Technische Universität Dresden: Qucosa
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High Gain Graphene Based Hot Electron Transistor with Record High Saturated Output Current Density
No full textHot electron transistors (HETs) represent an exciting new device for integration into semiconductor technology, holding the promise of high-frequency electronics beyond the limits of SiGe bipolar hetero transistors. With the exploration of 2D materials such as graphene and new device architectures, hot electron transistors have the potential to revolutionize the landscape of modern electronics. This study highlights a novel hot electron transistor structure with a record output current density of 800 A cm−2 and a high current gain α, fabricated using a scalable fabrication approach. The hot electron transistor structure comprises 2D hexagonal boron nitride and graphene layers wet transferred to a germanium substrate. The combination of these materials results in exceptional performance, particularly in terms of the highly saturated output current density. The scalable fabrication scheme used to produce the hot electron transistor opens up opportunities for large-scale manufacturing. This breakthrough in hot electron transistor technology holds promise for advanced electronic applications, offering high current capabilities in a practical and manufacturable device
Classical Invasive Description of Informationally-Complete Quantum Processes
No full textIn classical stochastic theory, the joint probability distributions of a stochastic process obey by definition the Kolmogorov consistency conditions. Interpreting such a process as a sequence of physical measurements with probabilistic outcomes, these conditions reflect that the measurements do not alter the state of the underlying physical system. Prominently, this assumption has to be abandoned in the context of quantum mechanics, yet there are also classical processes in which measurements influence the measured system. Here, conditions that characterize uniquely classical processes that are probed by a reasonable class of such invasive measurements are derived. We then analyze under what circumstances such classical processes can simulate the statistics arising from quantum processes associated with informationally-complete measurements. It is expected that this investigation will help build a bridge between two fundamental traits of non-classicality, namely, coherence and contextuality
Umweltkommunikation zum Waldzustand und zur Wiederherstellung von Waldlandschaften: Analyse von Online-Medien ausgewählter Akteure mit Waldbezug in Deutschland
No full textDiese Dissertation untersucht die Umweltkommunikation zum Waldzustand und zur Wiederherstellung von Waldlandschaften in Deutschland. Im Fokus steht die Online-Kommunikation auf den Webseiten verschiedener, waldbezogener Akteure, darunter Ministerien, Landesforstbetriebe, Umweltorganisationen, Interessenverbände und Forschungseinrichtungen. Ziel der Arbeit ist es, Umfang, sprachliche Gestaltung und Performanz der vermittelten Informationen zu analysieren und deren potenzielle Auswirkungen auf die öffentliche Meinungsbildung und forstpolitische Entscheidungen zu bewerten.
Die zentrale Forschungsfrage lautet: Welche Akteure kommunizieren online über den Waldzustand und die Wiederbewaldung, mit welchen Inhalten, in welcher sprachlichen Form und mit welcher medialen Performanz? Dazu wurden u.a. eine Inhaltsanalyse, eine Sprachintensitätsanalyse sowie eine Performanzanalyse der Webseiten durchgeführt. Ergänzend erfolgten eine Online-Befragung zur Wahrnehmung themenrelevanter Begriffe und eine Keyword-Analyse zur Ermittlung der Begriffsverwendung.
Die Ergebnisse zeigen, dass der Umfang und die Qualität der bereitgestellten Informationen zwischen den Akteursgruppen erheblich variieren. Staatliche Akteure bieten ausführliche, evidenzbasierte Inhalte zu Waldschäden und Wiederbewaldungsmaßnahmen an, die jedoch häufig in einem fachsprachlich komplexen und sachlichen Stil präsentiert werden. Die Performanzanalyse offenbart, dass viele Webseiten der staatlichen Akteure Mängel hinsichtlich einer optimalen User Experience aufweisen. Die Mängel liegen dabei insbesondere bei der visuellen Gestaltung, der Textlastigkeit, der geringen Einbindung anderer, eigener Informationskanäle wie Socialmedia, Videos und Publikationen sowie in der schwierigen Auffindbarkeit der hier relevanten Informationen. Die Webseiten der Umwelt- und Naturschutz-NGOs zeichnen sich ausnahmslos durch eine gute bis sehr gute User Experience aus, wodurch ihre Webseiten potenziell eine längere Verweildauer und deren Inhalte eine höhere Aufmerksamkeit erzielen. Umwelt- und Naturschutz-NGOs kommunizieren aktivierend, aber häufig selektiv. Sie setzen gezielt auf emotionalisierte Darstellungen und nutzen vereinfachte Narrative, um ihr Framing zu verstärken. Forstwirtschaftliche Verbände bzw. deren Informationsangebot und Webseiten-Performanz sind zwischen den staatlichen Akteuren und den Umwelt- und Naturschutz-NGOs einzuordnen.
Die Studie leistet einen Beitrag zur Forschung über waldbezogene Umweltkommunikation, indem sie aufzeigt, dass ein wissenschaftlich fundiertes, aber verständliches, nutzerfreundliches und visuell ansprechend aufbereitetes Informationsangebot notwendig ist, um Polarisierungen zu reduzieren, evidenzbasierte Diskurse zu fördern und einem möglichen Verlust von Akzeptanz forstwirtschaftlicher Aktivitäten vorzubeugen
Resilient by Design - Integrating Water and Climate in Higher Education for a Sustainable Future
No full textIntegrating climate adaptation strategies into water resources management is critical to safeguarding human well-being, ecological stability, and socio-economic development. As the impacts of climate change become increasingly pronounced, water systems are subject to heightened vulnerabilities such as flooding, drought, and infrastructural failure. At the same time, higher education institutions (HEIs) hold a unique potential to bridge the persistent gap between scientific knowledge and practical policy application. By leveraging their capacity for innovation, research, and capacity building, HEIs can drive forward sustainable water governance and climate resilience.
This policy brief explores key challenges, outlines a multi-layered adaptation strategy, and provides recommendations for embedding climate-responsive water policies into national and international frameworks. It further presents an expanded vision for cross-sectoral cooperation, identifies implementation bottlenecks, and proposes pathways for HEI’s engagement in policymaking, digital innovation, and public transformation. With the escalating urgency of water-related climate impacts, the role of adaptive knowledge infrastructures becomes not only strategic but indispensable.:Summary
Integrated Challenges and Opportunities in Climate-Water Governance
Strategic Adaptation Pathways for Resilient Water Systems
Cross-Sectoral Synergies and Nexus Approaches
Digital Transformation and Data-Driven Resilience
Institutional Barriers and Implementation Bottlenecks
Policy Recommendations: Toward Transformative Adaptation
Conclusion: A Call to Collective Action
References
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Modality-specific and modality-independent neural representations work in concert in predictive processes during sequence learning
No full textProbabilistic sequence learning supports the development of skills and enables predictive processing. It remains contentious whether visuomotor sequence learning is driven by the representation of the visual sequence (perceptual coding) or by the representation of the response sequence (motor coding). Neurotypical adults performed a visuomotor sequence learning task. Learning occurred incidentally as it was evidenced by faster responses to high-probability than to low-probability targets. To uncover the neurophysiology of the learning process, we conducted both univariate analyses and multivariate pattern analyses (MVPAs) on the temporally decomposed EEG signal. Univariate analyses showed that sequence learning modulated the amplitudes of the motor code of the decomposed signal but not in the perceptual and perceptual-motor signals. However, MVPA revealed that all 3 codes of the decomposed EEG contribute to the neurophysiological representation of the learnt probabilities. Source localization revealed the involvement of a wider network of frontal and parietal activations that were distinctive across coding levels. These findings suggest that perceptual and motor coding both contribute to the learning of sequential regularities rather than to a neither–nor distinction. Moreover, modality-specific encoding worked in concert with modality-independent representations, which suggests that probabilistic sequence learning is nonunitary and encompasses a set of encoding principles
Präzise Graphen-Nanostreifen Heteroübergänge durch Kettenwachstumspolymerisation
No full textGraphene-Nanostreifen (GNS, engl. GNR) werden als vielversprechende Kandidaten für Nanoelektroniken der nächsten Generation gehandelt. Besonders Heteroübergänge in diesen Materialien erhalten durch ihre exotischen topologischen elektronischen Phasen am Heteroübergang in letzter Zeit viel Aufmerksamkeit. Allerdings sind Synthesestrategien für die atompräzise Synthese noch am Beginn ihrer Entwicklung. Hier berichten wir von einer neuartigen Strategie zur Kettenwachstumspolymerisation für die Konstruktion von Heteroübergängen zwischen N=9 Sessel-GNR (engl. armchair, 9-AGNR) und chevron GNRs (cGNR). Die Synthese beinhaltet eine kontrollierte Suzuki–Miyaura Katalysatortransferpolymerisation (engl. SCTP) zwischen 2-(6′-bromo-4,4′′-ditetradecyl-[1,1′:2′,1′′-terphenyl]-3′-yl)boronsäureester (M1) und 2-(7-bromo-9,12-diphenyl-10,11-bis(4-tetradecylphenyl)-triphenylen-2-yl)boronsäureester (M2) um das Blockcopolymer poly-M1/M2 mit einem kontrollierten Mn (18 kDa) und einem schmalen Polydispersitätsindex Đ (1.45) zu erhalten. Darauf folgt eine Schollreaktion des Blockcopolymers zur Heterostruktur 9-AGNR/cGNR. NMR und SEC von poly-M1/M2 bestätigen die erfolgreiche Blockcopolymerisation. Die lösungsvermittelte Zyklodehydrierung von poly-M1/M2 zu 9-AGNR/cGNR wurde eindeutig über FT-IR, Raman und UV/Vis Spektroskopie nachgewiesen. Weiter konnten wir die Ausbildung von 9-AGNR/cGNR durch Oberflächenchemie des unsubstituierten Blockcopolymers mit Hilfe von Rastertunnelmikroskopie (RTM) direkt visualisieren
Journal of forest and landscape research
No full textJFLR is an international open access journal presenting current research into forest ecosystems and forest management in a landscape context.
The journal publishes original research papers, short communications, and review papers; presenting findings from experimental and empirical studies, modelling studies, and conceptual studies of forest ecosystems, plantations and trees in urban environments worldwide
Stegreifentwürfe: Entwurfsreihe Para Sport
No full textDie Stegreifreihe ist eine kurze Entwurfsaufgabe für Studierende. Ziel ist es in kurzer Zeit eine Idee und ein Konzept zu entwickeln und dieses zu präsentieren. Mit der Stegreifreihe wird eine praxisorientierte Ergänzung zum ARCH4HEALTH Student Research Lab geschaffen.
Im Sommersemester 2024 war das Ziel der Stegreifreihe die Möglichkeiten und Herausforderungen der Architektur im Bereich des Para Sports beim Fest der Begegnung der Stadt Dresden und beim Tag der Gesundheit der TU Dresden zu präsentieren und eine aktive Partizipation zu erzielen.
Im STEG 1: Die Idee wurden Ideen und Konzepte entwickelt. Diese wurden in STEG 2: Die Umsetzung an den beiden Festen umgesetzt und von den Teilnehmenden sehr positiv angenommen. Den Abschluss bildet STEG 3: Die Dokumentation mit einer Dokumentation der Feste und eine Reflexion für zukünftige Veranstaltungen. [... aus dem Text
Collective biomolecular timers: from development to aging
No full textIn biological systems, the development and maintenance of complex tissues require the precise timing of cell behavior. The control of timing spans processes spanning many orders of magnitude in space and time: from interactions of proteins with the DNA on a time scale of milliseconds to the systematic, decade-long progression of aging. How precise temporal scales emerge from orders of magnitude faster molecular events is generally not known.
In this thesis, we demonstrate how collective biomolecular processes lead to emergent timing across temporal scales. Specifically, by developing biophysical theories based on sequencing experiments, we show how subcellular processes establish the temporal scales controlling cell behavior in early human development, cellular reprogramming, and aging.
Aging is the functional decline of an organism over time. Whether it is the result of the accumulation of fast molecular events or slowly driven by an external process is unknown. Using the example of epigenetic modifications of the DNA (DNA methylation), we show that aging is the accumulation of fast molecular events. Specifically, we draw on a combination of experiments spanning different temporal scales of DNA methylation dynamics using genomic experiments. From these, we derive a biophysical theory comprising the coordination of molecular binding events to the DNA, noise, and the geometric conformation of the DNA. We show that this theory consistently predicts experimental quantifications of DNA methylation across temporal scales, namely the convergence to fixed points on the scale of a few rounds of cell divisions and stochastic transitions between these fixed points on the time scale of years. Our work provides a unified picture of epigenetic aging spanning the milliseconds scale to the time scale of the progression of aging.
A second example of the regulation of time scales is the maintenance of cell functions. Cells perform highly specialized tasks over long periods, but under specific signals, such as after injury, they can reprogram rapidly to different cell types. We show that the interplay between DNA geometry and the stochastic dynamics of chemical modifications of the DNA provides a mechanism for achieving simultaneously stable and plastic epigenetic marks on the DNA. To this end, we introduce a minimal field theoretical model that incorporates the dynamics of a one-dimensional field that interacts in three dimensions via contacts induced by fluctuations of a polymer. This system exhibits a phase diagram encompassing a stable and a plastic regime controlled by the statistical properties of the DNA geometry. Our work provides an exemplary mechanism for how the stability plasticity dilemma is resolved on a molecular scale.
In the context of development, complex organisms rely on the precise regulation of the timing of successive events. As a paradigmatic example, during the early stages of human development, pluripotent epiblast cells wait for around 14 days before they commit to differentiation into more specialized cell types. How subcellular processes measure this time interval is not known. So far, one molecular mechanism has been identified as a timekeeper in development: the genetic oscillator. Here, we identify a novel mechanism for molecular timekeeping: the transcriptional hourglass used in early human development. By using gene network inference on single-cell sequencing experiments, we first derived a mathematical model predicting gene expression dynamics during the developmental transition. By coarse-graining this model, we show that timing is controlled by a dynamical system comprising the convergence to an attractor, which is regulated by a bottleneck mechanism. The same mechanism predicts the much faster timing in the mouse embryo.
Overall, by combining genomic experiments with theoretical biophysics, our work unveils paradigms of how biomolecular processes collectively control timing. We expect that, due to their generality, these paradigms are employed by biological systems beyond the ones studied in this thesis
Zuverlässigkeit von ausscheidungshärtbaren und martensitischen Stählen im additiv gefertigten Zustand unter hochzyklischer mechanischer Beanspruchung
No full textThis dissertation deals with the reliability of precipitation-hardened martensitic steels under cyclic mechanical loading up to > 109 cycles. The experimental work explores the two typical representatives of the material group X3NiCoMoTi18 9 5 (1.2709) and X5CrNiCuNb17 4 4 (1.4548) manufactured by laser beam powder bed fusion (PBF LB) and in heat treated condition. In addition to the microstructural analysis and quasi-static investigations, the focus is on fatigue tests on typical laboratory fatigue specimens using ultrasonic fatigue testing technology. Thereby, specimens from a conventionally rolled process and a PBF-LB are compared. PBF-LB process parameters with different building directions and surface conditions as well as process-inherent irregularities are taken into account. The transferability of the determined fatigue strengths is evaluated using component-like cube-shaped scaffold structures with an edge length of 80 mm. The irregularities present in the material are quantified by metallographic cross-sections and fractographic analyses of failed samples. These methods are used to determine √area values according to the concept proposed by Murakami. With the support of the Kitagawa-Takahashi-diagram, √area values and experimental strength values are linked and can be compared.
The experimental findings show that both test materials exhibit similar behavior: Heat treatment in the form of solution annealing and aging results in a comparable microstructure for all material states considered. Irregularities present in the material are not only inhomogeneous in space but also logarithmically normally distributed in size. The irregularities cause a significantly reduced formability under quasi-static loading. Under cyclic loading, the irregularities determine the failure and reduce the strength. Corresponding to the irregularity distribution, the fatigue life or the endurable stress amplitude is also subject to a broad distribution. Thus typical laboratory fatigue test specimens are not suitable for characterizing the fatigue strength of materials using classic fatigue test methods. Large √area values of the samples with machined surfaces reach the dimension around 200 µm. The crack-initiating irregularities from the samples with an as built surface are also concentrated in this order of size. The Kitagawa-Takahashi-diagram shows that it is possible to determine a reliable long-term fatigue strength using the El Haddad-model. Thereby, the main challenge is to determine the largest irregularity present in the material. As a simple approximation, the size distribution of the irregularities in the material can be represented by using samples with process-typical surfaces. For the investigated materials, the largest √area value determined 215 µm results in long-term fatigue strengths of 146 MPa for the X3NiCoMoTi18-9-5 and 199 MPa for the X5CrNiCuNb17-4-4, independently of the sample surface and building direction. Compared to the rolled material, surface structure and irregularities cause a significant reduction of the long-term fatigue strength of approx. 450 respectively 300 MPa in PBF LB manufactured specimens.:Danksagung 1
Abstract 2
Kurzfassung 3
Symbolverzeichnis 5
Abkürzungsverzeichnis 7
Abbildungsverzeichnis 8
Tabellenverzeichnis 10
1 Einleitung 11
2 Stand der Wissenschaft 12
2.1 Additive Fertigung 12
2.2 Werkstoffermüdung 24
2.3 Schwingfestigkeitsvorhersage 35
2.4 Werkstoffe 43
3 Forschungsfragen 52
4 Methoden 53
4.1 Probenherstellung 53
4.2 Quasi-statische Kennwerte 57
4.3 Ermüdungsprüfung 58
4.4 Analytische Methoden 62
4.5 Ergebnisaufbereitung 63
5 Ergebnisse und Bewertung 68
5.1 Mikrostruktur 68
5.2 Quasi-statische Kennwerte 81
5.3 Wöhlerversuche 90
5.4 Fraktographie 102
5.5 Schwingfestigkeitsvorhersage 116
5.6 Überblick 128
6 Zusammenfassung 134
7 Literatur 135
Selbstständigkeitserklärung 147
Anhang 14