• Analysis and experimental evaluation of the frequency response of an indoor radiating cable in the UHF band

      Seseña Osorio, Jorge A.; Zaldívar Huerta, Ignacio E.; Aragón Zavala, Alejandro; Castañón Ávila, Gerardo A. (Springer Open, 10/02/2015)
      Abstract We present the modeling of the frequency response of the channel for a radiating cable system by using an autoregressive model for an indoor environment. The coefficients of the autoregressive model are determined from the experimental channel frequency response. Measurements were carried out in an indoor environment, in particular on the second floor of a university building in the frequency range of 1.3 to 1.8 GHz by using a vector network analyzer. It is demonstrated that the use of a second-order model provides a better representation of the behavior of the channel. In this context, the coherence bandwidth and the rms delay spread show dependence with the receiver position along the radiating cable length. This dependence is crucial and must be taken into account in the design and study of broadband systems with mobility because the rms delay spread and coherence bandwidth are used to describe the time dispersion and the frequency selectivity of the multipath fading channels, respectively.
    • The conceptual survey of electricity and magnetism: reliability analysis and study of most frequent difficulties

      Barniol, Pablo; Campos, Esmeralda; Zavala, Genaro (2018)
      La prueba The Conceptual Survey of Electricity and Magnetism (CSEM) ha sido ampliamente utilizada en el área de la educación de la física. Sin embargo, hasta la fecha no existe un estudio que presente el test en su versión en español. Este artículo tiene tres objetivos generales: 1) presentar el CSEM en su versión en español y analizar la confiabilidad y poder discriminatorio de este, 2) realizar un análisis detallado de las dificultades más frecuentes de los estudiantes en los conceptos evaluados en el test y 3) establecer recomendaciones para la investigación e instrucción de estos conceptos. El test fue implementado a 310 estudiantes que terminaban el curso Electricidad y Magnetismo de una universidad mexicana. El test en su versión en español, que presentamos en el proyecto Physport (physport.org), los análisis y las recomendaciones para la instrucción pueden ser utilizados por investigadores o por profesores de física de países hispanohablantes.
    • Identification of material properties using nanoindentation and surrogate modeling

      Li, Han; Gutierrez, Leonardo; Toda, Hiroyuki; Kuwazuru, Osamu; Liu, WenliHangai, Yoshihiko; Kobayashi, Masakazu; Batres Prieto, Rafael; Tecnologico de Monterrey (Elsevier, 2016)
      In theory, identification of material properties of microscopic materials, such as thin film or single crystal, could be carried out with physical experimentation followed by simulation and optimization to fit the simulation result to the experimental data. However, the optimization with a number of finite element simulations tends to be computationally expensive. This paper proposes an identification methodology based on nanoindentation that aims at achieving a small number of finite element simulations. The methodology is based on the construction of a surrogate model using artificial neural-networks. A sampling scheme is proposed to improve the quality of the surrogate model. In addition, the differential evolution algorithm is applied to identify the material parameters that match the surrogate model with the experimental data. The proposed methodology is demonstrated with the nanoindentation of an aluminum matrix in a die cast aluminum alloy. The result indicates that the methodology has good computational efficiency and accuracy.
    • Impelling research productivity and impact through collaboration: a scientometric case study of knowledge management

      Ceballos, Hector G.; Fangmeyer Jr, James Andrew; Galeano Sánchez, Nathalíe M.; Juarez, Erika; Cantú Ortíz, Francisco J.; Tecnologico de Monterrey (Palgrave Macmillan, 2017-07-11)
      A case study for impelling university research productivity and impact through collaboration is presented. Scientometric results support the hypothesis that a knowledge management model increased research collaboration and thereby boosted a university’s number of publications and citations. Results come from fifteen years of data at a Mexican university with 2400 researchers who produced 24,000 works in fifteen research disciplines. These data are treated with social network visualizations and algorithms to identify patterns of collaboration and clustering, as well as with normalizations to make disciplines comparable and to verify increasing citation impact. The knowledge management model implemented in the study may be a costeffective way for universities to intensify collaboration and improve research performance.
    • The mechanical waves conceptual survey: An analysis of university students' performance, and recommendations for instruction

      Barniol P. (Modestum, 2017-01-01)
      The Mechanical Waves Conceptual Survey (MWCS), presented in 2009, is the most important test to date that has been designed to evaluate university students' understanding of four main topics: propagation, superposition, reflection, and standing waves. In a literature review, we detected a significant need for a study that uses this test as an assessment tool and presents a complete analysis of students' difficulties on the test. This article addresses this need. We administered the MWCS at a private university in Mexico to 541 students. In this article, we present a complete description of these students' performance on the test, a description of their main difficulties, an elaboration of these main difficulties in terms of students' inappropriate conceptions, and recommendations for instruction based on the results obtained by the test. Our analyses may be used by instructors and researchers who intend to use the MWCS or create new instructional material.
    • MIMO channel capacity using antenna selection and water pouring

      Cuan Cortes, Jose V.; Vargas-Rosales, Cesar; Munoz Rodriguez, David (Springer Open, 30/12/2014)
      Abstract The use of multiple-input multiple-output (MIMO) communication systems has attracted considerable attention due to capacity and performance improvements without increasing the required bandwidth or transmission power. Although MIMO improves the transmission rate and provides reliable communication, these advantages come at a high cost, since multiple radio frequency (RF) chains have to be employed. Therefore, cost-effective implementation of MIMO systems remains as an important challenge. In this sense, antenna selection techniques (AST) can help reduce the high cost of MIMO systems, while retaining most of their benefits; and in order to improve channel capacity, transmission power can be allocated efficiently according to the channel experienced by each antenna element. In this paper, we show the channel capacity improvement of MIMO systems, by combining the use of AST and transmission power allocation through the water-pouring algorithm (WPA) for different antenna configurations. We apply WPA and allocate more power to the channel with better conditions, when the MIMO channel is Rayleigh distributed and noise is Gaussian. By employing these two techniques (AST and WPA), we show that channel capacity is significantly improved, with higher capacity values than those obtained using traditional systems which just spread equal power among all the transmit antennas. We also show that bounds on the capacity can be considered when these improvements are used in a MIMO system.
    • Modifying the test of understanding graphs in kinematics

      Zavala G. (The American Physical Society, 2017-08-31)
      In this article, we present several modifications to the Test of Understanding Graphs in Kinematics. The most significant changes are (i) the addition and removal of items to achieve parallelism in the objectives (dimensions) of the test, thus allowing comparisons of students’ performance that were not possible with the original version, and (ii) changes to the distractors of some of the original items that represent the most frequent alternative conceptions. The final modified version (after an iterative process involving four administrations of test variations over two years) was administered to 471 students of an introductory university physics course at a large private university in Mexico. When analyzing the final modified version of the test it was found that the added items satisfied the statistical tests of difficulty, discriminatory power, and reliability; also, that the great majority of the modified distractors were effective in terms of their frequency selection and discriminatory power; and, that the final modified version of the test satisfied the reliability and discriminatory power criteria as well as the original test. Here, we also show the use of the new version of the test, presenting a new analysis of students’ understanding not possible to do before with the original version of the test, specifically regarding the objectives and items that in the new version meet parallelisms. Finally, in the PhysPort project (physport.org), we present the final modified version of the test. It can be used by teachers and researchers to assess students’ understanding of graphs in kinematics, as well as their learning about them.
    • Un procedimiento basado en GRASP para un problema de asignación de equipos médicos de diagnóstico en una red de hospitales públicos

      Mendoza-Gómez, Rodolfo; Ríos-Mercado, Roger; Valenzuela Ocaña, Karla B.; F. Chávez de la O; M. R. Luque Baena; F. Luna; F. Fernández de la Vega; Tecnológico de Monterrey; Universidad Autónoma de Nuevo León (2015-02)
      En este artículo se introduce un modelo de programación entera para la planificación de equipos médicos de diagnóstico de alto costo en una red de hospitales públicos integrada por diferentes instituciones de salud. El modelo permite identificar en qué hospitales de cada institución se deben instalar equipos médicos minimizando los costos de inversión y operativos para satisfacer la demanda del servicio. Dada la inherente complejidad computacional del problema, se propone un GRASP. El esquema constructivo de GRASP consiste en dos etapas en cada iteración. En una primera etapa se van fijando decisiones de qué hospitales habilitar y su capacidad de equipos médicos. En una segunda etapa, se resuelve un problema de trasbordo relativamente fácil. Se resolvieron diferentes instancias de prueba que muestran que la heurística propuesta encuentra soluciones factibles de muy buena calidad. Las soluciones mejoran conforme aumenta el tamaño de la red y disminuye la capacidad de los equipos.