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Dissertation
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Power System Inertia
(2019)
System inertia is the instantaneous power reserve that stabilizes power systems after large-scale disturbances. It declines with increasing renewable generation, causing an increased risk of black-out unless action is taken. Providing additional inertia will be necessary to maintain security of supply at a reasonable level. To solve the problem of reduced inertia in a reliable and cost-efficient way, this thesis first systematically describes requirements on system level, as basis for the following evaluation of ...
Dissertation
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Long-term voltage stability of electric power systems hosting inverter-interfaced energy sources
(2021)
The study of power system dynamics refers to the motion of electro-mechanical and electro-magnetic quantities such as voltages, currents, rotational speeds, angles and powers under the action of forces caused by system disturbances. For decades, such dynamics have been extensively dominated by large Synchronous Generators (SGs). Not a surprising statement, considering that the power systems that we know today were built based on the SG concept since the closing decades of the 19th century. It all began in 1891, when ...
Dissertation
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Gast-Partikel in mikroskaligen, dreidimensionalen Wirts-Partikeln: Herstellung durch Nanoimprintlithographie und ihre Charakterisierung
(2020)
Die Verwendung von Partikeln spielt in vielen alltäglichen Bereichen eine essenzielle Rolle und ist daher im Laufe dieses Jahrhunderts immer mehr in den Fokus der Forschung gerückt. Aktuelle Forschungsarbeiten belegen, dass die Größe und Form der Partikel Einfluss auf verschiedene Anwendungen haben. Ein Beispiel ist die Verwendung als Medikamententräger. Forschungen zeigen, dass ellipsoide Partikel langsamer als sphärische Partikel von Makrophagen internalisiert werden und den Transport von Medikamenten innerhalb des ...
Dissertation
Multilayer Thin-film Structures with Distributed Cavity for Optical Filter and Laser Applications
(2018-12)
This work is aimed at the development of a fabrication process for realization of a chirped filter based laser device (called as coreSEL). Conventional vertical cavity surface emitting lasers (VCSELs) are based on Fabry-Pérot arrangement where the electric field of the resonant mode is mainly located in the cavity region (center) and often causes undesired effects such as mode-jumps. However, coreSEL is based on chirped optical filter which offers a resonant mode with wider spatial distribution of the electric field ...
Dissertation
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Entwicklung eines Nanoimprint-Prozesses zur Herstellung von dreidimensional strukturierten Nanopartikeln mit erhöhter mechanischer Stabilität
(2019)
The nanoimprint technology realizes already the production of two-dimensional (2D) shaped nanoparticles of different shapes and materials. These nanoparticles can be applied in advanced applications in material engineering, as well as in biology and particularly in drug-delivery systems. This work presents three-dimensional (3D) shaped nanoparticles with T-, L- and step-like cross-sections, implemented by substrate conformal imprint lithography (SCIL) and a manual soft-imprint technique. Further, 2D shaped nanoparticles ...
Dissertation
Development, Verification and Analysis of a Fault Injection Tool for Improving Dependability of FPGA Systems
(2019-11)
Field Programmable Gate Array (FPGA) has been involved in various applications in the last couple of decades, such as aerospace, biomedical instrumentation, safety-critical systems, and spacecraft, due to their remarkable features. These features include parallelism, reconfiguration, self-healing capabilities, availability, low cost and low design turn-around time. FPGA devices are sensitive to Single Event Effects (SEE), which can be caused by various sources, such as α-particles, cosmic rays, atmospheric neutrons, ...
Dissertation
Consistent Hierarchical Control in Cooperative Autonomous Driving
(2022)
This thesis is set within the context of the problem of motion planning in autonomous driving. Due to nonlinear system dynamics and non-convex constraints, this problem is challenging even under simplifying assumptions (e.g. non-cooperating traffic participants obey traffic rules, lossless inter-vehicle communication, absence of measuring errors). Typical solution approaches rely on a decomposition of the problem into subproblems which are easier to solve. This decomposition often results in a hierarchy of subproblems ...
Dissertation
Mikromechanisch durchstimmbare, dielektrische Fabry-Pérot-Filter im nahen Infrarot-Bereich: Konzept, Herstellung und Charakterisierung
(2013-12-13)
Das Ziel der vorliegenden Arbeit war die Herstellung und Charakterisierung mikromechanisch durchstimmbarer, dielektrischer Fabry-Pérot-Filter im nahen Infrarot-Bereich bei einer Zentralwellenlänge von λc = 950 nm.
Diese Bauelemente wurden auf Basis kostengünstiger Technologien realisiert, dank deren Entwicklung extreme Miniaturisierung und gleichzeitig hohe spektrale Anforderungen möglich sind. Der Vorteil solcher Filter liegt darin, dass sie direkt in einen Photodetektor integriert werden können und mit ganz wenigen ...
Dissertation
Spektrometrische Bestimmung der NO2-Konzentration im Abgas von Lastkraftwagen mit Dieselmotor unter Verwendung eines elektrostatisch durchstimmbaren Fabry-Pérot-Filters zur Reduzierung des Kraftstoffverbrauches und der Schadstoffemissionen
(2010-08-09)
Die Reduktion von Schadstoff-Emissionen und des Kraftstoffverbrauches sind für die Einhaltung von immer strenger werdenden Abgasgrenzwerten zum Schutz der menschlichen Gesundheit und der Vegetation von großer gesellschaftlicher Bedeutung. Ob Deutschland die innerstädtischen Immissionsgrenzwerte der Europäischen Union (EU) für Stickstoffdioxid (NO2) ab 2010 einhalten wird, ist fraglich. Vor allem Lastkraftwagen mit Dieselmotor emittieren einen Großteil dieses Schadstoffes, sodass man mit einer Senkung der NO2-Emissionen ...
Dissertation
Optimization of the Mechanical and Optical Properties of Tunable Optical Sensor Arrays (TOSA) for a Nanospectrometer in the Visible and Near Infrared Spectral Range
(2015-01-07)
Tunable Optical Sensor Arrays (TOSA) based on Fabry-Pérot (FP) filters, for high quality spectroscopic applications in the visible and near infrared spectral range are investigated within this work. The optical performance of the FP filters is improved by using ion beam sputtered niobium pentoxide (Nb2O5) and silicon dioxide (SiO2) Distributed Bragg Reflectors (DBRs) as mirrors. Due to their high refractive index contrast, only a few alternating pairs of Nb2O5 and SiO2 films can achieve DBRs with high reflectivity ...