10,716 research outputs found
Stability and collisions of moving semi-gap solitons in Bragg cross-gratings
We report results of a systematic study of one-dimensional four-wave moving
solitons in a recently proposed model of the Bragg cross-grating in planar
optical waveguides with the Kerr nonlinearity; the same model applies to a
fiber Bragg grating (BG) carrying two polarizations of light. We concentrate on
the case when the system's spectrum contains no true bandgap, but only
semi-gaps (which are gaps only with respect to one branch of the dispersion
relation), that nevertheless support soliton families. Solely zero-velocity
solitons were previously studied in this system, while current experiments
cannot generate solitons with the velocity smaller than half the maximum group
velocity. We find the semi-gaps for the moving solitons in an analytical form,
and demonstrated that they are completely filled with (numerically found)
solitons. Stability of the moving solitons is identified in direct simulations.
The stability region strongly depends on the frustration parameter, which
controls the difference of the present system from the usual model for the
single BG. A completely new situation is possible, when the velocity interval
for stable solitons is limited not only from above, but also from below.
Collisions between stable solitons may be both elastic and strongly inelastic.
Close to their instability border, the solitons collide elastically only if
their velocities c1 and c2 are small; however, collisions between more robust
solitons are elastic in a strip around c1=-c2.Comment: 16 pages, 7 figures, Physics Letters A, in pres
Adverse events following influenza immunization reported by healthcare personnel using active surveillance based on text messages
Studies have demonstrated that healthcare personnel (HCP) have concerns about the potential side effects of trivalent inactivate influenza vaccine (IIV3).1-3 A recent metaanalysis of reasons HCP refuse IIV3 indicates the strongest predictors of vaccine acceptance are belief that the vaccine is safe and belief the vaccine does not cause the disease it is meant to prevent.
Solitons in coupled Ablowitz-Ladik chains
A model of two coupled Ablowitz-Ladik (AL) lattices is introduced. While the
system as a whole is not integrable, it admits reduction to the integrable AL
model for symmetric states. Stability and evolution of symmetric solitons are
studied in detail analytically (by means of a variational approximation) and
numerically. It is found that there exists a finite interval of positive values
of the coupling constant in which the symmetric soliton is stable, provided
that its mass is below a threshold value. Evolution of the unstable symmetric
soliton is further studied by means of direct simulations. It is found that the
unstable soliton breaks up and decays into radiation, or splits into two
counter-propagating asymmetric solitons, or evolves into an asymmetric pulse,
depending on the coupling coefficient and the mass of the initial soliton.Comment: To appear in Phys. Lett.
Causal Bulk Viscous Dissipative Isotropic Cosmologies with Variable Gravitational and Cosmological Constants
We consider the evolution of a flat Friedmann-Robertson-Walker Universe,
filled with a causal bulk viscous cosmological fluid, in the presence of
variable gravitational and cosmological constants. The basic equation for the
Hubble parameter, generalizing the evolution equation in the case of constant
gravitational coupling and cosmological term, is derived, under the
supplementary assumption that the total energy of the Universe is conserved. By
assuming that the cosmological constant is proportional to the square of the
Hubble parameter and a power law dependence of the bulk viscosity coefficient,
temperature and relaxation time on the energy density of the cosmological
fluid, two classes of exact solutions of the field equations are obtained. In
the first class of solutions the Universe ends in an inflationary era, while in
the second class of solutions the expansion of the Universe is non-inflationary
for all times. In both models the cosmological "constant" is a decreasing
function of time, while the gravitational "constant" increases in the early
period of evolution of the Universe, tending in the large time limit to a
constant value.Comment: 14 pages, 15 figure
Biomarkers in acute coronary syndromes and their role in diabetic patients
Diabetic patients with acute coronary syndromes
are at high risk for cardiovascular complications
but risk stratification in these patients remains
challenging. Regularly, diabetic patients have a less typical
clinical presentation, which could lead to delayed
diagnosis and subsequent delayed initiation of treatment.
Since diabetic patients derive particular benefit
from aggressive anti-platelet therapy, early diagnostic
and therapeutic risk stratification of these patients is of
critical importance to improve their adverse outcome.
Although the electrocardiogram remains a pivotal
diagnostic tool in the evaluation of patients suspected of
having an acute coronary syndrome, only significant STsegment
changes provide reasonable prognostic information.
Therefore, repeated assessment of circulating
protein biomarkers represents a valuable diagnostic tool
for improving efficacy and safety of decision-making in
these patients. The combined use of biomarkers reflecting
distinct pathophysiological aspects, such as myocardial
necrosis, vascular inflammation, oxidative stress
and neurohumoral activation, may significantly improve
triage of patients with chest pain. These tools may identify
those patients that are at particularly high risk for
short-term and/or long-term cardiovascular events.
Eventually, tailored medical and interventional treatment
of diabetic patients should help to prevent these cardiac
events in a cost-effective manner
Slowdown and splitting of gap solitons in apodized Bragg gratings
We study the motion of gap solitons in two models of apodized nonlinear fiber
Bragg gratings (BGs), with the local reflectivity (LR) varying along the fiber.
A single step of LR, and a periodic array of alternating steps with opposite
signs (a "Bragg superstructure") are considered. A challenging possibility is
to slow down and eventually halt the soliton by passing it through the step of
increasing reflectivity, thus capturing a pulse of standing light. First, we
develop an analytical approach, assuming adiabatic evolution of the soliton,
and making use of the energy conservation and balance equation for the
momentum. Comparison with simulations shows that the analytical approximation
is quite accurate (unless the inhomogeneity is too steep): the soliton is
either transmitted across the step or bounces back. If the step is narrow,
systematic simulations demontrate that the soliton splits into transmitted and
reflected pulses (splitting of a BG soliton which hits a chirped grating was
observed in experiments). Moving through the periodic "superstructure", the
soliton accummulates distortion and suffers radiation loss if the structure is
composed of narrow steps. The soliton moves without any loss or irreversible
deformation through the array of sufficiently broad steps.Comment: to appear in a special issue on Wave-Optical Engineering, Journal of
Modern Optic
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