Electron-phonon interactions and high-temperature thermodynamics of vanadium and its alloys

Inelastic neutron scattering was used to measure the phonon densities of states (DOSs) for pure V and solid solutions of V with 6 to 7at% of Co, Nb, and Pt, at temperatures from 10 K to 1323 K. Ancillary measurements of heat capacity and thermal expansion are reported on V and V-7at%Co and used to help identify the different sources of entropy. Pure V exhibits an anomalous anharmonic stiffening of phonons with increasing temperature. This anharmonicity is suppressed by Co and Pt, but not by isoelectronic Nb solutes. The changes in phonon frequency with alloying and with temperature both correlate to the decrease in electron density of states (DOS) at the Fermi level as calculated using density functional theory. The effects of both temperature and alloying can be understood in terms of an adiabatic electron-phonon interaction (EPI), which broadens sharp features in the electron DOS. These results show that the adiabatic EPI can influence the phonon thermodynamics at temperatures exceeding 1000 K, and that thermal trends of phonons may help assess the strength of the EPI

Novel characterization method of impedance cardiography signals using time-frequency distributions

The purpose of this document is to describe a methodology to select the most adequate time-frequency distribution (TFD) kernel for the characterization of impedance cardiography signals (ICG). The predominant ICG beat was extracted from a patient and was synthetized using time-frequency variant Fourier approximations. These synthetized signals were used to optimize several TFD kernels according to a performance maximization. The optimized kernels were tested for noise resistance on a clinical database. The resulting optimized TFD kernels are presented with their performance calculated using newly proposed methods. The procedure explained in this work showcases a new method to select an appropriate kernel for ICG signals and compares the performance of different time-frequency kernels found in the literature for the case of ICG signals. We conclude that, for ICG signals, the performance (P) of the spectrogram with either Hanning or Hamming windows (P¿=¿0.780) and the extended modified beta distribution (P¿=¿0.765) provided similar results, higher than the rest of analyzed kernels.Peer ReviewedPostprint (published version

Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules

Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K are covered by ice mantles. A nonthermal desorption mechanism is invoked to explain the presence of gas-phase molecules in these environments, such as the photodesorption induced by irradiation of ice due to secondary ultraviolet photons. To quantify the effects of ice photoprocessing, an estimate of the photon absorption in ice mantles is required. In a recent work, we reported the vacuum-ultraviolet (VUV) absorption cross sections of nonpolar molecules in the solid phase. The aim was to estimate the VUV-absorption cross sections of nonpolar molecular ice components, including CH4, CO2, N2, and O2. The column densities of the ice samples deposited at 8 K were measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. We found that, as expected, solid N2 has the lowest VUV-absorption cross section, which about three orders of magnitude lower than that of other species such as O2, which is also homonuclear. Methane (CH4) ice presents a high absorption near Ly-alpha (121.6 nm) and does not absorb below 148 nm. Estimating the ice absorption cross sections is essential for models of ice photoprocessing and allows estimating the ice photodesorption rates as the number of photodesorbed molecules per absorbed photon in the ice.Comment: 9 pages, 6 figures, 7 table

El desarrollo de un programa de preservación ideal para documentos digitales

Se presenta una guía práctica de las etapas que llevan a cabo aquellos quienes se embarcan en el proceso de la preservación digital o que proyectan hacerlo. El objetivo del plan de preservación que aquí se describe es el de preservar la integridad de los objetos digitales para permitir a los usuarios su localización, visualización y en último término utilización de los mismos haciendo frente a constantes cambios tecnológicos. En este sentido, es una necesidad el preservar a lo largo del tiempo tanto el documento creado directamente en digital como aquel que ha sido reconvertido o digitalizado. El artículo analiza el elenco de opciones existentes en cuanto a la preservación digital se refiere determinando las habilidades requeridas por el profesional de la información para que éste sea capaz de preservar dichos objetos.This article intended to provide practical guidance to those undertaking digital preservation or considering doing so. The purpose of the following preservation planning is to preserve the integrity of digital objects and to retain the ability for users to retrieve, display, and otherwise use them in the face of constantly changing technology. There is therefore a need to preserve long term both born-digital and digital surrogate material. The report explores the range of options for digital preservation provides an analysis of the digital landscape, focusing on features that affect the integrity of digital information objects and which determine the ability of information professionals to preserve such objects over the long term