Effect of dielectric thickness on the bandwidth of planar transformers

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017This research has considered an idealistic non-interleaved planar transformer wherein only the electromagnetic parasitic capacitive and inductive elements arising out of the transformer geometry are taken into account, without considering material limitations. A suitable model for the planar transformer is used to analyse its frequency and power transfer characteristics; this model was validated by three dimensional electromagnetic simulations of various planar transformer structures in FEKO simulation software. The capacitive and inductive parasitics in this model have been found to be functions of the dielectric thickness. The theoretical bandwidth for the planar transformer is defined in this research as a function of dielectric thickness. The effect of dielectric thickness of the transformer windings on the bandwidth of the transformer is analysed, based on the premise that the inherent parasitic capacitive and inductive elements would affect the transfer characteristics of the transformer. Upon conclusion of this analysis, it is found that the dielectric thickness of a planar transformer can be optimised such as to present an optimised bandwidth. A closed form analytic expression for the optimum dielectric thickness value is derived and presented in this research. In a design example of a 4:1 50W transformer presented in this research, it has been shown that the bandwidth can be improved by 384%, along with a power density improvement of 45%, upon choosing of an optimum dielectric thickness of 0.156mm to replace a standard 0.4mm thick dielectric. It should be noted that the results derived in this research are purely theoretical, justified by many idealisations and assumptions that are argued throughout the research. It is thus expected that practical results should at best approach the theoretical results, due to the known non-ideal nature of reality.CK201

Ferromagnetism in SnO₂ Doped with Transition Metals (Fe, Mn and Ni) for Spintronics Application: A Review of Experimental Status

Due to their potential application in the field of spintronics, the discovery of various types of oxide-based dilute magnetic semiconductors (ODMS) materials that might work at practical room temperature ferromagnetism (RTFM) has recently attracted great attention. Among ODMS materials, transition metal™ doped tin oxide (SnO2) compounds are important for the investigation of ferromagnetism due to its special important property such as high chemical stability, high carrier density, n-type behavior and trait long range ferromagnetism. However, the question of understanding the mechanism of ferromagnetism (FM) process is still not fully understood in these materials, due to unable to know exactly whether its FM property arises from the nature of the intrinsic property or secondary phases of the material. According to the results from many literature surveys, the mechanism of magnetic ordering responsible for magnetic exchange interaction in these materials is highly affected by oxygen vacancy, defects, dopant types and concentration, temperature, sample preparation method and so on. In this chapter, we reviewed the mechanism of ferromagnetism observed of Ni, Mn and Fe-doped SnO2 materials

Fast and Coherent Control of Optically-Addressable Spin-Qubits in Diamond

Qubits are the basic building blocks of quantum computers. Although various qubit implementations exist and are subjects of various research and industry efforts, spin-based qubits are fast becoming an attractive candidate to build quantum processor architectures, mainly due to their simplicity. In this thesis I examine spin-qubits realized within color centers in diamond. Diamond as a host material provides a deep band gap, allowing optical transparency, whilst capable of hosting a variety of vacancy-type defects formed by implantation of nitrogen, silicon, as well as recently germanium and tin nuclei. These features allow diamond based color centers to be addressed using various optical measurement techniques involving suitable lasers. The thesis focuses on two core aspects of qubit control: speed and coherence. Fast control is required to perform gate operations within inherent coherence times of the qubit. Ideally, fast control is also paired with long coherence times. These concepts are explored experimentally and theoretically using qubit control strategies including spin-resonance, indirect control and dressed control in their respective chapters. The thesis thus contains three main chapters, respectively addressing the above three qubit control strategies: --Up to 48 MHz electron spin control of nitrogen-vacancy ensemble is experimentally demonstrated using a KTaO3 dielectric resonator at cryogenic temperatures. --Megahertz-rate Indirect control is theoretically shown to work in the host nuclear spin of a silicon-vacancy color center. --Dressed control using the SMART protocol is experimentally demonstrated to achieve high fidelity gates in nitrogen-vacancy centers at room temperature

All-electron ab-initio\mathrm{\textit{ab-initio}} hyperfine coupling of Si-, Ge- and Sn-vacancy defects in diamond

Colour centres in diamond are attractive candidates for numerous quantum applications due to their good optical properties and long spin coherence times. They also provide access to the even longer coherence of hyperfine coupled nuclear spins in their environment. While the NV centre is well studied, both in experiment and theory, the hyperfine couplings in the more novel centres (SiV, GeV, and SnV) are still largely unknown. Here we report on the first all-electron \textit{ab-initio} calculations of the hyperfine constants for SiV, GeV, and SnV defects in diamond, both for the respective defect atoms ($^{29}$Si, $^{73}$Ge, $^{117}$Sn, $^{119}$Sn), as well as for the surrounding $^{13}$C atoms. Furthermore, we calculate the nuclear quadrupole moments of the GeV defect. We vary the Hartree-Fock mixing parameter for Perdew-Burke-Ernzerhof (PBE) exchange correlation functional and show that the hyperfine couplings of the defect atoms have a linear dependence on the mixing percentage. We calculate the inverse dielectric constant to predict an \textit{ab-initio} mixing percentage. The final hyperfine coupling predictions are close to the experimental values available in the literature. Our results will help to guide future novel experiments on these defects.Comment: 8 pages, 3 figures. Supplementary data (Tables S1-S12) in sourc

Coherent control of NV- centers in diamond in a quantum teaching lab

The room temperature compatibility of the negatively-charged nitrogen-vacancy (NV-) in diamond makes it the ideal quantum system for a university teaching lab. Here, we describe a low-cost experimental setup for coherent control experiments on the electronic spin state of the NV- center. We implement spin-relaxation measurements, optically-detected magnetic resonance, Rabi oscillations, and dynamical decoupling sequences on an ensemble of NV- centers. The relatively short times required to perform each of these experiments (<10 minutes) demonstrate the feasibility of the setup in a teaching lab. Learning outcomes include basic understanding of quantum spin systems, magnetic resonance, the rotating frame, Bloch spheres, and pulse sequence development.Comment: 16 pages, 9 figure

Observing hyperfine interactions of NV centers in diamond in an advanced quantum teaching lab

The negatively charged nitrogen-vacancy (NV$^-$) center in diamond is a model quantum system for university teaching labs due to its room-temperature compatibility and cost-effective operation. Based on the low-cost experimental setup that we have developed and described for the coherent control of the electronic spin (Sewani et al.), we introduce and explain here a number of more advanced experiments that probe the electron-nuclear interaction between the \nv electronic and the \NN~and \CC~nuclear spins. Optically-detected magnetic resonance (ODMR), Rabi oscillations, Ramsey fringe experiments, and Hahn echo sequences are implemented to demonstrate how the nuclear spins interact with the electron spins. Most experiments only require 15 minutes of measurement time and can, therefore, be completed within one teaching lab.Comment: Extension of the teaching lab experiments described in Sewani et al., Coherent control of NV centers in diamond in a quantum teaching lab. American Journal of Physics 88, 1156 (2020). https://doi.org/10.1119/10.000190

Regulation of Monocyte Functional Heterogeneity by miR-146a and Relb

Monocytes serve as a central defense system against infection and injury but can also promote pathological inflammatory responses. Considering the evidence that monocytes exist in at least two subsets committed to divergent functions, we investigated whether distinct factors regulate the balance between monocyte subset responses in vivo. We identified a microRNA (miRNA), miR-146a, which is differentially regulated both in mouse (Ly-6C^(hi)/Ly-6C^(lo)) and human (CD14^(hi)/CD14^(lo)CD16^+) monocyte subsets. The single miRNA controlled the amplitude of the Ly-6C^(hi) monocyte response during inflammatory challenge whereas it did not affect Ly-6C^(lo) cells. miR-146a-mediated regulation was cell-intrinsic and depended on Relb, a member of the noncanonical NF-κB/Rel family, which we identified as a direct miR-146a target. These observations not only provide mechanistic insights into the molecular events that regulate responses mediated by committed monocyte precursor populations but also identify targets for manipulating Ly-6C^(hi) monocyte responses while sparing Ly-6C^(lo) monocyte activity

MiR-29b replacement inhibits proteasomes and disrupts aggresome+autophagosome formation to enhance the antimyeloma benefit of bortezomib

Evading apoptosis is a cancer hallmark that remains a serious obstacle in current treatment approaches. Although proteasome inhibitors (PIs) have transformed management of multiple myeloma (MM), drug resistance emerges through induction of the aggresome+autophagy pathway as a compensatory protein clearance mechanism. Genome-wide profiling identified microRNAs (miRs) differentially expressed in bortezomib-resistant myeloma cells compared with drug-naive cells. The effect of individual miRs on proteasomal degradation of short-lived fluorescent reporter proteins was then determined in live cells. MiR-29b was significantly reduced in bortezomib-resistant cells as well as in cells resistant to second-generation PIs carfilzomib and ixazomib. Luciferase reporter assays demonstrated that miR-29b targeted PSME4 that encodes the proteasome activator PA200. Synthetically engineered miR-29b replacements impaired the growth of myeloma cells, patient tumor cells and xenotransplants. MiR-29b replacements also decreased PA200 association with proteasomes, reduced the proteasome's peptidase activity and inhibited ornithine decarboxylase turnover, a proteasome substrate degraded through ubiquitin-independent mechanisms. Immunofluorescence studies revealed that miR-29b replacements enhanced the bortezomib-induced accumulation of ubiquitinated proteins but did not reveal aggresome or autophagosome formation. Taken together, our study identifies miR-29b replacements as the first-in-class miR-based PIs that also disrupt the autophagy pathway and highlight their potential to synergistically enhance the antimyeloma effect of bortezomib