184 research outputs found
Low-l CMB Analysis and Inpainting
Reconstruction of the CMB in the Galactic plane is extremely difficult due to
the dominant foreground emissions such as Dust, Free-Free or Synchrotron. For
cosmological studies, the standard approach consists in masking this area where
the reconstruction is not good enough. This leads to difficulties for the
statistical analysis of the CMB map, especially at very large scales (to study
for e.g., the low quadrupole, ISW, axis of evil, etc). We investigate in this
paper how well some inpainting techniques can recover the low- spherical
harmonic coefficients. We introduce three new inpainting techniques based on
three different kinds of priors: sparsity, energy and isotropy, and we compare
them. We show that two of them, sparsity and energy priors, can lead to
extremely high quality reconstruction, within 1% of the cosmic variance for a
mask with Fsky larger than 80%.Comment: Submitte
Geometric characterizations for strong minima with applications to nuclear norm minimization problems
In this paper, we introduce several geometric characterizations for strong
minima of optimization problems. Applying these results to nuclear norm
minimization problems allows us to obtain new necessary and sufficient
quantitative conditions for this important property. Our characterizations for
strong minima are weaker than the Restricted Injectivity and Nondegenerate
Source Condition, which are usually used to identify solution uniqueness of
nuclear norm minimization problems. Consequently, we obtain the minimum (tight)
bound on the number of measurements for (strong) exact recovery of low-rank
matrices.Comment: 41 page
Numerical simulation of solar cells besed CZTS buffer layer (ZnO1-XSX) using SCAPS-1D software
Cds buffer layer has many advantages such as large bandgap, and the carrier density. Otherwise, the presence of cadmium is an inconvenient. Research work, are shifted on the possibility of replacing CdS by a buffer layer devoid of cadmium. This manuscript presents the numerical study, using SCAPS-1D program, the effects of sulfur content in the buffer layer Zn (O,S) on the electrical parameters of the solar cell ZnO: Al / i-ZnO / Zn (O, S) / CZTS /. Changes in the band gap and electron affinity of Zn (O, S) were calculated from the law of Vegard. The numerical results of the thickness of the absorbent layer CZTS equal to 2.5μm, show that from the sulfur content equals to 45% we can find the same results with CdS, an efficiency varies slightly, about 19%.Keywords: CZTS; ZnO1-xSx; CdS; SCAPS; Solar cell
FASTLens (FAst STatistics for weak Lensing) : Fast method for Weak Lensing Statistics and map making
With increasingly large data sets, weak lensing measurements are able to
measure cosmological parameters with ever greater precision. However this
increased accuracy also places greater demands on the statistical tools used to
extract the available information. To date, the majority of lensing analyses
use the two point-statistics of the cosmic shear field. These can either be
studied directly using the two-point correlation function, or in Fourier space,
using the power spectrum. But analyzing weak lensing data inevitably involves
the masking out of regions or example to remove bright stars from the field.
Masking out the stars is common practice but the gaps in the data need proper
handling. In this paper, we show how an inpainting technique allows us to
properly fill in these gaps with only operations, leading to a new
image from which we can compute straight forwardly and with a very good
accuracy both the pow er spectrum and the bispectrum. We propose then a new
method to compute the bispectrum with a polar FFT algorithm, which has the main
advantage of avoiding any interpolation in the Fourier domain. Finally we
propose a new method for dark matter mass map reconstruction from shear
observations which integrates this new inpainting concept. A range of examples
based on 3D N-body simulations illustrates the results.Comment: Final version accepted by MNRAS. The FASTLens software is available
from the following link : http://irfu.cea.fr/Ast/fastlens.software.ph
Miscible displacement fronts of shear thinning fluids inside rough fractures
The miscible displacement of a shear-thinning fluid by another of same
rheological properties is studied experimentally in a transparent fracture by
an optical technique imaging relative concentration distributions. The fracture
walls have complementary self-affine geometries and are shifted laterally in
the direction perpendicular to the mean flow velocity {\bf U} : the flow field
is strongly channelized and macro dispersion controls the front structure for
P\'{e}clet numbers above a few units. The global front width increases then
linearly with time and reflects the velocity distribution between the different
channels. In contrast, at the local scale, front spreading is similar to Taylor
dispersion between plane parallel surfaces. Both dispersion mechanisms depend
strongly on the fluid rheology which shifts from Newtonian to shear-thinning
when the flow rate increases. In the latter domain, increasing the
concentration enhances the global front width but reduces both Taylor
dispersion (due to the flattening of the velocity profile in the gap of the
fracture) and the size of medium scale front structures
A review of fMRI simulation studies
Simulation studies that validate statistical techniques for fMRI data are challenging due to the complexity of the data. Therefore, it is not surprising that no common data generating process is available (i.e. several models can be found to model BOLD activation and noise). Based on a literature search, a database of simulation studies was compiled. The information in this database was analysed and critically evaluated focusing on the parameters in the simulation design, the adopted model to generate fMRI data, and on how the simulation studies are reported. Our literature analysis demonstrates that many fMRI simulation studies do not report a thorough experimental design and almost consistently ignore crucial knowledge on how fMRI data are acquired. Advice is provided on how the quality of fMRI simulation studies can be improved
Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)
The implicit objective of the biennial "international - Traveling Workshop on
Interactions between Sparse models and Technology" (iTWIST) is to foster
collaboration between international scientific teams by disseminating ideas
through both specific oral/poster presentations and free discussions. For its
second edition, the iTWIST workshop took place in the medieval and picturesque
town of Namur in Belgium, from Wednesday August 27th till Friday August 29th,
2014. The workshop was conveniently located in "The Arsenal" building within
walking distance of both hotels and town center. iTWIST'14 has gathered about
70 international participants and has featured 9 invited talks, 10 oral
presentations, and 14 posters on the following themes, all related to the
theory, application and generalization of the "sparsity paradigm":
Sparsity-driven data sensing and processing; Union of low dimensional
subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph
sensing/processing; Blind inverse problems and dictionary learning; Sparsity
and computational neuroscience; Information theory, geometry and randomness;
Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?;
Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website:
http://sites.google.com/site/itwist1
Wavelet penalized likelihood estimation in generalized functional models
The paper deals with generalized functional regression. The aim is to
estimate the influence of covariates on observations, drawn from an exponential
distribution. The link considered has a semiparametric expression: if we are
interested in a functional influence of some covariates, we authorize others to
be modeled linearly. We thus consider a generalized partially linear regression
model with unknown regression coefficients and an unknown nonparametric
function. We present a maximum penalized likelihood procedure to estimate the
components of the model introducing penalty based wavelet estimators.
Asymptotic rates of the estimates of both the parametric and the nonparametric
part of the model are given and quasi-minimax optimality is obtained under
usual conditions in literature. We establish in particular that the LASSO
penalty leads to an adaptive estimation with respect to the regularity of the
estimated function. An algorithm based on backfitting and Fisher-scoring is
also proposed for implementation. Simulations are used to illustrate the finite
sample behaviour, including a comparison with kernel and splines based methods
Impact of Continuous Axenic Cultivation in Leishmania infantum Virulence
Experimental infections with visceral Leishmania spp. are frequently performed referring to stationary parasite cultures that are comprised of a mixture of metacyclic and non-metacyclic parasites often with little regard to time of culture and metacyclic purification. This may lead to misleading or irreproducible experimental data. It is known that the maintenance of Leishmania spp. in vitro results in a progressive loss of virulence that can be reverted by passage in a mammalian host. In the present study, we aimed to characterize the loss of virulence in culture comparing the in vitro and in vivo infection and immunological profile of L. infantum stationary promastigotes submitted to successive periods of in vitro cultivation. To evaluate the effect of axenic in vitro culture in parasite virulence, we submitted L. infantum promastigotes to 4, 21 or 31 successive in vitro passages. Our results demonstrated a rapid and significant loss of parasite virulence when parasites are sustained in axenic culture. Strikingly, the parasite capacity to modulate macrophage activation decreased significantly with the augmentation of the number of in vitro passages. We validated these in vitro observations using an experimental murine model of infection. A significant correlation was found between higher parasite burdens and lower number of in vitro passages in infected Balb/c mice. Furthermore, we have demonstrated that the virulence deficit caused by successive in vitro passages results from an inadequate capacity to differentiate into amastigote forms. In conclusion, our data demonstrated that the use of parasites with distinct periods of axenic in vitro culture induce distinct infection rates and immunological responses and correlated this phenotype with a rapid loss of promastigote differentiation capacity. These results highlight the need for a standard operating protocol (SOP) when studying Leishmania species
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