1,720,958 research outputs found
NDT for the diagnosis of modern, historical and archaeological structures
Full text linkThis thesis has been developed with the aim to explore thoroughly potential and limit of the GPR and ERT methods for monitoring heterogeneous structures where different construction materials are combined together.
Firstly we analysed the GPR response, in various construction materials related to different modern, historical or archaeological structures. In particular, three real examples were investigated during the thesis, namely: the Pyramid of Caius Cestius, the Passage of Commodus and the Colle Oppio Ninpheum, all in Rome. According to the different types of material and frequency antennas, different GPR responses and therefore dissimilar degree of resolution and of attenuation was obtained.
In light of this, the interposition between the surface of the investigated medium and the GPR antenna of a dielectric material (e.g. Plexiglas) was performed in order to improve the resolution.
Furthermore, an application of the GPR and ERT methods for monitoring a load test executed on masonry samples was presented. This panels were built up in the laboratory controlled conditions using tuff and bricks (widespread materials employed in Italy for decades for masonry buildings) and also were reproduced in the phase of theoretical modeling. The laboratory samples are reinforced with a conductive fibre fabric, where a high-conductive material (steel wires) is combined together with a dielectric material (basalt fibre).
In order to improve the sample-antenna coupling in the presence of conductive reinforcements, a Plexiglas (polimetilmetacrilato - PMMA) plate was added underneath a 2 GHz antenna. GPR data were acquired along profiles spaced 0.1 m apart and ERT measurements were executed on a 0.1 m regular spaced grid with a dipole-dipole array operating in a three-dimensional configuration. GPR datasets were also analysed in non-conventional mode, by means of the picking of the reflection time of the EM wave from the rear face of the wall samples.
Results show that GPR and electrical resistivity tomography were both able to detect fractures and weakness zones caused by the load application, even though with a higher resolution for the georadar with respect to the geoelectrical method. Moreover, mapping the GPR data in terms of the dielectric constant and mean absolute amplitude is particularly diagnostic to detect the effective fracturing pattern, after the application of the diagonal load. Therefore, GPR and ERT methods can reduce the degree of uncertainty in the detection of fractures, voids or cavities, with respect to the standard processing, by the combined analysis of radargrams, time-slices and resistivity ERT models.
Furthermore, for the GPR laboratory data acquired directly on the reinforced face of samples, it is demonstrated how interposing a layer of dielectric material between the antenna and the structure can substantially improve the antenna coupling and consequently the capability to detect fractures and to reach the rear face of the sample, despite losing resolution in the case of shallow high-conductive layers.
Finally, three-dimensional synthetic simulations on the same samples validate the experimental evidences. Therefore, we demonstrate that this approach can be a reliable tool to monitor static load tests and it can be further extended to the whole load cycle (before, during and after the experiment)
Utilizzo di tecniche geofisiche non distruttive per la caratterizzazione dello strato di copertura e la localizzazione di biogas in discariche controllate
No full textLa crescente sensibilità ambientale, unita ad un razionale uso del territorio, pone come priorità conoscitiva la caratterizzazione e il monitoraggio nel tempo delle aree di discarica in cui al corpo rifiuti spesso si associano biogas e percolato, i quali determinano importanti variazioni di alcuni parametri fisico-chimici, individuabili mediante l’utilizzo di tecniche non invasive di tipo geofisico. Lo scopo del presente lavoro è l’analisi delle potenzialità e dei limiti dell’integrazione di differenti metodi geofisici (tomografia elettrica di resistività, metodi elettromagnetici a bassa frequenza e georadar) per la localizzazione di biogas in una discarica controllata costituita da rifiuti di tipo Car-Fluff. Dall’analisi dei profili di resistività ottenuti mediante le indagini di tomografia elettrica è stato possibile investigare i soli terreni di copertura posti al di sopra della membrana di impermeabilizzazione, in quanto quest’ultimo si comporta da isolante impedendo il passaggio della corrente elettrica. I metodi elettromagnetici e georadar hanno invece consentito di monitorare anche i sedimenti al di sotto del telo di impermeabilizzazione.
L’interpretazione integrata dei dati ottenuti con le diverse tecniche geofisiche ha consentito la localizzazione degli accumuli del biogas al di sopra del telo in polietilene ad alta densità e ha ovviato ai limiti dovuti alle
particolari condizioni specifiche legate al singolo metodo di indagine. Lo studio ha dimostrato che le tecniche geofisiche possono fornire un valido ausilio nell’ottimizzazione dello sfruttamento di biogas in discariche
controllate e nella riduzione dei rischi ad esso associati in discariche non controllate.In the last decades geophysical techniques have been used for detection, characterization and monitoring of landfills due to the high-flexibility and the costeffectiveness of these methods. The aim of this work is to analyze potential and limits of a new integrated approach, encompassing electrical resistivity tomography, georadar and low-frequency electromagnetic techniques, for the evaluation and the monitoring of biogas accumulation
in the subsoil. Experimental geophysical data are acquired in a closed controlled landfill which contains Car-Fluff waste. The electrical resistivity tomography investigation is able to investigate only the shallower layer
above the geomembrane, acting as an insulator. On the contrary, georadar and electromagnetic methods can monitor also the waste mass below the geomembrane, where biogas accumulations are likely to occur. Through the joint interpretation of geophysical data we are able to reduce the degree of uncertainty in interpretation of the single geophysical model and to provide a direct correlation between the change in the geophysical parameters and the effective presence of biogas. As a result the non-invasive geophysical techniques can be an important tool for biogas monitoring in controlled landfills and for reducing the associated risks in uncontrolled landfills
High-resolution investigation of masonry samples through GPR and electrical resistivity tomography
No full textThis paper aims to explore potential and limits of the combined use of ground penetrating radar (GPR) and electrical resistivity tomography (ERT) investigations for the characterization of reinforced masonry samples. To this aim, both techniques were applied on two laboratory small-scale wall samples before and after the application of a shear-compression diagonal load. Laboratory samples (1 × 1 × 0.25 m) are made of bricks and tuff respectively and reinforced with a thin high-strength and high-conductive fibre fabric. In order to improve the sample-antenna coupling in presence of conductive reinforcements, a Plexiglas plate was added underneath the 2 GHz antenna. GPR data were acquired along profiles spaced 0.1 m apart and ERT measurements were executed on a 0.1 m regular spaced grid with a dipole-dipole array operating in a three-dimensional configuration. GPR datasets were also analysed in non-conventional mode, by means of the picking of the reflection time of the EM wave from the rear face of the samples. Results show that GPR and electrical resistivity tomography were both able to detect fractures and weakness zones caused by the load application, even though with a higher resolution for the georadar with respect to the geoelectrical method. The use of a dielectric material between the GPR antenna and the investigated medium improves substantially the signal penetration in the case of shallow high-conductive layers. Finally, three-dimensional synthetic simulations on the same samples validate the experimental evidences. Therefore, we demonstrate that this approach can be a reliable tool to monitor static load tests and it can be extended to the whole load cycle (before, during and after the experiment)
Investigating the Foundation of the Amphiteatrum Flavium through the Passage of Commodus
Full text linkIn this work we present a non-invasive investigation of the Amphiteatrum Flavium, executed using the ground penetrating radar (GPR) technique, with the aim to improve the knowledge of the construction materials and techniques employed for building foundation. Therefore, the main goal of this work is to achieve quantitative and reliable information for assessing the seismic vulnerability of the structure. The GPR survey was performed through the Passage of Commodus, excavated within the foundation for a length of about 60 m. GPR data were acquired on the floor and on the lateral walls, using different antenna frequencies (80, 200, 600, 900 MHz) as they combine good resolution and depth of investigation.
On the floor dataset, we detected three equally-spaced anomalies related to old utilities parallel to the passageway, whose roof is located at a depth of 1 m. In addition to this, the GPR radargrams clearly highlight horizontal layers within the foundation, related to the sequential development of works at the time of construction.
GPR dataset acquired on the wall allowed us to detect the thickness of the concrete covering the foundation and to locate the extensions of the structural elements underground. Outside the foundation, the passage is built using bricks, with external walls about 1 m thick.
Therefore, GPR dataset revealed that the foundation of the Colosseum is a heterogeneous multi-layer element, with the presence of cavity networks and buried elements related to the plinths of the load-bearing structures. This work confirmed that foundation was built over time by means of subdivisions into small sectors, probably both in the horizontal and vertical directions
Pavement testing by integrated geophysical methods: Feasibility, resolution and diagnostic potential
Full text linkThis work is focused on the assessment of the diagnostic potential of several geophysical methods when applied to the investigation of a rigid airport pavement. The potential and limit of each technique are evaluated as well as the added value deriving from their integration. Firstly, we reconstruct a high-resolution image of the pavement by a large electromagnetic and georadar screening. An advanced processing of georadar data, implemented through the picking of the arrival times of reflections for each profile, provides a quantitative estimation of the deviation between the design and the as-built thickness of layers. Additionally, electrical tomography has been applied to unequivocally identify the anomalous zones, where higher values of resistivity would be associated to porous zones that are prone to degradation and failure. The seismic tomographic survey had the additional purpose to recover the mechanical properties of the pavement in terms of both P- and S-waves and consequently of elastic constants (Poisson's ratio), whose values were consistent with those recovered in literature. The anomalies detected by each technique are consistent in their indications and they can be correlated to failure phenomena occurring at layer interfaces within the pavement structure or to unexpected variations of the layer thicknesses. The cost-effective geophysical campaign has validated the four-layered system deduced from the original design and has been used to reconstruct a high-resolution map of the pavement in order to discriminate fractures, crack-prone areas or areas where the as-built differs from the original design
Indagini geofisiche integrate ad alta risoluzione per la diagnostica delle pavimentazioni aeroportuali
No full textNel corso della loro vita utile, le pavimentazioni aeroportuali devono garantire qualità, affidabilità e sicurezza, al fine di minimizzare eventuali rischi dovuti a fenomeni di rottura e cedimento strutturale. Tali pavimentazioni non devono altresì presentare irregolarità o caratteristiche che possano deteriorare le capacità di controllo direzionale dell’aeromobile, la capacità frenante dei sistemi antislittamento o condizionare la corsa di un velivolo (Manassero e Dominijanni, 2010). È quindi necessario valutare lo stato di conservazione e individuare i parametri fisicomeccanici del complesso pavimentazione-terreno di fondazione, al fine di verificare da una parte la conformità al progetto originale in fase di collaudo, nonché individuare zone usurate, anomale o potenzialmente soggette a cedimento durante l’utilizzo dell’infrastruttura. È pertanto di fondamentale importanza mettere a punto un’accurata e consistente attività di rilevamento e di monitoraggio dei principali parametri geometrici e fisico-meccanici della pavimentazione, che renda più affidabili le scelte manutentive da mettere in opera. In tal senso, i metodi non distruttivi ed in particolare i metodi geofisici permettono di effettuare test supavimentazioni in maniera rapida, totalmente non invasiva e a basso costo. Negli ultimi anni sono stati fatti significativi passi in avanti nel campo delle pavimentazioni stradali, utilizzando degli indicatori diretti della portanza strutturale attraverso una stima in sito dei valori tanto degli spessori quanto dei moduli elastici degli strati che costituiscono la pavimentazione (Goel e Das, 2008). Inoltre, tali proprietà possono essere anche monitorate nel tempo, fornendo così un utile strumento di valutazione nella fase di gestione e di progettazione di una pavimentazione stradale. Poiché una singola tecnica geofisica spesso non è in grado di raggiungere la totalità degli obiettivi richiesti in termini di accuratezza e univocità interpretativa, in molti casi si opta per un approccio integrato di più metodologie, come è prassi comune nei rilievi geofisici degli ultimi anni (Piro et al., 2001; Cardarelli et al., 2014). Il target richiesto per le indagini in ambito aeroportuale colloca le necessità diagnostiche nel campo dell’alta risoluzione. In particolare per la valutazione dell’integrità strutturale delle pavimentazioni aeroportuali sono necessari sia un grado di risoluzione elevato nel primo metro dal piano di campagna, al fine di individuare eventuali fratture nella pavimentazione, ma anche una buona penetrazione in profondità, per caratterizzare correttamente il suolo di fondazione. Sulla base di quanto sopra descritto, si è eseguito un rilievo geofisico integrato con l’obiettivo di ricavare i parametri necessari alle verifiche delle condizioni attuali di un piazzale di sosta prospiciente un hangar aeroportuale e integrare le conoscenze dedotte dagli elaborati di progetto. In particolare sono state eseguite indagini georadar (GPR), elettromagnetiche a bassa frequenza (EM), di tomografia elettrica (ERT) e di tomografia sismica a rifrazione (SRT) per verificare le capacità diagnostiche e le potenzialità di integrazione dei vari metodi. L’interprestazione integrata dei risultati delle indagini geofisiche eseguite nell’area d’indagine, ha costituito uno strumento utile per la determinazione di eventuali scostamenti tra il progetto originale e l’effettivamente costruito (as-built), per l’individuazione di eventuali anomalie relative a zone maggiormente deteriorate e conseguentemente per la pianificazione di successivi interventi di monitoraggio e/o messa in sicurezza delle piste aeroportuali
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
