69,771 research outputs found
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
Collaborative signal and information processing for target detection with heterogeneous sensor networks
In this paper, an approach for target detection and acquisition with heterogeneous sensor networks through strategic resource allocation and coordination is presented. Based on sensor management and collaborative signal and information processing, low-capacity low-cost sensors are strategically deployed to guide and cue scarce high performance sensors in the network to improve the data quality, with which the mission is eventually completed more efficiently with lower cost. We focus on the problem of designing such a network system in which issues of resource selection and allocation, system behaviour and capacity, target behaviour and patterns, the environment, and multiple constraints such as the cost must be addressed simultaneously. Simulation results offer significant insight into sensor selection and network operation, and demonstrate the great benefits introduced by guided search in an application of hunting down and capturing hostile vehicles on the battlefield
Array signal processing for maximum likelihood direction-of-arrival estimation
Emitter Direction-of-Arrival (DOA) estimation is a fundamental problem in a variety of applications including radar, sonar, and wireless communications. The research has received considerable attention in literature and numerous methods have been proposed. Maximum Likelihood (ML) is a nearly optimal technique producing superior estimates compared to other methods especially in unfavourable conditions, and thus is of significant practical interest. This paper discusses in details the techniques for ML DOA estimation in either white Gaussian noise or unknown noise environment. Their performances are analysed and compared, and evaluated against the theoretical lower bounds
Z-D Brane Box Models and Non-Chiral Dihedral Quivers
Generalising ideas of an earlier work \cite{Bo-Han}, we address the problem of constructing Brane Box Models of what we call the Z-D Type from a new point of view, so as to establish the complete correspondence between these brane setups and orbifold singularities of the non-Abelian G generated by Z_k and D_d under certain group-theoretic constraints to which we refer as the BBM conditions. Moreover, we present a new class of quiver theories of the ordinary dihedral group d_k as well as the ordinary exceptionals E_{6,7,8} which have non-chiral matter content and discuss issues related to brane setups thereof
Charmonium suppression by gluon bremsstrahlung in p-A and A-B collisions
Prompt gluons are an additional source for charmonium suppression in nuclear
collisions, in particular for nucleus-nucleus collisions. These gluons are
radiated as bremsstrahlung in N-N collisions and interact inelastically with
the charmonium states while the nuclei still overlap. The spectra and mean
number of the prompt gluons are calculated perturbatively and the
gluon-Psi inelastic cross section is estimated. The integrated cross sections
for AB --> J/Psi (Psi')X for p-A and A-B collisions and the dependence on
transverse energy for S-U and Pb-Pb can be described quantitatively with some
adjustment of one parameter \sigma(gPsi).Comment: 17 pages of Latex including 10 figure
Transport theory with self-consistent confinement related to the lattice data
The space-time development of a quark-gluon plasma is calculated from a
Vlasov equation for the distribution function of quasiparticles with medium
dependent masses. At each space-time point the masses are calculated
selfconsistently from a gap equation, whose form is determined by the
requirement that in thermal equilibrium and for a range of temperatures the
energy density of the quasi-particle system is identical to the one from
lattice calculations . The numerical solutions of the Vlasov equation display
confinement. Relations to effective theories like that by Friedberg Lee and
Nambu Jona-Lasinio are established.Comment: 9 pages, 12 figure
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Testing the uniqueness of the open bosonic string field theory vacuum
The operators K_n are generators of reparameterization symmetries of Witten's cubic open string field theory. One pertinent question is whether they can be utilised to generate deformations of the tachyon vacuum and thereby violate its uniqueness. We use level truncation to show that these transformations on the vacuum are in fact pure gauge transformations to a very high accuracy, thus giving new evidence for the uniqueness of the perturbatively stable vacuum. Equivalently, this result implies the vanishing of some discrete cohomology classes of the BRST operator in the stable vacuum
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