Untersuchung von Magnetostriktiven und Piezotronischen Mikrostrukturen und Materialien für biomagnetische Sensoren mittels Röntgenstrahlen

Detecting electric potential differences from the human physiology is an established technique in medical diagnosis, e.g., as electrocardiogram. It arises from a changing electrical polarization of living cells. Simultaneously, biomagnetism is induced and can be utilized for medical examinations, as well. Benefits in using magnetic signals are, no need for direct skin contact and an increased spatial resolution, e.g., for mapping brain activity, especially in combination with electrical examinations. But biomagnetic signals are very weak and, thus, highly sensitive devices are necessary. The development of small and easy to use biomagnetic sensors, with a sufficient sensitivity, is the goal of the Collaborative Research Centre 1261 - Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics. This thesis was written as part of this collaboration, with the main focus on the investigation of crystalline structures and structure related properties of piezotronic and magnetostrictive materials by utilizing a selection of X-ray techniques, i.e., X-ray diffraction (XRD), X-ray reflectivity (XRR) and coherent X-ray diffraction imaging (CXDI). Piezotronics, realized by combining piezoelectricity and Schottky contacts in one structure, provides a promising path to enhance sensor sensitivity. A first study investigated the crystalline structure of three piezotronic ZnO rods, spatially resolved by scanning nano XRD and combined with electrical examinations of their Schottky contact properties. It is found that the crystalline quality has a clear impact on the electrical properties of the related Schottky contact, probably due to crystalline defects. A complementary transmission electron microscopy (TEM) and XRD study performed on hybride vapor phase epitaxy (HVPE) grown GaN showed a slight, photoelectrochemical etching related relaxion of strain originating from crystal growth. In a separate study, CXDI was utilized for three-dimensional visualization of strain in a gold coated ZnO rod, with spatial resolution below 30 nm. A distinct strain distribution was found inside the rod, denoted to depletion and screening effects occurring in bent piezotronic structures, and a high strain at the interface may be related to Schottky contact formation. This interface strain agrees with results obtained from TEM. A succeeding CXDI study was conducted on a ZnO rod coated with magnetostrictive FeCoSiB and the possibility for the investigation of the Schottky contacts electrical properties. It was found that FeCoSiB sputtered on ZnO results in an ohmic contact and that an external magnetic field causes a change of the electrical properties, probably due to a strain change, visualized by CXDI. In a fifth study, magnetostrictive FeCo/TiN multilayer structures were investigated by a combined TEM and XRD/XRR approach, showing a relaxation of the structure due to an annealing process and a cube-on-cube structure of the FeCo and TiN layers

Evaluation of Energy Costs and Error Performance of Range-Aware Anchor-Free Localization Algorithms for Wireless Sensor Networks

This research examines energy and error tradeoffs in Anchor-Free Range-Aware Wireless Sensor Network (WSN) Localization algorithms. A concurrent and an incremental algorithm (Anchor Free Localization (AFL) and Map Growing) are examined under varying network sizes, densities, deployments, and range errors. Despite current expectations, even the most expensive configurations do not expend significant battery life (at most 0.4%), implying little energy can be conserved during localization. Due to refinement, AFL is twice as accurate, using 6 times the communication. For both, node degree affects communication most. As degree increases, Map Growing communication increases, while AFL transmissions drop. Nodes with more neighbors refine quicker with fewer messages. At high degree, many nodes receive the same message, overpowering the previous effect, and raising AFL received bits. Built from simulation data, the Energy Consumption Model predicts energy usage of incremental and concurrent algorithms used in networks with varying size, density, and deployments. It is applied to current wireless sensor nodes. Military WSNs should be flexible, cheap, and long lasting. Anchor-Free, Range-Aware algorithms best fit this need

Think Piece: Food Gardening and Intergenerational Learning in Times of Uncertainty

To people who base their livelihoods on land and animals, climate changes generate experiences of increased livelihood uncertainty. With the point of departure in a case story from the Amanzi for Food project in the Eastern Cape and older case material on community gardens in Port Elizabeth, in this paper I reflect on ways of experiencing and coping with uncertain livelihood conditions. The focus of discussion is the intergenerational interactions and learning processes involved in food gardening and their role in shaping responses to uncertainty which point towards ‘creative solutions’ rather than ‘debilitation’ (cf. Calkins, 2016:2)

Green Entrepreneurship an Hochschulen: Benchmarking und Best-Practices

[Ziele der Untersuchung] Um den aktuellen Stand der SPICE-Partner im Vergleich zu Aktivitäten an anderen Hochschulen zu erfassen, wurde ein Benchmarking-Sonderteil angestrebt, der sich ganz speziell dem Themengebiet des Green Entrepreneurship widmet. Nicht nur um die bereits geleistete Arbeit besser bewerten zu können und ihr ein Gewicht zu verleihen, sondern auch um für die Zukunft gut aufgestellt zu sein. So ist ein weiteres Ziel dieser Untersuchung, Best-Practice-Maßnahmen zu identifizieren und zu analysieren. Diese herausragenden Maßnahmen können bei zukünftigen Aktionen der beteiligten Partner mit einfließen und das akademische Angebot vor Ort dementsprechend prägen und verändern. [Gang der Untersuchung] Im zweiten Kapitel wird zunächst eine generelle Übersicht über die Angebote im Bereich des Green Entrepreneurship geboten, bevor es im dritten Kapitel mit einer näheren Analyse ausgesuchter Vergleichshochschulen weiter geht. Kapitel vier befasst sich mit einer genaueren Bestandsaufnahme der ausgewählten Best- Practice-Maßnahmen der zuvor untersuchten Hochschulen. In Kapitel 5 werden die Angebote der SPICE-Partner im Bereich Green Entrepreneurship dargestellt. Den Abschluss bildet Kapitel sechs, in dem vergleichende Schlussfolgerungen gezogen werden und Handlungsempfehlungen/Ansatzpunkte für zukünftige Aktivitäten im Bereich des Green Entrepreneurship abgeleitet werden

Unternehmenslandschaft der Erneuerbaren Energien im Strombereich in Schleswig-Holstein: Unternehmenspräsentationen und Meinungsbild

[Gegenstand und Ziel der Untersuchung] Ziel und Gegenstand der vorliegenden Untersuchung sind nicht, die bestehenden Studien zur aggregierten Wertschöpfung, zur aggregierten Beschäftigung oder der Gesamtzahl der Unternehmen der Erneuerbaren Energien in Schleswig-Holstein zu überprüfen oder zu komplettieren. Wer ernsthaft die Ziele zur Stärkung der Schleswig-Holsteiner Wirtschaft im Bereich der Erneuerbaren Energien und die Ziele der Schleswig-Holsteiner Energiewende verfolgen möchte, muss sich die Mühe machen, die Unternehmen dahinter in ihrer Vielfalt kennenzulernen und sich mit deren Meinung zu beschäftigen. Es ist daher vielmehr Gegenstand der Untersuchung, die Perspektive zu erweitern und die einzelnen Unternehmen als Erkenntnisgegenstand in den Fokus zu rücken, sie dem Leser vorzustellen und zudem die Unternehmer und Manager dieser Unternehmen im Interview zu Wort kommen zu lassen. In diesem Sinne ist es die erste Untersuchung dieser Art. Die Vorstellung von Unternehmen der Erneuerbaren Energien in Schleswig-Holstein ist das erste Kernziel der Untersuchung. Gegliedert nach den Kategorien der Erneuerbaren Energien werden Unternehmen in zwei Formaten präsentiert - Visitenkarten als Kompaktformat und Portraits als Großformat. Die Erstellung eines Meinungsbildes aus Sicht der Schleswig-Holsteiner Unternehmen der Erneuerbaren Energien ist das zweite Kernziel der Untersuchung. Unternehmer hinter diesen Unternehmen bzw. für diese Unternehmen verantwortliche Manager sollen im Interview zu Wort kommen. Deren Einschätzungen und Zukunftserwartungen zu Themen wie Wachstum, Branchentrends, Marktkräfte, strategische Faktoren, Hidden Champions und Standortfaktoren und deren geäußerte Maßnahmenvorschläge, Ansatzpunkte und Empfehlungen zur Sicherung und Hebung von Potenzialen der Erneuerbaren Energien in Schleswig-Holstein werden zu einem Meinungsbild aggregiert und dargestellt

Underwater 3D Reconstruction Based on Physical Models for Refraction and Underwater Light Propagation

In recent years, underwater imaging has gained a lot of popularity partly due to the availability of off-the-shelf consumer cameras, but also due to a growing interest in the ocean floor by science and industry. Apart from capturing single images or sequences, the application of methods from the area of computer vision has gained interest as well. However, water affects image formation in two major ways. First, while traveling through the water, light is attenuated and scattered, depending on the light's wavelength causing the typical strong green or blue hue in underwater images. Second, cameras used in underwater scenarios need to be confined in an underwater housing, viewing the scene through a flat or dome-shaped glass port. The inside of the housing is filled with air. Consequently, the light entering the housing needs to pass a water-glass interface, then a glass-air interface, thus is refracted twice, affecting underwater image formation geometrically. In classic Structure-from-Motion (SfM) approaches, the perspective camera model is usually assumed, however, it can be shown that it becomes invalid due to refraction in underwater scenarios. Therefore, this thesis proposes an adaptation of the SfM algorithm to underwater image formation with flat port underwater housings, i.e. introduces a method where refraction at the underwater housing is modeled explicitly. This includes a calibration approach, algorithms for relative and absolute pose estimation, an efficient, non-linear error function that is utilized in bundle adjustment, and a refractive plane sweep algorithm. Finally, if calibration data for an underwater light propagation model exists, the dense depth maps can be used to correct texture colors. Experiments with a perspective and the proposed refractive approach to 3D reconstruction revealed that the perspective approach does indeed suffer from a systematic model error depending on the distance between camera and glass and a possible tilt of the glass with respect to the image sensor. The proposed method shows no such systematic error and thus provides more accurate results for underwater image sequences