231 research outputs found
Malaria intervention scale-up in Africa : effectiveness predictions for health programme planning tools, based on dynamic transmission modelling
Scale-up of malaria prevention and treatment needs to continue to further important gains made in the past decade, but national strategies and budget allocations are not always evidence-based. Statistical models were developed summarizing dynamically simulated relations between increases in coverage and intervention impact, to inform a malaria module in the Spectrum health programme planning tool.; The dynamic Plasmodium falciparum transmission model OpenMalaria was used to simulate health effects of scale-up of insecticide-treated net (ITN) usage, indoor residual spraying (IRS), management of uncomplicated malaria cases (CM) and seasonal malaria chemoprophylaxis (SMC) over a 10-year horizon, over a range of settings with stable endemic malaria. Generalized linear regression models (GLMs) were used to summarize determinants of impact across a range of sub-Sahara African settings.; Selected (best) GLMs explained 94-97 % of variation in simulated post-intervention parasite infection prevalence, 86-97 % of variation in case incidence (three age groups, three 3-year horizons), and 74-95 % of variation in malaria mortality. For any given effective population coverage, CM and ITNs were predicted to avert most prevalent infections, cases and deaths, with lower impacts for IRS, and impacts of SMC limited to young children reached. Proportional impacts were larger at lower endemicity, and (except for SMC) largest in low-endemic settings with little seasonality. Incremental health impacts for a given coverage increase started to diminish noticeably at above ~40 % coverage, while in high-endemic settings, CM and ITNs acted in synergy by lowering endemicity. Vector control and CM, by reducing endemicity and acquired immunity, entail a partial rebound in malaria mortality among people above 5 years of age from around 5-7 years following scale-up. SMC does not reduce endemicity, but slightly shifts malaria to older ages by reducing immunity in child cohorts reached.; Health improvements following malaria intervention scale-up vary with endemicity, seasonality, age and time. Statistical models can emulate epidemiological dynamics and inform strategic planning and target setting for malaria control
Sloshing in High Speed Galaxy Interactions
Observations of lopsided spiral galaxies motivated us to explore whether the
rapid passage of a companion galaxy could cause them. We examine whether the
center of mass of the visible matter becomes displaced from the center of mass
of the dark halo during the intruder's passage, thereby causing an asymmetric
response and asymmetric structure. Two dimensional -body simulations
indicate that this can happen.
We also explore some consequences of this offset. These include the center of
mass of the visible disk following a decaying orbit around the halo center of
mass and the development of transient one-armed spirals that persist for up to
six rotation periods.
We then study the results of a variety of initial conditions based on such
offsets. We report on the results of several runs in which we initially offset
a disk from its halo's center of mass by an amount typical of the above
interaction. In some runs the halo is free to move, while in others it is held
fixed. We used three different mass distributions for the halo in these runs.
We find that the disk's center of mass spiraled inward creating a variety of
observed or observable phenomena including one-armed spirals, massive clumps of
particles, and counter-rotating waves. The systems settle into relatively
axisymmetric configurations. Whether or not the end states included a bar
depended on a variety of initial conditions.Comment: 20 text pages, 3 tables, 24 figures. A gzipped postscripped version
with higher resolution figures can be downloaded from
http://butch.umephy.maine.edu/kickers/Research/Sloshing/ . Accepted for
publication in The Astrophysical Journa
Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries
We analyze galactic black hole mergers and their emitted gravitational waves.
Such mergers have typically unequal masses with mass ratio of the order 1/10.
The emitted gravitational waves carry the inprint of spins and mass quadrupoles
of the binary components. Among these contributions, we consider here the
quasi-precessional evolution of the spins. A method of taking into account
these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5
PN and 2PN accurate spin contributions to the accumulated orbital phase is
developed.Comment: 10 pages, to appear in Class. Quantum Grav. GWDAW13 Proceedings
Special Issue, v2: no typos conjectur
Gravitating discs around black holes
Fluid discs and tori around black holes are discussed within different
approaches and with the emphasis on the role of disc gravity. First reviewed
are the prospects of investigating the gravitational field of a black
hole--disc system by analytical solutions of stationary, axially symmetric
Einstein's equations. Then, more detailed considerations are focused to middle
and outer parts of extended disc-like configurations where relativistic effects
are small and the Newtonian description is adequate.
Within general relativity, only a static case has been analysed in detail.
Results are often very inspiring, however, simplifying assumptions must be
imposed: ad hoc profiles of the disc density are commonly assumed and the
effects of frame-dragging and completely lacking. Astrophysical discs (e.g.
accretion discs in active galactic nuclei) typically extend far beyond the
relativistic domain and are fairly diluted. However, self-gravity is still
essential for their structure and evolution, as well as for their radiation
emission and the impact on the environment around. For example, a nuclear star
cluster in a galactic centre may bear various imprints of mutual star--disc
interactions, which can be recognised in observational properties, such as the
relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be
available from http://www.iop.org/EJ/journal/CQ
Kinematics of Ten Early-Type Galaxies from HST and Ground-Based Spectroscopy
We present stellar kinematics for a sample of 10 early-type galaxies observed
using the STIS aboard the Hubble Space Telescope, and the Modular Spectrograph
on the MDM Observatory 2.4-m telescope. The spectra are used to derive
line-of-sight velocity distributions (LOSVDs) of the stars using a Maximum
Penalized Likelihood method. We use Gauss-Hermite polynomials to parameterize
the LOSVDs and find predominantly negative h4 values (boxy distributions) in
the central regions of our galaxies. One galaxy, NGC 4697, has significantly
positive central h4 (high tail weight). The majority of galaxies have a central
velocity dispersion excess in the STIS kinematics over ground-based velocity
dispersions. The galaxies with the strongest rotational support, as quantified
with v_MAX/sigma_STIS, have the smallest dispersion excess at STIS resolution.
The best-fitting, general, axisymmetric dynamical models (described in a
companion paper) require black holes in all cases, with masses ranging from
10^6.5 to 10^9.3 Msun. We replot these updated masses on the BH/sigma relation,
and show that the fit to only these 10 galaxies has a slope consistent with the
fits to larger samples. The greatest outlier is NGC 2778, a dwarf elliptical
with relatively poorly constrained black hole mass. The two best candidates for
pseudobulges, NGC 3384 and 7457, do not deviate significantly from the
established relation between black hole and sigma. Neither do the three
galaxies which show the most evidence of a recent merger, NGC 3608, 4473, and
4697.Comment: 43 pages, accepted for publication in the Astrophysical Journal, high
resolution version found at http://hoku.as.utexas.edu/~gebhardt/pinkney.p
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
Host galaxies, clustering, Eddington ratios, and evolution of radio, X-ray, and infrared-selected AGNs
We explore the connection between different classes of active galactic nuclei
(AGNs) and the evolution of their host galaxies, by deriving host galaxy
properties, clustering, and Eddington ratios of AGNs selected in the radio,
X-ray, and infrared. We study a sample of 585 AGNs at 0.25 < z < 0.8 using
redshifts from the AGN and Galaxy Evolution Survey (AGES) and data in the radio
(WSRT 1.4 GHz), X-rays (Chandra XBootes), and mid-IR (IRAC Shallow Survey). The
radio, X-ray, and IR AGN samples show modest overlap, indicating that to the
flux limits of the survey, they represent largely distinct classes of AGNs. We
derive host galaxy colors and luminosities, as well as Eddington ratios
(lambda), for obscured or optically faint AGNs. We also measure the two-point
cross-correlation between AGNs and galaxies on scales of 0.3-10 h^-1 Mpc, and
derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly
found in luminous red galaxies, are strongly clustered (with M_halo ~ 3x10^13
h^-1 M_sun), and have very low lambda <~ 10^-3; (2) X-ray-selected AGNs are
preferentially found in galaxies in the "green valley" of color-magnitude space
and are clustered similarly to typical AGES galaxies (M_halo ~ 10^13 h^-1
M_sun), with 10^-3 <~ lambda <~ 1; (3) IR AGNs reside in slightly bluer, less
luminous galaxies than X-ray AGNs, are weakly clustered (M_halo <~ 10^12 h^-1
M_sun), and have lambda > 10^-2. We interpret these results in terms of a
simple model of AGN and galaxy evolution, whereby a "quasar" phase and the
growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a
critical mass between ~10^12 and 10^13 M_sun. Subsequently, star formation
ceases and AGN accretion shifts from radiatively efficient (optical- and IR-
bright) to radiatively inefficient (optically-faint, radio-bright) modes.Comment: 30 emulateapj pages, 21 figures, 3 tables, v2: minor changes match
version to appear in Ap
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