Characterization of mesostructure of natural rubber

To study NR mesostructure (macromolecular structure + aggregates or gels) (Figure 1), the NR sample is placed in a good solvent of polyisoprene (cyclohexane, toluene or tetrahydrofuran). In addition to a soluble fraction, there is always an insoluble fraction called macrogel (Figure 1) or gel depending on the authors [1-4]. The gel fraction of NR not only consists of an insoluble fraction or macrogel, but also includes a fair quantity of microaggregates or microgels (sphere-like or core-shell structure) distributed in the soluble fraction with the polyisoprene macromolecules (random coil structure) (Figure 1) [5]. The gel in NR formed because of associations between poly(cis-1,4-isoprene) chains due to interactions with non-isoprene compounds (proteins [6-7] and lipids [8]). The characterization of NR mesostructure by separative methods coupled to a multiangular light scattering (MALS) detector is presented. The separative methods used were size exclusion chromatography (SEC) [5,9] and asymmetrical field field-flow fractionation (AsFlFFF) [10]. These two techniques offer the opportunity to fully characterize NR mesostructure (average molar masses, size, microaggregates, conformation, and gel contents). Two examples of AsFlFFF-MALS use are presented: (i) characterization of NR mesostructure from different Hevea brasiliensis genotypes, (ii) characterization of the dynamic structuring of NR. A focus is on microaggregates with sizes smaller than 1 μm (Gel<1μ). They were purified by SEC and analyzed by TEM [11]. The different changes in the microaggregate structure after mastication (thermal or mechanical) were also studied [12]. Lastly, the relation with the protein content and crosslink density of the macrogel [13] is presented. (Résumé d'auteur

IMMERSION ET ENVIRONNEMENTS NUMÉRIQUES : UNE APPROCHE MÉTHODOLOGIQUE PAR L'EXPÉRIENCE VÉCUE

International audience— L'approche théorique et méthodologique développée dans ce texte a pour objectif d'analyser ce qui se joue dans les perceptions et les interactions de sujets qui utilisent des environnements numériques dits immersifs. Après avoir présenté ces environnements et le contexte de la recherche, il problématise la relation du corps des sujets à l'espace physique et l'espace numérique. Elle interroge le rapport de ces sujets à la technique. Nous proposons de caractériser ce rapport par une expérience vécue qui joue sur le sensoriel et l'imaginaire des sujets. Il s'agit ensuite de mobiliser une méthodologie originale pour analyser les usages de ces environnements. L'approche énactive est utilisée pour saisir ce qui se joue au niveau des perceptions et des interactions dans ces expériences. Associée à une approche interactionniste et sémio-pragmatique, cette recherche interroge aussi les publics, les contextes et les modalités sociales de ces expériences vécues par les sujets. Par la conjugaison de ces approches, la contribution tente d'identifier les éléments qui permettraient de clarifier, sur le plan méthodologique, le rapport des sujets à leur environnement numérique, et notamment sur ce qui pourrait relever dans cette relation, d'un couplage fort ou, au contraire, d'une opposition à celui-ci

Ecole, memoire et identite nationale en France: quand les minorites questionnent le pacte republicain

La nécessité d’ "enseigner la Nation" dans l ’un des rares pays, la France, où léducation est nationale renvoie à une histoire dans laquelle l’Ecole moderne est d’abord "affaire d’Etat" depuis plus d’un siècle, tout en revendiquant depuis la seconde de modernité sa neutralité politique, par un curieux paradoxe au coeur méme de notre histoireyesBelgorod State Universit

SEC-MALS characterization of natural rubber: Study of phenomena behind the abnormal elution profile

Natura/ and synthetic poly(cis-1,4-isoprene) were characterized by size exclusion chromatography coupled with an online multiangle light scattering detector (SEC-MALS) (Fig. 1). Different from SEC classic method, the absolute molar masses are directly determined according to the variation of scattered light intensities with detecting angles and by using Zimm plot method for zero-angle extrapolation. This technique allows us to obtain elution profiles of rubber samples. (Texte intégral

A Physically-Motivated Photometric Calibration of M Dwarf Metallicity

The location of M dwarfs in the V-K_s--M_Ks color-magnitude diagram (CMD) has been shown to correlate with metallicity. We demonstrate that previous empirical photometric calibrations of M dwarf metallicity exploiting this correlation systematically underestimate or overestimate metallicity at the extremes of their range. We improve upon previous calibrations in three ways. We use both a volume-limited and kinematically-matched sample of F and G dwarfs from the Geneva-Copehnagen Survey (GCS) to infer the mean metallicity of M dwarfs in the Solar Neighborhood, we use theoretical models of M dwarf interiors and atmospheres to determine the effect of metallicity on M dwarfs in the V-K_s--M_Ks CMD, and we base our final calibration purely on high-resolution spectroscopy of FGK primaries with M dwarf companions. As a result, we explain an order of magnitude more of the variance in the calibration sample than previous photometric calibrations. We non-parametrically quantify the significance of the observation that M dwarfs that host exoplanets are preferentially in a region of the V-K_s--M_Ks plane populated by metal-rich M dwarfs. We find that the probability p that planet-hosting M dwarfs are distributed across the V-K_s--M_Ks CMD in the same way as field M dwarfs is p = 0.06 +/- 0.008. Interestingly, the subsample of M dwarfs that host Neptune and sub-Neptune mass planets may also be preferentially located in the region of the V-K_s--M_Ks plane populated by high-metallicity M dwarfs. The probability of this occurrence by chance is p = 0.40 +/- 0.02, and this observation hints that low-mass planets may be more likely to be found around metal-rich M dwarfs. An increased rate of low-mass planet occurrence around metal-rich M dwarfs would be a natural consequence of the core-accretion model of planet formation. (abridged)Comment: 10 pages, 4 figures, and 1 table in A&A format; accepted for publication in A&

Closing the loop, expanding the circle: Educational outreach for institutional food waste on small farms

This project increased the awareness of summer camp visitors about alternatives to using public landfill facilities for disposing of food waste

Prospects for near-infrared characterisation of hot Jupiters with VSI

In this paper, we study the feasibility of obtaining near-infrared spectra of bright extrasolar planets with the 2nd generation VLTI Spectro-Imager instrument (VSI), which has the required angular resolution to resolve nearby hot Extrasolar Giant Planets (EGPs) from their host stars. Taking into account fundamental noises, we simulate closure phase measurements of several extrasolar systems using four 8-m telescopes at the VLT and a low spectral resolution (R = 100). Synthetic planetary spectra from T. Barman are used as an input. Standard chi2-fitting methods are then used to reconstruct planetary spectra from the simulated data. These simulations show that low-resolution spectra in the H and K bands can be retrieved with a good fidelity for half a dozen targets in a reasonable observing time (about 10 hours, spread over a few nights). Such observations would strongly constrain the planetary temperature and albedo, the energy redistribution mechanisms, as well as the chemical composition of their atmospheres. Systematic errors, not included in our simulations, could be a serious limitation to these performance estimations. The use of integrated optics is however expected to provide the required instrumental stability (around 10^-4 on the closure phase) to enable the first thorough characterisation of extrasolar planetary emission spectra in the near-infrared.Comment: 10 pages, 8 figures, Proc. SPIE conference 7013 "Optical and Infrared Interferometry" (Marseille 2008