12,575 research outputs found
A Sino-German 6cm polarisation survey of the Galactic plane IX. HII regions
Large-scale radio continuum surveys provide data to get insights into the
physical properties of radio sources. HII regions are prominent radio sources
produced by thermal emission of ionised gas around young massive stars. We
identify and analyse HII regions in the Sino-German 6cm polarisation survey of
the Galactic plane. Objects with flat radio continuum spectra together with
infrared and/or Halpha emission were identified as HII regions. For HII regions
with small apparent sizes, we cross-matched the 6cm small-diameter source
catalogue with the radio HII region catalogue compiled by Paladini and the
infrared HII region catalogue based on the WISE data. Extended HII regions were
identified by eye by overlaying the Paladini and the WISE HII regions onto the
6cm survey images for coincidences. The TT-plot method was employed for
spectral index verification. A total of 401 HII regions were identified and
their flux densities were determined with the Sino-German 6cm survey data. In
the surveyed area, 76 pairs of sources are found to be duplicated in the
Paladini HII region catalogue, mainly due to the non-distinction of previous
observations with different angular resolutions, and 78 objects in their
catalogue are misclassified as HII regions, being actually planetary nebulae,
supernova remnants or extragalactic sources that have steep spectra. More than
30 HII regions and HII region candidates from our 6cm survey data, especially
extended ones, do not have counterparts in the WISE HII region catalogue, of
which 9 are identified for the first time. Based on the newly derived radio
continuum spectra and the evidence of infrared emission, the previously
identified SNRs G11.1-1.0, G20.4+0.1 and G16.4-0.5 are believed to be HII
regions.Comment: version after some minor corrections and language editing, full Table
2 - 5 will appear in CDS, accepted for publication in A&
Prediction of infectious disease epidemics via weighted density ensembles
Accurate and reliable predictions of infectious disease dynamics can be
valuable to public health organizations that plan interventions to decrease or
prevent disease transmission. A great variety of models have been developed for
this task, using different model structures, covariates, and targets for
prediction. Experience has shown that the performance of these models varies;
some tend to do better or worse in different seasons or at different points
within a season. Ensemble methods combine multiple models to obtain a single
prediction that leverages the strengths of each model. We considered a range of
ensemble methods that each form a predictive density for a target of interest
as a weighted sum of the predictive densities from component models. In the
simplest case, equal weight is assigned to each component model; in the most
complex case, the weights vary with the region, prediction target, week of the
season when the predictions are made, a measure of component model uncertainty,
and recent observations of disease incidence. We applied these methods to
predict measures of influenza season timing and severity in the United States,
both at the national and regional levels, using three component models. We
trained the models on retrospective predictions from 14 seasons (1997/1998 -
2010/2011) and evaluated each model's prospective, out-of-sample performance in
the five subsequent influenza seasons. In this test phase, the ensemble methods
showed overall performance that was similar to the best of the component
models, but offered more consistent performance across seasons than the
component models. Ensemble methods offer the potential to deliver more reliable
predictions to public health decision makers.Comment: 20 pages, 6 figure
The Fragmenting Superbubble Associated with the HII Region W4
New observations at high latitudes above the HII region W4 show that the
structure formerly identified as a chimney candidate, an opening to the
Galactic halo, is instead a superbubble in the process of fragmenting and
possibly evolving into a chimney. Data at high Galactic latitudes (b > 5
degrees) above the W3/W4 star forming region at 1420 and 408 MHz Stokes I
(total power) and 1420 MHz Stokes Q and U (linear polarization) reveal an
egg-shaped structure with morphological correlations between our data and the
H-alpha data of Dennison, Topasna, & Simonetti. Polarized intensity images show
depolarization extending from W4 up the walls of the superbubble, providing
strong evidence that the radio continuum is generated by thermal emission
coincident with the H-alpha emission regions. We conclude that the parts of the
HII region hitherto known as W4 and the newly revealed thermal emission are all
ionized by the open cluster OCl 352. Assuming a distance of 2.35 kpc, the ovoid
structure is 164 pc wide and extends 246 pc above the mid-plane of the Galaxy.
The shell's emission decreases in total-intensity and polarized intensity in
various locations, appearing to have a break at its top and another on one
side. Using a geometric analysis of the depolarization in the shell's walls, we
estimate that a magnetic field line-of-sight component of 3 to 5 uG exists in
the shell. We explore the connection between W4 and the Galactic halo,
considering whether sufficient radiation can escape from the fragmenting
superbubble to ionize the kpc-scale H-alpha loop discovered by Reynolds,
Sterling & Haffner.Comment: 42 pages, 14 figures; Accepted for publication in Ap
Evaluation of remote sensing techniques on selected forest sites in Florida
There are no author-identified significant results in this report
G55.0+0.3: A Highly Evolved Supernova Remnant
Multi-frequency analysis has revealed the presence of a new supernova
remnant, G55.0+0.3, in the Galactic plane. A kinematic distance of 14 kpc has
been measured from HI spectral line data. The faint, clumpy half-shell is
non-thermal and has a physical radius of 70 pc. Using an evolutionary model,
the age of the remnant is estimated to be on the order of one million years,
which exceeds conventional limits by a factor of five. The remnant may be
associated with the nearby pulsar J1932+2020, which has a spin-down age of 1.1
million years. This work implies that the radiative lifetimes of remnants could
be much longer than previously suggested.Comment: 27 pages, 7 figures in 9 files (figures 1 and 2 require 2 files
each), Accepted for publication in The Astrophysical Journal (Jan. 20, 1998
volume
Observation of magnetism in Au thin films
Direct magnetization measurements of thin gold films are presented. These
measurements integrate the signal from the thin film under study and the
magnetic contribution of the film's interface with the substrate. The
diamagnetic contribution to the signal from the bulk substrate is of the same
order as the noise level. we find that thin gold films can exhibit positive
magnetization. The character of their magnetic behavior is strongly substrate
dependent.Comment: 9 pages, 4 figure
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