Bonding in uranium oxides: The role of 5f electrons

X-ray photoemission spectra of valence and bonding bands of UO₂, U₃O₈ and UO₃ are presented. The gradual transfer of localized 5f electrons into the bonding band as a function of oxygen content has been studied in these oxides.     

Epicocconone, A New Cell-Permeable Long Stokes' Shift Fluorescent Stain for Live Cell Imaging and Multiplexing

Epicocconone is a heterocyclic natural product from the fungus Epicoccum nigrum that fluoresces weakly in the green (520 nm). However, cells exposed to epicocconone rapidly absorb the dye and become bright orange fluorescent because the natural product reacts reversibly with proteins. The orange fluorescence is enhanced in lipophilic environments, allowing the visualization of membranous organelles and lipid rafts but does not stain oligonucleotides. As the unconjugated dye has no orange fluorescence, there is no need to wash out the excess fluorophore. Epicocconone is a neutral, non-toxic, small molecule that appears to diffuse readily into live of fixed cells without the need for permeabilization. These features enable the real-time imaging of live cells and the study of organelle movements. Cells stained with epicocconone are excitable by common lasers (UV, 405, 488, and 532 nm) and its long Stokes' shift allows multiplexing applications with more common short Stokes' fluorophores using a single light source.     

Low field63Cu NMR study of indirect nuclear spin-spin coupling in YBa2Cu3O6.9. A new approach to probe strong correlation effects in high-T c superconductors

The authors carried out a low field (6.3 kOe) NMR measurement of the Gaussian component of⁶³Cu nuclear spin-spin relaxation rate 1/T _2G at the planar Cu site in a high-T _c superconductor YBa₂Cu₃O_6.9 (T _c=92 K). They demonstrate that the results provide quantitative information concerning the static spin susceptibility χ′(q) at non-zero wave vector q. The detailed analysis of the data assuming a model susceptibility peaked at the corner of first Brillouin zone q=Q (Q=(π/a, θ/a),a: lattice constant) shows that χ′(q) satisfies a Curie-Weiss law around q=Q. Stoner enhancement over the calculated Lindhard function at q=Q is estimated to be of the order of ～10–20. They also demonstrate that combined analysis of 1/T ₁ and 1/T _2G allows one to judge whether anomalous shift of the low frequency spectral weight of χ″(Q,ω) to higher frequencies (i.e.pseudo gap) exists or not. Application of the method to YBa₂Cu₃O_6.9 revealed no appreciable pseudo gap in the material.