Conceptualización de área del rectángulo con la mediación del programa Cabri Geometry

En esta charla se presentará el trabajo realizado durante el año 2010 por el grupo Nuevas Tecnologías de EDUMAT-UIS coordinado por el Dr. Martín Eduardo Acosta Gempeler. El grupo viene realizando un trabajo de capacitación a profesores de varios colegios del área metropolitana de Bucaramanga en cuanto a la implementación de software de geometría dinámica en la enseñanza de diferentes conceptos geométricos en secundaria

N-dimensional sl(2)-coalgebra spaces with non-constant curvature

An infinite family of ND spaces endowed with sl(2)-coalgebra symmetry is introduced. For all these spaces the geodesic flow is superintegrable, and the explicit form of their common set of integrals is obtained from the underlying sl(2)-coalgebra structure. In particular, ND spherically symmetric spaces with Euclidean signature are shown to be sl(2)-coalgebra spaces. As a byproduct of this construction we present ND generalizations of the classical Darboux surfaces, thus obtaining remarkable superintegrable ND spaces with non-constant curvature.Comment: 11 pages. Comments and new references have been added; expressions for scalar curvatures have been corrected and simplifie

Enteric Methane and Nitrogen Emissions in Beef Cattle Grazing a Tannin-Containing Legume Relative to Feedlot and Traditional Pasture-Based Production Systems

Beef cattle production is highly criticized because of the high use of land and water resources, and by the pollution (e.g., the gas methane in a cow’s breath and nitrogen in urine) produced by cows fed in feedlots. In contrast to feedlots diets and grasses, some plants (e.g., legumes) contain bioactive compounds (condensed tannins) that reduce pollution and enhance animal nutrition. In my research, I observed that cows grazing a tannin-containing legume (birdsfoot trefoil; BFT) had methane emissions similar to cows fed a feedlot ration with comparable weight gains. Cows in the BFT treatment gained more weight than cows grazing grass (meadow brome) or a legume without tannins (cicer milkvetch). Additionally, I estimated the potential areas in the state of Utah than can sustain birdsfoot trefoil production, with 412,250 ha distributed mostly in the Box elder, Cache, Millard and Sanpete counties. Thus, feeding tannin-containing legumes to cows is a viable alternative to feedlot rations, with greater levels of productivity than other pasture-based systems, which can lead to a more sustainable production of beef

Precios y salarios en Castilla la Nueva: La construcción de un índice de salarios reales, 1501-1991

Editada en la Universidad Carlos IIIA partir de datos publicados e inéditos, referidos en su mayor parte al centro de la península y en especial a Madrid, se propone la construcción de índices anuales de Precios, salarios y salarios reales entre 1501 y 1991. Se ofrece una explicación detallada de la naturaleza de las fuentes y de los procedimientos utilizados en la construcción de los índices, evaluando la bondad de los ajustes introducidos. Las series resultantes delimitan con claridad la evolución cíclica a medio y largo plazo de precios y salarios en el centro de España. Al comparárselas con series temporales inglesas, destaca la similitud de tendencias en el conjunto del periodo estudiadoUsing published and unpublished data, mainly taken from the center of Spain and especially from Madrid, annual series of prices, wages and real wages between 1501-1991 have been constructed. A detailed explanation is given of the sources and procedures used in the construction of the series, and the reliability of the different adjustments is evaluated. The resulting time series clearly portray the medium and long-term trends of prices and wages in the center of Spain. When compared with English data, similar trends emerge.Publicad

On the influence of creativity in basic programming learning at a first-year Engineering course

Teaching fundamentals of programming is a complex task that involves the students’ acquisition of diverse knowledge and skills. It is also well known that programming often requires a certain degree of creativity. There are some studies on how to foster creativity with programming, but few studies have analyzed the influence of students creativity on their performance as programmers. In this paper we present the results of a study, with a sample of 89 freshmen engineering students. Our results suggest (p<0.01) that a high level of creativity is correlated with achieving excellence in programming. Creativity is a generic competence which is not currently covered with in most engineering curricula, and we conclude it should be taken into account. Females, diverse thinking student and some disadvantage groups may benefit from a free-thinking environment in the classroom, in particular at their first-year in college.Peer ReviewedPostprint (author's final draft

Exploración de metodologías para el cálculo del valor en riesgo del mercado de renta variable en Colombia

En el presente documento se describen metodologías para el cálculo del Riesgo del Mercado, algunas de estas metodologías parten de supuestos estrictamente teóricos y otras parten tanto de conceptos teóricos como prácticos. Adicional a esto se plantea un estudio comparativo de dichas metodologías, presentando en forma detallada las diferentes formas de encontrar los resultados teóricos para el Riesgo de Mercado, que puedan ayudar a los diversos interesados a tener una forma alterna en como calcular este riesgo. Se establece que puede haber una incidencia significativa tanto en el método usado para encontrar el riesgo como en la conformación de los portafolios óptimos. Esto último debido a que existe más de un coeficiente de correlación (insumo base para la matriz de covarianza, que a su vez es el insumo base para aplicar la teoría de Markowitz): Pearson, Kendall y Spearman. Como metodologías para el cálculo del riesgo se estudiaran: Delta – Normal, Teoría de Valores Extremos, Segundo Momento Estadístico de la Distribución Generalizada de Pareto y Aproximación por la Función de Distribución de Probabilidad Beta. Finalmente se realizará una comparación aplicando las estimaciones en un periodo considerable de tiempo (un año) utilizando los datos presentados de manera oficial por la Bolsa de Valores de Colombia, por medio de la metodología de backtesting. Coeficientes, Spearman, Kendall, Pearson, Mercado Accionario, Delta – Normal, Teoría de Valores Extremos

Do female motives for enrolling vary according to STEM profile?

Contribution: Stereotypes and immediate environment are the reasons for low enrollment of women in STEM studies. Background: The low number of women in STEM degree courses has been the subject of much research, which has found that the lack of female enrollment is not evenly distributed across all STEM studies. In some areas, such as computing, communications, and electrical and electronic engineering (CCEEE), not only has the number of women not increased, it has even fallen. Research Questions: Is there a stereotype for women taking STEM studies? Is this stereotype different between women taking CCEEE and non-CCEEE degrees? What are the main reasons that lead women to enroll in STEM studies? Methodology: A survey was sent to 3699 female students and STEM graduates belonging to the authors’ university in six schools with a lowest level of enrollment, and 1060 replies were received. A qualitative study based on data analysis triangulation was performed. Findings: The women surveyed consider social stereotypes (31.47%) and the immediate environment (14.5%) as the main reasons for the low enrollment of women in STEM studies. Surprisingly, the third reason (11.03%) is that women do not like engineering. New knowledge concerning what motivates female students to enroll in STEM studies, what stereotypes they must struggle against, and the existence of possible differences between CCEEE and STEM but non-CCEEE female students could help policy makers and academia to improve female enrollment in STEM and, in particular, in CCEEE studies.Peer ReviewedPostprin

Scalar charges and the first law of black hole thermodynamics

We present a variational formulation of Einstein-Maxwell-dilaton theory in flat spacetime, when the asymptotic value of the scalar field is not fixed. We obtain the boundary terms that make the variational principle well posed and then compute the finite gravitational action and corresponding Brown-York stress tensor. We show that the total energy has a new contribution that depends of the asymptotic value of the scalar field and discuss the role of scalar charges for the first law of thermodynamics. We also extend our analysis to hairy black holes in Anti-de Sitter spacetime and investigate the thermodynamics of an exact solution that breaks the conformal symmetry of the boundary.Comment: 13 pages, no figures;v2: a general boundary term added, ack. extende

Data Envelopment Analysis to measure relative performance based on key indicators from a supply network with reverse logistics

Introduction− Data Envelopment Analysis (DEA) is used to measure the relative performance of a series of distribution centers (DCs), using key indicators based on reverse logistics for a company that produces electric and electronic supplies in Colombia.Objective−The aim is to measure the relative perfor-mance of distribution centers based on Key Performance Indicators (KPI) from a supply network with reverse logistics.Methodology−A DEA model is applied through 5 steps: KPIs selection; Data collection for all 18 DCs in the net-work; Build and run the DEA model; Identify the DCs that will be the focus of improvement; Analyze the DCs that restrict or diminish the total performance of the system.Results− KPIs are defined, data is collected and KPI’s for each DCs are presented. The DEA model is run and the relative efficiencies for each DCs are determined. A frontier analysis is made and DCs that limit or reduce the performance of the system are analyzed to find options for improving the system.Conclusions−Reverse logistics, brings numerous ad-vantages for companies. The analysis of the indicators allows logistics managers involved to make relevant deci-sions for higher performance. The DEA model identifies which DCs have a relative superior and inferior perfor-mance, making it easier to make informed decisions to change, increase or decrease resources, and activities or apply best practices that optimize the performance of the network.Introducción− El análisis envolvente de datos (DEA), se usa para medir el desempeño relativo de una serie de centros de distribución (DCs), utilizando indicadores clave basados en logística inversa para una empresa que produce suministros eléctricos y electrónicos en Colombia.Objetivo− Medir el rendimiento relativo de los centros de distribución en función de indicadores clave (KPI) de una red de abastecimiento con logística inversa.Metodología− Se aplica un modelo DEA a través de 5 pasos: Selección de KPIs; Recopilación de datos para los 18 DCs en la red de distribución; Se construye y ejecuta el modelo DEA; Identificar los DCs que serán el foco de la mejora; Analizar los DCs que restringen o disminuyen el rendimiento total del sistema.Resultados− Inicialmente se definen KPI, a partir de los datos recolectados y se presentan los KPI para cada DCs. Se ejecuta el modelo DEA y se determinan las eficiencias relativas para cada DCs. Posteriormente, se realiza un análisis de la frontera y se analizan los DCs que limitan o reducen el rendimiento del sistema en busca de opciones para mejorar el sistema.Conclusiones− La logística inversa, trae numerosas ven-tajas para las empresas. El análisis de los indicadores permite a los gerentes de logística tomar decisiones rel-evantes para mejorar el desempeño del sistema. El mod-elo DEA identifica a los DCs que presentan rendimientos relativamente superiores e inferiores; lo cual facilita la toma de decisiones informadas para cambiar, aumentar o disminuir los recursos y las actividades, o aplicar las mejores prácticas que optimicen el rendimiento de la red