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Kwantumchemische methoden voor spectra en eigenschappen in de gecondenseerde fase
No full textComputational and theoretical chemistry has become an important pillar in our modern understanding of chemistry. The usage of mathematical models based, for example, on thermodynamic, kinetic, or quantum mechanical theories aids chemical research on a daily basis. Specifically, computational methods based on quantum mechanics are incredibly important because they enable access to information such as molecular structure, reaction paths, spectroscopic data, or molecular properties. However, these methods often require one to make a trade-off between accuracy and computational effort, often making it unfeasible to model realistic systems with the most robust theories. For this reason, the development of computational protocols designed for studying systems in condensed phases, where most of the chemistry actually takes place, while still using accurate quantum mechanical methods, is an active area of research for theoretical chemists.
This thesis aims to develop new computational protocols for modelling spectra and properties in condensed phase. In particular, Auger decay and electronic dipole polarizabilities were studied using the developed protocols. The proposed approaches have coupled-cluster theory as their foundation. For the description of Auger decay, coupled-cluster theory is combined with complex variable techniques based on non-Hermitian quantum mechanics, which provide a suitable framework for describing the transient nature of the metastable states involved in such processes. The computational protocols presented in this thesis streamline the modelling of Auger spectra from the results of these calculations, which was illustrated for organic molecules and heavy metals. Meanwhile, two different approaches that employ the projection-based quantum embedding method were proposed for the study of supermolecular properties of systems in condensed phase. Analytical derivatives serve as an efficient to compute molecular properties. For this reason, the implementation of first derivatives for coupled-cluster in density functional theory embedding was also addressed in this work.status: Publishe
Are consumers (approximately) rational? Shifting the burden of proof
No full textWe present a statistical test for the hypothesis of (approximate)
utility maximization on the basis of nonparametric revealed preference
conditions. We take as null hypothesis that the consumer behaves ran domly, and we reject this hypothesis only if the data provides sufficient
evidence to support the alternative hypothesis of approximate utility max imization. Our statistical test uses a permutation method to operationalize
the principle of random consumption behavior. We show that our test
(i) is valid for any sample size under the null and (ii) has an asymptotic
power of one. We also provide simulated power results and two empirical
applications.sponsorship: Fund of Scientific Research Flanders (FWO-Vlaanderen), Research Fund KU Leuven, Fonds De La Recherche Scientifique - FNRS, National Science Foundation of China|key project no. 72033006status: Published onlin
Autonome voertuigen in overtreding? Een prospectieve studie naar burgerlijke aansprakelijkheid en schadevergoeding in het Belgische, Franse, Britse/Engelse en EU-recht
No full textThese past years, advances in programming and data science, as well as increased computational power, have fostered the development of powerful intelligent software programs that are gradually being introduced in various fields. So called artificial intelligent (AI) technologies are booming throughout the world where these set of tools have many applications such as transportation.
The alleged benefits of embedding AI technologies in transport vehicles are multiple, ranging from enhanced safety, increased reliability to economic efficiency. Some authors have described it as a mobility revolution in the making. But however beneficial these technologies may seem, their intrinsically disruptive nature will challenge numerous psychological, social, ethical, economic and legal norms.
These autonomous vehicles' main features, inter alia, the autonomization of the decision-making process, their potentially self-learning and self-adaptive capacities, their increased reliance on data and connectivity, will highly challenge the current liability setting. Through the apprehension of autonomous cars as 'mobility systems', functions could be reshuffled and blurred, forcing a re-conceptualization of the field of transportation from a legal perspective.
From the focal point of extra-contractual civil liability and insurance law, the proposed study aims at assessing the legal impact of introducing autonomous transportation vehicles in the current European and selected national frameworks (BE, FR, UK), within the context of the wider mobility 'ecosystem'. After an initial analysis and evaluation, conclusions will be drawn on the suitability of these liability and insurance frameworks. Finally, recommendations for legal adaptations or normative evolutions will be considered.status: Publishe
Naar het begrijpen van spiermechanismen voor verminderde proprioceptie bij lagerugpijn
No full textLow back pain (LBP) is very prevalent, affecting more than 510 million people worldwide. Moreover, LBP is the leading cause of years lived with disability, and it is responsible for major socio-economic costs. In most people, LBP is non-specific, meaning that a pathological cause, such as trauma, cannot be determined. Since the underlying mechanisms of non-specific LBP remain poorly understood, it is a major challenge to provide personalized healthcare. Bio-psychosocial treatment with a focus on active therapy and exercise is therefore recommended to treat people with non-specific LBP. Unfortunately, recurrences remain high and because effect sizes are small, it is unclear which type of exercise therapy is more beneficial. Research should therefore focus on determining the underlying mechanisms of non-specific LBP and on how these mechanisms can be influenced by training.
One putative mechanism contributing to non-specific LBP is impaired lumbar proprioception. Our research group previously showed that people with LBP display a rigid, ankle-steered proprioceptive postural strategy and that this was associated with both the onset and maintenance of non-specific LBP. Yet, the contributing factors to impaired proprioception remain unclear. This doctoral project therefore aimed to investigate unexplored peripheral muscle characteristics in relation to impaired lumbar proprioception.
For instance, while one study previously showed that lower lumbar muscle oxygenation was related to an ankle-steered postural control, this has never been investigated in people with non-specific LBP. Moreover, it has often been suggested that people with LBP exhibit altered muscle activity, with either too "loose" or too "tight" postural control. This could be related to an "underactivation" or "overactivation" of lumbar musculature. However, it remains unclear if people show these changed levels of muscle activation throughout their daily postures and how this relates to other muscle characteristics. Likewise, it was previously suggested that impaired lumbar muscle size could be related to an ankle-steered postural control, but this was only investigated in a limited elderly population of people with spondylolysis. Moreover, the relation between lumbar muscle structure and clinical outcomes for LBP remains unclear. This could be because most previous studies only included single segmental lumbar level evaluations. This likely does not accurately reflect lumbar muscle structure. Additionally, a wide variety of measurement methods has often been used, with a general lack of standardization.
This doctoral project aimed to investigate (1) differences in lumbar muscle proprioception, macroscopic structure, oxygenation and activation, in people with and without recurrent non-specific LBP, and (2) explore the interrelation between impaired postural control and paraspinal muscle characteristics in people with LBP. Therefore intending to generate hypotheses for muscle-based mechanisms for impaired lumbar proprioception. To our knowledge, this was the first time that these muscle characteristics were combined.
The first objective of this doctoral project was to develop a reliable assessment of the lumbar multifidus with three-dimensional freehand ultrasound (3DfUS). In Chapter 1 and Supplementary Materials 1, we showed that 3DfUS can reliably be used to measure lumbar multifidus volume, with sufficient concurrent validity to MRI measurements. However, our results indicated that a single assessor is preferred for future studies. Additionally, to further improve reproducibility, Supplementary Materials 1 and Chapter 1 presented guidelines for 3DfUS acquisition and processing, together with a quality scoring system. In Chapter 2, we introduced a new processing method for echo-intensity with localized, intramuscular regions of interest. Both the intra- and inter- processor analysis showed excellent repeatability, with small measurement errors. This processing method showed great promise, as it was a fast and feasible analysis, even with relatively novel processors. Yet, baseline differences in multifidus echo-intensity indicated that acquisition may still introduce considerable variation and future studies should further improve the evaluation of echo-intensity.
The second objective of this doctoral project was to investigate differences in macroscopic lumbar muscle structure and function between people with and without LBP. In Chapter 2, we demonstrated incrementally greater multifidus size and worse multifidus composition from the upper to the lower lumbar segmental levels. This highlighted the importance of a multi-level segmental evaluation of multifidus structure. Moreover, people with recurrent LBP showed higher corrected multifidus echo-intensity or impaired muscle composition, but similar multifidus size compared to healthy controls. In Chapter 4, we showed that people with LBP displayed higher overall muscle activity in both the multifidus and iliocostalis lumborum, with decreased lumbar muscle oxygen extraction compared to healthy controls.
The third objective of this doctoral project was to explore the inter-relation of lumbar muscle characteristics with proprioceptive use in people with LBP. In Chapters 3 and 4, we confirmed that people with LBP showed a more rigid ankle-steered postural control, with decreased reliance on lumbar proprioceptive input. Moreover, in Chapter 3, we showed that impaired muscle composition, or higher echo-intensity, had a small correlation with a more rigid ankle-steered postural control. In Chapter 4, we demonstrated that impaired multifidus oxygenation and iliocostalis over-activation during standing showed small to moderate correlations with impaired lumbar proprioception.
Finally, the last objective of this doctoral project was to examine the reversibility of lumbar muscle impairments in people with LBP. If these multifidus characteristics would simultaneously improve with lumbar proprioception after proprioceptive training, this could provide a preliminary proof-of- Summary/ Samenvatting 7 principle, serving as a basis for future studies to further explore these characteristics as potential mechanisms for impaired lumbar proprioception. In Chapter 5, we performed a systematic review of the literature, showing that both low and high load exercise can improve lumbar muscle size, pain and disability in people with LBP. However, high load exercise might be more effective to improve disability and more studies should investigate the effect of exercise on muscle composition in people with LBP. In Chapter 6, we showed that low load proprioceptive training improved lumbar proprioception, postural control, disability and pain in people with recurrent LBP. Likewise, proprioceptive training seemed to improve muscle composition and a sub-analysis revealed that non-responders had worse multifidus after training and higher disability at baseline. Yet, caution is warranted as echo-intensity measures were not stable between repeated baseline measures and proprioceptive training had no effect on multifidus oxygenation. Therefore, future studies should investigate the effect of a longer duration of low load training or other exercise interventions, such as longer duration low load training, high load or aerobic training, to provide a proof-of-principle for multifidus oxygenation and composition as a potential mechanism for impaired proprioception.
In conclusion, this doctoral project highlighted the importance of lumbar muscle function and structure in people with recurrent LBP. Lumbar proprioception and postural control were impaired in people with LBP, and this could be related to iliocostalis lumborum overactivation, reduced multifidus oxygenation and impaired multifidus composition. Further, low load proprioceptive training provided additional evidence that improved muscle composition could be a potential mechanism to improve proprioception. Yet, further research is warranted to determine whether muscle composition can truly be improved by training, as baseline measurements were not stable and proprioceptive training had no effect on muscle oxygenation. In addition, to further improve sensorimotor control, muscle health and clinical outcomes it could be necessary to have longer duration of training or more high load and aerobic training. Besides, although our proprioceptive intervention aimed to incorporate exercises into daily activities of patients, we did not investigate whether participants showed behavioral changes during their daily life. Future studies may investigate whether these improvements in sensorimotor control, pain and disability could be explained by behavioral changes during daily life and whether these improvements could be sustained over a longer follow-up period. Additionally, future studies should probably use multi-level segmental evaluation of both multifidus size and composition. To achieve this, 3DfUS can be a useful tool, but future studies should attempt to further reduce variation due to acquisition in the definition of echo-intensity. This doctoral project could serve as a basis for future research and guide clinicians, as it improved our knowledge on lumbar muscle structure, function and proprioception and the reversibility of these characteristics with training in people with LBP.status: Publishe
Analyse van de dynamische respons van spoorwegbruggen aan de hand van bewegende lastmodellen en meerlichaamsmodellen van hogesnelheidstreinen
No full textThe investigation of dynamic responses of high-speed railway bridges is increasingly important due to the expanding stock of high-speed trains.Developments of new trains lead to insufficient coverage of dynamic effects by standards on bridge design.In this dissertation, the dynamic responses of railway bridges are studied based on extensive sets of moving load models as well as 2D multi-body models of high-speed passenger trains.
Moving load models allow a relatively fast evaluation of dynamic effects during bridge crossings and only require information of static axle loads and axle distances, which is available for a high number of trains. The moving load models of the currently operating high-speed passenger trains in the European network are used for the investigation of resonance excitations of bridges. The consideration of vehicle-bridge interaction effects requires a more detailed modeling of the trains using multi-body models with additional information about springs, dampers, and masses of the train. Multi-body models allow to take into account dynamic axle loads due to the movement of the train itself and therefore lead to calculation results closer to reality.
More than 3,000 moving load models for passenger trains are assembled and railway bridge responses are investigated using simplified calculation methods. Based on the dynamic train signature envelope of this train catalog, a new dynamic load model for high-speed trains is developed aiming for only 20 model trains to represent the dynamic effects of all operating passenger trains. Additionally, a preselection procedure for dynamically relevant trains is developed based on the simplified calculation methods of train signature and train spectra. The resulting 500 dynamically relevant trains can be used for more complex computations of dynamic bridge responses.
Vehicle-bridge interaction effects are recognized by comparing bridge responses of multi-body models, which cover interaction effects inherently, and moving load models, for which interaction effects can only be considered by an additional damping value which has to be calibrated. In calculations with moving loads the bridge damping ratio is increased by the additional damping value to account for the vehicle-bridge interaction. For the investigation of the vehicle-bridge interaction, multi-body models for more than 30 passenger trains (including conventional trains, trains with articulated bogies, and trains with equidistant wheelsets) are created. The algorithm for interaction calculations is implemented in MATLAB and the investigations are based on a parametric bridge set of about 100 single-span bridges. As only a small number of multi-body model parameters is publicly available and the correct representation of the dynamic train characteristics is uncertain, the eigenfrequencies of the theoretical multi-body models are validated based on measurements on stationary and moving trains. Beyond this, the influence of uncertainties in the data for stiffness and damping parameters in the multi-body models on the vehicle-bridge interaction is studied using a sensitivity analysis. The results of the comprehensive computational series of more than 1,000,000 bridge crossings are used to assess the validity of the additional damping method included in Eurocode 1 as well as further approaches for the additional damping given in literature.
This dissertation provides a new dynamic load model of 20 model trains based on the dynamic signature envelope of more than 3,000 operating passenger trains. The investigations of vehicle-bridge interaction effects lead to the conclusion that special attention should be paid to the primary spring parameter in the definition of multi-body models and an additional damping value needs to be defined based on detailed train characteristics.status: Publishe
Elliptic curves over Hasse pairs
No full textWe call a pair of distinct prime powers (q₁,q₂) = (p₁^a₁,p₂^a₂) a Hasse pair if |√(q₁)-√(q2)| ≤ 1.
For such pairs, we study the relation between the set Ε₁ of isomorphism classes of elliptic curves defined over Fq₁ with q₂ points, and the set Ε₂ of isomorphism classes of elliptic curves over Fq₂ with q₁ points. When both families contain only ordinary elliptic curves, we prove that their isogeny graphs are isomorphic. When supersingular curves are involved, we describe which curves might belong to these sets. We also show that if both q₁ and q₂ are odd and Ε₁∪Ε₂≠∅, then Ε₁∪Ε₂ always contains an ordinary elliptic curve. Conversely, if q₁ is even, then Ε₁∪Ε₂ may contain only supersingular curves precisely when q₂ is a given power of a Fermat or a Mersenne prime. In the case of odd Hasse pairs, we could not rule out the possibility of an empty union Ε₁∪Ε₂, but we give necessary conditions for such a case to exist. In an appendix, Moree and Sofos consider how frequently Hasse pairs occur using analytic number theory, making a connection with Andrica's conjecture on the difference between consecutive primes.sponsorship: European Research Council|ERC-669891, Fonds Wetenschappelijk Onderzoek|12ZZC23Nstatus: Published onlin
Het In Kaart Brengen van Cognitieve Controle in Gezond Verouderen
No full textCognitive control enables us to reach our goals, making this a crucial ability for daily life. However, cognitive control declines with aging. Living in an aging society, a comprehensive overview of how cognitive control changes with age is needed. Cognitive control is not a unitary construct. The Unity and Diversity framework distinguishes inhibition, updating and shifting as cognitive control subcomponents. The Dual Mechanisms of Control theory proposes that cognitive control can operate in a proactive and reactive mode. The onset, pace and trajectory of cognitive control declines with aging seem to depend on these specific subcomponents. The multitude of cognitive control tasks and operationalizations, small sample sizes and the focus on a single subcomponent in typical cross-sectional study designs complicate our current understanding of cognitive control in healthy aging. In Chapter 2, a uniform test battery assessing multiple subcomponents was developed and validated. Next, in a 3-year longitudinal study, we administered part of this test battery once a year in a large sample of older adults with a broad age span. At baseline, a group of young adults was tested as well. Findings of the first time point, reported in Chapter 3, showed declines in updating and shifting with age, but stable proactive control and even improved inhibition in older compared to young adults. Longitudinal declines in older age in interference control were observed in Chapter 4, whereas other components remained stable over time or even improved, possibly due to practice effects. Finally, Chapters 5 and 6 emphasized the detrimental impact of the COVID-19 pandemic on the wellbeing and subjective cognitive functioning of older adults. Depressive and anxiety symptoms as well as social network were exposed as important protective and risk factors for cognitive decline. This dissertation highlights the importance of assessing multiple cognitive control subcomponents in a large age span. Furthermore, capturing heterogeneity in cognitive aging with longitudinal designs and focusing on protective and risk factors were identified as potential ways forward in the field.status: Publishe
Indulging kleptocracy: British service providers, postcommunist elites, and the enabling of corruption
No full textstatus: Accepte
Contextualising Income-Based Poverty Measurement: The Needs-Based Cost of Childhood Disability in Belgium
No full textsponsorship: The authors want to thank all study participants for their valuable input in interviews, and the Centre of Expertise Budget and Financial Well-Being (CEBUD) for their consultancy role in the study. We also appreciate the critical and constructive feedback on the research process and preliminary results from participants of the European Network for Social Policy Analysis (ESPAnet) 2022, Foundation for International Studies of Social Security (FISS) 2022 and Nordic Network on Disability Research (NNDR) 2023, colleagues from the Research Group on Social Policy, Social Work, Public Opinion and Population Dynamics (ReSPOND), and everyone involved in the project of the Policy Research Centre Well-Being, Public Health, and Family. (Fonds Wetenschappelijk Onderzoek, Centre of Expertise Budget and Financial Well-Being (CEBUD)|2022, Centre of Expertise Budget and Financial Well-Being (CEBUD)|(NNDR) 2023, Foundation for International Studies of Social Security (FISS))status: Publishe
Ontwerp- en optimalisatiemethodologie voor kleinschalige bioraffinaderijen
No full textGlobal initiatives like the European Green Deal and the Circular Economy Action Plan highlight the urgent need to optimise resource recovery from waste streams. In particular, biowaste holds untapped potential for conversion into valuable products. Converting these renewable feedstocks into usable products requires a series of bioconversion processes, i.e., a biorefinery. While centralised, large-scale biorefineries are already implemented on an industrial scale, their capital-intensive nature and strict feedstock requirements often render them unsuitable for areas with diverse land usage or agricultural output. Small-scale biorefineries, on the other hand, require smaller investments and can be tailored to the specific area in which they will be employed. If suitably designed and operated, these facilities can convert community-generated biowaste into high-value products, resulting in both environmental benefits and local economic gains. However, small-scale biorefineries remain underutilised, often owing to limited awareness of such waste-processing solutions by stakeholders or a lack of trust in their (economic) sustainability, creating a reinforcing cycle of distrust and limited implementation.
This research seeks to break that cycle by proposing a holistic design and optimisation methodology for small-scale biorefineries in Western Europe. The methodology focuses on the three major aspects of any bioproduction process: (i) its supply chain, (ii) its process layout, and (iii) its optimality regarding multiple sustainability indicators. To model the small-scale biorefinery's supply chain, novel GIS methods were developed to assess the availability of kitchen, garden, and agricultural waste using only freely available datasets. Secondly, a customisable process superstructure flowsheet was introduced and simulated with adapted (kinetic) process models from literature, as well as surrogate energy models to account for energy consumption. Finally, custom genetic optimisation algorithms, capable of handling complex black-box multi-objective optimisation problems, were developed and used to optimise the resulting process layout for both profit and energy consumption. These three design and optimisation aspects were combined into one holistic methodology, which was additionally summarised in a proof-of-concept online decision support tool, to guide non-expert users in designing and optimising small-scale biorefineries that meet their requirements. Although initially calibrated for Western Europe, the proposed methodology can be easily adapted to diverse geographic contexts with varying feedstock and policy landscapes. By bridging the gap between complex engineering analyses and community-level decision-making, this holistic solution is expected to foster knowledge and trust in small-scale biorefinery systems, facilitating their broader implementation and accelerating the global transition to a circular carbon economy.status: Publishe