1,721,486 research outputs found
Higher-Order Operators on Networks: Hyperbolic and Parabolic Theory
No full textWe study higher-order elliptic operators on one-dimensional ramified structures (networks). We introduce a general variational framework for fourth-order operators that allows us to study features of both hyperbolic and parabolic equations driven by this class of operators. We observe that they extend to the higher-order case and discuss well-posedness and conservation of energy of beam equations, along with regularizing properties of polyharmonic heat kernels. A noteworthy finding is the discovery of a new class of well-posed evolution equations with Wentzell-type boundary conditions
La Carta delle unità di paesaggio e dei beni naturali e culturali dell’istituendo Parco dei Tacchi (Ogliastra, Sardegna centro-orientale)
No full textNell’ambito di una tesi di laurea elaborata presso il Dipartimento di Scienze della Terra dell’Università di Cagliari è stato condotto uno studio geomorfologico dell’area dei Tacchi con lo scopo di individuare, descrivere e valutare i geomorfositi ed il paesaggio geologico. L’area di studio si estende sulla quasi totalità dei tacchi Ogliastrini e della Barbagia di Seulo e ricade nei comuni di Arzana, Gairo, Jerzu, Lanusei, Osini, Seui, Ulàssai, Ussassai e Villagrande Strisaili.
Quest’area, interessata quasi per intero dalla recente proposta di istituzione del Parco dei Tacchi, è caratterizzata da un paesaggio geologico la cui identità è determinata da caratteristici altopiani carbonatici giurassici che dominano l’antico penepiano ercinico metamorfico e magmatico, inciso da profonde sinuose vallate dai versanti spesso franosi.
Questa regione, pur essendo stata da sempre molto isolata, presenta numerose testimonianze di antica e recente frequentazione umana, con peculiari adattamenti alle precipue caratteristiche del territorio, a dimostrazione che l’insediamento umano ha sempre tenuto in ampia considerazione le componenti del paesaggio.
Nell’area studiata sono stati individuati, descritti e catalogati 30 geomorfositi utili a far conoscere la storia geologica della regione e gli eventi che hanno determinato le forme e l’evoluzione del paesaggio. I risultati più significativi del lavoro sono contenuti in una Carta delle unità di paesaggio e dei beni naturali e culturali che riassume e distingue le aree con caratteristiche geoambientali complessivamente omogenee e più significative dell’area dei Tacchi e l’insieme dei beni naturali e culturali in esse presenti, la quale potrà costituire la base conoscitiva per futuri progetti di valorizzazione geoturistica di questo territorio, denso di segni di storia naturale e umana
Bi-Laplacians on graphs and networks
No full textWe study the fourth order differential operator acting on a connected network G along with
the square of the discrete Laplacian acting on a connected discrete graph. For both operators, we discuss
well-posedness of the associated linear parabolic problems on L^p(G) or ell^p(V), respectively, for 1 ≤ p ≤ ∞. In view of the well-known lack of parabolic maximum principle for all elliptic differential operators of order 2N for N > 1, our most surprising finding is that after some transient time, the parabolic equations driven by−A may display Markovian features, depending on the imposed transmission conditions in the vertices. Analogous results seem to be unknown in the case of general domains and even bounded intervals. Our analysis is based on a detailed study of bi-harmonic
functions complemented by simple combinatorial arguments. We elaborate on analogous issues for the
discrete bi-Laplacian; a characterization of complete graphs in terms of the Markovian property of the
semigroup generated by it is also presented
The effect of ash composition on gasification of poultry wastes in a fluidized bed reactor
No full textThe effect of ash composition on the fluidized bed gasification behaviour of poultry wastes was investigated by operating a pre-pilot scale reactor with two batches of manure obtained from an industrial chicken farm. The experimental runs were carried out by keeping the fluidized bed velocity fixed (at 0.4m s-1) and by varying the equivalence ratio between 0.27 and 0.40, so obtaining bed temperature values between 700 and 800 °C. The performance of the gasification process was assessed by means of mass balances as well as material and feedstock energy analyses, and reported in terms of cold gas efficiency (CGE), specific energy production, low heating value of obtained syngas and yield of undesired by-products. The experimental results indicate the crucial role of ash amount and composition of the two poultry wastes. In particular, higher ash content (25.1% instead of 17.2%) and higher fractions of calcium, phosphorous and potassium (with an increase of 24, 30 and 28%, respectively) induce a dramatic reduction of all the process performance parameters: CGE reduces from 0.63 to 0.33 and the specific energy from 2.1 to 1.1 kWh kgfuel-1. At the same time, the formation of alkali compounds and their behaviour inside the fluidized bed reactor determine an increase of feedstock energy losses, which is related to occurrence of sintering and bridging between bed particles. © The Author(s) 2014
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Technical Specification for a Synthetic Jet Experiment
No full textViene controllata la separazione della corrente attorno al profilo alare Naca 0024 mediante getti sintetici alle elvate incidenz
Fluidized bed gasification of a packaging derived fuel: Energetic, environmental and economic performances comparison for waste-to-energy plants
No full textA comparison of possible solutions for small scale (0.2-1. MWe) waste-to-energy gasification-based industrial application is presented. A pilot scale bubbling fluidized bed air blown gasifier, having a capacity of 500. kWe, provided experimental data: the syngas complete composition as well as the characterization of the bed material and contaminants downstream of the cyclone and wet scrubber. Mass and energy balances and material and substance flow analyses have been drawn to assess and compare design solutions utilizing a packaging derived fuel (PDF) obtained as scrap by food industrial processes. The related environmental, energetic and economic performances have been estimated on the basis of the experimental data and manufacturer's specifications. In the scale range analyzed, the best solution is that of a power gasification coupled with an internal combustion engine, which provides high reliability and high internal rate of return. © 2012 Elsevier Ltd
Gasification of a solid recovered fuel in a pilot scale fluidized bed reactor
No full textThe paper investigates the technical feasibility of an air gasification process of a Solid Recovered Fuel (SRF) obtained from municipal solid waste. A pilot scale bubbling fluidized bed gasifier, having a feedstock capacity of about 70 kg/h and a maximum thermal output of about 400 kW, provided the experimental data: the complete composition of the syngas (including the tar, particulate and acid/basic gas contents), the chemical and physical characterization of the bed material and that of entrained fines collected at the cyclone. The experimental runs were carried out by reaching a condition of thermal and chemical steady state under values of equivalence ratio ranging from 0.25 to 0.33. The results indicate that the selected SRF can be conveniently gasified, yielding a syngas of valuable quality for energy applications. The rather high content of tar in the syngas indicates that the more appropriate plant configuration should be that of a "thermal gasifier", with the direct combustion of the syngas in a burner ad hoc designed, coupled with an adequate energy-conversion device. © 2013 Elsevier Ltd. All rights reserved
Alla scoperta dei tesori geologici della Sardegna. Cala Domestica (Sardegna sud-occidentale). Geoitalia, Ottobre 2008, N° 24, pp. 38-39, Livorno
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