Time filter

Source Type

Vanbeveren D.,Vrije Universiteit Brussel | Vanbeveren D.,Groep T Leuven Engineering College | Mennekens N.,Vrije Universiteit Brussel | De Greve J.P.,Vrije Universiteit Brussel
Astronomy and Astrophysics | Year: 2012

Context. The chemical processes during the asymptotic giant branch (AGB) evolution of intermediate-mass single stars predict most of the observations of the different populations in globular clusters although some important questions still need to be further clarified. In particular, to reproduce the observed anticorrelations of Na-O and Al-Mg, chemically enriched gas lost during the AGB phase of intermediate-mass single stars must be mixed with matter with a pristine chemical composition. The source of this matter is still debated. Furthermore, observations reveal that a significant fraction of the intermediate-mass and massive stars are born as components of close binaries. Aims. We investigate the effects of binaries on the chemical evolution of globular clusters and on the origin of matter with a pristine chemical composition that is needed for the single-star AGB scenario to work. Methods. We used a population synthesis code that accounts for binary physics to estimate the amount and the composition of the matter returned to the interstellar medium of a population of binaries. Results. We demonstrate that the mass lost by a significant population of intermediate-mass close binaries in combination with the single-star AGB pollution scenario may help to explain the chemical properties of the different populations of stars in globular clusters. © 2012 ESO.

Deng Y.,Catholic University of Leuven | Van Acker K.,Catholic University of Leuven | Dewulf W.,Groep T Leuven Engineering College | Duflou J.R.,Catholic University of Leuven
Glocalized Solutions for Sustainability in Manufacturing - Proceedings of the 18th CIRP International Conference on Life Cycle Engineering | Year: 2011

This paper performs a cradle-to-gate LCA (Life Cycle Assessment) to compare the environmental impact between conventional PCB substrate (epoxy resins reinforced with glass fiber) and biobased PCB substrate, in case epoxidized linseed oil and flax fiber. The study reveals that the overall weighted environmental scores of substrate from biobased materials are significantly lower than the traditional materials, especially in impact categories of climate change, human tox-icity and fossil resources depletion. Since previous results showed satisfactory technical properties of the biobased materials as PCB substrate, they offer promising perspectives for final replacement of the conventional materials.

Van Caneghem J.,Catholic University of Leuven | Block C.,Groep T Leuven Engineering College | Vandecasteele C.,Catholic University of Leuven
Journal of Hazardous Materials | Year: 2010

The impact on human health of substances emitted to air by the Flemish industry was calculated with characterization factors (CFs) provided by the CML, Eco-indicator 99, EPS, EDIP and USEtox impact assessment methods. A comparison of the results pointed out that the choice of the CFs can greatly influence conclusions on the trend of the impact over time and on the relative contribution of the individual substances. If the impact on human health of organic substances and heavy metals was assessed separately, the differences between methods were less pronounced. In this case, the impacts on human health obtained by simply dividing the emitted masses of substances by the respective minimal risk concentrations or minimal risk doses, were comparable to those calculated with the CFs of the model-based methods. © 2010 Elsevier B.V.

Mennekens N.,Vrije Universiteit Brussel | Vanbeveren D.,Vrije Universiteit Brussel | Vanbeveren D.,Groep T Leuven Engineering College | De Greve J.P.,Vrije Universiteit Brussel | And 2 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. We investigate the contribution of different formation scenarios for type Ia supernovae in elliptical galaxies. The single-degenerate scenario (a white dwarf accreting from a late main-sequence or red giant companion) is tested against the double-degenerate scenario (the spiral-in and merging of two white dwarfs through the emission of gravitational wave radiation). Methods. We use a population-number synthesis code that incorporates the latest physical results in binary evolution and allows us to differentiate between certain physical scenarios (e.g. description of common-envelope evolution) and evolutionary parameters (e.g. mass-transfer efficiency during Roche-lobe overflow). The obtained theoretical distributions of the delay times of type Ia supernovae are compared, both in morphological shape and in absolute number of events, to those which are observed. The critical dependency of these distributions on certain parameters is used to constrain the values of the latter. Results. We find that the single-degenerate scenario alone cannot explain the morphological shape of the observational delay-time distribution, while the double-degenerate scenario (or a combination of both) can. Most of these double-degenerate type Ia supernovae are created through a normal quasi-conservative Roche-lobe overflow followed by a common-envelope phase, not through two successive common-envelope phases. This may cast doubt on the use in other studies of analytical formalisms to determine delay times. In terms of absolute number, theoretical supernova Ia rates in old elliptical galaxies lie a factor of at least three below the observed ones. We propose a solution involving the effect of rotation on the evolution of intermediate mass binaries. © 2010 ESO.

Kar S.,National Institute of Technology Durgapur | Nag K.,National Institute of Technology Durgapur | Nag K.,Jadavpur University | Dutta A.,Groep T Leuven Engineering College | And 2 more authors.
Chemical Engineering Science | Year: 2014

Based on a generalized Cellular Automata (CA) model which has the flexibility of reaction interactions between all possible two-agent combinations on both reactant and product side, in previous studies by the authors, probabilistic reaction events were combined in a multiplicative order and an exploratory study of the variability analysis was performed. However it was found that the probabilistic parameter values are extremely sensitive to the final model output. As such, NSGA-II based on a Multi-objective Genetic Algorithm (MOGA) is used in this study to obtain optimum sets of these probability parameter values within a feasible computational time. For each generation of the MOGA, the probability rules parameter values are updated (improved) based on the objective functions. Finally, a validation study is performed to indicate the applicability of the CA model to represent specific enzymatic reactions when coupled with the multi-objective optimization algorithm. © 2013 Elsevier Ltd.

Discover hidden collaborations