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At least 955 records · Page 53

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DOE OSTI2025

Time-resolved chemically-selective spectroscopic investigation of the redox reaction between hematite and aluminium

Thermite reactions –highly energetic redox processes between a metal and an oxide—are used in welding, propulsion, and the fabrication of advanced materials. When reduced to the nanoscale, these reactions exhibit enhanced energetic performance, but their ultrafast dynamics remain poorly understood. Gaining insight into charge transfer during these processes is essential for advancing applications in energy conversion and materials design. Here we show that the reaction between aluminium and hematite, a common iron oxide, can be tracked with femtosecond resolution using extreme ultraviolet (EUV) time-resolved absorption spectroscopy at the Fe M 2,3 and Al L 2,3 edges. By exciting the system with an ultrashort optical pulse and probing element-specific absorption changes, we observe an early spectral shift that reveals the formation of localized charge carriers (polarons). Comparing samples with different supporting substrates highlights ultrafast electron transfer from aluminium to hematite. These results demonstrate an approach to investigating charge flow in energetic materials and provide a basis for studying fast chemical reactions with chemical specificity.

Electron transfer↗

NASA NTRS1975

Demonstration of optical navigation measurements on Mariner 10

An experiment was performed on the Mariner 10 Venus/Mercury mission to assess the performance of the onboard television cameras and ground-based software used in the optical navigation measurement system. The elements of the system, calibration, and distortion are considered. The navigation technique requires detection of stars in the same field of view as the target body. The star detection capability is discussed with reference to required threshold, calibration factors, standard conditions, camera sensitivity, response uniformity, and the effect of image smearing. Tests conducted during the Mariner 10 encounters with Mercury demonstrated that a large bright planet can be imaged simultaneously with faint stars to provide accurate navigation data. Improvements are suggested in the system for the Mariner Jupiter/Saturn 1977 and later missions.

Stanton, R. H.↗

NASA NTRS1977

Electrically-controlled variable-color optical filters

Optical transmission characteristics of birefringent element are changed by applying voltage to plate. Filters are used on sequential-color television cameras and in color displays. Filters are more convenient and less costly than mechanical color wheels and crystal-based filters.

Miller, A.↗

NASA NTRS1982

The ionization structure of planetary nebulae. 3: NGC 7009

Spectrophotometric observations of emission line intensities were made in 8 positions in the planetary nebula NGC 7009. For the 6 brightest positions, the coverage is from 1400 A to 10,000 A. Standard equations used to correct for the existence of elements in other than the optical observable ionization stages give results over a wide range of ionization that are consistent and agree with abundances calculated using ultraviolet lines. This result is particularly gratifying for N because previously the standard formula gave inconsistent abundances in NGC 7009. The major outstanding problem is that the lambda 4267 CII line implies a C(2+) abundance as much as 12 times greater than that determined from the UV lines. This discrepancy is greatest nearest the central star, as is the case in the planetary nebula NGC 6720. The logarithmic abundances (relative to H=12.00) are: He=11.07, 0=8.68, N=8.10, Ne=8.16, C=8.18, Ar=6.36, and S=7.12. The average of the Ne, Ar, and S abundances agrees to within 5% of that for NGC 6720, but the O, N, nd C abundances average 1.9 times lower in NGC 7009, suggesting that here may have been mixing of processed material in the planetary precursor in NGC 6720.

Barker, T.↗

NASA NTRS1985

The ionization structure of planetary nebulae. Part 4: NGC 7662

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in five positions in the planetary nebula NGC 7662. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages show a consistent and approximate agreement with abundances calculated using ultraviolet lines. The abundances of C and N indicate that some mixing of CNO-processed material into the nebular shell may have occurred in NGC 7662; the low He abundance, however, indicates that little or no He enrichment occurred. The Ar, Ne, and O and S abundances appear to be low. It is suggested that the progenitor to NGC 7662 may have formed out of somewhat metal-poor material.

Barker, T.↗

NASA NTRS1985

Separability of boreal forest species in the Lake Jennette area, Minnesota

In order to exploit the use of thematic mapper (TM) data to obtain vegetation and net primary productivity maps in the boreal forest, three aircraft flights were undertaken over the area near Ely, MN, with the NS 001 Thematic Mapper Simulator. Attention is presently given to an analysis of these 1983 data, which attempted to separate coniferous trees from deciduous ones. Canopy reflectance models and measured optical properties of the scattering elements have been used to deepen understanding of this separability, and to relate the ratio of nadir view reflectances in TM bands 4 and 3 to the overstory leaf area index. A map that is proportional to the leaf area index for deciduous species is presented.

Shen, S. S.↗

NASA NTRS1985

Dynamic fracture mechanics

Dynamic fracture and crack propagation concepts for ductile materials are reviewed. The equations for calculating dynamic stress integrity and the dynamic energy release rate in order to study dynamic crack propagation are provided. The stress intensity factor versus crack velocity relation is investigated. The uses of optical experimental techniques and finite element methods for fracture analyses are described. The fracture criteria for a rapidly propagating crack under mixed mode conditions are discussed; crack extension and fracture criteria under combined tension and shear loading are based on maximum circumferential stress or energy criteria such as strain energy density. The development and use of a Dugdale model and finite element models to represent crack and fracture dynamics are examined.

Kobayashi, A. S.↗

NASA NTRS1988

The ionization structure of planetary nebulae. 9: NGC 1535

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in five positions in the planetary nebula NGC 1535. There is some evidence for variation in the Balmer decrements between these positions. The O(++) electron temperature varies little from 11500 K across these positions; the Balmer continuum electron temperature averages a few hundred K higher than this, but this difference is insignificant when compared to the measurement errors. As found for most of the other planetaries in this series, the wavelength 4267 C II line intensity near the central star implies a C(++) abundance that is several times higher that that determined from the wavelength 1906, 1909 C III lines. The discrepancy again decreases with increasing distance from the central star, again suggesting that the excitation mechanism for the wavelength 4267 C II is not understood. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions; there is no evidence for any abundance gradient in the nebula. The logarithmic abundances are He = 10.99, O = 8.51, N = 7.63, Ne = 7.89, C = 8.34, and Ar = 6.08. The abundances agree well with determinations by Aller and Czyzak and by Torres-Peimbert and Peimbert and are nearly identical to those found for NGC 6826. As for NGC 6826, the rather low abundances of He, N, and C suggest that there was little if any mixing of CNO-processed material into the nebular shell in the progenitor to NGC 1535. The O, Ne, Ar abundances appear to be somewhat low, suggesting that the progenitor to NGC 1535 may have formed out of somewhat metal-poor material.

Barker, Timothy↗

NASA NTRS1989

The ionization structure of planetary nebulae 10: NGC 2392

Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in six positions in the planetary nebula NGC 2392. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions that are in excellent agreement with abundances calculated using ultraviolet lines, and there is no evidence for any abundance gradient in the nebula. The logarithmic abundances agree well with determinations by Aller and Keyes.

Barker, Timothy↗

NASA NTRS1991

The ionization structure of planetary nebulae. X - NGC 2392

Barker, Timothy↗

NASA NTRS1991

Mixed application MMIC technologies - Progress in combining RF, digital and photonic circuits

Approaches for future 'mixed application' monolithic integrated circuits (ICs) employing optical receive/transmit, RF amplification and modulation and digital control functions are discussed. We focus on compatibility of the photonic component fabrication with conventional RF and digital IC technologies. Recent progress at Honeywell in integrating several parts of the desired RF/digital/photonic circuit integration suite required for construction of a future millimeter-wave optically-controlled phased-array element are illustrated.

Swirhun, S.↗

NASA NTRS1993

Correlated petrographic, electron microprobe, and ion microprobe studies of selected primitive and processed phase assemblages in meteorites

During the past three years we have received support to continue our research in elucidating the formation and alteration histories of selected meteoritic materials by a combination of petrographic, trace element, and isotopic analyses employing optical and scanning electron microscopes and electron and ion microprobes. The awarded research funds enabled the P.I. to attend the annual LPSC, the co-I to devote approximately 15 percent of his time to the research proposed in the grant, and partial support for a visiting summer post-doctoral fellow to conduct electron microprobe analyses of meteoritic samples in our laboratory. The research funds, along with support from the NASA Education Initiative awarded to P.I. G. Wasserburg, enabled the co-I to continue a mentoring program with inner-city minority youth. The support enabled us to achieve significant results in the five projects that we proposed (in addition to the Education Initiative), namely: studies of the accretional and post-accretional alteration and thermal histories in CV meteorites, characterization of periclase-bearing Fremdlinge in CV meteorites, characterization of Ni-Pt-Ge-Te-rich Fremdlinge in CV meteorites in an attempt to determine the constraints they place on the petrogenetic and thermal histories of their host CAI's, correlated electron and ion microprobe studies of silicate and phosphate inclusions in the Colomera meteorite in an attempt to determine the petrogenesis of the IE iron meteorites, and development of improved instrumental and correction procedures for improved accuracy of analysis of meteoritic materials with the electron microprobe. This grant supported, in part or whole, 18 publications so far by our research team, with at least three more papers anticipated. The list of these publications is included. The details of the research results are briefly summarized.

Albee, Arden L.↗

NASA NTRS1994

A proposition for the classification of carbonaceous chondritic micrometeorites

Classification of interplanetary dust particles (IDP's) should be unambiguous and, if possible, provide an opportunity to interrelate these ultrafine IDP's with the matrices of undifferentiated meteorites. I prefer a scheme of chemical groupings and petrologic classes that is based on primary IDP properties that can be determined without prejudice by individual investigators. For IDP's of 2-50 microns these properties are bulk elemental chemistry, morphology, shape, and optical properties. The two major chemical groups are readily determined by energy dispersive spectroscopic analysis using the scanning or analytical electron microscope. Refinement of chondritic IDP classification is possible using the dominant mineral species, e.g. olivine, pyroxene, and layer silicates, and is readily inferred from FTIR, and automated chemical analysis. Petrographic analysis of phyllosilicate-rich IDP's will identify smectite-rich and serpentine-rich particles. Chondritic IDP's are also classified according to morphology, viz., CP and CF IDP's are aggregate particles that differ significantly in porosity, while the dense CS IDP's have a smooth surface. The CP IDP's are characterized by an anhydrous silicate mineralogy, but small amounts of layer silicates may be present. Distinction between the CP and CF IDP's is somewhat ambiguous, but the unique CP IDP's are fluffy, or porous, ultrafine-grained aggregates. The CP IDP's, which may contain silicate whiskers, are the most carbon-rich extraterrestrial material presently known. The CF IDP's are much less porous that CP IDP's. Using particle type definitions, CP IDP's in the NASA JSC Cosmic Dust Catalogs are approx. 15 percent of all IDP's that include nonchondritic spheres. Most aggregate particles are of the CF type.

Rietmeijer, Frans J. M.↗

NASA NTRS1998

Electroformed Nickel Mirrors for the Next Generation Space Telescope

This paper summarizes the work to date on a novel mirror fabrication technique being developed at the Marshall Space Flight Center for potential use on the Next Generation Space Telescope (NGST). This technique involves forming an extremely lightweight mirror by electroplating nickel and nickel based alloys onto a highly polished precision mandrel. The resulting mirror shell can then be backed up with or attached to a lightweight structure to produce a mirror element that is on the order of 15 kg/sq m areal density. Since the mirrors are fabricated from a mandrel (or master), subsequent mirrors can be made with very high economy; this technique is particularly suited to segmented mirrors schemes whereby large apertures are achieved through the deployment of smaller segments. Control of the electroplating process is the key element for producing high quality optics; bath chemistry and real time control of the plating current density yields uniform grained electroforms with zero residual stress. To accomplish this, a special electronic sensor was developed whereby the residual stress can be monitored as the nickel is electrolytically deposited. This information is used in a feedback loop to modulate current density which, in turn, directly governs the residual stress. Details pertaining to this and other aspects of the fabrication of a half meter mirror will be published along with test results and metrology data.

Redmon, John W.↗

NASA NTRS2004

Gain-Assisted Superluminal Propagation in Coupled Optical Resonators

We predict superluminal pulse propagation in co-resonant coupled optical resonators, when a gain element is placed in the resonator closest to the excitation waveguide, provided the resonator farthest from the excitation waveguide is under-coupled.

Chang, Hong-Rok↗

NASA NTRS2004

A New On-Line Diagnosis Protocol for the SPIDER Family of Byzantine Fault Tolerant Architectures

This paper presents the formal verification of a new protocol for online distributed diagnosis for the SPIDER family of architectures. An instance of the Scalable Processor-Independent Design for Electromagnetic Resilience (SPIDER) architecture consists of a collection of processing elements communicating over a Reliable Optical Bus (ROBUS). The ROBUS is a specialized fault-tolerant device that guarantees Interactive Consistency, Distributed Diagnosis (Group Membership), and Synchronization in the presence of a bounded number of physical faults. Formal verification of the original SPIDER diagnosis protocol provided a detailed understanding that led to the discovery of a significantly more efficient protocol. The original protocol was adapted from the formally verified protocol used in the MAFT architecture. It required O(N) message exchanges per defendant to correctly diagnose failures in a system with N nodes. The new protocol achieves the same diagnostic fidelity, but only requires O(1) exchanges per defendant. This paper presents this new diagnosis protocol and a formal proof of its correctness using PVS.

Geser, Alfons↗

NASA NTRS2005

Gain-assisted Superluminal Propagation in Coupled Optical Resonators

We predict transparent superluminal pulse propagation in co-resonant coupled optical resonators, when a gain element is placed in the resonator closest to the excitation waveguide, provided the structure is over-coupled, but the resonator farthest from the excitation waveguide is under-coupled sufficiently to avoid lasing at the split modes. The effective steady-state absorptive and dispersive response of coupled resonators is derived, and the coupled-mode approximation is used to determine the conditions for transparent superluminal pulse propagation in these systems.

Chang, Hongrok↗

NASA NTRS2007

Dispersive Elements for Enhanced Laser Gyroscopy and Cavity Stabilization

We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the modulation to determine the conditions for cavity self-stabilization and enhanced gyroscopic sensitivity. We find an enhancement in the sensitivity of a laser gyroscope to rotation for normal dispersion, while anomalous dispersion can be used to self-stabilize an optical cavity. Our results indicate that atomic media, even coherent superpositions in multilevel atoms, are of limited use for these applications, because the amplitude and phase filters work against one another, i.e., decreasing the modulation frequency increases its amplitude and vice-versa. On the other hand, for optical resonators the dispersion reversal associated with critical coupling enables the amplitude and phase filters to work together. We find that for over-coupled resonators, the absorption and normal dispersion on-resonance increase the contrast and frequency of the beat-note, respectively, resulting in a substantial enhancement of the gyroscopic response. Under-coupled resonators can be used to stabilize the frequency of a laser cavity, but result in a concomitant increase in amplitude fluctuations. As a more ideal solution we propose the use of a variety of coupled-resonator-induced transparency that is accompanied by anomalous dispersion.

Smith, David D.↗