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Werner Nagel

Publications and source records attributed to Werner Nagel.

13 recordsLinked to original sources
arXiv2023

Tessellation-valued processes that are generated by cell division

Processes of random tessellations of the Euclidean space $\mathbb{R}^d$, $d\geq 1$, are considered which are generated by subsequent division of their cells. Such processes are characterized by the laws of the life times of the cells until their division and by the laws for the random hyperplanes that divide the cells at the end of their life times. The STIT tessellation processes are a reference model. In the present paper a generalization concerning the life time distributions is introduced, a sufficient condition for the existence of such cell division tessellation processes is provided and a construction is described. In particular, for the case that the random dividing hyperplanes have a Mondrian distribution -- which means that all cells of the tessellations are cuboids -- it is shown that the intrinsic volumes, except the Euler characteristic, can be used as the parameter for the exponential life time distribution of the cells.

math.PR↗
arXiv2018

The largest order statistics for the inradius in an isotropic STIT tessellation

A planar stationary and isotropic STIT tessellation at time $t>0$ is observed in the window $W_ρ={t^{-1}}\sqrt{π\ ρ}\cdot [-\frac{1}{2},\frac{1}{2}]^2$, for $ρ>0$. With each cell of the tessellation, we associate the inradius, which is the radius of the largest disk contained in the cell. Using the Chen-Stein method, we compute the limit distributions of the largest order statistics for the inradii of all cells whose nuclei are contained in $W_ρ$ as $ρ$ goes to infinity.

math.PR↗
arXiv2017

Regenerative processes for Poisson zero polytopes

Let $(M_t: t > 0)$ be a Markov process of tessellations of ${\mathbb R}^\ell$ and $({\cal C}_t:\, t > 0)$ the process of their zero cells (zero polytopes) which has the same distribution as the corresponding process for Poisson hyperplane tessellations. Let $a>1$. Here we describe the stationary zero cell process $(a^t {\cal C}_{a^t}:\, t\in {\mathbb R})$ in terms of some regenerative structure and we prove that it is a Bernoulli flow. An important application are the STIT tessellation processes.

math.PR↗
arXiv2017

Joseph Mecke's last fragmentary manuscripts - a compilation

Summarizing results from Joseph Mecke's last fragmentary manuscripts, the generating function and the Laplace transform for nonnegative random variables are considered. The concept of thickening of a random variable, as an inverse operation to thinning (which is usually applied to point processes) is introduced, based on generating functions, and a characterization of thickable random variables is given. Further, some new relations between exponential distributions and their interpretation in terms of Poisson point processes are derived with the help of the Laplace transform.

math.PR↗
arXiv2016

A Mecke-type formula and Markov properties for STIT tessellation processes

An analogue of the classical Mecke formula for Poisson point processes is proved for the class of space-time STIT tessellation processes. From this key identity the Markov property of a class of associated random processes is derived. This in turn is used to determine the distribution of the number of internal vertices of the typical maximal tessellation segment.

math.PR↗
arXiv2016

STIT Tessellations -- Ergodic Limit Theorems and Bounds for the Speed of Convergence

We consider homogeneous STIT tessellations in the $\ell$-dimensional Euclidean space ${\mathbb R}^\ell$. Based on results for the spatial $β$-mixing coefficient an upper bound for the variance of additive functionals of tessellations is derived, using results by Yoshihara and Heinrich. Moreover, ergodic theorems are applied to subadditive functionals.

math.PR↗
arXiv2014

STIT Process and Trees

We study several constructions of the STIT tessellation process in a window of $\RR^\ell$ and supply an exact formula for its transition probability.

math.PR↗
arXiv2014

On the capacity functional of excursion sets of Gaussian random fields on $\R^2$

When a random field $(X_t, \ t\in {\mathbb R}^2)$ is thresholded on a given level $u$, the excursion set is given by its indicator $~1_{[u, \infty)}(X_t)$. The purpose of this work is to study functionals (as established in stochastic geometry) of these random excursion sets, as e.g. the capacity functional as well as the second moment measure of the boundary length. It extends results obtained for the one-dimensional case to the two-dimensional case, with tools borrowed from crossings theory, in particular Rice methods, and from integral and stochastic geometry.

math.PR↗
arXiv2013

On the consistency of cell division processes

For a class of cell division processes, generating tessellations of the Euclidean space $\mathbb{R}^d$, spatial consistency is investigated. This addresses the problem whether the distribution of these tessellations, restricted to a bounded set $V$, depends on the choice of a larger region $W\supset V$ where the construction of the cell division process is performed. This can also be understood as the problem of boundary effects in the cell division procedure. In Nagel and Weiß (2005) it was shown that the STIT tessellations are spatially consistent There were hints that the STIT tessellation process might be the only translation-invariant cell division process that has such a consistency property. In the present paper it is shown that, within a reasonable wide class of cell division processes, the STIT tessellations are the only ones that are consistent.

math.PR↗
arXiv2012

STIT Tessellations have trivial tail σ-algebra

We consider homogeneous STIT tessellations Y in the \ell-dimensional Euclidean space and show the triviality of the tail σ-algebra. This is a sharpening of the mixing result by Lachièze-Rey.

math.PR↗
arXiv2011

Spatial STIT Tessellations -- Distributional Results for I-Segments

Three-dimensional random tessellations that are stable under iteration (STIT tessellations) are considered. They arise as a result of subsequent cell division, which implies that their cells are not face-to-face. The edges of the cell-dividing polygons are the so-called I-segments of the tessellation. The main result is an explicit formula for the distribution of the number of vertices in the relative interior of the typical I-segment. On the way of its proof other distributional identities for the typical as well as for the length-weighted typical I-segment are obtained. They provide new insight into the spatio-temporal construction process.

math.PR↗
arXiv2010

Ergodic Description of STIT Tessellations

Let (Y_t: t > 0) be the STIT tessellation process. We show that for all polytopes W with nonempty interior and all a>1, the renormalized random sequence (a^n Y_{a^n}: n integer) induced in W, is a finitary factor of a Bernoulli shift. As a corollary we get that the renormalized continuous time process (a^t Y_{a^t}: t real) induced in W is a Bernoulli flow.

math.PR↗