Diffusion induced decoherence of stored optical vortices

We study the coherence properties of optical vortices stored in atomic ensembles. In the presence of thermal diffusion, the topological nature of stored optical vortices is found not to guarantee slow decoherence. Instead the stored vortex state has decoherence surprisingly larger than the stored Gaussian mode. Generally, the less phase gradient, the more robust for stored coherence against diffusion. Furthermore, calculation of coherence factor shows that the center of stored vortex becomes completely incoherent once diffusion begins and, when reading laser is applied, the optical intensity at the center of the vortex becomes nonzero. Its implication for quantum information is discussed. Comparison of classical diffusion and quantum diffusion is also presented.Comment: 5 pages, 2 figure

Coherent Graphene Devices: Movable Mirrors, Buffers and Memories

We theoretically report that, at a sharp electrostatic step potential in graphene, massless Dirac fermions can obtain Goos-H\"{a}nchen-like shifts under total internal reflection. Based on these results, we study the coherent propagation of the quasiparticles along a sharp graphene \emph{p-n-p} waveguide and derive novel dispersion relations for the guided modes. Consequently, coherent graphene devices (e.g. movable mirrors, buffers and memories) induced only by the electric field effect can be proposed.Comment: 12 pages, 5 figure

To be or not to be? – An empirical study on dual-class share structure of US listed Chinese companies

Dual-class share structure (DCSS) is prohibited in Mainland China currently with the OSOV (one share one vote) principle clearly written in both the Chinese company law and listing rules . As a result, those American stock exchanges become attractive to Mainland Chinese companies due to their tolerance of takeover defences, in particular, DCSS. To seek the soft regulation with the issuance of multiple voting shares, dozens of Chinese companies chose the American stock exchanges as their IPO (initial public offering) venues. In this paper, empirical research will be conducted to analyse those US-listed Mainland Chinese companies with DCSS. This paper aims to assess those transnational companies, their characteristics and corporate performances. As to the range of data to be covered, only those companies listed after 2011 will be sampled in this paper. It is because some of those data of the Mainland Chinese companies on NYSE or NASDAQ listed prior to 2011 were not available or were inaccurate; counting them leads to misleading results. Furthermore, those data is dated for such a changing area of law. In order to reflect the up-to-date status accurately, this paper focuses its empirical study of data which date back to 2011

Calibrating the {\alpha} parameter of convective efficiency using observed stellar properties

Context. Synthetic model atmosphere calculations are still the most commonly used tool when determining precise stellar parameters and stellar chemical compositions. Besides three-dimensional models that consistently solve for hydrodynamic processes, one-dimensional models that use an approximation for convective energy transport play the major role. Aims. We use modern Balmer-line formation theory as well as spectral energy distribution (SED) measurements for the Sun and Procyon to calibrate the model parameter {\alpha} that describes the efficiency of convection in our 1D models. Convection was calibrated over a significant range in parameter space, reaching from F-K along the main sequence and sampling the turnoff and giant branch over a wide range of metallicities. This calibration was compared to theoretical evaluations and allowed an accurate modeling of stellar atmospheres. Methods. We used Balmer-line fitting and SED fits to determine the convective efficiency parameter {\alpha}. Both methods are sensitive to the structure and temperature stratification of the deeper photosphere. Results. While SED fits do not allow a precise determination of the convective parameter for the Sun and Procyon, they both favor values significantly higher than 1.0. Balmer-line fitting, which we find to be more sensitive, suggests that the convective efficiency parameter {\alpha} is $\approx$ 2.0 for the main sequence and quickly decreases to $\approx$ 1.0 for evolved stars. These results are highly consistent with predictions from 3D models. While the values on the main sequence fit predictions very well, measurements suggest that the decrease of convective efficiency as stars evolve to the giant branch is more dramatic than predicted by models.Comment: 14 pages, 16 figures, accepted for publication in A&