La termodinámica en los estudiantes de tecnología: una experiencia de aprendizaje cooperativo

Se describe el uso de la estrategia de aprendizaje cooperativo en la resolución de problemas basados en la primera ley de la termodinámica. Participaron 33 estudiantes de las carreras de Tecnología Mecánica y Mantenimiento Aeronáutico de la Universidad Simón Bolívar. Se describe la estrategia en función de dos indicadores (calidad en la resolución y trabajo grupal). Los estudiantes lograron en promedio resolver en más de un 70,90% los problemas de sistemas mecánicos y aeronáuticos planteados, y en 69,09% consideraron satisfactorio el desempeño en el trabajo grupal. Las respuestas mostraron dominio de las nociones básicas del tema, conceptos asociados y la habilidad para aplicarlos en un contexto relacionado con su área de formación. Se concluye que con la estrategia los estudiantes participaron activamente en la presentación de soluciones y auto-evaluaron su dominio del tema. Es ideal para trabajar con un gran número de estudiantes y minimizar el solapamiento de responsabilidades cuando se trabaja en grupos

Local Rheology Relation with Variable Yield Stress Ratio across Dry, Wet, Dense, and Dilute Granular Flows

Dry, wet, dense, and dilute granular flows have been previously considered fundamentally different and thus described by distinct, and in many cases incompatible, rheologies. We carry out extensive simulations of granular flows, including wet and dry conditions, various geometries and driving mechanisms (boundary driven, fluid driven, and gravity driven), many of which are not captured by standard rheology models. For all simulated conditions, except for fluid-driven and gravity-driven flows close to the flow threshold, we find that the Mohr-Coulomb friction coefficient $\mu$ scales with the square root of the local P\'eclet number $\mathrm{Pe}$ provided that the particle diameter exceeds the particle mean free path. With decreasing $\mathrm{Pe}$ and granular temperature gradient $M$, this general scaling breaks down, leading to a yield condition with a variable yield stress ratio characterized by $M$

Magnetorotational Instability in Core-Collapse Supernovae

We discuss the relevance of the magnetorotational instability (MRI) in core-collapse supernovae (CCSNe). Our recent numerical studies show that in CCSNe, the MRI is terminated by parasitic instabilities of the Kelvin-Helmholtz type. To determine whether the MRI can amplify initially weak magnetic fields to dynamically relevant strengths in CCSNe, we performed three-dimensional simulations of a region close to the surface of a differentially rotating proto-neutron star in non-ideal magnetohydrodynamics with two different numerical codes. We find that under the conditions prevailing in proto-neutron stars, the MRI can amplify the magnetic field by (only) one order of magnitude. This severely limits the role of MRI channel modes as an agent amplifying the magnetic field in proto-neutron stars starting from small seed fields.Comment: Proceedings in Acta Physica Polonica B, Proceedings Supplement, Vol. 10, No. 2, p.361, 4 pages, 1 figur

La termodinámica en los estudiantes de tecnología: una experiencia de aprendizaje cooperativo

Se describe el uso de la estrategia de aprendizaje cooperativo en la resolución de problemas basados en la primera ley de la termodinámica. Participaron 33 estudiantes de las carreras de Tecnología Mecánica y Mantenimiento Aeronáutico de la Universidad Simón Bolívar. Se describe la estrategia en función de dos indicadores (calidad en la resolución y trabajo grupal). Los estudiantes lograron en promedio resolver en más de un 70,90% los problemas de sistemas mecánicos y aeronáuticos planteados, y en 69,09% consideraron satisfactorio el desempeño en el trabajo grupal. Las respuestas mostraron dominio de las nociones básicas del tema, conceptos asociados y la habilidad para aplicarlos en un contexto relacionado con su área de formación. Se concluye que con la estrategia los estudiantes participaron activamente en la presentación de soluciones y auto-evaluaron su dominio del tema. Es ideal para trabajar con un gran número de estudiantes y minimizar el solapamiento de responsabilidades cuando se trabaja en grupos

Assessment of a new sub-grid model for magnetohydrodynamical turbulence. II. Kelvin-Helmholtz instability

The modelling of astrophysical systems such as binary neutron star mergers or the formation of magnetars from the collapse of massive stars involves the numerical evolution of magnetised fluids at extremely large Reynolds numbers. This is a major challenge for (unresolved) direct numerical simulations which may struggle to resolve highly dynamical features as, e.g. turbulence, magnetic field amplification, or the transport of angular momentum. Sub-grid models offer a means to overcome those difficulties. In a recent paper we presented MInIT, an MHD-instability-induced-turbulence mean-field, sub-grid model based on the modelling of the turbulent (Maxwell, Reynolds, and Faraday) stress tensors. While in our previous work MInIT was assessed within the framework of the magnetorotational instability, in this paper we further evaluate the model in the context of the Kelvin-Helmholtz instability (KHI). The main difference with other sub-grid models (as e.g. the alpha-viscosity model or the gradient model) is that in MInIT we track independently the turbulent energy density at sub-grid scales, which is used, via a simple closure relation, to compute the different turbulent stresses relevant for the dynamics. The free coefficients of the model are calibrated using well resolved box simulations of magnetic turbulence generated by the KHI. We test the model against these simulations and show that it yields order-of-magnitude accurate predictions for the evolution of the turbulent Reynolds and Maxwell stresses.Comment: 12 pages, 13 figures Accepted for publication in MNRA

Gasificación del aserrín de pino (Pinus arizonica) en un reactor de lecho fluidizado: Análisis de las variables del proceso

La gasificación hidrotérmica del aserrín de pino (Pinus arizonica) es un proceso de degradación termoquímica de sus macromoléculas poliméricas con el fin de producir principalmente hidrógeno y metano como biocombustibles. Este proceso puede ocurrir en un reactor de lecho fluidizado que permite un apropiado contacto gas-sólido, el adecuado manejo de la temperatura y una mayor velocidad de reacción. El propósito es modelar y simular las variables del proceso donde se gasifica esta biomasa forestal a partir del respectivo análisis de sensibilidad. Se obtiene que la conversión de reacción de gasificación del aserrín de pino crece a una temperatura mayor a los 900 °C, presentando un comportamiento que tiende a ser isotérmico, por lo que se sugiere un proceso energéticamente autosostenible. A su vez, la reacción mejoró para una alimentación de aserrín de pino con un diámetro óptimo de tamaño de partícula de 0,65 mm; se ve favorecida para bajas relaciones de vapor de agua/ biomasa alimentada alcanzando el óptimo en 2,375; y a bajas relaciones aire/biomasa con un valor óptimo de 0,289. Se evidencia que este proceso constituye una vía de aprovechamiento energético a partir de la conversión termoquímica de estos desechos y residuos forestales.The hydrothermal gasification of sawdust pine (Pinus arizonica) is a process of thermochemical degradation of polymeric macromolecules in order to produce mainly hydrogen and methane as biofuels. This process can occur in a fluidized bed reactor which allows an appropriate gas-solid, proper temperature management and a faster reaction. The purpose is to model and simulate process variables where this forest biomass is gasified from the respective sensitivity analysis. It is obtained that the conversion of gasification reaction of pine sawdust increases at temperature higher than 900°C, showing a behavior that tends to be isothermal, suggesting an energetically self-sustaining process. In turn, it improved reaction for pine sawdust feed with an optimum particle size diameter of 0,65 mm; it is favored for low ratios steam / biomass fed in reaching the optimal 2,375; and at low air / biomass relationship with an optimum value of 0,289. It is evident that this process is a way of harnessing energy from thermochemical conversion of these wastes and forestry residues

Factors to consider from education to promote an image of science and technology with a gender perspective

The image of science influences on the decision of girls when opting for studies related to STEM disciplines, since in many cases they are perceived as masculine, due to the image promoted from different areas of society, including the education system. Consequently, women do not feel identified with these disciplines, and prejudices and beliefs are generated that promote the well-known gender gap that exists in these areas. Therefore, this article sets out the considerations to be taken into account from science and technology education to avoid showing an image of science as individual, stereotyped and elitist, among other aspects, and, ultimately, to promote an image of science and technology with a gender perspective. It is necessary to transform curricular content and teacher training following these considerations, so that students perceive a realistic image of science and technology. This will have a positive influence by minimising the Pygmalion effect that occurs in girls and helping to combat social inequality that generates the under-representation of women in scientific-technological fields.This work was supported by Ministery of Science, Innovation and Universities of Spain Goverment [PGC2018-094114-A-I00]. // Funding for open access charge: Universidad de Málaga / CBU