Nonlinear wave conversion in electron-positron plasmas     

M. E. Gedalin  J. G. Lominadze  L. Stenflo  V. N. Tsytovich 《Astrophysics and Space Science》1985,108(2):393-400

Wave conversion mechanisms causing large-frequency shifts are considered for an electron-positron plasma in a strong magnetic field. In particular, we discuss the effects of the nonlinear erenkov as well as the cyclotron resonances in order to associate pulsar radio-emissions with our present model for nonlinear conversion of high-frequency radiation into the low-frequency region.  相似文献   

Radiation of a neutrino mechanism for type II supernovae     

I. V. Baikov  V. M. Suslin  V. M. Chechetkin  V. Bychkov  L. Stenflo 《Astronomy Reports》2007,51(4):274-281

We propose a new mechanism for type II supernova explosions. An important element of the model is large-scale convection that arises due to non-equilibrium neutronization of the matter in the central region of the proto-neutron star. Our analytical estimates and numerical simulations of the convection rate are in good mutual agreement. Large-scale convection leads to the rapid transport of neutrinos from the center of the star to the bounce shock formed during the pause in the collapse of the stellar matter in the proto-neutron star. The mean neutrino energy is 30–50 MeV. We analyze the dependence of the mean neutrino energy on the size of the convection cells—“bubbles.” Our computations of the interaction between the neutrinos and the shock show that the velocity of the shock along the rotational axis of the star exceeds the escape velocity. Thus, explosion of the envelope and a supernova with a very asymmetrical envelope structure become possible, leading to the formation of a neutron star.  相似文献   

Nonlinear interaction between acoustic gravity waves     

P. Axelsson  J. Larsson  L. Stenflo 《Annales Geophysicae》1996,14(3):304-308

The resonant interaction between three acoustic gravity waves is considered. We improve on the results of previous authors and write the new coupling coefficients in a symmetric form. Particular attention is paid to the low-frequency limit.  相似文献   

Interpretations of new features of time domain electric-field structures in the auroral acceleration region     

P. K. Shukla  L. Stenflo 《Annales Geophysicae》1998,16(7):889-890

Possible theoretical interpretations of the various nonlinear electric-field structures in the auroral acceleration region are provided.  相似文献   

Probability distribution functions for the Sun's magnetic field     

J.O. Stenflo 《Astronomische Nachrichten》2010,331(6):585-588

Magnetoconvection structures the Sun's magnetic field cover a vast range of scales, down to the magnetic diffusion scale that is orders of magnitude smaller than the resolution of current telescopes. The statistical properties of this structuring are governed by probability density functions (PDFs) for the flux densities and by the angular distribution functions for the orientations of the field vectors. The magnetic structuring on sub‐pixel scales greatly affects the field properties averaged over the resolution element due to the non‐linear relation between polarization and magnetic field. Here we use a Hinode SOT/SP data set for the quiet Sun disk center to explore the complex behavior of the 6301–6302 Å Stokes line profile system and identify the observables that allow us to determine the distribution functions in the most robust and least model dependent way. The angular distribution is found to be strongly peaked around the vertical direction for large flux densities but widens with decreasing flux density to become isotropic in the limit of zero flux density. The noise‐corrected PDFs for the vertical, horizontal, and total flux densities all have a narrowly peaked maximum at zero flux density that can be fitted with a stretched exponential, while the extended wings decline quadratically (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Pancake cyclones and anti-cyclones in the ionosphere     

V. I. Petviashvili  O. A. Pokhotelov  P. K. Shukla  L. Stenflo 《Astrophysics and Space Science》1993,202(2):363-372

The formation of pancake cyclones and anticyclones in the E-region of the Earth's ionosphere is considered. It is shown that the vortices can be maintained by the neutral winds or by chemical reactions including the energy release caused by the triple collisions of atomic oxygen with neutrals. It is found that the variations of the magnetic fields induced by the vortices are not localized and decrease slowly far from the vortex core. They can be easily detected by ground based magnetometers or by facilities on board the low-orbiting satellites.  相似文献   

Parametric coupling between electromagnetic ion-cyclotron and shear Alfvén waves     

P. K. Shukla  L. Stenflo 《Astrophysics and Space Science》1990,166(1):93-97

The nonlinear interaction between finite amplitude electromagnetic ion-cyclotron waves and shear-Alfvén waves is considered. It is shown that this process is governed by three coupled equations. They are here used to study modulational instabilities. The relevance of our investigation to low-frequency electromagnetic fluctuations in space plasmas is pointed out.  相似文献   

Filamentation instability of Alfvén waves     

P. K. Shukla  L. Stenflo 《Astrophysics and Space Science》1989,155(1):145-147

The filamentation instability of finite amplitude left-hand circularly polarized Alfvén waves has been investigated taking into account the second-order density and magnetic field perturbations that are created by the Alfvén wave pressure. The minimum scale length and time over which the filamentation occurs, are found. Our results are applied to Alfvén waves that should scatter cosmic rays in the interstellar medium (ISM).  相似文献   

Polarimetry in the Mg ii h and k lines     

W. Henze  J. O. Stenflo 《Solar physics》1987,111(2):243-254

The Ultraviolet Spectrometer and Polarimeter (UVSP) on the SMM satellite has been used to record the linear polarization profile across the Mgii h and k lines, including its center-to-limb variation. Linear polarization with an orientation of the electric vector parallel to the solar limb is detected in the line wings on the short wavelength side of the k line and on the long wavelength side of the h line, in agreement with theoretical predictions of Auer et al. (1980). The predicted negative polarization (electric vector perpendicular to the limb) between the h and k lines is however not confirmed by the observations. Instead values close to zero are indicated there, although the statistical significance of the results is marginal.We have examined possible explanations of such a discrepancy between theory and observations. After having rejected other alternatives (e.g., opacity effects, different continuum polarization, or deviations from a plane-parallel stratification), it is suggested that the solution may be found in a treatment of partial redistribution of the polarized radiation with the quantum-mechanical interference between the two scattering transitions being included as an integral part of the redistribution problem.  相似文献   

A fast and accurate guiding system     

G. Pålsgård  J. O. Stenflo 《Solar physics》1970,11(1):155-156

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