Diseño y construcción de un convertidor multinivel en cascada basado en celdas monofásicas de corriente

91 p.En este trabajo se presenta el desarrollo de la topología de un convertidor multinivel en cascada basado en celdas monofásicas de corriente. El trabajo de esta memoria consta de simular esta topología de convertidor multinivel en cascada, con el fin de obtener la base del desarrollo posterior del convertidor, el diseño de las celdas de corriente, la construcción de las tarjetas electrónicas correspondientes al rectificador e inversor, así como su interconexión y el montaje sobre el set-up para conformar las celdas a fin de conectarlas en cascada y la realización de pruebas de estas celdas monofásicas de corriente y ver el desempeño global del convertidor. Este informe muestra los aspectos fundamentales en las etapas correspondientes del desarrollo del convertidor, así como la comparación de los resultados proporcionados por las simulaciones y por las pruebas experimentale

La política monetaria única y sus efectos regionales.

El interés por el estudio de los efectos asimétricos que puede tener la política monetaria única (PMU) en los países integrantes de la eurozona ha dado origen a una ingente literatura, fundamentalmente de carácter empírico, que se ha ocupado de analizar las respuestas del output y los precios de los países europeos ante los supuestos shocks monetarios ocasionados por las decisiones de política monetaria adoptadas por el Banco Central Europeo (BCE). Buena parte de ella revela la existencia de importantes diferencias no sólo en el impacto total que los shocks monetarios ocasionaban en el output y los precios de distintos países, sino también en sus trayectorias temporales, lo cual era interpretado como un indicio de las asimetrías regionales que ocasionaría la puesta en marcha de la PMU en la eurozona. En este trabajo se realiza una síntesis del debate en torno a las asimetrías regionales de la PMU teniendo en cuenta la experiencia y la documentación empírica que se ha ido generando en estos casi quince años de trayectoria de la eurozona, con la doble intención de: propiciar una reflexión crítica al respecto de los resultados empíricos obtenidos hasta la fecha y apuntar algunos cambios que habría que introducir en el actual marco operativo de la PMU.Increasing interest in exploring the possible asymmetric effects of Single Monetary Policy (SMP) on euro zone countries has resulted in a great deal of research, most of it empirical in nature, into the response of GDP and prices in European countries in the face of the monetary shocks caused by the monetary policy measures adopted by the ECB. Much of this research points to the existence of major differences not just in the overall impact of monetary shocks on growth and prices in different countries but also in their timing. This has been interpreted as a sign of regional asymmetries that could be caused by implementing the SMP in the euro zone. Taking into account the experience and empirical evidence built up over the almost-fifteen-year history of the euro zone, proposals are made for changes that should be introduced in the current operational framework of the SMP with a view to palliating those asymmetries

Limitações teóricas da literatura convencional sobre impactos regionais de política monetária

The aim of this paper is to analyze the theoretical limitations of the mainstream’s Works related to the regional impacts of monetary policy. After a general presentation of the conventional framework, followed by the typology proposed in Dow & Rodríguez-Fuentes (1997), we present our arguments based on the Post-Keynesian theory against the traditional approach. In our view, the Post-Keynesian framework is the most appropriate for analyzing this type of dynamics. Its theoretical elements have the best explanation for the dynamics of the monetary policy at a regional level, once they take into account the role played by uncertainty and liquidity preference of economic agents and institutions, which are essential for the understanding the regional economics in a "center – periphery” context.regional monetary policy, liquidity preference, Post-Keynesian theory.

Male tilapia production techniques: A mini-review

Tilapia culture has been growing over the past decades as an excellent source of high-quality protein. Some of the Tilapia´s advantages are the ability to breed and produce new generations rapidly, tolerate shallow and turbid waters, resist a high level of disease and be flexible for culture under many different farming systems. These characteristics are the main reasons for its commercial success. However, one of them contributes to the major drawback of pond culture: the high level of uncontrolled reproduction that may occur in grow-out ponds. Uncontrolled reproduction yields to stunted growth and unmar-ketable fish due to offspring competing with the initial stock for food, besides other problems like less dissolved oxygen, greater release of ammonia and feces, heterogeneous sizes and overpopulation stress. Monosex production has been preferred in order to deal with these issues. Males are preferred because they grow almost twice as fast as the females. This paper reviews monosex male production techniques and their results, comprising environment manipulation, hybridization, sex reversal and genetic manipulation. The choice of a particular technique would depend on the legislation of each country. This review’s should help to select the appropriate technique depending on the market target and the commercial technology available.Keywords: Monosex production, hybridization, sex reversal, environmental and genetic sex determinationAfrican Journal of Biotechnology Vol. 12(36), pp. 5496-550

Infección por virus T-linfotrópico humano en donantes de sangre en un hospital nacional de Lima: Human T-lymphotropic virus infection among blood donors in a national hospital of Lima City

Introducción: Los virus linfotrópicos humanos (HTLV), particularmente el HTLV-1 están asociados a leucemia/linfoma de células T del adulto (ATLL) y mielopatía/paraparesia espástica tropical (HAM/TSP). En América del Sur el Perú es considerado área endémica. Objetivos: Determinar la seroprevalencia de infección por HTLV1-2 en donantes de sangre de un hospital nacional de Lima. Métodos: Estudio descriptivo basado en una fuente secundaria obtenida del banco de sangre del Hospital Nacional Dos de Mayo. La población estuvo conformada por donantes de sangre postulantes de ambos géneros en el periodo 2012 a 2015. Los criterios de inclusión fueron: contar con datos personales, edad, sexo, grupo sanguíneo y los resultados del examen de pesquisa para HTLV-1 y HTLV-2. De 28249 sujetos admitidos, 28084 cumplieron con los criterios del estudio. Resultados: La edad media de los participantes fue 33, 5 años (DS=10,02; mín. 17, máx. 70), predominaron los grupos de edad de 20-29 y 30-39 años con 34,6% (n=9727) y 30,9% (n=8685) respectivamente. El 70,6% (n=19825) estuvo representado por los varones y el 83,3% (n=23407) tenían el grupo sanguíneo O. La frecuencia de resultados reactivos para HTLV 1-2 tuvo una tendencia creciente desde 0,6% el 2012 hasta 1,4% el 2015. Considerando el acumulado del periodo 2012 a 2015, la frecuencia de resultados reactivos fue 1,1%. Los resultados reactivos se presentaron en mayor proporción en los varones (p=0,020) y en los grupo de edad de 30-39 años (p<0,001). Conclusiones: La seroprevalencia para HTLV en los postulantes admitidos como donante de sangre fue 1,1%. Los resultados reactivos se asociaron al grupo etario y al sexo masculino

Cognition and its relationship with endogenous and exogenous factors in engineering students

In this research, a relational study was carried out between student cognition with endogenous factors (student attitude and age) and exogenous (collegiate origin) in engineering students of the University of Cartagena. The project was carried out in three (3) phases where the survey allowed the desired information to be obtained from an estimated nine hundred sixty (960) students between 2014 and 2016. In the second phase, the instrument was used to collect the information, which was constituted the cognitive scale of the Self-Regulation Inventory for Learning (SRLI) and in the third phase, the independent endogenous and exogenous variables were crossed with the dependent one (student cognition), constructing the bar diagram of the relationship analysis; being possible to determine statistical significance with the attitude of the student to a level of confidence of 95% while with the age and collegial origin was not relevant

Escala de Miedo al Covid-19 en Estudiantes Universitarios Chilenos: Propiedades psicométricas e invarianza de medida

Los últimos acontecimientos relacionados con el Covid-19 han sido muy estresantes en la vida de los universitarios chilenos. A partir de lo anterior, es imperativo contar con un instrumento sólido para medir el miedo al Covid. Esta investigación tiene como objetivo estimar las propiedades psicométricas de la Escala de Miedo al Covid-19 (FCV-19S) en una muestra de 562 estudiantes universitarios chilenos y confirmar su estructura factorial. Se realizó un análisis factorial confirmatorio y se estimaron los parámetros del modelo utilizando el método de mínimos cuadrados ponderados diagonalmente (DWLS). La evaluación de FCV-19S tuvo valores satisfactorios (ω = .94; α = .93). Los resultados mostraron que el modelo de dos factores correlacionados se ajusta mejor a los datos CFI = .993, TLI = .989, RMSEA = .053, SRMR = .049. Estos hallazgos sugieren que la FCV-19S tiene las propiedades psicométricas adecuadas para su aplicación en estudiantes universitarios chilenos.The latest events in the lives of university students in Chile have been very stressful quarantines, online classes, and fear of contagion. It is imperative to have a solid instrument to measure the fear of Covid. This research aims to estimate the psychometric properties of the ‘Fear of Covid-19 Scale (FCV-19S)’ in a sample of 562 Chilean university students and to confirm its factorial structure. Confirmatory factorial analyses were performed and model parameters were estimated using the diagonally weighted least squares (DWLS) method. The assessment of FCV-19S had satisfactory values (ω = .94; α = .93). The results showed that the two-correlated factor model best fit the data CFI = .993, TLI = .989, RMSEA = .053, SRMR = .049. These findings suggest that FCV-19S has the proper psychometric properties for its application to Chilean university students.Fil: Martínez Líbano, Jonathan. Universidad Andrés Bello; ChileFil: TorresVallejos, Javier. Universidad Andrés Bello; ChileFil: Simkin, Hugo Andrés. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Oyanedel, Juan Carlos. Universidad Andrés Bello; ChileFil: Silva Fuentes, Alicia. Universidad de Las Américas.; EcuadorFil: Yeomans Cabrera, María Mercedes. Universidad de Las Américas.; Ecuado

Un modelo exploratorio de la intención de continuar estudiando en alumnos universitarios no-tradicionales

Background: Although academic achievement is believed to be an important factor in students’ decision to continue studying at university, research on this topic is limited. Method: The current study analyzed the relationship between academic achievement and the intention of 327 non-traditional students to continue studying at university, using a path model. Results: The central hypothesis of the study was confi rmed, as the intention to continue studying was determined by previous academic results, although the amount of variance explained was relatively low (13%). Conclusions: The results from this study indicate that the intention to continue studying at university depends less than expected on the performance achieved. So, universities should consider other variables such as the quality of the academic support offered to these students continue their studies.Antecedentes: a pesar de la importancia que se atribuye al rendimiento académico en la toma de decisión de los alumnos mayores de 25 años sobre si continuar o no sus estudios en la Universidad, la investigación sobre este tópico es limitada. Método: se analizó la relación entre el rendimiento académico y la intención de 327 alumnos no-tradicionales de continuar sus estudios en la Universidad mediante el ajuste de un modelo de relaciones causales. Resultados: la hipótesis central del estudio fue confi rmada en la medida en que la intención de continuar con los estudios resultó determinada por los resultados académicos previos, aunque la cantidad de varianza explicada fue relativamente escasa (un 13%). Conclusiones: de los resultados obtenidos en este estudio se concluyó que la intención de continuar en la Universidad depende menos de lo que se cree del rendimiento logrado, por lo que las universidades deberán dirigir su mirada también a otras variables como, por ejemplo, la calidad del apoyo que estos estudiantes reciben para continuar sus estudios

Hydroponic Lettuce Production and Minimally Processed Lettuce

Lettuce is a leafy vegetable most consumed in Brazil, and is considered the basis for salads and can be grown by hydroponics system. Hydroponics is a viable alternative to be implemented, with benefits for soil conservation and preservation of water sources. This work aimed to study the market of trailers snacks in Pelotas to analyze the economic feasibility of deploying an enterprise for the production of hydroponic lettuce, minimally processed, on a farm located in the city of Pelotas. The trailers were classified as small, medium and large, according to the consumption of lettuce. From market analysis, facilities and greenhouses for hydroponics area for processing of lettuce with flowchart of activities and mass balance were designed. The lettuce is produced from seeding to minimal processing, consisting of packing to delivery the whole lettuces and cut and pack the other portion, which will also be packaged for shipment. For the optimization of space in the greenhouses, a system of trails that allow them to glide over the stands, being compressed, opening corridors through which people ranging transplanting or harvest the lettuces, only where needed was created. The economic and financial analysis was performed using the indicators to establish the viability of the project or not. These indicators are: NPV (Net Present Value), IRR (Internal Rate of Return) and payback. The analysis was performed in a planning horizon of 10 years and considering a TMA (Average Attractiveness ) of 11.6 % pa Three scenarios for implementation of the project, the amount of greenhouses ranging from one to three different percentages of sales and production over time were studied. The project proved to be unfeasible with only a greenhouse, but two or three greenhouses is feasible to be implemented. However, when deployed, the project with two greenhouses in the first year, and three greenhouses in the first two years will profit. The best option would be two or three greenhouses, depending on the amount to be invested and the availability of capital to withstand years without profitability. Technically, the project proved feasible by enabling large area in a small amount of lettuce is produced by hydroponic system, hydroponic lettuce and minimally processed snack bars for an interesting product, as it is practical and hygienic. It is recommended to study whether the project would become more attractive with the production of other crops such as tomato, zucchini, among other hydroponic

Drying Tomatoes in a Small Tray Dryer

Drying tomatoes with high initial moisture content have advantages such as: maintenance of mineral constituents, inhibition of the action of microorganisms, reduction of the cost of transportation, handling, and storage and is an alternative to the problems of waste disposal and pollution. Moreover, dried products, besides the more economical and affordable package, is an option for light and quick meals. Small and low cost tray dryers are hard to find in the Brazilian market. Producing your own dehydrated food is a practice used in many countries for domestic consumption, as a gift, for small-scale enterprises, because some people appreciate handmade products that are related to a healthier product, without additives. The present study aimed to dry tomatoes and evaluates the characteristics such as: loss of final mass, drying time, and cost of drying in a portable low cost tray dryer. The dryer was built in plastic body and trays. Two heating conical resistors with 600 W each, and a 26W-fan were used. Approximately 1.4 kg of tomatoes was used in this test. They were previously sliced, washed, and the endocarp and seeds were removed. The weight loss during the process was obtained ​​by successive weightings of tomatoes in the trays each hour. The final drying was determined when the tomatoes were around 25% of moisture content. The initial moisture content of the tomatoes was determined by oven drying using 10 g of chopped tomatoes, dried at 95°C for 24h. To evaluate the drying cost the yield of dried tomatoes, the losses during the preparation of the fresh tomatoes slices, the drying time, and the rate of product ready for the drying period were determined. The energy cost was R$4,72, plus R$ 0,30 of osmotic solution, additional R$7.80/kg of tomatoes (off season). The final cost was R$ 12,82 (U$S 5.35) to process 1 kg of fresh tomatoes. During the season, one can buy tomatoes at R$ 1,00/kg, which reduces the cost to R$6.02/kg (U$S 2.50). Whereas the process reduces weight by 10.83 times, the pound of dried tomatoes would cost R$65,20 (U$S 27.15) in crop condition. As this portable dryer holds 2 kg of tomatoes by drying, the cost could be reduced to R$3.66/kg (U$S 1.55) considering fresh tomatoes or R$39,60/kg (U$S 16.50) dried tomatoes. The dryer presented the ideal medium parameters for drying fruits (51.6°C and 1.2 m/s) in a drying process of 8 hours. The cost per hour of drying in this experiment, due to be in between tomato crop season was considered high. However, there are conditions to reduce this cost at the harvest time and by increasing the density of tomatoes in the dryer trays