451 research outputs found
Near-field enhancement and sub-wavelength imaging in the optical region using a pair of two-dimensional arrays of metal nanospheres
Near-field enhancement and sub-wavelength imaging properties of a system
comprising a coupled pair of two-dimensional arrays of resonant nanospheres are
studied. The concept of using two coupled material sheets possessing surface
mode resonances for evanescent field enhancement is already well established in
the microwave region. This paper shows that the same principles can be applied
also in the optical region, where the performance of the resonant sheets can be
realized with the use of metallic nanoparticles. In this paper we present
design of such structures and study the electric field distributions in the
image plane of such superlens.Comment: 15 pages, 9 figure
Three-dimensional isotropic perfect lens based on LC-loaded transmission lines
An isotropic three-dimentional perfect lens based on cubic meshes of
interconnected transmission lines and bulk loads is proposed. The lens is
formed by a slab of a loaded mesh placed in between two similar unloaded
meshes. The dispersion equations and the characteristic impedances of the
eigenwaves in the meshes are derived analytically, with an emphasis on
generality. This allows designing of transmission-line meshes with desired
dispersion properties. The required backward-wave mode of operation in the lens
is realized with simple inductive and capacitive loads. An analytical
expression for the transmission through the lens is derived and the
amplification of evanescent waves is demonstrated. Factors that influence
enhancement of evanescent waves in the lens are studied and the corresponding
design criteria are established. A possible realization of the structure is
outlined.Comment: 22 pages, 15 figure
De Sitter stability in quadratic gravity
Quadratic curvature corrections to Einstein-Hilbert action lead in general to
higher-order equations of motion, which can induced instability of some
unperturbed solutions of General Relativity. We study conditions for stability
of de Sitter cosmological solution. We argue that simple form of this condition
known for FRW background in 3+1 dimensions changes seriously if at least one of
these two assumptions is violated. In the present paper the stability
conditions for de Sitter solution have been found for multidimensional FRW
background and for Bianchi I metrics in 3+1 dimensions.Comment: 12 pages with 4 figures; references adde
Spin connection and cosmological perturbations in gravity
In this paper we study cosmological perturbations in teleparallel gravity. We
discuss problems which appear in standard approach to gravity, and find
that these problems may be solved within covariant formulation of teleparallel
gravity, which take into account spin connection. We calculate spin connection
which symmetrize equation for perturbation and split diagonal and non-diagonal
part of equation of motion. We demonstrate that there is minimal solution for
spin connection, which lead to zero slip, however, in this case one additional
equation appears, so the system may become over-determined. After that, we show
that a more general solution exists, which is incompatible with zero slip, but
allows to write down the equations of motion for cosmological perturbation in a
self-consistent way without additional equations to be satisfied.Comment: 13 pages, no figures, final version to appear in Phys. Rev.
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