Resumen En este trabajo presentamos el modelamiento y simulación computacional de la oxidación del monóxido de carbono, proceso que tomamos como referente para analizar la importancia de describir la dinámica de los sitios activos en el rendimiento del proceso catalítico. Utilizamos el formalismo de los procesos de transporte y los balances poblaciones para desarrollar un modelo realístico que involucra el intercambio de calor, la transferencia de masa y de momentum, la reacción química y la desactivación del catalizador. El modelo propuesto se resuelve numéricamente y se hace un análisis comparativo de los resultados entre la aproximación de pseudo estado estacionario isotérmico y el estado no-estacionario no-isotérmico para el ciclo catalítico. Los resultados obtenidos muestran la importancia de considerar en el modelo la interfase de manera explícita, ya que la dinámica temporal de la reacción y de los sitios activos influyen de manera significativa en el rendimiento del proceso catalítico.

Abstract Modeling and computational simulation of the carbon monoxide oxidation process, taken as a key system to analyze the importance of the dynamic description of active sites into the process yield, are presented in this work. To this aim, the formalism of transport phenomena and population balances are used to implement a realistic model that involves heat exchange, transfer of mass and momentum, chemical reaction, and catalyst deactivation. The model is solved numerically, and the analysis is made by comparing isothermal pseudo-steady state approximation with non-isothermal non-steady state assumption for the catalytic cycle. The results show the advantage of considering the interface explicitly into the model since temporary changes of the reactive complex as well as the active sites of the catalyst have a great influence over the reaction yield. By considering this fact, the reaction description is made in a more proper way.

Abstract The present work is aimed to describe the ways of life in the Eastern part of Durango at the end of 19th century and the beginning of 20th’s, an epoch signaled by the railroad arrival. In particular, it describes the context and means by which the Martínez del Río family, owner of Santa Catalina del Alamo, the biggest Durango’s latifundium, appropriated El Zorrillo stream at the time of Las Mercedes Dam construction, an event that compelled a rearrangement of the relations between the Martínez del Río family and the Pasaje town inhabitants, who considered that the former had deprived them from their land and water.

Resumen El presente trabajo expone la dinámica que se vivía en el oriente de Durango a finales del siglo XIX y principios del XX, etapa marcada por la llegada del ferrocarril, y la manera en que enmarcados en dicho contexto, la familia Martínez del Río, dueña del latifundio más grande de la entidad, Santa Catalina del Álamo, se apropió del agua del afluente de El Zorrillo, gracias a la construcción de la presa Las Mercedes. Lo cual derivó en un reajuste en sus relaciones con los habitantes del pueblo de Pasaje, quienes consideraban que se les despojaba de su tierra y agua.

Traditionally, thermokinetic and chemical oscillations have been studied independently, but in cellular media recent studies have shown that cell’s temperature is not uniform. Thus, on this context it is possible to inquire about the influence of thermal effects on chemical oscillatory behavior and vice versa. To this end, in this paper we propose a dynamical model based on a modified Sal’nikov oscillator that can address both kinds of oscillatory behavior (thermokinetic and chemical). We found that the system modeled can jump from thermal oscillations to mixed chemical-thermal oscillations through a transition or bifurcation parameter. Thermokinetic oscillations are well defined in a limit cycle, while chemical-thermal oscillations appear in the form of a burst. The model could be useful in explaining biochemical energy recovery under cellular stress conditions.

Resumen En la naturaleza observamos una amplia variedad de colores, ritmos y formas, a toda escala y en sistemas animados e inanimados. Desde hace décadas los patrones y ritmos de la naturaleza han sido objeto de estudio y fuente de inspiración en el desarrollo tecnológico y en el bienestar del ser humano. Hoy entendemos que el diseño de los patrones de la naturaleza obedece a principios de funcionalidad y de eficiencia. En este artículo nos enfocamos en aspectos fisicoquímicos para mostrar cómo el estudio de los patrones espacio-temporales se convirtió en un área de gran interés e investigación en ciencias naturales. En particular, abordamos algunos sistemas donde la formación de patrones se explica mediante el acople entre procesos químicos y de transporte, tales como los jardines químicos, la precipitación periódica y los patrones de Turing. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat.

Abstract At all scales and both in animate and inanimate systems, nature displays a wide variety of colors, rhythms, and forms. For decades, these natural patterns and rhythms have been studied and used as a source of inspiration for the technological development and well-being of human beings. Today we understand that the design of these patterns responds to principles of functionality and efficiency. This article focuses on physicochemical aspects to show how the study of spatiotemporal patterns became such an important area of interest and research for natural sciences. In particular, we address some systems in which the formation of patterns is explained by the coupling between chemical and transport processes, such as chemical gardens, periodic precipitation and Turing patterns. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat.

We address the concept of steric effect in the pursuit of establishing quantitative correlations between reactivity of molecules and their molecular shape. To this end, a set of series of SN2 reactions were modeled to compute the energy barrier height and the molecular volume, atomic charges and dipole moment of molecules. We introduced the Kappa index to characterize the shape of molecules. Quantitative correlations between the change in the energy barrier with properties of molecules and Kappa index were presented and discussed.

A reação de Belousov-Jabotinsky clássica foi modificada pela adição de fenol como um segundo substrato orgânico que compete cineticamente com o ácido malônico na redução de Ce4+ para Ce3+ e na remoção de bromo molecular da reação. A reação oscilante de dois substratos exibiu oscilações abruptas e período oscilatório de longa duração. A análise de dados experimentais mostra um aumento do fenômeno abrupto, com pico maior e estado quiescente mais longo, como função do aumento da concentração de fenol inicial. Hipotetizou-se que o fenômeno de oscilação abrupta pode ser explicado pela introdução de um ciclo redox entre as espécies fenólicas reduzidas (hidroxifenois) e as oxidadas onas (quinonas). A hipótese foi testada experimentalmente e numericamente e dos resultados concluiu-se que o fenômeno oscilatório abrupto exibido pela reação oscilante de dois substratos é impulsionado principalmente por um ciclo redox p-di-hidroxi-benzeno/p-benzoquinona.

The classic Belousov-Zhabotinsky reaction was modified by adding phenol as a second organic substrate that kinetically competes with the malonic acid in the reduction of Ce4+ to Ce3+ and in the removal of molecular bromine of the reaction mixture. The oscillating reaction of two substrates exhibited burst firing and an oscillatory period of long duration. Analysis of experimental data shows an increasing of the bursting phenomenon, with a greater spiking in the burst firing and with a longer quiescent state, as a function of the initial phenol concentration increase. It was hypothesized that the bursting phenomenon can be explained introducing a redox cycle between the reduced phenolic species (hydroxyphenols) and the oxidized ones (quinones). The hypothesis was experimentally and numerically tested and from the results it is possible to conclude that the bursting phenomenon exhibited by the oscillating reaction of two substrates is mainly driven by a p-di-hydroxy-benzene/p-benzoquinone redox cycle.

A methodology is proposed for explaining one of the central questions in the teaching of general chemistry courses to freshman students: why do chemical transformations occur? The answer to this question is based on thermodynamics but we propose arriving at an answer in a more intuitive way by using computational tools in a bid to increase the motivation of students for learning chemistry.

Para un sistema con una fuente interna de generación de calor se analizan, en el marco de la termodinámica de los procesos irreversibles, las ecuaciones evolutivas que describen la transferencia de calor según la ley de enfriamiento de Newton. A partir del balance de flujo de entropía se muestra que la generación de entropía no es mínima en el estado estacionario descrito por la ley de enfriamiento de Newton. Igualmente, se discute cómo realizar el balance de flujos en el sistema, su conexión con los parámetros de control y su futura aplicación a procesos de optimización basados en la segunda ley de la termodinámica.

The thermodynamic theory of irreversible processes was applied to studying heat exchange described by Newton's cooling law. It is shown that the steady states described by Newton's law are not states having minimum entropy production; it is then proved that Newton's law is not a consequence of a linear relationship between fluxes and thermodynamic forces. Systems are often constrained and heat exchange can be optimised if entropy production is minimised according to the second law.