416 research outputs found
Stable multiple-charged localized optical vortices in cubic-quintic nonlinear media
The stability of two-dimensional bright vortex solitons in a media with
focusing cubic and defocusing quintic nonlinearities is investigated
analytically and numerically. It is proved that above some critical beam powers
not only one- and two-charged but also multiple-charged stable vortex solitons
do exist. A vortex soliton occurs robust with respect to symmetry-breaking
modulational instability in the self-defocusing regime provided that its radial
profile becomes flattened, so that a self-trapped wave beam gets a pronounced
surface. It is demonstrated that the dynamics of a slightly perturbed stable
vortex soliton resembles an oscillation of a liquid stream having a surface
tension. Using the idea of sustaining effective surface tension for spatial
vortex soliton in a media with competing nonlinearities the explanation of a
suppression of the modulational instability is proposed.Comment: 4 pages, 3 figures. Submitted to Journal of Optics A. The proceedings
of the workshop NATO ARW, Kiev 2003 Singular Optics 200
Gap solitons in a model of a hollow optical fiber
We introduce a models for two coupled waves propagating in a hollow-core
fiber: a linear dispersionless core mode, and a dispersive nonlinear
quasi-surface one. The linear coupling between them may open a bandgap, through
the mechanism of the avoidance of crossing between dispersion curves. The
third-order dispersion of the quasi-surface mode is necessary for the existence
of the gap. Numerical investigation reveals that the entire bandgap is filled
with solitons, and they all are stable in direct simulations. The gap-soliton
(GS) family is extended to include pulses moving relative to the given
reference frame, up to limit values of the corresponding boost ,
beyond which the solitons do not exists. The limit values are nonsymmetric for
and . The extended gap is also entirely filled with the
GSs, all of which are stable in simulations. Recently observed solitons in
hollow-core photonic-crystal fibers may belong to this GS family.Comment: 5 pages, 5 figure
Manipulations with early mouse embryos for generation of genetically modified animals
Recently, genome-editing technologies have become more efficient and accessible. The discovery of nucleases for directional genome editing (CRISPR/Cas9, TALEN, ZFNs) significantly accelerated and simplified the production of mice with targeted gene editing in the genome. Until last time, the CRISPR/Cas9 system noticeably simplified the preparation of knockout or transgenic mice. CRISPR/Cas9 technology was successfully applied for gene knockout and knock-in, generation of large deletions or directed insertions in targeted genome regions in embryonic stem cells (ESCs).When injected into blastocysts, such modified ESCs are able to generate chimeras producing gametes with an identical genotype with ESC. Thus, it can identify animals with modified genomes. More recently, CRISPR/Cas9 technology was successfully applied to mouse zygotes and the birth of genetic modified mice was observed, i. e., the time required for generating genome-modified animals decreased significantly. The CRISPR/Cas9 system allows making gene knockout, large deletions or directed insertions into the target region of the genome by cytoplasm or pronuclear microinjection into zygotes. In addition, this is faster and simpler than similar work with mouse ESCs. Meanwhile, methods of manipulation with early embryos and their transplantation to surrogate mothers may be somewhat tricky. Therefore, it is important to use modern technologies for directional genome editing and perfect mastery in the embryological technics. In this article, we describe the protocols of microinjection into the pronucleus or cytoplasm of zygotes and injection of embryonic stem cells into the blastocyst cavity. We also describe embryological methods, such as superovulation, preparation of early stage embryos, surgical operation, production of foster mice. In addition, we describe the assembly and necessary components for the isoflurane anesthetic apparatus and isoflurane anesthesia
Modulational instability of solitary waves in non-degenerate three-wave mixing: The role of phase symmetries
We show how the analytical approach of Zakharov and Rubenchik [Sov. Phys.
JETP {\bf 38}, 494 (1974)] to modulational instability (MI) of solitary waves
in the nonlinear Schr\"oedinger equation (NLS) can be generalised for models
with two phase symmetries. MI of three-wave parametric spatial solitons due to
group velocity dispersion (GVD) is investigated as a typical example of such
models. We reveal a new branch of neck instability, which dominates the usual
snake type MI found for normal GVD. The resultant nonlinear evolution is
thereby qualitatively different from cases with only a single phase symmetry.Comment: 4 pages with figure
Observation of bright polariton solitons in a semiconductor microcavity
Microcavity polaritons are composite half-light half-matter quasi-particles,
which have recently been demonstrated to exhibit rich physical properties, such
as non-equilibrium Bose-Einstein condensation, parametric scattering and
superfluidity. At the same time, polaritons have some important advantages over
photons for information processing applications, since their excitonic
component leads to weaker diffraction and stronger inter-particle interactions,
implying, respectively, tighter localization and lower powers for nonlinear
functionality. Here we present the first experimental observations of bright
polariton solitons in a strongly coupled semiconductor microcavity. The
polariton solitons are shown to be non-diffracting high density wavepackets,
that are strongly localised in real space with a corresponding broad spectrum
in momentum space. Unlike solitons known in other matter-wave systems such as
Bose condensed ultracold atomic gases, they are non-equilibrium and rely on a
balance between losses and external pumping. Microcavity polariton solitons are
excited on picosecond timescales, and thus have significant benefits for
ultrafast switching and transfer of information over their light only
counterparts, semiconductor cavity lasers (VCSELs), which have only nanosecond
response time
Critical sound attenuation in a diluted Ising system
The field-theoretic description of dynamical critical effects of the
influence of disorder on acoustic anomalies near the temperature of the
second-order phase transition is considered for three-dimensional Ising-like
systems. Calculations of the sound attenuation in pure and dilute Ising-like
systems near the critical point are presented. The dynamical scaling function
for the critical attenuation coefficient is calculated. The influence of
quenched disorder on the asymptotic behaviour of the critical ultrasonic
anomalies is discussed.Comment: 12 RevTeX pages, 4 figure
A molecular assembly system for presentation of antigens on the surface of HBc virus-like particles
AbstractHepatitis B virus-like particles, icosahedral structures formed by multiple core protein dimers, are promising immune-enhancing vaccine carriers for foreign antigens. Insertions into the surface-exposed immunodominant loop are especially immunogenic. However, the need to conserve the particulate structure to ensure high immunogenicity imposes restraints on the nature of the heterologous sequence that can be inserted. We propose a new approach to constructing HBc particles linked to the target epitopes that relies on non-covalent interactions between the epitope and pre-assembled unmodified HBc particles. Interaction was enabled by fusion of the epitope to the GSLLGRMKGA peptide, binding to the spike tips. This peptide may be used as a “binding tag” allowing in vitro construction of HBc particles carrying the target peptide. Such virus-like particles carrying multiple copies of the extracellular domain of the M2 protein of different influenza strains appeared to be highly immunogenic and protected immunised mice against a lethal influenza challenge
Pulse area theorem in a single mode waveguide and its application to photon echo and optical memory in Tm3+:Y3Al5O12
We derive the area theorem for light pulses interacting with inhomogeneously
broadened ensemble of two-level atoms in a single-mode optical waveguide and
present its analytical solution for Gaussian-type modes, which demonstrates the
significant difference from the formation of pulses by plane waves. We
generalize this theorem to the description of photon echo and apply it to the
two-pulse (primary) echo and the revival of silenced echo (ROSE) protocol of
photon echo quantum memory. For the first time, we implemented ROSE protocol in
a single-mode laser-written waveguide made of an optically thin crystal
. The experimental data obtained are satisfactorily
explained by the developed theory. Finally, we discuss the obtained
experimental results and possible applications of the derived pulse area
approach
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