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Computing the Exact Radius of Large Graphs
No full textThe radius of a graph is an important structural parameter which plays a key role in social network analysis and related applications. It measures the minimum shortest path distance that is required to reach all nodes in the graph from a single node. A node from which all other nodes are within a distance equal to the radius is called a center of the graph. In a graph with n nodes and m edges, the center and the radius can be determined in Õ(nm) by computing shortest path distances between all pairs of nodes. Fine-grained complexity results suggest that asymptotically faster algorithms are unlikely to exist. In this paper, we describe a novel randomized algorithm for exact radius computation in weighted digraphs with an expected running time in Õ(d³m) where d is the so-called combinatorial dimension. Our methodology is inspired by Clarkson’s algorithm for LP-type problems. The value of d denotes the size of a basis, which is a smallest subset of nodes which enforce the same radius as the whole node set. While we show that there exist graphs with d ∈ Θ(n), our empirical analysis reveals that even large real-world graphs have small combinatorial dimension. This allows us to compute the radius in near-linear time on such instances. The significantly improved scalability can be clearly observed in our experimental evaluation on a diverse set of benchmark graphs.publishe
Costs of reproduction in flowering plants
No full textCosts of reproduction arise when investments into current reproduction reduce future reproductive fitness. Studies on reproductive costs use diverse approaches, including the analysis of gene expression, physiology, trade‐offs between reproduction and growth/survival, and the impact of reproductive investments on population growth. These studies demonstrate that reproductive trade‐offs have far‐reaching effects on plants, affect their fitness, and are therefore important for shaping the evolution of life histories. However, not all studies have detected costs of reproduction, and c . 90% of these were conducted in natural populations, where controlling for variation in plant resource status is challenging. For dioecious plants, there is a common perception that fruit production should result in greater costs of reproduction for females than males, but divergent reproductive costs between the sexes are not supported by studies of reproductive trade‐offs in dioecious plants. Other aspects of reproductive costs remain poorly understood, including ecological costs of reproduction, the fitness effects of reproductive trade‐offs involving growth or physiological processes, and how the male sex role influences reproductive costs. Progress will be enabled by the use of measurements that allow for easier comparisons across studies and by more clearly distinguishing between the processes that contribute to current vs future reproductive fitness.publishe
Liegeplatzspezifischer Flächenverbrauch ausgewählter Bootsstationierungsanlagen am Starnberger See und Chiemsee (Bayern) : Bericht der Arbeitsgruppe Umweltphysik am Limnologischen Institut der Universität Konstanz für das SuBoLakes-Projekt der Deutschen Bundesstiftung Umwelt (DBU), Az. 35825/01
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Spin polarization of the two-dimensional electron gas at the EuO/SrTiO<sub>3</sub> (001) interface
No full textSpin-polarized two-dimensional electron gases (2DEGs) are of particular interest for functional oxide electronics applications. The redox-created 2DEG residing on the strontium titanate, SrTiO3 (STO), side of a europium monoxide (EuO)/SrTiO3 (001) interface is expected to be significantly spin polarized due to the proximity to the strong (7/..) Heisenberg ferromagnet EuO. We apply magnetic circular dichroism in the angular distribution (MCDAD) of photoemitted electrons to investigate whether and how the induced spin polarization of the 2DEG depends on the dimensionality of the overlaying EuO layer. The experimental data are complemented by density functional theory calculations with a Hubbard term (DFT+). We show that the EuO/STO interfacial 2DEG is spin polarized even for ultrathin EuO overlayers, starting at an EuO threshold thickness of only two monolayers. Additional EuO monolayers even increase the induced magnetic Ti moment and thus the spin polarization of the 2DEG. Our results and the potential to enhance the magnetic order of EuO by other proximity effects indicate that the EuO/STO(001) interface is an ideal template for creating (multi-)functional spin-polarized 2DEGs for application in oxide electronics.publishe
Potentiale der Normentheorie im Prozess der strafrechtlichen Internationalisierung
No full textDie Globalisierung fordert auch das Strafrecht heraus. Nationale Strafrechtsordnungen bestehen nicht mehr isoliert nebeneinander, sondern müssen koordiniert und sowohl praktisch als auch normativ vernetzt werden. Welche Potentiale die Normentheorie für den Prozess der Internationalisierung des Straf- und Strafprozessrechts birgt, wird in diesem Band von einem internationalen Kreis von Normentheoretiker:innen in grundlegender Weise sowie unter spezifischen Gesichtspunkten beleuchtet. Daraus ergibt sich ein facettenreiches Bild der Normentheorie als rechtsordnungsübergreifend anwendbarem Analysetool, das als gemeinsame Sprache der interrechtssystemischen Kommunikation und als Grammatik des Strafrechts im internationalen Kontext dienen kann. Mit Beiträgen von Prof. Dr. Stefanie Bock | Prof. Dr. Inês Fernandes Godinho, LL.M. |Prof. Dr. Kyriakos N. Kotsoglou, LL.M. | Prof. Dr. Juan Pablo Montiel | Prof. Dr. Yuki Nakamichi | Prof. Dr. Laura Katharina Sophia Neumann | Prof. Dr. Konstantina Papathanasiou, LL.M. | Dr. Zhiwei Tang, LL.M. | Prof. Dr. Markus Wagner | Prof. Dr. Liane Wörner, LL.M.publishe
A comprehensive atlas of the bonobo gut bacteriome and its associated host and exposome factors
No full textIn great apes, the gut bacteriome shapes key physiological functions and is influenced by both the exposome and the host. Yet, isolating these independent contributions remains challenging. We sequenced 644 fecal samples from 212 wild and zoo-housed bonobos (Pan paniscus), matched with detailed data collection on host and exposome factors. This standardized dataset reveals clear differences in gut bacterial diversity and composition between wild and captive bonobos. Within the controlled zoo-housed cohort, factors such as age, transit time, diet, early life adversity, and medication use influence gut bacterial structure. Notably, social contact emerges as a stronger predictor of bacteriome similarity than genetics or other exposome factors, while maternal effects persist even in non-cohabiting mother-offspring dyads. By offering a unique, comprehensive, and standardized dataset, our work paves the way for future research into microbiome ecology, providing insights with far-reaching implications for both human and animal health in an increasingly industrialized world.publishe
Approaches to Mitigate Edge Recombination Effects in Silicon Lifetime Samples With Emitter
No full textInsufficiently sized symmetric lifetime samples with pn-junction exhibit a specific injection-dependent effective charge carrier lifetime measured by photoconductance decay due to increased edge recombination, characterized by a strong decline toward low injection. In this study, various approaches are presented to suppress these edge effects in n-type Si samples with boron emitter. These approaches include edge passivation using AlOx from atomic layer deposition and the creation of an undiffused buffer layer between the central measurement area and recombination-active edges. For the latter, both an etch-back approach and a masked diffusion of the boron emitter (sunken emitter) are evaluated. Lifetime measurements and photoluminescence imaging demonstrate that the sunken emitter approach most effectively suppresses edge recombination in small-sized lifetime samples.publishe
Do European Capitals of Culture Influence Attitudes Towards and Identification with the European Union?
No full textThe European Capitals of Culture (ECoC) programme, a cornerstone of EU Cultural Policy, is designed to foster a sense of Europeanness amongst citizens and is described as a legitimizing tool for the EU. Although ECoCs cumulatively form the largest cultural event in Europe, their effectiveness in achieving these goals remains understudied. I contribute the first assessment of the effect of ECoCs on attitudes towards and identification with the EU by comparing ECoC regions before and after the event to non-winning competitors. Results from difference-in-differences regression on Eurobarometer data show that positive effects of ECoCs on attitudes towards and identification with the EU are limited both spatially to the hosting region and temporally to the immediate aftermath of the event. Thus, ECoCs are a tool to bring the EU closer to its citizens, but their effects could be amplified further by strengthening the European dimension of the events.publishe
Chimpanzees (Pan troglodytes) Indicate Mammalian Abundance Across Broad Spatial Scales
No full textOngoing ecosystem change and biodiversity decline across the Afrotropics call for tools to monitor the state of biodiversity or ecosystem elements across extensive spatial and temporal scales. We assessed relationships in the co‐occurrence patterns between great apes and other medium to large‐bodied mammals to evaluate whether ape abundance serves as a proxy for mammal diversity across broad spatial scales. We used camera trap footage recorded at 22 research sites, each known to harbor a population of chimpanzees, and some additionally a population of gorillas, across 12 sub‐Saharan African countries. From ~350,000 1‐min camera trap videos recorded between 2010 and 2016, we estimated mammalian community metrics, including species richness, Shannon diversity, and mean animal mass. We then fitted Bayesian Regression Models to assess potential relationships between ape detection rates (as proxy for ape abundance) and these metrics. We included site‐level protection status, human footprint, and precipitation variance as control variables. We found that relationships between detection rates of great apes and other mammal species, as well as animal mass were largely positive. In contrast, relationships between ape detection rate and mammal species richness were less clear and differed according to site protection and human impact context. We found no clear association between ape detection rate and mammal diversity. Our findings suggest that chimpanzees hold potential as indicators of specific elements of mammalian communities, especially population‐level and composition‐related characteristics. Declines in chimpanzee populations may indicate associated declines of sympatric medium to large‐bodied mammal species and highlight the need for improved conservation interventions.Changes in chimpanzee abundance likely precede extirpation of sympatric mammals.publishe
The defensive behaviour of honey bees (Apis mellifera) : individuality, social regulation, and neural mechanisms
No full textAmong all the different behaviours that animals exhibit, defensive behaviour lies at the intersection of survival of an individual, its kin, territory and resources. In both loosely aggregated and highly social animals, threats or predators are initially detected by guarding individuals, and an alarm signal is then communicated via visual, chemical or vibrational means to warn conspecifics. Depending on the nature of the group and the territory they protect, the defensive behaviour either sets off in a ‘flight’ or ‘fight’ response. Animals that choose the “flight” response either escape or hide themselves for a short period due to their inability to attack physically. In contrast, those that choose the “fight” response defend against their predators by physically assaulting them until the threat is deterred. Although defensive behaviour appears straightforward, it is not – as conspecifics can lose a limb or even die while defending their group and territory. The defensive behaviour in honey bees (Apis mellifera) operates similarly – individual bees sting their predators in an attempt to defend their colony; however, they die after stinging, creating a unique evolutionary paradox.
To balance out colony defence against loss of colony workforce, we must look beyond the ‘collective spirit’ of the hive to understand regulation at the individual level. Bees process sensory information in their individual brains, integrating cues from both the threat and surrounding environment. This information is likely weighed against competing factors, such as internal pre-dispositions, such as genetic predispositions and physiological conditions, to make a decision to either sting or not sting, which results in an efficient colony defence. My PhD research focuses on this aspect, on how bees regulate their individual and social factors, in the broad context of collective defensive behaviour. I cover different aspects of this theme, namely olfaction, individuality, social factors, and neural mechanisms, as elucidated in three chapters.
In Chapter 1, I explore via a literature review how insects, both solitary and social, defend against intruders by using their sense of olfaction. I detail how insects detect threats, deploy chemical 'weapons', and, in social insects, communicate danger through chemical signals called alarm pheromones. Further, I discuss the chemical properties of these alarm pheromones, their immediate behavioural as well as long-term physiological effects, along with their neural processing in the insect brain.
In Chapter 2, I asked whether individuals exhibit consistency in their stinging likelihood, which may suggest a predetermined bias to the threat, regardless of the defensiveness of the colony. I demonstrate that individual bees do vary in their stinging behaviours, and this variation persists in the presence of social factors. I further support these findings with explanations of an ‘internal state’. Moreover, I demonstrate that the stinging responsiveness of bees decreases upon exposure to the alarm pheromone over repeated trials, in contrast to their response to repeated visual stimuli of the threat. These findings suggest differential neurobiological mechanisms at the individual level for different stimuli. Finally, I confirm that group composition does not affect individual bees in their defensive decisions.
In Chapter 3, I investigate the neurobiological basis of defensive behaviour. Here, I focus on the biogenic amine, serotonin, which modulates aggression in a diverse range of invertebrates, including bees. Using higher spatial resolution techniques such as immunostaining, I map serotonergic activity in the bee brain following alarm pheromone exposure and stinging behaviour. With pharmacological manipulations, I identify a putative serotonergic receptor mediating stinging responses, providing preliminary evidence for a neural circuit underlying defensive behaviour.
Overall, my thesis advances our understanding of defensive behavior, which is one among the large behavioural repertoires of honey bees. My focus on behavioural and neurobiological perspectives in this topic have potential implications for understanding the evolution of social defense mechanisms in insects as well as other animals. Furthermore, it may also inform beekeeping practices on individual and colony defensiveness.publishe