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排序方式: 共有478条查询结果,搜索用时 15 毫秒
441.
442.
Stimulation of reductive dechlorination of hexachlorobenzene in soil by inducing the native microbial activity 总被引:16,自引:0,他引:16
The reductive dechlorination and behaviour of 14C-hexachlorobenzene (HCB) was investigated in an arable soil. The activity of the native anaerobic microbial communities could be induced by saturating the soil with water. Under these conditions high rates of dechlorination were observed. After 20 weeks of incubation only 1% of the applied 14C-HCB could be detected in the fraction of extractable residues. Additional organic substances, like wheat straw and lucerne straw, however considerably delayed and reduced the dechlorination process in the soil. The decline of HCB was not only caused by dechlorination but also by the formation of non-extractable residues, whereby their amounts varied with time depending on the experimental conditions. Several dechlorination products were detected, indicating the following main HCB transformation pathway: HCB → PCB → 1,2,3,5-TeCB → 1,3,5-TCB → 1,3-DCB, with 1,3,5-TCB as main intermediate dechlorination product. The other TeCB-, TCB- and DCB-isomers were also detected in low amounts, showing the presence of more than one dechlorination pathway. Since the methane production rates were lowest when the dechlorination rates were highest, it can be assumed that methanogenic bacteria were not involved in the dechlorination process of HCB. The established 14C-mass balances show, that with increasing dechlorination and incubation times, the 14C-recoveries decreased. 相似文献
443.
Jean E. Weber Martin M. Fogel Lucien Duckstein 《Journal of the American Water Resources Association》1976,12(1):1-17
ABSTRACT. Four commonly used models for predicting sediment yield are analyzed and compared using previously published data. Three of these models involve logarithmic transformations. Some of the problems involved in transforming data are discussed in the context of logarithmic transformations. These problems are illustrated using the results of standard regression analyses and economic loss function analyses. For the data analyzed, the linear model is preferable to each of the logarithmic models on the basis of each analysis, and the usual multiple objective nature of the model choice problem is thus modified. The extent to which these results can be generalized is discussed in the context of model choice. 相似文献
444.
Jean M. Sogbedji Gregory F. Mclsaac 《Journal of the American Water Resources Association》2002,38(6):1753-1765
ABSTRACT: Evaluation of the applicability and validity of hydrologic simulation models for various cropping systems in different hydrogeologic and soil conditions is needed for a range of spatial scales. We calibrated and tested the ADAPT model for simulating streamflow from 552 to 1,985 km2 watersheds in central Illinois, where more than 79 percent of the land is used for maize‐soybean production and tile drainage is common. Model calibration was performed with a seven year period (1987 through1993) of measured streamflow from one of the watersheds, and model testing was done using independent weather and measured streamflow data from the two neighboring watersheds for the same seven year period. Simulations of annual streamflow were accurate with a coefficient of determination and Willmott's index of agreement of 0.98 and 0.99, respectively. For simulation of monthly streamflow, Willmott's index of agreement ranged from 0.93 to 0.95. For simulation of daily streamflow, Willmott's index of agreement ranged from 0.84 to 0.85. The daily simulations challenged the temporal and spatial resolution of our measured precipitation data. Discrepancies between simulated and measured data may result from the model's inability to effectively address frozen soils and snowmelt runoff processes and in accurately representing evapotranspiration. 相似文献
445.
This study was conducted on the reactions of Pheidole megacephala scouts when finding liquid food sources situated on territories marked by competing dominant ant species or on unmarked, control areas to see if the number of recruited nestmates is affected and if soldiers behave in ways adapted to the situation. We show that scouts recruit more nestmates, particularly soldiers, on marked rather than on unmarked areas. This recruitment allows P. megacephala to organize the defence and rapid depletion of these food sources prior to any contact with competitors. Soldiers can carry liquid foods both (1) in their crops like other Myrmicinae and (2), in a new finding concerning myrmicine ants, under their heads and thoraxes like certain poneromorph genera because the droplets adhere through surface tension strengths. Later, the liquids stored in the crop are distributed to nestmates through regurgitations during trophallaxis and the external droplets are distributed through social buckets, or the mode of liquid food transfer common in poneromorphs. Their flexibility to use or not use the latter technique, based on the situation, corroborates other reports that Pheidole soldiers have a relatively large behavioral repertoire. 相似文献
446.
Catherine Donner MD Jean-Christophe Noel Françoise Rypens Jean van Kerkem Freddy Avni Frédéric Rodesch 《黑龙江环境通报》1995,15(1):60-63
A 29-year-old woman was referred for suspicion of twin-twin transfusion syndrome (TTTS). Several ultrasonographic and neonatal criteria of TTTS were encountered in this twin pregnancy. The peculiar observations in this case were, firstly, the demonstration of superficial anastomosis by Doppler ultrasound and, secondly, that one single therapeutic amniocentesis could have been sufficient to partially correct the progression of the syndrome, as after amniocentesis it was no longer possible to demonstrate the vascular communication. This observation suggests that superficial anastomoses could also have a role in the genesis of TTTS. Their effect could be monitored by Doppler ultrasound and could be more easily corrected by therapeutic amniocentesis. 相似文献
447.
Buffetaut E Grellet-Tinner G Suteethorn V Cuny G Tong H Kosir A Cavin L Chitsing S Griffiths PJ Tabouelle J Le Loeuff J 《Die Naturwissenschaften》2005,92(10):477-482
We report on very small fossil eggs from the Lower Cretaceous of Thailand, one of them containing a theropod embryo, which display a remarkable mosaic of characters. While the surficial ornamentation is typical of non-avian saurischian dinosaurs, the three-layered prismatic structure of the eggshell is currently known only in extant and fossil eggs associated with birds. These eggs, about the size of a goldfinch's, mirror at the reproductive level the retention of small body size that was paramount in the transition from non-avian theropods to birds. The egg-layer may have been a small feathered theropod similar to those recently found in China. 相似文献
448.
Joshua J. Lawler§ Denis White Jean C. Sifneos† Lawrence L. Master‡ 《Conservation biology》2003,17(3):875-882
449.
A process simulation of a high grade coated paper mill has been developed as part of a process integration study. Data necessary to calibrate and validate the simulation developed with the Cadsim Plus® software were obtained by: measurements, samples analysis and estimations through partial and local mass balances. The simulation was designed in a way that allows grade changes to reproduce the mill operation. The simulation is used to support process studies to optimise water and raw materials consumption and to evaluate results obtained by mathematical optimisation. Different scenarios were studied in order to evaluate the feasibility and the effects of process redesign of the mill's networks. 相似文献
450.
Olivier Maire Jean Claude Duchêne Jean Michel Amouroux Antoine Grémare 《Marine Biology》2007,151(2):737-749
The activity and surface sediment displacement by the terebellid polychaete Eupolymnia nebulosa were monitored, using new image acquisition and image analysis procedures. We used a video sensor mounted on a motorized
table, to acquire adjacent images of the whole studied aquarium within about 2 s. These images were then grouped within a
composite image acquired every 15 s. Consecutive composite images were compared to infer activity and surface sediment displacement.
This procedure proved efficient for E. nebulosa as indicated by (1) the continuity of the tentacles within composite images, and (2) the direct comparison of images and
detected activities. There were important temporal changes in the relative importance of the three main types of activity:
feeding, tube-building and (both partial and total) emergence from the tube, accounting, respectively, for 75, 15 and 10%
of the entire experiment duration. Activity intensity (cm2 min-1) was assessed through the surface of pixels with grey levels differing by more than 20 (on a 0–255 scale) between two consecutive
images. Feeding was associated with low activity intensity, whereas tube-building and emergence from the tubes were associated
with high activity intensities. Surface sediment displacement mostly resulted from tentacle activity both during feeding and
tube-building and was almost zero when worms emerged from their tube. We used our experimental set up to assess spatial changes
in activity intensity and particle displacements along the tentacles. Most of the activity occurred within the first 4–6 cm
from the tube aperture. Particle loss during their transfer along the tentacles preferentially affected larger particles as
postulated by the model of particle selection and transport in tentaculate deposit-feeders. Moreover, the speed of the particles
along the tentacles correlated negatively with their size. This contributed to increase in the residence time of larger particles
on the tentacles and thus, to further enhance their probability of being lost. The size distributions of particles during
feeding and tube-building did not differ significantly although visual observations confirmed the preferential use of larger
particles for tube-building. This suggests the existence of a sorting step occurring elsewhere than on the tentacles as already
demonstrated for spionid polychaetes. 相似文献