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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

On the biological hazard of galactic antinuclei

The interaction of antinuclei in the galactic cosmic-ray beam with biological systems is studied. A nuclei-antinuclei annihilation event observed in nuclear emulsion near the end of the slowing-down trajectories of singly charged particle is discussed. An annihilation event that occurred by capture of the antinucleus into an atomic orbital followed by cascade to or near the ground atomic state and subsequent annihilation with the nuclear material of the atom is described. Microdosimetric quantities relevant to potential biological hazards are estimated. The average linear-energy-transfer spectrum for galactic cosmic ray antinuclei annihilation events in tissues is presented. It is observed that the annihilation in tissues occurs mainly in O and the heavier elements around K.

Wilson, J. W.↗
NASA NTRS1993

A comparison of theoretical CIV emission line strengths with active region observations obtained with the solar EUV rocket telescope and spectrograph (SERTS)

Theoretical line ratios involving 2s 2S - 3p 2P, 2p 2p - 3s 2S, and 2p 2S - 3d 2D transitions in C IV between 312 and 420 A are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22 percent. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on board Skylab. The potential usefulness of the C IV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed.

Keenan, F. P.↗
NASA NTRS1973

Strength of Chemical Bonds

Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

Christian, Jerry D.↗
NASA NTRS2018

Determination of Trace Silicone Contamination on Composites by Quantitative XPS and LIBS

Surface treatment and surface characterization techniques are critical to ensure that adherends are chemically activated and free of contaminants prior to adhesive bonding. Silicone contamination from mold-release agents and other sources can interfere with interfacial bonding, decreasing the durability and performance of bonded composite structures. Tools and methods are needed that can be used in a production environment to reliably detect low levels of contaminants in a rapid, simple, and cost-effective manner to improve bond reliability. In this work, surface characterization of carbon fiber reinforced polymer (CFRP) composites was performed using laser induced breakdown spectroscopy (LIBS) and the results were compared with those obtained from X-ray photoelectron spectroscopy (XPS). The objective was to investigate the ability to quantify the surface species measured by LIBS since it offers many advantages over XPS in terms of ease of use, sample preparation, and real-time results. The as-processed CFRP panels had trace surface silicone contamination from the fabrication process, the source of which was not investigated. The composites were laser treated at select average laser power levels, resulting in varying levels of contamination reduction. The Si atomic percentage measurements using XPS were conducted both before and after laser ablation. The XPS results were compared with those obtained from LIBS to assess the reliability of each technique for surface contaminant characterization. The results showed an excellent correlation in Si atomic concentration between the two techniques.

Ledesma, Rodolfo↗
NASA NTRS1995

Relativistic timescale analysis suggests lunar theory revision

The SI second of the atomic clock was calibrated to match the Ephemeris Time (ET) second in a mutual four year effort between the National Physical Laboratory (NPL) and the United States Naval Observatory (USNO). The ephemeris time is 'clocked' by observing the elapsed time it takes the Moon to cross two positions (usually occultation of stars relative to a position on Earth) and dividing that time span into the predicted seconds according to the lunar equations of motion. The last revision of the equations of motion was the Improved Lunar Ephemeris (ILE), which was based on E. W. Brown's lunar theory. Brown classically derived the lunar equations from a purely Newtonian gravity with no relativistic compensations. However, ET is very theory dependent and is affected by relativity, which was not included in the ILE. To investigate the relativistic effects, a new, noninertial metric for a gravitated, translationally accelerated and rotating reference frame has three sets of contributions, namely (1) Earth's velocity, (2) the static solar gravity field and (3) the centripetal acceleration from Earth's orbit. This last term can be characterized as a pseudogravitational acceleration. This metric predicts a time dilation calculated to be -0.787481 seconds in one year. The effect of this dilation would make the ET timescale run slower than had been originally determined. Interestingly, this value is within 2 percent of the average leap second insertion rate, which is the result of the divergence between International Atomic Time (TAI) and Earth's rotational time called Universal Time (UT or UTI). Because the predictions themselves are significant, regardless of the comparison to TAI and UT, the authors will be rederiving the lunar ephemeris model in the manner of Brown with the relativistic time dilation effects from the new metric to determine a revised, relativistic ephemeris timescale that could be used to determine UT free of leap second adjustments.

Deines, Steven D.↗
NASA NTRS1990

Far-infrared spectroscopy of the DR 21 star formation region

Far-IR line and continuum observations of the DR 21 star formation region are presented. It is shown that the extended emission in the 63 micron forbidden O I, 35 micron forbidden Si II, and 158 micron forbidden C II lines is most likely produced in dense, warm photodissociation regions on the surfaces of atomic and molecular clumps of size smaller than 0.6 pc. The gas temperatures in these photoelectrically heated, predominantly atomic layers are 250-500 K and are maintained by FUV fluxes 10,000 or more times the average interstellar radiation field. Gas densities in the surface layers are in the range 10,000-50,000/cu cm. The gas phase abundance of Si(+) is inferred to be about 5 x 10 to the -6th relative to hydrogen, or about 0.15 of its solar abundance. The mass of atomic gas is at least 200 solar masses.

Lane, Adair P.↗
NASA NTRS1990

Theoretical study of the nitrogen-atom hyperfine coupling constant. II

The N hyperfine coupling constant has been computed using multireference configuration interaction (MRCI) and averaged coupled pair functional (ACPF) treatments in very large one-particle basis sets. Unlike previous calculations, no selection of configurations has been performed. The calculations again illustrate the difficulty of computing the N hyperfine coupling constant accurately. The best MRCI result of 10.7 MHz is larger than the accurate experimental value of 10.4509 MHz, while the best ACPF result (10.3 MHz) is smaller than experiment. The difference between this work and previous calculations is discussed.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1984

Pioneer 10 and Voyager observations of the interstellar medium in scattered emission of the He584 A and H Lya 1216 A lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 A was applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments in the same way as other earlier determinations based on the same method. However, the spacecraft data were combined with daily full sun averages of the H Lyman 1216 A line obtained by the Solar Mesospheric Explorer satellite to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a one year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are H = 0.12 cu cm and H = .016 cu cm, giving a density ratio close to the cosmic abundance value in contrast to some earlier results indicating a depletion of atomic hydrogen. Estimates were obtained of galactic background emissions in the signals of both spacecraft.

Shemansky, D. E.↗
NASA NTRS1984

Pioneer 10 and Voyager Observations of the Interstellar Medium in Scattered Emission of the He 584 a and H Lya 1216 a Lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 A was applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments in the same way as other earlier determinations based on the same method. However, the spacecraft data were combined with daily ll sun averages of the H Lyman 1216 A line obtained by the Solar Mesospheric Explorer satellite to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a one year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are H = 0.12/cu cm and H = .016/cu cm, giving a density ratio close to the cosmic abundance value in contrast to some earlier results indicating a depletion of atomic hydrogen. Estimates were obtained of galactic background emissions in the signals of both spacecraft.

Shemansky, D. E.↗
NASA NTRS1980

Interstellar depletions and far-ultraviolet extinction in the Rho Ophiuchi cloud

Copernicus ultraviolet data on six stars embedded in the well-studied Rho Ophiuchi cloud complex have been analyzed for interstellar abundances, densities, and far-ultraviolet extinction parameters, in an effort to determine how interstellar depletions depend on physical conditions. While there are variations within the cloud in the overall depletions, the pattern of depletions from element to element is constant for all six lines of sight. A picture is suggested in which the cloud core has a small velocity dispersion or is either so strongly depleted or so dense (hence not ionized) that the lines of first ions of heavy elements do not arise there, but rather form in a less-dense or less-depleted outer region. The cloud as a whole has substantial depletions, average to low far-ultraviolet extinction, and a low ratio of molecular to atomic hydrogen.

Snow, T. P., Jr.↗
NASA NTRS1985

Satellite observations of 557.7 NM airglow as a diagnostic technique to study the dynamics of the lower thermosphere

Photometric observations of the airglow limb at 557.7 nm have been made from the ISIS 2 satellite since 1971. From an analysis of 32,000 airglow limb observations obtained during the first two years of operation, the major temporal and spatial characteristics of the night airglow have been identified. Maxima occur in mid-October and mid-April at all latitudes. There is a marked variation with latitude during the equinox periods, with peak intensities near 35 degrees in autumn and near 25 degrees in spring. It is possible to gain considerable insight into the behavior of the lower thermosphere by combining the airglow observations with a simple model of the photochemical and dynamical processes. In this way a pattern of the latitude and temporal variation of atomic oxygen concentration at the peak of the layer as well as the eddy diffusion in this altitude region have been inferred. The concentration of atomic oxygen shows midlatitude peaks near equinox, and minima about one month after solstice. Average values at midlatitudes are about 1.3 times those at the equator. The amplitude of the semiannual component is about 20% of the mean value at 35 degrees as compared to 10% at the equator, and the amplitude of 12-month component is about 12% at 35 deg and 5% at the equator. The semiannual component has a minimum that occurs approximately 3 weeks (plus or minus) after solstice at all latitudes, while the 12-month component peaks in the summer hemisphere at solstice (plus or minus 2 months).

Cogger, L. L.↗
NASA NTRS1990

Physical conditions in photodissociation regions: Application to galactic nuclei

Infrared and sub-millimeter observations are used in a simple procedure to determine average physical properties of the neutral interstellar medium in Galactic photodissociation regions as well as in ensembles of clouds which exist in the nuclei of luminous infrared galaxies. The relevant observations include the Infrared Astronomy Satellite (IRAS) infrared continuum measurements, infrared spectroscopy of the fine-structure lines of SiII 35 microns, OI 63 microns, and CII 158 microns, and the 2.6 mm CO (J=1-0) rotational transition. The diagnostic capabilities of the OI 145 microns line is also addressed. Researchers attribute these emission lines as well as the continuum to the atomic/molecular photodissociation region on the surfaces of molecular clouds which are illuminated by strong ultraviolet fields. They use the theoretical photodissociation region models of Tielens and Hollenbach (1985, Ap. J., 291, 722) to construct simple diagrams which utilize line ratios and line to continuum ratios to determine the average gas density n, the average incident far-ultraviolet flux G sub o, and the temperature of the atomic gas T.

Wolfire, M. G.↗
NASA NTRS2023

Testing the Gravitational Redshift With an Inner Solar System Probe: the Veritas Case

The NASA Discovery-class mission VERITAS, selected in June 2021, will be launched towards Venus after 2027. In addition to the science instrumentation that will build global foundational geophysical datasets, VERITAS proposed to conduct a technology demonstration for the Deep Space Atomic Clock (DSAC-2). A first DSAC successfully operated in low-Earth orbit for more than two years, demonstrated the trapped ion atomic clock technology, and established a new level of performance for clocks in space. DSAC-2 would have further improvements in size, power, and performance. It would host a 1× 10 -13 grade USO to produce a frequency output with short-term stability of less than 2× 10 -13 /√ τ (where τ is the averaging time).However, due to funding shortfalls, DSAC-2, had to be canceled. The initially foreseen presence of an atomic clock on board the probe, however, raised the question whether this kind of instrumentation could be useful not only for navigation and time transfer but also for fundamental physics tests. In this work, we consider the DSAC-2 atomic clock and VERITAS mission as a specific example to measure possible discrepancies in the redshift predicted by General Relativity by using an atomic clock onboard an interplanetary spacecraft. In particular we investigate the possibility of measuring possible violations of the Local Lorentz Invariance and Local Position Invariance principles. We perform accurate simulations of the experiment during the VERITAS cruise phase. We consider different parametrizations of the possible violations of the General Relativity, different operational conditions, and several different assumptions on the expected measurement performance. We show that DSAC-2 onboard VERITAS would provide new and improved constraints with respect to the current knowledge. Our analysis shows the scientific value of atomic clocks like DSAC-2 hosted onboard interplanetary spacecraft.

Fabrizio De Marchi↗
NASA NTRS1989

Theoretical study of the structures and electron affinities of the dimers and trimers of the group IB metals (Cu, Ag, and Au)

The molecular structure of both the neutral and negatively charged diatomic and triatomic systems containing the Cu, Ag, and Au metals are determined from ab initio calculations. For the neutral triatomic systems, the lowest energy structure is found to be triangular. The relative stability of the 2A1 and 2B2 structures can be predicted simply by knowing the constituent diatomic bond distances and atomic electron affinities (EAs). The lowest energy structure is linear for all of the negative ions. For anionic clusters containing Au, the Au atom(s) preferentially occupy the terminal position(s). The EAs of the heteronuclear systems can be predicted relatively accurately from a weighted average of the corresponding homonuclear systems. Although the theoretical EAs are systematically too small, accurate predictions for the EAs of the triatomics are obtained by uniformly scaling the ab initio results using the accurate experimental EA values available for the atoms and homonuclear diatomics.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1984

Pioneer 10 and Voyager Observations of the Interstellar Medium in Scattered Emission of the H 584 A and H Lya 1216 A Lines

The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 AU have been applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments, in the same way as other earlier determinations based on the same method. However. we have combined the spacecraft data with daily full sun averages of the H Lya 1216 A line obtained by the Solar Mesospheric Explorer (SME) satellite, to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a 1 year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are (H) = 0.12 cm(sup 2) and (He) = .016 cm(sup 2), giving a density ratio close to the cosmic abundance value, in contrast to some earlier results indicating a depletion of atomic hydrogen. We have obtained estimates of galactic background emissions in the signals of both spacecraft.

Shemansky, D. E.↗
NASA NTRS2020

Global-scale distribution of ozone in the remote troposphere from ATom and HIPPO airborne field missions

Ozone is a key constituent of the troposphere, where it drives photochemical processes, impacts air quality, and acts as a climate forcer. Large-scale in situ observations of ozone commensurate with the grid resolution of current Earth system models are necessary to validate model outputs and satellite retrievals. In this paper, we examine measurements from the Atmospheric Tomography (ATom; four deployments in 2016–2018) and the HIAPER Pole-to-Pole Observations (HIPPO; five deployments in 2009–2011) experiments, two global-scale airborne campaigns covering the Pacific and Atlantic basins. ATom and HIPPO represent the first global-scale, vertically resolved measurements of O3 distributions throughout the troposphere, with HIPPO sampling the atmosphere over the Pacific and ATom sampling both the Pacific and Atlantic. Given the relatively limited temporal resolution of these two campaigns, we first compare ATom and HIPPO ozone data to longer-term observational records to establish the representativeness of our dataset. We show that these two airborne campaigns captured on average 53 %, 54 %, and 38 % of the ozone variability in the marine boundary layer, free troposphere, and upper troposphere–lower stratosphere (UTLS), respectively, at nine well-established ozonesonde sites. Additionally, ATom captured the most frequent ozone concentrations measured by regular commercial aircraft flights in the northern Atlantic UTLS. We then use the repeated vertical profiles from these two campaigns to confirm and extend the existing knowledge of tropospheric ozone spatial and vertical distributions throughout the remote troposphere. We highlight a clear hemispheric gradient, with greater ozone in the Northern Hemisphere, consistent with greater precursor emissions and consistent with previous modeling and satellite studies. We also show that the ozone distribution below 8 km was similar in the extra-tropics of the Atlantic and Pacific basins, likely due to zonal circulation patterns. However, twice as much ozone was found in the tropical Atlantic as in the tropical Pacific, due to well-documented dynamical patterns transporting continental air masses over the Atlantic. Finally, we show that the seasonal variability of tropospheric ozone over the Pacific and the Atlantic basins is driven year-round by transported continental plumes and photochemistry, and the vertical distribution is driven by photochemistry and mixing with stratospheric air. This new dataset provides additional constraints for global climate and chemistry models to improve our understanding of both ozone production and loss processes in remote regions, as well as the influence of anthropogenic emissions on baseline ozone.

ATom, aircraft profiles, Atlantic pollution, ozone↗
NASA NTRS1977

Investigation of possible lower hybrid emission from the NASA Lewis Bumpy Torus plasma

Radio frequency emission detected near the lower hybrid frequency of the NASA Lewis Bumpy Torus plasma is studied, using a simple detection system that consists of a spectrum analyzer and a 50-ohm miniature co-axial antenna concentrically located in a re-entrant quartz tube. The frequency shift of a broad emission peak is monitored as a function of the background pressure, electrode voltage, and the strength of the dc magnetic field. Simultaneous measurements of the average plasma density are made with a polarization diplexing microwave interferometer. Information from the experiment is discussed with particular reference to the role of atomic or molecular species of deuterium in the emissions, the strength of the dc magnetic field in the emitting region, the geometric location of the emitting region of the plasma, the lower hybrid plasma density as compared with the average plasma density, and the relation of the ion spoke geometry to the lower hybrid emission.

Mallavarpu, R.↗
NASA NTRS1972

Hydrogen/helium ratio in stars

The ratio of hydrogen-to-helium in main sequence B stars is analyzed. An attempt was made to match each observed neutral helium profile with a theoretically calculated profile. Observational results show an overall average of helium-to-hydrogen is roughly between 10% and 11% by number of atoms. Detailed results of each star examined are given in graphs. Theoretical and calculated results are in reasonable agreement.

Leckrone, D.↗