Universität Stuttgart

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Open Access
Advanced methods for a sustainable sediment management of reservoirs
(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2022) Haun, Stefan; Wieprecht, Silke (Prof. Dr.-Ing.)
As a result of an increasing demand on storing water, sustainable reservoir management will become more and more important in the future. Minimizing, or in the best case avoiding, the loss of storage due to sedimentation is a challenging task because each reservoir has unique boundary conditions. Hence, not every management strategy is suitable for a given reservoir. Due to the combination of state of the art measurement methods and hydro‐morphodynamic models, reservoir sedimentation can be better predicted in the future and the success of sediment management strategies can be assessed. The development of advanced measurement methods makes it possible to obtain data with a high accuracy, but also with a high spatial and temporal resolution. The combination of recent measurement approaches with reliable hydro‐morphodynamic numerical prediction models, enhances a highly accurate prediction and understanding of governing processes. This opens new possibilities for an objective selection of important parameters, essential spatial domains as well as for the temporal resolution of measurements. This will finally lead to more reliable predictions about the future of reservoirs that provide water for human life, health and wealth. The presented scientific work gives an overview of recent developments to investigate hydromorphological processes in reservoirs.
Open Access
Analysis and verification of systems with dynamically evolving structure
(2004) König, Barbara; Esparza, Javier (Prof. Dr.)
This thesis is concerned with verification and analysis techniques for software systems characterized by dynamically evolving structure, such as dynamic creation and deletion of objects, mobility and variable topology. Examples for such systems are pointer structures, object-based systems and communication protocols in which the number of participants is not constant. The approach taken here is based on graph transformation systems, an intuitive and---at the same time---powerful formalism for the modelling of distributed and mobile systems. So far there exists comparatively little research concerning the verification of graph rewriting. We will---in the first part of this thesis---introduce graph transformations and give an overview of existing analysis and verification methods, with a focus on the verification of systems with dynamically evolving structure. Then we will describe three original lines of research: behavioural equivalences, type systems and approximation by Petri nets, all of them concerned with the analysis of graph transformation systems. The second part consists of eight refereed research papers treating the previously introduced analysis and verification techniques in depth.
Open Access
The AnT project : on the simulation and analysis of dynamical systems
(2004) Schanz, Michael; Levi, Paul (Prof. Dr. rer. nat. habil.)
In this work, a the software project AnT is presented. This project is about a simulation and analysis tool for dynamical systems, whereby it was aimed right from the start, that not only a broad spectrum of dynamical systems is supported, but many investigation methods as well. This thesis is structured as follows: In chapter one (Introduction) a motivation and an overview about the main topics and the involved scientific disciplines is given and among others, the notions of simulation and analysis and their prerequisites are defined and described. The modeling and especially the mathematical modeling are considered in more detail as well as the tasks of interactive and non-interactive simulation. Chapter two (The AnT project) provides an overview about the software - its aims, requirements and features. Some historical and technical remarks are given together with some basic principles and facts about the functionality and a short guidance how to use this software and its features. In the third chapter (Supported classes of dynamical systems), the notion of a dynamical system is defined and described in this context and the most important classes of dynamical systems supported by the AnT software package including their main characteristic properties are listed. For each addresses class of dynamical systems at least one typical and illustrative representative is presented. In chapter four (Scanning dynamical systems), the notion of scanning is described and its importance in the field of nonlinear dynamics is emphasized. The different types of scan possibilities and procedures provided by the software are explained as well as the meaning of a scan item and a scan item sequence. Directly connected with the scanning of a dynamical system is the investigation or analysis of the dynamic behavior, because in most of the cases one is not only interested in the investigation under some fixed conditions but under varying conditions. For the analysis of dynamical systems, several methods are developed in the meanwhile. The methods, which are already implemented in the AnT software and hence available, are presented in chapter five (Supported investigation methods). The investigation of dynamical systems is the most important task in the field of nonlinear dynamics, because it represents the basis for prediction and forecasting of the dynamics as well as improvement and enhancement of the used or derived mathematical models. Therefore, a lot of examples are given in this chapter where the supported investigation methods are applied and illustrated. In chapter six (Simulating and investigating dynamical systems), a more detailed description of the software architecture and applied concepts is given. Especially the most important concepts of transitions and machines designed for the simulation and the investigation are explained and illustrated. The necessity of distributed computing is addressed to in chapter seven (Distributed computing), where the capability of the software to run in distributed mode to solve time consuming investigation tasks in parallel on several workstations or nodes of a cluster is described. The used client/server architecture is presented together with the developed network protocol. Many diagrams and figures in this work are based on the result of time consuming computations and could not have been prepared without the important distributed computing feature of the AnT software package. In chapters eight (AnT-gui: the graphical user interface) and nine (Visualization of dynamical systems), the graphical user interface, which guides a user through the initialization phase and the visualization capabilities of the software were presented, before in chapter ten (Numerical aspects of simulation) some remarks about numerics and scientific computing are elucidated. In chapter eleven (Examples), further illustrative examples of the functionality of the software are given including several scans not only with respect to system parameters but also with respect to initial values and even method parameters. The work closes with chapter twelve (Conclusion), where the main advantages of the AnT software package and the future extensions are presented, together with a short overview about related software projects.
Open Access
Applications of Cartan and tractor calculus to conformal and CR-geometry
(2007) Leitner, Felipe; Kühnel, Wolfgang (Prof.)
The main object of this Habilitationsschrift is the geometric study of solutions of overdetermined conformally invariant differential equations via the use of Cartan and tractor calculus. This study fits into the broader research field of conformal and parabolic invariant theory. Parts of our investigations take special attention to conformal Lorentzian and spin geometry, which provides a link to the theories of modern physics. The present text originated from a collection of research articles and other works of the author, which emerged since the year 2003. In order to make the text basically self contained with uniform notations and conventions I decided to prefix an extended introductory chapter. An English and German summary are included as well.
Open Access
Asymptotische Entwicklungen des Robbins-Monro-Prozesses
(1998) Dippon, Jürgen; Walk, Harro (Prof. Dr.)
Zur Schätzung der Nullstelle x einer unbekannten Regressionsfunktion, deren Funktionswert f(X(n)) an der Stelle X(n) nur mit einem zufälligen Fehler V(n) mittels Y(n)=f(X(n))-V(n) beobachtet werden kann, schlugen Robbins und Monro (1951) die Rekursion X(n+1)=X(n)-a/n Y(n) vor. In der vorliegenden Arbeit werden Edgeworth-Entwicklungen des Robbins-Monro-Prozesses vorgestellt, welche eine Approximation der Verteilungsfunktion von sqrt(n)(X(n)-x) mit Resttermen der Ordnung o(1/sqrt(n)) und o(1/n) ermöglichen. Ausgehend von einer Idee von Walk zur linearen Approximation des Robbins-Monro-Prozesses wird die Rekursion in eine Summe von Multilinearformen in den Beobachtungsfehlern V(n) aufgelöst. Die Gültigkeit dieser Darstellungen wird in Kapitel 1 für quasi- und sublineare Regressionsfunktionen nachgewiesen. In Kapitel 2 werden die Entwicklungen der ersten vier Kumulanten der Darstellungsformen ermittelt. Dadurch ist die Form der Edgeworth-Entwicklung bereits festgelegt. Die dort gefundene asymptotische Entwicklung der Verzerrung könnte auch für weitere stochastische Approximationsverfahren von Interesse sein, da sie eine Korrektur des rekursiven Schätzers erlaubt. Zum Nachweis der Gültigkeit der Edgeworth-Entwicklungen der Darstellungsformen werden in Kapitel 3 die Methode der charakteristischen Funktionen und das Smoothing Lemma von Esseen verwendet. Der Beweis baut auf Ideen von Helmers, Callaert, Janssen, Veraverbeke, Bickel, Goetze und van Zwet auf, die Edgeworth-Entwicklungen für L- und U-Statistiken untersucht haben. In Kapitel 4 werden diese Ergebnisse auf den Robbins-Monro-Prozess angewendet. Damit kann die Überdeckungswahrscheinlichkeit von Konfidenzintervallen für x mit einem Restterm der Ordnung O(1/n) angegeben werden. Weitere Folgerungen betreffen Cornish-Fisher-Entwicklungen der Quantilfunktion und eine Edgeworth-Korrektur der Verteilungsfunktion.
Open Access
Atomistic simulation of shock waves : from simple crystals to complex quasicrystals
(2005) Roth, Johannes Werner; Trebin, Hans-Rainer (Prof. Dr.)
This habilitation thesis describes molecular dynamics simulations of solids. The impact of shock waves on a number of solids is studied: In the first part binary icosahedral quasicrystals and Laves crystals are treated, in the second part monatomic dodecagonal quasicrystals and body centered cubic crystals are dealt with. The third part contains studies of intermediate phases and solitons which show up in the body centered cubic crystals if shocked along a three-fold axis. In all cases three ranges of different behavior are observed: if the shock waves are weak, elastic deformations occur, in a medium range elastic and plastic waves or phase transitions are observed. If the shock waves are strong, the initial structures are completely destroyed. In this work we are concerned especially with the range of medium strong shock waves. For the binary crystal structure fragmentation occurs. The emerging crystallites are rotated with respect to each other and separated by boundary layers which are several atomic distances thick. The main difference between crystal and quasicrystal are phason-like defects which lead to a continuous transition between the range of weak and medium shock waves. For the monatomic crystal structures the Dzugutov potential has been applied to stabilize the structures. Here we find in the range of medium shock waves phase transitions from quasicrystals and approximants to the body centered cubic structure. Depending on the orientation and strength of the shock waves the transition takes places within a few atomic layers or spread out across many layers. In the quasicrystal and the approximants atomic flips are observed in the elastically compress region. Body centered cubic crystals possess an inherent instability along the three-fold axes. In many materials, this leads to a phase transition to the so-called omega-phase. In our case the omega-phase is stable only in a small range of compression, thus a forth- and back-transformation from body centered cubic to the omega-phase takes place, as long as the phase transition front moves slower than the speed of sound. If this is no longer the case, solitons shock up which contain in their interior. In summary several differences could be observed between crystals and quasicrystals. The results obtained for the Dzugutov potentials are comparable to the outcome of simulation of shock waves in iron with materials-specific interactions.
Open Access
Biomimetische Grenzflächen mittels hierarchisch strukturierter Systeme zur molekularen Erkennung
(2004) Tovar, Günter; Roduner, Emil (Prof. Dr.)
So genannte biomimetische Grenzflächen wurden mit Hilfe synthetischer und biologischer Materialien als hierarchisch strukturierte Multischichtsysteme aufgebaut, chemisch und strukturell analysiert und für molekulare Erkennungsreaktionen eingesetzt. Als funktionelle Schichten an der Festkörperoberfläche ahmen die synthetischen Konstrukte das biologisch zentrale Prinzip der molekularen Erkennung an der Fest/Flüssig-Grenzfläche nach. Über drei unterschiedliche Wege wurden biologische Makromoleküle mit spezifischen Bindestellen chemisch kontrolliert an ultradünn organisch beschichteten anorganischen oder polymeren Festkörperoberflächen verankert. Alternativ dazu wurden synthetische Bindestellen während der Synthese polymerer Festkörper durch molekulares Prägen induziert. Die so erzeugten Funktionsmaterialien wurden entweder unmittelbar in bioanalytischen Verfahren eingesetzt oder zunächst zu mesoskopischen Strukturen weiterverarbeitet und dann als bioanalytische Funktionselemente verwendet. Die zur Oberflächenfunktionalisierung eingesetzten Moleküle, der Verlauf der Oberflächenreaktionen sowie die molekülspezifischen Bindeereignisse an den Oberflächen wurden mit Hilfe von auf die jeweiligen Materialien spezifisch angepassten Untersuchungsmethoden charakterisiert. Zur Analyse der chemischen Zusammensetzung und Struktur der Einzelmoleküle sowie deren Eigenschaften wurden Experimente mit Hilfe von FT-IR-Spektroskopie, 1H- und 13C-NMR-Spektroskopie, Isotherme Titrationsmikrokalorimetrie (ITC), Verbrennungselementaranalyse (EA), MALDI-TOF-MS, Wilhelmy-Waage-Grenzflächenspannungsmessungen und der Langmuir-Blodgett-Filmwaage durchgeführt. Die Kolloide wurden mit Hilfe von Dynamischer Lichtstreuung (DLS), Zetapotenzialmessungen, ITC, Partikelladungstitrationsmessungen (PCD), Rasterkraftmikroskopie (AFM), Raster- und Transmissionselektronenmikroskopie (REM/TEM), konfokaler Fluoreszenzmikroskopie, 1H- und 13C-NMR, EA und MALDI-TOF-MS untersucht. Zur Charakterisierung der planaren Oberflächen wurden Untersuchungen mittels Null-Ellipsometrie, Röntgenphotoelektronenspektroskopie (XPS), Kontaktwinkelmessungen, Optische Wellenleiterspektroskopie sowie AFM, REM, Licht- und Fluoreszenzmikroskopie durchgeführt. Durch den Einsatz dieses reichen Methodenspektrums konnten weitreichende Einsichten in Entstehung, Struktur und biomimetische Funktion der beschriebenen hierarchisch aufgebauten Materialien gewonnen werden. Die Molekül-spezifisch bindenden Oberflächen wurden nach zwei grundsätzlich verschiedenen Prinzipien aufgebaut: Entweder wurden durch chemische Prozesse an der Oberfläche reaktive Gruppen kontrolliert verankert, die mit Hilfe einer weiteren Reaktion biologische Rezeptormoleküle unter Erhalt deren biologischer Aktivität an der Oberfläche immobilisieren. Oder es wurden während der Entstehung der Festkörperoberfläche synthetische Erkennungsstellen für biologische Ligandenmoleküle durch eine Templatpolymerisation dargestellt. Diese chemischen Reaktionen zur Ausstattung der Oberflächen für die molekulare Erkennung fanden an sphärischen Kolloiden oder makroskopisch ausgedehnten planaren Trägern statt. Weiterhin wurden die mit molekularer Erkennungsfunktion ausgestatteten Kolloide zu Schichten an planaren Trägern abgeschieden. Dabei wurden diese Schichten mikrostrukturiert, so dass lateral aufgelöste Mikrostrukturen mit multifunktionaler Oberfläche entstanden. Die Kolloid-Multischichtsysteme wurden als Funktionselemente in bioanalytischen Verfahren zur spezifischen Molekülbindung eingesetzt. Kompositmembranen mit molekular erkennenden Kolloiden als Selektoren wurden zur spezifischen Festphasenextraktion in Membranverfahren eingesetzt. Die hier präsentierte Forschung an den dargestellten neuartigen nanoskopisch strukturierten Systemen führt zu einem weitreichenden Erkenntnisgewinn über die Struktur-Funktionsbeziehungen chemischer Systeme mit molekularer Erkennungsfunktion. Die vorliegende Arbeit leistet damit einen wesentlichen Beitrag zum weitergehenden Verständnis chemischer Funktionsmaterialien und erlaubt eine Erweiterung der Methoden zur Oberflächen-gestützten Analyse von Proben biologischen Ursprungs.
Open Access
Circuit complexity of group theoretic problems
(2021) Weiß, Armin; Diekert, Volker (Prof. Dr. rer. nat.)
In dieser kumulativen Habilitationsschrift werden sechs Arbeiten zum Thema "Schaltkreiskomplexität von Gruppentheoretischen Problemen" zusammengefasst. An vorderster Stelle steht hierbei das Wortproblem: Gegeben ein Wort über den Erzeugern einer Gruppe, ist die Frage, ob das Wort das Einselement der Gruppe darstellt. Daneben werden noch weitere Probleme, wie das Konjugationsproblem, das Power-Wortproblem (wie das Wortproblem, aber die Eingabe wird in komprimierter Form gegeben) und das Lösen von Gleichungen betrachtet. Die meisten der hier zusammengefassten Arbeiten betrachten die genannten Probleme für spezielle Klassen von Gruppen und klassifizieren deren Komplexität mit Methoden der Schaltkreiskomplexität. Eine Ausnahme bildet die letzte Arbeit zum Thema Gleichungen: hier liegt der Zusammenhang zur Schaltkreiskomplexität darin, dass sich das Erfüllbarkeitsproblem für Gleichungen in endlichen auslösbaren Gruppen ähnlich verhält wie das Erfüllbarkeitsproblem für CC^0 Schaltkreise.
Open Access
Computational and logical aspects of infinite monoids
(2003) Lohrey, Markus; Diekert, Volker (Prof. Dr.)
The present work contains a treatise of several computational and logical aspects of infinite monoids. The first chapter is devoted to the word problem for finitely generated monoids. In particular, the relationship between the the computational complexity of the word problem and the syntactical properties of monoid presentations is investigated. The second chapter studies Cayley-graphs of finitely generated monoids under a logical point of view. Cayley-graphs of groups play an important role in combinatorial group theory. We will study first-order and monadic second-order theories of Cayley-graphs for both groups and monoids. The third chapter deals with word equations over monoids. Using the graph product operation, which generalizes both the free and the direct product, we generalize the seminal decidability results of Makanin on free monoids and groups to larger classes of monoids.
Open Access
Concentrated patterns in biological systems
(2003) Winter, Matthias; Mielke, Alexander (Prof.)
We study pattern formation for reaction-diffusion systems of mathematical biology in the case of the Gierer-Meinhardt system. In this thesis we show that there is a critical growth rate of the inhibitor such that the position of boundary spikes is given by a linear combination of the boundary curvature and a Green function. There are two main results. The first one concerns the existence of boundary spikes for the activator. It says that the solutions are such that in the neighborhood of a boundary point for which the linear combination mentioned above possesses a nondegenerate critical point in tangential direction there is a spike (i.e. a peak whose spatial extension contracts but which after rescaling has a limit profile). Outside this boundary point the solutions are constant in first approximation. The proof uses Liapunov-Schmidt reduction, fixed point theorems and asymptotic analysis. The second main result concerns stability and says that the stability of this boundary spike depends on the parameters of the system. We assume that the linear combination from above possesses a nondegenerate local maximum at that boundary point. Then the stability depends on the size of a time relaxation constant. The proof studies small eigenvalues (i.e. they converge to zero) using asymptotic analysis. These small eigenvalue are connected with the second tangential derivatives of this linear combination. Large eigenvalues are explored using nonlocal eigenvalue problems.
Open Access
Continuum mechanics of multicomponent materials : modelling, numerics and applications for biological materials in the framework of the theory of porous media
(Stuttgart : Institut für Mechanik (Bauwesen), Lehrstuhl für Kontinuumsmechanik, Universität Stuttgart, 2021) Wagner, Arndt; Ehlers, Wolfgang (Prof. Dr.-Ing. Dr. h. c.)
Open Access
Contributions to the integral representation theory of groups
(2004) Hertweck, Martin; Kimmerle, Wolfgang (apl. Prof. Dr.)
This thesis contributes to the integral representation theory of groups. Topics treated include: the integral isomorphism problem --- if the group rings ZG and ZH are isomorphic, are the finite groups G and H isomorphic?, the Zassenhaus conjecture concerning automorphisms of integral group rings --- can each augmentation preserving automorphism of ZG be written as the product of an automorphism of G and a central automorphism?, and the normalizer problem --- in the unit group of ZG, is G only normalized by the obvious units? It is well known that these topics are closely related. Though counterexamples are known to each of these questions, our knowledge about such problems is still rather incomplete. A semilocal analysis of the known counterexample to the integral isomorphism problem is performed, which leads to new insight into the structure of the underlying groups. At the same time, this gives strong evidence for the existence of non-isomorphic groups of odd order having isomorphic semilocal group rings. It is shown how in the "semilocal case", counterexamples to the Zassenhaus conjecture can be produced with relatively minor effort. More importantly, it is shown for the first time that there is no local-global principle for automorphisms: An automorphism of a semilocal group ring (corresponding to an invertible bimodule M) need not give rise to a global automorphism (none of the modules in the genus of M is free from one side). In another part of this thesis, the normalizer problem for infinite groups is discussed. Research begun by Mazur is continued, and extensions of results of Jespers, Juriaans, de Miranda und Rogerio are obtained: By reduction to the finite group case, the normalizer problem is answered in the affirmative for certain classes of groups. The hypercenter of the unit group of RG, where G is a periodic group and R a G-adapted ring, is investigated too. If the hypercenter is not equal to the center, then G is a so called Q*-group, and then the hypercenter is described explicitly. The description in the R=Z case was obtained independently by Li and Parmenter, using different methods. The approach given here emphazises the connection to the normalizer problem and has a group-theoretical flavor. Moreover, it is shown that the second center of the unit group of ZG coincides with the finite conjugacy center. By way of contrast, the thesis ends with a little observation, intended to raise hopes that significant applications of integral representation theory to finite group theory will be found some day. In search of a proof of Glauberman's Z_p-star-Theorem (for odd p) which is independent from the classification, the following detail is noticed: If x is an element of order 3 in a finite group G which does not commute with any of its distinct conjugates, then chi(x), for any irreducible character chi of G, is an integral muliple of a root of unity.
Open Access
Datenanalysen für industrielle Anwendungsfälle : Datencharakteristika und Nutzung von Domänenwissen
(2025) Reimann, Peter; Mitschang, Bernhard (Prof. Dr.-Ing. habil.)
Der inhaltliche Schwerpunkt der vorliegenden Arbeit liegt im Bereich des Datenmanagements sowie der Datenanalyse für industrielle Anwendungsfälle aus dem produzierenden Gewerbe. Die in solchen industriellen Anwendungsfällen verfügbaren Daten weisen komplexe Charakteristika auf, die gängige Verfahren zum Datenmanagement und zur Datenanalyse vor Herausforderungen stellen. Beispiele für solche Datencharakteristika sind, dass häufig nur sehr wenige Daten zur Verfügung stehen oder dass die hohe Produktvielfalt in Unternehmen zu einer höheren Anzahl und Komplexität der in den Daten auftretenden Muster führen kann. In dieser Arbeit werden die häufigsten domänenspezifischen und komplexen Datencharakteristika vorgestellt und kategorisiert. Zudem wird aufgezeigt, dass diese Datencharakteristika, wenn sie nicht adäquat adressiert werden, zu mäßigen Analyseergebnissen führen, z.B. zu einer geringen Vorhersagegenauigkeit in einer Klassifikation. Als weiterer Schwerpunkt wird in dieser Arbeit der Stand der Wissenschaft hinsichtlich grundlegender Ansätze zur Nutzung von formal repräsentiertem Domänenwissen in die drei Schritte Datenakquise, Datenvorbereitung und Datenanalyse von Datenanalyseprozessen untersucht. Es wird diskutiert, inwieweit diese Ansätze die komplexen Datencharakteristika industrieller Anwendungsfälle adressieren können, um somit die Qualität von Analyseergebnissen zu erhöhen. Betrachtete Wissensrepräsentationsformen sind Fallbasen, Regelbasen, Glossare, semantische Netze wie Ontologien oder Wissensgraphen, probabilistische Graphen sowie mathematische Simulationsmodelle. Die untersuchten Ansätze schließen u.a. Ansätze zur Nutzung einer Regelbasis, semantischer Netze oder Simulationsmodelle zum Feature-Engineering, zur Festlegung der Labels in Daten oder für weitere Schritte der Datenakquise, Datenvorbereitung oder der Datenanalyse ein. Die Diskussionen werden mit Evaluationsergebnissen auf Basis realer industrieller Anwendungsfälle und Daten untermauert.
Open Access
Efficient modeling of environmental systems in the face of complexity and uncertainty
(2014) Oladyshkin, Sergey; Helmig, Rainer (Prof. Dr.-Ing.)
Strong industrial development of the last century has led to a significant increase in public demand for different types of energy and, as a consequence, to an enormous increase in demand for natural resources. Naturally, all types of nature resources form a part of our surrounding environment. In order to extract natural resources a wide variety of technologies has been developed. This has led to a strong rise in interventions in the environment continuing up to the present days. At the same time, environmental systems form one of the largest and most important classes of complex dynamic systems. For this reason, society needs a better understanding of the environment in order to have an efficient and safe interaction for the sake of maximized welfare and sustainability in resources management. In particular, the ability to predict how the environment changes over time or how it will react to planned interventions is indispensable. However our surroundings behave non-trivially in various time and spatial scales. Moreover, many environmental systems are heterogeneous, non-linear and dominated by real-time influences of external driving forces. Unfortunately, a complete picture of environmental systems is not available, because many of these systems cannot be observed directly and only can be derived using sparse measurements. Moreover, environmental data is hardly available and expensive to acquire. Overall, this leads to limited observability, and an inherent uncertainty in all modeling endeavors. Still, research over several decades has showed that modeling plays a very important role in reconstructing (as far as possible) the complete and complex picture of the environment systems and offers a unique way to predict behavior of such multifaceted systems. The current thesis contains research in the field of environmental modeling in the face of complexity and uncertainty. The presented thesis is divided into three parts and refers to diverse applications such as underground petroleum reservoirs, groundwater flow, radioactive waste deposits and storage of energy relevant gases. Part 1 focuses on physical concepts and offers several possibilities to accelerate the modeling process. Part 2 deals with efficient model reduction methodologies for uncertainty quantification. Part 3 demonstrates application to the storage of energy relevant gases in geological formations and discusses related challenges.
Open Access
Electron correlations in the 2D multilayer organic metal k-(BEDT-TTF)2I3 in magnetic fields
(2004) Balthes, Eduard; Schweitzer, Dieter (Prof. Dr.)
This work presents quantum oscillation experiments in quasi-twodimensional multilayer organic metals. They show that low integer Landau level filling factors nare present in the two-dimensional organic metal k-(BEDT-TTF)2I3 and give strong indications for the existence of the fractional filling factor n=½ in this material. By this the work shows the presence of electron localisation and electron correlation in a bulk metallic two-dimensional system. These effects are found in the normal conducting state of the organic superconductor k-(BEDT-TTF)2I3. The revolutionary discovery of the integer as well as the fractional quantum Hall effect in two-dimensional semiconducting single-layer systems invoked, i.a., the questions, whether these effects may also be present in other types of conductors and, especially, whether they may also occur in bulk three-dimensional crystals. Strong efforts were made to produce bilayer two-dimensional semiconductors, to control their interlayer coupling as well as electron tunnelling, to increase step by step the number of involved layers with the aim to realise the quantised Hall effects in 'bulk' multilayer and, finally, in 'infinite-layer' systems. Furthermore strong efforts are made in semiconducting two-dimensional systems to realise carrier densities above 1011/cm2 with mobilities exceeding 107cm2/Vs. k-(BEDT-TTF)2I3 is a metallic compound with a very high electron density of 2*1019/cm2 and a very high carrier mobility reaching about 5*108cm2/Vs. From its structural principle this organic material represents a system of 105 coupled metallic multilayers, which can be synthesised in very high purity and can be produced as three-dimensional bulk single crystals. Despite of this, the material shows strongly two-dimensional electronic properties under certain experimental conditions, as found in the frame of this work. In contrast to the characteristic situation in semiconducting two-dimensional systems, where (correlated) electrons move on a single quantised orbit, the strongly correlated carriers in k-(BEDT-TTF)2I3 move on various quantised orbits with even very different filling factors. These are the main conditions under which the above mentioned filling factors are found in k-(BEDT-TTF)2I3. Besides these characteristics, the present two-dimensional organic metal holds a number of further peculiarities, which may represent a challenge for the understanding of possible fractional filling factors and quantum limit in a macroscopic multilayer crystal with two-dimensional electronic properties. In addition, the present work resumes experiments on the influence of low-dimensionality onto the electronic properties of a number of low-dimensional multilayer organic conductors.
Open Access
Engineering AI planning systems
(2024) Georgievski, Ilche; Aiello, Marco (Prof. Dr.)
Planning and acting adaptively in complex environments is fundamental to human intelligence. We navigate such complexity by simulating, evaluating, and selecting among possible courses of action using internal models of the world. The field of AI planning seeks to computationally reproduce this form of intelligent behavior. This habilitation thesis presents research on engineering AI planning systems that can effectively address complex, real-world problems, with the broader objective of enabling users to design, develop, and operate such systems. The thesis offers and advocates for a holistic approach to AI planning, one that integrates algorithmic, knowledge, and systems engineering to support the entire lifecycle of planning technology, from conceptualisation to deployment. By bridging foundational research with real-world application, it strives to widen the academic dialogue around AI planning and to establish a pathway toward making AI planning technology a practical tool for innovation. The habilitation thesis is cumulative and accompanied by an executive summary synthesising insights from sixteen publications. The executive summary begins by outlining the research context, key challenges, and research approach employed. It then turns to the published contributions, with particular focus on systems engineering and knowledge engineering, including methodological and artefactual advancements. These contributions are supported by applied research in the domain of smart energy systems. The summary concludes by reflecting on the implications of the work and offering directions for future work.
Open Access
Experimentelle und numerische Beschreibung katalytischer Zünd- und Verbrennungsprozesse
(1999) Behrendt, Frank; Maas, Ulrich (Prof. Dr.)
In der hier vorgestellten Arbeit wird ein räumlich eindimensional behandelbares Modellsystem für die numerische Simulation und experimentelle Untersuchung der katalytischen Zündung und Verbrennung für verschiedene Brennstoffe und Katalysatoren vorgestellt. Darüberhinaus wird die Anwendbarkeit von Modell und Rechenprogramm für die Materialdeposition aus einer reaktiven Gasphase am Beispiel der Diamantabscheidung erfolgreich demonstriert. Das Rechenprogramm löst hierbei die zeitabhängigen Navier-Stokes-Gleichungen für eine Staupunktströmung, die auf eine reaktive Oberfläche gerichtet ist. Die Beschreibung der Oberflächenreaktionen und der daraus resultierenden Wärmefreisetzung bilden die Randbedingungen für die Integration der Erhaltungsgleichungen in der Gasphase. Auf der Oberfläche wie in der Gasphase wird das chemische Geschehen unter Zuhilfenahme detaillierter Mechanismen aus Elementarreaktionen beschrieben. Der Transport in der Gasphase sowie zwischer dieser und der Oberfläche wird durch ein vereinfachtes Multikomponenten-Transportmodell, das auch die Thermodiffusion berücksichtigt, erfaßt.
Open Access
Gas-solid reactions for energy storage and conversion
(2022) Linder, Marc; Thess, André (Prof. Dr.)
Reversible gas-solid reactions could offer relevant technological contributions to an energy system predominantly based on renewable energy. However, our current understanding of this technology is mainly based on fundamental material research and generic application concepts. Therefore, the first part of this work summarizes the current state of knowledge in order to identify unique advantages that could arise from reversible gas-solid reactions for energy storage and conversion. Starting with a technological differentiation between various reversible processes used for energy storage, a classification of different reactor designs and a generic approach for thermal integration and necessary reaction gas supply, three main directions are derived that currently seem most promising to transfer the specific properties of gas-solid reactions to technical systems: (1) open configurations to reduce system complexity, (2) utilization of available pressure differences to adjust the reaction temperature and (3) combination of abundant materials with the intrinsic possibility of lossless storage. Based on these considerations, the second part of this work summarizes our approach to transfer material properties to technical systems, e.g. by developing storages that utilize oxygen from air, by taking advantage of the pressure dependency of the reaction temperature of metal hydrides and salt hydrates or by combining the long-term energy storage possibility with abundant and costefficient reactants such as calcium oxide and water.
Open Access
Gegenseitige Simulation von Datenstrukturen
(2002) Petersen, Holger; Diekert, Volker (Prof. Dr.)
Die vorliegende Arbeit stellt einige Ergebnisse zusammen, welche das Verhältnis verschiedener Berechenbarkeitsmodelle zueinander betreffen. Hierbei wird einerseits der Zusatzaufwand (im Bezug auf die Zeitkomplexität) bei der gegenseitigen Simulation solcher Modelle untersucht. Andererseits werden untere Schranken bewiesen oder auch die Unmöglichkeit einer Simulation. Diese Untersuchungen lassen sich einem Bereich zuordnen, der als konkrete Komplexitätstheorie bezeichnet wird.
Open Access
General properties of ionic complex fluids
(2016) Bier, Markus; Dietrich, Siegfried (Prof. Dr.)