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Towards a new viewpoint on causality for time series
No full textInternational audienceCausation between time series is a most important topic in econometrics, financial engineering, biological and psychological sciences, and many other fields. A new setting is introduced for examining this rather abstract concept. The corresponding calculations, which are much easier than those required by the celebrated Granger-causality, do not necessitate any deterministic or probabilistic modeling. Some convincing computer simulations are presented.La causalité entre chroniques est un sujet capital en économétrie, ingénierie financière, sciences biologiques et psychologiques, et quantité d'autres domaines. On introduit ici une nouvelle approche pour traiter ce concept abstrait. Les calculs, qui sont beaucoup plus simples que ceux liés à la causalité de Granger, bien connue, ne nécessitent aucune modélisation déterministe ou probabiliste. On présente plusieurs simulations numériques réussies
Cross section and transverse single-spin asymmetry of η mesons in p↑+p collisions at s√=200 GeV at forward rapidity
No full textSee paper for full list of authorsInternational audienceWe present a measurement of the cross section and transverse single-spin asymmetry (AN) for η mesons at large pseudorapidity from s√=200 GeV p↑+p collisions. The measured cross section for 0.5<pT<5.0 GeV/c and 3.0<|η|<3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries AN have been measured as a function of Feynman-x (xF) from 0.2<|xF|<0.7, as well as transverse momentum (pT) from 1.0<pT<4.5 GeV/c. The asymmetry averaged over positive xF is ⟨AN⟩=0.061±0.014. The results are consistent with prior transverse single-spin measurements of forward η and π0 mesons at various energies in overlapping xF ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p↑+p collisions
TEMPERATURE INFLUENCE ON SMART STRUCTURES: A FIRST APPROACH
No full textInternational audienceWe study a linear coupled thermo-electromagnetoelastic problem and the nondi-mensionalization of the corresponding linear mixed parabolic-hyperbolic system. We deduce from the quasi-static equations a thin thermo-electromagnetoelastic plate model through the asymptotic expansions method
Building a 15-Year Cloud Climatology using Lidar in Space Observations: CALIOP and CloudSat now, EarthCARE next.
No full textInternational audienceToday, the CALIOP lidar and CloudSat radar have collected more than seven years of observations, and willhopefully still operate in 2016, after the EarthCARE-ATLID/CPR launch. Lidars and Radars in space providecutting edge information on the detailed vertical structure of clouds: a key element for both the evaluation ofthe description of clouds in climate models, and the survey of the clouds inter-annual evolution in variousclimatic conditions (El Nino, variation of North Atlantic Oscillations, polar regions, etc). For this purpose,the observations collected by CALIOP and by ATLID as well as CloudSat and EarthCARE CPR need to bemerged into a long-term (15 years) cloud climatology. Here, we examine the possibility of building such a climatology, with the aim of defining its accuracy andrelevance for cloud inter-annual studies. We examine the differences between the instruments (wavelengths,satellite’s altitudes, telescope fields of view, multiple scattering processes, spatial resolutions) and theirability to detect the same clouds consistently. Then, we define a set of cloud detection thresholds for ATLID,CALIOP, CloudSat and EarthCARE-CPR and test against synthetic cloud scenes (cirrus and shallowcumulus) over small areas (about 200km) produced by a lidar and radar instrument simulator (ECSIM)running on Large Eddy Simulations. Doing so, we verify that the fourth instruments will be able to detect thesame clouds despite their differences (e.g. their sensitivities to noise). Finally, we use the COSP lidar andradar simulator to predict the global scale cloud cover that ATLID, CALIOP, CloudSat and EarthCARE CPRwould observe if they were overflying the same atmosphere predicted by a GCM. Our results suggest that amerged CALIOP/ATLID and CloudSat/CPR cloud climatology could be to be useful for clouds inter-annualstudies, if the post-launch sensitivity of EarthCARE instruments is in line with what is predicted today
On the convective-absolute nature of river bedform instabilities
No full textInternational audienceRiver dunes and antidunes are induced by the morphological instability of stream-sediment boundary. Such bedforms raise a number of subtle theoretical questions and are crucial for many engineering and environmental problems. Despite their importance, the absolute/convective nature of the instability has never been addressed. The present work fills this gap as we demonstrate, by the cusp map method, that dune instability is convective for all values of the physical control parameters, while the antidune instability exhibits both behaviors. These theoretical predictions explain some previous experimental and numerical observations and are important to correctly plan flume experiments, numerical simulations, paleo-hydraulic reconstructions, and river works
Full-particle 2-D Simulations of the Ion Foreshock associated to a Supercritical Quasi-perpendicular Curved Collisionless Shock : Origin of Backstreaming Energetic Particles
No full textInternational audienceThe ion foreshock located upstream of the Earth's bow shock is populated with ions reflected back by the shock front. In-situ spacecraft measurements have clearly established the existence of two distinct populations in the upstream of the quasi-perpendicular shock region (i.e. for 45o ≤ ΘBn≤ 90o, where ΘBn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned ion beams (or 'FAB') characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions (or 'GPB') characterized by a NON gyrotropic distribution, which exhibits a non-vanishing perpendicular bulk velocity.The use of 2D PIC simulations where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described, has evidenced that the shock front itself can be the possible source of these two characteristic populations.A recent analysis has evidenced that both populations can be discriminated in terms of interaction time (Δtinter) with the shock front. 'GPB' and 'FAB' populations are characterized by a short (Δtinter ~ 1 τci) and much larger (Δtinter ≥ 2 τci) interaction time respectively, where τci is the ion upstream gyroperiod.In addition, present statistical results evidence that:(i) backstreaming ions are splitted into 'FAB' and 'GPB' populations depending on their injection angle when hitting the shock front (defined between the local normal to the shock front and the gyration velocity vector).(ii) As a consequence, ion trajectories strongly differ between the 'FAB' and 'GPB' populations at the shock front. In particular, 'FAB' ions suffer multi-bounces along the curved front whereas 'GPB' ions make only one bounce. Such differences may explain why the 'FAB' population loses their gyro-phase coherency and become gyrotropic which is not the case for the 'GPB'.Then, the differences observed between 'FAB' and 'GPB' populations do not involve some distinct reflection processes as often claimed in the literature but follow from different particle time histories at the shock front. Both 'FAB' and 'GPB' ions suffer the same reflection process but only 'FAB' population loose their initial phase coherency by suffering several bounces. This important result was not expected and greatly simplifies the question of their origin
Structural and functional studies of Bud23-Trm112 reveal 18S rRNA N7-G1575 methylation occurs on late 40S precursor ribosomes
No full textInternational audienceRibosomes are essential cellular nanomachines responsible for all protein synthesis in vivo. Efficient and faithful ribosome biogenesis requires a plethora of assembly factors whose precise role and timing of action remains to be established. Here we determined the crystal structure of Bud23–Trm112, which is required for efficient pre-rRNA processing steps leading to 18S rRNA synthesis and methylation of 18S rRNA at position G1575. For the first time, to our knowledge, we identified where on Bud23–Trm112 the contacts with precursor ribosomes occur. We further report that the essential helicase Dhr1 interacts directly with Bud23–Trm112, proposing a concerted action of these proteins in ribosome assembly. Finally, we reveal that the methyltransferase activity of Bud23–Trm112 and its requirement for pre-rRNA processing are disconnected in time
Vitamin D as an early predictor of multiple sclerosis activity and progression.
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Converse Lyapunov--Krasovskii Theorems for Uncertain Time-Delay Systems
No full textInternational audienceIn this article, we give a collection of converse Lyapunov-Krasovskii theorems for uncertain time-delay systems. We show that the existence of a weakly-degenerate Lyapunov-Krasovskii functional is necessary and sufficient condition for the global exponential stability of the time-delay systems. This is carried out using the switched system transformation approach