349 research outputs found
Three Dimensional Raman Cooling using Velocity Selective Rapid Adiabatic Passage
We present a new and efficient implementation of Raman cooling of trapped
atoms. It uses Raman pulses with an appropriate frequency chirp to realize a
velocity selective excitation through a rapid adiabatic passage. This method
allows to address in a single pulse a large number of non zero atomic velocity
classes and it produces a nearly unity transfer efficiency. We demonstrate this
cooling method using cesium atoms in a far-detuned crossed dipole trap.
Three-dimensional cooling of atoms down to K is
performed in 100 ms. In this preliminary experiment the final atomic density is
at/cm (within a factor of 2) and the phase-space
density increase over the uncooled sample is 20. Numerical simulations indicate
that temperatures below the single photon recoil temperature should be
achievable with this method.Comment: OSA TOPS on Ultracold Atoms and BEC 7 (1997) 5
Gene Similarity-based Approaches for Determining Core-Genes of Chloroplasts
In computational biology and bioinformatics, the manner to understand
evolution processes within various related organisms paid a lot of attention
these last decades. However, accurate methodologies are still needed to
discover genes content evolution. In a previous work, two novel approaches
based on sequence similarities and genes features have been proposed. More
precisely, we proposed to use genes names, sequence similarities, or both,
insured either from NCBI or from DOGMA annotation tools. Dogma has the
advantage to be an up-to-date accurate automatic tool specifically designed for
chloroplasts, whereas NCBI possesses high quality human curated genes (together
with wrongly annotated ones). The key idea of the former proposal was to take
the best from these two tools. However, the first proposal was limited by name
variations and spelling errors on the NCBI side, leading to core trees of low
quality. In this paper, these flaws are fixed by improving the comparison of
NCBI and DOGMA results, and by relaxing constraints on gene names while adding
a stage of post-validation on gene sequences. The two stages of similarity
measures, on names and sequences, are thus proposed for sequence clustering.
This improves results that can be obtained using either NCBI or DOGMA alone.
Results obtained with this quality control test are further investigated and
compared with previously released ones, on both computational and biological
aspects, considering a set of 99 chloroplastic genomes.Comment: 4 pages, IEEE International Conference on Bioinformatics and
Biomedicine (BIBM 2014
Building a Chaotic Proven Neural Network
International audienceChaotic neural networks have received a great deal of attention these last years. In this paper we establish a precise correspondence between the so-called chaotic iterations and a particular class of artificial neural networks: global recurrent multi-layer perceptrons. We show formally that it is possible to make these iterations behave chaotically, as defined by Devaney, and thus we obtain the first neural networks proven chaotic. Several neural networks with different architectures are trained to exhibit a chaotical behavior
Finding the Core-Genes of Chloroplasts
Due to the recent evolution of sequencing techniques, the number of available
genomes is rising steadily, leading to the possibility to make large scale
genomic comparison between sets of close species. An interesting question to
answer is: what is the common functionality genes of a collection of species,
or conversely, to determine what is specific to a given species when compared
to other ones belonging in the same genus, family, etc. Investigating such
problem means to find both core and pan genomes of a collection of species,
\textit{i.e.}, genes in common to all the species vs. the set of all genes in
all species under consideration. However, obtaining trustworthy core and pan
genomes is not an easy task, leading to a large amount of computation, and
requiring a rigorous methodology. Surprisingly, as far as we know, this
methodology in finding core and pan genomes has not really been deeply
investigated. This research work tries to fill this gap by focusing only on
chloroplastic genomes, whose reasonable sizes allow a deep study. To achieve
this goal, a collection of 99 chloroplasts are considered in this article. Two
methodologies have been investigated, respectively based on sequence
similarities and genes names taken from annotation tools. The obtained results
will finally be evaluated in terms of biological relevance
Atom interferometry and the Einstein equivalence principle
The computation of the phase shift in a symmetric atom interferometer in the
presence of a gravitational field is reviewed. The difference of action-phase
integrals between the two paths of the interferometer is zero for any
Lagrangian which is at most quadratic in position and velocity. We emphasize
that in a large class of theories of gravity the atom interferometer permits a
test of the weak version of the equivalence principle (or universality of free
fall) by comparing the acceleration of atoms with that of ordinary bodies, but
is insensitive to that aspect of the equivalence principle known as the
gravitational redshift or universality of clock rates.Comment: 5 pages, to appear in the proceedings of the "46th Rencontres de
Moriond and GPhyS Colloquium on Gravitational Waves and Experimental
Gravity", la Thuile, March 20-27, 201
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