Transport and metabolism of polyamines in Trypanosoma cruzi.

The epimastigotes (insect stage) of Trypanosoma cruzi, are unable to synthesize de novo the diamines putrescine and its analogue cadaverine, from their amino acid precursors. Therefore the metabolic pathways to polyamines (aliphatic bases) in T.cruzi, clone XI0/6 epimastigotes, have been studied by in vitro radiolabelling using these diamine precursors. [3H]Putrescine was rapidly taken up from the medium and incorporated in to the polyamines spermidine, spermine and the glutathione-polyamine conjugate N1, N2-bis(glutathionyl)spermidine(trypanothione). Likewise [3H]cadaverine was rapidly taken up by T.cruzi and converted into the analogous polyamines aminopropylcadaverine and bis(aminopropyl) cadaverine and the glutathione-polyamine conjugates glutathionylaminopropylcadaverine and N1, N2-bis(glutathionyl)- aminopropylcadaverine (homotrypanothione). Detailed analysis has revealed that T.cruzi epimastigotes (clone X10/6) transport exogenous [3H]putrescine and [3H]cadaverine by a rapid, high affinity, temperature dependent, diamine transport system which exhibits saturable kinetics (putrescine Km, - 2.0 μM, Vmax- 3.3nmol min-1 (10(8) cells)-1; cadaverine Km= 13.4 μM, V ■ 3.9 nmol min-1 (10(8) cells)-1). Diamine transport requires the presence of a proton gradient and thiol groups, does not utilise an amino acid transporter and its activity is altered as die cells proceed through the growth cycle. This transporter shows high specificity for the diamines, putrescine and cadaverine, but low specificity for the polyamines, spermidine and spermine. Hence polyamine metabolism in T.cruzi epimastigotes differs from other trypanosomadids ('Trypanosoma brucei, Leishmania and Crithidia fascicuiata) in three ways. Firstly T.cruzi lacks the ability to synthesize diamines de novo. Secondly both putrescine and cadaverine are rapidly taken up and can be converted into significant amounts of spermine and bis(aminopropyl) cadaverine respectively. Thirdly T.cruzi is able to synthesize homotrypanothione in addition to trypanothione. If the pattern of polyamine metabolism in the mammalian stages of T.cruzi is similar to that observed with the epimastigotes, these findings will have important implications with respect to future developmental strategies for the chemotherapy of Chagas’ disease

The geometry of some Beaufort group sandstones and its relationship to uranium mineralisation

Bibliography: pages 175-191.From field evidence gained whilst working on the Ptistetognathus/ Diictodon Assemblage Zone west of Beaufort West it is found that three discrete sandstone types called: A) straight channel sandstones, B) low sinuosity channel sandstones and C) transitional sandstones can be identified, in what has previously been considered as high sinuosity channel facies association sediments. Palaeocurrent analysis has demonstrated that the transitional sandstones were high sinuosity and were the larger fluvial systems; the straight channel and low sinuosity channel sandstones were generally much smaller and had as their names imply a much lower sinuosity. The palaeo-variability of current vectors in these systems, in the study area, is such that a standard deviation of greater than +40° is considered diagnostic of the transitional sandstones. Moreover in the study area only this type of sandstone is of importance in uranium exploration. From the palaeocurrent data and the reduction-oxidation states of the sandstone types it is proposed that the transitional sandstones represent semi-perennial fluvial systems flowing across an arid intracratonic basin, whilst the straight and low sinuosity channel sands are intrabasinal tributaries of the transitional sandstones. From this study of the sandstone geometry has evolved a new model of uranium mineralisation. It is proposed that the mineralisation is syngenetic and generated by reduction of uranyl carbonates on carbonaceous material. The carbonaceous material must however be lying closely below or within a weak REDOX front, since it is vital to transport complexes in an oxidising environment, and yet such an environment will not allow reduced uranium to be preserved for any length of time, as the carbonaceous material on which it reduced will eventually oxidize. Such a REDOX front, it is proposed, is created by the coalescence of two discrete sands. The upper sand is an oxidising active channel. The lower sand has been buried for some time and is weakly reducing due to anaerobic breakdown of its carbonaceous material by bacteria. Fluids in the two sands mix at the point of coalescence and uranium in transport in the upper sand is transported to and fixed at the REDOX front by carbonaceous material in the lower sand. Borehole data suggests that the correlation between coalescence of two discrete sandstones (the lower being a transitional sandstone) and mineralisation is very good. It is believed that the three sandstone types, whilst representing major fluvial systems and their tributaries, were undergoing water loss along their length such that distal portions of even the major (transitional) sandstones were likely ephemeral. Evidence for this is found in the arid climate, lack of in-channel vegetation, dominance of flat-bedded sandstones and clear evidence for bedload transport

Predicting reference points and associated uncertainty from life histories for risk and status assessment

To assess status of fish populations and the risks of overexploitation, management bodies compare fishing mortality rates and abundance estimates with reference points (RP). Generic, “data-poor” methods for estimating RP are garnering attention because they are faster and cheaper to implement than those based on extensive life history data. Yet data-poor RP are subject to many unquantified uncertainties. Here, we predict fishing mortality RP based on five levels of increasingly comprehensive data, to quantify effects of parameter and structural uncertainty on RP. Level I RP (least data) are estimated solely from species' maximum size and generic life history relationships, while level V RP (most data) are estimated from population-specific growth and maturity data. By estimating RP at all five data levels, for each of 12 North Sea populations, we demonstrate marked changes in the median RP values, and to a lesser extent uncertainty, when growth parameters come from data rather than life history relationships. As a simple rule, halving the median level I RP gives almost 90% probability that a level V median RP is not exceeded. RP and uncertainty were substantially affected by assumed gear selectivity; plausible changes in selectivity had a greater effect on RP than adding level V data. Calculations of RP using data for successive individual years from 1984 to 2014 showed that the median RP based on data for any given year would often fall outside the range of uncertainty for RP based on data from earlier or later years. This highlighted the benefits of frequent RP updates when suitable data are available. Our approach provides a quantitative method to inform risk-based management and decisions about acceptable targets for data collection and quality. Ultimately, however, the utility and extent of adoption of data-poor methods for estimating RP will depend on the risk aversion of managers

Bilateral Panner’s disease in sickle cell anaemia: Case report

Avascular necrosis is common in sickle cell disease in various vulnerable areas such as in the femoral or humeral heads. Panner’s disease however is described as avascular necrosis of the capitellum, which commonly occurs in a younger age group. It is a pathological process believed to be caused by interference in the blood supply to the growing capitellar epiphysis. A 17 year old boy with sickle cell disease presented with pain on pronation and supination of both elbows, particularly on the lateral side. These movements were restricted in both elbows. Plain radiograph of his elbows showed fragmentation of the capitellum with signs of revascularisation. We have performed a thorough literature search and have not found other reported cases of Panner’s avascular necrosis of the capitellum in association with sickle cell disease. We conclude that Panner’s disease is a possible complication of sickle cell anaemia

Evaluation and management implications of uncertainty in a multispecies size-structured model of population and community responses to fishing

1. Implementation of an ecosystem approach to fisheries requires advice on trade-offs among fished species and between fisheries yields and biodiversity or food web properties. However, the lack of explicit representation, analysis and consideration of uncertainty in most multispecies models has limited their application in analyses that could support management advice. 2. We assessed the consequences of parameter uncertainty by developing 78 125 multispecies size-structured fish community models, with all combinations of parameters drawn from ranges that spanned parameter values estimated from data and literature. This unfiltered ensemble was reduced to 188 plausible models, the filtered ensemble (FE), by screening outputs against fish abundance data and ecological principles such as requiring species' persistence. 3. Effects of parameter uncertainty on estimates of single-species management reference points for fishing mortality (FMSY, fishing mortality rate providing MSY, the maximum sustainable yield) and biomass (BMSY, biomass at MSY) were evaluated by calculating probability distributions of estimated reference points with the FE. There was a 50% probability that multispecies FMSY could be estimated to within ±25% of its actual value, and a 50% probability that BMSY could be estimated to within ±40% of its actual value. 4. Signal-to-noise ratio was assessed for four community indicators when mortality rates were reduced from current rates to FMSY. The slope of the community size spectrum showed the greatest signal-to-noise ratio, indicating that it would be the most responsive indicator to the change in fishing mortality F. Further, the power of an ongoing international monitoring survey to detect predicted responses of size spectrum slope was higher than for other size-based metrics. 5. Synthesis and applications: Application of the ensemble model approach allows explicit representation of parameter uncertainty and supports advice and management by (i) providing uncertainty intervals for management reference points, (ii) estimating working values of reference points that achieve a defined reduction in risk of not breaching the true reference point, (iii) estimating the responsiveness of population, community, food web and biodiversity indicators to changes in F, (iv) assessing the performance of indicators and monitoring programmes and (v) identifying priorities for data collection and changes to model structure to reduce uncertainty

Organic materials for photovoltaic devices

This thesis is a contribution towards the understanding of the operation of bilayer solar cells, and the development of a theoretical basis for the selection of suitable pairs of materials for the fabrication of such cells. The work is divided into two main areas: (a) theoretical calculations on materials used in solar cells (b) fabrication of devices to test the calculations. Practically, many devices were made using some previously untried materials, the most successful of which was formed from dibromoanthanthrone and titanyl phthalocyanine. This sample was 0.30% efficient under incident white light of intensity 20mW/cm2 and had an open circuit voltage of 0.39V. Measurements of the response time of the sample were also recorded which provided information on the quality of the device made. Theoretically, calculations were performed using the extended Huckel method on potential materials for photovoltaic devices. Initially, these provided information on the variation of bandwidth with inter-ring separation for cofacially stacked phthalocyanines. They were also used to predict the position of the HOMO/LUMO for different materials. Then by deducing the position of the Fermi level, it is possible to simulate the junction formed between the two materials. Predicted behaviour for the phthalocyanine/perylene interface agreed with that found experimentally from UPS and optical absorption measurements of the ionisation potentials, work functions and band gaps for a similar junction. The calculations have also demonstrated how substituting or changing the two layers alters the performance of the device. This allowed a set of criteria to be established that should enable a more systematic approach to choosing potential pairs and then optimising their performance in future solar cells

Development and selection of operational management strategies to achieve policy objectives

Since the reform of the EU Common Fisheries Policy in 2002, effort has been devoted to addressing the governance, scientific, social and economic issues required to introduce an ecosystem approach to fisheries management (EAFM) in Europe. Fisheries management needs to support the three pillars of sustainability (ecological, social and economic) and Fisheries Ecosystem Plans (FEPs) have been developed as a tool to assist managers considering the ecological, social and economic implications of their decision. Building upon previous studies (e.g. the FP5-funded European Fisheries Ecosystem Plan project), the core concept of the Making the European Fisheries Ecosystem Plan Operational (MEFEPO) project is to deliver operational frameworks (FEPs) for three regional seas. The project focus is on how best to make current institutional frameworks responsive to an EAFM at regional and pan-European levels in accordance with the principles of good governance. The regional seas selected for the project are the North Sea (NS), North Western Waters (NWW) and South Western Waters (SWW) RAC regions. The aim of this work package (WP5) was to develop operational objectives to achieve the ecological objectives identified for the 3 regional seas in WP2. This report describes the development and implementation of a transparent and formal process that should lead to identification of the “best” operational management strategies for an EAFM, based on sound scientific information and stakeholder involvement (e.g. regional industry groups, citizen groups, managers and other interest groups)