IRIS Università degli Studi dell'Aquila
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Sampled-data global asymptotic stabilization of globally Lipschitz retarded switched systems
Get PDFIn this paper, we address the sampled-data global asymptotic stabilization of nonlinear globally Lipschitz retarded switched systems under arbitrary Lebesgue measurable switching signals. In particular, we show that if a mode-independent, globally Lipschitz state feedback is available and acts as a global stabilizer in continuous time, then applying this feedback via sampling and holding ensures global asymptotic stability, given a sufficiently fast sampling. Moreover, when the class of piecewise-continuous switching signal is considered, we prove that suitably fast sampling also guarantees global exponential stability. Finally, an example is provided to illustrate the obtained results
Parameter identification of nonlinear dynamical systems through the Hilbert Huang Transform and the Multiple Scales Method
Get PDFEffect of concrete properties on cyclic behavior of poorly engineered RC beam-column wall joint
Get PDFPost-earthquake observations have shown the reinforced concrete beam-column joints of dated structures may result in premature brittle failure during earthquakes. These critical zones transfer complex combination of forces between beams and columns and their premature failure may cause the catastrophic collapse of structures even in areas from low to moderate seismic risk. External beam-column joints (i.e., "wall" and "corner" joints) of buildings constructed without or with insufficient transverse reinforcement are often involved in this types of collapses. The aim of this study is to investigate how the structural response of RC beam-column joints is affected by several mechanical parameters of the concrete, including: compressive strength, tensile strength, Young's modulus, Poisson ratio and fracture energy in tension of the concrete. Both experimental tests and numerical models have been carried out. In particular, four RC beam-column sub-assemblies with no shear reinforcement in the joint have been designed, constructed and tested un- der cyclic loads. In particular, to reproduce the worst possible condition for the beam-column joints, no axial load was applied to the column the tests were performed with no axial load in the column. Experimental results were then compared with those predicted through numerical simulation carried out with a 3D FEM model, able to describe crack propagation in concrete. Experimental structural ductility of the tested RC frames were found surprisingly high and force-displacement numerical curves were found to match experimental ones both in terms of initial stiffness and maximum strength capacity. Sensitivities analysis carried out with respect of various concrete properties showed: (i) the frame strength capacity and ductility to increase with fc; (ii) in case of low concrete strength classes, the collapse of RC frames is expected to be in shear mode; (iii) for high concrete strength classes the collapse of RC frames may be reached in the beam column joint in pressure-bending mode; (iiii) both the maximum strength capacity and the ductility of the RC frames increase as the concrete fracture energy increases; (iiiii) Poisson ratio and concrete tensile strength seem not to have much influence on the mechanical behavior of the RC frame
The Power of Social Sources on Students’ Well-being in Primary School The Role of Teachers and Peers in Classroom Positive Emotions and Perceptions of Future School Success
Get PDFThe present study examined the role of positive classroom relationships with teachers and
peers in students’ adaptation. Fifty-five students in the final year of an Italian primary
school (5th grade) participated in the study. The findings indicated that the quality of
the teacher-student relationship was significantly associated with students’ well-being, as
reflected by the frequency of positive emotions in the classroom and students’ self-efficacy
beliefs regarding their ability to successfully transition to lower secondary school. In
contrast, after accounting for the quality of the teacher-student relationship, classroom
cohesion was not associated with the outcomes considered. These results highlight the
crucial role of teachers in shaping students’ school experiences. They also underscore the
multidimensional nature of the teaching-learning process, which is essential not only for
promoting knowledge acquisition and ensuring academic learning but also for providing
students with the emotional support necessary for their overall development.Il presente studio ha analizzato il ruolo delle relazioni positive in classe, sia con gli insegnanti
sia con il gruppo dei pari, nell’adattamento degli studenti. Cinquantacinque studenti
dell’ultimo anno di una scuola primaria italiana (classi quinte) hanno partecipato
allo studio. I risultati hanno indicato che la qualità della relazione insegnante-studente
era significativamente associata al benessere degli studenti, come evidenziato dalla frequenza
delle emozioni positive in classe e dalle convinzioni di autoefficacia degli studenti
riguardo alla loro capacità di affrontare con successo il passaggio alla scuola secondaria
di primo grado. Al contrario, tenendo conto della qualità della relazione insegnantestudente,
la coesione tra pari in classe non risultava associata agli esiti considerati. Tali
risultati evidenziano il ruolo cruciale degli insegnanti nelle esperienze scolastiche degli
studenti, sottolineando la natura multidimensionale del processo di insegnamento-apprendimento,
fondamentale non solo per promuovere l’acquisizione di conoscenze e garantire
l’apprendimento, ma anche per offrire agli studenti il supporto emotivo necessario
al loro sviluppo
Chopped Basalt Fibers Reinforced Mortar for Strengthening the Architectural Heritage
Get PDFThe high seismic vulnerability of unreinforced masonry buildings urgently calls for researchers to develop sustainable reinforcing methods and materials. This paper presents an innovative lime-based mortar reinforced with randomly oriented basalt fibers for the reinforcement of masonry heritage. The main aim of this study is to understand the effect of the content and the length of basalt fibers on the mortar's mechanical behavior. As a cementitious material made mostly out of lime, the mortar is chemically compatible with the historical substrate and therefore suitable in cases of restoration works on architectural heritage. Moreover, the chopped basalt fibers are randomly oriented, and this characteristic makes the overall layer effective in all directions, as the state of stress induced by seismic action is directionally undetermined. The newly proposed reinforcement system is characterized by a twofold aspect related to sustainability: 30% of the aggregates composing the mortar mix design is a recycled result of the ruins of the 2009 L'Aquila earthquake, and the chopped fibers are made out of basalt, widely known for its environmentally supportable peculiarity. The study consists of testing samples characterized by two fiber lengths and six fiber contents, along with one set of plain mortar samples. Specimens measuring 160 mm x 40 mm x 40 mm are first tested in a three-point bending (TPB) configuration, aiming to determine the flexural strength and the post-peak capacity through the calculation of the fracture energy. Then, the two broken pieces resulting from the TPB tests, each measuring 80 mm x 40 mm x 40 mm, are tested in splitting and compression, respectively, aiming to compute the tensile and compressive strengths. Finally, to provide a trend for the mortar's mechanical properties, a regression analysis is performed by fitting the experimental data with simple linear, polynomial, and exponential regression models. Results show that: (i) both fiber content and fiber length are responsible for a linear increase of the flexural strength and the fracture energy; (ii) for both short- and long-fiber mortar samples, the tensile strength and the compressive strength parabolically increase with the fiber content; (iii) the increase in fiber content and fiber length always generates a reduction in the conglomerate workability. The fiber content (FC) optimization with respect to the mechanical properties leads to a basalt FC equal to 1.2% for long-fiber samples and an FC equal to 1.9% for short-fiber ones
On the Equivalence and Optimality of Transformations of Diffusive Systems
No full textIn this paper we introduce, inspired by Clausius and developing the ideas of [11], the concept of equivalence of transformations in non equilibrium theory of diffusive systems within the framework of macroscopic fluctuation theory. Besides providing a new proof of a formula derived in [3, 4], which is the basis of the equivalence, we show that equivalent quasistatic transformations can be distinguished in finite terms, by the renormalized work introduced in [1, 2, 3-4]. This allows us to tackle the problem of determining the optimal quasistatic transformation among the equivalent ones
Microbial Consortium of Streptomyces spp. from Mining Environments Enhances Phytoremediation Potential of Lemna minor L
Get PDFThe presence of substantial amounts of heavy metals in the environment can result in various significant ecological issues and human health risks. Currently, bioremediation employing microorganisms is garnering significant interest due to its effectiveness. The present investigation aimed to isolate actinobacterial strains from an Italian mine and to characterise them for heavy metals resistance and plant growth-promoting characteristics. The different samples were processed for DNA extraction and 16S rRNA gene metabarcoding to investigate the bacteria and archaea communities. Cultivable microbiota were isolated and evaluated for heavy metals tolerance and different PGP traits. The most pertinent strains were tested for compatibility, merged into a consortium, and tested on Lemna minor L. Metabarcoding analysis revealed that amplicon sequence variants (ASVs) at the phylum level were mostly assigned to proteobacteria and bacteroidota. Uncultured and unknown taxa were the most prevalent in the samples at the genus level. A total of ten strains were obtained from the culture-dependent approach exhibiting interesting heavy metals tolerance and plant growth-promoting traits. The best strains (MTW 1 and MTW 5) were selected and further characterised by 16S barcoding. These strains were identified as Streptomyces atratus (99.57% identity). An in planta experiment showed that the metal-tolerant consortium MTW 1-5 improved plant physiology by significantly optimising plant growth and tolerance to heavy metals. The experiment conducted provided evidence for the possibility of using actinobacteria as bioaugmentation agents to improve the phytoextraction abilities of L. minor
Fire resistance of wooden dowelled cross-laminated timber panels under in-plane loading
No full textThis paper addresses the fire resistance of adhesive-free Cross-Laminated Timber (CLT) panels assembled with beech wooden dowels. A 180 mm thick, unprotected sample composed of six layers, each 30 mm thick, with overall dimensions of 3 m×3 m, was subjected to a standard fire curve for 100 min. The panel was loaded in-plane with a uniformly distributed load of 50 kN/m2. During the large-scale fire test, the temperature on the unexposed side and deformations at various points were monitored. Additionally, the final reduction in cross-section along the panel's height was assessed. The overall fire performance of the wooden dowel CLT (WDCLT) panels was satisfactory, with no failure after 100 min of exposure. A thermomechanical analysis of the panel was conducted to simulate the panel's mechanical behaviour under fire. Since no temperature data within the panel or direct measurements of the evolving charring depth were available, validation was performed against the deformation history. The charring rate time history was indirectly estimated from the model. A parametric analysis was conducted to simulate the load-carrying capacity ratio over time for the WDCLT panels, considering multiple layups with 5, 6, and 7 layers, with respective thicknesses of 150 mm, 180 mm, and 210 mm. The performance of these WDCLT panels was also compared to that of models representative of glued CLT panels, discussing the sensitivity of the fire resistance to the charred layer fall-off
