A class of solutions of the low energy string theory in four dimensions is studied. This class admits a geodesic, shear-free null congruence which is non-twisting but in general diverging and the corresponding solutions in Einstein's theory form the Robinson-Trautman family together with a subset of the Kundt's class. The Robinson-Trautman conditions are found to be frame invariant in string th...

Peng-Robinson equation of state is widely used with the classical van der Waals mixing rules to predict vapor liquid equilibria for systems containing hydrocarbons and related compounds. This model requires good values of the binary interaction parameter kij . In this work, we developed a semi-empirical correlation for kij partly based on the Huron-Vidal mixing rules. We obtained values for the...

A PDAE model of a multicomponent gas pipeline has been formulated and solved using the ode15s solver of Matlab. The model with boundary conditions allows for reactions and di usion. Also, general cubic equations of state for pressure and enthalpy are described. To simplify the implementation at this stage, a non-reactive, non-di usional model with fixed feed composition is considered, and multi...

An analytical equation of state has been previously modified by Papari et al. for representing the volumetric properties of molecular fluids. However the performance of that EOS has not been yet well investigated for refrigerant fluids. This study extended that equation to 19 liquid refrigerants to predict their densities at isothermal and saturated states. Two temperature-independent parameter...

Sixty years ago the late William S. Robinson (1913–96) published his Ecological Correlations and the Behaviors of Individuals. 1 The paper became an all-time classic and it is one of the most influential methodological papers in social sciences. To underscore its impact on epidemiology , this classic was reprinted in this journal, 2 along with an original re-analysis of Robinson's data and conc...

Cubic equations of state combined with excess Gibbs energy predictive models (like UNIFAC) and equations of state based on applied statistical mechanics are among the main alternatives for phase equilibria prediction involving polar substances in wide temperature and pressure ranges. In this work, the predictive performances of the PC-SAFT with association contribution and Peng-Robinson (PR) co...