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Lipoate protein ligase A : a self-assembling protein with diverse catalytic functions for biological applications
No full textA block householder based algorithm for the QR decomposition of hierarchical matrices
No full textThis thesis introduces a new approach to compute QR factorizations of hierarchical matrices using block Householder transformations and a newly developed implicit storage scheme for them. The algorithm and the analysis of its numerical cost track low-rank factorizations in intermediate results. Numerical tests on several types of square matrices like 2D Laplacian boundary element matrices and different RBF kernel matrices show a good performance, although the algorithm struggles with rectangular matrices. A version of the H-LU decomposition is also implemented, demonstrating potential benefits.Diese Dissertation stellt einen neuen Ansatz zur Berechnung von QR-Faktorisierungen hierarchischer Matrizen vor, der Block-Householder-Transformationen und ein dafür neu entwickeltes implizites Speicherschema nutzt. Der Algorithmus und die nachgelagerte Abschätzung der numerischen Kosten verfolgen, in welchen Zwischenergebnissen Niedrigrang-Faktorisierungen möglich sind. Numerische Tests (u.A. an 2D Laplace BEM-Matrizen und RBF-Interpolationsmatrizen) zeigen eine gute Leistung, obwohl der Algorithmus bei rechteckigen Matrizen Schwierigkeiten hat. Eine neue Version der H-LU-Zerlegung ist ebenfalls implementiert
Domain of one’s own: learning scholarly writing and publishing with Zotero, Quarto and Hypothesis
No full textIn the age of AI, new approaches are required to encourage students to develop critical reading and writing skills, as well as a scholarly attitude. In the “Introduction to Information Technology” course for vocational school education students, a socio-technical environment was introduced for writing blog articles, with ongoing feedback from the group and teacher
Rapid multi-criteria screening of energy-integrated distillation processes for nonideal mixtures
No full textSeveral thousand distillation columns are industrially employed for various separations, accounting for a substantial share of the industrial energy demand. In order to reduce their energy requirements various means for energy integration, such as direct heat integration, multi-effect distillation, thermal coupling, or vapor recompression can be applied. Considering these options and combinations of these, several hundred possible process configurations can be designed even for separations into three product streams, while the choice for a best option depends strongly on the specific separation task and system properties. In order to enable a reliable case-specific evaluation, which avoids simplified heuristics or simplified thermodynamics, this article presents a computationally efficient, algorithmic framework for a multi-criteria evaluation of more than 750 energy-integrated distillation sequences for multicomponent separations in three product streams. The framework employs thermodynamically sound pinch-based shortcut models that do not rely on constant relative volatility and constant molar overflow assumptions, making it applicable to nonideal and azeotropic mixtures. Based on the minimum energy duties and the respective flowsheet information, classical estimation methods for equipment sizes, operating costs, and capital investment, are employed. Several case studies demonstrate the framework's applicability to azeotropic systems, its computational efficiency benefits that enable performing sensitivity analyses for varied process, thermodynamic, and economic scenarios
Automatic security-flaw detection - towards a fair evaluation and comparison
No full textThreat Modeling is an essential step in secure software system development. It is a (so far) manual, attacker-centric approach for identifying architecture-level security flaws during the planning phase of software systems. In recent years, academia has presented ideas to automate threat detection that do not focus on a particular class of security flaws but offer means of pattern-based security flaw descriptions. However, comparing presented ideas (tools) for automated threat detection contains the potential for unwilling bias or restricted information content. In this work, we investigate the process of comparing automatic security flaw detection tools, clarify common pitfalls during this process, and propose a fair, reproducible, and informative comparison approach to be used as a community standard. We additionally discuss the necessary steps for the community to effectively implement this approach and support improved comparisons and evaluations in the future. We use a previously published case study to determine problems with current comparison techniques and classify different levels of comparison to be used for future reference as our main contribution. As a consequence, we propose using a model-based approach for specifying security flaws and apply an existing natural language-based catalogue to this model-based approach. Furthermore, we introduce an inspection process model (for providing a standard to specify findings of a threat detection process) to streamline the evaluation and comparisons of automatic security flaw detection tools. We provide an exemplary evaluation of this detection guideline and inspection process model along the lines of both automatic approaches from the original case study. All artefacts of the work are publicly available to support the research community and to create a common baseline for future tool comparisons
Magnetic Resonance Imaging of Structured Packings: Overcoming Spatial, Signal, and Geometric Challenges
No full textStructured packings are widely employed in trickle beds to improve the mass transfer between the liquid and gas phases in absorption and distillation processes. While integral experiments, such as pressure drop measurements and collector experiments, offer overall insights, they lack spatial and temporal detail on liquid distribution. Magnetic Resonance Imaging (MRI) overcomes this by providing resolved flow visualization, though its application is challenged by low liquid content, the need for high temporal resolution, and difficulty achieving spatial resolution on the order of hundreds of micrometers with large-bore scanners. These issues are mitigated through optimized imaging sequences, doped aqueous solutions, and tailored radiofrequency coils, enabling MRI to deliver detailed insights into liquid behavior and packing efficiency.
All experiments were conducted with a 3 Tesla vertical large-bore MRI system with the ability to measure samples with a height of several meters. The trickle bed included a one meter structured packing bed with a diameter of 54 mm. 3D-printed corrugated sheet packings (480 m²/m³) were studied under varying gas and liquid loadings. To shorten T₁ relaxation time to 50 ms and match the magnetic susceptibility of the gas phase, which is air, the aqueous solution was doped with 16.27 mM dysprosium(III) nitrate and 1 mM gadolinium(III) chloride. The liquid distribution was measured using a gradient echo imaging sequence. Two coil designs were compared, the system-integrated Transmit - Receive bird cage body coil and a tailored single-channel surface coil.
The coils were compared with regard to signal-to-noise ratio (SNR) and spatiotemporal resolution. Unlike the body coil, which suffers from low spatial resolution and long acquisition times, the single-channel coil enables significantly higher spatiotemporal resolution (Fig. 1). The shortened T1 relaxation times allow faster signal recovery, enabling higher temporal resolution. Using a single-channel coil, doped aqueous solution, and gradient echo sequence enables MRI with spatial resolution up to 0.25 × 0.25 × 0.3 mm³. Combining data from partially and fully filled packings (Fig. 1) enables differentiation of liquid, gas, and structured packing, allowing the determination of the gas-liquid interfacial area, which is critical for the separation efficiency. MRI-derived maldistribution factors were validated against collector experiments at the column bottom, demonstrating good agreement.
This study shows the use of MRI for temporally and spatially resolved measurements of liquid distribution in structured packings within trickle beds. A tailored surface coil, doped aqueous solutions, and optimized imaging enabled high-resolution imaging. MRI allows to distinguish between gas, liquid, and packing phases, enabling the determination of the gas–liquid interfacial area. The comparison with collector experiments showed good agreement, with MRI offering enhanced insight along the column height and improved radial resolution
Non-destructive assessment of strain and mechanical fatigue in neat and glass fibre-reinforced epoxy via NIR spectroscopy
No full textIn this study, changes in the near-infrared (NIR) spectrum in neat epoxy and glass fibre-reinforced plastic under tensile stress and cyclic fatigue loading are investigated. Specimens were fabricated using resin transfer moulding. During mechanical testing, NIR spectra were collected at regular intervals, enabling monitoring of characteristic absorption bands. Results demonstrate that both material systems show measurable and reproducible shifts in the wavenumber of the absorbed light in specific NIR bands as a function of applied mechanical load. These shifts closely track the progression of damage accumulation, particularly in the context of mechanical fatigue. Overall, the findings underscore the potential of NIR spectroscopy as a powerful, non-destructive, in-situ monitoring tool for assessing the integrity and damage evolution of fibre-reinforced plastic under mechanical stress. This approach provides valuable insights for the development of advanced structural damage monitoring systems and contributes to improving the safety and reliability of composite materials in engineering applications
Development and validation of a novel stenosis model for percutaneous transluminal angioplasty training of the internal carotid artery
No full textIntroduction/Background: The rising demand for endovascular stroke therapy highlights the need for standardized training environments. Studies have shown the positive impact of simulator-based training for neurointerventional procedures. Given the frequent use of percutaneous transluminal angioplasty (PTA) of the internal carotid artery (ICA) in acute settings, specialized simulation training is crucial. This study evaluates the feasibility of a custom-made ICA stenosis model for PTA simulation. Methods: Internally developed 3D-printed circular clamps were attached to patient-based 3D printed ICA models and integrated into a previously described realistic whole-body neurovascular simulation model HANNES (Hamburg Anatomic Neurointerventional Endovascular Simulator) to simulate a proximal ICA stenosis. Participants (N = 5) of varying experience levels each performed three PTA procedures. Fluoroscopy time, radiation doses, and the extent of stenosis and balloon inflation pressure were assessed. After simulation, participants rated the model in terms of haptic, feasibility and applicability. Results: For statistical analysis, the participants were divided into two groups according to their experience level. There was a statistically significant difference in the procedure duration between both groups, U = 10.500, Z = −1.968, p < 0.05. Significant test results could also be demonstrated for radiation doses (DAP) among groups, Kolmogorov-Smirnov p < 0.05, U = 7.000, Z = −2.357, p < 0.05. No difference was shown between the total contrast volume (ml) among groups that was used during procedures (m = 11.67, SD 2.09). Conclusion: The authors propose a novel ICA stenosis simulation model for training of the cervical PTA. The model provides a realistic and replicable method for standardized procedural training