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Magnetic composites have received increasing attention for electromagnetic wave absorption (EMA) applications. However, the practical EMA performance of the materials is severely hampered by mismatching impedance characteristics and finite electromagnetic attenuation capacity. Controlling the components and building the architecture fabrication is necessary to solve these issues. Herein, a series of Fe3O4, Fe3O4&Fe and Fe microspheres with flower-like hierarchical structures were constructed through a solvothermal method followed by an annealed process. This hierarchical structure and the synergy effect of dielectric dissipation and magnetic loss capacity offer Fe3O4 a perfect impedance matching, providing an excellent EMA performance of an effective absorption bandwidth (EAB) of 4.0 GHz and a reflection loss (RL) of 67.9 dB. Meanwhile, the coordination of the hierarchical structures and the multiple components endow Fe3O4&Fe composites with an EAB as wide as 5.7 GHz (9.0–14.7 GHz) and a RL as strong as 78.7 dB at 1.88 mm, which covers 75% X and 45% Ku bands. Such a remarkable lightweight and broad properties is due to the decent X band impedance matching and appropriate attenuation capacity. Therefore, this work highlights the significant of regulating the hierarchical structure and components to enhance the EMA performances. [ABSTRACT FROM AUTHOR]

To achieve highly efficient electromagnetic wave absorber, elaborately designing magnetic–dielectric Co@TiO2 microspheres with core–shell configuration are successfully constructed through a facile sequential process of liquid phase reduction–sol–gel–annealing. Owing to the core–shell configuration and the synergistic effect among magnetic and dielectric components, the annealed sample shows outstanding electromagnetic wave absorption (EMA) in X and Ku band. Impressively, a maximum reflection loss (RLmax) is reached –56.6 dB at a coating thickness of 2.3 mm with corresponding effective absorption bandwidth (EAB10) of 7.2 GHz (including 65% of Ku band and 82.5% of X band), much stronger than those of as-prepared Co (EAB10 of 1.6 GHz, RLmax of 14.6 dB) and pristine Co@TiO2 (EAB10 of 2.9 GHz, RLmax of 16.3 dB). An EAB10 covering completely the whole X and Ku band could be obtained by controlling the thickness only from 2.0 mm to 2.5 mm. The composites have both outstanding RL and wide EAB10 with the thin coating thickness, reinforcing that fabricating core–shell configuration composites is an efficient strategy to boost the EMA efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Methane conversion to C2 hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C2 products. Pulsed spark discharges gives the highest acetylene yield (54%) and H2 yield (51%) with 69% of methane conversion in a pure methane system and at 10SCCM of flow rate and 12W of discharge power. In the two DBD processes, ethane is the major C2 products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H2 formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18–69%), 14–25, 35–65 and 10–17eV/molecule; in pulsed streamer discharges (methane conversion 19–41%), 17–21, 38–59, and 12–19eV/molecule; in pulsed DBD (methane conversion 6–13%), 38–57, 137–227 and 47–75eV/molecule; in AC DBD (methane conversion 5–8%), 116–175, 446–637, and 151–205eV/molecule, respectively. The immersion of the γ-Al2O3 pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C2 yield. [Copyright &y& Elsevier]

The spectrometer-based nitrogen (N) nutrition monitoring and diagnosis models for double-cropping rice in Jiangxi is important for recommending precise N topdressing rate, achieving high yield, improving grain quality and increasing economic efficiency. Field experiments were conducted in Jiangxi in 2016 and 2017, involving different early rice and late rice cultivars and N application rates. Plant N accumulation (PNA) and canopy spectral vegetation indices (VIs) were measured at tillering and jointing stages with two spectrometers, i.e., GreenSeeker (an active multispectral sensor containing 780 and 660 nm wavelengths) and crop growth monitoring and diagnosis apparatus (CGMD, a passive multispectral sensor containing 810 and 720 nm wavelengths). The VI-based models of PNA were established from a experimental dataset and then validated using an independent dataset. The N topdressing rates for tillering and jointing stages were calculated using the newly developed N spectral diagnosis model and higher yield cultivation experience of double-cropping rice. The results showed that the VIs from two spectrometers were strongly positively correlated with PNA at both growth stages, with the model performance for tillering or jointing stages was better than that for the early growth stages. The exponential equation of normalized difference vegetation index (NDVI (780,660) ) from GreenSeeker could be used to estimate PNA with a determination coefficient (R 2 ) in the range of 0.92-0.94, the root mean square error (RMSE), relative root mean square error (RRMSE) and correlation coefficient (r) of model validation in the range of 3.09-5.96 kg·hm -2 , 5.8%-18.5% and 0.92-0.98, respectively. The linear equation of difference vegetation index (DVI (810,720) ) from CGMD could be used to estimate PNA with a R 2 in the range of 0.90-0.93, the RMSE, RRMSE and r of model validation in the range of 3.71-6.33 kg·hm -2 , 11.7%-14.3% and 0.93-0.96, respectively. The recommended N topdressing rate with CGMD was higher than that with GreenSeeker. Compared with conventional farmer's plan, the precision N application plan reduced N fertilizer application rate by 5.5 kg·hm -2 , while N agronomic efficiency and net income was improved by 0.8% and 128 yuan·hm -2 , respectively. Application of the spectral monitoring and diagnosis method to guiding fertilization could reduce cost and increase grain yield and net income, and thus had great potential for guiding double-cropping rice production.

In this study, we developed a model for photosynthetic production in double cropping rice by integrating the advantages in current crop models (including the models of canopy structure, canopy light distribution, canopy photosynthesis and dry matter production). The canopy light distribution and dry matter accumulation were preliminarily validated with independent field experiment datasets. The distribution of direct radiation both on a level surface and on the leaf surface within canopy, the canopy daily photosynthate and its characteristics with varying leaf area index for three typical plant types (erect both upper and lower, upper erect and lower flat, and flat both upper and lower) were quantitatively analyzed by the model. The results indicated that there was a good agreement between the simulated and observed values. The root mean square error (RMSE), relative root mean square error (RRMSE) and correlation coefficient (r) of prediction of canopy light distribution in double cropping rice were 12.01 J ·m -2 ·s -1 , 8.2% and 0.9929, respectively. Meanwhile, the RMSE, RRMSE and r of prediction of dry matter accumulation were 0.83 t·hm -2 , 14.6% and 0.9772, respectively. It was indicated that the model had a performance. The upper erect and lower flat plant type had highest canopy daily photosynthate due to higher incident sun light received on the leaf surface, leaf photosynthetic efficiency and leaf area index.