601 research outputs found
Investigation techniques for the determination of sediment transport in the southern Bight of the North Sea
VHF discharges in storm cells producing microbursts
An experiment was carried out in which 3-D mapping of VHF sources was compared to a 3-D description of the reflectivity and dynamics of associated cloud cells observed by a radar network. Data from 61 microbursts were analyzed and it was found that, in 93 pct. of the cases, electrical activity precedes outflow development. The results confirm that the peak in intracloud activity precedes the maximum value of the outflow
South African congenital disorders data, 2006 - 2014
Background. The National Department of Health in South Africa (SA) routinely collects congenital disorder (CD) data for its national CD surveillance system. The current system has been implemented since 2006, but no reports on the data collected, methodology, achievements or challenges have been published to date.Objectives. To ascertain the effectiveness of the current national CD surveillance system and its implementation.Method. A descriptive, retrospective study using an audit of the current database was undertaken to evaluate the number of notifications received, types of CDs reported and the quality of reporting across SA for data received from 2006 to 2014.Results. A total of 14 571 notifications were received, including 13 252 CDs and 1 319 zero notifications, across all nine provinces. Commonly reported CDs included Down syndrome, cleft lip and palate, talipes equinovarus, neural tube defects and albinism.Conclusions. The major challenges identified included erratic compliance by health facilities and a lack of healthcare providers trained in human genetics related to CDs. This has led to misdiagnosed and undiagnosed CDs, collectively resulting in under-reporting of cases by >98% during the review period. Owing to limited human and financial resources, it is recommended that the surveillance system be modified into an electronic format. This should be piloted alongside relevant training in specific sentinel sites, to improve data coverage and quality for further evaluation
Preliminary risk assessment of common-use pesticides using PRIMET and PERPEST pesticide risk models in a semi-arid subtropical region
The pesticide risk in agriculture in developing countries has not been adequately studied due to the extent and fate of pesticides in the environment often being unknown. South Africa is a country that has significant pressure on its freshwater and agricultural resources, which increases the possibility of pesticide effects. Thus, the aim of this study was to evaluate the use of the PRIMET (Pesticide Risks in the Tropics to Man, Environment and Trade) and PERPEST (Predicting the Ecological Risk of PESTicides) models to predict pesticide exposure and effects on aquatic ecosystems due to spray drift. Vaalharts Irrigation Scheme is situated in the Northern Cape Province and receives water from the Vaal River for 43 000 ha of agricultural land. Crops in the area mostly consist of wheat, maize and groundnuts. Data gathered through household surveys with farmers were used in PRIMET as a first-tier estimate of the potential risk of the pesticides. The Predicted Effect Concentrations (PEC) calculated for the pesticides indicating a possible to definite risk were then used as input for PERPEST. PERPEST is a higher-tier model that predicts the potential effects of a pesticide on various grouped endpoints in the aquatic environment. The PRIMET results indicated most pesticides posed no risk to the environment, except the pyrethroid, deltamethrin. The ETR for deltamethrin indicated a possible to definite risk to the aquatic environment. The PERPEST results for deltamethrin indicated a high probability of clear effects on insects, micro- and macro-crustacean communities, with a lower probability for rotifers, algae, macrophytes and fish. PRIMET and PERPEST provided valid estimates of risk for pesticides and could be used effectively in South Africa.Keywords: pesticides, PRIMET, PERPEST, Vaalhart
Quasi full-disk maps of solar horizontal velocities using SDO/HMI data
For the first time, the motion of granules (solar plasma on the surface on
scales larger than 2.5 Mm) has been followed over the entire visible surface of
the Sun, using SDO/HMI white-light data.
Horizontal velocity fields are derived from image correlation tracking using
a new version of the coherent structure tracking algorithm.The spatial and
temporal resolutions of the horizontal velocity map are 2.5 Mm and 30 min
respectively .
From this reconstruction, using the multi-resolution analysis, one can obtain
to the velocity field at different scales with its derivatives such as the
horizontal divergence or the vertical component of the vorticity. The intrinsic
error on the velocity is ~0.25 km/s for a time sequence of 30 minutes and a
mesh size of 2.5 Mm.This is acceptable compared to the granule velocities,
which range between 0.3 km/s and 1.8 km/s. A high correlation between
velocities computed from Hinode and SDO/HMI has been found (85%). From the data
we derive the power spectrum of the supergranulation horizontal velocity field,
the solar differential rotation, and the meridional velocity.Comment: 8 pages, 11 figures, accepted in Astronomy and Astrophysic
A weakly-intrusive multi-scale substitution method in explicit dynamics
For virtual testing of composite structures, the use of fine modeling seems preferable to simulate complex mechanisms
like delamination. However, the associated computational costs are prohibitively high for large structures.
Multi-scale coupling techniques aim at reducing such computational costs, limiting the fine model only where necessary.
The dynamic adaptivity of the models represents a crucial feature to follow evolutive phenomena. Domain
decomposition methods would have to be combined with re-meshing strategies, that are considered intrusive implementations
within commercial software. Global-local approaches are considered less intrusive, because they allow
one to use a global coarse model on the overall structure and a fine local patch eventually adapted to cover the
interest zone. In our work, we developed a global-local coupling method for explicit dynamics, presented in [1] and
[2] and implemented in Abaqus/Explicit via the co-simulation technique for the simulation of delamination under
high velocity impact
A fast weakly intrusive multiscale method in explicit dynamics
This paper presents new developments on a weakly intrusive approach for the simplified implementation of space and time multiscale methods within an explicit dynamics software. The 'substitution' method proposed in previous works allows to take advantage of a global coarse model, typically used in an industrial context, running separate, refined in space and in time, local analyses only where needed. The proposed technique is iterative, but the explicit character of the method allows to perform the global computation only once per global time step, while a repeated solution is required for the small local problems only. Nevertheless, a desirable goal is to reach convergence with a reduced number of iterations. To this purpose, we propose here a new iterative algorithm based on an improved interface inertia operator. The new operator exploits a combined property of velocity Hermite time interpolation on the interface and of the central difference integration scheme, allowing the consistent upscaling of interface inertia contributions from the lower scale. This property is exploited to construct an improved mass matrix operator for the interface coupling, allowing to significantly enhance the convergence rate. The efficiency and robustness of the procedure are demonstrated through several examples of growing complexity. Copyright {\copyright} 2014 John Wiley \& Sons, Ltd
Rejection-free Geometric Cluster Algorithm for Complex Fluids
We present a novel, generally applicable Monte Carlo algorithm for the
simulation of fluid systems. Geometric transformations are used to identify
clusters of particles in such a manner that every cluster move is accepted,
irrespective of the nature of the pair interactions. The rejection-free and
non-local nature of the algorithm make it particularly suitable for the
efficient simulation of complex fluids with components of widely varying size,
such as colloidal mixtures. Compared to conventional simulation algorithms,
typical efficiency improvements amount to several orders of magnitude
Hanle effect in the solar Ba II D2 line: a diagnostic tool for chromospheric weak magnetic fields
The physics of the solar chromosphere depends in a crucial way on its
magnetic structure. However there are presently very few direct magnetic field
diagnostics available for this region. Here we investigate the diagnostic
potential of the Hanle effect on the Ba II D2 line resonance polarization for
the determination of weak chromospheric turbulent magnetic fields......Comment: In press in astronomy and astrophysic
South African congenital disorders data, 2006 - 2014
Background. The National Department of Health in South Africa (SA) routinely collects congenital disorder (CD) data for its national CD surveillance system. The current system has been implemented since 2006, but no reports on the data collected, methodology, achievements or challenges have been published to date.Objectives. To ascertain the effectiveness of the current national CD surveillance system and its implementation.Method. A descriptive, retrospective study using an audit of the current database was undertaken to evaluate the number of notifications received, types of CDs reported and the quality of reporting across SA for data received from 2006 to 2014.Results. A total of 14Â 571 notifications were received, including 13 252 CDs and 1 319 zero notifications, across all nine provinces. Commonly reported CDs included Down syndrome, cleft lip and palate, talipes equinovarus, neural tube defects and albinism.Conclusions. The major challenges identified included erratic compliance by health facilities and a lack of healthcare providers trained in human genetics related to CDs. This has led to misdiagnosed and undiagnosed CDs, collectively resulting in under-reporting of cases by >98% during the review period. Owing to limited human and financial resources, it is recommended that the surveillance system be modified into an electronic format. This should be piloted alongside relevant training in specific sentinel sites, to improve data coverage and quality for further evaluation
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