2,739 research outputs found
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 - from the substellar limit down to at least
20 M for zero reddening. Candidate BD were first selected
using wide field () band imaging with CFH12K, by reference to current
theoretical isochrones. Subsequently, 79 (33%) of the sample were found
to have near-infrared 2MASS photometry ( 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 ,, and
. We discuss the status and potential substellarity of a number of
relatively unreddened (A 5) likely low-mass members in our
sample, but in spite of the depth of our observations in , we are as yet
unable to unambiguously identify substellar candidates using only 2MASS data.
Nevertheless, there are excellent arguments for considering two faint (observed
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 {\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&
Geographical Analysis of US Green Sector Industry Concentration
This paper analyzes the geographic distribution of âgreen energyâ 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,
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
Trapping colloids near chemical stripes via critical Casimir forces
We study theoretically and experimentally the solvent-mediated critical
Casimir force acting on colloidal particles immersed in a binary liquid mixture
of water and 2,6-lutidine and close to substrates which are chemically
patterned with periodically alternating stripes of antagonistic adsorption
preferences. These patterns are experimentally realized via microcontact
printing. Upon approaching the critical demixing point of the solvent, normal
and lateral critical Casimir forces generate laterally confining effective
potentials for the colloids. We analyze in detail the rich behavior of the
spherical colloids close to such substrates. For all patterned substrates we
investigated, our measurements of these effective potentials agree with the
corresponding theoretical predictions. Since both the directions and the
strengths of the critical Casimir forces can be tuned by minute temperature
changes, this provides a new mechanism for controlling colloids as model
systems, opening encouraging perspectives for applications.Comment: Invited contribution to Molecular Physics Special Issue on Bob Evans'
65th birthda
The BOSS Emission-Line Lens Survey. III. : Strong Lensing of Ly Emitters by Individual Galaxies
We introduce the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line
Lens Survey (BELLS) for GALaxy-Ly EmitteR sYstems (BELLS GALLERY)
Survey, which is a Hubble Space Telescope program to image a sample of
galaxy-scale strong gravitational lens candidate systems with high-redshift
Ly emitters (LAEs) as the background sources. The goal of the BELLS
GALLERY Survey is to illuminate dark substructures in galaxy-scale halos by
exploiting the small-scale clumpiness of rest-frame far-UV emission in lensed
LAEs, and to thereby constrain the slope and normalization of the
substructure-mass function. In this paper, we describe in detail the
spectroscopic strong-lens selection technique, which is based on methods
adopted in the previous Sloan Lens ACS (SLACS) Survey, BELLS, and SLACS for the
Masses Survey. We present the BELLS GALLERY sample of the 21 highest-quality
galaxy--LAE candidates selected from galaxy spectra
in the BOSS of the Sloan Digital Sky Survey III. These systems consist of
massive galaxies at redshifts of approximately 0.5 strongly lensing LAEs at
redshifts from 2--3. The compact nature of LAEs makes them an ideal probe of
dark substructures, with a substructure-mass sensitivity that is unprecedented
in other optical strong-lens samples. The magnification effect from lensing
will also reveal the structure of LAEs below 100 pc scales, providing a
detailed look at the sites of the most concentrated unobscured star formation
in the universe. The source code used for candidate selection is available for
download as a part of this release.Comment: 14 pages, 5 figures, accepted for publication in the ApJ (ApJ, 824,
86). Minor edits to match the ApJ published versio
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