Time filter

Source Type

Preat J.,Belgian National Fund for Scientific Research | Hagfeldt A.,Uppsala University | Hagfeldt A.,KTH Royal Institute of Technology | Perpete E.A.,Belgian National Fund for Scientific Research
Energy and Environmental Science | Year: 2011

We have carried out theoretical investigation aiming at modelling the assessment of mechanisms of photoinduced processes in a recent p-type organic metal-free dye derived from the triphenylamine (P-1) structure. In the P-1 system, one uses the triphenylamine moiety as the electron donor, malononitrile as the electron acceptor, and a thiophene that plays the role of the conjugated chain. Basically, the difference between the P-1 dye and the common organic dyes used in the n-type DSSC field is the anchoring group located on the electron donor group. In a first step, DFT and TDDFT approaches have been exploited to calculate the key parameters controlling both the intramolecular charge transfer (ICT) and hole transfer rate constants in the Gurney-Gerischer-Marcus (GGM) formalism, for either a solvent-controlled adiabatic or a nonadiabatic electron transfer. These are: (i) the electronic coupling; (ii) the reorganization energies; and (iii) the variation of the Gibbs energy. The gathered results are in agreement with the experimental trends. (i) The vertical ICT excited states energy has been calculated at 2.67 eV, in perfect line with the experiment (2.65 eV). (ii) Two mechanisms can be conceived for the hole transfer and regeneration process. The first deals with the reduction of dye molecule at the excited state followed by an electron transfer from the reduced dye to the oxidized regenerator. The second implies a redox reaction between the excited dye and the oxidized regenerator, followed by an electron transfer from the cathode to the oxidized dye. (iii) Our theoretical investigation suggests that the first mechanism is dominant. Secondly, we propose structural modifications improving the TPA-based DSSCs hole transfer efficiency and we show that an additional -CN graft on the malononitrile unit combined to the functionalisation of the TPA moieties by -OMe groups (to give P-1b) should significantly improve the key parameters related to the electron injection. Indeed, for P-1b, we have noticed an increase of both the RLHE factor (0.907) and the injection driving force (-0.33 eV). This dye is therefore expected to be a very promising molecule in the p-type DSSC field. © 2011 The Royal Society of Chemistry.

Clobert M.,Catholic University of Louvain | Clobert M.,Belgian National Fund for Scientific Research | Saroglou V.,Catholic University of Louvain | Hwang K.-K.,National Taiwan University
Personality and Social Psychology Bulletin | Year: 2015

Does Buddhism really promote tolerance? Based on cross-cultural and cross-religious evidence, we hypothesized that Buddhist concepts, possibly differing from Christian concepts, activate not only prosociality but also tolerance. Subliminally priming Buddhist concepts, compared with neutral or Christian concepts, decreased explicit prejudice against ethnic, ideological, and moral outgroups among Western Buddhists who valued universalism (Experiment 1, N = 116). It also increased spontaneous prosociality, and decreased, among low authoritarians or high universalists, implicit religious and ethnic prejudice among Westerners of Christian background (Experiment 2, N = 128) and Taiwanese of Buddhist/Taoist background (Experiment 3, N = 122). Increased compassion and tolerance of contradiction occasionally mediated some of the effects. The general idea that religion promotes (ingroup) prosociality and outgroup prejudice, based on research in monotheistic contexts, lacks cross-cultural sensitivity; Buddhist concepts activate extended prosociality and tolerance of outgroups, at least among those with socio-cognitive and moral openness. © 2015 by the Society for Personality and Social Psychology, Inc

Sultan S.,University of Paris Descartes | Luminet O.,Catholic University of Louvain | Luminet O.,Belgian National Fund for Scientific Research | Hartemann A.,University Pierre and Marie Curie
Journal of Affective Disorders | Year: 2010

Background: Little systematic research into the diagnostic performance of instruments used to screen for clinical depression is available for people with diabetes. The objective of this study was to compare performances of the HADS and BDI-SF and their components in association with a standard diagnostic interview. Methods: In a sample of 298 French outpatients from a diabetes clinic (165 men, aged 59.4 ± 10.7 years), we assessed diagnoses of clinical depression (CD, n = 42) and major depression (MD, n = 30) using the MINI and administered the HADS and BDI-SF. Results: Cognitive symptoms from the BDI-SF (BDIcog) were more closely associated with MD than CD. BDIcog and HADS total scores performed best overall in identifying clinical depression (AUCs under ROC curve 85%). For identification of CD, the sensitivity/specificity of BDI cognitive symptoms was 88/71% (cutoff 3+) and for the HADS 83/65% (cutoff 13+). For identification of MD, BDIcog scored 83/80% (cutoff 4+) and HAD-A 80/76% (cutoff 9+). Logistic regression analyses further suggested that BDIcog and HAD-A discriminated between depressed and non-depressed patients better than the somatic and anhedonia items present in the same scales. The depression subscale of the HADS performed poorly. Limitations: The consecutive nature of the sample may limit the generalizability of our findings. Conclusion: Results suggest that, in addition to depressed mood, both negative thoughts and anxiety are core elements for the correct identification of clinical depression in chronic illnesses such as diabetes. It may be more appropriate to use the total score when applying the HADS and distinguish non-somatic symptoms within the BDI. © 2009 Elsevier B.V. All rights reserved.

Stephan A.,Belgian National Fund for Scientific Research | Stephan A.,Roosevelt University | Stephan A.,University of Melbourne | Crawford R.H.,University of Melbourne | de Myttenaere K.,Roosevelt University
Building and Environment | Year: 2013

Many cities are likely to expand in the coming decades and this expansion will probably include low-density neighbourhoods. There is an increasing pressure on cities worldwide to accommodate an increasing population. It is therefore crucial to assess the energy demand and related greenhouse gas emissions implications of such development.This paper uses a representative low-density neighbourhood in Melbourne, Australia, assesses its energy consumption and greenhouse gas emissions over 100 years and investigates various scenarios related to house size, transport technology, housing typology and the temporal evolution of parameters.Results show that the energy required to produce and replace building materials and infrastructures constitutes 26.9% of the total energy consumption, while operational and transport requirements represent 39.4% and 33.7% respectively. One of the analysed scenarios reveals that replacing half of the built area of the suburb with apartment buildings reduces the total energy consumption per capita by 19.6%, compared to a typical single storey detached house layout.Regardless of the uncertainty in the data, the main conclusion is that each of the embodied, operational and transport energy demand and associated greenhouse gas emissions can be reduced in order to improve the overall environmental performance of new urban neighbourhoods. © 2013 Elsevier Ltd.

Manard M.,University of Liège | Carabin D.,University of Liège | Jaspar M.,University of Liège | Collette F.,University of Liège | Collette F.,Belgian National Fund for Scientific Research
BMC Neuroscience | Year: 2014

Background: Research on cognitive control suggests an age-related decline in proactive control abilities whereas reactive control seems to remain intact. However, the reason of the differential age effect on cognitive control efficiency is still unclear. This study investigated the potential influence of fluid intelligence and processing speed on the selective age-related decline in proactive control. Eighty young and 80 healthy older adults were included in this study. The participants were submitted to a working memory recognition paradigm, assessing proactive and reactive cognitive control by manipulating the interference level across items.Results: Repeated measures ANOVAs and hierarchical linear regressions indicated that the ability to appropriately use cognitive control processes during aging seems to be at least partially affected by the amount of available cognitive resources (assessed by fluid intelligence and processing speed abilities).Conclusions: This study highlights the potential role of cognitive resources on the selective age-related decline in proactive control, suggesting the importance of a more exhaustive approach considering the confounding variables during cognitive control assessment. © 2014 Manard et al.; licensee BioMed Central Ltd.

Davydov D.M.,Catholic University of Louvain | Luminet O.,Catholic University of Louvain | Luminet O.,Belgian National Fund for Scientific Research | Zech E.,Catholic University of Louvain
International Journal of Psychophysiology | Year: 2013

This study was conducted to test the hypothesis that differences in alexithymia would moderate coupling in physiological and subjective-experiential responses to two affective films, which were shown to induce a common negative (sad) feeling, but to provoke different hyper- or hypo-arousal physiological responses (e.g., heart rate acceleration or deceleration) associated with antipathic or empathic context, respectively (Davydov et al., 2011). Only women were studied as persons showing more reactivity to sad films than men. Reactivity was evaluated for facial behavior, physiological arousal, and subjective experience. Some other affective and cognitive disposition factors (e.g., depression and defensiveness) were considered for evaluating their probable mediation of the alexithymia's effects. While subjective experience was not affected by alexithymia, high scorers on the externally-oriented thinking factor showed reduced physiological reactivity in both film conditions. These effects were mediated through different disposition factors: either low affectivity (low depressed mood), which mediated alexithymia's effect on hyper-arousal responses (e.g., decrease of heart rate acceleration), or impression management (other-deception), which mediated alexithymia's effect on hypo-arousal responses (e.g., decrease of heart rate deceleration). © 2012 Elsevier B.V.

Busoniu L.,Technical University of Delft | Ernst D.,Belgian National Fund for Scientific Research | Ernst D.,University of Liège | De Schutter B.,Technical University of Delft | Babuska R.,Technical University of Delft
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2011

This paper introduces an algorithm for direct search of control policies in continuous-state discrete-action Markov decision processes. The algorithm looks for the best closed-loop policy that can be represented using a given number of basis functions (BFs), where a discrete action is assigned to each BF. The type of the BFs and their number are specified in advance and determine the complexity of the representation. Considerable flexibility is achieved by optimizing the locations and shapes of the BFs, together with the action assignments. The optimization is carried out with the cross-entropy method and evaluates the policies by their empirical return from a representative set of initial states. The return for each representative state is estimated using Monte Carlo simulations. The resulting algorithm for cross-entropy policy search with adaptive BFs is extensively evaluated in problems with two to six state variables, for which it reliably obtains good policies with only a small number of BFs. In these experiments, cross-entropy policy search requires vastly fewer BFs than value-function techniques with equidistant BFs, and outperforms policy search with a competing optimization algorithm called DIRECT. © 2010 IEEE.

Stephan A.,Belgian National Fund for Scientific Research | Stephan A.,Roosevelt University | Stephan A.,University of Melbourne | Crawford R.H.,University of Melbourne | De Myttenaere K.,Roosevelt University
Energy and Buildings | Year: 2012

Current assessments of residential building energy demand focus mainly on operational energy, notably in thermal terms. The embodied energy of buildings and the transport energy consumption of their users are typically overlooked. Recent studies have shown that these two energy demands can represent more than half of the life cycle energy over 50 years. This article presents a framework which takes into account energy requirements at the building scale, i.e. the embodied and operational energy of the building and its refurbishment, and at the city scale, i.e. the embodied energy of nearby infrastructures and the transport energy (direct and indirect) of its users. This framework has been implemented through the development of a software tool which allows the rapid analysis of the life cycle energy demand of buildings at different scales. Results from two case studies, located in Brussels, Belgium and Melbourne, Australia, confirm that each of the embodied, operational and transport requirements are nearly equally important. By integrating these three energy flows, the developed framework and software provide building designers, planners and decision makers with a powerful tool to effectively reduce the overall energy consumption and associated greenhouse gas emissions of residential buildings. © 2012 Elsevier B.V. All rights reserved.

Stephan A.,Belgian National Fund for Scientific Research | Stephan A.,Roosevelt University | Stephan A.,University of Melbourne | Crawford R.H.,University of Melbourne | de Myttenaere K.,Roosevelt University
Applied Energy | Year: 2013

Certifications such as the Passive House aim to reduce the final space heating energy demand of residential buildings. The latter are responsible for a significant share of final energy consumption in Europe of which nearly 70% is associated with space conditioning, notably heating. The improvement of the energy efficiency of residential buildings, in terms of space heating, can therefore reduce their total energy demand.However, most certifications totally overlook other energy requirements associated with residential buildings. Studies on passive houses do not take into consideration the embodied energy required to manufacture the building materials, especially the large amount of insulation required to achieve high operational efficiencies. At an urban scale, most passive houses are single family detached houses located in low density suburbs with a high car usage, resulting in considerable transport related energy demand.This paper analyses the total life cycle energy demand of a typical Belgian passive house, comprising embodied, operational and transport energy. It relies on a comprehensive technique developed by Stephan et al. [1] and conducts a parametric analysis as well as a comparison to alternative building types.Results show that current building energy efficiency certifications might not ensure a lower energy demand and can, paradoxically result in an increased energy consumption because of their limited scope. More comprehensive system boundaries should be used to make sure that net energy savings do occur. The embodied energy of passive houses can represent up to 77% of the total embodied and operational energy over 100. years. Also passive houses can have nearly the same energy consumption as a standard new house with the same geometry, location and number of occupants. A retrofitted apartment in the city has an energy consumption 15.2% lower than the best passive house scenario. © 2013 Elsevier Ltd.

Libert B.,Catholic University of Louvain | Libert B.,Belgian National Fund for Scientific Research | Peters T.,Catholic University of Louvain | Yung M.,Columbia University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Group signatures are a central cryptographic primitive, simultaneously supporting accountability and anonymity. They allow users to anonymously sign messages on behalf of a group they are members of. The recent years saw the appearance of several constructions with security proofs in the standard model (i.e., without appealing to the random oracle heuristic). For a digital signature scheme to be adopted, an efficient revocation scheme (as in regular PKI) is absolutely necessary. Despite over a decade of extensive research, membership revocation remains a non-trivial problem in group signatures: all existing solutions are not truly scalable due to either high overhead (e.g., large group public key size), or limiting operational requirement (the need for all users to follow the system's entire history). In the standard model, the situation is even worse as many existing solutions are not readily adaptable. To fill this gap and tackle this challenge, we describe a new revocation approach based, perhaps somewhat unexpectedly, on the Naor-Naor-Lotspiech framework which was introduced for a different problem (namely, that of broadcast encryption). Our mechanism yields efficient and scalable revocable group signatures in the standard model. In particular, the size of signatures and the verification cost are independent of the number of revocations and the maximal cardinality N of the group while other complexities are at most polylogarithmic in N. Moreover, the schemes are history-independent: unrevoked group members do not have to update their keys when a revocation occurs. © 2012 International Association for Cryptologic Research.

Loading Belgian National Fund for Scientific Research collaborators
Loading Belgian National Fund for Scientific Research collaborators