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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Crack growth in Ti-8Al-1Mo-1V with real-time and accelerated flight-by-flight loading

Crack growth in Ti-8Al-1Mo-1V was measured and calculated for real-time and accelerated simulations of supersonic airplane loading and heating. Crack-growth rates calculated on the assumption that an entire flight could be represented by a single cycle predicted the experimental rates poorly. Calculated crack-growth rates were slower than the experimental rates for all tests with flight-by-flight loading. For room-temperature accelerated tests, the calculated rates agreed well with the experimental rates; but the calculations became progressively less accurate for progressively more complex test conditions (tests that included elevated temperature). Calculations of crack growth using the crack-closure concept can probably be improved through study of crack-opening stresses using finite-element models that account for variable-amplitude loading, residual stresses, and temperature effects. The calculations of crack growth could also be improved through detailed studies of material properties and interactions among stress, temperature, and time as appropriate for the real-time operating conditions of a supersonic transport airplane.

Imig, L. A.↗
NASA NTRS1985

On the observed properties and long-term structure and evolution of white dwarfs in cataclysmic variables

An attempt is made to explain the observed surface temperatures and luminosities of cataclysmic variable white dwarfs based on the cooling physics and time-averaged structure of the white dwarf in response to accretion. The evolutionary changes in core temperature and core luminosity as an accreting white dwarf evolves quasi-statically are compared with the cooling evolution of a nonaccreting, one solar mass, pure C-12 core. Then, the evolutionary behavior of the white dwarf envelope in mass and temperature, in response to long-term accretion, is used to predict temperatures and luminosities of white dwarfs during quiescent intervals between nova outbursts. It is shown that the observed luminosities and effective temperatures of the bare white dwarfs detected in some cataclysmic variables are the expected intrinsic values associated with classical nova thermonuclear outburst cycles. Two alternate interpretations of their observed surface temperatures and luminosities are assessed.

Sion, E. M.↗
DOE OSTI2024

High-temperature quantum valley Hall effect with quantized resistance and a topological switch

Edge states of a topological insulator can be used to explore fundamental science emerging at the interface of low dimensionality and topology. Achieving a robust conductance quantization, however, has proven challenging for helical edge states. In this work, we show wide resistance plateaus in kink states—a manifestation of the quantum valley Hall effect in Bernal bilayer graphene—quantized to the predicted value at zero magnetic field. The plateau resistance has a very weak temperature dependence up to 50 kelvin and is flat within a dc bias window of tens of millivolts. We demonstrate the electrical operation of a topology-controlled switch with an on/off ratio of 200. These results demonstrate the robustness and tunability of the kink states and its promise in constructing electron quantum optics devices.

Science & Technology - Other Topics↗
DOE OSTI2023

Ultrasmall Pd Clusters in FER Zeolite Alleviate CO Poisoning for Effective Low-Temperature Carbon Monoxide Oxidation

Ultra small Pd 4 clusters form in the micropores of FER zeolite during low temperature treatment (100 °C) in the presence of humid CO gas. They effectively catalyze CO oxidation below 100°C, whereas Pd nanoparticles are not active as they are poisoned by CO. Using catalytic measurements, infrared (IR) spectroscopy, X-ray absorption spectroscopy (EXAFS), microscopy, and density functional theory calculations we provide the molecular level insight into this previously unreported phenomenon. Pd nanoparticles get covered with CO at low temperatures which effectively blocks O 2 activation until CO desorption occurs. Small Pd clusters in zeolites, in contrast, demonstrate fluxional behavior in the presence of CO, which significantly increases their affinity for binding O 2 . In conclusion, our study shows a pathway for achieving low temperature CO oxidation activity on the basis of well-defined Pd/zeolite system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

Molecular column densities in selected model atmospheres

From an examination of predicted column densities, the following conclusions were drawn: (1) The SiO ought to be visible in carbon stars which were generated from triple alpha burning, but absent from carbon stars generated from the CNO bi-cycle. (2) Variation in the observed relative strengths of TiO and ZrO is indicative of real differences in the ratio Ti/Zr. (3) The TiO/ZrO ratio shows a small variation as C/O and effective temperature is changed. (4) Column density of silicon dicarbide (SiC2) is sensitive to abundance, temperature, and gravity; hence all relationships between the strength of SiC2 and other stellar parameters will show appreciable scatter. There is however, a substantial luminosity effect present in the SiC2 column densities. (5) Unexpectedly, SiC2 is anti-correlated with C2. (6) The presence of SiC2 in a carbon star eliminates the possibility of these stars having temperatures greater than or equal to 3000 K, or being produced through the CNO bi-cycle.

Johnson, H. R.↗
NASA NTRS1992

Vapor-liquid equilibrium thermodynamics of N2 + CH4 - Model and Titan applications

A thermodynamic model is presented for vapor-liquid equilibrium in the N2 + CH4 system, which is implicated in calculations of the Titan tropospheric clouds' vapor-liquid equilibrium thermodynamics. This model imposes constraints on the consistency of experimental equilibrium data, and embodies temperature effects by encompassing enthalpy data; it readily calculates the saturation criteria, condensate composition, and latent heat for a given pressure-temperature profile of the Titan atmosphere. The N2 content of condensate is about half of that computed from Raoult's law, and about 30 percent greater than that computed from Henry's law.

Thompson, W. R.↗
NASA NTRS1994

Analysis of Voyager spectra of the beta Cephei star nu Eridani

Voyager 500-1700 A spectrophotometric observations of the beta Cephei star nu Eri are presented and discussed. The Voyager observations were obtained in 1981 and cover six pulsation cycles of the star. These data are supplemented with a set of nine International Ultraviolet Explorer (IUE) SWP high-resolution observations covering one, earlier epoch, pulsation cycle. Light curves are derived from the Voyager data at 1055 and 1425 A. These light curves are found to be consistent in both shape and period with published optical curves. The 1055 A light curve also exhibits a phenomenon not seen in the optical curves: a small but highly significant systematic increase in the flux of the maximum light phases while maintaining a constant minimum light level over the interval of observation. Substantially larger errors in the longer wavelength data preclude discussion of this phenomenon in the 1425 A light curve. Examination of the far-UV continuum in nu Eri during this period shows that the color temperature is lower for the brighter maxima. Analysis of the far-UV continuum at maximum and minimum light yields an effective temperature difference between these two phases of 2200 + or - 750 K. Spectroscopically, three prominent features are seen in the Voyager data: a feature at 985 A mostly due to a blend of C III 977 A, H I Ly gamma 972 A, and N III 990 A; a feature at 1030 A due to H I Ly beta 1026 A and C II 1037 A; and the Si IV resonance doublet near 1400 A. A comparison of the 912-1700 A spectral region in nu Eri with a set of standard, i.e., nonpulsating stars, shows that nu Eri closely resembles the standard both in continuum shape and spectral line strengths with the possible exception of a slight flux excess between 912 and 975 A. The equivalent width of the 985 A feature is shown to vary in strength over the pulsation cycle in antiphase with the light curve and variations seen in the C IV 1548-1551 lines from the IUE data. This behavior of the 985 A feature is most likely caused by variations in the strength of the Ly gamma component of the blend. Comparisons are also made between nu Eri and the only other beta Cephei star studied in the far-UV, BW Vul, with the most notable differences between the two stars being the much larger delta(T(sub eff)) for BW Vul and the almost total absence of abnormalities in observed spectrum of nu Eri.

Porri, A.↗
NASA NTRS1994

Boundary-layer transition detection with infrared imaging emphasizing cryogenic applications

This paper reviews the technique of boundary-layer transition detection using infrared (IR) imaging, emphasizing cryogenic wind-tunnel testing. With the exception of the low-temperature effects on the IR radiation, the discussion is relevant to conventional wind-tunnel and flight testing as well. At low temperatures, IR imaging encounters a reduction in the radiated energy throughout the IR spectrum, combined with a shift to longer wavelengths of the bulk of the radiation. This radiation behavior affects the minimum resolvable temperature difference (MRTD) of the IR imaging system because of its fixed wave band sensitivity. In the absence of commercial long wavelength IR imaging systems, operating at wavelengths longer than 13 micron, some measures can be taken to alleviate the problem caused by the MRTD limitation. The thermal signature of transition can be enhanced by allowing a small and controlled temperature increase of the wind-tunnel flow that induces a transient heat transfer to the model. This action temporarily reveals the model area under the turbulent regime through its higher heating rate compared with the laminar regime. The contrast between the areas exposed to the two regimes can be enhanced by subtraction of thermograms (the equilibrium thermogram from the transient thermogram). Further visual improvement can be obtained through shade stretching or binary shading.

Gartenberg, Ehud↗
NASA NTRS2018

Detection of Photospheric Features in the Near-Infrared Spectrum of a Class 0 Protostar

We present a near-infrared K-band R ≃ 1500 Keck spectrum of S68N, a Class 0 protostar in the Serpens molecular cloud. The spectrum shows a very red continuum, CO absorption bands, weak or non-existent atomic metal absorptions, and H2 emission lines. The near-IR H2 emission is consistent with excitation in shocks or by X-rays but not by UV radiation. We model the absorption component as a stellar photosphere plus circumstellar continuum emission with wavelength-dependent extinction. A Markov Chain Monte Carlo analysis shows that the most likely model parameters are consistent with a low-temperature, low-gravity photosphere with signifi cant extinction and no more than modest continuum veiling. Its T(eff) ≃ 3260 K effective temperature is similar to that of older, more evolved pre-main-sequence stars, but its surface gravity log g ≃ 2:4 cm/sq.s is approximately 1 dex lower. This implies that the radius of this protostar is a factor of ~ 3 larger than that of 106 yr old T Tauri stars. Its low veiling is consistent with a circumstellar disk having intrinsic near-IR emission that is less than or equal to that of more evolved Class I protostars. Along with the high extinction, this suggests that most of the circumstellar material is in a cold envelope, as expected for a Class 0 protostar. This is the first known detection and analysis of a Class 0 protostar absorption spectrum.

Thomas P Greene↗
DOE OSTI2022

Universal van der Waals Force between Heavy Polarons in Superfluids

Here, we investigate the long-range behavior of the induced Casimir interaction between two spinless heavy impurities, or polarons, in superfluid cold atomic gases. With the help of effective field theory (EFT) of a Galilean invariant superfluid, we show that the induced impurity-impurity potential at long distance universally shows a relativistic van der Waals-like attraction (~1/r 7 ) resulting from the exchange of two superfluid phonons. We also clarify finite temperature effects from the same two-phonon exchange process. The temperature $\mathrm{T}$ introduces the additional length scale c s /$\mathrm{T}$ with the speed of sound c s . Leading corrections at finite temperature scale as $\mathrm{T}$ 6 /r for distances r$\ll$c s /$\mathrm{T}$ smaller than the thermal length. For larger distances the potential shows a nonrelativistic van der Waals behavior (~$\mathrm{T}$/r 6 ) instead of the relativistic one. Our EFT formulation applies not only to weakly coupled Bose or Fermi superfluids but also to those composed of strongly correlated unitary fermions with a weakly coupled impurity. The sound velocity controls the magnitude of the van der Waals potential, which we evaluate for the fermionic superfluid in the BCS-BEC crossover.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2009

Numerical and Physical Modeling of the Response of Resonator Liners to Intense Sound and Grazing Flow

Two significant advances have been made in the application of computational aeroacoustics methodology to acoustic liner technology. The first is that temperature effects for discrete sound are not the same as for broadband noise. For discrete sound, the normalized resistance appears to be insensitive to temperature except at high SPL. However, reactance is lower, significantly lower in absolute value, at high temperature. The second is the numerical investigation the acoustic performance of a liner by direct numerical simulation. Liner impedance is affected by the non-uniformity of the incident sound waves. This identifies the importance of pressure gradient. Preliminary design one and two-dimensional impedance models were developed to design sound absorbing liners in the presence of intense sound and grazing flow. The two-dimensional model offers the potential to empirically determine incident sound pressure face-plate distance from resonator orifices. This represents an important initial step in improving our understanding of how to effectively use the Dean Two-Microphone impedance measurement method.

Hersh, Alan S.↗
DOE OSTI2025

Particle-in-cell simulations of expanding high energy density plasmas with laser ray tracing

The design and analysis of high energy density (HED) laser experiments typically rely on radiation hydrodynamics simulations. However, some laser–plasma interaction regimes are not collisional and cannot be adequately modeled with hydrodynamics. For example, strongly driven magnetic reconnection and magnetized collisionless shock experiments possess extended hydrodynamic or even kinetic properties, necessitating first-principles kinetic simulations. In this paper, we present the benchmarking and first results obtained with a laser-ray-tracing and inverse bremsstrahlung absorption module implemented in the particle-in-cell code PSC. The simulation results are compared to radiation hydrodynamic simulations using the FLASH code as well as analytical estimates. We successfully benchmark the energy deposition model and overall hydrodynamic evolution of the systems. We also consider possible kinetic effects that may be expected from laser-target ablation in the HED regime, including non-local transport and two-temperature effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1971

Maximum temperatures for radiation from plasma waves.

Upper limits to radiation temperatures from plasma waves for emissions near the fundamental and second harmonic of the electron plasma frequency are derived in terms of effective temperature for plasma waves. Results are obtained that differ from those of Melrose (1970) by a factor that can exceed 40,000 for some plasmas.

Smith, D. F.↗
NASA NTRS1992

Effects of temperature-dependent molecular absorption coefficients on the thermal infrared remote sensing of the earth surface

The effect of temperature-dependent molecular absorption coefficients on thermal infrared spectral signatures measured from satellite sensors is investigated by comparing results from the atmospheric transmission and radiance codes LOWTRAN and MODTRAN and the accurate multiple scattering radiative transfer model ATRAD for different atmospheric profiles. The sensors considered include the operational NOAA AVHRR and two research instruments planned for NASA's Earth Observing System (EOS): MODIS-N (Moderate Resolution Imaging Spectrometer-Nadir-Mode) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer). The difference in band transmittance is as large as 6 percent for some thermal bands within atmospheric windows and more than 30 percent near the edges of these atmospheric windows. The effect of temperature-dependent molecular absorption coefficients on satellite measurements of sea-surface temperature can exceed 0.6 K. Quantitative comparison and factor analysis indicate that more accurate measurements of molecular absorption coefficients and better radiative transfer simulation methods are needed to achieve SST accuracy of 0.3 K, as required for global numerical models of climate, and to develop land-surface temperature algorithms at the 1-K accuracy level.

Wan, Zhengming↗
NASA NTRS1984

Time dependent land and vegetation canopy temperatures

A simple interactive biosphere is presented based on an electrical analog of turbulent transport processes that produce heat and moisture fluxes between land and the atmosphere. A network of resistances that effect temperature or vapor pressure fluxes are identified and entered into the quasi steady state equations. A set of solutions that depict a realistic diurnal cycle is included.

Sud, Y. C.↗
DOE OSTI2022

Experiments to Measure the Inversion Point of the Isothermal Reactivity Coefficient in a Water-Moderated Pin-Fueled Critical Assembly at Sandia [Slides]

Two experiment series are planned to measure temperature effects in the Sandia Critical Experiments. The first series (IER-304) will measure the critical size of a fuel rod configuration at several temperatures. The second series (IER-452) will measure the inversion temperature of the isothermal reactivity coefficient in the Sandia critical assembly. Each experiment in the second series will be preceded by one or more experiments in the first series. This presentation addresses the conceptual design of the inversion temperature experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗