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Item Open Access Hybrid plasmonic devices for sensing and thermal imaging(2015) Tittl, Andreas; Giessen, Harald (Prof. Dr.)Plasmonics is an emerging field in nanooptics, which focuses on the optical properties of resonant subwavelength metal nanoparticles. Historically, such geometries commonly employed noble metal nanoparticles to achieve a variety of effects ranging from nanofocusing of light to negative refraction. Building on these concepts, this thesis investigates hybrid nanoplasmonic devices, which combine passive noble metal nanostructures with chemically reactive or actively tunable materials to obtain novel functionalities. Utilizing various complex plasmonic geometries, this work pursues two complementary threads of research, covering the technological scale from fundamental science to device applications. On the one hand, it utilizes chemically synthesized hybrid plasmonic "smart dust" nanoprobes to detect progressively lower reagent concentrations. Starting from silica shell-isolated gold nanoparticles, which are used to map the catalytic reactions in adjacent extended palladium thin films, DNA-assembled bimetallic plasmonic nanosensors are investigated to resolve changes in sub-5nm Pd nanocrystals on the single antenna level, pushing the lower limit of chemical detection volume. On the other hand, it studies plasmonic perfect absorber structures, optical elements designed to absorb all radiation of a certain wavelength, which have shown promise for a variety of technological applications. Here, the focus is on both developing a theoretical model for the optical behavior of plasmonic perfect absorber structures, especially at large incident angles, as well as on the experimental realization of efficient gas sensors and active mid-infrared imaging devices.Item Open Access Aluminum-induced crystallization of semiconductor thin films(2015) Qu, Fei; Schmitz, Guido (Prof. Dr.)Thin film materials of the semiconductors, such as silicon (Si), germanium (Ge) or their alloys, are turning into the most promising functional materials in the energy technology. However, the morphologies of these semiconductor thin films must be varied to be suitable for the different applications, e.g. a large-grained layer as the seed layer of thin film solar cells, a porous structure for anode materials of high energy rechargeable lithium (Li) ion batteries. Due to the collective interdiffusion process during the aluminum (Al)-induced crystallization, in this thesis, the suitable morphologies are achieved for the corresponding applications under the different fabrication conditions. A large-grained Si layer can be formed by the crystallization of Si in a porous Al layer, which is obtained by applying a bias voltage. Since the Al grain boundaries are contaminated by e.g. oxygen (O), the diffusion of Si in the Al grain boundaries is retarded. It can lead to a reduction of the nucleation density of Si. At a certain high temperature, a collective diffusion process of Si in Al is activated. Consequently, a large-grained Si layer with (100) texture can be formed. By purposely interrupting the annealing of nanocrystalline Al/amorphous Si (a-Si) bilayers, a porous structure of the crystallized Si can be developed due to the incomplete intermixing of Si and Al. Due to the different dominant diffusion processes of Si in Al at the different annealing temperatures, the most Si diffuses along the different paths in the Al layer, such as triple junction, grain boundary and Al bulk. Therefore, it can develop the different morphologies of the porous Si layers after the selectively etching of Al. By introducing an amorphous Ge interlayer between the crystalline Al and amorphous Si layer, the Al grain boundaries are not essential for the crystallization of the amorphous Si in contrast to the case in Al/Si bilayer system. Si crystallizes continuously on the pre-crystallized Ge seeds which form initially at the original interface of crystalline Al and amorphous Ge. The thermodynamic models to interpret the fundamentals of these different crystallization behaviors of Si are established based on the change of the interface energy between the different phases of the whole system during the crystallization. Using the effective diffusivity, the dominant diffusion process of Si in Al can be investigated to explore the morphological dependence of the crystallized Si layer on the annealing conditions.Item Open Access Spin interactions in graphene-single molecule magnets hybrid materials(2015) Cervetti, Christian; Bogani, Lapo (Dr.)This thesis work employs magnetic molecules, belonging to the family of single molecule magnets (SMMs), as model systems to study the relaxation of mesoscopic spins on graphene, and their interaction with graphene charge carriers in real devices. Their large uniaxial anisotropy makes SMMs behave like giant spins, with relaxation times of years at low temperatures. Their spin dynamics combines a classical and a quantum relaxation mechanism, that can be selectively switched on and off by either applying an external magnetic Field or by varying the temperature. The work is organized as follows. The First part presents a thorough structural characterization of the SMMs-graphene hybrid materials via multiple techniques, including atomic force microscopy, x-ray photoelectrons spectroscopy, mass spectrometry, Raman spectroscopy, and electronic transport measurements on graphene-based Feld-effect transistors. The analysis of the dynamical arrangement of molecular adsorbates on graphene reveals new opportunities to control the supramolecular surface arrangement. A comprehensive study of the magnetization dynamics of SMMs on graphene is carried out by means of ac-susceptibility techniques in a broad temperature range (T = 4K - 13 mK). The details of the complex spin-graphene interaction are unraveled in the framework of a newly developed theoretical model that accounts for all the possible fundamental contributions and the two-dimensional nature of graphene. The focus of the second part is the design, fabrication and characterization of graphene-based spintronic devices. Diffrent strategies for the injection of spin-polarized carriers in graphene are implemented and tested down to very low temperatures (T = 300 mK). To conclude the first spin-transport and spin-relaxation measurements in SMMs-graphene devices are presented.Item Open Access Monotonicity-based methods for inverse parameter identification problems in partial differential equations(2015) Ullrich, Marcel; von Harrach, Bastian (Prof. Dr.)This work is concerned with monotonicity-based methods for inverse parameter reconstruction problems in partial differential equations. The first three chapters address the anomaly detection problem of electrical impedance tomography. While electrical impedance tomography aims on reconstructing the interior conductivity distribution of a conductive subject from boundary data, the goal of the specific anomaly detection problem is the reconstruction of areas inside a conductive subject where the conductivity differs from an expected reference conductivity. The considered boundary data can be understood as an operator that describes current-voltage measurements. In the final chapter we prove a novel uniqueness result for the inverse potential problem of the Schrödinger equation with partial data. For the development of anomaly detection methods, both known and novel variants of a monotonicity relation are used. Roughly speaking, these monotonicity relations particularly show that a pointwise decrease of the conductivity leads to larger boundary data (in sense of operator definiteness). At first glance, it is not obvious at all whether the converse of this implication holds also true, i.e., it is not clear whether larger boundary data could also result from a local decrease of the conductivity in some parts and a local increase in other parts. Assuming a local definiteness condition for the conductivity change we prove a partial converse of the monotonicity implication that holds for the case in which the measurements are modeled with the idealized continuum model. In the first chapter we develop novel anomaly detection methods for measurement data modeled with the continuum model. Moreover, fast linearized variants are presented that only require the computation of reference measurements for one homogeneous reference conductivity. We prove that all presented methods are capable of reconstructing the exact outer shape of conductivity anomalies. In realistic electrical impedance tomography settings in which measurement data is collected on a finite number of electrodes, the reconstruction of the exact outer shape of anomalies cannot be guaranteed anymore. On top of that, systematic errors resulting from imprecise knowledge of the setting parameters as well as additional random measurement errors need to be taken into account. In the second chapter we show that nevertheless certain resolution guarantees are principally possible for such settings. In the third chapter we develop a novel hybrid method that does not require the simulation of reference data. We apply an idealized model for ultrasound modulation that alters the conductivity uniformly in a test region and we develop a test criterion to check whether the test region is located inside an anomaly. The test criterion consists of a monotonicity-based comparison of ultrasound modulated and weighted frequency-difference measurements. Finally, in the fourth chapter, a local uniqueness result for the inverse potential problem of the Schrödinger equation on a bounded Lipschitz domain with partial boundary data is shown. More precisely, we show that positive-valued bounded potentials that do not completely coincide in a neighborhood of a potentially arbitrarily small part of the boundary can be distinguished from Cauchy data on this boundary part provided that a local definiteness condition is fulfilled.Item Open Access Regulation of endocytic membrane trafficking by the GTPase-activating protein Deleted in Liver Cancer 3 (DLC3)(2015) Braun, Anja Catharina; Olayioye, Monilola (Prof. Dr.)Small GTPases of the Rho family are key regulators of the actin and microtubule cytoskeleton, whereby many cellular functions including cell migration, adhesion and polarity, as well as cell cycle progression are controlled. Increasing evidence suggests that Rho proteins are also critically involved in the regulation of membrane trafficking pathways within exocytosis and endocytosis. Although the molecular mechanisms are not well understood, Rho GTPases apparently have to govern and finely tune cytoskeletal remodeling, in order to support the formation, fusion and motility of transport carriers. However, the identity of their regulators, the guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) that ensure the balanced GTPase activation in space and time is largely elusive. The ‘Deleted in Liver Cancer’ (DLC1/2/3) proteins are a structurally conserved subfamily of RhoGAP proteins that act as negative regulators of Rho GTPases. In addition to the catalytically active GAP domain, all DLC proteins contain a sterile alpha motif (SAM) and steroidogenic acute regulatory protein-related lipid transfer (START) domain. Expression of the best studied member, DLC1, is frequently lost in various types of human cancers and a tumor suppressive function associated with its RhoGAP activity has been established in vivo. Although DLC3 was also observed to be downregulated in several cancer cell lines and primary tumors, the cellular functions of DLC3 are still poorly characterized. So far, GAP activity for RhoA has only been demonstrated in vitro and, associated with its localization at cell-cell contacts, a Rho-regulatory role in adherens junction stability was described. Thus, the aims of this thesis were to further investigate the subcellular localization of DLC3 and to shed light on the role of DLC3 in the regulation of Rho-mediated cellular processes, in particular endocytic membrane trafficking. This study provides convincing evidence that DLC3 is a functional, Rho-specific GAP protein in living cells and that its loss enhances perinuclear RhoA activity. DLC3 is recruited to Rab8-positive membrane tubules and required for the integrity of the Rab8 and Golgi compartments. Depletion of DLC3 impairs the transport of internalized transferrin to the endocytic recycling compartment, which is restored by the simultaneous downregulation of RhoA and RhoB. As a consequence, DLC3 loss interferes with epidermal growth factor receptor (EGFR) degradation and causes prolonged receptor signaling. Furthermore, it was found that DLC3-depleted cells show reduced surface N-cadherin levels, leading to decreased cell aggregation. Together, these findings identify DLC3 as a novel component of the endocytic trafficking machinery, wherein it maintains organelle integrity and regulates membrane transport via the control of local Rho activity.Item Open Access Stadterneuerung und Stadtentwicklung im historischen Kontext : eine Untersuchung chinesischer und deutscher Strategien im Umgang mit dem „Genius Loci“(2015) Yang, Yinan; Bott, Helmut (Prof. Dr.-Ing)In China wird immer mehr Wert auf die historische Einzigartigkeit einer Stadt gelegt. Als Stadtteil mit besonderen historischen Informationen spielt der Altstadtkern eine wichtige Rolle in Stadtgestalt, Stadtkultur und Stadtfunktion. Mitte der 1990er Jahre wuchs der Tourismus in historischen Gebieten rasant. Besonders nach der „Olympiade 2008“ in Peking besichtigen immer mehr ausländische Touristen chinesische Altstädte. Dies spiegelt ein großes Interesse an regionaler Kultur und Stadtgestalt wider, welches den historischen Kontext immer mehr in den Vordergrund rückt. Die Zerstörung der meisten chinesischen Altstädte erfolgte in zwei Phasen: Im Laufe der Kulturrevolution 1966-1976 wurden zahlreiche Baudenkmäler, zumeist Buddhastatuen, von den „Roten Garden“ in der „Kampagne gegen die vier Alten“ zerstört. Während der marktwirtschaftlichen Zeit ab Anfang der 1990er Jahre wurde die Modernisierung durch den boomenden Immobiliensektor auch in den Altstädten vorangetrieben. Dieser Entwicklung fiel eine Vielzahl an Altstädten zum Opfer. Es ist zu erwarten, dass nach dieser Phase des enormen Wachstums - sowohl der Gesellschaft als auch der Stadtgestalt - eine Phase historischer Rückbesinnung aufkommen wird. Dies kündigt sich bereits in einigen Wiederaufbau- oder Umbauprojekten der letzten zehn Jahre an, wie z.B. dem Wiederaufbau des abgerissenen „Yongding-Tors“ in Peking oder dem Umbau des „Shuyuanmen-Quartiers“ in Xi’an. Dabei stellt sich die Frage, durch welche Umbaumethode und Erneuerungsstrategie der historische Kontext wieder hergestellt werden soll, zumal diese historisch orientierten Bauprojekte mit mehr oder weniger Kenntnis des geschichtlichen Charakters eines Ortes durchgeführt werden. In Europa und in Deutschland im Besonderen liegen bereits seit langem Erfahrungen über viele Epochen des Stadtumbaus und der Stadterneuerung vor, insbesondere über die Phase des Wiederaufbaus in der Nachkriegszeit und die Periode der erhaltenden Stadterneuerung ab Mitte der 1970er Jahre. Aber auch fast 70 Jahre nach den Kriegszerstörungen in Europa ist die Debatte über den Umbau und Rückbau vieler Innenstädte in Auseinandersetzung mit historischen Strukturen, auch wenn sie Jahrzehnte lang zerstört waren, wieder virulent. Dies zeigte sich beispielsweise an einigen Projekten wie der Internationalen Bauausstellung (IBA-Altbau) von 1987 in Berlin, dem Wiederaufbau der Frankfurter Altstadt zwischen Dom und Römerberg sowie der Realisierung der Neuen Mitte von Ulm. Diese Arbeit soll verschiedene Möglichkeiten von Methoden und Strategien der Stadterneuerung aufzeigen, um auf diese Weise mögliche Wege zur Wiederherstellung des historischen Kontexts bei der Altstadterneuerung in China zu finden.Item Open Access Stability of a laminar streaky boundary-layer behind a roughness element(2015) Shin, Yong-su; Rist, Ulrich (apl. Prof. Dr.-Ing.)Analysis of flow instability is of importance to understand laminar-turbulent transition which is a crucial factor for aerodynamic performance. The present study deals with influences of a roughness element on the flow instability of a laminar boundary-layer. Roughness elements in laminar boundary-layers generate localized disturbances. They grow transiently and formulate streamwise elongated streaky structures downstream. Spanwise periodicity of these streaky structures disturbs the streamwise development of two-dimensional Tollmien-Schlichting waves in a laminar boundary-layer. In this way, a delay of the laminar-turbulent transition is achieved (flow stabilization). On the other side, physically unavoidable velocity reduction behind the roughness elements brings on high shear layers in wall-normal direction at the same time. Also, separations or strong vortical structures occur occasionally depending on both shape of the roughness elements and flow conditions. They cause a flow destabilization and sometimes trigger a bypass transition. Because these two opposite phenomena happen concurrently and interact with each other, it is difficult to precisely understand the instability mechanisms provoked by the roughness elements. Therefore, the goal of the present work is to study the stability of a laminar streaky layer induced by a roughness element. This work consists of two parts: Bi-global linear stability analysis and experimental measurements. A complex instability procedure of the three-dimensional streaky layers arranged parallel in streamwise and periodical in spanwise direction can be analysed by a bi-global approach. Corroborating experiments were conducted in the laminar water channel at the University of Stuttgart. Simultaneous operation of two hot-film probes and signal processing enabled to find the theoretically calculated unstable eigenmodes in practical flow. In addition, observations of both velocity distribution in a complex flow field and nonlinear vortex structures were carried out by a flow visualization using a hydrogen-bubble method and Particle-Image-Velocimetry measurements. As a result, a streaky layer which includes streamwise elongated high- and low-speed streaks and a separation behind the roughness element was found by a CFD computation using a laminar solver and confirmed by time-averaged experimental velocity components. The bi-global LST identified two highly unstable eigenmodes. These eigenmodes oscillate symmetrically and asymmetrically with respect to the spanwise coordinates and were accordingly termed varicose and sinuous mode, respectively. Their streamwise evolution depends mainly on a streamwise development of the streaks. Experimental results confirmed the presence of these two unstable modal modes. The varicose mode dominants flow instability, and the sinuous mode has a smaller signal-to-noise ratio. Additionally, an external forcing was tried to increase the initial amplitude of the smaller sinuous mode with respect to the varicose one. Despite some deficiencies of the experimental setup, a separate artificial amplification of a specific eigenmode, i.e. the sinuous mode, was possible. In the latter part of the present study, the nonlinear behaviour of the streaky layer further downstream and the breakdown under an over-critical condition were explored. Because the linear theory cannot calculate nonlinear instability, complex three-dimensional flows and vortical structures were investigated by experimental flow visualization methods, and an evolution from nonlinear streaks to hairpin vortices was detected.Item Open Access Strömungsmechanische Untersuchungen zur Funktionsweise von Manschettendichtungen aus PTFE-Compounds mit Rückförderstrukturen(2015) Goujavin, Witalij; Haas, Werner (Prof. Dr.-Ing. habil.)Die Standardlösung zur Abdichtung von Wellen im Maschinenbau sind Radial-Wellendichtringe (RWDR) aus Elastomeren. Allerdings stoßen Elastomer-Werkstoffe in vielen Anwendungen an ihre Belastungsgrenzen. Durch Einsatz von PTFE-Compounds als Dichtungswerkstoff können die Einschränkungen von Elastomeren weitgehend überwunden werden. Daher werden in der Dichtungstechnik immer häufiger Manschettendichtungen aus PTFE-Compounds (PTFE-MD) eingesetzt. Im Gegensatz zu Elastomer-RWDR sind bei PTFE-MD Rückförderstrukturen (RS) erforderlich, um die dynamische Dichtheit zu gewährleisten. Für Anwendungen mit festgelegter Drehrichtung der Welle gehören PTFE-MD mit Spiralrille zum bewährten Stand der Technik. Die Spiralrille als RS ist aber nur für eine Drehrichtung der Welle geeignet. Bei wechselnder Wellendrehrichtung werden andere RS verwendet. Es gibt zwar bereits funktionierende PTFE-MD mit RS für beide Drehrichtungen der Welle, allerdings sind diese noch im Erforschungsstadium und weisen Optimierungspotenziale auf. Trotz des hohen potenziellen Nutzens für Dichtungsanwender durch die Verfügbarkeit von optimierten PTFE-MD mit RS, insbesondere für beide Drehrichtungen der Welle, gibt es kaum Fortschritte seitens der Dichtungshersteller. Dies liegt im Wesentlichen daran, dass die entsprechenden Funktionsmechanismen nicht hinreichend bekannt sind. Ohne Kenntnis der genauen Funktionsmechanismen ist eine gezielte Optimierung nicht möglich. Daher muss mit hohem experimentellem Aufwand durch „Versuch und Irrtum“ optimiert werden. Ziel der vorliegenden Arbeit ist es einen Beitrag zum besseren Verständnis der dynamischen Funktionsmechanismen von PTFE-MD mit RS, insbesondere für beide Drehrichtungen der Welle, zu leisten. Dabei liegt das Hauptaugenmerk der Arbeit auf der numerischen Untersuchung der nachfolgenden Zusammenhänge. • Analyse des Strömungsverlaufs und der Druckverteilung um RS und im Dichtspalt. Dies dient einem besseren Verständnis der Vorgänge im Bereich des Dichtspalts. • Untersuchung unterschiedlicher Einflüsse auf das Umlenk- und Fördervermögen von RS. Ziel ist dabei die Identifikation von relevanten Einflussgrößen auf das Fördervermögen von PTFE-MD mit RS. • Analyse des Förderverhaltens durch den hydrodynamischen Dichtspalt und durch lokale Erhöhungen des Dichtspalts. • Betrachtung der Einflüsse der Dichtspaltgeometrie auf den Förderwert einer PTFE-MD mit RS. • Untersuchung der Auswirkungen von Geometrievariationen am Übergang einer RS in den geschlossenen Ring auf das Druckaufbauvermögen und damit auch indirekt auf das Fördervermögen von PTFE-MD mit RS. Durch ein besseres Verständnis der obigen Zusammenhänge können die dynamischen Funktionsmechanismen von PTFE-MD mit RS besser nachvollzogen werden. Hieraus lassen sich besonders wirkungsvolle Maßnahmen zur Verbesserung des Fördervermögens und damit der dynamischen Dichtsicherheit von PTFE-MD mit RS ableiten. Damit ist eine effektivere Optimierung möglich, wodurch der experimentelle Aufwand bei der Weiterentwicklung von PTFE-MD mit RS reduziert werden kann.Item Open Access Stochastic and hydrological modelling for climate change prediction in the Lima region, Peru(2015) Chamorro Chávez, Alejandro; Bárdossy, András (Prof. Dr. rer. nat. Dr.-Ing.)Climate change has been an important field of research in the past years and certainly is a major concern in the present time. It involves a broad spectrum of subjects and significant different time scales, ranging from decades to thousands or millions of years. Generally speaking, in a climate change scenario a change in the pattern, average or extreme conditions of some variables is observed, and this can be due to many different causes as changing processes in the earth, human activities or extra terrestrial induced factors. This study concentrates on the influences on the climate due to human activities and focuses on the hydrological response to these influences or changes as a primarily goal, for the next few decades. The main motivation is the vulnerability and scarcity of the water availability in the capital of Peru, Lima, and how the area under study will respond to a change in the climate. An important focus of analysis in order to reduce the uncertainty in the predictions is the errors that appears when modeling a given variable or set of variables. This issue is addressed first in regionalization of precipitation and second in the calibration of hydrological models in which a robust parameter estimation is performed. In the first issue concerning to regionalization, External Drift Kriging is applied. In this part of the work the results of regionalization are analyzed with focus on the errors and systematic errors which appear during the modeling. The main goal here is the reduction of these errors through some proposed transformations. Here, three approaches are suggested, namely smoothing of the digital elevation model (DEM) considering a symmetric area, power transformation and smoothing considering a non symmetric area. The second issue concerning the uncertainty in the estimations (discharge) was addressed two-fold, namely by optimizing the objective function by means of a heuristic optimization procedure based on Monte Carlo simulation, and by means of a robust parameter estimation (ROPE) algorithm developed quite recently by Bárdossy and Singh, which in general terms can be used as a general multivariate optimization procedure. The algorithm offers a way of finding a set of “good” parameter vectors, which among other characteristics, are transferable in time. The final result comprises an ensemble of estimations for expected discharge variations accounting for the uncertainty in parameterization and processes description in the models. In this study HVB and HYMOD models are used. The assessment of the impact of climate change in precipitation and temperature is carried out by a statistical downscaling procedure based on a quantil-quantil transformation. Here the information given by the Global Climate Models (GCMs) outputs are transferred to the local scale. Two different GCMs and three scenarios are used in this step. This permitted the definition of a range for the expected future variations for temperature and precipitation. The last chapter of the study addresses the assessment of the discharge in the short term. The goal here is to “infer” the outcome of a random variable (discharge) in the next time step by taking information from past observations (previous steps). As we can regard the observations (time series) as a realization generated from a stochastic process, we can address this issue from a stochastic point of view. The task is addressed first by considering some of the existing autoregressive models (AR process), and second by considering a Copula-based autoregressive model. In order to perform the Copula-based autoregressive model, a given time series (modelled discharge) was transformed into three vectors representing the same original time series but shifted in time. A three dimensional Copula was then fitted to the univariate distributions. For this, a Gaussian model as well as a Beta kernel model expressed in terms of the Beta function was considered.Item Open Access Thermodynamics and kinetics of the oxidation of amorphous Al-Zr alloys(Stuttgart : Max-Planck-Institut für Intelligente Systeme (ehemals Max-Planck-Institut für Metallforschung), 2015) Weller, Katharina; Mittemeijer, Eric J. (Prof. Dr. Ir.)The present thesis presents a comprehensive investigation of the thermal oxidation of amorphous Al-Zr alloys. The oxide composition and microstructure, as well as the oxidation kinetics and oxidation mechanism of amorphous Al-Zr alloys upon thermal oxidation at relatively low oxidation temperatures of 350 - 400 °C and at high oxidation temperatures of 500 - 560 °C have been investigated. The phase and microstructural development upon oxidation of amorphous Al-Zr alloys, as well as the oxidation-induced changes in the alloy substrate, were investigated by a combinatorial experimental approach using X-ray diffraction (XRD), cross-sectional (analytical) transmission electron microscopy (TEM), Auger electron spectroscopy (AES) sputter-depth profiling and spectroscopic ellipsometry (SE). Furthermore, the corrosion behavior of as-deposited and oxidation-treated amorphous Al-Zr alloys have been investigated as function of the alloy composition and oxidation conditions by employing an electrochemical microcapillary technique.