Theoretical analysis of aliasing noises in cold atom Mach-Zehnder interferometers

We present a theoretical analysis of aliasing noises that might appear in cold atom Mach-Zehnder interferometers used for the measurement of various physical quantities. We focus more specifically on single cold atom gyroscopes. To evaluate the level of aliasing noises, we have developed a model based on the power spectral densities of the different identified noise sources as input parameters and which makes use of a servo-loop to realize a precise measurement of the rotation rate. The model allows one to take into account different modes of operation, like a continuous as well as a pulsed or even a multi-ball operation. For monokinetic atoms, we show that the intermodulation noise can be completely filtered out with a continuous mode of operation and an optimum modulation scheme for any modulation frequency but also with a pulsed operation however only for specific launching frequencies. In the case of a real continuous atomic beam having a velocity distribution, it comes out that a high attenuation can be reached which indicates clearly the potential stability improvement that can be expected from a continuous operatio

An experimental study of intermodulation effects in an atomic fountain frequency standard

The short-term stability of passive atomic frequency standards, especially in pulsed operation, is often limited by local oscillator noise via intermodulation effects. We present an experimental demonstration of the intermodulation effect on the frequency stability of a continuous atomic fountain clock where, under normal operating conditions, it is usually too small to observe. To achieve this, we deliberately degrade the phase stability of the microwave field interrogating the clock transition. We measure the frequency stability of the locked, commercial-grade local oscillator, for two modulation schemes of the microwave field: square-wave phase modulation and square-wave frequency modulation. We observe a degradation of the stability whose dependence with the modulation frequency reproduces the theoretical predictions for the intermodulation effect. In particular no observable degradation occurs when this frequency equals the Ramsey linewidth. Additionally we show that, without added phase noise, the frequency instability presently equal to 2x10-13 at 1s, is limited by atomic shot-noise and therefore could be reduced were the atomic flux increased

Caractérisation des qualités mécaniques du pin sylvestre.

Les caractéristiques mécaniques et physiques du pin sylvestre ont été mesurées sur 245 arbres répartis en Alsace, Auvergne, PACA, Limousin et Centre. Elles sont élevées et révèlent un fort potentiel d'utilisation en structure, avec des différences régionales marquées

A Functional Genomics Approach to Establish the Complement of Carbohydrate Transporters in Streptococcus pneumoniae

The aerotolerant anaerobe Streptococcus pneumoniae is part of the normal nasopharyngeal microbiota of humans and one of the most important invasive pathogens. A genomic survey allowed establishing the occurrence of twenty-one phosphotransferase systems, seven carbohydrate uptake ABC transporters, one sodium∶solute symporter and a permease, underlining an exceptionally high capacity for uptake of carbohydrate substrates. Despite high genomic variability, combined phenotypic and genomic analysis of twenty sequenced strains did assign the substrate specificity only to two uptake systems. Systematic analysis of mutants for most carbohydrate transporters enabled us to assign a phenotype and substrate specificity to twenty-three transport systems. For five putative transporters for galactose, pentoses, ribonucleosides and sulphated glycans activity was inferred, but not experimentally confirmed and only one transport system remains with an unknown substrate and lack of any functional annotation. Using a metabolic approach, 80% of the thirty-two fermentable carbon substrates were assigned to the corresponding transporter. The complexity and robustness of sugar uptake is underlined by the finding that many transporters have multiple substrates, and many sugars are transported by more than one system. The present work permits to draw a functional map of the complete arsenal of carbohydrate utilisation proteins of pneumococci, allows re-annotation of genomic data and might serve as a reference for related species. These data provide tools for specific investigation of the roles of the different carbon substrates on pneumococcal physiology in the host during carriage and invasive infection

Les gènes SEC61 et SEC62 de Yarrowia lipolytica

* INRA, centre GMP Diffusion du document : INRA, centre GMPNational audienc

Cloning the Yarrowia lipolytica homologue of the Saccharomyces cerevisiae SEC62 gene.

International audienc