On a poroviscoelastic model for cell crawling

In this paper a minimal, one–dimensional, two–phase, viscoelastic, reactive, flow model for a crawling cell is presented. Two–phase models are used with a variety of constitutive assumptions in the literature to model cell motility. We use an upper–convected Maxwell model and demonstrate that even the simplest of two–phase, viscoelastic models displays features relevant to cell motility. We also show care must be exercised in choosing parameters for such models as a poor choice can lead to an ill–posed problem. A stability analysis reveals that the initially stationary, spatially uniform strip of cytoplasm starts to crawl in response to a perturbation which breaks the symmetry of the network volume fraction or network stress. We also demonstrate numerically that there is a steady travelling–wave solution in which the crawling velocity has a bell–shaped dependence on adhesion strength, in agreement with biological observation

A comparative study on homogenization strategies for multi-scale analysis of materials

One of the most important engineering tasks over the years has been the design and manufacture of increasingly sophisticated structural materials as a result of the requirements related to the technological progress. In the last decades, the growing needs for improved properties of products have been partially solved through the development of composite materials. A key to the success of many modern structural components is the tailored behavior of the material to given applications. Therefore, research efforts in material science engineering have been focused in the design of new materials either through the creation of new structures at the scale of single atoms and molecules or through the development of structural materials by changing the composition, size, arrangement and topology of the constituents at larger scales: the microscopic/mesoscopic level. The development of new materials has been linked to the development of a new theoretical field within the mechanics of solids. This branch of the mechanical, known as Continuum Micromechanics, introduces a series of new concepts that are key to the definition of the macroscopic properties of composite materials on the basis of the definition of the characteristics of its components. Starting from the premise of separation of scales and the concept of Representative Volume Element, defined the so-called homogenization methods, whose number has been increasing as the Micromechanics is gone extend over the years. Such methods are many and varied, although especially there have been two that have been used and developed by the majority of authors: the so-called Mean-Homogenization techniques and the multi-scale based on Finite Element Approaches. Mean-fifieeld homogenization schemes are an efficient way to predict the behavior of heterogeneous materials. They range from the simplest hypotheses of the stress or strain sharing among the phases which do not require analytical solution on the associated boundary-value problem to more involved geometric models based on the solution of a boundary-value problem involving a single or composite inclusion embedded in an equivalent homogenized medium whose elastic module become part of the solution procedure. In general, they are based on analytical solutions of the boundary value problem defined in the microstructure level of the inhomogeneous material and provide good predictions for the mean values over the RVE. Although originally designed for elastic materials, some approaches to deal with elastoplastic materials and even with viscoplastic materials have been developed over the years and compared with the results obtained using Finite Element Approaches. The comparison between different methods of homogenization allows the definition of a range of validity between the different methods, which helps to discover the limitations of the various methods and aspects to take into account for future developments and research. The main goal of this work is, firstly, to present a general overview of the different techniques that have been developed in the last years in order to obtain a prediction of the behavior of elastoplastic composites by taking into account geometrical and mechanical aspects. Secondly, a comparison between the different approaches is carried out through a numerical implementation of such techniques. Both objectives will be carried out through eight different chapters. The first chapter serves as an introduction and historical review of the advances that have been made in the field of micromechanics. On the other hand, the second chapter deals with some important theoretical background that is important in the field of Continuum Micromechanics, as well as a short introduction of the different approaches that traditionally have been considered to solve the problem. One group of methods, based on analytical solutions { the so-called Mean Field Analysis { will be commented in chapter 3. Chapter 4 is devoted to the implementation and validation of a numerical tool that solves the mean-field homogenization using analytical schemes for elastoplastic materials. Subsequent chapters are devoted to the comparison of the results with the results given by the Finite Element Method. The general formulation of such method { applied to multi-scale problems { is presented in chapter 5 from a theoretical point of view, as well as the corresponding numerical examples. Finally, last chapter will be dedicated to enumerate some conclusions extracted from the present work, including some aspects that can be object of future works or improvements. The current work presents some important aspects about the theoretical concepts and the numerical implementation of some key approaches for solving the mechanical problem regarding composite materials. There exist a large number of possibilities to approximate the response of such complex materials, based in different assumptions. This document shows the general efficiency of the so-called mean-field homogenization schemes to capture correctly the macroscopic behavior of composites. Although these techniques show some limitations, like the incapability to provide results for the distribution of the different variables over the microgeometry or the low accuracy in the case of complex microgeometries (like porous materials), they represent an efficient way to predict the main general behavior of a composite material spending low computational effort. They are specially indicated to be used in the previous steps of an analysis or as a tool to validate the results with more involved approaches

Update on ultrasensitive technologies to facilitate research on blood biomarkers for central nervous system disorders

Most research on fluid biomarkers for central nervous system (CNS) disorders has so far been performed using cerebrospinal fluid (CSF) as the biomarker source. CSF has the advantage of being closer to the brain than serum or plasma with a relative enrichment of CNS-specific proteins that are present at very low concentrations in the blood and thus difficult to reliably quantify using standard immunochemical technologies. Recent technical breakthroughs in the field of ultrasensitive assays have started to change this. Here, we review the most established ultrasensitive quantitative technologies that are currently available to general biomarker laboratories and discuss their use in research on biomarkers for CNS disorders

Factores psicosociales influyentes en la ocurrencia de accidentes laborales

El objetivo del trabajo es la presentación de un modelo de predicción de la siniestralidad laboral basado en datos empíricos en un conjunto de variables susceptibles de intervención. El método empleado es un diseño transversal y correlacional, en el que a partir de una muestra representativa de más de 500 trabajadores de diferentes sectores de actividad de la provincia de Valencia, se cuantifica la importancia relativa de cada uno de los aspectos definidos como relevantes para predecir la ocurrencia de accidentes. El uso metodológico de modelos de ecuaciones estructurales permite la consideración simultánea de un gran número de variables, junto con un adecuado control estadístico, reflejando así con mayor fidelidad la problemática de la siniestralidad laboral. Los resultados muestran el impacto de la variables organizacionales y los riesgos sobre variables del trabajador, la importancia de éstas en la predicción de accidentes, junto con su papel mediador en los efectos de las variables organizacionales (clima de seguridad, formación en seguridad, sobrecarga de trabajo, etc.) sobre la ocurrencia de accidentes laborales. La conclusión es que los aspectos psicosociales son claves en la explicación de los accidentes laborales y abren vías para una intervención efica

Soot temperature characterization of spray a flames by combined extinction and radiation methodology

[EN] Even though different optical techniques have been applied on 'Spray A' in-flame soot quantification within Engine Combustion Network in recent years, little information can be found for soot temperature measurement. In this study, a combined extinction and radiation methodology has been developed with different wavelengths and applied on quasi-steady Diesel flame to obtain the soot amount and temperature distribution simultaneously by considering self-absorption issues. All the measurements were conducted in a constant pressure combustion chamber. The fuel as well as the operating conditions and the injector used were chosen following the guidelines of the Engine Combustion Network. Uncertainty caused by wavelength selection was evaluated. Additionally, temperature-equivalence ratio maps were constructed by combining the measurements with a 1D spray model. Temperature fields during the quasi-steady combustion phase show peak temperatures around the limit of the radiation field, in agreement with a typical diffusion flame structure. Effects of different operating parameters on soot formation and temperature were investigated. Soot temperature increases dramatically with oxygen concentration, but it shows much less sensitivity with ambient temperature and injection pressure, which on the other hand have significant effects on soot production. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.This study was partially funded by the Ministerio de Economia y Competitividad from Spain in the frame of the CHEST Project (TRA2017-89139-C2-1-R) and China Postdoctoral Science Foundation (2018M642176). This study was also partially supported by State Key Laboratory of Engines, Tianjin University.Xuan, T.; Desantes J.M.; Pastor, JV.; García-Oliver, JM. (2019). Soot temperature characterization of spray a flames by combined extinction and radiation methodology. Combustion and Flame. 204:290-303. https://doi.org/10.1016/j.combustflame.2019.03.02329030320