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Many patients are affected by facial deformities due to trauma or congenital disorders. Reconstruction using bone transplants has been the standard procedure to address many of these defects. In modern times, synthetic materials such as polymers have become widely used in facial reconstruction as medical implants to reconstruct the defective facial bony features. Conventional manufacturing methods can be used to produce polymeric implants, but literature has shown them to be limited in their applications. Many of these limitations can now be overcome by additive manufacturing technologies. This review paper presents an overview of different processes and polymeric materials that can be used to produce cosmetic facial implants.

The uptake of laser powder bed fusion for polymers has remained limited mainly because the interaction between material properties and process parameters is not well understood. The constraints of experimentally determining the optimal process parameters for new polymers in laser powder bed fusion include high expense, time-consumption, errors, and considerable effort. Hence, the need for using analytical and numerical models as alternatives. This paper starts with a summary on laser powder bed fusion of polymers, reviews the aspects of the process requiring the use of analytical and numerical tools, limitations, and possible improvements of the existing studies on the analytical models, and finally briefly explores approaches for numerical modelling of laser powder bed fusion of polymers. Some of the key aspects of the process that have been identified as being amenable to modelling include powder spreading and deposition of the layers, interaction between the laser beam and powder particles, melting and fusion of the particles, powder bed surface temperature, heat transfer through the powder, cooling phase, and the properties of printed parts. It is suggested in the study that the existing analytical and/or numerical models can be improved by increasing relevant variables (process parameters and material characteristics) used in them.

Development on dolomite poses a risk to people and their assets living on it. Although development in the Tlokwe City Council (TCC) broadly took cognisance of the presence of dolomite, some parts of the township had been developed on dolomite. Therefore, since the Council is accountable for safe development within its jurisdiction, a Dolomite Risk Management Programme (DRMPr) should be put in place according to prevailing legislation, standards and guidelines. For long-term mitigation measures to be implemented successfully, the DRMPr should be integrated and aligned within the existing structure and processes of the Council. This exercise is described, with some challenges identified and recommendations made, for consideration in the same or similar programmes in future.

Through seepage, dissolved uranium and other heavy metals migrate from tailings deposits of gold mines via groundwater into adjacent fluvial systems. The extent of associated stream contamination is determined, inter alia, by the retardation of dissolved contaminants along the pathway and the rate in which polluted groundwater enters the stream channel. Comparing several sediment-water systems of the aqueous pathway significantly higher immobilisation of U was found in (fast-flowing) surface water systems such as the stream than in (slow moving) alluvial groundwater of the floodplain. Mainly triggered by redox-initiated co-precipitation bottom sediments in streams act as geochemical barrier and long-term sink for U and other heavy metals from polluted groundwater. Real-time in situ measurements of hydraulic interactions between contaminated groundwater and streamwater suggest a highly dynamic water exchange between both water bodies, including daily inversions of the direction of flow in certain times of the year. This results in distinct diurnal differences of the associated stream contamination. The extent of subsequent downstream transport of U within the fluvial system is largely determined by pronounced diurnal oscillations of pH and redox potential in the stream, affecting U-speciation as well as adsorption and precipitation rates. In addition event-triggered fluctuations of both parameter impact on the fluvial transport of U.

Soos die titel van hierdie artikel aandui, beïnvloed ’n voetstootsklousule kontraktuele aanspreeklikheid en sluit dit die werking van kontraktuele remedies uit. Daar moet vanuit die staanspoor onderskei word tussen ex lege waarborge (naturalia) en ex consensu waarborge (incidentalia). Die rede hiervoor is dat die voetstootsklousule nie laasgenoemde waarborge kan uitsluit nie. Verder, indien die voetstootsklousule wel ingesluit word en die ex lege waarborg word uitgesluit, laat dit die koper sonder die aedilisiese aksies.

Dissolved uranium (U) from the tailings deposits of various gold mines in South Africa has been found to migrate via seepage and groundwater into adjacent streams. The extent of the associated non-point pollution depends on the concentration of U in the groundwater as well as the volume and rate of groundwater seepage into the stream channel. Whilst the U concentration in groundwater is relatively constant and comparatively easy to determine, the same is not true for the flux of groundwater into the stream. In order to track the water exchange at the groundwater-stream interface, real-time in situ measurements by data-logger controlled probes for gauging heights and electrical conductivity (EC) were taken at 10 min intervals. As a result of a steep hydraulic gradient between water-saturated tailings deposits and the receiving watercourse, exfiltration (base-flow) of contaminated groundwater generally dominates. However, short-term inversions of the flow direction (infiltration of stream water into the groundwater) were also observed. These are attributed to an artificial flow regime of the Koekemoerspruit, which results from a pumping scheme that discharges groundwater from underground mine workings into the stream. Differences in pumping rates lead to pronounced diurnal fluctuations of gauging heights in the stream, which in turn cause even higher fluctuations of the associated groundwater table. The hydraulic mechanisms of the stream-groundwater interaction, as well as implications for the aqueous transport of U are discussed. WaterSA Vol.30 (2) 2004: 227-232

Tailings deposits from gold and uranium (U) mining in the Witwatersrand basin often contain elevated levels of radioactive and chemo-toxic heavy metals. Through seepage, dissolved U and other metals migrate from tailings deposits via groundwater into adjacent fluvial systems. The subsequent transport through flowing surface water is one of the most effective pathways of distributing contaminants throughout the biosphere. Mechanisms of diffuse stream contamination, as well as the aqueous transportation of U were investigated. In this paper, geochemical data of water and sediment samples from the Koekemoerspruit (a typical example of a stream affected by gold and U mining in South Africa) are analysed with regards to possible transport and immobilisation mechanisms of U migrating in solution. Ratios between dissolved and solid phases of U for various water-sediment-systems along the aqueous pathway indicated, unexpectedly, significantly lower mobility of U in flowing surface water than in the groundwater system of the floodplain. Correlation of various geochemical parameters suggests co-precipitation of U along with calcium carbonate and iron/ manganese-compounds as the main reason for the higher immobilisation rate in the flowing water systems. Owing to redoxinitiated precipitation at the interface of reducing groundwater and oxygenated stream water within the bottom sediments, the latter act as a sink and geochemical barrier for U from groundwater sources. The low retention of U in the highly sorptive floodplain sediments on the other hand is explained by the formation of neutral uranyl-sulphate-complexes, which prevent the positively charged U ion from adsorbing onto negative surfaces of clay minerals and organic substances in the floodplain. Evidence for such complexes are sulphate crusts with extremely high U concentrations, which form on topsoil due to capillary fringe effects in dry periods. Due to their high solubility, these crusts are easily dissolved by rain, resulting in concentration peaks of dissolved U in surface runoff. WaterSA Vol.30 (2) 2004: 219-225

Once dissolved uranium (U) from tailings deposits enters adjacent streams, subsequent downstream transport is affected by the rate at which U is immobilised in sediments, thereby lowering its concentration in stream water. For aqueous phases immobilisation includes adsorption onto sediments and suspended solids, as well as precipitation and co-precipitation as insoluble compounds, all mechanisms being largely controlled by pH and redox potential (Eh) of the stream water. Using real-time in situ measurements pronounced diurnal oscillations of both parameters were found at the site described here. The influence of the position of probes in detecting such short-term variations of stream-water quality are analysed by comparing in-house with in-stream measurements. Diurnal pH-oscillations are mainly caused by photosynthesis-based shifts of the calcium carbonate - carbon dioxide equilibrium in the stream that, in turn, is influenced by geological features of the catchment, biological activity as well as meteorological factors. These oscillations are likely to affect the mobility of dissolved U as well as the rate and distance of the downstream transport of U and other heavy metals significantly. Apart from this, event-related changes of stream chemistry, such as a sudden fall in pH in response to acid rain, were also observed. The dynamics and possible impacts on re-mobilisation of U from contaminated sediments back into the stream water are explored. WaterSA Vol.30 (2) 2004: 233-239