Collineation groups irreducible on the components of a translation plane

We investigate finite translation planes of odd dimension over their kernels in which the translation complement induces on each component l a permutation group whose order is divisible by a p-primitive divisor. Using results of this investigation, we show that rank 3 affine planes of odd dimension over their kernels are either generalized André planes or semi-field planes. A similar result is given for translation planes having a collineation group which is doubly transitive on each affine line; besides the above two possibilities, there is a third possibility; the plane has order 27, the translation complement is doubly transitive on , and SL(2, 13) is contained in the translation complement.We also consider translation planes of odd dimension over their kernels which have a collineation group isomorphic to SL(2, w) with w prime to 5 and the characteristic, and having no affine perspectivity. We show that such planes have order 27, the prime power w=13, and the given group together with the translations forms a doubly transitive collineation group on {ie153-1}. This indicates quite strongly that the Hering translation plane of order 27 is unique with respect to the above properties.Both authors supported in part by NSF Grant No. MCS76-0661 A01.     

Deforming star-shaped polygons in the plane

Given a star-shaped polygon in the euclidean plane and a vertex v of the polygon, the author characterizes all those points w in the plane such that when the vertex v moves to w along a straight line path, while all other vertices of the polygon are fixed, the polygon remains star-shaped. An example is given to show that this characterization fails for the star-shaped polyhedral spheres in the 3-dimensional euclidean space.     

Analyticity of a Nonlinear Operator Associated to the Conformal Representation in Schauder Spaces. An Integral Equation Approach

We consider the Riemann map g_ζ,w of the complex unit disk to the plane domain 𝕀[ζ] enclosed by the Jordan curve ζ and normalized by the conditions g_ζ,w(0) = w, g′_ζ,w(0) > 0, where w is a point of 𝕀[ζ], and we present a nonlinear singular integral equation approach to prove that the nonlinear operator which takes the pair (ζ, w) to the map g^(–1)_ζ,w ○ ζ is real analytic in Schauder spaces.     

Unitals in the Hall plane

The unitals in the Hall plane are studied by deriving PG(2,q ²)and observing the effect on the unitals of PG(2,q ²).The number of Buekenhout and Buekenhout-Metz unitals in the Hall plane is determined. As a corollary we show that the classical unital is not embeddble in the Hall plane as a Buekenhout unital and that the Buekenhout unitals of H(q ²)are not embeddable as Buekenhout unitals in the Desarguesian plane. Finally, we generalize this technique to other translation planes.     

An extension of the Erdős-Szekeres theorem on large angles

The existence of a functionn(ε) (ε>0) is established such that given a finite setV in the plane there exists a subsetW⊆V, |W|<n(ε) with the property that for anyv εV\ W there are two pointsw ₁,w ₂ εW such that the angle ∢(w ₁ vw ₂)>π-ε.     

A structure theory for two-dimensional translation planes of order q 2 that admit collineation groups of order q 2

This paper is devoted to the study of translation planes of order q ² and kernel GF(q) that admit a collineation group of order q ² in the linear translation complement. We give a representation of this group by a suitable set of matrices depending on some functions over GF(q). Using this representation we obtain several results concerning the existence and the collineation group of the plane.     

Winkelmessung und Orientierung

In an affine plane oriented distance d and oriented angle w (between non-oriented lines) are introduced as mapping into , fulfilling certain axioms. Examples show, that the use of w is of advantage in elementary geometry. Axiomatic consequences of generalizing d, w to mappings into ordered abelian groups are considered.

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Herrn Helmut Salzmann zum 60. Geburtstag     

Simple continued fractions and cutting sequences

Abstract

The connection between cutting sequences of a directed geodesic in the tessellated hyperbolic plane ?², the modular group Γ = PSL(2, ?) and the simple continued fractions of an end point w of the geodesic have been established by Series [13]. In this paper we represent the simple continued fractions of w ∈ ? and the “L” and “R” codes of the cutting sequence in terms of modular and extended modular transformations. We will define a T ₀-path on a graph whose vertices are the set of Farey triangles, as the equivalent of the cutting sequence. The relationship between the directed geodesic with end point w on ?, the Farey tessellation and the simple continued fraction expansion of w ∈ ? _∞ then follows easily as a consequence of this redefinition. Finite, infinite and periodic simple continued fractions are subsequently examined in this light.     

Unitals and inversive planes

We show that if U is a Buekenhout-Metz unital (with respect to a point P) in any translation plane of order q ² with kernel containing GF(q), then U has an associated 2-(q²,q+1,q) design which is the point-residual of an inversive plane, generalizing results of Wilbrink, Baker and Ebert. Further, our proof gives a natural, geometric isomorphism between the resulting inversive plane and the (egglike) inversive plane arising from the ovoid involved in the construction of the Buekenhout-Metz unital. We apply our results to investigate some parallel classes and partitions of the set of blocks of any Buekenhout-Metz unital.     

Eine einfache Verallgemeinerung der Rayleigh-Grenzschicht

Summary A simple generalization of the theory of the compressible boundary layer near an infinite flat plate to the case with suction or blowing out is given if at the timet=0 the plate is set into motion in its own plane with velocityu _w t ⁿ. The normal velocity at the wall shall vary with time according tov _wt ^–1/2. In that case one gets similar boundary layer profiles for allt>0, which can be reduced to the profiles without suction or blowing (v _w=0) by a simple parallel displacement and stretching of the coordinates. As an example the Rayleigh boundary layer (n=0,u _w=const) is discussed.     

On Minimum-Weight k-Edge Connected Steiner Networks on Metric Spaces

For a given set of points P in a metric space, let w _k(P) denote the weight of minimum-weight k-edge connected Steiner network on P divided by the weight of minimum-weight k-edge connected spanning network on P, and let r _k=inf{w _k(P) |P}. We show in this paper that for any P, , for even k≥2 and , for odd k≥3. In particular, we prove that for any P in the Euclidean plane, w ₄(P) and w ₅(P) are greater than or equal to , and ; For any P in the rectilinear plane , for odd k≥5. In addition, we prove that there exists an O(|P|³)-time approximation algorithm for constructing a minimum-weight k-edge connected Steiner network which has approximation ratio of for even k and for odd k. Received: August 21, 1997 Revised: February 5, 1998     

Reduced Words and Plane Partitions

Let w ₀ be the element of maximal length in thesymmetric group S _n , and let Red(w ₀) bethe set of all reduced words for w ₀. We prove the identity which generalizes Stanley's [20] formula forthe cardinality of Red(w ₀), and Macdonald's [11] formula .Our approach uses anobservation, based on a result by Wachs [21], that evaluation of certainspecializations of Schubert polynomials is essentially equivalent toenumeration of plane partitions whose parts are bounded from above. Thus,enumerative results for reduced words can be obtained from the correspondingstatements about plane partitions, and vice versa. In particular, identity(*) follows from Proctor's [14] formula for the number of planepartitions of a staircase shape, with bounded largest part.Similar results are obtained for other permutations and shapes;q-analogues are also given.     

A decomposition of the beta distribution,related order and asymptotic behavior

Let β _{v, w} be any beta variate with p.d.f.(Γ(v+w)/Γ(v)Γ(w))x ^v−1(1−x) ^w−1 and letU _{v, w} =-log β _{v, w} . ThenU _v,w =U ^CM +U ^PF , whereU ^CM andU ^PF are independent with completely monotone andPF _∞ densities, respectively. It is shown thatU _{v, w} is infinitely divisible and β _{v, w} correspondingly infinitely factorable. The asymptotic behavior ofU _{v, w} and β _{v, w} for largev, w is described. For different modes of increase ofv andw,U _{v, w} is asymptotically normal, gamma or extreme value distributed. The decomposition is employed to provide an algorithm for generating random β _{v, w} distributed numbers. Many of the results are based on insights provided by the classical theory of the Gamma function in the complex plane. This work was supported in part by the United States Air Force, Office of Scientific Research, under grant No. AFOSR-79-0043.     

Szeg? theorem, Carathéodory domains, and boundedness of calculating functionals

Suppose that G is a bounded simply connected domain on the plane with boundary í\subseteq òln( \tfracdm_a dw ) dw = - ￥\int {\ln \left( {\tfrac{{d\mu _a }}{{d\omega }}} \right)} d\omega = - \infty     

On translation planes of orderq 3 that admit a collineation group of orderq 3

Let II be a translation plane of orderq ³, with kernel GF(q) forq a prime power, that admits a collineation groupG of orderq ³ in the linear translation complement. Moreover, assume thatG fixes a point at infinity, acts transitively on the remaining points at infinity andG/E is an abelian group of orderq ², whereE is the elation group ofG.In this article, we determined all such translation planes. They are (i) elusive planes of type I or II or (ii) desirable planes.Furthermore, we completely determined the translation planes of orderp ³, forp a prime, admitting a collineation groupG of orderp ³ in the translation complement such thatG fixes a point at infinity and acts transitively on the remaining points at infinity. They are (i) semifield planes of orderp ³ or (ii) the Sherk plane of order 27.     

On translation planes of orderq 3 that admit a collineation group of orderq 3, II

Let II be a translation plane of orderq ³ with kernel GF(q) that admits a collineation groupG of orderq ³ in the linear translation complement such thatG fixes a point at infinity and acts transitively on the remaining points at infinity.In this paper, we show that any such translation plane II is one of the following types of planes:     

Characterization of polyanalytic functions by meromorphic extensions from chains of circles

Let C _t = {z ∈ ℂ: |z − c(t)| = r(t), t ∈ (0, 1)} be a C ¹-family of circles in the plane such that lim _t→0+ C _t = {a}, lim _t→1− C _t = {b}, a ≠ b, and |c′(t)|² + |r′(t)|² ≠ 0. The discriminant set S of the family is defined as the closure of the set {c(t) + r(t)w(t), t ∈ [0, 1]}, where w = w(t) is the root of the quadratic equation ̅c′(t)w ² + 2r′(t)w + c′(t) = 0 with |w| < 1, if such a root exists.     

Spreads,ovoids andS 5

We consider translation planes of orderq ² (whereq andq ² - 1 are coprime to 30) such thatS ₅ acts on the line at infinity. It turns out that the Klein correspondence is in particular useful for the investigation of these planes. Representations of the planes, automorphisms and examples of low order are studied in detail. In view of a problem of Ostrom (Math. Z. 156 (1977), 59–71), series of translation planes are constructed with the following property: the translation complement is nonsolvable and has an order coprime to the characteristic of the plane.     

On the integral representation of superbiharmonic functions

We consider a nonnegative superbiharmonic function w satisfying some growth condition near the boundary of the unit disk in the complex plane. We shall find an integral representation formula for w in terms of the biharmonic Green function and a multiple of the Poisson kernel. This generalizes a Riesz-type formula already found by the author for superbihamonic functions w satisfying the condition 0 ⩽ w(z) ⩽ C(1-|z|) in the unit disk. As an application we shall see that the polynomials are dense in weighted Bergman spaces whose weights are superbiharmonic and satisfy the stated growth condition near the boundary. Research supported in part by IPM under the grant number 83310011.