558 research outputs found
Effective electric and magnetic properties of metasurfaces in transition from crystalline to amorphous state
In this paper we theoretically study electromagnetic reflection,
transmission, and scattering properties of periodic and random arrays of
particles which exhibit both electric-mode and magnetic-mode resonances. We
compare the properties of regular and random grids and explain recently
observed dramatic differences in resonance broadening in the electric and
magnetic modes of random arrays. We show that randomness in the particle
positioning influences equally on the scattering loss from both electric and
magnetic dipoles, however, the observed resonance broadening can be very
different depending on the absorption level in different modes as well as on
the average electrical distance between the particles. The theory is
illustrated by an example of a planar metasurface composed of cut-wire pairs.
We show that in this particular case at the magnetic resonance the array
response is almost not affected by positioning randomness due to lower
frequency and higher absorption losses in that mode. The developed model allows
predictions of behavior of random grids based on the knowledge of
polarizabilities of single inclusions.Comment: 13 pages, 5 figures, and submitted to PR
From inflation to dark energy in the non-minimal modified gravity
We consider the modified gravity non-minimally coupled with matter Lagrangian
for the description of early-time and late-time universe. Such ()
gravity in the absence of non-minimal coupling is viable theory which passes
the local tests and reproduces the CDM era. For qualitatively similar
choice of non-minimal gravitational coupling function it is shown that the
unified description of early-time inflation and late-time cosmic acceleration
is possible. It is interesting that matter (scalar) which supports the
inflationary era is gravitationally screened at late times. Hence, it may be
effectively invisible at current universe.Comment: LaTeX file, 10 pages, based on the talk given by S.D. Odintsov at
ICGA8 conference, Nara, Japa
Reconstruction and deceleration-acceleration transitions in modified gravity
We discuss the cosmological reconstruction in modified Gauss-Bonnet and F(R)
gravities. Two alternative representations of the action (with and without
auxiliary scalar) are considered. The approximate description of
deceleration-acceleration transition cosmologies is reconstructed. It is shown
that cosmological solution containing Big Bang and Big Rip singularities may be
reconstructed only using the representation with the auxiliary field. The
analytical description of the deceleration-acceleration transition cosmology in
modified Gauss-Bonnet gravity is demonstrated to be impossible at sufficiently
general conditions.Comment: LaTeX 8 pages, published version
On the Definition of Effective Permittivity and Permeability For Thin Composite Layers
The problem of definition of effective material parameters (permittivity and
permeability) for composite layers containing only one-two parallel arrays of
complex-shaped inclusions is discussed. Such structures are of high importance
for the design of novel metamaterials, where the realizable layers quite often
have only one or two layers of particles across the sample thickness. Effective
parameters which describe the averaged induced polarizations are introduced. As
an explicit example, we develop an analytical model suitable for calculation of
the effective material parameters and
for double arrays of electrically small electrically polarizable scatterers.
Electric and magnetic dipole moments induced in the structure and the
corresponding reflection and transmission coefficients are calculated using the
local field approach for the normal plane-wave incidence, and effective
parameters are introduced through the averaged fields and polarizations. In the
absence of losses both material parameters are purely real and satisfy the
Kramers-Kronig relations and the second law of thermodynamics. We compare the
analytical results to the simulated and experimental results available in the
literature. The physical meaning of the introduced parameters is discussed in
detail.Comment: 6 pages, 5 figure
Level of computer dependence at pupils of modern schools
In article the problem of formation of dependence on computer games at modern school students is considered. The state and level of dependence at pupils of 914 years is investigatedВ статье рассматривается проблема формирования зависимости от компьютерных игр у современных школьников. Исследуется состояние и уровень зависимости у учащихся 9–14 ле
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