Some observations on the use of D-glucose-2-³H as a tracer in turnover studies in Merino sheep

Bolus Injection of a mixture of D-g1ucose-2-³H and -(U)-¹⁴C into each sheep enabled a turnover rate to be calculated for each isotope and to be compared in the same animal. No statistically significant differences were found in pool size, or glucose space. The total entry rates calculated from the D-glucose-2-³H results were found to be significantly higher (P>0,95 paired t test) than those calculated from the D-glucose -(U)-¹⁴C results, the average difference being 18%. This difference indicated that the extent of glucose recycling was somewhat less than that reported for monogastric mammals (30%-Katz & Dunn, 1967) and similar to that found by Judson & Leng (1972) in sheep. Glycogen was isolated from skeletal, cardiac and smooth muscle as well as from the liver and the ³H:¹⁴C ratios determined. These ratios were found to be significantly higher than those reported for monogastric mammals such as the rat or dog.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acroabt XI was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

The separation of some volatile fatty acids on a "Sephadex" partition chromatogram

The suitability of Sephadex LH-20 as a solid support for the partition chromatography of acetic, propionic and butyric acids was investigated by using standard mixtures of 14C-labelled acids. The clear separation that was obtained between the acids was confirmed by the negligible cross contamination found between the acid peaks. Furthermore, the Sephadex LH-20 column gave a convenient elution volume and time similar to those found for a Celite Analytical Filter Aid column, without the progressive deterioration in separation normally associated with Celite.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

EFFECTIVENESS OF PRIMECAST® AND PMMA ADDITIVE MANUFACTURING PROCESSES TO PRODUCE PATTERNS FOR INVESTMENT CASTING

Conference ProceedingsInvestment casting produces parts that need little or no secondary machining operations. Wax patterns used for investment casting are typically produced through an injection moulding process with the accompanying tooling. However, cost and lead time to produce tooling can be high and complexity is limited by conventional machining ability. Additive manufacturing provides an alternative method for producing investment casting patterns that can provide dramatic time and cost savings. This paper reports on a study to determine the advantages and limitations of using PrimeCast® and PMMA patterns produced for investment casting by two different additive manufacturing technologies

BENCHMARKING OF FDM PRINTED REPLACEMENT PARTS FOR RURAL WHEELCHAIRS

ArticleMany disabled patients rely on wheelchairs for mobility to participate as equal citizens within society. Wheelchairs supplied through state healthcare are often not well suited to especially rural conditions and often break-down. This study investigates if entry level Fused Deposition Modelling (FDM) can be used to produce front caster wheels and seat post guides that commonly fail on wheelchairs. Results of the study has shown that these parts can be produced with good quality and at reasonable cost through FDM. The ability to manufacture custom made parts on request through FDM was shown to be a real advantage to supply hard to source wheelchair parts in the rural communities

Evaluating the Suitability of Alumide Tooling for Injection Moulding of Different Polymers

Published ArticleThis paper describes the possibility of using laser-sintered Alumide® as an alternative material for producing rapid tooling (RT) inserts. To determine the durability of Alumide® inserts for the injection moulding (IM) process, a product with geometrical features was developed, and Alumide® inserts were manufactured. Polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), and polyamide 6 (PA 6) were used for IM trials with the Alumide® inserts. From these trials, it was concluded that polymer materials with a processing temperature of about 230 ºC, similar to PP and ABS, can be used with Alumide® inserts as RT inserts for the IM process

Assessment of surface finish and dimensional accuracy of tools manufactured by metal casting in rapid prototyping sand moulds

Abstract In this paper, an initial assessment of the quality parameters of the surface finish and dimensional accuracy of tools made by metal casting in rapid prototyping (RP) sand moulds is undertaken. A case study from a local tool room, dealing with the manufacturing of an aluminium die for the lost wax process, is employed. Modern techniques, including surface roughness analysis and three dimensional scanning, are used to determine and understand how each manufacturing step influences the final quality of the cast tool. The best surface finish obtained for the cast die had arithmetic average roughness (Ra) and mean average roughness (Rz) respectively equal to 3.23μm and 11.38μm. In terms of dimensional accuracy, 82% of cast-die points coincided with the Computer Aided Design (CAD) data, which is within the typical tolerances of sand cast products

Volatile fatty acid metabolism in sheep. 1. Average daily volatile fatty acid production in the rumen of sheep fed lucerne hay

Changes in the total concentration of the volatile fatty acid (VFA) pool in the rumen were followed over a 24 hour period in 2 groups of sheep, 1 fed at 08h00 and the other twice daily at 08h00 and 20h00. Although similar maximum (143 and 147 meq/l) and average (100,3 and 102,1 meq/l) levels were found in the 12 and 24 h groups respectively, the twice daily feeding regimen resulted in a lower variation (S.D. = I7,0 meq/l and 28,9 meq/l respectively). It was concluded from changes in the percentage molar composition of the VFA pool over the same period that the order of VFA absorption from the rumen was propionate > acetate > butyrate for both groups, but that the differences were less marked for the twice daily fed sheep. Long term infusions of ¹⁴C labelled acetic, propionic and butyric acids into the rumen of sheep fed a total of I 600 g lucerne hay twice daily (08h00 and 20h00), gave an average net total VFA production rate of 4, 52 ± 1 ,01 moles/800 g/12 hours irrespective of the acid infused. The net individual turnover rates for acetic (2,81 moles/ 12 h), propionic acid (0,82 moles/12 h) and butyric acid (0 , 55 moles/12 h), derived by the subtraction of the inter-conversion factors from the gross production rates of the acids, and expressed as the percentage contribution of each acid to the total net VFA turnover (acetic= 62%, propionic= 18% and butyric= 12%) closely resembled the percentage molar composition of the VFA pool in the rumen (acetic= 60%, propionic=23% and butyric= 12%). The total net VFA production was found to be directly proportional to the total VFA concentration in the rumen (correlation coefficient = 0, 83), and the relationship can be described by the equation y = 0,034 x + 0,16 where y= VFA production in moles/ 12 hour and x = VFA concentration in meq/l. A specific VFA production rate of 0,85 moles per 100 g digestible organic matter was calculated from the average daily VFA production rate and the composition of the lucerne hay.The articles have been scanned in colour with a HP scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to final presentyation PDF-Format

A rapid quantitative colorimetric determination of blood acetone applied to the assessment of ketosis in fasted pregnant ewes

A simple, accurate, colorimetric method for determining blood acetone as an adjunct to the enzymic method of estimating the other ketones was developed and tested on a group of fasted pregnant ewes. Acetone reacted with 2-hydroxybenzaldehyde to form a stable coloured complex that followed Beer's Law up to an acetone concentration of at least 4 mg/ 100 ml of the test solution at 490 nm. While the optimum incubation time of the reaction mixture was found to be 3 h at 40 °C, it could also be left to incubate overnight at room temperature. When tested in a blood matrix, the method gave a mean within-batch coefficient of variation of 0,7%, and a day to day variation of 0, 3 – 1,2 %, while an overall recovery of 100,6 ± 1,4% was achieved over 5 concentration ranges (2,86 - 10,53 mg/100ml). The values obtained from this method corresponded closely to those from the diffusion technique previously employed and it considerably simplified the procedure. A direct linear relationship, y= 2,594x + 2,917 with a coefficient of determination r²= 0,958 for 49 pairs of data, was found between the acetone (= x mg/100 ml) and total ketone (= y mg/100 ml) concentrations in blood samples drawn from fasted pregnant sheep. This relationship can therefore be used to estimate accurately the degree of ketosis from the blood acetone concentration alone.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Glucose turnover, tolerance and insulin response in wethers, ewes and pregnant ewes in the fed and fasted state

Glucose turnover parameters were obtained in fed and fasted wethers, ewes and pregnant ewes in their 2nd and 3rd trimesters, using a jugular bolus injection of D-glucose-2-³H. Fasting significantly (P<0,05) reduced glucose turnover (c. 40%) in both the wether and the non-pregnant ewe. A somewhat larger difference (c. 54%) between the fed and fasted ewes was found in their 3rd trimester of pregnancy due to an increase when fed (c. 29% higher turnover than in the non-pregnant ewe) rather than a decrease when fasted, since there was no statistical difference (P< 0, 1) between glucose turnover values of pregnant or non-pregnant fasted ewes. Glucose tolerance was estimated from an intrajugular glucose load (1 g/kg⁰'⁷⁵ body mass) in these 3 groups of sheep under both fed and fasted conditions, and the resulting insulin response was followed for 4 h after the injection. Fasting reduced the plasma clearance rate of glucose by c. 63% in both the wether and the nonpregnant ewe while the reduction was somewhat smaller (c. 51%) during the 2nd trimester of pregnancy. Only the pregnant ewe group showed a corresponding reduction in the resulting insulin response of 46% which was similar in magnitude to the diminished clearance, indicating that factors other than insulin are responsible for the reduced glucose clearance associated with fasting in the weather and non-pregnant ewe. Despite similar baseline plasma glucose values the glucose load appeared to distribute in a space that was significantly less than that found in all 3 groups of fed sheep when trace amounts were injected.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Development Of An Improved Wood’S Alloy End-Frame Casting Unit For Electron Field Shaping In Radiotherapy

Journal ArticleAs the second leading cause of death, cancer is a harsh reality. Skin cancer is one of the most prevalent cancers in South Africa and is commonly treated using electron radiation in radiotherapy. The applied radiation field needs to be shaped to the size of the cancer-affected area on the patient. This can be achieved through end-frames that fit into applicators that attach to the treatment unit. The end-frames are produced by casting Wood’s alloy into commercially available jigs. However, producing these end-frames presents various shortcomings such as lack of dimensional accuracy, the inconsistent density of the castings and the high cost of the jigs. The aim of this study was to develop a Wood’s alloy casting unit that can be made available to local oncology departments to produce endframes that are superior to what can be produced through commercial jigs. This paper describes the development and manufacturing of the new casting equipment and experiments performed to evaluate end-frames produced. Results showed that end-frames cast in the newly developed casting equipment are dimensionally more accurate, have consistent high density, and can be produced in a shorter time