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排序方式: 共有426条查询结果,搜索用时 15 毫秒
41.
Late season nitrogen fertilization of soybeans: effects on leaf senescence, yield and environment 总被引:3,自引:0,他引:3
Flavio H. Gutiérrez-Boem Javier D. Scheiner Helena Rimski-Korsakov Raúl S. Lavado 《Nutrient Cycling in Agroecosystems》2004,68(2):109-115
Nitrogen demand from soybean seeds during seed filling is very high and has been proposed as the cause of nitrogen remobilization and leaf senescence. Previous research has not shown consistent effects of late season fertilization on seed yield, while its effects on leaf senescence have not been evaluated. Two field experiments were performed to determine the effects of a late season N fertilization on leaf senescence and fall, seed yield and its components, and residual soil nitrate, and to evaluate the potential risk of groundwater contamination. Two rates of nitrogen (50 and 100 kg N ha–1) were applied at the R3 and R5 development stages. Nitrogen fertilization, either at R3 or R5, increased soil nitrate availability during the seed-filling period. Seed yield, seed number and protein content were not affected by N fertilization. The addition of 100 kg N ha–1 produced a small delay of 1–2 days in the leaf fall, and slightly increased seed size (3.6%). Our results suggest that increasing soil N availability during the seed-filling period is not an effective way to delay leaf senescence or to increase seed growth and yield of soybean. Nitrogen fertilization increased the level of residual nitrate in the top soil at one site (the one with lowest seed yield), increasing the risk of nitrate leaching during subsequent fallow. 相似文献
42.
This paper presents a model for predicting damage evolution in heterogeneous viscoelastic solids under dynamic/impact loading.
Some theoretical developments associated with the model have been previously reported. These are reviewed briefly, with the
main focus of this paper on new developments and applications. A two-way coupled multiscale approach is employed and damage
is considered in the form of multiple cracks evolving in the local (micro) scale. The objective of such a model is to develop
the ability to consider energy dissipation due to both bulk dissipation and the development of multiple cracks occurring on
multiple length and time scales. While predictions of these events may seem extraordinarily costly and complex, there are
multiple structural applications where effective models would save considerable expense. In some applications, such as protective
devices, viscoelastic materials may be preferred because of the considerable amount of energy dissipated in the bulk as well
as in the fracture process. In such applications, experimentally based design methodologies are extremely costly, therefore
suggesting the need for improved models. In this paper, the authors focus on the application of the newly developed multiscale
model to the solution of some example problems involving dynamic and impact loading of viscoelastic heterogeneous materials
with growing cracks at the local scale. 相似文献
43.
44.
Federico Pallottino Paolo Menesatti Corrado Costa Graziella Paglia Flavio R. De Salvador Daniele Lolletti 《Food and Bioprocess Technology》2010,3(1):155-159
According to FAO statistics, in 2000, Italy was the second largest hazelnut (Corylus avellana, L. 1753) producer in the world. The price of the stock depends on the nut quality (kernel/nut ratio, nut and seed defect,
percentage of peeling, and taste panel scores). The evaluation of peeling efficiency after toasting is generally conducted
by trained operators in sight on 100 kernels. This work tests two alternative objective methods of after toasting peeling
evaluation based on image analysis. Eleven hazelnut cultivars were analyzed and results were compared with the ones assessed
by trained operators. Images were analyzed with two statistical approaches: fixed values of RGB thresholding and trained K
Nearest Neighbors (KNN). Root mean squared error (RMSE), estimating the comparison between operators and the two image analysis-based
techniques, shows better results for KNN (6.6) with respect to fixed threshold (15.9). 相似文献
45.
Flavio S. Damos 《Electrochimica acta》2007,53(4):1945-1953
The present work describes the construction of nanoporous assemblies based on single self-assembled monolayer (SAM) of mono-(6-deoxy-6-mercapto)-β-cyclodextrin (βCDSH) and two-component monolayers of βCDSH and 11-mercaptoundecanoic acid. An investigation of its supramolecular properties toward the tricyclic antidepressants drugs chlorprothixene and imipramine is also presented. The adsorption process was investigated by using surface plasmon resonance and the selectivity of the SAM was verified by using electroactive species permeable and not permeable into the cyclodextrin SAM, such as ferrocenemonocarboxylic acid, hexacyanoferrate, methylene blue and hexamineruthenium (II). The redox probe was chosen based on its capability to permeate the grafted cyclodextrin molecules and its electrochemical characteristics. It was applied to imipramine and chlorprothixene competitive assay by the mono-(6-deoxy-6-mercapto)-β-cyclodextrin self-assembled cavity. Finally, the pKa of the surface and its effects on thee host-guest interaction properties were also investigated. 相似文献
46.
Flavio Carbognani Felix Buergin Norbert Felber Hubert Kaeslin Wolfgang Fichtner 《Analog Integrated Circuits and Signal Processing》2008,56(1-2):5-12
The most widespread 16-bit multiplier architectures are compared in terms of area occupation, dissipated energy, and EDP (Energy-Delay Product) in view of low-power low-voltage signal processing for digital hearing aids and similar applications. Transistor-level simulations including back-annotated wire parasitics confirm that the propagation of glitches along uneven and re-convergent paths results in large unproductive node activity. Because of their shorter full-adder chains, Wallace-tree multipliers indeed dissipate less energy than the carry-save (CSM) and other traditional array multipliers (6.0 µW/MHz versus 10.9 µW/MHz and more for 0.25 µm CMOS technology at 0.75 V). By combining the Wallace-tree architecture with transmission gates (TGs), a new approach is proposed to improve the energy efficiency further (3.1 µW/MHz), beyond recently published low-power architectures. Besides the reduction of the overall capacitance, minimum-sized transmission gate full-adders act as RC-low-pass filters that attenuate undesired switching. Finally, minimum size TGs increase the V dd to ground resistance, hence decreasing leakage dissipation (0.55 nW versus 0.84 nW in CSM and 0.94 nW in Wallace). 相似文献
47.
Flavio De Martino Corrado Gisonni Willi H. Hager 《Canadian Metallurgical Quarterly》2002,128(6):397-400
Manholes often contain small drops for various reasons, the most important being submergence. While this may be appropriate for subcritical flow, its effect was considered doubtful for supercritical flow. This note aims at investigating the effect of a manhole drop on the hydraulics of sewer flow. Based on systematic experimental observations, the flow pattern associated with a manhole drop was established. A distinction was also made between small and intermediate drops. Then, the main wave features were analyzed to result in expressions that contain both the upstream filling ratio and the Froude number of the approach flow. In addition, the discharge capacity was also investigated, and selected photographs show typical drop flow in combined sewer manholes. The result of the present study is evident, based on these observations, and recommendations towards future design of combined sewer manholes are also made. 相似文献
48.
Analysis and behavior of steel storage drive-in racks 总被引:1,自引:0,他引:1
This work presents a general analysis of drive-in racks, evaluating the influence of each of their components on global stability. In this study, a full-scale test of a drive-in system was carried out. Finite element models were also developed to evaluate global structural stability and component influence on system behavior. The experimental and numerical results show that the connections and base plates have the most significant influence on the system's behavior. This influence is analyzed, an equation that predicts base plate resistance is then proposed, and its results are compared with experimental and numerical results. 相似文献
49.
50.
Cristina Benincá Eduardo Charao Boni Fabio Ferreira Gonçalves Ednei Gilberto Primel Flavio Bentes Freire 《Chemical Engineering Communications》2019,206(1):1-11
An initial set of 12 kinetic experiments was carried out to remove naphthalene from an aqueous effluent by photo-Fenton involving Fe0 and Fe2+ at two different concentrations of H2O2 (150 and 300?mg?L?1) and three different pHs (3, 5, and 7) (22×31 experiments). The rate constants (k) for the reaction of naphthalene degradation by involving Fe2+ as reactant were in general higher than those with Fe0, but the use of Fe2+ increased the concentration of naphthalene at equilibrium (Ce) when compared with the same response obtained with Fe0 at analogous conditions. A second set of twelve kinetic experiments of photo-Fenton degradation was also performed with persulfate as additive at the conditions already reported, but at a constant concentration of H2O2 of 150?mg?L?1 (21×31 experiments with NaCl +21×31 experiments without NaCl). In almost all the runs in which only the source of iron was varied, k from the kinetic data involving Fe2+ was higher than that involving Fe0, but no difference was observed in terms of Ce that was always zero. The addition of persulfate to treat the effluent either containing or not containing salt enhanced the chemical kinetics, and shifted the equilibrium toward the full removal of naphthalene. A final set of nine experiments of UV photo degradation of naphthalene by involving persulfate without iron, with Fe0 and Fe2+ in the pH range from 3 to 7 (32 experiments) mainly showed that the use of H2O2 may be avoided to remove rapidly and completely naphthalene from wastewater. 相似文献