Abstract:
We prove some limit properties of the harmonic mean of a random transition probability for finite Markov chains indexed by a homogeneous tree in a nonhomogeneous Markovian environment with finite state space. In particular, we extend the method to study the tree-indexed processes in deterministic environments to the case of random enviroments. 1. Introduction A tree is a graph which is connected and doesn't contain any circuits. Given any two vertices , let be the unique path connecting and . Define the graph distance to be the number of edges contained in the path . Let be an infinite tree with root . The set of all vertices with distance from the root is called the th generation of , which is denoted by . We denote by the union of the first generations of . For each vertex , there is a unique path from to and for the number of edges on this path. We denote the first predecessor of by . The degree of a vertex is defined to be the number of neighbors of it. If every vertex of the tree has degree , we say it is Cayley’s tree, which is denoted by . Thus, the root vertex has neighbors in the first generation and every other vertex has neighbors in the next generation. For any two vertices and of tree , write if is on the unique path from the root to . We denote by the farthest vertex from satisfying and . We use the notation and denote by the number of vertices of . In the following, we always let denote the Cayley tree . A tree-indexed Markov chain is the particular case of a Markov random field on a tree. Kemeny et al. [1] and Spitzer [2] introduced two special finite tree-indexed Markov chains with finite transition matrix which is assumed to be positive and reversible to its stationary distribution, and these tree-indexed Markov chains ensure that the cylinder probabilities are independent of the direction we travel along a path. In this paper, we omit such assumption and adopt another version of the definition of tree-indexed Markov chains which is put forward by Benjamini and Peres [3]. Yang and Ye[4] extended it to the case of nonhomogeneous Markov chains indexed by infinite Cayley’s tree and we restate it here as follows. Definition 1 (T-indexed nonhomogeneous Markov chains (see [4])). Let be an infinite Cayley tree, a finite state space, and a stochastic process defined on probability space , which takes values in the finite set . Let be a distribution on and a transition probability matrix on . If, for any vertex , then will be called -valued nonhomogeneous Markov chains indexed by infinite Cayley’s tree with initial distribution (1) and

Abstract:
We consider a sequence of Markov chains $(\mathcal X^n)_{n=1,2,...}$ with $\mathcal X^n = (X^n_\sigma)_{\sigma\in\mathcal T}$, indexed by the full binary tree $\mathcal T = \mathcal T_0 \cup \mathcal T_1 \cup ...$, where $\mathcal T_k$ is the $k$th generation of $\mathcal T$. In addition, let $(\Sigma_k)_{k=0,1,2,...}$ be a random walk on $\mathcal T$ with $\Sigma_k \in \mathcal T_k$ and $\widetilde{\mathcal R}^n = (\widetilde R_t^n)_{t\geq 0}$ with $\widetilde R_t^n := X_{\Sigma_{[tn]}}$, arising by observing the Markov chain $\mathcal X^n$ along the random walk. We present a law of large numbers concerning the empirical measure process $\widetilde{\mathcal Z}^n = (\widetilde Z_t^n)_{t\geq 0}$ where $\widetilde{Z}_t^n = \sum_{\sigma\in\mathcal T_{[tn]}} \delta_{X_\sigma^n}$ as $n\to\infty$. Precisely, we show that if $\widetilde{\mathcal R}^n \to \mathcal R$ for some Feller process $\mathcal R = (R_t)_{t\geq 0}$ with deterministic initial condition, then $\widetilde{\mathcal Z}^n \to \mathcal Z$ with $Z_t = \delta_{\mathcal L(R_t)}$.

Abstract:
We study systems of Kuramoto oscillators, driven by one pacemaker, on $d$-dimensional regular topologies like linear chains, rings, hypercubic lattices and Cayley-trees. For the special cases of next-neighbor and infinite-range interactions, we derive the analytical expressions for the common frequency in the case of phase-locked motion and for the critical frequency of the pacemaker, placed at an arbitrary position on the lattice, so that above the critical frequency no phase-locked motion is possible. These expressions depend on the number of oscillators, the type of coupling, the coupling strength, and the range of interactions. In particular we show that the mere change in topology from an open chain with free boundary conditions to a ring induces synchronization for a certain range of pacemaker frequencies and couplings, keeping the other parameters fixed. We also study numerically the phase evolution above the critical eigenfrequency of the pacemaker for arbitrary interaction ranges and find some interesting remnants to phase-locked motion below the critical frequency.

Abstract:
We study the mathematical aspects of the Bose Einstein Condensation for the pure hopping model describing arrays of Josephson junctions on non homogeneous networks. The graphs under investigation are obtained by adding density zero perturbations to the homogeneous Cayley Trees. The resulting topological model is described by the (opposite of the) adjacency operator on the graph. In the present paper we investigate some relevant spectral properties of the adjacency of the perturbed network, such the appearance of the hidden spectrum below the norm, the transience character and the Perron Frobenius distribution. All the mentioned properties have a mathematical interest in itself, and have natural applications for the investigation of the BEC of Bardeen Cooper Bosons on the networks under consideration.

Abstract:
A tree $T$ is said to be homogeneous if it is uniquely rooted and there exists an integer $b\geq 2$, called the branching number of $T$, such that every $t\in T$ has exactly $b$ immediate successors. We study the behavior of measurable events in probability spaces indexed by homogeneous trees. Precisely, we show that for every integer $b\geq 2$ and every integer $n\geq 1$ there exists an integer $q(b,n)$ with the following property. If $T$ is a homogeneous tree with branching number $b$ and $\{A_t:t\in T\}$ is a family of measurable events in a probability space $(\Omega,\Sigma,\mu)$ satisfying $\mu(A_t)\geq\epsilon>0$ for every $t\in T$, then for every $0<\theta<\epsilon$ there exists a strong subtree $S$ of $T$ of infinite height such that for every non-empty finite subset $F$ of $S$ of cardinality $n$ we have \[ \mu\Big(\bigcap_{t\in F} A_t\Big) \meg \theta^{q(b,n)}. \] In fact, we can take $q(b,n)= \big((2^b-1)^{2n-1}-1\big)\cdot(2^b-2)^{-1}$. A finite version of this result is also obtained.

Abstract:
By introducing the sample relative entropy rate as a measure of the deviation bewteen the arbitrary random fields and the Markov chain fields on Cayley trees, a class of small deviation theorems for the frequencies of state ordered couples are established. In the proof a new analytic technique in the study of the strong limit theorems for Markov chains is applied.

Abstract:
The green mineral dioptase Cu6Si6O18(H2O)6 has been known since centuries and plays an important role in esoteric doctrines. In particular, the green dioptase is supposed to grant the skill to speak with trees and to understand the language of birds. Armed with natural samples of dioptase, we were able to unravel the magnetic nature of the mineral (presumably with hidden support from birds and trees) and show that strong quantum fluctuations can be realized in an essentially framework-type spin lattice of coupled chains, thus neither frustration nor low-dimensionality are prerequisites. We present a microscopic magnetic model for the green dioptase. Based on full-potential DFT calculations, we find two relevant couplings in this system: an antiferromagnetic coupling J_c, forming spiral chains along the hexagonal c axis, and an inter-chain ferromagnetic coupling J_d within structural Cu2O6 dimers. To refine the J_c and J_d values and to confirm the proposed spin model, we perform quantum Monte-Carlo simulations for the dioptase spin lattice. The derived magnetic susceptibility, the magnetic ground state, and the sublattice magnetization are in remarkably good agreement with the experimental data. The refined model parameters are J_c = 78 K and J_d = -37 K with J_d/J_c ~ -0.5. Despite the apparent three-dimensional features of the spin lattice and the lack of frustration, strong quantum fluctuations in the system are evidenced by a broad maximum in the magnetic susceptibility, a reduced value of the Neel temperature T_N ~ 15 K >> J_c, and a low value of the sublattice magnetization m = 0.55 Bohr magneton. All these features should be ascribed to the low coordination number of 3 that outbalances the three-dimensional nature of the spin lattice.

Abstract:
We generalize the concept of ascending runs from permutations to Cayley trees and mappings. A combinatorial decomposition of the corresponding functional digraph allows us to obtain exact enumeration formulae that show an interesting connection to the Stirling numbers of the second kind. Using a bijective proof of Cayley's formula, we can show why the numbers of trees with a given number of ascending runs are directly linked to the corresponding numbers for mappings. Moreover, analytic tools allow a characterization of the limiting distribution of the random variable counting the number of ascending runs in a random mapping. As for permutations, this is a normal distribution with linear mean and variance.

Abstract:
A tree $T$ is said to be homogeneous if it is uniquely rooted and there exists an integer $b\meg 2$, called the branching number of $T$, such that every $t\in T$ has exactly $b$ immediate successors. A vector homogeneous tree $\mathbf{T}$ is a finite sequence $(T_1,...,T_d)$ of homogeneous trees and its level product $\otimes\mathbf{T}$ is the subset of the cartesian product $T_1\times ...\times T_d$ consisting of all finite sequences $(t_1,...,t_d)$ of nodes having common length. We study the behavior of measurable events in probability spaces indexed by the level product $\otimes\mathbf{T}$ of a vector homogeneous tree $\mathbf{T}$. We show that, by refining the index set to the level product $\otimes\mathbf{S}$ of a vector strong subtree $\bfcs$ of $\mathbf{S}$, such families of events become highly correlated. An analogue of Lebesgue's density Theorem is also established which can be considered as the "probabilistic" version of the density Halpern--L\"{a}uchli Theorem.

Abstract:
We study the size properties of a general model of fractal sets that are based on a tree-indexed family of random compacts and a tree-indexed Markov chain. These fractals may be regarded as a generalization of those resulting from the Moran-like deterministic or random recursive constructions considered by various authors. Among other applications, we consider various extensions of Mandelbrot's fractal percolation process.