171 research outputs found
Il culto di Iuppiter a Roma: spazi, tempo e attori
No full textLa ricerca ha come focus il culto di Iuppiter a Roma, indagato principalmente attraverso le fonti epigrafiche, e mira a fornire una lettura complessiva della sua fenomenologia storico-religiosa nel contesto urbano. Essa è articolata in due parti: nella prima parte vengono ripercorse le tappe della complessa genesi della figura divina e ne vengono analizzati l’iconografia, l’onomastica, il profilo funzionale, i rapporti con gli altri dèi e con gli uomini; la seconda parte è dedicata, invece, all’analisi archeologico-topografica delle aree sacre urbane riservate a Giove, alla ricostruzione del calendario festivo cittadino e della relativa pratica rituale, all’indagine storico-sociale e prosopografica dei professionisti del sacro e dei devoti
Realism and Truth from a Quinean point of view
No full textProblems of realism and truth in Quine's philosophy of science and language are discussed, with a particular focus on the naturalistic perspective defended by Quine
Low-frequency vibrational spectrum of mean-field disordered systems
No full textWe study a recently introduced and exactly solvable mean-field model for the density of vibrational states D(omega) of a structurally disordered system. The model is formulated as a collection of disordered anharmonic oscillators, with random stiffness kappa drawn from a distribution p(kappa), subjected to a constant field h and interacting bilinearly with a coupling of strength J. We investigate the vibrational properties of its ground state at zero temperature. When p(kappa) is gapped, the emergent D(omega) is also gapped, for small J. Upon increasing J, the gap vanishes on a critical line in the (h, J) phase diagram, whereupon replica symmetry is broken. At small h, the form of this pseudogap is quadratic, D(omega) similar to omega(2), and its modes are delocalized, as expected from previously investigated mean-field spin glass models. However, we determine that for large enough h, a quartic pseudogap D(omega) similar to omega(4), populated by localized modes, emerges, the two regimes being separated by a special point on the critical line. We thus uncover that mean-field disordered systems can generically display both a quadratic-delocalized and a quartic-localized spectrum at the glass transition
Biogas upgrading by adsorption onto activated carbon and carbon molecular sieves: Experimental and modelling study in binary CO2/CH4 mixture
No full textBiomethane, a renewable form of natural gas, can be produced by biogas upgrading and its utilization is incentivized to mitigate CO2 emissions. In this work, biogas upgrading via adsorption on commercial carbonaceous adsorbents, an activated carbon (AC) provided by Desotec and two carbon molecular sieves (CMSs) produced by Carbotech and Xintao, is experimentally investigated in a fixed-bed column, testing CO2/CH4 mixtures at different concentrations as feed gas. The experimental campaign highlights that AC has a higher adsorption capacity for both CO2 and CH4, as well as better kinetic performances (i.e. higher bed usage efficiency and lower desorption times), than CMSs. On the other hand, the CMSs show a much lower CH4 adsorption capacity than the AC due to their combined thermodynamic/kinetic sieving properties, which emerge from dynamic breakthrough curves and equilibrium adsorption data alike. Therefore, the CMSs show a much higher selectivity for the separation of the CO2/CH4 mixture, and Xintao sample shows a better overall performance thanks to its faster kinetics; moreover, experimental cyclic adsorption/desorption runs on Xintao confirmed its complete regenerability. Breakthrough curves modelling, performed in MATLAB environment and aimed at evaluating the CO2 mass transfer coefficients, points out that intraparticle diffusion is the rate-limiting step for CO2 adsorption process. It can be concluded that CMSs show better performances for biogas upgrading due to their high selectivity and despite their lower CO2 adsorption capacity, which cannot be taken as the main controlling parameter in the adsorbent selection devoted to this specific application
IDENTIFICATION AND INVESTIGATION OF SHALLOW PALEOCHANNELS IN THE CHAMELECON VALLEY (HONDURAS): 1D VS 2D ELECTRICAL RESISTIVITY SURVEYS
No full textElectrical Resistivity Tomography (ERT) and resistivity depth sounding surveys were undertaken at two sites located along the Chamelecòn Valley (Honduras). The objective of the surveys was to determine the occurrence, geometry and lithological properties of the Chamelecòn River’s shallow paleochannels. Following the interpretation of aerial photograms which indicated the likely presence of paleochannels, two sites were selected for the surveys. Resistivity depth soundings were used to achieve electro-stratigraphic sections obtained by interpolating 1D inverted data that would assist with assessing the occurrence of paleochannels at a large scale. The presence of paleochannels at the two sites was assessed through interpretation of the electro-stratigraphic sections. At Site 2, the abundant 1D data, the small distance between the soundings and the shallow target, allowed determining the course of the paleoriver as shown by resistivity and electrical transmissivity maps. The results from the 1D data, although affected by strong heterogeneities, are congruent with the 2D inverted models. ERT surveys confirmed the presence of paleochannels and allowed achieving detailed imaging of the alluvial geological bodies. Paleochannel deposits show resistivity values ranging between 70 and 100 ohm m at Site 1, while resistivity values range between 90 and 120 ohm m at Site 2. The latter resistivity values were affected by the presence of coarser deposits. Resistivity values suggest that at both sites paleochannel deposits have a clay content that is lower than 3 %. Other alluvial deposits in the area show resistivity values that range between 19 and 70 ohm m at Site 1, while resistivity values range between 30 and 90 ohm m at Site 2. These lower values suggest that clay content can be as high as 29 %. The presence of paleochannels assessed by means of 1D surveys and the lithological characterisation assessed by means of 2D surveys were confirmed by logs from boreholes drilled at the sites
Mean-field model of interacting quasilocalized excitations in glasses
No full textStructural glasses feature quasilocalized excitations whose frequencies ω follow a universal density of states D(ω)∼ω4
. Yet, the underlying physics behind this universality is
not fully understood. Here we study a mean-field model of quasilocalized excitations in
glasses, viewed as groups of particles embedded inside an elastic medium and described
collectively as anharmonic oscillators. The oscillators, whose harmonic stiffness is taken
from a rather featureless probability distribution (of upper cutoff κ0) in the absence of
interactions, interact among themselves through random couplings (characterized by
a strength J) and with the surrounding elastic medium (an interaction characterized
by a constant force h). We first show that the model gives rise to a gapless density
of states D(ω) = Ag ω4
for a broad range of model parameters, expressed in terms of
the strength of the oscillators’ stabilizing anharmonicity, which plays a decisive role in
the model. Then — using scaling theory and numerical simulations — we provide a
complete understanding of the non-universal prefactor Ag(h, J,κ0), of the oscillators’
interaction-induced mean square displacement and of an emerging characteristic frequency, all in terms of properly identified dimensionless quantities. In particular, we
show that Ag(h, J,κ0) is a non-monotonic function of J for a fixed h, varying predominantly exponentially with −(κ0h
2/3/J
2
) in the weak interactions (small J) regime —
reminiscent of recent observations in computer glasses — and predominantly decays as
a power-law for larger J, in a regime where h plays no role. We discuss the physical interpretation of the model and its possible relations to available observations in structural
glasses, along with delineating some future research directions
Following the Evolution of Hard Sphere Glasses in Infinite Dimensions under External Perturbations: Compression and Shear Strain
No full textWe consider the adiabatic evolution of glassy states under external perturbations. The formalism we use is very general. Here we use it for infinite-dimensional hard spheres where an exact analysis is possible. We consider perturbations of the boundary, i.e., compression or (volume preserving) shear strain, and we compute the response of glassy states to such perturbations: pressure and shear stress. We find that both quantities overshoot before the glass state becomes unstable at a spinodal point where it melts into a liquid (or yields). We also estimate the yield stress of the glass. Finally, we study the stability of the glass basins towards breaking into sub-basins, corresponding to a Gardner transition. We find that close to the dynamical transition, glasses undergo a Gardner transition after an infinitesimal perturbation
Application of 1D-2D electrical resistivity surveys to the identification and investigation of shallow paleochannels in the Chamelecòn Valley (Honduras)
No full textIl lavoro confronta i risultati ottenuti dall’utilizzo di due differenti metodi di prospezione elettrica, nell’ambito di uno studio finalizzato alla ricerca e caratterizzazione di paleoalvei presenti in due siti opportunamente selezionati lungo la valle del Rio Chamelecòn (Honduras). L’applicazione di sondaggi elettrici verticali (1D) ha permesso di determinare la presenza di paleoalvei; la caratterizzazione geometrica e litologica di questi è stata invece ottenuta mediante applicazione di indagini di tomografia elettrica 2D (ERT)
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