Volumen 24, Número 2
URI permanente para esta colección
Examinar
Envíos recientes
Ítem Síntesis y caraterización del ligando tris-(2-tiosalicilamidoetil)amina y sus complejos de hierro e indio(2009-01-13 00:00:00) Guerra García, Pedro Pablo; Valle Bourrouet, GrettelThe coordination chemistry of the hexadentate ligand, tris(2-thiosalicylamidoethyl)amine, (LH3), was studied. The reaction of the ligand trianion with iron(III) and indium(III) yields monomeric hexacoordinate complexes, LFe·HCl and LIn. The complexes were characterized by spectroscopic, magnetic and electrochemical methods.Ítem Lignanos de Zanthoxylum acuminatum(2009-01-13 00:00:00) Murillo Masís, Renato; Castro Araya, Víctor H.; Chavarría, Max; Poveda Álvarez, Luis JorgeFrom the aerial parts of Zanthoxylum acuminatum (Rutaceae) collected in Upala, Alajuela, Costa Rica were isolated the known lignans hinokinin, (+)-asarinin, (+)- piperitol, (+)-kobusin, and epi-kobusin. In addition to the lignans were isolated the triterpen lupeol and the steroid campesterol. All the separations were performed with chromatographic techniques and the structures were elucidated using 1D and 2D NMR techniques.Ítem Identificación de modelos de orden reducido a partir de la curvatura de reacción del proceso(2009-01-13 00:00:00) Alfaro Ruíz, Víctor M.A general identification procedure is given, for first and second orders plus time delay models, that uses two or three arbitrary points over the process reaction curve. Two simplified versions of the methods are described: the three points 123c identification method that uses the times required to arrive to the 25, 50 and 75% of the output total change, and the symmetrical method that uses points symmetrically distributed over the reaction curve. It is also described the use of the identification methods to obtain the optimal times for the model parameters identification. Using an example, the goodness of the models identified is compared.Ítem Nuevas lactonas sesquiterpénicas de Perymenium grande(2009-01-13 00:00:00) Murillo Masís, Renato; Castro Araya, Víctor H.; Araya, J.; Poveda Álvarez, Luis JorgeThree new sesquiterpenes lactonaes were isolated from the aerial parts of Perymenium grande Hemsl. (Asteraceae), collected around Rincón de la Vieja Volcano, Costa Rica. In addition to the three new lactones 1, 3 and 5; were isolated the additional five known sesquiterpenes lactones. The separation were performed with chromatographic techniques and the structures were elucidated by one- and two-dimensional nuclear magnetic resonance techniques.Ítem Aplicación de la tomografía axial computarizada para la detección de bolsas de humedad en madera seca de gmelina arborea (roxb.)(2009-01-13 00:00:00) Moya, Róger; Muñoz A., Freddy; Escalante, IvánDue to its excellent growth rate and productivity, Gmelina arborea (Roxb.) is widely used for commercial reforestation in Costa Rica. However during the lumber drying process, the wooden boards show non-uniform values of final moisture content (MC). The low uniformity in final MC is caused by the presence of "wet pockets", originated during the growing process of the tree. During the wood drying process, the regions with wet pockets present zones with a high MC, which are hard to detect with traditional methods for MC measurements. This article shows that it is possible to detect and to set the limits of the presence of wet wood in Gmelina arborea boards using scanning computed tomography (CT-scanning), a technique applied in medical diagnostic.Ítem Kinetics of the fischer esterification of palm fatty acids with isopropanol and butyl-cellosolve(2009-01-13 00:00:00) Moya León, Alonso; Viales Montero, Christian; Arias Carrillo, Maynor; Mata Segreda, Julio FranciscoFischer esterification of the mixture of palm fatty acids can be achieved in 80% conversion, under conditions of reactive distillation and methanesulphonic acid as catalyst. The volatility of the H2O/alcohol azeotrope by-product confines the kinetic acceleration, relative to batch conditions.Ítem La cinética de la esterificación de ácidos carboxílocos es de segundo orden con repecto al alcohol(2009-01-13 00:00:00) Arias Carrillo, Maynor; Céspedes Camacho, Isaac; Fatjó Rojas, DanielEsterification of carboxylic acids with alcohols is considered as AAC2 type reaction. The specific rate of esterification of acetic acid with methanol, in mixtures of acetonitrile-methanol showed a quadratic dependence on the alcohol concentration. This second order dependence suggests a general base catalyzed mechanism analogous to the [H2O]2 kinetic dependence observed in the acidcatalyzed hydrolysis of carboxylic esters, in highly aqueous media.Ítem Modelación de la emisión de compuestos orgánicos volátiles en sistemas de aereación mediante un modelo de dos zonas simplificado(2009-01-13 00:00:00) Durán Herrera, Esteban; Morales Lara, YenoryA new simplified mass-transfer model was developed to describe the volatile organic compounds (VOC) emission rates from diffused aeration systems. The model takes into consideration that the VOC mass transfer occurs in two separate mass-transfer zones instead of lumping the overall VOC transfer in the whole aeration tank as is done in the conventional ASCE-based model. A series of batch VOC emission tests were performed in a 1000 l tank equipped with a fine pore diffuser at 0,50 to 1,33 - 10-3 normal m3/s diffused air flow rate and a water temperature of 293 K. The unsteady-state dissolved concentrations of p-xylene, benzene, toluene, trichloroethylene and tetrachlorethylene were measured during the tests and these data were used to find the proportional coefficient Ψ and with it, the volumetric mass-transfer coefficients of the VOCs. It was found that the Ψ coefficients were not dependent upon the diffused air flow rate, but do depend on the nature of the volatile compound used. A semiempirical set of equations that predict successfully the Ψ coefficients based on the critical volume and the normal boiling temperature of the compound was found. It was concluded that the new model provides better insight of the VOC mass transfer process and requires only oxygen aeration performance data, besides the critical volume and the normal boiling point of the compound, to predict accurately the VOC emission rates.Ítem EEfecto de contaminantes sobre la transferencia de oxígeno en sistemas de aeración analizado mediante un modelo de dos zonas simplificado(2009-01-13 00:00:00) Durán Herrera, Esteban; Rojas Meza, GerardoA series of unsteady-state reaeration tests were performed in a 1000 l tank at 1-10-3 normal m3/s diffused-air flow rate and 298,65 K water temperature. Three different types of impurities: soybean oil, surfactant, and diatomaceous earth were doped to simulate the impurities in wastewaters and the effects of the impurities on the oxygen transfer rate were investigated. The ASCE and the new simplified two-zone oxygen mass-transfer models were used to analyze the unsteady-state reaeration data and the volumetric mass-transfer coefficients determined from them were correlated as a function of the impurity concentration. An empirical correlation that predicts successfully the volumetric oxygen-transfer coefficient in an aqueous system with mixed impurities was found. The results showed that the mass-transfer coefficients of the surface aeration zone are more sensitive to the impurity concentration than those of the gas bubble zone.Ítem Modelación de la transferencia de oxágeno en sistemas de aereación mediante un modelo de dos zonas simplificado(2009-01-13 00:00:00) Durán Herrera, Esteban; Rojas Meza, GerardoA new two zone simplified oxygen mass-transfer model with an analytical solution was proposed and used to analyze the unsteady state reaeration data of diffused reaeration systems in order to find the volumetric mass-transfer coefficients. Series of unsteady state reaeration tests in a 1000 l tank was performed to validate the model. The effect of the air flow rate and the temperature upon the mass-transfer coefficients was studied and empirical equations were used to successfully correlate them. The air flow rate was varied from 0,50 to 1,33 - 10-3 normal m3/s and the water temperature was varied from 293,25 to 303,25 K. It was found that the new model describes mathematically the aeration process very well and gives a better physical understanding of it.Ítem La lógica difusa en ingeniería: principios, aplicaciones y futuro(2009-01-13 00:00:00) Guzmán, D.; Castaño, V. M.Fuzzy logic is a mathematical tool that mimics the way humans manage and process information. It is a method of great simplicity for processing of information, decision making and process control. This article discusses the basic concepts and applications, and analyses pros and cons of this methodology.