The influence of material types on twist angles and torsion stability of a composite shaft

Prednost primjene kompozitnih materijala, u odnosu na konvencionalne materijale, ogleda se u mogućnosti širokog variranja praktično svih svojstava materijala od kojih su sastavljeni, što se postiže putem izbora sastavnih komponenata, njihove količine, rasporeda i orijentacije u okviru materijala, a s ciljem da se iskoriste njihova najbolja svojstva. U nekim slučajevima najbolji rezultati mogu biti postignuti uporabom kombinacije kompozita i tradicionalnih metalnih materijala. U radu su analizirana vratila dobivena kombinacijom aluminija s različitim kompozitnim materijalima – karbonska vlakna/epoksi smola, staklena vlakna/epoksi smola, aramidna vlakna/epoksi smola. Razmatran je njihov utjecaj na vrijednosti kutova uvijanja i kritične vrijednosti momenta uvijanja koje dovode do gubitka stabilnosti vratila. Provedena je i eksperimentalna analiza vratila koje je pokazalo najbolja svojstva (karbonska vlakna/epoksi smola).The advantages of composite materials over the conventional ones include the ability to vary their properties in order to ensure the best combination for each application. This is achieved through selection of their constituent materials, quantities, distribution and fibre orientation angle. In some cases, the best results can be achieved by using a combination of composite and traditional metal materials. This paper analyses shafts made from a combination of aluminium and different composite materials – carbon fibre/epoxy, glass fibre/epoxy, and aramid fibre/epoxy. The influence of these materials on twist angle values and critical torques that impair the shaft stability has also been discussed. Finally, an experimental analysis of the shaft that exhibited the best properties (carbon fibres/epoxy) has been performed

Removing Products of Thermal Degradation from Edible Oils by Zeolite and by Clinoptilolite - Comparison of Results

When edible oils are heated above 150°C, they undergo thermo-oxidative changes depending on a variety of factors, such as temperature, heating time, type of oil, etc. These changes cause a series of chemical reactions (hydrolysis, oxidation, polymerization, etc.) resulting in the formation of free fatty acids, an increase in the peroxide number and the acid number, a change of color and a decrease in the iodine number. This study investigates changes of the content of free fatty acids, the acid number, and the peroxide number in edible sunflower oil when heating at the temperature range from 110°C to 190°C for 30 minutes, as well as after the adsorption by a natural and a synthetic adsorbent (clinoptilolite and zeolite 4A). The results of the research show that these adsorbents are effective in removing the products of chemical reactions occurring in thermal degradation, which is particularly evident after the adsorption of oil heated at 190°C. Somewhat better results were achieved after the adsorption using clinoptilolite, with a 72 % reduction in the content of free fatty acids, 83 % reduction in the acid number, and 43 % reduction in the peroxide number. After the adsorption by zeolite 4A, the content of free fatty acids was reduced by 65%, the acid number by 76 %, and the peroxide number by 39 %. The results obtained open the possibilities of further research aiming at discovering the adsorbents which would be most suitable for the regeneration of used edible oils, after which they could be applied safely for different purposes. Keywords: edible oil, free fatty acids, acid number, peroxide number, adsorben

The effect of meteorological and chemical parameters on summer phytoplankton assemblages in an urban recreational lake

The summer phytoplankton community was studied across both vertical and temporal scales in relation to environmental factors in the shallowrecreational Sava Lake. The sampling was conducted weekly at four depths from mid-July until mid-September 2014, in order to detect short-term changes within the assemblages. Besides physical and chemical parameters, meteorological data was also included in the investigation, as that year was characterized with extreme rainfall, which caused serious flooding in the region. The community succession was characterized by a reverse in the cyanobacteria (Codon M) and chlorococcal green algae (Coda F and J). Statistical analyses (RDA) indicated that changes in the community composition and successional pattern could have been due to the mixing regime variations in the reservoir, most likely induced by weather disturbances, especially high precipitation and wind events. These events did not permit massive cyanobacterial development, although they most likely caused resuspension of dissolved phosphorus from the sediment. When observing functional groups, three groups could be distinguished by their response to the above-mentioned parameters: the first prefers high temperature and insolation(Lm, Y, Lo, Xph, W2andM), the second is correlated with precipitation and wind (Td, C, K, MP and X2), while the third group tolerates cloudiness (H1, F, N, X1, D, J and P)

Far infrared properties of PbTe doped with Hg

Single crystal samples of PbTe doped with Hg were grown using the Bridgman method. Far infrared reflectivity spectra were measured at room temperature for samples with 0.5 at. % Hg; 0.9 at. % Hg and 1.4 at. % Hg. The plasma frequency decreased when PbTe was doped with Hg and it was lowest for the PbTe sample doped with 0.5 at. % Hg. The values of the determined optical free carrier mobility increased and was the highest for PbTe doped with 0.5 at. % Hg

Far infrared and photoacoustic characterization of iodine doped PbTe

Single crystal samples of PbTe doped with PbI2 were made using the Bridgman technique. Far infrared reflectivity diagrams of PbTe doped with 0.4 at% and 0.6 at% Iodine were measured and numerically analyzed. A plasma resonance at about 650 cm(-1) with the reflectivity minima very close to zero was observed for both samples. Thermal diffusivity was determined for the same samples using the photoacoustic method with a transmission detection configuration and the values of the minority free carrier (holes) mobility were calculated

Far infrared properties of PbTe doped with Hg

Single crystal samples of PbTe doped with Hg were grown using the Bridgman method. Far infrared reflectivity spectra were measured at room temperature for samples with 0.5 at. % Hg; 0.9 at. % Hg and 1.4 at. % Hg. The plasma frequency decreased when PbTe was doped with Hg and it was lowest for the PbTe sample doped with 0.5 at. % Hg. The values of the determined optical free carrier mobility increased and was the highest for PbTe doped with 0.5 at. % Hg

Far infrared and photoacoustic characterization of iodine doped PbTe

Single crystal samples of PbTe doped with PbI2 were made using the Bridgman technique. Far infrared reflectivity diagrams of PbTe doped with 0.4 at% and 0.6 at% Iodine were measured and numerically analyzed. A plasma resonance at about 650 cm(-1) with the reflectivity minima very close to zero was observed for both samples. Thermal diffusivity was determined for the same samples using the photoacoustic method with a transmission detection configuration and the values of the minority free carrier (holes) mobility were calculated

Performance Analysis of Nonlinear Energy‐Harvesting DF Relay System in Interference‐Limited Nakagami‐

A decode‐and‐forward system with an energy‐harvesting relay is analyzed for the case when an arbitrary number of independent interference signals affect the communication at both the relay and the destination nodes. The scenario in which the relay harvests energy from both the source and interference signals using a time switching scheme is analyzed. The analysis is performed for the interference‐limited Nakagami‐m fading environment, assuming a realistic nonlinearity for the electronic devices. The closed‐form outage probability expression for the system with a nonlinear energy harvester is derived. An asymptotic expression valid for the case of a simpler linear harvesting model is also provided. The derived analytical results are corroborated by an independent simulation model. The impacts of the saturation threshold power, the energy‐harvesting ratio, and the number and power of the interference signals on the system performance are analyzed