New materials for high temperature turbines; ONERA's DS composites confronted with blade problems

ONERA's refractory DS composites were cited as materials required for use in advanced aircraft turbines, operating at high temperatures. These materials were found to be reliable in the construction of turbine blades. Requirements for a blade material in aircraft turbines operating at higher temperatures were compared with the actual performance as found in COTAC DS composite testing. The structure and properties of the more fully developed 74 and 741 types were specified. High temperature structural stability, impact of thermal and mechanical fatigue, oxidation resistance and coating capability were thoroughly evaluated. The problem of cooling passages in DS eutectic blades is also outlined

Recovery of surface reflectance spectra and evaluation of the optical depth of aerosols in the near-IR using a Monte-Carlo approach: Application to the OMEGA observations of high latitude regions of Mars

We present a model of radiative transfer through atmospheric particles based on Monte Carlo methods. This model can be used to analyze and remove the contribution of aerosols in remote sensing observations. We have developed a method to quantify the contribution of atmospheric dust in near-IR spectra of the Martian surface obtained by the OMEGA imaging spectrometer on board Mars Express. Using observations in the nadir pointing mode with significant differences in solar incidence angles, we can infer the optical depth of atmospheric dust, and we can retrieve the surface reflectance spectra free of aerosol contribution. Martian airborne dust properties are discussed and constrained from previous studies and OMEGA data. We have tested our method on a region at 90{\deg}E and 77{\deg}N extensively covered by OMEGA, where significant variations of the albedo of ice patches in the visible have been reported. The consistency between reflectance spectra of ice-covered and ice-free regions recovered at different incidence angles validates our approach. The optical depth of aerosols varies by a factor 3 in this region during the summer of Martian year 27. The observed brightening of ice patches does not result from frost deposition but from a decrease in the dust contamination of surface ice and (to a lower extent) from a decrease in the optical thickness of atmospheric dust. Our Monte Carlo-based model can be applied to recover the spectral reflectance characteristics of the surface from OMEGA spectral imaging data when the optical thickness of aerosols can be evaluated. It could prove useful for processing image cubes from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (MRO)

Water ice in the dark dune spots of Richardson crater on Mars

In this study we assess the presence, nature and properties of ices - in particular water ice - that occur within these spots using HIRISE and CRISM observations, as well as the LMD Global Climate Model. Our studies focus on Richardson crater (72{\deg}S, 179{\deg}E) and cover southern spring and summer (LS 175{\deg} - 17 341{\deg}). Three units have been identified of these spots: dark core, gray ring and bright halo. Each unit show characteristic changes as the season progress. In winter, the whole area is covered by CO2 ice with H2O ice contamination. Dark spots form during late winter and early spring. During spring, the dark spots are located in a 10 cm thick depression compared to the surrounding bright ice-rich layer. They are spectrally characterized by weak CO2 ice signatures that probably result from spatial mixing of CO2 ice rich and ice free regions within pixels, and from mixing of surface signatures due to aerosols scattering. The bright halo shaped by winds shows stronger CO2 absorptions than the average ice covered terrain, which is consistent with a formation process involving CO2 re-condensation. According to spectral, morphological and modeling considerations, the gray ring is composed of a thin layer of a few tens of {\mu}m of water ice. Two sources/processes could participate to the enrichment of water ice in the gray ring unit: (i) water ice condensation at the surface in early fall (prior to the condensation of a CO2 rich winter layer) or during winter time (due to cold trapping of the CO2 layer); (ii) ejection of dust grains surrounded by water ice by the geyser activity responsible for the dark spot. In any case, water ice remains longer in the gray ring unit after the complete sublimation of the CO2. Finally, we also looked for liquid water in the near-IR CRISM spectra using linear unmixing modeling but found no conclusive evidence for it

Composition of Syrtis Major volcanic plateau

Syrtis Major, a low-relief volcanic shield centered near 295 degrees 10 degrees N, is an old, well-preserved and exposed volcanic region on Mars which formed at the end of the heavy bombardment period. The composition of these volcanic materials has importance for understanding the thermal and chemical history of Mars. Imaging spectrometer data of the Syrtis Major volcanic plateau are used in this analysis to identify major compositional components. First and second order even channel reflectance spectra between 0.77 and 2.55 microns from four broad classes of materials on Syrtis Major are given. For the volcanic materials, there are three primary classes characterized by albedo, slope, and shape of the 10 micron band. To emphasize the latter, straight line continua were removed from each spectral segment and replotted in another figure. Each spectrum shows a band minima near 0.96 microns and 2.15 microns indicative of pyroxene mineral absorptions. Comparison of these band minima with studies of pyroxene reflectance spectra suggests that the pyroxenes in the volcanics of Syrtis Major are high calcium pyroxene with a Ca/(Mg+Fe+Ca) ratio of 0.2 to 0.3. The most likely pyroxene is an augite

Near-tropical subsurface ice on Mars

Near-surface perennial water ice on Mars has been previously inferred down to latitudes of about 45{\deg} and could result from either water vapor diffusion through the regolith under current conditions or previous ice ages precipitations. In this paper we show that at latitudes as low as 25{\deg} in the southern hemisphere buried water ice in the shallow (< 1 m) subsurface is required to explain the observed surface distribution of seasonal CO2 frost on pole facing slopes. This result shows that possible remnants of the last ice age, as well as water that will be needed for the future exploration of Mars, are accessible significantly closer to the equator than previously thought, where mild conditions for both robotic and human exploration lie

Léger comme le faon, fort comme un lion. Nouvelles considérations sur « La compétition des poètes » : la mise en abyme du poète dans le troisième conte (maḥberet) du Sefer ha‑meshalim de Yaakov ben Éléazar de Tolède

L’objet de cette étude est l’analyse du statut singulier du poète dans le troisième conte (maḥberet) du Sefer ha‑meshalim composé au xiiie siècle par Yaakov ben Éléazar. Elle se fonde sur l’examen de la frontière, parfois très mince, entre la réalité et la fiction. Il s’agit d’une compétition entre Lemuel, narrateur et protagoniste du conte mais aussi l’alter ego de Yaakov, l’auteur « historique », et le poète adverse. L’enjeu est d’améliorer un vers de la poésie de Yemima, le personnage d’une poétesse présent dans un autre conte. Le défi à relever est de composer un vers sur le même sujet avec autant d’images, puis de poursuivre le concours en augmentant le nombre de métaphores. On découvre à travers ce débat une représentation du poète, pris entre l’angoisse de l’échec et la confiance dans son talent, désireux d’être reconnu du public. L’analyse du fonctionnement de ce dispositif repose sur l’examen de la mise en scène de la compétition, des noms et prénoms donnés aux personnages, des métaphores choisies et donc de la virtuosité technique présente à chaque étape, ainsi que du statut de chacune des figures, tout particulièrement de celle de la poétesse.The purpose of this paper is to analyze the status of the poet in the third tale (maḥberet) of Sefer ha-Meshalim, by Yaakov ben Eleazar, written in the thirteenth century. This examination focuses on the very thin line between reality and fiction, as is reflected in the tale. The tale describes a competition between Lemuel (the narrator and protagonist of the tale but also the alter‑ego of Yaakov, the “historical” author) and the poet’s rival. Their challenge is to improve a verse written by Yemima (a poetess, the protagonist of another tale) by composing a verse on the same subject with the same number of images, and then to continue the contest by increasing the number of metaphors. Through this competition, the readers are introduced to a representation of the poet, caught between the anguish of failure and his confidence in his talent, eager to be recognized by the public. The article analyses these features based upon the staging of the competition, the names given to the characters, the interpretation of selected metaphors and the technical virtuosity demonstrated at each stage, as well as the status of each of the figures, especially that of the poetess.המאמר מנתח את מעמדו של המשורר במחברת השלישית של ספר המשלים ליעקב בן אלעזר, שנכתב במאה השלוש-עשרה. בחינה זו מתמקדת בקו הדק שבין המציאות לבדיה, כפי שהיא משתקפת ביצירה. המחברת מתארת תחרות בין למואל (המספר והגיבור, אך במקביל גם האלטר-אגו של יעקב, הסופר «ההיסטורי») לבין יריבו של המשורר. השניים מתחרים על  שורת שיר של המשוררת ימימה (גיבורת העלילה ממחברת אחרת) שלדעתם יש לשפרה, וזאת על-ידי כתיבת שורה חדשה, טובה יותר, שתכלול כמות זהה של דימויים. בשלבי התחרות השונים, על המשוררים להגדיל בכל פעם את כמות המטפורות בשורה הנדונה.  באמצעות ריב משוררים, נחשפים הקוראים לייצוגים השונים של דמות המשורר, הלכוד בין הפחד מכישלון לבין הביטחון העצמי בכישרונו, ובצורך שלו בהכרת הציבור. המאמר בוחן ומנתח את כל שלבי התחרות, את הקשר בין שמות הדמויות ותפקידיהן במחברת, מבחר מהדימויים השיריים המוצגים בכל שלב, תוך התייחסות לוירטואוזיות הפואטית של למואל

Scènes érotiques, écriture courtoise. La symbolique naturelle dansles Lais de Marie de France

Les Lais de Marie de France présentent un jeu subtil entre l’impossibilité de décrire l’acte charnel et l’utilisation d’un langage travaillé qui y fait allusion suivant les codes de la courtoisie. S’allonger l’un près de l’autre dans un lit, rire, jouer et parler, le pinceau de Marie de France n’ira pas plus loin. Mais l’intensité du désir sexuel sera dénotée par d’autres éléments symboliques appartenant au monde naturel (arbres, plantes, oiseaux). Les amants, captifs d’amours interdites et abandonnés à leurs plaisirs sensuels, risquent parfois la mort mais, dans une dialectique entre l’amour et la mort, leurs lits funéraires, posés l’un à côté de l’autre, rétablissent mythiquement l’amour par la promesse d’une fusion éternelle.Marie de France’s Lais presents a subtle play between the impossibility of describing the carnal act and the use of a studied language, which alludes to it, according to courtly codes. Lying down next to one another in a bed, laughing, playing, and talking, Marie de France’s paintbrush does not proceed any further. But the intensity of sexual desire is conveyed through symbolic elements belonging to the natural world (trees, plants, birds). The lovers during their lifetime – prisoners of forbidden loves and abandoned to their sensual pleasures – risk death, but, thanks to the dialectic between love and death, their funeral beds, placed side by side, restore love mythically through the promise of an eternal fusion