Structure and function of natural sulphide-oxidizing microbial mats under dynamic input of light and chemical energy

We studied the interaction between phototrophic and chemolithoautotrophic sulphide-oxidizing microorganisms in natural microbial mats forming in sulphidic streams. The structure of these mats varied between two end-members: one characterized by a layer dominated by large sulphur-oxidizing bacteria (SOB; mostly Beggiatoa-like) on top of a cyanobacterial layer (B/C mats) and the other with an inverted structure (C/B mats). C/B mats formed where the availability of oxygen from the water column was limited (<5 mu M). Aerobic chemolithotrophic activity of the SOB depended entirely on oxygen produced locally by cyanobacteria during high light conditions. In contrast, B/C mats formed at locations where oxygen in the water column was comparatively abundant (445 mu M) and continuously present. Here SOB were independent of the photosynthetic activity of cyanobacteria and outcompeted the cyanobacteria in the uppermost layer of the mat where energy sources for both functional groups were concentrated. Outcompetition of photosynthetic microbes in the presence of light was facilitated by the decoupling of aerobic chemolithotrophy and oxygenic phototrophy. Remarkably, the B/C mats conserved much less energy than the C/B mats, although similar amounts of light and chemical energy were available. Thus ecosystems do not necessarily develop towards optimal energy usage. Our data suggest that, when two independent sources of energy are available, the structure and activity of microbial communities is primarily determined by the continuous rather than the intermittent energy source, even if the time-integrated energy flux of the intermittent energy source is greater

Rapid tooling application for the evaluation of a greensand casting defect

Abstract: The ability to produce production quality tooling, directly from CAD data, through additive manufacturing (AM) processes has obvious advantages with regards to the reduced lead time and labour costs. This, together with the ability to simulate the metal casting process, opens new doors for researchers in the field of metal casting. This paper reviews the suitability of tooling produced in PA 2200 polyamide material, for use in a research environment, where the failure of greensand, a mixture of silica sand, bentonite (clay) and water, is to be replicated as it would occur in an industrial setting

Andragogy : a theoretical overview on learning theories that impact on benchmarking blended learning at the Central Univerity of Technology, Free State

Published ArticleBlended learning has shown enormous growth worldwide during the last decade. Blended learning initiatives expanded rapidly, as technological improvement and a greater demand from learners arose as a result of the need for life-long learning and changing demands in the world of work. Many higher education institutions use blended learning as an alternative for or additional to conventional face-to-face education. The changing needs of learners, and especially adults, forced institutions to upgrade their traditional courses and increasingly make use of technologically enhanced courses. The research problem encompasses the fact that the growth of blended learning poses many problems to higher education institutions, as the delivery by means of technology is complex. Many higher learning institutions were not prepared adequately to deliver education by using blended learning and did not have the required systems in place. The greatest concern was that staff was not familiar with the technology or its use and that the particular demands of staff arrangements to engage in blended learning programs were not taken into account. It appears that institutions did not plan or have systems and guidelines in place to implement programs at a distance using blended learning technology. Another concern was that most of the programs held traditional approaches and has not been adapted to suit the particular characteristics and needs of distance education by taking the planning, development and review of such programs into consideration. As part of ongoing research at the Central University of Technology, Free State appropriate research had to be undertaken. Consequently the following research question emanated from the research problem: Within the context of higher education in South Africa, what framework underpinned by andragogy, national education policies and blended learning theory, will benchmark and support the implementation of blended learning at the Central University of Technology, Free State

Andragogy : a theoretical overview on learning theories that impact on benchmarking blended learning at the Central Univerity of Technology, Free State

Published ArticleBlended learning has shown enormous growth worldwide during the last decade. Blended learning initiatives expanded rapidly, as technological improvement and a greater demand from learners arose as a result of the need for life-long learning and changing demands in the world of work. Many higher education institutions use blended learning as an alternative for or additional to conventional face-to-face education. The changing needs of learners, and especially adults, forced institutions to upgrade their traditional courses and increasingly make use of technologically enhanced courses. The research problem encompasses the fact that the growth of blended learning poses many problems to higher education institutions, as the delivery by means of technology is complex. Many higher learning institutions were not prepared adequately to deliver education by using blended learning and did not have the required systems in place. The greatest concern was that staff was not familiar with the technology or its use and that the particular demands of staff arrangements to engage in blended learning programs were not taken into account. It appears that institutions did not plan or have systems and guidelines in place to implement programs at a distance using blended learning technology. Another concern was that most of the programs held traditional approaches and has not been adapted to suit the particular characteristics and needs of distance education by taking the planning, development and review of such programs into consideration. As part of ongoing research at the Central University of Technology, Free State appropriate research had to be undertaken. Consequently the following research question emanated from the research problem: Within the context of higher education in South Africa, what framework underpinned by andragogy, national education policies and blended learning theory, will benchmark and support the implementation of blended learning at the Central University of Technology, Free State

Maceration Before and During Fermentation: Effect on Pinotage Wine Phenolic Composition, Total Antioxidant Capacity and Objective Colour Parameters

Low-temperature maceration treatments (1, 2 and 4 days at 10 and 15°C) before fermentation and juice/skin mixing treatments (punching-down, pumping-over and rotor action every hour and every 3 hours) duringfermentation were investigated in terms of their effects on Pinotage wine phenolic composition, total antioxidant capacity (TAC) and colour over three vintages (2000 to 2002). Results for pre-fermentation maceration were notconsistent between vintages. Very few significant differences in the phenolic content, TAC and objective colour parameters were observed between the control wines and wines subjected to different pre-fermentation macerationtreatments. Pre-fermentation maceration, especially at 15°C, resulted in wines with increased vitisin A content.  Improvement of wine quality when using pre-fermentation maceration treatments at 10°C was noted previously, while no detrimental effect on the wine TAC was observed. The pumping-over treatment yielded wines with lower TAC and phenol content, as well as less favourable objective colour values, indicating that the punching-down or rotor treatment would be preferred. Although mixing at hourly intervals yielded a higher content of some phenolic compounds compared to the 3-hour interval mixing, mixing frequency did not affect the TAC of the wine. The objective colour parameters, h* and b*, were slightly lower at the higher mixing frequency in 2002 indicating a shift in the direction of a magenta hue

In Situ Coral Reef Oxygen Metabolism: An Eddy Correlation Study

Quantitative studies of coral reefs are challenged by the three-dimensional hard structure of reefs and the high spatial variability and temporal dynamics of their metabolism. We used the non-invasive eddy correlation technique to examine respiration and photosynthesis rates, through O-2 fluxes, from reef crests and reef slopes in the Florida Keys, USA. We assessed how the photosynthesis and respiration of different reef habitats is controlled by light and hydrodynamics. Numerous fluxes (over a 0.25 h period) were as high as 4500 mmol O-2 m(-2) d(-1), which can only be explained by efficient light utilization by the phototrophic community and the complex canopy structure of the reef, having a many-fold larger surface area than its horizontal projection. Over diel cycles, the reef crest was net autotrophic, whereas on the reef slope oxygen production and respiration were balanced. The autotrophic nature of the shallow reef crests implies that the export of organics is an important source of primary production for the larger area. Net oxygen production on the reef crest was proportional to the light intensity, up to 1750 mu mol photons m(-2) s(-1) an d decreased thereafter as respiration was stimulated by high current velocities coincident with peak light levels. Nighttime respiration rates were also stimulated by the current velocity, through enhanced ventilation of the porous framework of the reef. Respiration rates were the highest directly after sunset, and then decreased during the night suggesting that highly labile photosynthates produced during the day fueled early-night respiration. The reef framework was also important to the acquisition of nutrients as the ambient nitrogen stock in the water had sufficient capacity to support these high production rates across the entire reef width. These direct measurements of complex reefs systems yielded high metabolic rates and dynamics that can only be determined through in situ, high temporal resolution measurements

Beyond persons: extending the personal / subpersonal distinction to non-rational animals and artificial agents

The distinction between personal level explanations and subpersonal ones has been subject to much debate in philosophy. We understand it as one between explanations that focus on an agent’s interaction with its environment, and explanations that focus on the physical or computational enabling conditions of such an interaction. The distinction, understood this way, is necessary for a complete account of any agent, rational or not, biological or artificial. In particular, we review some recent research in Artificial Life that pretends to do completely without the distinction, while using agent-centered concepts all the way. It is argued that the rejection of agent level explanations in favour of mechanistic ones is due to an unmotivated need to choose among representationalism and eliminativism. The dilemma is a false one if the possibility of a radical form of externalism is considered

Metabolic changes in the lungs after ischaemia

CITATION: Engelbrecht, F. M., Edwards, I. J. & De Beer, D. P. 1980. Metabolic changes in the lungs after ischaemia. South African Medical Journal, 58:409-413.The original publication is available at http://www.samj.org.zaThe effects of variable periods of ischaemia on the isolated lungs of rats and rabbits, stored for up to 6 hours at 4°C, 21°C and 37°C under standardized conditions, were investigated in vitro in terms of oxygen consumption, the rate of 1-14C-leucine incorporation into soluble proteins, and 1-14C-palmitate incorporation into total phospholipids and lipid fractions. The endogenous oxygen uptake of rat lung slices in an air phase, from tissues stored at 4°C and 21°C under ischaemic conditions for 6 hours and at 37°C for 4 hours, was significantly different from the control values. The oxygen uptake of lungs from animals anaesthetized with pentobarbitone prior to exsanguination and stored for only 2 hours at 37°C differed significantly from control values. Judged by the rate of incorporation of radiolabelled leucine into soluble proteins and that of palmitate into total lipids and phospholipids of lungs after storage for increasing periods at 4°C and 37°C, significant differences were already found after 1 1/2 hours. From this observation it would appear that these parameters are very sensitive indicators for assessing irreversible lung damage due to ischaemia.Publisher’s versio

Climatic Region and Vine Structure: Effect on Pinotage Wine Phenolic Composition, Total Antioxidant Capacity and Colour

The phenolic composition, total antioxidant capacity (TAC) and colour of Pinotage wines of the 2001, 2002 and 2003 vintages were investigated, using spectrophotometric, high-performance liquid chromatography (HPLC), free radical scavenging and objective colour analyses. Grapes were harvested from grapevines in three climatic regions ranging from cool to warm, with bush (20- and 30-cm trunk height) and trellised (30- and 60-cm trunk heights) vine treatments, on several vineyard sites in each climatic area. Climatic region had a significant effect on the content of several phenolic compounds; the concentration of anthocyanin monoglucosides, flavonols, flavan-3-ols and tartaric acid esters of hydroxycinnamic acids generally increased as the climatic region becomes cooler, while concentrations of acylated derivatives and free hydroxycinnamic acids decreased. Wines made from bush vines contained higher concentrations of flavonols, gallic acid and flavan-3-ols than those from trellised vines, but lower concentrations of some anthocyanin monoglucosides and acylated derivatives, as well as non-coloured polymers.  These trends resulted in differences in TAC and objective colour parameters, although the different vintages did not show the same trends in all cases. More vintages should therefore be investigated to clarify these effects. Wines from the cool climatic regions and from bush vines were generally darker coloured, with higher TAC than those from the warm climatic regions and bush vines, respectively. High TAC, therefore, coincided with higher colour quality. Variations in TAC were partly explained by trends for individual phenolic compounds, although unknown compounds played a major role

Postmortem tissue distribution of morphine and its metabolites in a series of heroin related deaths

The abuse of heroin (diamorphine) and heroin deaths are growing around the world. The interpretation of the toxicological results from suspected heroin deaths is notoriously difficult especially in cases where there may be limited samples. In order to help forensic practitioners with heroin interpretation we determined the concentration of morphine (M), morphine‐3‐glucuronide (M3G) and morphine‐6‐glucuronide (M6G) in blood (femoral and cardiac), brain (thalamus), liver (deep right lobe), bone marrow (sternum), skeletal muscle (psoas) and vitreous humor in 44 heroin related deaths. The presence of 6‐monoacetylmorphine (6‐MAM) in any of the postmortem samples was used as confirmation of heroin use. Quantitation was carried out using a validated LC‐MS/MS method with solid phase extraction. We also determined the presence of papaverine, noscapine and codeine in the samples, substances often found in illicit heroin and that may help determine illicit heroin use. The results of this study show that vitreous is the best sample to detect 6‐MAM (100% of cases), and thus heroin use. The results of the M, M3G and M6G quantitation in this study allow a degree of interpretation when samples are limited. However in some cases it may not be possible to determine heroin/morphine use as in 4 cases in muscle (3 cases in bone marrow) no morphine, morphine‐3‐glucuronide or morphine‐6‐glucuronide was detected, even though they were detected in other case samples. As always postmortem cases of suspected morphine/heroin intoxication should be interpreted with care and with as much case knowledge as possible