Quenched lattice calculation of the B --> D l nu decay rate

We calculate, in the continuum limit of quenched lattice QCD, the form factor that enters in the decay rate of the semileptonic decay B --> D l nu. Making use of the step scaling method (SSM), previously introduced to handle two scale problems in lattice QCD, and of flavour twisted boundary conditions we extract G(w) at finite momentum transfer and at the physical values of the heavy quark masses. Our results can be used in order to extract the CKM matrix element Vcb by the experimental decay rate without model dependent extrapolations.Comment: 5 pages, 4 figures, accepted for publication on Phys. Lett. B, corrected one typ

Colour and stellar population gradients in galaxies

We discuss the colour, age and metallicity gradients in a wide sample of local SDSS early- and late-type galaxies. From the fitting of stellar population models we find that metallicity is the main driver of colour gradients and the age in the central regions is a dominant parameter which rules the scatter in both metallicity and age gradients. We find a consistency with independent observations and a set of simulations. From the comparison with simulations and theoretical considerations we are able to depict a general picture of a formation scenario.Comment: 4 pages, 4 figures. Proceedings of 54th Congresso Nazionale della SAIt, Napoli 4-7 May 201

Online Independent Set Beyond the Worst-Case: Secretaries, Prophets, and Periods

We investigate online algorithms for maximum (weight) independent set on graph classes with bounded inductive independence number like, e.g., interval and disk graphs with applications to, e.g., task scheduling and spectrum allocation. In the online setting, it is assumed that nodes of an unknown graph arrive one by one over time. An online algorithm has to decide whether an arriving node should be included into the independent set. Unfortunately, this natural and practically relevant online problem cannot be studied in a meaningful way within a classical competitive analysis as the competitive ratio on worst-case input sequences is lower bounded by $\Omega(n)$. As a worst-case analysis is pointless, we study online independent set in a stochastic analysis. Instead of focussing on a particular stochastic input model, we present a generic sampling approach that enables us to devise online algorithms achieving performance guarantees for a variety of input models. In particular, our analysis covers stochastic input models like the secretary model, in which an adversarial graph is presented in random order, and the prophet-inequality model, in which a randomly generated graph is presented in adversarial order. Our sampling approach bridges thus between stochastic input models of quite different nature. In addition, we show that our approach can be applied to a practically motivated admission control setting. Our sampling approach yields an online algorithm for maximum independent set with competitive ratio $O(\rho^2)$ with respect to all of the mentioned stochastic input models. for graph classes with inductive independence number $\rho$. The approach can be extended towards maximum-weight independent set by losing only a factor of $O(\log n)$ in the competitive ratio with $n$ denoting the (expected) number of nodes

The multiplicative effect of combining alcohol with energy drinks on adolescent gambling

Purpose: There has been increased concern about the negative effects of adolescents consuming a combination of alcohol mixed with energy drinks (AmED). To date, few studies have focused on AmED use and gambling. The present study analyzed the multiplicative effect of AmED consumption, compared to alcohol alone, on the likelihood of at-risk or problem gambling during adolescence. Methods: Data from the ESPAD®Italia 2015 study, a cross-sectional survey conducted in a nationally representative sample of students (ages 15 to 19 years) were used to examine the association between self-reported AmED use (≥ 6 times, ≥ 10 times, and ≥ 20 times during the last month) and self-reported gambling severity. Multivariate models were used to calculate adjusted prevalence ratios to evaluate the association between alcohol use, AmED use, and gambling among a representative sample of adolescents who reported gambling in the last year and completed a gambling severity scale (n = 4495). Results: Among the 19% students classed as at-risk and problem gamblers, 43.9% were classed as AmED consumers, while 23.6% were classed as alcohol consumers (i.e. did not mix alcohol with energy drinks). In multivariate analyses that controlled for covariates, AmED consumers were three times more likely to be at-risk and problem gamblers (OR = 3.05) compared to non-consuming adolescents, while the effect became less pronounced with considering those who consumed alcohol without the addition of energy drinks (OR = 1.37). Conclusions: The present study clearly established that consuming AmED might pose a significantly greater risk of experiencing gambling-related problems among adolescents

Colour and stellar population gradients in galaxies: correlation with mass

We analyse the colour gradients (CGs) of ∼ 50 000 nearby Sloan Digital Sky Survey galaxies estimated by their photometrical parameters (Sérsic index, total magnitude and effective radius). From synthetic spectral models based on a simplified star formation recipe, we derive the mean spectral properties and explain the observed radial trends of the colour as gradients of the stellar population age and metallicity. CGs have been correlated with colour, luminosity, size, velocity dispersion and stellar mass. Distinct behaviours are found for early- and late-type galaxies (ETGs and LTGs), pointing to slightly different physical processes at work in different morphological types and at different mass scales. In particular, the most massive ETGs (M*≳ 1011 M☉) have shallow (even flat) CGs in correspondence of shallow (negative) metallicity gradients. In the stellar mass range (1010.3− 1010.5) ≲M*≲ 1011 M☉, the metallicity gradients reach their minimum of ∼ − 0.5 dex−1. At M*∼ 1010.3− 1010.5 M☉, colour and metallicity gradient slopes suddenly change. They turn out to anticorrelate with the mass, becoming highly positive at the very low masses, the transition from negative to positive occurring at M*∼ 109−9.5 M☉. These correlations are mirrored by similar trends of CGs with the effective radius and the velocity dispersion. We have also found that age gradients anticorrelate with metallicity gradients, as predicted by hierarchical cosmological simulations for ETGs. On the other side, LTGs have colour and metallicity gradients which systematically decrease with mass (and are always more negative than in ETGs), consistently with the expectation from gas infall and supernovae feedback scenarios. Metallicity is found to be the main driver of the trend of CGs, especially for LTGs, but age gradients are not negligible and seem to play a significant role too. Owing to the large data set, we have been able to highlight that older galaxies have systematically shallower age and metallicity gradients than younger ones. The emerging picture is qualitatively consistent with the predictions from hydrodynamical and chemodynamical simulations. In particular, our results for high-mass galaxies are in perfect agreement with predictions based on the merging scenario, while the evolution of LTGs and younger and less massive ETGs seems to be mainly driven by infall and supernovae feedbac

Packing Returning Secretaries

We study online secretary problems with returns in combinatorial packing domains with $n$ candidates that arrive sequentially over time in random order. The goal is to accept a feasible packing of candidates of maximum total value. In the first variant, each candidate arrives exactly twice. All $2n$ arrivals occur in random order. We propose a simple 0.5-competitive algorithm that can be combined with arbitrary approximation algorithms for the packing domain, even when the total value of candidates is a subadditive function. For bipartite matching, we obtain an algorithm with competitive ratio at least $0.5721 - o(1)$ for growing $n$, and an algorithm with ratio at least $0.5459$ for all $n \ge 1$. We extend all algorithms and ratios to $k \ge 2$ arrivals per candidate. In the second variant, there is a pool of undecided candidates. In each round, a random candidate from the pool arrives. Upon arrival a candidate can be either decided (accept/reject) or postponed (returned into the pool). We mainly focus on minimizing the expected number of postponements when computing an optimal solution. An expected number of $\Theta(n \log n)$ is always sufficient. For matroids, we show that the expected number can be reduced to $O(r \log (n/r))$, where $r \le n/2$ is the minimum of the ranks of matroid and dual matroid. For bipartite matching, we show a bound of $O(r \log n)$, where $r$ is the size of the optimum matching. For general packing, we show a lower bound of $\Omega(n \log \log n)$, even when the size of the optimum is $r = \Theta(\log n)$.Comment: 23 pages, 5 figure

The EPN-TAP protocol for the Planetary Science Virtual Observatory

International audienceA Data Access Protocol has been set up to search and retrieve Planetary Science data in general. This protocol will allow the user to select a subset of data from an archive in a standard way, based on the IVOA Table Access Protocol (TAP). The TAP mechanism is completed by an underlying Data Model and reference dictionaries. This paper describes the principle of the EPN-TAP protocol and interfaces, underlines the choices that have been made, and discusses possible evolutions