The thermo-oxidative stability of Jojoba wax (Simmondsia chinensis) was studied by differential scanning calorimetry in a dynamic oxygen atmosphere. The thermo-oxidation activation energy (Ea) was calculated by determining the maximum reaction temperature (Tm) at different heating rates (Hr) and using mathematical models previously proposed for dynamic systems. The value obtained was 21.84 Kcal/mol. The oxidation enthalpiesδHox were also calculated and a lineal relationship was found with the square root of the heating rate and the initial temperature of thermo-oxidation
The thermal behaviour of a series of oxovanadium(IV) complexes of halogenated derivatives of 8-hydroxyquinoline was investigated by means of TG and DTA measurements in oxygen atmosphere. V2O5 was the final pyrolysis residue in all cases.
Authors:V. González-González, R. O. Valero-Coss, and E. Campos-López
The thermal behaviour of Jojoba (Simmondsia chinensis) liquid wax was studied by differential scanning calorimetry (DSC), varying the annealing conditions. The fusion enthalpy (ΔHf) of the unannealed material was 27.1 cal/g; the relationship between heat capacity (Cp) and temperature could be expressed by the following equation:Cp=9.51×10−4 T+0.129. It was found that Jojoba wax presents four endothermic transitions (α, β, γ andδ) including fusionα, estimable at low heating rates (1 K/min); the activation energies (Ea) for transitionsα andγ were 51.18 and 64.82 Kcal/mole respectively; and it was observed that the transition temperaturesα andγ maintained a lineal relationship with the square root of the heating rate (Hr).
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:J. Griffith, R. Rosenberg, O. Díaz-Rizo, and E. González
Thermal and epithermal non-destructive activation analyses have been performed on samples of final molasses from 14 different sugar factories, covering the most important regions in Cuba. From the first measurement after irradiation at the Triga Mark reactor (VTT), the concentration of more than 15 elements is reported. The almost constant elemental composition shows that they can be used equally for different purposes as animal foodstuff and for the manufacture of biotechnological products. This work is part of a research project developed in order to establish a complete characterization of Cuban sugar molasses.
Authors:E. Quintero-Ponce, H. López-González, and L. Cervantes-Naranjo
The aim of this work was to determine the contamination of I-131 in milk samples by low background -spectrometry and low background -counting techniques in the vicinity of the Nuclear Center in Salazar, Mexico. The low background -spectrometry was done directly. The determination by low background -counting consisted of a radiochemical separation of I-131 by ion exchange from the milk samples followed by measurement in a low background -counting system. The results indicated that there was no contamination of I-131 in the samples.
Authors:H. López-González, E. Quintero-Ponce, and L. Cervantes-Naranjo
The conditions to measure the gross alpha and gross beta radioactivity in water samples from the surrounding of the Nuclear
Center (Instituto Nacional Investigaciones Nucleares, (ININ), and Collection, Treatment and Storage Center for Low Level Radioactive
Waste (Maquixco) in the State of Mexico were established. The samples were collected from 1987 to 1996. The gross alpha and
gross beta radioactivity in the samples were determined by a gas-flow proportional counter. The results indicated that the
gross alpha and gross beta radioactive contamination in water samples were below the maximum contaminant level (MCL).
Authors:A. Borhidi, I. García-González, and E. Martinez Salas
Three new taxa of the genus
L. (Rubiaceae, Gardenieae) are described, two of them from the dry areas less visited and collected of the State Oaxaca,
, related to
Wiggins. The third taxon is a subspecies of the polymorphic species
from the semi-desert area of Cuatrociénagas (Coahuila).
Authors:N. Garcia-Gonzalez, E. Ordóñez-Regil, E. Simoni, and C. Barrera-Díaz
Hydration of zirconium diphosphate (ZrP2O7) conduced to formation of active sites in solid/liquid interface. In ZrP2O7/NaClO4 0.5 M suspensions, active sites and their acidity constants are quite determined but the presence of some impurities is now
studied. This work was conducted to determine the surface properties changes produced by oxalic and citric acid during the
hydration process. Moreover the presence of organic acids with ZrP2O7 modified reveals an increase in uranium sorption constants. The zirconium diphosphate has been characterized using X-ray
powder diffraction (XRD), Scanning electron microscopy (SEM) and Particle induced X-ray emission and Neutron (PIXE). Furthermore,
the specific surface area, measured by the BET method, was 3.5 m2/g. The pH corresponding to the isoelectric point, determined by Zeta Potential measurements and mass titration was 3.6. The
sites density calculated using titration curves was around of 5.37 s/nm2 for NaClO4 0.5 M, 13.71 s/nm2 for NaClO4 0.5 M/citric acid 0.1 M and 7.33 s/nm2 NaClO4 0.5 M/oxalic acid 0.1 M. The surface acidity constants and species distribution in surface were calculated by means of simulation
of the titration curves with the FITEQL code (constant capacitance model), for ZrO and PO amphoteric sites of ZrP2O7. The uranyl sorption edge was determined for NaClO4 0.5 M. It spreads between pH 3 and 4.5 for complete sorption according to the previously published results. In the ZrP2O7–citrate modified surface, the uranyl sorption edge begin at pH 2 and was almost complete at pH 3.2 while ZrP2O7–oxalate modified surface edge started at 50% of sorption at pH of 1.5 and was complete at pH 3.