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Item Open Access Investigating superconductivity by tunneling spectroscopy using oxide heterostructures(2017) Fillis-Tsirakis, Evangelos; Mannhart, Jochen (Prof. Dr.)Item Open Access Nonlinear optical microspectroscopy with few-cycle laser pulses(2017) Wan, Hui; Wrachtrup, Jörg (Prof. Dr.)Nonlinear optical (NLO) microscopy is a powerful tool in physics, chemistry, and material science it probes intrinsic optical properties of the sample without the need of labeling. In order to investigate the ultrafast processes in nonlinear materials with high spatial resolution, we need to combine both ultrashort pulses and techniques focusing them to the diffraction limit. Previously, few-cycle laser pulses have often been tightly focused using conventional microscope objectives. However, the propagation of an ultrashort pulse in optical materials, particularly in the glass of a high numerical aperture (N.A.) microscope objective, results in spatial and temporal distortions of the pulse electric field, which can severely affect its quality in the focus. By purely passive group delay dispersion (GDD) and third-order dispersion (TOD) management, in this thesis, we experimentally demonstrate in-focus diffraction-limited and bandwidth-limited few-cycle pulses by using high N.A. objectives. Based on these achievements, the performance of a novel few-cycle NLO microscope for both second-harmonic generation (SHG) imaging and microspectroscopy in the frequency- and time-domains was characterized. The inverse linear dependence of SHG intensity on the in-focus pulse duration was demonstrated down to 7.1 fs for the first time. The application of shorter in-focus pulses for the enhancement of SHG image contrast was successfully demonstrated on a single collagen (type-I) fibril as a biological model system for studying protein assemblies under physiological conditions. Beyond imaging, a collagen fibril has been found to act as a purely non-resonant χ(2) soft matter under the present excitation conditions, and its ratio of forward- to epi-detected SHG intensities allowed for the estimation of the fibril thickness, which corresponds well with atomic force microscopy (AFM) measurements. The ultrafast dephasing of the localized surface plasmon resonance (LSPR) in the metallic nanoparticles, that only occurs on a time scale of a few femtoseconds, has gained a lot of attraction in the field of nanoplasmonics. This thesis is the first systematic experimental demonstration of time-resolving ultrashort plasmon dephasing in single gold nanoparticles by using interferometric SHG spectroscopy with in-focus 7.3 fs excitation pulses in combination with linear scattering spectroscopy performed on the same nanoparticle. For nanorods, nanodisks, and nanorectangles, strong plasmon resonance enhanced SHG is observed, where the SHG intensity strongly depends on the spectral overlap between the LSPR band and the excitation laser spectrum. For single nanorods and nanorectangles, the polarization dependence of the SHG intensity was found to follow second-order dipole scattering, and the effect of size and shape on the LSPR properties was directly observed in the time-domain. Good agreement between experimental and simulated values of dephasing times and resonance wavelengths is obtained, which confirms that a common driven damped harmonic oscillator model for the LSPR in the nanoparticle can qualitatively explain both the linear scattering spectra in the frequency-domain and the SHG response in the time-domain. Resonance bands in linear transmission and scattering spectra have also been observed for nanoholes with sizes smaller than the wavelength of the incident light in a metal film, which are assigned to LSPR modes of the electric field distribution around the nanohole with qualitatively similar resonance properties as a nanoparticle. The polarization-resolved nonlinear optical properties of the single nanoholes with different shapes and symmetries were also reported. The objective of this thesis has been systematic SHG studies of the size effect in the LSPR of single nanoholes in metal films and of their ultrafast dephasing dynamics. Although, enhancement of both the forward- and epi-detected SHG emissions from single rectangular nanoholes are observed,however,no ultrafast dephasing dynamics of LSPRs in rectangular nanoholes could be time-resolved with our in-focus 7.3 fs excitation laser pulses, which indicates that contributions from LSPR enhanced SHG to the detected SHG signal are negligible. More work needs to be done in order to overcome the current experimental limitations. However, in this thesis, the polarization dependence of the forward- and epi-detected SHG intensity from the single rectangular nanohole was found to follow that of a second-order dipole pattern. While the SHG dipole pattern observed for rectangular nanoparticles is oriented parallel to its long-axis, the SHG dipole pattern of its complementary rectangular nanohole is oriented perpendicular to its long-axis. This observation represents the first experimental demonstration of Babinet’s principle in second-order nonlinear scattering of a single rectangular nanohole in a gold film.Item Open Access Simultaneous optimization of office building facades in terms of both energy consumption and transparency in hot arid climates, analysed on the example of Cairo(2017) Mohamed, Tamer Awny Abd Elkader; Moro, José Luis (Prof. Dipl.-Ing.)Since the early days, buildings forms, types of construction, and development were closely responding to the local climatic conditions. However, the technical innovations during the last 150 years and the calls of modern architecture to transparency drove the building sector towards the extensive usage of glazed facades in commercial buildings and to the adoption of the international style buildings. Those building models can only function through the extensive intervention of technical equipment to guarantee the desired internal comfort conditions at any place of the world with the corresponding massive energy input, owing to the poor thermal performance of glazing and its selective property with respect to radiation permeability (greenhouse effect). Unfortunately, this situation is very apparent in Cairo. Contemporary commercial buildings are being increasingly designed and constructed based upon highly glazed building models originally conceived in, and for, countries with moderate climates. Such architecture is totally maladapted to the hot-arid climate, especially with the extensive solar radiation and the relatively high summer temperatures. However, on the other hand, transparency provides crucial psychological values and benefits to the occupants. It affects their comfort, sense of well-being, and affords them view and natural light. View provides the occupants with visual amenity, access to environmental information, relief from claustrophobia and monotony, and recovery from daily stress. While natural lighting has a direct influence on mood and cognition, and influences the production of hormones, it also regulates motivation, and improves productivity in the workplace. In addition, the proper use of natural day-light decreases the energy used for lighting and improves the environmental quality indoors. The research work aims to elaborate a scientific methodology in order to optimize the office facades configurations in hot-arid climates, analyzed on the example of Cairo. The research methodology is based on investigating the adequate balance between two critical, and at the same time conflicting requirements or tasks, which are: First: To provide the required level of transparency that provides the occupants with their psychological sense of satisfaction and general well-being. Second: To reduce the total energy consumption of the building through an energy-efficient concept based on a proposed solar protection strategy. Through a series of parametric analysis processes of the energetic performance of the selected solar protection variants (represented by their total annual energy consumption per square meter) with their corresponding visual quality (represented by their view index measures), the research provides an optimized definition for the configuration of office facades. The optimized façade designs achieved the required balancing ratio that gives the occupants psychological satisfaction and general well-being. The research proposes an Energy-Transparency Balancing Factor (ETBF) in order to compare and differentiate between the findings of these optimized configurations.Item Open Access Transformation von B. subtilis 168 : Optimierung und Regulation des Transkriptionsfaktors ComK(2017) Franzen, Regine; Mattes, Ralf (Prof. Dr. rer. nat.)Item Open Access Modeling and analysis of almost unidirectional flows in porous media(2017) Armiti, Alaa; Rohde, Christian (Prof. Dr.)Item Open Access Shape derivatives and shock capturing for the Navier-Stokes equations in discontinuous Galerkin methods(2017) Sonntag, Matthias; Munz, Claus-Dieter (Prof. Dr.)This work addresses two different topics, the shape derivatives for the compressible Navier-Stokes equations on the one hand and, on the other hand, the treatment of shocks or other flow discontinuities in Discontinuous Galerkin methods. There is a strong demand for very efficient methods for shape optimization in the aerospace industry, for example drag reduction or lift maximization of an aircraft. The use of gradient based optimization schemes requires derivatives of the cost function with respect to the shape of an object. With the shape derivatives presented in this work, these derivatives can be calculated independent of the parametrization of the object's shape, and, since the derivation takes place in the continuous space, they can be applied to almost any discretization. Nevertheless, one has to take the numerical scheme, which is later applied, into account. For methods based on the variational formulation a difference in the shape derivative, compared to the pointwise approach, arises, which cannot be neglected. Hence, one objective of this work is to derive the shape derivatives of the drag- and lift-coefficient for the Navier-Stokes equations in variational formulation and compare it with the pointwise approach both analytically and numerically. A discrepancy has to be expected, especially for flow phenomena with high gradients or discontinuities which do not fulfill the strong form of the governing equations. These flow phenomena require a special treatment in numerical methods of high order. In the second part of this work, a shock capturing for the Discontinuous Galerkin method is developed which prevents the oscillations originating from the approximation of discontinuities with high order polynomials. Therefore a hybrid approach is presented, where the original DG scheme is coupled with a second order Finite Volume method. In all elements containing shocks or discontinuities the operator of the DG method is replaced by the Finite Volume scheme. This scheme is, due to the use of slope limiters, well known for its strengths in handling shocks. However, in regions where the flow is smooth the Finite Volume method requires a finer resolution for the same accuracy than the Discontinuous Galerkin scheme. Using the same mesh for the FV method as for the DG scheme would lead to a big reduction in resolution. Hence, to compensate this loss the original elements of the mesh are divided into logical sub-cells. By associating exactly one Finite Volume sub-cell to each degree of freedom of a DG element, the same data structures can be used. This enables an efficient implementation of the outlined shock capturing designated for high performance computations. Therefore, not only the basic properties of this hybrid DG/FV sub-cell approach are investigated with several examples, but also studies regarding the parallel efficiency are performed.Item Open Access Die Bedeutung der Kontrolle über mikroskopische Freiheitsgrade für die Effizienz optimierter Maschinen(2017) Bauer, Michael; Seifert, Udo (Prof. Dr.)Item Open Access Bose-Einstein condensates with balanced gain and loss beyond mean-field theory(2017) Dast, Dennis; Wunner, Günter (Prof. Dr.)Most of the work done in the field of Bose-Einstein condensates with balanced gain and loss has been performed in the mean-field approximation using the non-Hermitian PT-symmetric Gross-Pitaevskii equation. However, the exchange of particles with the environment plays a crucial role in such systems which in general leads to deviations from the mean-field behavior. Thus, it is not clear whether a mean-field approach is appropriate. It is the purpose of this work to formulate and study a many-particle description of a Bose-Einstein condensate with balanced gain and loss. This is achieved by using a quantum master equation describing a double well where the incoupling of particles in one well and the outcoupling from the other are implemented with Lindblad superoperators. The in- and outcoupling rates are adjusted in an appropriate manner such that balanced gain and loss is achieved. It is shown that the mean-field limit of this master equation yields a PT-symmetric Gross-Pitaevskii equation. Furthermore the master equation supports the characteristic dynamical properties of PT-symmetric systems. There are, however, fundamental differences compared with the mean-field description revealing a new generic feature of PT-symmetric Bose-Einstein condensates. It is shown that the purity of the condensate periodically drops to small values but then is nearly completely restored, when the particles oscillate in the double well. Since in the mean-field limit a completely pure condensate is assumed, this effect cannot be covered by the Gross-Pitaevskii equation. These purity oscillations have a direct impact on the average contrast in interference experiments. In particular it is found that the extrema of the purity can be precisely measured since the average contrast at these points is not reduced by an imbalance of the particle distribution. To gain a detailed understanding of the purity oscillations, analytic solutions for the dynamics in the non-interacting limit are presented and the Bogoliubov backreaction method is used to discuss the influence of the on-site interaction. A central result is that the strength of the purity revivals does neither depend on the amount of particles in the system nor the interaction strength, but is almost exclusively determined by the strength of the in- and outcoupling processes. However, the strong revivals are shifted towards longer times for larger particle numbers. Without interaction this would make the purity oscillations unobservable for a realistic particle number, but by adjusting the interaction strength the strong revivals again occur earlier.Item Open Access An approach for automated detection and classification of pavement cracks(2017) Al-Mistarehi, Bara'; Schwieger, Volker (Prof. Dr.-Ing. habil.)Item Open Access Eignung von metallorganischen Gerüstverbindungen als stationäre Phase in der Hochleistungsflüssigchromatographie (HPLC)(2017) Lieder, Christian; Klemm, Elias (Prof. Dr.-Ing.)Anwendung von metallorganischen Gerüstverbindungen als stationäre Phase in der HPLC, Vergleich mit klassischen Silika-Materialien. Synthese der metallorganischen Gerüstverbindungen, Modifizierung. Befüllung chromatographischer Säulen und Gegenüberstellung der Füllmethoden. Methodenentwicklung, Einflüsse auf chromatographische Ergebnisse. Chirale Erkennung, Untersuchung der Wechselwirkungen. Theoretisch chemische Berechnungen der Wechselwirkungen.