Production of separation-nozzle systems for uranium enrichment by a combination of X-ray lithography and galvanoplastics

X-ray lithography using synchrotron radiation has been applied in a multi-step process for the production of plastic moulds to be used in the fabrication of separation nozzles by electrodeposition. For characteristic dimensions of a few microns a total height of the nozzle structure of about 400 μm has been achieved. Structural details of about 0.1 μm are being reproduced across the total thickness of the polymer layer. The surface finish of metallic separation nozzles produced by electrodeposition was equivalent to the high quality of the polymer surface. The separation-nozzle systems fabricated by the described method allow an increase by a factor three of the gas pressure in separationnozzle plants as compared to the present standard. This results in considerable savings in the enrichment of ²³⁵U for nuclear power production.     

Abiotic aging of water- soluble 3- hydroxybutyric acid oligomers as monitored by capillary zone electrophoresis

Oligomers of poly(3-hydroxybutyric acid) (P(3-HB)) were prepared by partial degradation of high molecular weight P(3-HB) dissolved in 1,2-dichloroethane/water mixture in the presence of p-toluene sulfonic acid (p-TSA). The water-soluble fraction of the resulting oligomers was extracted from the mixture with neutral sodium phosphate buffer. Capillary zone electrophoresis showed that the aqueous extracts were composed of two series of oligomers. The first one was composed of one to seven P(3-HB) oligomers (O(3-HB)). In contrast, the second series was composed of four oligomers characterized by the presence of a terminal C=C bond [O’(3-HB)]. Both series of oligomers behaved differently insofar as their fate in aqueous medium was concerned. The 0(3-HB) compounds were stable over a period of 2 months. On the other hand, the population of the O’(3-HB) oligomers varied, the proportion of oligomers increasing with aging time.     

A comparison of five pesticides adsorption and desorption processes in thirteen contrasting field soils

Batch adsorption and desorption experiments were performed using thirteen agricultural soil samples and five pesticides. Experimental data indicated a gradient in pesticide adsorption on soil: trifluralin > 2,4-D > isoproturon> atrazine > bentazone. Atrazine, isoproturon and trifluralin adsorption were correlated to soil organic matter content (r2 = 0.7, 0.82, 0.79 respectively). Conversely, bentazone adsorption was governed by soil pH (r2 = 0.68) while insignificant effect has been shown in the case of 2,4-D. Multiple linear regressions were used to combine relationships between the various soil parameters and the Freundlich adsorption coefficient (K(f)) of each pesticide. Then desorption was assessed since it may reflect some of the interactions involved between the pesticides and the soil components. Adsorbed molecules were released into aqueous solution in the following order: bentazone > atrazine> isoproturon> 2,4-D > trifluralin. The occurrence of hysteresis did not allow an accurate interpretation of the pesticide desorption data because of the possible interplay of several processes.     

Competition between alga (Pseudokirchneriella subcapitata), humic substances and EDTA for Cd and Zn control in the algal assay procedure (AAP) medium

The chemical speciation of trace metals in natural waters has important implications for their biogeochemical behavior. Trace metals are present in natural waters as dissolved species and associated with colloids and particles. The complexation of one trace metal (Cd and Zn at 200 and 390 microg/l respectively) with a green alga Pseudokirchneriella subcapitata in colloid-free algal culture medium and in presence of colloidal humic substances (HS) is presented. The influence of the nature of colloids was also addressed using three "standard" HS: fulvic acid (FA) and, soil (SHA) and peat humic acids (PHA). The chemical speciation model, MINTEQA2, was used to simulate the influence of pH and standardized culture medium on metal association with humic substances. The model was successfully modified to consider the differences in the metal complexation with fulvic (FA) and humic acids (HA). The deviations of concentrations of metals associated with HS between experimental results and model predictions were within a factor of approximately 2. The results of speciation model highlight the influence of the experimental conditions (pH, EDTA) used for alga bioassay on the behavior of Cd and Zn. The computed speciation suggests working with a pH buffered/EDTA-free mixture to avoid undesirable competition effects. The behavior of Cd and Zn in solution is more strongly influenced by HS than by alga. Metal-HS associations depend on metal and humic substance nature and concentration. Cd is complexed to a higher extent than Zn, in particular at larger HS concentration, and the complexation strength is in the order FA相似文献   

Comparison of the complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and produced by pure bacteria strains, for cadmium, lead and nickel

This paper provides information on the metal complexation potential of extracellular polymeric substances (EPS), extracted from activated sludges and from eight pure cultures of bacteria isolated from the same activated sludge. The EPS extracted from pure bacteria cultures are mainly composed of proteins and low quantities of polysaccharides and uronic acids in comparison with EPS extracted from activated sludges. The EPS studied present two apparent pK(a) and the IR spectra show the presence of the same functional groups on all the EPS studied. The ability of EPS to complex Cd, Pb and Ni, was studied at pH 7 with Chau and Ruzic's models using polarography titration. All of the EPS exhibited a greater ability to complex Pb than Ni, Cd showing the weakest affinity overall. The EPS extracted from the pure cultures of bacteria were less able to complex the metals than that extracted from activated sludges. Literature data, IR data and EPS phosphorous content, supported by the EPS pK(a), revealed that carboxylic and phosphoric groups may play a major role in binding to metals at pH 7. This study underlines the importance of metal exposure in order for bacteria to secrete or modify EPS. After exposure, the EPS then exhibit the greatest capacity to bind metal in order to protect bacteria from harmful effects of heavy metals.     

Analysis of six relevant toxaphene congeners in biological samples using ion trap MS/MS

Farmed and wild Scottish Atlantic salmon were obtained from retail suppliers, producers, and Stirling University in Scotland during January, 1999, for determination of 17 2,3,7,8-C1-substituted PCDDs and PCDFs, and seven nonortho- and mono-ortho-PCBs. The study confirms previous reports of relatively high concentrations of PCDDs, PCDFs and, especially, PCBs in farmed Scottish salmon. The results indicate that high consumption of salmon, particularly by children under 5 years, could lead to intakes above the tolerable daily intake (TDI) and tolerable weekly intake (TWI) for these chemicals, especially the PCBs, when combined with mean or high level intakes from the typical UK diet. These results suggest further investigation of farmed salmon and salmon feed, including feed fortified with fish oil and feed fortified with selected vegetable oils, is warranted.     

The FAIR model: A tool to analyse environmental and costs implications of regimes of future commitments

This article describes the policy decision-support tool, FAIR, to assess the environmental and abatement costs implications of international regimes for differentiation of future commitments. The model links long-term climate targets and global reduction objectives with regional emission allowances and abatement costs, accounting for the Kyoto Mechanisms used. FAIR consists of three sub-models: a simple climate model, an emission-allocation model and a cost model. The article also analyses ten different rule-based emission allocation schemes for two long-term concentration stabilisation targets for greenhouse gases. This analysis shows that evaluating regimes requires not only an assessment of the initial allocation, but also of the distribution of abatement costs and the impacts from emissions trading. The Multi-Stage approach (with a gradual increase of Parties adopting emission intensity or reductions targets) and the Triptych approach (with sectoral targets for all Parties) seem to provide the best prospects for most of the Parties when compared to the other allocation schemes analysed.     

The socioeconomic significance of nature-based recreation in Canada

In recognition of the many values that people ascribe to nature, federal, provincial, and territorial agencies worked inpartnership to complete the 'Survey on the Importance of Natureto Canadians' (SINC) in 1981, 1987, 1991, and 1996. Between 1981 and 1996, more than 80% of Canadians 15 years of age and older engaged in one or more nature-related activities. This paper describes the evolution of this cooperative monitoring program, defines a classification system as a context for the values examined by the SINC, highlights trends of some nature-related recreational activities measured by the survey, and comments onthe importance of this information to Canadians.     

Repartition du cadmium dans les enveloppes cellulaires d'une bacterie marine

Investigations were made on a Gram negative marine bacterium to describe the involvement of the different envelopes in the distribution of cadmium on cells. Cadmium content decreased from the outer to the inner layers of the cell wall, suggesting a protective effect of the different envelopes.