Discrete Fractional‐Order BAM Neural Networks with Leakage Delay: Existence and Stability Results

In this paper, a discrete model of fractional‐order bidirectional associative memory (BAM) neural networks with leakage delay is considered. Sufficient conditions are established for the existence, uniqueness and uniform stability of nontrivial solutions of the addressed model. Our approach is based on the implementation of the newly defined discrete fractional calculus, mathematical inequalities and fixed point theorems. We provide an example that supports the application of the theoretical results.     

Proton exchange membranes by grafting of styrene–acrylic acid onto FEP by preirradiation technique. I. Effect of synthesis conditions

Grafting of styrene–acrylic acid (sty–AA) polymer onto fluorinated ethylene propylene copolymer (FEP) was carried out by preirradiation of FEP with γ‐rays. Effect of reaction conditions on the degree of grafting such as total radiation dose, monomer concentration, temperature, and time of grafting has been studied. From the study, it is seen that the degree of grafting is strongly dependent on the reaction conditions. The rate dependence of 0.53 (～0.5) and 1.03 (～1) have been obtained with respect to total dose and monomer concentration, respectively indicating that radiation induced grafting follows free radical polymerization. The activation energy for the grafting in the temperature range of 60–90°C is found to be 33 kJ/mol. The results indicate that the grafting takes place by the front mechanism where the grafting starts at surface and slowly proceeds inwards by diffusion of the monomer through the swollen grafted chains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2572–2577, 2003     

Synthesis,characterization, and thermal and antimicrobial studies of newly developed transition metal–polychelates derived from polymeric Schiff base

Monomeric Schiff base derived from salicylaldehyde and 1,3‐diaminopropane was subjected to polycondensation reaction with formaldehyde and piperazine in basic medium. The resin was found to form polychelates readily with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) metal ions. The materials were characterized by elemental analysis, spectral studies (IR, ¹H‐NMR, ¹³C‐NMR, and UV–visible), magnetic moment measurements, and thermal analysis. The electronic spectra and magnetic moment measurements of the synthesized polychelates confirmed the geometry of the central metal ion. Metal–resin bonds were registered in the IR spectra of the polychelates. The thermogravimetric analysis data indicated that the polychelates were more stable than the corresponding polymeric Schiff base. All the synthesized metal–polychelates showed excellent antibacterial activities against the selected bacteria. The antimicrobial activities were determined by using the shaking flask method, where 25 mg/mL concentrations of each compound were tested against 10⁵ CFU/mL bacteria solutions. The number of viable bacteria was calculated by using the spread‐plate method, where 100 μL of the incubated antimicrobial agent in bacteria solutions were spread on agar plates, and the number of bacteria was counted after 24 h of incubation period at 37°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrochemical and XPS studies and the potential scan rate dependent pitting corrosion behavior of Zircaloy-2 in 5% NaCl solution

Electrochemical studies of Zircaloy-2 in 5% NaCl solution were carried out using polarization and electrochemical impedance spectroscopy (EIS). Scan rate dependent pitting behavior of Zircaloy-2 was observed when polarization experiments were carried out at different scan rates (5 mV/min, 50 mV/min and 500 mV/min). Polarization resistance, double layer capacitance, and the thickness of passive film were calculated from the EIS study. The slope of the Bode plot in the capacitive region showed non-ideal behaviour, suggesting formation of pits. A distribution of chloride concentration was seen at the surface of the electrode when the test solution was sampled from different parts of the sample surface and analyzed for chloride. Inclusion of chloride ions in the passive film was observed from the XPS study and the chloride concentration increases with the higher anodic polarization. The outermost layer of the passive film was rich in hydroxide and oxy-hydroxide. A bi-layer passive film structure on the alloy surface is proposed.     

Characterization of metals and salts‐based thermal energy storage materials using energy balance method

Thermal energy storage technologies minimize the imbalance between energy production and demand. In this context, latent heat storage materials are of great importance as they have a higher density of energy storage as compared with the sensible heat storage materials. The present study involves the characterization of energy storage materials using an energy balance cooling curve analysis method. The method estimates the convective heat transfer coefficient in the solidification range to characterize the phase change materials for applications in energy storage. The method is more beneficial than the Computer Aided Cooling Curve analysis methods as it eliminates baseline calculations and the associated fitting errors. Metals (Sn) and salts (KNO₃ and NaNO ₃) were used in the present work. Phase change characteristics like the rate of cooling, liquidus and solidus temperatures, time for solidification, and enthalpy of phase change were estimated for both metals and salts. It was observed that the energy balance cooling curve analysis method worked very well for metals but not well suited for low conductivity salts. Salts could not be characterized since the thermal gradient existing within the salt sample was not considered in this method.     

Chemically reactive solute transfer in a boundary layer slip flow along a stretching cylinder

This paper presents the distribution of a solute undergoing a first order chemical reaction in an axisymmetric laminar boundary layer flow along a stretching cylinder. Velocity slip condition at the boundary is used instead of no-slip condition. Similarity transformations are used to convert the partial differential equations corresponding to momentum and concentration into highly nonlinear ordinary differential equations. Numerical solutions of these equations are obtained by the shooting method. The velocity decreases with increasing slip parameter. The skin friction as well as the mass transfer rate at the surface is larger for a cylinder than for a flat plate.     

Electroinitiated copolymerization of N-vinylcarbazole and α-methylstyrene in a mixed biphasic medium

The electroinitiated copolymerization of N-vinylcarbazole and α-methylstyrene has been studied using a mixed biphasic system in which formamide together with some added electrolyte has been used as the polar phase and the monomer in bulk form or its solution in a nonpolar solvent as the nonpolar phase. The copolymer has been characterized by elemental analysis, and infrared and nuclear magnetic resonance spectroscopy. Molecular weights obtained from gel permeation chromatography were in the range of 20–25 × 10³. Generally the copolymer yield increased with increased applied current density. The effect of various other parameters such as dependence of copolymer yield on concentration of electrolyte and comonomer, temperature, and time of electrolysis have also been examined. The locus of polymerization is the anode compartment and a plausible mechanism based on the electrochemical formation of a radical-cation and a dication has been suggested.     

The properties of bismuth-doped vacuum-evaporated CdS films

The effect of doping with bismuth on various properties of vacuum-evaporated CdS films was studied. The properties specifically studied were (1) the dark conductivity and photoconductivity as functions of the temperature and doping concentration, (2) the Hall mobility and carrier concentration at room temperature, (3) the thermally stimulated current and (4) the optical absorption and spectral response. It was found that on doping with bismuth the dark conductivity decreases and the photosensitivity increases significantly. These phenomena probably arise from the formation of cadmium vacancies due to bismuth doping. Studies of the Hall effect show that the carrier concentration is reduced by doping with bismuth. Investigations of thermally stimulated currents for both pure and doped films show that the trap concentrations are reduced by doping.     

Synthesis and structural characterization of calcia-stabilized tetragonal zirconia

Synthesis of calcia-stabilized tetragonal zirconia by the reaction of precipitated zirconium hydroxide with calcium oxide at ∼1400 K is described. The unit cell parameters of the oxidea ₀=b ₀=0.3644 nm,c ₀=0.5092 nm andZ=2 are in good agreement with the high-temperature tetragonal crystallographic modification of pure zirconia.