2,015 research outputs found

    Information Spreading in Stationary Markovian Evolving Graphs

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    Markovian evolving graphs are dynamic-graph models where the links among a fixed set of nodes change during time according to an arbitrary Markovian rule. They are extremely general and they can well describe important dynamic-network scenarios. We study the speed of information spreading in the "stationary phase" by analyzing the completion time of the "flooding mechanism". We prove a general theorem that establishes an upper bound on flooding time in any stationary Markovian evolving graph in terms of its node-expansion properties. We apply our theorem in two natural and relevant cases of such dynamic graphs. "Geometric Markovian evolving graphs" where the Markovian behaviour is yielded by "n" mobile radio stations, with fixed transmission radius, that perform independent random walks over a square region of the plane. "Edge-Markovian evolving graphs" where the probability of existence of any edge at time "t" depends on the existence (or not) of the same edge at time "t-1". In both cases, the obtained upper bounds hold "with high probability" and they are nearly tight. In fact, they turn out to be tight for a large range of the values of the input parameters. As for geometric Markovian evolving graphs, our result represents the first analytical upper bound for flooding time on a class of concrete mobile networks.Comment: 16 page

    Proposed course of study in general science for non-college preparatory students

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    This item was digitized by the Internet Archive. Thesis (Ed.M.)--Boston Universit

    Donor/Acceptor Heterojunction Organic Solar Cells

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    The operation and the design of organic solar cells with donor/acceptor heterojunction structure and exciton blocking layer is outlined and results of their initial development and assessment are reported. Under halogen lamp illumination with 100 mW/cm2 incident optical power density, the devices exhibits an open circuit voltage VOC = 0.45 V, a short circuit current density JSC between 2 and 2.5 mA/cm2 with a fill factor FF ≈ 50%, an external quantum efficiency (electrons/s over incident photons/s) EQE ≈ 5% and a power conversion efficiency of about 0.5%. Measurements of the photoelectrical characteristics with time are also reported, confirming that non encapsulated organic solar cells have limited stability in ambient atmosphere

    Archaeobotanical analysis from the long-term rural settlement of Contrada Castro (Corleone, Palermo): preliminary data

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    The project ¿Harvesting Memories: Ecology and Archaeology of Monti Sicani landscapes¿ aims to analyse the long-term relationship of landscape dynamics and settlement patterns in a Mediterranean inland of Central-Western Sicily. The project combined different interdisciplinary approaches of vegetation science, landscape ecology, history and archaeology in order to diachronically understand and reconstruct the human- society-environment interactions. From 2017 to 2019 a new rural settlement has been investigated in Contrada Castro (Corleone, Palermo). The excavation in Contrada Castro showed a clear case of long-term occupation of an hill-top site during Late Archaic/Classical age (6 th -5 th c. BC) and the Byzantine and Islamic period (7 th -11 th c. AD). Soils from the archaeological excavation were sampled to obtain evidences about paleo-vegetation and vegetal paleo-diet. Archaeobotanical data (seeds and charcoal remains) represent an informative source in human-environmental dynamics to collect specific data on a small scale in terms of chronology and topography (Hastorf, Popper 1988; Pearsall 2009). Furthermore, presence of edible plants as cereals, pulses and fruit characterize their use as economical resources. Unfortunately, archaeobotanical analyses from archaeological sites in Sicily are still not very common (see http://brainplants.successoterra.net/sites.html). For the reconstruction of the paleo-environment and the use of arboreal resources from the three chronological phases of the site, a total of 239 liters of soils were analysed. Taxonomical identification was made by optical microscopy through the comparison with the reference collection and specific atlases (fig.). More than 400 wood charcoals were observed, about 80% of them was identified. Thanks to comparisons with the current vegetation, so far 8 species have been identified - Quercus cfr. ilex (fig.), Pistacia cfr. terebinthus, Rhamnus alathernus, Fraxinus ornus, Ulmus canescens, Acer cfr. campestris, Ostrya carpinifolia, Populus cf. nigra; identification reached the detail of genus or subfamily in 6 cases - Quercus cf. robur / pubescens, Phillyrea sp., Sorbus sp., Rosacea cfr. Pirus sp. and maybe Moracea. The arboreal vegetation is therefore represented by evergreen oaks, semi- and deciduous oaks, maples, ash trees, associated with riparian species such as elm, poplar and hornbeam, and shrub species such as backthorn, terebinth, sorb, plum. Cultivated species are mostly not represented. Despite the widespread presence of the evergreen oaks in the whole record, differences between the three chronological phases were identified, highlighting a selective use of the wild species present in the area and a specific collection of wood for the hearths. 1) Hastorf C.A., Popper V.F.1988, Current Paleoethnobotany. Analytical Methods and Cultural Interpretations of Archaeological Plant Remains, Chicago. ISBN: 978022631893 2) Pearsall D. M. 2009, Paleoethnobotany: A Handbook of Procedures, Second Edition, Walnut Creek. ISBN-10: 1598744720 3) BRAIN Network, http://brainplants.successoterra.net/sites.htmlFinanciación: beca "Juan de la Cierva-incorporación, IJCI-2017-31494, MINECO), IJCI-2017-31494" y proyecto "Harvesting Memories" de la Universidad de Palermo (financiado por Bona Furtuna LLC)

    Water Electrolysis for the Production of Hydrogen to Be Employed in the Ironmaking and Steelmaking Industry

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    The way to decarbonization will be characterized by the huge production of hydrogen through sustainable routes. Thus, the basic production way is water electrolysis sustained by renewable energy sources allowing for obtaining "green hydrogen". The present paper reviews the main available technologies for the water electrolysis finalized to the hydrogen production. We describe the fundamental of water electrolysis and the problems related to purification and/or desalinization of water before electrolysis. As a matter of fact, we describe the energy efficiency issues with particular attention to the potential application in the steel industry. The fundamental aspects related to the choice of high-temperature or low-temperature technologies are analyzed. Keywords: water electrolysis; ironmaking; steelmaking;

    Dynamic identification and model updating of an eight-storey CLT building

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    So far, few in situtests have been carried out to estimate the modal parameters of multi-storey Cross-Laminated-Timber (CLT) buildings: the understanding of their dynamic behaviour under operational conditions is still an open issue. In this paper, the results of the dynamic identification of an eight-storey CLT building are reported and interpreted in the light of a simplified shear-type analytical model. The structural model is calibrated on the experimental modal parameters, which are assessed using the Stochastic Subspace Identification (SSI). The SSI provides mode shapes, natural frequencies and damping factors of the structures in its first linear response range; The minimum of a modal-based objective function gives an estimation of the unknown parameters of the structural model. Given the results of the dynamic identification, the storey-masses are the chosen optimization parameters: the values of the experimental eigenfrequencies likely reveal a continuum-like behaviour of the building without connections. The identified storey masses are indeed realistic and confirm the negligible role of the connections in the low-amplitude dynamic response. The nonlinear effects of connections over the building response to higher displacements are discussed, providing simplified and practice-oriented correlations for the first natural frequency estimation.acceptedVersio

    A time multiscale based data-driven approach in cyclic elasto-plasticity

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    Within the framework of computational plasticity, recent advances show that the quasi-static response of an elasto-plastic structure under cyclic loadings may exhibit a time multiscale behaviour. In particular, the system response can be computed in terms of time microscale and macroscale modes using a weakly intrusive multi-time Proper Generalized Decomposition (MT-PGD). In this work, such micro-macro characterization of the time response is exploited to build a data-driven model of the elasto-plastic constitutive relation. This can be viewed as a predictor-corrector scheme where the prediction is driven by the macrotime evolution and the correction is performed via a sparse sampling in space. Once the nonlinear term is forecasted, the multi-time PGD algorithm allows the fast computation of the total strain. The algorithm shows considerable gains in terms of computational time, opening new perspectives in the numerical simulation of history-dependent problems defined in very large time intervals

    A time multiscale decomposition in cyclic elasto-plasticity

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    For the numerical simulation of time-dependent problems, recent works suggest the use of a time marching scheme based on a tensorial decomposition of the time axis. This time-separated representation is straightforwardly introduced in the framework of the Proper Generalized Decomposition (PGD). The time coordinate is transformed into a multi-dimensional time through new separated coordinates, the micro and the macro times. From a physical viewpoint, the time evolution of all the quantities involved in the problem can be followed along two time scales, the fast one (micro-scale) and the slow one (macro-scale). In this paper, the method is applied to compute the quasi-static response of an elasto-plastic structure under cyclic loadings. The study shows the existence of a physically consistent temporal decomposition in computational cyclic plasticity. Such micro-macro characterization may be particularly appealing in high-cycle loading analyses, such as aging and fatigue, addressed in a future work in progress
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