183 research outputs found
Asymptotic normality of kernel estimates in a regression model for random fields
We establish the asymptotic normality of the regression estimator in a
fixed-design setting when the errors are given by a field of dependent random
variables. The result applies to martingale-difference or strongly mixing
random fields. On this basis, a statistical test that can be applied to image
analysis is also presented.Comment: 20 page
Maximum a posteriori estimation through simulated annealing for binary asteroid orbit determination
This paper considers a new method for the binary asteroid orbit determination
problem. The method is based on the Bayesian approach with a global
optimisation algorithm. The orbital parameters to be determined are modelled
through an a posteriori distribution made of a priori and likelihood terms. The
first term constrains the parameters space and it allows the introduction of
available knowledge about the orbit. The second term is based on given
observations and it allows us to use and compare different observational error
models. Once the a posteriori model is built, the estimator of the orbital
parameters is computed using a global optimisation procedure: the simulated
annealing algorithm. The maximum a posteriori (MAP) techniques are verified
using simulated and real data. The obtained results validate the proposed
method. The new approach guarantees independence of the initial parameters
estimation and theoretical convergence towards the global optimisation
solution. It is particularly useful in these situations, whenever a good
initial orbit estimation is difficult to get, whenever observations are not
well-sampled, and whenever the statistical behaviour of the observational
errors cannot be stated Gaussian like.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Photometric redshift galaxies as tracers of the filamentary network
Galaxy filaments are the dominant feature in the overall structure of the
cosmic web. The study of the filamentary web is an important aspect in
understanding galaxy evolution and the evolution of matter in the Universe. A
map of the filamentary structure is an adequate probe of the web. We propose
that photometric redshift galaxies are significantly positively associated with
the filamentary structure detected from the spatial distribution of
spectroscopic redshift galaxies. The catalogues of spectroscopic and
photometric galaxies are seen as point-process realisations in a sphere, and
the catalogue of filamentary spines is proposed to be a realisation of a random
set in a sphere. The positive association between these sets was studied using
a bivariate function, which is a summary statistics studying clustering. A
quotient was built to estimate the distance distribution of the filamentary
spine to galaxies in comparison to the distance distribution of the filamentary
spine to random points in dimensional Euclidean space. This measure gives a
physical distance scale to the distances between filamentary spines and the
studied sets of galaxies. The bivariate function shows a statistically
significant clustering effect in between filamentary spines and photometric
redshift galaxies. The quotient confirms the previous result that smaller
distances exist with higher probability between the photometric galaxies and
filaments. The trend of smaller distances between the objects grows stronger at
higher redshift. Additionally, the quotient for photometric galaxies gives
a rough estimate for the filamentary spine width of about ~Mpc. Photometric
redshift galaxies are positively associated with filamentary spines detected
from the spatial distribution of spectroscopic galaxies.Comment: Accepted to Astronomy & Astrophysics. 13 pages and 9 figure
Method and Apparatus for Simultaneous Processing of Multiple Functions
Electronic logic gates that operate using N logic state levels, where N is greater than 2, and methods of operating such gates. The electronic logic gates operate according to truth tables. At least two input signals each having a logic state that can range over more than two logic states are provided to the logic gates. The logic gates each provide an output signal that can have one of N logic states. Examples of gates described include NAND/NAND gates having two inputs A and B and NAND/NAND gates having three inputs A, B, and C, where A, B and C can take any of four logic states. Systems using such gates are described, and their operation illustrated. Optical logic gates that operate using N logic state levels are also described
The bivariate J-function to analyse positive association between galaxies and galaxy filaments
International audienceThe compelling and intrinsic network of galaxies builds up a complex structure for the Universe. In this work positive association between long bridging structures named galaxy filaments and a photometric redshift galaxy dataset is under investigation. Possible positive association is studied by the use of a bivariate J-function.Le réseau de filaments formé par la position des galaxies est une des structures les plus fascinantes dans notre Univers. Dans cet article, nous étudions des possibles associations entre le réseau de filaments déjà détecté et des nouvelles observations. Ces observations très récentes sont obtenues à partir des mesures du décalage vers le rouge photométrique. L'utilisation de la fonction J-bivariée tend à indiquer une association positive entre les filaments existants et les nouvelles observations
Statistically bias-minimized peculiar velocity catalogs from Gibbs point processes and Bayesian inference
Galaxy peculiar velocities are excellent cosmological probes provided that
biases inherent to their measurements are contained before any study. This
paper proposes a new algorithm based on an object point process model whose
probability density is built to statistically reduce the effects of Malmquist
biases and uncertainties due to lognormal errors in radial peculiar velocity
catalogs. More precisely, a simulated annealing algorithm permits maximizing
the probability density describing the point process model. The resulting
configurations are bias-minimized catalogs. Tests are conducted on synthetic
catalogs mimicking the second and third distance modulus catalogs of the
Cosmicflows project from which peculiar velocity catalogs are derived. By
reducing the local peculiar velocity variance in catalogs by an order of
magnitude, the algorithm permits recovering the expected one while preserving
the small-scale velocity correlation. It also permits retrieving the expected
clustering. The algorithm is then applied to the observational catalogs. The
large-scale structure reconstructed with the Wiener-filter technique applied to
the bias-minimized observational catalogs matches with great success the local
cosmic web as depicted by redshift surveys of local galaxies. These new
bias-minimized versions of peculiar velocity catalogs can be used as a starting
point for several studies from possibly estimating the most probable Hubble
constant, H0, value to the production of simulations constrained to reproduce
the local Universe.Comment: Accepted for publication in A&A, 26 pages, 22 figures, 3 table
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