10,467 research outputs found
Estimation of means in graphical Gaussian models with symmetries
We study the problem of estimability of means in undirected graphical
Gaussian models with symmetry restrictions represented by a colored graph.
Following on from previous studies, we partition the variables into sets of
vertices whose corresponding means are restricted to being identical. We find a
necessary and sufficient condition on the partition to ensure equality between
the maximum likelihood and least-squares estimators of the mean.Comment: Published in at http://dx.doi.org/10.1214/12-AOS991 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Disjunct Lake Michigan Populations of Two Atlantic Coast Spiders, \u3ci\u3eDisembolus Bairdi\u3c/i\u3e and \u3ci\u3eGrammonota Pallipes\u3c/i\u3e (Araneae: Linyphiidae)
Two species of linyphiid spiders, Disembolus bairdi Edwards, 1999 and Grammonota pallipes Banks, 1895, were discovered along the southwestern coast of Lake Michigan in Lake County, Illinois representing an Atlantic Coastal Plain disjunct distribution. A brief discussion of known collection sites, habitat preferences, and possible modes of dispersal are given
Inference in Graphical Gaussian Models with Edge and Vertex Symmetries with the gRc Package for R
In this paper we present the R package gRc for statistical inference in graphical Gaussian models in which symmetry restrictions have been imposed on the concentration or partial correlation matrix. The models are represented by coloured graphs where parameters associated with edges or vertices of same colour are restricted to being identical. We describe algorithms for maximum likelihood estimation and discuss model selection issues. The paper illustrates the practical use of the gRc package.
On Exchangeability in Network Models
We derive representation theorems for exchangeable distributions on finite
and infinite graphs using elementary arguments based on geometric and
graph-theoretic concepts. Our results elucidate some of the key differences,
and their implications, between statistical network models that are finitely
exchangeable and models that define a consistent sequence of probability
distributions on graphs of increasing size.Comment: Dedicated to the memory of Steve Fienber
Thermocapillary Flow on Superhydrophobic Surfaces
A liquid in Cassie-Baxter state above a structured superhydrophobic surface
is ideally suited for surface driven transport due to its large free surface
fraction in close contact to a solid. We investigate thermal Marangoni flow
over a superhydrophobic array of fins oriented parallel or perpendicular to an
applied temperature gradient. In the Stokes limit we derive an analytical
expression for the bulk flow velocity above the surface and compare it with
numerical solutions of the Navier-Stokes equation. Even for moderate
temperature gradients comparatively large flow velocities are induced,
suggesting to utilize this principle for microfluidic pumping.Comment: 4 pages, 4 figure
Boltzmann Collision Term
We derive the Boltzmann equation for scalar fields using the
Schwinger-Keldysh formalism. The focus lies on the derivation of the collision
term. We show that the relevant self-energy diagrams have a factorization
property. The collision term assumes the Boltzmann-like form of scattering
probability times statistical factors for those self-energy diagrams which
correspond to tree level scattering processes. Our proof covers scattering
processes with any number of external particles, which come from self-energy
diagrams with any number of loops.Comment: 17 pages, 4 figure
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