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Optical wireless communications (OWC) has the potential to become a remedy for the shortage of the radio frequency (RF) spectrum. Especially in indoor environments, OWC could enable wireless home networking systems which offload data traffic from existing RF systems. In OWC, data is transmitted by modulating the intensity of light sources, typically incoherent light emitting diodes (LEDs). Thus, OWC systems employ intensity modulation (IM) and direct detection (DD) of the optical carrier. Since off-the-shelf LEDs have a limited modulation capability, the transmission bandwidth of practical OWC systems is restricted. Consequently, the available bandwidth has to be used efficiently. In this thesis, spectrally efficient optical wireless transmission techniques are evaluated. Firstly, multiple transmitter-receiver techniques are investigated. These multiple-input-multiple-output (MIMO) techniques provide high spectral efficiency, and therefore high data rates. Specifically, the MIMO techniques repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) are analysed for indoor OWC. The performance of these techniques is evaluated analytically and by means of computer simulations. It is shown that inducing power imbalance between the multiple optical transmitters can substantially improve the performance of optical MIMO techniques as the power imbalance improves the differentiability of the multiple channels. In addition, it is found that link blockage and the utilisation of transmitters having different optical wavelengths enhance channel differentiability as well. These methods enable the utilisation of optical MIMO techniques under conditions which typically disallow the application of MIMO schemes due to little differences between the multiple links. Secondly, a novel optical wireless transmitter concept is developed. This concept uses discrete power level stepping to generate intensity modulated optical signals, such as orthogonal frequency division multiplexing (OFDM) waveforms. The transmitter consists of several on-off-switchable LED groups which are individually controlled to emit scaled optical intensities. As a result, the digital-to-analogue conversion of the signals to be sent is done in the optical domain. This method enables the implementation of low-complex and power-efficient optical transmitter front-ends – the major shortcoming of conventional optical OFDM transmitters. Thirdly, a novel approach for wireless data transmission within an aircraft cabin is presented. The data is transferred by 2-dimensional visual code sequences. These sequences are displayed on the in-flight entertainment (IFE) screen and are captured by the built-in camera of a user device which acts as receiver. Transmission experiments within an aircraft cabin mock-up demonstrate the functionality of the implemented system under realistic conditions, such as ambient illumination and geometric configuration. Altogether, this thesis has analysed the potential of spectrally efficient optical wireless transmission techniques. It is shown that OWC systems can greatly benefit from these techniques.

Background: The colon is believed to salvage energy from unabsorbed starch especially when the capacity of the small intestine to digest it is limited. The extent to which this occurs is not known. Aims: The aim of this thesis was to determine site and relative extent of starch digestion and fermentation in young children using the individual and combined approaches of stable isotope breath tests and in vitro stool fermentation models. Stable Isotope Breath Test Methods: Thirteen children (10m, 3f), median (range) age 11.8 mo (7.6 -22.7 mo), took a starchy breakfast containing 13C labelled wheat flour following an overnight fast. Duplicate breath samples were obtained before breakfast and every 30 min for 12 h. Breath 13CO2 enrichment was measured by isotope ratio mass spectrometry and results were expressed as percentage dose recovered (PDR) for each 30 min. PDR data were analysed and mathematically curve fitted either assuming a constant estimate of CO2 production rate or adjusted for physical activity. Stable Isotope Breath Test Results: Mean ± SD cumulative 13C PDR (cPDR) at 12 h was 21.3% ± 8.4% for unadjusted data and 26.5% ± 11.6% for adjusted data. A composite fit of two curves fitted significantly better than a single curve. Curve fitting allowed estimation of cPDRs of small intestine (17.5% ± 6.5% and 22.7% ± 9.3% for unadjusted and adjusted data respectively) and colon (4.6% ± 2.9% and 6.3% ± 5.4 %). From these results it is speculated that the colon may account for up to 20% of starch digestion in young children. In Vitro Colonic Fermentation Methods: A simulated colonic environment was used to account for the fate of raw and cooked starch that was fermented in the colon of young children. A slurry was prepared from faecal samples of 6 infants (7-10 mo), 6 toddlers (16-21 mo) and 7 adults (24-56 years). Each slurry was anaerobically incubated with raw or cooked maize starch in MacCartney bottles in a shaking water bath. Parallel incubations were stopped at 4 and 24 h. The headspace gas volume was analysed for CO2 and methane. The culture supernatant was analyzed for the volatile short chain fatty acids acetate, propionate and butyrate (SCFA), lactate and residual starch. In Vitro Colonic Fermentation Results: There was a decreasing trend of SCFA production with age at 4 h which was not evident at 24 h. At 4 h, toddler stools produced the most CO2 followed by infants and then adults, but this trend was not seen at 24 h. Methane was detected in 3 adults only. Lactate was detected mainly at 4 h in children only. The production of SCFA at 4 h generally declined with age but the differences at 24 h were less marked, suggesting fermentation is a more rapid process in young children than in adults. A highly efficient energy salvage process may take place in the colon of young children. Calculations Using Both Data Sets and Conclusions: Using data from studies described in both parts of the dissertation, it has been possible to derive stoichiometric equations for the whole gut digestion of starch, and thereby calculate its potential energy. There are a number of limitations to the methodology and from assumptions that have been made, but this provides an attractive means to calculate relative roles of small intestine and colon to starch digestion in young children which in turn may form the scientific basis for nutritional advice given to mothers.

This thesis is concerned the development of useful engineering techniques for the characterisation and identification of nonlinear systems in terms of their Volterra Series representations. The Volterra series is presented and discussed in some detail. Various Techniques for deriving a system's Volterra kernels from a differential equation are discussed. An example of the extension of these procedures to distributed parameter systems is given in the form of the Burgers equation or nonlinear acoustic propagation. Mathematical criteria for the convergence of the series are presented and are compared with qualitaitve features of the system's behaviour which are shown to be necessary for convergence. In this way a number of criteria are developed in order to determine under what circumstance the Volterra series is suitable for the modelling of a particularly nonlinear system. Related functional series are discussed, in particular the Hermite functional series which is considered in a stochastic context. The properties of this series are used to allow an interpretation of a linear frequency response function estimator applied to a nonlinear system. A newer identification procedure is discussed which involves maximum length sequences. These are reviewed in such a way as to emphasise the important 'multiply and shift' property which makes this procedure work. A number of new results are presented which enable the experimenter to efficiently generate and manipulate such sequences. The identification procedure is examined in detail together wiht strategies to enhance its efficiency and reliability and to reduce the phenomenon of overlapping kernel slices. The procedure is tested in simulated data in order to demonstrate its properties. The same procedure is then used on a number of real nonlinear systems. The first is a small nonlinear amplifier whose second and third Volterra kernels are obtained. The second is the nonlinear path between acoustic stimulation of the human ear and measured otoacoustic (or cochlea) emissions.

Regular, everyday conversations do not occur in a vacuum. The physical and social context in which a conversation takes place is utilized through the course of that conversation—it is situated. The ways in which a context can be used vary. Sometimes we implicitly and unconsciously utilize context in interpreting others. While at a restaurant, you would effortlessly interpret “What are you going to have?” not as a general question disconnected from the current situation, but as a question about that particular restaurant’s menu. Other times we overtly utilize context to aid in communication. While out on a walk in the city, I might point to an ice cream cone that has fallen onto the street and say “Somebody’s having a bad day”, and it would be clear what I am talking about.I argue in this dissertation that the psychological category of attention is key for understanding how situated conversations operate. In contrast to viewing communication as a process of pure information exchange, I argue that communication is helpfully analyzed as a process of attention management. Our utterances, gestures, and facial expressions do not serve to merely convey information, but serve to coordinate our attentional states. I begin by focusing on a particular communicative phenomenon that I call rich demonstration. It is, roughly, a deictic (pointing) gesture that functions to communicate an entire thought, in contrast to fixing the reference of a demonstrative expression such as ‘that’. Just by making something salient, one can seemingly say something. I argue that rich demonstration is a speech act in its own right, and provide a formal semantic framework for modeling its communicative effect in discourse.I then proceed to analyze salience itself. The notion has proven useful for understanding a number of communicative phenomena, including reference resolution, certain kinds of pragmatic inference, quantifier domain restriction, and more. Focusing on cases of reference, I argue that the linguistic notion of salience is best understood in terms of the psychological notion of mutual attention. I discuss competing options, including mutual knowledge and varieties of joint attention that are weaker than mutual attention, and argue that only mutual attention suffices for establishing conversational salience. The picture that emerges is one on which conversational moves function in part to coordinate the attentional states of interlocutors.I take advantage of these considerations to argue that discourse information states are genuinely structured—they represent different types of information that can be updated independently. I argue that such structural models of conversation cannot be reasonably reduced to unstructured models, such as the Common Ground model, which flatten discourse information into one kind.This dissertation therefore develops a view of conversation as attention management. This is a perspective on situated conversation on which communicative acts are both restricted by facts about attention and function to coordinate the attentional states of interlocutors.

Lengyel, Christian M., PhD., December 2021History Greenbacks and Greybacks: Iconographic Depictions of Union and Confederate Nationalism on Civil War-Era Currency (335 pp.)Dissertation Advisor: Kevin AdamsNationalism studies have recently increased in popularity, and particularly those focused on the era of the U.S. Civil War. But for all the attention scholars have given to this specific area of research, no single investigation exists that directly compares and contrasts the visual patriotic impulses of the North and the South under the banner of one holistic work. Further, no authority has ever accomplished such a feat using the iconographies on both sides’ government-issued paper dollars as the main vehicles for inquiring into this important facet of the country’s history. The present dissertation utilizes those essential artifacts as a means of illustrating the Union and the Confederacy’s separate nationalistic philosophies and highlighting that, from the start of the struggle, they included different casts of characters, subjects, and symbols. These findings indicate that each body attempted to portray itself as a distinct entity who relied on inherently individualized sets of “signs” to exemplify its leaders’ divergent ideas about proper American patriotism. Therefore, by using the analytical technique of semiotics – as well as quantitative and qualitative assessments – to classify the images at-hand, the following review tests the significance, frequency, and type(s) of monetary vignettes that northern and southern Treasury officials employed to represent their respective nations. What it discovers is that the initial batteries of U.S. Greenbacks were far simpler, less inconsistent, and more unique in their appearance than early C.S.A. Greybacks, only showcasing added layers complexity when it became apparent that the North would emerge victorious. This project thus argues that contrary to the convoluted designs of Confederate bills, the fixed features of United States scrip simultaneously brought to the forefront and continued to mold citizens’ trust in the State which, in turn, helped to partially ensure the successes of the country and its currency.