The Scheldt estuary revisited: occurrence and behaviour of particulate polychlorinated biphenyls and polycyclic aromatic hydrocarbons

Temporal and spatial variations in particulate PolyChlorinated Biphenyl (PCB) and Polycyclic Aromatic Hydrocarbons (PAH) concentrations were studied in the Scheldt estuary during a one-year period (May 1995-June 1996). This sampling campaign was arecurrence of a campaign held almost a decade ago. Both PCB and PAH concentrations in the Scheldt river were substantially lower in the 90's, but the Scheldt is still one of the most severely polluted rivers in the North Sea area. The annual input into the estuary was approximately 40 kg for total PCBs (sum of 8 congeners) and 3300 kg for total PAHs (19 compounds). The fraction transported to the North Sea is relatively small: 10-20 %.In the most recent sampling campaign the behaviour of particulate PCBs and PAHs found earlier was confirmed: as a result of the mixing of riverine with marine particulates the concentrations of the micropollutants generally decrease with increasing salinities, The quicker restoration of dissolved oxygen in the upper estuary gave rise to a more intense degradation of organic matter, and, probably as a result of cometabolism, degradation of low molecuiar weight PAH. Typical calculated half lives were 260 days for pyrene and 390 for fluoranthene

Pyramiding of Meloidogyne hapla resistance genes in potato does not result in an increase of resistance

High levels of resistance against Meloidogyne hapla have been identified in wild species of tuber-bearing potatoes, but only QTL with partial effects have been identified so far in back crosses with cultivated potato. This study was designed to test if pyramiding of two previously identified resistance genes, R Mh-tar and R Mh-chc A, will result in improved or even an absolute level of resistance. R Mh-tar and R Mh-chc A introgressed from the wild tuber-bearing potato species Solanum tarijense and Solanum chacoense were combined in a segregating diploid Solanum tuberosum population. With the aid of AFLP markers, descendants from this segregating population were classified into four groups, carrying no R gene, with only R Mh-tar , with only R Mh-chc A and a group with the pyramided R Mh-tar and R Mh-chc A. Upon inoculation with M. hapla isolate Bovensmilde, the group containing only R Mh-chc A showed a decline of 88% in average number of developed egg masses compared to the group without R Mh-chc A and R Mh-tar . The group of genotypes containing only R Mh-tar , but not R Mh-chc A, showed a decline of 55% in the number of developed egg masses compared to the group without R Mh-chc A and R Mh-tar . Unfortunately, the latter effect of R Mh-tar was not significant. The effect of both loci, R Mh-tar and R Mh-chc A combined, did not further reduce the number of egg masses compared to the level of R Mh-chc A alon

Notes on determinations of nitrate in plant material.

The determination of nitrate in extracts of plants including grass, maize, sugarbeet leaves, lucerne, peas, cucumber, radish and lettuce by 3 different methods was tested. The methods based on nitration of O'-xylenol and dialysis of plant extracts and reduction of nitrate to nitrite ions by a Cu-Cd reductor were equally satisfactory. No influence of the extraction ratio was found. Extraction of plant material with water or electrolyte solution gave comparable results. Direct potentiometry gave too high results at lower nitrate ion levels. This phenomenon depends on the nature of plant material analysed and is apparently caused by organic anions. For spinach, the electrode can be used when the nitrate content is about 300 mmol nitrate/kg DM or higher. (Abstract retrieved from CAB Abstracts by CABI’s permission

The temperature and chronology of heavy-element synthesis in low-mass stars

Roughly half of the heavy elements (atomic mass greater than that of iron) are believed to be synthesized in the late evolutionary stages of stars with masses between 0.8 and 8 solar masses. Deep inside the star, nuclei (mainly iron) capture neutrons and progressively build up (through the slow-neutron-capture process, or s-process) heavier elements that are subsequently brought to the stellar surface by convection. Two neutron sources, activated at distinct temperatures, have been proposed: 13C and 22Ne, each releasing one neutron per alpha-particle (4He) captured. To explain the measured stellar abundances, stellar evolution models invoking the 13C neutron source (which operates at temperatures of about one hundred million kelvin) are favoured. Isotopic ratios in primitive meteorites, however, reflecting nucleosynthesis in the previous generations of stars that contributed material to the Solar System, point to higher temperatures (more than three hundred million kelvin), requiring at least a late activation of 22Ne. Here we report a determination of the s-process temperature directly in evolved low-mass giant stars, using zirconium and niobium abundances, independently of stellar evolution models. The derived temperature supports 13C as the s-process neutron source. The radioactive pair 93Zr-93Nb used to estimate the s-process temperature also provides, together with the pair 99Tc-99Ru, chronometric information on the time elapsed since the start of the s-process, which we determine to be one million to three million years.Comment: 30 pages, 10 figure

On the map: Nature and Science editorials

Bibliometric mapping of scientific articles based on keywords and technical terms in abstracts is now frequently used to chart scientific fields. In contrast, no significant mapping has been applied to the full texts of non-specialist documents. Editorials in Nature and Science are such non-specialist documents, reflecting the views of the two most read scientific journals on science, technology and policy issues. We use the VOSviewer mapping software to chart the topics of these editorials. A term map and a document map are constructed and clusters are distinguished in both of them. The validity of the document clustering is verified by a manual analysis of a sample of the editorials. This analysis confirms the homogeneity of the clusters obtained by mapping and augments the latter with further detail. As a result, the analysis provides reliable information on the distribution of the editorials over topics, and on differences between the journals. The most striking difference is that Nature devotes more attention to internal science policy issues and Science more to the political influence of scientists

CH in stellar atmospheres: an extensive linelist

The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 magnitudes in the $\lambda=$3000 -- 5500 \AA\ range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data.Comment: 33pages, 15 figures, accepted in A&A external data available at http://www.astro.ulb.ac.be/~spectrotools

Semantic Support for Automated Negotiation with Alliances

Companies can form alliances on the Internet to aggregate buying or selling power and create value. More concretely, together resources are shared or new possibilities are exploited that cannot be exploited individually. Most alliances are formed as a result of a negotiation process between the companies that form an alliance. This paper proposes a software framework that enables automated negotiation between alliances. Our framework allows for the semantic description of negotiation objects and their attributes, and provides a mean for the exchange of negotiation messages unambiguously interpretable by all parties involved. The proposed framework supports ad-hoc alliances by allowing parties with a common interest to negotiate on the proposal they want to make to other market participants first