Vapor pressures and osmotic coefficients of the acetone solutions of three bis(tetraalkylammonium)tetrathiomolybdates at 298.15 K measured by head-space gas chromatography

The vapor pressures and osmotic coefficients of solutions of (R₄N)₂[MoS₄] (R = ethyl, n-propyl and n-butyl) in acetone have been measured by head space-gas chromatography (HS-GC). Experimental data for the osmotic coefficients have been expressed by three thermodynamic models including the ionic interaction model of Pitzer, the electrolyte non-random two liquid (e-NRTL) model and the non-random factor (NRF) model. The ability of the models to fit the osmotic coefficient was compared on the basis of the standard deviation of the fittings. The results show that the considered models provide reliable results, but the Pitzer's model gives better results than the NRTL and the NRF methods, especially in the dilute region.     

A computational study of the electronic structure and the chemical activity of curcumin and some novel curcuminoids by density functional theory

Structural modification of curcumin represents a strategy to improve its stability, water solubility, pharmaceutical properties and bioactivity. In this context, numerous structural analogues of curcumin, including curcuminoids, have been developed. In this paper, the precise density functional theory computations were used for investigating the electronic and geometrical structure of curcumin and some of its derivatives. The chemical activity of the considered molecules was investigated with the help of the global softness and hardness concepts. Among the studied molecules, bisdemethoxycurcumin had the most chemical activity and hexahydrocurcumin had the most stable structure. Among two isomers of the curcumin, the enol isomer was found to be active.     

Bond graph modeling of a typical flapping wing micro-air-vehicle with the elastic articulated wings

In the present research, a new comprehensive model of a flexible articulated flapping wing robot using the bond graph approach is presented. The flapping kinematics of a two-section wing is introduced via the bond graph based approach on a hybrid mechanism providing amplitude and phase characteristics. The aerodynamic quasi-steady approach equipped with stall correlation is utilized according to the reduced flapping frequency and the angle of attack ranges. The local flow velocity and the wing position are calculated in both wing and body coordinates taking into account rotation and translation of the wing different parts. Estimation of the effective angle of attack is performed by calculating the instantaneous torque distribution on both wing sections. Aeroelastic modeling is employed in which the wing structure is assumed as an elastic Euler–Bernoulli beam at the leading edge with three linear torsional modes. In this novel integrated bond graph model, computation of the performance indices including the average lift and thrust, consumed and produced powers by flapping and mechanical efficiency are presented. Due to existence of the numerous geometric and kinematic parameters in articulated flexible flapping wing, such a model is essential for design and optimization. Consequently, an example of a typical parametric study and the results validation are carried out. It is indicated that the sensitivity of the bird performance to relative change in design variables would increase for out of phase flapping, second part stiffness, flapping amplitude, frequency and velocity respectively. It is interesting that by employing the reverse-phase flapping which is possible only via articulated wings, the maximum efficiency could be achieved. In addition, it is shown that adjusting the wing torsional stiffness is a crucial item in design of passive flapping robots. The key advantage of the two-section flapping wing is depicted as the controlling capability of the angle of attack in the outer part of the wing. Finally, the improved version of the bird is being addressed by approximately 15% progress in propulsive efficiency.

     

Osmotic and activity coefficients in the binary solutions of 1-butyl-3-methylimidazolium chloride and bromide in methanol or ethanol at T = 298.15 K from isopiestic measurements

Osmotic coefficients of the binary solutions of two room-temperature ionic liquids (1-butyl-3-methylimidazolium chloride and bromide) in methanol and ethanol have been measured at T = 298.15 K by the isopiestic method. The experimental osmotic coefficient data have been correlated using a forth-order polynomial in terms of (molality)^0.5, with both, ion interaction model of Pitzer and electrolyte non-random two liquid (e-NRTL) model of Chen. The values of vapor pressures of above-mentioned solutions have been calculated from the osmotic coefficients. The model parameters fitted to the experimental osmotic coefficients have been used for prediction of the mean ionic activity coefficients of those ionic liquids in methanol and ethanol.     

Comparative studies on the structure and electromagnetic properties of Ni−Zn ferrites prepared via co-precipitation and conventional ceramic processing routes

The magnetic and physical properties of ferrites are very sensitive to microstructure, which in turn critically depends on the manufacturing process. In this study, nickel zinc ferrite powder with composition Ni_0.8Zn_0.2Fe₂O₄ has been prepared via conventional ceramic processing and co-precipitation methods. The toroidal and pellet form samples were sintered at various temperatures such as 1100, 1200 and 1300 °C. The microstructure, magnetic and dielectric properties of both samples were studied. The X-ray diffraction patterns confirm the formation of single-phase cubic spinel structure for the co-precipitation technique after sintering. The microstructure studies of Ni_0.8Zn_0.2Fe₂O₄ show the grain size increases and the porosity decreases with temperature for both methods. The controlled permeability with small loss and wide operational frequency range are found in the co-precipitation samples. Dielectric constants decrease with increase of frequency and increase with sintering temperature in both methods. Consequently, the homogenous microstructure with the low-loss high-performance of nickel zinc ferrite has been discovered by means of co-precipitation method.     

Density functional theory (DFT) study of O<Subscript>3</Subscript> molecules adsorbed on nitrogen-doped TiO<Subscript>2</Subscript>/MoS<Subscript>2</Subscript> nanocomposites: applications to gas sensor devices

Density functional theory calculations were carried out to investigate the adsorption behaviors of O₃ molecules on the undoped and N-doped TiO₂/MoS₂ nanocomposites. With the inclusion of vdW interactions, which correctly account the long-range dispersion energy, the adsorption energies and final geometries of O₃ molecules on the nanocomposite surfaces were improved. For O₃ molecules on the considered nanocomposites, the binding sites were located on the fivefold coordinated titanium atoms of the TiO₂ anatase. The structural properties of the adsorption systems were examined in view of the bond lengths and bond angles. The variation of electronic structures was also discussed in view of the density of states, molecular orbitals and distribution of spin densities. The results suggest that the adsorption of the O₃ molecule on the N-doped TiO₂/MoS₂ nanocomposite is more favorable in energy than that on the pristine one, indicating that the N-doped nanocomposite has higher sensing capability than the pristine one. This implies that the N-doped TiO₂/MoS₂ nanocomposite would be an ideal O₃ gas sensor. However, our calculations thus provide a theoretical basis for the potential applications of TiO₂/MoS₂ nanocomposites as efficient O₃ sensors, leading to very interesting results in the context of air quality measurement.     

Vapor pressures and apparent molal volumes of the solutions of ZnCl2 in ethanol at 298.15 K

Vapor pressures and apparent molal volumes of solutions of ZnCl₂ in ethanol are reported at 298.15 K. The vapor pressure of ethanol has been evaluated from the osmotic coefficients measured by an improved isopiestic method. The experimental osmotic coefficients have been correlated with the Pitzer model and local composition models including electrolyte non-random two liquid (e-NRTL), non-random factor (NRF), modified NRTL (MNRTL) and extended Wilson (EW) models. Apparent molal volumes have been calculated from the densities of the solutions measured by a vibrating-tube densimeter, and fitted with the volumetric equations based on the Pitzer model and the local composition models. All of the models successfully correlate the experimental osmotic coefficients and apparent molal volume data.