2,786 research outputs found
Rapid Bayesian identification of sparse nonlinear dynamics from scarce and noisy data
We propose a fast probabilistic framework for identifying differential
equations governing the dynamics of observed data. We recast the SINDy method
within a Bayesian framework and use Gaussian approximations for the prior and
likelihood to speed up computation. The resulting method, Bayesian-SINDy, not
only quantifies uncertainty in the parameters estimated but also is more robust
when learning the correct model from limited and noisy data. Using both
synthetic and real-life examples such as Lynx-Hare population dynamics, we
demonstrate the effectiveness of the new framework in learning correct model
equations and compare its computational and data efficiency with existing
methods. Because Bayesian-SINDy can quickly assimilate data and is robust
against noise, it is particularly suitable for biological data and real-time
system identification in control. Its probabilistic framework also enables the
calculation of information entropy, laying the foundation for an active
learning strategy.Comment: 23 pages, 13 figure
Quantum cloning with an optical fiber amplifier
It has been shown theoretically that a light amplifier working on the
physical principle of stimulated emission should achieve optimal quantum
cloning of the polarization state of light. We demonstrate close-to-optimal
universal quantum cloning of polarization in a standard fiber amplifier for
telecom wavelengths. For cloning 1 --> 2 we find a fidelity of 0.82, the
optimal value being 5/6 = 0.83.Comment: 4 pages, 3 figure
High performance guided-wave asynchronous heralded single photon source
We report on a guided wave heralded photon source based on the creation of
non-degenerate photon pairs by spontaneous parametric down conversion in a
Periodically Poled Lithium Niobate waveguide. Using the signal photon at 1310
nm as a trigger, a gated detection process permits announcing the arrival of
single photons at 1550 nm at the output of a single mode optical fiber with a
high probability of 0.38. At the same time the multi-photon emission
probability is reduced by a factor of 10 compared to poissonian light sources.
Relying on guided wave technologies such as integrated optics and fiber optics
components, our source offers stability, compactness and efficiency and can
serve as a paradigm for guided wave devices applied to quantum communication
and computation using existing telecom networks
Ensemble of Hankel Matrices for Face Emotion Recognition
In this paper, a face emotion is considered as the result of the composition
of multiple concurrent signals, each corresponding to the movements of a
specific facial muscle. These concurrent signals are represented by means of a
set of multi-scale appearance features that might be correlated with one or
more concurrent signals. The extraction of these appearance features from a
sequence of face images yields to a set of time series. This paper proposes to
use the dynamics regulating each appearance feature time series to recognize
among different face emotions. To this purpose, an ensemble of Hankel matrices
corresponding to the extracted time series is used for emotion classification
within a framework that combines nearest neighbor and a majority vote schema.
Experimental results on a public available dataset shows that the adopted
representation is promising and yields state-of-the-art accuracy in emotion
classification.Comment: Paper to appear in Proc. of ICIAP 2015. arXiv admin note: text
overlap with arXiv:1506.0500
An in vitro anatomic model of the human cerebral arteries with saccular arterial aneurysms
Summary: Anin vitro model of the main human cerebral arteries with or without saccular arterial aneurysms is presented. A cast of the cerebral arteries was obtained in a human specimen. Three aneurysms were simulated and added to the cast. Wax copies of the cast were produced, and embedded with liquid resin solidifying into solid blocks. After evacuation of the wax, a model consisting of a hollow reproduction of the cast within the resin block was obtained. The model is reproducible and anatomically accurate. Since it is transparent to visible light, and compatible with x-ray, magnetic resonance and transcranial doppler techniques, it should prove useful for a wide range of haemodynamic and radiologic investigations. The reported technique may be adapted to any structure with a hollow configuration, allowing for the preparation of arterial and venous models from other vascular areas, as well as models from other anatomic systems, such as the biliary or urinary tract
Optimizing single-photon-source heralding efficiency at 1550 nm using periodically poled lithium niobate
We explore the feasibility of using high conversion-efficiency
periodically-poled crystals to produce photon pairs for photon-counting
detector calibrations at 1550 nm. The goal is the development of an appropriate
parametric down-conversion (PDC) source at telecom wavelengths meeting the
requirements of high-efficiency pair production and collection in single
spectral and spatial modes (single-mode fibers). We propose a protocol to
optimize the photon collection, noise levels and the uncertainty evaluation.
This study ties together the results of our efforts to model the single-mode
heralding efficiency of a two-photon PDC source and to estimate the heralding
uncertainty of such a source.Comment: 14 pages, 2 tables and 3 figures, final version accepted by
Metrologi
Inadequacies in the conventional treatment of the radiation field of moving sources
There is a fundamental difference between the classical expression for the
retarded electromagnetic potential and the corresponding retarded solution of
the wave equation that governs the electromagnetic field. While the boundary
contribution to the retarded solution for the {\em potential} can always be
rendered equal to zero by means of a gauge transformation that preserves the
Lorenz condition, the boundary contribution to the retarded solution of the
wave equation governing the {\em field} may be neglected only if it diminishes
with distance faster than the contribution of the source density in the far
zone. In the case of a source whose distribution pattern both rotates and
travels faster than light {\em in vacuo}, as realized in recent experiments,
the boundary term in the retarded solution governing the field is by a factor
of the order of {\em larger} than the source term of this solution in
the limit that the distance of the boundary from the source tends to
infinity. This result is consistent with the prediction of the retarded
potential that part of the radiation field generated by a rotating superluminal
source decays as , instead of , a prediction that is
confirmed experimentally. More importantly, it pinpoints the reason why an
argument based on a solution of the wave equation governing the field in which
the boundary term is neglected (such as appears in the published literature)
misses the nonspherical decay of the field
Theoretical analysis of the electronic structure of the stable and metastable c(2x2) phases of Na on Al(001): Comparison with angle-resolved ultra-violet photoemission spectra
Using Kohn-Sham wave functions and their energy levels obtained by
density-functional-theory total-energy calculations, the electronic structure
of the two c(2x2) phases of Na on Al(001) are analysed; namely, the metastable
hollow-site structure formed when adsorption takes place at low temperature,
and the stable substitutional structure appearing when the substrate is heated
thereafter above ca. 180K or when adsorption takes place at room temperature
from the beginning. The experimentally obtained two-dimensional band structures
of the surface states or resonances are well reproduced by the calculations.
With the help of charge density maps it is found that in both phases, two
pronounced bands appear as the result of a characteristic coupling between the
valence-state band of a free c(2x2)-Na monolayer and the
surface-state/resonance band of the Al surfaces; that is, the clean (001)
surface for the metastable phase and the unstable, reconstructed "vacancy"
structure for the stable phase. The higher-lying band, being Na-derived,
remains metallic for the unstable phase, whereas it lies completely above the
Fermi level for the stable phase, leading to the formation of a
surface-state/resonance band-structure resembling the bulk band-structure of an
ionic crystal.Comment: 11 pages, 11 postscript figures, published in Phys. Rev. B 57, 15251
(1998). Other related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
High coherence photon pair source for quantum communication
This paper reports a novel single mode source of narrow-band entangled photon
pairs at telecom wavelengths under continuous wave excitation, based on
parametric down conversion. For only 7 mW of pump power it has a created
spectral radiance of 0.08 pairs per coherence length and a bandwidth of 10 pm
(1.2 GHz). The effectively emitted spectral brightness reaches 3.9*10^5 pairs
/(s pm). Furthermore, when combined with low jitter single photon detectors,
such sources allow for the implementation of quantum communication protocols
without any active synchronization or path length stabilization. A HOM-Dip with
photons from two autonomous CW sources has been realized demonstrating the
setup's stability and performance.Comment: 12 pages, 4 figure
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