arXiv subjects

B. Shapiro

Publications and source records attributed to B. Shapiro.

60 records · Page 4Linked to original sources

arXiv1997

Connected components in the intersection of two open opposite Schubert cells in real complete flag manifold

In this paper we reduce the problem of counting the number of connected components in the intersection of two opposite open Schubert cells in the variety of real complete flags to a purely combinatorial question of counting the number of orbits of a certain intriguing group action in the space of upper triangular matrices with {0,1}-valued entries. The crucial step of our reduction uses the parametrization of the space of real unipotent totally positive upper triangular matrices introduced by Lusztig and Berenstein, Fomin, Zelevinski.

alg-geom↗

arXiv1996

On Young hulls of convex curves in R^{2n}

For a convex curve in an even-dimensional affine space we introduce a series of convex domains (called Young hulls), describe their structure and give a formulas fo the volume of the biggest of these domains. This paper is an attempt to generalize the classical isoperimetric inequality for the volume of the convex hull of a space curve due to I.Schoenberg.

dg-ga↗

arXiv1996

Orbital Magnetism in Two-dimensional Integrable Systems

We study orbital magnetism of a degenerate electron gas in a number of two-dimensional integrable systems, within linear response theory. There are three relevant energy scales: typical level spacing, the energy related to the inverse time of flight across the system, and the Fermi energy. Correspondingly, there are three distinct temperature regimes: microscopic, mesoscopic, and macroscopic. In the first two regimes there are large finite-size effects in the magnetic susceptibility, whereas in the third regime the susceptibility approaches its macroscopic value. In some cases, such as a quasi-one-dimensional strip or a harmonic confining potential, it is possible to obtain analytic expressions for the susceptibility in the entire temperature range.

cond-mat.mes-hall↗

arXiv1996

Giambelli-type formula for subbundles of the tangent bundle

Let us consider a generic n-dimensional subbundle V of the tangent bundle TM on some given manifold M. Given V one can define different degeneracy loci S_r(CV), r=(r_1<= r_2<= r_3<=...<=r_k) on M consisting of all points x in M for which the dimension of the subspace V^j(x) in TM(x) spanned by all length <= j commutators of vector fields tangent to V at x is less than or equal to r_j. We calculate 'explicitly' the cohomology classes dual to S_r(V) using determinantal formulas due to W.Fulton and the expression for the Chern classes of the associated bundle of free Lie algebras in terms of the Chern classes of V itself.

alg-geom↗

arXiv1996

Discriminants of convex curves are homeomorphic

For a given real generic curve $\ga: S^1\to \Bbb {RP}^n$ let $D_\ga$ denote the ruled hypersurface in $\Bbb {RP}^n$ consisting of all osculating subspaces to $\ga$ of codimension 2. A curve $\ga: S^1\to \Bbb {RP}^n$ is called convex if the total number of its intersection points (counted with multiplicities) with any hyperplane in $\Bbb {RP}^n$ does not exceed $n$. In this short note we show that for any two convex real projective curves $\ga_1:S^1\to\Bbb {RP}^n$ and $\ga_2:S^1\to\Bbb {RP}^n$ the pairs $(\Bbb {RP}^n,D_{\ga_1})$ and $(\Bbb {RP}^n,D_{\ga_2})$ are homeomorphic answering a question posed by V.Arnold.

dg-ga↗

arXiv1996

Intensity Fluctuations in Closed and Open Systems

We consider the intensity pattern, generated by a monochromatic source, in a disordered cavity coupled to the environment. For weak coupling, and when the source frequency is tuned to a resonance, the intensity distribution is close to Porter-Thomas distribution. When the coupling increases, gradually crosses over to the Rayleigh distribution. The joint probability distribution for intensities at two different points is also discussed.

cond-mat↗