Ústav fyzikálního inženýrství

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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%.
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.
Enhanced magnetic field concentration using windmill-like ferromagnets
(AIP Publishing, 2024-02-01) Bort-Soldevila, Natanael; Cunill-Subiranas, Jaume; Barrera, Aleix; Del-Valle, Nuria; Silhanek, Alejandro V.; Uhlíř, Vojtěch; Bending, Simon; Palau, Anna; Navau, Carles
Magnetic sensors are used in many technologies and industries, such as medicine, telecommunications, robotics, the Internet of Things, etc. The sensitivity of these magnetic sensors is a key aspect, as it determines their precision. In this article, we investigate how a thin windmill-like ferromagnetic system can hugely concentrate a magnetic field at its core. A magnetic sensor combined with such a device enhances its sensitivity by a large factor. We describe the different effects that provide this enhancement: the thickness of the device and its unique windmill-like geometry. An expression for the magnetic field in its core is introduced and verified using finite-element calculations. The results show that a high magnetic field concentration is achieved for a low thickness-diameter ratio of the device. Proof-of-concept experiments further demonstrate the significant concentration of the magnetic field when the thickness-diameter ratio is low, reaching levels up to 150 times stronger than the applied field. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Simulation of optomechanical interaction of levitated nanoparticle with photonic crystal micro cavity
(Optica Publishing Group, 2024-02-13) Maňka, Tadeáš; Šiler, Martin; Liška, Vojtěch; Zemánek, Pavel; Šerý, Mojmír; Brzobohatý, Oto
We propose and analyze theoretically a promising design of an optical trap for vacuum levitation of nanoparticles based on a one-dimensional (1D) silicon photonic crystal cavity (PhC). The considered cavity has a quadratically modulated width of the silicon wave guiding structure, leading to a calculated cavity quality factor of 8 x 105. An effective mode volume of approximately 0.16 mu m3 having the optical field strongly confined outside the silicon structure enables optical confinement on nanoparticle in all three dimensions. The optical forces and particle -cavity optomechanical coupling are comprehensively analyzed for two sizes of silica nanoparticles (100 nm and 150 nm in diameter) and various mode detunings. The value of trapping stiffnesses in the microcavity is predicted to be 5 order of magnitudes higher than that reached for optimized optical tweezers, moreover the linear single photon coupling rate can reach MHz level which is 6 order magnitude larger than previously reported values for common bulk cavities. The theoretical results support optimistic prospects towards a compact chip for optical levitation in vacuum and cooling of translational mechanical degrees of motion for the silica nanoparticle of a diameter of 100 nm.
Zero-field spin wave turns
(AIP Publishing, 2024-03-11) Klíma, Jan; Wojewoda, Ondřej; Roučka, Václav; Molnár, Tomáš; Holobrádek, Jakub; Urbánek, Michal
Spin-wave computing, a potential successor to CMOS-based technologies, relies on the efficient manipulation of spin waves for information processing. While basic logic devices such as magnon transistors, gates, and adders have been experimentally demonstrated, the challenge for complex magnonic circuits lies in steering spin waves through sharp turns. In this study, we demonstrate with micromagnetic simulations and Brillouin light scattering microscopy experiments, that dipolar spin waves can propagate through 90 degrees turns without distortion. The key lies in carefully designed in-plane magnetization landscapes, addressing challenges posed by anisotropic dispersion. The experimental realization of the required magnetization landscape is enabled by spatial manipulation of the uniaxial anisotropy using corrugated magnonic waveguides. The findings presented in this work should be considered in any magnonic circuit design dealing with anisotropic dispersion and spin wave turns.

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