Pokročilé instrumentace a metody pro charakterizace materiálů

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    On the non-universality of distance metrics in laser-induced breakdown spectroscopy
    (The Royal Society of Chemistry, 2025-06-05) Vrábel, Jakub; Képeš, Erik; Nedělník, Pavel; Záděra, Antonín; Pořízka, Pavel; Kaiser, Jozef
    The ability to measure similarity between high-dimensional spectra is crucial for numerous data processing tasks in spectroscopy. Many popular machine learning algorithms depend on, or directly implement, a form of similarity or distance metric. Despite its profound influence on algorithm performance and sensitivity to signal fluctuations, the selection of an appropriate metric remains often neglected within the spectroscopic community. This work aims to shed light on the metric selection process in Laser-Induced Breakdown Spectroscopy (LIBS) and study consequences for data analysis and analytical performance in selected applications. We studied six relevant distance metrics: Euclidean, Manhattan, cosine, Siamese, fractional, and mutual information. We assessed their response to changes in sample composition, additive noise, and signal intensity. Our results show specific vulnerabilities of commonly used metrics, such as the Euclidean metric's high sensitivity to additive noise and the cosine metric's sensitivity to spectral shifts. The Siamese metric stood out in the majority of studied cases and outperformed others in a direct comparison within the spectra classification task. This work provides basic guidelines for selecting metrics in various contexts. The methodology is general and can be directly extended to other spectroscopic techniques that possess comparable data properties.
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    Chlorine determination in cement paste samples using laser-induced breakdown spectroscopy and non-matching matrix calibration samples
    (Royal Society of Chemistry, 2025-06-05) Kratochvilová, Lucie; Prochazka, David; Opravil, Tomáš; Pořízka, Pavel; Kaiser, Jozef
    This paper deals with determining the chlorine content in cement matrixes using non-matching calibration samples made from microsilica and potassium chloride. We aimed to make easy-to-prepare calibration samples and determine the chlorine content in cement paste samples. To create proper cement paste samples, it is necessary to allow the concrete to mature for 28 days. Also, this methodology enables faster calibration and higher throughput in routine analysis. To suppress the matrix effect, we tested several strategies of signal normalization and then compared the reference (known) and the predicted chlorine content. Best results were obtained when we normalized the intensity of the chlorine line by a parameter proportional to the particle number density which was a priori determined by the intensity of the hydrogen emission line (H alpha) and full width at half-maximum (FWHM). With this parameter, we obtained a high-reliability coefficient for the calibration curve (R2 = 0.99) and the best prediction for total chloride content in cement paste, with a sum of mean squares of the prediction error of 0.22 wt%.
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    Investigating aquatic biodegradation and changes in the properties of pristine and UV-irradiated microplastics from conventional and biodegradable agricultural plastics
    (ELSEVIER SCI LTD, 2025-07-01) Putar, Ula; Fazlić, Aida; Brunnbauer, Lukas; Novak, Janja; Jemec Kokalj, Anita; Imperl, Jernej; Kučerík, Jiří; Procházková, Petra; Federici, Stefania; Hurley, Rachel; Sever Škapin, Andrijana; Modlitbová, Pavlína; Pořízka, Pavel; Kaiser, Jozef; Limbeck, Andreas; Kalčíková, Gabriela
    There is an increasing tendency to replace conventional agricultural plastic mulching films with biodegradable alternatives. However, while the latter biodegrade well under controlled conditions (e.g. industrial compost), their biodegradation in non-target environments (e.g. aquatic environments) is questioned and poorly understood. Therefore, in this study, microplastics derived from conventional polyethylene (PE) and biodegradable polybutylene adipate terephthalate starch blend (PBAT) mulching films were exposed to UV irradiation and subsequently tested for their ready biodegradability in an aqueous medium where changes in their characteristics were evaluated. The results showed limited biodegradation for pristine and UV-aged PE: no morphological, surface chemical or internal changes were observed. Pristine PBAT showed signs of initial biodegradation, while UV-aged PBAT biodegraded by up to 57%. New functional groups appeared on the PBAT surface after UV irradiation according to FTIR analysis and crystallinity increased after biodegradation. Elemental analysis revealed a range of metals in PE and PBAT microplastics. No changes in metal distribution analysed in micro-plastic after UV-aging or biodegradation were found, except that less titanium was present in PBAT after biodegradation indicating potential leaching. None of the PBAT microplastics had ecotoxic effects towards the aquatic plant Lemna minor. Pristine and UV-aged PE showed negative effects on roots, but these were not observed after biodegradation. Low biodegradation of pristine PBAT and possible leaching of metals demonstrated here raise questions about the sustainable use of biodegradable alternatives, especially when they enter non-target environments.
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    Porous titanium/hydroxyapatite interpenetrating phase composites with optimal mechanical and biological properties for personalized bone repair
    (Elsevier, 2025-01-01) Oliver Urrutia, Carolina; Kashimbetova, Adelia; Slámečka, Karel; Casas Luna, Mariano; Matula, Jan; Koledová, Zuzana; Kaiser, Jozef; Čelko, Ladislav; Montufar Jimenez, Edgar Benjamin
    This study introduces the first fabrication of porous titanium/hydroxyapatite interpenetrating phase composites through an innovative processing method. The approach combines additive manufacturing of a customized titanium skeleton with the infiltration of an injectable hydroxyapatite foam, followed by in situ foam hardening at physiological temperature. This biomimetic process circumvents ceramic sintering and metal casting, effectively avoiding the formation of secondary phases that can impair mechanical performance. Hydroxyapatite foams, prepared using two foaming agents (polysorbate 80 and gelatine), significantly reinforce the titanium skeleton while preserving the microstructural characteristics essential for osteoinductive properties. The strengthening mechanisms rely on the conformation of the foams to the titanium surface, thereby enabling stable mechanical interlocking and effective interfacial stress transfer. This, combined with the mechanical constriction of phases, enhances damage tolerance and mechanical reliability of the interpenetrating phase composites. In addition, the interpenetrating phase composites feature a network of concave pores with an optimal size for bone repair, support human osteoblast proliferation, and exhibit mechanical properties compatible with bone, offering a promising solution for the efficient and personalized reconstruction of large bone defects. The results demonstrate a significant advancement in composite fabrication, integrating the benefits of additive manufacturing for bone repair with the osteogenic capacity of calcium phosphate ceramics.
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    Automated detection of element-specific features in LIBS spectra
    (ROYAL SOC CHEMISTRY, 2024-11-27) Gajarská, Zuzana; Faruzelová, Anna; Képeš, Erik; Prochazka, David; Pořízka, Pavel; Kaiser, Jozef; Lohninger, Hans; Limbeck, Andreas
    This work introduces a novel semi-automatic approach to identify elemental lines in spectra obtained via laser-induced breakdown spectroscopy (LIBS). The algorithm is based on unique spectral fingerprints of individual elements that are configured into comb-like filters. The element-specific filters are then correlated with measured spectra for semi-supervised qualitative analysis of samples. Spectral variations are accommodated by adjusting the micro-parameters of the comb filter. This step ensures accurate results despite minor deviations from the instrument's ideal calibration due to instrumental fluctuations, e.g., drift in spectral calibration or line broadening. Additionally, the algorithm can autonomously detect spectral interference regions, aiding the analyst in verifying spectral lines where such interference may occur. The paper presents a comprehensive overview of the algorithm and discusses the main concepts, parameters, optimization steps, and limitations using Echelle spectra of two standard reference materials with different complexity: borosilicate glass (NIST 1411) and low-alloyed steel (SUS1R). Furthermore, the transferability of the approach to different scenarios and real-life applications is demonstrated using a single-channel Czerny-Turner spectrum of an amalgam filling extracted from a hyperspectral image of a human tooth. A demo of the algorithm is publicly available for non-commercial purposes.