24,354 research outputs found
Constraints on turbulent velocity broadening for a sample of clusters, groups and elliptical galaxies using XMM-Newton
Using the width of emission lines in XMM-Newton Reflection Grating
Spectrometer spectra, we place direct constraints on the turbulent velocities
of the X-ray emitting medium in the cores of 62 galaxy clusters, groups and
elliptical galaxies. We find five objects where we can place an upper limit on
the line-of-sight broadening of 500 km/s (90 per cent confidence level), using
a single thermal component model. Two other objects are lower than this limit
when two thermal components are used. Half of the objects examined have an
upper limit on the velocity broadening of less than 700 km/s. To look for
objects which have significant turbulent broadening, we use Chandra spectral
maps to compute the expected broadening caused by the spatial extent of the
source. Comparing these with our observed results, we find that Klemola 44 has
extra broadening at the level of 1500 km/s. RX J1347.5-1145 shows weak evidence
for turbulent velocities at 800 km/s. In addition we obtain limits on
turbulence for Zw3146, Abell 496, Abell 1795, Abell 2204 and HCG 62 of less
than 200 km/s. After subtraction of the spatial contribution and including a 50
km/s systematic uncertainty, we find at least 15 sources with less than 20 per
cent of the thermal energy density in turbulence.Comment: 17 pages, 17 figures, accepted by MNRAS. Includes minor edits to
proo
Searching for the missing iron in the core of the Centaurus cluster
We re-analyse a combined 198 ks Chandra observation of NGC4696, the brightest
galaxy of the Centaurus cluster. We extract temperature and metallicity
profiles from the data, and we confirm the presence of a sharp drop in iron
abundance, from ~1.8 Zsolar to ~0.4 Zsolar, within the central 5 kpc of the
cluster. We estimate that this abundance drop corresponds to a total "missing"
iron mass of 1.4e06 Msolar. We propose that part of this missing iron is locked
up in cool (~19 K) far-IR emitting dust, as found by Spitzer and Herschel
observations. This can occur if the iron injected by stellar mass loss in the
central region is in grains, which remain in that form as the injected dusty
cold gas mixes and joins the cold dusty filamentary nebula observed within the
same region. The bubbling feedback process observed in the cluster core then
drags filaments outward and dumps them at 10-20 kpc radius, where the
metallicity is high.Comment: 8 pages, accepted for publication in MNRA
Memetic Multilevel Hypergraph Partitioning
Hypergraph partitioning has a wide range of important applications such as
VLSI design or scientific computing. With focus on solution quality, we develop
the first multilevel memetic algorithm to tackle the problem. Key components of
our contribution are new effective multilevel recombination and mutation
operations that provide a large amount of diversity. We perform a wide range of
experiments on a benchmark set containing instances from application areas such
VLSI, SAT solving, social networks, and scientific computing. Compared to the
state-of-the-art hypergraph partitioning tools hMetis, PaToH, and KaHyPar, our
new algorithm computes the best result on almost all instances
Galactic metric, dark radiation, dark pressure and gravitational lensing in brane world models
In the braneworld scenario, the four dimensional effective Einstein equation
has extra terms which arise from the embedding of the 3-brane in the bulk.
These non-local effects, generated by the free gravitational field of the bulk,
may provide an explanation for the dynamics of the neutral hydrogen clouds at
large distances from the galactic center, which is usually explained by
postulating the existence of the dark matter. We obtain the exact galactic
metric, the dark radiation and the dark pressure in the flat rotation curves
region in the brane world scenario. Due to the presence of the bulk effects,
the flat rotation curves could extend several hundred kpc. The limiting radius
for which bulk effects are important is estimated and compared with the
numerical values of the truncation parameter of the dark matter halos, obtained
from weak lensing observations. There is a relatively good agreement between
the predictions of the model and observations. The deflection of photons is
also considered and the bending angle of light is computed. The bending angle
predicted by the brane world models is much larger than that predicted by
standard general relativistic and dark matter models. The angular radii of the
Einstein rings are obtained in the small angles approximation. The predictions
of the brane world model for the tangential shear are compared with the
observational data obtained in the weak lensing of galaxies in the Red-Sequence
Cluster Survey. Therefore the study of the light deflection by galaxies and the
gravitational lensing could discriminate between the different dynamical laws
proposed to model the motion of particles at the galactic level and the
standard dark matter models.Comment: 33 pages, 3 figures, accepted for publication in Ap
A volume-limited sample of X-ray galaxy groups and clusters - II. X-ray cavity dynamics
We present the results of our study of a volume-limited sample (z <= 0.071)
of 101 X-ray galaxy groups and clusters, in which we explore the X-ray cavity
energetics. Out of the 101 sources in our parent sample, X-ray cavities are
found in 30 of them, all of which have a central cooling time of less than3
Gyr. New X-ray cavities are detected in three sources. We focus on the subset
of sources that have a central cooling time of less than 3 Gyr, whose active
galactic nucleus (AGN) duty cycle is approximately 61 percent (30/49). This
rises to over 80 percent for a central cooling time of less than 0.5 Gyr. When
projection effects and central radio source detection rates are considered, the
actual duty cycle is probably much higher. In addition, we show that data
quality strongly affects the detection rates of X-ray cavities. After
calculating the cooling luminosity and cavity powers of each source with
cavities, it is evident that the bubbling process induced by the central AGN
has to be, on average, continuous, to offset cooling. We find that the radius
of the cavities, r, loosely depends on the ambient gas temperature as T^0.5,
above about 1.5 keV, with much more scatter below that temperature. Finally, we
show that, at a given location in a group or cluster, larger bubbles travel
faster than smaller ones. This means that the bubbles seen at larger distances
from cluster cores could be the result of the merging of several smaller
bubbles, produced in separate AGN cycles.Comment: Accepted for publication in MNRAS; 26 pages (including 10 pages of
images), 8 figures, 2 tables. Higher resolution images will be available as
online materia
BOOMERanG Data Suggest a Purely Baryonic Universe
The amplitudes of peaks in the angular power spectrum of anisotropies in the
microwave background radiation depend on the mass content of the universe. The
second peak should be prominent when cold dark matter is dominant, but is
depressed when baryons dominate. Recent microwave background data are
consistent with a purely baryonic universe with Omega(matter) = Omega(baryon) ~
0.03 and Omega(Lambda) ~ 1.Comment: 10 pages AASTeX with 1 color postscript figure. Accepted for
publication in ApJ Letters. And yes, the prediction was in the literature
before the dat
Effects of a multi-component exercise program and calcium–vitamin-D3-fortified milk on bone mineral density in older men : a randomised controlled trial
Summary We examined the independent and combined effects of a multi-component exercise program and calcium–vitamin-D3-fortified milk on bone mineral density (BMD) in older men. Exercise resulted in a 1.8% net gain in femoral neck BMD, but additional calcium–vitamin D3 did not enhance the response in this group of older well-nourished men.Introduction This 12-month randomised controlled trial assessed whether calcium–vitamin-D3-fortified milk could enhance the effects of a multi-component exercise program on BMD in older men.Methods Men (n  = 180) aged 50–79 years were randomised into: (1) exercise + fortified milk; (2) exercise; (3) fortified milk; or (4) controls. Exercise consisted of high intensity progressive resistance training with weight-bearing impact exercise. Men assigned to fortified milk consumed 400 mL/day of low fat milk providing an additional 1,000 mg/day calcium and 800 IU/day vitamin D3. Femoral neck (FN), total hip, lumbar spine and trochanter BMD and body composition (DXA), muscle strength 25-hydroxyvitamin D and parathyroid hormone (PTH) were assessed.Results There were no exercise-by-fortified milk interactions at any skeletal site. Exercise resulted in a 1.8% net gain in FN BMD relative to no-exercise (p < 0.001); lean mass (0.6 kg, p < 0.05) and muscle strength (20–52%, p < 0.001) also increased in response to exercise. For lumbar spine BMD, there was a net 1.4–1.5% increase in all treatment groups relative to controls (all p < 0.01). There were no main effects of fortified milk at any skeletal site.Conclusion A multi-component community-based exercise program was effective for increasing FN BMD in older men, but additional calcium–vitamin D3 did not enhance the osteogenic response.<br /
Engineering adiabaticity at an avoided crossing with optimal control
We investigate ways to optimize adiabaticity and diabaticity in the
Landau-Zener model with non-uniform sweeps. We show how diabaticity can be
engineered with a pulse consisting of a linear sweep augmented by an
oscillating term. We show that the oscillation leads to jumps in populations
whose value can be accurately modeled using a model of multiple,
photon-assisted Landau-Zener transitions, which generalizes work by Wubs et al.
[New J. Phys. 7, 218 (2005)]. We extend the study on diabaticity using methods
derived from optimal control. We also show how to preserve adiabaticity with
optimal pulses at limited time, finding a non-uniform quantum speed limit
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