Enhancing single-parameter quantum charge pumping in carbon-based devices

We present a theoretical study of quantum charge pumping with a single ac gate applied to graphene nanoribbons and carbon nanotubes operating with low resistance contacts. By combining Floquet theory with Green's function formalism, we show that the pumped current can be tuned and enhanced by up to two orders of magnitude by an appropriate choice of device length, gate voltage intensity and driving frequency and amplitude. These results offer a promising alternative for enhancing the pumped currents in these carbon-based devices.Comment: 3.5 pages, 2 figure

Caracterización química y mineral ógica de los sedimentos de los canales de Mira, Ílhavo y Ovar de la Laguna de Aveiro (Portugal)

The paleoenvironmental reconstruction of Aveiro Lagoon is being carried out based on the sedimentological, paleoecological, geochemical and mineralogical characterization of sediment samples collected systematically in the lagoon. This paper presents results concerning the changes in the chemical and mineralogical composition of the fine fraction (<63 μm) and the clay fraction (<2 μm) in sediment samples from Aveiro Lagoon, mainly collected from the lower intertidal plain and subtidal deposits located along the Mira, Ílhavo and Ovar channels. A zonography of the lagoon was established based on the parameters analyzed. The results show that the surface and near-surface sediments of Aveiro Lagoon trap relatively large quantities of trace metals, such as Cu, Pb, Co, Ni, Cd, Zn, Fe, Mn and Cr, considered to be partially adsorbed, particularly on silty and clayey particles, and co-precipitated on Fe and Mn oxyhydroxide forms precipitated in the topmost layers of sediments. Series of statistically significant relationships were established between trace metal concentrations and clay content and semi-quantitatively determined clay mineral species in the sediments.La reconstrucción paleoambiental de la Laguna de Aveiro se está realizando mediante la caracterización sedimentológica, paleoecológica, geoquímica y mineralógica de muestras de sedimento recogidas sistemáticamente en la misma. Este artículo presenta resultados relativos a las variaciones en la composición química y mineralógica de las fracciones fina (<63 μm) y arcillosa (<2 μm) de las muestras de sedimento de la Laguna de Aveiro, recogidas principalmente en las planicies intermareales bajas y depósitos submareales de los canales de Mira, Ílhavo y Ovar. Estos parámetros fueron utilizados para caracterizar los sedimentos de cada uno de los canales estudiados de la Laguna de Aveiro. Los sedimentos superficiales y subsuperficiales de esta laguna retienen cantidades relativamente elevadas de elementos vestigiales como Cu, Pb, Co, Ni, Cd, Zn, Fe, Mn y Cr, los cuales se consideran principalmente adsorbidos en partículas fangosas y arcillosas y en óxidos de Fe y Mn. Con base en los parámetros analizados se puede establecer una zonografía de la laguna. Se han encontrado relaciones entre las concentraciones de elementos vestigiales y el contenido de arcilla y las especies minerales de las arcillas en los sedimentos