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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Precision redshift-space galaxy power spectra using Zel'dovich control variates

Numerical simulations in cosmology require trade-offs between volume, resolution and run-time that limit the volume of the Universe that can be simulated, leading to sample variance in predictions of ensemble-average quantities such as the power spectrum or correlation function(s). Sample variance is particularly acute at large scales, which is also where analytic techniques can be highly reliable. This provides an opportunity to combine analytic and numerical techniques in a principled way to improve the dynamic range and reliability of predictions for clustering statistics. In this paper we extend the technique of Zel'dovich control variates, previously demonstrated for 2-point functions in real space, to reduce the sample variance in measurements of 2-point statistics of biased tracers in redshift space. We demonstrate that with this technique, we can reduce the sample variance of these statistics down to their shot-noise limit out to k ~ 0.2 h Mpc -1 . This allows a better matching with perturbative models and improved predictions for the clustering of e.g. quasars, galaxies and neutral Hydrogen measured in spectroscopic redshift surveys at very modest computational expense. We discuss the implementation of ZCV, give some examples and provide forecasts for the efficacy of the method under various conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Raman Interferometry between Autoionizing States to Probe Ultrafast Wave-Packet Dynamics with High Spectral Resolution

Photoelectron interferometry with femtosecond and attosecond light pulses is a powerful probe of the fast electron wave-packet dynamics, albeit it has practical limitations on the energy resolution. We show that one can simultaneously obtain both high temporal and spectral resolution by stimulating Raman interferences with one light pulse and monitoring the modification of the electron yield in a separate step. Applying this spectroscopic approach to the autoionizing states of argon, we experimentally resolved its electronic composition and time evolution in exquisite detail. Theoretical calculations show remarkable agreement with the observations and shed light on the light-matter interaction parameters. Using appropriate Raman probing and delayed detection steps, this technique enables highly sensitive probing and control of electron dynamics in complex systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1990

Upper atmosphere research: Reaction rate and optical measurements

The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

Stief, L. J.↗
NASA NTRS1996

Spectroscopic Analysis of Perfluoropolyether Lubricant Degradation During Boundary Lubrication

The degradation of a branched perfluoropolyether (PFPE) under boundary lubrication conditions was studied using mu-FTIR and mu-Raman spectroscopies. Stainless steel (440C) discs coated with thin (600A), uniform films of the PFPE were tested in a ball-on-disc apparatus until various levels of friction coefficient were attained. Discs were then examined using the above techniques. When the friction coefficient surpassed the value obtained with an un-lubricated control, the lubricant film had either been physically displaced or partially transformed in to a 'friction polymer'. Infrared analysis of this 'friction polymer' indicated the presence of a polymeric fluorinated acid species (R(sub f)COOH). Raman spectroscopy indicated the presence of amorphous carbon in the wear track and in the friction polymer. Some reaction mechanisms are suggested to explain the results.

Herrera-Fierro, Pilar↗
NASA NTRS2013

Spectroscopic Determination of Trace Contaminants in High-Purity Oxygen

Oxygen used for extravehicular activities (EVAs) must be free of contaminants because a difference in a few tenths of a percent of argon or nitrogen content can mean significant reduction in available EVA time. These inert gases build up in the extravehicular mobility unit because they are not metabolized or scrubbed from the atmosphere. A prototype optical emission technique capable of detecting argon and nitrogen below 0.1% in oxygen has been developed. This instrument uses a glow discharge in reduced-pressure gas to produce atomic emission from the species present. Because the atomic emission lines from oxygen, nitrogen, and argon are discrete, and in many cases well-separated, trace amounts of argon and nitrogen can be detected in the ultraviolet and visible spectrum. This is a straightforward, direct measurement of the target contaminants, and may lend itself to a device capable of on-orbit verification of oxygen purity. A glow discharge is a plasma formed in a low-pressure (1 to 10 Torr) gas cell between two electrodes. Depending on the configuration, voltages ranging from 200 V and above are required to sustain the discharge. In the discharge region, the gas is ionized and a certain population is in the excited state. Light is produced by the transitions from the excited states formed in the plasma to the ground state. The spectrum consists of discrete, narrow emission lines for the atomic species, and broader peaks that may appear as a manifold for molecular species such as O2 and N2, the wavelengths and intensities of which are a characteristic of each atom. The oxygen emission is dominated by two peaks at 777 and 844 nm.

Hornung, Steven↗
DOE OSTI2022

Nanostructures evolution assessment and spectroscopic properties modification induced by electronic energy loss in KTaO 3 crystal

Modifications of micro/nanostructure and photoelectric properties under swift ion irradiation (645 MeV Xe 35+ ) of KTaO 3 crystal with varying electronic energy losses (7.2–31.4 keV/nm) and ion velocities (0.18–5.00 MeV/u) have been studied by combining experimental and calculated approaches. The i-TS calculations combined with molecular dynamics simulations are compared with the experimental observations, revealing the inner track fine structures from individual spherical defects to continuous ion tracks with core–shell morphologies, and a quantitative relationship, including the melting (0.42 eV/atom), damage (0.75 eV/atom), and amorphous (1.71 eV/atom) thresholds, is established to successfully predict the inner disorder/amorphous proportions and track damage morphologies. The surface nanostructures of nanohillocks (isolated or partial overlaps) and nanopits (serious overlaps) directly depend on the combined action of the deposited potential and kinetic energies of incident ions, which induce local melting and sublimation in the near-surface region. Owing to the decreased recombination and the increased separation efficiency between electrons and holes, the higher photogenerated charge carrier mobility enhanced the photocurrent effect, further optimizing the photoconductivity performance in Xe 35+ -irradiated KTaO 3 . Therefore, controlled defect engineering using the ion irradiation technique, as an effective strategy, could design tailored nanostructure systems and regulate photoelectric properties, further promoting the development of novel technological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Discovering strongly lensed quasar candidates with catalogue-based methods from DESI Legacy Surveys

The Hubble tension, revealed by a ~5σ discrepancy between measurements of the Hubble-Lemaitre constant among observations of the early and local Universe, is one of the most significant problems in modern cosmology. In order to better understand the origin of this mismatch, independent techniques to measure H 0 , such as strong lensing time delays, are required. Notably, the sample size of such systems is key to minimising the statistical uncertainties and cosmic variance, which can be improved by exploring the datasets of large-scale sky surveys such as Dark Energy Spectroscopic Instrument (DESI). We identify possible strong lensing time-delay systems within DESI by selecting candidate multiply imaged lensed quasars from a catalogue of 24 440 816 candidate QSOs contained in the ninth data release of the DESI Legacy Imaging Surveys (DESI-LS). Using a friend-of-friends-like algorithm on spatial co-ordinates, our method generates an initial list of compact quasar groups. This list is subsequently filtered using a measure of the similarity of colours among a group’s members and the likelihood that they are quasars. A visual inspection finally selects candidate strong lensing systems based on the spatial configuration of the group members. We identified 620 new candidate multiply imaged lensed quasars (101 grade-A, 214 grade-B, 305 grade-C). This number excludes 53 known spectroscopically confirmed systems and existing candidate systems identified in other similar catalogues. When available, these new candidates will be further checked by combining the spectroscopic and photometric data from DESI.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Electro-optic sampling of classical and quantum light

Full characterization of electric-field waveforms in amplitude and phase is achieved across the terahertz to visible spectral range through interaction with an optical pulse shorter than a half-cycle period via the Pockels (linear electro-optic) effect. This technique of electro-optic sampling has become an indispensable tool in various areas, including ultrafast pump-probe, time-domain and frequency-comb spectroscopies, quantum optics, high-harmonic generation, and attosecond science, and holds great promise for further advances. Not only does it enable spectroscopic measurements with record dynamic range and temporal resolution, along with massively parallel real-time spectral data acquisition, but its remarkable sensitivity also allows the detection of vacuum fluctuations, i.e., “zero-point motion” of electric fields, profoundly impacting our understanding of the fundamental laws of nature.

Benea-Chelmus, Ileana-Cristina (ORCID:000000024814↗
NASA NTRS1987

Interstellar problems and matrix solutions

The application of the matrix isolation technique to interstellar problems is described. Following a brief discussion of the interstellar medium (ISM), three areas are reviewed in which matrix experiments are particularly well suited to contribute the information which is sorely needed to further understanding of the ISM. The first involves the measurement of the spectroscopic properties of reactive species. The second is the determination of reaction rates and the elucidation of reaction pathways involving atoms, radicals, and ions which are likely to interact on grain surfaces and in grain mantles. The third entails the determiantion of the spectroscopic, photochemical, and photophysical properties of interstellar and cometary ice analogs. Significant, but limited, progress has been made in these three areas, and a tremendous amount of work is required to fully address the variety of unique chemical and spectroscopic questions posed by the astronomical observations.

Allamandola, Louis J.↗
NASA NTRS2010

Characterization of Orbital Debris Photometric Properties Derived from Laboratory-Based Measurements

Capitalizing on optical data products and applying them to generate a more complete understanding of orbital space objects, is a key objective of NASA's Optical Measurement Program, and a primary objective for the creation of the Optical Measurements Center(OMC). The OMC attempts to emulate space-based illumination conditions using equipment and techniques that parallel telescopic observations and source-target-sensor orientations. The data acquired in the OMC are a function of known shape, size, and material. These three physical parameters are key to understanding the orbital debris environment in more depth. For optical observations, one must rely on spectroscopic or photometric measurements to ascertain an object's material type. Determination of an object s shape using remote observations is more complicated due to the various light scattering properties each object present and is a subject that requires more study. It is much easier to look at the periodicity of the light curve and analyze its structure for rotation. In order to best simulate the orbital debris population, three main sources were used as test fragments for optical measurements: flight-ready materials, destructive hypervelocity testing (simulating on-orbit collisions) and destructive pressure testing (simulating on-orbit explosions). Laboratory optical characteristics of fragments were measured, including light curve shape, phase angle dependence, and photometric and spectroscopic color indices. These characteristics were then compared with similar optical measurements acquired from telescopic observations in order to correlate remote and laboratory properties with the intent of ascertaining the intrinsic properties of the observed orbital debris

Cowardin, Heather↗
DOE OSTI2024

Challenges in the Use of AI-Driven Non-Destructive Spectroscopic Tools for Rapid Food Analysis

Routine, remote, and process analysis for foodstuffs is gaining attention and can provide more confidence for the food supply chain. A new generation of rapid methods is emerging both in the literature and in industry based on spectroscopy coupled with AI-driven modelling methods. Current published studies using these advanced methods are plagued by weaknesses, including sample size, abuse of advanced modelling techniques, and the process of validation for both the acquisition method and modelling. This paper aims to give a comprehensive overview of the analytical challenges faced in research and industrial settings where screening analysis is performed while providing practical solutions in the form of guidelines for a range of scenarios. After extended literature analysis, we conclude that there is no easy way to enhance the accuracy of the methods by using state-of-the-art modelling methods and the key remains that capturing good quality raw data from authentic samples in sufficient volume is very important along with robust validation. A comprehensive methodology involving suitable analytical techniques and interpretive modelling methods needs to be considered under a tailored experimental design whenever conducting rapid food analysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Characterizing Complex Gas–Solid Interfaces with in Situ Spectroscopy: Oxygen Adsorption Behavior on Fe–N–C Catalysts

Electrocatalysts for the oxygen reduction reaction within polymer electrolyte membrane fuel cells based on iron, nitrogen, and carbon elements (Fe–N–C) are receiving significant research attention as they offer an inexpensive alternative to catalysts based on platinum-group metals. Although both the performance and the fundamental understanding of Fe–N–C catalysts have improved over the past decade, there remains a need to differentiate the relative activity of different active sites. Toward this goal, our study is focused on characterizing the interactions between O 2 and a set of five structurally different Fe–N–C materials. Detailed characterization of the Fe speciation was performed with 57 Fe Mössbauer spectroscopy and soft X-ray absorption spectroscopy of the Fe L 3,2 -edge, whereas nitrogen chemical states were investigated with X-ray photoelectron spectroscopy (XPS). In addition to initial sXAS and XPS measurements performed in ultra-high vacuum (UHV), measurements were also performed (at the identical location) in an atmosphere of 100 mTorr of O 2 at 80 °C (O 2 -rich). XPS and sXAS results reveal the presence of several types of FeNxCy adsorption sites. FeNxCy sites that are proposed as the most active ones do not show significant change (based on the techniques used in this study) when their environment is changed from UHV to O 2 -rich. Correlation with Mössbauer and sXAS results suggests that this is most likely due to the persistence of strongly adsorbed O 2 molecules from their previous exposure to air. However, other species do show spectroscopic changes from UHV conditions to O 2 -rich. This implies that these sites have a weaker interaction with O 2 that results in their desorption in vacuum conditions and re-adsorption when exposed to the O 2 -rich environment. The nature of these weakly and strongly O 2 -adsorbing FeN x C y sites is discussed in the context of different synthetic and processing parameters employed to fabricate each of these five Fe–N–C materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ultrafast spectroscopic studies of vibrational energy transfer in energetic materials

Shock-induced detonation is a key property of energetic materials (EM) that remains empirically understood. One proposed mechanism of shock-initiation in EM is “phonon up-pumping” to initiate chemical reactions, where excitation of lattice phonon modes rapidly transfers energy into intramolecular vibrations, ultimately resulting in the breaking of chemical bonds. We are developing novel ultrafast laser spectroscopy techniques to study vibrational energy transfer from phonon modes to intramolecular vibrations (phonon up-pumping), as well as competing energy transfer pathways from intramolecular vibrations to phonon modes (vibrational cooling). Through combinations of plasma- generated supercontinuum infrared, tunable near- and mid-infrared, and terahertz pulses in pump-probe spectroscopy, supplemented with ab inito simulations, we can explore the energy transfer processes on a sub-picosecond time scale to elucidate vibrational energy transfer pathways and lifetimes in EM. In this work, we highlight recent progress, including the spectral and temporal characteristics of the infrared and THz sources as well as preliminary results on select EM.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Bragg crystal spectrometer for HEAO-B X-ray astronomy experiment

The X-ray astronomy experiment for the HEAO mission is described. The instrument to be flown on the satellite consists of two Bragg crystal spectrometers designed to make measurements with high spectral resolution in the energy range from 0.1 to 10 keV. No sharp spectroscopic features were detected directly in X-ray astronomy except emission lines in the sun; therefore, the objectives and design criteria of this instrument are based on the theoretical models of the different types of extra solar X-ray sources. From the point of view of instrumental techniques it is convenient to divide these into point or stellar sources, whose radiation is parallel, and diffuse sources, and to consider the possible spectral features in each type.

Angel, J. R. P.↗
NASA NTRS1975

Enhanced crystallinity of low temperature deposited silicon films on graphite subtrates

The previously developed technique of a sandwich coating for silicon crystallinity enhancement in silicon films deposited at low temperature is applied to graphite substrates. The measured increase in silicon crystallinity is comparable to that observed earlier using a quartz substrate. The distribution of aluminum in the silicon films is determined using Auger spectroscopic depth profiling. Carbon diffusion from the substrate into the silicon film is shown to be negligible at a substrate temperature of 600 C.

Chang, C. A.↗
NASA NTRS1989

Fast spectroscopic variations on rapidly-rotating, cool dwarfs. 3: Masses of circumstellar absorbing clouds on AB Doradus

New time-resolved H alpha, Ca II H and K and Mg II h and k spectra of the rapidly-rotating K0 dwarf star AB Doradus (= HD 36705). The transient absorption features seen in the H alpha line are also present in the Ca II and Mg II resonance lines. New techniques are developed for measuring the average strength of the line absorption along lines of sight intersecting the cloud. These techniques also give a measure of the projected cloud area. The strength of the resonance line absorption provides useful new constraints on the column densities, projected surface areas, temperatures and internal turbulent velocity dispersions of the circumstellar clouds producing the absorption features. At any given time the star appears to be surrounded by at least 6 to 10 clouds with masses in the range 2 to 6 x 10(exp 17) g. The clouds appear to have turbulent internal velocity dispersions of order 3 to 20 km/s, comparable with the random velocities of discrete filamentary structures in solar quiescent prominences. Night-to-night changes in the amount of Ca II resonance line absorption can be explained by changes in the amplitude of turbulent motions in the clouds. The corresponding changes in the total energy of the internal motions are of order 10(exp 29) erg per cloud. Changes of this magnitude could easily be activated by the frequent energetic (approximately 10(exp 34) erg) x ray flares seen on this star.

Cameron, A. Collier↗
NASA NTRS1994

Infrared spectroscopic measurements of the ethane (C2H6) total column abundance above Mauna Loa, Hawaii -- seasonal variations

About 200 i.r. solar spectra recorded at 0.01/cm resolution on 71 days between November 1991 and July 1993 at the Network for the Detection of Stratospheric Change (NDSC) station at Mauna Loa, Hawaii (latitude 19.53 deg N, longitude 155.58 deg W, elevation 3.459 km) have been analyzed with a nonlinear least-squares spectral fitting technique to study temporal variations in the total column of atmospheric ethane (C2H6) above the site. The results were derived from the analysis of the unresolved nu(sub 7) band (P)Q(sub 3) subbranch at 2976.8/cm. A distinct seasonal cycle is observed with a factor of 2 variation, a maximum total column of 1.16 x 10(exp 16) mol/sq cm at the end of winter, and a minimum total column of 0.53 x 10(exp 16) mol/sq cm at the end of summer. Our measurements are compared with previous observations and model predictions.

Rinsland, C. P.↗
NASA NTRS1994

Infrared Spectroscopic Measurements of the Ethane (C2H6) Total Column Abundance Above Mauna Loa, Hawaii: Seasonal Variations

About 200 i.r. solar spectra recorded at 0.01/ cm resolution on 71 days between November 1991 and July 1993 at the Network for the Detection of Stratospheric Change (NDSC) station at Mauna Loa, Hawaii (latitude 19.53 deg N, longitude 155.58 deg W, elevation 3.459 km) have been analyzed with a nonlinear least-squares spectral fitting technique to study temporal variations in the total column of atmospheric ethane (C2H6) above the site. The results were derived from the analysis of the unresolved nu(sub 7) band (sup P)Q(sub 3) subbranch at 2976.8/cm. A distinct seasonal cycle is observed with a factor of 2 variation, a maximum total column of 1.1 6 x 10(exp 16) mol /sq cm at the end of winter, and a minimum total column of 0.53 x 10(exp 16) mol/sq cm at the end of summer. Our measurements are compared with previous observations and model predictions.

Rinsland, C. P.↗