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A novel insulating cross-arm (ICA) has been developed for new and existing overhead transmission lines of up to 400 kV. The cross-arm consists of four insulating members, end fittings, field grading devices and a nose connection for the attachment of the conductor. The two main structural elements of the assembly have a unique non-cylindrical geometry which gives them improved mechanical characteristics compared to conventional overhead line insulators. The profile for the compression insulator has been designed. After examining six profile variations, it was determined that the lateral orientation which would give the best performance would be with the flat face of the core facing upwards and tilted by 6o. Using the results obtained from performing flashover tests on a conventional 145 kV insulator, the elevation angle for the compression insulator was set to 6o. The dimensions of the compression insulator were calculated based on the assumption that the ICA would be used to uprate an OHL with L3 towers from 275 kV to 400 kV. The optimal insulator profile was determined to be an alternating profile with three different shed sizes, an arcing distance of 3083 mm and a creepage distance of 12470 mm. Electric field grading devices for the ICA were designed. For the LV end, a grading device resembling a ring which follows the general shape of the cross-section of the insulator was designed. For the HV end, an iterative process yielded two designs. First, the ‘butterfly’ grading device was a unibody piece of cast aluminium for all four ICA members. FEA simulations and tests in the laboratory showed that it could effectively control the electric field at voltages of up to 132 kV. The design was patented and the device was used on six cross-arms installed on a live line in Scotland in August 2013. Second, the ‘M-W’ grading device, was a solution made out of four components for managing the field at voltages of up to 400 kV. The device was designed to be easy to install and service, easy and cheap to manufacture and to have minimal visual impact. The compression insulator and the cross-arm assembly were subjected to a multitude of tests adapted from international standards and the Technical Specifications of National Grid. The performed tests aimed to test the electrical characteristics of the cross-arm and the quality of the materials and manufacturing process of the compression insulator. All of the tests were completed successfully except from the corona extinction test for which the appropriate equipment was not available at the time. Two trials were commissioned to examine how the cross-arm performs in a service-like environment. The snow and ice accretion patterns recorded at the mechanical trial site were used for optimising the profile of the compression insulator. The results after a year of continuous monitoring of leakage current and weather conditions at the live trial site showed that there were humidity and visibility thresholds, above 93% for the former and below 400 m for the latter, which increased the average leakage current by 15% on the tension insulators and by 20% on the compression insulators. It was found that when the longitudinal axis of the cross-arm was perpendicular to the weather the leakage current was higher because more of its surface was exposed. The performance of the novel compression insulators was found to be as good as that of the industry standard tension insulators, reaffirming the potency of the design. Finally, on-site observations showed that the ‘butterfly’ grading device could not effectively manage the electric field on the cross-arm at 400 kV, confirming the results of the FEA simulations and testing.

Wide bandgap semiconductors are currently considered as the building blocks which revolutionized many areas of nanoscience and nanotechnologies. Among them, silicon carbide has been quickly emerging as one of the most interesting materials due to its remarkable physical, chemical, mechanical, electrical properties along with its biocompatibility and its feasibility for a wafer-scale production using standard MEMS processes. Inspired by these advantages, considerable number of studies have been devoted to the development of various SiC-based electronic devices over the past years. Despite these great achievements, however, it is realized that existing sensing devices usually rely on SiC in the forms of bulk or thin film, which still exhibit relatively poor sensitivity and unstable operation due to the limitation of their surface-to-volume ratios. Another key bottleneck of these existing sensing devices lies in the impossibility to integrate SiC onto soft and stretchable substrates due to its rigid and brittle nature, which significantly hamper the broader applications of SiC in the fast-emerging field of bioelectronics. Therefore, the research activities in the framework of my Ph.D. candidature aimed to establish reliable and sustainable protocols to overcome these two critical challenges. The focuses of my research work are placed on the fabrication of SiC nanowires on SiO2 insulators and stretchable SiC microstructures integrated onto polymeric substrates with a high level of structural perfection. Towards these goals, I have successfully fabricated Si NWs on insulator by using a combination of electron beam lithography and thermal wet oxidation techniques. The temperature sensing devices based on SiC NWs exhibit a high TCR compared to their bulk counterparts. On the other hand, I successfully established an effective protocol to transfer rigid SiC microstructures onto polymeric substrates and subsequently, enhanced their stretchability by taking advantages of structural design approaches.

We present results of investigations into the underlying mechanisms that drive the long observed phenomenon of contact electrification. Our experiments indicate identical single-crystal insulators are able to exchange charge at magnitudes comparable to charge transfer between dissimilar materials. Any complete theory of contact electrification must be held accountable to these observations, leading to significant constraints on possible underlying mechanisms of charge transfer between insulators. This self-charging behavior does not appear random when repeated contacts are made, suggesting the possibility of a nucleation-type event developing from seed charges. The confirmation of such a mechanism would require a probe capable of monitoring the charge distribution on the materials' surfaces without affecting the charge distribution. This effect could be direct (e.g. via polar interactions between the tip and sample or by encouraging discharges to the probe) or requiring substantial time to collect data between charging contacts, which could allow for charge redistribution or neutralization, obscuring information on the growth of charge patches.To this end, we demonstrate a novel non-destructive in-situ method of probing the charge distribution, including bipolar charging, on the surfaces of the contacting materials. This method also allows for determination of discharges and charge re-distribution during the experiment. This unprecedented understanding of charge carrier behavior immediately before and after contact provides key clues to the nature of the charge carriers in contact electrification and the underlying mechanism. These results provide constraints on both electron-dominant and ion-dominant theories of charge transfer and significantly narrows the field of possible mechanisms. Another significant aspect of this work is that it provides an explanation as to why a subject studied with so much interest for such a substantial period of time has failed to provide a definitive understanding of the topic. We find charge transfer is highly variable, even in the situation of like materials, and provides insight as to why the results of contact electrification experiments can have such high variation between runs or even individual contacts. We have found that the nature of the contact between two insulating materials, in terms of alignment and amount of rub, have dramatic effects on the charging behavior.

Germline stem cells (GSCs) are the progenitor cells for the entire population of an organism’s germline. In Drosophila, these cells reside in a well-defined cellular niche that is required for both their maintenance (self-renewal) and differentiation (asymmetric division resulting in a daughter cell that differs from the GSC). The stem-cell maintenance factor Stonewall (Stwl) has undergone adaptive evolution across the Drosophila phylogeny and has been implicated in heterochromatin maintenance. In the hopes of identifying potential drivers of selection at Stwl, we investigated the molecular functions of Stwl. We performed RNA-Seq on stwl mutant ovaries and testes to assay the transcript abundance of transposable elements in the absence of functional Stwl. We found that stwl mutant ovaries (but not testes) show significant de-repression of many transposon families, but that heterochromatic genes are not preferentially misregulated relative to euchromatic genes. We also found that testis-enriched genes, including the differentiation factor bgcn and a large cluster on chromosome 2, are upregulated in stwl mutant ovaries. This abnormal masculinization of the ovary was accompanied by ectopic expression of a number of testis- and somatic-enriched genes. Surprisingly, we also found that RNAi knockdown of stwl in S2 cells results in ectopic expression of these gene classes. In order to understand how Stwl regulates transcription, we developed antibodies against a Stwl epitope and thoroughly validated it prior to performing parallel ChIP-Seq and RNA-Seq experiments in S2 cells. Analysis of Stwl binding sites shows that Stwl binds upstream of transcription start sites and localizes to heterochromatic sequences. We also show that Stwl is enriched at repetitive sequences associated with telomeres. Finally, we identify binding motifs that are shared with known insulator binding proteins. We propose that Stwl affects gene regulation by binding insulators and establishing chromatin boundaries.

A large area, square-gate Metal-Oxide/Insulator-Semiconductor (MOS or MIS) structured `Spatial Light Modulator’ has been proposed for the Terahertz (THz) imaging at room temperature. This theoretical study has been done entirely by using the MATLAB platform. The 1D Poisson’s equation has been solved iteratively by Euler’s method with the exact Fermi-Dirac integral for n-doped Si-MOS and GaAs- MIS capacitors in deep accumulation mode. Free carrier density and the potential profile have been found for the degenerate case. The results have been compared with the analytical method, which is approximated by Boltzmann statistics, and clearly, show the difference between the degenerate case and non-degenerate Boltzmann approximation at higher bias. Then the sheet carrier density was calculated by performing the numerical integration over the depth of accumulation. The mobility was calculated for various scattering mechanisms at room temperature, and the total mobility was found by using Matthiessen’s rule. The mobility and free carrier density were then used for calculating the bulk conductivity of the device. The sheet conductance and sheet resistance were found by the numerical integration of the bulk conductivity over the depth of accumulation. The sheet resistance is the DC resistance and was scaled to THz frequencies by using the Drude model. Then a lossless two-port transmission line model was adopted for studying the transmittances of the THz signal through the MOS or MIS devices for different bias and doping concentration and calculated the depth of modulation was calculated Vs frequency between 0.1 and 1 THz. In contrast to the GaAs-MIS device, it has been found that the depth of modulation of the Si-MOS device is much higher.The switching time has been calculated as the 10% to 90% charging time of the interface capacitor by solving the equivalent large-signal RC circuit. The GaAs-MIS displays lower switching time than Si-MOS because GaAs-MIS offers lower interface capacitance than that of the Si-MOS at the same interface bias. The 3dB bandwidth of the modulator has been estimated by assuming the linear RC circuit relations. Although the GaAs-MIS exhibited higher bandwidth than that of Si-MOS, both devices are still promising for the possible fabrication of spatial light modulator for THz imaging.

Eukaryotic chromatin insulators play an essential role in regulating gene expression and modifying nuclear architecture by organizing the higher-order chromatin structure in response to cellular and developmental cues. The details on how insulators function in this capacity are not completely understood. Five different types of insulators have been identified in Drosophila. Each functional insulator consists of an insulator DNA response element bound by an insulator protein, which recognizes specific DNA sequences. Each type of insulator functions individually as well as collaboratively. Except for the Su(Hw) insulator protein, the other insulator proteins are necessary for viability considering loss of Su(Hw) only interrupts insulator function and causes female sterility. It has been suggested that Su(Hw) may play a separate role in these two functions. To gain a better understanding of Su(Hw), its functions were studied using female germline development as a model system, and the mechanisms of its regulation were studied using an in vitro cell culture system. This study examined the critical function of Su(Hw) in both gene regulation and genome organization during oogenesis. Chapter one describes a remarkable ring canal developmental defect phenotype first identified and characterized in su(Hw) mutants, and this phenotype may contribute to female infertility. Chapter two details a newly discovered role of Su(Hw) in maintaining the genome integrity of germline cells. Loss of Su(Hw) causes accumulation of double strand breaks (DSBs), further triggering DNA damage signaling. Genome instability causes developmental defects resulting in incomplete oogenesis and consequent female sterility. To understand insulator function regulatory mechanisms, Drosophila Schneider 2 cells (S2 cells), were used as the system for investigation. Chapter three demonstrates that Su(Hw) was identified at a novel sub-cellular location within the midbody during mitotic telophase, and SUMOylation and phosphorylation may play a role in the functional regulation and sub-cellular localization of Su(Hw). Our work proposes that in spite of regulating gene expression, the Su(Hw) insulator also plays a critical role in maintaining genome stability by directing higher-order organization of the chromatin structure. Moreover, the protein-protein interactions and sub-cellular localization of Su(Hw) may regulate its function, and this functionality control may be fine-tuned by post-translational modifications.

Chromatin insulators are short DNA sequences that, together with enhancers and silencers, orchestrate gene transcription through DNA-protein interactions in eukaryotic genomes. It has been proposed that insulators operate at the chromatin level by generating functionally independent higher-order chromatin domains. Insulators may maintain the integrity of such domains using two properties: blocking enhancer-promoter interactions and blocking heterochromatin spreading. The gypsy insulator of Drosophila was identified as a region of the gypsy retrovirus responsible for the production of tissue-specific mutations in many genes. The Suppressor of Hairy wing [Su(Hw)] protein contains 12 zinc fingers that specifically bind the gypsy insulator. Upon DNA binding, Su(Hw) recruits a second protein, Modifier of Mdg4 67.2 [Mod(mdg4) 67.2], and the interaction of both proteins is required for insulator function in vivo. We have found that three different arrays of gypsy retrovirus insertions in a yellow transgene result in unique yellow phenotypes, showing that the enhancer-blocking activity of the Drosophila gypsy insulators depends on the relative orientation of the gypsy retroviruses on the chromosome. We also observed from transgenic lines with gypsy retrovirus or insulator insertions that interaction of insulators may be regulated by active enhancers according to the relative positions of the insulators flanking the enhancers. Moreover, we show that gypsy insulators can positively modulate yellow activation and result in wild-type levels of expression when placed upstream of enhancers in yellow transgenes in which enhancers are placed out of context by &#:-DNA spacers and fail to reproduce the expression levels of yellow in wings and body cuticle. Our results provide evidence indicating that this phenomenon is independent of the boundary activity. Genetic analysis using mod(mdg4)67.2 mutant lines containing gypsy retrovirus insertions revealed that the gypsy insulator may be placed close to the yellow promoter region and be intimately involved in transcriptional activation and repression. Therefore, we suggest that insulators may also function by mediating long range interactions between enhancers and promoters.

Triboelectric charging, also known as contact charging, is a process that occurs when two initially neutral surfaces are in contact, transfer charge, and upon separation, remain electrically charged. This charging occurs in a wide range of contexts, including industrial applications such as fluidized beds, pharmaceuticals, dust explosions and pneumatic conveying, and natural phenomena such as sand storms, dust devils, lightning and volcanic plumes. The mechanism of triboelectrification of granular materials is poorly understood, especially in single component systems. Triboelectric charging of chemically uniform, insulating granular materials with a broad size distribution is generally known to exhibit bipolar charge segregation, characterized by smaller negatively-charged particle and larger positively-charge particles. This study focuses on the development of experiments to validate previously accepted theory and experimental observations of bipolar charging in these systems. Samples of soda lime glass beads with bimodal size distributions are initially charged in a flow apparatus that induces only particle-particle interactions in a controlled environment. Particles are separated and characterized by their charge polarity and sized using optical methods. Charging behavior is found to be intimately coupled to the relative size and mass concentration of the particle size distribution with smaller particles tending to charge negatively and larger particles charging positively. Several single component systems are examined where this phenomenon occurs including polyethylene resin particle, glass beads, and Mars simulant (JSC-1 Mars simulant). These results are explained by a population balance model, in which the charge segregation occurs from an asymmetrical transfer of a negative species (i.e. electrons or hydroxide ions) between small and large particles.

As scaling continues in the semiconductor industry, silicon-on-insulator (SOI) wafers are increasingly becoming the substrate of choice, due to higher channel mobility, effective device isolation, reduced short channel effects, minimized parasitic capacitance, and therefore higher speed, compared to a regular silicon wafer. Current methods of SOI wafer production, however, will have difficulty achieving the desired silicon device layer and buried oxide insulator layer thicknesses and eliminating interface roughness as scaling proceeds. We propose "Floating Epitaxy SOI" as a novel method of SOI production utilizing an all in-situ growth process. Floating Epitaxy SOI involves Molecular Beam Epitaxy deposition of an epitaxial template oxide, oxidizing through the epitaxial template layer to establish the insulation layer, and silicon growth on top of the epitaxial template oxide layer (which is now "floating" on top of an amorphous oxide layer). The key to this process is the epitaxial oxide template layer, which must deposit on the silicon substrate as an atomically smooth film with a lattice parameter close to that of silicon and must be sufficiently stable in both an oxygen an in vacuum annealing to relatively high temperature to achieve Floating Epitaxy SOI. Although many researchers have examined epitaxial oxides on silicon, this study focuses on epitaxial films over large area substrates, while virtually all other studies report on growth on small substrate sizes. Also, the oxide stability limits on silicon in vacuum have not been thoroughly established by previous work, and are investigated here. The growth and thermal stability of this epitaxial oxide template layer are discussed, as well as brief results for through-oxidation "floating" of the template oxide layer and silicon growth experiments. BaO, SrO, CaO, Ba[subscript 1-x]Sr[subscript x]O, SrTiO₃, CaTiO₃, and Ca[subscript 1-x]Sr[subscript x]TiO₃ were successfully epitaxially deposited on Si(001) substrates. A 64:36 Ba:Sr ratio was used for the solid solution of Ba[subscript 1-x]Sr[subscript x]O, in order to achieve close lattice matching with silicon; a 50:50 Ca:Sr ratio was used initially for the Ca[subscript 1-x]Sr[subscript x]TiO₃ solid solution, an attempt to mediate SrTiO₃'s 2% lattice mismatch with silicon and CaTiO₃'s orthorhombic structure. Alloying SrTiO₃ with calcium to alter the lattice parameter has not been studied much to this point in thin films, and this is the first demonstration of Ca[subscript 1-x]Sr[subscript x]TiO₃ and CaTiO₃ thin films grown directly on silicon. Reflection High Energy Electron Diffraction patterns of both Ba[subscript 1-x]Sr[subscript x]O and Ca[subscript 1-x]Sr[subscript x]TiO₃ indicated high quality 2D epitaxial films. A thin (3 monolayer) film of Ba[subscript 1-x]Sr[subscript x]O is stable on silicon to 535°C in vacuum, while a 5 monolayer Ca[subscript 1-x]Sr[subscript x]TiO₃ film survives to 740°C in vacuum, but roughens from a 2D toward a 3D surface above ˜650°C. Of the epitaxial oxides studied, the solid solution Ca[subscript 1-x}Sr[subscript x]TiO₃ would be the best choice for Floating Epitaxy SOI, based on epitaxial growth quality and stability. High-resolution TEM indicates the presence of an amorphous interfacial layer at the SrTiO₃Si interface, as grown. X-ray diffraction confirms an epitaxial film, with a lattice parameter larger than that of bulk SrTiO₃, likely due to oxygen deficiency in the film. Annealing 17.5nm SrTiO₃Si(001) at 800°C in 5.5 Torr of oxygen for 30 minutes results in an equivalent oxide thickness of 10.3nm, sufficient for scaling to 2020. X-ray diffraction after annealing reveals a still-epitaxial SrTiO₃ film, with sharper 2θ and χ peaks and a lattice parameter closer to that of bulk SrTiO₃. These results validate the "floating" epitaxy approach: an epitaxial film remains on top of an amorphous insulator, after through-oxidation of the substrate. Direct deposition of epitaxial silicon on Ca[subscript 1-x]Sr[subscript x]TiO₃ and solid-phase epitaxy of silicon on a CaTiO₃ film are promising, but interface engineering or a surfactant may be required to achieve a high quality, single crystal silicon layer.

This thesis investigates the electronic structure of 3d transition metal (TM) oxides. Many different electron spectroscopy and x-ray absorption spectroscopy (XAS) measurements have been performed on a sequence of transition metal oxides NiO, CoO, FeO, Fe$\sb2$O$\sb3$, Fe$\sb3$O$\sb4$, MnO, Cr$\sb2$O$\sb3$, (V$\sb{1-x}$M$\sb{x}$)$\sb2$O$\sb3$ (M = Cr,Ti), and Ti$\sb2$O$\sb3$. XAS and resonance photoemission spectroscopy (RESPES) studies were made at the TM 2p and oxygen 1s edges, and the photoemission spectroscopy (PES) work also includes high resolution, variation of temperature studies of the metal-insulator (MI) 'Verwey' transition in Fe$\sb3$O$\sb4$ and the famous MI transition in the V$\sb2$O$\sb3$ system. In this thesis, I present various new spectroscopic data, suggest a new physical picture for the early TM oxides in framework of the Anderson model Hamiltonian and discuss new interpretations of the two unsolved metal-insulator transition problems. The systematic study for the sequence leads to a reclassification of early TM oxides from a traditional Mott-Hubbard picture to one using the Anderson Hamiltonian with very strong metal-oxygen hybridization. The lowest lying PES states are not of the $d\sp{n-l}$ character, but are bound states of mixed configuration character pushed out of the oxygen band, toward the lowest one electron addition state. The occurrence of a gap is then controlled by the strong hybridization, which also pushes bound state satellites out of the oxygen 2p band at high binding energies. (V$\sb{1-x}$M$\sb{x}$)$\sb2$O$\sb3$ (M = Ti, Cr) system shows a complex phase diagram which contains antiferromagnetic insulating, paramagnetic metallic, and paramagnetic insulating phases. Varying the temperature through the MI transitions, I observed not only gap openings in the high resolution spectra but also spectral changes in all the measured spectra. The spectral changes through the MI transitions are well explained by the variation of the V $3d$-O2p hybridization T and the charge transfer energy $\Delta$ as proposed in the new picture. The new data also enable us to estimate the size of band gap in both the low T and the high T insulating phase. The spectroscopic study on the valence of the dopants in the (V$\sb{1-x}$M$\sb{x}$)$\sb2$O$\sb3$ system shows interesting results. The valence of Ti is not 3+, as in Ti$\sb2$O$\sb3$, but is 4+, as in SrTiO$\sb3$, while that of Cr is as expected 3+, as in Cr$\sb2$O$\sb3$. In Fe$\sb3$O$\sb4$, XAS and RESPES at the Fe 2p edge enable resolution and observation of separate Fe valence states even above the transition temperature T$\sb{V}$. On heating through T$\sb{V}$ the electrical gap is not collapsed, but merely reduced by $\sim$50meV, showing that a metal-insulator transition does not occur. This change in the gap is perfectly consistent with the two orders of magnitude conductivity jump at T$\sb{V}$. These new spectroscopic data allow us to construct an energy diagram in connection with the Verwey transition.

Microstrip-based monolithic microwave integrated circuits (MMIC's) are widely used; those fabricated on semiconducting substrates are compatible with optical and other control technologies where substrate losses can be appreciable. A general technique for analyzing shielded microstrip transmission structures fabricated on lossy, multiple layer substrates is developed to address problems of this type. The surface current maintained on the metallized microstrip region is obtained by solving an integral equation. The propagation constant and characteristic impedance of several metal-semiconductor-insulator (MIS) microstrip transmission lines are computed using the theory presented and compared to measured and published data. Various types of basic discontinuities are characterized in terms of generalized scattering parameters and the fractional powers dissipated by some MIS structures are investigated. Overall, the comparisons between theory and measurement are favorable and support the validity of the method given.