146 research outputs found
Recombination processes in the lower ionosphere
Rate of nitrogen oxide ion recombination in auror
Low frequency 1/f-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere
Ion-cyclotron turbulence and diagonal double layers in a magnetospheric plasma
A survey of current concepts regarding electrostatic ion-cyclotron turbulence (theory and experiment), and regarding inclined double potential layers in the magnetospheric plasma is presented. Anomalous resistance governed by electrostatic ion-cyclotron turbulence, and one-dimensional and two-dimensional models of double electrostatic layers in the magnetospheric plasma are examined
Magnetopause stand-off distance in dependence on the magnetosheath and solar wind parameters
International audienceA model of the magnetosheath structure proposed in a recent paper from the authors is extended to estimate the magnetopause stand-off distance from solar wind data. For this purpose, the relationship of the magnetopause location to the magnetosheath and solar wind parameters is studied. It is shown that magnetopause erosion may be explained in terms of the magnetosheath magnetic field penetration into the magnetosphere. The coefficient of penetration (the ratio of the magnetospheric magnetic field depression to the intensity of the magnetosheath magnetic field Bm?z=?Bmsin2?/2, is estimated and found approximately to equal 1. It is shown that having combined a magnetosheath model presented in an earlier paper and the magnetosheath field penetration model presented in this paper, it is possible to predict the magnetopause stand-off distance from solar wind parameters
Rate of steady-state reconnection in an incompressible plasma
The reconnection rate is obtained for the simplest case of 2D symmetric
reconnection in an incompressible plasma. In the short note (Erkaev et al.,
Phys. Rev. Lett.,84, 1455 (2000)), the reconnection rate is found by matching
the outer Petschek solution and the inner diffusion region solution. Here the
details of the numerical simulation of the diffusion region are presented and
the asymptotic procedure which is used for deriving the reconnection rate is
described. The reconnection rate is obtained as a decreasing function of the
diffusion region length. For a sufficiently large diffusion region scale, the
reconnection rate becomes close to that obtained in the Sweet-Parker solution
with the inverse square root dependence on the magnetic Reynolds number,
determined for the global size of the current sheet. On the other hand, for a
small diffusion region length scale, the reconnection rate turns out to be very
similar to that obtained in the Petschek model with a logarithmic dependence on
the magnetic Reynolds number. This means that the Petschek regime seems to be
possible only in the case of a strongly localized conductivity corresponding to
a small scale of the diffusion region.Comment: 11 pages, 3 figure
Low frequency 1/<i>f</i>-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere
Dissipationless Disk Accretion
We consider disk accretion resulting purely from the loss of angular momentum
due to the outflow of plasma from a magnetized disk. In this limiting case, the
dissipation due to the viscosity and finite electrical conductivity of the
plasma can be neglected. We have obtained self-consistent, self-similar
solutions for dissipationless disk accretion. Such accretion may result in the
formation of objects whose bolometric luminosities are lower than the flux of
kinetic energy in the ejected material.Comment: 17 pages, 6 figures, published in Astronomy Reports, Vol.49, No.1,
2005, p.57 (submitted September 13, 2003). Unfortunately, we did not upload
the paper to astro-ph before, but since the topic is now of interest we feel
that the paper would benefit the communit
Probabilistic forecasting of the disturbance storm time index: An autoregressive Gaussian process approach
Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 1. Insights from the estimation of effective population sizes
International audienceThe sustainability of modern agriculture relies on strategies that can control the ability of pathogens to overcome chemicals or genetic resistances through natural selection. This evolutionary potential, which depends partly on effective population size (Ne), is greatly influenced by human activities. In this context, wild pathogen populations can provide valuable information for assessing the long-term risk associated with crop pests. In this study, we estimated the effective population size of the beet cyst nematode, Heterodera schachtii, by sampling 34 populations infecting the sea beet Beta vulgaris spp. maritima twice within a one-year period. Only 20 populations produced enough generations to analyze the variation in allele frequencies, with the remaining populations showing a high mortality rate of the host plant after only one year. The 20 analyzed populations showed surprisingly low effective population sizes, with most having Ne close to 85 individuals. We attribute these low values to the variation in population size through time, systematic inbreeding, and unbalanced sex- ratios. Our results suggest that H. schachtii has low evolutionary potential in natural environments. Pest control strategies in which populations on crops mimic wild populations may help prevent parasite adaptation to host resistance
- …