1. The relationship between oil prices and stock prices of the European renewable energy companies : a vector autoregressive analysisEnis Slatina, Lejla Lazović-Pita, Ademir Abdić, Adem Abdić, 2023, original scientific article Abstract: This article aims to examine the potential relationship between Brent crude
oil futures prices and the index of the European renewable energy companies.
After the overview of the European legislation and the most recent literature
review on the topic, the article deploys a method of the Vector Autoregressive
Model (VAR). The analysis includes weekly data over eight years (2015-
2022). Our results indicate a positive correlation between Brent crude oil
futures prices and the value of the European Renewable Energy Total Return
(ERIX) index. The estimated bivariate VAR model indicates a statistically
significant relationship, meaning that past values of the ERIX Index may be
used to predict future Brent crude oil prices in the long run. Considering the
most recent systemic disturbance in the world’s commodity market, future
research should consider longer time series and possible relationships of
other macroeconomic factors.
Keywords: renewable energy, Brent crude oil, futures prices, ERIX index, VAR
Published in DKUM: 28.05.2025; Views: 0; Downloads: 0
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2. 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: 18
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3. Task-oriented evaluation of the feasible kinematic directional capabilities for robot machiningSaša Stradovnik, Aleš Hace, 2022, original scientific article Abstract: Performing the machining of complex surfaces can be a challenging task for a robot, especially in terms of collaborative robotics, where the available motion capabilities are greatly reduced
in comparison with conventional industrial robot arms. It is necessary to evaluate these capabilities
prior to task execution, for which we need efficient algorithms, especially in the case of flexible
robot applications. To provide accurate and physically consistent information about the maximum
kinematic capabilities while considering the requirements of the task, an approach called the Decomposed Twist Feasibility (DTF) method is proposed in this study. The evaluation of the maximum
feasible end-effector velocity is based on the idea of decomposition into the linear and angular motion
capabilities, considering a typical robot machining task with synchronous linear and angular motion.
The proposed DTF method is presented by the well-known manipulability polytope concept. Unlike
the existing methods that estimate the kinematic performance capabilities in arbitrarily weighted
twist space, or separately in the translation and the rotation subspace, our approach offers an accurate
and simple solution for the determination of the total kinematic performance capabilities, which is
often highly required, especially in the case of robot machining tasks. The numerical results obtained
in this study show the effectiveness of the proposed approach. Moreover, the proposed DTF method
could represent suitable kinematic performance criteria for the optimal placement of predefined tasks
within the robot workspace
Keywords: robot surface machining, task feasibility, task-dependent kinematic capability, kinematic performance evaluation, manipulability index, manipulability polytope, motion decomposition, Decomposed Twist Feasibility method, DTF method
Published in DKUM: 01.04.2025; Views: 0; Downloads: 2
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4. Trees with distinguishing index equal distinguishing number plus oneSaeid Alikhani, Sandi Klavžar, Florian Lehner, Samaneh Soltani, 2020, original scientific article Abstract: The distinguishing number (index) D(G) (D'(G)) of a graph G is the least integer d such that G has an vertex (edge) labeling with d labels that is preserved only by the trivial automorphism. It is known that for every graph G we have D'(G) \leq D(G) + 1. In this note we characterize finite trees for which this inequality is sharp. We also show that if G is a connected unicyclic graph, then D'(G) = D(G).
Keywords: automorphism group, distinguishing index, distinguishing number, tree, unicyclic graph
Published in DKUM: 11.03.2025; Views: 0; Downloads: 4
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5. Contract price change during the construction phase: unforeseen market conditionsNataša Šuman, Stanko Tominc, 2024, original scientific article Abstract: The unstable economic conditions that have been in place in the Slovenian and international construction markets reveal the problem of a disproportionate increase in the prices of construction materials and energy products. Such increases will therefore result in higher costs of construction services, which would ultimately affect the total value of the construction project. These events in turn bring uncertainty to the construction project and would negatively impact the business of construction companies and investors. Legal and construction practices have so far developed various ways to regulate contract changes arising due to unforeseen market conditions. The present paper offers a contribution to the contract price change solution during the construction phase. The introduction first presents the measures and guidelines that deal with the differences in contract prices in Slovenia and some other countries. Then, various methods of calculating price differences that have emerged in current Slovenian practice are described. As a result, a proposal for a hybrid method of monthly price difference calculation is presented. The hybrid method represents a balanced solution resulting from the unforeseen increase in construction material prices on the market and is applicable to all construction projects. The three methods, i.e., a calculation method, a method based on the GZS-ZGIGM index, and a hybrid method, are applied to a real example of a public contract. The calculation of the price valorisation, represented as an index of the recognised price increases of contract works, is carried out. The results are compared, and further solutions are proposed.
Keywords: connstruction contract, construction market, contract price, price index
Published in DKUM: 03.03.2025; Views: 0; Downloads: 6
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6. The Graovac-Pisanski index of connected bipartite graphs with applications to hydrocarbon moleculesMatevž Črepnjak, Martin Knor, Niko Tratnik, Petra Žigert Pleteršek, 2021, original scientific article Abstract: The Graovac-Pisanski index, also called the modified Wiener index, was introduced in 1991 and represents an extension of the original Wiener index, because it considers beside the distances in a graph also its symmetries. Similarly as Wiener in 1947 showed the correlation of the Wiener indices of the alkane series with the boiling points, in 2018 the connection between the GraovacPisanski index and the melting points of some hydrocarbon molecules was established. In this paper, we prove that the Graovac-Pisanski index of any connected bipartite graph as well as of any connected graph on an even number of vertices is an integer number. These results are applied to some important families of hydrocarbon molecules. By using a computer programme, the graphs with a non-integer Graovac-Pisanski index on at most nine vertices are counted. Finally, an infinite class of unicyclic graphs with a non-integer Graovac-Pisanski index is described.
Keywords: modified Wiener index, Graovac-Pisanski index, graph distance, automorphism group, hydrocarbons, carbon nanostructures
Published in DKUM: 14.02.2025; Views: 0; Downloads: 4
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8. International energy security risk index - analysis of the methodological settingsIztok Podbregar, Goran Šimić, Mirjana Radovanović, Sanja Filipović, Polona Šprajc, 2020, original scientific article Abstract: The main objective of this paper is to analyze model settings of the International Energy Security Risk Index developed by the U.S. Chamber of Commerce. The study was performed using stepwise regression, principal component analysis, and Promax oblique rotation. The conclusion of the regression analysis shows that Crude Oil Price and Global Coal Reserves are sufficient to explain 90% of the variance of the Index. However, if a model that explains 100% of the variance of the Index is chosen and other variables are added, Global Coal Reserves loses importance due to the presence of other parameters in which it is contained. Regardless of the chosen model of analysis, it is evident that there is room for revising the Index and removing variables that do not contribute to its precision. The research showed that the main disadvantage of the variables that make up the Index rests with the fact that the variables are of different degrees of generality, that is, one parameter is contained in other parameters (unclear which other). The research covers data for 25 countries over a 26-year period, with the first year of the research being 1980 and the last 2016 (the latest available report).
Keywords: international energy security risk index, analysis, stepwise regression, principal component analysis, Promax oblique rotation
Published in DKUM: 04.02.2025; Views: 0; Downloads: 17
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9. The international energy security risk index in sustainable energy and economy transition decision making - a reliability analysisIztok Podbregar, Goran Šimić, Mirjana Radovanović, Sanja Filipović, Damjan Maletič, Polona Šprajc, 2020, original scientific article Abstract: The world economy and society are in a complex process of transition characterized by a high degree of uncertainty. Therefore, further development and management of the transition will largely depend on the quality of the decisions made and, accordingly, on the decision-making process itself. The main goal of this study is to analyze the reliability of International Energy Security Risk Index as a tool to support the process of energy and economy transition decision making, as closely related and highly interdependent phenomena. The index is composed of 29 aggregated variables (grouped into eight categories), and the research is conducted on a research sample of 25 countries over a period of 36 years. The reliability assessment is performed by using Multiple Regression Analysis. Multicollinearity test, plus Multicollinearity test with Variance Inflation Factors, is used for methodological verification. The test results indicate a high degree of unreliability of the Index, as is concluded based on the observed errors in its methodological settings. These errors primarily relate to a high degree of multicollinearity in all 29 variables, whereby independent variables lose their independence and thus jeopardize reliability of the total Index. Out of the eight groups of variables, the fuel imports group is the only one that does not show big methodological errors. The paper presents a recommendation for the improvement of the observed Index (review of the role of individual variables found to be particularly methodologically indicative), as well as a recommendation for different distribution of weighting coefficients.
Keywords: energy and economy transition, decision making, international energy security risk index, multiple regression analysis, multicollinearity test, multicollinearity test with variance inflation factors
Published in DKUM: 04.02.2025; Views: 0; Downloads: 7
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10. Properties of large 2-crossing-critical graphsDrago Bokal, Markus Chimani, Alexander Nover, Jöran Schierbaum, Tobias Stolzmann, Mirko H. Wagner, Tilo Wiedera, 2022, original scientific article Keywords: crossing number, crossing-critical graph, chromatic number, chromatic index, treewidth
Published in DKUM: 04.02.2025; Views: 0; Downloads: 4
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