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'n Nuwe stratigrafiese indeling van die Ventersdorp-sisteem
(University of Pretoria, 1953) Matthysen, Johannes Louis
Mitochondrial DNA variability and geographic population structure in Pronolagus rupestris and P. randensis (Mammalia: Lagomorpha)
(University of Pretoria, 1993) Robinson, T.J.; Matthee, Conrad Adolf
Phylogeographic mitochondrial DNA (mtDNA) population structure was determined for Pronolagus rupestris and P. randensis, two species of red rock rabbit occurring in South Africa. The study revealed that P. randensis mtDNA patterns reflect phylogenetic continuity with partial spatial separation between populations, although this should be viewed with caution given the limited distributional range covered by the investigation. Eleven composite haplotypes were found in the 27 P. randensis specimens sampled. The relatively low sequence diversity of 0.74% (±0.21 %) was interpreted as reflecting limited intraspecific variation within the taxon, and is thought to be indicative of fairly recent range expansion. In the eastern Transvaal (Blyderivierspoort Nature Reserve) P. rupestris and P. randensis are found approximately 15 kilometers apart. No distributional overlap was detected even though extensive geographic sampling was undertaken in the presumed contact zone, a pattern which is thought to reflect competitive exclusion. An interesting observation was that previously documented mtDNA phylogeographic patterns recorded in the rock hyrax, Procavia capensis, coincide with the observed zone of contact between P. rupestris and P. randensis. The rock hyrax is a mammalian species of comparable body size which occurs sympatrically with Prono/agus and is similarly limited to outcrops of rock in the form of krantzes, rocky koppies or rocky hillsides. It is argued that similar vicariant events may have been implicated in shaping the evolutionary processes in these independent lineages. This hypothesis may hold for not only the taxa surveyed in this investigation, but for other mammal species with similar habitat and dispersal capabilities. The 55 P. rupestris specimens sampled showed pronounced intraspecific genetic structure with two well defined, virtually geographically contiguous clades; one situated in the north western Cape Province while the other follows the Great Escarpment extending along the southern and eastern seaboard of South Africa. These mitochondrially distinct clades were separated by 7.94% (±1 .40%) sequence divergence, a relatively high value which is thought to reflect inaccuracies in the currently accepted taxonomy of P. rupestris. The phylogeographic profiles of the two P. rupestris clades differ markedly from each other. The north western clades' matrilines are separated by few mutational steps between isolated populations, while those of the south eastern clade are characterized by deep divisions. Disruptive extrinsic factors between the two assemblages could not be identified and the clade specificity of the mtDNA haplotypes is thought to be due to competitive habitat exclusion and possibly the inability of the representatives of the two clades to interbreed.
An investigation of the pyroxenite marker and the associated rocks in the main zone of the eastern bushveld complex
(University of Pretoria, 1977) Snyman, C.P.; Marais, Constance Lougene
Optical investigation of the orthopyroxenes also revealed a compositional break in the differentiation sequence at the height of the Pyroxenite Marker. A reversal in the trend of iron enrichment is recorded at all four of the localities examined. At the same stratigraphic height, the orthopyroxene is poorer in iron in the north than in the south. The compositional trends of the plagioclase from the four localities resemble those of the orthopyroxene. Separated pyroxenes were analysed chemically by means of the energy dispersive analyses of x-rays (EDAX) method. Whole-rock samples were also analysed by means of EDAX. Quantitative trace-element analyses on the whole rock and on separated cumulus minerals were carried out by atomic absorption spectrometry (AAS) for the element’s barium, chromium, cobalt, copper, nickel, strontium and zinc, whereas ion exchange chromatography was used for titanium and vanadium. Variation in the chromium and nickel contents with fractionation was shown to conform with that predicted by crystal field theory. At the Pyroxenite Marker the reversal or the normal fractionation trend is borne out by the partitioning of chromium. The reversed fractionation trend, as well as the partitioning of the trace elements at the level of the Pyroxenite Marker, are inconsistent with the process of continuous fractionation within the magma chamber. The gradual addition of undifferentiated magma during crystallization of the upper part of Subzone B, followed by a larger, sudden influx of magma at the level of the Pyroxenite Marker, were probably responsible for the observed relationships.
Isolation and structure of the metabolites from diplodia maydis
(University of Pretoria, 1990) Vleggaar, Robert; Modro, T.A.; Marais, Stephanus Francois
Investigation of toxic extracts from cultures of the fungus Diplodia maydis (Berk.) Sacc. [ synonyms D. zeae (Schw.) Lev. and Stenocarpella maydis (Berk.)] led to the isolation of diplodiatoxin, a known metabolite, as well as four new metabolites viz. 3-hydroxydiplodiatoxin stenocarpin, steno-carpin 6-0-(4-0-methyl-orsellinate) and carpellin. The structure elucidation of the new compounds is based on a detailed analysis of their highfield 1H and 13 c nuclear magnetic resonance spectra. The relative configurations were deduced from the magnitude of the proton-proton coupling constants and the results obtained from homonuclear proton-proton nuclear Overhauser effect (n.O.e.) studies. The absolute configuration of stenocarpin 6 - 0- ( 4 - 0-methylorsellina te) was determined by the 'partial resolution' method of Horeau. The biosynthetic pathway leading to d±plodiatoxin was investigated by incorporation studies with 13 c-, 2 H and 18 0-labelled precursors.
The geology of the Bushveld complex on the Sekhukhune Plateau, Eastern Transvaal
(University of Pretoria, 1976) Coertze, F.J.; Snyman, C.P.; Von Gruenewaldt, G. (Gerhard), 1942-; Marlow Alan Gerald
This study comprises a general geological investigation of the rocks from an area 1 200 square km in size, situated about 50 km'north-east of Marble Hall. The area lies upon the Sekhukhune Plateau and is dominated by acid rocks of the Bushveld Complex. The oldest rocks in the area include hornfels and quartzite of the Pretoria Group which are present in the form of xenoliths in, the rocks of the Bushveld Complex, and also as part of the f uptiomed floor of the Complex in the Malope area. The quartzite which occurs in the form of xenoliths has been locally transformed to a pseudogranophyre by a process of feldspathtzation. Three suites of Bushveld rocks are present within the area investigated, namely the Rustenburg Layered Suite, the Rashoop Granophyre Suite and the Lebowa Granite Suite. The first out crop at the base of the Sekhukhune Escarpment which forms the eastern boundary to the area. They have also been discovered on the plateau around Malope to the south-east of the 0lifants River, where they appear to overlie the updomed floor of the Bushveld Complex. The rocks of the layered sequence exposed east of the Sekhukhune Escarpment belong to the Upper Zone, whilst the majority of those around Malope are typical of the Critical Zone, although rocks which typify the Upper Zone are also present. The latter seem to transgressively overlie the rocks of the Critical Zone. The Rashoop Granophyre Suite consists of granophyre and a fine-grained granophyric granite. These rocks are separated from the basic rocks of the layered sequence below by a thin layer of leptite which is considered to be metamorphosed Rooiberg felsite. The Lebowa Granite Suite consists of an older Nebo Granite and a younger Makhutso Granite. Four facies of the Nebo Granite have been recognized, viz. main, contact, granophyric and aplitic facies, and their textural, mineralogical and chemical differences are discussed. The Makhutso Granite also consists of four facies, namely the main facies, the contact facies and the aplitic facies, as well as the Koornkopje granite which is considered to be a variety of the Makhutso Granite. The Makhutso Granite which was previously only known to exist in the Dennilton area, has been found at seventeen separate localities on the Sekhukhune Plateau, and the intrusive relation= ships with the Nebo Granite are described. The Makhutso Granite differs from the Nebo Granite in its higher biotite content and its higher anorthite content of the plagioclase, and also in its trace element composition. It also differs from the main facies of the Nebo Granite in its abundance of zoned plagioclase phenocrysts. The Koornkopje granite differs from the main fadies of the Makhutso Granite in its persistent fine-grained nature, and in its lower biotite content and the lower anorthite content of the plagioclase.
Inductively-coupled plasma optical emission spectroscopic determination of trace impurities in zirconium oxide-powder
(University of Pretoria, 1996) Rademeyer, C.J.; Mandiwana, Khakhathi Leonard
Because of their extraordinary properties, advanced ceramic materials, e.g. ZrO2 , offer new possibilities to science and technology in such important areas as microelectronics, high temperature applications in reactors and motors and also medicine. Due to these, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) has been used for the determination of the most significant impurities (Cr, Fe, U and Th) in high-purity refractory powders of ZrO2 without matrix(Zr) separation. ZrO2 powders were decomposed by fusion with a 10-fold excess of NH4HSO4 and subsequent dissolution of the melt in either HNO3 or HF. ZrO2 samples were fused and dissolved in both HNO3 and HF. The results in the two acids were evaluated with respect to detection limits, blank values, interferences, accuracy and precision. The solution was then directly analyzed by ICP-OES, which was optimized for each independent analytical line. The calibration was performed by standard addition and matrix matching was not necessary. The detection limits in Zr02 in the two acids varied from 1.73μg/l(Fe) to 50μg/l(U). The standard deviations obtained were 1-10 % depending on the element and its concentration in the sample. There was no significant difference on the interferences and accuracy obtained in the two acids. The precision of the results in HN03 was poor as the results were not reproducible day after day due to precipitation. Except for Fe and Cr, the blank values encountered in HF were lower than in HNO3, but generally they were below the detection limits of the metals investigated. It was concluded that HF is the best acid to dissolve the fused ZrO2 powders as it results in stable sample solution. It was further investigated whether the presence of mineral acids, viz. HCl, HNO3 and H2SO4, at 0-50% (v/v) concentration has significant influence on the emission signal of Fe as one of the impurities determined in ZrO2. A number of solutions containing 1, 5, 10, 20 and 50μg/ml of Fe in acid concentrations of Oto 50% (v/v) were used. It has been found that HNO3 and HCl enhances the emission signal at low levels of Fe whereas H2SO4 depresses the emission signal of Fe at all levels. These effects are neither caused by the change in aerosol flow-rate nor the amount of aerosol reaching the plasma.
Fluorinated ferroelectric liquid crystals : synthesis, properties and fluorine-19 nmr
(University of Pretoria, 1993) Wessels, P.L.; Loubser, Christa
A series of new laterally fluorinated liquid crystals containing a single chiral centre on the terminal chain, was synthesised. All the compounds, with a single exception, exhibit a ferroelectric smectic C* phase. Their liquid crystalline properties were investigated using optical polarising microscopy and differential scanning calorimetry, while ferroelectric properties were studied electro-optically. The number/ position of the lateral fluoro-substituents greatly influence the incidence and range of the liquid crystalline phases. The 2,3 - difluorophenyl unit stabilises the cholesteric and smectic C* phases, but suppresses the formation of the smectic A phase. The 2' ,3 - difluorobiphenyl unit, in contrast, discourages the formation of helical phases. A helix inversion occurs in the cholesteric phase of (S)-4-n-octyloxy-2, 3-difluorobiphenyl-4' -yl 3-fluoro-4-(2-fluorooctanoyloxy) benzoate. Due to certain structural features, the phenomenon could not be explained in terms of the conventional model. Instead, competing conformer species created through interaction between fluoro-substituents on the core and at the chiral centre, are suggested. The influence of the lateral fluoro-substituents on the ferroelectric properties was investigated. Two of the compounds exhibit unusual tilt angle behaviour - the tilt angle decreases with decreasing temperature. A helix inversion takes place in the smectic C* phase of (S)-4-n-octyloxy-2' ,3- difluorobiphenyl-4' -yl 2-fluoro-4-(2-fluorooctanoyloxy)benzoate and is thought to be due to the presence of the 2',3-difluorobiphenyl unit. The orientational ordering of several of the liquid crystals was investigated using 19F nmr. A new technique was developed for this purpose and used to determine the order parameter as a function of temperature of (S)-4-n-octyloxy-2,3-difluorobiphenyl-4' -yl 4-(2-chloro-4-methylpentanoyloxy) benzoate from the dipolar coupling constant, DFF. The question of possible coupling between dipoles on the core and the chiral centre was addressed. For the first time it is experimentally shown that such an interaction does exist for two fluorosubstituents {1 9F - 19F dipolar coupling). Conformational analysis revealed a transverse electrostatic gradient. The conformation of the 2' ,3-difluorobiphenyl unit was investigated by using 19F nmr in conjunction with crystal structure data. It appears that the net dipole moment as well as the effective size of this unit play an important role.
Application of the enzyme-linked immunosorbent assay in the quality control of legume inoculants
(University of Pretoria, 1986) Steyn, P.L.; Strijdom, B.W.; Lochner, Hester Helena
Samples of each batch of legume inoculant manufactured in South-Africa, are tested by the Plant Protection Research Institute for the number of viable Rhizobium and Bradyrhizobium cells per gram peat, strain identity and possible contamination before marketing. Possible replacement of plate counts and serological identification tests by a single indirect or DAS ELISA test, to assess the quality of legume inoculants, was investigated. Six of the nine strains of rhizobia investigated, are currently used for inoculant production. Somatic agglutination titres of most antisera, measured by tube agglutination not always reactivity in tests, lead ELISA were high. Use of these antisera did to effective ELISA systems, as low were obtained with some antisera with high somatic agglutination titres. Due to low reactivity of the four Rhizobium strains in ELISA, only Bradyrhizobium strains were used. Optimal concentrations of immunoreactants differed for each antigen-antibody combination tested in ELISA. Consequently, optimal ELISA concentrations had to be determined for each new batch of immunoglobulin, antigen and conjugate prepared. The plate count, as well as the indirect ELISA test, were conducted on inoculant suspensions containing each of two Bradyrhizobium strains. The indirect ELISA tests were negative, but centrifuged suspensions gave rise to weak, but inconsistant indirect ELISA reactions. Colour gradients were obtained in DAS ELISA with higher dilutions of inoculant suspension, containing each of three Bradyrhizobium strains. In the lowest dilutions tested, inhibition of the DAS ELISA reaction occurred. By allowing peat particles in the first dilution to settle for 3 h, the inhibition effect was markedly reduced. The lowest concentration of rhizobia significantly detected above the peat control differed for the three Bradyrhizobium strains and ranged from 6, 0 X 10 to 4,0 X 10 colony forming units per gram (cfu.g ) peat. Reproducible results were obtained with suspensions of each laboratory produced inoculant tested by the plate count technique and DAS ELISA. Statistical analysis indicated that the relationship between A 405 values and the number of (cfu.g) peat differed among packets tested.
Die reaksie tussen plasma gedissosieerde sirkoon en hidrofluoorsuur
(University of Pretoria, 1993) Heyns, A.M.; Nel, Johannes T.; Lubbe, Solomon Johannes
Zircon is dissociated in a direct arc plasma to a chemically reactive form called Plasma Dissociated Zircon, which is dissolved in HF. Distillation of the mother liquor is controlled on the basis of the prevention of the formation of possibly Zr2F 12 polymeric groups. The degree of evaporation affects the purity of the zirconium fluoride crystals that are formed. These crystals are used in preparing fluorozirconate chemicals such as K 2ZrF 6 and (NH4 ) 2ZrF 6 • Further purifying can be done by recrystallisation in a water solution. Other zirconium chemicals can be prepared by breaking the stable zirconium-fluoride bond by precipitating and suspending the crystals in alkaline solutions. Fluoride-free zirconium chemicals can then be prepared by dissolving the precipitate in the corresponding mineral acid. High purity zirconium chemicals like K2ZrF 6, (NH4) 2ZrF 6, H2Zr0(S04) 2 .3H20 and Zr0Cl2.8H20 can be prepared in this way. During the fluoride recovery process, high value silica, that can be used as a filler in the rubber industry is prepared from H2SiF 6 solutions. Fluoride recovery is done by preparing aluminium fluoride from ammonium fluoride solutions. The properties of the aluminium fluoride are determined by the phase of the alumina used as starting material.
The sulphides in the layered sequence of the Bushveld igneous complex
(University of Pretoria, 1968) Willemse, J.; Visser, D.J.L.; Nel, H.J.; Liebenberg, Leon
The Bushveld Complex, which is the largest mafic and ultramafic complex of its kind in the world does not contain copper and nickeliferous ores, with the exception of the Merensky Reef and the sulphide pegmatoids of the Western Transvaal. Ores belonging to the latter type have almost been worked out. However, minor quantities of disseminated sulphides are found throughout the whole sequence of layered rocks of the Main Plutonic Phase, the Hypabyssal Phase, the Late Plutonic Phase and the Volcanic Phase. The investigation reported here is restricted to the rocks of the Main Plutonic Phase and the Late Hypabyssal Phase. From field observations and bore-hole investigations it is clear that cross-cutting relationships exist between the rocks of the Basal Zone and the sediments of the Pretoria Series in the Western Transvaal. Huge blocks of metasediment were lifted from the floor to form inclusions in the plutonic rocks. The bore-hole results reveal that in the deepest parts of the basin the floor of the Complex has not yet been explored, particularly in the region west of the Pilanesberg. It was found that disseminated sulphide seldom exceeds 2 per cent by volume of the rock. Abnormal concentrations of sulphide are known only from certain parts of the Basal Zone, from sulphide-bearing pegmatoids, from the Merensky Reef and from the mineralized anorthosites below the Main and the Uppermost Magnetitite Seams. Generally the sulphides constitute approximately O. 05 per cent by volume of the layered rocks. The sulphides are the three modifications of pyrrhotite (troilite, hexagonal and monoclinic pyrrhotite, distinguished from one another by X-ray diffraction and etching methods), pentlandite, chalcopyrite, cubanite, pyrite, mackinawite, zinc-blende, bornite, galena(?), safflorite-loellingite, linaeite, millerite, chalcopyrrhotite( ?) and the nickel-arsenic-bearing minerals, gersdorffite, maucherite, niccolite, rammelsbergite( ?) and ullmannite( ?) . The secondary minerals are valleriite, melnikowite-pyrite, bravoite and covellite. Not much attention was paid to the minerals containing the platinum group metals, although a few have been identified; sperrylite, braggite, cooperite and michenerite( ?) . A differentiation trend was established in the mineralogical composition of the sulphide phase. From the base to the top of the Main Plutonic Phase there is a decrease in pentlandite and an increase in chalcopyrite. In the Upper Zone chalcopyrite decreases with an increase of pyrrhotite. The sulphides in any pegmatoid, which is considered to be a differentiation product of the host-rock, are also enriched in copper sulphide and pyrrhotite in comparison with the adjoining country-rock. In addition to this differentiation trend, the sulphide of the mafic rock, which contains little sulphide (0. 1 %), consists mainly of chalcopyrite. Mackinawite in pentlandite appears in these rocks below the Merensky Reef, in association with metal-rich sulphides such as troilite and cubanite. Galena (?) is present only in higher horizons of the layered sequence. All the sulphides involved in the Fe-Ni-S system exsolved from a solid solution of the monosulphide (FeNi)1 –x S, above 863 C.
A taxonomic revision of Lachnaea L. (Thymelaeaceae)
(University of Pretoria, 2000) Van Wyk, Abraham Erasmus (Braam); Beyers, Josephine Bertha Pauline
Lachnaea L., a genus endemic to the Cape Floristic Region, occurs almost exclusively in fynbos vegetation. In this revision a brief taxonomic history of Lachnaea is presented. Palynology and chromosome numbers were found to be taxonomically insignificant at specific level. Evidence from macromorphology, leaf anatomy, ecology and geographical distribution is used as the basis for species delimitation. Circumscription of the genus is extended to include the species of Cryptadenia Meisn. Previously proposed sections in Lachnaea are not upheld. Four species and all varieties are reduced to synonymy; 12 species and two subspecies are newly described and one new name is proposed. Forty species and two subspecies are now recognised. Geographically most species are concentrated in the 3319 (Worcester) grid. A phylogenetic hypothesis of Lachnaea resulting from two cladistic analyses is presented. The results of the analyses show that Lachnaea is monophyletic and that the sections are paraphyletic. The two analyses produced mixed resolution regarding the solitary-flowered species and gave conflicting results with regard to the evolutionary pathway of certain characters. Allopatric speciation appears to have been the dominant process in Lachnaea. Additional variables that may have governed diversification are altitudinal difference, allochory and post-fire regeneration strategies. The taxonomic treatment includes keys to the species and subspecies, detailed descriptions with notes on nomenclature, diagnostic features, relationships, distribution, ecology and conservation status. Line drawings and a distribution map are provided for each species.
Die Eienskappe en korrelasie van steenkoollae in die Witbank - Bethal - Breyten-gebied
(University of Pretoria, 1985) Snyman, C.P.; Le Roux, Jacob Philippus
It has long been noticed that there appears to be stratigraphic equivalents for the major coal seams in the Witbank, Highveld and Eastern Transvaal coal fields. In order to correlate these seams, readily available coal properties (heat value, ash content, volatile content and moisture content) and other physical properties (elevation and thickness) were evaluated. It was found that no single property or even combinations of these in the form of variation diagrams could provide sufficient resolution between the seams. Discriminant analysis was used to form linear combinations (discriminant functions) of the properties which statistically provide the best possible resolution between the groups. It was thus established to a high degree of certainty that coal seams can be correlated between boreholes and even adjacent coal fields using this method. Discriminant functions were calculated for areas by which new cases can be correlated. Lateral variation in the coal properties was studied by means of geostatistical methods and it was found that the average range of influence was around 15 km. Anomalous values resulting from data errors, devolatilisation or oxidation of coal could be identified by means of a normal probability graph and the Seyler oiagram as adopted for South African coals. (Snyman et. al., 1983) Two dolerite factors, reflecting the metamorphic effect of the magma on the coal were tested but found useless for the identification of devolatilised coal in this area.
Die Rand van die bosveldstollingskompleks, suid van Burgersfort, insluitende sekere perikotiet-liggame en die gemetamorfoseerde serie Pretoria
(University of Pretoria, 1964) Willemse, J.; Liebenberg, Leon
Die horingfels en die kwartsiet van die boonste gedeelte van die Etage Magaliesberg suid van Burgersfort in Oos- Transvaal het baie aandag geniet in hierdie ondersoek. Die gesteentes was veral aan kontakmetamorfose onderworpe gewees, alhoewel die effekte van regionale metamorfe toestande ook op die kontak van 'n peridotietliggaam op Glen Ora herken kon word. Die volgende tipes horingfelse is onderskei: Chiastolietchloriet-, andalusietcordieriet-, granaatcordieriet-, s\illimanietcordieriet-, muskovietcordieriet- en kalksilikaathoringfels. In die lig van vorige navorsingswerk is die stabiliteitsverhouding en gevolglik die invloed wat chemiese samestelling en die graad van metamorfose op die verskyning van sekere kritieke minerale het, krities in oenskou geneem. Daar is gevind dat die vormingstoestande van andalusiet in die plek van chiastoliet, en sillimaniet in die plek van andalusiet, suiwer termaal van aard is. Granaat in granaatcordieriethoringfels verskyn by 'n mg-waarde groter as 0. 43. Die vermeerdering in cordieriet- en afname in andalusiet hoogop in die stratigrafiese opeenvolging word toegeskryf aan 'n toename in magnesium en 'n afname in aluminium. Die verskyning van mikroklien op hoer horisonte word ook deur die verandering in chemiese samestelling, naamlik 'n toename in Kalium, in plaas van verhoging in die graad van metamorfose, verklaar. In die metamorfe gesteentes is, op grond van tipiese mineraalassosiasies, die volgende metamorfe fasies herken: Albietepidoothoringfels-, horingblendehoringfels-, pirokseenhoringfels-, sanidiniet- en die sillimanietalmandietortoklaassubfasies van die almandietamfibolietfasies. Die kristallisasietoestande van peridotiet van die gebied is gevind dieselfde te wees as die van 'n tipiese harzburgiet met 'n poikilitiese tekstuur, naamlik kumulusolivien wat gemodifiseer is deur die interkumulusvloeistof. Ortopirokseen en plagioklaas het uitgekristalliseer as interkumulusmateriaal. Aangesien peridotietplutone in die metasedimente aanwesig is, is afgelei dat 'n peridotietmagma as sodanig bestaan het. Omdat nie genoegsame geologiese getuienis ingewin kon word oor die struk turele vorm van die peridotietliggame en die vloerkontak nie, is 'n gravimetriesE opname onderneem. 'n Transgressiewe verhouding van die Bosveldkompleks tot die omgewende sedimentere gesteentes kon bewys word. Volgens gravimetriesE en geologiese getuienis breek die ultramafiese gesteentes definitief deur die Magaliesbergkwartsiet.
'n Idiografiese beeld van standerdsesleerlinge met wiskunde-angs : 'n ortopedagogiese perspektief
(University of Pretoria, 1992) Viljoen, J.; Kruger, Jerome
Mathematics anxiety is a well-known phenomenon causing concern in both schools and the work place. The aim of this study is to investigate the occurrence of mathematics anxiety in standard 6 pupils. The research comprises a literature study with special attention being given to definitions of mathematics anxiety, criteria for the identification of mathematics anxiety, instruments for determining mathematics anxiety and a review of theories about mathematics anxiety. Interviews are conducted with selected pupils. Cumulative performance data documents, statistical analysis as well as a historical review of mathematics anxiety also form part of the research. Standard 6 pup i 1 s with mathematics anxiety are i dent i fi ed by means of a questionnaire. The mathematics anxiety of selected pupils are then studied by idiographic means. The study is concluded with an interpretation of the findings on mathematics anxiety and a number of recommendations are made.
Die invloed van gesimuleerde beweiding op die produksie van enkele efemeerplantspesies van Namakwaland
(University of Pretoria, 1997) Van Rooyen, M.W. (Margaretha W.), 1950-; Theron, G.K.; Kruger, Margaretha
The effect of various simulated grazing and water stress treatments were studied in three winter ephemeral species, namely Dimorphotheca sinuata, Grielum humifusum and Osteospermum hyoseroides by means of pot trials. The intensity of water stress, the intensity and frequency of grazing, as well as the phenophase of the plant, determined the reaction of plants to grazing. Grazing had a large effect on the production of the plants of all three species. Dimorphotheca sinuata and Osteospermum hyoseroides are strict ephemeral species and reacted similarly to grazing, while the reaction of Grielum humifusum, a facultative perennial species, differed considerably from the above-mentioned species. Grazing, in general, led to a decrease in the total biomass of D. sinuata and 0. Hyoseroides plants. High intensity grazing of mature plants led to a decrease in plant production. Frequent grazing of leaves, stems and reproductive organs led to delayed phenological development of plants. Light grazing before and at the time of bud formation, as well as high intensity grazing before bud formation, had the least disadvantage for D. sinuata and 0. hyoseroides. Weekly or continuous grazing on the other hand disadvantage D. sinuata and 0. hyoseroides plants. Grielum humifusum was not affected negatively by grazing. A single high or low intensity grazing treatment during bud formation or a weekly grazing treatment during the bud formation and flowering stages, in various ways benefitted G. humifusum plants. Grazing of G. humifusum led to higher reproductive allocation, whereas it led to a decrease in the fruit production of D. ,sinuata and 0. hyoseroides. Moderate water stress had no negative effect on the total production of Dimorphotheca sinuata plants. Grazing of moderately water stressed plants, should be limitted to the early phenological stages. For optimum utilization of D. sinuata and to ensure a good flowering display, it is therefore recommended that a moderate water stress treatment is combined with a single high intensity grazing during the earlier phenophases. Fieldwork, by means of exclusion plots, was done on the Goegap Nature Reserve in Namaqualand. Ephemeral plant species were utilized during the winter, as well as during summertime. The abundance of showy plant species was decreased under circumstances of high grazing intensities. Antelope preferred plant species such as grasses, Foveolina albida, Galenia sarcophyla, Arctotis fastuosa and Mesembryanthemum karrooense. In general to ensure the survival of the plant species; for maximum fruit production and a spectacular floral display, the ephemeral plants of Namaqualand should not be grazed intensively.
Structural analysis of fractures around underground excavations on a Witwatersrand gold-mine
(University of Pretoria, 1969) Kersten, Rudiger Welf Olgert
The interpretation of faults and joints on the bas is of stresses in the earth I s crust has been attempted on many occasions. The main problem encountered in such interpretations has been that the physical conditions, and the stress field, during the period of origin of these faults were imperfectly known. New information has become available with regard to the mechanisms involved in fracture processes, primarily in the development of the modified Griffith criterion of fracture initiation. The validity of this criterion is tested by comparing orientations of fractures as predicted with those measured in a known environment. Fractures in the hanging wall of a s tope were measured on a gold-mine in the Klerksdorp area. Comparison of predicted and measured orientations shows that the limits within which the orientation of fractures must be, can be predicted. However, minor variations within these limits indicate that a more elaborate model than an idealised slit in an elastic medium is necessary. The modified Griffith 1 s criterion of fracture is used to analyse the history of faulting at the Loraine Gold Mine in the Orange Free State. The studies show that it is possible to place certain limiting conditions on the physical properties of the material, and the stress fields existing at the time of origin of the fault systems.
Population biology of humpback dolphins in Richards bay, South Africa
(University of Pretoria, 1999) Bester, Marthan Nieuwoudt; Peddemors, V.M.; Keith, Mark
During the last 19 years a minimum of 72 humpback dolphins Sousa chinensis were retrieved from the Richards Bay shark nets. Recently developed acoustic warning devices led to the introduction of these devices (pingers) into the shark nets at Richards Bay in an attempt to reduce the number of humpback dolphins captured in the nets. With the KwaZulu-Natal population set at approximately 200 animals this step led to the conception of the Richards Bay Humpback Dolphin Project. The present study was designed to obtain data that would reflect the state of the humpback dolphin population frequenting the Richards Bay area. The study was conducted during April to October of 1998 at Richards Bay (28° 48' S, 032° 06' E), on the eastern coast of KwaZulu-Natal. Humpback dolphins frequented the Richards Bay area throughout the study period with the average group size being 8.72 (± 5.13). Data suggests that the Richards Bay area may be a suitable nursery are~ since "females" with calves in close attendance, were frequently sighted in the study area. Humpback dolphins were seen most frequently in the southern and harbour mouth region of the study area and these areas most likely represent preferred areas. Collection of biotic and abiotic data throughout the study are~ such as water visibility, water temperature and ocean depth were used to correlate any noticeable environmental differences in area utilisation of humpback dolphin groups found in the study area. Only water depth seemed to limit the distribution of this species. No preference for turbid waters were evident during the study. Little or no preference for certain water temperature regimes were evident. Analysis of capture data of humpback dolphins in the Richards Bay shark nets revealed an average capture rate of 3.79 (S.D. ± 3.08) dolphins per year during the 19- year period of installation. The number of dolphins captured in relation to the total length of nets in the particular installation do not seem to be correlated. Peaks in captures existed during the winter months (June to August). Humpback dolphin follows within the harbour and harbour mouth occurred primarily from June to August, the period which coincided with the dolphin captures of 1998 in the Richards Bay installation. Differences in seasonal utilisation and movement of humpback dolphins may lead to an increase in the number of dolphins caught during the winter months within the Richards Bay shark net installation. The number of newly identified individuals did not decrease with time, suggesting that the population sampled at Richards Bay may appear to be an open population. Using all identified individuals sighted during this study, a population of 213 (± 42.72 at the 95% confidence level) individuals was calculated. The continual discovery of new individuals in conjunction with some individuals exhibiting long distance movements along the coast, indicate that a large part of the sampled population does not constitute dolphins actually "resident" within the study area. As the majority of the identified individuals (63 % ) were only photographed once within the study area, unfamiliarity may be one of the main reasons contributing to the high humpback dolphin capture rate in the Richards Bay installation. Unfortunately, social structure estimates of humpback dolphins were severely hampered by irregular movements of dolphin groups. Active acoustic deterrent devices (pingers) were introduced during June 1998 into the Richards Bay shark net installation in an effort to reduce the rate of capture of humpback dolphins in the shark nets. Humpback dolphins frequented the netted areas with and without pingers in place and even though three dolphins were caught in the shark nets, no final conclusion could be made about to the efficacy of the pingers, as all three captures took place during non-active pinger (dummies) periods. Continued investigation into the efficacy of the pingers is therefore needed. The observed site fidelity and home ranges indicated that the Richards Bay area may be for some individuals a "core area" or "preferred area" while others individuals just pass through. Humpback dolphins studied in the Richards Bay area displayed differences in site fidelity and had distinct levels of residency to the study area, affected by various unknown factors. In conclusion, the continuous monitoring of the KZN humpback dolphin population is imperative, to ascertain any change in the current status, as population depletion in conjunction with mass habitat destruction, usually go un-noticed and unchallenged.
Application of inductively coupled plasma emission spectrometry in the analysis of environmental samples
(University of Pretoria, 1986) Strasheim, A.; Bohmer, R.G.; Kempster, Phillip Lyle
A discussion of the theory of inductively coupled plasma (ICP) emission spectrometry, with particular attention being paid to the question of detection limit, leads on to an overview of the analytical application of the ICP emission spectrometric technique in environmental sample analysis. Among the aspects which may influence accuracy are: (i) The sample matrix, in particular the acid matrix effect. (ii) The effect of sample uptake rate on excitation temperature and degree of ionization. Temperature was estimated by use of the two-line method. Inconsistencies in calculated temperatures illustrate the departure from local thermodynamic equilibrium in the ICP source. (iii) The effect of mains supply voltage changes on analyte emission intensity; with the effect on the radio frequency generator and spectrometer being considered separately. (iv) The effect of aerosol argon flow rate change on analyte emission intensity, where a correlation with excitation potential is shown to exist. Thereafter follows a study on the calibration of a twenty-eight channel ICP polychromator and the use of the software approach for interference correction. Second order polynomial interference correction coefficients were determined for interference from Ca, Mg, Fe and Mn. The importance of correction for drift in the concentration readout of a blank sample in analysis at trace concentrations is illustrated. An investigation into the memory-effect in the sample transport system of the polychromator showed that the dead volume displacement time is followed by a biphasic washout curve with both the fast and slow phases having a linear double logarithmic plot. The use of a weighted internal standardization method to correct for sensitivity change consequent to aerosol argon flow rate change was investigated as a possible means of improving accuracy and avoiding frequent recalibration. An investigation is also undertaken into the use of a scanning monochromator for quantitative analysis in the profile scan mode of measurement, where interference correction is carried out by background subtraction. A study is included on the use of an inverse Gaussian transformation as a means of estimating precision from a profile scan, and a discussion on the establishment and the influence of background structure on detection limits. An example is given on the determination of Pb and Cr in a sediment digest. The study is concluded with a discussion on quality control.
The metamorphosed sediments of the Pretoria group and the associated rocks northwest of Zeerust, Western Transvaal
(University of Pretoria, 1978) Snyman, C.P.; Von Gruenewaldt, G. (Gerhard), 1942-; Klop, Andre Alexander Cornelis
Part of the Transvaal Supergroup, viz. the upper formations of the Chuniespoort Group and the Pretoria Group between Zeerust and the border with Botswana, was mapped. The metamorphic aureole of the Bushveld Complex as developed in the Transvaal Supergroup in this area decreases in metamorphic grade both along and across the strike as a result of an apparent reduction in the thickness of the mafic rocks towards the west. The presence of the metamorphic index minerals tremolite, anthophyllite, cummingtonite, cordierite and almandine indicate rocks of the hornblende-hornfels facies in the east. West of long. 25°53'E (which transverses the strata), the metamorphic assemblages are typical of the albite-epidote-hornfels facies and contain minerals such as talc and epidote. Total fluid pressure in the mapped area is unlikely to have exceeded 4 kb. Temperatures are estimated to have been between 300 and 5oo 0 c for the albiteepidote- hornfels facies and between 500 hornblende-hornfels facies. 0 and 600 C for the Few of the complex structures present in adjoining Botswana enter South Africa. A low-angle strike fault zone is an exception, however, and enters South Africa to cut out a large part of the Malmani Subgroup. The port Bushveld linear structures, which are predominant in most-. of the mapped area as well as in a large part of the Kaapvaal province, viz. the NNW faults and the ENE photo-lineation’s, were formed under tensional conditions. EW faults are rare. Several lateral lithofacies changes in the sedimentary layers of the area indicate a higher energy environment in the west. This, together with an increase in the amount and size of detrital chert near Botswana, suggests a nearby original margin of the Transvaal basin in Botswana. Uplift and erosion of the Chuniespoort Group after its deposition did not remove the Penge Formation, with the result that the basal layer of the Pretoria Group is a chert conglomerate and not a residual chert breccia as elsewhere in the Transvaal basin. The sequence of the Rooihoogte Formation at Skilpadhek,as indicated by the cores of four boreholes, represents a delta partly destroyed by strong currents and superseded by linear elastic shore deposits. Lava of the Hekpoort Andesite Formation was extruded subaerially and has an upper, metamorphosed, residual paleosoil cover. Nsutite, a battery-active manganese dioxide, is mined between Skilpadhek and Livingstone's Poort. The ore body originated by replacement of a layer of stromatolitic1 dolomitic limestone in the Polo Ground Member of the Rooihoogte Formation and 0 has a dip of 15 to the north or northeast, a strike length of 10 km and a thickness of between O and 7 m. Ore formation could still be in progress in the oxygen-rich zone of the ground water, which would curtail the extent of the ore to between 30 and 40 groundwater level.
Die evaluering en verfyning van meetinstrumente en die gebruik AMONA in die modellering van latente veranderlike strukture
(University of Pretoria, 1966) Vivier, F.L.; Millard, Sollie M.; Julyan, Surika
In the Social Sciences, and recently also in other Sciences, constructs (latent variables) are being measured. It is however, not possible to know in advance whether the questions being asked will accurately measure the said construct. The measuring instrument that is being used to measure a construct should therefore first be refined before it is used in a model. Unrefined (raw) measuring instruments can have a major influence on the results of model fitting. The objective of the study was to refine measuring instruments and subsequently to build a model which will best fit the data and will reflect the causal relationship between constructs. Specific attention was paid to refining the measuring instruments for job satisfaction, job involvement and career orientation. a Psychometrical model was eventually built, which reflected the causal relationship between the different constructs and the biographical factors. In this study the refinement of measuring instruments (verification of reliability and validity) and model building were investigated. It was evident that the methods for the refinement of measuring instruments, that is Cronbach's Alpha and exploratory factor analysis, maximised the reliability and validity of an instrument. The measuring instruments were consequently successfully refined. It was finally also evident that RAMONA is a very successful computer package for the building of models.

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