Nikolai Nikolaevich Nekhoroshev (russian: Николай Николаевич Нехорошев; 2 October 1946 – 18 October 2008) was a prominent

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nation ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

n mathematician specializing in

classical mechanics Classical mechanics is a physical theory describing the motion of macroscopic objects, from projectiles to parts of machinery, and astronomical objects, such as spacecraft, planets, stars, and galaxies. For objects governed by classi ...

and dynamical systems. His research concerned

Hamiltonian mechanics Hamiltonian mechanics emerged in 1833 as a reformulation of Lagrangian mechanics. Introduced by Sir William Rowan Hamilton, Hamiltonian mechanics replaces (generalized) velocities \dot q^i used in Lagrangian mechanics with (generalized) ''momenta ...

perturbation theory In mathematics and applied mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem. A critical feature of the technique is a middl ...

celestial mechanics Celestial mechanics is the branch of astronomy that deals with the motions of objects in outer space. Historically, celestial mechanics applies principles of physics (classical mechanics) to astronomical objects, such as stars and planets, to ...

integrable system In mathematics, integrability is a property of certain dynamical systems. While there are several distinct formal definitions, informally speaking, an integrable system is a dynamical system with sufficiently many conserved quantities, or first ...

s, dynamical systems, the quasiclassical approximation, and

singularity theory In mathematics, singularity theory studies spaces that are almost manifolds, but not quite. A string can serve as an example of a one-dimensional manifold, if one neglects its thickness. A singularity can be made by balling it up, dropping it ...

. He proved, in particular, a stability result in KAM-theory stating that, under certain conditions, solutions of nearly integrable systems stay close to invariant tori for exponentially long times . Nekhoroshev was professor of the

Moscow State University M. V. Lomonosov Moscow State University (MSU; russian: Московский государственный университет имени М. В. Ломоносова) is a public research university in Moscow, Russia and the most prestigious ...

and

University of Milan The University of Milan ( it, Università degli Studi di Milano; la, Universitas Studiorum Mediolanensis), known colloquially as UniMi or Statale, is a public research university in Milan, Italy. It is one of the largest universities in Europe ...

. He was an alumnus of Moscow's boarding school no. 18 (1964).

References

* . * . * . {{DEFAULTSORT:Nekhoroshev, Nikolay Moscow State University alumni Moscow State University faculty Russian mathematicians Soviet mathematicians 1946 births 2008 deaths Dynamical systems theorists