Electrical, structural and optical properties of fluorine-doped zinc oxide thin films: Effect of the solution aging time

In this paper ageing effects of the solution used to prepare fluorine-doped ZnO films by the spray pyrolysis technique were investigated, concerning its role on the structure, the electrical and optical properties of films produced. The data reveal that the sheet resistance of the ZnO:F thin film decreases with the age of the solution used, reaching a minimum of 24 Ω/□, after 15 days. On the other hand the optical transmittance increases for films deposited using 6 days aging solution, decreasing afterwards as the aging time increases, being the optical transmittance in the visible range below 55%, for films deposited from solutions 36 days in age. The X-ray diffraction spectra show that the aged films are polycrystalline in nature with a [100] predominant orientation. The data also show that the intensity of (100) peak increases as the time of solution age increases, which is related to an improvement of the film crystallinity.     

The study of adsorption characteristics Cu and Pb ions onto PHEMA and P(MMA-HEMA) surfaces from aqueous single solution

The adsorption characteristics of Cu²⁺ and Pb²⁺ ions onto poly2-hydroxyethyl methacrylate (PHEMA) and copolymer 2-hydroxyethyl methacrylate with monomer methyl methacrylate P(MMA-HEMA) adsorbent surfaces from aqueous single solution were investigated with respect to the changes in the pH of solution, adsorbent composition (changes in the weight percentage of MMA copolymerized with HEMA monomer), contact time and the temperature in the individual aqueous solutions. The linear correlation coefficients of Langmuir and Freundlich isotherms were obtained. The results revealed that the Langmuir isotherm fitted the experimental results better than the Freundlich isotherm. Using the Langmuir model equation, the monolayer adsorption capacity of PHEMA surface was found to be 0.840 and 3.037 mg/g for Cu²⁺ and Pb²⁺ ions and adsorption capacity of (PMMA-HEMA) was found to be 31.153 and 31.447 mg/g for Cu²⁺ and Pb²⁺ ions, respectively. Changes in the standard Gibbs free energy (ΔG⁰), standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) show that the adsorption of mentioned ions onto PHEMA and P(MMA-HEMA) are spontaneous and exothermic at 293–323 K.     

Mixing performance of transverse hydrogen/air multi-jet through coaxial injector arrays in supersonic crossflow

Increasing the fuel mixing performance substantially improves the overall performance of the scramjet engine for a long-distance flight. In this paper, the influence of coaxial injector arrays of hydrogen/air multi-jet on the mixing performance of the fuel in supersonic crossflow is fully investigated. Our main goal is to examine the impacts of air and fuel coaxial injector on fuel distribution and penetration downstream of injectors in different operating conditions. In this study, fuel and air are simultaneously injected through coaxial multi-jet at sonic condition while of free-stream Mach number is 4. Computational Fluid Dynamic is applied for simulation of the transverse coaxial jet at supersonic crossflow. The effect of jet diameter with the same mass flow rate of air and hydrogen on fuel mixing is also investigated. The mixing efficiency of different jet spaces and pressures is also examined to obtain an optimum jet arrangement in the combustor chamber. Our study shows that the injection of the coaxial air/hydrogen jet noticeably improves mixing downstream by augmentation of fuel interaction with an air jet. Our results also show that fuel jet space of 7 Dj offers maximum fuel mixing by the formation of multi vortices with uniform strength.     

Characterization of a New Structured Packing by Computational Fluid Dynamics

The novel wire gauze structured packing PACK‐1300Y with high specific surface area was characterized by computational fluid dynamics. The main features of PACK‐1300Y were investigated including the dry and wet pressure drop as well as the height equivalent to a theoretical plate (HETP). Moreover, the flow structure of this packing was described via numerical simulations. To evaluate the amount of HETP and dry and wet pressure drop, 3D computational fluid dynamic modeling with respect to the Eulerian‐Eulerian multiphase approach was applied. The average relative errors were determined between the findings achieved from computational fluid dynamic simulation and experimental findings for mass transfer efficiency and wet and dry pressure drop, respectively.     

Effect of particle size on the optical properties of lead zirconate titanate nanopowders

Nanopowder samples of lead zirconate titanate (Pb_1.1Zr_0.52Ti_0.48O₃ or PZT) were prepared by the sol‐gel method with controlled pH values. The samples were characterized using FTIR spectroscopy, XRD, FE‐SEM, and TEM techniques. Most of the peaks in the XRD pattern were related to the coexistence of tetragonal‐rhombohedral phases and confirmed the formation of PZT with a perovskite structure. Also, the crystallite size of PZT nanopowders was in a range of 17‐28 nm. FTIR spectroscopy revealed a longitudinal optical (LO) and transverse optical (TO) phonon modes corresponding to the stretching vibration of Ti‐O and Zr‐O bonds. The influence of pH values on the LO and TO phonon modes, LO‐TO splitting, refractive index n(ω), extinction coefficient k(ω), and the real ?₁(ω) and imaginary ?₂(ω) parts of dielectric function was discussed. These properties were investigated in the mid‐infrared region (450‐750 cm^?1). The energy loss function Im[?1/(?)] of PZT nanopowders was obtained by Kramers‐Kronig dispersion relations. The TO phonon frequency decreases with increasing crystallite size of the PZT samples. This effect does not happen at pH 8 to pH 9. As the crystallite size increased from 17.26 nm (at pH 5) to 27.25 nm (at pH 7), the LO‐TO splitting increased as well. This result showed that the optimum pH for absorption of IR radiation and optical application was at pH 7.     

Effect of simultaneous ultrasound/pulsed electric field pretreatments on the oil extraction from sunflower seeds

In this study, the individual and synergistic effects of ultrasound (US) and pulsed electric field (PEF) on the oil yield and content of functional food ingredients of sunflower oil were evaluated. The application of a PEF treatment (1.1 kV/cm) to the sunflower suspension significantly increased the extraction yield by 12.7%, with respect to hexane extraction. However, US/PEF treatment led to a reduction in oil yield as compared with US- and PEF-treated samples. Furthermore, the content of α-tocopherol was slightly higher for the oil after applying PEF-assisted extraction and a slight decrease in this content was observed for US- and US/PEF-assisted extraction.     

Shape memory alloy based controllable multi-port microvalve

This paper describes an innovative miniature multi-port valve with a thin foil of shape memory alloy (SMA) as actuator for switching and dosing gaseous and liquid media. The normally closed (NC) microvalve has two structured SMA actuators that are switched independently of each other and either two inputs and one output or one input and two outputs. In addition to switching the media in the 3/4-way arrangement, it can also be used with a flow sensor in a closed loop control for dosing. Furthermore, the valve design is layer-based so that individual components can be manufactured according to given requirements or using different manufacturing technologies depending on the batch size. The SMA multi-port microvalve showed flow rates of about 2300 ml/min (nitrogen gas) and about 45 ml/min (water) for an applied pressure difference of 200 kPa and a heating current of about 400 mA. For flow regulation a closed loop control was realized and evaluated for a pressure difference of 100 kPa and a setpoint value of 900 ml/min.

     

Structural,Electronic and Magnetic Properties of NaKZ (Z = N,P, As,and Sb) Half-Heusler Compounds: a First-Principles study

The electronic and magnetic properties of the half-Heusler compounds of NaKZ (Z = N, P, As, and Sb) are investigated on the basis of density functional theory. The spin-polarized calculations indicate that these materials are half-metallic ferromagnets with an integer magnetic moment of 1 μ _B at their equilibrium lattice constants. The mechanism that leads to half-metallicity in these materials is also investigated. It is found that these compounds are half-metallic ferromagnets on a wide range of lattice constants, and as a result, they could be used in the spintronic devices that contain heterojunctions of half-metal/semiconductors. The Curie temperatures of NaKN, NaKP, NaKAs, and NaKSb are estimated to be 526.3, 494.7, 475.9, and 358.1 K in the mean field approximation, respectively.