Many wireless sensor network (WSN) applications depend on knowing the position of nodes within the network if they are to function efficiently. Location information is used, for example, in item tracking, routing protocols and controlling node density. Configuring each node with its position manually is cumbersome, and not feasible in networks with mobile nodes or dynamic topologies. WSNs, therefore, rely on localisation algorithms for the sensor nodes to determine their own physical location. The basis of several localisation algorithms is the theory that the higher the number of reference nodes (called “references”) used, the greater the accuracy of the estimated position. However, this approach makes computation more complex and increases the likelihood that the location estimation may be inaccurate. Such inaccuracy in estimation could be due to including data from nodes with a large measurement error, or from nodes that intentionally aim to undermine the localisation process. This approach also has limited success in networks with sparse references, or where data cannot always be collected from many references (due for example to communication obstructions or bandwidth limitations). These situations require a method for achieving reliable and accurate localisation using a limited number of references. Designing a localisation algorithm that could estimate node position with high accuracy using a low number of references is not a trivial problem. As the number of references decreases, more statistical weight is attached to each reference’s location estimate. The overall localisation accuracy therefore greatly depends on the robustness of the selection method that is used to eliminate inaccurate references. Various localisation algorithms and their performance in WSNs were studied. Information-fusion theory was also investigated and a new technique, rooted in information-fusion theory, was proposed for defining the best criteria for the selection of references. The researcher chose selection criteria to identify only those references that would increase the overall localisation accuracy. Using these criteria also minimises the number of iterations needed to refine the accuracy of the estimated position. This reduces bandwidth requirements and the time required for a position estimation after any topology change (or even after initial network deployment). The resultant algorithm achieved two main goals simultaneously: accurate location discovery and information fusion. Moreover, the algorithm fulfils several secondary design objectives: self-organising nature, simplicity, robustness, localised processing and security. The proposed method was implemented and evaluated using a commercial network simulator. This evaluation of the proposed algorithm’s performance demonstrated that it is superior to other localisation algorithms evaluated; using fewer references, the algorithm performed better in terms of accuracy, robustness, security and energy efficiency. These results confirm that the proposed selection method and associated localisation algorithm allow for reliable and accurate location information to be gathered using a minimum number of references. This decreases the computational burden of gathering and analysing location data from the high number of references previously believed to be necessary. / Thesis (PhD(Eng))--University of Pretoria, 2011. / Electrical, Electronic and Computer Engineering / unrestricted

Far-field optical spectroscopy allows for measurement of plasmonic resonances on metallic nanostructures of various shapes and sizes when illuminated by continuous light. Employing dark-field microscopy makes it possible to measure scattering on a localised plasmon excited on a single, isolated nanostructure. For the purpose of these measurements an apparatus based on commercial dual microscope system Nanonics has been put together. Experiments carried out during work on this thesis have shown a great sensitivity of the apparatus in its present form, allowing to measure a plasmonic resonance of a single nanoparticle. Proposed improvements of the apparatus should lead to even greater sensitivity and precision of measurements in the near future.

Le graphène, plan d'atomes de carbone agencés en nid d'abeille, possède des propriétés physico-chimiques remarquables, en particulier une excellente mobilité électronique, qui en font un matériau d'avenir pour de nombreuses applications. Si la synthèse par dépôt chimique en phase vapeur (CVD) est une méthode prometteuse en vue d'une production de graphène de qualité à grande échelle, il reste difficile de contrôler les caractéristiques du graphène formé. L'objectif de ce travail expérimental est à la fois de développer la croissance de graphène par CVD à pression atmosphérique et température modérée (600°C à 900°C) sur un substrat de cobalt et d'analyser le graphène formé par des techniques d'analyse complémentaires afin de déterminer ses caractéristiques physico-chimiques et structurales.Une étude de l'influence de plusieurs paramètres de synthèse sur les caractéristiques du graphène formé (nombre de couches, taux de recouvrement, défauts et taille des domaines cristallins) a été réalisée. En utilisant des feuilles de cobalt commerciales et en travaillant à 850°C avec une forte vitesse de refroidissement et un apport faible en carbone, un film continu de graphène de trois couches a été obtenu. De plus, en étudiant la distribution des atomes de carbone dans le cobalt après synthèse, nous avons mis en évidence une concentration de carbone extrêmement élevée, environ 100 fois supérieure à la solubilité du carbone dans le cobalt à 850°C.L'influence du cobalt sur les caractéristiques structurales a été étudiée par diffraction des rayons X sur source synchrotron. Pour cela, du graphène a été synthétisé par CVD à pression atmosphérique sur des films minces de cobalt. L'étude structurale de ce système a révélé un empilement des feuillets de graphène de type graphite turbostratique et des domaines cristallins présentant deux orientations différentes par rapport au cobalt.L'étude du système graphène/cobalt est complétée par une analyse multi-techniques et localisée du graphène permettant d'analyser la même zone de graphène lorsqu'elle est sur cobalt puis sur SiO2, après transfert. La caractérisation est réalisée par microcopie et par spectroscopie Raman. L'influence du substrat de cobalt sur le graphène formé, notamment des contraintes mécaniques et du dopage électronique, est mise en évidence.Une étude de l'influence de plusieurs paramètres expérimentaux sur les caractéristiques du graphène formé (nombre de couches, taux de recouvrement, défauts et taille des domaines cristallins) a été réalisée. En utilisant des feuilles de cobalt commerciales et en travaillant à 850°C avec une forte vitesse de refroidissement et un apport faible en carbone, un film continu de graphène de trois couches a été obtenu. De plus, en étudiant la distribution des atomes de carbone dans le cobalt après synthèse, nous avons mis en évidence une concentration de carbone extrêmement élevée, environ 100 fois supérieure à la solubilité du carbone dans le cobalt à 850°C.L'influence du cobalt sur la croissance du graphène a été étudiée par diffraction des rayons X sur source synchrotron. Pour cela, du graphène a été synthétisé par CVD à pression atmosphérique sur des films minces de cobalt. L'étude structurale de ce système a révélé un empilement des feuillets de graphène de type graphite turbostratique. De plus, il a été montré que 95 % des domaines cristallins du graphène sont orientés à 20° ± 7° par rapport au cobalt tandis que 5 % des domaines est très bien orientée à 30° ± 0,6°.L'étude du système graphène/cobalt est complétée par une analyse multi-techniques et localisée du graphène permettant d'analyser la même zone de graphène lorsqu'elle est sur cobalt puis sur SiO2, après transfert. L'influence, notamment mécanique, du substrat de croissance sur le graphène formé est mise en évidence. / Graphene, a two-dimensional material composed of carbon atoms arranged in hexagonal lattice, has outstanding physical and chemical properties, i.e. its exceptional electronic mobility. This material is thus promising for many applications in the future. However, if chemical vapour deposition (CVD) is a very promising method for large-scale graphene growth , it is still very challenging to control graphene characteristics. The objective of this experimental work is both to develop graphene growth by CVD at atmospheric pressure and moderate temperature (600°C / 850°C) on cobalt and to analyse grown graphene with complementary techniques to determine its physical, chemical and structural characteristics.A study of the influence of different synthesis parameters on graphene characteristics (number of layer, coverage, defect and crystallite size) has been achieved. By combining the use of commercial cobalt foils with growth temperature of 850°C, a high cooling rate (100°C/min) and a low carbon supply, a continuous graphene film of three layers has been synthesized. Moreover, by measuring carbon distribution in the cobalt substrate after graphene growth, we have highlighted a carbon concentration about 100 times higher than carbon solubility in cobalt at 850 °C.The influence of cobalt on graphene structure was studied by X-ray diffraction using a synchrotron beamline. Prior to experiments, graphene was grown by CVD at atmospheric pressure on cobalt thin film. The structural study of this system has revealed a turbostratic stacking of graphene and two different orientations for graphene domains with respect to cobalt.The study of the graphene/cobalt system is completed by a multi-technique and localised characterisation of graphene which enables to analyse a same area of graphene when it is on cobalt and then after transfer on SiO2 substrate. Sample characterisation is based on microscopy and Raman spectroscopy. The influence of cobalt substrate on grown graphene, especially on mechanical strain and electronic doping, is highlighted.

Das maligne Melanom ist für 90 % der Sterbefälle bei Hautkrebs verantwortlich (Garbe et al., 2022). Verschiedene Mutationen wirken sich auf die Signalwege aus und fördern die Karzinogenese, was zu einem ständigen Wandel der Melanomtherapie führt. Zusätzlich zu der, in frühen Stadien kurativen, chirurgischen Therapie, erzielt die zielgerichtete Therapie mit BRAF- und MEK-Inhibitoren in den letzten Jahren durchschlagende Erfolge für das Gesamtüberleben der Patienten, bei nicht-resezierbaren Metastasen wird weiterhin die Chemotherapie empfohlen. Zunehmende Therapieresistenzen schränken die Melanomtherapie ein. Müller et al. (2020) weisen auf Wildtyp p53 exprimierende Tumorzellen hin, die mithilfe der Expression von nukleärer Caspase-8 den G2/M-Zellzyklusarrest umgehen und so die Proliferation und Expansion entarteter Tumorzellen fördern. Bei der Untersuchung von 16 Melanomzellproben, die sich in ihrem BRAF-/NRAS- und p53 Mutationsstatus, sowie in ihren klinischen Vortherapien unterscheiden, konnte die potenziell klinische Relevanz der nukleären Caspase-8 herausgearbeitet werden. Wir konnten bestätigen, dass nukleär lokalisierte Caspase-8 bei Wildtyp p53 exprimierenden Tumorzellen zu Chemoresistenz und auch in geringem Maß zur Resistenz gegenüber zielgerichteten Therapien führt. Zunächst wurde die subzelluläre Lokalisation von Caspase-8 in den vorhandenen 16 Melanomzellproben mithilfe immunzytochemischer Färbung bestimmt, wobei sich herausstellte, dass die Melanomzellproben mit nukleärer Caspase-8, alle von Metastasen stammen. Das hohe Metastasierungspotenzial dieser Zellproben wurde weiterhin dadurch betont, dass die Melanomzellproben mit nukleär lokalisierter Caspase-8 die stärkste Migration aufwiesen. Dem gegenüberstehend präsentierten sie die geringste Proliferation, was den direkten Zusammenhang zwischen migrativen und proliferativen Eigenschaften bei Tumorzellen unterstreicht. Ebenso zeigten BRAF-mutierte Zellproben die stärkste Migration und bekräftigen, dass Melanompatienten mit BRAF-Mutation früher Metastasen entwickeln. Das stärkste Wachstum zeigten hingegen die Zellproben mit diffus lokalisierter Caspase-8, was die protektive Relevanz der diffusen Caspase-8 für Tumorzellen verdeutlicht. Ein Einfluss des p53-Mutationsstatus auf die Proliferation und Migration konnte ebenfalls nachgewiesen werden. Die Zellproben mit Wildtyp p53 migrierten stärker, wohingegen die Zellprobe mit mutp53(E285K) stark proliferierte. Bei Korrelation der subzellulären Caspase-8-Lokalisation mit der Caspase-8- und p53-Expression der Melanomzellproben mithilfe Westernblotanalysen zeigte sich, dass metastatische Zellproben verstärkt Caspase-8 exprimieren. Dies betraf besonders die metastatischen Zellproben mit nukleär lokalisierter Caspase-8, die kein p53 oder wenig Wildtyp p53 exprimieren. Diese inverse Korrelation der Caspase-8- und p53 Expression konnte ebenfalls bei den unstimulierten Zellproben mit zytoplasmatischer Caspase-8 festgestellt werden. Zellprobe M31 mit mutp53(E285K) exprimiert konstant stark p53 und wies Chemoresistenz auf. Bei Untersuchung des Zelltods 24 h und 48 h nach Cisplatinstimulation, sowie 48 h nach Stimulation mit Dabrafenib, Trametinib und deren Kombination mithilfe des IncuCyte® Readers, wurde deutlich, dass die Zellproben mit nukleär lokalisierter Caspase-8 chemoresistenter sind als die restlichen Zellproben, wobei die Zellproben mit diffus lokalisierter Caspase-8 am resistentesten gegenüber den zielgerichteten Therapeutika sind. Die protektive Rolle der diffusen Caspase-8 für die Tumorzellen konnte unterstützend durch die Zunahme der Apoptose bei einigen Zellproben nach Herunterregulierung von Caspase-8 nachgewiesen werden. Hervorzuheben ist, dass die Zellproben mit zytoplasmatischer Caspase-8 am sensitivsten, sowohl auf zielgerichtete Therapeutika als auch auf Chemotherapie reagierten. Insgesamt induzierte Cisplatin deutlich mehr Zelltod als die zielgerichteten Therapien, weshalb die potenzielle Überlegenheit der Chemotherapie, besonders bei rezidivierten Melanomen bedacht werden muss. Es bestätigte sich ebenfalls die Relevanz des BRAF-/NRAS Mutationsstatus für die Therapiesensitivität, wobei BRAF-mutierte Zellproben die größte Chemosensitivität präsentierten und NRAS-mutierte Zellproben vor allem nach der Stimulation mit Trametinib und der Kombination Dabrafenib + Trametinib Zelltod aufwiesen. Überraschenderweise zeigten sich die Zellproben vortherapierter Melanompatienten sensitiver gegenüber Dabrafenib und Cisplatin als die Zellproben therapienaiver Melanompatienten, was die Bedeutung von Chemotherapie und Dabrafenib für vortherapierte, rezidivierte Tumore bzw. Metastasen hervorhebt. Weiterhin konnte der Impact des p53-Mutationsstatus herausgearbeitet werden. Die Zellproben mit mutiertem oder ohne p53 wiesen die größte Cisplatinresistenz auf, wohingegen die Zellproben mit Wildtyp p53 am meisten Zelltod zeigten, gefolgt von den Zellproben mit dem Einzelnukleotidpolymorphismus (wt(P72R)). Nach Herunterregulierung des mutierten p53 nahm die Apoptose nach Cisplatinstimulation hoch signifikant zu. Dahingegen zeigten besonders die Zellproben mit zytoplasmatischer Caspase-8 und Wildtyp p53 eine Hochregulierung von p53 nach Cisplatinstimulation im Westernblot. Wir konnten nachweisen, dass die Wildtyp p53 exprimierende Zellprobe M40 nukleär lokalisierte Caspase-8 aufweist und die stärkste Chemoresistenz zeigte, wohingegen die Zellproben mit diffus oder zytoplasmatisch lokalisierter Caspase-8, die Wildtyp p53 oder den Einzelnukleotidpolymorphismus (wt(P72R)) exprimieren, am chemosensitivsten waren. Die Therapieresponsivität von Melanomen wird durch eine Vielzahl an Faktoren beeinflusst, die für die optimale Behandlung der Patienten bei Beginn einer Therapie möglichst genau bestimmt werden sollten. Wir empfehlen für die Risikostratefizierung und Prognose des Krankheitsverlaufes, sowie für die Entscheidung des Therapiewegs, die Bestimmung der subzellulären Caspase-8-Lokalisation in Kombination mit dem p53-Mutationsstatus. Weiterhin weisen wir auf die Bedeutung des BRAF-/NRAS-Mutationsstatus sowie mögliche Vortherapien in Bezug auf Therapieresistenz hin und stellen die Bedeutung der Chemotherapie, besonders für rezidivierte, BRAF-mutierte Melanompatienten bei Resistenzentwicklung gegen BRAF- und/oder MEK-Inhibitoren heraus. / Malignant melanoma is responsible for 90 % of skin cancer deaths (Garbe et al., 2022). Various mutations affect the signaling pathways and promote carcinogenesis, which leads to a constant change in melanoma therapy. In addition to surgical therapy, which is curative in the early stages, targeted therapy with BRAF and MEK inhibitors has achieved resounding successes for the overall survival of patients in recent years while chemotherapy is still recommended for non-resectable metastases. Increasing therapy resistance limits melanoma therapy, with Müller et al. (2020) pointing to wild-type p53-expressing tumor cells that use the expression of nuclear caspase-8 to bypass the G2/M cell cycle arrest and thus promote the proliferation and expansion of degenerated tumor cells. By investigating 16 melanoma cell samples differing in their BRAF/NRAS and p53 mutation status, as well as in their prior clinical therapies, the potential clinical relevance of nuclear caspase-8 could be elaborated. We were able to confirm that nuclear localized caspase-8 in wild-type p53-expressing tumor cells leads to chemoresistance and, to a lesser extent, to resistance to targeted therapies. First, the subcellular localization of caspase-8 in the existing 16 melanoma cell samples was determined using immunocytochemical staining, which revealed that the melanoma cell samples with nuclear caspase-8 all originated from metastases. The high metastatic potential of these cell samples was further emphasized by the fact that the melanoma cell samples with nuclear localized caspase-8 showed the strongest migration. In contrast, they presented the lowest proliferation, underlining the direct correlation between migratory and proliferative properties in tumor cells. Likewise, BRAF-mutated cell samples showed the strongest migration and verified that melanoma patients with BRAF mutations develop metastases earlier. In contrast, the cell samples with diffusely localized caspase-8 showed the strongest growth, which illustrates the relevance of diffusely localized caspase-8 in its protective function in tumor cells. The impact of the p53 mutation status on proliferation and migration could also be demonstrated. The cell samples with wild-type p53 migrated stronger, whereas the cell samples with mutp53(E285K) showed stronger proliferation. Correlation of subcellular caspase-8 localization with caspase-8 and p53 expression of melanoma cell samples using western blot analysis showed that metastatic cell samples express more caspase-8. This was particularly true for the metastatic cell samples with nuclearly localized caspase-8, which express little wild-type p53 or no p53. This inverse correlation of caspase-8 and p53 expression was also observed in the unstimulated cell samples with cytoplasmically localized caspase-8, respectively. Cell sample M31 with mutp53(E285K) consistently expressed high levels of p53 and exhibited chemoresistance. When examining cell death 24 h and 48 h after cisplatin stimulation, as well as 48 h after stimulation with dabrafenib, trametinib and their combination using the IncuCyte® Reader, it became clear that the cell samples with nuclearly localized caspase-8 are the most chemoresistant, whereby the cell samples with diffusely localized caspase-8 are the most resistant to the targeted therapeutics. The protective role of diffusely localized caspase-8 for the tumor cells was supportively demonstrated by the increase in apoptosis in some cell samples after downregulation of caspase-8. It should be emphasized that the cell samples with cytoplasmically localized caspase-8 responded most sensitively to both targeted therapies and chemotherapy. Overall, cisplatin induced significantly more cell death than the targeted therapies, which is why the potential superiority of chemotherapy, especially in recurrent melanoma, must be considered. The relevance of BRAF/NRAS mutation status for therapy sensitivity was also confirmed, with BRAF-mutated cell samples presenting the greatest chemosensitivity and NRAS-mutated cell samples showing cell death particularly after stimulation with trametinib and the combination dabrafenib + trametinib. Surprisingly, the cell samples of pre-treated melanoma patients were more sensitive to dabrafenib and cisplatin than the cell samples of treatment-naive melanoma patients, which highlights the importance of chemotherapy and dabrafenib for pre-treated, recurrent tumors and metastases. Furthermore, the impact of the p53 mutation status could be worked out. The cell samples with mutated or no p53 showed the highest cisplatin resistance, whereas the cell samples with wild-type p53 showed the highest cell death, followed by the cell samples with the single nucleotide polymorphism (wt(P72R)). After downregulation of mutant p53, apoptosis increased highly significantly after cisplatin stimulation. In contrast, especially the cell samples with cytoplasmically localized caspase-8 and wild-type p53 showed an upregulation of p53 in the Western blot after cisplatin stimulation. We demonstrated that wild-type p53 and nuclear caspase-8 expressing cell sample M40 exhibited the strongest chemoresistance, whereas the cell samples with diffusely or cytoplasmically localized caspase-8 expressing wild-type p53 or the single nucleotide polymorphism (wt(P72R)) were the most chemosensitive. In summary, it is clear that the treatment response of melanoma is influenced by a variety of factors that should be determined as precisely as possible for the optimal treatment of patients at the start of therapy. We recommend the determination of subcellular caspase-8 localization in combination with the p53 mutation status for risk stratification and prognosis of disease progression, as well as for the optimal therapy. Furthermore, we point out the importance of BRAF/NRAS mutation status and possible prior therapies with regard to therapy resistance and emphasize the importance of chemotherapy, especially for relapsed, BRAF-mutated melanoma patients who developed resistance to BRAF and/or MEK inhibitors.

Inspired by graphene, I investigate the properties of several different real and artificial Dirac materials. Firstly, I consider a two-dimensional honeycomb lattice of metallic nanoparticles, each supporting localised surface plasmons, and study the quantum properties of the collective plasmons resulting from the near field dipolar interaction between the nanoparticles. I analytically investigate the dispersion, the effective Hamiltonian and the eigenstates of the collective plasmons for an arbitrary orientation of the individual dipole moments. When the polarisation points close to normal to the plane the spectrum presents Dirac cones, similar to those present in the electronic band structure of graphene. I derive the effective Dirac Hamiltonian for the collective plasmons and show that the corresponding spinor eigenstates represent chiral Dirac-like massless bosonic excitations that present similar effects to those of electrons in graphene, such as a non-trivial Berry phase and the absence of backscattering from smooth inhomogeneities. I further discuss how one can manipulate the Dirac points in the Brillouin zone and open a gap in the collective plasmon dispersion by modifying the polarisation of the localized surface plasmons, paving the way for a fully tunable plasmonic analogue of graphene. I present a phase diagram of gapless and gapped phases in the collective plasmon dispersion depending on the dipole orientation. When the inversion symmetry of the honeycomb structure is broken, the collective plasmons become gapped chiral Dirac modes with an energy-dependent Berry phase. I show that this concept can be generalised to describe many real and artificial graphene-like systems, labeling them Dirac materials with a linear gapped spectrum. I also show that biased bilayer graphene is another Dirac material with an energy dependent Berry phase, but with a parabolic gapped spectrum. I analyse the relativistic phenomenon of Klein Tunneling in both types of system. The Klein paradox is one of the most counter-intuitive results from quantum electrodynamics but it has been seen experimentally to occur in both monolayer and bilayer graphene, due to the chiral nature of the Dirac quasiparticles in these materials. The non-trivial Berry phase of pi in monolayer graphene leads to remarkable effects in transmission through potential barriers, whereas there is always zero transmission at normal incidence in unbiased bilayer graphene in the npn regime. These, and many other 2D materials have attracted attention due to their possible usefulness for the next generation of nano-electronic devices, but some of their Klein tunneling results may be a hindrance to this application. I will highlight how breaking the inversion symmetry of the system allows for results that are not possible in these system's inversion symmetrical counterparts.

Metal nanoparticles have recently gained popularity in many research areas due to their nanosize-related properties. Depending on the size of the metal nanoparticle, their mode of interaction with electromagnetic radiation and the outcome of this interaction vary; in turn the effect exerted on a protein which is conjugated to a nanoparticle varies, because different sized nanoparticles demonstrate different modes of energy transfer with electromagnetic radiation and molecules conjugated to them. Very small cluster with sizes around 1 – 1.2 nm tend to get excited by incident light and emit fluorescence, whereas larger nanoparticles absorb the incoming light very strongly due to their LSPR. In this study we observed the outcomes of the interaction between two types of nanoparticles, namely gold and gold/silver alloyed nanoparticles with the fluorescence emission of two fluorophores, namely eGFP and rPhiYFP; and demonstrated a bioassay where the fluorescence modulation by gold nanoparticles can be used as the sensing strategy. Lastly, we demonstrated the potential of autofluorescent gold nanoparticles as intracellular reporters.

This project predominantly investigated the implications of spatial heterogeneity in the ecological processes of competition and infection. Empirical analysis of spatial heterogeneity was carried out using the lepidopteran species Plodia interpunctella. Using differently viscous food media, it was possible to alter the movement rate of larvae. Soft Foods allow the movement rate of larvae to be high, so that individuals can disperse through the environment and avoid physical encounters with conspecifics. Harder foods lower the movement rate of larvae, restricting the ability of individuals to disperse away from birth sites and avoid conspecifics encounters. Increasing food viscosity and lowering movement rate therefore has the effect of making uniform distributed larval populations more aggregated and patchy. Different spatial structures changed the nature of intraspecific competition, with patchy populations characterised by individuals experiencing lower growth rates and greater mortality because of the reduced food and space available within densely packed aggregations. At the population scale, the increased competition for food individuals experience in aggregations emerges as longer generational cycles and reduced population densities. Aggregating individuals also altered the outcome of interspecific competition between Plodia and Ephestia cautella. In food media that allowed high movement rates, Plodia had a greater survival rate than Ephestia because the larger movement rate of Plodia allowed it to more effectively avoid intraspecific competition. Also the faster growth rate, and so larger size, of Plodia allowed it to dominate interspecific encounters by either predating or interfering with the feeding of Ephestia. In food that restricts movement, the resulting aggregations cause Plodia to experience more intraspecific encounters relative to interspecific, reducing its competitive advantage and levelling the survival of the two species. Spatial structure also affected the dynamics of a Plodia-granulosis virus interaction and the evolution of virus infectivity. Larval aggregation forced transmission to become limited to within host patches, making the overall prevalence of the virus low. However potentially high rates of cannibalism and multiple infections within overcrowded host aggregations caused virus-induced mortality to be high, as indicated by the low host population density when virus is presented. Also aggregated host populations cause the evolution of lower virus infectivity, where less infective virus strains maintain more susceptible hosts within the aggregation and so possess a greater transmission rate. The pattern of variation in resistance of Plodia interpunctella towards its granulosis virus was found using two forms of graphical analysis. There was a bimodal pattern of variation, with most individuals exhibiting either low or high levels of resistance. This pattern was related to a resistance mechanism that is decreasingly costly to host fitness.

Effective focusing of electromagnetic (EM) energy to nanoscale regions is one of the major challenges in nano-photonics and plasmonics. The strong localization of the optical energy into regions much smaller than allowed by the diffraction limit, also called nanofocusing, offers promising applications in nano-sensor technology, nanofabrication, near-field optics or spectroscopy. One of the most promising solutions to the problem of efficient nanofocusing is related to surface plasmon propagation in metallic structures. Metallic tapered rods, commonly used as probes in near field microscopy and spectroscopy, are of a particular interest. They can provide very strong EM field enhancement at the tip due to surface plasmons (SP’s) propagating towards the tip of the tapered metal rod. A large number of studies have been devoted to the manufacturing process of tapered rods or tapered fibers coated by a metal film. On the other hand, structures such as metallic V-grooves or metal wedges can also provide strong electric field enhancements but manufacturing of these structures is still a challenge. It has been shown, however, that the attainable electric field enhancement at the apex in the V-groove is higher than at the tip of a metal tapered rod when the dissipation level in the metal is strong. Metallic V-grooves also have very promising characteristics as plasmonic waveguides. This thesis will present a thorough theoretical and numerical investigation of nanofocusing during plasmon propagation along a metal tapered rod and into a metallic V-groove. Optimal structural parameters including optimal taper angle, taper length and shape of the taper are determined in order to achieve maximum field enhancement factors at the tip of the nanofocusing structure. An analytical investigation of plasmon nanofocusing by metal tapered rods is carried out by means of the geometric optics approximation (GOA), which is also called adiabatic nanofocusing. However, GOA is applicable only for analysing tapered structures with small taper angles and without considering a terminating tip structure in order to neglect reflections. Rigorous numerical methods are employed for analysing non-adiabatic nanofocusing, by tapered rod and V-grooves with larger taper angles and with a rounded tip. These structures cannot be studied by analytical methods due to the presence of reflected waves from the taper section, the tip and also from (artificial) computational boundaries. A new method is introduced to combine the advantages of GOA and rigorous numerical methods in order to reduce significantly the use of computational resources and yet achieve accurate results for the analysis of large tapered structures, within reasonable calculation time. Detailed comparison between GOA and rigorous numerical methods will be carried out in order to find the critical taper angle of the tapered structures at which GOA is still applicable. It will be demonstrated that optimal taper angles, at which maximum field enhancements occur, coincide with the critical angles, at which GOA is still applicable. It will be shown that the applicability of GOA can be substantially expanded to include structures which could be analysed previously by numerical methods only. The influence of the rounded tip, the taper angle and the role of dissipation onto the plasmon field distribution along the tapered rod and near the tip will be analysed analytically and numerically in detail. It will be demonstrated that electric field enhancement factors of up to ~ 2500 within nanoscale regions are predicted. These are sufficient, for instance, to detect single molecules using surface enhanced Raman spectroscopy (SERS) with the tip of a tapered rod, an approach also known as tip enhanced Raman spectroscopy or TERS. The results obtained in this project will be important for applications for which strong local field enhancement factors are crucial for the performance of devices such as near field microscopes or spectroscopy. The optimal design of nanofocusing structures, at which the delivery of electromagnetic energy to the nanometer region is most efficient, will lead to new applications in near field sensors, near field measuring technology, or generation of nanometer sized energy sources. This includes: applications in tip enhanced Raman spectroscopy (TERS); manipulation of nanoparticles and molecules; efficient coupling of optical energy into and out of plasmonic circuits; second harmonic generation in non-linear optics; or delivery of energy to quantum dots, for instance, for quantum computations.

Strong light matter interactions in metallic nanoparticles (NPs), especially those made of noble metals such as Gold and Silver is at the heart of much ongoing research in nanoplasmonics. Individual NPs can support collective excitations (Plasmon’s) of the electron plasma at certain wavelengths, known as the localized surface Plasmon resonance (LSPR) which provides a powerful platform for various sensing, imaging and therapeutic applications. For a collection of NPs their optical properties can be signify cannily different from isolated particles, an effect which originates in the electromagnetic interactions between the localised Plasmon modes. An interesting aspect of such interactions is their strong dependence on the geometry of NP collection and accordingly new optical properties can arise. While this problem has been well considered in one and two dimensions with periodic as well as with random arrays of NPs, three dimensional systems are yet to be fully explored. In particular, there are challenges in the successful de-sign and fabrication of three dimensional (3D) plasmonic metamaterials at optical frequencies. In the work presented in this thesis we present a detail investigation of the theoretical and experimental aspects of plasmonic interactions in two geometrically different three dimensional plasmonic nanostructured systems - a chiral system consisting of achiral plasmonic nanoparticles arranged in a helical geometry and an achiral system consisting of achiral plasmonic nanoparticle arrays stacked vertically into three dimensional geometry. The helical arrangement of achiral plasmonic nanoparticles were realised using a wafer scale technique known as Glancing Angle Deposition (GLAD). The measured chiro-optical response which arises solely from the interactions of the individual achiral plasmonic NPs was found to be one of the largest reported value in the visible. Semi analytical calculation based on couple dipole approximation was able to model the experimental chiro-optical response including all the variabilities present in the experimental system. Various strategies based on antiparticle spacing, oriented elliptical nanoparticles, dielectric constant value of the dielectric template were explored such as to engineer a strong and tunable chiro-optical response. A key point of the experimental system despite the presence of variabilities, was that the measured chiro-optical response showed less than 10 % variability along the sample surface. Additionally we could exploit the strong near held interactions of the plasmonic nanoparticles to achieve a strongly nonlinear circular differential response of two photon photoluminescent from the helically arranged nanoparticles. In addition to these plasmonic chiral systems, our study also includes investigation of light matter interactions in purely dielectric chiral systems of solid and core shell helical geometry. The chiro-optical response was found to be similar for both the systems and depend strongly on their helical geometry. A core-shell helical geometry provides an easy route for tuning the chiro-optical response over the entire visible and near IR range by simply changing the shell thickness as well as shell material. The measured response of the samples was found to be very large and very uniform over the sample surface. Since the material system is based entirely on dielectrics, losses are minimal and hence could possibly serve as an alternative to conventional plasmonic chiro-optical materials. Finally we demonstrated the used of an achiral three dimensional plasmonic nanostructure as a SERS (surface enhance Raman spectroscopy) substrate. The structure consisted of porous 3D metallic NP arrays that are held in place by dielectric rods. For practically important applications, the enhancement factor, as well as the spatial density of the metallic NPs within the laser illumination volume, arranged in a porous 3D array needs to be large, such that any molecule in the vicinity of the metal NP gives rise to an enhanced Raman signal. Having a large number of metallic NPs within the laser illumination volume, increases the probability of a target molecule to come in the vicinity of the metal NPs. This has been achieved in the structures reported here, where high enhancement factor (EF) in conjunction with large surface area available in a three dimensional structure, makes the 3D NP arrays attractive candidates as SERS substrates.

Failure modes for sandwich beams of GFRP laminate skins and Nomex honeycomb core are investigated. Theoretical models using honeycomb mechanics and classical beam theory are described. A failure mode map for loading under 3-point bending, is constructed, showing the dependence of failure mode and load on the ratio of skin thickness to span length and honeycomb relative density. Beam specimens are tested in 3-point bending. The effect of honeycomb direction is also examined. The experimental data agree satisfactorily with the theoretical predictions. The results reveal the important role of core shear in a sandwich beam's bending behaviour and the need for a better understanding of indentation failure mechanism. High order sandwich beam theory (HOSBT) is implemented to extract useful information about the way that sandwich beams respond to localised loads under 3-point bending. 'High-order' or localised effects relate to the non-linear patterns of the in-plane and vertical displacements fields of the core through its height resulting from the unequal deformations in the loaded and unloaded skins. The localised effects are examined experimentally by Surface Displacement Analysis of video images recorded during 3-point bending tests. A new parameter based on the intrinsic material and geometric properties of a sandwich beam is introduced to characterise its susceptibility to localised effects. Skin flexural rigidity is shown to play a key role in determining the way that the top skin allows the external load to pass over the core. Furthermore, the contact stress distribution in the interface between the central roller and the top skin, and its importance to an indentation stress analysis, are investigated. To better model the failure in the core under the vicinity of localised loads, an Arcan- type test rig is used to test honeycomb cores under simultaneous compression and shear loading. The experimental measurements show a linear relationship between the out-of-plane compression and shear in honeycomb cores. This is used to derive a failure criterion for applied shear and compression, which is combined with the high order sandwich beam theory to predict failure caused by localised loads in sandwich beams made of GFRP laminate skins and Nomex honeycomb under 3-point bending loading. Short beam tests with three different indenter's size are performed on appropriately prepared specimens. Experiments validate the theoretical approach and reveal the nature of pre- and post-failure behaviour of these sandwich beams. HOSBT is used as a compact computational tool to reconstruct failure mode maps for sandwich panels. Superposition of weight and stiffness contours on these failure maps provide carpet plots for design optimisation procedures.