Fast acoustic streaming in standing waves : Generation of an additional outer streaming cell

Rayleigh streaming in a cylindrical acoustic standing waveguide is studied both experimentally and numerically for nonlinear Reynolds numbers from 1 to 30. Streaming velocity is measured by means of laser Doppler velocimetry in a cylindrical resonator filled with air at atmospheric pressure at high intensity sound levels. The compressible Navier-Stokes equations are solved numerically with high resolution finite difference schemes. The resonator is excited by shaking it along the axis at imposed frequency. Results of measurements and of numerical calculation are compared with results given in the literature and with each other. As expected, the axial streaming velocity measured and calculated agrees reasonably well with the slow streaming theory for small ReNL but deviates significantly from such predictions for fast streaming (ReNL > 1). Both experimental and numerical results show that when ReNL is increased, the center of the outer streaming cells are pushed toward the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes

Au seuil de l’écrit, au seuil de l’oral

En m’appuyant sur mon expérience personnelle du livre et de l’écrit, mais aussi sur ma posture d’ethnographe pendant plusieurs décennies dans le Centre-Ouest de la France, je me suis attaché à évoquer quelques attitudes assez bien partagées, engendrées par les livres, du moins par certains d’entre eux, désignés à la vindicte. Puis, je me suis arrêté sur des exemples d’ethnotextes où s’entrelacent écrit et oral, enfin j’ai voulu rappeler certains tabous linguistiques élémentaires, parfois très anciens, du domaine de la culture de l’oralité. Le rapprochement d’anecdotes et de signes qui relèvent de l’intime, dispersés dans le quotidien rural, dénote une « mémoire longue » et bien enracinée qui transfère des savoirs anciens jusqu’à nous.Based on my personal experience of books and writing and on my position as ethnographer in west central France, I have tried to evoke some of the shared attitudes generated by those books designated as condemnable. I then focused on samples of ethnotexts that mingle the oral and written. Then, I decided to recall certain basic linguistic taboos, some quite ancient, belonging to the area of oral culture. By bringing together anecdotes and signs stemming from the intimate sphere and dispersed in the rural everyday, one denotes a “long memory” that is well rooted and that transfers ancient knowledge to our very day

Reliable microsatellite genotyping of the Eurasian badger (Meles meles) using faecal DNA

The potential link between badgers and bovine tuberculosis has made it vital to develop accurate techniques to census badgers. Here we investigate the potential of using genetic profiles obtained from faecal DNA as a basis for population size estimation. After trialling several methods we obtained a high amplification success rate (89%) by storing faeces in 70% ethanol and using the guanidine thiocyanate/silica method for extraction. Using 70% ethanol as a storage agent had the advantage of it being an antiseptic. In order to obtain reliable genotypes with fewer amplification reactions than the standard multiple-tubes approach, we devised a comparative approach in which genetic profiles were compared and replication directed at similar, but not identical, genotypes. This modified method achieved a reduction in polymerase chain reactions comparable with the maximumlikelihood model when just using reliability criteria, and was slightly better when using reliability criteria with the additional proviso that alleles must be observed twice to be considered reliable. Our comparative approach would be best suited for studies that include multiple faeces from each individual. We utilized our approach in a well-studied population of badgers from which individuals had been sampled and reliable genotypes obtained. In a study of 53 faeces sampled from three social groups over 10 days, we found that direct enumeration could not be used to estimate population size, but that the application of mark–recapture models has the potential to provide more accurate results

Mesures de vent acoustique dans un moteur thermoacoustique à onde stationnaire par vélocimétrie laser

International audienceLa vélocimétrie par images de particules et l'anémométrie laser Doppler sont utilisées pour étudier le vent acoustique de Rayleigh dans un moteur thermoacoustique. Le vent acoustique est un écoulement station- naire de second ordre superposé à l'écoulement acoustique oscillant du premier ordre. La mesure de ce type d'écoulement, même dans un résonateur vide, nécessite des techniques spéciales de post-traitement. Dans les moteurs thermoacoustiques réels, deux défis supplémentaires sont rencontrés lors de la mesure de la vitesse moyenne du second ordre. Tout d'abord, du fait du lien étroit entre vent acoustique et équilibre thermique, le temps requis pour atteindre le régime permanent est relativement long et, par conséquent, la densité des particules d'ensemencement (piégées à l'intérieur du résonateur) est significativement réduite à l'issu de ce temps d'établissement. Deuxièmement, la non-uniformité de distribution de température à la paroi du résonateur du moteur crée un flux de convection naturel qui se superpose au vent acoustique. Dans la présente étude, deux solutions sont proposées pour surmonter ces défis. Tout d'abord, le préchauffage du moteur est utilisé pour raccourcir le temps nécessaire pour atteindre les conditions d'équilibre. Deuxième- ment, une méthode de découplage des différents écoulements moyens dans le moteur thermoacoustique est présentée. L'utilisation de ces techniques aide à mieux comprendre le comportement du vent acoustique de Rayleigh et de la convection naturelle dans un moteur thermoacoustique réel

Widely rhythmic transcriptome in Calanus finmarchicus during the high Arctic summer solstice period

Solar light/dark cycles and seasonal photoperiods underpin daily and annual rhythms of life on Earth. Yet, the Arctic is characterized by severalmonths of permanent illumination (‘‘midnight sun’’). To determine the persistence of 24h rhythms during the midnight sun, we investigated transcriptomic dynamics in the copepod Calanus finmarchicus during the summer solstice period in the Arctic, with the lowest diel oscillation and the highest altitude of the sun’s position. Here we reveal that in these extreme photic conditions, a widely rhythmic daily transcriptome exists, showing that very weak solar cues are sufficient to entrain organisms. Furthermore, at extremely high latitudes and under sea-ice, gene oscillations become re-organized to include <24h rhythms. Environmental synchronization may therefore be modulated to include non-photic signals (i.e. tidal cycles). The ability of zooplankton to be synchronized by extremely weak diel and potentially tidal cycles, may confer an adaptive temporal reorganization of biological processes at high latitudes

Daily transcriptomes of the copepod Calanus finmarchicus during the summer solstice at high Arctic latitudes

The zooplankter Calanus finmarchicus is a member of the so-called “Calanus Complex”, a group of copepods that constitutes a key element of the Arctic polar marine ecosystem, providing a crucial link between primary production and higher trophic levels. Climate change induces the shift of C. finmarchicus to higher latitudes with currently unknown impacts on its endogenous timing. Here we generated a daily transcriptome of C. finmarchicus at two high Arctic stations, during the more extreme time of Midnight Sun, the summer solstice. While the southern station (74.5 °N) was sea ice-free, the northern one (82.5 °N) was sea ice-covered. The mRNAs of the 42 samples have been sequenced with an average of 126 ± 5 million reads (mean ± SE) per sample, and aligned to the reference transcriptome. We detail the quality assessment of the datasets and the complete annotation procedure, providing the possibility to investigate daily gene expression of this ecologically important species at high Arctic latitudes, and to compare gene expression according to latitude and sea ice-coverage

Mendelian Inheritance Pattern and High Mutation Rates of Microsatellite Alleles in the Diatom Pseudo-nitzchia multistriata

The diatom Pseudo-nitzschia multistriata exhibits a diplontic life cycle composed of an extensive phase of vegetative cell division and a brief phase of sexual reproduction. To explore genotypic stability, we genotyped seven polymorphic microsatellite loci in 26 monoclonal strains over 3–16 months in a culture maintenance regime. Moreover, to assess inheritance patterns of the microsatellite alleles, we genotyped 246 F1 strains resulting from four mating experiments between parental strains of know genotype. Results generally conformed expectations according to Mendelian inheritance patterns, but deviations were detected indicating mutations during sexual reproduction. A total of forty-two mutations were detected in the clonal cultures over time. Microsatellites with more core-repeats accumulated mutations faster. The mutation rate varied significantly across loci and strains. A binomial mass function and a computer simulation showed that the mutation rate was significantly higher during the first months of culture (μ≈3×10-3 per locus per cell division) and decreased to μ≈1×10-3 in the strains kept for 16 months. Our results suggest that genetic mutations acquired in both the vegetative phase and sexual reproduction add to the allelic diversity of microsatellites, and hence to the genotypic variation present in a natural population