11,586 research outputs found
On the Existence of Jenkins-Strebel Differentials Using Harmonic Maps from Surfaces to Graphs
We give a new proof of the existence (\cite{HM}, \cite{Ren}) of a
Jenkins-Strebel differential on a Riemann surface \SR with prescribed
heights of cylinders by considering the harmonic map from \SR to the leaf
space of the vertical foliation of , thought of as a Riemannian graph.
The novelty of the argument is that it is essentially Riemannian as well as
elementary; moreover, the harmonic maps existence theory on which it relies is
classical, due mostly to Morrey (\cite{Mo}).Comment: 8 pages, 2 figures available upon reques
Dynamical Entropy Production in Spiking Neuron Networks in the Balanced State
We demonstrate deterministic extensive chaos in the dynamics of large sparse
networks of theta neurons in the balanced state. The analysis is based on
numerically exact calculations of the full spectrum of Lyapunov exponents, the
entropy production rate and the attractor dimension. Extensive chaos is found
in inhibitory networks and becomes more intense when an excitatory population
is included. We find a strikingly high rate of entropy production that would
limit information representation in cortical spike patterns to the immediate
stimulus response.Comment: 4 pages, 4 figure
Spectrum Estimation: A Unified Framework for Covariance Matrix Estimation and PCA in Large Dimensions
Covariance matrix estimation and principal component analysis (PCA) are two
cornerstones of multivariate analysis. Classic textbook solutions perform
poorly when the dimension of the data is of a magnitude similar to the sample
size, or even larger. In such settings, there is a common remedy for both
statistical problems: nonlinear shrinkage of the eigenvalues of the sample
covariance matrix. The optimal nonlinear shrinkage formula depends on unknown
population quantities and is thus not available. It is, however, possible to
consistently estimate an oracle nonlinear shrinkage, which is motivated on
asymptotic grounds. A key tool to this end is consistent estimation of the set
of eigenvalues of the population covariance matrix (also known as the
spectrum), an interesting and challenging problem in its own right. Extensive
Monte Carlo simulations demonstrate that our methods have desirable
finite-sample properties and outperform previous proposals.Comment: 40 pages, 8 figures, 5 tables, University of Zurich, Department of
Economics, Working Paper No. 105, Revised version, July 201
Polynomial cubic differentials and convex polygons in the projective plane
We construct and study a natural homeomorphism between the moduli space of
polynomial cubic differentials of degree d on the complex plane and the space
of projective equivalence classes of oriented convex polygons with d+3
vertices. This map arises from the construction of a complete hyperbolic affine
sphere with prescribed Pick differential, and can be seen as an analogue of the
Labourie-Loftin parameterization of convex RP^2 structures on a compact surface
by the bundle of holomorphic cubic differentials over Teichmuller space.Comment: 64 pages, 5 figures. v3: Minor revisions according to referee report.
v2: Corrections in section 5 and related new material in appendix
Non-Existence of Geometric Minimal Foliations in Hyperbolic Three-Manifolds
In this paper we show that every three-dimensional closed hyperbolic manifold
admits no locally geometric -parameter family of closed minimal surfaces.Comment: Commentarii Mathematici Helvetici, to appea
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