Distributed Robotic Vision for Calibration, Localisation, and Mapping

This dissertation explores distributed algorithms for calibration, localisation, and mapping in the context of a multi-robot network equipped with cameras and onboard processing, comparing against centralised alternatives where all data is transmitted to a singular external node on which processing occurs. With the rise of large-scale camera networks, and as low-cost on-board processing becomes increasingly feasible in robotics networks, distributed algorithms are becoming important for robustness and scalability. Standard solutions to multi-camera computer vision require the data from all nodes to be processed at a central node which represents a significant single point of failure and incurs infeasible communication costs. Distributed solutions solve these issues by spreading the work over the entire network, operating only on local calculations and direct communication with nearby neighbours. This research considers a framework for a distributed robotic vision platform for calibration, localisation, mapping tasks where three main stages are identified: an initialisation stage where calibration and localisation are performed in a distributed manner, a local tracking stage where visual odometry is performed without inter-robot communication, and a global mapping stage where global alignment and optimisation strategies are applied. In consideration of this framework, this research investigates how algorithms can be developed to produce fundamentally distributed solutions, designed to minimise computational complexity whilst maintaining excellent performance, and designed to operate effectively in the long term. Therefore, three primary objectives are sought aligning with these three stages

Geometrical and Kitaev Frustration in Spin-Orbit Coupled Magnets

In materials with significant interactions between magnetic spins, the reduction of temperature below the scale of the magnetic interaction of the spins $J\approx k_BT$ generally results in the formation of static spin textures. Frustration between interactions can result in either the significant reduction of the ordering temperature or the formation of an exotic and long sought after spin-liquid state. The origin of the frustration originates from the arrangement of spins on lattices with geometric frustration, such as the triangular and kagome lattices, where no ordered state can satisfy all interactions. Exchange anisotropy induced by strong spin-orbit coupling has emerged as another route towards frustration in so-called Kitaev materials. In this dissertation, the low energy properties of five different strongly spin-orbit coupled frustrated magnets are investigated experimentally. Through a variety of measurements and theoretical studies, we achieve an understanding of the unusual forms of magnetism in Ba$_4$Nb(Ru,Ir)$_3$O$_{12}$, $\beta$-Li$_2$IrO$_3$, D$_3$LiIr$_2$O$_6$, and BaCo$_2$(AsO$_4$)$_2$, all of which are investigated for potential spin-liquid behaviour. Ba$_4$NbRu$_3$O$_{12}$ and Ba$_4$NbIr$_3$O$_{12}$ are "traditional" quantum spin-liquid candidates in that the origin of their frustrated interactions lies in the triangular lattice upon which (Ru,Ir)$_3$O$_{12}$ J$_{eff}=\frac{1}{2}$ trimers sit. Neutron scattering measurements and bulk characterization are used to characterize the magnetic ground states and excitations in each material. The lithium iridates $\beta$-Li$_2$IrO$_3$ and D$_3$LiIr$_2$O$_6$ are Kitaev materials in which strong ferromagnetic bond-dependent interactions are the result of the strong spin-orbit coupled Ir$^{4+}$ ions in octahedral crystal fields on a honeycomb lattice. Isotope enriched powder samples are examined by inelastic neutron scattering, and both materials show evidence of Kitaev interactions. D$_3$LiIr$_2$O$_6$ in particular does not show any evidence of magnetic order, and polarized inelastic neutron scattering combined with THz spectroscopy reveal low energy excitations suggestive of a Kitaev spin-liquid ground state. The final part of the thesis describes extensive work on BaCo$_2$(AsO$_4$)$_2$, a material recently examined for its potential realization of Kitaev physics. Detailed analysis of single crystal inelastic neutron spectroscopy in an in-plane field is performed by the application of linear spin-wave theory and molecular dynamics simulations, and we rigorously show that BCAO is not a Kitaev material but instead is driven by competing interactions between first and third neighbors with an XXZ type planar anisotropy

Natural drivers of multidecadal Arctic sea ice variability over the last millennium

This is the final version. Available from Nature Research via the DOI in this record.The climate varies due to human activity, natural climate cycles, and natural events external to the climate system. Understanding the different roles played by these drivers of variability is fundamental to predicting near-term climate change and changing extremes, and to attributing observed change to anthropogenic or natural factors. Natural drivers such as large explosive volcanic eruptions or multidecadal cycles in ocean circulation occur infrequently and are therefore poorly represented within the observational record. Here we turn to the first high-latitude annually-resolved and absolutely dated marine record spanning the last millennium, and the Paleoclimate Modelling Intercomparison Project (PMIP) Phase 3 Last Millennium climate model ensemble spanning the same time period, to examine the influence of natural climate drivers on Arctic sea ice. We show that bivalve oxygen isotope data are recording multidecadal Arctic sea ice variability and through the climate model ensemble demonstrate that external natural drivers explain up to third of this variability. Natural external forcing causes changes in sea-ice mediated export of freshwater into areas of active deep convection, affecting the strength of the Atlantic Meridional Overturning Circulation (AMOC) and thereby northward heat transport to the Arctic. This in turn leads to sustained anomalies in sea ice extent. The models capture these positive feedbacks, giving us improved confidence in their ability to simulate future sea ice in in a rapidly evolving Arctic.Natural Environment Research Council (NERC)Natural Environment Research Council (NERC)Natural Environment Research Council (NERC)Leverhulme TrustAustralian Research CouncilEuropean Union’s Horizon 202

Population screening for colorectal cancer means getting FIT:the past, present, and future of colorectal cancer screening using the fecal immunochemical test for hemoglobin (FIT)

Fecal immunochemical tests for hemoglobin (FIT) are changing the manner in which colorectal cancer (CRC) is screened. Although these tests are being performed worldwide, why is this test different from its predecessors? What evidence supports its adoption? How can this evidence best be used? This review addresses these questions and provides an understanding of FIT theory and practices to expedite international efforts to implement the use of FIT in CRC screening

Inconsistent strategies to spin up models in CMIP5: implications for ocean biogeochemical model performance assessment

International audienceDuring the fifth phase of the Coupled Model Inter-comparison Project (CMIP5) substantial efforts were made to systematically assess the skill of Earth system models. One goal was to check how realistically representative marine biogeochemical tracer distributions could be reproduced by models. In routine assessments model historical hind-casts were compared with available modern biogeochemi-cal observations. However, these assessments considered neither how close modeled biogeochemical reservoirs were to equilibrium nor the sensitivity of model performance to initial conditions or to the spin-up protocols. Here, we explore how the large diversity in spin-up protocols used for marine biogeochemistry in CMIP5 Earth system models (ESMs) contributes to model-to-model differences in the simulated fields. We take advantage of a 500-year spin-up simulation of IPSL-CM5A-LR to quantify the influence of the spin-up protocol on model ability to reproduce relevant data fields. Amplification of biases in selected biogeochemical fields (O2, NO3, Alk-DIC) is assessed as a function of spin-up duration. We demonstrate that a relationship between spin-up duration and assessment metrics emerges from our model results and holds when confronted with a larger ensemble of CMIP5 models. This shows that drift has implications for performance assessment in addition to possibly aliasing estimates of climate change impact. Our study suggests that differences in spin-up protocols could explain a substantial part of model disparities, constituting a source of model-to-model uncertainty

Antilymphoid antibody preconditioning and tacrolimus monotherapy for pediatric kidney transplantation

Objective: Heavy post-transplant immunosuppression may contribute to long-term immunosuppression dependence by subverting tolerogenic mechanisms; thus, we sought to determine if this undesirable consequence could be mitigated by pretransplant lymphoid depletion and minimalistic post-transplant monotherapy. Study design: Lymphoid depletion in 17 unselected pediatric recipients of live (n = 14) or deceased donor kidneys (n = 3) was accomplished with antithymocyte globulin (ATG) (n = 8) or alemtuzumab (n = 9). Tacrolimus was begun post-transplantation with subsequent lengthening of intervals between doses (spaced weaning). Maintenance immunosuppression, morbidity, graft function, and patient/graft survival were collated. Results: Steroids were added temporarily to treat rejection in two patients (both ATG subgroup) or to treat hemolytic anemia in two others. After 16 to 31 months (mean 22), patient and graft survival was 100% and 94%, respectively. The only graft loss was in a nonweaned noncompliant recipient. In the other 16, serum creatinine was 0.85 ± 0.35 mg/dL and creatinine clearance was 90.8 ± 22.1 mL/1.73 m2. All 16 patients are on monotherapy (15 tacrolimus, one sirolimus), and 14 receive every other day or 3 times per week doses. There were no wound or other infections. Two patients developed insulin-dependent diabetes. Conclusion: The strategy of lymphoid depletion and minimum post-transplant immunosuppression appears safe and effective for pediatric kidney recipients. © 2006 Elsevier Inc. All rights reserved

Cost-effectiveness of Pharmaceutical-based Pandemic Influenza Mitigation Strategies1

Population prepandemic vaccine and antiviral treatment strategies may be cost-effective

Syndromic Surveillance and Bioterrorism-related Epidemics

To facilitate rapid detection of a future bioterrorist attack, an increasing number of public health departments are investing in new surveillance systems that target the early manifestations of bioterrorism-related disease. Whether this approach is likely to detect an epidemic sooner than reporting by alert clinicians remains unknown. The detection of a bioterrorism-related epidemic will depend on population characteristics, availability and use of health services, the nature of an attack, epidemiologic features of individual diseases, surveillance methods, and the capacity of health departments to respond to alerts. Predicting how these factors will combine in a bioterrorism attack may be impossible. Nevertheless, understanding their likely effect on epidemic detection should help define the usefulness of syndromic surveillance and identify approaches to increasing the likelihood that clinicians recognize and report an epidemic