Linda Prinsloo - Academia.edu (original) (raw)

Papers by Linda Prinsloo

Journal of Archaeological Science

ABSTRACT Publication currently in press.

ChemInform, 1993

ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

SADJ : journal of the South African Dental Association = tydskrif van die Suid-Afrikaanse Tandheelkundige Vereniging, 2000

The degree of polymerisation (DP) of modern resin cements has a significant role to play in deter... more The degree of polymerisation (DP) of modern resin cements has a significant role to play in determining the ultimate physical and mechanical properties of the material. This study was undertaken to determine the DP of three adhesive resin cements, viz. 3M Opal Cement (3M), Enforce (E, Caulk/Dentsply) and C epsilon tB-Metabond (CB, Parkell). Spectra of both light-cured (3M and E) and self-cured (3M, E and CB) samples were obtained at different time intervals from 3 minutes after mixing the cement up to 24 hours, using a Dilor Raman Confocal Microprobe. The DP of the different cement specimens was calculated from the spectra and statistically analysed (ANOVA). There was a statistically significant difference (P < 0.01) between the DP of 3M and E in the two different activation modes. The light-cured specimens attained a statistically higher degree of polymerisation. CB obtained a statistically significant higher degree of polymerisation (P < 0.01) compared with 3M and E at 24 ho...

The Journal of the Dental Association of South Africa = Die Tydskrif van die Tandheelkundige Vereniging van Suid-Afrika, 1997

Highly filled luting resins are recommended for bonding porcelain restorations to tooth structure... more Highly filled luting resins are recommended for bonding porcelain restorations to tooth structure. This in vitro investigation was undertaken to determine the degree of cure of a 82 per cent filled dual-curing luting resin, after it was cured through various thicknesses of Cerec Vita Mark II porcelain. Infrared, as well as micro-Raman spectroscopy were used to determine the degree of cure of the cement at different time intervals after mixing and exposure to the curing light. The results indicated that Cerec porcelain thicknesses greater than 3 mm adversely affected the degree of cure of the luting resin, even at 24 hours after mixing the cement.

Archéologie 56 • La Recherche | mArs 2012 • nº 462 savoirs nº 462 • mArs 2012 | La Recherche • 57... more Archéologie 56 • La Recherche | mArs 2012 • nº 462 savoirs nº 462 • mArs 2012 | La Recherche • 57 AFRIQUE DU SUD NAMIBIE ANGOLA BOTSWANA ZAMBIE ZIMBABWE MOZAMBIQUE Pretoria Mapungubwe Grand Zimbabwe © A. CARR

Thermochimica Acta, 1994

Using a heating rate of 5°C min-', 010, decomposes between 300 and 350°C according to the reactio... more Using a heating rate of 5°C min-', 010, decomposes between 300 and 350°C according to the reaction 2CsIO,(s) +2CsIO,(s) + O,(g), with an enthalpy change of -57 kJ mol-' CsIO,. The reaction occurs in two distinct parts. First a maximum number of nuclei (approx. 14 per pm') forms at a constant rate according to the power law. Then these nuclei grow according to the contracting area equation. Using isothermal decomposition data, an activation energy value of 226 kJ mol-' and In A of 40.9 were calculated for the first part of the reaction where nuclei are formed, while the activation energy value for the growth of the nuclei is 138 kJ mall'

Surface and Coatings Technology, 2002

ABSTRACT Damage profiles in diamond due to implantation of argon and krypton ions at liquid nitro... more ABSTRACT Damage profiles in diamond due to implantation of argon and krypton ions at liquid nitrogen temperature were determined by α-particle channeling in a backscattering geometry. Energies and fluences were chosen to obtain similar damage energies in the surface region as obtained for a 75 keV carbon implant, investigated and discussed in a previous paper. The damage profiles before and after annealing at 1500 K were compared with those of the carbon implants. Raman spectroscopic analyses and channeling results prove that, contrary to the carbon implants, no irreversible transition to the graphitic phase takes place at comparable damage energies. Critical damage energies are obviously higher for argon and krypton ions than for the lighter carbon ions. This can be explained by a strong annealing effect of the combined inelastic energy transfer by the ion and its associated recoil atoms due to electronic stopping.

Nanophotonic Materials VIII, 2011

ABSTRACT In this research we studied the resonant reflection of circularly polarized light from a... more ABSTRACT In this research we studied the resonant reflection of circularly polarized light from a chiral stack of twisted ultra-thin birefringent layers such as found in the exocuticle of the beetle Proagoderus brucei. This beetle is interesting as it belongs to a very small group of species exhibiting different colors on different parts of its body. Measurements were compared with a computer model of the structure. In this way observations could be explained, some unknown parameters could be quantified and the properties of similar artificial structures with possible practical applications can be predicted.

Brazilian Journal of Physics, 2014

Thin films and Schottky diodes dots of ruthenium (Ru) on bulk-grown n-type-6-hexagonal-silicon ca... more Thin films and Schottky diodes dots of ruthenium (Ru) on bulk-grown n-type-6-hexagonal-silicon carbide (6H-SiC) were annealed isochronally in a vacuum furnace at temperatures ranging from 500-1,000°C. Rutherford backscattering spectroscopy analysis of the thin films showed formation of ruthenium silicide (Ru 2 Si 3 ) at 800°C, while diffusion of Ru into 6H-SiC commenced at 800°C. Raman analysis of the thin films annealed at 1,000°C showed clear D and G carbon peaks which was evidence of formation of graphite. At this annealing temperature, the Schottky contact was observed to convert to an ohmic contact, as evidenced by the linearity of current-voltage characteristic, thereby, rendering the diode unusable. The transformation from Schottky contact to ohmic contact is attributed to graphite formation at the interface.

Applied Surface Science, 2014

South African coal-fired power stations produce about 25 million tons of fly ash per annum, of wh... more South African coal-fired power stations produce about 25 million tons of fly ash per annum, of which only approximately 5% is currently reused. A growing concern about pollution and increasing landfill costs stimulates research into new ways to utilize coal fly ash for economically beneficial applications. Fly ash particles may be used as inorganic filler in polymers, an application which generally requires the modification of their surface properties. In order to design experiments that will result in controlled changes in surface chemistry and morphology, a detailed knowledge of the bulk chemical and mineralogical compositions of untreated fly ash particles, as well as their morphology and surface properties, is needed. In this paper, a combination of complementary bulk and surface techniques was explored to assess the physicochemical properties of a classified, ultrafine coal fly ash sample, and the findings were discussed in the context of polymer application as fillers. The sample was categorized as a Class F fly ash (XRF). Sixty-two percent of the sample was an amorphous glass phase, with mullite and quartz being the main identified crystalline phases (XRD, FTIR). Quantitative carbon and sulfur analysis reported a total bulk carbon and sulfur content of 0.37% and 0.16% respectively. The spatial distribution of the phases was determined by 2D mapping of Raman spectra, while TGA showed a very low weight loss for temperatures ranging between 25 and 1000 • C. Individual fly ash particles were characterized by a monomodal size distribution (PSD) of spherical particles with smooth surfaces (SEM, TEM, AFM), and a mean particle size of 4.6 m (PSD). The BET active surface area of this sample was 1.52 m 2 /g and the chemical composition of the fly ash surface (AES, XPS) was significantly different from the bulk composition and varied considerably between spheres. Many properties of the sample (e.g. spherical morphology, small particle size, thermal stability) appeared to be suitable for its applicability as filler in polymers, although the wide variation in surface composition between individual particles may challenge the development of a suitable surface modification technique. The observation that the bulk and surface compositions of the particles were so intrinsically different, strongly suggested that surface characterization is important when considering compatibility between matrices when applying fly ash as filler in polymers. (E.M. van der Merwe). disposed of and managed on ash dumps or slurry dams; or it can be utilized in a number of applications. FA is usually classified by particle size, creating a relatively uniform fine gray powder of which the particles are predominantly spherical in shape. Depending on the source and type of coal being combusted, the FA composition may differ considerably, but its chemical nature remains predominantly glassy or amorphous .

Powder Technology, 2014

The application of coal fly ash as mineral filler in polymers is hampered by the aggregation of t... more The application of coal fly ash as mineral filler in polymers is hampered by the aggregation of the ash particles and a lack of interaction between the ash and polymer. Therefore surface treatment is usually performed on mineral fillers to enhance workability and compatibility between the polymer and filler. In this study, a commercially available South African coal fly ash sample was surface modified under a variety of conditions with an anionic surfactant, sodium lauryl sulphate (SLS), with the aim to alter the surface properties of the ash. The properties of the modified products were compared to those of the untreated samples by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA-IR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF). A small shift of the S\O stretch vibration in FTIR spectra of SLS treated fly ash is indicative of interaction between fly ash and SLS. Although the overall chemical composition of the SLS modified coal fly ash sample was not altered extensively, significant changes could be observed in its physical properties. Contact angle measurements indicated that the hydrophilic surface of untreated fly ash was rendered hydrophobic after SLS treatment. SEM and TEM results showed agglomerates on the surface of most of the fly ash spheres. Feasibility tests of using fly ash samples as filler in PVC indicated that SLS treated fly ash can successfully replace CaCO 3 as filler in PVC under conditions of low filler loadings.

Surface and Interface Analysis, 2008

Many scarabus beetles, such as Gymnopleurus virens exhibit exceptionally bright iridescent colour... more Many scarabus beetles, such as Gymnopleurus virens exhibit exceptionally bright iridescent colours caused by a Bragg resonance in the thin-layered structure of the exocuticle. These layers are rotated by a small angle with respect to each other resulting in a helcoidal stack, which reflects circularly polarised light with the same sense of rotation as that of the stack. Previous work assumed a smooth chiral structure, but in this work we explicitly include the effect of discrete layers and twist angles and investigate the effect of different layer densities on the reflectance spectrum. By comparing modelled results to experimentally recorded spectra it is possible to estimate the actual layer density found in this scarabus beetle.

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012

In South Africa traditional medicine plays an important role in primary health care and therefore... more In South Africa traditional medicine plays an important role in primary health care and therefore it is very important that the medicinal use of plants is scientifically tested for toxicity and effectiveness. It was established that the ethanolic extract of the leaves of Crotalaria agatiflora, as well as the isolated compound madurensine, is moderately toxic against leukemic U-937 cells. Light microscopic investigations indicated that symptoms of cell death are induced during treatments, but flow cytometry analysis of treated cells, using annexin-V and propidium iodide, showed that apoptosis and necrosis are insignificantly induced. The Raman results suggested that protein extraction and DNA melting occur in the cells during treatment with the ethanolic extracts (IC 50 value 73.9 lg/mL), drastically changing the molecular content of the cells. In contrast, treatment with madurensine (IC 50 value 136.5 lg/mL), an isolated pyrrolizidine alkaloid from the ethanolic extract of the leaves, did not have the same effect. The results are also compared to that of cells treated with actinomycin D, a compound known to induce apoptosis.

Phosphorus, Sulfur, and Silicon and the Related Elements, 1996

IR spectroscopic studies of hydrogen bonding (intra- vs intermolecular) in selected mixed phospho... more IR spectroscopic studies of hydrogen bonding (intra- vs intermolecular) in selected mixed phosphoric-carboxylic imides (RO) 2P(O)NR′C(O)R″ 1, R = Et, R′ = H, alkyl, R″ = OEt, Ph, are presented.

Minerals Engineering, 1995

A significant portion of the gold in Witwatersrand ores may occur in the pyritic fraction, which ... more A significant portion of the gold in Witwatersrand ores may occur in the pyritic fraction, which selabm comprises more than 4% of the ore. Consequently, pyrite recovery through flotation offers the opportunity to improve gold recoveries through further treatment of the pyritic concentrate. The traditional processing routes are no longer economically viable due' to the high cost of acid treatment to overcome the depressing influence of cyanide on xanthate flotation. Amines were identified as possible alternative collectors for pyrite flotation in the presence of cyanide. In this work the influence of cyanide on pyrite flotation with dodecylamine (DDA) acetate was investigated by means of electrochemical impedance measurements, flotation tests, and in-situ Raman spectroscopy.

Minerals Engineering, 1998

Conflicting results have been reported on the infrared spectroscopic (IRS) analysis of the sorpti... more Conflicting results have been reported on the infrared spectroscopic (IRS) analysis of the sorption products of gold di-cyanide onto activated carbon. The present paper reports on our infrared spectroscopic findings. The infrared peak of CN in Au(CN) 2-at 2140 cm -1 was detected in mixtures of activated carbon and solid KAu( CN) 2 and also in activated carbon that was exposed to highly concentrated solutions of gold di-cyanide, but they were very weak in the second instance even though the gold concentrations on the carbon were of the same order as in the former case. It was not detected in activated carbon that was exposed to dilute solutions of gold di-cyanide. It is shown that the detected peaks could be due to KAu(CN) 2 salt that crystallised from the concentrates solution during drying. It is concluded that once the gold is adsorbed the IRS technique may not be sensitive enough to detect the adsorbed species.

Journal of Molecular Structure, 2012

A study of ethnobiological, archaeological, linguistic and historical ethnographic data shows tha... more A study of ethnobiological, archaeological, linguistic and historical ethnographic data shows that notions about the cultural and symbolic significance of the African rhinoceros were widely shared among southeastern Bantu speakers and had considerable time depth. African farming communities could draw upon the traits of both the more aggressive and solitary black rhino (Diceros bicornis) and the more sociable and territorial white rhino (Ceratotherium simum) in their conceptualisation of the qualities of leadership. The Mapungubwe gold rhino served as an emblem of sacred leadership in a class-based society. In less-stratified Sotho-Tswana society, the importance of this pachyderm was reflected in its appropriation as a leadership referent in chiefly praise poems, the use of rhino figurines as didactic tools during initiation schools, as well as a plethora of vernacular names and a complex folk taxonomy. Meat cut from the breast of the rhino was the preserve of a chief and a special club of rhino horn was widely employed as a marker of chiefly status. Rhino horns and bones also featured in rainmaking rituals. Monoliths adorning the central courts of nineteenth-century Tswana towns, as well as the walls or courts of Zimbabwe culture and Venda capitals, most probably signified rhino horns, thereby architecturally encapsulating the key qualities of power, danger and protection traditionally associated with African leadership.

Journal of Human Evolution, 2014

Siliceous rocks that were not heated to high temperatures during their geological formation displ... more Siliceous rocks that were not heated to high temperatures during their geological formation display improved knapping qualities when they are subjected to controlled heating. Experimental heat treatment of South African silcrete, using open fires of the kind used during the Middle Stone Age, shows that the process needed careful management, notwithstanding recent arguments to the contrary. Silcrete blocks fractured when heated on the surface of open fires or on coal beds, but were heated without mishap when buried in sand below a fire. Three silcrete samples, a control, a block heated underground with maximum temperature between 400 and 500 C and a block heated in an open fire with maximum temperature between 700 and 800 C, were analysed with X-ray powder diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, and both Fourier transform infrared (FTIR) and Raman spectroscopy.