Finite-range effects in dilute Fermi gases at unitarity

We develop a theoretical method going beyond the contact-interaction approximation frequently used in mean-field theories of many-fermion systems, based on the low-energy T-matrix of the pair potential to rigorously define the effective radius of the interaction. One of the main consequences of our approach is the possibility to investigate finite-density effects, which are outside the range of validity of approximations based on delta-like potentials. We apply our method to the calculation of density dependent properties of an ultracold gas of 6Li atoms at unitarity, whose two-body interaction potential is calculated using ab initio quantum chemistry methods. We find that density effects will be significant in ultracold gases with densities one order of magnitude higher than those attained in current experiments.Comment: 7 pages, 3 figures. v2: Corrected typos in the main text and in the reference

Theoretical Estimates of Stellar e-Captures. I. The half-life of 7Be in Evolved Stars

The Li enrichment in the Universe still presents various puzzles to astrophysics. One open issue is that of obtaining estimates for the rate of e-captures on 7Be, for T and rho conditions different from solar. This is important to model the Galactic nucleosynthesis of Li. In this framework, we present a new theoretical method for calculating the e-capture rate in conditions typical of evolved stars. We show how our approach compares with state-of-the-art techniques for solar conditions, where various estimates are available. Our computations include: i) "traditional" calculations of the electronic density at the nucleus, to which the e-capture rate for 7Be is proportional, for different theoretical approaches including the Thomas--Fermi, Poisson--Boltzmann and Debye--Hueckel (DH) models of screening, ii) a new computation, based on a formalism that goes beyond the previous ones, adopting a mean-field "adiabatic" approximation to the scattering process. The results obtained with our approach as well as with the traditional ones and their differences are discussed in some detail, starting from solar conditions, where our method and the DH model converge to the same solution. We then analyze the applicability of the various models to a rather broad range of T and rho values, embracing those typical of red giant stars. We find that, over a wide region of the parameter space explored, the DH approximation does not stand, and the more general method we suggest is preferable. We then briefly reanalyze the 7Li abundances in RGB and AGB stars of the Galactic Disk using the new Be-decay rate. We also underline that the different values of the electron density at the nucleus we find should induce effects on electron screening (for p-captures on Li itself, as well as for other nuclei) so that our new approach might have wide astrophysical consequences.Comment: Astrophts. Journal Feb. 1, 201

Ab initio melting curve of molybdenum by the phase coexistence method

We report ab initio calculations of the melting curve of molybdenum for the pressure range 0-400 GPa. The calculations employ density functional theory (DFT) with the Perdew-Burke-Ernzerhof exchange-correlation functional in the projector augmented wave (PAW) implementation. We present tests showing that these techniques accurately reproduce experimental data on low-temperature b.c.c. Mo, and that PAW agrees closely with results from the full-potential linearized augmented plane-wave implementation. The work attempts to overcome the uncertainties inherent in earlier DFT calculations of the melting curve of Mo, by using the ``reference coexistence'' technique to determine the melting curve. In this technique, an empirical reference model (here, the embedded-atom model) is accurately fitted to DFT molecular dynamics data on the liquid and the high-temperature solid, the melting curve of the reference model is determined by simulations of coexisting solid and liquid, and the ab initio melting curve is obtained by applying free-energy corrections. Our calculated melting curve agrees well with experiment at ambient pressure and is consistent with shock data at high pressure, but does not agree with the high pressure melting curve deduced from static compression experiments. Calculated results for the radial distribution function show that the short-range atomic order of the liquid is very similar to that of the high-T solid, with a slight decrease of coordination number on passing from solid to liquid. The electronic densities of states in the two phases show only small differences. The results do not support a recent theory according to which very low dTm/dP values are expected for b.c.c. transition metals because of electron redistribution between s-p and d states.Comment: 27 pages, 10 figures. to be published in Journal of Chemical Physic

L'Utopia di André Gorz. Per una rilettura complessiva del suo pensiero.

Il saggio mira ad una globale ripensamento del pensiero e dell’esperienza culturale e politica di André Gorz, intellettuale che nei lontani anni cinquanta fu prossimo a Sartre nella condivisione dei temi dell’esistenzialismo e che tentò una rivisitazione del marxismo in chiave critica rispetto alla vulgata dell’epoca. La sua opera continuò negli anni settanta fino alla morte nel 2007, con un particolare interesse verso i temi dell’economia, del lavoro e dell’ecologia. Rispetto alle categorie dominanti del sapere economico e alle prassi del sistema capitalistico avanzato, Gorz si pose in modo polemico, elaborando strategie alternative che tenessero conto dei nuovi bisogni emergenti e dei nuovi soggetti sociali comparsi sulla storia. Il saggio nella sua parte principale e più estesa prende le mosse dagli inizi dell’attività di Gorz e dei suoi esordi, in particolare con il romanzo autobiografico "Il Traditore", ricostruisce il retroterra filosofico entro cui il pensatore si muove ed in seguito scandaglia le opere più tarde ove l’autore abbraccia convintamente il tema dell’economia politica, dell’ecologia, dell’abitare dell’uomo e delle trasformazioni del lavoro negli ultimi decenni, anche in seguito all’avvento del mondo del digitale e dell’immateriale. Da ultimo viene studiato e analizzato l’ultimo tratto della vita di Gorz, legato alla vicenda umana del legame strettissimo e complesso con la moglie Dorine e alla morte della donna in seguito ad un male incurabile. Gorz stesso pose fine alla sua vita non sopportando la scomparsa della compagna. L’ultima opera di Gorz "Lettera a D." (oggetto della postilla di Roberto Taioli) ha il valore di una estrema testimonianza umana ed è al contempo ricca di rimandi diretti ed indiretti alla precedente esperienza culturale e politica, tale da poter essere letta come una ricapitolazione della sua intera esperienza. Il saggio mira altresì a mettere in evidenza la sostanziale unità e continuità del pensiero di Gorz, pur nelle differenze di stagioni culturali e di interessi di studio che hanno segnato la sua vita

Seasonal Variations of Complete Blood Count and Inflammatory Biomarkers in the US Population - Analysis of NHANES Data

BACKGROUND: Recent studies reported seasonal differences in gene expression in white blood cells, adipose tissue, and inflammatory biomarkers of the immune system. There is no data on the seasonal variations of these biomarkers in the US general population of both children and adults. Then aim of this study is to explore the seasonal trends in complete blood count (CBC), and C-reactive protein (CRP) in a large non-institutionalized US population. METHODS: Seven cross-sectional data collected in the National Health and Nutrition Examination Survey (NHANES) during 1999-2012 were aggregated; participants reporting recent use of prescribed steroids, chemotherapy, immunomodulators and antibiotics were excluded. Linear regression models were used to compare levels of CBC and CRP between winter-spring (November-April) and summer-fall (May-October), adjusting for demographics, personal behavioral factors, and chronic disease conditions. RESULTS: A total of 27,478 children and 36,644 adults (\u3e/=18 years) were included in the study. Levels of neutrophils, white blood cell count (WBC), and CRP were higher in winter-spring than summer-fall (

A Bird's Eye View on the Concept of Multichannel Scattering with Applications to Materials Science, Condensed Matter, and Nuclear Astrophysics

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