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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Rapid Rebuilding of the Outer Radiation Belt

Recent observations by the radiation monitor (RDM) on the spacecraft Akebono have shown several cases of greater than 2.5 MeV radiation belt electron enhancements occurring on timescales of less than a few hours. Similar enhancements are also seen in detectors on board the NOAA/POES and TWINS 1 satellites. These intervals are shorter than typical radial diffusion or wave-particle interactions can account for. We choose two so-called "rapid rebuilding" events that occur during high speed streams (4 September 2008 and 22 July 2009) and simulated them with the Space Weather Modeling Framework configured with global magnetosphere, radiation belt, ring current, and ionosphere electrodynamics model. Our simulations produce a weaker and delayed dipolarization as compared to observations, but the associated inductive electric field in the simulations is still strong enough to rapidly transport and accelerate MeV electrons resulting in an energetic electron flux enhancement that is somewhat weaker than is observed. Nevertheless, the calculated flux enhancement and dipolarization is found to be qualitatively consistent with the observations. Taken together, the modeling results and observations support the conclusion that storm-time dipolarization events in the magnetospheric magnetic field result in strong radial transport and energization of radiation belt electrons.

Glocer, A.↗
NASA NTRS2021

Ultraviolet line profiles of slowly rotating massive star winds using the ‘analytic dynamical magnetosphere’ formalism

Recent large-scale spectropolarimetric surveys have established that a small but significant percentage of massive stars host stable, surface dipolar magnetic fields with strengths on the order of kG. These fields channel the dense, radiatively driven stellar wind into circumstellar magnetospheres, whose density and velocity structure can be probed using ultraviolet (UV) spectroscopy of wind-sensitive resonance lines. Coupled with appropriate magnetosphere models, UV spectroscopy provides a valuable way to investigate the wind–field interaction, and can yield quantitative estimates of the wind parameters of magnetic massive stars. We report a systematic investigation of the formation of UV resonance lines in slowly rotating magnetic massive stars with dynamical magnetospheres. We pair the analytic dynamical magnetosphere (ADM) formalism with a simplified radiative transfer technique to produce synthetic UV line profiles. Using a grid of models, we examine the effect of magnetosphere size, the line strength parameter, and the cooling parameter on the structure and modulation of the line profile. We find that magnetic massive stars uniquely exhibit redshifted absorption at most viewing angles and magnetosphere sizes, and that significant changes to the shape and variation of the line profile with varying line strengths can be explained by examining the individual wind components described in the ADM formalism. Finally, we show that the cooling parameter has a negligible effect on the line profiles.

C Erba↗
NASA NTRS2014

Open Boundary Particle-in-Cell Simulation of Dipolarization Front Propagation

First results are presented from an ongoing open boundary 2-1/2D particle-in-cell simulation study of dipolarization front (DF) propagation in Earth's magnetotail. At this stage, this study is focused on the compression, or pileup, region preceding the DF current sheet. We find that the earthward acceleration of the plasma in this region is in general agreement with a recent DF force balance model. A gyrophase bunched reflected ion population at the leading edge of the pileup region is reflected by a normal electric field in the pileup region itself, rather than through an interaction with the current sheet. We discuss plasma wave activity at the leading edge of the pileup region that may be driven by gradients, or by reflected ions, or both; the mode has not been identified. The waves oscillate near but above the ion cyclotron frequency with wavelength several ion inertial lengths. We show that the waves oscillate primarily in the perpendicular magnetic field components, do not propagate along the background magnetic field, are right handed elliptically (close to circularly) polarized, exist in a region of high electron and ion beta, and are stationary in the plasma frame moving earthward. We discuss the possibility that the waves are present in plasma sheet data, but have not, thus far, been discovered.

dipolarization front↗
DOE OSTI2025

Fluorine-free strongly dipolar polymers exhibit tunable ferroelectricity

Current research on ferroelectric polymers centers predominantly on poly(vinylidene fluoride) (PVDF)–based fluoropolymers because of their superior performance. However, they are considered “forever chemicals” with environmental concerns. Here, we describe a family of rationally designed fluorine-free ferroelectric polymers, featuring a polyoxypropylene main chain and disulfonyl alkyl side chains with a C3 spacer: −SO 2 CH 2 CHRCH 2 SO 2 − (R = −H or −CH 3 ). Both experimental and simulation results demonstrate that strong dipole-dipole interactions between neighboring disulfonyl groups induce ferroelectric ordering in the condensed state, which can be tailored by changing the R group: ferroelectric for R = −H or relaxor ferroelectric for R = −CH 3 . At low electric fields, the relaxor polymer exhibits electroactuation and electrocaloric performance comparable with those of state-of-the-art PVDF-based tetrapolymers.

36 MATERIALS SCIENCE↗
NASA NTRS2013

Rovibrational Spectroscopic Constants and Fundamental Vibrational Frequencies for Isotopologues of Cyclic and Bent Singlet HC2N isomers

Through established, highly-accurate ab initio quartic force fields (QFFs), a complete set of fundamental vibrational frequencies, rotational constants, and rovibrational coupling and centrifugal distortion constants have been determined for both the cyclic 1(sup 1) 1A' and bent 2(sup 1)A' DCCN, H(C13)CCN, HC(C-13)N, and HCC(N-15) isotopologues of HCCN. Spectroscopic constants are computed for all isotopologues using second-order vibrational perturbation theory (VPT2), and the fundamental vibrational frequencies are computed with VPT2 and vibrational configuration interaction (VCI) theory. Agreement between VPT2 and VCI results is quite good with the fundamental vibrational frequencies of the bent isomer isotopologues in accord to within a 0.1 to 3.2 / cm range. Similar accuracies are present for the cyclic isomer isotopologues. The data generated here serve as a reference for astronomical observations of these closed-shell, highly-dipolar molecules using new, high-resolution telescopes and as reference for laboratory studies where isotopic labeling may lead to elucidation of the formation mechanism for the known interstellar molecule: X 3A0 HCCN.

molecular data↗
NASA NTRS2017

The Magnetospheric Source Region of the Bright Proton Aurora

The bright proton aurora is generally understood to be the projection of the Central Plasma Sheet where there is sufficient particle energy to cause auroral luminosity and strong pitch angle scattering (presumably due to field line curvature). This region is often interpreted as the transition region between dipolar and tail-like magnetic topologies. The location of auroral features relative to the peak in the proton aurora has been used, for example, to argue that the substorm onset arc lies on field lines that thread this transition region. In this paper, we present statistics of proton aurora luminosity computed from Time History of Events and Macroscale Interactions in Substorms electrostatic analyzer measurements for various radial distances in the magnetotail. These results are compared to ground observations of proton auroral luminosity and used to derive a statistical source region of the bright proton aurora.

Spanswick, E.↗
DOE OSTI2026

Magnon-Magnon Interaction Induced by Dynamic Coupling in a Hybrid Magnonic Crystal

We report a combined experimental and numerical investigation of spin-wave dynamics in a hybrid magnonic crystal consisting of a CoFeB artificial spin ice (ASI) of stadium-shaped nanoelements patterned atop a continuous NiFe film separated by a 5 nm Al 2 O 3 spacer. Using Brillouin light scattering spectroscopy, we probe the frequency dependence of thermal spin waves as functions of applied magnetic field and wavevector, revealing the decisive role of interlayer dipolar coupling in the magnetization dynamics. Micromagnetic simulations complement the experiments, showing a strong interplay between ASI edge modes and backward volume modes in the NiFe film. The contrast in saturation magnetization between CoFeB and NiFe enhances this coupling, leading to a pronounced hybridization manifested as a triplet of peaks in the BLS spectra predicted by simulations and observed experimentally. This magnon−magnon coupling persists over a wide magnetic field range, shaping both the spin-wave dispersion at fixed fields and the full frequency-field response throughout the magnetic hysteresis loop. Our findings establish how ASI geometry can selectively enhance specific spin-wave wavelengths in the underlying film, thereby boosting their amplitude and identifying them as preferential channels for spin wave transmission and manipulation.

Brillouin light scattering spectroscopy↗
DOE OSTI2025

Interstitial Atoms and the Frustrated and Allowed Structural Transitions Principle: Tunability in the Electronic Structure of AuCu 3 ‐type Frameworks in Dy 4 T 1− x Ga 12 (T = Ag, Ir)

In this Article, we explore how the chemical pressure (CP) features of an intermetallic phase may provide opportunities to couple perturbations in electron count with the stabilization of the underlying geometrical structure. AuCu 3 ‐type LnGa 3 (Ln = lanthanide or group 3 metal) phases contain octahedral cavities of negative CP held open by overly compressed Ln–Ga interactions, leading to a series of transition metal‐stuffed derivatives. We present new additions to this family with the synthesis and crystal structures of Dy 4 T 1−x Ga 12 with (T, x) = (Ag, 0.29) and (Ir, 0.15), adopting Y 4 PdGa 12 ‐type superstructures of the AuCu 3 ‐type. density functional Ttheory (DFT)‐CP calculations, when adjusted to avoid dipolar CP features, affirm that T atom incorporation provides a mechanism for the relief of packing tensions, while electronic density of states distributions illustrate that the T atoms serve largely as electron or hole donors to the band structure, as needed for them to attain d 10 configurations. The maximum obtainable value for x may be limited by a mismatch between the Fermi energy and pseudogap, in line with the balance of factors envisioned by the frustrated and allowed structural transitions principle. Furthermore, trends in resistivity measurements on T = Ir, Pd, and Ag compounds are interpretable in terms of the varying degrees of disorder arising from x < 1.0.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1980

Motion of trapped electrons and protons in Saturn's inner magnetosphere

A summary is given of basic formulas for the guiding center motion of energetic charged particles trapped in a dipolar magnetic field. These formulas for longitudinal drift rates, latitudinal bounce periods, equatorial gyroradii, and equatorial gyroperiods are then stated in convenient numerical form for electrons and protons as functions of kinetic energy E, magnetic shell parameter L, and equatorial pitch angle alpha 0 for a slightly simplified model of the observed magnetic field of Saturn. To aid in the study of the interaction of charged particles with the rings and inner satellites of Saturn, additional formulas are given for the time interval between successive encounters of charged particles with a satellite in a circular prograde orbit and for the energy of electrons whose longitudinal angular velocity is resonant, or synchronous, with the Keplerian angular velocity of such a satellite.

Thomsen, M. F.↗
DOE OSTI2024

Deep-Learning Interatomic Potential Connects Molecular Structural Ordering to the Macroscale Properties of Polyacrylonitrile

Polyacrylonitrile (PAN) is an important commercial polymer, bearing atactic stereochemistry resulting from nonselective radical polymerization. As such, an accurate, fundamental understanding of governing interactions among PAN molecular units is indispensable for advancing the design principles of final products at reduced processability costs. While ab initio molecular dynamics (AIMD) simulations can provide the necessary accuracy for treating key interactions in polar polymers, such as dipole–dipole interactions and hydrogen bonding, and analyzing their influence on the molecular orientation, their implementation is limited to small molecules only. Herein, we show that the neural network interatomic potentials (NNIPs) that are trained on the small-scale AIMD data (acquired for oligomers) can be efficiently employed to examine the structures and properties at large scales (polymers). NNIP provides critical insight into intra- and interchain hydrogen-bonding and dipolar correlations and accurately predicts the amorphous bulk PAN structure validated by modeling the experimental X-ray structure factor. Furthermore, the NNIP-predicted PAN properties, such as density and elastic modulus, are in good agreement with their experimental values. Overall, the trend in the elastic modulus is found to correlate strongly with the PAN structural orientations encoded in the Hermans orientation factor. In conclusion, this study enables the ability to predict the structure–property relations for PAN and analogues with sustainable ab initio accuracy across scales.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Particle acceleration by electromagnetic ion cyclotron turbulence

The LF EM-turbulence which furnishes energy for the acceleration of ions in various regions of the earth's magnetosphere efficiently accomplishes its transfer of energy from waves to particles through ion cyclotron resonance (ICR) with the left-hand polarized component of the turbulence; the result of this interaction is a heating of the particle distribution. A general theoretical treatment of ICR heating in a weakly inhomogeneous magnetic geometry is presented, en route to a more detailed examination of auroral ion conics' formation. A substantial simplification of the analysis of the altitude-asymptotic form of the conic distribution is obtained via the similarity transformation introduced into the properties of the electric field spectral density and the earth's dipolar magnetic field.

Crew, G. B.↗
NASA NTRS2010

Recent Developments in the Radiation Belt Environment Model

The fluxes of energetic particles in the radiation belts are found to be strongly controlled by the solar wind conditions. In order to understand and predict the radiation particle intensities, we have developed a physics-based Radiation Belt Environment (RBE) model that considers the influences from the solar wind, ring current and plasmasphere. Recently, an improved calculation of wave-particle interactions has been incorporated. In particular, the model now includes cross diffusion in energy and pitch-angle. We find that the exclusion of cross diffusion could cause significant overestimation of electron flux enhancement during storm recovery. The RBE model is also connected to MHD fields so that the response of the radiation belts to fast variations in the global magnetosphere can be studied.Weare able to reproduce the rapid flux increase during a substorm dipolarization on 4 September 2008. The timing is much shorter than the time scale of wave associated acceleration.

Fok, M.-C.↗
NASA NTRS1996

Comparison of lightning observations from the KSC LDAR system with radar observations from the NCAR CP-2 radar

This grant supported observations of thunderstorms at Kennedy Space Center during the summer of 1995. In particular, we obtained detailed observations of lightning-producing storms over KSC with the CP2 radar of the National Center for Atmospheric Research (NCAR), for the purpose of comparing these with observations from KSC's Lightning Detection and Ranging (LDAR) system. The NCAR radar was a special purpose dual-polarization system for studying the development of precipitation in storms and was at KSC for another project, the Small Cumulus Microphysics Study - SCMS. We used the radar on a non-interference basis to obtain the desired observations. In addition we recorded the electrostatic field change of the lightning discharges at two locations. Subsequent to the field observational period we compared the LDAR lightning observations with the storm structure as indicated by the radar. The results obtained to date are summarized briefly as follows: (1) The initial lightning sequence in a small developing storm was observed to occur in a region of the storm where supercooled raindrops had frozen within the previous few minutes. This is consistent with the idea that the storm electrification is produced by interactions between ice particles. (2) The lightning discharges tended to avoid regions of supercooled liquid raindrops, possibly indicating that corona from the drops reduces any electrification in the vicinity of the drops. (3) 'Bilevel' lightning discharges within storms have been confirmed to be between the level of negative charge at mid-levels in the storm and the upper storm level. This is consistent with and expands upon our understanding that storms have a basic dipolar charge structure. (4) The upward channels of the intracloud lightning discharges are often aligned with shafts of strong precipitation, and often begin just above the upper extent of 40 dBZ reflectivity in the precipitation shaft. This is consistent with a precipitation-based mechanism of electrification.

Krehbiel, Paul↗
DOE OSTI2024

Size matters: altering the metal-surface coordination in micropores via structural confinement effects

Solid-state NMR experiments were used to investigate the dynamics of supported complexes grafted to a series of silica gel materials of varied pore sizes. Through dipolar recoupling measurements, we found that ligand dynamics were impeded in the more confined environments, as would be expected. A new form of motion involving the complex as a whole, however, appeared in the most restricted environment consisting of 22 Å diameter pores. These motions persisted down to –100 °C at which point the ligands were frozen on the NMR timescale. The newly observed dynamics could only result from the breaking of secondary dative metal–siloxane interactions that otherwise lock the complex in a preferred orientation on the surface. Crucially, these results show that confinement effects alone can be sufficient to reduce a grafted metal's effective coordination number in direct analogy to the synthesis of undercoordinated complexes using bulky ligands. Finally, this finding could have important implications in the synthesis of more active heterogeneous catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Does the Coherent Lidar System Corroborate Non-Interaction of Waves (NIW)?

The NIW (non-interaction of waves) property has been proposed by one of the coauthors. The NIW property states that in the absence of any "obstructing" detectors, all the Huygens-Fresnel secondary wavelets will continue to propagate unhindered and without interacting (interfering) with each other. Since a coherent lidar system incorporates complex behaviors of optical components with different polarizations including circular polarization for the transmitted radiation, then the question arises whether the NIW principle accommodate elliptical polarization of light. Elliptical polarization presumes the summation of orthogonally polarized electric field vectors which contradicts the NIW principle. In this paper, we present working of a coherent lidar system using Jones matrix formulation. The Jones matrix elements represent the anisotropic dipolar properties of molecules of optical components. Accordingly, when we use the Jones matrix methodology to analyze the coherent lidar system, we find that the system behavior is congruent with the NIW property.

Prasad, Narasimha S.↗
DOE OSTI2025

Symmetry breaking forms split-off flat bands in quantum oxides controlling metal versus insulator phases

The crystal structure used as input to electronic structure calculation of conventionally bonded solids consists primarily of the standard crystallographic degrees of freedom. Quantum solids sometimes have additional microscopic degrees of freedom (m-DOF) nested within the crystallographic structure. These might include local motifs including positional (Peierls dimers, deformed octahedra, Jahn-Teller distortions), magnetic (local moment configurations) and dipolar (local ferroelectric configurations). Such motifs can be observed experimentally via local probes that avoid averaging, and theoretically as distinct total energy lowering features relative to more simplified “average crystallographic structures”. Here we examine the ability of electronic structure methods independent of strong correlation physics to explain the broad phenomenology of metal-insulator selectivity in quantum oxides by energy-lowering symmetry breaking. We do this by avoiding the restriction of considering only (i) electron-electron interactions in a fixed unresponsive lattice—as done in Mott strong correlation explanations—allowing, however, (ii) local positional and magnetic motifs that coexist within a crystallographic landscape. We find in a broad range of quantum oxides with different symmetry breaking modes the formation of split-off flat bands that can also control metallic versus insulating characteristics. The split-off band effect is common to magnetic and non-magnetic materials, including both binary and ternary oxides. One finds that when such local symmetry breaking motifs are considered in mean-field-like (e.g. density functional theory) electronic structure calculations of quantum oxides, they explain many of the observed trends in metal vs insulator phases discussed otherwise in prior literature via strong correlation in symmetry unbroken view.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Polarization‐Engineered Near‐Field Generation Using a Hybrid Tip–Antenna System

Precise control of light polarization at the nanoscale is critical for accessing chiral optical responses and manipulating spin–photon interactions in advanced materials. Yet, conventional scattering-type near-field probes predominantly generate out-of-plane linear polarization and offer little control over phase or polarization state. Here, in this study, we introduce a polarization-engineered near-field methodology based on a combined metallic tip and planar dipole nanoantenna system. Using full-wave electromagnetic simulations, we show that the tip acts as a vertically oriented plasmonic resonator, while the antenna supports an in-plane dipolar mode. By tuning the tip–antenna geometry and tip height, the two orthogonal field components attain comparable amplitudes and a controllable ∼90° phase offset, producing circularly polarized nano-light in the antenna gap. The proposed system effectively functions as a nanoscale quarter-wave plate, converting linearly polarized illumination into circularly polarized hotspots without external polarization optics. This method establishes an experimentally accessible route toward polarization-programmable near-field nanoscopy, enabling chiral spectroscopy, selective excitation of spin/valley degrees of freedom, and quantum optical investigations at the nanoscale.

36 MATERIALS SCIENCE↗
NASA NTRS1988

A computer model of the earth's magnetosphere

The interaction of the solar wind with the earth magnetosphere is investigated theoretically by means of three-dimensional MHD simulations, with a focus on the effects of changes in the Bz component of the IMF. A high-resolution (0.5 earth radii) version of the model of Ogino et al. (1986) is employed, and the results are presented in a series of computer-generated maps and diagrams and characterized in detail. Bz of -5 nT is found to be associated with dipolar magnetic-field lines near the earth and very concave lines in the magnetotail, while Bz of +5 nT produces a narrow finger of closed field lines extending into the polar cap. Both IMF orientations have sunward convection near the noon-midnight meridian and region-1-type field-aligned currents on both sides of the plasma-sheet extension.

Ogino, Tatsuki↗