Electrical properties of ZnO varistors prepared by direct mixing of constituent phases

Varistor samples containing different amounts of constituent phases were prepared by direct mixing of constituent phases. Detailed electrical characterization was performed to explain the influence of minor phases (spinel and intergranular phases) on overall properties. Characterization included investigation of the non-linear coefficients (α), breakdown electric field (EB), leakage currents (JL), grain boundary barrier hight (ΦB) and constant β from current-voltage characteristics, as well as calculation of activation energies for conduction (EA) from ac impedance spectroscopy in the temperature interval 30-410°C. Varistors sintered at 1100 °C for 1 h showed pronounced differences in electrical properties depending on relative molar ratios of the phases. Results were discussed in the sense of possible reduction of the content of minor phases in ZnO varistors

EFFECTIVE DOSE FOR REAL POPULATION EXPOSED TO INDOOR RADON IN DWELLINGS OF THE FORMER URANIUM MINE AREA KALNA (EASTERN SERBIA)

This paper deals with calculated effective doses that members of real population received from radon gas and its short lived progeny during air inhalation in their dwellings at field site Kalna in Eastern Serbia. There are two crucial parameters in effective dose calculation: Dose Conversion Factor (DCF) for particular subjects (including real gender, age and physical activity level) and indoor concentration of radon and its short lived progeny in field area. According to the results of indoor radon measurements in the area of former uranium mine, Kalna, the effective dose for this real population was estimated by using the dosimetric lung model, developed by authors according ICRP Publication 66. Authentic software was developed for determination of effective dose per unit inhaled activity of radon progeny, DCF expressed in unit [mSv/WLM]. The results, obtained according to ICRP 66 dosimeter lung model, were compared with results calculated according to ICRP Publication 65. The dosimetric results were, also, compared and discussed with epidemiological approach data, according to UNSCEAR

REACTION OF TABLE GRAPE VARIETIES TO LOW WINTER TEMPERATURES

The aim ofthis study was toinvestigate theresistanceof winter buds to lowwinter temperatures oneighttablevarieties of differentripening time. The study was conducted during vine dormancy at three testing dates during winter i.e. over the last ten days of the three winter months of December, January and February. At the first, second and third dates, the air temperature in the freezing chamber was reduced to - 15oC, -20oC, and -10oC, respectively.The analysis of the average values for the study period shows that Muscat Hamburg and Smederevo Muscat had the lowest and highest average percentage of completely frozen buds (48.97% and 58.84%, respectively). The average values for partly frozen buds ranged from 29.17 % in Afuz-Ali to 33.11 % in Muscat Hamburg. The evaluation of the data on unfrozen buds suggests that the average values were within the range of 11.15 % (Smederevo Muscat) to 17.91 % (Muscat Hamburg)

Interactive histogenesis of axonal strata and proliferative zones in the human fetal cerebral wall

Development of the cerebral wall is characterized by partially overlapping histogenetic events. However, little is known with regards to when, where, and how growing axonal pathways interact with progenitor cell lineages in the proliferative zones of the human fetal cerebrum. We analyzed the developmental continuity and spatial distribution of the axonal sagittal strata (SS) and their relationship with proliferative zones in a series of human brains (8-40 post-conceptional weeks; PCW) by comparing histological, histochemical, and immunocytochemical data with magnetic resonance imaging (MRI). Between 8.5 and 11 PCW, thalamocortical fibers from the intermediate zone (IZ) were initially dispersed throughout the subventricular zone (SVZ), while sizeable axonal "invasion" occurred between 12.5 and 15 PCW followed by callosal fibers which "delaminated" the ventricular zone-inner SVZ from the outer SVZ (OSVZ). During midgestation, the SS extensively invaded the OSVZ, separating cell bands, and a new multilaminar axonal-cellular compartment (MACC) was formed. Preterm period reveals increased complexity of the MACC in terms of glial architecture and the thinning of proliferative bands. The addition of associative fibers and the formation of the centrum semiovale separated the SS from the subplate. In vivo MRI of the occipital SS indicates a "triplet" structure of alternating hypointense and hyperintense bands. Our results highlighted the developmental continuity of sagittally oriented "corridors" of projection, commissural and associative fibers, and histogenetic interaction with progenitors, neurons, and glia. Histogenetical changes in the MACC, and consequently, delineation of the SS on MRI, may serve as a relevant indicator of white matter microstructural integrity in the developing brain

Chemical stability and electrical properties of Nb doped BaCe 0.9Y 0.1O 3-δ as a high temperature proton conducting electrolyte for IT-SOFC

BaCe 0.9-xNb xY 0.1O 3-δ (where x=0, 0.01, 0.03 and 0.05) powders were synthesized by solid-state reaction to investigate the influence of Nb concentration on chemical stability and electrical properties of the sintered samples. The dense electrolyte pellets were formed from the powders after being uniaxially pressed and sintered at 1550 °C. The electrical conductivities determined by impedance measurements in temperature range of 550-750 °C in different atmospheres (dry argon and wet hydrogen) showed a decreasing trend with an increase of Nb content. For all samples higher conductivities were observed in the wet hydrogen than in dry argon atmosphere. The chemical stability was enhanced with increasing of Nb concentration. It was found that BaCe 0.87Nb 0.03Y 0.1O 3-δ is the optimal composition that satisfies the opposite demands for electrical conductivity and chemical stability, reaching 0.8×10 -2 S cm -1 in wet hydrogen at 650 °C compared to 1.01×10 -2 S cm -1 for undoped electrolyte. © 2012 Elsevier Ltd and Techna Group S.r.l

Enhanced stability in CO2 of Ta doped BaCe0.9Y 0.1O3-δ electrolyte for intermediate temperature SOFCs

The influence of Ta concentration on the stability of BaCe 0.9-xTaxY0.1O3-δ (where x=0.01, 0.03 and 0.05) powders and sintered samples in CO2, their microstructure and electrical properties were investigated. The ceramic powders were synthesized by the method of solid state reaction, uniaxially pressed and sintered at 1550 °C to form dense electrolyte pellets. A significant stability in CO2 indicated by the X-ray analysis performed was observed for the samples with x≥0.03. The electrical conductivities determined by impedance measurements in the temperature range of 550-750 °C and in various atmospheres (dry argon, wet argon and wet hydrogen) increased with temperature but decreased with Ta concentration. The highest conductivities were observed in the wet hydrogen atmosphere, followed by those in wet argon, while the lowest were obtained in the dry argon atmosphere for each dopant concentration. The composition with Ta content of 3 mol% showed satisfactory characteristics: good resistance to CO2 in extreme testing conditions, while a somewhat reduced electrical conductivity is still comparable with that of BaCe0.9Y0.1O3-δ. © 2012 Elsevier Ltd and Techna Group S.r.l

Modeling of kinetics of pertechnetate removal by amino-functionalized glycidyl methacrylate copolymer

Technetium-99 comprises a significant health risk, since edible plants can bioaccumulate and convert it to more lipophilic species that cannot be excreted through urine. Batch kinetics of pertechnetate removal from aqueous solutions by two samples of crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) functionalized with diethylene triamine (PGME-deta) was investigated at the optimum pH value of 3.0, and the initial solution activity of 325 MBq dm(-3). PGME-deta was characterized by elemental analysis, mercury intrusion porosimetry, and scanning electron microscopy. Five kinetic models (pseudo-first, pseudo-second order, Elovich, Bangham, and intraparticle diffusion) were used to determine the best-fit equation for pertechnetate sorption. After 24 h, PGME-deta samples sorbed more than 98% of pertechnetate present, with maximum sorption capacity of 25.5 MBq g(-1), showing good potential for remediation of slightly contaminated groundwater

Effective Dose for Real Population Exposed to Indoor Radon in Dwellings of the Former Uranium Mine Area Kalna (Eastern Serbia)

This paper deals with calculated effective doses that members of real population received from radon gas and its short lived progeny during air inhalation in their dwellings at field site Kalna in Eastern Serbia. There are two crucial parameters in effective dose calculation: Dose Conversion Factor (DCF) for particular subjects (including real gender, age and physical activity level) and indoor concentration of radon and its short lived progeny in field area. According to the results of indoor radon measurements in the area of former uranium mine, Kalna, the effective dose for this real population was estimated by using the dosimetric lung model, developed by authors according ICRP Publication 66. Authentic software was developed for determination of effective dose per unit inhaled activity of radon progeny, DCF expressed in unit [mSv/WLM]. The results, obtained according to ICRP 66 dosimeter lung model, were compared with results calculated according to ICRP Publication 65. The dosimetric results were, also, compared and discussed with epidemiological approach data, according to UNSCEAR.1st East European Radon Symposium (FERAS), Sep 02-05, 2012, Cluj Napoca, Romani

The indoor radon survey in Serbian schools: can it reflect also the general population exposure?

A systematic indoor radon survey in elementary schools of Serbia is underway since 2008. Its current first phase covers all elementary schools in predominantly rural communities of Southern Serbia. The design of the survey, its implementation and the current state of its realization is shortly described. Part of this paper is devoted to discussion of the question if this survey could produce results representative also of the radon concentration in dwellings and of radon exposure of the general population, discussing some statistical aspects of representativity which arose during the work, namely, if the implementation leads to an unbiased estimate of the targeted quantities