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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Light Absorption Properties and Radiative Effects of Primary Organic Aerosol Emissions

Organic aerosols (OAs) in the atmosphere affect Earth's energy budget by not only scattering but also absorbing solar radiation due to the presence of the so-called "brown carbon" (BrC) component. However, the absorptivities of OAs are not represented or are poorly represented in current climate and chemical transport models. In this study, we provide a method to constrain the BrC absorptivity at the emission inventory level using recent laboratory and field observations. We review available measurements of the light-absorbing primary OA (POA), and quantify the wavelength-dependent imaginary refractive indices (k(OA), the fundamental optical parameter determining the particle's absorptivity) and their uncertainties for the bulk POA emitted from biomass/biofuel, lignite, propane, and oil combustion sources. In particular, we parametrize the k(OA) of biomass/biofuel combustion sources as a function of the black carbon (BC)-to-OA ratio, indicating that the absorptive properties of POA depend strongly on burning conditions. The derived fuel-type-based k(OA) profiles are incorporated into a global carbonaceous aerosol emission inventory, and the integrated k(OA) values of sectoral and total POA emissions are presented. Results of a simple radiative transfer model show that the POA absorptivity warms the atmosphere significantly and leads to similar to 27% reduction in the amount of the net global average POA. cooling compared to results from the nonabsorbing assumption.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Enhancement of Emission from Lanthanide Dopants in Perovskite Nanocrystals through a Temperature-Dependent Phase Transformation of the Perovskite Lattice

The excited states of lanthanide ions (Ln 3+ ) exhibit ultranarrow emission and long spin dephasing lifetimes suitable for optoelectronic and quantum applications but are not directly optically accessible. One effective strategy to excite Ln 3+ ions is to dope them into a semiconductor host lattice, which acts as a photosensitizer. This work describes enhancement of emission intensity by a factor of 19 with decreasing temperature (from 300 to S K) from Sm 3+ ions in CsPbCl 3 nanocrystal hosts. Structural characterization over the same temperature region reveals that this enhancement is primarily due to a symmetry-lowering cubic-to-orthorhombic phase transition of the host lattice, which reduces the local site symmetry of the dopant and increases the Sm 3+ * emission quantum yield.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Phenyl Ring Dynamics in a Tetraphenylethylene-Bridged Metal-Organic Framework: Implications for the Mechanism of Aggregation-Induced Emission

Molecules that exhibit emission in the solid state, especially those known as aggregation-induced emission (AIE) chromophores, have found applications in areas as varied as light-emitting diodes and biological sensors. Despite numerous studies, the mechanism of fluorescence quenching in AIE chromophores is still not completely understood. To this end, much interest has focused on understanding the low-frequency vibrational dynamics of prototypical systems, such as tetraphenylethylene (TPE), in the hope that such studies would provide more general principles toward the design of new sensors and electronic materials. We hereby show that a perdeuterated TPE-based metal–organic framework (MOF) serves as an excellent platform for studying the low-energy vibrational modes of AIE-type chromophores. In particular, we use solid-state 2 H and 13 C NMR experiments to investigate the phenyl ring dynamics of TPE cores that are coordinatively trapped inside a MOF and find a phenyl ring flipping energy barrier of 43(6) kJ/mol. DFT calculations are then used to deconvolute the electronic and steric contributions to this flipping barrier. Finally, we couple the NMR and DFT studies with variable-temperature X-ray diffraction experiments to propose that both the ethylenic C=C bond twist and the torsion of the phenyl rings are important for quenching emission in TPE, but that the former may gate the latter. To conclude, we use these findings to propose a set of design criteria for the development of tunable turn-on porous sensors constructed from AIE-type molecules, particularly as applied to the design of new multifunctional MOFs.

Shustova, Natalia B↗
DOE OSTI2023

Dinitrogen Emissions Dominate Nitrogen Gas Emissions From Soils With Low Oxygen Availability in a Moist Tropical Forest

Lowland tropical forest soils are relatively N rich and are the largest global source of N 2 O (a powerful greenhouse gas) to the atmosphere. Despite the importance of tropical N cycling, there have been few direct measurements of N 2 (an inert gas that can serve as an alternate fate for N 2 O) in tropical soils, limiting our ability to characterize N budgets, manage soils to reduce N 2 O production, or predict the future role that N limitation to primary productivity will play in buffering against climate change. We collected soils from across macro‐ and micro‐topographic gradients that have previously been shown to differ in O 2 availability and trace gas emissions. We then incubated these soils under oxic and anoxic headspaces to explore the relative effect of soil location versus transient redox conditions. No matter where the soils came from, or what headspace O 2 was used in the incubation, N 2 emissions dominated the flux of N gas losses. In the macrotopography plots, production of N 2 and N 2 O were higher in low O 2 valleys than on more aerated ridges and slopes. In the microtopography plots, N 2 emissions from plots with lower mean soil O 2 (5%–10%) were greater than in plots with higher mean soil O 2 (10%–20%). We estimate an N gas flux of ∼37 kg N/ha/yr from this forest, 99% as N 2 . These results suggest that N 2 fluxes may have been systematically underestimated in these landscapes, and that the measurements we present call for a reevaluation of the N budgets in lowland tropical forest ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Emission from quantum-dot high-β microcavities: transition from spontaneous emission to lasing and the effects of superradiant emitter coupling

Measured and calculated results are presented for the emission properties of a new class of emitters operating in the cavity quantum electrodynamics regime. The structures are based on high-finesse GaAs/AlAs micropillar cavities, each with an active medium consisting of a layer of InGaAs quantum dots (QDs) and the distinguishing feature of having a substantial fraction of spontaneous emission channeled into one cavity mode (high β-factor). This paper demonstrates that the usual criterion for lasing with a conventional (low β-factor) cavity, that is, a sharp non-linearity in the input–output curve accompanied by noticeable linewidth narrowing, has to be reinforced by the equal-time second-order photon autocorrelation function to confirm lasing. The article also shows that the equal-time second-order photon autocorrelation function is useful for recognizing superradiance, a manifestation of the correlations possible in high-β microcavities operating with QDs. In terms of consolidating the collected data and identifying the physics underlying laser action, both theory and experiment suggest a sole dependence on intracavity photon number. Evidence for this assertion comes from all our measured and calculated data on emission coherence and fluctuation, for devices ranging from light-emitting diodes (LEDs) and cavity-enhanced LEDs to lasers, lying on the same two curves: one for linewidth narrowing versus intracavity photon number and the other for g( 2 )(0) versus intracavity photon number.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Radiative emission enhancement using nano-antennas made of hyperbolic metamaterial resonators

A hyperbolic metamaterial (HM) resonator is analyzed as a nano-antenna for enhancing the radiative emission of quantum emitters in its vicinity. It has been shown that the spontaneous emission rate by an emitter near a hyperbolic metamaterial substrate is enhanced dramatically due to very large density of states. However, enhanced coupling to the free-space, which is central to applications such as solid-state lighting, has not been investigated significantly. Here, we numerically demonstrate approximately 100 times enhancement of the free-space radiative emission at 660 nm wavelength by utilizing a cylindrical HM resonator with a radius of 54 nm and a height of 80 nm on top of an opaque silver-cladded substrate. We also show how the free-space radiation enhancement factor depends on the dipole orientation and the location of the emitter near the subwavelength resonator. Furthermore, we calculate that an array of HM resonators with subwavelength spacings can maintain most of the enhancement effect of a single resonator.

36 MATERIALS SCIENCE↗
DOE OSTI2012

VARIABILITY OF DISK EMISSION IN PRE-MAIN SEQUENCE AND RELATED STARS. II. VARIABILITY IN THE GAS AND DUST EMISSION OF THE HERBIG Fe STAR SAO 206462

We present 13 epochs of near-infrared (0.8-5 {mu}m) spectroscopic observations of the pre-transitional, 'gapped' disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Br{alpha}, Br{gamma}, Pa{beta}, Pa{gamma}, Pa{delta}, Pa{epsilon}, and the 0.8446 {mu}m line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1} was derived from the Br{gamma} and Pa{beta} lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only {approx}30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 {mu}m was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on timescales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer timescales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on timescales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer timescales that have been sampled so far.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A COUPLED CHEMISTRY-EMISSION MODEL FOR ATOMIC OXYGEN GREEN AND RED-DOUBLET EMISSIONS IN THE COMET C/1996 B2 HYAKUTAKE

The green (5577 Angstrom-Sign ) and red-doublet (6300, 6364 Angstrom-Sign ) lines are prompt emissions of metastable oxygen atoms in the {sup 1}S and {sup 1}D states, respectively, that have been observed in several comets. The value of the intensity ratio of green to red-doublet (G/R ratio) of 0.1 has been used as a benchmark to identify the parent molecule of oxygen lines as H{sub 2}O. A coupled chemistry-emission model is developed to study the production and loss mechanisms of the O({sup 1}S) and O({sup 1}D) atoms and the generation of red and green lines in the coma of C/1996 B2 Hyakutake. The G/R ratio depends not only on photochemistry, but also on the projected area observed for cometary coma, which is a function of the dimension of the slit used and the geocentric distance of the comet. Calculations show that the contribution of photodissociation of H{sub 2}O to the green (red) line emission is 30%-70% (60%-90%), while CO{sub 2} and CO are the next potential sources contributing 25%-50% (<5%). The ratio of the photoproduction rate of O({sup 1} S) to O({sup 1} D) would be around 0.03 ({+-}0.01) if H{sub 2}O is the main source of oxygen lines, whereas it is {approx}0.6 if the parent is CO{sub 2}. Our calculations suggest that the yield of O({sup 1} S) production in the photodissociation of H{sub 2}O cannot be larger than 1%. The model-calculated radial brightness profiles of the red and green lines and G/R ratios are in good agreement with the observations made on the comet Hyakutake in 1996 March.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Reduction of CO2 Emissions Due to Wind Energy - Methods and Issues in Estimating Operational Emission Reductions

This paper presents ways of estimating CO2 reductions of wind power using different methodologies. Estimates based on historical data have more pitfalls in methodology than estimates based on dispatch simulations. Taking into account exchange of electricity with neighboring regions is challenging for all methods. Results for CO2 emission reductions are shown from several countries. Wind power will reduce emissions for about 0.3-0.4 MtCO2/MWh when replacing mainly gas and up to 0.7 MtCO2/MWh when replacing mainly coal powered generation. The paper focuses on CO2 emissions from power system operation phase, but long term impacts are shortly discussed.

17 WIND ENERGY↗
DOE OSTI2022

Connecting Low- and High-redshift Weak Emission-line Quasars via Hubble Space Telescope Spectroscopy of Lyα Emission

We present ultraviolet spectroscopy covering the Lyα + N v complex of six candidate low-redshift (0.9 < z < 1.5) weak emission-line quasars (WLQs) based on observations with the Hubble Space Telescope. The original systematic searches for these puzzling Type 1 quasars with intrinsically weak broad emission lines revealed an N ≈ 100 WLQ population from optical spectroscopy of high-redshift (z > 3) quasars, defined by a Lyα + N v rest-frame equivalent width (EW) threshold <15.4 Å. Identification of lower-redshift (z < 3) WLQ candidates, however, has relied primarily on optical spectroscopy of weak broad emission lines at longer rest-frame wavelengths. With these new observations expanding existing optical coverage into the ultraviolet, we explore unifying the low- and high-z WLQ populations via EW[Lyα+N v]. Two objects in the sample unify with high-z WLQs, three others appear consistent with the intermediate portion of the population connecting WLQs and normal quasars, and the final object is consistent with typical quasars. The expanded wavelength coverage improves the number of available line diagnostics for our individual targets, allowing a better understanding of the shapes of their ionizing continua. The ratio of EW[Lyα+N v] to EW[Mg ii] in our sample is generally small but varied, favoring a soft ionizing continuum scenario for WLQs, and we find a lack of correlation between EW[Lyα+N v] and the X-ray properties of our targets, consistent with a "slim-disk" shielding gas model. We also find indications that weak absorption may be a more significant contaminant in low-z WLQ populations than previously thought.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Non-methane organic gas emissions from biomass burning: identification, quantification, and emission factors from PTR-ToF during the FIREX 2016 laboratory experiment

Volatile and intermediate-volatility non-methane organic gases (NMOGs) released from biomass burning were measured during laboratory-simulated wildfires by proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF). We identified NMOG contributors to more than 150 PTR ion masses using gas chromatography (GC) pre-separation with electron ionization, H 3 O + chemical ionization, and NO + chemical ionization, an extensive literature review, and time series correlation, providing higher certainty for ion identifications than has been previously available. Our interpretation of the PTR-ToF mass spectrum accounts for nearly 90 % of NMOG mass detected by PTR-ToF across all fuel types. The relative contributions of different NMOGs to individual exact ion masses are mostly similar across many fires and fuel types. The PTR-ToF measurements are compared to corresponding measurements from open-path Fourier transform infrared spectroscopy (OP-FTIR), broadband cavity-enhanced spectroscopy (ACES), and iodide ion chemical ionization mass spectrometry (I - CIMS) where possible. The majority of comparisons have slopes near 1 and values of the linear correlation coefficient, R 2 , of > 0.8, including compounds that are not frequently reported by PTR-MS such as ammonia, hydrogen cyanide (HCN), nitrous acid (HONO), and propene. The exceptions include methylglyoxal and compounds that are known to be difficult to measure with one or more of the deployed instruments. The fire-integrated emission ratios to CO and emission factors of NMOGs from 18 fuel types are provided. Finally, we provide an overview of the chemical characteristics of detected species. Non-aromatic oxygenated compounds are the most abundant. Furans and aromatics, while less abundant, comprise a large portion of the OH reactivity. The OH reactivity, its major contributors, and the volatility distribution of emissions can change considerably over the course of a fire.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1982

Theoretical quasar emission-line ratios. V - Balmer continuum emission

Isothermal, isobaric models of quasar emission line regions are presented which include an improved treatment of radiative transfer in the bound-free continua, based on a generalization of frequency-integrated line transfer techniques and on the use of a probabilistic radiative transfer equation which explicitly distinguishes between the flux divergence coefficient and the photon escape probability. It is found that Balmer continuum emission can be obtained without compromising observed line ratios. It is also established that optically thin or thick Balmer continuum emission models with blended Fe II line are consistent with 4000-2000 A 'blue bump' observations, and that the improved radiative transfer treatment makes order-of-magnitude corrections to level populations and local cooling rates calculated with past techniques.

Puetter, R. C.↗
NASA NTRS1982

X-ray emission from young supernova remnants - Nonionization equilibrium abundances and emissivities

X-ray line emission from hot, low-density plasma in young supernova remnants is strongly enhanced by departures from ionization equilibrium. The X-ray emission from a Sedov blast wave has been calculated using a nonequilibrium evolutionary treatment of the ionization structure, and the resulting spectrum has been fitted to HEAO 2 SSS data for Tycho's remnant. These models yield dramatically different elemental abundances for heavy elements (Ne, Mg, Si, S, Ar, Ca, and Fe), compared with two-temperature component equilibrium models of Becker et al. (1979, 1980). Nonequilibrium broad-band X-ray emissivities result in lower mass determinations for the supernova ejecta. Areas of further improvement of remnant X-ray modeling are suggested.

Shull, J. M.↗
NASA NTRS1985

Electron emission and acoustic emission from the fracture of graphite/epoxy composites

In past studies it has been shown that the fracture of materials leads to the emission of a variety of species, including electrons, ions, neutral molecules, and photons, all encompassed by the term 'fractoemission' (FE). In this paper, electron emission (EE) from the fracture of single graphite fibers and neat epoxy resin is examined. Measurements of EE are also combined with the detection of acoustic emission (AE) during the testing of graphite-epoxy composite specimens with various fiber orientation. The characteristics of these signals are related to known failure mechanisms in fiber-reinforced plastics. This study suggests that by comparing data from AE and FE measurements, one can detect and distinguish the onset of internal and external failure in composites. EE measurements are also shown to be sensitive to the locus of fracture in a composite material.

Dickinson, J. T.↗
NASA NTRS1985

Theoretical quasar emission-line ratios. VIII - Implications of free-free emission for QSO clouds

A range of simple theoretical models is presented which explores the effects of high densities in the broad-line clouds on near-IR free-free emission. These calculations demonstrate in a qualitiative way that large near-IR fluxes can result from high densities without compromising the observed hydrogen line spectrum. It is suggested that high density in the emission-line region provides a plausible explanation of several features seen in the spectra of QSOs and active galaxies, including (1) the 3-micron bump and/or the near-IR spectral break seen in many QSOs, (2) the low observed Pa-alpha broad-line fluxes seen in some objects, and (3) the highly depressed Br-gamma broad-line fluxes seen in active galaxies. It is also found that free-free emission in such clouds can be an important coolant.

Puetter, R. C.↗
NASA NTRS1985

Implications of the 1400 MHz flare emission from AD Leo for the emission mechanism and flare environment

High brightness temperature spikes have been observed during a radio flare on the M-dwarf flare star AD Leo (Lang et al., 1983). Their high brightness temperature (greater than 10 to the 13th K) and circular polarization indicate that a coherent radiation mechanism must be responsible for the spike emission. The underlying flare emission, which is identified with a low polarization, gradual component, was found not to be spiky to within the 200 ms time resolution of the observations. This note is concerned primarily with this nonspiky emission.

Holman, G. D.↗