BIOMERIT Research Centre (BRC) - Doctoral Theses

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    Investigation of the high-frequency effects in Mn-Zn ferrites for EMI filter applications
    (University College Cork, 2022-08-22) Kącki, Marcin; Hayes, John G.; Ryłko, Marek S.; Sullivan, Charles R.; SMA Magnetics sp. z o.o.
    This thesis focuses on the analysis, identification, and experimental investigation of the high-frequency effects encountered within the magnetic core when used in high-frequency, high-power electromagnetic interference (EMI) filters. These applications require cost-optimized, high-performance, and high-power-density magnetic components. As the manufacturers’ material specifications usually do not provide sufficient information to optimize the design, this thesis develops new methods to determine the high-frequency properties of Mn-Zn ferrites up to 20 MHz. Complex permeability and permittivity, as well as specific power loss, are typically provided as one value by the manufacturer, regardless of the core shape and size. Therefore, various magnetic materials are characterized for their complex permeability and permittivity. These two parameters are of differentiated physical origins, and so two independent measurement fixtures are developed and built. The impacts of physical size, temperature and force on complex permeability and permittivity are also considered. The detailed analysis of magnetic flux is introduced based on a 1-D analytical model, a novel shell-based transmission-line model, and finally, based on the FEM and Maxwell 3D eddy-current field solver. These models are used to calculate the complex permeability characteristics for various core sizes made of two materials: 3E10 and 3F36. A complete experimental validation is presented for the calculated values. The analytical methods show a very good correlation with the experimental measurements. The novel shell-based transmission-line model has the best accuracy, and the calculation can be implemented into simulation of a higher-order system or into any other magnetic component design algorithm. Flux verification methods are developed which use precisely-bored cores to accurately predict flux distribution. The results of the flux propagation, starting from the simple three-hole model up to the advanced four-section model confirm that the magnetic flux distribution is affected by frequency-dependent dynamic effects. Flux distributions was experimentally measured for T50 and T80 cores made of 3E10 and 3F36 material. Results are consistent with the FEM simulations and help in the development of a more accurate analytical model. A novel laminated-core common mode choke (CMC) is developed and presented in this thesis. The presented CMC core structure divides the conduction path into sub-regions which allowing for the reduction of the high-frequency effects. Laminated cores, made of several Mn-Zn ferrite materials, were tested and special attention is paid to the effect of magnetic material selection, core size and lamination thickness on the core high-frequency performance. Common mode insertion loss characteristic for the novel CMC shows that laminated ferrite structure give rise to significant attenuation improvement.
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    Understanding the molecular mechanism through which aspirated bile triggers chronic Pseudomonas aeruginosa infections in respiratory disease
    (University College Cork, 2019) Flynn, Stephanie; O'Gara, Fergal; Reen, F.Jerry; Irish Research Council for Science, Engineering and Technology
    The opportunistic pathogen Pseudomonas aeruginosa is the leading cause of morbidity and mortality in Cystic Fibrosis (CF) patients. Extensive genomic adaptation of this organism facilitates its emergence as a dominant organism within the lung microbial community and to its ability to chronically persist within the CF airways. The environmental and host factors contributing to the success of this species in vivo have been the subject of intensive research efforts. Gastro-oesophageal reflux (GOR) has recently emerged as a major co-morbidity in CF and a range of other respiratory conditions and is associated with the presence of bile acids in the lungs of CF patients, a consequence of micro-aspiration of refluxed gastric contents. This thesis aimed to investigate the impact that bile exerts on the global lung microbiota and the key CF associated pathogen P. aeruginosa. The detection of bile acids in paediatric CF patients using liquid chromatography mass spectrometry (LC-MS) analysis correlated with a reduction in lung microbial biodiversity and the emergence of dominant respiratory pathogens including P. aeruginosa. Bile acids may contribute to the progressive restructuring of the lung microbiota towards a pathogen dominated state associated with worse clinical outcomes. Bile and the active component bile acids were found to be capable of triggering P. aeruginosa to transition to a chronic, antibiotic tolerant lifestyle through a combination of transcriptional and phenotypic responses. Functional screens based on biofilm formation and growth on bile identified key two component systems mediating the biofilm response to bile with a connection to central metabolism becoming apparent. The latter screen identified the glyoxylate shunt as a key breakpoint in the suppression of redox potential as part of the bile response. Bile was also found to be capable of selecting for genetic variants in an in vitro system known to mimic conditions found within the CF lung environment. Pigmented derivatives emerged exclusively in the presence of bile with genome sequencing identifying single nucleotide polymorphisms (SNPs) in quorum sensing (lasR) and both the pyocyanin (phzS) and pyomelanin (hmgA) biosynthetic pathways. These mutations have been previously described in various clinical isolates of P. aeruginosa. Loss of Pseudomonas Quinolone Signal (PQS) production in the pigmented variants underpinned the loss of redox suppression in response to bile, perhaps a consequence of the anti-oxidant/pro-oxidant activities attributed to the PQS signalling molecule. Bile is therefore capable of influencing the evolutionary trajectory of this respiratory pathogen, a key finding in understanding the emergence of genotypic and phenotypic heterogeneity within the lungs of patients with respiratory disease. Collectively, this research supports the role for bile in the progression of chronic infection in CF through its impact on P. aeruginosa and other respiratory pathogens. Therefore, the early detection and profiling of bile acids utilising rapid point of care devices could lead to the identification of high risk paediatric patients and to the development of increasingly effective intervention strategies to prevent the establishment of chronic respiratory microbiota.