We consider subsets of the (symbolic) sequence space that are invariant under
the action of the semigroup of multiplicative integers. A representative
example is the collection of all 0-1 sequences $(x_k)$ such that $x_k x_{2k}=0$
for all $k$. We compute the Hausdorff and Minkowski dimensions of these sets
and show that they are typically different. The proof proceeds via a
variational principle for multiplicative subshifts.
Let $\nu_\lambda^p$ be the distribution of the random series
$\sum_{n=1}^\infty i_n \lambda^n$, where $i_n$ is a sequence of i.i.d. random
variables taking the values 0,1 with probabilities $p,1-p$. These measures are
the well-known (biased) Bernoulli convolutions.
In this paper we study the multifractal spectrum of $\nu_\lambda^p$ for
typical $\lambda$. Namely, we investigate the size of the sets
\[ \Delta_{\lambda,p}(\alpha) = \left\{x\in\R: \lim_{r\searrow 0} \frac{\log
\nu_\lambda^p(B(x,r))}{\log r} =\alpha\right\}. \]
We consider self-affine tilings in the Euclidean space and the associated
tiling dynamical systems, namely, the translation action on the orbit closure
of the given tiling. We investigate the spectral properties of the system.
We show that for multi-colored Delone point sets with finite local complexity
and uniform cluster frequencies the notions of pure point diffraction and pure
point dynamical spectrum are equivalent.
There is a growing body of results in the theory of discrete point sets and
tiling systems giving conditions under which such systems are pure point
diffractive. Here we look at the opposite direction: what can we infer about a
discrete point set or tiling, defined through a primitive substitution system,
given that it is pure point diffractive? Our basic objects are Delone multisets
and tilings, which are self-replicating under a primitive substitution system
of affine mappings with a common expansive map $Q$.
We consider linear iterated function systems (IFS) with a constant
contraction ratio in the plane for which the ``overlap set'' $\Ok$ is finite,
and which are ``invertible'' on the attractor $A$, the sense that there is a
continuous surjection $q: A\to A$ whose inverse branches are the contractions
of the IFS. The overlap set is the critical set in the sense that $q$ is not a
local homeomorphism precisely at $\Ok$. We suppose also that there is a
rational function $p$ with the Julia set $J$ such that $(A,q)$ and $(J,p)$ are
conjugate.