Primary cilia are cellular organelles that protrude into the extracellular space, acting as antennas. They detect a wide range of chemical cues, including SHH and PDGF, as well as fluid flow, and they modulate downstream signalling systems, such as WNT and ERK. Due to this cue-sensing ability and the close association of the primary cilium with the centrosome the organelle is able to influence both cell cycle progression and cell migration. This work investigated the effect of mutations on two genes associated with primary cilia: Arl13b and Ift172. The effects of the HNN genotype of Arl13b and the WIM genotype of Ift172 on cell migration were assessed uniquely within the context of direct current electric fields. Both cell lines showed a decreased migratory response when compared to WT cells, despite no clear involvement of cilia in sensing the direction of the electric field. This corroborated with previous data of in vivo Arl13b cellular migration. Through the use of in utero electroporation the migratory deficits of IFT172 knock down were then confirmed in vivo in the developing mouse neocortex. Further in vitro investigation revealed a slower proliferation rate of HNN and WIM cells, though this was not confirmed in vivo after IFT172 knock down using a standard BrDU protocol. Nevertheless, further in vitro investigations revealed a wide variety of cell cycle and intracellular changes within both cell lines. The commonalities included lower numbers of cells in the S-phase and lower MAPK3 phosphorylation compared to WT, and differences such as GSK3β phosphorylation on Ser9. This work showed for the first time that ciliopathies affect galvanotaxis, and revealed fundamental commonalities in cell migration and proliferation between various ciliary mutations, as well as differences in specific signalling pathways. This will hopefully aid in developing future therapeutic interventions for ciliary diseases.

Assumindo elétrons e buracos se movimentando em suas bandas próprias e centros de recombinação independente para ambos, Hughes e Sokel calcularam as características e distribuição de cargas para o oxido de chumbo (PbO) quando este se encontra sob radiação. O cálculo também inclui a corrente de difusão e segundo os autores, esta possui um importante papel em muitos aspectos. Neste trabalho a característica para o PbO foi recalculado sem considerar a contribuição da corrente de difusão e essencialmente foi obtido o mesmo resultado. Foram desenvolvidos aproximações para baixo e alto campo. Em seguida, foram assumidos iguais parâmetros para ambos portadores (isto é, iguais mobilidades, tempos de captura, coeficientes de recombinação e densidades de centros de captura) e obtido as características para 18 combinações de três conjuntos de parâmetros convenientemente definidos. Aproximações de campo baixo e campo alto foram também derivadas para este caso / Assuming electron and hole bands and independent recombination centers or both carriers, Hughes and Sokel calculated the characteristics and charge distributions for lead oxide PbO under irradiation. The calculation also included the diffusion current and it was asserted that such a current was important in some aspects. In this work the characteristic for PbO was recalculated without the diffusion component and essentially the same result was obtained. Side this; approximations were derived for low and high fields. Next, assuming equal parameters for both carriers (that is, equal mobilities, trapping times, recombination rates and density of trap), characteristics were obtained for 18 combinations of three conveniently defined set of parameters. Low and high field approximation were also derived for this case

[pt] Este trabalho examina a viabilidade de construção, utilizando tecnologia nacional, de um sensor eletromagnético de velocidade e direção de fluidos, sendo considerado o caso particular de correntes marinhas. O projeto do sensor e os problemas técnicos de produção são apresentados e discutidos, assim como as medidas efetuadas em um protótipo. Considerações gerais sobre o tratamento dos sinais fornecidos pelo sensor também são expostas. / [en] This thesis presents a study of the feasibility of industrial production of an electromagnetic sensor for the measurement of fluid flow, using national available technology. The project of a prototype is developed for the special case of marine currents. The problems concerning the project and its implementation, as well as the measurements obtained from the prototype, are presented and discussed. The sensor signals processing is also examined in its general aspects.

Abstract Eddy currents and susceptibility differences are the most important sources that interfere with the quality of MR images in the presence of an artificial macroscopic object in the volume to be imaged. In this study, both of these factors have been examined. The findings show that the RF field is the most important cause of induced eddy currents when gradients with relatively slow slew rates are used. The induced eddy currents amplify or dampen the RF field with the result that the flip angle changes. At the proximal end in the vicinity of the hip prosthesis surface, there have been areas where the flip angle is nearly threefold compared to the reference flip angle. Areas with decreased flip angles have also been found near the surface of the prosthesis top. The incompleteness of the image due to eddy currents manifests as signal loss areas. Two different methods based on MRI were developed to estimate the susceptibility of a cylindrical object. One of them is based on geometrical distortions in SE magnitude images, while the other takes advantage of phase differences in GRE phase images. The estimate value of the Profile™ test hip prosthesis is χ = (170 ± 13) 10-6. A remapping method was selected to correct susceptibility image distortions. Correction was accomplished with pixel shifts in the frequency domain. The magnetic field distortions were measured using GRE phase images. The method was tested by simulations and by imaging a hip prosthesis in a water tank and in a human pelvis. The main limitations of the method described here are the loss of a single-valued correction map with higher susceptibility differences and the problems with phase unwrapping in phase images. Modulation transfer functions (MTF) were exploited to assess the effect of correction procedure. The corrected image of a prosthesis in a human hip after total hip arthroplasty appears to be equally sharp or slightly sharper than the corresponding original images. The computer programs written for this study are presented in an appendix.

M.Ing. / Along with the increased use of power-electronic devices, there has been an increase in the magnitudes of distorted currents. Much of the power-theory in use today was devised many decades ago, mostly for AC-systems with clean sinusoidal voltages and currents. Modem loads are more often no longer mostly linear. Against the background of a study in the basic mathematics underlying AC power theory, a few techniques concerned with per-frequency power were examined. In addition certain concerns surrounding the use of correlation indexes for the purposes of load identification were also examined.

Rip currents present a severe hazard to water users worldwide, resulting in over 100 drownings and thousands of lifeguard rescues annually. This thesis examines the demographics of who is effected by rip currents in the UK, what activity they are undertaking, when and where incidents occur, how much the public know, what people have experienced, and how best to educate them. Analysis of 7909 rip current lifeguard rescues (16777 people) across the UK between 2006-2013 highlighted the most at risk group, and subsequent target audience for education, to be male teenagers aged between 13-17 years old (n=2906, 17%). Geographically, the highest incidents occurred on the beaches in the Southwest of England (n=6911, 87%). Incidents mostly occurred outside of lifeguard flagged areas (n=4302, 54%) and mainly involved those using bodyboards (n=5290, 52%). Through the analysis of 407 public beach-based rip current and beach safety questionnaires, it was established that beach users have a poor understanding of rip currents (n=263, 65%) but a good perception of the beach safety flags (n=389, 96%). People with greater knowledge were typically educated by a lifeguard, enter the sea more frequently or have been caught in rip currents themselves. The experiences of 553 people caught in rip currents were analysed using an online questionnaire. The gender split was 69% male (n= 382) to 31% female (n= 171), indicating that males are caught in rip currents more than females. Swimming directly to shore against the rip followed an initial panic (n=108, 34%) for most people caught in a rip. Swimming parallel to the beach was the most remembered, advised, utilised, and promoted safety message. Respondents advocated the use of lifeguards to disseminate rip current safety messages. A new and unique rip current education programme was developed from the synthesis of these results. A lifeguard delivered a pilot programme to 185 teenagers in three schools and two community groups in the Southwest of England. This interactive pilot consisted of exercises using videos, photographs, news reports, and a swimming machine. Levels of rip current knowledge were evaluated before and after, and at regular intervals, to assess knowledge retention. The short-term effects after 3 months were positive, showing statistically significant (p < 0.0005) improvements in mean knowledge levels. This thesis provides a new contribution to the expanding field of social and behavioural rip current research. The development of a unique rip current education programme presents an alternative method for increasing public awareness, and supports the worldwide prevention of rip current incidents and fatalities.

The work described in this thesis consists of an investigation into the behaviour of the critical current density (Jc) of several different high temperature superconductors (HTSCs) as a function of temperature and applied magnetic field. The focus of this research has been to investigate the discrepancies which generally exist between magnetic and transport measurements on HTSCs. In order to do this a number of systems were selected with different weak link strengths, overall alignment and pinning characteristics. Systematic studies were carried out on these systems using both transport and magnetic techniques. The results obtained were compared to obtain a coherent picture of the relation between critical currents in HTSCs, their granularity and structure, and how this accounts for the differences in magnetic and transport measurements. The Jc of granular bulk sintered YBCO was measured as a function of magnetic field and orientation, and attempts made to fit the results obtained to theory. The results obtained indicate that hysteresis of Jc with field cannot be explained by flux trapping alone. Jc measurements were carried out on the 'hub-and-spoke' (H-S) grains of melt-processed YBCO thick films. These indicated that within each H-S grain the current is constrained to radial paths through the centre of the grain. This has major implications for the analysis of any measurements carried out on these samples, as well as for applications, as only a small fraction of the sample carries the applied current. Silver-clad tapes of Tl:1223 and Tl:2223 were measured in different temperatures, applied magnetic fields and orientations. The variation of Jc along the tape length was also measured to provide an estimate of their homogeneity. It was found that the processing route used in the production of these tapes had not aligned the superconductor within them, and also that the tape properties were not homogenous along their length. This probably arises from the crystal structure of the thallium materials. The Jcs of melt-processed thick films of Bi:2212 on silver substrates were measured as a function of temperature and applied magnetic field, and compared with results obtained from magnetic measurements obtained from a VSM. Attempts were made to fit these results to theory. The results obtained show clear scaling behaviour of Jc with T at constant B and imply that the variation in the form of the Jc versus T curves is due simply to the suppression of Tc with increasing applied field.

Current transfer behaviour in anisotropic superconducting bodies is the central topic of this thesis and focuses on the effect that the nonlinearity of the electric field dependence upon the local current density value and anisotropy have on the nature of current transport. The main motivation for this work was the desire for a better understanding of the conceptually difficult behaviour of current transport in superconducting bodies and examines current transfer quantitatively for a number of important problems on the macroscopic and microscopic scale. This behaviour is examined both experimentally and using computer models. The successful development of a powerful, robust and adaptable numerical model for analysing the complex current transfer behaviour has been the primary aim of this work. The range of parameters appropriate to macroscopic models of the Bi-2212 CRT system has been experimentally examined using a specifically constructed apparatus for the measurement of current transport characteristics. A study of the self-field properties of the Bi-2212 CRT material using a new experimental technique and mathematical analysis is presented and has allowed the importance of the self-field effect in the numerical model to be assessed. An essential requirement for the practical application of high current superconducting devices is the development of low resistance current contacts. The research presented examines this macroscopic current transfer problem and aims to explain experimentally observed current transfer characteristics at high applied currents. Existing models cannot explain these characteristics. Current transfer on the microscopic scale is also examined. Models of current transfer have been developed from descriptions of specific microstructures that are thought to characterise the microstructure of Bi-2223 and Bi-2212 silver-sheathed tapes. This thesis specifically presents modelling of current transfer between c-axis, low-angle c-axis and edge-on c-axis tilt oriented grain interfaces; the principal current transfer paths between individual current elements of the microstructural models of current flow in polycrystalline HTSs.

The method of magnetotellurics (MT) uses surface measurements of naturally-occurring electromagnetic fields to investigate the conductivity distribution within the Earth. In many interpretations it is adequate to represent the conductivity structure by a one-dimensional (1-D) model. Inferring information about this model from surface field measurements is a non-linear inverse problem. In this thesis, linearized construction and appraisal algorithms are developed for the 1-D MT inverse problem. To formulate a linearized approach, the forward operator is expanded in a generalized Taylor series and second-order terms are neglected. The resulting linear problem may be solved using techniques of linear inverse theory. Since higher-order terms are neglected, the linear problem is only approximate, and this process is repeated iteratively until an acceptable model is achieved. Linearized methods have the advantage that, with an appropriate transformation, a solution may be found which minimizes a particular functional of the model known as a model norm. By explicitly minimizing the model norm at each iteration, it is hypothesized that the final constructed model represents the global minimum of this functional; however, in practice, it is difficult to verify that a global (rather than local) minimum has been found. The linearization of the MT problem is considered in detail in this thesis by deriving complete expansions in terms of Fréchet differential series for several choices of response functional, and verifying that the responses are indeed Fréchet differentiable. The relative linearity of these responses is quantified by examining the ratio of non-linear to linear terms in order to determine the best choice for a linearized approach. In addition, the similitude equation for MT is considered as an alternative formulation to linearization and found to be inadequate in that it implicitly neglects first-order terms. Appropriate choices of the model norm allow linearized inversion algorithms to be formulated which minimize a measure of the model structure or of the deviation from a (known) base model. These inversions construct the minimum-structure and smallest-deviatoric model, respectively. In addition, minimizing I₂ model norms lead to smooth solutions which represent structure in terms of continuous gradients, whereas minimizing I₁ norms yield layered conductivity models with structural variations occurring discontinuously. These two formulations offer complementary representations of the Earth, and in practice, a complete interpretation should consider both. The algorithms developed here consider the model to be either conductivity or log conductivity, include an arbitrary weighting function in the model norm, and fit the data to a specified level of misfit: this provides considerable flexibility in constructing 1-D models from MT responses. Linearized inversions may also be formulated to construct extremal models which minimize or maximize localized conductivity averages of the model. These extremal models provide bounds for the average conductivity over the region of interest, and thus may be used to appraise model features. An efficient, robust appraisal algorithm has been developed using linear programming to extremize the conductivity averages. For optimal results, the extremal models must be geophysically reasonable, and bounding the total variation in order to limit unrealistic structure is an important constraint. Since the extremal models are constructed via linearized inversion, the possibility always exists that the computed bounds represent local rather than global extrema. In order to corroborate the results, extremal models are also computed using simulated annealing optimization. Simulated annealing makes no approximations and is well known for its inherent ability to avoid unfavourable local minima. Although the method is considerably slower than linearized analysis, it represents a general and interesting new appraisal technique. The construction and appraisal methods developed here are illustrated using synthetic test cases and MT field data collected as part of the LITHOPROBE project. In addition, the model construction techniques are used to analyze MT responses measured at a number of sites on Vancouver Island, Canada, to investigate the monitoring of local changes in conductivity as a precursor for earthquakes. MT responses measured at the same site over a period of four years are analyzed and indicate no significant changes in the conductivity (no earthquakes of magnitude greater than 3.0 occurred in this period). Conductivity profiles at a number of sites are also considered in an attempt to infer the regional structure. Finally, a method of correcting linearized inversions is developed. The corrections consist of successively approximating an analytic expression for the linearization error. The method would seem to represent a novel and practical approach that can significantly reduce the number of linearized iterations. In addition, a correspondence between the correction steps and iterations of the modified Newton's method for operators is established. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Problem: Biofilms are a community of bacteria that cause infections which are resistant to the immune system and antimicrobial treatments, posing a significant threat for patients with implantable and indwelling medical devices. Purpose: The purpose of this research is to effectively treat biofilms utilizing electric currents assisted by antibiotics. Method: Evaluated the impact of direct electric current with or without vancomycin against Staphylococcus epidermidis biofilms. Results: (1) Electric current reduced the S. epidermidis biofilm and (2) increased the effectiveness of vancomycin. (3) Older biofilms had an increased resistance to vancomycin treatments. (4) Higher electric current intensities and (5) longer duration treatments were more effective against biofilms. Conclusion: Electric current increased the effectiveness of vancomycin against S. epidermidis biofilms.