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1.
Optical and magnetic properties of PbTe(Ni)
Nebojša Romčević, J. Trajić, M. Romčević, D. Stojanović, T. A. Kuznetsova, D. Khokhlov, W. Dobrowolski, Rebeka Rudolf, Ivan Anžel, 2009, published scientific conference contribution

Abstract: Far-infrared and magnetic properties of Ni doped PbTe (ZNi = 1 £ 1019 at./cm3)single crystal are investigated in a broad range of temperature and magnetic elds. Far-infrared re°ection spectra were analyzed using a tting procedure based on the modi ed plasmon{two phonon interaction model. Together with the strong plasmon{two longitudinal optical phonon coupling we obtained a local mode of Ni at about 180 cm¡1. This mode intensity depends on temperature. Magnetic measurements shows that PbTe alloys doped with Ni reveals weak ferromagnetic interaction between magnetic ions.
Keywords: semiconductor compounds, PbTe(Ni)
Published: 31.05.2012; Views: 1086; Downloads: 58
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2.
Low-frequency Raman scattering from ZnO(Fe) nanoparticles
R. Kostić, Nebojša Romčević, M. Romčević, B. Hadžić, Rebeka Rudolf, I. Kuryliszyn Kudelska, W. Dobrowolski, U. Narkiewicz, D. Sibera, 2009, published scientific conference contribution

Abstract: Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine the sample composition and the mean crystalline size. Low frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum aproximation, which considers nanoparticle as homogeneous elastic sphere.
Keywords: nanocrystalline samples, Raman modes
Published: 31.05.2012; Views: 914; Downloads: 68
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3.
Raman spectroscopy of multiphonon emission process in Ni-doped PbTe
Nebojša Romčević, J. Trajić, B. Hadžić, M. Romčević, D. Stojanović, Z. Lazarević, T. A. Kuznetsova, D. Khokhlov, Rebeka Rudolf, Ivan Anžel, 2009, published scientific conference contribution

Abstract: In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1* 1019 at./cm3. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm-1. The modes at 126 and 143 cm-1, which are also observed in other telluride compounds, originate from vibrations in TeO2. We assume that the mode at about 181 cm-1 is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni3+ state). Modes at about 362 cm-1 and 724 cm-1 are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
Keywords: crystals, Raman scattering
Published: 31.05.2012; Views: 1047; Downloads: 78
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4.
Ellipsometric measurements of plastically deformed copper
M. Mirić, Rebeka Rudolf, Ivan Anžel, B. Hadžić, M. Romčević, J. Trajić, Nebojša Romčević, 2009, published scientific conference contribution

Abstract: Chemically pure copper (99.99) prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm was extremely plastically deformed with the repeated application of equal channel angular pressing. Equal channel angular pressing was applied as an effective technique for producing bulk nanoscaled structures. It is well known that severe plastic deformation of metallic materials often leads to microstructure with ultrafine grains and cross-sections which remain about equal before and after deformation. Optical properties of the sample were studied using spectroscopic ellipsometry in UV-VIS range. The parameters of the sample like copper oxide and surface roughness overlayer were calculated using two-film model together with the Bruggeman effective medium approximation.
Keywords: hydrometallurgical extraction of metals, copper
Published: 31.05.2012; Views: 989; Downloads: 83
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5.
Optical properties of plastically deformed copper
J. Trajić, Rebeka Rudolf, Ivan Anžel, M. Romčević, N. Lazarević, M. Mirić, Z. Lazarević, B. Hadžić, Nebojša Romčević, 2010, published scientific conference contribution

Abstract: Pure copper (99.99), prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of 7 cm¡1) and wide ( 40 cm¡1) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen.
Keywords: plastically deformed copper, hydrometallurgical extraction of metals
Published: 31.05.2012; Views: 1144; Downloads: 65
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6.
Optical properties of plastically deformed copper : an ellipsometric study
Nebojša Romčević, Rebeka Rudolf, J. Trajić, M. Romčević, B. Hadžić, Dana Vasiljević-Radović, Ivan Anžel, 2011, original scientific article

Abstract: In this paper the results of optical properties investigations on plastically deformed copper are presented. The optical properties of the plastically deformed copper were studied using spectroscopic ellipsometry in the ultraviolet-visible (UV-VIS) range. Chemically pure copper was deformed by applying the Equal Channel Angular Pressing (ECAP) technique. During the last decade, equal-channel angular pressing procedure was used for the fabrication of ultrafine-grained metals and alloys. The plastic deformation of metallic materials leads to the production of bulk nano-scale structures with ultrafine grains and cross-sections, which remain about equal before and after deformation. The parameters of the sample were calculated using a two-film model together with the Bruggeman effective medium approximation.
Keywords: ellipsometric spectroscopy, atomic force microscopy, copper, amorphisation
Published: 01.06.2012; Views: 1182; Downloads: 40
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7.
Genetic programming approach for the material flow curve determination of copper alloy - CuCrZr
Leo Gusel, Miran Brezočnik, Rebeka Rudolf, Ivan Anžel, Z. Lazarević, Nebojša Romčević, 2010, original scientific article

Abstract: For the control of the forming process it is necessary to know as precisely as possible the flow curve of the formed material. The paper presents the determination of the equation for the flow curve of cooper alloy (CuCrZr) with artificial intelligence approach. The genetic programming method (GP) was used. It is an evolutionary optimization technique based on the Darwinist principles of the evolution of species and the survival of the fittest organisms. The main characteristic of GP is its non- deterministic way of computing. It is probably the most general approach out of evolutionary computation methods. The comparison between the experimental results, analytical solution and the solution obtained genetically clearly shows that the genetic programming method is a very promising approach.
Keywords: forming, flow curve, copper alloys, genetic programming
Published: 01.06.2012; Views: 873; Downloads: 11
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8.
In-vitro evaluation of the retention of different prefabricated posts luted with different cements
Miloš Maksimović, Aleksandra Špadijer Gostović, Aleksandar Todorović, Nebojša Romčević, Rebeka Rudolf, Ana Todorović, 2012, original scientific article

Abstract: The aim of this study was to assess and compare the mechanical resistance and the retentive force of metal and composite post systems cemented with different types of cements. Three different designs of prefabricated titanium alloy posts were used in the study, i.e., active, passive and combined, as well as AgPd cast posts and two different fibre-reinforced composite post systems. In accordance with the experimental design these posts were cemented with zinc phosphate, self-curing composite resin or self-adhesive, self-etching, luting agent. Comparing the results between the different metal post designs, cemented with zinc phosphate, a statistically significant difference in the retention was found between all the analysed posts. The best results with the pull-out test were obtained with the active posts, then the passive, followed by the combined posts. The metal cast posts cemented conventionally with Zn-phosphate demonstrated the lowest retentive force value, based on all the measurements. The bond strengths between the post and the root dentine were influenced statistically by the post design (active, passive, combined or cast) and material, metal vs. composite. The active Ti posts showed significantly superior retention in combination with all the cements. The Ti alloy posts achieved higher retentive force values than the composite posts, in general. The composite cements compared to the Zn-phosphate ensure a better retentive strength for all the posts, including individually cast posts.
Keywords: retention, prefabricated titanium posts, fibre-reinforced composite posts, cements, pull-out testing
Published: 10.07.2015; Views: 411; Downloads: 46
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9.
Mechanical properties of the materials for bruxoguards
Vojkan Lazić, Aleksandra Špadijer Gostović, Nebojša Romčević, Igor Đorđević, Ana Todorović, Rebeka Rudolf, 2014, original scientific article

Abstract: The aim of this study is to investigate the mechanical properties of polymethyl methacrylate (PMMA) and thermoplastic polycarbonate (TPC) materials in order to produce night bruxoguards. For this purpose we used a static tensile test. In the next step the microstructures of PMMA and TPC were observed. Within this framework special attention was paid to the examination of the tensile-test tube fracture surfaces for both materials. This approach revealed that PMMA is a brittle and TPC is a plastic material. Certain mechanical properties and a review of the crucial areas confirmed that the TPC material is extremely favourable for making occlusal splints.
Keywords: polymers, mechanical properties, characterization, bruxoguards, polymethyl methacrylate, thermoplastic polycarbonate
Published: 16.03.2017; Views: 470; Downloads: 55
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10.
Determination of microstructural changes by severely plastically deformed copper-aluminum alloy
Nebojša Romčević, M. Gilić, Ivan Anžel, Rebeka Rudolf, Miodrag Mitrić, M. Romčević, B. Hadžić, D. Joksimović, Milica Petrović Damjanović, Matija Kos, 2014, original scientific article

Abstract: Our work deals with the problem of producing a complex metal-ceramic composite using the processes of internal oxidation (IO) and severe plastic deformation. For this purpose, Cu-Al alloy with 0.4wt.% of Al was used. IO of sample serves in the first step of the processing as a means for attaining a fine dispersion of nanosized oxide particles in the metal matrix. Production technology continues with repeated application of severe plastic deformation (SPD) of the resulting metal matrix composite to produce the bulk nanoscaled structural material. SPD was carried out with equal channel angular pressing (ECAP), which allowed that the material could be subjected to an intense plastic strain through simple shear. Microstructural characteristics of one phase and multiphase material was studied on internally oxidized Cu with 0.4wt.% of Al sample composed of one phase copper-aluminum solid solution in the core and fine dispersed oxide particles in the same matrix in the mantle region. In this manner AFM, X-ray diffraction and Raman spectroscopy were used. Local structures in plastically deformed samples reflect presence of $Cu$, $CuO$, $Cu_2O$, $Cu_4O_3$ or $Al_2O_3$ structural characteristics, depending on type of sample.
Keywords: metals, oxides, atomic force microscopy, Raman spectroscopy, microstructure
Published: 08.08.2017; Views: 396; Downloads: 63
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