9,497 research outputs found
Global well-posedness of a conservative relaxed cross diffusion system
We prove global existence in time of solutions to relaxed conservative cross
diffusion systems governed by nonlinear operators of the form where the represent
density-functions, is a spatially regularized form of
and the nonlinearities are merely assumed to be
continuous and bounded from below. Existence of global weak solutions is
obtained in any space dimension. Solutions are proved to be regular and unique
when the are locally Lipschitz continuous
Efficient filtering of adult content using textual information
Nowadays adult content represents a non negligible proportion of the Web
content. It is of the utmost importance to protect children from this content.
Search engines, as an entry point for Web navigation are ideally placed to deal
with this issue.
In this paper, we propose a method that builds a safe index i.e.
adult-content free for search engines. This method is based on a filter that
uses only textual information from the web page and the associated URL
Non-Uniform Time Sampling for Multiple-Frequency Harmonic Balance Computations
A time-domain harmonic balance method for the analysis of almost-periodic (multi-harmonics) flows is presented. This method relies on Fourier analysis to derive an efficient alternative to classical time marching schemes for such flows. It has recently received significant attention, especially in the turbomachinery field where the flow spectrum is essentially a combination of the blade passing frequencies. Up to now, harmonic balance methods have used a uniform time sampling of the period of interest, but in the case of several frequencies, non-necessarily multiple of each other, harmonic balance methods can face stability issues due to a bad condition number of the Fourier operator. Two algorithms are derived to find a non-uniform time sampling in order to minimize this condition number. Their behavior is studied on a wide range of frequencies, and a model problem of a 1D flow with pulsating outlet pressure, which enables to prove their efficiency. Finally, the flow in a multi-stage axial compressor is analyzed with different frequency sets. It demonstrates the stability and robustness of the present non-uniform harmonic balance method regardless of the frequency set
Properties of selected mutations and genotypic landscapes under Fisher's Geometric Model
The fitness landscape - the mapping between genotypes and fitness -
determines properties of the process of adaptation. Several small genetic
fitness landscapes have recently been built by selecting a handful of
beneficial mutations and measuring fitness of all combinations of these
mutations. Here we generate several testable predictions for the properties of
these landscapes under Fisher's geometric model of adaptation (FGMA). When far
from the fitness optimum, we analytically compute the fitness effect of
beneficial mutations and their epistatic interactions. We show that epistasis
may be negative or positive on average depending on the distance of the
ancestral genotype to the optimum and whether mutations were independently
selected or co-selected in an adaptive walk. Using simulations, we show that
genetic landscapes built from FGMA are very close to an additive landscape when
the ancestral strain is far from the optimum. However, when close to the
optimum, a large diversity of landscape with substantial ruggedness and sign
epistasis emerged. Strikingly, landscapes built from different realizations of
stochastic adaptive walks in the same exact conditions were highly variable,
suggesting that several realizations of small genetic landscapes are needed to
gain information about the underlying architecture of the global adaptive
landscape.Comment: 51 pages, 8 figure
How informative are single well tracing experiments? : an assessment using Bayesian evidential learning
ATHEN
Effect of disorder close to the superfluid transition in a two-dimensional Bose gas
We experimentally study the effect of disorder on trapped quasi
two-dimensional (2D) 87Rb clouds in the vicinity of the
Berezinskii-Kosterlitz-Thouless (BKT) phase transition. The disorder
correlation length is of the order of the Bose gas characteristic length scales
(thermal de Broglie wavelength, healing length) and disorder thus modifies the
physics at a microscopic level. We analyze the coherence properties of the
cloud through measurements of the momentum distributions, for two disorder
strengths, as a function of its degeneracy. For moderate disorder, the
emergence of coherence remains steep but is shifted to a lower entropy. In
contrast, for strong disorder, the growth of coherence is hindered. Our study
is an experimental realization of the dirty boson problem in a well controlled
atomic system suitable for quantitative analysis
All optical cooling of K to Bose Einstein condensation
We report the all-optical production of Bose Einstein condensates (BEC) of
K atoms. We directly load atoms in a large volume
optical dipole trap from gray molasses on the D1 transition. We then apply a
small magnetic quadrupole field to polarize the sample before transferring the
atoms in a tightly confining optical trap. Evaporative cooling is finally
performed close to a Feshbach resonance to enhance the scattering length. Our
setup allows to cross the BEC threshold with atoms every 7s. As
an illustration of the interest of the tunability of the interactions we study
the expansion of Bose-Einstein condensates in the 1D to 3D crossover
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