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.     

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.     

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.     

Experimental manipulation of colony genetic diversity had no effect on short-term task efficiency in the Argentine ant Linepithema humile

Genetic diversity might increase the performance of social groups by improving task efficiency or disease resistance, but direct experimental tests of these hypotheses are rare. We manipulated the level of genetic diversity in colonies of the Argentine ant Linepithema humile, and then recorded the short-term task efficiency of these experimental colonies. The efficiency of low and high genetic diversity colonies did not differ significantly for any of the following tasks: exploring a new territory, foraging, moving to a new nest site, or removing corpses. The tests were powerful enough to detect large effects, but may have failed to detect small differences. Indeed, observed effect sizes were generally small, except for the time to create a trail during nest emigration. In addition, genetic diversity had no statistically significant impact on the number of workers, males and females produced by the colony, but these tests had low power. Higher genetic diversity also did not result in lower variance in task efficiency and productivity. In contrast to genetic diversity, colony size was positively correlated with the efficiency at performing most tasks and with colony productivity. Altogether, these results suggest that genetic diversity does not strongly improve short-term task efficiency in L. humile, but that worker number is a key factor determining the success of this invasive species.Communicated by L. Sundström     

Fate of the veterinary medicine ivermectin in soil

We investigated the fate of the drug ivermectin in the soil. We found that ivermectin was transformed solely by photos, leading to the formation of two ivermectin isomers. We indeed failed to detect any biotransformation reaction of the chemical either in the soil or in fungal liquid cultures. According to its limited water solubility, the bioavailability of ivermectin was very low in the soil solution. Here, we show that ivermectin, transferred to the soil from faeces of drug-treated cattle, could be stored for long periods in the soil.     

Social synchronization of circadian rhythms in deer mice (Peromyscus maniculatus)

Summary Deer mice (Peromyscus maniculatus), kept in individual cages under constant dim-light conditions, displayed steady free-running rhythms of activity, the period of which varied between individuals.When two previously isolated mice with different rhythms were placed in a common enclosure, under the same constant light conditions, they soon displayed a mutual synchronization of their activity rhythms. When separated again, the mice lost mutual synchronization (Figs. 1 and 2)The process by which mutual synchronization was attained in the common enclosure is typical of entrainment by an external synchronizer (Zeitgeber). Our results suggest that the activity rhythm of the dominant mouse entrains the activity rhythm of the subordinate, and is thus a social Zeitgeber.