306,418 research outputs found
Determination of water retention properties of silty sands by means of combined commercial techniques
No full textA recent increase in frequency and severity of exceptional climatic events is of concern for the stability of natural and artificial slopes. These undergo continuous evaporation and infiltration cycles, which change the suction distribution and trigger shrinkage, swelling, cracking, and surfi-cial erosion, overall decreasing the soil strength. To assess the impact of these climatic stresses, the determination of water retention properties is a priority. Although advanced techniques have been proposed in the last few decades to this end, simpler commercially available techniques allow col-lecting data for a larger number of samples in a shorter time, thus enabling a basic description of the water retention properties for a larger database of soils. Data on two silty sands, coming from very different climatic environments in Europe, were collected with a combination of two simple commercial devices, and the results were modelled with a van Genuchten’s law. The fitted pa-rameters were found to correlate well with the amount of fines, irrespective of the different origin and composition of the two soils. Eventually, the limitation of the approach is discussed based on the results of cyclic drying–wetting tests.</p
Terreni collassabili e processi di instabilità nella Valle dei Templi
No full textIl complesso sacrale ellenistico della Valle dei Templi di Agrigento, Patrimonio UNESCO dell’Umanità, si snoda lungo la cresta
di un banco di calcarenite, poggiante su un livello di sabbie. I costoni, in corrispondenza delle pareti calcarenitiche, risultano frequentemente
in condizioni di equilibrio limite anche in prossimità delle principali strutture archeologiche, fra cui il Tempio di
Giunone, il Tempio della Concordia, e il Tempio di Vulcano, le aree dei Donari e del Santuario Rupestre dedicato a Demetra, e la
Necropoli Paleo–Cristiana. Tali strutture sono minacciate da fenomeni di instabilità e, in taluni casi, dall’arretramento del versante
sino ad ora attribuito alla mesostruttura ed a fenomeni di erosione selettiva e scalzamento al piede. Recenti studi hanno individuato
per le sabbie parzialmente sature, sovrastate dalle calcareniti, il tipico comportamento dei terreni collassabili caratterizzati da
struttura aperta e metastabile, nei quali un incremento del contenuto d’acqua può innescare notevoli variazioni volumetriche. Sulla
base di rilievi in sito, di prove di laboratorio e di analisi numeriche agli elementi finiti è stato possibile ipotizzare il ruolo attivo delle
sabbie nei fenomeni di dissesto consentendo una nuova lettura e interpretazione dei fenomeni di instabilità
Sensing Properties of E-Beam Evaporated Nanostructured Pure and Iron-Doped Tungsten Oxide Thin Films
No full textGas sensing properties of nanostructured pure and iron-doped WO(3) thin films are discussed. Electron beam evaporation technique has been used to obtain nanostructured thin films of WO(3) and WO(3):Fe with small grain size and porosity. Atomic force microscopy has been employed to study the microstructure. High sensitivity of both films towards NO(2) is observed. Doping of the tungsten oxide film with Fe decreased the material resistance by a factor of about 30 when exposed to 5 ppm NO(2). The high sensitivity is attributed to an improved microstructure of the films obtained through e-beam evaporation technique, and subsequent annealing at 300 degrees C for 1 hour
Palcoscenici dell'essere. Le comunicazioni di bambini e adolescenti nelle piazze virtuali
No full textL’Osservatorio sulla Comunicazione Adolescenziale tra Reale e Virtuale (OSCARV@bg) ha condotto tra il 2017 e il 2019 la quarta campagna di indagine sulle modalità di comunicazione e di relazione degli adolescenti. Il volume propone i dati raccolti e le riflessioni del gruppo di lavoro dell’Osservatorio. A partire dall’esperienza delle campagne di indagine condotte dal 2008, si è ampliato il raggio d’azione su base territoriale, allargando lo sguardo a province confinanti con Bergamo; e su base anagrafica, indagando gli alunni di quarta e quinta della scuola primaria. Il gruppo di lavoro ha coinvolto, in modalità d’indagine diverse, oltre 9000 persone tra adolescenti, genitori, docenti, educatori
Intercultura online e offline: autorappresentazione dell'identità e della diversità di adolescenti con background migratorio fuori e dentro Facebook
No full textIn a globalized world characterized by human migrations that affect every social level, the possibility to stay connected by Internet represented an important revolution. Nowadays this opportunity has been magnified by the spread of social networks that defined new ways of placing ourselves in the virtual world. Among these media, Facebook, drew the attention of researchers, because it also created a social space where people can represent their identities and their relationships. “Virtual” and “real” are categories that do not fit in this context. In fact, online and offline are two strongly connected faces of the same reality, they are two different ways to be and to stay in the world.
In a social place that has proved to be very important for relationship among peers and for the definition of the self, how does the question of cultural diversity come into play? Is this a place of interculturality intended as reciprocal exchange? This research, by the combination of quantitative and qualitative methods, aims at defining how adolescents with migration backgrounds manage the complexity of a multiple identity
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The behaviour of a gap graded sand with mixed mineralogy
No full textThe compression and shearing behaviour in mixtures of soils of different granulometries and/or mineralogies has been researched extensively. The focus of the research has been to identify the key factors that might lead the behaviour to change from transitional to not transitional, where transitional behaviour is characterised by non-convergent compression paths and critical state lines that might be non-unique. A review of mixtures of different soils revealed a complex pattern of behaviour, in which transitional behaviour can be caused by relatively small changes in the proportion or nature of the soil particles. It was then assumed that the mineralogy of the matrix composed by larger grains determines the mode of behaviour. If there is a strong and stiff matrix made of quartz sand particles either larger than or at least of a similar size to the other component, then non-convergent compression paths and/or not unique CLSs are likely to occur. This paper presents the results of triaxial and oedometer tests on a range of mixtures of a quartz sand and a carbonate sand, but with a larger weaker carbonate sand component. As predicted, no transitional behaviour was seen in any mixture
Determination of water retention properties of silty sands by means of combined commercial techniques
No full textA recent increase in frequency and severity of exceptional climatic events is of concern for the stability of natural and artificial slopes. These undergo continuous evaporation and infiltration cycles, which change the suction distribution and trigger shrinkage, swelling, cracking, and surfi-cial erosion, overall decreasing the soil strength. To assess the impact of these climatic stresses, the determination of water retention properties is a priority. Although advanced techniques have been proposed in the last few decades to this end, simpler commercially available techniques allow col-lecting data for a larger number of samples in a shorter time, thus enabling a basic description of the water retention properties for a larger database of soils. Data on two silty sands, coming from very different climatic environments in Europe, were collected with a combination of two simple commercial devices, and the results were modelled with a van Genuchten’s law. The fitted pa-rameters were found to correlate well with the amount of fines, irrespective of the different origin and composition of the two soils. Eventually, the limitation of the approach is discussed based on the results of cyclic drying–wetting tests
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