2-D and 3-D Radiation Transfer Models of High-Mass Star Formation

2-D and 3-D radiation transfer models of forming stars generally produce bluer 1-10 micron colors than 1-D models of the same evolutionary state and envelope mass. Therefore, 1-D models of the shortwave radiation will generally estimate a lower envelope mass and later evolutionary state than multidimensional models. 1-D models are probably reasonable for very young sources, or longwave analysis (wavelengths > 100 microns). In our 3-D models of high-mass stars in clumpy molecular clouds, we find no correlation between the depth of the 10 micron silicate feature and the longwave (> 100 micron) SED (which sets the envelope mass), even when the average optical extinction of the envelope is >100 magnitudes. This is in agreement with the observations of Faison et al. (1998) of several UltraCompact HII (UCHII) regions, suggesting that many of these sources are more evolved than embedded protostars. We have calculated a large grid of 2-D models and find substantial overlap between different evolutionary states in the mid-IR color-color diagrams. We have developed a model fitter to work in conjunction with the grid to analyze large datasets. This grid and fitter will be expanded and tested in 2005 and released to the public in 2006.Comment: 10 pages, 8 figures, to appear in the proceedings of IAU Symp 227, Massive Star Birth: A Crossroads of Astrophysics, (Cesaroni R., Churchwell E., Felli M., Walmsley C. editors

Utilisation d'un «indice de réflexion» pour l'analyse rapide des sédiments lacustres

L'indice de réflexion ou réflectance donne une mesure de la teinte du sédiment entre le blanc (100 %) et le noir (0 %). Sa valeur est directement liée à la teneur en matières organiques.Les relations entre l'indice de réflexion et les teneurs en carbone organique, en azote Kjeldahl et en carbonates sont données pour les sédiments de dix lacs différents.Une étude particulière de prélèvements superficiels et de prélèvements profonds montre qu'une simple mesure de la réflectance donne une valeur approchée de la composition chimique.Thorough studies on many lakes in Franche-Comté, especially chemical and physical investigations concerning sediments, have been carried out for several years. Seventy-one sediment samples have been extracted at different points and depths of ten lakes in Franche-Comté. The upper stratum between 0 and - 2,5 cm were isolated and studied.A comparison of visual observations and results of chemical analysis have shown that the darkest sediments are those which contain the greatest amount of organic matter. This finds its origin in a particularity of Franche-Comté lake sediments, which are often composed of dark black organic matter in different evolutionary states, and clear mineral compounds such as calcium carbonate and detrital particles.Differences in colouration were particularly difficult to determine, so colours were defined by the reflexion factor of the sediment surfaces, after the sediments had been well dried and homogeneized.The reflectance index was measured with a reftectometer, which is generally used for determinations of dark smokes in air pollution. The reflectance index was defined between the values 0 and 100. The value 0 was obtained with a standard black glass and the value 100 with a white filter paper.Comparing reflectance indices and ignition loss has shown that there is an exponential relationship between these two parameters. These relationships were found to exist between the reflectance index and organic carbon, Kjeldahl nitrogen and carbonates.Ignition loss, organic carbon and Kjeldahl nitrogen proportions increase, but, on the contrary, carbonate proportions decrease when the reflexion index increases.The values calculated and observed were then compared and generally the difference does not appear to be too great. Once, relationships have been established, it becomes possible to use them, after measuring reflexion indices, to obtain quickly and easily a good approximation of the composition.Special relationships may also be calculated for an individual lake, as shown for St-Point Lake. If one mineral constituent prevails in the composition, it is possible to obtain a good estimation of this component.For this lake twenty-eight sediment samples were extracted and for each sample three strata were separated. The reflectance index was again defined between the values 0 and 100, but the value 100 was now obtained by using a flat calcium carbonate surface, as the principal mineral part of St-Point Lake consists of calcium carbonate.Recent results obtained from two lake sediments of the Massif Central indicate that such relationships also exist for these lakes and that this method of estimating the chemical composition can be generalised.The calculated composition may often be sufficient to estimate values required for others studies on the same lakes, especially biological studies, thus avoiding laborious and extensive chemical determinations

Influence of coating on the thermal resistance of a Ni-Based superalloy

In this paper, the influence of M-CrAlY polycrystalline coating on the thermal fatigue behavior of a Nickel-base superalloy has been investigated. A special device using a rotating bending machine and two thermal sources has been used to perform thermo-mechanical tests. The two thermal sources have been set to obtain temperature variations between 750 and 1120 °C in the central part of the specimens, with a frequency of 0.1 Hz. The results showed a deleterious effect of the coating on the fatigue resistance. Numerical simulations have been carried out on SAMCEF to determine the thermo-mechanical field of the so-tested specimens. Calculated thermo-mechanical cycles of critical sites are associated with microstructure evolution and damage by cracking observed on the specimens. Damage mechanisms related to the presence of coating are discussed

Endosymbiosis morphological reorganization during metamorphosis diverges in weevils

Virtually all animals associate with beneficial symbiotic bacteria. Whether and how these associations are modulated across a host’s lifecycle is an important question in disentangling animal-bacteria interactions. We recently reported a case of complete morphological reorganization of symbiosis during metamorphosis of the cereal weevil, Sitophilus oryzae. In this model, the bacteriome, a specialized organ that houses the intracellular bacterium Sodalis pierantonius, undergoes a two-phase remodeling program synchronously driven by host and endosymbiont, resulting in a localization shift and the formation of multiple new bacteriomes. Here, we provide comparative data in a closely-related coleopteran, the red palm weevil Rhynchophorus ferrugineus, which is associated with the ancestral endosymbiont Nardonella. Using cell imaging experiments, we show that the red pal weevil bacteriome remains unchanged during metamorphosis, hence contrasting with what we reported in the cereal weevil S. oryzae. These findings highlight the complexity and divergence of host-symbiont interactions and their intertwining with host development, even in closely-related species. Abbreviations: DAPI: 4′,6-diamidino-2-phenylindole; FISH: Fluorescence in situ hybridization; T3SS: Type III secretion system

Detection of x-rays from galaxy groups associated with the gravitationally lensed systems PG 1115+080 and B1422+231

Gravitational lenses that produce multiple images of background quasars can be an invaluable cosmological tool. Deriving cosmological parameters, however, requires modeling the potential of the lens itself. It has been estimated that up to a quarter of lensing galaxies are associated with a group or cluster which perturbs the gravitational potential. Detection of X-ray emission from the group or cluster can be used to better model the lens. We report on the first detection in X-rays of the group associated with the lensing system PG 1115+080 and the first X-ray image of the group associated with the system B1422+231. We find a temperature and rest-frame luminosity of 0.8 +/- 0.1 keV and 7 +/- 2 x 10^{42} ergs/s for PG 1115+080 and 1.0 +infty/-0.3 keV and 8 +/- 3 x 10^{42} ergs/s for B1422+231. We compare the spatial and spectral characteristics of the X-ray emission to the properties of the group galaxies, to lens models, and to the general properties of groups at lower redshift.Comment: Accepted for publication in ApJ. 17 pages, 5 figures. Minor changes to tex

Structural and magnetic properties of E-Fe_{1-x}Co_xSi thin films deposited via pulsed laser deposition

We report pulsed laser deposition synthesis and characterization of polycrystalline Fe1-xCox Si thin films on Si (111). X-ray diffraction, transmission electron, and atomic force microscopies reveal films to be dense, very smooth, and single phase with a cubic B20 crystal structure. Ferromagnetism with significant magnetic hysteresis is found for all films including nominally pure FeSi films in contrast to the very weak paramagnetism of bulk FeSi. For Fe1-xCoxSi this signifies a change from helimagnetism in bulk, to ferromagnetism in thin films. These ferromagnetic thin films are promising as a magnetic-silicide/silicon system for polarized current production, manipulation, and detection.Comment: 12 pages, 4 figures accepted in the Applied Physics Letter

Speeding up Simplification of Polygonal Curves using Nested Approximations

We develop a multiresolution approach to the problem of polygonal curve approximation. We show theoretically and experimentally that, if the simplification algorithm A used between any two successive levels of resolution satisfies some conditions, the multiresolution algorithm MR will have a complexity lower than the complexity of A. In particular, we show that if A has a O(N2/K) complexity (the complexity of a reduced search dynamic solution approach), where N and K are respectively the initial and the final number of segments, the complexity of MR is in O(N).We experimentally compare the outcomes of MR with those of the optimal "full search" dynamic programming solution and of classical merge and split approaches. The experimental evaluations confirm the theoretical derivations and show that the proposed approach evaluated on 2D coastal maps either shows a lower complexity or provides polygonal approximations closer to the initial curves.Comment: 12 pages + figure