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Large-scale live imaging of adult neural stem cells in their endogenous niche
No full textInternational audienceLive imaging of adult neural stem cells (aNSCs) in vivo is a technical challenge in the vertebrate brain. Here, we achieve long-term imaging of the adult zebrafish telencephalic neurogenic niche and track a population of >1000 aNSCs over weeks, by taking advantage of fish transparency at near-infrared wavelengths and of intrinsic multiphoton landmarks. This methodology enables us to describe the frequency, distribution and modes of aNSCs divisions across the entire germinal zone of the adult pallium, and to highlight regional differences in these parameters
Identification of magnetic deposits in 2-D axisymmetric eddy current models via shape optimization
No full textInternational audienceThe non-destructive control of steam generators is an essential task for the safe and failure-free operation of nuclear power plants. Due to magnetite particles in the cooling water of the plants, a frequent source for failures are magnetic deposits in the cooling loop of steam generators. From eddy current signals measured inside a U-tube in the steam generator, we propose and analyze a regularized shape optimization algorithm to identify magnetic deposits outside the U-tube with either known or unknown physical properties. Motivated by the cylindrical geometry of the U-tubes we assume an axisymmetric problem setting, reducing Maxwell's equations to a 2-D elliptic eddy current problem. The feasibility of the proposed algorithms is illustrated via numerical examples demonstrating in particular the stability of the method with respect to noise
Water impacting on superhydrophobic macrotextures
No full textInternational audienceIt has been recently shown that the presence of macrotextures on superhydrophobic materials can markedly modify the dynamics of water impacting them, and in particular significantly reduce the contact time of bouncing drops, compared with what is observed on a flat surface. This finding constitutes a significant step in the maximization of water repellency, since it enables to minimize even further the contact between solid and liquid. It also opens a new axis of research on the design of super-structures to induce specific functions such as anti-freezing, liquid fragmentation and/or recomposition, guiding, trapping and so on. Here we show that the contact time of drops bouncing on a repellent macrotexture takes discrete values when varying the impact speed. This allows us to propose a quantitative analysis of the reduction of contact time and thus to understand how and why macrotextures can control the dynamical properties of bouncing drops
The physics of badminton
No full textInternational audienceThe conical shape of a shuttlecock allows it to flip on impact. As a light and extended particle, it flies with a pure drag trajectory. We first study the flip phenomenon and the dynamics of the flight and then discuss the implications on the game. Lastly, a possible classification of different shots is proposed
Slot Machines: an approach to the Strategy Challenge in SMT solving (presentation only)
No full textInternational audienceIn this short introduction we briefly describe the relevance of Psyche's system description [GL13] to the Strategy Challenge set by L. de Moura and G. O. Passmore for SMT solving
On the nature of MHD and kinetic scale turbulence in the magnetosheath of Saturn: Cassini observations
No full textInternational audienceLow frequency turbulence in Saturn’s magnetosheath is investigated using in-situ measurements of the Cassini spacecraft. We focus on the magnetic en- ergy spectra computed in the frequency range ∼ [10−4 , 1]Hz. Three main results are reported: 1) The magnetic energy spectra showed a ∼ f−1 scaling at MHD scales followed by an ∼ f−2.6 scaling at the sub-ion scales without forming the so-called inertial range, breaking the universality of the Kolmogorov spectrum in the magnetosheath; 2) The magnetic com- pressibility and the cross-correlation between the par- allel component of the magnetic field and density fluctuations C(δn, δB||) indicate the dominance of the compressible magnetosonic slow modes at MHD scales rather than the Alfvén mode [3] ; 3) Higher order statistics revealed a monofractal (resp. multi- fractal) behaviour of the turbulent flow behind a quasi- perpendicular (resp. quasi-parallel) shock at the sub- ion scales
Seasonalities and cycles in time series: A fresh look with computer experiments
No full textInternational audienceRecent advances in the understanding of time series permit to clarify seasonalities and cycles, which might be rather obscure in today's literature. A theorem due to P. Cartier and Y. Perrin, which was published only recently, in 1995, and several time scales yield, perhaps for the first time, a clear-cut definition of seasonalities and cycles. Their detection and their extraction, moreover, become easy to implement. Several computer experiments with concrete data from various fields are presented and discussed. The conclusion suggests the application of this approach to the debatable Kondriatev waves
Temperature-precipitation extremes relationship in the Mediterranean: past climate assessment and projection in anthropogenic scenarios
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Modularity maximization clustering with cohesion conditions
No full textInternational audienceThe study of systems composed of interacting components through their representation as graphs is attracting a growing attention in a wide variety of domains. A modular structure characterizes many of these systems, that means that they contain subgroups of entities sharing some common properties. Therefore, a topic of particular interest is the identification of modules, called clusters or communities. The problem can be formulated using mathematical programming, where the idea is to optimize a function expressing the quality of the clustering partition. The most studied of these functions is the so-called modularity. We consider modularity maximization, formulated as a mixed-integer quadratic optimization problem that has a convex continuous relaxation. We address the problem of combining different clustering criteria and the corresponding impact on the optimization problem. Defining a good clustering criterion is in fact difficult. On the one hand, quality functions to be optimized have been proposed, and on the other hand, properties to be satisfied by each cluster of a partition have been suggested. It has recently been observed that one of the best known such properties, i.e., the weak condition [Proc. Natl. Acad. Sci. USA, 2004] was not satised by one or more clusters in a partition which maximizes some of the best known criteria. We consider five cluster-defining conditions, that we call cohesion conditions (including the weak one). We then modify the modularity optimization problem to add these conditions, one at a time, as constraints. These can be expressed as linear constraints (applying, for one of the considered conditions, a Fortet's linearization). Then, the obtained optimization models are still mixed-integer quadratic optimization problems that we solve by exact methods. We thus discuss the solution of the new models that enable to understand the impact of cohesion conditions on modularity maximization
Recollision-Induced Superradiance of Ionized Nitrogen Molecules
No full textInternational audienceWe propose a new mechanism to explain the origin of optical gain in the transitions between the excited and ground states of the ionized nitrogen molecule following irradiation of neutral nitrogen molecules with an intense ultrashort laser pulse. An efficient transfer of population to the excited state is achieved via field-induced multiple recollisions. We show that the proposed excitation mechanism must lead to a superradiant emission, a feature that we confirm experimentally