For some fractal measures it is a very difficult problem in general to prove
the existence of spectrum (respectively, frame, Riesz and Bessel spectrum). In
fact there are examples of extremely sparse sets that are not even Bessel
spectra. In this paper we investigate this problem for general fractal measures
induced by iterated function systems (IFS). We prove some existence results of
spectra associated with Hadamard pairs.
In this paper, we study the moduli space of $1|2$-dimensional complex
associative algebras, which is also the moduli space of codifferentials on the
tensor coalgebra of a $2|1$-dimensional complex space. We construct the moduli
space by considering extensions of lower dimensional algebras. We also
construct miniversal deformations of these algebras. This gives a complete
description of how the moduli space is glued together via jump deformations.
We study Fourier frames of exponentials on fractal measures. We prove that,
for affine iterated function system measures, the Beurling dimension of a
Fourier frame must coincide with the Hausdorff dimension of the fractal. We
present necessary and/or sufficient conditions for a set of frequencies to form
a Bessel sequence or a frame of exponential functions.
In this paper, we study the moduli space of $2|1$-dimensional complex
associative algebras, which is also the moduli space of codifferentials on the
tensor coalgebra of a $1|2$-dimensional complex space. We construct the moduli
space by considering extensions of lower dimensional algebras. We also
construct miniversal deformations of these algebras. This gives a complete
description of how the moduli space is glued together via jump deformations.