Dokument: Orientational topology of layered systems and reinforcement learning in active matter
| Titel: | Orientational topology of layered systems and reinforcement learning in active matter | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=63219 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20230731-132013-0 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Monderkamp, Paul [Autor] | |||||||
| Dateien: |
| |||||||
| Beitragende: | Prof. Dr. Löwen, Hartmut [Gutachter] Prof. Dr. Horbach, Jürgen [Gutachter] | |||||||
| Stichwörter: | Liquid Crystals, Reinforcement Learning | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibungen: | The largest fraction of research attention in this thesis is dedicated to the study of topological defects in the regular layered structure of colloidal smectic liquid crystals. Liquid crystals are materials which, due to characteristic particle shapes, display a plethora of interesting ordered phases, depending on, for instance, density. At intermediate densities, elongated particles tend to align, into so-called nematic
ordering. Additionally, at high densities, they display a tendency to reside in layers, called a smectic phase. These ordered phases are accompanied by local disruptions in their ordered structure, so-called topological defects. In ch. 1, I introduce the necessary fundamentals to understand the topological concepts, applied in the corresponding publications in ch. 3. Furthermore, the Monte-Carlo simulation protocol is elaborated, which marks my main contribution to the scientific publications on smectic liquid crystal topology (P1, P2, P3 and P4). Over the course of these scientific publications, we investigate how the concept of topological defect charges, known from nematic liquid crystals, generalises to the defects, which are inherent to smectics (P1,P3). We present how grain boundaries can be classified with these charges. We furthermore show that the rigidity of the smectic structure causes the formation of so-called tetratic defect pairs. These resemble points in two, and line defects in three dimensions. Even though, in three dimensions, topological charge is not strictly conserved, we find that it can result from the smectic rigidity (P2). Lastly, in this part on liquid crystals, we explore how graph-theoretical approaches can be used to interpret the structure of systems composed of chiral particles (P4). This thesis contains a study of the application of reinforcement learning to an active swimmer. In our case, we equip single microswimmers in Brownian dynamics simulations with the means to intelligent steering via tabular Q-learning (P5). Details on the physical model as well as a simple, illustrative example for a problem, solved with tabular Q-learning algorithm, can be found in ch. 2. Our research provides a model for the understanding of autonomous decision-making in biological microorganisms, as well as for the design of intelligent microrobotic machines. The swimmer utilises his capabilities to learn to navigate through complicated, random environments. We find, that it not only outperforms suitable reference cases, but the strategy also generalises well to classes of environments, unknown until after the training. The last scientific publication in this thesis comprises a study of the equilibrium statistics of carrier-cargo complexes (P6). These represent microscopic particles, which possess the ability to engulf smaller cargo particles. This is relevant, for instance, for quantitative methods in medicine or the study of biological objects such as vesicles or phagocytes. The main findings of this work are obtained via density functional theory: the formation of carrier-cargo complexes can be tuned by carrier and cargo densities. Furthermore, the theory predicts structural properties of the mixture. The theoretical results are complimented by Monte-Carlo simulation. The Monte-Carlo simulation protocol, which I contribute to this work is the same, which is applied in the equilibration of liquid crystal phases, summarised in ch. 1.4. The theory itself is extensively discussed in the main text of the publication.The largest fraction of research attention in this thesis is dedicated to the study of topological defects in the regular layered structure of colloidal smectic liquid crystals. Liquid crystals are materials which, due to characteristic particle shapes, display a plethora of interesting ordered phases, depending on, for instance, density. At intermediate densities, elongated particles tend to align, into so-called nematic ordering. Additionally, at high densities, they display a tendency to reside in layers, called a smectic phase. These ordered phases are accompanied by local disruptions in their ordered structure, so-called topological defects. In ch. 1, I introduce the necessary fundamentals to understand the topological concepts, applied in the corresponding publications in ch. 3. Furthermore, the Monte-Carlo simulation protocol is elaborated, which marks my main contribution to the scientific publications on smectic liquid crystal topology (P1, P2, P3 and P4). Over the course of these scientific publications, we investigate how the concept of topological defect charges, known from nematic liquid crystals, generalises to the defects, which are inherent to smectics (P1,P3). We present how grain boundaries can be classified with these charges. We furthermore show that the rigidity of the smectic structure causes the formation of so-called tetratic defect pairs. These resemble points in two, and line defects in three dimensions. Even though, in three dimensions, topological charge is not strictly conserved, we find that it can result from the smectic rigidity (P2). Lastly, in this part on liquid crystals, we explore how graph-theoretical approaches can be used to interpret the structure of systems composed of chiral particles (P4). This thesis contains a study of the application of reinforcement learning to an active swimmer. In our case, we equip single microswimmers in Brownian dynamics simulations with the means to intelligent steering via tabular Q-learning (P5). Details on the physical model as well as a simple, illustrative example for a problem, solved with tabular Q-learning algorithm, can be found in ch. 2. Our research provides a model for the understanding of autonomous decision-making in biological microorganisms, as well as for the design of intelligent microrobotic machines. The swimmer utilises his capabilities to learn to navigate through complicated, random environments. We find, that it not only outperforms suitable reference cases, but the strategy also generalises well to classes of environments, unknown until after the training. The last scientific publication in this thesis comprises a study of the equilibrium statistics of carrier-cargo complexes (P6). These represent microscopic particles, which possess the ability to engulf smaller cargo particles. This is relevant, for instance, for quantitative methods in medicine or the study of biological objects such as vesicles or phagocytes. The main findings of this work are obtained via density functional theory: the formation of carrier-cargo complexes can be tuned by carrier and cargo densities. Furthermore, the theory predicts structural properties of the mixture. The theoretical results are complimented by Monte-Carlo simulation. The Monte-Carlo simulation protocol, which I contribute to this work is the same, which is applied in the equilibration of liquid crystal phases, summarised in ch. 1.4. The theory itself is extensively discussed in the main text of the publication. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Bezug: | 2019-2023 | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Theoretische Physik Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Physik der kondensierten Materie | |||||||
| Dokument erstellt am: | 31.07.2023 | |||||||
| Dateien geändert am: | 31.07.2023 | |||||||
| Promotionsantrag am: | 19.04.2023 | |||||||
| Datum der Promotion: | 18.07.2023 |
