25 research outputs found
Cosmology with Weak Lensing Surveys
Weak gravitational lensing surveys measure the distortion of the image of
distant sources due to the deflections of light rays by the fluctuations of the
gravitational potential along the line of sight. Since they probe the
non-linear matter power spectrum itself at medium redshift such surveys are
complimentary to both galaxy surveys (which follow stellar light) and cosmic
microwave background observations (which probe the linear regime at high
redshift). Ongoing CMB experiments such as WMAP and the future Planck satellite
mission will measure the standard cosmological parameters with unprecedented
accuracy. The focus of attention will then shift to understanding the nature of
dark matter and vacuum energy: several recent studies suggest that lensing is
the best method for constraining the dark energy equation of state. During the
next 5 year period ongoing and future weak lensing surveys such as the Joint
Dark Energy Mission (JDEM, e.g. SNAP) or the Large-aperture Synoptic Survey
Telescope (LSST) will play a major role in advancing our understanding of the
universe in this direction. In this review article we describe various aspects
of weak lensing surveys and how they can help us in understanding our universe.Comment: 15 pages, review article to appear in 2005 Triennial Issue of Phil.
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A SOM-based analysis of the drivers of the 2015–2017 Western Cape drought in South Africa
The multi-year (2015–2017) drought in the South West of the Western Cape (SWC) caused a severe water shortage in the summer of 2017–2018, with damaging impacts on the local and regional economy, and Cape Town being in the news one of the first major cities to potentially run out of water. Here, we assess the links between the rainfall deficits during the drought and (a) large scale circulation patterns, (b) moisture transport, and (c) convective available potential energy (CAPE). We used self-organising maps (SOM) analysis to classify daily ERA-interim 850 hPa geopotential height for the period 1979–2017 (March–October) into synoptic types. This allowed us to identify the dominant synoptic states over Southern Africa that influence the local climate in the area affected by the drought. The results show that (a) the frequency of nodes with rain-bearing circulation types decreased during the drought; (b) the amount of rain falling on days that did have rain-bearing circulation types was reduced, especially in the shoulder seasons (March–May and August–October); (c) the rainfall reduction was also associated with anomalously low moisture transport, and convective energy (CAPE), over SWC. These results add to the existing knowledge of drivers of the Cape Town drought, providing an understanding of underlying synoptic processes
The effect of incentive spirometry on postoperative pulmonary function following laparotomy a randomized clinical trial
Importance: Changes in pulmonary dynamics following laparotomy are well documented. Deep breathing exercises, with or without incentive spirometry, may help counteract postoperative decreased vital capacity; however, the evidence for the role of incentive spirometry in the prevention of postoperative atelectasis is inconclusive. Furthermore, data are scarce regarding the prevention of postoperative atelectasis in sub-Saharan Africa. Objective: To determine the effect of the use of incentive spirometry on pulmonary function following exploratory laparotomy as measured by forced vital capacity (FVC). Design, Setting, and Participants: Thiswas a single-center, randomized clinical trial performed at Kamuzu Central Hospital, Lilongwe, Malawi. Study participants were adult patients who underwent exploratory laparotomy and were randomized into the intervention or control groups (standard of care) from February 1 to November 30, 2013. All patients received routine postoperative care, including instructions for deep breathing and early ambulation.We used bivariate analysis to compare outcomes between the intervention and control groups. Intervention: Adult patients who underwent exploratory laparotomy participated in postoperative deep breathing exercises. Patients in the intervention group received incentive spirometers Main outcomes and measures: We assessed pulmonary function using a peak flow meter to measure FVC in both groups of patients. Secondary outcomes, such as hospital length of stay and mortality, were obtained from the medical records. Results: A total of 150 patients were randomized (75 in each arm). The median age in the intervention and control groups was 35 years (interquartile range, 28-53 years) and 33 years (interquartile range, 23-46 years), respectively. Men predominated in both groups, and most patients underwent emergency procedures (78.7%in the intervention group and 84.0%in the control group). Mean initial FVC did not differ significantly between the intervention and control groups (0.92 and 0.90 L, respectively; P = .82 [95%CI, 0.52-2.29]). Although patients in the intervention group tended to have higher final FVC measurements, the change between the first and last measured FVC was not statistically significant (0.29 and 0.25 L, respectively; P = .68 [95%CI, 0.65-1.95]). Likewise, hospital length of stay did not differ significantly between groups. Overall postoperative mortality was 6.0%, with a higher mortality rate in the control group compared with the intervention group (10.7%and 1.3%, respectively; P = .02 [95%CI, 0.01-0.92]). Conclusions and Relevance: Education and provision of incentive spirometry for unmonitored patient use does not result in statistically significant improvement in pulmonary dynamics following laparotomy.We would not recommend the addition of incentive spirometry to the current standard of care in this resource-constrained environment. Trial registration: clinicaltrials.gov Identifier: NCT01789177
The effect of seasonality on burn incidence, severity and outcome in Central Malawi
Introduction In much of the world, burns are more common in cold months. However, few studies have described the seasonality of burns in sub-Saharan Africa. This study examines the effect of seasonality on the incidence and outcome of burns in central Malawi. Methods A retrospective analysis was performed at Kamuzu Central Hospital and included all patients admitted from May 2011 to August 2014. Demographic data, burn mechanism, total body surface area (%TBSA), and mortality were analyzed. Seasons were categorized as Rainy (December–February), Lush (March–May), Cold (June–August) and Hot (September–November). A negative binomial regression was used to assess the effect of seasonality on burn incidence. This was performed using both the raw and deseasonalized data in order to evaluate for trends not attributable to random fluctuation. Results A total of 905 patients were included. Flame (38%) and Scald (59%) burns were the most common mechanism. More burns occurred during the cold season (41% vs 19–20% in the other seasons). Overall mortality was 19%. Only the cold season had a statistically significant increase in burn. The incidence rate ratios (IRR) for the hot, lush, and cold seasons were 0.94 (CI 0.6–1.32), 1.02 (CI 0.72–1.45) and 1.6 (CI 1.17–2.19), respectively, when compared to the rainy season. Burn severity and mortality did not differ between seasons. Conclusion The results of this study demonstrate the year-round phenomenon of burns treated at our institution, and highlights the slight predominance of burns during the cold season. These data can be used to guide prevention strategies, with special attention to the implications of the increased burn incidence during the cold season. Though burn severity and mortality remain relatively unchanged between seasons, recognizing the seasonal variability in incidence of burns is critical for resource allocation in this low-income setting
Interatomic potentials for atomistic simulations of the Ti-Al system
Semi-empirical interatomic potentials have been developed for Al, alpha-Ti,
and gamma-TiAl within the embedded atomic method (EAM) by fitting to a large
database of experimental as well as ab-initio data. The ab-initio calculations
were performed by the linear augmented plane wave (LAPW) method within the
density functional theory to obtain the equations of state for a number of
crystal structures of the Ti-Al system. Some of the calculated LAPW energies
were used for fitting the potentials while others for examining their quality.
The potentials correctly predict the equilibrium crystal structures of the
phases and accurately reproduce their basic lattice properties. The potentials
are applied to calculate the energies of point defects, surfaces, planar faults
in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al
system, the proposed potentials provide reasonable description of the lattice
thermal expansion, demonstrating their usefulness in the molecular dynamics or
Monte Carlo studies at high temperatures. The energy along the tetragonal
deformation path (Bain transformation) in gamma-TiAl calculated with the EAM
potential is in a fairly good agreement with LAPW calculations. Equilibrium
point defect concentrations in gamma-TiAl are studied using the EAM potential.
It is found that antisite defects strongly dominate over vacancies at all
compositions around stoichiometry, indicating that gamm-TiAl is an antisite
disorder compound in agreement with experimental data.Comment: 46 pages, 6 figures (Physical Review B, in press
Weak lensing, dark matter and dark energy
Weak gravitational lensing is rapidly becoming one of the principal probes of
dark matter and dark energy in the universe. In this brief review we outline
how weak lensing helps determine the structure of dark matter halos, measure
the expansion rate of the universe, and distinguish between modified gravity
and dark energy explanations for the acceleration of the universe. We also
discuss requirements on the control of systematic errors so that the
systematics do not appreciably degrade the power of weak lensing as a
cosmological probe.Comment: Invited review article for the GRG special issue on gravitational
lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). V3: subsection on
three-point function and some references added. Matches the published versio
Three-Dimensional Mapping of the Dark Matter
We study the prospects for three-dimensional mapping of the dark matter to
high redshift through the shearing of faint galaxies images at multiple
distances by gravitational lensing. Such maps could provide invaluable
information on the nature of the dark energy and dark matter. While in
principle well-posed, mapping by direct inversion introduces exceedingly large,
but usefully correlated noise into the reconstruction. By carefully propagating
the noise covariance, we show that lensing contains substantial information,
both direct and statistical, on the large-scale radial evolution of the density
field. This information can be efficiently distilled into low-order
signal-to-noise eigenmodes which may be used to compress the data by over an
order of magnitude. Such compression will be useful for the statistical
analysis of future large data sets. The reconstructed map also contains useful
information on the localization of individual massive dark matter halos, and
hence the dark energy from halo number counts, but its extraction depends
strongly on prior assumptions. We outline a procedure for maximum entropy and
point-source regularization of the maps that can identify alternate
reconstructions.Comment: 11 pages, 5 figures, submitted to PR