12,938 research outputs found
Stellar populations -- the next ten years
The study of stellar populations is a discipline that is highly dependent on
both imaging and spectroscopy. I discuss techniques in different regimes of
resolving power: broadband imaging (R~4), intermediate band imaging (R~16, 64),
narrowband spectral imaging (R~256, 1024, 4096). In recent years, we have seen
major advances in broadband all-sky surveys that are set to continue across
optical and IR bands, with the added benefit of the time domain, higher
sensitivity, and improved photometric accuracy. Tunable filters and integral
field spectrographs are poised to make further inroads into intermediate and
narrowband imaging studies of stellar populations. Further advances will come
from AO-assisted imaging and imaging spectroscopy, although photometric
accuracy will be challenging. Integral field spectroscopy will continue to have
a major impact on future stellar population studies, extending into the near
infrared once the OH suppression problem is finally resolved. A sky rendered
dark will allow a host of new ideas to be explored, and old ideas to be
revisited.Comment: Invited review, IAUS 241, "Stellar Populations as Building Blocks of
Galaxies," eds. Vazdekis, Peletier. 12 pages, 1 table. (The sideways table
should print ok; there are 10 columns.
Simulation test results for lift/cruise fan research and technology aircraft
A flight simulation program was conducted on the flight simulator for advanced aircraft (FSAA). The flight simulation was a part of a contracted effort to provide a lift/cruise fan V/STOL aircraft mathematical model for flight simulation. The simulated aircraft is a configuration of the Lift/Cruise Fan V/STOL research technology aircraft (RTA). The aircraft was powered by three gas generators driving three fans. One lift fan was installed in the nose of the aircraft, and two lift/cruise fans at the wing root. The thrust of these fans was modulated to provide pitch and roll control, and vectored to provide yaw, side force control, and longitudinal translation. Two versions of the RTA were defined. One was powered by the GE J97/LF460 propulsion system which was gas-coupled for power transfer between fans for control. The other version was powered by DDA XT701 gas generators driving 62 inch variable pitch fans. The flight control system in both versions of the RTA was the same
Astrochemistry and Astrophotonics for an Antarctic Observatory
Due to its location and climate, Antarctica offers unique conditions for
long-period observations across a broad wavelength regime, where important
diagnostic lines for molecules and ions can be found, that are essential to
understand the chemical properties of the interstellar medium. In addition to
the natural benefits of the site, new technologies, resulting from
astrophotonics, may allow miniaturised instruments, that are easier to
winterise and advanced filters to further reduce the background in the
infrared.Comment: 4 pages, to be published in EAS Publications Series, Vol. 40, Proc.
of 3rd ARENA conferenc
Successful paediatric HIV treatment in rural primary care in Africa
<p>Objective: Clinical outcomes of HIV-infected children on antiretroviral treatment (ART) in a decentralised, nurse/counsellor-led programme.</p>
<p>Design: Clinical cohort.</p>
<p>Setting: KwaZulu-Natal, South Africa.</p>
<p>Patients: HIV-infected children aged <= 15 years on ART, June 2004-2008.</p>
<p>Main outcome measures: Survival according to baseline characteristics including age, WHO clinical stage, haemoglobin and CD4%, was assessed in Kaplan-Meier analyses. Hazard ratios for mortality were estimated using Cox proportional hazards regression and changes in laboratory parameters and weight-for-age z scores after 6-12 months' treatment were calculated.</p>
<p>Results: 477 HIV-infected children began ART at a median age of 74 months (range 4-180), median CD4 count (CD4%) of 433 cells/mm(3) (17%) and median HIV viral load of log 4.2 copies/ml; 105 (22%) were on treatment for tuberculosis and 317 (76.6%) were WHO stage 3/4. There were significant increases after ART initiation in CD4% (17% vs 22%; p<0.001), haemoglobin (9.9 vs 11.7 g/l; p <= 0.001) and albumin (30 vs 36 g/l; p <= 0.001). 32 (6.7%) children died over 732 child-years of follow-up (43.7 deaths/1000 child-years; 95% CI 32.7 to 58.2), 17 (53.1%) within 90 days of treatment initiation; median age of death was 84 (IQR 10-181) months. Children with baseline haemoglobin <= 8 g/l were more likely to die (adjusted HR 4.5; 95% CI 1.6 to 12.3), as were those aged <18 months compared with >60 months (adjusted HR 3.2; 95% CI 1.2 to 9.1).</p>
<p>Conclusions Good clinical outcomes in HIV-infected children on ART are possible in a rural, decentralised service. Few young children are on ART, highlighting the urgent need to identify HIV-exposed infants.</p>
MMTF: The Maryland-Magellan Tunable Filter
This paper describes the Maryland-Magellan Tunable Filter (MMTF) on the
Magellan-Baade 6.5-meter telescope. MMTF is based on a 150-mm clear aperture
Fabry-Perot (FP) etalon that operates in low orders and provides transmission
bandpass and central wavelength adjustable from ~5 to ~15 A and from ~5000 to
over ~9200 A, respectively. It is installed in the Inamori Magellan Areal
Camera and Spectrograph (IMACS) and delivers an image quality of ~0.5" over a
field of view of 27' in diameter (monochromatic over ~10'). This versatile and
easy-to-operate instrument has been used over the past three years for a wide
variety of projects. This paper first reviews the basic principles of FP
tunable filters, then provides a detailed description of the hardware and
software associated with MMTF and the techniques developed to observe with this
instrument and reduce the data. The main lessons learned in the course of the
commissioning and implementation of MMTF are highlighted next, before
concluding with a brief outlook on the future of MMTF and of similar facilities
which are soon coming on line.Comment: 38 pages, 12 figures, 3 tables, now accepted for publication to the
Astronomical Journa
Agreement between methods of measurement with multiple observations per individual
Limits of agreement provide a straightforward and intuitive approach to agreement between different methods for measuring the same quantity. When pairs of observations using the two methods are independent, i.e., on different subjects, the calculations are very simple and straightforward. Some authors collect repeated data, either as repeated pairs of measurements on the same subject, whose true value of the measured quantity may be changing, or more than one measurement by one or both methods of an unchanging underlying quantity. In this paper we describe methods for analysing such clustered observations, both when the underlying quantity is assumed to be changing and when it is not
The Smith Cloud: high-velocity accretion and dark-matter confinement
The Smith Cloud is a massive system of metal-poor neutral and ionized gas
M_gas >= 2x10^6 M_sun) that is presently moving at high velocity (V_GSR ~300 km
s^-1) with respect to the Galaxy at a distance of 12 kpc from the Sun. The
kinematics of the cloud's cometary tail indicates that the gas is in the
process of accretion onto the Galaxy, as first discussed by Lockman et al.
(2008). Here, we re-investigate the cloud's orbit by considering the
possibility that the cloud is confined by a dark matter halo. This is required
for the cloud to survive its passage through the Galactic corona. We consider
three possible models for the dark matter halo (NFW, Einasto, Burkert)
including the effects of tidal disruption and ram-pressure stripping during the
cloud's infall onto and passage through the Galactic disk. For the NFW and
Einasto dark-matter models, we are able to determine reasonable initial
conditions for the Smith Cloud, although this is only marginally possible with
the Burkert model. For all three models, the progenitor had an initial
(gas+dark matter) mass that was an order of magnitude higher than inferred
today. In agreement with Lockman et al. (2008), the cloud appears to have
punched through the disk ~70 Myr ago. For our most successful models, the
baryon to dark matter ratio is fairly constant during an orbital period but
drops by a factor of 2-5 after transiting the disk. The cloud appears to have
only marginally survived its transit, and is unlikely to retain its integrity
during the next transit ~30 Myr from now.Comment: 9 pages, 7 figures. ApJ, accepte
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