Equations of low-degree projective surfaces with three-divisible sets of cusps

We determine the equations of surfaces of degrees 6 carrying a minimal, non-empty, three-divisible set of cusps.Mathematics Subject Classification (2000): 14J25, 14J17Supported by the DFG Schwerpunktprogramm Global methods in complex geometry. The second author is supported by a Fellowship of the Foundation for Polish Science and KBN Grant No. 2 P03A 016 25.     

Remez-type inequality on sets with cusps

A Remez-type inequality is proved for a large family of sets with cusps in R^N${\mathbb{R}}^N$, including compact, fat and semialgebraic (or subanalytic) sets.     

On the period function of reversible quadratic centers with their orbits inside quartics

This paper is concerned with the monotonicity of the period function for a class of reversible quadratic centers with their orbits inside quartics. It is proved that such a system has a period function with at most one critical point.     

Some elementary examples of quartics with finite-dimensional motive

This small note contains some easy examples of quartic hypersurfaces that have finite-dimensional motive. As an illustration, we verify a conjecture of Voevodsky (concerning smash-equivalence) for some of these special quartics.     

On convex projective manifolds and cusps

This study of properly or strictly convex real projective manifolds introduces notions of parabolic, horosphere and cusp. Results include a Margulis lemma and in the strictly convex case a thick–thin decomposition. Finite volume cusps are shown to be projectively equivalent to cusps of hyperbolic manifolds. This is proved using a characterization of ellipsoids in projective space.     

On the norm of singular integral operator on curves with cusps

Applying the results on singular integral operators with the complex conjugation on curves with cusps (see R. Duduchava, T. Latsabidze, A. Saginashvili, 1992, 1994) the explicit formula for the local norm of the Cauchy singular integral operator on a curve with cusps in a Lebesgue space with an exponential weightL ₂ (, ) is obtained. For curves with angles the formula was already known (see R. Avedanio, N. Krupnik, 1988).     

On the number of moduli of plane sextics with six cusps

Let be the variety of irreducible sextics with six cusps as singularities. Let be one of irreducible components of . Denoting by the space of moduli of smooth curves of genus 4, we consider the rational map sending the general point [Γ] of Σ, corresponding to a plane curve , to the point of parametrizing the normalization curve of Γ. The number of moduli of Σ is, by definition the dimension of Π(Σ). We know that , where ρ(2, 4, 6) is the Brill–Noether number of linear series of dimension 2 and degree 6 on a curve of genus 4. We prove that both irreducible components of have number of moduli equal to seven.      

Uniqueness of exceptional singular quartics

We prove that given a general collection of 14 points of ( an infinite field) there is a unique quartic hypersurface that is singular on .

This completes the solution to the open problem of the dimension of a linear system of hypersurfaces of that are singular on a collection of general points.

     

Fano surfaces of real quartics

We prove certain properties of the Fano surface of bitangents to the real quartic in projective 3-space. In particular, we estimate the dimension of the cohomology of the real part of this surface in terms of the dimension of the cohomology of the real part of the quartic, and compute its Euler characteristic.     

On the asymptotic behaviour of capillary surfaces in cusps

Concus and Finn [2] discovered that capillary surfaces rise to infinity in corners with sufficiently small opening angle. They also found the leading term of an asymptotic expansion. Miersemann [5] improved this result to obtain a complete asymptotic expansion. In the present paper we will apply the methods of the above authors to discuss asymptotic behaviour of capillarities in cusps, which is a corner with opening angle 0. A large variety of asymptotic formulas will be provided. The general comparison theorem from Concus and Finn will play an important role in the proofs.     

Hyperbolization of cusps with convex boundary

We prove that for every metric on the torus with curvature bounded from below by ?1 in the sense of Alexandrov there exists a hyperbolic cusp with convex boundary such that the induced metric on the boundary is the given metric. The proof is by polyhedral approximation. This was the last open case of a general theorem: every metric with curvature bounded from below on a compact surface is isometric to a convex surface in a 3-dimensional space form.     

Plane quartics with Jacobians isomorphic to a hyperelliptic Jacobian

We show how for every integer one can explicitly construct distinct plane quartics and one hyperelliptic curve over all of whose Jacobians are isomorphic to one another as abelian varieties without polarization. When we say that the curves can be constructed ``explicitly', we mean that the coefficients of the defining equations of the curves are simple rational expressions in algebraic numbers in whose minimal polynomials over can be given exactly and whose decimal approximations can be given to as many places as is necessary to distinguish them from their conjugates. We also prove a simply-stated theorem that allows one to decide whether or not two plane quartics over , each with a pair of commuting involutions, are isomorphic to one another.