Red luminescence from hydrothermally synthesized Eu-doped ZnO nanoparticles under visible excitation

Eu-doped ZnO nanoparticles were synthesized by hydrothermal method. The Eu-dopant concentration has been varied by varying the amount of Eu-dopant concentration. These nanoparticles were structurally characterized by X-ray diffraction, transmission electron microscopy and selected area electron diffraction and it confirms the formation of nanoparticles having standard wurtzite structure. Photoluminescence studies show that these nanoparticles exhibit a sharp red luminescence due to the intra-4f transitions of Eu³⁺ ions at an excitation of 397 nm and 466 nm. Luminescence quenching is observed in the nanoparticles as the Eu-dopant concentration increases. Incorporation of Eu in the nanoparticles was confirmed by the energy dispersive X-ray studies.     

Optimal Selection of Predictor Variables in Statistical Downscaling Models of Precipitation

Two screening methods aimed at selection of predictor variables for use in a statistical downscaling (SD) model developed for precipitation are proposed and evaluated in this study. The SD model developed in this study relies heavily on appropriate predictors chosen and accurate relationships between site-specific predictand (i.e. precipitation) and general circulation model (GCM)-scale predictors for providing future projections at different spatial and temporal scales. Methods to characterize these relationships via rigid and flexible functional forms of relationships using mixed integer nonlinear programming (MINLP) formulation with binary variables, and artificial neural network (ANN) methods respectively are developed and evaluated in this study. The proposed methods and three additional methods based on the correlations between predictors and predictand, stepwise regression (SWR) and principal component analysis (PCA) are evaluated in this study. The screening methods are evaluated by employing them in conjunction with an SD model at 22 rain gauge locations in south Florida, USA. The predictor variables that are selected by different predictor selection methods are used in a statistical downscaling model developed in this study to downscale precipitation at a monthly temporal scale. Results suggest that optimal selection of variables using MINLP and ANN provided improved performance and error measures compared to two other models that did not use these methods for screening the variables. Results from application and evaluations of screening methods indicate improved downscaling of precipitation is possible by SD models when an optimal set of predictors are used and the selection of the predictors is site-specific.     

Study of Shubnikov-de Haas oscillations and measurement of hole effective mass in compressively strained InXGa1−XSb quantum wells

In_XGa_1−XSb has the highest hole mobility amongst all III-V semiconductors which can be enhanced further with the use of strain. The use of confinement and strain in In_XGa_1−XSb quantum wells lifts the degeneracy between the light and heavy hole bands which leads to reduction in the hole effective mass in the lowest occupied band and an increase in the mobility. We present magnetotransport measurements on compressively strained In_XGa_1−XSb and GaSb quantum wells. Hall-bar and Van de Pauw structures were fabricated and Shubnikov-de Haas oscillations in the temperature range of T = 2-10 K for magnetic fields of B = 0-9 T were measured. The reduction of effective hole mass with strain was quantified. These results are in excellent agreement with modeling results from band structure calculations of the effective hole mass in the presence of strain and confinement.     

Interaction of energetic clusters (Au3, Au400 and C60) with organic material and adsorbed gold nanoparticles

Using molecular dynamics simulations (MD), this contribution compares the interaction of three energetic clusters (Au₃, Au₄₀₀ and C₆₀) with a hybrid surface of crystalline polyethylene (PE) covered by a layer of gold nanoparticles. This model system mimics the situation encountered in metal-assisted secondary ion mass spectrometry. The chosen impact points are representative of the PE surface, the metal particles and the frontier between the metal and the polymer. The simulations show the differences between the impact over the Au nanoparticle and the polymer surface, in terms of projectile penetration, crater formation and sputtering yield of PE and gold species. For C₆₀ and Au₃ projectiles, a simple correlation is found between the quantity of energy deposited in the top polymeric layers and the quantity of sputtered polymer material, including all the impact points. The results obtained with Au₄₀₀ do not fit on this line, indicating that other physical parameters are prevalent. The mechanistic view of the interaction provided by the MD helps explain the differences. In short, while C₆₀ and Au₃ quickly break apart, creating energetic recoils and severing many bonds in the surface, Au₄₀₀, with the largest total momentum by far (∼10 times larger than the others) and the lowest energy per atom (25 eV), tends to act and implant in the solid as a single entity, pushing the polymeric material downwards and breaking few bonds in the surface.     

Numerical modelling of isothermal release and distribution of helium and hydrogen gases inside the AIHMS cylindrical enclosure

Hydrogen is a highly flammable gas and accidental release in confined space can pose serious combustion hazards. Numerical studies are required to assess the formation of flammable hydrogen cloud within confined spaces. In the present study, numerical investigations on the release of helium and hydrogen gases as high-velocity jets and their subsequent distribution inside an unventilated cylindrical enclosure (AIHMS facility) has been carried out as a first step towards numerical studies on hydrogen distribution in confined spaces for safety assessments. Experimental data for jet release of helium at volume Richardson number 0.1 and subsequent distribution has been used as benchmark data. Sensitivity studies on the influence of grid sizes, time-steps and turbulence models are performed. The performance of the validated numerical model is evaluated using statistical performance parameters. Similarity relations are used to determine input parameters for hydrogen jet for corresponding experimental data with helium jets. Finally, the mixing and flammability aspects of hydrogen distribution inside the enclosure are studied using four numerical indices that quantify mixing and deflagration potential of a distribution. It is concluded that the helium experiments can be used for validation of numerical models for hydrogen safety studies and any one of the similarity relationships, viz., equal buoyancy, equal volumetric flow, or equal concentration can be used for assessing the behaviour of hydrogen release and distribution within confined spaces.     

The impact of feature selection on maintainability prediction of service-oriented applications

Service-oriented development methodologies are very often considered for distributed system development. The quality of service-oriented computing can be best assessed by the use of software metrics that are considered to design the prediction model. Feature selection technique is a process of selecting a subset of features that may lead to build improved prediction models. Feature selection techniques can be broadly classified into two subclasses such as feature ranking and feature subset selection technique. In this study, eight different types of feature ranking and four different types of feature subset selection techniques have been considered for improving the performance of a prediction model focusing on maintainability criterion. The performance of these feature selection techniques is evaluated using support vector machine with different types of kernels over a case study, i.e., five different versions of eBay Web service. The performances are measured using accuracy and F-measure value. The results show that maintainability of the service-oriented computing paradigm can be predicted by using object-oriented metrics. The results also show that it is possible to find a small subset of object-oriented metrics which helps to predict maintainability with higher accuracy and also reduces the value of misclassification errors.     

Structural Properties and Ionic Conductivity of Nanocrystalline Zr5Ti7O24 Ceramic Synthesized by Autoignited Combustion Technique

Nanoparticles of Zr₅Ti₇O₂₄ ceramic have been prepared by the autoignited combustion technique. The phase purity of the ceramic was examined by x-ray diffraction method, yielding lattice parameters of a = 14.3 Å, b = 5.2 Å, and c = 5.1 Å. A narrow size distribution of the nanoparticles was determined by transmission electron microscopy with a peak at 21.55 nm. Coexistence of Zr/TiO₆ octahedra and Zr/TiO₄ tetrahedra was observed in the Raman spectrum. The optical bandgap of the ceramic was found to be 2.36 eV. The sample was pressed into a circular pellet and sintered at 1490°C, obtaining 94.7% of theoretical density. The microstructure of the sintered pellet was analyzed by scanning electron microscopy, and the elemental composition was confirmed by energy-dispersive spectrometry. Impedance spectroscopic analysis of the sample showed that ions are the main source of conduction. Two semicircles in the Cole–Cole plot provide evidence of grain and grain boundary contributions to the conductivity. The total ionic conductivity of the sample was 5.57 × 10^?1 S/m at 700°C. The activation energies of grains and grain boundaries above 500°C were 1.08 eV and 0.72 eV, respectively. Nanocrystalline Zr₅Ti₇O₂₄ ceramic is a promising material for use as an electrolyte in solid oxide fuel cells.     

Effect of zeolites on thermal decomposition of ammonia borane

Chemical hydrides due to their light weight and high storage capacity are considered to be promising hydrogen storage materials for both mobile and stationary applications. Ammonia Borane (AB) is a novel material with very high hydrogen content (19.6 wt %) per mass. The decomposition of AB takes place in three steps at desorption temperatures of about 100 °C, 140 °C and above 1000 °C respectively releasing 1 mol of hydrogen in each step. The major obstacle towards the use of AB as a hydrogen store is its irreversibility and slow kinetics. With the additives the decomposition temperature could be reduced and the kinetics can be improved. Effect of addition of Zeolites on decomposition of Ammonia Borane at different temperatures is reported in this paper. It was observed that the kinetics behaviour is greatly affected by addition of Zeolites with considerable reduction in the induction or warm-up period.     

Adsorption of Cr(III) ions using 2-(ureylenemethyl)pyridine functionalized MCM-41

Journal of Porous Materials - Modified MCM-41 material with uniform meropore channels was prepared by surfactant-directed synthesis strategy and post functionalized with 3-(triethoxysilyl)propyl...