Students' seminar

Conical intersections (CIs) are key features of molecular potential energy surfaces that govern how molecules behave after absorbing light. Acting as “doorways” between electronic states, they play a central role in determining chemical outcomes on ultrafast timescales. Yet, directly observing CIs remains a major challenge in spectroscopy.We use quantum dynamics simulations to uncover how CI-driven processes leave distinct fingerprints in spectroscopic signals. By modeling molecules like furan and its derivatives, we predict how different reaction pathways—such as ring puckering vs. ring opening—can be distinguished using time-resolved photoelectron spectroscopy, X-ray spectroscopy, and ultrafast electron diffraction.In a second example, we study the photodissociation of methyl iodide, a benchmark system in ultrafast science. We discover that quantum coherences formed at the CI surprisingly survive long after the molecule splits, showing up in the atomic products. To probe these hidden dynamics, we propose a novel approach using heterodyne-detected four-wave mixing, which not only captures CI-induced coherence but also enables a form of quantum state tomography. [more]

Cardiovascular diseases like the aortic dissection and atherosclerose in the carotid artey are a leading cause of worldwide mortality, yet current risk assessment is based on arbitrary treshhold and lack patient-specific precision. By using Computational Fluid Dynamics to govern the blood flow and Fluid-Structure-Interaction considering the flexibility of artery walls as well as the Windkessel effect multiphysical numerical models for personalized risk assessment are developed. Patient-specific arterial geometries are reconstructed from high-quality CT Angiography (CTA) scans and processed using automated segmentation tools. Then the numerical models are used to get insights into problematic flow patterns and endothelial stress responsible for inflammatory response by the artery wall. In collaboration with the Universitätsmedizin Mainz the predictive power of those models is evaluated. For example, already demonstrating that patient-specific simulated Oscillating Shear successfully predicts sites of aortic dissection when comparing pre- and post-dissection states. Also, Histological analysis conducted by the Universitätsmedizin confirms tissue degradation in numerically predicted high-shear zones. [more]

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Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios are used for the reconstruction of past diet and environments. δ¹³C of herbivores can differentiate between browsers and grazers as well as indicate prey preference of carnivores. δ¹⁵N shows trophic level: carnivores are 3 – 6 ‰ enriched compared to herbivores. δ¹³C is measured on the inorganic portion of tooth enamel, as enamel is highly robust to alteration. δ¹⁵N is measured on the organic fraction of collagen, which only rarely preserves past 50 ka. In 2021, a method was established at the MPIC that allows for the measurement of the small fraction of organic nitrogen within the mineral structure of enamel. Sterkfontein is a cave site in the Cradle of Humankind, South Africa, where all three hominin genera have been found. My project focusses on three infills of the cave. The Jacovec Cavern (3.6 Ma) has yielded Australopithecus fossils. Member 5 Oldowan (2.1 – 1.7 Ma) contained Paranthropus fossils, and Member 5 Acheulean (1.7 – 1.4 Ma) yielded early Homo specimens. I sampled tooth enamel of herbivores, carnivores, and hominins from each infill and measured δ¹³C and δ¹⁵N to reconstruct dietary behavior and the potential onset of meat consumption. [more]

Numerical simulations of atmospheric models resolve slow (advection) and fast (gravity and sound) modes, creating significant challenges in handling multiple time scales under CFL restrictions. In this work, we develop time-space flux splitting schemes for the two-dimensional compressible Euler equations. We introduce flux splitting within the framework of the multirate infinitesimal step (MIS) method and formulate the proposed schemes using the discontinuous Galerkin flux-differencing approach to ensure compatibility with high-order spatial discretizations. We integrate the advective terms using a Runge-Kutta method with a macro time step constrained by the CFL condition, while we treat sound wave terms with smaller time steps to satisfy stability requirements dictated by the speed of sound. Additionally, the fast waves are resolved using a Rosenbrock-type method, where the Jacobian is constructed as one-dimensional operator in the vertical direction. We investigate different approaches, present an extension to curvilinear coordinates, analyze the stability properties of the new schemes, and present several atmospheric test cases, comparing the results to existing methods. [more]