Short-range order of compressed amorphous GeSe2

The structure of amorphous GeSe2 (a-GeSe2) has been studied by means of a combination of two-edges X-ray absorption spectroscopy (XAS) and angle-dispersive X-ray diffraction under pressures up to about 30 GPa. Multiple-edge XAS data-analysis of a-GeSe2 at ambient conditions allowed us to reconstruct and compare the first-neighbor distribution function with previous results obtained by neutron diffraction with isotopic substitution. GeSe2 is found to remain amorphous up to the highest pressures attained, and a reversible 1.5 eV red-shift of the Ge K-edge energy indicating metallization, occurs between 10 GPa and 15 GPa. Two compression stages are identified by XAS structure refinement. First, a decrease of the first-neighbor distances up to about 10 GPa, in the same pressure region of a previously observed breakdown of the intermediate-range order. Second, an increase of the Ge-Se distances, bond disorder, and of the coordination number. This stage is related to a reversible non-isostructural transition involving a gradual conversion from tetra- to octa-hedral geometry which is not yet fully completed at 30 GPa

Investigation of the phase diagram of selenium by means of Raman spectroscopy

We report a detailed and systematic Raman scattering investigation of the high pressure - high temperature (350–620 K, 0–20 GPa) phase diagram of elemental selenium starting from its trigonal structure (Se-I). Phase transitions to the tetragonal Se-VII phase were identified by the measured Raman pattern along several isotherms, upon pressurization and depressurization. A wide hysteresis region (∼10–15 GPa) has been observed at 350 K, gradually reducing to about 3 GPa at 620 K. These results extend previous scattered determinations of the phase diagram and shifts the Se-I Se-VII transition line up to about 3 GPa at lower pressures and ∼150 K at lower temperatures

New Graphical User Interface for EXAFS analysis with the GNXAS suite of programs

International audienceGNXAS is a suite of programs based on multiple scattering calculations which performs a structural refinement of EXAFS spectra. It can be used for any system although it has been mainly developed to determine the local structure of disordered substances. We developed a user-friendly graphical user interface (GUI) to facilitate use of the codes by using wxPython. The developed GUI and the codes are multiplatform running on Windows, Macintosh and Linux systems, and are free shareware (http://gnxas.unicam.it). In this work we illustrate features and potentials of this newly developed version of GNXAS (w-GNXAS)

Structural evolution mechanisms of amorphous and liquid As2Se3 at high pressures

The elusive structure of compressed, melt-quenched As 2 Se 3 was studied in both its liquid and amorphous form up to 4.4 and 30 GPa, respectively, by means of x-ray absorption spectroscopy and diffraction. The evolution of the short-range structure is studied by As and Se multiple K-edge extended x-ray absorption fine structure (EXAFS) refinement, while changes in intermediate-range ordering are revealed by x-ray diffraction and near-edge structures. In the liquid, at the nearest-neighbor length scales, a gradual disordering and slight elongation of the As-Se average distances is observed, preserving the local coordination upon increasing pressure, whereas substantial compression and disordering are observed at intermediate distances. Similarly, in the amorphous form we found a progressive slight elongation and disordering of the first-neighbor As-Se average distance R (from ̊ 2 ) upon increasing pressures up to 30 GPa. ̊ and bond variance σ 2 (from ∼0.004 to 0.008 A ∼2.42 to 2.44 A) On the other hand, gradual shortening of the second and farther neighbor distances, more evident below 15 GPa, are compatible with data analysis. No sign of crystallization and gradual metallization are observed for amorphous a-As 2 Se 3 up to 30 GPa. The emerging picture for the structure evolution under high pressures is a compaction mechanism involving mainly changes at intermediate distances, weakly affecting the first-neighbor bonding character

Reflectivity enhancement in titanium by ultrafast XUV irradiation

The study of highly photo-excited matter at solid state density is an emerging field of research, which is benefitting the development of free-electron-laser (FEL) technology. We report an extreme ultraviolet (XUV) reflectivity experiment from a titanium (Ti) sample irradiated with ultrafast seeded FEL pulses at variable incident photon fluence and frequency. Using a Drude formalism we relate the observed increase in reflectivity as a function of the excitation fluence to an increase in the plasma frequency, which allows us to estimate the free electron density in the excited sample. The extreme simplicity of the experimental setup makes the present approach potentially a valuable complementary tool to determine the average ionization state of the excited sample, information of primary relevance for understanding the physics of matter under extreme conditions

Tocilizumab for patients with COVID-19 pneumonia. The single-arm TOCIVID-19 prospective trial

BackgroundTocilizumab blocks pro-inflammatory activity of interleukin-6 (IL-6), involved in pathogenesis of pneumonia the most frequent cause of death in COVID-19 patients.MethodsA multicenter, single-arm, hypothesis-driven trial was planned, according to a phase 2 design, to study the effect of tocilizumab on lethality rates at 14 and 30 days (co-primary endpoints, a priori expected rates being 20 and 35%, respectively). A further prospective cohort of patients, consecutively enrolled after the first cohort was accomplished, was used as a secondary validation dataset. The two cohorts were evaluated jointly in an exploratory multivariable logistic regression model to assess prognostic variables on survival.ResultsIn the primary intention-to-treat (ITT) phase 2 population, 180/301 (59.8%) subjects received tocilizumab, and 67 deaths were observed overall. Lethality rates were equal to 18.4% (97.5% CI: 13.6-24.0, P=0.52) and 22.4% (97.5% CI: 17.2-28.3, P<0.001) at 14 and 30 days, respectively. Lethality rates were lower in the validation dataset, that included 920 patients. No signal of specific drug toxicity was reported. In the exploratory multivariable logistic regression analysis, older age and lower PaO2/FiO2 ratio negatively affected survival, while the concurrent use of steroids was associated with greater survival. A statistically significant interaction was found between tocilizumab and respiratory support, suggesting that tocilizumab might be more effective in patients not requiring mechanical respiratory support at baseline.ConclusionsTocilizumab reduced lethality rate at 30 days compared with null hypothesis, without significant toxicity. Possibly, this effect could be limited to patients not requiring mechanical respiratory support at baseline.Registration EudraCT (2020-001110-38); clinicaltrials.gov (NCT04317092)