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Amtliche Bekanntmachungen, 55. Jahrgang, Nr. 71
No full textOrdnung zur Änderung der Prüfungsordnung für die konsekutiven Masterstudiengänge „Geologie“, „Paläontologie“ und „Geochemie/Petrologie“ der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vom 3. September 202
One-dimensional aggregates of the organic dye quinacridone on metallic and dielectric surfaces
No full textThe present work deals with the question to what extent the motif of intermolecular hydrogen bonds (H-bonds) can be used to generate isolated one-dimensional (1D) structures, i.e. "chains", of organic molecules on surfaces through self-assembly. For this purpose, the structures of quinacridone (QA) were investigated using LEED and STM. Of particular interest was the question of whether such molecular chains can be formed not only on metallic substrates, but also on thin layers of insulating materials, where they may be electronically decoupled from the underlying metallic substrate.
First, the self-assembled structures of QA on the Ag(100) and Cu(111) surfaces were investigated. It was found that QA forms homochiral molecular chains that are held together by intermolecular H-bonds. These chains are metastable and are stabilized by a kinetic barrier. During annealing, the molecular chains on both surfaces transform into heterochiral structures. These heterochiral structures contain fewer H-bonds per molecule, which is overcompensated by stronger bonds between the molecules and the substrates. The kinetic barriers are given by the breaking of the intermolecular H-bonds and presumably by a slight reconstruction of the first layers of the metal substrates.
The second step consisted of electronically decoupling the molecular chains of QA from the underlying metal substrates. For this purpose, QA was evaporated onto thin films of insulating materials, namely KCl on Ag(100) and hBN on Cu(111), where the interactions between substrate and adsorbate are usually weaker. Interestingly, molecular chains of QA with different azimuthal orientations were observed on both thin KCl layers and a single hBN layer, which are stabilized by additional van der Waals interactions with the substrate. On thicker KCl layers, 3D clusters are formed instead of molecular chains, since the additional stabilization by the metal substrate is not given there.
In addition, it was investigated whether the QA structures on KCl layers can be stabilized by introducing a larger number of steps into the system, which can serve as favorable nucleation sites. For this purpose, the growth of epitaxial KCl layers on a vicinal Ag(100) surface was investigated. The KCl layer grows over the step edges of the vicinal surface in a carpet-like growth, which leads to a slight deformation of the KCl lattice. This has an effect on the growth of QA structures on the KCl layer. The deformation of the KCl lattice leads to more possible adsorption configurations for QA molecules and thus to a wider range of azimuthal chain orientations.
Overall, the studies in the present work show that the formation of intermolecular H-bonds is a powerful motif that can be used to create one-dimensional organic structures on metal surfaces and thin films of insulating materials. However, the substrate also plays an important role, as all observed structures are the result of a delicate balance between the intermolecular and substrate-adsorbate interactions
Amtliche Bekanntmachungen, 55. Jahrgang, Nr. 55
No full textPrüfungsordnung für den Bachelorstudiengang „Agrarwissenschaften“ der Agrar-, Ernährungs- und Ingenieurwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vom 20. August 202
Plural Sustainabilities : Reflections and Ways Ahead
Get PDF"Sustainability" is a diverse and contested concept that cannot be reduced to a single definition or practice. We propose the concept of "plural sustainabilities" to raise awareness of how different worldviews, knowledge systems, and values shape understandings of sustainability, recognizing the context-specific and culturally rooted approaches to sustainability found across the globe. Thereby, we use the concept of sustainability as a "boundary object"—a flexible term that connects different perspectives—and illustrates a plurality of sustainability concepts and practices through examples from various countries, including Bolivia, Colombia, Chile, Indonesia, Ghana, Germany, Tanzania, and China. These examples highlight how local knowledge, cultural philosophies, national narratives, grassroots initiatives, and international policy frameworks contribute to sustainability. Through our discussions, we advocate for a "scientific multilingualism"— a more inclusive and pluralistic approach to sustainability research that values diverse way of living, interacting with, and making sense of the world. "Plural sustainabilities" calls on researchers to critically assess the development models advanced in the name of sustainability, particularly those influenced by national governments and international organizations. These models often, whether intentionally or not, perpetuate the same extractive practices and socio-environmental injustices they aim to resolve. A truly critical approach must go beyond surface-level commitments and explore how political decisions and institutional practices—both public and private—shape sustainability efforts in ways that may reinforce existing power structures. Recognizing and challenging this political use of sustainability is essential to support alternative, context-based responses grounded in plural worldviews, local knowledge, and transformative action
Associated production of a top-quark and a Higgs-boson in the <em>H</em>→ττ decay channel in <em>pp</em> collisions at √<em>s</em> = 13 TeV using the ATLAS detector
No full textSince the discovery of the Higgs-boson in 2012, experiments at the LHC have focused on studying and precisely measuring this particle's properties. Of particular interest is the Yukawa coupling between the Higgs-boson and the heaviest known elementary particle, the top-quark. Besides the coupling's magnitude, its relative sign with respect to the Higgs-boson's coupling to gauge bosons is also of importance. Both aspects can be probed by analysing the associated production of a top-quark and a Higgs-boson (tH). In the Standard Model, a positive sign of this Yukawa coupling is predicted, causing a destructive interference in the tH channel, thereby lowering the cross-section. The simultaneous presence of large background processes makes the search for tH events particularly challenging. However, certain hypotheses beyond the Standard Model allow for an inverted coupling, resulting in a constructive interference that would significantly enhance the tH cross-section. This thesis probes both hypotheses by investigating the tH production in H→ττ decay channels, using pp collisions at √s = 13 TeV, recorded by the ATLAS detector. The analysis is conducted in channels with either one or two hadronically decaying tau-leptons. After applying a common preselection, a categorical neural network is used in each channel to improve the background rejection and thereby to enhance the sensitivity of the analysis. To ensure reliable results, the modelling of all dominant background processes is validated and corrected in dedicated control regions. The cross-section estimation is performed via a binned profile likelihood fit, testing both the Standard Model and the inverted coupling hypothesis
Dense Gas and Star Formation from the Milky Way to Nearby Galaxies
No full textGalaxies are the building blocks of the universe, which come in different sizes and shapes. Driven by dark matter, galaxies can interact and merge to form bigger galaxies across cosmic time. Across the cosmos, there are billions of galaxies that can be divided into two main classes - ellipticals and spirals. Spiral galaxies contain large gas reservoirs and show active star formation, while ellipticals are often depleted of gas and quenched in star formation. Galaxies contain hundreds of millions of stars that light up the universe. Everything between the stars is called the interstellar medium - a complex, turbulent subject containing various components and phases. One of the most interesting component are molecular clouds, which are the sites of star formation.
Star formation is at the heart of many astrophysical processes from planet formation to galaxy evolution that is intimately connected to the cycle of matter in galaxies, dominating its energy budget and chemical composition. At the same time, star formation is one of the most complex processes in the universe and hence only poorly understood. One of the key science questions is whether star formation proceeds in a universal way across the universe or if it varies across galaxies. Gaining a deeper understanding of the process of star formation requires the study of molecular gas in galaxies, which is the fuel for star formation. While it is known that stars form in the densest parts of giant molecular clouds, it is not very well understood how fast and efficiently gas is converted into stars and if and how star formation varies between and within galaxies.
Answering these questions requires observations of the densest parts of giant molecular clouds in a representative sample of star-forming galaxies. While hardly observable at optical wavelength, the interstellar medium shines at radio wavelength in molecular line emission. Only recently, radio observatories such as ALMA and the IRAM facilities have opened up a golden age of radio astronomy, allowing the detailed study of the interstellar medium in galaxies. This thesis makes use of the novel capabilities of ALMA to present the largest sample of dense gas observations across the local universe paired with multi-wavelength observations from state-of-the-art telescopes such as the VLT and JWST, allowing the most detailed view of dense gas and star formation in nearby galaxies.
In this thesis, we connect dense molecular gas, star formation, galactic environment and molecular cloud properties in a comprehensive way using new observations of nearby, star-forming galaxies. We find that the efficiency of converting dense gas into stars is not the same across galaxies, but varies with galactic environment and dynamical properties of molecular clouds in agreement with turbulent clouds models. On the one hand, these findings suggest that more extreme, dense, high-pressure, turbulent environments, typically found towards galaxy centres, might convert dense gas less efficiently into stars compared to the discs where clouds tend to decouple from the environment and show higher star formation efficiencies. On the other hand, these results also indicate that the tracers used to infer the mass of dense gas might become less trustworthy in these extremer environments. Therefore, we test the capabilities and limitations of these dense gas tracers, using new radio observations of molecular clouds in the Milky Way that provide a robust, high-resolution view of the physical conditions of molecular clouds and their associated line emission. We find that typical extragalactic dense gas tracers can also trace lower-density gas, questioning their utilisation as robust tracers of dense gas. Nevertheless, we show that these tracers are still sensitive to density and hence powerful extragalactic tools.Dichtes Gas und Sternentstehung in der Milchstraße und nahen Galaxien
Galaxien sind die Bausteine des Universums, die in verschiedenen Größen und Formen vorkommen. Beeinflusst von dunkler Materie können Galaxien interagieren und verschmelzen, um im Laufe der kosmischen Zeit größere Galaxien zu bilden. Im gesamten Kosmos gibt es Milliarden von Galaxien, die in zwei Hauptklassen unterteilt werden können – elliptische und spiralförmige Galaxien. Spiralgalaxien enthalten große Gasreservoirs und zeigen aktive Sternentstehung, während elliptische Galaxien oft gasarm und in der Sternentstehung erloschen sind. Galaxien enthalten Hunderte Millionen von Sternen, die das Universum erleuchten. Alles zwischen den Sternen wird als interstellares Medium bezeichnet -- eine komplexe, turbulente Substanz, die verschiedene Komponenten und Phasen enthält. Eine der interessantesten Komponenten sind molekulare Wolken, in welchen Sternentstehung passiert.
Die Sternentstehung steht im Zentrum vieler astrophysikalischer Prozesse von der Planetenbildung bis zur Galaxienentwicklung, die eng mit dem Materiekreislauf in Galaxien verbunden ist und das Energiebudget und die chemische Zusammensetzung dominiert. Gleichzeitig ist die Sternentstehung einer der komplexesten Prozesse im Universum und daher nur unzureichend verstanden. Eine der wichtigsten wissenschaftlichen Fragen ist, ob die Sternentstehung im gesamten Universum auf eine universelle Weise abläuft oder ob sie von Galaxie zu Galaxie variiert. Ein tieferes Verständnis des Prozesses der Sternentstehung erfordert das Studium von molekularem Gas in Galaxien, das den Treibstoff für die Sternentstehung liefert. Während bekannt ist, dass Sterne in den dichtesten Teilen von riesigen Molekülwolken entstehen, ist es noch nicht gut verstanden, wie schnell und effizient Gas in Sterne umgewandelt wird und ob und wie sich die Sternentstehung zwischen und innerhalb von Galaxien unterscheidet.
Um diese Fragen zu beantworten, sind Beobachtungen des dichten Gases von Molekülwolken in einer repräsentativen Stichprobe von sternbildenden Galaxien erforderlich. Im optischen Wellenlängenbereich kaum beobachtbar, leuchtet das interstellare Medium im Radiowellenbereich in Form von molekularer Linienemission. Erst kürzlich haben Radioobservatorien wie ALMA und die IRAM-Observatorien ein goldenes Zeitalter der Radioastronomie eingeläutet, das die detaillierte Untersuchung des interstellaren Mediums in Galaxien ermöglicht. Diese Arbeit nutzt die revolutionären Fähigkeiten von ALMA, um die größte Stichprobe von Beobachtungen des dichten Gases im lokalen Universum zu präsentieren. Kombiniert mit Beobachtungen von hochmodernen Teleskopen wie dem VLT und JWST, bildet diese Studie eines der detailliertesten Blicke auf dichtes Gas und Sternentstehung in nahegelegenen Galaxien.
In dieser Arbeit werden dichtes molekulares Gas, Sternentstehung, galaktische Umgebung und die Eigenschaften von Molekülwolken auf umfassende Weise verknüft. Daber werden neue Beobachtungen von nahegelegenen, sternbildenden Galaxien verwendet. Wir finden, dass die Effizienz der Umwandlung von dichtem Gas in Sterne nicht in allen Galaxien gleich ist, sondern mit der galaktischen Umgebung und den dynamischen Eigenschaften von Molekülwolken in Übereinstimmung mit Modellen turbulenter Wolken variiert. Einerseits deuten diese Ergebnisse darauf hin, dass in extremen, dichten, turbulenten Umgebungen mit hohem Druck, die typischerweise in Galaxienzentren zu finden sind, dichtes Gas weniger effizient in Sterne umgewandelt wird als in Galaxienscheiben, in denen sich die Molekülwolken von der Umgebung entkoppeln und höhere Sternentstehungseffizienzen zeigen. Andererseits weisen diese Ergebnisse auch darauf hin, dass die Indikatoren, die verwendet werden, um die Masse von dichtem Gas abzuleiten, in diesen extremeren Umgebungen weniger zuverlässig sein könnten. Daher testen wir die Fähigkeiten und Einschränkungen dieser Indikatoren für dichtes Gas unter Verwendung neuer Radiobeobachtungen von Molekülwolken in der Milchstraße, die einen robusten, hochauflösenden Blick auf die physikalischen Bedingungen von Molekülwolken und deren zugehörige Linienemission bieten. Wir stellen fest, dass typische extragalaktische Indikatoren für dichtes Gas auch Gas mit niedrigerer Dichte nachweisen können, was ihre Verwendung als robuste Indikatoren für dichtes Gas in Frage stellt. Nichtsdestotrotz zeigen wir, dass diese Indikatoren dennoch empfindlich auf Dichte reagieren und somit mächtige extragalaktische Werkzeuge sind
Amtliche Bekanntmachungen, 55. Jahrgang, Nr. 44
No full textPrüfungsordnung für den Bachelorstudiengang „Law and Economics“ der Rechts- und Staatswissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vom 9. Juli 202
Singular Brascamp-Lieb Forms and Multilinear Fourier Multipliers with Rough or Oscillatory Multipliers
Get PDFIn this thesis, we study the boundedness of several multilinear operators including singular Brascamp-Lieb forms and certain multilinear Fourier multipliers with rough or oscillatory multipliers. Several important multilinear singular integral operators in harmonic analysis such as the Coifman-Meyer multipliers, the bilinear Hilbert transform, and twisted paraproducts all fall within the class of singular Brascamp-Lieb forms. The boundedness of a singular Brascamp-Lieb form is invariant under certain linear changes of variables. Given specific dimension data, we classify singular Brascamp-Lieb forms up to equivalence and characterize their boundedness in this setting. Typically, for a given singular Brascamp-Lieb form, one imposes the Mihlin's condition on its multiplier, which is the Fourier transform of the singular kernel. This Mihlin's condition can be generalized to Hormander's condition, which allows for fractional regularity. Naturally, this raises the question: what is the minimal regularity required of the multiplier to ensure boundedness? We address this question for multipliers that may exhibit Lipschitz-type singularities. Furthermore, the linear projections appearing in singular Brascamp-Lieb forms can be replaced by nonlinear maps. This line of research traces back to the 1970s, when singular Radon transforms were first studied. We also explore multilinear generalizations of the singular Radon transform, where the associated multipliers may exhibit oscillatory behavior. A crucial step in establishing the boundedness of such multilinear oscillatory multipliers is to prove a suitable smoothing inequality. We provide partial answers regarding which classes of multilinear oscillatory multipliers admit such smoothing effects
Epigenetische Regulation und klinische Relevanz der Immuncheckpoints PD-L1, CTLA-4, LAG-3 und BTLA in Kopf-Hals- und Blasenkarzinom
Get PDFDie vorliegende Dissertation untersucht die epigenetische Regulation und klinische Relevanz von Immuncheckpoints in Plattenepithelkarzinomen des Kopf-Hals-Bereichs ("head and neck squamous cell carcinoma", HNSCC) und in Urothelkarzinomen ("urothelial carcinoma", UC). Die Arbeit zeigt, dass eine niedrige Methylierung des programmierten Zelltod-Liganden 1 ("programmed cell death ligand-1", PD-L1) bei Urothelkarzinomen mit einem besseren Ansprechen auf die Immuncheckpoint-Blockade sowie verlängertem progressionsfreiem und Gesamtüberleben korreliert. Zudem wird die epigenetische Regulation des zytotoxischen T-Lymphozyten-assoziierten Proteins 4 ("cytotoxic T-lymphocyte associated protein 4", CTLA-4) durch Promotormethylierung nachgewiesen, was insbesondere in HNSCC mit Therapieansprechen und progressionsfreiem Überleben unter Anti-PD-1-Therapie verbunden ist. Die Ergebnisse legen nahe, dass die Methylierung von Immuncheckpoints eine wichtige Rolle im Therapieansprechen spielt und die Methylierung von CTLA-4 als potenzieller prädiktiver Biomarker für personalisierte Immuntherapien in HNSCC weiter erforscht werden sollte. Insgesamt unterstreicht die Arbeit die Bedeutung von Genmethylierung als Mechanismus zur Beeinflussung der Immuncheckpoint-Expression und damit des Behandlungserfolges bei HNSCC und UC
Exploring Plant Responses to Changing Environments: Integrating Phenotyping and Modeling Across Scales
No full textClimate change and the depletion of essential resources like phosphorus are challenging agriculture by reducing water and fertilizer availability and ultimately threatening the security of the human food supply. Knowledge of how plants respond to changing environmental conditions is required to cope with these challenges. Plant growth information and corresponding environmental data are key to unraveling stress responses and revealing the underlying mechanisms. Understanding architectural and functional plant adaptations to stresses, such as water and nutrient limitation, is crucial to exploring new pathways to sustainable agriculture. It is vital to consider all organs, including the often-overlooked root system and surrounding soil, that are essential for water and nutrient uptake. Plant phenotyping and functional-structural plant modeling are key technologies for understanding plant responses to changing environments, making their continued development and application imperative. This doctoral project is dedicated to advancing the field of plant research by 1. developing a novel in situ phenotyping method for roots, 2. applying this method to assemble a comprehensive collection of in-field root and soil data, 3. investigating the architectural responses of Zea mays to phosphorus deficiency, 4. gaining a deeper understanding of the responses to stress by investigating the effects of phosphorus deficiency on the root system’s conductance, and 5. placing the findings into an overall context.
First, a new method combining deep neural networks and automated feature extraction was developed and validated to analyze root images, reducing processing time by 98% while achieving high precision compared to manual annotation (r=0.9). Second, besides other technologies, this method was applied to assemble a comprehensive collection of in-field root and soil data over time in two minirhizotron facilities in distinct soil domains. The resulting open-access, time-series dataset includes dynamic crosshole ground-penetrating radar, minirhizotron camera measurements, and static soil sensor observations at a high temporal and spatial resolution over five years of Zea mays and Triticum aestivum experiments, including drought stress treatments and crop mixtures trials. Third, a combined approach of the developed phenotyping workflow and functional-structural plant modeling was used to investigate the responses of Zea mays to varying phosphorus availability. Combining measured architectural plant parameters with root hydraulic properties enabled time-dependent simulations of plant growth and root system conductance under different phosphorus regimes, revealing that only plants with optimal phosphorus availability sustained a high root system conductance. In contrast, all other phosphorus levels led to significantly lower root system conductance under light and severe phosphorus deficiency. It was also shown that root system organization is critical for its function rather than mere total size. Finally, this thesis contributes to collaborative studies aiming to enhance phenotyping methods and further investigate Zea mays responses to environmental changes. We found that ground-penetrating radar could be employed as a root-sensing tool in the future. By linking aboveground crop data to the belowground dataset, we revealed that maize responses to water stress vary significantly with soil conditions. We combined the automated analysis method with functional-structural modeling to show that Zea mays domestication was driven by water availability, with seminal root number emerging as a critical adaptation trait, possibly providing key information for breeding drought-tolerant varieties. Lastly, we applied an in silico approach using a game engine that visualizes plant models in high-performance computing environments to generate virtual data for neural networks, enhancing their precision and informative power.
This work explores different methods, data, and models to understand plant responses to a changing environment across scales and provides new insights into the combined stress responses and development of Zea mays