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Lukic M.J.,Serbian Academy of Science and Arts | Jovalekic C.,Institute for Multidisciplinary Studies | Markovic S.,Serbian Academy of Science and Arts | Uskokovic D.,Serbian Academy of Science and Arts
Materials Research Bulletin | Year: 2014

Correlation between high-temperature electrical response and microstructural properties of dense hydroxyapatite with average grain size from micrometer to nanometer level in heating/cooling cycle was investigated. Grain interior and grain boundary contributions to overall conductivity were determined. Nanostructured hydroxyapatite exhibited enhanced grain interior conductivity, with significantly higher activation energy (∼2.4 eV) than that of coarsed microstructures (∼1.7 eV). This difference in activation energies is explained by the possible influence of dehydroxylation during materials fabrication procedure, which affected the amount of OH- ions as the main charge carriers. Grain boundary conductivity was similar for all microstructures, with activation energy above ∼2 eV, implying the OH- ions migration across grain boundaries. Electrical response in cooling cycle confirmed the trends found during heating. © 2014 Elsevier B.V. All rights reserved.

Nikolic L.M.,University of Belgrade | Rokic M.B.,Institute for Multidisciplinary Studies | Todorovic N.V.,University of Belgrade | Kartelija G.S.,University of Belgrade | And 2 more authors.
Biological Research | Year: 2010

The effect of extremely low frequency magnetic felds (50 Hz, 0.5 mT) - ELF-MF, on phosphate metabolism has been studied in the isolated ganglions of the garden snail Helix pomatia, after 7 and 16 days of snail exposure to ELF-MF. The infuence of ELF-MF on the level of phosphate compounds and intracellular pH was monitored by 31P NMR spectroscopy. Furthermore, the activity of enzymes involved in phosphate turnover, total ATPases, Na +/K +-ATPase and acid phosphatase has been measured. The exposure of snails to the ELF-MF for the period of 7 days shifted intracellular pH toward more alkaline conditions, and increased the activity of investigated enzymes. Prolonged exposure to the ELF-MF for the period of 16 days caused a decrease of PCR and ATP levels and decreased enzyme activity, compared to the 7-day treatment group. Our results can be explained in terms of: 1. increase in phosphate turnover by exposure to the ELF-MF for the period of 7 days, and 2. adaptation of phosphate metabolism in the nervous system of snails to prolonged ELF-MF exposure.

Boskovic S.,Vinča Institute of Nuclear Sciences | Zec S.,Vinča Institute of Nuclear Sciences | Brankovic G.,Institute for Multidisciplinary Studies | Brankovic Z.,Institute for Multidisciplinary Studies | And 3 more authors.
Ceramics International | Year: 2010

Multiply doped ceria nanopowders were synthesized by applying MGNP (modified glycine/nitrate procedure). The overall concentration of dopants was kept constant (x = 0.2) whereby Gd ion as the main dopant was gradually substituted by Sm and by Sm + Y. The compositions of solid solutions were calculated by applying defect model introducing anion vacancy radius. Characterization of powders involved BET, TEM, XRD and chemical analyses. Densification was performed at 1500 °C, in an oxygen atmosphere for 1 h. The results showed that with increasing number of dopants, specific surface area of powders increased, followed by decrease of crystallite and grain sizes. Densification degree was also found to rise with increasing number of dopants. According to impedance measurements it was found that ionic conductivity was the highest 1.14 × 10-3 S cm-1 at 450 °C in sample doped with Gd, Sm and Y simultaneously. © 2009 Elsevier Ltd and Techna Group S.r.l.

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