An alternative marginal likelihood estimator for phylogenetic models

Bayesian phylogenetic methods are generating noticeable enthusiasm in the field of molecular systematics. Many phylogenetic models are often at stake and different approaches are used to compare them within a Bayesian framework. The Bayes factor, defined as the ratio of the marginal likelihoods of two competing models, plays a key role in Bayesian model selection. We focus on an alternative estimator of the marginal likelihood whose computation is still a challenging problem. Several computational solutions have been proposed none of which can be considered outperforming the others simultaneously in terms of simplicity of implementation, computational burden and precision of the estimates. Practitioners and researchers, often led by available software, have privileged so far the simplicity of the harmonic mean estimator (HM) and the arithmetic mean estimator (AM). However it is known that the resulting estimates of the Bayesian evidence in favor of one model are biased and often inaccurate up to having an infinite variance so that the reliability of the corresponding conclusions is doubtful. Our new implementation of the generalized harmonic mean (GHM) idea recycles MCMC simulations from the posterior, shares the computational simplicity of the original HM estimator, but, unlike it, overcomes the infinite variance issue. The alternative estimator is applied to simulated phylogenetic data and produces fully satisfactory results outperforming those simple estimators currently provided by most of the publicly available software

Low energy quantum regimes of 1D dipolar Hubbard model with correlated hopping

We apply the bosonization technique to derive the phase diagram of a balanced unit density two-component dipolar Fermi gas in a one dimensional lattice geometry. The considered interaction processes are of the usual contact and dipolar long-range density-density type together with peculiar correlated hopping terms which can be generated dynamically. Rigorous bounds for the transition lines are obtained in the weak coupling regime. In addition to the standard bosonization description, we derive the low energy phase diagram taking place when part of the interaction is embodied non-perturbatively in the single component Hamiltonians. In this case the Luttinger liquid regime is shown to become unstable with respect to the opening of further gapped phases, among which insulating bond ordered wave and Haldane phases, the latter with degenerate edge modes.Comment: 6 pages, 1 figur

Price vs quantity in a duopoly supergame with nash punishments

We examine the endogenous choice between price and quantity behaviour in a duopoly supergame with product differentiation. We find that (i) if cartel profits are evenly split between firms, then only symmetric equilibria obtains; (i) if instead the additional profits available through collusion are split according to the Nash bargaining solution, there are parameter regions where all subgame perfect equilibria are asymmetric, with firms colluding in price-quantity supergames

A LEGAL REVIEW OF ITALIAN MODEL OF INTERCULTURAL EDUCATION

The aim of this work is to repeat in another european scientific context an overview of intercultural education in Italian school starting from the legal perspectives. Unlike Italy, in many European countries, since the middle of the 900, the issue of interculturality, in field of education, has become a real emergency. In this perspective, the Council of Europe and UNESCO, in the Eighties of the last century, have focused their attention on this issue by adopting various pronouncements and recommendations. In Italy, however, the National Council of Education (CNPI) has ruled in favor of intercultural education much later – by means of different standards and ministerial circulars that have treated this issue explicitly – and only recently has defined a national model of intercultural integration in the school. The Molise, as region with special characteristics, is trying to find its own model of integration through a research called Plism entrusted by the Region at the University of Molise

Radio recombination lines from obscured quasars with the SKA

We explore the possibility of detecting hydrogen radio recombination lines from 0 < z < 10 quasars. We compute the expected Hnalpha flux densities as a function of absolute magnitude and redshift by considering (i) the range of observed AGN spectral indices from UV to X-ray bands, (ii) secondary ionizations from X-ray photons, and (iii) stimulated emission due to nonthermal radiation. All these effects are important to determine the line fluxes. We find that the combination of slopes: alpha_X,hard = -1.11, alpha_X,soft = -0.7, alpha_EUV = -1.3, alpha_UV = -1.7, maximizes the expected flux, f_Hnalpha = 10 microJy for z = 7 quasars with M_AB = -27 in the n = 50 lines; allowed SED variations produce variations by a factor of 3 around this value. Secondaries boost the line intensity by a factor of 2 to 4, while stimulated emission in high-z quasars with M_AB = -26 provides an extra boost to RRL flux observed at nu = 1 GHz if recombinations arise in HII regions with T_e = 10^3-5 K, n_e = 10^3-5 cm^-3. We compute the sensitivity required for a 5sigma detection of Hnalpha lines using the SKA, finding that the SKA-MID could detect sources with M_AB < -27 (M_AB < -26) at z < 8 (z < 3) in less than 100 hrs of observing time. These observations could open new paths to searches for obscured SMBH progenitors, complementing X-ray, optical/IR and sub-mm surveys.Comment: 11 pages, 9 figures; to be published in Monthly Notices of the Royal Astronomical Society Main Journa

Cryptocurrencies activity as a complex network: Analysis of transactions graphs

The number of users approaching the world of cryptocurrencies exploded in the last years, and consequently the daily interactions on their underlying distributed ledgers have intensified. In this paper, we analyze the flow of these digital transactions in a certain period of time, trying to discover important insights on the typical use of these technologies by studying, through complex network theory, the patterns of interactions in four prominent and different Distributed Ledger Technologies (DLTs), namely Bitcoin, DogeCoin, Ethereum, Ripple. In particular, we describe the Distributed Ledger Network Analyzer (DiLeNA), a software tool for the investigation of the transactions network recorded in DLTs. We show that studying the network characteristics and peculiarities is of paramount importance, in order to understand how users interact in the DLT. For instance, our analyses reveal that all transaction graphs exhibit small world properties

DiLeNA: Distributed Ledger Network Analyzer

This paper describes the Distributed Ledger Network Analyzer (DiLeNA), a new software tool for the analysis of the transactions network recorded in Distributed Ledger Technologies (DLTs). The set of transactions in a DLT forms a complex network. Studying its characteristics and peculiarities is of paramount importance, in order to understand how users interact in the distributed ledger system. The tool design and implementation is introduced and some results are provided. In particular, the Bitcoin and Ethereum blockchains, i.e. the most famous and used DLTs at the time of writing, have been analyzed and compared.Comment: Proceeding of the 3rd Workshop on Cryptocurrencies and Blockchains for Distributed Systems (CryBlock 2020

Steplength selection in gradient projection methods for box-constrained quadratic programs

The role of the steplength selection strategies in gradient methods has been widely in- vestigated in the last decades. Starting from the work of Barzilai and Borwein (1988), many efficient steplength rules have been designed, that contributed to make the gradient approaches an effective tool for the large-scale optimization problems arising in important real-world applications. Most of these steplength rules have been thought in unconstrained optimization, with the aim of exploiting some second-order information for achieving a fast annihilation of the gradient of the objective function. However, these rules are successfully used also within gradient projection methods for constrained optimization, though, to our knowledge, a detailed analysis of the effects of the constraints on the steplength selections is still not available. In this work we investigate how the presence of the box constraints affects the spectral properties of the Barzilai\u2013Borwein rules in quadratic programming problems. The proposed analysis suggests the introduction of new steplength selection strategies specifically designed for taking account of the active constraints at each iteration. The results of a set of numerical experiments show the effectiveness of the new rules with respect to other state of the art steplength selections and their potential usefulness also in case of box-constrained non-quadratic optimization problems

Homogeneous and domain-wall topological Haldane conductors with dressed Rydberg atoms

The interplay between antiferromagnetic interaction and hole motion is capable of inducing conducting Haldane phases with topological features described by a finite nonlocal string order parameter. Here we show that these states of matter are captured by the one-dimensional t − J z model, which can be experimentally realized with dressed Rydberg atoms trapped onto a one-dimensional optical lattice. In the sector with vanishing total magnetization, exact calculations associated with the bosonization technique allow us to predict that both metallic and superconducting topological Haldane states can be achieved. With the addition of an appropriate magnetic field, the system enters a domain-wall structure with finite total magnetization. In this regime, the conducting Haldane states are confined in domains separated by regions where a fully polarized Luttinger liquid occurs. A procedure to dynamically stabilize such topological phases starting from a confined Ising state is also described