245 research outputs found
Les conditions du milieu et la morphologie de la plante en fin de croissance chez le haricot, Phaseolus vulgaris L.
Le nombre d'entre-noeuds est déterminé très tôt, à la levée germinative, par les facteurs du milieu. Il est limité au maximum à 7 pour toutes les variétés naines et, le plus souvent, à un nombre supérieur pour les variétés à rames. La notion de croissance illimitée a été expliquée. L'entre-noeud "moyen", le premier entre-noeud, à partir de la base, à présenter une longueur supérieure à la longueur moyenne de tous les entre-noeuds de la tige, admet un seuil (9 cm chez les variétés naines) au-dessous duquel la plante est érigée et au-dessus duquel elle est volubile. Lors de la pleine croissance de cet entre-noeud apparaît le port futur (érigé ou volubile) de la plante suivant que la longueur de celui-ci est inférieure ou supérieure au seuil. Il n'y a pas de relation de cause à effet entre la longueur et le port de la plante. (Résumé d'auteur
The IRIS network of excellence: future directions in interactive storytelling
The IRIS Network of Excellence (NoE) started its work in January 2009. In this paper we highlight some new research directions developing within the network: one is revisiting narrative formalisation through the use of Linear Logic and the other is challenging the conventional framework of basing Interactive Storytelling on computer graphics to explore the content-based recombination of video sequences
Polymorphic evolution sequence and evolutionary branching
We are interested in the study of models describing the evolution of a
polymorphic population with mutation and selection in the specific scales of
the biological framework of adaptive dynamics. The population size is assumed
to be large and the mutation rate small. We prove that under a good combination
of these two scales, the population process is approximated in the long time
scale of mutations by a Markov pure jump process describing the successive
trait equilibria of the population. This process, which generalizes the
so-called trait substitution sequence, is called polymorphic evolution
sequence. Then we introduce a scaling of the size of mutations and we study the
polymorphic evolution sequence in the limit of small mutations. From this study
in the neighborhood of evolutionary singularities, we obtain a full
mathematical justification of a heuristic criterion for the phenomenon of
evolutionary branching. To this end we finely analyze the asymptotic behavior
of 3-dimensional competitive Lotka-Volterra systems
Developmental morphology of seedlings of Dioscorea cayenensis-D. rotundata complex
L'étude morphologique des plantes issues de graines, de l'Igname du complexe #Dioscorea cayenensi - D. rotundata$, a été réalisée par examen en microscopie optique de leur développement, depuis l'embryon dans la graine jusqu'à la jeune plante âgée de deux mois. Au cours du premier mois après le semis des graines, les organes liés étroitement avec la partie basale axiale de la jeune plante s'initient et/ou se développent ; ce sont le cotylédon, les trois premières feuilles, le système racinaire et le tubercule. La première feuille, présente dans l'embryon, est particulière parce qu'elle ne possède pas de bourgeon axillaire. La deuxième feuille devient une écaille à l'aisselle de laquelle se développe un système axillaire important. L'entrenoeud sous-jacent à la troisième feuille est le premier allongement de la tige. Des racines adventives naissent dans la partie axiale basale ; Dès le quinzième jour après le semis, la formation du tubercule est initiée par des divisions anticlines et périclines dans le parenchyme de la région axiale située entre la racine principale et le cotylédon, et enfermée à ce stade dans la gaine cotylédonaire. Deux mois après le semis, le très jeune tubercule s'est structuré avec un apex à vaste méristème couvrant du parenchyme et des faisceaux provasculaires. (Résumé d'auteur
Direct competition results from strong competiton for limited resource
We study a model of competition for resource through a chemostat-type model
where species consume the common resource that is constantly supplied. We
assume that the species and resources are characterized by a continuous trait.
As already proved, this model, although more complicated than the usual
Lotka-Volterra direct competition model, describes competitive interactions
leading to concentrated distributions of species in continuous trait space.
Here we assume a very fast dynamics for the supply of the resource and a fast
dynamics for death and uptake rates. In this regime we show that factors that
are independent of the resource competition become as important as the
competition efficiency and that the direct competition model is a good
approximation of the chemostat. Assuming these two timescales allows us to
establish a mathematically rigorous proof showing that our resource-competition
model with continuous traits converges to a direct competition model. We also
show that the two timescales assumption is required to mathematically justify
the corresponding classic result on a model consisting of only finite number of
species and resources (MacArthur, R. Theor. Popul. Biol. 1970:1, 1-11). This is
performed through asymptotic analysis, introducing different scales for the
resource renewal rate and the uptake rate. The mathematical difficulty relies
in a possible initial layer for the resource dynamics. The chemostat model
comes with a global convex Lyapunov functional. We show that the particular
form of the competition kernel derived from the uptake kernel, satisfies a
positivity property which is known to be necessary for the direct competition
model to enjoy the related Lyapunov functional
A simple mathematical model of gradual Darwinian evolution: Emergence of a Gaussian trait distribution in adaptation along a fitness gradient
We consider a simple mathematical model of gradual Darwinian evolution in
continuous time and continuous trait space, due to intraspecific competition
for common resource in an asexually reproducing population in constant
environment, while far from evolutionary stable equilibrium. The model admits
exact analytical solution. In particular, Gaussian distribution of the trait
emerges from generic initial conditions.Comment: 21 pages, 2 figures, as accepted to J Math Biol 2013/03/1
The monomer-dimer problem and moment Lyapunov exponents of homogeneous Gaussian random fields
We consider an "elastic" version of the statistical mechanical monomer-dimer
problem on the n-dimensional integer lattice. Our setting includes the
classical "rigid" formulation as a special case and extends it by allowing each
dimer to consist of particles at arbitrarily distant sites of the lattice, with
the energy of interaction between the particles in a dimer depending on their
relative position. We reduce the free energy of the elastic dimer-monomer (EDM)
system per lattice site in the thermodynamic limit to the moment Lyapunov
exponent (MLE) of a homogeneous Gaussian random field (GRF) whose mean value
and covariance function are the Boltzmann factors associated with the monomer
energy and dimer potential. In particular, the classical monomer-dimer problem
becomes related to the MLE of a moving average GRF. We outline an approach to
recursive computation of the partition function for "Manhattan" EDM systems
where the dimer potential is a weighted l1-distance and the auxiliary GRF is a
Markov random field of Pickard type which behaves in space like autoregressive
processes do in time. For one-dimensional Manhattan EDM systems, we compute the
MLE of the resulting Gaussian Markov chain as the largest eigenvalue of a
compact transfer operator on a Hilbert space which is related to the
annihilation and creation operators of the quantum harmonic oscillator and also
recast it as the eigenvalue problem for a pantograph functional-differential
equation.Comment: 24 pages, 4 figures, submitted on 14 October 2011 to a special issue
of DCDS-
Distinct roles of Hoxa2 and Krox20 in the development of rhythmic neural networks controlling inspiratory depth, respiratory frequency, and jaw opening
<p>Abstract</p> <p>Background</p> <p>Little is known about the involvement of molecular determinants of segmental patterning of rhombomeres (r) in the development of rhythmic neural networks in the mouse hindbrain. Here, we compare the phenotypes of mice carrying targeted inactivations of <it>Hoxa2</it>, the only <it>Hox </it>gene expressed up to r2, and of <it>Krox20</it>, expressed in r3 and r5. We investigated the impact of such mutations on the neural circuits controlling jaw opening and breathing in newborn mice, compatible with Hoxa2-dependent trigeminal defects and direct regulation of <it>Hoxa2 </it>by Krox20 in r3.</p> <p>Results</p> <p>We found that <it>Hoxa2 </it>mutants displayed an impaired oro-buccal reflex, similarly to <it>Krox20 </it>mutants. In contrast, while <it>Krox20 </it>is required for the development of the rhythm-promoting parafacial respiratory group (pFRG) modulating respiratory frequency,<it> Hoxa2 </it>inactivation did not affect neonatal breathing frequency. Instead, we found that <it>Hoxa2</it><sup>-/- </sup>but not <it>Krox20</it><sup>-/- </sup>mutation leads to the elimination of a transient control of the inspiratory amplitude normally occurring during the first hours following birth. Tracing of r2-specific progenies of <it>Hoxa2 </it>expressing cells indicated that the control of inspiratory activity resides in rostral pontine areas and required an intact r2-derived territory.</p> <p>Conclusion</p> <p>Thus, inspiratory shaping and respiratory frequency are under the control of distinct <it>Hox</it>-dependent segmental cues in the mammalian brain. Moreover, these data point to the importance of rhombomere-specific genetic control in the development of modular neural networks in the mammalian hindbrain.</p
Super-resolution in map-making based on a physical instrument model and regularized inversion. Application to SPIRE/Herschel
We investigate super-resolution methods for image reconstruction from data
provided by a family of scanning instruments like the Herschel observatory. To
do this, we constructed a model of the instrument that faithfully reflects the
physical reality, accurately taking the acquisition process into account to
explain the data in a reliable manner. The inversion, ie the image
reconstruction process, is based on a linear approach resulting from a
quadratic regularized criterion and numerical optimization tools. The
application concerns the reconstruction of maps for the SPIRE instrument of the
Herschel observatory. The numerical evaluation uses simulated and real data to
compare the standard tool (coaddition) and the proposed method. The inversion
approach is capable to restore spatial frequencies over a bandwidth four times
that possible with coaddition and thus to correctly show details invisible on
standard maps. The approach is also applied to real data with significant
improvement in spatial resolution.Comment: Astronomy & Astrophysic
Use of a Priori Information for the Deconvolution of Ultrasonic Signals
The resolution of pulse-echo imaging technique is limited by the band-width of the transducer impulse response (IR). For flaws sizing or thickness measurement simple and accurate methods exist if the echoes do not overlap. These classical methods break if the echoes can not be separated in time domain
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