240 research outputs found
Position and Mode Dependent Optical Detection Back-Action in Cantilever Beam Resonators
Optical detection back-action in cantilever resonant or static detection
presents a challenge when striving for state-of-the-art performance. The origin
and possible routes for minimizing optical back-action have received little
attention in literature. Here, we investigate the position and mode dependent
optical back-action on cantilever beam resonators. A high power heating laser
(100 {\mu}W) is scanned across a silicon nitride cantilever while its effect on
the first three resonance modes is detected via a low-power readout laser (1
{\mu}W) positioned at the cantilever tip. We find that the measured effect of
back-action is not only dependent on position but also the shape of the
resonance mode. Relevant silicon nitride material parameters are extracted by
fitting the temperature-dependent frequency response of the first three modes
to finite element (FE) simulations. In a second round of simulations, using the
extracted parameters, we successfully fit the FEM results with the measured
mode and position dependent back-action. Finally, different routes for
minimizing the effect of this optical detection back-action are described,
allowing further improvements of cantilever-based sensing in general
The wind speed profile at offshore wind farm sites
Using Monin-Obukhov theory the vertical wind speed profile can be predicted from the wind speed at one height, when the two parameters Monin-Obukhov length and sea surface roughness are known. The applicability of this theory for wind power prediction at offshore sites is investigated using data from the measurement program Rdsand in the Danish Baltic Sea. Different methods to estimate the two parameters are discussed and compared. Significant deviations to the theory are found for near-neutral and stable conditions, where the measured wind shear is larger than predicted. A simple correction method to account for this effect has been developed and tested. As
A G1-like globular cluster in NGC 1023
The structure of a very bright (MV = -10.9) globular cluster in NGC 1023 is
analyzed on two sets of images taken with the Hubble Space Telescope. From
careful modeling of King profile fits to the cluster image, a core radius of
0.55+/-0.1 pc, effective radius 3.7+/-0.3 pc and a central V-band surface
brightness of 12.9+/-0.5 mag / square arcsec are derived. This makes the
cluster much more compact than Omega Cen, but very similar to the brightest
globular cluster in M31, G1 = Mayall II. The cluster in NGC 1023 appears to be
very highly flattened with an ellipticity of about 0.37, even higher than for
Omega Cen and G1, and similar to the most flattened clusters in the Large
Magellanic Cloud.Comment: 14 pages, 3 figures, 1 table. Accepted for AJ, Oct 200
Sizes and Shapes of Young Star Cluster Light Profiles in M83
We measure the radii and two-dimensional light profiles of a large sample of
young, massive star clusters in M83 using archival HST/WFC3 imaging of seven
adjacent fields. We use GALFIT to fit the two-dimensional light profiles of the
clusters, from which we find effective (half-light) radii, core radii, and
slopes of the power-law (EFF) profile (). We find lognormal distributions
of effective radius and core radius, with medians of 2.5 pc and
1.3 pc, respectively. Our results provide strong evidence for a
characteristic size of young, massive clusters. The average effective radius
and core radius increase somewhat with cluster age. Little to no change in
effective radius is observed with increasing galactocentric distance, except
perhaps for clusters younger than 100 Myr. We find a shallow correlation
between effective radius and mass for the full cluster sample, but a stronger
correlation is present for clusters 200-300 Myr in age. Finally, the majority
of the clusters are best fit by an EFF model with index . There is
no strong evidence for change in with cluster age, mass, or
galactocentric distance. Our results suggest that clusters emerge from early
evolution with similar radii and are not strongly affected by the tidal field
of M83. Mass loss due to stellar evolution and/or GMC interactions appear to
dominate cluster expansion in the age range we study.Comment: 34 pages, 11 figures, 3 tables, accepted by MNRAS. Machine-readable
table attached (full version of Table 3). To obtain, download the source file
from the "Other formats" link abov
2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable -ray emission
We present optical photometric and spectroscopic observations of the likely
stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT)
-ray source 2FGL J0846.0+2820, selected for study based on positional
coincidences of optical variables with unassociated LAT sources. Using optical
spectroscopy from the SOAR telescope, we have identified a late-G giant in an
eccentric ( = 0.06) 8.133 day orbit with an invisible primary. Modeling the
spectroscopy and photometry together lead us to infer a heavy neutron star
primary of and a partially stripped giant secondary of . H emission is observed in some of the spectra, perhaps
consistent with the presence of a faint accretion disk. We find the
-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009,
accompanied by an increased variation in the optical brightness, and since then
it has not been detected by \emph{Fermi}. The long period and giant secondary
are reminiscent of the -ray bright binary 1FGL J1417.7--4407, which
hosts a millisecond pulsar apparently in the final stages of the pulsar
recycling process. The discovery of 2FGL J0846.0+2820 suggests the
identification of a new subclass of millisecond pulsar binaries that are the
likely progenitors of typical field millisecond pulsars.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Ap
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