Marija Savic

On Explanation of the Double-Valued Paschen-Like Curve for RF Breakdown in Argon

This paper represents an investigation of the dependence of the breakdown voltage on the gas pressure in radio-frequency argon discharges under conditions when ion-induced secondary electron production is negligible. Calculations were performed by using a Monte Carlo collision code including electrons only. Our simulation results clearly show a region, occurring at low pressure, where multiple values of the breakdown voltage exist at a given pressure, in agreement with previous experimental observations. The two different regimes of operation, each satisfying the breakdown condition, may be best analyzed in contour plots of electron density, ionization rate, and mean energy.

Numerical Modeling of Thermalization of Positrons in Gas-Filled Surko Traps

In this paper, we present the results of our Monte Carlo-based numerical simulation of a Penning-Malmberg-Surko positron trap. The results of simulations show the effect that various processes (such as positronium (Ps) formation, annihilation, losses on walls, etc.) have on trapping efficiency. The thermalization profile is shown, along with the evolution of the energy distribution that morphs from a particle beam to a broad swarm-type distribution.

Assessment of the ISO 9001 functioning on an example of relations with suppliers development: empirical study for transitional economy conditions

In this paper, a model for the development of relationships with suppliers in order to create long-term partnerships, while following the requirements of ISO 9001 standard, was defined. Research has shown that the same relations with suppliers that exist between standardised companies (SC) and non-standardised companies (NSC) within the set of suppliers, also exist between NSC and NSC within the set of companies. Creating partnerships between SC and NSC suppliers is not possible, while obtained results show the opposite, which clearly indicates that the certification in the studied economy is being performed pro forma.

Episodes of extremely high concentrations of SO2 and particulate matter in the urban environment of Bor, Serbia.

This paper presents the extremely high concentrations of SO2 and particulate matter measured in the urban area of the town Bor (Serbia) during August 2011. Concentrations of SO2 above 125 μg m(-3) and concentrations of particulate matter above 200 μg m(-3) recorded over several days indicate significant risk to human health and the ecosystem in this region.

ANFIS-Based Prediction of the Decomposition of Sodium Aluminate Solutions in the Bayer Process

This article presents the results of nonlinear statistical modeling of the decomposition process of sodium aluminate solution, as part of the Bayer technology for the production of alumina. Based on the data collected in 2011 and 2012 from industrial production in the Birač Alumina Factory, Zvornik (Bosnia and Herzegovina), nonlinear statistical modeling of the industrial processes was derived. The model was developed as an attempt to define the dependence of the degree of decomposition of sodium aluminate solution as a function of the input parameters of the leaching process: caustic ratio (αk) of the solution; ratio of the crystallization; content of Na2O(caustic) in the solution; the initial temperature of the solution; the final temperature of the solution; average diameter of the crystallized seeds; and duration of the crystallization process. As a tool for statistical modeling, Adaptive Network Based Fuzzy Inference System (ANFIS) was applied. The defined model using ANFIS methodology expressed a high level of fitting, and could be used to effectively predict the degree of decomposition of the sodium aluminate solution as a function of the input process under industrial conditions.

Multi-Criteria Decision Support System for Optimal Blending Process in Zinc Production

The formation of input batch zinc concentrates is one of the key processes on which the quality and efficiency of all subsequent operations during the production of zinc cathodes directly depends. The optimization of the formation of a mixed batch aims at making a selection between the zinc concentrates that have different contents of useful and harmful components and to determine their share in the optimal mix. A multi criteria optimization model, which can be a good support for the defined problem of determining the optimal mixture of zinc concentrates, was developed in this study. For an evaluation of this model, according to four different research scenarios, the PROMETHEE/GAIA methodology was used to rank the considered zinc concentrates and determine their optimal share in the mix batch. In addition, the determination of the significance of the criteria in the optimization model was performed by application of the subjective AHP approach and the objective entropic approach. The results of this study, which were obtained during an analysis of a real case from the practice of a zinc production facility, indicate that the choice and formation of the optimal mixture of concentrates directly depends on the subjective or objective type of assessment of the significance of several chemical components in the zinc concentrates, and on the market price of the considered concentrates.

New phenomenology of gas breakdown in DC and RF fields

This paper follows a review lecture on the new developments in the field of gas breakdown and low current discharges, usually covered by a form of Townsends theory and phenomenology. It gives an overview of a new approach to identifying which feedback agents provide breakdown, how to model gas discharge conditions and reconcile the results with binary experiments and how to employ that knowledge in modelling gas discharges. The next step is an illustration on how to record volt-ampere characteristics and use them on one hand to obtain the breakdown voltage and, on the other, to identify the regime of operation and model the secondary electron yields. The second aspect of this section concerns understanding the different regimes, their anatomy, how those are generated and how free running oscillations occur. While temporal development is the most useful and interesting part of the new developments, the difficulty of presenting the data in a written form precludes an easy publication and discussion. Thus, we shall only mention some of the results that stem from these measurements. Most micro discharges operate in DC albeit with complex geometries. Thus, parallel plate micro discharge measurements were needed to establish that Townsends theory, with all its recent extensions, is still valid until some very small gaps. We have shown, for example, how a long-path breakdown puts in jeopardy many experimental observations and why a flat left-hand side of the Paschen curve often does not represent good physics. We will also summarize a kinetic representation of the RF breakdown revealing a somewhat more complex picture than the standard model. Finally, we will address briefly the breakdown in radially inhomogeneous conditions and how that affects the measured properties of the discharge. This review has the goal of summarizing (rather than developing details of) the current status of the low-current DC discharges formation and operation as a discipline which, in spite of its very long history, is developing rapidly.

An Linear Programming Model for Batch Optimization in the Ecological Zinc Production

This paper presents a mathematical model for solving the blending composition problem used in the zinc smelting process. The model proposes an objective function maximizing profit in terms of the total income from the sale of zinc on the market and the cost of producing zinc. In addition to the constraints contained in the basic mathematical model, the constraints, which are in accordance with the specific production process of zinc and environmental requirements, are developed. This paper proposes a model that can align three contradictory demands (technological, economic, and environmental) present in zinc production. The results, obtained by numerical experiments, confirm the assumption that it is possible to assemble such an optimal batch that will “reconcile” all contradictory demands. This model can be applied to other similar processes of production with minor changes.

Statistical modeling of copper losses in the silicate slag of the sulfide concentrate smelting process

Abstract This article presents the results of the statistical modeling of copper losses in the silicate slag of the sulfide concentrates smelting process. The aim of this study was to define the correlation dependence of the degree of copper losses in the silicate slag on the following parameters of technological processes: SiO2, FeO, Fe3O4, CaO and Al2O3 content in the slag and copper content in the matte. Multiple linear regression analysis (MLRA), artificial neural networks (ANNs) and adaptive network based fuzzy inference system (ANFIS) were used as tools for mathematical analysis of the indicated problem. The best correlation coefficient (R2 = 0.719) of the final model was obtained using the ANFIS modeling approach.