A note on a property of a weak self-similar perfect set

Let S be a compact, weak self-similar perfect set based on a system of weak contractions f_j, j=1,…,m each of which is characterized by a variable contraction coefficient _j(l) as d(f_j(x),f_j(y)) _j(l)d(x,y), d(x,y)<l, l>0. If the relation ∑^m_j=1j(l₀)<1 holds at at least one point l₀, then every nonempty compact metric space is a continuous image of the set S.     

An estimate of the Hausdorff dimension of a weak self-similar set

We propose an estimate to quantitatively evaluate the Hausdorff dimension of a self-similar set based on a system of weak contractions each of whose contraction coefficient is not a constant but a function of a parameter. Using the estimate, we investigate the topological structures specific to this weak self-similar set.     

On the open set condition for self-similar fractals

For self-similar sets, the existence of a feasible open set is a natural separation condition which expresses geometric as well as measure-theoretic properties. We give a constructive approach by defining a central open set and characterizing those points which do not belong to feasible open sets.

     

Surface homeomorphisms with zero-dimensional singular set

We prove that if ƒ is an orientation-preserving homeomorphism of a closed orientable surface M² whose singular set Σ(ƒ) is totally disconnected, then ƒ is topologically conjugate to a conformal transformation.     

Euclidean self-similar sets generated by geometrically independent sets

For every integer n>0, we consider all iterated function systems generated by n+1 Euclidean similarities acting on Rn whose fixed points form the set of vertices of an n-simplex, and characterize the nature of attractors of such iterated function systems in terms of contractivity factors of their generators.     

On the semilattice of weak orders of a set

Order theoretic and combinatorial properties of the semilattice of weak orders on a set are developed. In the case of a finite set, an order theoretic characterization of this semilattice is obtained.     

Relation between spectral classes of a self-similar Cantor set

A self-similar Cantor set is completely decomposed as a class of the lower (upper) distribution sets. We give a relationship between the distribution sets in the distribution class and the subsets in a spectral class generated by the lower (upper) local dimensions of a self-similar measure. In particular, we show that each subset of a spectral class is exactly a distribution set having full measure of a self-similar measure related to the distribution set using the strong law of large numbers. This gives essential information of its Hausdorff and packing dimensions. In fact, the spectral class by the lower (upper) local dimensions of every self-similar measure, except for a singular one, is characterized by the lower or upper distribution class. Finally, we compare our results with those of other authors.     

Hausdorff measure of infinitely generated self-similar sets

We analyze self-similarity with respect to infinite sets of similitudes from a measure-theoretic point of view. We extend classic results for finite systems of similitudes satisfying the open set condition to the infinite case. We adopt Vitali-type techniques to approximate overlapping self-similar sets by non-overlapping self-similar sets. As an application we show that any open and bounded set with a boundary of null Lebesgue measure always contains a self-similar set generated by a countable system of similitudes and with Lebesgue measure equal to that ofA.     

On the exact Hausdorff measure of a class of self-similar sets satisfying open set condition

In this paper,we provide a new effective method for computing the exact value of Hausdorff measures of a class of self-similar sets satisfying the open set condition(OSC).As applications,we discuss a self-similar Cantor set satisfying OSC and give a simple method for computing its exact Hausdorff measure.     

On the connectivity of the Julia set of a finitely generated rational semigroup

In this paper we show that the Julia set of a finitely generated rational semigroup is connected if the union of the Julia sets of generators is contained in a subcontinuum of . Under a nonseparating condition, we prove that the Julia set of a finitely generated polynomial semigroup is connected if its postcritical set is bounded.

     

Open set condition for graph directed self-similar structure

Graph directed self-similar structure generalizes the concept of self-similar set and contains some important instants of fractal sets. We characterize the open set condition (OSC), which is fundamental in the study of self-similar set, for graph directed self-similar structure in terms of the post critical set. Using this characterization, we establish the relations between OSC and other separation conditions including post-critically finite, finitely ramified condition and finite preimage property. It turns out that whether the intrinsic metric is doubling makes difference. In particular, finitely ramified condition implies OSC in case of doubling metric but does not in case of non-doubling metric.     

Multifractal formalism for self-similar measures with weak separation condition

For any self-similar measure μ on satisfying the weak separation condition, we show that there exists an open ball U₀ with μ(U₀)>0 such that the distribution of μ, restricted on U₀, is controlled by the products of a family of non-negative matrices, and hence μ|_U0 satisfies a kind of quasi-product property. Furthermore, the multifractal formalism for μ|_U0 is valid on the whole range of dimension spectrum, regardless of whether there are phase transitions. Moreover the dimension spectra of μ and μ|_U0 coincide for q0. This result unifies and improves many of the recent works on the multifractal structure of self-similar measures with overlaps.     

Weighted weak type estimates involving spaces generated by blocks

The problem studied in this paper is how to establish weighted estimates of weak type near L¹ for those operators that are not of weak type (1,1). The first author is supported by the NSFC (Tian Yuan) and the second is supported by NSF grant DMS-9007491.