1,528,115 research outputs found
Averaged shelling for quasicrystals
The shelling of crystals is concerned with counting the number of atoms on
spherical shells of a given radius and a fixed centre. Its straight-forward
generalization to quasicrystals, the so-called central shelling, leads to
non-universal answers. As one way to cope with this situation, we consider
shelling averages over all quasicrystal points. We express the averaged
shelling numbers in terms of the autocorrelation coefficients and give explicit
results for the usual suspects, both perfect and random.Comment: 4 pages, several figures, 2 tables; updated version with minor
corrections and improvements; to appear in the proceedings of ICQ
Averaged Template Matching Equations
By exploiting an analogy with averaging procedures in fluid
dynamics, we present a set of averaged template matching equations.
These equations are analogs of the exact template matching equations
that retain all the geometric properties associated with the diffeomorphismgrou
p, and which are expected to average out small scale features
and so should, as in hydrodynamics, be more computationally efficient
for resolving the larger scale features. Froma geometric point of view,
the new equations may be viewed as coming from a change in norm that
is used to measure the distance between images. The results in this paper
represent first steps in a longer termpro gram: what is here is only
for binary images and an algorithm for numerical computation is not
yet operational. Some suggestions for further steps to develop the results
given in this paper are suggested
The anisotropic averaged Euler equations
The purpose of this paper is to derive the anisotropic averaged Euler
equations and to study their geometric and analytic properties. These new
equations involve the evolution of a mean velocity field and an advected
symmetric tensor that captures the fluctuation effects. Besides the derivation
of these equations, the new results in the paper are smoothness properties of
the equations in material representation, which gives well-posedness of the
equations, and the derivation of a corrector to the macroscopic velocity field.
The numerical implementation and physical implications of this set of equations
will be explored in other publications.Comment: 24 pages, 1 figur
On Incompressible Averaged Lagrangian Hydrodynamics
This paper is devoted to the geometric analysis of the incompressible
averaged Euler equations on compact Riemannian manifolds with boundary. The
equation also coincides with the model for a second-grade non-Newtonian fluid.
We study the analytical and geometrical properties of the Lagrangian flow map.
We prove existence and uniqueness of smooth-in-time solutions for initial data
in , by establishing the existence of smooth geodesics of a
new weak right invariant metric on new subgroups of the volume-preserving
diffeomorphism group. We establish smooth limits of zero viscosity for the
second-grade fluids equations even on manifolds with boundary. We prove that
the weak curvature operator of the weak invariant metric is continuous in the
topology for , thus proving existence and uniqueness for the
Jacobi equation. We show that this new metric stabilizes the Lagrangian flow of
the original Euler equations by changing the sign of the sectional curvature.Comment: 35 page
Generalization bounds for averaged classifiers
We study a simple learning algorithm for binary classification. Instead of
predicting with the best hypothesis in the hypothesis class, that is, the
hypothesis that minimizes the training error, our algorithm predicts with a
weighted average of all hypotheses, weighted exponentially with respect to
their training error. We show that the prediction of this algorithm is much
more stable than the prediction of an algorithm that predicts with the best
hypothesis. By allowing the algorithm to abstain from predicting on some
examples, we show that the predictions it makes when it does not abstain are
very reliable. Finally, we show that the probability that the algorithm
abstains is comparable to the generalization error of the best hypothesis in
the class.Comment: Published by the Institute of Mathematical Statistics
(http://www.imstat.org) in the Annals of Statistics
(http://www.imstat.org/aos/) at http://dx.doi.org/10.1214/00905360400000005
Panchromatic Averaged Stellar Populations: PaasP
We study how the spectral fitting of galaxies, in terms of light fractions
derived in one spectral region translates into another region, by using results
from evolutionary synthesis models. In particular, we examine propagation
dependencies on Evolutionary Population Synthesis (EPS, {\sc grasil}, {\sc
galev}, Maraston and {\sc galaxev}) models, age, metallicity, and stellar
evolution tracks over the near-UV---near infrared (NUV---NIR, 3500\AA\ to
2.5\mc) spectral region. Our main results are: as expected, young (
400 Myr) stellar population fractions derived in the optical cannot be directly
compared to those derived in the NIR, and vice versa. In contrast, intermediate
to old age ( 500 Myr) fractions are similar over the whole spectral
region studied. The metallicity has a negligible effect on the propagation of
the stellar population fractions derived from NUV --- NIR. The same applies to
the different EPS models, but restricted to the range between 3800 \AA\ and
9000 \AA. However, a discrepancy between {\sc galev}/Maraston and {\sc
grasil}/{\sc galaxev} models occurs in the NIR. Also, the initial mass function
(IMF) is not important for the synthesis propagation. Compared to {\sc
starlight} synthesis results, our propagation predictions agree at 95%
confidence level in the optical, and 85% in the NIR. {\bf In summary,
spectral fitting} performed in a restricted spectral range should not be
directly propagated from the NIR to the UV/Optical, or vice versa. We provide
equations and an on-line form ({\bf Pa}nchromatic {\bf A}veraged {\bf S}tellar
{\bf P}opulation - \paasp) to be used for this purpose.Comment: 13 pages and 10 figures. Accepted by MNRA
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