Influence of mechanical activation on synthesis of zinc metatitanate

Investigations of a ZnO-TiO2 binary oxide mixture during mechanical treatment were mainly focused on obtaining orthotitanate Zn2TiO4 with a spinel structure. Due to the specific way of energy transfer during mechanical treatment using a high-energy ball mill, the system passes through low temperature ZnTiO3 metatitanate phase formation. Mechanical activation was performed on an equimolar ratio mixture of ZnO and TiO2. The anatase phase was previously submitted to heat treatment for achieving a starting mixture rich in a rutile phase. Milling conditions were preset for observing the formation of a low temperature ZnTiO3 phase with a perovskite structure. The powder microstructure was characterized using scanning electron microscopy. A nitrogen gas sorption analyzer with the BET method was used to determine the specific surface area and porosity, indicating changes of powder sample properties during mechanical activation. Also, X ray powder diffractometry was applied to obtain the phase composition. Powders were then pressed into pellets and their compressibility was observed through density changes. According to microstructures obtained by scanning electron microscopy analysis, the system underwent a primary and secondary agglomeration process. Specific surface area measurements supported that conclusion. Compressibility investigations established the difference between compressibility of the non-activated mixture and activated powders. X-ray diffraction analysis revealed that a perovskite structure forms simultaneously with a spinel phase during the process of mechanical activation

Investigation of zinc stannate synthesis using photoacoustic spectroscopy

Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200°C with a heating rate of 5°C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained a correlation between thermal diffusivity and experimental conditions as well the samples microstructure characteristics was discussed.

Influence of nuclear radiation and laser beams on optical fibers and components

The influence of nuclear radiation and particles has been the object of investigation for a long time. For new materials and systems the research should be continued. Human activities in various environments, including space, call for more detailed research. The role of fibers in contemporary communications, medicine, and industry increases. Fibers, their connections and fused optics components have one type of tasks - the transmission of information and power. The other type of tasks is reserved for fiber lasers: quantum generators and amplifiers. The third type of tasks is for fiber sensors, including high energy nuclear physics. In this paper we present some chosen topics in the mentioned areas as well as our experiments with nuclear radiation and laser beams to fiber and bulk materials of various nature (glass, polymer, metallic, etc.)

Electrical conductivity of plasmas of DB white dwarf atmospheres

The static electrical conductivity of non-ideal, dense, partially ionized helium plasma was calculated over a wide range of plasma parameters: temperatures $1\cdot 10^{4}\textrm{K} \lesssim T \lesssim 1\cdot 10^{5}\textrm{K}$ and mass density $1 \times 10^{-6} \textrm{g}/\textrm{cm}^{3} \lesssim \rho \lesssim 2 \textrm{g}/\textrm{cm}^{3}$. Calculations of electrical conductivity of plasma for the considered range of plasma parameters are of interest for DB white dwarf atmospheres with effective temperatures $1\cdot 10^{4}\textrm{K} \lesssim T_{eff} \lesssim 3\cdot 10^{4}\textrm{K}$. Electrical conductivity of plasma was calculated by using the modified random phase approximation and semiclassical method, adapted for the case of dense, partially ionized plasma. The results were compared with the unique existing experimental data, including the results related to the region of dense plasmas. In spite of low accuracy of the experimental data, the existing agreement with them indicates that results obtained in this paper are correct

Klinički aspekti stražnjeg uveitisa kod očne sarkoidoze

Two clinical forms of the “white spot” syndrome in patients with posterior uveitis in definitive and presumable ocular sarcoidosis were analyzed. Group 1 was characterized by periphlebitis and discrete white spots around the vein of the retina, so-called “candle-wax”, whereas group 2 showed yellow-orange solitary nodules located at the choroid, i.e. multifocal choroiditis. Visual acuity and the severity of clinical presentation were assessed in both groups. Visual acuity, Snellen equivalent was 0.52±0.36 in group 1 and 0.82±0.39 in group 2 with lesions at the level of choroid. One-way analysis of variance ANOVA showed a statistically significant between-group difference in visual acuity (p=0.03). The mean severity of clinical presentation was 11.80±2.04 points in group 1 and 5.80±4.18 points in group 2. T-test for independent samples yielded a statistically significant difference between the groups (p=0.02). A statistically significant difference in visual acuity was the result of vasculitis in the group with the “candle-wax” phenomenon, which is associated with retinal vasculitis and causes cystoid macular edema and reduction of visual acuity. Complications such as cataract, glaucoma and neovascularization, which also decrease visual acuity, were more frequent in group 1.Analizirana su dva klinička oblika sindroma “bijelih točaka“ kod bolesnika sa stražnjim uveitisom u okviru definitivne i pretpostavljane sarkoidoze oka. Prva skupina je imala periflebitis i diskretne bijele mrlje oko venula mrežnice, tzv. “kapi svijeće“. Druga skupina je imala žuto-narančaste solitarne čvoriće na razini koroida, tj. multifokalni koroiditis. Ispitana je vidna oštrina i težina kliničke slike obiju skupina. Vidna oštrina, Snellenov ekvivalent bio je 0,52±0,36 u prvoj skupini i 0.82±0,39 u drugoj skupini s lezijama na razini koroida. Jednosmjerna analiza varijance ANOVA je pokazala statistički značajnu razliku u vidnoj oštrini (p=0,03). Težina kliničke slike bila je 11,80±2,04 bodova za prvu skupinu i 5,80±4,18 bodova za drugu skupinu. T-testom za nezavisne uzorke izračunata je statistički značajna razlika između skupina (p=0,02). Statistički značajna razlika u vidnoj oštrini bila je rezultat vaskulitisa u skupini s fenomenom “kapi svijeće“ koji je povezan s vaskulitisom mrežnice te uzrokuje cistoidni edem makule i smanjenje vidne oštrine. Komplikacije kao što su katarakta, glaukom i neovaskularizacija koje također utiču na smanjenje vidne oštrine bili su češći u prvoj skupini

Novel Meteor Simulation and Observation Techniques that Emerged from Big-Sky-Earth COST Action

The cooperation of scientists in Big-Sky-Earth COST Action creates an emergent group of researchers with relation to meteor science. Selected cases of development of novel approaches and techniques for meteor simulation and observation are presented

Atom-Rydberg atom chemi-ionization/recombination processes in the hydrogen clouds in Broad Line Region of AGNs

International audienc

The collisional atomic processes of Rydberg alkali atoms in geo-cosmical plasmas

International audienc

The Influence of Solar Spectral Lines on Electron Concentration in Terrestrial Ionosphere

One of the methods of detection and analysis of solar flares is observing the time variations of certain solar spectral lines. During solar flares, a raise of electron concentration occurs in Earth’s ionosphere which results in amplitude and phase variations of the recorded very low frequency (VLF) waves. We compared the data obtained by the analysis of recorded VLF signals and line spectra for different solar flares. In this paper we treated the DHO VLF signal transmitted from Germany at the frequency of 23.4 kHz recorded by the AWESOME system in Belgrade (Serbia) during solar flares in the period between 10:40 UT and 13:00 UT on 2011 April 22