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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Photospheric Fluorescence and Resonance Scattering: Non Classical Diagnostics and the Future of X-ray Stellar Spectroscopy

High resolution AXAF and XMM observations of stellar coronae will yield a wealth of X-ray plasma line diagnostics that will provide a giant leap forward in our understanding of coronal densities, abundance anomalies and emission measure distributions. Unfortunately, there is one very basic unanswered question in the physics of active stellar coronae that the usual plasma diagnostics cannot address directly: What are the spatial characteristics of stellar coronae-the scale height and filling factor? What do other stellar coronae actually look like? I will discuss two novel diagnostics of coronal geometry and their application to future X-ray spectra: photospheric fluorescence and resonance line optical depths.

Drake, Jeremy↗
NASA NTRS1977

Ultraviolet absorption: Experiment MA-059

A technique devised to permit the measurement of atmospheric species concentrations is described. This technique involves the application of atomic absorption spectroscopy and the quantitative observation of resonance fluorescence in which atomic or molecular species scatter resonance radiation from a light source into a detector. A beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation was sent from Apollo to Soyuz. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Results of postflight analysis of the resonance fluorescence data are discussed.

Donahue, T. M.↗
NASA NTRS1979

Rate constant for the reaction H + NO2 from 195 to 400 K with FP-RF and DF-RF techniques

Measurements are made of the rate constant for the reaction H + NO2 yielding OH + NO over significant temperature ranges with the flash photolysis-resonance fluorescence (FP-RF) technique and also with the discharge flow-resonance fluorescence (DF-RF) technique. Since it is important to study chemical reactions with more than one technique, the above reaction is investigated with the FP-RF technique over the temperature range 230-400 K. The results reported do not agree with earlier determinations. Accordingly, a separate set of measurements is made with the DF-RF technique over the temperature range 195-368 K; the results are also reported. The reaction is also considered theoretically, especially with regard to the question of temperature dependence and absolute magnitude of the rate constant.

Michael, J. V.↗
NASA NTRS1977

Statistical equilibrium in cometary C2. I

Swan-band emission from the C2 molecule provides important information for a study of the physical processes occurring in comets. It is, therefore, a disturbing factor that many quantitative Swan-band observations are in clear contradiction of predictions of resonance fluorescence excitation of the Swan bands. A description is presented of an investigation involving an application of resonance fluorescence theory to C2. The investigation takes into account all important electronic transitions which determine the population distribution of the lowest energy states. It is found that the previous discrepancy for the brighter band sequences disappears.

Swamy, K. S. K.↗
NASA NTRS1976

Ultraviolet absorption experiment MA-059

The ultraviolet absorption experiment performed during the Apollo Soyuz mission involved sending a beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation, all filling the same 3 deg-wide field of view from the Apollo to the Soyuz. The radiation struck a retroreflector array on the Soyuz and was returned to a spectrometer onboard the Apollo. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Information concerning oxygen densities was also obtained by observation of resonantly fluorescent light. The absorption experiments for atomic oxygen and atomic nitrogen were successfully performed at a range of 500 meters, and abundant resonance fluorescence data were obtained.

Donahue, T. M.↗
NASA NTRS1978

Rate constant for the reaction of atomic chlorine with methane

The rate constant and temperature dependence of the Cl + CH4 reaction have been investigated by the techniques of competitive chlorination of CH4/C2H6 mixtures and by discharge-flow/mass spectroscopy. The objectives were to determine an accurate value for the rate constant for use in stratospheric modeling, and to clarify discrepancies in results previously obtained by different techniques. The results deduced from the competitive chlorination study are in good agreement with the absolute values measured by the mass spectrometric method, and at temperatures above 300 K are in good agreement with measurements by other techniques based on resonance fluorescence detection of atomic chlorine. However, in the 220-300 K region, the competitive experiments indicate lower rate constants than those obtained by resonance fluorescence methods, and do not reproduce the curved Arrhenius plots seen in some of those studies.

Lin, C. L.↗
NASA NTRS1980

Pressure dependence of the absolute rate constant for the reaction OH + C2H2 from 228 to 413 K

The pressure dependence of the absolute rate constant for the reaction of the hydroxyl radical with acetylene, important in both atmospheric and combustion chemistry, is determined for temperatures between 228 and 413 K. The flash photolysis-resonance fluorescence technique was employed at five temperatures over wide ranges of pressure and acetylene concentrations, with the OH produced by water photolysis and hydroxyl resonance fluorescent photons measured by multiscaling techniques. Results indicate that, except at the lowest temperature, the bimolecular rate constant for the reaction depends strongly on total pressure, with the pressure effect becoming more pronounced with increasing temperature. At limiting high pressures, the rate constant is found to be equal to 6.83 + or - 1.19 x 10 to the -12th exp (-646 + or - 47/T) cu cm/molecule per sec, where T is the temperature. Results thus demonstrate the importance of environmental conditions in theoretical studies of atmospheric and combustion product compositions

Michael, J. V.↗
NASA NTRS1976

Absolute rate parameters for the reaction of ground state atomic oxygen with dimethyl sulfide and episulfide

It is pointed out that the investigated reaction of oxygen with dimethyl sulfide may play an important role in photochemical smog formation and in the chemical evolution of dense interstellar clouds. Kinetic data were obtained with the aid of the flash photolysis-resonance fluorescence method. The photodecomposition of molecular oxygen provided the oxygen atoms for the experiments. The decay of atomic oxygen was studied on the basis of resonance fluorescence observations. Both reactions investigated were found to be fast processes. A negative temperature dependence of the rate constants for reactions with dimethyl sulfide was observed.

Lee, J. H.↗
NASA NTRS1993

Laser flash photolysis studies of atmospheric free radical chemistry using optical diagnostic techniques

Some recent studies carried out in our laboratory are described where laser flash photolytic production of reactant free radicals has been combined with reactant and/or product detection using time-resolved optical techniques to investigate the kinetics and mechanisms of important atmospheric chemical reactions. Discussed are (1) a study of the radical-radical reaction O + BrO yields Br + O2 where two photolysis lasers are employed to prepare the reaction mixture and where the reactants O and BrO are monitored simultaneously using atomic resonance fluorescence to detect O and multipass UV absorption to detect BrO; (2) a study of the reaction of atomic chlorine with dimethylsulfide (CH3SCH3) where atomic resonance fluorescence detection of Cl is employed to elucidate the kinetics and tunable diode laser absorption spectroscopy is employed to investigate the HCl product yield; and (3) a study of the aqueous phase chemistry of Cl2(-) radicals where longpath UV absorption spectroscopy is employed to investigate the kinetics of the Cl2(-) + H2O reaction.

Wine, Paul H.↗
NASA NTRS1981

A laser flash photolysis kinetics study of the reaction OH + H2O2 yields HO2 + H2O

Absolute rate constants for the reaction are reported as a function of temperature over the range 273-410 K. OH radicals are produced by 266 nm laser photolysis of H2O2 and detected by resonance fluorescence. H2O2 concentrations are determined in situ in the slow flow system by UV photometry. The results confirm the findings of two recent discharge flow-resonance fluorescence studies that the title reaction is considerably faster, particularly at temperatures below 300 K, than all earlier studies had indicated. A table giving kinetic data from the reaction is included.

Wine, P. H.↗
DOE OSTI2025

Theory of resonant x-ray scattering with ultrafast intense pulses

Here, we present a time-dependent Schrödinger equation approach within a nonrelativistic quantum electrodynamics framework to investigate resonant x-ray scattering driven by intense x-ray pulses. This method enables us to explore how coherent x-ray electron dynamics influence scattering signals from Ne + . We account for both resonance fluorescence and elastic scattering channels, while also considering competing photoionization and inner-shell decay processes. By computing the angular distribution and energy spectrum of scattered photons, we uncover interference effects between elastic scattering and resonance fluorescence pathways. Notably, this interference results in a small asymmetry in the energy spectrum. We discuss the experimental potential for detecting signatures of interference. Our findings demonstrate that the x-ray Rabi dynamics can be used to control scattering responses and provide insights into interference mechanisms and scattering efficiency in high-intensity x-ray regimes.

Venkatesh, Akilesh [Argonne National Laboratory (A↗
NASA NTRS1997

Calculated hydroxyl A2 sigma --> X2 pi (0, 0) band emission rate factors applicable to atmospheric spectroscopy

A calculation of the A2 sigma --> X2 pi (0, 0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant fluorescence in the terrestrial atmosphere is presented in this paper. The most accurate available line parameters have been used. Special consideration has been given to the solar input flux because of its highly structured Fraunhofer spectrum. The calculation for the OH atmospheric emission rate factor in the solar resonant fluorescent case is described in detail with examples and intermediate results. Results of this calculation of OH emission rate factors for individual rotational lines are on average 30% lower than the values obtained in an earlier work.

NASA Discipline Exobiology↗
NASA NTRS2015

Development of a Sodium LIDAR for Spaceborne Missions

We are currently developing laser and electro-optic technologies to remotely measure Sodium (Na) by adapting existing lidar technology with space flight heritage. The developed instrumentation will serve as the core for the planning of a Heliophysics mission targeted to study the composition and dynamics of Earths mesosphere based on a spaceborne lidar that will measure the mesospheric Na layer. There is a pressing need in the Ionosphere Thermosphere - Mesosphere (ITM) community for high-resolution measurements that can characterize small-scale dynamics (i.e. Gravity Waves with wavelengths smaller than a few hundred km) and their effects in the Mesosphere-Lower-Termosphere (MLT) on a global basis. This is compelling because they are believed to be the dominant contributors to momentum transport and deposition in the MLT, which largely drive the global circulation and thermal structure and interactions with the tides and planetary waves in this region. We are developing a spaceborne remote sensing technique that will enable acquisition of global Na density, temperature and wind measurements in the MLT with the spatial and temporal resolution required to resolve issues associated with the structure, chemistry, dynamics, and energetics of this regionA nadir-pointing spaceborne Na Doppler resonance fluorescence LIDAR on board of the ISS will essentially make high-resolution, in time and space, Na density, temperature and vertical wind measurements, from 75-115 km (MLT region). Our instrument concept consisted of a high-energy laser transmitter at 589 nm and highly sensitive photon counting detector that allows for range-resolved atmospheric-sodium-temperature profiles. The atmospheric temperature is deduced from the linewidth of the resonant fluorescence from the atomic sodium vapor D2 line as measured by our tunable laser. We are currently developing a high power energy laser that allows for some day time sodium lidar observations with the help of a narrow bandpass filter based on etalon or atomic sodium Faraday filter with 5 to 10 pm optical bandwidth. The current baseline detector for the lidar instrument is a 16-channel Photomultiplier Tube with receiver electronics that has been space-qualified for the ICESat-2ATLAS mission. Our technique uses the 16-channels as a photon-number-resolving single detector to provide the required full-spectroscopic sodium lineshape waveform for recovering Mesospheric temperature profiles. In this paper, we will describe our instrument concept for a future Heliophysics space mission based on board of the International Space Station (ISS).

lidar↗
NASA NTRS1997

Kinetics and Thermochemistry of Reversible Adduct Formation in the Reaction of Cl((sup 2)P(sub J)) with CS2

Reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with CS2 has been observed over the temperature range 193-258 K by use of time-resolved resonance fluorescence spectroscopy to follow the decay of pulsed-laser-generated Cl((sup 2)P(sub J)) into equilbrium with CS2Cl. Rate coefficients for CS2Cl formation and decomposition have been determined as a function of temperature and pressure; hence, the equilbrium constant has been determined as a function of temperature. A second-law analysis of the temperature dependence of Kp and heat capacity corrections calculated with use of an assumed CS2Cl structure yields the following thermodynamic parameters for the association reaction: Delta-H(sub 298) = -10.5 +/- 0.5 kcal/mol, Delta-H(sub 0) = -9.5 +/- 0.7 kcal/mol, Delta-S(sub 298) = -26.8 +/- 2.4 cal/mol.deg., and Delta-H(sub f,298)(CS2Cl) = 46.4 +/- 0.6 kcal/mol. The resonance fluorescence detection scheme has been adapted to allow detection of Cl((sup 2)P(sub J)) in the presence of large concentrations of O2, thus allowing the CS2Cl + Cl + O2 reaction to be investigated. We find that the rate coefficient for CS2Cl + O2 reaction via all channels that do not generate Cl((sup 2)P(sub J)) is less than 2.5 x 10(exp-16) cu cm/(molecule.s) at 293 K and 300-Torr total pressure and that the total rate coefficient is less than 2 x 10 (exp -15) cu cm/(molecule.s) at 230 K and 30-Torr total pressure. Evidence for reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with COS was sought but not observed, even at temperatures as low as 194 K.

Nicovich, J. M.↗
NASA NTRS1973

A new effect in the depolarization of resonant light scattering from molecules in the vapor phase: I2

Theoretical discussions of the depolarization ratios in two types of resonance processes are given. These processes are discrete state resonance fluorescence, and Raman scattering when the resonance is between a bound state and evanescent-dissociative states. Theory predicts a dramatic difference for these two cases due to a quantum mechanical phase cancellation in the case of virtual dissociative states. The predictions have been verified experimentally.

Silverstein, S. D.↗
DOE OSTI2025

Luminescent Zn 2 GeO 4 :Mn 2+ Nanoparticles with High Quantum Yield for Salivary Protein Detection

Zinc germanate doped with Mn 2+ (Zn 2 GeO 4 :Mn 2+ ) is known to be a green luminescence phosphor with many applications in biosensing and bioimaging. This study presents a simple method for creating small size Zn 2 GeO 4 :Mn 2+ nanoparticles using a combination of the coprecipitation–molten salt synthesis method. These nanoparticles exhibit bright green luminescence under UV excitation. After surface functionalization, these nanoparticles were then used to develop a fluorescence resonance energy transfer (FRET)-based immunoassay. This immunoassay shows a detection range of 5–20 ng/mL of C-reactive protein (CRP), which suggests its potential for simple solution CRP detection and broader applications in protein biosensing.

biosensing↗
DOE OSTI2024

Sequence-specific dynamic DNA bending explains mitochondrial TFAM’s dual role in DNA packaging and transcription initiation

Abstract Mitochondrial transcription factor A (TFAM) employs DNA bending to package mitochondrial DNA (mtDNA) into nucleoids and recruit mitochondrial RNA polymerase (POLRMT) at specific promoter sites, light strand promoter (LSP) and heavy strand promoter (HSP). Herein, we characterize the conformational dynamics of TFAM on promoter and non-promoter sequences using single-molecule fluorescence resonance energy transfer (smFRET) and single-molecule protein-induced fluorescence enhancement (smPIFE) methods. The DNA-TFAM complexes dynamically transition between partially and fully bent DNA conformational states. The bending/unbending transition rates and bending stability are DNA sequence-dependent—LSP forms the most stable fully bent complex and the non-specific sequence the least, which correlates with the lifetimes and affinities of TFAM with these DNA sequences. By quantifying the dynamic nature of the DNA-TFAM complexes, our study provides insights into how TFAM acts as a multifunctional protein through the DNA bending states to achieve sequence specificity and fidelity in mitochondrial transcription while performing mtDNA packaging.

59 BASIC BIOLOGICAL SCIENCES↗