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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Study of ball bearing torque under elastohydrodynamic lubrication

Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used, a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 10 lbs to 90 lbs. An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes.

Townsend, D. P.↗
NASA NTRS1984

Estimation of aerodynamic forces and moments on a steadily spinning airplane

A semiempirical method is presented for the estimation of aerodynamic forces and moments on a steadily rotating airplane model in a spin tunnel. The approach is based on the application of strip theory to determine a part of the aerodynamic coefficient (including rotational velocity) and then estimation of increments to these coefficients because of rotational flow over the stalled airplane. The theory is applied to a light, single-engine, general aviation airplane and the results are compared with the corresponding spin tunnel rotary balance test data.

Pamadi, B. N.↗
DOE OSTI2023

Spin canting and lattice symmetry in La 2 CuO 4

While the dominant magnetic interaction in La 2 CuO 4 is superexchange between nearest-neighbor Cu moments, the pinning of the spin direction depends on weak anisotropic effects associated with spin-orbit coupling. The symmetry of the octahedral tilt pattern allows an out-of-plane canting of the Cu spins, which is compensated by an opposite canting in nearest-neighbor layers. A strong magnetic field applied perpendicular to the planes can alter the spin canting pattern to induce a weak ferromagnetic phase. In light of recent evidence that the lattice symmetry is lower than originally assumed, we take another look at the nature of the field-induced spin-rotation transition. Comparing low-temperature neutron diffraction intensities for several magnetic Bragg peaks measured in fields of 0 and 14 T, we find that a better fit is provided by a model in which spins rotate within both neighboring planes but by different amounts, resulting in a noncollinear configuration. Finally, this model allows a more consistent relationship between lattice symmetry and spin orientation at all Cu sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1973

Study of ball bearing torque under elastohydrodynamic lubrication

Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used - a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 45 newtons (10 lb) to 403 newtons (90 lb). An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes.

Townsend, D. P.↗
DOE OSTI2022

Solvable 3D Kondo Lattice Exhibiting Pair Density Wave, Odd-Frequency Pairing, and Order Fractionalization

The Kondo lattice model plays a key role in our understanding of quantum materials, but a lack of small parameters has posed a long-standing problem. We present a 3 dimensional S= 1 2 Kondo lattice model describing a spin liquid within an electron sea. Strong correlations in the spin liquid are treated exactly, enabling a controlled analytical approach. Like a Peierls or BCS phase, a logarithmically divergent susceptibility leads to an instability into a new phase at arbitrarily small Kondo coupling. Our solution captures a plethora of emergent phenomena, including odd-frequency pairing, pair density wave formation and order fractionalization. The ground-state state is a pair density wave with a fractionalized charge e, S = 1/2 order parameter, formed between electrons and Majorana fermions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Dipolar spin-exchange and entanglement between molecules in an optical tweezer array

Ultracold polar molecules are promising candidate qubits for quantum computing and quantum simulations. Their long-lived molecular rotational states form robust qubits, and the long-range dipolar interaction between molecules provides quantum entanglement. In this work, we demonstrate dipolar spin-exchange interactions between single calcium monofluoride (CaF) molecules trapped in an optical tweezer array. We realized the spin- 1 2 quantum XY model by encoding an effective spin- 1 2 system into the rotational states of the molecules and used it to generate a Bell state through an iSWAP operation. Conditioned on the verified existence of molecules in both tweezers at the end of the measurement, we obtained a Bell state fidelity of 0.89(6). Using interleaved tweezer arrays, we demonstrate single-site molecular addressability.

Science & Technology - Other Topics↗
DOE OSTI2020

Block–spiral magnetism: An exotic type of frustrated order

Significance Magnetic frustration in spin or electronic models emerges from the failure of the system to fulfill simultaneously conflicting local requirements. The latter typically arise from the lattice geometry or are induced by special spin–spin interactions in the system at various distances. Here we show that the competing energy scales of the seemingly nonfrustrated orbital-selective Mott phase of the low-dimensional multiorbital Hubbard model can originate a “block–chiral magnetism,” i.e., a state with rigidly rotating spin–magnetic islands. Furthermore, we show how such an exotic spin state influences the electronic properties of the system, revealing parity-breaking quasiparticles.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Testing shell-model interactions at high excitation energy and low spin: Nuclear resonance fluorescence in Ge 74

With their complex low-spin structure, the germanium isotopes have accrued a large number of experimental data which challenge nuclear models. The structure of the 74 Ge isotope is investigated here with nuclear resonance fluorescence as part of an extensive campaign of experimental tests of the shell model in the germanium isotopic chain using a number of complementary techniques. Levels were excited with 3.10 – 5.44 MeV photon beams provided by the High Intensity Gamma-Ray Source at TUNL. Many new levels were identified and their spins, parities, branching ratios, and associated scattering cross section values were determined. Large-scale shell-model calculations, which include jj44b and JUN45 effective interactions developed to describe nuclei in this mass region, predict the new data satisfactorily. Herein this study extends the validation of these two interactions, which are candidates for computation of matrix elements to be used in the interpretation of neutrinoless double-β decay experiments in 76 Ge, into the low-spin, high excitation energy domain.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Direct local parametrization of nuclear state densities using the back-shifted Bethe formula

Level densities are often parametrized using the back-shifted Bethe formula (BBF) for nuclei that possess experimental data for s-wave neutron resonance average spacings and a complete discrete level sequence at low excitation energies. However, these parametrizations require the additional modeling of the dependence of the spin-cutoff parameter on excitation energy. Here, in this work, we avoid the need to model the spin distribution of level densities by using the experimental data to parametrize directly the state densities, for which the BBF does not depend on the spin-cutoff parameter. This approach allows for a local parameterization of state densities that is independent of the spin-cutoff parameter. We provide these parameters in a tabulated form for applications in nuclear reaction calculations and for testing microscopic approaches to state densities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1975

Investigation of low-latitude hydrogen emission in terms of a two-component interstellar gas model

High-resolution 21-cm hydrogen line observations at low galactic latitude are analyzed to determine the large-scale distribution of galactic hydrogen. Distribution parameters are found by model fitting, optical depth effects are computed using a two-component gas model suggested by the observations, and calculations are made for a one-component uniform spin-temperature gas model to show the systematic departures between this model and data obtained by incorrect treatment of the optical depth effects. Synthetic 21-cm line profiles are computed from the two-component model, and the large-scale trends of the observed emission profiles are reproduced together with the magnitude of the small-scale emission irregularities. Values are determined for the thickness of the galactic hydrogen disk between half density points, the total observed neutral hydrogen mass of the galaxy, and the central number density of the intercloud hydrogen atoms. It is shown that typical hydrogen clouds must be between 1 and 13 pc in diameter and that optical thinness exists on large-scale despite the presence of optically thin gas.

Baker, P. L.↗
NASA NTRS1981

Global weather research

Modeling, prediction, and analysis of global meteorological phenomena influencing the large scale behavior of the atmosphere are summarized. Prediction of global weather phenomena based on satellite data is discussed and models of global phenomena developed. The atmospheric general circulation model (AGCE) is reviewed, axisymmetric flow calculated, and axisymmetric states in cylindrical, spherical, three dimensional, and spin up numerical models for AGCE described. The role of latent heat release in baroclinic waves, latent heat and cyclonic systems, and a theoretical study of baroclinic flow related to the AGCE and the flow regime were studied with a simplified general circulation model. AGCE and the geophysical fluid flow cell (GFFC) instrumentation are discussed. Investigation of solar and planetary convection for GFFC is described. The utilization of satellite cloud observations to diagnose the energy state and transformations in extratropical cyclones is reviewed.

Source record↗
DOE OSTI2025

Dissipation-assisted steady-state entanglement engineering based on electron transfer models

Here, we propose a series of dissipation-assisted entanglement generation protocols that can be implemented on a trapped-ion quantum simulator. Our approach builds on the single-site molecular electron transfer (ET) model recently realized in experiment [So et al., Sci. Adv. 10, eads8011 (2024)]. This model leverages spin-dependent boson displacement and dissipation controlled by sympathetic cooling. We show that, when coupled to external degrees of freedom, the ET model can be used as a dissipative quantum control mechanism, enabling the precise tailoring of both spin and boson steady states of a target subsystem. We derive simplified analytical formalisms that offer intuitive insights into the dissipative dynamics. Using realistic interactions in a trapped-ion system, we develop a protocol for generating 𝑁-qubit and 𝑁-boson 𝑊 states. Additionally, we generalize this protocol to realize generic 𝑁-qubit Dicke states with tunable excitation numbers. Finally, we outline a realistic experimental setup to implement our schemes in the presence of noise sources.

chemical charge transfer↗
NASA NTRS1975

Stabilization of large-scale systems - A spinning flexible spacecraft

Stabilization of high-order constant systems by multilevel control is proposed in the framework of the decomposition-aggregation method for stability analysis of large-scale systems. An 11-order linear model of a spinning flexible spacecraft is stabilized by the method using both the passive and the active stabilization devices. The method can take advantage of the special structural features of the model to provide the best estimate of the stability region for an important parameter which couples the wobble and the spin motion of the spacecraft.

Siljak, D. D.↗
DOE OSTI2021

Theoretical methods to design and test quantum simulators for the compact Abelian Higgs model

The lattice compact Abelian Higgs model is a nonperturbative regularized formulation of low-energy scalar quantum electrodynamics. In 1+1 dimensions, this model can be quantum simulated using a ladder-shaped optical lattice with Rydberg-dressed atoms. In this setup, one spatial dimension is used to carry the angular momentum of the quantum rotors. One can use truncations corresponding to spin-2 and spin-1 to build local Hilbert spaces associated with the links of the lattice. We argue that ladder-shaped configurable arrays of Rydberg atoms can be used for the same purpose. We make concrete proposals involving two and three Rydberg atoms to build one local spin-1 space (a qutrit). We show that the building blocks of the Hamiltonian calculations are models with one and two spins. We compare target and simulators using perturbative and numerical methods. The two-atom setup provides an easily controllable simulator of the one-spin model while the three-atom setup involves solving nonlinear equations. We discuss approximate methods to couple two spin-1 spaces. The article provides analytical and numerical tools necessary to design and build the proposed simulators with current technology.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Contributing to Sunny open source code

The Sunny package is an existing open source software to support the simulation of magnetic spin systems. It is available online under the MIT license here: https://github.com/SunnySuite/Sunny.jl The package aims to include the following features: - Analysis for symmetry-allowed interactions - Monte Carlo algorithms for simulating equilibrium configurations. - Schemes for integrating spin dynamics. - Inference of model Hamiltonians - Support for generalized SU(N) spins - Tools for interpreting experimental data, such as diffraction data, magnetization curves, and heat capacity data

Barros, Kipton↗
DOE OSTI2022

The Variability of the Black Hole Image in M87 at the Dynamical Timescale

The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the u–v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗