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Aktuellste Veröffentlichungen

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    KI-Systeme instrumentell verstehen
    (2026) Mann, Sara; Schmidt, Eva; Kästner, Lena
    Viele moderne KI-Systeme sind epistemisch opak. Das Forschungsfeld der erklärbaren KI (XAI) versucht, diese Opazität durch die Entwicklung von Erklärbarkeitsmethoden zu reduzieren und relevante Aspekte von KI-Systemen für verschiedene Stakeholder verständlich zu machen. Häufig wird angenommen, dass das resultierende Verstehen als Mediator zwischen Erklärbarkeit und der Erfüllung gesellschaftlicher Desiderata (z.B. Fairness von KI, Wahrung menschlicher Verantwortlichkeit bei KI-gestützten Entscheidungen) fungieren kann. Doch bleibt in der XAI-Literatur weitestgehend offen, worin dieses Verstehen besteht und wie es seiner Mediatorrolle gerecht werden kann. Diese Dissertation entwickelt mithilfe von Conceptual Engineering und auf Grundlage aktueller erkenntnis- und wissenschaftstheoretischer Debatten einen kontextsensitiven Verstehensbegriff, der speziell auf erklärbare KI zugeschnitten ist und die behauptete Mediatorrolle von Verstehen in XAI-Kontexten erklärt. Das entscheidende Merkmal dieses Verstehens ist sein zweckgerichteter Charakter: Es dient der Erfüllung legitimer gesellschaftlicher Desiderata und heißt daher „instrumentelles Verstehen“. Instrumentelles Verstehen wird durch zwei notwendige und zusammen hinreichende Bedingungen definiert. Diese verlangen ein gerechtfertigtes, moderat faktives Überzeugungssystem über systembezogene Aspekte sowie das Verfügen über verstehensbezogene Fähigkeiten und berücksichtigen den Einfluss mehrerer Kontextfaktoren. Weiterhin argumentiert diese Arbeit, dass so genannte „Exemplare“ besonders vorteilhafte Mittel sind, um instrumentelles Verstehen zu erwerben. Exemplare zeichnen sich dadurch aus, dass sie kontextuell relevante Aspekte exemplifizieren und besonders leicht zu interpretieren sind. Der Begriff instrumentellen Verstehens konkretisiert ein wichtiges epistemisches Ziel in XAI-Kontexten. Exemplare bieten wiederum einen Ausgangspunkt, um XAI-Erklärungen und andere Verstehensermöglicher in Hinblick auf ihre Eignung für den instrumentellen Verstehenserwerb zu evaluieren.
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    Glycerol-mediated improvement of heterologous aurachin D production in E. coli
    (Springer Science and Business Media LLC, 2026-05-30) Korb, Jonas; Demir, Büsra; Graw, Kai; Nett, Markus
    Neglected tropical diseases and the increasing prevalence of antibiotic resistance in nosocomial infections represent a major challenge in medicine. Intensive research into bioactive compounds has identified the myxobacterial natural product aurachin D as promising drug candidate due to its potent antibiotic and antiprotozoal properties. The biosynthesis of aurachin D from 2-methyl-1H-quinolin-4-one (MQO) is catalyzed by the membrane-bound farnesyltransferase AuaA. Recently, this enzymatic conversion was reconstructed in the heterologous host Escherichia coli, yielding an aurachin D titer of 17 mg L−1. In this study, we investigated the influence of the medium on aurachin D biosynthesis in E. coli in order to improve the product titer. Our analyses revealed that the glycerol concentration has a major impact on both the growth of the production host and the biocatalytic formation of aurachin D. After switching to a glycerol-based minimal medium and adjustment of the MQO precursor concentration, an aurachin D titer of 124 mg L−1 was achieved in a microbioreactor system, highlighting the superior performance of minimal over complex medium as well as the beneficial effect of glycerol compared to glucose. Further studies were conducted to elucidate the mechanism underlying glycerol’s effects. While improved growth and substrate solubilization were found to be insignificant for increasing the product titer, it was demonstrated that glycerol supplementation positively influenced the expression of the enzyme AuaA. Using a folding reporter, we were able to show that the availability of correctly folded AuaA increased until growth defects of the host, presumably resulting from osmotic stress, began to appear. Key points • Product toxicity is negligible in the production of aurachin D using E. coli • The media supplement glycerol improves the availability of the enzyme AuaA • Aurachin D titers increase after switching to a minimal medium
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    In situ observation of the pore formation during laser-based reactive air brazing of alumina
    (Springer Science and Business Media LLC, 2024-03-16) Wojarski, Lukas; Ulitzka, Henrik; Geldmacher, Anna; Ulitzka, Tim; Tillmann, Wolfgang
    Reactive air brazing (RAB) is a low-cost process for joining ceramic composites in air. However, due to the comparably low strength values that can be achieved by RAB, the process is only used in special applications like solid oxide fuel cells as a sealant. The limited strength values are the result of a severe pore formation during the brazing operation that remain in the brazing fillet after the solidification of the brazing filler. In this work, the formation of the pores during RAB brazing of alumina using a paste containing Ag4CuO powder and various binders was investigated. The formation and evolution of the pores were observed and quantified in in situ X-ray measurements. It could be observed that during debinding, pores have developed in the filler metal. The pore structure depends on the binder and the heating rate in the debinding stage. With the melting of the filler metal, many pores are closed by the melt flow. But it seems that the wetting of the alumina was hindered by the pores. The change of porosity during cooling is comparatively low.
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    Integer optimal control with fractional perimeter regularization
    (Springer Science and Business Media LLC, 2024-07-01) Antil, Harbir; Manns, Paul
    Motivated by many applications, optimal control problems with integer controls have recently received a significant attention. Some state-of-the-art work uses perimeter-regularization to derive stationarity conditions and trust-region algorithms. However, the discretization is difficult in this case because the perimeter is concentrated on a set of dimension d - 1 for a domain of dimension d. This article proposes a potential way to overcome this challenge by using the fractional nonlocal perimeter with fractional exponent 0 < α < 1 . In this way, the boundary integrals in the perimeter regularization are replaced by volume integrals. Besides establishing some non-trivial properties associated with this perimeter, a Γ-convergence result is derived. This result establishes convergence of minimizers of fractional perimeter-regularized problem, to the standard one, as the exponent α tends to 1. In addition, the stationarity results are derived and algorithmic convergence analysis is carried out for α ∈ (0.5, 1) under an additional assumption on the gradient of the reduced objective. The theoretical results are supplemented by a preliminary computational experiment. We observe that the isotropy of the total variation may be approximated by means of the fractional perimeter functional.
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    Non-local synchronization of continuous time crystals in a semiconductor
    (Springer Science and Business Media LLC, 2026-07-22) Greilich, Alex; Kopteva, Nataliia E.; Korenev, Vladimir L.; Haude, Philipp A.; Kunze, Linus; Grobecker, Ben W.; Anghel, Sergiu; Betz, Markus; Bayer, Manfred
    Synchronization resulting in unified collective behavior of the individual elements of a system that are weakly coupled to each other has long fascinated scientists. Examples range from the periodic oscillation of coupled pendulum clocks to the rhythmic behavior in biological systems. Here we demonstrate this effect in a solid-state platform: spatially remote, auto-oscillating electron-nuclear spin systems in a semiconductor. When two such oscillators separated by up to 40 μm are optically pumped, their individually different frequencies lock to a common value, revealing long-range coupling. For larger separations, the synchronization breaks. The interaction distance matches the electron spin diffusion length, identifying spin transport as the coupling-mediating mechanism and maintaining correlated behavior over mesoscopic distances. As a consequence, a wide-area optical pump drives all oscillators within the illuminated spot into a single synchronized state, despite their inhomogeneity. This synchronization accounts for the exceptional stability of the resulting auto-oscillations, enabling collective motion in distributed spin systems and paving the way toward spin networks in spintronics.