University of Konstanz
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Conventional versus singlet-triplet Kondo effect in Blatter radical molecular junctions : Zero-bias anomalies and magnetoresistance
No full textThe Blatter radical has been suggested as a building block in future molecular spintronic devices because of its radical character and expected long spin lifetime. However, whether its radical character is maintained in single-molecule junctions depends on the environment. Here, we demonstrate the ability to retain the open-shell nature of the Blatter radical in a two-terminal device by the appearance of a Kondo resonance in transport spectroscopy. Additionally, a high negative magnetoresistance is observed in junctions that do not reveal a zero-bias anomaly. By combining distance-dependent and magnetic-field-dependent measurements and accompanying quantum-chemical and quantum-transport calculations, we show that both findings, the negative magnetoresistance and the Kondo features, can be consistently explained by a singlet-triplet Kondo model. Our findings provide the possibility of using the Blatter radical in a two-terminal system under cryogenic conditions and also reveal the magnetotransport properties emerging from different configurations of the molecule inside a junction.publishe
Multi-Criteria Route Planning with Little Regret
No full textMulti-criteria route planning arises naturally in real-world navigation scenarios where users care about more than just one objective - such as minimizing travel time while also avoiding steep inclines or unpaved surfaces or toll routes. To capture the possible trade-offs between competing criteria, many algorithms compute the set of Pareto-optimal paths, which are paths that are not dominated by others with respect to the considered cost vectors. However, the number of Pareto-optimal paths can grow exponentially with the size of the input graph. This leads to significant computational overhead and results in large output sets that overwhelm users with too many alternatives. In this work, we present a technique based on the notion of regret minimization that efficiently filters the Pareto set during or after the search to a subset of specified size. Regret minimizing algorithms identify such a representative solution subset by considering how any possible user values any subset with respect to the objectives. We prove that regret-based filtering provides us with quality guarantees for the two main query types that are considered in the context of multi-criteria route planning, namely constrained shortest path queries and personalized path queries. Furthermore, we design a novel regret minimization algorithm that works for any number of criteria, is easy to implement and produces solutions with much smaller regret value than the most commonly used baseline algorithm. We carefully describe how to incorporate our regret minimization algorithm into existing route planning techniques to drastically reduce their running times and space consumption, while still returning paths that are close-to-optimal.publishe
Rising beliefs but descending self-efficacy when preparing in-service teachers for linguistically responsive teaching – insights from a longitudinal intervention study
No full textFostering teacher beliefs (TB) and self-efficacy (TSE) towards multilingualism in class is key for the successful implementation of linguistically responsive teaching (LRT) aiming to support multilingual students, who are often disadvantaged in class. However, TB and TSE towards multilingualism have not been examined together within a longitudinal LRT intervention. Therefore, 44 teachers were trained in a professional development (PD) workshop about LRT, which they then implemented in their regular German classes. TB and TSE were measured longitudinally (TB pre-PD, post-PD and post-implementation, TSE post-PD and post-implementation). TB significantly improved through PD and remained stable during implementation, while TSE significantly decreased, probably due to unexpected challenges to motivate multilingual students to use their family languages. TB and TSE were moderately correlated when measured at the same time. Longitudinally, post-PD TSE had a positive effect on post- implementation TB when controlling for post-PD TM, but post-PD TB had no effect on post-implementation TSE when controlling for post-PD TSE. Overall, TB remained positive during the implementation of LRT without decreasing along with TSE. Hence, this study makes optimistic for improving TB through PD, but also emphasises that TSE needs further support during implementation.publishe
Drivers of the range expansion of the European catfish (Silurus glanis) within its native distribution
No full textThe European catfish Silurus glanis L. continues to spread as an invasive species in Europe. Meanwhile, increasing abundance and range expansions are also suspected within its native distribution. The objective of this study was to characterize the feeding, growth and abundance of S. glanis in 12 lakes and 12 rivers within its European native range in relation to environmental changes that may explain population trends over time. The results suggest a shift in factors limiting the carrying capacity of catfish habitats within this range, leading to increases in growth and abundance. Statistical modelling identified warming and increasing population density of invasive gobies as likely contributors to this shift. Given that catfish predation on native species can be expected to increase dramatically, there is an urgent need for new management strategies. It is recommended that catfish removal rates should be increased, especially in areas of high importance for native fish and crayfish species, such as spawning grounds and at bottlenecks for migration.publishe
Seasonal genotypic and phenotypic differentiation of a cosmopolitan freshwater diatom
No full textMost ecosystems are characterized by seasonality, which, through biotic and abiotic changes, influences species biomass dynamics. Recent studies have shown that ecologically important traits can evolve rapidly in response to environmental changes, resulting in eco-evolutionary dynamics with consequences for population and community dynamics. Evidence for seasonal effects on intraspecific variation is still scarce and understanding eco-evolutionary dynamics in the presence of seasonal fluctuations remains a major challenge. Following the phytoplankton spring bloom in Lake Constance, we investigated how seasonal changes influence the intraspecific diversity of Asterionella formosa both at genotypic and phenotypic levels. We found a moderate degree of genetic and phenotypic differentiation characterizing the Asterionella population, explained by a clustering of the isolates into early and late spring according to lake thermal stratification. Yet, most traits related to environmental parameters as well as fitness in different seasonal environments did not show a clear response to seasonality (i.e., temperature and nutrients). The changes in genetic patterns observed after a peak in parasite relative abundance suggested that seasonal changes in biotic interactions (i.e., parasitic chytrids) might be an important driver of the observed seasonal shift in Asterionella genotypes. Our results highlight the importance of studying eco-evolutionary processes for understanding variations in population and community dynamics in response to seasonal environmental fluctuations.publishe
Long‐term changes in intra‐ and interspecific trait variability of a small herbivore in a deep perialpine lake
No full textAnalyses of trait dynamics provide new insights into the dynamics of communities and ecosystems. While zooplankton traits—and especially the defensive traits—of zooplankton are well studied in the laboratory, there are hardly any studies analyzing long‐term dynamics of zooplankton traits. Here, we study species turnover and trait dynamics of three species of the genus Bosmina , Bosmina coregoni , Bosmina longispina , and Bosmina longirostris , at the genus and species levels during three decades of environmental changes in Lake Constance. We showed that Bosmina species turnover substantially influenced genus‐level body size distributions and key defensive traits, including mucro and antennule sizes. Results also showed that mean species traits more effectively predicted genus‐level traits when interspecies trait differences were large, making them particularly reliable in species‐rich contexts. In contrast, when trait differences among species were small, intraspecific variations may obscure genus‐level temporal patterns. In addition, we found within‐species trait changes that partially paralleled those observed at the genus level, but also within‐species trait changes that partially differed from those observed at the genus level. While a large reduction of nutrients during two decades appeared not to be strongly associated with changes in Bosmina species composition and trait dynamics, large and rapid species turnover and trait changes coincided with 7 yr of increased stickleback densities in the pelagic zone of the lake.publishe
Rhetorical action in a liberal international order in crisis : theorising EU and NATO enlargements post-2022
No full textThe Russian invasion of Ukraine has thrust the issue of European Union and NATO enlargement back into the political spotlight. However, it remains uncertain whether established theoretical frameworks are still applicable in today’s rapidly changing world. In response to this uncertainty, this debate section brings together five short reflection pieces, with a response from Frank Schimmelfennig, to assess the relevance of the theory of ‘rhetorical action’ in light of recent developments in European and international politics. How effectively does rhetorical action explain current EU and NATO enlargement processes, as well as broader forms of international cooperation? The authors find strong overall support for the theory’s continued validity. However, they caution that the increasing politicisation of issues, the rising competition from populist, non-liberal forces, and the broader crisis of the Liberal International Order require more careful reflection and specification of the scope conditions that define the theory’s limits.publishe
Modulation of sub-optical cycle photocurrents in an ultrafast near-infrared scanning tunnelling microscope
No full textLightwave-driven scanning tunnelling microscopy (STM) at near-IR frequencies promises an unprecedented combination of atomic spatial resolution and temporal resolution approaching the attosecond range. To achieve this goal, high-sensitivity optical control and detection of sub-cycle tunnelling currents must be achieved at the STM junction. Here, we demonstrate the generation and detection of coherent ultrafast currents across the junction of an STM illuminated by near-infrared single-cycle pulses. We introduce a modulation scheme that avoids time-dependent thermal loading while selectively isolating carrier-envelope phase (CEP)-dependent photocurrents. All artifacts arising from periodic modulation of laser power and thermal coupling are efficiently suppressed, enabling a clean readout of the coherent portion of the ultrafast tunneling current.publishe
PbI<sub>2</sub> Crystallization for Perovskite Solar Cell Fabrication Using Spin-Coating and APCVD
No full textThis doctoral thesis investigates the optimization of the two-step deposition method for metal halide perovskite solar cells (PSCs), a critical technology for next-generation photovoltaics. The research focuses on the morphological and structural evolution of the lead iodide (PbI2) precursor layer and its subsequent conversion into the photoactive perovskite phase. A significant portion of the work is dedicated to the wet-chemical optimization of Cs-doped PbI2 films. Furthermore, the thesis presents a novel, scalable approach for depositing PbI2 using Atmospheric Pressure Chemical Vapor Deposition (APCVD), marking the first successful application of an industrial APCVD tool for this material class.
In the first phase, the study systematically analyzes the annealing process of spin-coated Cs0.05PbI2.05 precursor films. The solvent system utilized a mixture of DMF and DMSO. A key finding is that standard annealing temperatures (≥ 80°C) lead to incomplete substrate coverage and the formation of holes, which persist in the final perovskite layer. Consequently, a reduced annealing temperature of 50°C was established. This lower temperature regime allows for precise control over the crystallization kinetics. Initially, excess unbound DMSO evaporates within the first 3 minutes. Subsequently, PbI2-DMSO complexes dissociate, releasing PbI2 for crystallization. It was demonstrated that amorphous precursor films—resulting from short annealing durations (1–3 min)—retain a higher DMSO content. This facilitates a more reliable conversion into high-quality perovskite films via an intermolecular exchange mechanism between DMSO and formamidinium iodide (FAI).
The second step, converting the precursor to the perovskite composition Cs0.05MA0.28FA0.67Pb(I0.96Br0.04)3, revealed significant temperature sensitivities. The study highlights a trade-off during the conversion annealing at 150°C. While necessary for phase formation, this temperature induces the degradation of the perovskite via the volatilization of the organic cation methylammonium (MA+), leaving behind a crystalline PbI2 phase and reducing the bandgap energy. Contrarily, reducing the conversion annealing time to 1 minute prevented decomposition while achieving complete conversion. A remarkable phenomenon was observed when converting highly crystalline PbI2 precursors (annealed for 30 min): the high conversion rate led to the formation of exceptionally large perovskite grains (up to 7.4 µm). However, these large grains were found to be thermally unstable, fragmenting into smaller domains upon prolonged annealing. Simulations confirmed that the grain size is inversely proportional to the nucleation density, which is governed by the conversion rate.
A major contribution of this work is the introduction of APCVD for the deposition of PbI2 layers. This method operates at atmospheric pressure, offering a distinct advantage over vacuum-based Physical Vapor Deposition (PVD) regarding throughput and cost. The APCVD process produced high-crystallinity PbI2 films characterized by large, hexagonal platelets (> 1 µm) oriented along the (001) direction. A deposition rate of (55.5 ± 2.3) nm min-1 was achieved, surpassing many existing vapor-phase techniques. The deposition mechanism suggests growth primarily at the crystal edges due to the high collision rate at atmospheric pressure. While deposition on the hole-selective layer NiO resulted in unfavorable vertical growth due to poor adhesion, deposition on MeO-2PACz yielded planar films suitable for device integration. Subsequent conversion of these APCVD-PbI2 layers into perovskite resulted in absorber films with implied open-circuit voltages (iVoc) of up to 1.13 V, demonstrating the high potential of this industrial manufacturing route.
The thesis provides a comprehensive understanding of the interplay between precursor morphology, solvent evaporation, and thermal processing in the two-step fabrication of perovskites. It identifies MA+ evaporation as a critical degradation pathway during fabrication and proposes optimized, low-thermal-budget protocols. Finally, the successful implementation of APCVD for PbI2 paves the way for scalable, high-throughput manufacturing of perovskite solar cells.publishe
Citizen scientists for MoveApps : Innovations and insights from volunteer coders in wildlife conservation
No full text1. Amidst numerous global crises, decision-makers have recognized the critical need for fact-based advice, driving unprecedented data collection. However, a significant gap persists between data availability and knowledge generation, primarily due to time and resource constraints. To bridge this gap, we propose involving a novel group of citizen scientists: volunteer code developers.
2. Utilizing the modular, open-source analysis platform MoveApps, we were able to engage 12 volunteer coders in a challenge to create tools for movement ecology, aimed at animal conservation. These volunteers developed functioning applications capable of analysing animal tracking data to identify stationary behaviour, estimate ranges and movement corridors and assess human–wildlife conflicts using data sets from human infrastructure, such as OpenStreetMap.
3. Engaging citizen scientists in developing code has surfaced three primary challenges: (i) Community Building—attracting the right participants; (ii) Community Involvement—maintaining quality standards and directing tasks effectively; and (iii) Community Retention—ensuring long-term engagement. We explore strategies to overcome these challenges and share lessons learnt from our coding challenge experience. Our approaches include engaging the community through their own preferred channels, providing an accessible open-source tool, defining specific use cases in detail, ensuring quality through feedback, fostering self-organized community exchanges and prominently illustrating the impact of contributions.
4. We also advocate for other disciplines to consider leveraging volunteer involvement, alongside artificial intelligence, for data analysis and generating state-of-the-art, fact-based insight to address critical issues such as the global decline in biodiversity.publishe