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We consider the impact of varying the aspect ratio A of carbon nanotubes (CNT) on the rheological properties of isotactic polypropylene/CNT nanocomposites. Specifically, we focus on multiwall CNT having a relatively low aspect ratio (A in the range from 22 to 45), since previous work (Kharchenko et al., Nature Mater. 2004) has emphasized the rheological properties of relatively high aspect ratio multiwall CNT nanocomposites (A from 300 to 400). Correspondingly, we find that the formation of a nonequilibrium CNT network structure occurs at a higher CNT concentration in our low A CNT nanocomposites, as theoretically expected. The proposed mechanism for the large apparent negative normal stress differences (∆N) described by Kharchenko et al. relies on the capacity of the "struts" of the CNT network to rotate about their impingement junctions, much like the links of a deformed chain link fence. This model implies the absence of appreciable negative ∆N at low CNT concentrations where the network does not yet exist and also for short CNT and at high concentrations of CNT where the mesh size of the network becomes too small to accommodate appreciable rotational distortion. In conformity with this simple mechanical model, we observe only a positiVe apparent ∆N in our CNT/iPP nanocomposites, even well above the CNT gelation concentration. This striking change in the rheology of CNT nanocomposites with a change in A has been further confirmed in die-swell measurements, where a large die swell has been seen in the short CNT nanocomposites, rather than the die-shrinkage found before for the large A or the highly "entangled" CNT network counterpart.

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Yield and nutrient acquisition advantages are frequently found in intercropping systems. However, there are few published reports on soil fertility in intercropping relative to monocultures. A field experiment was therefore established in 2009 in Gansu province, northwest China. The treatments comprised maize/faba bean, maize/soybean, maize/chickpea and maize/turnip intercropping, and their correspoding monocropping. In 2011 (the 3rd year) and 2012 (the 4th year) the yields and some soil chemical properties and enzyme activities were examined after all crop species were harvested or at later growth stages. Both grain yields and nutrient acquisition were significantly greater in all four intercropping systems than corresponding monocropping over two years. Generally, soil organic matter (OM) did not differ significantly from monocropping but did increase in maize/chickpea in 2012 and maize/turnip in both years. Soil total N (TN) did not differ between intercropping and monocropping in either year with the sole exception of maize/faba bean intercropping receiving 80 kg P ha−1 in 2011. Intercropping significantly reduced soil Olsen-P only in 2012, soil exchangeable K in both years, soil cation exchangeable capacity (CEC) in 2012, and soil pH in 2012. In the majority of cases soil enzyme activities did not differ across all the cropping systems at different P application rates compared to monocrops, with the exception of soil acid phosphatase activity which was higher in maize/legume intercropping than in the corresponding monocrops at 40 kg ha−1 P in 2011. P fertilization can alleviate the decline in soil Olsen-P and in soil CEC to some extent. In summary, intercropping enhanced productivity and maintained the majority of soil fertility properties for at least three to four years, especially at suitable P application rates. The results indicate that maize-based intercropping may be an efficient cropping system for sustainable agriculture with carefully managed fertilizer inputs.