Publication Server of Constructor University Library
Not a member yet
858 research outputs found
Sort by
Multiscale and geometric methods for linear elliptic and parabolic partial differential equations
No full textIn this thesis a variety of linear elliptic and parabolic boundary value probelms with general geometries are investigated. In chapter 3 and chapter 4, we derive a fictitious domain/penalty method for parabolic PDE with Dirichlet and Neumann conditions, got some convergence results and error estimates. In chapter 5, we construct a fictitious domain/successive approximation approach to a variety of BVP and present multigrid algorithms. In chapter 6, a modified wavelet sampling formulae is established and used for a class of anisotropic problems to get a robust fast solver
Molecular dynamics simulation of water near structured hydrophobic surfaces
No full textThe main focus of the thesis is to study the enhancement in the hydrophobicity of an already hydrophobic surface by creating surface structuring on the surface of the crystal. The local structuring and the free energy of interfacial water at the crystal/water interface is analysed by molecular dynamics simulation. An alkane crystal has been taken as the parent model for a hydrophobic surface. Surface structuring were created by either indenting pits on the surface of the crystal or by raising a protrusion on the surface of the crystal. Around all structures the water density was lower and the number of contacts between water and the surface of the crystal decreased due to surface structuring. The difference in the free energy of hydration between planar surface and the structured surface also revealed the increase in the hydrophobicity of the already hydrophobic crystal. Finally a study on the hydrophobicity of a perfluoro-n-alkane crystal is discussed in the final chapter. A qualitative comparison of the water structuring near an alkane and a perfluoro-n-alkane crystal show a higher htdrophobicity in case of a perfluoro-n-alkane crystal than an alkane crystal
On the dynamical fine structure of entire transcendental functions
No full textIn this thesis we give several answers to questions of Fatou and Eremenko. For a large class of transcendental entire functions we show that all components of the set of escaping points are path connected. In particular we show that for all bounded type functions of finite order and their finite compositions, the set of escaping points is organized in terms of dynamic rays. Ruthermore we show that, in logarithmic coordinates, the strong version of Eremenko's conjecture is false. That is, there exists a function F such that the according set of escaping points contains a point which can not be connected to infinity by a curve contained in the escaping set. For the example of the family of cosine functions a exp(z)+b exp(-z) we give an explicit parameterization of the dynamic rays. We also describe the dimension paradox: the set of escaping points on rays has Hausdorff dimension 1, while the set of escaping landing points has Hausdorff dimension 2 and even positive planar Lebesgue measure
Selbstbezogene Weisheit : ein Instrument zur Messung von Persönlichkeitsreife : Entwicklung, Validierung und Alterseffekte
No full textThe goals of this study were to develop a conception of self-related wisdom as one form of maturity, to develop and validate an instrument for measuring it and to examine age effects in self-related wisdom. Existing conceptions of personal maturity were examined for overlapping aspects and the extracted characteristics were integrated with the Berlin Wisdom Paradigm. The resulting concept of self-related wisdom is defined by 5 criteria, 2 basic-criteria: self-knowledge and growth- and self-regulation; and 3 meta-criteria: interrelating the self, self-relativism and tolerance of ambiguity. In a structured interview 161 adults, 83 between 20-40, 78 between 60-80, were asked to think aloud about the question "how are you as a friend?".10 raters (2 per criterion) rated the protocols according to the criteria of self-related wisdom on a Likert-scale. The results showed satisfactory interraterreliability. Indicators of maturity predicted self-related wisdom significantly better than indicators of adaptivity. Life events and fluid intelligence showed an inverted u-shaped relationship with self-related wisdom, crystalline intelligence was linearly positively related to it. Self-transcendent values were positively associated with self-related wisdom, whereas self-centered values were not. Concerning mean-level differences older adults performed lower in the metacriteria, which was partly due to their lower fluid intelligence and openness for experience. In the basic criteria older adults showed a tendency to perform better than younger adults. The correlational patterns confirmed the hypotheses and the construct validity of the new measure. The age differences are interpreted as resulting from a complex interplay of developmental tasks, age-related deficits causing a change of goals, and cohort effects like different upbringing and societal developments. It is discussed whether older adults tend to be experts in leading an adaptive life, rather than in self-related wisdom
Neural and biochemical networks : organization, development, and robustnes
No full textIn this work, I studied the organization, development and robustness of cortical, as well as other biological networks, using methods of network analysis. First, I examined the organization of neural systems and important constraints for shaping them. Area positions in the macaque cortical as well as the C. elegans neural networks could be rearranged so that total wiring length can be reduced by up to 64% of the original value. Although causing such non-optimal wiring, long-distance connections help to minimize the number of intermediate nodes, which leads to lower time delay, less interference, and higher synchrony in the network. Second, I observed growth of networks in space. I designed a developmental algorithm that takes into account distance between nodes and which yields networks that are alike various spatial networks from metabolic networks to the German highway system. Such spatial growth can generate networks that are comparable to cat and macaque cortical networks. In addition, the inclusion of time windows for development can lead to a defined cluster architecture. Finally, I analyzed the measurement of robustness in biological networks as well as possible underlying causes for high robustness towards unspecific removal of edges or nodes. The existence of clusters and of highly-connected nodes results in enhanced average-case robustness after removal of edges or nodes. Using multiple lesions, I found that in some cases the effect differed from the effect that was predicted from single lesions. Therefore, multiple lesion analysis could become a framework to predict or explain 'unexpected' effects of experimental lesions (or multiple gene knock-outs in metabolic systems)
Development of potential scaling methods to improve prediction of loops and binding interfaces at homology modelling and docking
No full textIn comparative modelling a protein structure can be predicted based on the structure of another protein if both proteins share sufficient sequence similarity. In the present work two potential scaling methods based on molecular dynamics (MD) simulations have been developed in order to improve structure prediction at comparative modelling of proteins and docking between proteins and small peptide ligands. The first method, presented in chapter Project 1, refers to prediction of conformation of protein loops and cyclic peptides. To accelerate the conformational sampling the rotational energy barriers of the dihedral main-chain angles and the 1-4 van der Waals and electrostatic interactions were lowered at the beginning and smoothly rescaled during the following MD simulation until the standard potential was reached. The second method, presented in chapter Project 2, was developed for modelling of side-chain conformations within protein cores and within protein-peptide interfaces. The present method uses a consecutive set of potential scaling MD simulations where the buried residues are free and the remaining protein regions are highly flexible but preserved within their overall conformation using weak positional restraints. At the beginning the non-bonded van der Waals and electrostatic interactions of selected buried side-chains were strongly alleviated and smoothly rescaled during the following steps until the total force field applied in standard MD simulations was used. In chapter Project 3 a structural model of the extracellular part of protein human Toll-like receptor 5 (TLR5) is presented, which was generated by applying comparative modelling. An X-ray structure of flagellin, the bacterial binding partner of TLR5, served subsequently for a docking approach of both components using the program ATTRACT. The docking procedure was supported by literature-based knowledge of residues located at the binding sites of both proteins
Communicative exploration : a multi-robot exploration approach
No full textExploration is one of the main research topics in the field of mobile robotics. Multiple robots have been applied for different exploration algorithms In most of the these algorithms the robots exchange data via wireless communication assuming perfect data transmission in the whole environment. Unfortunately, this assumption does not always hold, as e.g. the range of wireless communication is limited. In this thesis Communicative Exploration is presented, which is based on Frontier-Based Exploration. For communicative exploration a group of robots is exploring unknown environments and maintain communication throughout the whole exploration process. The robots form a mobile ad-hoc network that is fully connected for the entire exploration. The motion of the robots is controlled via a heuristic utility function which assigns values to a population of configurations. The configuration with the highest utility value defines the motions of the robots. Different versions of communicative exploration are presented. In the first version a basestation is located outside the environment, from where a human operator can control or supervise the group of robots. During exploration the robots also maintain communication with the basestation. An extension to this version is presented where an improved motion control algorithm is implemented. By calculating a distance transform over the environment the robots are guided better towards the unknown areas of the environment. In a different version the basestation is omitted from the setup to enlarge the reachability of the robots. The group of robots explores the environment acting as a robot pack. Surprisingly, this version introduce situations where the robots get stuck in the environment in deadlock situations. Strategies are introduced that try to avoid or recover from these deadlocks
Cucurbiturils as Molecular Containers The Mechanism of Complexation of Small guests, the Effects of the Inclusion on their Photophysical Properties, and Potential Applications
No full textIn this thesis the mechanism of complexation of small guest by the cavity of cucurbiturils has been investigated, as well as the effect provoked by the inclusion on their photophysical properties. Special attention has been paid to potential applications of these host-guest systems. Detailed mechanistic studies on the host-guest complexation of organic cations inside the core of cucurbit[6]uril (CB6) based on kinetic and thermodynamic considerations have been accomplished. The binding constants and complexation rate constants for organic amine and ammonium compounds were found to vary in a contrasting manner with pH, due to a different complexation mechanism and stability of the host-guest system. The studies as a function of guest size indicated that the effective container volume of the CB6 cavity is approximately 100 Å3. It is suggested that larger guests are excluded for two reasons: a high activation barrier for ingression imposed by the tight CB6 portals and a destabilization of the complex due to steric repulsion inside. The association of metal cations at the portals and the CB6 molecular recognition capacity has been explored. When the concentration of the inorganic salt present (necessary to dissolve CB6) was increased, the binding constant of the guest decreased due to a competitive binding of the metal ion and the ammonium site of the guest with the ureido carbonyl portals of CB6. Other factors such as the 10 size of the cation have been studied, and indicate that the guest binding constants decrease with an increase in cation binding constant. The "inner phase" of cucurbiturils - in particular the larger cucurbit[7]uril (CB7) - and Crams hemicarcerands have been investigated by studying the polarizability inside them. For this purpose, the azoalkane 2,3 - diazabicyclo[2.2.2]oct-2-ene (DBO) and biacetyl were included as guest molecules, and bulk polarizability-dependent solvatochromic shifts were measured in comparison with different solvents. The extreme ,olarizability obtained for CB7 (0.12) and hemicarcerands (0.45) reinforce the hypothesis that these cavities may behave like a new phase of matter. The possibilities of CBn have been expanded by using CB7 as a chemical tool to discriminate between different fluorescence quenching mechanisms in the interaction between DBO and nucleotides, establishing exciplex formation and hydrogen abstraction as the main mechanisms depending on the base. "Throughdistance" quenching mechanisms common for most of the cases described in the literature could therefore be disregarded. Finally, potential applications of the CB7 DBO host-guest system have been considered based on its extremely long fluorescence lifetime in solution - more than 1 μs in aerated water. Its use as a sensor in applications based on long-lived fluorescence in screening assays, e.g., for metal ions, has been evaluated