1,020 research outputs found
Quantitation in men of suppressive effects of fluocortolone and prednisolone by evaluation of diurnal rhythms of serum cortisol
Autonomous, high-resolution observations of particle flux in the oligotrophic ocean
© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 10 (2013): 5517-5531, doi:10.5194/bg-10-5517-2013.Observational gaps limit our understanding of particle flux attenuation through the upper mesopelagic because available measurements (sediment traps and radiochemical tracers) have limited temporal resolution, are labor-intensive, and require ship support. Here, we conceptually evaluate an autonomous, optical proxy-based method for high-resolution observations of particle flux. We present four continuous records of particle flux collected with autonomous profiling floats in the western Sargasso Sea and the subtropical North Pacific, as well as one shorter record of depth-resolved particle flux near the Bermuda Atlantic Time-series Study (BATS) and Oceanic Flux Program (OFP) sites. These observations illustrate strong variability in particle flux over very short (~1-day) timescales, but at longer timescales they reflect patterns of variability previously recorded during sediment trap time series. While particle flux attenuation at BATS/OFP agreed with the canonical power-law model when observations were averaged over a month, flux attenuation was highly variable on timescales of 1–3 days. Particle fluxes at different depths were decoupled from one another and from particle concentrations and chlorophyll fluorescence in the immediately overlying surface water, consistent with horizontal advection of settling particles. We finally present an approach for calibrating this optical proxy in units of carbon flux, discuss in detail the related, inherent physical and optical assumptions, and look forward toward the requirements for the quantitative application of this method in highly time-resolved studies of particle export and flux attenuation.M.L.E. was
supported by a WHOI Postdoctoral Scholar fellowship, and the
floats used in this project were funded by the above NASA grant
and by ONR (DURIP, N00014-10-1-0776)
Estimating the maritime component of aerosol optical depth and its dependency on surface wind speed using satellite data
Six years (2003-2008) of satellite measurements of aerosol parameters from the Moderate Resolution Imaging Spectroradiometer (MODIS) and surface wind speeds from Quick Scatterometer (QuikSCAT), the Advanced Microwave Scanning Radiometer (AMSR-E), and the Special Sensor Microwave Imager (SSM/I), are used to provide a comprehensive perspective on the link between surface wind speed and marine aerosol optical depth over tropical and subtropical oceanic regions. A systematic comparison between the satellite derived fields in these regions allows to: (i) separate the relative contribution of wind-induced marine aerosol to the aerosol optical depth; (ii) extract an empirical linear equation linking coarse marine aerosol optical depth and wind intensity; and (iii) identify a time scale for correlating marine aerosol optical depth and surface wind speed. The contribution of wind induced marine aerosol to aerosol optical depth is found to be dominated by the coarse mode elements. When wind intensity exceeds 4 m/s, coarse marine aerosol optical depth is linearly correlated with the surface wind speed, with a remarkably consistent slope of 0.009±0.002 s/m. A detailed time scale analysis shows that the linear correlation between the fields is well kept within a 12 h time frame, while sharply decreasing when the time lag between measurements is longer. The background aerosol optical depth, associated with aerosols that are not produced in-situ through wind driven processes, can be used for estimating the contributions of terrestrial and biogenic marine aerosol to over-ocean satellite retrievals of aerosol optical depth
A Search for Cold Dust around Neutron Stars
We present observations of nine radio pulsars using the
Heinrich-Hertz-Telescope at \lambda 0.87mm and the IRAM 30-m telescope at
\lambda 1.2mm in search for a cold dust around these sources. Five of the
program pulsars have been observed for the first time at the mm-wavelengths.
The results are consistent with the absence of circumpulsar disks that would be
massive enough () to support planet formation according to
the scenarios envisioned for solar-type stars, but they do not exclude lower
mass () disks for a wide range of grain sizes. These
conclusions confirm the previously published results and, together with the
current lack of further detections of pulsar planets, they suggest that planet
formation around neutron stars is not a common phenomenon.Comment: 5 pages, 1 figure, accepted for publication in A&
Astrometric and photometric monitoring of GQ Lup and its sub-stellar companion
Neuhaeuser et al. (2005) presented direct imaging evidence for a sub-stellar
companion to the young T Tauri star GQ Lup. Common proper motion was highly
significant, but no orbital motion was detected. Faint luminosity, low gravity,
and a late-M/early-L spectral type indicated that the companion is either a
planet or a brown dwarf. We have monitored GQ Lup and its companion in order to
detect orbital and parallactic motion and variability in its brightness. We
also search for closer and fainter companions. We have taken six more images
with the VLT Adaptive Optics instrument NACO from May 2005 to Feb 2007, always
with the same calibration binary from Hipparcos for both astrometric and
photometric calibration. By adding up all the images taken so far, we search
for additional companions. The position of GQ Lup A and its companion compared
to a nearby non-moving background object varies as expected for parallactic
motion by about one pixel (2 \pi with parallax \pi). We could not find evidence
for variability of the GQ Lup companion in the K-band (standard deviation being
\pm 0.08 mag), which may be due to large error bars. No additional companions
are found with deep imaging. There is now exceedingly high significance for
common proper motion of GQ Lup A and its companion. In addition, we see for the
first time an indication for orbital motion (about 2 to 3 mas/yr decrease in
separation, but no significant change in the position angle), consistent with a
near edge-on or highly eccentric orbit. We measured the parallax for GQ Lup A
to be \pi = 6.4 \pm 1.9 mas (i.e. 156 \pm 50 pc) and for the GQ Lup companion
to be 7.2 \pm 2.1 mas (i.e. 139 \pm 45 pc), both consistent with being in the
Lupus I cloud and bound to each other.Comment: A&A in pres
An emission ring at 20 microns around the HAEBE star AB Aurigae: unveiling the disc structure
Isolated HAEBE stars are believed to represent an intermediate stage of
objects between young stellar objects surrounded by massive, optically thick,
gaseous and dusty disks and Vega like stars surrounded by debris disks. The
star AB Aur is already known for being surrounded by an intermediate-stage dust
disk emitting a fairly large infrared and (sub-)millimetric excess. Until now,
the outer disk structure has only been resolved at millimeter wavelengths and
at optical wavelength coronographic imaging. We have obtained 20 microns images
which show an unexpected ellipse-shaped disk structure in emission at a
distance of about 260 AU from the central star. Large azimuthal asymmetries in
brightness can be noticed and the center of the ellipse does not coincide with
the star. A simple, pure geometrical model based on an emission ring of uniform
surface brightness, but having an intrinsic eccentricity succeeds in fitting
the observations. These observations give for the first time clues on a very
peculiar structure of pre-main-sequence disk geometry, i.e. a non uniform
increase in the disk thickness unlike the common usual sketch of a disk with a
constant flaring angle. They provide also valuable informations on the disk
inclination as well as its dust composition; at such a large distance from the
star, only transient heating of very small particles can explain such a bright
ring of emission at mid-infrared wavelengths. Finally, the increase of
thickness inferred by the model could be caused by disk instabilities; the
intrinsic eccentricity of the structure might be a clue to the presence of a
massive body undetected yet
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