Search results for "STeMA"
showing 9 items of 10049 documents
An experimental model for mimicking biological systems: the Belousov-Zhabotinsky reaction in Lipid membranes
2006
Un compendio de Investigaciones en economia de la educacion
2012
Este artículo presenta los principales temas abordados por los economistas de la educación a lo largo de los últimos cincuenta años. Después de recordar brevemente los antecedentes de la disciplina, se describen las aportaciones teóricas y empíricas realizadas a raíz del desarrollo de la teoría del capital humano, que es el fundamento de la economía de la educación. Más allá de los trabajos que tratan de los efectos externos de la educación, el artículo repasa también las principales aportaciones efectuadas en el análisis de los sistemas de enseñanza y en la evaluación de las políticas educativas.
Chemical composition and biological activity of the essential oil of Ballota hispanica (L.) Benth. growing wild in Sicily
2015
Ballota L. comprises several relevant species largely used for their excellent therapeutic properties. Ballota hispanica (L.) Benth. is widely used in herbal medicine, and it is sold in herbalist shops for its sedative and antispasmodic properties. Considering its traditional medicinal use and the lack of scientific studies on the volatile components of this species as well as on its biological activities, in this study the chemical composition of the essential oil from aerial parts of B. hispanica, collected in Sicily, was evaluated by gas chromatography and gas chromatographyâmass spectrometry. α-Elemol was the most abundant component of the oil (10.9%), followed by α-ylangene (8.5%),…
Malus Mill. drawings
1980
Profesora Voldemāra Langenfelda (1923–2007) sagatavots mācību materiāls par ābeļu ģinti (Mallus Mill.). Zīmējusi viņa sieva Astrīda Langenfelde. Komplektā trūkst 1. kartītes. Materiāls glabājās Latvijas Universitātes Muzeja Botānikas un mikoloģijas kolekcijā.
Late Jurassic (Kimmeridgian–Tithonian) stable isotopes (δ18O, δ13C) and Mg/Ca ratios: New palaeoclimate data from Helmsdale, northeast Scotland
2010
Abstract The data presented here provide the first detailed stable isotope ( δ 18 O, δ 13 C) and geochemical (Mg/Ca) investigation of Kimmeridgian–Tithonian belemnites from the Helmsdale Coast, Scotland, UK. Oxygen and carbon stable isotope values from well preserved specimens range from − 2.8 to + 0.3‰ and from − 2.3 to + 2.8‰ respectively. The oxygen isotope data are consistent with palaeotemperatures of up to 24 °C in the Early Kimmeridgian cymodoce Zone and down to 11 °C in the Mid Tithonian rotunda–fittoni Zones. These estimates are strongly supported by the Mg/Ca data, which also indicate a cooling episode (and very similar palaeotemperatures, 11–22 °C) at this time. The cooling event…
A 2600-year record of past polycyclic aromatic hydrocarbons (PAHs) deposition at Holzmaar (Eifel, Germany)
2014
Polycyclic aromatic hydrocarbons (PAHs) are a proxy for climate- and human-related historical fire activity which has rarely been used beyond 1800 AD. We explored the concentration and composition patterns of PAHs together with other proxies (charcoal, C, N, S, δ13C, δ15N, and δ34S) in a sediment core of Holzmaar as indicators of variations in climate and anthropogenic activity over the past 2600 years. The concentrations of pyrogenic PAHs remained low (< 500 ng g− 1) from the pre-Roman Iron Age (600 BC) until the first significant increases to ca. 1000–1800 ng g− 1 between 1700 and 1750 AD related to regional iron production. The highest increases in pyrogenic PAH concentrations occurred w…
Unraveling environmental histories from skeletal diaries — Advances in sclerochronology
2013
High-resolution proxy archives from aquatic settings are essential to better understand processes and mechanisms of global change. During the last decade, it has become increasingly evident that calcified tissues of bivalve mollusks and cold-water corals, in particular, can significantly increase our knowledge of seasonal to multi-decadal paleoclimate and paleoenvironmental variability in the extratropical oceans and coastal marine settings. Daily, tidal, fortnightly and annual growth patterns of periodically formed skeletal hard parts provide a means to place the proxy record in a precise temporal context. Their extreme longevity coupled with the running similarity between growth increment…
Variation in Sr uptake in the shell of the freshwater gastropod Bithynia tentaculata from Lake Arreo (northern Spain) and culture experiments
2010
The Sr uptake features in Bithynia tentaculata aragonite shells from monthly collections in Lake Arreo (northern Spain) over a two-year period are compared with those from the same species grown in culture experiments with similar waters under controlled temperature. The shell aragonite of B. tentaculata from Lake Arreo formed in isotopic equilibrium with the lake water. A comparison of the stable oxygen isotope values (δ18O) from the shells and waters allowed the selection of suitable shells for Sr uptake studies. The Sr/Ca molar ratio in B. tentaculata shells (Sr/Cashell) from the lake and from the culture experiments positively correlate with some chemical parameters like conductivity an…