92 research outputs found
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
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