Soliton dynamics in a two-level medium with pumping

A perturbation theory is developed for a system of evolution equations close to integrable systems in the method of inverse scattering with a spectral parameter depending on variables. This theory is used for analyzing the evolution features for soliton light pulses in a two-level medium with the upper level pumping taking into account linear and nonlinear losses as well as dispersion. Various modes of soliton evolution (including the random mode) in such a system are investigated numerically. It is shown that anomalies in the dependence of soliton parameters on the length of the laser medium appear in the presence of nonuniform broadening in the case when the upper level pumping rate and inverse population losses are functions of detuning. The contribution from the radiative component of the solution is also analyzed taking into account perturbations; it is shown that this contribution can be disregarded in a certain range of parameters.     

Dynamics of solitons in periodic systems with different nonlinear media

To analyze pulse dynamics in an optical system consisting of a periodic sequence of nonlinear media, a composite model is used. It includes a model of the resonance interaction of an ultrashort light pulse with the energy transition of the medium with allowance made for an upper level pump and an almost integrable model that describes the propagation of the light field in the other medium with a cubic nonlinearity and dispersion. Additional allowance is made for losses and other kinds of interaction by introducing perturbation terms. On the bases of the inverse scattering transform and perturbation theory, a simple method for analyzing specific features of soliton evolution in periodic systems of this kind is developed. It is used to describe various modes of soliton evolution in such a system, including chaotic dynamics.     

Control of excitons in a bent bunch of molecular aggregates by dipole–dipole interaction with quantum dots

The nonlocal dipole–dipole interaction is studied between excitations in chromophores forming a bunch or a tube of J-aggregates and closely spaced quantum dots (QDs). Equations describing the evolution of exciton pulses in a quasi-one-dimensional medium are derived taking into account the interaction with the transition resonant to nanoparticles. It is shown that the efficient controllable resonance energy transfer can occur in the system between QDs and an exciton pulse. The efficiency of this process significantly increases if the bunch of aggregates is deformed to bend nanoparticles round. It is shown that the interaction of permanent dipole moments of QDs and chromophores leads to the formation of a potential barrier or a well. It is found that the combined influence of these factors can be used to efficiently control the dynamics of pulses in aggregates.     

Electrochemical and Mass Transport Characteristics of the Strongly Basic MA-41 Membrane Modified by Poly-N,N-Diallylmorpholinium

Russian Journal of Electrochemistry - Poly-N,N-diallylmorpholinium bromide is synthesized and characterized using the methods of IR and NMR spectroscopy. The surface modification of MA-41...     

Mass transfer mechanism and chemical stability of strongly basic anion-exchange membranes under overlimiting current conditions

The dynamics of changes in overall and partial voltammetric characteristics with respect to chloride and hydroxide ions is studied by the method of rotating membrane disk (RMD) under the conditions of stabilized diffusion layer thickness for the original strongly basic MA-41P and homogeneous AMX membranes and also for the modified heterogeneous MA-41P-M membrane at high current densities. For unmodified anion-exchange membranes at currents exceeding the limiting value, the hydrolysis of fixed ammonium bases produces secondary and ternary amino groups which are catalytically active in the reaction of water molecule dissociation. The hydrolysis of amino groups in the membrane surface layer is the mechanism of degradation of electrochemical characteristics of strongly basic membranes. This results in the increase of transport numbers with respect to hydroxide ions and weakening of mass transfer with respect to salt ions. For the surface-modified heterogeneous anion-exchange membranes, no degradation of electrochemical characteristics is observed. The characteristics of the surface-modified MA-41P-M membrane remain stable: after long-term operation of the energized membrane, the partial currents with respect to hydroxide ions are close to zero and the mass transfer with respect to salt ions is considerably intensified. The dependences of the thickness of the hydrolyzed layer of a strongly basic anion-exchange membrane on the time of its exposure to solutions of high pH are determined. An original method is developed for determination of the hydrolyzed layer thickness for strongly-basic anion-exchange membranes, which is based on the copper ability to form stable complex compounds with weakly basic amino groups of anion-exchange membranes.     

Superradiant properties of a suspension of composite nanoparticles

The characteristics of gold nanoparticles coated with silicon dioxide containing embedded dye molecules are experimentally investigated at room and liquid-nitrogen temperatures. The origin of the observed narrowing of the luminescence line upon cooling is discussed. Model analysis of the nanosystem under study indicates that the observed behavior cannot be related to the temperature dependence of individual parameters of the components of the medium. The effect is explained by the occurrence of nonlinear feedback that leads to the enhancement of phase synchronization between the polarizations of the active transitions in the dye molecules and plasmons. This effect is an analog of plasmon polariton superradiance.     

Solvation of lithium chloride in aqueous and mixed solutions of an aprotic solvent

The dynamic hydration and solvation numbers of lithium chloride are estimated on the basis of experimental data on the limiting electrodialysis concentration of an electrolyte from aqueous and aqueousorganic solutions containing aprotic solvent N,N-dimethylacetamide. It is established that the dependence of the hydration numbers of the salt on the volume fraction of the aprotic solvent is of an extreme character, and its solvation number on N,N-dimethylacetamide does not depend on the composition of the mixed solution.     

Role of nonlinear refraction in the generation of terahertz field pulses by light fields

The generation of microwave (terahertz) pulses without any envelope in a four-level quasi-resonant medium is considered. Two intense quasi-monochromatic laser fields lead to a partial upper-level population. Microwave field pulses cause the transition between these levels. For appropriately chosen scales, the evolution of the fields is shown to be described by the pseudo-spin evolution equations in a microwave field with the inclusion of nonlinear refraction caused by an adiabatic upper-level population. The evolution of terahertz field pulses is described outside the scope of the slow-envelope approximation. When a number of standard approximations are taken into account, this system of equations is shown to be equivalent to an integrable version of the generalized reduced Maxwell-Bloch equations or to the generalized three-wave mixing equations. The soliton solution found by the inverse scattering transform method is used as an example to show that nonlinear refraction leads to a strong compression of the microwave (terahertz) field soliton.     

Strongly regular growth of entire functions of order zero

For entire functions of order zero we introduce a new concept of regularity of growth, which is shown to possess properties similar to those which characterize the concept of totally regular growth of entire functions of finite order in the sense of Levin-Pflüger. Translated fromMatematicheskie Zameiki, Vol. 63, No. 2, pp. 196–208, February, 1998. This research was partially supported by the International Science Foundation under grant No. UCR000.