Reversible Band Gap Engineering in Carbon Nanotubes by Radial Deformation

We present a systematic analysis of the effect of radial deformation on the atomic and electronic structure of zigzag and armchair single wall carbon nanotubes using the first principle plane wave method. The nanotubes were deformed by applying a radial strain, which distorts the circular cross section to an elliptical one. The atomic structure of the nanotubes under this strain are fully optimized, and the electronic structure is calculated self-consistently to determine the response of individual bands to the radial deformation. The band gap of the insulating tube is closed and eventually an insulator-metal transition sets in by the radial strain which is in the elastic range. Using this property a multiple quantum well structure with tunable and reversible electronic structure is formed on an individual nanotube and its band-lineup is determined from first-principles. The elastic energy due to the radial deformation and elastic constants are calculated and compared with classical theories.Comment: To be appear in Phys. Rev. B, Apr 15, 200

Anomalous electron spin resonance behavior of single-walled carbon nanotubes

International audienceWe have studied the electron spin resonance (ESR) of single-walled carbon nanotubes (SWNTs) both in their pristine state and after irradiation with fast electrons in order to detect the signal of conduction electrons. No metallic Pauli contribution was observed in the global spin susceptibility, the ESR signal of the conduction electrons is undetectable because it is broadened by magnetic impurities. We measured a paramagnetic contribution from localized states, with an effective Curie constant decreasing when the temperature increases, following a deactivation law of the type A-B exp(-E-a/k(B)T). This behavior is supposed to be characteristic of semiconducting SWNTs interacting with metallic impurities from the catalys

DÉVELOPPEMENT D'UNE INSTRUMENTATION D'ÉVALUATION EN BIOMASSE DE STOCKS PISCICOLES

Afin d'élaborer un modèle prédictif de gestion d'une retenue d'eau (naturelle ou artificielle) il est nécessaire d'estimer de la manière la plus précise le stock piscicole. Des travaux ont mis en évidence l'intérêt d'une méthode d'échosondage pour l'évaluation de la biomasse. Toutefois, la lourdeur de l'instrumentation ainsi que les incertitudes sur l'exploitation des enregistrements nous ont amenés à envisager l'étude d'une instrumentation plus performante, plus précise et en outre transportable. Dans le cadre du développement de cette instrumentation nous avons réalisé une maquette axée sur le recensement de population aquatique et le traitement numérique des signaux reçusTo set up a predictive management model for a water reservoir (natural or artificial), it is necessary to make a most precise estimate of its stock of fish. Previous works have pointed out the advantages of using an echo-sounding method to estimate the biomass. However, the cumbersome nature of the instrumentation and the uncertainty involved in the exploitation of the recordingled us to envisage studying instrumentation that would give better performance and higher accuracy, whilst also being easier to transport. Within the development work for this instrumentation, we realized one model centred on counting the aquatic population, and numerical processing of the signals received

Médicaments anticancéreux et médecine vétérinaire. Retour d'expérience du Centre hospitalier universitaire vétérinaire d'Alfort

International audienceLe développement des chimiothérapies en médecine vétérinaire expose le personnel à des risques de contamination par les médicaments cytotoxiques. Après une campagne de prélèvements surfaciques montrant une contamination de l'environnement et une exposition des personnels, en particulier au niveau des gants, le Centre hospitalier universitaire vétérinaire d'Alfort a mis en place des actions correctrices, notamment en dédiant une salle à ce type de traitement et en réorganisant le nettoyage. Une nouvelle campagne de prélèvements montre que les niveaux d'exposition se sont réduits et tendent vers un niveau le plus bas techniquement possible

When capacitive transduction meets the thermomechanical limit: Towards femto-newton force sensors at very high frequency

International audienceWe show that the capacitive transduction of a MEMS device using a setup based on a microwave detection scheme achieves the measurement of the thermomechanical noise spectrum of a high-frequency (>10 MHz) high-stiffness (>10 5 N/m) resonator, reaching the outstanding displacement resolution of 1 fm/√Hz. This result paves the way for vibrating sensors with exquisite force resolution in the fN/vHz range, enabling large-bandwidth measurements of mechanical interactions at small scale and rheology of fluids at very high frequency. An example of application is given and concerns atomic force microscopy images of biomolecular assemblies