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Thermodynamisch‐analytische Modellierung der Karbonatisierung in Betonen aus klinkerreduzierten Zementen
Get PDFDas Bestreben, die Umwelteinwirkungen von Zement und Beton zu verringern, wird zukünftig zum vermehrten Einsatz klinkerreduzierter Zemente führen. Etablierte Modelle zur Vorhersage der Karbonatisierungstiefe (xc) sind aber häufig auf Betone aus handelsüblichem Zement beschränkt. In diesem Beitrag werden die Karbonatisierungsraten von Beton aus Zement mit bis zu 60 Gew.‐% Kalksteinmehl (LS) und w/z‐Werten von 0,3 bis 0,75 untersucht. Zur Abschätzung der xc wurde ein gekoppeltes analytisch‐thermodynamisches Modell entwickelt. Der vorgeschlagene Modellierungsansatz beinhaltet die thermodynamische Berechnung der effektiven CO2‐Bindekapazität und einen analytischen Ansatz zur Abschätzung des CO2‐Diffusionskoeffizienten. Die gute Übereinstimmung zwischen berechneten und experimentell (XRD und TGA) ermittelten Phasenzusammensetzungen zeigt, dass thermodynamische Teilmodelle eine Möglichkeit bieten die Vorhersagegenauigkeit der xc zu verbessern. Die größten Abweichungen zwischen simulierten und tatsächlichen xc wurden bei dichtem Beton beobachtet. Die Untersuchungen und Modellierungen ergaben, dass die betontechnologisch optimierten, klinkerreduzierten Betone mit bis zu 60 Gew.‐% Kalksteinmehl ähnlich hohe Karbonatisierungswiderstände aufweisen können wie Beton aus CEM I 52.5 R
Enhancing coherent transport in a photonic network using controllable decoherence
Get PDFTransport phenomena on a quantum scale appear in a variety of systems, ranging from photosynthetic complexes to engineered quantum devices. It has been predicted that the efficiency of coherent transport can be enhanced through dynamic interaction between the system and a noisy environment. We report an experimental simulation of environment-assisted coherent transport, using an engineered network of laser-written waveguides, with relative energies and inter-waveguide couplings tailored to yield the desired Hamiltonian. Controllable-strength decoherence is simulated by broadening the bandwidth of the input illumination, yielding a significant increase in transport efficiency relative to the narrowband case. We show integrated optics to be suitable for simulating specific target Hamiltonians as well as open quantum systems with controllable loss and decoherence
Stability Analysis and Mitigation of Thermo-Hydraulic Oscillations in Multi-Supplier District Heating Systems
Get PDFIn fourth-generation district heating systems (DHSs), the supply temperature of modern heat sources such as heat pumps and waste heat can potentially be reduced by mixing in hot water from combustion-based producers, thereby increasing efficiency and facilitating integration into networks with unrenovated buildings. However, this approach introduces the risk of thermo-hydraulic oscillations driven by mixing dynamics, transport delays, and mass flow adjustments by consumers. These oscillations can increase wear and cost and may potentially lead to system failure. This study addresses the asymptotic stability of multi-supplier DHSs by combining theoretical analysis and practical validation. Through linearization and Laplace transformation, we derive the transfer function of a system with two suppliers. Using pole-zero analysis, we show that transport delay can cause instability. We identify a new control law, demonstrating that persisting oscillations depend on network temperatures and low thermal inertia and enabling stabilization through careful temperature selection, thorough choice of the slack supplier, or installation of buffer tanks. We validate our findings using dynamic simulations of a nonlinear delayed system in Modelica, highlighting the applicability of such systems to real-world DHSs. These results provide actionable insights for designing robust DHSs and mitigating challenges in multi-supplier configurations by relying on thoughtful system design rather than complex control strategies
Einsatzszenarien und mögliche Effekte STACK-basierter Mathematikaufgaben im Ingenieurstudium des ersten Studienjahres
Get PDFDie vorliegende Arbeit beschreibt die Untersuchung von möglichen Effekten STACK-basierter Mathematikaufgaben auf das Lernverhalten und den Lernerfolg von Studierenden im Ingenieurstudium des ersten Studienjahres. Dazu werden im Sinne des Design-Based Research Ansatzes zunächst der Übergang von Lernenden von der Schule zur Universität beschrieben und Probleme sowie bereits bestehende Interventionsmöglichkeiten in der Studieneingangsphase in Bezug auf das mathematikhaltige Studium benannt.
Zentral ist die theoretisch fundierte Entwicklung einer digitalen Aufgabendatenbank mathematischer Übungsaufgaben mit Hilfe des Computer-Algebra-Systems STACK und deren Einsatzmöglichkeiten in universitären Lehrveranstaltungen. Zudem stellt die empirische Untersuchung der Effektivität dieser digitalen Übungsaufgaben auf das Lernverhalten und den Lernerfolg von Studierenden sowie auf die Arbeitsbelastung von Übungsleitenden in ingenieurwissenschaftlichen Mathematiklehrveranstaltungen im ersten Studienjahr einen Fokus dieser Arbeit dar. Die Begriffe Lernstrategien und Lernverhalten werden auf Grundlage kognitionspsychologischer Theorien konzeptualisiert und durch die Entwicklung eines Lernstrategiefragebogens operationalisiert. Die Operationalisierung wird im Rahmen einer nicht-randomisierten kontrollierten Längsschnittstudie über einem Zeitraum von fünf Semestern erprobt und evaluiert. Anhand der Ergebnisse dieser empirischen Untersuchungen können positive Effekte auf das Anwenden von ausgewählten Lernstrategien, insbesondere von metakognitiven Lernstrategien und auf den Lernerfolg von Studierenden sowie eine geringere Arbeitsbelastung von Übungsleitenden beobachtet werden
Optimized Smart Charging of Electric Bus Fleets for Greenhouse Gas Emission Minimization
Get PDFThe EU has set the goal to reduce the greenhouse gas emissions of the transport sector. The electrification of the public transport sector in Europe is underway to contribute to this goal. By 2030, approximately 90 % of new sales of buses have to be zero-emission vehicles, e. g., electric buses. Compared with conventional fossil driven buses, they have the advantage of reducing local noise pollution and avoiding local greenhouse gas emissions. However, when one considers the full lifecycle, the emissions for electricity generation have to be considered. The greenhouse gas emissions stemming from electricity generation fluctuate depending on the share of the different types of generation. As the expansion of renewable energy sources in Europe continues, the overall potential for a reduction of greenhouse gas emissions increases, but so does the volatility of the generation. Therefore, the targeted timing of electricity consumption, e. g., charging processes, can contribute to an overall emission reduction in the electricity and the transport sector. Based on an exact solution approach we identify the greenhouse gas emission minimization potentials for three charging strategies of an electric bus fleet with 80 buses and compare them to an uncontrolled fleet charging strategy. The optimizations run over 3 years of historical price and CO2emission factor data for electricity. When minimizing the procurement cost of electricity at the day-ahead and intraday power markets, cumulative greenhouse gas emissions can be reduced by 23.5 % and, when minimizing the emissions directly, up to 31 % can be reduced. A further reduction can be achieved with a holistic scope, if the bus depot feeds electricity back to the grid at suitable times
Cyber Attack Prevention and Detection for Electric Vehicle Charging
Get PDFThe increasing adoption of Electric Vehicles (EVs) is transforming the automotive landscape, driven by the need for a more sustainable transportation sector. To support the widespread use of EVs, an efficient and reliable charging infrastructure is essential. For this, several related communication protocols and backend systems have been established to manage power delivery, authorization, and billing. The main goals are the security of charge session payments and a power grid-friendly scheduling of EV charging loads.
The charging of EVs, however, also involves various security risks in associated use-cases. On the one hand, regarding the use-case of charge authorization and billing, existing protocols fail to protect against relevant adversaries. As a result, backend operators are exposed to the risk of significant financial damages and EV users are exposed to severe privacy risks. On the other hand, regarding the use-case of charge session power control and load balancing, existing processes can be manipulated by compromised systems. As a result, adversaries may be able to cause severe physical damage to involved systems and potentially harm power grid operations.
In this dissertation, we address selected security risks. For charge authorization and billing, we present three solutions to enhance the preventive security of EV charging protocols. More specifically, we present concepts (i) for the integration of crypto-agility and the use of Post-Quantum Cryptography (PQC), (ii) for the use of Self-Sovereign Identities (SSIs) to enhance EV user privacy, and (iii) for the adoption of a standardized authorization framework to reduce existing complexity. Regarding manipulations of charge session control, we present several concepts for the analysis, detection, and mitigation of related attacks. More specifically, we present (i) a feasibility analysis of resulting attacks on grid stability and a related co-simulation framework, (ii) different anomaly detection concepts for either large-scale coordinated attacks on the grid or attacks in individual charging sessions, (iii) approaches for improving detection performance, including a Generative Adversarial Network (GAN)-based Intrusion Detection System (IDS) optimization and a combination of large-scale and session-based detection, and (iv) methods for attack mitigation based on IDS outputs.
All presented concepts are implemented and evaluated with regard to relevant criteria. Concepts for EV charging protocol security are evaluated regarding performance/usability criteria based on proof-of-concept implementations and regarding security/privacy criteria based on formal protocol analyses using the Tamarin prover. Concepts for the analysis, detection, and mitigation of session control-related attacks are implemented with simulation-based approaches to evaluate their effect on involved systems and their detection/mitigation performance. Used Tamarin models and simulation data are published for reproducibility and future use in related studies. Overall, our results show the presented concepts can provide a significant benefit to the security of EV charging in the sector’s future
Introspection in Problem Solving
Get PDFProblem solving research has encountered an impasse. Since the seminal work of Newell und Simon (1972) researchers do not seem to have made much theoretical progress (Batchelder and Alexander, 2012; Ohlsson, 2012). In this paper we argue that one factor that is holding back the field is the widespread rejection of introspection among cognitive scientists. We review evidence that introspection improves problem solving performance, sometimes dramatically. Several studies suggest that self-observation, self-monitoring, and self-reflection play a key role in developing problem solving strategies. We argue that studying these introspective processes will require researchers to systematically ask subjects to introspect. However, we document that cognitive science textbooks dismiss introspection and as a consequence introspective methods are not used in problem solving research, even when it would be appropriate. We conclude that research on problem solving would benefit from embracing introspection rather than dismissing it
Investigating Interaction Dynamics of an Enantioselective Peptide‐Catalyzed Acylation Reaction
Get PDFModern nuclear magnetic resonance (NMR) methods like carbon relaxation dispersion in the rotating frame (¹³C−R₁ₚ) and proton chemical exchange saturation transfer (¹H‐CEST) are key methods to investigate molecular recognition in biomacromolecules and to detect molecular motions on the μs to s timescale, revealing transient conformational states. Changes in kinetics can be linked to binding, folding, or catalytic events. Here, we investigated whether these methods allow detection of changes in the dynamics of a small, highly selective peptide catalyst during recognition of its enantiomeric substrates. The flexible tetrapeptide Boc‐L‐(π‐Me)−His−ᴬGly‐L−Cha−L‐Phe−OMe, used for the monoacetylation of cycloalkane‐diols, is probed at natural abundance using ¹³C‐R₁ₚ and ¹H‐CEST. Indeed, we detected differences in dynamics of the peptide upon interaction with the diol. Importantly, these differ depending on the enantiomer of the substrate used. These enantiospecific influences of the substrates on the dynamics of the peptide are rationalized using computational techniques. We find that even though one enantiomer reacts faster, as confirmed by reaction monitoring, the other is more tightly bound in DCM (as confirmed by ¹H‐saturation transfer difference (STD) measurements). These findings provide insights into the recognition of the substrates and explain the selectivity differences observed between the solvents toluene and DCM
Dislocation‐induced local symmetry reduction in single‐crystal KNbO₃ observed by Raman spectroscopy
Get PDFIn recent years, dislocation‐tuned functionalized ceramics have become one of the focal points of modern materials research due to their outstanding properties. These range from improved electrical conductivity and ferroelectric properties to dislocation‐enhanced toughening and superconductivity, caused by local strain fields. The aim of this work is to investigate the dislocation‐induced structural changes in single‐crystal KNbO₃ by micro‐Raman spectroscopy. Dislocation‐rich regions with tailored densities have been generated using the Brinell indenter scratching method. The influence of the dislocations on the single‐crystal structure can be observed in the Raman spectra. The activation of additional Raman modes is observed, which does not occur in regions of low dislocation density. This observation is confirmed by DFT calculations of vibrational modes and is attributed to a reduction in the crystal symmetry due to increased defect densities in plastically deformed KNbO₃. In addition, an increase in compressive stress at higher dislocation densities can be demonstrated by a blueshift in Raman mode positions
Vampyrella crystallifera sp. nov., an Amoeba That Dissolves Entire Algal Cells at a Remarkable Speed
Get PDFThe vampyrellid amoebae (Order Vampyrellida, Rhizaria) comprise predatory microeukaryotes that inhabit freshwater, marine, and terrestrial habitats. They are known to consume a wide array of prey, which includes microalgae, fungi, and even microscopic animals such as nematodes. Members of the popular genus Vampyrella phagocytize the cell contents of filamentous green algae after localized perforation of the cell wall. This feeding strategy, named protoplast extraction, is the hallmark of Vampyrella species and vampyrellid amoebae in general. Here, we report on a new species from a German spring fen, Vampyrella crystallifera sp. nov., which specifically preys on a unicellular zygnematophyte green alga (Nucleotaenium sp.) isolated from the same microhabitat. In contrast to its closest relatives (V. lateritia and V. pendula), V. crystallifera does not feed by protoplast extraction but engulfs whole algal cells, followed by the dissolution of the entire prey cell wall. Given the recalcitrant, plant‐like cell walls of the zygnematophytes, this is a remarkable process that might involve enzymes also used by the closely related protoplast feeders. The discovery of V. crystallifera again showcases the exceptional diversity of predator–prey interactions found in the Vampyrellida and adds to our knowledge of protist diversity in temperate moorlands