SPATIAL CHARACTERIZATION OF TELECOMMUNICATION SATELLITES VISIBLE ABOVE THE REPUBLIC OF SERBIA

This paper deals with the general technical, spatial, and temporal characteristics of satellite telecommunications systems. Particular attention was paid to the peculiarities of the territory of the Republic of Serbia in terms of implementation and use of modern satellite telecommunication infrastructure. The overview shows how and on which way to use various satellite telecommunication systems to configure and exploit next-generation networks, especially modern communications such as 5G technology and IoT. Their work cannot be imagined without the high speeds and high frequencies that allow us to transmit a wealth of information - from short messages/news to HD video on a mobile phone. We need either a base station network or in the case of the high seas or areas where the base station system is difficult to imagine, we need satellite communication. The paper presents data that give a numerical and graphical overview of geostationary satellites visible from the territory of the city of Belgrade, depending on the orbital position and the associated angle of azimuth and elevation, which would also be valid for the leading territory of Serbia.

FUNCTIONAL TRANSFORMATION OF WEST MORAVA VALLEY DISTRICT SETTLEMENTS

The existing territorial layout and the current demographic situation in the settlements of West Morava Valley District during the late 20th century and at the beginning of the 21st century are the result of the synchronized action of the process of industrialization, deagrarization and urbanization. They conditioned the selective transformation of urban and rural space, which led to the concentration of the population in urban and suburban settlements and the depopulation of the rural part of the West Morava Valley District. Within the studied region, the hierarchy of municipal centers, subcenters and communities of settlements was observed. Based on important theoretical and methodological assumptions and indicators, the paper analyzes the functional transformation of the settlements of West Morava Valley in the period between 1971- 2011. It was determined by certain quantitative methods that the changes went in the direction of reducing the share of purely agrarian settlements and increasing the share of industrial and service settlements.

ON THE STARK BROADENING OF Os II SPECTRAL LINES

Stark broadening parameters, full widths at half maximum (FWHM) and shifts for 13 Os II lines have been calculated. The plasma parameters are: electron density of 1017 cm-3 and temperatures from 5 000 K to 80 000 K. Calculations have been performed with the simplified modified semiempirical (SMSE) approach. The results are also used for the consideration of Strak width and shift regularities within the Os II 6s6D-6p6Do multiplet.

MATHEMATICS TEACHER’S PERCEPTIONS ABOUT INFLUENCE OF DIFFERENT ICT USAGE STRATEGIES ON THEIR COMPETENCIES

Teacher competencies are among the key factors of a successful mathematics instruction. The main goal of the study was to compare teachers’ beliefs and attitudes affected by different strategies in organizing the instruction process. The study gives a comparison of teachers’ competencies in three groups of teachers – one teaching mathematics without ICT, the second using ready-made GeoGebra applets and the third one developing their own GeoGebra applets in cooperation with their students. The survey includes 65 mathematics teachers working in 21 primary and secondary schools in southern regions of Serbia. We observed, assessed and compared affective-motivational characteristics of teachers – their beliefs and professional motivation. Results indicate that the teachers’ affective-motivational characteristics depend on the way they employ technology in representing the content they teach. If the technology is used in an inappropriate manner it can impede the students’ creativity, but it also obstructs teachers in deploying their full abilities in the process. The results also bring to the fore issues concerning ways to maintain positive effects achieved through ICT empowered instruction organized in the way the third group of teachers did.

ELEMENTAL CONCENTRATIONS AND SOIL-TO-MOSS TRANSFER FACTORS OF RADIONUCLIDES IN THE ENVIRONMENT OF NORTH KOSOVO AND METOHIJA

This paper deals with investigations of elemental concentrations and soil-to-moss transfer factors of radionuclides in area of municipalities Kosovska Mitrovica and Zubin Potok. Twelve samples of soil and moss Hypnum cupressiforme Hedw. were collected during May 2018. Transfer factors of radionuclides: 226Ra, 232Th, 40Kand 137Cs were calculated with regard to elemental concentrations of radionuclides in soil and moss samples. Analysis was done in order to indicate the different ways of adopting radionuclides by mosses. According to calculated transfer factors and analysis, authors concluded that the soil is dominant source of natural radionuclides and their concentration in moss occurred due to resuspension of soil particles, while artificial 137Cs is present in soil and moss samples as a consequence of atmospheric dry and wet deposition.

SOME MATHEMATICAL CONCEPTS IN GEOMETRY OF MASSES

The study of the distribution of geometrical points, loaded by some scalars plays an important role in various fields of science, of theoretical and practical character. Since such study was first applied and studied when mass had the role of played a scalar, the mass loaded point was named material point, and the discipline dealing with the arrangement of material points in space is called the geometric mass. In that discipline, in the general case under mass one should imply a scalar of arbitrary nature, which can be negative as well. For example, the discipline includes the study of distribution of magnetic or electrical masses, which can be positive and negative. This paper presents some concepts from the geometry of masses that play an important role, particularly in mechanics and physics.

COVID-19 RISK ASSESSMENT IN PUBLIC TRANSPORT USING AMBIENT SENSOR DATA AND WIRELESS COMMUNICATIONS

Covid-19 causes one of the most alarming global health and economic crises in modern times. Countries around the world establish different preventing measures to stop or control Covid-19 spread. The goal of this paper is to present methods for the evaluation of indoor air quality in public transport to assess the risk of contracting Covid-19. The first part of the paper involves investigating the relationship between Covid-19 and various factors affecting indoor air quality. The focus of this paper relies on exploring existing methods to estimate the number of occupants in public transport. It is known that increased occupancy rate increases the possibility of contamination as well as indoor carbon dioxide concentration. Wireless data collection schemes will be defined that can collect data from public transportation. Collected data are envisioned to be stored in the cloud for data analytics. We will present novel methods to analyze the collected data by considering the historical data and estimate the virus contagion risk level for each public transportation vehicle in service. The methodology is expected to be applicable for other airborne diseases as well. Real-time risk levels of public transportation vehicles will be available through a mobile application so that people can choose their mode of transportation accordingly.

CONTEMPORARY CHANGES IN THE ETHNIC STRUCTURE OF THE POPULATION IN THE AUTONOMOUS PROVINCE OF KOSOVO AND METOHIJA

Twenty years (1999 - 2019) after the end of the conflict in the Autonomous Province of Kosovo and Metohija, it can be stated that nowhere in Europe is there such ethnic segregation of the population as is the case with the AP of Kosovo and Metohija. Following the withdrawal of pumped security forces from the entire territory of Kosovo and Metohija and the entry of the United Nations peacekeeping force into the Serbian Autonomous Province, Kosovo Albanians carried out their persecution from Kosovo through terrorist attacks on Serbs and other non-Albanian populations (Montenegrins, Gorans, Roma, Ashkali) carried out their persecution from Kosovo and Metohija and fundamentally changed the ethnic structure of the Province. An insight into the majority of 223.081 exiles and displaced persons from Kosovo and Metohija indicates an exodus against the Serbs. The number of displaced Roma, Ashkali and Egyptians is estimated at about 100.000. The mass persecution of the Serb and other non-Albanian populations has resulted in tremendous changes in the ethnic structure of the Province, which today, with 93% of the total population, is dominated by Albanians, while other ethnic communities have a participation of 7%.

SPECTROPHOTOMETRIC DETERMINATION OF ASCORBIC ACID BY HORSERADISH PEROXIDASE

L-ascorbic acid is one of the essential nutrients and most common food supplements, fortificants, and preservatives. It is commercially available as solutions, drops, tablets, capsules, crystal powder, beverage mixtures, multivitamin formulations, and multi antioxidant formulations. The usual daily dose is from 25 mg to 1.5 g. Ascorbic acid is a distinctly reducing agent with low redox potential (0.18 and 0.08 V at pH 4.5 and 6.4, respectively). Based on ascorbate property, numerous methods for its quantitative determination are developed, from titrimetric, electrochemical, and chromatographic methods, to fluorometric and kinetic ones. Enzyme peroxidase is interfered with by ascorbic acid, which decreases the oxidation speed of its co-substrates during hydrogen peroxide decomposition by peroxidase. Absorbance changes at the wavelength of corresponding reagents are in correlation with ascorbate concentration. During this study, benzidine and o-tolidine have been used as chromogenic reagents. Reaction conditions were optimized for various buffer systems, calibration curves were constructed, and limits of detection (0.04 μmol/L) and quantification (0.12 μmol/L) were calculated. Using calibration charts, it was possible to detect ascorbic acid within limits from 0.4 to 10 μmol/L. The optimized method was applied for the determination of ascorbic acid in pharmaceutical products. The method was characterized by exceptional sensitivity and accuracy, but only for preparations not containing substances that affect enzyme peroxidase.

MORPHOLOGICAL VARIABILITY AND SEXUAL DIMORPHISM OF NOBLE CRAYFISH Astacus astacus FROM THE BALKANA LAKE

This paper presents the information about morphological variability and sex dimorphism of the Noble crayfish (Astacus astacus) in the area of the Balkana Lake in Mrkonjic Grad. The crayfish were caught by hand made baited traps from October 9nd 2018. until May 31th 2019. A total of 58 crayfish were caught, of which 38 males and 20 females. The eight morphometric characteristics: body weight (W), body length (TBL), claw length (CLL), cephalothorax length (CFL), carapace width (CPW), abdomen length (ABL), rostrum length (ROL) and rostrum width (ROW) were measured, both in males and females. Also, the body condition was determined for all specimens. The results of morphometric characteristics partially matched into the already known range of variations. These data represent first ones for the observed area. The t-test showed that there were significant differences between the sexes in W, TBL, CLL, CFL and CPW which are explained by the emphasized sex dimorphism of the noble crayfish.