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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Simultaneous measurements of sunspot umbral oscillations in the photosphere, chromosphere, and transition region

Measurements of umbral oscillations in a sunspot were made simultaneously from space (with the SMM/UVSP instrument) in the C IV transition-region line and from the ground (with the tower telescope at NSO/sunspot) in spectral lines formed in the photosphere and chromosphere. The power spectra of velocity and intensity variations show multiple peaks in the 3 min band (4.5-10 mHz). A strong oscillation at 5.5 mHz is coherent between the chromosphere and transition region. Another strong oscillation mode at 7.5 mHz is coherent between the photosphere and transition region and appears to have a node in the chromosphere. The rms velocity in the 3 min band is a little over 12 km/sec in both the chromosphere and transition region, but the kinetic energy density is lower in the transition region (by a factor of 10 or more) due to the lower mass density there. These measurements of amplitude and phase of the waves at different heights provided a new, independent method of testing or fitting models of the vertical temperature distribution in the umbral chromosphere and transition regions.

Thomas, John H.↗
NASA NTRS2024

Development and Testing of a Superconducting Ground Plane on Transition Edge Sensors

Much of the normal matter in the universe is thought to exist as diffuse hot gas near 1.0 × 10 6 K, which can be detected through its 0.1–0.5 keV line emission. Distinguishing among multiple temperature regions and emission mechanisms along a line of sight requires resolving individual spectral lines in this particularly crowded spectral range. This requires 1–2 eV spectral resolution, which is currently only possible using grating spectrometers, which are suitable only for point sources, but not for the diffuse sources we wish to observe. We aim to measure individual spectral lines in this energy band using transition edge sensors (TES) that have the required 1–2 eV non-dispersive spectral resolution on a sounding rocket. While TESs offer sufficient energy resolution, they are very sensitive to ambient magnetic fields, e.g. from earth’s field and stray fields from the adiabatic demagnetization refrigerator (ADR) that is used to cool TESs to their ∼70 mK transition temperature. Strict space and weight limitations on the sounding rocket payload will limit the use of conventional high permeability magnetic shielding. Further design challenges arise in designing shielding with at least a 45∘ field of view, which is required to maintain a large enough throughput to obtain a useful spectrum on a brief (∼300 s) sounding rocket flight. Here we explore adding a superconducting ground plane (SGP) to the backside of the TES to reduce its field sensitivity and minimize attenuation requirements for the external shielding, which is based on prior work from (de Wit et al. 2022). We tested the feasibility of SGPs with novel materials, geometries, and on larger TESs with different biasing conditions.

Astrophysics↗
NASA NTRS2012

Enthalpy-Based Thermal Evolution of Loops: III. Comparison of Zero-Dimensional Models

Zero dimensional (0D) hydrodynamic models, provide a simple and quick way to study the thermal evolution of coronal loops subjected to time-dependent heating. This paper presents a comparison of a number of 0D models that have been published in the past and is intended to provide a guide for those interested in either using the old models or developing new ones. The principal difference between the models is the way the exchange of mass and energy between corona, transition region and chromosphere is treated, as plasma cycles into and out of a loop during a heating-cooling cycle. It is shown that models based on the principles of mass and energy conservation can give satisfactory results at some, or, in the case of the Enthalpy Based Thermal Evolution of Loops (EBTEL) model, all stages of the loop evolution. Empirical models can lead to low coronal densities, spurious delays between the peak density and temperature, and, for short heating pulses, overly short loop lifetimes.

Cargill, P. J.↗
NASA NTRS2024

The Impact of Decarbonization on Particulate Soiling of Solar Panels

Climate researchers have examined many impacts of climate change on energy supply and demand under various scenarios. However, the effect of changing particulate deposition onto solar panel surfaces on solar power production efficiency (i.e., soiling) has not been studied. We therefore characterize probabilistic outcomes across multiple climate models and scenarios. We find large current regional losses (up to 40% without manual cleaning, up to 20% with monthly cleaning and rain removal) in generation that grow slightly under a high-emission scenario, largely due to regional increases in windblown dust. In contrast, under a low-emissions scenario, potential production increases significantly (2–8% interquartile range with only rain removal) due to reduced soiling, especially in regions of Asia and Africa where anthropogenic aerosols are major contributors to soiling. Projected changes vary widely across models in many dusty areas outside of the Sahara and Arabia. Differences can also be large in regions dominated by anthropogenic aerosols, such as Nigeria, eastern China, and northern India, where the full range across modeled potential power production changes extends from −1 to +11% for the end of the century (without manual cleaning), underscoring the need to consider multiple climate models. With large increases in projected solar power deployment, the relatively small potential production increases reported here could nevertheless represent a large dividend in additional energy production. Hence, reductions in air pollution attributable to decarbonization could provide positive feedback under which a greater deployment of solar power (or other renewables) increases the production of solar power, facilitating the transition to renewable energy.

renewable energy↗
NASA NTRS1977

Color of kerogen as index of organic maturity

Kerogen from the Tanner basin off southern California was heated under nitrogen at different temperatures and times and subsequently was studied under the transmitted light microscope. Samples darken in color from yellow through shades of brown to black with increasing thermal maturation. The transition from dark brown to very dark brown marks the range of maximum n-alkane generation where the residue attains an atomic H/C of about 0.80 plus or minus 0.05. The apparent activation energy for this transition was about 45 plus or minus 5 kcal per mole.

Peters, K. E.↗
NASA NTRS1978

The excitation of electronic transverse energy levels in an intense magnetic field

Observations of the X-ray pulsar Hercules X-1 show a line emission feature at about 60 keV, which has been interpreted as the fundamental electron cyclotron line in a magnetic field of around six trillion gauss. In this interpretation, the line radiation results from transitions between transverse energy levels, which are quantized by the field. The expected line luminosity from the excitation of these levels by protons which are falling into the polar cap of a neutron star are calculated. They are assumed to attain kinetic energies up to around 200 MeV, the gravitational potential energy at the surface. The cross sections for high energy Coulomb encounters between small pitch angle protons and electrons in a strong field are measured and used to calculate the energy loss rate of the infalling protons. This rate, together with the rate of elastic nuclear proton collisions, is then used to calculate the number of line photons an infalling proton can be expected to produce, directly or indirectly. The results are applied to Hercules X-1.

Bussard, R. W.↗
NASA NTRS1990

Large-eddy simulation of transitional channel flow

A large-eddy simulation (LES) of transition in plane channel flow was carried out. The LES results were compared with those of a fine direct numerical simulation (DNS), and with those of a coarse DNS that uses the same mesh as the LES, but does not use a residual stress model. While at the early stages of transition, LES and coarse DNS give the same results: the presence of the residual stress model was found to be necessary to predict accurately mean velocity and Reynolds stress profiles during the late stages of transition (after the second spike stage). The evolution of single Fourier modes is also predicted more accurately by the LES than by the DNS. As small scales are generated, the dissipative character of the residual stress starts to reproduce correctly the energy cascade. As transition progresses, the flow approaches its fully developed turbulent state, the subgrid scales tend towards equilibrium, and the model becomes more accurate.

Piomelli, Ugo↗
NASA NTRS1991

Use of scaled external correlation, a double many-body expansion, and variational transition state theory to calibrate a potential energy surface for FH2

New ab initio results and a double many-body expansion formalism have been used to parameterize a new FH2 potential energy surface with improved properties near the saddle point and in the region of long-range attraction. The functional form of the new surface includes dispersion forces by a double many-body expansion. Stationary point properties for the new surface are calculated along with the product-valley barrier maxima of vibrationally adiabatic potential curves for F + H2 - HF(nu-prime = 3) + H, F + HD - HF(nu-prime = 3) + D, and F + D2 - DF(nu-prime = 4) + D. The new surface should prove useful for studying the effect on dynamics of a low, early barrier with a wide, flat bend potential.

Lynch, Gillian C.↗
NASA NTRS1969

Self-consistent many-electron theory of electron work functions and surface potential characteristics for selected metals

Electron work functions, surface potentials, and electron number density distributions and electric fields in the surface region of 26 metals were calculated from first principles within the free electron model. Calculation proceeded from an expression of the total energy as a functional of the electron number density, including exchange and correlation energies, as well as a first inhomogeneity term. The self-consistent solution was obtained via a variational procedure. Surface barriers were due principally to many-body effects; dipole barriers were small only for some alkali metals, becoming quite large for the transition metals. Surface energies were inadequately described by this model, which neglects atomistic effects. Reasonable results were obtained for electron work functions and surface potential characteristics, maximum electron densities varying by a factor of over 60.

Smith, J. R.↗
NASA NTRS1990

Determination of molecular spectroscopic parameters and energy-transfer rates by double-resonance spectroscopy

The spectroscopy of small to medium-size polyatomic molecules can be extremely complex, especially in higher-lying overtone and combination vibrational levels. The high density of levels also complicates the understanding of inelastic collision processes, which is required to model energy transfer and collision broadening of spectral lines. Both of these problems can be addressed by double-resonance spectroscopy, i.e., time-resolved pump-probe measurements using microwave, infrared, near-infrared, and visible-wavelength sources. Information on excited-state spectroscopy, transition moments, inelastic energy transfer rates and propensity rules, and pressure-broadening parameters may be obtained from such experiments. Examples are given for several species of importance in planetary atmospheres, including ozone, silane, ethane, and ammonia.

Steinfeld, J. I.↗
NASA NTRS2002

Near Infrared Emission of Highly Electronically Excited CO: A Sensitive Probe to Study the Interstellar Medium??

Among the various spectroscopic features of the second most abundant molecule in the space, CO, "the triplet - triplet transitions involving the lowest triplet state a(sup 3)II and the higher-lying a(sup 1)3 SIGMA (sup +), d(sup 3) (DELTA), e (sup 3) SIGMA (sup -) states spanning near-UV to mid-IR spectral range" have so far not been explored in astrophysical observations. The energies of these transitions are highly sensitive to the surroundings in which CO exists, i.e. gas-phase, polar or non-polar condensed phase. It is proposed here that these triplet-triplet emission/absorption bands can be used as a sensitive probe to investigate the local environments of CO, whether in the planetary atmosphere, stellar atmosphere or interstellar medium.

Gudipati, Murthy S.↗
NASA NTRS1977

Influence of temperature and the role of chromium on the kinetics of sulfidation of 310 stainless steel

The sulfidation of 310 stainless steel was studied over the temperature range from 910 K to 1285 K. By adjusting the ratio of hydrogen sulfide, variations in sulfur potential were obtained. The effect of temperature on sulfidation was determined at three different sulfur potentials: 39/sqNm, 0.014/sqNm, and 0.00015/sqNm. All sulfide scales contained one or two surface layers in addition to a subscale. The second outer layer (OL-II), furthest from the alloy, contained primarily Fe-Ni-S. The first outer layer (OL-I), nearest the subscale, contained FE-Cr-S. The subscale consisted of sulfide inclusions in the metal matrix. At a given temperature and sulfur potential, the weight gain data obeyed the parabolic rate law after an initial transient period. The parabolic rate constants obtained at the sulfur potential of 39/sqNm did not show a break when the logarithm of the rate constant was plotted as a function of the inverse of absolute temperature. Sulfidation carried out at sulfur potentials below 0.02/sqNm, however, did show a break at 1145 K, which is termed as the transition temperature. This break was found to be associated with the changes which had occurred in the Fe:Cr ratio of OL-I. Below the transition temperature the activation energy was found to be approximately 125 kj/mole. Above the transition temperature the rate of sulfidation decreased with temperature but dependent on the Fe:Cr ratio in the iron-chromium-sulfide layers of the OL-I. A reaction mechanism consistent with the experimental results has been proposed.

Rao, D. B.↗
NASA NTRS2003

Heats of Segregation of BCC Binaries from Ab Initio and Quantum Approximate Calculations

We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.

Good, Brian S.↗
NASA NTRS2003

Surface Segregation Energies of BCC Binaries from Ab Initio and Quantum Approximate Calculations

We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy method. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameterization. Quantum approximate segregation energies are computed with and without atomistic relaxation. The ab initio calculations are performed without relaxation for the most part, but predicted relaxations from quantum approximate calculations are used in selected cases to compute approximate relaxed ab initio segregation energies. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with other quantum approximate and ab initio theoretical work, and available experimental results.

Good, Brian S.↗
NASA NTRS2011

Hg-201 (+) CO-Magnetometer for HG-199(+) Trapped Ion Space Atomic Clocks

Local magnetic field strength in a trapped ion atomic clock is measured in real time, with high accuracy and without degrading clock performance, and the measurement is used to compensate for ambient magnetic field perturbations. First and second isotopes of an element are co-located within the linear ion trap. The first isotope has a resonant microwave transition between two hyperfine energy states, and the second isotope has a resonant Zeeman transition. Optical sources emit ultraviolet light that optically pump both isotopes. A microwave radiation source simultaneously emits microwave fields resonant with the first isotope's clock transition and the second isotope's Zeeman transition, and an optical detector measures the fluorescence from optically pumping both isotopes. The second isotope's Zeeman transition provides the measure of magnetic field strength, and the measurement is used to compensate the first isotope's clock transition or to adjust the applied C-field to reduce the effects of ambient magnetic field perturbations.

Burt, Eric A.↗
NASA NTRS1993

Rotational structure in the near-infrared absorption spectrum of ozone

The lowest energy members of the near-IR absorption bands of ozone possess fine structure which is probably due to the rotation of the molecule in the upper vibronic state, suggesting that this state is metastable. A preliminary analysis of the structures as rotational subbands supports a recent theoretical assignment of the near-IR vibronic features to the 3A2 - 1A1 electronic transition. A binding energy of about 0.1 eV is inferred from the breakoff in the observed structure.

Anderson, Stuart M.↗