As near-Earth space becomes increasingly crowded with spacecraft and debris, the need for improved space situational awareness has become paramount. Contemporary ground-based systems are limited in the detection of very small or dim targets. In contrast, space-based systems, above most atmospheric interference, can achieve significant improvements in dim target detection by observing targets against a clutter-free space background, i.e. targets above the horizon (ATH). In this study, numerical methods for the evaluation of ATH coverage provided by constellations of satellites are developed. Analysis of ATH coverage volume is reduced to a planar analysis of cross-sectional coverage area in the orbit plane. The coverage model performs sequences of boolean operations between polygons representing cross-sections of satellite sensor coverage regions and regions of interest, returning the coverage area at the desired multiplicity. This methodology allows investigation of any coverage multiplicity for planar constellations of any size, and use of arbitrary sensor profiles and regions of interest. The implementation is applied to several constellation design problems demonstrating the utility of the numerical ATH coverage model in a constellation design process. / text

The importance of humus form or forest floor as a principal component of terrestrial forest ecosystems has led to the development of a taxonomic classification of humus forms for BC (first approximation: Klinka et al. 1981; second approximation: Green et al. 1993). This classification, as all others, is based on the field-observable (morphological) features because we expect that they reflect differences in the nature and development of humus forms. However, there is a continuing need to test (1) whether humus forms that appear different are in fact different in their physical, chemical, and biotic properties, and (2) the portability of the classification outside the area in which it was developed. As a result of recent studies of the biotic component of humus forms and recent testing of the classification outside British Columbia (Scandinavia, southeastern Russia, and northeastern China), we have recognized several new diagnostic horizons, and hence new taxa. In this pamphlet, we present synopsis of the third approximation of the classification for review and testing. For more detailed information on the background, methodology, and classification of humus forms, the readers should consult Green et al. (1993). Each humus form is represented by the sequence of organic and mineral horizons that constitute the humus form profile. Identification of a humus form, i.e., giving it a name, requires description of the humus form profile – the identification of master and subordinate horizons. For this reason we have included a description of the horizon designations as well as a synopsis of the classification and a key to the identification of humus forms.

No description available.

This thesis considers the links between identity and landscape in key works by American artist Roni Horn, focusing on a selection of her photo-installations and books. In particular it argues that Horn approaches landscape as a performative category through which to address the performativity of identity, and that in doing so her work privileges the viewer as an embodied participant. Drawing on a feminist approach grounded in phenomenology, the thesis locates androgyny as a key structuring principle in the artist’s work. Identifying herself as neither male nor female, Horn employs the notion of in-between-ness to negotiate gender binaries of male/female and to describe the indeterminate and contingent nature of androgynous being. Importantly, the thesis argues that Horn addresses these issues of identity by staging experiences in her work that invite the viewer to perform the very processes by which identity is defined and played out. This strategy is examined through concepts of doubling, the sublime, horizons and dwelling, each of which in their own way involve a sense of orientation and disorientation that gestures toward the in-between-ness of androgyny. The thesis also considers the tensions between visuality and embodiment in Horn’s work. Her use of photographic images within an installation practice is one that establishes a complex set of relations between the opticality of the photograph and the actuality of ‘real’ space. It is argued that the experiential potential of Horn’s photo-installations and books is only realised through the dialectical relation between visuality and embodiment in which both are equally privileged. / Full thesis with illustrations can be requested via Inter-Library Loan.

Previous studies have come to contrasting conclusions regarding nutrient limitation of hydrocarbon biodegradation in the Gulf of Mexico, and rate measurements are needed to support oil plume modeling. Thus, this study investigates the rates and controls of biodegradation in seawater and sediments, largely in the deepsea. Sediment and seawater samples were collected on research cruises in the northern Gulf from 2012 to 2014, where the seafloor was impacted by the Deepwater Horizon (DWH) oil spill. Biodegradation was clearly limited by both nitrogen and phosphorus availability in surface waters with significant rates of CO₂ production (100 μmol CO₂ l⁻¹ d⁻¹) only observed in treatments amended with ammonium and phosphate. In deepsea sediments, nutrient amendments resulted in an average of 6 fold higher degradation rates (0.49 μmol CO₂ g sed⁻¹ d⁻¹) compared to unamended controls. Microbial communities responded to oil contamination rapidly in a series of enrichment cultures, and selection was observed for populations of native hydrocarbon-degrading bacteria. Temperature was shown to be a major factor in controlling microbial community composition in the enrichments. At room temperature, community diversity in the enrichments was significantly reduced in the presence of oil, while under 4 °C, the community diversity and evenness remained relatively high upon oil amendment. From the same deepsea sediments, 30 strains of known oil-degrading bacteria (Rhodococcus and Halomonas) were enriched and isolated with hexadecane, phenanthrene, and Macondo oil as the sole carbon and energy source. Detection of these strains in sequence libraries indicates that they may have contributed to the degradation of oil deposited onto the sediments. Rhodococccus strain PC20 degraded approximately one-third of total petroleum hydrocarbons amended into cultures within 7 days. This work elucidates the controls of biodegradation and we provide model pure cultures to further elucidate the ecophysiology of hydrocarbon degradation, focusing on deepsea sediments of the northern Gulf of Mexico.

Extant research finds inconclusive evidence about the CEO horizon problem. One possibility is that compensation committees design CEO compensation in a way that discourages retiring CEOs from opportunistic earnings management and R&D reduction. However, compensation committees dominated by co-opted directors may not be as effective as those with fewer co-opted directors in mitigating the CEO horizon problem, because directors co-opted by the CEO tend to bias their decisions in favor of the CEO. I find that compensation committees dominated by co-opted directors are associated with higher CEO compensation packages. I document R&D reduction and accruals management in firms with retiring CEOs and compensation committees dominated by co-opted directors, and find that R&D reduction and income-increasing accruals are less discouraged by compensation committees dominated by co-opted directors when deciding CEO compensation. I also examine the effect of boards of directors and compensation committee characteristics on CEO compensation and on mitigating the CEO horizon problem. I find that CEO compensation positively associates with CEO power, director independence, and the percentage of busy directors, and negatively associates with board of directors and committee size and director ownership. Moreover, I find that retiring CEOs are more likely to reduce R&D expenditures when CEOs have more power, and director tenure is longer; retiring CEOs in firms with large boards of directors and compensation committees are less likely to manage accruals.

Variable Horizon Model Predictive Control (VH-MPC) is a form of predictive control that includes the horizon length as a decision variable in the constrained optimisation problem solved at each iteration. It has been recently applied to completion problems, where the system state is to be steered to a closed set in finite time. The behaviour of the system once completion has occurred is not considered part of the control problem. This thesis is concerned with three aspects of robustness and optimality in VH-MPC completion problems. In particular, the thesis investigates robustness to well defined but unpredictable changes in system and controller parameters, robustness to bounded disturbances in the presence of certain input parameterisations to reduce computational complexity, and optimal robustness to bounded disturbances using tightened constraints. In the context of linear time invariant systems, new theoretical contributions and algorithms are developed. Firstly, changing dynamics, constraints and control objectives are addressed by introducing the notion of feasible contingencies. A novel algorithm is proposed that introduces extra prediction variables to ensure that anticipated new control objectives are always feasible, under changed system parameters. In addition, a modified constraint tightening formulation is introduced to provide robust completion in the presence of bounded disturbances. Different contingency scenarios are presented and numerical simulations demonstrate the formulation’s efficacy. Next, complexity reduction is considered, using a form of input parameterisation known as move blocking. After introducing a new notation for move blocking, algorithms are presented for designing a move-blocked VH-MPC controller. Constraints are tightened in a novel way for robustness, whilst ensuring that guarantees of recursive feasibility and finite-time completion are preserved. Simulations are used to illustrate the effect of an example blocking scheme on computation time, closed-loop cost, control inputs and state trajectories. Attention is now turned towards mitigating the effect of constraint tightening policies on a VH-MPC controller’s region of attraction. An optimisation problem is formulated to maximise the volume of an inner approximation to the region of attraction, parameterised in terms of the tightening policy. Alternative heuristic approaches are also proposed to deal with high state dimensions. Numerical examples show that the new technique produces substantially improved regions of attraction in comparison to other proposed approaches, and greatly reduces the maximum required prediction horizon length for a given application. Finally, a case study is presented to illustrate the application of the new theory developed in this thesis to a non-trivial example system. A simplified nonlinear surface excavation machine and material model is developed for this purpose. The model is stabilised with an inner-loop controller, following which a VH-MPC controller for autonomous trajectory generation is designed using a discretised, linearised model of the stabilised system. Realistic simulated trajectories are obtained from applying the controller to the stabilised system and incorporating the ideas developed in this thesis. These ideas improve the applicability and computational tractability of VH-MPC, for both traditional applications as well as those that go beyond the realm of vehicle manœuvring.

A UAV swarm is simulated using Horizon Simulation Framework. The asset utilized for the swarm agent is a simplified model of the MQ-1 Predator, a large fixed-wing aircraft. The simulated swarm utilizes a decentralized cooperative control approach to command the assets through the use of digital pheromones and a pheromone map. Each vehicle operates at steady-state flight conditions of 36 m/s with an altitude of 1,800 m, and utilize an LQR set-point controller to maneuver through the pheromone map. All pheromone and aircraft related models are written in Python to expand the HSF scripting capability and include airborne scenarios. The simulation study focuses in the variation of three parameters in the repelling pheromone model. The first two are the update and deposit parameters with values of 2, 10, and 18. The third is the threshold parameter with values of 1e-02, 1e-10, and 1e-18. The lower parameter values provide more time-on-target while the higher parameters allow the swarm to search the surrounding area by only visiting the grid-space once.

Architecture exists where the world of ideas meets the world of materials. From its general scheme all the way to the joinery of the floorboards, the proposed building should serve a guiding idea. Otherwise, architecture is not architecture but simply functional construction. Theater exists within a similar framework, whereby the actor's work is a mundane manifestation of the elements extracted from the world of ideas, making it the perfect conduit to examine the reconciliation of these oppositions: the mundane and the ethereal, the quotidian and the philosophical, the earth and the heavens… By examining the dichotomous relationship between the tectonic and the stereotomic, the project proposed within these pages provides for a spatial experience that will aid its audience in shedding the entrapments of their daily lives as they proceed towards the auditorium to watch a play. As they move through the building, they will walk through six-foot thick brick walls of heavy stereotomy towards a lighter tectonic environment.  As they approach the architectonic auditorium, the horizon, which they could initially only see through small openings within the massive brick walls, becomes more prominent, reminding them of the spherical nature of our world and the existence of an entire universe outside of our frame of reference - a phenomenon which is symbolic of the world of ideas that provides us with theater and architecture. / Master of Architecture

This set of drawings, paintings, and photographs explores the realms of knowledge and experience in architecture through analytical and perceptual means. In other words, how physical, material considerations inform the experience of moving through space, the perception of space, and the memory of place. These themes and questions are considered through the design of an observation tower that punctuates the ambiguous joint between land and water, earth and sky on the southwestern most point on the Isle of Skye, Scotland, UK. / Master of Architecture