Ambipolar Nernst effect in NbSe2_2

The first study of Nernst effect in NbSe$_2$ reveals a large quasi-particle contribution with a magnitude comparable and a sign opposite to the vortex signal. Comparing the effect of the Charge Density Wave(CDW) transition on Hall and Nernst coefficients, we argue that this large Nernst signal originates from the thermally-induced counterflow of electrons and holes and indicates a drastic change in the electron scattering rate in the CDW state. The results provide new input for the debate on the origin of the anomalous Nernst signal in high-T$_c$ cuprates.Comment: 5 pages including 4 figure

Heat transport in Bi_{2+x}Sr_{2-x}CuO_{6+\delta}: departure from the Wiedemann-Franz law in the vicinity of the metal-insulator transition

We present a study of heat transport in the cuprate superconductor Bi_{2+x}Sr_{2-x}CuO_{6+\delta} at subkelvin temperatures and in magnetic fields as high as 25T. In several samples with different doping levels close to optimal, the linear-temperature term of thermal conductivity was measured both at zero-field and in presence of a magnetic field strong enough to quench superconductivity. The zero-field data yields a superconducting gap of reasonable magnitude displaying a doping dependence similar to the one reported in other families of cuprate. The normal-state data together with the results of the resistivity measurements allows us to test the Wiedemann-Franz(WF) law, the validity of which was confirmed in an overdoped sample in agreement with previous studies. In contrast, a systematic deviation from the WF law was resolved for samples displaying either a lower doping content or a higher disorder. Thus, in the vicinity of the metal-insulator cross-over, heat conduction in the zero-temperature limit appears to become significantly larger than predicted by the WF law. Possible origins of this observation are discussed.Comment: 9 pages including 7 figures, submitted to Phys. Rev.

Eosinophilic granulomatosis with polyangiitis (Churg–Strauss) (EGPA) Consensus Task Force recommendations for evaluation and management

AbstractObjectiveTo develop disease-specific recommendations for the diagnosis and management of eosinophilic granulomatosis with polyangiitis (Churg–Strauss syndrome) (EGPA).MethodsThe EGPA Consensus Task Force experts comprised 8 pulmonologists, 6 internists, 4 rheumatologists, 3 nephrologists, 1 pathologist and 1 allergist from 5 European countries and the USA. Using a modified Delphi process, a list of 40 questions was elaborated by 2 members and sent to all participants prior to the meeting. Concurrently, an extensive literature search was undertaken with publications assigned with a level of evidence according to accepted criteria. Drafts of the recommendations were circulated for review to all members until final consensus was reached.ResultsTwenty-two recommendations concerning the diagnosis, initial evaluation, treatment and monitoring of EGPA patients were established. The relevant published information on EGPA, antineutrophil-cytoplasm antibody-associated vasculitides, hypereosinophilic syndromes and eosinophilic asthma supporting these recommendations was also reviewed.DiscussionThese recommendations aim to give physicians tools for effective and individual management of EGPA patients, and to provide guidance for further targeted research

Socializing One Health: an innovative strategy to investigate social and behavioral risks of emerging viral threats

In an effort to strengthen global capacity to prevent, detect, and control infectious diseases in animals and people, the United States Agency for International Development’s (USAID) Emerging Pandemic Threats (EPT) PREDICT project funded development of regional, national, and local One Health capacities for early disease detection, rapid response, disease control, and risk reduction. From the outset, the EPT approach was inclusive of social science research methods designed to understand the contexts and behaviors of communities living and working at human-animal-environment interfaces considered high-risk for virus emergence. Using qualitative and quantitative approaches, PREDICT behavioral research aimed to identify and assess a range of socio-cultural behaviors that could be influential in zoonotic disease emergence, amplification, and transmission. This broad approach to behavioral risk characterization enabled us to identify and characterize human activities that could be linked to the transmission dynamics of new and emerging viruses. This paper provides a discussion of implementation of a social science approach within a zoonotic surveillance framework. We conducted in-depth ethnographic interviews and focus groups to better understand the individual- and community-level knowledge, attitudes, and practices that potentially put participants at risk for zoonotic disease transmission from the animals they live and work with, across 6 interface domains. When we asked highly-exposed individuals (ie. bushmeat hunters, wildlife or guano farmers) about the risk they perceived in their occupational activities, most did not perceive it to be risky, whether because it was normalized by years (or generations) of doing such an activity, or due to lack of information about potential risks. Integrating the social sciences allows investigations of the specific human activities that are hypothesized to drive disease emergence, amplification, and transmission, in order to better substantiate behavioral disease drivers, along with the social dimensions of infection and transmission dynamics. Understanding these dynamics is critical to achieving health security--the protection from threats to health-- which requires investments in both collective and individual health security. Involving behavioral sciences into zoonotic disease surveillance allowed us to push toward fuller community integration and engagement and toward dialogue and implementation of recommendations for disease prevention and improved health security

Transport d'entropie, thermoélectricité dans les supraconducteurs non conventionnels

During these last fifteen years, Nernst effect has attracted much attention. This was particularly due to its behavior in high Tc superconducting hole doped cuprates. Indeed, it has been reported in these compounds that a finite Nernst effect persists, in magnetic field and in temperature, outside of the superconducting phase, although Nernst effet is supposed to be, in the case of simple metals, nonzero only in the vortex phase. This result was of importance because it supported experimentally, among other results, a scenario of preformed pairs and vortex-like excitations in the normal phase of the hole doped cuprates. However, the interpretation of the Nernst effect suffer from a lack of experimental datas in other strongly correlated electrons systems. This has initiated the work of this thesis, which contains results obtained from 2001 to 2004 in the Laboratoire de Physique Quantique - ESPCI in Paris, and which consists mostly in measurements of Nernst effect in another class of strongly correlated electrons compounds : the heavy fermions. More precisely, we performed measurements of Nernst effet at zero pressure for temperatures lying between 1.5K and 50K and for magnetic fields below 12T, in three different compounds : CeCoIn5, URu2Si2 and CeRu2Si2. These measurements are, nowadays, the sole results of Nernst effect available on heavy fermions compounds. \vspace(12pt) In the three cases, we discovered in the metallic phase the emergence of a giant Nernst effect which amplitude (some µV/KT) is by several order of magnitude higher than what is expected in a simple metal, and which reaches the characteristic size of the vortex signal in the mixed phase of cuprates. More precisely, CeCoIn5 hosts a very large \emph(negative) Nernst effect in the non Fermi liquid part of its phase diagram associated to the presence of a quantum critical point at B_c=5T. However, the Nernst effet does not show any anomaly at B_c, but much more in the B=0 limit where the Nernst coefficient reaches 1µV/KT. The emergence of a strong positive Nernst effect in URu2Si2 in concomitant to the entrance in the so called hidden order phase. Here again, the Nernst coefficient reaches its maximum of 4µV/KT at low field, and is the largest Nernst effect ever measured in a metallic phase. Finally, the Nernst effect seems to be strongly affected by the metamagnetism in CeRu2Si2. Indeed, it presents, at the metamagnetic transition, a change of sign which coincides with the maximum in specific heat. Very strikingly, in the three compounds, the emergence of a large Nernst effect coincide with the presence of a large Hall effect ; moreover, especially in CeCoIn5 and CeRu2Si2, the structure of Hall and Nernst effect are quite similar. The existence of this signal still remains intriguing, particularly in absence of systematic measurements in other heavy fermions compounds. However, but in a very simple way, we showed that the mass renormalisation might be an ingredient at the origin of this giant Nernst effect. Moreover, for each compound, several scenarios can be proposed to explain this emergence : proximity to a quantum critical point, antiferromagnetic fluctuations, density waves... We have discussed at the end of this thesis several scenarios and proposed possible measurements to confirm or infirm this propositions.L'effet Nernst a connu, ces quinze dernières années, un regain d'attention, en particulier en raison de son comportement dans les cuprates supraconducteurs à haute température critique dopés aux trous. En effet, on observe dans ces composés la persistance tant en température qu'en champ magnétique d'un signal Nernst fini en dehors de la phase supraconductrice, alors que ce dernier n'est censé être non nul, dans le cas de métaux simples, que dans la phase vortex. Ce résultat a revêtu une certaine importance en ce sens qu'il appuyait expérimentalement, parmi d'autres résultats, un scénario de type paires préformées et excitations de type vortex dans la phase normale des cuprates dopés aux trous. Cependant, l'interprétation de l'effet Nernst souffre d'un manque de données expérimentales dans d'autres systèmes à électrons fortement corrélés. C'est initialement ce qui a motivé le travail de cette thèse, qui rassemble des résultats obtenus de 2001 à 2004 au Laboratoire de Physique Quantique - ESPCI à Paris, et qui est majoritairement constitué de mesures d'effet Nernst dans une autre classe de composés à électrons fortement corrélés : les fermions lourds. Plus particulièrement, nous avons mesuré l'effet Nernst à pression nulle dans une fenêtre de température comprise entre 1,5K et 50K et pour des champs magnétiques de 0 à 12T, dans trois composés : CeCoIn5, URu2Si2 et CeRu2Si2. Ces mesures constituent, à l'heure actuelle, les seules mesures d'effet Nernst effectuées sur des fermions lourds. Dans les trois cas, nous avons découvert dans la phase métallique l'émergence d'un effet Nernst géant dont l'amplitude dépasse de plusieurs ordres de grandeur la taille du signal attendu dans un métal simple, et qui atteint celle caractéristique des vortex dans la phase mixte des cuprates, à savoir quelques µV/KT. Plus particulièrement, CeCoIn5 héberge un effet Nernst négatof très important dans la partie non liquide de Fermi de son diagramme de phase, associée à la présence d'un point critique à Bc=5T. Cependant, l'effet Nernst que nous avons mesuré ne présente aucune anomalie à Bc, mais plutôt dans la limite B=0T, où le coefficient Nernst atteint 1µV/KT. L'émergence d'un effet Nernst positif important dans URu2Si2 coïncide avec l'entrée dans la phase ordre caché, et encore ici c'est à bas champ que le coefficient Nernst atteint son maximum de 4µV/KT, qui constitue le plus grand effet Nernst jamais mesuré dans une phase métallique. Enfin, c'est le métamagnétisme de CeRu2Si2 qui semble particulièrement affecter l'effet Nernst, puisque celui-ci présente, à Hm, un changement de signe particulièrement prononcé et coïncidant avec le maximum de chaleur spécifique. Par ailleurs, une des caractéristiques générales frappantes de cette émergence est qu'elle coïncide, dans les trois composés, avec la présence d'un angle de Hall également très élevé, et dont, en particulier dans CeCoIn5 et CeRu2Si2, la structure est assez proche de celle de l'effet Nernst. La présence de ce signal reste encore aujourd'hui particulièrement intrigante, en particulier en l'absence de mesures systématiques sur d'autres composés aux fermions lourds. Cependant, mais de façon très schématique, nous avons montré que la renormalisation de la masse pouvait être un ingrédient à l'origine de cet effet Nernst géant. De plus, pour chacun des composés des pistes peuvent être avancées pour déterminer l'origine de cet émergence : proximité d'un point critique quantique, fluctuations antiferromagnétiques, ondes de densité... Nous discutons en fin de cette thèse les divers scénarios et proposons des mesures futures afin de confirmer ou d'infirmer ces diverses propositions

Transport d'entropie, thermoélectricité dans les supraconducteurs non conventionnels

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Calendrier vaccinal, recommandations et conseils associés à la vaccination anti-amarile chez le voyageur

MONTPELLIER-BU Pharmacie (341722105) / SudocSudocFranceF

A Novel Thermoplastic Composite for Marine Applications: Comparison of the Effects of Aging on Mechanical Properties and Diffusion Mechanisms

International audienceThis article investigates and compares the effects of hydrothermal aging on carbon fibre / Elium™ thermoplastic composite and on carbon fibre / vinylester thermoset composite for marine application. Accelerated aging tests are performed by immersion in deionised water at 70 °C. Water diffusion, monitored by regular weighing, shows that both composites as well as Elium™ resin exhibit non-Fickian behaviour. Analytical models are proposed to fit the experimental curves and to identify and compare diffusion parameters. The aging effects on the microstructure are evaluated using SEM, while irreversibility of degradation mechanisms is investigated by desiccation tests. Mechanical tensile tests, performed before and after aging, show the slight impact of water on tensile modulus and tensile strengths for both materials. Furthermore, it was found that shear modulus and interlaminar shear strength undergo significant alteration related to irreversible physicochemical degradation of the matrix. Studied materials have shown different diffusion behaviours, but similar mechanical properties evolutions

Durability of an acrylic thermoplastic carbon fibre reinforced composite

International audienceElium resin from Arkema is an excellent substitute for many thermosetting resins used in the manufacture of structural composites. Indeed, it offers mechanical properties very similar to those of its competitors, but it stands out above all because of its recyclability potential, thus offering the possibility of recovering the fibres at the end of the composites' life for reuse. This opportunity makes it a prime candidate for the eco-design of tomorrow's composite structures, particularly in the transport sector.The aim of this work is to study the durability of a carbon fibre reinforced Elium composite in a wet environment through accelerated ageing tests. The evolution of its mechanical properties was monitored over time, and the reversibility of ageing was also evaluated by completely drying the aged material.It was thus shown that this carbon fibre reinforced Elium composite had good durability properties under harsh ageing conditions, with a loss of longitudinal properties after ageing of less than 10% and in shear of around 20%, but above all an almost complete recovery of its properties after drying