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Planetization: Five Theses
No full textInternational audienceThe expansion of the human sphere beyond Earth has larger repercussions for understanding the present than is usually acknowledged. The outcome of a collaboration between a historian and a philosopher, this paper proposes Teilhard de Chardin’s 1946 notion of ‘planetization’ as a key analytical concept. Planetizing history amounts to situating it within a dynamically transforming horizon, emphasizing the significance of extra-terrestrial technology including robotic spacecraft and orbital infrastructures for the environmental, social and political histories of what is commonly theorized as globalization. To planetize history, then, is to show that the history of the globalized present cannot be written from an exclusively terrestrial point of view
Use of Chromene or Chromane Derivatives as Herbicidal Agents
No full textThe present invention is applicable to the field of herbicides useful for controlling the proliferation of undesired plants. In particular, the invention relates to the use of at least one compound derived from chromene or chromane as a herbicidal agent, to a phytotoxic composition comprising said compound, as well as to a method for treating and/or controlling plants using such a compound
Spatio-temporal couplings for controlling group velocity in longitudinally pumped seeded soft X-ray lasers
No full textInternational audienc
Variational methods for solving numerically magnetostatic systems
No full textInternational audienceIn this paper, we study some techniques for solving numerically magnetostatic systems. We consider fairly general assumptions on the magnetic permeability tensor. It is elliptic, but can be nonhermitian. In particular, we revisit existing classical variational methods and propose new numerical methods. The numerical approximation is either based on the classical edge finite elements, or on continuous Lagrange finite elements. For the first type of discretization, we rely on the design of a new, mixed variational formulation that is obtained with the help of -coercivity. The numerical method can be related to a perturbed approach for solving mixed problems in electromagnetism. For the second type of discretization, we rely on an augmented variational formulation obtained with the help of the Weighted Regularization Method
A new method for in vivo assessment of corneal transparency using spectral-domain OCT
No full textInternational audienceCorneal transparency is essential to provide a clear view into and out of the eye, yet clinical means to assess such transparency are extremely limited and usually involve a subjective grading of visible opacities by means of slit-lamp biomicroscopy. Here, we describe an automated algorithm allowing extraction of quantitative corneal transparency parameters with standard clinical spectral-domain optical coherence tomography (SD-OCT). Our algorithm employs a novel pre-processing procedure to standardize SD-OCT image analysis and to numerically correct common instrumental artifacts before extracting mean intensity stromal-depth ( z ) profiles over a 6-mm-wide corneal area. The z -profiles are analyzed using our previously developed objective method that derives quantitative transparency parameters directly related to the physics of light propagation in tissues. Tissular heterogeneity is quantified by the Birge ratio B r and the photon mean-free path ( l s ) is determined for homogeneous tissues (i.e., B r ~1 ). SD-OCT images of 83 normal corneas (ages 22–50 years) from a standard SD-OCT device (RTVue-XR Avanti, Optovue Inc.) were processed to establish a normative dataset of transparency values. After confirming stromal homogeneity ( B r <10), we measured a median l s of 570 μm (interdecile range: 270–2400 μm). By also considering corneal thicknesses, this may be translated into a median fraction of transmitted (coherent) light T coh(stroma) of 51% (interdecile range: 22–83%). Excluding images with central saturation artifact raised our median T coh(stroma) to 73% (interdecile range: 34–84%). These transparency values are slightly lower than those previously reported, which we attribute to the detection configuration of SD-OCT with a relatively small and selective acceptance angle. No statistically significant correlation between transparency and age or thickness was found. In conclusion, our algorithm provides robust and quantitative measurements of corneal transparency from standard SD-OCT images with sufficient quality (such as ‘Line’ and ‘CrossLine’ B-scan modes without central saturation artifact) and addresses the demand for such an objective means in the clinical setting
A combination of Kohn-Vogelius and DDM methods for a geometrical inverse problem
No full textInternational audienceWe consider the inverse geometrical problem of identifying the discontinuity curve of an electrical conductivity from boundary measurements. This standard inverse problem is used as a model to introduce and study a combined inversion algorithm coupling a gradient descent on the Kohn-Vogelius cost functional with a domain decomposition method that includes the unknown curve in the domain partitioning. We prove the local convergence of the method in a simplified case and numerically show its efficiency for some two dimensional experiments
Standoff detection of an electric field by bidirectional nitrogen lasing
No full textInternational audienceWe report on standoff detection of dc electric field by bidirectional cavity-free lasing emission of neutral nitrogen molecules excited by intense circularly polarized femtosecond laser pulses. We observed that both the backward and forward 337.4 nm coherent lasing emission present a monotonous dependence on the strength of a remotely applied dc field up to ∼ 1 kV/cm field strength. Moreover, this method shows a dependence on the polarity of the external dc field, providing a sensitive method for remote characterization of the electric field amplitude and direction. We attribute the underlying mechanism of lasing signal modulation to the electric field induced electron acceleration and deceleration, which results in a variation of the kinetic energy of the free electrons and a modulation of the population inversion responsible for the nitrogen molecules’ lasing.The polarity-sensitive detection anisotropy is interpreted by the symmetry breaking of the electron motion in the plane perpendicular to the laser propagation due to the injection of a weak second harmonic laser field produced in the quarter-wave plate for a circularly polarized pump laser. Numerical simulations based on the two-dimensional time-dependent Schrödinger equation for electron kinetic energy support our interpretation.This study provides a proof-of-principle method for standoff detection of electric fields based on nitrogen lasing, which can be potentially useful for atmospheric and metrological applications
