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Tor Strömgren 《Journal of experimental marine biology and ecology》1980,48(3):225-231
The increase in length of apices of Ascophyllum nodosum (L.) Le Jolis was measured in paired combinations of Cu, Hg, and Zn.Significant antagonistic effects appeared with exposure to Cu + Zn after 3 days (P < 0.001), and with Hg and Zn after 4 days (P < 0.01). When Cu and Hg were combined, only a weak antagonistic effect was indicated after 7 days of exposure. It is supposed that the observed detoxificating effect of Zn to Cu and Hg is partly related to the relative number of ions present. 相似文献
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James G. Abbott Lisa M. Campbell Clinton J. Hay Tor F. Næsje John Purvis 《Human ecology: an interdisciplinary journal》2007,35(5):559-574
This paper examines small-scale fish vending in a southern African floodplain from two perspectives: as a link between natural
resource use and consumption, and as a livelihood in itself. We used a combination of observation, surveys and semistructured
interviews in a market in Katima Mulilo, Namibia, to determine sources of fish, preferences and constraints to vending, average
investment and profit, as well different routes into fish vending and perceptions regarding vending. Most vendors come from
fishing households, but their stock is often an accumulation of purchases from other fishers. There is little evidence of
formal arrangements between fishers and vendors, yet most adapt to the highly variable natural and social environments of
the region. Although all vendors ranked selling fish as their most important livelihood activity, a wide range of investment
and profit exists among individuals. Our findings indicate that fisheries management proposed for the area must be developed
with a careful understanding of how changes in access and use will affect vending livelihoods.
相似文献
John PurvisEmail: |
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Structural polysaccharides of the alginate family form gels in aqueous Ca2+-containing solutions by lateral association of chain segments. The effect of adding oligomers of alpha-l-guluronic acid (G blocks) to gelling solutions of alginate was investigated using rheology and atomic force microscopy (AFM). Ca-alginate gels were prepared by in situ release of Ca2+. The gel strength increased with increasing level of calcium saturation of the alginate and decreased with increasing amount of free G blocks. The presence of free G blocks also led to an increased gelation time. The gel point and fractal dimensionalities of the gels were determined based on the rheological characterization. Without added free G blocks the fractal dimension of the gels increased from df = 2.14 to df = 2.46 when increasing [Ca2+] from 10 to 20 mM. This increase was suggested to arise from an increased junction zone multiplicity induced by the increased concentration of calcium ions. In the presence of free G blocks (G block/alginate = 1/1) the fractal dimension increased from 2.14 to 2.29 at 10 mM Ca2+, whereas there was no significant change associated with addition of G blocks at 20 mM Ca2+. These observations indicate that free G blocks are involved in calcium-mediated bonds formed between guluronic acid sequences within the polymeric alginates. Thus, the added oligoguluronate competes with the alginate chains for the calcium ions. The gels and pregel situations close to the gel point were also studied using AFM. The AFM topographs indicated that in situations of low calcium saturation microgels a few hundred nanometers in diameter develop in solution. In situations of higher calcium saturation lateral association of a number of alginate chains are occurring, giving ordered fiber-like structures. These results show that G blocks can be used as modulators of gelation kinetics as well as local network structure formation and equilibrium properties in alginate gels. 相似文献
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David Vela-Corcía Diego Romero Juan Antonio Torés Antonio De Vicente Alejandro Pérez-García 《BMC microbiology》2015,15(1)