Quasi-chemical approximation for polyatomic mixtures.

The statistical thermodynamics of binary mixtures of polyatomic species was developed based on a generalization in the spirit of the lattice-gas model and the quasi-chemical approximation (QCA). The new theoretical framework is obtained by combining: (i) the exact analytical expression for the partition function of non-interacting mixtures of linear k-mers and l-mers (species occupying k sites and l sites, respectively) adsorbed in one dimension, and its extension to higher dimensions; and (ii) a generalization of the classical QCA for multicomponent adsorbates and multisite-occupancy adsorption. This process is analyzed using the partial adsorption isotherms corresponding to both species of the mixture. Comparisons with analytical data from Bragg-Williams approximation (BWA) and Monte Carlo simulations are performed in order to test the validity of the theoretical model. Even though a good fitting is obtained from BWA, it is found that QCA provides a more accurate description of the phenomenon of adsorption of interacting polyatomic mixtures.

A semiempirical model for adsorption of binary mixtures.

The statistical thermodynamics of polyatomic species mixtures adsorbed on two-dimensional lattices was developed based on generalization of the semiempirical approximation for the adsorption of single components [Romá, F. et al., Langmuir, 2006, 22, 3192-3197]. In this scheme, the partial adsorption isotherms are obtained using a correction function C[combining tilde], which relates to the conditional probability of finding the ith empty site to a lattice with i- 1 already vacant sites. This approximation allows us to write a new theoretical model using a combination of the correction functions corresponding to exact 1-D calculations and the Guggenheim-DiMarzio approach. Finally, comparisons with MC simulations and experimental data of methane-ethane and ethane-propylene mixtures on activated carbon are used to test the accuracy and reliability of the proposed model. The obtained results indicate that the new thermodynamic description is significantly better than the existing theoretical models developed to treat adsorption of interacting binary mixtures of polyatomics.

[Intestinal infarction in the newborn]. / Infarto intestinal en el lactante

Intestinal infarction was studied in 20 children with acute gastroenteritis. Eighteen cases (90%) died and 2 (10%) recovered. The disease was most frequently seen in infants under one month of age (85%) and in malnourished cases with subnormal weight at birth. It was suspected only in four patients and in the rest, it was a surgical or post mortem finding. No clinical or radiological findings were detected to orient diagnosis. The following signs are considered jointly to support a diagnostic suspicion; prolonged paralytic ileus, abdominal vascular distress, peritoneal irritation, shock and history of diarrhea. Considerations are made on its pathology, clinical picture and treatment, stressing the fact that an early surgical treatment may increase survival possibilities.