We study the structure of two contrasting alpine forest.pasture ecotones located in the Central Pyrenees (sites Ordesa and Tessó). We define ecotone structure as the spatial distribution of trees of different size classes and growth-forms, and the relationship between these aspects and the spatial distribution of understory vegetation and substrate. The studied ecotones are dominated by Pinus uncinata and have been little affected by recent anthropogenic disturbances (logging, grazing). One rectangular plot (30 x 140 m2) was located within each site encompassing treeline and timberline with its longest side parallel to the slope. The distribution of size and growth-form classes at Ordesa followed a clear sequence of increasing size downslope, from shrubby krummholz individuals to bigger arborescent trees. At Ordesa, regeneration was concentrated near the krummholz area and over rocky substrates. At Tessó, regeneration was abundant above the treeline, where the cover of the dominant understory shrub (Rhododendron ferrugineum) decreased. Detrended canonical correspondence analysis of tree and plant cover data, with respect to spatial location in the ecotone and substrate cover, demonstrated that elevation was an important factor controlling the distribution of trees and understory plants in both ecotones. Finally, k-means clustering with spatial constraint revealed abrupt spatial clusters along the slope at Ordesa. However, the ecotone at site Tessó was composed of elongated downslope spatial clusters suggesting greater spatial heterogeneity and subtle gradual changes due to other factors in addition to the altitudinal gradient (snow avalanches). These contrasting structures correspond well with the ecotone (sharp boundary, Ordesa) and ecocline (gradual transition, Tessó) concepts. This suggests the dominant role of different local environmental factors: wind at site Ordesa and avalanches at Tessó. Positive feedbacks, like facilitation among P. uncinata individuals (nurse effect), may maintain and intensify the sharpness of the ecotone at Ordesa.
A sufficient condition for the strict insertion of a continuous function between two comparable upper and lower semicontinuous
functions on a normal space is given. Among immediate corollaries are the classical insertion theorems of Michael and Dowker.
Our insertion lemma also provides purely topological proofs of some standard results on closed subsets of normal spaces which
normally depend upon uniform convergence of series of continuous functions. We also establish a Tietze-type extension theorem
characterizing closed Gδ-sets in a normal space.
Authors:J. Gutierrez Garcia, I. Mardones-Pérez and M. De Prada Vicente
Monotone normality is usually defined in the class of T1 spaces. In this paper new characterizations of monotone normality, free of T1 axiom, are provided and it is shown that in this context it is not a hereditary property. Also, a Tietze-type extension theorem
for lattice-valued functions for this class of spaces is given.
Authors:Y. Ladino-Ospina, L. Giraldo-Gutierréz and J. C. Moreno-Piraján
Summary This work shows the result of the study of the Pb(II) and Cr(VI) ions adsorption by means of a Calvet type calorimeter of heat conduction that can operate at 150şC. The calorimeter was electrically calibrated to establish its sensitivity and reproducibility, obtaining K=12.95±0.05 W V-1 and chemically it was examined with tris-(hydroxymethyl)-aminomethane (THAM)-HCl system, obtaining ΔH= -30.91±0.03 kJ mol-1. The activated carbon sample obtained from coffee husk and the calorimetric results obtained were related to other techniques used to perform this type of studies.
Authors:S. Otin, J. M. Lozano and C. Gutierrez Losa
Excess molar enthalpies,HE, at atmospheric pressure and 303.15 K are reported for binary mixtures of 1-chlorohexane with diethyl oxalate, diethyl malonate, diethyl succinate, diethyl glutarate, diethyl adipate, diethyl pimelate and diethyl sebacate. These experimental results, together with those obtained previously on the excess enthalpies of aliphatic diester+n-hexane mixtures, are interpreted in terms of molecular surface interactions between aliphatic, chlorinated and carboxylate groups. Comparison of the enthalpy interchange parameters reveals a decrease of the intermolecular interactions with decreasing intramolecular COO-COO distance in the diester molecule.
Authors:C. González, J. I Gutiérrez, J. R. González-Velasco, A. Cid, A. Arranz and J. F. Arranz
Thermal decomposition of various synthetic manganese oxides (MnO, Mn3O4, Mn2O3, MnOOH) and a natural manganese dioxide (MnO2) from Gabon was studied with the help of termogravimetry in inert, oxidizing and reducing atmospheres. The compounds were characterized by XRD and electrochemical activity was tested by cyclic voltammetry using a carbon paste electrode. The natural manganese dioxide showed the best oxidizing and reducing capacity, confirmed by the lower temperatures of the transitions, the extent of the reactions and electrochemical performance in cyclic voltammograms.
Authors:J. I. Gutiérrez-Ortiz, B. de Rivas, R. López-Fonseca and J. R. González-Velasco
Summary The catalytic properties of ceria-zirconia mixed oxides have been characterized using temperature-programmed techniques such as temperature-programmed desorption of ammonia and water, and temperature-programmed reduction with hydrogen. The acidity and hydrophobicity of these materials increased with zirconia content while the reducibility was maximum for Ce0.5Zr0.5O2 sample.
Authors:J. Gutiérrez-Ortiz, Beatriz de Rivas, R. López-Fonseca and J. González-Velasco
The catalytic behaviour of ceria, zirconia
and ceria–zirconia mixed oxides in the temperature-programmed degradation
of toluene and n-hexane was analysed by
means of evolved gas analysis (mass spectrometry). Pure cerium oxide resulted
the most active catalyst in the oxidation of both compounds. This fact revealed
the crucial role of the surface oxygen species in the decomposition of this
type of hydrocarbons. The low affinity of CeO2 for
H2O and CO2, the major oxidation
products, may be also responsible for the observed highly active catalytic