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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Measurement and analysis of the far infrared absorption spectrum of the gaseous mixture H2-CH4

The collision-induced absorption of H2-CH4 mixtures was measured from 20 to 900/cm at 195 and 297 K. By subtracting the absorption due to H2-H2 and CH4-CH4 collisions from that of the mixture, the absorption due to H2-CH4 collisions was obtained. This spectrum was analyzed using the BC model line shape to provide a way of estimating the far-IR spectrum of H2-CH4 for various concentrations of H2 and CH4. Theoretical spectral moments were computed with different potential functions and compared with experimental values.

Birnbaum, George↗
NASA NTRS1979

Investigation of effects of background water on upwelled reflectance spectra and techniques for analysis of dilute primary-treated sewage sludge

In an effort to improve understanding of the effects of variations in background water on reflectance spectra, laboratory tests were conducted with various concentrations of sewage sludge diluted with several types of background water. The results from these tests indicate that reflectance spectra for sewage-sludge mixtures are dependent upon the reflectance of the background water. Both the ratio of sewage-sludge reflectance to background-water reflectance and the ratio of the difference in reflectance to background-water reflectance show spectral variations for different turbid background waters. The difference in reflectance is the only parameter considered.

Whitlock, C. H.↗
NASA NTRS2005

Digital Equivalent Data System for XRF Labeling of Objects

A digital equivalent data system (DEDS) is a system for identifying objects by means of the x-ray fluorescence (XRF) spectra of labeling elements that are encased in or deposited on the objects. As such, a DEDS is a revolutionary new major subsystem of an XRF system. A DEDS embodies the means for converting the spectral data output of an XRF scanner to an ASCII alphanumeric or barcode label that can be used to identify (or verify the assumed or apparent identity of) an XRF-scanned object. A typical XRF spectrum of interest contains peaks at photon energies associated with specific elements on the Periodic Table (see figure). The height of each spectral peak above the local background spectral intensity is proportional to the relative abundance of the corresponding element. Alphanumeric values are assigned to the relative abundances of the elements. Hence, if an object contained labeling elements in suitably chosen proportions, an alphanumeric representation of the object could be extracted from its XRF spectrum. The mixture of labeling elements and for reading the XRF spectrum would be compatible with one of the labeling conventions now used for bar codes and binary matrix patterns (essentially, two-dimensional bar codes that resemble checkerboards). A further benefit of such compatibility is that it would enable the conversion of the XRF spectral output to a bar or matrix-coded label, if needed. In short, a process previously used only for material composition analysis has been reapplied to the world of identification. This new level of verification is now being used for "authentication."

Schramm, Harry F.↗
DOE OSTI2015

Quantitative acetylene measurements in laminar and turbulent flames using 1D Raman/Rayleigh scattering

Our research presents the extension of the established detection of seven major species in 1D Raman/Rayleigh measurements to incorporate acetylene (C 2 H 2 ) as an eighth species. Acetylene is an important soot precursor which is generated in hydrocarbon flames as an intermediate species following decomposition. It occurs over a broad temperature range in flames and has been identified as a potentially detectable species in 1D Raman/Rayleigh measurements. In this paper, we discuss the Raman spectral signature of acetylene, its temperature dependence, calibration procedures, and the interference with other Raman-active species, C 2 and broadband interferences, all of which are essential to quantify for accurate data processing. In this regard, Raman measurements in laminar and turbulent dimethyl ether flames were acquired. The data are spectrally analyzed and low-temperature calibrations of the Raman response are combined with an extrapolation model for high temperatures in order to place the acetylene signals on an absolute scale. Single-shot and conditional-mean values are presented as a function of mixture fraction for a laminar partially-premixed DME/air flame. Measurements from the laminar flame are compared to a 1D laminar flame calculation to assess the accuracy of the calibration and analysis procedures. Furthermore, detection limits, signal-to-noise, and signal-to-interference ratio of the C 2 H 2 measurement are discussed, and single-shot measurements of acetylene in a turbulent DME/air jet flame are demonstrated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Hyperspectral Detection of the Fluorescence Shift between Chirality-Sorted Empty and Water-Filled Single-Wall Carbon Nanotube Enantiomers

Single-wall carbon nanotubes (SWCNTs) have extraordinary electronic and optical properties that depend strongly on their exact chiral structure and their interaction with their inner and outer environment. The fluorescence (PL) of semiconducting SWCNTs, for instance, will shift depending on the molecules with which the SWCNT’s hollow core is filled. These interaction-induced shifts are challenging to resolve on the ensemble level in samples containing a mixture of different filling contents due to the relatively large inhomogeneous line width of the ensemble SWCNT PL compared to the size of these shifts. To circumvent this inhomogeneous broadening, single-tube spectroscopy and hyperspectral imaging are often applied, which until now required time-consuming statistical studies. Here, we present hyperspectral PL microscopy combined with automated SWCNT segmenting based on either principal component analysis or a convolutional neural network, capable of both spatially and spectrally resolving the PL along the length of many individual SWCNTs at the same time and automatically fitting peak positions and line widths of individual SWCNTs. The methodology is demonstrated by accurately determining the emission shifts and line widths of thousands of left- and right-handed empty and water-filled SWCNTs coated with a chiral surfactant, resulting in four statistical distributions which cannot be resolved in ensemble spectroscopy of unsorted samples. The results demonstrate a robust method to quickly probe ensemble properties with single-enantiomer spectral resolution. Moreover, it promises to be an absolute quantitative method to characterize the relative abundances of SWCNTs with different handedness or filling content in macroscopic samples, simply by counting individual species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

Determination of Spectral Line Parameters in Selected Portions of the Infrared Spectrum of Water Vapor

Pressure broadening and pressure-induced shift coefficients due to water and nitrogen have been determined for water vapor transitions in the CO2 region of interest to Project HALOE. The temperature dependences of the widths and shifts have also been determined for selected transitions in this region. Results have been compared with values available in the literature. The line parameters have been obtained from the analysis of room temperature recordings of the spectrum of pure water and recordings of the spectra of heated water/nitrogen mixtures. The recordings of the water vapor spectrum were obtained with Fourier Transform Spectrometers at Kitt Peak and at the Justus-Liebig-Universitat Giessen. Up to eighteen spectra have been fitted simultaneously with a multispectrum nonlinear least-squares fitting technique developed by Dr. D. Chris Benner and colleagues.

Albert, Karen Keppler↗
NASA NTRS1992

Preliminary total dose measurements on LDEF

After spending nearly six years in Earth's orbit twenty stacks consisting of radiation detectors and biological objects are now back on Earth. These Free Flyer Biostack experiments are part of the Long Duration Exposure Facility (LDEF). The major objective of the experiments are to investigate the biological effectiveness of single heavy ions of the cosmic radiation in various biological systems and to provide information about the spectral composition of the radiation field and the total dose received in the LDEF orbit. The preliminary analysis of the thermoluminescence dosimeters (TLD) yields maximum absorbed dose rates of 2.24 mGy day(exp -1) behind 0.7 g cm(exp -2) shielding and 1.17 mGy day(exp -1) behind 12 g cm(exp -2) shielding. A thermal neutron fluence of 1.7 n cm(exp -2)s(exp -1) is determined from the differences in absorbed dose for different isotopic mixtures of lithium. The results of this experiment on LDEF are especially valuable since LDEF stayed for almost six years in the prospected orbit of the Space Station Freedom.

Reitz, G.↗
NASA NTRS1993

Expert system-based mineral mapping in northern Death Valley, California/Nevada, using the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)

Integrated analysis of imaging spectrometer data and field spectral measurements were used in conjunction with conventional geologic field mapping to characterize bedrock and surficial geology at the northern end of Death Valley, California and Nevada. A knowledge-based expert system was used to automatically produce image maps showing the principal surface mineralogy from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data. Linear spectral unmixing of the AVIRIS data allowed further determination of relative mineral, abundances and identification of mineral assemblages and mixtures. The imaging spectrometer data show the spatial distribution of spectrally distinct minerals occurring both as primary rockforming minerals and as alteration and weathering products. Field spectral measurements were used to verify the mineral maps and field mapping was used to extend the remote sensing results. Geographically referenced image maps produced from these data form new base maps from which to develop improved understanding of the processes of deposition and erosion affecting the present land surface.

Kruse, F. A.↗
DOE OSTI2018

Deep data analysis via physically constrained linear unmixing: universal framework, domain examples, and a community-wide platform

Abstract Many spectral responses in materials science, physics, and chemistry experiments can be characterized as resulting from the superposition of a number of more basic individual spectra. In this context, unmixing is defined as the problem of determining the individual spectra, given measurements of multiple spectra that are spatially resolved across samples, as well as the determination of the corresponding abundance maps indicating the local weighting of each individual spectrum. Matrix factorization is a popular linear unmixing technique that considers that the mixture model between the individual spectra and the spatial maps is linear. Here, we present a tutorial paper targeted at domain scientists to introduce linear unmixing techniques, to facilitate greater understanding of spectroscopic imaging data. We detail a matrix factorization framework that can incorporate different domain information through various parameters of the matrix factorization method. We demonstrate many domain-specific examples to explain the expressivity of the matrix factorization framework and show how the appropriate use of domain-specific constraints such as non-negativity and sum-to-one abundance result in physically meaningful spectral decompositions that are more readily interpretable. Our aim is not only to explain the off-the-shelf available tools, but to add additional constraints when ready-made algorithms are unavailable for the task. All examples use the scalable open source implementation from https://github.com/ramkikannan/nmflibrary that can run from small laptops to supercomputers, creating a user-wide platform for rapid dissemination and adoption across scientific disciplines.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Standoff detection of turbulent chemical mixture plumes using a swept external cavity quantum cascade laser

We demonstrate standoff detection of turbulent mixed-chemical plumes using a broadly-tunable external cavity quantum cascade laser (ECQCL). The ECQCL was directed through plumes of mixed methanol/ethanol vapor to a partially-reflective surface located 10 m away. The reflected power was measured as the ECQCL was swept over its tuning range of 930-1065 cm-1 (9.4-10.8 µm) at rates up to 200 Hz. Analysis of the transmission spectra though the plume was performed to determine chemical concentrations with time resolution of 0.005 s. Comparison of multiple spectral sweep rates of 2 Hz, 20 Hz, and 200 Hz shows that higher sweep rates reduce effects of atmospheric and source turbulence, resulting in lower detection noise and more accurate measurement of the rapidly-changing chemical concentrations. Detection sensitivities of 0.13 ppm*m for MeOH and 1.2 ppm*m for EtOH are demonstrated for a 200 Hz spectral sweep rate, normalized to 1 s detection time.

Phillips, Mark C.↗
NASA NTRS1986

Feasibility experiments on time-resolved fluorosensing applied to oil slicks

The introduction of time resolved observations can provide a very penetrating tool in the practice of laser fluorosensing. The investigations have demonstrated a relevance of multispectral, time resolved analysis for oil fingerprinting. By comparative studies on a variety of crude oils and their most significant fractions, it was found that the process of time decay in a composite oil is characterized by a few steps, which are associated with specific components in the medium light range. The average decay times of these pure fractions are markedly differentiated as to absolute values and spectral spread; as a consequence, the corresponding parameters in the resultant crude are quite sensitive to the particular mixture of these components. Measurements of the time response give then a finer discrimination between oil classes, depending on the relative content of certain fractions. Experiments were pursued with an improved fluorosensor facility, in order to test the application of time resolved fluorosensing to remote samples on water.

Camagni, P.↗
NASA NTRS2013

Mid-Infrared Study of Samples from Multiple Stones from the Sutters Mill Meteorite

The Sutter's Mill meteorite fell in N. California on April 22, 2012 and numerous pieces have been recovered and studied. We present Fourier transform infrared (FTIR) spectra of fragments from several stones of the meteorite. Methods and analysis: Infrared spectra of the samples were recorded with a Nicolet iN10 MX FTIR microscope in the mid-IR range (4000-675/cm; spectral resolution 4/cm). All samples were deposited on a clean glass slide, crushed with a stainless steel roller tool, and placed directly on the focal plane of the microscope. IR spectra were collected by averaging 128 scans. Results: Preliminary IR spectra of the non-fusion crust samples show mineral compositions that are dominated by phyllosilicates, carbonates, or mixtures of both [2]. The carbonates display a dominant, broad band centered at 1433/cm, with additional bands at 2515/cm, 1797/cm, 882/cm, and 715/cm). Features associated with phyllosilicates include a symmetric Si-O stretching mode band centered at 1011/cm and several O-H stretching mode bands. The O-H shows up in two forms (1) a broadband centered at 3415/cm that is probably largely due to adsorbed H2O and (2) a much weaker, narrower feature centered near 3680/cm due to structural -OH. Features observed in the 2985-2855/cm range suggest the presence of aliphatic -CH3 and -CH2- groups. The relative intensities of the bands in this range are somewhat unusual. Typically, the asymmetric aliphatic CH stretching bands are stronger than the symmetric stretching bands, but in this case the reverse is true. This unusual pattern is well matched by the aliphatic features seen in the spectrum of a terrestrial calcite (CaCO3) standard. This observation, and the fact that the strength of the carbonate and aliphatic bands seem to correlate, suggest the organics are associated with the carbonates. Conclusions: IR spectra of samples from the Sutter's Mill meteorite show absorption features associated with carbonates, phyllosilicates, and organics. Both the unusual band profile of the aliphatic C-H stretching mode bands and their correlation with the strength of the carbonate bands suggests the organics and the carbonates are associated in some manner.

Sutter's mill↗
DOE OSTI2018

Fast Decomposition of Three-Component Spectra of Fluorescence Quenching by White and Grey Methods of Data Modeling

‘White’ and ‘grey’ methods of data modeling have been employed to resolve the heterogeneous fluorescence from a fluorophore mixture of 9-cyanoanthracene (CNA), 10-chloro-9-cyanoanthracene (ClCNA) and 9,10-dicyanoanthracene (DCNA) into component individual fluorescence spectra. The three-component spectra of fluorescence quenching in methanol were recorded for increasing amounts of lithium bromide used as a quencher. The associated intensity decay profiles of differentially quenched fluorescence of single components were modeled on the basis of a linear Stern-Volmer plot. These profiles are necessary to initiate the fitting procedure in both ‘white’ and ‘grey’ modeling of the original data matrices. ‘White’ methods of data modeling, called also ‘hard’ methods, are based on chemical/physical laws expressed in terms of some well-known or generally accepted mathematical equations. The parameters of these models are not known and they are estimated by least squares curve fitting. ‘Grey’ approaches to data modeling, also known as hard-soft modeling techniques, make use of both hard-model and soft-model parts. In practice, the difference between ‘white’ and ‘grey’ methods lies in the way in which the ‘crude’ fluorescence intensity decays of the mixture components are estimated. In the former case they are given in a functional form while in the latter as digitized curves which, in general, can only be obtained by using dedicated techniques of factor analysis. In the paper, the initial values of the Stern-Volmer constants of pure components were evaluated by both ‘point-by-point’ and ‘matrix’ versions of the method making use of the concept of wavelength dependent intensity fractions as well as by the rank annihilation factor analysis applied to the data matrices of the difference fluorescence spectra constructed in two ways: from the spectra recorded for a few excitation lines at the same concentration of a fluorescence quencher or classically from a series of the spectra measured for one selected excitation line but for increasing concentration of the quencher. The results of multiple curve resolution obtained by all types of the applied methods have been scrutinized and compared. In addition, the effect of inadequacy of sample preparation and increasing instrumental noise on the shape of the resolved spectral profiles has been studied on several datasets mimicking the measured data matrices. .

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2022

Simulated Lunar Surface Hydration Measurements using Multispectral Lidar at 3 µm

Accurately measuring the variability of spectroscopic signatures of hydration (H2O + OH) on the illuminated lunar surface at 3 µm as a function of latitude, lunar time of day, and composition is crucial to determining the generation and destruction mechanisms of OH species and understanding the global water cycle. A prime complication in analysis of the spectroscopic feature is the accurate removal of thermal emission, which can modify or even eliminate the hydration feature depending on the data processing methods used and assumptions made. An orbital multispectral lidar, with laser illumination at key diagnostic wavelengths, would provide uniform, zero-phase geometry, complete latitude and time of day coverage from a circular polar orbit, and is agnostic to the thermal state of the surface. We have performed measurement simulations of a four-wavelength multispectral lidar using spectral mixtures of hydrated mid-ocean ridge basalt (MORB) glasses and lunar regolith endmembers to assess the lidar performance in measuring hydration signatures on the lunar surface. Our results show a feasible system with wavelengths at 1.5 µm, 2.65 µm, 2.8 µm, and 3.1 µm can measure lunar hydration with a precision of 52 ppm (1σ) or better. These results, combined with the uniform measurement capabilities of multispectral lidar make it a valuable spectroscopic technique for elucidating mechanisms of OH/H2O generation, migration, and destruction.

D. R. Cremons↗
NASA NTRS1984

An analysis of the effect of biological and physical parameters of a wetlands grass biome on the spectral modeling of phytomass and primary productivity

Aircraft simulated thematic mapper data and field data were acquired in the fall and spring to analyze the relationship of spectral response and biomass for the marsh grass Spartina patens. Regression results indicate no simple relationship exists for TMS spectral response and biomass with a high R sq. However, results show a consistent relationship between spectral response and the percent live vegetation (by weight) and percent interstitial standing surface water (by area) as independent variables. It is suggested that the reflected energy of a pixel represents a mixture of surface constituents. It is recommended that alternative remote sensors be employed to account for the pixel constituents of live and dead vegetation, litter, and standing water.

Butera, M. K.↗
NASA NTRS2010

X-Ray Variation Statistics and Wind Clumping in Vela X-1

We investigate the structure of the wind in the neutron star X-ray binary system Vela X-1 by analyzing its flaring behavior. Vela X-1 shows constant flaring, with some flares reaching fluxes of more than 3.0 Crab between 20-60 keV for several 100 seconds, while the average flux is around 250 mCrab. We analyzed all archival INTEGRAL data, calculating the brightness distribution in the 20-60 keV band, which, as we show, closely follows a log-normal distribution. Orbital resolved analysis shows that the structure is strongly variable, explainable by shocks and a fluctuating accretion wake. Analysis of RXTE ASM data suggests a strong orbital change of N. Accreted clump masses derived from the INTEGRAL data are on the order of 5 x 10(exp 19)-10(exp 21) g. We show that the lightcurve can be described with a model of multiplicative random numbers. In the course of the simulation we calculate the power spectral density of the system in the 20-100 keV energy band and show that it follows a red-noise power law. We suggest that a mixture of a clumpy wind, shocks, and turbulence can explain the measured mass distribution. As the recently discovered class of supergiant fast X-ray transients (SFXT) seems to show the same parameters for the wind, the link between persistent HMXB like Vela X-1 and SFXT is further strengthened.

Furst, Felix↗
NASA NTRS1984

Ice-Soil Mixtures: Visual and Near-Infrared Remote Sensing Techniques

The spectral properties of ice soil mixtures are reviewed. Water ice has an absorption coefficient which varies by several orders of magnitude in the visual and near infrared, and has several prominent overtone absorptions. Different wavelengths can be used to probe to different depths in the surface as well as for different mineral impurity concentrations. Empirical and/or theoretical models might be used to derive characteristics grain size of the ice or of the impurity minerals and to derive abundance of the ice and rock or soil components. Quantitative analysis of remotely obtained reflectance spectra can only be performed by using absorption features in the spectra of ice and soil, and not by broadband response. It is suggested that this might be done by special selection of several narrow band filters in the near infrared which will adequately define the ice absorptions.

Clark, R. N.↗
NASA NTRS2016

Physical State and Distribution of Materials at the Surface of Pluto from New Horizons LEISA Imaging Spectrometer

From Earth based observations Pluto is known to be the host of N2, CH4 and CO ices and also a dark red material. Very limited spatial distribution information is available from rotational visible and near-infrared spectral curves obtained from hemispheric measurements. In July 2015 the New Horizons spacecraft reached Pluto and its satellite system and recorded a large set of data. The LEISA spectro-imager of the RALPH instruments are dedicated to the study of the composition and physical state of the materials composing the surface. In this paper we report a study of the distribution and physical state of the ices and non-ice materials on Pluto's illuminated surface and their mode and degree of mixing. Principal Component analysis as well as various specific spectral indicators and correlation plots are used on the first set of 2 high resolution spectro-images from the LEISA instrument covering the whole illuminated face of Pluto at the time of the New Horizons encounter. Qualitative distribution maps have been obtained for the 4 main condensed molecules, N2, CH4, CO, H2O as well as for the visible-dark red material. Based on specific spectral indicators, using either the strength or the position of absorption bands, these 4 molecules are found to indicate the presence of 3 different types of ices: N2-rich:CH4:CO ices, CH4-rich(:CO:N2?) ices and H2O ice. The mixing lines between these ices and with the dark red material are studied using scatter plots between the various spectral indicators. CH4 is mixed at the molecular level with N2, most probably also with CO, thus forming a ternary molecular mixture that follows its phase diagram with low solubility limits. The occurrence of a N2-rich - CH4-rich ices mixing line associated with a progressive decrease of the CO/CH4 ratio tells us that a fractionation sublimation sequence transforms one type of ice to the other forming either a N2-rich - CH4-rich binary mixture at the surface or an upper CH4-rich ice crust that may hide the N2-rich ice below. The strong CH4-rich - H2O mixing line witnesses the subsequent sublimation of the CH4-rich ice lag left behind by the N2:CO sublimation (N spring-summer), or a direct condensation of CH4 ice on the cold H2O ice (S autumn). The weak mixing line between CH4-containing ices and the dark red material and the very sharp spatial transitions between these ices and this non-volatile material are probably due to thermal incompatibility. Finally the occurrence of a H2O ice - red material mixing line advocates for a spatial mixing of the red material covering H2O ice, with possibly a small amount intimately mixed in water ice. From this analysis of the different materials distribution and their relative mixing lines, H2O ice appears to be the substratum on which other ices condense or non-volatile organic material is deposited from the atmosphere. N2-rich ices seem to evolve to CH4-dominated ices, possibly still containing traces of CO and N2, as N2 and CO sublimate away. The spatial distribution of these materials is very complex. The high spatial definition of all these composition maps, as well as those at even higher resolution that will be soon available, will allow us to compare them with Pluto's geologic features observed by LORRI panchromatic and MVIC multispectral imagers to better understand the geophysical processes in action at the surface of this astonishingly active frozen world.

Schmitt, B.↗