Loline alkaloids (LA) are secondary metabolites produced by Epichloandamp;euml; (anamorph, Neotyphodium) grass endophytes. They are toxic and deterrent to a broad range of herbivorous insects but not to livestock. This protective bioactivity has spurred considerable research into the LA biosynthetic pathway. LOL, the gene cluster containing nine genes, is required for LA biosynthesis. The regulation of LOL genes during LA production in culture and in symbio is of interest. In this study, coordinate regulation between LOL gene expression and LA production level was investigated in both MM culture and symbiota. Results showed that expression of LOL genes in N. uncinatum MM culture were tightly correlated with each other (p andamp;lt; 0.0005), and all presented a significant temporal quadratic pattern during LA production. Gene expression started before LA were detectable, and increased while LA accumulated. The highest gene expression level was reached before the highest amounts of LA were detected, and gene expression level declined to a very low level after amounts of LA plateaued. Observations suggested that the hierarchical clusters based on the correlation coefficient could help to predict the roles of LOL genes in the LA pathway. In symbiota, coordinate coregulation of LOL gene expression with LA was found in E. festucae-meadow fescue inflorescences and stromata, whereby lower LOL gene expression corresponded with the lower LA level in stromata. In N. uncinatum (or N. siegelii)-meadow fescue vegetative tissues, dramatically higher LA levels were found in younger leaf tissue than in older leaf tissue, yet no evidence was found to relate this difference to LOL gene expression differences. Instead, substrate availability may regulate the LA level. In particular, asparagine was more than 10-fold higher in young leaf tissue than in old tissue, although proline was significantly lower in young tissue. Therefore, different regulatory mechanisms underlie LOL gene expression and LA production in different circumstances. The GUS activity of Pro-lolC2-GUS and Pro-lolA2-GUS in Neotyphodium species was almost undetectable in culture, though the activity could be detected in symbiota. The mRNA of GUS did not exhibit the same pattern as lolC2 or lolA2 in culture during LA production time course. A Pro-lolC2-cre transgene was expressed in complex medium, in which lolC2 mRNA was not detectable. These results suggest that proper regulation of LOL genes in culture or symbiota is dependent on the LOL cluster.

There are currently three known crystal packing motifs of boronsubphthalocyanine derivatives. Each motif is associated with a particular class of BsubPc derivatives, and none are ideal for organic electronic applications according to the criteria we defined for evaluation: having a continuous pathway for charge-carrier conduction in the solid-state, resistance to hydrolysis, good electrochemical and optical properties, and possession of a robust crystal form. In this thesis, we present five methods for altering the crystal packing structure of phenoxy-BsubPc derivatives in order to meet the above four criteria. We find that neither addition of steric bulk to the axial derivative nor changing the symmetry of the compounds is sufficient for creating a new crystal packing motif. We do find that reducing the symmetry of the axial group does increase the solubility greatly, however. We identify a new motif for BsubPc crystals that occurs when the intermolecular interactions between the axial phenoxy segment and the BsubPc ligand are increased. We present two methods for achieving this new motif, one is through addition of a π-Br interaction and the other is through creation of a strong π-acid/ π-base stacking by making the axial phenoxy more π-electron rich. Unfortunately, the p-bromophenoxy-BsubPc forms this new motif as a kinetic product, isolation of which is unreliable. Attaching a naphthol fragment axially to the BsubPc creates a stable version of this new motif. We also synthesized a new class of BsubPc pseudohalides based on sulfonate derivatives. Of the derivatives in this new class, we found that mesylate-BsubPc forms into a crystal packing structure that possesses a one-dimensional pathway for charge carrier mobility, but is still resistant to hydrolysis under the conditions tested. Overall, we show four compounds that meet the criteria for further study as organic electronic materials: p-methoxyphenoxy-BsubPc, α-naphthoxy-BsubPc, β-naphthoxy-BsubPc, and mesylate-BsubPc.

There are currently three known crystal packing motifs of boronsubphthalocyanine derivatives. Each motif is associated with a particular class of BsubPc derivatives, and none are ideal for organic electronic applications according to the criteria we defined for evaluation: having a continuous pathway for charge-carrier conduction in the solid-state, resistance to hydrolysis, good electrochemical and optical properties, and possession of a robust crystal form. In this thesis, we present five methods for altering the crystal packing structure of phenoxy-BsubPc derivatives in order to meet the above four criteria. We find that neither addition of steric bulk to the axial derivative nor changing the symmetry of the compounds is sufficient for creating a new crystal packing motif. We do find that reducing the symmetry of the axial group does increase the solubility greatly, however. We identify a new motif for BsubPc crystals that occurs when the intermolecular interactions between the axial phenoxy segment and the BsubPc ligand are increased. We present two methods for achieving this new motif, one is through addition of a π-Br interaction and the other is through creation of a strong π-acid/ π-base stacking by making the axial phenoxy more π-electron rich. Unfortunately, the p-bromophenoxy-BsubPc forms this new motif as a kinetic product, isolation of which is unreliable. Attaching a naphthol fragment axially to the BsubPc creates a stable version of this new motif. We also synthesized a new class of BsubPc pseudohalides based on sulfonate derivatives. Of the derivatives in this new class, we found that mesylate-BsubPc forms into a crystal packing structure that possesses a one-dimensional pathway for charge carrier mobility, but is still resistant to hydrolysis under the conditions tested. Overall, we show four compounds that meet the criteria for further study as organic electronic materials: p-methoxyphenoxy-BsubPc, α-naphthoxy-BsubPc, β-naphthoxy-BsubPc, and mesylate-BsubPc.

Nanometer-scale-thick films of metals and semiconductor heterostructures are used increasingly in modern technologies, from microelectronics to various areas of nanofabrication. Processing of such ultrathin-film materials generates structural defects, including voids and cracks, and may induce structural transformations. Furthermore, the mechanical behavior of these small-volume structures is very different from that of bulk materials. Improvement of the reliability, functionality, and performance of nano-scale devices requires a fundamental understanding of the atomistic mechanisms that govern the thin-film response to mechanical loading in order to establish links between the films' structural evolution and their mechanical behavior. Toward this end, a significant part of this study is focused on the analysis of atomic-scale mechanisms of plastic deformation in freestanding, ultrathin films of face-centered cubic (fcc) copper (Cu) that are subjected to biaxial tensile strain. The analysis is based on large-scale molecular-dynamics simulations. Elementary mechanisms of dislocation nucleation are studied and several problems involving the structural evolution of the thin films due to the glide of and interactions between dislocations are addressed. These problems include void nucleation, martensitic transformation, and the role of stacking faults in facilitating dislocation depletion in ultrathin films and other small-volume structures of fcc metals. Void nucleation is analyzed as a mechanism of strain relaxation in Cu thin films. The glide of multiple dislocations causes shearing of atomic planes and leads to formation of surface pits, while vacancies are generated due to the glide motion of jogged dislocations. Coalescence of vacancy clusters with surface pits leads to formation of voids. In addition, the phase transformation of fcc Cu films to hexagonal-close packed (hcp) ones is studied. The resulting martensite phase nucleates at the film's free surface and grows into the bulk of the film due to dislocation glide. The role of surface orientation in the strain relaxation of these strained thin films under biaxial tension is discussed and the stability of the fcc crystalline phase is analyzed. Finally, the mechanical response during dynamic tensile straining of pre-treated fcc metallic thin films with varying propensities for formation of stacking faults is analyzed. Interactions between dislocations and stacking faults play a significant role in the cross-slip and eventual annihilation of dislocations in films of fcc metals with low-to-medium values of the stable-to-unstable stacking-fault energy ratio, γs/γu. Stacking-fault-mediated mechanisms of dislocation depletion in these ultrathin fcc metallic films are identified and analyzed. Additionally, a theoretical analysis for the kinetics of strain relaxation in Si 1-x Ge x (0 ≤ x ≤ 1) thin films grown epitaxially on Si(001) substrates is conducted. The analysis is based on a properly parameterized dislocation mean-field theoretical model that describes plastic-deformation dynamics due to threading dislocation propagation; the analysis addresses strain relaxation kinetics during both epitaxial growth and thermal annealing, including post-implantation annealing. The theoretical predictions for strain relaxation as a function of film thickness in Si 0.80 Ge 0.20 /Si(001) samples annealed after growth, either unimplanted or after He + implantation, are in excellent agreement with reported experimental measurements.

For organic electronic device applications materials are needed which display good charge carrier mobility, good processability, and stability towards oxygen and moisture. Alkynylated N-Heteroacenes fulfill many of these requirements. Substitution with alkyne groups as well as the introduction of the pyrazine subunit both inhibits oxidative degradation at sensitive position in the molecules. Additionally the trialkylsilylethynyl group aides in directing the packing motif as well as vastly increases the solubility over unsubstituted analogues. A requisite precursor in the synthesis of alkynylated N-heteroacenes is alkynylated acenothiadiazoles. These thiadiazoles display interesting photophysical properties and can be functionalized to produce a wide range of properties in closely related materials. The acenothiadiazoles themselves have potential applications as an N-type semiconductor. Optical gaps and calculated HOMO-LUMO gaps show that these molecules, when compared to known N-type materials, should be easily injected with electrons. Additionally the crystal packing of these compounds shows favorable π-orbital overlap which should provide excellent charge carrier mobilities.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Construction Management, Department of Construction Management and Quantity Surveying In the Faculty of Engineering, At the Cape Peninsula University of Technology / Sustainable buildings are structures produced to meet the present housing needs of a society without compromising the ability of the future generation to meet their future needs. Based on the findings derived from the reviewed literature, the production process and the operational lifecycle of sustainable buildings promote a healthy well-being for the inhabitants and environmental balance through the effective management of energy, water, land and materials resources at every stage of construction. However, ineffective construction materials procurement strategy was found in literature as a major factor that constrains the production of sustainable buildings; leading to project failures or production cost and time overrun. Thus, the production cost of sustainable buildings is influenced by the total cost of construction materials acquisition, which amounts to about 65% of the total cost of building production. This factor on cost has over the years been a significant barrier to the adoption of sustainable building principles in the construction industry. This prompted the need to establish an effective strategy for construction materials procurement towards the enhancement of sustainable building production in Western Cape, South Africa. The research study adopted a mixed methodological approach, which involved the use of semi-structured qualitative interviews and closed-ended quantitative questionnaires administered to construction stakeholders (contractors and consultants) in the Western Cape Province of South Africa. SPSS version 23 software was used to analyse the quantitative data collected and ‘content analysis’ method was used to analyse the information collected through qualitative interview conducted.

No description available.

This thesis is centred around the study materials with novel electronic properties, including transition metals interacting with semiconductors and unique molecular systems. The idea of advancing modern computing is the basis for motivating the work in that the projects all have potential to be used in novel applications that would impact the efficiency and/or execution of current technology. We have studied two variations of transition metals as they appear in materials and two molecular systems. As for the transition metals interacting with semiconductors, we first discuss transition metal atoms introduced as impurities to a semiconductor lattice, and second, we discuss transition metal oxides that are naturally semiconducting. We have used a number of experimental and theoretical techniques to better understand these groups of materials. Materials prepared through high quality synthesis techniques were studied using x-ray spectroscopy made possible by synchrotron light sources. Computational software then allowed for the experiments to be interpreted by comparing them to the simulations. In the study of transition metals as impurities, we chose the Co:MoS2 system because MoS2 has had promising results with other transition metal dopants. We examined the electronic structure for two purposes: (1) to determine the local bonding environment and locations of the cobalt atoms in order to better understand the behaviour of Co as an impurity; and (2) the overall band gap of the system so that we could evaluate the system’s potential for use in applications. Experimental results combined with our theoretical simulations led us to conclude that the samples available were all metallic, and at low concentrations cobalt atoms were able to substitute directly into the MoS2 lattice. An examination of copper (II) oxide allowed us to investigate the ability to tune the band gap of a known semiconductor through a synthesis process that applied axial pressure to the sample. For a collection of samples prepared at different pressures, x-ray spectroscopy methods showed an increasing band gap with increasing synthesis pressure, a result that is most encouraging for the field of band gap engineering. Using soft x-ray spectroscopy to examine the conduction and valence bands of the two molecular systems, the potassium-doped hydrocarbons and Li2RuO3, was important for drawing conclusions about the materials’ composition and behaviour. Results showed the introduction of new states at the lower edge of the conduction band of K:phenanthrene, a possible reason for its low-temperature superconductivity. Li2RuO3’s electronic structure was examined and compared to calculations performed by collaborators.

No description available.

Microwave tubes are the choice of a wide range of high power and millimeter wave applications in radar, electronic warfare and communication systems. Advances in these devices are due to device innovation, improved modeling, and development of advanced materials. In a microwave tube, electron emitter is the source of electron beam and it is one of the vital components determining the life & performance of the device. High power, high frequency microwave tubes require electron emitters with high emission density. The present thesis aims at developing the materials for high emission density electron emitters. It is aimed to improve the emission density of thermionic cathodes for use in conventional microwave tubes and to develop cold emitters like ferroelectric cathodes for high power microwave devices. The work reported in the present thesis is a modest attempt of the author towards this aim. The thesis is organized in six chapters. Chapter 1 gives a brief introduction of thermionic and ferroelectric emitters. Different types of electron emission mechanisms and a brief background of thermionic and ferroelectricemitters are discussed in this chapter. The genesis of the problem taken up and its importance as well as the plan and scope of the work is also given in this chapter. In Chapter 2, the basic experimental techniques used in the present work are discussed. Preparation of mixed metal matrix and M- type dispenser cathodes and their characterization techniques has been discussed in this chapter. Subsequently, ferroelectric materials preparation and characterization for their material properties and electron emission has been discussed. A brief introduction to FEM software ANSYS, used for thermal analysis of dispenser cathodes and electrostatic field analysis of ferroelectric cathodes, has been given at the end of this chapter. Thermal analysis, development process, emission characterization, work function distribution, of W-Ir mixed metal matrix (MM type) cathodes and a simple innovative technique to estimate the barium evaporation rate from the emission data of the dispenser cathodes is presented in Chapter 3. Under normal microwave tube operating conditions, the cathode of the electron gun has to be heated up to 1050°C to obtain stable thermionic electron emission. Thermal analysis is a first step in the development process of cathodes, optimizing its structure for improved performance with respect to its operating power, warm-up time and efficiency. Thermal analysis of a dispenser cathode in electron gun environment using the FEM software ANSYS and its experimental validation are presented. Development of porous W-Ir mixed metal matrix material required for dispenser cathode applications has been discussed. Determination of pore size, pore density and pore uniformity has been carried out. The performance of the cathodes made with these pellets is at par with the results reported in the literature. The surface of mixed metal pellet is an inherently two-phase structure consisting of tungsten solid solution phase and W-Ir ε phase causing more spread in the spatial distribution of work function. W-Ir mixed metal matrix cathodes have been realized and their work function distribution has been determined form the measured I-V characteristics. Also in this chapter, a novel technique for estimation of barium evaporation rate for dispenser cathodes from their I-V characteristics is presented. Results of life test carried out on these cathodes are given at the end of the chapter. In Chapter 4, work carried out on enhancing the emission properties of mixed metal matrix cathodes by suitably modifying the impregnant mix is discussed. W-Ir MM type cathodes discussed in the previous chapter give a emission current density of ~ 7.5A/cm2 with a work function of 1.99 eV. Thesevalues are very close to that of B-type cathode. In this chapter, it is explored to suitably dope the 5BaO:3CaO:2Al2O3 impregnant mix to reduce the work function of W-Ir cathodes. Lithium and Scandium oxides have been added to the 5:3:2 imp regnant mix. Lithium oxide doped impregnated MM type cathodes have given more than 30 A/cm2 current density at 1050oC. For scandium oxide doped MM type cathodes current density has increased to 15 A/cm2 at the same temperature. In Chapter 5, Electron emission from the ferroelectric cathodes has been discussed. FEM simulation of Ferroelectric cathodes to study the electrical excitation effects on emission. Triple point electric field in FE Cathodes is very large and can lead to field emission from the metallic grid at triple points. FEM simulation has been carried out to find out the effect of grid thickness on triple junction electric field using ANSYS software. From FEM modeling it is also seen that if a dielectric layer of lower dielectric constant (εr≤10) is placed between the grid and the ferroelectric material the triple junction electric field increases three fold. Use of dielectric layer can also reduce the secondary electron coefficient (δ) and surface plasma generation. Lanthanum doped PZT has been chosen for the study and these materials have been tested in diode configuration for emission characterization in demountable vacuum systems. Repeatable electron emission has been achieved for all the three compositions of PLZT (x/65/35) material (x = 7, 8, 9). However, it has been observed that when the ferroelectric is subjected to repetitive unipolar electrical excitation, fatigue is set in and cathode material is cracking. To study the effect of domain switching on the residual stress in the ferroelectric material, XRD studies have been carried out. Shift in XRD peaks for fresh and emission tested samples has been used to calculate the residual stress developed in the samples. Details of High current switch realized using ferroelectric cathodes have been discussed. Chapter 6 gives the Summary of the work done and suggestions for further research on W-Ir mixed metal matrix cathodes and ferroelectric cathodes.