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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Nanomechanics of Carbon and CxByNz Nanotubes: Via a Quantum Molecular Dynamics Method

Nanomechanics of single-wall C, BN and BC$_3$ and B doped C nanotubes under axial compression and tension are investigated through a generalized tight-binding molecular dynamics (GTBMD) and {\it ab-initio} electronic structure methods. The dynamic strength of BN, BC$_3$ and B doped C nanotubes for small axial strain are comparable to each other. The main difference is in the critical strain at which structural collapse occurs. For example, even a shallow doping with B lowers the value of critical strain for C nanotubes. The critical strain for BN nanotube is found to be more than that for the similar C nanotube. Once the structural collapse starts to occur we find that carbon nanotubes irreversibly go into plastic deformation regime via the formation of tetrahedral (four-fold coordinated) bonds at the location of sharp pinches or kinks. This finding is considerably different from the classical MD (molecular dynamics) simulation results known so far. The energetics and electronic densities of states of the collapsed structures, investigated with {\it ab-initio) methods, will also be discussed.

Srivastava, Deepak↗
NASA NTRS1972

Magnetospheric electrons

Coupling of source, transport, and sink processes produces a fairly accurate model for the macroscopic structure and dynamics of magnetospheric electrons. Auroral electrons are controlled by convective transport from a plasma sheet source coupled with a precipitation loss due to whistler and electrostatic plasma turbulence. Outer and inner zone electrons are governed by radial diffusion transport from convection and acceleration sources external to the plasmapause and by parasitic precipitation losses arising from cyclotron and Landau interactions with whistler and ion cyclotron turbulence.

Coroniti, F. V.↗
NASA NTRS1988

Auroral energy deposition rate, characteristic electron energy, and ionospheric parameters derived from Dynamics Explorer 1 images

Auroral images obtained by the Spin Scan Auroral Imager (SAI) aboard the DE-1 satellite were used to derive auroral energy deposition rate, characteristic electron energy, and ionospheric parameters. The principles involved in the imaging technique and the physical mechanisms that underlie the relationship between the spectral images and the geophysical parameters are discussed together with the methodology for implementing such analyses. It is shown that images obtained with the SAI provide global parameters at 12-min temporal resolution; the spatial resolution is limited by the field of view of a pixel. The analysis of the 12-min images presented yielded a representation of ionospheric parameters that was better than can be obtained using empirical models based on local measurements averaged over long periods of time.

Rees, M. H.↗
NASA NTRS1986

Plasma waves and continuum radiation in planetary magnetospheres

Voyager data on whistler mode waves and electron cyclotron harmonic emissions are analyzed to understand the interaction of the waves with the dynamics of the electrons. The occurrence and characteristics of Jovian whistler mode chorus and the interactions with the plasma in and near the Io torus are emphasized. Bernstein waves, especially those near the upper hybrid or plasma frequency are discussed to provide insight into an important plasma diagnostic tool and to compare the relevant portions of the electron distribution function at Earth, Jupiter, and Saturn. The nonthermal continuum radiation common to the magnetospheres of Earth, Jupiter, and Saturn is considered. Because of the very low frequency of these radio waves and their close association with upper hybrid resonance emissions, continuum radiation is often associated more closely with the plasma wave spectrum of a planetary magnetosphere than with the planet's radio spectrum.

Kurth, W. S.↗
NASA NTRS1987

The role of ring current O(+) in the formation of stable auroral red arcs

Observations of thermal and energetic ion populations by the Dynamics Explorer 1 satellite in the magnetospheric energy source region as well as nearly simultaneous Langmuir probe measurements of enhanced electron temperatures by Dynamics Explorer 2 within the stable auroral red (SAR) arc at F region heights are used to examine the role of heavy ions in the formation of SAR arcs. It is found that sufficient energy is transferred to the electron gas at high altitudes via Coulomb collisions between the observed ring current ions and thermal electrons to support the enhanced F region electron temperatures measured on these field lines. The latitudinal variation in the electron heating rates calculated using observed ion populations is consistent with the observed variation in electron temperature across the SAR arc. In all cases, ring current O(+) is the major source of energy for the SAR arcs.

Kozyra, J. U.↗
NASA NTRS2004

Inner Radiation Belt Representation of the Energetic Electron Environment: Model and Data Synthesis Using the Salammbo Radiation Belt Transport Code and Los Alamos Geosynchronous and GPS Energetic Particle Data

The highly energetic electron environment in the inner magnetosphere (GEO inward) has received a lot of research attention in resent years, as the dynamics of relativistic electron acceleration and transport are not yet fully understood. These electrons can cause deep dielectric charging in any space hardware in the MEO to GEO region. We use a new and novel approach to obtain a global representation of the inner magnetospheric energetic electron environment, which can reproduce the absolute environment (flux) for any spacecraft orbit in that region to within a factor of 2 for the energy range of 100 KeV to 5 MeV electrons, for any levels of magnetospheric activity. We combine the extensive set of inner magnetospheric energetic electron observations available at Los Alamos with the physics based Salammbo transport code, using the data assimilation technique of "nudging". This in effect input in-situ data into the code and allows the diffusion mechanisms in the code to interpolate the data into regions and times of no data availability. We present here details of the methods used, both in the data assimilation process and in the necessary inter-calibration of the input data used. We will present sample runs of the model/data code and compare the results to test spacecraft data not used in the data assimilation process.

Friedel, R. H. W.↗
NASA NTRS1994

Electrotastic Solitary Waves (ESW) in the magnetotail: BEN wave forms observed by GEOTAIL

Wave forms of BEN (Broadband Electrostatic Noise) in the geomagnetic tail were first detected by the Wave Form Capture reciever on the GEOTAIL spacecraft. The results show that most of the BEN in the plasma sheet boundary layer (PSBL) are not continuous broadband noise but are composed of a series of solitary pulses having a special form which we term 'Electrostatic Solitary Waves (ESW)'. A nonlinear BGK potential model is proposed as the generation mechanism for the ESW based upon a simple particle simulation which considers the highly nonlinear evolution of the electron beam instability. The wave forms produced by this simulation are very similar to those observed by GEOTAIL and suggest that the nonlinear dynamics of the electron beam play an essential role in the generation of ESW.

Matsumoto, H.↗
NASA NTRS1998

Carbon Nanotube Based Molecular Electronics and Motors: A View from Classical and Quantum Dynamics Simulations

The tubular forms of fullerenes popularly known as carbon nanotubes are experimentally produced as single-, multiwall, and rope configurations. The nanotubes and nanoropes have shown to exhibit unusual mechanical and electronic properties. The single wall nanotubes exhibit both semiconducting and metallic behavior. In short undefected lengths they are the known strongest fibers which are unbreakable even when bent in half. Grown in ropes their tensile strength is approximately 100 times greater than steel at only one sixth the weight. Employing large scale classical and quantum molecular dynamics simulations we will explore the use of carbon nanotubes and carbon nanotube junctions in 2-, 3-, and 4-point molecular electronic device components, dynamic strength characterization for compressive, bending and torsional strains, and chemical functionalization for possible use in a nanoscale molecular motor. The above is an unclassified material produced for non-competitive basic research in the nanotechnology area.

Srivastava, Deepak↗
NASA NTRS1988

F region electron temperature signatures of the plasmapause based on Dynamics Explorer 1 and 2 measurements

A large DE 1 and 2 database covering all local times is used to explore the relationship between electron temperature (Te) signatures in the F region and plamaspheric density structures. The quiet time Te signature remains in the vicinity of 60 deg invariant latitude at all local times, while the plasmapause is found to bulge to about 60 deg at 1500 LT. The plasmasphere in the bulge region is shown to exhibit an internal feature in the vicinity of 60 deg which takes the form of a sharp H(+) gradient. It is suggested that the light-ion gradient may represent a recently created sharp boundary between an old plasmasphere and a new plasmasphere. The present Te characteristics are consisent with plasmasphere depletion and refilling time constants.

Brace, L. H.↗
NASA NTRS1985

Test particle modeling of wave-induced energetic electron precipitation

A test particle computer model of the precipitation of radiation belt electrons is extended to compute the dynamic energy spectrum of transient electron fluxes induced by short-duration VLF wave packets traveling along the geomagnetic field lines. The model is adapted to estimate the count rate and associated spectrum of precipitated electrons that would be observed by satellite-based particle detectors with given geometric factor and orientation with respect to the magnetic field. A constant-frequency wave pulse and a lightning-induced whistler wave packet are used as examples of the stimulating wave signals. The effects of asymmetry of particle mirror heights in the two hemispheres and the atmospheric backscatter of loss cone particles on the computed precipitated fluxes are discussed.

Chang, H. C.↗
NASA NTRS1977

Cosmic rays in a dynamical halo. I - Age and matter traversal distributions and anisotropy for nuclei. II - Electrons

Recent measurements of the mean lifetime of galactic cosmic rays (at least 10 million yr) have suggested a dynamical halo model of cosmic-ray confinement to the Galaxy. A one-dimensional version of the model is analyzed to determine the ranges of parameters required to give self-consistent values of the mean lifetime, matter traversed, anisotropy, and interstellar gamma-ray flux. It is found that the ranges of the parameters are: disk scale height of 4000-10,000 pc, average convection velocity of no more than 60 km/s, and diffusion coefficient of (3-10) by 10 to the 28th power sq cm/sec for particles with charges of the order of 10 GV. Some consequences for this model of a much shorter lifetime are also discussed. The energy spectrum and spatial distribution of electrons in the dynamical halo model are considered. A gradual steepening of the electron energy spectrum beginning at several GeV energy is found, as indicated by observations. The decrease of electron density with height in the halo depends on the particle energy and may be much steeper than that for nuclei. The models give a halo with a scale height of the order of 3 kpc for several-GeV electrons, which is shown to be consistent with radio observations.

Owens, A. J.↗
NASA NTRS1990

The electron signature of parallel electric fields

Dynamics Explorer I High-Altitude Plasma Instrument electron data are presented. The electron distribution functions have characteristics expected of a region of parallel electric fields. The data are consistent with previous test-particle simulations for observations within parallel electric field regions which indicate that typical hole, bump, and loss-cone electron distributions, which contain evidence for parallel potential differences both above and below the point of observation, are not expected to occur in regions containing actual parallel electric fields.

Burch, J. L.↗
NASA NTRS2003

Flywheels Upgraded for Systems Research

With the advent of high-strength composite materials and microelectronics, flywheels are becoming attractive as a means of storing electrical energy. In addition to the high energy density that flywheels provide, other advantages over conventional electrochemical batteries include long life, high reliability, high efficiency, greater operational flexibility, and higher depths of discharge. High pulse energy is another capability that flywheels can provide. These attributes are favorable for satellites as well as terrestrial energy storage applications. In addition to energy storage for satellites, the several flywheels operating concurrently can provide attitude control, thus combine two functions into one system. This translates into significant weight savings. The NASA Glenn Research Center is involved in the development of this technology for space and terrestrial applications. Glenn is well suited for this research because of its world-class expertise in power electronics design, rotor dynamics, composite material research, magnetic bearings, and motor design and control. Several Glenn organizations are working together on this program. The Structural Mechanics and Dynamics Branch is providing magnetic bearing, controls, and mechanical engineering skills. It is working with the Electrical Systems Development Branch, which has expertise in motors and generators, controls, and avionics systems. Facility support is being provided by the Space Electronic Test Engineering Branch, and the program is being managed by the Space Flight Project Branch. NASA is funding an Aerospace Flywheel Technology Development Program to design, fabricate, and test the Attitude Control/Energy Storage Experiment (ACESE). Two flywheels will be integrated onto a single power bus and run simultaneously to demonstrate a combined energy storage and 1-degree-of-freedom momentum control system. An algorithm that independently regulates direct-current bus voltage and net torque output will be experimentally demonstrated.

Jansen, Ralph H.↗
NASA NTRS2005

The Dynamics of Thermospheric Composition and Ionospheric Total Electron Content During Geomagnetic Storms

The geomagnetic storms of April 17-21,2002 and May 29-30,2003 caused large decreases in the O/N2 column density ratio in the thermosphere. For these storms, O/N2 column density decreases of greater than 50% were observed to extend to mid-to-low latitudes with the FUV sensitive Earth Camera of the Visible Imaging System (VIS) on the Polar spacecraft. Simultaneously in these same regions, the ground-based GPS network observed approximately 80% reductions in the Total Electron Content (TEC) of the ionosphere. The reduction in the O/N2 column density ratio is due mainly to increases in the molecular species that have welled-up into the thermosphere from the lower levels of the atmosphere due to auroral heating. The geomagnetic-storm driven increase in molecular densities at typical ionospheric heights rapidly charge exchange with the ambient ionized atoms and subsequently dissociatively recombine with the ionospheric electrons leading to a reduction in the total charge density. The transition boundaries between high and low regions of O/N2 as well as TEC can be tracked in the images and the thermospheric winds may be inferred from the motion of the boundaries. The motion of these boundaries during the development of the geomagnetic storm will be discussed.

Sigwarth, John B.↗
NASA NTRS2018

Intense Electric Fields and Electron-Scale Substructure Within Magnetotail Flux Ropes as Revealed by the Magnetospheric Multiscale Mission

Three flux ropes associated with near-Earth magnetotail reconnection are analyzed using Magnetospheric Multiscale observations. The flux ropes are Earthward propagating with sizes from ∼3 to 11 ion inertial lengths. Significantly different axial orientations are observed, suggesting spatiotemporal variability in the reconnection and/or flux rope dynamics. An electron-scale vortex, associated with one of the most intense electric fields (E) in the event, is observed within one of the flux ropes. This E is predominantly perpendicular to the magnetic field (B); the electron vortex is frozen-in with E × B drifting electrons carrying perpendicular current and causing a small-scale magnetic enhancement. The vortex is ∼16 electron gyroradii in size perpendicular to B and potentially elongated parallel to B. The need to decouple the frozen-in vortical motion from the surrounding plasma implies a parallel E at the structure's ends. The formation of frozen-in electron vortices within reconnection-generated flux ropes may have implications for particle acceleration.

Magnetospheric Multiscale↗
NASA NTRS2010

The Role of Kinetic Processes in Magnetospheric Dynamics

The question of whether the micro scale controls the macro scale or vice-versa remains one of the most challenging problems in plasmas. A particular topic of interest within this context is collisionless magnetic reconnection, where both points of views are espoused by different groups of researchers. This presentation will focus on this topic. We will begin by analyzing the global properties of magnetic reconnection. Following that, we discuss properties of electron diffusion region dynamics both for guide field and antiparallel reconnection, and how they can be scaled to different inflow conditions. As a next step, we will study typical temporal variations of the microscopic dynamics with the objective of understanding the potential for secular changes to the macroscopic system. The research will be based on a combination of analytical theory and numerical modeling.

Hesse, Michael↗