Results of a self-triggered prototype system for radio-detection of extensive air showers at the Pierre Auger Observatory

We describe the experimental setup and the results of RAuger, a small radio-antenna array, consisting of three fully autonomous and self-triggered radio-detection stations, installed close to the center of the Surface Detector (SD) of the Pierre Auger Observatory in Argentina. The setup has been designed for the detection of the electric field strength of air showers initiated by ultra-high energy cosmic rays, without using an auxiliary trigger from another detection system. Installed in December 2006, RAuger was terminated in May 2010 after 65 registered coincidences with the SD. The sky map in local angular coordinates (i.e., zenith and azimuth angles) of these events reveals a strong azimuthal asymmetry which is in agreement with a mechanism dominated by a geomagnetic emission process. The correlation between the electric field and the energy of the primary cosmic ray is presented for the first time, in an energy range covering two orders of magnitude between 0.1 EeV and 10 EeV. It is demonstrated that this setup is relatively more sensitive to inclined showers, with respect to the SD. In addition to these results, which underline the potential of the radio-detection technique, important information about the general behavior of self-triggering radio-detection systems has been obtained. In particular, we will discuss radio self-triggering under varying local electric-field conditions.Comment: accepted for publication in JINS

The effect of multiple paternity on genetic diversity during and after colonisation

In metapopulations, genetic variation of local populations is influenced by the genetic content of the founders, and of migrants following establishment. We analyse the effect of multiple paternity on genetic diversity using a model in which the highly promiscuous marine snail Littorina saxatilis expands from a mainland to colonise initially empty islands of an archipelago. Migrant females carry a large number of eggs fertilised by 1 - 10 mates. We quantify the genetic diversity of the population in terms of its heterozygosity: initially during the transient colonisation process, and at long times when the population has reached an equilibrium state with migration. During colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in comparison with the case of single paternity. The equilibrium state, by contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 % higher heterozygosity compared with single paternity. Further we find that far from the mainland, new mutations spreading from the mainland cause bursts of high genetic diversity separated by long periods of low diversity. This effect is boosted by multiple paternity. We conclude that multiple paternity facilitates colonisation and maintenance of small populations, whether or not this is the main cause for the evolution of extreme promiscuity in Littorina saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia

Analytical and numerical stability analysis of Soret-driven convection in a horizontal porous layer

We present an analytical and numerical stability analysis of Soret-driven convection in a porous cavity saturated by a binary fluid. Both the mechanical equilibrium solution and the monocellular flow obtained for particular ranges of the physical parameters of the problem are considered. The porous cavity, bounded by horizontal infinite or finite boundaries, is heated from below or from above. The two horizontal plates are maintained at different constant temperatures while no mass flux is imposed. The influence of the governing parameters and more particularly the role of the separation ratio, characterizing the Soret effect and the normalized porosity, are investigated theoretically and numerically. From the linear stability analysis, we find that the equilibrium solution loses its stability via a stationary bifurcation or a Hopf bifurcation depending on the separation ratio and the normalized porosity of the medium. The role of the porosity is important, when it decreases, the stability of the equilibrium solution is reinforced. For a cell heated from below, the equilibrium solution loses its stability via a stationary bifurcation when the separation ratio >0(Le,), while for 0, while a stationary or an oscillatory bifurcation occurs if mono the monocellular flow loses stability via a Hopf bifurcation. As the Rayleigh number increases, the resulting oscillatory solution evolves to a stationary multicellular flow. For a cell heated from above and <0, the monocellular flow remains linearly stable. We verified numerically that this problem admits other stable multicellular stationary solutions for this range of parameters

Quantization codebook optimization for color image under psychophysical constraints

The information contained into an image is spatially, spectrally and perceptually redundant . In the context of the color Vector Quantization (VQ) compression scheme, this redundancy is a handicap in terms of performances (complexity, quality and compression rate) . Combining perceptual and classification criteria, one can improve the codebook quality when reduce construction time associated . In this paper, we propose a training set reduction method . Associating to vectors of the training set a perceptually relevant measure, one can extract a subset from it . A classification step is then applied on this subset . Finally, the codebook is construct using the LBG algorithm on each obtained cluster, and joining together all code vectors . Psychophysics and statistical measures of image quality allow us to validate our method in terms of construction time, reconstructed image quality and compression rate .L'information contenue dans une image couleur est redondante spatialement, spectralement et perceptuellement. Dans le contexte de la compression d'image couleur par quantification vectorielle, cette redondance devient rapidement un handicap en termes de performances (complexité, qualité, taux de compression). En combinant des éléments de perception et de classification, il est possible d'améliorer la qualité du dictionnaire tout en réduisant le temps de construction associé. Dans cet article, nous proposons une méthode de réduction de la base d'apprentissage. En associant aux éléments de cette base une mesure perceptuellement significative, nous en extrayons un sous-ensemble représentatif. Une étape de classification reposant sur un modèle paramétrique de la mesure est ensuite appliquée sur ce sous-ensemble. Pour chacune des classes obtenues, un dictionnaire est déterminé en appliquant l'algorithme LBG. L'ensemble de ces dictionnaires constitue le dictionnaire final. L'utilisation de tests psychophysiques et de mesures statistiques de la qualité nous ont permis de valider notre approche en termes de temps de calcul, de qualité des images reconstruites et du taux de compression

Color image segmentation by unsupervised 2D histogram clustering and Dempster-Shafer region merging

In this paper, a color image segmentation method based on a new approach called bimarginal is proposed.To overcome the drawbacks of the classical marginal approaches, color components are considered in pairs in order to have a partial view of their inner correlation. Working with color images, the three possible combinations are considered as three independant information sources. Each pairwise component combination is firstly analyzed according to an unsupervised morphologic clustering which looks for the dominant colors of a 2D histogram. This leads to obtain three segmentation maps combined by intersection after being simplified. The intersection process itself producing an over-segmentation of the image, a pairwise region merging is done according to a similarity criterion with the Dempster-Shafer theory up to a termination criterion. To fully automate the segmentation, an energy function is proposed to quantify the segmentation quality. The latter acts as a performance indicator and is used all over the segmentation to tune its parameters.Dans cet article nous proposons une méthode de segmentation d'images couleur selon une nouvelle approche que nous appelons bi-marginale. Afin de pallier les défauts des approches marginales classiques, nous considérons les composantes couleur deux à deux afin d'avoir une vue partielle de leur corrélation. Travaillant selon cette vision bi-composante, nous considérons les trois combinaisons possible comme trois sources d'informations indépendantes. Chaque information bi-composante est tout d'abord analysée selon un schéma de coalescence morphologique non supervisé qui recherche les couleurs dominantes d'un histogramme bidimensionnel. Cela permet de construire trois cartes de segmentation distinctes qui sont combinées par intersection après avoir été simplifiées. L'intersection produisant une sur-segmentation, une fusion des régions deux à deux est opérée selon un critère de similarité et selon la combinaison de Dempster-Shafer jusqu'à un critère de terminaison. Afin d'automatiser la méthode de segmentation, une mesure d'énergie est proposée afin de quantifier la qualité d'une segmentation, celle-ci sert tout au long de la méthode proposée comme indicateur de performance de la segmentation afin d'en régler les différents paramètres

Adaptations of a native Subantarctic flightless fly to dehydration stress: more plastic than we thought? ( Short Communication)

Water conservation is a critical aspect affecting the survival, distribution and abundance of terrestrial arthropods. In this study we investigate mechanisms of dehydration tolerance of the native, flightless fly, Calycopteryx moseleyi, inhabiting contrasting environments at two localities in the Kerguelen Islands. We compare the survival abilities and management of body water content of adult flies from two different ecophenotypes when exposed to conditions of low relative humidity. Our results suggest a broad plasticity in the responses of C. moseleyi to desiccation, showing distinct local adaptations to environmental conditions

Understanding “green” multicellularity: do seaweeds hold the key?

International audienceLiving organisms are unicellular, composed of a single cell, or multicellular, where a group of up to ~1012 cells functions co-operatively (Kaiser, 2001). All multicellular organisms evolved from single-celled ancestors; every individual organism arises from a unicell and reproduces by forming unicells. Multicellularity enables competitive advantages, and may have shaped our oxygen-rich atmosphere (Grosberg and Strathmann, 1998; Kaiser, 2001; Schirrmeister et al., 2013). Multicellularity has evolved multiple times: animals, plants, algae, amoebae, fungi, and bacteria are or can all be multicellular (King, 2004; Grosberg and Strathmann, 2007; Rokas, 2008; Claessen et al., 2014). Multicellularity can be clonal (arising from division of a single cell) or aggregative (aggregation of genetically diverse cells), with clonal multicellularity considered evolutionarily more stable (Grosberg and Strathmann, 1998). The molecular mechanisms by which organisms become multicellular are not well understood. In this article, we outline eukaryotic multicellular evolution, and discuss how to increase our future understanding

Evaluation of Sweet Grain Sorghum Silage for Dairy Cows as an Alternative to Irrigated Maize Silage

Under European dairy cattle rearing conditions, whole plant maize silage is the main part of the dairy cow\u27s diet especially during the winter season. Nevertheless maize production can be limited in some areas because summer rainfall is insufficient and so irrigation is necessary. Grain sorghum hybrids, and especially sweet sorghum types, are potentially of great interest to avoid this water consumption (Lemaire et al., 1996, Legarto, 2000). For this reason we evaluated in 2003 the benefits and limits of a sweet grain sorghum silage for dairy milk production, compared to an irrigated maize silage. We paid particularl attention to forage quality and yield, environmental effects and animal performance

On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble ewline transition metals

The rate of consumption of dithiothreitol (DTT) is increasingly used to measure the oxidative potential of particulate matter (PM), which has been linked to the adverse health effects of PM. While several quinones are known to be very reactive in the DTT assay, it is unclear what other chemical species might contribute to the loss of DTT in PM extracts. To address this question, we quantify the rate of DTT loss from individual redox-active species that are common in ambient particulate matter. While most past research has indicated that the DTT assay is not sensitive to metals, our results show that seven out of the ten transition metals tested do oxidize DTT, as do three out of the five quinones tested. While metals are less efficient at oxidizing DTT compared to the most reactive quinones, concentrations of soluble transition metals in fine particulate matter are generally much higher than those of quinones. The net result is that metals appear to dominate the DTT response for typical ambient PM&lt;sub&gt;2.5&lt;/sub&gt; samples. Based on particulate concentrations of quinones and soluble metals from the literature, and our measured DTT responses for these species, we estimate that for typical PM&lt;sub&gt;2.5&lt;/sub&gt; samples approximately 80% of DTT loss is from transition metals (especially copper and manganese), while quinones account for approximately 20%. We find a similar result for DTT loss measured in a small set of PM&lt;sub&gt;2.5&lt;/sub&gt; samples from the San Joaquin Valley of California. Because of the important contribution from metals, we also tested how the DTT assay is affected by EDTA, a chelator that is sometimes used in the assay. EDTA significantly suppresses the response from both metals and quinones; we therefore recommend that EDTA should not be included in the DTT assay