A novel approach for high precision rapid potentiometric titrations: application to hydrazine assay

We propose a high precision rapid personal computer (PC) based potentiometric titration technique using a specially designed mini-cell to carry out redox titrations for assay of chemicals in quality control laboratories attached to industrial, R&D, and nuclear establishments. Using this technique a few microlitre of sample (50-100 μl) in a total volume of ~2 ml solution can be titrated and the waste generated after titration is extremely low comparing to that obtained from the conventional titration technique. The entire titration including online data acquisition followed by immediate offline analysis of data to get information about concentration of unknown sample is completed within a couple of minutes (about 2 min). This facility has been created using a new class of sensors, viz., pulsating sensors developed in-house. The basic concept in designing such instrument and the salient features of the titration device are presented in this paper. The performance of the titration facility was examined by conducting some of the high resolution redox titrations using dilute solutions--hydrazine against KIO(3) in HCl medium, Fe(II) against Ce(IV) and uranium using Davies-Gray method. The precision of titrations using this innovative approach lies between 0.048% and 1.0% relative standard deviation in different redox titrations. With the evolution of this rapid PC based titrator it was possible to develop a simple but high precision potentiometric titration technique for quick determination of hydrazine in nuclear fuel dissolver solution in the context of reprocessing of spent nuclear fuel in fast breeder reactors.     

Theoretical study of conjugate heat transfer effects on temperature profiles in parallel flow with embedded heat sources

A two-dimensional model for heat transfer in a “simulated flame” modeled as an embedded heat source is developed along with an analytical solution that relates the temperature field in the channel to the flow Pe number. The solution is derived from first principles by modeling the flame as a volumetric heat source and by applying “jump conditions” across the heat release zone. The model explores the role of heat recirculation via the structure of the device by accounting for the thermal coupling between the structure and the gas. The unique aspect of the model is that it solves for the two-dimensional temperature fields in both the structure and the gas simultaneously. The solution is obtained using separation of variables in the streamwise (x) and the transverse (y) directions. Thermal coupling between the structure and gas is achieved by requiring that the temperatures and heat fluxes match at the interface. The outer structure boundary can be either adiabatic or have a convective heat loss based on Newton’s law of cooling. The resulting solution is a Fourier series (for both structure and gas temperature fields) which depends on the flow Pe and the outer structure boundary condition. This simple model and the resulting analytical solution provide an extremely computationally efficient tool for exploring the effects of varying channel height and gas velocity on the temperature distribution associated with reacting (combusting) flow in a channel. Understanding these tradeoffs is important for developing miniaturized, combustion-based power sources.     

Characterization of a reverse molding sequence at the mesoscale for in‐mold assembly of revolute joints

In‐mold assembly and miniature molding have been combined to realize miniature assemblies. Our previous work has shown that for realizing in‐mold assembly at the mesoscale, the molding sequence is the reverse of that used at the macroscale. Moreover, special features are needed in the mold to prevent plastic bending of the pin because of the pressure exerted by the second stage melt. This article presents novel mold designs and computational methods to enable the use of the reverse molding sequence to prevent: (1) plastic bending of the premolded component, and (2) joint jamming during the mesoscale in‐mold assembly process. The computational methods are also validated through experimentation. Results reported in this article show that for making in‐mold assembled revolute joints with the polymer combination of ABS and LDPE, a reversed molding sequence needs to be used for joints sizes less than 1.5 mm. POLYM. ENG. SCI., 50:1843–1852, 2010. © 2010 Society of Plastics Engineers     

Analytical model for the design of volumetric solar flow receivers

The development of efficient solar thermal receivers has received significant interest for solar to electrical power conversion and heating applications. Volumetric flow receivers, where the incoming solar radiation is absorbed in the volume of a heat transfer fluid (HTF), promise reduced heat loss at the surface compared to surface absorbers. In order to efficiently store the thermal energy in the volume, nanoparticles can be suspended in the HTF to absorb the incoming radiation. In such systems, compact models are needed to design and optimize the performance. This paper presents an analytical model that investigates the effect of heat loss, particle loading, solar concentration and channel height on receiver efficiency. The analytical model was formulated by modeling the absorption of solar radiation by the suspended nanoparticles as a volumetric heat release inside the flowing HTF. The energy equation was solved with the surface heat losses modeled using a combined radiative and convective heat loss coefficient. The analytical solution provides a convenient tool for predicting the effect of different parameters, in terms of dimensionless numbers (Pe, Nu_E, $\overline{G}$, and θ_amb), on two-dimensional temperature profiles and system performance. By combining the receiver efficiency with a power generation efficiency, idealized by the Carnot efficiency, an optimum receiver length where the total efficiency is maximized is determined. However, in practice, the maximum efficiency depends on the maximum allowable temperature of the working HTF. As a case study, predictions were made for Therminol® VP-1 with suspended graphite nanoparticles in a 1 cm deep channel with a solar concentration of 10. The model predicts an optimum total system efficiency of 0.35 for a dimensionless receiver length of 0.86. Finally, the analytical model was used to estimate the optimum efficiency and the corresponding optimum receiver length for different design configurations with varying Nu_E and $\overline{G}$. The results from this paper will help guide experimental design of volumetric flow receivers for solar thermal based power systems.     

Application of the one-dimensional Ising model to the secondary structures in globular proteins. Prediction of beta-regions

An attempt has been made to predict the beta-regions in 16 globular proteins by applying the one-dimensional Ising model theory of Lifson & Roig (8). The parameters for the theory have been derived from the statistical data on globular proteins given by Chou & Fasman (5). Comparison of our results with the data available from the X-ray crystallographic studies indicates a prediction accuracy which is comparable to those of several other methods, especially in view of the limitations in our method for considering the other secondary structures. It is pointed out that not considering the long-range interactions in our and other methods based on short-range interactions would make these methods incomplete and incapable of being uniformly applicable to all proteins.     

Interaction of calcium channel antagonists with calcium: structural studies on verapamil and its Ca2+ complex

The conformation of the calcium channel antagonist verapamil has been determined in acetonitrile, in the absence and presence of Ca2+, using two-dimensional 1H-NMR and molecular modeling techniques. Interproton connectivities in the drug molecule were identified from the observed NOESY cross peaks and interproton distances were estimated from the magnitudes of the volume integrals of the cross peaks. The molecular modeling program utilized the Monte Carlo simulation to generate a random ensemble of conformers complying with the NOESY-derived distance constraints. The energies of these conformers were subsequently computed. The minimum-energy structure of the free drug obtained in this manner exhibited some significant differences from the structure of verapamil determined by X-ray crystallography. In particular, the torsional angles in the middle region of the molecule containing the aliphatic "backbone" were such that the two aromatic rings at either end of the drug molecules were moved farther apart from each other in solution than in the crystal structure. The nearly perpendicular orientation of the aromatic rings seen in the crystal was, however, maintained in the solution structure as well. The addition of Ca2+ to a solution of verapamil in acetonitrile caused marked changes in the difference absorbance of the drug in the 200-300-nm region and in many of its 1H-NMR resonances. The changes were most significant up to a mole ratio of about 0.5 Ca2+:drug. Analysis of the binding data at 25 degrees C showed the presence of both 2:1 and 1:1 drug:Ca2+ complexes in equilibrium, the former "sandwich" complex being dominant at the lower cation concentrations with an estimated dissociation constant of about 300 microM. All of the NOESY cross peaks of the free drug remained on addition of 0.5 mol ratio of Ca2+ to verapamil in deuterated acetonitrile and only two new connectivities were observed. Using the interproton distances calculated from these NOESY data, molecular modeling of the 2:1 drug:Ca2+ complex was carried out to yield the minimum-energy conformer. In this conformer, Ca2+ was coordinated to two methoxy oxygens from each of the two drug molecules. The implications of the verapamil-Ca2+ interaction are discussed in terms of available experimental data on the binding of verapamil to the dihydropyridine-sensitive channel and in terms of a hypothesis on the formation of a drug-Ca(2+)-receptor complex in the lipid bilayer environment.     

Venturi Scrubber Modelling and Optimization

An improved algorithm that optimizes Pease‐Anthony type venturi scrubber performance is presented in this work. This approach predicts the minimum pressure drop needed to achieve the desired collection efficiency by optimizing key operating and design parameters such as liquid‐to‐gas ratio, throat gas velocity, number of nozzles, nozzle diameter, and throat aspect ratio. A detailed assessment of four established pressure drop models and an extension of two of the models by providing an empirical algorithm to give better prediction of pressure drop in the venturi throat have been conducted by validating them with experimental data. This optimization algorithm provides a stepwise, effective, and accurate approach to optimizing both existing and new scrubbers.     

Flame speed predictions in planar micro/mesoscale combustors with conjugate heat transfer

An analytical model for flame stabilization in meso-scale channels is developed by solving the two-dimensional partial differential equations associated with heat transport in the gas and structure and species transport in the gas. It improves on previous models by eliminating the need to assume values for the Nusselt numbers in the pre and post-flame regions. The effects of heat loss to the environment, wall thermal conductivity, and wall geometry on the burning velocity and extinction are explored. Extinction limits and fast and slow burning modes are identified but their dependence on structure thermal conductivity and heat losses differ from previous quasi one-dimensional analyses. Heat recirculation from the post-flame to the pre-flame is shown to be the primary mechanism for flame stabilization and burning rate enhancement in micro-channels. Combustor design parameters like the wall thickness ratio, thermal conductivity ratio, and heat loss to the environment each influence the flame speed through their influence on the total heat recirculation. These findings are used to propose a simple methodology for preliminary micro-combustor design.     

Studies in antifertility agents: 10. Secosteroids 4: synthesis of 2-methyl-2-(2-(6-hydroxy-1,2,3,4-tetrahydro-1-naphthyl) -ethyl)cyclopentan-1-one and -1-o1

Sythesis of 8,14-secoestrone, its 3-methoxy-, its 17-hydroxy- and its 17-rho-beta-pyrrolidino ethyl ether were achieved by desulfuration of the methoxymonothioketal, followed by demethylation and borohydride reduction. None of these had any antiimplantation activity at 10 mg/kg in rats.     

The rat liver ecto-ATPase is also a canalicular bile acid transport protein

A approximately 110-kDa glycoprotein purified from canalicular vesicles by bile acid affinity chromatography has been identified as the canalicular bile acid transport protein. Internal amino acid sequence and chemical and immunochemical characteristics of this protein were found to be identical to a rat liver canalicular ecto-ATPase. In order to definitively determine whether these were two activities of a single polypeptide, we examined the possibility that transfection of cDNA for the ecto-ATPase would confer bile acid transport characteristics, as well as ecto-ATPase activity, on heterologous cells. The results show that transfection of the ecto-ATPase cDNA conferred on COS cells de novo synthesis of a approximately 110-kDa polypeptide, as immunoprecipitated by antibody to the purified canalicular bile acid transport protein and conferred on COS cells the capacity to pump out [3H]taurocholate with efflux characteristics comparable with those previously determined in canalicular membrane vesicles (Km = 100 microM; Vmax = 200 pmol/mg of protein/20 s). A truncated ecto-ATPase cDNA, missing the cytoplasmic tail, was targeted correctly to the cell surface but did not confer bile acid transport activity on COS cells. The results of this study also show that the canalicular ecto-ATPase/bile acid transport protein is phosphorylated on its cytoplasmic tail and that its phosphorylation is stimulated by activation of protein kinase C and inhibited by inhibitors of protein kinase C activation. Moreover, inhibition of protein kinase C activation by staurosporine completely abrogates bile acid transport but does not affect ATPase activity. This study, therefore, demonstrates that the rat liver canalicular ecto-ATPase is also a bile acid transport protein, that the capacity to pump out bile acid can be conferred on a heterologous cell by DNA-mediated gene transfer, and that phosphorylation within the cytoplasmic tail of the transporter is essential for bile acid efflux activity but not for ATPase activity.