The concentrations of trifluoroacetic acid (TFA) were measured in urban landscape waters, tap water and snows in Beijing, China in 2012. Compared with the 2002 measurements, a 17-fold increase from 23–98 ng L−1 to 345–828 ng L−1 was observed for TFA concentrations in urban landscape waters, and an obvious increase from not detected (n.d.) to 155 ng L−1 occurred to TFA in tap water. By flux estimation between air and water interface, the remarkable increase of TFA was attributable to dry and wet deposition. The quantitative water–air–sediment interaction (QWASI) model simulated TFAs in various environmental media and showed that, over 99% of TFA distributed in water bodies. Our results recommend that measures are needed to control the increase of TFA in China.
This paper presents a detailed review of both theory and algorithms for the Cheeger cut based on the graph $1$-Laplacian. In virtue of the cell structure of the feasible set, we propose a cell descend (CD) framework for achieving the Cheeger cut. While plugging the relaxation to guarantee the decrease of the objective value in the feasible set, from which both the inverse power (IP) method and the steepest descent (SD) method can also be recovered, we are able to get two specified CD methods. Comparisons of all these methods are conducted on several typical graphs.
