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Gomez-Ortiz A.,University of Barcelona | Oliva M.,University of Lisbon | Palacios D.,Universidadcomplutense Of Madrid | Salvador-Franch F.,University of Barcelona | And 3 more authors.
Cuadernos de Investigacion Geografica | Year: 2015

The large number of studies of Sierra Nevada’s environmental history since the Last Pleistocene glacial period makes it one of the most intensively analysed massifs in the Iberian Peninsula. The early geomorphological descriptions have been complemented in recent decades with absolute dating techniques that have allocated in time the sequence of environmental events occurred in Sierra Nevada during the last millennia. The maximum expansion of the glaciers during the Last Glaciation took place around 30-32 ka, with a subsequent re-advance by 19-20 ka. The process of deglaciation was very fast, and around 14-15 ka the ice had almost completely retreated from the massif. Since then, with greater or less intensity and extent, periglacial processes have driven the environmental change in the massif. The coldest and wettest phases during the Holocene have favoured the development of small glaciers in the highest northern cirques. The last of these phases was the Little Ice Age, where abundant historical sources and sedimentary records exist. During the mid XX century the last glaciers melted, resulting in the complete deglaciation of the massif. © Universidad de La Rioja.

Ortega Y.,University of Kiel | Ortega Y.,Universidadcomplutense Of Madrid | Dieker C.H.,University of Kiel | Jager W.,University of Kiel | And 2 more authors.
Nanotechnology | Year: 2010

ZnO nanorods containing different hollow structures have been grown by a thermal evaporation-deposition method with a mixture of ZnS and SnO2 powders as precursor. Transmission electron microscopy shows rods with rows of voids as well as rods with empty channels along the growth axis. The presence of Sn nanoprecipitates associated with the empty regions indicates, in addition, that these are generated by diffusion processes during growth, probably due to an inhomogeneous distribution of Sn. The mechanism of forming voids and precipitates appears to be based on diffusion processes similar to the Kirkendall effect, which can lead to void formation at interfaces of bulk materials or in core-shell nanostructures. In some cases the nanorods are ZnO tubes partially filled with Sn that has been found to melt and expand by heating the nanotubes under the microscope electron beam. Such metal-semiconductor nanostructures have potential applications as thermal nanosensors or as electrical nanocomponents. © 2010 IOP Publishing Ltd.

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