Modelovanje Etveševog tenzora primenom normalnog polja potencijala teže i digitalnih modela terena

Предмет овог рада је истраживање могућности моделовања градијената убрзања теже Земље, елемената тзв. Етвешевог тензора. Анализирани концепт подразумијева моделовање које се врши без коришћења било каквих резултата гравиметријских или сличних мјерења. Умјесто тога, модел се искључиво ослања на директно моделовање утицаја маса тијела Земље. Масе су подијељене на три дијела, масу нормалне Земље, топографске масе и масе између геоида и елипсоида. Утицај масе нормалне Земље срачунат је на основу нормалног поља и других извода нормалног потенцијала теже, док су друга два сегмента моделована њиховом дискретизацијом и апроксимацијом помоћу призми као правилних геометријских тијела. У ту сврху коришћени су дигитални модели терена и званични модел квазигеоида, као и глобални геопотенцијални модели. Практично истраживање спроведено је за територију Србије. У директној провјери модела, срачунати градијенти су упоређени са резултатима мјерења торзионом вагом у полигону код Новог Сада. За стандардно одступање градијената добијене су вриједности од 15 E – 20 E, односно 1.5 Gal/m - 2 Gal/m . Вертикални градијенти су тестирани на основу мјерења широм Србије, те је утврђено стандардно одступање од око 230 E. За све градијенте срачунате су и вриједности из глобалног геопотенцијалног модела, те је утврђено да на изразито равничарском терену имају исту или бољу сагласност са мјерењима у односу на вриједности из модела. Модел је тестиран и посредно, у оквиру гравиметријког полигона у Бору, рачунањем компоненти одступања вертикала из моделованих градијената. Ове вриједности упоређене су са компонентама оцијењеним из званичног модела квазигеоида. Установљена је врло добра сагласност оцијењених компоненти са познатим, уз стандардно одступање мање од једне лучне секунде по компоненти. На основу ових резултата извшена је оцјена тачности градијената, те су за њихова стандардна одступања добијене вриједности од 30 E – 40 E. Добијени резултати су показали да је примјеном предложеног концепта могуће остварити тачност моделовања градијената на нивоу тачности мјерења, или за један ред величине мању. На крају су дата додатна запажања о оствареној тачности и потенцијалним изворима грешака, као и препоруке за даља истраживања и унапређење модела.The subject of this thesis is research into the possibility of modeling Earth’s gravity gradients, the elements of the so-called of the Eöetvös tensor. The analyzed concept implies modeling that is performed without using any results of gravimetric or similar measurements. Instead, the model relies exclusively on forward modeling of the effects of the Earth's masses. The masses are divided into three parts, the mass of the normal Earth, the topographic masses and the masses between the geoid and the ellipsoid. The influence of the mass of the normal Earth was calculated on the basis of the normal gravity field and second derivatives of the normal gravity potential, while the other two segments were modeled by their discretization and approximation using prisms as regular geometric bodies. For this purpose, digital terrain models and the official quasigeoid model, as well as global geopotential models, were used. Practical research was conducted for the territory of Serbia. In the direct verification of the model, the calculated gradients were compared with the results of torsion balance measurements in the polygon near Novi Sad. For the standard deviation of the gradients, values of 15 E - 20 E were obtained, that is, . Vertical gravity gradients were tested based on measurements across Serbia, and a standard deviation of about 230 E was determined. For all gradients, values from the global geopotential model were also calculated, and it was determined that on extremely flat terrain they have the same or better agreement with measurements compared to modeled values. The model was also tested indirectly, within the gravimetric polygon in Bor, by calculating the vertical deflections components based on modeled gradients. These values were compared with the components estimated from the official quasigeoid model. A very good agreement of the evaluated components with the known ones was established, with a standard deviation of less than one arcsecond per component. Based on these results, the accuracy of the gradients was evaluated, and values of 30 E - 40 E were obtained for their standard deviations. The obtained results showed that by applying the proposed concept, it is possible to achieve the accuracy of modeling gradients at the level of measurement accuracy, or one order of magnitude lower. At the end, additional observations are given about the achieved accuracy and potential sources of errors, as well as recommendations for further research and improvement of the model

Structural properties and antisite defect formation in monoclinic Li2FeSiO4 – a DFT aspect

Properties of monoclinic Li2FeSiO4, which is a prominent candidate for future use as a cathode in lithium ion batteries, have been investigated by DFT+U method, using GGAPBE approximation, plane wave basis set and periodic boundary conditions. All calculations were performed in an antiferromagnetic state, which has been found to be energetically slightly more stable than ferromagnetic. Optimized lattice parameters and atomic coordinates have been compared to the literature data in order to verify the model. In addition, a particular attention was paid to the possibility of the formation of an antisite defect, which was introduced as the interchange between Fe and Li ions at both Li1 and Li2 crystallographic positions. The concentration of defect was varied from 0 to 25 molar per cent. Changes of structural, energetic, and magnetic properties of monoclinic Li2FeSiO4 upon increase of Li1-Fe and Li2-Fe antisite defect concentration have been analyzed and discussed in light of available experimental results

Age as demographic determinant of household consumption in Serbia

Предмет истраживања јесте потрошња домаћинстава на чији ниво и структуру, између осталог, утичу старост носиоца домаћинства и демографске карактеристике чланова домаћинства. Опште прихваћен начин увођења старости у разматрање потрошње домаћинстава јесте преко старости носиоца домаћинства, који се иначе користи у економетријским истраживањима потрошње становништва. Са друге стране, циљ овог истраживања је да на примеру домаћинстава у Србији утврди утицај старости као демографске одреднице на структуру личне потрошње, као и да објасни смер и интензитет утицаја посматраних демографских карактеристика домаћинстава. Промене у демографским структурама неминовно воде и до промена у структури личне потрошње. Отуда би објашњење утицаја старосне структуре на структуру личне потрошње водило потпунијем разумевању промена у обиму и структури личне потрошње...The main objective of this research is identification and explanation of changes in the structure of private consumption as a function of the age of an individual. However, it is not possible to isolate and measure the consumption of individual which is being realized within the household. Yet, it is possible to make a compromise and instead of an individual, as an observation unit to take the household. The reason why in this type of research individual can not be the subject of research, lies in the definition of the household. Generally accepted way of introducing age into household consumption research is through the age of the household head, which is used in econometric studies of household consumption. On the other hand, the aim of this study is to, in the case of households in Serbia, determine the influence of age as the demographic characteristics of the structure of private consumption, as well as to explain the direction and intensity of the impact of the observed demographic characteristics of households. Changes in the demographic structure will inevitably lead to changes in the structure of private consumption. Hence, the explanation of the impact of the population age structure on the structure of private consumption would led to a more complete understanding of changes in the scope and structure of household consumption..

Improvement possibilities of the I-V characteristics of PIN photodiodes damaged by gamma irradiation

This paper presents the behavior of PIN photodiodes after combined gamma and neutron irradiation. Different types of PIN photodiodes have been exposed first to gamma and then to neutron irradiation. I-V characteristics (current dependence on voltage) of photodiodes have been measured after each of these irradiations. It has been noted that the photocurrent level after the neutron irradiation is higher than before it, which is not consistent with the current theories about the effects of neutron radiation on semiconductors. In order to explain this behavior of the photodiodes, the Monte Carlo simulation of photon transport through the material has been used. It is proposed that a possible cause for current enhancement are defects in semiconductor created by gamma irradiation and effects of neutron irradiation on these defects. The results can be explained by an intercentre transfer of charge between defects in close proximity to each other. The aim of this paper is to investigate the improvement possibilities of the I-V characteristics of PIN photodiodes, and photodetectors in general, damaged by gamma irradiation. [Projekat Ministarstva nauke Republike Srbije, br. 171007

An insight into the efficient dimethoate adsorption on graphene-based materials—a combined experimental and dft study

The development of highly efficient methods for removing hazardous substances from the environment attracts increasing attention. Understanding the basic principles of the removal processes using graphene materials is equally essential to confirm their application efficiency and safety. (2) Methods: In this contribution, adsorption of pesticide dimethoate (DMT) on graphene-based materials has been investigated on the molecular level. (3) Results: The experimental results’ analysis revealed a cooperative binding mechanism of the DMT on the adsorption sites of investigated materials—graphene oxide (GO) and industrial graphene (IG). The adsorption data were analyzed using various adsorption isotherms to determine the thermodynamics of the adsorption process. The experimental results were correlated with Density Functional Theory (DFT) calculations of DMT adsorption on the model surfaces that appropriately describe the graphene materials’ reactive features. (4) Conclusions: Considering experimental results, calculated adsorption energies, optimized adsorption geometries, and electronic structure, it was proposed that the dispersive interactions determine the adsorption properties of DMT on plain graphene sites (physisorption). Additionally, it was shown that the existence of vacancy-type defect sites on the surfaces could induce strong and dissociative adsorption (chemisorption) of DMT. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Aging of the geiger-muller counter due to particle conductance in an insulating gas

In this paper, the aging effect of commercially available Geiger-Muller counters under working conditions is being considered from both theoretical and experimental point of view. In the experimental part lifetime curves for the commercial Geiger-Muller counter chamber are first recorded. After detection of the aging phenomena, the commercial chamber response to an impulse voltage is tested along with recording of the same response of the Geiger-Muller chamber model with conductive particles included. The law of similarity for the gaseous discharge is fulfilled both by the commercial Geiger-Muller chamber and by the chamber model with conductive particles. The results obtained from the U-test indicate that the aging of the Geiger-Muller chamber is mainly caused by the occurrence of a great number of conductive particles hovering inside the chamber. Some suggestions of how to reduce the aging effect due to conductive particles inside the Geiger-Muller chamber are given in the conclusion

Aging of the geiger-muller counter due to particle conductance in an insulating gas

In this paper, the aging effect of commercially available Geiger-Muller counters under working conditions is being considered from both theoretical and experimental point of view. In the experimental part lifetime curves for the commercial Geiger-Muller counter chamber are first recorded. After detection of the aging phenomena, the commercial chamber response to an impulse voltage is tested along with recording of the same response of the Geiger-Muller chamber model with conductive particles included. The law of similarity for the gaseous discharge is fulfilled both by the commercial Geiger-Muller chamber and by the chamber model with conductive particles. The results obtained from the U-test indicate that the aging of the Geiger-Muller chamber is mainly caused by the occurrence of a great number of conductive particles hovering inside the chamber. Some suggestions of how to reduce the aging effect due to conductive particles inside the Geiger-Muller chamber are given in the conclusion