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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Photoionization of lithium

The photoionization of lithium from threshold to 50 eV above threshold is calculated using the method of polarized orbitals. The method is applied in as orthodox a manner as possible; this means that total wave functions are constructed as by Temkin and Lamkin (1961) using only the static dipole part of the perturbation of core electrons by the outer part of the external electron. According to other previously given prescriptions, both initial (bound) and final (continuum) wave functions are so polarized, only the length form of the matrix is calculated, and bilinear terms from the polarization contributions are retained (although their effect in this calculation is small). The results themselves are essentially identical to those of a recent diagrammatic calculation of Chang and Poe (1975) (in the region below 5 eV where thay have calculated), and as such they differ in certain significant components from exchange-adiabatic and extended-polarization results of Matese and LaBahn (1969) (although their overall result is similar). The s- and p-wave e-Li(+) phase shifts, which are derived as by-products of this calculation, are also presented and compared with other phase-shift calculations.

Bhatia, A. K.↗
NASA NTRS1995

Consideration of the Martian magnetotail as evidence for an intrinsic magnetic field

It has been suggested by Verigin et al. (1993) that the response of the Martian magnetotail to changes in the solar wind ram pressure indicates the presence of an intrinsic dipole magnetic field. 3-D hybrid particle simulations of Mars were performed including the magnetotail regions. The simulations are in agreement with published Phobos 2 data from the 3 elliptical orbits and reproduce the magnetopause diameter dependence on the solar wind ram pressure reported by Verigin et al. (1993). However, the simulations were performed with no intrinsic field present, indicating that the dependence of the magnetotail width on ram pressure, is not a discriminator for the presence of the intrinsic field.

Brecht, Stephen H.↗
DOE OSTI2021

Non-Loudon-Fleury Raman scattering in spin-orbit coupled Mott insulators

In this work we revisit the theory of magnetic Raman scattering in Mott insulators with strong spin-orbit coupling, with a major focus on Kitaev materials. We show that Kitaev materials with bond-anisotropic interactions are generally expected to show both one- and two-magnon responses. It is further shown that, in order to obtain the correct leading contributions to the Raman vertex operator R, one must take into account the precise, photon-assisted microscopic hopping processes of the electrons and that, in systems with multiple hopping paths, R contains terms beyond those appearing in the traditional Loudon-Fleury theory. Most saliently, a numerical implementation of the revised formalism to the case of the three-dimensional hyperhoneycomb Kitaev material β– Li 2 Ir O 3 reveals that the non-Loudon-Fleury scattering terms actually dominate the Raman intensity. In addition, they induce a qualitative modification of the polarization dependence, including, e.g., the emergence of a sharp one-magnon peak at low energies, which is not expected in the traditional Loudon-Fleury theory. This peak is shown to arise from microscopic photon-assisted tunneling processes that are of similar type with the ones leading to the symmetric off-diagonal interaction Γ (known to be present in many Kitaev materials), but take the form of a bond-directional magnetic dipole term in the Raman vertex. These results are expected to apply across all Kitaev materials and mark a drastic change of paradigm for the understanding of Raman scattering in materials with strong spin-orbit coupling and multiple exchange paths.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1973

Electromagnetic evidence concerning the lunar interior and its evolution

Reviews of the evidence for magnetization of the moon found from discovery of remanence in lunar samples, direct measurements of fields on the surface of the moon, and direct and indirect determination of fields from lunar orbit. It is shown that the evidence implies that the fields are not only local but that regional properties are found though there is still no direct evidence for a global dipole moment. Limits on the detectibility of a global dipole are given and it is shown that the strength of magnetization for reasonable thermal gradients places possible dipole moments just below the threshold of detectibility of current experiments. The hypothesis of plate magnetics is reviewed. Current ideas regarding the source of the background magnetic field presumed responsible for the magnetization are critically considered. These are the dynamo hypothesis and primordial magnetization. Consequences of both are discussed and finally the constraints placed upon the thermal evolution of the moon are considered.

Sonett, C. P.↗
NASA NTRS1993

Theoretical characterization of the reaction CH3 +OH yields CH3OH yeilds products: The (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO channels

The potential energy surface (PES) for the CH3OH system has been characterized for the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels using complete-active-space self-consistent-field (CASSCF) gradient calculations to determine the stationary point geometries and frequencies followed by CASSCF/internally contracted configuration-interaction (CCI) calculations to refine the energetics. The (1)CH2 + H2O channel is found to have no barrier. The long range interaction is dominated by the dipole-dipole term, which orients the respective dipole moments parallel to each other but pointing in opposite directions. At shorter separations there is a dative bond structure in which a water lone pair donates into the empty a" orbital of CH2. Subsequent insertion of CH2 into an OH bond of water have barriers located at -5.2 kcal/mol and 1.7 kcal/mol, respectively, with respect to CH3 + OH. From comparison of the computed energetics of the reactants and products to known thermochemical data it is estimated that the computed PES is accurate to plus or minus 2 kcal/mol.

Walch, Stephen P.↗
NASA NTRS1993

Theoretical characterization of the reaction CH3 + OH yields CH3OH yields products - The (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO channels

The potential energy surface (PES) for the CH3OH system has been characterized for the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels using complete-active-space self-consistent-field (CASSCF) gradient calculations to determine the stationary point geometries and frequencies followed by CASSCF/internally contracted configuration-interaction (CCI) calculations to refine the energetics. The (1)CH2 + H2O channel is found to have no barrier. The long range interaction is dominated by the dipole-dipole term, which orients the respective dipole moments parallel to each other but pointing in opposite directions. At shorter separations there is a dative bond structure in which a water lone pair donates into the empty 'a' orbital of CH2. Subsequent insertion of CH2 into an OH bond of water have barriers located at -5.2 kcal/mol and 1.7 kcal/mol, respectively, with respect to CH3 + OH. From comparison of the computed energetics of the reactants and products to known thermochemical data it is estimated that the computed PES is accurate to plus or minus 2 kcal/mol.

Walch, Stephen P.↗
DOE OSTI2021

Strong-field physics in three-dimensional topological insulators

We investigate theoretically the strong-field regime of light-matter interactions in the topological-insulator class of quantum materials. In particular, we focus on the process of nonperturbative high-order harmonic generation from the paradigmatic three-dimensional topological insulator bismuth selenide (Bi 2 Se 3 ) subjected to intense midinfrared laser fields. We analyze the contributions from the spin-orbit-coupled bulk states and the topological surface bands separately and reveal a major difference in how their harmonic yields depend on the ellipticity of the laser field. Furthermore, bulk harmonics show a monotonic decrease in their yield as the ellipticity increases, in a manner reminiscent of high harmonic generation in gaseous media. However, the surface contribution exhibits a highly nontrivial dependence, culminating with a maximum for circularly polarized fields. We attribute the observed anomalous behavior to (i) the enhanced amplitude and the circular pattern of the interband dipole and the Berry connections in the vicinity of the Dirac point and (ii) the influence of the higher-order, hexagonal warping terms in the Hamiltonian, which are responsible for the hexagonal deformation of the energy surface at higher momenta. The latter are associated directly with spin-orbit-coupling parameters. Our results thus establish the sensitivity of strong-field-driven high harmonic emission to the topology of the band structure as well as to the manifestations of spin-orbit interaction.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1983

Geomagnetic excursions and climate change

Rampino argues that although Kent (1982) demonstrated that the intensity of natural remanent magnetism (NRM) in deep-sea sediments is sensitive to changes in sediment type, and hence is not an accurate indicator of the true strength of the geomagnetic field, it does not offer an alternative explanation for the proposed connections between excursions, climate, and orbital parameters. Kent replies by illustrating some of the problems associated with geomagnetic excursions by considering the record of proposed excursions in a single critical core. The large departure from an axial dipole field direction seen in a part of the sample is probably due to a distorted record; the drawing and storage of the sample, which is described, could easily have led to disturbance and distortion of the record.

Rampino, M. R.↗
NASA NTRS1989

The COBE cosmic 3 K anisotropy experiment: A gravity wave and cosmic string probe

Among the experiments to be carried into orbit next year, by the COBE satellite, are differential microwave radiometers. They will make sensitive all-sky maps of the temperature of the cosmic microwave background radiation at three frequencies, giving dipole, quadrupole, and higher order multipole measurements of the background radiation. The experiment will either detect, or place significant constraints on, the existence of cosmic strings and long wavelength gravity waves.

Bennett, Charles L.↗
NASA NTRS1995

On the injection of fine dust from the Jovian magnetosphere

Using a simple aligned dipole model of the Jovian magnetic field, and exploiting integrals of the gravito-electrodynamic equation of motion of charged dust, we obtain an analytic result which characterizes the nature of the orbits of grains of different (fixed) charge-to-mass ratios launched at different velocities from different radial distances from Jupiter. This enables us to consider various possible sources of the dust-streams emanating from Jupiter which have been observed by the Ulysses spacecraft. We conclude that Jupiter's volcanically active satellite Io is the likely source, in agreement with the earlier calculations and simulations of Horanyi et al. using a detailed three-dimensional model of the Jovian magnetosphere. Our estimates of the size range and the velocity range of these dust grains are also in good agreement with those of the above authors and are within the error bars of the observations.

Maravilla, D.↗
NASA NTRS1980

Saturn's magnetosphere, rings, and inner satellites

The discovery of the Saturn magnetosphere and its characterization by Pioneer 11 are reported, and findings on the planet's rings and satellites obtained by energetic charged particle measurements within the inner magnetosphere are presented. Bow shock crossings identified by the Pioneer plasma analyzer and magnetometer at distances of 24.1, 23.1 and 20.0 Saturn radii indicate the presence of a magnetosphere with physical dimensions and charged particle populations intermediate between those of the earth and Jupiter, with a scale more similar to that of the earth. Particle angular distributions on the inbound leg of the trajectory are consistent with a dipole magnetic field approximately perpendicular to the planet's equator, while on the outbound leg the distributions indicate the presence of an equatorial current sheet. Charged particle absorption features are detected at the orbits of Dione and Mimas, encompassing the orbits of Tethys and Enceladus, and at 2.534 and 2.343 Saturn radii indicating the presence of satellites of diameters greater than 170 km. Charged particle measurements also confirm the Pioneer division in the rings between 2.292 and 2.336 Saturn radii, a suspected satellite at 2.82 Saturn radii, the presence of the F ring between 2.336 and 2.371 Saturn radii and the outer radius of the A ring at 2.292 Saturn radii.

Van Allen, J. A.↗
NASA NTRS1995

Generation of Venus' nightside ionospheric structure by particle streams from cosmoids

A newly discovered source of energetic particle streams directed at Venus' nightside may cause several exosphere phenomena. The streams evolve from dispersed cosmoids, a surreptitious population of meteoroids in nearly hyperbolic orbits, measured with three dust experiments on Pioneer 10/11. Loose fragile comet-like ensembles of frozen volatile material, they are orders of magnitude more populous than short-period meteoroids. Dispersion is forced near a planet masking the meteor signature at Earth, but recently terrestrial exosphere interactions have been detected principally from VLF radar returns and as suddenly formed layers of neutral sodium and iron probed by lidar. Venus influx is estimated greater than 10(exp -14)(g)/((sq cm)(s)) with nightside directed kinetic power of greater than 0.3 (erg)/((sq cm)s)). Compared to Earth, Venus, lacking a dipole field with almost no rotation, has a readily recognized set of nightside interaction signatures of these downward energetic particle streams: i.e., density depressions of the neutral thermosphere, hydrogen and helium bulges, a non-disappearing ionosphere, electron holes, nightglows, VLF bursty signals, and local magnetic fields. From Pioneer Venus Orbiter (PVO) measurements, the cosmoid population, its temporal and solar azimuthal variation may be determined.

Dubin, M.↗
DOE OSTI2020

Pseudospin versus magnetic dipole moment ordering in the isosceles triangular lattice material K 3 Er(VO 4 ) 2

Spin- 1 / 2 antiferromagnetic triangular lattice models are paradigms of geometrical frustration, revealing very different ground states and quantum effects depending on the nature of anisotropies in the model. Due to strong spin orbit coupling and crystal field effects, rare-earth ions can form pseudospin- 1 / 2 magnetic moments with anisotropic single-ion and exchange properties. Thus, rare-earth-based triangular lattices enable the exploration of this interplay between frustration and anisotropy. Here we study one such case, the rare-earth double vanadate glaserite material K 3 Er ( VO 4 ) 2 , which is a quasi-two-dimensional (2D) isosceles triangular antiferromagnet. Our specific heat and neutron powder diffraction data from K 3 Er ( VO 4 ) 2 reveal a transition to long range magnetic order at T N = 155 ± 5 mK which accounts for all R ln 2 entropy. Furthermore, we observe what appears to be a coexistence of three-dimensional (3D) and quasi-2D order below T N . The quasi-2D order leads to an anisotropic Warren-like peak profile for ( h k 0 ) reflections, while the 3D order is best-described by layers of antiferromagnetic b -aligned moments alternating with layers of zero moment. Our magnetic susceptibility data reveal that Er 3 + takes on a strong X Y single-ion anisotropy in K 3 Er ( VO 4 ) 2 , leading to vanishing moments when pseudospins are oriented along c . Thus, the magnetic structure, when considered from the pseudospin point of view could comprise of alternating layers of b -axis and c -axis aligned antiferromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Orbital angular momentum at small $x$ revisited

We revisit the problem of the small Bjorken-x asymptotics of the quark and gluon orbital angular momentum (OAM) distributions in the proton utilizing the revised small-x helicity evolution derived recently in [1]. We relate the quark and gluon OAM distributions at small x to the polarized dipole amplitudes and their (first) impact-parameter moments. To obtain the OAM distributions, we derive novel small-x evolution equations for the impact-parameter moments of the polarized dipole amplitudes in the double-logarithmic approximation (summing powers of α s ln 2 (1/x) with α s the strong coupling constant). We solve these evolution equations numerically and extract the leading large-N c , small-x asymptotics of the quark and gluon OAM distributions, which we determine to be ${L}_{q+\overline{q}}\left(x,{Q}^2\right)\sim {L}_G\left(x,{Q}^2\right)\sim \Delta \Sigma \left(x,{Q}^2\right)\sim \Delta G\left(x,{Q}^2\right)\sim {\left(\frac{1}{2}\right)}^{3.66\sqrt{\frac{\alpha_s{N}_c}{2_π}}}$in agreement with [2] within the precision of our numerical evaluation. (Here N c is the number of quark colors.) We also investigate the ratios of the quark and gluon OAM distributions to their helicity distribution counterparts in the small-x region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1989

Feasibility of using high temperature superconducting magnets and conventional magnetic loop antennas to attract or repel objects at the space station

A study was undertaken to see if magnetic forces can be used at the Space Station to attract or repel spacecrafts such as the Orbital Manuevering Vehicle (OMV) or the Orbiter. A large magnet, in the form of a current loop, is assumed to be placed at the Space Station and another one on the spacecraft. The expression for the force between the two dipoles (loops) is obtained. Using a force of 15 Newtons (3.4 pounds) in order to move the spacecraft, the number of ampere-turn needed in the current loops was calculated at various distances between them. The expression for the force of attraction between a current loop and a soft magnetic material was also examined and the number of amp-turn needed to provide a force of one-tenth of a pound at various distances is also calculated. This one tenth of a pound force would be used in a life line system for the retrieval of an adrift crewman or tool at the Space Station. The feasibility of using conventional antenna on the Station and the incoming vehicle for attraction or repulsion was also examined.

Randhawa, Manjit S.↗
NASA NTRS2002

A Revolution in Mars Topography and Gravity and Magnetic Fields

Since the arrival of the Mars Global Surveyor (MGS) at Mars in September 1997 and the subsequent beginning of observations of the planet there has been a constant stream of surprises and puzzling observations that have kept scientists looking at new 'out of the box' explanations. Observations of the shape and topography have shown a planet with one hemisphere, the southern, several kilometers higher than the north and a northern hemisphere that is so flat and smooth in places that it's difficult to imagine it was not once the bottom of an ocean. And yet the ocean idea presents some enormous difficulties. The measurements of gravity derived from the tracking of MGS have shown that several Mars volcanoes are enormous positive gravity anomalies much larger than we see on Earth and revealed small errors in the orbit of Mars and or Earth. And the magnetic field is found to be composed of a number of extremely large crustal anomalies; but as far as can be ascertained there is no main dipole field such as we have on Earth. Understanding these diverse observations and placing them in the sequence of the evolution of the planet will be a long, challenging but rewarding task.

Smith, David E.↗
NASA NTRS2013

Ionospheric Simulation System for Satellite Observations and Global Assimilative Modeling Experiments (ISOGAME)

ISOGAME is designed and developed to assess quantitatively the impact of new observation systems on the capability of imaging and modeling the ionosphere. With ISOGAME, one can perform observation system simulation experiments (OSSEs). A typical OSSE using ISOGAME would involve: (1) simulating various ionospheric conditions on global scales; (2) simulating ionospheric measurements made from a constellation of low-Earth-orbiters (LEOs), particularly Global Navigation Satellite System (GNSS) radio occultation data, and from ground-based global GNSS networks; (3) conducting ionospheric data assimilation experiments with the Global Assimilative Ionospheric Model (GAIM); and (4) analyzing modeling results with visualization tools. ISOGAME can provide quantitative assessment of the accuracy of assimilative modeling with the interested observation system. Other observation systems besides those based on GNSS are also possible to analyze. The system is composed of a suite of software that combines the GAIM, including a 4D first-principles ionospheric model and data assimilation modules, an Internal Reference Ionosphere (IRI) model that has been developed by international ionospheric research communities, observation simulator, visualization software, and orbit design, simulation, and optimization software. The core GAIM model used in ISOGAME is based on the GAIM++ code (written in C++) that includes a new high-fidelity geomagnetic field representation (multi-dipole). New visualization tools and analysis algorithms for the OSSEs are now part of ISOGAME.

Pi, Xiaoqing↗
NASA NTRS1994

Charged dust in planetary magnetospheres: Hamiltonian dynamics and numerical simulations for highly charged grains

We use a combination of analytical and numerical methods to investigate the dynamics of charged dust grains in planetary magnetospheres. Our emphasis is on obtaining results valid for particles that are not necessarily dominated either by gravitational or electromagnetic forces. A Hamiltonian formulation of the problem yields exact results, for all values of charge-to-mass ratio, when we introduce two constraints: particles remain in the equatorial plane and the magnetic field is taken as axially symmetric. In particular, we obtain locations of equilibrium points, the frequencies of stable periodic orbits, the topology of separatrices in phase space, and the rate of longitudinal drift. These results are significant for specific applications: motion in the nearly aligned dipolar field of Saturn, and the trajectories of arbitrarily charged particles in complex magnetic fields for limited periods of time after ejection from parent bodies. Since the model is restrictive, we also use numerical integrations of the full three-dimensional equations of motion and illustrate under what conditions the constrained problem yields reasonable results. We show that a large fraction of the intermediately charged and highly charged (gyrating) particles will always be lost to a planet's atmosphere within a few hundred hours, for motion through tilted-dipole magnetic fields. We find that grains must have a very high charge-to-mass ratio in order to be mirrored back to the ring plane. Thus, except perhaps at Saturn where the dipole tilt is very small, the likely inhabitants of the dusty ring systems are those particles that are either nearly Keplerian (weakly charged) grains or grains whose charges place them in the lower end of the intermediate charge zone. Fianlly, we demonstrate the effect of plasma drag on the orbits of gyrating particles to be a rapid decrease in gyroradius followed by a slow radial evolution of the guiding center.

Schaffer, L.↗