Volumen 28, Números 1 y 2
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Item Acumulación de cobre en plantas silvestres de zonas agrícolas contaminadas con el metal(2013-06-28 15:00:39) Hernández Colorado, Ramón Rigoberto; Alvarado Gámez, Ana Lorena; Romero Chacón, Rosaura MaríaCopper is an essential nutrient that is known to result in toxic damages to organisms. Copper salts have been utilized as fungicide because of its protective effect against several diseases in plants, but the repeated use of it has caused contamination of many Costa Rican agricultural lands. This study evaluated the potential of twenty most abundant species growing on two contaminated sites in Alajuela and Siquirres. Plants and associated soil samples were collected and analyzed for total metal concentrations using flame atomic adsorption technique. None of the species was identified as hyperaccumulator. Plant total Cu concentration varied from 19,0 to 170 mg kg-1 and in the soil ranged from 60,0 to 307 mg kg-1 . Among the plants, Portulaca oleracea had the higher bioconcentration factor (BCF): 2,5. This specie could be suitable for phytoextracting of sites contaminated with copper.Item Producción de jarabe de fructosa con enzimas inmobilizadas en un proceso continuo a partir de tiquisque (Xanthosoma sagittifolium)(2013-06-28 15:00:39) Quesada Salazar, Melissa; Hernández Peñaranda, Alicia MaríaHigh fructose corn syrups (HFCS) are mainly used by the food industry and are produced by enzymatic hydrolysis from cornstarch. The main objective of this project was to produce fructose syrups using tiquisque starch (Xanthosoma sagittifolium) as new source. Conditions to produce tiquisque glucose syrup were obtained in a previous study. Fructose was produced using a column packed isomerase (Sweetzyme IT). The effect of flow rate (0.5 and 1.0 mL/min), glucose syrup concentration (40 and 45 °Brix) and hydrolysis temperature (55 and 60 °C) were studied using a 23 factorial design. Response variables were fructose and glucose concentrations, fructose yield and conversion degree. All variables were statistically significant (p < 0.05), and flow rate presented the main effect on response variables. Higher conversion degree (99.16 %) was achieved using 40 °Brix glucose syrup and a flow rate of 0.5 mL/min at 60 °C. Fructose syrups obtained experimentally presented higher fructose content than commercial syrup (HFCS-42).Item La naturaleza del enlace químico 2013 ¡No existe tal cosa llamada orbital!(2013-06-28 15:00:39) Ogilvie, John F.Despite the fact that the chemical bond is a fiction, although convenient and nearly harmless, it plays an enormous role in the thinking, and especially the education, of chemists at all levels. Much further fiction has accumulated during the past 85 years; although, when the ideas about bonds, orbitals, hybridization and related topics originated and became widely known, largely through the verbal and written efforts of Pauling, they seemed plausible and helpful, the powerful experiments and calculations now available show those efforts and concepts to lack a firm foundation. Their continued promulgation is counterproductive to a profound understanding and communication of chemical knowledge. In this essay we discuss the origin and amplification of various ideas and terms that are common in textbooks of chemistry and in the lessons of instructors of chemistry but that are no longer acceptable as scientific truth.Item Caracterización del producto del proceso de viscoreducción, para la conversión de aceite vegetal, aceite de alga y búnker(2013-06-28 15:00:39) Davis Barquero, Alexander; Ulate Brenes, Adolfo MauricioThrough the use of a high pressure and high temperature reactor conditions a visbreaking is simulated, with the purpose of producing green fuels, replacing a fraction fuel oil #6 with vegetable oils. A 25% (m/m) of palm (Elaeis guineensis), castor (Ricinus communis), jatropha (Jatropha curcas) and 10% algae (Undaria pinatifida) oils, 450 ° C and 5 min of reaction time were utilize and the products were compared with the standards used by RECOPE. The replacement of 25% m/m by vegetable oil, increases by 6,1% the fraction of total diesel oil, improves the cetane index, decreases viscosity the amount of aromatic material and the amount of sulphur respect to 100% bunker The use of fluidized bed reactors or hydrogen mix for increase the saturated products are recommended for future research.