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  • 1
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    High temperature strain gage apparent strain compensation (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Once an installed strain gage is connected to a strain indicating device and the instrument is balanced, a subsequent change in temperature of the gage installation will generally produce a resistance change in the gage. This purely temperature-induced resistance will be registered by the indicating device as a strain and is referred to as 'apparent strain' to distinguish it from strain due to applied stress. One desirable technique for apparent strain compensation is to employ two identical gages with identical mounting procedures which are connected with a 'half bridge' configuration where gages see the same thermal environment but only one experiences a mechanical strain input. Their connection in adjacent arms of the bridge will then balance the thermally induced apparent strains and, in principle, only the mechanical strain remains. Two approaches that implement this technique are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: The 1992 NASA Langley Measurement Technology Conference: Measurement Technology for Aerospace Applications in High-Temperature Environments; p 211-222
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  • 2
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    Large-Scale Structure of Magnetospheric Plasma (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Recent investigations of magnetospheric plasma structure are summarized under the broad categories of empirical models, transport across boundaries, formation, and dynamics of the plasma sheet. This report reviews work in these areas during the period 1991 to 1993. Fully three-dimensional empirical models and simulations have become important contributors to our understanding of the magnetospheric system. Some new structural concepts have appeared in the literature: the 'entry boundary' and 'geo-pause', the plasma sheet 'region 1 vortices', the 'low-energy layer', the 'adia-baticity boundary' or 'wall region', and a region in the tail to which we refer as the 'injection port'. Traditional structural concepts have also been the subject of recent study, notably the plasmapause, the magnetopause, and the plasma sheet. Significant progress has been made in understanding the nature of plasma sheet formation and dynamics, but the acceleration of electrons to high energy remains somewhat mysterious.
    Keywords: Astrophysics
    Type: NASA-TM-111866 , NAS 1.15:111866
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  • 3
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    Strain gage calibration (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A temporary bonding system for accurately predetermining the individual apparent strain curve characteristics of the gages is used, and subsequently employs a computer to watch the apparent strain curves of the individual gages to determine which gages should be used together on transducers. The temporary bonding system requires a test block on which the gages are temporarily bonded, several thermocouples for monitoring temperature, and a data acquisition system for recording apparent strain data. Initially, a group of strain gages are attached to the test block using a bonding agent that disintegrates at high temperatures. The gages are then wired to an appropriate data acquisition and data, collected throughout a predetermined temperature excursion. Once the data is obtained, the test block is heated until the bonding agent disintegrates freeing the gages from the test block. The gages are then disconnected from the data acquisition system and cleaned, thereby ready for use on transducers.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 4
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    Interferometric phase velocity measurements (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Phase velocities of plasma waves near the lower hybrid frequency were measured with an interferometer composed of two spatially separated electron-density probes. The plasma waves were produced in the F-region ionosphere by an argon ion beam. By calculating the normalized cross spectrum of the plasma waves a coherency of .98 was estimated along with a maximum phase difference of pi/3 radians between the two probes. This implies that the wavelength was 6 meters compared to an O(+) gyroradius of 3.8 meters, and that the phase velocity was 45 km/sec compared to an ion-beam velocity of 12.4 km/sec. These numbers compare favorably with recent predictions of a nonresonant mode produced by a dense ion beam.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 19-22
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  • 5
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    Force instrumentation for cryogenic wind tunnels using one-piece strain-gage balances (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Materials and techniques for a transducer capable of obtaining accurate force measurements at cryogenic temperatures (down to 77 K) and high pressures (up to 9 atm) have been determined. Areas of high stress concentration are minimized by balance design, and model and sting attachment methods able to withstand cryogenic temperatures are used. Maraging 200 is the material used for the balances, due to its high impact strength and simple heat treatment procedure. Test results verify that the balances produce reliable, repeatable, and predictable data from 300 K to 110 K under steady state conditions. Techniques have been developed to reduce the temperature-induced bridge output, such as the use of bridges with two gages mounted transverse to the principal stress direction. Under these conditions, the results given by the balances should be equally good during transient temperatures on five of the six components. The work will be used at the National Transonic Facility (NTF) at NASA Langley.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: International Instrumentation Symposium; Apr 27, 1981 - Apr 30, 1981; Indianapolis, IN
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  • 6
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    Evidence for Spiral Magnetic Structures at the Magnetopause: A Case for Multiple Reconnections (2003)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: We analyze plasma structures within the low latitude boundary layer (LLBL) observed by the lnterball Tail spacecraft under southward interplanetary magnetic field. Ion velocity distributions observed in the LLBL under these conditions fall into three categories: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counterstreaming magnetosheath-type, and (c) distributions with three components where one of them has nearly zero velocity parallel to magnetic field (VlI), while the other two are counter-streaming components. D-shaped ion velocity distributions (a) correspond to magnetosheath plasma injections into reconnected flux tubes, as influenced by spacecraft location relative to the reconnection site. Simultaneous counter-streaming injections (b) suggest multiple reconnections. Three-component ion velocity distributions (c) and theii evolution with decreasing number density in the LLBL are consistent v behavior expected on long spiral flux tube islands at the magnetopaus as has been proposed and found to occur in magnetopause simulatior We interpret these distributions as a natural consequence of the formation of spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and magnetospheric plasmas. We suggest that multiple reconnections pla! an important role in the formation of the LLBL.
    Keywords: Astrophysics
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  • 7
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    Short Large-Amplitude Magnetic Structures (SLAMS) at Venus (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: We present the first observation of magnetic fluctuations consistent with Short Large-Amplitude Magnetic Structures (SLAMS) in the foreshock of the planet Venus. Three monolithic magnetic field spikes were observed by the Venus Express on the 11th of April 2009. The structures were approx.1.5-〉11s in duration, had magnetic compression ratios between approx.3-〉6, and exhibited elliptical polarization. These characteristics are consistent with the SLAMS observed at Earth, Jupiter, and Comet Giacobini-Zinner, and thus we hypothesize that it is possible SLAMS may be found at any celestial body with a foreshock.
    Keywords: Astrophysics
    Type: GSFC.JA.7467.2012
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  • 8
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    Long-term stability of a Fabry-Perot interferometer used for measurement of stellar Doppler shift (1990)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The use of a fiber-optic-link CCD-detector Fabry-Perot interferometer (McMillan et al., 1985, 1986, and 1988) to obtain high-accuracy measurements of stellar Doppler shifts at KPNO is described in detail and illustrated with sample data. Particular attention is given to accuracy requirements and techniques for reducing errors, resolution (orders of 50 mA at wavelength 4300 A are separated by 640 mA), CCD sensitivity, observing and data-processing operations, and the control of environmental conditions. Standard-deviation data and statistics on seven solar-type stars are presented in tables, and the time evolution of the radial velocity of Beta Com is shown in a graph.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Instrumentation in Astronomy VII; Feb 13, 1990 - Feb 17, 1990; Tucson, AZ; United States
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  • 9
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    Magnetic Reconnection and Modification of the Hall Physics Due to Cold Ions at the Magnetopause (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohms law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the v x B drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN41004 , Geophysical Research Letters (ISSN 0094-8276); 43; 13; 6705–6712
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  • 10
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    Shift of the Magnetopause Reconnection Line to the Winter Hemisphere Under Southward IMF Conditions: Geotail and MMS Observations (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: At 02:13 UT on 18 November 2015 when the geomagnetic dipole was tilted by -27deg, the MMS spacecraft observed southward reconnection jets near the subsolar magnetopause under southward and dawnward interplanetary magnetic field conditions. Based on four-spacecraft estimations of the magnetic field direction near the separatrix and the motion and direction of the current sheet, the location of the reconnection line was estimated to be approx.1.8 R(sub E) or further northward of MMS. The Geotail spacecraft at GSM Z approx. 1.4 R(sub E) also observed southward reconnection jets at the dawnside magnetopause 30-40 min later. The estimated reconnection line location was northward of GSM Z approx.2 R(sub E). This crossing occurred when MMS observed purely southward magnetic fields in the magnetosheath. The simultaneous observations are thus consistent with the hypothesis that the dayside magnetopause reconnection line shifts from the subsolar point toward the northem (winter) hemisphere due to the effect of geomagnetic dipole tilt.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN41266 , Geophysical Research Letters (ISSN 0094-8276); 43; 11; 5581–5588
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