31,020 research outputs found
Charge transport in underdoped bilayer cuprates
Within the t-J model, we study the charge transport in underdoped bilayer
cuprates by considering the bilayer interaction. Although the bilayer
interaction leads to the band splitting in the electronic structure, the
qualitative behavior of the charge transport is the same as in the case of
single layer cuprates. The conductivity spectrum shows a low-energy peak and
the unusual midinfrared band. This midinfrared band is suppressed severely with
increasing temperatures, while the resistivity in the heavily underdoped regime
is characterized by a crossover from the high temperature metallic-like to the
low temperature insulating-like behaviors, which are consistent with the
experiments.Comment: 5 pages, Revtex, three figures are include
UAV Swarm-Enabled Aerial CoMP: A Physical Layer Security Perspective
Unlike aerial base station enabled by a single unmanned aerial vehicle (UAV),
aerial coordinated multiple points (CoMP) can be enabled by a UAV swarm. In
this case, the management of multiple UAVs is important. This paper considers
the power allocation strategy for a UAV swarm-enabled aerial network to enhance
the physical layer security of the downlink transmission, where an eavesdropper
moves following the trajectory of the swarm for better eavesdropping. Unlike
existing works, we use only the large-scale channel state information (CSI) and
maximize the secrecy throughput in a whole-trajectory-oriented manner. The
overall transmission energy constraint on each UAV and the total transmission
duration for all the legitimate users are considered. The non-convexity of the
formulated problem is solved by using max-min optimization with iteration. Both
the transmission power of desired signals and artificial noise (AN) are derived
iteratively. Simulation results are presented to validate the effectiveness of
our proposed power allocation algorithm and to show the advantage of aerial
CoMP by using only the large-scale CSI
Joint radar-communication waveform designs using signals from multiplexed users
Joint radar-communication designs are exploited in applications where radar and communications systems share the same frequency band or when both radar sensing and information communication functions are required in the same system. Finding a waveform that is suitable for both radar and communication is challenging due to the difference between radar and communication operations. In this paper, we propose a new method of designing dual-functional waveforms for both radar and communication using signals from multiplexed communications users. Specifically, signals from different communications users multiplexed in the time, code or frequency domains across different data bits are linearly combined to generate an overall radar waveform. Three typical radar waveforms are considered. The coefficients of the linear combination are optimized to minimize the mean squared error with or without a constraint on the signal-to-noise ratio (SNR) for the communications signals. Numerical results show that the optimization without SNR constraint can almost perfectly approximate the radar waveform in all the cases considered, giving good dual-functional waveforms for both radar and communication. Also, among different multiplexing techniques, time division multiple access is the best option to approximate the radar waveform, followed by code division multiple access and orthogonal frequency division multiple access
Quasiparticle scattering in two dimensional helical liquid
We study the quasiparticle interference (QPI) patterns caused by scattering
off nonmagnetic, magnetic point impurities, and edge impurities, separately, in
a two dimensional helical liquid, which describes the surface states of a
topological insulator. The unique features associated with hexagonal warping
effects are identified in the QPI patterns of charge density with nonmagnetic
impurities and spin density with magnetic impurities. The symmetry properties
of the QPI patterns can be used to determine the symmetry of microscopic
models. The Friedel oscillation is calculated for edge impurities and the decay
of the oscillation is not universal, strongly depending on Fermi energy. Some
discrepancies between our theoretical results and current experimental
observations are discussed.Comment: 12 pages, appendices added. Accepted for publication in Physical
Review B (submitted, October 2009
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