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Ivens J.,Lessius University College Antwerp | Ivens J.,Catholic University of Leuven | Urbanus M.,Catholic University of Leuven | De Smet C.,University College Ghent
Express Polymer Letters | Year: 2011

A shape memory polymer (SMP) can be deformed from a permanent to a temporary shape above their transformation temperature. Upon reheating, the SMP spontaneously returns to the permanent shape. SMP's show high deformability, but the recovery stresses are very low, thus limiting the size of the components. This paper presents the first results of an ongoing research to develop large sized components based on SMP. To achieve higher recovery stresses, asymmetric fibre reinforced shape memory composites were produced (SMPC) using resin transfer moulding. The results show a 30- fold increase in recovery stress, compared to the neat SMP resin. The recovery stress is independent of the deformation temperature, but is strongly affected by the degree of deformation. At higher deformation levels, crazing occurs. Even though the visible effects of the crazing disappear during reheating, it does influence the recovery stress. This indicates that the ability to recover the permanent shape might change in cyclic loading. All composites tested show complete recovery upon reheating. The rate of shape recovery is higher when the fibre reinforcement is loaded in compression. © BME-PT. Source

Goossens L.,Ghent University | Braet C.,Ghent University | Bosmans G.,Katholieke University Leuven andreas Vesaliusstraat 2 | Decaluwe V.,Lessius University College Antwerp
Eating Behaviors | Year: 2011

Objective: The present study aimed to add to the limited literature on the role of self-esteem and attachment for the explanation of loss of control over eating (LC) among pre-adolescent boys and girls. Method: Self-report questionnaires were administered to a community sample of 555 children (8-11. years; 47% female). Results: Children reporting LC (17.6% of the sample) were characterized by a lower self-esteem and less secure attachment toward both of their parents. No gender differences emerged. Moreover, the relation between self-esteem and LC was fully mediated by attachment toward mother and partially mediated by attachment toward father. Discussion: The present study provides preliminary evidence for the idea that the influence of self-esteem on LC seems to operate through a third variable that is an insecure relationship with the parents. Longitudinal research is needed to further elucidate the influence of interpersonal factors on the development of LC. © 2011 Elsevier Ltd. Source

Boudt K.,Catholic University of Leuven | Boudt K.,Lessius University College Antwerp | Croux C.,Catholic University of Leuven
Computational Statistics and Data Analysis | Year: 2010

The Gaussian quasi-maximum likelihood estimator of Multivariate GARCH models is shown to be very sensitive to outliers in the data. A class of robust M-estimators for MGARCH models is developed. To increase the robustness of the estimators, the use of volatility models with the property of bounded innovation propagation is recommended. The Monte Carlo study and an empirical application to stock returns document the good robustness properties of the M-estimator with a fat-tailed Student t loss function. © 2009 Elsevier B.V. All rights reserved. Source

Jacquemyn H.,Catholic University of Leuven | Honnay O.,Catholic University of Leuven | Cammue B.P.A.,Catholic University of Leuven | Brys R.,Research Institute for Nature and Forest | And 2 more authors.
Molecular Ecology | Year: 2010

Most orchid species rely on mycorrhizae to complete their life cycle. Despite a growing body of literature identifying orchid mycorrhizal associations, the nature and specificity of the association between orchid species and mycorrhizal fungi remains largely an open question. Nonetheless, better insights into these obligate plant-fungus associations are indispensable for understanding the biology and conservation of orchid populations. To investigate orchid mycorrhizal associations in five species of the genus Orchis (O. anthropophora, O. mascula, O. militaris, O. purpurea, and O. simia), we developed internal transcribed spacer-based DNA arrays from extensive clone library sequence data sets, enabling rapid and simultaneous detection of a wide range of basidiomycetous mycorrhizal fungi. A low degree of specificity was observed, with two orchid species associating with nine different fungal partners. Phylogenetic analysis revealed that the majority of Orchis mycorrhizal fungi are members of the Tulasnellaceae, but in some plants, members of the Thelephoraceae, Cortinariaceae and Ceratobasidiaceae were also found. In all species except one (O. mascula), individual plants associated with more than one fungus simultaneously, and in some cases, associations with ≥3 mycorrhizal fungi at the same time were identified. Nestedness analysis showed that orchid mycorrhizal associations were significantly nested, suggesting asymmetric specialization and a dense core of interactions created by symmetric interactions between generalist species. Our results add support to the growing literature that multiple associations may be common among orchids. Low specificity or preference for a widespread fungal symbiont may partly explain the wide distribution of the investigated species. © 2010 Blackwell Publishing Ltd. Source

Soetens T.,Ghent University | Van Gysel A.,Lessius University College Antwerp | Matthys S.,Ghent University | Taerwe L.,Ghent University
Construction and Building Materials | Year: 2013

The residual post-cracking tensile strength of conventional steel fibre reinforced concrete is directly related to both the amount of fibres crossing a crack and the individual pull-out responses of all activated fibres. Therefore, the knowledge of the single pull-out behaviour is essential to understand the uni-axial or bending behaviour of SFRC when it is considered as a full-fledged composite. Since hooked-end steel fibres are considered to be the most suitable fibre type for structural purposes, the need to accurately predict the pull-out response of these type of fibres, is of great practical importance. In this paper, an experimental investigation of the pull-out response of both straight and hooked-end steel fibres is discussed. Based on the obtained experimental data, a semi-analytical model is developed to predict the fibre pull-out behaviour. The ability of the model to deal with different geometrical and mechanical fibre characteristics as well as the influence of orientation, embedded length and matrix compressive strengths, reflects its overall quality. © 2013 Elsevier Ltd. All rights reserved. Source

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