111,146 research outputs found

    Cooperative learning in multi-agent systems from intermittent measurements

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    Motivated by the problem of tracking a direction in a decentralized way, we consider the general problem of cooperative learning in multi-agent systems with time-varying connectivity and intermittent measurements. We propose a distributed learning protocol capable of learning an unknown vector μ\mu from noisy measurements made independently by autonomous nodes. Our protocol is completely distributed and able to cope with the time-varying, unpredictable, and noisy nature of inter-agent communication, and intermittent noisy measurements of μ\mu. Our main result bounds the learning speed of our protocol in terms of the size and combinatorial features of the (time-varying) networks connecting the nodes

    Velocity map imaging of the dynamics of the CH3 + HCl -> CH4 + Cl reaction using a dual molecular beam method

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    International audienceThe reactions CH3 + HCl → CH4 + Cl(<sup>2</sup>P<sub>3/2</sub>) and CD<sub>3</sub> + HCl → CD<sub>3</sub>H + Cl(<sup>2</sup>P<sub>3/2</sub>) have been studied by photo-initiation (by CH<sub>3</sub>I or CD<sub>3</sub>I photolysis at 266 nm) in a dual molecular beam apparatus. Product Cl(<sup>2</sup>P</sub>3/2</sub>) atoms were detected using resonance enhanced multi-photon ionisation and velocity map imaging, revealing product translational energy and angular scattering distributions in the centre-of-mass frame. Image analysis is complicated by the bimodal speed distribution of CH<sub>3</sub> (and CD<sub>3</sub>) radicals formed in coincidence with I(<sup>2</sup>P<sub>3/2</sub>) and I(<sup>2</sup>P<sub>1/2</sub>) atoms from CH<sub>3</sub>I (CD<sub>3</sub>I) photodissociation, giving overlapping Newton diagrams with displaced centre of mass velocities. The relative reactivities to form Cl atoms are greater for the slower CH<sub>3</sub> speed group than the faster group by factors of ~1.5 for the reaction of CH<sub>3</sub> and ~2.5 for the reaction of CD<sub>3</sub>, consistent with the greater propensity of the faster methyl radicals to undergo electronically adiabatic reactions to form Cl(<sup>2</sup>P<sub>1/2</sub>). The average fraction of the available energy becoming product translational energy is = 0.48 ± 0.05 and 0.50 ± 0.03 for reaction of the faster and slower sets of CH<sub>3</sub> radicals, respectively. The Cl atoms are deduced to be preferentially forward scattered with respect to the HCl reagents, but the angular distributions from the dual beam imaging experiments require correction for under-detection of forward scattered Cl products

    Femtosecond real-time probing of reactions. VIII. The bimolecular reaction Br+I2

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    In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atom–molecule Br+I_2 reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 (1991)], we report on the observed transients and lifetimes for the collision complex, the nature of the transition state, and the dynamics near threshold. Classical trajectory calculations provide a framework for deriving the global nature of the reactive potential energy surface, and for discussing the real-time, scattering, and asymptotic (product-state distribution) aspects of the dynamics. These experimental and theoretical results are compared with the extensive array of kinetic, crossed beam, and theoretical studies found in the literature for halogen radical–halogen molecule exchange reactions

    Complex Berry phase instability in PT-symmetric coupled waveguides

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    We show that the analogue of the geometric phase for non-Hermitian coupled waveguides with PT-symmetry and at least one periodically varying parameter can be purely imaginary, and will consequently result in the manifestation of an instability in the system. The instability peaks seen in the spectrum of the system's eigenstates after evolution along the waveguides can be directly mapped to the spectrum of the derivative of the geometric function. The instabilities are magnified as the exceptional point of the system is approached, and non-adiabatic effects begin to appear. As the system cannot evolve adiabatically in the vicinity of the exceptional point, PT-symmetry will be observed breaking earlier than theoretically predicted

    Bifurcation Dodge: Avoidance of a Thermoacoustic Instability under Transient Operation

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    Varying one of the governing parameters of a dynamical system may lead to a critical transition, where the new stable state is undesirable. In some cases, there is only a limited range of the bifurcation parameter that corresponds to that unwanted attractor, while the system runs problem-less otherwise. In this study, we present experimental results regarding a thermoacoustic system subject to two consecutive and mirrored supercritical Hopf bifurcations: the system exhibits high amplitude thermoacoustic limit cycles for intermediate values of the bifurcation parameter. Changing quickly enough the bifurcation parameter, it was possible to dodge the unwanted limit cycles. A low-order model of the complex thermoacoustic system was developed, in order to describe this interesting transient dynamics. It was afterward used to assess the risk of exceeding an oscillation amplitude threshold as a function of the rate of change of the bifurcation parameter

    Loss of molecules in magneto-electrostatic traps due to nonadiabatic transitions

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    We analyze the dynamics of a paramagnetic, dipolar molecule in a generic "magneto-electrostatic'' trap where both magnetic and electric fields may be present. The potential energy that governs the dynamics of the molecules is found using a reduced molecular model that incorporates the main features of the system. We discuss the shape of the trapping potentials for different field geometries, as well as the possibility of nonadiabatic transitions to untrapped states, i.e., the analog of Majorana transitions in a quadrupole magnetic atomic trap. Maximizing the lifetime of molecules in a trap is of great concern in current experiments, and we assess the effect of nonadiabatic transitions on obtainable trap lifetimes.Comment: 13 pages, 6 figure

    Codes as fractals and noncommutative spaces

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    We consider the CSS algorithm relating self-orthogonal classical linear codes to q-ary quantum stabilizer codes and we show that to such a pair of a classical and a quantum code one can associate geometric spaces constructed using methods from noncommutative geometry, arising from rational noncommutative tori and finite abelian group actions on Cuntz algebras and fractals associated to the classical codes.Comment: 18 pages LaTeX, one png figur
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