The clearing of tropical rain forest in the Amazon basin has created large areas of cattle pasture that are now declining in productivity. Practices adopted by ranchers to restore productivity to degraded pastures have the potential to alter soil N availability and gaseous N losses from soils. We examined how soil inorganic N pools, net N mineralization and net nitrification rates, nitrification potential and NO and N2O emissions from soils of a degraded pasture responded to the following restoration treatments: (1) soil tillage followed by replanting of grass and fertilization, (2) no-till application of non-selective herbicide, planting of rice, harvest followed by no-till replanting of grass and fertilization, and (3) the same no-till sequence with soybeans instead of rice. Tillage increased soil NH4+ and NO3? pools but NH4+ and NO3? pools remained relatively constant in the control and no-till treatments. Cumulative rates of net N mineralization and net nitrification during the first 6 months after treatment varied widely but were hightest in the tilled treatment. Emissions of NO and N2O fluxes increased with tillage and with N fertilization. There were no clear relationships among rates of N fertilizer application, net N mineralization, net nitrification, NO, N2O and total N oxide emissions. Our results indicate that pasture restoration sequences involving tilling and fertilizing will increase emissions of N oxides, but the magnitude of the increase is likely to differ based on timing of fertilizer application relative to the presence of plants and the magnitude of plant N demand. Emissions of N oxides appear to be decreased by the use of restoration sequences that minimize reductions in pasture grass cover. 相似文献
DGEBA-based epoxy nanocomposites filled with various amounts of fumed silica nanopowders (10, 20 and 30 phr corresponding to 3.3, 6.4 and 9.2% by volume) were prepared by a solvent assisted dispersion procedure. The obtained nanocomposites were analyzed by means of differential scanning calorimetry, dynamic-mechanical thermal analysis, uniaxial tensile tests on un-notched samples and three-point bending tests on notched samples.
All the thermal and mechanical properties showed non-monotonic trends with relative minima as the silica content increased. A trend inversion in the physical properties was detected at the highest filler level tested, which was not previously observed for epoxy systems filled with comparable amounts of unmodified silica. The behavior could be explained by considering a reduction of cross-linking degree of the epoxy matrix due to the huge viscosity increase induced by the silica nanoparticles during composites preparation. On the other hand, the physical immobilization of the cross-linked matrix can be supposed to be responsible for the inversion of the properties trend at the highest filler level, which is presumably very close to the percolation threshold. 相似文献
This paper presents an analysis of Laser Sintering (LS) process from an energy standpoint. LS has a potential as an environmental benign alternative to traditional processes but only few authors deal with the process optimization including the energy aspects. This work evaluates the effect of the energy density in processing of two polymeric materials: polyamide powder and a phenolic resin coated sand. The different behaviour of the two materials is studied by analysing the geometrical features (depth and width) of linear sintered structures. In particular the volumetric productivity and the energy intensity of the process are calculated to characterize the sintering process.It is shown how an upper limit to the energy consumption can be remarked. Measurements reveal that within the energy density range of 0.02-0.1 J/mm2 the whole energy input is useful for the agglomeration process. The use of higher energy density produces different results for both the cases analysed. A proper selection of energy density maintains the energy requirement below the level of 106 J/kg which is considered a lower limit for manufacturing process. 相似文献
In order to elucidate the role of this element in superalloy metallurgy, the binding energy of Re–Re pairs and the stability of small Re clusters in the nickel face-centred cubic (fcc) lattice is investigated using ab initio density functional theory. It is shown that the formation of Re–Re nearest neighbour pairs is energetically unfavourable, and that this repulsive energy is dramatically reduced as soon as the solute atoms move further apart from one another. Furthermore, small nearest neighbour and second neighbour Re clusters are found to be unstable. The calculations are repeated for W and Ta, which lie beside Re in the periodic table; the results are essentially the same, except that some Ta–Ta higher order pairs have a positive binding energy, consistent with the Ni–Ta binary phase diagram exhibiting several ordered intermetallics. The predictions show that Re clusters are unstable in fcc Ni and it is unlikely that clustering has a role in improving creep and fatigue properties (the rhenium-effect) in Ni-based superalloys. 相似文献
A panel of new potential Ras ligands was generated by decorating a tricyclic levoglucosenone‐derived scaffold with aromatic moieties. Some members of the panel show in vitro inhibitory activity toward the nucleotide exchange process on Ras and are toxic to some human cancer cell lines.
Carbonate on polymer is a valuable solid supported reagent (SSR) to promote, under eco‐friendly conditions, the preparation of 2H‐1,4‐benzoxazin‐2‐one derivatives starting from β‐nitroacrylates and aminophenols via a domino process. 相似文献
ZSM-5 zeolite films were grown on Si substrates by a two-step hydrothermal synthesis consisting of in situ seeding and secondary crystal growth. The films were 8–13 μm thick and partly oriented with the c-axis perpendicular to the substrate surface. After ion exchange with sodium ions, one film was applied as solid electrolyte in a potentiometric hydrocarbon gas sensor. A fast and reversible voltage response of the sensor to varying propane concentrations (100 ppm – 10%) was observed in O2/CO2/N2 gas mixtures at 723 K. 相似文献
The synthesis and carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity of two series of aromatic sulfonamides and their Cu(II) derivatives, incorporating metal-complexing moieties of the DTPA, DOTA, and TETA type are reported. The new compounds were designed in such a way as to possess high affinity for Cu(II) ions, exploiting four pendant carboxylate moieties in the DTPA derivatives, as well as the cyclen/cyclam macrocyles, and three pendant acetate moieties in the DOTA and TETA derivatives. The new derivatives showed modest inhibition of the cytosolic isoform CA I (K(I) values in the range of 66-2130 nM), were better CA II inhibitors (K(I) values in the range of 21-360 nM), and excellent inhibitors of the tumor-associated isoform CA IX (K(I) values in the range of 4.1-110 nM), with selectivity ratios for the inhibition of the tumor (CA IX) over the cytosolic (CA II) isozyme in the range of 10.74-20.88 for the best derivatives. Copper complexes were more inhibitory than the corresponding ligand sulfonamides, and showed membrane impermeability, thus, having the possibility to specifically target the transmembrane CA IX that has an extracellular active site. Incorporation of radioactive copper isotopes in this type of CA inhibitor may lead to interesting diagnostic/therapeutic applications for such compounds. 相似文献
Two sets of emulsion particles have been synthesized. In the first set, surfactant free emulsion was used to directly synthesize PS‐PNIPAAM copolymer particles. In the second set, polystyrene particles with an ATRP initiator shell were first synthesized and subsequently grafted with PNIPAAM brushes. Swelling/deswelling behavior of both sets of particles was studied with respect to temperature and time. Monoliths with two different porosities were also formed by grafting and crosslinking of PNIPAAM chains on the aggregated particles and characterized. In all cases, swelling kinetics is sufficiently fast to use these supports for separation driven by temperature changes only. However, hindrance and cross‐linking is sensibly reducing the material performance.