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Recent Submissions

A microstructural investigation of Fe-oxides for developing high-temperature corrosion lifetime prediction models
(2026) Flora Alto, Alexandra
The aim of this study was to investigate the microstructure of oxide scales formed in environments relevant to biomass- and waste boilers used for superheater appli cations. It also investigated how KCl can a!ect both the corrosion kinetics and mi crostructure, specifically the characteristics of oxide grain boundaries. The obtained data provides insights into high-temperature corrosion and ultimately help improve high-temperature corrosion lifetime prediction models for superheater tubes. The study starts with a literature review about corrosion and analytical methods. To simulate the environment that exists for the superheater tubes of biomass- and waste power plants, the furnace’s environment was prepared to attain constant levels of the following: 20 % water vapor, 5 % O2 and 75 % N2 at 400 °C. Each exposure of the sample groups was performed according to four phases, namely sample prepara tion, exposure to simulation of the environment, preparation before SEM analysis, and SEM analysis. Results showed that pure Fe samples exposed longer to the simulated environment experienced the corrosion process to a greater extent, which results in a thicker ox ide scale on the Fe sample surface. In addition, KCl appears to have increased the corrosion rate, as demonstrated by the greater oxide scale thickness, the higher mass gain of the samples, and the observability of oxide grains after both exposure times. The combined use of SEM-EDS (EDX) made it possible to perform EDX mapping and EDX point analysis of the exposed samples. This facilitated the identification of the Fe sample surface, the Fe-rich oxide scales, and the KCl layer located on top of the oxide scales. The flat BIB milling technology implemented during sample preparation prior to SEM imaging enabled the identification and di!erentiation of oxide grains, BIB milling marks, and mechanical polishing scratches. This indicates that there is a need for improvement in the flat BIB milling technique, which could be achieved by testing variations in the accelerating voltage, the angle of incidence of the ion beam, and the flat BIB milling exposure time. In conclusion, the flat BIB milling method, when combined with SEM, has the potential to reveal oxide grains at the nanoscale, making the observation of these oxide grains in the oxide scale more accessible than with widely utilized conventional technologies. Nevertheless, this study also shows that the method requires further development. Therefore, future work should focus on optimizing the BIB parameters to achieve the best possible Fe surface finish. Lastly, exposure time and the presence of KCl appears to have a positive e!ect on the detection of oxide grains and the growth of the oxide scale on pure Fe samples.
Encapsulation of carbonic anhydrase in metal-organic frameworks to facilitate CO2 capture
(2026) Sjöstrand, Ellen
Reducing carbon emissions is crucial to stop global warming. The current methods to capture and store carbon dioxide are expensive and energy demanding. Therefore, a new technique using the enzyme carbonic anhydrase was evaluated in this project. Five protocols were tested to encapsulate SazCA, which is a carbonic anhydrase from the thermophilic bacterium Sulfurihydrogenibium azorense, in metal-organic frameworks (MOFs) called zeolitic imidazolate framework-8 (ZIF-8). Encapsulating enzymes in metal-organic frameworks has previously been shown to increase their reusability and thermostability. The enzyme was first produced through heterologous expression from Escherichia coli and purified with affinity chromatography. The MOF was then synthesized together with SazCA. It was confirmed through X-ray diffraction that two of the protocols were successful in producing pure SazCA@ZIF-8. The structure was then identified with scanning electron microscopy, which showed that the protocol with a ratio of 70:1 of the precursors 2-methylimidazole and zinc nitrate hexahydrate had particles with the most desirable cubical shape and were also mostly uniform in size. However, evaluation of the enzymatic activity with Wilbur-Anderson units assay after the encapsulation showed that it only reached about 2-5 % of the activity in free SazCA. This was shown to most likely partly be because the free zinc ions were inhibiting the enzyme. However, it was also shown that the activity improved with 122.41 % by introducing sonication, which increases the diffusion rate. Finally the thermostability was tested and compared to that of free SazCA at the temperatures 75, 85 and 95 ◦C for 1 and 4 hours. At 85 ◦C it was observed that the thermostability in the encapsulated SazCA was higher than in the free SazCA. After 1 h at this temperature the relative activity compared to the free SazCA was 11.85 ± 0.72 %, compared to 1.97 ± 0.30 %, which it was initially. In conclusion, even though the SazCA encapsulated in ZIF-8 lost most of its original activity, important design principles were identified, which could benefit future research within the field.
Evaluating the Performance of Transfer Function Models for Identifying Groundwater Disturbances in Infrastructure Projects
(2026) Alfredsson, Viktor; Blomquist, Ella
Hydrogeology is inherently challenged by the difficulty of making direct observa tions. To address this, numerical groundwater models are commonly developed to simulate hydrogeological conditions at specific study sites. However, such models require extensive input data and are often time- and resource-intensive. As a result, alternative, data-driven modeling techniques are of growing interest. This study evaluates the performance of a data-driven Transfer Function model in identifying and analyzing groundwater head disturbances caused by underground excavation activities. The transfer function model used for this project is the open-source Python package Pastas. Focusing on the Haga Station site within the Västlänken infrastructure project in Gothenburg, Sweden, the research compares transfer function models with a numerical benchmark model developed using MOD FLOW. Synthetic and constructed disturbance scenarios in the form of excavation shafts were modeled in the benchmark model to generate time series of groundwater head, leakage and infiltration. These time series were then used to test the transfer function model’s ability to detect controlled disturbances. To validate the results, a qualitative assessment was also performed using observed field data. The findings demonstrate that transfer function models developed using Pastas can replicate general groundwater trends and detect some disturbance signals. However, the models showed significant variation between different well simulations, with in consistencies in how disturbances were interpreted. Additional limitations include the overestimation of recharge and the underestimation of leakage into shafts fol lowing transfer function model calibration. Despite these challenges, the transfer function approach shows promise due to its low data requirements and its ability to model complex hydrogeologic study sites. This work contributes to a better under standing of transfer function model capabilities and their potential application in hydrogeological assessments of infrastructure projects.
Study of the Effect of Impurities from Nuclear Fuel Reprocessing on the Neutronics of a Fast-Spectrum Generation IV Nuclear Reactor
(2026) Ndulue, Hazel
Green, sustainable, and clean are ubiquitous terms in modern energy discourse, yet their meaningful realization remains a profound challenge. Throughout history, electrification has been a catalyst for human progress—symbolizing not only access to dignity but also the foundation for economic and intellectual growth. While renewable energy sources dominate global decarbonization strategies, nuclear power currently offers the most reliable and scalable pathway to large-scale emissions reduction. However, its full sustainability is constrained by persistent concerns across the nuclear fuel cycle, particularly the long-term radiotoxicity and heat generation of spent nuclear fuel. Closing the fuel cycle is therefore central to aligning nuclear energy with the United Nations Sustainable Development Goal 7—“ensure access to affordable, reliable, sustainable, and modern energy for all”—by addressing both resource conservation and intergenerational equity. This master’s thesis investigates one crucial dimension of that challenge: the impact of reprocessinginduced impurities on the neutronic behavior of sodium-cooled fast reactor fuel assemblies, with a focus on the SPX Superphénix reference design. Building on the CHALMEX separation process and the internal gelation route for fuel fabrication, the work examines how residual actinides, fission products, and trace elements carried over from reprocessing alter the final fuel composition and performance. A literature review is combined with microscopic cross-section analysis of selected impurities using the OECD/NEA JANIS database. Lattice depletion and branch calculations are then performed with the Monte Carlo code Serpent 2 on SPX-type assemblies, with and without impurities, to quantify their effects on reactivity coefficients, neutron flux distributions, absorption behavior, and burnup characteristics. By identifying tolerance thresholds and impurity-driven deviations in key neutronic parameters, this thesis assesses the operational viability of reprocessed fuels and proposes directions for optimizing separation and fabrication processes. The results support the safe, efficient, and genuinely sustainable deployment of Generation-IV fast reactors within a closed fuel cycle framework, contributing evidence-based insights for future reactor development and fuel cycle strategies. i
Design Features and Clinical Considerations of Orthopedic Knee Rehabilitation Exoskeletons: A Systematic Literature Review and Analysis
(2026) Wei, Zikun
As rehabilitation robotics expands from neurorehabilitation to orthopedics, the biomechanical suitability of existing devices remains unclear. This paper systematically reviews 57 wearable knee exoskeletons (2015–2025) to evaluate their clinical compatibility. It highlights the critical design divergence between the “repurposing strategy” of neuro-derived systems and the “specialized design philosophy” of orthopedic-specific solutions. Using a novel five-dimensional evaluation framework, this study reveals a significant design "mismatch." While systems relying on a generalist, neuro-adapted approach offer advanced control, their architectures often lack the kinematic compatibility and structural support required for vulnerable orthopedic joints. In contrast, "specialized" designs have seen explosive growth, prioritizing unilateral modularity and anatomical protection. However, a "valley of death" persists in translational research: over 60% of orthopedic-specific devices remain at Technology Readiness Level (TRL) 4, failing to reach clinical patient trials. The study concluded that most current cases of transplanting neurological rehabilitation equipment for orthopedic use cannot address the specific needs and limitations of orthopedics. Future development should adopt an "orthopedic-first" philosophy— prioritizing multi-DOF stability, modular adaptability, and pain-aware control. These shifts are imperative to reduce adverse events and optimize treatment outcomes in orthopedic rehabilitation. In addition, another systematic review should be conducted on mature and cuttingedge neurosurgical exoskeletons that do not claim to include orthopedic rehabilitation functions to analyze their potential to meet orthopedic rehabilitation needs.