Sobre la definición y cálculo de la Energía de Falla de Apilamiento

Los aceros austeníticos de alto contenido en manganeso (Mn > 20%) de estructura FCC, pertenecen a la nueva generación de aceros avanzados de alta resistencia, esto por su buen comportamiento mecánico global. Las mejores propiedades de estos materiales se deben a la competencia entre los distintos mecanismos de deformación que pueden manifestarse, estando estos relacionados con la Energía de Falla de Apilamiento (EFA), que define la prevalencia de un mecanismo por sobre otro, siendo estos el deslizamiento de dislocaciones, el maclado mecánico y la transformación de austenita-γ a martensita-ε. Este artículo explica el concepto de la Energía de Falla de Apilamiento dentro de materiales FCC, los métodos de obtención y los mecanismos de deformación que son regidos por esta, para finalizar con el planteo del modelo de Olson y Cohen y su aplicación en un acero específico de composición Fe-22%Mn-0,6%C en un rango de temperatura entre 50 a 600 [K]. Se demuestra que la EFA es proporcional a la temperatura y que se relaciona principalmente con la interacción de los elementos de aleación. Palabras Clave: Aceros TWIP; Energía de falla de apilamiento; Austenita; Martensita

INDUSTRIALISED STRUCTURES AS AN INNOVATIVE ELEMENT UNDER THE CONTRAST OF ENGINEERS' PERCEPTIONS

The objective of the research was to make known the experiences of calculating engineers in the face of the behavior of industrialized buildings in earthquakes of great magnitude in the departments of Santander and Norte de Santander, Colombia. This industrialized construction system for houses was taken as object of study due to its novel implantation in the departments. The planning, execution and application of the 2010 seismic standard applied in Colombia in the field of building construction was analyzed. In addition to the field experiences of the professionals and university professors of both departments, the research was based mainly on the technical knowledge of the specialists. These two characteristics were taken into account due to the absence of information on the structural behavior under earthquakes of great magnitude of the buildings constructed with the system in the departments. The interpretative method was used with the support of the computer-assisted qualitative analysis program ATLAS.ti, which allowed the association of codes through the relationships of the interviews. The results concluded in the feasibility of implementing the system as a method of construction of buildings resistant to earthquakes of great magnitude subject to strict monitoring of the parameters described in the relevant regulations for the country, however the information provided is of great importance for individuals and contractors in the construction area in Colombia, since the expert engineers in calculations have some contradictions as for the industrialized system, and this can be factor of incidences in the response to earthquakes of these buildings, it is for that reason that the information revealed is a novelty to take into account the types of systems that calculate them the same but really have many structural differences and this could be a key element in an earthquake of great magnitude

Extending effective medium theory to finite size systems: theory and simulation for permeation in mixed-matrix membranes

We present a novel theory for estimation of the effective permeability of pure gases in flat mixed-matrix membranes (MMMs), in which effective medium theory (EMT) is extended to systems with finite filler size and membrane thickness. We introduce an inhomogeneous filler volume fraction profile, which arises due to depletion of the filler in regions adjacent to the membrane ends, into the MMM permeation model. In this way, the effective medium approach (EMA) can still be applied to systems where the dispersant size is not small in comparison to the membrane thickness, and for which a permeability profiles arises in the MMM that is dependent on both filler size and membrane thickness, besides the filler-polymer equilibrium constant. It is found that increase in particle size reduces the effective membrane permeability at fixed membrane thickness, and that the effective membrane permeability increases with increase of the membrane thickness to asymptotically reach the value predicted by existing models. The present theory is validated against detailed simulations of the transport in MMMs, and theoretical predictions are found to be in agreement with those obtained from the exact calculations. Further, comparison of the exact effective permeability at different filler volume fractions is made for different packing configurations, showing variations in dispersant packing structure to have only a very weak effect on MMM performance

Concentration-dependent transport in finite sized composites: modified effective medium theory

Current models for transport in dispersions, while grounded in well-established effective medium theory (EMT), rely on the assumption of uniformity of the driving force. As consequence, theoretical approaches cannot accommodate driving force inhomogeneities as well as variations over the space occupied by the dispersed phase particles, and existing EMT-based models therefore fail to represent finite particle size effects. Moreover, because transport coefficients are generally considered uniform, such models largely pertain to the Henry's law region. Here, using the context of permeation in mixed-matrix membranes (MMMs), we introduce a self-consistent theory for transport in dispersion-based composites, which captures effects of isotherm nonlinearity and dispersant size without introducing fitting parameters, and accurately predicts concentration-dependent permeabilities. The model is validated against rigorous 3d simulations of transport in filler-polymer composite MMMs, with excellent agreement between theoretical results and those from simulation. Both model and simulations confirm isotherm nonlinearities to have a very significant effect on effective MMM permeability, which is found to be more sensitive to isotherm nonlinearity in the filler phase than in the continuous phase. These effects disappear when the filler phase is much more permeable than the continuous phase, although additional system size effects related to exclusion regions at the ends due to finite particle size lead to decrease in permeability with increase in particle size even for linear isotherms

Comparison of hollow fiber and flat mixed-matrix membranes: theory and simulation

We extend effective medium theory (EMT) to composite hollow fiber mixed matrix membranes, considering the asymmetric filler volume fraction profile arising from finite system size. This volume fraction profile leads to strong variation of the driving force (i.e. pseudo-bulk concentration gradient) in the regions adjacent to the composite ends, and to sensitivity of the effective permeability of the composite to the geometrical configuration. The new theory is validated against rigorous simulations of the transport in mixed-matrix membranes (MMMs) using both concentration-independent and concentration-dependent diffusivities in the MMM constituent phases. Both theory and simulations show that flat mixed-matrix membranes (F-MMMs) have higher effective overall permeability than hollow fiber mixed-matrix membranes (HF-MMMs), upon comparison of systems having identical operating conditions, filler phase loading and particle size. Furthermore, we show here that the sensitivity to the geometry vanishes with increase of inner radius of the hollow fiber membrane at fixed thickness, and the effective permeability of a HF-MMM is found to asymptotically approach that of a F-MMM

Socialización parental y ciberviolencia en estudiantes de una Institución Educativa De Chiclayo

La familia y sus procesos se constituyen en elementos trascendentales en la formación integral de los adolescentes, incluyendo procesos disfuncionales; por ello, desde la socialización es necesario la promoción de buenas prácticas que coadyuven en el control de la violencia y ciberviolencia. En tal sentido, se ha desarrollado la presente investigación que tuvo como objetivo determinar la relación entre socialización parental y ciberviolencia en estudiantes de una institución educativa de Chiclayo. El diseño de investigación fue no experimental, de enfoque cuantitativo y tipología básica y correlacional. La muestra estuvo constituida por 105 estudiantes de entre 12 y 17 años de edad (M=15; DE=1.4), de ambos sexos (65 varones y 40 mujeres). Los instrumentos de recolección de datos fueron la escala de socialización parental de Musitu y García (2001) y la escala de ciberviolencia de Caba y Buelga (2018). Los resultados han demostrado que, existe relación entre socialización parental, específicamente en el componente coerción-imposición y ciberacoso perpetrado y cibervictimización (p<.05); asimismo, los padres son percibidos bajo es estilo autoritario (41%), mientras que las madres bajo el estilo indulgente (37.1%); así también, en los varones predominan los niveles altos de ciberacoso perpetrado (38.5%), mientras que en las mujeres el nivel bajo (55%); y en ambos sexos, la cibervictimización predominante se clasifica en un nivel medio. Se concluye que, la dinámica familia, y específicamente la forma en que los padres socializan con sus hijos, se asocian con la concepción de violencia, incluyendo aquella que se desarrolla por medio de las tecnologías modernas.Tesi

Simulation of multicomponent gas transport through mixed-matrix membranes

We extend the Maxwell-Stefan (M-S) formulation of irreversible thermodynamics to multicomponent transport in mixed-matrix membranes (MMMs), using a simulation-based rigorous modeling approach (SMA) through finite-element method (FEM) solution of the three-dimensional (3-d) transport problem in full-scale MMMs. In the new approach, we generalize the dual-mode/partial immobilization (DM/PI) theory for the local permeability in glassy polymers to describe multicomponent permeation in pure glassy polymer membranes and MMMs, by reformulating the M-S constitutive equations in the Onsager formalism considering concentration-dependent transport diffusivities and non-uniform concentration gradients across the MMM. In this way, the new M-S formulation explicitly considers effects of intrinsic MMM features such as finite filler particle size and isotherm nonlinearity in the MMM constituent phases, as well as mixture-related effects, such as competitive adsorption and friction amongst permeants, on the calculation of the mixture fluxes (permeabilities). This is achieved without introduction of empirical fitting parameters in the MMM permeability calculation and only requiring single-gas experimental or simulation-based adsorption and permeation data on the individual MMM materials to predict the mixture perm-selectivity in the MMM as a whole. Further, we validate the new approach by using available experimental permeation data for the separation of an equimolar binary mixture of propylene (C H ) and propane (C H ) in ZIF‑8/PIM-6FDA-OH MMMs, with the rigorous simulation results showing very good agreement with both experimental single and mixed-gas permeabilities and perm-selectivities

Model-based scale-up methodology for aerobic fed-batch bioprocesses: application to polyhydroxybutyrate (PHB) production

This work presents a general model-based methodology to scale-up fed-batch bioprocesses. The idea behind this approach is to establish a dynamics hierarchy, based on a model of the process, that allows the designer to determine the proper scale factors as well as at which point of the fed-batch the process should be scaled up. Here, concepts and tools of linear control theory, such as the singular value decomposition of the Hankel matrix, are exploited in the context of process design. The proposed scale-up methodology is first described in a bioprocesses general framework highlighting its main features, key variables and parameters. Then, it is applied to a polyhydroxybutyrate (PHB) fed-batch bioreactor and compared with three empirical criteria, that are traditionally employed to determine the scale factors of these processes, showing the usefulness and distinctive features of this proposal. Moreover, this methodology provides theoretical support to a frequently used empirical rule: scale-up aerobic bioreactors at constant volumetric oxygen transfer coefficient. Finally, similar process dynamic behavior and PHB production set at the laboratory scale are predicted at the new operating scale, while it is also determined that is rarely possible to reproduce similar dynamic behavior of the bioreactor using empirical scale-up criteria.Facultad de IngenieríaInstituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

Analysis of sloppiness in model simulations: unveiling parameter uncertainty when mathematical models are fitted to data

This work introduces a Bayesian approach to assess the sensitivity of model outputs to changes in parameter values, constrained by the combination of prior beliefs and data. This novel approach identifies stiff parameter combinations that strongly affect the quality of the model-data fit while simultaneously revealing which of these key parameter combinations are informed primarily from the data or are also substantively influenced by the priors. We focus on the very common context in complex systems where the amount and quality of data are low compared to the number of model parameters to be collectively estimated, and showcase the benefits of our technique for applications in biochemistry, ecology, and cardiac electrophysiology. We also show how stiff parameter combinations, once identified, uncover controlling mechanisms underlying the system being modeled and inform which of the model parameters need to be prioritized in future experiments for improved parameter inference from collective model-data fitting

ABLATOR NANOCOMPUESTO DE RESINAS POLIMÉRICAS TERMOFIJAS REFORZADO CON MICRO Y NANOESTRUCTURAS EN APLICACIONES DE PROTECCIÓN TÉRMICA AERONÁUTICA E INDUSTRIAL

Un material ablativo es un material diseñado para proteger y resistir al daño térmico [1]. En ésta investigación se decidió diseñar un grupo de ablatores poliméricos, por su buena relación peso- resistencia en aeronáutica y automotriz. Cuando un ablator polimérico termofijo se expone a la llama o gases de combustión, es decir, a altas temperaturas, se carboniza creando una capa cerámica porosa que servirá de protección térmica asociada a su índice de aislamiento. Hay diversos tipos de materiales ablativos; ablatores de sublimación, ablatores de fusión y de degradación [2]. El tipo de ablator que se desarrolló es uno de degradación o carbonización, este se hace a partir de resinas termofijas como las resinas epóxicas y poliéster [3], por esta razón, se decidió desarrollar una serie de experimentaciones con estas dos resinas combinando cargas cerámicas, fibras y nanotubos de carbono funcionalizados, con el fin de observar, en los ensayos termomecánicos por llama, su efecto en la forma, mecanismos y velocidad de degradación térmica así como su nivel de protección medido en términos de un gradiente térmico lineal