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Structural properties and thermal stability of cobalt- and chromium-doped $α-MnO_2$ nanorods
Romana Cerc Korošec, Polona Umek, Alexandre Gloter, Jana Padežnik Gomilšek, Peter Bukovec, 2017, izvirni znanstveni članek

Opis: $α-MnO_2$ nanorods were synthesized via the hydrothermal decomposition of $KMnO_4$ in an acidic environment in the presence of $Co^{2+}$ and $Cr^{3+}$ ions. Reactions were carried out at three different temperatures: 90, 130 and 170 °C. All prepared samples exhibit a tetragonal $MnO_2$ crystalline phase. SEM–EDS analysis shows that cobalt cations are incorporated to a higher degree into the $MnO_2$ framework than chromium ions, and that the content of the dopant ions decreases with increasing reaction temperature. The oxidation of $Co^{2+}$ to $Co^{3+}$ during the reaction was proved by an XANES study, while EXAFS results confirm that both dopant ions substitute $Mn^{4+}$ in the center of an octahedron. The K/Mn ratio in the doped samples synthesized at 170 °C is significantly lower than in the undoped samples. Analysis of an individual cobalt-doped $α-MnO_2$ nanorod with HAADF-STEM reveals that the distribution of cobalt through the cross-section of the nanorod is uniform. The course of thermal decomposition of the doped nanorods is similar to that of the undoped ones. Dopant ions do not preserve the $MnO_2$ phase at higher temperatures nor do they destabilize the cryptomelane structure.
Ključne besede: $α-MnO_2$, manganese dioxide, doping, EXAFS, nanorods, XANES
Objavljeno: 10.08.2017; Ogledov: 280; Prenosov: 35
.pdf Celotno besedilo (8,24 MB)

Effects of ultrasound irradiation on the preparation of ethyl cellulose nanocapsules containing spirooxazine dye
Julija Volmajer Valh, Simona Vajnhandl, Lidija Škodič, Aleksandra Lobnik, Matejka Turel, Bojana Vončina, 2017, izvirni znanstveni članek

Opis: This article presents the influence of low frequency, high intensity ultrasonic irradiation on the characteristics (average size, polydispersity index) of ethyl cellulose nanocapsules encapsulating a photochromic dye. Photochromic nanocapsules were prepared by the emulsion-solvent evaporation method. The acoustic densities entering the system were systematically studied with respect to their abilities to modify and reduce the average sizes and polydispersity indexes of the nanocapsules. Scanning electron microscope, confocal laser microscope, and dynamic light scattering were utilised to characterise the structure, shape, size, and polydispersity of ethyl cellulose photochromic nanocapsules. We were able to tailor the size of the photochromic nanocapsules simply by varying the acoustic densities entering the system. At an acoustic density of 1.5 W/mL and 60 s of continuous irradiation, we were able to prepare an almost monodispersed population of the nanocapsules with an average size of 193 nm.
Ključne besede: encapsulation, ethyl cellulose microcapsules, nanocapsules
Objavljeno: 09.08.2017; Ogledov: 336; Prenosov: 37
.pdf Celotno besedilo (3,31 MB)

Dependence of warm or cold feeling and heat retention ability of knitwear from digital print parameters
Mladen Stančić, Dragana Grujić, Dragoljub Novaković, Nemanja Kašiković, Branka Ružičić, Jelka Geršak, 2014, izvirni znanstveni članek

Opis: Textile materials are increasingly being subjected to the process of printing. The printing process with its parameters significantly affects the properties of textile materials and clothes made from these materials. This paper examines the effect of the parameters of digital printing on thermo-physiological characteristics of printed textile materials. As the essential print parameters were selected tone value and a different number of passes. In this research were used knitted fabric materials of 100% cotton fibers (100% CO), 100% polyester fibers (100% PES) and their mixture (50%CO/50% PES). The influence of print parameters to thermo-physiological properties of the material is evaluated through a warm or cold feeling and heat retention ability. Results of the research demonstrated that, in addition to material composition, the printing process with its parameters have a significant influence on the thermo-physiological characteristics of textile materials.
Ključne besede: digital printing, textile materials, thermo-physiological comfort, warm of cold feeling, heat retention ability
Objavljeno: 09.08.2017; Ogledov: 173; Prenosov: 25
.pdf Celotno besedilo (934,30 KB)

Force measurements on teeth using fixed orthodontic systems
Rebeka Rudolf, Janko Ferčec, 2013, pregledni znanstveni članek

Opis: The fixed orthodontic appliance consists of brackets that are bonded to the teeth. When the wire is engaged in the slot of the brackets, it generates forces for orthodontic tooth movement. The change in periodontal blood supply provides a biological response which leads to remodelling of the alveolar bone and the orthodontic tooth movement. Many variables influencing orthodontic treatment cannot be controlled fully, such as growth and tissue response to appliances. However, the force placed on the tooth should be a controllable variable, and a careful study of the physics underlying clinical applications can help in reducing undesirable side effects. The properties of orthodontic wires such as: strength, stiffness, elasticity and spring-back define their clinical usefulness. The ideal orthodontic wire should exhibit the following properties: large spring-back, low stiffness, good formability, high stored energy, biocompatibility and environmental stability, low surface friction, and the capability of being welded or soldered to auxiliaries. The ideal arch wire has not been introduced yet. Once the wire is activated or bent, it is the unloading or deactivating forces that produce the orthodontic tooth movement. For these reasons, it is necessary to know the force level caused by each individual wire used in orthodontic treatment. Finally, the purpose of this paper is a presentation of force measurements which are generated by different super-elasticity NiTi wires.
Ključne besede: force measurements, orhodontic system, teeth, NiTi alloys
Objavljeno: 09.08.2017; Ogledov: 164; Prenosov: 18
.pdf Celotno besedilo (1,33 MB)

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, izvirni znanstveni članek

Opis: 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.
Ključne besede: metals, oxides, atomic force microscopy, Raman spectroscopy, microstructure
Objavljeno: 08.08.2017; Ogledov: 206; Prenosov: 42
.pdf Celotno besedilo (596,63 KB)

Deformation and energy parameters of fracture of steel of the main gas pipeline
P. O. Maruščak, Sergey Panin, Ulyana Polyvana, Tomaž Vuherer, Anna Guzanová, Janette Brezinová, 2015, izvirni znanstveni članek

Opis: By example of steel 17G1S, the regularities in the impact fracture of Charpy specimens at normal and low temperatures are described. The relationship between the energy parameters of fracture (impact toughness) and the deformation response of the material (the height of shear lips) of the specimens from the pipe steel is established. The micromechanisms of impact fracture of the material are described. At 20 °C and –30 °C, focal splitting of the material was observed on the fracture surface of specimens; at –60 °C, the material failed in a brittle manner by the mechanism of cleavage.
Ključne besede: impact toughness, main gas pipeline, failure analysis
Objavljeno: 08.08.2017; Ogledov: 196; Prenosov: 42
.pdf Celotno besedilo (2,03 MB)

The correlation between pain perception among patients with six different orthodontic archwires and the degree of dental crowding
Evgenija Marković, Janko Ferčec, Ivana Ščepan, Branislav Glišič, Nenad Nedeljković, Jovana Juloski, Rebeka Rudolf, 2015, izvirni znanstveni članek

Opis: Introduction: Forces generated in orthodontic treatment with fixed appliances create tension and compression zones in the periodontal ligament resulting in a painful experience for patients. In the first phase of orthodontic treatment, when leveling of teeth is needed, nickel-titanium (NiTi) archwires can be completely engaged in brackets, even in the cases of extreme crowding, exerting small forces. There is a great individual variation in the pain perception related to the application of orthodontic forces. Objective: The aim of this study was to investigate the pain perception among patients with dental crowding after insertion of six different NiTi orthodontic archwires as a part of fixed appliances in the first stage of orthodontic treatment. Methods: The study was conducted on a sample of 189 orthodontic patients receiving one of six different either superelastic or heat activated NiTi archwires, in the first phase of orthodontic treatment. Pain perception was evaluated in groups of patients with different degree of crowding. The modified McGill Pain Questionnaire with Visual Analogue Scale was used to evaluate the quality and intensity of pain. Statistical analysis was performed using simple descriptive statistics, and Pearson`s chi-square test with statistical significance of p<0.05. Results: Majority of patients reported pain as discomfort or pressure of moderate intensity caused by chewing or biting, started within 12 hours, carried on for 3-4 days, and decreased over time without self-medication. Conclusion: No correlation was found between pain perception among patients with different types of NiTi archwires and the degree of crowding.
Ključne besede: nickel-titanium archwires, pain, dental crowding, orthodontics
Objavljeno: 04.08.2017; Ogledov: 203; Prenosov: 28
.pdf Celotno besedilo (258,88 KB)

Lagrangian particle tracking in velocity-vorticity resolved viscous flows by subdomain BEM
Jure Ravnik, Matjaž Hriberšek, Janez Lupše, 2016, izvirni znanstveni članek

Opis: A numerical study of particle motion in a cubic lid driven cavity is presented. As a computational tool, a boundary element based flow solver with a Lagrangian particle tracking algorithm is derived. Flow simulations were performed using an in-house boundary element based 3D viscous flow solver. The Lagrangian particle tracking algorithm is capable of simulation of dilute suspensions of particles in viscous flows taking into account gravity, buoyancy, drag, pressure gradient and added mass. The derived algorithm is used to simulate particle behaviour in a cellular flow field and in a lid driven cavity flow. Simulations of particle movement in a cellular flow field were used to validate the algorithm. The main goal of the paper was to numerically simulate the flow behaviour of spheres of different densities and different diameters, as experimentally observed in work of Tsorng et al.The study of slightly buoyant and non-buoyant particles in a lid driven cavity was aimed at discovering cases when particles leave the primary vortex and enter into secondary vortices, a phenomenon described in the work of Tsorng et al. A parametric study of this phenomenon was preformed. The presented computational results show excellent agreement with experiments, confirming the accuracy of the developed computational method.
Ključne besede: dispersed two phase flow, Lagrangian particle tracking, cellular flow, lid driven cavity, boundary element method
Objavljeno: 04.08.2017; Ogledov: 144; Prenosov: 21
.pdf Celotno besedilo (13,57 MB)

Analysis of the effect of the swirl flow intensity on combustion characteristics in liquid fuel powered confined swirling flames
Marko Klančišar, Tim Schloen, Matjaž Hriberšek, Niko Samec, 2016, izvirni znanstveni članek

Opis: This article examines the implementation of CFD technology in the design of the industrial liquid fuel powered swirl flame burner. The coupling between the flow field and the combustion model is based on the eddy dissipation model. The choice of the LES (Large Eddy Simulation) turbulence model over standard RANS (Reynolds Averaged Navier-Stokes) offers a possibility to improve the quality of the combustion-flow field interaction. The Wall Adapting Local Eddy-Viscosity (WALE) sub-grid model was used. The reaction chemistry is a simple infinitely fast one step global irreversible reaction. The computational model was setup with the Ansys-CFX software. Through the detailed measurements of industrial size burner, it was possible to determine the natural operational state of the burner according to the type of fuel used. For the inlet conditions, axial and radial velocity components were calculated from known physical characteristics of both the fuel and air input, with the initial tangential velocity of the fuel assumed as 18% of the initial axial fuel velocity. Different swirl number (S) values were studied. Addition of a surplus (in comparison to conventional flame stabilization) of tangential air velocity component (W), the rotational component increases itself with a considerably high magnitude, contributing to the overall flame stabilization. The level of S especially influences the turbulent energy, its dissipation rate and turbulent (Reynolds) stresses. In the case of high swirl number values (S > 0,65) it is possible to divide the flow field in three principle areas: mixing area (fuel-air), where exothermal reactions are taking place, central recirculation area and outer recirculation area, which primarily contains the flow of burnt flue gases. The described model was used to determine the flow and chemical behavior, whereas the liquid atomization was accounted for by LISA (Linear Instability Sheet Atomization) model incorporating also the cavitation within injection boundary condition. The boundary conditions were determined based on the data from the experimental hot water system. Depending on system requirements, especially with continuous physical processes as well as the results of experimental measurements, the paper reports on determination of the mixing field and its intensity in the turbulent flow, the description of heat release and interaction of turbulent flow field and chemical kinetics in the case of confined swirling flames.
Ključne besede: CFD, fluid dispersion, combustion, industrial burner, confined swirling flame, two-phase flow
Objavljeno: 04.08.2017; Ogledov: 297; Prenosov: 27
.pdf Celotno besedilo (1,08 MB)

Product lifecycle management through innovative and competitive business environment
Valentina Gečevska, Paolo Chiabert, Zoran Anišić, Franco Lombardi, Franc Čuš, 2010, objavljeni znanstveni prispevek na konferenci

Opis: Product Lifecycle Management (PLM) is the process of managing the whole life cycle of a product starting from generating an idea, concept description, business analyzes, product design and solution architecture and technical implementation, to the successful entrance to the market, service, maintenance and product improvement. At present, a wide range of stakeholders including consumers, regulators, shareholders and public bodies are demanding that companies address product management through all life cycle in a more comprehensive and sustainable way. However, even if a company actually wishes innovate its processes for improving the way to account for project management, it will face relevant difficulties to deal with different guidelines, tools and methods currently addressing the matter from various points of view. The purpose of this paper is to review literature on PLM from an operational point of view with the objective to help companies to answer to the main market needs.
Ključne besede: product lifecycle management, business process, competitiveness
Objavljeno: 04.08.2017; Ogledov: 152; Prenosov: 14
.pdf Celotno besedilo (241,81 KB)

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