Biomedical subjects

M Gorkunov

Publications and source records attributed to M Gorkunov.

5 recordsLinked to original sources

PubMed2005

Regimes of feedback-controlled beam coupling.

The introduction of certain electronic feedback loops into photorefractive wave-coupling schemes makes them noise free and leads to dramatic changes of the whole nonlinear behavior. The familiar steady states can be transformed into periodic states that are characterized by ultimately high and low values of the diffraction efficiency eta of the recorded index grating or into quasisteady states with small values of eta. These transformations possess thresholds with respect to controllable experimental parameters like the coupling strength and the input intensity ratio. We present a general analysis of the threshold behavior for different modes of the feedback operation and different types of the nonlinear photorefractive response. The results obtained (analytical and numerical) allow one to predict the regions of stability for feedback-controlled steady states and the observable characteristics of the system, including the output amplitudes and diffraction efficiency of the spatial grating, beyond these regions. They extend strongly the potentialities of the feedback-controlled wave coupling.

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PubMed2004

Three-wave coupling of microwaves in metamaterial with nonlinear resonant conductive elements.

We consider a metamaterial possessing nonlinear magnetic response owing to nonlinear electronic components inserted into resonant conductive elements. We imply that the insertions operate in an essentially nonlinear regime, so that a nonlinear magnetic susceptibility cannot be introduced and separate analysis is required for different nonlinear processes. Here we develop an approach for analyzing three-wave coupling processes with a strong pump wave and two weak signals. We discuss the peculiarities of coupling arising from use of insertions with variable resistance or variable capacitance. We estimate that extremely strong nonlinear coupling can be achieved using typical diodes reported in the literature.

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PubMed2003

Origin of stretched exponential relaxation for hopping-transport models.

We propose a novel geometric approach to the description of the relaxation phenomena in complex condensed-matter systems. It is shown within a fairly general random site hopping model that the stretched exponential decay law, exp([-(t/tau)(beta)], originates from the simple and general geometric features of a random distribution of transport and trapping sites in the 3D space. The value of the variable stretching index beta is determined by the localization radius of hopping electrons. The possibilities for generalization of the obtained results and interpretation of the relevant experimental data are discussed.

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PubMed2003

Nonlinearity of a metamaterial arising from diode insertions into resonant conductive elements.

We consider a possibility to create a metamaterial with nonlinear magnetic response in the microwave frequency range. Such a metamaterial is a regular periodic three-dimensional-array of resonant conductive elements with diodes as nonlinear insertions. We calculate the arising quadratic nonlinear susceptibility and show how it is controlled by the properties and arrangement of the structure elements as well as by the type and characteristics of the diode. We discuss the requirements for the diode necessary to optimize the nonlinear response of the proposed metamaterial.

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PubMed2002

Surface effects in thin films of antiferroelectric smectic liquid crystals in terms of the short-pitch long-pitch competition model.

A theoretical model based on the competition between short-pitch and long-pitch types of helical order is developed for thin films of antiferroelectric smectic liquid crystals. In the case of the "bookshelf" structure of the film and non-polar surfaces, subsurface perturbations of the ordering are found out analytically. Corresponding contributions to the free energies of the different phases are analysed. The possibility of sufficient influence of the boundaries on phase sequences is predicted even in the case of weak surface anchoring. A consistent explanation of the controversial experimental information is given; further ways of experimental justification of the model assumptions are discussed.

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