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Exponential finite element shape functions for a phase field model of brittle fracture

  • Kuhn, Charlotte
  • Müller, Ralf
In phase field models for fracture a continuous scalar field variable is used to indicate cracks, i.e. the value 1 of the phase field variable is assigned to sound material, while the value 0 indicates fully broken material. The width of the transition zone where the phase field parameter changes between 1 and 0 is controlled by a regularization parameter. As a finite element discretization of the model needs to be fine enough to resolve the crack field and its gradient, the numerical results are sensitive to the choice of the regularization parameter in conjunction with the mesh size. This is the main challenge and the computational limit of the finite element implementation of phase field fracture models. To overcome this limitation a finite element technique using special shape functions is introduced. These special shape functions take into account the exponential character of the crack field as well as its dependence on the regularization length. Numerical examples show that the exponential shape functions allow a coarser discretization than standard linear shape functions without compromise on the accuracy of the results. This is due to the fact, that using exponential shape functions, the approximation of the surface energy of the phase field cracks is impressively precise, even if the regularization length is rather small compared to the mesh size. Thus, these shape functions provide an alternative to a numerically expensive mesh refinement.

Investigation of the structure and properties of flexible polymeric materials for integration with thin heat conductors

  • Cherunova, Irina V.
  • Stenkina, Maria P.
  • Cherunov, Pavel V.
This article presents the results of analysis of the methods of connecting heaters with materials. Limitations and disadvantages of the ways of integration of materials with heat conductors are revealed. The method of glueless thermoplastic fixing has been proposed. The thermophysical characteristics of the selected polymeric materials were experimentally determined. Experimental studies of the maximum strength for selected materials were carried out. Recommendations for creating heat-protective garments with polymeric materials have been obtained.

Physical visualization of math concepts using Lego Mindstorms

  • Suárez-Gómez, Andrés-David
  • Pérez-Holguín, Wilson Javier
Educational robotics has become one of the most effective methods to teach STEM concepts in a practical and didactic way at all educational level. In this context, the LEGO Mindstorms robotic platforms have been widely used due to their versatility ease of use and modularity. Despite this, most of the papers focus on K-12 and undergraduate levels, with little information reported in the literature about educational experiences at the graduate level. This article deals with the use of educational robotics for the teaching of mathematical concepts at the graduate level, and more specifically on the physical visualization of metrics (Euclidean, Taxicab, and Infinity), and the convergence of Cauchy sequence using a mobile robots LEGO Mindstorms NXT. The educational experience was applied to a group of graduate students who offered good comments on this type of educational activity and its usefulness to understand the mathematical concepts addressed. It was observed that this type of educational experiences motivates students to use mathematical concepts in interdisciplinary problems and encourages them to understand their functionality and application in the real world, Peer Reviewed

Análisis y aplicación de diversos métodos y técnicas de previsión de ventas

  • Camara Roldan, Sofia
El objetivo de este proyecto es describir una metodología de previsión de ventas que permita establecer un modelo de previsión adecuado dada una casuística concreta. Por ello, se realizan diversos análisis con el fin de conocer el impacto de las previsiones de ventas y qué técnicas de previsión son las más adecuadas para cada caso particular. La metodología descrita y los resultados de los análisis son aplicados a un caso práctico en el que se desea predecir las ventas de un establecimiento minorista de la compañía Walmart. La metodología de previsión de ventas presentada considera diversos métodos de previsión. Con el fin de conocer qué métodos son los más adecuados para cada casuística, es importante conocer y entender el impacto de las previsiones de venta en la gestión de la cadena de suministro. Por ello, se analiza, considerando diferentes tipologías de producto, el impacto que las previsiones generan en los niveles de existencias y en la gestión de las actividades de todos los actores que forman la cadena de abastecimiento. Con el fin de mejorar la eficiencia de la cadena de suministro, se concluye que es importante predecir con una precisión elevada y en todas las etapas de la cadena, las ventas de productos que generan un gran número de ventas y/o ingresos, que tienen un elevado coste de stock, un alto riesgo a generar stock obsoleto o un tiempo de abastecimiento alto. Con el fin de conocer que métodos de previsión deben ser considerados al aplicar la metodología descrita en un caso particular, se realiza un análisis de los diversos métodos y técnicas de previsión de ventas existentes. De este análisis se destaca que las ventas pueden ser previstas mediante métodos cualitativos o mediante métodos cuantitativos. Los segundos son en general más precisos y deben ser considerados cuando se dispone de un histórico de datos. Los métodos cuantitativos se dividen en métodos estadísticos basados en el análisis de series de tiempo y en métodos causales. Tradicionalmente las ventas son previstas utilizando modelos de series temporales; entre los que destacan las variaciones de los modelos autorregresivos integrados de medias móviles (ARIMA) y de los modelos de alisado exponencial. A pesar de ello, en el presente trabajo, se analizan también métodos causales de aprendizaje automático los cuales permiten, en general, la obtención de resultados más precisos. En la resolución del caso práctico, donde se aplica la metodología presentada y se analiza la precisión de las previsiones aplicando diferentes modelos de previsión, se define un modelo de aprendizaje automático para realizar las previsiones de venta del establecimiento Walmart considerado. El modelo propuesto se basa en el aprendizaje combinado y considera las previsiones de un modelo de bosques aleatorios, en un 70%, y las de un modelo de regresión lineal, en un 30%; y, presenta una precisión del 96, 57 %. En el caso práctico, se valora también el impacto de aplicar el modelo de ventas propuesto en el establecimiento Walmart.

A demand based algorithm for rapid updating of replicas

  • Acosta Elías, J. Jesús
  • Navarro Moldes, Leandro
In many Internet scale replicated system, not all replicas can be dealt with in the same way, since some will be in greater demand than others. In the case of weak consistency algorithms, we have observed that updating first replicas having most demand, a greater number of clients would gain access to updated content in a shorter period of time. In this work we have investigated the benefits that can be obtained by prioritizing replicas with greater demand, and considerable improvements have been achieved. In zones of higher demand, the consistent state is reached up to six times quicker than with a normal weak consistency algorithm, without incurring the additional costs of the strong consistency., Peer Reviewed


  • Borràs García, M. Rosa

Dielectric properties of liquid ethanol: a computer simulation study

  • Saiz, L
  • Guàrdia Manuel, Elvira
  • Padro Cardenas, Joan Angel
Static and dynamic dielectric properties of liquidethanol have been studied as a function of the wave-vector number by computer simulation.Molecular dynamics simulations at room temperature have been performed using the optimized potentials for liquid simulations (OPLS) potential model proposed by Jorgensen [J. Phys. Chem. 90, 1276 (1986)]. The time dependent correlation functions of the longitudinal and transverse components of the dipole density as well as the individual and total dipole moment autocorrelation functions have been calculated. The infrared spectra and the dielectric relaxation of the liquid have been also analyzed. Results have been compared with the available experimental data. Special attention has been dedicated to investigate the molecular origin of the different analyzed properties.

Towards distributed architecture for collaborative cloud services in community networks

  • Khan, Muhammad Amin
  • Selimi, Mennan
  • Freitag, Fèlix
Internet and communication technologies have lowered the costs for communities to collaborate, leading to new services like user-generated content and social computing, and through collaboration, collectively built infrastructures like community networks have also emerged. Community networks get formed when individuals and local organisations from a geographic area team up to create and run a community-owned IP network to satisfy the community’s demand for ICT, such as facilitating Internet access and providing services of local interest. The consolidation of today’s cloud technologies offers now the possibility of collectively built community clouds, building upon user-generated content and user-provided networks towards an ecosystem of cloud services. To address the limitation and enhance utility of community networks, we propose a collaborative distributed architecture for building a community cloud system that employs resources contributed by the members of the community network for provisioning infrastructure and software services. Such architecture needs to be tailored to the specific social, economic and technical characteristics of the community networks for community clouds to be successful and sustainable. By real deployments of clouds in community networks and evaluation of application performance, we show that community clouds are feasible. Our result may encourage collaborative innovative cloud-based services made possible with the resources of a community., Peer Reviewed

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