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De Afrikaanse turquoise killivis als model voor letsel-geïnduceerde neuroregeneratie: van cellulair herstel tot functionele regeneratie
No full textAs the global population ages, there is a growing burden of neurodegenerative diseases and traumatic brain injuries (TBIs), both of which lead to progressive neuronal loss. Understanding how to counteract this loss is critical, especially since the adult mammalian brain only has a limited capacity to generate new neurons. Teleost fish, including the short-lived and rapidly aging African turquoise killifish, possess remarkable regenerative abilities, making them valuable models for studying age-dependent brain regeneration. This PhD research focused on how especially young killifish regenerate neurons after TBI in the Dm zone of the telencephalon, a brain region involved in learning and memory. To assess the extent and rate of maturation and integration of new neurons into brain circuits, a viral vector labeling method was optimized to track dividing progenitor cells and their progeny. Morphological and electrophysiological analyses confirmed that new injury-induced neurons in young adults could mature and functionally integrate into neural circuits. Behavioral tests, using a conditioned place avoidance assay, showed that injured fish were able to relearn the task but only after a 45-60 day period of cellular maturation. The study also revealed new diversity among the progenitor and glial cells in terms of morphology and connectivity. Overall, this work established new tools in killifish and demonstrated that young adults can achieve functional neuroregeneration, offering insights that may guide future therapies for neuronal loss in humans.status: Publishe
Op de rand van het bestaan: Het ontrafelen van de verbanden tussen existentiële zorgen en depressieve symptomen in oudere volwassenen die in woonzorgcentra wonen
No full textDepressive symptoms seem to be common in older adults living in nursing homes, with rates ranging from 14% to 82%. To identify and support nursing home residents who may be struggling with depressive symptoms, it is essential to understand the risk factors contributing to these symptoms. Although various risk factors have been proposed, existential concerns - particularly meaning in life and existential loneliness - have received limited attention despite their relevance in the nursing home context. The dissertation aimed to investigate the relationship between these existential concerns and depressive symptoms, combining cross-sectional, longitudinal and qualitative approaches.
The Introduction outlines the current state of research on meaning in life, existential loneliness, and depressive symptoms. Chapter 1 offers a conceptual exploration of meaning in life in older adults through a scoping review. Our findings indicated that current conceptualisations of meaning in life are generally not tailored to older adults, despite some studies suggesting potentially unique components relevant to this life stage. Chapter 2 presents the cross-sectional relationship between meaning in life and depressive symptoms, with a specific focus on the experience of bodily disconnection, in 242 residents from 22 Flemish (Belgian) nursing homes. Residents experiencing greater bodily disconnection reported less meaning in life and more depressive symptoms, suggesting that moving beyond purely physical terms may be crucial when approaching and caring for the body of older adults. Chapter 3 qualitatively explores the entanglement between meaning in life, existential loneliness and depressive symptoms by analysing 24 residents' narratives to identify whether, and which, depressive symptoms were present in their narratives. We also examined whether these depressive references differed between residents with a high versus low score on a depressive symptom questionnaire. We found that certain depressive symptoms are more frequently used to express existential concerns, yet, at the same time, depressive symptoms and existential concerns are much entangled. Chapter 4 longitudinally examines the relationships between meaning in life, existential loneliness, and depressive symptoms across three annual measurement points in the sample of 243 nursing home residents from the 22 Flemish nursing homes, using random-intercept cross lagged panel models. At the between-level, residents who reported more meaning in life and less existential loneliness tended to experience fewer depressive symptoms. However, at the within-person level, these relationships were inconsistent and unexpected, suggesting the need to further explore these within-person dynamics, potentially on a shorter timescale. The Discussion of this dissertation integrates our findings into the broader literature, and discusses some limitations and directions for future research.status: Publishe
Een verkenning van de diversiteit van Saccharomyces cerevisiae-stammen als celfabrieken voor limoneenproductie
No full textGenetically engineered microbes are increasingly utilized to produce a broad range of high-value compounds. However, most studies start with only a very narrow group of genetically tractable type strains that have not been selected for maximum titers or industrial robustness. In this study, we used high-throughput screening and parallel metabolic engineering to identify and optimize Saccharomyces cerevisiae chassis strains for limonene production, a monoterpene with applications in flavors, fragrances, and biofuels. We screened 921 genetically and phenotypically distinct S. cerevisiae strains for limonene tolerance and lipid content to identify optimal chassis strains for precision fermentation of limonene. In parallel, we also evaluated 16 different plant limonene synthases. Our results revealed that two of the selected strains showed approximately a 2-fold increase in titers compared to CEN.PK2-1C, the type strain that is often used as a chassis for limonene production, with the same genetic modifications in the mevalonate pathway. Intriguingly, the most effective engineering strategy proved strain-specific. Metabolic profiling revealed that this difference is likely explained by differences in native mevalonate production. Ultimately, by using strain-specific engineering strategies, we achieved 1412 mg/L in a new strain, which is 83% higher than the optimal titer (770 mg/L) achieved in CEN.PK2-1C. Our findings demonstrate the potential of leveraging genetic diversity in S. cerevisiae for monoterpene bioproduction and highlight the necessity for tailoring metabolic engineering strategies to specific strains.status: Publishe
Gefocuste aandachtsmeditatie door de lens van neuroviscerale dynamiek en neurofeedback
No full textCross frequency coupling between brain oscillations has been extensively studied and is thought to underlie cross-talk between distinct neural processes. Recent accounts suggest that not only the rhythms of the brain interact through cross-frequency coupling, but that also the frequencies of body oscillations (e.g. heart and respiratory rhythms) are impacted by and aligned with oscillations at the level of the brain (Binary hierarchy brain body oscillation theory). The current PhD project will further explore the functional relevance of cross-frequency dynamics of neural and bodily rhythms from a basic science perspective and in the context of stress regulation and meditation. A deeper understanding of brain-body cross-frequency dynamics will allow the identification of novel neurophysiological indices for the evaluation of promising stress relief interventions (e.g. oxytocin treatment, mindfulness-based stress reduction), and will inform the development of novel bio-feedback protocols targeting self-regulation of brain-body cross-frequency dynamics.status: Accepte
Marking similarity “in the style of ”: Czech prepositional phrases with (non-)taxonomic nouns in contrast with Polish
No full textThis paper compares Czech and Polish prepositional phrases formed with non-taxonomic abstract nouns such as styl ‘style’ or duch ‘spirit’. It analyzes their syntactic functions, surrounding contexts (especially co-occurrence with indefinite pronouns), and semantic-pragmatic extensions, including similarity, exemplification, and quotative uses. While Polish shows broad grammaticalization (of variable advancement) of both taxonomic and non-taxonomic nouns into similative, exemplifying and quotative constructions, Czech limits such developments to a small set of manner-based nouns, which brings further evidence that the semantic domain of ‘manner’ is a productive source for the emergence of similative and quotative constructions, even in the absence of analogical models based on taxonomic nouns in Czech. The findings contribute to a more nuanced understanding of how similarity and related meanings are grammatically expressed in Slavic languages.status: Accepte
Betrouwbaarheidsonderzoek van Monolithische GaAs-op-Si Fotonische Componenten voor Datacommunicatie
No full textAs we move on towards the 'More than Moore' era and the Internet Of Things is becoming an important part of our life, the need of heterogenous integration and reduced power consumption becomes critical. Even though copper-based interconnects have served us well over the years, they cannot follow the frantic pace of data transmission rates, so high-speed optical transmission systems are required. This is where Silicon-based Photonic Integration appears, having as a leverage the, already, mature CMOS Si industry, combining the best existing processes and tools. The widely known, Si and Ge, materials continue to be popularly used for the basic building blocks of Si Photonics, like modulators and photodiodes. But, when it comes to the laser integration, they have not been efficient due to their limitation to emit light. So, the research interest has turned into the III-V group of materials that has been widely used in commercial laser devices. The so-called Monolithic integration (direct growth of III-V on Si) is targeting to a superior active device functionality, including on-chip light emission and improved modulation and detection capability. However, along with the advancements in the semiconductor industry, additional reliability issues have emerged. Defects induced by the fabrication process (mainly epitaxy) or the ageing of the device under stress, can lead to the degradation of the device's characteristics and have a tremendous impact on the laser performance. So, it is of great importance to benchmark their reliability in order to continue their development over the years and be confident that the designed products will not fail after a short time. The purpose of this thesis is, therefore, to deeply investigate the impact of the aforementioned induced defects, on the III-V laser devices developed in imec, from a fundamental reliability perspective. The project will, mainly, consist of an in-depth electrical & optical characterization of these devices in order to fully understand the key parameters that could affect the device characteristics and how their initial properties could change as a function of electrical and optical stress. The systematic and statistical analysis will enable us to better understand the underlying physics and to propose adequate modeling towards the lifetime prediction at operating conditions. Following the process flow of the relevant devices is important in a bid to understand the processing challenges and their impact on the resultant device characteristics and indeed reliability, towards the design and fabrication of a more robust and reliable technology.status: Publishe
Analyse en ontwerp van cryptografische protocollen voor IoT-apparaten
No full textThe Internet of Things already counts into the tens of billions of devices, outnumbering people and spreading into every corner of daily life. Yet no single body owns the definition of ``IoT''. The Internet Engineering Task Force (IETF) frames it in terms of end-to-end connectivity between resource-constrained devices. The European Commission stresses economic and social impact. Industrial alliances focus on seamless interoperability. All these perspectives acknowledge the same hard facts: embedded processors have only a few kilobytes of memory, batteries must last for years, and user interfaces often shrink to a lone status LED, without any input/output ports for usual authentication or pairing. These limits sharpen an old tension between cryptographic rigour, ease of use and large-scale deployment. Heavy public-key arithmetic drains power. Manual key entry discourages adoption. Extra security chips increase cost and reduce openness. The central question of this thesis is therefore how to design and analyse protocols that respect all three pressures while relying only on hardware that manufacturers already ship.
The design part of the work contributes a family of protocols that address different faces of the problem. First, an access-control architecture for implantable medical devices moves the vulnerable, ad-hoc setting towards a secure arrangement in which access control for the implant is outsourced to a companion smartphone (handset) that the patient already owns. The implant itself performs only a lightweight token check and one short-field Diffie-Hellman operation. A formal model in Verifpal and ProVerif proves authentication, forward secrecy and resistance to replay without relying on fresh randomness inside the implant. Second, a zero-interaction geofencing protocol, to help in IoT commissioning, constructs a fingerprint of a room from received-signal-strength (RSS) measurements. Using an autoencoder, the system verifies whether a live trace belongs to the learned geofence and, by binding a public key to the radio-channel geometry, grants or revokes access automatically when a user crosses the boundary. The scheme works with the Bluetooth and Wi-Fi radios already present in most access points and phones and needs no calibration, extra beacons or user actions. Third, a quorum-based location proof distributes a cryptographic secret across several heterogeneous sensors that happen to share the same room. Only when a defined subset of those sensors concur on co-presence can the secret be reconstructed and an authorisation token released. Together, these three designs demonstrate that modern public-key techniques and physical context can be combined to achieve strong guarantees while keeping interaction overhead close to zero.
The final part of the thesis focuses on the security analysis of an industry standard that already appears in millions of smart-home products. A full symbolic model of its commissioning workflow is built in applied- calculus and checked with ProVerif. The proofs identify unwritten assumptions about salt freshness and identity binding that, if violated, break secrecy and authenticity. Laboratory tests on certified devices confirm that implementations deviate from the idealised model in exactly those places. The resulting attacks allow an intruder to hijack an onboarding session or to resume a stale session under weaker keys. A responsible-disclosure process coordinated with the standard body and major vendors has led to clarified specification text, patched software development kits and a global update campaign that reached a product range numbering in the many millions. The study shows that formal verification is not limited to academic protocols. When applied carefully, it can reveal subtle design gaps in commercial ecosystems before those gaps turn into large-scale breaches.
The thesis thus provides a concrete foundation for building IoT systems that are secure, usable and readily deployable at a global scale.status: Publishe
Optische karakterisering van perceptuele oppervlakteglans
No full textIn many applications, customers make purchase decisions based on functional requirements, performance and experiential considerations. The visual appearance - the visual sensation resulting from an interaction between the shape of objects, their optical properties, and the illumination - strongly contributes to this assessment task. In essence, a high quality product must nowadays also look alike, or it will simply not be as attractive as other (cheaper) alternatives with elaborated surface finish or packaging. For this reason, all manufacturing industries are concerned with appearance control: from cars or yachts, to any electronic device or home appliance, paints, cosmetics, flooring, and even food products. Realistic visual appearance is also required for reality perception in today's digital world. In this sense, guiding frameworks for the quantification of visual appearance have become essential for industry to ensure reproducibility and uniformity in appearance descriptions. The optical characterization of visual appearance is however tremendously complex, even though human individuals can easily and continuously asses it in crowded scenes. An international team of scientists dealt with the topic in 2006, introducing four essential attributes: colour, gloss, translucency and texture.
This dissertation focuses on the optical characterization of the attribute gloss. Gloss is generally associated with specular reflection (mirror reflection) at the front surface (first interface between the surrounding medium (i.e. air) and an object) of objects. Contributing to the visual appearance, gloss influences our impression of - and interaction with - the surrounding world. In particular, industrial gloss control on visible product surfaces often pursuits a sense of high quality or prestige. A unanimous consensus for the perceptual and optical characterization of gloss is however yet non-existent. In this manuscript, an extensive review of existing research on the visual perception of gloss and its instrumental characterization is provided. A custom framework is suggested for a next generation of gloss meters, consisting of five main attributes: specular gloss, distinctness of the reflected image ('DOI'), haziness of the image ('haze'), contrast and surface-uniformity gloss. Standardized measurement methods for most attributes have been around for a long time. As such, they are mostly based on outdated photo-electric technology and not considering the technological potential of contemporary compact imaging hardware and software. Furthermore, the industrial evaluation of gloss is mainly performed with a simple handheld specular gloss meter, whose evaluations often correlate poorly with the actual gloss appraisal. A dedicated visual inspection thus remains indispensable for a trustful judgement, leading to uncertainties and subjectivity in the process. As a solution, instrument manufacturers developed more modern gloss meters with linear or twodimensional sensors that can combine standard evaluation methods for specular gloss, DOI and haze, with some customized capabilities. Other application-specific and appearance-oriented instruments with camera technology exist, but they are very expensive.
Industry would benefit from an affordable gloss meter that could quantify every aspect of surface gloss. In the process towards such a multifunctional and cost-effective gloss meter, two image-based gloss meters (iGMs) have been developed in this project. With CMOS camera sensors, they incorporate arbitrary image-processing algorithms. Their optical geometry is based upon the classical specular gloss meter, providing backward compatibility for industry. The first iGM with a colour camera sensor and two light sources is capable of evaluating image-based metrics for four of the five defined gloss attributes (specular gloss, DOI, haze and contrast). An evaluation of the contrast attribute is a particular novelty of the device. A second extended iGM instrument, additionally equipped with an extra camera sensor and various light sources, was developed to also incorporate the last gloss attribute (surface-uniformity gloss). It includes evaluations of the physical texture, sparkle (glitter), surface defects, material grooves and orange peel (surface waviness). Consisting of compact and cheap components, both instruments are cost-effective and handheld. The applicability and appropriateness of many gloss evaluation algorithms based on measurement image data of both devices was illustrated on a variety of industrially relevant materials. An introductory study was performed on the impact of local surface curvature on specular gloss evaluation. Indeed, despite the complex threedimensional shape of nowadays products, all gloss evaluation standards still assume a flat surface geometry. Based on measurements and ray-tracing simulations, the iGM was adapted to the measurement of specular gloss on non-flat surfaces.
The unavailability of the ground truth perception of stimuli complicates a conclusion on the appropriateness of iGM gloss evaluations. As sample haziness has been rarely studied yet, focus was laid on the psychophysical validation of hazy specimen. In a psychophysical experiment, perceptual scales for the glossiness and its two mainly recognized attributes (DOI and contrast) were determined for a batch of hazy surfaces. In the search for a suitable (image-based) representation, the perceptual data was correlated with metrics of the iGM and other optical instruments. In particular, the study indicates the relevance of 'contrast-based' evaluations in describing the perceived glossiness of hazy surfaces. In addition, novel haze and DOI metrics of the iGM provide the best description of the perceived glossiness and DOI, respectively. Future work is required to investigate the generalization of these findings.
Finally, the performed research also resulted in the development of a commercialized embodiment of the iGM in collaboration with the company Rhopoint Instruments ltd. Rhopoint is one of the world-wide market leaders in optical instrumentation, with multiple gloss and appearance related devices in their product portfolio. The commercial iGM, with measurement capabilities for each of the five gloss attributes, will be launched in early 2024.status: Publishe
Het dichten van de hiaten in de ammoniak supply chain: katalytische routes voor synthese uit NOx en kraken tot groene waterstof
No full textAmmonia is a promising hydrogen carrier due to its high hydrogen density, but a missing link is an energy-efficient technology for ammonia cracking to produce hydrogen gas. The most explored option is thermocatalytic cracking, but this solution requires high temperatures to achieve near complete conversion, especially when using noble metal-free catalysts. Plasma cracking of ammonia is not limited by the same thermodynamic equilibrium as the applied electrical energy selectively heats electrons, due to their small mass, creating a thermal non-equilibrium. The highly energetic electrons can break up ammonia molecules and achieve higher conversions at lower bulk temperatures. The main downside of plasma cracking is the relatively high energy cost. During this PhD, a process, which combines the benefits of thermocatalytic and plasma cracking, will be explored. A packed bed reactor partly converts ammonia to H2 and N2 (>50 %). The outlet of the catalytic reactor is sent to the plasma reactor, where the remaining ammonia is converted as much as possible (aiming at > 99%). The first objective of this PhD is to develop a noble metal-free catalysts with high activity for ammonia cracking, without aiming at complete conversion. The second objective is to join the catalytic and plasma reactor and find the optimal combination of process parameters (temperatures, flow rates, conversion efficiencies, energy requirements) to minimize total energy cost and maximize synergy production rate.status: Accepte