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The marine calcifying algae Emiliania huxleyi (coccolithophores) was grown in laboratory cultures under varying conditions with respect to the environmental parameters of temperature and carbonate ion concentration [CO32-] concentration. The Ca isotope composition of E. huxleyi's coccoliths reveals new insights into fractionation processes during biomineralization. The temperature-dependent Ca isotope fractionation resembles previous calibrations of inorganic and biogenic calcite and aragonite. Unlike inorganically precipitated calcite, the [CO32-] concentration of the medium has no significant effect on the Ca isotope composition of the coccoliths. These results indicate a decoupling of the chemical properties of the bulk medium and the calcifying vesicle. Cellular Ca pathways of E. huxleyi indicate that fractionation cannot occur at the crystal surface, as occurs during inorganic precipitation. The dominant processes leading to the observed Ca isotope fractionation pattern in E. huxleyi are most likely the dehydration of the Ca aquocomplex at the plasma membrane and the attachment of dissolved Ca to proteins of Ca channels. The independence of Ca isotope fractionation from [CO32-] and the small temperature dependence of E. huxleyi are also important for defining the isotopic signature of the oceanic Ca sink. Since coccolithophores contribute to about half the global CaCO3 production, a relatively uniform isotopic composition of the oceanic Ca sink is further supported.

Two haptophyte algae, Emiliania huxleyi and Gephyrocapsa oceanica, were cultured at different temperatures and salinities to investigate the impact of these factors on the hydrogen isotopic composition of long chain alkenones synthesized by these algae. Results showed that alkenones synthesized by G.oceanica were on average depleted in D by 30 compared to those of E.huxleyi when grown under similar temperature and salinity conditions. The fractionation factor, αalkenones-H2O, ranged from 0.760 to 0.815 for E.huxleyi and from 0.741 to 0.788 for G.oceanica. There was no significant correlation of αalkenones-H2O with temperature but a positive linear correlation was observed between αalkenones-H2O and salinity with ~3 change in fractionation per salinity unit and a negative correlation between αalkenones-H2O and growth rate. This suggests that both salinity and growth rate can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments.

Microstructure changes during annealing of nano-crystalline silver and amorphous silicon multilayers (Ag/a-Si) have been studied by X-ray diffraction and transmission electron microscopy. The dc-magnetron sputtered Ag/a-Si multilayers remained stable even after annealing at 523 K for 10 h, and microstructural changes occurred only above 600K. The degradation of Ag/a-Si multilayers can be described by the increase of size of Ag grains, formation of grooves and pinholes at Ag grain boundaries and by the diffusion of silicon atoms through the silver grain boundaries and along the Ag/a-Si interfaces. This results in thinning of a-Si layers, and in formation of Ag granulates after longer annealing times.újratöltve - BIBFORM008828

Two haptophyte algae, Emiliania huxleyi and Gephyrocapsa oceanica, were cultured at different temperatures and salinities to investigate the impact of these factors on the hydrogen isotopic composition of long chain alkenones synthesized by these algae. Results showed that alkenones synthesized by G. oceanica were on average depleted in D by 30 per mil compared to those of E. huxleyi when grown under similar conditions. The fractionation factor, ?alkenones-H2O, ranged from 0.760 to 0.815 for E. huxleyi and from 0.741 to 0.788 for G. oceanica. There was no significant correlation of ?alkenones-H2O with temperature but a positive linear correlation was observed between ?alkenones-H2O and salinity with ~3 per mil change in fractionation per salinity unit. This suggests that salinity can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments and, vice versa, that ?D can possibly be used as a proxy to estimate paleosalinity.

Het huidige Kabinet gaat de komende twee jaar de Wet sociale werkvoorziening (Wsw) moderniseren. De eerste stap in dit moderniseringstraject is de overdracht op 1 oktober 2004 van de Wsw-indicatiestelling naar het CWI. De bedoeling is dat door de landelijke aansturing van het CWI een meer onafhankelijke, uniforme en efficiënte indicatiestelling ontstaat. TNO Arbeid heeft voor het CWI een ontwerp-werkproces ontwikkeld met inbreng van het uitvoeringsveld en mede gebaseerd op eerder opgedane kennis en ervaringen met de uitvoering van de indicatiestelling. Dit ontwerp-werkproces is op zeven pilotlocaties getest. In een schema is het definitieve procesvoorstel van TNO Arbeid weergegeven, hetgeen bestaat uit drie procesonderdelen. Het betreft: aanmelding & advisering; onderzoek & beoordeling en indicatiebesluit & overdracht. In de rapportage zijn deze procesonderdelen verder uitgewerkt. De bij deze rapportage horende bijlagen zijn afzonderlijk gepubliceerd.

By employing two different spectroscopic techniques we have mapped out the variable ISM dust extinction endemic to globular cluster M4. We derive an average E(B-V) reddening of 0.33 +/- 0.01 and R = 3.4 +/- 0.4, both in good agreement with previous studies of M4. For individual stars in the most heavily reddened regions of M4, we find E(B-V) values significantly higher than those inferred by studies of interstellar gas; for heavily reddened regions, the gas measured in column density measurements may not completely trace the dust., Comment: 4 pages, 1 figure, to appear in Revista Mexicana de Astronomia y Astrofisica Serie de Conferencias: ``The Seventh Texas-Mexico Conference on Astrophysics: Glows, Flows & Blows'' April 6-8, 2000, Austin, Texas

The effect of anomalous couplings in $����\to W^+ W^-$ is studied for different energies of the $����$ mode of the next linear collider. The analysis based on the maximum likelihood method exploits the variables in the four-fermion semi-leptonic final state. Polarised differential cross sections based on the complete set of diagrams for these channels with the inclusion of anomalous couplings are used and compared to an approximation based on $����\to W^+ W^-$ with full spin correlations. To critically compare these results with those obtained in $e^+ e^-$ we perform an analysis based on the complete calculation of the four-fermion semi-leptonic final state. The anomalous couplings that we consider are derived from the next-to-leading order operators in the non-linear realisation of symmetry breaking., paper in LATEX, 36 pages, 11 figures. Complete psfile also available via anonymous ftp at ftp://lapphp0.in2p3.fr/pub/preprints-theorie/enslapp636.uu or at http://lapphp0.in2p3.fr/preplapp/psth/enslapp636.ps.gz

We calculate the process $����\rightarrow e^- \bar��_e u \bar{d}$ with the full set of Feynman diagrams. We consider different implementations of the $W$ width and different combinations of the photon polarisations. The results of an improved narrow width approximation based on $����\rightarrow W^+ W^-$ with full spin-correlations that takes into account different angular cuts as well as cuts on the invariant masses are compared to those of the complete calculation., paper in LATEX, 19 pages, 3 figures. Complete psfile available via anonymous ftp at ftp://lapphp0.in2p3.fr/pub/preprints-theorie/enslapp635.uu or at http://lapphp0.in2p3.fr/preplapp/psth/enslapp635.ps.gz