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Povzetek: We study lightlikeness preserving mappings from the $4$-dimensional Minkowski spacetime $\mathcal{M}_4$ to itself under no additional regularity assumptions like continuity, surjectivity, or injectivity. We prove that such a mapping $\phi$ satisfies one of the following three conditions. (1) The mapping $\phi$ can be written as a composition of a Lorentz transformation, a multiplication by a positive scalar, and a translation. (2) There is an event $r\in \mathcal{M}_4$ such that $\phi(\mathcal{M}_4\setminus\{r\})$ is contained in one light cone. (3) There is a lightlike line $\ell$ such that $\phi(\mathcal{M}_4\setminus \ell)$ is contained in another lightlike line. Here, a line that is contained in some light cone in $\mathcal{M}_4$ is called a lightlike line. We also give several similar results on mappings defined on a certain subset of $\mathcal{M}_4$ or the compactification of $\mathcal{M}_4$.
Ključne besede: fundamental theorem of chronogeometry, special relativity, coherency preserving mapping
Objavljeno v DiRROS: 16.10.2025; Ogledov: 192; Prenosov: 79
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Ključne besede: gozdarstvo, znanstvena komunikacija
Objavljeno v DiRROS: 16.10.2025; Ogledov: 271; Prenosov: 149
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Povzetek: Understanding material transformations at the nano- and microscale is essential for advancing electrocatalysis, energy storage, and other applications. Conventional SEM imaging, which captures random locations before and after treatment, struggles to distinguish real transformations from inherent sample heterogeneity. Identical Location SEM (IL-SEM) overcomes this by enabling re-imaging of the exact same region, offering clear evidence of localized changes in morphology, structure, and composition. Despite its simplicity and wide applicability, IL-SEM remains underutilized. This article presents a detailed, practical guide to implementing IL-SEM reliably, including sample alignment, multiscale imaging, and consistent re-localization. Key methodological tips and solutions to common challenges are provided, making the approach accessible even for non-expert users. To showcase its versatility, we present case studies involving electrocatalysts, alloys, and nanostructured materials. Moreover, by integrating IL-SEM with energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD), we demonstrate how compositional and crystallographic evolution can be tracked alongside morphological changes. This optimized workflow offers a powerful, non-destructive method for visualizing dynamic material behavior and provides a foundation for IL-SEM to become a standard technique for studying structural evolution across diverse materials research fields.
Ključne besede: electrocatalysis, identical location electron microscopy, IL-SEM, materials characterization, scanning electron microscopy, surface analysis
Objavljeno v DiRROS: 15.10.2025; Ogledov: 291; Prenosov: 145
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Povzetek: Clay-based materials typically require high-temperature processing (>900 ◦C), resulting in high energy consumption. This study explores cold sintering of metakaolin (MK) powders to achieve high mechanical strength at significantly lower processing temperatures. By applying uniaxial pressure of 400 MPa and heating to only 240 ◦ C in the presence of 15 mol/L NaOH solution, successful densification of structurally sound and dense samples with an average density of 2.16 g/cm³ and a biaxial flexural strength of ~35 MPa was achieved. This strength surpasses that of conventionally sintered MK (1470 ◦C) by ~30 %. Densification was found to be governed by synergistic mechanisms involving MK exfoliation, conformal sintering around aggregates, and the precipitation of an amorphous sodium aluminosilicate hydrate phase. Crack formation was avoided through process optimization and verified using X-ray micro-computed tomography. These findings offer new insights into the chemo- mechanical mechanisms of cold sintering and demonstrate its potential as an efficient route for producing structural materials.
Ključne besede: cold sintering, metakaolin, geopolymer, delaminations, exfoliation
Objavljeno v DiRROS: 15.10.2025; Ogledov: 201; Prenosov: 91
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Povzetek: Carbon capture plays an important role in the decarbonation of the building sector. One way to capture carbon is through mineral carbonation, in which Ca and Mg compounds react with CO2 to form stable carbonate minerals such as calcite, dolomite, magnesite and/or siderite, permanently sequestering CO2. Various techniques are available to measure the amount of permanently bound CO2 and quantify the carbonation potential. The suitability and accuracy of a particular method are very important, as the accurate determination of CO2 is crucial to correctly assess the sequestration potential of different materials. This study compares the three methods: calcimetric, gravimetric and thermogravimetric analysis used for CO2 determination in different types of ash, slag and natural rock. While the CO2 content in natural rock is stable, the CO2 content in slag and ash can change over time as the contained minerals gradually absorb CO2 (by natural or accelerated carbonation) until they are fully carbonated. To avoid errors in testing the CO2 uptake, as-received samples were first exposed to the full carbonation process and then tested. The comparison of calcimeter, thermogravimetric and gravimetric analysis of ground and sieved samples with a particle size below 125 μm shows that the results usually differ by less than 2 %. Higher deviations could be caused by non-carbonate minerals (especially in slags) that can react with hydrochloric acid during the calcimetric and gravimetric tests and/or decompose in the range where carbonates decompose, contributing to inaccurate CO2 measurements. The measurement uncertainty was calculated for all three quantitative methods to allow a practical comparability.
Ključne besede: CO2 sequestration, ash, slags, natural rocks, TGA, calcimetry, measurement uncertainty
Objavljeno v DiRROS: 15.10.2025; Ogledov: 204; Prenosov: 106
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