Integrable billiards model important integrable cases of rigid body dynamics

Abstract—A generalized billiard is considered, in which a point moves on a locally flat surface obtained by isometrically gluing together several plane domains along boundaries being arcs of confocal quadrics. Under this motion, a point moves from one domain to another, passing through the glued boundaries. Many integrable cases of rigid body dynamics with appropriate parameter values at certain levels of integrals are modeled by classical or generalized billiards; in the paper, Liouville equivalence is proved by comparing Fomenko–Zieschang invariants.     

Topology of Liouville Foliations for Integrable Billiards in Non-Convex Domains

Plane billiards are studied in non-convex domains bounded by arcs of confocal quadrics and in domains bounded by segments of mutually perpendicular straight lines. The topology of isoenergetic surfaces of such billiards is studied by calculating rough Liouville equivalence invariants known as Fomenko molecules.     

Fomenko–Zieschang Invariants of Topological Billiards Bounded by Confocal Parabolas

A topological (Liouville) classification of integrable billiards in locally flat compact domains bounded by arcs of confocal parabolas is obtained by methods of Fomenko–Zieschang invariants of integrable systems theory.     

The behavior of conformal maps of domains near convex boundary arcs

The behavior of the derivatives of conformal maps of the unit disk onto simply connected domains in the complex plane whose boundaries contain convex or concave attainable arcs, as well as the behavior of the derivatives of the inverse maps, is studied. It is proved that these derivatives exist and are bounded on the corresponding arcs and near them; a criterion for their continuity at points of these arcs is stated and proved.     

Periodic trajectories in 3-dimensional convex billiards

 We give a lower bound on the number of periodic billiard trajectories inside a generic smooth strictly convex closed surface in 3-space: for odd n, there are at least 2(n-1) such trajectories. Convex plane billiards were studied by G. Birkhoff, and the case of higher dimensional billiards is considered in our previous papers. We apply a topological approach based on the calculation of cohomology of certain configuration spaces of points on 2-sphere. Received: 11 June 2001 / Revised version: 26 February 2002     

Combinatorial cell complexes and Poincaré duality

We define and study a class of finite topological spaces, which model the cell structure of a space obtained by gluing finitely many Euclidean convex polyhedral cells along congruent faces. We call these finite topological spaces, combinatorial cell complexes (or c.c.c). We define orientability, homology and cohomology of c.c.c’s and develop enough algebraic topology in this setting to prove the Poincaré duality theorem for a c.c.c satisfying suitable regularity conditions. The definitions and proofs are completely finitary and combinatorial in nature.     

Whitney differentiability of optimal-value functions for bound-constrained convex programming problems

ABSTRACT

In the spirit of the Whitney Extension Theorem, consider a function on a compact subset of Euclidean space to be ‘Whitney-differentiable’ if it is a restriction of a continuously Fréchet-differentiable function with an open domain. Whitney-differentiable functions have been shown to have useful (yet possibly nonunique) derivatives and calculus properties even on the boundaries of their domains. This article shows that optimal-value functions for bound-constrained convex programmes with Whitney-differentiable objective functions are themselves Whitney-differentiable, even when the linear-independence constraint qualification is not satisfied. This result extends classic sensitivity results for convex programmes, and generalizes recent work. As an application, sufficient conditions are presented for generating continuously differentiable convex underestimators of nonconvex functions for use in methods for deterministic global optimization in the multivariate McCormick framework. In particular, the main result is applied to generate Whitney-differentiable convex underestimators for quotients of functions with known Whitney-differentiable relaxations.     

On the Rigidity of a Class of Glued Surfaces

The method of integral formulas is applied to prove the rigidity of a class of closed nonconvex surfaces obtained by gluing together regular pieces of surfaces of positive Gaussian curvature with smooth boundaries.     

Modeling Nondegenerate Bifurcations of Closures of Solutions for Integrable Systems with Two Degrees of Freedom by Integrable Topological Billiards

It is well known that surgeries of closures of solutions for integrable nondegenerate Hamiltonian systems with two degrees of freedom at a level of constant energy are classified by the so-called 3-atoms. These surgeries correspond to singular leaves of the Liouville foliation of three-dimensional isoenergetic surfaces. In this paper we prove the Fomenko conjecture that all such surgeries are modeled by integrable topological two-dimensional billiards (billiard books).     

Heisenberg Model in Pseudo-Euclidean Spaces II

In the review we describe a relation between the Heisenberg spin chain model on pseudospheres and light-like cones in pseudo-Euclidean spaces and virtual billiards. A geometrical interpretation of the integrals associated to a family of confocal quadrics is given, analogous to Moser’s geometrical interpretation of the integrals of the Neumann system on the sphere.     

Symmetric Periodic Orbits and Uniruled Real Liouville Domains

A real Liouville domain is a Liouville domain with an exact anti-symplectic involution. The authors call a real Liouville domain uniruled if there exists an invariant finite energy plane through every real point. Asymptotically, an invariant finite energy plane converges to a symmetric periodic orbit. In this note, they work out a criterion which guarantees uniruledness for real Liouville domains.     

On typical degenerate convex surfaces

Various properties are given concerning geodesics on, and distance functions from points in, typical degenerate convex surfaces; i.e., surfaces obtained by gluing together two isometric copies of typical (in the sense of Baire category) convex bodies, by identifying the corresponding points of their boundaries.     

Representation of torus homeotopies by simple polyhedra with boundary

In 1991, Turaev and Viro constructed a quantum topological linear representation of mapping class groups of closed surfaces. To the mappings of a surface into itself, they assigned simple polyhedra whose boundaries consisted of two simple graphs cutting the surface into cells. The computational complexity of the Turaev-Viro representations strongly depends on the choice of suitable sets of simple polyhedra. In this paper, simple polyhedra for the torus are constructed. One of the reasons why they are convenient is that they all are obtained by gluing along boundary of copies of the same simple polyhedron. Translated fromMatematicheskie Zametki, Vol. 66, No. 4, pp. 533–539, October, 1999.     

Generation of structured difference grids in two-dimensional nonconvex domains using mappings

Generation of structured difference grids in two-dimensional nonconvex domains is considered using a mapping of a parametric domain with a given nondegenerate grid onto a physical domain. For that purpose, a harmonic mapping is first used, which is a diffeomorphism under certain conditions due to Rado’s theorem. Although the harmonic mapping is a diffeomorphism, its discrete implementation can produce degenerate grids in nonconvex domains with highly curved boundaries. It is shown that the degeneration occurs due to approximation errors. To control the coordinate lines of the grid, an additional mapping is used and universal elliptic differential equations are solved. This makes it possible to generate a nondegenerate grid with cells of a prescribed shape.     

Global stress regularity of convex and some nonconvex variational problems

We derive a global regularity theorem for stress fields which correspond to minimizers of convex and some special nonconvex variational problems with mixed boundary conditions on admissible domains. These are Lipschitz domains satisfying additional geometric conditions near those points, where the type of the boundary conditions changes. In the first part it is assumed that the energy densities defining the variational problem are convex but not necessarily strictly convex and satisfy a convexity inequality. The regularity result for this case is derived with a difference quotient technique. In the second part the regularity results are carried over from the convex case to special nonconvex variational problems taking advantage of the relation between nonconvex variational problems and the corresponding (quasi-) convexified problems. The results are applied amongst others to the variational problems for linear elasticity, the p-Laplace operator, Hencky elasto-plasticity with linear hardening and for scalar and vectorial two-well potentials (compatible case).      

Bifurcations of Steiner minimal trees and minimal fillings for non-convex four-point boundaries and Steiner subratio for the Euclidean plane

Bifurcation diagrams for topologies of Steiner minimal trees and minimal fillings for nonconvex four-point boundaries in the Euclidean plane are constructed. Using this result, the four-pointed Steiner subratio of the Euclidean plane is obtained. All configurations which it is attained at are found.     

Minimax inequalities and fixed points of expansive set-valued mappings with noncompact and nonconvex domains and ranges in topological spaces

Some minimax inequalities involving two bifunctions with noncompact and nonconvex domains are first proved in finite continuous topological spaces (in short, FC$FC$-spaces) without convexity structure. As applications some new Fan–Browder type fixed point theorems for expansive set-valued maps with noncompact and nonconvex domains and ranges are obtained in general topological spaces. These results generalize some known results in the recent literature.     

Seifert unions of solid tori

We obtain a list of all 3-manifolds that can be obtained by gluing 3-balls and solid tori along mutually disjoint surfaces in their boundaries. Received: 22 February 2001; in final form: 18 October 2001 / Published online: 4 April 2002