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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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Dynamics of ion temperature gradient turbulence and transport with a static magnetic island
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Low frequency fully kinetic simulation of the toroidal ion temperature gradient instability
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Gyrokinetic simulation on the effect of radio frequency waves on ion-temperature-gradient-driven modes: Part II – transport analysis
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Examination of stiff ion temperature gradient mode physics in simulations of DIII-D H-mode transport
This paper presents comparisons of predictions from two models of turbulent transport in tokamaks. The focus is on assessing how close a reduced but significantly less computationally demanding model (TGLF) does in matching the more detailed model (CGYRO) in predicting scalings with driving gradient ("stiffness"). The impacts of other physics mechanisms such as flow shear, fast ions, and electromagnetic fluctuations on these predictions is also studied. Overall, while there are clear differences in the scaling, these do not appear to significantly impact the fidelity of the reduced model in prediction the experimental conditions studied relative to the more advanced model.
Community structure explains antibiotic resistance gene dynamics over a temperature gradient in soil
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Plane-stress analysis of an edge-stiffened rectangular plate subjected to loads and temperature gradients
Mechanical and thermal stress in elastic edge- stiffened plate under edge loading
Convection and magnetic fields in an atmosphere with constant temperature gradient. I - Hydrodynamic flows
In order to deduce the fluid and field conditions deep in the supergranules from the fluid motions and magnetic fields observed in the solar photosphere, it is necessary to have some idea of the depth to which the supergranules extend and the form of their internal fluid velocities. Toward this end a number of analytic solutions of the Navier-Stokes equations are given for circumstances possessing various facets of the supergranule environment in the sun. These solutions, together with the earlier work by others, shows that the granules extend to depths in excess of their mean diameters, that the convective velocities probably do not diminish much, if any, with depth, and that across the tops of the supergranules at the photosphere the horizontal velocity is more or less independent of depth.
Convection and magnetic fields in an atmosphere with constant temperature gradient. II - The supergranules and magnetic fields
The hydrodynamic properties of convective motions in a stratified atmosphere suggest that the supergranules in the solar photosphere extend to depths in excess of their horizontal diameters. The calculations presented here show that the weak fields which appear at the photosphere are as strong as, or stronger than, the horizontal fields anywhere in the supergranules below the surface. Hence the general 10 to 100 gauss azimuthal field of the sun, whose presence is indicated by the emerging bipolar magnetic regions, must lie below the base of the supergranules, i.e., below a depth probably of the order of 20,000 to 50,000 km. Presumably then the azimuthal field is generated by nonuniform rotation below the supergranule convection and does not appear in the supergranule layer because of the high rate of turbulent diffusion loss from that layer.
Empirical relations between seasonal changes in meridional temperature gradients and meridional fluxes of heat
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Non-Maxwellian velocity distribution functions associated with steep temperature gradients in the solar transition region. I - Estimate of the electron velocity distribution functions. II - The effect of non-Maxwellian electron distribution functions on ionization equilibrium calculations for carbon, nitrogen and oxygen
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Temperature gradient and electric field driven electrostatic instabilities
The stability of electrostatic waves to thermodynamic and electric potential gradients was investigated. It is shown that thermodynamic gradients drive instabilities even when the internal electric field vanishes. Skewing of the distribution function is not included in the dielectric.
Effect of design variables, temperature gradients and speed of life and reliability of a rotating disk
A generalized methodology to predict the fatigue life and reliability of a rotating disk such as used for aircraft engine turbines and compressors is advanced. The approach incorporates the computed life of elemental stress volumes to predict system life and reliability. Disk speed and thermal gradients as well as design variables such as disk diameter and thickness and bolt hole size, number and location are considered.
Vertical temperature gradients on Uranus - Implications for layered convection
Analyses of Voyager IR spectroscopy and radio occultation measurements confirm ground-based observations that the deep lapse rate of Uranus exceeds that for an adiabat of H2 in thermodynamic equilibrium. However, in approximately the same region of the atmosphere, Voyager IR and ground-based observations also indicate that the ratio of ortho to para hydrogen is near the equilibrium value. These two sets of observations can be reconciled by postulating the existence of rapid convective overturning within layers which are thin in comparison to a pressure scale height. Two forms of layered convection are examined. In one case, deposition of kinetic energy results in thin, rapidly overturning layers. Possible kinetic energy sources include braking waves and local instabilities. In the second case considered, molecular-weight discontinuities due to CH4 stratification stabilize the interfaces of thin layers. It is argued that both forms may be important in the convective portion of the Uranus atmosphere.
Effect of design variables, temperature gradients, and speed on life and reliability of a rotating disk
A generalized methodology to predict the fatigue life and reliability of a rotating disk such as used for aircraft engine turbines and compressors is advanced. The approach incorporates the computed life of elemental stress volumes to predict system life and reliability. Disk speed and thermal gradients as well as design varibles such as disk diameter and thickness and bolt hole size, number and location are considered.
Lower solar chromosphere-corona transition region. I - Theoretical models with small temperature gradients
A study of transition region models including the effects of classical thermal conduction, heating, and radiative cooling is carried out with attention directed toward the problem of understanding the observed emission in the lower transition region. It is found that the observationally inferred emission measure curve implies a near-balance between heating and radiative cooling in the lower transition region, and that the presence of strong hydrogen Ly-alpha cooling leads to the existence of singularities in the solutions of the force balance and energy balance equations when such a near-balance between heating and cooling is assumed. These singularities place strong constraints on the nature of viable models of the lower transition region and must be considered when Ly-alpha cooling is important. Previously suggested explanations of the observed emission from the lower transition region are considered in the context of the results of the present study, and conditions for the applicability of these suggested explanations are discussed.