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WRAP: Warwick Research Archive Portal: No conditions. Results ordered -Date Deposited.

Total ring depopulation is sometimes used as a management strategy for emerging infectious diseases in livestock, which raises ethical concerns regarding the potential slaughter of large numbers of healthy animals. We evaluated a farm-density-based ring culling strategy to control foot-and-mouth disease (FMD) in the United Kingdom (UK), which may allow for some farms within rings around infected premises (IPs) to escape depopulation. We simulated this reduced farm density, or "target density", strategy using a spatially-explicit, stochastic, state-transition algorithm. We modeled FMD spread in four counties in the UK that have different farm demographics, using 740,000 simulations in a full-factorial analysis of epidemic impact measures (i.e., culled animals, culled farms, and epidemic length) and cull strategy parameters (i.e., target farm density, daily farm cull capacity, and cull radius). All of the cull strategy parameters listed above were drivers of epidemic impact. Our simulated target density strategy was usually more effective at combatting FMD compared with traditional total ring depopulation when considering mean culled animals and culled farms and was especially effective when daily farm cull capacity was low. The differences in epidemic impact measures among the counties are likely driven by farm demography, especially differences in cattle and farm density. To prevent over-culling and the associated economic, organizational, ethical, and psychological impacts, the target density strategy may be worth considering in decision-making processes for future control of FMD and other diseases.

Co-infection is the simultaneous infection of a host by multiple pathogen species. This thesis explores the use of co-infection models in understanding how interactions between multiple pathogens have affected human evolution and history. I use a malaria co infection model to explore the interaction between α thalassaemia and Plasmodium vivax and P. falciparum in different settings, and demonstrate that both of these species of malaria parasite could have played a role in generating the heterogeneity of α thalassaemia frequencies in different populations. I also analyse the roles of P. vivax and P. falciparum in the evolution of Duffy negativity, showing that the frequency of the Duffy negative mutation can be driven down by the presence of P. falciparum before Duffy negativity reaches its maximum frequency in a population. Finally, I utilise a measles co-infection model to explore the possibility of the unique mortality pattern of the measles outbreak on Rotuma in 1911 being due to the immunosuppressive effect of measles and its interaction with the diversity of gut microbes present in the Rotuman population at the time. The thesis highlights that considering co-infection can give us a deeper understanding of both human population genetics and historical disease outbreaks.

We study whether Chief Executive Officer (CEO) narcissism affects a firm's share repurchase announcements and their implementations. Using signature characteristics as a measure of narcissism, we find that US firms with narcissist CEOs are more likely to make repurchase announcements and announce higher repurchase dollar amounts. However, these firms are less likely to follow through. Actual repurchases by these firms are less frequent, and they use a smaller amount of cash for share buyback because they have a higher cashflow sensitivity of cash. Narcissist CEOs' repurchase announcements are less driven by market timing and have a lower announcement effect compared to those by other CEOs. The higher rate and amount of repurchase announcements are more pronounced in poorly governed firms with narcissistic CEOs. These results are robust to various specifications including a difference-in-difference set-up using CEOs' exogenous turnover, controlling for other CEO traits and using an alternative measure of narcissism based on pronoun usage in CEO communications. Collectively, the results presented in this study demonstrate that narcissist CEOs play a critical role in the intensity of share repurchase announcements and their executions, particularly for firms with weaker governance structures.

We conjecture that a convex polytope is uniquely determined up to isometry by its edge-graph, edge lengths and the collection of distances of its vertices to some arbitrary interior point, across all dimensions and all combinatorial types. We conjecture even stronger that for two polytopes $P\subset {\mathbb {R}}^{d}$ and $Q\subset {\mathbb {R}}^{e}$ with the same edge-graph it is not possible that $Q$ has longer edges than $P$ while also having smaller vertex-point distances. We develop techniques to attack these questions and we verify them in three relevant special cases: $P$ and $Q$ are centrally symmetric, $Q$ is a slight perturbation of $P$, and $P$ and $Q$ are combinatorially equivalent. In the first two cases the statements stay true if we replace $Q$ by some graph embedding $q:V(G_{P})\to {\mathbb {R}}^{e}$ of the edge-graph $G_{P}$ of $P$, which can be interpreted as local resp. universal rigidity of certain tensegrity frameworks. We also establish that a polytope is uniquely determined up to affine equivalence by its edge-graph, edge lengths and the Wachspress coordinates of an arbitrary interior point. We close with a broad overview of related and subsequent questions.

We introduce and analyze a class of forward performance criteria in incomplete markets in the presence of model ambiguity. Incompleteness stems from general investment constraints, while model uncertainty is represented by a convex and compact set of plausible model parameter processes. Following the max-min criteria in traditional (backward) robust control, we formulate similar criteria for the robust forward performance processes and focus on the rich class of time-monotone processes. We provide a novel PDE characterization and a semi-explicit saddle-point construction of the robust forward performance criteria and their optimal policies. Furthermore, we present additional results within the class of homothetic constant relative risk aversion (CRRA) processes. Within this class, we investigate the relationship between forward performance processes on wealth and those on consumption, establishing an interesting dominance through time.

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