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Supported by RS and GIS technology, combining the former achievements in scientific research and lots of field investigations, we used IRS image of 2000 and Landsat-TM images of 1984, 1989, 1992, 1996, 1998, 2002 and 2004 as information source, then, with the help of GIS and RS software, interpreted the images and built up Beijing wetland resource and ecological environment information system. On the basis of it, we can dynamic monitor wetland resource and wetland change trend of Beijing region in the past twenty years, including the wetland type, area and distribution; wetland biodiversity; wetland exploitation, etc. After all of these, analyze the actual state of wetland resource and the dynamic change of wetland in Beijing region. Keyword--GIS, RS, Beijing wetland resource, dynamic monitor

Hall thruster plasma discharge channels interact with wall forming sheath, and different secondary electron emission coefficients of wall material can considerably affect sheath characteristics. In this paper, we establish a two-dimensional physical model in wall sheath area to study the secondary electron emission characteristics of three different wall materials which are boron nitride (BN), silicon carbide (SiC) and aluminium oxide (Al2O3), and SiC material secondary electron emission model is improved. On the basis of improved secondary electron emission model, the relationship between the wall secondary electron emission coefficient and both electron temperature and magnetic field intensity is discussed by the particle in cell simulation method, and the different sheath properties of three materials (BN, SiC and Al2O3), are also investigated. The results show that fitting curve is consistent with the experimental results; at the same electron temperature, the values of secondary electron emission coefficient and electron density of three materials (BN, SiC and Al2O3) increase but the values of sheath electric field and sheath potential drop decrease in their sequence. The BN material has the appropriate secondary electron radiation coefficient, which makes the thruster work steadily under low current condition.