Polypyrrole (Ppy) was synthesized using Ferric Chloride (FeCl 3) as oxidant. The ratio of monomer to oxidant was 1:2.4. The polymerization was carried out at 5˚C. Attempts were made to increase the electrical conductivity by using various dopants viz. Lithium per Chlorate (LiClO 4), para-Toluene Sulfonate (p-TS) and Napthalene Sulfonic acid (NSA). The materials were characterized using FTIR, X-Ray diffraction and SEM. The electrical conductivity was measured by two probe method and was found to be in the range of 10 −3 to 10 −2 S/cm. Thin films of these preparations were casted on the interdigited electrodes to study the detection of gases such as ammonia and LPG. It was found that for the pure Ppy and one doped with LiClO 4 , when ammonia gas was allowed to flow in, there was a sudden increase in the current, which decreased rapidly when gas was stopped. This behavior is in contradiction to that observed in earlier investigations where Ppy was prepared by electrochemical method. However when Ppy doped with p-TS and NSA were used, the trend was reversed. Similarly it was noted that for pure Ppy and one doped with LiClO 4 , p-TS and NSA there was an increase in the current when LPG gas was brought in. However the response to LPG was somewhat low as compared ammonia gas.

Silver nanoparticles were synthesized by chemical reduction method. The Ag nanoparticles (AgNP) were characterized using UV-Vis spectroscopy which shows an absorption band at 420 nm confirming the formation of nanoparticles. For any practical application of the silver nanoparticles it is necessary to stabilize it which can be done by making a composite. In the present studies three polymers were chosen such that AgNP could be put to some practical use. Polyvinyl Alcohol (PVA), Polypyrrole (Ppy) and Carboxymethyl cellulose (CMC) are important for use in textiles, electronics and food/drug technologies respectively. Polymeric composites of PVA, PPy, and CMC were prepared by mixing the aqueous solutions of the respective polymers and the colloidal suspension of preformed silver nanoparticles. Various compositions containing 1% to 5% of Ag nanoparticles were prepared. Thin films of these composites were characterized by UV-Vis spectroscopy, X-ray diffraction and Scanning electron microscopy. X-ray diffraction showed the presence of the peaks at 2θ values of 38.1°, 44.2°, 64.4 and 78.2° corresponding to cubic phase of silver metal. SEM photographs revealed the presence of Ag nanoparticles of sizes varying from 40 to 80 nm. The electrical conductivity of these materials was studied using the four probe method. The conductivity was found to increase from 10^–6 for control samples to 10^–3 S/cm after the formation of the nanocomposites

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A realization of voltage-mode transfer functions with feedforward input signal for third-order active-R filter using an oprational amplifier has been presented. This filter is useful for high frequency operation, monolithic IC implementation and is easy to design. The single circuit gives three filter functions, low pass, high pass and band pass. This filter circuit can be used for different Q and f 0 with high passband gain. This gives better stop band attenuation and sharper cutoff at the edge of the passband.

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