Modellgestützte Interpretation der elektrochemischen Charakteristik von Festoxid-Brennstoffzellen mit Ni/YSZ-Cermetanoden

In dieser Arbeit wird die Entwicklung, Validierung und Anwendung von Multiskalenmodellen für die detaillierte Beschreibung einer Festoxid-Brennstoffzelle (Solid Oxide Fuel Cell, SOFC) mit Ni/YSZ (Nickel/Yttriumoxid-stabilisiertes Zirkonoxid)-Cermetanoden gezeigt. Ziel ist es, die chemisch-physikalischen Prozesse innerhalb einer SOFC zu identifizieren, die sich in Form von Polarisationsverlusten in den Impedanzspektren und Polarisationskurven zeigen. Das Modell der SOFC umfasst eine elementarkinetische Beschreibung der Elektrochemie einschließlich der Bildung einer elektrischen Doppelschicht an der Elektrode/Elektrolyt-Phasengrenze der Cermetanode, eine homogenisierte Beschreibung des Ladungs- und Gasphasentransports in den Elektroden sowie eine makroskopische Beschreibung des konvektiven und diffusiven Gastransports über den Elektroden. Durch den Vergleich mit Impedanzmessungen an symmetrischen Zellen (Universität Karlsruhe) liefert dieses Modell erstmals eine vollständige Beschreibung des Impedanzverhaltens einer diffusiv gasversorgten Cermetanode, die die Identifizierung der drei dominierenden Verlustprozesse ermöglicht. Die Erweiterung des Modells auf die Beschreibung einer segmentierten SOFC zeigt in Übereinstimmung mit Messungen (Deutsches Zentrum für Luft und Raumfahrt) starke Gradienten der Stromdichte und Gaskonzentrationen

Phase estimation of single tones next to modulated signals in the medium frequency R-mode system

Position, navigation, and timing information are critical to today’s infrastructures; as a result, the possibility of estimating ranges is being explored in more and more radio systems. One way to achieve this is to extend the modulation with time-synchronised aiding carriers and to estimate their phase at the receiver side. In this paper, we present two ways to minimise the negative influence of the modulation on the phase estimation. We show that the classical maximum likelihood estimator is still an efficient estimator for our problem, using a medium-frequency R-Mode signal as an example, and is therefore used in receiver designs. We then describe two possible ways to precondition the signal to increase the accuracy for short observations. As a first approach, we describe how window functions can positively change the signal-to-noise ratio for our estimation. As a second approach, we show the use of a narrowband bandpass filter. Finally, we show that these approaches, applied to real measurements, improve the variance of the estimate by up to two orders of magnitude

Investigation of the ubiquitin-specific protease UBP41 and of the lysosomal cysteine proteases cathepsin-L and cathepsin-B as potential mediators of proapoptotic signalling

Two projects are described within the scope of this thesis. The first project characterizes the ubiquitin-specific protease UBP41 as a protein which upon overexpression causes apoptosis induction in several mammalian cancer cell lines. The second project investigates a possible involvement of the lysosomal cysteine proteases cathepsin-L and cathepsin-B in apoptosis pathways induced by distinct death stimuli, in particular by the tumor necrosis factor a (TNF-a). Therefore, both projects examine a possible regulation of apoptosis induction by proteases that are part of one of the two major systems of protein degradation. UBP41 as a protease with deubiquitylating activity is expected to play a role in the ubiquitin/proteasome system which is the major proteolytic apparatus for the degradation of cytosolic proteins. Cathepsins, on the other hand, are lysosomal proteases that participate in the breakdown of membrane-associated proteins and of extracellular proteins that are taken up by endocytosis. Both, the ubiquitin/proteasome system as well as lysosomal proteases have been previously implicated in the regulation and mediation of apoptosis, and it therefore appeared particularly attractive to further study the effect of UBP41 and cathepsins on cell death signalling in more detail.Mittels eines genetischen cDNA Screening-Verfahren wurden neuartige, bislang noch nicht identifizierte dominant proapoptotische Faktoren isoliert. Darunter war ein cDNA Klon, welcher für die Ubiquitin-spezifische Protease UBP41 kodierte, sowie ein weiterer cDNA Klon, welcher für die lysosomale Protease Cathepsin-L kodierte. Es wurden im weiteren der proapoptotische Effekt von UBP41 sowie der mögliche Zusammenhang zwischen Cathepsin-Expressionsleveln und der Sensitiviät von Tumorzellen gegenüber Apoptose-Induktion studiert. Die Dissertation leistet einen Beitrag zu der in der aktuellen Apoptoseforschung intensiv diskutierten Fragestellung, ob und auf welche Weise Nicht-Caspase Cystein-Proteasen einen Einfluss auf die Vermittlung apoptotischer Signalwege haben

Worldwide Availability of Maritime Medium-Frequency Radio Infrastructure for R-Mode-Supported Navigation

The Ranging Mode (R-Mode), a maritime terrestrial navigation system under development, is a promising approach to increase the resilient provision of position, navigation and timing (PNT) information for bridge instruments, which rely on Global Navigation Satellite Systems (GNSS). The R-Mode utilizes existing maritime radio infrastructure such as marine radio beacons, which support maritime traffic with more reliable and accurate PNT data in areas with challenging conditions. This paper analyzes the potential service, which the R-Mode could provide to the mariner if worldwide radio beacons were upgraded to broadcast R-Mode signals. The authors assumed for this study that the R-Mode is available in the service area of the 357 operational radio beacons. The comparison with the maritime traffic, which was generated from a one-day worldwide Automatic Identification System (AIS) Class A dataset, showed that on average, 67% of ships would operate in a global R-Mode service area, 40% of ships would see at least three and 25% of ships would see at least four radio beacons at a time. This means that R-Mode would support 25% to 40% of all ships with position and 67% of all ships with PNT integrity information. The relatively high number of supported ships compared to the total radio beacon coverage of about 9% of the earth’s surface is caused by the good coverage of busy ports and areas such as the coast of China, North Sea and Baltic Sea. These numbers emphasize the importance of marine radio beacons for the R-Mode system

Availability of Maritime Radio Beacon Signals for R-Mode in the Southern Baltic Sea

This paper presents an overview of the development of a terrestrial positioning system called Ranging Mode (R-Mode) in the Southern Baltic Sea region which utilizes already existing maritime radio infrastructure. Here, an R-Mode testbed is planned to be set up until 2020 that meets maritime user needs for resilient PNT. First measurements of radio beacon signals on-board a vessel sailing in the Southern Baltic Sea show the good availability of beacon signals in this region. A comparison of received signals with a coverage prediction based on the nominal range of radio beacons shows the shortcoming of this approach and emphasizes the need for more elaborated coverage predictions which consider all effects of medium frequency wave propagation at day and night. In the measurements results the skywave has a major impact on the beacon signal stability in the night. The time stability of the signal amplitude seems to be a good indicator for disturbed reception conditions

Prediction of Ground Wave Propagation Delay for MF R-Mode

Time delays caused by ground wave propagation are the primary source of systematic error limiting the performance of the medium-frequency R-Mode radionavigation system. To achieve the desired ranging accuracy and compensate these delays, we have conceived a comprehensive correction scheme based on the prediction and application of the Atmospheric and Ground wave Delay Factor (AGDF). The AGDF was computed and mapped in 2D for a number of MF R-Mode transmitters in the Baltic Sea that were embedded into the receiver and evaluated during a large-scale measurement campaign. Our results show that the proposed AGDF approach is valid for the MF R-Mode system and provides accurate corrections of ground wave propagation delays within the performance requirements

Improving MF R-Mode ranging performance with measureemnt-based correction factors

The advent of global satellite navigation systems (GNSS) has revolutionized the provision of position, navigation and timing (PNT) information. Thought to be always available and reliable, these systems may experience outages and they can be threatened by interference events. In such cases, alternative positioning, navigation and timing (APNT) systems play a key role. In the maritime domain Ranging Mode, called R-Mode, is a rising terrestrial alternative to GNSS. R-Mode exploits medium frequency (MF) signals transmitted by maritime radio beacons in one possible implementation. It is well-known that MF radio waves are affected by attenuation and distortion caused by a change in the electrical properties of the ground along the propagation path. Additionally, terrain elevation variation and large metallic infrastructures introduce further distortions in the signal, decreasing the overall ranging performance. In this paper we propose a novel approach to compensate for this effect based on direct range measurements. The theory is explained in depth and a test case, based on real measurement campaign data, to validate the technique is also presented

Performance Assessment of the Medium Frequency R-Mode Baltic Testbed at Sea near Rostock

Global Navigation Satellite Systems (GNSS) are the primary source of position, navigation and timing (PNT) information in the maritime domain. Nevertheless, there is a pressing need for alternative absolute position information to serve as a backup when GNSS is not trustworthy or usable. One possible alternative navigation system is the terrestrial Ranging Mode, also known as the R-Mode. It reuses medium frequency (MF) radio beacons and base stations of the very high frequency data exchange system (VDES) for the transmission of synchronised signals in the service areas of those stations. A large-scale R-Mode testbed is available in the southern Baltic Sea with eight MF radio beacons transmitting R-Mode signals. These signals suffer the self-interference generated by the reflection of the radio wave from the ionosphere at night. The reflected signal, known as the sky wave in the literature, is a form of multipath, which decreases the accuracy of the system. In our work, we present the analysis of measurements obtained with the research vessel Deneb. The horizontal accuracy achieved in the optimal condition was 15.1 m (95%), whereas under the sky wave, the accuracy decreased to 55.3 m. The results are a starting point for the further development of the MF R-Mode system

Improving MF R-Mode ranging performance with measureemnt-based correction factors

The advent of global satellite navigation systems (GNSS) has revolutionized the provision of position, navigation and timing (PNT) information. Thought to be always available and reliable, these systems may experience outages and they can be threatened by interference events. In such cases, alternative positioning, navigation and timing (APNT) systems play a key role. In the maritime domain Ranging Mode, called R-Mode, is a rising terrestrial alternative to GNSS. R-Mode exploits medium frequency (MF) signals transmitted by maritime radio beacons in one possible implementation. It is well-known that MF radio waves are affected by attenuation and distortion caused by a change in the electrical properties of the ground along the propagation path. Additionally, terrain elevation variation and large metallic infrastructures introduce further distortions in the signal, decreasing the overall ranging performance. In this paper we propose a novel approach to compensate for this effect based on direct range measurements. The theory is explained in depth and a test case, based on real measurement campaign data, to validate the technique is also presented