scholarly journals Anisotropic Electron Fluid Closure Validated by in situ Spacecraft Observations in the far Exhaust of Guide‐Field Reconnection

2020 ◽  
Author(s):  
Blake A. Wetherton ◽  
Jan Egedal ◽  
Ari Lê ◽  
William Daughton
Keyword(s):  
Electron Fluid ◽  
Guide Field

scholarly journals Validation of Anisotropic Electron Fluid Closure Through In Situ Spacecraft Observations of Magnetic Reconnection

2019 ◽  
Vol 46 (12) ◽  
pp. 6223-6229
Author(s):  
Blake A. Wetherton ◽  
Jan Egedal ◽  
Ari Lê ◽  
William Daughton
Keyword(s):  
Magnetic Reconnection ◽  
Electron Fluid

scholarly journals Energy cascade rate in isothermal compressible magnetohydrodynamic turbulence

2018 ◽  
Vol 84 (4) ◽  
Author(s):  
N. Andrés ◽  
F. Sahraoui ◽  
S. Galtier ◽  
L. Z. Hadid ◽  
P. Dmitruk ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Rotation Group ◽  
Energy Cascade ◽  
Relative Importance ◽  
Dominant Contribution ◽  
Magnetohydrodynamic Turbulence ◽  
Guide Field ◽  
Small Scales ◽  
Spurious Results

Three-dimensional direct numerical simulations are used to study the energy cascade rate in isothermal compressible magnetohydrodynamic turbulence. Our analysis is guided by a two-point exact law derived recently for this problem in which flux, source, hybrid and mixed terms are present. The relative importance of each term is studied for different initial subsonic Mach numbers$M_{S}$and different magnetic guide fields$\boldsymbol{B}_{0}$. The dominant contribution to the energy cascade rate comes from the compressible flux, which depends weakly on the magnetic guide field$\boldsymbol{B}_{0}$, unlike the other terms whose moduli increase significantly with$M_{S}$and$\boldsymbol{B}_{0}$. In particular, for strong$\boldsymbol{B}_{0}$the source and hybrid terms are dominant at small scales with almost the same amplitude but with a different sign. A statistical analysis undertaken with an isotropic decomposition based on the SO(3) rotation group is shown to generate spurious results in the presence of$\boldsymbol{B}_{0}$, when compared with an axisymmetric decomposition better suited to the geometry of the problem. Our numerical results are compared with previous analyses made within situmeasurements in the solar wind and the terrestrial magnetosheath.

Rendez vous with Saturn's rings

1984 ◽  
Vol 75 ◽  
pp. 743-759 ◽  
Author(s):  
Kerry T. Nock
Keyword(s):  
Solar Energy ◽  
Electric Propulsion ◽  
Power Source ◽  
Propulsion System ◽  
Low Thrust ◽  
Ring Plane ◽  
The Earth ◽  
Total Impulse ◽  
Saturn's Rings

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.

The Use of Advanced Analytical Techniques for Characterization of the Chemical, Physical, and Crystallographic Nature of a Surface

1973 ◽  
Vol 31 ◽  
pp. 132-133 ◽  
Author(s):  
R. E. Herfert
Keyword(s):  
Surface Characterization ◽  
Analytical Techniques ◽  
X Ray Diffraction ◽  
Depth Of Penetration ◽  
X Ray ◽  
The Past ◽  
Transmission Electron ◽  
Scanning Electron

Studies of the nature of a surface, either metallic or nonmetallic, in the past, have been limited to the instrumentation available for these measurements. In the past, optical microscopy, replica transmission electron microscopy, electron or X-ray diffraction and optical or X-ray spectroscopy have provided the means of surface characterization. Actually, some of these techniques are not purely surface; the depth of penetration may be a few thousands of an inch. Within the last five years, instrumentation has been made available which now makes it practical for use to study the outer few 100A of layers and characterize it completely from a chemical, physical, and crystallographic standpoint. The scanning electron microscope (SEM) provides a means of viewing the surface of a material in situ to magnifications as high as 250,000X.

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