851 research outputs found
Dust properties inside molecular clouds from coreshine modeling and observations
Context. Using observations to deduce dust properties, grain size
distribution, and physical conditions in molecular clouds is a highly
degenerate problem. Aims. The coreshine phenomenon, a scattering process at 3.6
and 4.5 m that dominates absorption, has revealed its ability to explore
the densest parts of clouds. We want to use this effect to constrain the dust
parameters. The goal is to investigate to what extent grain growth (at constant
dust mass) inside molecular clouds is able to explain the coreshine
observations. We aim to find dust models that can explain a sample of Spitzer
coreshine data. We also look at the consistency with near-infrared data we
obtained for a few clouds. Methods. We selected four regions with a very high
occurrence of coreshine cases: Taurus-Perseus, Cepheus, Chameleon and
L183/L134. We built a grid of dust models and investigated the key parameters
to reproduce the general trend of surface bright- nesses and intensity ratios
of both coreshine and near-infrared observations with the help of a 3D
Monte-Carlo radiative transfer code. The grid parameters allow to investigate
the effect of coagulation upon spherical grains up to 5 m in size derived
from the DustEm diffuse interstellar medium grains. Fluffiness (porosity or
fractal degree), ices, and a handful of classical grain size distributions were
also tested. We used the near- and mostly mid-infrared intensity ratios as
strong discriminants between dust models. Results. The determination of the
background field intensity at each wavelength is a key issue. In particular, an
especially strong background field explains why we do not see coreshine in the
Galactic plane at 3.6 and 4.5 m. For starless cores, where detected, the
observed 4.5 m / 3.6 m coreshine intensity ratio is always lower than
0.5 which is also what we find in the models for the Taurus-Perseus and
L183 directions. Embedded sources can lead to higher fluxes (up to four times
greater than the strongest starless core fluxes) and higher coreshine ratios
(from 0.5 to 1.1 in our selected sample). Normal interstellar radiation field
conditions are sufficient to find suitable grain models at all wavelengths for
starless cores. The standard interstellar grains are not able to reproduce
observations and, due to the multi-wavelength approach, only a few grain types
meet the criteria set by the data. Porosity does not affect the flux ratios
while the fractal dimension helps to explain coreshine ratios but does not seem
able to reproduce near-infrared observations without a mix of other grain
types. Conclusions. Combined near- and mid-infrared wavelengths confirm the
potential to reveal the nature and size distribution of dust grains. Careful
assessment of the environmental parameters (interstellar and background fields,
embedded or nearby reddened sources) is required to validate this new
diagnostic
New Young Star Candidates in BRC 27 and BRC 34
We used archival Spitzer Space Telescope mid-infrared data to search for
young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed
clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These
regions both appear to be actively forming young stars, perhaps triggered by
the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of
the 26 YSOs or YSO candidates identified in the literature, and identify 16 new
YSO candidates that appear to have IR excesses. In BRC 34, the one
literature-identified YSO has an IR excess, and we suggest 13 new YSO
candidates in this region, including a new Class I object. Considering the
entire ensemble, both BRCs are likely of comparable ages, within the
uncertainties of small number statistics and without spectroscopy to confirm or
refute the YSO candidates. Similarly, no clear conclusions can yet be drawn
about any possible age gradients that may be present across the BRCs.Comment: 54 pages, 19 figures, accepted by A
Nanostructuring Titania by Embossing with Polymer Molds Made from Anodic Alumina Templates
Photometric Accretion Signatures Near the Substellar Boundary
Multi-epoch imaging of the Orion equatorial region by the Sloan Digital Sky
Survey has revealed that significant variability in the blue continuum persists
into the late-M spectral types, indicating that magnetospheric accretion
processes occur below the substellar boundary in the Orion OB1 association. We
investigate the strength of the accretion-related continuum veiling by
comparing the reddening-invariant colors of the most highly variable stars
against those of main sequence M dwarfs and evolutionary models. A gradual
decrease in the g band veiling is seen for the cooler and less massive members,
as expected for a declining accretion rate with decreasing mass. We also see
evidence that the temperature of the accretion shock decreases in the very low
mass regime, reflecting a reduction in the energy flux carried by the accretion
columns. We find that the near-IR excess attributed to circumstellar disk
thermal emission drops rapidly for spectral types later than M4. This is likely
due to the decrease in color contrast between the disk and the cooler stellar
photosphere. Since accretion, which requires a substantial stellar magnetic
field and the presence of a circumstellar disk, is inferred for masses down to
0.05 Msol we surmise that brown dwarfs and low mass stars share a common mode
of formation.Comment: 37 pages, 14 figures, accepted by A
Three-dimensional modeling of acoustic backscattering from fluid-like zooplankton
Author Posting. © Acoustical Society of America, 2002. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 111 (2002): 1197-1210, doi:10.1121/1.1433813.Scattering models that correctly incorporate organism size and shape are a critical component for the remote detection and classification of many marine organisms. In this work, an acoustic scattering model has been developed for fluid-like zooplankton that is based on the distorted wave Born approximation (DWBA) and that makes use of high-resolution three-dimensional measurements of the animal's outer boundary shape. High-resolution computerized tomography (CT) was used to determine the three-dimensional digitizations of animal shape. This study focuses on developing the methodology for incorporating high-resolution CT scans into a scattering model that is generally valid for any body with fluid-like material properties. The model predictions are compared to controlled laboratory measurements of the acoustic backscattering from live individual decapod shrimp. The frequency range used was 50 kHz to 1 MHz and the angular characteristics of the backscattering were investigated with up to a 1° angular resolution. The practical conditions under which it is necessary to make use of high-resolution digitizations of shape are assessed.This work was supported
in part by the Woods Hole Oceanographic Institution
Education Office
A 24 hour naproxen dose on gastrointestinal distress and performance during cycling in the heat
Using a double-blind, randomized and counterbalanced, cross-over design, we assessed naproxen's effects on gastrointestinal (GI) distress and performance in eleven volunteers (6 male, 5 female). Participants completed 4 trials: 1) placebo and ambient); 2) placebo and heat; 3) naproxen and ambient; and 4) naproxen and heat. Independent variables were one placebo or 220 mg naproxen pill every 8 h (h) for 24 h and ambient (22.7 ± 1.8°C) or thermal environment (35.7 ± 1.3°C). Participants cycled 80 min at a steady heart rate then 10 min for maximum distance. Perceived exertion was measured throughout cycling. Gastrointestinal distress was assessed pre-, during, post-, 3 h post-, and 24 h post-cycling using a GI index for upper, lower, and systemic symptoms. No statistically significant differences occurred between conditions at any time for GI symptoms or perceived exertion, distance, or heart rate during maximum effort. A 24 h naproxen dose did not significantly affect performance or cause more frequent or serious GI distress when participants were euhydrated and cycling at moderate intensity in a thermal environment
Management of systemic lupus erythematosus
No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37693/1/1780050510_ftp.pd
Relationship between photonic band structure and emission characteristics of a polymer distributed feedback laser
G. A. Turnbull, P. Andrew, M. J. Jory, William L. Barnes, and I. D. W. Samuel, Physical Review B, Vol. 64, article 125122 (2001). "Copyright © 2001 by the American Physical Society."We present an experimental study of the emission characteristics and photonic band structure of a distributed feedback polymer laser, based on the material poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. We use measurements of the photonic band dispersion to explain how the substrate microstructure modifies both spontaneous and stimulated emission. The lasing structure exhibits a one-dimensional photonic band gap around 610 nm, with lasing occurring at one of the two associated band edges. The band edge (frequency) selection mechanism is found to be a difference in the level of output coupling of the modes associated with the two band edges. This is a feature of the second-order distributed feedback mechanism we have employed and is clearly evident in the measured photonic band structur
Photonic mode dispersion of a two-dimensional distributed feedback polymer laser
G. A. Turnbull, P. Andrew, William L. Barnes, and I. D. W. Samuel, Physical Review B, Vol. 67, article 165107 (2003). "Copyright © 2003 by the American Physical Society."We present an analysis of the photonic mode dispersion of a two-dimensional (2D) distributed feedback polymer laser based on the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. We use a combination of a simple model, together with experimental measurements of the photonic mode dispersion in transmission and emission, to explain the operating characteristics of the laser. The laser was found to oscillate at 636 nm on one edge of a photonic stop band in the photonic dispersion. A 2D coupling of modes traveling perpendicular to the orthogonal gratings was found to lead to a low divergence laser emission normal to the waveguide. At pump energies well above the oscillation threshold for this mode, a divergent, cross-shaped far-field emission was observed, resulting from a distributed feedback occurring over a wide range of wave vectors in one band of the photonic dispersion
Electrospun amplified fiber optics
A lot of research is focused on all-optical signal processing, aiming to
obtain effective alternatives to existing data transmission platforms.
Amplification of light in fiber optics, such as in Erbium-doped fiber
amplifiers, is especially important for an efficient signal transmission.
However, the complex fabrication methods, involving high-temperature processes
performed in highly pure environment, slow down the fabrication and make
amplified components expensive with respect to an ideal, high-throughput and
room temperature production. Here, we report on near infrared polymer fiber
amplifiers, working over a band of about 20 nm. The fibers are cheap, spun with
a process entirely carried out at room temperature, and show amplified
spontaneous emission with good gain coefficients as well as low optical losses
(a few cm^-1). The amplification process is favoured by the high fiber quality
and low self-absorption. The found performance metrics promise to be suitable
for short-distance operation, and the large variety of commercially-available
doping dyes might allow for effective multi-wavelength operation by electrospun
amplified fiber optics.Comment: 27 pages, 8 figure
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