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Dang V.K.,University of Strasbourg | Dang V.K.,Ha Noi National University of Education | Doubre C.,University of Strasbourg | Weber C.,University of Strasbourg | And 2 more authors.
Natural Hazards and Earth System Sciences | Year: 2014

Since the 1990s the land subsidence due to the rapid urbanization has been considered a severely destructive hazard in the center of Hanoi City. Although previous studies and measurements have quantified the subsiding deformation in Hanoi center, no data exist for the newly established districts in the south and the west, where construction development has been most significant and where groundwater pumping has been very intensive over the last decade. With a multioral InSAR approach, we quantify the spatial distribution of the land subsidence in the entire Hanoi urban region using ALOS images over the 2007-2011 period. The map of the mean subsidence velocity reveals that the northern bank of the Red River appears stable, whereas some areas in southern bank are subsiding with a mean vertical rate up to 68.0 mm yr-1, especially within the three new urban districts of Hoang Mai, Ha Dong-Thanh Xuan and Hoai Duc-Tu Liem. We interpret the spatial distribution of the surface deformation as the combination of the nature of the unsaturated layer, the lowering of groundwater in the aquifers due to pumping withdrawal capacity, the increase of built-up surfaces and the type of building foundation. The piezometric level in Qp aquifer lowers particularly after 2008, whereas the groundwater level in Qp aquifer remains steady, even if it loses its seasonal fluctuation in urban areas and drawdowns in neighboring water production plants. The time evolution deduced from the InSAR time series is consistent with previous leveling data and shows that the lowering rate of the surface slightly decreases till 2008. The analysis of groundwater levels in instrumented wells shows a correlation between the behavior of groundwater with the urban development and the acceleration of groundwater withdrawal. Also, the time variations suggest that the deformation became non-stationary, with upward and downward transient displacements related to the charge and discharge of the aquifers.© Author(s) 2014. CC Attribution 3.0 License. Source


Cam L.M.,Ha Noi National University of Education | Huyen N.D.,Ha Noi National University of Education | Ha N.N.,Ha Noi National University of Education
Journal of Chemistry | Year: 2013

The catalytic performance of vanadia catalysts with 15 wt% V supported on TiO2 and (15 wt% V + 4.6 wt% La) supported on TiO2 in oxidative dehydrogenation (ODH) of n-butane was investigated. The catalysts were characterized by means of TPD-NH3, TPR-H2, UV-Vis, and BET. Testing of samples showed that vanadia catalysts were active for the reaction. It was found that La doping of V/TiO2 catalyst had a negative effect on the dispersion of V species and led to formation of V 2O5 clusters. This resulted in a loss of activity. Although slight improvement of selectivity was observed in comparison to undoped V/TiO2 samples due to lower acidity of La-doped -V/TiO2, this could not compensate the loss of activity and finally did not lead to higher butene yields. © 2013 Le Minh Cam et al. Source

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