262 research outputs found
The OGLE View of Microlensing towards the Magellanic Clouds. II. OGLE-II SMC data
The primary goal of this paper is to provide the evidence that can either
prove or falsify the hypothesis that dark matter in the Galactic halo can clump
into stellar-mass compact objects. If such objects existed, they would act as
lenses to external sources in the Magellanic Clouds, giving rise to an
observable effect of microlensing. We present the results of our search for
such events, based on the data from the second phase of the OGLE survey
(1996-2000) towards the SMC. The data set we used is comprised of 2.1 million
monitored sources distributed over an area of 2.4 square degrees. We found only
one microlensing event candidate, however its poor quality light curve limited
our discussion on the exact distance to the lensing object.
Given a single event, taking the blending (crowding of stars) into account
for the detection efficiency simulations, and deriving the HST-corrected number
of monitored stars, the microlensing optical depth is tau=(1.55+-1.55)10e-7.
This result is consistent with the expected SMC self-lensing signal, with no
need of introducing dark matter microlenses. Rejecting the unconvincing event
leads to the upper limit on the fraction of dark matter in the form of MACHOs
to f<20 per cent for deflectors' masses around 0.4 Msun and f<11 per cent for
masses between 0.003 and 0.2 Msun (95 per cent confidence limit). Our result
indicates that the Milky Way's dark matter is unlikely to be clumpy and form
compact objects in the sub-solar-mass range.Comment: Accepted for publication in MNRAS. Data in electronic form are
available on the OGLE's website: http://ogle.astrouw.edu.pl
Finite temperature calculations for the bulk properties of strange star using a many-body approach
We have considered a hot strange star matter, just after the collapse of a
supernova, as a composition of strange, up and down quarks to calculate the
bulk properties of this system at finite temperature with the density dependent
bag constant. To parameterize the density dependent bag constant, we use our
results for the lowest order constrained variational (LOCV) calculations of
asymmetric nuclear matter. Our calculations for the structure properties of the
strange star at different temperatures indicate that its maximum mass decreases
by increasing the temperature. We have also compared our results with those of
a fixed value of the bag constant. It can be seen that the density dependent
bag constant leads to higher values of the maximum mass and radius for the
strange star.Comment: 21 pages, 2 tables, 12 figures Astrophys. (2011) accepte
Reaching the poor with health interventions: programme-incidence analysis of seven randomised trials of women's groups to reduce newborn mortality in Asia and Africa
Efforts to end preventable newborn deaths will fail if the poor are not reached with effective interventions. To understand what works to reach vulnerable groups, we describe and explain the uptake of a highly effective community-based newborn health intervention across social strata in Asia and Africa
Strange Quark Matter and Compact Stars
Astrophysicists distinguish between three different types of compact stars.
These are white dwarfs, neutron stars, and black holes. The former contain
matter in one of the densest forms found in the Universe which, together with
the unprecedented progress in observational astronomy, make such stars superb
astrophysical laboratories for a broad range of most striking physical
phenomena. These range from nuclear processes on the stellar surface to
processes in electron degenerate matter at subnuclear densities to boson
condensates and the existence of new states of baryonic matter--like color
superconducting quark matter--at supernuclear densities. More than that,
according to the strange matter hypothesis strange quark matter could be more
stable than nuclear matter, in which case neutron stars should be largely
composed of pure quark matter possibly enveloped in thin nuclear crusts.
Another remarkable implication of the hypothesis is the possible existence of a
new class of white dwarfs. This article aims at giving an overview of all these
striking physical possibilities, with an emphasis on the astrophysical
phenomenology of strange quark matter. Possible observational signatures
associated with the theoretically proposed states of matter inside compact
stars are discussed as well. They will provide most valuable information about
the phase diagram of superdense nuclear matter at high baryon number density
but low temperature, which is not accessible to relativistic heavy ion
collision experiments.Comment: 58 figures, to appear in "Progress in Particle and Nuclear Physics";
References added for sections 1,2,3,5; Equation (116) corrected; Figs. 1 and
58 update
Mobilise-D insights to estimate real-world walking speed in multiple conditions with a wearable device
This study aimed to validate a wearable device's walking speed estimation pipeline, considering complexity, speed, and walking bout duration. The goal was to provide recommendations on the use of wearable devices for real-world mobility analysis. Participants with Parkinson's Disease, Multiple Sclerosis, Proximal Femoral Fracture, Chronic Obstructive Pulmonary Disease, Congestive Heart Failure, and healthy older adults (nâ=â97) were monitored in the laboratory and the real-world (2.5Â h), using a lower back wearable device. Two walking speed estimation pipelines were validated across 4408/1298 (2.5Â h/laboratory) detected walking bouts, compared to 4620/1365 bouts detected by a multi-sensor reference system. In the laboratory, the mean absolute error (MAE) and mean relative error (MRE) for walking speed estimation ranged from 0.06 to 0.12Â m/s and -â2.1 to 14.4%, with ICCs (Intraclass correlation coefficients) between good (0.79) and excellent (0.91). Real-world MAE ranged from 0.09 to 0.13, MARE from 1.3 to 22.7%, with ICCs indicating moderate (0.57) to good (0.88) agreement. Lower errors were observed for cohorts without major gait impairments, less complex tasks, and longer walking bouts. The analytical pipelines demonstrated moderate to good accuracy in estimating walking speed. Accuracy depended on confounding factors, emphasizing the need for robust technical validation before clinical application.Trial registration: ISRCTN - 12246987
Laboratory and free-living gait performance in adults with COPD and healthy controls
BACKGROUND
Gait characteristics are important risk factors for falls, hospitalisations and mortality in older adults, but the impact of COPD on gait performance remains unclear. We aimed to identify differences in gait characteristics between adults with COPD and healthy age-matched controls during 1) laboratory tests that included complex movements and obstacles, 2) simulated daily-life activities (supervised) and 3) free-living daily-life activities (unsupervised).
METHODS
This case-control study used a multi-sensor wearable system (INDIP) to obtain seven gait characteristics for each walking bout performed by adults with mild-to-severe COPD (n=17; forced expiratory volume in 1â
s 57±19% predicted) and controls (n=20) during laboratory tests, and during simulated and free-living daily-life activities. Gait characteristics were compared between adults with COPD and healthy controls for all walking bouts combined, and for shorter (â€30â
s) and longer (>30â
s) walking bouts separately.
RESULTS
Slower walking speed (-11â
cm·s, 95% CI: -20 to -3) and lower cadence (-6.6 steps·min, 95% CI: -12.3 to -0.9) were recorded in adults with COPD compared to healthy controls during longer (>30â
s) free-living walking bouts, but not during shorter (â€30â
s) walking bouts in either laboratory or free-living settings. Double support duration and gait variability measures were generally comparable between the two groups.
CONCLUSION
Gait impairment of adults with mild-to-severe COPD mainly manifests during relatively long walking bouts (>30â
s) in free-living conditions. Future research should determine the underlying mechanism(s) of this impairment to facilitate the development of interventions that can improve free-living gait performance in adults with COPD
Deletion of chromosome 4q predicts outcome in Stage II colon cancer patients
Background: Around 30% of all stage II colon cancer patients will relapse and die of their disease. At present no objective parameters to identify high-risk stage II colon cancer patients, who will benefit from adjuvant chemotherapy, have been established. With traditional histopathological features definition of high-risk stage II colon cancer patients is inaccurate. Therefore more objective and robust markers for prediction of relapse are needed. DNA copy number aberrations have proven to be robust prognostic markers, but have not yet been investigated for this specific group of patients. The aim of the present study was to identify chromosomal aberrations that can predict relapse of tumor in patients with stage II colon cancer
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
Light cone effect on the reionization 21-cm signal â II. Evolution, anisotropies and observational implications
Measurements of the H I 21-cm power spectra from the reionization epoch will be influenced by the evolution of the signal along the line-of-sight direction of any observed volume. We use numerical as well as seminumerical simulations of reionization in a cubic volume of 607 Mpc across to study this so-called light-cone effect on the H I 21-cm power spectrum. We find that the light-cone effect has the largest impact at two different stages of reionization: one when reionization is âŒ20 per cent and other when it is âŒ80 per cent completed. We find a factor of âŒ4 amplification of the power spectrum at the largest scale available in our simulations. We do not find any significant anisotropy in the 21-cm power spectrum due to the light-cone effect. We argue that for the power spectrum to become anisotropic, the light-cone effect would have to make the ionized bubbles significantly elongated or compressed along the line of sight, which would require extreme reionization scenarios. We also calculate the two-point correlation functions parallel and perpendicular to the line of sight and find them to differ. Finally, we calculate an optimum frequency bandwidth below which the light-cone effect can be neglected when extracting power spectra from observations. We find that if one is willing to accept a 10 per cent error due to the light-cone effect, the optimum frequency bandwidth for k = 0.056 Mpcâ1 is âŒ7.5 MHz. For k = 0.15 and 0.41 Mpcâ1, the optimum bandwidth is âŒ11 and âŒ16 MHz, respectively
Unexpected Fine-Scale Population Structure in a Broadcast-Spawning Antarctic Marine Mollusc
Several recent empirical studies have challenged the prevailing dogma that broadcast-spawning species exhibit little or no population genetic structure by documenting genetic discontinuities associated with large-scale oceanographic features. However, relatively few studies have explored patterns of genetic differentiation over fine spatial scales. Consequently, we used a hierarchical sampling design to investigate the basis of a weak but significant genetic difference previously reported between Antarctic limpets (Nacella concinna) sampled from Adelaide and Galindez Islands near the base of the Antarctic Peninsula. Three sites within Ryder Bay, Adelaide Island (Rothera Point, Leonie and Anchorage Islands) were each sub-sampled three times, yielding a total of 405 samples that were genotyped at 155 informative Amplified Fragment Length Polymorphisms (AFLPs). Contrary to our initial expectations, limpets from Anchorage Island were found to be subtly, but significantly distinct from those sampled from the other sites. This suggests that local processes may play an important role in generating fine-scale population structure even in species with excellent dispersal capabilities, and highlights the importance of sampling at multiple spatial scales in population genetic surveys
- âŠ