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Search Results: 1 - 10 of 15208 matches for " Marco Piastra "
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A Growing Self-Organizing Network for Reconstructing Curves and Surfaces
Marco Piastra
Computer Science , 2008, DOI: 10.1109/IJCNN.2009.5178709
Abstract: Self-organizing networks such as Neural Gas, Growing Neural Gas and many others have been adopted in actual applications for both dimensionality reduction and manifold learning. Typically, in these applications, the structure of the adapted network yields a good estimate of the topology of the unknown subspace from where the input data points are sampled. The approach presented here takes a different perspective, namely by assuming that the input space is a manifold of known dimension. In return, the new type of growing self-organizing network presented gains the ability to adapt itself in way that may guarantee the effective and stable recovery of the exact topological structure of the input manifold.
Gradient of the Objective Function for an Anisotropic Centroidal Voronoi Tessellation (CVT) - A revised, detailed derivation
Giacomo Parigi,Marco Piastra
Computer Science , 2014,
Abstract: In their recent article (2010), Levy and Liu introduced a generalization of Centroidal Voronoi Tessellation (CVT) - namely the Lp-CVT - that allows the computation of an anisotropic CVT over a sound mathematical framework. In this article a new objective function is defined, and both this function and its gradient are derived in closed-form for surfaces and volumes. This method opens a wide range of possibilities, also described in the paper, such as quad-dominant surface remeshing, hex-dominant volume meshing or fully-automated capturing of sharp features. However, in the same paper, the derivations of the gradient and of the new objective function are only partially expanded in the appendices, and some relevant requisites on the anisotropy field are left implicit. In order to better harness the possibilities described there, in this work the entire derivation process is made explicit. In the authors' opinion, this also helps understanding the working conditions of the method and its possible applications.
Explicit excluded volume of cylindrically symmetric convex bodies
Marco Piastra,Epifanio G. Virga
Physics , 2015, DOI: 10.1103/PhysRevE.91.062503
Abstract: We represent explicitly the excluded volume Ve{B1,B2} of two generic cylindrically symmetric, convex rigid bodies, B1 and B2, in terms of a family of shape functionals evaluated separately on B1 and B2. We show that Ve{B1,B2} fails systematically to feature a dipolar component, thus making illusory the assignment of any shape dipole to a tapered body in this class. The method proposed here is applied to cones and validated by a shape-reconstruction algorithm. It is further applied to spheroids (ellipsoids of revolution), for which it shows how some analytic estimates already regarded as classics should indeed be emended.
Pediatric Intensive Care Unit admission criteria for haematooncological patients: a basis for clinical guidelines implementation
Marco Piastra,Giuliana Fognani,Alessia Franceschi
Pediatric Reports , 2011, DOI: 10.4081/pr.2011.e13
Abstract: Cancer remains a major death cause in children, though outcomes have considerably improved over the past decades (1-3). Outcomes for children diagnosed with cancer have changed since ’70 from 80% mortality to 80% survival (2); while children with solid tumors 5-year survival has been reported as 67%, cure rates for childhood leukemia now approach 90% [4-5). Moreover, hematopoietic stem cell transplantation (HSCT) indications are still expanding for both malignant and non-malignant diseases.
Retraction With Face Saving: modelling conversational interaction through dynamic hypermedia
Anthony Baldry,Marco Piastra,Roberto Bolognesi
Research in Learning Technology , 1994, DOI: 10.3402/rlt.v2i2.9580
Abstract: This paper describes RWFS (Retraction With Face Saving), a hypermedia application which models an interview between a lawyer and his client - a lorry driver - facing court charges of reckless driving. At one level RWFS takes the form of a sophisticated game in which different outcomes to the interview are possible according to the learner's degree of skill. At another level, RWFS is designed to encourage the language learner's awareness and understanding of the pragmatic features of conversation. RWFS runs on HyperContext, a hybrid hypertextlexpert system developed in Pavia by two of the authors, Marco Piastra and Roberto Bolognesi, and which supports dynamic hypermedia units. HyperContext's dynamic linking capacity plays a vital role in simulating significant conversational features such as the conditioning of a current move in the conversation by information acquired much earlier in the course of the interview. In this connection, the paper discusses the contribution of RMCI (Re-usable Model of Conversational Interaction), a re-usable application-independent applied model of interaction on which the game is based, and which links a tactical level (the conversation) to a metalevel which provides a moveby- move commentary on interactional theory. In its turn, RMCFs metalevel is linked to a strategic level which interprets the structure of the conversation in terms of a pyramid-like hierarchy of increasingly abstract theoretical concepts.
Some Further Evidence about Magnification and Shape in Neural Gas
Giacomo Parigi,Andrea Pedrini,Marco Piastra
Computer Science , 2015, DOI: 10.1109/IJCNN.2015.7280550
Abstract: Neural gas (NG) is a robust vector quantization algorithm with a well-known mathematical model. According to this, the neural gas samples the underlying data distribution following a power law with a magnification exponent that depends on data dimensionality only. The effects of shape in the input data distribution, however, are not entirely covered by the NG model above, due to the technical difficulties involved. The experimental work described here shows that shape is indeed relevant in determining the overall NG behavior; in particular, some experiments reveal richer and complex behaviors induced by shape that cannot be explained by the power law alone. Although a more comprehensive analytical model remains to be defined, the evidence collected in these experiments suggests that the NG algorithm has an interesting potential for detecting complex shapes in noisy datasets.
A Multi-signal Variant for the GPU-based Parallelization of Growing Self-Organizing Networks
Giacomo Parigi,Angelo Stramieri,Danilo Pau,Marco Piastra
Computer Science , 2015, DOI: 10.1007/978-3-319-03500-0_6
Abstract: Among the many possible approaches for the parallelization of self-organizing networks, and in particular of growing self-organizing networks, perhaps the most common one is producing an optimized, parallel implementation of the standard sequential algorithms reported in the literature. In this paper we explore an alternative approach, based on a new algorithm variant specifically designed to match the features of the large-scale, fine-grained parallelism of GPUs, in which multiple input signals are processed at once. Comparative tests have been performed, using both parallel and sequential implementations of the new algorithm variant, in particular for a growing self-organizing network that reconstructs surfaces from point clouds. The experimental results show that this approach allows harnessing in a more effective way the intrinsic parallelism that the self-organizing networks algorithms seem intuitively to suggest, obtaining better performances even with networks of smaller size.
Ex Vivo Effect of Varespladib on Secretory Phospholipase A2 Alveolar Activity in Infants with ARDS
Daniele De Luca, Angelo Minucci, Marco Piastra, Paola E. Cogo, Francesca Vendittelli, Laura Marzano, Leonarda Gentile, Bruno Giardina, Giorgio Conti, Ettore D. Capoluongo
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0047066
Abstract: Background Secretory phospholipase A2 (sPLA2) plays a pivotal role in acute respiratory distress syndrome (ARDS). This enzyme seems an interesting target to reduce surfactant catabolism and lung tissue inflammation. Varespladib is a specifically designed indolic sPLA2 inhibitor, which has shown promising results in animals and adults. No specific data in pediatric ARDS patients are yet available. Methods We studied varespladib in broncho-alveolar lavage (BAL) fluids obtained ex vivo from pediatric ARDS patients. Clinical data and worst gas exchange values during the ARDS course were recorded. Samples were treated with saline or 10–40–100 μM varespladib and incubated at 37°C. Total sPLA2 activity was measured by non-radioactive method. BAL samples were subjected to western blotting to identify the main sPLA isotypes with different sensitivity to varespladib. Results was corrected for lavage dilution using the serum-to-BAL urea ratio and for varespladib absorbance. Results Varespladib reduces sPLA2 activity (p<0.0001) at 10,40 and 100 μM; both sPLA2 activity reduction and its ratio to total proteins significantly raise with increasing varespladib concentrations (p<0.001). IC50 was 80 μM. Western blotting revealed the presence of sPLA2-IIA and –IB isotypes in BAL samples. Significant correlations exist between the sPLA2 activity reduction/proteins ratio and PaO2 (rho = 0.63;p<0.001), PaO2/FiO2 (rho = 0.7; p<0.001), oxygenation (rho = ?0.6; p<0.001) and ventilation (rho = ?0.4;p = 0.038) indexes. Conclusions Varespladib significantly inhibits sPLA2 in BAL of infants affected by post-neonatal ARDS. Inhibition seems to be inversely related to the severity of gas exchange impairment.
Cosmogenic activation of xenon and copper
Laura Baudis,Alexander Kish,Francesco Piastra,Marc Schumann
Physics , 2015,
Abstract: Rare event search experiments using liquid xenon as target and detection medium require ultra-low background levels to fully exploit their physics potential. Cosmic ray induced activation of the detector components and, even more importantly, of the xenon itself during production, transportation and storage at the Earth's surface, might result in the production of radioactive isotopes with long half-lives, with a possible impact on the expected background. We present the first dedicated study on the cosmogenic activation of xenon after 345 days of exposure to cosmic rays at the Jungfraujoch research station at 3470m above sea level, complemented by a study of copper which has been activated simultaneously. We have directly observed the production of 7Be, 101Rh, 125Sb, 126I and 127Xe in xenon, out of which only 125Sb could potentially lead to background for a multi-ton scale dark matter search. The production rates for five out of eight studied radioactive isotopes in copper are in agreement with the only existing dedicated activation measurement, while we observe lower rates for the remaining ones. The specific saturation activities for both samples are also compared to predictions obtained with commonly used software packages, where we observe some underpredictions, especially for xenon activation.
Enhancement of Light Yield and Stability of Radio-Pure Tetraphenyl-Butadiene Based Coatings for VUV Light Detection in Cryogenic Environments
Laura Baudis,Giovanni Benato,Rugard Dressler,Francesco Piastra,Ilya Usoltsev,Manuel Walter
Physics , 2015, DOI: 10.1088/1748-0221/10/09/P09009
Abstract: The detection of VUV scintillation light, e.g. in (liquid) argon detectors, commonly includes a reflector with a fluorescent coating, converting UV photons to visible light. The light yield of these detectors depends directly on the conversion efficiency. Several coating/reflector combinations were produced using VM2000, a specular reflecting multi layer polymer, and Tetratex, a diffuse reflecting PTFE fabric, as reflector foils. The light yield of these coatings was optimised and has been measured in a dedicated liquid argon setup built at the University of Zurich. It employs a small, 1.3 kg LAr cell viewed by a 3-inch, low radioactivity PMT of type R11065-10 from Hamamatsu. The cryogenic stability of these coatings was additionally studied. The optimum reflector/coating combination was found to be Tetratex dip coated with Tetraphenyl-butadiene with a thickness of 0.9 mg/cm$^2$ resulting in a 3.6 times higher light yield compared to uncoated VM2000. Its performance was stable in long term measurements, ran up to 100 days, in liquid argon. This coated reflector was further investigated concerning radioactive impurities found to be suitable for current and upcoming low-background experiments. Therefore it is used for the liquid argon veto in Phase II of the GERDA neutrinoless double beta decay experiment.
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