has been focused on the features that enhance the fluidization state. The experimental results showed that the fluidized state was enhanced in polydispersed and fine enriched pyroclastic mixtures. In particular, the occurrence of a shear flow during the experiment improved the quality of the fluidization and enhanced its stabilization.

Pyroclastic flows have been frequently addressed in the recent volcanological literature as far as the depositional mechanisms and the field features of the related deposits are concerned. Much less attention has been paid to phenomena that control the dynamic of pyroclastic flow motion. The peculiar feature of pyroclastic flows, hence focused, is the onset of an intense upflow of gas, whose velocity may be so large that a fluidized state may be established in the granular phase. The fluidization behaviour of granular synthetic mixtures has been studied in a broad range of conditions, mostly driven by the widespread use of fluidized beds in the process industry. However, experimental studies focused on fluidization of natural granular mixtures are lacking. The aim of this paper is the characterization of the fluidization behaviour of natural pyroclastic mixtures. In particular, mixing and segregation of granular mixtures of natural origin and fluidization-induced abrasion/fragmentation of pyroclastic particles have been investigated. A pyroclastic mixture extracted from a pumice fall deposit has been used as the starting material, as it is representative of the whole material of a plinian column immediately before collapse and emplacement of the pyroclastic flow deposits. Experimental tests have been also performed using the granular material extracted from pyroclastic flow deposits. Incipient and complete fluidization velocities, onset of particle segregation due to size and density polydispersity of the samples, elutriation of attrition-induced fine particulates and attrition-induced changes of particle size distributions have been characterized. When comparing the segregation propensity of the pumice fall and of the pyroclastic flow starting material, it is concluded that only the former exhibits significant segregation. Results of elutriation and attrition experiments highlight the transient nature of particle attrition phenomena: generation of fines by attrition of relatively coarse granular solids is at a maximum in the early stage of fluidization and decays significantly thereafter.

Pyroclastic flows are fluidized mixtures of solid particles and gases undergoing rapid gravity-driven motion. Upflow of gas across the flow is a common feature of a pyroclastic density current. The ascent velocity of the gas across the current may be large to the point that a fluidized state establishes in the granular phase. Accordingly, defining the fluidization behaviour of pyroclastic granular solids is relevant to the assessment of pyroclastic flows. The fluidization behaviour of pyroclastic granular mixtures has been the subject of renewed interest over the last decade. Studies addressed the effect of temperature (Druitt et al., 2004), the occurrence of fragmentation and attrition (Gravina et al., 2004), and the initial conditions of a pyroclastic flow (Roche et al., 2004). The experimental campaign of Gravina et al. (2004) highlighted the occurrence of extensive attrition by abrasion between particles, which determined the generation of a new fine grain size population. The production of fine particles stopped after a few minutes. Moreover, the experimental campaign highlighted that only part of the newly formed grain size fractions was elutriated. This experimental evidence, applied to the internal dynamics of pyroclastic flows, suggests that the fine fraction produced by attrition during the propagation of a pyroclastic flow might enhance fluidization of coarse-grained solids. Starting from this recent experimental evidence, the aim of the present work is to study the conditions that enhance the fluidized state of granular solids in pyroclastic flows. Characterization of the fluidization of pyroclastic natural mixtures has been undertaken with the aid of the “bed collapse” tests. The specific concern was the assessment of the role of the fine fractions and of the establishment of shear flow in the fluidization of pyroclastic currents. The experimental campaign was carried by means of an experimental facility where a fluidized bed could be held under continuous shear flow between two co-axial cylinders, the inner one being rotated while the other was stationary. The outer cylinder was subdivided into five cylindrical segments so that retrieval of solids from each of them and size analysis was possible, in order to study axial segregation of particles along the bed. The first phase of the experimental campaign was based on the use of synthetic materials (glass beads, porous catalyst). This study made it possible to: 1)Recognize the existence of distinct fluidization regimes corresponding to different gas superficial velocities; 2) Compare the fluidization behaviour in absence and in presence of mechanical agitation, i.e. shear flow. The same experimental procedure was extended to the characterization of the fluidization behaviour of pyroclastic natural mixtures. In particular, the role of shear flow in the fluidization and segregation phenomena, and on the attrition and generation of fine particles was addressed.

Le informazioni concernenti lo stato dell'ambiente sono acquisite dal grande pubblico attraverso i mass media (televisione, radio,
giornali), che mirano a impressionare il lettore ma che usano spesso un approccio superficiale. Le stesse problematiche
ambientali sono affrontate in maniera più approfondita su riviste di settore "peer reviewed" che, a differenza del giornalismo non
specializzato, riportano dati oggettivi senza voler creare sensazioni nel lettore. Tuttavia il linguaggio utilizzato in tali riviste
spesso non è comprensibile per il grande pubblico. Negli ultimi anni c'è stata una vera rivoluzione "digitale" con l'avvento della
rete internet; attraverso il world wide web è possibile comunicare tematiche scientifiche sia da parte di centri di ricerca, che di
singoli interessati alla scienza. La crescita di questo nuovo settore d'informazione ha creato molte possibilità nell'ambito della
comunicazione scientifica, ma ha aumentato anche il rischio di diffondere informazioni scorrette e non verificate. In tale settore
non sono molto presenti le Università italiane, i cui siti sono ricchi di informazioni burocratiche, ma quasi privi di notizie
relative alle ricerche svolte in un linguaggio fruibile dal grande pubblico. La divulgazione delle ricerche svolte in campo
ambientale dalle Università o da altre istituzioni di ricerca potrebbe avere un ruolo molto importante perché, da un lato,
garantirebbe l'affidabilità delle informazioni, dall'altro, utilizzando un linguaggio adatto al grande pubblico, consentirebbe la
comprensione delle problematiche ambientali da parte della popolazione, favorendo lo sviluppo di comportamenti responsabili.
Sulla base di queste considerazioni nasce il presente progetto, che ha come obiettivo la divulgazione scientifica dei risultati di
alcuni prodotti della ricerca svolta da studiosi afferenti all'ex Dipartimento di Scienze Ambientali, in parte confluito nel
Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche (DiSTABiF) della Seconda Università di Napoli
(SUN). Per la divulgazione dei prodotti della ricerca è stato implementato uno spazio web (SUstaiNability), nel dominio unina2,
con caratteristiche e grafica pensate per valorizzare i contenuti presentati e renderli fruibili ad un'audience non specializzata.
Parallelamente allo sviluppo web, è stata eseguita una ricerca bibliografica sull'Anagrafe della Ricerca della SUN e sono state
scelte alcune pubblicazioni su tematiche ambientali (preferibilmente relative al territorio casertano), ma anche su aspetti legati a
nutrizione e salute, tenendo conto dell'intima connessione esistente tra ambiente, nutrizione e salute. I contenuti web sviluppati
sono stati pubblicizzati attraverso i principali social network (FACEBOOK e TWITTER). Infine sono stati monitorati l'accesso
ai contenuti su web per 28 giorni e la tipologia di utenti, in termini demografici e geografici. Al termine di questo intervallo di
tempo è stato analizzato il flusso dei contatti al sito SUstaiNability ed alle pagine sui social network.

L'analisi dei dati relativi alla visualizzazione dei materiali ha mostrato che sono stati raggiunti molti utenti (circa 62600)
attraverso i social network; le visualizzazioni del sito SUstaiNability sono state molto inferiori (3306), ma gli apprezzamenti
sono stati molto superiori rispetto a quelli ottenuti attraverso i social network. L'analisi demografica e geografica ha messo in
evidenza che gli utenti dei social network sono distribuiti prevalentemente nel territorio campano e hanno un'età compresa tra
18 e 44 anni. Questi dati consentono di affermare che i social network sono utili per ampliare l'audience e promuovere i
contenuti del sito web, ma per divulgare dati scientifici è necessario presentare le ricerche in modo completo e affidabile, come
attraverso un sito web all'interno di un dominio istituzionale.

I risultati delle ricerche in campo ambientale raggiungono il grande pubblico principalmente attraverso i mass
media, che usano spesso un approccio superficiale. D’altra parte le riviste specializzate "peer reviewed"
utilizzano un linguaggio incomprensibile ai non addetti ai lavori. La rete internet offre l’opportunità di
divulgare dati scientifici, ma non sempre garantisce l’affidabilità delle informazioni. Attraverso il web le
Università italiane diffondono informazioni su aspetti burocratici, ma generalmente non sui risultati delle
ricerche svolte. Questo lavoro propone un modello di divulgazione di ricerche scientifiche rivolto al grande
pubblico. Alcuni articoli scientifici su tematiche ambientali, prodotti da ricercatori della Seconda Università di
Napoli, sono stati rielaborati, usando un linguaggio divulgativo, e pubblicati in un sito web istituzionale
(http://www.sunability.unina2.it/), che è stato pubblicizzato attraverso i social network FACEBOOK e TWITTER.
Sono stati poi monitorati, per 28 giorni, il numero e la tipologia di utenti. I social network hanno permesso di
raggiungere molti più utenti rispetto al sito web (62600 vs 3306), ma il maggior numero di apprezzamenti alle
ricerche proposte è stato registrato sul sito web. Pertanto i social network sono risultati utili per ampliare
l’audience, ma per divulgare dati scientifici è necessario presentare le ricerche in modo esaustivo e affidabile,
come attraverso un sito web all’interno di un dominio istituzionale.

The Italian coastline is about 7,500 km long; approximately 53% of the coastlines are low or deltaic coastlines,
while 3,240 km were mainly composed of sand or gravel beaches. Most of the Italian coastal environment suffers
from intense and growing urbanization, tourism and industry pressure, which could partly explain that 42% of
Italian beaches experience erosion.
Terracina is situated Lazio (Central Italy), a region strongly impacted by coastal erosion, and for this reason
we organized a teaching activity, carried out with fourth year high school classes, in order to help students to
understand sand beach dynamics, acquisition of geology issues and land conservation and preservation skills. We
decided to focus our activity on the mineralogical composition of beach sand in order to relate beach formations
with the geological evolution of the territory. Sand beach minerals were used as tracers in order to support students
to understand dynamics that influence beach formations. In addition to mineral characteristic recognition, this
activity allows us to introduce the beach balance concept and the phenomena that regulate sediment balance,
in order to allow students to consider beaches as a resource which needs to be preserved. Sand mineralogical
composition data is treated in a worksheet to elaborate simple statistical analysis in order to recognize the mineral
composition of Terracina beach sand’s rock sources. This exercise allows students to find relationships between
regional geology and beach sand’s composition. Finally, statistical evidence could be compared with geological
maps of the area in order to find the probable provenance of sand’s rock source and rocks recognition thanks to
related morphologies.
Our main purpose was to help students to understand that beaches are dynamic systems subject to anthropogenic
pressure and for this reason they needed to be preserved. Proposed teaching activities involve topics related to
students’ living territory and to introduce pupils to the importance of observing environmental characteristics and
trying to relate them to geological processes in action.

Social networks enable anyone to publish potentially boundless amounts of information. However, such information is also highly prone to creating and/or diffusing mistakes and misunderstandings in scientific issues. In 2013 we produced a website (www.sunability.unina2.it) reporting on some research outputs from the University of Campania Luigi Vanvitelli (formerly the Second University of Naples, SUN), and shared it on Facebook and Twitter to analyse the effectiveness of these platforms in scientific dissemination. The study results suggest that (i) a regular update of the web-site stimulates the user's interest, (ii) Campania's citizens are more concerned with pollution problems than natural hazards , and (iii) direct involvement of researchers effectively enhances web-mediated scientific dissemination.

The Italian National Association of Science Teachers (ANISN), established in 1979, aims to promote excellent performance in science among students. For this reason, annually the ANISN organizes a national competition for high school students. The 14th edition was held in 2016: 500 Italian schools took part in this contest. Within all them, 3000 students participated in the regional phases, while 129 students achieved the national phases. For the first time 16-19 years old students could decide to participate in two different competitions focusing on Biology or Earth Sciences. This article resumes the results of the first year of Italian Earth Sciences Olympiad, aims at drawing the state of art of Earth Sciences competition for students in Italy and suggests some reflections for teachers in order to address students interested in participating in this competition.