The Microstructure,Texture and Mechanical Properties of Friction Stir Welded Aluminum Alloy

Russian Journal of Non-Ferrous Metals - The microstructure and texture of 7075-T6 FSW weld with optimal parameters are investigated using optical microscopy, electron back scatter diffraction and...     

Mixed convection and entropy production of a hybrid nanofluid in a porous cylindrical enclosure with rotating top wall

A numerical study is carried out to investigate heat transfer and entropy production of a hybrid nanofluid in a porous cylindrical enclosure with a rotating top wall. The bottom wall of the cylinder is taken as hot, the sidewall is adiabatic, except the top wall is considered cold and rotates at an angular velocity (ΩR). The effects of a hybrid nanofluid flow on heat transfer and entropy generation are examined for an aspect ratio (H/R = 1). A FORTRAN program was elaborated for solving the governing equations based on the finite volume method. Good agreement was found when comparing results from this study against published data. Our results are presented for different Reynolds number values (100 ≤ Re ≤ 1500), nanoparticle fraction NP (0 ≤ ϕ ≤ 0.08), Darcy number (10⁻⁴ ≤ Da ≤ 10⁻¹) and porosity of the porous medium (0.2 ≤ ε ≤ 0.99) for Ri = 0.5, 1,5 and 8, where (Ri = Gr/Re2). They reveal that the heat transfer increases with Re, ϕ, Da, Ri, and decreasing ε. The simulation data were used to propose four different correlations for $\overline{\mathit{Nu}}$ and S_tot as Re, Da, Ri, ϕ, and ε.     

Effects of process parameters on the synthesis of palladium membranes

In this study, palladium film plating was carried out on porous glass supports using the electroless plating technique. This technique was applied to study the effects of bath temperature and reducing agent concentration on the amount and the structure of palladium plated. Hydrazine concentration was fixed at 10 ml/L in the baths using 1 M hydrazine solution while the temperature was changed between 25 and 50 °C. The total mass gain and Pd/Si ratio (wt/wt%) on the surface were obtained as 7.76 mg/cm² and 68.7 in a bath temperature of 35 °C, respectively. With the help of LM microscope analysis, thickness of the membrane prepared at this temperature was determined as 31 μm. In the studies in which the bath temperature was examined as a parameter, the minimum total mass gain was obtained in a plating bath temperature of 43 °C. In the second part of this study, in order to study the concentration effect of hydrazine, hydrazine concentration was increased to 15 and 20 ml/L at a bath temperature of 43 °C. It was shown that as a result of increasing the hydrazine concentration from 10 ml/L to 15 ml/L, total mass gain increased more than twice and a denser plating was obtained. On the contrary to expectations, a result less successful than in the study of 10 ml/L concentration was obtained through increasing hydrazine concentration to 20 ml/L. This study showed that bath temperature of 25 °C was too low to carry out effectively autocatalytic reaction on the activated surface. Plating bath decomposed in plating studies performed at 43 °C and 50 °C. In the studies where hydrazine concentrations were examined as a parameter, it was observed that the stability of the bath could not be maintained in each of the three baths throughout the plating time. The highest decomposition rate was also predicted for the study carried out at a hydrazine concentration of 20 ml/L. Decomposition seen at high temperatures and high hydrazine concentrations was explained as a consequence of insufficient EDTA concentrations in plating baths.     

The role of pH and boron doping on the characteristics of sol gel derived ZnO films

Undoped and boron doped ZnO films (nominal volume B/Zn ratio = 1%, 3% and 5%) were deposited onto glass substrates by the sol gel method using spin coating technique. Zinc acetate dihydrate (ZnAc), 2-methoxyethanol and monoethanolamine (MEA) were used as a starting material, solvent and stabilizer, respectively. Trimethyl borate (TMB) was used as a dopant source. The pH value of the sol was adjusted with glacial acetic acid and ammonia and it changed from acid to base in nature. The effect of pH value and B dopant on the structural, morphological and optical properties of the films was investigated. The crystalline structure and orientation of the films were investigated using XRD study. The crystallite size of the films was determined. The XRD analyses showed that the undoped ZnO film crystallinity enhanced when pH of the precursor sol was increased from 5.05 to 7.00. Surface morphology was studied by a field emission scanning electron microscope (FESEM), and the effects of the doping concentration and pH values on the microstructure of the films were investigated. The optical band gap values on the surface morphology of the films were determined. The absorption edge shifted depending on the pH values and the B dopant.     

The effects of Al doping on the optical constants of ZnO thin films prepared by spray pyrolysis method

Aluminum doped ZnO (AZO) thin films doped with different aluminum concentrations have been prepared by spray pyrolysis method onto glass substrates. The optical and structural properties of the films have been investigated by X-ray diffraction and optical characterization methods. The X-ray diffraction spectra showed that all of the thin films are of polycrystalline nature. The thin films have (002) as the preferred orientation. The optical band gaps of the films were calculated. The E _g values decrease with increasing Al doping concentration. The refractive index, the extinction coefficient, and the real and imaginary components of dielectric constant are calculated. The obtained results show that all optical parameters keep constant in the visible region, whereas in the ultraviolet region, doping concentration strongly affects the optical parameters of AZO thin films. Optical constants tend to decrease with increasing doping concentration.     

Influence of Internal and External Parameters in Temperature of Hybrid PV/T Water Collector

The combination of photovoltaic system with a thermal to form the hybrid PVT （photovoltaic thermal）, which together will generate electricity and heat. This energy depends on the input that is to say the energy of solar radiation, temperature and speed wind and output which is the operating temperature of the system. This production also depends on the mode of heat removal. The authors present in this article; a study by a numerical simulation of the thermal behavior of a prototype hybrid sensor through the development of an energy balance that involves heat exchange between the different components of the hybrid sensor, and it will allow us to study the influence of internal and external parameters on the temperature variation in the different layers of the prototype PV/T studied.     

A methodology for implementing decimator FIR filters on FPGA

This paper presents a methodology which can be used to implement any decimator symmetric/antisymmetric (S/A) finite impulse response (FIR) filter. Two varieties are developed: a classic distributed arithmetic (CDA) based and a modified distributed arithmetic (MDA) based one. Both exploit the polyphase structure and the symmetry/antisymmetry of the filter and are evaluated in terms of area efficiency, speed and power consumption. The choice of the algorithm depends on the performance metrics targeted. The methodology has been applied to implement the filter bank CDF9/7 which constitutes a one dimensional (1D) and one level discrete wavelet transform (DWT). The filter bank also known as the bior4.4 biorthogonal wavelets is recommended by the JPEG2000 standard for lossy compression of images and video. The architecture has been implemented on an Altera field programmable gate array (FPGA) and the simulations run in Matlab, Modelsim and Altera Quartus II. The results prove the efficiency of the algorithms and show the tradeoff between the area occupied, the throughput and the power consumption.     

The effects of substrate temperature on refractive index dispersion and optical constants of CdZn(S0.8Se0.2)2 alloy thin films

The effect of substrate temperature on optical properties of CdZn(S_0.8Se_0.2)₂ thin films deposited onto glass substrates by the spray pyrolysis method has been investigated. The average optical transmittance of the films was over 74% in the visible range. The optical absorption studies reveal that the transition is direct with band gap energy values between 2.86 and 2.92 eV. The optical constants such as refractive index and dielectric constant of the films were determined. According to variation of the substrate temperature, the important changes in absorption edge, refractive index and the dielectric constant were observed. The refractive index dispersion curves of the films obey the single oscillator model and oscillator parameters changed with substrate temperature. The most significant result of the present study is to indicate that substrate temperature of the film can be used to modify in the optical band gaps and optical constants of CdZn(S_0.8Se_0.2)₂ thin films.     

Comparison of antioxidant capacity of cow and ewe milk kefirs

This research aimed to evaluate the effects of using either grain or commercial starter culture on the antioxidative capacity of cow and ewe milk kefirs. The antioxidant capacity of kefir samples during fermentation and 21 d of storage was assessed by using 3 assays: 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical cation decolorization; 2,2-diphenyl-1-picrylhydrazyl (DPPH^?) radical scavenging activity assay; and Fe⁺³-reducing power (ferric reducing antioxidant power assay, FRAP). Vitamin E and β-carotene contents were also quantified. All kefir samples exhibited varying values for DPPH, ABTS, and FRAP assays depending on the starter culture and milk type. Vitamin E and β-carotene contents were similar in all kefir samples during storage. The results of this study suggest that milk type (cow or ewe) and culture type (kefir grains or commercial starter) were the significant parameters for the antioxidative activity of kefir.