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Investigating Quasiparticle Interactions in the Far-Infrared
(2026) Anders, Daniel
This dissertation investigates ultrafast charge-carrier dynamics and quasiparticle interactions in semiconductors using terahertz (THz) spectroscopy. The THz spectral range provides direct access to low-energy excitations such as intraexcitonic transitions and free-carrier dynamics, making it a powerful probe of many-body interactions in photoexcited semiconductor systems. Using optical pump–terahertz probe spectroscopy and broadband THz emission measurements, several aspects of carrier dynamics in bulk and low-dimensional semiconductors are explored. First, broadband and gapless THz radiation is generated in bulk germanium via phase-controlled quantum interference currents driven by two-color optical excitation. This approach enables efficient emission across the entire THz spectral range and provides insight into the underlying photocurrent generation mechanisms. The dissertation further investigates the formation dynamics of excitons in (Ga,In)As multi-quantum wells following nonresonant optical excitation. Time-resolved THz spectroscopy reveals that excitons emerge from an initially created electron–hole plasma on two distinct timescales: a fast component of approximately 10 ps and a slower component of about 250 ps. By introducing a differential probing method based on weak and strong THz fields, the longstanding discrepancy in reported exciton formation times is resolved. In addition, the interaction of incoherent excitons with an additional electron–hole plasma is studied using a double optical pump–THz probe scheme. The results show that elastic and inelastic scattering processes are governed primarily by the excess energy of the additional carriers rather than their density. Despite excitation energies exceeding the exciton binding energy, inelastic scattering occurs only when suitable final states are available, consistent with predictions from Fermi’s golden rule. The screening of excitonic states by additional charge carriers is investigated by monitoring the transient shift of the intraexcitonic 1s–2p transition. The measurements provide direct access to the time-dependent exciton binding energy and reveal that the screening strength scales linearly with carrier density while the screening time is determined by the carrier excess energy. Finally, transient excitonic states induced by intense optical fields are demonstrated. Detuned optical excitation produces short-lived excitonic resonances that exist only during the temporal overlap of pump and probe pulses and manifest as blue-shifted THz absorption features. Together, these results provide new insight into ultrafast exciton formation, many-body interactions, and THz generation mechanisms in semiconductor systems, highlighting the capabilities of terahertz spectroscopy as a powerful tool for probing quasiparticle dynamics in condensed matter.
Fighting Poverty with Sheep in Armenia: The Role of Hope
(2026) Weichbrodt, Louisa Joline
Half of the world's population lives in poverty, yet eradicating poverty remains the first Sustainable Development Goal by 2030. Studies evaluating poverty traps and livestock often overlook the role of hope in their analyses, a factor that has recently been recognised as vital in combating poverty. Non-Governmental Organisations implement livestock transfer projects to help families escape poverty and restore hope. To understand the role of hope in these projects, a qualitative approach with interviews was employed, combined with observations of multidimensional poverty indicators to reveal participants' experiences of hope and changes in poverty. The study found that hope is essential for participants' responses to the project and, consequently, supports their exit from poverty. Levels of hope significantly influence perceptions and in turn, actions during participation. Moreover, individual hope was enhanced through livestock transfers, affecting goals, mood, and perception of the future. Subtle changes in multidimensional poverty related to housing and health expenditure planning were also observed. Additionally, development projects can nurture hope by improving mental health, addressing multiple dimensions of poverty, and actively supporting participants' aspirations. Policies can influence both external and internal constraints on poverty and foster hope: firstly, by providing structural grounds for hope; secondly, by informing about available opportunities; and thirdly, by encouraging and supporting aspirations. The government can use policies to promote hopefulness. The fact remains that people living in poverty are not necessarily hopeless. Further research could offer quantitative insights into hope within development contexts. Overall, recognising the role of hope is crucial for designing holistic and effective development projects.
Trafficking and Sorting of Proteins to the Parasitophorous Vacuolar Membrane of Plasmodium falciparum: PfEXP1 as a Model
(2026) Abbasi, Amin
During the asexual blood stage of malaria infection, Plasmodium falciparum develops inside a membrane-bound compartment within the host red blood cell. The membrane surrounding this compartment, the parasitophorous vacuolar membrane (PVM), forms an important interface between parasite and host cell. In addition to exporting soluble effector proteins, the parasite must also direct a specific set of membrane proteins to the PVM. PfEXP1 is a well- established membrane protein of the PVM, but the sequence features that govern its trafficking to this membrane remain unclear. The aim of this thesis was therefore to identify PfEXP1 sequence features that contribute to its targeting to the PVM. To address this question, a panel of plasmid-expressed PfEXP1 variants was generated and analyzed by immunofluorescence microscopy in two parasite developmental stages. In parallel, a biochemical fractionation assay was used to compare whether the different variants behaved mainly as soluble or membrane-associated proteins. Across the construct panel, distal C-terminal truncations generally retained PVM-like localization under the assay conditions used. These variants showed staining patterns consistent with PVM localization and were enriched in the membrane-associated fraction, suggesting that they remained capable of stable membrane association. This indicates that the distal C-terminus is not a dominant determinant of this behavior. In contrast, disruption of the N-terminal region more often resulted in less distinct localization and weaker biochemical evidence for stable membrane association. The transmembrane domain replacement experiments further showed that not all membrane anchors behaved in the same way. Constructs combining the PfEXP1 N-terminal region with a parasite-derived transmembrane segment were more often consistent with PVM-like localization, whereas constructs containing artificial hydrophobic helices did not reproduce clear PVM localization even when flanked by PfEXP1-derived N- and C-terminal regions. These findings argue against a model in which hydrophobicity alone is sufficient for correct targeting. An important limitation of this study was the unexpected predominantly soluble behavior of the exogenous full-length PfEXP1 reference construct, indicating that construct architecture, including tag and linker context, can substantially affect the experimental readout. Taken together, the data support a model in which correct PfEXP1 targeting depends on N-terminal context acting together with an appropriate membrane anchor, whereas the distal C-terminal region appears broadly dispensable in this assay context. More broadly, this work highlights the need for follow-up experiments that directly resolve protein topology, particularly protease- protection assays.
Essays on Monetary Policy, Non-Bank Financial Intermediation and Financial Stability
(2025) Tiza Mimun, Anisa
This dissertation provides an empirical examination of the relationship between monetary policy and non-bank financial intermediaries, commonly referred to as nonbanks.
Microbiological and physical properties of biofilm-active PMMA bone cements in arthroplasty
(2026) Humez, Martina Anneliese
Periprosthetic joint infection (PJI) remains one of the most serious complications in arthroplasty, associated with high morbidity, mortality, and substantial socioeconomic burden. Antibiotic‑loaded bone cements (ALBCs) play a central role in both the prevention and treatment of PJI. In primary arthroplasty, they enable high local antibiotic concentrations at the implant-tissue interface, reducing early bacterial adhesion and lowering infection risk. In revision surgery, especially for established infection, ALBCs facilitate targeted antimicrobial delivery as cement spacers, while simultaneously providing mechanical stability for temporary or definitive fixation. Despite decades of clinical experience with ALBCs, fundamental questions remain incompletely understood: the selection of the most appropriate antimicrobial drugs for admixing to acrylic bone cements, pharmacokinetic carrier elution aspects, cement matrix interactions, antibiotic admixing methodology, and antibiotic dose limitations. Furthermore, it is not clear to which extent laboratory experiences can be transferred to the clinical setting. These knowledge gaps are particularly relevant in the context of rising antimicrobial resistances, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin‑resistant enterococci (VRE), for which therapeutic options are increasingly restricted. This cumulative dissertation integrates material science, microbiology, and translational in-vivo modelling to advance the evidence-based use of ALBCs in arthroplasty and revision surgery. Across four studies, the work systematically examines (i) the feasibility of formulating novel daptomycin-loaded poly-methyl-methacrylate (PMMA) cements for PJIs caused by vancomycin-resistant bacteria, (ii) the mechanical, chemical, and kinetic consequences of manual antibiotic admixing, (iii) the impact of the cement matrix on antibiotic release and long-term antimicrobial activity, and (iv) the translational antimicrobial efficacy of commercial single antibiotic-loaded bone cements (SALBCs) and dual-antibiotic loaded bone cements (DALBCs) in a validated Galleria mellonella implant infection model. A fifth investigation, presented at the EBJIS (European Bone & Joint Infection Society) congress and published as abstract, proposes an optimal daptomycin dosage and suitable PMMA cement matrix for spacer applications using the Galleria mellonella biofilm model. The results demonstrate that acrylic bone cements are not interchangeable materials: the polymer composition and additives, hydrophilicity, viscosity, sterilisation method and manufacturing process collectively determine the antibiotic elution, antimicrobial efficacy and mechanical stability. DALBCs consistently outperformed SALBCs in infection prevention, achieving superior antibiofilm effects, and providing markedly increased survival in larvae infected with multi-drug-resistant Staphylococcus aureus and Enterococcus faecalis. High local antibiotic concentrations generated by antibiotic elution from acrylic bone cements were able to overcome resistance phenotypes, emphasising the unique pharmacodynamic environment of ALBC. Systematic evaluation of manual admixing revealed that dry mixing of the powder in cartridge mixing devices did neither improve mechanical stability nor antibiotic release. It generated abrasive plastic debris capable of embedding into the cement highlighting previously unrecognised risks. Fractionated bowl mixing was identified as the only safe and reproducible preparation method when manual admixing is unavoidable. Cement brand was found to be a dominant predictor of antibiotic release, with the polymer composition in Palacos® cements consistently outperforming the one in Simplex® cements across all antibiotics tested. Finally, integrating in-vitro release kinetics with the Galleria mellonella biofilm model enabled the identification of 1.5 g daptomycin per 40 g PMMA (Palacos® R+G and Simplex® T) as the optimal risk-benefit balance between antimicrobial efficacy and mechanical integrity for cement spacers in VRE caused infections. In summary, this thesis provides a comprehensive evidence base for the rational selection, mixing, and clinical application of ALBCs. It clarifies the material dependent performance and establishes best‑practice standards for manual admixing, validates an efficient in-vivo screening platform for cement performance, and supports the development of future daptomycin-loaded DALBC formulations capable of addressing the growing challenge of multi-drug-resistant PJI. These results are of high clinical relevance for surgeons who deal with these difficult-to-treat orthopaedic infections.