The ground state of binary boson mixtures

We consider the ground-state configurations of mixtures of strongly interacting bosons using a variational ansatz: the average correlation approximation (ACA). Using this ansatz, we are able to obtain explicit expressions for the first and second concentration derivatives of the enthalpy which can then be used to interpret the detailed numerical results. The range of ACA accuracy is ascertained by examining the mixtures in the weakly correlated limit. For those systems for which the potential energy core sizes are equal, the ACA gives reliable enthalpy upper bounds and second derivatives. A detailed comparative analysis is made between mixture calculations at fixed pressure and mixture calculations at fixed volume. A hard-sphere boson mixture is used to illustrate relevant points.     

The study of disordered systems by EXAFS: Limitations

The correct treatment of the spatial averaging procedure in the EXAFS formalism reveals the need for sizeable corrections in many cases of interest. The consequences of the new formalism, together with the absence of low momentum transfer information, results in serious limitations in the study of disordered systems by the EXAFS technique.     

An ab initio study of the in-plane harmonic force fields and fundamental vibration frequencies of cis- and trans-1,3-butadiene

The structure, in-plane force field, and fundamental vibration frequencies of trans- and cis-1,3-butadiene are calculated ab initio using the 4-31G basis set. Using a scaling procedure based on computational results from smaller molecules, the vibration frequencies for the trans-conformer calculated from the ab initio force constant matrix are found on average to be within 2.2% of the experimental values “harmonized” according to Dennison's rule. The values predicted for the cis-conformer, for which experimental spectroscopic data are only now becoming available, should facilitate the complete in-plane assignment of fundamentals in the near future.     

A thermobalance for high pressure process studies

A DuPont 950 TG has been modified to permit operation at up to 30 atm, 1100°C, with corrosive atmospheres, and steam partial pressures up to 20 atm.The major areas of instrument development included: weight and temperature measurement at high pressures in a dynamic flow system; modification of a TG to accept corrosive gas atmospheres containing high partial pressures of steam; design of a pressure balanced flow system for safe introduction of corrosive gas atmospheres; design of a working steam generation system for low flows.Process studies illustrating the utility of the high presure thermobalance include the cyclic CO₂-acceptor reaction for half-calcined dolomite

and the cyclic H₂S absorption and regeneration reaction for half-calcined dolomite