2,908 research outputs found
Evaluation of noise immunity of high orbital satellite telecommunication systems with broadband noise-like sign
HIn with this regard article assesses the noise immunity of high-orbit satellite telecommunication systems with code division of addresses when using a number of broadband noise-like signals with linear frequency modulation as information carrier
Noncommutative Field Theories and (Super)String Field Theories
In this lecture notes we explain and discuss some ideas concerning
noncommutative geometry in general, as well as noncommutative field theories
and string field theories. We consider noncommutative quantum field theories
emphasizing an issue of their renormalizability and the UV/IR mixing. Sen's
conjectures on open string tachyon condensation and their application to the
D-brane physics have led to wide investigations of the covariant string field
theory proposed by Witten about 15 years ago. We review main ingredients of
cubic (super)string field theories using various formulations: functional,
operator, conformal and the half string formalisms. The main technical tools
that are used to study conjectured D-brane decay into closed string vacuum
through the tachyon condensation are presented. We describe also methods which
are used to study the cubic open string field theory around the tachyon vacuum:
construction of the sliver state, ``comma'' and matrix representations of
vertices.Comment: 160 pages, LaTeX, 29 EPS figures. Lectures given by I.Ya.Aref'eva at
the Swieca Summer School, Brazil, January 2001; Summer School in Modern
Mathematical Physics, Sokobanja, Yugoslavia, August 2001; Max Born Symposium,
Karpacz, Poland, September, 2001; Workshop "Noncommutative Geometry, Strings
and Renormalization", Leipzig, Germany, September 2001. Typos corrected,
references adde
Sub-wavelength imaging at optical frequencies using canalization regime
Imaging with sub-wavelength resolution using a lens formed by periodic
metal-dielectric layered structure is demonstrated. The lens operates in
canalization regime as a transmission device and it does not involve negative
refraction and amplification of evanescent modes. The thickness of the lens
have to be an integer number of half-wavelengths and can be made as large as
required for ceratin applications, in contrast to the other sub-wavelength
lenses formed by metallic slabs which have to be much smaller than the
wavelength. Resolution of at 600 nm wavelength is confirmed by
numerical simulation for a 300 nm thick structure formed by a periodic stack of
10 nm layers of glass with and 5 nm layers of metal-dielectric
composite with . Resolution of is predicted for a
structure with same thickness, period and operating frequency, but formed by
7.76 nm layers of silicon with and 7.24 nm layers of silver with
.Comment: 4 pages, 4 figures, submitted to PR
On homogenization of electromagnetic crystals formed by uniaxial resonant scatterers
Dispersion properties of electromagnetic crystals formed by small uniaxial
resonant scatterers (magnetic or electric) are studied using the local field
approach. The goal of the study is to determine the conditions under which the
homogenization of such crystals can be made. Therefore the consideration is
limited by the frequency region where the wavelength in the host medium is
larger than the lattice periods. It is demonstrated that together with known
restriction for the homogenization related with the large values of the
material parameters there is an additional restriction related with their small
absolute values. From the other hand, the homogenization becomes allowed in
both cases of large and small material parameters for special directions of
propagation. Two unusual effects inherent to the crystals under consideration
are revealed: flat isofrequency contour which allows subwavelength imaging
using canalization regime and birefringence of extraordinary modes which can be
used for beam splitting.Comment: 16 pages, 12 figures, submitted to PR
About signals allowing to provide sustainability to impacts of short-term and or focused on spectrum interference
It is proposed to use basic functions in the work in the work to combat short-term interference in comparison with signal duration. One of the function fragments can be calculated from the others. In its turn, one should use basic functions in order to combat narrow-band interference, some fragments of the Fourier spectra of which can be calculated from the other
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