Monitoring of Laser Powder Bed Fusion by Acoustic Emission: Investigation of Single Tracks and Layers

Quality concerns in laser powder bed fusion (L-PBF) include porosity, residual stresses and deformations during processing. Single tracks are the fundamental building blocks in L-PBF and their shape and geometry influence subsequent porosity in 3D L-PBF parts. The morphology of single tracks depends primarily on process parameters. The purpose of this paper is to demonstrate an approach to acoustic emission (AE) online monitoring of the L-PBF process for indirect defect analysis. This is demonstrated through the monitoring of single tracks without powder, with powder and in layers. Gas-borne AE signals in the frequency range of 2–20 kHz were sampled using a microphone placed inside the build chamber of a L-PBF machine. The single track geometry and shape at different powder thickness values and laser powers were studied together with the corresponding acoustic signals. Analysis of the acoustic signals allowed for the identification of characteristic amplitudes and frequencies, with promising results that support its use as a complementary method for in-situ monitoring and real-time defect detection in L-PBF. This work proves the capability to directly detect the balling effect that strongly affects the formation of porosity in L-PBF parts by AE monitoring

Qualification of Ti6Al4V ELI Alloy Produced by Laser Powder Bed Fusion for Biomedical Applications

Published ArticleTi6Al4V ELI samples were manufactured by Laser Powder Bed Fusion (LPBF) in vertical and horizontal directions and subjected to various heat treatments. Detailed analyses of porosity, microstructure, residual stress, tensile properties, fatigue and fractured surfaces were performed based on X-ray micro computed tomography, scanning electron microscopy and X-ray diffraction methods. Types of fractures and tensile fracture mechanisms in LPBF Ti6Al4V ELI alloy were studied. Detailed analysis of the microstructure and the corresponding mechanical properties were compared with standard specifications for conventional Ti6Al4V alloy (grade 5 and 23) for surgical implant applications. Conclusions regarding mechanical properties and heat treatment of LPBF Ti6Al4V ELI for biomedical applications were made

Foraging strategies of coexisting lacertid lizards in the arid Tankwa Karoo Basin of South Africa

The original publication is available at http://africanzoology.journals.ac.za/pubFour lacertid lizards, Pedioplanis laticeps, P. lineo-ocellata, Meroles knoxii and Nucras tessellata, occur sympatrically on the arid plains of the Tankwa Karoo Basin in South Africa. The aim of this study was to evaluate the significance of foraging strategy in resource partitioning among the four species, allowing them to co-occur in a structurally simple system with a limited number of potential niches. Previous workers already identified P. lineo-ocellata and M. knoxii as sit-and-wait foragers and N. tessellata as an active forager. We recorded data on three foraging variables: movements per minute, proportion of time spent moving, and proportion of attacks on prey whilst moving, for juveniles and adults of P. laticeps. By comparing the foraging data obtained for P. laticeps to those for other lacertid species, we were able to demonstrate that adult P. laticeps are ambush foragers.We also noted a significant ontogenetic shift in foraging behaviour in P. laticeps, and, due to a significantly higher frequency of short brief movements, we classified juveniles as mixed foragers. The sharing of an ambush foraging strategy by at least three of the four lacertid species co-occurring on the Tankwa plains, suggests considerable overlap along the trophic dimension of ecological space. This overlap presumably promotes occupation of separate microhabitats by the three ambush foragers in the Tankwa Karoo Basin.Publisher's versio

Field-testing of the revised, draft South African Paediatric Food-Based Dietary Guidelines among Siswati-speaking mothers/caregivers of children aged 0–36 months in Kabokweni, Mpumalanga province, South Africa

Objectives: To determine the appropriateness and understanding of the revised, draft South African Paediatric Food-Based Dietary Guidelines (SA-PFBDG) among siSwati speaking mothers/caregivers of children aged 0–36 months. Previous exposure to guidelines with similar messages, barriers and enablers to following the guidelines were also assessed. Design: A descriptive, cross-sectional qualitative research approach was followed. Purposive and snowball sampling were used to recruit a total of 75 participants. Data were collected by means of focus-group discussions from 12 groups. Setting: Kabokweni, Mpumalanga, South Africa. Subjects: The study population included mothers/caregivers older than 18 years who provided informed consent. Results: The participants were generally aware of messages similar to those contained in the revised, draft SA-PFBDG. They reported exposure to these messages at clinics/hospitals, radio/television, and the Road-to-Health booklet. Participants showed good understanding of guidelines on breastfeeding, complementary feeding, inclusion of protein-rich and starchy foods as well as fruit and vegetables in the diets of young children as well as hygiene practices. The guidelines on avoiding tea, coffee and sugar drinks and high-sugar, high-fat salty snacks, being active and providing five small meals were less well understood. Enablers to following the guidelines were its perceived importance and positive impact on children’s health. Barriers included misinterpretation of the guidelines and lack of money and resources. Conclusion: The revised, draft SA-PFBDGs are appropriate for the age group 0–36 months. A degree of rewording is suggested to aid understanding. The guidelines can be used as an educational tool to improve the nutritional status of children in South Africa

Experiences and attitudes of dietitians during the first compulsory community service year (2003)

Objectives. This study was undertaken to investigate the experiences and attitudes of dietitians during the first compulsory community service (CS) year (2003), to determine their perception of the success of the year as a whole and to assess whether the knowledge and skills of graduates improved. Subjects and design. Data were collected by means of an anonymous questionnaire posted to the CS dietitians (N = 126). The questionnaire consisted of four sections: general information, demographic and logistical information, professional duties and competencies, and personal experience. Results. Ninety dietitians returned the completed questionnaire, giving a 71% response. Thirty-nine per cent of dietitians were placed during the first round of allocation, with 48% placed during the third round or after further deliberations. Eighty-eight per cent of the dietitians reported a safe working environment. Full competency was reported by 26% of dietitians for therapeutic nutrition, 47% for food service management and 30% for community nutrition. Only 7% of dietitians found it very difficult to execute their daily duties. At the outset, 55% of dietitians had a positive attitude regarding the year, with this percentage increasing to 67% towards the end of the year. Negative attitudes decreased from 17% to 15%. Ninety-one per cent of dietitians reported that their knowledge improved and 95% reported an improvement in skills. Most dietitians (92%) felt that the CS year was a successful institution. Conclusions. The majority of dietitians experienced the CS year positively and felt that their knowledge and skills improved. The vast majority of dietitians reported the CS year to be a successful institution. South African Journal of Clinical Nutrition Vol. 19(1) 2006: 10-1

Mangiferin: A Promising Anticancer Bioactive

Of late, several biologically active antioxidants from natural products have been investigated by the researchers in order to combat the root cause of carcinogenesis, i.e., oxidative stress. Mangiferin, a therapeutically active C-glucosylated xanthone, is extracted from pulp, peel, seed, bark and leaf of Mangifera indica. These polyphenols of mangiferin exhibit antioxidant properties and tend to decrease the oxygen-free radicals, thereby reducing the DNA damage. Indeed, its capability to modulate several key inflammatory pathways undoubtedly helps in stalling the progression of carcinogenesis. The current review article emphasizes an updated account on the patents published on the chemopreventive action of Mangiferin, apoptosis induction made on various cancer cells, along with proposed antioxidative activities and patent mapping of other important therapeutic properties. Considering it as promising polyphenol, this paper would also summarize the diverse molecular targets of Mangiferin

LOOKING INSIDE VOTIVE CREATURES: COMPUTED TOMOGRAPHY (CT) SCANNING OF ANCIENT EGYPTIAN MUMMIFIED ANIMALS IN IZIKO MUSEUMS OF SOUTH AFRICA: A PRELIMINARY REPORT

The ancient Egyptians mummified many more animals than humans. The study of ancient Egyptian animal mummies is varied and extensive. Currently new methodologies and modern technology are being used to unlock the secrets of animal mummies. Recently five animal mummies housed in the Egyptian collection of Iziko Museums of South Africa in Cape Town were scanned using a state of the art computed tomography (CT) scanner at Stellenbosch University. Preliminary results revealed two complete bird skeletons, a claw, a fake and the partial skeleton of what appears to be a cat

Preliminary investigation into the cause of acid mine water induced seismicity in Johannesburg

A preliminary investigation was done into the possible causes of the increased seismic activity in the Witwatersrand Basin. The paper focuses on approximated underground mining areas, groundwater mobility, rock types and the proximity of fault lines to seismic events. These parameters were mapped and correlated with observed seismicity in the area. There is some indication that the presence of underground mining areas has a positive relationship with the occurrence of seismic events. The other parameters exhibit a negative relationship with seismic activity. However, more detailed investigations are required before final conclusions can be drawn. An approach to risk assessment of possible earthquake scenarios in the City of Johannesburg (CoJ) is proposed. The approach aims to assess potential damage to infrastructure and loss of life in the case of an earthquake. The results of such an assessment may provide justification for more detailed investigations

Production and Charaterization of PQQ- Dependent Alcohol and Aldehyde Dehydrogenases on Assembly of BioFuel Cells

In the arid sweetveld regions of South Africa producers are marketing beef steers increasingly as long weaners (ca. 12 months of age) or finishing them on the natural grazing to a ready-to-slaughter stage at between 18 and 30 months of age. Limited production norms in this regard are available since most growth and carcass studies have been conducted in the sourveld regions of the country. In this study steers from four different beef maturity types which differ in body frame size were used, viz. Simmentaler crosses (large, >500 kg mature weight), Bonsmara crosses (large-medium, 450-500 kg mature weight), the Afrikaner (small-medium, 400-450 kg mature weight) and the Nguni (small

Stirring of sea ice meltwater enhances submesoscale fronts in the Southern Ocean

In the sea ice-impacted Southern Ocean, the spring melt of sea ice modifies the upper ocean. These modified waters subduct and enter the global overturning circulation. Submesoscale processes act to modulate the stratification of the mixed layer and therefore mixed layer properties. Sparse observations mean that the role of submesoscales in exchange across the base of the mixed layer in this region is not well constrained. The goal of this study is to determine the interplay between sea ice melt, surface boundary layer forcing, and submesoscale flows in regulating the mixed layer structure in the Antarctic Marginal Ice Zone. High-resolution observations suggest that fine-scale lateral fronts, representative of submesoscale mixed layer eddies (MLEs), arise from mesoscale gradients produced by northwards advecting sea ice meltwater. The strong salinity-driven stratification at the base of the mixed layer confined the MLEs to the upper ocean, limiting submesoscale vertical fluxes across the mixed layer base. This strong stratification prevents the local subduction by submesoscale flow of these modified waters, suggesting that the subduction site that links to the global overturning circulation does not correspond with the location of sea ice melt. However, the presence of MLEs enhanced the magnitude of lateral gradients through stirring and increased the potential for Ekman-driven cross-frontal flow to modulate the stability of the mixed layer and mixed layer properties. The inclusion, particularly of submesoscale Ekman Buoyancy Flux parameterizations, in coupled-climate models, may improve the representation of mixed layer heat and freshwater transport in the ice-impacted Southern Ocean during summer