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Search Results: 1 - 10 of 1269 matches for " Donato Jhon "
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Limnology in El Dorado: some surprising aspects of the regulation of phytoplankton productive capacity in a high-altitude Andean lake (Laguna de Guatavita, Colombia)
Jhon Donato,Paola Jimenez,Colin Reynolds
Revista de Biología Tropical , 2012,
Abstract: High-altitude mountain lakes remain understudied, mostly because of their relative inaccessibility. Laguna de Guatavita, a small, equatorial, high-altitude crater lake in the Eastern Range of the Colombian Andes, was once of high cultural importance to pre-Columban inhabitants, the original location of the legendary El Dorado. We investigated the factors regulating the primary production in Laguna de Guatavita (4°58’50” N - 73°46’43” W, alt. 2 935m.a.s.l., area: 0.11km2, maximum depth: 30m), during a series of three intensive field campaigns, which were conducted over a year-long period in 2003-2004. In each, standard profiles of temperature, oxygen concentration and light intensity were determined on each of 16-18 consecutive days. Samples were collected and analysed for chlorophyll and for biologically-significant solutes in GF/F-filtered water (NH4+, NO3- , NO2-; soluble reactive phosphorus). Primary production was also determined, by oxygen generation, on each day of the campaign. Our results showed that the productive potential of the lake was typically modest (campaign averages of 45-90mg C/m2.h) but that many of the regulating factors were not those anticipated intuitively. The lake is demonstrably meromictic, reminiscent of karstic dolines in higher latitudes, its stratification being maintained by solute- concentration gradients. Light penetration is poor, attributable to the turbidity owing to fine calcite and other particulates in suspension. Net primary production in the mixolimnion of Laguna de Guavita is sensitive to day-to-day variations in solar irradiance at the surface. However, deficiencies in nutrient availability, especially nitrogen, also constrain the capacity of the lake to support a phytoplankton. We deduced that Laguna de Guatavita is something of a limnological enigma, atypical of the common anticipation of a “mountain lake”. While doubtlessly not unique, comparable descriptions of similar sites elsewhere are sufficiently rare to justify the presentation of the data from Laguna de Guatavita that our studies have revealed so far. Los factores que regulan la producción primaria en un lago remoto, peque o, ecuatorial y de elevada altitud en la región Oriental de los Andes Colombianos (4°58’50” N - 73°46’43” W, altura 2 935m.s.n.m., área 0.11km2 y profundidad máxima 30m), que también tuvo importancia cultural para los indígenas precolombinos y los orígenes de la leyenda de El Dorado, fueron investigados. La relativa lejanía del lugar requirió una serie de tres campa as intensivas de estudio, en un periodo de un a o (2003-2004). Dur
Comparation of Spectrophotometric and Fluorometric Measurements of Chlorophyll-a Comparación de la estimación de la Clorofila-a mediante los métodos espectrofotométrico y fluorométrico
Rivera R. Carlos,Zapata A. ángela,Pinilla Gabriel,Donato Jhon
Acta Biológica Colombiana , 2005,
Abstract: In four mountain aquatic ecosystems of altiplano Cundiboyacense, Colombia, we compared through analysis regression data set of chlorophyll-a obtained with spectoropho-tometric (tricromatic formula) and fluorometric (Welschmeyer) methods. The analysis showed that the spectrophotometric method overestimated the chlorophyll-a concen-tration, but it could be used with precaution in the lower trophic environments. An equation that relates the two chlorophyll-a measures was obteined. En cuatro ecosistemas acuáticos de monta a del altiplano Cundiboyacense, Colombia, se compararon mediante un análisis de regresión los datos de clorofila-a obtenidos a partir de los métodos espectrofotométrico (fórmula tricromática) y fluorométrico (método de Welschmeyer). El análisis demostró que el método espectrofotométrico sobreestimó la concentración de clorofila-a, pero se puede utilizar con precaución en ambientes de baja trofia. Se halló una ecuación que permite relacionar las medidas de clorofila-a obtenidas con las dos metodologías.
Acta Biológica Colombiana , 2010,
Abstract: morphometric characteristics of the lake guatavita were investigated in order to disclose possible connections with its ecological functioning and discuss some hypotheses that exist about the origin of this lake. the lake has a basin with a conical shape, low perimeter development, maximum depth of 30 m and relative depth of 7.9%. the hypsographic curve reveals a constant increase of the sectional area with depth. the lake shape promotes a permanent thermal stratification during eight months of the year with a hypoxic hypolimnion and a strong vertical gradient in the conductivity and ammonium concentration. these results indicate an important role of depth on the physical and chemical lake characteristics which in turn explain the dynamics of biological communities and are responsible for a relatively low phytoplankton primary productivity.
Acta Biológica Colombiana , 2005,
Abstract: in four mountain aquatic ecosystems of altiplano cundiboyacense, colombia, we compared through analysis regression data set of chlorophyll-a obtained with spectorophotometric (tricromatic formula) and fluorometric (welschmeyer) methods. the analysis showed that the spectrophotometric method overestimated the chlorophyll-a concentration, but it could be used with precaution in the lower trophic environments. an equation that relates the two chlorophyll-a measures was obtained.
Rivera Rondón Carlos Alberto,Zapata Anzola Angela María,Donato Rondón Jhon Charles
Acta Biológica Colombiana , 2010,
Abstract: En el lago Guatavita se estudiaron sus características morfométricas con el objeto de analizar implicaciones de la morfología sobre su funcionamiento y discutir algunas hipótesis que existen sobre el origen del lago. El lago presenta una cubeta con una forma cónica, bajo desarrollo del perímetro, profundidad máxima de 30m y profundidad relativa de 7.9%. La curva hipsográfica indica que el lago presenta un aumento constante del área de la sección con respecto a la profundidad. La forma del lago promueve una estratificación térmica que se mantiene durante ocho meses del a o, con un hipolimnio hipóxico y un fuerte gradiente en la conductividad y en la concentración de amonio. Estos resultados indican un papel muy importante de la profundidad sobre las características físicas y químicas del lago que a su vez determinan la dinámica de las comunidades biológicas y una baja productividad primaria del sistema.
Donato R Jhon Charles,Morales-Duarte Silvia Juliana,Castro-Rebolledo Maria Isabel,Chaparro Hooz Angela
Acta Biológica Colombiana , 2010,
Modus vivendi, overlapping consensus and stability
Discusiones Filosóficas , 2010,
Abstract: in this paper, i show how the political theory of a non-liberal giant of the western philosophy canon, hobbes, can be interpreted as having a commitment to some form of neutrality. in recognizing the role neutrality plays in hobbes's thought we come to see that a neutrality requirement is not exclusive to liberalism. beyond this, however, i intend to show that consideration of hobbes in this context reveals certain helpful points of comparison with rawls's later work that raise concerns about the viability of his political liberalism. i argue that rawls's political liberalism, while not a modus vivendi solution to political justification, is ill suited for the securing stability.
Characterisation of Moringa peregrina Arabia seed oil
Tsaknis, Jhon
Grasas y Aceites , 1998,
Abstract: Oil content of Moringa peregrina seeds (from Saudi Arabia) was 49.8%. Results of some physical and chemical characteristics of extracted oil were: refractive index (40 °C) 1.460, density (24 °C) 0.906, acidity (as oleic) 0.30%, iodine value 69.6, saponification number 185 and peroxide value 0.4 meq/kg. Moringa peregrina seed oil was found to contain high levels of oleic (70.52%), followed by gadoleic (1.5%), while the dominant saturated acids were palmitic (8.9%) and stearic (3.82%). α- γ- and δ-tocopherols were detected at levels of 145,58 and 66 mg/kg respectively. The induction period (at 120 °C) of tomato seed oil was 10.2 hours and reduced to 8.1 hours after degumming. Specific extinctions at 232 and 270 nm were 1.66 and 0.19 respectively, β-sitosterol was found as the most predominant component of the sterolic fraction of the oil. Other sterols found in percentages higher than 1.5% were 24-methylenecholesterol, campesterol, stigmasterol and Δ5-avenasterol. In addition, trace to minor anaounts of brassicasterol, campestanol, Δ7-campestanol, clerosterol, Δ5,24-stigmastadienol, Δ7-stigmastanol and Δ7-avenasterol were found. El contenido de aceite de semilla Moringa peregrina (de Arabía Saudí) fue del 49.8%. Los resultados de algunas características físicas y químicas del aceite extraído fueron: índice de refracción (40 °C) 1.460, densidad (24 °C) 0.906, acidez (como oleico) 0.30%, índice de yodo 69.6, índice de saponificación 185 e índice de peróxido 0.4 meq/Kg. El aceite de semilla Moringa peregrina tuvo altos niveles de oleico (70.52%), seguido por el gadoleico (1.5%), mientras los ácidos saturados dominantes fueron palmítico (8.9%) y esteárico (3,82%). Los α- γ- y δ-tocoferoles fueron detectados a niveles de 145,58 y 66 mg/Kg respectivamente. El período de inducción (a 120 °C) de aceite de semilla de tomate fue de 10.2 horas y se redujo a 8.1 horas después del desgomado. Las extinciones específicas a 232 y 270 nm fueron 1.66 y 0.19 respectivamente. El β-sitosterol fue el componente más predominante de la fracción esterólica del aceite. Otros esteroles encontrados en porcentajes mayores del 1.5% fueron 24-metiIenecolesterol, campesterol, estigmasterol y Δ5-avenasterol. Además se encontraron trazos con componentes menores de brasicasterol, campestanol, Δ7- campestanol, clerosterol, Δ5,24-estigmastadienol, Δ7-estigmastanol y Δ7-avenasterol.
Description of Asphondylia Helianthi-Globulus
Jhon Marten
Psyche , 1888, DOI: 10.1155/1888/23515
Molecular Dynamics Study of the Mechanical Behavior of Few Layer Graphene
Young In Jhon,Myung S. Jhon
Physics , 2012,
Abstract: Atomistic simulation was performed to study the mechanical properties of few layer graphene (FLG) in conjunction with monlayer graphene (MLG) under uniaxial elongation by systematically increasing the layer number from one to six. We found that the ultimate tensile strength and strain increased in these FLGs for both zigzag and armchair-directional elongations when compared with the results of MLG. We also found that the largest increments were obtained in bi- or tri-layer graphene for all the FLG systems we studied. Using atomic stress distribution analysis, it is observed that the width of the distribution became narrower, thus the maximum stress decreased in FLG compared to MLG at respective stages of identical tensile stress. It indicates that locally-driven highly elevated atomic stress of FLG has been effectively relaxed to the atoms in other layers through cooperative interlayer interaction. This effect explains the reason for synergetic mechanical strengthening of FLG since tensile failure is critically influenced by maximum atomic stress. Furthermore, the Young's moduli were slightly smaller for all FLGs compared to MLG.
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