Polygonal deformation of a metallic foil subjected to impact by an axisymmetric indenter

When a stack consisting of layers of soft elastomer and thin metallic film is subjected to low intensity impact by releasing an axisymmetric spherical indenter from a vertical height, the foils buried within the stack undergoes large deformation and fracture. The shape of the deformed area nevertheless remains circular, its radius first increases with the depth from the surface of the stack and then decreases. In contrast, here we show that the symmetry of the deformed area breaks down when instead of a smooth elastomeric layer, one with topographical patterns is used in the stack. The metallic foil deforms through a polygonal area. The size and shape of the polygonal area vary with the flexibility of foil, geometry and dimension of the patterns and the intensity of the impact. For example, for one elastomeric layer decorated with pillars arranged in a square array, the damaged area turns rectangular to hexagonal and then to octagonal with increasing severity of impact, very much similar to polygonal wetting and spreading by a liquid on a patterned substrate.     

Studies on the dehydration kinetics and rehydration of YAG precursor powder in the hydroxyhydrogel form

YAG precursor powder was prepared in the hydroxyhydrogel form. Dehydration kinetic study and rehydration experiment was carried out to know the behavior of water molecules and hydroxide bonds present in the hydroxyhydrogel network structure with temperature. Rate constants and activation energies for dehydration and dehydroxylation were evaluated by static thermogravimetry. Percent rehydration was determined at different heat treatment temperatures. The results obtained were explained, correlated to establish the thermal stability of hydroxyhydrogel network structure and finally supported by the FTIR analysis.     

The Einstein relation in nanostructured materials: simplified theory and suggestion for experimental determination

An attempt is made to study the Einstein relation for the diffusivity–mobility ratio (DMR) in quantum wells (QWs) and quantum well wires (QWWs) of tetragonal compounds on the basis of a newly formulated electron energy spectrum taking into account the combined influences of the anisotropies in effective electron mass, the spin–orbit splitting, and the presence of crystal field splitting, respectively. The results for quantum-confined III–V compounds form a special case of our generalized analysis. The DMR has also been studied for QWs and QWWs of II–VI and IV–VI materials. Taking QWs and QWWs of CdGeAs₂, InAs, CdS and PbSe as examples, it was found that the DMR increases with increasing carrier statistics and decreasing film thickness respectively in various oscillatory manners emphasizing the influence of dimensional quantizations and the energy band constants in different cases. An experimental method of determining the DMR in nanostructures with arbitrary dispersion laws has also been suggested and the present simplified analysis is in agreement with the suggested relationship. The well-known results for nanostructures with parabolic energy bands have also been obtained as special cases from this generalized analysis under certain limiting conditions.     

Evolutionary optimization of Haferman carpet fractal patterned antenna array

This article investigates radiation characteristics of a new type of fractal shaped antenna array based on Haferman carpet geometry. An iterative feed matrix eases the complexity of array factor calculation that makes the array factor suitable for the application of any evolutionary optimization techniques. It is seen that Haferman carpet array produces peak side lobe level (PSLL) better than Sierpinski carpet that produces ?10 dB PSLL at every stage of growth. Optimization techniques have been applied for array element reduction and PSLL minimization at different stages of growth. Here, PSLL is minimized by turning off array elements and also by varying inter element spacing between the array elements. The optimized version of Haferman carpet array produces better characteristics (49.38% thinning with ?20.5 dB PSLL for stage‐2, 46.3% thinning with ?22 dB PSLL for stage‐3 and 42.3% thinning with ?21dB PSLL for stage‐4) than its original counterpart in terms of reduced element count and PSLL. Numerical results for obtaining optimized array performance exploit both DE as well as PSO. A comparative study on the performance is also presented. As a whole, Haferman carpet is seen to be more effective approach than Sierpinski carpet in fractal antenna paradigm. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:719–729, 2015.     

Prediction of creep curve of HP40Nb steel using artificial neural network

Neural Computing and Applications - Simulation of creep curves using data obtained from a limited number of short-time creep tests is helpful for predicting the long-time creep life of materials by...     

Thermelectric power in ultrathin films ofA 3 II B 2 V semiconductors in the presence of a quantizing magnetic field

An attempt is made to study theoretically the thermoelectric power in ultrathin films ofA ₃ ^II B ₂ ^V semiconductors in the presence of a quantizing magnetic field by formulating a new magneto-dispersion law, within the framework ofk · p formalism incorporating the anisotropies in the band parameters. It is found, taking ultrathin films ofn-Cd₃P₂ as an example, that the same power decreases with increasing surface electron concentration and changes in an oscillatory manner with film thickness and quantizing magnetic field. In addition, the well-known results for parabolic energy bands have also obtained from our expressions as special cases.     

Exact solutions for TM modes in graded index slab waveguides

Three continuous profiles for the dielectric constant are derived, which allow exact solutions of the vector wave equation, including all terms in the gradient of the profile, for both TE and TM modes on slab waveguides. The dielectric constant has been assumed to be a scalar quantity; i.e., the medium is isotropic.     

Planar optical waveguides with arbitrary index profile: an accuratemethod of analysis

We present here an improvement of the existing modified Airy function (MAF) method. The results of our study show that the improvement gives extremely accurate propagation constants and also the modal fields for planar waveguides with arbitrary index profile     

Calculated fiber attenuation: a general method yielding stationaryvalues

A method of calculating the attenuation constant of an optical fiber under very general but weakly guiding conditions is derived. The method, based on Galerkin's formalism, allows a nonuniform and complex refractive-index profile. The real and imaginary parts of the refractive index are allowed to vary independently and arbitrarily as a function of radius. The result is the predicted complex propagation constant. The results are inherently stationary