Global Wilson-Fisher fixed points

The Wilson-Fisher fixed point with $O(N)$ universality in three dimensions is studied using the renormalisation group. It is shown how a combination of analytical and numerical techniques determine global fixed point solutions to leading order in the derivative expansion for real or purely imaginary fields with moderate numerical effort. Universal and non-universal quantitites such as scaling exponents and mass ratios are computed, for all $N$, together with local fixed point coordinates, radii of convergence, and parameters which control the asymptotic behaviour of the effective action. We also explain when and why finite-$N$ results do not converge pointwise towards the exact infinite-$N$ limit. In the regime of purely imaginary fields, a new link between singularities of fixed point effective actions and singularities of their counterparts by Polchinski are established. Implications for other theories are indicated.Comment: 28 pages, 10 figures, v2: explanations and refs added, to appear (NPB

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Parental proportions maximizing the mean value of a parameter in a panmictic population can be useful in plant breeding

De nombreux travaux de sélection portent sur la valeur moyenne d'un paramètre dans un ensemble de génotypes (ou d'échantillons). Ce paramètre peut caractériser les génotypes eux-mêmes (distances entre génotypes, diversité génétique de l'ensemble, résistance d'un mélange de lignées à un ensemble de pathogènes) ou la descendance de ces génotypes par panmixie (rendement d'une variété synthétique, hétérosis moyen). La plupart du temps, la valeur moyenne est calculée avec des fréquences égales des génotypes. Le présent article propose de déterminer les proportions des génotypes qui maximisent la valeur moyenne dans le mélange panmictique de façon à augmenter l'efficacité des méthodes de sélection. L'intérêt de cette procédure est illustré par une application en gestion des ressources génétiques et par des simulations en sélection récurrente assistée par marqueurs. La procédure a permis de supprimer toute redondance dans une collection restreinte (core collection) en augmentant la diversité moyenne de 81 % et de réduire de 38 % le temps et l'argent requis dans une sélection récurrente conventionnelle assistée par marqueurs. Elle invite à formuler de nombreux problèmes de sélection en termes de maximisation de formes quadratiques. (Résumé d'auteur

Infrared properties of scalar field theories

Phase transitions and critical phenomena are of central importance in quantum field theory and statistical physics. We investigate the low energy properties of O(N) symmetric scalar field theories using functional renormalisation group methods for all N. This modern formulation of Wilson's renormalisation group allows a continuous interpolation between short and long distance physics without resorting to a weak coupling expansion. To leading order in the derivative expansion, we study the phase transition and the approach to convexity in the deep infrared limit. In the limit of infinite N, the fluctuations of the Goldstone modes dominate allowing for a complete analytical discussion of the effective potential. For finite N, the radial fluctuations become important and we resort to systematic series expansions. In both cases a systematic and thorough analysis of the diverse fixed point solutions is carried out. This leads to a comprehensive picture of the scaling potential for a large number of universality classes. We also study the dependence of our results on the regularisation scheme. Finally, we establish that the infrared completion of the effective potential in the broken phase is driven by a fixed point that leads to the flattening of the non-convex part of the potential

Wild pearl millet population (Pennisetum glaucum, Poaceae) integrity in agricultural Sahelian areas : an example from Keita (Niger)

La structure génotypique de mils pénicillaires cultivés et spontanés poussant côte à côte à Keita au Niger a été observée sur des caractères morphologiques et enzymatiques pour évaluer leur degré d'isolement reproductif. Le champ de mils cultivés montre pour les caractères de domestication une distribution continue unimodale entre un type extrême domestiqué et un type semblable à un hybride cultivé et sauvage. Cependant, toute cette diversité semble le produit de recombinaisons génétiques au sein des mils cultivés sans que des hybridations avec les mils spontanés voisins aient pu être mises en évidence. Au contraire, les mils spontanés montrent deux groupes distincts : un groupe typique des mils sauvages et un groupe hybride des mils sauvages et des mils cultivés du champ. Le maintien des mils spontanés d'année en année induit à supposer l'élimination naturelle rapide des génotypes non conformes au type sauvage. (Résumé d'auteur

Assessing the Role of Social Media and Digital Technology in Violence Reporting

The use of social media and digital technologies has radically changed the way that information about violence is captured, reported, analysed and acted upon. People’s use of social media played a significant role in the Egyptian revolution, post-election violence in Kenya, and drug-cartel violence in Mexico. Social media can be used to provide humanitarian agencies, policymakers and academics seeking to understand and respond to violent crises with data unavailable from other sources. After an initial period of uncritical optimism regarding the potential of social media and digital technologies there is now, however, a growing recognition that they come with new practical, ethical and methodological limitations. Indeed, social media content is often the target of conscious distortions, manipulations, or censorship by a range of actors. Bias of several kinds can significantly distort social media data and reduce their representativeness. This paper assesses the role of social media and digital technologies in the reporting of violent events, and evaluates their relative strengths and weaknesses as compared to other means available. It seeks to understand how social media and digital technology data are collated, how reliable the data are, and what practical and ethical issues are associated with their collection and use.ESR

NAPP: the Nucleic Acid Phylogenetic Profile Database

Nucleic acid phylogenetic profiling (NAPP) classifies coding and non-coding sequences in a genome according to their pattern of conservation across other genomes. This procedure efficiently distinguishes clusters of functional non-coding elements in bacteria, particularly small RNAs and cis-regulatory RNAs, from other conserved sequences. In contrast to other non-coding RNA detection pipelines, NAPP does not require the presence of conserved RNA secondary structure and therefore is likely to identify previously undetected RNA genes or elements. Furthermore, as NAPP clusters contain both coding and non-coding sequences with similar occurrence profiles, they can be analyzed under a functional perspective. We recently improved the NAPP pipeline and applied it to a collection of 949 bacterial and 68 archaeal species. The database and web interface available at http://napp.u-psud.fr/ enable detailed analysis of NAPP clusters enriched in non-coding RNAs, graphical display of phylogenetic profiles, visualization of predicted RNAs in their genome context and extraction of predicted RNAs for use with genome browsers or other software