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- PublicaciónSólo datosRegional employment cycles in Colombia: Interregional dependence 2001-2006(Ensayos Sobre Politica Económica, 2009-01-01) Bohórquez Olarte, Lilian Carol; Godoy Bejarano, Jesús María; Téllez Falla, Diego FernandoThis work studies the interdependence relationship presented in employment cycles of some cities against the cycle of the rest of Colombian cities. Irrestrictive VAR models usage allowed us to identify those cities whose employment cycles are adapted faster to the aggregate cycle of the other cities in a national level or the aggregate cycles of similar cities. It was also concluded that some cities inside the groups precede statistically the behavior of the other cities in the group, what could be useful to measure labor indicators in cities where home survey hasn't been implemented yet.
- PublicaciónSólo datosDimensions of scientific collaboration and its contribution to the academic research groups' scientific quality(Research Evaluation, 2009-08-01) Bermeo Andrade, Helga; de los Reyes López, Ernesto; Bonavia Martín, TomasThis article analyzes, under several dimensions, whether collaboration contributes to the production of high-quality scientific results. It examines the proportion of scientific quality (measured by impact and relevance) gained by ISI publications considering the presence of a particular form of collaboration. As an application case, this paper offers a micro-level analysis of the academic research groups (ARGs) of a technical university. Results indicate that there are positive and significant benefits in scientific quality received by ARGs as product of international and inter-sector collaboration, and in a broader sense, from the presence of inter-institutional collaboration.
- PublicaciónSólo datosCompacidad en reductores mecánicos de un paso utilizando ejes huecos(Información Tecnológica, 2010-01-01) Araque de los Ríos, Oscar; Cabello, Juan J.En este trabajo se identifica la incidencia de la reducción de peso en elementos de máquina integrados, como ejes de transmisión, sobre su resistencia mecánica y sobre la compacidad de reductores mecánicos compuestos por engranajes de un paso. Se han considerado diversas variaciones geométricas, como ejes huecos, y se determinó su incidencia sobre la geometría y la variación del peso de cada uno de los elementos constitutivos de los reductores afectados por el cambio geométrico de los árboles de salida. Para el caso de ejes macizos y huecos de igual sección circular y resistencia la disminución del área fue superior al 12% y la del módulo de resistencia a la flexión, del 11%. Para ejes de sección circular con chavetero el área disminuyó en más del 30%, mientras que el módulo de resistencia a la flexión, en 10%. Se concluye que el uso de árboles huecos con incrementos de hasta el 50% en su diámetro interior, no incide significativamente en la compacidad de reductores mecánicos de un paso.
- PublicaciónSólo datosDiseño e implementación de una estrategia de control predictivo para el secado de arroz paddy(Revista Facultad De Ingeniería Universidad De Antioquia, 2010-08-01) Barrero-Mendoza, Oscar; Cubillos-Varela, AlfonsoEste artículo trata sobre la modelación y control del proceso de secado de arroz Paddy en silo inclinado usando técnicas de control predictivo. Para esto se usa un secador a escala 1:10 con capacidad de 25 kilos de grano, totalmente instrumentado donde se puede medir en línea la temperatura y humedad del grano de arroz y del medio ambiente. Además, permite medir y manipular el flujo y temperatura del aire de secado. Con el fin de diseñar el controlador, primero se obtiene un modelo dinámico basado en el principio de capa delgada, luego se diseña e implementa la estrategia de control predictivo, conocida como DMC (Dynamic Matriz Control) la cual utiliza la respuesta paso y repuesta libre del sistema para calcular la acción de control óptima. Como consecuencia de este proceso se obtienen resultados prometedores del uso de este tipo de tecnología en el secado de arroz Paddy: a) reducción del tiempo de secado, b) evitar la pérdida de masa por sobresecado, c) garantizarun secado más homogéneo y por lo tanto una mejora en la calidad del arroz y la productividad de la industria molinera de la Región.
- PublicaciónSólo datosAbout regional logistics operator in Tolima under SCOR model approach(61st Annual IIE Conference and Expo Proceedings, 2011-05-11) García-León, Andrés Alberto; Bermeo-Andrade, Helga PatriciaLogistics is an opportunity area to gain productivity and competitiveness in regions with geographical and commercial strategic position. Tolima is a central region of Colombia, which due to its location near to the major cities of consumption, is the region with higher demand and operation of goods and cargo flows in the country. In this region, the presence of logistics operators is a critical factor for effective operation of productive chains that have a total or partial presence in the zone. In this study, 32 logistics operators (sample 80% representative of the sector) were initially characterized according to their service portfolio and outsourcing level as 2PL, 3PL or 4PL. Then, they were analyzed under the guidelines of 25 selected good practices identified by the SCOR reference model. The results suggest that the level of service of most of these operators is basic and limited to transportation activity, and their infrastructure is weak to create added-value on goods. In general, the evidence shows that this sector has a limited capacity to contribute to the competitiveness of supply chains operating in the Tolima region.
- PublicaciónSólo datosLogistics management in cotton agro-industry sector of Tolima region in Colombia(61st Annual IIE Conference and Expo Proceedings, 2011-05-22) Tovar-Perilla, Nelson; Bermeo-Andrade, Helga PatriciaMarket evolution has made it harder for companies to meet consumers' needs in the global context of economy, communications and business. This fact has transformed logistics activity as a key factor for competitiveness of any productive chain, particularly for agro-industrial chains. The appropriation and adoption of engineering and technological tools to support logistics management is increasingly a potential source of improvement in productivity and competitiveness, since they help to generate solutions at three decision levels: strategic, tactical and operational. In this article we study the cotton chain and its derivatives, in Tolima region, which is one of the main agro-industrial chains of one of the most traditional agricultural regions in Colombia. Considering the best practices defined by the SCOR1 reference model, we study and characterize the tools that support logistics work into representative companies of each link of the analyzed chains. The results suggest the absence in some cases, or limited use in some others, of the recommended tools for effective logistics operation along supply chains.
- PublicaciónSólo datosIBSE as a pedagogical proposal: Lessons from a particular Latin American context(Revista Española de Pedagogía, 2011-09-01) Meisel-Donoso, Jose D.; Bermeo-Andrade, Helga Patricia; Patiño, LuceliScience teaching among the student population is a key factor so that a country may count with a critic mass of citizens, scientifically knowledgeable, capable of facilitating and promoting the technological, economical and social development of a nation under a sustainable approach. This article is orientated to show the implementation details of the teaching proposal of the inquiry-based science education (IBSE), a proposal that is internationally positioning itself as an effective tool for the development of scientific, technological and citizen competences among students, within a particular Latin American context: The Small Scientists Project (SSP) in the Tolima Region of Colombia. The results make evident the importance of exogenous factors in the classroom as the institutional context, as well as the presence of endogenous factors linked to the teacher and the student for the success of the Program in this region. Similarly, the main findings propose a methodology on behalf of the teachers and changes in the learning atmosphere of science classes.
- PublicaciónSólo datosPVECLAB: Interactive power electronics training, teaching and experimentation tool(Proceedings of the 2011 14th European Conference on Power Electronics and Applications, 2011-09-15) López-Santos, OswaldoNowadays, thanks to the development of communications and systems, the interactivity has taken a fundamental role in engineering education. An important challenge is the effective use of computer tools that allow associating the teaching methods with the new way the students learn. In power electronics area, recognizing different concepts of switching converters is more simple thanks to simulation and experimentation tools. Nevertheless, the general-purpose tools applied in the analysis and simulation of electronic circuits and systems do not take advantage properly of the interactivity that computer applications can offer. As a consequence it is necessary to develop modern tools with specific capacities as complementation of teaching and researching processes in power electronics. This article presents the results of the development of a tool for researching and teaching activities in power electronics area, implemented in LabVIEW called PVCLAB. It contains different dedicated modules to provide interactive conceptual training for analysis, design, simulation and control of DC/DC switching power converters. The state-space models of these converters include resistors in inductors, capacitors, MOSFET and diodes.
- PublicaciónSólo datosOrganizational learning and the effective management of complexity(Proceedings of 2011 IEEE International Conference on Grey Systems and Intelligent Services, 2011-10-13) Reyes Alvarado, AlfonsoAn experience of a profound change in the structure of a small non-for-profit private university in Colombia will be used to show the relationship between organizational learning and the need to improve its management of complexity [Beer 1979; 1985; Espejo 1992; Espejo & Reyes 2011]. Organizational learning relates to processes increasing an organization's capacity for effective action in a particular domain.Organizations learn through their individuals, however, individual learning does not imply (necessarily) organizational learning. Both structure and culture affect this learning. The author's experience transforming the already mentioned university, over a number of years, is at the core of his presentation. The author uses techniques from variety engineering [Espejo & Reyes 2011] to show how organizational learning needs a requisite structure to happen. At the same time, he illustrates how learning loops contribute to the viability of a project.
- PublicaciónSólo datosAssimilation of ozone measurements in the air quality model AURORA by using the Ensemble Kalman Filter(2011 50th IEEE Conference on Decision and Control and European Control Conference, 2011-12-12) Barrero Mendoza, OscarThis paper presents the results of using the Ensemble Kalman Filter (EnKF) for improving the ozone estimations of the air quality model AURORA. The EnKF is built around a stochastic formulation of the model, where some of its parameters are assumed to be uncertain. These uncertainties turn out to be the main reason behind the differences between the model predictions and the real measurements. The filter estimates these parameters as well as the ozone concentration field by using ground-based measurements from the Airbase database. The assimilation experiments are carried out over a region that consists of Belgium, Luxembourg, and some small parts of Germany, France and the Netherlands. The simulations results show that the EnKF significantly reduces the error of the ozone estimations.
- PublicaciónSólo datosElectronic band structure of the Pt(1 1 1) surface: An ab initio and tight-binding study – I(Computational Materials Science, 2012-04-01) Herrera-Suárez, Hernán Javier; Rubio–Ponce, Alberto; Olguín, DanielThe electronic band structure of ideal Pt(1 1 1) surface was studied using density functional theory and the empirical tight-binding method. A detailed discussion of the surface- and resonance-states is given. It is shown that the calculated surface- and resonance-states of ideal Pt(1 1 1) surface agree very well with the available experimental data. The density functional calculations were performed using the full potential linearized augmented plane wave method, and the empirical calculations were performed using the tight-binding method and Surface Green’s Function Matching Method.
- PublicaciónSólo datosPhysicochemical characterization of traditional and commercial instant corn flours prepared with thresched white corn(CYTA - Journal of Food, 2012-05-10) Pineda Gómez, Posidia; Acosta Osorio, Andrés Antonio; Coral, Diego Fernando; Rosales Rivera, Andrés; Sánchez-Echeverry, Luz Adriana; Rojas-Molina, I.; Rodríguez-García, Mario EnriqueThe aim of this work is to study the physicochemical characterization of commercial instant corn flour (CICF) and traditional instant corn flour (TICF) prepared with threshed corn. The chemical analysis shows that there are a few amounts of fat, fiber, and minerals but the protein shows small variations in relation to the threshed corn. The CICF is characterized by coarse particles. Differential scanning calorimeter corroborated that the flours are gelatinized; but in the case of CICF the starch granules are partially disrupted and some of them are integer, producing structural changes which are identified using X-ray diffraction. A pasting analysis based on the pasting curves was conducted in order to study the apparent viscosity of these flours. The CICF shows quick water absorption at low temperatures and major values in peak viscosity than the threshed corn flour which may be related to presence of hydrocolloids. The TICF apparent viscosity showed a complete gelatinized starch.
- PublicaciónSólo datosPhotoluminescence from germanate glasses containing silicon nanocrystals and erbium ions(Applied Physics B, 2012-08-01) da Silva, Diego Silvério; Naranjo, Luz Patrícia; Pires Kassab, Luciana Reyes; de Araújo, Cid B.We report the first observation of photolumines-cence enhancement in Er 3+ doped GeO 2-Bi 2O 3 glasses containing silicon nanocrystals (Si-NCs) excited by a laser operating at 980 nm. The growth of ≈ 200% in the intensity of the Er 3+ transition 4S 3/2 → 4I 15/2 (545 nm) and of ≈ 100% for transitions 2H 11/2 → 4I 15/2 (525 nm), 4F 9/2 → 4I 15/2 (660 nm), and 4I 5/2 → 4I 13/2 (1530 nm) was observed in comparison with a reference sample that does not contain Si-NCs. The results open a new road for obtaining efficient Stokes and anti-Stokes emissions in germanate composites doped with rare-earth ions.
- PublicaciónSólo datosOrganizational learning and the effective management of complexity(Kybernetes, 2012-08-01) Reyes, AlfonsoThe purpose of this paper is to show, through a case study, the relationship between organizational learning and the need to improve the organization's management of complexity. Design/methodology/approach A case study is used. Findings The case study illustrates both how organizational learning needs a requisite structure to occur and how learning loops contribute to the viability of a project. Originality/value This case study shows that designing learning loops requires setting up the structural conditions for a Human Communication System in the organization.
- PublicaciónSólo datosAnálisis de las propiedades psicométricas de la versión en español del Internet Addiction Test(Trastornos Adictivos, 2012-10-15) Puerta-Cortés, Diana Ximena; Carbonell, Xavier; Chamarro, AndrésEl Internet Addiction Test (IAT) ha sido adaptado a diferentes lenguas, convirtiéndose en uno de los cuestionarios más empleados para la evaluación de los síntomas de la adicción a Internet. Sin embargo, la versión en lengua española carece de estudios psicométricos en aplicaciones online. El objetivo del estudio fue analizar las características psicométricas de la versión en lengua española del IAT. Material y método . 1.117 usuarios de Internet de nacionalidad colombiana completaron online el cuestionario de datos demográficos y uso de Internet y el IAT. La fiabilidad fue establecida con el coeficiente Alfa de Cronbach y para analizar la estructura del test se aplicó un análisis factorial exploratorio. Resultados Los resultados muestran una alta consistencia interna del test. Se extrajeron tres factores (consecuencias por el uso de Internet, dimensión cognitiva-emocional y control del tiempo) que correlacionaron positivamente con las horas de acceso diario a la red y negativamente con la edad. Conclusiones La versión en lengua española del IAT ha demostrado una alta fiabilidad, es un instrumento adecuado para evaluar el impacto del uso de Internet en las interacciones sociales y la influencia del uso de Internet en la vida diaria. Se recomienda seguir investigando las dimensiones subyacentes del test.
- PublicaciónSólo datosElectronic band structure of platinum low-index surfaces: An abinitio and tight-binding study. II(Revista Mexicana De Fisica , 2012-12-01) Herrera-Suárez, Hernán Javier; Rubio–Ponce, Alberto; Olguín, Daniel
- PublicaciónSólo datosDigital control of a single-phase boost rectifier with power factor correction using a dsPIC(2012 IEEE 4th Colombian Workshop on Circuits and Systems (CWCAS), 2013-01-11) Lopez-Santos, Oswaldo; Murcia, Harold; Barrero, John MauricioA digital implementation of a boost rectifier with power factor correction (PFC) is presented. The proposed control involves a current control loop and a voltage control loop. The current control loop is implemented with two different methods: (a) linear compensation; and (b) ON-OFF control. The voltage control loop is implemented with a proportional-integral (PI) controller. Several Simulink/MATLAB simulations of the converter operating with both current control methods are presented. An assessment of the total harmonic distortion (THD) measurements shows the advantages of the simple ON-OFF controller. Finally, experimental results obtained from a 100W prototype using a low-cost 16-bit microcontroller are included and discussed.
- PublicaciónSólo datosSliding-mode indirect control of the quadratic boost converter operating in continuous conduction mode or discontinuous conduction mode(2012 IEEE 4th Colombian Workshop on Circuits and Systems (CWCAS), 2013-01-11) Lopez-Santos, Oswaldo; García, Germain; Martínez-Salamero, Luis; Valderrama-Blavi, HugoThis paper presents the analysis of the quadratic boost converter operating in sliding-mode control in order to obtain high DC-gain. This approach uses a indirect control of the output voltage based on the use of a sliding surface defined with the input inductor current. The control law is argued through a stability test. The proposed control was implemented in MATLAB simulations with a quadratic boost operating in continuous conduction mode (CCM), and another one in discontinuous conduction mode (DCM). The results validate the theoretical approach and illustrate the advantages and drawbacks of two operational modes.
- PublicaciónSólo datosEfficiency Analysis of a Sliding-Mode Controlled Quadratic Boost Converter(IET Power Electronics, 2013-02-01) Lopez-Santos, Oswaldo; Martínez-Salamero, Luis; García, Germain; Valderrama-Blavi, Hugo; Mercuri, Daniel O.A quadratic boost converter with high DC gain to step up the voltage of a standard photovoltaic panel up to 400 V is analysed. First of all, a comparative analysis among boost, quadratic boost and cubic boost reveals that the quadratic boost exhibits the best trade-off between duty ratio range and converter efficiency. A hysteretic comparator is employed as a modulator to ensure the converter operation with high values of the duty ratio without risk of modulation saturation. A twoloop sliding-mode control is used to regulate the output voltage. An internal loop controls cycle by cycle the input current whose reference is established by an outer loop that processes the output voltage error by means of a proportional-integral compensating network. The measured results in a 100 W prototype operating in continuous conduction mode of average values, ripples, frequency and efficiency for different equilibrium points are in good agreement with the theoretical predictions.
- PublicaciónSólo datosInstrumentation and design of a supervisory system for an Anaerobic Biodigestor(2012 IEEE International Symposium on Alternative Energies and Energy Quality (SIFAE), 2013-03-14) Hernández, José; Medina, Robinson; Hernández Sarabia, MauricioHis paper presents the design of a supervisory system of an Anaerobic Biodigestor pilot plant located at Universidad de Ibagué in Colombia to produce Biogas. This contribution includes the design of a reliable low-cost instrumentation; whereby, the correct selection, implementation, and calibration of sensors of temperature, pH, CO 2 , CH 4 , and gas flow play an important role in accomplishing a good design. The supervisory system is used to perform tasks of fault-detection and on-line measuring; where the last one is essential for modeling by extracting kinetic information of the degradation process and automatic control. Labview ® was chosen as the software platform to develop the supervisory system.