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1.
Synthesis of PMMA/ZnO nanoparticles composite used for resin teeth
Danica Popović, Rajko Bobovnik, Silvester Bolka, Miroslav Vukadinovič, Vojkan Lazić, Rebeka Rudolf, 2017, original scientific article

Abstract: Wear resistance is one of the most important physical properties of the artificial teeth used in acrylic dentures. The goal of this research was to synthesize a new composite material made of matrix Poly-(methyl methacrylate)-PMMA with different percentages (2 % and 3 % of volume fractions) of zinc-oxide nanoparticles (ZnO NPs) as reinforcing elements, to improve its mechanical properties. The dynamic mechanical behaviour of this composite was studied through the DMA method in comparison to the pure PMMA supported by the characterization of their microstructures. Then the wear resistance was analysed on the samples, which were prepared in the form of teeth. In this context their vertical height loss was measured after 100,000 chewing cycles on a chewing simulator, before and after the artificial thermal ageing. Investigations showed that the PMMA/ZnO NP composites dampened the vibrations better than the pure PMMA, which could be assigned to the homogenous distribution of ZnO NPs in the PMMA matrix. It was found that the mean vertical height loss for the pure PMMA teeth was significantly higher (more than 4 times) compared to composite teeth made with ZnO NPs. Introducing the thermal artificial ageing led to the finding that there was no effect on the height loss by the composite material with 3 % of volume fractions of ZnO NPs. Based on this it was concluded that PMMA/ZnO NPs composites showed improved in-vitro wear resistance compared to acrylic-resin denture teeth, so this new composite material should be preferred when occlusal stability is considered to be of high priority.
Keywords: poly-methyl methacrylate, PMMA, zinc-oxide nanoparticles, composite, resin teeth
Published: 12.12.2017; Views: 824; Downloads: 346
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2.
Experimental testing of single APM spheres
Matej Vesenjak, Lovre Krstulović-Opara, 2010, published scientific conference contribution

Abstract: Advanced pore morphology (APM) foam, consisting of sphere-like metallic foam elements, proves to have advantageous mechanical properties and unique application adjustability. Since the APM foam manufacturing procedure has been developed recently, the mechanical characterization of these materials is still very limited. Therefore, the purpose of this research was to determine the behaviour of APM spheres and its composites when subjected to quasi-staticand dynamic compressive loading. The results of the performed research have shown valuable mechanical properties of the composite APM foam structures, offering new possibilities for their use in general engineering applications.
Keywords: advanced pore morphology, foam, composite APM foam structures
Published: 26.07.2017; Views: 733; Downloads: 291
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3.
Weak k-reconstruction of Cartesian products
Wilfried Imrich, Blaž Zmazek, Janez Žerovnik, 2003, original scientific article

Abstract: By Ulam's conjecture every finite graph ▫$G$▫ can be reconstructed from its deck of vertex deleted subgraphs. The conjecture is still open, but many special cases have been settled. In particular, one can reconstruct Cartesian products. We consider the case of ▫$k$▫-vertex deleted subgraphs of Cartesian products and prove that one can decide whether a graph ▫$H$▫ is a ▫$k$▫-vertex deleted subgraph of a Cartesian product ▫$G$▫ with at least ▫$k+1$▫ prime factors on at least ▫$k+1$▫ vertices each, and that ▫$H$▫ uniquely determines ▫$G$▫. This extends previous works of the authors and Sims. This paper also contains a counterexample to a conjecture of MacAvaney.
Keywords: mathematics, graph theory, reconstruction problem, Cartesian product, composite graphs
Published: 31.03.2017; Views: 834; Downloads: 295
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4.
Synthesis of NiTi/Ni-TiO[sub]2 composite nanoparticles via ultrasonic spray pyrolysis
Peter Majerič, Rebeka Rudolf, Ivan Anžel, Jelena Bogovic, Srečko Stopić, Bernd Friedrich, 2015, original scientific article

Abstract: In this paper we present the production of NiTi/Ni-TiO2 composite nanoparticles via the synthesis method called ultrasonic spray pyrolysis (USP). The precursor solution for the synthesis of spherical NiTi particles was prepared from an orthodontic wire with a chemical composition of Ni (amount fraction x = 51.46 %) and Ti (x = 48.54 %). TEM microscopy, in combination with EDX analyses, was used for a detailed characterization of the obtained NiTi nanoparticles. The results showed the nanoparticle sizes ranging from 60 nm to 600 nm, depending on the parameters of the production procedure. This showed the versatility of the new USP synthesis procedure, proving its usefulness for different materials and applications.
Keywords: ultrasonic spray pyrolysis, NiTi/Ni-TiO2 composite nanoparticles, characterization, Transmission electron microscope (TEM), TEM microscopy
Published: 23.03.2017; Views: 781; Downloads: 88
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5.
Synthesis of micro-composite beads with magnetic nano-particles embedded in porous CaCO[sub]3 matrix
Alenka Vesel, Aljoša Košak, David Haložan, Kristina Eleršič, 2012, original scientific article

Abstract: A method for synthesis of soft magnetic microbeads is presented. The microbeads are made from magnetic nanoparticles dispersed in CaCO3 (calcium carbonate) matrix. The composite beads are almost perfectly spherical with a diameter of few micrometers. The majority of the composite beads consists of a porous CaCO3 matrix. Magnetic nanoparticles with a size of about 10-15 nm are made of Fe2O3. They are captured inside the pores of CaCO3 matrix during its formation. CaCO3 matrix is formed by crystallization from saturated solution of sodium carbonate and calcium chloride. The composite beads are coated with a layer of functionalized polymer. The magnetic microbeads were characterized by SEM and XPS. Different functional groups were detected by XPS measurements including SO3–,NH3+,NH2,CO32– and OH groups. The results indicate that the iron oxide particles are absent on the surface and that the polymer coating serves as a good biocompatible film.
Keywords: composite, surface characterization, XPS, functionalization, Fe nanoparticles, microbeads
Published: 23.03.2017; Views: 665; Downloads: 69
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6.
Computer Modelling of Porous Composite Structures with Advanced Pore Morphology
Aljaž Kovačič, 2016, doctoral dissertation

Abstract: Advanced pore morphology (APM) structures are composite metal foams, which are assembled from a large number of small spherical elements with cellular structure, and are bonded into a composite with polymeric adhesive. The result of such composition is a wide spectrum of achievable mechanical behaviour in APM structures. To explore their full potential, efficient computational models are needed, which allow for simple parameter variation. Unfortunately, the current computer models do not allow for efficient simulations of porous composite structures with advanced pore morphology, as they employ complex discretisation approaches. A new approach to simulation is presented in this work, based on the discrete particle method (DPM), where every element of APM structure is discretised with a single node. This enables more efficient simulations of APM structures, while still allowing for simple variation of structural parameters. The DPM method was augmented with constitutive models of normal and tangential contact behaviour of APM elements and bonds between them, which were formulated based on an extensive experimental study of APM structure's geometry and mechanical behaviour. Consequently, the models enable simulations of large APM structure's behaviour by modelling the contact behaviour of individual elements. The implementation of new models was verified on a set of analytically solvable examples, and the accuracy of the models was validated with very good correspondence between computational and experimental results. Moreover, the models were validated on a wide set of examples, also taking into account the various strain rates and the absence of the bonds. The applicability of new models was demonstrated in a comprehensive parametrical study, where the influential structural parameters and properties were identified for low and high strain rate deformations. The study also demonstrated the possibility of customising the mechanical behaviour with property gradation, and with introduction of regular, as well as geometrically complex APM element assemblies. The possibility of coupled discrete particle method and finite element method simulations was also addressed. The newly developed models represent a breakthrough in the field of computational investigation of APM structures, and provide for simpler and more efficient investigations of APM structures in the future.
Keywords: Metal foams, advanced pore morphology, composite materials, mechanical properties, contact modelling, discrete particle methods, computer simulations
Published: 11.03.2016; Views: 1623; Downloads: 132
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7.
Direct enthalpy exchange between process utilities
Zorka Novak-Pintarič, Peter Glavič, 2002, professional article

Abstract: This paper presents an application of the improved pinch methodology by performing a simplified exergy analysis in a real-size ammonia plant. Besides the well known pinch technics like composite curves and grand composite curve, the improved approach with the extended grand composite curve was implemented. The latter presents the most energy intensive units in the process separated from the process background as well as the direct transfer of enthalpy from hot utilities to cold utilities. Based on this presentation the synthesis of modified heat exchanger network was performed which results in considerable decrease of utilities demand.
Keywords: chemical engineering, process design, exergy analysis, ammonia plant, pinch methodology, extended hrand composite curve method, enthalpy exchange, distillation column, heat exchanger network
Published: 10.07.2015; Views: 997; Downloads: 56
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8.
Weak reconstruction of strong product graphs
Blaž Zmazek, Janez Žerovnik, 2007, original scientific article

Abstract: We prove that any nontrivial connected strong product graph can be uniquely reconstructed from each of its one vertex deleted subgraphs.
Keywords: matematika, teorija grafov, problem rekonstrukcije, šibka rekonstrukcija, krepki produkt grafov, mathematics, graph theory, reconstruction problem, strong product, composite graphs
Published: 10.07.2015; Views: 519; Downloads: 346
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9.
On the weak reconstruction of strong product graphs
Blaž Zmazek, Janez Žerovnik, 2003, published scientific conference contribution

Abstract: We prove that any nontrivial connected strong product graph can be uniquely reconstructed from each of its one vertex deleted subgraphs.
Keywords: matematika, teorija grafov, problem rekonstrukcije, šibka rekonstrukcija, krepki produkt grafov, mathematics, graph theory, reconstruction problem, strong product, composite graphs
Published: 10.07.2015; Views: 544; Downloads: 62
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10.
Weak k-reconstruction of Cartesian products graphs
Wilfried Imrich, Blaž Zmazek, Janez Žerovnik, 2001, published scientific conference contribution abstract

Abstract: Po Ulamovi domnevi je mogoče vsak končen graf ▫$G$▫ rekonstruirati iz množice vseh podgrafov ▫$G$▫ brez ene točke. Znano je, da je mogoče rekonstruirati kartezične produkte. Obravnavan je soroden problem, imenovan šibka rekonstrukcija. Dokazano je, da je mogoče odločiti, ali se da dani graf ▫$H$▫ dobiti iz nekega kartezičnega produkta ▫$g$▫ z odstranitvijo ▫$k$▫ točk, če privzamemo, da ima ▫$G$▫ vsaj ▫$k+1$▫ faktorjev s po ▫$k+1$▫ točkami. V tem rimeru ▫$H$▫ enolično določa ▫$G$▫. Dan je tudi protiprimer za MacAvaneyjevo domnevo.
Keywords: matematika, teorija grafov, kartezični produkt, problem rekonstrukcije, sestavljeni grafi, mathematics, graph theory, reconstruction problem, Cartesian product, composite graphs
Published: 10.07.2015; Views: 662; Downloads: 8
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