Pulse propagation in the pulmonary and systemic arteries

The one-dimensional model of Olufsen (2000) [*] for blood flow in the systemic arteries has been extended and built upon in a number of ways. Firstly, it has been applied to hypotheses of diseases of the systemic circulation, and that of the microcirculation. With a view to better understanding the microcirculation (the smallest vessels of the systemic circulation) and its diseases, the model has been extended to provide predictions of the propagating pressure pulse and flow rate in small arteries. Secondly, Olufsen’s model has been used as a base upon which to build a model of the pulmonary circulation, incorporating both the pulmonary arterial and venous circulations, with detailed simulations of pressure and flow predicted in the large pulmonary arteries and large pulmonary veins. To this end, a new model has been eveloped to describe a connected network of small arteries and small veins, replacing the small arterial model used as an outflow condition in the original model. A new outflow condition to describe the return of blood from the pulmonary venous system to the left atrium of the heart has also been implemented. Finally, this new pulmonary model has been applied to various hypotheses as to the causes of diseases and disorders of the pulmonary circulation, providing predictions of pressure and flow in the large pulmonary arteries and veins in both normal and abnormal circumstances, and showing agreement with clinical observations. [*] M.S. Olufsen at al. Numerical simulation and experimental validation of blood flow in arteries with structured-tree outflow conditions. Ann Biomed Eng, 28:1281–1299, 2000

Minor planet astrophotometry

Historically, the Minor Planet Center (MPC) has concentrated on improving the quality of the astrometric observations and the resulting orbits of minor planets. In light of long-standing complaints in the literature about the quality of the photometric parameters for the minor planets, there has been a need to improve the quality of the absolute magnitudes, H, and slope parameters, G. However, this task is complex, as the bulk of the minor-planet magnitude estimates are suppl ied by the astrometric observers. These observations are not made through standard fillers and are made with respect to the (indifferent) magnitudes in numerous astrometric reference catalogues. Such magnitude estimates are labelled "astrophotometry", to reflect their low quality. This thesis describes a method for correcting the catalogue- and observer-specific errors present in the astrophotometry. This method was applied to more than 70 million astrometric observations with magnitude estimates. New H determinations have been made for 322 607 numbered minor planets, while new G determinations have been made for 64 348 numbered minor planets. New assumed G values have been determined for 258 259 numbered minor planets. Analysis of the results shows that the problems identified in the literature have been removed, particularly the -0.5 magnitude offset at H≈14 that is present in the current MPC HG data set. Implications of the new H magnitudes on the albedos determined by the WISE space mission and on the differential H distributions of various types of solar-system object are discussed

Application of Analytical Electron Microscopy to the Physical and Chemical Characterisation of Ferrihydrites

Ferrihydrite is a poorly crystalline iron (oxy)hydroxide which exists exclusively in a disordered nanocrystalline form. Lacking long range three-dimensional structural order, possessing a high density of defects and displaying variable composition depending on origin has meant that to date a clear consensus regarding a structural model has yet to be reached. A departure from traditional means of crystallographic investigation is therefore required prompting the exploration of hitherto unexplored and potentially novel methods in refining this elusive structure. Recent years have witnessed significant interest in the investigation of ferrihydrites formed in the presence of compounds such as phosphate and citrate. Novel forms of ferrihydrite have been reported, produced by the hydrothermal treatment of these modified ferrihydrites, which have the potential to increase understanding of ferrihydrite in general. This work demonstrates the application of the latest generation of aberration corrected electron microscopes to the structural and chemical characterisation of ferrihydrite produced both in vitro and within the protein cage of ferritin. Two-line ferrihydrite (2LFh), coprecipitated in the presence of varying concentrations of phosphorus (P-doped) and subject to hydrothermal and dry air annealing heat treatments, has also been investigated. By way of a thorough characterisation additional physicochemical characterisation techniques have been applied to confirm the phase purity of specimens and benchmark them against those reported in the literature. The effects of prolonged exposure to the 200 keV electron beam of the transmission electron microscope (TEM) has been investigated by the simultaneous acquisition of Fe-L and O-K edge electron energy-loss (EELS), EELS and energy dispersive X-ray (EDX) compositional and selected-area electron diffraction (SAED) data. A safe fluence level of 108 electrons nm-2 has been established, below which both 2LFh and P-doped 2LFh can be observed in their pristine state. Beyond the safe fluence limit alteration of both pristine 2LFh and the P-doped 2LFh proceeds by preferential loss of oxygen, reduction of iron and concomitant phase transformation to a material with characteristics similar to that of magnetite. A novel low-electron fluence method of scanning TEM EELS acquisition (SmartAcquisition) has been developed and its applicability to the characterisation of ferrihydrite nanoparticles proven. Results here are consistent with independently published data which confirm ferrihydrite to be a predominantly Fe(III) bearing iron-oxide material in which the iron atoms reside in six-fold coordination with oxygens and/or hydroxyls. Fe-L EELS edge analysis provides support for a new and controversial model for the structure of ferrihydrite in which a significant fraction of iron is in four fold coordination. High-angle aberration corrected scanning electron microscopy is used to investigate the morphology of ferritin mineral cores. Atomically resolved sub-unit structure is observed with individual cores comprising several crystalline units which appear to have nucleated independently of one another. The principle aim of this work it to explore the applicability of the latest generation of analytical electron microscopes for the elucidation of chemical and structural properties of challenging nanoparticulate systems

Cooperation, social selection, and language change: an experimental investigation of language divergence

In this thesis, I use an experimental model to investigate the role of social pressures in stimulating language divergence. Research into the evolution of cooperation has emphasised the usefulness of ingroup markers for swiftly identifying outsiders, who pose a threat to cooperative networks. Mechanisms for avoiding cheats and freeriders, which tend to rely on reputation, or on (explicit and implicit) contracts between individuals, are considerably less effective against short-term visitors. Outsiders, moreover, may behave according to different social norms, which may adversely affect cooperative interactions with them. There are many sources of markers by which insiders and outsiders can be distinguished, but language is a particularly impressive one. If human beings exploit linguistic variation for this purpose, we might expect the exploitation to have an influence on the cultural evolution of language, and to be involved in language divergence, since it introduces a selective pressure, by which linguistic variants are selected on the basis of their social significance. However, there is also a neutral, mechanistic model of dialect formation that relies on unconscious accommodation between interlocutors, coupled with variation in the frequency of interaction, to account for divergence. In studies of real-world communities, these factors are difficult to tease apart. The model described in this thesis put real speakers in the artificial environment of a computer game. A game consisted of a series of rounds in which players were paired up with each other in a pseudo-random order. During a round, pairs of players exchanged typed messages in a highly restricted artificial "alien language". Each player began the game with a certain number of points, distributed between various resources, and the purpose of sending messages was to negotiate to exchange these resources. Any points given away were worth double to the receiver, so, by exchanging resources, players could accumulate points for their team. However, the pairings were anonymous: until the end of a round, players were not told who they had been paired with. This basic paradigm allowed the investigation of the major factors influencing language divergence, as well as the small-scale individual strategies that contribute to it. Two major factors were manipulated: frequency of interaction and competitiveness. In one condition, all players in a game were working together; in another condition, players were put into teams, such that giving away resources to teammates was advantageous, but giving them to opponents was not. This put a pressure on players to use variation in the alien language to mark identity. A combination of this pressure and a minimum level of interaction between teammates was found to be sufficient for the alien language to diverge into "dialects". Neither factor was sufficient on its own. The results of these experiments suggest that a pressure for the socially based selection of linguistic variants can lead to divergence in a very short time, given sufficient levels of interaction between members of a group

Nitrogen enrichment in macroalgae following mass coral mortality

Scleractinian corals are engineers on coral reefs that provide both structural complexity as habitat and sustenance for other reef-associated organisms via the release of organic and inorganic matter. However, coral reefs are facing multiple pressures from climate change and other stressors, which can result in mass coral bleaching and mortality events. Mass mortality of corals results in enhanced release of organic matter, which can cause significant alterations to reef biochemical and recycling processes. There is little known about how long these nutrients are retained within the system, for instance, within the tissues of other benthic organisms. We investigated changes in nitrogen isotopic signatures (δ15N) of macroalgal tissues (a) ~ 1 year after a bleaching event in the Seychelles and (b) ~ 3 months after the peak of a bleaching event in Mo’orea, French Polynesia. In the Seychelles, there was a strong association between absolute loss in both total coral cover and branching coral cover and absolute increase in macroalgal δ15N between 2014 and 2017 (adjusted r2 = 0.79, p = 0.004 and adjusted r2 = 0.86, p = 0.002, respectively). In Mo’orea, a short-term transplant experiment found a significant increase in δ15N in Sargassum mangarevense after specimens were deployed on a reef with high coral mortality for ~ 3 weeks (p < 0.05). We suggest that coral-derived nutrients can be retained within reef nutrient cycles, and that this can affect other reef-associated organisms over both short- and long-term periods, especially opportunistic species such as macroalgae. These species could therefore proliferate on reefs that have experienced mass mortality events, because they have been provided with both space and nutrient subsidies by the death and decay of corals. © 2021, The Author(s)

Redox interactions of Tc(VII), U(VI), and Np(V) with microbially reduced biotite and chlorite

Technetium, uranium, and neptunium are contaminants that cause concern at nuclear facilities due to their long half-life, environmental mobility, and radiotoxicity. Here we investigate the impact of microbial reduction of Fe(III) in biotite and chlorite and the role that this has in enhancing mineral reactivity toward soluble TcO4 -, UO2 2+, and NpO2 +. When reacted with unaltered biotite and chlorite, significant sorption of U(VI) occurred in low carbonate (0.2 mM) buffer, while U(VI), Tc(VII), and Np(V) showed low reactivity in high carbonate (30 mM) buffer. On reaction with the microbially reduced minerals, all radionuclides were removed from solution with U(VI) reactivity influenced by carbonate. Analysis by X-ray absorption spectroscopy (XAS) confirmed reductive precipitation to poorly soluble U(IV) in low carbonate conditions and both Tc(VII) and Np(V) in high carbonate buffer were also fully reduced to poorly soluble Tc(IV) and Np(IV) phases. U(VI) reduction was inhibited under high carbonate conditions. Furthermore, EXAFS analysis suggested that in the reaction products, Tc(IV) was associated with Fe, Np(IV) formed nanoparticulate NpO2, and U(IV) formed nanoparticulate UO2 in chlorite and was associated with silica in biotite. Overall, microbial reduction of the Fe(III) associated with biotite and chlorite primed the minerals for reductive scavenging of radionuclides: this has clear implications for the fate of radionuclides in the environment

The Antarctic Peninsula Under a 1.5°C Global Warming Scenario

Warming of the Antarctic Peninsula in the latter half of the twentieth century was greater than any other terrestrial environment in the Southern Hemisphere, and clear cryospheric and biological consequences have been observed. Under a global 1.5°C scenario, warming in the Antarctic Peninsula is likely to increase the number of days above 0°C, with up to 130 of such days each year in the northern Peninsula. Ocean turbulence will increase, making the circumpolar deep water (CDW) both warmer and shallower, delivering heat to the sea surface and to coastal margins. Thinning and recession of marine margins of glaciers and ice caps is expected to accelerate to terrestrial limits, increasing iceberg production, after which glacier retreat may slow on land. Ice shelves will experience continued increase in meltwater production and consequent structural change, but not imminent regional collapses. Marine biota can respond in multiple ways to climatic changes, with effects complicated by past resource extraction activities. Southward distribution shifts have been observed in multiple taxa during the last century and these are likely to continue. Exposed (ice free) terrestrial areas will expand, providing new habitats for native and non-native organisms, but with a potential loss of genetic diversity. While native terrestrial biota are likely to benefit from modest warming, the greatest threat to native biodiversity is from non-native terrestrial species

The seasonal cycle of ocean-atmosphere CO2 Flux in Ryder Bay, West Antarctic Peninsula

Approximately 15 million km2 of the Southern Ocean is seasonally ice covered, yet the processes affecting carbon cycling and gas exchange in this climatically important region remain inadequately understood. Here, 3 years of dissolved inorganic carbon (DIC) measurements and carbon dioxide (CO2) fluxes from Ryder Bay on the west Antarctic Peninsula (WAP) are presented. During spring and summer, primary production in the surface ocean promotes atmospheric CO2 uptake. In winter, higher DIC, caused by net heterotrophy and vertical mixing with Circumpolar Deep Water, results in outgassing of CO2 from the ocean. Ryder Bay is found to be a net sink of atmospheric CO2 of 0.59–0.94 mol C m−2 yr−1 (average of 3 years). Seasonal sea ice cover increases the net annual CO2 uptake, but its effect on gas exchange remains poorly constrained. A reduction in sea ice on the WAP shelf may reduce the strength of the oceanic CO2 sink in this region

Antarctic Peninsula mesoscale cyclone variability and climatic impacts influenced by the SAM

The frequency of mesoscale cyclones in the Western Antarctic Peninsula (WAP) region during 1991-94 is correlated with the Southern Hemisphere Annular Mode (SAM) index, most strongly during winter and spring. Also, during periods of positive SAM index polarity there is a shift in the storm tracks to favor more east-bound trajectories, consistent with strengthening of circumpolar westerlies. The presence of mesoscale cyclones is associated with positive near-surface-air temperature anomalies in the WAP region year-round, largest during winter