A geometric realization without self-intersections does exist for Dyck's regular map

Even in our decade there is still an extensive search for analogues of the Platonic solids. In a recent paper Schulte and Wills [13] discussed properties of Dyck's regular map of genus 3 and gave polyhedral realizations for it allowing self-intersections. This paper disproves their conjecture in showing that there is a geometric polyhedral realization (without self-intersections) of Dyck's regular map {3, 8}₆ already in Euclidean 3-space. We describe the shape of this new regular polyhedron.     

Geometric conditions of differentiability for a regular locally Lipschitz function

The differentiability of a norm of a Banach space may be characterized by its unit sphere. This paper generalizes these geometric conditions of norm's differentiability to the case of a regular locally Lipschitz function. Supported by the National Natural Science Foundation of China     

Maximum genus of regular graphs

This paper provides tight lower bounds on the maximum genus of a regular graph in terms of its cycle rank. The main tool is a relatively simple theorem that relates lower bounds with the existence (or non-existence) of induced subgraphs with odd cycle rank that are separated from the rest of the graph by cuts of size at most three. Lower bounds on the maximum genus are obtained by bounding from below the size of these odd subgraphs. As a special case, upper-embeddability of a class of graphs is caused by an absence of such subgraphs. A well-known theorem stating that every 4-edge-connected graph is upper-embeddable is a straightforward corollary of the employed method.     

Geometric realizations of curvature models by manifolds with constant scalar curvature

We show any pseudo-Riemannian curvature model can be geometrically realized by a manifold with constant scalar curvature. We also show that any pseudo-Hermitian curvature model, para-Hermitian curvature model, hyper-pseudo-Hermitian curvature model, or hyper-para-Hermitian curvature model can be realized by a manifold with constant scalar and -scalar curvature.     

The generalized Verschiebung map for curves of genus 2

Let C be a smooth curve, and M _r (C) the coarse moduli space of vector bundles of rank r and trivial determinant on C. We examine the generalized Verschiebung map induced by pulling back under Frobenius. Our main result is a computation of the degree of V ₂ for a general C of genus 2, in characteristic p > 2. We also give several general background results on the Verschiebung in an appendix.This paper was partially supported by fellowships from the National Science Foundation and Japan Society for the Promotion of Sciences.     

Geometric properties of the scattering map of a normally hyperbolic invariant manifold

Given a normally hyperbolic invariant manifold Λ for a map f, whose stable and unstable invariant manifolds intersect transversally, we consider its associated scattering map. That is, the map that, given an asymptotic orbit in the past, gives the asymptotic orbit in the future.We show that when f and Λ are symplectic (respectively exact symplectic) then, the scattering map is symplectic (respectively exact symplectic). Furthermore, we show that, in the exact symplectic case, there are extremely easy formulas for the primitive function, which have a variational interpretation as difference of actions.We use this geometric information to obtain efficient perturbative calculations of the scattering map using deformation theory. This perturbation theory generalizes and extends several results already obtained using the Melnikov method. Analogous results are true for Hamiltonian flows. The proofs are obtained by geometrically natural methods and do not involve the use of particular coordinate systems, hence the results can be used to obtain intersection properties of objects of any type.We also reexamine the calculation of the scattering map in a geodesic flow perturbed by a quasi-periodic potential. We show that the geometric theory reproduces the results obtained in [Amadeu Delshams, Rafael de la Llave, Tere M. Seara, Orbits of unbounded energy in quasi-periodic perturbations of geodesic flows, Adv. Math. 202 (1) (2006) 64-188] using methods of fast-slow systems. Moreover, the geometric theory allows to compute perturbatively the dependence on the slow variables, which does not seem to be accessible to the previous methods.     

Nonorientable genus of cartesian products of regular graphs

A special type of surgery developed by A. T. White and later used by the author to construct orientable quadrilateral embeddings of Cartesian products of graphs is here expanded to cover the nonorientable case as well. This enables the nonorientable genus of many families of Cartesian products of triangle-free graphs to be computed.     

Handle removal on a compact Riemann surface of genus 2

A degeneration of a compact, two-sheeted, Riemann surface in genus 2 is studied. Two branch points coalesce when the period matrix for the surface is degenerated. A Siegel modular transformation is applied to give the degenerating period matrix in the form of a corner matrix.     

Geometric effects on surface roughness in electrodeposition

^** Email: ranga{at}ufl.edu Our aim is to understand the early stages of roughness growthin electrodeposition. We present a study of the branching ofsteady planar electrode surfaces to steady non-planar electrodesurfaces as the voltage imposed at a cathode is decreased throughits critical value. We aim to discover the type of branchingand to learn whether or not the new branches can be detectedby measuring the current. The cross-sectional shape of the electrodemakes a difference. Circular electrodes lead to transcriticalbranching; ordinarily, rectangular electrodes lead to a pitchfork,sometimes forward and sometimes backward.     

Enumeration of maps regardless of genus: Geometric approach

We use the conceptual idea of “maps on orbifolds” and the theory of the non-Euclidean crystallographic groups (NEC groups) to enumerate rooted and unrooted maps (both sensed and unsensed) on surfaces regardless of genus. As a consequence we deduce a formula for the number of chiral pairs of maps. The enumeration principle used in this paper is due to Mednykh (2006) [15], it counts the number of conjugacy classes of subgroups in NEC groups which are in one-to-one correspondence with unrooted (sensed or unsensed) maps.     

Recent progress in classification of regular maps on a given compact surface

We give a brief overview of the state-of-the art of clasification of regular maps on a given compact surface and outline recent results for surfaces of Euler characteristic equal to the negative of a small multiple of a prime.     

The Riemann problem on a finite-sheeted Riemann surface of infinite genus

LetR be the Riemann surface of the functionu(z) specified by the equationu ⁿ=P(z) withn ε ℕ,n ≥ 2, andz ε ℂ, whereP(z) is an entire function with infinitely many simple zeros. OnR, the Riemann boundary-value problem for an arbitrary piecewise smooth contour Γ is considered. Necessary and sufficient conditions for its solvability are obtained, and its explicit solution is constructed. Translated fromMatematicheskie Zametki, Vol. 67, No. 1, pp. 25–35, January, 2000.     

Degeneration of a compact Riemann surface of genus 2

A problem in the degeneration of a compact, two-sheeted, Riemann surface of genus 2 is studied, using theta function techniques. The three moveable branch points coalesce to the fourth branch point on the first limiting surface while the triangles formed by these points are all essentially similar. Applying a conformal map, we see that these points represent the finite branch points on the second of the limiting surfaces.     

Geometric and arithmetic properties of the Hénon map

Research partially supported by NSF DMS-9121727     

Real forms of a Riemann surface of even genus

Natanzon proved that a Riemann surface of genus has at most conjugacy classes of symmetries, and this bound is attained for infinitely many genera . The aim of this note is to prove that a Riemann surface of even genus has at most four conjugacy classes of symmetries and this bound is attained for an arbitrary even as well. An equivalent formulation in terms of algebraic curves is that a complex curve of an even genus has at most four real forms which are not birationally equivalent.