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91.
Karine Vallee-Rehel Valérie Langlois Philippe Guerin 《Journal of Polymers and the Environment》1998,6(4):175-186
Specific polymeric material applications as bioactive molecules delivery systems involve a strictly controlled degradation of polymer matrixes. One possibility to obtain a zero-order kinetic for small molecules release consists in a simple hydrolysis of ester groups contained in the macromolecular structure. The chemical degradation can lead to the continuous surface erosion of the formulated resins without loss of their mechanical properties and to a permanent activity of the delivery systems. Hydrolysis is a very well-known reaction in the case of organic molecules containing ester groups. The mechanism seems to be more complicated when ester groups are located in macromolecular structures. With the aim of antifouling applications, acrylic acid polymers bearing lateral ester groups of different chemical structures (hydrophilic, hydrophobic, hydrolyzable) have been prepared, characterized, and immersed in water, at pH 8, and their hydrolysis has been studied. Experimental data display two parameters, at least, which must be taken into account: the reactivity of the ester groups toward hydrolysis and the hydrophilic/hydrophobic balance of the polymer. The susceptibility of the acrylic polymers to hydrolysis has been compared to the erosion characteristics of the corresponding films. The results confirm that hydrolysis is necessary to obtain a regular degradation of the films without loss of mechanical properties. A relationship has been observed between the characteristics of hydrolysis and erosion for each studied polymer. 相似文献
92.
Cebeci Havva Hande Açıkalın Korkut Figen Aysel Kantürk 《Journal of Material Cycles and Waste Management》2023,25(4):2205-2221
Journal of Material Cycles and Waste Management - The current study aimed to determine the characteristics and kinetic parameters for the pyrolysis of printed circuit board (PCB) wastes including... 相似文献
93.
The spatial and temporal organization of ecological processes and features and the scales at which they occur are central topics to landscape ecology and metapopulation dynamics, and increasingly regarded as a cornerstone paradigm for understanding ecological processes. Hence, there is need for computational approaches which allow the identification of the proper spatial or temporal scales of ecological processes and the explicit integration of that information in models. For that purpose, we propose a new method (multiscale codependence analysis, MCA) to test the statistical significance of the correlations between two variables at particular spatial or temporal scales. Validation of the method (using Monte Carlo simulations) included the study of type I error rate, under five statistical significance thresholds, and of type II error rate and statistical power. The method was found to be valid, in terms of type I error rate, and to have sufficient statistical power to be useful in practice. MCA has assumptions that are met in a wide range of circumstances. When applied to model the river habitat of juvenile Atlantic salmon, MCA revealed that variables describing substrate composition of the river bed were the most influential predictors of parr abundance at 0.4-4.1 km scales whereas mean channel depth was more influential at 200-300 m scales. When properly assessed, the spatial structuring observed in nature may be used purposefully to refine our understanding of natural processes and enhance model representativeness. 相似文献
94.
T. Gallé 《Environmental Sciences Europe》2010,22(6):656-660
The Water Framework Directive’s (WFD) choice of good ecological status as a metric of the immission situation in water bodies implicitly considers the exposure of biota to pollutants. However, the exposure concept lacks consequent links to food webs and substance cycles where sediments and suspended matter play an important role. This is traceable in monitoring as well as in evaluation schemes. This article identifies the major challenges towards a process-oriented approach. 相似文献
95.
John M. Logan Enrique Rodríguez-Marín Nicolas Goñi Santiago Barreiro Haritz Arrizabalaga Walter Golet Molly Lutcavage 《Marine Biology》2011,158(1):73-85
Atlantic bluefin tuna (Thunnus thynnus) are highly migratory predators whose abundance, distribution, and somatic condition have changed over the past decades.
Prey community composition and abundance have also varied in several foraging grounds. To better understand underlying food
webs and regional energy sources, we performed stomach content and stable isotope analyses on mainly juvenile (60–150 cm curved
fork length) bluefin tuna captured in foraging grounds in the western (Mid-Atlantic Bight) and eastern (Bay of Biscay) Atlantic
Ocean. In the Mid-Atlantic Bight, bluefin tuna diet was mainly sand lance (Ammodytes spp., 29% prey weight), consistent with historic findings. In the Bay of Biscay, krill (Meganyctiphanes norvegica) and anchovy (Engraulis encrasicolus) made up 39% prey weight, with relative consumption of each reflecting annual changes in prey abundance. Consumption of anchovies
apparently declined after the local collapse of this prey resource. In both regions, stable isotope analysis results showed
that juvenile bluefin tuna fed at a lower trophic position than indicated by stomach content analysis. In the Mid-Atlantic
Bight, stable isotope analyses suggested that >30% of the diet was prey from lower trophic levels that composed <10% of the
prey weights based upon traditional stomach content analyses. Trophic position was similar to juvenile fish sampled in the
NW Atlantic but lower than juveniles sampled in the Mediterranean Sea in previous studies. Our findings indicate that juvenile
bluefin tuna targeted a relatively small range of prey species and regional foraging patterns remained consistent over time
in the Mid-Atlantic Bight but changed in relation to local prey availability in the Bay of Biscay. 相似文献
96.
Eva Friis Møller Christian Marc Andersen Borg Sigrún H. Jónasdóttir Suree Satapoomin Cornelia Jaspers Torkel Gissel Nielsen 《Marine Biology》2011,158(3):677-688
The vertical distribution of copepods, fecal pellets and the fecal pellet production of copepods were measured at seven stations
across the Southern Indian Ocean from productive areas off South Africa to oligotrophic waters off Northern Australia during
October/November 2006. We quantified export of copepod fecal pellet from surface waters and how much was retained. Furthermore,
the potential impact of Oncaea spp. and harpacticoid copepods on fecal pellets degradation was evaluated and found to be regional substantial. The highest
copepod abundance and fecal pellet production was found in the western nutrient-rich stations close to South Africa and the
lowest at the central oligotrophic stations. The in situ copepod fecal pellet production varied between 1 and 1,000 μg C m−3 day−1. At all stations, the retention of fecal pellets in the upper 400 m of the water column was more than 99% and the vertical
export of fecal pellets was low (<0.02 mg m−2 day−1). 相似文献
97.
Maria Clara P. Amorim José Miguel Simões Vitor C. Almada Paulo J. Fonseca 《Behavioral ecology and sociobiology》2011,65(4):707-716
Signal attributes should show different degrees of variability depending on the information to be conveyed. Species identity
is usually associated with stereotyped features of a signal, whereas other types of information such as individual quality
and motivation are associated with signal plasticity. Lusitanian toadfish males form aggregations during the breeding season
and emit a tonal advertisement call (the boatwhistle) to attract mates to their nests. We test the hypothesis that the boatwhistle
can convey information both on individual identity and motivation by checking how signal parameters vary with time. We study
how the physical (tide level) and social (calling alone or in a chorus) environments and male calling rate affect this advertisement
signal and how all these external and internal factors (environment, social and male motivation) blend to modulate the Lusitanian
toadfish’s advertisement call. Boatwhistles of each male were very stereotyped in short periods of time (minutes), but intra-male
signal variability greatly increased in a longer time scale (days). Nevertheless, significant differences among males could
still be found even in a long time scale. Pulse period was the acoustic feature that most contributed to discriminate among
males. Tide level and male calling rate modulated boatwhistle characteristics, and there was a differential effect of tide
on call attributes depending on male calling rate. Social acoustic environment only affected calling rate. These results suggest
that inter-individual differences in call characteristics and call plasticity may mediate both male–male assessment and mate
choice. 相似文献
98.
Age effect on the antioxidant activity of Daphnia magna (Anomopoda: Daphniidae): does younger mean more sensitivity? 总被引:1,自引:0,他引:1
Alberto AC Rocío OB Fernando MJ 《Journal of environmental biology / Academy of Environmental Biology, India》2011,32(4):481-487
It has been accepted that for most species newborns and senescent organisms are more sensitive than other ages to environmental stressors. Nevertheless, it must be considered that there are several biochemical and physiological compensatory processes which are not expressed with the same magnitude during the whole life cycle. With this aim, Daphnia magna individuals of different age were exposed to hexavalent chromium, Cr (VI), at two different sublethal concentrations (0.032 and 0.0064 mg l(-1)), and the activity of some antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and glutathione peroxidase (GPx) were evaluated during most of the life cycle of this cladoceran. The antioxidant enzymatic activity showed an inverse relationship with respect to age. The activity of CAT, GR and GPx were increased in the two treated groups, at all life stages tested. On the other hand, the activity of SOD decreased in the same groups. Both, increase and decrease in the antioxidant enzymatic activities, showed significant differences with respect to the control group, being higher for the 0.032 mg l(-1) group. The Cr (VI) LC50 was also estimated for these age groups, finding statistical differences among them. Even though adults exhibited higher responses, these enzymatic activity changes should not be interpreted as higher sensitivity, since the daphnids acute chromium toxicity followed a different pattern, with increasing LC50 values according to age. 相似文献
99.
Plant biomass and plant abundance can be controlled by aboveground and belowground natural enemies. However, little is known about how the aboveground and belowground enemy effects may add up. We exposed 15 plant species to aboveground polyphagous insect herbivores and feedback effects from the soil community alone, as well as in combination. We envisaged three possibilities: additive, synergistic, or antagonistic effects of the aboveground and belowground enemies on plant biomass. In our analysis, we included native and phylogenetically related range-expanding exotic plant species, because exotic plants on average are less sensitive to aboveground herbivores and soil feedback than related natives. Thus, we examined if lower sensitivity of exotic plant species to enemies also alters aboveground-belowground interactions. In a greenhouse experiment, we exposed six exotic and nine native plant species to feedback from their own soil communities, aboveground herbivory by polyphagous insects, or a combination of soil feedback and aboveground insects and compared shoot and root biomass to control plants without aboveground and belowground enemies. We observed that for both native and range-expanding exotic plant species effects of insect herbivory aboveground and soil feedback added up linearly, instead of enforcing or counteracting each other. However, there was no correlation between the strength of aboveground herbivory and soil feedback. We conclude that effects of polyphagous aboveground herbivorous insects and soil feedback add up both in the case of native and related range-expanding exotic plant species, but that aboveground herbivory effects may not necessarily predict the strengths of soil feedback effects. 相似文献
100.
Marcelo de O. Milfont Epifania Emanuela M. Rocha Afonso Odério N. Lima Breno M. Freitas 《Environmental Chemistry Letters》2013,11(4):335-341
This is the first report showing that using honeybee (Apis mellifera) and wild pollinators complementary pollination can enhance soybean productivity (Glycine max). Current industrial production of soybean involves autopollination and high loads of pesticides. Therefore, growers have neglected possible biotic pollination despite suggestions that soybean benefit from insect pollinators. Reports advocating possible biotic pollination are based on experiments where bees are caged with flowering plants and the absence of pesticides, thus not in field conditions. Therefore, here we compared in field conditions soybean yield produced (1) independently of biotic pollinators, (2) with wild pollinators and (3) with honeybee colonies. Results showed an increase of +6.34 % of soybean yield in areas where wild pollinators had free access to flowers. The introduction of honeybee colonies further raised the yield of +18.09 %. Our findings therefore show that, though soybean is autogamous, allowing pollination by wild pollinators leads to higher yields. Moreover, adding honeybee mitigates pollination deficits and improves yield compared to current practices. 相似文献