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The most important stratified screes of the Iberian Range are found in Sierra de Albarracín. These slope deposits have been traditionally considered, without absolute datings, as having been formed during various Pleistocene cold phases. The aim of this paper is to establish the sedimentological, morphological, chronological, and paleoenvironmental characteristics of these deposits through the study of four profiles recorded in the Calomarde canyon (El Rollo, El Molino, and Royuela) and Toril. The most representative profile is that of El Rollo as it is formed by basal tufa and stratified scree layers separated by paleosoils. Radiocarbon datings obtained from paleosoil samples show that the sequence ranges between the early and middle Holocene. The profiles from El Molino and Royuela, as well as the upper levels of Toril, complete the sequence showing deposits from upper Holocene (Bronze Age and ‘Little Ice Age’). These data show the oscillations during the Holocene between colder phases, represented by the stratified screes, and warmer–wetter phases with soil development and local tufa deposits. This geomorphological and pedological response to the Holocene climatic variability shows its clearest records in the canyons. However, there are almost no Pleistocene accumulations – with the exception of that of Toril (minimum age of <43.5 ka BP). The possibility of relating this succession of Holocene environmental changes to known regional and global climatic stages converts these accumulations into the most important Holocene paleoenvironmental record from the Iberian Ranges and the most complete sequence of Holocene stratified screes from the Mediterranean area. [ABSTRACT FROM AUTHOR]

The tsscds method, recently developed in our group, discovers chemical reaction mechanisms with minimal human intervention. It employs accelerated molecular dynamics, spectral graph theory, statistical rate theory and stochastic simulations to uncover chemical reaction paths and to solve the kinetics at the experimental conditions. In the present review, its application to solve mechanistic/kinetics problems in different research areas will be presented. Examples will be given of reactions involved in photodissociation dynamics, mass spectrometry, combustion chemistry and organometallic catalysis. Some planned improvements will also be described. [ABSTRACT FROM AUTHOR]

The existence of different growth forms (tall and short) in various species of the genus Spartina has, on occasion, been attributed to differences in the availability of nutrients. In the present work, macronutrient (N, P, K, Mg, Ca, S) and micronutrient (Fe, Mn, Zn, Cu) contents of the soils and tissues (leaves and stems) of three populations of S. maritima from the NW Iberian Peninsula were studied. The results obtained showed that although there were differences in the physicochemical properties of the soils and in the concentration of nutrients in soils and plants at the different locations, these do not explain the different growth forms of S. maritima. Since other authors have found that the growth forms displayed by different species of the same genus are in part due to genotypic differences, ecotypic differentiation, along with other environmental factors that were not assessed in this research, may control the differences in height and biomass of S. maritima. However, more detailed studies of this species are required in order to assess the importance of environmental (e.g., fertilization experiments) and genetic factors (e.g., RAPD analysis) that influence the growth form of natural populations of Spartina maritima. [ABSTRACT FROM AUTHOR]

A number of species of Spartina show two clearly distinguishable growth forms, tall and short. Several authors have suggested that the differences in height reflect differences in soil properties. In the present study, we determined mean shoot height, shoot density, and standing crop in three populations of Spartina maritima in northwest Spain. Soil properties were also determined at each site. Shoot density was significantly correlated with redox potential and sulfide concentration, but height was not significantly correllated with any of the soil properties considered. This latter result suggests that the observed variability in height among the study populations may be of genetic origin. [ABSTRACT FROM AUTHOR]