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761.
762.
Sofie Vandendriessche Gina De Keersmaecker Magda Vincx Steven Degraer 《Marine Biology》2006,149(6):1499-1507
The species composition of macrofauna associated with floating seaweed rafts is highly variable and influenced by many factors like spatial and temporal variation, period since detachment and probably also the seaweed species. The presence of seaweed preferences was assessed by a combination of in situ seaweed samplings and multiple-choice aquarium experiments in a controlled environment, using the seaweed-associated grazing organisms Idotea baltica and Gammarus crinicornis. Results from the sampling data confirm that the seaweed composition influences macrofaunal species composition and abundance: samples dominated by Sargassum muticum displayed higher densities but lower diversities compared to samples dominated by Ascophyllum nodosum and Fucus vesiculosus. Seaweed preference was also apparent from the multiple-choice experiments, but did not exactly match the results of the community analysis: (1) I. baltica had high densities in seaweed samples (SWS) dominated by F. vesiculosus and A. nodosum, while in the experiments, this isopod was most frequently associated with Enteromorpha sp. and F. vesiculosus, and fed mostly on S. muticum, A. nodosum and Enteromorpha sp.; (2) G. crinicornis had high densities in SWS dominated by F. vesiculosus, while in the experiments, this amphipod was most frequently associated with S. muticum, but fed most on A. nodosum and F. vesiculosus. It is clear from the laboratory experiments that preference for habitat (shelter) and food can differ among seaweed species. However, food and habitat preferences are hard to assess because grazer preference may change if choices are increased or decreased, if different sizes of grazers are used, or if predators or other grazers are added to the experiments. The effects of seaweed composition may also be blurred due to the obligate opportunistic nature of a lot of the associated macrofaunal species. 相似文献
763.
Laboratory experiments tested whether the cardiac activity of two species of limpets (Cellana spp.), co-occurring on the rocky shores of Hong Kong but having different zonal distributions, was differently affected by variations in physical environmental characteristics. Experiments reproduced exposure of limpets to dehydration, high water temperature and reduced salinity, all conditions that can occasionally be faced by animals during low tides. Cardiographic traces were obtained using a non-invasive method based on infrared light sensors glued onto the limpet shell in a position directly over the heart. The signals were filtered and amplified, viewed on portable oscilloscopes and automatically transferred to computer. When tested under acclimation temperatures, the lower shore C. toreuma had faster heart rates than the upper shore C. grata, both in air and when submerged in seawater. Regular alternation of heartbeating and acardia were observed in C. grata exposed to both dry and saturated air, whilst C. toreuma showed transient acardia only during exposure to dry air. Both species showed a similar increase in heart rate with increasing temperature (Q10~1.8 in the range 25-34°C). When submerged in freshwater, C. grata regularly alternated acardia with beating at a rate slightly lower than in seawater, whilst C. toreuma showed strong bradycardia with reduction of beat amplitude, followed by steady acardia. Recovery of heartbeating after return to initial salinity was faster in C. grata, whilst C. toreuma, initially bradycardic, showed a consistent return to tachycardia. Overall, this study shows that the two congeneric species exhibit different cardiac responses to variations in environmental characteristics, which may be related to their differing vertical distribution. 相似文献
764.
765.
F. Devillard F. Prieur M. Delhomme-Bachy B. De Freminville B. Lauras C. P. Brizard J. Fraisse Dr M. F. Bertheas 《黑龙江环境通报》1992,12(7):613-618
Since 1987, we have had experience with 13 prenatal diagnoses of 11 women at risk for the fragile X syndrome by cytogenetic studies on amniotic fluid cultures. The induction method included TC 199 medium and methotrexate. Results were obtained in all cases. Ten were males and three were prenatally diagnosed as being affected. Three were females and none of them was fra(X)-positive. Results were confirmed in 10/13 cases. In these cases, we had neither false-positive nor false-negative results. 相似文献
766.
Humic substances (HS) produced during the aerobic decomposition of polysaccharides still need to be recognized as such and characterized. Humic (HA) and fulvic (FA) acids extracted at different time intervals during composting of cotton residues from carding, where no decomposition of lignin occurred, were investigated by scanning electron microscopy (SEM) size exclusion chromatography and infrared spectroscopy. Throughout the experiment, fulvic acids possessed a larger number of carboxyl groups but a lower number of weak acidic groups (negatively charged acid groups at pH 11) than humic acids. the number of carboxyl groups increased with time in both fulvic and humic acids, while that of phenolic groups decreased. Infrared spectra showed that the ratio between carboxyl and methyl groups decreased from 8.5 to 4 in FA after 18 days. This change corresponded with the disappearance of flat sheet structures observed by SEM at pH 6. Our results suggest that the shape of humic molecules as observed by SEM reflects the strength of hydrophilic/hydrophobic interactions with the solvent molecules. About 80% of FA molecules had a molecular weight lower than 3500 as deduced from column calibration with HS standards obtained by ultrafiltration. About 40% of humic acids were composed of small molecules; only 20% HA had a molecular weight larger than 45000. Polysaccharide-derived HS may not be limited to the high molecular weight poorly transformed fraction containing bonded polysaccharide structures, but may also consist of low molecular weight components with no structural similarity to the original material. 相似文献
767.
768.
Thermal hazard in a batch process involving hydrogen peroxide 总被引:1,自引:0,他引:1
P. De Filippis C. Giavarini R. Silla 《Journal of Loss Prevention in the Process Industries》2002,15(6):449-453
Hydrogen peroxide is a versatile and interesting reagent for many industrial processes; nevertheless, it is very sensitive to impurities that can catalyze its decomposition, so that the desired reaction could be accompanied by undesired parallel and consecutive reactions. As an example, the butadiene free radical polymerization with hydrogen peroxide in the presence of an organic solvent was studied. Batch polymerization occurs in the liquid phase at about 120 °C. Because of the involved reactive compounds and the relatively high temperature, this is an intrinsically dangerous reaction. Therefore calorimetric data can give important information about safety and process optimization during the scale-up. The aim of this research project was to study the influence of impurities on the overall heat of reaction. The experiments were made in a high-pressure reaction calorimeter. The study has revealed that impurities do indeed affect the reaction course. Most importantly, the presence of carboxylic acids and/or ionic iron must be avoided and the recycle of unreacted reagents must be carefully controlled to minimize the build-up of these impurities. 相似文献
769.
Naiara Albaina Jeanine L. Olsen Lucía Couceiro José Miguel Ruiz Rodolfo Barreiro 《Marine Biology》2012,159(9):1871-1884
Because marine species respond differentially to factors governing survival and gene flow, closely related taxa may display dissimilar phylogeographic histories. New data for the patchily distributed gastropod Nassarius nitidus throughout its Atlantic–Mediterranean range (collected during 2008 and 2009) were used to investigate its phylogeography and recent demography. Results based on mitochondrial COI sequences of 422?N. nitidus individuals from 15 localities revealed contrasting phylogeographic and demographic patterns among N. nitidus populations from each basin. Data suggest the existence of two glacial refugia, one in the Atlantic, around the Iberian Peninsula, and the other in the Paleo-Mediterranean Sea (Adriatic). Bayesian skyline reconstructions suggest that the Adriatic population of N. nitidus remained largely unaffected by the Last Glacial Maximum (LGM), whereas the Iberian Atlantic region experienced dramatic exponential growth after its conclusion. Contemporary North Sea populations of N. nitidus are the endpoint of a leading-edge recolonization process from a southern position. Additionally, a reanalysis of pre-existing material for the continuously distributed close congener N. reticulatus was used to compare both species in the late histories. In contrast to N. nitidus, N. reticulatus prospered during the LGM and experienced an earlier Atlantic expansion during the previous interglacial period. Despite similar life history and dispersal potential, the results here presented suggest that subtle differences in microhabitat requirements between the two species have had important consequences for their particular distribution in response to glacial events. 相似文献
770.