97 research outputs found
Frequency spectra of the sources 3C 295 and 3C 380
Interferometric flux density measurements on stellar light source
The Effect of Air Density on Atmospheric Electric Fields Required for Lightning Initiation from a Long Airborne Object
The purpose of the work was to determine minimum atmospheric electric fields required for lightning initiation from an airborne vehicle at various altitudes up to 10 km. The problem was reduced to the determination of a condition for initiation of a viable positive leader from a conductive object in an ambient electric field. It was shown that, depending on air density and shape and dimensions of the object, critical atmospheric fields are governed by the condition for leader viability or that for corona onset. To establish quantitative criteria for reduced air densities, available observations of spark discharges in long laboratory gaps were analyzed, the effect of air density on leader velocity was discussed and evolution in time of the properties of plasma in the leader channel was numerically simulated. The results obtained were used to evaluate the effect of pressure on the quantitative relationships between the potential difference near the leader tip, leader current and its velocity; based on these relationships, criteria for steady development of a leader were determined for various air pressures. Atmospheric electric fields required for lightning initiation from rods and ellipsoidal objects of various dimensions were calculated at different air densities. It was shown that there is no simple way to extend critical ambient fields obtained for some given objects and pressures to other objects and pressures
A moving boundary problem motivated by electric breakdown: I. Spectrum of linear perturbations
An interfacial approximation of the streamer stage in the evolution of sparks
and lightning can be written as a Laplacian growth model regularized by a
`kinetic undercooling' boundary condition. We study the linear stability of
uniformly translating circles that solve the problem in two dimensions. In a
space of smooth perturbations of the circular shape, the stability operator is
found to have a pure point spectrum. Except for the zero eigenvalue for
infinitesimal translations, all eigenvalues are shown to have negative real
part. Therefore perturbations decay exponentially in time. We calculate the
spectrum through a combination of asymptotic and series evaluation. In the
limit of vanishing regularization parameter, all eigenvalues are found to
approach zero in a singular fashion, and this asymptotic behavior is worked out
in detail. A consideration of the eigenfunctions indicates that a strong
intermediate growth may occur for generic initial perturbations. Both the
linear and the nonlinear initial value problem are considered in a second
paper.Comment: 37 pages, 6 figures, revised for Physica
Spontaneous Branching of Anode-Directed Streamers between Planar Electrodes
Non-ionized media subject to strong fields can become locally ionized by
penetration of finger-shaped streamers. We study negative streamers between
planar electrodes in a simple deterministic continuum approximation. We observe
that for sufficiently large fields, the streamer tip can split. This happens
close to Firsov's limit of `ideal conductivity'. Qualitatively the tip
splitting is due to a Laplacian instability quite like in viscous fingering.
For future quantitative analytical progress, our stability analysis of planar
fronts identifies the screening length as a regularization mechanism.Comment: 4 pages, 6 figures, submitted to PRL on Nov. 16, 2001, revised
version of March 10, 200
Glow corona generation and streamer inception at the tip of grounded objects during thunderstorms: revisited
The lightning swept stroke along an aircraft in flight. Part II: numerical simulations of the complete process
Transition between breakdown regimes in a temperature-dependent mixture of argon and mercury using 100 kHz excitation
Recovery of the parameters of a lightning current pulse from measurements of the electromagnetic field in the far wave zone
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