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From HX-groups to HX-polygroups
Seyed S. Mousavi, Morteza Jafarpour, Irina Elena Cristea, 2023, izvirni znanstveni članek

Ključne besede: HX-group, hypercompositional structure, coset, polygroup, regularity, uniformity, essentiality, double coset
Objavljeno v RUNG: 22.12.2023; Ogledov: 750; Prenosov: 7
.pdf Celotno besedilo (340,31 KB)
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Spine-sheath jet model for low-luminosity AGNs
Margot Boughelilba, Anita Reimer, Lukas Merten, Jon Paul Lundquist, 2023, objavljeni znanstveni prispevek na konferenci

Opis: In several jetted AGNs, structured jets have been observed. In particular spine-sheath configurations where the jet is radially divided into two or more zones of different flow velocities. We present a model based on the particle and radiation transport code CR-ENTREES. Here, interaction rates and secondary particle and photon yields are pre-calculated by Monte Carlo event generators or semi-analytical approximations. These are then used to create transition matrices, that describe how each particle spectrum evolves with time. This code allows for arbitrary injection of primary particles, and the possibility to choose which interaction to include (photo-meson production, Bethe-Heitler pair-production, inverse-Compton scattering, �-� pair production, decay of all unstable particles, synchrotron radiation — from electrons, protons, and all relevant secondaries before their respective decays — and particle escape). In addition to the particle and radiation interactions taking place in each homogeneous zone, we implement the feedback between the two zones having different bulk velocities. The main mechanism at play when particles cross the boundary between the two zones is shear acceleration. We follow a microscopic description of this acceleration process to create a corresponding transition matrix and include it in our numerical setup. Furthermore, each zone’s radiation field can be used as an external target photon field for the other zone’s particle interactions. We present here the first results of the effect of a two-zone spine-sheath jet, by applying this model to typical low-luminosity AGNs.
Ključne besede: active galactic nuclei, low-luminosity jetted AGN, spine-sheath jet structure
Objavljeno v RUNG: 24.08.2023; Ogledov: 762; Prenosov: 4
.pdf Celotno besedilo (461,21 KB)
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Preface to the special issue ʺAlgebraic structures and graph theoryʺ : editorial
Irina Elena Cristea, Hashem Bordbar, 2023, drugi znanstveni članki

Ključne besede: algebraic structure, graphs
Objavljeno v RUNG: 27.07.2023; Ogledov: 899; Prenosov: 6
.pdf Celotno besedilo (205,60 KB)
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The avidin-theophylline complex : a structural and computational study
Angelo Spinello, Fabio Lapenta, Matteo De March, 2023, izvirni znanstveni članek

Ključne besede: avidin, theophillyn, crystal structure
Objavljeno v RUNG: 24.07.2023; Ogledov: 859; Prenosov: 2
.pdf Celotno besedilo (1,52 MB)
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Efficiency of the grid energy storage technology based on iron-chloride material cycle
Uroš Luin, doktorska disertacija

Opis: Future high-capacity energy storage technologies are crucial for a highly renewable energy mix, and their mass deployment must rely on cheap and abundant materials, such as iron chloride. The iron chloride electrochemical cycle (ICEC), suitable for long-term grid energy storage using a redox potential change of Fe2+/Fe, involves the electrolysis of a highly concentrated aqueous FeCl2 solution yielding solid iron deposits. For the high overall energy efficiency of the cycle, it is crucial maximizing the energy efficiency of the electrolysis process. The thesis presents a study of the influence of electrolysis parameters on energy efficiency, performed in an industrial-type electrolyzer system. We studied the conductivity of the FeCl2 solution as a function of concentration and temperature and correlated it with the electrolysis energy efficiency as a function of current density. The contribution of the resistance polarization increases with the current density, causing a decrease in overall energy efficiency. The highest energy efficiency of 89 ±3 % was achieved using 2.5 mol dm-3 FeCl2 solution at 70 °C and a current density of 0.1 kA m-2. In terms of the energy input per Fe mass, this means 1.88 Wh g-1. The limiting energy input per mass of the Fe-deposit, calculated by extrapolating experimental results toward Eocell potential, was found to be 1.76 Wh g-1. For optimal long-duration electrolysis efficiency and performance, the optimal catholyte concentration range is 1-2 mol dm-3 FeCl2. We performed in situ X-ray absorption spectroscopy experimental studies to validate theoretical conclusions from literature related to the population and structure of Fe-species in the FeCl2 (aq) solution at different concentrations (1 - 4 mol dm-3) and temperatures (25 - 80 °C). This revealed that at low temperature and low FeCl2 concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five H2O at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical H2O is substituted by a Cl ion to yield a neutral Fe[Cl2(H2O)4]0. The transition from the charged Fe[Cl(H2O)5]+ to the neutral Fe[Cl2(H2O)4]0 causes a significant drop in the solution conductivity, which well correlates with the existing state-of-the-art conductivity models. An additional steric impediment of the electrolytic cell is caused by the predominant neutral species present in the catholyte solution at high concentration. This correlates with poor electrolysis performance at a very high catholyte concentration (4 mol dm-3 FeCl2), especially at high current densities (> 1 kA m-2). The neutral Fe[Cl2(H2O)4]0 complex negatively affects the anion exchange membrane ion (Cl-) transfer and lowers the concentration of electroactive species (Fe[Cl(H2O)5]+) at the cathode surface. The kinetics of hydrogen evolution from the reaction between Fe powder and HCl acid was studied under the first-order reaction condition. The activation energy was determined to be 55.3 kJ mol-1.
Ključne besede: ICEC, Power-to-Solid, energy storage, hydrogen, ferrous chloride, electrolysis, Fe deposition, efficiency, XAS, structure and population, ionic species, ion association, conductivity
Objavljeno v RUNG: 18.04.2023; Ogledov: 1502; Prenosov: 25  (1 glas)
.pdf Celotno besedilo (4,34 MB)

Dependence relations and grade fuzzy set
Alessandro Linzi, Irina Elena Cristea, 2023, izvirni znanstveni članek

Opis: With the aim of developing the recent theory of dependence relations, we elaborate a procedure to measure the strength of the influence of an element on another with respect to a given dependence relation on a finite set. We call this measure the degree of influence. Its definition is based on a partial hyperoperation and a directed graph which we associate with any dependence relation. We compute the degree of influence in various examples and prove some general properties. Among these properties, we find symmetries that have the potential to be applied in the realization of effective algorithms for the computations.
Ključne besede: dependence relation, degree of influence, grade fuzzy set, hypercompositional structure, hyperoperation
Objavljeno v RUNG: 23.01.2023; Ogledov: 1475; Prenosov: 3
.pdf Celotno besedilo (304,05 KB)
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Correlation between FeCl2 electrolyte conductivity and electrolysis efficiency
Uroš Luin, Matjaž Valant, Iztok Arčon, 2022, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: The electrolysis efficiency is an important aspect of the Power-to-Solid energy storage technology (EST) based on the iron chloride electrochemical cycle [1]. This cycle employs an aqueous FeCl2 catholyte solution for the electro-reduction of iron. The metal iron deposits on the cathode. The energy is stored as a difference in the redox potential of iron species. Hydrogen, as an energy carrier, is released on demand over a fully controlled hydrogen evolution reaction between metallic Fe0 and HCl (aq) [1]. Due to these characteristics, the cycle is suitable for long-term high-capacity and high-power energy storage. In a previous work [2] we revealed that the electrolyte conductivity linearly increases with temperature. Contrary, the correlation between the electrolyte concentration and efficiency is not so straightforward. Unexpectedly small efficiency variations were found between 1 and 2.5 mol dm-3 FeCl2 (aq) followed by an abrupt efficiency drop at higher concentrations. To explain the behavior of the observed trends and elucidate the role of FeCl2 (aq) complex ionic species we performed in situ X-ray absorption studies. We made a dedicated experimental setup, consisting of a tubular oven and PMMA liquid absorption cell, and performed the measurements at the DESY synchrotron P65 beamline. The XAS investigation covered XANES and EXAFS analyses of FeCl2 (aq) at different concentrations (1 - 4 molL-1) and temperatures (25 - 80 °C). We found that at low temperature and low FeCl2 concentration the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å [3]. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl2(H2O)4]0. The transition from the single charged Fe[Cl(H2O)5]+ to the neutral Fe[Cl2(H2O)4]0 causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models [3]. [1] M. Valant, “Procedure for electric energy storage in solid matter. United States Patent and Trademark Office. Patent No. US20200308715,” Patent No. US20200308715, 2021. [2] U. Luin and M. Valant, “Electrolysis energy efficiency of highly concentrated FeCl2 solutions for power-to-solid energy storage technology,” J. Solid State Electrochem., vol. 26, no. 4, pp. 929–938, Apr. 2022, doi: 10.1007/S10008-022-05132-Y. [3] U. Luin, I. Arčon, and M. Valant, “Structure and Population of Complex Ionic Species in FeCl2 Aqueous Solution by X-ray Absorption Spectroscopy,” Molecules, vol. 27, no. 3, 2022, doi: 10.3390/molecules27030642.
Ključne besede: Iron chloride electrochemical cycle, Power-to-Solid energy storage, XANES, EXAFS, electrical conductivity, electrolyte complex ionic species structure and population
Objavljeno v RUNG: 26.09.2022; Ogledov: 1685; Prenosov: (1 glas)
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Stefan Subotić, magistrsko delo

Opis: The master thesis aims to find the optimal model for a new energy company that considers regional potential, supports sustainable development, and fits the circular economy concept in a region. The idea of sustainable development is crucial today when we have more city areas and less countryside around the globe. Increased global population, industrial trends and modern living style are some of the reasons why the burden on our environment is more significant than ever in the history of humanity. The idea is to launch the new company in the Croatian region Osijek-Baranja, which is less developed and not attractive to tourists. A newly established company will produce electric energy from renewable energy sources. The multi-criterion decision support methods were used to determine the optimal energy source between wind, biogas and sun. Results show that the biogas has the most significant sustainable potential in chosen boundary conditions. The cash flows and other economic indicators are shown for a farm of 500 milking cows in the chosen region as a source of biogas. The risk assessments method estimated the boundaries of the company success and adaptability to possible changes. One of the critical aspects of the project is the company's organizational structure, where a vertical hierarchy with a flexible and fluid, circular organization model with network culture was proposed. Clear communication about the project will help establish trust with the local community. Based on the biogas plant, the proposed company reduces biodegradable waste in the green energy production process. It is shown quantitatively that besides being economically sustainable, it also suits the region's potential, supports energy self-supply, and involves local people - it aims to the long-term sustainable growth of the region, rather than short-term capital growth.
Ključne besede: Circular economy, sustainable development, regional potential, renewable energy sources, company structure, communication
Objavljeno v RUNG: 18.02.2022; Ogledov: 2599; Prenosov: 67
.pdf Celotno besedilo (2,75 MB)

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