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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Background Measurements and Simulations of the ComPair Balloon Flight

ComPair, a prototype of the All-sky Medium Energy Gamma-ray Observatory (AMEGO), completed a short-duration high-altitude balloon campaign on 27 August 2023 from Fort Sumner, New Mexico, USA. The goal of the balloon flight was to demonstrate ComPair as both a Compton and Pair telescope in flight, reject the charged particle background, and measure the background γ-ray spectrum. This analysis compares measurements from the balloon flight with Monte Carlo simulations to benchmark the instrument. The comparison finds good agreement between the measurements and simulations and supports the conclusion that ComPair accomplished its goals for the balloon campaign. Additionally, two charged particle background rejection schemes are discussed: a soft ACD veto that records a higher charged particle event rate but with less risk of event loss, and a hard ACD veto that limits the charged particle event rate on board. There was little difference in the measured spectra from the soft and hard ACD veto schemes, indicating that the hard ACD veto could be used for future flights. The successes of ComPair’s engineering flight will inform the development of the next generation of ComPair with upgraded detector technology and larger active area.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Spectroscopic Determination of Stellar Parameters and Oxygen Abundances for Hyades/Field G–K Dwarfs

It has been suggested that Fe abundances of K dwarfs derived from Fe i and Fe ii lines show considerable discrepancies, and oxygen abundances determined from high-excitation O i 7771–5 triplet lines are appreciably overestimated (the problem becoming more serious toward lower T {sub eff}), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G–K dwarfs (Hyades cluster stars and field stars) by assuming the classical Fe i/Fe ii ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to O i 7771–5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in T {sub eff} and logg from the well-determined solutions of Hyades dwarfs are mostly ≲100 K and ≲0.1 dex). Likewise, the oxygen abundances of Hyades stars are around [O/H] ∼ +0.2 dex (consistent with the metallicity of this cluster) without exhibiting any systematic T {sub eff}-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha–Boltzmann equation for Fe i/Fe ii) and oxygen abundances can be reliably determined from the O i 7771–5 triplet for K dwarfs as far as stars of T {sub eff} ≳ 4500 K are concerned. We suspect that previously reported strongly T {sub eff}-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper T {sub eff} scale.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

DSN research and technology support

The ongoing activities at the Venus Station (DSS 13) and the Microwave Test Facility (MTF) discussed include: (1) equipment implementation for unattended operation at DSS 13; (2) salvaging of a 20-kW klystron, at a cost savings of several thousand dollars by the DSN High Power Transmitter Facility; (3) extensive tracking activities with the 26-m antenna including DSN Platform Parameters, Multistation Planetary Radar, Helios II Spectrum Broadening Analysis, VLBI Validation, Planetary Radio Astronomy, and Pulsar Rotation Constancy, for a total time of 219-1/4 observing hours; (4) clock synchronization transmissions from the DSS 13 master clock to the overseas 64-m antenna complexes and special implementation activities in support of PV-78; and (5) implementation of a hydrogen maser frequency standard and the pathfinder installation of a utility control system (UCS) and significant station modification and maintenance.

Jackson, E. B.↗
NASA NTRS1978

Kinetic model of turbulence in an incompressible fluid

A statistical description of turbulence in an incompressible fluid obeying the Navier-Stokes equations is proposed, where pressure is regarded as a potential for the interaction between fluid elements. A scaling procedure divides a fluctuation into three ranks representing the three transport processes of macroscopic evolution, transport property, and relaxation. Closure is obtained by relaxation, and a kinetic equation is obtained for the fluctuation of the macroscopic rank of the distribution function. The solution gives the transfer function and eddy viscosity. When applied to the inertia subrange of the energy spectrum the analysis recovers the Kolmogorov law and its numerical coefficient.

Tchen, C. M.↗
NASA NTRS1983

LANDSAT-4 thematic mapper Modulation Transfer Function (MTF) evaluation

A power spectrum (PS) analysis technique was used to compare thematic mapper (TM) A and P-tape data for a Washington, DC scene in two orthogonal directions, along scan and along track. The resulting effective modulation transfer functions (MTF) between the A and P data are repeatable from area to area and consistent with theoretical expectations. The average x-direction (along scan) MTF calculated with the PS technique is compared to the MTF of the cubic convolution resampling function used to create P data from A data. The two curves are nearly identical, indicating that the major factor affecting the image quality of P data relative to A data is the cubic convolution resampling.

Schowengerdt, R.↗
NASA NTRS1991

A rapid energetic X-ray flare in the quasar PKS0558 - 504

A recent observation from the Ginga satellite of the quasar PKS0558 - 504 is reported during which the X-ray flux increased by 67 percent in the space of only three minutes. There was no significant change in the spectrum. Comprehensive analysis of the data strongly indicates that this was a genuine X-ray flare originating in the quasar. The implied rate of change in luminosity in the 2-10 keV range, assuming a Hubble constant of 70 km/s/Mpc, and a cosmological deceleration parameter q0 = 0.5, is 3.2 x 10 to the 42nd erg/sq s, the highest value measured for a quasar. When photon scattering is considered, this is about 16 times greater than could be produced, with a three-minute rise time, in an isotropically emitting plasma. It is argued that the apparent luminosity must be enhanced by relativistic beaming. This is the first indication of beaming in an 'ordinary' unpolarized quasar.

Remillard, R. A.↗
NASA NTRS1993

Applications of wavelet-based compression to multidimensional Earth science data

A data compression algorithm involving vector quantization (VQ) and the discrete wavelet transform (DWT) is applied to two different types of multidimensional digital earth-science data. The algorithms (WVQ) is optimized for each particular application through an optimization procedure that assigns VQ parameters to the wavelet transform subbands subject to constraints on compression ratio and encoding complexity. Preliminary results of compressing global ocean model data generated on a Thinking Machines CM-200 supercomputer are presented. The WVQ scheme is used in both a predictive and nonpredictive mode. Parameters generated by the optimization algorithm are reported, as are signal-to-noise (SNR) measurements of actual quantized data. The problem of extrapolating hydrodynamic variables across the continental landmasses in order to compute the DWT on a rectangular grid is discussed. Results are also presented for compressing Landsat TM 7-band data using the WVQ scheme. The formulation of the optimization problem is presented along with SNR measurements of actual quantized data. Postprocessing applications are considered in which the seven spectral bands are clustered into 256 clusters using a k-means algorithm and analyzed using the Los Alamos multispectral data analysis program, SPECTRUM, both before and after being compressed using the WVQ program.

Bradley, Jonathan N.↗
NASA NTRS1955

Apparatus for Measurements of Time and Space Correlation

A brief review is made of improvements to an experimental apparatus for time and space correlation designed for study of turbulence. Included is a description of the control of the measurements and a few particular applications.

TURBULENCE - SPECTRUM ANALYSIS↗
NASA NTRS1998

PCA/HEXTE Observations of Coma and A2319

The Coma cluster was observed in 1996 for 90 ks by the PCA and HEXTE instruments aboard the RXTE satellite, the first simultaneous, pointing measurement of Coma in the broad, 2-250 keV, energy band. The high sensitivity achieved during this long observation allows precise determination of the spectrum. Our analysis of the measurements clearly indicates that in addition to the main thermal emission from hot intracluster gas at kT=7.5 keV, a second spectral component is required to best-fit the data. If thermal, it can be described with a temperature of 4.7 keV contributing about 20% of the total flux. The additional spectral component can also be described by a power-law, possibly due to Compton scattering of relativistic electrons by the CMB. This interpretation is based on the diffuse radio synchrotron emission, which has a spectral index of 2.34, within the range allowed by fits to the RXTE spectral data. A Compton origin of the measured nonthermal component would imply that the volume-averaged magnetic field in the central region of Coma is B =0.2 micro-Gauss, a value deduced directly from the radio and X-ray measurements (and thus free of the usual assumption of energy equipartition). Barring the presence of unknown systematic errors in the RXTE source or background measurements, our spectral analysis yields considerable evidence for Compton X-ray emission in the Coma cluster.

Rephaeli, Yoel↗
NASA NTRS2003

New Ground-based Spectral Observations of Mercury and Comparison with the Moon

Spectroscopic observations (400-670 nm) of Mercury were made at La Palma with the Nordic Optical Telescope (NOT) in June and July of 2002. Extensive observations of solar analog standard stars and validation spectra of 7 Iris and a variety of locations on the Moon were also collected. The 2002 Mercury data were also combined with previous observations (520-970 nm) from the Swedish Solar Vacuum Telescope (SVST). A spectrum (400-970 nm) calibrated to standard bidirectional geometry (alpha=i=30deg, e=0deg) was constructed based on the spectral slopes from 2002. The combined spectrum permits analysis with the Lucey lunar abundance relations for FeO and TiO2.

Blewett, D. T.↗
NASA NTRS2004

Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astronometry Program

We present preliminary trigonometric parallaxes and proper motions for 22 L dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager on the US naval Observatory (USNO) 1.55 m Strand Astrometric Reflector. The results presented here are based on observations obtained between 2000 September and 2002 November; about half of the objects have an observational time baseline of t 1:3 yr and half t 2:0 yr. Despite these short time baselines, the astrometric quality is sufficient to produce significant new results, especially for the nearer T dwarfs. Seven objects are in common with the USNO optical CCD parallax program for quality control and seven in common with the European Southern Observatory 3.5 m New Technology Telescope parallax program. We compare astrometric quality with both of these programs. Relative to absolute parallax corrections are made by employing Two Micron All Sky Survey and/or Sloan Digital Sky Survey photometry for reference-frame stars. We combine USNO infrared and optical parallaxes with the best available California Institute of Technology (CIT) system photometry to determine MJ , MH, and MK values for 37 L dwarfs between spectral types L0 and L8 and 19 T dwarfs between spectral types T0.5 and T8 and present selected absolute magnitude versus spectral type and color diagrams, based on these results. Luminosities and temperatures are estimated for these objects. Of special interest are the distances of several objects that are at or near the L-T dwarf boundary so that this important transition can be better understood. The previously reported early to mid T dwarf luminosity excess is clearly confirmed and found to be present at J, H, and K. The large number of objects that populate this luminosity-excess region indicate that it cannot be due entirely to selection effects. The T dwarf sequence is extended to MJ 16:9 by 2MASS J041519 0935, which, at d 5:74 pc, is found to be the lluminous LOG (L=L )pa

L DWARFS↗
NASA NTRS2002

Plasma-enhanced chemical vapor deposition of multiwalled carbon nanofibers

Plasma-enhanced chemical vapor deposition is used to grow vertically aligned multiwalled carbon nanofibers (MWNFs). The graphite basal planes in these nanofibers are not parallel as in nanotubes; instead they exhibit a small angle resembling a stacked cone arrangement. A parametric study with varying process parameters such as growth temperature, feedstock composition, and substrate power has been conducted, and these parameters are found to influence the growth rate, diameter, and morphology. The well-aligned MWNFs are suitable for fabricating electrode systems in sensor and device development.

Nanotechnology/instrumentation/methods↗
NASA NTRS2003

Raman-atomic force microscopy of the ommatidial surfaces of Dipteran compound eyes

The ommatidial lens surfaces of the compound eyes in several species of files (Insecta: Diptera) and a related order (Mecoptera) were analyzed using a recently developed Raman-atomic force microscope. We demonstrate in this work that the atomic force microscope (AFM) is a potentially useful instrument for gathering phylogenetic data and that the newly developed Raman-AFM may extend this application by revealing nanometer-scale surface chemistry. This is the first demonstration of apertureless near-field Raman spectroscopy on an intact biological surface. For Chrysopilus testaceipes Bigot (Rhagionidae), this reveals unique cerebral cortex-like surface ridges with periodic variation in height and surface chemistry. Most other Brachyceran flies, and the "Nematoceran" Sylvicola fenestralis (Scopoli) (Anisopodidae), displayed the same morphology, while other taxa displayed various other characteristics, such as a nodule-like (Tipula (Triplicitipula) sp. (Tipulidae)) or coalescing nodule-like (Tabanus punctifer Osten Sacken (Tabanidae)) morphology, a smooth morphology with distinct pits and grooves (Dilophus orbatus (Say) (Bibionidae)), or an entirely smooth surface (Bittacus chlorostigma MacLachlan (Mecoptera: Bittacidae)). The variation in submicrometer structure and surface chemistry provides a new information source of potential phylogenetic importance, suggesting the Raman-atomic force microscope could provide a new tool useful to systematic and evolutionary inquiry.

Eye/ultrastructure↗
NASA NTRS2002

Atmospheric pressure chemical ionization studies of non-polar isomeric hydrocarbons using ion mobility spectrometry and mass spectrometry with different ionization techniques

The ionization pathways were determined for sets of isomeric non-polar hydrocarbons (structural isomers, cis/trans isomers) using ion mobility spectrometry and mass spectrometry with different techniques of atmospheric pressure chemical ionization to assess the influence of structural features on ion formation. Depending on the structural features, different ions were observed using mass spectrometry. Unsaturated hydrocarbons formed mostly [M - 1]+ and [(M - 1)2H]+ ions while mainly [M - 3]+ and [(M - 3)H2O]+ ions were found for saturated cis/trans isomers using photoionization and 63Ni ionization. These ionization methods and corona discharge ionization were used for ion mobility measurements of these compounds. Different ions were detected for compounds with different structural features. 63Ni ionization and photoionization provide comparable ions for every set of isomers. The product ions formed can be clearly attributed to the structures identified. However, differences in relative abundance of product ions were found. Although corona discharge ionization permits the most sensitive detection of non-polar hydrocarbons, the spectra detected are complex and differ from those obtained with 63Ni ionization and photoionization. c. 2002 American Society for Mass Spectrometry.

Non-NASA Center↗
NASA NTRS1999

Neutron yields from 155 MeV/nucleon carbon and helium stopping in aluminum

Neutron fluences have been measured from 155 MeV/nucleon 4He and 12C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon 4He stopping in Al and 155 MeV/nucleon 12C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the 12C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 +/- 0.03) as does the 4He + Al system (1.02 +/- 0.04), despite the fact that 12C has three times as many neutrons as does 4He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the 4He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon 4He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.

NASA Discipline Radiation Health↗