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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

High-latitude distributions of plasma waves and spatial irregularities from DE 2 alternating current electric field observations

The high-latitude spatial distributions of average signal intensities in 12 frequency channels between 4 Hz and 512 kHz as measured by the ac electric field spectrometers on the DE-2 spacecraft are analyzed for 18 mo of measurements. In MLT-INL (magnetic local time-invariant latitude) there are three distinct distributions that can be identified with 4-512 Hz signals from spatial irregularities and Alfven waves, 256-Hz to 4.1-kHz signals from ELF hiss, and 4.1-64 kHz signals from VLF auroral hiss, respectively. Overlap between ELF hiss and spatial irregularity signals occurs in the 256-512 Hz band. VLF hiss signals extend downward in frequency into the 1.0-4.1 kHz band and upward into the frequency range 128-512 kHz. The distinctly different spatial distribution patterns for the three bands, 4-256 Hz, 512-1204 Hz, and 4.1-64 kHz, indicate a lack of any causal relationships between VLF hiss, ELF hiss, and lower-frequency signals from spatial irregularities and Alfven waves.

Heppner, J. P.↗
NASA NTRS1993

Measurement of direct current electric fields and plasma flow speeds in Jupiter's magnetosphere

During the encounter of Ulysses with Jupiter, we have measured two components of the dc electric field and deduced from them the flow speed in the Io toms, as well as the presence of a polar cap region end what we interpret as a cleft region. Within the toms the flow speed is approximately equal to the speed of a plasma corotating with Jupiter but has significant deviations. The dominant deviations have an apparent period of the order of Jupiter's rotation period, but this might be a latitudinal effect. Other important periods are about 40 min and less than 25 min.

Kellogg, Paul J.↗
NASA NTRS1994

Loop heating by D.C. electric current and electromagnetic wave emissions simulated by 3-D EM particle zone

We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions.

Sakai, J. I.↗
NASA NTRS1982

Relationships between the Birkeland currents, ionospheric currents, and electric fields

Currents and electric fields in the ionosphere are calculated using a global model of the electron density including conjugate coupling along field lines. Incoherent scatter and rocket measurements of high-latitude electron densities are used to derive realistic variations of the polar conductivities as a function of magnetic activity. The Birkeland currents are specified in terms of three indices, and the relationship between these parameters and the auroral electrojets indices is examined along with the polar cap potential and the electric field at lower latitudes. A mathematical model of the currents, electric fields, and energy inputs produced by field aligned currents is developed, which is consistent with and specifiable in terms of measured geophysical indices.

Bleuler, E.↗
NASA NTRS1981

Dynamics Explorer dual spacecraft to be launched on July 31

Plans for the launch of the Dynamics Explorers A and B are announced. The mission of the spacecraft is described. Specific knowledge about the coupling of energy, electric currents, electric fields, and plasmas between the magnetosphere, the ionosphere, and the atmosphere is sought. The instrumentation of the spacecraft is described and the spacecraft and Delta 3918 launch vehicle characterized. Detailed background information amplifying the mission is included.

Source record↗
NASA NTRS1981

NASA launches dual Dynamics Explorer spacecraft

A Delta launch vehicle was used to insert Dynamics Explorer A into a highly elliptical polar orbit, ranging from 675 to 24,945 km, and Dynamics Explorer B satellite into a low polar orbit, ranging from 306 to 1,300 km. The two spacecraft are designed to provide specific knowledge about the interaction of energy, electric currents, electric fields, and plasmas between the magnetosphere, the ionosphere, and the atmosphere.

Source record↗
NASA NTRS1981

Dynamics Explorer spacecraft and ground operations systems

The Dynamics Explorer program of NASA is designed to study the coupling of energy, electric currents, electric fields, and plasmas between the atmosphere, ionosphere, and the magnetosphere. The program is composed of two well instrumented polar orbiting satellites and ground operations and data handling systems which have been designed to acquire, process, and make readily available to the scientists of the program the data sets necessary for analysis to accomplish the science objectives. These systems are described with emphasis placed on the relationship of the two instrumented spacecraft and the ground systems to their roles in meeting the program requirements. In addition, the characteristics of the orbits selected are specified.

Hoffman, R. A.↗
NASA NTRS1982

The polar ionosphere

Self-consistent concepts which in many cases demonstrate the required relationships between electric currents, conductivity and electric fields are emerging from International Magnetospheric Study period research on the polar ionosphere and its role in the coupling between the ionosphere and the magnetopause. Observed phenomena may now be explained in terms of realistic variations in the electric current, conductivity and electric field parameters, and the distribution and composition of plasma can be reconciled with large scale plasma motion and ion production regions. Gaps remain, however, in the current understanding of the polar ionosphere's electrodynamic and plasma properties.

Heelis, R. A.↗
NASA NTRS1975

Instrumentation for measurement of aircraft noise and sonic boom

A jet aircraft noise and sonic boom measuring device which converts sound pressure into electric current is described. An electric current proportional to the sound pressure level at a condenser microphone is produced and transmitted over a cable, amplified by a zero drive amplifier and recorded on magnetic tape. The converter is comprised of a local oscillator, a dual-gate field-effect transistor (FET) mixer and a voltage regulator/impedance translator. A carrier voltage that is applied to one of the gates of the FET mixer is generated by the local oscillator. The microphone signal is mixed with the carrier to produce an electrical current at the frequency of vibration of the microphone diaphragm by the FET mixer. The voltage of the local oscillator and mixer stages is regulated, the carrier at the output is eliminated, and a low output impedance at the cable terminals is provided by the voltage regulator/impedance translator.

Zuckerwar, A. J.↗
NASA NTRS1978

Currents and electric fields in the ionosphere due to field-aligned auroral currents

Birkeland (1908, 1913) did a detailed analysis of the upper atmospheric current system in the high-latitude region, and suggested that field-aligned currents flowing into and out of the auroral ionosphere were the driving mechanism for this current system. In the present paper, static electric field and current patterns due to the field-aligned Birkeland currents are examined, using a model in which currents approximating those reported by Iijima and Potemra (1976) are used as input to a global model of the ionospheric conductivities, in which interhemispheric coupling along field lines is included. The model reproduces the main features of the high-latitude current and voltage system and the penetration of these currents within the plasmasphere.

Nisbet, J. S.↗
NASA NTRS2005

Two SMA-Actuated Miniature Mechanisms

The figures depict two miniature mechanisms actuated by strips made of shape-memory alloy (SMA). A typical SMA is a nickel-titanium alloy known by the trade name "Flexinol" or "Nitinol." In preparation for a typical application, a suitably sized and shaped piece of an SMA is deformed by a predetermined amount at the lower of two operating temperatures, then mounted in a mechanism. When stroking of the mechanism in one direction is desired, the piece of SMA is heated above a transition temperature to make it return to the "remembered" undeformed state. When stroking of the mechanism in the opposite direction is desired, the SMA is cooled below the transition temperature to make it return to the deformed state. Also, the SMA alloy chosen for a specific application is one that has a transition temperature somewhat above the ambient temperature, so that stroking in one direction or the opposite direction can be achieved by heating the SMA, or refraining from heating the SMA, respectively, above the transition temperature. In the present mechanisms as in typical other SMA mechanisms, the heating is effected by electric currents applied via electrical contacts at the ends of the SMA strips. The purpose served by the mechanism of Figure 1 is to lock or release a flexible latch attachment. In preparation for use in this mechanism, two initially straight SMA strips are deformed into curved springs that, when mounted in the mechanism at ambient temperature, clamp the knob at the lower end of the flexible latch attachment. When heated above their transition temperature by an electric current, the SMA strips return to their original straight configuration, thereby releasing the knob. This mechanism is redundant in the sense that as long as at least one of the two SMA strips straightens when commanded to do so, the knob is released. The mechanism of Figure 2 is suited to any of a variety of applications in which there are requirements for a small mechanism that affords lowtorque rotary actuation through a finite angular range. As shown here, the mechanism is used to rotate a coverlatch pin to a release position. In this case, a straight and flat SMA strip is torsionally deformed to a twist angle of about 90deg by use of a torsion bias spring. When the SMA strip is heated, it rotates to its original straight and flat condition.

Willey, Cliff E.↗
NASA NTRS2006

Method for manufacturing high quality carbon nanotubes

A non-catalytic process for the production of carbon nanotubes includes supplying an electric current to a carbon anode and a carbon cathode which have been securely positioned in the open atmosphere with a gap between them. The electric current creates an electric arc between the carbon anode and the carbon cathode, which causes carbon to be vaporized from the carbon anode and a carbonaceous residue to be deposited on the carbon cathode. Inert gas is pumped into the gap to flush out oxygen, thereby preventing interference with the vaporization of carbon from the anode and preventing oxidation of the carbonaceous residue being deposited on the cathode. The anode and cathode are cooled while electric current is being supplied thereto. When the supply of electric current is terminated, the carbonaceous residue is removed from the cathode and is purified to yield carbon nanotubes.

Benavides, Jeanette M.↗
NASA NTRS2011

Radiation Shielding Systems Using Nanotechnology

A system for shielding personnel and/or equipment from radiation particles. In one embodiment, a first substrate is connected to a first array or perpendicularly oriented metal-like fingers, and a second, electrically conducting substrate has an array of carbon nanostructure (CNS) fingers, coated with an electro-active polymer extending toward, but spaced apart from, the first substrate fingers. An electric current and electric charge discharge and dissipation system, connected to the second substrate, receives a current and/or voltage pulse initially generated when the first substrate receives incident radiation. In another embodiment, an array of CNSs is immersed in a first layer of hydrogen-rich polymers and in a second layer of metal-like material. In another embodiment, a one- or two-dimensional assembly of fibers containing CNSs embedded in a metal-like matrix serves as a radiation-protective fabric or body covering.

Chen, Bin↗
NASA NTRS1986

Static current-sheet models of quiescent prominences

A particular class of theoretical models idealize the prominence to be a discrete flat electric-current sheet suspended vertically in a potential magnetic field. The weight of the prominence is supported by the Lorentz force in the current sheet. These models can be extended to have curved electric-current sheets and to vary three-dimensionally. The equation for force balance is 1 over 4 pi (del times B) times Bdel p- p9 z=zero. Using Cartesian coordinates we take, for simplicity, a uniform gravity with constant acceleration g in the direction -z. If we are interested not in the detailed internal structure of the prominence, but in the global magnetic configuration around the prominence, we may take prominence plasma to be cold. Consideration is given to how such equilibrium states can be constructed. To simplify the mathematical problem, suppose there is no electric current in the atmosphere except for the discrete currents in the cold prominence sheet. Let us take the plane z =0 to be the base of the atmosphere and restrict our attention to the domain z greater than 0. The task we have is to solve for a magnetic field which is everywhere potential except on some free surface S, subject to suit able to boundary conditions. The surface S is determined by requiring that it possesses a discrete electric current density such that the Lorentz force on it is everywhere vertically upward to balance the weight of the material m(S). Since the magnetic field is potential in the external atmosphere, the latter is decoupled from the magnetic field and its plane parallel hydrostatic pressure and density can be prescribed.

Wu, F.↗