Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “molecular”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Fast Molecular Outflows in Luminous Galaxy Mergers: Evidence for Quasar Feedback from Herschel

We report the results from a systematic search for molecular (OH 119 micron) outflows with Herschel/PACS in a sample of 43 nearby (z < 0.3) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. We find that the character of the OH feature (strength of the absorption relative to the emission) correlates with that of the 9.7 micron silicate feature, a measure of obscuration in ULIRGs. Unambiguous evidence for molecular outflows, based on the detection of OH absorption profiles with median velocities more blueshifted than−50 km/s, is seen in 26 (70%) of the 37 OH-detected targets, suggesting a wide-angle (approx. 145 deg.) outflow geometry. Conversely, unambiguous evidence for molecular inflows, based on the detection of OH absorption profiles with median velocities more redshifted than +50 km/s is seen in only four objects, suggesting a planar or filamentary geometry for the inflowing gas. Terminal outflow velocities of approx. −1000 km/s are measured in several objects, but median outflow velocities are typically approx.−200 km/s−1. While the outflow velocities show no statistically significant dependence on the star formation rate, they are distinctly more blueshifted among systems with large active galactic nucleus (AGN) fractions and luminosities [log (L(sub AGN)/L(sub solar)) => 11.8 +/- 0.3]. The quasars in these systems play a dominant role in driving the molecular outflows. However, the most AGN dominated systems, where OH is seen purely in emission, show relatively modest OH line widths, despite their large AGN luminosities, perhaps indicating that molecular outflows subside once the quasar has cleared a path through the obscuring material.

Outfows↗
NASA NTRS2018

Preliminary Testing of NASA's Molecular Adsorber Coating Technology for Future Missions to Mars

The Molecular Adsorber Coating (MAC) is a sprayable coatings technology that was developed at NASA Goddard Space Flight Center (GSFC). The coating is comprised of highly porous, zeolite materials that help capture outgassed molecular contaminants on spaceflight applications. The adsorptive capabilities of the coating can alleviate molecular contamination concerns on or near sensitive surfaces and instruments within a spacecraft. This paper will discuss the preliminary testing of NASA’s MAC technology for use on future missions to Mars. The study involves evaluating the coating’s molecular adsorption properties in simulated test conditions, which include the vacuum environment of space and the Martian atmosphere. MAC adsorption testing was performed using a commonly used plasticizer called dioctyl phthalate (DOP) as the test contaminant.

CO2↗
NASA NTRS2018

Preliminary Testing of NASA's Molecular Adsorber Coating Technology for Future Missions to Mars

The Molecular Adsorber Coating (MAC) is a sprayable coatings technology that was developed at NASA Goddard Space Flight Center (GSFC). The coating is comprised of highly porous, zeolite materials that help capture outgassed molecular contaminants on spaceflight applications. The adsorptive capabilities of the coating can alleviate molecular contamination concerns on or near sensitive surfaces and instruments within a spacecraft. This paper will discuss the preliminary testing of NASA's MAC technology for use on future missions to Mars. The study involves evaluating the coating's molecular adsorption properties in simulated test conditions, which include the vacuum environment of space and the Martian atmosphere. MAC adsorption testing was performed using a commonly used plasticizer called dioctyl phthalate (DOP) as the test contaminant.

outgassing↗
NASA NTRS1978

Star formation in molecular clouds

A general overview is presented of the findings of molecular line and infrared astronomy regarding star formation. Beginning with the statement that stars, and therefore, planets, form from molecular clouds, it is argued that the growing body of data on conditions in molecular clouds should serve as input parameters for theoretical calculations of star and planet formation. The fact that the gravitational potential energy of molecular clouds far exceeds their thermal energy implies that the required rate of star formation is easily explained. Indeed the most important problem in this field is that the rate of star formation predicted from molecular cloud studies is too high. Until this problem is understood, additional modes of inducing star formation, while they may be occurring, only add to the existing difficulties.

Evans, N. J., II↗
NASA NTRS1980

Molecular clouds and galactic spiral structure

Two large-scale 2.6 mm CO surveys of the galactic plane, one in the first quadrant (l = 12 to 60 deg, b = -1 to +1 deg), the other in the second (l = 105 to 139 deg, b = -3 to +3 deg), have provided evidence that, contrary to previous findings, molecular clouds constitute a highly specific tracer of spiral structure. Molecular counterparts of five of the classical 21-cm spiral arms have been identified: the Perseus arm, the local arm (including Lindblad's local expanding ring), the Sagittarius arm, the Scutum arm, and the 4-kpc arm. The region between the local arm and the Perseus arm is apparently devoid of molecular clouds, and the interarm regions of the inner Galaxy appear largely so. CO spiral structure implies that the mean lifetime of molecular clouds cannot be greater than 100 million years, the time required for interstellar matter to cross a spiral arm. Conservation of mass then sets a limit on the fraction of the interstellar medium in the form of molecular clouds: it cannot exceed one-half at any distance from the galactic center in the range 4-12 kpc.

Cohen, R. S.↗
NASA NTRS1982

Thermal- and plasma-induced molecular redistribution on the icy satellites

The molecular transport of condensed gas species across the surfaces of the icy satellites of Jupiter and Saturn is examined with the view of describing, in part, certain gross visual features associated with these bodies. Molecular redistribution induced by thermal sublimation and magnetospheric plasma-ion impact on satellites with negligible atmospheres is calculated by assuming that the molecules follow ballistic trajectories and by statistically selecting initial molecular velocities and points of origin. Erosion/deposition profiles so calculated are compared for a variety of satellite sizes and environments in order to understand the relative importance of sublimation and cold corotating plasma-ion- and fast plasma-ion-induced transport. The erosion/deposition profiles are used to discuss the appearance of a polar frost on Ganymede. A balance of magnetospheric-ion implantation and ion-induced molecular redistribution is used to discuss the observation of embedded SO2 and the darkening of the trailing side on Europa. Ion-induced molecular transport may also limit the deposition of SO2 frost in the polar regions of Io and may be a source of heavy particles in the Jovian and Saturnian magnetospheres.

Sieveka, E. M.↗
NASA NTRS1983

Organic molecules as chemical fossils - The molecular fossil record

The study of biochemical clues to the early earth and the origin of life is discussed. The methods used in such investigation are described, including the extraction, fractionation, and analysis of geolipids and the analysis of kerogen. The occurrence of molecular fossils in the geological record is examined, discussing proposed precursor-product relationships and the molecular assessment of deep sea sediments, ancient sediments, and crude petroleums. Alterations in the molecular record due to diagenesis and catagenesis are considered, and the use of microbial lipids as molecular fossils is discussed. The results of searches for molecular fossils in Precambrian sediments are assessed.

Eglinton, G.↗
NASA NTRS1983

A large molecular cloud toward the SNR W50 and SS 433

The CO 1 yields 0 transition at 115 GHz has been mapped over an area of more than 6 deg sq toward W50, the extended SNR surrounding the peculiar object SS 433. W50 is found to lie at the end of a filamentary molecular cloud 4 deg long and 1 deg wide that closely matches a conspicuous dust lane on the Palomar Sky Survey; the cloud's kinematic distance is within 0.7 of 2.2 kpc, in agreement with the distance 2-3.3 kpc estimated for the SNR, and its mass is about 120,000 solar masses. Though there is little evidence of star formation in the molecular filament, or evidence of an interaction between the filament and W50 (or SS 433), the positional coincidence of the two, their similar distance, and their displacement nearly two molecular scale heights from the plane all suggest a physical relationship or common origin. One possibility is that both the molecular filament and the stellar progenitor of W50 were ejected from a large active molecular complex lying in the plane at l = 40 deg.

Huang, Y.-L.↗
NASA NTRS1985

Far-infrared line intensities of H2O and CO from warm molecular clouds

Takahashi et al. (1983) have studied the role of H2O in the overall energetics of warm molecular clouds with large optical depths. It was found that in molecular clouds associated with nearby or embedded luminosity sources, the dust is likely to be warmer than the molecular gas. Thus, the warm dust represents the primary source of heat for the gas. In some cases, H2O was found to cool the gas. Takahashi et al. (1983) have presented the formalism for treating H2O in an optically thick molecular cloud with embedded sources of luminosity. The total H2O heating and cooling rates were also calculated. In the present investigation, the emergent intensities of far-infrared lines of H2O and excited, rotational CO transitions from relatively warm molecular clouds based on the large-velocity gradient model of the previous study are calculated. It is found that the dominant submillimeter CO transitions are related to emission, while the H2O transitions can be either absorption or emission lines.

Takahashi, T.↗
NASA NTRS1984

Molecular processes in a high temperature shock layer

Models of the shock layer encountered by an Aeroassisted Orbital Transfer Vehicle require as input accurate cross sections and rate constants for the atomic and molecular processes that characterize the shock radiation. From the estimated atomic and molecular densities in the shock layer and the expected residence time of 1 m/s, it can be expected that electron-ion collision processes will be important in the shock model. Electron capture by molecular ions followed by dissociation, e.g., O2(+) + e(-) yields 0 + 0, can be expected to be of major importance since these processes are known to have high rates (e.g., 10 to the -7th power cu/cm/sec) at room temperature. However, there have been no experimental measurements of dissociative recombination (DR) at temperatures ( 12000K) that are expected to characterize the shock layer. Indeed, even at room temperature, it is often difficult to perform experiments that determine the dependence of the translational energy and quantum yields of the product atoms on the electronic and vibrational state of the reactant molecular ions. Presented are ab initio quantum chemical studies of DR for molecular ions that are likely to be important in the atmospheric shock layer.

Guberman, S. L.↗
NASA NTRS1986

Molecular microenvironments: Solvent interactions with nucleic acid bases and ions

The possibility of reconstructing plausible sequences of events in prebiotic molecular evolution is limited by the lack of fossil remains. However, with hindsight, one goal of molecular evolution was obvious: the development of molecular systems that became constituents of living systems. By understanding the interactions among molecules that are likely to have been present in the prebiotic environment, and that could have served as components in protobiotic molecular systems, plausible evolutionary sequences can be suggested. When stable aggregations of molecules form, a net decrease in free energy is observed in the system. Such changes occur when solvent molecules interact among themselves, as well as when they interact with organic species. A significant decrease in free energy, in systems of solvent and organic molecules, is due to entropy changes in the solvent. Entropy-driven interactioins played a major role in the organization of prebiotic systems, and understanding the energetics of them is essential to understanding molecular evolution.

Macelroy, R. D.↗
NASA NTRS1985

Molecular cloud evolution and star formation

The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

Silk, J.↗
NASA NTRS1986

CO mapping of the Orion molecular cloud: The influence of star formation on cloud structure

Regions of massive star formation have long been believed to have a profound influence on the structure of their surrounding molecular clouds. The ways in which massive star formation has altered the structure and kinematics of the Orion Molecular Cloud are discussed. The data to be discussed consists of a large scale map of the CO J=1-0 emission from approximately 3 square degrees of OMC-1. During 1985, the Five College Radio Astronomy Observatory 14M antenna was used to map a 2 deg x 1 deg region centered on alpha(1950) = 5(h)33(m)00(s) delta(1950) = -5 deg 30 min. The region mapped in 1985 covers the well known HII regions M42, M43, and NGC1977, and the CO map contains abundant evidence of the interaction between these regions and the molecular cloud. Indeed, the global structure of the cloud appears to have been strongly influenced by the continuous formation of massive stars within the cloud. Individual instances of some of these features are discussed. There appear to be two classes of features which are indicative of this interaction: CO bright rims and CO holes. During 1986, we have undertaken further mapping of OMC-1 to the south of the region covered by the 1985 map. This portion of the cloud contains significant regions of star formation, but O star formation has not occured and large HII regions have not developed to alter the appearance of the cloud. A detailed map of this region is thus an opportunity to view the structure of the molecular cloud before it has been altered by massive star formation. Preliminary analysis of data obtained in this region suggests that the structure and kinematics of the southern portion of the Orion cloud are indeed dramatically different from those of the region previously mapped. Comparison of the two regions thus supports models of the development of structure in molecular clouds through interaction with the HII regions formed within them.

Schloerb, F. P.↗
NASA NTRS1987

Masses, luminosities and dynamics of galactic molecular clouds

Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

Solomon, P. M.↗
NASA NTRS1987

Submillimeter and Far-Infrared Spectroscopy of M17 and S106: UV-Heated, Quiescent Molecular Gas?

Measurements of CO line emission toward the interface between molecular cloud and HII region in M17, and the center of the bipolar nebula S106 are discussed. The warm quiescent molecular gas is in the interface between the exciting OB stars and the surrounging molecular cloud. Comparison of the submillimeter, far-IR, and millimeter CO line intensities and profiles suggests a model in which clumps of relatively cool gas (T = 50 K) have warm surfaces or are embedded in a warm surrounding medium. Heating of the warm, quiescent molecular gas by collisions with dust grains can be excluded. Slow shocks or heating by photoelectrons are possible. The most promising mechanism is photoelectric heating. The existence of a substantial amount of warm, quiescent molecular gas in UV illuminated regions may be of importance locally in most OB star formation regions and globally in external galaxies with large rates of star formation.

Harris, A. I.↗
NASA NTRS1986

Clump 1 - An unusual molecular cloud complex near the Galactic center

The properties of the (C-12)O and (C-13)O emission from Clump I, a complex of molecular clouds which shows the largest noncircular velocities of any molecular material known in the Milky Way, are studied. Observations of the J = 1-0 rotational transitions of the above molecules are reported, and the large-scale distribution and kinematics of the molecular gas in the direction of Clump I are discussed. The small-scale structure is described based on one arcmin resolution of (C-13)O data. Physical properties of the molecular material are derived, and the dynamics of the Clump I clouds are discussed in the context of their stability against Galactic tidal forces. It is concluded that all the clouds in the complex are gravitationally bound, although their outer envelopes may be tidally disrupted by the Galactic potential. The relative motion of the clouds is qualitatively similar to giant molecular cloud complexes in spiral arms of the outer Galactic disk, but the velocities are higher.

Bania, T. M.↗
NASA NTRS1989

Fast molecular shocks. I - Reformation of molecules behind a dissociative shock

The physical and chemical processes that operate in the cooling gas behind a fast, dissociative, single-fluid shock propagating in a dense interstellar cloud are discussed. The treatment extends previous theoretical work on fast molecular shocks by including the effects of the conversion of Ly-alpha photons into radiation of the two-photon continuum and into H2 Lyman band emission lines, the effects of CO photodissociation following line absorption, and the formation and destruction of molecules containing the elements nitrogen, silicon, and sulphur, and of the complex hydrocarbons. Abundance profiles for the molecular species of interest are presented. After molecular hydrogen begins to reform, by means of gas phase and grain surface processes, the neutral species OH, H2O, O2, CO, CN, HCN, N2, NO, SO, and SiO reach substantial abundances. The molecular ions HeH(+), OH(+), SO(+), CH(+), H2(+), and H3(+), are produced while the gas is still hot and partially ionized. Emissions from them provide a possible diagnostic probe of fast molecular shocks.

Neufeld, David A.↗
NASA NTRS1989

A close-up view of the S87 molecular outflow

Observations of the S87 star-forming region have been made at optical, far-infrared, centimeter, and millimeter wavelengths in order to explain the origin of the previously discovered supersonic molecular gas in this source. S87/IRS 1 is a massive, pre-main-sequence object still embedded in its parent molecular cloud, but disrupting its surroundings through the action of its powerful stellar wind. The shocked wind gas provides the force required to accelerate the surrounding molecular gas to supersonic velocities. An ordered, large-scale magnetic field is postulated to set up an initially anisotropic pressure distribution which channels the flow into two oppositely directed lobes and provides some further acceleration to the already supersonic molecular gas. Only 5 percent of the molecular gas actually reaches escape velocity.

Barsony, M.↗