Partially balanced incomplete block designs from weakly divisible nearrings

In [[6] Riv. Mat. Univ. Parma 11 (2) (1970) 79-96] Ferrero demonstrates a connection between a restricted class of planar nearrings and balanced incomplete block designs. In this paper, bearing in mind the links between planar nearrings and weakly divisible nearrings (wd-nearrings), first we show the construction of a family of partially balanced incomplete block designs from a special class of wd-nearrings; consequently, we are able to give some formulas for calculating the design parameters.     

Composition rings from formal power series rings

We study the ideals in some Dickson nearrings of polynomials and formal power series. For some of their related quotients, we introduce variants and generalizations, and construct composition rings also.     

Topological nearrings whose additive groups are Euclidean

Let (G,+) be a group with a locally compact Hausdorff topology for which the binary operation + is continuous. Those, binary operation * onG for which (G, +, *) is a topological nearring are described. In the case whereG is abelian, those binary operations * for which (G, +, *) is a topological ring are also described. Versions of these results are then obtained in the special case where the group is the topological Euclideann-group,R ⁿ. A family of binary operations * for which (R ⁿ, +, *)_is a topological nearring is then investigated in some detail. Most of these nearrings turn out to be planar. Their ideals are completely determined and we characterize those nearrings which are simple. The multiplicative semi-groups (R ⁿ, *) of these nearrings are then investigated. Green's relations are completely determined and it is shown that a number of familiar properties of semigroups are equivalent for these particular semigroups. Finally, all those binary operations * for which (R, +, *) is a topological nearring are completely described. It is determined when any two of these nearrings are isomorphic and for each of these nearrings, its automorphism group, is completely determined.     

Planar nearrings on the Euclidean plane

Planar near-rings are generalized rings which can serve as coordinate domains for geometric structures in which each pair of nonparallel lines has a unique point of intersection. It is known that all planar nearrings can be constructed from regular groups of automorphisms of groups which can be viewed as the “action groups” of the planar nearring. In this article, we study planar nearrings whose additive group is \({(\mathbb{R}^n,+)}\) , in particular, n = 1 and 2. It is natural to study topological planar nearrings in this context, following ideas of the late Kenneth D. Magill, Jr. In the case of n = 1, we characterize all topological planar nearrings by their action groups \({(\mathbb{R}^*, \cdot)}\) or \({(\mathbb{R}^+, \cdot)}\) . For n = 2, these action groups and the circle group \({(\mathbb{U}, \cdot)}\) seem to be the most interesting cases, but the last case can be excluded completely. As a consequence, we obtain characterizations of the semi-homogeneous continuous mappings from \({\mathbb{R}^n}\) to \({\mathbb{R}}\) for n = 1 and 2. Such a mapping f enjoys the property that f(f(u)v) = f(u)f(v) for all \({u,v \in \mathbb{R}^n}\) . When \({f(\mathbb{R}^n) = \mathbb{R}^+}\) , f is a positive homogeneous mapping of degree 1.     

Two Dimensional Nilpotent Euclidean Nearrings

We find all multiplications on the two dimensional Euclidean group (IR²,+) such that (IR², +, ·) is a nilpotent topological nearring of rank three. We determine the left, right, and two sided ideals of these nearrings and we determine when two of these nearrings are isomorphic. As a consequence, we are able to conclude that there are infinitely many isomorphism classes of such nearrings. This is in considerable contrast to the case for rings. There are only eight isomorphism classes of topological rings with additive group (IR²,+).AMS Subject Classification (2000) 16Y30     

Local Nearrings with Multiplicative Shmidt Group

Ukrainian Mathematical Journal - We propose a classification of finite local nearrings with multiplicative Shmidt group. Moreover, it is shown that there are no nearrings with identity on the...     

Nearrings whose set of N-subgroups is linearly ordered

We consider zerosymmetric right nearrings whose lattice of N-subgroups is linearly ordered by inclusion and in which for every n ∈ N, there is x ∈ N such that x * n = n. All such nearrings with finitely many N-subgroups are constructed.     

Segments in a planar nearring

Suppose (N,+,·) is a finite (left) planar nearring. Define the (line) segment in N with endpoints a and b by

We prove that under many circumstances we have

which is the same phenomenon as in the Euclidean plane.     

On Polynomials Over Rickart Rings and Their Generalizations I

This paper continues the investigation of polynomials and formal power series over a ring with various annihilator conditions which were originally used by Rickart and Kaplansky to abstract the algebraic properties of von Neumann algebras. Results of Armendariz on polynomial rings over a PP ring are extended to analogous annihilator conditions in nearrings of polynomials and nearrings of formal power series. These results are somewhat striking since, in contrast to the polynomial ring case, the nearring of polynomials or formal power series has substitution for its “multiplication” operation. These investigations provide an alternative viewpoint in illustrating the structure of polynomials and formal power series. Extensions of Rickart rings to formal power series rings are also discussed. The author was partially supported by the National Science Council, Taiwan under the grant number NSC 93-2115-M-143-001.     

Projective Klingenberg planes over nearrings

In the first section the definition of a PK-nearring is given and it is shown that every PK-nearring is a local ternary ring. Then a PK-nearring is used to construct PK-planes and further algebraic properties of PK-nearrings are related to geometrical ones of the corresponding PK-planes. Finally, a wide class of PK-nearrings is presented by applying the Dickson-process to the ring of formal power series.Throughout the following all nearrings shall be left-distributive. For the notation and basic properties of nearrings the reader is referred to Pilz [5].Dedicated to Professor Helmut Karzel on the occasion of his 65. birthday     

PRME AND k-PRIME IDEALS IN Ω-GROUPS

Abstract

In this paper we define two concepts of prime ideals for Ω-groups. The first generalizes the definitions of prime ideal in rings, nearrings, Γ-rings, associative algebras and Lie algebras. The second generalizes a concept defined for groups by ??ukin ([21]). We show that both lead to radicals in the sense of Hoehnke ([10]). Furthermore in the case of rings, Γ-rings, abelian zero-symmetric nearrings and cubic rings these two definitions coincide, thus obtaining a new characterization for the prime ideal. Zero-symmetric Ω-groups are defined analogously to the nearring case and a new characterization in term of ideals is given.     

直角平面内圆孔对稳态SH波的散射

利用复变函数方法和多极坐标移动技术，研究了直角平面内圆孔在直边分布有反平面稳态载荷时的sH波散射问题．首先构造出直角平面内不含有圆孔时满足边界应力条件的Green函数解；其次提出直角平面内存在圆孔时满足边界应力自由条件的散射波解，并利用叠加原理写出问题的位移总波场．借助于多极坐标移动技术和圆孔边界处应力自由条件，列出求解散射波解中未知系数的无穷代数方程组，在满足计算精度的前提下，通过有限项截断进行求解．作为算例，具体讨论了圆孔边界处的环向动应力随不同波数、圆孔位置及载荷分布位置和分布范围大小的变化情况，算例结果说明了算法的有效实用性．     

Factorizations of groups and related topics

This is a survey of some recent progress in the theory of groups with factorizations. Some of the methods can be used to obtain information about finite groups in general, nilpotent algebras and nearrings.      

On circular designs

Summary A general method of analysis of circular designs (Das [3]) is suggested. Average efficiency factors of these designs have been tabulated.A-optimality of circular designs has been studied in comparison to group divisible incomplete block designs.     

Some remarks on filtrations of hopf algebras

In this paper, the problem of nontrivial nearring multiplications on groups is closely investigated with a different approach. By using the notions of 5, 0-acts and the language of model theory, we give a detailed discussion on a large class of groups that possesses nontrivial nearring multiplications. In the last section, we apply our results to the theory of centralizer nearrings of a single endomorphism which is mainly due to the work of C. Maxson and K. Smith [28, 29]     

平面图的循环色数与临界性

循环着色是普通着色的推广。本文中,我们研究了一类平面图的循环着色问题,并证明了这类平面图是循环色临界的,但不是普通色临界的,同时,我们还研究了循环着色与图G_k~d中的链之间的关系．     

A Möbius-Invariant Power Diagram and Its Applications to Soap Bubbles and Planar Lombardi Drawing

We use three-dimensional hyperbolic geometry to define a form of power diagram for systems of circles in the plane that is invariant under Möbius transformations. By applying this construction to circle packings derived from the Koebe–Andreev–Thurston circle packing theorem, we show that every planar graph of maximum degree three has a planar Lombardi drawing (a drawing in which the edges are drawn as circular arcs, meeting at equal angles at each vertex). We use circle packing to construct planar Lombardi drawings of a special class of 4-regular planar graphs, the medial graphs of polyhedral graphs, and we show that not every 4-regular planar graph has a planar Lombardi drawing. We also use these power diagrams to characterize the graphs formed by two-dimensional soap bubble clusters (in equilibrium configurations) as being exactly the 3-regular bridgeless planar multigraphs, and we show that soap bubble clusters in stable equilibria must in addition be 3-connected.     

Drawing planar graphs with circular arcs

In this paper we address the problem of drawing planar graphs with circular arcs while maintaining good angular resolution and small drawing area. We present a lower bound on the area of drawings in which edges are drawn using exactly one circular arc. We also give an algorithm for drawing n -vertex planar graphs such that the edges are sequences of two continuous circular arcs. The algorithm runs in O(n) time and embeds the graph on the O(n)\times O(n) grid, while maintaining Θ(1/d(v)) angular resolution, where d(v) is the degree of vertex v . Since in this case we use circular arcs of infinite radius, this is also the first algorithm that simultaneously achieves good angular resolution, small area, and at most one bend per edge using straight-line segments. Finally, we show how to create drawings in which edges are smooth C ¹ -continuous curves, represented by a sequence of at most three circular arcs. Received September 30, 1999, and in revised form March 27, 2000. Online publication October 26, 2000.     

Circular list colorings of some graphs

The circular list coloring is a circular version of list colorings of graphs. Let χinc,l denote the circular choosability(or the circular list chromatic number). In this paper, the circular choosability of outer planar graphs and odd wheel is discussed.