8 research outputs found
Testing the statistical isotropy of the universe using radio survey data
>Magister Scientiae - MScThe Cosmological Principle forms part of one of the most fundamental hypotheses
of modern Cosmology. So it is very important to assess whether it holds true using
observational data, or whether it consists of a mathematical simplification. We probe
the statistical isotropy of the Universe using the existing radio continuum data, by
means of a local variance estimator. In order to investigate this, we analyse the number
count variance of the radio catalog by looking at patches of approximately 10,
15, 20 & 25 degrees in radii, and thus comparing it to mock catalogs which reproduce the
matter density power spectrum, as well as the same sky coverage of the real data.
We establish criteria for accepting patches that have more than 90%, 70% & 50% of
their pixels not masked. We make use of the NRAO VLA Sky Survey (NVSS), whose
operational frequency is 1.4 GHz. We perform statistical tests for detecting possible
departures from statistical isotropy using galaxy number counts with flux limits of
20 < SNVSS < 1000 mJy. We also compare the real data to the mock catalogs of the
radio data in order to assess the statistical significance of our results. We use the
local variance estimator for testing the statistical isotropy of our data sample. We
find that the statistical properties of our sample are in reasonable agreement with
the standard cosmological model. The mean of the distribution for the data falls
well within the 95% confidence interval of the average of the simulated mocks. For
all the radii and acceptance criteria for the patches, we found no significant deviations
beyond those allowed by the standard model. As expected there were no
large discrepancies between our mocks and the data. The results are consistent with
statistical isotropy
Testing the Cosmological Principle in the radio sky
The Cosmological Principle states that the Universe is statistically
isotropic and homogeneous on large scales. In particular, this implies
statistical isotropy in the galaxy distribution, after removal of a dipole
anisotropy due to the observer's motion. We test this hypothesis with number
count maps from the NVSS radio catalogue. We use a local variance estimator
based on patches of different angular radii across the sky and compare the
source count variance between and within these patches. In order to assess the
statistical significance of our results, we simulate radio maps with the NVSS
specifications and mask. We conclude that the NVSS data is consistent with
statistical isotropy.Comment: 7 pages, 3 figures. To appear in JCA
Characterization of in vivo anti-rotavirus activities of saponin extracts from Quillaja saponaria Molina
Integrating elements of teddy bear therapy into cognitive behavioral therapy for a child with obsessive–compulsive disorder: A case study
The ASOS Surgical Risk Calculator: development and validation of a tool for identifying African surgical patients at risk of severe postoperative complications
Background:
The African Surgical Outcomes Study (ASOS) showed that surgical patients in Africa have a mortality twice the global average. Existing risk assessment tools are not valid for use in this population because the pattern of risk for poor outcomes differs from high-income countries. The objective of this study was to derive and validate a simple, preoperative risk stratification tool to identify African surgical patients at risk for in-hospital postoperative mortality and severe complications.
Methods:
ASOS was a 7-day prospective cohort study of adult patients undergoing surgery in Africa. The ASOS Surgical Risk Calculator was constructed with a multivariable logistic regression model for the outcome of in-hospital mortality and severe postoperative complications. The following preoperative risk factors were entered into the model; age, sex, smoking status, ASA physical status, preoperative chronic comorbid conditions, indication for surgery, urgency, severity, and type of surgery.
Results:
The model was derived from 8799 patients from 168 African hospitals. The composite outcome of severe postoperative complications and death occurred in 423/8799 (4.8%) patients. The ASOS Surgical Risk Calculator includes the following risk factors: age, ASA physical status, indication for surgery, urgency, severity, and type of surgery. The model showed good discrimination with an area under the receiver operating characteristic curve of 0.805 and good calibration with c-statistic corrected for optimism of 0.784.
Conclusions:
This simple preoperative risk calculator could be used to identify high-risk surgical patients in African hospitals and facilitate increased postoperative surveillance.
© 2018 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.Medical Research Council of South Africa gran
Maternal and neonatal outcomes after caesarean delivery in the African Surgical Outcomes Study: a 7-day prospective observational cohort study.
BACKGROUND: Maternal and neonatal mortality is high in Africa, but few large, prospective studies have been done to investigate the risk factors associated with these poor maternal and neonatal outcomes. METHODS: A 7-day, international, prospective, observational cohort study was done in patients having caesarean delivery in 183 hospitals across 22 countries in Africa. The inclusion criteria were all consecutive patients (aged ≥18 years) admitted to participating centres having elective and non-elective caesarean delivery during the 7-day study cohort period. To ensure a representative sample, each hospital had to provide data for 90% of the eligible patients during the recruitment week. The primary outcome was in-hospital maternal mortality and complications, which were assessed by local investigators. The study was registered on the South African National Health Research Database, number KZ_2015RP7_22, and on ClinicalTrials.gov, number NCT03044899. FINDINGS: Between February, 2016, and May, 2016, 3792 patients were recruited from hospitals across Africa. 3685 were included in the postoperative complications analysis (107 missing data) and 3684 were included in the maternal mortality analysis (108 missing data). These hospitals had a combined number of specialist surgeons, obstetricians, and anaesthetists totalling 0·7 per 100 000 population (IQR 0·2-2·0). Maternal mortality was 20 (0·5%) of 3684 patients (95% CI 0·3-0·8). Complications occurred in 633 (17·4%) of 3636 mothers (16·2-18·6), which were predominantly severe intraoperative and postoperative bleeding (136 [3·8%] of 3612 mothers). Maternal mortality was independently associated with a preoperative presentation of placenta praevia, placental abruption, ruptured uterus, antepartum haemorrhage (odds ratio 4·47 [95% CI 1·46-13·65]), and perioperative severe obstetric haemorrhage (5·87 [1·99-17·34]) or anaesthesia complications (11·47 (1·20-109·20]). Neonatal mortality was 153 (4·4%) of 3506 infants (95% CI 3·7-5·0). INTERPRETATION: Maternal mortality after caesarean delivery in Africa is 50 times higher than that of high-income countries and is driven by peripartum haemorrhage and anaesthesia complications. Neonatal mortality is double the global average. Early identification and appropriate management of mothers at risk of peripartum haemorrhage might improve maternal and neonatal outcomes in Africa. FUNDING: Medical Research Council of South Africa.Medical Research Council of South Africa