Nenad Sakan

Institute of Physics Belgrade | IPB

The desire to model diverse atmospheric plasmas ranging from medium to strong non-ideality prompted additional research of the optical features of such systems. This submission presents a more comprehensive set of results and properties for such systems. Our research methodology, as well as the existing and prospective applications, are outlined.

In order to describe a dense plasma the approach of cut-off Coulomb potential was used. After testing of model the step further was made. Inclusion of more complex models has been conducted with the help of Hartree-Fock generated potentials. Although the potentials were a good way to describe a complex emitters in a plasma the step forward in descr...

The interest in the modeling of laboratory and astrophysical plasma behavior from mid up to strong non-ideality (NI), e.g., plasma in which a Coulomb interaction becomes dominant, led us to further investigate the optical properties of such systems. An expanded set of results and properties like wave functions, dipole matrix elements, etc., for suc...

This research is focused on the assessment of the pollution status of river and lake sediments near Pb, Zn, and Cu mines and tailings in the southeastern part of Serbia—Krajište area. The study is based on hypothesis that investigated rivers and lakes in the Krajište area could be polluted by potentially toxic elements (PTEs) and that these element...

Nanostructured thin films on a silicon substrate were obtained by high-frequency periodic pulse f ~ 6–10 kHz action of laser radiation with wavelength λ = 1.064 μm and power density q = 120 MW/cm2 on zirconium in a vacuum chamber at pressure p = 2.2 Pa. The morphology of the thin films of zirconium was studied by atomic-force microscopy. The transm...

The optimized three-step sequential extraction procedure for the fractionation of micro- and macroelements, was conducted to determine fractional characteristics of PTEs (potentially toxic elements) in surface sediments of rivers in the Vlasina watershed. The sequential extraction results, which enable the evaluation of mobility of the studied elem...

Stark broadening parameters for four Sn III spectral line obtained by using semiclassical perturbation approach and Stark widths for this transitions obtained by using modified semiempirical approach have been compared with available experimental and semiempirical data and used for the consideration of the influence of the Stark broadening effect i...

Artificial neural networks are gaining a momentum for solving complex problems in all sorts of data analysis and classification matters. As such, idea of determining their usability on complex plasma came up. The choice for the input data for the analysis is a set of stellar spectral data. It consists of complex composition plasma under vast variet...

Stark broadening parameters - full widths at half maximum (FWHM) and shifts for 11 Re II lines have been calculated. The plasma parameters used were electron density of 1017 cm⁻³ and temperature from 5 000 K to 80 000 K. Calculations were performed using the simplified modified semiempirical (SMSE) approach and compared with calculations by Cowley’...

In this manuscript, samples of Kupa River sediments were examined using three different extraction agents. The aim of this study was to evaluate the applicability of single extraction procedures to investigate the bioavailability and mobility of major and trace elements (Al, As, Ba, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, S, Si, Sr, Ti, V...

Comparison of discharge channel temperature in gaseous hydrogen of high density with current amplitude of ~ 1 MA at initial gas pressure of 5–7 MPa, determined by two methods, was done under stage of its maximal contraction. In the first case determination of the temperature value of 72–73 eV was made by intensity of soft x-ray radiation from the c...

In this work, we present the data of Stark widths of rare-earth element Nb iii, calculated for 21 spectral lines by using the modified semi-empirical method. Obtained results have been used to study the influence of Stark broadening on spectral lines in hot stars atmospheres such as A-type star and DA and DB white dwarfs.

The need for further research into potentially toxic elements in Serbian rivers led to an investigation of distributions, sources, and ecological risks in a sample base of sediments from 15 rivers. The analyses were carried out through both experimental and theoretical methods. Geochemical fractionation of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, As, V, and...

The free-free i.e. electron-ion inverse “Bremsstrahlung” characteristics are determined for the case of the solar atmosphere as well as solar interior where such plasma characteristics as plasma density and temperature change in wide region. We demonstrate that determination of these characteristics such as the absorption coefficients and Gaunt fac...

Potentially harmful trace elements pollution in aquatic ecosystems is a worldwide environmental problem that has received increasing attention over the last few decades because of its adverse effects. Sediments pollution by toxic elements is related to different kinds of human activities such as industrial production, agricultural operations, burni...

In the process of inclusion of the bound-bound photo absorption processes within cut-off Coulomb potential model some of the numerical errors appeared. The analysis of the source of numerical errors led to conclusion about avoiding them and also led to the procedure for inclusion of more complex atom models.

In this work, we present a study dedicated to determination of the inverse bremsstrahlung absorption coefficients and the corresponding Gaunt factor of dense hydrogen-like stellaratmosphere plasmas where electron density and temperature change in a wide range. A method suitable for this wide range is suggested and applied to the inner layers of the...

In this contribution, we present results of bound state transition modeling using the cutoff Coulomb model potential. The cutoff Coulomb potential has proven itself as a model potential for the dense hydrogen plasma. The main aim of our investigation include further steps of improvement of the usage of model potential. The results deal with partial...

In this work we determine the electron–ion inverse bremsstrahlung characteristics for the case of the white dwarf atmospheres where such plasma characteristics as plasma density and temperature change in wide region. It is presented that determination of these characteristics, i.e. the absorption coefficients and Gaunt factors can be successfully p...

The HF characteristics of astrophysical plasmas was determined on the basis of numerically calculated values for the dense plasma conductivity in an external HF electric field. The examined range of plasma frequencies covers the IR, visible and UV regions and considers electronic number density and temperature important for different stellar models...

Here are presented results of bound state transition modeling using the cutoff Coulomb model potential. The cutoff Coulomb potential has proven itself as a model potential for the dense hydrogen plasma. The main aim of our investigation include a further steps of improvement of the usage of model potential. The results deal with partially ionized d...

The paper aims to research the orientation possibilities of an object in the horizontal plane, from its start course into a required orientating recourse, by using simplified navigation methods. The object’s directed motion uses controlling powering impulses, variable distributed in time, during constrained motion time. Three logical decision-makin...

This investigation examines surface sediment samples from rivers and artificial lakes (Serbia) to quantify levels of potentially harmful elements (As, Hg, and Se) and several ancillary elements (Al, Fe, Mn, Ca, Mg, C, H, N, and S). These data provide the first global analysis of Hg, As and Se levels in a well-studied system. Combination of differen...

In this work is examined a new modeling way of describing the continuous absorption of electromagnetic (EM) radiation in a dense partially ionized hydrogen plasmas with electron densities about $5\cdot10^{18}$ cm$^{-3}$ - $1.5\cdot10^{19}$cm$^{-3}$ and temperatures about $1.6 \cdot10^{4}$ K - $2.5 \cdot 10^{4}$ K in the wavelength region $300 \text...

In this paper we present the method of determination of the electron-ion inverse Bremsstrahlung characteristics in order to cover the corresponding stellar atmosphere models. The used method is based on cutoff Coulomb model potential. It is shown that determination of these characteristics i.e. the absorption coefficients and Gaunt factors can be s...

On the basis of numerically calculated values for the dense plasma conductivity in an external HF electric field, we determine the HF characteristics of plasmas under extreme conditions. The examined range of frequencies covers the IR, visible and UV regions and consider electronic number density and temperature are in the ranges of $10^{21} \textr...

Metals in sediments are present in different chemical forms which affect their ability to transfer. The objective of this body of work was to compare different extraction methods for the bioavailability evaluation of some elements, such as Ba, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, V and Zn from Serbian river sediments. A bioavailability risk asses...

In our previous research, it has been demonstrated that inelastic processes in atom Rydberg-atom collisions, such as chemi-ionization and (n−n′) mixing, should be considered together. Here we will review the present state-of-the-art and the actual problems. In this context, we will consider the influence of the (n−n′)-mixing during a symmetric atom...

The electron–ion inverse Bremsstrahlung is considered here as a factor of the influence on the opacity of the different stellar atmospheres and other astrophysical plasmas. It is shown that this process can be successfully described in the frames of cut-off Coulomb potential model within the regions of the electron densities and temperatures. The r...

The presented study was carried out in order to evaluate risk assessment of selected heavy metals (Cd, Cu, Mn, Cr, Ni, Pb, Zn, Co and V) in river sediments in Serbia. The purpose of this chapter is to describe a new approach in ecological geochemistry assessment of heavy metal pollution using different pollution indices for estimation the anthropog...

Geochemical normalization with conservative elements has been effectively used for assessing the enrichment of metal pollutants and distinguishing their natural and anthropogenic sources. Without correcting for textural and mineralogical variability, a comparison of heavy metal data with regional background is complicated because of large variablit...

The purpose of this study was to evaluate sediment heavy metals (Cd, Cu, Co, Mn, Cr, Ni, Pb and Zn) related to pollution in freshwater sediments in Serbia. The heavy metal enrichment determination in studied sediments was conducted by using total metal content with strong acidic digestion (HCl + HNO3 + HF), a calculated enrichment factor (EF), and...

In the present study, concentrations of heavy metals (Cd, Cu, Co, Mn, Cr, Ni, Pb, and Zn) were determined at 35 river sediments in Serbia. The anthropogenic heavy metals input and quantification of the metal enrichment degree in sediments were estimated by calculating geo-accumulation indices (I geo) and enrichment factors (EF). These pollution ind...

The contaminated sediment serves as a long-term source of toxic elements, since that mobility and transport in the environment of these elements are strongly influenced to associated solid phase. In this study, the modified Tessier sequential extraction procedure was applied for the fractionation of Cd, As, Hg, Cu, Zn, Cr, Pb, Ni and V in the sedim...

We present an analysis of the procedure for plasma electron number density, Ne, diagnostics based on the comparison of theoretical and experimental shape or width of hydrogen Balmer lines. Low Ne diagnostics, requiring an extension of available theoretical Stark broadening data tables was examined first. The difficulties encountered during experime...

A new modeling way of describing the continuous absorption of electromagnetic (EM) radiation in dense partially ionized hydrogen plasma is tested in this work. It is shown that the obtained results give a possibility of calculating spectral absorption coefficients which characterize the relevant absorption processes in partially ionized hydrogen pl...

Extensive work was done in the application of a cut-off Coulomb model on the description of the optical processes of the photo ionization and inverse bremsstrahlung. Presented work deals with a usage of a cut-off Coulomb model pseudo potential for the calculation of the optical absorption process in dense hydrogen plasma as a entirely quantum mecha...

The main aim of this work is to estimate the total contribution to the opacity of DB white dwarf atmosphere of the processes of the He{sub 2}{sup +} molecular ion photo-dissociation and He+He{sup +} collisional absorption charge exchange, and compare it with the contribution of He{sup -}, and other relevant, radiative absorption processes included...

Elementary processes in astrophysical phenomena traditionally attract researchers attention. At first this can be attributed to a group of hemi-ionization processes in Rydberg atom collisions with ground state parent atoms. This processes might be studied as a prototype of the elementary process of the radiation energy transformation into electrica...

The main aim of this work is to estimate the total contribution of the processes of molecular ion photodissociation and collisional absorption charge exchange to the opacity of DB white dwarf atmospheres, and compare this with the contribution of and other relevant radiative absorption processes included in standard models. The method for the calcu...

The method of moments is used to calculate the dynamic conductivity of strongly coupled fully ionized hydrogen plasmas. The electron density ne and temperature T vary in the domains 1021 < ne < 1024 cm−3, 104 K < T < 106 K. The results are compared to some theoretical data.

We present the results of a spectroscopic study of hydrogen Balmer line shapes and intensities in a microwave-induced discharge generated in an Evenson resonant cavity at 2.45 GHz in pure hydrogen and hydrogen-argon and hydrogen-helium gas mixtures. The Balmer line shapes do not show signs of excessive Doppler broadening. The discharge parameters—D...

This paper presents a study of the usability of the Coulomb cut-off potential for the calculation of bound-free and free-free cross sections. It covers the condition in dense plasma where there is no good theory that covers the optical properties of dense plasma. The presented quantum mechanical model has given a good agreement with the experimenta...

In this work the previously developed method of calculation of HF electro-conductivity of non-ideal plasma is applied to the area of higher electron densities, up to 1024 cm-3 and in the temperature range 30 000 K ≤ T ≤ 200 000 K. The computations are carried out in the frequency range (0, 1·ωp), ωp being the plasma frequency. A good agreement with...

This work presents the cut-off Coulomb potential approach for the modeling of the dense hydrogen plasma of mid and high non ideality, where the self sphere radius is close to Debye radius. The cutoff Coulomb potential has given us the possibility to finish all necessary calculation without any additional approximations besides the numerical calcula...

On the basis of numerically calculated values for the dense plasma dynamic conductivity in an external HF electric field, we determine the electrical permeability and the coefficients of refractivity and reflectivity of dense non-ideal plasmas. We consider electronic number density and temperature in the ranges of 10^{21} < N_{e} 10^{23} < cm^{−3}...

In this work, the previously developed method for calculation of HF electroconductivity of non-ideal plasma is applied to the area of high electron densities: 10(21) <= N-e <= 10(23) cm(-3) and in the temperature range 20000 K <= T <= 1000 000 K. This is enabled by the improvement of the numerical procedure. The real and imaginary parts of the HF c...

Aims. To estimate the total contribution of the absorption processes λ + H + 2 (X 2 Σ + g) ⇒ H(1s) + H + and λ + H(1s) + H + ⇒ H + + H(1s) to the opacity of Solar atmosphere in UV and VUV region, and compare it with the contribution of other relevant radiative processes included in standard models. Methods. The strict quantum-mechanical method was...

The continuous optical spectrum of dense hydrogen plasma is modeled with the complete quantum mechanical model based on the cut-off Coulomb potential. Here are presented the results of calculation of a continuous optical spectra of dense hydrogen plasma and compared with the experimental results obtained in ``Laboratory for dense plasma'' at the Pi...

The radiative charge exchange processes in H+ + H(1s) and He+(1s) + H(1s2) collisions at intermediate ion–atom impact velocities were treated in this paper from a spectroscopic aspect as new sources of UV and VUV emission. These processes were characterized by the cross-section spectral densities. In the case of hydrogen the corresponding spectral...

The dynamic electric conductivity, dielectric permeability and refraction and reflection coefficients of a completely ionized gaseous plasma in a high frequency (HF) external electric field are calculated. These results are obtained within the self-consistent field approach developed earlier for the static conductivity determination. The plasma ele...

In this work we present the method of determnination of HF electroconductivity, dielectrical permeability and reflection coefficients of fully ionized plasmas which is based on previously developed modified RPA theory of non-ideal plasma transport processes. Here we have treated two-component plasma, which consists of free electrons and one kind of...

In this paper, we present the results of the calculations of high-frequency electroconductivity, dielectric permeability and refraction and reflection coefficients of a fully ionized gaseous plasma in an external electric field. The electron density, Ne, and temperature, Te, varied in the domains 1017≤Ne≤1019 cm-3 and 10 000≤Te≤50 000 K, while the...