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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Quasi-static evolution of force-free magnetic fields and a model for two-ribbon solar flares

It is shown that a two-dimensional force-free field in the solar corona can evolve in a quasi-static manner toward an open configuration, assuming the coronal field is invariant with respect to translations parallel to the x-axis. The theoretical result is applied to the quantitative theory of the evolution of two-ribbon solar flares of Kopp and Pneuman (1976), and the results are discussed. It is concluded that the two-dimensional force is the principal mechanism for the opening of the coronal magnetic field prior to reconnection during a solar flare.

Aly, J. J.↗
NASA NTRS1987

Cosmic ray variations and magnetic field fluctuations in the outer heliosphere

It is formally confirmed that Galactic-cosmic-ray intensity variations measured by Voyager 2 during recovery from solar maximum are caused by traveling compressions and rarefactions in the mean interplanetary magnetic field. Voyager magnetic-field data are used as input to a time-independent, spherically symmetric, cosmic-ray-transport equation in the force-field approximation. The solutions closely followed the count rate of cosmic rays greater than 75 MeV/nucleon over 4 years, during the recovery phase of the 11-year solar-driven cosmic-ray cycle. This strongly supports prior theoretical assertions that turbulent interaction regions traveling with the solar wind are the major cause of the solar-cycle variation of Galactic cosmic rays in the ecliptic region.

Perko, J. S.↗
NASA NTRS1996

Motor function in microgravity: movement in weightlessness

Microgravity provides unique, though experimentally challenging, opportunities to study motor control. A traditional research focus has been the effects of linear acceleration on vestibular responses to angular acceleration. Evidence is accumulating that the high-frequency vestibulo-ocular reflex (VOR) is not affected by transitions from a 1 g linear force field to microgravity (<1 g); however, it appears that the three-dimensional organization of the VOR is dependent on gravitoinertial force levels. Some of the observed effects of microgravity on head and arm movement control appear to depend on the previously undetected inputs of cervical and brachial proprioception, which change almost immediately in response to alterations in background force levels. Recent studies of post-flight disturbances of posture and locomotion are revealing sensorimotor mechanisms that adjust over periods ranging from hours to weeks.

NASA Program Flight↗
NASA NTRS2002

Effects of Structural Deformation and Tube Chirality on Electronic Conductance of Carbon Nanotubes

A combination of large scale classical force-field (UFF), density functional theory (DFT), and tight-binding Green's function transport calculations is used to study the electronic properties of carbon nanotubes under the twist, bending, and atomic force microscope (AFM)-tip deformation. We found that in agreement with experiment a significant change in electronic conductance can be induced by AFM-tip deformation of metallic zigzag tubes and by twist deformation of armchair tubes. The effect is explained in terms of bandstructure change under deformation.

Svizhenko, Alexei↗
NASA NTRS1960

The Motion of a Satellite of the Moon

The motion of a satellite of the Moon depends on the potential field due to the Moon as well as the gravitational effects of the Earth and Sun. If one chooses a frame of reference attached to the Moon, it can be shown that the force field resulting from the Sun can be neglected when compared with the perturbing field of the Moon resulting from its oblateness. The effect of the Earth's field on the satellite is of the some order of magnitude as the Moon's perturbing field and must be included in an analysis of the motion of a satellite of the Moon. We will assume that the distance between Earth and Moon remains constant, and we will consider satellite orbits of small eccentricity. It will be shown that a nearly circular polar orbit will digress less than 1 deg from a polar orbit and that the change in eccentricity is less than a factor of e in one year.

Lass, Harry↗
NASA NTRS1991

A model of the formation of high-salinity shelf water on polar continental shelves

This study presents a model of the flow and salinity fields forced by sea-surface salinity flux and wind stress curl and examines the processes that create High-Salinity Shelf Water (HSSW). To investigate the relative effects of wind stress and buoyancy forcing in HSSW production, the polynya freezing rate in the model is varied from 0.0 to 0.30 m/d, and the Ekman pumping derived from the wind stress curl is varied independently from 0.0 to 1.8 x 10 exp 6 m/s. The Ekman pumping was found to control the magnitude of the circulation, while the polynya freezing rate controlled the extent of salinization in the shelf water. The flux of HSSW increases linearly with increasing Ekman pumping above 0.3 x 10 exp -6 m/s. The modeled flux of HSSW and the flux of derived Botttom Water for the present estimates of the forcings (a peak freezing rate of 0.10 m/d and Ekman pumping of 0.2 x 10 exp -6 m/s) agree with the fluxes inferred from physical and chemical observations in the deep Weddel Sea by oceanographic field programs.

Grumbine, Robert W.↗
NASA NTRS1992

Intensity variations in the interplanetary magnetic field measured by Voyager 2 and the 11-year solar cycle modulation of galactic cosmic rays

New evidence is presented to support the hypothesis that the 11-yr solar cycle modulation of galactic cosmic rays is caused by strong diffusion inside long-lived merged interaction regions. To test this hypothesis, the 1D force-field approximation of the cosmic ray modulation equation is solved. It is assumed that a constant solar wind speed convects magnetic field compressions and rarefactions unchanged through a model heliosphere. The result is a reasonable simulation of the integrated high-energy cosmic ray intensity profile from about 1982 to mid-1989. This period encompasses both the full recovery portion of the last profile from about 1982 to mid-1989. This model responds to the Voyager 2 magnetic field data by correctly timing the beginning of the new modulation cycle in late 1987. It is concluded that the present hypothesis is consistent with the results of this simulation.

Perko, J. S.↗
DOE OSTI2025

Efficient calculation of self magnetic field, self-force, and self-inductance for electromagnetic coils with rectangular cross-section

Abstract For designing high-field electromagnets, the Lorentz force on coils needs to be computed in order to design suitable support structures, and the inductance should be computed to evaluate the stored energy and dynamics. Also, the magnetic field and its variation inside the conductor is of interest for computing stress and strain, and due to superconducting quench limits. For these force, inductance, energy, and internal field calculations, the coils cannot be naively approximated as infinitesimally thin filaments due to divergences when the source and evaluation points coincide, so more computationally demanding calculations are usually required, resolving the finite cross-section of the conductors. Here, we present a new alternative method that enables the internal magnetic field vector, self-force, and self-inductance to be computed rapidly and accurately within a 1D filament model. The method is applicable to coils for which the curve center-line can have general noncircular shape, as long as the conductor width is small compared to the radius of curvature. This paper extends a previous calculation for circular-cross-section conductors (Hurwitz et al 2024 IEEE Trans. Magn. ) to consider the case of rectangular cross-section. The reduced model is derived by rigorous analysis of the singularity, regularizing the filament integrals such that they match the true high-dimensional integrals at high coil aspect ratio. The new filament model exactly recovers analytic results for a circular coil, and is shown to accurately reproduce full finite-cross-section calculations for a non-planar coil of a stellarator magnetic fusion device. Due to the efficiency of the model here, it is well suited for use inside design optimization.

Landreman, Matt (ORCID:000000027233577X)↗
NASA NTRS1984

On some properties of force-free magnetic fields in infinite regions of space

Techniques for solving boundary value problems (BVP) for a force free magnetic field (FFF) in infinite space are presented. A priori inequalities are defined which must be satisfied by the force-free equations. It is shown that upper bounds may be calculated for the magnetic energy of the region provided the value of the magnetic normal component at the boundary of the region can be shown to decay sufficiently fast at infinity. The results are employed to prove a nonexistence theorem for the BVP for the FFF in the spatial region. The implications of the theory for modeling the origins of solar flares are discussed.

Aly, J. J.↗
NASA NTRS1989

Nucleation in the presence of long-range interactions

Unlike droplet nucleation near a liquid-gas critical point, the decay of metastable phases in crystalline materials is strongly affected by the presence of long-range forces. Field quench experiments performed on the ferroelectric barium titanate indicate that nucleation in this material is markedly different from that observed in liquids. In this paper, a theory for nucleation at a first-order phase transition in which the mediating forces are long range is presented. It is found that the long-range force induces cooperative nucleation and growth processes, and that this feedback mechanism produces a well-defined delay time with a sharp onset in the transformation to the stable phase. Closed-form expressions for the characteristic onset time and width of the transition are developed, in good agreement with numerical and experimental results.

Chandra, P.↗
DOE OSTI2026

Phase instability-coupled fracture behavior in garnet LLZO solid electrolytes: a machine learning-enabled atomistic study

Fracture in the garnet-type solid electrolyte Li 7 La 3 Zr 2 O 12 (LLZO) poses a critical threat to both the performance and safety of solid-state batteries. To unravel the coupled chemomechanical processes that govern fracture in LLZO under external loading, we carry out large-scale molecular-dynamics simulations with a validated machine-learning force field. Our results demonstrate that triaxial stresses at crack flanks trigger a localized cubic-to-tetragonal phase transformation, which is accompanied by Li-ion rearrangement. The emergent tetragonal domains feature lattice contraction normal to the fracture plane, imposing coherent misfit strains that provide an additional driving force for further crack propagation. Crucially, introducing Li deficiencies stabilizes the cubic phase, postponing the phase transition and thereby delaying fracture initiation. These findings highlight the role of intrinsic phase instability in dictating LLZO's fracture resistance and its critical connection to local Li concentration. This chemomechanical coupling points toward targeted strategies to enhance the mechanical robustness of garnet electrolytes, including tuning Li content, ensuring dopant homogeneity, and refining processing protocols.

Materials science↗
DOE OSTI2025

3D Continuous Forcing Dataset from 3D Constrained Variational Analysis at SGP

The continuous 3D large-scale forcing (VARANAL3D) data set derived from 3D constrained variational analysis (3DCVA) extends the conventional constrained variational analysis method by incorporating multiple sub-columns within the analysis domain. This advancement introduces spatial variability into the large-scale forcing fields, thereby enriching the data set’s applicability. The VARANAL3D data set spans from 2004 to 2018 and covers a region of 5˚×4.5˚ domain around the ARM SGP site. The analysis domain is divided into 10×9 sub-columns with 0.5˚ resolution. The 3D large-scale forcing data provides necessary variables to drive and evaluate single-column models (SCM), cloud-resolving models (CRM) ,and large-eddy simulations (LES), as well as information for testing model sensitivity to spatial variability of the large-scale forcing data, facilitating more rigorous testing and refinement of physical processes in SCM/CRM/LES.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Systematic softening in universal machine learning interatomic potentials

Machine learning interatomic potentials (MLIPs) have introduced a new paradigm for atomic simulations. Recent advancements have led to universal MLIPs (uMLIPs) that are pre-trained on diverse datasets, providing opportunities for universal force fields and foundational machine learning models. However, their performance in extrapolating to out-of-distribution complex atomic environments remains unclear. In this study, we highlight a consistent potential energy surface (PES) softening effect in three uMLIPs: M3GNet, CHGNet, and MACE-MP-0, which is characterized by energy and force underprediction in atomic-modeling benchmarks including surfaces, defects, solid-solution energetics, ion migration barriers, phonon vibration modes, and general high-energy states. The PES softening behavior originates primarily from the systematically underpredicted PES curvature, which derives from the biased sampling of near-equilibrium atomic arrangements in uMLIP pre-training datasets. Our findings suggest that a considerable fraction of uMLIP errors are highly systematic, and can therefore be efficiently corrected. We argue for the importance of a comprehensive materials dataset with improved PES sampling for next-generation foundational MLIPs.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Viscosity of Xenon Examined in Microgravity

Why does water flow faster than honey? The short answer, that honey has a greater viscosity, merely rephrases the question. The fundamental answer is that viscosity originates in the interactions between a fluid s molecules. These interactions are so complicated that, except for low-density gases, the viscosity of a fluid cannot be accurately predicted. Progress in understanding viscosity has been made by studying moderately dense gases and, more recently, fluids near the critical point. Modern theories predict a universal behavior for all pure fluids near the liquid-vapor critical point, and they relate the increase in viscosity to spontaneous fluctuations in density near this point. The Critical Viscosity of Xenon (CVX) experiment tested these theories with unprecedented precision when it flew aboard the Space Shuttle Discovery (STS-85) in August 1997. Near the critical point, xenon is a billion times more compressible than water, yet it has about the same density. Because the fluid is so "soft," it collapses under its own weight when exposed to the force of Earth s gravity - much like a very soft spring. Because the CVX experiment is conducted in microgravity, it achieves a very uniform fluid density even very close to the critical point. At the heart of the CVX experiment is a novel viscometer built around a small nickel screen. An oscillating electric field forces the screen to oscillate between pairs of electrodes. Viscosity, which dampens the oscillations, can be calculated by measuring the screen motion and the force applied to the screen. So that the fluid s delicate state near the critical point will not be disrupted, the screen oscillations are set to be both slow and small.

Zimmerli, Gregory A.↗
NASA NTRS2004

Modeling the interaction Between Ethylene Diamine and Water Films on the Surface of a Carbon Nanotube

It has been observed that a carbon nanotube (CNT) AFM tip coated with ethylene diamine (EDA) penetrates the liquid water-air interface more easily than an uncoated nanotube tip. The EDA coating remains intact through repeated cycles of dipping and removal. In order to understand the physical basis for this observation, we use ab initio quantum chemistry calculations to study the EDA-CNT-water interaction and to parameterize a force field describing this system. Molecular dynamics (MD) simulations are carried out for EDA-water mixtures and an EDA-coated carbon nanotube immmed in water. These simulations are similar to our earlier MD study that characterized the CNT-water interface. The attractive CNT-EDA and CNT-water interactions arise primarily from van der Waals forces, and the EDA-EDA, EDA-water and water-water interactions are mainly due to hydrogen bond formation. The binding energ of single EDA molecule to the nanotube is nearly three times larger than the corresponding value found for water (4.3 versus 1.5 kcal mol, respectively). The EDA molecules readily stick to and diffuse along the CNT surface. As a resulf mixing of the EDA and water films does not occur on the timescale of the MD simulations. The EDA film reduces the hydrophobicity of the nanotube surface and acts like a prototypical surfactant in stabilizing the suspension of carbon nanotubes in water. For this presentation, we use the MD simulations to determine how the presence of the carbon nanotube surface perturbs the properties of EDA-water mixtures.

Jaffe, Richard L.↗
NASA NTRS1993

Gravity as a probe for understanding pattern specification

Amphibian eggs from Xenopus laevis were employed as a model system. Xenopus embryos were demonstrated to be sensitive to novel force fields. Under clinostat-simulated weightlessness the location of the third cleavage furrow was shifted towards the equator; the dorsal lip was shifted closer to the vegetal pole; and head and eye dimensions of hatching tadpoles were enlarged. Effects of centrifuge-simulated hypergravity were the opposite of those of simulated weightlessness. Those morphological alterations had their own force-sensitive period, and a substantial spawning-to-spawning variation in sensitivity was observed. Despite those dramatic differences in embryogenesis, tadpoles at the feeding stage were largely indistinguishable from controls.

Malacinski, George M.↗
NASA NTRS1985

Influence of rotation and pretwist on cantilever fan blade flutter

The fundamental and lowest frequency natural modes in a cantilever fan blade exhibit significant amounts of flexure and torsion coupled by pretwist and operation in a rotational force field. Consequently the flutter estimation of such blades requires an accurate structural description that incorporates these two effects, amongst others. A beam-type finite element model is used in this study with up to six spanwise elements, each element being pretwisted. Coalescence-type flutter is found with subsonic aerodynamics. Evidence of the aerodynamic resonance phenomenon is exhibited and the importance of including radially varying aerodynamic forces is brought out.

Sisto, F.↗