33,817 research outputs found
Magnetohydrodynamic turbulence in the solar wind
Recent work in describing the solar wind as an MHD turbulent fluid has shown that the magnetic fluctuations are adequately described as time stationary and to some extent as spatially homogeneous. Spectra of the three rugged invariants of incompressible MHD are the principal quantities used to characterize the velocity and magnetic field fluctuations. Unresolved issues concerning the existence of actively developing turbulence are discussed
On the variational homotopy perturbation method for nonlinear oscillators
In this paper we discuss a recent application of a variational homotopy
perturbation method to rather simple nonlinear oscillators . We show that the
main equations are inconsistent and for that reason the results may be of
scarce utility
Reusable silica surface-insulation material
Material was specifically developed for manufacture of insulating tiles, but it can be molded into other shapes as required. Basic raw materials are high-purity silica fiber, fumed-silica powder, and reagent-grade starch. Only purest materials are used, and care must be taken to avoid contamination during processing
Bi-Directional Energy Cascades and the Origin of Kinetic Alfv\'enic and Whistler Turbulence in the Solar Wind
The observed sub-proton scale turbulence spectrum in the solar wind raises
the question of how that turbulence originates. Observations of keV energetic
electrons during solar quite-time suggest them as possible source of free
energy to drive the turbulence. Using particle-in-cell simulations, we explore
how free energy in energetic electrons, released by an electron two-stream
instability drives Weibel-like electromagnetic waves that excite wave-wave
interactions. Consequently, both kinetic Alfv\'enic and whistler waves are
excited that evolve through inverse and forward magnetic energy cascades.Comment: 12 pages, 5 figures, Submitted to Physical Review Letter
Stationarity of magnetohydrodynamic fluctuations in the solar wind
Solar wind research and studies of charged particle propagation often assume that the interplanetary magnetic field represents a stationary random process. The extent to which ensemble averages of the solar wind magnetic fields follow the asymptotic behavior predicted by the ergodic theorem was investigated. Several time periods, including a span of nearly two years, are analyzed. Data intervals which span many solar rotations satisfy the conditions of weak stationarity if the effects of solar rotation are included in the asymptotic analysis. Shorter intervals which include a small integral number of interplanetary sectors also satisfy weak stationarity. The results are illustrated using magnetometer data from the ISEE-3, Voyager and IMP spacecraft
Fibrous refractory composite insulation
A refractory composite insulating material was prepared from silica fibers and aluminosilicate fibers in a weight ratio ranging from 1:19 to 19:1, and about 0.5 to 30% boron oxide, based on the total fiber weight. The aluminosilicate fiber and boron oxide requirements may be satisfied by using aluminoborosilicate fibers and, in such instances, additional free boron oxide may be incorporated in the mix up to the 30% limit. Small quantities of refractory opacifiers, such as silicon carbide, may be also added. The composites just described are characterized by the absence of a nonfibrous matrix
Effect of velocity slip at a porous boundary on the performance of an incompressible porous bearing
Effect of velocity slip at porous boundary on performance of incompressible porous bearin
An effective Hamiltonian for 2D black hole Physics
In another application of the methods of Henneaux, Teitelboim, and Vergara
developed for diffeomorphisms invariant models, the CGHS theory of 2D black
holes is focused in order to obtain the true degrees of freedom, the simplectic
structure and the {\it effective} Hamiltonian that rules the dynamics in
reduced phase-space.Comment: To appear in Europhysics Letter
Silica reusable surface insulation
A reusable silica surface insulation material is provided by bonding amorphous silica fibers with colloidal silica at an elevated temperature. The surface insulation is ordinarily manufactured in the form of blocks (i.e., tiles)
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