Comparative Mössbauer study of high Tc superconductors

¹⁵¹Eu,¹¹⁹Sn and⁵⁷Fe Mössbauer spectroscopy was used to study high T_c superconductors. Mössbauer spectra of Sn substituted EuBa₂Cu₃O_7–y, YBa₂Cu₃O_7–y and TlBaCaCuO_4.5+y as well as of Fe Substituted TlBaCaCuO_4.5+y were compared. The Sn and Fe ions replace the regular Cu positions in the YBa₂Cu₃O_7–y and in TlBaCaCuO_4.5+y materials, fespectively, while the localization of tin atoms in both the¹¹⁹Sn doped EuBa₂Cu₃O_7–y and TlBaCaCuO_4.5+y superconductors is different from that of previous cases. Up to our knowledge, this is the first publication on a Mössbauer study of a Tl-containing superconductor.     

Characterization of a new qQq-FTICR mass spectrometer for post-translational modification analysis and top-down tandem mass spectrometry of whole proteins

The use of a new electrospray qQq Fourier transform ion cyclotron mass spectrometer (qQq-FTICR MS) instrument for biologic applications is described. This qQq-FTICR mass spectrometer was designed for the study of post-translationally modified proteins and for top-down analysis of biologically relevant protein samples. The utility of the instrument for the analysis of phosphorylation, a common and important post-translational modification, was investigated. Phosphorylation was chosen as an example because it is ubiquitous and challenging to analyze. In addition, the use of the instrument for top-down sequencing of proteins was explored since this instrument offers particular advantages to this approach. Top-down sequencing was performed on different proteins, including commercially available proteins and biologically derived samples such as the human E2 ubiquitin conjugating enzyme, UbCH10. A good sequence tag was obtained for the human UbCH10, allowing the unambiguous identification of the protein. The instrument was built with a commercially produced front end: a focusing rf-only quadrupole (Q0), followed by a resolving quadrupole (Q1), and a LINAC quadrupole collision cell (Q2), in combination with an FTICR mass analyzer. It has utility in the analysis of samples found in substoichiometric concentrations, as ions can be isolated in the mass resolving Q1 and accumulated in Q2 before analysis in the ICR cell. The speed and efficacy of the Q2 cooling and fragmentation was demonstrated on an LCMS-compatible time scale, and detection limits for phosphopeptides in the 10 amol/muL range (pM) were demonstrated. The instrument was designed to make several fragmentation methods available, including nozzle-skimmer fragmentation, Q2 collisionally activated dissociation (Q2 CAD), multipole storage assisted dissociation (MSAD), electron capture dissociation (ECD), infrared multiphoton induced dissociation (IRMPD), and sustained off resonance irradiation (SORI) CAD, thus allowing a variety of MS(n) experiments. A particularly useful aspect of the system was the use of Q1 to isolate ions from complex mixtures with narrow windows of isolation less than 1 m/z. These features enable top-down protein analysis experiments as well structural characterization of minor components of complex mixtures.     

Charmonium sum rules andη c production in two-photon reactions

The coupling of the pseudoscalar charmonium stateη _c to two photons is calculated using the charmonium sum rules. The resulting value of the two-photon decay width is Λ=5.6 KeV (±10%). If the virtualness of one of the photons is increased from |k ₁ ² |=0 to |k ₁ ² |=1 GeV² the coupling decreases about 10%.     

Surface energy properties of lignin particles studied by inverse gas chromatography and interfacial adhesion in polyester composites with electromagnetic transparency

We introduce a simple spray drying method for the scaleup production of spherical organic (lignin) particles with sizes between 0.85 and 1.57 µm. We assess the surface energy of the lignin particles by inverse gas chromatography to reveal their role in composites synthesized with unsaturated polyester. Such nanocomposites are shown to be transparent to electromagnetic irradiation (millimeter wave bands). The permittivity and tanδ of the composite material reached values 3.01 and 0.01 at 28 GHz with 10% lignin content. Vinyl groups were introduced on the surface of the particles to achieve enhanced interfacial adhesion, and resulted in a reduced relative permittivity (2.75). Together with wave interactions, the mechanical and thermal properties of the composites are put in perspective, opening new opportunities in the development of bio-based devices for 5G high-speed communication.

     

Surfactant-mediated growth revisited

The x-ray structure analysis of the oxygen-surfactant-mediated growth of Ni on Cu(001) identifies up to 0.15 monolayers of oxygen in subsurface octahedral sites. This questions the validity of the general view that surfactant oxygen floats on top of the growing Ni film. Rather, the surfactant action is ascribed to an oxygen-enriched zone extending over the two topmost layers. Surface stress measurements support this finding. Our results have important implications for the microscopic understanding of surfactant-mediated growth and the change of the magnetic anisotropy of the Ni films.