4,259 research outputs found
Effect of the short-term temperature changes on Diagnostic Indicator in online insulation monitoring by parametric identification
International audienceElectrical generators of offshore wind or tidal current turbines are exposed to harsh marine and operating conditions. Predictive maintenance is therefore a key issue for the competitiveness of these energy generation systems. Generally speaking, the predictive maintenance is based on the monitoring of a Diagnostic Indicator (DI): the interpretation of its value or drift is used for the optimal planning of the corrective maintenance. In this work, we present briefly our new online monitoring technique of electrical machine winding insulation. This model-based approach consists in monitoring the drift of a DI built from the in-situ estimation of high-frequency electrical model parameters. The involved model structures are derived from the RLC network modeling of the winding insulation, with more or less lumped parameters. In the second part of the work, we investigate the effects of temperature changes on the estimated parameters of diagnostic models. A 1.5 kW low power wound stator is exposed to different temperature levels, from 30°C to 160°C, and for each temperature a series of experimental acquisitions is realized. Identification results show that resistance and inductance of a simple HF model structure are almost independent of temperature changes, while insulation capacitance increases with temperature increases: at 160°C it is 8% higher than its initial value at room temperature
Energy release associated with a first-order phase transition in a rotating neutron star core
We calculate energy release associated with a first order phase transition at
the center of a rotating neutron star. The results are based on precise
numerical 2-D calculations, in which both the polytropic equations of state
(EOS) as well as realistic EOS of the normal phase are used. Presented results
are obtained for a broad range of metastability of initial configuration and
size of the new superdense phase core in the final configuration. For small
radii of the superdense phase core analytical expressions for the energy
release are obtained. For a fixed "overpressure" dP (the relative excess of
central pressure of collapsing metastable star over the pressure of equilibrium
first-order phase transition) the energy release remarkably does not depend on
the stellar angular momentum and coincides with that for nonrotating stars with
the same dP. The energy release is proportional to dP^2.5 for small dPs, when
sufficiently precise brute force 2-D numerical calculations are out of
question. For higher dPs, results of 1-D calculations of energy release for
non-rotating stars are shown to reproduce, with very high precision, the exact
2-D results for rotating stars.Comment: 8 pages, 8 figures, submitted to A&
Multicritical continuous random trees
We introduce generalizations of Aldous' Brownian Continuous Random Tree as
scaling limits for multicritical models of discrete trees. These discrete
models involve trees with fine-tuned vertex-dependent weights ensuring a k-th
root singularity in their generating function. The scaling limit involves
continuous trees with branching points of order up to k+1. We derive explicit
integral representations for the average profile of this k-th order
multicritical continuous random tree, as well as for its history distributions
measuring multi-point correlations. The latter distributions involve
non-positive universal weights at the branching points together with fractional
derivative couplings. We prove universality by rederiving the same results
within a purely continuous axiomatic approach based on the resolution of a set
of consistency relations for the multi-point correlations. The average profile
is shown to obey a fractional differential equation whose solution involves
hypergeometric functions and matches the integral formula of the discrete
approach.Comment: 34 pages, 12 figures, uses lanlmac, hyperbasics, eps
Global existence of classical solutions to the Vlasov-Poisson system in a three dimensional, cosmological setting
The initial value problem for the Vlasov-Poisson system is by now well
understood in the case of an isolated system where, by definition, the
distribution function of the particles as well as the gravitational potential
vanish at spatial infinity. Here we start with homogeneous solutions, which
have a spatially constant, non-zero mass density and which describe the mass
distribution in a Newtonian model of the universe. These homogeneous states can
be constructed explicitly, and we consider deviations from such homogeneous
states, which then satisfy a modified version of the Vlasov-Poisson system. We
prove global existence and uniqueness of classical solutions to the
corresponding initial value problem for initial data which represent spatially
periodic deviations from homogeneous states.Comment: 23 pages, Latex, report #
The Cauchy problem for the 3-D Vlasov-Poisson system with point charges
In this paper we establish global existence and uniqueness of the solution to
the three-dimensional Vlasov-Poisson system in presence of point charges in
case of repulsive interaction. The present analysis extends an analogeous
two-dimensional result by Caprino and Marchioro [On the plasma-charge model, to
appear in Kinetic and Related Models (2010)].Comment: 28 page
Synthesis of 4-Piperidinoflavan
A study of the reaction of flavylium perchlorate with piperidine showed that piperidine perchlorate was formed plus two other compounds. One of these appears to be 4-piperidinoflavene which should be reducible to 4-piperidinoflavan. This compound had not been described previously, hence its synthesis was undertaken. Flavanone was prepared according to the method of Kostanecki (1). Catalytic reduction of flavanone with hydrogen and a platinum catalyst gave a 79% yield of a compound melting at 145- 147°. This corresponds to the, B-isomer of 4-hydroxyflavan originally obtained by Karrar, Yen and Reichstein (2) as the result of a titanous chloride reduction of flavanone. Mozingo and Adkins (3) also obtained this ,B-isomer by catalytic reduction of flavanone but used copper-chromium oxide at 120° and hydrogen at 100-200 atm. Treatment of the 4-hydroxyflavan with phosphorus tribromide at 0° gave a 52% yield of 4-bromoflavan. An ether solution of this bromo-compound reacted with two equivalents of piperidine to form piperidinium hydrobromide and {3-4 piperidinoflavan. Upon recrystallization from ether, colorless needles were obtained melting at 137-138° which had the correct analysis for this compound
Herbicides for corn
"Federal regulations regarding herbicide use change frequently, so keep informed about the status of label registration. Based upon available information this guide sheet conforms to laws and regulations in effect at the time it was written. It is essential that you read and understand the label of the herbicide you plan to use."--First page.L.E. Anderson, O. Hale Fletchall, David Guethle, Harold Kerr, E.J. Peters, Zane Helsel, James Schaeffer (Department of Agronomy, College of Agriculture)Revised 1/84/15
Waves attractors in rotating fluids: a paradigm for ill-posed Cauchy problems
In the limit of low viscosity, we show that the amplitude of the modes of
oscillation of a rotating fluid, namely inertial modes, concentrate along an
attractor formed by a periodic orbit of characteristics of the underlying
hyperbolic Poincar\'e equation. The dynamics of characteristics is used to
elaborate a scenario for the asymptotic behaviour of the eigenmodes and
eigenspectrum in the physically relevant r\'egime of very low viscosities which
are out of reach numerically. This problem offers a canonical ill-posed Cauchy
problem which has applications in other fields.Comment: 4 pages, 5 fi
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