Raman spectroscopy and molecular dynamics simulations of aqueous two-phase systems for the purification of phosphoric acid.

In this work, Raman spectroscopy and molecular dynamics simulations were used to elucidate key interactions between polyethylene glycol (PEG) and phosphoric acid (H3PO4) in aqueous two-phase systems for the extraction of phosphoric acid. Extensive molecular dynamics simulations were performed, and radial distribution functions as well as hydrogen bonds between PEG and other molecules were measured. Experimental data were used in combination with the slope method to infer PEG-H3PO4 interactions, and the interpretation is consistent with molecular simulation results. Based on our experimental and simulation results, we propose a solvation mechanism governed by hydrogen bonding interactions: at low concentrations of H3PO4 within the polymer-rich aqueous solution, entropy dominates and phosphoric acid molecules have weak interactions with PEG; as the concentration of phosphoric acid increases above a certain critical value, enthalpy dominates with PEG molecules interacting strongly with H3PO4 molecules via hydrogen bonds.

Multi-objective optimization of process conditions in the manufacturing of banana (Musa paradisiaca L.) starch/natural rubber films.

Multi-objective optimization was used to evaluate the effect of adding banana (Musa paradisiaca L.) starch and natural rubber (cis-1,4-poliisopreno) at different ratios (1-13w/w) to the manufacturing process of biodegradable films, specifically the effect on the biodegradability, crystallinity and moisture of the films. A structural characterization of the films was performed by X-ray diffraction, Fourier transform infrared spectroscopy and SEM, moisture and biodegradability properties were studied. The models obtained showed that degradability vs. moisture tend to be inversely proportional and crystallinity vs. degradability tend to be directly proportional. With respect to crystallinity vs. moisture behavior, it is observed that crystallinity remains constant when moisture values remain between 27 and 41%. Beyond this value there is an exponential increase in crystallinity. These results allow for predictions on the mechanical behavior that can occur in starch/rubber films.

Numerical simulation of Gaussian chains near hard surfaces.

We present a coarse grain representation for Gaussian chains in the presence of hard surfaces. Whereas a Gaussian chain in the bulk can be represented by a bead-spring model with a quadratic potential between adjacent beads, the presence of a surface reduces the number of allowed chain configurations and modifies the effective potential between the beads. We derive the corrected potentials for several surface geometries: a single wall, two parallel walls (slit), and a spherical or cylindrical object (nanoparticle). Those potentials can be used in any model that includes a Gaussian chain, regardless of the simulation method. As an illustration, we consider a coarse grain model of a polymeric melt and, using Monte Carlo simulations, we compute the density profiles for (i) a melt confined in a slit and (ii) a melt in the vicinity of a nanoparticle. The case of a polymeric solution confined within a slit is also addressed, and the proposed approach is shown to yield results in qualitative agreement with those obtained with field-theoretic simulations.

Violation of the zeroth law of thermodynamics in systems with negative specific heat.

We show that systems with negative specific heat can violate the zeroth law of thermodynamics. By both numerical simulations and by using exact expressions for free energy and microcanonical entropy, it is shown that if two systems with the same intensive parameters but with negative specific heat are thermally coupled, they undergo a process in which the total entropy increases irreversibly. The final equilibrium is such that two phases appear; that is, the subsystems have different magnetizations and internal energies at temperatures which are equal in both systems, but that can be different from the initial temperature.

Systems with negative specific heat in thermal contact: violation of the zeroth law.

Using both numerical simulations and exact expressions for the free energy and microcanonical entropy for a modified Hamiltonian mean-field (HMF) model, we show that when two similar systems with the same intensive parameters but with negative specific heat are weakly coupled, they undergo a process in which the total entropy increases irreversibly. We find that the final equilibrium is such that two phases appear at a temperature (equal in both systems) that is generally different from the initial temperature. We corroborate our results using two different kinds of couplings between the HMF systems. We confirm that our results hold also for the Ising model with long- and short-range interactions, which also has a parameter region with negative specific heat in the microcanonical ensemble. Further, we show that we can couple each system having negative specific heat to a third system that can be used as a thermometer, as long as this thermometer is small enough not to drive the system out of the microcanonical ensemble. Therefore, we show an instance of violation of the zeroth law of thermodynamics.

[Presence of ferruginous bodies in cancerous pulmonary tissue]. / Presencia de cuerpos ferruginosos en tejido pulmonar canceroso.

The correlation between high counts of ferruginous bodies (FB) and pulmonary cancer was investigated. Autopsy cases between 1982 and 1988 were chosen, and studied at Instituto Nacional de Enfermedades Respiratorias. Two grams of lung tissue were digested with sodium hypochlorite. We found no differences in the histologic types of cancer: 18.0 FB per gram (FB/g) for the adenocarcinoma group and 16.0 FB/g for both the epidermoid and anaplastic groups. The asbestos core was predominant in all FB analysed (greater than 85%). Males, Mexico city residents and smokers showed to higher amounts of FB. We concluded that there is an environmental exposure to particles in the cases studied.