Development of FEM/BEM and SEA models from experimental results for structural elements with attached equipment

This work focuses on the analysis of a structural element of MetOP-A satellite. Given the special interest in the influence of equipment installed on structural elements, the paper studies one of the lateral faces on which the Advanced SCATterometer (ASCAT) is installed. The work is oriented towards the modal characterization of the specimen, describing the experimental set-up and the application of results to the development of a Finite Element Method (FEM) model to study the vibro-acoustic response. For the high frequency range, characterized by a high modal density, a Statistical Energy Analysis (SEA) model is considered, and the FEM model is used when modal density is low. The methodology for developing the SEA model and a compound FEM and Boundary Element Method (BEM) model to provide continuity in the medium frequency range is presented, as well as the necessary updating, characterization and coupling between models required to achieve numerical models that match experimental results

Surface acoustic wave velocity and elastic constants of cubic GaN

We present high-resolution surface Brillouin scattering measurements on cubic GaN layers grown on GaAs substrate. By using a suitable scattering geometry, scattering by surface acoustic waves is recorded for different azimuthal angles, and the surface acoustic wave velocities are determined. A comparison of experimental results with numerical simulations of the azimuthal dependence of the surface wave velocity shows good agreement and allows a consistent set of elastic constants for c-GaN to be determined

Antiferromagnetism in doped anisotropic two-dimensional spin-Peierls systems

We study the formation of antiferromagnetic correlations induced by impurity doping in anisotropic two-dimensional spin-Peierls systems. Using a mean-field approximation to deal with the inter-chain magnetic coupling, the intra-chain correlations are treated exactly by numerical techniques. The magnetic coupling between impurities is computed for both adiabatic and dynamical lattices and is shown to have an alternating sign as a function of the impurity-impurity distance, hence suppressing magnetic frustration. An effective model based on our numerical results supports the coexistence of antiferromagnetism and dimerization in this system.Comment: 5 pages, 4 figures; final version to appear in Phys. Rev.

Influence of nanoparticles on elastic and optical properties of a polymeric matrix: Hypersonic studies on ethylene-vinyl alcohol copolymer-titania nanocomposites

High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene-vinyl alcohol copolymer (EVOH) and TiO2 nanoparticles present anomalous dependence with concentration, while Young's modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO2 nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO2 nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH-TiO2 nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene-TiO2 nanocomposites proves that EVOH-TiO2 nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO2 nanoparticles. © 2009 Elsevier Ltd. All rights reserved.Dr. A. Kubacka and Ms. C. Serrano thank, respectively, the CSIC and MEC for I3P postdoctoral and PFU predoctoral grants. This work was supported by the CSIC under the projects PIF200580F0101, PIF200580F0102, PIF200560F0103 and PIF200560F0102.Peer Reviewe

Do tunneling states and boson peak persist or disappear in extremely stabilized glasses?

We review and concurrently discuss two recent works conducted by us, which apparently give opposite results. Specifically, we have investigated how extreme thermal histories in glasses can affect their universal properties at low temperatures, by studying: (i) amber, the fossilized natural resin, which is a glass which has experienced a hyperaging process for about one hundred million years; and (ii) ultrastable thin-film glasses of indomethacin. Specific heat Cp measurements in the temperature range 0.07 K < T < 30 K showed that the amount of two-level systems, assessed from the linear term at the lowest temperatures, was exactly the same for the pristine hyperaged amber glass as for the subsequently rejuvenated samples, whereas just a modest increase of the boson-peak height (in Cp/T³) with increasing rejuvenation was observed, related to a corresponding increase of the Debye coefficient. On the other hand, we have observed an unexpected suppression of the two-level systems in the ultrastable glass of indomethacin, whereas conventionally prepared thin films of the same material exhibit the usual linear term in the specific heat below 1 K ascribed to these universal two-level systems in glasses. By comparing both highly-stable kinds of glass, we conclude that the disappearance of the tunneling two-level systems in ultrastable thin films of indomethacin may be due to the quasi-2D and anisotropic behavior of this glass, what could support the idea of a phonon-mediated interaction between two-level systems

Solution synthesis of BiFeO3 thin films onto silicon substrates with ferroelectric, magnetic, and optical functionalities

Single-BiFeO3 perovskite films onto Pt-coated silicon substrates have been fabricated by chemical solution deposition using a synthesis strategy based on the use of nonhazardous reagents. Different routes were tested to obtain precursors for the deposition of the films, inferring that bismuth (III) nitrate and iron (III) 2,4-pentanedionate dissolved in acetic acid and 1,3-propendiol led to the best solution. Ferroelectric, magnetic, and optical functionalities were demonstrated in these films, obtaining a high ferroelectric polarization at room temperature, ~67 μC × cm-2, a dependence of the magnetization with the film thickness, 0.60 and 2.50 emu × g-1 for the ~215 and ~42-nm-thick films, and a direct band gap in the visible range, Eg ~2.82 eV. These results support the interest of solution methods for the fabrication of BiFeO3 thin films onto the silicon substrates required in microelectronic devices. © 2013 The American Ceramic Society.Funded by: Spanish project. Grant Number: MAT2010-15365; Magnetic characterization. Grant Number: MAT2011-27470-C02-02; IMAGINE. Grant Number: CSD2009-00013; FPU and FPI. Grant Number: BES-2008-010132.Peer Reviewe

Photochemical solution deposition of β-Bi2O3 thin films

The non-equilibrium β-Bi2O3 polymorph is stabilized in thin films by a photochemical synthesis method. A strong ultraviolet-absorbing bismuth(III)-N-methyldiethanolamine complex is synthesized in solution as an ideal precursor for the β-Bi2O3 phase. Ultraviolet-light induces the formation of an amorphous —Bi—O—Bi— continuous network in the films deposited from the former solution that easily converts into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The room temperature stabilization of the β-Bi2O3 phase is confirmed by their structural characterization using four-circle X-ray diffractometry. This study unequivocally identified the tetragonal crystal structure of the β-Bi2O3 polymorph in the films. The high phase purity of these β-Bi2O3 films is responsible for their exceptional visible-light photocatalytic activity, thus enabling the applications of the films of this metastable phase at room-temperature conditions.This work has been financed by the Spanish Project MAT2013-40489-P and MAT2016-76851-R. I.B. acknowledges the financial support by Fundación General CSIC (Spanish ComFuturoProgramme).MINECO/ICTI2013-2016/MAT2016-76851-

Photochemical solution processing of films of metastable phases for flexible devices: the β-Bi 2 O 3 polymorph

The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi O polymorph. The pure β-Bi O phase is thermodynamically stable at high temperature (450-667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a -Bi-O-Bi- continuous network in the deposited layers and the further conversion into the β-Bi O polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi O films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi O films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases.This work was financed by Spanish Project MAT2013-40489-P and MAT2016-76851-R. The COST Action IC1208 also contributed to this study. I.B. acknowledges the financial support by Fundación General CSIC (Spanish ComFuturo Programme)

Biocidal Capability Optimization in Organic-Inorganic Nanocomposites Based on Titania

Optimization of the interfacial agent content in biocidal titania−isotactic polypropylene nanocomposites is performed by evaluating their structural, thermal, optical, and biocidal properties. The balance between the photochemistry (photokilling) behavior and the thermal properties is achieved in the nanocomposites with an incorporation of 2 wt.% in inorganic nanoparticles (TiO2) using a compatibilizer content ranging from 50 to 80 wt.% with respect to the titania amount

Biocidal capability optimization in organic - Inorganic nanocomposites based on titania

Optimization of the interfacial agent content in biocidal titania - isotactic polypropylene nanocomposites is performed by evaluating their structural, thermal, optical, and biocidal properties. The balance between the photochemistry (photokilling) behavior and the thermal properties is achieved in the nanocomposites with an incorporation of 2 wt.% in inorganic nanoparticles (TiO2) using a compatibilizer content ranging from 50 to 80 wt.% with respect to the titania amount. © 2009 American Chemical Society.Peer Reviewe