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A facile route was proposed to synthesize polyaniline (PANI) uniformly deposited on bagasse fiber (BF) via a one-step in situ polymerization of aniline in the dispersed system of BF. Correlations between the structural, electrical, and electromagnetic properties were extensively investigated. Scanning electron microscopy images confirm that the PANI was coated dominantly on the BF surface, indicating that the as-prepared BF/PANI composite adopted the natural and inexpensive BF as its core and the PANI as the shell. Fourier transform infrared spectra suggest significant interactions between the BF and PANI shell, and a high degree of doping in the PANI shell was achieved. X-ray diffraction results reveal that the crystallization of the PANI shell was improved. The dielectric behaviors are analyzed with respect to dielectric constant, loss tangent, and Cole-Cole plots. The BF/PANI composite exhibits superior electrical conductivity (2.01 ± 0.29 S·cm), which is higher than that of the pristine PANI with 1.35 ± 0.15 S·cm. The complex permittivity, electromagnetic interference (EMI), shielding effectiveness (SE) values, and attenuation constants of the BF/PANI composite were larger than those of the pristine PANI. The EMI shielding mechanisms of the composite were experimentally and theoretically analyzed. The absorption-dominated total EMI SE of 28.8 dB at a thickness of 0.4 mm indicates the usefulness of the composite for electromagnetic shielding. Moreover, detailed comparison of electrical and EMI shielding properties with respect to the BF/PANI, dedoped BF/PANI composite, and the pristine PANI indicate that the enhancement of electromagnetic properties for the BF/PANI composite was due to the improved conductivity and the core-shell architecture. Thus, the composite has potential commercial applications for high-performance electromagnetic shielding materials and also could be used as a conductive filler to endow polymers with electromagnetic shielding ability.

Land use/cover change induced by human activities has emerged as a "global" phenomenon with Earth system consequences. Northeast China is an area where the largest land cultivation activities by migrants have happened in China during the past 300 years. In this paper, methods including documentary data calibration and multi-sourced data conversion model are used to reconstruct historical cropland cover change in Northeast China during the past 300 years. It is concluded that human beings have remarkably changed the natural landscape of the region by land cultivation in the past 300 years. Cropland area has increased almost exponentially during the past 300 years, especially during the past 100 years when the ratio of cropland cover changed from 10% to 20%. Until the middle of the 19th century, the agricultural area was still mainly restricted in Liaoning Province. From the late 19th century to the early 20th century, dramatic changes took place when the northern boundary of cultivation had extended to the middle of Heilongjiang Province. During the 20th century, three agricultural regions with high ratio of cropland cover were formed after the two phases of spatial expansion of cropland area in 1900s-1930s and 1950s-1980s. Since 1930s-1940s, the expansion of new cultivated area have invaded the forest lands especially in Jilin and Heilongjiang Provinces.past 300 years, Northeast China, cropland, land cover, environmental change

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Development of highly efficient electromagnetic interference (EMI) shielding materials with tunable properties is essential for the modern electronics industry against severe electromagnetic pollution. Herein, a series of novel heterostructured bagasse fiber/polyaniline (BF/PANI) composites are successfully synthesized via a facile in situ polymerization method and both their EMI shielding effectiveness (SE) and mechanisms were analyzed experimentally and theoretically. The results show that the conductivity and EMI shielding properties of BF/PANI composites can be tailored by adjusting the component, microstructure, and electromagnetic parameter, which can be easily tuned by modulating the weight ratio of aniline monomer and BF. More significantly, the BF/PANI heterostructures exhibit remarkable enhanced EMI shielding capabilities compared with the pristine PANI. The BF/PANI heterostructure prepared with an aniline volume of 7 mL shows an electrical conductivity of 6.07 S·cm–1 and the best EMI shielding capabilities of 35.73 dB. The excellent microwave attenuation capacity can be attributed to the cooperation of interface polarization, conductivity, skin depth effect, and the novel heterostructure. Considering their fascinating performance, these BF/PANI composites are proving to be the promising candidates as highly efficient EMI shielding materials.

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