Etude par spectrométrie Mössbauer d'alliages Fe-Si-B amorphes

Amorphous Fe100-x-ySi yBx alloys have been studied by Môssbauer Spectroscopy. The fitting methods and some possible origins of the asymmetric broadenings of the peaks are discussed. A comparison of the hyperfine field distributions in alloys with and without silicon suggests that iron and silicon are located in similar sites (for the studied y values, y ≤ 9) while boron occupies interstitial sites with ≃ 9 iron atoms nearest neighbours. Crystallisation steps and mechanisms have been studied in Fe82Si3B15 and Fe76Si9B15 alloys. They differ from those found in Fe-B alloys because metastable borides are not observed.Des alliages amorphes Fe100-x- ySiyBx ont été étudiés par spectrométrie Môssbauer. Les méthodes de calcul et les origines possibles des dissymétries des spectres sont discutées. La comparaison des distributions de champ hyperfin des alliages avec et sans silicium suggère que le silicium et le fer occupent des sites semblables (pour les valeurs de y étudiées, y ≤ 9) alors que le bore occupe une position interstitielle avec ≃ 9 atomes de fer proches voisins. Les alliages Fe-B sont fortement stabilisés par le silicium. Les étapes et les mécanismes de cristallisation d'alliages Fe82Si3B 15 et Fe76Si9B15 ont été précisés. Ils diffèrent de ceux observés dans les alliages Fe-B car il ne se forme pas de borures métastables

Topological correlations in soap froths

Correlation in two-dimensional soap froth is analysed with an effective potential for the first time. Cells with equal number of sides repel (with linear correlation) while cells with different number of sides attract (with NON-bilinear) for nearest neighbours, which cannot be explained by the maximum entropy argument. Also, the analysis indicates that froth is correlated up to the third shell neighbours at least, contradicting the conventional ideas that froth is not strongly correlated.Comment: 10 Pages LaTeX, 6 Postscript figure

Debye temperature of disordered bcc-Fe-Cr alloys

Debye temperature, TD, of Fe100-xCrx disordered alloys with 0<x<99.9 was determined from the temperature dependence of the centre shift of 57Fe Mossbauer spectra recorded in the temperature range of 80-300K. Its compositional dependence shows an interesting non-monotonous behaviour. For 0<x<~45 as well as for ~75<x<~95 the Debye temperature is enhanced relative to its value of a metallic iron, and at x=~3 there is a local maximum having a relative height of ~12% compared to a pure iron. For ~45~95 the Debye temperature is smaller than the one for the metallic iron, with a local minimum at x=~55 at which the relative decrease of TD amounts to ~12%. The first maximum coincides quite well with that found for the spin-waves stiffness coefficient, D0, while the pretty steep decrease observed for x>~95 which is indicative of a decoupling of the probe Fe atoms from the underlying chromium matrix is likely related to the spin-density waves which constitute the magnetic structure of chromium in that interval of composition. The harmonic force constant calculated from the Debye temperature of the least Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of a pure chromium.Comment: 15 pages, 7 figures, 26 reference

All-dielectric photonic metamaterials operating beyond the homogenization regime

Photonic metamaterials made of graded photonic crystals operating near the bandgap frequency region are proposed for field manipulation around l=1.5μm. Proof-of-concept structures have been studied using Hamiltonian optics and FDTD simulation, fabricated, and characterized using farfield optical measurements. Experimental results are in good agreement with predictions, showing the interest of graded photonic crystals as an (ultra-low loss) alternative solution to the use of metamaterials combining dielectric and metallic materials with sub-wavelength unit cells

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. VII. Ophiuchus Observed with MIPS

We present maps of 14.4 deg^2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high-quality maps depict both numerous point sources and extended dust emission within the star-forming and non–star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 μm and 81 sources at 70 μm at the 10 σ level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus color-magnitude diagrams, as compared to 24 μm detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all those with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates

DEFECTS IN Fe7C3 TYPE CARBIDE FORMED DURING THE CRYSTALLIZATION OF AMORPHOUS HIGH CARBON ALLOYS AND THEIR RELATION WITH THE AMORPHOUS STATE

Les carbures de type M7C3 ont une structure orthorhombique (R. FRUCHART et al.). Cette structure peut être masquée par des défauts qui sont propres au mode de préparation. Dans le cas du carbure Fe7C3 formé lors de la recristallisation d'un alliage amorphe Fe75C25 préparé par sputtering, la taille des défauts (inférieure à 100 Å) est du même ordre de grandeur que celle des domaines allongés suivant certaines directions. Pour les carbures primaires présents dans les fontes blanches et les aciers au carbone, les domaines sont environ cent fois plus grands. Ces résultats suggèrent que la croissance des domaines est bloquée pendant la cristallisation de l'amorphe. Un très grand nombre de germes peut déjà exister dans l'état amorphe ou se former très rapidement. L'apparition de Fe7C3 est discutée dans le cadre du modèle de GASKELL.M7C3 type carbides have an orthorhombic structure, as proposed by R. FRUCHART et al. This structure may be hidden by defects which are typical of the preparation method. In Fe7C3 formed by crystallization of sputter-deposited amorphous Fe75C25 alloys, the defects are only consistent with elongated domains whose size is less than [MATH] 100 Å, the order of the defect size. In primary M7C3 carbides, present in white cast-iron and chromium steels, domains are about 100 times larger than in the latter case. Both results suggest that domain growth is impeded during the crystallization of amorphous Fe75C25. Nuclei may thus already exist in or be easily formed with a large density from the amorphous state. The formation of Fe7C3 is discussed within the frame of the GASKELL model

[Comprehensive geriatric assessment and complications after resection for lung cancer].

International audienceBACKGROUND: With the expanding elderly population comes an increasing prevalence of lung cancer. Surgery remains the mainstay of treatment for early-stage non-small cell lung cancer. Standard treatment strategies have mostly been validated in young adults. Curative resection is feasible in older patients but careful preoperative evaluation is needed, taking into account the physiologic changes that occur with ageing. A tool used by geriatricians, a comprehensive geriatric assessment, can contribute to our understanding of physiologic age through an evaluation of prognostic factors that are independent predictors of morbidity. PATIENTS: Study 08-05 of the French Lung Oncology Group is a prospective, national, multicentre study. All patients aged over 70 years with a suspicion of lung cancer, receiving curative lung resection, will be included. After inclusion, a comprehensive geriatric assessment (evaluating such diverse areas as functional status, nutritional status, cognition, psychological functioning, and social support) will be performed. The primary outcome is the value of the comprehensive geriatric assessment in predicting the risk of post-operative complications after lung resection for cancer. Post-operative morbidity at 30-days after pulmonary resection will be graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. The follow-up period is one year. EXPECTED RESULTS: This global assessment may help to initiate specific care plans for the management of lung cancer in the elderly