Středoevropský technologický institut VUT
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- ItemHigh-Temperature Creep Resistance of FeAlOY ODS Ferritic Alloy(MDPI, 2024-10-01) Dymáček, Petr; Jarý, Milan; Bártková, Denisa; Luptáková, Natália; Gamanov, Štěpán; Bořil, Petr; Georgiev, Vjačeslav; Svoboda, JiříA significant effort in optimizing the chemical composition and powder metallurgical processing led to preparing new-generation ferritic coarse-grained ODS alloys with a high nano-oxide content. The optimization was aimed at high-temperature creep and oxidation resistance at temperatures in the range of 1100-1300 degrees C. An FeAlOY alloy, with the chemical composition Fe-10Al-4Cr-4Y2O3 (wt. %), seems as the most promising one. The consolidation of the alloy is preferably conducted by hot rolling in several steps, followed by static recrystallization for 1 h at 1200 degrees C, which provides a stable coarse-grain microstructure with homogeneous dispersion of nano-oxides. This represents the most cost-effective way of production. Another method of consolidation tested was hot rotary swaging, which also gave promising results. The compression creep testing of the alloy at 1100, 1200, and 1300 degrees C shows excellent creep performance, which is confirmed by the tensile creep tests at 1100 degrees C as well. The potential in such a temperature range is the target for possible applications of the FeAlOY for the pull rods of high-temperature testing machines, gas turbine blades, or furnace fan vanes. The key effort now focuses on expanding the production from laboratory samples to larger industrial pieces.
- ItemGreen synthesis and the stablization of selenium nanoparticles using carboxylmethyl starch(Tanger, 2020-12-28) Vishakha, Vishakha; Abdellatif, Abdelmohsen Moustafa; Jančář, JosefThe growing interest in biodegradable products paves the way for the safest sustainable earth. Starch is an extensively studied, cost-effective, easily accessible, and highly trusted resource to produce biodegradable products in the present and future. However, the exploitation of these starch in several fields requires substantial changes in its chemical functionalities and related properties. Here, we investigated the conditions (pH, temperature, the concentration of starch, concentration of chloroacetate, time, the ratio between starch/sodium hydroxide, etc.) that affect the preparation of carboxymethyl starch (CMS). The chemical structure and degree of substitution of native starch and CMS were confirmed by Fourier transform infrared ( FTIR), X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), potentiometric titration, Scanning electron microscope (SEM), and Nuclear magnetic resonance spectroscopy (NMR ). CMS's rheological properties show that CMS's intrinsic viscosity increased with increased degrees of substitutions (DS) from CMS (0.05 to 0.45). The CMS with different DS (0.05 to 0.45) was used for the first time to stabilize selenium nanoparticles (Se-NPs), showing spherical shape with a high homogenous size of Se-NPs (approx. 50 nm). The NPs shape and size stability were investigated and confirmed by different techniques like Dynamic light scanning (DLS), SEM, and Transmission electron microscope (TEM)
- ItemInvestigation into the Effect of Molds in Grasses on Their Content of Low Molecular Mass Thiols(MDPI, 2012-10-24) Skládanka, Jiří; Adam, Vojtěch; Zítka, Ondřej; Kryštofová, Olga; Beklová, Miroslava; Kizek, René; Havlíček, Zdeněk; Sláma, Petr; Nawrath, adamThe aim of this study was to investigate the effect of molds on levels of low molecular mass thiols in grasses. For this purpose, the three grass species Lolium perenne, Festulolium pabulare and Festulolium braunii were cultivated and sampled during four months, from June to September. The same species were also grown under controlled conditions. High-performance liquid chromatography with electrochemical detection was used for quantification of cysteine, reduced (GSH) and oxidized (GSSG) glutathione, and phytochelatins (PC2, PC3, PC4 and PC5). Data were statistically processed and analyzed. Thiols were present in all examined grass species. The effect of fungicide treatments applied under field conditions on the content of the evaluated thiols was shown to be insignificant. Species influenced (p < 0.05) PC3 and GSSG content. F. pabulare, an intergeneric hybrid of drought- and fungi-resistant Festuca arundinacea, was comparable in PC3 content with L. perenne and F. braunii under field conditions. Under controlled conditions, however, F. pabulare had higher (p < 0.05) PC3 content than did L. perenne and F. braunii. Under field conditions, differences between the evaluated species were recorded only in GSSG content, but only sampling in June was significant. F. pabulare had higher (p < 0.05) GSSG content in June than did L. perenne and F. braunii.
- ItemElectrical Performance of a Piezo-inductive Device for Energy Harvesting with Low-Frequency Vibrations(MDPI, 2019-07-16) Vargas, Carlos Alberto; Tinoco Navarro, Hector AndresThis study presents the experimental evaluation of a piezo-inductive mechanical system for applications of energy harvesting with low-frequency vibrations. The piezo-inductive vibration energy harvester (PI-VEH) device is composed of a voice coil motor (VCM) extracted from a hard disk drive. The proposed design allows the integration of different element types as beams and masses. The dynamic excitations in the system produce a pendular motion carried out by a hybrid arm (rigid-flexible) that generates energy with the rotations (with a coil) and the beam strains (with a piezoelectric material). The electrical assessment was performed through different working modes classified as inductive, inductive with magnetic instabilities, and piezo-inductive. The instabilities in the harvester refer to external forces induced by two magnets that repel each other. The first two inductive configurations were designed as a function of three parameters (length, mass, instability angle) to debug these using the maximum output voltage. The selected experiments were conducted in a piezo-inductive configuration. The results showed two effects on the output voltage-the first one is related to a system without resonances (higher broadband), and the second effect is associated with a multi-resonant system. As a final conclusion, it is pointed out that the electrical performance can be improved with the magnetic instabilities since these considerably amplified the output voltages.
- ItemNAND Flash Memory Organization and Operations(Omics, 2015-06-30) Novotný, Radovan; Kadlec, Jaroslav; Kuchta, RadekNAND flash memories are well known for their uncomplicated structure, low cost, and high capacity. Their typical characteristics include architecture, sequential reading, and high density. NAND flash memory is a non-volatile type of memory and has low power consumption. The erasing of NAND Flash memory is based on a block-wise base. Since cells in a ash chip will fail after a limited number of writes, limited write endurance is a key characteristic of flash memory. There are many noise causes such as read or program disturbs, retention process, charge leakage, trapping generation, etc. Preferably, all errors in the storage would be adjusted by the ECC algorithm. The conclusion of all mentioned parasitic factors creates a set of external and internal influences which affects variable behaviour of memory in time. To prepare a review of all the important factors that affect the reliability and life-cycle endurance of NAND flash memories and was our main motivation for this paper.