1,721,032 research outputs found
A computational investigation on singlet and triplet exciton couplings in acene molecular crystals
No full textQuantum chemical calculations (DFT, TDDFT and ZINDO/S) of singlet and triplet exciton couplings are presented and discussed for some acene derivatives (such as anthracene, tetracene, 9,10-di(phenyl) anthracene and 9,10-bis(phenylethynyl) anthracene). An accurate excited state single molecule characterization has been carried out followed by an analysis of the inter-molecular excitonic interactions, taking place in the crystalline phase. These have been correlated to exciton coupling terms obtaining guidelines for the choice of molecular materials with large exciton couplings. Such organic systems are likely to show multiexciton processes such as singlet fission (SF) and triplet-triplet annihilation (TTA) which are useful in energy conversion phenomena to be exploited in photonic and optoelectronic devices
Assessing the effect of tsunami-induced vertical loads on RC frames
Full text linkThe increasing number of people, structures and economic activities being exposed to tsunami hazards
makes it important to estimate the effects of this hazard on coastal developments. Tsunami onshore
flow generates significant loading on buildings and infrastructure, which can lead to structural failure.
Literature works recently proposed a non-linear static analysis method, called Variable Depth Pushover
(VDPO), for assessing the performance of buildings under the lateral pressures induced by a tsunami
onshore flow. This methodology was developed under the assumption that the building is watertight.
However, in the case of buildings with breakaway cladding (e.g., masonry infills), the water flow passing through the building induces vertical loads on horizontal structural members, due to uplift and
buoyancy pressures, that should be considered during the analysis. Thus, to address this phenomenon,
in this paper a numerical investigation is performed considering a combination of tsunami-induced
horizontal and vertical loads on a case-study reinforced concrete (RC) moment-resisting frame with
breakaway infills, typical of Mediterranean construction. The building model is subjected to a VDPO
analysis that applies different types and sizes of vertical loading on the horizontal elements of the building, as the tsunami inundation depth increases. From the results of this analysis, the effects of tsunamiinduced vertical load components on the case-study building in terms of damage propagation and failure
mode are discussed, and the significance of considering vertical loading is proven
Ductility improvement of existing RC columns strengthened with CFRP
No full textExisting reinforced concrete (RC) columns, designed according to obsolete
standards, often show premature failures due to longitudinal bars buckling or loss of bond when
subjected to horizontal cyclic loads. This kind of failure modes significantly reduces the
deformation capacity and the relevant ductility of existing RC columns and leads to poor
performances during seismic events. In order to improve the seismic performance of existing RC
columns, the effectiveness of external confinement with carbon fiber reinforcement polymers
(CFRP) was investigated in this work. Four square RC columns with deformed bars, designed
according to obsolete standards, were strengthened in the plastic hinge region with one and two
plies of uniaxial CFRP sheets. The columns were tested under horizontal cyclic load combined
with a constant compressive axial load. The performance of strengthened columns has been
compared with an unstrengthened control column. The test results have been analyzed and
compared in terms of failure modes and ductility improvement. Particular attention has been
focused on the strain distribution recorded on the CFRP strips; the strain profiles along the crosssection
perimeter in case of axial load and bending moment interaction are presented and
discussed at different drift levels
Effetti dei metalli pesanti su germinazione e crescita iniziale di Zannichellia palustris L.
No full textLa presenza di determinate associazioni vegetali può rappresentare un valido indice di valutazione dello stato di salute dell'ambiente da esse colonizzato. Esiste infatti un preciso rapporto fra gli organismi viventi e le caratteristiche chimico-fisiche dell'habitat, per il quale la sopravvivenza o meno di alcune specie può permettere di ottenere buone informazioni sulla presenza di contaminanti o altri fattori di stress nei diversi substrati. Da ciò si comprende come sia importante l'individuazione in natura di nuove specie utilizzabili come indicatori biologici, intendendo con questo termine sia le entità sensibili a un determinato fattore di stress (elevata salinità del substrato, presenza di metalli pesanti e/o sostanze inquinanti), sia quelle ad esso resistenti. Sulla base di tali considerazioni è stato sviluppato un programma di ricerca volto alla valutazione della presenza, in alcune specie spontanee, di quelle particolari caratteristiche che permettano di utilizzare tali specie come "bioindicatori". A tale proposito, per il nostro studio, è stata scelta una popolazione di Zannichellia palustris L. un'Idrofita moderatamente alofila che ritroviamo nelle acque dolci o moderatamente salate dei ruscelli di tutta Italia; in particolare il materiale da noi utilizzato, appartenente alla subsp. pedicellata, distribuita in acque salmastre lungo il litorale, è stato raccolto nei mesi di Maggio e Giugno 1997 in località Patanella (Laguna di Orbetello). Per la valutazione dei limiti di tolleranza della specie, sono state eseguite prove di germinazione e crescita iniziale (radice e germoglio) in presenza di metalli pesanti, quali CuSO4 e CdSO4, alle concentrazioni di 1, 2.5, 5, 10 e 20μM con controllo in acqua deionizzata; tali prove sono state condotte per 10 giorni in termostato alla temperatura di 20°C e fotoperiodo di 12/12h luce/buio. La % di germinati sul totale diminuisce proporzionalmente all'aumentare della concentrazione di Cd nel substrato mentre in presenza di Cu i valori di germinazione sono simili o addirittura superiori a quelli del controllo sino alla concentrazione di 10μM, superata la quale la capacità germinativa diminuisce. Un simile andamento si osserva anche a livello della crescita del germoglio; diversamente la crescita della radice è negativamente influenzata dalla presenza di entrambi i metalli nel substrato e in modo particolare dal Cd. I risultati ottenuti, come già osservato in altri generi quali Typha, Juncus etc., mettono in luce la possibilità di utilizzare Zannichellia palustris come "bioindicatore" per mettere rapidamente in evidenza livelli tossici di metalli pesanti nell'ambiente
Analysis of FRCM and CRM parameters for the in-plane shear strengthening of different URM types
No full textFabric Reinforced Cementitious Matrix and Composite Reinforced Mortar, are amongst relatively new type of inorganic composites. Several precedent research programs have investigated the effectiveness of inorganic composite materials to enhance in-plane shear capacity of unreinforced masonry (URM) walls. A database consisting of 406 diagonal compression test results was prepared using experimental results reported in literature with the aim of investigating the role of strengthening parameters on the effectiveness of solutions for enhancing the in-plane shear capacity of masonry panels. The experimental results were analysed for different masonry typologies and effects of masonry texture, mesh reinforcement, matrix properties and strengthening configurations were investigated to provide useful indication for the design of such systems. Furthermore, the accuracy of current design equations for FRCM was evaluated based on experimental data. Shear stress amplification factors were also proposed. The results showed that both the axial stiffness of mesh reinforcement and the mechanical properties of the matrix affected the shear capacity of strengthened panels. Furthermore, based on obtained results, topics for future research are also recommended
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