Lorentzian-Corrected Apparent Exchange-Dependent Relaxation (LAREX) Ω-Plot Analysis—An Adaptation for qCEST in a Multi-Pool System: Comprehensive In Silico,In Situ,and In Vivo Studies

Based on in silico, in situ, and in vivo studies, this study aims to develop a new method for the quantitative chemical exchange saturation transfer (qCEST) technique considering multi-pool systems. To this end, we extended the state-of-the-art apparent exchange-dependent relaxation (AREX) method with a Lorentzian correction (LAREX). We then validated this new method with in situ and in vivo experiments on human intervertebral discs (IVDs) using the Kendall-Tau correlation coefficient. In the in silico experiments, we observed significant deviations of the AREX method as a function of the underlying exchange rate (k_ba) and fractional concentration (f_b) compared to the ground truth due to the influence of other exchange pools. In comparison to AREX, the LAREX-based Ω-plot approach yielded a substantial improvement. In the subsequent in situ and in vivo experiments on human IVDs, no correlation to the histological reference standard or Pfirrmann classification could be found for the f_b (in situ: τ = −0.17 p = 0.51; in vivo: τ = 0.13 p = 0.30) and k_ba (in situ: τ = 0.042 p = 0.87; in vivo: τ = −0.26 p = 0.04) of Glycosaminoglycan (GAG) with AREX. In contrast, the influence of interfering pools could be corrected by LAREX, and a moderate to strong correlation was observed for the fractional concentration of GAG for both in situ (τ = −0.71 p = 0.005) and in vivo (τ = −0.49 p < 0.001) experiments. The study presented here is the first to introduce a new qCEST method that enables qCEST imaging in systems with multiple proton pools.     

Dislocation‐Free and Atomically Flat GaN Hexagonal Microprisms for Device Applications

III‐nitrides are considered the material of choice for light‐emitting diodes (LEDs) and lasers in the visible to ultraviolet spectral range. The development is hampered by lattice and thermal mismatch between the nitride layers and the growth substrate leading to high dislocation densities. In order to overcome the issue, efforts have gone into selected area growth of nanowires (NWs), using their small footprint in the substrate to grow virtually dislocation‐free material. Their geometry is defined by six tall side‐facets and a pointed tip which limits the design of optoelectronic devices. Growth of dislocation‐free and atomically smooth 3D hexagonal GaN micro‐prisms with a flat, micrometer‐sized top‐surface is presented. These self‐forming structures are suitable for optical devices such as low‐loss optical cavities for high‐efficiency LEDs. The structures are made by annealing GaN NWs with a thick radial shell, reforming them into hexagonal flat‐top prisms with six equivalents either m‐ or s‐facets depending on the initial heights of the top pyramid and m‐facets of the NWs. This shape is kinetically controlled and the reformation can be explained with a phenomenological model based on Wulff construction that have been developed. It is expected that the results will inspire further research into micron‐sized III‐nitride‐based devices.     

Gegenüberstellung der statischen Berechnungen einer Stahlbrücke nach DIN ‐Fachberichten und bisher gültigem Regelwerk

Structural analysis and design of a steel bridge – comparing the new standards with the previous ones. The DIN ‐Fachberichte were adopted in 2003 as new standards for structural analysis and design of bridges. Their application results in changes of loading, design methods and design of bridges compared to the previous regulations. This contribution will illustrate the effects of the new standards on the steel construction of a railway bridge by comparing its structural analysis and design both according to new standards and previous ones. As a result the comparison shows that mainly due to more conservative load distribution in the road bed the trackway needs to be reinforced.     

An integrated approach to Deacon chemistry on RuO2-based catalysts

Rationally designed RuO₂-based Deacon catalysts can contribute to massive energy saving compared to the current electrolysis process in chemically recycling HCl to produce molecular chlorine. Here, we report on our integrated approach between state-of-the-art experiments and calculations. The aim is to understand industrial Deacon catalyst in its realistic surface state and to derive mechanistic insights into this sustainable reaction. We show that the practically relevant RuO₂/SnO₂ consists of two major RuO₂ morphologies, namely 2–4 nm-sized particles and 1–3-ML-thick epitaxial RuO₂ films attached to the SnO₂ support particles. A large fraction of the small nanoparticles expose {1 1 0} and {1 0 1} facets, whereas the film grows with the same orientations, due to the preferential surface orientation of the rutile-type support. Steady-state Deacon kinetics indicate a medium-to-strong positive effect of the partial pressures of reactants and deep inhibition by both water and chlorine products. Temporal Analysis of Products and in situ Prompt Gamma Activation Analysis strongly suggest a Langmuir–Hinshelwood mechanism and that adsorbed Cl poisons the surface. Under relevant operation conditions, the reactivity is proportional to the coverage of a specific atomic oxygen species. On the extensively chlorinated surface that can be described as surface oxy-chloride, oxygen activation is the rate-determining step. DFT-based micro-kinetic modeling reproduced all experimental observations and additionally suggested that the reaction is structure sensitive. Out of the investigated models, the 2 ML RuO₂ film-covered SnO₂ gives rise to significantly higher reactivity than the (1 0 1) surface, whereas the 1 ML film seems to be inactive.