A representation formula for radially weighted biharmonic functions in the unit disc

Let w : D → (0, ∞) be a radial continuous weight function. We consider the weighted biharmonic equation ∆w −1 ∆u = 0 in D with Dirichlet boundary conditions u = f0 and ∂n u = f1 on T = ∂D. Under some extra conditions on the weight function w, we establish existence and uniqueness of a distributional solution u of this biharmonic Dirichlet problem. Furthermore, we give a representation formula for the solution u. The key to our analysis is a series representation of Almansi type

EMBRACE@Nancay: An Ultra Wide Field of View Prototype for the SKA

A revolution in radio receiving technology is underway with the development of densely packed phased arrays for radio astronomy. This technology can provide an exceptionally large field of view, while at the same time sampling the sky with high angular resolution. Such an instrument, with a field of view of over 100 square degrees, is ideal for performing fast, all-sky, surveys, such as the "intensity mapping" experiment to measure the signature of Baryonic Acoustic Oscillations in the HI mass distribution at cosmological redshifts. The SKA, built with this technology, will be able to do a billion galaxy survey. I will present a very brief introduction to radio interferometry, as well as an overview of the Square Kilometre Array project. This will be followed by a description of the EMBRACE prototype and a discussion of results and future plans.Comment: to appear in proceedings of the INFIERI Summer School INtelligent Signal Processing for FrontIEr Research and Industry, Paris 201

Gas signatures of Herbig Ae/Be disks probed with Herschel SPIRE spectroscopy

Herbig Ae/Be objects, like their lower mass counterparts T Tauri stars, are seen to form a stable circumstellar disk which is initially gas-rich and could ultimately form a planetary system. We present Herschel SPIRE 460-1540 GHz spectra of five targets out of a sample of 13 young disk sources, showing line detections mainly due to warm CO gas.Comment: to be published in proceedings of IAU symposium 299 (Victoria, BC, Canada, June 2013

Molecular gas in high-mass filament WB673

We studied the distribution of dense gas in a filamentary molecular cloud containing several dense clumps. The center of the filament is given by the dense clump WB673. The clumps are high-mass and intermediate-mass star-forming regions. We observed CS(2-1), 13CO(1-0), C18O(1-0) and methanol lines at 96GHz toward WB673 with the Onsala Space Observatory 20-m telescope. We found CS(2-1) emission in the inter-clump medium so the clumps are physically connected and the whole cloud is indeed a filament. Its total mass is $10^4$ M$_{\odot}$ and mass-to-length ratio is 360 M$_{\odot}$pc$^{-1}$ from 13CO(1-0) data. Mass-to-length ratio for the dense gas is $3.4-34$ M$_{\odot}$pc$^{-1}$ from CS(2-1) data. The PV-diagram of the filament is V-shaped. We estimated physical conditions in the molecular gas using methanol lines. Location of the filament on the sky between extended shells suggests that it could be a good example to test theoretical models of formation of the filaments via multiple compression of interstellar gas by supersonic waves

Near-infrared observations of water-ice in OH/IR stars

A search for the near-infrared water-ice absorption band was made in a number of very red OH/IR stars which are known to exhibit the 10um silicate absorption. As a by-product, accurate positions of these highly reddened objects are obtained. We derived a dust mass loss rate for each object by modelling the spectral energy distribution and the gas mass loss rate by solving the equation of motion for the dust drag wind. The derived mass loss rates show a strong correlation with the silicate optical depth as well as that of the water-ice. The stars have a high mass loss rate (> 1.0E-4 Msun/yr) with an average gas-to-dust mass ratio of 110. In objects which show the 3.1um water-ice absorption, the near-IR slope is much steeper than those with no water-ice. Comparison between our calculated mass loss rates and those derived from OH and CO observations indicates that these stars have recently increased their mass loss rates.Comment: 10 pages, 6 figures : accepted for publication in A&

Characterization of a dense aperture array for radio astronomy

EMBRACE@Nancay is a prototype instrument consisting of an array of 4608 densely packed antenna elements creating a fully sampled, unblocked aperture. This technology is proposed for the Square Kilometre Array and has the potential of providing an extremely large field of view making it the ideal survey instrument. We describe the system,calibration procedures, and results from the prototype.Comment: 17 pages, accepted for publication in A&

Modeling Growth and Telomere Dynamics in Saccharomyces Cerevisiae

A general branching process is proposed to model a population of cells of the yeast Saccharomyces cerevisiae following loss of telomerase. Previously published experimental data indicate that a population of telomerase-deficient cells regain exponential growth after a period of slowing due to critical telomere shortening. The explanation for this phenomenon is that some cells engage telomerase-independent pathways to maintain telomeres that allow them to become “survivors.” Our model takes into account random variation in individual cell cycle times, telomere length, finite lifespan of mother cells, and survivorship. We identify and estimate crucial parameters such as the probability of an individual cell becoming a survivor, and compare our model predictions to experimental data

Discovery of Molecular Gas in the Outflow and Tidal Arms around M82

We present the first fully sampled map of 12CO (1-0) emission from M82 covering the entire galaxy. Our map contains a 12 x 15 kpc^2 area. We find that extraplanar CO emission, previously reported at short distances above the galactic plane, extends to heights of up to 6 kpc above the disk. Some of this emission is associated with tidal arms seen in HI, implying either that M82 contained substantial amounts of molecular gas in the outer disk, or that molecular gas formed after the tidal features. CO emission along the direction of the outflow extends to distances of 3 kpc above and below the disk. At this distance, the line is shifted in velocity about 100 km/s, and has the same sense as the galactic outflow from the central starburst. This implies that molecular gas may be entrained into the outflow.Comment: 4 pages, 6 figures. Uses emulateapj5. Accepted by ApJ Letter

Where is the warm H2 ? A search for H2 emission from disks around Herbig Ae/Be stars

Mid-IR emission lines of H2 are useful probes to determine the mass of warm gas present in the surface layers of disks. Numerous observations of Herbig Ae/Be stars (HAeBes) have been performed, but only 2 detections of mid-IR H2 toward HD97048 and AB Aur have been reported. We aim at tracing the warm gas in the disks of 5 HAeBes with gas-rich environments and physical characteristics close to those of AB Aur and HD97048, to discuss whether the detections toward these 2 objects are suggestive of peculiar conditions for the gas. We search for the H2 S(1) emission line at 17.035 \mu\m with VISIR, and complemented by CH molecule observations with UVES. We gather the H2 measurements from the literature to put the new results in context and search for a correlation with some disk properties. None of the 5 VISIR targets shows evidence for H2 emission. From the 3sigma upper limits on the integrated line fluxes we constrain the amount of optically thin warm gas to be less than 1.4 M_Jup in the disk surface layers. There are now 20 HAeBes observed with VISIR and TEXES instruments to search for warm H2, but only two detections (HD97048 and AB Aur) were made so far. We find that the two stars with detected warm H2 show at the same time high 30/13 \mu\m flux ratios and large PAH line fluxes at 8.6 and 11.3 \mu\m compared to the bulk of observed HAeBes and have emission CO lines detected at 4.7 \mu\m. We detect the CH 4300.3A absorption line toward both HD97048 and AB Aur with UVES. The CH to H2 abundance ratios that this would imply if it were to arise from the same component as well as the radial velocity of the CH lines both suggest that CH arises from a surrounding envelope, while the detected H2 would reside in the disk. The two detections of the S(1) line in the disks of HD97048 and AB Aur suggest either peculiar physical conditions or a particular stage of evolution.Comment: accepted for publication in A&A : 10 pages, 6 figure