Studium des resonanz falles bei systemen linearer gewöhnlicher differentialgleichungen

Ohne Zusammenfassung     

Über den Resonanzbegriff bei systemen von n linearen gewöhnlichen Differentialgleichungen erster ordnung

Ohne ZusammenfassungTeil einer bei der Naturwissenschaft-Philosophischen Fakultät der Technischen Hochschule Braunschweig eingereichten Dissertation. Referenten: Professor Dr. R. Iglisch und Prof. Dr. H-J. Kanold. Auch Herrn Dr. H. Eltermann bin ich für wertvolle Ratschläge zu Dank verpflichtet.     

Mechanical and lattice dynamical properties of the Re2C compound

In this work, density functional theory calculations on the structural, mechanical, and lattice dynamical properties of Re₂C within ReB₂‐type structure are reported. The generalized gradient approximation has been used for modeling exchange–correlation effects. We have predicted the lattice constants, bulk modulus, bond distances, elastic constants, shear modulus, Young's modulus, Poisson's ratio, hardness, Debye temperature, and sound velocities of this compound. Furthermore, the band structure, phonon dispersion curves and corresponding density of states are computed. The obtained results are in good agreement with the available experimental and other theoretical data. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical investigations on vibrational properties and thermal conductivities of ternary antimonides TiXSb,ZrXSb and HfXSb (X = Si,Ge)

We have performed density functional calculations of the vibrational and thermodynamic properties of the ternary antimonides TiXSb, ZrXSb and HfXSb (X = Si, Ge). The direct method is used to calculate the phonon dispersion relation and phonon density of states for these compounds as well as their infrared and Raman active mode frequencies for the first time. Their dynamical stability is confirmed by phonon spectra. The lattice thermal conductivities of these compounds have been calculated from third-order force constants and plotted as a function of temperature. We have also evaluated the high temperature thermal conductivity by means of the Clarke’s model and Cahill’s model. Some selected thermodynamical properties, e.g. Gibbs free energy, entropy and heat capacity at constant volume are predicted theoretically and discussed. We have showed the relationships between thermodynamical properties and temperature.     

Monte Carlo simulation of the structure of mono- and bidisperse polyethylene nanocomposites

The structure of bidisperse polyethylene(PE) nanocomposite mixtures of 50:50(by mole) of long and short chains of C160H322/C80H162 and C160H322/C40H82 filled with spherical nanoparticles were investigated by a coarse-grained, on lattice Monte Carlo method using rotational isomeric state theory for short-range and Lennard-Jones for long-range energetic interactions. Simulations were performed to evaluate the effect of wall-to-wall distance between fillers(D), polymer-filler interaction(w) and polydispersity(number of short chains in the mixture) on the behavior of the long PE chains. The results indicate that long chain conformation statistics remain Gaussian regardless of the effects of confinement, interaction strength and polydispersity. The various long PE subchain structures(bridges, dangling ends, trains, and loops) are influenced strongly by confinement whereas monomer-filler interaction and polydispersity did not have any impact. In addition, the average number of subchain segments per filler in bidisperse PE nanocomposites decreased by about 50% compared to the nanocomposite system with monodisperse PE chains. The presence of short PE chains in the polymer matrix leads to a reduction of the repeat unit density of long PE chains at the interface suggesting that the interface is preferentially populated by short chains.     

Self-tuning fuzzy logic control of crane structures against earthquake induced vibration

Self-tuning fuzzy logic controllers (STFLC) for the active control of Marmara Kocaeli Earthquake excited crane structures are studied in this paper. Vibration control using intelligent controllers, such as fuzzy logic has attracted the attention of structural control engineers during the last few years, because fuzzy logic can handle, uncertainties and heuristic knowledge and even non-linearities effectively and easily. The improved seismic control performance can be achieved by converting a simply designed static gain into a real time variable dynamic gain through a self-tuning mechanism. A self-tuning fuzzy logic controller is designed to reduce the vibrations of the crane structure. The simulated system has a five degrees-of-freedom and modeled system was simulated against the ground motion of the Marmara Kocaeli Earthquake (M _w =7.4) in Turkey on August 17, 1999. At the end of the study, the time history of the crane bridge and portal legs displacements, accelerations, and frequency responses of the both uncontrolled and controlled cases are presented. Additionally, the performance of the designed STFLC is also compared with a PD controller. Simulations of an earthquake excited bridge and portal legs are performed to prove the validity of proposed control strategy.     

Rayleigh-Wave Propagation in a Half-Plane Covered with a Prestressed Layer under Complete and Incomplete Interfacial Contact

Under a plane-strain state in a half-plane covered with a homogeneous prestressed layer, the Rayleigh-wave propagation along the layer is investigated. The investigations are carried out within the framework of a piecewise homogeneous body model with the use of the three-dimensional linearized theory of elasticity. Complete and incomplete contact conditions between the layer and half-plane are considered. Numerical results relating to the dispersion of the waves are obtained for the case where the layer and half-plane are isotropic and homogeneous.     

A study on chemical behaviors of some 4‐pyrones synthesized by one‐step reactions towards various amines

Cycloaddition of acetylbenzoyl ketene generated in situ as an intermediate during one‐step reaction between excess benzoylacetone and oxalylchloride to C=C double bond of cyclic enol form of benzoylacetone gave 3‐acetyl‐5‐benzoyl‐6‐methyl‐2‐phenyl‐4(4H)‐pyrone 1a . Condensation reactions of 1a together with 3,5‐dibenzoyl‐2,6‐diphenyl‐4(4H)‐pyrone 1b and 3‐benzoyl‐5‐ethoxycarbonyl‐2,6‐diphenyl‐4(4H)‐pyrone 1c with two‐fold excess primary amines provided a series of 3‐benzoyl‐1‐alkyl‐5‐(1‐alkylimino‐ethyl)‐6‐phenyl‐2‐methyl‐4(1H)‐pyridinone 2 , 3,5‐dibenzoyl‐1‐alkyl‐2,6‐diphenyl‐4(1H)‐pyridinone 3a‐c and 3‐benzoyl‐1‐alkyl‐5‐ethoxycarbonyl‐2,6‐diphenyl‐4(1H)‐pyridinone 3d,e derivatives, respectively. In addition, while prolonged reaction of n‐pentylamine with unsymmetrical pyrone derivative 1a gives a symmetrical pyridinone derivative namely 3,5‐dibenzoyl‐2,6‐dimethyl‐1‐pentyl‐4(1H)‐pyridinone 5 , much prolonged action n‐pentylamine and then aqueous n‐pentylamine on 1b resulted in degradation of the 4‐pyrone ring to give dibenzoylmethane.     

Flow and structure development behavior of bar soaps containing synthetic detergent

Many bar soaps are processed using continuous processing technologies, including single and twin screw extrusion. However, in spite of the industrial importance of the extrusion-based processing of bar soaps the rheological behavior of bar soaps is poorly understood. Here, the shear viscosity and the formation of gross surface irregularities upon extrusion of the bar soap were investigated using steady torsional, rectangular slit, and capillary flows. Furthermore, the structure development aspects were investigated using wide-angle X-ray diffraction and scanning electron microscopy. It is revealed that the flow and deformation behavior of bar soaps is complicated by the ubiquitous presence of wall slip, viscoplasticity, gross surface irregularities, and various structuring aspects. The orientation of crystallites and the shear stress dependent fracture of a crystalline component of the formulation at the wall during flow were identified as some of the contributing effects to the development of the structure of the bar soap during flow and deformation.