Este artículo presenta resultados de tres proyectos desarrollados por el Grupo de Investigación en Electrónica de Altas Frecuencias y Telecomunicaciones, de la Universidad Nacional de Colombia (CMUN), en los cuales se han implementado sistemas de telecomunicaciones inalámbricos, basados en tecnologías de identificación por radiofrecuencia (RFID), para el entrenamiento médico de estudiantes de neonatología, manejo de logística de eventos y monitoreo de rutas y arribo de vehículos de transporte de pasajeros. El primer proyecto permitió mejorar la tecnología de telecomunicaciones de los simuladores de entrenamiento para estudiantes de medicina y enfermería en el área de neonatología de la Universidad de Colombia. Con el sistema para apoyo a labores de logística se logró una herramienta que controla autónomamente el ingreso de asistentes a las diversas actividades de un evento y recolecta de modo remoto datos para obtener estadísticas de participación de los asistentes en cada actividad programada. En el último proyecto se implementó un sistema que identifica vehículos que circulan a una distancia máxima de 100 m de un punto de control, con el fin de verificar el cumplimiento de rutas y de horarios del parque automotor de una empresa sin la presencia de un operador. Al final del artículo se hace un análisis de los principales logros alcanzados en cada uno de los proyectos realizados con tecnologías RFID.

Radio frequency identification (RFID) technology, from its beginning in the 1980s, has provided solutions in areas in which no identification (ID) technology has done so before. This paper presents three applications in areas having an issue in common: an RFID technology-based solution; these fields were academic topics, logistic support for an event and passenger land transport. Each project identified a problem which needed resolving, the methods and electronic devices used for such solution and the outcomes achieved. The developments shown in this paper indicated the multidisciplinary nature of RFID technology because it achieved new solutions for identifying objects or people in many contexts and not just the consumer goods trade which is the application nowa-days most known for using this technology. These projects were developed by members of the Universidad Nacional de Colombia's High Frequency Electronics and Telecommunications Research Group (CMUN) (website: http://www.cmun.unal.edu.co).

In this work an operation alternative and controllability was studied by simulation of a stirred tank continuous isothermic crystallizer through of its dynamic characterization. The process model is based on the moments technique. The methodological process consisted on the implementation of a SISO (single input-single output) feedback servocontrol algorithm and a PID (proportional-integral-derivative) controller. The tuning was carried out with the strategies of internal model control (IMC). The process variable to control was the average diameter in % volume D(4,3) = μ4 / μ3, because is a useful variable in both commercial and industrial environment; the manipulate variable in isothermic operation and for cooling was the solute concentration in the feeder and cooling temperature, respectively. Since static analysis were obtained zones where the presence of limits cycle exists and values of more favorable residence times to operate and control the crystallization process for isothermic and cooling operation. Feedback PID controller in the two operations was satisfactory eliminating the deviations between the adjustment point and the response of the controllable variable.

En este trabajo se caracterizó dinámicamente un cristalizador continuo tipo tanque agitado en estado isotérmico y por enfriamiento vía simulación, y se estudiaron alternativas de operación y controlabilidad del proceso. El modelo matemático del proceso está basado en el método de momentos. El proceso metodológico consistió en la implementación de un servocontrol SISO (única entrada-única salida) retroalimentado con controlador PID (proporcional-integral-derivativo). Los parámetros de sintonía del controlador se obtuvieron con las estrategias de un modelo de control interno (IMC). La variable del proceso a controlar fue el diámetro promedio relativo en % volumen D(4,3) = μ4 / μ3, ya que es una variable muy usada en el ámbito comercial e industrial; la variable manipulable en el caso isotérmico y por enfriamiento fue la concentración del soluto en la alimentación y la temperatura de enfriamiento, respectivamente. Del análisis estático se observan las zonas donde existe la presencia de ciclos límites y los valores de tiempos de residencia más favorables para operar y controlar la cristalización isotérmica y por enfriamiento. Se concluye que el controlador PID retroalimentado que se implementó en los dos casos fue satisfactorio eliminando las desviaciones entre el punto de ajuste y la respuesta de la variable controlable.

With the purpose of contributing to the energetic valuation of the solid wastes generated by the Colombian agricultural industry, a practical methodology for the design of a fluidized bed gasifier for rice husk on pilot scale was developed. The gasifier equipment, made up of a reaction chamber of 0.3 m of internal diameter and 3 m of overall height, was designed from theoretical and experimental information available in the literature and from the past experiences of the research group. A design procedure was elaborated for each one of the seven parts or subsystems in which the gasifier equipment was divided, intending to produce an energetic gas with aproximately 70 kW of useful energetic power. Experimental tests performed with a gasifier fabricated according to the designs showed that the developed procedure was adequate, with a maximum deviation close to 50% for the operational performance variables. Therefore, the basic model developed in this work shows that it is helpful for preliminary prediction of the equivalence ratio, low heating value, volumetric yield, gas power and cold efficiency obtained in experimental atmospheric bubbling fluidized bed biomass gasification tests.

Variações vertical, nictemeral e entre os dias de amostragem das formas de nitrogênio, fósforo e sílica solúvel reativa (SRS) foram estudadas no lago das Garças, reservatório tropical raso situado na cidade de São Paulo, sudeste do Brasil. Excetuado o N-NH4, todas as demais formas inorgânicas de nitrogênio (N-NO2, N-NO3 e N total) diminuíram de teor no sentido do fundo do reservatório. Da mesma maneira, todas as formas de nitrogênio apresentaram diferenças significativas quanto às horas de amostragem, aumentando seus valores durante a noite, em razão da ausência de fotossíntese nesse período. Essas formas diminuíram seus teores no dia de amostragem da primavera, graças à floração de Microcystis registrada nesse período. Os valores das três formas de fósforo estudadas (solúvel reativo, particulado e total) apresentaram variação vertical significativa, exceto no dia da amostragem de outono. No dia de amostragem de verão ocorreu aumento dos valores de P total e particulado, sendo que este último constituiu mais de 70% do P total durante todos os dias de amostragem. Considerando as horas, a variação dos teores de fósforo foi significativa nos dias das amostragem de primavera, de outono e de inverno. A variação vertical da sílica reativa solúvel foi significativa em todos os dias de amostragem, menos no da primavera. Essa variação também foi diferente entre as horas e os dias de amostragem.

The vertical and diurnal variation of nitrogen and phosphorus forms, as well as that of soluble reactive silica (SRS), were studied in four sampling days at Garças reservoir, a shallow tropical one located in the city of São Paulo, in southeastern Brazil. Except for N-NH4, all other inorganic forms of nitrogen (N-NO2, N-NO3, and total N) demonstrated decreased concentrations toward the bottom of reservoir. Similarly, all showed significant diurnal differences on every sampling day, with increased values during the night due to absence of photosynthetic assimilation during that period. In the sampling days, these forms decreased on the spring sampling day due to the bloom of Microcystis registered during this period of the year. All three forms of phosphorus (SRP, particulate P, and total P) showed significant vertical variation, except on the fall sampling day. On the summer sampling day there was an increase of both total P and particulate P, the latter because it constitutes more than 70% of the total P during all sampling days. Hourly phosphorus variation was significant during all sampling days, except for the summer one. The SRS vertical variation was significant during all sampling days, except for that in the spring. It was also different hourly on sampling days.

Foram estudadas as variações espacial e temporal das características climáticas e físicas em um reservatório tropical raso situado na cidade de São Paulo e sua possível influência na dinâmica da comunidade fitoplanctônica. Foram retiradas amostras da coluna d'água (subsuperfície, 10% Io, 1% Io, 2 m e fundo) a intervalos de 4 horas (6, 10, 14, 18, 22, 2 e 6 h) durante o verão (3-4 de março), outono (13-14 de junho), inverno (29-30 de agosto) e primavera (29-30 de novembro) de 1994. Concluiu-se que o Reservatório das Garças (23º39'S, 46º37'W) é um sistema cinético turbulento, altamente influenciado pelo vento, com estratificações térmicas que podem durar dias ou semanas, sofrendo períodos de mistura mais de uma vez ao ano. O padrão térmico desse tipo é comparável ao polimítico quente descontínuo. Do ponto de vista de suas propriedades ópticas, o reservatório foi classificado como um ecossistema de turbidez moderada, que diminui basicamente pelo aumento na concentração de feopigmentos na primavera. O reservatório é um sistema sob estresse e a intensidade do estresse para a comunidade fitoplanctônica deve-se à pouca penetração de luz, a qual aumenta do verão para a primavera.

Spatial and temporal variation of climatic and physical characteristics in a shallow tropical reservoir in the city of São Paulo, Southeastern Brazil, and their possible influence on the dynamics of the phytoplankton population. Samples were taken at 5 depths of the water column (subsurface: 1% Io, 10% Io, 2 m, and bottom) and at 4 hour intervals (6:00, 10:00, 14:00, 18:00, 22:00, 2:00, and 6:00 h) during summer (March 3-4), fall (June 13-14), winter (August 29-30), and spring (November 29-30) of 1994 at a single sampling station. Garças Reservoir (23º39'S, 46º37'W) is a kinetic turbulent system, highly influenced by winds, with stratification that may last for days or weeks, and which undergoes mixing periods more than once in a year. A thermal pattern of this type is comparable to the warm discontinuous polymictic. Considering its optical properties, the water body was classified as an ecosystem with moderate turbidity, which decreases basically due to increased phaeopigment concentration during the spring. Also, the reservoir is an ecosystem whose phytoplanktonic community is subjected to stress, the degree of which depends on level of light penetration.