Electrical properties of mechanically activated zinc oxide

Microstructural properties of a commercial zinc oxide powder were modified by mechanical activation in a high-energy vibro-mill. The obtained powders were dry pressed and sintered at 1100 degrees C for 2 h. The electrical properties of grain boundaries of obtained ZnO ceramics were studied using an ac impedance analyzer. For that purpose, the ac electrical response was measured in the temperature range from 23 to 240 degrees C in order to determine the resistance and capacitance of grain boundaries. The activation energies of conduction were obtained using an Arrhenius equation. Donor densities were calculated from Mott-Schottky measurements. The influence of microstructure, types and concentrations of defects on electrical properties was discussed

Modification of the structural and optical properties of commercial ZnO powder by mechanical activation

Mechanical activation was used as a method for modification of the structural and optical properties of commercial ZnO powder. For this purpose zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Starting and modified ZnO samples were characterized using XRD, BET and TEM measurements. Optical properties of these samples were investigated by Raman and photoluminescence (PL) spectroscopy. The color of commercial ZnO powder was white while mechanically activated ZnO powder was dark yellow, indicating the presence of nonstoichiometry. In the Raman spectra of non-activated sample Raman modes of bulk ZnO were observed, while the spectra of modified samples point out structural and stoichiometric changes. The PL spectra of modified samples excited by 325 and 442 nm lines of a He-Cd laser show great difference with respect to the spectra of the original sample. This study confirms that change in the defect structure of the ZnO crystal lattice introduced by mechanical activation affects the optical properties of this material

The effects of nonstoichiometry on optical properties of oxide nanopowders

In this paper we illustrate the change of optical properties of mechanically activated wurtzite ZnO powder and laser synthesized anatase TiO2 nanopowder due to the nonstoichiometry caused by mechanical activation and/or laser irradiation in vacuum. Both of the investigated materials are widely used in optoelectronics and the examination of their optical properties under different preparation and environmental conditions is of great practical interest

Evaluation of the patients with Grave's ophthalmopathy after the corticosteroids treatment

Background/Aim. Graves' ophthalmopthy is one of the most common causes of exophthalmos as well as the most common manifestation of Graves' disease. The treatment of Graves' ophthalmopathy includes ophthalmological and endocrinological therapy. The aim of this study was to clinically evaluate the patients with Graves' ophthalmopathy treated with corticosteroids. Methods. Evaluation of 21 patients was performed in the Ophthalmology Clinic and Endocrinology Clinic, Clinical Centre Kragujevac, in the period from 2009 to 2010. They were treated with pulse doses of intravenous corticosteroids. They were referred to ophthalmologist by endocrinologist in euthyroid condition in the active phase of Graves' ophthalmopathy (ultrasonography of orbit findings and positive findings of antithyroid stimulating hormone receptor antibody - anti-TSH R Ab). The clinical activity score (CAS) and NO SPECS classification for evaluation of disease severity were used. Ophthalmological examination includes: best corrected visual acuity, slit-lamp exam, Hertels' test, direct ophthalmoscopy and ultrasonography of the orbit. Results. According to our results 76.19% of the patients were female; mean age of the patients was 35.2 ± 5.6 years. According to CAS classification after 6 months of the treatment recovery was shown in 23.81% of the patients, partial amelioration in 47.62% and no clinical amelioration in 28.57% of the patients. We achieved better results with male, young patients with high clinical activity score. Good results were observed after the first dose of corticosteroids, much better CAS after the third dose, which maintained until 6 months after the first treatment. Conclusion. Our results signify that intravenous pulse dose of corticosteroids treatment of the patients with Graves' ophthalmopthy is safe, comfortable, clinically justified and accessible for the clinicians and patients. Positive results are achieved after the first dose with increasing trend up to the third dose, which was maintained for the next three months

Influence of gaseous laser in continuous-wave and pulse regimes on biomaterial characteristics

Aromatic plants and laser beam wavelength in the red range of visible spectra (623.8 nm), most commonly used for treating plant species, were selected. As there is not much information in the references, it is necessary to set a scale with qualitative and partially quantitative evaluations of the results. Specimens of thyme seed (Thymus vulgaris) were selected as aromatic plants for studying the effect of low-power lasers on plant development, and continuous He-Ne laser, with irradiation times in the range of minutes

Taeniosis and cysticercosis in Serbia, 1990-2018: Significance of standard of living

Objectives: As is the case for all of Southeast Europe, Serbia is an area traditionally endemic for Taenia saginata and Taenia solium infections. This study was performed to analyse the epidemiological data on taeniosis and cysticercosis in Serbia for the period 1990-2018. Methods: Data on cases of T. saginata and T. solium infection were collected via a systematic search of published articles, the grey literature, and official reports, as well as by performing clinical observational studies of patients treated in the departments for infectious diseases of hospitals and university clinics in Serbia. Results: A total of 212 cases of taeniosis were reported, all between 1997 and 2004 when taeniosis was notifiable (incidence range 0.04-0.9/100 000 population/year). From 1990 to 2018, 170 cases of cysticercosis (all but one of neurocysticercosis), were registered (incidence range 0-0.29/100 000 population/year), with a strong decrease since 2000 and a single case in the last 9 years. The annual number of cases of both taeniosis (Pearson's r = 0.914, p = 0.001) and cysticercosis (Pearson's r = 0.582, p = 0.014) correlated with the consumer price index. Conclusions: In Serbia, T. saginata and T. solium infections are autochthonous but occur only sporadically. However, the potential for re-emergence exists, depending on the socio-economic state of the country

Children’s Internet use and physical and psychosocial development

IntroductionInternet use (IU) commonly refers to sedentary lifestyle and may be addictive, especially among children. The aim of this study was to investigate the relationship between IU and some aspects of child physical and psychosocial development.MethodologyWe conducted a cross-sectional survey by using a screen-time based sedentary behavior questionnaire and Strengths and Difficulties Questionnaire (SDQ)—among 836 primary school children in the Braničevo District. The children’s medical records were analysed for vision problems and spinal deformities. Their body weight (BW) and height (BH) were measured and body mass index (BMI) was calculated as BW in kilograms divided by BH in meters squared (kg/m2).ResultsThe average age of respondents was 13.4 (SD 1.2) years. The mean duration of daily Internet use and sedentary behavior was 236 (SD 156) and 422 (SD 184) minutes, respectively. There was no significant correlation between daily IU and vision problems (near sightedness, farsightedness, astigmatism, strabismus), and spinal deformities. However, daily Internet use is significantly associated with obesity (p < 0.001) and sedentary behavior (p = 0.01). There was significant correlation between emotional symptoms with total Internet usage time, and total sedentary score (p < 0.001 for both, r = 0.141 and r = 0.132, respectively). There was a positive correlation between the total sedentary score of children and hyperactivity/inattention (r = 0.167, p < 0.001), emotional symptoms (r = 0.132, p < 0.001), and conduct problems (r = 0.084, p < 0.01).ConclusionIn our study, children’s Internet use was associated with obesity, psychological disturbances and social maladjustment

Microstructural characterization of mechanicallyactivated ZnO powders

In this paper, changes of microstructural characteristics of disperse systems during mechanical activation of zinc oxide (ZnO) have been investigated. ZnO powder was activated by grinding in a planetary ball mill in a continuous regime in air during 300 min at the basic disc rotation speed of 320 rpm and rotation speed of bowls of 400 rpm but with various balls-to-powder mass ratios. During ball milling in a planetary ball mill, initial ZnO powder suffered high-energy impacts. These impacts are very strong, and large amounts of microstructural and structural defects were introduced in the milled powders. The morphology and dispersivity of particles and agglomerates of all powders were investigated by scanning electron microscopy and scanning transmission electron microscopy. The specific surface area of initial ZnO powder was determined as 3.60 m(2) g(-1) and it increased to 4.42 m(2) g(-1) in mechanically activated powders. An increase of the ball-to-powder mass ratio led to a decrease of particle dimensions as well as increased the tendency for joining into quite compact agglomerates, that is aggregates, compared with the very loose, soft initial agglomerates. The obtained results pointed out that activation of ZnO powders produces a highly disperse, nano-scaled mixture of small particles, that is crystallites with sizes in the range of 10-40 nm. Most of these particles are in the form of aggregates with dimensions of 0.3-0.1 mu m. The crystallite and aggregate size strongly depend on milling conditions, that is ball-to-powder mass ratio, as shown in this investigation

Preparation of ultrathin PZT films by a chemical solution deposition method from a polymeric citrate precursor

Ultrathin PZT film was prepared using a chemical solution deposition method from polymeric citrate precursors. The PZT solution was spin-coated on an amorphous silica layer formed on a Si(l 0 0) substrate. The films were thermally treated from the substrate side with a low heating rate (1 degrees/min) up to 700 degrees C and finally annealed for 10 h. Ultrathin PZT films without microstructural instability were prepared in spite of high temperature and long annealing time. AFM and HRTEM investigations revealed the formation of a well-developed dense microstructure consisting of spherical crystallites (4-7 nm). Low roughness (2.2 nm) of a similar to 26 nm thick layer was obtained for a two-layered PZT film. The grazing incidence X-ray diffraction (GIXRD) measurements confirmed the polycrystalline structure of ultrathin PZT films. Also, GIXRD and electron energy dispersive X-ray (EDS) analysis showed that compositional variations were smaller than expected, in spite of the long annealing time

Defect induced variation in vibrational and optoelectronic properties of nanocrystalline ZnO powders

Structural disorder of ZnO nanopowders with mean crystallite size down to 15 nm, produced by mechanical activation in high energy mills, has been analyzed by x-ray diffraction and Raman spectroscopy. The influence of such disorder on optical and electronic properties of activated ZnO nanopowders has been investigated using photoluminescence spectroscopy and spectroscopic ellipsometry. A revised interpretation of the resonant enhancement of the first and second order Raman scattering by the E-1(LO) phonons in highly disorder ZnO nanopowders has been proposed. Detailed analysis of resonant Raman effects in ZnO powders under sub band gap excitation has given valuable information about defect induced electronic states in the band gap of ZnO. Systematic trend in the electron-phonon coupling strength, with the correlation length which depends on lattice disorder in ZnO, has been also demonstrated