Long Range Binding in Alkali-Helium Pairs

Variational calculations are performed to search for bound rovibrational states of diatomic molecules formed from alkali atoms and helium in the very shallow Σ2 electronic ground state. Examination of a recent set of potential surfaces and several older potentials indicates that all pairs possess a single very diffuse bound state with J=0. Such marginally bound states will have profound effects on low energy collisions between alkali atoms and helium atoms. The sensitivity of these states with respect to retardation effects has been studied. The variational calculations employ a basis set of generalized Laguerre functions and new analytical expressions for kinetic energy matrix elements

Coherent control of the spin current through a quantum dot

73.63.Kv Quantum dots, 85.35.Be Quantum well devices (quantum dots, quantum wires, etc.),

Functional Rotation of the Transporter AcrB: The Essentials of Peristaltic Motion and Subsequent Substrate Extrusion

Bacteria, such as E. coli, use multidrug efflux pumps to export toxic substrates through their cell membranes, including antibiotics. The RND transporter of the AcrAB-TolC efflux pump is able to export structurally and chemically different substrates via a functional rotation. The three major states of this rotation cycle were found in several asymmetric crystal structures. After initially analyzing the basic mechanisms of opening of the TolC channel [1] and of substrate extrusion by AcrB [2] separately, we have continued the analysis of the latter one. Thereby, we have focused both on the local interactions between substrate and protein, the properties of the extrusion pathway, as well as the principal subdomain movements which lead to the peristaltic motion. Furthermore, we have investigated the possibility to pull the substrate from the final state of the previous simulations out of the exit gate to estimate whether the substrate is already free to leave the protein via diffusion, which is usually beyond the time scale of computer simulations. [1] R. Schulz, U. Kleinekathöfer, Biophys. J. 96, 3116 (2009) [2] R. Schulz, A. Vargiu, F. Collu, U. Kleinekathöfer, P. Ruggerone, submitte