17,708 research outputs found
Multichromatic colour-magnitude diagrams of the globular cluster NGC 6366
We present multichromatic isochrone fits to the colour-magnitude data of the
globular cluster NGC 6366, based on Hubble Space Telescope Advanced Camera for
Surveys/Wide Field Channel and Southern Astrophysical Research photometric
data. We corrected the photometric data for differential reddening and
calculated the mean ridge line of the colour-magnitude diagrams. We compared
the isochrones of Dartmouth Stellar Evolution Database and PAdova and TRieste
Stellar Evolution Code both with microscopic diffusion starting on the main
sequence. Bracketing all previous determinations of this cluster, we tested
metallicities from [Fe/H]=-1.00 to [Fe/H]=-0.50, and ages from 9 to 13 Gyr.
After determining the total to selective extinction ratio only from stars
belonging to this cluster, R_V=3.06+/-0.14, we found the parameters for this
cluster to be E(B-V)=0.69+/-0.02(int)+/-0.04(ext),
(m-M)_V=15.02+/-0.07(int)+/-0.13(ext), Age=11+/-1.15 Gyr. Evolutionary models
fail to reproduce the low-Teff sequence in multiband colour-magnitude diagrams,
indicating that they still have an incomplete physics. We found that the
Dartmouth Stellar Evolution Database isochrones better fit the subgiant branch
and low main sequence than the PAdova and TRieste Stellar Evolution Code.Comment: 9 pages, 5 figure
Analysis of dependence among size, rate and duration in internet flows
In this paper we examine rigorously the evidence for dependence among data
size, transfer rate and duration in Internet flows. We emphasize two
statistical approaches for studying dependence, including Pearson's correlation
coefficient and the extremal dependence analysis method. We apply these methods
to large data sets of packet traces from three networks. Our major results show
that Pearson's correlation coefficients between size and duration are much
smaller than one might expect. We also find that correlation coefficients
between size and rate are generally small and can be strongly affected by
applying thresholds to size or duration. Based on Transmission Control Protocol
connection startup mechanisms, we argue that thresholds on size should be more
useful than thresholds on duration in the analysis of correlations. Using
extremal dependence analysis, we draw a similar conclusion, finding remarkable
independence for extremal values of size and rate.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS268 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Illuminating Solutions: The Youth Violence Reduction Partnership
Over the last decade, P/PV has undertaken several studies of the Philadelphia-based Youth Violence Reduction Partnership (YVRP), an intensive collaboration that targets young people deemed at highest risk of being involved in a homicide. YVRP provides young probationers with enhanced supervision and support, with the goal of keeping them out of trouble and putting them on a path toward productive adulthood
Phenomenological Analysis of and Elastic Scattering Data in the Impact Parameter Space
We use an almost model-independent analytical parameterization for and
elastic scattering data to analyze the eikonal, profile, and
inelastic overlap functions in the impact parameter space. Error propagation in
the fit parameters allows estimations of uncertainty regions, improving the
geometrical description of the hadron-hadron interaction. Several predictions
are shown and, in particular, the prediction for inelastic overlap
function at TeV shows the saturation of the Froissart-Martin
bound at LHC energies.Comment: 15 pages, 16 figure
Ultrahigh Transmission Optical Nanofibers
We present a procedure for reproducibly fabricating ultrahigh transmission
optical nanofibers (530 nm diameter and 84 mm stretch) with single-mode
transmissions of 99.95 0.02%, which represents a loss from tapering of
2.6 10 dB/mm when normalized to the entire stretch. When
controllably launching the next family of higher-order modes on a fiber with
195 mm stretch, we achieve a transmission of 97.8 2.8%, which has a loss
from tapering of 5.0 10 dB/mm when normalized to the
entire stretch. Our pulling and transfer procedures allow us to fabricate
optical nanofibers that transmit more than 400 mW in high vacuum conditions.
These results, published as parameters in our previous work, present an
improvement of two orders of magnitude less loss for the fundamental mode and
an increase in transmission of more than 300% for higher-order modes, when
following the protocols detailed in this paper. We extract from the
transmission during the pull, the only reported spectrogram of a fundamental
mode launch that does not include excitation to asymmetric modes; in stark
contrast to a pull in which our cleaning protocol is not followed. These
results depend critically on the pre-pull cleanliness and when properly
following our pulling protocols are in excellent agreement with simulations.Comment: 32 pages, 10 figures, accepted to AIP Advance
Topological insulator particles as optically induced oscillators: towards dynamical force measurements and optical rheology
We report the first experimental study upon the optical trapping and
manipulation of topological insulator (TI) particles. By virtue of the unique
TI properties, which have a conducting surface and an insulating bulk, the
particles present a peculiar behaviour in the presence of a single laser beam
optical tweezers: they oscillate in a plane perpendicular to the direction of
the laser propagation, as a result of the competition between radiation
pressure and gradient forces. In other words, TI particles behave as optically
induced oscillators, allowing dynamical measurements with unprecedented
simplicity and purely optical control. Actually, optical rheology of soft
matter interfaces and biological membranes, as well as dynamical force
measurements in macromolecules and biopolymers, may be quoted as feasible
possibilities for the near future.Comment: 6 pages, 5 figures. Correspondence and requests for Supplementary
Material should be addressed to [email protected]
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