Channel Estimation for Ambient Backscatter Communication Systems with Massive-Antenna Reader

Ambient backscatter, an emerging green communication technology, has aroused great interest from both academia and industry. One open problem for ambient backscatter communication (AmBC) systems is channel estimation for a massive-antenna reader. In this paper, we focus on channel estimation problem in AmBC systems with uniform linear array (ULA) at the reader which consists of large number of antennas. We first design a two-step method to jointly estimate channel gains and direction of arrivals (DoAs), and then refine the estimates through angular rotation. Additionally, Cramer-Rao lower bounds (CRLBs) are derived for both the modulus of the channel gain and the DoA estimates. Simulations are then provided to validate the analysis, and to show the efficiency of the proposed approach.Comment: 5 figures, submitted to IEEE Transactions on Vehicular Technology, 29 March, 201

Exceptional and Anisotropic Transport Properties of Photocarriers in Black Phosphorus

We show that black phosphorus has room-temperature charge mobilities on the order of 10$^4$ cm$^2$V$^{-1}$s$^{-1}$, which are about one order of magnitude larger than silicon. We also demonstrate strong anisotropic transport in black phosphorus, where the mobilities along the armchair direction are about one order of magnitude larger than zigzag direction. A photocarrier lifetime as long as 100 ps is also determined. These results illustrate that black phosphorus is a promising candidate for future electronic and optoelectronic applications.Comment: 5 pages, 4 figure

The Simulation of Non-Abelian Statistics of Majorana Fermions in Ising Chain with Z2 Symmetry

In this paper, we numerically study the non-Abelian statistics of the zero-energy Majorana fermions on the end of Majorana chain and show its application to quantum computing by mapping it to a spin model with special symmetry. In particular, by using transverse-field Ising model with Z2 symmetry, we verify the nontrivial non-Abelian statistics of Majorana fermions. Numerical evidence and comparison in both Majorana-representation and spin-representation are presented. The degenerate ground states of a symmetry protected spin chain therefore previde a promising platform for topological quantum computation.Comment: 5 pages,4 figure

RR-band host galaxy contamination of TeV γ\gamma-ray blazar Mrk 501: effects of the aperture size and seeing

We simulated the $R$-band contribution of the host galaxy of TeV $\gamma$-ray BL Lac object Mrk 501 in different aperture sizes and seeing conditions . The intensive observations were run with the 1.02 m optical telescope at Yunnan Observatories from 2010 May 15 to 18. Based on the host subtraction data presented in Nilsson et al. (2007), the subtraction of host galaxy contamination results in significant seeing-brightness correlations. These correlations would lead to illusive large amplitude variations at short timescales, which will mask the intrinsic micro variability, thus gives rise to difficulty in detecting the intrinsic micro variability. Both aperture size and seeing condition influence the flux measurements, but aperture size impact the result more significantly. Based on the parameters of elliptical galaxy provided in Nilsson et al. (1999), we simulated the host contributions of Mrk 501 in the different aperture sizes and seeing conditions. Our simulation data of the host galaxy obviously weaken these significant seeing-brightness correlations for the host-subtracted brightness of Mrk 501, and can help us discover the intrinsic short timescale micro variability. The pure nuclear flux is $\sim$ 8.0 $\rm{mJy}$ in \emph{R} band, i.e., AGN has a magnitude of $R\sim13^{m}_{\cdot}96$.Comment: accepted for publication in Research in Astronomy and Astrophysics, 8 figures, 6 table

The Deep Optical Imaging of the Extended Groth Strip

We present $u'g'R$ optical images taken with the MMT/Megacam and the Subaru/Suprime of the Extended Groth Strip survey. The total survey covers an area of about $\sim 1$ degree$^2$, including four sub-fields and is optimized for the study of galaxies at $z\sim3$. Our methods for photometric calibration in AB magnitudes, the limiting magnitude and the galaxy number count are described. A sample of 1642 photometrically selected candidate LBGs to an apparent $R_{AB}$ magnitude limit of 25.0 is present. The average sky surface density of our LBGs sample is $\sim$ 1.0 arcmin$^{-2}$, slightly higher than the previous finding.Comment: Accepted for publication by RA