Spin-phonon coupling in single Mn doped CdTe quantum dot

The spin dynamics of a single Mn atom in a laser driven CdTe quantum dot is addressed theoretically. Recent experimental results\cite{Le-Gall_PRL_2009,Goryca_PRL_2009,Le-Gall_PRB_2010}show that it is possible to induce Mn spin polarization by means of circularly polarized optical pumping. Pumping is made possible by the faster Mn spin relaxation in the presence of the exciton. Here we discuss different Mn spin relaxation mechanisms. First, Mn-phonon coupling, which is enhanced in the presence of the exciton. Second, phonon-induced hole spin relaxation combined with carrier-Mn spin flip coupling and photon emission results in Mn spin relaxation. We model the Mn spin dynamics under the influence of a pumping laser that injects excitons into the dot, taking into account exciton-Mn exchange and phonon induced spin relaxation of both Mn and holes. Our simulations account for the optically induced Mn spin pumping.Comment: 17 pages, 11 figures, submitted to PR

Would Global Patent Protection be too Weak without International Coordination?

This paper analyzes the setting of national patent policies in the global economy. In the standard model with free trade and social-welfare-maximizing governments à la Grossman and Lai (2004), cross-border positive policy externalities induce individual countries to select patent strengths that are weaker than is optimal from a global perspective. The paper introduces three new features to the analysis: trade barriers, firm heterogeneity in terms of productivity and political economy considerations in setting patent policies. The first two features (trade barriers interacting with firm heterogeneity) tend to reduce the size of cross-border externalities in patent protection and therefore make national IPR policies closer to the global optimum. With firm lobbying creating profit-bias of the government, it is even possible that the equilibrium strength of global patent protection is greater than the globally efficient level. Thus, the question of under-protection or not is an empirical one. Based on calibration exercises, we find that there would be global under-protection of patent rights when there is no international policy coordination. Furthermore, requiring all countries to harmonize their patent standards with the equilibrium standard of the most innovative country (the US) does not lead to global over-protection of patent rights.intellectual property rights, patents, TRIPS, harmonization

Evidence for a Functional Interaction between Integrins and G Protein-activated Inward Rectifier K+ Channels

Heteromultimeric G protein-activated inward rectifier K+ (GIRK) channels, abundant in heart and brain, help to determine the cellular membrane potential as well as the frequency and duration of electrical impulses. The sequence arginine-glycine-aspartate (RGD), located extracellularly between the first membrane-spanning region and the pore, is conserved among all identified GIRK subunits but is not found in the extracellular domain of any other cloned K+ channels. Many integrins, which, like channels, are integral membrane proteins, recognize this RGD sequence on other proteins, usually in the extracellular matrix. We therefore asked whether GIRK activity might be regulated by direct interaction with integrin. Here, we present evidence that mutation of the RGD site to RGE, particularly on the GIRK4 subunit, decreases or abolishes GIRK current. Furthermore, wild-type channels can be co-immunoprecipitated with integrin. The total cellular amount of expressed mutant GIRK channel protein is the same as the wild-type protein; however, the amount of mutant channel protein that localizes to the plasma membrane is decreased relative to wild-type, most likely accounting for the diminished GIRK current detected. GIRK channels appear to bind directly to integrin and to require this interaction for proper GIRK channel membrane localization and function