1,454 research outputs found
Differential fast fixed-point algorithms for underdetermined instantaneous and convolutive partial blind source separation
This paper concerns underdetermined linear instantaneous and convolutive
blind source separation (BSS), i.e., the case when the number of observed mixed
signals is lower than the number of sources.We propose partial BSS methods,
which separate supposedly nonstationary sources of interest (while keeping
residual components for the other, supposedly stationary, "noise" sources).
These methods are based on the general differential BSS concept that we
introduced before. In the instantaneous case, the approach proposed in this
paper consists of a differential extension of the FastICA method (which does
not apply to underdetermined mixtures). In the convolutive case, we extend our
recent time-domain fast fixed-point C-FICA algorithm to underdetermined
mixtures. Both proposed approaches thus keep the attractive features of the
FastICA and C-FICA methods. Our approaches are based on differential sphering
processes, followed by the optimization of the differential nonnormalized
kurtosis that we introduce in this paper. Experimental tests show that these
differential algorithms are much more robust to noise sources than the standard
FastICA and C-FICA algorithms.Comment: this paper describes our differential FastICA-like algorithms for
linear instantaneous and convolutive underdetermined mixture
Renormings of
We investigate the best order of smoothness of . We prove in
particular that there exists a -smooth bump function on if
and only if and are both even integers and is a multiple of .Comment: 18 pages; AMS-Te
Smooth Approximation of Lipschitz functions on Riemannian manifolds
We show that for every Lipschitz function defined on a separable
Riemannian manifold (possibly of infinite dimension), for every continuous
, and for every positive number , there exists
a smooth Lipschitz function such that
for every and
. Consequently, every separable
Riemannian manifold is uniformly bumpable. We also present some applications of
this result, such as a general version for separable Riemannian manifolds of
Deville-Godefroy-Zizler's smooth variational principle.Comment: 10 page
Extended Red Emission and the evolution of carbonaceaous nanograins in NGC 7023
Extended Red Emission (ERE) was recently attributed to the photo-luminescence
of either doubly ionized Polycyclic Aromatic Hydrocarbons (PAH), or
charged PAH dimers. We analysed the visible and mid-infrared (mid-IR) dust
emission in the North-West and South photo-dissociation regions of the
reflection nebula NGC 7023.Using a blind signal separation method, we extracted
the map of ERE from images obtained with the Hubble Space Telescope, and at the
Canada France Hawaii Telescope. We compared the extracted ERE image to the
distribution maps of the mid-IR emission of Very Small Grains (VSGs), neutral
and ionized PAHs (PAH and PAH) obtained with the Spitzer Space
Telescope and the Infrared Space Observatory. ERE is dominant in transition
regions where VSGs are being photo-evaporated to form free PAH molecules, and
is not observed in regions dominated by PAH. Its carrier makes a minor
contribution to the mid-IR emission spectrum. These results suggest that the
ERE carrier is a transition species formed during the destruction of VSGs.
Singly ionized PAH dimers appear as good candidates but PAH molecules
seem to be excluded.Comment: Accepted for publication in A&
Large-eddy simulation of the flow in a lid-driven cubical cavity
Large-eddy simulations of the turbulent flow in a lid-driven cubical cavity
have been carried out at a Reynolds number of 12000 using spectral element
methods. Two distinct subgrid-scales models, namely a dynamic Smagorinsky model
and a dynamic mixed model, have been both implemented and used to perform
long-lasting simulations required by the relevant time scales of the flow. All
filtering levels make use of explicit filters applied in the physical space (on
an element-by-element approach) and spectral (modal) spaces. The two
subgrid-scales models are validated and compared to available experimental and
numerical reference results, showing very good agreement. Specific features of
lid-driven cavity flow in the turbulent regime, such as inhomogeneity of
turbulence, turbulence production near the downstream corner eddy, small-scales
localization and helical properties are investigated and discussed in the
large-eddy simulation framework. Time histories of quantities such as the total
energy, total turbulent kinetic energy or helicity exhibit different evolutions
but only after a relatively long transient period. However, the average values
remain extremely close
Reply to the correspondence: "On the fracture toughness of bioinspired ceramic materials"
This is a reply to the correspondence of Prof. Robert Ritchie: "On the
fracture toughness of bioinspired ceramic materials", submitted to Nature
Materials, which discusses the fracture toughness values of the following
papers: Bouville, F., Maire, E., Meille, S., Van de Moort\`ele, B., Stevenson,
A. J., & Deville, S. (2014). Strong, tough and stiff bioinspired ceramics from
brittle constituents. Nature Materials, 13(5), 508-514 and Le Ferrand, H.,
Bouville, F., Niebel, T. P., & Studart, A. R. (2015). Magnetically assisted
slip casting of bioinspired heterogeneous composites. Nature Materials, 14(11),
1172-1172.Comment: 5 pages, 2 figure
Interaction of multiple particles with a solidification front : from compacted particle layer to particle trapping
The interaction of solidification fronts with objects such as particles,
droplets, cells, or bubbles is a phenomenon with many natural and technological
occurrences. For an object facing the front, it may yield various fates, from
trapping to rejection, with large implications regarding the solidification
pattern. However, whereas most situations involve multiple particles
interacting with each other and the front, attention has focused almost
exclusively on the interaction of a single, isolated object with the front.
Here we address experimentally the interaction of multiple particles with a
solidification front by performing solidification experiments of a monodisperse
particle suspension in a Hele-Shaw cell, with precise control of growth
conditions and real-time visualization. We evidence the growth of a particle
layer ahead of the front at a close-packing volume fraction and we document its
steady state value at various solidification velocities. We then extend single
particle models to the situation of multiple particles by taking into account
the additional force induced on an entering particle by viscous friction in the
compacted particle layer. By a force balance model, this provides an indirect
measure of the repelling mean thermomolecular pressure over a particle entering
the front. The presence of multiple particles is found to increase it following
a reduction of the thickness of the thin liquid film that separates particles
and front. We anticipate the findings reported here to provide a relevant basis
to understand many complex solidification situations in geophysics,
engineering, biology, or food engineering, where multiple objects interact with
the front and control the resulting solidification patterns.Comment: 13 pages, 10 figures, submitted to Langmui
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