High-pressure study of X-ray diffuse scattering in ferroelectric perovskites

We present a high-pressure x-ray diffuse scattering study of the ABO$_3$ ferroelectric perovskites BaTiO_3 and KNbO_3. The well-known diffuse lines are observed in all the phases studied. In KNbO_3, we show that the lines are present up to 21.8 GPa, with constant width and a slightly decreasing intensity. At variance, the intensity of the diffuse lines observed in the cubic phase of BaTiO_3 linearly decreases to zero at $\sim 11$ GPa. These results are discussed with respect to x-ray absorption measurements, which leads to the conclusion that the diffuse lines are only observed when the B atom is off the center of the oxygen tetrahedron. The role of such disorder on the ferroelectric instability of perovskites is discussed.Comment: 4 pages, Accepted in PR

Leflunomide treatment for patients hospitalised with COVID-19: DEFEAT-COVID randomised controlled trial

Objective To evaluate the clinical efficacy and safety of leflunomide (L) added to the standard-of-care (SOC) treatment in COVID-19 patients hospitalised with moderate/critical clinical symptoms. Design Prospective, open-label, multicentre, stratified, randomised clinical trial. Setting Five hospitals in UK and India, from September 2020 to May 2021. Participants Adults with PCR confirmed COVID-19 infection with moderate/critical symptoms within 15 days of onset. Intervention Leflunomide 100 mg/day (3 days) followed by 10–20 mg/day (7 days) added to standard care. Primary outcomes The time to clinical improvement (TTCI) defined as two-point reduction on a clinical status scale or live discharge prior to 28 days; safety profile measured by the incidence of adverse events (AEs) within 28 days. Results Eligible patients (n=214; age 56.3±14.9 years; 33% female) were randomised to SOC+L (n=104) and SOC group (n=110), stratified according to their clinical risk profile. TTCI was 7 vs 8 days in SOC+L vs SOC group (HR 1.317; 95% CI 0.980 to 1.768; p=0.070). Incidence of serious AEs was similar between the groups and none was attributed to leflunomide. In sensitivity analyses, excluding 10 patients not fulfilling the inclusion criteria and 3 who withdrew consent before leflunomide treatment, TTCI was 7 vs 8 days (HR 1.416, 95% CI 1.041 to 1.935; p=0.028), indicating a trend in favour of the intervention group. All-cause mortality rate was similar between groups, 9/104 vs 10/110. Duration of oxygen dependence was shorter in the SOC+L group being a median 6 days (IQR 4–8) compared with 7 days (IQR 5–10) in SOC group (p=0.047). Conclusion Leflunomide, added to the SOC treatment for COVID-19, was safe and well tolerated but had no major impact on clinical outcomes. It may shorten the time of oxygen dependence by 1 day and thereby improve TTCI/hospital discharge in moderately affected COVID-19 patients

X-ray absorption coefficient of rubidium in the K-edge region

A high-resolution absorption spectrum of rubidium vapor in the vicinity of K edge is converted to absolute absorption coefficient by a set of measurements on a RbNO3 solution. Specific problems arising in absolute absorption measurements with synchrotron light and with conventional X-ray sources are discussed

Elements of a Model Function for the Atomic Absorption Background in EXAFS Spectra

From the study of multielectron photoexcitations in atoms, a specific ansatz for the EXAFS atomic background is derived, to improve or replace the conventional spline approximation. The elements of the ansatz describe multielectron resonances, edges and shake-off features at proper theoretical energies. The approach is tested on the atomic background of Rb ion and on EXAFS-free absorption spectra of rubidium vapor and krypton

Elements of a Model Function for the Atomic Absorption Background in EXAFS Spectra

From the study of multielectron photoexcitations in atoms, a specific ansatz for the EXAFS atomic background is derived, to improve or replace the conventional spline approximation. The elements of the ansatz describe multielectron resonances, edges and shake-off features at proper theoretical energies. The approach is tested on the atomic background of Rb ion and on EXAFS-free absorption spectra of rubidium vapor and krypton

EXAFS and XANES study of the incorporation of Mn cations into a chabazite-like AlPO molecular sieve

The incorporation of Mn(II) cations into a chabazite-like MnAIPO material is studied with Mn K-edge XANES and EXAFS. Both methods show that Mn(II) is inserted exclusively into the tetrahedrally coordinated aluminum sites. Calcination and rehydration of the as-synthesized MnAIPO cause a partial oxidation of Mn(ll) as well as a change of its coordination geometry to a distorted octahedron

FLUORESCENCE YIELD OF DOUBLE K VACANCIES IN KRYPTON

The formation of double K-shell vacancy in absorption of single photon is studied in krypton. A multiwire wall-less proportional counter filled with a mixture of krypton and propane is used to detect the double vacancies separately according to their mode of decay. The analysis of spectra of pulses demonstrated the independent particle model of decay to be inappropriate. Using the collective model the probabilities for radiative, radiative-nonradiative and nonradiative modes in the decay of double vacancy state were preliminary determined as < 0.1 ± 0.1, 0.35 ± 0.05 and 0.54 ± 0.05, respectively. The double K-shell ionization cross section at the edge was determined to be less than 8.2(E-3) of the total photoelectric cross section