Thermopower in the strongly overdoped region of single-layer Bi2Sr2CuO6+d superconductor

The evolution of the thermoelectric power S(T) with doping, p, of single-layer Bi2Sr2CuO6+d ceramics in the strongly overdoped region is studied in detail. Analysis in term of drag and diffusion contributions indicates a departure of the diffusion from the T-linear metallic behavior. This effect is increased in the strongly overdoped range (p~0.2-0.28) and should reflect the proximity of some topological change.Comment: 4 pages, 4 figure

Infrared and Raman spectra of LiV2O5 single crystals

The phonon dynamics of LiV2O5 single crystals is studied using infrared and Raman spectroscopy techniques. The infrared-active phonon frequencies and dielectric constants are obtained by oscillator fitting procedure of the reflectivity data measured at room temperature. The Raman scattering spectra are measured at room temperature and at T=10 K in all nonequivalent polarized configurations. The assignment of the phonons is done by comparing the infrared and Raman spectra of LiV2O5 and NaV2O5. The factor-group-analysis of the LiV2O5 crystal symmetry and of its constituent layers is performed to explain the symmetry properties of the observed modes. We concluded that layer symmetry dominates in the vibrational properties of this compound.Comment: 10 pages, 5 figure

Biofilm formation of achromobacter xylosoxidans on contact lens

Achromobacter spp. may contaminate lenses, lens cases, and contact lens solutions and cause ocular infections. The aim of this study was to investigate the possibility of isolated strain of Achromobacter xylosoxidans to form biofilm on the surface of soft contact lenses (CL), to quantify the production of the formed biofilm, and compare it with the reference strains (Pseudomonas aeruginosa, Staphylococcus aureus, and Haemophilus influenzae). Bacterial strain isolated from one contact lens case was identified as A. xylosoxidans using Vitek2 Automated System. Biofilm forming capacity of isolated strain of A. xylosoxidans and reference strains of P. aeruginosa, S. aureus, and H. influenzae on soft CL were analyzed by commonly used microtitre plate method. Our results showed that isolated strain of A. xylosoxidans was capable to form biofilm on the surface of soft contact lens. A. xylosoxidans was strong biofilm producer while all examined reference strains were moderate biofilm producers. A. xylosoxidans appears to be superior biofilm producer on soft CL compared to reference strains

Failure of the empirical OCT law in the Bi2Sr2CuO6+d compound

We have studied the evolution of the thermoelectric power S(T) with oxygen doping of single-layered Bi2Sr2CuO6+d thin films and ceramics in the overall superconducting (Tc, S290K) phase diagram. While the universal relation between the room-temperature thermopower S290K and the critical temperature is found to hold in the strongly overdoped region (d>0.14), a strong violation is observed in the underdoped part of the phase diagram. The observed behaviour is compared with other cuprates and the different scenarios are discussed.Comment: 7 pages, 5 figure

Interfacial effects in La2/3Sr1/3MnO3 thin films with different complex oxide capping layers

Interfacialeffects in sputtered La2/3Sr1/3MnO3thin films with different capping layers (MgO, LaAlO3, SrTiO3, NdGaO3, and Au) have been locally investigated by means of x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Mn L3,2-edge. Data were acquired by using the total electron yield detection mode thus guaranteeing maximum sensitivity to the interface. The data show that LaAlO3 capping almost does not modify the bulklike Mn valence at the interface. In case of SrTiO3 and Au, the presence of divalent Mn is detected, whereas MgO and NdGaO3 capping lead to an increase of the Mn valence oxidation state. The modification of the nominal Mn valence state leads to depressed surfacemagnetization.We acknowledge financial support from the Spanish MEC (MAT2009-08024 and MAT2008-04931/NAN), CONSOLIDER (CSD2007-00041) and FEDER program. The research leading to these results has received funding from the European Community’s Seventh Framework Program (FP7/2007-2013) under Grant No. 226716. Z.K. thanks the Spanish MEC for the financial support through the RyC program.Peer reviewe

Particle growing mechanisms in Ag-ZrO2 and Au-ZrO2 granular films obtained by pulsed laser deposition

Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO2 matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08<x(Ag)<0.28 and 0.08<x(Au)<0.52). High resolution transmission electron microscopy (TEM) showed regular distribution of spherical Au and Ag nanoparticles having very sharp interfaces with the amorphous matrix. Mean particle size determined from X-ray diffraction agreed with direct TEM observation. The silver mean diameter increases more abruptly with metal volume content than that corresponding to gold particles prepared under the same conditions. Two mechanisms of particle growing are observed: nucleation and particle coalescence, their relative significance being different in both granular systems, which yields very different values of the percolation threshold (xc(Ag)~0.28 and xc(Au)~0.52).Comment: 6 figure

Quantification of biofilm formation on silicone intranasal splints: An in vitro study

Objectives: Biofilms are associated with persistent infections and resistant to conventional therapeutic strategies. The aim of this study was to investigate the quantity of biofilm produced on silicone intranasal splints. Methods: Quantity of biofilm formation on silicone splints (SS) was tested on 15 strains of Staphylococcus aureus and Moraxella catarrhalis, respectively. Antimicrobial susceptibility testing was performed in accordance with European Committee on Antimicrobial Susceptibility Testing recommendations. Results: All tested strains formed different amounts of biofilm on SS: 66.7% S. aureus and 93.3% M. catarrhalis were weak biofilm producers and 33.3% S. aureus and 6.7% M. catarrhalis were moderate biofilm producers. S. aureus formed significantly higher quantity of biofilm compared with M. catarrhalis (p  Conclusion: Quantity of biofilm on SS is highly dependent on bacterial species and their resistance patterns. Future studies are needed to ascertain another therapeutic option for prophylaxis prior to SS placement

Lattice vibrations of alpha'-NaV_2O_5 in the low-temperature phase. Magnetic bound states?

We report high resolution polarized infrared studies of the quarter-filled spin ladder compound alpha'-NaV_2O_5 as a function of temperature (5K <= T <= 300K). Numerous new modes were detected below the temperature T_c=34K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at T_c and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2, 1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.Comment: 15 pages, 13 Postscript figure

Charge-ordering and optical transitions of LiV2O5 and NaV2O5

We present the measurements of the polarized optical spectra of NaV2O5 and LiV2O5. In an energy range from 0.5 to 5.5 eV we observe similar peaks in the E parallel a spectra of LiV2O5 and NaV2O5, which suggests similar electronic structure along the a axis in both materials. On the other hand, we find an almost complete suppression of the peaks in sigma_b of LiV2O5 around 1 and 5 eV. We attribute this suppression to the charge localization originating from the existence of double-chain charge-ordering patterin in LiV2O5.Comment: 7 pages, 3 figures final version, to appear in PR

Optical properties and electronic structure of Ca-doped alpha'-NaV2O5

The dielectric function of alpha'-Na(1-x)Ca(x)V2O5 (0 < x < 20%) was measured for the a and b axes in the photon energy range 0.8-4.5 eV at room temperature. By varying the Ca-concentration we control the relative abundancy of V4+ and V5+. We observe that the intensity of the main optical absorption peak at 1 eV is proportional to the number of V5+ ions. This rules out the interpretation as a V4+ d-d excitation, and it establishes that this is the on-rung bonding-antibonding transition.Comment: 6 pages, ReVTeX, 5 figures in encapsulated postscript forma