Stochastic point processes relevant to the theory of long-range aperiodic
order are considered that display diffraction spectra of mixed type, with
special emphasis on explicitly computable cases together with a unified
approach of reasonable generality. The latter is based on the classical theory
of point processes and the Palm distribution. Several pairs of autocorrelation
and diffraction measures are discussed which show a duality structure analogous
to that of the Poisson summation formula for lattice Dirac combs.
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 $Q$.
A linear deformation of a Meyer set $M$ in $\RR^d$ is the image of $M$ under
a group homomorphism of the group $[M]$ generated by $M$ into $\RR^d$. We
provide a necessary and sufficient condition for such a deformation to be a
Meyer set. In the case that the deformation is a Meyer set and the deformation
is injective, the deformation is pure point diffractive if the orginal set $M$
is pure point diffractive.