scholarly journals Direct measurements of the 3D plasma velocity in single-helical-axis RFP plasmas

2021 ◽  
Vol 28 (1) ◽  
pp. 012510
Author(s):  
J. Boguski ◽  
M. D. Nornberg ◽  
U. Gupta ◽  
K. J. McCollam ◽  
A. F. Almagri ◽  
...  
Keyword(s):  
Helical Axis ◽  
Plasma Velocity ◽  
Direct Measurements

scholarly journals Control of ionospheric plasma velocities by thermospheric winds

2021 ◽  
Author(s):  
Thomas Immel ◽  
Brian Harding ◽  
Roderick Heelis ◽  
Astrid Maute ◽  
JM Forbes ◽  
...  
Keyword(s):  
Ionospheric Plasma ◽  
Middle Atmosphere ◽  
Equatorial Ionosphere ◽  
Plasma Velocity ◽  
Technological Systems ◽  
Plasma Environment ◽  
Adverse Impacts ◽  
Direct Measurements ◽  
Plasma State ◽  
Thermospheric Winds

Abstract Earth’s equatorial ionosphere exhibits significant and unpredictable day-to-day variations in density and morphology . This presents difficulties in preparing for adverse impacts on technological systems even 24 hours in advance . This behavior is now theoretically understood as a manifestation of thermospheric weather, where conditions in the upper atmosphere respond strongly to changes in the spectrum of atmospheric waves that propagate into space from the lower and middle atmosphere, modifying the electrodynamic environment that exerts control over the creation of plasma . The NASA Ionospheric Connection Explorer (ICON) makes the first coordinated space-based observations of the wind-driven dynamo and the plasma state to understand the relation of the plasma environment to the thermospheric weather below. Here we show the first direct measurements of the effects of a wind-driven dynamo in space, where a clear relationship is found between the vertical plasma velocities measured at the magnetic equator near 600 km and the thermospheric winds much farther below, with substantial correlations found between the plasma velocity and thermospheric winds during each of several successive precession cycles of the observatory’s orbit. Prediction of thermospheric winds in the 100 – 150 km range emerges as a key to improved prediction of the Earth’s plasma environment.

Feasibility of Molecular Structure Determination With a High Resolution Electron Microscope

1968 ◽  
Vol 26 ◽  
pp. 338-339
Author(s):  
T. A. Welton
Keyword(s):  
Electron Microscope ◽  
Substrate Surface ◽  
Helical Axis ◽  
Base Plane ◽  
Resolution Electron ◽  
High Resolution Electron Microscope ◽  
High Degree ◽  
Degree Of Order ◽  
Purine Pyrimidine

An ultimate design goal for an improved electron microscope, aimed at biological applications, is the determination of the structure of complex bio-molecules. As a prototype of this class of problems, we propose to examine the possibility of reading DNA sequence by an imaginable instrument design. This problem ideally combines absolute importance and relative simplicity, in as much as the problem of enzyme structure seems to be a much more difficult one.The proposed technique involves the deposition on a thin graphite lamina of intact double helical DNA rods. If the structure can be maintained under vacuum conditions, we can then make use of the high degree of order to greatly reduce the work involved in discriminating between the four possible purine-pyrimidine arrangements in each base plane. The phosphorus atoms of the back bone form in projection (the helical axis being necessarily parallel to the substrate surface) two intertwined sinusoids. If these phosphorus atoms have been located up to a certain point on the molecule, we have available excellent information on the orientation of the base plane at that point, and can then locate in projection the key atoms for discrimination of the four alternatives.

The restoration of blurred electron micrographs

1986 ◽  
Vol 44 ◽  
pp. 180-181
Author(s):  
Bridget Carragher ◽  
David A. Bluemke ◽  
Michael J. Potel ◽  
Robert Josephs
Keyword(s):  
Cross Section ◽  
Electron Micrographs ◽  
Relative Motion ◽  
Finite Thickness ◽  
Image Plane ◽  
Helical Axis ◽  
Thin Sections ◽  
Structural Details

We have investigated the feasibility of restoring blurred electron micrographs. Two related problems have been considered; the restoration of images blurred as a result of relative motion between the specimen and the image plane, and the restoration of images which are rotationally blurred about an axis. Micrographs taken while the specimen is drifting result in images which are blurred in the direction of motion. An example of rotational blurring arises in micrographs of thin sections of helical particles viewed in cross section. The twist of the particle within the finite thickness of the section causes the image to appear rotationally blurred about the helical axis. As a result, structural details, particularly at large distances from the helical axis, will be obscured.

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