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581.
582.
Martin Pichler Georg Guggenberger Robert Hartmann Wolfgang Zech 《Environmental science and pollution research international》1996,3(1):24-31
The behavior of 20 PAH in the organic layers of a L mull, an Of mull and a mor was assessed by a combined approach of a soil
profile study, and the analysis of particle-size separates. Increasing PAH concentrations with depth in the mor profile (L,
866 μg kg−3; Of, 2902 μg kg−1; Oh, 10489 ug kg−1) were assigned to selective enrichment during organic matter decomposition. PAH were further highly enriched within the finer
separates. For the L horizons, significant positive correlations were established between the enrichment of individual PAH
(as observed from the decomposition gradient between the >2-mm fraction and the < 0.05-mm fraction), and the KOW for each compound. The slope of the regression line, m, described the degree of differentiation between low- and high-molecular
PAH during litter decomposition. Since m was greatest in the most biologically active humus type (L mull, 0.33) and smallest
in the most inactive (mor, 0.20), microbial breakdown was assumed as the dominating process for this differentiation. The
results also indicated that decomposition processes had already taken place in the L horizons, leading to morphological and
chemical changes of organic matter, and to an enrichment of high molecular PAH. 相似文献
583.
584.
Pigeons released away from their loft usually fly around at the release site for a while before they finally leave. Visual
observations had suggested that the moment when the birds decide to head home is associated with a certain change in flying
style. To see whether this change is also reflected by GPS-recorded tracks, a group of pigeons equipped with flight recorders
was released at two sites about 10 km from their home loft. The initial part of their flight paths was analyzed in order to
find objective criteria indicating the point of decision. We selected the highest increase in steadiness as the best estimate
for the moment of decision. This criterion allows us to divide the pigeons’ paths in two distinct phases, an initial phase
and the homing phase, with the moment of decision, on an average, 2 min after release. The moment of decision marks a change
in behavior, with a significant increase in steadiness and flying speed and headings significantly closer to the home direction.
The behavior of the individual birds at the two sites was not correlated, suggesting no pronounced individual traits for the
length of the initial phase. The behavior during this phase seems to be controlled by flight preparation, exploration, and
non-navigational motivations rather than by navigational necessities alone.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
585.
Guillermo Palau-Salvador Manuel García-Villalba Wolfgang Rodi 《Environmental Fluid Mechanics》2011,11(6):611-625
This paper presents a large eddy simulation of mass transfer in the flow around a surface-mounted finite-height circular cylinder.
The study was carried out for a cylinder with height-to-diameter ratio of 2.5 and a Reynolds number based on the cylinder
diameter of 44000. The approach flow boundary layer had a thickness of about 10% of the cylinder height. A tracer was released
at various levels upstream of the cylinder. The effect of the release position in the subsequent spreading and dilution of
the plumes is analyzed. It is found that a tracer released at the top or at mid-height is entrained into the recirculation
zone behind the cylinder, and therefore presents similar plume evolution in the far wake in both cases. If the tracer is released
at around three-quarters of the height of the cylinder, it is not significantly entrained by the main recirculation region,
leading to smaller rates of spreading of the plume. Finally, if the tracer is released near the floor, the plume is entrained
by the horseshoe vortex that wraps around the cylinder, leading to a large lateral spreading of the plume, remaining always
near the floor. 相似文献
586.
Gnandi K Musa Bandowe BA Deheyn DD Porrachia M Kersten M Wilcke W 《Journal of environmental monitoring : JEM》2011,13(7):2033-2041
The state of contamination of tropical environments, particularly in Africa, remains a relatively under explored subject. Here, we determined polycyclic aromatic hydrocarbon (PAH) and trace metal concentrations in coastal sediment and biota samples (fish and mussels) from Togo (West Africa). In the sediments, the ∑21 PAH concentrations ranged from <4 ng g(-1) to 257 ng g(-1), averaging 92 ng g(-1). Concentration ratios of low molecular weight PAHs (2-3 rings) versus high molecular weight PAHs (≥4 rings) were always lower than 1 (ranging from 0.08 to 0.46) indicating that high molecular weight PAHs were dominant in all sediment samples, and that PAHs originated mainly from anthropogenic combustion activities. The sediments were also analyzed for major elements and a total of 15 trace metals, which were found in elevated concentrations. The calculated enrichment factor (EF) values relative to the Earth's crust show that the contamination is extremely severe for Cd (EF = 191), severe for Cr (EF = 18) and U (EF = 17.8), moderately severe for Zr (EF = 8.8), for Ni (EF = 6.8), Sr (EF = 5.9) and Ba (EF = 5.4), and moderate for V (EF = 3.6) and Zn (EF = 3.4). Sediments sampled in areas affected by the dumping of phosphorite mine tailings showed particularly high concentrations of trace metals. Overall, concentrations of both PAHs and trace metals in sediment tend to increase from the coastline to the open sea (2 km offshore). This is attributable to the increasingly finer texture of coastal sediment found offshore, which has a terrigenous origin and appears loaded with various contaminants through adsorption processes. Such high loads of trace metals were also found in the biota (fish and mussels). The ratio of measured trace metal concentrations in biota to threshold limits set by the World Health Organization herein defined as relative health factor (RHF) was high. Average RHF values in fish were highest for Se (470), As (250), Ag (97), Ni (78), Mn (63), Fe (53), Pb (36), Cd (10), and Cr (7) while lowest for Cu (0.08) and Zn (0.03). Cd and Al did not bioaccumulate in the analyzed fish species. In mussels, the RHF values were highest for Fe (9,108), As (295), Pb (276), Se (273), Mn (186), Ni (71), Ag (70), Cd (14), and Cu (4). 相似文献
587.
Avian magnetic compass: fast adjustment to intensities outside the normal functional window 总被引:1,自引:0,他引:1
To determine how fast birds can adapt to magnetic intensities outside the normal functional window of their magnetic compass,
we tested migratory birds in a magnetic field of 92,000 nT, twice the intensity of the local geomagnetic field at the test
site in Frankfurt a.M., Germany. In the local field, robins showed a significant preference of their southerly migratory direction,
whereas in the 92,000-nT field, they were initially disoriented. However, when the birds were preexposed to 92,000 nT for
1 h before being tested, they were able to orient under this intensity, and their behavior did not differ from that in the
geomagnetic field. These data show that birds require only a short time to adjust to magnetic intensities, which they cannot
spontaneously use for orientation. Interpreting these findings in view of the radical pair model (Ritz et al. 2000), this means that they can learn rather quickly to interpret novel activation patterns on their retina. 相似文献
588.
Recent Industrial Applications of Lignin: A Sustainable Alternative to Nonrenewable Materials 总被引:10,自引:0,他引:10
Lignin represents a vastly under-utilized natural polymer co-generated during papermaking and biomass fractionation. Different types of lignin exist, and these differ with regard to isolation protocol and plant resource (i.e., wood type or agricultural harvesting residue). The incorporation of lignin into polymeric systems has been demonstrated, and this depends on solubility and reactivity characteristics. Several industrial utilization examples are presented for sulfur-free, water-insoluble lignins. These include materials for automotive brakes, wood panel products, biodispersants, polyurethane foams, and epoxy resins for printed circuit boards. 相似文献