Magnification as a Tool in Weak Lensing

Weak lensing surveys exploit measurements of galaxy ellipticities. These measurements are subject to errors which degrade the cosmological information that can be extracted from the surveys. Here we propose a way of using the galaxy data themselves to calibrate the measurement errors. In particular, the cosmic shear field, which causes the galaxies to appear elliptical, also changes their sizes and fluxes. Information about the sizes and fluxes of the galaxies can be added to the shape information to obtain more robust information about the cosmic shear field. The net result will be tighter constraints on cosmological parameters such as those which describe dark energy.Comment: 4 pages, 2 figure

A deep, wide-field search for substellar members in NGC 2264

We report the first results of our ongoing campaign to discover the first brown dwarfs (BD) in NGC 2264, a young (3 Myr), populous star forming region for which our optical studies have revealed a very high density of potential candidates - 236 in $<$ 1 deg$^2$ - from the substellar limit down to at least $\sim$ 20 M$_{\rm Jup}$ for zero reddening. Candidate BD were first selected using wide field ($I,z$) band imaging with CFH12K, by reference to current theoretical isochrones. Subsequently, 79 (33%) of the $I,z$ sample were found to have near-infrared 2MASS photometry ($JHK_s$ $\pm$ 0.3 mag. or better), yielding dereddened magnitudes and allowing further investigation by comparison with the location of NextGen and DUSTY isochrones in colour-colour and colour-magnitude diagrams involving various combinations of $I$,$J$,$H$ and $K_s$. We discuss the status and potential substellarity of a number of relatively unreddened (A$_{\rm v}$ $<$ 5) likely low-mass members in our sample, but in spite of the depth of our observations in $I,z$, we are as yet unable to unambiguously identify substellar candidates using only 2MASS data. Nevertheless, there are excellent arguments for considering two faint (observed $I$ $\sim$ 18.4 and 21.2) objects as cluster candidates with masses respectively at or rather below the hydrogen burning limit. More current candidates could be proven to be cluster members with masses around 0.1 M$_{\odot}$ {\it via} gravity-sensitive spectroscopy, and deeper near-infrared imaging will surely reveal a hitherto unknown population of young brown dwarfs in this region, accessible to the next generation of deep near-infrared surveys.Comment: 10 pages, 12 figures, accepted by A&

Proximity effect between two superconductors spatially resolved by scanning tunneling spectroscopy

We present a combined experimental and theoretical study of the proximity effect in an atomic-scale controlled junction between two different superconductors. Elaborated on a Si(111) surface, the junction comprises a Pb nanocrystal with an energy gap of 1.2 meV, connected to a crystalline atomic monolayer of lead with a gap of 0.23 meV. Using in situ scanning tunneling spectroscopy we probe the local density of states of this hybrid system both in space and in energy, at temperatures below and above the critical temperature of the superconducting monolayer. Direct and inverse proximity effects are revealed with high resolution. Our observations are precisely explained with the help of a self-consistent solution of the Usadel equations. In particular, our results demonstrate that in the vicinity of the Pb islands, the Pb monolayer locally develops a finite proximity-induced superconducting order parameter, well above its own bulk critical temperature. This leads to a giant proximity effect where the superconducting correlations penetrate inside the monolayer a distance much larger than in a non-superconducting metal.Comment: 13 pages, 14 figures, accepted for publication in Physical Review

Geographical Analysis of US Green Sector Industry Concentration

This paper analyzes the geographic distribution of “green energy” sector clustering in the lower 48 United States using recent developments in industry concentration analysis. Evidence suggests that the ten green energy subsectors and the aggregate of the firms comprising the green energy sector are regionally concentrated. Positive changes in industry concentration from 2002 to 2006 tended to be greatest in non-metropolitan counties, suggesting comparative advantage with respect to site location for the composite of firms making up these sectors.Agglomeration, Location Quotient, Renewable Energy, Community/Rural/Urban Development, Industrial Organization, Research and Development/Tech Change/Emerging Technologies,

HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-Hα\alpha 569

We present new HST ACS observations and detailed models for a recently discovered edge-on protoplanetary disk around ESO H$\alpha$ 569 (a low-mass T Tauri star in the Cha I star forming region). Using radiative transfer models we probe the distribution of the grains and overall shape of the disk (inclination, scale height, dust mass, flaring exponent and surface/volume density exponent) by model fitting to multiwavelength (F606W and F814W) HST observations together with a literature compiled spectral energy distribution. A new tool set was developed for finding optimal fits of MCFOST radiative transfer models using the MCMC code emcee to efficiently explore the high dimensional parameter space. It is able to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties. We confirm that ESO H$\alpha$ 569 is an optically thick nearly edge-on protoplanetary disk. The shape of the disk is well described by a flared disk model with an exponentially tapered outer edge, consistent with models previously advocated on theoretical grounds and supported by millimeter interferometry. The scattered light images and spectral energy distribution are best fit by an unusually high total disk mass (gas+dust assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap

Topography and lithology of the Mendocino Ridge

Twenty-two slope-corrected bathymetric profiles of the Mendocino Ridge between 125°W and 129°W are presented, and the method of their development is discussed. The crest of this Ridge lies at an average depth of 2000 m, falling off to 3200 m on the north and to 4400 m on the south. A short, steep scarp, fresh dredge-haul material lacking manganiferous crusts, and earthquake epicenters suggest recent faulting on the north...

Effect of kinetic resonances on the stability of Resistive Wall Mode in Reversed Field Pinch

The kinetic effects, due to the mode resonance with thermal particle drift motions in the reversed field pinch (RFP) plasmas, are numerically investigated for the stability of the resistive wall mode, using a non-perturbative MHD-kinetic hybrid formulation. The kinetic effects are generally found too weak to substantially change the mode growth rate, or the stability margin, re-enforcing the fact that the ideal MHD model is rather adequate for describing the RWM physics in RFP experiments.Comment: Submitted to: Plasma Phys. Control. Fusio

Dust disks around old Pre Main-Sequence stars: HST/NICMOS2 scattered light images and modeling

We present recent near-infrared detections of circumstellar disks around the two old PMS Herbig stars HD 141569 and HD 100546 obtained with the HST/NICMOS2 camera. They reveal extended structures larger than 350-400 AU in radius. While the HD 100546 disk appears as a continuous disk down to 40 AU, the HD 141569 environment seems more complex, splitted at least into two dust populations. As a convincing example, the full modeling of the disk surrounding HR 4796, another old PMS star, is detailed and confronted with more recent observations.Comment: 6 page