An Investigation of the Postsubiculum’s role in Spatial Cognition

The hippocampal formation has been implicated in spatial formation for many decades. The hippocampus proper has received the most attention but other regions of the hippocampal formation contribute largely to spatial cognition. This thesis concentrated on one such region, the postsubiculum. The postsubiculum is considered important because it contains head direction cells and because it thought to be a major input to the hippocampus, via the entorhinal cortex. This thesis aims to test the functional role of the rat postsubiculum under two types of situation: one where the rat must rely on idiothetic cues for navigation, and another where the rat has visual cues present and can rely on these for orientation. The thesis also investigates hippocampal place cells and their stability over time after short exposures to novel environments. Chapter 3 of this thesis aimed to test whether the postsubiculum is necessary for path integration during a homing task. Rats were trained on a homing task on a circular platform maze. Once the task was acquired, rats were given lesions of the postsubiculum or sham lesions and then re-tested on the path integration task. The homing performance of rats with lesions of the postsubiculum was as good as that of the sham rats. A series of manipulations suggests that the rats were homing by path integration, confirmed by probe tests. The rats were then tested on a forced-choice delayed alternation T-maze task that revealed a significant impairment in alternation with delays of 5, 30, and 60 seconds. This suggests that the postsubiculum is not necessary for path integration in a homing task but is necessary for avoiding previously visited locations as is necessary in an alternation task. The experiments in Chapters 4 and 5 of this thesis aimed to investigate the effects of postsubiculum pharmacological inactivation on hippocampal CA1 place cells when rats were introduced to a novel environment with visual cues. A necessary first step was to assess place cells without any manipulation of the postsubiculum (Chapter 4) and then use information gained from this in the design of experiments in Chapter 5. Rats chronically implanted with recording electrodes in the CA1 region of the hippocampus were exposed to novel cue-rich environments whilst place fields were recorded. Following delays of 3, 6, or 24 hours, the same cells were recorded again in the same environment but with the cues rotated by 90°. Pixel-by-pixel correlations of the place fields show that stability of the place fields was significantly lower at 24 hours than at 3 hours. Stability after 6 hours was not significantly different from 3 hours. In the third set of experiments, rats were implanted with drug infusion cannulae in the postsubiculum and recording electrodes in CA1. Following infusions of either the AMPA receptor antagonist CXQX, the NMDA receptor antagonist D-AP5 or a control infusion of ACSF, place field stability was assessed as rats were exposed to a cylindrical environment with a single polarising cue card for 3 x 10 minute sessions and then again 6 hours later. There were no differences in place field correlations between the 3 drug conditions, although there was evidence of larger changes in spatial information content between cells in the CNQX and AP5 drug condition, but not the ACSF condition. The results suggest that, under the present testing conditions, place fields stability did not depend upon AMPA receptor-mediated transmission nor did it depend on NMDA receptor-mediated synaptic plasticity

Profitability of Indigenous Chicken: The Case of Producers in Makueni County, Kenya

Indigenous Chicken(IC) (Gallus domestica) is increasingly becoming an essential component of diets in urban centers. This increase in demand is accompanied by an increase in production by smallholder farmers. These farmers rely on the indigenous chicken for food security, household income, employment and quick funds in emergencies. The profit associated with the production of indigenous chicken, constitutes part of the contribution of the Agriculture sector to the Gross Domestic Product (GDP) of Kenya. However, in Makueni County there is little information on the amount of profit from production of IC or its relationship with socioeconomic factors. The objectives of this study was to calculate the profit of IC in Makueni and to determine the relationship between socio economic factors and profit from IC.A total of 130 households were sampled using multi stage sampling after which data was collected using a pre tested questionnaire in a house hold survey. These data was then analysed using budgetary analysis and multiple regression in STATA 11. The results showed that the profit from IC production in Makueni was Ksh. 5347/100 birds (1US$= Ksh86.70).Age, education, access to credit, flock size, price and years in farmer group had a significant relationship with the profit. Therefore it is recommended to form marketing groups that will engage in contractual agreements with final buyers of indigenous chicken. Key words: Indigenous chicken, food security, profitability, flock size, credi

Determinants of Consumer Perception towards Genetically Modified (GM) Foods in Higher Learning Institutions in Kenya

Genetically modified organisms (GMOs) have been developed to ensure food and security nutrition in the world, income generation and environmental protection for resource poor farmers. However, there are some unquantifiable risks and claims associated with GMOs. In spite of these risks, the benefits of using GMOs still outweigh the risks associated with their use. Persistent controversies and claims that GMOs are harmful to human health and the environment have led to uncertainty in their adoption by most countries especially in Sub-Saharan Africa (SSA), where hunger is most prevalent. Therefore, this is a clear indication that the benefits of GMOs are unlikely to be realized. In most industrialized countries public perception of GMOs has been thoroughly investigated. In Africa, consumers  have a negative perception towards GMO products. Therefore it was on this basis that the study was conducted to assess the consumer perception of genetically modified tomato at Kenyatta University. A total of 100 respondents were sampled using random sampling among various faculties. A questionnaire was administered online and the data analyzed in STATA 11. The results showed that 67% of the respondents were male and there was a significant difference in education level (p<0.001). In addition, the willingness to pay for GM free tomato, GM tomato attributes, acceptance of GM tomato, GM tomato production techniques and consumer awareness on: GM tomato importation, GM tomato safety and knowledge had an influence on consumer perception towards GM tomatoes. It is recommended to focus on establishing information hubs; integrating organic farming approach into extension services and diversification of the marketing strategy to improve on consumer perceptions. Keywords: Risks, malnutrition, perception, premium, controversie

Spatial, seasonal and climatic predictive models of Rift Valley fever disease across Africa

Understanding the emergence and subsequent spread of human infectious diseases is a critical global challenge, especially for high-impact zoonotic and vector-borne diseases. Global climate and land-use change are likely to alter host and vector distributions, but understanding the impact of these changes on the burden of infectious diseases is difficult. Here, we use a Bayesian spatial model to investigate environmental drivers of one of the most important diseases in Africa, Rift Valley fever (RVF). The model uses a hierarchical approach to determine how environmental drivers vary both spatially and seasonally, and incorporates the effects of key climatic oscillations, to produce a continental risk map of RVF in livestock (as a proxy for human RVF risk). We find RVF risk has a distinct seasonal spatial pattern influenced by climatic variation, with the majority of cases occurring in South Africa and Kenya in the first half of an El Niño year. Irrigation, rainfall and human population density were the main drivers of RVF cases, independent of seasonal, climatic or spatial variation. By accounting more subtly for the patterns in RVF data, we better determine the importance of underlying environmental drivers, and also make space- and time-sensitive predictions to better direct future surveillance resources

Coupled ice/ocean interactions during future retreat of West Antarctic ice streams in the Amundsen Sea sector

The Amundsen Sea sector has some of the fastest-thinning ice shelves in Antarctica, caused by high, ocean-driven basal melt rates, which can lead to increased ice stream flow, causing increased sea level rise (SLR) contributions. In this study, we present the results of a new synchronously coupled ice-sheet/ocean model of the Amundsen Sea sector. We use the WAVI ice sheet model to solve for ice velocities and the MITgcm to solve for ice thickness and three-dimensional ocean properties, allowing for full mass conservation in the coupled ice/ocean system. The coupled model is initialised in the present day and run forward under idealised warm and cold ocean conditions with a fixed ice front. We find that Thwaites Glacier dominates the future SLR from the Amundsen Sea sector, with a SLR that evolves approximately quadratically over time. The future evolution of Thwaites Glacier depends on the life-span of small pinning points that form during the retreat. The rate of melting around these pinning points provides the link between future ocean conditions and the SLR from this sector and will be difficult to capture without a coupled ice/ocean model. Grounding-line retreat leads to a progressively larger Thwaites iceshelf cavity, leading to a positive trend in total melting, resulting from the increased ice basal surface area. Despite these important sensitivities, Thwaites Glacier retreats even in a scenario with zero ocean-driven melting. This demonstrates that atipping point may have been passed in these simulations and some SLR from this sector is now committed

Environmental limits of Rift Valley fever revealed using ecoepidemiological mechanistic models.

Vector-borne diseases (VBDs) of humans and domestic animals are a significant component of the global burden of disease and a key driver of poverty. The transmission cycles of VBDs are often strongly mediated by the ecological requirements of the vectors, resulting in complex transmission dynamics, including intermittent epidemics and an unclear link between environmental conditions and disease persistence. An important broader concern is the extent to which theoretical models are reliable at forecasting VBDs; infection dynamics can be complex, and the resulting systems are highly unstable. Here, we examine these problems in detail using a case study of Rift Valley fever (RVF), a high-burden disease endemic to Africa. We develop an ecoepidemiological, compartmental, mathematical model coupled to the dynamics of ambient temperature and water availability and apply it to a realistic setting using empirical environmental data from Kenya. Importantly, we identify the range of seasonally varying ambient temperatures and water-body availability that leads to either the extinction of mosquito populations and/or RVF (nonpersistent regimens) or the establishment of long-term mosquito populations and consequently, the endemicity of the RVF infection (persistent regimens). Instabilities arise when the range of the environmental variables overlaps with the threshold of persistence. The model captures the intermittent nature of RVF occurrence, which is explained as low-level circulation under the threshold of detection, with intermittent emergence sometimes after long periods. Using the approach developed here opens up the ability to improve predictions of the emergence and behaviors of epidemics of many other important VBDs.The work was partially supported by the National Institute for Health Research (NIHR) Health Protection Research Unit in Environmental Change and Health at the London School of Hygiene and Tropical Medicine in partnership with Public Health England (PHE) and in collaboration with the University of Exeter, University College London, and the Met Office. European Union FP7 Project ANTIGONE (Contract 278976). Royal Society Wolfson Research Merit Award. The Alborada Trust

Skilful seasonal prediction of winter gas demand

In Britain, residential properties are predominantly heated using gas central heating systems. Ensuring a reliable supply of gas is therefore vital in protecting vulnerable sections of society from the adverse effects of cold weather. Ahead of the winter, the grid operator makes a prediction of gas demand to better anticipate possible conditions. Seasonal weather forecasts are not currently used to inform this demand prediction. Here we assess whether seasonal weather forecasts can skilfully predict the weather-driven component of both winter mean gas demand and the number of extreme gas demand days over the winter period. We find that both the mean and the number of extreme days are predicted with some skill from early November using seasonal forecasts of the large-scale atmospheric circulation (r > 0.5). Although temperature is most strongly correlated with gas demand, the more skilful prediction of the atmospheric circulation means it is a better predictor of demand. If seasonal weather forecasts are incorporated into pre-winter gas demand planning, they could help improve the security of gas supplies and reduce the impacts associated with extreme demand events

Internal alignments of red versus blue discs in dark matter haloes

Large surveys have shown that red galaxies are preferentially aligned with their haloes, while blue galaxies have a more isotropic distribution. Since haloes generally align with their filaments, this introduces a bias in the measurement of the cosmic shear from weak lensing. It is therefore vitally important to understand why this difference arises. We explore the stability of different disc orientations within triaxial haloes. We show that, in the absence of gas, the disc orientation is most stable when its spin is along the minor axis of the halo. Instead when gas cools on to a disc, it is able to form in almost arbitrary orientation, including off the main planes of the halo (but avoiding an orientation perpendicular to the halo's intermediate axis). Substructure helps gasless galaxies reach alignment with the halo faster, but has less effect on galaxies when gas is cooling on to the disc. Our results provide a novel and natural interpretation for why red, gas poor galaxies are preferentially aligned with their halo, while blue, star-forming, galaxies have nearly random orientations, without requiring a connection between galaxies' current star formation rate and their merger history

Optoelectronic Characterisation of Intermediate Band Solar Cells by Photoreflectance Comparison to Other Advanced Architectures.

The fabrication and design of novel materials and devices for advanced photovoltaics, like the intermediate-band solar cell (IBSC), requires the use of specific characterization tools providing information about their optoelectronic properties. We have tested the suitability of photoreflectance for the characterization of IBSC prototypes based on quantum dots and compared the results obtained with those predicted by the theory. Nonidealities in operative devices have been identified and detailed information has been obtained about the electronic structure of the materials. We have compared PR spectra of IBSCs with those obtained from alternative device architectures, namely a triple-junction solar cell and a multi-quantum well structure. Some general conclusions are drawn demonstrating the potential of the technique

The impact of the Amundsen Sea freshwater balance on ocean melting of the West Antarctic Ice Sheet

The Amundsen Sea has the highest thinning rates of ice shelves in Antarctica. This imbalance is caused by changes in ocean melting induced by warm Circumpolar Deep Water (CDW) intrusions. The resulting changing freshwater balance could affect the on‐shelf currents and mixing. However, a clear understanding of the sources and sinks of freshwater in the region is lacking. Here we use a model of the Amundsen Sea, with passive freshwater tracers, to investigate the relative magnitudes and spatial distributions of the different freshwater components. In the surface layer and as a depth average, all freshwater tracer concentrations are of comparable magnitude, though on a depth average, sea ice and ice shelf are largest. The total freshwater tracer distribution is similar to that of the ice‐shelf tracer field. This implies a potential for ice‐shelf meltwater feedbacks, whereby abundant ice‐shelf meltwater alters the ocean circulation and stratification, affecting melting. Ice‐shelf and sea‐ice freshwater fluxes have the largest interannual variability. The effect of including grounded icebergs and iceberg freshwater flux are studied in detail. The presence of icebergs increases CDW intrusions that reach the base of ice shelves. This suggests another possible feedback mechanism, whereby more icebergs induce greater ice‐shelf melting and hence more icebergs. However, the strength of this potential feedback is dependent on poorly constrained sea‐ice model parameters. These results imply that poorly constrained parameters relating to the ocean freshwater balance, such as those relating to icebergs and sea ice, impact predictions for melting of the West Antarctic Ice Sheet