Gliding Arc in Noble Gases Under Normal and Hypergravity Conditions

This paper describes the gliding arc operated in four different noble gases (helium, neon, argon, and krypton) under normal gravity and hypergravity conditions up to 18 g. We studied the influence of gas flow, gas properties, and gravity-dependent buoyancy on the gliding arc behavior

Hypergravity influence on gliding arc in noble gases

The effects of increased artificial gravity (in the range 1g-18g) on gliding arcs in four noble gases (He, Ne, Ar, Kr) were the subject of this experimental study

Advanced mathematical and statistical methods in evaluating instrumented indentation measurements

This publicly available research report provides a detailed overview of the results achieved within the TACR project TJ02000203 "Advanced mathematical and statistical methods in evaluating instrumented indentation measurements". The introductory section contains necessary background on instrumented indentation data evaluation procedures using the method due to Oliver and Pharr, as described in ISO 14577 standard. The next section provides detailed derivation of a novel algorithm "OEFPIL" for nonlinear data regression with errors in both variables, as well as guidelines for efficient implementation of the algorithm. The algorithm calculates both the optimum estimate of function parameters and an estimate of the parameter covariance matrix. The algorithm performance is demonstrated on reference data for nonlinear regression, and validated by comparison to another method. In the next section some existing advanced methods for uncertainty propagation (higher-order uncertainty propagation, Latin hypercube sampling for Monte Carlo) are also discussed. The last section presents application of the aforementioned methods for data regression and uncertainty propagation in processing data from instrumented indentation measurements. These methods have been newly added to the the free software tool Niget to improve data fitting of the unloading curve and to provide capability for indenter contact area function calibration. Combination of the regression and uncertainty propagation methods enables a better insight into evaluation of indentation data and provides basis for e.g. identifying main sources of measurement uncertainty or designing measurement strategy. Although the methods were designed and assessed with Oliver and Pharr's evaluation method in mind, they can be easily adapted to other evaluation models, too. All software developed and used in this project is freely available.Tato veřejně dostupná výzkumná zpráva obsahuje detailní přehled o výsledcích dosažených v rámci TAČR projektu TJ02000203 "Pokročilé matematické a statistické metody ve vyhodnocování měření instrumentovanou indentací". Úvodní sekce obsahuje nezbytný úvod k procedurám vyhodnocení dat instrumentované indentace, které využívají metodu Olivera a Pharra, jež je popsána v normě ISO 14577. Další kapitola poskytuje detailní odvození nového algoritmu OEFPIL pro nelineární regresi s chybami v obou proměnných a také návod pro efektivní implementaci algoritmu. Algoritmus počítá jak optimální odhad funkčních parametrů, tak odhad kovarianční matice parametrů. Použití algoritmu je demonstrováno na referenčních datech pro nelineární regresi a je ověřeno porovnáním s jinou metodou. Další kapitola se zabývá některými existujícími pokročilými metodami šíření nejistot (šíření nejistot vyšších řádů a metodou tzv. "Latin hypercube sampling" pro Monte Carlo). V poslední části najdeme aplikace výše zmíněných metod pro datovou regresi a propagaci nejistot ve zpracování dat získaných z měření instrumentovanou indentací. Tyto metody byly nově přidány do zdarma dostupného softwaru Niget k vylepšení prokládání dat odtěžovací křivky a k poskytnutí možnosti kalibrace funkce kontaktní plochy indentoru. Kombinace metod regrese a šíření nejistot dovoluje lepší náhled na vyhodnocování indentačních dat a poskytuje základ pro např. identifikování hlavních zdrojů nejistot měření nebo pro dizajn strategie získávání měření. Ačkoli byly metody navrženy a ověřeny pomocí Oliverovy a Pharrovy metody, mohou být lehce upraveny na jiné vyhodnocovací modely. Všechen software, který byl vyvinut a použit v tomto projektu, je volně dostupný

Hypergravity diagnostics and material synthesis in noble gas gliding arc plasma

The behaviour of gliding arc discharge in argon and helium has been studied under normal gravity and hypergravity conditions. The similar influence of increased gas flow and increased gravity is reported. The measured electrical quantities show the differences between glide arc in argon and helium. Material synthesis of carbon nanomaterial has been carried out in mixture of helium with methane in both normal gravity and hypergravity

Hypergravity effects on glide arc plasma

The behaviour of a special type of electric discharge – the gliding arc plasma – has been investigated in hypergravity (1g –18g) using the Large Diameter Centrifuge (LDC) at ESA/ESTEC. The discharge voltage and current together with the videosignal from a fast camera have been recorded during the experiment. The gliding of the arc is governed by hot gas buoyancy and by consequence, gravity. Increasing the centrifugal acceleration makes the glide arc movement substantially faster. Whereas at 1g the discharge was stationary, at 6g it glided with 7 Hz frequency and at 18g the gliding frequency was 11 Hz. We describe a simple model for the glide arc movement assuming low gas flow velocities, which is compared to our experimental results

Shifted laser surface texturing for bearings applications

Laserové texturování povrchů, založené na vytváření mikroobjektů s definovanou geometrií může pozitivně ovlivnit koeficient tření i opotřebení. V praxi je použití omezeno z důvodů malé rychosti aplikace. Nová metoda, založené na posuvném laserovém texturování (sLST) je rychlejší a tím i pro průmyslové využití atraktivnější. V článku je využití metody pro texturování Al-Sn-Si kluzných ložisek. Jejich tribologické charakteristiky byly hodnoceny pomocí laboratorních testů ASTM G-77 i testů blízkým reálným podmínkám. Testy prokázaly zlepšení chování vlivem textury a naznačily další směr vývoje texturovaných ložisek.The laser surface texturing (LST) technologies, based on creation of micro-pattern with pre-defined geometry can positively influence both the friction and wear of tribo-elements. In practice, the integration of LST technology is often limited due to its slowness. The new method, so called shifted laser surface texturing (sLST) with increased process speed was developed to make the technology more attractive for the industrial application. In the paper, the texture created by sLST technology was applied onto the steel samples and Al-Sn-Si surface of sliding bearings. Both block-on-ring (ASTM G-77) laboratory tests of steel samples and highloaded working application tests on Al-Sn-Si bearings surface were carried out to evaluate the influence of texture on tribological behaviour. The ASTM G-77 laboratory tests showed a positive effect of the texture on friction behaviour. Under the high-loaded testing conditions, the positive effect was observed in initial stages of the tests, decreasing the torque of textured bearings compared to the untreated one. Lately, the texture was worn out and have no influence on the overall wear of the bearings. Based on the above mentioned observations, the use of alternative bearing material with higher hardness or application of protective layer over the created texture was suggested to exploit the texture benefits

Plasma synthesized iron oxide nanoparticles with outlook to potential application in MRI

We report on iron oxide based nanoparticles synthesized in single step process by plasma enhanced chemical vapor deposition (PECVD) using low-pressure microwave discharge from iron pentacarbonyl Fe(CO)5 precursor. The product was analyzed by SEM, XRD and AFM and tested for suitability as MRI contrast agent

Gliding arc subjected to hypergravity

We studied the influence of hypergravity on gliding arc plasma in noble gases. The hypergravity affected the plasma channel propagation

Experimental study of gliding arc plasma channel motion: buoyancy and gas flow phenomena under normal and hypergravity conditions

The details of plasma channel motion are investigated by frame-by-frame image analysis of high speed recording of a gliding arc. The gliding arc is operated in several noble gases at various flow rates, voltages and artificial gravity levels. Several peculiarities in evolution of individual glides are observed, described and discussed, such as accelerating motion of plasma channel or shortcutting events of various kinds. Statistics of averaged parameters are significantly different for buoyancy and gas drag dominated regimes, which is put into relation with differing flow patterns for hypergravity and high gas flow