The controls on earthquake ground motion in foreland-basin settings: The effects of basin and source geometry

SUMMARYRapid urban growth has led to large population densities in foreland basin regions, and therefore a rapid increase in the number of people exposed to hazard from earthquakes in the adjacent mountain ranges. It is well known that earthquake-induced ground shaking is amplified in sedimentary basins. However, questions remain regarding the main controls on this effect. It is, therefore, crucial to identify the main controls on earthquake shaking in foreland basins as a step towards mitigating the earthquake risk posed to these regions. We model seismic-wave propagation from range-front thrust-faulting earthquakes in a foreland-basin setting. The basin geometry (depth and width) and source characteristics (fault dip and source-to-basin distance) were varied, and the resultant ground motion was calculated. We find that the source depth determines the amount of near-source ground shaking and the basin structure controls the propagation of this energy into the foreland basin. Of particular importance is the relative length scales of the basin depth and dominant seismic wavelength (controlled by the source characteristics), as this controls the amount of dispersion of surface-wave energy, and so the amplitude and duration of ground motion. The maximum ground motions occur when the basin depth matches the dominant wavelength set by the source. Basins that are shallow compared with the dominant wavelength result in low-amplitude and long-duration dispersed waveforms. However, the basin structure has a smaller effect on the ground shaking than the source depth and geometry, highlighting the need for understanding the depth distribution and dip angles of earthquakes when assessing earthquake hazard in foreland-basin settings.EPSRC iCASE PhD Studentship in collaboration with Ove Arup and Partners Ltd

Reality as a simulation of reality: robot illusions, fundamental limits, and a physical demonstration

We consider problems in which robots conspire to present a view of the world that differs from reality. The inquiry is motivated by the problem of validating robot behavior physically despite there being a discrepancy between the robots we have at hand and those we wish to study, or the environment for testing that is available versus that which is desired, or other potential mismatches in this vein. After formulating the concept of a convincing illusion, essentially a notion of system simulation that takes place in the real world, we examine the implications of this type of simulability in terms of infrastructure requirements. Time is one important resource: some robots may be able to simulate some others but, perhaps, only at a rate that is slower than real-time. This difference gives a way of relating the simulating and the simulated systems in a form that is relative. We establish some theorems, including one with the flavor of an impossibility result, and providing several examples throughout. Finally, we present data from a simple multi-robot experiment based on this theory, with a robot navigating amid an unbounded field of obstacles

Systematic derivation of a surface polarization model for planar perovskite solar cells

Increasing evidence suggests that the presence of mobile ions in perovskite solar cells can cause a current-voltage curve hysteresis. Steady state and transient current-voltage characteristics of a planar metal halide CH$_3$NH$_3$PbI$_3$ perovskite solar cell are analysed with a drift-diffusion model that accounts for both charge transport and ion vacancy motion. The high ion vacancy density within the perovskite layer gives rise to narrow Debye layers (typical width $\sim$2nm), adjacent to the interfaces with the transport layers, over which large drops in the electric potential occur and in which significant charge is stored. Large disparities between (I) the width of the Debye layers and that of the perovskite layer ($\sim$600nm) and (II) the ion vacancy density and the charge carrier densities motivate an asymptotic approach to solving the model, while the stiffness of the equations renders standard solution methods unreliable. We derive a simplified surface polarisation model in which the slow ion dynamic are replaced by interfacial (nonlinear) capacitances at the perovskite interfaces. Favourable comparison is made between the results of the asymptotic approach and numerical solutions for a realistic cell over a wide range of operating conditions of practical interest.Comment: 32 pages, 7 figure

Running: A Flexible Situated Study

This paper describes a situated study of personal informatics applications for running that had to be conducted in a flexible and pragmatic way to adjust for the context of use. A qualitative situated study highlighted important differences in runners' motivations, uncovering markedly different uses and preferences between people who run either for health or for pleasure, but also underscored how the physical nature of the interaction impacted data collection. By adjusting the method to be sensitive to the physical nature of the interaction and the preferences of the participants, a pragmatic situated approach provided insights into how these technologies are actually used

Habitat selection, numbers and demographics of large mammalian herbivores in Ithala Game Reserve, KwaZulu-Natal.

Thesis (M.Sc.)-University of KwaZulu-Natal, 2005.With the purpose of improving the conservation management of Ithala Game Reserve and other similar reserves, the aims of this study were to determine the reserve's large mammalian herbivores' habitat occupancy, numbers and demographics, to investigate the feasibility of road strip counts as a census method for the same herbivores and to establish what environmental factors influence their habitat occupancy, numbers and demographics. Four years of demographic data were collected by vehicle transects on giraffe, kudu, wildebeest and impala. During the final two years additional positional data, using GPS, were collected on these and the reserve's other large herbivores. Sightings were recorded on the basis of habitat type occupied, a GIS was then used to define area sampled and hence derive habitat occupancy densities. GIS was further used to determine both absolute population sizes and, by over-laying other available GIS data, the relevance of distance to surface water, soil type and degree of slope to species' habitat preferences. Species showed non-random, significant habitat selections broadly in line with established preferences. Deterioration in habitat quality in winter generally lead to changes in habitat selection and the extent and nature of these changes related to the severity of resource pressure for individual species. This in turn was influenced by the species digestive strategy i.e. ruminant versus non-ruminant, grazer versus browser. Generally species showed a dry season move down the slope, moving, in some cases, onto heavier soils. Hartebeest, warthog, wildebeest and impala were strongly attracted to winter grass flushes. Lack of predation may be influencing the habitat selection decisions of impala and giraffe and kudu females, as well as allowing giraffe, wildebeest and impala to attain comparatively high densities. Giraffe density (effectively 1.8 km - 2) was abnormally high and their habitat quality poor, leading to a decline in numbers and low fecundity-related demographics. Wildebeest density (6 km -2) was also abnormally high and this may be instrumental in the poor performance of the rare tsessebe population, which is in decline and shows low fecundity-related demo graphics, increased dry season pressure on other grazers in general and impala 111 unexpectedly preferring browse habitats, rather than grasslands, in the wet season. Wildebeest fecundity declined in response to lower rainfall over the early period of lactation. Herbivores with an open social structure generally showed a dry season decrease in group size, although wildebeest and hartebeest showed, atypically, an Increase. Giraffe, zebra and impala adult sex ratios were comparatively less female biased, probably due to minimal predation. Territorial behaviour, virtually year round by wildebeest bulls and over the rut by impala bulls, imposed spatial sexual segregation between breeding and bachelor herds in these species. Outside of these periods, and generally in species not exhibiting territoriality, social sexual segregation was maintained and appeared to relate to differing activity budgets. Areas of concern for management are highlighted. Numbers results were generally acceptable and the method is proposed as a cost effective alternative in reserves with diverse topography. Underlying environmental determinants of habitat occupancy, numbers and demographics, together with associated annual or seasonal changes, were habitat quality, competition and predation