31,246 research outputs found
Statistical analysis on high-dimensional spheres and shape spaces
We consider the statistical analysis of data on high-dimensional spheres and
shape spaces. The work is of particular relevance to applications where
high-dimensional data are available--a commonly encountered situation in many
disciplines. First the uniform measure on the infinite-dimensional sphere is
reviewed, together with connections with Wiener measure. We then discuss
densities of Gaussian measures with respect to Wiener measure. Some nonuniform
distributions on infinite-dimensional spheres and shape spaces are introduced,
and special cases which have important practical consequences are considered.
We focus on the high-dimensional real and complex Bingham, uniform, von
Mises-Fisher, Fisher-Bingham and the real and complex Watson distributions.
Asymptotic distributions in the cases where dimension and sample size are large
are discussed. Approximations for practical maximum likelihood based inference
are considered, and in particular we discuss an application to brain shape
modeling.Comment: Published at http://dx.doi.org/10.1214/009053605000000264 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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The oxygen isotopic composition of water extracted from carbonaceous chondrites
The oxygen isotopic composition of water from carbonaceous chondrites suggests that close to isotopic equilibrium was attained on CI and CM parent bodies. This is more consistent with a closed system than one with fluid flow. Tagish Lake does not display such equilibrium
Bayesian matching of unlabelled point sets using Procrustes and configuration models
The problem of matching unlabelled point sets using Bayesian inference is
considered. Two recently proposed models for the likelihood are compared, based
on the Procrustes size-and-shape and the full configuration. Bayesian inference
is carried out for matching point sets using Markov chain Monte Carlo
simulation. An improvement to the existing Procrustes algorithm is proposed
which improves convergence rates, using occasional large jumps in the burn-in
period. The Procrustes and configuration methods are compared in a simulation
study and using real data, where it is of interest to estimate the strengths of
matches between protein binding sites. The performance of both methods is
generally quite similar, and a connection between the two models is made using
a Laplace approximation
An analysis of HCN observations of the Circumnuclear Disk at the galactic centre
The Circumnuclear Disk (CND) is a torus of dust and molecular gas rotating
about the galactic centre and extending from approximately 1.6pc to 7pc from
the central massive black hole, SgrA*. Large Velocity Gradient modelling of the
intensities of the HCN 1-0, 3-2 and 4-3 transitions is used to infer hydrogen
density and HCN optical depth. From HCN observations we find the molecular
hydrogen density ranges from 0.1 to 2 10 cm, about an
order of magnitude less than inferred previously. The 1-0 line is weakly
inverted with line-centre optical depth approx 0.1, in stark contrast to
earlier estimates of 4. The estimated mass of the ring is approximately 3 4
10M consistent with estimates based on thermal dust
emission. The tidal shear in the disk implies that star formation is not
expected to occur without some significant triggering event.Comment: 17 pages, 8 figures, 7 tables (including 3 landscape tables generated
with 2 separate Latex files
SKA Engineering Change Proposal: Gridded Visibilities to Enable Precision Cosmology with Radio Weak Lensing
This document was submitted as supporting material to an Engineering Change
Proposal (ECP) for the Square Kilometre Array (SKA). This ECP requests gridded
visibilities as an extra imaging data product from the SKA, in order to enable
bespoke analysis techniques to measure source morphologies to the accuracy
necessary for precision cosmology with radio weak lensing. We also discuss the
properties of an SKA weak lensing data set and potential overlaps with other
cosmology science goals.Comment: Comments welcome. 4 pages, 3 figures. Progress can be tracked at the
SKA ECP register https://skaoffice.atlassian.net/wiki/display/EP/ECP+Registe
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New data on carbon isotopic compositions of some ureilites
We have collected new C data from high resolution stepped combustion analyses of 5 ureilites to better constrain their relationships with O and mineralogical/petrographic groupings. This may help the future development of petrogenetic models
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