Pensamiento intuitivo en química: suposiciones implícitas y reglas heurísticas

El objetivo central de este trabajo es el de ilustrar en qué medida el razonamiento de los estudiantes de ciencias, en particular de los alumnos de química, puede estar restringido por suposiciones implícitas sobre las propiedades y el comportamiento de las entidades en un sistema, o por atajos de razonamiento (heurísticos) que les ayudan a disminuir el esfuerzo cognitivo. Los resultados de nuestras investigaciones indican de manera consistente que, aun a nivel universitario, el pensamiento de los estudiantes está dominado por conocimientos y formas de razonamiento intuitivos. Desde esta perspectiva, cualquier agenda en la educación de las ciencias que se privilegie debe reconocer la importancia de crear oportunidades en el aula para cuestionar y reflexionar sobre los alcances y limitaciones de estas formas de pensar.The central goal of this work is to illustrate the extent to which science students' reasoning is constrained by a) implicit assumptions about the properties and behavior of the relevant entities in the domain, and b) shortcut reasoning procedures (heuristics) in order to build explanations, generate inferences, and make predictions and decisions with limited time and knowledge. Results from our research consistently suggest that, even at college level, students' thinking is largely controlled by these types of cognitive constraints. Solving problems, generating explanations, or building inferences seems to involve the activation or instantiation of a spectrum of constraints, from domain-general to domain-specific, from implicit to explicit, which may act in complementary or competitive ways. The goal is not necessarily to achieve conceptual coherence, but rather local explanatory coherence during a specific task in a determined context. The characterization of students' intuitive thinking is thus of central importance in the development of curriculum and teaching strategies that better support student learning in science, as well as in the design of assessment tools to gather valid evidence of student understanding

Desarrollando pensamiento químico en contextos sociales y ambientales

En aquest treball es descriu una proposta educativa alternativa per a l'ensenyament de la química general en l'àmbit universitari. El currículum se centra en el desenvolupament de formes de pensament químic útils per resoldre problemes en contextos socials i ambientals. En particular, les metes educatives s'adrecen a preparar estudiants que puguin identificar el tipus de preguntes que la química ens ajuda a respondre, els recursos intel·lectuals i experimentals existents per afrontar aquests reptes i els costos i beneficis d'utilitzar la química per resoldre els nostres roblemes.This work describes an alternative educational approach for the teaching of general chemistry at the college level. The curriculum is focused on the development of chemical ways of thinking that are useful for solving problems in social and environmental contexts. In particular, the educational goals are directed at preparing students who can identify the types of questions that chemistry helps us answer, the intellectual and experimental resources that are available to face such challenges, and the costs and benefits of using chemistry to solve our problems.En este trabajo se describe una propuesta educativa alternativa para la enseñanza de la química general a nivel universitario. El currículo se centra en el desarrollo de formas de pensamiento químico útiles para resolver problemas en contextos sociales y ambientales. En particular, las metas educativas se dirigen a preparar estudiantes que puedan identificar el tipo de preguntas que la química nos ayuda a responder, los recursos intelectuales y experimentales existentes para enfrentar tales retos y los costos y beneficios de usar la química para resolver nuestros problemas

Construyendo puentes conceptuales entre las varias escalas y dimensiones de los modelos químicos

En aquest treball es descriuen algunes de les dificultats que els estudiants de química tenen per relacionar conceptes i idees a través de les diferents escales i dimensions en les quals es defineixen els diversos models químics. També es discuteixen alguns elements de l'ensenyament tradicional de la disciplina que tendeixen a agreujar aquestes dificultats i es presenten eines didàctiques computacionals dissenyades per donar suport a l'aprenentatge en aquesta àrea.This paper describes some of the difficulties that chemistry students face when trying to connect concepts and ideas across the different scales and dimensions, from which many chemical models are defined. We also discuss some of the features of traditional chemistry education that tend to aggravate these problems, and we present a set of computer- based educational tools, which are designed to scaffold learning in this area.En este trabajo se describen algunas de las dificultades que los estudiantes de química tienen para relacionar conceptos e ideas a través de las diferentes escalas y dimensiones en las que los diversos modelos químicos se definen. También se discuten algunos elementos de la enseñanza tradicional de la disciplina que tienden a exacerbar estas dificultades y se presentan herramientas didácticas computacionales diseñadas para apoyar el aprendizaje en esta área

Homogeneous nucleation near a second phase transition and Ostwald's step rule

Homogeneous nucleation of the new phase of one transition near a second phase transition is considered. The system has two phase transitions, we study the nucleation of the new phase of one of these transitions under conditions such that we are near or at the second phase transition. The second transition is an Ising-like transition and lies within the coexistence region of the first transition. It effects the formation of the new phase in two ways. The first is by reducing the nucleation barrier to direct nucleation. The second is by the system undergoing the second transition and transforming to a state in which the barrier to nucleation is greatly reduced. The second way occurs when the barrier to undergoing the second phase transition is less than that of the first phase transition, and is in accordance with Ostwald's rule.Comment: 11 pages, 5 figure

Design rules for the self-assembly of a protein crystal

Theories of protein crystallization based on spheres that form close-packed crystals predict optimal assembly within a `slot' of second virial coefficients and enhanced assembly near the metastable liquid-vapor critical point. However, most protein crystals are open structures stabilized by anisotropic interactions. Here, we use theory and simulation to show that assembly of one such structure is not predicted by the second virial coefficient or enhanced by the critical point. Instead, good assembly requires that the thermodynamic driving force be on the order of the thermal energy and that interactions be made as nonspecific as possible without promoting liquid-vapor phase separation.Comment: 5 pages, 4 figure

México 2019: política personalista y neoliberalismo desde la izquierda

This article analyzes President Andrés Manuel López Obrador’s (AMLO) first year in power. It argues that his government is hostage to deep-seated fragilities in the Mexican state apparatus, which are structurally constraining its ability to deliver results. Yet rather than addressing institutional deficiencies, decisions made by the new government have further compromised the state’s weak capabilities. Under the premise of extirpating the old neoliberal order, AMLO has centralized decision-making in the national executive, cultivated personalistic linkages, discarded inherited institutions, and implemented an aggressive fiscal austerity program. These measures have impaired the functioning of the bureaucracy and limited the prospects for greater social inclusion. Fiscal austerity, a quasi-religious moralizing discourse, and an increased reliance on the military for policy implementation mark a conservative turn. Attempts to weaken independent centers of power and AMLO’s propensity to demonize opponents may not escalate into a full authoritarian reversal, but they have eroded the conditions for pluralistic politics andrational public deliberation. Overall, the “Fourth Transformation” has missed opportunities to democratically strengthen the state and lay the groundwork for progressive social change.Este artículo analiza el primer año del presidente Andrés Manuel López Obrador (AMLO) en el poder. Sostiene que su gobierno es rehén de profundas fragilidades en el aparato estatal, que están limitando estructuralmente su capacidad de dar resultados. Sin embargo, en vez de abordar las deficiencias institucionales, las decisiones tomadas por el nuevo gobierno han comprometido aún más las débiles capacidades del Estado. Bajo la premisa de extirpar el viejo orden neoliberal, AMLO ha centralizado la toma de decisiones en el ejecutivo nacional, cultivado formas de vinculación personalista, descartado instituciones heredadas e implementado un agresivo programa de austeridad fiscal. Estas medidas han perjudicado el funcionamiento de la burocracia y limitado las perspectivas de una mayor inclusión social. La austeridad fiscal, un discurso moralizador cuasirreligioso y una mayor dependencia de los militares para la implementación de políticas configuran un giro conservador. Los intentos de debilitar centros independientes de poder y la propensión de AMLO a demonizar a sus opositores pueden no llegar a una reversión autoritaria completa, pero han erosionado las condiciones para la política pluralista y la deliberación pública racional. En suma, la "Cuarta Transformación" ha perdido oportunidades para fortalecer democráticamente al Estado y sentar las bases para un cambio social progresista

Lattice model of gas condensation within nanopores

We explore the thermodynamic behavior of gases adsorbed within a nanopore. The theoretical description employs a simple lattice gas model, with two species of site, expected to describe various regimes of adsorption and condensation behavior. The model includes four hypothetical phases: a cylindrical shell phase (S), in which the sites close to the cylindrical wall are occupied, an axial phase (A), in which sites along the cylinder's axis are occupied, a full phase (F), in which all sites are occupied, and an empty phase (E). We obtain exact results at T=0 for the phase behavior, which is a function of the interactions present in any specific problem. We obtain the corresponding results at finite T from mean field theory. Finally, we examine the model's predicted phase behavior of some real gases adsorbed in nanopores

Homogeneous nucleation of a non-critical phase near a continuous phase transition

Homogeneous nucleation of a new phase near a second, continuous, transition, is considered. The continuous transition is in the metastable region associated with the first-order phase transition, one of whose coexisting phases is nucleating. Mean-field calculations show that as the continuous transition is approached, the size of the nucleus varies as the response function of the order parameter of the continuous transition. This response function diverges at the continuous transition, as does the temperature derivative of the free energy barrier to nucleation. This rapid drop of the barrier as the continuous transition is approached means that the continuous transition acts to reduce the barrier to nucleation at the first-order transition. This may be useful in the crystallisation of globular proteins.Comment: 6 pages, 1 figur

Esquemas de conocimiento que guían el razonamiento sobre cómo y por qué ocurren las reacciones químicas

Els resultats de les investigacions en educació química en els darrers 50 anys proporcionen informació valuosa sobre el raonament dels estudiants sobre com i per què tenen lloc les reaccions químiques. L’anàlisi d’aquests resultats permet inferir esquemes de coneixement que semblen guiar el raonament de la majoria dels estudiants en aquesta àrea en diferents etapes de la seva formació. Aquest article descriu aquests esquemes dominants i les barreres conceptuals que generen en el procés d’aprenentatge. Aquesta caracterització fa evident la complexitat dels coneixements que volem que els estudiants desenvolupin i ressalta la urgència de fer canvis en currículums, mètodes d’ensenyament i estratègies d’avaluació tradicionalment utilitzats en l’ensenyament de la química.Results from research in chemistry education in the last 50 years provide valuable insights into how students reason about how and why chemical reactions happen. The analysis of these results allows us to infer knowledge schemas that seem to guide student reasoning in this area at different stages in their schooling. This paper describes these dominant knowledge schemas and the conceptual barriers they create during the learning process. This characterization makes explicit the complexity of the understandings we want students to develop and highlights the urgent need for changes in traditional curricula, teaching practices, and assessment strategies in chemistry education.Los resultados de las investigaciones en educación química en los últimos 50 años proporcionan información valiosa sobre el razonamiento de los estudiantes acerca de cómo y por qué ocurren las reacciones químicas. El análisis de estos resultados permite inferir esquemas de conocimiento que parecen guiar el razonamiento de la mayoría de los estudiantes en esta área en diferentes etapas de su formación. En este artículo se describen estos esquemas dominantes y las barreras conceptuales que generan en el proceso de aprendizaje. Esta caracterización hace evidente la complejidad de los conocimientos que queremos que los estudiantes desarrollen y resalta la urgencia de realizar cambios en currículos, métodos de enseñanza y estrategias de evaluación tradicionalmente utilizados en la enseñanza de la química

Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions

Excess contributions to the free energy due to interfaces occur for many problems encountered in the statistical physics of condensed matter when coexistence between different phases is possible (e.g. wetting phenomena, nucleation, crystal growth, etc.). This article reviews two methods to estimate both interfacial free energies and line tensions by Monte Carlo simulations of simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is based on thermodynamic integration. This method is useful to study flat and inclined interfaces for Ising lattices, allowing also the estimation of line tensions of three-phase contact lines, when the interfaces meet walls (where "surface fields" may act). A generalization to off-lattice systems is described as well. The second method is based on the sampling of the order parameter distribution of the system throughout the two-phase coexistence region of the model. Both the interface free energies of flat interfaces and of (spherical or cylindrical) droplets (or bubbles) can be estimated, including also systems with walls, where sphere-cap shaped wall-attached droplets occur. The curvature-dependence of the interfacial free energy is discussed, and estimates for the line tensions are compared to results from the thermodynamic integration method. Basic limitations of all these methods are critically discussed, and an outlook on other approaches is given