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Inflammation is a biological response to injury – a fundamental part of which involves the influx of leukocytes to the affected area. Circulating neutrophils are typically the first responders to an inflammatory insult. Orchestrated interactions between neutrophils and the underlying endothelium and occurs in a process termed the “multi-step leukocyte adhesion cascade”. L-selectin, a cell adhesion molecule, expressed on all circulating neutrophils, and facilitates the initial tethering and rolling events. Previously, L-selectin on CD14-positive (“inflammatory”) monocytes was shown to undergo ectodomain “shedding”, exclusively during transendothelial migration (TEM) and not before. The consequence of this was to establish monocyte polarity within the subendothelial space. The primary aim of this project was to determine if L-selectin shedding during TEM was exclusive to monocytes or extended to neutrophils. Perfusion of primary human neutrophils over activated endothelial monolayers revealed that L-selectin shedding was also activated specifically during TEM. Ectopic expression of L-selectin tagged to green fluorescent protein (GFP) in HL-60 cells (a neutrophil-like cell line that does not express endogenous L-selectin) significantly increased their invasive potential across activated endothelial cells under flow. Blocking L-selectin shedding (either pharmacologically in primary neutrophils or genetically in HL60 cells) promoted cell elongation in fully transmigrated cells, which significantly impacted cell polarity and directional persistence in 2D and 3D collagen scaffolds. Additionally, manufacturing bespoke microfluidic flow chamber devices revealed that blocking L-selectin shedding impacted the neutrophil chemotaxis towards classic “end-stage chemoattractants”, such as fMLP. Taken together, L-selectin shedding ensures that fully transmigrated neutrophils can establish front-back polarity so that they can home optimally to their inflamed targets. As fMLP is secreted during sterile injury, the potential therapeutic targeting of L-selectin shedding in the setting of myocardial infarction is discussed.

The High Redundancy Actuator (HRA) project investigates a novel approach to fault tolerant actuation, which uses a high number of small actuation elements, assembled in series and parallel in order to form a single intrinsically fault tolerant actuator. Element faults affect the maximum capability of the overall actuator, but through control techniques, the required performance can be maintained. This allows higher levels of reliability to be attained in exchange for less over-dimensioning in comparison to conventional redundancy techniques. In addition, the combination of both serial and parallel elements provides intrinsic accommodation of both lock-up and loose faults. Research to date has concentrated on HRAs based on electromechanical technology, of relatively low order, controlled through passive Fault Tolerant Control (FTC) methods. The objective of this thesis is to expand upon this work. HRA configurations of higher order, formed from electromagnetic actuators are considered. An element model for a moving coil actuator is derived from first principles and verified experimentally. This element model is then used to form high-order, non-linear HRA models for simulation, and reduced-order representations for control design. A simple, passive FTC law is designed for the HRA configurations, the results of which are compared to a decentralised, active FTC approach applied through a framework based upon multi-agent concepts. The results indicate that limited fault tolerance can be achieved through simple passive control, however, performance degradation occurs, and requirements are not met under theoretically tolerable fault levels. Active FTC offers substantial performance improvements, meeting the requirements of the system under the vast majority of theoretically tolerable fault scenarios. However, these improvements are made at the cost of increased system complexity and a reliance on fault detection. Fault Detection (FD) and health monitoring of the HRA is explored. A simple rule-based FD method, for use within the active FTC, is described and simulated. An interacting multiple model FD method is also examined, which is more suitable for health monitoring in a centralised control scheme. Both of these methods provide the required level of fault information for their respective purposes. However, they achieve this through the introduction of complexity. The rule-based method increases system complexity, requiring high levels of instrumentation, and conversely the interacting multiple model approach involves complexity of design and computation. Finally, the development of a software demonstrator is described. Experimental rigs at the current project phase are restricted to relatively low numbers of elements for practical reasons such as cost, space and technological limitations. Hence, a software demonstrator has been developed in Matlab/Simulink which provides a visual representation of HRAs with larger numbers of elements, and varied configuration for further demonstration of this concept.

Humans activities are dominant drivers of the biogeochemical cycling of carbon (C), nitrogen (N) and phosphorus (P) in terrestrial ecosystems worldwide. Atmospheric N deposition can reduce biodiversity and have long-lasting consequences for plants and soils alike. While the ecological consequences of elevated CO2 (eCO2) are less certain, the unprecedented rise in C availability may have important ramifications for ecosystems, particularly when combined with N. As C and N pollution continue to increase, understanding their effects on ecosystem functioning and biogeochemical cycling of one of the largest and most important ecosystems; grasslands, is of paramount importance. Most research focusses on N-limited grasslands, but due to considerable differences between N and P cycling, we require a separate understanding for grasslands whose productivity is limited by P availability, for which we know very little. This thesis combines empirical and computational methodology to investigate the consequences of N pollution, eCO2, and their combination, for P-limited grasslands. It does so by utilising a state-of-the-art CO2 fumigation experiment on two contrasting grasslands from a long-term nutrient manipulation experiment. Specifically, it explores their effects on soil C sequestration, P cycling and nutrient limitation, biodiversity, and plant nutrient stoichiometry. Responses of plants and soils consistently differed between grasslands, suggesting contrasts in soil conditions and plant communities may contribute to grassland responses to biogeochemical perturbations. Nitrogen deposition strongly influenced soil organic C storage and the cycling of P, where access to organic P forms by plants may play a key role in determining the response of P-limited grasslands to N deposition. Combinations of eCO2 and N deposition considerably affected grassland communities and foliar C, N and P content of a multitude of plant species. To conclude, this thesis contributes to the pressing need to understand the responses of P-limited ecosystems to a future of high C and N availability.