Vrije Universiteit Brussel

About: Vrije Universiteit Brussel is a education organization based out in Brussels, Belgium. It is known for research contribution in the topics: Population & Context (language use). The organization has 14295 authors who have published 38258 publications receiving 1203970 citations. The organization is also known as: VUB.

Understanding the Woodward-Hoffmann rules by using changes in electron density.

Abstract: The Woodward-Hoffmann rules for pericyclic reactions are explained entirely in terms of directly observable physical properties of molecules (specifically changes in electron density) without any recourse to model-dependent concepts, such as orbitals and aromaticity. This results in a fundamental explanation of how the physics of molecular interactions gives rise to the chemistry of pericyclic reactions. This construction removes one of the key outstanding problems in the qualitative density-functional theory of chemical reactivity (the so-called conceptual DFT). One innovation in this paper is that the link between molecular-orbital theory and conceptual DFT is treated very explicitly, revealing how molecular-orbital theory can be used to provide "back-of-the-envelope" approximations to the reactivity indicators of conceptual DFT.

Arranging language features for more robust pattern-based crosscuts

Abstract: A crosscut language is used to describe at which points an aspect crosscuts a program. An important issue is how these points can be captured using the crosscut language without introducing tight coupling between the aspect and the program. Such tight coupling harms the evolvability of the program and the reusability of the aspect. Current pattern-based capturing already offers a certain decoupling between aspects and the program but it may still suffer from what we call the arranged pattern problem. In this paper, we discuss this problem and present a logic-based crosscut language from which we distill what language features are beneficial to avoid this problem.

Linearity of calibration curves: use and misuse of the correlation coefficient

Abstract: The correlation coefficient is commonly used to evaluate the de- gree of linear association between two variables. However, it can be shown that a correlation coefficient very close to one might also be ob- tained for a clear curved relation- ship. Other statistical tests, like the Lack-of-fit and Mandel's fitting test thus appear more suitable for the validation of the linear calibration model. A number of cadmium cali- bration curves from atomic absorp- tion spectroscopy were assessed for their linearity. All the investigated calibration curves were characterized by a high correlation coefficient (r >0.997) and low quality coeffi- cient (QC <5%), but the straight-line model was systematically rejected at the 95% confidence level on the ba- sis of the Lack-of-fit and Mandel's fitting test. Furthermore, significant- ly different results were achieved be- tween a linear regression model (LRM) and a quadratic regression (QRM) model in forecasting values for mid-scale calibration standards. The results obtained with the QRM did not differ significantly from the theoretically expected value, while those obtained with the LRM were systematically biased. It was con- cluded that a straight-line model with a high correlation coefficient, but with a lack-of-fit, yields signifi- cantly less accurate results than its curvilinear alternative.

Cell biology of liver endothelial and Kupffer cells.

Abstract: Endothelial cells Liver sinusoidal endothelial cells (LSEC) form a continuous, but fenestrated lining of the hepatic sinusoids.1 Figure 1 shows rat liver endothelial lining as seen by scanning electron microscopy. The fenestrae are grouped in sieve plates. In rat liver, the fenestrae have an average diameter of about 150 nm in the centrilobular areas of the liver and of 175 nm in the periportal areas when measured in plastic embedded ultrathin sections in transmission electron microscopy. The shrinkage of the tissue due to the sample preparation is shown in results of scanning microscopy, with the diameters of fenestrae 105 to 1 10 nm.2 Fenestrae form open connections between the lumen of the sinusoid and the space of Disse (Fig 2).I It is assumed that the transport and exchange of fluid, solutes, and particles between the sinusoidal lumen and the space of Disse containing the parenchymal cell surface occur through these open fenestrae.2-4 This transport can be influenced by modulation of the diameter of the fenestrae by a variety of agents such as cytochalasin B,5 dimethyl nitrosamine,6 thioacetamide,7 ethyl alcohol,8 pantethine,9 nicotine,10 and extracellular matrix.' 1 These agents change the diameter or number of fenestrae, or both. Data obtained by fluorescence microscopy show that the cytoskeleton of LSEC plays an important part in the modulation of fenestrae.'2 13 Little information is available about mechanisms that regulate the diameter and number of fenestrae. The fenestrated endothelial lining inhibits the passage of chylomicrons larger than 200-250 nm. Chylomicrons up to the size of fenestrae are present in the space of Disse, although larger chylomicrons are present in the blood, suggesting a filtration effect.4 14 Chylomicrons lose a