Electromagnetic radiation from VDT units: Study of the effectiveness of an active shielding device

Measurements of extremely low frequency electromagnetic fields and low frequency magnetic fields emitted by a set of video display terminal (VDT) units are reported. The field values measured at the position normally occupied by the user are below the safety limits. This is because the field amplitudes decrease rapidly (following a 1/R-3 law) with the distance from the source, as has been verified in this work. Measurements with a commercial shielding device consisting of small plastic balls filled with a water solution of rare earth elements were also performed. The only physical mechanism that could be hypothesized to produce an active suppression of the VDT field is that rare earth atoms, which probably were chosen due to their large magnetic moment, behave as oscillating magnetic dipoles capable of emitting a secondary magnetic field that, along some particular directions, has a phase that is opposite to that of the exciting field. Unfortunately, if one analyzes this mechanism quantitatively, it is easy to show that the secondary magnetic field is absolutely negligible, as was confirmed by experimental measurements performed in this study

Multi-functional, high-performing fuel electrode for dry methane oxidation and CO2 electrolysis in reversible solid oxide cells

Intermittency of renewable energy sources can be profitably faced using efficient energy storage systems. Reversible solid oxide cells (RSOCs) able to operate with carbon-containing species are likely among the most appealing choices. Energy can be obtained by natural gas and/or biogas (SOFC mode), with useful recovery of CO2 in the exhausts. Besides, if the electrode is also active towards CO2 electrolysis (SOEC mode), CO2 is reduced to CO and O2. In this work a composite material with in-situ formed Ni-Fe alloy catalyst consisting of La1.2Sr0.8Fe0.6Mn0.4O4 Ruddlesden-Popper perovskite and Ni-Ce0.85Sm0.15O2-δ fluorite was developed as a multi-functional fuel-electrode for RSOCs. The composite electrode was tested in SOFC mode as anode for hydrogen, dry methane and carbon monoxide oxidation and showed power density outputs of 657, 668 and 527 mW/cm2 at 850 °C, respectively, together with redox stability and coking tolerance for over 120 h. In SOEC mode, it was tested as cathode and delivered 2.66 A/cm2 at 2 V in a 95:5 CO2:CO mixture, retaining a current density of 1 A/cm2 for more than 40 h

X-ray and UV photoelectron spectroscopy of Ag nanoclusters

The main purpose of the present work is to analyze a series of Ag nanoparticles (NPs) with different size or ligand functionalization by using X-ray photoelectron spectroscopy (XPS) and to identify the differences in the band-shape and energy peak position of photoemission spectra due to the particle dimension. A transmission electron microscopy characterization was performed, to verify the consistency of the results. Three types of samples were prepared starting from AgNO3 water solution and adding different capping agents. In the first two cases, the formation of NPs was promoted by the reduction of silver ions Ag+1 to metallic Ag-0 through the addition of sodium borohydride, whereas in the last case, it was triggered by the exposure to UV light. Depending on the size of the NPs, a different physical behavior can be recognized. NPs with diameter of about 5 nm are characterized by the phenomenon of localized surface plasmon resonance (LSPR). The other type of samples having a diameter of about 1.5 nm presents discrete energy levels instead of electronic bands, and in this case, a typical fluorescence phenomenon can be observed. In the latter case, we can refer to such systems as nanoclusters. The XPS analyses were focused on the Ag 3D spectra looking for the possible shifts of the Ag doublet as a function of the particles size. The ultraviolet photoelectron spectroscopy with He II source was used for the investigation of possible changes in the valence band

Experimental Evidence of Single-Stranded DNA Adsorption on Multiwalled Carbon Nanotubes

Noncovalent DNA functionalization is one of the most used routes for the easy dispersion of carbon nanotubes (CNTs) yielding DNA-CNTs complexes with promising applications. Definition of the structure of adsorbed DNA is crucial, but the organization of polymer at the carbon interface is far from being understood. In comparison to single-walled nanotubes, not much effort has been devoted to assessing the structure of the adsorbed DNA on multiwalled carbon nanotubes (MWCNTs), where their metallic nature, large size, and polydispersity represent serious obstacles for both experimental and theoretical studies. As a contribution to fill this lack in these aspects, we investigated DNA-MWCNT complexes by dielectric spectroscopy (DS) which is sensitive to even small changes in the charge distribution at charged interfaces and was largely employed in studying the electric and conformational properties of polyelectrolytes, such as DNA, in aqueous solutions and at interfaces. The dielectric relaxation in the MHz range is the signature of DNA adsorption on CNTs and sheds light on its conformational properties. A detailed analysis of the conductivity of the DNA-MWCNT suspensions unequivocally proves that DNA is adsorbed in a single-stranded conformation while excess DNA reassociates without interfering with the stability of the complexes

A redox stable Pd-doped perovskite for SOFC applications

Structural and microstructural investigations of Pd-doped lanthanum strontium ferrite with stoichiometry La0.6Sr0.4Fe0.95Pd0.05O3d (LSFPd) were carried out under oxidizing and reducing conditions using XRD, Rietveld refinement, XPS, SEM, and TEM analyses. LSFPd exhibited a smart behaviour with a reversible redox structural transformation occurring upon switching from air to hydrogen and then back to air. Exsolution of nanometric metal particles was observed after reduction, and reincorporation of metal cations onto the perovskite structure was confirmed after reoxidation. The electrochemical performances were evaluated on electrolyte supported cells using LSFPd as symmetric electrodes. The self-regenerating redox process largely improved the anodic performance of LSFPd-based SOFCs because it mitigates the coarsening of metallic electrocatalysts at high temperature promoting a redox stable behaviour. Fuel cell tests revealed promising performance in terms of maximum power output and redox stability