A note on Lambert's theorem
Lambert theorem application to particle motion in gravitational central force field
GRAVITATIONAL FIELD↗
SEARCH · Search NASA
Results for “FORCE FIELD”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A constant-alpha force-free-field analysis of the active region AR 4711 of February, 1986
The theory of Yang et al. (1983) is used to analyze the large active region AR 4711 of Feb. 1986. This region stored between 0.01 x 10 to the 32nd and 5.36 x 10 to the 32nd erg of extractable free magnetic energy, sufficient to supply the energies of the observed flare activities in this region. The region was an energetic quadrupolar sunspot group, occurring during solar minimum; this group was strongly twisted and produced many intense flares.
Yang, Hai-Shou↗
Erratum: “Abrupt Changes in the Photospheric Magnetic Field, Lorentz Force, and Magnetic Shear during 15 X-class Flares” (2019, ApJS, 240, 11)
Explore the source record for details and available documents.
Gordon J. D. Petrie↗
Galactic cosmic ray modulation from 1965-1970.
Numerical solutions of the cosmic-ray equation of transport within the solar cavity and including the effects of diffusion, convection, and energy losses due to adiabatic deceleration, have been used to reproduce the modulation of galactic electrons, protons, and helium nuclei observed during the period from 1965 to 1970. Kinetic energies between 10 and 10,000 MeV/nucleon are considered. Computed and observed spectra are given for the years 1965, 1968, 1969, and 1970 together with the diffusion coefficients. These diffusion coefficients are assumed to be of separable form in rigidity and radial dependence, and are consistent with the available magnetic-field power spectra. The force-field solutions are given for these diffusion coefficients and galactic spectra and are compared with the numerical solutions. It is shown that the energy losses and convection lead to near-earth nuclei spectra at kinetic energies less than or equal to 100 MeV/nucleon in which the differential intensity is proportional to the kinetic energy with little dependence on the form of the galactic spectrum. This dependence is in agreement with the observed spectra of all species of atomic nuclei and it is argued that this provides strong observational evidence for the presence of energy losses in the propagation process, and for the exclusion of low-energy galactic nuclei from near earth.
Urch, I. H.↗
Simulation of the fluctuating field of a forced jet
The fluctuating field of a jet excited by transient mass injection is simulated numerically. The model is developed by expanding the state vector as a mean state plus a fluctuating state. Nonlinear terms are not neglected and the effect of nonlinearity is studied. The results show a significant spectral broadening in the flow field due to the nonlinearity. In addition, large scale structures are broken down into smaller scales.
Bayliss, A.↗
Simulation of the fluctuating field of a forced jet
The fluctuating field of a jet excited by transient mass injection is simulated numerically. The model is developed by expanding the state vector as a mean state plus a fluctuating state. Nonlinear terms are not neglected and the effect of nonlinearity is studied. The results show a significant spectral broadening in the flow field due to the nonlinearity. In addition, large scale structures are broken down into small scales. Previously announced in STAR as N82-34191
Bayliss, A.↗
Electromagnetic forces on space structures
Axial and tensile stresses on conducting loop structures either isolated or in presence of other electromagnetic force fields
ELECTRIC CONDUCTOR↗
Evolving force-free magnetic fields. III - States of nonequilibrium and the preflare stage
The paper considers whether a neighboring magnetostatic equilibrium exists to allow a magnetic field initially in a force-free configuration to accommodate any imposed weak pressure. The following problem is treated. The foot points of the field are fixed and the plasma is frozen into the field lines under the approximation of infinite electrical conductivity. A weak pressure is introduced. It is determined infinitesimal plasma displacements exist to adjust the field lines to a new equilibrium without changing the field line connectivity. The analysis is carried out for the bipolar force-free fields forming one of two evolutionary sequences modeling the development of the preflare stage. It was found that for the force-free field corresponding to the quasi-static stage of evolution, the neighboring magnetostatic equilibrium always exists and the imposed gas pressure can be accommodated with a slight departure of the field from being exactly force free.
Low, B. C.↗
The precession and nutation of deformable bodies. II - The form of distorted configurations
Derivation of explicit equations governing deformations of self-gravitating viscous bodies in external force field for application to physical librations of moon
NUTATIONAL OSCILLATION↗
Response of gravity level fluctuations on the Gravity Probe-B Spacecraft propellant system
The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled fluids in a rotating dewar under microgravity environment have been investigated. Results show that there is a group of wave trains, both in longitudinal and transverse modes, with various frequencies and wavelengths of slosh waves generated by the restoring force field of gravity jitters and centrifugal forces in this study. The longest wave periods of slosh waves, either the longitudinal or transverse modes, are responsible for the production of wave modes with highest ratio of maximum wave amplitude to wavelength. Also, the lower frequency slosh waves are the wave modes with higher wave energy than that of the higher frequency slosh waves.
Hung, R. J.↗
Slosh wave excitation in gravity Probe-B spacecraft experiment
The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled fluids in a rotating dewar under microgravity environment have been investigated. Results show that there is a group of wave trains, both in longitudinal and transverse modes, with various frequencies and wavelengths of slosh waves generated by the restoring force field of gravity jitters and centrifugal forces in this study.
Hung, R. J.↗
The role of global cloud climatologies in validating numerical models
Global maps of the monthly mean net upward longwave radiation flux at the ocean surface were obtained for April, July, October 1985 and January 1986. These maps were produced by blending information obtained from a combination of general circulation model cloud radiative forcing fields, the top of the atmosphere cloud radiative forcing from ERBE and TOVS profiles and sea surface temperature on ISCCP C1 tapes. The fields are compatible with known meteorological regimes of atmospheric water vapor content and cloudiness. There is a vast area of high net upward longwave radiation flux (greater than 80/sq Wm) in the eastern Pacific Ocean throughout most of the year. Areas of low net upward longwave radiation flux ((less than 40/sq Wm) are the tropical convective regions and extra tropical regions that tend to have persistent low cloud cover.The technique used relies on General Circulation Model simulations and so is subject to some of the uncertainties associated with the model. However, all input information regarding temperature, moisture, and cloud cover is from satellite data having near global coverage. This feature of the procedure alone warrants its consideration for further use in compiling global maps of longwave radiation.
HARSHVARDHAN↗
Applications of Nickelate perovskites for neuromorphic computing from electronic structure and Machine Learning
While the limit of Moore's law is presently being reached with current microelectronic technologies, we need to develop new paradigms that overcome this limitation. In that respect, neuromorphic computing is a concept that emulates the neural behavior and response of the human brain, and it has been recognized as a promising alternative approach. In this research project, we will perform multi-fidelity scale bridging to explore the potential use of materials with metal to insulator transition for neuromorphic applications. In particular, rare earth nickelates are promising for such purposes, as the transition in these materials is quite sensitive to a broad set of different external stimuli. Our multi-fidelity approach will bridge the high-fidelity electronic structure calculations with classical potentials. We will bridge dynamical mean field theory with a classical atomistic representation via a deep learning force field. The neural network is trained with energies, charges, and forces obtained by accurate electronic structure theories based on Dynamical Mean Field Theory. The configurational space is generated from known crystal phases, ab initio molecular dynamics with exchange-correlation functionals corrected with the Hubbard model, disordered phases with different concentrations of oxygen vacancies, and nonsymmetrical positions and induced strain by grain interfaces or contact with a substrate. Strategies to train the model with a reduced number of training examples are obtained from active learning methods, and new structures for improving the learning process are generated by using machine learning autoencoders. This classical potential will be validated through a diversity of electronic structure methods and represents an important step to combine the flexibility and accuracy of first-principles with the speed of classical potentials. The generated multi-fidelity surrogate model will be used to understand the role of strain, oxygen vacancies, proton doping, the variation of the crystal phase, substrate effects, vibrational effects as the octahedral rotation, grain boundaries and defect effects on the response of a Metal to Insulator Transition (MIT) in correlated materials. Long time and large-scale simulations will help understand the role of different stimuli to control the hysteresis of the MIT, as it has been experimentally suggested. Selected configurations will be analyzed with higher-level theories to provide an accurate electronic description and to study how the orbitals and charges are rearranged under different conditions.
36 MATERIALS SCIENCE↗
Hierarchical Reinforcement Learning of a Short-Range Bond-Order Potential for Silica: Analytic Embedding of Coordination with Classical Efficiency
Reinforcement learning (RL) has recently emerged as a data-efficient strategy to parametrize short-range interatomic potentials. Building on our past RL optimization of pairwise silica models, we extend the framework to a bond-order (Tersoff-type) potential that provides an analytic embedding of local coordination through a three-body term. A hierarchical RL workflow combining continuous-action Monte Carlo Tree Search and property-based rewards efficiently explores the 26-dimensional parameter space, sequentially optimizing lattice parameters, densities, angles, and cohesive energies of 21 silica polymorphs. The resulting models, Q-Tersoff and ML-Tersoff, reproduce the energetic ordering of low-energy phases and capture the angular correlations and amorphous structure factors of silica with improved fidelity over pairwise force fields, while remaining orders of magnitude faster than high-dimensional machine-learned potentials. Both models underperform for elastic constants and high-energy frameworks, delineating the limits of the current analytic form. The approach establishes a general and interpretable route to angle-aware, short-range potentials that bridge physics-based and machine-learned descriptions of silicate materials.
36 MATERIALS SCIENCE↗
Anharmonic Rovibrational Calculations of Singlet Cyclic C4 Using a New Ab Initio Potential and a Quartic Force
We report a CCSD(T)/cc-pCV5Z quartic force field (QFF) and a semi-global CCSD(T)-F12b/aug-cc-pVTZ potential energy surface (PES) for singlet, cyclic C4. Vibrational fundamentals, combinations and overtones are obtained using vibrational second-order perturbation theory (VPT2) and the vibrational configurationinteraction (VCI) approach. Agreement is within 10 cm(exp −1) between the VCI calculated fundamentals on the QFF and PES using the MULTIMODE (MM) program, and VPT2 and VCI results agree for the fundamentals. The agreement between VPT2- QFF and MM-QFF results is also good for the C4 combinations and overtones. The J = 1 and J = 2 rovibrational energies are reported from both VCI (MM) on the PES and VPT2 on the QFF calculations. The spectroscopic constants of (12)C4 and two C(sub 2v)-symmetry, single (13)C-substituted isotopologues are presented, which may help identification of cyclic C4 in future experimental analyses or astronomical observations.
quartic force field↗
Nonlinear force-free magnetic fields: Calculation and applicatin to astrophysics
The problem concerned in this work is that of calculating magnetic field configurations in which the Lorentz force (vector)j x (vector)B is everywhere zero, subject to specified boundary conditions. The magnetic field is represented in terms of Clebsch variables in the form (vector)B = del alpha x del beta. These variables are constant on any field line. The most appropriate choice of boundary conditions is to specify the values of alpha and beta on the bounding surface. It is proposed that the field lines move in the direction of local Lorentz force and relax towards a force-free field configuration. This concept leads to an iteration procedure for modifying the variables alpha and beta that tends asymptotically towards the force-free state. This method is first applied to a simple problem in two rectangular dimensions; the calculation shows that the convergence of magnetic field energy to a minimum state (force-free) is close to exponential. This method is then applied to study some astrophysical force-free magnetic fields, such as the structures and evolution of magnetic fields of rotating sunspots and accretion disks. The implication of the results, as related to the mechanisms of solar flares, extragalactic radio sources and radio jets, are discussed.
Yang, Wei-Hong↗
Excited Vibrational Level Rotational Constants for SiC2: A Sensitive Molecular Diagnostic for Astrophysical Conditions
Silacyclopropynylidene, SiC2, is a known and highly abundant circumstellar molecule. Its spectrum has been established as a major component of lines observed toward the carbon-rich star IRC +10216 (CW Leonis). It has been detected in its low-lying v(sub 3) = 1 and 2 vibrational states as well as in various isotopic compositions. Increasing sensitivity and spatial resolution will enable many more emission or absorption lines to be detected. In order to detect new molecular species, unassigned lines of known species must be identified. This work uses established ab initio quartic force fields to produce data necessary for this classification of lines related to SiC2. Agreement between the theoretical vibrational frequencies and known rotational and spectroscopic constants is quite good, as good as 5 cm(exp -1) and 3 MHz, respectively in some cases. Additionally, experimentally unknown vibrational frequencies and rotational constants are provided for the first overtones and combination bands in addition to 3(sub v3), the second overtone of the low-lying antisymmetric stretch/carbide rotation mode. Frequencies of v(sub 3) = 3 low-J rotational transitions of the main isotopic species are also estimated from published data for v(sub 3) ≤ 2. Further, we determine rotational and centrifugal distortion parameters for which in most cases vibrational effects due to the v(sub 3) mode were reduced to first, and in several cases also to second order. These values may approximate equilibrium values better than the ground state values. The data produced herein will aid in the experimental and observational characterization of this known astromolecule in order to identify some of the unassigned lines for a known entity.
Astrochemistry↗
Mechanisms and stability of Li dynamics in amorphous Li-Ti-P-S-based mixed ionic–electronic conductors: A machine learning molecular dynamics study
Mixed ionic–electronic conductors (MIECs) exhibit both high ionic and electronic conductivity to improve the battery performance. In this work, we investigate the mechanism and stability of transport channels in our recently developed MIEC material, amorphous Ti-doped lithium phosphorus sulfide (LPS), using molecular dynamics (MD) simulations with a 99% accurate machine-learning force field (MLFF) trained on ab initio MD data. The achieved MLFF helps efficient large-scale MD simulations on LPS with three Ti concentrations (10%, 20%, and 30%) and six temperatures (25°C to 225°C) to calculate ionic conductivity, activation energy, Li-ion transport mechanism, and configurational entropy. Results show that ionic conductivities and activation energies are consistent with our recent experimental values. Moreover, Li-ion transport occurs via free-volume diffusion facilitated by the formation of disordered Li-S polyhedra. The enhanced stability of transport channels at 10% and 20% Ti doping, compared to 0% and 30%, is observed by analyzing the vibrational and configurational entropy of these disordered Li-S polyhedra. Overall, this study highlights the utility of MLFF-based large-scale MD simulations in explaining the transport mechanism and the stability of Li-ion in Ti-doped LPS electrolyte with significant computational efficiency.
And configuration entropy↗