Gratings: Theory and Numeric Applications

International audienceThe book containes 11 chapters written by an international team of specialist in electromagnetic theory, numerical methods for modelling of light diffraction by periodic structures having one-, two-, or three-dimensional periodicity, and aiming numerous applications in many classical domains like optical engineering, spectroscopy, and optical telecommunications, together with newly born fields such as photonics, plasmonics, photovoltaics, metamaterials studies, cloaking, negative refraction, and super-lensing. Each chapter presents in detail a specific theoretical method aiming to a direct numerical application by university and industrial researchers and engineers

USING VIRTUAL REALITY TO INVESTIGATE ‘PROTEAN’ ANTI-PREDATOR BEHAVIOUR

Prey animals have evolved a wide variety of behaviours to combat the threat of predation, many of which have received considerable empirical and theoretical attention and are generally well understood in terms of their function and mechanistic underpinning. However, one of the most commonly observed and taxonomically widespread antipredator behaviours of all has, remarkably, received almost no experimental investigation: so-called ‘protean’ behaviour. This is defined as ‘behaviour that is sufficiently unpredictable to prevent a predator anticipating in detail the future position or actions of its prey’. In this thesis, I have elucidated the mechanisms that allow protean behaviour to be an effective anti-predatory response. This was explored with two approaches. Firstly, through the novel and extremely timely use of virtual reality to allow human ‘predators’ to attack and chase virtual prey in three-dimensions from a first-person perspective, thereby bringing the realism that has been missing from previous studies on predator-prey dynamics. Secondly through the three-dimensional tracking of protean behaviour in a highly tractable model species, the painted lady butterfly (Vanessa cardui). I explored this phenomenon in multiple contexts. Firstly, I simulated individual protean prey and explored the effects of unpredictability in their movement rules with respect to targeting accuracy of human ‘predators’ in virtual reality. Next, I examined the concept of ‘protean insurance’ via digitised movements of the painted lady butterfly, exploring the qualities of this animals’ movement paths related to human targeting ability. I then explored how the dynamics of animal groupings affected protean movement. Specifically, I investigated how increasing movement path complexity interacted with the well-documented ‘confusion effect’. I explored this question using both an experimental study and a VR citizen science game disseminated to the general public via the video game digital distribution service ‘Steam’. Subsequently, I explored another phenomenon associated with groupings of prey items; the ‘oddity effect’, which describes the preferential targeting of phenotypically odd individuals by predators. Typically, this phenomenon is associated with oddity of colouration or size. In this case, I investigated whether oddity of protean movement patterns relative to other group members could induce a ‘behavioural oddity effect’. Finally, I used a specialised genetic algorithm (GA) that was driven by human performance with respect to targeting prey items. I investigated the emergent protean movement paths that resulted from sustained predation pressure from humans. Specifically, I examined the qualities of the most fit movement paths with respect to control evolutions that were not under the selection pressure of human performance (randomised evolution). In the course of this thesis, I have gained a deeper understanding of a near ubiquitous component of predator prey interactions that has until recently been the subject of little empirical study. These findings provide important insights into the understudied phenomenon of protean movement, which are directly applicable to predator –prey dynamics within a broad range of taxa

Gratings: Theory and Numeric Applications, Second Revisited Edition

International audienceThe second Edition of the Book contains 13 chapters, written by an international team of specialist in electromagnetic theory, numerical methods for modelling of light diffraction by periodic structures having one-, two-, or three-dimensional periodicity, and aiming numerous applications in many classical domains like optical engineering, spectroscopy, and optical telecommunications, together with newly born fields such as photonics, plasmonics, photovoltaics, metamaterials studies, cloaking, negative refraction, and super-lensing. Each chapter presents in detail a specific theoretical method aiming to a direct numerical application by university and industrial researchers and engineers.In comparison with the First Edition, we have added two more chapters (ch.12 and ch.13), and revised four other chapters (ch.6, ch.7, ch.10, and ch.11

Fabrication of bio-mimetic multi-voided polystyrene particles acting as broad-band light scatterers

Titanium dioxide is the main white pigment used in the paint industry. It is the most efficient broad-band light scattering material due to the high refractive index and its ability to scatter light across the entire visible range of the electromagnetic spectrum. However, the high production costs and the high carbon footprint associated with this compound constitute a motivation for investigating alternative materials. Polymeric particles have the potential to become a competitive alternative considering both their physical properties and the comparatively low production costs. The objective of this work was the identification of a simple and cost effective system for the production of bio-mimetic multi-voided polymeric particles, to be introduced in paint formulation as a partial replacement for the industrial white material titanium dioxide. Nature does not rely on titanium dioxide to produce striking examples of white and is particularly ingenious in designing structures that are capable of maximising the amount of scattering in very little material, producing a remarkable white in very thin tissues. Some of the most relevant structures displaying exceptional white are the scales of the Cyphochilus and Lepidiota stigma beetles, consisting of isotropic networks of rod-like filaments of chitin and air-filled voids, and the foam-like structures found in the feathers of the Garrulus glandarius (Eurasian jay) bird, consisting in spherical air-filled voids within a keratin matrix. Those were identified as the target structures for the synthetic work. An effective way of producing porous structures in polymer materials is based on the possibility of inducing phase separation in an initially homogeneous polymer solution. The phase separation process can be initiated by the introduction of a non-solvent (NIPS) into the system and can proceed by a mechanism of nucleation and growth, producing closed pores within a polymer matrix resembling the foam-like structures of the Garrulus glandarius, or by spinodal decomposition, producing interconnected polymer-pore domains, similar to the networks found in the Cyphochilus and Lepidiota stigma beetles’ scales. Polystyrene was the polymer selected for the synthetic work, due to a good compromise between costs, refractive index and a large selection of good solvents. The first attempt at fabricating polystyrene multi-voided particles by NIPS involved a simple ternary system with tetrahydrofuran as the solvent and deionised water as the non-solvent. The process was successful in achieving porosity, but particles size and shape were difficult to control. The fabrication process was upgraded by employing an Ink-Jet apparatus, capable of reducing and standardising the size of the polystyrene solution droplets. The Ink-Jet provided a way to control particles’ shape and size, but presented a fatal flaw in the fact that the production was limited to a very small amount of material and the process was not industrially scalable. In order to overcome these limitations, a modification of the fabrication process was necessary, whereby the ability to control shape and size of the polymer solution droplets would not rely on the mechanical capabilities of the equipment employed, but rather on the intrinsic properties of the chemical system. An emulsion system was considered, where the polystyrene in toluene solution was finely dispersed into a continuous phase of deionised water. The spherical shape of the droplets was achieved by the action of the surface tension and the droplets’ size could be controlled by the level of shear applied to the emulsion mixing. The emulsion method allowed the production of particles with the desired specifications and was a scalable process. The scale up was performed in the AkzoNobel® laboratories. The polystyrene multi-voided particles, along with titanium dioxide and the extender Ropaque, were implemented in paint formulations. The paints were spread on substrates to produce paint films of a desired thickness. The reflectance of the paint films was measured using a spectrophotometer and their density calculated. The reflectance and density data allowed the calculation of the scattering coefficient of the paints. A factorial design analysis of the scattering results was performed in order to compare the scattering power of the polystyrene multi-voided particles with those of titanium dioxide and Ropaque, and to highlight any synergistic effects between these materials. The analysis concluded that polystyrene multi-voided particles have a scattering power of 57-60% that of the Ropaque extender and of 6-8% that of titanium dioxide

What does the honeybee see? And how do we know?

This book is the only account of what the bee, as an example of an insect, actually detects with its eyes. Bees detect some visual features such as edges and colours, but there is no sign that they reconstruct patterns or put together features to form objects. Bees detect motion but have no perception of what it is that moves, and certainly they do not recognize “things” by their shapes. Yet they clearly see well enough to fly and find food with a minute brain. Bee vision is therefore relevant to the construction of simple artificial visual systems, for example for mobile robots. The surprising conclusion is that bee vision is adapted to the recognition of places, not things. In this volume, Adrian Horridge also sets out the curious and contentious history of how bee vision came to be understood, with an account of a century of neglect of old experimental results, errors of interpretation, sharp disagreements, and failures of the scientific method. The design of the experiments and the methods of making inferences from observations are also critically examined, with the conclusion that scientists are often hesitant, imperfect and misleading, ignore the work of others, and fail to consider alternative explanations. The erratic path to understanding makes interesting reading for anyone with an analytical mind who thinks about the methods of science or the engineering of seeing machines

Conceptual-associative system in Aboriginal English : a study of Aboriginal children attending primary schools in metropolitan Perth

National measures of achievement among Australian school children suggest that Aboriginal students, considered as a group, are those most likely to end their schooling without achieving minimal acceptable levels of literacy and numeracy. In view of the fact that many Aboriginal students dwell in metropolitan areas and speak English as a first language, many educators have been unconvinced that linguistic and cultural difference have been significant factors in this underachievement. This study explores the possibility that, despite intensive exposure to non-Aboriginal society, Aboriginal students in metropolitan Perth may maintain, through a distinctive variety of English, distinctive conceptualisation which may help to account for their lack of success in education. The study first develops a model of conceptualisations that emerge at the group level of cognition. The model draws on the notion of distributed representation to depict what are here termed cultural conceptualisations. Cultural conceptualisations are conceptual structures such as schemas and categories that members of a cultural group draw on in approaching experience. The study employs this model with regard to Aboriginal and non-Aboriginal students attending schools in the Perth Metropolitan area. A group of 30 Aboriginal primary school students and a matching group of non-Aboriginal students participated in this study. A research technique called Association-Interpretation was developed to tap into cultural conceptualisations across the two groups of participants. The technique was composed of two phases: a) the \u27association\u27 phase, in which the participants gave associative responses to a list of 30 everyday words such as \u27home\u27 and \u27family\u27, and b) the \u27interpretation\u27 phase, in which the responses were interpreted from an ethnic viewpoint and compared within and between the two groups. The informants participated in the task individually. The analysis of the data provided evidence for the operation of two distinct, but overlapping, conceptual systems among the two cultural groups studied. The two systems are integrally related to the dialects spoken by Aboriginal and non-Aboriginal Australians, that is, Aboriginal English and Australian English. The discrepancies between the two systems largely appear to be rooted in the cultural systems which give rise to the two dialects while the overlap between the two conceptual systems appears to arise from several phenomena such as experience in similar physical environments and access to \u27modem\u27 life style. A number of responses from non-Aboriginal informants suggest a case of what may be termed conceptual seepage, or a permeation of conceptualisation from one group to another due to contact. It is argued, in the light of the data from this study, that the notions of dialect and \u27code-switching\u27 need to be revisited in that their characterisation has traditionally ignored the level of conceptualisation. It is also suggested that the results of this study have implications for the professional preparation of educators dealing with Aboriginal students

Light control and microcavity lasers based on quantum wires integrated in photonic-crystal cavities

Novel light-emitting devices and micro-optical-circuit elements will rely upon understanding and control of light-matter interaction at the nanoscale. Recent advances in nanofabrication and micro-processing make it possible to develop integrable solid-state structures where the optical- and quantum-confinement effects determine the density and distribution of the energy states, allowing for mastering the output characteristics. In semiconductor nanostructures, such as quantum wires or quantum dots (sometimes referred even to as "artificial atoms") produced by epitaxy, with characteristic dimensions of 10÷20 nm, the quantization determines light absorbtion and emission spectra. Unlike the bulk matter, these important properties depend on the size and shape of the object, which is designed by nanotechnology. In photonic crystals and photonic-crystal micro-resonators, on the other hand, due to pronounced bandgap effects acting on light, unprecedented control over reflectivity, transmission and such a fundamental quantum-mechanical property as the density of electromagnetic vacuum-field fluctuations is achieved, the latter defining the rates of spontaneous emission of an embedded source. Based on these ideas, a number of passive and active optical and optoelectronic devices is anticipated practically, in particular, semiconductor microlasers with extremely low threshold pump-powers and ultimate conversion efficiency. Within the framework of this thesis we successfully integrated site-controlled quantum wires (QWRs) in 2D photonic-crystal (PhC) microcavities, examined the basic spectral and dynamics properties of the system, implemented the QWRs as a testing light source and probed interesting cavity configurations, and finally achieved stimulated emission and lasing. Starting from the previous studies of the QWR nanostructures, we, first, designed the geometry patterns adapted for implementation in the PhC-cavity system. Crystal growth (by metal-organic vapor-phase epitaxy) of InGaAs/GaAs QWRs on such patterns was verified; single and triple vertically stacked identical wires were obtained integrated within a 260-nm thin GaAs membrane. The basic properties of such QWRs were checked by photoluminescence spectroscopy. Spectra, power-dependent blueshift and temperature dependence consistent with previous studies were evidenced. Relatively long radiative lifetimes were found (at low – 20K – temperature) in transient spectroscopy, suggesting exciton localization effects and the effective dimensionality in between 0D and 1D. Identified as the most practically feasible way of exploiting the PhC bandgap effects for achieving high-Q truly single-mode resonators, the membrane approach in 2D photonic crystals was then implemented. In our nanofabrication effort we succeeded in incorporating the QWRs into such PhC cavities with very good site-control. The site control is apparently crucial, as light-matter coupling in an optical cavity and the spontaneous-emission properties are determined by the spatial and spectral matching. Cavity Q-factors of ∼ 5000÷6000 were reached. Our technology can be readily extended to schemes involving multiple site-controlled nanostructures in single or multiple (e.g. coupled) cavities that are currently of interest for various experiments in quantum physics. We then examined several interesting cavity configurations including coupled and 1D-like PhC cavities, exploiting QWRs as an embedded local light source. Such cavity geometries are relevant to on-chip photon-transfer lines, single-photon sources, coupled-cavity lasers and quantum-optics experiments. While with 1D-like cavities we were able to track the 0D-1D transition of the photonic states and observe important implications due to distributed disorder, we also found out experimentally and analyzed numerically that in the formation of the coupled states an important feature of loss splitting appears having implications on the energy transfer. On a more fundamental level, we examined PhC-cavity and bandgap effects on the QWR spontaneous emission. It was found experimentally that, at low temperature, the QWR spontaneous emission resonantly coupled to the cavity mode can be enhanced by factors of ∼ 2 ÷ 2.5. In addition, the off-resonance part is inhibited by a factor of ∼ 3. Such measured factors suggest that the output stems from an ensemble of emitters, which is consistent with a regular QWR inhomogeneous broadening and exciton localization picture. Nevertheless, the enhancement of the spontaneous emission into the cavity mode with respect to any other available modes is then a factor of ∼ 6, which is important for microcavity laser concept based on the spontaneous-emission control. Finally, multi- and single-mode lasing is experimentally demonstrated (for the first time). In order to verify the observation of the stimulated emission and lasing, complex analysis of spectral and photon-dynamics characteristics was undertaken and compared to a rate-equation model. Significantly low threshold values of ≲ 1 μW (incident power) were achieved, with relatively high spontaneous-emission coupling factors of ∼ 0.3