Automation of metallographic sample cleaning process
Čermák, Jan; Ambrož, Ondřej; Jozefovič, Patrik; Mikmeková, Šárka
2022 - English
Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual sample handling. An etchant or electrolyte results in inhomogeneous surface quality because the solution runs off the specimen surface during its removal from the beaker. High-quality specimen cleaning is absolutely crucial for the acquisition of the specimen suitable for characterization by a scanning electron microscope operated at very low landing energies of the primary electrons (SLEEM). The SLEEM technique is a powerful tool for the characterization of advanced steels, as described by many scientific papers. The SLEEM requires the specimen absolutely free of water and any organic residues on the surface. This work presents a novel unique apparatus enabling automatic specimen cleaning and drying after the etching or electropolishing processes. Automation reduces the influence of dependent variables that would be introduced into the process by the metallographer. These variables include cleaning time, kinematics, and motion dynamics, but the process can also be affected by variables that are not obvious. Performed experiments clearly demonstrate our in-house designed apparatus as a useful tool improving efficiency and consistency of the sample cleaning process. The high quality of the specimen surface is verified using a light optical microscope, an electron scanning microscope, and above mentioned SLEEM technique.
Keywords:
metallography; sample cleaning; process automation; repeatability
Fulltext is available at external website.
Automation of metallographic sample cleaning process
Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual ...
Correction of gradient pulse shape distortions in radial MRI
Vitouš, Jiří
2022 - English
This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may produce phase distortion in the resulting image and also signal loss in the acquired signal. A method for correction is proposed based on the Nelder-Mead algorithm followed by coordinate ascent search in the neighborhood of the found solution. The adjustment is evaluated using a simple Fast low angle shot (FLASH) sequence with radial readout. The results show a significant improvement in the Free induction decay (FID) signal magnitude, echo stability, and an improvement in the homogeneity of image phase.
Keywords:
MRI; gradient; Nelder–Mead; slice; adjustment
Fulltext is available at external website.
Correction of gradient pulse shape distortions in radial MRI
This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may ...
Unfolded Low-rank + Sparse Reconstruction for MRI
Mokrý, O.; Vitouš, Jiří
2022 - English
We apply the methodology of deep unfolding on the problem of reconstruction of DCE-MRI data. The problem is formulated as a convex optimization problem, solvable via the primal-dual splitting algorithm. The unfolding allows for optimal hyperparameter selection for the model. We examine two approaches - with the parameters shared across the layers/iterations, and an adaptive version where the parameters can differ. The results demonstrate that the more complex model can better adapt to the data.
Keywords:
DCE-MRI; proximal splitting algorithms; deep unfolding; L+S model
Fulltext is available at external website.
Unfolded Low-rank + Sparse Reconstruction for MRI
We apply the methodology of deep unfolding on the problem of reconstruction of DCE-MRI data. The problem is formulated as a convex optimization problem, solvable via the primal-dual splitting ...
Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters
Burda, Daniel; Knápek, Alexandr
2022 - English
This research aims to obtain a more in-depth understanding of the field emission properties of tungsten single-tip field emitters (STFEs) coated with a several tens of nanometer thin barrier of Al2O3. The introduction of an additional barrier into the metal-vacuum interface system of the emitter can be beneficial to improve its performance. The tungsten emitters were prepared using a two-step electrochemical drop-off etching technique. Thin oxide barrier coatings were prepared by using low-temperature atomic layer deposition (ALD), a chemical vapor deposition technique. Field emission was studied in an internally developed field emission microscope (FEM) working in UHV vacuum (< 1·10−7 Pa), and the experimental field emission data were analyzed by the so-called Murphy-Good plotsThe value of the local work function of the grown oxide layer were investigated using Ultra-violet photoelectron spectroscopy (UPS).
Keywords:
Cold field emission; single-tip field emitters; tungsten tip; aluminum oxide; dielectric coatings; Murphy-Good plot
Fulltext is available at external website.
Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters
This research aims to obtain a more in-depth understanding of the field emission properties of tungsten single-tip field emitters (STFEs) coated with a several tens of nanometer thin barrier of Al2O3. ...
Electron beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy
Rončák, Ján; Adam, O.; Müller, P.; Zobač, Martin
2022 - English
Eutectic high-entropy alloys have become a significantly studied type of material due to their combination of strength and ductility. However, previous research has focused primarily on manufacture, solidification behaviour and mechanical properties. Only a small part of the research has been devoted to welding. This paper is focused on evaluating the weldability of eutectic high-entropy alloy AlCoCrFeNi2.1 in the as-cast state without further heat treatment. The electron beam welding process was performed twice at the same parameters, except for the beam current. Properties such as the depth of the remelted layer, the formation of the heat-affected zone, and the presence of undesirable defects in the welded joints were observed using light and electron microscopy. At the same time, material properties in the form of microstructural stability, chemical composition, and hardness of the welded joints were evaluated.
Keywords:
AlCoCrFeNi2.1; electron beam welding; eutectic high-entropy alloys; microstructure
Fulltext is available at external website.
Electron beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy
Eutectic high-entropy alloys have become a significantly studied type of material due to their combination of strength and ductility. However, previous research has focused primarily on manufacture, ...
Nové metody přípravy vzorků pro moderní rastrovací elektronovou mikroskopii
Ambrož, Ondřej; Čermák, Jan; Mikmeková, Šárka
2021 - Czech
Moderní rastrovací elektronové mikroskopy (SEM) jsou vybaveny velmi sofistikovaným detekčním systémem, který umožňuje detekovat signální elektrony současně pomocí několika různě umístěných detektorů. Tímto způsobem dochází k filtraci signálních elektronů podle energie a úhlu. Efektivní filtrace signálu v rastrovací elektronové mikroskopii současně s možností použití velmi nízkých dopadových energií primárního svazku vede k extrémní citlivosti této metody na kvalitu povrchu vzorku a jeho stav. Současné metalografické metody přípravy vzorků začínají být nedostatečné pro pokročilé zobrazování v moderních SEM instrumentech. Klasická příprava vzorků se ukazuje jako nevhodná zejména pro nízkonapěťovou rastrovací elektronovou mikroskopii. V práci budou prezentovány první výsledky experimentů vlivu běžných metod přípravy na stav povrchu a možnost odlišení jednotlivých fází TRIP oceli pomocí pokročilých technik elektronové mikroskopie a budou také nastíněny možnosti nových postupů využívajících například robotizace. Modern scanning electron microscopes (SEM) are equipped with a very sophisticated detection system that allows the detection of signal electrons by several differently located detectors simultaneously. Signal electrons are filtered according to energy and angle. Effective signal filtering in SEM together with the possibility of using very low impact energies of the primary beam leads to the extreme sensitivity of this method to the quality of the sample surface. Current metallographic methods of sample preparation are becoming insufficient for advanced imaging in modern SEM instruments. Classical sample preparation proves to be completely unsuitable especially for low-voltage scanning electron microscopy. The work will present the first results of the influence of preparation methods on the surface condition and the possibility of differentiating the individual phases of TRIP steel using advanced electron microscopy techniques. The possibilities of new procedures using robotics will be shown.
Keywords:
TRIP steel; SEM; automation
Fulltext is available at external website.
Nové metody přípravy vzorků pro moderní rastrovací elektronovou mikroskopii
Moderní rastrovací elektronové mikroskopy (SEM) jsou vybaveny velmi sofistikovaným detekčním systémem, který umožňuje detekovat signální elektrony současně pomocí několika různě umístěných detektorů. ...
Deep learning for magnetic resonance spectroscopy quantification: A time frequency analysis approach
Shamaei, Amirmohammad
2020 - English
Magnetic resonance spectroscopy (MRS) is a technique capable of detecting chemical compounds from localized volumes in living tissues. Quantification of MRS signals is required for obtaining the metabolite concentrations of the tissue under investigation. However, reliable quantification of MRS is difficult. Recently deep learning (DL) has been used for metabolite quantification of MRS signals in the frequency domain. In another study, it was shown that DL in combination with time-frequency analysis could be used for artifact detection in MRS. In this study, we verify the hypothesis that DL in combination with time-frequency analysis can also be used for metabolite quantification and yields results more robust than DL trained with MR signals in the frequency domain. We used the complex matrix of absolute wavelet coefficients (WC) for the time-frequency representation of the signal, and convolutional neural network (CNN) implementation for DL. The comparison with DL used for quantification of data in the frequency domain is presented.
Keywords:
magnetic resonance spectroscop; quantification; deep learning; machine learning
Fulltext is available at external website.
Deep learning for magnetic resonance spectroscopy quantification: A time frequency analysis approach
Magnetic resonance spectroscopy (MRS) is a technique capable of detecting chemical compounds from localized volumes in living tissues. Quantification of MRS signals is required for obtaining the ...
Měření a simulace zpětně odraženého záření při penetračním laserovém svařování
Horník, Petr; Mrňa, Libor; Šarbort, Martin; Šebestová, Hana
2019 - Czech
Laserový svařovací proces je doprovázen množství záření, jak ve viditelné části spektra, tak tepelné záření svarové lázně a v neposlední řadě i vlastní laserové záření. Při laserovém svařování se často používá penetrační režim, při kterém se tvoří paroplynový kanál – keyhole. Většina laserového záření je vícenásobným odrazem pohlcena uvnitř keyhole, avšak malá část se odráží zpět a prochází optickou soustavou svařovací hlavy a dopravním vláknem. Zpětně odražené laserové záření je také monitorováno přímo v laseru z důvodu ochrany rezonátoru a dalších optických komponent. Signál je snadno přístupný a takto získaných dat se dá využít i během svařovacího procesu. Proto byl navržen experiment, při kterém byla zjišťována souvislost mezi rozměry svaru, polohou ohniska a zpětně odraženým laserovým zářením. Dále pak byly výsledky měření porovnány se simulací. The laser welding process is accompanied by a wide range of radiation, both in the visible part of the spectrum and thermal radiation of the weld pool, and last but not least, the laser radiation itself. During penetration laser welding mode, which is often used, the keyhole is created. Most of the laser radiation is absorbed by the multiple reflections inside the keyhole, but a small portion is reflected back and passes through the welding head and the optical fiber. Back-reflected laser radiation is also monitored directly in the laser to protect the resonator and other optical components. The signal is easily accessible and obtained data can be used for monitoring during the welding process. Therefore, we designed experiment in which the relationship between weld dimensions, focal position, and back-reflected laser radiation was investigated. Furthermore, the measurement results were compared with the simulation.
Keywords:
laser welding; focus position; back-reflected radiation; ray-tracing simulation
Fulltext is available at external website.
Měření a simulace zpětně odraženého záření při penetračním laserovém svařování
Laserový svařovací proces je doprovázen množství záření, jak ve viditelné části spektra, tak tepelné záření svarové lázně a v neposlední řadě i vlastní laserové záření. Při laserovém svařování se ...
Vliv teploty na spektrální valstnosti optických tenkých vrstev v laserové spetroskopii s absorpčními kyvetami
Oulehla, Jindřich; Pokorný, Pavel; Hrabina, Jan; Holá, Miroslava; Číp, Ondřej; Lazar, Josef
2019 - Czech
Studujeme vlic teploty na spektrální vlastnosti optických tenkých vrstev, které jsou využívány v laserové spektroskopii s absorpčními kyvetami. Jedná se zejména o vliv teploty na polohu minima zbytkové odrazivosti ve spektru a na pronikání pracovního plynu do struktury tenké vrstvy v závislosti na použité depoziční technologii.\n We stude the influence of thermal annealing on the optical performance of thin film coatings used in laser spectroscopy with iodine-filled absorption cells. We are particulary interested in the temperature influence on the position of the residual reflection minimum in the spectrum and on the permeation of the working gas into the coating structure depending on the coating technology used.\n
Keywords:
absolute frequency-measurement standard; thin film optics, coatings; evaporation; PIAD
Fulltext is available at external website.
Vliv teploty na spektrální valstnosti optických tenkých vrstev v laserové spetroskopii s absorpčními kyvetami
Studujeme vlic teploty na spektrální vlastnosti optických tenkých vrstev, které jsou využívány v laserové spektroskopii s absorpčními kyvetami. Jedná se zejména o vliv teploty na polohu minima ...
Teplotní gradienty při laserovém svařování
Šebestová, Hana; Horník, Petr; Mrňa, Libor
2019 - Czech
Předmětem tohoto příspěvku je měření teplotních cyklů při svařování oceli S460MC o tloušťce 3 mm vláknovým laserem IPG YLS 2000 pomocí termočlánků. Zjištěné teplotní gradienty jsou porovnány s výsledky MKP simulace teplotních polí při svařování laserem, provedené v programu SYSWELD. This contribution concludes results of thermocouples-based measurement of thermal cycles during IPG YLS 2000 fiber laser welding of S460MC steel with thickness 3 mm. Measured thermal gradients are compared with results of temperature field distribution simulation performed in FEM software SYSWELD.
Keywords:
laser welding; temperature gradient; thermocouple; simulation
Fulltext is available at external website.
Teplotní gradienty při laserovém svařování
Předmětem tohoto příspěvku je měření teplotních cyklů při svařování oceli S460MC o tloušťce 3 mm vláknovým laserem IPG YLS 2000 pomocí termočlánků. Zjištěné teplotní gradienty jsou porovnány s ...
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