Universität Stuttgart
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Item Open Access Rigorous compilation for near-term quantum computers(2024) Brandhofer, Sebastian; Polian, Ilia (Prof.)Quantum computing promises an exponential speedup for computational problems in material sciences, cryptography and drug design that are infeasible to resolve by traditional classical systems. As quantum computing technology matures, larger and more complex quantum states can be prepared on a quantum computer, enabling the resolution of larger problem instances, e.g. breaking larger cryptographic keys or modelling larger molecules accurately for the exploration of novel drugs. Near-term quantum computers, however, are characterized by large error rates, a relatively low number of qubits and a low connectivity between qubits. These characteristics impose strict requirements on the structure of quantum computations that must be incorporated by compilation methods targeting near-term quantum computers in order to ensure compatibility and yield highly accurate results. Rigorous compilation methods have been explored for addressing these requirements as they exactly explore the solution space and thus yield a quantum computation that is optimal with respect to the incorporated requirements. However, previous rigorous compilation methods demonstrate limited applicability and typically focus on one aspect of the imposed requirements, i.e. reducing the duration or the number of swap gates in a quantum computation. In this work, opportunities for improving near-term quantum computations through compilation are explored first. These compilation opportunities are included in rigorous compilation methods to investigate each aspect of the imposed requirements, i.e. the number of qubits, connectivity of qubits, duration and incurred errors. The developed rigorous compilation methods are then evaluated with respect to their ability to enable quantum computations that are otherwise not accessible with near-term quantum technology. Experimental results demonstrate the ability of the developed rigorous compilation methods to extend the computational reach of near-term quantum computers by generating quantum computations with a reduced requirement on the number and connectivity of qubits as well as reducing the duration and incurred errors of performed quantum computations. Furthermore, the developed rigorous compilation methods extend their applicability to quantum circuit partitioning, qubit reuse and the translation between quantum computations generated for distinct quantum technologies. Specifically, a developed rigorous compilation method exploiting the structure of a quantum computation to reuse qubits at runtime yielded a reduction in the required number of qubits of up to 5x and result error by up to 33%. The developed quantum circuit partitioning method optimally distributes a quantum computation to distinct separate partitions, reducing the required number of qubits by 40% and the cost of partitioning by 41% on average. Furthermore, a rigorous compilation method was developed for quantum computers based on neutral atoms that combines swap gate insertions and topology changes to reduce the impact of limited qubit connectivity on the quantum computation duration by up to 58% and on the result fidelity by up to 29%. Finally, the developed quantum circuit adaptation method enables to translate between distinct quantum technologies while considering heterogeneous computational primitives with distinct characteristics to reduce the idle time of qubits by up to 87% and the result fidelity by up to 40%.Item Open Access Investigations and technical development of adsorption thermal energy storage systems with simulation and different control strategies(2021) Abou Elfadil, Mazen; Hirth, Thomas (Prof. Dr.)Thermal energy storage (TES) has been receiving an increasing worldwide attention, especially with the growing concerns about environmental problems caused by an inefficient utilization of energy. A major part of the energy consumption is considered as low temperature thermal energy. Thus, a better management of this energy by using thermal energy storage could provide a significant contribution to improve the overall efficiency of energy utilization in industrial processes and economies. The thermal energy can be stored in different forms e.g. sensible heat, latent heat or thermo-chemical, allowing variety of choices depending on the application. While the sensible and latent heat storage technologies are standard products, the thermo-chemical energy storage is still under development. Based on the method used, thermo-chemical energy storage can be divided into absorptive and adsorptive thermal energy storage systems. The adsorptive thermal energy storage systems have a great potential in both daily (short term) and seasonal (long term) applications. However, their implementation is still limited due to their low degree of applicability caused by lack of scientific knowledge on the thermal analysis level, as well as the absence of knowledge on the level of system integration, which has prevented the heat storage systems from reaching their maximum potential and from being fully commercialized. Consequently, there is still a big necessity for research and development in this field [Salvatore Vasta, 2018]. The principle of the adsorption storage system is based on a gaseous working fluid (e.g. water resp. vapor) which gets adsorbed by a highly porous material (e.g. zeolite). This adsorption process is an exothermal one, thus heat is being released and can be transferred and used. In order to recharge the heat storage system, desorption of the working fluid is done by heating the porous material. The heat storage system consists mainly of a reactor (where the porous material is located), a condenser/evaporator and other auxiliary components (e.g. water tank, pumps, sensors…). Efforts of development of the adsorptive TES were concentrated mainly on developing the adsorptive material, as the performance of the storage material has been the priority so far [Salvatore Vasta, 2018]. Little focus was put on heat power analysis and temperature behavior in the different system components, which have an impact on the overall system efficiency. Thus, system approach is still needed in order to combine and integrate this technology into industrial applications and products [Hauer, Andreas 2020] [Michelangelo Di Palo 2020]. With the aim of improving the heat storage efficiency (recovered heat to stored heat ratio), both numerical (simulations) and experimental (technical modifications) approaches were applied, which have enabled the system to achieve an optimal operational status in terms of energy utilization and efficiency. These approaches were later on used to define a fully automated control system assisting the adsorption TES to instantly react with the continuously varying parameters in such a way to assure an optimal performance. Hence, in the first stage of this investigation, process-modeling and simulation of the whole heat storage system were carried out, so that the total performance of the heat storage system can be predicted and evaluated for any future applications, including the possibility of combining different reactors or heat storage units. In the second stage, different experiments and technical modifications of the system were conducted. This includes testing various possibilities of TES setups (e.g. storage cascades), where the different pressure and temperature behavior in the reactor were evaluated. With the help of experiments, a detailed numerical 3D-model of the packed bed was created, giving an insight into the heat and mass transfer in the reactor during both adsorption and desorption. As a result, a new heat exchanger design was developed, which has improved the temperature distribution and the heating/cooling power. Additionally, the simulation’s results suggested the separation between the evaporator and the condenser to achieve an enhanced water vapor transfer between the reactor and condenser. On a parallel stage of this investigation, comprehensive heat power analysis during both adsorption and desorption processes was carried out, which has showed that the sensible heat left in the reactor, contributes to ca. 50% of the total stored heat. Consequently, multiple reactor concept was introduced, in order to enable the sensible heat recovery. As a conclusion, process simulation enabled tests with different parameters to be performed within much shorter time than the real experimental time. Thus, it was possible to cover numerous application-scenarios and help improving the system overall efficiency. The experimental results have shown that the developed heat exchanger design has increased the maximum power of the heat exchanger about 74%. Moreover, by improving the fluid dynamics between the reactor and condenser, the efficiency of desorption ηd and overall efficiency ηo were increased by 32% and 9% respectively. Furthermore, about 36% of the sensible heat left in the reactor after desorption was recovered by using multiple reactors with sequential configuration, which has led to a reduction in the total invested heat by ca. 9%. For future work it’s recommended to investigate the possibility of controlling the amount of discharged heat from the system by regulating the water uptake during adsorption. In addition, trying a different approach to the reactor’s design (e.g. moving bed reactor) could bring significant improvements to the system.Item Open Access Computational studies of massively separated wake flows of transport aircraft(2021) Waldmann, Andreas; Krämer, Ewald (Prof. Dr.)This work focuses on the investigation of flow phenomena associated with low speed stall using a representative commercial transport aircraft configuration. Subsonic stall at high Reynolds number involves a highly complex turbulent flow field, which is difficult to analyze in ist entirety via experimental methods. Various computational approaches based on URANS and hybrid RANS/LES were evaluated, utilizing validation data from the European Transonic Windtunnel. Scale-resolving computational approaches were leveraged to gain deeper insight into the processes occurring in such a wake. DDES-based methods were found to be able to resolve the flow features occurring at the separation location and in the wake. An extensive study on the impact of solver settings, computational grids, model geometry and inflow Reynolds number was carried out in order to permit a validation of the chosen approach. Using these findings, the massively separated wake flow was studied at three angles of attack in post stall conditions. Three different regimes of formation of the separated wake were identified via the main locations where turbulence kinetic energy is produced. Analysis of anisotropy, turbulence length scales and signal characteristics provided insight into the propagation of the wake and the mixing processes. Modal analysis of the wake dynamics enabled the detection of a near-wing recirculation area and a von Kármán vortex street in the wake. Flow structures associated with both phenomena result in tailplane load fluctuations at their respective characteristic frequencies.Item Open Access The benefit of muscle-actuated systems : internal mechanics, optimization and learning(Stuttgart : Institut für Modellierung und Simulation Biomechanischer Systeme, Computational Biophysics and Biorobotics, 2023) Wochner, Isabell; Schmitt, Syn (Prof. Dr.)We are facing the challenge of an over-aging and overweight society. This leads to an increasing number of movement disorders and causes the loss of mobility and independence. To address this pressing issue, we need to develop new rehabilitation techniques and design innovative assistive devices. Achieving this goal requires a deeper understanding of the underlying mechanics that control muscle-actuated motion. However, despite extensive studies, the neural control of muscle-actuated motion remains poorly understood. While experiments are valuable and necessary tools to further our understanding, they are often limited by ethical and practical constraints. Therefore, simulating muscle-actuated motion has become increasingly important for testing hypotheses and bridge this knowledge gap. In silico, we can establish cause-effect relationships that are experimentally difficult or even impossible to measure. By changing morphological aspects of the underlying musculoskeletal structure or the neural control strategy itself, simulations are crucial in the quest for a deeper understanding of muscle-actuated motion. The insights gained from these simulations paves the way to develop new rehabilitation techniques, enhance pre-surgical planning, design better assistive devices and improve the performance of current robots. The primary objective of this dissertation is to study the intricate interplay between musculoskeletal dynamics, neural controller and the environment. To achieve this goal, a simulation framework has been developed as part of this thesis, enabling the modeling and control of muscle-actuated motion using both model-based and learning-based methods. By utilizing this framework, musculoskeletal models of the arm, head-neck complex and a simplified whole-body model are investigated in conjunction with various concepts of motor control. The main research questions of this thesis are therefore: 1. How does the neural control strategy select muscle activation patterns to generate the desired movement, and can we use this knowledge to design better assistive devices? 2. How does the musculoskeletal dynamics facilitate the neural control strategy in accomplishing this task of generating desired movements? To address these research questions, this thesis comprises a total of five journal and conference articles. More specifically, contributions I-III of this thesis focus on addressing the first research question which aims to understand how voluntary and reflexive movements can be predicted. First, we investigate various optimality principles using a musculoskeletal arm model to predict point-to-manifold reaching tasks. By using predictive simulations, we demonstrate how the arm would move towards a goal if, for example, our neural control strategy would minimize energy consumption. The main finding of this contribution shows that it is essential to include muscle dynamics and consider tasks with more openly defined targets to draw accurate conclusions about motor control. Through our analysis, we show that a combination of mechanical work, jerk and neuronal stimulation effort best predicts point-reaching when compared to human experiments. Second, we propose a novel method to optimize the design of exoskeleton power units taking into account the load cycle of predicted human movements. To achieve this goal, we employ a forward dynamic simulation of a generic musculoskeletal arm model, which is first scaled to represent different individuals. Next, we predict individual human motions and employ the predicted human torques to scale the electrical power units employing a novel scalability model. By considering the individual user needs and task demands, our approach achieves a lighter and more efficient design. In conclusion, our framework demonstrates the potential to improve the design of individual assistive devices. The third contribution focuses on predicting reflexive movements in response to sudden perturbations of the head-neck complex. To achieve this, we conducted experiments in which volunteers were placed on a table while supporting their heads with a trapdoor. This trapdoor was then suddenly released leading to a downward movement of the head until the reflexive reaction of the muscles stops the head from falling. We analyzed the results of these experiments, presenting characteristic parameters and highlighting differences between separate age and gender groups. Using this data, we also set up benchmark validations for a musculoskeletal head-neck model, including reflex control strategies. Our main findings are that there are large individual differences in reflexive responses between participants and that the perturbation direction significantly affects the reflexive response. Furthermore, we show that this data can be used as a benchmark test to validate musculoskeletal models and different muscle control strategies. While the first three contributions focus on the research question (1), contributions IV-V focus on (2) whether and how the musculoskeletal dynamics facilitate the learning and control task of various movements. We utilize a recently introduced information-theoretic approach called control effort to quantify the minimally required information to perform specific movements. By applying this concept, we can for example quantify how much biological muscles reduce the neuronal information load compared to technical DC-motors. We present a novel optimization algorithm to find this control effort and apply it to point-reaching and walking tasks. The main finding of this contribution is that the musculoskeletal dynamics reduce the control effort required for these movements compared to torque-driven systems. Finally, we hypothesize that the highly nonlinear muscle dynamics not only facilitate the control task but also provide inherent stability that is beneficial for learning from scratch. To test this, we employed various learning strategies for multiple anthropomorphic tasks, including point-reaching, ball-hitting, hopping, and squatting. The results of this investigation demonstrate that using muscle-like actuators improves the data-efficiency of the learning tasks. Additionally, including the muscle dynamics improves the robustness towards hyperparameters and allows for a better generalization towards unknown and unlearned perturbations. In summary, this thesis enhances existing methods to control and learn muscle-actuated motion, quantifies the control effort needed to perform certain movements and demonstrates that the inherent stability of the muscle dynamics facilitates the learning task. The models, control strategies, and experimental data presented in this work aid researchers in science and industry to improve their predictions in various fields such as neuroscience, ergonomics, rehabilitation, passive safety systems, and robotics. This allows us to reverse-engineer how we as humans control movement, uncovering the complex relationship between musculoskeletal dynamics and neural controller.Item Open Access Interfacial mechanics and liquid crystal structure of liquid gallium(2021) Yunusa, Muhammad; Sitti, Metin (Prof. Dr.)This dissertation aims to shed light on the fundamental aspects of supercooled liquid gallium. First, the mechanical properties of the oxide skin encapsulating the supercooled liquid gallium droplet is investigated. By leveraging the supercooling behavior of gallium and the formation of its oxide skin, we characterized the emergence of wrinkling at the interface and adhesion energy between the liquid gallium and rigid substrate. An interfacial energy of 0.238 ± 0.008 J m-2 was measured between gallium droplet and flat glass. Second, seed induced crystallization of supercooled liquid gallium on the different substrate materials revealed the dependence of the kinetics of crystallization on thermal behavior of the substrate. Such approach further elucidates on the importance of interface temperature during crystallization with a preferred orientation. The third part of the dissertation reports an unprecedented liquid crystal structure in supercooled liquid gallium. By the use of techniques applied in liquid crystal (LC) research, observation of LC texture in supercooled liquid gallium was realized. Reflective polarized optical microscopy (R-POM) on liquid gallium sandwiched between glasses treated with rubbed polymers reveals the onset of an anisotropic reflection of possible dimer molecules or clusters at 120°C that increases on cooling and persists down to room temperature or below. On the other hand, when gallium is sandwiched between substrates that align conventional liquid crystal molecules normal to the surface, the reflection is isotropic. This observation of LC structure of a highly electrically conductive supercooled liquid gallium provides an unexpected new field of materials science and liquid crystal research.Item Open Access Selektive Elektrodynamische Fragmentierung : Zerkleinerungsmechanismen und Einsatzmöglichkeiten zur Rückgewinnung von Wertstoffen(2020) Pestalozzi, Samuel Fadri; Hirth, Thomas (Prof. Dr. rer. nat.)Aufschluss und Sortierung sind zentrale Schritte moderner Recyclingtechnologien. Eine treibende Kraft für die Suche nach neuen Aufbereitungsverfahren ist die Zusammensetzung moderner Produkte, welche eine zunehmende Stoffvielfalt aufweisen, was für herkömmliche Recyclingtechnologien eine erhebliche Schwierigkeit darstellt. Parallel dazu steigen auch die Anforderungen an Aufbereitungsverfahren durch steigende Verwertungsquoten. Bei der im Feststoff-Recycling bisher weit verbreiteten mechanischen Zerkleinerung wird zwar die Korngröße des Aufgabegutes verringert, die einzelnen Körner bestehen dann aber teilweise noch immer aus einem Konglomerat verschiedener Stoffe. Als alternatives Verfahren zu mechanischen Zerkleinerungstechnologien wird in dieser Arbeit die Fragmentierung mittels Hochspannungsentladungen (HSE) in Wasser untersucht. Bei der elektrodynamischen Fragmentierung (EDF, SelFrag Lab S2.1) werden mittels hoher Spannungen (90-200 kV) bei kurzer Pulsanstiegszeit (150-200 ns) Feststoffdurchschläge ermöglicht. Im Gegensatz dazu erreichen die Entladungen bei der elektrohydraulischen Fragmentierung (EHF, ImpulsTec EHF-100) geringere Spannungswerte (30-50 kV) bei längerer Pulsanstiegszeit (500-2 000 ns), was zu Durchschlägen im Arbeitsmedium führt. Die thermische Expansion im Entladungskanal (bis 10^4 K) führt in beiden Fällen zu Druckschwankungen (bis 10^10 Pa), welche die erwünschte Fragmentierung verursachen. Bei Feststoffdurchschlägen werden die Druckschwankungen innerhalb des Materials ausgelöst (Zugkräfte). Bei Entladungen im Arbeitsmedium propagieren die Druckschwankungen durch das Medium und treffen von außen auf die Probenoberfläche (Druckkräfte). Elektropulsverfahren werden für die Auftrennung von Mineralien zwar seit Jahren eingesetzt, ihre Anwendung im Recyclingbereich ist jedoch bisher wenig wissenschaftlich untersucht worden. Ein wesentlicher Vorteil beim Einsatz von HSE gegenüber mechanischer Zerkleinerung ist die verbesserte Selektivität beim Feststoff-Aufschluss. Dies birgt somit das Potential, den nachgeschalteten Trennprozess effizienter zu gestalten. Ziel dieser Arbeit ist ein grundlegendes Prozessverständnis der Fragmentierung von Verbundmaterialien mittels HSE. Die Erforschung von Zerkleinerungsmechanismen bildet dabei den ersten Schritt in der Entwicklung eines Verfahrens zur Kreislaufführung von Verbundmaterialien durch HSE. Als Forschungs- und Entwicklungslücke hinsichtlich ausgewählter sekundärer Stoffströme wurde die Anwendung zur Aufbereitung von Dünnschicht-Photovoltaik-Modulen identifiziert und durch die vorliegende Arbeit geschlossen. Die Beiträge zum theoretischen Prozessverständnis umfassten Grundlagenuntersuchungen zur Festlegung und Bestimmung von Kennwerten zum Aufbereitungserfolg, systematische Aufbereitungsuntersuchungen sowie Übertragbarkeitsuntersuchungen mit weiteren Werkstoffen. Dabei wurden drei Haupt-Kennwerte verwendet. Der Zerkleinerungsgrad (Z) beschreibt das Verhältnis der medianen Korngröße vor und nach einem Zerkleinerungsvorgang. Der Funkenwirkungsgrad (ηPF) beschreibt das Verhältnis von in der Anlage eingesetzter Pulsenergie zu im Prozessgefäß umgesetzter Funkenenergie. Der Liberationsgrad (L) quantifiziert den Aufbereitungserfolg durch einen Vergleich zwischen der Masse eines freigelegten Zielwerkstoffes und dessen gesamter Masse im Werkstoffverbund. Das Prozessverständnis wurde durch Versuche mit kugelförmigen Modell-Probenkörpern aus der Verfahrenstechnik (Bruchkugeln mit Durchmesser 16 mm) erweitert. Als Modellmaterialien wurden Kalk-Natron-Glas (Glas) und Aluminiumoxid (Keramik) verwendet. Zur Quantifizierung einzelner Zerkleinerungsmechanismen wurden neben Bruchkugeln aus Glas oder Keramik auch bruchfeste Kugeln aus Naturkautschuk verwendet. Auf Basis dieser Versuche wurde die Zerkleinerungswirkung des elektrodynamischen Effektes quantitativ mit einer Überlagerung aus elektrohydraulischem Effekt und autogenem Mahleffekt verglichen. Als Modellparameter wurde hierzu der jeweils erreichte Zerkleinerungsgrad (Z) der massenspezifisch umgesetzten Zerkleinerungsenergie (EZ) gegenübergestellt (dZ/dEZ). Zur getrennten Betrachtung des elektrodynamischen Zerkleinerungsmechanismus einerseits und einer Überlagerung aus Elektrohydraulik und autogener Mahlung andererseits wurde eine Positionierhilfe aus ABS verwendet. Für Versuche mit Glaskugeln stieg der elektrodynamische Anteil am Zerkleinerungserfolg von 53 % mit Positionierhilfe auf 67 % ohne Positionierhilfe an. Bei der Fragmentierung von Keramikkugeln wurde eine rein elektrodynamische Fragmentierung ohne messbaren Beitrag des elektrohydraulischen Effektes und des autogenen Mahleffektes nachgewiesen. Dieses Ergebnis wurde auch durch die Tatsache gestützt, dass nach Entnahme der Positionierhilfe der Wert für dZ/dEZ bei Glas um den Faktor 5,7 anstieg, wohingegen der Anstieg bei Keramik mit einem Faktor von 1,4 deutlich geringer ausfiel. Im Gegensatz zu einer mechanischen Zekleinerung mittels Prallmühlen wurden im Verlauf einer Fragmentierung mittels HSE zunächst sinkende Werte für dEZ/dD50 gemessen. Im weiteren Zerkleinerungsverlauf stiegen die dEZ/dD50-Werte bei HSE dann ähnlich wie bei einer mechanischen Zekleinerung fortlaufend an. Als mögliche Gründe für diesen atypischen Zerkleinerungsverlauf wurden neben der in der Literatur beschriebenen Vorschwächung aufgrund hoher induzierter Dehnraten die bei der EDF wirkenden Zugkräfte identifiziert. Ein Übergang von sinkenden zu steigenden dEZ/dD50-Werten könnte somit ein Hinweis auf eine vermehrte elektrohydraulische Fragmentierung sein, da diese wie bei mechanischer Aufbereitung auf Druckkräften beruht. Eine Hypothese aus der Literatur besagt, dass sich Werkstoffverbunde mit größerer interner Permittivitätsdifferenz mittels EDF besser auftrennen lassen als homogener aufgebaute Verbunde. Zur Überprüfung dieser Hypothese wurden Anwendungsversuche mit Photovoltaik-Modulen (Typ CdTe und CIS), Glasfaserverbundwerkstoffen sowie Proben aus dem Elektrogerätebereich (Steckerverbindungen und Lautsprechermodule) mit unterschiedlicher interner Permittivitätsdifferenz durchgeführt. Die interne Permittivitätsdifferenz wurde über die Grenzflächenpolarisation (dε) nach Debye definiert. Aus der EDF dieser Proben ergab sich für eine Grenzflächenpolarisation über dε=100 ein Prozessfenster, in welchem eine Liberation von L > 80 % erreicht wurde. Dieses Modellvorgehen erlaubt somit die Einteilung noch unerforschter Werkstoffverbunde in zwei Gruppen zur Aufschlusszerkleinerung mittels entweder EDF oder EHF. Bei der Fragmentierung von Dünnschicht-Photovoltaik-Modulen (DPV) vom Typ CIS konnte festgestellt werden, dass die Liberation der enthaltenen Halbleitermetalle nicht vom Spannungsniveau, sondern lediglich von der total umgesetzten Pulsenergie abhängig war. Bei demselben Energieumsatz von 121-125 J/g erreichten sowohl die EHF als auch die EDF vergleichbare Liberationswerte über 80 %. Bei CIS-DPV wurde somit trotz eines hohen Wertes von dε=2900 entgegen der Hypothese aus der Literatur kein verbessertes Trennergebnis der EDF gegenüber der EHF beobachtet. Da für Pulse höherer Spannung ein anlagenspezifisch größerer Aufwand nötig ist, ist somit eine Fragmentierung von CIS-DPV bei tieferen Spannungen und somit die EHF der EDF vorzuziehen. Im Ergebnis zeigte diese Arbeit, dass ein Einsatz von HSE zur erhöhten Selektivität beim Feststoff-Aufschluss unter Berücksichtigung des Entladungstypus (EDF oder EHF) erfolgen muss. Mit Hilfe von Modellsubstanzen konnte der elektrodynamische Anteil einer Zerkleinerung stoffspezifisch auf 100 % (Keramik) resp. 53 bis 67 % (Glas) quantifiziert werden. Dies schließt ungeeignete Werkstoffe ohne elektrohydraulische Zerkleinerungswirkung wie etwa Keramik von einer EHF aus. Im Zusammenhang mit einer Fragmentierung durch HSE wurde in der Literatur nebem der Permittivität auch die akustische Impedanz als wichtige Einflussgröße genannt, welche sich somit als weiterer Modellierungsansatz anbietet. Im Rahmen dieser Promotion wurden neben Grundlagen- und Anwendungsuntersuchungen zusätzlich noch Ansätze zur Erweiterung des Prozessfensters der Fragmentierung mittels HSE aufgezeigt. Zur Spektroskopie während der EDF wurde eine Prozessgefäßmodifikation mit Sichtfenster umgesetzt und die Plasmatemperatur aus den aufgenommenen Emissionsspektren mit 6 800-7 700 K bestimmt. Mittels Kalibration der Spektrogramme durch Fragmentierung bekannter Reinststoffe könnte diese Modifikation in einem möglichen Folgevorhaben zur Elementidentifikation eingesetzt werden. Zur Fragmentierung in alternativen Prozessmedien wurde des Weiteren ein Autoklav entwickelt und ein erster Prototyp gefertigt, dessen Konstruktion derzeit zur Sicherstellung eines erfolgreichen Entladungsverlaufes überarbeitet wird.Item Open Access Resilience of quantum optimization algorithms(2024) Ji, Yanjun; Polian, Ilia (Prof. Dr.)Quantum optimization algorithms (QOAs) show promise in surpassing classical methods for solving complex problems. However, their practical application is limited by the sensitivity of quantum systems to noise. This study addresses this challenge by investigating the resilience of QOAs and developing strategies to enhance their performance and robustness on noisy quantum computers. We begin by establishing an evaluation framework to assess the performance of QOAs under various conditions, including simulated noise-free and error-modeled environments, as well as real noisy hardware, providing a foundation for guiding the development of enhancement strategies. We then propose innovative techniques to improve the performance of algorithms on near-term quantum devices characterized by limited qubit connectivity and noisy operations. Our study introduces an effective compilation process that maximizes the utilization of classical and quantum resources. To overcome the restricted connectivity of hardware, we develop an algorithm-oriented qubit mapping approach that bridges the gap between heuristic and exact methods, providing scalable and optimal solutions. Additionally, we demonstrate, for the first time, selective optimization of quantum circuits on real hardware by optimizing only gates implemented with low-quality native gates, providing significant insights for large-scale quantum computing. We also investigate error mitigation strategies and their dependence on hardware features and algorithm implementation details, emphasizing the synergistic effects of error mitigation and circuit design. While error mitigation can suppress the effects of noise, hardware quality and circuit design are ultimately more critical for achieving high performance. Building upon these insights, we explore the cooptimization of algorithm design and hardware implementation to achieve optimal performance and resilience. By optimizing gate sequences and parameters at the algorithmic level and minimizing error-prone two-qubit gates during compilation, we demonstrate significant improvements in QOA performance. Finally, we explore the practical application of QOAs in real-world problems, emphasizing the importance of optimizing parameters in problem instances to identify optimal solutions. With extensive experiments conducted on real devices, this dissertation makes a substantial contribution to the field of quantum optimization, providing both theoretical foundations and practical strategies for addressing the challenges posed by near-term quantum hardware. Our findings pave the way for the realization of practical quantum computing applications and unlock the full potential of QOAs.Item Open Access Adaptive error control for stratospheric long-distance optical links(2024) Parthasarathy, Swaminathan; Kirstädter, Andreas (Prof. Dr.-Ing.)Free-space optical (FSO) communication plays a crucial role in aerospace technology, utilizing lasers to establish high-speed, wireless connections over long distances. FSO surpasses conventional RF wireless technology in various aspects and supports high-data-rate connectivity for services such as Internet access, data transfer, voice communication, and image transfer. High-Altitude Platforms (HAPs) have emerged as ideal hosts for FSO communication networks, offering ultra-high data rates for applications like high-speed Internet, video conferencing, telemedicine, smart cities, and autonomous driving. FSO via HAPs ensures minimal latency, making it suitable for real-time tasks like remote surgery and autonomous vehicle control. The swift, long-distance communication links with low delays make FSO-equipped HAPs ideal for RF-congested areas, providing cost-effective solutions in remote regions and contributing to environmental monitoring. This thesis explores the use of adaptive code-rate Hybrid Automatic Repeat Request (HARQ) methods and channel state information (CSI) to improve the transmission efficiency of Free-Space Optical (FSO) links between High Altitude Platforms (HAPs). The study looks at channel problems like atmospheric turbulence and static pointing errors, focusing on the weak fluctuation regime of atmospheric turbulence. It explores the reciprocal behavior in bidirectional FSO channels to improve performance efficiency, providing evidence of channel reciprocity. The research proposes using HARQ, an adaptive Reed-Solomon (RS) code-rate technique, and different CSI types to address these impairments. Simulations of various situations are used to test how well these methods work. This helps us learn more about how efficient HARQ protocols are in inter-HAP FSO links, how important different CSI is in adaptive rate HARQ, and possible ways to make the system more efficient. This thesis looks at the channel model for inter-High Altitude Platform (HAP) Free-Space Optical (FSO) links in great detail, taking atmospheric conditions and static pointing errors into account. The channel is modeled as a lognormal fading channel under a weak fluctuation regime. The principle of channel reciprocity and the measures used to quantify it are discussed, providing a foundational understanding for the subsequent investigations. Forward Error Correction (FEC) schemes, with a specific emphasis on the Reed-Solomon (RS) scheme, and various Automatic Repeat reQuest (ARQ) schemes are thoroughly examined. A meticulous comparison of different ARQ schemes highlights that Selective Repeat ARQ (SR-ARQ) is the most efficient for high-error-rate channels, making it the preferred choice for inter-HAP FSO channels. Conversely, Stop and Wait ARQ (SW-ARQ) and Go-Back-N ARQ (GBN-ARQ) are found to be less suitable for these channels. An innovative approach is introduced, leveraging various types of Channel State Information (CSI) to adjust the Reed-Solomon Forward Error Correction (FEC) code-rate. Four types of CSI: perfect CSI (P-CSI), reciprocal CSI (R-CSI), delayed CSI (D-CSI), and fixed mean CSI (F-CSI) are employed. The adaptation of the Reed-Solomon FEC code-rate, aligned with Selective Repeat ARQ, is explored, and the optimal power selection is identified through rigorous analysis. It shows simulation models that use OMNET++ and gives information about the inter-HAP channel and the event-based selective repeat HARQ model. The study demonstrates reciprocity in the longest recorded ground-to-ground bidirectional Free-Space Optical (FSO) link, holding promise to mitigate signal scintillation caused by atmospheric turbulence. It evaluates the performance of different ARQ protocols and adaptive Hybrid Automatic Repeat Request (HARQ) schemes in inter-HAP FSO communication systems. The results show how channel state information, turbulence in the atmosphere, and pointing errors affect the performance of the system. They also suggest ways to improve system efficiency, such as using CSI prediction and soft combining. These findings offer valuable insights for the design and optimization of ARQ and HARQ schemes in inter-HAP FSO communication systems and suggest promising avenues for future research.