1,721,103 research outputs found
Characterization of palygorskite in dust of desert source collected in aerosols and rain in Sardinia, Western Mediterranean
No full textNell'atmosfera del Mediterraneo occidentale sono stati campionati aggregati di fibre di palygorskite con dimensioni del silt e dell'argilla grossolana (6-40 µm). Utilizzando un microscopio elettronico a scansione interfacciato ad un sistema a dispersione di energia a raggi X, è stato possibile caratterizzare la morfologia e la tessitura dei granuli di palygorskite. La palygorskite è stata generalmente rinvenuta in granuli dalla forma eolica, come superficie fibrosa formata da lamine fini e come riempimento di pori e ricoprimento di particelle. Tutte queste forme sono il risultato di un'alterazione meccanica dovuta al processo eolico. Il ritrovamento di questi aggregati di palygorskite a grande distanza dalla zona di origine è prova della loro resistenza meccanica e perciò di una possibile loro utilizzazione negli studi paleoclimatici. Sono state osservate tessiture diverse della palygorskite nelle polveri a deposizione secca ed umida. Inoltre, nella deposizione secca, sono stati trovati clorite, illite, e caolinite intrappolate negli aggregati di palygorskite; tali aggregati presentano forma da arrotondata ad ovale con fibre di lunghezza da 1 a 2 µm e larghezza da 0,05 a 0,1 µ.m. entre nella deposizione umida i minerali intrappolati sono: quarzo, calcite e dolomite e gli aggregati di palygorskite mostrano una superficie tipo feltro, ad elevata porosità con fibre >1 µm di lunghezza e larghezza 0,02 µm. Tutte queste differenze morfologiche indicano aree sorgenti diverse per i due tipi di deposizione. Le aree in cui si origina la palygorskite sono generalmente gli alvei dei fiumi e dei laghi prosciugati e i laghi salati dell'Africa nord-occidentale. Anche le traiettorie delle masse d'aria che hanno trasportato le polveri atmosferiche e che si sono poi depositate in modo secco ed umido hanno indicato due aree di origine diverse.
Palygorskite aggregated grains occur in aerosol dust samples in western Mediterranean Sea, predominantly in silty a)1d coarse clay fractions (6-40 µm). We have characterized morphology and texture of palygorskite grains using analytical scanning electron microscope (SEM) with attached X-ray energy dispersive system (EDS). Palygorskite occurs as rounded aggregate grains (wind-shaped), as interwoven fibrous mats forming fine laminae, and as porefilling and pore-bridging cements that commonly coat detrital grains and occur among them. The shape and surficial felt-like structure of wind shaped grains result from the mechanical processes of eolian mobilization. Survival of the fiber-structures ofpalygorskite that have been transported for a long distance attests to their mechanical strength and therefore to their utility in the paloeclimatic studies. Our results show distinct and characteristic textures of palygorskite in dry (aerosol in air) and wet (precipitation) deposition. Modes moreover, in dry mode chlorite, illite, and kaolinite are trapped within aggregated palygorskite grains; those grains areround to oval in shape with a crust of flat fibers (some are 1-2 µm long; 0.05-0.1 µm wide). In wet mode, additional minerals such as quartz, calcite, and dolomite are trapped; palygorskite aggregate grains show an irregular meshwork, a high porosity of intervowen fibrous mats with mostly long thin fibers (> 1 µm long; about 0.02 µm wide). These differences highlight that two separate source areas sup- plied the dry and wet depositions. The main sources of this clay mineral are the dry rivers, late beds, salt lakes, and argillaceous bed-rocks in northwestern Africa. Air mass trajectories calculation independently indicate two different source areas
La Sardinia in età antonina: riflessioni su un testo da Bithia (ICO Sard. n. 8NP)
No full textThe well-known inscription from Bithia (ICO Sard. n. 8NP) is perhaps dated to 176 AD thanks to the identification of the proconsul M. Peducaeus Plautius Quintillus, son-in-law of Marcus Aurelius, who was probably supported in his office by an official of senatorial or equestrian rank C. Pompeius Felix. The text, although drafted in Neo-Punic, allows us to recognize a society by now deeply influenced by the Latin culture in the small but rich community of the Sulcis, which perhaps uses a late variant of the language of Carthage only for cultual purposes
Il mondo militare
No full textIl lavoro descrive l'esercito romano in Sardegna fra l'età repubblicana e il VI secolo d.C., con particolare attenzione all'età imperiale, soffermandosi sui singoli reparti, i loro spostamenti, i compiti, gli effettivi, gli accampament
Mechanical models of cellular solids: parameters identification from experimental tests - part II
Full text linkVenationes e miti classici nei mosaici della “Casa degli Struzzi” ad Hadrumetum (odierna Sousse, Tunisia)
No full textIn the House of the Ostriches in the Roman colony of Hadrumetum, the mosaic floors of the second phase –which can be attributed to the years immediately after the mid-3rd century – are marked by a total reorganization of the decoration. As in the previous phase, this is based on geometrical schemes, to which, however, wonderful figural mosaics have now been added in the large triclinium complex. These mosaics have often been considered simply as proof of the commitment of the dominus who gave the munus, while in reality they are inseparable elements of a complex semantic question that is not only visual but also ideological. In this representative space, in fact, the mosaicist put together images taken from the daily life of the venationes in the amphitheatres and set them against the myth of the Amazons, thus comparing the legendary past with the real
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L’admirable spectacle offert par monsieur Magerius à ses concitoyens: nuove riflessioni su un enigmatico mosaico dalla regione di Sousse (Tunisia centro-orientale)
No full textIl grande mosaico rinvenuto a Smirat, nelle campagne non molto distanti da Sousse (Tunisia) racconta per parole e immagini la venatio offerta da Megerius ai suoi concittadini in un momento imprecisato della seconda metà del III secolo: la narrazione ha il compito non solo di fornire la cronaca dello spettacolare atto evergetico, rimasto nella memoria di quanti frequentavano la villa rustica di Megerius, ma anche di glorificare il dominus ed editor e della sua famiglia. Ne sortisce una fotografia interessante della cultura e della società della Byzaena nel III secolo, di organizzatori, attori, pubblico coinvolti nell'evento, dei costi di queste operazioni, della tensione che circondava l'evento e che poteva sfociare nel dramma e nel lazzo irrispettoso
Mechanical models of cellular solids: parameters identification from experimental tests
No full textCellular materials have large use in many components acting as impact energy absorbers. These components have to be designed on the basis of the kind of impact, of the involved energy amount and of the maximum admissible load. The choice of the most suitable density for the selected type of foam is based on stress-strain behaviour, obtained by means of experimental tests and/or models. Only a few micro-mechanical models, as the Gibson model, take into account the density effects. These models could result quite complex to manage because of the need of, at least, a rough analysis of the actual foam structure. Conversely, most of the models used for numerical simulations are phenomenological models and have simple parameter identification based on fitting of experimental data, but they do not account for density effect. Experimental uniaxial compression tests performed for several types of foams, namely EPP, PUR (Bayfill EA), EPS and PPO/PS (Noryl GTX), at different density levels are used in order to identify, with an optimisation procedure devoted to the minimisation of the fitting residual evaluated by the least square method, the parameters of four cellular solid models. The considered models are four: the Gibson model [Gibson LJ, Ashby MF. Cellular solids. Structure and properties. Cambridge: Cambridge University Press; 1997], the Rusch model [Rusch KC. Load-compression behavior of flexible foams. J Appl Polym Sci 1969;13:2297-311; Rusch KC. Energy-absorbing characteristics of foamed polymers. J Appl Polym Sci 1969;14:1133-47; Rusch KC. Load-compression behavior of brittle foams. J Appl Polym Sci 1970;14:1263-73], a modified version of the Gibson model and a new empirical model. The third and fourth models have been developed in order to better fit the experimental stress-strain curve. The obtained improvements in terms of weighted sum of the squared errors are shown. The experimental data are a good representation of the typical behaviour of these kinds of foams and can be useful for the validation of models and the comparison of their performance. Moreover the large basis of experimental data for different types of foams at different densities could be used for the analysis of the influence of the density on the model parameters. Explicit empirical formulations are proposed to express the dependency of the phenomenological model parameters on the foam density. These relationships permit the identification of whatever density foam derived from the same solid material and with the same micro-structure by means of a minimum set of experimental tests. At the same time the availability of a large quantity of experimental data is helpful to reach a higher level of confidence in the model parameter values. Finally the identified parameters vs. density laws for the considered types of foam could be used in order to assist the design of a given absorber and to find the optimum density for the specific application. Closed form expression for the specific energy W and the efficiency E can be obtained, based on the resulting identified phenomenological model
MONTE TIMIDONE: AALENIAN-BAJOCIAN LIMESTONES. TIMIDONELLS BEDS (NORTH-WESTERN SARDINIA, ITALY).
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Provincia Sardinia et Corsica
No full textRoman tribus are absent in Corsica. They are rare in Sardinia and mostly present on the coastal regions. The predominance of the tribe Collina in Turris Libisonis, the prevalence of Quirina in Karales and the variety of evidences in Sulci could be related to the processes which led to the institution of colonia and municipia. Isolated presences presumably pertain to soldiers and incola
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