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Biomedical subjects

D Vasudevan

Publications and source records attributed to D Vasudevan.

6 recordsLinked to original sources
PubMed2006

A rare case of Guillain-Barre syndrome with pregnancy.

Guillain-Barre syndrome is a rare neuorological disorder affecting 6-24/ 1,00,000 population during pregnancy. The case involved a 29-year-old woman conceived after 14 years of marriage presenting with 16 weeks pregnancy and clinical symptoms of Guillain-Barre syndrome. It was confirmed by nerve conduction test and patient was started on intravenous immunoglobulin. She had a rapid recovery following therapy and subsequent follow-up 3 months later showed complete recovery and healthy ongoing pregnancy. Various diagnostic and treatment options are discussed.

Adult↗
PubMed2001

Tracer-grade rhodamine WT: structure of constituent isomers and their sorption behavior.

Rhodamine WT (RWT), a fluorescent xanthene dye, is often used as a conservative tracer in aquifer characterization and as a surrogate or sorbing tracer for contaminant fate and transport. Quantitative tracing employing RWT is confounded by the presence of two major fluorescent constituents in the tracer-grade mixture. Here, we have confirmed that the two constituents are isomers of RWT, elucidated their molecular structures and their percent mass distribution in the tracer-grade mixture, and examined their individual sorption behavior onto soil solids. The energy-minimized geometry of the meta isomer indicates that it possesses a greater potential for (i) hydrophobic exclusion from bulk solution, (ii) electrostatic attraction to the solid phase, and (iii) surface complexation with surface-bound Al and Fe ions as compared with the para isomer. Hence, the meta isomer consistently sorbs to a higher extent onto the mineral phases examined. The para isomer has the potential to be a nearly conservative tracer, and the meta isomer has the potential to be a nonconservative tracer. To facilitate RWT use as a conservative tracer and comparison of tracer tests at different locations, we recommend modification of the RWT manufacturing process toward production of 100% of the para isomer. Alternatively, appropriately designed tests with tracer-grade RWT have the potential for simultaneous estimation of hydraulic parameters and contaminant fate and transport.

Absorption↗
PubMed2001

Adsorption of hydroxy pyridines and quinolines at the metal oxide-water interface: role of tautomeric equilibrium.

We have identified compound physical-chemical properties and structural criteria required to facilitate the adsorption of hydroxypyridines, quinolines, and pyrimidines onto aluminum(III), iron(III), and titanium(IV) oxides. We achieved this by measuring the adsorption behavior of a number of structurally related compounds, each with a nearly isolated variation in molecular structure, and systematically evaluating the effect of structural change on the nature and extent of adsorption. We find that the adsorption at the metal oxide-water interface is significant only when the oxo-hydroxy (keto-enol) tautomeric equilibrium in aqueous solution favors the hydroxy tautomer. Lack of adsorption of the oxo tautomer can be attributed to the absence of favorable electrostatic interactions between the compound and the surface, the absence of ligand groups capable of surface complexation, and the presence of strong intermolecular hydrogen bonding between ligand groups (carbonyl and amide) and water molecules. We find that adsorption of hydroxy tautomers with ortho-substituted cyclic N and -OH groups (such as trichloropyridinol) likely occurs via nonspecific electrostatic interactions, while non-ortho-substituted hydroxy tautomers (such as 8-hydroxyquinoline) and compounds such as (2-hydroxy-methylpyridine) likely adsorb via surface complexation. This study demonstrates that for compounds classified as tautomeric heterocycles it is imperative to accurately represent the predominant tautomer in aqueous solution so that the appropriate physical-chemical properties and reactivities are utilized in the evaluation of environmental fate.

Adsorption↗
PubMed1999

Solution-Membrane Equilibrium at Metal-Deposited Cation-Exchange Membranes: Chronopotentiometric Characterization of Metal-Modified Membranes.

Copper- and lead-deposited interpolymer cationic membranes have been prepared by electroless plating by an ion-exchange method and characterized by chronopotentiometry and cyclic voltammetry. The parameters such as transition time (tau), Itau1/2, the potential drop (E0) across these membranes immediately after the application of constant current (I), and the height of the potential jump (DeltaE) across the membrane at tau have been measured by chronopotentiometry and compared with those of plain membranes. The approximate percentage of metal coverage and the number of ionic sites masked by the deposited metal in terms of NaCl concentration have been estimated from the differences in Itau1/2 values of plain and metal-deposited membranes. The quantity of metal deposited in a unit area of the membrane surface was measured by differential pulse polarography. The oxidation and reduction peak potentials corresponding to Cu(0)/Cu(II) and Pb(0)/Pb(II) couples were identified by cyclic voltammetry at pH 2.8 and 4.5 of 0.2 M CH3COONa-H2SO4. Copyright 1999 Academic Press.

Journal Article↗
PubMedDate not supplied

Determination of closed form solution for acceptance sampling using ANN.

Tabled sampling schemes such as MIL-STD-105D offer limited flexibility to quality control engineers in designing sampling plans to meet specific needs. We describe a closed form solution to determine the AQL indexed single sampling plan using an artificial neural network (ANN). To determine the sample size and the acceptance number, feed-forward neural networks with sigmoid neural function are trained by a back propagation algorithm for normal, tightened, and reduced inspections. From these trained ANNs, the relevant weight and bias values are obtained. The closed form solutions to determine the sampling plans are obtained using these values. Numerical examples are provided for using these closed form solutions to determine sampling plans for normal, tightened, and reduced inspections. The proposed method does not involve table look-ups or complex calculations. Sampling plan can be determined by using this method, for any required acceptable quality level and lot size. Suggestions are provided to duplicate this idea for applying to other standard sampling table schemes.

Algorithms↗