2,204 research outputs found
A forward unprovability calculus for intuitionistic propositional logic
No full textThe inverse method is a saturation based theorem proving technique; it relies on a forward proof-search strategy and can be applied to cut-free calculi enjoying the subformula property. This method has been successfully applied to a variety of logics. Here we apply this method to derive the unprovability of a goal formula G in Intuitionistic Propositional Logic. To this aim we design a forward calculus FRJ(G) for Intuitionistic unprovability. From a derivation of G in FRJ(G) we can extract a Kripke countermodel for G. Since in forward methods sequents are not duplicated, the generated countermodels do not contain redundant worlds and are in general very concise
Time-variation of Newton's constant and the age of globular clusters
No full textA variation of Newton's constant G over cosmological time scales would modify the main-squence time of globular cluster (GC) stars. We have calculated the evolution of low-mass stars typical for GCs both for standard nonvarying G and under the assumption of a linear variation of G. The age of the isochrones resulting from the latter models then was chosen such that the isochrones mimicked the standard ones at the turnoff. Since they are indistinguishable from the standard isochrones for ages higher than a few Gyrs, they themselves cannot be used to limit G/G alone. Assuming additionally that the true age of GCs is between 8 and 20 Gyr, and because their apparent age is between 14 and 18 Gyr, we find that today -35x10(-12) yr(-1) less than or similar to G/G less than or similar to 7x10(-12) yr(-1). The upper limit (gravity weaker in the past) is competitive with direct present-day bounds from celestial mechanics. Within independently determined G/G limits a time-varying G as an explanation for the discrepancy between the cosmic expansion age and the apparent GC ages is conceivable
E le rimanenti cose. Eccetera tra reticenza e inferenza.
No full textIl contributo approfondisce gli usi e le funzioni del general extender eccetera in italiano contemporaneo, analizzando in particolare dati di italiano parlato tratti dal corpus LIP
Vibrational stability of graphene under combined shear and axial strains
No full textWe study the vibrational properties of graphene under combined shear and uniaxial tensile strain using density-functional perturbation theory. Shear strain always causes rippling instabilities with strain-dependent direction and wavelength; armchair strain contrasts this instability, enabling graphene stability in a large range of combined strains. A complementary description based on membrane elasticity theory nicely clarifies the competition of shear-induced instability and uniaxial tension. We also report the large strain-induced shifts of the split components of the G optical phonon line, which may serve as a shear diagnostic. As to the electronic properties, we find that conical intersections move away from the Brillouin zone border under strain, and they tend to coalesce at large strains, making the opening of gaps difficult to assess. By a detailed search, we find that even at large strains, only small gaps in the tens-of-meV range open at the former Dirac points
Forward refutation for Gödel-Dummett Logics
No full textWe propose a refutation calculus to check the unprovability of a formula in Gödel-Dummett logics. From refutations we can directly extract countermodels for unprovable formulas, moreover the calculus is designed so to support a forward proof-search strategy that can be understood as a top-down construction of a model
Efficient SAT-based Proof Search in Intuitionistic Propositional Logic
No full textWe present an efficient proof search procedure for Intuitionistic Propositional Logic which involves the use of an incremental SATsolver. Basically, it is obtained by adding a restart operation to the system intuit by Claessen and Ros ́en, thus we call our implementation intuitR. We gain some remarkable advantages: derivations have a simple structure; countermodels are in general small; using a standard benchmarks suite, we outperform intuit and other state-of-the-art provers
Amphibole as window on the Archean mantle composition
No full textThe Archean mantle is among the few reservoirs on Earth preserving records of the early differentiation of the planet. Because the Archean mantle is poorly preserved, only Archean komatiites and few other mantle-derived rocks of Archean age are the only source of information on the Archean mantle composition we presently have (Sossi et al., 2016). However, these rocks generally have strong metamorphic overprints that cause the bulk rock composition to be poorly representative of the original chemical signature, in particular for volatile elements and elements with high fluid mobility. Furthermore, olivine, orthopyroxene or clinopyroxene - the major constituents of these ultramafic rocks - are all minerals that operate a significant filter in the uptake of trace elements, thus hindering precious information on the Archean mantle. Here we propose a novel approach in deciphering the Archean mantle geochemical signature based on the geochemical characterisation of amphibole which is a mineral capable to incorporate a large number of petrologically relevant elements including volatiles (Tiepolo et al., 2007; Giesting et al., 2014). Several studies have shown the presence of primary hydro-magmatic amphiboles among accessory minerals of Archean ultra-mafic rocks (Stone et al., 2003; Fiorentini et al., 2012). We have selected amphibole-bearing samples from komatiites of the Agnew-Wiluna greenstone belt (Western Australia), from the tholeiitic and Fe-picritic suites of the Abitibi greenstone belt (Canada) and from the ferropicrites of the Pechenga complex (Russia). Phanerozoic amphiboles from mafic and ultramafic rocks were also considered for comparison. We have characterised amphiboles for major-, trace- and volatile element contents. The δD and δ18O isotopic composition of amphibole has been also determined by HR-SIMS. Results suggest plume-related origin for the selected Archean ultramafic rocks and point to a significant change in mantle source composition at the origin of Archean and Phanerozoic primary mantle melts. Moreover, elemental and isotopic results on volatiles reveal the occurrence of hydrous deep mantle sources in the Archean. Hence results have significant implications for the debated “wet or dry” signature of komatiites
Cooperativa Mutualistica e Impresa Sociale-Dal calabrone al cigno nero?
No full textAnalisi sistematica, con approccio economico aziendale e definizione dei tipi di imprese sociali non profit. Si analizzano le caratteristiche della formula imprenditoriale dell’ impresa sociale non profi
La Compagnia reale del Teatro de’ Fiorentini di Napoli al servizio di sua Maestà Ferdinando I di Borbone (1816-1824)
No full textL'attività dell'impresario Salvatore Fabbrichesi, direttore della Compagnia reale del Teatro de’ Fiorentini di Napoli al servizio di
Ferdinando I di Borbone dal 1816 al 1824.The activity of the impresario Salvatore Fabbrichesi, director of the Royal Company of the Teatro de' Fiorentini of Naples in the service of Ferdinand I of Bourbon from 1816 to 1824
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