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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The effect of latent heat release on synoptic-to-planetary scale wave interactions and implications for satellite observations: Observational study

Researchers have been exploring methods to facilitate the prediction of rapidly intensifying surface cyclones. Recognizing that synoptic-scale systems, such as these cyclones, are less predictable at medium range and beyond than are planetary-scale circulations, researchers propose that the planetary-scale environment for explosive cyclogenesis could be better predicted than the cyclones themselves. Researchers have therefore constructed a planetary-scale climatology of explosive cyclogenesis by compositing together filtered 500 mb height fields (retaining planetary waves only) corresponding to a large sample of rapidly intensifying surface cyclones, stratified geographically and according to the direction of 500 mb geostrophic flow (southwesterly, northwesterly or westerly) over the cyclone center. The composites are calculated from five days preceding to five days following each rapid cyclogenesis event, and have climatology subtracted so that the evolution of planetary-scale anomalies before and after cyclogenesis can be followed. Whether the anomalies are distinct from background variability and thus provide predictive value is now being evaluated. Following explosive cyclogenesis over which the filtered 500 mb flow is southwesterly, there appear in the composites large positive 500 mb height anomalies downstream. In some cases, these anomalies are associated with blocking patterns. Whether the objectively-defined blocking patterns in the data set are preceded by upstream intense surface cyclone activity is being investigated. Finally, the contribution of synoptic-scale processes, notably warm air advection, to planetary-scale height rises during a block formation following an explosive cyclogenesis event is being diagnosed. Researchers hope to eventually evaluate the impact of satellite derived latent heat release upon the warm air advection in this case.

Colucci, Stephen J.↗
NASA NTRS1986

A numerical simulation of barotropic instability. III - Wave-wave interaction in the presence of dissipation

A fully nonlinear model of barotropic instability including dissipation is used to investigate the evolution of the integrated enstrophy and vorticity. The dissipation independent limits on the integrated enstrophy and the long period oscillation in the integrated enstrophy found by Schoeberl and Lindzen are verified. The enstrophy oscillations are similar to those previously noted for two-dimensional Kelvin-Helmholtz instabilities. They are produced by advection of the vorticity back and forth across the region of instability by the largest scale wave. A simple expression that accurately estimates the period of these oscillations is derived using the saturation theory.

Schoeberl, M. R.↗
NASA NTRS1999

The Atmospheric Effects of HSCT Emissions Simulated by a 3-Wave Interactive Model

An interactive model which couples a semi-spectral dynamical model, a radiative transfer code and a two-dimensional chemistry transport model (2-D CTM), is used to assess the atmospheric effects of the High-Speed Civil Transport (HSCT) engine emissions. The residual mean meridional circulation, the zonal-mean temperature and the eddy diffusion coefficients are calculated using zonal means and three longest zonal waves of dynamical variables integrated in the semi-spectral dynamical model. They are used in the 2-D CTM to simulate the distribution of trace gases in the atmosphere. The simulated ozone is sent to the radiative transfer code to calculate the heating rates, which drive the dynamics. This radiative coupling connects the dynamical and photochemical processes and creates feedback when the atmosphere is perturbed. It is found that in most areas the ozone depletion caused by HSCT emissions calculated using the 3-wave model has the features similar to, but with significantly larger magnitude than that calculated by the AER 2-D CTM with prescribed transport parameters and temperature. The difference is mostly due to the differences in the circulation in the two models. The radiative feedback effects are investigated by comparing the ozone depletion calculated with the baseline dynamics and with the dynamics perturbed by the HSCT emissions. The feedback through changes in the residual mean meridional circulation and the eddy diffusion coefficients has moderate effects on the simulated ozone depletion. It reduced the ozone depletion by 20-30% in northern mid and high-latitudes. However, the feedback through changes in the zonal- mean temperature is negligible.

Shia, R.-L.↗
NASA NTRS1990

Numerical simulation of particle-wave interaction in boundary layers

The effects of wall injection and particle motion on the spatial stability of two-dimensional plane channel flow are investigated. For this purpose, an accurate Navier-Stokes solver to simulate the space-time evolution of disturbances in three-dimensional flows has been developed. The code is operational on the NASA Langley CRAY2 and can be ported to any other supercomputer. The code has been tested extensively in tracking the spatial evolution of two-dimensional disturbances in plane channel flow and provided excellent agreement with the linear theory including at the inflow/outflow boundaries. Preliminary calculations have been performed to investigate the effects of stationary and moving sources of vortical disturbances simulating a particle traveling in the flow field. Results suggest that even at very low amplitudes, vortical disturbances act as amplifiers on the Tollmien-Schlichting waves promoting rapid instability. It is also found that slow moving particles are more dangerous than both stationary and fast moving particles for the same disturbance levels.

Biringen, S.↗
DOE OSTI2018

Spontaneous Separation in Trapped Fermi Gas with p-Wave Interactions: Due to the Mass-Imbalance

Based on density functional theory, the spontaneous separation in the mass-imbalanced Fermi–Fermi mixture is studied. The ground-state energy density functional is constructed with the effective contact interaction, with which the ground-state density profiles of the mixture are calculated under different conditions of mass-imbalance and coupling strength. The influence of mass-imbalance on the separation and the cloud size is analyzed. In addition, the system with both mass- and population-imbalance is also calculated and studied. Despite our rough treatment in the Thomas–Fermi approximation, it is hoped that the results may provide new clues to understand the nature of phase separation of a trapped ultracold gas in both theoretical and experimental researches in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Repulsion and total reflection with mismatched three-wave interaction of noncollinear optical beams in quadratic media

The phenomenon of the total reflection of a weak signal beam from a high-power reference beam due to noncollinear mismatched parametric interaction in a quadratic medium is demonstrated. In a planar geometry the conditions of the signal beam reflection from the optical inhomogeneity induced by the reference beam are found. The analytical expression for the critical value of the signal beam tilt is obtained, and it is shown that total reflection occurs if the initial tilt is less than the critical value. The influence of the walk-off and the reference beam focusing on interaction dynamics are discussed. It is shown that in a bulk medium the beam reflection turns into scattering by an induced inhomogeneity. If reflection conditions are fulfilled, the cylindrical reference beam acts as a convex mirror and lunate distortions of the reflected beam profile occur.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Indication of subdominant d-wave interaction in superconducting CaKFe 4 As 4

We report inelastic light scattering results on the stoichiometric and fully ordered superconductor CaKFe 4 As 4 as a function of temperature and light polarization. In the energy range between 10 and 315 cm -1 (1.24 and 39.1 meV) we observe the particle-hole continuum above and below the superconducting transition temperature T c and seven of the eight Raman active phonons. The main focus is placed on the analysis of the electronic excitations. Below T c all three symmetries projected with in-plane polarizations display a redistribution of spectral weight characteristic for superconductivity. The energies of the pair-breaking peaks in A 1g and B 2g symmetry are in approximate agreement with the results from photoemission studies. In B 1g symmetry the difference between the normal and superconducting state is most pronounced, and the feature is shifted downwards with respect to those in A 1g and B 2g symmetry. The maximum peaking at 134 cm -1 (16.6 meV) has a substructure on the high-energy side. We interpret the peak at 134 cm -1 in terms of a collective Bardasis-Schrieffer (BS) mode and the substructure as a remainder of the pair-breaking feature on the electron bands. Finally, there is a very weak peak at 50 cm -1 (6.2 meV) which is tentatively assigned to another BS mode.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Two-nucleon 𝑆-wave interactions at the SU(3) flavor-symmetric point with 𝑚 𝑢⁢𝑑 ≈ 𝑚$^{phys}_𝑠$: A first lattice QCD calculation with the stochastic Laplacian Heaviside method

We report on the first application of the stochastic Laplacian Heaviside method for computing multiparticle interactions with lattice QCD to the two-nucleon system. Like the Laplacian Heaviside method, this method allows for the construction of interpolating operators which can be used to construct a set of positive-definite two-nucleon correlation functions, unlike nearly all other applications of lattice QCD to two nucleons in the literature. It also allows for a variational analysis in which optimal linear combinations of the interpolating operators are formed that couple predominantly to the eigenstates of the system. Utilizing such methods has become of paramount importance to help resolve the discrepancy in the literature on whether two nucleons in either isospin channel form a bound state at pion masses heavier than physical, with the discrepancy persisting even in the SU(3)-flavor-symmetric point with all quark masses near the physical strange quark mass. This is the first in a series of papers aimed at resolving this discrepancy. In the present work, we employ the stochastic Laplacian Heaviside method without a hexaquark operator in the basis at a lattice spacing of 𝑎 ≈0.086 fm, lattice volume of 𝐿 = 48⁢𝑎 ≈ 4.1 fm and pion mass 𝑚 𝜋 ≈ 714 MeV. With this setup, the observed spectrum of two-nucleon energy levels strongly disfavors the presence of a bound state in either the deuteron or dineutron channel.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗