Optimización multi-objetivo del desempeño y consumo energético de procesos de destilación intensificados para sistemas cuaternarios

Este artículo presenta el diseño y optimización multiobjetivo de sistemas de destilación convencionales e intensificados para la separación de mezclas cuaternarias. Tres casos de estudio fueron utilizados para demostrar las ventajas y limitaciones de las configuraciones de destilación convencionales, nonsharp e intensificadas en términos de la optimización simultánea de la composición de un compuesto clave y el consumo energético para su separación. Los resultados indican que el desempeño de estos esquemas de destilación puede variar sustancialmente cuando la pureza y eficiencia energética del proceso son los objetivos en conflicto. La secuencia convencional de destilación directa puede igualar o incluso mejorar el desempeño de algunos procesos intensificados en las mezclas analizadas. En este trabajo se resalta la importancia de realizar un diseño robusto de secuencias de separación multicomponente con la finalidad de evaluar sus ventajas y limitaciones

CO oxidation: effect of Ce and Au addition on MnOx catalysts

The effect of cerium and/or gold addition to a manganese oxide which was greatly active in CO oxidation was studied. The catalysts obtained by this way were characterized by N2 adsorption, XRF, XRD and TPR, and their catalytic activity was measured in the CO oxidation reaction. The pure MnOx catalyst was active in the CO oxidation but the addition of 5 wt % cerium decreased their catalytic activity. Adding 2 wt % gold improved the activity of MnOx and Ce/MnOx and caused a slight decrease of the catalyst specific area and of the average oxidation state of manganese in catalysts, which was found between 3.3 and 3.6. The order of activity found on the basis of T50 for the four catalysts was: Au/MnOx > Au/Ce/MnOx > MnOx > Ce/MnOx, with T50 of 89, 95, 99 and 139 ºC, respectively. The solids Au/MnOx and Au/Ce/MnOx presented a T10 of 30 and 49 ºC, indicating that gold favored the conversion at room temperature. The effect of water vapor on the reaction was also analyzed, finding a decrease in the catalytic activity of all catalysts, due to the blocking of active sites in the catalyst surfaceUnión Europea AlBan UE E06D101739C

Activated Random Walkers: Facts, Conjectures and Challenges

We study a particle system with hopping (random walk) dynamics on the integer lattice $\mathbb Z^d$. The particles can exist in two states, active or inactive (sleeping); only the former can hop. The dynamics conserves the number of particles; there is no limit on the number of particles at a given site. Isolated active particles fall asleep at rate $\lambda > 0$, and then remain asleep until joined by another particle at the same site. The state in which all particles are inactive is absorbing. Whether activity continues at long times depends on the relation between the particle density $\zeta$ and the sleeping rate $\lambda$. We discuss the general case, and then, for the one-dimensional totally asymmetric case, study the phase transition between an active phase (for sufficiently large particle densities and/or small $\lambda$) and an absorbing one. We also present arguments regarding the asymptotic mean hopping velocity in the active phase, the rate of fixation in the absorbing phase, and survival of the infinite system at criticality. Using mean-field theory and Monte Carlo simulation, we locate the phase boundary. The phase transition appears to be continuous in both the symmetric and asymmetric versions of the process, but the critical behavior is very different. The former case is characterized by simple integer or rational values for critical exponents ($\beta = 1$, for example), and the phase diagram is in accord with the prediction of mean-field theory. We present evidence that the symmetric version belongs to the universality class of conserved stochastic sandpiles, also known as conserved directed percolation. Simulations also reveal an interesting transient phenomenon of damped oscillations in the activity density

Managing carious lesions:consensus recommendations on terminology

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HPM Approximations for Trajectories: From a Golf Ball Path to Mercury’s Orbit

In this work, we propose the approximated analytical solutions for two highly nonlinear problems using the homotopy perturbation method (HPM). We obtained approximations for a golf ball trajectory model and a Mercury orbit’s model. In addition, to enlarge the domain of convergence of the first case study, we apply the Laplace-Padé resummation method to the HPM series solution. For both case studies, we were able to obtain approximations in good agreement with numerical methods, depicting the basic nature of the trajectories of the phenomena