A microcomputer software package was written to calculate the tranmission and reflection characteristics of multilayer thin films on a substrate. The program was written to be as "user-friendly", versatile and modular as possible. To test the program, a transparent oxide-type heat-mirror film capped with an antireflection coating was studied for greenhouse applications. Si0₂ and ZnO were considered as representative antireflection and heat-mirror materials respectively. The results of calculations of heat transfer coefficient and transmittance of the glazing construction polyethylene/air gap/Si0₂/ZnO/polyethylene are presented. The resulting structure is shown to give a visible light transmission spectrum which closely matches the plant sensitivity curve for plant growth and has higher thermal insulation compared to uncoated polyethylene. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The magnetic behavior of cubic B20 crystal structure FeSi thin film has been previously probed at macroscopic level using a magnetometer. The results revealed ferromagnetic state with significant hysteresis. This is contrary to the bulk with the same cubic B20 crystal structure that is paramagnetic. The origin of ferromagnetism in thin films in contrast to paramagnetism in the bulk is unclear and unexplained. Electron spin resonance technique (ESR) was used as a tool to characterize the magnetic behavior of FeSi thin films at microscopic level. With ESR technique, B20 crystalline FeSi show microwave power absorption centred at zero field (HDC = 0) termed low-field microwave absorption (LFA) in addition to usual ferromagnetic resonance (FMR) typical of magnetic materials. LFA was observed as a distinct signal in these films. This signal has been observed in several other materials other than FeSi thin films. However in FeSi thin films it was for the first time that LFA signal was observed. The LFA is closely connected to the magnetization process that occurs at low applied field. LFA is a new technique that has recently been used to detect the magnetic transition in materials, sensitive detection of magnetic order and more importantly to distinguish between different dynamics of microwave absorption centres. The LFA measurements were made at 9.4 GHz (X-band) on pulse laser deposited (PLD) polycrystalline B20 cubic structure FeSi thin film grown on Si (111) substrate. PLD is regarded as a powerful tool for thin film growth. The LFA properties of the films were investigated as a function of DC field, temperature, microwave power and orientation of DC field with respect to the film surface. The LFA signal is very strong when the DC field is parallel to the film surface and diminishes at higher angles. This is attributed to induced anisotropy field (IAF) and surface anisotropy field (SAF) contributing to total anisotropy field (TAF). The LFA signal strength increases as the microwave power is increased, such increase is due to impedance and thus showing that LFA and magnetoimpedance (MI) has common origin. The LFA signal disappears around 340 K which can be attributed to the disappearance of long range order giving us a positive signature of surviving magnetic state well above room temperature in these films. We believe that domain structure evolution in low-fields, which in turn modifies the low field permeability as well as the anisotropy, could be the origin of LFA observed in these films. MI and LFA can be understood as the absorption of electromagnetic radiation by spin systems that are modified by domain configuration and strongly depend on anisotropy field. The observation of LFA opens the possibility of FeSi films to be used as potential candidates of low magnetic field sensors in the microwave and radio frequency regions. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Physics / unrestricted

Billions of people rely solely on groundwater for drinking and daily use. In the last few decades, groundwater was shown to be contaminated with arsenic in high concentrations, especially in Asian countries such as Bangladesh. Arsenic (As) is ranked the first among 20 toxic substances by the Agency for Toxic Substances and Disease Registry (ATSDR) and United States Environmental Protection Agency (USEPA). Because many diseases and deaths were linked to consumption of arsenic-contaminated groundwater, the world health organization (WHO) reduced the arsenic standard level for drinking water from 50 to 10 µg L-1. Urgent demands for safe drinking water lead to developing potential technologies for removal of arsenic from groundwater. Arsenic is mainly present as uncharged As(III) in groundwater, which makes it difficult to be efficiently removed by conventional treatment methods. Therefore, membrane technology could be a promising potential solution. Because membrane technology has not been widely tested for arsenic removal, a novel in-house defect-free interfacially-polymerized (IP) cross-linked polyamide thin-film composite (TFC) nanofiltration membrane, namely, PIP-KRO1, was tested in this research. Two commercial TFC membranes, namely Dow NF270 and Sepro RO4, were also tested and compared to PIP-KRO1. The membranes were tested at four different pH conditions (4, 6, 8, and 10) in a cross-flow flat sheet membrane unit. The experiments were divided into two parts: (i) the membranes were tested for water permeance and salt (NaCl) removal and (ii) tested for As(III) removal in the presence of 250 ppm NaCl. The results in this study showed strong size sieving rejection for RO4 and a combination of size sieving and charge exclusion mechanisms for PIP-KRO1 and NF270. In general, the rejection trend was RO4 > PIP-KRO1 > NF270 for both NaCl and As(III). In contrast, the trend for water permeance was NF270 > PIP-KRO1 > RO4. The minimum and maximum salt rejection at pH 4 and pH 10, respectively, were 85 and 98.8% for RO4, 57 and 89% for PIP-KRO1, and 34 and 76.8% for NF270. In addition, the TFC membranes demonstrated a maximum As(III) rejection of 98.7, 69.5, and 46.3% for RO4, PIP-KRO1, and NF270, respectively. Based on the characterizations of the membranes, PIP-KRO1 had the highest cross-linking (N/O ratio) followed by RO4 and NF270, respectively. The same trend was observed for the thickness of the polyamide selective layer (PIP-KRO1 > RO4 > NF270). The zeta potential for NF270 was slightly higher than that for PIP-KRO1; RO4 had much lower membrane surface charge. In terms of surface roughness, the following trend was observed: RO4 > PIP-KRO1 > NF270.

Today, thin client applications often rely on the infrastructure of the WWW to deliver their user interfaces (UIs) to clients. While this approach does not require the deployment of application logic on the client, web-based UIs typically do not provide the same level of usability as window-based UIs. We therefore present a UI framework that combines the flexibility of a thin presentation logic with the usability of a full-featured UI: Our approach uses an XMPP-based instant messaging infrastructure to exchange XUL interface descriptions and events between the application logic on the server and a generic UI rendering engine on the client.

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No description available.

ABSTRACT The belief that herbal remedies are less invasive on the human body than conventional medicine and the return of the consumer to a more natural lifestyle, has led to the development of a multitude of remedies, with many different uses. Because the use of these herbal remedies has increased drastically in the last decade, it is essential that the quality and efficacy of these products are well regulated. One of the objectives in this study includes the investigation of the presence of marker metabolites in five herbal remedies, namely Serenoa repens, Silybum marianum, Hypericum perforatum, Echinacea purpurea and Gingko biloba. Although most of the brands tested contained the active ingredients assayed for, a few exceptions were found. However, because this study used only thin layer chromatography for analysis of products, verification of these results should be obtained using other more modern methods for example high pressure liquid chromatography. Four brands of Serenoa repens were selected and assayed for the presence of -sitosterol. All four brands tested indicated the presence of -sitosterol. Five brands of Hypericum perforatum were selected and assayed for the presence of hypericin, rutin and chlorogenic acid. Four of the five products tested indicated the presence of hypericin, while three of five products indicated the presence of rutin and chlorogenic acid. Five brands of Echinacea purpurea were selected and assayed for the presence of -sitosterol, chlorogenic and caffeic acid. Three of the five products indicated the presence of -sitosterol, while only one of the five products contained chlorogenic acid. Caffeic acid was present in 3 of the 5 products. Seven brands of Gingko biloba were selected and assayed for the presence of rutin and bilobalide. Five of the seven products indicated the presence of rutin and bilobalide. Four brands of Silybum marianum were selected and assayed for the presence of both taxifolin and sylibin. Only two of the four products contained both taxifolin and silybin. The second objective of this study is to provide a literature review of the five herbal remedies mentioned above. Amongst the topics discussed were uses of these plants, evidence from studies conducted, chemistry and mechanism of action of the active molecules contained in the plants.

No description available.

No description available.

Spintronic-based magnetic random-access memory (MRAM) implementing the tunnel magnetoresistance (TMR) effect has various advantages over conventional semiconductor base memory devices, such as non-volatility and potentially high density and scalability. Traditional MRAM design implemented in-plane magnetic switching for the read/write operation which is now recognized to suffer from poor scalability below 60 nm. With the discovery of the spin-transfer torque (STT) effect, where the spin-polarized current is used to switch the ferromagnet, the MRAM design simplified considerably as it eliminated one of the two current-carrying wires that are used to generate the magnetic field required for switching. The thermal stability is further enhanced by using magnetic materials with perpendicular magnetic anisotropy (PMA). In current devices, perpendicular anisotropy is developed at the free magnetic layer (CoFeB) interface with the tunnel barrier (MgO). It is called interfacial-perpendicular anisotropy. However, it has been shown that this design has scaling issues below 20 nm. Materials with volume (bulk) perpendicular magnetic anisotropy should show better scaling without compromising on thermal stability.This dissertation work is focused on growth and physical property investigations of thin films of novel magnetic and electronic materials which are promising for MRAM devices. Leveraging on prior identified materials (both theory and bulk materials experiment) with tetragonal and hexagonal symmetry that support PMA, we have successfully implemented several manganese-based hexagonal Heusler-like Mn3-xFexSn (X=0,1,2) alloys predicted to be high PMA materials. While Mn3Sn thin films are reported in the literature, we are not aware of any thin film reports elsewhere on Fe2MnSn and Mn2FeSn thin films discussed here. All these materials are stabilized in the hexagonal structure which inherently supports perpendicular anisotropy. Specifically, we found that Mn3Sn has low saturation magnetization and high Tc but low magnetic anisotropy. Mn2FeSn has a moderate magnetic moment but low Tc (272 K). Fe2MnSn is the most favorable material among our investigations, with high magnetic anisotropy and high Curie temperature of 548 K, but with a higher than desired magnetization value. The magnetic anisotropy value of Fe2MnSn is estimated to be 0.56 MJ/m3. Such value is in the desirable range for MRAM devices. Our thermal stability calculations indicate that STT-MRAM with Fe2MnSn free layer can scale below 20 nm lateral size for 3nm free layer thickness. While the scaling behavior remains to be investigated experimentally, my work has demonstrated that research into new materials is always an exciting prospect particularly if combined with a theory-driven design approach.