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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Design of the focal plane array assembly for the Mars Observer/Visual and Infrared Mapping Spectrometer (MO/VIMS)

A unique focal plane array (FPA) assembly combining both electronic and optical components in a single hermetically sealed hybrid package has been designed to meet the performance requirements imposed on the focal plane assembly in the Visual and Infrared Mapping Spectrometer (VIMS) for the Mars Observer (MO) mission. Inside the FPA package is a configuration of three multiplexed linear arrays containing 320 detector elements, a combination of Si and InSb, allowing continuous spectral coverage from 0.35 to 5.14 microns. An optical subassembly consisting of two spectral order-sorting filters with intrinsic field-of-view apertures requiring critical optical alignment is also internal to the hybrid. Several engineering issues arose during the MO/VIMS FPA development phase which had challenging design ramifications. FPA performance requirements, design approach, and critical issues are discussed.

Niblack, Curtiss A.↗
NASA NTRS1990

A composition comparison between comets P/Halley and P/Brorsen-Metcalf

The appearance of comet Brorsen-Metcalf in 1989 following only a few years on the heels of comet Halley in 1986 gave an unusual opportunity to compare two comets of similar orbital elements but potentially different physical and chemical characteristics. Photometric spectral data were acquired for Brorsen-Metcalf on two dates: 13 July 1989 and 2 August 1989. The observations were performed with the 154 cm Catalina Telescope of the University of Arizona Observatories. The spectrum for 13 July 1989 is compared to a Halley spectrum. The general appearance of the spectra is very similar, both comets showing emission due to C2, NH2, OI(D-1), and CN. Neither displays any emission features that are exclusive to only one of the two. Since water is now reasonably well established as the major driving force in the activity of a comet, the H2O production rate for comet Brorsen-Metcalf was calculated. The relative ratios between the production rates of the various species obtained from the data are presented. Results are summarized in tabular form. All species are compared to the H2O production rate of the two comets. The results indicate that C2 originates from an extended source of dust particles or small polymers in addition to parent molecules. The lower production rates of C2 and CN in Brorsen-Metcalf correlate well with both the lower dust production and their smaller increase as the comet approaches the sun. Even without a mode, the spectroscopic observations of Brorsen-Metcalf allowed significant compositional conclusions to be drawn. The NH2 abundance is lower by about a factor of three which appears to be independent of heliocentric distance. Both C2 and CN are less abundant in Brorsen-Metcalf than in Halley and do not seem to participate as much in the strong increase as the comet approaches the sun. The lower H2O production rate implies that the active surface area of the comet Brorsen-Metcalf is much smaller, or equivalently the comet as a whole is much smaller. The substantially lower continuum level for Brorsen-Metcalf cannot readily be explained by smaller or larger active surface area, and must be intrinsic to the comet's embedded dust-to-ice ratio, or to an overall smaller-sized dust grain population.

Disanti, Michael A.↗
NASA NTRS1991

X-ray optics. II - A technique for high resolution spectroscopy

A novel combination of optical elements and properties is combined to achieve high-spectral resolution using grazing incidence optics of modest quality. Analysis and ray tracing of examples show that using radial groove gratings at high blaze angles in the manner of an echelle spectrograph can provide high spectral resolution. This arrangement is compared to the conventional in-plane designs to show that the off-plane is superior in nearly every respect. Cross dispersion can be provided by the energy resolution of a CCD detector. Additional resolution can be squeezed from the system by strategic placement of gratings to take advantage of the azimuthal response of a Wolter X-ray optic.

Cash, Webster C., Jr.↗
NASA NTRSDate not supplied

Heavy-metal Abundances in DO-type White Dwarfs

Spectral lines of a variety of trans-iron elements were identified in high-resolution ultraviolet spectra of DO-type white dwarfs. Abundance determinations by means of non-local thermodynamic equilibrium stellar-atmosphere techniques have shown that, without exception, their abundances are unexpectedly strong supersolar, much higher than predicted by asymptotic-giant-branch nucleosynthesis calculations. We present our analyses and discuss the photospheric trans-iron element prominence.

Thomas Rauch↗
DOE OSTI2023

Development of a Low-Cost, Sensitivity-Optimized Fluorescence Sensor for Visible Spectrum Analysis

This paper presents an economically viable, sensitivity-optimized fluorescence sensor for detecting low concentrations of fluorophores in the visible spectrum range. The sensor employs a deep ultraviolet (DUV) 275-nm LED and a dichroic mirror to establish a co-axial optical path for excitation and emission. Instead of utilizing a general-purposed spectrometer optimized for high spectral resolution, the sensor strikes a balance between resolution and sensitivity by using an appropriate aperture size and optimized optical design tailored for the spectral characteristics of fluorophores. Here, the manuscript demonstrates measurements of ppb-level rare earth element (REE) samples containing terbium (Tb), europium (Eu), dysprosium (Dy), and samarium (Sm) in aqueous solutions. Through balanced design that optimizes collection of fluorescence emission without losing spectral information, this work shows the feasibility of developing a low-cost, compact, and highly sensitive fluorescence sensors with improved detection sensitivity when compared to bench-top commercial spectrofluorometers at far higher costs.

47 OTHER INSTRUMENTATION↗
NASA NTRS2017

Relaxation Matrix for Symmetric Tops with Inversion Symmetry: Line Coupling and Line Mixing Effects on NH3 Lines in the V4 Band

Line shape parameters including the half-widths and the off-diagonal elements of the relaxation matrix have been calculated for self-broadened NH3 lines in the perpendicular v4 band. As in the pure rotational and the parallel v1 bands, the small inversion splitting in this band causes a complete failure of the isolated line approximation. As a result, one has to use formalisms not relying on this approximation. However, due to differences between parallel and perpendicular bands of NH3, the applicability of the formalism used in our previous studies of the v1 band and other parallel bands must be carefully verified. We have found that, as long as potential models only contain components with K1 equals K2 equals 0, whose matrix elements require the selection rule delta k equals 0, the formalism is applicable for the v4 band with some minor adjustments. Based on both theoretical considerations and results from numerical calculations, the non-diagonality of the relaxation matrices in all the PP, RP, PQ, RQ, PR, and RR branches is discussed. Theoretically calculated self-broadened half-widths are compared with measurements and the values listed in HITRAN 2012. With respect to line coupling effects, we have compared our calculated intra-doublet off-diagonal elements of the relaxation matrix with reliable measurements carried out in the PP branch where the spectral environment is favorable. The agreement is rather good since our results do well reproduce the observed k and j dependences of these elements, thus validating our formalism.

Absorption coefficient↗
NASA NTRS1984

Spectral methods for exterior elliptic problems

Spectral approximations for exterior elliptic problems in two dimensions are discussed. As in the conventional finite difference or finite element methods, the accuracy of the numerical solutions is limited by the order of the numerical farfield conditions. A spectral boundary treatment is introduced at infinity which is compatible with the infinite order interior spectral scheme. Computational results are presented to demonstrate the spectral accuracy attainable. Although a simple Laplace problem is examined, the analysis covers more complex and general cases.

Canuto, C.↗
NASA NTRS2009

Electro-optic imaging Fourier transform spectrometer

An Electro-Optic Imaging Fourier Transform Spectrometer (EOIFTS) for Hyperspectral Imaging is described. The EOIFTS includes an input polarizer, an output polarizer, and a plurality of birefringent phase elements. The relative orientations of the polarizers and birefringent phase elements can be changed mechanically or via a controller, using ferroelectric liquid crystals, to substantially measure the spectral Fourier components of light propagating through the EIOFTS. When achromatic switches are used as an integral part of the birefringent phase elements, the EIOFTS becomes suitable for broadband applications, with over 1 micron infrared bandwidth.

Chao, Tien-Hsin↗
NASA NTRS2004

CHANDRA Detection of the AM CVn Binary ES Cet (KUV 01584-0939)

We report on Chandra ACE observations of the ultracompact AM CVn binary ES Cet. This object has a 10.3 minute binary period and is the most compact of the confirmed AM CVn systems. We have, for the first time, unambiguously detected the X-ray counterpart to ES Cet. In a 20 ksec ACIS-S image a point-like X-ray source is found within 1 sec. of the catalogued optical position. The mean countrate in ACIS-S is 0.013/s, and there is no strong evidence for variability. We folded the X-ray data using the optical ephemeris of Warner & Woudt, but did not detect any significant modulation. If an approx. = 100% modulation similar to those seen in the ultracompact candidates V407 Vu1 and Rx J0806.3+1527 were present then we would have detected it. The upper limit (3(sigma)) to any modulation at the putative orbital period is approx. 40% (rms). We extract the first X-ray spectrum from ES Cet, and find that it is not well described by simple continuum models. We find suggestive evidence for discrete spectral components at approx. 470 and 890 eV, that can be modelled as gaussian emission lines. In comparison with recent X-ray detections of nitrogen and neon in another AM CVn system (GP Com), it appears possible that these features may represent emission lines from these same elements; however, deeper spectroscopy will be required to confirm this. Our best spectral model includes a black body continuum with kT = 0.8 keV along with the gaussian lines. The 0.2 - 5 keV X-ray flux was approx. 7 x 10(exp -14) ergs/sq cm s. The luminosity implied by this flux for any reasonable distance is much smaller than that expected for a mass accretion rate as high as m = 10(exp -8) solar mass/yr, suggesting that the bulk of the accretion luminosity is below 100 eV and not seen with Chandra. We discuss the implications of our results for the nature of ES Cet.

Strohmayer, Tod E.↗
NASA NTRS1973

Effect of contamination on the optical properties of transmitting and reflecting materials exposed to a MMH/N2O4 rocket exhaust

The changes are presented in spectral transmittance, and reflectance due to exposure of various optical materials to the exhaust plume of a 5-pound thrust bipropellant rocket. The engine was fired in a pulsed mode for a total exposure of 223.7 second. Spectral optical properties were measured in air before and after exposure to the exhaust plume in vacuum. The contaminating layer resulted in both absorption and scattering effects which caused changes as large as 30-50% for transmitting elements and 15% for mirrors in the near ultraviolet wavelengths. The changes in spectral properties of materials exposed to the exhaust plume for 44 and 223.7 seconds are compared and found to be similar.

Bowman, R. L.↗
NASA NTRS1990

Model atmosphere analysis of the DZ white dwarf K789 - 37

This paper presents new observations and an analysis using model atmosphere techniques of the recently discovered DZA white dwarf K789 - 37. The effective temperature derived is 9500 + or - 500 K. Abundances are determined for the elements hydrogen, magnesium, calcium, and iron, as well as upper limits for carbon and silicon. The abundances are very low compared to solar values and within the range typical for this spectral class. The implications of the results for the currently accepted explanation of trace elements in cool white dwarfs in terms of the diffusion/accretion scenario are discussed. It is concluded that the accreted matter cannot have had solar composition.

Koester, D.↗
NASA NTRS2007

Optical Design of a Compact Imaging Spectrometer for Planetary Mineralogy

We present the design of a compact, wide-angle pushbroom imaging spectrometer suitable for exploration of solar system bodies from low orbit. The spectrometer is based on a single detector array with a broadband response that covers the range 400 to 3000 nm and provides a spectral sampling of 10 nm. The telescope has a 24-deg field of view with 600 spatially resolved elements (detector pixels). A specially designed convex diffraction grating permits optimization of the signal-to-noise ratio through the entire spectral band. Tolerances and design parameters permit the achievement of high uniformity of response through field and wavelength. The spectrometer performance is evaluated in terms of predicted spectral and spatial response functions and from the point of view of minimizing their variation through field and wavelength. The design serves as an example for illustrating the design principles specific to this type of system.

space optics↗
NASA NTRS1997

High precision computing with charge domain devices and a pseudo-spectral method therefor

The present invention enhances the bit resolution of a CCD/CID MVM processor by storing each bit of each matrix element as a separate CCD charge packet. The bits of each input vector are separately multiplied by each bit of each matrix element in massive parallelism and the resulting products are combined appropriately to synthesize the correct product. In another aspect of the invention, such arrays are employed in a pseudo-spectral method of the invention, in which partial differential equations are solved by expressing each derivative analytically as matrices, and the state function is updated at each computation cycle by multiplying it by the matrices. The matrices are treated as synaptic arrays of a neural network and the state function vector elements are treated as neurons. In a further aspect of the invention, moving target detection is performed by driving the soliton equation with a vector of detector outputs. The neural architecture consists of two synaptic arrays corresponding to the two differential terms of the soliton-equation and an adder connected to the output thereof and to the output of the detector array to drive the soliton equation.

Barhen, Jacob↗
NASA NTRS2002

Combining S-space and image spatial information for characterization of land-cover elements using AVIRIS data

Imaging spectroscopy data provides information that is both spatially and spectrally rich. However,hyperspectral classification and identification procedures are generally based solely on the spectral data. The S-space concept treats the spectrum as a 'spatial' dimension thereby facilitating the exploration of a relationship between the spectral and spatial image domains. This paper presents the ideas that will be researched as well as some preliminary results.

AVIRIS image spectroscopy↗
NASA NTRS1990

Fiber-coupled high resolution infrared array spectrometer for the Kuiper Airborne Observatory

A novel cryogenic grating spectrometer (FCAS) is being designed for observations of volatiles in cometary and planetary atmospheres, and in newly forming planetary systems. The instrument features two-dimensional detector arrays coupled to a high-dispersion echelle by infrared fibers, and will achieve a spectral resolving power of about 40,000. The primary observational platform for this instrument will be the Kuiper Airborne Observatory, but it will also be configured for use at ground-based observatories. Initially, the spectrometer will use a 58 x 62, 1- to 5-micron InSb array. Larger-format IR arrays and arrays of different composition, will later be incorporated as they become available. The instrument will be used in two modes. The first uses a large format IR array in the spectral image plane for the customary one-dimensional spectral-one-dimensional spatial coverage. In the second mode, a massive, coherent bundle of infrared transmitting ZrF4 fibers will be installed after the dispersive element, to reformat the two-dimensional array into an elongated one-dimensional array for wide spectral coverage, allowing multiple lines to be measured in a single integration with high sensitivity. The overall instrument design is discussed, and the system sensitivity is estimated.

Glenar, D. A.↗
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 OSTI2020

A partial-volume correction for quantitative spectral x-ray radiography

The technique of spectral radiography has been shown to accurately discriminate a materials elemental composition by using known x-ray physics. This is achieved with a state-of-the-art pixelated spectrometer and a high-fidelity physical model. Similar to other radiographs, the system suffers from partial volume attenuation where the sample projection onto a pixel is only a fraction of the pixel area, leaving the rest unattenuated. This study updates the physical model to account for fractional area which presents new challenges to the existing algorithm. We present how this update is made and explore approaches to stabilize the algorithm through parameter scaling, constrained optimization, and hyperparameter selection.

Gillis, Wesley C.↗
DOE OSTI2022

The MASSIVE Survey. XVI. The Stellar Initial Mass Function in the Center of MASSIVE Early-type Galaxies

The stellar initial mass function (IMF) is a fundamental property in the measurement of stellar masses and galaxy star formation histories. In this work, we focus on the most massive galaxies in the nearby universe $\mathrm{log}({M}_{\star }/\,{M}_{\odot })\gt 11.2$. We obtain high-quality Magellan/LDSS-3 long-slit spectroscopy with a wide wavelength coverage of 0.4–1.01 μm for 41 early-type galaxies (ETGs) in the MASSIVE survey and derive high signal-to-noise spectra within an aperture of R e /8. Using detailed stellar synthesis models, we constrain the elemental abundances and stellar IMF of each galaxy through full spectral modeling. All the ETGs in our sample have an IMF that is steeper than a Milky Way (Kroupa) IMF. The best-fit IMF mismatch parameter, α IMF = (M/L)/(M/L) MW , ranges from 1.1 to 3.1, with an average of $\langle$α IMF $\rangle$ = 1.84, suggesting that on average, the IMF is more bottom heavy than Salpeter. Comparing the estimated stellar masses with the dynamical masses, we find that most galaxies have stellar masses that are smaller than their dynamical masses within the 1σ uncertainty. We complement our sample with lower-mass galaxies from the literature and confirm that $\mathrm{log}({\alpha }_{\mathrm{IMF}})$ is positively correlated with $\mathrm{log}(\sigma )$, $\mathrm{log}({M}_{\star })$, and $\mathrm{log}({M}_{\mathrm{dyn}})$. From the combined sample, we show that the IMF in the centers of more massive ETGs is more bottom heavy. In addition, we find that $\mathrm{log}({\alpha }_{\mathrm{IMF}})$ is positively correlated with both [Mg/Fe] and the estimated total metallicity [Z/H]. We find suggestive evidence that the effective stellar surface density Σ Kroupa might be responsible for the variation of α IMF . We conclude that σ, [Mg/Fe], and [Z/H] are the primary drivers of the global stellar IMF variation.

79 ASTRONOMY AND ASTROPHYSICS↗