35 research outputs found

    SCIENCECRAFT

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    The technological capabilities are now at hand to design an integrated system that combine science instruments, spacecraft and propulsion elements into a single system. The authors have called this a Sciencecraft since it is intended to provide automatic scientific observations of planetary and astrophysical objects. Integration of function allows lower mass and cost and supports a short development cycle. A specific science mission is described in this paper, a flyby of Neptune, Triton and an object in the Kuiper belt. The SCIENCECRAFT system is described. It has electric propulsion and is capable of measuring the surface constituents and morphology of the objects visited and characterizing their atmospheres both in emission and absorption (against the sun). Miniature fields and particles experiments are incorporated that will provide interplanetary information together with details of the magnetic and electric attributes of each object. The SCIENCECRAFT is Delta launched and has a flight time to the Kuiper belt of 7 years. The design is such that the craft functions in a largely autonomous mode to provide low cost mission operations

    Ethnicity and prediction of cardiovascular disease: performance of QRISK2 and Framingham scores in a U.K. tri-ethnic prospective cohort study (SABRE--Southall And Brent REvisited).

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    OBJECTIVE: To evaluate QRISK2 and Framingham cardiovascular disease (CVD) risk scores in a tri-ethnic U.K. population. DESIGN: Cohort study. SETTING: West London. PARTICIPANTS: Randomly selected from primary care lists. Follow-up data were available for 87% of traced participants, comprising 1866 white Europeans, 1377 South Asians, and 578 African Caribbeans, aged 40-69 years at baseline (1998-1991). MAIN OUTCOME MEASURES: First CVD events: myocardial infarction, coronary revascularisation, angina, transient ischaemic attack or stroke reported by participant, primary care or hospital records or death certificate. RESULTS: During follow-up, 387 CVD events occurred in men (14%) and 78 in women (8%). Both scores underestimated risk in European and South Asian women (ratio of predicted to observed risk: European women: QRISK2: 0.73, Framingham: 0.73; South Asian women: QRISK2: 0.52, Framingham: 0.43). In African Caribbeans, Framingham over-predicted in men and women and QRISK2 over-predicted in women. Framingham classified 28% of participants as high risk, predicting 54% of all such events. QRISK2 classified 19% as high risk, predicting 42% of all such events. Both scores performed poorly in identifying high risk African Caribbeans; QRISK2 and Framingham identified as high risk only 10% and 24% of those who experienced events. CONCLUSIONS: Neither score performed consistently well in all ethnic groups. Further validation of QRISK2 in other multi-ethnic datasets, and better methods for identifying high risk African Caribbeans and South Asian women, are required

    Denitrification and indirect N2O emissions in groundwater: Hydrologic and biogeochemical influences

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    peer-reviewedIdentification of specific landscape areas with high and low groundwater denitrification potential is critical for improved management of agricultural nitrogen (N) export to ground and surface waters and indirect nitrous oxide (N2O) emissions. Denitrification products together with concurrent hydrogeochemical properties were analysed over two years at three depths at two low (L) and two high (H) permeability agricultural sites in Ireland. Mean N2O–N at H sites were significantly higher than L sites, and decreased with depth. Conversely, excess N2–N were significantly higher at L sites than H sites and did not vary with depth. Denitrification was a significant pathway of nitrate (NO3−–N) reduction at L sites but not at H sites, reducing 46–77% and 4–8% of delivered N with resulting mean NO3−–N concentrations of 1–4 and 12–15 mg N L− 1 at L and H sites, respectively. Mean N2O–N emission factors (EF5g) were higher than the most recent Intergovernmental Panel on Climate Change (IPCC, 2006) default value and more similar to the older IPCC (1997) values. Recharge during winter increased N2O but decreased excess dinitrogen (excess N2–N) at both sites, probably due to increased dissolved oxygen (DO) coupled with low groundwater temperatures. Denitrifier functional genes were similar at all sites and depths. Data showed that highly favourable conditions prevailed for denitrification to occur — multiple electron donors, low redox potential (Eh < 100 mV), low DO (< 2 mg L− 1), low permeability (ks < 0.005 m·d− 1) and a shallow unsaturated zone (< 2 m). Quantification of excess N2–N in groundwater helps to close N balances at the local, regional and global scales.Department of Agriculture, Food and Marine, Ireland - Research Stimulus Fund Programme (Grant RSF 06383); The University of Dublin, Trinity College Dublin

    Combinatorial Network Abstractionby Trees and Distances

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    Abstract We draw attention to network abstraction as a fundamental problem within network analysisand visualization. A combinatorial network abstraction problem is specified by a class P of pattern graphs and a real-valued similarity measure % based on certain graph properties. For fixedP and %, the optimization task on any graph G is finding a subgraph G0 which belongs to Psuch that %(G, G0) is minimal. In this work, we consider this problem for the natural case oftrees (as the class of pattern graphs) and similarity-measures based on distances. In particular--with respect to the most standard vector and matrix norms--we systematically study sub-treesof graphs that minimize distances, approximate distances, and approximate closeness-centrality. Although these similarity measures lead to reasonable results, the complexity analysis of findingoptimal trees is discouraging: we prove that all problems are NP-complete independent of thenorms used, except for the case of minimizing distances with respect to the L1 matrix-normwhich was already known to have a polynomial algorithm
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