open_UMR

Aaron Beller

Welcome to open_UMR!

Open_UMR is a cross faculty publication hub. We collect scientific publications, resources, research data and software from members of Philipps-University Marburg and make it openly accessible. To ensure high standards of quality and re-usability, submissions to open_UMR are subject to curation.

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Recent Submissions

Presentation

Open Access

Introduction to Research Data Management

(Philipps-Universität Marburg) Röder, Juliane; Lenze, Stefan; Ortwein, Tobias

This presentation was part of a 4 h workshop on basic aspects of research data management for participants of the “IMPRS Welcome week for new doctoral researchers”, organised by the Max Planck Institute for Terrestrial Microbiology. In this workshop, members of the Marburg University eResearch Service Center discussed day-to-day handling of research data along the data life cycle (DLC), data management plans (DMPs), electronic lab notebooks (ELNs), and introduced version control with Git, the Marburg University GitLab instance, and the Marburg University Jupyter instance. The presentation is designed as a collection of useful resources for further studies.

Thesis

Open Access

"Es wird künftig nur noch einen Adel geben..." Aristokratismus in Nationalsozialismus und "Drittem Reich"

(2025-07-09) Thiel, Daniel; Conze, Eckart; Strobel, Jochen

Die Arbeit beschäftigt sich mit den Semantiken von Adel und Aristokratie in Nationalsozialismus und „Drittem Reich“. Entgegen dem ausdrücklich formulierten Anspruch, „Künftig nur noch einen Adel“ zu kennen (nämlich jenen „der Arbeit“), existierten im NS mehrere, zum Teil miteinander konkurrierende Adelsentwürfe. Die Arbeit untersucht, wie diese Ideen und Konzepte semantisch gefüllt waren, wie sie an den Aristokratismus der Hochmoderne anknüpften und welche Funktion sie innerhalb des nationalsozialistischen Ideologiearsenals einnahmen. Dazu wird zunächst der breit (und zum Teil kontrovers) geführte Diskurs um (neuen) Adel in der Weimarer Republik dargestellt, in dessen Kontext auch die Adelskonzepte des NS entstanden. Daran anknüpfend werden jene Gruppen untersucht, die im „Dritten Reich“ zum Adel gehören sollten. Abschließend werden Konzepte von Adeligkeit im Widerstand analysiert.

Thesis

Open Access

Ultrafast processes in organic semiconductors: From spectral and spatial dynamics in model systems towards heterostructures

(2025-09-26) Muth, Dominik; Gerhard, Marina; Witte, Gregor

Compared to conventional semiconductors, organic semiconductors host a number of unique properties that give rise to a variety of interesting optical and electronic phenomena. These include singlet fission and excimer formation, both of which are processes highly desirable in certain technological applications in the realms of solar cells and illuminants. Although extensively studied in various systems, the specific effects of temperature and material quality on the above-mentioned kinetic processes are still unclear in many cases. In order to properly exploit the aforementioned qualities of organic semiconductors, detailed investigations of the underlying mechanisms are required. This dissertation aims to address these aspects, using time- and polarization-resolved experimental studies of model systems, complemented by theoretical calculations and kinetic models. The soft lattice in molecular crystals results in strong electron-phonon coupling, which significantly affects the energetic relaxation dynamics. However, how these processes take place microscopically is still unknown in many cases. In particular, part of this thesis deals with the investigation of the phonon-driven relaxation pathways between different excitonic states originating from the Davydov splitting in oligoacene single crystals. Calculations are performed on pentacene and tetracene to compare their relaxation dynamics. Complementary time- as well as polarization-resolved photoluminescence (PL) and absorption measurements are conducted on a thin tetracene single crystal at different temperatures to compare the Davydov peak characteristics with the calculations. It is found that optically dark states play a vital role as intermediates in the transition from the higher to the lower Davydov state. Additionally, in pentacene an accumulation of excitons in a dark state is observed, leading to a phonon-bottleneck. However, this seems to be absent in tetracene, most likely due to the lower energetic separation between the two states compared to pentacene, making energetic relaxation via electron-phonon scattering more efficient. The obtained model could thus be a valuable tool for predicting the occurrence of phonon-bottlenecks in other oligoacene systems. Likewise, the time- and polarization-resolved PL and absorption measurements used provide a way to experimentally confirm the presence of this phenomenon in a given system. Tetracene is a material in which endothermic singlet fission is known to occur, along with the reverse triplet-triplet annihilation process. The resulting interconversion between singlet and triplet excitons has been demonstrated to have a significant impact on the total diffusion lengths, which could be beneficial for the design of organic solar cells. However, the exact effect of temperature on the fission process is still unknown, as is the role of crystal quality, which has been shown to significantly affect spectral signatures. Part of this work focuses on investigating these factors, by performing spectrally-, spatially- and time-resolved photoluminescence measurements on two tetracene single crystals of different quality at varying temperatures. In order to elucidate the underlying temporal population changes and to extract the kinetic parameters governing the exciton diffusion and transition processes, a kinetic model is fit to the experimental data. Crystal quality is shown to strongly affect spectral as well as spatial dynamics at decreased temperatures, spectrally shifting the emission signature and modifying the total singlet diffusion length. The model reveals that the temperature-activated step for the process of singlet fission is the dissociation of the correlated triplet-pair. It also suggests that a single radiative emission and fission constant is insufficient to explain the observed dynamics in the pristine sample. Instead, the model must rely on multiple species with different kinetic parameters to accurately reproduce the experimental data. The study reveals crystal quality and temperature to act as possible turning knobs for optimizing singlet fission in tetracene. Moreover, the derived kinetic model is suitable for obtaining robust sets of parameters by simultaneously reproducing several experimental datasets. Even though organic semiconductors exhibit the unique qualities mentioned previously, they also have some significant drawbacks compared to their inorganic counterparts, one of which being their exciton transport properties. One way to remedy this issue is to integrate organic semiconductors in a heterostructure with materials that complement their weak points, such as monolayer transition metal dichalcogenides (TMDs). Although theoretically a fascinating proposition, to date not much experimental research has been performed on such systems. One reason for this is a lack of available heterostructures with controlled orientation of the molecular lattice. The final part of this thesis deals with the construction of a heterostructure consisting of an ionic organic crystal, pyrenemethylammonium chloride, and a monolayer of tungsten disulphide via physical stacking. The structure is studied using time- as well as polarization-resolved and steady-state photoluminescence measurements at different temperatures to probe for evidence of successful electronic coupling between the compounds. A significant quenching of the PL of the organic crystal is observed in the heterostructure. Interestingly, this trend is observed both for the mobile excitonic as well as the localized excimer species. This, together with the emergence of a red-shifted, linearly polarized emission, seemingly arising from an interfacial state, suggests the presence of efficient electronic coupling. The study thus provides a method for the controlled fabrication of organic/TMD heterostructures.

Thesis

Open Access

From Dense to Sparse Design: Optimal Rates under the Supremum Norm in Functional Data Analysis

(2025-09-17) Berger, Max Jannis; Holzmann, Hajo; Birke, Melanie

We establish minimax-optimal rates of convergence in the supremum norm for estimating key components of functional data from repeatedly observed stochastic processes at discrete, synchronous design points - namely the mean function, the covariance kernel, and their partial derivatives. The supremum norm is employed as it controls the estimation error uniformly over the entire interval and forms the basis for constructing uniform confidence bands. The smoothness of the mean function, the stochastic processes and the covariance kernel is characterised by Hölder classes. Under dense designs, meaning sufficiently many design points per curve, the estimators for the mean function and the covariance kernel achieve the parametric √n rate without additional logarithmic factors and corresponding central limit theorems are derived. In sparse settings, the discretisation error dominates while between the sparse and dense regimes an additional regime appears, driven by measurement errors which is unique to the use of the supremum norm. For the estimation of partial derivatives sufficiently smooth sample paths of the stochastic processes are crucial to obtain the √n rate, whereas paths of lower order differentiability necessarily lead to a slower rate of convergence in the dense regime. The theoretical analysis is conducted with abstract weights; however, we show that local polynomial estimators satisfy the required assumptions and their practical performance is demonstrated through simulations and real-data applications.

Thesis

Open Access

Reaction-diffusion in a 2D array of cell mimics, perfused by a microfluidic biochemostat

(Philipps-Universität Marburg, 2025-11-06) Banlaki, Imre; Niederholtmeyer, Henrike (Prof. Dr. rer. nat.)

In biological systems, the spatio-temporal localization, of biochemical reactions, is the constituent force generating compartmentalized living entities. This work is part of the collective effort, of bottom-up synthetic biology, to create synthetic cells and communities from first principles. In this work, I used porous polymer cell mimics to compartmentalize discrete DNA packages. I employed these properties to execute gene regulatory networks, programmed within the cell mimics, using cell free transcription and translation (TXTL). I developed a multilayer microfluidic chip to perfuse a 2D array of cell mimics immobilizing a reaction diffusion gene regulatory network.