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Now showing items 11-20 of 69
Dissertation
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 ...
Konferenzveröffentlichung
Weight reduction of DC/DC converters using controllable inductors
(VDE Verlag, 2019-07)
Controllable inductors can be realized by introducing auxiliary windings into the device that partially saturate the core and allow variation of the inductance value. This can be used to achieve zero-voltage switching in a DC/DC converter over a wide load range while at the same time the weight of the inductor is reduced. In this paper the possible size and weight reduction and the influence on the efficiency is calculated and compared to other solutions. The results are verified in a prototype.
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
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 ...
Aufsatz
Effect of Auger recombination and leakage on the droop in InGaN/GaN quantum well LEDs
(Optical Society of America, 2014)
We investigate the effect of the epitaxial structure and the acceptor doping profile on the efficiency droop in InGaN/GaN LEDs by the physics based simulation of experimental internal quantum efficiency (IQE) characteristics. The device geometry is an integral part of our simulation approach. We demonstrate that even for single quantum well LEDs the droop depends critically on the acceptor doping profile. The Auger recombination was found to increase stronger than with the third power of the carrier density and has ...
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, ...
Buch
Strom – fit für die Zukunft?
(Görich & Weiershäuser, 2019-04-02)
Das 2008 in gedruckter Form und als pdf veröffentlichte Buch liegt hier in neuester Überarbeitung vom 02.04.2019 vor.
Es stellt mögliche Komponenten eines "integrierten Balancing-Management" vor, das die Sekundärregelung unter Einbeziehung aller Flexibilitätsoptionen, insbesondere der gesamten Verbrauchsseite, ressourcenoptimiert realisieren könnte. Mehrere denkbare Instrumente für das verteilte Handling von (drohenden) Überlastungs- und Notfallsituationen (auch langdauernde extreme Dunkelflauten) werden beschrieben.
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 ...