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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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NASA NTRS2014

The LBTI Hunt for Observable Signatures of Terrestrial Systems (HOSTS) Survey: a Key NASA Science Program on the Road to Exoplanet Imaging Missions (SPIE Proceedings 2)

Telescope Interferometer (LBTI) will survey nearby stars for faint exozodiacal dust (exozodi). This warm circumstellar dust, analogous to the interplanetary dust found in the vicinity of the Earth in our own system, is produced in comet breakups and asteroid collisions. Emission and or scattered light from the exozodi will be the major source of astrophysical noise for a future space telescope aimed at direct imaging and spectroscopy of terrestrial planets (exo- Earths) around nearby stars. About 20 of nearby field stars have cold dust coming from planetesimals at large distances from the stars (Eiroa et al. 2013, AA, 555, A11; Siercho et al. 2014, ApJ, 785, 33). Much less is known about exozodi; current detection limits for individual stars are at best 500 times our solar system's level (aka. 500 zodi). LBTI-HOSTS will be the first survey capable of measuring exozodi at the 10 zodi level (3). Detections of warm dust will also reveal new information about planetary system architectures and evolution. We will describe the motivation for the survey and progress on target selection, not only the actual stars likely to be observed by such a mission but also those whose observation will enable sensible extrapolations for stars that will not be observed with LBTI. We briefly describe the detection of the debris disk around Crv, which is the first scientific result from the LBTI coming from the commissioning of the instrument in December 2013, shortly after the first time the fringes were stabilized.

exozodiacal dust↗

NASA NTRS1980

The interaction of T-Tauri stars with molecular clouds

Winds from T-Tauri stars may provide an important dynamical input into cold molecular clouds. If the frequency of T-Tauri stars exceeds 20/cu pc, wind-driven shells collide and form ram-pressure-confined clumps. The supersonic clump motions can account for cloud line widths. Clumps collide inelastically, coalescing and eventually becoming Jeans unstable. For characteristic dark cloud temperatures low-mass stars form, and it is speculated that in this manner clouds can be self-sustaining for 10 million to 100 million yr. Only when either the gas supply is exhausted or an external trigger stimulates massive star formation (for example, by heating the cloud or enhancing the clump collision rate), will the cloud eventually be disrupted. A natural consequence of this model is that dark cloud lifetimes are identified with the duration of low-mass star formation, inferred to exceed 10 million yr from studies of nearby star clusters. Other implications include the prediction of the existence of embedded low-mass stars in turbulent cloud cores, the presence of an internal source of radiation in dark clouds, and a clumpy structure for cold molecular clouds.

Silk, J.↗

NASA NTRS1973

Current distribution on an infinite tubular antenna immersed in a cold collisional magnetoplasma.

Based upon a boundary-value formulation, a new approximate expression is derived for the total axial current on an infinite antenna immersed in an unbounded, cold, collisional magnetoplasma with a dc magnetic field oriented parallel to the antenna. Numerical results are presented for the current distributions over plasma parameters corresponding to each of the eight regions of the Clemmow-Mullaly-Allis diagram and for different values of the collision frequency.

Bhat, B.↗

DOE OSTI2024

Exploring the chemical dynamics of phenanthrene (C 14 H 10 ) formation via the bimolecular gas-phase reaction of the phenylethynyl radical (C 6 H 5 CC) with benzene (C 6 H 6 )

The exploration of the fundamental formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) is crucial for the understanding of molecular mass growth processes leading to two- and three-dimensional carbonaceous nanostructures (nanosheets, graphenes, nanotubes, buckyballs) in extraterrestrial environments (circumstellar envelopes, planetary nebulae, molecular clouds) and combustion systems. While key studies have been conducted exploiting traditional, high-temperature mechanisms such as the hydrogen abstraction–acetylene addition (HACA) and phenyl addition–dehydrocyclization (PAC) pathways, the complexity of extreme environments highlights the necessity of investigating chemically diverse mass growth reaction mechanisms leading to PAHs. Employing the crossed molecular beams technique coupled with electronic structure calculations, we report on the gas-phase synthesis of phenanthrene (C 14 H 10 )—a three-ring, 14π benzenoid PAH—via a phenylethynyl addition–cyclization–aromatization mechanism, featuring bimolecular reactions of the phenylethynyl radical (C 6 H 5 CC, X 2 A 1 ) with benzene (C 6 H 6 ) under single collision conditions. The dynamics involve a phenylethynyl radical addition to benzene without entrance barrier leading eventually to phenanthrene via indirect scattering dynamics through C 14 H 11 intermediates. The barrierless nature of reaction allows rapid access to phenanthrene in low-temperature environments such as cold molecular clouds which can reach temperatures as low as 10 K. Furthermore, this mechanism constitutes a unique, low-temperature framework for the formation of PAHs as building blocks in molecular mass growth processes to carbonaceous nanostructures in extraterrestrial environments thus affording critical insight into the low-temperature hydrocarbon chemistry in our universe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Organisation of Diverse Mechanisms of Secondary Ice Production among Basic Convective and Stratiform Cloud-types

This 3-year DoE-funded joint project had the over-arching aim of understanding how ice is initiated in clouds of various types. Focus was given to processes of fragmentation of pre-existing ice, which can occur in positive feedback loops (‘ice multiplication’). A basic question to address was which fragmentation processes prevail in which basic cloud-types. The approach was to use cloud models and field observations, while pioneering our own lab observations of ice initiation to break the deadlock from the past lack of lab observations. Historically, the tendency of the cloud physics community to avoid doing lab observations has allowed a vast gap in knowledge about ice initiation to persist for decades. During the first part of the project, new formulations were created to treat two overlooked types of fragmentation of ice. First, sublimational breakup of ice was treated based on a theoretical formula that we fitted to a pooled dataset of lab observations published previously in the literature. Second, a new mode of fragmentation of freezing raindrops was treated, which involves a supercooled drop being hit by a more massive ice particle. Some of the secondary droplets from the impact freeze. This work was done at Manchester University by Co-I Connolly. Then during the second part, both formulations were implemented in our ‘aerosol-cloud model’ (AC). AC has a hybrid bin/bulk microphysics scheme, and now represents four processes of SIP. The accuracy of AC was evaluated for four cases typifying four basic cloud-types: slightly cold-based stratiform cloud and cold-, warm- and very warm-based convective clouds. We discovered that the warmth of cloud-base, especially in the tropics, promotes SIP processes of raindrop-freezing fragmentation and rime-splintering, and surprisingly, sublimational breakup too. It was found that breakup in ice-ice collisions is ubiquitous. Finally, a portable laboratory chamber was constructed at Lund and deployed in northern Sweden to observe breakup in graupel-snow collisions outdoors. This was seen to be even more prolific than treated in our 2018 formulation. Papers describing results are either published or soon to be published.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2026

Formation of 1 H -Phenalene (C 13 H 10 ) in the Taurus Molecular Cloud via Methylidyne Addition-Cyclization-Aromatization (MACA)

The formation of 1H-phenalene (C 13 H 10 ) in cold molecular clouds, such as the Taurus Molecular Cloud-1 (TMC-1), presents a significant challenge to traditional astrochemical models, which predominantly suggest high-temperature pathways for polycyclic aromatic hydrocarbon (PAH) formation. In this study, we explore computationally the Methylidyne Addition-Cyclization-Aromatization (MACA) mechanism as a viable, barrierless pathway for phenalene synthesis under low-temperature conditions. Through electronic structure calculations and Rice–Ramsperger–Kassel–Marcus (RRKM) statistical methods, we demonstrate that the reaction of 1-vinylnaphthalene (C 10 H 7 C 2 H 3 ) with the methylidyne radical (CH) leads to the formation of 1H-phenalene via a bimolecular reaction, a process that is exoergic and without entrance barrier. The MACA mechanism facilitates the growth of the aromatic carbon backbone via a [5 + 1] ring annulation, providing a new insight into PAH formation in cold molecular clouds. Notably, the MACA mechanism has previously been shown to form indene (C9H8), which was detected in TMC-1 as well, via a [4 + 1] annulation, demonstrating its potential to produce a variety of complex PAHs by addition of a five- and six-membered ring to a benzene moiety via [4 + 1] and [5 + 1] annulation, respectively. As a result, this work highlights the importance of barrierless, exoergic reactions involving MACA in the synthesis of complex aromatic molecules in space, expanding our physicochemical understanding of carbon-rich chemistry in cold molecular clouds.

Aromatic compounds↗

NASA NTRS1985

Plasma-gas interactions studies in a hybrid plume plasma rocket

Plasma-gas interaction was investigated and the basic mechanisms for energy and particle transport. The solution approach assumes cylindrical geometry and includes a multiplicity of atomic reactions, and the presence of a strong magnetic field is described. The principal reactions are electron and ion impact ionization, and charge exchange between hot ions and cold neutrals. Radial particle and energy transport is mainly by diffusion. A modified Bohm diffusion model for plasma in the core of the plume, and classical neutral particle diffusion in the cooler regions of the flow are presented. Neutrals are allowed to free stream in the low density regions, where the collision mean-free-path becomes comparable, or even larger than the characteristic dimensions of the system.

Chang, F. R.↗

NASA NTRS1983

Apparent electrostatic ion cyclotron waves in the diffuse aurora

Emissions that have properties consistent with electrostatic ion cyclotron (EIC) waves have been observed at low altitude in the diffuse aurora by a sounding rocket payload. Peaks were observed in the power spectrum of the electric field near the hydrogen and oxygen ion cyclotron frequencies. Doppler shift and polarization analyses have been performed using EIC wave parameters derived from linear theory. Both analyses indicated that these emissions had properties consistent with those expected for H(+) and O(+) EIC waves. The two analyses indicated that both emission bands were due to waves propagating eastward parallel to the poleward boundary of the diffuse aurora. The large local cold plasma density and resulting Landau damping require that the source be local. Magnetometer data indicated the presence of a downward parallel current density of 5 microamps/sq m. Sufficient free energy for the waves was available from this current, although the waves were observed frequently at altitudes where the ion-neutral collision frequency exceeded the oxygen cyclotron frequency.

Bering, E. A.↗

NASA NTRS1985

Numerical modeling of the hybrid plume plasma rocket

This paper reports on ongoing research in the area of numerical simulations of hybrid plume dynamics, and describes the basic mechanisms for energy and particle transport. The solution approach assumes cylindrical geometry and includes a multiplicity of atomic reactions, as well as the presence of a strong magnetic field. The principal reactions are electron impact ionization, and resonant charge exchange between hot ions and cold neutrals. Radial particle and energy transport is mainly by diffusion. The present description includes a modified Bohm diffusion model for plasma in the core of the plume, and classical neutral particle diffusion in the cooler regions of the flow. Neutrals are allowed to 'free stream' in the low density regions, where the collision mean-free-path becomes comparable, or even larger than the characteristic dimensions of the system. A parameteric scan of the various regimes of interest has been completed and the most significant results are presented.

Chang, F. R.↗

DOE OSTI2025

Binding the Power of Cycloaddition and Cross-Coupling in a Single Mechanism: An Unexpected Bending Journey to Radical Chemistry of Butadiynyl with Conjugated Dienes

What if an experiment could combine the power of cycloaddition and cross-coupling with the in situ formation of an aromatic molecule in a single collision? Crossed molecular beam experiments augmented with electronic structure and statistical calculations provided compelling evidence on a novel radical route involving 1,3-butadiynyl (HCCCC; X 2 Σ + ) radicals synthesizing (substituted) arylacetylenes in the gas phase upon reactions with 1,3-butadiene (CH 2 CHCHCH 2 ; X 1 Ag) and 2-methyl-1,3-butadiene (isoprene; CH 2 C(CH 3 )CHCH 2 ; X 1 A'). Furthermore, this elegant mechanism de facto merges two previously disconnected concepts of cross-coupling and cycloaddition–aromatization in a single collision event via the formation of two new C(sp 2 )–C(sp 2 ) bonds and bending the 180° moiety of the linear 1,3-butadiynyl radical out of the ordinary by 60° to 120°. In addition to its importance to fundamental organic chemistry, this unconventional mechanism links two previously separated routes of gas-phase molecular mass growth processes of polyacetylenes and polycyclic aromatic hydrocarbons (PAHs), respectively, in low-temperature environments such as in cold molecular clouds like the Taurus Molecular Cloud (TMC-1) and in hydrocarbon-rich atmospheres of planets and their moons such as Titan, what revises the established understanding of low-temperature molecular mass growth processes in the Universe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2000

Apse-Alignment of the Uranian Rings

An explanation of the dynamical mechanism for apse-alignment of the eccentric Uranian rings is necessary before observations can be used to determine properties such as ring masses, particle sizes, and elasticities. The leading model relies on the ring self-gravity to accomplish this task, yet it yields equilibrium masses which are not in accord with Voyager radio measurements. We explore possible solutions such that the self-gravity and the collisional terms are both involved in the process of apse-alignment. We consider limits that correspond to a hot and a cold ring, and show that pressure terms may play a significant role in the equilibrium conditions for the narrow Uranian rings. In the cold ring case, where the scale height of the ring near periapse is comparable to the ring particle size, we introduce a new pressure correction pertaining to a region of the ring where the particles are locked in their relative positions and jammed against their neighbors, and the velocity dispersion is so low that the collisions are nearly elastic. In this case, we find a solution such that the ring self-gravity maintains apse-alignment against both differential precession (m = 1 mode) and the fluid pressure. We apply this model to the Uranian alpha ring, and show that, compared to the previous self-gravity model, the mass estimate for this ring increases by an order of magnitude. In the case of a hot ring, where the scale height can reach a value as much as fifty times larger than a particle size, we find velocity dispersion profiles that result in pressure forces which act in such a way as to alter the ring equilibrium conditions, again leading to a ring mass increase of an order of magnitude; however, such a velocity dispersion profile would require a different mechanism than is currently envisioned for establishing heating/cooling balance in a finite-sized, inelastic particle ring. Finally, we introduce an important correction to the model of Chiang and Goldreich.

Mosqueira, I.↗

NASA NTRS1981

Computations of ion diffusion coefficients from the Boltzmann-Fokker-Planck equation

The Boltzmann-Fokker-Planck equation is solved with the Chapman-Enskog method of analysis for the velocity distribution functions of helium, carbon, nitrogen, and oxygen. The analysis is a perturbation scheme based on the assumption of a collision-dominated gas, and the calculations are carried out to first order. The elements considered are treated as trace constituents in an electron-proton gas. From the resulting distribution functions, diffusion coefficients are computed which are found to be 20-30% less than those obtained by Chapman and Burgers. In addition, it is shown that the return current of cold electrons needed to maintain quasi-neutrality in a plasma with a temperature gradient contributes a term in the thermal diffusion coefficient omitted erroneously in previous works. This added term resolves the longstanding controversy over the discrepancy between the coefficients of Chapman and Burgers, which are seen to be completely equivalent in the light of this analysis. The viscosity coefficient for an electron-proton gas is also computed and found to be 7% less than that obtained by Braginskii.

Roussel-Dupre, R.↗

NASA NTRS1990

Hot and cold gas toward young stellar objects

High-resolution M band spectra are presented for the seven embedded IR sources W3 IRS 5, S140 IRS1, NGC 7538 IRS 1, NGC 7538 IRS 9, GL 2136, LkH-alpha 101, and MWC 349A, and the data are combined with previously published work for W33A and GL 2591. Cold CO is seen toward all nine sources, with temperatures from 11 K to 66 K. Column densities of cold CO are presented. Hot gas is seen toward eight of the nine objects with temperatures from 120 K to 1010 K. New lower limits to the hot gas density are obtained. The hot gas toward GL 2591, GL 2136, W3 IRS 5, and S140 IRS 1 is probably very near the central source and heated via gas-grain collisions. The optical depth in the silicate feature is strongly correlated with the (C-13)O column density, confirming that silicate optical depth is a useful measure of gas column density. The ratio of solid-to-gaseous CO is obtained for seven sources.

Mitchell, George F.↗

NASA NTRS1984

Atomic hydrogen maser measurements with wall surfaces of carbon tetrafluoride

The principal objectives of the Smithsonian Astrophysical Observatory cold maser research programs are given. This work is aimed principally at understanding more about the interaction of hydrogen atoms with wall coatings of fluorinated ethylene propylene (Dupont Teflon FEP-120 co-polymer) and of carbon tetrafluoride (CE4). The principal measured quantity in these experiments is the wall shift of the maser's output frequency. The wall shift per atomic collision was calculated from the measured wall frequency shift. This assumes that the wall surface area is smooth on a molecular scale.

Vessot, R. F. C.↗

NASA NTRS1987

Mass extinction caused by large bolide impacts

A history and development status assessment is presented for the hypothesis that the great extinction of living species 65 million years ago, at the boundary between the Tertiary and Cretaceous geological ages, was due to the collision of a meteoroid, asteroid, or comet with the earth. The initial, deeply suggestive indication of the extraterrestial origin of the extinction-initiating mechanism was the detection of an exceptionally high concentration of iridium at the stratigraphic position of the extinction. Detailed computer modeling of the atmospheric effect of such a bolide impact has shown that the earth would have first grown intensely cold during a period of darkness due to particulate debris clouds in the upper atmosphere, followed by an enormous increase in global temperatures as the debris cleared, created by the persistence of greenhouse-effect gases; this heating would have been especially lethal to numerous forms of life.

Alvarez, Luis W.↗

NASA NTRS2010

Formation of Benzene in the Interstellar Medium

Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block-the aromatic benzene molecule-has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C6H6) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3- butadiene, C2H + H2CCHCHCH2 --> C6H6, + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadlene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.

Jones, Brant M.↗

NASA NTRS2022

Dilution of Boundary Layer Cloud Condensation Nucleus Concentrations by Free Tropospheric Entrainment During Marine Cold Air Outbreaks

Recent aircraft measurements over the northwest Atlantic enable an investigation of how entrainment from the free troposphere (FT) impacts cloud condensation nucleus (CCN) concentrations in the marine boundary layer (MBL) during cold-air outbreaks (CAOs), motivated by the role of CCN in mediating transitions from closed to open-cell regimes. Observations compiled over eight flights indicate predominantly far lesser CCN concentrations in the FT than in the MBL. For one flight, a fetch-dependent MBL-mean CCN budget is compiled from estimates of sea-surface fluxes, entrainment of FT air, and hydrometeor collision-coalescence, based on in-situ and remote-sensing measurements. Results indicate a dominant role of FT entrainment in reducing MBL CCN concentrations, consistent with satellite-observed trends in droplet number concentration upwind of CAO cloud-regime transitions over the northwest Atlantic. Relatively scant CCN may widely be associated with FT dry intrusions, and should accelerate cloud-regime transitions where underlying MBL air is CCN-rich, thereby reducing regional albedo.

Boundary Layer Cloud Condensation Nucleus Concentr↗

NASA NTRS1981

Origin of Ca-Al-rich inclusions. II - Sputtering and collisions in the three-ph8se interstellar medium

The theory put forward by Clayton (1977) for the formation of the Ca-Al-rich inclusions within C3 meteorites is extended to an evolutionary history in a three-phase interstellar medium. Widespread supersonic turbulence in the hot interstellar medium is maintained by supernova shock waves, giving rise to heavy sputtering of the refractory dust. Subsequent reaccumulation with varying dust/gas ratios or varying particle sizes produces isotopically fractionated Ca-Al-rich accumulates. It is thought that the Ca-Al-rich inclusions themselves are formed by the following sequence in the solar system: (1) cold accumulation of larger-than-average Ca-Al-rich particles containing supernova condensate cores into macroscopic (approximately 1 cm) Ca-Al-rich agglomerates, probably by sedimentation; and (2) fusion of the supernova condensates into macroscopic minerals by exothermic chemical reactions that begin when the accumulate has been warmed, thereby releasing energy from the unequilibrated forms accumulated from the interstellar medium.

Clayton, D. D.↗