http://hdl.handle.net/10900/42133 2026-07-27T18:21:10Z http://hdl.handle.net/10900/181882 The Sun as an X-ray Star: Spectral Models of Solar Coronal Regions and Their Application to Stellar Coronae Joseph, Wilhelmina Maryann Understanding stellar coronae requires connecting the integrated X-ray emis- sion I observe from unresolved stars to the physical magnetic structures pro- ducing that emission. The Sun uniquely enables this connection: I can ob- serve both its spatially resolved coronal structures and its integrated X-ray spec- trum as it would appear from a stellar distance. This dissertation develops a new implementation of the "Sun as an X-ray Star" (SaXS) methodology that di- rectly retrieves the surface coverage (filling factors) of different coronal region types—background corona, active regions, cores, and flares—from X-ray spec- tral fitting. I construct spectral models for XSPEC from emission measure distributions derived from Yohkoh observations of solar coronal regions. Each region type becomes a multi-temperature model with fixed temperature structure and free normalization corresponding to its projected surface area. This direct fitting ap- proach eliminates the computational overhead of synthetic spectral grids while providing transparent physical interpretation: fitted normalizations immedi- ately yield filling factors without intermediate parameter-space matching. I validate the method on the Sun itself using full-disk soft X-ray spectra from the DAXSS (Dual Aperture X-ray Solar Spectrometer) CubeSat instrument at two activity levels. Comparing spectral-fit-derived filling factors with the actual spatial distribution visible in contemporaneous Hinode/XRT images demon- strates that the method successfully recovers known coronal structure. The qui- escent Sun shows ∼21% active region coverage (with refined fits using variable abundances), while flaring periods show ∼15% active region coverage, ∼3% core coverage, and ∼0.07% flare coverage (with refined fits using variable abundances and non-equilibrium ionization for flares). Spectral filling factors systematically exceed image-based measurements because spectra naturally in- clude limb emission extending to coronal scale heights, providing a more com- plete picture of total coronal output as seen from stellar distances. Application to AD Leo, a nearby active M3.5V dwarf, reveals both capa- bilities and limitations of solar-derived templates. During quiescent periods, the corona appears dominated by hot cores with significant background but minimal active region contribution, suggesting either fundamentally different magnetic structures or templates that incompletely capture stellar active re- gions. The star exhibits continuous low-level flaring even in nominally qui- escent phases. The spectacular November 2021 "November 2021 Great Flare" (GOES X1445 equivalent) produces systematic high-energy residuals: even our hottest solar flare template (X9.0, ∼30 MK) cannot reproduce emission above 2–3 keV. Adding thermal components reaching several tens of MK eliminates residuals, demonstrating that AD Leo’s superflares produce plasma significantly hotter than any solar analog. This analysis reveals a fundamental degeneracy in X-ray spectral analysis: for fixed emission measure, electron density and filling factor trade off (EM ∝ n2 e f ). Initial density estimates from literature extrapolation yielded unphysi- cally small filling factors, requiring iterative density refinement constrained by the requirement that regions occupy at least one coronal loop’s projected area. Breaking this degeneracy definitively requires independent density measure- ments from high-resolution spectroscopy, underscoring the importance of com- plementary observations for future applications. The dissertation establishes that solar-derived spectral models can charac- terize stellar coronae in terms of physical magnetic structures, validates the filling factor retrieval methodology through direct comparison with spatially resolved solar observations, and identifies critical limitations—particularly the need for expanded emission measure libraries extending to super-solar temper- atures and independent density constraints—that must be addressed for robust application to active stellar populations. 2026-07-27T00:00:00Z http://hdl.handle.net/10900/181865 Investigating the Factors Affecting Endotoxin Masking in Human Blood Plasma: Internal and External Contributions Burgmaier, Luisa Endotoxin detection is essential for pharmaceutical safety and clinical diagnostics, but remains challenging due to interference with formulation components and biological matrices. This thesis investigates factors affecting detection, focusing on storage conditions, the effect of lipopolysaccharide (LPS) structural variants on low endotoxin recovery (LER), and masking mechanisms in human plasma. First, the influence of container materials on (1→3)-β-D-glucan (BDG) recovery was assessed, as BDG interferes with endotoxin measurements by falsely activating the Limulus amebocyte lysate (LAL) cascade via factor G. While short-term storage had no effect, long-term storage at -20°C reduced recoveries, especially in polyethylene containers. This highlights the importance of storage material selection for reliable BDG detection. Next, the effect of LPS structural diversity on endotoxin masking was analysed using rough LPS mutants (Ra – Re) from S. minnesota and E. coli. Polysaccharide length influenced masking susceptibility: rough mutants, with a lower hydrophilic/hydrophobic ratio and stronger negative charge, showed greater resistance to masking due to enhanced cation binding and stabilised supramolecular structures, resulting in higher recovery rates. Masking kinetics varied between detection systems, with LAL and recombinant Factor C (rFC) assays showing similar masking behaviour, while the Monocyte Activation Test (MAT) showed improved recovery. Finally, endotoxin detection in human blood was investigated, where plasma proteins contribute to masking. While previous research has emphasised electrostatic interactions, this study found that highly charged LPS structures, such as Re LPS, are less susceptible to masking, suggesting additional contributing factors. Overall, this dissertation advances the understanding of endotoxin masking, structural influences on detection and external factors affecting test reliability. These findings will help to optimise endotoxin testing, reduce false negatives and improve pharmaceutical and clinical safety. 2026-07-27T00:00:00Z http://hdl.handle.net/10900/181863 Crop Husbandry and Storage Practices in the Bronze and Iron Age Levant: Diversification between Coastal and Inland Regions Demeulenaere, Eline Agriculture played a central role in Levantine societies during the Bronze and Iron Age (ca. 3700-332 BCE), providing food security and enabling surplus production that supported social organization and trade. Agricultural strategies were shaped by the region’s diverse environments and climates, influencing crop choices and land use. Archaeobotany, which analyzes preserved plant remains, provides evidence to reconstruct crop husbandry, storage practices, and human-plant interactions. While this field has significantly advanced understanding of Levantine Bronze and Iron Age crop husbandry, some challenges and gaps still remain. This dissertation investigates crop husbandry and storage practices across the Levant using new archaeobotanical data from Kamid el-Loz, Tel Kinrot, Tel Lachish, Tel Dan, and Tel Dor, combined with comparative datasets based on ADEMNES. Multivariate statistical analyses are used to identify regional and chronological shifts in crop patterns, with particular attention to differences between inland and coastal regions, and their link to environmental and socio-political influences. The results indicate a stable core set of crops, primarily cereals, pulses, and fruits, alongside notable chronological and regional variation. A key chronological shift is the transition from hulled to free-threshing wheat between the Bronze and Iron Age, which likely reflects changing political and economic conditions. Regional differences are also evident. Inland areas tended to focus on cereal-pulse agriculture, whereas coastal regions placed additionally greater emphasis on fruit cultivation, particularly olives and grapes. In the northern Levant, agriculture centered on cereals and pulses, while in the southern Levant fruit trees and flax played a more prominent role. Most central Levantine sites align with the southern Levantine pattern, with Kamid el-Loz, an inland site, standing out as an exception. These patterns can be linked primarily to environmental factors, but in some cases also to economic and political influences. Storage practices formed a fundamental component of crop husbandry. Archaeobotanical evidence suggests that cereals were often stored in large communal facilities, pulses in household-level containers, and fruits mainly in processed forms such as oil or wine. These patterns underscore the importance of storage for surplus management, redistribution, and integration into urban and administrative networks. The similarity of chronological and regional trends observed in both storage and non-storage datasets indicates that environmental variables, particularly rainfall and elevation, played a key role in shaping both crop selection and storage strategies, alongside socio-political and economic factors. Overall, the study demonstrates that Levantine agriculture was in a way constant but also dynamic and adaptive, shaped by environmental conditions, economic networks, and political change. By integrating new archaeobotanical data with comparative datasets, it contributes to a more nuanced understanding of agricultural strategies, storage systems, and daily life in the ancient Levant.; Die Dissertation ist gesperrt bis zum 15. Juli 2027 ! 2027-07-15T00:00:00Z http://hdl.handle.net/10900/181845 Scandium Methyl and Methylidene Complexes Zug, Gernot T. L. Synthesis and characterization of scandium methyl and methylidene complexes as well as lanthanide phenyl complexes.; Die Dissertation ist gesperrt bis zum 30. Juni 2027 ! 2027-06-30T00:00:00Z