2,367 research outputs found
Convergence of U-statistics for interacting particle systems
The convergence of U-statistics has been intensively studied for estimators
based on families of i.i.d. random variables and variants of them. In most
cases, the independence assumption is crucial [Lee90, de99]. When dealing with
Feynman-Kac and other interacting particle systems of Monte Carlo type, one
faces a new type of problem. Namely, in a sample of N particles obtained
through the corresponding algorithms, the distributions of the particles are
correlated -although any finite number of them is asymptotically independent
with respect to the total number N of particles. In the present article,
exploiting the fine asymptotics of particle systems, we prove convergence
theorems for U-statistics in this framework
A Backward Particle Interpretation of Feynman-Kac Formulae
We design a particle interpretation of Feynman-Kac measures on path spaces
based on a backward Markovian representation combined with a traditional mean
field particle interpretation of the flow of their final time marginals. In
contrast to traditional genealogical tree based models, these new particle
algorithms can be used to compute normalized additive functionals "on-the-fly"
as well as their limiting occupation measures with a given precision degree
that does not depend on the final time horizon.
We provide uniform convergence results w.r.t. the time horizon parameter as
well as functional central limit theorems and exponential concentration
estimates. We also illustrate these results in the context of computational
physics and imaginary time Schroedinger type partial differential equations,
with a special interest in the numerical approximation of the invariant measure
associated to -processes
Multi-GPU maximum entropy image synthesis for radio astronomy
The maximum entropy method (MEM) is a well known deconvolution technique in
radio-interferometry. This method solves a non-linear optimization problem with
an entropy regularization term. Other heuristics such as CLEAN are faster but
highly user dependent. Nevertheless, MEM has the following advantages: it is
unsupervised, it has a statistical basis, it has a better resolution and better
image quality under certain conditions. This work presents a high performance
GPU version of non-gridding MEM, which is tested using real and simulated data.
We propose a single-GPU and a multi-GPU implementation for single and
multi-spectral data, respectively. We also make use of the Peer-to-Peer and
Unified Virtual Addressing features of newer GPUs which allows to exploit
transparently and efficiently multiple GPUs. Several ALMA data sets are used to
demonstrate the effectiveness in imaging and to evaluate GPU performance. The
results show that a speedup from 1000 to 5000 times faster than a sequential
version can be achieved, depending on data and image size. This allows to
reconstruct the HD142527 CO(6-5) short baseline data set in 2.1 minutes,
instead of 2.5 days that takes a sequential version on CPU.Comment: 11 pages, 13 figure
On the spectrum of a matrix model for the D=11 supermembrane compactified on a torus with non-trivial winding
The spectrum of the Hamiltonian of the double compactified D=11 supermembrane
with non-trivial central charge or equivalently the non-commutative symplectic
super Maxwell theory is analyzed. In distinction to what occurs for the D=11
supermembrane in Minkowski target space where the bosonic potential presents
string-like spikes which render the spectrum of the supersymmetric model
continuous, we prove that the potential of the bosonic compactified membrane
with non-trivial central charge is strictly positive definite and becomes
infinity in all directions when the norm of the configuration space goes to
infinity. This ensures that the resolvent of the bosonic Hamiltonian is
compact. We find an upper bound for the asymptotic distribution of the
eigenvalues.Comment: 11 pages, LaTe
On the Stability and the Approximation of Branching Distribution Flows, with Applications to Nonlinear Multiple Target Filtering
We analyse the exponential stability properties of a class of measure-valued
equations arising in nonlinear multi-target filtering problems. We also prove
the uniform convergence properties w.r.t. the time parameter of a rather
general class of stochastic filtering algorithms, including sequential Monte
Carlo type models and mean eld particle interpretation models. We illustrate
these results in the context of the Bernoulli and the Probability Hypothesis
Density filter, yielding what seems to be the first results of this kind in
this subject
Degenerate neutrinos from a supersymmetric A_4 model
We investigate the supersymmetric A_4 model recently proposed by Babu, Ma and
Valle. The model naturally gives quasi-degenerate neutrinos that are bi-largely
mixed, in agreement with observations. Furthermore, the mixings in the quark
sector are constrained to be small, making it a complete model of the flavor
structure. Moreover, it has the interesting property that CP-violation in the
leptonic sector is maximal (unless vanishing). The model exhibit a close
relation between the slepton and lepton sectors and we derive the slepton
spectra that are compatible with neutrino data and the present bounds on
flavor-violating charged lepton decays. The prediction for the branching ratio
of the decay tau -> mu gamma has a lower limit of 10^{-9}. In addition, the
overall neutrino mass scale is constrained to be larger than 0.3 eV. Thus, the
model will be tested in the very near future.Comment: 11 pages, 6 figures. Talk given at the International Workshop on
Astroparticle and High Energy Physics (AHEP), Valencia, Spain, 14-18 Oct.
200
On Chern-Simons Quivers and Toric Geometry
We discuss a class of 3-dimensional N=4 Chern-Simons (CS) quiver gauge models
obtained from M-theory compactifications on singular complex 4-dimensional
hyper-Kahler (HK) manifolds, which are realized explicitly as a cotangent
bundle over two-Fano toric varieties V^2. The corresponding CS gauge models are
encoded in quivers similar to toric diagrams of V^2. Using toric geometry, it
is shown that the constraints on CS levels can be related to toric equations
determining V^2.Comment: 14pg, 1 Figure, late
Aplication of LED technology for food quality control
Motivation: Currently, there are numerous chemical methods to analyze compounds, however, these involve a large investment and highly qualified personnel. In this work, Light Emission Diode has been used as a cheap and simple method to easily detect, the existence of: a) cheese whey in different representative samples of water b) rice syrup in different types of commercial honeys.Methods: Six different colour LEDs (orange, pink, ultraviolet, blue, green and white) were used in this research as a light source to measure the emission spectra of water and honey samples. The water and honey samples were prepared adding known concentrations of cheese whey( from 1% to 20%, 1800 samples) and rice syrup (1%-8%, 480 samples), to waters from five different rivers and reservoirs in Madrid; and to five different honeys, respectively. The phenomenon measured with this technology is fluorescence. The emited fluorescence is measured at a right angle from the light source, using a fiber spectrometer. The output of the spectrometer is collected in a computer. It is necessary to apply a linear regression model to obtain the concentration from the intensity values.This information is taken from a fluorescence emission spectrum.Results: In the whey emission spectra (for each LED), the increase in cheese whey concentrations were seen by an increase in its intensity. The honey spectra have different profiles as well as intensities for each honey, so the difference in syrup concentration is also detected by an intensity increase.In addition, the analysis of the measurements has obtained an efficiency of approximately 90%.Conclusions: It has been demonstrated that LED technology can be a potencial and important first approach to determine contaminants or adulterants in water and honey samples. It is also a cheap and user-friendly technique which could be useful in the food quality control sector
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