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The mobility of the microcapsules in saturated granular media was estimated on the basis of conventional breakthrough experiments in vertical columns packed with sands for various physical and chemical conditions. Four types of microcapsules have been tested, all of them were found to have reasonable mobility in clean quartz sand, but not in sandy soil. The immobility in the sandy soil was attributed to some production deficiencies in terms of shape, size and quality of the coating surface. The size of the microcapsules should be considerably smaller than those produced with an order of magnitude of a few micrometers. They should also be more spherical and with a smoother surface. The addition of a proper dispersant had stabilized the microcapsules suspension, and facilitated their transport in the sand. A major flow factor affecting microcapsules mobility is the water flux. The microcapsules should be applied at a high irrigation rate, which also implies a high water content in the soil profile. Considering solely the mobility aspect, it seems that the prospect for successful application of the new method for weed control is limited to granular soils with a high hydraulic conductivity at/or near saturation. However, for the time being the most limiting problem is the production of quality microcapsules with good physical and chemical properties. 相似文献
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Longley NP Bode CR Border PM Courant H DeMuth DM Gray RN Johns K Kasahara SM Lowe MJ Marshak ML Miller WH Mualem L Peterson EA Roback DM Ruddick K Schmid DJ Schub MH Shupe MA Vassiliev V Villaume G Werkema SJ Ayres DS Fields TH Gallagher HM Goodman MC Lopez FV May EN Price LE Seidlein RV Thron JL Trost H Uretsky JL Allison WW Barr GD Brooks CB Cobb JH Giller GL Stassinakis A Thomson MA West N Wielgosz U Alner GJ Cockerill DJ Cotton RJ Garcia-Garcia C Litchfield PJ Pearce GF Ewen B Kafka T 《Physical review D: Particles and fields》1995,52(5):2760-2765
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A classical random walker starting on a node of a finite graph will always reach any other node since the search is ergodic, namely it fully explores space, hence the arrival probability is unity. For quantum walks, destructive interference may induce effectively non-ergodic features in such search processes. Under repeated projective local measurements, made on a target state, the final detection of the system is not guaranteed since the Hilbert space is split into a bright subspace and an orthogonal dark one. Using this we find an uncertainty relation for the deviations of the detection probability from its classical counterpart, in terms of the energy fluctuations. 相似文献
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The effects of rainfall-induced soil seals on drying processes and on infiltration following drying intervals are simulated for two different soils, a loam and a sandy loam. The simulated drying processes include water content redistribution without evaporation and under a constant evaporation rate of 5 mm day–1. During evaporation, the water content at the seal surface decreases rapidly. A high water content gradient develops within the seal, which increases along the drying interval. It indicates that, at least during the first hours of drying, the seal layer fulfilled all the evaporation demand and therefore dries faster that an unsealed soil where the evaporation is supplied by a much deeper zone of the soil profile. This phenomenon is more accentuated in the loam than in the sandy loam soil. Considering the subsequent infiltration curves during rainfall following different drying intervals, the ponding time and the post-ponding infiltration rates increase when the antecedent drying period is longer, but no significant effect on the final infiltration is found following drying intervals of few days. Also, the water content at the sealed soil surface before rainfall seems to play a major role on infiltration. Very close infiltration curves were obtained after different drying intervals that ended with similar surface water content. 相似文献
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The soil water hysteresis model proposed by Poulovassilis and Kargas (Soil Sci. Soc. Am. J. 64:1947–1950, 2000) is considered
in the present study. According to this model, the bivariate domain density distribution function f can be derived by partitioning the slopes of either of two main curves proportionally to the slopes of another. Accordingly,
there are two possible ways of deriving function f. The basic claim of Poulovassilis and Kargas is that both possibilities lead to the same resultant function f, which can be evaluated using integral equation presented by them. The present study shows that the above two ways of determining
function f actually lead to two incompatible partitioning models yielding different domain density distribution functions. Moreover,
none of these two partitioning models can reproduce the measured hysteresis loop used for calibration. Whether the partitioning
of the main wetting curve slopes proportionally to the main drying curve slopes or vice versa is applied, most of the predicted
primary scanning curves deviate considerably from the measured ones, cross out the measured boundary loop and do not converge
at an appropriate edge of the loop. The present study reveals that the above-mentioned integral equation, presented by Poulovassilis
and Kargas, appears to be at variance with both partitioning models. It is shown herein that this integral equation unambiguously
follows from Mualem (Water Resour. Res. 9:1324–1331, 1973) similarity hypothesis and, accordingly, the correspondent domain
density distribution function derived as the unique analytical solution of this equation is evidently identical to that obtained
by Mualem (1973). The predicted curves presented by Poulovassilis and Kargas are not obtained when any of the two partitioning
models is applied, but when using the integral equation of Mualem’s (1973) model. 相似文献
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