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Turitsyn S.K.,Aston University | Rubenchik A.M.,Lawrence Livermore National Laboratory | Fedoruk M.P.,Institute of Computational Technologies
Optics Letters | Year: 2010

The modulation instability (MI) in optical fiber amplifiers and lasers with anomalous dispersion leads to cw radiation breakup. This can be both a detrimental effect limiting the performance of amplifiers and an underlying physical mechanism in the operation of MI-based devices. Here we revisit the analytical theory of MI in fiber optical amplifiers. The results of the exact theory are compared with the previously used adiabatic approximation model, and the range of applicability of the latter is determined. © 2010 Optical Society of America.


Rubenchik A.M.,Lawrence Livermore National Laboratory | Turitsyn S.K.,Aston University | Fedoruk M.P.,Institute of Computational Technologies
Optics Express | Year: 2010

The modulation instability (MI) is one of the main factors responsible for the degradation of beam quality in high-power laser systems. The so-called B-integral restriction is commonly used as the criteria for MI control in passive optics devices. For amplifiers the adiabatic model, assuming locally the Bespalov-Talanov expression for MI growth, is commonly used to estimate the destructive impact of the instability. We present here the exact solution of MI development in amplifiers. We determine the parameters which control the effect of MI in amplifiers and calculate the MI growth rate as a function of those parameters. The safety range of operational parameters is presented. The results of the exact calculations are compared with the adiabatic model, and the range of validity of the latest is determined. We demonstrate that for practical situations the adiabatic approximation noticeably overestimates MI. The additional margin of laser system design is quantified. © 2010 Optical Society of America.


Bednyakova A.E.,Novosibirsk State University | Fedoruk M.P.,Institute of Computational Technologies | Kurkov A.S.,RAS A.M. Prokhorov General Physics Institute | Sholokhov E.M.,RAS A.M. Prokhorov General Physics Institute | Turitsyn S.K.,Aston University
Laser Physics | Year: 2011

A Raman converter based on an active fiber with variable mode structure is experimentally and theoretically studied. It is demonstrated that a conventional telecommunication fiber with variable mode structure can be used to construct Raman converters © Pleiades Publishing, Ltd., 2011.


Liseykina T.V.,University of Rostock | Liseykina T.V.,Institute of Computational Technologies | Dudnikova G.I.,Institute of Computational Technologies | Vshivkov V.A.,Institute of Computational Mathematics and Mathematical Geophysics | Malkov M.A.,University of California at San Diego
Journal of Plasma Physics | Year: 2015

Non-relativistic collisionless shock waves are widespread in space and astrophysical plasmas and are known as efficient particle accelerators. However, our understanding of collisionless shocks, including their structure and the mechanisms whereby they accelerate particles, remains incomplete. We present here the results of numerical modelling of an ion-acoustic collisionless shock based on the one-dimensional kinetic approximation for both electrons and ions with a real mass ratio. Special emphasis is paid to the shock-reflected ions as the main driver of shock dissipation. The reflection efficiency, the velocity distribution of reflected particles and the shock electrostatic structure are studied in terms of the shock parameters. Applications to particle acceleration in geophysical and astrophysical shocks are discussed. © 2015 Cambridge University Press.


Shary S.P.,Institute of Computational Technologies
Journal of Global Optimization | Year: 2015

The work is devoted to application of global optimization in data fitting problem under interval uncertainty. Parameters of the linear function that best fits intervally defined data are taken as the maximum point for a special (“recognizing”) functional which is shown to characterize consistency between the data and parameters. The new data fitting technique is therefore called “maximum consistency method”. We investigate properties of the recognizing functional and present interpretation of the parameter estimates produced by the maximum consistency method. © 2015 Springer Science+Business Media New York


Shary S.P.,Institute of Computational Technologies
Studies in Computational Intelligence | Year: 2014

The work advances a new class of global optimization methods, called graph subdivision methods, that are based on simultaneous adaptive subdivision of both the function's domain of definition and the range of values. An application to interval linear systems is given. © 2014 Springer International Publishing Switzerland.


Sharaya I.A.,Institute of Computational Technologies | Shary S.P.,Institute of Computational Technologies
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

The paper considers the interval linear inclusion Cx ⊆ d in the Kaucher interval arithmetic. We introduce a quantitative measure of its fulfillment, called “reserve”, and investigate its properties and application. We show that the reserve proves useful in the study of AE-solutions and quantifier solutions to interval linear problems. In particular, using the reserve can help to recognize position of a point with respect to the solution set, emptiness of the solution set and of its interior, etc. © Springer International Publishing Switzerland 2016.


Medvedev S.,Institute of Computational Technologies | Zeitlin V.,Ecole Normale Superieure de Paris
IUTAM Bookseries | Year: 2010

We revisit the well-known analogy between the effects of stratification and rotation in hydrodynamics, and between both and the external magnetic field in magnetohydrodynamics. After sketching the similarities among models in what concerns linear and nonlinear stationary waves, we show that the Hamiltonian structure of the 2D versions of the models is the same, and use this fact to 1) find a canonical (skew-diagonal) form of the Hamiltonian equations, and 2) to treat in a unified manner the problem of weak turbulence of, respectively, internal gravity, gyroscopic, and Alfvén waves in scale-invariant limits. We thus find stationary energy spectra in the long- and short-wave limits for all three types of waves. © 2010 Springer Science+Business Media B.V.


Kovenya V.M.,Institute of Computational Technologies | Kudryashov A.S.,Novosibirsk State University
Journal of Applied and Industrial Mathematics | Year: 2016

Some implicit difference scheme of approximate factorization is proposed for numerical solution of the Navier–Stokes equations for an incompressible liquid in curvilinear coordinates. Testing of the algorithm is carried out on the solution of the problems concerning the Couette and Poiseuille flows; and the results are presented of numerical simulation of a flow between the rotating cylinders with covers. © 2016, Pleiades Publishing, Ltd.


Sharaya I.A.,Institute of Computational Technologies | Shary S.P.,Institute of Computational Technologies
Reliable Computing | Year: 2011

We develop a technique for computing tolerable solution set for interval linear systems with convex polyhedral ties upon its coefficients. The tolerable solution set in the above problem is proved to be the intersection of finite number of hyperstripes, i.e. a solution set to a finite system of two-sided nonstrict linear inequalities. For some specific ties on the coefficients, we propose simplified variants of the general method.

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