The rechargeable Li-O2 battery has attracted interest due to its high theoretical energy density (about 10 times better than today’s Li-ion batteries). In this PhD thesis the cycling instability of the Li-O2 battery has been studied. Degradation of the battery has been followed by studying the interface between the electrodes and electrolyte and determining the chemical composition and quantity of degradation products formed after varied cycling conditions. For this in-house and synchrotron based Photoelectron Spectroscopy (PES) were used as a powerful surface sensitive technique. Using these methods quantitative and qualitative information was obtained of both amorphous and crystalline compounds. To make the most realistic studies the carbon cathode pore structure was optimised by varying the binder to carbon ratio. This was shown to have an effect on improving the discharge capacity. For Li-O2 batteries electrolyte decomposition is a major challenge. The stability of different electrolyte solvents and salts were investigated. Aprotic carbonate and ether based solvents such as PC, EC/DEC, TEGDME, and PEGDME were found to decompose during electrochemical cycling of the cells. The carbonate based electrolytes decompose to form a 5-10 nm thick surface layer on the carbon cathode during discharge which was then removed during battery charging. The degradation products of the ether based electrolytes consisted mainly of ether and carbonate based surface species. It is also shown that Li2O2 as the final discharge product of the cell is chemically reactive and decomposes carbonate and ether based solvents. The stability of lithium electrolyte salts (such as LiPF6, LiBF4, LiB(CN)4, LiBOB, and LiClO4) was also studied. The PES results revealed that all salts are unstable during the cell cycling and in contact with Li2O2. Decomposition layers thinner than 5 nm were observed on Li2O2. Furthermore, it is shown that the stability of the interface on the lithium anode is a chief issue. When compared to Li batteries (where oxygen levels are below 10 ppm) working in the presence of excess oxygen leads to the decomposition of carbonate based electrolytes to a larger degree.

The tandem solar cell concept is a promising approach to improve the efficiency of photovoltaic devices. However, characterization of tandem solar cell devices is challenging since correct efficiency determination demands special experimental infrastructure as well as suitable characterization procedures. Even though the appropriate IEC and ASTM measurement standards define all that very precisely, they cannot be applied without special care to organic photovoltaics (OPV) because they were originally developed for inorganic devices. As a consequence, nowadays almost all tandem organic solar cell publications are not using correct characterization procedures, often resulting in questionable efficiency values. The aim of this work is developing a measurement procedure for tandem organic solar cells assuring their correct characterization. Therefore, at first the existing standards and measurement procedures for tandem solar cells are reviewed and challenges when applying these standards to organic solar cells are identified. As main challenges the relatively low fill factors and distinct nonlinearities of organic solar cells are identified. As preliminary experiments, single junction organic solar cells are investigated to analyze the influence of measurement parameters like bias irradiance, bias voltage, and chopper frequency on the external quantum efficiency (EQE) of organic solar cells. This results in parameter sets assuring minimized artifacts for the subsequent EQE determination of the subcells of tandem organic solar cells. The main part of this thesis presents the detailed characterization of a tandem OPV example device. First, EQE is measured and validated by two independent institutes. The EQE results are used to calculate the illumination conditions to reach AM1.5g conditions for both subcells with a multi-source sun simulator. The resulting efficiency value under standard reporting conditions (SRC) is found to be 5% lower than the efficiency measured with a single-source sun simulator. A full spectrometric characterization shows that differing fill factors of the subcells are the reason for this behavior. To overcome the main reason for the complicated measurement procedure of tandem solar cells, the inaccessibility of the individual subcells, three different approaches for the jV-characteristics determination of the subcells are presented. The so-called Bias Voltage Approach is based on EQE-measurements under varying bias voltage and needs no additional electrical contacts. Therefore, it can be applied to existing devices. The Voltage Contact Approach as well as the Current Contact Approach require in changed stack designs. Therefore, they cannot be applied to existing devices but give more accurate results. Finally, a procedure for characterizing tandem organic solar cells is formulated. This procedures aims at giving practical advice how to characterize tandem organic solar cells to achieve results conforming to the measurement standards and being as accurate and reproducible as possible. Hence, this thesis attempts to establish standards for a correct measurement of tandem organic solar cells of which other emerging solar cell technologies can profit as well.

It is perhaps paradoxical that many material properties arise from the absence of material rather than the presence of it. For example, the strength, stiffness, and toughness of a concrete are related to its pore structure. Furthermore, the volume, size distribution, and interconnectivity of porosity is important for understanding permeability, diffusivity, and capillary action occurring in concrete, which are necessary for predicting service lives in aggressive environments. This research advances the state-of-the-art of multiscale characterization of cement-based materials, and uses this characterization information to model the material behavior under competing durability concerns. In the first part of this research, a novel method is proposed to characterize the entrained air void system. In the second and third parts of this research, microstructural characterization is used in tandem with mechanical models to investigate the behavior of cementitious materials when exposed to rapid rates of loading and to cyclic freezing and thawing. First, a novel analytical technique is presented which reconstructs the 3D entrained air void distribution in hardened concrete using 2D image analysis. This method proposes a new spacing factor, which is believed to be more sensitive to microstructural changes than the current spacing factor commonly utilized in practiced, and specified in ASTM C457, as a measure of concrete's ability to resist to damage under cyclic freeze/thaw loading. This has the potential to improve economy by improving the quality of petrographic assessment and reducing the need for more expensive and time-consuming freeze/thaw tests, while also promoting the durability of concrete. Second, quantitative measurements of the sizes, shapes, and spatial arrangements of flaws which are through to drive failure at strain rates above 100/s were obtained in order to model mortar subjected to high strain-rate loading (i.e., extremes in load rate). A micromechanics model was used to study the ways in which flaw geometry and flaw interaction govern damage. A key finding suggests that dynamic strength may be multimodal, with larger flaws shifting the dynamic strength upwards into the highest strength failure mode. Third, a robust theoretical approach, based upon poroelasticity, is presented to further validate the utility of the novel spacing factor proposed this research. The model is truly multiscale, using in its formulation pore size data ranging from the nanoscale to the micro-scale, entrained air data from the micro-scale to the millimeter scale, and infers a representative volume element on the centimeter scale. The results provide an underlying physical basis for the performance of the novel spacing factor. Furthermore, the framework could be used as a forensic tool, or as a tool to optimize the entrained air void system against freeze/thaw damage.

Radiation safety is the biggest concern of the nuclear industry, and co-robots are a crucial component to insuring that safety. Currently, radiation mapping data is typically gathered using hand held detectors or other detection systems requiring constant human interaction. This results in direct exposure to radiation of the individual performing the survey. Co-robots can coordinate computer algorithms and human input to determine the most efficient and accurate methods of surveying these same regions while eliminating health hazards. These surveying methods can then be adapted for multiple uses in the industry including nonproliferation, maintenance, and accident response scenarios. This work describes the process by which two vehicles were modified to detect radiation with minimal human interaction. An algorithm was developed to control the robot and to navigate the area of interest while ensuring that all sources are found. A compact detector system was used to keep the vehicles as small and light as possible. The vehicles were constructed to satisfy the requirements of the detector system and relay the necessary information back to the control station. The process, which is nearly fully autonomous, can map an area of interest and proceed to characterize the radiation materials that are found using neutron and gamma spectroscopy. The vehicles were tested in several scenarios which included obstacles, multiple sources, and shielding of the sources to determine the practicality of these co-robots. The evaluation of these co-robots was critical, as the future of radiation safety lies in the research and construction of small autonomous radiation detection systems to minimize the risk that radiation exposure poses to humans.

The advancement of photonics technologies depends on synthesis of novel materials and processes for device fabrication. The characterization techniques of the optical, electrical and magnetic properties of the synthesized materials and devices, by non-contact, non-invasive and nondestructive methods plays a significant role in development of new photonics technologies. The research reported in this thesis focuses on two such aspects of photonic materials characterization: Magneto-Optic characterization and Spectroscopic Ellipsometry. The theoretical and experimental basis of these two techniques, and experimental data analysis are presented in two parts. In Part 1, the changes in magneto-optic parameters of FePT PS-P2VP block copolymer nanocomposites with increasing concentrations of FePt nanoparticles in the block copolymer are analyzed. We present the results of change in MO anisotropy factor with the wt% of FePt and try to analyze these changes with further experimentation. Part 2 presents the results of spectroscopic ellipsometry of group III-IV multilayered thin film materials to give their precise thicknesses and optical constants. Both these techniques are unique ways to understand novel material characteristics for future use in device development.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Parameterized data from ARTM channel sounding test flights are used to derive a parameter-based estimate of the scattering function. The Doppler bandwidth and Doppler spread, important measures of channel dynamics, can be estimated from such a scattering function. Data collected from ARTM Flight 11 suggest that the Doppler bandwidth is larger than 6.7 Hz. Even for very small collections of parameterized data, surprising agreement is shown to non-parametric scattering function estimates. This confirms modeling assumptions and offers a way to achieve significant reductions of storage requirements.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / In an effort to determine a more accurate characterization of the multipath fading effects on telemetry signals, the BYU telemetering group is implementing an inexpensive data acquisition system to measure these effects. It is designed to measure important signals in a diversity combining system. The received RF envelope, AGC signal, and the weighting signal for each beam, as well as the IRIG B time stamp will be sampled and stored. This system is based on an 80x86 platform for simplicity, compactness, and ease of use. The design is robust and portable to accommodate measurements in a variety of locations including aircraft, ground, and mobile environments.

The objective of the proposed research is to develop a framework for the signal reconstruction algorithm with sub-Nyquist sampling rate and the low-cost hardware design in system level. A further objective of the proposed research is to monitor the device-under-test (DUT) and to adapt its behaviors. The key contribution of this research is that the high-speed signal acquisition is done by direct subsampling. As the signal is directly sampled without any front-end radio-frequency (RF) components such as mixers or filters, the cost of hardware is reduced. Furthermore, the distortion and the nonlinearity from the RF components can be avoided. The first proposed work is wideband signal reconstruction by dual-rate time-interleaved subsampling hardware and Multi-coset signal reconstruction. Using the combination of the dual-rate hardware and the multi-coset algorithm, the number of sampling channel is significantly reduced compared to the conventional multi-coset works. The second proposed work is jitter tracking by accurate period estimation with incoherent subsampling. In this work, the long-term jitter in PRBS is tracked without hardware synchronization and clock-data-recovery (CDR) circuits. The third proposed work is eye-monitoring and time-domain-reflectometry (TDR) by monobit receiver signal reconstruction. Using a monobit receiver based on incoherent subsampling and time-variant threshold signal, high resolution of reconstructed signal in both amplitude and time is achieved. Compared to a multibit-receiver, the scalability of the test-system is significantly increased.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Proteins from various sources, including grape berry cells, yeast, bacteria and fining agents e.g. albumin and casein, have previously been identified in wine. These proteins play various critical roles in the functioning and survival of the organisms that produced them but also exhibit oenological properties, once secreted in the juice/wine. Some of them can indeed be beneficial to winemaking, by releasing aroma compounds from grape-derived precursors, or detrimental to wine quality, by causing protein haze. Yeasts contribute significantly to the protein pool during and after alcoholic fermentation. However, while the extracellular proteins of Saccharomyces cerevisiae, the main wine yeast species, have been characterised, those of non-Saccharomyces yeasts remain largely unknown, especially under winemaking conditions. Although specific extracellular enzymes released by non-Saccharomyces yeasts have been the focus of many studies in recent years, the targeted approaches used have restricted our knowledge to these specific enzymes and excluded the other secreted proteins. A more comprehensive insight into entire secretomes could improve our understanding of how yeasts survive in wine and interact with other species in mixed culture fermentations. This study aims to characterise the exo-proteome of Saccharomyces and selected non-Saccharomyces yeasts in pure and mixed cultures in a wine-like medium. Fermentation kinetics were monitored and the extracellular proteins isolated at the end of fermentation. M. pulcherrima hardly fermented whereas L. thermotolerans fermented slowly but steadily. As expected S. cerevisiae completed the fermentation rapidly. In sequential fermentations, the kinetics resembled those of the non-Saccharomyces yeasts for a period before switching to that of S. cerevisiae. This period varied from 4 to 15 days for M. pulcherrima and L. thermotolerans respectively. Visual observations of the protein content of the medium at the end of fermentation using 1D and 2D SDS-PAGE gels as well as identification of these proteins using mass fingerprinting revealed the large variety of proteins secreted and the influence of yeast interactions on each other’s secretome. The fermentation kinetics observed could partially be explained by the extent of the contribution of the different yeast to the protein content. Proteins secreted by non-Saccharomyces yeasts lowered the potential of wine to form protein haze, with both M. pulcherrima and L. thermotolerans in pure and mixed culture fermentations showing lower haze formation than S. cerevisiae. As far as we know, this is the first report on the secretome of non-Saccharomyces under winemaking condition and the influence non-Saccharomyces proteins have on the protein haze potential of wine, providing the basis for future investigations. / AFRIKAANSE OPSOMMING: Proteïene vanaf verskeie bronne (insluitend druiwe korrels, gis, bakterieë en verhelderings agente bv. albumien en kaseïen) is reeds in wyn identifiseer. Hierdie proteïene speel verskeie rolle in die funksionering en oorlewing van die organismes wat dit produseer, maar beskik ook oor wynkundige eienskappe sodra dit in die sap of wyn uitgeskei word. Hoewel sommige proteïene in wyn wel voordelig mag wees as gevolg van die vrystelling van aroma komponente vanuit druif‐voorlopers, kan dit ook nadelig wees vir wyn kwaliteit deur die troebelheid wat dit kan veroorsaak Gis dra aansienlik by tot die totale proteïen inhoud van wyn, beide gedurende asook na alkoholiese fermentasie. Alhoewel die ekstrasellulêre proteïene van Saccharomyces cerevisiae (die mees algemeen gebruikte gis vir wynmaak) reeds goed gekarakteriseer is, is die proteïene van nie-Saccharomyces giste grootliks onbekend, veral die wat tydens wynmaak vrygestel word. Gedurende die laaste paar jaar het verskeie studies gefokus op spesifieke ekstrasellulêre ensieme wat deur nie-Saccharomyces giste produseer word, maar geteikende benaderings het ons kennis beperk tot net hierdie spesifieke ensieme, en enige ander afgeskeide proteïene uitgesluit. ʼn Meer omvattende insig oor die algehele afgeskeide proteoom kan ons begrip van hoe gis in wyn oorleef en interaksies tussen gis spesies in gemengde kultuur fermentasies verbeter Hierdie studie streef om die sekretoom van Saccharomyces en geselekteerde nie-Saccharomyces giste in suiwer en gemengde kultuur fermentasies van sintetiese wyn medium te karakteriseer. Fermentasie kinetika is gemonitor en die ekstrasellulêre proteïene is teen die einde van fermentasie geïsoleer. Metschnikowia pulcherrima het swak fermenteer terwyl Lachancea thermotolerans stadig tog reëlmatig fermenteer het. Soos verwag, het S. cerevisiae vinnig tot droog fermenteer. In agtereenvolgend geïnokuleerde fermentasies is die kinetika vir ʼn tydperk soortgelyk aan die van die nie-Saccharomyces giste voordat dit oorskakel na die van S. cerevisiae. Hierdie tydperk wissel respektiewelik vanaf 4 tot 15 dae vir M. pulcherrima en L. thermotolerans. Visuele waarnemings van die proteïen-inhoud van die medium aan die einde van die gisting met behulp van 1D en 2D SDS-PAGE gels asook identifisering van hierdie proteïene met behulp van massa vingerafdrukke onthul die groot verskeidenheid proteïene wat afgeskei word, asook die invloed van die giste se interaksies op mekaar se sekretoom. Die fermentasie kinetika waargeneem kan gedeeltelik verklaar word deur die omvang van die bydrae van die verskillende gis tot die proteïen-inhoud. Proteïene wat afgeskei word deur nie-Saccharomyces giste verlaag die potensiaal van wyn om proteïen troebelheid te vorm, met beide M. pulcherrima en L. thermotolerans (in suiwer en gemengde kultuur fermentasies) wat minder troebelheid vorm as fermentasies met S. cerevisiae. Sover ons kennis strek, is hierdie die eerste verslag oor die sekretoom van nie- Saccharomyces onder wynmaak toestande en ook oor die invloed wat nie-Saccharomyces proteïene op die proteïen troebelheid van wyn het, en vorm die basis vir toekomstige navorsing. / Winetech and THRIP

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Sulfated galactans (agarans and carrageenans) are accumulated in the cell wall of various red algae (Rhodophyta) species. These polysaccharides are of commercial importance in the food, pharmaceutical and biotechnology industries due to their unique physicochemical properties. Although having received significant research attention over the last 20 years, events regarding their biosynthesis have not been elucidated. Aiming for the identification of galactosyltransferase (GalT) genes involved in sulfated galactan biosynthesis, cDNA expression libraries were constructed from the prolific agar-producing South African red seaweed Gelidium pristoides (Turner) Kützing and screened by functional complementation of UDP-galactose 4-epimerase deficient mutants (E. coli and S. cerevisiae). Regretfully, no GalTs were identified. The study however yielded the first UGE enzyme described for a red seaweed. Southern hybridization indicated the presence of two UGE copies and confirmed the gene originated from G. pristoides. Bioinformatic analysis of G. pristoides UGE shows amino acid sequence homology to known UGEs from various organisms. The enzyme was shown to be functional in E. coli crude extracts and showed affinity for UDP-D-galactose, similar to other UDP-galactose 4-epimerases. Further, the isolated G. pristoides UGE (GpUGE) was biochemically characterized and its kinetic parameters determined. We found that there was no kinetic difference between this enzyme and previously described UGE enzymes except enhanced activity in the presence of exogenously added NAD+. The UDP-galactose 4-epimerase (UDP-glucose 4-epimerase, UGE, EC 5.1.3.2) is an essential Leloir pathway enzyme facilitating the catalytic inter-conversion between UDP-D-glucose and UDP-D-galactose. UDP-D-galactose is the nucleotide sugar required by galactosyltransferases for the production of red algae sulfated galactans. UGE is suspected as being responsible for supplying UDP-D-galactose for the synthesis of sulfated galactans. In planta monitoring of GpUGE transcript levels with respect to dark and light cycling indicated high expression of the enzyme at night, while expression diminished during the day. The occurrence of increased nocturnal UGE expression correlates with floridean starch breakdown at night. Evidence for hydrolysis of floridean starch is also reflected in obtained G. pristoides transcriptome sequence data. In red algae, floridean starch degradation coincides with sulfated galactan production. The detection of starch hydrolysis enzyme transcripts alongside increased expression of GpUGE suggests the enzyme plays a role in supplying UDP-Dgalactose for sulfated galactan production. As far as we know, this the first report of sequencing and biochemical characterization of a UGE from red seaweed.