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Ageing effects due to inactivity for magnetorheological seismic dampers: a 10-year experimental investigation
No full textThe proposed work gives a response, based on the experimental evidence, to the issue of long-term magnetorheological (MR) dampers' behavior, when they are applied for structural control of earthquake induced vibrations. MR control devices, designed for infrequent dynamic loads as earthquakes, might be dormant for most of their life until a seismic event hits the hosting controlled structure. Two prototype MR devices have been tested three times, first in 2008, then in 2013 after five years of absolute inactivity, and finally in 2017 after further four years of rest. The comparison between the results of the three experimental testing activities is made in terms of force-displacement loops, dissipated energy and maximum reacting force. It is shown that only the first stroke of the damper is characterized by an unexpected mechanical response. However, after this first movement, the damper comes back to behave similarly to what was before the rest, with only a slight not reversible decrease of the damping force. This reduction results to be more significant (about 5%) for larger currents, while less significant in the case of zero feeding current. From a civil engineering perspective, this performance decay is definitely acceptable, even if it is referred to a possible cause, deeply studied in literature, that could continue endangering the mechanical response of the devices over time. The paper shows the experimental results, but the possible causes of mechanical deterioration of the dampers will be discussed also
Learning-based approach to segment pigment signs in fundus images for Retinitis Pigmentosa analysis
No full textThe automatic segmentation of variations in fundus images is being increasingly developed to establish retinal health, and to diagnose and monitor retinal abnormality. Fundus images can be acquired by low-cost and easy access diagnostic systems also in resource limited countries. In this paper, we focus on the segmentation of pigment signs in retinal fundus images, which is an important step in the diagnosis and monitoring of Retinitis Pigmentosa. At present, most of the existing approaches adopted for this purpose are based on the analysis of Optical Coherence Tomography (OCT) data, with only a few algorithms working on fundus images. The contribution of this paper is twofold. First, we propose a supervised segmentation technique for pigment sign detection in fundus images, which exploits the ensemble classifiers for both bagged and boosted decision trees, namely Random Forests and AdaBoost.M1. The ensemble classifiers are trained on feature vectors encoding the information of a set of regions obtained by partitioning a pre-processed image, so that each region is labeled as either normal fundus or pigment sign. Secondly, we have collected a large dataset of retinal images, in which the pigment signs have been segmented manually and we are making this publicly available to the research community. The performance of the classifiers has been evaluated on the proposed dataset and can be considered as a baseline for comparison. Our results demonstrate the high effectiveness of a machine learning approach as a suitable tool for automated Retinitis Pigmentosa analysis
Heterotrophic components of biofilms on wood artefacts
No full textHeterotrophic components of biofilms on wood artefacts were studied at the Conservation Laboratory for Wood Artefacts of the University Suor Orsola Benincasa of Naples, Italy. The aim of the study was to add new information on the micro-habitats represented by biofilms formed by wood-dwelling organisms. Light and electron microscopy of histological features of woods used to make the artefacts showed that the woods belonged to species of lime (Tilia sp.), poplar (Populus sp.) and pear (Pyrus sp.). A Denaturing Gradient Gel Electrophoresis analysis performed on heterotrophic microorganisms colonizing the artefacts led to identify four species of bacteria, namely Bacillus cereus, B. mycoides, B. subtilis and Microbacterium oleivorans, and seven species of fungi, namely Alternaria alternata, Aspergillus fumigans, A. versicolor, Cladosporium cladosporioides, C. oxysporum, Fusarium oxysporum and Penicillium chrysogenum. Based on its morphological features, an insect found on some artefacts was identified as the xylophagous beetle Nicobium castaneum (Anobiidae). The influence of wood type and environmental conditions on the diversity of microorganisms was discussed
Observation of Centrality-Dependent Acoplanarity for Muon Pairs Produced via Two-Photon Scattering in Pb plus Pb Collisions at root s(NN)=5.02 TeV with the ATLAS Detector
No full textThis Letter presents a measurement of gamma gamma -> mu(+)mu(-)-
production in Pb + Pb collisions recorded by the ATLAS detector at the
Large Hadron Collider at root s(NN) = 5.02 TeV with an integrated
luminosity of 0.49 nb(-1). The azimuthal angle and transverse momentum
correlations between the muons are measured as a function of collision
centrality. The muon pairs are produced from gamma gamma through the
interaction of the large electromagnetic fields of the nuclei. The
contribution from background sources of muon pairs is removed using a
template fit method. In peripheral collisions, the muons exhibit a
strong back-to-back correlation consistent with previous measurements of
muon pair production in ultraperipheral collisions. The angular
correlations are observed to broaden significantly in central
collisions. The modifications arc qualitatively consistent with
rescattering of the muons while passing through the hot matter produced
in the collision
