84 research outputs found

    Effetto di mineralogia e granulometria sul comportamento di transizione di miscele di sabbia.

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    Il comportamento di transizione è stato identificato per diverse tipologie di terreno, dai terreni con lacuna granulometrica a limi e sabbie ben gradate. Tale comportamento è caratterizzato dall’esistenza di percorsi di compressione non convergenti e dalla non unicità della linea di stato critico, con localizzazione fortemente dipendente dalla densità iniziale dei campioni. Sebbene in letteratura tale comportamento sia stato inizialmente attribuito a terreni di granulometria intermedia, è stato mostrato come questo sembrerebbe manifestarsi anche in presenza di terreni aventi granulometria mista, con lacuna granulometrica o ben gradati, e per miscele composte da particelle di diversa natura o diversa mineralogia. La diversa tipologia di terreni in cui tale comportamento è stato osservato evidenzia l’elevata difficoltà nell’individuazione dei fattori chiave che lo determinano. Uno studio recente ha mostrato la mancata convergenza dei percorsi di compressione per alcune miscele di sabbia create artificialmente utilizzando materiali di differente mineralogia: sabbia di quarzo e sabbia carbonatica. Con lo scopo di verificare l’effetto della composizione mineralogica, delle dimensioni e resistenza relative dei grani e natura delle particelle sul manifestarsi o meno del comportamento di transizione, la presente nota approfondisce i risultati del precedente studio utilizzando miscele di sabbia caratterizzate da proporzioni variabili delle componenti mineralogiche e granulometriche

    Unsaturated sand in the stability of the cuesta of the Temple of Hera (Agrigento)

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    In the Valle dei Templi in Agrigento seven Doric temples stand lengthwise the crest of a rigid calcarenite cuesta over a layer of carbonate sand which lies along a thick stratum of clays. The environment is highly prone to landslides since topplings of calcarenite blocks often occur. The rock slopes are moving back and the slope edge draw near to the foundation of the Temple of Hera Lacinia contributing to increase their perilous condition. To assess the role of unsaturated sands in the instability processes, after the compositional and textural analysis of the material, direct shear tests and oedometer tests have been carried out on sand samples initially at the natural state, with low or very low values of natural water content, and finally at full saturation. The mechanical behaviour of sands seems one of the main causes of the instability influenced by the presence of an open metastable structure, which develops through bonding mechanisms generated via suctions and/or through cementing material such as clay or salts

    The safety of an industrial archaeological heritage: The underground quarries in Marsala (Sicily)

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    The present paper analyses an underground and inactive quarry of calcarenite, which belong to a localised area called Cave di calcarenite in Contrada Cuccidenna that has been recognised as a typical example of industrial archaeological heritage. The study of this typical quarry is finalised to the preservation and safe fruition of this site, which represents the history of manufacturing technologies of rocky ashlars. Rock samples from the pillars have been collected and, at first, a petrographic characterisation has been performed. The strength parameters have been estimated by means of triaxial and isotropic compression tests. Through a finite element analysis, the mechanical characterization has been then used to assess the stability and safety conditions of the structure. The influence of several parameters has been considered: e.g. mesostructure of the rock mass, shape of the underground quarry and effects, in close areas, of human interventions

    The role of particle mineralogy in mixtures of sands

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    Several recent studies on mixtures of sands of different granulometries and/or mineralogies have focused on the key factors that might lead the behaviour to change from transitional to not transitional, where a transitional behaviour is characterised by non-convergent compression paths and critical state lines that might be non-unique. The authors present a review of mixtures of different soils showing a complex pattern of compression and shearing behaviour in which transitional behaviour can be caused by relatively small varia- tions to the proportion or nature of soil particles. Laboratory investigations, carried out by means of oedometer tests, have confirmed the role of the mineralogy of the matrix composed by larger grains. This determines the mode of behaviour so that, if there is a strong and stiff matrix made of quartz sand particles, which are either larger than or at least of similar size to the other component, then non-convergent compression paths are likely to occur, no matter whether particle breakage occurs or not

    New Synthetic Analogues of Natural Polyphenols as Sirtuin 1-Activating Compounds

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    NAD+-dependent deacetylase SIRT1 regulates many different biological processes, thus being involved in pathogenic conditions such as metabolic diseases, neurogenerative disorders and cancer. Notably, experimental evidence underlined that the activation of SIRT1 had promising cardioprotective effects. Consequently, many efforts have been so far devoted to finding new SIRT1 activators, both derived from natural sources or prepared by synthetic procedures. Herein, we discovered new SIRT1-activating derivatives, characterized by phenolic rings spaced by sulfur, nitrogen or oxygen-based central linkers. The newly synthesized derivatives were analyzed in enzymatic assays to determine their ability to activate SIRT1, as compared with that of resveratrol. Among the tested molecules, bisarylaniline compound 10 proved to be the most efficient SIRT1 activator. An evaluation of the effects caused by focused structural variations revealed that its para-hydroxy-substituted diphenyl moiety of 10 was the fundamental structural requirement for achieving good SIRT1 activation. Compound 10 was further investigated in ex vivo studies in isolated and perfused rat hearts submitted to ischemia/reperfusion (I/R), where it showed significant protection of the myocardium against I/R injury. Molecular modeling studies suggest the binding mode of 10 within SIRT1 in the presence of the p53-AMC peptide. Our findings reveal that this chemical scaffold may be used as the starting point to develop a new class of more potent SIRT1 activators as cardioprotective agents

    Determination of water retention properties of silty sands by means of combined commercial techniques

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    A 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

    The mechanics of silty soils from the Po river embankments. PhD thesis.

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    Dottorato in Ingegneria Geotecnica consorziato fra UniversitĂ  degli Studi di Parma, UniversitĂ  degli Studi di Brescia, UniversitĂ  degli Studi di Ferrara e UniversitĂ  degli Studi di Bologna XVII Ciclo
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