Produzione di spugne di acciaio tramite metallurgia delle polveri

I materiali cellulari sono caratterizzati da un’interessante combinazione di proprietà fisiche e meccaniche. Inquesto contesto, le schiume metalliche in acciaio possono essere impiegate come alternativa alle leghe leggerein tutte quelle applicazioni dove si necessita un buon compromesso tra leggerezza e resistenza meccanica. Inquesto studio viene presentato un nuovo approccio per la realizzazione di spugne in acciaio tramite metallurgiadelle polveri utilizzando sfere di SiC come riempitivo. Terminato il processo produttivo le particelle ceramichesono state rimosse tramite lisciviazione e le spugne sono state caratterizzate dal punto di vista morfologico,microstrutturale e meccanico. Il risultato della caratterizzazione ha dimostrato la fattibilità del processoproduttivo per l’ottenimento di spugne metalliche in acciaio

New perspective in steelmaking activity to increase competitiveness and reduce enviromental impact

The competitiveness of the European steel industry is strictly related to the introduction of high performanceproducts and to the increase in process efficiency and to the reduction in environmental impact. Thesechallenges can be faced to ensure a future to the area’s important industrial assets and some actions need to beidentified. Several aspects about steelmaking plants, processes and steel products have been highlighted andnowadays, they may become the object of innovative action and efforts in order to achieve and maintain a highlevel of competitiveness and to solve this serious industrial crisis

A review of Monte Carlo simulations of polymers with PERM

In this review, we describe applications of the pruned-enriched Rosenbluth method (PERM), a sequential Monte Carlo algorithm with resampling, to various problems in polymer physics. PERM produces samples according to any given prescribed weight distribution, by growing configurations step by step with controlled bias, and correcting "bad" configurations by "population control". The latter is implemented, in contrast to other population based algorithms like e.g. genetic algorithms, by depth-first recursion which avoids storing all members of the population at the same time in computer memory. The problems we discuss all concern single polymers (with one exception), but under various conditions: Homopolymers in good solvents and at the $\Theta$ point, semi-stiff polymers, polymers in confining geometries, stretched polymers undergoing a forced globule-linear transition, star polymers, bottle brushes, lattice animals as a model for randomly branched polymers, DNA melting, and finally -- as the only system at low temperatures, lattice heteropolymers as simple models for protein folding. PERM is for some of these problems the method of choice, but it can also fail. We discuss how to recognize when a result is reliable, and we discuss also some types of bias that can be crucial in guiding the growth into the right directions.Comment: 29 pages, 26 figures, to be published in J. Stat. Phys. (2011

The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)

The Pliensbachian-Toarcian (Early Jurassic) fossil record is an archive of natural data of benthic community response to global warming and marine long-term hypoxia and anoxia. In the early Toarcian mean temperatures increased by the same order of magnitude as that predicted for the near future; laminated, organic-rich, black shales were deposited in many shallow water epicontinental basins; and a biotic crisis occurred in the marine realm, with the extinction of approximately 5% of families and 26% of genera. High-resolution quantitative abundance data of benthic invertebrates were collected from the Cleveland Basin (North Yorkshire, UK), and analysed with multivariate statistical methods to detect how the fauna responded to environmental changes during the early Toarcian. Twelve biofacies were identified. Their changes through time closely resemble the pattern of faunal degradation and recovery observed in modern habitats affected by anoxia. All four successional stages of community structure recorded in modern studies are recognised in the fossil data (i.e. Stage III: climax; II: transitional; I: pioneer; 0: highly disturbed). Two main faunal turnover events occurred: (i) at the onset of anoxia, with the extinction of most benthic species and the survival of a few adapted to thrive in low-oxygen conditions (Stages I to 0) and (ii) in the recovery, when newly evolved species colonized the re-oxygenated soft sediments and the path of recovery did not retrace of pattern of ecological degradation (Stages I to II). The ordination of samples coupled with sedimentological and palaeotemperature proxy data indicate that the onset of anoxia and the extinction horizon coincide with both a rise in temperature and sea level. Our study of how faunal associations co-vary with long and short term sea level and temperature changes has implications for predicting the long-term effects of “dead zones” in modern oceans

Population response during an Oceanic Anoxic Event: The case of Posidonotis (Bivalvia) from the Lower Jurassic of the Neuquén Basin, Argentina

Benthonic marine species show a wide range of biological reactions to seawater chemical changes through time, from subtle adjustments to extinction. The Early Toarcian Oceanic Anoxic Event (T-OAE) was recently recognized in the Neuquén Basin, Argentina, confirming its global scope. The event was identified chemostratigraphically on the basis of a relative increase in marine organic carbon and a characteristic negative carbonisotope excursion (δ13Corg) in bulk rock and fossil wood in the upper Pliensbachian-lower Toarcian interval in the Arroyo Lapa section (Neuquén). Simultaneously with collection of lithological samples, a high-resolution biostratigraphical survey was carried out, and the scarce benthonic fauna was collected in order to check the biotic response to changing marine geochemical conditions. We present here an analysis of size and abundance data from the T-OAE interval in the Neuquén Basin for the dominant bivalve species, the paper-clam Posidonotis cancellata (Leanza), and relate these data to geochemical proxies (%TOC and δ13Corg) obtained at the same locality. The abundance of P. cancellata increased when the rest of the benthos diminished, reaching a maximum at the onset level of the T-OAE, and then decreasing. Size-frequency distributions show a noteworthy lack of juvenile shells. Shell size shows a positive correlation with %TOC in the whole section, though over the T-OAE interval proper, it decreases below the level where the maximum %TOC value is attained and increases above it. Posidonotis cancellata shows features of opportunistic species, such as high tolerance to hypoxia, strong dominance in impoverished environments and a strong dependence on primary productivity, but at the same time had a reproductive strategy more similar to equilibrium species, with relatively low juvenile mortality rates. Several anatomical features suggest adaptation to permanently dysaerobic environments. The species disappeared just before the minimum negative carbon-isotope value was reached; and by the same time the genus became extinct worldwide

The equivalent of the “Faraoni Level” (uppermost Hauterivian, Lower Cretaceous) recorded in the eastern part of Trento Plateau (Venetian Southern Alps, Italy)

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Calcareous nannofossil fluctuations during the late Hauterivian in the Cismon core (Venetian Alps, northeastern Italy) and in selected sections of the Umbria-Marche Basin (central Italy) : paleoceanographic implications of the Faraoni Level

Calcareous nannofossil quantitative analyses were carried out on upper Hauterivian sediments from the Cismon core and results from the uppermost Hauterivian "Faraoni Level" were compared to nannofloral fluctuations in abundance and composition recorded in the S.S. Arceviese road and Palazzo D'Arcevia sections, Umbria-Marche Basin (central Italy). Fragile taxa are generally absent since the preservation is poor in all lithologies analyzed, but dissolution-resistant taxa show remarkable fluctuations. Smear-slide investigations reveal that limestones are characterized by high abundances of nannoconids (principally narrow-canal nannoconids) suggesting oligotrophic conditions throughout the interval investigated. Conversely, nannoconids are rare or absent in black shales, whereas Assipetra infracretacea and Rucinolithus terebrodentarius are prevailing. In addition, high abundances of pentaliths are recorded in limestones through the interval preceding the deposition of the Faraoni Level. This finding possibly suggests a decrease in salinity of surface waters. Different paleoceanographic regimes seem to have triggered repetitive changes in abundance and composition of nannofloral assemblages. Limestones were plausibly deposited under oligotrophic conditions, whilst black shales may suggest increasing primary productivity. Thin section investigations show a drop in abundance of pentaliths and a marked decrease of narrow-canal nannoconids starting definitively before and reaching a minimum in the Faraoni Level. In the black shales bounding the ammonite-rich Guide Bed, A. infracretacea and R. terebrodentarius become dominant. Such nannofloral changes may suggest enhanced primary productivity and more arid conditions associated with dysoxic bottom waters. We stress the fact that nannofloral variations recorded in the Faraoni Level are not exclusive, but match the repetitive nannofloral-lithological fluctuations preceding and following it. Perhaps, the paleoenvironmental changes triggering the Faraoni event were not affecting calcareous phytoplankton or represent the over-reaching of threshold conditions after gradual and progressive modifications in nutrient availability