3,313 research outputs found
Quantum Broadening of k-Strings from the AdS/CFT Correspondence
We study the quantum broadening (width) of k-strings. We generalise an old
result by Luscher, Munster and Weisz to the case of a k-string, by using the
gauge/gravity correspondence. When the fundamental QCD-string is replaced by a
bound state of k strings, the bound state is better described by a wrapped
D-brane. We calculate the width of the k-string (the wrapped D-brane) in
several AdS/CFT backgrounds by using a D-brane probe and find universally that
omega_k ^2 = 1 / (2\pi \sigma_k) log R/r .Comment: 13 pages, LaTex. v2: minor changes, references added. To appear in
Nucl.Phys.
GLM permutation - nonparametric inference for arbitrary general linear models
Introduction: Permutation methods are finding growing use in neuroimag-
ing data analyses (e.g. randomise in FSL, SnPM in SPM,
XBAMM/BAMM/CAMBA, etc). These methods provide ex-
act control of false positives, make only weak assumptions, and
allow nonstandard types of statistics (e.g. smoothed variance t-
test). With fast and inexpensive computing, there would seem
few reasons not to use nonparametric methods.
A significant limitation of these methods, however, is the lack of
flexibility with respect to the experimental design and nuisance
variables. Each specific design dictates the type of exchange-
ability of null data, and hence how to permute. Nuisance effects
(e.g. age) render data non-exchangeable even when the effect of
interest is null. Hence, even something as simple as ANCOVA
has no exact permutation test.
Recently there has been an active literature on approximateâ
but accurateâpermutation tests for 2-variable regression, one
effect of interest, one nuisance (see review by Anderson &
Robinson [1]). Here we extend and evaluate these methods
for use with an arbitrary General Linear Model (GLM)
Deep Spectroscopy in the Field of 3C 212
We present the results of longslit and multiaperture spectroscopy of faint
galaxies in the field of the z=1.049 quasar 3C212. We show that an apparently
aligned optical feature beyond the NW radio lobe has a redshift z=0.928, and a
similarly aligned feature just beyond the SE radio lobe has a redshift z=1.053,
quite close to that of the quasar. While the NW optical component is extremely
well aligned with the radio jet and has a morphology that is very similar to
that of the radio lobe lying 3" interior to it, the fact that we find three
other field galaxies with closely similar redshifts indicates that it is most
likely a member of an intervening group rather than an unusual example of true
alignment with the radio structure. In addition, we have found two galaxies
(besides the one near the SE radio lobe) having redshifts close to that of
3C212. We have firm or probable redshifts for 66 out of 82 galaxies we have
observed in this field. Comparison with the redshift distribution of faint
field galaxies indicates that a large fraction of the remaining 16 galaxies are
likely to be at redshifts >1.4. There are at least two low-redshift dwarf
starburst galaxies showing low metal abundance and high ionization in our
sample; such galaxies are likely to be relatively common in very faint samples,
and, under certain conditions, they could be confused with high-redshift
objects.Comment: 15 pages, 4 figures, one of which is a separate JPEG plate. To be
published in the April 1998 issue of The Astronomical Journa
An investigation of some theological interpretations of Pentecost, with special reference to Spirit-Baptism
https://place.asburyseminary.edu/ecommonsatsdissertations/2049/thumbnail.jp
Diffeomorphic Demons using Normalised Mutual Information, Evaluation on Multi-Modal Brain MR Images
The demons algorithm is a fast non-parametric non-rigid registration method. In recent years great efforts have been made to improve the approach; the state of the art version yields symmetric inverse-consistent large-deformation diffeomorphisms. However, only limited work has explored inter-modal similarity metrics, with no practical evaluation on multi-modality data. We present a diffeomorphic demons implementation using the analytical gradient of Normalised Mutual Information (NMI) in a conjugate gradient optimiser. We report the first qualitative and quantitative assessment of the demons for inter-modal registration. Experiments to spatially normalise real MR images, and to recover simulated deformation fields, demonstrate (i) similar accuracy from NMI-demons and classical demons when the latter may be used, and (ii) similar accuracy for NMI-demons on T1w-T1w and T1w-T2w registration, demonstrating its potential in multi-modal scenarios
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