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The theme of this dissertation is to advance safety hazard mitigation by detecting and characterizing hidden targets of concern. Ground-penetrating radar (GPR) is used to detect and characterize hidden targets that pose safety hazards at Earth's surface, within shallow soil, and within rock. The resulting images detect unexploded ordnance (UXO) and detect fractures that pose collapse hazards in a mine. Detecting and characterizing fractures and voids within rock prior to excavation can enable mitigation of mine collapse hazards. GPR data were acquired on the wall of a pillar in an underground mine. Strong radar reflections in the field data correlate with fractures and a cave exposed on the pillar walls. Pillar wall roughness was included in migration, a wavefield imaging algorithm, to quantitatively locate fractures and voids and map their spatial relationships within the rock. Quantifying the radar reflection amplitudes enabled mapping the distance between fracture walls. Detecting and characterizing UXO and landmines from a safe distance can enable de-mining. Migration was used to improve GPR imaging for unmanned aerial vehicle (UAV) data acquisitions. Existing algorithms were adapted for UAV flight irregularities and surface topography, and a new algorithm was developed that does not depend on the unknown soil wavespeed. Errors associated with wavespeed and raypath assumptions were quantified. The algorithms were tested with real and synthetic datasets. The improved and new algorithms are more successful than previous algorithms. To detect linear targets at all orientations, fully polarized GPR data are needed. Polarity combinations were investigated to optimize the detection of surface and subsurface small targets and linear targets. Scattering caused by topographic roughness is the primary shallow subsurface noise. For subsurface targets, detection is optimized by migration plus a polarity combination that captures all scattered energy. Strong reflection and scattering from the air-ground boundary can hide surface targets. Detection is optimized by removing the strong isotropic surface scattering, imaging targets by their anisotropic scattering. / Doctor of Philosophy / The theme of this dissertation is to advance safety hazard mitigation by detecting and characterizing hidden targets of concern. Ground-penetrating radar (GPR) is used to detect and characterize hidden targets that pose safety hazards at Earth's surface, within shallow soil, and within rock. The resulting images detect unexploded ordnance (UXO)/landmines and detect fractures that pose collapse hazards in a mine. Detecting and characterizing fractures and voids within rock prior to mining can enable mitigation of mine collapse hazards. GPR data were acquired on the wall of a pillar in an underground mine. Strong radar reflections in the field data correlate with fractures and a cave exposed on the pillar walls. Pillar wall roughness was included in migration, a wavefield imaging algorithm, to quantitatively locate fractures and voids and map their spatial relationships within the rock. Quantifying the radar reflection amplitudes enabled mapping the distance between fracture walls. Detecting and characterizing UXO, landmines from a safe distance can enable de-mining. Migration was used to improve GPR imaging for an unmanned aerial vehicle (drone) data acquisition. Existing algorithms were adapted for drone flight irregularities and surface topography, and a new algorithm was developed that does not depend on the unknown soil properties. Errors associated with the algorithms' assumptions were quantified. The algorithms were tested with real and computer-generated datasets. The improved and new algorithms are more successful than previous algorithms. To detect all targets regardless of their orientation, GPR data need to be acquired with antenna pointing in multiple directions (different polarities). Polarity combinations were investigated to optimize the detection of surface and subsurface small targets and linear targets. Scattering caused by topographic roughness is the primary shallow subsurface noise. For subsurface targets, detection is optimized by migration plus a polarity combination that captures all scattered energy. Strong radar reflection from the air-ground boundary can hide surface targets. Detection is optimized by removing the strong ground surface from the data, and imaging targets by differences in their radar scattering.

yes / Controlling polymer thin-film morphology and crystallinity is crucial for a wide range of applications, particularly in thin-film organic electronic devices. In this work, the crystallization behavior of a model polymer, poly(ethylene oxide) (PEO), during spincoating is studied. PEO films were spun-cast from solvents possessing different polarities (chloroform, THF and methanol) and probed via in situ grazing incidence wide angle x-ray scattering. The crystallization behavior was found to follow the solvent polarity order (where chloroform < THF < methanol) rather than the solubility order (where THF > chloroform > methanol). When spun-cast from non-polar chloroform, crystallization largely followed Avrami kinetics, resulting in the formation of morphologies comprising large spherulites. PEO solutions cast from more polar solvents (THF and methanol) do not form well-defined highly crystalline morphologies and are largely amorphous with the presence of small crystalline regions. The difference in morphological development of PEO spun-cast from polar solvents is attributed to clustering phenomena that inhibit polymer crystallization. This work highlights the importance of considering individual components of polymer solubility, rather than simple total solubility, when designing processing routes for the generation of morphologies with optimum crystallinities or morphologies.

Maintenance of apico-basal polarity is essential for epithelial integrity and requires particular reinforcement during tissue morphogenesis, when cells are reorganised, undergo shape changes and remodel their junctions. It is well established that epithelial integrity during morphogenetic processes depends on the dynamic exchange of adherens junction components, but our knowledge on the dynamics of other proteins and their dynamics during these processes is still limited. The early Drosophila embryo is an ideal system to study membrane dynamics during morphogenesis. Here, morphogenetic activities differ along the anterior-posterior axis, with the extending germband showing a high degree of epithelial remodelling. We developed a Fluorescence Recovery After Photobleaching (FRAP) assay with a higher temporal resolution, which allowed the distinction between a fast and a slow component of recovery of membrane proteins during the germband extension stage. We show for the first time that the recovery kinetics of a general membrane marker, SpiderGFP, differs in the anterior and posterior parts of the embryo, which correlates well with the different morphogenetic activities of the respective embryonic regions. Interestingly, absence of crumbs, a polarity regulator essential for epithelial integrity in the Drosophila embryo, decreases the fast component of SpiderGFP and of the apical marker Stranded at Second-Venus specifically in the anterior region. We suggest that the defects in kinetics observed in crumbs mutant embryos are the first signs of tissue instability in this region, explaining the earlier breakdown of the head epidermis in comparison to that of the trunk, and that diffusion in the plasma membrane is affected by the absence of Crumbs.

Until recently, numerical modulation models for the solar modulation of cosmic rays have been based primarily on finite difference approaches; however, models based on the solution of an appropriate set of stochastic differential equations have become increasingly popular. This study utilises such a spatially three-dimensional and time-stationary model, based on that of Strauss et al. (2011b). The remarkable numerical stability and powerful illustrative capabilities of this model are utilised extensively and in a distinctly comparative fashion to enable new insights into the processes of modulation. The model is refined to provide for both the Smith-Bieber (Smith and Bieber, 1991) and Jokipii-Kota (Jokipii and Kota, 1989) modifcations to the Parker heliospheric magnetic field (Parker, 1958) and the implications for modulation are investigated. During this investigation it is conclusively illustrated that the Parker field is most conducive to drift dominated modulation, while the Jokipii-Kota and Smith-Bieber modifcations are seen to induce successively larger contributions from diffusive processes. A further refinement to the model is the incorporation of a different profile for the heliospheric current sheet. This profile is defined by its latitudinal extent given by Kota and Jokipii (1983), as opposed to the profile given by Jokipii and Thomas (1981). An extensive investigation into current sheet related matters is launched, illustrating the difference between these current sheet geometries, the associated drift velocity fields and the effect on modulation. At high levels of solar activity, such that the current sheet enters deep enough into the polar regions, the profile of Kota and Jokipii (1983) is found to significantly reduce the effective inward (outward) drifts of positively (negatively) charged particles during A > 0 polarity cycles. The analogous effect is true for A < 0 polarity cycles and the overall effect is of such an extent that the A > 0 and A < 0 solutions are found to coincide at the highest levels of solar activity to form a closed loop. This is a result that has never before been achieved without having to scale down the drift coefficient to zero at solar maximum, as was done by e.g. Ndiitwani et al. (2005). Furthermore, it is found that the drift velocity fields associated with these two current sheet profiles lead to significant differences in modulation even at such low levels of solar activity where no difference in the geometries of these profiles are yet in evidence. The model is finally applied to reproduce four observed galactic proton spectra, selected from PAMELA measurements (Adriani et al., 2013) during the atypical solar minimum of 2006 to 2009; a new proton local interstellar spectrum was employed. The results are found to be in accordance with that found by other authors and in particular Vos (2011), i.e. the diffusion was required to consistently increase from 2006 to 2009 and, in addition, the rigidity dependence below ~ 3 GV was required to change over this time so that the spectra became increasingly softer. / MSc (Space Physics), North-West University, Potchefstroom Campus, 2015

Until recently, numerical modulation models for the solar modulation of cosmic rays have been based primarily on finite difference approaches; however, models based on the solution of an appropriate set of stochastic differential equations have become increasingly popular. This study utilises such a spatially three-dimensional and time-stationary model, based on that of Strauss et al. (2011b). The remarkable numerical stability and powerful illustrative capabilities of this model are utilised extensively and in a distinctly comparative fashion to enable new insights into the processes of modulation. The model is refined to provide for both the Smith-Bieber (Smith and Bieber, 1991) and Jokipii-Kota (Jokipii and Kota, 1989) modifcations to the Parker heliospheric magnetic field (Parker, 1958) and the implications for modulation are investigated. During this investigation it is conclusively illustrated that the Parker field is most conducive to drift dominated modulation, while the Jokipii-Kota and Smith-Bieber modifcations are seen to induce successively larger contributions from diffusive processes. A further refinement to the model is the incorporation of a different profile for the heliospheric current sheet. This profile is defined by its latitudinal extent given by Kota and Jokipii (1983), as opposed to the profile given by Jokipii and Thomas (1981). An extensive investigation into current sheet related matters is launched, illustrating the difference between these current sheet geometries, the associated drift velocity fields and the effect on modulation. At high levels of solar activity, such that the current sheet enters deep enough into the polar regions, the profile of Kota and Jokipii (1983) is found to significantly reduce the effective inward (outward) drifts of positively (negatively) charged particles during A > 0 polarity cycles. The analogous effect is true for A < 0 polarity cycles and the overall effect is of such an extent that the A > 0 and A < 0 solutions are found to coincide at the highest levels of solar activity to form a closed loop. This is a result that has never before been achieved without having to scale down the drift coefficient to zero at solar maximum, as was done by e.g. Ndiitwani et al. (2005). Furthermore, it is found that the drift velocity fields associated with these two current sheet profiles lead to significant differences in modulation even at such low levels of solar activity where no difference in the geometries of these profiles are yet in evidence. The model is finally applied to reproduce four observed galactic proton spectra, selected from PAMELA measurements (Adriani et al., 2013) during the atypical solar minimum of 2006 to 2009; a new proton local interstellar spectrum was employed. The results are found to be in accordance with that found by other authors and in particular Vos (2011), i.e. the diffusion was required to consistently increase from 2006 to 2009 and, in addition, the rigidity dependence below ~ 3 GV was required to change over this time so that the spectra became increasingly softer. / MSc (Space Physics), North-West University, Potchefstroom Campus, 2015

The compositional technique of cross partitioning is one of Luigi Dallapiccola's most used twelve-tone devices. Through a detailed analysis of three contrapuntal canonic movements from Dallapiccola's Quaderno Musicale di Annalibera, I examine his use of cross partitioning as a motivic tool and as a referential collection. The development of the BACH motive and the derivation of tone-row statements reflects on Dallapiccola's extensive use of cross partitioning and his compositional principles used to achieve a sense of polarity. Upon a preliminary analysis based on set-theory analysis set out by Joseph Straus I draw an interpretive analysis through Alegant's cross partitioning model as well as develop my own set of parameters for interpretation in regards to polarity which is based on intervallic stability.

La voie de la polarité planaire cellulaire (PCP), aussi connue sous le nom de la voie non-canonique du Frizzled/Dishevelled, contrôle le processus morphogénétique de l'extension convergente (CE) qui est essentiel pour la gastrulation et la formation du tube neural pendant l'embryogenèse. La signalisation du PCP a été récemment associée avec des anomalies du tube neural (ATN) dans des modèles animaux et chez l'humain. Prickle1 est une protéine centrale de la voie PCP, exprimée dans la ligne primitive et le mésoderme pendant l'embryogenèse de la souris. La perte ou le gain de fonction de Prickle1 mène à des mouvements de CE fautifs chez le poisson zèbre et la grenouille. PRICKLE1 interagit directement avec deux autres membres de la voie PCP, Dishevelled et Strabismus/Vang. Dans notre étude, nous avons investigué le rôle de PRICKLE1 dans l'étiologie des ATN dans une cohorte de 810 patients par le re-séquençage de son cadre de lecture et des jonctions exon-intron. Le potentiel pathogénique des mutations ainsi identifiées a été évalué par des méthodes bioinformatiques, suivi par une validation fonctionnelle in vivo dans un système poisson zèbre. Nous avons identifié dans notre cohorte un total de 9 nouvelles mutations dont sept: p.Ile69Thr, p.Asn81His, p.Thr275Met, p.Arg682Cys et p.Ser739Phe, p.Val550Met et p.Asp771Asn qui affectent des acides aminés conservés. Ces mutations ont été prédites in silico d’affecter la fonction de la protéine et sont absentes dans une large cohorte de contrôles de même origine ethnique. La co-injection de ces variantes avec le gène prickle1a de type sauvage chez l’embryon de poisson zèbre a démontré qu’une mutation, p.Arg682Cys, modifie dans un sens négatif le phénotype du défaut de la CE produit par pk1 de type sauvage. Notre étude démontre que PK1 peut agir comme facteur prédisposant pour les ATN chez l’humain et élargit encore plus nos connaissances sur le rôle des gènes de la PCP dans la pathogenèse de ces malformations. / The planar cell polarity pathway (PCP) or the non-canonical Frizzled/Dishevelled pathway controls the morphogenetic process of convergent extension (CE) that is essential during embryogenesis for gastrulation and neural tube formation. Recently, PCP signalling was associated with neural tube defects (NTD) in humans and animal models. The core PCP protein, Prickle1, is expressed in the primitive streak and mesoderm during mouse embryogenesis. Both gain and loss of function of Prickle1 cause faulty CE movements in zebrafish and the frog. PRICKLE1 physically interacts with two other core PCP members, Dishevelled and Strabismus/Vang. In the present study we investigated the role of PRICKLE1 in the aetiology of NTDs in a large cohort of 810 patients through resequencing of its open reading frame and exon-intron junctions. The pathogenicity of the identified mutations was assessed through bioinformatics methods followed by a functional validation in a zebrafish system, in vivo. We identified in our cohort a total of nine novel mutations, of which seven affected conserved amino acids: p.Ile69Thr, p.Asn81His, p.Thr275Met, p.Arg682Cys, p.Ser739Phe, p.Val550Met and p.Asp771As. These mutations were predicted to affect the function of the protein in silico and were absent in a large cohort of ethnically-matched controls. Co-injection of these variants with the wild type pk1 in zebrafish oocytes revealed that one mutation, p.Arg682Cys, antagonized the CE phenotype induced by the wild-type zebrafish prickle1a in a dominant fashion. Our study demonstrates that PRICKLE1 can represent a predisposing factor for human NTDs and further expands our knowledge on the role that PCP genes in the pathogenesis of these malformations.

No description available.

Comment les cellules établissent leurs formes et organisations internes est un problème biologique fondamental. Au cours de cette thèse, j’ai étudié le développement de la forme cellulaire et de la polarité chez la cellule de levure fissipare. Ces études sont fondées sur l’exploration de la façon dont les petites spores symétriques de levures se développent et s’organisent pour briser la symétrie pour la définition de leur tout premier axe de polarité. Dans une première partie, j’ai étudié les couplages entre la mécanique de surface de la paroi cellulaire des spores et la stabilité de domaines de polarité de Cdc42 qui contrôlent les aspects spatio-temporelles de la brisure de symétrie de ces spores. Dans une seconde partie, j’ai étudié les mécanismes par lesquels ces domaines de polarité contrôlent leur taille et l'adapte à la géométrie de la cellule, un processus vraisemblablement pertinents pour comprendre comment des domaines fonctionnels corticaux s’adaptent à la taille des cellules. Globalement, ces nouvelles recherches focalisant sur la façon dont les cellules développent dynamiquement leur forme et polarité de novo, permettent de mettre en évidence des couplages complexes dans la morphogenèse qui ne peuvent pas être testés en regardant les cellules à « l’état stationnaire» ou avec des outils génétiques. / How cells establish their proper shapes and organization is a fundamental biological problem. In this thesis, I investigated the dynamic development of cellular form and polarity in the rod-shape fission yeast cell. These studies are based on monitoring how small symmetric fission yeast spores grow and self-organize to break symmetry for the definition of their very first polarity axis. In a first part, I studied interplays between surface mechanics of the spore cell wall and the stability of Cdc42-based polarity domains which control spatio-temporal aspects of spore symmetry breaking. In a second part, I studied mechanisms by which these polarity domains control their width and adapt it to cell surface geometry, a process likely relevant to understand how functional cortical domains scale to cell size. Overall these novel investigations focusing on how cells dynamically develop their form and polarity de novo highlight complex feedbacks in morphogenesis that cannot be evidenced by looking at cells at “steady state” or with genetics.