Faculty of Technical Sciences, Čačak
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The Faculty is accredited and it offers accredited Undergraduate, Integrated, Master and Doctoral study programmes. The cooperation with leading domestic and International companies such as Oracle, Microsoft, Intergraph, Fujitsu and Schneider-electric enabled our students to gain skills through practice in well-known companies, and prompted our graduates to be distinguished experts in modern technologies.
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Browsing Faculty of Technical Sciences, Čačak by Issue Date
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Item Optimal spares availability strategy for power transformer components(2010) Mijailovic, VladicaThe paper suggests a method to optimize the spare amount of power transformer components. The proposed strategy is conceived to provide minimum annual cost consisting of expected failures renewal cost, capital cost for spares and load curtailment cost. The method identifies minor and major failures. Minor failures are repairable, while major failures can be repairable or unrepairable. Power transformer is a complex system, consisting of six components (functional parts). It is assumed that each component has two independent, competing failure modes: wear-out failure mode, modelled by two-parameter Weibull distribution, and a chance failure mode, characterized by an exponential distribution. The application of the method suggested and the benefits it provides are demonstrated for one transformer station (TS) 110/x kV/kV with 2×31.5MVA transformers. In addition, the influence of performing power transformer refurbishment on expected total cost has also been analyzed. © 2010 Elsevier B.V. All rights reserved.Item Properties of MnZn ferrites prepared by powder injection molding technology(2010) Zlatkov B.; Mitrovic, Nebojsa; Nikolic, Maria; Maricic, Aleksa; Danninger, Herbert; Aleksić O.; Halwax E.In this work, manganese zinc ferrite components were manufactured by powder injection molding - PIM technology. A fine powder consisting of Mn 1-xZnxFe2O4 with small addition of hematite α-Fe2O3 as used in mass ferrite production was mixed with an organic binder (Solvent System) to form ferrite feedstock for powder injection molding - PIM technology. Excess of Fe2O3 was present in the starting powder in order to suppress conversion of Fe 3+ to Fe2+ ions which would lower the permeability. The ferrite feedstock was injected in a mold with a cavity shaped like a small cylinder with a hole on the main axis. Injection molded samples were then solvent and thermally debinded and sintered in different atmospheres: air, argon and nitrogen. The starting powder, injected green samples and sintered samples were characterized using X-ray diffractometry, scanning electron microscopy, thermogravimetry, differential thermal analysis as well as by magnetic measurements. Rietveld refinement of measured X-ray patterns was done to detect possible phase transformations of Fe2O3 to other iron oxides through reduction by binder residues (carbon) at elevated temperatures during thermal debinding and sintering. Finally, the magnetic properties were measured by hysteresis graph and mutually compared for the injected samples that were sintered in air, argon and nitrogen. The obtained magnetic characteristics where found to be comparable with commercial samples prepared by traditional sintering technology. © 2010 Elsevier B.V.Item The weak asymptotic equivalence and the generalized inverse(2010) Đurčić, Dragan; Nikolić, Rale; Torgašev A.In this paper, we discuss the relationship between the weak asymptotic equivalence relation and the generalized inverse in the class A{\mathcal{A}} of all nondecreasing and unbounded functions, defined and positive on a half-axis [a,+∞) (a > 0). In the main theorem, we prove a proper characterization of the functional class ORV ÇA{{ORV} \cap \mathcal{A}} , where ORV is the class of all O{\mathcal{O}} -regularly varying functions (in the sense of Karamata). Keywordsregular variation-generalized inverse-weak asymptotic equivalence MSC26A12Item A few remarks on divergent sequences: Rates of divergence II(2010) Đurčić, Dragan; Kocinac, Ljubisa; Žižović, MališaWe continue (and, in a sense, close) our investigation begun in the paper Djurčić et al. (2009) [10] concerning quotient speed of divergence of sequences of positive real numbers and its relations with selection principles and games. By the way, we show a theorem of the generalized Galambos-Bojanić-Seneta type. © 2009 Elsevier Inc. All rights reserved.Item Reasoning with linguistic preferences using NPN logic(2010) Devedzic, Goran; Milošević, Danijela; Ivanović, Lozica; Adamovic, Dragan; Manić M.Negative-positive-neutral logic provides an alternative framework for fuzzy cognitive maps development and decision analysis. This paper reviews basic notion of NPN logic and NPN relations and proposes adaptive approach to causality weights assessment. It employs linguistic models of causality weights activated by measurement-based fuzzy cognitive maps' concepts values. These models allow for quasi-dynamical adaptation to the change of concepts values, providing deeper understanding of possible side effects. Since in the real-world environments almost every decision has its consequences, presenting very valuable portion of information upon which we also make our decisions, the knowledge about the side effects enables more reliable decision analysis and directs actions of decision maker.Item Electrodeposition of co-ni-mo xo y powders: Part I. the influence of deposition conditions on powder composition and morphology(2010) Stevanovic J.; Stajić-Trosić J.; Ćosović V.; Panić, Vladimir; Pešić, Olivera; Jordović BrankaThe Co-Ni-Mo xO y powders were obtained electrochemically at a constant current density from ammonia electrolyte. Ni and Co were anomalously deposited, inducing Mo deposition, which cannot be deposited separately from aqueous solutions. The obtained Co-Ni-Mo xO y powders were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electon microscope (SEM) methods. Based on the obtained experimental results, it was concluded that the particle size of deposited powders is influenced by the chemical composition of the electrolyte and current density imposed. XRD results suggested that obtained powders were of amorphous structure, although a Co 3Mo compound can be formed if certain experimental conditions are applied. © The Author(s) 2009.Item Summability of Sequences and Selection Properties(Hindawi Publishing Corporation, 2011) Đurčić, Dragan; Kocinac, Ljubisa; Žižović, MališaItem Interdependence of fundamental and applied research in material science(2011) Kosanović, Darko; Maricic, Aleksa; Mitrovic, Nebojsa; Runić Ristić M.Development of materials with desirable properties essentially depends on realization of interdependence: natural science ⇔ technical sciences. Taking this into account, in order to develop of new advanced materials it is essential to determine principles that characterize this interdependency. Therefore, in this article the principles of fundamental research and the importance of obtained results are considered and implemented in the field of technical realizations.Item Congruence openings of additive Green's relations on a semiring(2011) Damljanovic, Nada; Ciric, Miroslav; Bogdanovic V.In a series of papers, Green's relations on the additive and multiplicative reducts of a semiring proved to be a very useful tool in the study of semirings. However, in the vast majority of cases, Green's relations are not congruences, and we show that in such cases it is much more convenient to use the congruence openings of Green's relations, instead of the Green's relations themselves. By means of these congruence openings we define and study several very interesting operators on the lattices of varieties of semirings and additively idempotent semirings, and, in particular, we establish order embeddings of the lattice of varieties of additively idempotent semirings into the direct products of the lattices of open (resp. closed) varieties with respect to two opening (resp. closure) operators on this lattice that we introduced. © 2010 Springer Science+Business Media, LLC.Item Determining the optimum orientation of a greenhouse on the basis of the total solar radiation availability(2011) Dragicevic, SnezanaThis paper presents an approach to determining the optimum orientation of a greenhouse for year round applications for different climatic conditions. The most commonly used uneven-span single shape of greenhouse in east-west and north-south orientation have been selected for comparison. Total solar radiation input to each wall, included surfaces and roofs, is computed for both solar greenhouse orientation and compared for each month of the year at different latitudes at the northern hemisphere. Experimental validation is carried out for the measured global solar radiation data for horizontal surface and south wall at (44° N and 20° E), Belgrade, Serbia. The predicted and measured values are in close agreement. Results shows that east-west orientation of uneven-span solar greenhouse is the best suited during each months for all analyzed latitudes.Item Analysis of square coaxial lines by using Equivalent Electrodes Method(2011) Milovanović, Alenka; Koprivica, BrankoIn this paper the application of the Equivalent Electrodes Method (EEM) for the analysis of square coaxial lines has been presented. The capacitance per unit length, for different shapes and sizes, has been calculated. The results obtained by EEM have been compared with those reported in the literature, obtained by other methods, and those obtained by using software package COMSOL Multiphysics. These results have been found to be in very good agreement. © 2011 IEEE.Item Approximate calculation of capacitance of lines with multilayer medium(2011) Milovanović, Alenka; Bjekic, MiroslavIn this paper calculations of the capacitance per unit length of one or multilayer dielectric lines are presented. Special attention is given to the calculations of the capacitance per unit length of lines with rectangular cross sections, whose electrodes may be in different or the same layers of a two layer dielectric line. For the purpose of performing the above, several numerical methods are used and simple approximate expressions are proposed. © 2011 FEI STU.Item A wireless ECG sensor node based on Huffman data encoder(2011) Pešović, Uroš; Randjić, Siniša; Stamenković Z.The paper presents design and implementation of a wireless sensor node suitable for medical applications. As physiological signals are highly redundant, the data compression algorithms (Huffman's coding) are used to save energy and improve the node performance. Design is based on the ARM Cortex M1 processor and implemented in FPGA. © 2011 IEEE.Item The weak and the strong equivalence relation and the asymptotic inversion(2011) Đurčić, Dragan; Mitrović I.; Janjić M.In this paper we discuss the relationship between the weak and the strong asymptotic equivalence relation and the asymptotic inversion, for positive and measurable functions defined on a half-axis [a, + ∞) (a > 0). As the main results, we prove a certain characterizations of the functional class of all rapidly varying functions, as well as some other functional classes.Item Determination of electric and magnetic properties of commercial LTCC soft ferrite material(2011) Blaz N.; Maric A.; Radosavljevic, Gordana; Mitrovic, Nebojsa; Atassi I.; Smetana W.; Ẑivanov L.This paper offers an effective, accurate, and simple method for permittivity and permeability determination of an LTCC (low temperature cofired ceramic) ferrite sample. The presented research can be of importance in the fields of ferrite component design and application, as well as for RF and microwave engineering. The characterization sample is a stack of LTCC tapes forming a toroid. Commercially available ferrite tape ESL 40012 was used and standard LTCC processing was applied for the sample fabrication. For the first time, the electrical properties of a ferrite toroid sample of ESL 40012 LTCC ferrite tape is presented at various frequencies. The electrical properties of LTCC ferrite materials, permittivity and specific resistivity, are shown in a frequency range from 10 kHz to 1 MHz using the capacitive method. The hysteresis properties of this material are also determined. B-H hysteresis loops were measured applying a maximum excitation of 2 kA/m and frequencies of 50 Hz, 500 Hz, and 1000 Hz. Permeability is determined in the frequency range from 10 kHz to 1 GHz and a characterization procedure is divided in two segments, for low and high frequencies. Low frequency measurements (from 10 kHz to 1 MHz) are performed using LCZ meter and discrete turns of wire, while a short coaxial sample holder and vector network analyzer were used for the higher frequency range (from 300 kHz to 1 GHz). In addition, another important factor required for the practical design of devices is presented, the temperature variation of the permeability dispersion parameters. Copyright © International Microelectronics and Packaging Society. Copyright © 2013 International Microelectronics and Packaging Society.Item A FPGA system for QRS complex detection based on Integer Wavelet Transform(2011) Stojanović R.; Karadaglic D.; Mirković M.; Milošević, DanijelaDue to complexity of their mathematical computation, many QRS detectors are implemented in software and cannot operate in real time. The paper presents a real-time hardware based solution for this task. To filter ECG signal and to extract QRS complex it employs the Integer Wavelet Transform. The system includes several components and is incorporated in a single FPGA chip what makes it suitable for direct embedding in medical instruments or wearable health care devices. It has sufficient accuracy (about 95%), showing remarkable noise immunity and low cost. Additionally, each system component is composed of several identical blocks/cells what makes the design highly generic. The capacity of today existing FPGAs allows even dozens of detectors to be placed in a single chip. After the theoretical introduction of wavelets and the review of their application in QRS detection, it will be shown how some basic wavelets can be optimized for easy hardware implementation. For this purpose the migration to the integer arithmetic and additional simplifications in calculations has to be done. Further, the system architecture will be presented with the demonstrations in both, software simulation and real testing. At the end, the working performances and preliminary results will be outlined and discussed. The same principle can be applied with other signals where the hardware implementation of wavelet transform can be of benefit.Item Exponents of Convergence and Games(2011) Đurčić, Dragan; Kocinac, Ljubisa; Žižović, MališaThe notion of exponents of convergence has many applications in different mathematical disciplines. In this paper we consider exponents of convergence of sequences of positive real numbers in connection with games and selection principles.Item The weak and strong asymptotic equivalence relations and the generalized inverse*(2011) Đurčić, Dragan; Nikolić, Rale; Torgašev A.We discuss the relationship between the weak and strong asymptotic equivalence relations and the generalized inverse in the class A of all nondecreasing unbounded positive functions on a half-axis [a,+∞) (a > 0). As a main result, we prove a proper characterization of the functional class R ∞ ∩ A, where R ∞ is the class of all rapidly varying functions. Also, we prove a characterization of the functional class PI * ∩ A.Item The effect of temperature and frequency on magnetic properties of the Fe81B13Si4C2 amorphous alloy(2011) Djukic D.; Maričić V.; Kalezić-Glišović, Aleksandra; Ribić-Zelenović L.; Randjić, Siniša; Mitrovic, NebojsaIn this study it was investigated influence of temperature and frequency on permeability, coercivity and power loses of Fe81B13Si4C2 amorphous alloy. Magnetic permeability measurements performed in nonisothermal and isothermal conditions was confirmed that efficient structural relaxation was occurred at temperature of 663 K. This process was performed in two steps, the first one is kinetic and the second one is diffuse. Activation energies of these processes are: Ea1 = 52.02 kJ/mol for kinetic and Ea2 = 106.9 kJ/mol for diffuse. It was shown that after annealing at 663 K coercivity decrease about 30% and therefore substantial reduction in power loses was attained. Investigated amorphous alloy satisfied the criteria for signal processing devices that work in mean frequency domain.Item Development of new material for the environmental-friendly energy generation processes(2011) Ristic J.; Jovicevic, Ana; Kocić Sanja; Spasojević M.; Maricic, AleksaThe aim of this study was to develop a new material which has high hydrogen storage capacity and hydrogen absorption/desorption rate. This material, which is based on cobalt powder onto which palladium was chemically deposited can be used in environmentally friendly energy generation processes, thus ensuring preventive protection of human health. Hydrogen absorption was investigated using differential scanning calorimetry (DSC) and by measuring hydrogen pressure under isothermal and non-isothermal conditions in a chamber containing either pure cobalt powder either cobalt powder onto which palladium was chemically deposited (Co-0.003 Pd). The mechanism of hydrogen absorption has been described. It was noticed that palladium catalyses hydrogen absorption by dissociating the adsorbed H2 molecules into H atoms more rapidly on its own atoms than on cobalt ones. The catalysis of dissociation of H2 molecules enabled hydrogen absorption into Co-0.003 Pd powder to occur at lower temperatures. The results of this study enable integration of technological and public health investigation in order to ensure preventive protection of human health through enviromental protection.