Universität Stuttgart
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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 Visual prediction of quantitative information using social media data(2017) Fatehi Ebrahimzadeh, HamedIn recent years, the availability of a vast amount of user-generated data via social media, has given an opportunity to researchers for analyzing these data sources and discovering meaningful information. However, processing and understanding this immense amount of data is challenging and calls for automated approaches, and involvement of field experts to use their field knowledge and experience to enhance the data analysis. So far, existing approaches only enable the detection of indicative information from the data such as the occurrence of critical incidents, relevant situation reports etc. Consequently, the next step would be to better relate the user provided information to the real-world quantities. In this work, a predictive visual analytics approach is developed that offers semi-automated methods to estimate quantitative information (e.g. number of people who participate in a public event). At first, the approach provides interactive visual tools to explore social media data in time and space and select features required as input for training and prediction interactively. Next, a suitable model can be trained based on these feature sets and applied for prediction. Finally, the approach also allows to visually explore prediction results and measure quality of predictions with respect to the ground truth information obtained from past observations. The result of this work is a generic visual analytics approach, that provides expert user with visual tools for a constant interaction between human and machine, for producing quantitative predictions based on social media data. The results of predictions are promising, especially in cases that the location, time and other related information to public events are considered together with the content of user-generated data.Item Open Access Integration of IoT devices via a blockchain-based decentralized application(2017) Ahmad, AfzaalBlockchains are shared, immutable ledgers for recording the history of transactions. They foster a new generation of transactional applications that establish trust, accountability, and transparency. It enables contract partners to secure a deal without involving a trusted third party. Initially, the focus was on financial industry for digital assets trading like Bitcoin, but with the emergence of Smart Contracts, blockchain becomes a complete programmable platform. Many research and commercial organization start diving into blockchain world, bringing new ideas of its application in different sectors like supply chain, Health, and autonomous shopping. This thesis presents an idea to integrate Internet of Things (IoT) devices via a blockchain based decentralize application based on Ethereum. The application consists of front-end application which can be deployed to any web server, and a smart contract which will be deployed on a private blockchain network comprises of Peer-to-Peer (P2P) connected IoT devices acting as full Ethereum node. The application emulates the digital transport ticketing system where the asset is a ticket which can be purchased and paid by the user using ether in their Ethereum account on the blockchain. Once the purchase transaction is mined, it is propagated to all the peers. Ticket can now be accessed locally without requesting any centralized system, which makes the system easily accessible and safe because of the security, data integrity and decentralization of the blockchain-based systems.Item Open Access Grundsätze hochschuldidaktischer Arbeit : am Zentrum für Lehre und Weiterbildung(Stuttgart : Universität Stuttgart, Zentrum für Lehre und Weiterbildung, 2017) Braun, Thorsten; Kröber, Edith; Loewe, Simone; Qekaj, Avni; Rapp, Sonja; Kröber, Edith; Braun, Thorsten (Redaktion)Der Artikel befasst sich mit aktuellen, programmatischen Grundsätzen hochschuldidaktischer Arbeit, wie sie durch das Zentrum für Lehre und Weiterbildung der Universität Stuttgart verfolgt und umgesetzt werden. Ausgehend von einer Skizze des Europäischen Hochschulraums wird das Programmziel des "Lebenslangen Lernens" kritisch diskutiert und reflektiert. Anschließend werden die zentralen, thematischen Orientierungspunkte für praktische, hochschuldidaktische Arbeit vorgestellt und knapp umrissen. Der Artikel richtet sich an Hochschullehrende sowie Hochschuldidaktikerinnen und Hochschuldidaktiker.Item Open Access A MATLAB toolbox for the Scintrex CG-5 gravimeter at GIS(2017) Gu, SiyunThis thesis is about a MATLAB toolbox for the Scintrex CG-5 gravimeter. The aim of this toolbox is to offer a basic data process for gravity measurement, which is compatible for most applications in geodesy. In particular, the toolbox covers: 1. data selection, 2. adjustment, 3. gravity gradient computation, 4. gravity visualization, 5. calibration factor estimation. A graphical user interface enables users without deeper programming knowledge to operate this toolbox and obtain the results like adjusted values or figures.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 Erweiterung und Evaluation einer lupenbasierten Technik zur Exploration von Textsammlungen(2017) Assenov, IvanIn recent years there has been a sharp increase in the amount of text publicly accessible in digital form. The primary cause for this is widespread access to the Internet, the popularity of e-mail and social networking websites and collaborative efforts to preserve and share knowledge. These developments have inspired the creation of a wide variety of information visualization techniques that focus on large-scale text data and facilitate its exploration and analysis. One popular approach represents individual documents as glyphs on a 2D surface, with pairwise distances corresponding to semantic similarities. The metaphor of a moveable lens that summarizes the contents of texts underneath it has been proposed as a method of interaction targeted at free exploration tasks. The main goal of this master’s thesis project is to extend the basic technique by adding labels to the visualization that guide its users towards regions of interest more quickly without negatively impacting the lens’ usefulness. Also, an automatic framework that determines the tool’s effectiveness under different parameter settings is developed. Finally, the proposed improvements and the overall technique are evaluated by means of a think-aloud user study.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 Crawling hardware for OpenTOSCA(2017) Choudhury, PushpamHeterogeneity is the essence of the IoT paradigm. There is heterogeneity in communication and transport protocols, in network infrastructure, and even among the interacting devices themselves. Managing discovery of the different devices in such a paradigm is an extremely complex task. The typical solutions include an abstraction layer, commonly known as the middleware layer, that handles this complexity for the devices, thereby, allowing them to interact with one another. One major limitation of the existing middleware solutions is in their ability to allow for an easily configurable approach required to handle the tremendous scale of heterogeneous components in the IoT. The objective of this thesis is to develop such a highly configurable discovery middleware approach. The proposed approach aims to discover a variety of heterogeneous devices and services depending on a multi-level plugin layer, consisting of independent plugins that interact with each other based on the pipes and filters architectural pattern. To allow for the dynamic configuration of the middleware, a discovery configuration is developed. The output from the middleware includes a list of devices and their capabilities and is accessible via a web interface which can interact with a range of different clients. The proposed approach is validated on a scenario in a real-life environment.