Authors:J. M. Criado, F. Gonzalez, and M. Gonzalez
Kinetic analysis has been performed on TG and DTG diagrams of the forward reaction MnCO3⇌ MnO + CO2, recorded at different pressures of CO2 ranging form 2.6. 10−4 Pa to 26.6 kPa. The results obtained show that this reaction follows a first-order kinetic law, independently of the CO2 pressure used in carrying out the experiments. On the other hand, the activation energy increases on increase of the CO2 pressure, from 117 kJ/mol up to an asymptotic value of 292 kJ/mol at about 26.6 Pa. This finding cannot be explained by considering the influence of the reverse reaction of formation of MnCO3, for under the described experimental conditions the ratio
to zero. A mechanism that takes into account the adsorption of CO2 on the phase boundary has been proposed in order to interpret the results.
Authors:C. González-Gómez, J. López-González, and M-A. Ferro-García
In the present work a study was made for determining colour intensities using as luminous non-monochromatic source the Cherenkov
emission produced in the walls of a glass capillary which acts as luminous source itself inside of a coloured solution to
be evaluated. The reproducibility of this method has been compared with the spectrophotometric assay; the relative errors
of both analytical methods have been calculated for different concentrations of congo red solution in the range of minimal
error, according to Ringbom's criterion. The sensitivity of this analytical method has been studied for the two β-emitters
Authors:M. González-Martín, B. Jańczuk, and J. Bruque
Calorimetric measurements were made of the heat of immersion in water of cassiterite that was either untreated or treated
with 60% HNO3. The heats of immersion of cassiterite and fluorite were also calculated theoretically from the surface Gibbs energy components,
and compared with the heat of immersion measured for cassiterite and that taken from the literature for fluorite. The results
of the measurements and calculation revealed that the heat of immersion depends on the degree of hydration of the surface
of cassiterite and fluorite. It was also found that it is possible to predict the heats of immersion in water of cassiterite
and fluorite from the Lifshitz-van der Waals and acid-base components of the surface Gibbs energy.
Four new derivatives of uranium with propionic acid, ammonium and various divalent cations have been synthesized, whose general formula corresponds to NH4M[UO2(C2H5COO)3]3nH2O, (M=Mn++, Co++, Ni++ and Zn++). These compounds have been studied by X-ray diffraction, differential thermal and thermogravimetric analysis, so as to identify the different solid phases isolated during heat treatment. The existence of a new double oxide of uranium and cobalt with fluorite type structure has also been shown.
Authors:J.M. González, E. Friero, L. Selfa, S. Froilán, and N. Jouve
This work reports a rapid procedure of comparing root development among different genotypes of Brachypodium spp., using three plant growth supports: gel chamber, ‘Termita’ chamber and Whatman paper. Eight variables of the root system architecture (RSA) (number of seminal roots, number of lateral roots, total length of the roots, length of the primary root, mean diameter of the roots, mean diameter of the primary root, total surface area and total volume of the roots) were studied in seedling of four genotypes each of Brachypodium distachyon, B. stacei and B. hybridum. Correlations between pairs of growth supports in terms of the eight variables examined were highly significant. In all three supports, B. stacei showed the greatest root system development while B. distachyon showed the least; B. hybridum, an allotetraploid species derived from hybridization between B. distachyon and B. stacei, showed intermediate development. ANOVA and LSD tests showed that significant differences exist between the supports, species and genotypes with respect to all the variables analysed. A cluster analysis was conducted to determine if the RSA traits could be used to differentiate the species and genotypes of Brachypodium. This analysis allowed differentiated between the three species and twelve genotypes of Brachypodium spp., although a certain overlap between species was observed. The Whatman paper support was the easiest to use, and is recommended for the characterization of large collections of genotypes.
Authors:A. Sanchez-Ocampo, H. Lopez-Gonzalez, and M. Jimenez-Reyes
The behavior of uranyl ion and tervalent Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu in the solvent extraction system: M–HCl–H2O–TBP has been studied together with chromatographic elution of the first nine of these rare earth elements using DOWEX 50Wx8 resin. >99.5% of the rare earth elements, with a single exception, remained in the aqueous phase of the solvent extraction system where the initial concentration of hydrochloric acid was between 4 and 6 M. Under these conditions uranyl ions were readily extracted by TBP. The rare earth elements were quantitatively eluted from the chromatographic column using 6M hydrochloric acid solution and the uranyl ions in a 0.75M sulfuric acid solution.
Authors:L. Bernal-gonzález, M. Calderón-Moreno, and J. Prado-Bassas
We characterize various kinds of cyclicity of sequences of coefficient multipliers, which are operators defined on spaces
of holomorphic functions. In the case of a single coefficient multiplier we characterize its cyclicity, which contrasts with
the fact that such operators are never supercyclic. Moreover, it is proved that for each cyclic function there is a dense
part of the linear span of its orbit all of whose vectors are cyclic.
Authors:M. Monge, R. Pareja, R. González, and Y. Chen
Low-temperature positron lifetime and Doppler broadening measurements were made in MgO crystals containing D– or H– ions in order to investigate the temperature dependence of the positron trapping by D– and H– ions and elucidate the possible formation of PsD (PsH) states. Positrons are trapped at D– and H– ions once the oxygen vacancies, which are more effective positron traps, are eliminated by annealing the crystals at high temperatures in a reducing atmosphere. From the temperature dependence of the annihilation parameters the positron trapping coefficients for D– and H– centers were shown to increase with temperature between 100–300 K. The lifetime of the PsD (PsH) state is (650±30) ps and temperature independent. The dissociation rate of the PsD (PsH) state into D (H) and Ps is also temperature independent. No isotopic effect was observed.