Topological Quantum Phase Transition in 5dd Transition Metal Oxide Na2_2IrO3_3

We predict a quantum phase transition from normal to topological insulators in the 5$d$ transition metal oxide Na$_2$IrO$_3$, where the transition can be driven by the change of the long-range hopping and trigonal crystal field terms. From the first-principles-derived tight-binding Hamiltonian we determine the phase boundary through the parity analysis. In addition, our first-principles calculations for Na$_2$IrO$_3$ model structures show that the interlayer distance can be an important parameter for the existence of a three-dimensional strong topological insulator phase. Na$_2$IrO$_3$ is suggested to be a candidate material which can have both a nontrivial topology of bands and strong electron correlations

Hawking temperature from scattering off the charged 2D black hole

The charged 2D black hole is visualized as presenting an potential barrier $V^{OUT}(r^*)$ to on-coming tachyon wave. Since this takes the complicated form, an approximate form $V^{APP}(r^*)$ is used for scattering analysis. We calculate the reflection and transmission coefficients for scattering of tachyon off the charged 2D black hole. The Hawking temperature is also derived from the reflection coefficient by Bogoliubov transformation. In the limit of $Q \to 0$, we recover the Hawking temperature of the 2D dilaton black hole.Comment: 12 pages 3 figures, RevTeX, to obtain figures contact author ([email protected]

Opportunistic Scheduling and Beamforming for MIMO-OFDMA Downlink Systems with Reduced Feedback

Opportunistic scheduling and beamforming schemes with reduced feedback are proposed for MIMO-OFDMA downlink systems. Unlike the conventional beamforming schemes in which beamforming is implemented solely by the base station (BS) in a per-subcarrier fashion, the proposed schemes take advantages of a novel channel decomposition technique to perform beamforming jointly by the BS and the mobile terminal (MT). The resulting beamforming schemes allow the BS to employ only {\em one} beamforming matrix (BFM) to form beams for {\em all} subcarriers while each MT completes the beamforming task for each subcarrier locally. Consequently, for a MIMO-OFDMA system with $Q$ subcarriers, the proposed opportunistic scheduling and beamforming schemes require only one BFM index and $Q$ supportable throughputs to be returned from each MT to the BS, in contrast to $Q$ BFM indices and $Q$ supportable throughputs required by the conventional schemes. The advantage of the proposed schemes becomes more evident when a further feedback reduction is achieved by grouping adjacent subcarriers into exclusive clusters and returning only cluster information from each MT. Theoretical analysis and computer simulation confirm the effectiveness of the proposed reduced-feedback schemes.Comment: Proceedings of the 2008 IEEE International Conference on Communications, Beijing, May 19-23, 200

Discovering Chemical Structure with Linus Pauling

This poster for the Natural Sciences Poster Session provides a brief history and description of structural chemistry, the science dealing with the molecular structure of chemical substances, with a focus on Linus Pauling, the only scientist to have received two unshared Nobel Prizes