Platten-Modellversuche zur Erklärung des Entstehens von Eigenspannungen beim Schweißen

Ermittlung von Temperaturverteilung, Abkühlungsverlauf, Gefüge, Härte und Eigenspannungen bei mittig erwärmten Stahlplatten aus St 37-3 und StE 70. Einfluß des Umwandlungsverhaltens auf die Eigenspannungen. Deutung der Eigenspannungsentstehung beim Zusammenwirken von Wärme- und Umwandlungsspannungen.     

Der Einfluß des Umwandlungsverhaltens auf die Schweißeigenspannungen bei Stahl

Untersuchung des Schrumpfungs- und Umwandlungsverhaltens von Schweißproben aus austenitischem und hochfestem Grund- und Schweißzusatzwerkstoff. Messung von Eigenspannungen im Schweißnahtbereich. Erklärung der Eigenspannungen aus Temperaturverläufen und Härtemessungen im Schweißnahtbereich sowie aus Weg-Zeit-Aufschreibungen für das freie Ende einseitig eingespannter Schweißproben. Deutung der Umwandlungsvorgänge durch Zeit-Temperatur-Umwandlungsschaubilder.     

Activity of α‐Aminoadipate Reductase Depends on the N‐Terminally Extending Domain

L ‐α‐Aminoadipic acid reductases catalyze the ATP‐ and NADPH‐dependent reduction of L ‐α‐aminoadipic acid to the corresponding 6‐semialdehyde during fungal L ‐lysine biosynthesis. These reductases resemble peptide synthetases with regard to their multidomain composition but feature a unique domain of elusive function—now referred to as an adenylation activating (ADA) domain—that extends the reductase N‐terminally. Truncated enzymes based on NPS3, the L ‐α‐aminoadipic acid reductase of the basidiomycete Ceriporiopsis subvermispora, lacking the ADA domain either partially or entirely were tested for activity in vitro, together with an ADA‐adenylation didomain and the ADA domainless adenylation domain. We provide evidence that the ADA domain is required for substrate adenylation: that is, the initial step of the catalytic turnover. Our biochemical data are supported by in silico modeling that identified the ADA domain as a partial peptide synthetase condensation domain.     

Kinetically Stable Oxide Overlayers on Mo3P Nanoparticles Enabling Lithium–Air Batteries with Low Overpotentials and Long Cycle Life

The main drawbacks of today's state-of-the-art lithium–air (Li–air) batteries are their low energy efficiency and limited cycle life due to the lack of earth-abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo₃P) nanoparticles with an exceptional activity—ORR and OER current densities of 7.21 and 6.85 mA cm⁻² at 2.0 and 4.2 V versus Li/Li⁺, respectively—in an oxygen-saturated non-aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance—Tafel slopes of 35 and 38 mV dec⁻¹ for ORR and OER, respectively—resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li–air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo₃P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.     

Fluorescence Lifetime Imaging Microscopy (FLIM) of Intracellular Transport by Means of Doubly Labelled siRNA Architectures

For monitoring the intracellular pathway of small interfering RNA (siRNA), both strands were labelled at internal positions by two ATTO dyes as an interstrand Förster resonance energy transfer pair. siRNA double strands show red emission and a short donor lifetime as readout, whereas siRNA antisense single strands show green emission and a long donor lifetime. This readout signals if GFP silencing can be expected (green) or not (red). We attached both dyes to three structurally different alkyne anchors by postsynthetic modifications. There is only a slight preference for the ribofuranoside anchors with the dyes at their 2’-positions. For the first time, the delivery and fate of siRNA in live HeLa cells was tracked by fluorescence lifetime imaging microscopy (FLIM), which revealed a clear relationship between intracellular transport using different transfection methods and knockdown of GFP expression, which demonstrates the potential of our siRNA architectures as a tool for future development of effective siRNA.     

Epitaxial Strain Control of Relaxor Ferroelectric Phase Evolution

Understanding and ultimately controlling the large electromechanical effects in relaxor ferroelectrics requires intimate knowledge of how the local‐polar order evolves under applied stimuli. Here, the biaxial‐strain‐induced evolution of and correlations between polar structures and properties in epitaxial films of the prototypical relaxor ferroelectric 0.68PbMg_1/3Nb_2/3O₃–0.32PbTiO₃ are investigated. X‐ray diffuse‐scattering studies reveal an evolution from a butterfly‐ to disc‐shaped pattern and an increase in the correlation‐length from ≈8 to ≈25 nm with increasing compressive strain. Molecular‐dynamics simulations reveal the origin of the changes in the diffuse‐scattering patterns and that strain induces polarization rotation and the merging of the polar order. As the magnitude of the strain is increased, relaxor behavior is gradually suppressed but is not fully quenched. Analysis of the dynamic evolution of dipole alignment in the simulations reveals that, while, for most unit‐cell chemistries and configurations, strain drives a tendency toward more ferroelectric‐like order, there are certain unit cells that become more disordered under strain, resulting in stronger competition between ordered and disordered regions and enhanced overall susceptibilities. Ultimately, this implies that deterministic creation of specific local chemical configurations could be an effective way to enhance relaxor performance.     

Mix and Match: Organic and Inorganic Ions in the Perovskite Lattice

Materials science evolves to a state where the composition and structure of a crystal can be controlled almost at will. Given that a composition meets basic requirements of stoichiometry, steric demands, and charge neutrality, researchers are now able to investigate a wide range of compounds theoretically and, under various experimental conditions, select the constituting fragments of a crystal. One intriguing playground for such materials design is the perovskite structure. While a game of mixing and matching ions has been played successfully for about 150 years within the limits of inorganic compounds, the recent advances in organic–inorganic hybrid perovskite photovoltaics have triggered the inclusion of organic ions. Organic ions can be incorporated on all sites of the perovskite structure, leading to hybrid (double, triple, etc.) perovskites and inverse (hybrid) perovskites. Examples for each of these cases are known, even with all three sites occupied by organic molecules. While this change from monatomic ions to molecular species is accompanied with increased complexity, it shows that concepts from traditional inorganic perovskites are transferable to the novel hybrid materials. The increased compositional space holds promising new possibilities and applications for the universe of perovskite materials.