A simple algorithm for probes positioning in BTT systems
Tchawou Tchuisseu, Eder Batista; Procházka, Pavel; Maturkanič, Dušan
2020 - anglický The Blade Tip Timing (BTT), a non-contact method for measuring the blade tip displacement through the time of arrival, is studied in this article. This work proposes a simple algorithm based on the minimization of the coherence and the condition number of the sensingmatrix for defining the best probe positioning in the case of synchronous and asynchronous vibrations. Klíčová slova: BTT systems; probe positioning; condition number; coherence Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. A simple algorithm for probes positioning in BTT systems

The Blade Tip Timing (BTT), a non-contact method for measuring the blade tip displacement through the time of arrival, is studied in this article. This work proposes a simple algorithm based on the ...

Tchawou Tchuisseu, Eder Batista; Procházka, Pavel; Maturkanič, Dušan
Ústav termomechaniky, 2020

Adhesion of PVD Coatings on Surface of Small Arm
Joska, Z.; Rak, L.; Daniel, Josef; Horníček, J.; Tříska, V.; Nguyen, C.H.
2020 - anglický This work deals with the possibility of increasing the utility properties of the functional part of the weapon by deposition of PVD coating. These coatings are widely known for their high hardness and abrasion resistance without affecting the anticorrosion properties. The experimental part evaluates the created duplex coating on the piston of the assault rifle Sa vz. 58. Duplex coating adhesion, surface morphology and coating thickness was evaluated on opto digital microscope Olympus DSX 500. The impact resistance of the coating was evaluated by dynamic impact test. The durability tests of the coatings were carried out during the training of students in the military training. The results showed the application of PVD coating significantly reduced piston head wear and increased user comfort in the form of shortening time of the cleaning and maintenance process after firing. Klíčová slova: adhesion of PVD Coatings Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Adhesion of PVD Coatings on Surface of Small Arm

This work deals with the possibility of increasing the utility properties of the functional part of the weapon by deposition of PVD coating. These coatings are widely known for their high hardness and ...

Joska, Z.; Rak, L.; Daniel, Josef; Horníček, J.; Tříska, V.; Nguyen, C.H.
Ústav přístrojové techniky, 2020

Stability of a bar influenced by small and large imperfections
Náprstek, Jiří; Fischer, Cyril
2020 - anglický The geometrical and physical imperfections of systems can drastically reduce their critical loading. These imperfections are usually of stochastic character and, therefore, they act as random parametric perturbations of coefficients of corresponding differential equations. In this paper, the imperfections are introduced as multidimensional statistics on the set of a large number of realizations of the same system. As far as the amount of information is small or the imperfections themselves cannot be considered small, the convex analysis is preferable. The paper compares results obtained by both stochastic and convex analyses for hyperprism and demonstrates when each of them is more convenient to be used. Besides of the hyper-prism, the possibilities and properties of other modifications of convex method are considered, especially those based on the definition of imperfection zone marked as a centric hyper-ellipsoid or as an eccentric hyper-ellipsoid. The analytical background was brought up to the level when only a few configurations of imperfections are sufficient to be evaluated numerically. These configurations are obtained by means of the convex analysis as points of extreme critical loading using the Lagrange method of constrained extremes. Klíčová slova: convex domain method; system stability; hyper-prism and hyper-ellipsoid domains Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Stability of a bar influenced by small and large imperfections

The geometrical and physical imperfections of systems can drastically reduce their critical loading. These imperfections are usually of stochastic character and, therefore, they act as random ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2020

CrystalCMP: examples of use
Rohlíček, Jan
2020 - anglický The program CrystalCMP can be used for comparison of crystal structures containing separated molecular objects as it is, for instance, in molecular crystals or some metal-organic compounds. The program can be useful in many different situations. This article shows the use of the program CrystalCMP on three basic exam ples for which the program was primarily intended. Klíčová slova: molecular packing; comparison; similarity Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. CrystalCMP: examples of use

The program CrystalCMP can be used for comparison of crystal structures containing separated molecular objects as it is, for instance, in molecular crystals or some metal-organic compounds. The ...

Rohlíček, Jan
Fyzikální ústav, 2020

Slovo geologa.
Žák, Karel
2020 - český Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Slovo geologa.

Žák, Karel
Geologický ústav, 2020

Recurrence analysis of spinning particles in the Schwarzschild background
Zelenka, Ondřej; Lukes-Gerakopoulos, Georgios; Witzany, Vojtěch
2020 - anglický In this work the dynamics of a spinning particle moving in the Schwarzschild background is studied. In particular, the methods of Poincaré section and recurrence analysis are employed to discern chaos from order. It is shown that the chaotic or regular nature of the orbital motion is reflected on the gravitational waves. Klíčová slova: black holes; spinning particles; chaos Dokument je dostupný na externích webových stránkách. Recurrence analysis of spinning particles in the Schwarzschild background

In this work the dynamics of a spinning particle moving in the Schwarzschild background is studied. In particular, the methods of Poincaré section and recurrence analysis are employed to discern ...

Zelenka, Ondřej; Lukes-Gerakopoulos, Georgios; Witzany, Vojtěch
Astronomický ústav, 2020

Understanding the iron K alpha line emissivity profile with GR radiative transfer code
Zhang, Wenda; Dovčiak, Michal; Bursa, Michal; Svoboda, Jiří; Karas, Vladimír
2020 - anglický In this work, we present calculations of the illumination and the iron K alpha emissivity profiles performed with the GR radiative transfer code Monk that employs the Monte Carlo method. In most previous studies the distinction between the illumination and emissivity profiles was not clearly made. For AGN discs, the emissivity profile has a similar shape with the illumination profile, but in the inner most region the former is steeper than the latter, where as for accretion discs in black hole X-ray binaries, the distinction between the two profiles is more dramatic. We find out that the different behavior between AGN and black hole X-ray binary discs is due to the different energy spectra of the illuminating radiation. This suggests that the emissivity profile of the iron Kαline cannot be determined by black hole spin and corona geometry alone and the energy spectrum of the illuminating radiation has to be taken into account. We also study the dependence of the emissivity profile on the geometry of the corona. Klíčová slova: emissivity profiles; accretion discs; radiative transfer Dokument je dostupný na externích webových stránkách. Understanding the iron K alpha line emissivity profile with GR radiative transfer code

In this work, we present calculations of the illumination and the iron K alpha emissivity profiles performed with the GR radiative transfer code Monk that employs the Monte Carlo method. In most ...

Zhang, Wenda; Dovčiak, Michal; Bursa, Michal; Svoboda, Jiří; Karas, Vladimír
Astronomický ústav, 2020

Comparison of power control method for B4 converter connected to unbalanced grid
Šimek, Petr; Valouch, Viktor
2020 - anglický The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power control with a finite set of control values, the results obtained using a modified direct power control strategy, and the results obtained using a generalized predictive control are compared and discussed.\n Klíčová slova: power control; B4 converter; unbalanced grid Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Comparison of power control method for B4 converter connected to unbalanced grid

The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power ...

Šimek, Petr; Valouch, Viktor
Ústav termomechaniky, 2020

Nanopowders of R.sub.2./sub.Fe.sub.14./sub.B-type compounds in high magnetic fields: The effects of substitutional and interstitial atoms on inter-sublattice exchange interaction
Paukov, M.; Ivanov, L.; Tereshina, I.; Tereshina-Chitrova, Evgenia; Gorbunov, D.; Andreev, A. V.; Pyatakov, A.P.; Granovsky, S.A.; Doerr, M.; Drulis, H.
2020 - anglický The fundamental magnetic characteristics of R2Fe14B intermetallics are highly sensitive to atomic substitutions and interstitial absorption of light elements. In this work, both were combined, and the influence of the substitutions in the R-sublattice and hydrogen absorption on the magnetization of (RR’) 2Fe14BHx (R is Tm or Er, and R’ is Nd) in magnetic fields up to 58 T was studied. By using direct hydrogen absorption, (R0.5Nd0.5)2Fe14BHx compounds were obtained with hydrogen content 0≤x≤5.5. Magnetic measurements were carried out on nanopowders. The strength of the inter-sublattice coupling in (R0.5Nd0.5)2Fe14B and their hydrides is estimated by analysing high-field magnetization data. It is shown that hydrogenation weakens the inter-sublattice exchange interaction up to 45 %. Klíčová slova: rare earth; intermetallics; powder metallurgy; magnetism in solids; hydride properties Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Nanopowders of R.sub.2./sub.Fe.sub.14./sub.B-type compounds in high magnetic fields: The effects of substitutional and interstitial atoms on inter-sublattice exchange interaction

The fundamental magnetic characteristics of R2Fe14B intermetallics are highly sensitive to atomic substitutions and interstitial absorption of light elements. In this work, both were combined, and the ...

Paukov, M.; Ivanov, L.; Tereshina, I.; Tereshina-Chitrova, Evgenia; Gorbunov, D.; Andreev, A. V.; Pyatakov, A.P.; Granovsky, S.A.; Doerr, M.; Drulis, H.
Fyzikální ústav, 2020

Nanosecond laser damage of metallic mirrors
Muresan, Mihai-George; Pilná, Kateřina; Čech, Pavel; Mydlář, Martin; Vanda, Jan; Navrátil, Petr
2020 - anglický Laser surface processing is an established method to introduce surface functionalities on solid surfaces with the required throughputs for a commercial process. Fabrication of laser induced surface structures in an effective matter is done by laser interaction studies, which reveal the best processing parameters (laser wavelength, fluence, repetition, together with the processing speed and environment). Customized solutions are providing the best yields and they are being implemented faster than ever. However, the optics manufacturers are not being to keep up the pace with the new requirements, so they turn instead on older, but safer technology. In order to get a better understanding of optics capabilities, thorough testing is required. Common laser metallic mirrors, commercially available, are being rigorously tested using a nanosecond Yb:YAG laser and the results are compared with the vendor’s information.\n Klíčová slova: laser patterning; metallic mirrors; LIDT; nanosecond laser testing Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Nanosecond laser damage of metallic mirrors

Laser surface processing is an established method to introduce surface functionalities on solid surfaces with the required throughputs for a commercial process. Fabrication of laser induced surface ...

Muresan, Mihai-George; Pilná, Kateřina; Čech, Pavel; Mydlář, Martin; Vanda, Jan; Navrátil, Petr
Fyzikální ústav, 2020