1. School of Geoscience and Surveying Engineering China University of Mining and Technology Beijing 100083 P. R. China
2. Department of Chemical and Biomolecular Engineering and Polymer Program Institute of Materials Science University of Connecticut Storrs CT 06269 USA
3. School of Environmental Science and Engineering Chang'an University Xi'an 710054 P. R. China
4. Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region of the Ministry of Education Chang'an University Xi'an 710054 P. R. China