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An ultracompact X-ray source based on a laser-plasma undulator
No full textInternational audienceThe capability of plasmas to sustain ultrahigh electric fields has attracted considerable interest over the last decades and has given rise to laser-plasma engineering. Today, plasmas are commonly used for accelerating and collimating relativistic electrons, or to manipulate intense laser pulses. Here we propose an ultracompact plasma undulator that combines plasma technology and nanoengineering. When coupled with a laser-plasma accelerator, this undulator constitutes a millimetre-sized synchrotron radiation source of X-rays. The undulator consists of an array of nanowires, which are ionized by the laser pulse exiting from the accelerator. The strong charge-separation field, arising around the wires, efficiently wiggles the laser-accelerated electrons. We demonstrate that this system can produce bright, collimated and tunable beams of photons with 10-100 keV energies. This concept opens a path towards a new generation of compact synchrotron sources based on nanostructured plasmas
Towards a free electron laser based on laser plasma accelerators
No full textInternational audienceThe recent advances in developing compact laser plasma accelerators that deliver high quality electron beams in a more reliable way offer the possibility to consider their use in designing a compact free electron laser (FEL). Because of the particularity of these beams (especially concerning the divergence and the energy spread), specific electron beam handling is proposed in order to achieve FEL amplification
Contextes cognitifs
No full textInternational audienceLa stratégie d'entreprise est perçue comme un processus cognitif central et décisif de toute organisation. Ce chapitre explore la relation très distante qu’ont pourtant entretenue les sciences administratives avec les sciences cognitives. Perçue d'abord comme un obstacle ou un filtre déformant à l'établissement d'une vérité scientifique, la cognition est entrée dans le champ de la stratégie d'abord comme variable modératrice ou de contexte pour ensuite s'imposer comme un élément central avec la cybernétique, à travers les fondateurs des sciences de gestion comme Herbert Simon ou James March
Modulation of ionization front propagation velocity in a µs plasma gun helium discharge with nitrogen admixture
No full textInternational audienceThe propagation velocity modification of μs helium plasma gun (PG) discharge with nitrogen gas admixture in the helium buffer is studied in relation with ionization front imaging and helium-nitrogen plasma features. From 0,1 % to 0,8 % of N2, the ionization front is faster, more extended and with strong luminous intensity, compared to the high purity helium. The velocity has an optimum, for approximately 0,3 % of N2. Above 0,3 %, the velocity is progressively slowing down, and finally gets slower than the pure helium case above 0,9 %. The velocity evolution may be linked with kinetic and energy transfer predominantly on N2+ or N2 according to the increase of N2 %. Consequently, a local reinforcement of electric field in the front of the discharge is suspected for low N2 percentage, involving velocity increase of the discharge
Rôle des nuages dans l'anomalie de température de l'hiver 2007 en Europe
No full textInternational audienceL'hiver 2007 chaud sans anomalie particulière de la circulation, semble pouvoir s'expliquer par des anomalies significatives des nuages
Functionalization of nanochannels by radio-induced grafting polymerization on PET track-etched membranes
No full textInternational audienceIrradiated PET foils with swift-heavy ions were etched and grafted in a step-by-step process. Grafting polymerization was performed on the remaining active sites after etching. Track-etched PET membranes were fluorescently labeled by chemical functionalization. Functionalized track-etched PET membranes were analyzed by fluorescence and confocal microscopy. a b s t r a c t The application of swift-heavy ion bombardment to polymers is a well-established technique to manufacture micro-and nanopores onto polymeric films to obtain porous membranes. A few years ago, it was realized that, during ion bombardment, the high energy deposition along the ion path through the polymer reached cylindrical damage regions corresponding to the core trace and the penumbra. After the etching procedure, there are still enough active sites left in the penumbra that can be used to initiate a polymerization process selectively inside the membrane pores. In this study, we report the grafting polymerization of glycidyl methacrylate onto etched PET foils to obtain functionalized nanochannels. Grafted polymers were labeled with a fluorescent tag and analyzed by different fluorescence techniques such as direct fluorescence, fluorescence microscopy and confocal microscopy. These techniques allowed identifying and quantifying the grafted regions on the polymeric foils.
Study of the unknown HONO daytime source at a European suburban site during the MEGAPOLI summer and winter field campaigns
No full textInternational audienceNitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NOx , O3 , photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity , wind speed and wind direction), black carbon concentration , total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h−1 and 0.25 ppb h−1 , during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J (NO2) and the product between J (NO2) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground. Published by Copernicus Publications on behalf of the European Geosciences Union. 2806 V. Michoud et al.: Study of the unknown HONO daytime sourc
Hydro-mechanical properties of chemically altered limestones using 2D and 3D full-field multi-scale investigations
No full textInternational audienc
Fluid-solid-electric couplings and efficiency of piezoelectric flags
No full textInternational audienceThe spontaneous and self-sustained flapping of a flexible plate in an axial flow can be used for energy harvesting applications by placing piezoelectric patches on its surface, that periodically deform with the plate, generating an electrical current. These piezoelectric elements also introduce a feedback of the output circuit on the fluid-solid dynamics and may modify its flapping behavior. To better understand the dynamics of these piezoelectric flags, the resulting energy transfers and their harvesting efficiency, numerical simulations of the fluid-solid-electric problem were carried out using an explicit description of the energy harvesting mechanism and simple output circuits. In the case of purely resistive circuits, a tuning mechanism is identified between the circuit's time scale and the flapping frequency. When the circuit possesses its own dynamics (e.g. in-ductive/resonant circuits), a lock-in mechanism is observed that leads to an effective control of the flapping frequency by the output circuit over a large range of parameters and a significant increase in the energy harvesting performance of the device
Study of hadronic event-shape variables in multijet final states in pp collisions at sqrt(s) = 7 TeV
No full textReplaced with published version. Added journal reference and DOI, see paper for full list of authorsInternational audienceEvent-shape variables, which are sensitive to perturbative and nonperturbative aspects of quantum chromodynamic (QCD) interactions, are studied in multijet events recorded in proton-proton collisions at sqrt(s) = 7 TeV. Events are selected with at least one jet with transverse momentum pt > 110 GeV and pseudorapidity abs(eta) < 2.4, in a data sample corresponding to integrated luminosities of up to 5 inverse femtobarns. The distributions of five event-shape variables in various leading jet pt ranges are compared to predictions from different QCD Monte Carlo event generators