86,883 research outputs found
Uno sguardo sulla necropoli di Chiavari dall’Etruria Meridionale: spunti e osservazioni
No full textAttraverso l'esame dei contesti della necropoli di Chiavari e della circolazione di una precisa forma in ceramica depurata il contributo è volto a mettere in luce i contatti con l'Etruria meridionale nella prima metà del VII secolo a.C., le forze in gioco nel Tirreno settentrionale una generazione prima della fondazione di Marsiglia e l'apertura del centro anche a contatti con la cultura di Golasecca.Il lavoro consiste in una disamina in prospettiva contestuale degli indicatori della necropoli di Chiavari che sono stati a suo tempo considerati da N. Lamboglia di area etrusco meridionale, via via ripresi come tali e discussi nella critica.
Attraverso l’esame dei contesti il contributo si propone di contribuire a definire portata e modalità dei contatti sottesi (G. Bagnasco Gianni), di cui la “kylix” della tomba 60.D rappresenta uno degli aspetti più interessanti (G. Spadea Noviero). Essa, come emerge nel lavoro, porta inevitabilmente a concentrare l’attenzione sulle forze in gioco nel Tirreno settentrionale almeno una generazione prima della fondazione di Marsiglia
Main complications of photorefractive keratectomy and their management
No full textPhotorefractive keratectomy (PRK) was the first surface ablation procedure introduced for the treatment of refractive errors and has been proven to be effective and safe. In some cases, however, the patient may not be totally satisfied with the final result and retreatment may be necessary. We performed a literature review to describe the main conditions that may arise following PRK that may require retreatment and new promising techniques to allow customized and effective treatments for patients. There is currently no gold standard for retreatment of residual refractive error after PRK. The surgeon must take into account the patient’s history and type of problem when choosing the most appropriate technique. LASIK and PRK are the main options. Haze can be treated with good results with phototherapeutic keratectomy and mytomicin C. High order aberrations and decentration may be addressed with topographically-guided excimer photoablation or with wavefront-guided PRK
Beam-Column connection for FRP structures
No full textThe use of FRP profiles is appropriate and advantageous for construction of industrial and low-rise residential buildings as well as temporary structures built in emergency situations. But for FRP composite structures to be competitive with structures made of traditional materials, they must be safe, serviceable, durable and economical. Structural safety and serviceability depend on the structural members’, as well as on their joints’ or connections’, strength and stiffness. Currently, the connections in FRP structures are commonly made using bolted connections [1-2], akin to those used in steel structures while, as stipulated in a recent European guideline [3], bonded connections are not allowed for primary load bearing components.
Figure 1. a) Connection tested in [4], b) new connection.
With respect to bonded beam-to-column moment resisting connections, the authors in a recent paper [4] demonstrated that this prohibition appears to be unjustified. An identical pultruded GFRP I-profile was used to form the beam and the column elements. The two elements were connected by epoxy adhesive, and GFRP seat angles, bonded to the column compression flange and the beam tension and compression flanges. In addition, stiffeners were used in the connection region to strengthen the column flange and web. The beam, acting as a cantilever, was loaded by a point load near its free end, which subjected the connection to combined bending and shear. The connection (Figure 1a) failed by debonding within the adhesive, achieving nearly the same percentage of the GFRP profile ultimate moment capacity as in the best performing bolted connections tested by others.
As a follow up to the previous work, in order to further enhance the forgoing connection strength and stiffness, in this study the column and the seating angle bonded to the beam tension face and the column are strapped together using a carbon wrap as depicted in Figure 2b. The new connection is loaded identically to the previously tested connection, and, compared to the companion unwrapped connection, the results of the improved connection show increase in both the ultimate moment resistance and rotational stiffness. This improvement makes adhesive connections an even more appealing choice for practical applications.
[1] L.C. Bank, A.S. Mosallam, G.T. McCoy, Journal of Reinforced Plastics and Composites, 15, 1052 (1994).
[2] S.J. Smith, I.D. Parsons, K.D. Hjelmstad, Journal of Composite for Construction, 3, 20 (1999).
[3] Report EUR 27666 EN, Prospect for new guidance in the design of FRP. JRC Science for Policy Report, 2016.
[4] F. Ascione, M. Lamberti, A.G. Razaqpur, S. Spadea, S., J. Comp. Struct., 160, 1248 (2017)
Effects of recycled PET fibres on the mechanical properties and seawater curing of Portland cement-based concretes
No full textThis paper deals with an experimental study on the mechanical properties of recycled polyethylene terephthalate fibre-reinforced concrete (RPETFRC) and its durability in an aggressive seawater environment. A Portland limestone cement-based concrete with a 0.38 water/cement ratio is used to cast cubic and prismatic specimens, in association with two different PET fibres obtained through extrusion of recycled PET flakes (R-PET). Some of these specimens were conditioned in the Salerno harbour seawater for a period of 6/12 months. Compressive strength and four-point bending tests are performed in order to investigate the mechanical properties of such RPETFRCs. Comparison of the present results and those in the literature for air-cured RPETRCs highlights the influence of the analysed R-PET fibres on the mechanical properties of concretes showing different water/cement ratios and binders. The given results for seawater-cured specimens demonstrate that such a curing condition slightly modifies the first-crack strength and markedly reduces the toughness of the RPETFRCs examined in the present work. © 2014 Elsevier Ltd. All rights reserved
Source characteristics of the basement rocks from the Sulu and Celebes Basins (Western Pacific): chemical and isotopic evidence
No full textBuckling behavior of curved composite beams with different elastic response in tension and compression
No full textA geometrically nonlinear finite element model of a composite curved beam is presented, accounting for moderately large rotations of the cross-sections, moderately large shear strains, small axial strains, and different elastic response of the material in tension and compression (bimodular behavior). A path following procedure in displacement control is employed to compute the stability points and the post-buckling response of the given model. Several comparisons are established with different numerical approaches available in the literature, showing the accuracy of the proposed finite element scheme in the unimodular case. Some original results on the in-plane and out-of-plane buckling of bimodular arches highlight that the post-buckling response of such structures is strongly influenced by the ratios between tensile and compressive moduli. © 2013 Elsevier Ltd
Source characteristics of the basement rocks from the Sulu and Celebes Basins (Western Pacific): Chemical and isotopic evidence
No full textNew Sr- Nd- and Pb-isotopic and trace element data are presented on basalts from the Sulu and Celebes Basins, and the submerged Cagayan Ridge Arc (Western Pacific), recently sampled during Ocean Drilling Program Leg 124. Drilling has shown that the Sulu Basin developed about 18 Ma ago as a backarc basin, associated with the now submerged Cagayan Ridge Arc, whereas the Celebes Basin was generated about 43 Ma ago, contemporaneous with a general plate reorganisation in the Western Pacific, subsequently developing as an open ocean receiving pelagic sediments until the middle Miocene. In both basins, a late middle Miocene collision phase and the onset of volcanic activity on adjacent arcs in the late Miocene are recorded. Covariations between 87Sr/86Sr and 143Nd/144Nd show that the seafloor basalts from both the Sulu and Celebes Basins are isotopically similar to depleted Indian mid-ocean ridge basalts (MORB), and distinct from East Pacific Rise MORB, defining a single negative correlation. The Cagayan Arc volcanics are different, in that they have distinctly lower ɛNd(T) for a given ɛSr(T), compared to Sulu and Celebes basalts. In the 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, the Celebes, Sulu and Cagayan rocks all plot distinctly above the Northern Hemisphere Reference Line, with high Δ7/4 Pb (5.3–9.3) and D8/4 Pb (46.3–68.1) values. They define a single trend of radiogenic lead enrichment from Celebes through Sulu to Cagayan Ridge, within the Indian Ocean MORB data field. The data suggest that the overall chemical and isotopic features of the Sulu, Cagayan and Celebes rocks may be explained by partial melting of a depleted asthenospheric N-MORB-type (“normal”) mantle source with isotopic characteristics similar to those of the Indian Ocean MORB source. This asthenospheric source was slightly heterogeneous, giving rise to the Sr-Nd isotopic differences between the Celebes and Sulu basalts, and the Cagayan Ridge volcanics. In addition, a probably slab-derived component enriched in LILE and LREE is required to generate the elemental characteristics and low Nd(T) of the Cagayan Ridge island arc tholeiitic and calcalkaline lavas, and to contribute to a small extent in the backarc basalts of the Sulu Sea. The results of this study confirm and extend the widespread Indian Ocean MORB signature in the Western Pacific region. This signature could have been inherited by the Indian Ocean mantle itself during the rupture of Gondwanaland, when fragments of this mantle could have migrated towards the present position of the Celebes, Sulu and Cagayan sources
A crack growth strategy based on moving mesh method and fracture mechanics
No full textA numerical model based on moving mesh strategy is proposed to simulate the evolution of internal material discontinuities in a continuum medium. The approach combines concepts arising from structural mechanics and moving mesh methodology, which are implemented in a unified framework to predict crack growth on the basis of Fracture Mechanics variables. In particular, moving computational nodes are modified starting from a fixed referential coordinate system on the basis of a crack growth criterion to predict directionality and displacement of the tip front. The use of rezoning mesh methods coupled with a proper advancing crack growth scheme ensures the consistency of mesh motion with small distortions and an unaltered mesh typology. In addition, the moving grid is modified from the initial configuration in such a way that the recourse to re-meshing procedures is strongly reduced. The numerical formulation and its computational implementation show how the proposed approach can be easily embedded in classical finite element software. Finally, numerical examples in the presence of internal material discontinuities and comparisons with existing data obtained by advanced numerical approaches and experimental data are proposed to check the validity of the formulation.</p
On the elastic properties of PVC foam
No full textIn the last decade, sandwich structures spread a great interest in civil engineering applications. However, despite their excellent mechanical performance, they can be affected by macroscopic and microscopic damages, which may trigger catastrophic failure modes. Detailed understanding of the physical and mechanical properties is needed in order to allow refined numerical models to describe structural behaviour under intensive loading conditions, accurately. The elastic and fracture characterisation of the core material is particularly relevant because cracking phenomenon strongly reduces the capacity of the sandwich structures to carry out loads. PVC foams, typically used as the inner core in a structural application, are investigated over a range of foam densities. PVC foams H100, H130, and H200, produced by DIAB. The elastic properties of foams under compressive uni-axial loading are measured using the full-field methodology
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