Local symmetry in liquid metals probed by x-ray absorption spectroscopy

The nature of local point symmetry in simple monoatomic liquids has been a fundamental open question for almost 40 years of computational and experimental studies. We present original results of local ordering in different monoatomic liquids obtained by x-ray absorption spectroscopy (XAS), exploiting its high sensitivity to short-range ordering. We used Reverse Monte Carlo (RMC) analysis (RMC-GNXAS package) for obtaining structural models compatible with XAS experimental data (and diffraction techniques for long-range ordering). Pair, bond-angle distributions and suitable indicators for point symmetry are calculated for different liquid metals

Spectrometer for X-ray emission experiments at FERMI free-electron-laser

A portable and compact photon spectrometer to be used for photon in-photon out experiments, in particular x-ray emission spectroscopy, is presented. The instrument operates in the 25\u2013800 eV energy range to cover the full emissions of the FEL1 and FEL2 stages of FERMI. The optical design consists of two interchangeable spherical varied-lined-spaced gratings and a CCD detector. Different input sections can be accommodated, with/without an entrance slit and with/without an additional relay mirror, that allow to mount the spectrometer in different end-stations and at variable distances from the target area both at synchrotron and at free-electron-laser beamlines. The characterization on the Gas Phase beamline at ELETTRA Synchrotron (Italy) is presented

The structure of liquid metals probed by XAS

X-ray absorption spectroscopy (XAS) is a powerful technique to investigate the short-range order around selected atomic species in condensed matter. The theoretical framework and previous applications to undercooled elemental liquid metals are briefly reviewed. Specific results on undercooled liquid Ni obtained using a peak fitting approach validated on the spectra of solid Ni are presented. This method provides a clear evidence that a signature from close packed triangular configurations of nearest neighbors survives in the liquid state and is clearly detectable below k ≈ 5 Å−1, stimulating the improvement of data-analysis methods that account properly for the ensemble average, such as Reverse Monte Carlo

Glass polymorphism in amorphous germanium probed by first-principles computer simulations

The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions

The structure of liquid metals probed by XAS

X-ray absorption spectroscopy (XAS) is a powerful technique to in- vestigate the short-range order around selected atomic species in condensed matter. The theoretical framework and previous applications to undercooled elemental liquid metals are briefly reviewed. Specific results on undercooled liquid Ni obtained using a peak fitting approach validated on the spectra of solid Ni are presented. This method provides a clear evidence that a signature from close packed triangular configurations of nearest neighbors survives in the liquid state and is clearly detectable below k ≈ 5 Å −1 , stimulating the improve- ment of data-analysis methods that account properly for the ensemble average, such as Reverse Monte Carlo

Structure and atomic correlations in molecular systems probed by XAS reverse Monte Carlo refinement

The Reverse Monte Carlo (RMC) algorithm for structure refinement has been applied to x-ray absorption spectroscopy (XAS) multiple-edge data sets for six gas phase molecular systems (SnI2, CdI2, BBr3, GaI3, GeBr4, GeI4). Sets of thousands of molecular replicas were involved in the refinement process, driven by the XAS data and constrained by available electron diffraction results. The equilibrated configurations were analysed to determine the average tridimensional structure and obtain reliable bond and bond-angle distributions. Detectable deviations from Gaussian models were found in some cases. This work shows that a RMC refinement of XAS data is able to provide geometrical models for molecular structures compatible with present experimental evidence. The validation of this approach on simple molecular systems is particularly important in view of its possible simple extension to more complex and extended systems including metal-organic complexes, biomolecules, or nanocrystalline systems. © 2018 Author(s)

An investigation of the structure of liquid Zn by X-ray absorption spectroscopy

Abstract The structure of liquid zinc has been investigated by X-ray absorption spectroscopy (XAS) up to 1.6 GPa. The melting temperature was measured at two different pressures from the discontinuity of the X-ray absorption coefficient at the solid-liquid transition. The data of liquid Zn with increasing pressure have been interpreted using an advanced data-analysis method leading to the reliable determination of the main peak of the pair distribution function g ( r ) compared with previous experimental determinations

The growing impact of alpha-fetoprotein in the field of liver transplantation for hepatocellular cancer. Time for a revolution

The role of alpha-fetoprotein (AFP) in the specific setting of the diagnosis and prognosis of patients with hepatocellular cancer (HCC) waiting for liver transplantation (LT) is still controversial. Recently, a marked interest for this marker has been reported, mainly related to its ability to predict the outcome of HCC patients after LT. The growing number of papers in PubMed indicates that AFP has begun a "second life" in the particular context of LT. Looking at the most recent International Guidelines on HCC, it looks obvious that time is ripe to reevaluate the value of AFP in relation to its prognostic ability to identify HCC patients at high-risk for drop-out before and recurrence after LT. Many discrepancies exist worldwide regarding the use of biomarkers in HCC. In contrast to the Western world, AFP is widely used in Asian countries, the reason why being unclear. Indeed, in the (merely Western-dominated) HCC treatment algorithms, the role of AFP as a prognostic tumor marker is still considered to be "under investigation". One should however realize that the underestimation of the value of AFP in the LT context will hamper further refinements of both the liver allograft allocation process and the selection of the best candidates for this procedure. Moreover, AFP has an important role to play in the monitoring of bridging and/or downstaging procedures bringing eventually the patient to transplantation. So, time has come to reconsider the role and value of AFP (dynamics) in the field of transplant oncology