Study of the catalytic combustion of lean hydrogen-air mixtures in a monolith reactor

This paper presents an experimental study of catalytic hydrogen combustion that used commercial catalysts containing Pt in a honeycomb monolith reactor in a plug flow configuration. The emphasis is on determining global kinetics in the case of low hydrogen content. Measurements of the temperature and composition of the reaction product at the outlet in the steady state condition at the different initial compositions of hydrogen and total volumetric feed rates were performed. The conversion of hydrogen was determined in parallel to the composition of the reaction product at the outlet using GC as well as by means of the thermodynamic approach using material and energy balances. The influence of the flow rate and initial molar fraction of hydrogen on hydrogen conversion is shown. A kinetic expression of the Arrhenius type is proposed with the reaction first order in hydrogen and zero order in oxygen for the overall process of the oxidation of hydrogen in lean hydrogen-air mixtures. The determined activation energy was in good agreement with the desorption activation energy for O₂ from graphene-covered Pt(111) surfaces using temperature-programmed desorption. This result shows transport-limitations for heterogeneous hydrogen conversion in catalytic hydrogen combustion.     

Sustainable Syngas Production by High-Temperature Co-electrolysis

High-temperature co-electrolysis shows comparable performance to steam electrolysis. Current densities above 1 A cm⁻² can be reached between 700 °C and 800 °C. Tailor-made syngas is produced, mainly determined by the reactant ratio. The experimental results are supported by modeling. Durability tests with cathode-supported cells show increased voltage degradation rates during electrolysis compared to fuel cell operation. Nickel depletion is found to be the main cause.     

Synthesis,Chiral Separation,Absolute Configuration Assignment,and Biological Activity of Enantiomers of Retro‐1 as Potent Inhibitors of Shiga Toxin

The Shiga toxin (Stx) family is composed of related protein toxins produced by the bacteria Shigella dysenteriae and certain pathogenic strains of E. coli. No effective therapies for Stx intoxication have been developed yet. However, inhibitors that act on the intracellular trafficking of these toxins may provide new options for the development of therapeutic strategies. This study reports the synthesis, chromatographic separation, and pharmacological evaluation of the two enantiomers of Retro‐1, a compound active against Stx and other such protein toxins. Retro‐1 works by inhibiting retrograde transport of these toxins inside cells. In vitro experiments proved that the configuration of the stereocenter at position 5 is not crucial for the activity of this compound. X‐ray diffraction data revealed (S)‐Retro‐1 to be slightly more active than (R)‐Retro‐1.     

Urban traffic modeling and pattern detection using online map vendors and self-organizing maps

Typical traffic modeling approaches, such as network-based methods and simulation models, have been shown inadequate for urban-scale studies due to the fidelity issue of models. As a go-around, data-driven models have received increasing attention recently. However, most data-driven methods have been restricted by their data source and cannot be scaled up to manage urban- and regional-scale studies. Regarding this issue, this research proposes a pipeline that collects traffic data from online map vendors to bypass data limitations for large-scale studies. The study consists of two experiments: 1) recognizing the dominant traffic patterns of cities and 2) site-specific predictions of typical traffic or the most probable locations of patterns of interests. The experiments were conducted on 32 Swiss cities using traffic data that were collected for a two-month period. The results show that dominant patterns can be extracted from the temporal traffic data, and similar patterns exist not only in various parts of a city but also in different cities. Moreover, the results reveal that a country-level lockdown decreased traffic congestions in regional highways but increased those connections near the city centers and the country borders.     

Advances in macro-scale laser processing

Laser material processing is a technology with an increasing number of industrial applications, especially for aviation and automotive. The present keynote paper focusses on the advances in macro-scale laser processing, meaning that the laser generated structures are large enough to be visible with the naked eye. Next to that, also the reasons for the advances, especially the improvements regarding the power and the beam quality of the laser sources, the higher capabilities of the systems technologies and an increasing process understanding are shown. Nevertheless, challenges like a holistic understanding of the physical phenomena and the evolution of defects in some processing methods remain to be solved in future.     

Vertrauensvolle E-Mail-Kommunikation

Der ?elektronische Brief“ bzw. die elektronische Mail (E-Mail) ist seit über 30 Jahren im privaten wie beruflichen Umfeld im Einsatz. Behörden, Steuerbüros, Krankenhäuser, Finanzinstitute und viele weitere Gruppen versenden und empfangen E-Mails, um Informationen auszutauschen. Innerhalb kurzer Zeit findet eine E-Mail ihren Weg vom Sender in Deutschland zum Empfänger in beispielsweise den USA. Wie funktioniert das? Und was hat es mit E-Mail-Verschlüsselung auf sich? Dieser Artikel betrachtet die grundlegende technische Funktionsweise der E-Mail sowie Hintergründe und Funktionsweise der Verschlüsselung mit S/MIME und PGP.     

Fusion of indigenous knowledge and gamma spectrometry for soil mapping to support knowledge-based extension in Tanzania

Food shortages often threaten central Tanzania. Sustainable action adapted to local environmental conditions is desperately needed. In the framework of the TransSEC project, two food value chains in the Dodoma region of Tanzania were inspected in order to make propositions for improvement , spanning from soil preparation to product consumption. Therefore, soil mapping approaches were required to obtain rapid and reliable information. This would enable local farmers to participate in the development of upgrading strategies and extensionists to develop recommendations that take local soil conditions into account. In this study, a combination of participatory soil mapping and gamma ray spectrometry-assisted transect mapping was applied to establish local soil maps of two villages in the Dodoma region. Participatory mapping included key informant interviews, group discussions and transect walks. Local farmers indicated reference profiles for local soil types. Their gamma radiation signatures delivered base information for further soil exploration and soil unit delineation in the field. Finally, high resolution satellite images were used to establish the village soil maps. This approach allows capture of the major soil differences within a village territory and reduction of the costs of chemical analyses. Challenges were soil unit separation with gamma ray spectrometry due to erosional redistribution processes at the surface, correct translation of specific terms from local tongues as well as variable individual soil knowledge of local participants. Ultimately, the combination of local soil knowledge with innovative scientific mapping yielded quick results with sufficient spatial resolution for extension work.     

Eine abgeschirmte Schleifdrahtbrücke zur Feinmessung von Verlustwinkeln an hochwertigen flüssigen Isolierstoffen

Zusammenfassung Die Verwendung von Schleifdrähten mit vollkommen gleicher Zeitkonstante als untere Brückenzweige ermöglichte es, eine Verlustwinkelmeßbrücke nach dem Schering-Prinzip zu entwickeln, bei der die Einwirkung der Zeitkonstantenänderung auf den Verlustwinkel, die infolge der Verstellung vonR ₃ auftritt, vermieden wird. Durch einen zweiten Abgriff anR ₃ wurde erreicht, daß der Widerstand, der sich sonst mit der Prüfkapazität in Reihe schalten und so einen größeren Verlustwinkel vortäuschen würde, kurzgeschlossen wird. Der Einfluß der Störkapazitäten, die sich parallel zu den unteren Brückenzweigen legen, wird durch Anwendung der doppelten Abschirmung und Kompensation der Störkapazität parallelR ₄ mittels astatischer Gegeninduktivität beseitigt. Hierdurch wird bewirkt, daß ein Hilfszweig nach K. W. Wagner nicht benötigt wird.Bei dem neuen Aufbau der Mauschen Brücke wurde in den Nullzweig ein Übertrager gelegt, um eine bessere Anpassung an den hohen Innenwiderstand der Brücke zu erreichen. Ein Meßbereichschalter in der Hilfsbrücke ermöglicht die Messung von Prüfkapazitäten vom 1/60 fachen bis zum6fachen Betrag des Vergleichskondensators. Im dritten Brückenzweig wurde der Widerstand, der zum Abgleich des tg dient, vor den verlustlosen Kondensator gelegt. Hierdurch wird der Einfluß der Verlustkapazität, die sich vom Verbindungspunkt Widerstand—Normalkapazität nach Erde hin legt, vernachlässigbar klein.Von der Fakultät für Maschinenwesen der T. H. Hannover genehmigte Dissertation.Diese Arbeit wurde im Elektro-Institut I der Technischen Hochschule Hannover ausgeführt. Für die stete Förderung der Arbeit und die wertvollen Anregungen bin ich Herrn Prof. Dr. Schering zu tiefem Dank verpflichtet.Den Firmen Hartmann & Braun und Siemens & Halske möchte ich an dieser Stelle ebenfalls meinen Dank dafür aussprechen, daß sie zum Aufbau der Brücke verwendetes Material kostenlos zur Verfügung stellten.