High-frequency collective excitations in molten and glassy Te studied by inelastic neutron scattering

7 págs.; 5 figs.; 1 tab. ; PACS number s : 61.25.Mv, 61.43.Er, 61.20.Lc, 61.12. qhttp://dx.doi.org/10.1103/PhysRevB.73.094201The spectra of collective excitations of liquid and glassy tellurium have been studied by means of inelastic neutron scattering. Here we report on the dynamics of liquid Te as measured at two different temperatures, just above melting (Tm =723 K) and at ∼1000 K as well as the glass that is studied at room temperature. Estimates for the velocity of propagating excitations for both temperatures have been obtained from the experimental data, and a contrasting behavior is found with respect to anomalies shown by the adiabatic sound velocity measured by ultrasound methods. The origin of such differences is finally discussed. © 2006 The American Physical Society.This work was supported in part by Grant No. MAT2002- 04178-C04 SpainPeer Reviewe

Molecular Deuterion crystallitation under cuasi-1D confienment

ECNS 2015, Zaragoza (Spain), August 30th-September 4th 2015A particularly interesting aspect of Carbon Nanotubes is their use as nearly one-dimensional nano-containers. Apart of their possibilities for controlled chemistry in nano- fluidics devices new phenomena induced by confinement are also expected, such as liquid like ordered structures or exotic crystalline phases. Here, we present a series of neutron diffraction measurements (instrument D20, ILL, Grenoble) of molecular deuterium confined within Multiple Wall Carbon Nanotubes (MWCTNs). Bulk liquid D2 at its vapour pressure crystallises in an hcp structure at ~18.7 K. At low uptakes we have found a clear depression of the solidification temperature down to ~13.25 K. Interestingly, at the lowest uptake the diffraction pattern is consistent with the minimal fcc lattice compatible with a cylindrical symmetry.Peer Reviewe

Crystallization of para-Hydrogen: a quantum phase transition at finite temperature?

4 págs.; 3 figs.; Open Access funded by Creative Commons Atribution Licence 3.0; 7th Meeting of the Spanish Neutron Scattering Association (SETN)Recent neutron scattering measurements have revealed that para-Hydrogen prepared in its fundamental state solidifies in a crystal that do not show temperature response (temperature independent molecular displacement and first rotational level linewidth as well as negligible thermal expansion). Here, it is argued that such unique behaviour in the crystal phase can be understood if the crystallization is driven by pure quantum fluctuations.Work supported in part by grants MAT2007-65711-C04-01 and MAT2012-33633 from the Spanish Ministerio de Economía y Competitividad.Peer Reviewe

Microscopic dynamics in molten Ni: Experimental scrutiny of embedded-atom-potential simulations

11 págs.; 10 figs. ; PACS number s : 66.10. x, 66.20. d, 63.20.LsThe stochastic dynamics in molten nickel is studied by neutron scattering. The quasielastic spectrum shows two distinct components having disparate linewidths. The wave-vector dependence of the narrow component is shown to arise from incoherent scattering at low momentum transfers. In turn, the spectral half-width of the wider component shows a modulation with wave vector characteristic of coherent quasielastic scattering. The analysis of both components provides direct experimental estimates for the self-diffusion coefficient, as well as the effective particle diameter. The experimental data are then used to validate computer simulation results which are derived using an embedded-atom potential. Such results are also employed to explore regions in frequency-wave-vector space not easily amenable to experiment. In addition, simulation results are also compared with data pertaining to the collective motions. Such an exercise reveals the need to develop a further level in the memory function expansion of the coherent dynamic structure factor. The implications of such findings for our current understanding of the dynamics of liquid metals are finally assessed. © 2007 The American Physical Society.Peer Reviewe

Electron-beam deposited boron coatings for the extreme ultraviolet

Boron films deposited by evaporation with an electron-beam were found to have a relatively high reflectance in the extreme ultraviolet with values similar to those of ion-beam-sputtered (IBS) SiC and IBS B4C . The largest reflectance was measured for an 11¿nm thick boron film. Some reflectance degradation was observed for boron films stored in a desiccator. Reflectance degradation varied from sample to sample and was found to be either similar to that of IBS SiC and IBS B4C or larger. © 2008 Optical Society of AmericaThis work was supported by the National Programme for Space Research, Subdirección General de Proyectos de Investigación, Ministerio de Ciencia y Tecnología, project number ESP2005-02650. M. Fernández-Perea is thankful to Consejo Superior de Investigaciones Científicas (Spain) for funding under the Programa I3P (Ref. I3P-BPD2004) partially supported by the European Social Fund. We acknowledge the technical assistance of José M. Sánchez-Orejuela. M. Vidal-Dasilva is thankful to Ministerio de Educación y Ciencia for funding under the FPI BES-2006- 14047 fellowship.Peer Reviewe

What are the letters e and é in a language with vowel reduction? the case of Catalan

Although the Latin-based orthographies of most Western languages employ vowels with accent marks (e.g., é vs. e), extant models of letter and word recognition are agnostic as to whether these accented letters and their non-accented counterparts are represented by common or separate abstract units. Recent research in French with a masked priming alphabetic decision task was interpreted as favoring the idea that accented and non-accented vowels are represented by separate abstract orthographic units (orthographic account: é↛e and e↛é; Chetail & Boursain, 2019). However, a more parsimonious explanation is that salient (accented) vowels are less perceptually similar to non-salient (non-accented) vowels than vice versa (perceptual account: e→é, but é↛e; Perea et al., 2021a; Tversky, 1977). To adjudicate between the two accounts, we conducted a masked priming alphabetic decision experiment in Catalan, a language with a complex orthography-to-phonology mapping for non-accented vowels (e.g., e→/e/, /ə/, / /). Results showed faster responses in the identity than in the visually similar condition for accented targets (é-É < e-É), but not for non-accented targets (e-E = é-E). Neither of the above accounts can fully capture this pattern. We propose an explanation based on the rapid activation of both orthographic and phonological codes

Static structure factor of liquid parahydrogen

7 págs.; 5 figs. ; PACS number~s!: 61.20.2p, 61.12.2q, 78.70.2gThe single-differential neutron-scattering cross section of liquid parahydrogen has been measured at 15.2 K and 2 bars of applied pressure by means of low-energy neutron diffraction. Our experimental conditions enable the direct observation of the peak of the liquid structure factor and therefore largely improve the signal-to-noise ratio with respect to measurements carried out using higher-energy neutron diffraction. This avoids the need of performing corrections of approximate nature to the measured cross section that is dominated by molecular rotational components if measured by conventional neutron diffraction. ©2004 American Physical SocietyPeer Reviewe

Rotational dynamics in the plastic-crystal phase of ethanol: Relevance for understanding the dynamics during the structural glass transition

12 págs.; 14 figs.; 1 tab.; 1 apéndiceThe reorientational dynamics within the rotationally disordered cubic plastic phase of solid ethanol is investigated by means of the concurrent use of computer molecular dynamics and quasielastic neutron scattering. Motions involving widely different time scales are shown to take place above the calorimetric >glass transition> which is centered at Tg≈97 K. These correspond to well-defined reorientations belonging to the cubic point group. The dynamics of this solid exhibits features remarkably close to those of the supercooled liquid that can exist at the same temperature. Such similitude of dynamic behavior serves to provide some clues for the understanding of the nature of molecular motions at temperatures close to the canonical liquid→glass transition. ©2000 The American Physical Society.This work was supported in part by Grant No. DGICYTPB95- 0072-C03 (Spain). Work at ANL was supported by the U.S. Department of Energy, BES–Materials Sciences, under Contract No. W-31-109-ENG-38.Peer Reviewe

Optical constants of evaporation-deposited silicon monoxide films in the 7.1-800 eV photon energy range

8 págs.; 11 figs.The transmittance of silicon monoxide films prepared by thermal evaporation was measured from 7.1 to 800 eV and used to determine the optical constants of the material. SiO films deposited onto C-coated microgrids in ultrahigh vacuum conditions were measured in situ from 7.1 to 23.1 eV. Grid-supported SiO films deposited in high vacuum conditions were characterized ex situ from 28.5 to 800 eV. At each photon energy, transmittance, and thickness data were used to calculate the extinction coefficient k. The obtained k values combined with data from the literature, and with interpolations and extrapolations in the rest of the electromagnetic spectrum provided a complete set of k values that was used in a Kramers-Kronig analysis to obtain the real part of the index of refraction, n. Two different sum-rule tests were performed that indicated good consistency of the data. © 2009 American Institute of Physics.This work was supported by the National Programme for Space Research, Subdirección General de Proyectos de Investigación, Ministerio de Ciencia y Tecnología, Project Nos. ESP2002-01391 and ESP2005-02650. This work was also performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Berkeley National Laboratory under Contract No. DE-AC03-76F00098 and by the University of California Lawrence Livermore National Laboratory under Contract No. DE-AC52- 07NA27344. M.F.-P. is thankful to Consejo Superior de Investigaciones Científicas Spain for funding under the Programa I3P Contract No. I3P-BPD2004, partially supported by the European Social Fund. M.V.-D. acknowledges financial support from a FPI Contract No. BES-2006-14047 fellowship.Peer Reviewe