Energy storage systems for wave energy converters and microgrids

The thesis initially gives an overview of the wave industry and the current state of some of the leading technologies as well as the energy storage systems that are inherently part of the power take-off mechanism. The benefits of electrical energy storage systems for wave energy converters are then outlined as well as the key parameters required from them. The options for storage systems are investigated and the reasons for examining supercapacitors and lithium-ion batteries in more detail are shown. The thesis then focusses on a particular type of offshore wave energy converter in its analysis, the backward bent duct buoy employing a Wells turbine. Variable speed strategies from the research literature which make use of the energy stored in the turbine inertia are examined for this system, and based on this analysis an appropriate scheme is selected. A supercapacitor power smoothing approach is presented in conjunction with the variable speed strategy. As long component lifetime is a requirement for offshore wave energy converters, a computer-controlled test rig has been built to validate supercapacitor lifetimes to manufacturer’s specifications. The test rig is also utilised to determine the effect of temperature on supercapacitors, and determine application lifetime. Cycle testing is carried out on individual supercapacitors at room temperature, and also at rated temperature utilising a thermal chamber and equipment programmed through the general purpose interface bus by Matlab. Application testing is carried out using time-compressed scaled-power profiles from the model to allow a comparison of lifetime degradation. Further applications of supercapacitors in offshore wave energy converters are then explored. These include start-up of the non-self-starting Wells turbine, and low-voltage ride-through examined to the limits specified in the Irish grid code for wind turbines. These applications are investigated with a more complete model of the system that includes a detailed back-to-back converter coupling a permanent magnet synchronous generator to the grid. Supercapacitors have been utilised in combination with battery systems for many applications to aid with peak power requirements and have been shown to improve the performance of these energy storage systems. The design, implementation, and construction of coupling a 5 kW h lithium-ion battery to a microgrid are described. The high voltage battery employed a continuous power rating of 10 kW and was designed for the future EV market with a controller area network interface. This build gives a general insight to some of the engineering, planning, safety, and cost requirements of implementing a high power energy storage system near or on an offshore device for interface to a microgrid or grid.

The Rpf/DSF system and the regulation of virulence in the plant pathogen Xanthomonas campestris

The full virulence of Xanthomonas campestris pv. campestris (Xcc) to plants depends upon cell-to-cell signalling mediated by the signal molecule DSF (for diffusible signal factor), that has been characterised as cis-11-methyl-2-dodecenoic acid. DSF-mediated signalling regulates motility, biofilm dynamics and the synthesis of particular virulence determinants. The synthesis and perception of the DSF signal molecule involves products of the rpf (regulation of pathogenicity factors) gene cluster. DSF synthesis is fully dependent on RpfF, which encodes a putative enoyl-CoA hydratase. A two-component system, comprising the complex sensor histidine kinase RpfC and the HD-GYP domain regulator RpfG, is implicated in DSF perception. The HD-GYP domain of RpfG is a phosphodiesterase working on cyclic di-GMP; DSF perception is thereby linked to the turnover of this intracellular second messenger. The full range of regulatory influences of the Rpf/DSF system and of cyclic di-GMP in Xcc has yet to be established. In order to further characterise the Rpf/DSF regulatory network in Xcc, a proteomic approach was used to compare protein expression in the wildtype and defined rpf mutants. This work shows that the Rpf/DSF system regulates a range of biological functions that are associated with virulence and biofilm formation but also reveals new functions mediated by DSF regulation. These functions include antibiotic resistance, detoxification and stress tolerance. Mutational analysis showed that several of these regulated protein functions contribute to virulence in Chinese radish. Interestingly, it was demonstrated that different patterns of protein expression are associated with mutations of rpfF, rpfC and rpfG. This suggests that RpfG and RpfC have broader roles in regulation other than perception and transduction of DSF. Taken together, this analysis indicates the broad and complex regulatory role of Rpf/DSF system and identifies a number of new functions under Rpf/DSF control, which were shown to play a role in virulence.

Thuricin CD: a potential therapeutic targeted against Clostridium difficile-associated diarrhea (CDAD)

Clostridium difficile is mainly a nosocomial pathogen and is a significant cause of antibioticassociated diarrhea. It is also implicated in the majority of cases of pseudomembranous colitis. The main etiological agent of C. difficile-associated diarrhea (CDAD) is perturbations to the gut microbiota by broad-spectrum antibiotics. Recently, thuricin CD, a two-peptide narrow spectrum sactibiotic bacteriocin with potent activity against C. difficile has been discovered. It is produced by Bacillus thuringiensis DPC6431. The efficacy of thuricin CD against a range of C. difficile clinical isolates has been determined in the form of minimum inhibitory concentration (MIC) values and compared to metronidazole, vancomycin, ramoplanin and actagardine in this thesis. Furthermore, by assessing paired combinations of the above-mentioned antimicrobials, it was determined that ramoplanin and actagardine function in a synergistic manner against the majority of C. difficile isolates. The functions of the genes in the thuricin CD gene cluster have also been elucidated by cloning the cluster and expressing thuricin CD in a heterologous Bacillus subtilis host and are described herein. In addition, the immunity mechanisms employed by the B. thuringiensis DPC6431 producer to protect itself from the antimicrobial actions of thuricin CD have also been elucidated. It has been shown that a small immunity peptide, TrnI, is involved in thuricin CD immunity, most likely by intercepting the thuricin CD peptides and/or blocking their access to the thuricin CD receptor. This immunity peptide and also the ABC-transporter system TrnFG serve to protect the B. thuringiensis host against thuricin CD.

Psychosocial well-being of African migrant children in Ireland: a cultural orientation

This thesis explores the psychosocial wellbeing of sub-Saharan African migrant children in Ireland. A sociocultural ecological (Psychosocial Working Group, 2003) and resilience lens (Masten & Obradovic, 2008; Ungar, 2011) is used to analyse the experiences of African migrant children in Ireland. The research strategy employs a mixed-methods design, combining both an etic and emic perspective. Grounded theory inquiry (Strauss and Corbin, 1994) explores the experiences of African migrant children in Ireland by drawing on multi-sited observations over a period of six months in 2009, and on interviews and focus group discussions conducted with African children (aged 13-18), mothers and fathers. An emically derived ‘African Migrant Child Psychosocial Well-being’ scale was developed by drawing on data gathered through rapid ethnographic (RAE) free listing exercises carried out in Cork, Dublin and Dundalk with sixty-one participants (N=21 adults, N=28 15-18-year-olds, N=12 12-14-year-olds) and three African community key informants to elicit local understandings of psychosocial well-being. This newly developed scale was used alongside standardised measures of well-being to quantitatively measure the psychosocial adjustment of 233 African migrant children in Cork, Dublin and Dundalk aged 11-18. Findings indicate that the psychosocial wellbeing of the study population is satisfactory when benchmarked against the psychosocial health profile of Irish youth (Dooley & Fitzgerald, 2012). These findings are similar to trends reported in international literature in this field (Georgiades et al., 2006; Gonneke, Stevens, Vollebergh, 2008; Sampson et al., 2005). Study findings have implications for advancing psychosocial research methods with non-Western populations and on informing the practice of Irish professionals, mainly in the areas of teaching, psychology and community work.