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Grade retention : helpful or harmful? A contextual study towards the non-cognitive outcomes of grade retention from a cross-national perspective
No full textNovel freestanding carbons for micropollutants removal through sustainable processes
No full textNowadays, the occurrence of organic micropollutants (OMPs), especially pharmaceuticals, in water bodies has caused widespread concerns due to their negative impacts, e.g., bioaccumulating in living organisms and developing antibiotic-resistant bacteria and genes. On the other hand, conventional wastewater treatment plants, including a main biological step, fail to efficiently remove highly mobile and recalcitrant pharmaceuticals, posing new challenges for the clean water supply. This thesis introduces novel freestanding carbons that can serve as an adsorbent, an electrode, or both to remove OMPs via adsorption, (electro-)Fenton-based oxidation, or a combination of them in a so-called cyclic process, respectively. Such self-standing carbon materials can facilely incorporate different catalysts nanoparticles inside their structure. Two self-standing carbon microtubes were synthesized using carbon nanotubes (CNT) as the main constituent, mixed with powdered activated carbons (PAC) and Fe3O4 nanoparticles to serve as a micro-and mesoporous adsorbent (PAC/CNT microtube) and a Fe-incorporated carbon electrode (Fe3O4 /CNT microtube), respectively. The addition of PAC to the CNT matrix increased the specific surface area by introducing micropores as high energy centers for OMPs removal, especially at low equilibrium concentrations. A temperature-assisted Fenton oxidation was proposed to regenerate the SMX-saturated PAC/CNT microtube and reuse it for 12 consecutive cycles. Compared to the room temperature oxidation, the temperature-assisted Fenton showed an enhanced regenerated capacity in each cycle and extended durability of the adsorbent by mitigating the adsorption of undesired compounds during the Fenton process. Fe3O4 /CNT microtubes proved to degrade CBZ as an efficient cathode for heterogeneous electro-Fenton (HEF) with good reusability and minimal catalysts leaching in acidic environments. Moreover, as a green alternative to CNT-based carbons, a novel synthesis method to fabricate monolithic carbons was introduced using chitosan and sucrose as bio-based precursors. Final monolithic carbons possess high specific surface areas (up to 703 m2/g), a hierarchical porosity, and nitrogen and oxygen as heteroatoms. Monolithic carbons served as an adsorbent with adequate separation properties to adsorb SMX, being comparable to commercial granular carbons despite having 50 % less specific surface area. Furthermore, cylindrical and tubular carbons were deployed directly as electrodes and gas diffusion electrodes (GDE), respectively. Next, successful incorporation of Fe3O4 into bio-based carbons was carried out, and final Fe-containing carbons were used as electrodes and GDEs and proved to remove both SMX and CBZ and a mixture of them effectively at pH 3 and 7. This thesis emphasizes the advantages of self-standing carbons, with scaling-up perspectives, to develop efficient, more sustainable, and cost-effective processes for clean water supply and pave the way for implementing tangible (micro) tubular reactors
Numerical tools for fatigue lifetime assessment of large-scale welded steel structures
No full textVermoeiing is één van de meest voorkomende schademechanismen bij grote gelaste constructies. Wereldwijd wordt men alsmaar vaker geconfronteerd met de gevolgen van verouderende infrastructuur. Om ervoor te zorgen dat deze constructies veilig in gebruik kunnen blijven, is er nood aan betrouwbare methodes om de resterende levensduur te berekenen met inachtneming van huidige en toekomstige eisen. Hierbij moet onderscheid gemaakt worden tussen structuren met én zonder scheuren. Voor gelaste verbindingen die (nog) geen scheuren vertonen werden algoritmes ontwikkeld die toelaten om een volautomatische levensduur analyse uit te voeren op basis van de zogenaamde 'hot spot' spanning. Dit voor plaat- en buis verbindingen. Hierbij werd ook een diepgaand numeriek en experimenteel onderzoek verricht naar schade accumulatie modellen. Deze zijn essentieel voor een schatting van de resterende levensduur. In het tweede deel van het proefschrift wordt de focus verlegd naar de vermoeiingsanalyse van constructies die één of meerdere scheuren bevatten. Een robuuste numerieke tool werd ontwikkeld die toelaat om de multi-axiale, niet-planaire vermoeiingsscheurgroei te simuleren in grootschalige driedimensionale modellen. In samenwerking met industriële partners werden drie stalen structuren (een kraanbaan, spoorwegbrug en offshore jacket) geïnstrumenteerd en gemodelleerd. Op basis van de experimentele data werden de numerieke modellen en ontwikkelde tools gevalideerd
Power exhaust and plasma divertor interaction study by means of a 2D edge numerical code
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Impact of implant retained overdenture treatment and speech, oromyofunction, social participation and quality of life
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