1,267 research outputs found
Hurwitz equivalence of braid monodromies and extremal elliptic surfaces
We discuss the equivalence between the categories of certain ribbon graphs
and subgroups of the modular group and use it to construct
exponentially large families of not Hurwitz equivalent simple braid monodromy
factorizations of the same element. As an application, we also obtain
exponentially large families of {\it topologically} distinct algebraic objects
such as extremal elliptic surfaces, real trigonal curves, and real elliptic
surfaces
Evolutionary constraints on the complexity of genetic regulatory networks allow predictions of the total number of genetic interactions
Genetic regulatory networks (GRNs) have been widely studied, yet there is a
lack of understanding with regards to the final size and properties of these
networks, mainly due to no network currently being complete. In this study, we
analyzed the distribution of GRN structural properties across a large set of
distinct prokaryotic organisms and found a set of constrained characteristics
such as network density and number of regulators. Our results allowed us to
estimate the number of interactions that complete networks would have, a
valuable insight that could aid in the daunting task of network curation,
prediction, and validation. Using state-of-the-art statistical approaches, we
also provided new evidence to settle a previously stated controversy that
raised the possibility of complete biological networks being random and
therefore attributing the observed scale-free properties to an artifact
emerging from the sampling process during network discovery. Furthermore, we
identified a set of properties that enabled us to assess the consistency of the
connectivity distribution for various GRNs against different alternative
statistical distributions. Our results favor the hypothesis that highly
connected nodes (hubs) are not a consequence of network incompleteness.
Finally, an interaction coverage computed for the GRNs as a proxy for
completeness revealed that high-throughput based reconstructions of GRNs could
yield biased networks with a low average clustering coefficient, showing that
classical targeted discovery of interactions is still needed.Comment: 28 pages, 5 figures, 12 pages supplementary informatio
Mapping tori of free group automorphisms are coherent
The mapping torus of an endomorphism \Phi of a group G is the HNN-extension
G*_G with bonding maps the identity and \Phi. We show that a mapping torus of
an injective free group endomorphism has the property that its finitely
generated subgroups are finitely presented and, moreover, these subgroups are
of finite type.Comment: 17 pages, published versio
The Fiedler connection to the parametrized modularity optimization for community detection
This paper presents a comprehensive analysis of the generalized spectral
structure of the modularity matrix , which is introduced by Newman as the
kernel matrix for the quadratic-form expression of the modularity function
used for community detection. The analysis is then seamlessly extended to the
resolution-parametrized modularity matrix , where denotes
the resolution parameter. The modularity spectral analysis provides fresh and
profound insights into the -dynamics within the framework of modularity
maximization for community detection. It provides the first algebraic
explanation of the resolution limit at any specific value. Among the
significant findings and implications, the analysis reveals that (1) the maxima
of the quadratic function with as the kernel matrix always reside
in the Fiedler space of the normalized graph Laplacian or the null space of
, or their combination, and (2) the Fiedler value of the graph Laplacian
marks the critical value in the transition of candidate community
configuration states between graph division and aggregation. Additionally, this
paper introduces and identifies the Fiedler pseudo-set (FPS) as the de facto
critical region for the state transition. This work is expected to have an
immediate and long-term impact on improvements in algorithms for modularity
maximization and on model transformations.Comment: 11 pages, 3 figures, 1 tabl
A combinatorial Li-Yau inequality and rational points on curves
We present a method to control gonality of nonarchimedean curves based on graph theory. Let k denote a complete nonarchimedean valued field.We first prove a lower bound for the gonality of a curve over the algebraic closure of k in terms of the minimal degree of a class of graph maps, namely: one should minimize over all so-called finite harmonic graph morphisms to trees, that originate from any refinement of the dual graph of the stable model of the curve. Next comes our main result: we prove a lower bound for the degree of such a graph morphism in terms of the first eigenvalue of the Laplacian and some “volume” of the original graph; this can be seen as a substitute for graphs of the Li–Yau inequality from differential geometry, although we also prove that the strict analogue of the original inequality fails for general graphs. Finally,we apply the results to give a lower bound for the gonality of arbitraryDrinfeld modular curves over finite fields and for general congruence subgroups Γ of Γ (1) that is linear in the index [Γ (1) : Γ ], with a constant that only depends on the residue field degree and the degree of the chosen “infinite” place. This is a function field analogue of a theorem of Abramovich for classical modular curves. We present applications to uniform boundedness of torsion of rank two Drinfeld modules that improve upon existing results, and to lower bounds on the modular degree of certain elliptic curves over function fields that solve a problem of Papikian
- …