Alexander S. Kovalev, Leading Researcher.

Tel. +38 (0572) 340 21 05.

Was born in Ulan–Ude (USSR) in 1945.
Graduated from Kharkov State University in1967.
PhD Phys & Math, Kharkov State University, 1975. DrS Phys&Math, ILTPE NANU,1989.Professor degrees in Theoretical physics in ILTPE, 2001. Now is the Leading Researcher in ILTPE (theoretical department) and the professor in Kharkov National University (E.M.Lifshits theoretical physics department). Area of expertise is the nonlinear waves and soliton dynamics of magnetically ordered and elastic media, nonlinear phenomena in dynamical systems, mathematical aspects of nonlinear mechanics. Is the author and co-author of 2 monographs, 3 reviews and 180 articles. Lecturer activity: lecturing on theoretical mechanics and nonlinear physics at Kharkov National University. Foreign activity: scientific visitor in universities of Regensburg, Bayreuth (Germany), Paris (France), Canberra (Australia), Birmingham (UK) and Linchoping (Sweden) during the years 1994-2004. Scientific adviser of 6 PhDs. Avards: Ukrainian A.S.Davydov award in theoretical physics (2006), Letter of commendation from Ukrainian parliament (2010) and Ukrainian State award (2012).

Main current research interests: theory of nonlinear structures and waves in solid state.

(I) Investigation of nonlinear surface waves during last years includes studying of nonlinear surface shear waves (It was demonstrated the importance of a spatial dispersion of elastic media and criteria of stability for NSSW and surface shear solitons were formulated); the SSS were studied as a general problem of 2D and 3D solitons in media with acoustic spectrum and the special asyptotical procedures for them were proposed; the different surface Rayleigh solitons with a stationary profile were investigated near perfect surface and surface covered with thin film or monolayer. In the last cases the nonlinear non-local ID evolution equations were derived and their unusual soliton solutions were obtained. Recently some special problems for nonlinear elastic surface waves were investigated: propagation of envelope SRS, properties of "gap" SRS near the corrugated surface, propagation of exotic solitons with combined polarization in nonlinear elastic plates with effective nonlinear dispersion, derivation of nonlinear evolution equations for nonlinear elastic systems with restricted geometry and second-order nonlinearity. Some results were obtained for nonlinear elastic waves and solitons near the surface in the incommensurate state.

(II) Nonlinear dynamics of magnets is a traditional field of interest: the specific nonlinear excitations - "magnetic solitons" were studying and the novel conception of magnetic soliton as a bound state of magnons was formulated. In this area some important results were obtained: the exact solutions for ID solitons in ferro- and anti-feromagnets; exact many-solitons solutions in ID FM; numerical solutions for many-dimensional magnetic solitons; 2D skirmions and vortices in FM. Later some specific phenomena of nonlinear magnetic structure and dynamics was investigated: magnetic solitons in thin films and nonlinear surface spin waves, magnetic frustrations in HTSC, complicated topological solitons in AFM with dislocations, dynamical and topological solitons and internal modes in quasi 2D essentially discrete FM, exotic magnetic solitons, magnetic structure and dynamics of FM/AFM perfect and imperfect interfaces (especially exchange bias phenomenon). Recently the main interests are concentrated on the structure and dynamics of magnetic vortices, vortex pairs and their interaction with spin waves and external fields, magnetic vortices in magnetic nanodots, magnetic solitons interaction with the point sources of external high frequency field.

(III) Special problems of nonlinear mechanic and mathematical aspects of solitonic theory were studied including: some asymptotic techniques for envelope solitons in ID- 2D- and finite size systems; Hirota transformation, N-solitons solutions and spin-wave spectrum in the presence of domain walls; exact solutions for incommensurated systems; the connection of solitons in the systems with distributed parameters with their quasi-soliton analogous in the systems with finite number degrees of freedom. Recently some problems of nonlinear optical pulse propagation in fibers were intensively studied. Another "optical activity" is connected with propagation of nonlinear optical beams through spatial periodic media and properties of optical "supersolitons”. The particular attention is devoted to investigation of "gap-solitons" and their discrete analogs.

Main publications:

1. A.M.Kosevich, B.A.Ivanov, A.S.Kovalev, Nonlinear waves of magnetization. Dynamical and topological solitons, Kiev, Naukova Dumka (1983).

2. A.M.Kosevich, B.A.Ivanov, A.S.Kovalev, Magnetic solitons: A new type of collective excitations in magnetically ordered systems, Sov.Sci.Rev., A6,161-260 (1985).

3. A.M.Kosevich, B.A.Ivanov, A.S.Kovalev, Magnetic solitons, Phys.Rep., v.194, N3/4, 117-238 (1990).

4. A.M.Kosevich, A.S.Kovalev, Introduction in nonlinear physical mechanics, Kiev, Naukova dumka (1989).

Main last publications:

1. А.Г.Гречнев, А.С.Ковалев, М.Л.Панкратова, «Влияние обменного сдвига на гистерезис полевой зависимости намагниченности ферромагнитной пленки, контактирующей с антиферромагнетиком». ФНТ, т.39, №12, 1361 (2013).

2. E.S.Sokolova, A.P.Mayer, A.S.Kovalev, “Second-order nonlinearity of wedge acoustic waves in anisotropic media”, Wave Motion, v.50, N2, 246 (2013).

3. E.S.Sokolova, R.Timler, A.S.Kovalev, A.P.Mayer, “On the dispersion of wedge acoustic wave”, Wave Motion, v.50, N2, 233 (2013).

4. В.Н.Белан, А.С.Ковалев, А.А.Перетятько,«Влияние диссипации на структуру квазисолитонных состояний при высокочастотном точечном воздействии на нелинейные магнитоупорядоченные среды», ФНТ, т.39, №2, 186 (2013).

5. S.A.Gredeskul, S.A.Derevyanko, A.S.Kovalev, J.E.Prilepsky, “ Soliton propagation through a disordered system: Statistics of the transmission delay”, Phys.Rev. E, v.81, N 3, 036608 (2010).