Novetats

A 3-D volume-of-fluid advection method based on cell-vertex velocities for unstructured meshes

UPCommons - dj., 06/22/2017 - 16:39
A 3-D volume-of-fluid advection method based on cell-vertex velocities for unstructured meshes Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro González, Jesús; Oliva Llena, Asensio A new geometrical Volume-of-Fluid (VOF) method for capturing interfaces on three-dimensional (3-D) Cartesian and unstructured meshes is introduced. The method reconstructs interfaces as first- and second-order piecewise planar approximations (PLIC), and advects volumes in a single unsplit Lagrangian–Eulerian (LE) geometrical algorithm based on constructing flux polyhedrons by tracing back the Lagrangian trajectories of the cell-vertex velocities. In this way, the situations of overlapping between flux polyhedrons are minimized, consequently, the accuracy in the solution of the advection equation is improved by minimizing the creation of overshoots (volume fractions over one), undershoots (volume fractions below zero) and wisps (fluid in void regions or vice versa). However, if not treated carefully, the use of cell-vertex velocities may result in the construction of flux polyhedrons that contain nonplanar faces and that do not conserve volume. Therefore, this work explains in detail a set of geometric algorithms necessary to overcome these two drawbacks. In addition, the new VOF method is analyzed numerically on 3-D Cartesian and unstructured meshes, first, by reconstructing the interface of spherical geometries and, second, by evaluating the final advection result of a sphere placed in a rotation, shear and deformation field.
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Evolución de un dispositivo inalámbrico para el registro de la actividad electromiográfica del músculo diafragma

UPCommons - dj., 06/22/2017 - 15:53
Evolución de un dispositivo inalámbrico para el registro de la actividad electromiográfica del músculo diafragma Ràfols de Urquía, Magda; Estévez Piorno, Josep; Torres Cebrián, Abel; Estrada, Luis; Jané Campos, Raimon La evaluación clínica y deportiva requiere el desarrollo de sistemas de adquisición de señales biomédicas de alta calidad. Sin embargo, estos sistemas implican una gran limitación: los datos deben ser registrados en laboratorios. En los últimos años se han desarrollado dispositivos inalámbricos multimodales que pueden poner fin a estos problemas. En este proyecto se han evaluado señales electromiográficas de los músculos respiratorios, en especial del diafragma (EMGdi), obtenidas a partir de un dispositivo inalámbrico. De forma simultánea se han adquirido las mismas señales con un sistema estándar de adquisición de señales biomédicas, para realizar un estudio comparativo de parámetros e información fisiológica extraída de dichas señales. Las señales han sido registradas en 9 sujetos sanos que siguieron un protocolo respiratorio. Estas señales han sido filtradas y procesadas usando técnicas basadas en el dominio frecuencial y temporal. El ritmo cardíaco ha sido estimado tanto a partir de la medida directa del registro ECG, como indirectamente a partir de las señales electromiografícas respiratorias, mientras que el ritmo respiratorio y la fuerza del músculo han sido estimados a partir de la amplitud de las señales EMGdi durante la contracción respiratoria. Los resultados obtenidos de los datos registrados por sistemas inalámbricos son muy similares a los obtenidos mediante sistemas convencionales con cables, demostrando ser una alternativa que permite adquisiciones y estudios fuera de los laboratorios en situaciones mucho más reales.
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Sillas fantasmas: una antología hegemónica

UPCommons - dj., 06/22/2017 - 15:22
Sillas fantasmas: una antología hegemónica Arias Laurino, Daniela; Marciani, Florencia; Moisset, Inés; Muxí Martínez, Zaida A través de la silla como mueble icónico que determinó momentos clave del diseño del siglo XX, el presente artículo analiza las antologías en términos de género con el objetivo de identificar el problema de la invisibilidad de las diseñadoras. Desvelar la ausencia de estas mujeres y hacer una revisión crítica sobre las historias de ellas, sus contribuciones y de las propias sillas, implica generar nuevos relatos que impidan la réplica de modelos y estereotipos en la profesión.; Through the chair as an iconic furniture that found key moments of 20th century design, this paper analyzes the anthologies in terms of gender with the aim of identifying the invisibility of women designers. Unveil the absence of these women and make a critical review of their histories, their contributions, and the chairs they had design, involves a construction of new narratives in order to avoid reproducing stereotypes and professional roles.
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Improving transversal competences by using wikis in collaborative work

UPCommons - dj., 06/22/2017 - 13:28
Improving transversal competences by using wikis in collaborative work Guinau Sellés, Marta; Playà Pous, Elisabet; Aulinas Juncà, Meritxell; Rosell Ortiz, Laura; Rivero Marginedas, Lluís Work on transversal competences in university degrees is a teaching line entirely established since the implementation of the European Credit Transfer System (ECTS). Nevertheless, undergraduate students present shortcomings in the development of some of these competences, especially on collaborative work, time management, oral and writing expression, and on the use of information resources. This paper presents a virtual tool and associated guidelines to enhance the information management during the development of collaborative works, and to facilitate the information availability among the students. Moreover, this tool and the guideline improve the individual monitoring and evaluation of the contributions of the students to the work. The proposal presented in this work belongs to a teaching innovation project carried out in the Earth Sciences Faculty of the Universitat de Barcelona, and implemented in the subjects General Geology (first-year in the Engineering Geology degree, 6 ECTS) and Geochemistry (third-year course in the Geology degree, 9 ECTS)
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Power system stability analysis under increasing penetration of photovoltaic power plants with synchronous power controllers

UPCommons - dj., 06/22/2017 - 12:55
Power system stability analysis under increasing penetration of photovoltaic power plants with synchronous power controllers Remón Rodríguez, Daniel; Mir Cantarellas, Antoni; Mauricio, J.M.; Rodríguez Cortés, Pedro The utilisation of renewable sources brings many benefits to electric power systems, but also some challenges such as the impact that renewable power plants employing power electronics have on the grid, which is gaining importance as the penetration of this type of generating stations increases, driven by the construction of large wind or solar photovoltaic (PV) power plants. This study analyses the impact of large-scale PV power plants on a transmission grid for different penetration levels. The analysis considers power plants formed by a number of power converters employing synchronous power controllers (SPCs), that allow them to have a harmonious interaction with the grid, and compares their performance with that of conventional power converter controllers, assuming in both cases that the power plants participate in frequency and voltage regulation. The study addresses both the small-signal stability of the system and its response to large disturbances that alter the active power balance and frequency stability. The results of the analysis show that PV power plants using SPCs are able to limit frequency deviations, improve the oscillation damping, and reduce the stress of other generating units, thus having a beneficial impact on the power system.
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Room escape at class: escape games activities to facilitate the motivation and learning in computer science

UPCommons - dj., 06/22/2017 - 12:52
Room escape at class: escape games activities to facilitate the motivation and learning in computer science Borrego, Carlos; Fernández, Cristina; Blanes, Ian; Robles, Sergi Real-life room-escape games are ludic activities in which participants enter a room in order to get out of it only after solving some riddles. In this paper, we explain a Room Escape teaching experience developed in the Engineering School at Universitat Autònoma de Barcelona. The goal of this activity is to increase student’s motivation and to improve their learning on two courses of the second year in the Computer Engineering degree: Computer Networksand Information and Security
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Synchronized access to streams in multiprocessors

UPCommons - dj., 06/22/2017 - 12:32
Synchronized access to streams in multiprocessors Peiron Guàrdia, Montse; Valero Cortés, Mateo; Ayguadé Parra, Eduard; Lang, Tomás The synchronized and simultaneous access to several vectors that form a single stream occurs in SIMD vector multiprocessors as well as in MIMD superscalar multiprocessors with decoupled access. In this paper we propose a block-interleaved storage scheme and an out-oforder access mechanism that allows conflict-free access to streams with an arbitrary initial address and constant stride between elements. A maximal number of conflict-free families including the most commonly used strides can be obtained. We consider the use of a crossbar interconnection network, although the method applies also for the case of a multistage interconnection network.
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Computing size-independent matrix problems on systolic array processors

UPCommons - dj., 06/22/2017 - 11:59
Computing size-independent matrix problems on systolic array processors Navarro Guerrero, Juan José; Llaberia Griñó, José M.; Valero Cortés, Mateo A methodology to transform dense to band matrices is presented in this paper. This transformation, is accomplished by triangular blocks partitioning, and allows the implementation of solutions to problems with any given size, by means of contraflow systolic arrays, originally proposed by H.T. Kung. Matrix-vector and matrix-matrix multiplications are the operations considered here.The proposed transformations allow the optimal utilization of processing elements (PEs) of the systolic array when dense matrix are operated. Every computation is made inside the array by using adequate feedback. The feedback delay time depends only on the systolic array size.
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A gamification experience to improve engineering students' performance through motivation

UPCommons - dj., 06/22/2017 - 11:57
A gamification experience to improve engineering students' performance through motivation Sánchez-Carmona, Adrián; Robles, Sergi; Pons, Jordi The students' lack of motivation is a usual problem. The students value more the obtention of the degree than the developing of competences and skills. In order to fight this, we developed a gamification's experience based on merits and leaderboards. The merits are linked to the attainment of skills and competences that students usually do not appreciate. During the year 2016, we are carrying out a pilot involving 950 students at the Graduate of Engineering in Computer Science at the Autonomous University of Barcelona (UAB)
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Estudio de las propiedades físicas y mecánicas de un lote de vigas de madera procedentes de un derribo mediante técnicas no destructivas

UPCommons - dj., 06/22/2017 - 11:40
Estudio de las propiedades físicas y mecánicas de un lote de vigas de madera procedentes de un derribo mediante técnicas no destructivas Bobadilla Fonollá, Tomás En el siguiente trabajo de investigación se agrupan los estudios, las observaciones, los resultados y las conclusiones que se han obtenido en la realización de: Una clasificación visual, una batería de ensayos no destructivos y cuasi no destructivos y un ensayo de rotura de un grupo de vigas de madera aserrada de gran escuadría. La población a estudiar consiste en un pequeño grupo de 15 vigas de madera de conífera aserrada procedente de un derribo con unas dimensiones medias aproximadas de 220x75mm de sección y 4500mm de longitud. Dentro del grupo encontramos dos especies diferentes de madera, el Abeto, Abies Alba, del que se disponen 12 ejemplares, y el Pinus Nigra muy similar al Pino Laricio del que solo se disponen 3 muestras. El primer paso realizado es una clasificación visual exhaustiva que ha dado lugar a una ficha de clasificación visual individualizada donde se marcan los defectos más reseñables. Para esta clasificación se han seguido las directrices establecidas en la norma UNE 56544/2011. Finalmente y en función de la clasificación y de la tipología de madera se le ha asignado una clase resistente. Posteriormente se han realizado una serie de ensayos no destructivos y cuasi no destructivos de diversas tipologías: ultrasonidos, análisis de vibraciones, de impacto etc., para obtener y tratar de determinar la humedad, la densidad y el módulo de elasticidad dinámico. Finalmente se han llevado las piezas a rotura para contraponer los resultados reales con los obtenidos con los ensayos y probar así su capacidad predictiva y su fiabilidad. Las principales conclusiones han sido que: los criterios de la clasificación visual ofrecen resultados demasiado conservadores, por lo que se han reclasificado dejándose de considerar una serie de factores con lo que el porcentaje de rechazo se redujo notablemente. En cuanto a la predicción de la densidad la principal conclusión fue que la extracción de microprobetas es el sistema que ofrece mejores resultados, mientras que en los ensayos de impacto, Pilodyn y Woodpecker, se obtiene una R2 bastante baja. Finalmente de cara a la predicción del módulo de elasticidad local y la tensión de rotura se ha concluido que en todos los casos los datos obtenidos de velocidad de propagación mediante los ensayos de ultrasonidos y análisis de vibraciones guardan una mayor relación con el ensayo del módulo de elasticidad que con la tensión de rotura. Asimismo si también tenemos en cuenta el factor de la densidad conjuntamente con la velocidad de propagación, es decir el módulo de elasticidad dinámico, los valores de correlación aumentan considerablemente.
Categories: Novetats

Generating domain-restricted resources for web interaction in several languages: hindi, english and spanish

UPCommons - dt., 06/20/2017 - 15:22
Generating domain-restricted resources for web interaction in several languages: hindi, english and spanish Gatius Vila, Marta; Paliwal, Piyush The aim of our research is to develop domain-restricted resources for web interaction supporting different languages: English, Hindi and Spanish. Many practical natural language systems use linguistic resources adapted to a specific domain because the processing is faster and more robust against errors. Besides, those grammars can be adapted to the language used by different types of users. To facilitate the process of generating linguistic resources for each domain and language, we use ontologies representing the entities and relations in a specific domain. The use of domain ontologies also favors the integration of knowledge from several web sites. For developing the grammar rules for each domain and language, we use Grammar Framework, a powerful tool for writing multilingual grammars that supports several alphabets. Our work is focused on the generation of assisting the user when accessing the web in two different scenarios: searching for information on cultural events and searching for a new medical specialist.
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Aplicación Extensométrica. Análisis de la propulsión en el remo de banco fijo. LLagut Català de la FNB. Parte II

UPCommons - dt., 06/20/2017 - 15:09
Aplicación Extensométrica. Análisis de la propulsión en el remo de banco fijo. LLagut Català de la FNB. Parte II Moreno Martinez, Juan Antonio
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Tokyo: interstice as urban structure

UPCommons - dt., 06/20/2017 - 15:08
Tokyo: interstice as urban structure Muxí Martínez, Zaida; Massip Bosch, Enric
Categories: Novetats

Aplicación Extensométrica. Análisis de la propulsión en el remo de banco fijo. Parte 1.

UPCommons - dt., 06/20/2017 - 15:06
Aplicación Extensométrica. Análisis de la propulsión en el remo de banco fijo. Parte 1. Moreno Martinez, Juan Antonio
Categories: Novetats

A teaching proposal for the study of Eigenvectors and Eigenvalues

UPCommons - dt., 06/20/2017 - 14:48
A teaching proposal for the study of Eigenvectors and Eigenvalues Beltrán Meneu, María José; Murillo Arcila, Marina; Jordá Mora, Enrique In this work, we present a teaching proposal which emphasizes on visualization and physical applications in the study of eigenvectors and eigenvalues. These concepts are introduced using the notion of the moment of inertia of a rigid body and the GeoGebra software. The proposal was motivated after observing students’ difficulties when treating eigenvectors and eigenvalues from a geometric point of view. It was designed following a particular sequence of activities with the schema: exploration, introduction of concepts, structuring of knowledge and application, and considering the three worlds of mathematical thinking provided by Tall: embodied, symbolic and formal
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Numerical homogenization and experimental validation of a composite plate using modal analysis

UPCommons - dt., 06/20/2017 - 14:28
Numerical homogenization and experimental validation of a composite plate using modal analysis Pérez Martínez, Marco Antonio; Gil Espert, Lluís; Hammami, Farah; Neifar, Mondher; Chafra, Moez A Finite Element (FE) simulation and an experimental (EXP) test are performed for the validation of the homogenized global elastic properties of a composite material plate. Composite material homogenization is based on several assumptions. Thus its validation through an independent procedure from the initial homogenization simulation is of great interest especially when materials are used in critical components such as in aerospace applications. As an application case, a Carbon/Epoxy unidirectional laminated plate is studied. Tow FE models (abaqus) are designed. First, homogenized mechanical properties are computed through a Representative Volume Element (RVE) model. Then, the computed homogenized mechanical properties are introduced to a modal analysis model of the composite plate. The resultant numerical natural frequencies and mode shapes are compared to the EXP modal analysis results. The results in this study show an interesting FE and EXP validation through a Vibration Based Method (VBM). The methodology presented in this paper can be applied to several composite material geometries and materials.
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Efficient three-dimensional building-soil model for the prediction of ground-borne vibrations in buildings

UPCommons - dt., 06/20/2017 - 14:09
Efficient three-dimensional building-soil model for the prediction of ground-borne vibrations in buildings Clot Razquin, Arnau; Arcos Villamarín, Robert; Romeu Garbí, Jordi This paper proposes a new efficient model for the prediction of low-amplitude ground-borne vibrations in buildings. The model takes into account the three-dimensional nature of the building structure by analytical and semianalytical means, making it ideal for performing parametric studies or large-scale vibrations predictions. Its formulation assumes that the principal component in floor vibrations is the vertical one and assumes that the vibrations are transmitted to the various floors through the building columns. The correctness of the model is tested by comparing, in two 3-story building examples, its results with those obtained using a numerical model. Results regarding the isolation efficiency of implementing a thicker lower floor or columns with a larger cross section are also presented. The building-soil coupling is formulated considering piled foundations in a stratified soil. To ensure the computational efficiency of the calculations, the piles’ response to an incident wavefield is modeled considering the Novak pile model for a layered half-space. Finally, a study of the importance of the soil mechanical parameters in the considered problem is conducted using the building-soil coupled model.
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Estudio del condicionamiento de piezas termoplásticas

UPCommons - dt., 06/20/2017 - 13:30
Estudio del condicionamiento de piezas termoplásticas Adame López, José Este proyecto muestra un estudio empírico del comportamiento de piezas inyectadas con poliamida una vez se condicionan con humedad. Este condicionamiento tiene el objetivo de aumentar o disminuir la ductilidad con el fin de ajustar los esfuerzos necesarios para que las piezas cumplan una función determinada, por ejemplo, reducir ciertos esfuerzos de introducción para luego, perdiendo un porcentaje de esa humedad, los esfuerzos de extracción sean más altos. Se trata de, a partir de unas nociones básicas, determinar la realidad del comportamiento mediante ensayos realizados en piezas reales con unas condiciones de comportamiento reales. Además, se proponen mejoras para paliar errores actuales del sistema de producción, desde que las piezas se inyectan hasta que llegan a su destino final. Todo este estudio ha sido realizado con piezas y en las instalaciones de ITW España. Esta sección de la empresa se dedica a desarrollar y producir componentes plásticos para la industria automovilística.
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Tanatori a Montjuïc

UPCommons - dt., 06/20/2017 - 13:27
Tanatori a Montjuïc Martí Mercader, Marçal
Categories: Novetats

TFET-Based power management circuit for RF energy harvesting

UPCommons - dt., 06/20/2017 - 13:22
TFET-Based power management circuit for RF energy harvesting Nunes Cavalheiro, David Manuel; Moll Echeto, Francisco de Borja; Valtchev, Stanimir This paper proposes a Tunnel FET (TFET)-based power management circuit (PMC) for ultra-low power RF energy harvesting applications. In contrast with conventional thermionic devices, the band-to-band tunneling mechanism of TFETs allows a better switching performance at sub-0.2 V operation. As a result, improved efficiencies in RF-powered circuits are achieved, thanks to increased rectification performance at low power levels and to the reduced energy required for a proper PMC operation. It is shown by simulations that heterojunction TFET devices designed with III-V materials can improve the rectification process at received power levels below -20 dBm (915 MHz) when compared to the application of homojunction III-V TFETs and Si FinFETs. For an available power of -25 dBm, the proposed converter is able to deliver 1.1 µW of average power (with 0.5 V) to the output load with a boost efficiency of 86%.
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