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

NON-DESTRUCTIVE TESTING OF THE PARTS MANUFACTURED BY DIRECT METAL LASER SINTERING

Published Conference ProceedingsInterest in Additive Manufacturing (AM) has grown considerably in the past decades. The industry has gained the great benefits from this type of technologies. The main advantages being geometrical freedom that allows designing parts with complex shape, which are difficult or impossible to produce by conventional technology, shortened design to product time, customization and possible use of several materials in one process. Direct Metal Laser Sintering (DMLS) is one of the most promising AM techniques that utilize metal materials. Due to the complex nature of the DMLS process, one of the drawbacks is the high residual stress in the manufactured parts. This can result to the formation of internal cracks and eventually to a substantial deterioration of the mechanical properties of the products and their application properties. For this reason it is very important to identify defective parts before enrolling into service. Non-destructive testing (NDT) is effective for detection of internal defects without causing damage. NDT also covers a wide group of methods of analysis used to evaluate the properties of a material. NDT techniques like ultrasonic inspection, acoustic emission, visual inspection, thermography, X-ray and 3D computed tomography (CT) inspection, etc. are now widely used for various industrial applications. For the detection of defects and to study the properties of the material each of these methods uses different physical principles that have their advantages and disadvantages. In this study some of the NDT techniques in terms of their applicability to the inspection of parts manufactured by DMLS technology are considered

Die diskoers van kerst en andere liefdesverhalen deur Kristien Hemmerechts

Die doel van hierdie studie was om aan te toon hoe 'n linguistiese beskouing van 'n literere teks kan meehelp om tot gefundeerde insigte in 'n teks te kom en om langs hierdie weg die beskuldiging dat literatuurstudie grotendeels 'n 'anything-goes-dissipline' is, te omseil. Om hierdie rede is daar van die standpunt uitgegaan dat kennis oor die presiese aard van die tekslinguistiek kan meehelp in die toepassing daarvan. Dit dien as motivering vir die uitgebreide diachroniese situering van die tekslinguistiek van die eerste hoofstuk. Hier word geredeneer dat die tekslinguistiek iets soos 'n pseudo-literatuurteorie is wat kan meehelp in die lees en interpretasie van en kommentaar oor 'n literere teks. Daar is grotendeels gefokus op die literere benaderings wat die ontwikkeling van die tekslinguistiek voorafgegaan en be'invloed het. Daar was drie hoofstrominge t.o.v. tekstuele benadering, nl. (i) tekssentriese (outonomistiese), (ii) linguistiese (taalsentriese), en (iii) lesersentriese benaderings. Die vemaamste tekssentriese (outonomistiese) benaderings is die Russiese Formalisme, New Criticism en Stilistiek op taalkundige grondslag. In die bespreking van hierdie benaderings is dit tel kens in verband gebring met die bestaande teorie oor die tekslinguistiek ten einde die diachroniese aard van die ontwikkelingsgang daarvan, te karteer. Die vernaan1ste eksponente van die linguistiese (taalsentriese) benaderings is die Strukteralisme, Poststrukturalisme en die Semiotiek. Daar is in hierdie afdeling duidelik aangestip hoe die standaarde van tekstualiteit (De Beaugrande en Dressler, 1981), en spesifiek die standaard kohesie, terug te vind is in hierdie benadering tot teksstudie. Die Resepsie-estetika en Referensiele benadering is bespreek as eksponente van die sg. lesersentriese benadering. Die doel hiervan was om aan te dui hoe intertekstualiteit, kontekstualiteit en informatiwiteit as standaarde van tekstualiteit, in hierdie benadering terug te vind is. Met die diachroniese situering in gedagte, is daar in die tweede deel van Hoofstuk Een oorgegaan tot 'n sinchroniese karakterisering van wat die tekslinguistiek behels. In hierdie hoofstuk is daar voortgegaan met die beredenering dat die term diskoerslinguisliek • n meer akkurate benaming is vir 'n dissipline wat meer as net ' teks' in ag neem. Diskoers kan beskou word as 'n reeks taaluitinge wat 'n taalhandeling vorm. Hoewel diskoerslinguisliek die term tekslinguistiek in hierdie studie vervang, is daar duidelik aangetoon dat dit nie die doel het om aardskuddend veranderend te wees nie. Die werkswyse wat in hierdie studie gevolg is, is steeds die van die tekslinguistiek. Om hierdie rede is hierdie gedeelte van die studie grootliks teoreties, dit bespreek die interdissiplinere aard van tekslinguistiekldiskoerslinguistiek, definieer dit, en identifiseer die studieveld van 'teks'. Hierdie identifisering (sintaktiese eenheid, semantiese eenheid en pragmatiese eenheid) funksioneer breedweg as die hoofuiteensetting van hierdie studie. Tog word daar in hierdie studie aangetoon dat daar verskil word van die De Beaugrande en Dressler-aanname dat daar sewe standaarde van tekstualiteit bestaan, en word dit hier gereduseer tot twee superstandaarde, nl. kohesie en koherensie. Koherensie beskik oor sg. 'voorwilardes', nl. intensionaliteit, aanvaarbaarheid, informatiwiteit, kontekstualiteit en intertekstualiteit. Op hierdie wyse word die meganistiese indeling van die oorspronklike sewe standaarde oorkom. In Hoofstuk Twee word die teorie rondom die superstandaard kohesie toegepas op die Nederlandse teks deur Kristien Hemmerechts, Kerst en andere liefdesverhalen. Hierdie hoofstuk het die implisiete doel om aan te toon hoe 'n suiwer strukturalistiese ondersoek na 'n tekstuele gegewe kan meehelp in die identifisering van bepaalde linguistiese patrone wat, indien gesitueer in 'n pragmatiese milieu, bepaalde betekeniswaarde verkry. Verskeie aspekte rondom die konsep 'kohesie' word hier bespreek, o.a. 'n by trek van sg. storiegrammatika van die liefdesverhaal en sprokie ten einde bepaalde taalpatrone te identifiser wat pragmatiese betekenislading het. Hierbenewens word daar suiwer struktureel met die teks omgegaan met 'n identifisering van bepaalde patrone in die adjektief-aanwending, die gebruik van saakname, verwysing, polisemie, sinonimie, teenoorgesteldheid, antonimie, komplementeerbaarheid, ruimtelike opposisie en hiponimie. 'Hierbenewens word kohesiewe-bindingspatronesoos ellips, semantiese rolle en sg. tematiese kontinuHeit bespreek. Die daaropvolgende hoofstuk is 'n bye en bring van die ge"identi±iseerde talige patrone van Hoofstuk Twee en 'n situering daarvan in 'n pragmatiese raamwerk. Koherensie is die somtotaal van eenheid en betekenis soos wat dit in diskoers ervaar word. Dit het betrekking op dit wat bydra dat 'n teks vir taalgebruikers sin maak en samehang vertoon. Aangesien koherensie grootliks steun op die pragmatiek, is die fokus van hierdie afdeling van die studie grootliks pragmaties en word daar aangedui hoe die bestaan van bepaalde koordinate, 'n beginsel van samewerking en 'n spraakhandelingsteorie kan bydra tot gefundeerde insigte in die onderhawige teks

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

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

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

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