Aberrations in shift-invariant linear optical imaging systems using partially coherent fields

Here the role and influence of aberrations in optical imaging systems employing partially coherent complex scalar fields is studied. Imaging systems require aberrations to yield contrast in the output image. For linear shift-invariant optical systems, we develop an expression for the output cross-spectral density under the space-frequency formulation of statistically stationary partially coherentfields. We also develop expressions for the output cross{spectral density and associated spectral density for weak-phase, weak-phase-amplitude, and single-material objects in one transverse spatial dimension

Description des captures au filet tramail sur le cours supérieur du Sinnamary (Guyane Française)

Le Sinnamary est un fleuve de Guyane Française, de moyenne importance (6565 km2). Il peut être divisé en trois zones : l'estuaire, le cours inférieur et le cours supérieur. Une série de pêches expérimentales a été réalisée dans le cours supérieur de ce fleuve, à l'aide de filets tramails de maille comprise entre 10 et 65 mm. La sélectivité des filets utilisés s'est avérée très forte, et la composition des captures fort différente selon la taille de la maille. Quatre espèces représentent 68% des prises #(Leporinus friderici, Curimata cyprinoides, Triporteus rotundadus, Myleus ternetzy)$ et l'analyse des captures montre que le nombre d'individus capturés par unité d'effort est supérieur en saison des pluies. L'origine de ces variations saisonnières de captures est discutée. (Résumé d'auteur

Zonation longitudinale du peuplement ichtyque du fleuve Sinnamary (Guyane Française)

Le Sinnamary est un fleuve de moyenne importance (bassin de 6565 km2) de la Guyane Française. A l'aide de divers critères d'ordre géologique, pédologique, hydrologique et phytosociologique, nous avons pu diviser le fleuve en 3 zones distinctes : la partie haute, le cours inférieur et l'estuaire. Un important effort d'échantillonnage, réparti dans le temps et mettant en jeu plusieurs techniques de pêche, a été consenti dans chacune de ces 3 zones. A l'aide de ce travail, le peuplement ichtyologique a pu être décrit : il s'avère très différent, tant du point de vue de la richesse spécifique, que dans sa composition, entre les différentes zones. (Résumé d'auteur

SiO collimated outflows driven by high-mass YSOs in G24.78+0.08

We imaged the molecular outflows towards the cluster of high-mass young stellar objects G24.78+0.08 at high-angular resolution using SiO emission, which is considered the classical tracer of protostellar jets. We performed SiO observations with the VLA interferometer in the J = 1-0 v=0 transition and with the SMA array in the 5-4 transition. A complementary IRAM 30-m single-dish survey in the (2-1), (3-2), (5-4), and (6-5) SiO lines was also carried out. Two collimated SiO high-velocity outflows driven by the A2 and C millimeter continuum massive cores have been imaged. On the other hand, we detected no SiO outflow driven by the young stellar objects in more evolved evolutionary phases that are associated with ultracompact (B) or hypercompact (A1) HII regions. The LVG analysis reveals high-density gas (10^3-10^4 cm-3), with well constrained SiO column densities (0.5-1 10^15 cm-2). The driving source of the A2 outflow is associated with typical hot core tracers such as methyl formate, vinyl cyanide, cyanoacetilene, and acetone. The driving source of the main SiO outflow in G24 has an estimated luminosity of a few 10^4 Lsun (typical of a late O-type star) and is embedded in the 1.3 mm continuum core A2, which in turn is located at the centre of a hot core that rotates on a plane perpendicular to the outflow main axis. The present SiO images support a scenario similar to the low-mass case for massive star formation, where jets that are clearly traced by SiO emission, create outflows of swept-up ambient gas usually traced by CO.Comment: Astronomy & Astrophysics, in pres

Search for massive protostar candidates in the southern hemisphere: II. Dust continuum emission

In an ongoing effort to identify and study high-mass protostellar candidates we have observed in various tracers a sample of 235 sources selected from the IRAS Point Source Catalog, mostly with dec < -30 deg, with the SEST antenna at millimeter wavelengths. The sample contains 142 Low sources and 93 High, which are believed to be in different evolutionary stages. Both sub-samples have been studied in detail by comparing their physical properties and morphologies. Massive dust clumps have been detected in all but 8 regions, with usually more than one clump per region. The dust emission shows a variety of complex morphologies, sometimes with multiple clumps forming filaments or clusters. The mean clump has a linear size of ~0.5 pc, a mass of ~320 Msolar for a dust temperature Td=30 K, an H_2 density of 9.5E5 cm-3, and a surface density of 0.4 g cm-2. The median values are 0.4 pc, 102 Msolar, 4E4 cm-3, and 0.14 g cm-2, respectively. The mean value of the luminosity-to-mass ratio, L/M ~99 Lsolar/Msolar, suggests that the sources are in a young, pre-ultracompact HII phase. We have compared the millimeter continuum maps with images of the mid-IR MSX emission, and have discovered 95 massive millimeter clumps non-MSX emitters, either diffuse or point-like, that are potential prestellar or precluster cores. The physical properties of these clumps are similar to those of the others, apart from the mass that is ~3 times lower than for clumps with MSX counterpart. Such a difference could be due to the potential prestellar clumps having a lower dust temperature. The mass spectrum of the clumps with masses above M ~100 Msolar is best fitted with a power-law dN/dM proportional to M-alpha with alpha=2.1, consistent with the Salpeter (1955) stellar IMF, with alpha=2.35.Comment: 83 pages, 10 figures, 3 tables. Accepted for publication by A&A. The full paper, including Fig.2 with the maps of all the individual regions, complete Tables 1 and 2 can be found at http://www.arcetri.astro.it/~starform/publ2005.ht

The AgResults Nigeria Aflasafe TM Challenge Project: 2019 Annual Report

This report documents the key activities that were carried under the AgResults Aflasafe Pilot Project during the 2018/ 2019 maize-growing season on the verification process to trigger premium payments for successfully harvested and aggregated Aflasafe™-treated maize