Effect of trace additions of Sn on microstructure and mechanical properties of Al–Cu–Mg alloys

The work is aimed at investigating the influence of trace additions of Tin (Sn) on the microstructure, mechanical properties and age-hardening behavior of Al–6.2%Cu–0.6%Mg alloy system. Al–6.2%Cu–0.6%Mg alloys containing varying weight percentages (from 0 to 0.1 wt.%) of Sn were prepared by casting technique. The mechanical properties and microstructure of these alloys were investigated in the as-cast as well as different heat treated conditions. The composition of the different phases present in the microstructure was determined by energy dispersive X-ray (EDS) analysis. The average grain size of the annealed alloy was found to be maximum with trace content of 0.06 wt.% Sn. The hardness and strength of the alloy increased but the ductility reduced with increase in Sn content up to 0.06 wt.%. Precipitation hardening behavior of the alloys was investigated by analyzing the aging time required to attain the peak hardness value. Addition of trace percentage of Sn was observed to have no significant influence on the peak ageing time of the investigated alloy system.     

Spontaneous fracture of growing precipitates with large misfit strain

Precipitates that form as a result of phase transformation are studied with regard to mechanical behaviour and initiation of internal cracks. The focus is on precipitates occupying a larger volume than the surrounding matrix. Further the study is restricted to precipitates growing by incorporating material transformed from being matrix material to the phase of the precipitate. The phase transformation is here treated as a simple homogeneous swelling. The classical solutions for expanding inclusions predict that the inclusion becomes subjected to a constant homogeneous hydrostatic compression. During the process analysed here, added transformed material progressively relieve the compressive stress in the interior of the precipitate. As the process continues the stresses change from compression to tension in both radial and tangential directions in the centre of the precipitate. Further, growth of cracks in precipitates with poor fracture mechanical properties are studied. To simplify the analysis it is assumed that the fracture toughness is insignificant. The prediction is that around a third of the precipitate will fracture. The presence of a crack only has an insignificant effect on the load exerted by the swelling precipitate on the matrix.     

PSKA: Usable and Secure Key Agreement Scheme for Body Area Networks

A body area network (BAN) is a wireless network of health monitoring sensors designed to deliver personalized healthcare. Securing intersensor communications within BANs is essential for preserving not only the privacy of health data, but also for ensuring safety of healthcare delivery. This paper presents physiological-signal-based key agreement (PSKA), a scheme for enabling secure intersensor communication within a BAN in a usable (plug-n-play, transparent) manner. PSKA allows neighboring nodes in a BAN to agree to a symmetric (shared) cryptographic key, in an authenticated manner, using physiological signals obtained from the subject. No initialization or predeployment is required; simply deploying sensors in a BAN is enough to make them communicate securely. Our analysis, prototyping, and comparison with the frequently used Diffie–Hellman key agreement protocol shows that PSKA is a viable intersensor key agreement protocol for BANs.      

Optimization of support insulators used in HV systems using support vector machine

In this paper support vector machine (SVM) has been used for optimization of electric field along the support insulators used in high voltage (HV) systems. To illustrate the effectiveness of SVM in optimizing electric field problems, two axi-symmetric cases have been considered one having an insulator with a contour that is quarter ellipse and the second one having a porcelain core solid insulator. The training and the test data for the SVM have been prepared by electrostatic field computation using indirect boundary element method (BEM). It is observed that once the SVM is trained it is able to give results with mean absolute error of less than 1.5% when compared with the analytically obtained results. The SVM designed for insulator contour optimization is first trained with the results obtained from electric field computation for some predetermined contours of the arrangements under consideration. Then the trained SVM is used to produce an optimized insulator contour in such a way that the desired stress distribution can be obtained on the insulator surface. The results obtained from the present study show that the trained SVM is adequately efficient to optimize insulator contours in order to have the desired stress distribution along the insulator surface     

Effect of agglomeration during coprecipitation: Delayed spinellization of magnesium aluminate hydrate

Precipitation of magnesium aluminate hydrate with faster addition of ammonia at desired pH causes agglomeration. Agglomerated powder, without any further treatment, on calcination forms intermediate compounds at low temperatures (≤ 900°C). The intermediate compounds on further heat treatment (≥ 1000°C) decompose into MgO, MgAl₂O₄ and α-Al₂O₃. Effect of agglomeration and absorption of foreign ions such as Cl⁻, SO₄²⁻, and NH₄⁺ in complex compounds probably cause loss of Al³⁺ and Mg²⁺ ions during heat treatment, and stoichiometry changes. Powders prepared by continuous method with better control of process parameters than batch process yields better spinellization.     

Circularly polarized spin current assisted fast resonant switching in magnetic tunnel junctions with perpendicular anisotropy

We propose a mechanism to substantially enhance spin transfer torque induced switching in perpendicular anisotropy magnetic tunnel junctions. Our method is based on injecting an additional assisting DC current with circular spin polarization into a magnetic free layer at frequencies that are resonant with its normal ferromagnetic resonance frequencies. We observe 80 % reduction in switching delays at constant switching currents and 2× improvement in critical switching current density. Spin current polarization chirality and spin polarization efficiency dependencies are investigated. Further, a device structure to experimentally realize the mechanism proposed in this letter is presented.     

Development and characterization of gelatin‐based hydrogels,emulsion hydrogels,and bigels: A comparative study

This study was designed to examine the physicochemical and electrical properties of gelatin‐based hydrogels, emulgels, and bigels. The chemical studies suggested an increase in hydrogen bonding in the emulgel and bigel when sesame oil (SO; representative vegetable oil) and SO organogel (OG; representative OG) were incorporated within the gelatin matrix. The emulgel and bigel showed better mechanical properties and higher electrical impedances compared to the hydrogel. The hydrogel showed similar swelling at pH 1.2 and 7.2. The swelling of the emulgel and bigel was higher at pH 7.2. The formulations were found to be highly hemocompatible; this indicated their biocompatible nature. Ciprofloxacin, a model antimicrobial drug, was incorporated within the formulations. The release of the drug was found to be diffusion‐mediated. The antimicrobial efficiency of all of the drug‐loaded formulations was found to be equivalent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41502.     

γ Irradiation effects on optical,thermal, and mechanical properties of polysulfone/MWCNT nanocomposites in argon atmosphere

Polymer‐based composites find use in many nuclear and space application for their ease of fabrication, tailor made properties and light weight. Certain polymers like PTFE, unfilled polyesters and polyamides are prone to degradation in presence of high energy radiation while polymers like epoxies, polyimides, and poly‐ether ether ketone have good stability to ionizing radiation. Incorporation of fillers like carbon nanotubes (CNTs) is likely to improve the radiation resistance of the polymers. In this work, polysulfone (PSU)‐based nanocomposites were fabricated using multiwalled carbon nanotube (MWCNT) by solution mixing process. The morphology of the PSU/ MWCNT nanocomposites films were studied using Field Emission Scanning Electron Microscopy (FESEM). The prepared films were subjected to γ radiation in an argon environment (to avoid the effect of air/oxygen). Different techniques were used to understand the radiation‐induced changes. Gel Permeation Chromatography (GPC) traces of neat PSU before and after exposure to radiation shows a decrease in molecular weight. Infrared spectroscopy shows changes in chemical structure. Differential Scanning Calorimetry (DSC) thermograms reveal dose‐related changes. For neat PSU, a decrease in T_g was observed with increase in dose. For PSU/ MWCNT nanocomposites, the increase in MWCNT content and dose (up to 1.5 MGy) increased the T_g. Thermo Gravimetric Analysis (TGA) showed a marginal decrease in thermal stability for pristine PSU as well as PSU/MWCNT nanocomposites with irradiation. Tensile strength increased with increasing MWCNT content but decreased with dose. Elongation at break decreased with MWCNT content as well as radiation dose. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42017.     

Twin jets in cross-flow

An experimental study and numerical investigation of thermal mixing are carried out on tandem twin jets in cross flow. Experiments were carried out for velocity ratios 1, 2 and 4 for 15 °C temperature difference between main pipe and jet fluid. Velocity and temperature fields are measured using Hot Film Anemometer (HFA). Three dimensional steady state Computational Fluid Dynamics (CFD) simulations have been carried out to predict the velocity and temperature fields. The predicted velocity and temperature fields are in good agreement with the experimental measurements. Temperature fluctuations have been predicted using temperature variance model. The effect of jet spacing for different velocity ratios is studied. For jet spacing equal to twice the jet diameter, both the jets influence each other. Increase in the jet spacing decreases the effect of jets on each other.     

Studies and characterization of RESOL/VAc–EHA/HMMM IPN systems in aqueous medium

Resol was solution‐blended with vinyl acetate‐2‐ethylhexyl acrylate (VAc–EHA) resin in an aqueous medium, in varying weight fractions, with hexamethoxymethylmelamine (HMMM) as a crosslinker and the data were compared with a control. The present work was aimed to obtain an optimum combination of high‐temperature resistance by synthesis of an interpenetrating network (IPN) of the resins. The control gave a semi‐IPN system, in which the resol crosslinked, while the acrylic did not, whereas the blend, where HMMM was the crosslinker, gave a full‐IPN system. FTIR spectra of the blends of resol/VAc–EHA/HMMM indicated the formation of new stretching, which was generated due to crosslinking reactions among VAc–EHA and the crosslinker HMMM. TGA showed that, with an increase in the VAc–EHA percent in semi‐IPNs, the decomposition temperature decreased gradually, whereas in case of full‐IPNs, the decomposition temperature increased with increase in the VAc–EHA percent. However, the full‐IPNs had a higher decomposition temperature than that of the semi‐IPNs, at the same resol/(VAc–EHA) ratio. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3581–3588, 2002