12,198 research outputs found
Nonparametric Bayesian Mixed-effect Model: a Sparse Gaussian Process Approach
Multi-task learning models using Gaussian processes (GP) have been developed
and successfully applied in various applications. The main difficulty with this
approach is the computational cost of inference using the union of examples
from all tasks. Therefore sparse solutions, that avoid using the entire data
directly and instead use a set of informative "representatives" are desirable.
The paper investigates this problem for the grouped mixed-effect GP model where
each individual response is given by a fixed-effect, taken from one of a set of
unknown groups, plus a random individual effect function that captures
variations among individuals. Such models have been widely used in previous
work but no sparse solutions have been developed. The paper presents the first
sparse solution for such problems, showing how the sparse approximation can be
obtained by maximizing a variational lower bound on the marginal likelihood,
generalizing ideas from single-task Gaussian processes to handle the
mixed-effect model as well as grouping. Experiments using artificial and real
data validate the approach showing that it can recover the performance of
inference with the full sample, that it outperforms baseline methods, and that
it outperforms state of the art sparse solutions for other multi-task GP
formulations.Comment: Preliminary version appeared in ECML201
A note on the Gauge Symmetries of Unimodular Gravity
The symmetries of Unimodular Gravity are clarified somewhat.Comment: 4 pages, v2: acknowledgments correcte
Combining interactive GIS tools and expert knowledge in validation of tree species models
Poster presented at XIII Congreso Forestal Mundial. FAO, Buenos Aires (Argentina). 18-25 Oct 200
Quantum Corrections to Unimodular Gravity
The problem of the cosmological constant appears in a new light in Unimodular
Gravity. In particular, the zero momentum piece of the potential (that is, the
constant piece independent of the matter fields) does not automatically produce
a cosmological constant proportional to it. The aim of this paper is to give
some details on a calculation showing that quantum corrections do not
renormalize the classical value of this observable.Comment: 34 page
Effect of deformation on two-neutrino double beta decay matrix elements
We study the effect of deformation on the two-neutrino double beta decay for
ground state to ground state transitions in all the nuclei whose half-lives
have been measured. Our theoretical framework is a deformed QRPA based in
Woods-Saxon or Hartree-Fock mean fields. We are able to reproduce at the same
time the main characteristics of the two single beta branches, as well as the
double beta matrix elements. We find a suppression of the double beta matrix
element with respect to the spherical case when the parent and daughter nuclei
have different deformations
- …