1,950 research outputs found
Elastic contact to nearly incompressible coatings -- Stiffness enhancement and elastic pile-up
We have recently proposed an efficient computation method for the
frictionless linear elastic axisymmetric contact of coated bodies [A. Perriot
and E. Barthel, J. Mat. Res. 19 (2004) 600]. Here we give a brief description
of the approach. We also discuss implications of the results for the
instrumented indentation data analysis of coated materials. Emphasis is laid on
incompressible or nearly incompressible materials (Poisson ratio ): we
show that the contact stiffness rises much more steeply with contact radius
than for more compressible materials and significant elastic pile-up is
evidenced. In addition the dependence of the penetration upon contact radius
increasingly deviates from the homogeneous reference case when the Poisson
ratio increases. As a result, this algorithm may be helpful in instrumented
indentation data analysis on soft and nearly incompressible layers
Genomes are covered with ubiquitous 11 bp periodic patterns, the "class A flexible patterns"
BACKGROUND: The genomes of prokaryotes and lower eukaryotes display a very strong 11 bp periodic bias in the distribution of their nucleotides. This bias is present throughout a given genome, both in coding and non-coding sequences. Until now this bias remained of unknown origin. RESULTS: Using a technique for analysis of auto-correlations based on linear projection, we identified the sequences responsible for the bias. Prokaryotic and lower eukaryotic genomes are covered with ubiquitous patterns that we termed "class A flexible patterns". Each pattern is composed of up to ten conserved nucleotides or dinucleotides distributed into a discontinuous motif. Each occurrence spans a region up to 50 bp in length. They belong to what we named the "flexible pattern" type, in that there is some limited fluctuation in the distances between the nucleotides composing each occurrence of a given pattern. When taken together, these patterns cover up to half of the genome in the majority of prokaryotes. They generate the previously recognized 11 bp periodic bias. CONCLUSION: Judging from the structure of the patterns, we suggest that they may define a dense network of protein interaction sites in chromosomes
The small quantum cohomology of a weighted projective space, a mirror D-module and their classical limits
We first describe a canonical mirror partner (B-model) of the small quantum
orbifold cohomology of weighted projective spaces (A-model) in the framework of
differential equations: we attach to the A-model (resp. B-model) a D-module on
the torus and we show that these two D-modules are isomorphic. This makes the A
and B-models mirror partners and yields, in this situation, an explicit and
finer version of a recent result of Iritani. Then we study, using the theory of
the Kashiwara-Malgrange filtration, their degenerations at the origin and we
apply our results to the construction of (classical, limit, logarithmic)
Frobenius manifolds.Comment: 35 pages, Supersedes the paper arXiv:0806.2011, v2: minor
corrections, v3:minor corrections accepted for publication in Geometriae
Dedicat
UV-visible absorption study of the selfassociation of non-ionic chromonic triphenylenes TP6EOnM (n = 2, 3, 4) in dilute aqueous solutions:Impact of chain length on aggregation
A series of triphenylenes with oligoethoxy chains of various length, TP6EOnM with n = 2, 3, 4, has been synthesised and purified by HPLC. The self-association of these disc-shaped molecules in dilute aqueous solutions (?10–7 to ?4 × 10–4
M) has been studied by UV-visible absorption spectroscopy. The free energy of association decreases as the length of the chains increases. As a result, for a given concentration, the average size of aggregate diminishes as the chain length increases. While the absorption properties of the
monomer are identical for the three molecules, the extinction coefficients of solutions of the three triphenylenes at a given concentration are significantly different and are directly linked to the average size of the aggregates. The change of epsilon values upon aggregation could explain
the trend generally observed with dyes for solar cells substituted with chains of increasing length showing increasing extinction coefficient values
Formal Validation of Pattern Matching code
When addressing the formal validation of generated software, two main
alternatives consist either to prove the correctness of compilers or
to directly validate the generated code. Here, we focus on directly
proving the correctness of compiled code issued from powerful
pattern matching constructions typical of ML like languages or
rewrite based languages such as ELAN, MAUDE or Tom.
In this context, our first contribution is to define a general
framework for anchoring algebraic pattern-matching capabilities
in existing languages like C, Java or ML. Then, using a just enough
powerful intermediate language, we formalize the behavior of compiled
code and define the correctness of compiled code with respect to
pattern-matching behavior. This allows us to prove the equivalence of
compiled code correctness with a generic first-order proposition whose
proof could be achieved via a proof assistant or an automated theorem
prover. We then extend these results to the multi-match situation
characteristic of the ML like languages.
The whole approach has been implemented on top of the Tom compiler
and used to validate the syntactic matching code of the Tom compiler
itself
Ampelovirus and Vitivirus relationships in grapevine
Ampelovirus and Vitivirus relationships in grapevine. 16e Rencontres de Virologie Végétal
Stripping a debris disk by close stellar encounters in an open stellar cluster
A debris disk is a constituent of any planetary system surrounding a main
sequence star. We study whether close stellar encounters can disrupt and strip
a debris disk of its planetesimals in the expanding open cluster of its birth
with a decreasing star number density over 100 Myrs. Such stripping would
affect the dust production and hence detectability of the disk. We tabulated
the fractions of planetesimals stripped off during stellar flybys of miss
distances between 100 and 1000 AU and for several mass ratios of the central to
passing stars. We then estimated the numbers of close stellar encounters over
the lifetime of several expanding open clusters characterized by their initial
star densities. We found that a standard disk, with inner and outer radii of 40
and 100 AU, suffers no loss of planetesimals over 100 Myrs around a star born
in a common embedded cluster with star density <1000 pc^-3. In contrast, we
found that such a disk is severely depleted of its planetesimals over this
timescale around a star born in an Orion-type cluster where the star density is
>20 000 pc^-3. In this environment, a disk loses >97% of its planetesimals
around an M-dwarf, >63% around a solar-type star, and >42% around an A-dwarf,
over 100 Myrs. We roughly estimate that two-thirds of the stars may be born in
such high star density clusters. This might explain in part why fewer debris
disks are observed around lower mass stars.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics ; v2 abstract complemente
On the plastic deformation of soda-lime glass - a Cr3+ luminescence study of densification
International audienceSilicate glasses are known to experience an anomalous plastic behavior at micron-scale: 1) they exhibit densification when flowing plastically and 2) hydrostatic pressure affects the yield point. We have previously shown (A. Perriot et al. J. Am. Ceram. Soc. 89 (2006) 596) that densification maps are useful to infer a reliable constitutive law for the plastic response of silicate glasses. It is shown here that for soda-lime glass Cr3+ luminescence microspectroscopy may be used for that purpose. We also show that the constitutive law we have previously developed for amorphous silica provides a qualitative description of normal glasses although it is unable to account for the finer details. More work is needed to quantitatively model normal-glass plasticity at the continuum length-scale
Using early data to estimate the actual infection fatality ratio from COVID-19 in France (Running title: Infection fatality ratio from COVID-19)
The first cases of COVID-19 in France were detected on January 24, 2020. The
number of screening tests carried out and the methodology used to target the
patients tested do not allow for a direct computation of the real number of
cases and the mortality rate.In this report, we develop a
'mechanistic-statistical' approach coupling a SIR ODE model describing the
unobserved epidemiological dynamics, a probabilistic model describing the data
acquisition process and a statistical inference method. The objective of this
model is not to make forecasts but to estimate the real number of people
infected with COVID-19 during the observation window in France and to deduce
the mortality rate associated with the epidemic.Main results. The actual number
of infected cases in France is probably much higher than the observations: we
find here a factor x 15 (95%-CI: 4-33), which leads to a 5.2/1000 mortality
rate (95%-CI: 1.5 / 1000-11.7/ 1000) at the end of the observation period. We
find a R0 of 4.8, a high value which may be linked to the long viral shedding
period of 20 days
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