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Search Results: 1 - 10 of 209 matches for " Mickael Guinet "
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Absolute frequency measurement of an SF6 two-photon line using a femtosecond optical comb and sum-frequency generation
Anne Amy-Klein,Andrei Goncharov,Mickael Guinet,Christophe Daussy,Olivier Lopez,Alexander Shelkovnikov,Christian Chardonnet
Physics , 2005, DOI: 10.1364/OL.30.003320
Abstract: We demonstrate a new simple technique to measure IR frequencies near 30 THz using a femtosecond (fs) laser optical comb and sum-frequency generation. The optical frequency is directly compared to the distance between two modes of the fs laser, and the resulting beat note is used to control this distance which depends only on the repetition rate fr of the fs laser. The absolute frequency of a CO2 laser stabilized onto an SF6 two-photon line has been measured for the first time. This line is an attractive alternative to the usual saturated absorption OsO4 resonances used for the stabilization of CO2 lasers. First results demonstrate a fractional Allan deviation of 3.10-14 at 1 s.
First direct determination of the Boltzmann constant by an optical method
Christophe Daussy,Mickael Guinet,Anne Amy-Klein,Khelifa Djerroud,Yves Hermier,Stephan Briaudeau,Christian J. Bordé,Christian Chardonnet
Physics , 2007, DOI: 10.1103/PhysRevLett.98.250801
Abstract: We have recorded the Doppler profile of a well-isolated rovibrational line in the \nu2 band of 14NH3. Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant, kB, by laser spectroscopy. A relative uncertainty of 2x10-4 has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin.
Long-distance frequency dissemination with a resolution of 10-17
Christophe Daussy,Olivier Lopez,Anne Amy-Klein,Andréi N. Goncharov,Mickael Guinet,Christian Chardonnet,Fran?ois Narbonneau,Michel Lours,Damien Chambon,Sébastien Bize,André Clairon,Georgio Santarelli,Mike E. Tobar,Andre N. Luiten
Physics , 2005, DOI: 10.1103/PhysRevLett.94.203904
Abstract: We use a new technique to disseminate microwave reference signals along ordinary optical fiber. The fractional frequency resolution of a link of 86 km in length is 10-17 for a one day integration time, a resolution higher than the stability of the best microwave or optical clocks. We use the link to compare the microwave reference and a CO2/OsO4 frequency standard that stabilizes a femtosecond laser frequency comb. This demonstrates a resolution of 3.10-14 at 1 s. An upper value of the instability introduced by the femtosecond laser-based synthesizer is estimated as 1.10-14 at 1 s.
La construction d’une intimité religieuse. Les pratiques paraliturgiques des fidèles dans la cathédrale de Tirana
Mickael Wilmart
Antrocom : Online Journal of Anthropology , 2008,
Abstract: L’article se propose de suivre les fidèles dans la cathédrale Saint-Paul de Tirana (Albanie), de décrire précisément leurs déplacements, leurs gestes et leurs attitudes en dehors de la liturgie. Après avoir montré comment ils s’approprient et définissent par cette appropriation l’espace véritablement sacré du sanctuaire, l’auteur propose une relecture de leurs gestes, que l’on pourrait à première vue qualifier de banaux ou lier à la piété populaire, avec l’idée de montrer comment l’espace public qu’est la cathédrale peut se faire lieu d’intimité entre le croyant et le divin.
Turbulent pair dispersion as a ballistic cascade phenomenology
Mickael Bourgoin
Physics , 2014,
Abstract: Since the pioneering work of Richardson in 1926, later refined by Batchelor and Obukhov in 1950, it is predicted that the rate of separation of pairs of fluid elements in turbulent flows with initial separation at inertial scales, grows ballistically first (Batchelor regime), before undergoing a transition towards a super-diffusive regime where the mean-square separation grows as t^3 (Richardson regime). Richardson empirically interpreted this super-diffusive regime in terms of a non-Fickian process with a scale dependent diffusion coefficient (the celebrated Richardson's "4/3rd" law). However, the actual physical mechanism at the origin of such a scale dependent diffusion coefficient remains unclear. The present article proposes a simple physical phenomenology for the time evolution of the mean square relative separation in turbulent flows, based on a scale dependent ballistic scenario rather than a scale dependent diffusive. This phenomenology accurately retrieves most of the known features of relative dispersion ; among others : (i) it is quantitatively consistent with recent numerical simulations and experiments (both for the short term Batchelor regime and the long term Richardson regime, and for all initial separations at inertial scales), (ii) it gives a simple physical explanation of the origin of the super diffusive t^3 Richardson regime which naturally builts itself as an iterative process of elementary short-term-scale-dependent ballistic steps, (iii) it shows that the Richardson constant is directly related to the Kolmogorov constant (and eventually to a ballistic persistence parameter) and (iv) in a further extension of the phenomenology, taking into account third order corrections, it robustly describes the temporal asymmetry between forward and backward dispersion, with an explicit connection to the cascade of energy flux across scales.
Differential Puiseux theorem in generalized series fields of finite rank
Mickael Matusinski
Mathematics , 2009,
Abstract: We study differential equations $F(y,...,y^{(n)})=0$ where $F(Y_0,...,Y_n)$ is a formal series in $Y_0,...,Y_n$ with coefficients in some field of \emph{generalized power series} $\mathds{K}_r$ with finite rank $r\in\mathbb{N}^*$. Our purpose is to understand the connection between the set of exponents of the coefficients of the equation $\textrm{Supp} F$ and the set $\textrm{Supp} y_0$ of exponents of the elements $y_0\in\mathds{K}_r$ that are solutions.
Automated synthesis of reliable and efficient systems through game theory: a case study
Mickael Randour
Computer Science , 2012,
Abstract: Reactive computer systems bear inherent complexity due to continuous interactions with their environment. While this environment often proves to be uncontrollable, we still want to ensure that critical computer systems will not fail, no matter what they face. Examples are legion: railway traffic, power plants, plane navigation systems, etc. Formal verification of a system may ensure that it satisfies a given specification, but only applies to an already existing model of a system. In this work, we address the problem of synthesis: starting from a specification of the desired behavior, we show how to build a suitable system controller that will enforce this specification. In particular, we discuss recent developments of that approach for systems that must ensure Boolean behaviors (e.g., reachability, liveness) along with quantitative requirements over their execution (e.g., never drop out of fuel, ensure a suitable mean response time). We notably illustrate a powerful, practically useable algorithm for the automated synthesis of provably safe reactive systems.
Design of Fuzzy Controller for Robot Manipulators Using Bacterial Foraging Optimization Algorithm  [PDF]
Mickael Aghajarian, Kourosh Kiani, Mohammad Mehdi Fateh
Journal of Intelligent Learning Systems and Applications (JILSA) , 2012, DOI: 10.4236/jilsa.2012.41005
Abstract: Trial and error method can be used to find a suitable design of a fuzzy controller. However, there are many options including fuzzy rules, Membership Functions (MFs) and scaling factors to achieve a desired performance. An optimiza-tion algorithm facilitates this process and finds an optimal design to provide a desired performance. This paper presents a novel application of the Bacterial Foraging Optimization algorithm (BFO) to design a fuzzy controller for tracking control of a robot manipulator driven by permanent magnet DC motors. We use efficiently the BFO algorithm to form the rule base and MFs. The BFO algorithm is compared with a Particle Swarm Optimization algorithm (PSO). Performance of the controller in the joint space and in the Cartesian space is evaluated. Simulation results show superiority of the BFO algorithm to the PSO algorithm.
Plasma Exchange in Severe Attacks of Neuromyelitis Optica
Mickael Bonnan,Philippe Cabre
Multiple Sclerosis International , 2012, DOI: 10.1155/2012/787630
Abstract: Background. Neuromyelitis optica (NMO) attacks are poorly controlled by steroids and evolve in stepwise neurological impairments. Assuming the strong humoral response underlying NMO attacks, plasma exchange (PLEX) is an appropriate technique in severe NMO attacks. Objective. Presenting an up-to-date review of the literature of PLEX in NMO. Methods. We summarize the rationale of PLEX in relation with the physiology of NMO, the main technical aspects, and the available studies. Results. PLEX in severe attacks from myelitis or optic neuritis are associated with a better outcome, depending on PLEX delay (“time is cord and eyes”). NMO-IgG status has no influence. Finally, we build up an original concept linking the inner dynamic of the lesion, the timing of PLEX onset and the expected clinical results. Conclusion. PLEX is a safe and efficient add-on therapy in NMO, in synergy with steroids. Large therapeutic trials are required to definitely assess the procedure and define the time opportunity window. 1. Introduction Neuromyelitis optica (NMO) is an inflammatory disorder restricted to the spinal cord and optic nerves. Contrary to multiple sclerosis (MS), relapses of NMO are often strikingly severe and most NMO patients present stepwise neurological impairments. NMO treatments are aimed to prevent the relapses with the administration of various promising immunosuppressive drugs. However, relapse treatment is still a tricky problem. Since the largely used steroid treatment usually fails to control severe attacks, specific add-on treatments have to be considered in order to limit the stepwise increase of residual impairment. Given that a strong humoral response characterizes NMO physiology, one might assume plasma exchange (PLEX) to be particularly well adapted in severe NMO relapses. We here propose to outline the rationale of the PLEX treatment based on physiological grounds and summarize the relevant data of PLEX studies in the setting of NMO spectrum disorder, assessing the results obtained in each type of attacks. Finally we will try to build up an original concept linking the inner dynamic of the lesion, the timing of PLEX, onset, and the expected clinical results. 2. Physiopathology of NMO 2.1. Pathology of NMO Lesions A characteristic pathological pattern has been described in NMO [1]. Lesions are infiltrated by neutrophils and eosinophils and wall capillaries are hyalinized. A vasculocentric pattern of activated complement and immunoglobulin of IgG and IgM types is observed that mirrors the normal expression of AQP4. AQP4 expression is definitely
Equilibrium and dynamical properties of two dimensional self-gravitating systems
Alessandro Torcini,Mickael Antoni
Physics , 1998, DOI: 10.1103/PhysRevE.59.2746
Abstract: A system of N classical particles in a 2D periodic cell interacting via long-range attractive potential is studied. For low energy density $U$ a collapsed phase is identified, while in the high energy limit the particles are homogeneously distributed. A phase transition from the collapsed to the homogeneous state occurs at critical energy U_c. A theoretical analysis within the canonical ensemble identifies such a transition as first order. But microcanonical simulations reveal a negative specific heat regime near $U_c$. The dynamical behaviour of the system is affected by this transition : below U_c anomalous diffusion is observed, while for U > U_c the motion of the particles is almost ballistic. In the collapsed phase, finite $N$-effects act like a noise source of variance O(1/N), that restores normal diffusion on a time scale diverging with N. As a consequence, the asymptotic diffusion coefficient will also diverge algebraically with N and superdiffusion will be observable at any time in the limit N \to \infty. A Lyapunov analysis reveals that for U > U_c the maximal exponent \lambda decreases proportionally to N^{-1/3} and vanishes in the mean-field limit. For sufficiently small energy, in spite of a clear non ergodicity of the system, a common scaling law \lambda \propto U^{1/2} is observed for any initial conditions.
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