bluuebunny/crossref_metadata_2025 huggingface dataset:
Bydraes van Darwin se voorgangers tot die Ewolusieteorie
Authors: Swanepoel J. H.
Published: July 2013

A review of the literature with respect to ideas and hypotheses on evolution, prior to Darwin’s Origin of Species, reveals that many biologists long before Darwin postulated theories similar to his natural selection theory. The relation between phylogenetic classification and evolution, as well as the epigenetic theory of evolution, was postulated nearly fifty years be­fore Darwin. With this review of the literature an attempt is made to put Darwin and his forerunners in a better perspective with each other.
Woordeboek vir Tuinboukunde (Ingeslote Plantname)
Authors: Holtzhausen L. C. , Genis L. A.
Published: July 2013

Die vak Tuinboukunde kan gedefinieer word as die wetenskap en/of kuns wat hom bemoei met die kweek van vrugte, groente, blomme, sierstruike en - bome en die gepaardgaande bestuur daarvan in ’n tuin, boord of landgoed. Die tuinboubedryf dra tans meer as drie miljard rand tot die ekonomie van die land by.
Die invloed van endotoksienbesmetting op die uitkoms van ’n in vitro - bevrugtingsprogram
Authors: Fourie F. Le R. , Huyser C. , Visser D. , Esterhuizen A. , Peters E.
Published: July 2013

Gedurende 1988 het ’n betekenisvolle daling in biochemiese swangerskappe per embrioterugplasing (ET) voorgekom (28,2% vs 8,33%). Die weeklikse kwaliteitskontroles wat geimplementeer word (muisembrioverdeling, spermoorlewing en biochemiese profiel van die voorbereide medium), het geen betekenisvolle kwaliteitsafname getoon nie.
Omgewingstoksikologie - ’n nuwe uitdaging
Authors: Office Editorial
Published: July 2013

Kommer oor die uitwerking van toksiese chemiese stowwe op die plant - en dierelewe in die omgewing het gelei tot die ontwikkeling van ’n lewenskragtige nuwe studierigting aan verskeie Europese en Amerikaanse universiteite, nl. die ekotoksikologie.
Ondersoek na vruggroei van Minneola tangelo (Citrus paradisi x C. reticulata)
Authors: Esterhuizen H. J. , Holtzhausen L. C. , Swart E.
Published: July 2013

The influence of gibberellic acid (GA₃) on the fruit growth pattern of the Minneola tungelo was investigated. The growth pattern follows a S-curve, similar to other citrus cultivars but the growth rate differs. GA₃, applied at low concentrations caused a slightly slower fruit growth rate compared to controls, resulting in smaller fruit. In the case of GA₃ , applied at 15ppm, fruit numbers exceeded those of the control. GA₃ treatment of fruit resulted in a slight decrease in average seed con­tent. GA₃, had no significant effect on juice quality.
Evaluasie van bestaande seleksiekriteria vir beeste in terme van totale kuddedoeltreffendheid
Authors: Scholtz M. M. , Roux C. Z.
Published: July 2013

Breeding should always be aimed at the improvement of total herd efficiency. Selection criteria were evaluated from this viewpoint. In dairy cattle there was a marked increase in production traits in the 10 year period studied. During this period calving interval was also shortened by 5%. It was indicated that these changes probably led to an improvement in total herd efficiency. Thus, it seems that performance testing and selection criteria are utilized in the correct manner by dairy cattle breeders. In beef cattle no improvement was found in performance under farming conditions.
’n Plastiek Cartesiese duiker as respirometer
Authors: Van Aardt W. J.
Published: July 2013

The working principles of the Cartesian diver as a respirometer for terrestrial micro-athropods are discussed. The advan­tages and disadvantages of Perspex as thermoplastic diver material are compared with those of Pyrex or Jena glass. With the aid of diagrammes on which physical dimensions are indicated, the functional parts of a Perspex diver with a diver cons­tant of about 80 microliters are described. Stepwise instructions for the operation of the diver system (flotation vessel, manometer, glassmanifold) within the enclosed waterbath are presented to enable one to measure the equilibrium pressure (ΔP) of each individual animal with a mass less than 1 mg. The calculations used to determine the diver constant for each diver are fully described. Practical examples are used to enable one to calculate the oxygen consumption rate (VO₂) for a mite species from the equilibrium pressure measurement.
Ultrastrukturele kwantifisering van mikrotubuli in volledige selprofiele
Authors: Crous A. , De Beer A. M.
Published: July 2013

The ultrastructural morphometric quantification of cytoplasmic microtubular distribution densities requires electron micro­graph magnifications whereby only small cytoplasmic areas are included per negative. Consecutive electron micrographs can be composed in montages to attain complete profiles of high magnification cell sections. Conventional morphometric methods are not suitable for application on areas that may be as great or even greater than 1 m² in size. Modifications of conventional morphometric technology to facilitate investigations of this nature are described. Statistical comparison of results obtained with this method and a standard method reflect the soundness of the modifications.
Liggaamsoriëntasie van blesbokke in ’n skadulose omgewing
Authors: Van Aswegen C. H. J.
Published: July 2013

The body orientation of blesbok Damaliscus dorcas phillipsi in relation to sun angle and wind direction was investigated in a shadeless environment in the central Orange Free State. During early morning and late afternoon, when the sun’s altitude and ambient temperature are relatively low, the antelope evidently orientate laterally towards the sun. As the temperature increases during midday, the antelope show a tendency to orientate in line with the incoming radiation but laterally in rela­tion to wind direction.
Die effekte van melatonien op molekulêre vlak
Authors: Haag M. , Theron J. J.
Published: July 2013

The indole hormone melatonin is secreted in a biphasic circadian rhythm by the pineal gland. This review presents a summary of recent results concerning — (i) factors that influence melatonin synthesis; (ii) the existence of melatonin receptors in brain tissue; (iii) the effects of melatonin as a modulator of dopaminergic, noradrenergic, GABAergic and opioidergic neurotransmitter processes; (iv) the influence of melatonin on the electric activity and metabolic rate of certain brain nuclei; and (v) melatonin effects on hormone secretion in the hypothalamic-pituitary axis. A basic mechanism of melatonin action via cyclic nucleotides and thus protein phosphorylation is presented.
Sirkadiese sekresiepatrone van ß-endorfien en leusienenkefalien
Authors: De Wet E. H. , Oosthuizen J. M. C.
Published: July 2013

ß-endorphin and leucine enkephalin are neuropeptides with potent opioid activity. In a study to investigate the circadian secretion patterns of the above-mentioned, blood samples were collected hourly from 12 healthy males who were subjected to the experiment for 24 hours. Radioimmunoassays were used in the analysis of plasma samples for ß-endorphin and leucine enkephalin. Peak concentrations of ß-endorphin were demonstrated from 08:00-09:00, while peak concentrations of leucine enkephalin occured from 23:00-07:00. Trough concentrations of ß-endorphin occurred from 24:00-05:00, while trough con­centrations of leucine enkephalin were demonstrated from 09:00-12:00. The illustrated circadian secretion pattern for ß-endorphin simulates the well-known circadian rhythm of cortisol. The answer to this may be in the fact that ß-endorphin and corticotropin stem from the same precursor. The illustrated circadian secretion pattern for leucine enkephalin simulates that of melatonin. The reason for this is unclear.
Aspekte van die hersiening van die Fisikawoordeboek I
Authors: Louw D. F.
Published: July 2013

In die vorige uitgawe van hierdie tydskrif is aangedui dat ’n Redaksiekomitee onder die vleuels van die Departement van Nasionale Opvoeding se Nasionale Vakterminologie - diens (NVD) benoem is om die tweetalige Fisikawoor­deboek - te hersien.
Die Nasionale Vakterminologiediens (NVD)
Authors: Genis L. A.
Published: July 2013

Die Nasionale Vakterminologiediens (NVD) ressorteer onder die Hoofdirektoraat Kultuur en Vakkundige Hulp- dienste van die Departement van Nasionale Opvoeding. Die hoofdoelwit van die NVD is die skepping van ’n fijnksionele vakwoordeskat in veral Afrikaans, parallel met die inter- nasionaal gebruikte terminologieë.
Die evaluering van vyftien doringlose turksvykultivars (Opuntia ficus-indica (L.) Mill.) vir varsvrugteproduksie in die Pretoriagebied
Authors: Wessels A. B.
Published: July 2013

Fifteen spineless prickly pear cultivars (Opuntia ficus-indica) were evaluated for three successive seasons at the University of Pretoria Research Farm. Yields were recorded and external and internal fruit quality factors were identified and considered. Following this investigation, minimum standards were suggested and the cultivars under review were compared. The cultivars Morado, Algerian, Fusicaulis van Heerden, Fresno, Mexican and Nudosa met all or most of the standards set. It is concluded that for fresh fruit production these cultivars are best suited for planting in the Pretoria region and in areas with similar climatic conditions.
Die verband tussen die ontwerp en prestasie van seilplanke
Authors: Kriel K. F.
Published: July 2013

The shapes and performances of the 175 most recently designed sailboards recorded by testers in different sailboard magazines are statistically correlated to establish whether shapes are in fact responsible for performances as claimed by designers and manufacturers. Different shapes are correlated with different aspects of performance, namely up-wind, reach, broad reach, light- wind performance, medium-wind performance, strong-wind performance and jibes. Statistical analysis by means of different stages of multiple regression showed that different shapes of board collectively contributed in some cases to explaining up to 59% of the variance between certain types of performance.
Die gebruik van anaboliese steroïede by ramlammers
Authors: Greyling J. P. C.
Published: July 2013

The effect of anabolic steroids on certain body parameters in ram lambs was investigated. Twenty Ile de France ram lambs were allocated at random to two groups after weaning (3 months). One group (n = 10) was treated weekly with an intramuscular injection of an anabolic steroid (50 mg nandrolone laurate)for a 12-week period. The second group (n = 10) served as a control. Parameters recorded weekly included scrotal circumference, scrotal volume, shoulder width, body length, shoulder height, body weight and serum testosterone concentration. Treatment with steroids did not significantly increase the mean shoulder width (22,8 vs 22,0 cm), shoulder height (61,7 vs. 60.8 cm), body length (72,8 vs. 70,2 cm) or body weight (42,5 vs. 39,8 kg). Scrotal circumference and volume were significantly (P <0,01) less in the treated group - a decrease of 24,5% and 51,2%. respectively.
Wanneer is ’n pyp nie ’n buis nie?
Authors: Scribante P.
Published: July 2013

No abstract
Die toekoms van die biologiese wetenskappe
Authors: Office Editorial
Published: July 2013

No Absract
Die optimisering van die snyproses van diamante met behulp van ’n YAG - laser
Authors: Lubbe A. J.
Published: July 2013

A laser cannot, as generally assumed by the layman, cut right through a diamond with a single cut. A couple of hundred cuts may be necessary to "chip carve" through a diamond. There are several parameters, for example cutting speed, focus point, overlapping of cuts, etc., that influence the cutting process. With a view to optimizing the cutting process, laser cuts in diamonds were studied in a systematic way with the aid of an electron microscope. The method, technique and the results of the research are discussed in this article.
Intra - en interindividuele variasies in LP(a) - konsentrasies in hiper - lipidemiese Afrikaners
Authors: Kellerman J. A. , Vorster H. H. , Venter C. S. , Oosthuizen W.
Published: July 2013

No abstract
EENHEID IN DIE WETENSKAP, ’N WETENSKAPSTAAL EN AFRIKAANS AS WETENSKAPSTAAL: ’N REAKSIE
Authors: Office Editorial
Published: July 2013

No abstract
Die evolusie van gametangiofore in Suider - Afrikaanse Marchantiales (Hepaticae): ’ n hipotese
Authors: Perold S. M.
Published: July 2013

Members of the thallose liverwort order, Marchantiales, display great diversity in their gametangiophores (specialized gametangium-bearing branches), as well as in their sporophytes (typically consisting of a foot, seta and spore-containing capsule). An attempt is made to trace the phylogeny or evolutionary history of Southern African members of the order by examining and comparing the aforementioned structures in a few key examples such as the genera Oxymitra, Exormotheca, Targionia, Riccia, Lunularia, Asterella, Cryptomitrium and Marchantia. It is concluded that there is a mosaic of primitive and advanced characters in the gametangiophores of the examples cited and that a linear mode of descent is not acceptable, but that a branched type of configuration is more probable.
Struktuur en funksie van peroksisome
Authors: Theron J. J. , Van Papendorp D. H.
Published: July 2013

Peroxisomes found in most pro - and eucaryotic cells are usually round or oval cytoplasmic structures of varying size with a finely granular matrix surrounded by a single membrane. Crystalline inclusions described as nucleoids or marginal plates that consist of aggregates of enzyme molecules such as urate oxidase or L-a-hydroxyacid oxidase respectively, are found in some peroxisomes. Biogenesis of peroxisomes occurs through the translocation of proteins from the cytosol across the limiting membrane of the organelle and a carboxyterminal tripeptide signal, SKL, or minor modifications of this motif, is required for this process.
Die genetiese manipulasie van die gis Saccharomyces cerevisiae vir die moontlike omskakeling van polisakkariedryke landbougewasse en nywerheidsafval na enkelselproteien en brandstofetanol
Authors: Pretorius I. S.
Published: July 2013

The world’s problem with overpopulation and environmental pollution has created an urgent demand for alternative protein and energy sources. One way of addressing these burning issues is to produce single-cell protein (for food and animal feed supplements) and fuel ethanol from polysaccharide-rich agricultural crops and industrial waste by using baker’s yeast.
Die byniere van die Afrika-olifant (Loxodonta africana): enkele waarnemings. 2. Die zona reticularis, medullêre kapsel, F - laag en medulla
Authors: Strassberger F. G. W. , Nel M. M. , Nel P. P. C.
Published: July 2013

The structure of the zona reticularis, medullary capsule, F-zone and medulla of the African elephant (Loxodonta africana) is described. Three types of cells, arranged as described in other mammals, are found in the zona reticularis. Organelles in this zone are as descibed for other cells that secrete steroids. The ultrastructure of the cells in the F-zone is very similar to that of cells that secrete steroids. Two types of cells, roughly similar to those of other mammals, are found in the medulla.
Tegnologie vir ten volle geoutomatiseerde melking van koeie
Authors: Gouws J.
Published: July 2013

Since dairy farming is a very labour intensive, seven-days-per-week activity, increasing emphasis is being placed on the use of advanced technology in dairying throughout the world. Dairy mechanisation has been well established for many years, whereas dairy automation has only started to gain momentum fairly recently. An important milestone was the introduction of systems for automatic animal identification in the 1970’s. That paved the way for all further dairy automation activities. An analysis of the current status of the fully automated milking of cows shows that the automated attachment of a milking machine’s teat cups to a cow ’s teats is the most important task in dairying that remains to be automated.
Verbetering van numeriese modelle met behulp van eksperimentele data
Authors: Gorbler D. Z.
Published: July 2013

There is a growing interest in techniques for the updating of numerical structural models using experimental data. This work investigates the application of two fundamentally different approaches to the problem through a practical example. In one case the structural matrices are directly adjusted to force the eigenvalues and eigenvectors of the numerical model the same as the measured values. In the second case physical design variables are adjusted to improve the agreement between the eigenvalues. Although the direct adjustment of the structural matrices is much simpler to implement than the adjustment of physical design variables and also leads to better correspondence, the application thereof is restricted because of the changes in the physical structure of the matrices and it is suggested that further research be focused on the adjustment of physical parameters.
Afrikaanse tandheelkundige vaktaal
Authors: Germishuys P. J.
Published: July 2013

No abstract
Die reptielhart as oorgangstadium: ’n kort oorsig
Authors: Visser M. H. C.
Published: July 2013

The anatomical and functional significance for evolution of a lepidosaurian - and archosaurian-type of heart are discussed. In the light of cladistics the acceptance of a lepidosaurian-type of heart, as such, as ancestral to an archosaurian type, is questioned. The interventricular septum, right atrioventricular valves and conducting system of the heart of crocodilians, birds and mammals are pointed out as areas where homologies are uncertain. The evolutionary development of the heart and aortic arches of reptiles, birds and mammals is summarised in a cladogram corresponding with one based on characters derived from fossils as well as data derived from soft anatomical characters.
Die toepassing van wasige logika in industriële beheerstelsels
Authors: Shaw I. S.
Published: July 2013

The theory of fuzzy sets is a methodology for the handling of qualitive, inexact, imprecise information in a systematic and rigorous way. Conventional control approaches require a mathematical model of the process or system to be controlled. However, when an accurate knowledge of the process dynamics is not available, or the process is highly complex or non­ linear, conventional techniques do not give satisfactory results and human control operators must still be used. In contrast, fuzzy logic captures and utilizes the accumulated empirical know-how of human operators expressed in qualitative, inexact, imprecise ways.
Forum vir nuwe Afrikaanse chemieterminologie
Authors: Office Editorial
Published: July 2013

No abstract
Die invloed van ouderdom op die komposterings - koers van organiese materiaal deur Eisenia fetida (Oligochaeta)
Authors: Office Editorial
Published: July 2013

One of the main objectives of a vermicomposting plant is to achieve a maximum composting rate of organic waste. Apart from population densities, substrate characteristics and environmental factors, age structure of the population is expected to affect the rate of composting. The composting rate of worms was studied in the laboratory under optimal conditions over a period of 55 days. Growth and sexual maturity were monitored as well as the composting rate during various stages of the life-cycle of Eisenia fetida. The composting rate was initially slow and reached a maximum peak when the worms were pre-clitellate.
Bevolkingsgroei, ekonomiese ontwikkeling en drakapasiteit van die omgewing — is hulle versoenbaar of in konflik?
Authors: Heydom A. E. F.
Published: July 2013

In South Africa, as in many other countries, human population growth is currently reaching levels which render competition for basic human needs such as land and water, inevitable. Concurrent to population growth is the absolute necessity for economic development and job opportunities which, in turn, make tremendous demands upon the environment and natural resource base. As a consequence ever greater emphasis is placed by the news media on apparent conflicts between industrial development and social needs on the one hand, and conservation of the environment and natural resources on the other.
Simulasie van veilige projektielbewapening deur vliegwieltipe aanslagbuise
Authors: Office Editorial
Published: July 2013

Rounds of ammunition are normally armed with a fuse. In this study, a fuse is developed which uses a flywheel-type mechanism controlled by time or distance. Due to its simplicity of operation and construction, the concept is expected to have high reliabil­ity. The dynamic response of all the components of this flywheel-type fuse is mathematically modelled. Simulation software was developed which connects the mathematical models of the various components. With the definition of boundary values, the response of the projectile, flywheel and other components can be determined continuously for firing and in-flight conditions.
Die gebruik van rekenaars in tersiere chemieonderrig
Authors: Steyn M. M. de V
Published: July 2013

The implementation of computers in chemistry education since 1960 is described. Computers can be applied effectively to redress weaknesses in the basic scientific knowledge of students, as well as to augment their practical experience of chemical processes. Often the description or the explanation of chemical processes relies on mathematical and physical models that are three dimensional and dynamic and that can be presented elegantly with digitized images on computer. Current demands on lecturers and students, as well as didactic applications of computers in tertiary teaching are briefly described under the follow­ing headings: computer literacy, subject or task specific applications, computer aided testing, computer aided learning, inter­active multimedia, the use of electronic media for lecture presentations, Internet, and mass education.
Eriophyid-myte (Acari: Eriophyoidea: Eriophyidae) as moontlike beheeragente van ongewenste uitheemse plante in Suid-Afrika
Authors: Craemer C.
Published: July 2013

Eriophyid mites are probably present on most higher plants and generally show a high degree of host specificity. A few are sufficiently damaging to be considered for use in control programmes against unwanted plants. General interest in using eriophyids for weed control developed only recently. Five eriophyid species have already been used, generally successfully, in weed control programmes in other countries. Eriophyid mites have not yet been utilized as weed control agents in South Africa. Seventeen species causing appre­ciable damage, which may be of value in the biological control of 12 alien, invasive plants in South Africa are listed and discussed. The weeds are: Acacia saligna (Port Jackson), Acroptilon repens (Russian knapweed), Cardaria draba (hoary cress), Chromolaena odorata (triffid weed), Convolvulus arvensis (field bindweed), Cuscuta epithymum (dodder), Hypericum perforatum (St. John's wort), Lantana camara (lantana), Melia azedarach (syringa), Opuntia inermis (prickly-pear), Solanum elaeagnifolium(silverleaf nightshade), S. mauritianum (bugweed), and Spartium junceum (Spanish broom). Some of these eriophyids warrant special investigation as possi­ble weed control agents in South Africa.
Die katalitiese siklotrimerisasie van asetileen
Authors: Linde J. J. , Du Plessis J. A. K.
Published: July 2013

The compounds R₄NTaCI₆ with R = CH₃ or were synthesized by refluxing R₄NCI and TaCl₅ in SOCl₂ If C₂H₅AICI is added to R₄NTaCI₆ (Al/Ta molar ratio = 2,5) a suitable catalytic system is formed for the cyclotrimerization of acetylene to produce benzene.
Nuwe patogene in die voedselbedryf
Authors: Ehlers M. M.
Published: July 2013

A “new generation" of food pathogens has emerged which can cause problems in the food industry. These organisms are very adapt­able and existing food processing techniques are not always effective in controlling their growth, especially the refrigeration of the food. Clostridium botulinum type E, enterotoxigenic Escherichia coli, Listeria monocytogenes and Aeromonas hydrophila are capable of growing in food below 5 °C. Campylobacter jejuni and Brucella can survive at 5 °C and a third group of organisms namely Salmonella, Staphylococcus aureus, Vibrio parahaemolyticus and Vibrio vulnificus may grow or survive at temperatures between 5 °C and 12 °C and their presence is an indication of the interruption of the cold chain.
Die herleiding van ’n datapuntkonsentrasie - afhanklike gewigsfunksie vir interpolasie na reënval - roosterpuntvelde
Authors: Rautenbach C. J. de W.
Published: July 2013

Several interpolation algorithms have been developed to create homogeneous gridfields from heterogeneously distributed data. A shortcoming in most of these algorithms is the assumption that data field concentrations are fairly homogeneous over the grid field area. The method for constructing the weight functions as discussed here overcomes this problem by including a variable dependent on the concentration of data points in the weight function. A rainfall data field for South Africa is compiled by this algorithm. The concentration of climate stations in South Africa varies significantly.
Verdedigingsekresies van die graanstinkluis Macchiademus diplopterus (Heteroptera: Lygaeidae)
Authors: Office Editorial
Published: July 2013

Macchiademus diplopterus is a pest of wheat in South Africa. Large numbers of insects were collected from underneath exfolia­ting bark of Eucalyptus spp. growing near wheat fields in the Western Cape Province during January to March 1995. Volatile substances were collected with charcoal or Ambersorb as trapping agent. The adsorbent and the appropriate controls were eluted sequentially with dichloromethane and benzene.
Sanitêre ingenieurswese en legioensiekte
Authors: Office Editorial
Published: July 2013

In 1976 het sowat 200 van die 4 000 deelnemers aan die jaarlikse byeenkoms van die “American Legion” (’n vereniging vir oudsoldate) in Philadelphia longontsteking opgedoen en bykans 30 het gesterf. In die longe van die betrokkenes is ’n verwekker gevind wat reeds vir ’n geruime tyd bekend was en sowat tien jaar tevore met ’n longsiekte in verband gebring is, maar wat tot dusver nog nie ondersoek is nie. Die verwekker is toe die naam “legionella pneumophila” gegee en die siekte het bekend geword as “legioensiekte”.
Fisiologie en patofisiologie van selorganelle
Authors: Theron J. J. , Claasen N. , Panzer A. , Lizamore N.
Published: July 2013

Lysosomes are found in the cytoplasm of all eucaryotic cells except mature red blood cells. The matrix of the organelle is separated from the surrounding cytoplasm by a trilaminar unit membrane and contains a variety of acid hydrolytic enzymes. Morphologically primary (recently formed from the Golgi-complex) are distinguished from secondary lysosomes. The latter type is formed after fusion of a vacuole with a primary lysosome and is ultrastructurally extremely heterogeneous due to the large variety of substrates (macro­ molecules ) incorporated in the matrix of the organelle. The acid hydrolases of lysosomes are divided into the following five groups: phosphatases, nucleases, polysaccharide- and glycosaminoglycans (GAG)-liydrolases, proteases and lipases.
Atmosferiese stikstofopname deur sojaboonkultivars in kombinasie met Bradyrhizobium japonicum-rasse
Authors: Botha A. D. P
Published: July 2013

A pot experiment was conducted, using three soyabean (Giycinc max (L.) Merrill) cultivars (Forrest, Prima and A5409) inoculated at planting, with no (0) and two Bradyrhizobium japonicum strains (WB1 and WB74). The objectives were to investigate the effect of cultivar-rhizobial strain combinations on biomass and N derived from the atmosphere (Ndfa) and to compare the atmospheric N uptake determined by the isolope technique, with the conventional method.
Normtoets, selfdoenopleiding, superkritiek en nog baie meer
Authors: De Villiers W. Van Z.
Published: July 2013

No abstract
Bees Spongiforme Enkefalopatie (BSE, Malkoeisiekte)
Authors: Bruckner G. K.
Published: July 2013

Mad Cow Disease or BSE (Bovine Spongiform Encephalopathy) became a household name internationally and also in South Africa. International hysteria resulted following reports of a possible link between a disease diagnosed in cattle in Britain and a variant of the disease diagnosed in humans after the presumed ingestion or contact with meat from infected cattle. The European Union instituted a ban on the importation of beef from the United Kingdom during March 1996 that had a severe effect on the beef industry in the UK and also resulted in a world wide consumer resistance against beef consumption.
Fisiologie en patofísiologie van selorganelle
Authors: Theron J. J. , Claasen N. , Panzer A.
Published: July 2013

Congenital absence of one or more lysosomal hydrolases results in accumulation of the relevant substrate and development of the so- called lysosomal storage diseases (LSD). Approximately 22 different types of LSD are known, which are divided into three groups according to the chemical nature of the specific substrate: sphingolipidoses, mucopolvsaccharridoses (defective hydrolysis of glycosaminoglycans) and glycoproteinoses. Other lysosomal clinical syndromes may result from defects in the biogenesis of the organelle or abnormalities in transport of metabolites across the lysosomal membrane.
Episode - en chronometriese tydperk-tabelle: implikasies vir provinsies soos die Kaapvaal
Authors: Winter H. De la R.
Published: July 2013

An accurate basin analysis and knowledge of its evolutionary development being a prerequisite framework for metallogenic model­ling, a procedure was developed for the Kaapvaal Province to maximise quantitative observational data and constrain assumptions and interpretations. Employing an episodes chart to display various events interactively and its conversion to a geochronometric chart as the geological model, the method was applied to existing stratigraphic studies.
Normtoets en ander terme: lesers se kommentaar
Authors: De Villiers W. Van Z.
Published: July 2013

No abstract
Die migrasie en bewaring van voëls in ’n Suider - Afrikaanse konteks
Authors: Bouwman H. , Evans S. W.
Published: July 2013

The migration of birds is a phenomenon that has been studied for more than two thousand years. Almost half of the extant bird species undertake migration, covering distances of a few tens of kilometres, up to a calculated 50 000 km per year, sometimes at heights exceeding 9 000 m, at very low temperatures, during the day or night. Some species fly actively and continuously for more than a 100 hours, whilst making efficient use of energy. A variety of strategies and physiological mechanisms are used to perform such feats, but many remain to be studied.
Die invloed van seisoene en streeksverskille op die samestelling van koeimelk in die RSA
Authors: Bester J. A. , De Lange D. J. , Van Rensburg L. , Smith M. F , De Beer W. H. J.
Published: July 2013

Canonical variate analysis was used to attain a better understanding of seasonal and regional factors which could contribute to variation in the milk nutrient content of milk in the RSA.
Die invloed van koolstofpartikels op die vernietiging van Mycobacterium bovis deur die alveolêre makrofaag
Authors: Office Editorial
Published: July 2013

Diagnostic bronchoscopies done on untreated indigenous African patients with tuberculosis revealed a majority of alveolar macrophages that were filled with carbon particles. The aim of this investigation was to determine whether intracellular carbon particles could inhibit the killing of Mycobacterium bovis (M. bovis) by the alveolar macrophage.
Die beheer van ’n elektriese kragnetwerk - vervormingskompensator - hibried deur ’n kunsmatige neurale netwerk
Authors: Shaw I. S. , Van Wyk J. D. , Pretorius R. W.
Published: July 2013

Increased interest in the elimination of distortion in electrical power networks has led to the development of various compensator topologies. The increasing cost of electrical energy necessitates the cost-effective operation of any of these topologies. This paper considers the development of an artificial neural network based controller, trained by means of the backpropagation method, that ensures the cost-effective operation of the hybrid compensator consisting of various converters and filters.
Seladhesie
Authors: Meij H. S.
Published: July 2013

Cell-to-cell adhesion and cell adhesion to the intercellular matrix materials underlie the way in which cells are organised in tissues. Cell-cell interaction through cell adhesion molecules (CAMs) is not only needed to maintain the structural and functional integrity of tissues, but dynamic changes in cell adhesion also participate in tissue growth, development and repair Adhesion mechanisms are furthermore intimately related to cell motility and cell migration, which are essential in the defence processes of the body.
Visparasiete - indikators vir metaalbesoedeling?
Authors: Avenant-Oldewage A.
Published: July 2013

No abstract
Tegnologie vir ’n geïntegreerde gedeeltelik serieresonante mutator
Authors: Brand J. M.
Published: July 2013

No abstract
Die ekologiese relevansie van chemiese stres op die "gesondheid” van die biologiese omgewing
Authors: Reinecke A. J.
Published: July 2013

The term “environmental health” is frequently and confusingly used to refer both to the “health" or optimal functioning of the natural environment or ecosystems and also to the quality of the environment for human health.
Hersiklering van soliede afval in die tekstiel - en klerebedryf in Suid-Afrika
Authors: Larney M.
Published: July 2013

The need for recycling of textile and apparel waste is motivated by the increased costs of landfills, the decreased availability of landfill space and the dwindling of our natural resources.
Die bourekenaar as waardebestuurder
Authors: Siglé H. M. , Klopper C. H. , Visser R. N.
Published: July 2013

The technique of value management could enable the quantity surveyor to offer more comprehensive and efficient economic and financial management services.
Navorsingswerk en spesialiteitsgebiede in die Departement Elektriese en Elektroniese Ingenieurswese aan die Universiteit van Pretoria
Authors: Craig I. K.
Published: July 2013

This article gives an overview of the research performed in the Department of Electrical and Electronic Engineering at the University of Pretoria.
Outomatisasie: konsepte en verskillende beskouings
Authors: Gouws J.
Published: July 2013

Different people have different views on automation normally somewhere on a spectrum between miracle and evil.
Veertig stappe in die saamstel van ’n vakwoordeboek
Authors: Alberts M.
Published: July 2013

No abstract
Die invloed van N-bemesting en waterstremming op die droëmateriaalopbrengs en blaaroppervlakeienskappe van Panicum maximum cv. Gatton
Authors: Pieterse P. A.
Published: July 2013

The investigation was conducted in the form of a pot trial in a controlled environment.
Newel-pseudotopologiese vektorruimtes
Authors: Muller M. A.
Published: July 2013

Pseudo-topological spaces (i.e. limit spaces) were defined by Fischer in 1959. In this paper the theory of fuzzy pseudo-topological spaces is applied to vector spaces. We introduce the concept of boundedness in fuzzy pseudo-topological vector spaces.
Partisies van versamelings in metriese en normeerde ruimtes geïnduseer deur konsentriese sfere en ewewydige hipervlakke
Authors: Swanepoel K. J.
Published: July 2013

A covering of a set A in a metric space (M,d) by finitely many distinct concentric spheres induces a partition on A.
Spindigtheidsgolfgedrag van Cr-Si- en Cr-Ga-allooi-enkelkristalle
Authors: Prinsloo A. R. E.
Published: July 2013

The spin-density-wave (SDW) effects in Cr-Si and Cr-Ga alloy single crystals were investigated by means of thermal expansion, electrical resistivity and ultrasonic wave velocity measurements. The complete temperature-concentration and temperature-pressure magnetic phase diagrams of Cr-Ga were constructed.
Skistosomose, ’n onderskatte en verwaarloosde probleem, selfs in die endemiese gebiede van die Republiek van Suid-Afrika
Authors: Wolmarans C. T.
Published: July 2013

It is estimated that between three and four million people in the RSA are infected with parasites that cause human schistosomiasis. These estimates are based mainly on the incidence of schistosomiasis in school children in the schistosomiasis endemic areas of the country.
Die frekwensie van laat voltooiing op bouprojekte in die Republiek van Suid-Afrika
Authors: Klopper C. H. , Brϋmmer D. G.
Published: July 2013

An investigation was launched to determine whether building projects in the Republic of South Africa are generally completed timeously and, if that is not the case, what the potential impact of late completion holds for the parties to the contract.
Gebruik van ’n ekspertstelsel vir die identifikasie van Lithops
Authors: Gouws J.
Published: July 2013

It is often very difficult for non-botanists to distinguish between and identify closely related plants. This article provides an overview of the use of a computer-based expert system for this purpose, specifically applied to Lithops - a group of succulents that presents numerous interspecific resemblances as well as intra-specific differences.
Perspektief vir genestelde klimaatmodellering oor suidelike Afrika
Authors: Engelbrecht F. A.
Published: July 2013

The climate of southern Africa is fundamentally affected by mesoscale circulation patterns that are not adequately simulated by global atmospheric general circulation models (AGCMs). The technique of nested climate modelling (NCM) utilises high-resolution limited area models (LAMs) to obtain climate simulations of the mesoscale from essentially synoptical scale AGCM results.
Die bepaling van intrasellulere vry kalsium in die neutrofiel met die fluoressente kalsiumindikators, fura-2 en fura-PE3
Authors: Koorts A. M. , Viljoen M. , Kruger M. C.
Published: July 2013

A large number of fluorescent calcium indicators are available for the determination of intracellular free calcium concentrations. The best known of these is fura-2. However, the employment of fura-2, amongst others, for the determination of intracellular free calcium is not problem-free.
Die histologie en ultrastruktuur van die hepatopankreas van die bloukurper Oreochromis mossambicus
Authors: Nel M. M. , Swanepoel J. H. , Geyer H. J.
Published: July 2013

The histology and ultrastructure of the hepatopancreas of the Mozambique tilapia O. mossambicus are described. The liver is surrounded by a thin connective tissue capsule. The hepatocyte arrangement shows as lobules, with the hepatocyte cords that radiate and anastomose from a central vein. Borders of individual liver lobules do not show clearly, as do the few triads found in the liver of O. mossambicus. Each hepatocyte contains a single round nucleus with a prominent nucleolus. The rough endoplasmic reticulum appears in two or more rows around the nuclei and in close proximity to the plastnalemma of the hepatocytes. The remaining cytoplasmic organelles are scattered throughout the hepatocyte cytoplasm. The exocrine pancreas cells are centred around the portal veins. The nuclei of these cells are spherical and hasally situated in the cubiform to cylindriform cells. Well developed rough endoplasmic reticula - vesicular, tubular and circular in appearance - as well as secretory granules, apically situated in the cells, are present.
Verklarende lys van plantpatologiese terme
Authors: Gorter G. J. M. A
Published: July 2013

Die vinnige ontwikkeling van plantpatologie as wetenskap het aanleiding gegee tot die gebruik van ’n reeks terme wat nie altyd op die korrekte wyse aangewend word nie. Om hierdie probleem te oorkom het komitees in die V.S. A. en in Engeland en Nederland verklarende lyste opgestel om die betekenis van plantsiektekundige terme soveel moontlik te standaardiseer.
Absoluut sommerende vermenigvuldigers en die Dvoretzky-Rogers - stelling
Authors: Fourie J. H.
Published: July 2013

The space M(E) of absolutely summing multipliers of a Banach space E is considered. For some special types of Banach spaces E it turns out that M (E) can he characterized as an lᴾ-space of absolutely summable scalar sequences. We provide some important examples of Banach spaces for which the lᴾ-characterizations of M(E) hold true. The well known Dvoretzky-Rogers theorem plays an important role in these characterizations. An “alternative" version of the last men­tioned theorem is discussed.
Die kardiorespiratoriese effek van detomidien in die primaat (Papio ursinus)
Authors: Bosman H.
Published: July 2013

Detomidine is a novel imidazole derivative with a high affinity for a₂-adrenoceptors. The cardiorespiratory effects of this drug were evaluated in the primate (Papio ursinus) under ketamine anaesthesia. The release of noradrenalin is modulated by a₂-adrenoceptors, and this resulted in a longer duration of anaesthesia when ketamine was combined with detomidine in comparison with ketamine alone. Detomidine caused a marked bradycardia, which was not reflex induced, but probably the result of a decreased sympathetic outflow. Various conducting disturbances were observed in the electrocardiogram, also probably the result of decreased sympathetic tone to the heart. The effect of detomidine on the respiratory system was minimal. Detomidine proved to be a useful drug to use in combination with ketamine for the induction of anaesthesia in primates. It should, however, not be used during cardiovascular studies.
Regionale mikrotermometriese databasis vir die Proterosoïese gesteentes van die Noordwes-Kaap
Authors: Schoch A. E. , Klatt E. , Elsmere D.
Published: July 2013

First results from fluid inclusion studies of the Proterozoic rocks of the Northwestern Cape, indicate unique characteristics for the fugitive constituents connected to the most important late to post-tectonic geological processes in the Namaqua mobile belt. A broad fluid consanguinity is present in different structural terranes, in spite of possibly contrasting early PT histories.
Katalogus van vakwoordeboeke
Authors: Office Editorial
Published: July 2013

Die onderstaande lys vakwoordeboeke wat vir natuurwetenskaplikes van belang sal wees, is ’n uittreksel uit die jongste Katalogus van vakwoordeboeke. Die katalogus wat deur die Nasionale Vakterminologiediens van die Departement van Nasionale Opvoeding uitgegee word, bevat ’n volledige lys van vakwoordeboeke (in die handel beskikbaar of uit druk), sowel as die pryse.
Generation of soil drainage equations from an artificial neural network-analysis approach
Authors: Zhao Zhengyong , MacLean David A. , Bourque Charles P.-A. , Swift D. Edwin , Meng Fan-Rui
Published: July 2013

Zhao, Z., MacLean, D. A., Bourque, C. P.-A., Swift, D. E. and Meng, F.-R. 2013. Generation of soil drainage equations from an artificial neural network-analysis approach. Can. J. Soil Sci. 93: 329–342. Soil properties, especially soil drainage, are known to be related to topo-hydrologic variables derived from digital elevation models (DEM), such as vertical slope position, slope steepness, sediment delivery ratio, and topographic wetness index. Such relationships typically are strongly non-linear and thus difficult to define with conventional statistical methods. In this study, we used artificial neural network (ANN) models to establish relationships between soil drainage classes and DEM-generated topo-hydrologic variables and subsequently formulated the relationships to generate soil drainage equations for soil mapping. A high-resolution field soil map of the Black Brook Watershed in northwest New Brunswick, Canada, was used to calibrate/validate the ANN models, and the obtained equations. Independent data from an experimental farm, about 180 km away, were also used for validation. Results indicated that vertical slope position was the best predictor of soil drainage classes (r=0.55), followed by slope steepness (r=0.44), sediment delivery ratio (r=0.39), and topographic wetness index (r=0.38). The obtained soil drainage equations fitted well to the ANN model predictions (r2=0.78–0.99; root mean squared error=0.39–4.55). Analyses indicated that soil drainage equations clearly reflected the actual relationships between soil drainage classes and DEM-generated topo-hydrologic variables, and have the potential to minimize bias originated from over-training the ANN models when applied outside the area of calibration, especially when the ranges of input variables were outside of the range of calibration data.
Rapid turnover of organic acids in a Dystric Brunisol under a spruce–lichen forest in northern Saskatchewan, Canada
Authors: Fujii Kazumichi , Morioka Kokoro , Hangs Ryan , Funakawa Shinya , Kosaki Takashi , Anderson Darwin W.
Published: July 2013

Fujii, K., Morioka, K., Hangs, R., Funakawa, S., Kosaki, and Anderson, D. W. 2013. Rapid turnover of organic acids in a Dystric Brunisol under a spruce–lichen forest in northern Saskatchewan, Canada. Can. J. Soil Sci. 93: 295–304. Organic acids released by lichen play an important role in mineral weathering and podzolization in the Boreal–Tundra transition zone of Canada; however, importance of low-molecular-weight organic acids in the soil carbon (C) cycle in the black spruce–lichen forests remains unclear. We examined soil solution composition and mineralization kinetics of 14C-radiolabelled oxalate and citrate to quantify the C fluxes from organic acid mineralization in a Dystric Brunisol under a spruce–lichen forest in northern Saskatchewan. Oxalate concentration in soil solution was greatest in the lichen layer, while the high levels of citrate were observed in the lichen and organic (O) layers to the Ae horizon with the lowest sorption capacity. Oxalate and citrate were rapidly mineralized within the lichen and O layers and had short mean residence times (0.5 to 2.7 h). Substantial C fluxes due to citrate mineralization were observed both within the lichen and O layers, but oxalate mineralization led to C flux in the lichen layer only. The contribution of citrate and oxalate to microbial respiration was large (up to 57%) in the surface soil layers. Citrate was the dominant substrate for microbial respiration of the surface soil; however, it appears that oxalate could also be an important microbial substrate within the lichen layer, at least in summer months. We conclude that the exudation of low-molecular-weight organic acids by lichenous fungi, followed by their rapid mineralization, could play an important role in the C cycles of the sandy soils under spruce–lichen forest.