85,187 research outputs found
Conservation laws and open systems on higher-dimensional networks
We discuss a framework for defining physical open systems on higher-dimensional complexes. We start with the formalization of the dynamics of open electrical circuits and the Kirchhoff behavior of the underlying open graph or 1-complex. It is discussed how the graph can be closed to an ordinary graph, and how this defines a Dirac structure on the extended graph. Then it is shown how this formalism can be extended to arbitrary k-complexes, which is illustrated by a discrete formulation of heat transfer on a two-dimensional spatial domain.
On the diameter and incidence energy of iterated total graphs
The total graph of , is the graph whose set of vertices is
the union of the sets of vertices and edges of , where two vertices are
adjacent if and only if they stand for either incident or adjacent elements in
. Let , the total graph of . For
, the iterated total graph of , , is
defined recursively as If
is a connected graph its diameter is the maximum distance between any pair
of vertices in . The incidence energy of is the sum of the
singular values of the incidence matrix of . In this paper for a given
integer we establish a necessary and sufficient condition under which
. In addition, bounds for the
incidence energy of the iterated graph are obtained,
provided to be a regular graph. Finally, new families of non-isomorphic
cospectral graphs are exhibited
Cluster formation in mesoscopic systems
Graph-theoretical approach is used to study cluster formation in mesocsopic
systems. Appearance of these clusters are due to discrete resonances which are
presented in the form of a multigraph with labeled edges. This presentation
allows to construct all non-isomorphic clusters in a finite spectral domain and
generate corresponding dynamical systems automatically. Results of MATHEMATICA
implementation are given and two possible mechanisms of cluster destroying are
discussed
Duality and free energy analyticity bounds for few-body Ising models with extensive homology rank
We consider pairs of few-body Ising models where each spin enters a bounded number of interaction terms (bonds) such that each model can be obtained from the dual of the other after freezing k spins on large-degree sites. Such a pair of Ising models can be interpreted as a two-chain complex with k being the rank of the first homology group. Our focus is on the case where k is extensive, that is, scales linearly with the number of bonds n. Flipping any of these additional spins introduces a homologically nontrivial defect (generalized domain wall). In the presence of bond disorder, we prove the existence of a low-temperature weak-disorder region where additional summation over the defects has no effect on the free energy density f(T) in the thermodynamical limit and of a high-temperature region where an extensive homological defect does not affect f(T). We also discuss the convergence of the high- and low-temperature series for the free energy density, prove the analyticity of limiting f(T) at high and low temperatures, and construct inequalities for the critical point(s) where analyticity is lost. As an application, we prove multiplicity of the conventionally defined critical points for Ising models on all { f, d} tilings of the infinite hyperbolic plane, where df/(d + f) \u3e 2. Namely, for these infinite graphs, we show that critical temperatures with free and wired boundary conditions differ, Tc(f)T(f)
Beyond graph energy: norms of graphs and matrices
In 1978 Gutman introduced the energy of a graph as the sum of the absolute
values of graph eigenvalues, and ever since then graph energy has been
intensively studied.
Since graph energy is the trace norm of the adjacency matrix, matrix norms
provide a natural background for its study. Thus, this paper surveys research
on matrix norms that aims to expand and advance the study of graph energy.
The focus is exclusively on the Ky Fan and the Schatten norms, both
generalizing and enriching the trace norm. As it turns out, the study of
extremal properties of these norms leads to numerous analytic problems with
deep roots in combinatorics.
The survey brings to the fore the exceptional role of Hadamard matrices,
conference matrices, and conference graphs in matrix norms. In addition, a vast
new matrix class is studied, a relaxation of symmetric Hadamard matrices.
The survey presents solutions to just a fraction of a larger body of similar
problems bonding analysis to combinatorics. Thus, open problems and questions
are raised to outline topics for further investigation.Comment: 54 pages. V2 fixes many typos, and gives some new materia
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