The Karoo sand sea in changing climates: Early Jurassic interdune lakes and erg dynamics in southern Africa

Aeolian systems have a particular sensitivity to climate change, and where these are preserved in the geological record, they can provide insights into palaeo-climatic drivers of erg dynamics through time. This thesis investigates the sedimentary geology of the southern extension of a vast ancient desert system that was active over Pangaea and formed part of one of the largest known sand seas in Earth's history. The Lower Jurassic Clarens Formation in the main Karoo Basin of southern Africa has been interpreted as an aeolian succession that is dominated by massive sandstones in the lower and upper parts of the unit, whereas large-scale cross-bedded sandstones are mostly associated with its middle part. Lenticular mudstones and sandstones with ripple marks, ripple crosslamination, horizontal lamination and desiccation cracks have also been reported from the lower and upper parts of the succession. Based on the stratigraphic distribution of the sedimentary facies, the formation is informally subdivided into 3 zones that seem to reflect a wet-dry-wet climate megacycle. To date, the age of the formation is based on a very small detrital zircon dataset, the bioand chronostratigraphy of the conformably underlying Elliot Formation and the radioisotopic dates of Drakensberg Group basalts that are conformably overlying the Clarens Formation. Thus far, few investigations have targeted the evolution of this Early Jurassic fluvio-lacustrine-aeolian system, and the origin of massive sandstone facies that dominates parts of the formation. Therefore, this study re-evaluates the origin and basinal distribution of the sedimentary facies, and the spatiotemporal controls on erg development during the deposition of the Clarens Formation. Moreover, this study provides the first robust chronostratigraphic framework and provenance history for this iconic Early Jurassic aeolian system of southwestern Gondwana. The wet-dry-wet climate megacycle is not only corroborated herein, but using maximum depositional ages from detrital zircons, these climatic changes are now better dated. The results show a Late Sinemurian wet phase, an larly Pliensbachian dry phase and a late Pliensbachian wet phase during Clarens times. Newly documented field evidence shows that ponds and large lakes coexisted with aeolian dunes, with sand sheets, loess plains and fluvial systems having been established downwind. The size of the late Sinemurian ponds and lakes were controlled by their proximity to the erg margin, such that small ponds developed close to the erg centre, and large lakes were established along the erg margin. By the Early Pliensbachian, an intensification of the arid conditions led to the increased availability of sediments for aeolian entrainment, resulting in expansion of the erg eastward. Wet conditions ensued once again in the Late Pliensbachian, and lead to the contraction of the erg and expansion of loess plains with seasonally wet interdunes. Sediment, mostly supplied from the west, was overwhelmingly recycled from pre-existing, Karoo-age deposits and sedimentary rocks associated with the Pan-African orogeny, although evidence for some non-sedimentary and young, syn-Clarens sources are also present. The youngest zircon population show subtle temporal and spatial trends that can be used as proxies for the erg development. The late Sinemurian signal is identified in the lower zone in the south of the basin and is incorporated in subsequent zones in the central and northern parts of the basin, suggesting that, although the main wind direction was from the west northwest, the basin was filled from south to north. This newly established temporal framework of the wet-dry-wet climate cycle in the Clarens Formation corresponds well with the palaeoclimatic trends interpreted for the Tethyan margin of Gondwana, signifying that this may have been a global trend in the Early Jurassic

FPGA Based Diagnostics for the Mega-Amp Spherical Tokamak Upgrade

Terrestrial fusion power is a low carbon alternative to conventional power sources with reduced waste and proliferation concerns relative to fission power. The complexity of fusion research devices means that many high performance diagnostics are necessary to investigate the underlying physics of the environment. Field Programmable Gate Array technology provides a powerful and flexible option when designing bespoke instrumentation

A Study of Gradient Climbing Technique Using Cluster Space Control of Multi-Robot Systems

The design of the multi-robot system for distributed sensing and gradient climbing focuses on the capability to optimize the performance of tasks simultaneously. The strategy is to utilize the cluster’s redundancy and flexibility to gain and maximize the overall coverage of surveying parameters so as to surpass the performance of any single robot. The collaborative nature of the cluster provides a more efficient and effective platform for collecting data and conducting fieldwork. The purpose of this study is to explore the existing cluster space control technique to show effective gradient-based navigation, particularly that of climbing a gradient in a sensed parameter field to the local maximum. In order to achieve positive results, we need to estimate the gradient direction based on real-time measurements captured by sensors on the distributed robotic network, and then maneuver the cluster to travel in the estimated direction. Verification and characterization of this technique has been performed through both simulation and hardware-in-the-loop experimentation. In these tests, the gradient controller enabled the cluster to sense and climb the gradient in a parameterized field using kayaks in a marine environment and utilizing wheeled robots in a land based system. The successful outcome of these demonstrations proves the value of the cluster space control technique and showcases how it can be used for efficiently locating minimum and maximum features in a parameter field

The relationship between vocabularies, general and specific, and performance on specified tests

Thesis (Ed.M.)--Boston Universit

Flow rate--pressure drop relation for deformable shallow microfluidic channels

Laminar flow in devices fabricated from soft materials causes deformation of the passage geometry, which affects the flow rate--pressure drop relation. For a given pressure drop, in channels with narrow rectangular cross-section, the flow rate varies as the cube of the channel height, so deformation can produce significant quantitative effects, including nonlinear dependence on the pressure drop [{Gervais, T., El-Ali, J., G\"unther, A. \& Jensen, K.\ F.}\ 2006 Flow-induced deformation of shallow microfluidic channels.\ \textit{Lab Chip} \textbf{6}, 500--507]. Gervais et. al. proposed a successful model of the deformation-induced change in the flow rate by heuristically coupling a Hookean elastic response with the lubrication approximation for Stokes flow. However, their model contains a fitting parameter that must be found for each channel shape by performing an experiment. We present a perturbation approach for the flow rate--pressure drop relation in a shallow deformable microchannel using the theory of isotropic quasi-static plate bending and the Stokes equations under a lubrication approximation (specifically, the ratio of the channel's height to its width and of the channel's height to its length are both assumed small). Our result contains no free parameters and confirms Gervais et. al.'s observation that the flow rate is a quartic polynomial of the pressure drop. The derived flow rate--pressure drop relation compares favorably with experimental measurements.Comment: 20 pages, 6 figures; v2 minor revisions, accepted for publication in the Journal of Fluid Mechanic

Howard, George Elliott (1849-1928)

George Elliott Howard, a distinguished social scientist trained initially in history, rose to the presidency of the American Sociological Society in 1917. Howard earned the A.B. in 1876 at the University of Nebraska. Following two years of advanced study in Germany, Howard joined the Nebraska faculty in 1879. Howard\u27s most prominent Nebraska student from this period, Amos Griswold Warner, later wrote American Charities (1894) - a standard classic in the field. Howard was named to the prestigious First Faculty of Stanford University in 1891

The effects of collaboration scripts on the number and quality of student interactions in a social annotation tool

[EN] Social Annotation (SA) tools can be used to facilitate active and collaborative learning when students have to study academic texts. However, making these tools available does not ensure students participate in argumentative discussions. Scaffolding students by means of collaborations scripts geared towards collaboration and discussion encourages students to engage in meaningful, high-quality interactions. We conducted an experiment with students (n=59) in a course running at a Dutch university, using the SA tool Perusall. A control group received normal instructions, while an experimental group received scaffolding through collaboration scripts. The results showed a significant increase in the number of responses to fellow students for the experimental group compared to the control group. The quality of the annotations, measured on levels of Bloom’s taxonomy, increased significantly for the experimental group compared to both its baseline measurement and the control group. However, when scaffolding was faded out over subsequent assignments these differences became non-significant. The experimental groups’ increased quality of annotations did not remain over time, suggesting that internalization of the scripts was not achieved.De Boer, V.; Spoelstra, H. (2021). The effects of collaboration scripts on the number and quality of student interactions in a social annotation tool. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 967-974. https://doi.org/10.4995/HEAd21.2021.12862OCS96797

Spatial Frequency Response of Acrylamide Based Holographic Photopolymer

It has been shown that photopolymers are useful in holographic optical elements [1] and holographic interferometry [2]. However, the list of potential applications increases greatly if reflection holography is possible. Reflection holography requires a material that has the potential to record high spatial frequencies. Here we studied the spatial frequency response of an acrylamide based dye sensitized holographic photopolymer. We have investigated the effect of molecular weight of the binder and concentration of crosslinking monomer on diffusion using real time monitoring of the holographic grating formation. The effect of uniform pre-exposure on diffusion was also investigated. We have also demonstrated that reflection holograms can be recorded in the material