Estimating fossil fuel carbon dioxide (ffCO2) emissions in the Rhine Valley metropolitan region from local atmospheric observations in Heidelberg

This cumulative dissertation investigates the potential of radiocarbon (14C)-based and carbon monoxide (∆CO)-based fossil fuel CO2 (∆ffCO2) estimates from the urban observation site Heidelberg to deduce the seasonal cycle of the ffCO2 emissions in the Rhine Valley. For this, the CarboScope inversion system is used to investigate the benefit of few but accurate 14C-based ∆ffCO2 estimates from about 100 hourly flask samples collected in 2019 and 2020, compared to a continuous ∆CO-based ∆ffCO2 record with about 4 times larger uncertainty. The urban observation site with large ffCO2 point sources in the vicinity places special demands on the transport model. Therefore, a method is developed for the high-resolution Weather Research and Forecasting - Stochastic Time-Inverted Lagrangian Transport model (WRF-STILT) to represent the effective emission heights of point sources. This work shows that the 14C-based ∆ffCO2 observations contain the seasonal cycle of the ffCO2 emissions, but do not lead to robust inversion results. In contrast, the continuous ∆CO-based ∆ffCO2 estimates provide robust and data-driven seasonal cycles that show the distinct COVID-19 signal in 2020 and are suitable for validating the amplitude and phasing of the seasonal cycle of the emission inventories in the main footprint of Heidelberg

The role of string-like, supramolecular assemblies in reentrant supernematic liquid crystals

Using a combination of isothermal-isobaric Monte Carlo and microcanonical molecular dynamics we investigate the relation between structure and self-diffusion in various phases of a model liquid crystal using the Gay-Berne-Kihara potential. These molecules are confined to a mesoscopic slit-pore with atomically smooth substrate surfaces. As reported recently [see M. G. Mazza {\em et al.}, Phys. Rev. Lett. {\bf 105}, 227802 (2010)], a reentrant nematic (RN) phase may form at sufficiently high pressures/densities. This phase is characterized by a high degree of nematic order and a substantially enhanced self-diffusivity in the direction of the director $\hat{\bm{n}}$ which exceeds that of the lower-density nematic and an intermittent smectic A phase by about an order of magnitude. Here we demonstrate that the unique transport behavior in the RN phase may be linked to a confinement-induced packing effect which causes the formation of supramolecular, string-like conformations. The strings consist of several individual molecules that are capable of travelling in the direction of $\hat{\bm{n}}$ as individual "trains" consisting of chains of molecular "cars". Individual trains run in parallel and may pass each other at sufficiently high pressures.Comment: 24 page

Entropy-driven enhanced self-diffusion in confined reentrant supernematics

We present a molecular dynamics study of reentrant nematic phases using the Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities above those characteristic of smectic A phases, reentrant nematic phases form that are characterized by a large value of the nematic order parameter $S\simeq1$. Along the nematic director these "supernematic" phases exhibit a remarkably high self-diffusivity which exceeds that for ordinary, lower-density nematic phases by an order of magnitude. Enhancement of self-diffusivity is attributed to a decrease of rotational configurational entropy in confinement. Recent developments in the pulsed field gradient NMR technique are shown to provide favorable conditions for an experimental confirmation of our simulations.Comment: 10 pages, 5 figure

Heterogeneous Pd catalysts as emulsifiers in Pickering emulsions for integrated multistep synthesis in flow chemistry

Within the “Compartmentalised Smart Factory” approach of the ONE-FLOW project the implementation of different catalysts in “compartments” provided by Pickering emulsions and their application in continuous flow is targeted. We present here the development of heterogeneous Pd-catalysts that are ready to be used in combination with biocatalysts for catalytic cascade syntheses of active pharmaceutical ingredients (APIs). In particular, we focus on the application of the catalytic systems for Suzuki-Miyaura cross coupling reactions, which is the key step in the syntheses of the targeted APIs valsartan and sacubitril. An immobilised enzyme will accomplish the final product formation via hydrolysis. In order to create large interfacial area for the catalytic reactions and to keep the reagents separated until required, the catalyst particles are used to stabilise Pickering emulsions of oil and water. A set of Ce-Sn-Pd-oxides with the molecular formula Ce0.99-xSnxPd0.01O2-(x= 0-0.99) has been prepared utilising a simple single-step solution combustion method. The high applicability of the catalysts for different functional groups and their minimal leaching behaviour is demonstrated with various Suzuki-Miyaura cross coupling reactions in batch as well as in continuous flow employing the so-called “Plug & Play reactor”. Finally, we demonstrate the use of these particles as the sole emulsifier of oil + water emulsions for a range of oils

User Roles on Peer-to-Peer Sharing Platforms: A Critical Review of the Literature and Recommended Remedies

The success of sharing platforms such as Airbnb and Uber sparked interests in research, practice, and legislation in equal measures. However, studies about user roles on sharing platforms are very heterogeneous and have yet not dived into the theoretical complexity of these roles. In order to prevent incomparability of results and scattered theory building, this study reviews existing literature and identifies flaws in terminology and conceptualization of user roles and in applied measurement approaches. We discuss why these flaws matter and how they can be resolved. Finally, we propose a research agenda and emphasize to study the role of the prosumer, why different user roles lead to differences in constructs, and how the transition of user roles takes place

Oxide Free Wire Arc Sprayed Coatings—An Avenue to Enhanced Adhesive Tensile Strength

Conventionally, thermal spraying processes are almost exclusively carried out in an air atmosphere. This results in oxidation of the particles upon thermal spraying, and thus, the interfaces of the splats within the coating are oxidized as well. Hence, a full material bond strength cannot be established. To overcome this issue, a mixture of monosilane and nitrogen was employed in the present study as the atomising and environment gas. With this approach, an oxygen partial pressure corresponding to an extreme-high vacuum was established in the environment and oxide-free coatings could be realized. It is shown that the oxide-free particles have an improved substrate wetting behaviour, which drastically increases the adhesive tensile strength of the wire arc sprayed copper coatings. Moreover, the altered deposition conditions also led to a significant reduction of the coating porosity