Large Eddy Simulation of separating flows from curved surfaces

PhDThe capabilities and limitations of LES in predicting separation from curved surfaces at high Reynolds number are at the centre of this Thesis. Issues of particular interest are mesh resolution, subgrid-scale modelling and near-wall approximations aiming to reduce the computational cost. Two cases are examined: a flow separating in a channel with streamwise periodic constrictions (hills), and the flow around a single-element, high-lift aerofoil at a Reynolds number of 2.1 . 106. Prior to these studies, fully-developed channel-flow simulations are considered. These show substantial differences among subgrid-scale models in terms of the subgrid-scale viscosity magnitude and its wall-asymptotic variation. Modelling and numerical errors appear to counteract each other, thus reducing the total error. Wall functions axe shown to be a cost-effective approach, providing a reasonably accurate approximation in near-equilibrium conditions. Adequate resolution remains critical, however, in achieving successful simulations. In the hill flow, separation occurs downstream of the hill crest, reattachment takes place about half-way between two consecutive hills and partial recovery occurs prior to a re-acceleration on the following hill. A highly-resolved simulation, performed to produce -benchmark data, permits an extensive study of the flow properties. Coarser mesh simulations are then compared with the former. These highlight the influence of the streamwise discretisation around the separation point and the role played by the implementation details of the wall treatments, while the subgrid-scale models influence is less significant. The aerofoil, which features transition and separation, is extremely challenging and at the edge of current LES capabilities. None of the simulations reproduce 2 the experimental data well. Indications on the sensitivity to various parameters, including the numerical scheme, the mesh resolution and the spanwise extent, are extracted, however. The studies indicate the need for a structured mesh of about 80 million nodes to achieve the required accuracy. For the present study, this was unaffordable

Burden of fetal alcohol syndrome in a rural West Coast area of South Africa

Background. Fetal alcohol syndrome (FAS) is common in parts of South Africa; rural residence is a frequently cited risk factor. We conducted a FAS school prevalence survey of an isolated rural community in a West Coast village of Western Cape Province, so obtaining the first directly measured rate, focusing specifically on a South African rural area, of FAS and partial FAS (PFAS). Methods. The study area (Aurora village), a community of about 2 500 people in a grain-producing region, has one primary school. All learners were eligible for study inclusion. Initial anthropometry screening was followed by a diagnostic stage entailing examination by a dysmorphologist for features of FAS, neurodevelopmental assessment, and an interview assessing maternal alcohol consumption. Results. Of 160 learners screened, 78 (49%) were screen-positive, of whom 63 (81%) were clinically assessed for FAS. The overall FAS/PFAS rate among the screened learners was 17.5% (95% confidence interval 12.0 - 24.2%), with 16 (10.0%) children having FAS and 12 (7.5%) PFAS. High rates of stunting, underweight and microcephaly were noted in all learners, especially those with FAS or PFAS. Five (18%) mothers of affected children were deceased by the time of assessment. Conclusion. We describe very high rates of FAS/PFAS in an isolated rural part of the Western Cape that is not located in a viticultural region. Our study suggests that the prevalence of FA S may be very high in isolated communities, or in particular hot-spots. It adds to the growing evidence that FAS/PFAS is a significant, and underestimated, health problem in South Africa. Expanded screening and surveillance programmes, and preventive interventions, are urgently needed

Pressure Induced Charge Disproportionation in LaMnO3_{3}

We present a total energy study as a function of volume in the cubic phase of LaMnO$_{3}$. A charge disproportionated state into planes of Mn$^{3+}$O$_{2}$/Mn$^{4+}$O$_{2}$ was found. It is argued that the pressure driven localisation/delocalisation transition might go smoothly through a region of Mn$^{3+}$ and Mn$^{4+}$ coexistence.Comment: 3 pages, 1 figure, Conference Proceedings: Nanospintronics: Design and Realization (Kyoto, Japan 24-28 May, 2004

Testate amoebae as proxy for water level changes in a brackish tidal marsh

Few studies have examined testate amoebae assemblages of estuarine tidal marshes. This study investigates the possibility of using soil testate amoebae assemblages of a brackish tidal marsh (Scheldt estuary, Belgium) as a proxy for water level changes. On the marsh surface an elevation gradient is sampled to be analyzed for testate amoebae assemblages and sediment characteristics. Further, vegetation, flooding frequency and soil conductivity have been taken into account to explain the testate amoebae species variation. The data reveal that testate amoebae are not able to establish assemblages at the brackish tidal marsh part with flooding frequencies equal to or higher than 36.5%. Further, two separate testate amoebae zones are distinguished based on cluster analysis. The lower zone’s testate amoebae species composition is influenced by the flooding frequency (~ elevation) and particle size, while the species variability in the higher zone is related to the organic content of the soil and particle size. These observations suggest that the ecological meaning of elevation shifts over its range on the brackish tidal marsh. Testate amoeba assemblages in such a brackish habitat show thus a vertical zonation (RMSEP: 0.19 m) that is comparable to the vertical zonation of testate amoebae and other protists on freshwater tidal marshes and salt marshes

Quality at the centre of universal health coverage

The last decade of the MDG era witnessed substantial focus on reaching the bottom economic quintiles in low and middle income countries. However, the inordinate focus on reducing financial risk burden and increasing coverage without sufficient focus on expanding quality of services may account for slow progress of the MDGs in many countries. Human Resources for Health underlie quality and service delivery improvements, yet remains under-addressed in many national strategies to achieve Universal Health Coverage. Without adequate investments in improving and expanding health professional education, making and sustaining gains will be unlikely. The transition from the Millennium Development Goals (MDG) to the Sustainable Development Goals (SDG), with exciting new financing initiatives such as the Global Financing Facility brings the potential to enact substantial gains in the quality of services delivered and upgrading human health resources. This focus should ensure effective methodologies to improve health worker competencies and change practice are employed and ineffective and harmful ones eliminated (including undue influence of commercial interests)

Spatio-temporal development of vegetation die-off in a submerging coastal marsh

In several places around the world, coastal marsh vegetation is converting to open water through the formation of pools. This is concerning, as vegetation die-off is expected to reduce the marshes\u27 capacity to adapt to sea level rise by vegetation-induced sediment accretion. Quantitative analyses of the spatial and temporal development of marsh vegetation die-off are scarce, although these are needed to understand the bio-geomorphic feedback effects of vegetation die-off on flow, erosion, and sedimentation. In this study, we quantified the spatial and temporal development of marsh vegetation die-off with aerial images from 1938 to 2010 in a submerging coastal marsh along the Blackwater River (Maryland, U.S.A). Our results indicate that die-off begins with conversion of marsh vegetation into bare open water pools that are relatively far (\u3e 75 m) from tidal channels. As vegetation die-off continues, pools expand, and new pools emerge at shorter and shorter distances from channels. Consequently larger pools are found at larger distances from the channels. Our results suggest that the size of the pools and possibly the connection of pools with the tidal channel system have important bio-geomorphic implications and aggravate marsh deterioration. Moreover, we found that the temporal development of vegetation die-off in moderately degraded marshes is similar as the spatial die-off development along a present-day gradient, which indicates that the contemporary die-off gradient might be considered a chronosequence that offers a unique opportunity to study vegetation die-off processes

Effects of free maternity service policy in Kenya: an interrupted time series analysis

Background: In Kenya, more than 6000 maternal deaths, and 35000 stillbirths occur each year. In June, 2013, the Government of Kenya abolished user fees for maternity care in all public health facilities under the Free Maternity Service (FMS) policy, to make maternity services accessible and affordable, and to reduce maternal and perinatal deaths. This study aims to establish whether the FMS policy has influenced use of, access to, and quality of maternity care in Kenya. Methods: We did an observational retrospective study in three counties in Kenya. We used daily maternity registers in 90 public health facilities to extract monthly observations for six maternal health indicators in the time period 2 years before and 2 years after the introduction of the FMS policy. We used interrupted time series analysis with a single group to assess the effects of the FMS policy. Standard linear regression using generalised least squares model was used to run the final results for each of the six variables. We calculated absolute and relative changes using model coefficients. Findings: A total of 82962 women from Kilifi, Turkana, and Wajir counties were included in the study. Data were collected between June, 2011, and July, 2015. After policy implementation, there was an increase in antenatal care visits, health facility deliveries, and livebirths of 98% (p=0·0008), 97% (p\u3c0·0001), and 89% (p\u3c0·0001), respectively. The six maternal health output indicators were observed 24 months before implementation of the free maternity service policy (June, 2011, to May, 2013) and 25 months after implementation (June, 2013, to June, 2015), giving 49 observations. We noted an immediate and significant increase of 27% in women who received emergency obstetric care in the first month after policy implementation (p=0·0149). No significant change was observed in rates of stillbirth (p=0·4985) or caesarean section (p=0·4361). Interpretation: The 2013 introduction of free maternity services in Kenya saw an immediate, and then sustained, increase in the use of skilled care during pregnancy and childbirth. This sharp rise in the uptake of services suggest that the hospital cost is the main expense incurred by most women and their families when seeking maternity care services and that this cost is, therefore, a barrier to uptake of maternity care. Funding: Afya Bora Consortium fellowship career development award