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Search Results: 1 - 10 of 500 matches for " Quentin Baudouin "
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Steady-state signatures of radiation trapping by cold multilevel atoms
Quentin Baudouin,Nicolas Mercadier,Robin Kaiser
Physics , 2012, DOI: 10.1103/PhysRevA.87.013412
Abstract: In this paper, we use steady-state measurements to obtain evidence of radiation trapping in an optically thick a cloud of cold rubidium atoms. We investigate the fluorescence properties of our sample, pumped on opened transitions. The intensity of fluorescence exhibits a non trivial dependence on the optical thickness of the media. A simplified model, based on rate equations self-consistently coupled to a diffusive model of light transport, is used to explain the experimental observations in terms of incoherent radiation trapping on one spectral line. Measurements of atomic populations and fluorescence spectrum qualitatively agree with this interpretation.
A cold-atom random laser
Quentin Baudouin,Nicolas Mercadier,Vera Guarrera,William Guerin,Robin Kaiser
Physics , 2013, DOI: 10.1038/nphys2614
Abstract: Conventional lasers make use of optical cavities to provide feedback to gain media. Conversely, mirrorless lasers can be built by using disordered structures to induce multiple scattering, which increases the effective path length in the gain medium and thus provides the necessary feedback. These so-called random lasers potentially offer a new and simple mean to address applications such as lighting. To date, they are all based on condensed-matter media. Interestingly, light or microwave amplification by stimulated emission occurs also naturally in stellar gases and planetary atmospheres. The possibility of additional scattering-induced feedback (that is, random lasing) has been discussed and could explain unusual properties of some space masers. Here, we report the experimental observation of random lasing in a controlled, cold atomic vapour, taking advantage of Raman gain. By tuning the gain frequency in the vicinity of a scattering resonance, we observe an enhancement of the light emission of the cloud due to random lasing. The unique possibility to both control the experimental parameters and to model the microscopic response of our system provides an ideal test bench for better understanding natural lasing sources, in particular the role of resonant scattering feedback in astrophysical lasers.
The Bright Side of Coulomb Blockade
Max Hofheinz,Fabien Portier,Quentin Baudouin,Philippe Joyez,Denis Vion,Patrice Bertet,Patrice Roche,Daniel Esteve
Physics , 2011,
Abstract: We explore the photonic (bright) side of dynamical Coulomb blockade (DCB) by measuring the radiation emitted by a dc voltage-biased Josephson junction embedded in a microwave resonator. In this regime Cooper pair tunneling is inelastic and associated to the transfer of an energy 2eV into the resonator modes. We have measured simultaneously the Cooper pair current and the photon emission rate at the resonance frequency of the resonator. Our results show two regimes, in which each tunneling Cooper pair emits either one or two photons into the resonator. The spectral properties of the emitted radiation are accounted for by an extension to DCB theory.
évolutions récentes du droit européen des marchés publics de Défense
Baudouin Heuninckx
Pyramides : Revue du Centre d'Etudes et de Recherches en Administration Publique , 2012,
Abstract: Cet article présente, dans leur contexte politique et économique, les évolutions du droit européen des marchés publics de défense au cours des cinq dernières années, en particulier la nouvelle directive applicable aux marchés de défense et de sécurité et le régime intergouvernemental qui peut être appliqué lorsque l’exemption de l’art. 346 du Traité sur le Fonctionnement de l’Union Européenne, qui permet d’exclure de l’application du droit européen certaines mesures nécessaires à la protection des intérêts essentiels de sécurité de l’état et liées à la production ou au commerce de matériel militaire, est appliqué. Ces innovations représentent sans doute la plus vaste évolution du droit des marchés publics de défense au sein de l’Union Européenne, et ont non seulement le potentiel d’ouvrir les marchés nationaux de l’armement à la concurrence, mais également de modifier de manière fondamentale le travail des acheteurs dans le domaine de la défense. Notre article aide à définir le droit applicable aux marchés publics de défense au sein de l’Union Européenne, et discute les récentes évolutions de ce droit en fonction de la spécificité des marchés d’armements et de leur impact politique et économique.
Systèmes coutumiers, centralisme juridique de l'Etat et usages du droit
Baudouin Dupret
Chroniques Yéménites , 2000,
Abstract: Il est de notoriété qu'au Yémen la justice coutumière est encore active, prépondérante, voire exclusive dans certaines régions. Pourtant, il existe peu de travaux la prenant pour objet et tachant de mesurer l'impact de la construction étatique - et de son corollaire, l'instauration d'une justice civile centralisée - sur cette justice. Ce n'est pas tant que la recherche anthropologique se soit désintéressée du Yémen, loin s'en faut. Il suffit, à cet égard, de citer les travaux de Serjea...
Lipschitz stability in an inverse problem for the wave equation
Lucie Baudouin
Mathematics , 2011,
Abstract: We are interested in the inverse problem of the determination of the potential $p(x), x\in\Omega\subset\mathbb{R}^n$ from the measurement of the normal derivative $\partial_\nu u$ on a suitable part $\Gamma_0$ of the boundary of $\Omega$, where $u$ is the solution of the wave equation $\partial_{tt}u(x,t)-\Delta u(x,t)+p(x)u(x,t)=0$ set in $\Omega\times(0,T)$ and given Dirichlet boundary data. More precisely, we will prove local uniqueness and stability for this inverse problem and the main tool will be a global Carleman estimate, result also interesting by itself.
Trehalose: an intriguing disaccharide with potential for medical application in ophthalmology
Luyckx J, Baudouin C
Clinical Ophthalmology , 2011, DOI: http://dx.doi.org/10.2147/OPTH.S18827
Abstract: ehalose: an intriguing disaccharide with potential for medical application in ophthalmology Review (4607) Total Article Views Authors: Luyckx J, Baudouin C Published Date May 2011 Volume 2011:5 Pages 577 - 581 DOI: http://dx.doi.org/10.2147/OPTH.S18827 Jacques Luyckx1, Christophe Baudouin2 1Thea Laboratories, Clermont-Ferrand, 2Quinze-Vingts National Hospital and Vision Institute, University Paris 6, Paris, France Abstract: Trehalose is a naturally occurring disaccharide comprised of two molecules of glucose. The sugar is widespread in many species of plants and animals, where its function appears to be to protect cells against desiccation, but is not found in mammals. Trehalose has the ability to protect cellular membranes and labile proteins against damage and denaturation as a result of desiccation and oxidative stress. Trehalose appears to be the most effective sugar for protection against desiccation. Although the exact mechanism by which trehalose protects labile macromolecules and lipid membranes is unknown, credible hypotheses do exist. As well as being used in large quantities in the food industry, trehalose is used in the biopharmaceutical preservation of labile protein drugs and in the cryopreservation of human cells. Trehalose is under investigation for a number of medical applications, including the treatment of Huntington's chorea and Alzheimer's disease. Recent studies have shown that trehalose can also prevent damage to mammalian eyes caused by desiccation and oxidative insult. These unique properties of trehalose have thus prompted its investigation as a component in treatment for dry eye syndrome. This interesting and unique disaccharide appears to have properties which may be exploited in ophthalmology and other disease states.
Challenges in the clinical measurement of ocular surface disease in glaucoma patients
Pflugfelder SC, Baudouin C
Clinical Ophthalmology , 2011, DOI: http://dx.doi.org/10.2147/OPTH.S24410
Abstract: llenges in the clinical measurement of ocular surface disease in glaucoma patients Review (3159) Total Article Views Authors: Pflugfelder SC, Baudouin C Published Date November 2011 Volume 2011:5 Pages 1575 - 1583 DOI: http://dx.doi.org/10.2147/OPTH.S24410 Stephen C Pflugfelder1, Christophe Baudouin2,3 1Ophthalmology-Ocular Surface Center, Baylor College of Medicine, Houston, TX, USA; 2Department of Ophthalmology, Quinze-Vingts Hospital, Paris, France; 3Vision Institute, Paris, France Abstract: Ocular surface disease (OSD) is common among glaucoma patients. Clinical assessment of OSD can be challenging. This review focuses on some of the limitations relating to both subjective and objective measures of OSD, including dry eye. A survey of the literature was conducted to identify the caveats associated with different methods of assessing OSD. The effect of preservatives on the ocular surface, with respect to glaucoma patients in particular, was also reviewed. Objective methods for assessing ocular surface health and disease include the Schirmer test, tear break-up time, fluorescein turnover, corneal and conjunctival staining, tear osmolarity, and vital dyes. These measures all have limitations in terms of their ability to grade the severity of OSD. Previous studies using the OSD Index showed a mild-to-moderate correlation to dry eye disease severity. Other scoring systems for dry eye have shown a relationship to patient symptom scores or quality of life. Due to the challenges clinicians face concerning both subjective and objective ocular surface health assessments, discerning clinical improvement in ocular surface disease can be a challenge. Further research is needed in order to optimize existing clinical methods and/or identify alternative techniques for assessing OSD in the glaucoma population.
Challenges in the clinical measurement of ocular surface disease in glaucoma patients
Pflugfelder SC,Baudouin C
Clinical Ophthalmology , 2011,
Abstract: Stephen C Pflugfelder1, Christophe Baudouin2,3 1Ophthalmology-Ocular Surface Center, Baylor College of Medicine, Houston, TX, USA; 2Department of Ophthalmology, Quinze-Vingts Hospital, Paris, France; 3Vision Institute, Paris, France Abstract: Ocular surface disease (OSD) is common among glaucoma patients. Clinical assessment of OSD can be challenging. This review focuses on some of the limitations relating to both subjective and objective measures of OSD, including dry eye. A survey of the literature was conducted to identify the caveats associated with different methods of assessing OSD. The effect of preservatives on the ocular surface, with respect to glaucoma patients in particular, was also reviewed. Objective methods for assessing ocular surface health and disease include the Schirmer test, tear break-up time, fluorescein turnover, corneal and conjunctival staining, tear osmolarity, and vital dyes. These measures all have limitations in terms of their ability to grade the severity of OSD. Previous studies using the OSD Index showed a mild-to-moderate correlation to dry eye disease severity. Other scoring systems for dry eye have shown a relationship to patient symptom scores or quality of life. Due to the challenges clinicians face concerning both subjective and objective ocular surface health assessments, discerning clinical improvement in ocular surface disease can be a challenge. Further research is needed in order to optimize existing clinical methods and/or identify alternative techniques for assessing OSD in the glaucoma population. Keywords: dry eye, glaucoma, ocular surface disease, ocular surface disease index, preservatives, tear break-up time
An inverse problem for Schr?dinger equations with discontinuous main coefficient
Lucie Baudouin,Alberto Mercado
Mathematics , 2008,
Abstract: This paper concerns the inverse problem of retrieving a stationary potential for the Schr\"odinger evolution equation in a bounded domain of RN with Dirichlet data and discontinuous principal coefficient a(x) from a single time-dependent Neumann boundary measurement. We consider that the discontinuity of a is located on a simple closed hyper-surface called the interface, and a is constant in each one of the interior and exterior domains with respect to this interface. We prove uniqueness and lipschitz stability for this inverse problem under certain convexity hypothesis on the geometry of the interior domain and on the sign of the jump of a at the interface. The proof is based on a global Carleman inequality for the Schr\"odinger equation with discontinuous coefficients, result also interesting by itself.
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