Dynamic response of rocking cracked masonry walls

The behaviour of masonry constructions results to be very far from the one characterizing ductile structures. In masonry constructions, the seismic action activates a rocking motion rather than a dissipating mechanism. A strength resource of masonry structures, properly reinforced in order to avoid early local failures, consists in exhibiting rocking behaviour, until a failure condition is attained. Aim of the paper is to investigate the dynamic behaviour of masonry single storey walls, according to Housner’s studies and innovatively introducing the effect of diagonal cracks developing from the toes of the piers and shown by typical post-earthquake cracking patterns. The proposed procedure can be easily applied to the case of multi-storey regular masonry walls with openings representing the main resistant structural components of a masonry building. Starting from the evaluation of the incipient rocking acceleration of the system, the free and forced motions of the wall are examined. In the paper, according to the classical Housner’s approach, the energy dissipation occurring during the impact is modelled. Finally, a numerical application, considering a simple constant horizontal acceleration impulse of given duration has been carried out.

     

A basis for the linear theory of elastic stability of structures

Summary In this paper a consistent linear theory of stability of elastic structures is given and the problem of the neutral equilibrium of a continuum composed by an elastic material with high stiffness to the strains is studied. All the particular cases, as the buckling of beams, plates, shells etc., ensue and their classification in regard of their significance is given. There are comparisons with other theories.

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Sommario In questa Nota viene formulata una consistente teoria lineare della stabilità dell'equilibrio delle strutture elastiche e si tratta il problema dell'equilibrio indifferente di un continuo costituito da un materiale elastico con elevata rigidità alla deformazione. Tutti i casi particolari di instabilità euleriana delle travi, piastre, gusci ecc., discendono come casi particolari e di questi viene fornita una classifica nei riguardi della loro importanza. Si fanno infine confronti con altre trattazioni.

     

How chromophore shape determines the spectroscopy of phenylene-vinylenes: origin of spectral broadening in the absence of aggregation

Single oligo(phenylene-vinylene) molecules constitute model systems of chromophores in disordered conjugated polymers and can elucidate how the actual conformation of an individual chromophore, rather than that of an overall polymer chain, controls its photophysics. Single oligomers and polymer chains display the same range of spectral properties. Even heptamers support pi-electron conjugation across approximately 80 degrees curvature, as revealed by the polarization anisotropy in excitation and supported by quantum chemical calculations. As the chain becomes more deformed, the spectral linewidth at low temperatures, often interpreted as a sign of aggregation, increases up to 30-fold due to a reduction in photophysical stability of the molecule and an increase in random spectral fluctuations. The conclusions aid the interpretation of results from single-chain Stark spectroscopy in which large static dipoles were only observed in the case of narrow transition lines. These narrow transitions originate from extended chromophores in which the dipoles induced by backbone substituents do not cancel out. Chromophores in conjugated polymers are often thought of as individual linear transition dipoles, the sum of which make up the polymer's optical properties. Our results demonstrate that, at least for phenylene-vinylenes, it is the actual shape of the individual chromophore rather than the overall chromophoric arrangement and form of the polymer chain that dominates the spectroscopic properties.     

QSAR models for biocides: The example of the prediction of Daphnia magna acute toxicity

ABSTRACT

Biocides are multi-component products used to control undesired and harmful organisms able to affect human or animal health or to damage natural and manufactured products. Because of their widespread use, aquatic and terrestrial ecosystems could be contaminated by biocides. The environmental impact of biocides is evaluated through eco-toxicological studies with model organisms of terrestrial and aquatic ecosystems. We focused on the development of in silico models for the evaluation of the acute toxicity (EC₅₀) of a set of biocides collected from different sources on the freshwater crustacean Daphnia magna, one of the most widely used model organisms in aquatic toxicology. Toxicological data specific for biocides are limited, so we developed three models for daphnid toxicity using different strategies (linear regression, random forest, Monte Carlo (CORAL)) to overcome this limitation. All models gave satisfactory results in our datasets: the random forest model showed the best results with a determination coefficient r² = 0.97 and 0.89, respectively, for the training (TS) and the validation sets (VS) while linear regression model and the CORAL model had similar but lower performance (r² = 0.83 and 0.75, respectively, for TS and VS in the linear regression model and r² = 0.74 and 0.75 for the CORAL model).     

Virtual displacements principle,existence and uniqueness for elastic no tension bodies

Aim of this paper is the formulation of the virtual displacement principle, and some its applications, for bodies made of masonry like–material, i.e. the elastic no tension material (ENT). In place of the common adoption of continuously diffused smeared cracks, used to include both cracks and fracture strains, the paper considers the direct presence of discontinuities of the displacement fields, i.e. the cracks occurring in masonry bodies. The paper makes use of the notion of the new boundary of the body which includes the fractures, following the approach of Volpert and Hudjaev (Analysis in classes of discontinuous functions and equations of mathematical physics, Nijhoff, Dordrecht, 1985). In this framework the paper extends to the ENT bodies a previous formulation of the principle of virtual displacements, given by the Author, for the simpler case of the rigid no tension bodies. The consequent study of the existence and uniqueness of the admissible equilibrium concludes the paper.     

Tuning the excitonic and plasmonic properties of copper chalcogenide nanocrystals

The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions.     

Strains by shearing stresses in continuum media

Summary On the basis of the slip theory of the plasticity of metals a general formulation of strain of continuum bodies subjected to shearing stresses is given in incremental form. The isotropic and incompressible elastic body and the strain-hardening plastic body are then studied as particular cases.

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Sommario Sui fondamenti della teoria degli slip della plasticità dei metalli viene formulata in forma incrementale una teoria generale della deformazione dei mezzi continui soggetti all'azione di tensioni tangenziali. Vengono poi trattati, come casi particolari, il corpo elastico isotropo e incompressibile e il corpo plastico incrudente.

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This work has been sponsored by C.N.R. (the Italian Council of Research).     

Stability,buckling, and postbuckling of elastic structures

Summary This paper is the continuation of a research on the stability and postbuckling behaviour of elastic structures; in the first Part [n. 4, Vol. X, 1975 of this Journal], the potential energy of elastic tridimensional bodies has been defined in a suitable configuration space, and its properties of regularity have been studied. According to the program given in the previous Paper, we examine now the potential energy functional for some monodimensional and bidimensional structural models. Then the Part II of this research is developed so that the Liapunov stability of the equilibrium configuration of continuous elastic structures is analyzed by means of suitable energy criteria.

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Sommario Questo lavoro costituisce il proseguimento di uno studio sulle stabilità e comportamento postcritico delle strutture elastiche; nel precedente lavoro, pubblicato sul n. 4, vol. X, 1975 di questa rivista, è stato esaminato il problema della definizione dell'energia potenziale di un corpo elastico tridimensionale in un opportuno spazio funzionale delle configurazioni, e sono state esaminate le proprietà di regolarità di questo funzionale. Proseguendo il programma formulato nel lavoro precedente, viene ora innanzitutto completato lo studio del funzionale energia potenziale con riferimento a modelli strutturali mono e bidimensionali. Viene poi sviluppata la Parte II e cioè l'analisi della stabilità secondo Liapunov di una configurazione di equilibrio attraverso opportune formulazioni dei criteri dell'energia.

     

Immobilized catalase on CoFoam hydrophilic polyurethane composite

Catalase from bovine liver was covalently immobilized on hydrophilic polyurethane composite (CoFoam). The activity of the enzyme was assayed in the decomposition of H₂O₂ at pH 7.0 and 25°C. The effects of water-to-prepolymer ration the addition of a crosslinking agent, and the utilization of a spacer on enzyme, activity were examined. The results of immobilization of the enzyme in a large-scale unit are reported. The advantage of the CoFoam composite lies in the low drop in pressure in a packed-bed reactor at fairly large flow rates. For example, at flow rates of 10–12 L/min, the drop in pressure is typically 3 kPa. Enzymes immobilized on CoFoam represent a novel use as catalysts in packed-bed reactors owing to the low drop in pressure.