Génie végétal contre l'érosion des berges de cours d'eau dans un contexte de changement climatique : quelles nouvelles espèces utiliser ?

National audienceL'érosion des berges est un phénomène naturel participant activement aux processus de dynamique fluviale. Toutefois, afin de protéger des enjeux riverains (habitations, infrastructures de transport,) il est parfois nécessaire de fixer les berges avec des ouvrages de protection. Pour se faire, le génie végétal est aujourd'hui de plus en plus employé. Il s'agit de mettre en place des matériaux végétaux vivants qui vont stabiliser les berges. Ces ouvrages comprennent notamment des boutures de saules, dont les racines vont fixer la zone érodée. Les saules, sont des espèces qui apprécient l'eau et restent inféodées à la nappe phréatique. Or la sécheresse est une des causes majeures d'échec des ouvrages de génie végétal, et ces dernières devraient s'aggraver avec le changement climatique. Il apparaît donc particulièrement intéressant de tester de nouvelles espèces présentant à la fois de bonnes capacités en termes de génie végétal et une meilleure résistance à la sécheresse. Myricaria germanica et Tamarix gallica, deux espèces pionnières des bords de cours d'eau, présentent à priori de telles caractéristiques, mais leurs patrons de développement ainsi que leur capacité de résistance à la sécheresse sont peu connues. Les comportements de boutures de ces deux espèces ont été comparés avec celle d'un saule dans trois expérimentations en laboratoire et sur le terrain. On a ainsi pu déterminer les dynamiques de croissance des parties aériennes et souterraines en fonction de différentes modalités de sécheresse. Myricaria germanica et Tamarix gallica montrent généralement un taux de reprise au bouturage élevé et proche de celui du saule, et un investissement dans les racines supérieur en cas de sécheresse, Cependant la croissance de Myricaria germanica apparaît nettement plus faible que celles des deux autres espèces Ces deux espèces présentent un fort potentiel pour le génie végétal, notamment dans un contexte de changement climatique. Elles s'adaptent bien aux conditions de sècheresse et disposent de bonnes capacités de stabilisation. Leur utilisation dans ce domaine devrait contribuer à augmenter la biodiversité des ouvrages

Detection of arcs in Saturn's F ring during the 1995 Sun ring-plane crossing

Observations of the November 1995 Sun crossing of the Saturn's ring-plane made with the 3.6m CFH telescope, using the UHAO adaptive optics system, are presented here. We report the detection of four arcs located in the vicinity of the F ring. They can be seen one day later in HST images. The combination of both data sets gives accurate determinations of their orbits. Semi-major axes range from 140020 km to 140080 km, with a mean of 140060 +- 60 km. This is about 150 km smaller than previous estimates of the F ring radius from Voyager 1 and 2 data, but close to the orbit of another arc observed at the same epoch in HST images.Comment: 8 pages, 3 figures, 1 table, To appear in A&A, for comments : [email protected]

Axon Myelin Transfer of a Non-Enveloped Virus

We showed previously that Theiler's virus, a neurotropic non-enveloped picornavirus of mouse, traffics from the axon of infected neurons into the surrounding myelin. When this traffic is interrupted, as in the shiverer mouse which bears a mutation in the myelin basic protein gene, the virus is unable to persist in the central nervous system. In the present work, we used the Wlds mutant mouse, a strain in which axonal degeneration is considerably slowed down, to show that axon to myelin traffic takes place in the absence of axon degeneration. Our results suggest the existence of a mechanism of transfer of axonal cytoplasm into the myelin which Theiler's virus might exploit to ensure its persistence

Integration of Lie 2-algebras and their morphisms

Given a strict Lie 2-algebra, we can integrate it to a strict Lie 2-group by integrating the corresponding Lie algebra crossed module. On the other hand, the integration procedure of Getzler and Henriques will also produce a 2-group. In this paper, we show that these two integration results are Morita equivalent. As an application, we integrate a non-strict morphism between Lie algebra crossed modules to a generalized morphism between their corresponding Lie group crossed modules.Comment: 19 pages, Lett. Math. Phys. 102 (2), (2012.11), 223-24

Free particle scattering off two oscillating disks

We investigate the two-dimensional classical dynamics of the scattering of point particles by two periodically oscillating disks. The dynamics exhibits regular and chaotic scattering properties, as a function of the initial conditions and parameter values of the system. The energy is not conserved since the particles can gain and loose energy from the collisions with the disks. We find that for incident particles whose velocity is on the order of the oscillating disk velocity, the energy of the exiting particles displays non-monotonic gaps of allowed energies, and the distribution of exiting particle velocities shows significant fluctuations in the low energy regime. We also considered the case when the initial velocity distribution is Gaussian, and found that for high energies the exit velocity distribution is Gaussian with the same mean and variance. When the initial particle velocities are in the irregular regime the exit velocity distribution is Gaussian but with a smaller mean and variance. The latter result can be understood as an example of stochastic cooling. In the intermediate regime the exit velocity distribution differs significantly from Gaussian. A comparison of the results presented in this paper to previous chaotic static scattering problems is also discussed.Comment: 9 doble sided pages 13 Postscript figures, REVTEX style. To appear in Phys. Rev.

NN-body Simulation of Planetesimal Formation Through Gravitational Instability of a Dust Layer

We performed N-body simulations of a dust layer without a gas component and examined the formation process of planetesimals. We found that the formation process of planetesimals can be divided into three stages: the formation of non-axisymmetric wake-like structures, the creation of aggregates, and the collisional growth of the aggregates. Finally, a few large aggregates and many small aggregates are formed. The mass of the largest aggregate is larger than the mass predicted by the linear perturbation theory. We examined the dependence of system parameters on the planetesimal formation. We found that the mass of the largest aggregates increase as the size of the computational domain increases. However the ratio of the aggregate mass to the total mass $M_\mathrm{aggr}/M_\mathrm{total}$ is almost constant $0.8-0.9$. The mass of the largest aggregate increases with the optical depth and the Hill radius of particles.Comment: 34 pages, 11 figures. Accepted for publication in Ap

Cassini Observes the Active South Pole of Enceladus

Cassini has identified a geologically active province at the south pole of Saturn's moon Enceladus. In images acquired by the Imaging Science Subsystem (ISS), this region is circumscribed by a chain of folded ridges and troughs at ∼55°S latitude. The terrain southward of this boundary is distinguished by its albedo and color contrasts, elevated temperatures, extreme geologic youth, and narrow tectonic rifts that exhibit coarse-grained ice and coincide with the hottest temperatures measured in the region. Jets of fine icy particles that supply Saturn's E ring emanate from this province, carried aloft by water vapor probably venting from subsurface reservoirs of liquid water. The shape of Enceladus suggests a possible intense heating epoch in the past by capture into a 1:4 secondary spin/orbit resonance

Minimizing off-target signals in RNA fluorescent in situ hybridization

Fluorescent in situ hybridization (FISH) techniques are becoming extremely sensitive, to the point where individual RNA or DNA molecules can be detected with small probes. At this level of sensitivity, the elimination of ‘off-target’ hybridization is of crucial importance, but typical probes used for RNA and DNA FISH contain sequences repeated elsewhere in the genome. We find that very short (e.g. 20 nt) perfect repeated sequences within much longer probes (e.g. 350–1500 nt) can produce significant off-target signals. The extent of noise is surprising given the long length of the probes and the short length of non-specific regions. When we removed the small regions of repeated sequence from either short or long probes, we find that the signal-to-noise ratio is increased by orders of magnitude, putting us in a regime where fluorescent signals can be considered to be a quantitative measure of target transcript numbers. As the majority of genes in complex organisms contain repeated k-mers, we provide genome-wide annotations of k-mer-uniqueness at http://cbio.mskcc.org/∼aarvey/repeatmap