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David Makowski Jean-Baptiste Denis Laurent Ruck Annette Penaud 《Crop Protection》2008,27(8):1187-1193
The proportion of diseased plant organs measured before chemical treatment is often used to make an assessment of the need for crop protection in agricultural plots, but such diagnostic tests are not perfect and sometimes lead to incorrect decisions. The area under the receiver operating characteristic (ROC) curve is a popular index of the overall performance of a test. It can be interpreted as the probability that the test value for a randomly chosen diseased subject will exceed that of a randomly chosen disease-free subject. In this paper, we present a Gaussian/Binomial model to assess the accuracy of diagnostic test based on a measured proportion of diseased plant organs. The model parameters were estimated from a real dataset and the model was used to analyse the accuracy of a diagnostic test based on a measured proportion of oilseed rape flowers contaminated by Sclerotinia sclerotiorum. The results showed that the accuracy of the test depends on the number of collected flowers, but that it is not necessary to collect more than 40 flowers per plot. A simulation study showed that the bias of the estimator of the area under the ROC curve was near zero for all size of dataset and that its mean-square error decreased in function of the number of experimental plots used in the ROC analysis. A major interest of our approach is that it allows one to study the effect of the sample size of the organs on the accuracy of the test. It can also be used to estimate the probability of disease occurrence, and to determine a decision threshold according to the sensitivity and specificity values. 相似文献
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When leaves of M.III rootstocks were momentarily dipped in 0·004M copper sulphate solution there was an immediate rapid uptake at a rapidly declining rate (phase I), complete within a minute ; no further significant uptake occurred, though about 80% of the copper initially retained by the leaf could still be washed off its surface.When, after a suitable interval (three minutes or more), such leaves were re-treated with the same solution there was another cycle of immediate rapid uptake, similar to phase I, but leading to rather less copper being taken up. This process could be repeated again and again, and though the copper which entered the leaf did so in a series of discrete increments of phase I uptake, the overall pattern showed all of the changes of phase that occur when a leaf is immersed in solution for long periods.It is postulated that when leaves are dipped for the first time the copper taken up in phase I is adsorbed to two sites, only one of which (site Ia) communicates with the further sites (site II, etc.) which are eventually filled up when copper is continuously supplied to the leaves. Normally these sites are filled up through site Ia but, when the copper supply at the leaf surface is interrupted, site Ia becomes denuded of copper, and can be filled up again in another cycle of phase I when the leaves are re-treated.Leaves treated with 0·004M copper sulphate solution under field conditions took up copper additional to the initial uptake over a period of days, presumably when the surface deposit was brought into solution by rain or dew. However, in spite of numerous occasions on which rain or dew fell, there was no further uptake over the last six days of the experiment though about a third of the copper initially present could still be washed off the leaf surface. 相似文献
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Amirbahman Aria Ruck Philip L. Fernandez Ivan J. Haines Terry A. Kahl Jeffery S. 《Water, air, and soil pollution》2004,152(1-4):315-331
This study compares mercury (Hg) and methylmercury (MeHg) distribution in the soils of two forested stream watersheds at Acadia National Park, Maine, U.S.A. Cadillac Brook watershed, which burned in 1947, has thin soils and predominantly deciduous vegetation. It was compared to the unburned Hadlock Brook watershed, with thicker soil and predominantly coniferous vegetation. Soils in both watersheds were primarily well drained. The fire had a significant impact on the Cadillac watershed, by raising the soil pH, altering the vegetation, and reducing carbon and Hg pools. Total Hg content was significantly higher (P > 0.05) in Hadlock soils (0.18 kg Hg ha-1) compared to Cadillac soils (0.13 kg Hg ha-1). Hadlock O horizon had an average Hg concentration of 134±48 ng Hg g-1 dry weight, compared to 103±23 ng Hg g-1 dry weight in Cadillac O horizon. Soil pH was significantly higher in all soil horizons at Cadillac compared to Hadlock soils. This difference was especially significant in the O horizon, where Cadillac soils had an average pH of 3.41±0.22 compared to Hadlock soils with an average pH of 2.99±0.13.To study the mobilization potential of Hg in the O horizons of the two watersheds, batch adsorption experiments were conducted, and the results were modeled using surface complexation modeling. The results of Hg adsorption experiments indicated that the dissolved Hg concentration was controlled by the dissolved organic carbon (DOC) concentration. The adsorption isotherms suggest that Hg is more mobile in the O horizon of the unburned Hadlock watershed because of higher solubility of organic carbon resulting in higher DOC concentrations in that watershed.Methylmercury concentrations, however, were consistently higher in the burned Cadillac O horizon (0.20±0.13 ng Hg g-1 dry weight) than in the unburned Hadlock O horizon (0.07±0.07 ng Hg g-1 dry weight). Similarly, Cadillac soils possessed a higher MeHg content (0.30 g MeHg ha-1) than Hadlock soils (0.16 g MeHg ha-1). The higher MeHg concentrations in Cadillac soils may reflect generally faster rates of microbial metabolism due to more rapid nutrient cycling and higher soil pH in the deciduous forest. In this research, we have shown that the amount of MeHg is not a function of the total pool of Hg in the watershed. Indeed, MeHg was inversely proportional to total Hg, suggesting that landscape factors such as soil pH, vegetation type, or land use history (e.g., fire) may be the determining factors for susceptibility to high Hg in biota. 相似文献
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Knol JJ van Loon WA Linssen JP Ruck AL van Boekel MA Voragen AG 《Journal of agricultural and food chemistry》2005,53(15):6133-6139
A kinetic model for the formation of acrylamide in a glucose-asparagine reaction system is pro-posed. Equimolar solutions (0.2 M) of glucose and asparagine were heated at different temperatures (120-200 degrees C) at pH 6.8. Besides the reactants, acrylamide, fructose, and melanoidins were quantified after predetermined heating times (0-45 min). Multiresponse modeling by use of nonlinear regression with the determinant criterion was used to estimate model parameters. The proposed model resulted in a reasonable estimation for the formation of acrylamide in an aqueous model system, although the behavior of glucose, fructose, and asparagine was slightly underestimated. The formation of acrylamide reached its maximum when the concentration of sugars was reduced to about 0. This supported previous research, showing that a carbonyl source is needed for the formation of acrylamide from asparagine. Furthermore, it is observed that acrylamide is an intermediate of the Maillard reaction rather than an end product, which implies that it is also subject to a degradation reaction. 相似文献
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Experimental investigations in an atmospheric boundary layer wind tunnel were carried out in order to study both the influence
of the windward edge structure and the stand density on the flow characteristics near the canopy top of forest edges. For
the edge structure investigation, two different types of forest edges were used. The taper angle was varied three times for
both edge types, and all tapered edges were combined with both dense and sparse forest stands. In addition, a configuration
was investigated where the airflow in the trunk space of the dense forest was blocked completely by an impermeable wall. In
order to study the influence of stand density, forest stands were varied three times by removing whole rows of the originally
dense model forest. The measurements show that a forest edge induces strong disturbances in the flow field at the near-edge
region leading to an increased momentum transfer and to an increased wind loading on trees. The region of significant disturbances
extends to a distance of about eight tree heights. Both edge density and taper angle determine the amount of volume influx
through the edge, which seems to be primarily responsible for the flow field properties near the canopy top. It was found
that for sparse forest stands, sloping tapered edges reduce the wind velocities nearest to the canopy. It could also be shown
that the positive skewness of the near-canopy longitudinal velocity distribution is diminished with decreasing taper angle
indicating that higher wind velocity fluctuations are reduced. 相似文献
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