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21.
The effects of time and temperature on the release kinetics of water‐dispersible colloids (WDCs) from three German silt loam topsoils in deionized water were investigated in batch experiments under low‐energy rotating shaking conditions. The measured critical coagulation concentrations of Ca2+ and Na+ for extracted WDC were much larger than the experimental ionic conditions. This indicates a fast dispersion rate in the first detachment step of WDC mobilization from soil aggregates. The cumulative released WDC fraction F(t) (released WDC/clay content in bulk soil) was satisfactorily fitted to the square root of shaking time by a linear function in three soils with a similar clay content. This implies diffusion‐controlled release kinetics in the second step of the WDC mobilization process. The mobilization kinetics were modelled by considering a diffusion‐controlled transport through an immobile water layer in the macropores of soil aggregates formed by silt and sand particles. The effects of temperature on the mobilization kinetics and sedimentation volumes of saturated soils were compared at 7, 23 and 35°C. A linear correlation was found between immobile water layer thickness in soil macropores (lt) and the water volume (Vwater) in soil sediment, which indicates a strong dependence of lt on the soil texture. Temperature‐sensitive lt and Vwater influenced the effect of temperature on WDC release, which counteracts the estimated effect of temperature on particle diffusion according to the Stokes‐Einstein relation. A larger decrease in F(t) was found in grassland and forest soils than in an arable soil and can be related to greater stagnant water contents (larger lt and Vwater) in soil macropores, where particulate organic matter and polyvalent cations in their oxide forms at acidic pH will thus contribute to water immobilization. 相似文献
22.
Field study on colloid transport using fluorescent microspheres 总被引：1，自引：1，他引：0
M. Burkhardt R. Kasteel J. Vanderborght & H. Vereecken 《European Journal of Soil Science》2008,59(1):82-93
Understanding colloid movement through the vadose zone is important, because colloids may facilitate transport of some less mobile contaminants. Experimental evidence of colloid transport in the vadose zone, especially at the field scale, is rare. We developed and tested a method to detect and quantify local concentrations of fluorescent microspheres (MS) with a diameter of 1 μm in unsaturated soil based on fluorescent microscopy. The detection limit was 400 × 106 MS kg?1 field‐moist soil for an automated counting method, and 20 × 103 MS kg?1 for manual counting. To test the method in the field, we applied a 40‐mm pulse with an input concentration of 14.6 × 109 MS litre?1 on two plots during 6 hours, together with bromide (Br?) and the food dye Brilliant Blue (BB). The concentrations of MS were determined on horizontal cross‐sections by a randomly distributed sampling scheme, either directly after application or 90 days after application and a rainfall of 100 mm. Mass recoveries for the MS of 85 and 65% were acceptable in view of the field conditions. Even after infiltration of particle‐free water, the largest MS concentrations were measured at the soil’s surface, which pointed at physical retention mechanisms. An additional selective sampling of hydrologically active preferential flow pathways, guided by the dye infiltration patterns, revealed that the MS were transported to similar depths as BB, that is 0.80 m directly after irrigation and 1.7 m after 90 days. This implies that also a small fraction of the particulate tracers was rapidly transported to larger depths, regardless of their physico‐chemical properties. 相似文献
23.
Sequence analysis demonstrates the conservation of fimH and variability of fimA throughout avian pathogenic Escherichia coli (APEC) 总被引：2，自引：0，他引：2
Vandemaele F Vandekerchove D Vereecken M Derijcke J Dho-Moulin M Goddeeris BM 《Veterinary research》2003,34(2):153-163
In this study we sequenced and analysed the fimH and fimA genes of 24 avian pathogenic Escherichia coli (APEC) isolates, in order to investigate their possible conserved nature. Additional parameters (serotype, presence of aerobactin receptor, expression of F1 pili and virulence for chickens) were investigated to look for correlations with the obtained sequences. The sequence analysis demonstrated that FimH is highly conserved among all investigated APEC strains (>99% homology), whereas the major subunit FimA is less conserved, presenting 6 variable regions distributed along the protein. A hydrophilicity analysis suggested several variable domains of FimA to be potential epitopes. We were able to classify the investigated strains into three main groups, on the basis of the amino-acid sequences of the variable regions. This grouping was consistent throughout all variable regions and was independent of serotype, leading to an improved classification of the F1 pili. No correlation was found between the fimH and fimA sequences and the following parameters: avian species, organ of isolation, serotype, presence of aerobactin receptor and virulence for chickens. This study elucidated the molecular structure and the degree of conservation of FimH and FimA among various avian pathogenic E. coli strains. 相似文献
24.
Vereecken J Foubert I Smith KW Dewettinck K 《Journal of agricultural and food chemistry》2007,55(19):7793-7801
The objective of this study is to investigate the architecture to feature physical functionality of filling fats. This means an investigation of the different structure levels (crystallization, microstructure, macrostructure, etc.) that lead to good technological functionality. The isothermal crystallization behavior of two filling fats (one trans-containing and one trans-free) was examined by differential scanning calorimetry and microscopy. Furthermore, the hardness of the samples was examined after cooling in a water bath at two different temperatures and at three different storage times. The trans-containing filling fat crystallized faster and in smaller crystals as compared to the trans-free filling fat. The crystallization behavior of the trans-free filling fat was more complex, with the formation of different polymorphic forms. The hardness of the fillings was not only governed by the amount of solid fat present in the network but also by the structure of this network. The filling matrix components seem to have a pronounced influence on the microstructure and thus on the macroscopic properties. 相似文献
25.
Graf A Weihermüller L Huisman JA Herbst M Vereecken H 《Science (New York, N.Y.)》2011,331(6022):1265; author reply 1265
Mahecha et al. (Reports, 13 August 2010, p. 838) estimated the temperature sensitivity of ecosystem respiration (Q(10)) and showed that temperature sensitivity and its site-to-site variability are lower than previously reported. We demonstrate that their Q(10) value of 1.4 is an underestimate if interpreted as the averaged sensitivities of all ecosystem components, because fast temperature fluctuations penetrate poorly into the soil. 相似文献
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27.
The radioactive liquid waste (RLW) system in Ontario Hydro's pressurised heavy water reactors collects drainage from a variety of sources ranging from floor drains to laundry waste. RLW effluent was intermittently toxic to rainbow trout andDaphnia magna during the first phase of Ontario's Municipal Industrial Strategy for Abatement (MISA) Program, apparently as a result of the interaction of a variety of known and unknown organic and inorganic compounds. Accordingly, we employed a tmatment-based approach to reducing its toxicity, supplemented by chemical analysis. Two series of toxicity reduction tests were conducted. The fast series explored the potential for sorption of the possible toxicants, while the accord series incorporated a wider variety of treatments. Of the 24 samples in the first test series, 17 were toxic (D. magna mortality ≥ 50%). Of the toxic samples, only 7 of 17 were still toxic after passage through an activated carbon column, but 5 of 6 samples tested remained toxic after passage through a metal chelating resin column. In the second series, at least one of the treatments was effective in reducing toxicity of all samples which were initially toxic (16 of 24 samples), but no one treatment was effective for all toxic samples. Three treatments (UV/H2O2 photo-oxidation with prior pH adjustment, or passage through a column of either a non-functioalized (N-F) resin or a mixture of N-F resin and a weak base (W-B) anion exchange rain), were effective in reducing the toxicity of more than 50% of the toxic samples; yet roughly 25% of these samples remained toxic after treatment O2 sparging, UV/H2O2 photo-oxidation without prior pH adjustment, and passage through a column of the W-B Resin were less effective, as more than 50% of the samples remained toxic after treatment. Filtering was not effective, as all of the treated samples (9/9) retained their toxicity. There was no obvious correspondence between toxicity and the concentrations of metals (Cu, Zn, Fe, Al and Cd) nor were any simple relationships apparent between toxicity and Total Organic Carbon or NH3 concentrations. At stations where radioactive liquid wastes are segregated, toxicity was also segregated, suggesting that we may be able to address the problem at source through a combination of Best Management Practices and smaller scale treatment facilities. 相似文献
28.
A. E. Berns M. Bertmer A. Schäffer R. J. Meier H. Vereecken & H. Lewandowski 《European Journal of Soil Science》2007,58(4):882-888
DFT calculations are a powerful tool to support NMR studies of xenobiotics such as decomposition studies in soil. They can help interpret spectra of bound residues, for example, by predicting shifts for possible model bonds. The described bound‐residue models supported the hypothesis of a free amino side chain already suspected by comparison with the experimental data of the standards. No match was found between the calculated shifts of amide bondings of the amino side chains (free or substituted) and the experimental NMR shifts of a previous study. In the present paper, first‐principles quantum chemical calculations were used to support and check the interpretation of the 15N cross polarization‐magic angle spinning nuclear magnetic resonance (15N‐CPMAS NMR) spectra of simazine and its metabolites. Density functional theory (DFT) calculations were performed using Gaussian 03 and the nuclear magnetic shielding tensors were calculated using the Gauge‐Independent Atomic Orbital (GIAO) method and B3LYP/6–311+G(2d,p) model chemistry. Good agreement was reached between the calculated and measured chemical shifts of the core nitrogens and the lactam and lactim forms of the hydroxylated metabolites could be clearly distinguished. The calculated spectra showed that these metabolites exist preferentially in the lactam form, an important fact when considering the possible interactions of such hydroxylated metabolites with the soil matrix. Although the calculated bound‐residue models in the present study only partly matched the experimental data, they were nevertheless useful in helping to interpret the experimental NMR results of a previous study. To get a better match between the calculated and the measured shifts of the side‐chain nitrogens the calculations need to be further developed, taking into account the influence of neighbouring molecules in the solid state. Altogether, quantum chemical calculations are very helpful in the interpretation of NMR spectra. In the future, they can also be very useful for the prediction of NMR shifts, in particular when it is not possible to measure the metabolites due to a lack of material or in cases where practical experiments cannot be conducted. 相似文献
29.
C. Tudorache P. Viaene R. Blust H. Vereecken G. De Boeck 《Ecology of Freshwater Fish》2008,17(2):284-291
Abstract – Migrating fish species with different swimming capacities and energy use show different capacities for passing obstacles between habitats, such as culverts and fish ladders. Here, we present an integrated study on swimming capacity and energetic use in seven European freshwater fish species with different ranges of migration (brown trout Salmo trutta L., European perch Perca fluviatilis L., roach Rutilus rutilus L., common carp Cyprinus carpio L., gudgeon Gobio gobio L., bullhead Cottus gobio L. and stone loach Barbatula barbatula L.). Critical ( U crit ), optimal ( U opt ) and maximum ( U max ) swimming speed and oxygen consumption ( M O2 ) were analysed and showed values correlated to migration capacity with highest swimming capacities in trout and roach and lowest in stone loach and bullhead. The resulting data can be used to make estimates of maximum passable water speeds in culverts. In conclusion, long-distance migrators show higher swimming capacities and can potentially clear obstacles easier than short distance migrators with lower swimming capacities. Even small obstacles (<25 cm) could be a barrier for genetic exchange between populations in short-distance migrators. 相似文献
30.
Foubert I Vereecken J Smith KW Dewettinck K 《Journal of agricultural and food chemistry》2006,54(19):7256-7262
The objective of this study is to gain further understanding into the relationship between crystallization behavior, microstructure, and macroscopic properties in coating fats. The isothermal crystallization behavior of two coating fats (one trans containing and one trans free) was examined, both as pure fats and in coatings, by DSC and microscopy. Furthermore, the hardness of the samples was examined after cooling in a water bath at two different temperatures and at three different storage times. Both fats seemed to show an alpha-mediated beta' crystallization at lower temperatures and a direct beta' crystallization at higher temperatures. The trans free coating fat clearly crystallized faster and in smaller crystals. The hardness was governed not only by the amount of solid fat present in the network but also by the structure of this network. The coating matrix components seem to have a pronounced influence on the microstructure and thus on the macroscopic properties. 相似文献