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Search Results: 1 - 10 of 484271 matches for " Fernando álvarez Mejía "
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ANáLISIS BIOMECáNICO DE ESPALDA Y BRAZOS PARA EL DESARROLLO DE HERRAMIENTAS PORTáTILES
López Fisco,Hugo Andrés; Sanz Uribe,Juan Rodrigo; álvarez Mejía,Fernando;
Revista Facultad Nacional de Agronomía, Medellín , 2008,
Abstract: in semi-mechanized agricultural labors such as fertilization, pesticide application, harvesting and others, operators usually carry loads in backpacks and a tool in one of their hands. this work estimated the stresses that result in the shoulder and in the inter-vertebral disk l5-s1 of an average operator performing agricultural labors with back-mounted equipment. in order to perform the analysis it was developed a computational tool called homo, which considers the most common positions of the arm and the most common inclinations of the backbone when using back-mounted equipment. this analysis determined that a 12 kg load on the operator?s back, combined with a 0,5 kg tool in the operator?s hand, are not harmful for the studied joints.
ANáLISIS BIOMECáNICO DE ESPALDA Y BRAZOS PARA EL DESARROLLO DE HERRAMIENTAS PORTáTILES BIOMECHANICAL ANALYSIS OF ARMS AND BACK FOR THE DEVELOPMENT OF PORTABLE TOOLS
Hugo Andrés López Fisco,Juan Rodrigo Sanz Uribe,Fernando álvarez Mejía
Revista Facultad Nacional de Agronomía, Medellín , 2008,
Abstract: Cuando se realizan labores agrícolas semimecanizadas como fertilización, fumigación, cosecha y otras, los operarios regularmente llevan una carga en su espalda y una herramienta en una de sus manos. En este trabajo se estimaron los esfuerzos que se generan en las articulaciones del hombro y del disco intervertebral L5-S1, para una persona promedio realizando labores agrícolas con herramientas portátiles de este tipo. Para hacer el análisis se desarrolló una herramienta computacional denominada HOMO, en la cual se consideran las posiciones más comunes del brazo e inclinaciones más comunes del eje de la columna vertebral cuando se usan equipos de espalda. El análisis determinó que una carga en la espalda de 12 kg combinada con un elemento de 0,5 kg en la mano, no son perjudiciales para la salud de los trabajadores agrícolas. In semi-mechanized agricultural labors such as fertilization, pesticide application, harvesting and others, operators usually carry loads in backpacks and a tool in one of their hands. This work estimated the stresses that result in the shoulder and in the inter-vertebral disk L5-S1 of an average operator performing agricultural labors with back-mounted equipment. In order to perform the analysis it was developed a computational tool called HOMO, which considers the most common positions of the arm and the most common inclinations of the backbone when using back-mounted equipment. This analysis determined that a 12 kg load on the operator’s back, combined with a 0,5 kg tool in the operator’s hand, are not harmful for the studied joints.
CORRELACIóN ENTRE PROPIEDADES ANATóMICAS, RESISTENCIA A FLEXIóN ESTáTICA Y ENERGíA REQUERIDA PARA EL CORTE DE LA CA?A DE AZúCAR (Saccharum officinarum L.)
González Sánchez,Hugo Alberto; Toro Betancur,Alejandro; álvarez Mejía,Fernando; Cortés Marín,Elkin Alonso;
Revista Facultad Nacional de Agronomía, Medellín , 2008,
Abstract: the microstructure, anatomical structure, bending resistance and the energy required to cut stems of three varieties of sugar cane cultivated in the valle del cauca ( colombia ), were studied in order to have useful data for the development of cutting blades. microestructural and anatomical characterization tasks were performed by optical microscopy ( om), and scanning electron microscopy (sem). the physical and mechanical properties were determined after adaptation of astm standards (which were developed for wood), while the consumption of energy during cutting was evaluated by using a modified charpy type impact pendulum. the fibers and silica particles showed different geometry and distribution in the stems of the three studied varieties, and a relation was established between the microstructure of the stems and the energy required to cut them in the modified charpy pendulum. generally speaking, cutting the internodes required higher specific energy than cutting the nodes, and the use of blades with cutting angle of 20° led to lower levels of energy consumption. also, a relation of proportionality between the effective cross-sectional area of fibers (atef) and the specific energy consumed in cutting, as well as between the flexibility coefficient and the modulus of elasticity in bending were found.
CORRELACIóN ENTRE PROPIEDADES ANATóMICAS, RESISTENCIA A FLEXIóN ESTáTICA Y ENERGíA REQUERIDA PARA EL CORTE DE LA CA A DE AZúCAR (Saccharum officinarum L.) CORRELATIONS AMONG ANATOMIC PROPERTIES, BENDING RESISTANCE AND ENERGY REQUIRED TO CUT SUGAR CANE (Saccharum officinarum L.)
Hugo Alberto González Sánchez,Alejandro Toro Betancur,Fernando álvarez Mejía,Elkin Alonso Cortés Marín
Revista Facultad Nacional de Agronomía, Medellín , 2008,
Abstract: La microestructura, estructura anatómica, la resistencia a la flexión y la energía requerida durante el corte de los tallos de tres variedades de ca a de azúcar cultivadas en el Valle del Cauca (Colombia), fueron estudiados con el propósito de adquirir información útil para el desarrollo de cuchillas para corte de esta especie. Las labores de caracterización microestructural y anatómica se apoyaron en las técnicas de microscopía óptica y electrónica de barrido. Las propiedades mecánicas se determinaron adaptando algunas normas ASTM para maderas, mientras que la energía al corte se evaluó usando un péndulo de impacto tipo Charpy modificado. En los tallos de las tres variedades estudiadas se observaron diferentes distribuciones y dimensiones geométricas de las fibras y se verificó la presencia de partículas de sílice. Se presentó en general mayor requerimiento de energía específica al corte en los entrenudos que en los nudos y un menor consumo específico de energía al corte con las cuchillas con ángulo de afilado de 20°. Se establecieron relaciones entre la microestructura de los tallos, comportamiento a la flexión y al corte, destacándose la relación proporcional entre el área transversal efectiva de fibra (ATEF) y la energía específica al corte, así como entre el coeficiente de flexibilidad y el módulo de elasticidad en flexión. The microstructure, anatomical structure, bending resistance and the energy required to cut stems of three varieties of sugar cane cultivated in the Valle del Cauca ( Colombia ), were studied in order to have useful data for the development of cutting blades. Microestructural and anatomical characterization tasks were performed by optical microscopy ( OM), and scanning electron microscopy (SEM). The physical and mechanical properties were determined after adaptation of ASTM standards (which were developed for wood), while the consumption of energy during cutting was evaluated by using a modified Charpy type impact pendulum. The fibers and silica particles showed different geometry and distribution in the stems of the three studied varieties, and a relation was established between the microstructure of the stems and the energy required to cut them in the modified Charpy pendulum. Generally speaking, cutting the internodes required higher specific energy than cutting the nodes, and the use of blades with cutting angle of 20° led to lower levels of energy consumption. Also, a relation of proportionality between the effective cross-sectional area of fibers (ATEF) and the specific energy consumed in cutting, as well as between the fl
DESARROLLO DE UN SEPARADOR DE OBJETOS DUROS EN EL CAFé A PARTIR DE LAS VIBRACIONES PRODUCIDAS EN PLACAS DELGADAS DEVELOPMENT OF A SEPARATOR IN THE COFFEE HARD OBJECTS FROM THE VIBRATIONS PRODUCED IN THIN PLATES
Diego Agudelo Gómez,Carlos Eugenio Oliveros Tascón,Jorge Hernán Estrada Estrada,Fernando álvarez Mejìa
Revista Facultad Nacional de Agronomía, Medellín , 2008,
Abstract: En Cenicafé se dise aron y construyeron prototipos electromecánicos denominados PESELOD (pescador electrónico de objetos duros) para la protección de las máquinas despulpadoras. Este nuevo módulo, localizado antes de la despulpadora, está conformado por un alimentador, un cuerpo vibrante (placa delgada o cono metálico), una compuerta, un recipiente para los objetos duros desalojados y un circuito para la detección y separación automática del objeto duro. Su principio de funcionamiento se basa en la diferencia de los parámetros de amplitud y frecuencia de las vibraciones producidas en el impacto del café y de los objetos duros contra el cuerpo vibrante. Se realizó el análisis histórico en los espectros de las aceleraciones que se indujeron teniendo en cuenta variaciones del material, espesor y apoyo. En la caracterización se encontraron mejores características de separación para placas de 2,5 mm de espesor, simplemente soportada y de material acerado. Los prototipos presentaron eficacias superiores al 80% y rendimientos entre 300 y 2.000 kg h-1 de café en cereza. De igual manera se realizaron variaciones tendientes a mejorar su operabilidad, relacionada con la limpieza de las placas para lo cual se construyó otro prototipo cuyo cuerpo vibrante lo constituía un cono acerado. Electromechanical experimental models of an electronic separator of hard objects, denominated PESELOD (pescador electrónico de objetos duros, Spanish) were designed and constructed in Cenicafé to protect the coffee processing machines. The module, located before the pulping machine, includes a feeder, a vibrant body (thin plate or metallic cone), a gate, a hard objects container and a circuit for both hard objects detection and automatic separation. Its principle of operation is based on the difference of amplitude and frequency of the vibrations produced by impact of coffee fruits and hard objects against a vibrant body. The historical analysis was made in the spectrums of the accelerations that were induced on different materials, thicknesses and boundary conditions. The device worked better with steel plates, 2.5 mm thick, simply supported. The model presented effectiveness greater than 80% and yields between 300 and 2.000 kg h-1 of coffee fruits. To improve their operability related to dirty plates, another model was constructed with a truncated cone vibrant body.
Resistencia de Mycobacterium tuberculosis a los fármacos antituberculosos en menores de 15 a?os en Colombia
Llerena,Claudia; Fadul,Santiago Elías; Garzón,María Consuelo; Mejía,Graciela; Orjuela,Dora Leticia; García,Luz Mary; álvarez,Hilda Beatriz; Ruiz,Fernando Javier;
Biomédica , 2010,
Abstract: introduction. tuberculosis is a widespread and increasingly important infectious disease. a third of the world-wide population is infected. every year nine million cases occur in the world, one million of them appearing in children under 15 years old. in colombia alone, 719 cases were reported for the year 2008. objective. the incidence of mycobacterium tuberculosis resistant forms was characterized in children under 15 years old in colombia. materials and methods. mycobacterium tuberculosis drug susceptibility test data from 2001 to mid year 2009 were analyzed at the laboratorio nacional de referencia, instituto nacional de salud, bogotá, colombia. cases were evaluated by patient age, disease geographic location, and type of sample, as well as the proportions of tb/hiv coinfections and drug resistance. results. of the 128 patients examined, 66 were female (52%) and 62 were male (48%). the age group 0 to 5 years old consisted of 59 cases (46%), 21 cases were 6 to 10 years old (16%) and 48 cases 11 to 14 years old (37.5%). the types of disease were 89 (69.6%) pulmonary, 34 (26.4%) extrapulmonary, and 5 (3.9%) cases without data. tb/vih coinfection cases were 7(5.4%). 123 (96%) untreated cases and 5 (2.34%) cases previously treated. global resistance among the untreated cases was 21.1% and mdr-tb was 6.5%. conclusion. this analysis demonstrated weaknesses in following established procedures in the tb treatment process, thereby impeding the diagnosis and the identification of drug resistance s in children under 15 years old. approaches to improving treatment standards is a topic which requires further exploration.
Variables físicas que explican la variabilidad de suelo aluvial y su comportamiento espacial
Jaramillo, Daniel Francisco Jaramillo;Gómez, María Luisa Anaya;Moná, Carlos Andrés Restrepo;Sánchez, Hugo Alberto González;Mejía, Fernando álvarez;
Pesquisa Agropecuária Brasileira , 2011, DOI: 10.1590/S0100-204X2011001200017
Abstract: the objective of this work was to use the principal component and semivariance analyses to select physical variables that could explain the variability of an alluvial soil, in order to establish the spatial behavior of the chosen variables so that the location of experimental plots could be technically defined to study the abrasiveness effect on the wearing away of farm equipment. field tests were performed in 2008, on a 6,000 m2 flat lot with medium to heavy soil texture (vertic haplustepts). an intensive sampling was done in a grid of 10x14 m. the variables which had the most weight on the first three principal components were the contents of silt, fine and intermediate sand, intermediate gravel, soil moisture at field capacity, and the hygroscopic coefficient. except for the half sand and the field capacity, the other properties showed a high spatial dependence, and their distribution showed that in the experimental plot there are three sectors of differential accumulation of silt and fine sand. the combination of principal component analysis and geostatistics allowed for defining the soil properties involved in the wear of tools, their spatial pattern and the most appropriate way of distributing plots to study soil abrasiveness.
DESARROLLO DE UN SEPARADOR DE OBJETOS DUROS EN EL CAFé A PARTIR DE LAS VIBRACIONES PRODUCIDAS EN PLACAS DELGADAS
Agudelo Gómez,Diego; Oliveros Tascón,Carlos Eugenio; Estrada Estrada,Jorge Hernán; álvarez Mejìa,Fernando; Sanz Uribe,Juan Rodrigo;
Revista Facultad Nacional de Agronomía, Medellín , 2008,
Abstract: electromechanical experimental models of an electronic separator of hard objects, denominated peselod (pescador electrónico de objetos duros, spanish) were designed and constructed in cenicafé to protect the coffee processing machines. the module, located before the pulping machine, includes a feeder, a vibrant body (thin plate or metallic cone), a gate, a hard objects container and a circuit for both hard objects detection and automatic separation. its principle of operation is based on the difference of amplitude and frequency of the vibrations produced by impact of coffee fruits and hard objects against a vibrant body. the historical analysis was made in the spectrums of the accelerations that were induced on different materials, thicknesses and boundary conditions. the device worked better with steel plates, 2.5 mm thick, simply supported. the model presented effectiveness greater than 80% and yields between 300 and 2.000 kg h-1 of coffee fruits. to improve their operability related to dirty plates, another model was constructed with a truncated cone vibrant body.
COSECHA DEL CAFé CON VIBRADORES PORTáTILES DEL TALLO COFFEE HARVEST WITH PORTABLE STEM VIBRATORS
Carlos Eugenio Oliveros Tascón,Robin Benítez Mora,Fernando álvarez Mejía,Iván Darío Aristizábal Tórres
Revista Facultad Nacional de Agronomía, Medellín , 2005,
Abstract: Los vibradores portátiles del tallo (VPT′s) son herramientas con gran potencialidad para ser empleadas en la cosecha de café en Colombia, en los pases con mayor producción (más de 800 g/árbol) y concentración de frutos maduros por árbol (más del 60 %). Por su relativo bajo peso y tama o se pueden operar fácilmente en el interior de plantaciones con distancia entre surcos superiores a 1,2 m, en suelo húmedo con pendiente de hasta del 50 %. Para obtener la mejor calidad de cosecha y el mayor rendimiento de recolección, el tiempo de vibración por árbol debe ser inferior a 5 segundos. Por facilidad de operación, el vibrador se debe acoplar al tallo en la mitad de su altura. La recolección debe realizarse en equipos constituidos por dos VPT′s y cuatro personas, dos para operar los vibradores y dos para manejar las mallas de captura de los frutos desprendidos. El rendimiento potencial con esta tecnología varió en el rango 288 a 504 kg/h/vibrador. El rendimiento efectivo, incluyendo el tiempo para recoger el café con mallas, varió en el rango 53 a 67 kg/h/operario, que con relación al promedio observado en pases pico en cosecha manual tradicional (12 kg/h/operario) representa un incremento del 341,7 a 458,3 %, respectivamente. Aunque estos resultados muestran un aumento notorio en la eficiencia de la mano de obra en cosecha del café, la eficiencia global de recolección (rendimiento efectivo/rendimiento potencial) fue muy baja (0,13) y, por lo tanto, se requiere desarrollar métodos más eficientes para la captura de los frutos desprendidos. Portable stem vibrators (PSVs) are tools with great potential for use in coffee harvesting in Colombia, in the passes of greatest production (> 800 g/tree) and concentrations of mature fruits (> 60 %). Their relative low weight and size permits easy operation within plantations with distances between furrows greater than 1,2 m, in humid soils with slopes of up to 50 %. In order to obtain maximum harvest quality and greatest harvesting yield, the vibration time per tree must be less than 5 seconds. To operate easily, the vibrator should be fastened to the stem at half its height. Harvesting should be conducted in teams of two PSVs and four people, two to operate the PSVs and two to handle the fruit capture nets. The potential yield of this technology ranged from 288 to 504 kg/h/vibrator. The effective yield, including the time to remove the coffee from the nets, ranged from 53 to 67 kg/h/person, that in relation to the mean observed during peak passes using traditional manual harvest methods (12 kg/h/person) represents an incr
Growth Hormone Improves Growth Retardation Induced by Rapamycin without Blocking Its Antiproliferative and Antiangiogenic Effects on Rat Growth Plate
óscar álvarez-García, Enrique García-López, Vanessa Loredo, Helena Gil-Pe?a, Natalia Mejía-Gaviria, Julián Rodríguez-Suárez, Flor á. Ordó?ez, Fernando Santos
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0034788
Abstract: Rapamycin, an immunosuppressant agent used in renal transplantation with antitumoral properties, has been reported to impair longitudinal growth in young individuals. As growth hormone (GH) can be used to treat growth retardation in transplanted children, we aimed this study to find out the effect of GH therapy in a model of young rat with growth retardation induced by rapamycin administration. Three groups of 4-week-old rats treated with vehicle (C), daily injections of rapamycin alone (RAPA) or in combination with GH (RGH) at pharmacological doses for 1 week were compared. GH treatment caused a 20% increase in both growth velocity and body length in RGH animals when compared with RAPA group. GH treatment did not increase circulating levels of insulin-like growth factor I, a systemic mediator of GH actions. Instead, GH promoted the maturation and hypertrophy of growth plate chondrocytes, an effect likely related to AKT and ERK1/2 mediated inactivation of GSK3β, increase of glycogen deposits and stabilization of β-catenin. Interestingly, GH did not interfere with the antiproliferative and antiangiogenic activities of rapamycin in the growth plate and did not cause changes in chondrocyte autophagy markers. In summary, these findings indicate that GH administration improves longitudinal growth in rapamycin-treated rats by specifically acting on the process of growth plate chondrocyte hypertrophy but not by counteracting the effects of rapamycin on proliferation and angiogenesis.
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