Covering the Plane with Congruent Copies of a Convex Body

It is shown that every plane compact convex set K with an interiorpoint admits a covering of the plane with density smaller thanor equal to 8(23 – 3)/3 = 1.2376043.... For comparison,the thinnest covering of the plane with congruent circles isof density 2 / 27 = 1.209199576.... (see R. Kershner [3]), whichshows that the covering density bound obtained here is closeto the best possible. It is conjectured that the best possibleis 2 / 27. The coverings produced here are of the double-latticekind consisting of translates of K and translates of —K.     

Unavoidable Crossings in a Thinnest Plane Covering with Congruent Convex Disks

Two convex disks K and L in the plane are said to cross each other if the removal of their intersection causes each disk to fall into disjoint components. Almost all major theorems concerning the covering density of a convex disk were proved only for crossing-free coverings. This includes the classical theorem of L. Fejes Tóth (Acta Sci. Math. Szeged 12/A:62–67, 1950) that uses the maximum area hexagon inscribed in the disk to give a significant lower bound for the covering density of the disk. From the early seventies, all attempts of generalizing this theorem were based on the common belief that crossings in a plane covering by congruent convex disks, being counterproductive for producing low density, are always avoidable. Partial success was achieved not long ago, first for “fat” ellipses (A. Heppes in Discrete Comput. Geom. 29:477–481, 2003) and then for “fat” convex disks (G. Fejes Tóth in Discrete Comput. Geom. 34(1):129–141, 2005), where “fat” means of shape sufficiently close to a circle. A recently constructed example will be presented here, showing that, in general, all such attempts must fail. Three perpendiculars drawn from the center of a regular hexagon to its three nonadjacent sides partition the hexagon into three congruent pentagons. Obviously, the plane can be tiled by such pentagons. But a slight modification produces a (non-tiling) pentagon with an unexpected covering property: every thinnest covering of the plane by congruent copies of the modified pentagon must contain crossing pairs. The example has no bearing on the validity of Fejes Tóth’s bound in general, but it shows that any prospective proof must take into consideration the existence of unavoidable crossings.     

Covering a Convex Polygon by Triangles

According to a theorem of A. V. Bogomolnaya, F. L. Nazarov and S. E. Rukshin, if n points are given inside a convex n-gon, then the points and the sides of the polygon can be numbered from 1 to n so that the triangles spanned by the ith point and the ith side(i=1....,n ) cover the polygon. In this paper, we prove that the same can be done without assuming that the given points are inside the convex n-gon. We also show that in the general case at least [(n/3)] mutually nonoverlapping triangles can be constructed in the same manner.     

Minimal Convex k-Gons Containing a Given Convex Polygon

There is a k-gon of minimal area containing a given convex n-gon (k<n) such that k-1 sides of the n-gon lie on the sides of the k-gon. All midpoints of the sides of the k-gon belong to the n-gon. Bibliography: 3 titles.     

Covering a Rectangle With Equal Circles

Recently, Tarnai and Gáspár [22] used mechanically inspired computer simulations to construct thin coverings of a square with up to ten equal circles. We generalise the problem to rectangles and determine the thinnest coverings of a general rectangle with up to five equal circles. Partial results are presented for coverings with seven circles.     

The Densest Packing of 19 Congruent Circles in a Circle

Dense packings of n congruent circles in a circle were given by Kravitz in 1967 for n = 2,..., 16. In 1969 Pirl found the optimal packings for n 10, he also conjectured the dense configurations for 11 n 19. In 1994, Melissen provided a proof for n = 11. In this paper we exhibit the densest packing of 19 congruent circles in a circle with the help of a technique developed by Bateman and Erdös.     

Tilings of Convex Polygons with Congruent Triangles

By the spectrum of a polygon A we mean the set of triples (??,??,??) such that A can be dissected into congruent triangles of angles ??,??,??. We propose a technique for finding the spectrum of every convex polygon. Our method is based on the following classification. A tiling is called regular if there are two angles of the triangles, ?? and ?? such that at every vertex of the tiling the number of triangles having angle ?? equals the number of triangles having angle ??. Otherwise the tiling is irregular. We list all pairs (A,T) such that A is a convex polygon and T is a triangle that tiles A regularly. The list of triangles tiling A irregularly is always finite, and can be obtained, at least in principle, by considering the system of equations satisfied by the angles, examining the conjugate tilings, and comparing the sides and the area of the triangles to those of A. Using this method we characterize the convex polygons with infinite spectrum, and determine the spectrum of the regular triangle, the square, all rectangles, and the regular N-gons with N large enough.     

Packings of Unequal Circles in a Convex Set

   Abstract. In the Euclidean plane let T be a convex set, and let K ₁ , ..., K _n be a family of n ≥ 2 circles packed into T . We show that the density of each such packing is smaller than

Optimal Covering of Plane Domains by Circles Via Hyperbolic Smoothing

We consider the problem of optimally covering plane domains by a given number of circles. The mathematical modeling of this problem leads to a min–max–min formulation which, in addition to its intrinsic multi-level nature, has the significant characteristic of being non-differentiable. In order to overcome these difficulties, we have developed a smoothing strategy using a special class C^∞ smoothing function. The final solution is obtained by solving a sequence of differentiable subproblems which gradually approach the original problem. The use of this technique, called Hyperbolic Smoothing, allows the main difficulties presented by the original problem to be overcome. A simplified algorithm containing only the essential of the method is presented. For the purpose of illustrating both the actual working and the potentialities of the method, a set of computational results is presented.     

Covering Convex Bodies by Cylinders and Lattice Points by Flats

In connection with an unsolved problem of Bang (1951) we give a lower bound for the sum of the base volumes of cylinders covering a d-dimensional convex body in terms of the relevant basic measures of the given convex body. As an application we establish lower bounds on the number of k-dimensional flats (i.e. translates of k-dimensional linear subspaces) needed to cover all the integer points of a given convex body in d-dimensional Euclidean space for 1≤k≤d−1. K. Bezdek and A.E. Litvak are partially supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant.     

Splitting a Concave Domain to Convex Subdomains

1.IntroductionTurninglargescaleproblemtosmallscalesubproblemsandregularizingirregularproblemaretwomainsubjectsofdomaindecomposition.Inregularization,regularizingirregularregionisoffirstimportance.Irregularityoftenmeansconcavity,forexample,L-shaped,T--shapedandC-shapeddomainsareirregulardomains.Inthispaperswewillstudydomaindecompositionmethodforellipticproblemsdefinedonirregularregion.SchwarzalternatingInethodisthebasisofalmostalldomaindecompositionmethoddeveloped.Othermethodsarevariationsof…     

平面圆盘覆盖方法的改进

本文提出了用两种半径不等的圆来覆盖平面的方法 ,将覆盖效率由 3 3 2 / π≈ 83 %提高到 1 83 / 1 1 π≈ 90 % .     

Common Sections with Given Properties for a Finite Set of Convex Compacta

Let be convex compacta and let O be their common interior point. It is proved that there exists a 2-plane H through O such that for in–2 an affine image of a given centrally symmetric hexagon is inscribed in K_iH and has center at O. Furthermore, there exist n–3 2-planes H₁,...,H_n-3 through O lying at the same time in a 3-plane such that for in–3 an affine image of a regular octagon is inscribed in H_iK_i and has center at O. Bibliography: 9 titles.     

多元函数定点处偏导数的求解方法

针对多元函数定点处偏导数的计算,采用不同知识点、思路给出了此类问题的四种解法.     

Boundedness of the Hessian of a Biharmonic Function in a Convex Domain

We consider the Dirichlet problem for the biharmonic equation on an arbitrary convex domain and prove that the second derivatives of the variational solution are bounded in all dimensions.     

Best Approximations of Convex Compact Sets by Balls in the Hausdorff Metric

We deduce an upper bound for the Hausdorff distance between a nonempty bounded set and the set of all closed balls in a strictly convex straight geodesic space X of nonnegative curvature. We prove that the set $\chi \left[ {\rm M} \right]$ of centers of closed balls approximating a convex compact set in the Hausdorff metric in the best possible way is nonempty _X [M] and is contained in M. Some other properties of $\chi \left[ {\rm M} \right]$ also are investigated.     

Convex Hulls of Orbits and Orientations of a Moving Protein Domain

We study the facial structure and Carathéodory number of the convex hull of an orbit of the group of rotations in ℝ³ acting on the space of pairs of anisotropic symmetric 3×3 tensors. This is motivated by the problem of determining the structure of some proteins in an aqueous solution.