In this work we report the results of analysis of the acoustic signal generated by the interaction of a nanosecond laser pulse (30 mJ, 1064 nm) with various residues placed on a silica wafer. The signal was captured by a unidirectional microphone placed 30 mm from the laser-generated plasma. The examined sample classes, other than the clean wafer, included particles from soils and rocks, carbonates, nitro precursors, ash, coal, smeared diesel, and particles of explosives. We tested three types of explosives, namely PETN, RDX, and HMX, having different origins. For the explosives, the acoustic signal showed a faster rise, larger amplitude, different width, and attenuation compared with the other sample classes. By subtracting the acoustic signal from the wafer at the same position, obtained after four cleaning laser pulses, the contribution of echoes was eliminated and true differences between the residue and substrate became evident. Through four different features in the subtracted signal, it was possible to classify explosives without the presence of false positives; the estimated limit of detection was 15 ng, 9.6 ng, and 18 ng for PETN, RDX, and HMX, respectively, where the mass was extrapolated from nano-printed samples and LIBS spectra acquired simultaneously. Furthermore, HMX was distinguished from the other two explosives in 90% of the cases; diesel and coal were also recognized. We also found that explosives deposited through wet transfer behaved as inert substances for the tested masses up to 30 ng.

Plasma source for beryllium spectral line studies in the presence of beryllium dust particles was realised. The guideline during construction was to prevent exposure to formed dust, considering the toxicity of beryllium. Plasma source characterization through determination of optimal working conditions is described. The necessary conditions for Be spectral line appearance and optimal conditions for line shape measurements are found. It is proven experimentally that under these conditions dust appears coincidently with the second current maximum. The electron density measured after discharge current maximum is determined from the peak separation of the hydrogen Balmer beta spectral line, and the electron temperature is determined from the ratios of the relative intensities of Be spectral lines emitted from successive ionized stages of atoms. Maximum values of electron density and temperature are measured to be 9.3 × 10²² m⁻³ and 16 800 K, respectively. Construction details and testing of the BeO discharge tube in comparison with SiO₂ and Al₂O₃ discharge tubes are also presented in this paper.

Considering that the Republic of Serbia has a surplus in the foreign trade of fruits, the problem of this research refers to the perception of the importance of the foreign trade of fruit of the Republic of Serbia. The subject of the research includes the analysis of previous and future trends in the value of exports and imports of fruits, as one of the most important agro-industrial products. The aim of the research is to determine future trends, as well as to forecast future values of fruit imports and exports using econometric methodology in the field of analysis of variations of time series, i.e. statistical methods of linear trend. The contribution of this research study is multiple, in scientific terms it enriches the existing scientific literature, given that research studies that have addressed this issue are very rare, while in practical terms it provides guidance to producers and exporters of fruits and agricultural policy makers, especially in terms of encouraging fruit exports from the Republic of Serbia in the coming period.

This paper presents a study and comparison of surface effects induced by picosecond and nanosecond laser modification of a Ti6Al4V alloy surface under different ambient conditions: air and argon- and nitrogen-rich atmospheres. Detailed surface characterization was performed for all experimental conditions. Damage threshold fluences for picosecond and nanosecond laser irradiation in all three ambient conditions were determined. The observed surface features were a resolidified pool of molten material, craters, hydrodynamic effects and parallel periodic surface structures. Laser-induced periodic surface structures are formed by multi-mode-beam nanosecond laser action and picosecond laser action. Crown-like structures at crater rims are specific features for picosecond Nd:YAG laser action in argon-rich ambient conditions. Elemental analysis of the surfaces indicated nitride compound formation only in the nitrogen-rich ambient conditions. The constituents of the formed plasma were also investigated. Exploring the impact of process control parameters on output responses has been undertaken within the context of laser modification under different environmental conditions. Parametric optimization of the nanosecond laser modification was carried out by implementing an advanced method based on Taguchi’s parametric design and multivariate statistical techniques, and optimal settings are proposed for each atmosphere.

Modern international economic relations, among other things, are characterized by establishing bilateral and multilateral cooperation between countries in order to liberalize trade relations. The implementation of reached free trade agreements affects economic trends in the signatory countries, the intensification of their foreign trade as wll as the increase in the attractiveness of countries as investment destinations. From 2000 onwards, Serbia has signed several free trade agreements with European countries and the United States. Ten years ago, a free trade agreement was signed with the Republic of Kazakhstan in order to encourage the development of mutual trade and economic relations, accelerate economic development, improve living and working conditions, increase employment and establish fair competition between economic entities from Serbia and Kazakhstan. The subject of the mentioned trade relations are also agri-food products, whose production in Serbia is supported by an excellent raw material base, and has always been a part of national tradition and culture. The research subject of this paper is foreign trade of agricultural products between Serbia and Kazakhstan with regard to free trade agrrements. The research aim is to determine the differences in the movement of exports and imports between the mentioned countries in the period before and after the signing of the free trade agreement.