37 research outputs found
Direct observation of charge order in triangular metallic AgNiO2 by single-crystal resonant X-ray scattering
We report resonant X-ray scattering measurements on the orbitally-degenerate
triangular metallic antiferromagnet 2H-AgNiO2 to probe the spontaneous
transition to a triple-cell superstructure at temperatures below 365 K. We
observe a strong resonant enhancement of the supercell reflections through the
Ni K-edge. The empirically extracted K-edge shift between the
crystallographically-distinct Ni sites of 2.5(3) eV is much larger than the
value expected from the shift in final states, and implies a core-level shift
of ~1 eV, thus providing direct evidence for the onset of spontaneous honeycomb
charge order in the triangular Ni layers. We also provide band-structure
calculations that explain quantitatively the observed edge shifts in terms of
changes in the Ni electronic energy levels due to charge order and
hybridization with the surrounding oxygens.Comment: 5 pages, 4 figure
Microscopic theory of colour in lutetium hydride
Nitrogen-doped lutetium hydride has recently been proposed as a
near-ambient-conditions superconductor. Interestingly, the sample transforms
from blue to pink to red as a function of pressure, but only the pink phase is
claimed to be superconducting. Subsequent experimental studies have failed to
reproduce the superconductivity, but have observed pressure-driven colour
changes including blue, pink, red, violet, and orange. However, discrepancies
exist among these experiments regarding the sequence and pressure at which
these colour changes occur. Given the claimed relationship between colour and
superconductivity, understanding colour changes in nitrogen-doped lutetium
hydride may hold the key to clarifying the possible superconductivity in this
compound. Here, we present a full microscopic theory of colour in lutetium
hydride, revealing that hydrogen-deficient LuH is the only phase which
exhibits colour changes under pressure consistent with experimental reports,
with a sequence blue-violet-pink-red-orange. The concentration of hydrogen
vacancies controls the precise sequence and pressure of colour changes,
rationalising seemingly contradictory experiments. Nitrogen doping also
modifies the colour of LuH but it plays a secondary role compared to
hydrogen vacancies. Therefore, we propose hydrogen-deficient LuH as the key
phase for exploring the superconductivity claim in the lutetium-hydrogen
system. Finally, we find no phonon-mediated superconductivity near room
temperature in the pink phase.Comment: 3 figures + Supplementary Information, published versio
Fermi surface of IrTe2 in the valence-bond state as determined by quantum oscillations
We report the observation of the de Haas-van Alphen effect in IrTe2 measured
using torque magnetometry at low temperatures down to 0.4 K and in high
magnetic fields up to 33T. IrTe2 undergoes a major structural transition around
283 K due to the formation of planes of Ir and Te dimers that cut diagonally
through the lattice planes, with its electronic structure predicted to change
significantly from a layered system with predominantly three-dimensional
character to a tilted quasi-two dimensional Fermi surface. Quantum oscillations
provide direct confirmation of this unusual tilted Fermi surface and also
reveal very light quasiparticle masses (less than 1 me), with no significant
enhancement due to electronic correlations. We find good agreement between the
angular dependence of the observed and calculated de Haas-van Alphen
frequencies, taking into account the contribution of different structural
domains that form while cooling IrTe2.Comment: Latex, 4 pages, 3 figure
Tracing amino acid exchange during host-pathogen interaction by combined stable-isotope time-resolved Raman spectral imaging
This study investigates the temporal and spatial interchange of the aromatic amino acid phenylalanine (Phe) between human retinal pigment epithelial cell line (ARPE-19) and tachyzoites of the apicomplexan protozoan parasite Toxoplasma gondii (T. gondii). Stable isotope labelling by amino acids in cell culture (SILAC) is combined with Raman micro-spectroscopy to selectively monitor the incorporation of deuterium-labelled Phe into proteins in individual live tachyzoites. Our results show a very rapid uptake of L-Phe(D8) by the intracellular growing parasite. T. gondii tachyzoites are capable of extracting L-Phe(D8) from host cells as soon as it invades the cell. L-Phe(D8) from the host cell completely replaces the L-Phe within T. gondii tachyzoites 7–9 hours after infection. A quantitative model based on Raman spectra allowed an estimation of the exchange rate of Phe as 0.5–1.6 × 104 molecules/s. On the other hand, extracellular tachyzoites were not able to consume L-Phe(D8) after 24 hours of infection. These findings further our understanding of the amino acid trafficking between host cells and this strictly intracellular parasite. In particular, this study highlights new aspects of the metabolism of amino acid Phe operative during the interaction between T. gondii and its host cell
Distal Versus Conventional Radial Access for Coronary Angiography and Intervention: The DISCO RADIAL Trial.
BACKGROUND: Currently, transradial access (TRA) is the recommended access for coronary procedures because of increased safety, with radial artery occlusion (RAO) being its most frequent complication, which will increasingly affect patients undergoing multiple procedures during their lifetimes. Recently, distal radial access (DRA) has emerged as a promising alternative access to minimize RAO risk. A large-scale, international, randomized trial comparing RAO with TRA and DRA is lacking. OBJECTIVES: The aim of this study was to assess the superiority of DRA compared with conventional TRA with respect to forearm RAO. METHODS: DISCO RADIAL (Distal vs Conventional Radial Access) was an international, multicenter, randomized controlled trial in which patients with indications for percutaneous coronary procedure using a 6-F Slender sheath were randomized to DRA or TRA with systematic implementation of best practices to reduce RAO. The primary endpoint was the incidence of forearm RAO assessed by vascular ultrasound at discharge. Secondary endpoints include crossover, hemostasis time, and access site-related complications. RESULTS: Overall, 657 patients underwent TRA, and 650 patients underwent DRA. Forearm RAO did not differ between groups (0.91% vs 0.31%; PÂ =Â 0.29). Patent hemostasis was achieved in 94.4% of TRA patients. Crossover rates were higher with DRA (3.5% vs 7.4%; PÂ =Â 0.002), and median hemostasis time was shorter (180 vs 153Â minutes; PÂ < 0.001). Radial artery spasm occurred more with DRA (2.7% vs 5.4%; PÂ =Â 0.015). Overall bleeding events and vascular complications did not differ between groups. CONCLUSIONS: With the implementation of a rigorous hemostasis protocol, DRA and TRA have equally low RAO rates. DRA is associated with a higher crossover rate but a shorter hemostasis time