An efficient edge based data structure for the compressible Reynolds-averaged Navier–Stokes equations on hybrid unstructured meshes

An efficient edge based data structure has been developed in order to implement an unstructured vertex based finite volume algorithm for the Reynolds-averaged Navier–Stokes equations on hybrid meshes. In the present approach, the data structure is tailored to meet the requirements of the vertex based algorithm by considering data access patterns and cache efficiency. The required data are packed and allocated in a way that they are close to each other in the physical memory. Therefore, the proposed data structure increases cache performance and improves computation time. As a result, the explicit flow solver indicates a significant speed up compared to other open-source solvers in terms of CPU time. A fully implicit version has also been implemented based on the PETSc library in order to improve the robustness of the algorithm. The resulting algebraic equations due to the compressible Navier–Stokes and the one equation Spalart–Allmaras turbulence equations are solved in a monolithic manner using the restricted additive Schwarz preconditioner combined with the FGMRES Krylov subspace algorithm. In order to further improve the computational accuracy, the multiscale metric based anisotropic mesh refinement library PyAMG is used for mesh adaptation. The numerical algorithm is validated for the classical benchmark problems such as the transonic turbulent flow around a supercritical RAE2822 airfoil and DLR-F6 wing-body-nacelle-pylon configuration. The efficiency of the data structure is demonstrated by achieving up to an order of magnitude speed up in CPU times.     

Thermal performances and stabilities of nanofluids in an electrical oil heater

Journal of Thermal Analysis and Calorimetry - In this study, different nanofluids synthesized with aluminium oxide (alumina) and titanium dioxide in mass ratios of 1%, 3%, and 5% were tested in an...     

SOME SUBGROUPS OF THE EXTENDED HECKE GROUPS (λ_q)

The authors consider the extended Hecke groups H(λq) generated by T(z) = -1 / z, S(z) = -1/(z + λq,) and R(z) = 1 / z with A, = 2 cos(π/q) for q≥3 an integer. In this paper, the even subgroup He(λq), the second commutator subgroup H (λq) and the principal congruence subgroups Hp(λq) of the extended Hecke groups H(λq) are studied. Also, relations between them are given.     

Quantitative analysis of sea-bed sediments from Eastern Black Sea by EDXRF spectrometry

Sea-bed sediments from Eastern Black Sea have been analyzed for their Fe, Ba and Sr contents using the methods of standard addition and energy dispersive X-ray fluorescence (EDXRF). Samples were prepared from powder sifted by a 200 mesh sieve. An annular 100 mCi²⁴¹Am radioactive source emitting 59.543 keV photons was used for excitation and a Ge(Li) detector, which has a 190 eV FWHM for 5.9 keV photons was used for intensity measurements. 2048 channels of the MCA are employed for 20 or 30 min. Dried and ground sea-bed sediments are found to contain 2.95–7.50% Fe, 0.032–0.268% Ba and about 73–273 ppm Sr. These results agree with those obtained via atomic absorption methods.     

Synthesis of polyimides by photoaddition of bismaleimides to benzene

Polyimides have been synthesized by the sensitized photoaddition of aliphatic and aromatic bismaleimides to benzene. The reaction involves 2+2 cycloaddition to give homoannular diene intermediate followed by Diels-Alder addition to give polymer. Proof of structure is based mainly on a comparison of infrared spectra with those of the corresponding polyimides prepared from maleic anhydride-benzene photoadduct and diamines. The very low solubility of the polymers indicates that crosslinking probably occurred during photolysis. All the polyimides appear to decompose by decyclization at about 420–485°C. Polymer yield was dependent on bismaleimide structure.     

A phenolate-induced trans influence: crystallographic evidence for unusual asymmetric coordination of an alpha-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands

Three mononuclear ternary complexes of iron(III) with an alpha-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L3-) have been synthesized and characterized by magnetic susceptibility measurements, electron paramagnetic resonance (EPR) spectroscopy, vibrational spectroscopy, and electronic absorption spectroscopy. Single-crystal X-ray structure determinations of the pseudo-octahedral complexes [Fe(bipy)L] x MeCN [L = (3,5-Br2)-L3- or (5,3-Cl,Me)-L3-] revealed a considerable and consistent distortion in the coordination of bipy to iron(III) attributable largely to electronic effects. In both crystal structures, the Fe-N(pyridyl) bond trans to the phenolate oxygen is 0.133 A longer than the other one positioned trans to the tertiary amine nitrogen, a relatively weaker donor. This coordination behavior of bipy is of structural interest and has not been observed previously for iron(III). The electronic and EPR spectra of the compounds [Fe(L'-L')L] x MeCN (L'-L' = bipy or phen) are consistent with the spin state of the central metal atom (S = 5/2). The charge-transfer transitions arising from the strong interactions of the phenolate moieties with the ferric ion have been identified as phenolate (p(pi)) --> iron(III) (d(pi*)) (lambda(max) approximately 500 nm, epsilon approximately 3000 M(-1) cm(-1)) and phenolate (p(pi)) --> iron(III) (d(sigma*) (lambda(max) approximately 320 nm, epsilon approximately 5200 M(-1) cm(-1)). The presence of the phenolate moieties in the quadridentate hetero-donor tripodal ligands, H3L, lends these iron(III) ternary complexes the potential to model the specific metal-coordination, metal-substrate interactions, and physicochemical behaviors of several iron-tyrosinate proteins.     

Selective pre-concentration of selenite from aqueous samples using mercapto-silica

Silica gel modified with 3-mercaptopropyl-trimethoxysilane was used for the selective separation and pre-concentration of selenite (Se(IV)) from aqueous solutions containing Se(IV) and selenate (Se(VI)). Over a wide range of acidity, from 2 mol l⁻¹ HCl to pH 9.00, Se(IV) was taken up by the mercaptopropyl-silica with nearly 100% efficiency; Se(VI) however was unretained. Se(IV) content was determined by hydride generation atomic absorption spectrometry (HGAAS), following batch release of the selenium from the pre-concentration medium by acidic periodate. The overall pre-concentration efficiency, including both take-up and elution, in the range of 89-106%. The method was applied to spiked seawater samples containing as low as 800 ng l⁻¹ Se in selenite form. This solid-phase extraction system offers several major advantages over conventional solvent extraction procedures. It firstly exhibits high selectivity for Se(IV) over Se(VI). Using the solid-phase media, pre-concentration of Se(IV) in dilute water samples can be carried out in the field, stabilizing the selenite-selenium in a convenient form for transport and storage. In addition, selenium stored on silica is derived solely from Se(IV) overcoming problems of selenium redox speciation changes and loss during storage.     

Effects of processing parameters on the mechanical properties of polypropylene random copolymer

The mechanical properties of polypropylene random copolymer (PP-R) with different processing parameters were studied. Special attention is devoted to the investigation of the influence of masterbatch addition on the variation in the mechanical properties of injection moulded PP-R. Tensile, instrumented Charpy impact, Shore D hardness, differential scanning calorimeter (DSC) and Vicat softening temperature (VST) tests were conducted on the test samples containing different colour masterbatches varying from 0.5 to 10 wt%. The observed changes in the mechanical behaviour are explained by the type and level of masterbatch content. The natural UV weathering performance of the PP-R material was studied from the masterbatch type point of view. The effect of processing parameters on material performance was studied on samples which were directly obtained from extruded pipes and on injection moulded samples.

Finally, the effects of storage time on the polymer properties were investigated.     

Some Aspects of Magnetic Filtration Theory for Removal of Fine Particles from Aqueous Suspensions

The magnetic filtration theory was evaluated to intensify the filtration of industrial fluids by magnetic filters. Effects of filtration velocity and external magnetic field intensity on filter performance were investigated and the dependence of the logarithmic efficiency coefficient on filtration velocity was questioned. It was concluded that change in the magnetic susceptibility of the dispersion particles, caused by external magnetic field, and change in the flow rate properties of the liquid alongside the filter pores are the most essential factors to be considered in the design, development, and modeling of magnetic filtration systems in various industrial areas.