Properties of sol–gel synthesized n-ZnO/n-GaN (0001) isotype heterojunction

The electronic and optical properties of sol–gel synthesized n-ZnO/n-GaN (0001) isotype heterojunction were reported. By incorporating ZnO–GaN with the same wurtzite structure and the similar lattice constant, a heterojunction was fabricated. The junction properties were evaluated by measuring the electrical characteristics. The n-ZnO/n-GaN heterostructure exhibits a non-ideal I–V behavior with the ideality factor greater than unity that could be ascribed to the interfacial layer, interface states and series resistance. The forward turn on voltage is about 0.7 V and the reverse breakdown voltage is more than 2 V. The optical band gaps of the ZnO film and GaN using optical absorption method were found to be 3.272 eV and 3.309 eV, respectively. The fundamental absorption edge in the film is formed by the direct allowed transitions.     

The elasto-plastic impact analysis of functionally graded circular plates under low-velocities

In this study, three-dimensional elasto-plastic analysis of functionally graded (FG) circular plates under low-velocity impact loads is presented. The FG circular plate is composed of ceramic (SiC) and metal (Al) phases, varying in a predetermined fashion through the plate thickness. The elasto-plastic behaviour of the FG circular plate is described by the TTO model. In the analyses, the ceramic phase is taken to be an isotropic elastic material whereas the metal phase is taken to be elasto-plastic material in accordance with the TTO model. The locally effective material properties were evaluated using homogenization method which is based on the Mori–Tanaka scheme. The effects of compositional gradient exponent and impactor velocity on the elasto-plastic impact response of the FG circular plates are investigated, and results are presented graphical form. The compositional gradient exponent and impactor velocity have significant effects on the elasto-plastic impact response of the FG circular plates. The elasto-plastic impact response of FG circular plates is similar to those of homogeneous plates. Therefore, the TTO model can be used to describe the mechanical behaviour of FG plates beyond the elastic range, assuming that the material response is essentially governed by the spreading of plasticity in the metal phase.     

Adsorptive removal of phenol from aqueous solutions on activated carbon prepared from tobacco residues: equilibrium, kinetics and thermodynamics

This study consists of producing high surface area activated carbon from tobacco residues by chemical activation and its behavior of phenol removal from aqueous solutions. K(2)CO(3) and KOH were used as chemical activation agents and three impregnation ratios (50, 75 and 100 wt.%) were applied on biomass. Maximum BET surface areas of activated carbons were obtained from impregnation with 75 wt.% of K(2)CO(3) and 75 wt.% of KOH as 1635 and 1474 m(2)/g, respectively. Optimum adsorption conditions were determined as a function of pH, adsorbent dosage, initial phenol concentration, contact time and temperature of solution for phenol removal. To describe the equilibrium isotherms the experimental data were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models. Pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were used to find out the kinetic parameters and mechanism of adsorption process. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated for predicting the nature of adsorption. According to the experimental results, activated carbon prepared from tobacco residue seems to be an effective, low-cost and alternative adsorbent precursor for the removal of phenol from aqueous solutions.     

Insights into research on phytochemistry and biological activities of Prunus armeniaca L. (apricot)

Prunus armeniaca L. (Rosaceae) is an important medicinal edible plant species commonly known as “apricot”. Apricot is one of the most delicious and commercially traded fruits in the world. The plant is rich in mono- and polysaccharides, polyphenols, fatty acids and sterol derivatives, carotenoids, cyanogenic glucosides, and volatile components due to its appealing smell. P. armeniaca has been also investigated for various biological activities such as antimicrobial, antimutagenic, inhibitory activity against several enzymes, cardioprotective, anti-inflammatory and antinociceptive as well as antioxidant activity. Among these activities, antioxidant activity of apricot has been studied extensively and the plant displayed a high antioxidant effect in both in vitro and in vivo test systems. In this review, the relevant literature summary is given on phytochemistry and biological activity reports published on apricot. The literature survey for this review was performed using the key words “Prunus armeniaca and apricot” through the search Scopus, ScienceDirect, Pubmed, and Web of Science data bases between 1950 and 2010.     

Determining optimum tilt angles and orientations of photovoltaic panels in Sanliurfa, Turkey

The performance of a photovoltaic (PV) panel is affected by its orientation and its tilt angle with the horizontal plane. This is because both of these parameters change the amount of solar energy received by the surface of the PV panel. A mathematical model was used to estimate the total solar radiation on the tilted PV surface, and to determine optimum tilt angles for a PV panel installed in Sanliurfa, Turkey. The optimum tilt angles were determined by searching for the values of angles for which the total radiation on the PV surface was maximum for the period studied. The study also investigated the effect of two-axis solar tracking on energy gain compared to a fixed PV panel. This study determined that the monthly optimum tilt angle for a PV panel changes throughout the year with its minimum value as 13° in June and maximum value as 61° in December. The results showed that the gains in the amount of solar radiation throughout the year received by the PV panel mounted at monthly optimum tilt angles with respect to seasonal optimum angles and tilt angel equal to latitude were 1.1% and 3.9%, respectively. Furthermore, daily average of 29.3% gain in total solar radiation results in an daily average of 34.6% gain in generated power with two-axis solar tracking compared to a south facing PV panel fixed at 14° tilt angle on a particular day in July in Sanliurfa, Turkey.     

Polymer-immobilized palladium supported on TiO2 (Pd-PVB-TiO2) as highly active and reusable catalyst for hydrogen generation from the hydrolysis of unstirred ammonia-borane solution

Herein we report the preparation, characterization and the catalytic use of the polymer-immobilized palladium catalyst supported on TiO₂ (Pd-PVB-TiO₂) in the hydrolysis of unstirred ammonia-borane solution. The polymer-immobilized palladium catalyst is stable enough to be isolated as solid materials and characterized by XRD, SEM, and EDX. The immobilized palladium catalyst supported on TiO₂ is found highly active, isolable, and reusable in the hydrolysis of unstirred ammonia-borane even at low concentrations and temperature. The work reported here also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 55.9 kJ/mol) and the effects of catalyst and substrate concentration on the rate for the hydrolysis of unstirred ammonia-borane solution. Maximum H₂ generation rate of ∼642 mL H₂ min⁻¹ (g Pd)⁻¹ and ∼4367 mL H₂ min⁻¹ (g Pd)⁻¹ was measured by the hydrolysis of AB at 25 °C and 55 ± 0.5 °C, respectively.     

Random forest-based tuberculosis bacteria classification in images of ZN-stained sputum smear samples

In this paper, we present a robust hybrid watermarking method applied to color images for authentication, which presents robustness against several distortions. Due to the different nature of common signal processing and geometrical attacks, two different techniques for embed a same watermark are used in this method. In the first one, the luminance component (Y) information is used to embed the watermark bit sequence into the magnitude of the middle frequencies of the Discrete Fourier Transform (DFT). In the second one, a selected region of 2D histogram composed by blue-difference and red-difference (Cb–Cr) chrominance components is modified according to the watermark bit sequence. The quality of the watermarked image is measured using the following well-known indices peak signal to noise ratio (PSNR), visual information fidelity (VIF) and structural similarity index (SSIM). The difference color of the watermarked image is obtained using the normalized color difference (NCD) measure. The experimental results show that the proposed method provides robustness against several geometric distortions, signal processing operations, combined distortions and photo editing. The comparison with the previously reported methods based on different techniques is also provided.     

Optimal temperature control of solar heating systems

Temperature control systems based on solar and wind energy differ in two important ways from existing fossil fuel systems. One is that solar systems, at least active solar systems, all have some kind of energy storage, the other is that the source of energy in a solar and wind energy system is variable and uncontrollable. Because of these added complications and the high capital investment required for solar and wind energy systems, considerably more sophisticated techniques are required for the design of those systems. In this study, a new technique is applied to the optimal control problem of solar heating systems.