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Analytical electron microscopy analysis of insulating and metallic phases in nanostructured vanadium dioxide
(Royal Society of Chemistry, 2024-05-03) Krpenský, Jan; Horák, Michal; Kabát, Jiří; Planer, Jakub; Kepič, Peter; Křápek, Vlastimil; Konečná, Andrea
Vanadium dioxide (VO2) is a strongly correlated material that exhibits the insulator-to-metal transition (IMT) near room temperature, which makes it a promising candidate for applications in nanophotonics or optoelectronics. However, creating VO2 nanostructures with the desired functionality can be challenging due to microscopic inhomogeneities that can significantly impact the local optical and electronic properties. Thin lamellas, produced by focused ion beam milling from a homogeneous layer, provide a useful prototype for studying VO2 at the truly microscopic level using a scanning transmission electron microscope (STEM). High-resolution imaging is used to identify structural inhomogeneities while electron energy-loss spectroscopy (EELS) supported by statistical analysis helps to detect VxOy stoichiometries with a reduced oxidation number of vanadium at the areas of thickness below 70 nm. On the other hand, the thicker areas are dominated by vanadium dioxide, where the signatures of the IMT are detected in both core-loss and low-loss EELS experiments with in situ heating. The experimental results are interpreted with ab initio and semi-classical calculations. This work shows that structural inhomogeneities such as pores and cracks present no harm to the desired optical properties of VO2 samples. We utilize analytical electron microscopy with in situ heating to observe the insulator-metal transition in vanadium dioxide and to identify additional vanadium oxides across the sample exhibiting nanoscopic pores and cracks.
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Case Study on Thermal Management of Planar Elements with Various Polymeric Heat Exchangers: Experiment and Simulation
(Springer Nature, 2024-05-02) Hvožďa, Jiří; Mráz, Kryštof; Raudenský, Miroslav; Vakhrushev, Alexander; Karimi-Sibaki, Ebrahim; Boháček, Jan
A reliable battery thermal management system (BTMS) is essential to ensure proper performance, a long life span, and high electric vehicle safety. The primary objective of BTMS is to maintain the cells’ temperature in the range of 15–35 °C while limiting the temperature spread between cells to below 5 °C. Active thermal management with polymeric hollow fibers (PHFs) has been reported in a few articles, but its tremendous flexibility is mainly advantageous for cylindrical cells. Extruded polymeric cold plate heat exchangers with rounded rectangle channels (RRCs) are proposed as a more elegant solution for planar batteries. Heat exchangers using PHFs and RRCs were experimentally compared, with a strong focus on minimizing the maximum temperature and temperature spread of the experimental setup while simultaneously achieving minimal pressure drops. The system behaviour with different parameters, including materials, geometry, and thermophysical properties, was further studied using properly validated CFD models.
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Impact of digital procurement on economic resilience of enterprises during COVID-19
(Centre of Sociological Research, 2024-05-03) Chytilová, Ekaterina; Talíř, Milan; Straková, Jarmila; Dobrovič, Ján
The main objective of this paper was to determine whether digital procurement positively affected the economic resilience of firms in the manufacturing industry during the COVID-19 pandemic. Hence, qualitative research was conducted in Czech industrial enterprises by means of a questionnaire survey in 2021. Based on the research question, 3 hypotheses were formed, which focused on the impact that investing in digital procurement had on the economic resilience of enterprises in selected industries. The parametric two sample one-factor ANOVA and Pearson's Chi-squared test were used to test the hypotheses. The findings rejected the association between investment in digital procurement and the economic performance of the firm during the pandemic. They also failed to confirm the association between digital purchasing and economic resilience of businesses during the pandemic. Another important result was also that digitization of purchasing did not have a greater impact on the economic resilience of firms in the manufacturing industry compared to firms in the construction and agriculture sectors. The research results can be practically implemented in determining the expected benefits of digitizing procurement. The research implications are limited by the fact that it only investigates companies from the manufacturing industry in the Czech Republic and focuses exclusively on the period of the COVID-19 pandemic. © 2024, Centre of Sociological Research. All rights reserved.
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Methods for detecting the frequency of centers of Hydrogen-Cyanine (HCN) hyperfine transitions using a tunable laser in the range 1527 nm to 1563 nm
(Vysoké učení technické v Brně. Fakulta strojního inženýrství, ) Hošek, Martin; Číp, Ondřej; Peterka, Pavel; Vojtěch, Josef
Kyanovodík (HCN) je médiem, jehož absorpční spektrum pokrývá celé telekomunikační C-pásmo. To dělá z HCN vhodného kandidáta pro použití při frekvenční stabilizaci laserů. Tato práce se zaměřuje na přesné měření středů absorpčních čar HCN, což povede k zvýšení užitečnosti tohoto plynu v praxi. Cíle práce je dosaženo pomocí dvou metod laserové spektroskopie, a to lineární absorpční spektroskopie a saturované absorpční spektroskopie. Je sestavena tabulka absorpčních čar HCN, kde nejistota frekvence středů čar dosahuje čtyřicetinásobného zlepšení oproti doposud neměřené nejistotě.
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Shallow foundation design: a comparative study of partial safety factors and full probabilistic methods
(Springer Nature, 2024-06-13) Vořechovský, Miroslav; Miča, Lumír; Boštík, Jiří
In the past two decades, Europe has witnessed a significant transition in the design codes used for assessing foundation structures, with the widespread adoption of the Eurocodes (EC). This shift remains a pertinent topic within the engineering community, particularly concerning the transition from traditional design methodologies to those prescribed by the Eurocodes, as well as the potential for fully probabilistic design. While the Eurocodes’ methodology is described as probabilistic, it is crucial to recognize that the achievement of the target reliability level is predominantly facilitated through a system of partial safety factors. These factors are integrated into the calculation algorithm as fixed values, rendering the process essentially deterministic. To refine these calculations for more accurate reliability estimates—expressed in terms of failure probability—a genuinely probabilistic framework is required, termed as fully probabilistic computation. This paper aims to elucidate the fully probabilistic calculation approach for the broader professional community, using the geotechnical application of shallow foundations as an illustrative example. We present a comparative analysis of this advanced approach with the standard foundation design according to EC7 and ČSN 731001, the latter being a precursor in Europe for implementing the partial safety factor method. The discussion extends to a practical demonstration of full probabilistic design juxtaposed against the conventional partial safety factor method, using a shallow foundation case study. Furthermore, the paper delves into the impact of the tail behavior of uncertain or spatially varying soil parameters on the theoretical probability of failure, underscoring its significance in foundation design.