2024-07-27
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QUANTUM-MECHANICAL STUDY OF INTERNAL STRUCTURAL TRANSFORMATIONS IN Pb-SUPERSATURATED Pb-Sn ALLOYS
Friák, Martin ; Čípek, Petr ; Pavlů, J. ; Roupcová, Pavla ; Miháliková, Ivana ; Msallamová, Š. ; Michalcová, A.
Motivated by a decades-long controversy related to the crystal structure of Pb-supersaturated solid solutions of Pb in Sn, we have performed a quantum-mechanical study of these materials. Focusing on both body-centred-tetragonal beta-Sn and simple-hexagonal gamma-Sn structures, we have computed properties of two alloys with the chemical composition Pb5Sn11, i.e. 31.25 at. % Pb, which is close to the composition of the experimentally found alloy (30 at. % Pb). The 16-atom computational supercells were designed as multiples of the elemental beta- and gamma-Sn unit cells, where the Pb atoms were distributed according to the special quasi-random structure (SQS) concept. Full structural relaxations of both beta- and gamma-phase-based alloys resulted in very significant re-arrangements into structures which do not exhibit any apparent structural features typical for the original alloys, and are, therefore, difficult to classify. The formation energies of the beta- and gamma-phase-originating equilibrium phases are 50 meV/atom and 53 meV/atom, respectively. Therefore, they are not stable with respect to the decomposition into the elemental lead and tin. Moreover, our calculations of elastic constants of both phases revealed that they are close to mechanical instability. Our results indicate that the studied Pb-supersaturated Pb-Sn solid solutions may be prone to structural instability, transformations into different phases and decomposition. Our findings may contribute into the identification of the reason why the subsequent experimental studies did not reproduce the initial published data.
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2024-07-27
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QUANTUM-COMPUTING STUDY OF THE ELECTRONIC STRUCTURE OF CRYSTALS: THE CASE STUDY OF SI
Ďuriška, Michal ; Miháliková, Ivana ; Friák, Martin
Quantum computing is newly emerging information-processing technology which is foreseen to be exponentially faster than classical supercomputers. Current quantum processors are nevertheless very limited in their availability and performance and many important software tools for them do not exist yet. Therefore, various systems are studied by simulating the run of quantum computers. Building upon our previous experience with quantum computing of small molecular systems (see I. Mihalikova et al., Molecules 27 (2022) 597, and I. Mihalikova et al., Nanomaterials 2022, 12, 243), we have recently focused on computing electronic structure of periodic crystalline materials. Being inspired by the work of Cerasoli et al. (Phys. Chem. Chem. Phys., 2020, 22, 21816), we have used hybrid variational quantum eigensolver (VQE) algorithm, which combined classical and quantum information processing. Employing tight-binding type of crystal description, we present our results for crystalline diamond-structure silicon. In particular, we focus on the states along the lowest occupied band within the electronic structure of Si and compare the results with values obtained by classical means. While we demonstrate an excellence agreement between classical and quantum-computed results in most of our calculations, we further critically check the sensitivity of our results with respect to computational set-up in our quantum-computing study. A few results were obtained also using quantum processors provided by the IBM.
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2024-07-27
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EFFECT OF STEEL COMPOSITION ON ITS BEHAVIOUR IN THE LIQUID LEAD ENVIRONMENT
Pazderova, M. ; Hojná, A. ; Vít, J. ; Hadraba, Hynek ; Čižek, J.
Ferritic-martensitic Eurofer-97 and oxide dispersion strengthened (ODS) Eurofer steels are potential candidates for structural applications in advanced nuclear reactors. Influence of scandium, yttrium, and aluminum addition was studied at 600 degrees C using 10-6 wt.% oxygen concentration. Microstructure and corrosion behaviour was evaluated after 500 h and 1000 h of exposure to liquid lead. Microscopical investigation identified oxidation, solution- based attack, and Pb penetration into the material. Addition of scandium and aluminum changed the mechanism of corrosion attack. Eurofer-97 was partially protected by outer oxide and inner oxidation and Pb penetration was found. In contrast ODS-Eurofer steels after 1000 h of exposure showed mainly inner oxidation and SBA including Pb penetration into the steel. The inner oxidation consisted of Pb+Cr-O and Cr-O+Al-O layers mixture. Degradation of ODS steel was significantly lower than Eurofer-97. It seems that the inner oxidation layer beneath the surface did not prevent the Pb penetration but protected the surface from dissolution.
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2024-07-27
00:02 |
MINOR PHASES IN TIN-RICH HISTORICAL MATERIALS
Michalcová, A. ; Msallamová, Š. ; Fink, D. ; Friák, Martin
The historical organ pipes used to be manufactured from tin and tin-lead alloys. The tin-rich organ pipes usually contained copper as alloying elements, which make them similar to modern lead free soldering materials. The historical organ pipe materials can be used as model materials for natural ageing of soldering materials. Tin pest is a term for modification from white tin to grey tin, which leads to degradation of tin or tin-rich alloys. The influence of individual alloying elements has not been reliably described, yet. Not only on the concentration of the alloying element, but also the distribution may play the important role. In dependence on heat-treatment, the Cu can be in the Sn matrix present in these forms: i) as large intermetallic particles after casting (Cu6Sn5), ii) as solid solution after homogenization annealing and iii) as fine precipitates after ageing. The microstructure of the real historical organ-pipes material was studied and it was proven that contradictionary to the equilibrium phase diagram the Cu enriched was observed.
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2024-07-27
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EFFECT OF OXIDE DISPERSION ON ELECTRIC CONDUCTIVITY OF ROTARY SWAGED POWDER-BASED COPPER COMPOSITES
Kunčická, Lenka ; Benč, Marek ; Kačor, P. ; Marek, M.
Copper is a very popular electro-conductive material, however, the mechanical properties of pure Cu are low. They can be typically improved by (micro)alloying, or via structure modifications introduced by optimized deformation and thermomechanical treatments. Designing a Cu-based composite, possibly strengthened by a dispersion of fine oxides, is another way how to favourably improve the strength properties of Cu. In this study, we performed mechanical alloying of a Cu powder with a powder of Al2O3 oxide, which is known to have strengthening effects on metallic materials. After mixing, we sealed the powder mixture into evacuated tubular Cu containers (i.e. cans). As for the consolidation procedure, we applied direct consolidation of the canned powders via the intensive plastic deformation method of rotary swaging, performed under warm conditions. Subsequently, we subjected the swaged conductors to measurements of electric conductivity and detailed structure observations. The results revealed that the applied swaging ratio was sufficient to fully consolidate the canned powders as the final conductor was unrecognizable from a cast alloy from the viewpoints of visual and structure assessment. In other words, the structure did not exhibit any voids or remnants of unconsolidated powder particles. The observed fine grains with homogeneous dispersion of Al2O3 oxide particles provided improvement of the mechanical properties, as proven by microhardness measurements. Moreover, the electric properties remained favourable.
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2024-07-21
00:01 |
Lidar systems testing considerations for field use
Picmausová, Helena ; Farlík, Jan ; Eichhorn, Marc ; Kieleck, Christelle
The aim of this paper is to offer a perspective on testing a commercially available lidar system in order to determine its suitability for various practical tasks including mapping, object recognition, and the potential in its coupling with another sensor, in this case a camera. Several mapping missions were carried out over the course of the experiment, with both the lidar and the camera mounted on an Unmanned Aircraft System. Aside from mapping ordinary objects like trees, vehicles, people, and ground elevation, a standardized test target was designed for the purposes of the experiment, and placed in detection area. Influence of external factors on system performance was evaluated, e.g. atmospheric conditions and material properties of scanned surfaces, especially their reflectivity. Post processing of obtained data was carried out, demonstrating the potential of overlaying multiple sensor data for easier object recognition, and an optimal use case for the system is suggested.
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2024-07-21
00:01 |
Experimental audio effect based on dynamic signal filtering
Leitgeb, David
This paper deals with an audio effect that utilizes multiple types of digital signal processing to creatively produce various sound colors with musical signal as its input. Used signal processing techniques include: frequency filters, delay line with signal interpolation, low-frequency oscillators. The paper includes description of the structure of the proposed audio effect, approaches used during the implementation process and several examples of the functionality of its individual features. The proposed effect was developed using Matlab and its Audio Toolbox extension.
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2024-07-21
00:01 |
NANOBLAST: Python Tool for Raw Nanopore Signal Processing
Suriak, Martin ; Nykrýnová, Markéta
Oxford Nanopore Technologies’ sequencers enable direct real-time DNA/RNA sequencing. While numerous tools aid in analyzing the nanopore output data, offering functions such as visualizing raw signals with highlighted nucleotide positions, none provide a complete solution for exporting analyzed data into a clear, comprehensive file. In response, a Python tool has been developed to streamline various tasks. This includes searching for specific nucleotide sequences using BLAST, plotting raw signals with detected nucleotide bases, and generating a comprehensive file containing all essential information. The tool integrates components for handling raw nanopore data, extracting crucial information from the basecalling process using SAM file handlers, and utilizing a BLAST search engine. Employing a comprehensive algorithm, it can handle both the old FAST5 and the novel POD5 formats, enabling the identification of any nucleotide sequence and its corresponding signal.
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2024-07-21
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Steady-state Thermal Analysis of Fault-tolerant PMSM During the Open-phase Mode of Operation
Sizonenko, Vitaliy
In this paper, the initial outline of lumped-parameter thermal network and steady-state thermal finite element analysis for the fault-tolerant permanent magnet synchronous machine is demonstrated. The calculations show that the faulty operational mode with two open phases leads to substantial overheating of the machine when the need for the constant or overload torque is present. This challenge can be overcome by utilizing the machine’s restricted operating time, with implementing transient thermal finite element analysis. Alternatively, the machine has the option to operate continuously at a reduced torque.
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2024-07-21
00:01 |
Optical ray propagation through turbulent underwater space
Bartoň, Jan
This paper is aimed at the description of an optical ray propagating through underwater turbulent environment. In the first part, the description of the properties of underwater turbulence and its impact on the optical beam is presented. In the second part of the paper, method based upon Snell’s law is presented. In the third part, an approach using Ray tracing matrices is shown. The outcome of this thesis is a procedure for calculating the propagation of the optical beam through a turbulent underwater environment.
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