Electrophysical properties of microalloyed alumo-silicate ceramics as active dielectric

In this paper, electrophysical properties of porous alumo-silicate ceramics, modified by alloying with magnesium and microalloying with aluminum, were investigated. Complex multiphase system, as active microalloyed ceramics, has specific behavior under influence of external electrical field, which involves changes of dielectric losses and impedance, depending on frequency and temperature. Dielectric properties were measured in the frequency range 20 Hz - 1 MHz. Values for permittivity (εr) ranged between 140 - 430. Order of magnitude for electrical resistivity was about 106 Ωm, for impedance 104 - 108 Ω, and loss tangent had values about and greater than 0.05. Current flow through active dielectric takes place through dielectric barrier and throughout conduction bands of thin aluminum and magnesium metal films. Permittivity has nonlinear distribution and complex functional dependences because of significant nonhomogeneity of active microalloyed ceramics. Lower values of electrical resistivity are the result of complex electron and ion transfer of charge through solid phase and pores, with decreased potential barriers height, due to the influence of additives, ingredients and defects. [Projekat Ministarstva nauke Republike Srbije, br. III 45012 i br. ON 172057

The effects of colloidal SiO2 and inhibitor on the solid deposit formation in geothermal water of low hardness

Low solubility of SiO2 and its occurrence in geothermal waters in the form of ionic, colloidal and suspended state are the main cause of the solid deposit occurrence. Certain chemical types of silica, under the influence of Fe2+, Al3+, F−, OH- ions and other micro-constituents, and due to significantly decreased solubility of SiO2, stimulate nucleation, particle growth and solid deposit formation. The aim of this paper is to inhibit the process of nucleation and solid deposit formation by adding originally designed inhibitor in the form of an emulsion, when the total concentration of the present and added colloidal SiO2 is beyond the solubility limit (120 mg/dm3). By turbidimetric, SEM, EDS and XRD analysis, the processes of solid deposit formation were investigated in Vranjska Banja (Serbia) spa geothermal water source (water hardness of 4ºdH), and theoretical and practical conclusions were made

Application of Minkowski layer for microalloyed alumo-silicate ceramics grains fractal analysis

Porous aluminium-silicate ceramics, modified by alloying with magnesium and microalloying with alluminium belongs to a group of advanced multifunctional ceramics materials. This multiphase solid-solid system has predominantly amorphous microstructure and micro morphology. Intergranular and interphase areas are very complex, because they represent areas, where numbered processes and interactions take place, making new boundaries and regions with fractal nature. Solid contact between grains is actually very complex configuration of microcontacts with fractal nature. Fractal analysis of intergranular microstructure has included application of Minkowski layer. This layer is in correlation with fractal dimension, and defines grains contact probability. It represents convex layer of grains contour roughness and irregularity. Considering the fractal nature of intergranular contacts, it is possible to establish correlation between material electrical properties and fractal analysis, as a tool for future correlation with microstructure characterization

The influence of multifunctional microalloyed ceramics microstructure on its capacity properties

Modified porous alumo-silicate ceramics, alloyed with magnesium and microalloyed with aluminum, belongs to modern multifunctional ceramic materials. Microalloying has led to important changes in dielectric and electrical properties of ceramics, such as dielectric constant and electrical resistance. These changes are conditioned by the microstructural properties of modified porous ceramics. The obtained results have shown the unity of the influence of composition, structure, morphology and application of microalloyed multifunctional alumosilicate ceramics on electrophysical properties. Microstructural investigations have shown that this type of ceramics has an amorphous-crystal structure, which causes important changes in its electrical properties and affects its activity. Therefore the ceramics can be considered as an active dielectric. A correlation between microstructural properties and structurally sensitive, i.e. electrophysical properties of microalloyed multifunctional alumo-silicate ceramics, was confirmed

Dielectric characterization of microalloyed alumo-silicate ceramics by using linear regression model

In this paper, dielectric characterization of porous alumo-silicate ceramics, modified by alloying with magnesium and microalloying with aluminum, was investigated. Microstructure investigations have revealed non-uniform and highly porous structure with broad distribution of grain size, specifically shaped grains and high degree of agglomeration. Complex multiphase system, as active microalloyed ceramics, has specific behavior under external electrical field influence. Dielectric properties (the changes of permittivity, electrical resistivity, dielectric losses and impedance) were measured in the frequency range 20 Hz – 1 MHz. All characteristics showed nonlinear distribution and complex functional dependences because of significant nonhomogeneity of active microalloyed ceramics. Values for permittivity ranged between 140 – 430. Order of magnitude for electrical resistivity was about 106 Ωm, for impedance 104 – 108 Ω, and loss tangent had values much greater than 0.05. Mathematical model of linear regression was applied on the dielectric characterization results. Consistency with experimental data was approved, since the values for correlation coefficient r and determination coefficient r2 were obtained near value 1

FITNESS PARAMETERS AND MORPHOLOGICAL CHARACTERISTICS OF OVERWEIGHT AND OBESE CHILDREN AGED SEVEN

The aim of the research was to determine the correlation of morphological characteristics and fitness parameters of overweight and obese boys aged seven. The sample of participants consisted of 198 pupils (boys) aged seven years, from elementary schools from the territory of the city of Niš, Paraćin, Bela Palanka, Leskovac and others, classified as a category with increased body mass or obesity. Morphological characteristics were determined by measuring parameters of longitudinal (3), transversal, (3) circular dimensions (3) and body mass and measurement of subcutaneous fat tissue (3). For the assessment of muscular fitness, body composition and cardiorespiratory fitness, the following tests were used: the plyometric leap, precancer-turn-off, percentage of body fat and Body Mass Index (BMI); a shuttle run test based on the calculated VO2max (L) and VO2max (ml/kg/min) values. A canonical correlation analysis was used to determine the correlation between morphological characteristics and fitness parameters. The level of statistical significance was set at .05. The results of the study showed that there is a statistically significant association (p˂.01) between morphological characteristics and fitness parameters in overweight and obese boys aged seven. Participants who have higher values of voluminosity and body width have higher values of fat percentage in the body as well as BMI. Smaller explosive power was found in participants with higher values of skin folds. It has been determined that body mass and voluminosity positively affects the strength of the arm and shoulders, that is, they adversely affect the VO2max values

THE IMPORTANCE OF MOTOR COORDINATION ABILITIES FOR PERFORMANCE IN RHYTHMIC GYMNASTICS

Abstract. Rhythmic gymnastics (RG) is a difficult and complex sport which requires increased space-time coordination between body movements and apparatus handling, thus making specific motor coordination a vital part of technical preparation in RG with an important role in creating the preconditions necessary for allowing the gymnast to learn many RG techniques. The purpose of the research was to test and/or determine the possibility of predicting success in RG performance on the basis of gymnasts’ coordination skills. One hundred and twenty-seven national- and international-level rhythmic gymnasts (age: 11.93±3.09 years, body height: 147.65±14.6 cm, body mass:37.67±11.7 kg, BMI: 16.78±2.26 kg/m2, training experience: 5.85±2.81 years), distributed in five age categories (22 beginners, aged 7-9 years; 39 intermediate, aged 9-12 years; 26 advanced, aged 12-14 years; 25 juniors, aged 14-16 years; 15 seniors, aged 16 years and older), volunteered to participate in the study. Their baseline characteristics (age, body height, body mass, BMI, years of training experience, Success) were established, as well as their specific coordination skills (B-ROL, R-TCJ, H-SKP and C-JUG). By means of a Multiple regression analysis the specific coordination skills’ statistically significant influence on Success was established only in the group of advanced and intermediate gymnasts (p<0.018 and p<0.000, respectively), with an explanation of 42%, i.e. 50% of success in RG. Also, the Regression analysis emphasized the significant independent contributions, to the prediction of the dependent variable, of three independent variables: ball rolling (intermediate gymnasts: p=0.03), hoop skipping (intermediate gymnasts: p=0.03 and sample in total: p=0.02) and clubs juggling (intermediate gymnasts: p=0.03 and sample in total: p=0.02), with positive relationship among these independent variables and dependent variable. This study has confirmed the importance of coordination skills for success in RG, but only for younger age categories.Key words: rhythmic gymnasts, age categories, specific coordination, regression

Removal of cationic dye from water by activated pine cones

Adsorption of a cationic phenothyazine dye methylene blueonto activated carbon prepared from pine cones was investigated with the variation in parameters of contact time, dye concentration and pH. The kinetic data were found to follow the pseudo-second-order kinetic modelclosely. The equilibrium data were best represented by the Langmuir isotherm with maximum adsorption capacity of 233.1 mg g-1. Adsorption was favored by using a higher solution pH. Textural analysis by nitrogen adsorption was used to determine specific surface area and pore structure of the obtained carbon. Boehm titrations revealed that carboxylic groups are present in the highest degree on the carbon surface. The results indicate that the presented method for activation of pine cones could yield activated carbon with significant porosity, developed surface reactivity and considerable adsorption affinity toward cationic dye methylene blue

Leaching of chromium from chromium contaminated soil: Speciation study and geochemical modeling

Distribution of chromium between soil and leachate was monitored. A natural process of percolating rainwater through the soil was simulated in the laboratory conditions and studied with column leaching extraction. Migration of chromium in the soil is conditioned by the level of chromium soil contamination, the soil organic matter content, and rainwater acidity. Chromium (III) and chromium(VI) were determined by spectrophotometric method with diphenilcarbazide in acidic media. Comparing the results of chromium speciation in leachate obtained by experimental model systems and geochemical modelling calculations using Visual MINTEQ model, a correlation was observed regarding the influence of the tested parameters. Leachate solutions showed that the concentration of Cr depended on the organic matter content. The influence of pH and soil organic matter content is in compliance after its definition through experimental and theoretical way. The computer model - Stockholm Humic Model used to evaluate the leaching results corresponded rather well with the measured values