Effect of TiO2 addition on microstructure and mechanical properties of alumina-based cores prepared by sol-gel method

Alumina-based ceramic cores have widespread applications especially in the investment casting of turbine blades due to chemical inertness with most of the superalloys, capability of machining in the green state, and their mechanical stability at high temperatures. The present work studied the effects of TiO₂ addition to the alumina-based cores. These cores were prepared via the sol-gel method process by mixing alumina powders with NH₄Cl and silica sol. The effects of adding different amounts of titania from 5 to 30 wt% and different sintering procedures on mechanical, physical, thermal, chemical, and microstructural features of the bodies were investigated. According to the results of rheology measurements of the slurries and flexural strength of the green bodies, the suitable amount of solid loading was 45 vol. %. The results showed that there is an optimum content for TiO₂ addition. The specimen contained 15 wt. % titania and sintered at 1400°C for 2 hours had the thermal expansion coefficient as low as 4.8 × 10⁻⁶/°C (25-900°C), suitable mechanical properties as a result of tialite formation, and apparent porosity of 28 vol. %, respectively. The result of creep deformation test showed that this specimen had near zero deformation at 1650°C.     

Highly-Directional,Highly-Efficient Solution-Processed Light-Emitting Diodes of All-Face-Down Oriented Colloidal Quantum Well Self-Assembly

Semiconductor colloidal quantum wells (CQWs) provide anisotropic emission behavior originating from their anisotropic optical transition dipole moments (TDMs). Here, solution-processed colloidal quantum well light-emitting diodes (CQW-LEDs) of a single all-face-down oriented self-assembled monolayer (SAM) film of CQWs that collectively enable a supreme level of IP TDMs at 92% in the ensemble emission are shown. This significantly enhances the outcoupling efficiency from 22% (of standard randomly-oriented emitters) to 34% (of face-down oriented emitters) in the LED. As a result, the external quantum efficiency reaches a record high level of 18.1% for the solution-processed type of CQW-LEDs, putting their efficiency performance on par with the hybrid organic-inorganic evaporation-based CQW-LEDs and all other best solution-processed LEDs. This SAM-CQW-LED architecture allows for a high maximum brightness of 19,800 cd m⁻² with a long operational lifetime of 247 h at 100 cd m⁻² as well as a stable saturated deep-red emission (651 nm) with a low turn-on voltage of 1.7 eV at a current density of 1 mA cm⁻² and a high J₉₀ of 99.58 mA cm⁻². These findings indicate the effectiveness of oriented self-assembly of CQWs as an electrically-driven emissive layer in improving outcoupling and external quantum efficiencies in the CQW-LEDs.     

Optimization of process conditions in casting aluminum matrix composites via interconnection of artificial neurons and progressive solutions

A genetic algorithm is a machine learning technique that was inspired by the analogy of biological evolution which generates solutions by repeatedly mutating and recombining parts of the best currently known solutions. In order to model and optimize the properties of A356 matrix composites, a finite element method (FEM) with artificial neural network based genetic algorithm (ANN-GA) model was developed. The tribological and mechanical properties of the aluminum matrix composite were also experimentally investigated. The results verified the accuracy of the proposed model to find the optimal process conditions in aluminum matrix composite materials.     

Spectrophotometric determination of some vic-diol containing drugs using ion-exchange resins

Periodic acid and its salts have been widely used for the quantitative oxidation of vic-diol containing compounds including carbohydrates and catecholamine drugs. The advantage of using a polymeric resin (periodate form) over free periodate ions is that the resin quantitatively retains both unconsumed periodate ions and the iodate ions produced in the oxidation and, hence, enables one to undertake further studies on the structural, synthetic or preparative work. The resin (periodate form) was found to be a clean and sensitive chromogenic reagent for the spectrophotometric determination of some catecholamine drugs. The calibration graphs of absorption versus concentration in the range studied (5-50 ppm) were linear.     

Effect of grain refinement on the microstructure and tensile properties of thin 319 Al castings

The structural examinations and tensile properties of thin-section Al castings (319 Al alloy) have been investigated by applying a pattern with different cross sections (2–12 mm). Al–5Ti–1B and Al–5Zr grain refiners were added to the molten Al alloy to produce different levels of Ti (0.01%, 0.05%, 0.1% and 0.15%) and Zr (0.05%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%) in the castings. From macrostructural studies, it was found that Al–5Zr is less effective in grain refining of 319 alloy in comparison with Al–5Ti–1B master alloy. The optimum levels of grain refiners were selected for determination of tensile properties. T6 heat treatment was applied for selected specimens before tensile testing. Further structural results also showed that thinner sections are less affected by grain refiners. This observation was found to be in a good agreement with tensile test results, where tensile properties of the base and grain refined alloys did not show considerable differences in thinner sections (<6 mm).     

Effect of long‐term exposure of silver nanoparticles on growth indices,hematological and biochemical parameters and gonad histology of male goldfish (Carassius auratus gibelio)

Studying the impact of emerging pollutants such as nanoparticles is necessary to reveal the adverse effect. In this study, the effects of silver nanoparticles (Ag‐NPs) on hematological, biochemical, and gonad histopathological indices of male goldfish were examined. Sublethal toxicity were calculated based on acute toxicity and three dosages were selected. Live specimen of Carassius auratus gibelio larval were treated in 1, 2, and 3 ppm Ag‐NP with one control group. Blood and tissue samples were extracted after 6 months exposure to sublethal concentrations. Results showed that Ag‐NPs have reduced growth rate and effected on all blood indices significantly. Biochemical analysis revealed that Ag‐NPs significantly reduced blood glucose and total protein than in comparison to the control group and caused significantly differences in the concentrations of serum cholesterol (p < .05). Furthermore, histological observation of intestine after 6 months exposure showed definite alterations in tissue and maximum hypertrophy injuries were found after long‐term exposure to 3 ppm Ag‐NPs concentration. In addition, indicated that long‐term exposure to Ag‐NPs postponed sexual maturity in male gibel carp.     

Effects of hydrogen level and cooling rate on ultimate tensile strength of Al A319 alloy

The present study investigated the effects of initial Hydrogen level and cooling rate on ultimate tensile strength of commercial Al-A319 alloys. Three hydrogen levels (0.01, 0.2, and 0.41 mL/100 grams of melt) and five cooling rate were studied. Total of 45 tensile test bars was prepared (three hydrogen levels × five cooling rate × three repeats). The UTS of the samples was determined though uniaxial tension tests. Furthermore, the microstructures of the samples were studied by standard metallographic technique and image analysis software. Finally the relationship between UTS and microstructurai features—SDAS and fraction of porosity (Fp%)—of the alloys was investigated. Results of tensile test revealed: (i) UTS of the alloy decreased with increasing of hydrogen level or decreasing of cooling rate and (ii) Increasing of cooling rate beyond a certain value increased the UTS of the alloy significantly. Results of image analysis showed that the Fp% increased with increasing of hydrogen level and decreasing of cooling rate. Finally a Matrix Index [= ?SDAS (μm) ? 68.7 Ln (Fp%) + 275] was defined to correlate the tensile strength and microstructurai features of the alloy. It was shown that the UTS of the alloys had a linear dependence on matrix index according the below equation: $UTS(MPa) = 0.916M.I. + 265.17R^2 = 0.95$      

Flood Frequency Analysis of Interconnected Rivers by Copulas

Flood frequency analysis (FFA) considering the confluence of interconnected rivers is important for hydraulic structures (such as dams or diversions) design, but it has received little attention. This study develops a copula-based method for FFA and quantile estimation considering the confluence of two interconnected rivers, along with the uncertainty estimation by a nonparametric bootstrapping algorithm. Flood probability distribution and return periods are estimated for the two rivers by mapping from bivariate to univariate peak flow quantile estimation. The methodology is applied to the case study of Qezel Ozan and Shahrud Rivers which merge to one of the largest reservoir dams in Iran: Sefidrud (Manjil) dam. According to the results from Peak flow records from Gilvan station (GPF) at Qezel Ozan River and from Loshan station (LCF) at Shahrud River, Gaussian copula with Weibull and gamma margins fits best. Also, it shows that some peak flow quantiles with the same magnitudes have a different probability of occurrences at the confluence of the rivers, and the bivariate estimation uncertainty usually plays an important role in FFA. These findings suggest the use of bivariate instead of univariate distributions to the peak flows at the confluence of interconnected rivers, in which the sampling uncertainty should be considered.