Kondo quantum dot coupled to ferromagnetic leads: Numerical renormalization group study

We systematically study the influence of ferromagnetic leads on the Kondo resonance in a quantum dot tuned to the local moment regime. We employ Wilson's numerical renormalization group method, extended to handle leads with a spin asymmetric density of states, to identify the effects of (i) a finite spin polarization in the leads (at the Fermi-surface), (ii) a Stoner splitting in the bands (governed by the band edges) and (iii) an arbitrary shape of the leads density of states. For a generic lead density of states the quantum dot favors being occupied by a particular spin-species due to exchange interaction with ferromagnetic leads leading to a suppression and splitting of the Kondo resonance. The application of a magnetic field can compensate this asymmetry restoring the Kondo effect. We study both the gate-voltage dependence (for a fixed band structure in the leads) and the spin polarization dependence (for fixed gate voltage) of this compensation field for various types of bands. Interestingly, we find that the full recovery of the Kondo resonance of a quantum dot in presence of leads with an energy dependent density of states is not only possible by an appropriately tuned external magnetic field but also via an appropriately tuned gate voltage. For flat bands simple formulas for the splitting of the local level as a function of the spin polarization and gate voltage are given.Comment: 18 pages, 18 figures, accepted for publication in PR

Approaches and Frameworks for Managing Contaminated Sediments - A European Perspective

Sediment is an essential, integral and dynamic part of the hydrologic system. In natural and agricultural basins, sediment is derived from the weathering and erosion of minerals, organic material and soils in upstream areas and from the erosion of river banks and other in-stream sources. As surface-water flow rates decline in lowland areas, transported sediment settles along the river bed and banks by sedimentation. However, because sediments are the ultimate reservoir for the numerous potential chemical and biological contaminants that may be contained in effluents originating from urban, agricultural, and industrial lands and recreational activities, contaminated sediments in rivers and streams, lakes, coastal harbors, and estuaries have the potential to pose ecological and human health risks. The management of sediment quality and quantity in support of ecological and socioeconomic goals is a cause of extensive research, investment and regulatory and public scrutiny, both in Europe and internationally. This chapter examines the management of sediment from a European perspective. The first section discusses the role of sediment management in achieving European ecosystem objectives. Section two summarizes the findings of the EC-funded, demand driven European Sediment Research Network (SedNet). Section three describes a framework risk assessment and management in a major European region, the Venice Lagoon. The next three sections describe aspects of sediment management in an EC accession country, and the host country for this workshop - Slovakia. Section four describes river and lake sediment contamination and related legislation in Slovakia. Section five discusses the assessment and management of Persistent Organic Pollutants (POPs), a major risk driver in Slovakia. Section six discusses a specific class of POPs - PCBS in sediments of a specific region of Slovakia. Finally, Section seven discusses some barriers to successful sediment risk assessment and management, and lists science and infrastructure needs to address these barriers. Whilst all the authors of this chapter are living and/or working in Europe, and the focus is on European perspectives, much work has benefited from international collaborations and we feel that many of the observations and recommendations will have relevance to a broader audience

Venezuelan tepuis: their caves and biota

From the Preface: The world at the top of the tepuis of Venezuela is amazing. Ever since Sir Arthur Conan Doyle wrote The Lost World , the enigma of the South American steep and isolated table-mountains have attracted many people. Everyone in our research team dreamt about exploring these blank spaces on the map . However, despite this great attraction, scientific literature concerning tepuis has remained rather scarce. We are therefore proud to present this scientific monograph on tepuis, which is considered to be only the second issue of its kind, following the work of Huber (1992). This volume summarizes the main scientific results of expeditions to these tepuis between 2002 and 2011. The major research described in this monograph is dedicated to the great caves discovered in Roraima and Churí tepuis. The geological research was accompanied by biological research on cave and surface fauna, with a special focus on malacofauna, herpetofauna and insects. Although some of the data from this research has been previously published in scientific articles, it did not always obtain the justifiable space to present all gathered documentation and to elucidate all relevant scientific problems from a greater perspective. It is therefore our great pleasure to present this monograph containing detailed information on all research currently performed by our interdisciplinary research team. This is accompanied by a large number of fascinating photographs and several informative maps and diagrams. The greatest benefits to be gained from this combined monograph compared to short scientific publications is that more space is available to discuss currently unresolved problems, to ponder new intriguing questions and to envisage future necessary research. It is our sincere hope that all our readers will appreciate the unique information presented in this manner, and we hope you will really enjoy this monograph and find interesting topics for your research. Open Access See Extended description for more information