Assessing temperature effects on multipole contributions and angular dependence in core-level spectroscopies

This study aims at assessing the thermal nuclei motion effects on the multipole transition channels involved in two core-level spectroscopies, x-ray absorption spectroscopy (XAS) and x-ray Raman scattering (XRS). Temperature effects on the 1s -> s monopole, 1s -> p dipole, and 1s -> d quadrupole transitions are investigated using two reference systems for which we present original experimental data: alpha-Al2O3 at the Al K edge probed by XRS at room temperature and rutile TiO2 at the Ti K pre-edge probed by XAS at temperatures ranging from 6 to 700 K. Through the latter, this work enlightens the part of the pre-edge peak enhancement due to temperature in the K pre-edge region of 3d transition metal, which is known to be routinely used to determine the concentration, valence or symmetry of the probed element in a given sample. Nuclear thermal fluctuations are taken into account using a method based on density functional theory that consists in averaging spectra over atomic configurations, generated within the harmonic approximation and obeying quantum statistics at finite temperature. Since only a finite number of such configurations are used, the numerically averaged spectra generally lose the symmetry of the equilibrium crystal positions. In this paper, we demonstrate that the physical average has to be symmetric and propose a method to restore the physical angular dependence of the spectra. The approach is successfully applied to investigate the angular dependent XAS spectra in rutile as a function of temperature. The two systems under study allow to draw general conclusions regarding the effect of nuclear quantum fluctuations on the different transition channels available to both core-level spectroscopies.Peer reviewe

Risk-based inspection as a cost-effective strategy to reduce human exposure to cysticerci of Taenia saginata in low-prevalence settings

Taenia saginata cysticercus is the larval stage of the zoonotic parasite Taenia saginata, with a life-cycle involving both cattle and humans. The public health impact is considered low. The current surveillance system, based on post-mortem inspection of carcasses has low sensitivity and leads to considerable economic burden. Therefore, in the interests of public health and food production efficiency, this study aims to explore the potential of risk-based and cost-effective meat inspection activities for the detection and control of T. saginata cysticercus in low prevalence settings

X-ray Absorption Near-Edge Structure calculations with pseudopotentials. Application to K-edge in diamond and alpha-quartz

We present a reciprocal-space pseudopotential scheme for calculating X-ray absorption near-edge structure (XANES) spectra. The scheme incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole interaction through large supercells (hundreds of atoms). The method is compared with recently developed Bethe-Salpeter approach. The method is applied to the carbon K-edge in diamond and to the silicon and oxygen K-edges in alpha-quartz for which polarized XANES spectra were measured. Core-hole effects are investigated by varying the size of the supercell, thus leading to information similar to that obtained from cluster size analysis usually performed within multiple scattering calculations.Comment: 11 pages, 4 figure

Study of ligand substituent effects on the rate and stereoselectivity of lactide polymerization using aluminum salen-type initiators.

A series of aluminum salen-type complexes [where salen is N,N′-bis(salicylaldimine)-1,2-ethylenediamine] bearing ligands that differ in their steric and electronic properties have been synthesized and investigated for the polymerization of rac-lactide. X-ray crystal structures on key precatalysts reveal metal coordination geometries intermediate between trigonal bipyramidal and square-based pyramidal. Both the phenoxy substituents and the backbone linker have a significant influence over the polymerization. Electron-withdrawing groups attached to the phenoxy donor generally gave an increased polymerization rate, whereas large ortho substituents generally slowed down the polymerization. The vast majority of the initiators afforded polylactide with an isotactic bias; only one exhibited a bias toward heteroselectivity. Isoselectivity generally increases with increased flexibility of the backbone linker, which is presumed to be better able to accommodate any potential steric clashes between the propagating polymer chain, the inserting monomer unit, and the substituents on the phenoxy donor

Influence of the 6^1S_0-6^3P_1 Resonance on Continuous Lyman-alpha Generation in Mercury

Continuous coherent radiation in the vacuum-ultraviolet at 122 nm (Lyman-alpha) can be generated using sum-frequency mixing of three fundamental laser beams in mercury vapour. One of the fundamental beams is at 254 nm wavelength, which is close to the 6^1S_0-6^3P_1 resonance in mercury. Experiments have been performed to investigate the effect of this one-photon resonance on phasematching, absorption and the nonlinear yield. The efficiency of continuous Lyman-alpha generation has been improved by a factor of 4.5.Comment: 8 pages, 7 figure

Projet NoBaby : Apprentissage de la conception/réalisation de produits en mode projet

L'Institut Supérieur d'ingénieur de Franche-Comté est une jeune école d'ingénieurs spécialisée dans le génie biomédical. Les étudiants recrutés viennent d'horizons et de cultures scientifique et technique très différents. Dans le cadre des enseignements de construction mécanique, on propose de concevoir et réaliser un système mécanique. Les étudiants doivent concevoir un prototype fonctionnel du produit. Il est ensuite réalisé par prototypage rapide. On propose ici de donner la structuration pédagogique de ce type de projet et des démarches à suivre

Quadrupole moment of the 6− isomeric state in 66Cu: Interplay between different nuclear deformation driving forces

AbstractWe have measured the spectroscopic quadrupole moment of the 6− isomeric state in 66Cu to be |Qs|=18.6(12) efm2. This state results from a weak coupling of the πp3/2 and the νg9/2 orbitals, which lead to sizable deformation at oblate and prolate shapes, correspondingly, in the 68Ni region. The interplay between these two different deformation-driving orbitals is observed at N=37 for the 6− state resulting in a most probable oblate shape

Annihilation of low energy antiprotons in silicon

The goal of the AE$\mathrm{\bar{g}}$IS experiment at the Antiproton Decelerator (AD) at CERN, is to measure directly the Earth's gravitational acceleration on antimatter. To achieve this goal, the AE$\mathrm{\bar{g}}$IS collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a velocity of a few 100 m/s and measure the magnitude of the vertical deflection of the beam from a straight path. The final position of the falling antihydrogen will be detected by a position sensitive detector. This detector will consist of an active silicon part, where the annihilations take place, followed by an emulsion part. Together, they allow to achieve 1$$ precision on the measurement of $\bar{g}$ with about 600 reconstructed and time tagged annihilations. We present here, to the best of our knowledge, the first direct measurement of antiproton annihilation in a segmented silicon sensor, the first step towards designing a position sensitive silicon detector for the AE$\mathrm{\bar{g}}$IS experiment. We also present a first comparison with Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table