41,885 research outputs found
Two-dimensional plasmons in the random impedance network model of disordered thin-film nanocomposites
Random impedance networks are widely used as a model to describe plasmon
resonances in disordered metal-dielectric nanocomposites. In order to study
thin films, two-dimensional networks are often used despite the fact that such
networks correspond to a two-dimensional electrodynamics [J.P. Clerc et al, J.
Phys. A 29, 4781 (1996)]. In the present work, we propose a model of
two-dimensional systems with three-dimensional Coulomb interaction and show
that this model is equivalent to a planar network with long-range capacitive
connections between sites. In a case of a metal film, we get a known dispersion
of plane-wave two-dimensional plasmons. In the
framework of the proposed model, we study the evolution of resonances with
decreasing of metal filling factor. In the subcritical region with metal
filling lower than the percolation threshold , we observe a gap with
Lifshitz tails in the spectral density of states (DOS). In the supercritical
region , the DOS demonstrates a crossover between plane-wave
two-dimensional plasmons and resonances associated with small clusters.Comment: 8 pages, 3 figures, revtex; references adde
Spectral Renormalization Group for the Gaussian model and theory on non-spatial networks
We implement the spectral renormalization group on different deterministic
non-spatial networks without translational invariance. We calculate the
thermodynamic critical exponents for the Gaussian model on the Cayley tree and
the diamond lattice, and find that they are functions of the spectral
dimension, . The results are shown to be consistent with those from
exact summation and finite size scaling approaches. At , the lower
critical dimension for the Ising universality class, the Gaussian fixed point
is stable with respect to a perturbation up to second order. However,
on generalized diamond lattices, non-Gaussian fixed points arise for
.Comment: 16 pages, 14 figures, 5 tables. The paper has been extended to
include a interactions and higher spectral dimension
Maximum-Likelihood Sequence Detection of Multiple Antenna Systems over Dispersive Channels via Sphere Decoding
Multiple antenna systems are capable of providing high data rate transmissions over wireless channels. When the channels are dispersive, the signal at each receive antenna is a combination of both the current and past symbols sent from all transmit antennas corrupted by noise. The optimal receiver is a maximum-likelihood sequence detector and is often considered to be practically infeasible due to high computational complexity (exponential in number of antennas and channel memory). Therefore, in practice, one often settles for a less complex suboptimal receiver structure, typically with an equalizer meant to suppress both the intersymbol and interuser interference, followed by the decoder. We propose a sphere decoding for the sequence detection in multiple antenna communication systems over dispersive channels. The sphere decoding provides the maximum-likelihood estimate with computational complexity comparable to the standard space-time decision-feedback equalizing (DFE) algorithms. The performance and complexity of the sphere decoding are compared with the DFE algorithm by means of simulations
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