This study investigated a new potential hot-pressing method for wood modification, in which densification, drying, and heat-treatment were carried out in sequence. The effects of heat treatment on the chemical components of wood were evaluated. The specimens were treated at different temperatures (180 to 220 °C) for 2 to 5 h. Holocellulose, α-cellulose, and lignin were extracted from the treated and untreated milled wood. The changes in these components were analyzed by thermogravimetry (TG) and Fourier-transform infrared spectroscopy (FTIR). Due to its amorphous structure, most hemicelluloses were degraded when it was exposed to 220 °C for 3 h and to 200 °C for 5 h. Conversely, the lignin contents increased continuously throughout the treatment due to the loss of polysaccharides and the formation of cross-links. Because of the crystallinity, α-cellulose degradation was slight. According to the analysis of functional groups, FTIR showed treated wood was more hydrophobic than the untreated one.
Gas discharge in heterogeneous porous dielectric (PD) is becoming a reliable and popular low-temperature plasma technique in surface modification and plasma catalysis. However, the exact breakdown characteristics in the porous dielectric are not well studied due to experimental and diagnostic limitations. In this paper, a fluid model is then used to simulate the gas breakdown characteristics in real PD. It is found that the breakdown will selectively occur in porous dielectrics. The spatial distribution of PD determines regions of local breakdown. Varitions in pressure result in the rearrangement of breakdown probability in each region of PD so that breakdown regions will change. In order to explain the selective breakdown phenomenon, based on the assumption that a porous dielectric can be simplified into a network consisting of multiple curved capillaries, we developed a theoretical model of the breakdown in a capillary network. Three geometrical factors, i.e., capillary tortuosity, capillary radius, and line porosity, are taken into the model to account for the effect of electric field distortion and electron loss on the dielectric walls in the presence of PD. The calculated results explain the selective breakdown phenomenon occurring in the numerical simulation. This paper simulates the breakdown in a real porous dielectric and provides a quantitative theoretical model to analyze the effect of porous dielectric geometry on the breakdown. This paper will also provide insights into the design of optimal parameters for porous dielectric discharge (PDD) in surface modification and plasma catalysis.
Distance higher education plays a critical role in the promotion of regional equality in China by contributing to the availability of higher education. However, unbalanced regional development of distance higher education can lead to a widening of educational inequity. The study on which this article reports sheds light on the issue of unbalanced regional development of distance higher education in China, using provincial data that spans from 2008 to 2018. A dual‐index method with Gini coefficient and Theil index was employed to measure regional inequality of distance higher education in China. The findings show that tertiary correspondence education and tertiary radio and television education represent a comparatively small percentage of the regional inequality in distance higher education. Online tertiary education contributes to a greater extent to regional inequality in distance higher education. Intra‐regional inequality constituted a large percentage of the total inequality. Also, intra‐regional inequality in tertiary correspondence education has increased in western, and central China from 2008 to 2018. Inequality in tertiary radio and television education has also increased in central China from 2008 to 2016. Intra‐regional inequality in online tertiary education was marked in all three regions, while inter‐regional inequality in online tertiary education decreased from 2008 to 2018.
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