How to calculate correlation functions of Heisenberg chains

We describe a method for calculating dynamical spin-spin correlation functions in the finite isotropic and anisotropic antiferromagnetic Heisenberg models. Our method is able to produce results with high accuracy over the full parameter space.Comment: Proceedings of the "Tenth Training Course in the Physics of Correlated Electron Systems and High-Tc Superconductors", Salerno, Oct 200

Computation of dynamical correlation functions of Heisenberg chains in a field

We compute the momentum- and frequency-dependent longitudinal spin structure factor for the one-dimensional spin-1/2 $XXZ$ Heisenberg spin chain in a magnetic field, using exact determinant representations for form factors on the lattice. Multiparticle contributions are computed numerically throughout the Brillouin zone, yielding saturation of the sum rule to high precision.Comment: 4 pages, 14 figure

Mise en œuvre du MDE pour la conception de systèmes embarqués: premiers résultats et perspectives du projet Lambda

National audienceDémarré en juin 2008, Lambda est un projet de recherche collaboratif rassemblant 14 partenaires industriels, PME et académiques. Le projet se focalise sur la modélisation de plateformes d'exécutions dans le contexte de la conception de systèmes embarqués. Il vise des assemblages complexes de composants sur étagère, dans le cadre de cas de test représentatifs des problèmes actuels rencontrés par les intégrateurs système (contrôle de latences réseau, configuration des tâches et ordonnancement). Un premier objectif est de démontrer la faisabilité technique, ainsi que l'intérêt, de la modélisation de plateformes, comme un moyen de valider le déploiement et la configuration des composants du système. Un second objectif vise à réconcilier les standards appropriés (SysML, MARTE, AADL, IP-XACT) avec les standards de facto (déjà implémentés dans des outils d'analyse ou de simulation largement répandus). Un an et demi après son démarrage, Lambda fourni déjà des résultats visibles. Une utilisation intensive de SysML/MARTE dans des expérimentations de modélisation a permis d'identifier des bonnes pratiques, ainsi qu'un sous-ensemble de MARTE applicable dans un contexte d'ingénierie système. Les problématiques clés liées au déploiement massif du MDE dans l'industrie (MCO des ateliers de modélisation, passage à l'échelle) ont commencé à être adressées. Des actions concrètes d'alignement des standards (SysML, MARTE, AADL) et la convergence entre standards et outils commerciaux conduit à un panorama plus clair dans ce domaine. L'article décrit le contexte technique ainsi que les problématiques adressées par le projet Lambda. Après avoir présenté les objectifs du projet et le partenariat, il détaille les travaux en cours et présente une vue d'ensemble des premiers résultats. En conclusion, l'article évoque le travail restant dans le projet, ainsi que les perspectives pour les partenaires impliqués

Computation of dynamical correlation functions of Heisenberg chains: the gapless anisotropic regime

We compute all dynamical spin-spin correlation functions for the spin-1/2 $XXZ$ anisotropic Heisenberg model in the gapless antiferromagnetic regime, using numerical sums of exact determinant representations for form factors of spin operators on the lattice. Contributions from intermediate states containing many particles and string (bound) states are included. We present modified determinant representations for the form factors valid in the general case with string solutions to the Bethe equations. Our results are such that the available sum rules are saturated to high precision. We Fourier transform our results back to real space, allowing us in particular to make a comparison with known exact formulas for equal-time correlation functions for small separations in zero field, and with predictions for the zero-field asymptotics from conformal field theory.Comment: 14 page

Community-Level Responses to Iron Availability in Open Ocean Plankton Ecosystems

Predicting responses of plankton to variations in essential nutrients is hampered by limited in situ measurements, a poor understanding of community composition, and the lack of reference gene catalogs for key taxa. Iron is a key driver of plankton dynamics and, therefore, of global biogeochemical cycles and climate. To assess the impact of iron availability on plankton communities, we explored the comprehensive bio-oceanographic and bio-omics data sets from Tara Oceans in the context of the iron products from two state-of-the-art global scale biogeochemical models. We obtained novel information about adaptation and acclimation toward iron in a range of phytoplankton, including picocyanobacteria and diatoms, and identified whole subcommunities covarying with iron. Many of the observed global patterns were recapitulated in the Marquesas archipelago, where frequent plankton blooms are believed to be caused by natural iron fertilization, although they are not captured in large-scale biogeochemical models. This work provides a proof of concept that integrative analyses, spanning from genes to ecosystems and viruses to zooplankton, can disentangle the complexity of plankton communities and can lead to more accurate formulations of resource bioavailability in biogeochemical models, thus improving our understanding of plankton resilience in a changing environment

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

The ostracods of the Givetian (Middle Devonian) of the Ardenne. Palaeobiodiversity, palaeoecology and bioevents : biotic response to environmental changes of a carbonate platform

Cette étude porte sur les ostracodes du Givétien de l’Ardenne. A cette période, l’Ardenne est une vaste plate-forme carbonatée récifale et tropicale s’étendant le long de la marge sud-laurussienne (océan Rhéno-Hercynien). La faune de trois régions de l’Ardenne (Aisemont, Givet et Aisne), représentant trois emplacements sur la plate-forme givétienne, est caractérisée. La faune de trois provinces plus éloignées (Asturies, Massif de Mouthoumet et Saoura), appartenant à des plates-formes différentes au Givétien, est analysée dans un but comparatif. Environ 50 000 ostracodes ont été extraits par acétolyse à chaud. Au total, 376 taxons répartis en 9 genres sont identifiés. Dans le Givétien de l’Ardenne, 245 taxons sont recensés et 1 nouveau genre et 5 nouvelles espèces sont proposés. L’analyse de la répartition stratigraphique et de la biodiversité des ostracodes montre une faune relativement riche et stable durant le Givétien inférieur et moyen. Dans tous les sites étudiés, une chute dans l’abondance et la biodiversité des ostracodes est observable à la fin du Givétien moyen. Elle est suivie par une période où les faunes sont rares, puis par un renouvellement faunique avec l’installation de taxons nouveaux dans le Givétien supérieur. Ce phénomène, d’ampleur supra-régionale, est la conséquence de la crise du Taghanic. Cette crise affecte de façon conséquente les ostracodes benthiques néritiques. Au niveau spécifique, environ 90% des taxons connus dans le Givétien inférieur et moyen ne sont plus retrouvés dans le Givétien supérieur. Dans la Saoura, un autre bioévénement est retrouvé dans le Givétien moyen : les événements pumilio. Les ostracodes ne semblent aucunement perturbés par ce bioévénement. Enfin, en Ardenne, quelques marqueurs biostratigraphiques sont reconnus dans le Givétien. Des groupes écologiques d’ostracodes sont caractérisés sur la plate-forme ardennaise en fonction de l’environnement. Les affinités écologiques des espèces rencontrées sont analysées, permettant de mettre en avant quelques marqueurs environnementaux et des taxons ubiquistes. Parmi ces taxons ubiquistes, des espèces polymorphes sont observées. Une analyse quantitative de l’espèce Cavellina rhenana Krömmelbein, 1954 met en avant que l’environnement a une influence majeure sur la morphologie de la carapace. De tels taxons écomorphes peuvent permettre d’affiner les reconstitutions paléoenvironnementales. Une base de données sur les ostracodes du Givétien a été compilée et inclut 920 espèces de 18 régions. L’analyse de ces informations sous un angle paléobiogéographique permet de mettre en avant l’existence d’une province faunique Rhéno-Hercynienne au Givétien. Durant cette période, les échanges fauniques sont favorisés avec les régions plus méridionales. Le dernier volet de cette étude traite de la découverte de deux niveaux à microsphérules dans le Givétien ardennais. Les caractéristiques de ces niveaux permettent de penser qu’il s’agit d’éjectas distaux déposés suite à deux impacts météoritiques au cours du Givétien.This study deals with the ostracodes of the Givetian of the Ardenne. During this period, the Ardenne was a wide reefal carbonate platform in tropical realm, extending along the south-laurrusian margin (Rheno-Hercynian Ocean). The fauna from three areas of the Ardenne (Aisemont, Givet and Aisne), representing three different places on the givetien platform, are characterized. Other faunas from three farther areas (Asturias, Mouthoumet Massif and Saoura) which belong to other carbonate platforms during the Givetian are also analyzed to compare with the Ardenne. About 50,000 ostracodes were extracted by the hot acetolysis method. In all, 376 taxa belonging to 91 genera have been identified. In the Givetian of the Ardenne, 245 taxa have been recognized, of which 1 new genus and 5 new species. Analyses of the stratigraphical distribution and the biodiversity of ostracodes show a relatively rich and stable fauna from the Early to the Middle Givetian. For all the studied areas, the abundance and the biodiversity of ostracodes decrease in the late Middle Givetian. It is followed by a time interval where faunas are rare. Then, a faunal renewal occurs, with the appearance of new taxa in the Late Givetian. This supraregional phenomenon is a consequence of the global Taghanic Biocrisis. This crisis deepdly disturb the neritic benthic ostracodes communities. Ne arly 90% of the species know in the Early and the Middle Givetian are no longer found in the Late Givetian. In the Saoura, another bioevent is recognized: the pumilio events. Ostracodes communities are not affected by this bioevent. Finally, in the Ardenne, some biostratigraphical markers are proposed in the Givetian. Ecological groups of ostracodes on the ardennean platform are characterized in regards to environment. Ecological affinities of the species are analysed and allow recognizing both valuable environmental markers and ubiquists taxa. Among these ubiquists taxa, polymorphic species are present. Quantitative analyses performed on the species Cavellina rhenana Krömmelbein, 1954 put forwards that the environment strongly influences the carapace morphology. Such ecomorphs may be useful to refine paleoenvironmental reconstructions. A database on givetian ostracodes has been compiled. It includes 920 species from 18 areas. Analyses of this database evidence that a Rheno-Hercynian faunal province existed during Givetian. During this period, faunal exchanges were favoured with the more southern areas. The last part focuses on the finding of two microspherules layers in the Givetian of the Ardenne. The characteristics of these levels suggest that they are distal ejectas deposited following two asteroid impacts during the Givetian

The origin of terrestrial isopods (Crustacea: Isopoda: Oniscidea)

Living isopods of the suborder Oniscidea (commonly called woodlice) are the only group of Crustacea almost entirely composed of terrestrial forms. Furthermore, woodlice are completely independent from the aquatic environment from which they originally arose. From marine ancestors, woodlice are a key taxon to study the conquest of the land among arthropods because of their interesting gradation of morphological, physiological and behavioral adaptations for terrestriality. However, the origin and evolution of this model group are still poorly known. Herein, we provide a synthesis of the oniscidean fossil record to replace this group in a deep-time context. Because members of the Oniscidea are difficult to fossilize, their fossil record alone is undoubtedly fragmentary and not representative of their complete evolutionary history, but it maintains an important relevance by providing reference points. To date, the first attested occurrences of Oniscidea are recorded from the Early Cretaceous. At this time, woodlice were already widely distributed (from Western Europe to Eastern Asia) with several species. By evaluating phylogenetic studies, palaeobiogeographic context of fossil specimens and current biological considerations, we discuss and support a pre-Pangaean origin of the Oniscidea, in the Late Paleozoic-most likely during the Carboniferous. © 2012 Springer Science+Business Media Dordrecht.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The monotonicity formula in geometric measure theory, and an application to a partially free boundary problem

To appear in: Springer Lecture Notes in MathematicsSIGLETIB Hannover: RO 5389(35) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman