Searcharxiv⌕ Search

arXiv subjects

Seonhee Lim

Publications and source records attributed to Seonhee Lim.

29 records · Page 2Linked to original sources
arXiv2017

Continued fraction algorithm for Sturmian colorings of trees

Factor complexity $b_ϕ(n)$ for a vertex coloring $ϕ$ of a regular tree is the number of colored $n$-balls up to color-preserving automorphisms. Sturmian colorings are colorings of minimal unbounded factor complexity $b_ϕ(n) = n+2$. In this article, we prove an induction algorithm for Sturmian colorings using colored balls in a way analogous to induction algorithm of Sturmian words. Furthermore, we characterize Sturmian colorings in terms of the data for the induction algorithm.

math.DS↗
arXiv2016

Integrated multimodal network approach to PET and MRI based on multidimensional persistent homology

Finding the underlying relationships among multiple imaging modalities in a coherent fashion is one of challenging problems in the multimodal analysis. In this study, we propose a novel multimodal network approach based on multidi- mensional persistent homology. In this extension of the previous threshold-free method of persistent homology, we visualize and discriminate the topological change of integrated brain networks by varying not only threshold but also mixing ratios between two different imaging modalities. Moreover, we also pro- pose an integration method for multimodal networks, called one-dimensional projection, with a specific mixing ratio between modalities. We applied the proposed methods to PET and MRI data from 21 autism spectrum disorder (ASD) children and 10 pediatric control subjects. From the results, we found that the brain networks of ASD children and controls differ significantly, with ASD showing asymmetrical changes of connected structures between PET and MRI. The integrated MRI and PET networks showed that ASD children had weaker connections than controls within the visual cortex, between dorsal and ventral parts of the temporal pole, between frontal and parietal regions, and between the left perisylvian and other brain regions. These results provide a multidimensional homological understanding of disease-related PET and MRI networks that discloses the network association with ASD.

q-bio.QM↗
arXiv2014

Farey map, Diophantine approximation and Bruhat-Tits tree

Based on Broise-Alamichel and Paulin's work on the Gauss map corresponding to the principal convergents, we continue the study of the Gauss map via Farey maps to contain all the intermediate convergents. We define the geometric Farey map, which is given by time-1 map of the geodesic flow. We also define algebraic Farey maps, better suited for arithmetic properties, which produce all the intermediate convergents. Then we obtain the ergodic invariant measures for the Farey maps and the convergent speed.

math.DS↗
arXiv2012

Subword complexity and Sturmian colorings of regular trees

In this article, we study subword complexity of colorings of regular trees. We characterize colorings of bounded subword complexity and study Sturmian colorings, which are colorings of minimal unbounded subword complexity. We classify Sturmian colorings using their type sets. We show that any Sturmian coloring is a lifting of a coloring on a quotient graph of the tree which is a geodesic or a ray with loops possibly attached, thus a lifting of an "infinte word". We further give a complete characterization of the quotient graph for eventually periodic ones.

math.DS↗
arXiv2010

On the distribution of orbits of geometrically finite hyperbolic groups on the boundary (with appendix by Francois Maucourant)

We investigate the distribution of orbits of a non-elementary discrete hyperbolic group acting on the n-dimensional hyperbolic space and its geometric boundary. In particular, we show that if the group $Γ$ admits a finite Bowen-Margulis-Sullivan measure (for instance, if it is geometrically finite), then every $Γ$-orbit in the hyperbolic space is equidistributed with respect to the Patterson-Sullivan measure supported on the limit set of $Γ$.The appendix by Maucourant is the extension of a part of his thesis where he obtains the same result as a simple application of Roblin's theorem. Our approach is via establishing the equidistribution of solvable flows on the unit tangent bundle of the quotient manifold, which is of independent interest.

math.DS↗
arXiv2009

On Commensurizer Growth

We study new asymptotic invariant of a pair consisting of a group and a subgroup, which we call Commensurizer Growth. We compute the commensurizer growth for several examples, concentrating mainly on the case of a locally compact topological group and a lattice inside it.

math.GR↗
arXiv2009

Volume entropy of hyperbolic buildings

We characterize the volume entropy of an arbitrary regular building as the topological pressure of the geodesic flow on an apartment. We show that the Liouville measure is not entropy maximizing measure for regular hyperbolic buildings. As a consequence, we obtain a strict lower bound on the volume entropy in terms of the branching numbers and the volume of the boundary polyhedrons.

math.DS↗
arXiv2007

Covering theory for complexes of groups

We develop an explicit covering theory for complexes of groups, parallel to that developed for graphs of groups by Bass. Given a covering of developable complexes of groups, we construct the induced monomorphism of fundamental groups and isometry of universal covers. We characterize faithful complexes of groups and prove a conjugacy theorem for groups acting freely on polyhedral complexes. We also define an equivalence relation on coverings of complexes of groups, which allows us to construct a bijection between such equivalence classes, and subgroups or overgroups of a fixed lattice $Γ$ in the automorphism group of a locally finite polyhedral complex $X$.

math.GR↗
arXiv2005

Minimal volume entropy on graphs

Among the normalized metrics on a graph, we show the existence and the uniqueness of an entropy-minimizing metric, and give explicit formulas for the minimal volume entropy and the metric realizing it.

math.GR↗
arXiv2005

Counting overlattices in automorphism groups of trees

We give an upper bound for the number of ``overlattices'' in the automorphism group of a tree, containing a fixed lattice with index n. For an example of a lattice in the automorphism group of a 2p-regular tree whose quotient is a loop, we obtain a lower bound of the asymptotic behavior as well.

math.GR↗