Université libre de Bruxelles

About: Université libre de Bruxelles is a education organization based out in Brussels, Belgium. It is known for research contribution in the topics: Population & Breast cancer. The organization has 24974 authors who have published 56969 publications receiving 2084303 citations. The organization is also known as: ULB.

Interactions between rainfall, deforestation and fires during recent years in the Brazilian Amazonia

Abstract: Understanding the interplay between climate and land-use dynamics is a fundamental concern for assessing the vulnerability of Amazonia to climate change In this study, we analyse satellite-derived monthly and annual time series of rainfall, fires and deforestation to explicitly quantify the seasonal patterns and relationships between these three variables, with a particular focus on the Amazonian drought of 2005 Our results demonstrate a marked seasonality with one peak per year for all variables analysed, except deforestation For the annual cycle, we found correlations above 90% with a time lag between variables Deforestation and fires reach the highest values three and six months, respectively, after the peak of the rainy season The cumulative number of hot pixels was linearly related to the size of the area deforested annually from 1998 to 2004 (r 2 Z084, pZ0004) During the 2005 drought, the number of hot pixels increased 43% in relation to the expected value for a similar deforested area (approx 19 000 km 2 ) We demonstrated that anthropogenic forcing, such as land-use change, is decisive in determining the seasonality and annual patterns of fire occurrence Moreover, droughts can significantly increase the number of fires in the region even with decreased deforestation rates We may expect that the ongoing deforestation, currently based on slash and burn procedures, and the use of fires for land management in Amazonia will intensify the impact of droughts associated with natural climate variability or human-induced climate change and, therefore, a large area of forest edge will be under increased risk of fires

Dispersion and pollution of the FEM solution for the Helmholtz equation in one, two and three dimensions

Abstract: For high wave numbers, the Helmholtz equation suffers the so-called 'pollution effect'. This effect is directly related to the dispersion. A method to measure the dispersion on any numerical method related to the classical Galerkin FEM is presented. This method does not require to compute the numerical solution of the problem and is extremely fast. Numerical results on the classical Galerkin FEM (p-method) is compared to modified methods presented in the literature. A study of the influence of the topology triangles is also carried out. The efficiency of the different methods is compared. The numerical results in two of the mesh and for square elements show that the high order elements control the dispersion well. The most effective modified method is the QSFEM [1, 2] but it is also very complicated in the general setting. The residual-free bubble [3, 4] is effective in one dimension but not in higher dimensions. The least-square method [1, 5] approach lowers the dispersion but relatively little. The results for triangular meshes show that the best topology is the 'criss-cross' pattern. Copyright © 1999 John Wiley & Sons, Ltd.

The human Rhesus-associated RhAG protein and a kidney homologue promote ammonium transport in yeast.

Abstract: The Rhesus blood-group antigens are defined by a complex association of membrane polypeptides that includes the non-glycosylated Rh proteins (RhD and RhCE) and the RHag glycoprotein, which is strictly required for cell surface expression of these antigens. RhAG and the Rh polypeptides are erythroid-specific transmembrane proteins belonging to the same family (36% identity). Despite their importance in transfusion medicine, the function of RhAG and Rh proteins remains unknown, except that their absence in Rh(null) individuals leads to morphological and functional abnormalities of erythrocytes, known as the Rh-deficiency syndrome. We recently found significant sequence similarity between the Rh family proteins, especially RhAG, and Mep/Amt ammonium transporters. We show here that RhAG and also RhGK, a new human homologue expressed in kidney cells only, function as ammonium transport proteins when expressed in yeast. Both specifically complement the growth defect of a yeast mutant deficient in ammonium uptake. Moreover, ammonium efflux assays and growth tests in the presence of toxic concentrations of the analogue methylammonium indicate that RhAG and RhGK also promote ammonium export. Our results provide the first experimental evidence for a direct role of RhAG and RhGK in ammonium transport. These findings are of high interest, because no specific ammonium transport system has been characterized so far in human.