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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

A C(18)O survey of dense cores in the Taurus molecular cloud: Signatures of evolution and protostellar collapse

We have mapped 11 dense cores in the Taurus molecular cloud in the C(18)O J = 2 goes to 1 line at a linear resolution of 0.02 pc. The core masses derived from C(18)O range from 0.06 to 5 solar mass. Five of them have embedded infrared sources, and six do not. Dense cores without infrared sources show multiple emission peaks. In contrast, dense cores with infrared sources have a single peak and smaller sizes. The cores with infrared sources have line widths that are 2-3 times the value expected from correlations found in previous surveys. This enhancement may be accounted for by models of gravitational collapse. The data are consistent with the idea that dense cores evolve first toward smaller sizes and smaller line width along the line width-size relation, and then toward larger line width and constant or smaller sizes as an infrared source becomes observable. A good collapse candidate, L1527, is identified based on the shapes of C(18)O and H2CO lines.

Zhou, Shudong↗
NASA NTRS1993

Continental water recycling and H2(18)-O concentrations

Using a General Circulation Model (GCM) fitted with tracer diagnostics, we examine how continental moisture recycling affects the stable water isotope content of precipitation, focusing on its contribution to the 'noise' in the well-established relationship between temperature and delta O-18. On a global basis, for temperatures between -30 and 15 C, continental recycling explains more than a third of the variability in annual delta O-18 that is not explained by temperature. Recycling appears almost as important as temperature in defining delta O-18 distributions during northern hemisphere summer.

Koster, Randal D.↗
NASA NTRS1994

Dust extinction and molecular gas in the dark cloud IC 5146

In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution (1 min .7) as our molecular-line observations. This enabled a direct comparison of (13)CO, C(18)O, and CS integrated intensities and column densities with A(sub V) for more than 500 positions in the cloud, corresponding to a range in A(sub V) between 0 to 32 mag of extinction. We found the integrated intensities of (13)CO, C(18)O, and CS to be roughly linearly correlated with extinction over different ranges of extinction. However, for all three molecules we find the scatter in the observed relations to be larger than can be accounted for by instrumental error, suggesting that there are large intrinsic variations in the abundances or excitation of the molecules through the cloud. Mean abundances for all the molecules relative to hydrogen were directly derived from the data. The ratio of (13)CO to C(18)O abundances was found to be significantly higher than the terrestrial ratio in regions where extinction is less than 10 mag. In the same region, the dispersion in the abundance ratio is also found to be very large, suggesting that the abundances of one or both molecules are very unstable even at relatively large cloud optical depths. Beyond 10 mag of extinction the abundances of both species appear very stable with their ratio close to the terrestrial value.

Lada, Charles J.↗
NASA NTRS1986

Determination of band oscillator strengths of atmospheric molecules from high resolution vacuum ultraviolet cross section measurements

An account is given of progress in work on (1) the determination of band oscillator strengths of the Schumann-Runge absorption bands of (16)O2 and (18)O2 from cross section measurements conducted at 79 K; (2) the determination of the absolute absorption cross section of the Schumann-Runge bands of (16)O(18)O from optical depth measurements performed on mixtures of (16)O2, (18)O2 and (16)O(18)O at 79K; and (3) the influence of Schumann-Runge linewing contributions on the determination of the Herzberg continuum absorption cross section of (16)O2 in the wavelength region 194 to 204 nm. The experimental investigations are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (EWHM = 0.0013 nm), uniquely suitable for cross section measurements of molecular bands with discrete rotational structure. Absolute cross sections, which are independent of the instrumental function and from which band oscillator strengths are directly determined, are measured for the absorption bands that are most predissociated. Such measurements are needed for (1) accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photopredissociation of (18)O(16)O by solar radiation penetrating between the absorption lines of (16)O2; (2) elucidation of the mechanism of predissociation of the upper state of the Schumann-Runge bands; and (3) determination of the true shape of the Herzberg continuum cross section.

Parkinson, W. H.↗
NASA NTRS1990

Submillimeter and millimeter observations of solar system objects

Microwave spectroscopy of solar system objects was supported. It necessarily involves millimeter and submillimeter wavelengths where rotational transitions reside. The existing national facilities are at OVRO, the 12-meter at Kitt Peak, UC array at Hat Creek, the Caltech CSO on Mauna Kea, and the 14-meter at the Univ. of Massachusetts, near Amherst. The group used all of these instruments in the last year except the Univ. of Massachusetts 14-meter. This wavelength range (0.3 to 3 mm) is about to enjoy an explosion of interest as submillimeter receivers become better and easier to use. This region of the spectrum is rich in transitions of molecules that exist in the planetary atmospheres which can be studied for temperature-pressure profiles, wind tracers, and atmospheric chemistry. The list of solar system objects that have been recently addressed with these techniques include: (1) Venus: CO studies of T-P profiles, winds, and photochemistry; SO2 detections; Continuum mapping remains to be done at 1 mm; (2) Earth H2O, CO, NO, NO2, O(18)O, etc. as a test bed for other atmospheres; (3) Mars: H2O, CO, O(18)O studies of T-P profiles, winds (fall of 1990), and photochemistry; (4) Saturn: Same as Jupiter plus submillimeter and millimeter mapping of the ring system; (5) Uranus and Neptune: Continuum thermal mapping; and (6) Titan: CO, HCN, and HC3NT-P information and photochemistry. Recent results are given.

Muhleman, Duane O.↗
NASA NTRS1994

Rovibrational intensities of the minor isotopes of the CO X (sup 1)Sigma (sup +) state for v less than or equal to 20 and J less than or equal to 150

Electric dipole transition matrix elements for rovibrational transitions in the X (sup 1)Sigma(sup +) state of the CO minor isotopes (14)C(16)O and (13)C(17)O are calculated for the first time for all the delta v = +1, +2, and +3 transitions for which v less than or equal to 20 and J less than or equal to 150. Improved electric dipole transition matrix elements are also calculated for the minor isotopes (12)C(17)O, (12)C(18)O, (13)C(18)O. We have fitted polynomials to these matrix elements as a function of the parameter m which is defined in terms of the lower state angular momentum quantum number J; the convenient to use polynomial representations are given in tabular form. These results for the minor species of CO complement those previously reported by us for (12)C(16)O and (13)C(16)O.

Goorvitch, D.↗
NASA NTRS1994

Infrared CO line for the X 1 Sigma(+) state

A complete line list with improved accuracy for all the rotation-vibration transitions of the fundamental, first, and second overtone bands up to v = 20 and J = 149 of the gradual state X 1 Sigma(+) of the seven CO isotopes -- (12)C(16)O, (13)C(16)O, (12)C(17)O, (12)C(18)O, (13)C(18)O, (14)C(16)O, and (13)c(17)O -- is made available to the astronomical community. A line list of the pure rotational transitions up to v = 5 and J = 60 is also made available for these seven isotopes. This line list contains the transition frequency, the lower state energy, the Einstein A-value, the g f-value, the transition strength at 3000 K or 1000 K for the pure rotational transitions, the expectation value of the effective dipole moment operator, and the quantum numbers of each transition. Individual partition functions are reported in the temperature range of 500 to 10,000 K. This line list is available as four text files from the author using an anonymous file transfer protocol (ftp) transfer and in computer-readable form in the AAS CD-ROM Series, Vol. 3.

Goorvitch, D.↗
NASA NTRSDate not supplied

First N 2 Profile for Venus’ Deep Lower Atmosphere

We present the first N 2 profile for Venus’ deep lower atmosphere (<15 km) and a constrained isotopic composition for cloud N 2 [1]. This work directly addresses unresolved questions for Venus using legacy observations. Prior to this work, there were no reported measurements for N 2 abundances at <15 km and the isotopic composition remained unconstrained [2]. The N 2 parameters are critical to understanding the evolution and thermal properties of the atmosphere [3-7]. Our N 2 results were obtained by re-analysis of data acquired in 1978 by the Pioneer Venus Large Probe Neutral Mass Spectrometer (LNMS) [8]. The archived mass spectra from 64.2 to 0.2 km were treated using the analytical procedures specifically developed for the LNMS [9-11]. Judicious peak fitting permitted disambiguation of (A) N 2 + and CO + at 28 u and (B) 14 N 15 N+, 13 CO + , and C 2 H 5 + at 29 u. Quality controls included comparing the (A) LNMS CO + /CO 2 + ratios to the NIST database and literature and (B) fitted counts for CO + to the expected counts of CO + calculated from C 18 O + and 13 CO + using the LNMS 16 O/ 18 O and 12 C/ 13 C ratios (obtained from CO 2 ). Our results show that N 2 is uniformly mixed across the deep lower atmosphere between ~0.2 and 15 km (2.49 ± 0.10 v%). In contrast, N 2 is non-uniformly mixed across the sub-cloud atmosphere and clouds (~15–59 km), where N 2 abundances increase by ~ 2-fold between ~15 km (2.45 ± 0.32 v%) and ~59-51 km (5.21 ± 0.18 v%). Using the cloud data, we also obtained a constrained 15 N/ 14 N ratio (2.93×10 -3 ± 0.13×10 -3 ) and δ 15 N value (-204 ± 35‰). Thus, the LNMS results [1] suggest that (A) the atmosphere is unstable at <15 km, (B) N 2 is not well-mixed >15 km, and (C) the cloud δ 15 N falls between Earth and the solar wind [12, 13]. Comparisons of the N 2 abundances and isotopic compositions for nitrogen, carbon, and oxygen to other Venus measurements will be discussed.

deep lower atmosphere↗
NASA NTRS1972

Laboratory measurement of the 2-centimeter, 2/11/-2/12/ transition of normal formaldehyde and its carbon-13 and oxygen-18 species.

Beam-maser spectrometric measurements to an accuracy of about 100 Hz have been conducted of the 2(11)-2(12) transition for the isotopic species of greatest astronomical interest - i.e., H2CO, H2(13)CO, and H2C(18)O. The samples used were not isotopically enriched, monomeric formaldehyde vapors. For these species, all the coupling constants required to calculate the hyperfine structure of any rotational transition have been determined.

Tucker, K. D.↗
NASA NTRS1976

Effects of water immersion to the neck on pulmonary circulation and tissue volume in man

A rapid noninvasive breathing method is used to obtain serial measurements of the pulmonary capillary blood flow, diffusing capacity per unit of alveolar volume, combined pulmonary tissue plus capillary volume, functional residual capacity, and oxygen consumption in five normal subjects undergoing 6 h of sitting, 4 h of sitting while immersed to the neck in thermoneutral water, and 4 h of lying in thermoneutral water to the neck. The rebreathing method employed a test gas mixture containing 0.5% C2H2, 0.3% C(18)O, 10% He, 21% O2, and balance N2. It is shown that immersion to the neck in the seated posture results in significant increases in sodium excretion cardiac output, and diffusing capacity per unit of alveolar volume. The pulmonary tissue plus capillary volume did not change, demonstrating that the central vascular engorgement induced by water immersion is not accompanied by significant extravasation of fluid into the pulmonary interstitial space.

Begin, R.↗
NASA NTRS1987

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

Detailed study of the first interstellar hydrocarbon ring, cyclopropenylidene (C3H2), is continuing. The singly deuterated isotope of this molecule, C3HD, was observed in several cold interstellar clouds. The results of a large survey for C3H2 in galactic sources of various types will soon be completed. It appears that cyclopropenylidene is present in virtually all interstellar clouds of at least moderate density. In order to make the first determinations of the CO2/CO abundance ratio in interstellar sources, observations of protonated CO2 were pursued. The spectrum from 18.5 to 22 GHz for several interstellar clouds is being systematically measured. Particular attention is being given to the cold, dark clouds TMC-1 and L124N, which may be formation sites for solar mass stars. The phenomena of maser emission from molecules of methanol is being studied in certain interstellar clouds. A comparison of 1 millimeter continuum emission from dust with the column density of carbon monoxide as determined from the rare C(18)O isotope for 4 molecular clouds in the Galaxy is nearing completion. Papers published during the period of this report are listed.

Irvine, William M.↗
NASA NTRS1989

Isotopic study of oxygen diffusion in oxide coatings

Diffusion of oxygen in thin films of silicon dioxide was studied using oxygen isotopically enriched in oxygen of atomic mass 18 (O-18). This subject is of interest because thin films of dielectrics such as SiO2 are proposed for use as a protective coatings for solar mirrors in low Earth orbit, which is a strongly oxidizing environment. Films of this material were prepared with a direct current magnetron using reactive sputtering techniques. To produce (O-18)- enriched SiO2, a standard 3.5-in.-diameter silicon wafer was reactively sputtered using (O-18)-enriched (95 percent) oxygen as the plasma feed gas. The films were characterized using Rutherford backscattering and Secondary Ion Mass Spectrometer (SIMS) to establish stoichiometry and purity. Subsequently, the films were exposed to an air-derived oxygen plasma in a standard laboratory plasma reactor for durations of up to 10 hr. The concentration ratio of O-16 as a function of depth was determined using SIMS profiling and compared to a baseline, nonplasma exposed sample. A value for the diffusivity of oxygen near the surface of these films was obtained and found to be about 10(-15)sq cm/sec.

Gulino, Daniel A.↗
NASA NTRS1993

Inter- and intra-crystalline oxygen isotope distribution of fassaites in Allende CAI

Calcium, aluminum-rich inclusions (CAI's) from carbonaceous chondrite are believed to be among the first solids to have formed in the early solar system and thus to preserve a record of conditions and processes that prevailed early in the solar nebula. We have measured inter- and intra- crystalline oxygen isotope distribution of fassaite in Type B1 CAI of Allende meteorite. Secondary ion mass spectrometry (SIMS) using negative Au primary ion was applied to in situ oxygen isotope ratio analysis on a polished thin section of the CAI. Present data indicate that O isotope composition is homogeneous inside of fassaite grains as well as among grains in the HN3-1 CAI, and that the delta(exp 18) O value (-24.14 percent relative to SMOW) determined previously could be applied to most fassaite grains. The results suggest that most fassaite grains are preexisting solids like spinel grains.

Yurimoto, Hisayoshi↗
NASA NTRS1994

Interstellar carbon monoxide toward zeta Ophiuchi

Interstellar CO A-X bands in the spectrum of zeta Oph were recorded at high Sound-to-Noise (S/N) with grating G160M of the Goddard High Resolution Spectrograph on the Hubble Space Telescope. Isotopic fractionation of CO is severe: CO-12/CO-13 = 167, C(16)O/C(18)O approximately equal to 1550 and C(16)O/C(17)O is greater than 5900 are found where C-12/C-13 = 70, O-16/O-18 = 500, and O-16.O-17 = 2600 are observed or expected. Standard models of the zeta Oph cloud predict CO-12/CO-13 is less than or approximately 70. The higher observed ratio suggests that photodissociation of CO, not the isotopic charge exchange reaction ((13)C(+) + CO reversible reaction (12)C(+) + (13)(CO), is the dominant influence on the CO-12/CO-13 ratio.

Lambert, David L.↗
NASA NTRS1994

Multiple outflows in the bipolar planetary nebula M1-16: A molecular line study

Extensive observations of the molecular gas in the young, compact planetary nebula M1-16 have been made, using the Swedish-ESO-Submillimeter Telescope. A map of the CO J = 2-1 emission shows that the molecular envelope contains both a slow and a fast outflow with expansion velocities of 19 km/s and greater than 34 km/s, respectively. The slow outflow is mildly elliptical, while the fast molecular outflow is bipolar. This fast outflow is roughly aligned with the very fast outflows recently found in the optical, while the long axis of the slow elliptical outflow is roughly orthogonal to the optical outflow axis. The kinematic timescales for the CO fast outflow and the optical very fast outflow agree closely, supporting the view that the former represents material in the slow outflow accelerated by the very fast outflow. The kinematic signature of a disk expanding with about 15.5 km/s can also be seen in the CO J = 2-1 data. The mass-loss rate (a) for the slow outflow is greater than or equal to 2.8 x 10(exp -5) solar mass/yr and possibly as large as 9 x 10(exp -5) solar mass/yr, (b) for the fast outflow is greater than or equal to 5 x 10(exp -6) solar mass/yr, and (c) for the very fast optically visible outflow is approximately equal 5 x 10(exp -7) solar mass/yr. The disk mass is approximately equal 6 x 10(exp -3) solar mass. Grain photoelectric heating results in temperatures of 20-70 K in molecular gas of the slow outflow. The (13)C/(12)C abundance ratio in M1-16 is found to be 0.33, quite possibly the highest found for any evolved object. Upper limits for the (18)O/(16)O and (17)O/(16)O ratios were found to be consistent with the values found in AGB stars. A search for other molecular species in M1-16 resulted in the detection of the high-excitation species HCN, CN, (13)CN, HCO(+), and H(13)CO(+) and possibly N2H(+). Both the HCO(+)/HCN and CN/HCN line-intensity ratios are enhanced, the former by a very large factor, over the values found in the envelopes of AGB stars, probably as a result of enhancement of the CN and HCO(+) abundances due to photochemistry induced by the stellar UV. The CS J = 2-1, SiO J = 2-1 (v = 0), and SiS J = 6-5 lines were not detected to low levels. For the high-excitation molecules, adequate collisional excitation of rotational levels and survival against photodissociation by the UV radiation requires significant clumping of the molecular gas into clumps with H2 densities approximately 10(exp 5)/cu cm. The IRAS fluxes of M1-16, assuming negligible contribution from line emission, imply the presence of about (1.7-0.4) x 10(exp -3) solar mass of cool dust (temperature around 50 K) and a smaller quantity, (2.7-3.1) x 10(exp -6) solar mass, of warmer dust (temperature around 125 K) for a power-law emissivity index p = 1-2. The evolutionary nature of M1-16 cannot be explained by existing single-star models of post-AGB evolution. The very high (13)C/(12)C abundance ratio in M1-16 suggests a possible evolutionary connection between M1-16 and the rare class of J-type silicate-carbon stars which also have high (13)C/(12)C ratios and are thought to be binary systems with accretion disks.

Sahai, Raghvendra↗
NASA NTRS1992

Effect of bolus fluid intake on energy expenditure values as determined by the doubly labeled water method

The doubly labeled water (DLW, 2H(2)18O) method is a highly accurate method for measuring energy expenditure (EE). A possible source of error is bolus fluid intake before body water sampling. If there is bolus fluid intake immediately before body water sampling, the saliva may reflect the ingested water disproportionately, because the ingested water may not have had time to mix fully with the body water pool. To ascertain the magnitude of this problem, EE was measured over a 5-day period by the DLW method. Six subjects were dosed with 2H2(18)O. After the reference salivas for the two-point determination were obtained, subjects drank water (700-1,000 ml), and serial saliva samples were collected for the next 3 h. Expressing the postbolus saliva enrichments as a percentage of the prebolus value, we found 1) a minimum in the saliva isotopic enrichments were reached at approximately 30 min with the minimum for 2H (95.48 +/- 0.43%) being significantly lower than the minimum for 18O (97.55 +/- 0.44, P less than 0.05) and 2) EE values calculated using the postbolus isotopic enrichments are appreciably higher (19.9 +/- 7.5%) than the prebolus reference values. In conclusion, it is not advisable to collect saliva samples for DLW measurements within approximately 1 h of bolus fluid intake.

NASA Discipline Musculoskeletal↗