Identificación de patrones geomorfológicos a través de la interpretación de las razones entre bandas TM

7 páginas, 2 figuras, 18 referencias. Este trabajo se encuentra dentro del capítulo: Estratigrafía, Sedimentología y Geomorfología del Cuaternario. Desde el año 1972, AEQUA organiza Reuniones Nacionales de Cuaternario cada cuatro años. Se tiene una colaboración activa con el Grupo de Trabajo Portugués del Cuaternario (GTPEQ), con el que celebra cuatrianualmente congresos conjuntos denominados Reuniones del Cuaternario Ibérico. La referenciada es la II Reunión del Cuaternario Ibérico, Madrid, 25-29 septiembre, 1989. El ISBN de la obra completa: 84-7840-155-5.[EN]: A test area of 512 x 512 pixels, in the Doñana National Park, has been studied throug a Thematic Mapper image taken in February 1986. Three bands have been selected (TM3, TM4 and TM7) as well as two of their ratios (TM7/TM4 and TM4/TM3) containing enough information for the environmental study proposed. Different geomorphological and soil patterns have been identified, as well as their associated vegetation. Finally, these results have been compared with data Observed "in situ" to test their reliability.[ES]: Se realiza el estudio de un área test de 512 x 512 pixels, situada dentro del Parque Nacional de Doñana, a partir de una imagen tomada por el Thematic Mapper en febrero de 1986. Se seleccionan las bandas TM3, TM4 Y TM7, con las que se efectúan las razones TH1/TM4 y TM4/TM3 para la caracterizaci6n del medio físico. A partir de dichas bandas y combinaciones se identifican los principales patrones geomorfológicos, características edáficas y asociaciones vegetales de la zona. Estos resultados son posteriormente comparados y comprobados con observaciones sobre el terreno.Peer reviewe

Large quantum nonlinear dynamic susceptibility of single-molecule magnets

The nonlinear dynamical response of Mn$_{12}$ single-molecule magnets is experimentally found to be very large, quite insensitive to the spin-lattice coupling constant, and displaying peaks reversed with respect to classical superparamagnets. It is shown that these features are caused by the strong field dependence of the relaxation rate due to the detuning of energy levels between which tunneling takes place. The nonlinear susceptibility technique, previously overlooked, is thus proposed as a privileged probe to ascertain the occurrence of quantum effects in mesoscopic magnetic systems.Comment: 4 pages, 4 figure

Cambios edáficos en las Marismas de Doñana y su relación con la invasión de Azolla filiculoide

2 páginas, 7 referencias. En el Capítulo: Degradación de suelos y desertificación. Simposio celebrado en Fuerteventura, 16-20, septiembre, 2007. Los editores son del Departamento de Edafología y Geología, Universidad de La Laguna.La Marisma de de Doñana es una extensa planicie dominada por suelos arcillosos, calcáreos y salinos (Clemente et al., 1998) que se inunda estacionalmente -por efecto de la lluvia y de algunos arroyos- y acoge a una de las poblaciones de aves acuáticas más importantes de Europa (Clemente et al. 2004). En 2001 uno de los autores (J.L. Espinar) documentó por primera vez la presencia del helecho de origen americano Azolla filliculoides, una especie invasora con capacidad para fijar el N atmosférico, que acabó extendiéndose por el humedal en los años siguientes (Cobo y Bañuls, 2005) En este trabajo se analizan los cambios ambientales ocurridos en la marisma de Doñana con anterioridad a la invasión, en relación con lo acaecido en anteriores episodios de invasión por Azolla de otras áreas naturales.Peer reviewe

Changes in organic matter, nitrogen, phosphorus and cations in soil as a result of fire and water erosion in a Mediterranean landscape

10 páginas, 7 figuras, 9 tablas.Fire affects large parts of the dry Mediterranean shrubland, resulting in erosion and losses of plant nutrients. We have attempted to measure these effects experimentally on a calcareous hillside representative of such shrubland. Experimental fires were made on plots (4 m x 20 m) in which the fuel was controlled to obtain two different fire intensities giving means of soil surface temperature of 439 degrees C and 232 degrees C with temperatures exceeding 100 degrees C lasting for 36 min and 17 min. The immediate and subsequent changes induced by fire on the soil's organic matter content and other soil chemical properties were evaluated, together with the impact of water erosion. Seven erosive rain events, which occurred after the experimental fires (from August 1995 to December 1996), were selected, and on them runoff and sediment produced from each plot were measured. The sediments collected were weighed and analysed. Taking into account the variations induced by fire on the soil properties and their losses by water erosion, estimates of the net inputs and outputs of the soil system were made. Results show that the greatest losses of both soil and nutrients took place in the 4 months immediately after the fire. Plots affected by the most intense fire showed greater losses of soil (4077 kg ha(-1)) than those with moderate fire intensity (3280 kg ha(-1)). The unburned plots produced the least sediment (72.8 kg ha(-1)). Organic matter and nutrient losses by water erosion were related to the degree of fire intensity. However, the largest losses of N-NH4+ and N-NO3- by water erosion corresponded to the moderate fire (8.1 and 7.5 mg N m(-2), respectively).Peer reviewe

Helophyte germination in a Mediterranean salt marsh: gut-passage by ducks changes seed response to salinity

8 pages, 3 figures, 3 tables.Questions: In seeds which are regularly consumed by waterbirds in the field, how does gut–passage modify their response to salinity gradients? Locations: Doñana National Park salt marsh, south-west of Spain. Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non-ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0-32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed. Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut passage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (£2 dS/m) but decreased it at high salinities (≥4 dS/m). Conclusion: Gut-passage by ducks significantly changes seed response to salinity. The outcome of plant-animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results.Financial support from the Spanish Ministry of Environment (MMA, project 05/99) and the Junta de Andalucía (research group #4086) has enabled us to carry out the present work.Peer reviewe

Software engineering standards and guides for very small entities: implementation in two start-ups

Very small entities, enterprises, organizations, projects or departments with up to 25 people, are very important to the worldwide economy. However it has ben established that such entities often do not utilize existing standards and frameworks. To address the needs of Very Small Entities (VSEs), a set of international standards and guides known as ISO/IEC 29110 has been developed. In this paper we present the results of early trials of this standard in two IT start-ups VSEs. A Peruvian VSE was recently audited and issued an ISO/IEC 29110 certificate of conformity

Demo 25. Movimiento de electrones en campos E y B: el ciclotrón

Objetivo:1.- Observar el proceso de generación de cargas libres. 2.- Observar el movimiento de cargas en campos eléctricos y magnéticos. Estudio experimental del movimiento de electrones en un campo magnético uniforme. Demostración de la Fuerza de Lorentz sobre electrones mediante la observación y medida de la trayectoria circular generada en un campo magnético uniforme, habiendo acelerado previamente los electrones con un campo eléctrico. Medida de la relación carga/masa de los electrones

Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical

We present an experimental study of the {\em nonlinear} susceptibility of Mn$_{12}$ single-molecule magnets. We investigate both their thermal-equilibrium and dynamical nonlinear responses. The equilibrium results show the sensitivity of the nonlinear susceptibility to the magnetic anisotropy, which is nearly absent in the linear response for axes distributed at random. The nonlinear dynamic response of Mn$_{12}$ was recently found to be very large and displaying peaks reversed with respect to classical superparamagnets [F. Luis {\em et al.}, Phys. Rev. Lett. {\bf 92}, 107201 (2004)]. Here we corroborate the proposed explanation -- strong field dependence of the relaxation rate due to the detuning of tunnel energy levels. This is done by studying the orientational dependence of the nonlinear susceptibility, which permits to isolate the quantum detuning contribution. Besides, from the analysis of the longitudinal and transverse contributions we estimate a bound for the decoherence time due to the coupling to the phonon bath.Comment: 13 pages, 8 figures, resubmitted to Phys. Rev. B with minor change