Thermodynamic behavior of the system benzene-ethylene dichloride

The Maron theory of nonelectrolyte solutions has been used to analyze the thermodynamic behavior of the system benzene-ethylene dichloride. Excellent agreement with experiment has been obtained for all the thermodynamic properties involved. The analysis also shows that the interaction parameter for this system is small and positive, but it varies sharply with both concentration and temperature. As a result the system is nonideal and complex in behavior, despite the fact that vapor pressure data would tend to suggest near ideality.     

Nuclear magnetic resonance spectroscopic method for the estimation of competitive equilibrium constants

A nuclear magnetic resonance method is described which yields precise estimates of competitive equilibrium constants for systems in which two or more complexing agents compete for common species. Chemical-shift data under rapid exchange conditions are required, but neither analytical not equilibrium concentrations are needed. The method is demonstrated by estimating equilibria of proton exchange between aniline and pyridinium ion, proton exchange between triethylamine and diisopropylammonium ion, and cyclohexaamylose exchange between m- and p-hydroxybenzoic acids. The precisions of the equilibrium constants are similar to or better than those obtained from classical methods and are relatively free from interferences.     

Decycling graphs

In this paper, we introduce the decycling number of a graph as the minimum number of vertices that must be removed in order to eliminate all cycles. After proving some general results, we focus on two families of graph products, the grids and the hypercubes. © 1997 John Wiley & Sons, Inc. J Graph Theory 25: 59–77, 1997     

Water-soluble polymers for hostile environment enhanced oil recovery applications

This paper describes polymerization and properties of a number of water-soluble polymers suitable for enhanced oil recovery applications. The polymers described here can tolerate long-term exposure to hostile environment conditions of elevated temperatures and high salinity and hardness levels encountered in deeper petroleum reservoirs. The stable polymers reported here, in principle contain two or more of the following monomers: acrylamide, N-vinyl-2-pyrrolidone, sodium 2-acrylamido-2-methylpropanesulfonate and N,N-dimethylacrylamide in proper ratios. The polymers reported here can be used directly to increase the viscosity of the injected water and consequently reducing its mobility to recover additional oil from petroleum reservoirs. Alternatively, these polymers can be used in combination with a suitable crosslinker to produce gels in-situ to block high permeability channels or fractures under hostile environment applications.     

An algebraic characterization of projective‐planar graphs

We give a detailed algebraic characterization of when a graph G can be imbedded in the projective plane. The characterization is in terms of the existence of a dual graph G* on the same edge set as G, which satisfies algebraic conditions inspired by homology groups and intersection products in homology groups. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 320–331, 2003     

Crystal structure of bromofluoroacetic acid: a chiral molecule

The crystal structure of bromofluoroacetic acid has been determined from three-dimensional counter data, and refined by full-matrix least-squares techniques. The crystals belong to the monoclinic space groupP2₁/c, witha = 8.529(4),b = 5.632(3),c = 9.500(4) Å, = 105.52(4) °, andD _x = 2.37 g cm^–3 forZ = 4. The finalR factor for 654 independent observed reflections is 0.081. The compound exists as hydrogen-bonded dimers in the solid state.     

A gas chromatographic analysis for SO2 oxidation

Summary An improved method of determining yields of sulphur trioxide in sulphur dioxide oxidations is reported. The method relies on the absorption of SO₃ from the reaction gases. An all-teflon system incorporating a gas density balance is used. Separation of SO₂ and O₂ is effected on a Porapak PS column at ambient temperature.