The University of Niš (Serbian: Универзитет у Нишу, romanized: Univerzitet u Nišu) is a public university in Serbia. It was founded in 1965 and consists of 13 faculties with 1,492 academic staff and around 20,500 students (as of 2018–19 school year). Since its founding, the university diploma has been acquired by more than 50,000 students, including 1,300 foreigners.It has a university library "Nikola Tesla"; the Faculty of Technology is located in Leskovac, Pedagogy Faculty in Vranje and Agriculture Faculty in Kruševac.
The σ-irregularity index of a graph is defined as the sum of squared degree differences over all edges and provides a sensitive measure of structural heterogeneity. In this paper, we study the problem of maximizing σ(T) among all trees of fixed order n and prescribed maximum degree Δ≥4. By expressing the problem in terms of edge–degree multiplicities, we derive a linear programming formulation and analyze its dual. This approach yields sharp upper bounds for σ(T) and leads to a detailed description of extremal degree–pair distributions. We show that the extremal problem can be completely resolved for the congruence classes n≡1(modΔ) and n≡0(modΔ). When n≡1(modΔ), the linear program admits an integral optimal solution, and the bound for σ(T) is tight. When n≡0(modΔ), the linear relaxation is not attainable by any tree; nevertheless, by introducing a penalty function derived from dual slack variables, we determine the exact maximum value of σ(T). In both cases, all extremal trees are characterized explicitly and consist exclusively of vertices of degrees 1, 2, and Δ, with edges incident to Δ-vertices playing a dominant role.
This study investigates a sustainable route for biodiesel production from waste plum kernel oil (PKO) using a heterogeneous, waste-derived catalyst (35% CaO supported on coal fly ash-derived zeolite), in the presence of a green deep eutectic solvent (DES), triethanolamine:menthol (TEA:M, 1:2 mol/mol), as a cosolvent. The catalyst exhibited a high specific surface area, developed porosity, and abundant strong basic sites, ensuring effective transesterification activity. PKO, characterized by low acid value (1.95 +/- 0.03 mg KOH/g) and high oleic acid content (73.8 +/- 2.5%), proved to be a suitable feedstock for biodiesel production. The incorporation of TEA:M DES into the reaction system significantly enhanced fatty acid methyl ester (FAME) formation by improving mass transfer during the initial reaction period. Transesterification was conducted at 60 degrees C under atmospheric pressure by varying the catalyst amount (2-10% based on oil mass), DES amount (1-9% based on oil mass), and methanolto-oil molar ratio (6:1-12:1 mol/mol). A maximum FAME content of 96.7% was achieved under optimized reaction conditions (8% catalyst, 5% DES, 6:1 methanol-to-oil ratio). Transesterification followed a pseudo-firstorder kinetics with rate constants of 0.032-0.152 min(-1) and an activation energy of 42.67 kJ/mol. The catalyst maintained high activity over five reuse cycles, with only a slight decrease in FAME content from 96.7 +/- 1.0% to 94.5 +/- 0.5%. Cost analysis confirmed process feasibility ((sic)1.24/kg), demonstrating the potential of integrating waste-derived catalysts with green cosolvents for sustainable biodiesel production and providing a promising pathway toward a circular economy.
This paper establishes exact expressions for the Drazin inverse of the modified tensor A-C & lowast;N DD & lowast;N 13 via the Einstein product, formulated using the Drazin inverse of A and the generalized Schur complement D-13 & lowast;N AD & lowast;N C, providing a comprehensive generalization and unification of existing results in the literature for the case when the tensors are of order two. Furthermore, the findings reduce to the classical Sherman-Morrison-Woodbury formula in the special case of second-order tensors. Finally, we provide two examples to illustrate our new explicit expressions.
Background: Efficient electrochemical reduction of hydrogen peroxide is important for catalytic, sensing, and energy-related electrochemical applications, while understanding the underlying electrode mechanism remains essential for the rational design of high-performance materials. Methods: An Ag@SnO2/MWCNT hybrid nanocomposite was synthesized hydrothermally using SnCl2 and silver acetate precursors, with citric acid as a complexing agent. Physico-chemical characterization confirmed the formation of SnO2 nanostructures integrated with conductive multiwalled carbon nanotubes (MWCNTs), while Ag incorporation provided additional active sites and improved the electrode kinetics. The obtained composite was employed as a modified electrode for H2O2 reduction in an alkaline medium. Significant findings: Cyclic voltammograms recorded between 20 and 100 mV s-1 in the presence of 4 mM H2O2 exhibited nearly invariant profiles with minimal current variation, indicating a complex electrocatalytic mechanism. The observed behaviour suggests surface-mediated disproportionation of H2O2 on Ag sites, generating O2 that is subsequently reduced electrochemically, thereby maintaining the interfacial H2O2 concentration during catalysis. Additionally, cyclic voltammetry and square-wave voltammetry indicate an EC '-type mechanism at the Ag/SnO/SnO2 heterojunction, where the SnO/SnO2 redox couple acts as a mediator facilitating electron transfer. The developed electrode exhibited improved electrocatalytic performance toward H2O2 reduction.
Industrial hemp (Cannabis sativa L.) production and the hemp-based industry are set for expansion. Hemp is cultivated for valuable fibers from stems and oil from seeds, used in various industrial applications. Recently, hemp has been grown for energy production due to its high biomass and seed yields. Hemp oil is suitable for biodiesel production through transesterification, while hemp biomass serves as a solid fuel or raw material for bioethanol, biohydrogen, and biogas production. This paper provides a comprehensive review of hemp seed and biomass pretreatment, oil extraction, and biofuel production methods. Pretreatment methods for hemp seed and biomass are largely unexplored, and innovative methods require detailed economic analysis before commercialization. Research on hemp oil extraction is sparse and lacks comparative analyses of different techniques regarding yield and quality. Advanced methods yield more oil in shorter times than conventional techniques. Advanced solvent extraction yields more oil than screw pressing and maceration but less than Soxhlet extraction. Transesterification of hemp oil for biodiesel typically uses base catalysts, either homogeneous or heterogeneous, but novel methods have yet to be applied. Other biofuels are produced by thermochemical (torrefaction, pyrolysis, gasification) and biological (fermentation, anaerobic digestion) processes. A comparative analysis of biofuel yields and primary energy recovery potentials of different hemp components is needed to optimize biomass utilization in bioenergy production. Despite the substantial benefits of hemp biofuel production, challenges such as legal and regulatory barriers, economic competition with high-value products, production costs, environmental trade-offs, technological advancement, and public perception need to be addressed.
