Complex filters are multi-input, multi-output networks designed to discriminate based upon the relative phase difference between input signals. Complex filters find application in modern wireless systems for single sideband transmission and image-reject reception. This thesis presents one active complex filter implementation using two operational amplifiers per stage, termed “type-II” topology. The “type-II” originates from the passive RC-CR polyphase topology presented by Gingell in his 1973 paper, “Single sideband modulation using sequence asymmetric polyphase networks.” This new topology gains several advantages over existing complex filter implementations, namely “cascadability” (multiple sections placed in series to create a higher-order response) without altering the characteristics of each individual stage. In addition to describing the derivation of the topology and its performance relative to existing topologies, this thesis investigates the passband characteristics of a general higher-order filter and provides a passband-centric design approach through derivations of closed form expressions for passband gain and bandwidth. The thesis includes a five-stage design example using this approach in addition to an implementation, its characterization, and its comparison to the derived expressions and simulations.

The human eye is a conspicuous and unique component of facial appearance. From other mammalian eyes it is set apart mainly by its unusual shape, visible white sclera, and a wide range of iris colours, which is something unique within a single species. Whether alone or in the context of the face as a whole, eye colour is an underexplored area within research into the perception of various personality traits. In this thesis, the author first reviews the physiological factors connected with eye colour and reported correlations between eye colour and different psychological and behavioural conditions. This is followed by an investigation of a possible relationship between eye colour and perceived dominance and attractiveness. The first and second study examines whether and to what extent eye colour is associated with facial morphology responsible for perceived dominance. The results are ambiguous. A cross-cultural comparison in the third study revealed that faces with blue eyes are judged as more attractive only in populations where individuals with darker eyes predominate. It is thus discussed whether this population-specific pattern is the consequence of a negative frequency-dependent selection that may have contributed to the present-day eye colour diversity. In short, the aim of this thesis was to...

La sélection fréquence-dépendante est un mécanisme d’évolution selon lequel l’aptitude d'un type varie en fonction de sa fréquence dans la population. Ce mécanisme joue un rôle important dans de nombreuses interactions autant interspécifiques (parasitisme, prédation, compétition), qu'intra-spécifiques entre les différents phénotypes d'une même espèce. La sélection fréquence-dépendante peut être positive ou négative et favoriser alors les phénotypes communs ou rares, respectivement. Elle a été mise en évidence dans le contexte du choix de partenaire chez plusieurs espèces, notamment chez certaines espèces d'insectes (ex.: demoiselles, drosophiles, cantharide de Pennsylvanie) et de poissons (ex.: guppys, xiphos), mais elle a été aussi récemment découverte chez l’humain. L'importance de la sélection fréquence-dépendante dans le choix de partenaire chez les espèces monogames reste tout de même peu explorée et cette étude vise à combler cette lacune en utilisant le diamant mandarin, un passereau monogame, comme modèle biologique. Nous avons étudié l'importance de ce mécanisme lorsqu'un trait est neutre et lorsque celui-ci constitue un indicateur de qualité. De plus, nous avons tenté de déterminer si la présence de rivales peut modifier la préférence initiale des femelles pour les phénotypes rares ou communs. / Frequency-dependant selection is an evolution mechanism in which the fitness of a type depend of its frequency in the population. This mechanism play an important role in several interspecific (parasitism, predation, competition) and intraspecific interactions within different phenotypes of a same species. Frequency-dependant selection can be positive or negative and favor, respectively, either common or rare phenotype. This selection has been found in context of mated choice of several species, especially in insects (damselfly, drosophila, soldier beetle) and fishes (guppy, swordtail) and it has even been recently discover in humans. The significance of frequency-dependent selection in mated choice of monogamous species is still less explored and this study used the zebra finches (a monogamous passerine) in order to explored this field. We studied the significance of this mechanism when a character is neutral and when it is rather a quality cue. Also, we attempt to establish if rivals' presence affect or modify the initial preference of females for common or rare phenotypes.

The vacuum, as described by Quantum Field Theory, is not as empty as classical physics once led us to believe. In fact, it is characterised by an infinite energy stored in the ground state of its constituent fields. This infinite energy has real, tangible effects on the macroscopic clusters of matter that make up our universe. Moreover, the configuration of these clusters of matter within the vacuum in turn influences the form of the vacuum itself and so forth. In this work, we shall consider the changes to the quantum vacuum brought about by the presence of time-dependent dielectrics. Such changes are thought to be responsible for phenomena such as the simple and dynamical Casimir effects and Quantum Friction. After introducing the physical and mathematical descriptions of the electromagnetic quantum vacuum, we will begin by discussing some of the basic quasi-static effects that stem directly from the existence of an electromagnetic ground state energy, known as the \textit{zero-point energy}. These effects include the famous Hawking radiation and Unruh effect amongst others. We will then use a scenario similar to that which exhibits Cherenkov radiation in order to de-mystify the 'negative frequency' modes of light that often occur due to a Doppler shift in the presence of media moving at a constant velocity by showing that they are an artefact of the approximation of the degrees of freedom of matter to a macroscopic permittivity function. Here, absorption and dissipation of electromagnetic energy will be ignored for simplicity. The dynamics of an oscillator placed within this moving medium will then be considered and we will show that when the motion exceeds the speed of light in the dielectric, the oscillator will begin to absorb energy from the medium. It will be shown that this is due to the reversal of the 'radiation damping' present for lower velocity of stationary cases. We will then consider how the infinite vacuum energy changes in the vicinity, but outside, of this medium moving with a constant velocity and show that the presence of matter removes certain symmetries present in empty space leading to transfers of energy between moving bodies mediated by the electromagnetic field. Following on from this, we will then extend our considerations by including the dissipation and dispersion of electromagnetic energy within magneto-dielectrics by using a canonically quantised model referred to as 'Macroscopic QED'. We will analyse the change to the vacuum state of the electromagnetic field brought about by the presence of media with an arbitrary time dependence. It will be shown that this leads to the creation of particles tantamount to exciting the degrees of freedom of both the medium and the electromagnetic field. We will also consider the effect these time-dependencies have on the two point functions of the field amplitudes using the example of the electric field. Finally, we will begin the application of the macroscopic QED model to the path integral methods of quantum field theory with the purpose of making use of the full range of perturbative techniques that this entails, leaving the remainder of this adaptation for future work.

The European rewardless orchid Dactylorhiza sambucina commonly produces yellow- and purple-flowered individuals in frequencies that in different populations range from balanced to very unbalanced ones (we can find even monochromatic populations). I studied an effect of abiotic factors (soil pH, hydrolimits, slope and altitude of the locality), biotic factors (weight and viability of the seeds obtained from crossing between and within morphs) and the size of the populations on corolla colour of two morphs in European populations (the Czech Republic, Italy, Austria, Germany, France).