On the intersection of Hermitian curves and of Hermitian surfaces

Kestenband [Unital intersections in finite projective planes, Geom. Dedicata 11(1) (1981) 107–117; Degenerate unital intersections in finite projective planes, Geom. Dedicata 13(1) (1982) 101–106] determines the structure of the intersection of two Hermitian curves of PG(2,q²), degenerate or not. In this paper we give a new proof of Kestenband's results. Giuzzi [Hermitian varieties over finite field, Ph.D. Thesis, University of Sussex, 2001] determines the structure of the intersection of two non-degenerate Hermitian surfaces and of PG(3,q²) when the Hermitian pencil defined by and contains at least one degenerate Hermitian surface. We give a new proof of Giuzzi's results and we obtain some new results in the open case when all the Hermitian surfaces of the Hermitian pencil are non-degenerate.     

On a special case of the intersection of quadric and cubic surfaces

The intersection curve between two surfaces in three-dimensional real projective space RP³ is important in the study of computer graphics and solid modelling. However, much of the past work has been directed towards the intersection of two quadric surfaces. In this paper we study the intersection curve between a quadric and a cubic surface and its projection onto the plane at infinity. Formulas for the plane and space curves are given for the intersection of a quadric and a cubic surface. A family of cubic surfaces that give the same space curve when we intersect them with a quadric surface is found. By generalizing the methods in Wang et al. (2002) [6] that are used to parametrize the space curve between two quadric surfaces, we give a parametrization for the intersection curve between a quadric and a cubic surface when the intersection has a singularity of order 3.     

The intersection form of the result of gluing manifolds with degenerate intersection forms

It is proved that the intersection form of the result of gluing together two compact oriented 4k-dimensional manifolds along their boundaries can be (noncanonically) represented as the direct sum of a split form, whose rank is determined by the images of the inclusions of the free parts of the middle homology groups of the boundaries, and a form which is the result of gluing together nondegenerate parts of the intersection forms of the initial manifolds. Bibliography: 6 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 231, 1995, pp. 169–179. Translated by O. A. Ivanov and N. Yu. Netsvetaev.     

On maximization of quadratic form over intersection of ellipsoids with common center

We demonstrate that if A ₁,...,A _m are symmetric positive semidefinite n×n matrices with positive definite sum and A is an arbitrary symmetric n×n matrix, then the relative accuracy, in terms of the optimal value, of the semidefinite relaxation of the optimization program is not worse than . It is shown that this bound is sharp in order, as far as the dependence on m is concerned, and that a~feasible solution x to (P) with can be found efficiently. This somehow improves one of the results of Nesterov [4] where bound similar to (*) is established for the case when all A_i are of rank 1. Received August 13, 1998 / Revised version received May 25, 1999? Published online September 15, 1999     

On the inner curvature of the second fundamental form of helicoidal surfaces

Let M be a helicoidal surface in E ³, free of points of vanishing Gaussian curvature. Let H be the mean curvature and K _II the curvature of the second fundamental form. In this note it is shown that the helicoidal surfaces satisfying K _II =H are locally characterized by constancy of the ratio of the principal curvatures. Moreover it is proved that these helicoidal surfaces are determined by a first order differential equation. Research supported by E.E.C. contract CHRX-CT92-0050.     

On intersection and mixed intersection bodies

Duals of the basic projection and mixed projection inequalities are established for intersection and mixed intersection bodies.      

Verlinde algebras and the intersection form on vanishing cycles

We prove Zuber's conjecture [Z] establishing connections of the fusion rules of the su( N )_k WZW model of conformal field theory and the intersection form on vanishing cycles of the associated fusion potential.     

On the fuzzy intersection rule

The paper provides a complete exposition of the fuzzy intersection rule in variational analysis and its applications to generalized differentiation theory. New forms of the rule and further applications are presented.     

On the intersection of maximalm-convex subsets

A subsetS of a real linear spaceE is said to bem-convex providedm≧2, there exist more thanm points inS, and for eachm distinct points ofS at least one of the ( ₂ ^m ) segments between thesem points is included inS. InE, letxy denote the segment between two pointsx andy. For any pointx inSυE, letS _x ={y: xyυS}. The kernel of a setS is then defined as {xεS: S _x=S}. It is shown that the kernel of a setS is always a subset of the intersection of all maximalm-convex subsets ofS. A sufficient condition is given for the intersection of all the maximalm-convex subsets of a setS to be the kernel ofS.     

Line bundles on arithmetic surfaces and intersection theory

For line bundles on arithmetic varieties we construct height functions using arithmetic intersection theory. In the case of an arithmetic surface, generically of genusg, for line bundles of degreeg equivalence is shown to the height on the Jacobian defined by Θ. We recover the classical formula due to Faltings and Hriljac for the Néron-Tate height on the Jacobian in terms of the intersection pairing on the arithmetic surface.     

On the intersection of modular correspondences

Oblatum 28-I-1992 & 29-X-1992     

On the intersection of infinite matroids

We show that the infinite matroid intersection conjecture of Nash-Williams implies the infinite Menger theorem proved by Aharoni and Berger in 2009.We prove that this conjecture is true whenever one matroid is nearly finitary and the second is the dual of a nearly finitary matroid, where the nearly finitary matroids form a superclass of the finitary matroids.In particular, this proves the infinite matroid intersection conjecture for finite-cycle matroids of 2-connected, locally finite graphs with only a finite number of vertex-disjoint rays.