Volumen 27, Números 1 y 2

URI permanente para esta colección

Examinar

Envíos recientes

Mostrando 1 - 8 de 8
  • Ítem
    SYNTHESIS, CHARACTERIZATION AND REDOX BEHAVIOUR OF MIXED LIGAND COPPER(II) SACCHARINATE COMPLEXES
    (2012-11-26 11:29:40) Valle Bourrouet, Grettel; Falvello, Larry R.; Gómez, Julio
    Three mixed-­ligand complexes of Cu(II) with saccharin (sac), pyrazole, (Hpz), imidazole, (Himid) were synthesized and characterized on the basis of elemental analysis, FT-­IR spectroscopy, magnetic susceptibility, EPR spectra, and X-­ray diffraction. The reaction of [Cu(sac)2(H2O)4] ⋅ 2H2O with pyrazol in methanol resulted in a mononuclear pentacoordinated compound [Cu(sac)2(Hpz)3] (1) and a trinuclear N,N.bridged compound [Cu3(sac)2(Hpz)3(pz)3)2(OH)] (2), forming a nine membered [-Cu-­N-­N-­]3 ring and μμ3-­‐‐OH bridge; each Cu(II) ion is tetracoordinated, with weak axial interactions from saccharinate ions.The Himidazole compound [Cu2(sac)4(Himid)4] (3) has a dinuclear structure with two saccharinate ions as bridge; each Cu(II) ions has a penta-­coordination sphere, two N-­coordinated and one O-­coordinated saccharinate ions on the equatorial plane, and two imidazole molecules in the axial positions.
  • Ítem
    VISCOUS-­FLOW MECHANISM OF #6 FUEL OIL – PALM OLEIN MIXTURES
    (2012-11-26 11:37:12) Lezcano-­González, Ritzela E.; Mata Segreda, Julio Francisco
    The viscosities of mixtures of #6 fuel oil and palm olein at 60 °C do not obey Kendall-­‐‐Monroe equation. Molecular considerations predict deviation from ideal-­‐‐mixture behaviour for this kind of “binary” material. It is proposed that the observed positive deviations are mainly due to looser molecular packing in the mixtures than in the “pure” components. Thus, mixing results in a lesser degree of hindrance for the viscous-­‐‐flow process. The empirical fit of fluidity as a function of olein mass fraction (x) is ln [Φmix/Φolein] = (2,72±0,05) + (5,6±0,3) x -­‐‐ (2,9±0,3) x2; r2 = 0,992, p < 0,01.
  • Ítem
    SOLUCIÓN DE UNA ECUACIÓN DIFERENCIAL PARCIAL DE DIFUSIÓN
    (2012-11-26 00:00:00) Céspedes Álvarez, Julio
    Utilizing the Laplace transform, an algorithm is shown that solves the partial differential equation, product from the application of the Fick ́s second law of diffusion. The solution of the equation is simple and does not require potential or Fourier series, among other arguments, and it can be easily used for diffusion processes through cellular membranes.
  • Ítem
    THE LEGACY OF VAN DER WAALS
    (2012-11-26 10:49:40) Ogilvie, John F.
    The physical implications of the form and nature of the van der Waals equation of state are explained. The relation of this equation to so-­‐‐called van der Waals forces and radii is discussed. The conclusion is drawn that the van der Waals equation of state is practically worthless and its use should be abandoned. *** Resumen Se explican las implicaciones físicas de la forma y la naturaleza de la ecuación de estado de van der Waals. Además, se discute la relación entre esta ecuación y las llamadas fuerzas y radios van der Waals. Se llega a la conclusión de que la ecuación de estado de van der Waals no es útil y que no debería utilizarse.
  • Ítem
    Evaluation of three chroroplastic markers for barcoding and for phylogenetic reconstruction purposes in native plants of Costa Rica
    (2012-11-26 10:33:45) Vindas ­Rodríguez, Milton; Rojas Jiménez, Keilor Osvaldo; Tamayo Castillo, Giselle
    DNA barcoding has been proposed as a practical and standardized tool for species identification. However, the determination of the appropriate marker DNA regions is still a major challenge. In this study, we extracted DNA from 27 plant species belonging to 27 different families native of Costa Rica, amplified and sequenced the plastid genes matK and rpoC1 and the intergenic spacer trnH-­psbA. Bioinformatic analyses were performed with the aim of determining the utility of these markers as possible barcodes to discriminate among species and for phylogenetic reconstruction. From the markers selected, the trnH-­psbA spacer was the most variable in terms of genetic distance and the most promising region for barcoding. However, it presented a limited use for constructing phylogenies due to the complexity of its alignment. The locus matK was less variable but was also useful for species discrimination and for phylogenetic tree generation. The rpoC1 region was highly conserved and suitable for phylogenetic studies, but presented a limited utility as a barcode. The marker combination matK and rpoC1 provided the best resolution for establishing valid phylogenetic relationships among the analyzed plant families. In conclusion, more than one marker should be used for plant barcoding purposes, to provide complementary and variable information for the interespecific species discrimination.
  • Ítem
    IMPACTO DEL CRECIMIENTO ECONÓMICO INDUSTRIAL SOBRE LOS RECURSOS ENERGÉTICO E HÍDRICO EN COSTA RICA
    (2012-11-26 00:00:00) Díaz Sánchez, Luisa M.; Morales ­Carvajal, Pedro A.
    An empirical relationship between water consumption, energy consumption and industrial GDP was established, for the case of Costa Rica. This relationship may be useful in predicting the pressure exerted on natural resources by the effects derived from growth of GDP. These predictions will make possible to establish public and sectorial policies related to water and energy management, and assesses the sector in order to achieve the national goal of carbon neutrality by 2021. Additionally, indicators of energy intensity (7,1 ± 0,5) TJ / million dollars of GDPi), water intensity ((1,0 ± 0,4) 10 5 m3 / million dollars of GDPi) and carbon intensity (217 CO2 kg equivalent / million dollars of GNP i) for the industrial sector of Costa Rica were established and could be used as reference for environmental assessment of the industrial sector in the future. *** Palabras clave: indicador de intensidad energética; indicador de intensidad hídrica; intensidad de carbono; elasticidad hídrica y energética
  • Ítem
    COMPARACIÓN DE METODOLOGÍAS DE EXTRACCIÓN PARA LIMONENO Y CARVONA EN Lippia alba USANDO CROMATOGRAFÍA DE GASES.
    (2012-11-26 00:00:00) Medina López, Ligia A.; Araya Barrantes, Juan José; Tamayo Castillo, Giselle; Romero Chacón, Rosaura María
    Abstract Different plants drying procedures, hydrodistillation and solvent extraction by sonication were evaluated for the essential oil extraction of Lippia alba. Quantitative analysis of the markers limonene and carvone was performed in the extracts by gas chromatograph with flame ionization detection (GC-­FID). Experimental precision, accuracy, specificity, linearity, limits of detection and quantitation were addressed. Lyophilization as a drying procedure and solvent extraction by sonication using ethyl acetate showed the best results regarding the highest concentration for marker compounds.
  • Ítem
    Graph Theory and simple Hueckel Theory applied to benzene
    (2012-11-26 09:53:47) Lamoureux Lamontagne, Guy; Ogilvie, John F.
    We compare the results of application of graph theory and of simple Hueckel theory in its traditional form to benzene, as an instance of a conjugated molecular system. The identity of the results of solution of eigenvalues of the vertex adjacency matrix and characteristic values of the Hueckel determinant prove the isomorphism of these two formalisms. Because of the gross deficiencies of the Hueckel theory, we advocate its elimination from the teaching of chemistry in favour of graph theory that has many applications to molecular topology.