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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
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NASA NTRS2020

Exploring the Limits of the Data-Model-Theory Synergy: “Hot” MW Transitions for Rovibrational IR Studies

In order to further improve the accuracy of rovibrational IR line lists generated from the “Best Theory +Reliable High-resolution Experiment” (BTRHE) strategy from 0.01-0.05 cm-1, or 300-1500 MHz, to ~10 MHz, we explore the current limits of the Data-Model-Theory synergy by examining the accuracy and consistency of existing data, then propose that “hot” bands in microwave (MW) spectra is the solution we need for future enhancements. The Ames SO2 J=0-20 rovibrational energy levels computed on the semi-empirically refined Ames-2 potential energy surface (PES) are fit to the Effective Hamiltonian (EH) model regularly used in the experimental infrared (IR) analysis for SO2 isotopologues. In the fitted EH(Ames) model, the rotational constants A/B/C and all 5 quartic centrifugal distortion constants display clear, systematic, and consistent patterns along the vibrational state energy or quanta. Such consistent patterns may facilitate the vibrational assignments for MW hot bands and extract more information from high temperature MW spectra. Some EH(Expt) analyses were carried out with the lowest order Coriolis Coupling term, C1. Their constants should not be directly compared with other EH(Expt) and EH(Ames) results. After excluding them, our  = EH(Ames)- EH(Expt) analyses for 5 isotopologues (626, 636, 646, 628 and 828) indicates some loss of accuracy and consistency starting from vibrational states as low as 22 or 1000 cm-1. Some EH parameters, e.g. K, may have relative deviations as large as 50-100% and totally lose any recognizable patterns. This simply means that current EH(Expt) models do not have the system-wide consistency we need to further refine the EH(Ames) and Ames rovibrational IR line lists. A large part of such defects are probably inherited from the limited precision of experimental line positions, i.e. 1E-3 ~ 1E-4 cm-1, or 3-30 MHz. This is confirmed in a series of truncation tests using the Ames data. Although the EH(Ames) consistency may help identify unreliable rovibrational EH(Expt) parameters, and make reliable predictions for minor isotopologues and unobserved vibrational bands, we believe only the highly accurate “hot” MW transitions can provide real enhancements for EH(Expt) accuracy and consistency. “Hot” MW spectra should play a more significant role in the future synergy of Data, Model, and Theory in the field of rovibrational IR studies.

Xinchuan Huang↗
NASA NTRS1973

Theory of satellite structures on spectral-line profiles.

A systematic comparison with experiment of various explanations for the problem of satellite-band formation on spectral-line profiles was initiated. The experiments were performed under a variety of conditions in an effort to construct a consistent model of entire line shapes. A composite theory is detailed which is the result of the insights of many individuals. The calculations indicate that the main features of the problem, the line, the high-intensity red satellites, and the blue satellite can be described simultaneously. The results also indicate that widely different potentials can lead to very similar line profiles. Ancillary conclusions are presented concerning the role of Lennard-Jones potentials in line-shape calculations.

Atakan, A. K.↗
NASA NTRS1972

A study of microwave leakage through perforated flat plates.

A simple formula useful for predicting leakage through a circular hole array in a metallic flat plate is presented. A correction is given for plate thickness. The formula is applicable to arrays having either a 60-deg (staggered) or 90-deg (square) hole pattern, but is restricted to the case of (1) an obliquely incident plane wave with the E field polarized normal to the plane of incidence, and (2) large transmission loss. When theoretical values were compared to experimental data obtained on test samples having transmission losses greater than 20 dB, the agreement between theory and experiment was typically better than 1 dB at S band and 2 dB at X band.

Otoshi, T. Y.↗
NASA NTRS1973

Vibrational relaxation of carbon monoxide studied by two-wavelength infrared emission

Experimental results are presented for the vibrational relaxation of pure carbon monoxide behind incident shock waves over the temperature range 4000 to 6300 K. The data were obtained as infrared emission from the fundamental and overtone vibrational band systems (in some of the experiments the two-band systems were recorded simultaneously). The data are consistent with present theories for the vibrational relaxation of diatomic molecules and can be interpreted in terms of an initial Boltzmann vibrational distribution relaxing toward final equilibrium via a continuous sequence of intermediate Boltzmann distributions.

Chackerian, C., Jr.↗
NASA NTRS1985

An experimental TE sub 12 - TE sub 11 circular waveguide mode converter

Theoretical and experimental results for a prototype TE sub 12 to TE sub 11 circular waveguide mode converter are discussed. The system which requires such device, the high power Ka-Band transmitter is described briefly. A short review of coupled mode theory is given, and the theoretical performance of the final converter design is given. Experimental results for the fabricated converter are presented and compared with theory. A method of identifying the various circular waveguide modes in a multimode device is described. Given the close agreement between the theoretical predictions and experimental results, the computer code may be used with confidence in the design of future multimode tapers and mode converters.

Hoppe, D.↗
NASA NTRS1984

Ultrapressure materials science

Three active areas of research at ultra pressure are pursued, i.e., diffraction studies with the Cornell High Energy Synchrotron Source (CHESS), band gap and absorption edge effects, indentor-anvil experiments and theory and research to attain higher pressures. The range over which X-ray diffraction data and absorption edge data are obtained is extended to 700 kbars. Using the indentor technique pressures of 2.1 Mbars are obtained. Research results and methods are discussed.

Ruoff, A. L.↗
NASA NTRS1988

Interstellar dust and the IUE

Understanding of the physical nature of interstellar dust, as modified by observations of extinction obtained with IUE, is considered. Properties of extinction laws along various lines of sight, with emphasis on the bump, are reviewed. Correlations of the UV and optical/near infrared extinction are discussed. Other diagnostics of interstellar dust, such as the near infrared emission bands, polarization, far infrared thermal emission, and depletions are mentioned, and theories are summarized.

Mathis, John S.↗
NASA NTRS1990

Surface electrons in inverted layers of p-HgCdTe

Anodic oxide passivation of p-type HgCdTe generates an inversion layer. Extremely high Hall mobility data for electrons in this layer indicated the presence of a two-dimensional electron gas. This is verified by use of the Shubnikov-de Haas effect from 1.45 to 4.15 K. Data are extracted utilizing a numerical second derivative of dc measurement. Three sub-bands are detected. Their relative occupancies are in excellent agreement with theory and with experimental results obtained on anodic oxide as accumulation layers of n-type HgCdTe. The effective mass derived is comparable to what was expected.

Schacham, Samuel E.↗
NASA NTRS2013

On Multiscale Modeling: Preserving Energy Dissipation Across the Scales with Consistent Handshaking Methods

A mesh objective crack band model was implemented within the generalized method of cells micromechanics theory. This model was linked to a macroscale finite element model to predict post-peak strain softening in composite materials. Although a mesh objective theory was implemented at the microscale, it does not preclude pathological mesh dependence at the macroscale. To ensure mesh objectivity at both scales, the energy density and the energy release rate must be preserved identically across the two scales. This requires a consistent characteristic length or localization limiter. The effects of scaling (or not scaling) the dimensions of the microscale repeating unit cell (RUC), according to the macroscale element size, in a multiscale analysis was investigated using two examples. Additionally, the ramifications of the macroscale element shape, compared to the RUC, was studied.

Pineda, Evan J.↗
NASA NTRS1982

Theory of the fine structure of auroral kilometric radiation

Recent data from ISEE 1 show auroral kilometric radiation (AKR) with finely separated bands in frequency. The observation that the AKR fine structure frequency separation is about equal to the ion cyclotron frequency at the AKR source is strong evidence for the interaction of AKR and electrostatic ion cyclotron (EIC) waves in the source, as proposed by Grabbe et al. (1980) to explain the origin of AKR. It is pointed out that no other wave of frequency close to the band separation is known to exist in the auroral source region. The fine structure observed in the source region AKR is the first evidence for EIC waves in the lower source region (3000 - 5000 km attitude), as required in the theory of Grabbe et al.

Grabbe, C. L.↗
NASA NTRS2017

The Spectral Invariant Approximation Within Canopy Radiative Transfer to Support the Use of the EPIC/DSCOVR Oxygen B-band for Monitoring Vegetation

EPIC (Earth Polychromatic Imaging Camera) is a 10-channel spectroradiometer onboard DSCOVR (Deep Space Climate Observatory) spacecraft. In addition to the near-infrared (NIR, 780 nm) and the 'red' (680 nm) channels, EPIC also has the O2 A-band (764+/-0.2 nm) and B-band (687.75+/-0.2 nm). The EPIC Normalized Difference Vegetation Index (NDVI) is defined as the difference between NIR and 'red' channels normalized to their sum. However, the use of the O2 B-band instead of the 'red' channel mitigates the effect of atmosphere on remote sensing of surface reflectance because O2 reduces contribution from the radiation scattered by the atmosphere. Applying the radiative transfer theory and the spectral invariant approximation to EPIC observations, the paper provides supportive arguments for using the O2 band instead of the red channel for monitoring vegetation dynamics. Our results suggest that the use of the O2 B-band enhances the sensitivity of the top-of-atmosphere NDVI to the presence of vegetation.

Alexander Marshak↗
NASA NTRS1972

Infrared laboratory studies of synthetic planetary atmospheres

The initial stages of the research were involved with a test of Burch's law of multiplicative transmittance for mixed absorbing gases when their lines are broadened by H2 and He, which are constituents of the atmospheres of the major planets. The broadening of individual lines in the CO fundamental by various gases was investigated. Line strength and half-width for individual CO lines were studied as a function of temperature. Measurements of total band absorptance as a function of absorber thickness and total effective pressure were made at various temperatures for bands of CO and N2O. Attempts were made to develop a phenomenological theory of line broadening that would account for the phenomena observed for the CO fundamental and those reported for more highly polar gases. Laboratory measurements of nitric acid vapor absorptance were compared with balloon measurements in arriving at an estimate of the quantity of nitric acid vapor present in the earth's atmosphere in the region of the ozone layer.

Williams, D.↗
NASA NTRS1975

Hydrogen interactions with metals

Review of the literature on the nature and extent of hydrogen interactions with metals and the role of hydrogen in metal failure. The classification of hydrogen-containing systems is discussed, including such categories as covalent hydrides, volatile hydrides, polymeric hydrides, and transition metal hydride complexes. The use of electronegativity as a correlating parameter in determining hydride type is evaluated. A detailed study is made of the thermodynamics of metal-hydrogen systems, touching upon such aspects as hydrogen solubility, the positions occupied by hydrogen atoms within the solvent metal lattice, the derivation of thermodynamic functions of solid solutions from solubility data, and the construction of statistical models for hydrogen-metal solutions. A number of theories of hydrogen-metal bonding are reviewed, including the rigid-band model, the screened-proton model, and an approach employing the augmented plane wave method to solve the one-electron energy band problem. Finally, the mechanism of hydrogen embrittlement is investigated on the basis of literature data concerning stress effects and the kinetics of hydrogen transport to critical sites.

Mclellan, R. B.↗
NASA NTRS1978

Signal detection in l/f noise of SQUID magnetometers

It is shown that the variance on the SQUID power spectrum in the l/f low frequency region is well behaved, i.e., any small frequency band may be treated as white noise in standard power spectrum estimation theory. Specifically a calibration signal is examined at 0.017 Hz with an equivalent energy referred to the SQUID input coil of 1 times 10 to the -30th J and a digitally recorded and analyzed record of 140 hr duration obtained an optimum S/N better than 400. The results are in good agreement with theory. In addition no deviation from the l/f dependence of the noise energy spectrum is seen down to frequencies below 10 to the -5th Hz. A commercially available SQUID and electronics system were used.

Cabrera, B.↗
NASA NTRS1983

Influence of radiative recombination on the minority-carrier transport in direct band-gap semiconductors

When a semiconductor sample is irradiated by means of an external source, emitting photons or electrons, excess carriers are produced which distribute themselves throughout the sample. One of the parameters which determine the distribution of the carriers is the surface recombination velocity. The present investigation is concerned with the recombination lifetime tau. The predominant mechanism for recombination in wide band-gap semiconductors is described by the Shockley-Read-Hall (SRH) theory. The transport equations are derived for free carriers and the radiation field. The considered theory is applied to a semiinfinite, one-dimensional semiconductor slab irradiated by light of a given frequency. Some numerical considerations based on n-type GaAs are presented. Attention is given to a determination of the radiation transmitted through the surface of the sample.

Von Roos, O.↗
NASA NTRS1985

Reassignment of the Iron (3) Absorption Bands in the Spectra of Mars

Absorption features in the near-infrared and visible region reflectance spectra of Mars have been assigned to specific Fe (3+) crystal-field and o(2-) yields Fe(3+) charge transfer transitions. Recently, near-ultraviolet absorption spectra of iron oxides were obtained and the energies of o(2-) yields Fe(3+) charge-transfer (LMCT) transitions were determined from accurate SCF-X # alpha-SW molecular orbital calculations on (FeO6)(9-) and (FeO4)(5-) clusters. Both the theoretical and experimental results, together with existing data in the literature, show that some of the previous Fe(3+) band assignments in the spectra of Mars need to be revised. The theory of Fe(3+) spectra in minerals is discussed and applied to the spectrum of Mars.

Sherman, D. M.↗