Land degradation,unbalanced nutrition,change in climate and its extreme variability are the factors affecting the sustainability of agriculture and food security.In North-west Pakistan,more than 50%of the cultivated a...Land degradation,unbalanced nutrition,change in climate and its extreme variability are the factors affecting the sustainability of agriculture and food security.In North-west Pakistan,more than 50%of the cultivated area is rain-fed and the crop productivity is low.Conservation agriculture reduces greenhouse gas emissions by enhancing soil carbon sequestration and then improved soil fertility,WUE and crop productivity.A field experiment展开更多
As potential wave-transparent materials applied at high temperatures,3D BNf/Si3N4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition(LPCVI/CVD) process from SiCl4-NH3-H2-...As potential wave-transparent materials applied at high temperatures,3D BNf/Si3N4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition(LPCVI/CVD) process from SiCl4-NH3-H2-Ar gas precursor at 800℃. The densification process, microstructure and dielectric properties of 3D BNf/Si3N4 composites were investigated. The results indicated that 3D BNf/Si3N4 was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/cm3. Densification kinetics of 3D BNf/Si3N4 is a typical exponential pattern. The Si3N4 matrix was uniformly infiltrated into porous BNf preform. The deposited Si3N4 matrix was amorphous by XRD analysis. Introduction of BN fiber into Si3N4 ceramic lowered the permittivity of Si3N4. The fabricated BNf/Si3N4 composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below400℃. Transmission coefficient of BNf/Si3N4 composite is 0.57 and keeps stable below 400℃. BNf/Si3N4 can be fabricated at low temperature and may be candidates for the microwave transparent materials.展开更多
文摘Land degradation,unbalanced nutrition,change in climate and its extreme variability are the factors affecting the sustainability of agriculture and food security.In North-west Pakistan,more than 50%of the cultivated area is rain-fed and the crop productivity is low.Conservation agriculture reduces greenhouse gas emissions by enhancing soil carbon sequestration and then improved soil fertility,WUE and crop productivity.A field experiment
基金Funded by the National Natural Science Foundation of China(Nos.51472201,51602258,and 51632007)
文摘As potential wave-transparent materials applied at high temperatures,3D BNf/Si3N4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition(LPCVI/CVD) process from SiCl4-NH3-H2-Ar gas precursor at 800℃. The densification process, microstructure and dielectric properties of 3D BNf/Si3N4 composites were investigated. The results indicated that 3D BNf/Si3N4 was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/cm3. Densification kinetics of 3D BNf/Si3N4 is a typical exponential pattern. The Si3N4 matrix was uniformly infiltrated into porous BNf preform. The deposited Si3N4 matrix was amorphous by XRD analysis. Introduction of BN fiber into Si3N4 ceramic lowered the permittivity of Si3N4. The fabricated BNf/Si3N4 composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below400℃. Transmission coefficient of BNf/Si3N4 composite is 0.57 and keeps stable below 400℃. BNf/Si3N4 can be fabricated at low temperature and may be candidates for the microwave transparent materials.
