Magnetic anomalies in the spin chain system, Sr3_3Cu1−x_{1-x}Znx_xIrO6_6

We report the results of ac and dc magnetization (M) and heat-capacity (C) measurements on the solid solution, Sr$_3$Cu$_{1-x}$Zn$_x$IrO$_6$. While the Zn end member is known to form in a rhombohedral pseudo one-dimensional K$_4$CdCl$_6$ structure with an antiferromagnetic ordering temperature of (T$_N$ =) 19 K, the Cu end member has been reported to form in a monoclinically distorted form with a Curie temperature of (T$_C$ =) 19 K. The magnetism of the Zn compound is found to be robust to synthetic conditions and is broadly consistent with the behavior known in the literature. However, we find a lower magnetic ordering temperature (T$_o$) for our Cu compound (~ 13 K), thereby suggesting that T$_o$ is sensitive to synthetic conditions. The Cu sample appears to be in a spin-glass-like state at low temperatures, judged by a frequency dependence of ac magnetic susceptibility and a broadening of the C anomaly at the onset of magnetic ordering, in sharp contrast to earlier proposals. Small applications of magnetic field, however, drive this system to ferromagnetism as inferred from the M data. Small substitutions for Cu/Zn (x = 0.75 or 0.25) significantly depress magnetic ordering; in other words, T$_o$ varies non-monotonically with x (T$_o$ ~ 6, 3 and 4 K for x = 0.25, 0.5, and 0.67 respectively). The plot of inverse susceptibility versus temperature is non-linear in the paramagnetic state as if correlations within (or among) the magnetic chains continuously vary with temperature. The results establishComment: 7 pages, 7 figures, Revte

Bottom mixed layer oxygen dynamics in the Celtic Sea

The seasonally stratified continental shelf seas are highly productive, economically important environments which are under considerable pressure from human activity. Global dissolved oxygen concentrations have shown rapid reductions in response to anthropogenic forcing since at least the middle of the twentieth century. Oxygen consumption is at the same time linked to the cycling of atmospheric carbon, with oxygen being a proxy for carbon remineralisation and the release of CO2. In the seasonally stratified seas the bottom mixed layer (BML) is partially isolated from the atmosphere and is thus controlled by interplay between oxygen consumption processes, vertical and horizontal advection. Oxygen consumption rates can be both spatially and temporally dynamic, but these dynamics are often missed with incubation based techniques. Here we adopt a Bayesian approach to determining total BML oxygen consumption rates from a high resolution oxygen time-series. This incorporates both our knowledge and our uncertainty of the various processes which control the oxygen inventory. Total BML rates integrate both processes in the water column and at the sediment interface. These observations span the stratified period of the Celtic Sea and across both sandy and muddy sediment types. We show how horizontal advection, tidal forcing and vertical mixing together control the bottom mixed layer oxygen concentrations at various times over the stratified period. Our muddy-sand site shows cyclic spring-neap mediated changes in oxygen consumption driven by the frequent resuspension or ventilation of the seabed. We see evidence for prolonged periods of increased vertical mixing which provide the ventilation necessary to support the high rates of consumption observed

Oxygen dynamics in shelf seas sediments incorporating seasonal variability

Shelf sediments play a vital role in global biogeochemical cycling and are particularly important areas of oxygen consumption and carbon mineralisation. Total benthic oxygen uptake, the sum of diffusive and faunal mediated uptake, is a robust proxy to quantify carbon mineralisation. However, oxygen uptake rates are dynamic, due to the diagenetic processes within the sediment, and can be spatially and temporally variable. Four benthic sites in the Celtic Sea, encompassing gradients of cohesive to permeable sediments, were sampled over four cruises to capture seasonal and spatial changes in oxygen dynamics. Total oxygen uptake (TOU) rates were measured through a suite of incubation experiments and oxygen microelectrode profiles were taken across all four benthic sites to provide the oxygen penetration depth and diffusive oxygen uptake (DOU) rates. The difference between TOU and DOU allowed for quantification of the fauna mediated oxygen uptake and diffusive uptake. High resolution measurements showed clear seasonal and spatial trends, with higher oxygen uptake rates measured in cohesive sediments compared to the permeable sediment. The significant differences in oxygen dynamics between the sediment types were consistent between seasons, with increasing oxygen consumption during and after the phytoplankton bloom. Carbon mineralisation in shelf sediments is strongly influenced by sediment type and seasonality

Development and Applications of Fluorogen/Light-Up RNA Aptamer Pairs for RNA Detection and More.

The central role of RNA in living systems made it highly desirable to have noninvasive and sensitive technologies allowing for imaging the synthesis and the location of these molecules in living cells. This need motivated the development of small pro-fluorescent molecules called "fluorogens" that become fluorescent upon binding to genetically encodable RNAs called "light-up aptamers." Yet, the development of these fluorogen/light-up RNA pairs is a long and thorough process starting with the careful design of the fluorogen and pursued by the selection of a specific and efficient synthetic aptamer. This chapter summarizes the main design and the selection strategies used up to now prior to introducing the main pairs. Then, the vast application potential of these molecules for live-cell RNA imaging and other applications is presented and discussed.journal article2020importe

Auslegung eines Windkanalmodells mittels numerischer Strömungssimulationen

Der Triebwerkseinlauf stellt für Hyperschall-Raumflugzeuge (z.B. ELAC) eine leistungsbestimmende Baugruppe dar. In der Abteilung Windkanäle Köln-Porz des Deutschen Zentrums für Luft- und Raumfahrt werden daher im Rahmen eines Teilprojektes des DFG Sonderforschungsbereiches 253 solche Hyperschall-Einlaufsysteme optimiert. Da ein Hyperschall-Einlaufsystem über einen weiten Bereich betrieben werden muß, ist eine Anpassung an die verschiedenen Flugmachzahlen erforderlich. Die Untersuchung der hierzu erforderlichen Maßnahmen wie z.B. Rampenverstellung oder Absaugung soll zunächst im Bereich der Außenverdichtung anhand eines Prinzipmodells im Hyperschall-Windkanal des DLR durchgeführt werden. Dieses Windkanalmodell, bestehend aus zwei verstellbaren Rampen, wird mit Hilfe von numerischen Strömungssimulationen ausgelegt und anschließend konstruiert. Bei dem eingesetzten numerischen Verfahren handelt es sich um einen modernen 2D-Finite-Element-Strömunslöser, wobei die Rechnung auf unstrukturierten, adaptiven Netzen unter Annahme laminarer Grenzschichten erfolgt. Basierend auf einfachen, reibungsfreien Vorstudien werden in den daran anschließenden Navier-Stokes-Berechungen die Parameter der Anströmung sowie die Geometrie des Modells variiert, um so zu einer optimierten Modellauslegung zu gelangen. Abschließend wurde der Entwurf eines Windkanalmodells erarbeitet. Im einzelnen werden hier folgende Arbeitsschritte vorgestellt: Analytische und numerische Vorstudien, Strömungsberechnung auf adaptiven Netzen, Auswertung und Interpretation sowie der Entwurf eines Windkanalmodell

Manipulation of shock/boundary layer interactions in hypersonic inlets

Possibilities to manipulate shock/boundary layer interactions are demonstrated with regard to an application for hypersonic inlets. Experiments on generic models have been carried out in the hypersonic wind tunnel H2K of DLR at Mach number 6 and laminar flow conditions. Experimental results were validated by numerical flow simulations using a 2D finite element scheme. An analytical method has been developed for the pre-design of bleed configurations. In case of shock induced boundary layer separation it could be shown, that the implementation of bleed leads to a reduction of the separation bubble thickness by almost 50%. Further experimental investigations dealt with the achivable reduction of the heat loads on the wall surface depending on the amount and the position of the boundary layer bleed. These examinations were extended to three-dimensional corner flows. By this, favorable design parameters for a boundary layer bleed set-up were found. Finally, the results obtained using the generic models were transferred to a hypersonic inlet model. There the application of a correctly designed and positioned bleed system showed a significant increase of the attainable total pressure recover

Protein-RNA interactions: structural characteristics and hotspot amino acids

Structural information about protein-RNA complexes supports the understanding of crucial recognition processes in the cell, and it can allow the development of high affinity ligands to interfere with these processes. In this respect, the identification of amino acid hotspots is particularly important. In contrast to protein-protein interactions, in silico approaches for protein-RNA interactions lag behind in their development. Herein, we report an analysis of available protein-RNA structures. We assembled a data set of 322 crystal and NMR structures and analyzed them regarding interface properties. In addition, we describe a computational alanine-scanning approach which provides interaction scores for interface amino acids, allowing the identification of potential hotspots in protein-RNA interfaces. We have made the computational approach available as an online tool, which allows interaction scores to be calculated for any structure of a protein-RNA complex by uploading atomic coordinates to the PRI HotScore web server (https://pri-hotscore.labs.vu.nl)