Overview of the coordinated ground-based observations of Titan during the Huygens mission

Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Saturnian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental importance for the interpretation of results from the Huygens mission

Croissance de diamant nano-cristallin (NCD) par procédés plasmas en configuration matricielle de sources élémentaires (MEPS) microondes

La croissance de diamant sur des matériaux non réfractaires nécessite le développement de procédés innovants capables de couvrir de grandes surfaces tout en optimisant l'apport énergétique. L'objectif principal de cette thèse est d'explorer les possibilités de croissance de diamant nano-cristallin sur des surfaces complexes de métaux non réfractaires ou des structures en 3D à fort rapport d'aspect. La contrainte principale est que le procédé doit respecter une gamme de température 50 µm) gravées dans du silicium (puits, tranchées avec un rapport d'aspect de 1:7). Les propriétés de ces dépôts sont reliées aux paramètres de contrôle du procédé afin, à termes, d'être capable d'optimiser le procédé. Ainsi, a-t'il été mis évidence que l'utilisation d'un réseau matriciel d'applicateurs microondes ponctuels est facilement transposable pour le changement d'échelle. Ceci permet donc d'envisager un transfert de technologie vers une/des application(s) industrielle(s).Diamond growth on non-refractory materials requires the development of innovative processes capable of covering large surfaces while optimizing the energy input. The main objective of this thesis is to explore the possibilities of nano-crystalline diamond growth on complex surfaces of non-refractory metals or high aspect ratio 3D structures. The main constraint is to find a process with a temperature range 50 µm) etched in silicon (wells, trenches with an aspect ratio of 1:7). The properties of these deposits are linked to process control parameters in order to be able to optimize the process. Thus, it has been shown that the use of a matrix network of microwave applicators is easily transposable for the upscaling. This, therefore, allow to think a transfer of technology to one or more industrial application(s)

Are Deicing Salts Necessary to Promote Scaling in Concrete?

International audienceThe main purpose of the present study is to investigate the role of the material parameters such as permeability, thermal diffusivity, and pore size distribution on the mechanical behavior of cementitious structures submitted to frost action, such as surface scaling. An experimental device, in which a cement paste specimen is exposed to freezing-thawing cycles under a thermal gradient, has been developed. The experimental results show that under high thermal gradient (up to 1.5°C/mm), skin damage can occur without a saline layer in contact with the frozen surface. This can be explained and quantified in the framework of poromechanics. The model is based on the coupling between liquid-ice crystal thermodynamic equilibrium, liquid water transport, thermal conduction, and elastic properties of the different phases that form the saturated porous material. It eventually predicts that a less permeable sample is more susceptible to damage by surface defacement, which explains the observed experimental result

Foundations of continuous agent-based modelling frameworks for pedestrian dynamics and their implications

This paper addresses the theoretical foundations of pedestrian models for crowd dynamics. While the topic gains momentum, widely different mathematical approaches are actually in use, even if we only consider continuous agent-based models. To clarify their underpinning, we first rephrase the common hierarchical decomposition into strategic, tactical, and operational levels and show the practical interest in preserving the continuity between the latter two levels by working with a floor field, rather than way-points. Turning to local navigation, we clarify how three archetypical approaches, namely, reactive models, anticipatory models based on the idea of times to collision (exemplified by the recently proposed ANDA model), and game theory, differ in their extrapolation of future trajectories, and insist on the oft-overlooked distinction between processes pertaining to decision-making and mechanical effects in dense settings. The differences are illustrated with a comparison of the numerical predictions of instances of these models in the simple scenario of head-on collision avoidance between agents, by varying the walking speed and the reaction times, notably

Isolement acoustique de parois aux basses fréquences (programmation d'outils prédictifs et confrontations expérimentales dans le cas de planchers solivés en bois)

Dans le domaine de l acoustique du bâtiment, la structuredes constructions en bois est légère et ses capacités d isolementacoustique sont faibles en particulier pour les basses fréquencesen comparaison à d autres techniques de constructioncomme le béton. Les travaux de cette thèse se donc sont centréssur l élaboration d un outil prédictif visant à déterminer lesperformances acoustiques des planchers solivés en bois afin decompléter les outils prédictifs actuellement sur le marché. Laméthode des éléments finis est adaptée pour résoudre ce problèmevibro-acoustique car le comportement basses fréquencesest de type modal. Pour gagner en temps de calcul, une résolutionmixte éléments finis formulation intégrale d Huygens etdifférentes optimisations ont été mises en place. Grâce à l utilisationde la méthode des éléments finis, il a été possible demettre en évidence des résonances de ce problème couplé quifont chuter localement la valeur de l affaiblissement ; celles-cine peuvent être prises en compte par la méthode des matricesde transfert. Néanmoins, ces deux méthodes fournissent des alluresmoyennes de courbes d affaiblissement équivalentes, enparticulier lors d une étude en tiers d octave. Pour aborder leproblème des transmissions latérales, nous avons montré lafaisabilité de la détermination expérimentale des propriétés mécaniqueséquivalentes d un élément de jonction courant entreles planchers et les murs : le sabot métallique. Un modèle mécaniquesimplifié par éléments finis permet ainsi un couplagemécanique entre les solives et les poutres en intégrant les effetslocaux de dissipation présents pour ce type de jonction.In building acoustics, the structure of wooden construction islightweight and sound insulation at low frequency are weakcompared to other construction techniques like concrete. Thework of this thesis is focus on the development of predictivetools for determining the acoustic performance of wooden joistfloors to complete the existing predictive tools available on themarket. The finite element method (FEM) is adapted to solvethis vibro-acoustic problem because behavior at low frequenciesis modal. To save computation time, a mixed resolutionfinite element with Huygens integral formulations and severaloptimizations were implemented. We could note the interest ofthe FEM : we observed that resonances of the coupled systemdrive locally down the value of the TL, which can not be takeninto account by the method of transfer matrices. However, wenote that these two methods provide equivalent average curveshapes of TL s spectrum. To deal with the problem of flankingtransmissions, penalizing the lightweight construction, we experimentalydetermine the mechanical properties of a equivalentjunction element between floors and walls : the wood joisthanger. Through a simplified mechanical model, this numericalfinite element model allows a mechanical coupling between thejoists and beams by incorporating the local effects of dissipationpresent for this type of junction.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

SKI2 mediates degradation of RISC 5'-cleavage fragments and prevents secondary siRNA production from miRNA targets in <i>Arabidopsis</i>

Small regulatory RNAs are fundamental in eukaryotic and prokaryotic gene regulation. In plants, an important element of post-transcriptional control is effected by 20–24 nt microRNAs (miRNAs) and short interfering RNAs (siRNAs) bound to the ARGONAUTE1 (AGO1) protein in an RNA induced silencing complex (RISC). AGO1 may cleave target mRNAs with small RNA complementarity, but the fate of the resulting cleavage fragments remains incompletely understood. Here, we show that SKI2, SKI3 and SKI8, subunits of a cytoplasmic cofactor of the RNA exosome, are required for degradation of RISC 5′, but not 3′-cleavage fragments in Arabidopsis. In the absence of SKI2 activity, many miRNA targets produce siRNAs via the RNA-dependent RNA polymerase 6 (RDR6) pathway. These siRNAs are low-abundant, and map close to the cleavage site. In most cases, siRNAs were produced 5′ to the cleavage site, but several examples of 3′-spreading were also identified. These observations suggest that siRNAs do not simply derive from RDR6 action on stable 5′-cleavage fragments and hence that SKI2 has a direct role in limiting secondary siRNA production in addition to its function in mediating degradation of 5′-cleavage fragments

SKI2 mediates degradation of RISC 5′-cleavage fragments and prevents secondary siRNA production from miRNA targets in Arabidopsis

Small regulatory RNAs are fundamental in eukaryotic and prokaryotic gene regulation. In plants, an important element of post-transcriptional control is effected by 20-24 nt microRNAs (miRNAs) and short interfering RNAs (siRNAs) bound to the ARGONAUTE1 (AGO1) protein in an RNA induced silencing complex (RISC). AGO1 may cleave target mRNAs with small RNA complementarity, but the fate of the resulting cleavage fragments remains incompletely understood. Here, we show that SKI2, SKI3 and SKI8, subunits of a cytoplasmic cofactor of the RNA exosome, are required for degradation of RISC 5′, but not 3′-cleavage fragments in Arabidopsis. In the absence of SKI2 activity, many miRNA targets produce siRNAs via the RNA-dependent RNA polymerase 6 (RDR6) pathway. These siRNAs are low-abundant, and map close to the cleavage site. In most cases, siRNAs were produced 5′ to the cleavage site, but several examples of 3′-spreading were also identified. These observations suggest that siRNAs do not simply derive from RDR6 action on stable 5′-cleavage fragments and hence that SKI2 has a direct role in limiting secondary siRNA production in addition to its function in mediating degradation of 5′-cleavage fragment

Comportement au gel-dégel d'une structure en ciment

Ce travail vise à l'étude du comportement au gel-dégel des matériaux cimentaires. Le model poromécanique développé dans cette optique permet d'étudier l'influence sur la mécanique du couplage entre le changement de phase eau/glace, les transports en milieu poreux, la conduction thermique et le comportement de chacune des phases en présence. Nous pouvons ainsi prédire une pression de pore maximale au voisinage de la surface soumise au gel-dégel pouvant induire un endommagement localisé superficiel. Par la suite, l'influence relative des différents phénomènes physiques responsables de l'endommagement au gel-dégel est étudiée, permettant d'identifier les pressions hydrauliques de Powers comme prépondérantes

Functional characterization of Arabidopsis ARGONAUTE 3 in reproductive tissues

Arabidopsis encodes ten ARGONAUTE (AGO) effectors of RNA silencing, canonically loaded with either 21‐22 nucleotide (nt) long small RNAs (sRNA) to mediate post‐transcriptional‐gene‐silencing (PTGS) or 24nt sRNAs to promote RNA‐directed‐DNA‐methylation. Using full‐locus constructs, we characterized the expression, biochemical properties, and possible modes of action of AGO3. Although AGO3 arose from a recent duplication at the AGO2 locus, their expression patterns differ drastically, with AGO2 being expressed in both male and female gametes whereas AGO3 accumulates in aerial vascular terminations and specifically in chalazal seed integuments. Accordingly, AGO3 down‐regulation alters gene expression in siliques. Similar to AGO2, AGO3 binds sRNAs with a strong 5’‐adenosine bias, but unlike Arabidopsis AGO2, it binds most efficiently 24nt sRNAs. AGO3 immunoprecipitation experiments in siliques revealed that these sRNAs mostly correspond to genes and intergenic regions in a manner reflecting their respective accumulation from their loci‐of‐origin. AGO3 localizes to the cytoplasm and co‐fractionates with polysomes to possibly mediate PTGS via translation inhibition