14,251 research outputs found
A clever elimination strategy for efficient minimal solvers
We present a new insight into the systematic generation of minimal solvers in
computer vision, which leads to smaller and faster solvers. Many minimal
problem formulations are coupled sets of linear and polynomial equations where
image measurements enter the linear equations only. We show that it is useful
to solve such systems by first eliminating all the unknowns that do not appear
in the linear equations and then extending solutions to the rest of unknowns.
This can be generalized to fully non-linear systems by linearization via
lifting. We demonstrate that this approach leads to more efficient solvers in
three problems of partially calibrated relative camera pose computation with
unknown focal length and/or radial distortion. Our approach also generates new
interesting constraints on the fundamental matrices of partially calibrated
cameras, which were not known before.Comment: 13 pages, 7 figure
Beyond Gr\"obner Bases: Basis Selection for Minimal Solvers
Many computer vision applications require robust estimation of the underlying
geometry, in terms of camera motion and 3D structure of the scene. These robust
methods often rely on running minimal solvers in a RANSAC framework. In this
paper we show how we can make polynomial solvers based on the action matrix
method faster, by careful selection of the monomial bases. These monomial bases
have traditionally been based on a Gr\"obner basis for the polynomial ideal.
Here we describe how we can enumerate all such bases in an efficient way. We
also show that going beyond Gr\"obner bases leads to more efficient solvers in
many cases. We present a novel basis sampling scheme that we evaluate on a
number of problems
The Neutrino mass matrix after Kamland and SNO salt enhanced results
An updated analysis of all available neutrino oscillation evidence in Solar
experiments including the latest SNO ES,CC and NC data (254d live time, NaCL
enhanced efficiency) is presented. We obtain, for the fraction of active
oscillating neutrinos:
sin^2alpha=(\Phi_{NC}-\Phi_{CC})/(\Phi_{SSM}-\Phi_{CC})=0.94^{+0.0.065}_{-0.060}
nearly 20\sigma from the pure sterile oscillation case. The fraction of
oscillating sterile neutrinos cos^2\alpha \lsim 0.12 (1 sigma CL). At face
value, these results might slightly favour the existence of a small sterile
oscillating sector. In the framework of two active neutrino oscillations we
determine individual neutrino mixing parameters and their errors we obtain
Delta m^2= 7.01\pm 0.08 \times 10^{-5} eV^2, tan^2 theta=0.42^{+0.12}_{-0.07}.
The main difference with previous analysis is a better resolution in parameter
space. In particular the secondary region at larger mass differences (LMAII) is
now excluded at 95% CL. The combined analysis of solar and Kamland data
concludes that maximal mixing is not favoured at 4-5 sigma. This is not
supported by the antineutrino reactor results alone. We estimate the individual
elements of the two neutrino mass matrix, writing M^2=m^2 I+M_0^2, we obtain (1
sigma errors):
M_0^2=10^{-5} eV^2\pmatrix{
2.06^{+0.29}_{-0.31} & 3.15^{+0.29}_{-0.35} \cr
3.15^{+0.29}_{-0.35} & 4.60^{+0.56}_{-0.44} }
Testing Chern-Simons modified gravity with observations of extreme-mass-ratio binaries
Extreme-Mass-Ratio Inspirals (EMRIs) are one of the most promising sources of
gravitational waves (GWs) for space-based detectors like the Laser
Interferometer Space Antenna (LISA). EMRIs consist of a compact stellar object
orbiting around a massive black hole (MBH). Since EMRI signals are expected to
be long lasting (containing of the order of hundred thousand cycles), they will
encode the structure of the MBH gravitational potential in a precise way such
that features depending on the theory of gravity governing the system may be
distinguished. That is, EMRI signals may be used to test gravity and the
geometry of black holes. However, the development of a practical methodology
for computing the generation and propagation of GWs from EMRIs in theories of
gravity different than General Relativity (GR) has only recently begun. In this
paper, we present a parameter estimation study of EMRIs in a particular
modification of GR, which is described by a four-dimensional Chern-Simons (CS)
gravitational term. We focus on determining to what extent a space-based GW
observatory like LISA could distinguish between GR and CS gravity through the
detection of GWs from EMRIs.Comment: 10 pages, JPCS of the Amaldi 9 and NRDA 201
Modelling the Interfacial Flow of Two Immiscible Liquids in Mixing Processes
This paper presents an interface tracking method for modelling the flow of immiscible metallic liquids in mixing processes. The methodology can provide an insight into mixing processes for studying the fundamental morphology development mechanisms for immiscible interfaces. The volume-of-fluid (VOF) method is adopted in the present study, following a review of various modelling approaches for immiscible fluid systems. The VOF method employed here utilises the piecewise linear for interface construction scheme as well as the continuum surface force algorithm for surface force modelling. A model coupling numerical and experimental data is established. The main flow features in the mixing process are investigated. It is observed that the mixing of immiscible metallic liquids is strongly influenced by the viscosity of the system, shear forces and turbulence. The numerical results show good qualitative agreement with experimental results, and are useful for optimisating the design of mixing casting processes
ASTErIsM - Application of topometric clustering algorithms in automatic galaxy detection and classification
We present a study on galaxy detection and shape classification using
topometric clustering algorithms. We first use the DBSCAN algorithm to extract,
from CCD frames, groups of adjacent pixels with significant fluxes and we then
apply the DENCLUE algorithm to separate the contributions of overlapping
sources. The DENCLUE separation is based on the localization of pattern of
local maxima, through an iterative algorithm which associates each pixel to the
closest local maximum. Our main classification goal is to take apart elliptical
from spiral galaxies. We introduce new sets of features derived from the
computation of geometrical invariant moments of the pixel group shape and from
the statistics of the spatial distribution of the DENCLUE local maxima
patterns. Ellipticals are characterized by a single group of local maxima,
related to the galaxy core, while spiral galaxies have additional ones related
to segments of spiral arms. We use two different supervised ensemble
classification algorithms, Random Forest, and Gradient Boosting. Using a sample
of ~ 24000 galaxies taken from the Galaxy Zoo 2 main sample with spectroscopic
redshifts, and we test our classification against the Galaxy Zoo 2 catalog. We
find that features extracted from our pipeline give on average an accuracy of ~
93%, when testing on a test set with a size of 20% of our full data set, with
features deriving from the angular distribution of density attractor ranking at
the top of the discrimination power.Comment: 20 pages, 13 Figures, 8 Tables, Accepted for publication in the
Monthly Notices of the Royal Astronomical Societ
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