METAL ADDITIVE MANUFACTURING OF BLENDED ELEMENTAL Ti-6Al-4V POWDERS

ArticleSouth Africa primarily produces titanium raw material as a TiO2 rich slag of which most is exported, without further value addition to the mineral. Therefore, powder development becomes a significant aspect of research with possibilities of growth within the titanium metal industry in South Africa. Commercially pure titanium has been successfully blended in conventional powder metallurgy processing, but the use of blended elemental powder to produce Ti-6Al-4V powder for metal additive manufacturing alloy parts has not been demonstrated yet. The objective of this study is to determine the feasibility of using blended elemental Ti-6Al-4V powder for use in a powder bed additive manufacturing (AM) system. In this paper a literature review and proposed methodology are presented and the expected outcomes are discussed

Sublethal effects of manganese on the carbohydrate metabolism of Oreochromis mossambicus after acute and chronic exposure

Carbohydrate metabolism variables of Oreochromis mossambicuswere investigated after acute and chronic sublethal manganese exposure. The sublethal concentrations were determined from the LC50 value of manganese. After the exposures, the fish were carefully netted and blood was drawn from the caudal aorta. The differences in the values of carbohydrate metabolism variables of exposed fish were measured against control values and statistically analysed to prove statistically significant differences in variable values, caused by the metal pollutant (P < 0.05). The results obtained showed changes in the carbohydrate metabolism variables (glucose, lactate, glucose-6-phosphate dehydrogenase and pyruvate kinase concentrations). These alterations are produced as a result of increased levels of Cortisol and catecholamines, as well as hypoxic conditions. The latter induce hyperglycemia and increased lactate levels. Hypoxia may be a result of the damaging effect of manganese on the gills after exposure. The enzymes involved in the carbohydrate metabolism are sensitive to metal exposure and therefore enzyme concentrations fluctuated after the exposure to manganese. Enzyme function plays an important role in the catalysing of chemical reactions in an organism and the disturbance thereof could lead to death. Fish enzyme levels are therefore important biomarkers in the event of metal pollution in a water source

EVALUATION OF THE COMPRESSIVE MECHANICAL PROPERTIES OF CELLULAR DMLS STRUCTURES FOR BIOMEDICAL APPLICATIONS

Published Conference ProceedingsThe type of material used in biomedical applications depends on specific implant applications; different types of implant need different mechanical properties. Since the architectures of bone tissues in the human body are not completely dense and solid, it is desirable to produce biomimic structures as a replacement for damaged bone tissues. Learning from nature, it can be understood that cellular structures would be more preferable for biomedical implants than dense solid structures. Verification of mechanical properties of DMLS PA 2200 cellular structures should be conducted since scaffolds from this material have been proven for biomedical applications. Ti6Al4V alloy is well known to have a superior track record as leading material for bone replacement since it is a light-weight and biocompatible material, but the density of human cortical bone is less than half that of solid Ti6Al4V implants. The mismatch of the elastic modulus between such implants and bone tissue is one of the major causes of stress shielding, bone resorption and implant loosening. Finite element analysis showed big differences in strains of jaw bone and an implanted solid Ti6Al4V part. The elastic modulus of lattice structures was used to simulate a complex mandible to obtain foreknowledge of manufacturing advanced light-weight implants with suitable biomechanical properties. Compressive properties of proposed cellular structures were determined to demonstrate the viability of attaining different effective elastic moduli for Ti6Al4V implants

Population genetics of a lethally managed medium-sized predator

Globally, levels of human–wildlife conflict are increasing as a direct consequence of the expansion of people into natural areas resulting in competition with wildlife for food and other resources. By being forced into increasingly smaller pockets of suitable habitat, many animal species are at risk of becoming susceptible to loss of genetic diversity, inbreeding depression and the associated inability to adapt to environmental changes. Predators are often lethally controlled due to their threat to livestock. Predators such as jackals (black backed, golden and side striped; Canis mesomelas, C. aureus and C. adustus, respectively), red foxes (Vulpes vulpes) and coyotes (C. latrans) are highly adaptable and may respond to ongoing persecution through compensatory reproduction such as reproducing at a younger age, producing larger litters and/or compensatory immigration including dispersal into vacant territories. Despite decades of lethal management, jackals are problematic predators of livestock in South Africa and, although considered a temporary measure, culling of jackals is still common. Culling may affect social groups, kinship structure, reproductive strategies and sex-biased dispersal in this species. Here, we investigated genetic structure, variation and relatedness of 178 culled jackals on private small-livestock farms in the central Karoo of South Africa using 13 microsatellites. Genetic variation was moderate to high and was similar per year and per farm. An absence of genetic differentiation was observed based on STRUCTURE, principal component analysis and AMOVA. Relatedness was significantly higher within farms (r = 0.189) than between farms (r = 0.077), a result corroborated by spatial autocorrelation analysis. We documented 18 occurrences of dispersal events where full siblings were detected on different farms (range: 0.78–42.93 km). Distance between identified parent–offspring varied from 0 to 36.49 km. No evidence for sex-biased dispersal was found. Our results suggest that in response to ongoing lethal management, this population is most likely able to maintain genetic diversity through physiological and behavioural compensation mechanisms.APPENDIX S1. Supplementary methods.SUPPLEMENTARY TABLES. TABLE S1. Primer details for microsatellite loci used to genotype black-backed jackals (Canis Mesomelas). TABLE S2. Per-locus summary statistics as calculated in Cervus v3.0.7. The non-exclusion probabilities and combined non-exclusion probabilities (final row, italics) are relevant indicators of the power of the loci for parentage and sibship analyses. TABLE S3. Summary statistics for 20 sampling localities (farms) with >1 sample and for all farms pooled. Produced using the basicStats command of the diveRsity package v1.9.90 in R v3.6.2 and RStudio v1.2.5033. Standard deviation was calculated across loci in Microsoft Excel (stdev.s). Sampling localities with only one sample are not shown. TABLE S4. Summary statistics per year and for all years pooled. Produced using the basicStats command of the diveRsity package v1.9.90 in R v3.6.2 and RStudio v1.2.5033. Standard deviation was calculated across loci in Microsoft Excel (STDEV.S). TABLE S5. Pairwise FST values between farms with the full dataset (below diagonal) and associated significance at a level of 0.05 (above diagonal), where significant values are indicated by a “+” and non-significant values by a “−”. Calculated in Arlequin 3.5.2.2. TABLE S6. Pairwise FST values between farms with relatives removed (below diagonal) and associated significance at a level of 0.05 (above diagonal), where significant values are indicated by a “+” and non-significant values by a “−”. Calculated in Arlequin 3.5.2.2. TABLE S7. Comparison of mean pairwise relatedness (r) between years and mean individual inbreeding coefficients (F) between years. P-values for the Wilcoxon tests for difference in means are shown on the inside of the table (bordered by grey), with P-values for inbreeding comparisons shown below the diagonal (bottom left) and P-values for relatedness comparisons shown above the diagonal (top right). The mean F for each year is shown in the left-most column “outside” the main table, with the mean r for each year shown in the top row “outside” the main table. The numbers in parentheses after each year are the number of observations/data points for that year (number of samples for F and number of pairwise relatedness comparisons for r).SUPPLEMENTARY FIGURES. FIGURE S1. STRUCTURE HARVESTER results for (a) Delta K values and (b) probability (-LnPr) of K = 1–27 averaged over 20 runs and (c) genetic differentiation between the jackal sample locations (farms) based on STRUCTURE analysis (performed with K = 2–6) of 1 = GV, 2 = BB, 3 = BR, 4 = BD, 5 = DS, 6 = GG, 7 = HK, 8 = KD, 9 = KW, 10 = KK, 11 = KT, 12 = NG, 13 = ND, 14 = OG, 15 = RV, 16 = RE, 17 = RT, 18 = RD, 19 = SG, 20 = SK, 21 = VR, 22 = WK, 23 = CL, 24 = KR, 25 = WB and 26 = TD. FIGURE S2. STRUCTURE HARVESTER results for (a) Delta K values and (b) probability (-LnPr) of K = 1–27 averaged over 20 runs and (c) genetic differentiation between the jackal sample locations (farms) based on STRUCTURE analysis (performed with K = 2–6 and K = 14) of 1 = GV, 2 = BB, 3 = BD, 4 = DS, 5 = GG, 6 = HK, 7 = KW, 8 = KT, 9 = NG, 10 = ND, 11 = OG, 12 = RV, 13 = RE, 14 = RD, 15 = SG, 16 = SK, 17 = VR, 18 = WK and 19 = CL. After removing relatives, some localities had no samples, hence fewer sampling localities as compared to the full dataset. Note: The Evanno method (DeltaK) does not evaluate K = 1. FIGURE S3. Principal component analysis (PCA) of the different jackal sampling locations (farms) with related individuals removed. FIGURE S4. Plot comparing the relatedness estimates using six estimators and simulated individuals of known relatedness. Di, Dyadic likelihood estimator “DyadML”; LL, Lynch-Li estimator; LR, Lynch and Ritland estimator; QG, Queller and Goodnight estimator; Tri, Triadic likelihood estimator “TrioML”; W, Wang estimator. Plot produced with ggplot2 3.3.0 (Wickham, 2016). FIGURE S5. Results of the spatial autocorrelation analysis for A females and B males. The blue line indicates the autocorrelation coefficient of the data, with the 95% confidence interval at each distance class indicated by the black error bars, as determined by 1000 bootstrap resampling replicates. The red dashed lines indicate the 95% confidence interval around the null hypothesis (no spatial structure, i.e. rauto = 0), as determined by permutation (999 steps). Thus, if the error bars around the blue line do not overlap with the red dashed lines in a distance class, then genotypes were more (positive rauto) or less (negative rauto) similar than expected under the null hypothesis in that distance class. Such cases are indicated with an asterisk (*).The National Zoological Gardens, Pretoria and the University of South Africa.https://zslpublications.onlinelibrary.wiley.com/journal/14697998hj2023BiochemistryGeneticsMicrobiology and Plant Patholog

Development of chemical-based reference standards for rooibos and honeybush aroma lexicons

CITATION: du Preez, B.V.P. et al. 2020. Development of chemical-based reference standards for rooibos and honeybush aroma lexicons. Food Research International, 127. doi:10.1016/j.foodres.2019.108734.The original publication is available at https://www.sciencedirect.com/journal/food-research-internationalThe honeybush sensory wheel was revised, using a large sample set (n = 585) comprising of the major commercial Cyclopia species, i.e. C. intermedia, C. subternata and C. genistoides. Only positive and negative aroma attributes were included in the wheel. Chemicals were identified to serve as reference standards for the honeybush (Cyclopia spp.) lexicon. Similarly, chemical-based reference standards were identified for the rooibos (Aspalathus linearis) lexicon. From a comprehensive literature search and gas chromatography–mass spectrometry analyses, chemicals were screened by an expert panel for their suitability in terms of typicality of the target aroma. Each chemical was evaluated in a ‘base tea’ and compared to a specific ‘reference tea’ exhibiting a high intensity of the target aroma. A total of 30 and 44 chemicals for rooibos and honeybush, respectively, were selected for validation by a trained panel. Descriptive sensory analysis was conducted to assign typicality and intensity scores for each chemical representing a target aroma attribute. Several chemicals were identified as suitable reference standards for the following aroma notes: isophorone (‘rooibos-woody’), maltyl isobutyrate (‘caramel’), cis-3-hexenol (‘green grass’), 4-oxoisophorone (‘seaweed’) and 2,4,6-trichloroanisole (‘musty/mouldy’) for rooibos; and 2-acetyl-5-methylfuran (‘woody’), levulinic acid (‘fynbos-sweet’), maltyl isobutyrate (‘caramel’), and 2-acetylpyrrole (‘nutty’) for honeybush.https://www.sciencedirect.com/science/article/pii/S0963996919306209Publishers versio

The incidence of skin cancer in relation to climate change in South Africa

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Apolipoprotein E and sex modulate fatty acid metabolism in a prospective observational study of cognitive decline

Background: Fatty acids play prominent roles in brain function as they participate in structural, metabolic and signaling processes. The homeostasis of fatty acids and related pathways is known to be impaired in cognitive decline and dementia, but the relationship between these metabolic disturbances and common risk factors, namely the ɛ4 allele of the apolipoprotein E (ApoE-ɛ4) gene and sex, remains elusive. Methods: In order to investigate early alterations associated with cognitive decline in the fatty acid-related serum metabolome, we here applied targeted metabolomics analysis on a nested case-control study (N=368), part of a prospective population cohort on dementia. Results: When considering the entire study population, circulating levels of free fatty acids, acyl-carnitines and pantothenic acid were found to be increased among those participants who had greater odds of cognitive decline over a 12-year follow-up. Interestingly, stratified analyses indicated that these metabolomic alterations were specific for ApoE-ɛ4 non-carriers and women. Conclusions: Altogether, our results highlight that the regulation of fatty acids and related metabolic pathways during ageing and cognitive decline depends on complex inter-relationships between the ApoE-ε4 genotype and sex. A better understanding of the ApoE-ɛ4 and sex dependent modulation of metabolism is essential to elucidate the individual variability in the onset of cognitive decline, which would help develop personalized therapeutic approaches

Flexible patches for mm-wave holography

Funding: This work was supported by DSTL (DASA grant ACC6004053). J.B. and A.D.F. acknowledge support from EPSRC (Grant Nos. EP/M508214/1 and EP/L017008/1). A.D.F is supported by the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme (grant agreement No. 819346).In this work, we demonstrate, in simulation and experiment, reflection metasurface holograms operating in the millimeter wavelength range.Flexible holographic metasurface patches are the ideal platform to retrofit existing millimeter wavelength equipment to enhance and extendtheir functionality, e.g., for antennas and electromagnetic shielding. We present both a rigid and flexible implementation of the holographic metasurfaces, where the meta-atom is based on a three-layered structure with a gold c-ring as the polarization conversion element.PostprintPeer reviewe