Ionic switching in mehanochemically synthesized Ag2S-Sb2S3 amorphous superionic conductor

Highly ionically conducting amorphous samples of Ag₂S·xSb₂S₃ (x=0.15−0.40) are mechanochemically synthesized and characterized by X-ray diffraction (XRD), DTA/DSC, electrical and electrochemical methods. The electrical conductivity measurements are carried out as a function of frequency (5 Hz – 13 MHz) and temperature (300 – 380 K). While the ac conductivity of x=0.40 composition obeys the well-known power law σ (ω)=σ (0) + A ωⁿ over the whole frequency range, the x=0.30 sample obeys the above relation only at lower temperatures. The compositions x=0.20 and 0.15 do not follow the famous dispersion relation at higher (MHz) frequencies. The conductivity isotherms of these a-SICs do not superimpose upon application of Summerfield scaling. The scaling behaviour and the variation of ac conductivity with frequency for x=0.20 and 0.15 are explained in terms of switching from the predominantly ionic (at lower frequencies) to the predominantly electronic conduction (at higher frequencies). Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Channai, India, Nov. 28–30, 2003.     

Effect of finite ion temperature on modulational instability of ion-acoustic waves

A nonlinear Schrödinger equation for ion-acoustic waves in a collision free plasma, consisting of warm ions and hot isothermal electrons is derived using the KBM method. It is found that for finite ion temperature these waves are modulationally unstable only in a range of wave numbers. As the ratio of ion to electron temperature increases, the range of the unstable region decreases and shifts towards small wave numbers.     

Kinetics and mechanism of oxidation of diethyl ketone by N-bromosuccinimide

Oxidative kinetics of diethyl ketone in perchloric acid media in the presence of mercuric acetate have been studied by using N-bromosuccinimide (NBS) as oxidant in the temperature range of 25°-50°C. It has been found that the order with respect to NBS is zero while with respect to diethyl ketone and [H⁺], it is unity. Succinimide, sodium perchlorate, and mercuric acetate have an insignificant effect on the reaction rate, while the dielectric effect was negative. A solvent isotope effect (k0_D2O/k0_H2O = 1.6–1.8) at 35°C has been observed. On the basis of the available evidences a suitable mechanism consistent with the experimental results has been proposed in which it is suggested that the mechanistic route for NBS oxidation in an acidic medium is through the enol form of the ketone. The magnitude of the solvent effect also supports the mechanism. Various activation parameters have been calculated, and the 1,2-dicarbonyl compound has been identified as the end product of the reaction.     

Bianchi Type-III Cosmological Models with Gravitational Constant G and the Cosmological Constant ∧

Einstein field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for the Bianchi type-Ⅲ universe by assuming conservation law for the energy-momentum tensor. Exact solutions of the field equations are obtained by using the scalar of expansion proportional to the shear scalar θ∝σ, which leads to a relation between metric potential B = Cn, where n is a constant. The corresponding physical interpretation of the cosmological solutions are also discussed.     

Enhanced luminance efficiency of polymer light emitting diode by blending with ionic solid electrolytes

In this letter, we demonstrate that luminance efficiency of polymer light emitting diode can be significantly enhanced by adding a small amount of ionic solid electrolytes. Heterojunction polymer device, consist of MEH-PPV, C₆₀, methanofullerene([6,6}-phenyl C61-butyric acid methyl ester) PCBM and/or PEO as the active materials. It has been found that blending of ionic solid electrolytes, such as polyethylene oxide into active layer, enhances the luminance efficiency of polymer device. It is believed that the optimized polymer morphology improves carrier mobility of MEH-PPV. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Laser induced surface damage, thermal transport and microhardness studies on certain organic and semiorganic nonlinear optical crystals

N-alkyl-2,6-dimethyl-4(1H)-pyridinones, salts of 4-dimethylaminopyridine and 2-amino-5-nitropyridine are considered to be potential candidates for nonlinear optical (NLO) applications, in particular for the generation of blue-green laser radiation. Single crystals were grown following the slow evaporation technique at constant temperature. Single-shot laser-induced surface damage thresholds in the range 3–10 GW/cm² were measured using a 18 ns Q-switched Nd:YAG laser. The surface morphologies of the damaged crystals were examined under an optical microscope and the nature of damage identified. The Vicker’s microhardness was determined at a load of 98.07 mN. The thermal transport properties, thermal diffusivity (α), thermal effusivity (e), thermal conductivity (K) and heat capacity (C_p), of the grown crystals were measured by an improved photopyroelectric technique at room temperature. All the results are presented and discussed. PACS 42.70.Mp; 61.66.Hq; 67.80.Gb; 42.65.-k     

Effect of ultrasound processing on anthocyanins and color of red grape juice

Grape juice samples were sonicated with processing variables of amplitude level (24.4–61.0 μm) and treatment time (0–10 min) at a constant frequency of 20 kHz and pulse durations of 5 s on and 5 s off. A full factorial experimental design with regression modeling was employed to investigate the main effects of amplitude level and treatment time on anthocyanins and color parameters. Significant effects of sonication on major anthocyanins cyanidin-3-O-glucosides (CA), malvanidin-3-O-glucosides (MA) and delphinidin-3-O-glucosides (DA), color values (L*, a*, b*) and color index (CI) were observed. Prediction models were found to be significant (p < 0.05) with low standard errors and high coefficients of determination (R²). Model predictions for critical quality parameters of anthocyanins (CA; MA; DA), color values (L*, a*, b*), TCD and CI inactivation were closely correlated to the experimental results obtained. Significant retention of anthocyanin content in grape juice was observed for CA (97.5 %); MA (48.2 %) and DA (80.9%) during sonication. CI and other color combinations (L*a*b*, L*a*/b* and L*b*/a*) were found to be strongly correlated with anthocyanin content. This study shows that sonication could be employed for as a preservation technique for fruit juice processing where anthocyanin retention is desired.