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Mon, 27 Apr 2015 08:33:27 +0200Mon, 27 Apr 2015 08:33:27 +0200A Viscosity Adaptive Lattice Boltzmann Method
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4058
The present thesis describes the development and validation of a viscosity adaption method for the numerical simulation of non-Newtonian fluids on the basis of the Lattice Boltzmann Method (LBM), as well as the development and verification of the related software bundle SAM-Lattice.
By now, Lattice Boltzmann Methods are established as an alternative approach to classical computational fluid dynamics
methods. The LBM has been shown to be an accurate and efficient tool for the numerical simulation of weakly compressible or incompressible fluids. Fields of application reach from turbulent simulations through thermal problems to acoustic calculations among others. The transient nature of the method and the need for a regular grid based, non body conformal discretization makes the LBM ideally suitable for simulations involving complex solids. Such geometries are common, for instance, in the food processing industry, where fluids are mixed by static mixers or agitators. Those fluid flows are often laminar and non-Newtonian.
This work is motivated by the immense practical use of the Lattice Boltzmann Method, which is limited due to stability issues. The stability of the method is mainly influenced by the discretization and the viscosity of the fluid. Thus, simulations of non-Newtonian fluids, whose kinematic viscosity depend on the shear rate, are problematic. Several authors have shown that the LBM is capable of simulating those fluids. However, the vast majority of the simulations in the literature are carried out for simple geometries and/or moderate shear rates, where the LBM is still stable. Special care has to be taken for practical non-Newtonian Lattice Boltzmann simulations in order to keep them stable. A straightforward way is to truncate the modeled viscosity range by numerical stability criteria. This is an effective approach, but from the physical point of view the viscosity bounds are chosen arbitrarily. Moreover, these bounds depend on and vary with the grid and time step size and, therefore, with the simulation Mach number, which is freely chosen at the start of the simulation. Consequently, the modeled viscosity range may not fit to the actual range of the physical problem, because the correct simulation Mach number is unknown a priori. A way around is, to perform precursor simulations on a fixed grid to determine a possible time step size and simulation Mach number, respectively. These precursor simulations can be time consuming and expensive, especially for complex cases and a number of operating points. This makes the LBM unattractive for use in practical simulations of non-Newtonian fluids.
The essential novelty of the method, developed in the course of this thesis, is that the numerically modeled viscosity range is consistently adapted to the actual physically exhibited viscosity range through change of the simulation time step and the simulation Mach number, respectively, while the simulation is running. The algorithm is robust, independent of the Mach number the simulation was started with, and applicable for stationary flows as well as transient flows. The method for the viscosity adaption will be referred to as the "viscosity adaption method (VAM)" and the combination with LBM leads to the "viscosity adaptive LBM (VALBM)".
Besides the introduction of the VALBM, a goal of this thesis is to offer assistance in the spirit of a theory guide to students and assistant researchers concerning the theory of the Lattice Boltzmann Method and its implementation in SAM-Lattice. In Chapter 2, the mathematical foundation of the LBM is given and the route from the BGK approximation of the Boltzmann equation to the Lattice Boltzmann (BGK) equation is delineated in detail.
The derivation is restricted to isothermal flows only. Restrictions of the method, such as low Mach number flows are highlighted and the accuracy of the method is discussed.
SAM-Lattice is a C++ software bundle developed by the author and his colleague Dipl.-Ing. Andreas Schneider. It is a highly automated package for the simulation of isothermal flows of incompressible or weakly compressible fluids in 3D on the basis of the Lattice Boltzmann Method. By the time of writing of this thesis, SAM-Lattice comprises 5 components. The main components are the highly automated lattice generator SamGenerator and the Lattice Boltzmann solver SamSolver. Postprocessing is done with ParaSam, which is our extension of the
open source visualization software ParaView. Additionally, domain decomposition for MPI
parallelism is done by SamDecomposer, which makes use of the graph partitioning library MeTiS. Finally, all mentioned components can be controlled through a user friendly GUI (SamLattice) implemented by the author using QT, including features to visually track output data.
In Chapter 3, some fundamental aspects on the implementation of the main components, including the corresponding flow charts will be discussed. Actual details on the implementation are given in the comprehensive programmers guides to SamGenerator and SamSolver.
In order to ensure the functionality of the implementation of SamSolver, the solver is verified in Chapter 4 for Stokes's First Problem, the suddenly accelerated plate, and for Stokes's Second Problem, the oscillating plate, both for Newtonian fluids. Non-Newtonian fluids are modeled in SamSolver with the power-law model according to Ostwald de Waele. The implementation for non-Newtonian fluids is verified for the Hagen-Poiseuille channel flow in conjunction with a convergence analysis of the method. At the same time, the local grid refinement as it is implemented in SamSolver, is verified. Finally, the verification of higher order boundary conditions is done for the 3D Hagen-Poiseuille pipe flow for both Newtonian and non-Newtonian fluids.
In Chapter 5, the theory of the viscosity adaption method is introduced. For the adaption process, a target collision frequency or target simulation Mach number must be chosen and the distributions must be rescaled according to the modified time step size. A convenient choice is one of the stability bounds. The time step size for the adaption step is deduced from the target collision frequency \(\Omega_t\) and the currently minimal or maximal shear rate in the system, while obeying auxiliary conditions for the simulation Mach number. The adaption is done in the collision step of the Lattice Boltzmann algorithm. We use the transformation matrices of the MRT model to map from distribution space to moment space and vice versa. The actual scaling of the distributions is conducted on the back mapping, because we use the transformation matrix on the basis of the new adaption time step size. It follows an additional rescaling of the non-equilibrium part of the distributions, because of the form of the definition for the discrete stress tensor in the LBM context. For that reason it is clear, that the VAM is applicable for the SRT model as well as the MRT model, where there is virtually no extra cost in the latter case. Also, in Chapter 5, the multi level treatment will be discussed.
Depending on the target collision frequency and the target Mach number, the VAM can be used to optimally use the viscosity range that can be modeled within the stability bounds or it can be used to drastically accelerate the simulation. This is shown in Chapter 6. The viscosity adaptive LBM is verified in the stationary case for the Hagen-Poiseuille channel flow and in the transient case for the Wormersley flow, i.e., the pulsatile 3D Hagen-Poiseuille pipe flow. Although, the VAM is used here for fluids that can be modeled with the power-law approach, the implementation of the VALBM is straightforward for other non-Newtonian models, e.g., the Carreau-Yasuda or Cross model. In the same chapter, the VALBM is validated for the case of a propeller viscosimeter developed at the chair SAM. To this end, the experimental data of the torque on the impeller of three shear thinning non-Newtonian liquids serve for the validation. The VALBM shows excellent agreement with experimental data for all of the investigated fluids and in every operating point. For reasons of comparison, a series of standard LBM simulations is carried out with different simulation Mach numbers, which partly show errors of several hundred percent. Moreover, in Chapter 7, a sensitivity analysis on the parameters used within the VAM is conducted for the simulation of the propeller viscosimeter.
Finally, the accuracy of non-Newtonian Lattice Boltzmann simulations with the SRT and the MRT model is analyzed in detail. Previous work for Newtonian fluids indicate that depending on the numerical value of the collision frequency \(\Omega\), additional artificial viscosity is introduced due to the finite difference scheme, which negatively influences the accuracy. For the non-Newtonian case, an error estimate in the form of a functional is derived on the basis of a series expansion of the Lattice Boltzmann equation. This functional can be solved analytically for the case of the Hagen-Poiseuille channel flow of non-Newtonian fluids. The estimation of the error minimum is excellent in regions where the \(\Omega\) error is the dominant source of error as opposed to the compressibility error.
Result of this dissertation is a verified and validated software bundle on the basis of the viscosity adaptive Lattice Boltzmann Method. The work restricts itself on the simulation of isothermal, laminar flows with small Mach numbers. As further research goals, the testing of the VALBM with minimal error estimate and the investigation of the VALBM in the case of turbulent flows is suggested.Daniel Conraddoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4058Mon, 27 Apr 2015 08:33:27 +0200A Consistent Large Eddy Approach for Lattice Boltzmann Methods and its Application to Complex Flows
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4056
Lattice Boltzmann Methods have shown to be promising tools for solving fluid flow problems. This is related to the advantages of these methods, which are among others, the simplicity in handling complex geometries and the high efficiency in calculating transient flows. Lattice Boltzmann Methods are mesoscopic methods, based on discrete particle dynamics. This is in contrast to conventional Computational Fluid Dynamics methods, which are based on the solution of the continuum equations. Calculations of turbulent flows in engineering depend in general on modeling, since resolving of all turbulent scales is and will be in near future far beyond the computational possibilities. One of the most auspicious modeling approaches is the large eddy simulation, in which the large, inhomogeneous turbulence structures are directly computed and the smaller, more homogeneous structures are modeled.
In this thesis, a consistent large eddy approach for the Lattice Boltzmann Method is introduced. This large eddy model includes, besides a subgrid scale model, appropriate boundary conditions for wall resolved and wall modeled calculations. It also provides conditions for turbulent domain inlets. For the case of wall modeled simulations, a two layer wall model is derived in the Lattice Boltzmann context. Turbulent inlet conditions are achieved by means of a synthetic turbulence technique within the Lattice Boltzmann Method.
The proposed approach is implemented in the Lattice Boltzmann based CFD package SAM-Lattice, which has been created in the course of this work. SAM-Lattice is feasible of the calculation of incompressible or weakly compressible, isothermal flows of engineering interest in complex three dimensional domains. Special design targets of SAM-Lattice are high automatization and high performance.
Validation of the suggested large eddy Lattice Boltzmann scheme is performed for pump intake flows, which have not yet been treated by LBM. Even though, this numerical method is very suitable for this kind of vortical flows in complicated domains. In general, applications of LBM to hydrodynamic engineering problems are rare. The results of the pump intake validation cases reveal that the proposed numerical approach is able to represent qualitatively and quantitatively the very complex flows in the intakes. The findings provided in this thesis can serve as the basis for a broader application of LBM in hydrodynamic engineering problems.Andreas Schneiderdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4056Mon, 27 Apr 2015 08:24:57 +0200New N,N,P-Ligands and Their Heterobimetallic Complexes
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4052
The aim of this work was to synthesize and characterize new bidentate N,N,P-ligands and their corresponding heterobimetallic complexes. These bidentate pyridylpyrimidine aminophosphine ligands were synthesized by ring closure of two different enaminones ( 3-(dimethylamino)-1-(pyridine-2-yl)-prop-2-en-1-one or 3-(dimethylamino)-1-(pyridine-2-yl)-but-2-en-1-one) with excess amount of guanidinium salts in the presence of base. The novel phosphine functionalized guanidinium salts were prepared from 2-(diphenylphosphinyl)ethylamine or 3-(diphenyl-phosphinyl)propylamine. These bidentate N,N,P-ligands contain hard and soft donor sites which allows the coordination of two different metal centers and bimetallic complexes. These bimetallic complexes can exhibit a unique behavior as a result of a cooperation between the two metal atoms. First, the gold(I) complexes of all these four different ligands were synthesized. The gold metal coordinates only to the phosphorus atom. It was proved by X-Ray crystallography technique and 31P NMR spectroscopy. Addition to the gold(I)-monometallic complexes, trans- coordinated rhodium complex of (2-amino)pyridylpyrimidine aminophosphine ligand was successfully prepared. The characterization of this complex was achieved by NMR and IR spectroscopy. Reacting the mono gold(I) complexes with the different metal salts like Pd(PhCN)2Cl2, ZnCl2, [Ru(p-cymene)Cl2] dimer gave the target heterobimetallic complexes. The second metal centers coordinated to the N,N donor site which was proved by the help of NMR spectroscopy and ESI-MS measurements. The Au(I) and Au-Zn complexes of N,N,P-ligands were examined as catalysts for the hydroamidation reaction of cyclohexene with p-toluenesulfonamide. They did not show activities under the tested conditions. Further studies are necessary to understand the catalytic activities and cooperativity between the two metal atoms. In addition, bi-and trimetallic complexes with the rhodium compound could be synthesized and tested in different organic transformations. Furthermore, the chiral hydroxyl[2.2]paracyclophane substituted with five different aminopyrimidines were accomplished. These aminopyrimidine ligands were synthesized by a cyclization reaction with hydroxyl[2.2]paracyclophane substituted enaminone and excess amount of corresponding guanidinium salts under basic conditions. In the last part of this work, kinetic studies of cyclopalladation reaction of the 2-(arylaminopyrimidin-4-yl)pyridine ligands with Pd(PhCN)2 These measurements were carried out by using UV-Vis spectroscopy. The spectral studies of cyclometallation step showed that the reaction fits a second order kinetics. In addition to this, a full kinetic investigation was performed at different temperatures and the activation parameters of complex formation were calculated.
Merve Cayirdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4052Tue, 21 Apr 2015 13:14:32 +0200User-Centered Collaborative Visualization
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4051
The last couple of years have marked the entire field of information technology with the introduction of a new global resource, called data. Certainly, one can argue that large amounts of information and highly interconnected and complex datasets were available since the dawn of the computer and even centuries before. However, it has been only a few years since digital data has exponentially expended, diversified and interconnected into an overwhelming range of domains, generating an entire universe of zeros and ones. This universe represents a source of information with the potential of advancing a multitude of fields and sparking valuable insights. In order to obtain this information, this data needs to be explored, analyzed and interpreted.
While a large set of problems can be addressed through automatic techniques from fields like artificial intelligence, machine learning or computer vision, there are various datasets and domains that still rely on the human intuition and experience in order to parse and discover hidden information. In such instances, the data is usually structured and represented in the form of an interactive visual representation that allows users to efficiently explore the data space and reach valuable insights. However, the experience, knowledge and intuition of a single person also has its limits. To address this, collaborative visualizations allow multiple users to communicate, interact and explore a visual representation by building on the different views and knowledge blocks contributed by each person.
In this dissertation, we explore the potential of subjective measurements and user emotional awareness in collaborative scenarios as well as support flexible and user- centered collaboration in information visualization systems running on tabletop displays. We commence by introducing the concept of user-centered collaborative visualization (UCCV) and highlighting the context in which it applies. We continue with a thorough overview of the state-of-the-art in the areas of collaborative information visualization, subjectivity measurement and emotion visualization, combinable tabletop tangibles, as well as browsing history visualizations. Based on a new web browser history visualization for exploring user parallel browsing behavior, we introduce two novel user-centered techniques for supporting collaboration in co-located visualization systems. To begin with, we inspect the particularities of detecting user subjectivity through brain-computer interfaces, and present two emotion visualization techniques for touch and desktop interfaces. These visualizations offer real-time or post-task feedback about the users’ affective states, both in single-user and collaborative settings, thus increasing the emotional self-awareness and the awareness of other users’ emotions. For supporting collaborative interaction, a novel design for tabletop tangibles is described together with a set of specifically developed interactions for supporting tabletop collaboration. These ring-shaped tangibles minimize occlusion, support touch interaction, can act as interaction lenses, and describe logical operations through nesting operations. The visualization and the two UCCV techniques are each evaluated individually capturing a set of advantages and limitations of each approach. Additionally, the collaborative visualization supported by the two UCCV techniques is also collectively evaluated in three user studies that offer insight into the specifics of interpersonal interaction and task transition in collaborative visualization. The results show that the proposed collaboration support techniques do not only improve the efficiency of the visualization, but also help maintain the collaboration process and aid a balanced social interaction.Daniel Cerneadoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4051Mon, 20 Apr 2015 14:18:00 +0200Robustness for regression models with asymmetric error distribution
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4046
In this work we focus on the regression models with asymmetrical error distribution,
more precisely, with extreme value error distributions. This thesis arises in the framework
of the project "Robust Risk Estimation". Starting from July 2011, this project won
three years funding by the Volkswagen foundation in the call "Extreme Events: Modelling,
Analysis, and Prediction" within the initiative "New Conceptual Approaches to
Modelling and Simulation of Complex Systems". The project involves applications in
Financial Mathematics (Operational and Liquidity Risk), Medicine (length of stay and
cost), and Hydrology (river discharge data). These applications are bridged by the
common use of robustness and extreme value statistics.
Within the project, in each of these applications arise issues, which can be dealt with by
means of Extreme Value Theory adding extra information in the form of the regression
models. The particular challenge in this context concerns asymmetric error distributions,
which significantly complicate the computations and make desired robustification
extremely difficult. To this end, this thesis makes a contribution.
This work consists of three main parts. The first part is focused on the basic notions
and it gives an overview of the existing results in the Robust Statistics and Extreme
Value Theory. We also provide some diagnostics, which is an important achievement of
our project work. The second part of the thesis presents deeper analysis of the basic
models and tools, used to achieve the main results of the research.
The second part is the most important part of the thesis, which contains our personal
contributions. First, in Chapter 5, we develop robust procedures for the risk management
of complex systems in the presence of extreme events. Mentioned applications use time
structure (e.g. hydrology), therefore we provide extreme value theory methods with time
dynamics. To this end, in the framework of the project we considered two strategies. In
the first one, we capture dynamic with the state-space model and apply extreme value
theory to the residuals, and in the second one, we integrate the dynamics by means of
autoregressive models, where the regressors are described by generalized linear models.
More precisely, since the classical procedures are not appropriate to the case of outlier
presence, for the first strategy we rework classical Kalman smoother and extended
Kalman procedures in a robust way for different types of outliers and illustrate the performance
of the new procedures in a GPS application and a stylized outlier situation.
To apply approach to shrinking neighborhoods we need some smoothness, therefore for
the second strategy, we derive smoothness of the generalized linear model in terms of
L2 differentiability and create sufficient conditions for it in the cases of stochastic and
deterministic regressors. Moreover, we set the time dependence in these models by
linking the distribution parameters to the own past observations. The advantage of
our approach is its applicability to the error distributions with the higher dimensional
parameter and case of regressors of possibly different length for each parameter. Further,
we apply our results to the models with generalized Pareto and generalized extreme value
error distributions.
Finally, we create the exemplary implementation of the fixed point iteration algorithm
for the computation of the optimally robust in
uence curve in R. Here we do not aim to
provide the most
exible implementation, but rather sketch how it should be done and
retain points of particular importance. In the third part of the thesis we discuss three applications,
operational risk, hospitalization times and hydrological river discharge data,
and apply our code to the real data set taken from Jena university hospital ICU and
provide reader with the various illustrations and detailed conclusions.Daria Pupashenkodoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4046Thu, 16 Apr 2015 13:53:08 +0200Worst-Case Portfolio Optimization: Transaction Costs and Bubbles
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4045
In this thesis we extend the worst-case modeling approach as first introduced by Hua and Wilmott (1997) (option pricing in discrete time) and Korn and Wilmott (2002) (portfolio optimization in continuous time) in various directions.
In the continuous-time worst-case portfolio optimization model (as first introduced by Korn and Wilmott (2002)), the financial market is assumed to be under the threat of a crash in the sense that the stock price may crash by an unknown fraction at an unknown time. It is assumed that only an upper bound on the size of the crash is known and that the investor prepares for the worst-possible crash scenario. That is, the investor aims to find the strategy maximizing her objective function in the worst-case crash scenario.
In the first part of this thesis, we consider the model of Korn and Wilmott (2002) in the presence of proportional transaction costs. First, we treat the problem without crashes and show that the value function is the unique viscosity solution of a dynamic programming equation (DPE) and then construct the optimal strategies. We then consider the problem in the presence of crash threats, derive the corresponding DPE and characterize the value function as the unique viscosity solution of this DPE.
In the last part, we consider the worst-case problem with a random number of crashes by proposing a regime switching model in which each state corresponds to a different crash regime. We interpret each of the crash-threatened regimes of the market as states in which a financial bubble has formed which may lead to a crash. In this model, we prove that the value function is a classical solution of a system of DPEs and derive the optimal strategies.
Christoph Belakdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4045Tue, 07 Apr 2015 10:17:10 +0200Optimal Multilevel Monte Carlo Algorithms for Parametric Integration and Initial Value Problems
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4044
We intend to find optimal deterministic and randomized algorithms for three related problems: multivariate integration, parametric multivariate integration, and parametric initial value problems. The main interest is concentrated on the question, in how far randomization affects the precision of an approximation. We want to understand when and to which extent randomized algorithms are superior to deterministic ones.
All problems are studied for Banach space valued input functions. The analysis of Banach space valued problems is motivated by the investigation of scalar parametric problems; these can be understood as particular cases of Banach space valued problems. The gain achieved by randomization depends on the underlying Banach space.
For each problem, we introduce deterministic and randomized algorithms and provide the corresponding convergence analysis.
Moreover, we also provide lower bounds for the general Banach space valued settings, and thus, determine the complexity of the problems. It turns out that the obtained algorithms are order optimal in the deterministic setting. In the randomized setting, they are order optimal for certain classes of Banach spaces, which includes the L_p spaces and any finite dimensional Banach space. For general Banach spaces, they are optimal up to an arbitrarily small gap in the order of convergence.Thomas Daundoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4044Tue, 07 Apr 2015 10:06:18 +0200Metallacetylide und mehrkernige Komplexe mit neuen chelatisierenden Alkinylliganden
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4040
Metallacetylide sind Verbindungen aus Metallen und Liganden, die durch Deprotonierung terminaler Alkine entstehen. Komplexe dieser Art weisen eine Vielzahl verschiedener Eigenschaften und Verwendungsmöglichkeiten auf. Der lineare Charakter der Acetylideinheit und ihre π-ungesättigte Natur macht sie zu geeigneten Bildungskomponenten für die Herstellung molekularer Leiter oder organometallischer oligo- sowie polymerer Materialien mit Eigenschaften wie z. B. optischer Nichtlinearität, Lumineszenz, elektrischer Leitfähigkeit und Flüssigkristallinität. Zwar existieren zahlreiche Arbeiten zur Herstellung von Metall-acetylidkomplexen, die Möglichkeit Liganden zu synthetisieren, die eine mehrzähnige, sogenannte chelatisierende Funktion mit einer terminalen Alkinyleinheit kombinieren, wurde jedoch nur von wenigen Gruppen verfolgt. Mit Hilfe solcher Liganden ist es nicht nur möglich, durch kovalente Anbindung eines Metalls an die C-C-Dreifachbindung Metallacetylide zu erhalten, sondern diese durch Koordination weiterer Metallzentren an die Chelatfunktion effizient zu stabilen, mehrkernigen Metallkomplexen zu erweitern. Im Rahmen dieser Arbeit wurden zwei Liganden synthetisiert, die derartige Eigenschaften besitzen: Das zweizähnige Alkin 2-(1-(Prop-2-yn-1-yl)-1H-pyrazol-3-yl)pyridin und das dreizähnige Diin 2,6-Bis(1(prop-2-yn-1-yl)-1H-pyrazol-3-yl)pyridin. Die Liganden wurden unter steter Optimierung der Reaktionsbedingungen durch Propargylierung von 2-Pyrazolylpyridin bzw. 2,6-Bispyrazolylpyridin synthetisiert. In einer Reihe von Versuchen mit verschiedenen Übergangsmetallen wurde das Monoalkin auf seine Fähigkeit hin untersucht, sowohl Metallacetylide als auch Komplexe durch Koordination an die chelatisierenden Stickstoffatome zu bilden. Dabei wurden ein Gold(I)monoacetylid mit Triphenylphosphan als Neutralligand sowie zwei Platindiacetylide erhalten. Die Platinkomplexe unterscheiden sich durch ihre Neutralliganden: es wurde einerseits Triphenylphosphan, andererseits ein dppe eingesetzt. Die unterschiedliche Natur der Phosphanliganden wirkt sich auf die Konformation der Komplexe aus: Während die einzähnigen Triphenylphosphanmoleküle die Positionierung der Alkinylliganden in trans-Stellung erlauben, liegt der dppe-haltige Komplex in einer cis-Konformation vor. Aus beiden Komplexen wurden durch Koordination weiterer Metallzentren dreikernige Verbindungen synthetisiert. Dabei konnte das Produkt aus trans-Komplex mit Ruthenium(II) isoliert und charakterisiert werden, während das cis-Produkt nur analytisch nachgewiesen, jedoch nicht erfolgreich von den Nebenprodukten abgetrennt werden konnte. Für das dppe-haltige Platindiacetylid wurde die Fähigkeit Zink zu koordinieren in verschiedenen Versuchsreihen überprüft, die unter Variation der Zinkkonzentration und auch des Lösungsmittels durchgeführt wurden. Mit Hilfe von ESI-MS-Messungen konnte belegt werden, dass Zink(II)-Kationen an das Diacetylid koordinieren und in Abhängigkeit der
Zinkkonzentration verschiedene Produkte erhalten werden. Das Lösungsmittel zeigt ebenfalls einen Einfluss auf Produktbildung. Während in Aceton nur zwei verschiedene Zinkaddukte beobachtet werden können, wird in Acetonitril sogar die Bildung von Ketten und Clustern beobachtet. Der dreizähnige Diinligand wurde erfolgreich mit Ruthenium umgesetzt, sodass ein oktaedrischer Komplex entsand, bei dem der Ruthenium(II)-Kern dreifach an den von mir synthetisierten Liganden koordiniert war und neben einem Triphenylphosphan auch zwei Chloridoliganden trug. Mit diesem wurde die katalytische Transferhydrierung von Acetophenon mit Isopropanol durchgeführt, wobei die zur Deprotonierung des Alkohols zugegebene Menge an Base variiert wurde. Die Aktivität des Komplexes in der Transferhydrierung konnte bewiesen werden. Die zugegebene Basenmenge zeigte bei der angewendeten Versuchsdurchführung nur einen geringen Einfluss auf den Umsatz.Caroline Wilhelmidoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4040Wed, 01 Apr 2015 12:05:32 +0200Schwingfestigkeit und Mikrostruktur von ultrafeinkörnigem C45
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4038
Es gibt vielfache Ansätze, die mechanischen Eigenschaften von Werkstoffen zu verbessern, wobei in den meisten Fällen mit einer Erhöhung der quasistatischen Festigkeit eine Verringerung der Duktilität einhergeht. Bei ultrafeinkörnigen Werkstoffen ist diese Verringerung des Verformungsvermögens, aufgrund des dominierenden Verfestigungsmechanismus der Korngrenzenverfestigung, nicht zwangsläufig die Folge. Bei der Forschung mit Werkstoffen, die eine sehr kleine Korngröße aufweisen, stellt dieser Aspekt die Hauptmotivation dar.
Im Rahmen der aktuellen Arbeit wurden mehrere ultrafeinkörnige Modifikationen des Vergütungsstahles C45 mikrostrukturell, mit Hilfe von Raster- sowie Transmissionselektronenmikroskopie, aber auch Nanoindentation charakterisiert. Es konnten verbreitet Korngrößen unter 1 µm festgestellt werden, was der Definition ultrafeinkörnig entspricht. Anschließend folgte eine Korrelation der zyklischen Eigenschaften, welche mittels 4-Punkt-Mikrobiegeversuchen untersucht wurden und der Mikrostruktur. Da die hochfesten Ausprägungen der ultrafeinkörnigen Modifikationen in großen Teilen Rissinitiierung an nichtmetallischen Einschlüssen zeigten, erfolgte eine bruchmechanische Betrachtung mittels Spannungsintensitätsfaktoren. Als Quintessenz der vorliegenden Arbeit steht ein Modell, welches die Ermüdungseigenschaften von ultrafeinkörnigen Werkstoffen zusammenfasst. Mehrere Eigenschaften, wie das Auftreten von innerer Rissinitiierung, sowie insgesamt die extrem hohen Härten und Ermüdungsfestigkeiten (vergleichbar mit bainitisiertem 100Cr6), wurden im Rahmen der Arbeit erstmals bei diesen Modifikationen nachgewiesen und gehörten zuvor nicht zum Stand der Technik.
Christoph Ruffingdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4038Thu, 26 Mar 2015 15:30:31 +0100Modern dehydrogenative amination reactions
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4037
Nitrogen element is preponderant in Nature. Found in its simplest form as diatomic gas in the air, as well as in elaborated molecules such as the double helix of DNA, this element is indisputably essential for life. Indeed, nitrogen is omnipresent in all metabolic pathways.
With the advent of green chemistry, researchers attempt to functionalize arenes without pre-functionalization of the later for the establishment of C-C bond formation. Why not C-N bond formation?
We investigated new oxidative amination reactions by cross-dehydrogenative-coupling. Concerned by atom economy and green processes, our objectives were: 1) to obviate pre-activation or pre-oxidation of both C-H coupling partner and N-aminating agent. 2) to avoid the use of chelating directing group.
We achieved C-N bond formation for some classes of amines. Thus, we will describe the reactivity of cyclic secondary amines: carbazole, in presence of catalytic amount of ruthenium (II) and copper (II) to build the challenging C-N bond between two carbazoles. The initial mechanistic experiments will be present and discuss.
Then, we will describe more challenging hetero-coupling formation between diarylamines and carbazoles. The new ruthenium (II)/ copper (II) catalytic system allowed forming the ortho-N-carbazolation of diarylamines. This reaction performed under mild conditions (O2 as terminal oxidant) displays an unusual intramolecular N-H••N interaction in the novel class of compounds.
Finally, we will present a surprising metal free C-N bond formation between the ubiquitous phenols and the phenothiazines. Initially conducted in the presence of transition metals (RuII/CuII), this reaction proved to be efficient with the only effect of cumene and O2. Those components suggest a mechanism initiated by a Hock process. An initial infra-red analysis might point out a strong intramolecular O-H••N interaction in the resulting products.
These first elements of reactivity, developed within the laboratory for “modern dehydrogenative amination reactions”, will be presented and discussed.
Marie-Laure Louillat Habermeyerdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4037Wed, 25 Mar 2015 11:25:07 +0100Certification-Cognizant Mixed-Criticality Scheduling in Time-Triggered Systems
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4030
In embedded systems, there is a trend of integrating several different functionalities on a common platform. This has been enabled by increasing processing power and the arise of integrated system-on-chips.
The composition of safety-critical and non-safety-critical applications results in mixed-criticality systems. Certification Authorities (CAs) demand the certification of safety-critical applications with strong confidence in the execution time bounds. As a consequence, CAs use conservative assumptions in the worst-case execution time (WCET) analysis which result in more pessimistic WCETs than the ones used by designers. The existence of certified safety-critical and non-safety-critical applications can be represented by dual-criticality systems, i.e., systems with two criticality levels.
In this thesis, we focus on the scheduling of mixed-criticality systems which are subject to certification. Scheduling policies cognizant of the mixed-criticality nature of the systems and the certification requirements are needed for efficient and effective scheduling. Furthermore, we aim at reducing the certification costs to allow faster modification and upgrading, and less error-prone certification. Besides certification aspects, requirements of different operational modes result in challenging problems for the scheduling process. Despite the mentioned problems, schedulers require a low runtime overhead for an efficient execution at runtime.
The presented solutions are centered around time-triggered systems which feature a low runtime overhead. We present a transformation to include event-triggered activities, represented by sporadic tasks, already into the offline scheduling process. Further, this transformation can also be applied on periodic tasks to shorten the length of schedule tables which reduces certification costs. These results can be used in our method to construct schedule tables which creates two schedule tables to fulfill the requirements of dual-criticality systems using mode changes at runtime. Finally, we present a scheduler based on the slot-shifting algorithm for mixed-criticality systems. In a first version, the method schedules dual-criticality jobs without the need for mode changes. An already certified schedule table can be used and at runtime, the scheduler reacts to the actual behavior of the jobs and thus, makes effective use of the available resources. Next, we extend this method to schedule mixed-criticality job sets with different operational modes. As a result, we can schedule jobs with varying parameters in different modes.Jens Theisdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4030Mon, 23 Mar 2015 12:38:23 +0100SAHARA - A Structured Approach for Hazard Analysis and Risk Assessments
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4027
In this thesis, an approach is presented that turns the currently unstructured process of automotive hazard analysis and risk assessments (HRA), which relies on creativity techniques, into a structured, model-based approach that makes the HRA results less dependent on experts' experience, more consistent, and gives them higher quality. The challenge can be subdivided into two steps. The first step is to improve the HRA as it is performed in current practice. The second step is to go beyond the current practice and consider not only single service failures as relevant hazards, but also multiple service failures. For the first step, the most important aspect is to formalize the operational situation of the system and to determine its likelihood. Current approaches use natural-language textual descriptions, which makes it hard to ensure consistency and increase efficiency through reuse. Furthermore, due to ambiguity in natural language, it is difficult to ensure consistent likelihood estimates for situations.
The main aspect of the second step is that considering multiple service failures as hazards implies that one needs to analyze an exponential number of hazards. Due to the fact that hazard assessments are currently done purely manually, considering multiple service failures is not possible. The only way to approach this challenge is to formalize the HRA and make extensive use of automation support.
In SAHARA we handle these challenges by first introducing a model-based representation of an HRA with GOBI. Based on this, we formalized the representation of operational situations and their likelihood assessment in OASIS and HEAT, respectively. We show that more consistent situation assessments are possible and that situations (including their likelihood) can be efficiently reused. The second aspect, coping with multiple service failures, is addressed in ARID. We show that using our tool-supported HRA approach, 100% coverage of all possible hazards (including multiple service failures) can be achieved by relying on very limited manual effort. We furthermore show that not considering multiple service failures results in insufficient safety goals.Sören Kemmanndoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4027Wed, 18 Mar 2015 11:15:06 +0100Erfolgsfaktoren für die Entwicklung ländlicher Regionen in Rheinland-Pfalz
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4025
In Rheinland-Pfalz kommt den ländlichen Regionen eine hohe Bedeutung als Lebens-, Wirtschafts-, Natur- und Erholungsraum zu. Bei ihrer Entwicklung kann festgestellt werden, dass diese Regionen sowohl Schrumpfungstendenzen wie einen Rückgang der Bevölkerungszahl, zum Teil aber auch positive Entwicklungsdynamiken wie positive bevölkerungsstrukturelle und sozio-ökonomische Entwicklungen aufweisen. In jenen Regionen die positive Entwicklungsdynamiken verzeichnen stellt sich insbesondere die Frage nach „den Erfolgsfaktoren“, die diese Entwicklung begünstigt haben.
Die Bundesraumordnung hat das Potenzial dieser Räume, einen gesamtwirtschaftlichen Wachstumsbeitrag zu liefern, erkannt. Im Jahr 2010 und 2013 hat die Ministerkonferenz für Raumordnung den Beschluss gefasst, die Leitbilder für die Raumentwicklung in Deutschland dahingehend zu konkretisieren und weiterzuentwickeln, dass die Rolle und Bedeutung ländlicher Räume als „eigenständige Wirtschafts-, Kultur- und Lebensräume, die ihre Potenziale durch die Entwicklung eigener Stärken, aber auch durch Verflechtung und Vernetzung besser zur Geltung bringen können“, noch stärker herausgearbeitet werden soll. Im aktuellen Entwurf der Leitbilder und Handlungsstrategien für die Raumentwicklung in Deutschland 2013 zeigt sich, dass im vorgesehenen Leitbild „Wettbewerbsfähigkeit stärken“ sowohl ländliche als auch verstädterte wirtschaftliche Wachstumsräume außerhalb der Metropolregionen verortet werden, die im Rahmen einer Raumentwicklungsstrategie als Wirtschafts-, Innovations- und Technologiestandorte gestärkt werden sollen.
Somit stellt sich für ländliche Regionen insbesondere die Frage, welches die maßgeblichen Faktoren sein können, um eine eigene positive Entwicklungsdynamik zu fördern. Die vorliegende Dissertation identifiziert im Bundesland Rheinland-Pfalz, für das ländliche Regionen in exemplarischer Weise von Bedeutung sind, Landkreise die positive Entwicklungsdynamiken aufzeigen und untersucht sie hinsichtlich ihrer Erfolgsfaktoren. Dabei handelt es sich um den Donnersbergkreis, den Rhein-Hunsrück-Kreis und den Landkreis Südliche Weinstraße einschließlich der Stadt Landau in der Pfalz.
Um sich der Thematik der Erfolgsfaktoren in theoretischer Weise zu nähern, werden zunächst Ansätze zur Erklärung unterschiedlicher regionaler Entwicklungsdynamiken betrachtet und Kriterien abgeleitet, die dazu dienen, bereits bestehende Ansätze, Programme und Projekte zur Förderung solcher Entwicklungen in ländlichen Regionen zu bewerten. Der Untersuchung liegen ferner empirische Erhebungen wie leitfadengestützte Gespräche mit Experten, regionalen Akteuren aus Verwaltung und Wirtschaft sowie mit regionalen und kommunalen Entscheidungsträgern und eine schriftliche Befragung der Bevölkerung in allen drei Landkreisen zugrunde, um weitere Erkenntnisse über (spezifische) Erfolgsfaktoren zu erhalten.
Es zeigt sich dabei, dass die positiven Entwicklungsdynamiken durch die unterschiedlichen Rahmenbedingungen, wie die Lage der Landkreise im Raum, verkehrsinfrastrukturelle und naturräumliche Ausstattung, historische Entwicklungspfade sowie durch bestimmte Unternehmensansiedlungen und ein strategisches Handeln regionaler und kommunaler Akteure, maßgeblich beeinflusst wird. Im Zusammenhang mit dem Thema der europäischen Metropolregionen bleibt zu sagen, dass die untersuchten Räume auch von der Nähe zu diesen Räumen profitieren. Hierbei spielen vor allem eine gut ausgebaute Verkehrsinfrastruktur, Arbeitsplätze und Hochschulen eine wichtige Rolle.
Weiterhin zeigt sich, dass sich beispielsweise eine wirtschaftsnahe Verwaltung und die Etablierung von Netzwerken zwischen Politik, Wirtschaft und Verwaltung unterstützend auswirken. Ein weiteres Hauptaugenmerk im Zusammenhang mit positiven Entwicklungsdynamiken ist auf die Existenz hochinnovativer, vielfach klein- und mittelständischer Unternehmen zu richten. Als maßgeblich für die Entwicklung eines Raumes ist aber auch das hohe Engagement einzelner Personen zu betrachten, die oftmals eine wichtige Rolle als die treibenden Kräfte bei der regionalen Entwicklung einnehmen. Darüber hinaus spielt in den untersuchten ländlichen Regionen, die stark durch den produzierenden Sektor geprägt sind, die betriebliche Aus- und Weiterbildung sowie eine frühzeitige Berufsorientierung in Schulen und die Vermittlung von Praktika eine wichtige Rolle und trägt zur Sicherung der Fachkräftebasis in den Regionen bei. Die durchgeführte Haushaltsbefragung verdeutlicht, dass die Räume eine sehr hohe Wohn- und Lebensqualität aufweisen, welche die Bevölkerung verstärkt an den Raum bindet.
Aufbauend auf den identifizierten Erfolgsfaktoren werden Handlungsansätze der Raumordnung, Landes- und Regionalplanung sowie der Regionalentwicklung und relevanter Politikfelder erarbeitet. Hierbei steht insbesondere die Frage im Vordergrund, wie vorhandene Entwicklungsdynamiken unterstützt, ausgebaut und in anderen Regionen angestoßen werden können. In Hinblick auf die Übertragbarkeit auf andere Regionen ist zu erwähnen, dass dies durchaus möglich ist, wobei die identifizierten Erfolgsfaktoren vielfach von den spezifischen Rahmenbedingungen des Raumes abhängig sind. Wesentlich ist, dass die genannten Handlungsansätze und -strategien eine Orientierung ermöglichen. Berücksichtigt werden muss beim Verfolgen der dargestellten Strategien jedoch, dass sich die Entwicklungen in den Untersuchungsräumen über einen langen Zeitraum vollzogen haben. Somit sollte auch an einer „Strategie der kleinen Schritte“ angesetzt werden.
Claudia Boltedoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4025Wed, 18 Mar 2015 11:00:32 +0100Visual Learning of Socio-Video Semantics
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4023
Today's ubiquity of visual content as driven by the availability of broadband Internet, low-priced storage, and the omnipresence of camera equipped mobile devices conveys much of our thinking and feeling as individuals and as a society. As a result the growth of video repositories is increasing at enourmous rates with content now being embedded and shared through social media. To make use of this new form of social multimedia, concept detection, the automatic mapping of semantic concepts and video content has to be extended such that concept vocabularies are synchronized with current real-world events, systems can perform scalable concept learning with thousands of concepts, and high-level information such as sentiment can be extracted from visual content. To catch up with these demands the following three contributions are made in this thesis: (i) concept detection is linked to trending topics, (ii) visual learning from web videos is presented including the proper treatment of tags as concept labels, and (iii) the extension of concept detection with adjective noun pairs for sentiment analysis is proposed.
In order for concept detection to satisfy users' current information needs, the notion of fixed concept vocabularies has to be reconsidered. This thesis presents a novel concept learning approach built upon dynamic vocabularies, which are automatically augmented with trending topics mined from social media. Once discovered, trending topics are evaluated by forecasting their future progression to predict high impact topics, which are then either mapped to an available static concept vocabulary or trained as individual concept detectors on demand. It is demonstrated in experiments on YouTube video clips that by a visual learning of trending topics, improvements of over 100% in concept detection accuracy can be achieved over static vocabularies (n=78,000).
To remove manual efforts related to training data retrieval from YouTube and noise caused by tags being coarse, subjective and context-depedent, this thesis suggests an automatic concept-to-query mapping for the retrieval of relevant training video material, and active relevance filtering to generate reliable annotations from web video tags. Here, the relevance of web tags is modeled as a latent variable, which is combined with an active learning label refinement. In experiments on YouTube, active relevance filtering is found to outperform both automatic filtering and active learning approaches, leading to a reduction of required label inspections by 75% as compared to an expert annotated training dataset (n=100,000).
Finally, it is demonstrated, that concept detection can serve as a key component to infer the sentiment reflected in visual content. To extend concept detection for sentiment analysis, adjective noun pairs (ANP) as novel entities for concept learning are proposed in this thesis. First a large-scale visual sentiment ontology consisting of 3,000 ANPs is automatically constructed by mining the web. From this ontology a mid-level representation of visual content – SentiBank – is trained to encode the visual presence of 1,200 ANPs. This novel approach of visual learning is validated in three independent experiments on sentiment prediction (n=2,000), emotion detection (n=807) and pornographic filtering (n=40,000). SentiBank is shown to outperform known low-level feature representations (sentiment prediction, pornography detection) or perform comparable to state-of-the art methods (emotion detection).
Altogether, these contributions extend state-of-the-art concept detection approaches such that concept learning can be done autonomously from web videos on a large-scale, and can cope with novel semantic structures such as trending topics or adjective noun pairs, adding a new dimension to the understanding of video content.Damian Borthdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4023Wed, 18 Mar 2015 10:50:50 +0100Statistical Language Modeling for Historical Documents using Weighted Finite-State Transducers and Long Short-Term Memory
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4022
The goal of this work is to develop statistical natural language models and processing techniques
based on Recurrent Neural Networks (RNN), especially the recently introduced Long Short-
Term Memory (LSTM). Due to their adapting and predicting abilities, these methods are more
robust, and easier to train than traditional methods, i.e., words list and rule-based models. They
improve the output of recognition systems and make them more accessible to users for browsing
and reading. These techniques are required, especially for historical books which might take
years of effort and huge costs to manually transcribe them.
The contributions of this thesis are several new methods which have high-performance computing and accuracy. First, an error model for improving recognition results is designed. As
a second contribution, a hyphenation model for difficult transcription for alignment purposes
is suggested. Third, a dehyphenation model is used to classify the hyphens in noisy transcription. The fourth contribution is using LSTM networks for normalizing historical orthography.
A size normalization alignment is implemented to equal the size of strings, before the training
phase. Using the LSTM networks as a language model to improve the recognition results is
the fifth contribution. Finally, the sixth contribution is a combination of Weighted Finite-State
Transducers (WFSTs), and LSTM applied on multiple recognition systems. These contributions
will be elaborated in more detail.
Context-dependent confusion rules is a new technique to build an error model for Optical
Character Recognition (OCR) corrections. The rules are extracted from the OCR confusions
which appear in the recognition outputs and are translated into edit operations, e.g., insertions,
deletions, and substitutions using the Levenshtein edit distance algorithm. The edit operations
are extracted in a form of rules with respect to the context of the incorrect string to build an
error model using WFSTs. The context-dependent rules assist the language model to find the
best candidate corrections. They avoid the calculations that occur in searching the language
model and they also make the language model able to correct incorrect words by using context-
dependent confusion rules. The context-dependent error model is applied on the university of
Washington (UWIII) dataset and the Nastaleeq script in Urdu dataset. It improves the OCR
results from an error rate of 1.14% to an error rate of 0.68%. It performs better than the
state-of-the-art single rule-based which returns an error rate of 1.0%.
This thesis describes a new, simple, fast, and accurate system for generating correspondences
between real scanned historical books and their transcriptions. The alignment has many challenges, first, the transcriptions might have different modifications, and layout variations than the
original book. Second, the recognition of the historical books have misrecognition, and segmentation errors, which make the alignment more difficult especially the line breaks, and pages will
not have the same correspondences. Adapted WFSTs are designed to represent the transcription. The WFSTs process Fraktur ligatures and adapt the transcription with a hyphenations
model that allows the alignment with respect to the varieties of the hyphenated words in the line
breaks of the OCR documents. In this work, several approaches are implemented to be used for
the alignment such as: text-segments, page-wise, and book-wise approaches. The approaches
are evaluated on German calligraphic (Fraktur) script historical documents dataset from “Wan-
derungen durch die Mark Brandenburg” volumes (1862-1889). The text-segmentation approach
returns an error rate of 2.33% without using a hyphenation model and an error rate of 2.0%
using a hyphenation model. Dehyphenation methods are presented to remove the hyphen from
the transcription. They provide the transcription in a readable and reflowable format to be used
for alignment purposes. We consider the task as classification problem and classify the hyphens
from the given patterns as hyphens for line breaks, combined words, or noise. The methods are
applied on clean and noisy transcription for different languages. The Decision Trees classifier
returns better performance on UWIII dataset and returns an accuracy of 98%. It returns 97%
on Fraktur script.
A new method for normalizing historical OCRed text using LSTM is implemented for different texts, ranging from Early New High German 14th - 16th centuries to modern forms in New
High German applied on the Luther bible. It performed better than the rule-based word-list
approaches. It provides a transcription for various purposes such as part-of-speech tagging and
n-grams. Also two new techniques are presented for aligning the OCR results and normalize the
size by using adding Character-Epsilons or Appending-Epsilons. They allow deletion and insertion in the appropriate position in the string. In normalizing historical wordforms to modern
wordforms, the accuracy of LSTM on seen data is around 94%, while the state-of-the-art combined rule-based method returns 93%. On unseen data, LSTM returns 88% and the combined
rule-based method returns 76%. In normalizing modern wordforms to historical wordforms, the
LSTM delivers the best performance and returns 93.4% on seen data and 89.17% on unknown
data.
In this thesis, a deep investigation has been done on constructing high-performance language
modeling for improving the recognition systems. A new method to construct a language model
using LSTM is designed to correct OCR results. The method is applied on UWIII and Urdu
script. The LSTM approach outperforms the state-of-the-art, especially for unseen tokens
during training. On the UWIII dataset, the LSTM returns reduction in OCR error rates from
1.14% to 0.48%. On the Nastaleeq script in Urdu dataset, the LSTM reduces the error rate
from 6.9% to 1.58%.
Finally, the integration of multiple recognition outputs can give higher performance than a
single recognition system. Therefore, a new method for combining the results of OCR systems is
explored using WFSTs and LSTM. It uses multiple OCR outputs and votes for the best output
to improve the OCR results. It performs better than the ISRI tool, Pairwise of Multiple Sequence and it helps to improve the OCR results. The purpose is to provide correct transcription
so that it can be used for digitizing books, linguistics purposes, N-grams, and part-of-speech
tagging. The method consists of two alignment steps. First, two recognition systems are aligned
using WFSTs. The transducers are designed to be more flexible and compatible with the different symbols in line and page breaks to avoid the segmentation and misrecognition errors.
The LSTM model then is used to vote the best candidate correction of the two systems and
improve the incorrect tokens which are produced during the first alignment. The approaches
are evaluated on OCRs output from the English UWIII and historical German Fraktur dataset
which are obtained from state-of-the-art OCR systems. The Experiments show that the error
rate of ISRI-Voting is 1.45%, the error rate of the Pairwise of Multiple Sequence is 1.32%, the
error rate of the Line-to-Page alignment is 1.26% and the error rate of the LSTM approach has
the best performance with 0.40%.
The purpose of this thesis is to contribute methods providing correct transcriptions corresponding to the original book. This is considered to be the first step towards an accurate and
more effective use of the documents in digital libraries.
Mayce Al Azawidoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4022Thu, 12 Mar 2015 14:57:16 +0100Context Awareness for Enhancing Heterogeneous Access Management and Self-Optimizing Networks
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4021
The heterogeneity of today's access possibilities to wireless networks imposes challenges for efficient mobility support and resource management across different Radio Access Technologies (RATs). The current situation is characterized by the coexistence of various wireless communication systems, such as GSM, HSPA, LTE, WiMAX, and WLAN. These RATs greatly differ with respect to coverage, spectrum, data rates, Quality of Service (QoS), and mobility support.
In real systems, mobility-related events, such as Handover (HO) procedures, directly affect resource efficiency and End-To-End (E2E) performance, in particular with respect to signaling efforts and users' QoS. In order to lay a basis for realistic multi-radio network evaluation, a novel evaluation methodology is introduced in this thesis.
A central hypothesis of this thesis is that the consideration and exploitation of additional information characterizing user, network, and environment context, is beneficial for enhancing Heterogeneous Access Management (HAM) and Self-Optimizing Networks (SONs). Further, Mobile Network Operator (MNO) revenues are maximized by tightly integrating bandwidth adaptation and admission control mechanisms as well as simultaneously accounting for user profiles and service characteristics. In addition, mobility robustness is optimized by enabling network nodes to tune HO parameters according to locally observed conditions.
For establishing all these facets of context awareness, various schemes and algorithms are developed and evaluated in this thesis. System-level simulation results demonstrate the potential of context information exploitation for enhancing resource utilization, mobility support, self-tuning network operations, and users' E2E performance.
In essence, the conducted research activities and presented results motivate and substantiate the consideration of context awareness as key enabler for cognitive and autonomous network management. Further, the performed investigations and aspects evaluated in the scope of this thesis are highly relevant for future 5G wireless systems and current discussions in the 5G infrastructure Public Private Partnership (PPP).Andreas Kleindoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4021Wed, 11 Mar 2015 09:20:39 +0100Context-Enabled Optimization of Energy-Autarkic Networks for Carrier-Grade Wireless Backhauling
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4020
This work establishes the novel category of coordinated Wireless Backhaul Networks (WBNs) for energy-autarkic point-to-point radio backhauling. The networking concept is based on three major building blocks: cost-efficient radio transceiver hardware, a self-organizing network operations framework, and power supply from renewable energy sources. The aim of this novel backhauling approach is to combine carrier-grade network performance with reduced maintenance effort as well as independent and self-sufficient power supply. In order to facilitate the success prospects of this concept, the thesis comprises the following major contributions: Formal, multi-domain system model and evaluation methodology
First, adapted from the theory of cyber-physical systems, the author devises a multi-domain evaluation methodology and a system-level simulation framework for energy-autarkic coordinated WBNs, including a novel balanced scorecard concept. Second, the thesis specifically addresses the topic of Topology Control (TC) in point-to-point radio networks and how it can be exploited for network management purposes. Given a set of network nodes equipped with multiple radio transceivers and known locations, TC continuously optimizes the setup and configuration of radio links between network nodes, thus supporting initial network deployment, network operation, as well as topology re-configuration. In particular, the author shows that TC in WBNs belongs to the class of NP-hard quadratic assignment problems and that it has significant impact in operational practice, e.g., on routing efficiency, network redundancy levels, service reliability, and energy consumption. Two novel algorithms focusing on maximizing edge connectivity of network graphs are developed.
Finally, this work carries out an analytical benchmarking and a numerical performance analysis of the introduced concepts and algorithms. The author analytically derives minimum performance levels of the the developed TC algorithms. For the analyzed scenarios of remote Alpine communities and rural Tanzania, the evaluation shows that the algorithms improve energy efficiency and more evenly balance energy consumption across backhaul nodes, thus significantly increasing the number of available backhaul nodes compared to state-of-the-art TC algorithms.Christian Mannweilerdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4020Tue, 10 Mar 2015 12:22:33 +0100Modeling and design optimization of textile-like materials via homogenization and one-dimensional models of elasticity
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4019
The work consists of two parts.
In the first part an optimization problem of structures of linear elastic material with contact modeled by Robin-type boundary conditions is considered. The structures model textile-like materials and possess certain quasiperiodicity properties. The homogenization method is used to represent the structures by homogeneous elastic bodies and is essential for formulations of the effective stress and Poisson's ratio optimization problems. At the micro-level, the classical one-dimensional Euler-Bernoulli beam model extended with jump conditions at contact interfaces is used. The stress optimization problem is of a PDE-constrained optimization type, and the adjoint approach is exploited. Several numerical results are provided.
In the second part a non-linear model for simulation of textiles is proposed. The yarns are modeled by hyperelastic law and have no bending stiffness. The friction is modeled by the Capstan equation. The model is formulated as a problem with the rate-independent dissipation, and the basic continuity and convexity properties are investigated. The part ends with numerical experiments and a comparison of the results to a real measurement.
Vladimir Shiryaevdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4019Mon, 09 Mar 2015 14:42:08 +0100An Automata-Theoretic Approach to Open Actor System Verification
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4018
Open distributed systems are a class of distributed systems where (i) only partial information about the environment, in which they are running, is present, (ii) new resources may become available at runtime, and (iii) a subsystem may become aware of other subsystems after some interaction. Modeling and implementing such systems correctly is a complex task due to the openness and the dynamicity aspects. One way to ensure that the resulting systems behave correctly is to utilize formal verification.
Formal verification requires an adequate semantic model of the implementation, a specification of the desired behavior, and a reasoning technique. The actor model is a semantic model that captures the challenging aspects of open distributed systems by utilizing actors as universal primitives to represent system entities and allowing them to create new actors and to communicate by sending directed messages as reply to received messages. To enable compositional reasoning, where the reasoning task is reduced to independent verification of the system parts, semantic entities at a higher level of abstraction than actors are needed.
This thesis proposes an automaton model and combines sound reasoning techniques to compositionally verify implementations of open actor systems. Based on I/O automata, the model allows automata to be created dynamically and captures dynamic changes in communication patterns. Each automaton represents either an actor or a group of actors. The specification of the desired behavior is given constructively as an automaton. As the basis for compositionality, we formalize a component notion based on the static structure of the implementation instead of the dynamic entities (the actors) occurring in the system execution. The reasoning proceeds in two stages. The first stage establishes the connection between the automata representing single actors and their implementation description by means of weakest liberal preconditions. The second stage employs this result as the basis for verifying whether a component specification is satisfied. The verification is done by building a simulation relation from the automaton representing the implementation to the component's automaton. Finally, we validate the compositional verification approach through a number of examples by proving correctness of their actor implementations with respect to system specifications.Ilham W. Kurniadoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4018Mon, 09 Mar 2015 10:14:58 +0100Modeling and Simulation of a Moving Rigid Body in a Rarefied Gas
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4012
We present a numerical scheme to simulate a moving rigid body with arbitrary shape suspended in a rarefied gas micro flows, in view of applications to complex computations of moving structures in micro or vacuum systems. The rarefied gas is simulated by solving the Boltzmann equation using a DSMC particle method. The motion of the rigid body is governed by the Newton-Euler equations, where the force and the torque on the rigid body is computed from the momentum transfer of the gas molecules colliding with the body. The resulting motion of the rigid body affects in turn again the gas flow in the surroundings. This means that a two-way coupling has been modeled. We validate the scheme by performing various numerical experiments in 1-, 2- and 3-dimensional computational domains. We have presented 1-dimensional actuator problem, 2-dimensional cavity driven flow problem, Brownian diffusion of a spherical particle both with translational and rotational motions, and finally thermophoresis on a spherical particles. We compare the numerical results obtained from the numerical simulations with the existing theories in each test examples. Samir Shresthadoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4012Wed, 04 Mar 2015 11:43:53 +0100Visual Processing in Reading and Dyslexia
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4007
The present research combines different paradigm in the area of visual perception of letter and words. These experiments aimed to understand the deficit underlying the problem associated with the faulty visual processing of letters and words. The present work summarizes the findings from two different types of population: (1) Dyslexics (reading-disabled children) and (2) Illiterates (adults who cannot read). In order to compare the results, comparisons were made between literate and illiterate group; dyslexics and control group (normal reading children). Differences for Even related potentials (ERP’s) between dyslexics and control children were made using mental rotation task for letters. According to the ERP’s, the effect of the mental rotation task of letter perception resulted as a delayed positive component and the component becomes less positive when the task becomes more difficult (Rotation related Negativity – RRN). The component was absent for dyslexics and present for controls. Dyslexics also showed some late effects in comparison to control children and this could be interpreted as problems at the decision stage where they are confused as to the letter is normal or mirrored. Dyslexics also have problems in responding to the letters having visual or phonological similarities (e.g. b vs d, p vs q). Visually similar letters were used to compare dyslexics and controls on a symmetry generalization task in two different contrast conditions (low and high). Dyslexics showed a similar pattern of response, and were overall slower in responding to the task compared to controls. The results were interpreted within the framework of the Functional Coordination Deficit (Lachmann, 2002). Dyslexics also showed delayed response in responding to the word recognition task during motion. Using red background decreases the Magnocellular pathway (M-pathway) activity, making more difficult to identify letters and this effect was worse for dyslexics because their M-pathway is weaker. In dyslexics, the M-pathway is worse; using a red background decreases the M activity and increases the difficulty in identifying lexical task in motion. This effect generated worse response to red compared to the green background. The reaction times with red were longer than those with green background. Further, Illiterates showed an analytic approach to responding to letters as well as on shapes. The analytic approach does not result from an individual capability to read, but is a primary base of visual organization or perception.Gunjan Kheradoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4007Tue, 03 Mar 2015 14:12:00 +0100Adaptive Real-Time Scheduling and Resource Management on Multicore Architectures
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4008
Real-time systems are systems that have to react correctly to stimuli from the environment within given timing constraints.
Today, real-time systems are employed everywhere in industry, not only in safety-critical systems but also in, e.g., communication, entertainment, and multimedia systems.
With the advent of multicore platforms, new challenges on the efficient exploitation of real-time systems have arisen:
First, there is the need for effective scheduling algorithms that feature low overheads to improve the use of the computational resources of real-time systems.
The goal of these algorithms is to ensure timely execution of tasks, i.e., to provide runtime guarantees.
Additionally, many systems require their scheduling algorithm to flexibly react to unforeseen events.
Second, the inherent parallelism of multicore systems leads to contention for shared hardware resources and complicates system analysis.
At any time, multiple applications run with varying resource requirements and compete for the scarce resources of the system.
As a result, there is a need for an adaptive resource management.
Achieving and implementing an effective and efficient resource management is a challenging task.
The main goal of resource management is to guarantee a minimum resource availability to real-time applications.
A further goal is to fulfill global optimization objectives, e.g., maximization of the global system performance, or the user perceived quality of service.
In this thesis, we derive methods based on the slot shifting algorithm.
Slot shifting provides flexible scheduling of time-constrained applications and can react to unforeseen events in time-triggered systems.
For this reason, we aim at designing slot shifting based algorithms targeted for multicore systems to tackle the aforementioned challenges.
The main contribution of this thesis is to present two global slot shifting algorithms targeted for multicore systems.
Additionally, we extend slot shifting algorithms to improve their runtime behavior, or to handle non-preemptive firm aperiodic tasks.
In a variety of experiments, the effectiveness and efficiency of the algorithms are evaluated and confirmed.
Finally, the thesis presents an implementation of a slot-shifting-based logic into a resource management framework for multicore systems.
Thus, the thesis closes the circle and successfully bridges the gap between real-time scheduling theory and real-world implementations.
We prove applicability of the slot shifting algorithm to effectively and efficiently perform adaptive resource management on multicore systems.Stefan Schorrdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4008Tue, 03 Mar 2015 11:18:21 +0100Modellgestützter Vergleich hydraulischer Konzepte zur Reduzierung des Energiebedarfs mobiler Arbeitsmaschinen unter Berücksichtigung variabler, kundenspezifischer Nutzungsprofile am Beispiel eines Baggers
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4009
Der Energiebedarf von Mobilbaggern während des Betriebs hängt neben dem kundenspezifischen Einsatz unter anderem stark vom verwendeten hydraulischen Systemkonzept ab. Durch die sukzessive Weiterentwicklung der Komponenten und hydraulischen Systeme existiert dazu mittlerweile eine Vielzahl an verschiedenen Konzepten und Teillösungen, mit denen die Energieeffizienz der Maschine gesteigert werden kann. Jedoch handelt es sich oftmals um eine komplexe Aufgabe, aus den vorhandenen Einzellösungen ein für den Kunden verbrauchsoptimales Gesamtsystemkonzept zu erstellen. Um dies zu erleichtern, ist eine Unterstützung des Konzeptauswahlprozesses mittels hydraulischer Systemsimulationen möglich, sodass der Energieverbrauch verschiedener Konzepte und Konzeptkombinationen im Gesamtsystemzusammenhang schon frühzeitig im Produktentwicklungsprozess abgeschätzt werden kann.
Um dies effizient durchzuführen, wird in dieser Arbeit ein methodischer Ansatz entwickelt, mit dem ein Vergleich verschiedener hydraulischer Konzepte modellgestützt durchgeführt werden kann. Im Fokus stehen dabei die Entwicklung eines modular aufgebauten Simulationsmodells für eine vereinfachte Implementierung von Konzepten in ein Gesamtsystemmodell sowie die Einbindung eines variablen, kundenspezifischen Nutzungsprofils in den Bewertungsprozess.
Dazu wird zunächst auf die Modellerstellung und Modularisierung eingegangen und die Validierung und Verifikation des Modells beschrieben. Im Anschluss werden exemplarische Konzepte vorgestellt, die durch eine Bewertung unter Berücksichtigung des realen Einsatzes beim Kunden hinsichtlich ihres Energieverbrauchs miteinander verglichen werden.
Christian Schollerdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4009Tue, 03 Mar 2015 11:02:11 +0100Structural Decomposition of STGs
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/3999
Specification of asynchronous circuit behaviour becomes more complex as the
complexity of today’s System-On-a-Chip (SOC) design increases. This also causes
the Signal Transition Graphs (STGs) – interpreted Petri nets for the specification
of asynchronous circuit behaviour – to become bigger and more complex, which
makes it more difficult, sometimes even impossible, to synthesize an asynchronous
circuit from an STG with a tool like petrify [CKK+96] or CASCADE [BEW00].
It has, therefore, been suggested to decompose the STG as a first step; this
leads to a modular implementation [KWVB03] [KVWB05], which can reduce syn-
thesis effort by possibly avoiding state explosion or by allowing the use of library
elements. A decomposition approach for STGs was presented in [VW02] [KKT93]
[Chu87a]. The decomposition algorithm by Vogler and Wollowski [VW02] is based
on that of Chu [Chu87a] but is much more generally applicable than the one in
[KKT93] [Chu87a], and its correctness has been proved formally in [VW02].
This dissertation begins with Petri net background described in chapter 2.
It starts with a class of Petri nets called a place/transition (P/T) nets. Then
STGs, the subclass of P/T nets, is viewed. Background in net decomposition
is presented in chapter 3. It begins with the structural decomposition of P/T
nets for analysis purposes – liveness and boundedness of the net. Then STG
decomposition for synthesis from [VW02] is described.
The decomposition method from [VW02] still could be improved to deal with
STGs from real applications and to give better decomposition results. Some
improvements for [VW02] to improve decomposition result and increase algorithm
efficiency are discussed in chapter 4. These improvement ideas are suggested in
[KVWB04] and some of them are have been proved formally in [VK04].
The decomposition method from [VW02] is based on net reduction to find
an output block component. A large amount of work has to be done to reduce
an initial specification until the final component is found. This reduction is not
always possible, which causes input initially classified as irrelevant to become
relevant input for the component. But under certain conditions (e.g. if structural
auto-conflicts turn out to be non-dynamic) some of them could be reclassified as
irrelevant. If this is not done, the specifications become unnecessarily large, which
intern leads to unnecessarily large implemented circuits. Instead of reduction, a
new approach, presented in chapter 5, decomposes the original net into structural
components first. An initial output block component is found by composing the
structural components. Then, a final output block component is obtained by net
reduction.
As we cope with the structure of a net most of the time, it would be useful
to have a structural abstraction of the net. A structural abstraction algorithm
[Kan03] is presented in chapter 6. It can improve the performance in finding an
output block component in most of the cases [War05] [Taw04]. Also, the structure
net is in most cases smaller than the net itself. This increases the efficiency of the
decomposition algorithm because it allows the transitions contained in a node of
the structure graph to be contracted at the same time if the structure graph is
used as internal representation of the net.
Chapter 7 discusses the application of STG decomposition in asynchronous
circuit design. Application to speed independent circuits is discussed first. Af-
ter that 3D circuits synthesized from extended burst mode (XBM) specifications
are discussed. An algorithm for translating STG specifications to XBM specifi-
cations was first suggested by [BEW99]. This algorithm first derives the state
machine from the STG specification, then translates the state machine to XBM
specification. An XBM specification, though it is a state machine, allows some
concurrency. These concurrencies can be translated directly, without deriving
all of the possible states. An algorithm which directly translates STG to XBM
specifications, is presented in chapter 7.3.1. Finally DESI, a tool to decompose
STGs and its decomposition results are presented.
Benedictus Benyamin Kangsahdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/3999Thu, 26 Feb 2015 08:27:56 +0100Testrig optimization by block loads: Remodelling of damage as Gaussian functions and their clustering method
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4003
In automotive testrigs we apply load time series to components such that the outcome is as close as possible to some reference data. The testing procedure should in general be less expensive and at the same time take less time for testing. In my thesis, I propose a testrig damage optimization problem (WSDP). This approach improves upon the testrig stress optimization problem (TSOP) used as a state of the art by industry experts.
In both (TSOP) and (WSDP), we optimize the load time series for a given testrig configuration. As the name suggests, in (TSOP) the reference data is the stress time series. The detailed behaviour of the stresses as functions of time are sometimes not the most important topic. Instead the damage potential of the stress signals are considered. Since damage is not part of the objectives in the (TSOP) the total damage computed from the optimized load time series is not optimal with respect to the reference damage. Additionally, the load time series obtained is as long as the reference stress time series and the total damage computation needs cycle counting algorithms and Goodmann corrections. The use of cycle counting algorithms makes the computation of damage from load time series non-differentiable.
To overcome the issues discussed in the previous paragraph this thesis uses block loads for the load time series. Using of block loads makes the damage differentiable with respect to the load time series. Additionally, in some special cases it is shown that damage is convex when block loads are used and no cycle counting algorithms are required. Using load time series with block loads enables us to use damage in the objective function of the (WSDP).
During every iteration of the (WSDP), we have to find the maximum total damage over all plane angles. The first attempt at solving the (WSDP) uses discretization of the interval for plane angle to find the maximum total damage at each iteration. This is shown to give unreliable results and makes maximum total damage function non-differentiable with respect to the plane angle. To overcome this, damage function for a given surface stress tensor due to a block load is remodelled by Gaussian functions. The parameters for the new model are derived.
When we model the damage by Gaussian function, the total damage is computed as a sum of Gaussian functions. The plane with the maximum damage is similar to the modes of the Gaussian Mixture Models (GMM), the difference being that the Gaussian functions used in GMM are probability density functions which is not the case in the damage approximation presented in this work. We derive conditions for a single maximum for Gaussian functions, similar to the ones given for the unimodality of GMM by Aprausheva et al. in [1].
By using the conditions for a single maximum we give a clustering algorithm that merges the Gaussian functions in the sum as clusters. Each cluster obtained through clustering is such that it has a single maximum in the absence of other Gaussian functions of the sum. The approximate point of the maximum of each cluster is used as the starting point for a fixed point equation on the original damage function to get the actual maximum total damage at each iteration.
We implement the method for the (TSOP) and the two methods (with discretization and with clustering) for (WSDP) on two example problems. The results obtained from the (WSDP) using discretization is shown to be better than the results obtained from the (TSOP). Furthermore we show that, (WSDP) using clustering approach to finding the maximum total damage, takes less number of iterations and is more reliable than using discretization.Chhitiz Buchasiadoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4003Tue, 24 Feb 2015 11:08:29 +0100