410 research outputs found
SIGGMA: A Survey of Ionized Gas in the Galaxy, Made with the Arecibo Telescope
A Survey of Ionized Gas in the Galaxy, made with the Arecibo telescope
(SIGGMA) uses the Arecibo L-band Feed Array (ALFA) to fully sample the Galactic
plane (30 < l < 75 and -2 < b < 2; 175 < l < 207 and -2 < b < 1) observable
with the telescope in radio recombination lines (RRLs). Processed data sets are
being produced in the form of data cubes of 2 degree (along l) x 4 degree
(along b) x 151 (number of channels), archived and made public. The 151
channels cover a velocity range of 600 km/s and the velocity resolution of the
survey changes from 4.2 km/s to 5.1 km/s from the lowest frequency channel to
the highest frequency channel, respectively.RRL maps with 3.4 arcmin resolution
and line flux density sensitivity of 0.5 mJy will enable us to identify new HII
regions, measure their electron temperatures, study the physics of
photodissociation regions (PDRs) with carbon RRLs, and investigate the origin
of the extended low density medium (ELDM). Twelve Hn{\alpha} lines fall within
the 300 MHz bandpass of ALFA; they are resampled to a common velocity
resolution to improve the signal-to-noise ratio (SN) by a factor of 3 or more
and preserve the line width. SIGGMA will produce the most sensitive fully
sampled RRL survey to date. Here we discuss the observing and data reduction
techniques in detail. A test observation toward the HII region complex
S255/S257 has detected Hn{\alpha} and Cn{\alpha} lines with SN>10
Planetary Nebulae as Probes of Stellar Evolution and Populations
Planetary Nebulae (PNe) have been used satisfactory to test the effects of
stellar evolution on the Galactic chemical environment. Moreover, a link exists
between nebular morphology and stellar populations and evolution. We present
the latest results on Galactic PN morphology, and an extension to a distance
unbiased and homogeneous sample of Large Magellanic Cloud PNe. We show that PNe
and their morphology may be successfully used as probes of stellar evolution
and populations.Comment: to appear in: Chemical Evolution of the Milky Way: stars versus
clusters, ed. F. Giovannelli and F. Matteucci, Kluwer (2000), in pres
High resolution radio continuum survey of M33: I. The radio maps
We study the exponential scale length of total radio emission, the spectral
index distribution, and the linear radio polarization in the Scd galaxy M33.
Observations were carried out using the 3.6 cm dual channel and the 6.2 cm four
channel receivers of the 100--m Effelsberg telescope along with the L-band VLA
D--array at 20 cm. High spatial resolution and sensitivity in both total and
linearly polarized radio continuum emission from M33 were achieved. We found
considerable extended emission, not only from the main arms I S and I N, but
also from the weaker arms. The large--scale magnetic field exhibits
well--ordered spiral structure with almost the same orientation as that of the
optical spiral arms, however, it does not show a clear structural correlation
or anti--correlation with the optical arms. There is a north-south asymmetry in
polarization that is frequency-dependent. We found that the ring mean spectral
index versus radius increases faster beyond = 4 kpc. At each wavelength,
the exponential scale length is larger inside than outside = 4 kpc. From
the larger scales lengths at 4 kpc, we conclude that star forming
regions are mainly spread over the region 4 kpc without a dominant
nuclear concentration. Furthermore, at 4 kpc, a spatial correlation
between cosmic rays and star forming regions may exist. From the behaviour of
the mean spectral indices obtained from different pairs of the radio continuum
data at 3.6, 6.2, and 20 cm, we confirm that a decrease in the thermal fraction
causes an increase in the spectral index. The frequency-dependent asymmetry in
the polarization hints to an asymmetry in Faraday depolarization.Comment: 16 pages, 13 figures, accepted for publication in the Astronomy and
Astrophysics Journa
Hubble-type outflows of the high-excitation, poly-polar planetary nebula NGC 6302 -- from expansion proper motions
The ouflowing proper motions of fifteen knots in the dominant northwestern
lobe of the high-excitation poly-polar planetary nebula NGC 6302 have been
determined by comparing their positions relative to those of faint stars in an
image taken at the San Pedro Martir Observatory in 2007 to those in a South
African Astronomical Observatory archival plate obtained by Evans in 1956. The
Hubble-type expansion of this lobe is now directly confirmed in a model
independent way from these measurements. Furthermore, an unambiguous distance
to NGC 6302 of 1.17 +/- 0.14 kpc is now determined. Also all the velocity
vectors of the fifteen knots (and two others) point back to the central source.
An eruptive event from within the central torus, approximately 2200 years
previously must have created the high speed lobes of NGC 6302.Comment: 12 pages, 5 figures, MNRAS in pres
Public health surveillance after the 2010 Haiti earthquake: the experience of Médecins Sans Frontières
Background In January 2010, Haiti was struck by a powerful earthquake, killing and wounding hundreds of thousands and leaving millions homeless. In order to better understand the severity of the crisis, and to provide early warning of epidemics or deteriorations in the health status of the population, Médecins Sans Frontières established surveillance for infections of epidemic potential and for death rates and malnutrition prevalence. Methods Trends in infections of epidemic potential were detected through passive surveillance at health facilities serving as sentinel sites. Active community surveillance of death rates and malnutrition prevalence was established through weekly home visits. Results There were 102,054 consultations at the 15 reporting sites during the 26 week period of operation. Acute respiratory infections, acute watery diarrhoea and malaria/fever of unknown origin accounted for the majority of proportional morbidity among the diseases under surveillance. Several alerts were triggered through the detection of immediately notifiable diseases and increasing trends in some conditions. Crude and under-5 death rates, and acute malnutrition prevalence, were below emergency thresholds. Conclusion Disease surveillance after disasters should include an alert and response component, requiring investment of resources in informal networks that improve sensitivity to alerts as well as on the more common systems of data collection, compilation and analysis. Information sharing between partners is necessary to strengthen early warning systems. Community-based surveillance of mortality and malnutrition is feasible but requires careful implementation and validation
Use of National Standards to Monitor HIV Care and Treatment in a High Prevalence City-Washington, DC.
We sought to benchmark the quality of HIV care being received by persons living with HIV in care in Washington, DC and identify individual-level and structural-level differences. Data from the DC Cohort, an observational HIV cohort of persons receiving outpatient care in DC, were used to estimate the Institute of Medicine (IOM) and Department of Health and Human Services (HHS) quality of care measures. Differences in care by demographics and clinic type were assessed using χ2 tests and multivariable regression models. Among 8,047 participants, by HHS standards, 69% of participants were retained in care (RIC), 95% were prescribed antiretroviral therapy (ART), and 84% were virally suppressed (VS). By IOM standards, 84% were in continuous care; and 78% and 80% underwent regular CD4 and VL monitoring, respectively. Screening for syphilis, chlamydia, and gonorrhea was 51%, 31%, and 26%, respectively. Older participants were 1.5 times more likely to be RIC compared to younger participants (OR: 1.5; 95% CI: 1.3, 1.8). Participants enrolled in community-based clinics were more likely to be RIC (OR: 1.7; 95% CI: 1.4, 2.0) versus those enrolled at hospital-based clinics. Older participants were more likely to achieve VS than younger participants (OR: 1.8; 95% CI: 1.5, 2.2) while Black participants were less likely compared to white participants (OR: 0.4; 95% CI: 0.3, 0.5). Despite high measures of quality of care, disparities remain. Continued monitoring of the quality of HIV care and treatment can inform the development of public health programs and interventions to optimize care delivery
Frontiers in Pigment Cell and Melanoma Research
We identify emerging frontiers in clinical and basic research of melanocyte
biology and its associated biomedical disciplines. We describe challenges and
opportunities in clinical and basic research of normal and diseased melanocytes
that impact current approaches to research in melanoma and the dermatological
sciences. We focus on four themes: (1) clinical melanoma research, (2) basic
melanoma research, (3) clinical dermatology, and (4) basic pigment cell
research, with the goal of outlining current highlights, challenges, and
frontiers associated with pigmentation and melanocyte biology. Significantly,
this document encapsulates important advances in melanocyte and melanoma
research including emerging frontiers in melanoma immunotherapy, medical and
surgical oncology, dermatology, vitiligo, albinism, genomics and systems
biology, epidemiology, pigment biophysics and chemistry, and evolution
Measuring The Mass Loss Evolution at The Tip of The Asymptotic Giant Branch
In the final stages of stellar evolution low- to intermediate-mass stars lose
their envelope in increasingly massive stellar winds. Such winds affect the
interstellar medium and the galactic chemical evolution as well as the
circumstellar envelope where planetary nebulae form subsequently.
Characteristics of this mass loss depend on both stellar properties and
properties of gas and dust in the wind formation region. In this paper we
present an approach towards studies of mass loss using both observations and
models, focusing on the stage where the stellar envelope is nearly empty of
mass. In a recent study we measure the mass-loss evolution, and other
properties, of four planetary nebulae in the Galactic Disk. Specifically we use
the method of integral field spectroscopy on faint halos, which are found
outside the much brighter central parts of a planetary nebula. We begin with a
brief comparison between our and other observational methods to determine
mass-loss rates in order to illustrate how they differ and complement each
other. An advantage of our method is that it measures the gas component
directly requiring no assumptions of properties of dust in the wind. Thereafter
we present our observational approach in more detail in terms of its validity
and its assumptions. In the second part of this paper we discuss capabilities
and assumptions of current models of stellar winds. We propose and discuss
improvements to such models that will allow meaningful comparisons with our
observations. Currently the physically most complete models include too little
mass in the model domain to permit a formation of winds with as high mass-loss
rates as our observations show.Comment: 7 pages, workshop in honour of Agnes Acker, Legacies of the
Macquarie/AAO/Strasbourg Halpha Planetary Nebula project, ed. Q.Parker and
D.Frew, PASA, in press; clarified some parts and added some additional
reference
A search for periodicity in the light curves of selected blazars
We present an analysis of multifrequency light curves of the sources 2223-052
(3C 446), 2230+114 (CTA 102), and 2251+158 (3C 454.3), which had shown evidence
of quasi-periodic activity. The analysis made use of data from the University
of Michican Radio Astronomy Observatory (USA) at 4.8, 8, and 14.5 GHz, as well
as the Metsahovi Radio Astronomy Observatory (Finland) at 22 and 37 GHz.
Application of two different methods (the discrete autocorrelation function and
the method of Jurkevich) both revealed evidence for periodicity in the flux
variations of these sources at essentially all frequencies. The periods derived
for at least two of the sources -- 2223-052 and 2251+158-- are in good
agreement with the time interval between the appearance of successive VLBI
components. The derived periods for 2251+158 (P = 12.4 yr and 2223-052 (P = 5.8
yr) coincide with the periods found earlier by other authors based on optical
light curves.Comment: 27 pages, 11 figures, accepted for publication in Astronomy Report
The GALFA-HI Survey: Data Release 1
We present the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) survey, and
its first full data release (DR1). GALFA-HI is a high resolution (~ 4'), large
area (13000 deg^2), high spectral resolution (0.18 km/s), wide band (-700 <
v_LSR < +700 km/s) survey of the Galactic interstellar medium in the 21-cm line
hyperfine transition of neutral hydrogen conducted at Arecibo Observatory.
Typical noise levels are 80 mK RMS in an integrated 1 km/s channel. GALFA-HI is
a dramatic step forward in high-resolution, large-area Galactic HI surveys, and
we compare GALFA-HI to past, present, and future Galactic HI surveys. We
describe in detail new techniques we have developed to reduce these data in the
presence of fixed pattern noise, gain variation, and inconsistent beam shapes,
and we show how we have largely mitigated these effects. We present our first
full data release, covering 7520 square degrees of sky and representing 3046
hours of integration time, and discuss the details of these data.Comment: Accepted to the ApJ
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