756 research outputs found
Geavanceerde computerondersteuning van kwantitatief onderzoek
Kwantitatief onderzoek vindt in belangrijke mate op de computer plaats. Toch is de computerondersteuning van kwantitatief onderzoek niet ideaal. Er zijn meerdere, ongekoppelde systemen nodig en veel informatie blijft impliciet en dus niet toegankelijk voor automatische verwerking. De oplossing schuilt in semantische ontsluiting van de kwantitatieve informatie. Daartoe werd een kwantitatief vocabulaire ontwikkeld, die daarna werd toegepast in ontwikkelde tools, waarna het gebruik van deze tools met kwantitatieve onderzoekers werd geëvalueer
Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. II: anisotropy
We investigate the effects of stochasticity in the spatial and temporal
distribution of supernova remnants on the anisotropy of cosmic rays observed at
Earth. The calculations are carried out for different choices of the diffusion
coefficient D(E) for propagation in the Galaxy. The propagation and spallation
of nuclei are taken into account. At high energies we assume that
, with and being the
reference scenarios. The large scale distribution of supernova remnants in the
Galaxy is modeled following the distribution of pulsars with and without
accounting for the spiral structure of the Galaxy. Our calculations allow us to
determine the contribution to anisotropy resulting from both the large scale
distribution of SNRs in the Galaxy and the random distribution of the nearest
remnants. The naive expectation that the anisotropy amplitude scales as D(E) is
shown to be an oversimplification which does not reflect in the predicted
anisotropy for any realistic distribution of the sources. The fluctuations in
the anisotropy pattern are dominated by nearby sources, so that predicting or
explaining the observed anisotropy amplitude and phase becomes close to
impossible. We find however that the very weak energy dependence of the
anisotropy amplitude below GeV and the rise at higher energies, can
best be explained if the diffusion coefficient is . Faster
diffusion, for instance with , leads in general to an exceedingly
large anisotropy amplitude. The spiral structure introduces interesting trends
in the energy dependence of the anisotropy pattern, which qualitatively reflect
the trend seen in the data. For large values of the halo size we find that the
anisotropy becomes dominated by the large scale regular structure of the source
distribution, leading indeed to a monotonic increase of with energy.Comment: 21 Pages, to appear in JCA
Abyssal upwelling in the Indian Ocean: Radiocarbon diagnostics
The GEOSECS Indian Ocean radiocarbon and carbonate chemistry data set are used to estimate the mean upwelling transport of bottom water in the Indian Ocean north of 30S. The study uses an adjusted radiocarbon concentration which is corrected for the effects of addition of particulate radiocarbon to the deep ocean. The cross-basin uniformity in the vertical gradients of adjusted radiocarbon allows quantification of vertical transfer processes using horizontally averaged concentration and fluxes. The estimated total upwelling flux, north of 30S, is 8.2 ± 1.5 × 106 m3 s-1. The mean upwelling velocity and the vertical diffusivity, in the 3000-4500 m depth range, are estimated as 3 × 106 m s-1 and 2.5 × 10-4 m2 s-1, respectively. The results also suggest faster upwelling in the western Indian Ocean
Boeren voor natuur; scenario's voor het landelijk gebied
Deze publicatie over boeren voor natuur is een beleidsgeoriënteerde samenvatting bij een binnenkort te verschijnen boek over de mogelijke rol van de landbouw bij de inrichting en het beheer van het landelijke gebied. De discussie hieromtrent is onder andere door de recente problemen in de landbouw actueel. De visie laat zien dat bij een alternatieve aanwending van beschikbare financiële middelen een duurzame, op de natuur gerichte landbouw mogelijk is
Swine Influenza A Outbreak, Fort Dix, New Jersey, 1976
Published literature and events surrounding the outbreak are reviewed
The Microcirculation Is Unchanged in Neonates with Severe Respiratory Failure after the Initiation of ECMO Treatment
Purpose. Venoarterial extracorporeal membrane oxygenation (VA-ECMO) is known to improve cardiorespiratory function and outcome in neonates with severe respiratory failure. We tested the hypothesis that VA-ECMO therapy improves the microcirculation in neonates with severe respiratory failure. Methods. This single-center prospective observational pilot study took place in an intensive care unit of a level III university children's hospital. Twenty-one-term neonates, who received VA-ECMO treatment, were included. The microcirculation was assessed in the buccal mucosa, using Orthogonal Polarization Spectral imaging, within 24 hours before (T1) and within the first 24 hours after initiation of ECMO treatment (T2). Data were compared to data of a ventilated control group (N = 7). Results. At baseline (T1), median functional capillary density (FCD), microvascular flow index (MFI), and heterogeneity index (HI) did not differ between the ECMO group and the control group. At T2 the median FCD was lower in the control group (median [range]: 2.4 [1.4–4.2] versus 4.3 [2.8–7.4] cm/cm2; P value <0.001). For MFI and HI there were no differences at T2 between the two groups. Conclusion. The perfusion of the microcirculation does not change after initiation of VA-ECMO treatment in neonates with severe respiratory failure
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