609 research outputs found
Dynamics of subpicosecond dispersion-managed soliton in a fibre: A perturbative analysis
A model is studied which describes a propagation of a subpicosecond optical
pulse in dispersion-managed fibre links. In the limit of weak chromatic
dispersion management, the model equation is reduced to a perturbed modified
NLS equation having a nonlinearity dispersion term. By means of the
Riemann--Hilbert problem, a perturbation theory for the soliton of the modified
NLS equation is developed. It is shown in the adiabatic approximation that
there exists a unique possibility to suppress the perturbation-induced shift of
the soliton centre at the cost of proper matching of the soliton width and
nonlinearity dispersion parameter. In the next-order approximation, the
spectral density of the radiation power emitted by a soliton is calculated.Comment: 16 pages, 3 figures, to appear in J. Mod. Optic
Optical Fibers Based on Modified Silver Halide Crystals for Nuclear Power
We investigated the possibility of the deployment of AgBr – TlBr0.46I0.54MIR fibers in high ionizing radiation environment. For this purpose, we exposed plate samples made of AgBr – TlBr0.46I0.54crystals to β-ionizing radiation at a dose of 100 kGy. We revealed the radiation-induced translucence effect for these materials and assumed its nature. As the investigation showed the suitability of the fibers for the application in high ionizing radiation environment, the authors propose to use these fibers jointly with FTIR spectrometers for the online monitoring of various chemical processes at the nuclear power plants.
Keywords: modified silver halides, MIR fibers, FTIR spectroscopy, ionizing radiation resistanc
Hamiltonian formalism and the Garrett-Munk spectrum of internal waves in the ocean
Wave turbulence formalism for long internal waves in a stratified fluid is
developed, based on a natural Hamiltonian description. A kinetic equation
appropriate for the description of spectral energy transfer is derived, and its
self-similar stationary solution corresponding to a direct cascade of energy
toward the short scales is found. This solution is very close to the high
wavenumber limit of the Garrett-Munk spectrum of long internal waves in the
ocean. In fact, a small modification of the Garrett-Munk formalism includes a
spectrum consistent with the one predicted by wave turbulence.Comment: 4 pages latex fil
Does nitrate reductase play a key role in photoinduction of carotenoid synthesis in Neurospora crassa?
Does nitrate reductase play a key role in photoinduction of caroteniod synthesis in Neurospora crassa
Modeling Kelvin wave cascades in superfluid helium
We study two different types of simplified models for Kelvin wave turbulence on quantized vortex lines in superfluids near zero temperature. Our first model is obtained from a truncated expansion of the Local Induction Approximation (Truncated-LIA) and it is shown to possess the same scalings and the essential behaviour as the full Biot-Savart model, being much simpler than the later and, therefore, more amenable to theoretical and numerical investigations. The Truncated-LIA model supports six-wave interactions and dual cascades, which are clearly demonstrated via the direct numerical simulation of this model in the present paper. In particular, our simulations confirm presence of the weak turbulence regime and the theoretically predicted spectra for the direct energy cascade and the inverse wave action cascade. The second type of model we study, the Differential Approximation Model (DAM), takes a further drastic simplification by assuming locality of interactions in k-space via using a differential closure that preserves the main scalings of the Kelvin wave dynamics. DAMs are even more amenable to study and they form a useful tool by providing simple analytical solutions in the cases when extra physical effects are present, e.g. forcing by reconnections, friction dissipation and phonon radiation. We study these models numerically and test their theoretical predictions, in particular the formation of the stationary spectra, and closeness of numerics for the higher-order DAM to the analytical predictions for the lower-order DAM
Energy spectra of the ocean's internal wave field: theory and observations
The high-frequency limit of the Garrett and Munk spectrum of internal waves
in the ocean and the observed deviations from it are shown to form a pattern
consistent with the predictions of wave turbulence theory. In particular, the
high frequency limit of the Garrett and Munk spectrum constitutes an {\it
exact} steady state solution of the corresponding kinetic equation.Comment: 4 pages, one color figur
Gold nanoparticles formation in solid polyelectrolyte: The catalytic effect of halloysite nanotubes
© Copyright 2017 American Scientific Publishers All rights reserved.Clay nanotubes are kaolinite rolled-up sheets, discovered few years ago and, up to now, mainly exploited as carriers for drug delivery. Although available in tons, biocompatible and nontoxic, they remain sophisticated and novel natural nanomaterials. The possibility to mix them with polymers, both polar and not, opens many functional biocomposites developments. In this paper we report a novel property of this interesting material: a catalytic effect of gold dissolution when added to a polyethylene oxide gel doped with a lithium salt. We proved that the resulting material, placed between two gold electrodes, has anisotropic features and, more interestingly, over a certain voltage threshold, can speed up the formation of gold nanoparticles coming out from the gold electrodes. Fitting the electrical measurements we also have found that gold nanoparticles contribute to the total current flow and this effect can be described by adding an intercept in the function of the current trend
Vortical and Wave Modes in 3D Rotating Stratified Flows: Random Large Scale Forcing
Utilizing an eigenfunction decomposition, we study the growth and spectra of
energy in the vortical and wave modes of a 3D rotating stratified fluid as a
function of . Working in regimes characterized by moderate
Burger numbers, i.e. or , our results
indicate profound change in the character of vortical and wave mode
interactions with respect to . As with the reference state of
, for the wave mode energy saturates quite quickly
and the ensuing forward cascade continues to act as an efficient means of
dissipating ageostrophic energy. Further, these saturated spectra steepen as
decreases: we see a shift from to scaling for
(where and are the forcing and dissipation scales,
respectively). On the other hand, when the wave mode energy
never saturates and comes to dominate the total energy in the system. In fact,
in a sense the wave modes behave in an asymmetric manner about .
With regard to the vortical modes, for , the signatures of 3D
quasigeostrophy are clearly evident. Specifically, we see a scaling
for and, in accord with an inverse transfer of energy, the
vortical mode energy never saturates but rather increases for all . In
contrast, for and increasing, the vortical modes contain a
progressively smaller fraction of the total energy indicating that the 3D
quasigeostrophic subsystem plays an energetically smaller role in the overall
dynamics.Comment: 18 pages, 6 figs. (abbreviated abstract
Investigating the light stability of solid-solution-based AgCl-AgBr and AgBr-TlI crystals
For the development of mid-infrared fiber-optical elements, one needs light-stable, flexible materials that are transparent within this spectral band. Solid solutions of silver and monadic thallium halides prove to be the most suitable crystalline media for these needs. We study the light stability variation of high-purity AgCl1-xBrx(0 ≤ x ≤ 1) and Ag1-xTlxBr1-xIx (0 ≤ x ≤ 0.05) crystals by measuring the optical transmission change as functions of the composition and UV exposure time. The former is executed in a broad spectral range from 6500 - 350 cm-1, within which we choose three wavelengths to trace the transmission change. For thalliummonoiodide-containing samples, an effect is observed that we assumed to be translucence. © 2016 Chinese Optics Letters
- …