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Nonlinear Bessel vortex beams for applications
No full textInternational audienceWe investigate experimentally and numerically the nonlinear propagation of intense Bessel–Gauss vortices in transparent solids. We show that nonlinear Bessel–Gauss vortices preserve all properties of nonlinear Bessel–Gauss beams while their helicity provides an additional control parameter for single-shot precision micro structuring of transparent solids. For sufficiently large cone angle, a stable hollow tube of intense light is formed, generating a plasma channel whose radius and density are increasing with helicity and cone angle, respectively. We assess the potential of intense Bessel vortices for applications based on the generation of hollow plasma channels
Generation of long-lived underdense channels using femtosecond filamentation in air
No full textInternational audienceUsing femtosecond laser pulses at 800 and 400 nm, we characterize the formation of underdense channels in air generated by laser filamentation at the millijoule energy level by means of transverse interferometry. We find that using tight focusing conditions, filamentation generates a shock wave and that the resulting low-density channel lasts for more than 90 ms. Comparison of these results with hydrodynamic simulations using an Eulerian hydrodynamic code gives an good agreement and allows us to estimate the initial gas peak temperature at ∼ 1000 K. The influence of experimental parameters such as the focusing conditions for the ultrashort laser pulse, its polarization or the wavelength is studied and linked to previous characterizations of filamentation-generated plasma columns
Validation of CO2 Retrievals from GOSAT SWIR TANSO-FTS data, and Evaluation of Advanced spectral SWIR/TIR Synergistic Methodologies for Lowermost Tropospheric CO2 Retrieval.
No full textInternational audienceThe retrieval of the lowermost tropospheric content of greenhouse gases such as CO2 and CH4 is a critical issue for characterizing their sources and sinks. One key question lies in the methods to extract the best information of the concentration of these gases in the lower troposphere from satellite observations.We present first a validation of our atmospheric CO2 products retrieved from SWIR TANSO-FTS data on board GOSAT. This validation is based on the comparison between our CO2 products with TCCON products and other CO2 products from GOSAT data provided by several research groups (ACOS, NIES, SRON/KIT, and Univ. of Leicester).Then, we present spectral synergy methodologies exploiting SWIR and TIR spectral bands of TANSO-FTS and we discuss their expected added value to improve the retrieval of the lower tropospheric CO2 product. A specific approach combining SWIR and TIR level 2 products is compared with a more classical SWIR/TIR level 1 synergy algorithm and preliminary results are presented using synthetic TIR and SWIR GOSAT measurements
Lecture notes on BSDEs Main existence and stability results
No full textDoctoralBackward stochastic differential equations (BSDEs) are the non-Markovian (stochastic) counterpart of semi-linear parabolic equations. They have a wide range of applications in economics, and more generally in optimal control. In mathematical finance, the standard hedging theory can be written in terms of BSDEs (possibly reflected or with constraints), but they are also naturally associated to risk measures (g-expectations), utility maximization under constraints, or recursive utilities. These lectures are an introduction to the theory of BSDEs and to their applications. We will concentrate on various existence and stability results, starting from the classical Lipschitz continuous case up to quadratic BSDEs, and BSDEs with constraints.Our aim is to present the techniques rather than the results by themselves, so that the reader can enter the subject and further study the references we provide
Classification in Twitter via Compressive Sensing
No full textInternational audienceIn this paper we introduce a novel low dimensional method to perform topic detection and classification in Twitter. The proposed method first employs Joint Complexity to perform topic detection. Then, based on the nature of the data, we apply the theory of Compressive Sensing to perform topic classification by recovering an indicator vector, while reducing significantly the amount of information from tweets. In this paper we exploit datasets in various languages collected by using the Twitter streaming API, and achieve increased classification accuracy when comparing to state-of-the-art methods based on bag-of- words, along with several reconstruction techniques
Search for dark photons from neutral meson decays in p+p and d+Au collisions at =200 GeV
No full textInternational audienceThe standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g−2)μ deviates from SM calculations by 3.6σ. Several theoretical models attribute this to the existence of a “dark photon,” an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in π0,η→γe+e− decays and obtained upper limits of O(2×10−6) on U−γ mixing at 90% C.L. for the mass range 30<mU<90 MeV/c2. Combined with other experimental limits, the remaining region in the U−γ mixing parameter space that can explain the (g−2)μ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29<mU<32 MeV/c2 remaining
Socrate consultant ? Ou de la maïeutique
No full textInternational audienceA link has often be en drawn between the art of modem consultation and the socratic maieutics. Relying on Plato's work (Socrates Apology, Meno, Theaetetus) and on commentators (Maurice Clavel, Soren Kierkegaard, Wladimir Jankélévitch), the paper aims at highlighting similarities and dissimilarities between the art of modern consulting and Socrates maieutics.L’art du consultant a été souvent rapproché de la figure de Socrate et de la maïeutique. L’article fait un retour sur cette figure, à partir des textes de Platon (Apologie de Socrate, Ménon et Thééthète essentiellement) et de commentateurs (Maurice Clavel, Søren Kierkegaard, Wladimir Jankélévitch), pour comprendre comment un rapprochement est possible entre les consultants modernes et la maïeutique socratique, et mettre en lumière les différence
Transport of tropospheric ozone and precursors to the Arctic: lessons from a multi-model evaluation using aircraft, satellite and surface data
No full textInternational audienceChanges in abundances of short-lived climate pollutants such as tropospheric ozone and aerosol may have contributed significantly to observed rapid Arctic warming in recent decades. Ozone in the Arctic troposphere is influenced by long-range transport of polluted air from Europe, Asia and N. America, and in summer from boreal wildfires. Our understanding of how different sources contribute to Arctic tropospheric ozone is limited, and is reliant on sparse observations and models of atmospheric transport and chemistry. In particular, our confidence in future high latitude tropospheric ozone response to projected changes in mid-latitude emissions, and subsequent climate impacts, is informed by the ability of models to accurately simulate poleward export from source regions, long-range transport to high latitudes, and photochemical transformation of ozone and its precursors during such events
The spatial distribution of [i]Mustelidae[/i] in France.
No full text[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASAREWe estimated the spatial distribution of 6 Mustelidae species in France using the data collected by the French national hunting and wildlife agency under the "small carnivorous species logbooks" program. The 1500 national wildlife protection officers working for this agency spend 80% of their working time traveling in the spatial area in which they have authority. During their travels, they occasionally detect dead or living small and medium size carnivorous animals. Between 2002 and 2005, each car operated by this agency was equipped with a logbook in which officers recorded information about the detected animals (species, location, dead or alive, date). Thus, more than 30000 dead or living animals were detected during the study period. Because a large number of detected animals in a region could have been the result of a high sampling pressure there, we modeled the number of detected animals as a function of the sampling effort to allow for unbiased estimation of the species density. For dead animals -- mostly roadkill -- we supposed that the effort in a given region was proportional to the distance traveled by the officers. For living animals, we had no way to measure the sampling effort. We demonstrated that it was possible to use the whole dataset (dead and living animals) to estimate the following: (i) the relative density -- i.e., the density multiplied by an unknown constant -- of each species of interest across the different French agricultural regions, (ii) the sampling effort for living animals for each region, and (iii) the relative detection probability for various species of interest
Discovery of variable VHE gamma-ray emission from the binary system 1FGL J1018.6-5856
No full textAccepted for publication in A&AInternational audienceRe-observations with the H.E.S.S. telescope array of the very-high-energy (VHE) source HESS J1018-589 A coincident with the Fermi-LAT -ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9, and the detection of variability (/ of 238.3/155) in the emitted -ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy -ray binary detected by Fermi-LAT, and also confirms the point-like source as a new very-high-energy binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index . Emission is detected up to ~20 TeV. The mean differential flux level is TeV cm s at 1 TeV, equivalent to ~1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night lightcurve. When folded on the orbital period of 16.58 days, the rebinned lightcurve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the H.E.S.S. phaseogram to a constant flux provides evidence of periodicity at the level of 3. The shape of the VHE phaseogram and measured spectrum suggest a low inclination, low eccentricity system with a modest impact from VHE -ray absorption due to pair production ( < 1 at 300 GeV)