University of Basel

About: University of Basel is a education organization based out in Basel, Basel-Stadt, Switzerland. It is known for research contribution in the topics: Population & Transplantation. The organization has 25084 authors who have published 52975 publications receiving 2388002 citations. The organization is also known as: Universität Basel & Basel University.

Andreev tunneling, Coulomb blockade, and resonant transport of nonlocal spin-entangled electrons

Abstract: We propose and analyze a spin-entangler for electrons based on an s-wave superconductor coupled to two quantum dots, each of which is coupled to normal Fermi leads We show that in the presence of a voltage bias and in the Coulomb blockade regime two correlated electrons provided by the Andreev process can coherently tunnel from the superconductor via different dots into different leads The spin singlet coming from the Cooper pair remains preserved in this process, and the setup provides a source of mobile and nonlocal spin-entangled electrons The transport current is calculated and shown to be dominated by a two-particle Breit-Wigner resonance that allows the injection of two spin-entangled electrons into different leads at exactly the same orbital energy, which is a crucial requirement for the detection of spin entanglement via noise measurements The coherent tunneling of both electrons into the same lead is suppressed by the on-site Coulomb repulsion and/or the superconducting gap, while the tunneling into different leads is suppressed through the initial separation of the tunneling electrons In the regime of interest the particle-hole excitations of the leads are shown to be negligible The Aharonov-Bohm oscillations in the current are shown to contain single- and two-electron periods with amplitudes that both vanish with increasing Coulomb repulsion albeit differently fast

Interaction of Alzheimer beta-amyloid peptide(1-40) with lipid membranes.

Abstract: The β-amyloid peptide βAP(1−40), a 40-amino acid residues peptide, is one of the major components of Alzheimer's amyloid deposits. βAP(1−40) exhibits only a limited solubility in aqueous solution and undergoes a concentration-dependent, cooperative random coil ⇄ β-structure transition for Cpep > 10 μM [Terzi, E., Holzemann, G., and Seelig, J. (1995) J. Mol. Biol. 252, 633−642]. In the presence of acidic lipid, the equilibrium is shifted further toward β-structured aggregates. We have now characterized the lipid−peptide interaction using circular dichroism (CD) spectroscopy, lipid monolayers, and deuterium and phosphorus-31 solid-state nuclear magnetic resonance (NMR). CD spectroscopy revealed a distinct interaction between βAP(1−40) and negatively charged unilamellar vesicles. In addition to the random coil ⇄ β-structured aggregate equilibrium at low lipid-to-peptide (L/P) ratios, a β-structure → α-helix transition was observed at L/P > 55. βAP(1−40) was found to insert into acidic monolayers provided the...

The role of legumes as a component of biodiversity in a cross‐European study of grassland biomass nitrogen

Abstract: To investigate how plant diversity loss affects nitrogen accumulation in above-ground plant biomass and how consistent patterns are across sites of different climatic and soil conditions, we varied the number of plant species and functional groups (grasses, herbs and legumes) in experimental grassland communities across seven European experimental sites (Switzerland, Germany, Ireland, United Kingdom (Silwood Park), Portugal, Sweden and Greece). Nitrogen pools were significantly affected by both plant diversity and community composition. Two years after sowing, nitrogen pools in Germany and Switzerland strongly increased in the presence of legumes. Legume effects on nitrogen pools were less pronounced at the Swedish, Irish and Portuguese site. In Greece and UK there were no legume effects. Nitrogen concentration in total above-ground biomass was quite invariable at 1.66 ± 0.03% across all sites and diversity treatments. Thus, the presence of legumes had a positive effect on nitrogen pools by significantly increasing above-ground biomass, i.e. by increases in vegetation quantity rather than quality. At the German site with the strongest legume effect on nitrogen pools and biomass, nitrogen that was fixed symbiotically by legumes was transferred to the other plant functional groups (grasses and herbs) but varied depending on the particular legume species fixing N and the non-legume species taking it up. Nitrogen-fixation by legumes therefore appeared to be one of the major functional traits of species that influenced nitrogen accumulation and biomass production, although effects varied among sites and legume species. This study demonstrates that the consequences of species loss on the nitrogen budget of plant communities may be more severe if legume species are lost. However, our data indicate that legume species differ in their N 2 fixation. Therefore, loss of an efficient N 2 -fixer (Trifolium in our study) may have a greater influence on the ecosystem function than loss of a less efficient species (Lotus in our study). Furthermore, there is indication that P availability in the soil facilitates the legume effect on biomass production and biomass nitrogen accumulation.