Digital library of University of Maribor

    Yield strength modelling of formed material using evolutionary computational method

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    In this paper we propose an evolutionary computation approach for the modelling of yield strength in formed material. One of the most general evolutionary computation methods is genetic programming, which was used in our research. Genetic programming is an automated method for creating a working computer program from a problemćs high-level statement. Genetic programming does this by genetically breeding a population of computer programs using the principles of Darwinianćs natural selection and biologically inspired operations. During our research, material was cold formed by drawing using different process parameters and then determining yield strengths (dependent variable) of the specimens. On the basis of a training data set, various different genetic models for yield strength distribution were developed during simulated evolution. The accuracies of the best models were proved by a testing data set and comparing between the genetic and regression models. The research showed that very accurate genetic models can be developed by the proposed approach

    Notranja oksidacija Cu-C in Ag-C kompozitov

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    The internal oxidation in copper-carbon and silver-carbon composites occurs when they are exposed to air or oxygen at high temperature. Solubility of carbon in copper or in silver is very low. The kinetics of oxidation at high temperature and activation energy were determined and the mechanism of internal oxidation was analysed. The kinetics of internal oxidation was determined for both cases and it is depended from the diffusion of oxygen following parabolic time dependence according to Wagner\u27s theory. The activation energy for Cu-C composite is 70.5 kJ/mol, and for Ag-C composite is 50.1 kJ/mol, what is in both cases close to the activation energy for the volume diffusion of oxygen in copper or in silver. In both cases gas products are formed during the internal oxidation of composites. In the internal oxidation zone pores, bubbles occur. The carbon oxidates directly with the oxygen from solid solution as long there is a contact, which breaks down with the presence of gas products. Then the oxidation occurs over the gas mixture of CO and CO2.Pri visokih temperaturah kompoziti bakra in srebra z ogljikom na zraku ali v kisiku reagirajo po mehanizmu notranje oksidacije. Topnost ogljika v trdnem bakru in trdnem srebru je zelo majhna. Analizirali smo kinetiko oksidacije kompozitov, določili aktivacijsko energijo in mehanizem notranje oksidacije. Kinetika oksidacije je pri obeh skupinah materialov odvisna od difuzije kisika in sledi parabolični odvisnosti od časa v skladu z Wagnerjevo teorijo. Aktivacijska energija procesa je za kompozit Cu-C enaka 70,5 kJ/mol, za kompozit Ag-C pa 50,1 kJ/mol, kar je blizu aktivacijski energiji za volumsko difuzijo kisika v trdnem bakru oziroma srebru. Pri oksidaciji kompozita nastajajo plinski produkti. Oksidacija ogljika poteka neposredno s kisikom iz trdne raztopine, ko pa se zaradi nastanka plinske faze stik prekine, pa preko plinske zmesi CO in CO2

    Removal of inorganic As5+ from a small drinking water system

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    The drinking water from a small drinking water system contained arsenic in a concentration of about 50 ▫mumu▫g/L. Chemical analyses showed that the pentavalent form of arsenic was present. Since the MCL value is 10 ▫mumu▫g/L, it was necessary to implement a technological treatment to make the water suitable for drinking. In order to do so, two technologies were suggested: activated alumina and ▫alphaalpha▫-FeOOH (TehnoArz, TA) adsorption media. Experiments using both adsorption media were performed on a laboratory scale. It was possible to remove arsenic to below 1 ▫mumu▫g/L. The maximal adsorption capacity was found to be 12.7 mg of As5+ per gram of ▫alphaalpha▫-FeOOH. Moreover, all the important physico- chemical parameters of the water remained practically unchanged after the treatment. Only a slight release of iron from the media was observed. The Fe-As bond was studied by means of chemical analysis and X-ray powder diffraction. Finally, in addition to showing the capability of arsenic removalby ▫alphaalpha▫-FeOOH, a comprehensive optimization of the technological parameters of the selected technology is provided

    Wavelets in electrochemical noise analysis

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    Adsorption and antibacterial activity of soluble and precipitated chitosan on cellulose viscose fibers

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    The aim and novelty of this work was to compare the adsorption of totally-soluble chitosan (acidic solution) against the adsorption of precipitated chitosan, onto cellulose fibers. The influences of both these chitosan-adsorption procedures on a final amino groupćs content in functionalized cellulose fibers were studied, using potentiometric titration and the conventional spectrophotometric C.I. Acid Orange 7 method. Surface modification and adsorption of chitosan were, in addition, monitored by determining XPS spectra. The antimicrobial activities of both chitosan- functionalised cellulose fibers were examined, in regard to pathogen bacteria and fungus

    Power losses in synchronous reluctance motors

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    V članku smo najprej predstavili osnovne lastnosti, zgradbo in delovanje sinhronskega reluktančnega motorja, nato pa v okviru dvoosne teorije zapisali vezni model obravnavanega električnega stroja. Reluktančni navor omogoča vrtenje rotorja v sinhronizmu z glavnim vrtilnim poljem. Pri takšnem načinu delovanja (sinhronsko vrtenje) je v rotorju gostota magnetnega pretoka vedno enosmerna, kar narekuje brezizguben rotor. Vendar imamo zaradi statorskih utorov spremembo magnetne upornosti zračne reže, kar pri vrtenju povzroči utorske pulzacije magnetnega polja in s tem površinske izgube na rotorju. Na podlagi temeljnih elektromagnetnih zakonitosti smo izpeljali enačbo in z njo ovrednotili površinske izgube na rotorju motorja. Z obremenilnim preizkusom in preskusom prostega teka smo analizirali obratovalne karakteristike in izgube motorja. Kot posledico izgub smo nastalo temperaturno polje v motorju in na njem prikazali v obliki temperaturne slike.The aim of this paper is to present power losses in synchronous reluctance motors (SRM). Generally speaking, this type of motors is an unexcited synchronous machine with stator windings and a stator similar to any regular induction machine. The rotor is cross-laminated and contains flux barriers placed equidistantly around the air gap (Fig. 1). They serve to diminish the quadrature (q-axis) flux flowing between poles and at the same time they permit the direct axis flux to flow largely unimpeded through the poles. On the basis of the Parkćs theory, an impedance model of SRM for stationary operating modes is presented in a matrix form (Eq. 1). Further, the paper devotes special attention to surface power losses. The main flux of synchronous reluctance motors rotates at the same speed as the rotor. The presence of the stator openings gives rise to permeance variations causing a ripple in the main flux (Fig. 2) through which the rotor is driven and resulting in induced losses on the rotor surface. The same is going on on the stator surface due to the permeance variations in the rotor slot opening range. At normal tooth ripple frequencies, only eddy current components of these losses are of any significance and histeresis losses may be ignored. Eqs. (2-5) describe the magnetic flux density distribution and penetration into the rotor. Fundamental electromagnetic equtions (6-8) are used to calculate the eddy current distribution (Eq. 9) on a thin surface layer of a laminated rotor. Surface losses are calculated with Eq. 10 and presented in Figs. (3-4). The measured torque and current characteristics of SRM for asynchronous run are shown in Fig. 5. and for synchronous run in Fig. 7. The principle of the rotor load angle measurement is given in Fig. 6. No-load characteristics of SRM and power losses separation are presented in Fig. 8. Power losses at no-load operation of the measured prototype are separated and given in Table 1. To establish the surface losses impact on rotor temperature variations the temperature measurements (Fig. 9) were made. They are presentedin Table 2. Temperature variations for the SRM stator winding at a nominal load are given in Fig. 11

    PUBLIC OPINION ON MIGRANTS AND REFUGEES IN THE REPUBLIC OF SLOVENIA

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    V diplomskem delu je predstavljeno soočanje Republike Slovenije z različnimi migracijskimi tokovi od njene osamosvojitve do danes. Opravili smo analizo raziskav javnega mnenja o migrantih in begunci od leta 1991 do 2016. Podrobneje smo primerjali javno mnenje o migrantih in beguncih v 90. letih, ki so prihajali iz držav nekdanje Jugoslavije, z javnim mnenjem o migrantih in beguncih danes, ki prihajajo iz neevropskih držav. Prav tako smo na podlagi zbranih podatkov ugotavljali, ali na odnos do migrantov in beguncev vplivajo različni dejavniki kot so spol, izobrazba in politična usmerjenost. Rezultati analize javnega mnenja kažejo na to, da se javno mnenje v 90. letih o migrantih in beguncih, ki so prihajali iz držav nekdanje Jugoslavije, v primerjavi z javnim mnenjem do migrantov in beguncev danes, ki prihajajo iz neevropskih držav, ni občutno spremenilo. Pričakovano rezultati kažejo na to, da so ženske, visoko izobražene osebe ter podporniki levo usmerjenih političnih strank bolj naklonjeni migrantom in beguncem kot moški, osebe s poklicno izobrazbo ter podporniki desno usmerjenih političnih strank.This thesis presents the confrontation of the Republic of Slovenia with different migration flows from its independence until today. We performed analyses of the research of public opinion on migrants and refugees from 1991 to 2016 and compared the public opinion on migrants and refugees who migrated from the countries of the former Yugoslavia in the nineties with the public opinion on migrants and refugees who are migrating from non-European countries today. Based on the collected data we also examined if different factors such as gender, education, and political orientation affect the attitude towards migrants and refugees. The results of the analyses of public opinion show that the public opinion on migrants and refugees who migrated from countries of the former Yugoslavia in the nineties compared with the public opinion on migrants and refugees who are migrating from non-European countries today has not changed significantly. As expected, the results are showing that women, well educated people, and the supporters of leftist parties are more inclined to migrants and refugees than men, less educated people, and the supporters of right-wing parties
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