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Results for “EMISSION SPECTRA”

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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The galactic gamma-ray flux in the 0.06 to 5 MeV range

Gamma ray emission from the longitude range -50 deg less than or equal to lambda less than or equal to 22 deg recorded by the Apollo gamma-ray spectrometer and by individual observers is discussed. Agreement of the galactic emission spectra near 1 MeV with hard X-ray observations of the galactic central regions suggests that an ensemble of point sources is responsible for the emissions. Apollo 16 upper limits to the cosmic 4.4 MeV line flux imply that the ratio of line strength to continuum emission for the region observed by Haymes et al is higher than the galactic average.

Gilman, D. A.↗
NASA NTRS1987

Spectroscopy and nonthermal processes

Stellar spectra are analyzed to determine nonthermal processes for cool stars. A shock wave crossing model is supported by a study of the behavior of absorption and emission spectra. The shock waves are attributed to atmospheric kinetics. Circumstellar spectral lines are studied for information about gaseous circumstellar layers. The description of stellar envelopes is carried on through circumstellar dust. Characteristic properties of polarization in the dust are described in the case of specific stars, emphasizing narrowband observations in Mira, semiregular, and supergiant stars. Finally, the direct approach to measuring the angular diameters of stars and mapping the distribution of circumstellar dust and gas by lunar occultation or interferometry is discussed, using two prototype stars, an M supergiant and a dusty carbon star.

Querci, Monique↗
NASA NTRS2003

Constraints on the Composition and Petrogenesis of the Martian Crust

Spectral interpretation that silicic rocks are widespread on Mars implies that Earth's differentiated crust is not unique. Evaluation of observations bearing on the composition of the Martian crust (Martian meteorite petrology and a possible crustal assimilant, analysis of Mars Pathfinder rocks, composition of Martian fines, interpretation of spacecraft thermal emission spectra, and inferred crustal densities) indicates that the crust can be either basalt plus andesite or basalt plus weathering products. New calculated chemical compositions for Thermal Emission Spectrometer (TES) global surface units indicate that surface type 1 has basaltic andesite composition and surface type 2 has the composition of andesite. If these materials represent volcanic rocks, their calc-alkaline compositions on a FeO*/MgO versus silica diagram suggest formation by hydrous melting and fractional crystallization. On Earth, this petrogenesis requires subduction, and it may suggest an early period of plate tectonics on Mars. However, anorogenic production of andesite might have been possible if the primitive Martian mantle was wet. Alternatively, chemical weathering diagrams suggest that surface type 2 materials could have formed by partial weathering of surface type 1 rocks, leading to depletion in soluble cations and mobility of silica. A weathered crust model is consistent with the occurrence of surface type 2 materials as sediments in a depocenter and with the alpha proton X-ray spectrometer (APXS) analysis of excess oxygen suggesting weathering rinds on Pathfinder rocks. If surface type 1 materials are also weathered or mixed with weathered materials, this might eliminate the need for hydrous melting, consistent with a relatively dry Martian mantle without tectonics.

McSween, Harry Y., Jr.↗
NASA NTRS1990

Predicted extreme-ultraviolet and X-ray spectrum of a microflare-heated corona

Sturrock et al. (1990) have proposed that a distribution of microflares produces the solar coronal and transition-region emission. This paper presents computed EUV and X-ray emission spectra from that distribution, including the effects of time-dependent ionization. The overall agreement of the predicted spectrum with observations is fairly good, although the predicted emission from the upper transition region is high by a factor of 2. Time-dependent ionization greatly enhances the He II 304-A line, improving the agreement with observation compared with ionization equilibrium models. The predicted effects on temperature-sensitive line ratios of other ions cannot yet be tested against observations due to uncertainties in instrumental calibration and atomic rates.

Raymond, John C.↗
DOE OSTI2022

Interference between Franck–Condon and Herzberg–Teller Terms in the Condensed-Phase Molecular Spectra of Metal-Based Tetrapyrrole Derivatives

The commonly used Franck-Condon (FC) approximation is inadequate for explaining the electronic spectra of compounds that possess vibrations with substantial Herzberg-Teller (HT) couplings. Metal-based tetrapyrrole derivatives, which are ubiquitous natural pigments, often exhibit prominent HT activity. In this paper, we compare the condensed phase spectra of zinc-tetraphenylporphyrin (ZnTPP) and zinc-phthalocyanine (ZnPc), which exhibit vastly different spectral features in spite of sharing a common tetrapyrrole backbone. The absorption and emission spectra of ZnTPP are characterized by a lack of mirror symmetry and nontrivial temperature dependence. In contrast, mirror symmetry is restored, and the nontrivial temperature-dependent features disappear in ZnPc. We attribute these differences to FC-HT interference, which is less pronounced in ZnPc because of a larger FC component in the dipole moment that leads to FC-dominated transitions. A single minimalistic FC-HT vibronic model reproduces all the experimental spectral features of these molecules. These observations suggest that FC-HT interference is highly susceptible to chemical modification.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1983

Temperatures of shock-induced shear instabilities and their relationship to fusion curves

New emission spectra for MgO and CaAl2Si2O8 (glass) are observed from 430 to 820 nm. Taken with previous data, it is suggested that transparent solids display three regimes of light emission upon shock compression to successively higher pressures: (1) characteristic radiation such as observed in MgO and previously in other minerals, (2) heterogeneous hot spot (greybody) radiation observed in CaAl2Si2O8 and previously in all transparent solids undergoing shock-induced phase transformations, and (3) blackbody emission observed in the high pressure phase regime in NaCl, SiO2, CaO, CaAl2Si2O8, and Mg2SiO4. The onset of the second regime may delineate the onset of shock-induced polymorphism whereas the onset of the third regime delineates the Hugoniot pressure required to achieve local thermal equilibrium in the shocked solid. It is also proposed that the hot spot temperatures and corresponding shock pressures determined in the second regime delineate points on the fusion curves of the high pressure phase.

Schmitt, D. R.↗
NASA NTRS1987

Raman spectra of adsorbed layers on space shuttle and AOTV thermal protection system surface

Surfaces of interest to space vehicle heat shield design were struck by a 2 W argon ion laser line while subjected to supersonic arc jet flow conditions. Emission spectra were taken at 90 deg to the angle of laser incidence on the test object. Results showed possible weak Raman shifts which could not be directly tied to any particular parameter such as surface temperature or gas composition. The investigation must be considered exploratory in terms of findings. Many undesirable effects were found and corrected as the project progressed. For instance, initial spectra settings led to ghosts which were eliminated by closing the intermediate of filter slit of the Spex from 8 to 3 mm. Further, under certain conditions, plasma lines from the laser were observed. Several materials were also investigated at room temperature for Raman shifts. Results showed Raman shifts for RCC and TEOS coated materials. The HRSI materials showed only weak Raman shifts, however, substantial efforts were made in studying these materials. Baseline materials showed the technique to be sound. The original goal was to find a Raman shift for the High-temperature Reusable Surface Insulation (HRSI) Reaction Cured borosilicate Glass (RCG) coated material and tie the amplitude of this peak to Arc jet conditions. Weak Raman shifts may be present, however, time limitations prevented confirmation.

Willey, Ronald J.↗
NASA NTRS1994

Very high energy gamma rays from active galactic nuclei: Cascading on the cosmic background radiation fields and the formation of pair halos

Recent high-energy gamma-ray observations (E(sub gamma) greater than 100 MeV) of blazar Active Galactic Nuclei (AGNs) show emission spectra with no clear upper energy cutoff. AGNs, considered to be possible sources for the observed flux of cosmic rays beyond 10(exp 19) eV, may well have emission extending into the very high energy (VHE), (E(sub gamma) greater than 100 GeV) domain. Because VHE gamma-rays are absorbed by pair production on the intergalactic background radiation fields, much of this emission may not be directly visible. The electromagnetic cascades initiated by absorbed VHE gamma-rays, however, may be observable. Since, most probably, the velocities of (e(+), e(-)) pairs produced in a cascade are quickly isotropized by an ambient random magnetic field, extended 'halos' (R greater than 1 Mpc) of pairs will be formed around AGNs with VHE emission. The cascade radiation from these pair halos is emitted isotropically and should be observable at energies below a few TeV. The halo radiation can be distinguished by its characteristic variation in spectrum and intensity with angular distance from the central source. This variation depends weakly on the details of the central source model, e.g., the orientation and beaming/opening angle of an emitting jet. Limiting or determining the intensity of the pair halo can thus serve as a model-independent bound on or measure of the VHE power of AGNs. Next-generation Cherenkov telescopes may be able to image a pair halo.

Aharonian, F. A.↗
DOE OSTI2020

Amplified spontaneous emission in the extreme ultraviolet by expanding xenon clusters

Focused short-wavelength free-electron laser (FEL) pulses interacting with gas phase samples can induce by inner-shell ionization a short-lived population inversion, followed by coherent collective emission of directed, short, and strong radiation bursts. We extend our studies into the warm-dense matter (WDM) regime by investigating the nanoplasmas produced in an ensemble of nanometer-sized clusters by FEL irradiation. Here, additional pathways can also lead to strong, laserlike emission: Electron-ion collisions can yield a long-lived population inversion, and subsequent amplified spontaneous emission. We observe amplified spontaneous emission (ASE) in the extreme ultraviolet in xenon clusters excited by soft x-ray FEL pulses, we diagnose the generated nanoplasmas by fluorescence spectroscopy, and we study under various cluster and FEL parameters the directed ASE from the Xe 2+ 65 nm line. We show its exponential increase as a function of FEL irradiation power, and an accompanying collisional broadening of the emission spectra. These findings are corroborated by extensive numerical simulations based on theory, combining detailed hydrodynamic and kinetic simulations with time-dependent calculations of radiation transport, amplification, and collective emission in the WDM nanoplasma. Furthermore, our theoretical findings underline that population inversion is due to electron-ion collisions and that the observed decoherence processes can be empirically characterized by a phenomenological decoherence time in the range of 100–200 fs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

The origin of the diffuse galactic IR/submm emission: Revisited after IRAS

Balloon observations are compared with Infrared Astronomy Satellite observations. There was good agreement for the longitudinal profiles. However, the dust emission observed by IRAS, contrary to the balloon observations which show dust emission only within the absolute value of b is equal to or less than 3 degrees, extends all the way to the galactic pole. The model fits were repeated using more recent parameters for the distribution of interstellar matter in the galactic disk and central region. The IR luminosities are derived for the revised galactic distance scale of solar radius - 8.5 Kpc. A total IR luminosity of 1.2 E10 solar luminosity is obtained, which is about one third of the estimated stellar luminosity of the Galaxy. The dust emission spectrum lambdaI(sub lambda) attains it maximum at 100 microns. A secondary maximum in the dust emission spectrum occurs at 10 microns, which contains 15% of the total IR luminosity of the Galaxy. The galactic dust emission spectrum was compared with the dust emission spectra of external IRAS galaxies. The warm dust luminosity relates to the present OB star formation rate, while flux densities observed at longer submm wavelengths are dominated by cold dust emission and thus can be used to estimate gas masses.

Cox, P.↗
DOE OSTI2021

Photophysical properties of zero-dimensional perovskites studied by PBE0 and GW+BSE methods

Due to the exceptional photophysical properties and great potential applications in solid state lighting, zero-dimensional halide perovskites with broadband emitting have recently attracted much attention. In this work, to reveal the origin of the broadband absorption and emission spectra of 0D (C 4 N 2 H 14 Br) 4 SnBr x I 6-x (x = 3), the ground state and exciton dynamics properties have been studied by hybrid PBE0 functional and the GW+BSE method. Different self-trapped excitons (STEs) are obtained, and their emission energies by PBE0 are consistent well with experimental data. By considering the vibrational broadening of emission, our calculated full width at half maximum of emission accords well with the experiment. The absorption of free exciton and STEs is also calculated by considering the quasiparticle and excitonic effect. Our results show that these light-induced trapped states can be observed by experiments, as confirmed in other similar systems by the femtosecond transient absorption spectra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set

In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz (λ = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars—which typically exhibit steep emission spectra—are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (≲2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2013

Automating Hyperspectral Data for Rapid Response in Volcanic Emergencies

In a volcanic emergency, time is of the essence. It is vital to quantify eruption parameters (thermal emission, effusion rate, location of activity) and distribute this information as quickly as possible to decision-makers in order to enable effective evaluation of eruption-related risk and hazard. The goal of this work was to automate and streamline processing of spacecraft hyperspectral data, automate product generation, and automate distribution of products. Visible and Short-Wave Infrared Images of volcanic eruption in Iceland in May 2010." class="caption" align="right">The software rapidly processes hyperspectral data, correcting for incident sunlight where necessary, and atmospheric transmission; detects thermally anomalous pixels; fits data with model black-body thermal emission spectra to determine radiant flux; calculates atmospheric convection thermal removal; and then calculates total heat loss. From these results, an estimation of effusion rate is made. Maps are generated of thermal emission and location (see figure). Products are posted online, and relevant parties notified. Effusion rate data are added to historical record and plotted to identify spikes in activity for persistently active eruptions. The entire process from start to end is autonomous. Future spacecraft, especially those in deep space, can react to detection of transient processes without the need to communicate with Earth, thus increasing science return. Terrestrially, this removes the need for human intervention.

Davies, Ashley G.↗
DOE OSTI2021

Li Isotope Signatures using Optical Spectroscopies

The primary goal of this work is to investigate the detection capabilities of laser ablation molecular isotopic spectrometry (LAMIS) and Raman spectroscopy for lithium isotopic determination as related to Li enrichment activities. LAMIS is an emerging spectroscopic technique that takes advantage of the fact that molecules exhibit much larger isotopic wavelength shifts in molecular emission spectra than their atomic counterparts. Raman spectroscopy has been shown to exhibit isotopic shifts if a given molecular vibration involves the isotope of interest. Both techniques are comprised of the same basic hardware: a spectrometer, a laser system (pulsed for LAMIS, pulsed or CW for Raman), and an intensified charge-coupled device (ICCD). Shifts in Raman spectra due to lithium isotopes in Li 2 C0 3 and LiOH*H 2 0 were observed. LAMIS measurements of the same compounds have not been successful yet, as no lithium containing molecular emissions have been identified to this point. However, an isotopic shift of the self-reversal of an atomic lithium emission was observed, which is another optical technique used to measure isotopes.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1977

Nonthermal galactic emission below 10 MHz

The Radio Astronomy Explorer-2 (RAE-2) satellite has provided new measurements of the nonthermal galactic radio emission at frequencies below 10 MHz. Measurements of the emission spectra are presented for the center, anticenter, north polar, and south polar directions at 22 frequencies between 0.25 and 9.18 MHz. Survey maps of the spatial distribution of the observed low frequency galactic emission at 1.31, 2.20, 3.93, 4.70, 6.55, and 9.18 MHz are presented. The observations were obtained with the 229-meter traveling-wave V-antenna on this lunar orbiting spacecraft. The improved frequency coverage offers additional insights into structure of the local galactic neighborhood.

Novaco, J. C.↗
NASA NTRS1997

High-Resolution Studies of Extreme-Ultraviolet Emission from CO by Electron Impact

We report a high-resolution study (0.0036 nm full width at half maximum) of electron-impact-induced emission spectra of CO at 30-, 75-, and 100-eV electron-impact energies. The spectral features were acquired in optically thin conditions. At the specified resolution, attainable with our 3-m vacuum ultraviolet spectrometer, we observe rotationally resolved emission bands of CO in the extreme ultraviolet, from the vibronic states B (sup 1)sigma(sup +)(0), C (sup 1)sigma(sup+)(0), and E (sup 1)pi(0), to the ground state X (sup 1)sigma(sup +)(0). A simple model of these bands, based on the Honl-London factors and the rotational constants, is constructed and is shown to be in good agreement with the observed spectra. The predissociation yield for the E (sup 1)pi electronic state has been determined, showing that the E state has the largest predissociation cross section of CO for all singlet-state Rydberg series members. The excitation function of the [E (sup 1)pi(0) yields X (sup 1)sigma(sup +)(0)] transition, in the 0-800-eV impact energy range, is measured, permitting determination of the oscillator strength by using a modified Born approximation analytical fit.

Ciocca, Marco↗