Effect of superradiance on transport of diffusing photons in cold atomic gases

We show that in atomic gases cooperative effects like superradiance and subradiance lead to a potential between two atoms that decays like 1/r. In the case of superradiance, this potential is attractive for close enough atoms and can be interpreted as a coherent mesoscopic effect. The contribution of superradiant pairs to multiple scattering properties of a dilute gas, such as photon elastic mean free path and group velocity, is significantly different from that of independent atoms. We discuss the conditions under which these effects may be observed and compare our results to recent experiments on photon transport in cold atomic gases.     

GaN/LiNbO3 (0 0 0 1) interface formation calculated from first-principles

The stable adsorption sites for both Ga and N ions on the ideal and on the reconstructed LiNbO₃ (0 0 0 1) surface are determined by means of first-principle total energy calculations. A single N layer is found to be more strongly bound to the substrate than a single Ga layer. The adsorption of a GaN monolayer on the polar substrate within different orientations is then modeled. On the basis of our results, we propose a microscopic model for the GaN/LiNbO₃ interface. The GaN and LiNbO₃ (0 0 0 1) planes are parallel, but rotated by 30° each other, with in-plane epitaxial relationship [1 0 0]_GaN‖ [1 1  0]_LiNbO3. In this way the (0 0 0 1) plane lattice mismatch between GaN and LiNbO₃ is minimal and equal to 6.9% of the GaN lattice constant. The adsorbed GaN and the underlying LiNbO₃ substrate have parallel c-axes.     

Quantifying indium with ion chromatography in hydro‐ and biohydrometallurgical leaching solutions

A methodology has been developed to chromatographically quantify indium in polymetallic (bio)hydrometallurgical processing solutions using the Dionex IonPac CS5A column and pyridine‐2,6‐dicarboxylic acid eluent. Cu(II) and In(III) could be separated by elevating the column temperature to 45°C. The comparatively low stability constant of the In‐eluent complex (log K₂ = 3.8) required typical leaching samples to be diluted in the eluent rather than acid or water to overcome ligand competition between components of the sample solution and the eluent. The methodology was applied to leachates from (bio)hydrometallurgical processing of oxidic flue dust residues and sulfidic zinc ores, where both are promising candidates for the recovery of indium from low grade ores and metallurgical wastes. Indium, ferrous iron, ferric iron, copper, zinc, nickel, and manganese concentrations could be simultaneously quantified. The method was found suitable for samples containing at least 0.25 mg/L indium and an iron to indium ratio of up to 100:1.     

Adsorption and stability of streptavidin on cluster-assembled nanostructured TiOx films

The study of the adsorption of proteins on nanostructured surfaces is of fundamental importance to understand and control cell-surface interactions and, notably, cell adhesion and proliferation; it can also play a strategic role in the design and fabrication of nanostructured devices for postgenomic and proteomic applications. We have recently demonstrated that cluster-assembled nanostructured TiO x films produced by supersonic cluster beam deposition possess excellent biocompatibility and that these films can be functionalized with streptavidin, allowing the immobilization of biotinylated retroviral particles and the realization of living-cell microarrays for phenotype screening. Here we present a multitechnique investigation of the adsorption mechanisms of streptavidin on cluster-assembled TiO x films. We show that this nanostructured surface provides an optimal balance between adsorption efficacy and protein functionality. By using low-resolution protein arrays, we demonstrate that a layer of adsorbed streptavidin can be stably maintained on a cluster-assembled TiO x surface under cell culture conditions and that streptavidin retains its biological activity in the adsorbed layer. The adsorption mechanisms are investigated by atomic force microscopy in force spectroscopy mode and by valence-band photoemission spectroscopy, highlighting the potential role of the interaction of the exposed carboxyl groups on streptavidin with the titanium atoms of the nanostructured surface.     

Optical response of the Cu2S2 diamond core in (NGuaS)2Cl2

Density functional theory (DFT) and time‐dependent DFT calculations are presented for the dicopper thiolate complex Cu₂(NGuaS)₂Cl₂ [NGuaS=2‐(1,1,3,3‐tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu₂S₂Cl₂ core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the Cu_A center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural Cu_A models. The spectrum can be roughly divided in the known regions of metal d‐d absorptions and metal to ligand charge transfer regions. Nevertheless the chloride ions play an important role as electron donors, with the thiolate groups as electron acceptors. The bonding mechanism is dissected by means of charge decomposition analysis which reveals the large covalency of the Cu₂S₂ diamond core mediated between Cu and S‐S π and π* orbitals forming Cu‐S σ bonds. Measured resonant Raman spectra are shown for 360‐ and 720‐nm excitation wavelength and interpreted using the calculated vibrational eigenmodes and frequencies. The calculations help to rationalize the varying resonant behavior at different optical excitations. Especially the phenylene rings are only resonant for 720 nm. © 2016 Wiley Periodicals, Inc.