383 research outputs found
Nonlinear waves of polarization in two-component Bose-Einstein condensates
Waves with different symmetries exist in two-component Bose-Einstein
condensates (BECs) whose dynamics is described by a system of coupled
Gross-Pitaevskii (GP) equations. A first type of waves corresponds to
excitations for which the motion of both components is locally in phase. In the
second type of waves the two components have a counter-phase local motion. In
the case of different values of inter- and intra-component interaction
constants, the long wave-length behavior of these two modes corresponds to two
types of sound with different velocities. In the limit of weak nonlinearity and
small dispersion the first mode is described by the well-known Korteweg-de
Vries (KdV) equation. We show that in the same limit the second mode can be
described by the Gardner (modified KdV) equation, if the intra-component
interaction constants have close enough values. This leads to a rich
phenomenology of nonlinear excitations (solitons, kinks, algebraic solitons,
breathers) which does not exist in the KdV description.Comment: 10 pages, 5 figure
Stable one-dimensional periodic waves in Kerr-type saturable and quadratic nonlinear media
We review the latest progress and properties of the families of bright and
dark one-dimensional periodic waves propagating in saturable Kerr-type and
quadratic nonlinear media. We show how saturation of the nonlinear response
results in appearance of stability (instability) bands in focusing (defocusing)
medium, which is in sharp contrast with the properties of periodic waves in
Kerr media. One of the key results discovered is the stabilization of
multicolor periodic waves in quadratic media. In particular, dark-type waves
are shown to be metastable, while bright-type waves are completely stable in a
broad range of energy flows and material parameters. This yields the first
known example of completely stable periodic wave patterns propagating in
conservative uniform media supporting bright solitons. Such results open the
way to the experimental observation of the corresponding self-sustained
periodic wave patterns.Comment: 29 pages, 10 figure
Stabilization of dipole solitons in nonlocal nonlinear media
We address the stabilization of dipole solitons in nonlocal nonlinear
materials by two different approaches. First, we study the properties of such
solitons in thermal nonlinear media, where the refractive index landscapes
induced by laser beams strongly depend on the boundary conditions and on the
sample geometry. We show how the sample geometry impacts the stability of
higher-order solitons in thermal nonlinear media and reveal that dipole
solitons can be made dynami-cally stable in rectangular geometries in contrast
to their counterparts in thermal samples with square cross-section. Second, we
discuss the impact of the saturation of the nonlocal nonlinear response on the
properties of multipole solitons. We find that the saturable response also
stabi-lizes dipole solitons even in symmetric geometries, provided that the
input power exceeds a criti-cal value.Comment: 29 pages, 8 figures, to appear in Phys. Rev.
Vortex soliton tori with multiple nested phase singularities in dissipative media
We show the existence of stable two- and three-dimensional vortex solitons
carrying multiple, spatially separated, single-charge topological dislocations
nested around a vortex-ring core. Such new nonlinear states are supported by
elliptical gain landscapes in focusing nonlinear media with two-photon
absorption. The separation between the phase dislocations is dictated mostly by
the geometry of gain landscape and it only slightly changes upon variation of
the gain or absorption strength.Comment: 17 pages, 5 figures, to appear in Physical Review
Nonlinear photonic lattices in anisotropic nonlocal self-focusing media
We analyze theoretically and generate experimentally two-dimensional
nonlinear periodic lattices in a photorefractive medium. We demonstrate that
the light-induced periodically modulated nonlinear refractive index is highly
anisotropic and nonlocal, and it depends on the lattice orientation relative to
the crystal axis. We discuss stability of such induced photonic structures and
their guiding properties.Comment: 3 pages, 3 figure
Nonlinear optics and light localization in periodic photonic lattices
We review the recent developments in the field of photonic lattices
emphasizing their unique properties for controlling linear and nonlinear
propagation of light. We draw some important links between optical lattices and
photonic crystals pointing towards practical applications in optical
communications and computing, beam shaping, and bio-sensing.Comment: to appear in Journal of Nonlinear Optical Physics & Materials (JNOPM
Компьютерная программа дистанционного образования в непрерывной подготовке врача лучевой диагностики
This article highlights the need for a programming product for distant education and online testing of medical students, postgraduates or practicing doctors. The structure of such product is thoroughly described both from client and server sides as well as the required functionality for professors and students.Обсуждается программный продукт для дистанционного обучения и онлайн-тестирование по лучевой диагностике студентов, аспирантов и практикующих врачей. Состав такого продукта рассмотрен как с клиентской, так и серверной сторон также как и необходимая функциональность для преподавателей и студентов
Laminated Wave Turbulence: Generic Algorithms II
The model of laminated wave turbulence puts forth a novel computational
problem - construction of fast algorithms for finding exact solutions of
Diophantine equations in integers of order and more. The equations to
be solved in integers are resonant conditions for nonlinearly interacting waves
and their form is defined by the wave dispersion. It is established that for
the most common dispersion as an arbitrary function of a wave-vector length two
different generic algorithms are necessary: (1) one-class-case algorithm for
waves interacting through scales, and (2) two-class-case algorithm for waves
interacting through phases. In our previous paper we described the
one-class-case generic algorithm and in our present paper we present the
two-class-case generic algorithm.Comment: to appear in J. "Communications in Computational Physics" (2006
Single-shot nanosecond-resolution multiframe passive imaging by multiplexed structured image capture
The Multiplexed Structured Image Capture (MUSIC) technique is used to demonstrate single-shot multiframe passive imaging, with a nanosecond difference between the resulting images. This technique uses modulation of light from a scene before imaging, in order to encode the target’s temporal evolution into spatial frequency shifts, each of which corresponds to a unique time and results in individual and distinct snapshots. The resulting images correspond to different effective imaging gate times, because of the optical path delays. Computer processing of the multiplexed single-shot image recovers the nanosecond-resolution evolution. The MUSIC technique is used to demonstrate imaging of a laser-induced plasma. Simultaneous single-shot measurements of electron numbers by coherent microwave scattering were obtained and showed good agreement with MUSIC characterization. The MUSIC technique demonstrates spatial modulation of images used for passive imaging. This allows multiple frames to be stacked into a single image. This method could also pave the way for real-time imaging and characterization of ultrafast processes and visualization, as well as general tracking of fast objects
Soliton topology versus discrete symmetry in optical lattices
We address the existence of vortex solitons supported by azimuthally
modulated lattices and reveal how the global lattice discrete symmetry has
fundamental implications on the possible topological charges of solitons. We
set a general ``charge rule'' using group-theory techniques, which holds for
all lattices belonging to a given symmetry group. Focusing in the case of
Bessel lattices allows us to derive also a overall stability rule for the
allowed vortex solitons.Comment: 4 pages, 3 figures. To appear in Phys. Rev. Let
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