Comparative analysis of numerical computational techniques for determination of the wind turbine aerodynamic performances

The purpose of this paper is to explore and define an adequate numerical setting for the computation of aerodynamic performances of wind turbines of various shapes and sizes, which offers the possibility of choosing a suitable approach of minimal complexity for the future research. Here, mechanical power, thrust, power coefficient, thrust coefficient, pressure coefficient, pressure distribution along the blade, relative velocity contoure, at different wind speeds and streamlines were considered by two different methods: the blade element momentum and CFD, within which three different turbulence models were analyzed. The estimation of the mentioned aerodynamic performances was carried out on two different wind turbine blades. The obtained solutions were compared with the experimental and nominal (up-scaled) values, available in the literature. Although the flow was considered as steady, a satisfactory correlation between numerical and experimental results was achieved. The comparison between results also showed, the significance of selection, regarding the complexity and geometry of the analyzed wind turbine blade, the most appropriate numerical approach for computation of aerodynamic performances

Reconstructed Malacothermometer July Paleotemperatures from the Last Nine Glacials over the South-Eastern Carpathian Basin (Serbia)

In this study, the compiled malacological record of the two most important loess–palaeosol sequences (LPS) in Serbia was used to reconstruct the Malacothermometer July Paleotemperature (MTJP) of the last nine glacials. The sieved loess samples yielded shells of 11 terrestrial gastropod species that were used to estimate the MTJP. Veliki Surduk (covering the last three glacial cycles) and Stari Slankamen (covering the last fourth to ninth glacial cycle) LPSs previously lacked the malacological investigations. After the sieving, a total of 66,871 shells were found, from which 48,459 shells were used for the estimation of the MTJP. Through the studied period, the reconstructed MTJP was ranging from 14.4 °C to 21.5 °C. The lowest temperature was recorded during the formation of the loess unit L5, equivalent to the Marine Isotope Stage (MIS) 12. The second-coldest summers were occurring during the MIS 16 glacial. Although the warmest glacial was L8 (MIS 20) according to MTJP, these July temperatures might be overestimated due to only two samples from the poorly preserved L8 unit. The malacological material derived from the loess units at Veliki Surduk and Stari Slankamen LPSs showed great potential for July temperature reconstruction, as the comparison with other regional records showed similar climate changes. Further work is necessary to validate the age scale of the oldest samples, and a higher resolution sampling could lead to more detailed July temperature fluctuations, as was shown for the youngest glacial in this study. Likewise, estimating the July temperature using different proxies (e.g., pollen) from the same LPSs could be used to confirm the observed climate trends

Poboljšana adhezija akrilnih adheziva sa zubnim tkivom uz dodatak čestica na bazi aluminijum oksida

Composite materials based on acrylate UV-cured polymers (Bis-GMA/TEGDMA) as a matrix and reinforcements that can be selected in order to adjust the properties of the obtained composite are used in the field of dental technology. The role of reinforcement is to adjust the mechanical properties, but also to control the shrinkage during curing. As reinforcement, alumina particles doped with iron oxide (Al2O3 Fe) synthesized using the sol-gel technique were selected. In order to simulate the process of adhesive application in real conditions, in vitro testing technique and adhesion properties of synthesized adhesive were used, where tooth tissue was used as a substrate. Comparison with standard adhesives used in dentistry was used to compare adhesion. The quality of the adhesive joint was evaluated using the microhardness testing method using different loads where it is estimated how the adhesive makes a connection with the substrate. It was shown that the synthesized adhesive showed significantly enhanced adhesion compared to the standard adhesive used in dentistry (836%).Kompozitni materijali na bazi akrilatnih fotopolimerizujućih polimera, (Bis-GMA/TEGDMA) koji predstavljaju matricu i ojačanja koja se mogu odabrati sa ciljem podešavanja svojstava dobijenih kompozita, koriste se u oblasti dentalne tehnologije. Uloga ojačanja je podešavanje mehaničkih svojstava, ali i kontrola skupljanja tokom očvršćavanja. Kao ojačanje odabrane su čestice aluminijum-oksida dopirane gvožđe oksidom (Al2O3 Fe), sintetisane korišćenjem sol-gel tehnike. U cilju simuliranja procesa primene adheziva u realnim uslovima korišćena je in vitro tehnika ispitivanja adhezije sintetisanog adheziva pri čemu je kao substrat korišćeno tkivo zuba. Dobijene vrednosti adhezije poređene su sa komercijalnim adhezivima koji se koriste u stomatologiji. Kvalitet adhezivnog spoja ocenjen je merenjem mikrotvrdoće primenom različitih opterećenja, pri čemu je procenjen način kako se ostvaruje spoj između filma i podloge. Pokazalo se da je sintetisani adheziv imao višestruko jaču adheziju u poređenju sa standardnim adhezivom korišćenim u stomatologiji (836 %)

Ionization energies of K2X (X=F, Cl, Br, I) clusters

The electronic structure and properties of dipotassiummonohalides are important for understanding the unique physical and chemical behavior of MnX systems. In the present study, K2X (here X=F, Cl, Br, I) clusters were generated in the vapor over salts of the corresponding potassium halide, using a magnetic sector thermal ionization mass spectrometer. The ionization energies obtained for K2F, K2Cl, K2Br, and K2I molecules were 3.82 +/- 0.1eV, 3.68 +/- 0.1eV, 3.95 +/- 0.1eV, and 3.92 +/- 0.1, respectively. These experimental values of ionization energies for K2X (X=F, Br, and I) are presented for the first time. The ionization energy of K2Cl determined by thermal ionization corresponds to previous results obtained by photoionization mass spectrometry, and it agrees with the theoretical ionization energy calculated by the ab initio method. The presently obtained results support previous theoretical predictions that the excess electron in dipotassiummonohalide clusters is delocalized over two potassium atoms, which is characteristic for F-center clusters. Copyright (C) 2011 John Wiley and Sons, Ltd

A Glacial–Interglacial Malacofauna Record from the Titel Loess Plateau, Serbia, between ~350 and 250 ka

We present data on molluscan fauna within the L3 loess unit (and partially within the S3 paleosol) from the key loess section of Veliki Surduk in Serbia. The section correlates to Marine Isotope Stage (MIS) 8 and late MIS 9 and, thus, spans the time frame from ~350 to 250 ka. The Veliki Surduk loess–paleosol sequence (LPS) is located on the northwestern margin of the Titel loess plateau and comprises ~30 m of sediments. Our focus is on a 5.4 m thick sedimentary interval, which was sampled at 20 cm increments, each sample covering approximately 2 ky. Nine mollusk species were identified in the loess sequence: Granaria frumentum, Helicopsis striata, Pupilla triplicata, Chondrula tridens, Pupilla muscorum, Succinella oblonga, Punctum pygmaeum, Vallonia costata, and Vitrina pellucida, as well as a few unidentified slug taxa (Limacidae, Agriolimacidae, and Milacidae). The majority of the snail assemblage occurs at the transition between MIS 9 and MIS 8, suggesting a mostly dry climate and an open and steppe-like habitat. The fauna identified in the upper part of the paleosol layer S3, below the L3 unit, indicated aridification