Tuning electronic structure of graphene via tailoring structure: theoretical study

Electronic structures of graphene sheet with different defective patterns are investigated, based on the first principles calculations. We find that defective patterns can tune the electronic structures of the graphene significantly. Triangle patterns give rise to strongly localized states near the Fermi level, and hexagonal patterns open up band gaps in the systems. In addition, rectangular patterns, which feature networks of graphene nanoribbons with either zigzag or armchair edges, exhibit semiconducting behaviors, where the band gap has an evident dependence on the width of the nanoribbons. For the networks of the graphene nanoribbons, some special channels for electronic transport are predicted.Comment: 5 figures, 6 page

Quantifying admissible undersampling for sparsity-exploiting iterative image reconstruction in X-ray CT

Iterative image reconstruction (IIR) with sparsity-exploiting methods, such as total variation (TV) minimization, investigated in compressive sensing (CS) claim potentially large reductions in sampling requirements. Quantifying this claim for computed tomography (CT) is non-trivial, because both full sampling in the discrete-to-discrete imaging model and the reduction in sampling admitted by sparsity-exploiting methods are ill-defined. The present article proposes definitions of full sampling by introducing four sufficient-sampling conditions (SSCs). The SSCs are based on the condition number of the system matrix of a linear imaging model and address invertibility and stability. In the example application of breast CT, the SSCs are used as reference points of full sampling for quantifying the undersampling admitted by reconstruction through TV-minimization. In numerical simulations, factors affecting admissible undersampling are studied. Differences between few-view and few-detector bin reconstruction as well as a relation between object sparsity and admitted undersampling are quantified.Comment: Revised version that was submitted to IEEE Transactions on Medical Imaging on 8/16/201

Robust H∞ feedback control for uncertain stochastic delayed genetic regulatory networks with additive and multiplicative noise

The official published version can found at the link below.Noises are ubiquitous in genetic regulatory networks (GRNs). Gene regulation is inherently a stochastic process because of intrinsic and extrinsic noises that cause kinetic parameter variations and basal rate disturbance. Time delays are usually inevitable due to different biochemical reactions in such GRNs. In this paper, a delayed stochastic model with additive and multiplicative noises is utilized to describe stochastic GRNs. A feedback gene controller design scheme is proposed to guarantee that the GRN is mean-square asymptotically stable with noise attenuation, where the structure of the controllers can be specified according to engineering requirements. By applying control theory and mathematical tools, the analytical solution to the control design problem is given, which helps to provide some insight into synthetic biology and systems biology. The control scheme is employed in a three-gene network to illustrate the applicability and usefulness of the design.This work was funded by Royal Society of the U.K.; Foundation for the Author of National Excellent Doctoral Dissertation of China. Grant Number: 2007E4; Heilongjiang Outstanding Youth Science Fund of China. Grant Number: JC200809; Fok Ying Tung Education Foundation. Grant Number: 111064; International Science and Technology Cooperation Project of China. Grant Number: 2009DFA32050; University of Science and Technology of China Graduate Innovative Foundation

Microscopic origin of local moments in a zinc-doped high-TcT_{c} superconductor

The formation of a local moment around a zinc impurity in the high-$T_{c}$ cuprate superconductors is studied within the framework of the bosonic resonating-valence-bond (RVB) description of the $t-J$ model. A topological origin of the local moment has been shown based on the phase string effect in the bosonic RVB theory. It is found that such an $S=1/2$ moment distributes near the zinc in a form of staggered magnetic moments at the copper sites. The corresponding magnetic properties, including NMR spin relaxation rate, uniform spin susceptibility, and dynamic spin susceptibility, etc., calculated based on the theory, are consistent with the experimental measurements. Our work suggests that the zinc substitution in the cuprates provide an important experimental evidence for the RVB nature of local physics in the original (zinc free) state.Comment: The topological reason of local moment formation is given. One figure is adde

Temperature dependence of the impurity-induced resonant state in Zn-doped Bi_2Sr_2CaCu_2O8+δ_{8+\delta} by Scanning Tunneling Spectroscopy

We report on the temperature dependence of the impurity-induced resonant state in Zn-doped Bi_2Sr_2CaCu_2O$_{8+\delta}$ by scanning tunneling spectroscopy at 30 mK < T < 52 K. It is known that a Zn impurity induces a sharp resonant peak in tunnel spectrum at an energy close to the Fermi level. We observed that the resonant peak survives up to 52 K. The peak broadens with increasing temperature, which is explained by the thermal effect. This result provides information to understand the origin of the resonant peak.Comment: 4 pages, 3 figures, to appear in Phys. Rev.

Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet

The specific heat and thermal conductivity of the insulating ferrimagnet Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured down to 50 mK. The ferromagnetic magnon specific heat $C$$_m$ shows a characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward deviation is observed, which is attributed to the magnetic dipole-dipole interaction with typical magnitude of 10$^{-4}$ eV. The ferromagnetic magnon thermal conductivity $\kappa_m$ does not show the characteristic $T^2$ dependence below 0.8 K. To fit the $\kappa_m$ data, both magnetic defect scattering effect and dipole-dipole interaction are taken into account. These results complete our understanding of the thermodynamic and thermal transport properties of the low-lying ferromagnetic magnons.Comment: 5 pages, 5 figure

Sublogarithmic deterministic selection on arrays with a reconfigurable optical bus

The linear array with a reconfigurable pipelined bus system (LARPBS) is a newly introduced parallel computational model, where processors are connected by a reconfigurable optical bus. In this paper, we show that the selection problem can be solved on the LARPBS model deterministically in O((loglogN)2/ log log log N) time. To our best knowledge, this is the best deterministic selection algorithm on any model with a reconfigurable optical bus.Yijie Han, Yi Pan and Hong She

Suppression of low-energy Andreev states by a supercurrent in YBa_2Cu_3O_7-delta

We report a coherence-length scale phenomenon related to how the high-Tc order parameter (OP) evolves under a directly-applied supercurrent. Scanning tunneling spectroscopy was performed on current-carrying YBa_2Cu_3O_7-delta thin-film strips at 4.2K. At current levels well below the theoretical depairing limit, the low-energy Andreev states are suppressed by the supercurrent, while the gap-like structures remain unchanged. We rule out the likelihood of various extrinsic effects, and propose instead a model based on phase fluctuations in the d-wave BTK formalism to explain the suppression. Our results suggest that a supercurrent could weaken the local phase coherence while preserving the pairing amplitude. Other possible scenarios which may cause the observed phenomenon are also discussed.Comment: 6 pages, 4 figures, to appear in Physical Review