1. Organization of efficient energy security managementBojana Vasić, 2024, doctoral dissertation Abstract: The main problem this research addresses is the EU energy policy, which focuses on a critical analysis of strategic energy management in all process phases. Particular emphasis is placed on strategic control, which is a key phase of the management process. Strategic control includes evaluating the effectiveness of implementing planned measures and making decisions about necessary adjustments or changes. The purpose of the study is to assess how well EU energy management strategies are aligned with policy objectives, in particular, to ensure energy security, sustainability and economic competitiveness, and at the same time to identify areas where improvements are needed to address current challenges.
Energy management in the European Union is a crucial aspect of its energy policy, which focuses on ensuring energy security, sustainability and efficiency. Since the middle of the 20th century, organisations' increasing energy intensity has emphasized the need for a comprehensive and flexible approach. Energy management involves controlling the entire life cycle of energy - from extraction, conversion and distribution to consumption and waste disposal - in a complex environment shaped by various external factors. These challenges become even more pronounced in regions that experience frequent environmental, economic or geopolitical changes.
Designing a universal model for global energy management is difficult because of the different conditions, regulations, and energy needs worldwide. Adaptable and adaptive strategies are essential to respond to supply and demand fluctuations, integrate renewable energy sources, manage geopolitical risks and achieve sustainability goals. Therefore, energy management must evolve to respond to a dynamic global environment.
The EU prioritizes energy security but lacks a unified approach, which creates challenges in defining and measuring energy security. The absence of standardized criteria makes it difficult to strategically evaluate policies and make decisions, which could have long-term consequences for both energy and national security. Initially, energy security was focused on stable supply for economic growth, but global changes – such as rising demand, geopolitical tensions and environmental concerns – have made it more complex.
The recent years have underscored significant vulnerabilities in global energy security and the sustainability of energy systems, particularly in Europe. The dual crises of the COVID-19 pandemic and the conflict in Ukraine have highlighted the urgency of addressing these challenges, pushing the European Union to accelerate its efforts toward more sustainable and secure energy practices. In response, the EU has diversified energy sources and strengthened energy security to reduce its dependence on politically unstable suppliers.
Given the complexity of the geopolitical situation, disrupted supply chains and the EU's clear official commitment to decarbonisation by 2050, the above should be viewed from different angles. EU energy policy (short-term and long-term) is conditioned by the action of many factors, which differ in type, intensity of action and effect (positive or negative) - but the need to analyse existing and define new methodologies for evaluating the effectiveness of EU energy policy is evident. The doctoral dissertation examines the above and suggests improvements.
Keywords: Energy management, sustainable management, energy security, aggregate index, composite indicator
Published in DKUM: 10.04.2025; Views: 0; Downloads: 15
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2. Effect of micro- and nano-lignin on the thermal, mechanical, and antioxidant properties of biobased PLA–lignin composite filmsSofia P. Makri, Eleftheria Xanthopoulou, Panagiotis A. Klonos, Alexios Grigoropoulos, Apostolos Kyritsis, Konstantinos Tsachouridis, Antonios Anastasiou, Ioanna Deligkiozi, Nikolaos P. Nikolaidis, Dimitrios Bikiaris, 2022, original scientific article Abstract: Bio-based poly(lactic acid) (PLA) composite films were produced using unmodified soda
micro- or nano-lignin as a green filler at four different contents, between 0.5 wt% and 5 wt%. The PLA–
lignin composite polymers were synthesized by solvent casting to prepare a masterbatch, followed by
melt mixing. The composites were then converted into films, to evaluate the effect of lignin content
and size on their physicochemical and mechanical properties. Differential scanning calorimetry
(DSC), supported by polarized light microscopy (PLM), infrared spectroscopy (FTIR-ATR), X-ray
diffraction (XRD), and transmission electron microscopy (TEM) were employed to investigate the
PLA crystallization and the interactions with Lignin (L) and Nanolignin (NL). The presence of
both fillers (L and NL) had a negligible effect on the glass transition temperature (chain diffusion).
However, it resulted in suppression of the corresponding change in heat capacity. This was indicative
of a partial immobilization of the PLA chains on the lignin entities, due to interfacial interactions,
which was slightly stronger in the case of NL. Lignin was also found to facilitate crystallization, in
terms of nucleation; whereas, this was not clear in the crystalline fraction. The addition of L and
NL led to systematically larger crystallites compared with neat PLA, which, combined with the
higher melting temperature, provided indications of a denser crystal structure in the composites. The
mechanical, optical, antioxidant, and surface properties of the composite films were also investigated.
The tensile strength and Young’s modulus were improved by the addition of L and especially NL.
The UV-blocking and antioxidant properties of the composite films were also enhanced, especially
at higher filler contents. Importantly, the PLA–NL composite films constantly outperformed their
PLA–L counterparts, due to the finer dispersion of NL in the PLA matrix, as verified by the TEM
micrographs. These results suggest that bio-based and biodegradable PLA films filled with L, and
particularly NL, can be employed as competitive and green alternatives in the food packaging
industry.
Keywords: poly(lactic acid), PLA, lignin, nanolignin, composite films, nucleation, mechanical properties, antioxidant activity, food packaging
Published in DKUM: 26.03.2025; Views: 0; Downloads: 1
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3. Reinforcing ethyl cellulose aerogels with poly(lactic acid) for enhanced bone regenerationGabrijela Horvat, Jan Rožanc, Uroš Maver, Matjaž Finšgar, Željko Knez, Zoran Novak, 2024, original scientific article Abstract: Developing double porous biodegradable and biocompatible scafolds that can incorporate and release drugs in a controlled manner holds immense potential in regenerative medicine. This study presents a synthesis method for preparing a macro-mesoporous scafold, where poly(lactic acid) adds to the macroporous region and mechanical properties, and ethyl cellulose adds to the surface area (182 m2 /g). High surface area enables the incorporation of model drug indomethacin with an entrapment efciency of 17.0% and its later controlled release profle. The resulting scafold has desirable mechanical properties in the range of a natural trabecular bone with a compressive modulus of 22.4 MPa. The material is stable in the simulated body fuids for 120 days before the slow degradation starts. In vitro studies demonstrate the material’s ability to support bone cell adhesion, proliferation, and diferentiation, promoting osteogenic activity. Overall, the unique combination of poly(lactic acid) and ethyl cellulose produces advanced materials with tailored macro and mesopore properties, remarkable mechanical properties, optimal degradation rate, and drug delivery potential, making it a promising candidate for bone scafolds in regenerative medicine and tissue engineering
Keywords: bio composite, polymer-matrix composites (PMCs), polymers, porosity/voids, secondary ion mass spectrometry
Published in DKUM: 23.08.2024; Views: 130; Downloads: 9
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4. Innovative structural systems for timber buildings : A comprehensive review of contemporary solutionsMiroslav Premrov, Vesna Žegarac Leskovar, 2023, review article Abstract: The remarkable development of timber construction technologies in recent decades has led to an increase in the number of timber buildings worldwide, including multi-storey buildings. The design of timber buildings, especially those of greater height, is relatively demanding and, even in the context of architectural expression, has certain constraints due to the specific structural and physical properties of this material. Thus, it is important for designers to have an overview of existing timber structural systems and their specificities to be able to make the right design decisions during the design process. Unfortunately, there is a lack of scientific literature that systematically addresses the essential features of contemporary timber structural systems. Within the aims of this paper to provide the systematic review of contemporary structural systems, both the scientific and professional literature are comprehensively reviewed. This paper presents a systematic classification and description of the following structural systems of timber buildings: all-timber and hybrid timber structural systems with an additional description of constituent structural elements, while examples of completed multi-storey timber buildings are also given for each structural system. The findings provide a broader view of the knowledge of contemporary solutions of timber structural systems and their application, thus representing a novelty in the field of timber construction review.
Keywords: timber structural systems, hybrid timber structural system, timber-concrete composite, timber-steel composite, timber-timber composite, timber structural elements, timber buildings, multi-storey timber buildings
Published in DKUM: 09.02.2024; Views: 261; Downloads: 53
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5. Synthesis of PMMA/ZnO nanoparticles composite used for resin teethDanica Popović Antić, 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 in DKUM: 12.12.2017; Views: 1876; Downloads: 446
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6. Experimental testing of single APM spheresMatej 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 in DKUM: 26.07.2017; Views: 1428; Downloads: 379
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7. Weak k-reconstruction of Cartesian productsWilfried 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 in DKUM: 31.03.2017; Views: 1558; Downloads: 479
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8. Synthesis of NiTi/Ni-TiO[sub]2 composite nanoparticles via ultrasonic spray pyrolysisPeter 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 in DKUM: 23.03.2017; Views: 1610; Downloads: 134
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9. Synthesis of micro-composite beads with magnetic nano-particles embedded in porous CaCO[sub]3 matrixAlenka 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 in DKUM: 23.03.2017; Views: 1335; Downloads: 116
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10. Computer Modelling of Porous Composite Structures with Advanced Pore MorphologyAljaž 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 in DKUM: 11.03.2016; Views: 2635; Downloads: 250
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