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Aaron Beller

Willkommen auf open_UMR!

Open_UMR ist ein digitales Repositorium: Ein fachübergreifendes Publikationsportal, das wissenschaftliche Textpublikationen, Ressourcen, Forschungsdaten und Software von Universitätsangehörigen der Philipps-Universität sammelt, verfügbar hält und im open access offen zugänglich macht. Im Sinne einer hohen Qualität sowie einer potentiellen Nachnutzbarkeit ist dieses Repositorium kuratiert.

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Dissertation

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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.

Dissertation

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Optimization of neural response in the primate dorsal visual pathway

(Philipps-Universität Marburg, 2025-11-06) Kreß, Alexander (0000-0003-0646-5952); Bremmer, Frank (Prof. Dr.)

The human brain is frequently characterized as a "black box" in the context of comprehending sensory processing and neural optimization. The relationship between input stimuli and the brain's neuronal responses, such as spike rate, tends to remain obscured until it's measured through experiments. This challenge is further compounded by the intrinsic variability of neural responses, which are subject to biological noise, resulting in varying responses even when the same stimulus is repeatedly presented (Goris et al., 2014; Stein et al., 2005). This thesis focuses on the dorsal visual pathway of primates, a region of the brain that plays a crucial role in interpreting self-motion not only from visual but also from vestibular, tactile and even auditory cues (NHP physiology: Bremmer et al., 2002b; Chen et al., 2011; Schlack et al., 2002; Human fMRI: Bremmer et al., 2001; Huk et al., 2002; Krala et al., 2019; Rosenblum et al., 2023). Non-human primate (NHP) experiments have shown that neurons within this pathway exhibit sensitivity to specific directions of self-motion and typically demonstrate peak activation when the stimuli align with their preferred heading. The directional tuning properties have been the subject of extensive research, focusing especially on the medial superior temporal (MST) area (Bremmer et al., 2010; Duffy and Wurtz, 1995; Lappe et al., 1996; Maunsell and Van Essen, 1983) and the ventral intraparietal area (VIP) (Bremmer et al., 2002b, 2002a; Kaminiarz et al., 2014). Understanding which stimuli evoke the strongest average responses from such neurons can offer critical insights into the functional organization of the underlying brain area (Dayan and Abbott, 2005). In line with this, tuning curve analysis and reverse correlation techniques have proven instrumental in characterizing preferred stimulus features (Kaminiarz et al., 2014; Kriegeskorte and Wei, 2021; Ringach and Shapley, 2004). To explore stimulus-response dynamics for visual self-motion stimuli more systematically, I developed a closed-loop optimization framework that adaptively generates visual stimuli to maximize neural activation in real time. At the heart of this approach is a Variational Autoencoder (VAE), which captures the essential structure of complex self-motion stimuli in a compact latent space (Kingma and Welling, 2022). Using the VAE’s decoder, the system can generate new stimuli from any point within this latent space, enabling a focused and efficient search across possible visual inputs. For optimization, I used a Covariance Matrix Adaptation Evolution Strategy (CMA-ES), an evolutionary algorithm well-suited for high-dimensional, noisy problems (Hansen and Ostermeier, 2001). Here, the optimization objective was defined by neural output, such as spike rate or model-based neural activation, and aimed to find the latent parameters that would drive these outputs as high as possible. To validate the framework, I applied it to a 3D-ResNet model (He et al., 2016), using its internal filters as stand-ins for actual neural responses. The system successfully identified input patterns that activated specific filters near their tuning peaks, offering the possibility for valuable insights into which features most strongly drive neural-like behavior (Olah et al., 2018), proving the approach suitable for identifying optimal stimuli for in-vivo studies.

Dissertation

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Synthesis and Characterization of High-Valent Organoiron complexes

(Philipps-Universität Marburg, 2025-11-06) Souilah El Hadri, Charafa (000-0003-4066-6168); Casitas, Alicia (Prof. Dr.)

High-valent iron compounds in oxidation states of +4 and +5 have been proposed as key intermediates in numerous biological processes catalyzed by metalloenzymes. Bioinorganic chemists have successfully synthesized a wide range of high-valent iron complexes stabilized by strong electron-donating ancillary ligands in combination with strong π-donor ligands such as oxido (O2-), imido (RN2-) or nitride (N3-). These complexes are typically synthesized using traditional group-transfer two-electron oxidants, such as iodosylbenzene (PhIO) and tosylimidoiodanes (i.e., PhINTS). However, studies exploring the reactivity of iron complexes with other iodine(III) compounds, such as azide, cyanide, trifluoromethyl or fluoro λ3-iodanes, remain scarce. The activation of iodine(III) compounds with iron complexes offers an opportunity to develop environmentally friendly bond-forming catalytic reactions, owing to the high abundance, low cost, and low toxicity of iron. Despite their potential, the broader application of iron-catalyzed group transfer reactions in sustainable synthesis is limited by the lack of mechanistic understanding. The synthesis of Fe(IV) complexes remains challenging due to their inherent thermal instability. In particular, limited examples of organometallic Fe(IV) complexes containing metal-carbon -bonds have been isolated and thoroughly characterized by spectroscopic methods. Organometallic iron(IV) complexes have been proposed as catalytically active species in only few reactions, such as in Gif processes or in certain C–C cross-coupling reactions. Aiming at designing organometallic iron(IV) compounds that are relevant to catalytic C–C and C–X bond forming reactions, the carbon atom of the Fe–C bond cannot belong to the ancillary ligand but rather should be part of a labile exogenous substrate to enable intermolecular reactions. This work focuses on the synthesis of organoiron(IV) complexes featuring exogenous and labile Fe–C bonds to perform mechanistic investigations on C–C bond forming reactions. In addition, gaining knowledge in the synthesis and reactivity of organoiron(IV) complexes could pave the way for designing catalytic cycles proceeding via organoiron(IV) intermediates. Furthermore, this thesis explores the use of iodine(III) reagents to synthesize high-valent iron complexes through oxidative group-transfer reactions. The use of the electron-donating nitrogen-based ligand tris(N-tert butyldimethylsilyl-2-amidoethyl)amine (N3N′3-) facilitates the synthesis of iron complexes in high oxidation state. Thus, the investigation of the reactivity of iron(II) and iron(III) precursors bearing the N3N’3- ligand offers an opportunity to synthesize iron(IV) complexes using iodine(III) reagents by oxidative group-transfer reactions. In Chapter III, the investigation of the reactivity of iron(II) and iron(III) complexes bearing the N3N'3- ligand with cyanobenziodoxolone (CBX) and cyano-3,3-dimethyl-1,2 benziodoxole (CDBX) is presented. This work demonstrates that CBX and CDBX react with these iron complexes as cyano-transfer agents and one-electron oxidants. Whereas the reaction of CDBX with iron(II) affords the synthesis of iron(III) cyanide complexes, the oxidation of iron(II) with the most oxidizing CBX forms a highly electrophilic and thermally unstable Fe(IV) cyanide complex. Single-crystal X-ray diffraction confirms the solid-state structure of the Fe(III) and Fe(IV) cyanide complexes, while their electronic structures are elucidated through 57Fe Mössbauer spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, and computational analyses. The synthesis of Fe(IV) alkynylide complexes through the reaction of iron(II) with ethynylbenziodoxo(on)es (EBX) was hampered by the complex spectroscopic analysis of the crude reactions. Therefore, in Chapter IV, the Fe(IV) alkynylide complexes are synthesized through a more conventional approach, which is based on the transmetalation of an iron(III) complex bearing the N3N′3- ligand with lithium alkynylides, followed by one-electron oxidation. The alkynylferrates(III) and Fe(IV) alkynylides prepared in this thesis are rare examples of organoiron(IV) complexes where the C based ligand is not part of the chelating ligand. Their electronic structure has been thoroughly characterized by nuclear magnetic resonance (NMR), electronic paramagnetic resonance (EPR), 57Fe Mössbauer spectroscopy, X-ray emission (XES) and absorption (XAS) spectroscopies, as well as computational studies. While Fe(III) alkynylferrates show very limited reactivity towards C–C bond formation, Fe(IV) alkynylides decompose to give 1,3-diynes at room temperature. Based on mechanistic investigations, it is proposed that the Fe(IV) alkynylides undergo bimolecular C–C reductive elimination to form the 1,3-diynes. These findings contribute to the fundamental understanding of high-valent organoiron complexes and their role in C–C bond-forming processes, offering new pathways for their application in catalysis and synthetic methodologies.

Dissertation

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Evolving industrial clusters – A multi-dimensional investigation of influential factors

(Philipps-Universität Marburg, 2025-11-06) König, Tobias Julian (0000-0002-9623-0200); Brenner, Thomas (Prof. Dr. Dr.)

Since the popularization of the cluster terminology more than two decades ago, cluster research has attracted interest across different disciplines, resulting in a variety of theoretical perspectives, empirical approaches, and research agendas. This popularity is not limited to academia, as the term is also widely used by economic development and regional policy actors in order to support industrial clusters and enhance their positive economic effects. Ideally, this leads to the growth and sustainment of clusters, which, among other things, increases the resilience of the regional economy and its ability to cope with internal and external challenges. As industrial clusters are not binary entities that either exist or do not exist, clusters – like other business locations – must constantly adapt to changing socio-economic conditions to remain competitive, avoid downturns, and renew themselves. As a result, clustered firms, organizations, networks, and institutions associated with them are subject to constant change. In order to achieve a comprehensive understanding of the relevant driving factors, the research articles consider different theoretical perspectives, spatial scales, and empirical approaches to address evolving industrial clusters and related factors. The first article examines the phenomenon of co-located industrial clusters with different industry cores in one region. The empirical results show different patterns of collaboration and competition: on the one hand, the hiring of employees, especially in the segment of (highly) skilled labor, is an important concern for firms facing a tight labor market of co-located clusters. Consequently, filling vacant positions is challenging for firms of both industrial clusters, which results in a competitive environment including labor poaching. On the other hand, the linkages between firms are influenced by the institutional setting, such as changing regulatory environment, leading to more collaboration, even though an intense rivalry between participating firms has existed for decades. The second article takes up the regional findings from the labor market and examines the connection between the shortage of skilled workers and the degree of agglomeration of German firms in clusters. Such bottlenecks are a reality for many firms and organizations, with negative consequences for employees, firms and the economy as a whole. Up to now, it is unclear whether skill shortages in industrial agglomerations are more intense due to competitive labor poaching or less intense due to labor pooling. The empirical results show that firms located in an industrial cluster have a significantly lower probability of experiencing skill shortages in terms of vacancies for skilled jobs. At the same time, clustered firms face more difficulties in filling vacancies when they are struggling more with skill shortages. The third article additionally examines the influence of various factors on the decline or renewal of mature industrial clusters. Therefore, this study identifies different factors: preconditions, triggering events, and self-augmenting processes, and examines their influence on declining or renewing industrial clusters. The empirical results show, firstly, that the decline and renewal of industrial clusters is driven by different preconditions, triggering events, and self-augmenting processes. Secondly, these factors change over time and may have both positive and negative dimensions. Thirdly, the decline of industrial clusters is more often associated with unfavorable preconditions and triggering events, while self- augmenting processes are more often found in the context of cluster renewal. Finally, policy recommendations are derived on the basis of these findings. In addition to the empirical findings, these recommendations are based on the following general requirements for cluster policy: a greater consideration of theoretical findings, contextual factors, development phases, relevant stakeholders and monitoring/evaluation options. The ten specific policy recommendations aim at both existing and future cluster policy approaches and cover different areas, which is why the level of abstraction varies. For example, the first recommendation aims to take greater account of the cluster context in policy design, while another recommendation specifically mentions financial support for trade fair visits by SMEs. As usual, the results of this this and the included research articles are subject to a number of limitations, most of which are of a methodological nature. The concluding research outlook identifies article-specific starting points for future research projects and concludes with general considerations. Among other things, cluster research, especially with a focus on cluster policy, should be continued in the future, although there is a general need for conceptual unification of existing approaches addressing agglomerated economic areas.

Dissertation

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Climate Adaptation, Gender Dynamics, and Decision-Making in Vulnerable Communities: Experimental Insights from Bangladesh

(Philipps-Universität Marburg, 2025-11-06) Tahzeeda,Jasia; Vollan, Björn (Prof. Dr.)

Climate change poses severe challenges for climate vulnerable regions of developing countries, such as coastal Bangladesh. The study area is Shyamnagar upazila of Satkhira District of Bangladesh. The study is situated in a highly climate vulnerable coastal area of Bangladesh where natural disasters have historically been prevalent and have escalated due to climate change along with burgeoning freshwater scarcity. This study explores climate adaptation preferences and decision making among affected communities in coastal Bangladesh. We summarize here findings from three distinct studies, each exploring different facets of decision making. The first two chapters focus on clima te change adaptation, providing a comprehensive overview of the intergenerational, gender specific, and socio economic dimensions of adaptation strategies in this region. The third chapter focuses on how unpaid care work and different socioeconomic variabl es affect women's decision making agency in the study area. Chapter 1 investigates preferences for climate change adaptation among individuals in climate vulnerable regions of Bangladesh through experimental games. This research explores how individuals c ooperate for donation to climate adaptation for present and future generations in the study area. It tries to understand how exposure to cooperative behaviors targeted at the current generation's adaptation influences the donation for adaptation for the be nefit of future generations, and vice versa. Additionally, the study investigates the nature of the relationship between the levels of cooperation directed towards the adaptation of present generations and the adaptation for future generations. This resear ch employs a multi person Public Good Game with a threshold focused on the current generation and a multi person Dictator Game with a threshold oriented towards future generations. For this study, 316 respondents were selected from 10 unions of Shyamnaagr Upazilla using cluster sampling based on geography and stratified sampling based on gender. The sample selection details are based on unions and wards. The selection ensured a balanced representation, with 48.42% female (153 samples) and 51.58% male (163 s amples) participants. Two groups were prepared which are Threshold Public Good Game First Group (TPGG first group) and the Threshold Dictator Game First Group (TDG first group). In total, 136 participants participated in the TPGG first group (80 male and 5 6 female). They played two rounds, where they first engaged in the public good game, followed by the dictator game for future generations. A total of 180 participants, composed of 83 males and 97 females, played in the TDG first group. They also played two rounds, first engaging in a dictator game for future generations, followed by a public good game. The study finds a significant relationship between investments in public good games and donations in dictator games, showing that individuals who are more al truistic tend to be more cooperative. The study utilizes the Network of Action Situations ( approach to show that prior exposure to the dictator game, which focuses on future generations' adaptation, leads to less cooperation in the public good game fo r the present generation due to the spillover effect of the strategic uncertainty. Additionally, prior exposure to the public good game for the present generation did not significantly influence donations in the dictator game for future generations due to the learning effect resulting from the outcome revelation of the previous game. However, a dependency between investment behavior and the level of endowment was found to be significant. Chapter 2 explores gender specific cooperation and perceptions regarding climate change adaptation by utilizing experimental games in coastal Bangladesh. The study aims to investigate the impact of gender relations on decision making related to climate change adaptation of individuals in a cooperative within a climate vulnerable patriarchal society. It examines how men and women make decisions in both intr agenerational and intergenerational adaptation with threshold public good game ( and threshold dictator game for future generation ( respectively. These games are organized based on the gender composition of the groups, which include single sex groups and mixed sex groups. In the threshold public good game ( participants were distributed across three group compositions: 40 participants in 2 male only groups, 24 participants in 1 female only group, and 72 participants in 4 mixed sex groups. In the threshold dictator game for future generations ( the allocation included 27 participants in 2 male only groups, 54 participants in 3 female only groups, and 99 participants in mixed sex groups. The mixed sex groups in the TDGF were further div ided into subcategories: 48 participants in 2 male dominated mix groups, 15 participants in 1 female dominated mix group, and 36 participants in 2 groups with equal male and female representation. Findings reveal that gender dynamics significantly influenc e cooperative behaviors. Men show greater optimism and higher investments in single sex groups in the TDG, while both genders vi investinvest moremore inin mixedmixed--sexsex groupsgroups inin thethe TPGG.TPGG. TheThe qualitativequalitative analysisanalysis highlightedhighlighted societalsocietal normsnorms andand genderedgendered perceptionsperceptions asas signisignificantficant factorsfactors shapingshaping thesethese dynamics.dynamics. SocietalSocietal normsnorms influenceinfluence thesethese behaviors,behaviors, withwith men,men, perceivedperceived asas primaryprimary earners,earners, beingbeing expectedexpected toto contributecontribute more,more, whilewhile womenwomen oftenoften prioritizeprioritize collectivecollective benefitbenefit overover individualindividual gain.gain. MalesMales inin thethe TDGFTDGF werewere moremore opoptimistictimistic aboutabout singlesingle--sexsex groupsgroups andand pessimisticpessimistic aboutabout mixedmixed--sexsex groups.groups. OnOn thethe otherother hand,hand, females’females’ unconditionalunconditional contributionscontributions toto thethe TDGFTDGF reflectreflect societalsocietal expectationsexpectations ofof caregivingcaregiving andand intergenerationalintergenerational prioritization,prioritization, asas emphasizedemphasized inin feministfeminist ecologiecologicalcal economics.economics. Chapter 3, adopting a feminist ecological economics perspective, investigates the impact of unpaid care work and socio economic factors on women's decision making agencies in climate vulnerable rural Bangladesh. The study collected data fro m 316 households in 2022 (153 women and 156 men) and 385 households in 2021 (52 women and 333 men) from Shyamnagar Upazila. Decision making agency variables including economic, family, and social domains are analyzed. Economic domains include spending for oneself, spending for parents, economic participation, and land transactions. Family domains include children’s education, participation in decision making in family matters, and participation in family planning. The decision making agency variables relate d to social domains are going out alone, participating in social work, and purchasing household goods. The study identifies a positive correlation between unpaid care work and women's decision making agency in all three social, economic, and family domains emphasizing how caregiving responsibilities enhance their agency within households. However, entrenched patriarchal norms and climate induced challenges exacerbate gender inequalities, limiting women's agency. By applying the Institutional Analysis and D evelopment ( framework, the study elucidates the intricate feedback loops between unpaid care work and decision making agency, providing a nuanced understanding of women's roles in household and community level adaptation strategies. These studies underscore the complex interplay among intergenerational perspectives, gender dynamics, and socio-economic factors influencing decision-making and climate adaptation behaviors in coastal Bangladesh. They highlight the necessity of incorporating intergenerational equity, gender sensitivity, and socio-economic considerations into policy vii frameworks to enhance the effectiveness and sustainability of adaptation efforts in vulnerable regions.