Quantum Metallicity on the High-Field Side of the Superconductor-Insulator Transition

We investigate ultrathin superconducting TiN films, which are very close to the localization threshold. Perpendicular magnetic field drives the films from the superconducting to an insulating state, with very high resistance. Further increase of the magnetic field leads to an exponential decay of the resistance towards a finite value. In the limit of low temperatures, the saturation value can be very accurately extrapolated to the universal quantum resistance h/e^2. Our analysis suggests that at high magnetic fields a new ground state, distinct from the normal metallic state occurring above the superconducting transition temperature, is formed. A comparison with other studies on different materials indicates that the quantum metallic phase following the magnetic-field-induced insulating phase is a generic property of systems close to the disorder-driven superconductor-insulator transition.Comment: 4 pages, 4 figures, published versio

SIGLA - Sistema Integrato per il Monitoraggio e Gestione di Lagune ed Ambiente, sotto-azione CARLA Parte I : CARatterizzazione chimica e chimico-fisica e qualità acque LAguna di Cabras e Golfo di Oristano

È stata effettuata una prima caratterizzazione chimica e chimico-fisica della colonna d’acqua nella Laguna di Cabras tramite l’analisi di dati raccolti in precedenti indagini. Tali studi sono stati completati con campionamenti di acqua e misure in situ delle variabili idrologiche nella laguna e nel golfo di Oristano. Su questo set di dati sono state effettuate le analisi per individuare le relazioni tra le variabili misurate e per studiare le variabilità stagionali delle caratteristiche chimico-fisiche della colonna d’acqua. Lo studio ha permesso la compilazione di un protocollo metodologico di indagine e di monitoraggio dello stato trofico e di salute di ambienti lagunari costieri. I dati più recenti hanno mostrato come rispetto alle medie storiche, si sia avuto un aumento della temperatura e una diminuzione della salinità. Quest’ultima viene associata ad un limitato scambio tra la laguna ed il mare. I valori di ossigeno e pH non sono indicativi di un elevato stress ambientale, infatti non sono state rilevate condizioni di ipossia o anossia, e valori di pH superiori alla norma. Tuttavia in precedenti campionamenti nell’estate 2002 sono stati descritti al fondo valori ipossici. Tali valori hanno indicato come la laguna sia periodicamente soggetta a crisi anossiche. Il netto calo di nutrienti rispetto agli anni ottanta-novanta è associato ad una diminuzione degli input d’acqua dolce nel periodo monitorato. Inoltre non è trascurabile l’influenza degli scambi tra sedimento e colonna d’acqua. In conclusione, dagli studi condotti si può dedurre come nello specifico, nella Laguna di Cabras, lo stato trofico del sistema sia principalmente condizionato dagli input d’acqua dolce, e come questi condizionino anche gli scambi con il golfo. In aggiunta, data la diminuzione degli input di acqua dolce nel periodo monitorato e vista la relazione positiva tra volumi e nutrienti in entrata, il loro abbattimento in entrata tramite depurazione delle acque sembra essere un valido strumento di mitigazione e di recupero

Coarsened Lattice Spatial Disorder in the Thermodynamic Limit

In this Rapid Research Note the application of recently introduced [Physica A 277 (2000) 157] entropic measure S_Delta of spatial disorder for systems of finite-sized objects is presented. In the thermodynamic limit the critical behaviour of coarsened lattice model of random two-phase systems is illustrated for certain grain size distributions (GSDs) and chosen parameters. Also the changes of spatial disorder, quantified by S_Delta, between the limit GSDs clearly show that the topological equivalence of the two phases is broken.Comment: 3 pages, 1 figur

Gas turbine prime movers fuelled by LNG as a future alternative for sustainable power in marine propulsion: current emission policy assessment and exhaust quality evaluation

In recent years, climate change has dramatically shown its effects in terms of fluctuations of temperatures because of increased global warming due to greenhouse gas emissions. Pollution control is strongly linked to atmospheric acidification and contaminants in combustion exhausts. In such a contest, marine propulsion is actually a key player that is accounting for a substantial contribution to pollution. Kyoto protocol’s obligations established decarbonisation as a compulsory commitment and contaminant constraints are defined by current emission policy and regulations both on a global and on a regional basis. In this paper, a study is carried out in order to develop a framework for current emission policy and assessment of exhausts due to constraints imposed on fuel choice. Gas fuelled marine propulsion, implemented through state-of-the-art GT areoderivative prime movers, powered by LNG, is analysed from the environmental point of view. The pollutant emissions from various size GT models are evaluated through both GT datasheets and commercial (as well as self-coded) software, in order to assess the validity of LNG as an alternative fuel option for future sustainable marine applications

Feasibility of mini combined cycles for naval applications

The objective of energy production with low environmental impact will have, in the near future, high potential of development also for naval applications. The containment of pollutant emissions can be achieved by the combined use of an innovative mini gas-steam combined cycle with thermal energy cogeneration to feed the ship thermal utilities, in place of the current Diesel engine application, and liquefied natural gas as fuel (LNG). The present work is focused on the definition of the architecture of the plant, by selecting optimal distribution of pressure and temperature and repartition of power between Gas Turbine (GT), Steam Turbine (ST) and thermal utilities, as well as on the choice and sizing of the individual components. The main purpose is the definition of a compact, high efficiency, system. The proposed basic mini-cycle ranges from 2 MW to 10 MW electric power. Thanks to the combined heat and power cogeneration plant adopted, for an overall electrical efficiency of about 30%, a total return (thermal + electricity) of about 75% can be achieved. An example of plant providing large power, in a partially modular arrangement is also proposed