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Poulose S.,Indian Institute of Technology Madras | Panda T.,Indian Institute of Technology Madras | Nair P.P.,Government Engineering College at Thrissur | Theodore T.,Institute of Chemical Technology
Journal of Nanoscience and Nanotechnology | Year: 2014

Metal nanoparticles have unique optical, electronic, and catalytic properties. There exist well-defined physical and chemical processes for their preparation. Those processes often yield small quantities of nanoparticles having undesired morphology, and involve high temperatures for the reaction and the use of hazardous chemicals. Relatively, the older technique of bioremediation of metals uses either microorganisms or their components for the production of nanoparticles. The nanoparticles obtained from bacteria, fungi, algae, plants and their components, etc. appear environment-friendly, as toxic chemicals are not used in the processes. In addition to this, the formation of nanoparticles takes place at almost normal temperature and pressure. Control of the shape and size of the nanoparticles is possible by appropriate selection of the pH and temperature. Three important steps are the bioconversion of Ag+ ions, conversion of desired crystals to nanoparticles, and nanoparticle stability. Generally, nanoparticles are characterized by the UV-visible spectroscopy and use of the electron microscope. Silver nanoparticles are used as antimicrobial agents and they possess antifungal, anti-inflammatory, and anti-angiogenic properties. This review highlights the biosynthesis of silver nanoparticles by various organisms, possible mechanisms of their synthesis, their characterization, and applications of silver nanoparticles. © 2014 American Scientific Publishers.

Kamath P.M.,Government Engineering College at Thrissur | Kamath P.M.,Indian Institute of Technology Madras | Balaji C.,Indian Institute of Technology Madras | Venkateshan S.P.,Indian Institute of Technology Madras
International Communications in Heat and Mass Transfer | Year: 2014

This paper reports the results of experimental investigations of convective heat transfer in a vertical channel lined up with three discrete heat sources on one vertical wall of a vertical channel and cooled by air. The channel is filled with a metallic foam. The objective of the study is to investigate the heat transfer enhancement with the presence of metal foam and to identify the ratio of heat sources so as to achieve near isothermality of the heat source surfaces. The results of the study show that with the presence of a metal foam over the discrete heat sources the temperature variation among the heat sources drastically reduces which can be further optimized using a coupled artificial neural network (ANN)-genetic algorithm (GA) hybrid technique for a given velocity and heat input condition. A sensitivity analysis of the optimum thus obtained was also carried out to study the effect of inlet velocity and heat input on the isothermality of the heater surfaces. © 2014 Elsevier Ltd.

Ahammed M.M.,Sardar Vallabhbhai National Institute of Technology, Surat | Meera V.,Government Engineering College at Thrissur
Journal of Hazardous Materials | Year: 2010

The present study was conducted to compare the performance of a dual-media filter consisting of manganese oxide-coated (MOCS) and iron hydroxide-coated sand (IOCS) with that of IOCS filter and uncoated sand filter in treating water contaminated by microorganisms, heavy metals and turbidity with a view to its use in simple household water purification devices in developing countries. Long-duration column tests were conducted using two natural waters namely, roof-harvested rainwater and canal water. Performance of the filters showed that dual-media filter was more efficient in removing bacteria and heavy metals compared to IOCS filter, while uncoated sand filter showed very poor performance. The average effluent levels for dual-media filter when tested with rainwater were: turbidity 1.0 ± 0.1. NTU; total coliforms 3 ± 2. MPN/100. mL; heterotrophic plate count 170 ± 20. CFU/mL; zinc 0.06 ± 0.01. mg/L, while that for IOCS filter were: turbidity 1.0 ± 0.1. NTU; total coliforms 4 ± 2. MPN/100. mL; heterotrophic plate count 181 ± 37. CFU/mL; zinc 0.20 ± 0.07. mg/L. Similar results were obtained for canal water also. Up to 900 bed volumes (BV) could be treated without affecting the efficiency in the case of rainwater, while the filter operation had to be terminated after 500. BV due to excessive headloss in the case of canal water. The study thus showed the potential of the dual-media for use in low-cost household water filters for purification of natural waters. © 2010 Elsevier B.V.

Prasanthkumar K.P.,Government Engineering College at Thrissur | Alvarez-Idaboy J.R.,National Autonomous University of Mexico
RSC Advances | Year: 2014

Oxidation of 2-aminopyrimidine (2Apy) by hydroxyl radicals (•OH) in aqueous medium has been studied using pulse radiolysis coupled to optical absorption and M05-2X/6-311++G(d,p) level DFT calculations aimed at elucidation of the reaction mechanism. The rate constant (k) 2.76 ± 0.06 × 109 M-1 s-1 determined by the pulse radiolysis method for the title reaction at neutral pH reflects a diffusion-controlled process. The maximum absorption wavelength (λmax 330 and 550 nm) of transient(s) remains intact in the pH range 10.5-7. Radical adduct formation (RAF) reactions with N1 (N3 is an identical site), C2, C4 (C6 is an identical site) and C5 as the target atoms, hydrogen transfer (HT) reaction with amino group and single electron transfer (SET) of 2Apy with •OH were modelled theoretically. Lowest Gibbs free energy of activation (ΔG ≠) in solution, 1.72 kcal mol-1, was calculated for RAF at C5; the computed k value for this process is 2.0 × 109 M-1 s-1 using the transition state theory (TST). The relative yield (87%) of this major product predicted from the computed k value shows excellent agreement with the results of the pulse radiolysis redox titrations. Subsequently, the possibilities for other RAF reactions, HT and SET were ruled out. As an extension to the above work, we have carried out a theoretical survey of the reactivity of •OH with 4-aminopyrimidine (4Apy); wherein the RAF at C5 is proposed as the most probable mechanism with a ΔG≠ of 2.15 kcal mol-1. © 2014 The Royal Society of Chemistry.

Sudharshan Kaarthik R.,Indian Institute of Science | Gopakumar K.,Indian Institute of Science | Mathew J.,Government Engineering College at Thrissur | Undeland T.,Norwegian University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2015

Multilevel inverters with dodecagonal (12-sided polygon) voltage space vector structure have advantages, such as complete elimination of fifth and seventh harmonics, reduction in electromagnetic interference, reduction in device voltage ratings, reduction of switching frequency, extension of linear modulation range, etc., making it a viable option for high-power medium-voltage drives. This paper proposes two power circuit topologies capable of generating multilevel dodecagonal voltage space vector structure with symmetric triangles (for the first time) with minimum number of dc-link power supplies and floating capacitor H-bridges. The first power topology is composed of two hybrid cascaded five-level inverters connected to either side of an open-end winding induction machine. Each inverter consists of a three-level neutral-point-clamped inverter, which is cascaded with an isolated H-bridge making it a five-level inverter. The second topology is for a normal induction motor. Both of these circuit topologies have inherent capacitor balancing for floating H-bridges for all modulation indexes, including transient operations. The proposed topologies do not require any precharging circuitry for startup. A simple pulsewidth modulation timing calculation method for space vector modulation is also presented in this paper. Due to the symmetric arrangement of congruent triangles within the voltage space vector structure, the timing computation requires only the sampled reference values and does not require any offline computation, lookup tables, or angle computation. Experimental results for steady-state operation and transient operation are also presented to validate the proposed concept. © 2014 IEEE.

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