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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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A novel optical architecture (based on holographic optical elements) for making high speed tomographic measurements is presented. The system is designed for making density or species concentration measurements in a nonsteady fluid or combustion flow. Performance evaluations of the optical system are discussed, and a test phase object was successfully reconstructed using this optical arrangement.
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Problems on the identification of two-dimensional spatial domains arising in the detection and characterization of structural flaws in materials are considered. For a thermal diffusion system with external boundary input, observations of the temperature on the surface are used in a output least squares approach. Parameter estimation techniques based on the method of mappings are discussed and approximation schemes are developed based on a finite element Galerkin approach. Theoretical convergence results for computational techniques are given and the results are applied to experimental data for the identification of flaws in the thermal testing of materials.
Results are reported from an investigation of the resolving power of ISC/NEIC P travel-time data in tomographic inversions for the geometry of the subduction zones in the NW Pacific. From thermal models for the Kurile, Janan, Izu-Bonin, Mariana, and Ryukyu slabs, three-dimensional synthetic velocity anomalies for subducting slabs are generated and projected onto a cell model for the uppermost 1400 km of the mantle. These synthetic models are used to compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data, add Gaussian noise, invert the synthetic data, and compare the resulting velocity structure to the initial synthetic models. This comparison is illustrated for sections through the Kuriles and the Mariana arcs. A variety of resolution artifacts are observed, which in many cases resemble features visible in the tomographic results obtained from inverting the actual ISC/NEIC data.
The long-wavelength thermal anomalies in the lower mantle have been mapped out using several seismic tomographic models in conjunction with thermodynamic parameters derived from high-pressure mineral physics experiments. These parameters are the depth variations of thermal expansivity and of the proportionality factor between changes in density and seismic velocity. The giant plume-like structures in the lower mantle under the Pacific Ocean and Africa have outer fringes with thermal anomalies around 300-400 K, but very high temperatures are found in the center of the plumes near the base of the core-mantle boundary. These extreme values can exceed +1500 K and may reflect large hot thermal anomalies in the lower mantle, which are supported by recent measurements of high melting temperatures of perovskite and iron. Extremely cold anomalies, around -1500 K, are found for anomalies in the deep mantle around the Pacific rim and under South America. Numerical simulations show that large negative thermal anomalies in the mid-lower mantle have modest magnitudes of around -500 K. correlation pattern exists between the present-day locations of cold masses in the lower mantle and the sites of past subduction since the Cretaceous. Results from correlation analysis show that the slab mass-flux in the lower mantle did not conform to a steady-state nature but exhibited time-dependent behavior.
Progress in development of the methods required to study bone remodeling as a function of time is reported. The following topics are presented: 'A New Methodology for Registration Accuracy Evaluation', 'Registration of Serial Skeletal Images for Accurately Measuring Changes in Bone Density', and 'Precise and Accurate Gold Standard for Multimodality and Serial Registration Method Evaluations.'
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As the world-wide civil aviation fleet continues to age, methods for accurately predicting the presence of structural flaws-such as hidden corrosion-that compromise airworthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical-waveguide physics. Our work focuses on using a variety of different tomographic reconstruction techniques to graphically represent the Lamb wave data in images that can be easily interpreted by technicians. Because the velocity of Lamb waves depends on thickness, we can convert the travel times of the fundamental Lamb modes into a thickness map of the inspection region. In this paper we show results for the identification of single or multiple back-surface corrosion areas in typical aluminum aircraft skin structures.
We discovered correlated rapid variability between the optical/UV and X-ray emission for the first time in a soft X-ray transient, GRO J1655-40. Hubble Space Telescope light curves show features similar to those seen by the Rossi X-ray Timing Explorer, but with a mean delay of up to 10 - 20 s. We interpret the correlation as the result of reprocessing of X-rays into optical and UV emission, with a delay owing to finite light travel time; this assumption enables us to perform echo mapping of the system. The time-delay distribution has a mean of 14.6 +/-1.4 s and a dispersion of 10.5+/-1.9 s at binary phase 0.4. This establishes that the reprocessing region is the accretion disk around the compact star, rather than the mass-donating secondary. These results have been published.
A paper based on the RXTE results contents the following and are ready for submission to ApJ: "Possible Detection of Companion Star Reflection from Hercules X-1 with RXTE". A paper combining July 1998 and July 1999 observations (including the RXTE results for both years) is nearly ready for submission to ApJ: The July 1998 and July 1999 Multiwavelength Campaigns on Hercules X-I/HZ Herculis. The July 1999 observations took place during an anomalous X-ray low state and the RXTE and EUVE data are consistent with X_ray reflected from the surface of the companion star.
Under this project, a variety of accretion problems have been studied, with two in particular. In the first, astrophysical jets are observed in many objects ranging from young stars to Active Galactic Nuclei. A major unsolved problem is how do these jets originate from accretion disks. In a series of works, I have examined the launching of outflows from magnetized disks, the extraction of energy from black holes, and the formation of jets in systems like Cataclysmic Variables and supermassive accreting black holes. The results of these works were published in a number of papers. In the second, I examined the potential role of vortices in accretion disks around Young Stellar Objects, for the formation of planets and for angular momentum transport. I showed that vortices are surprisingly stable, and that they are able to concentrate dust in their cores. I also examined the development of spiral shocks in disks. Finally, I studied the evolution of magnetically layered protoplanetary disks, and showed that they exhibit outbursts which could 'pump' the jets that are observed in Herbig-Haro objects. The results of these works were published in a number of papers as well. Additional information on the published papers is contained in the original abstract.
Understanding the light-harvesting properties of algae and higher plants are a fundamental topic in photosynthesis research. Using thick sections obtained from fixed and embedded cultures of colonial P antarctica, we calculate tomographic reconstructions of individual chloroplasts under light-limiting and saturating conditions for net photosynthesis. Our goal is to gain an understanding of the continuity of thylakoid membranes and understand the spatial relationship between the pyrenoid, the starch containing organelle, and thylakoid membranes. We found that Phaeocystis showed considerable morphological and physiological flexibility in response to environmental light levels. We found that the thylakoids generally run parallel to the chloroplast membrane with many junctures and bifurcations, many of which are in contact with the chloroplast membrane itself. The considerable flexibility in the. thylakoid membranes allows for the accommodation of the pyrenoid structure. The arrangement of the thylakoids within these structures resemble those found in new structures of mitochondria cristae. We present a new structural model for algal chloroplasts which greatly revises current concepts of thylakoid membrane structure in relation to photoacclimation.
A list of research papers and reports completed on this final report are provided.
A new method of estimating temperatures and gas species concentrations (CO2 and H2O) in a laminar flame is reported. The path-integrated, spectral radiation intensities emitted from a laminar flame at multiple wavelengths and view angles are calculated using a narrow band radiation model. Synthetic data, in the form of radial profiles of temperature and gas concentrations, are used in these calculations. The calculations mimic measurements that would theoretically be obtained using a mid-infrared spectrometer with a scanner. The path integrated spectral radiation intensities are deconvoluted using a maximum likelihood estimation method in conjunction with an iterative scheme. The deconvolution algorithm accounts for the self-absorption of radiation by the intervening gases, and provides the local temperature and gas species concentrations. The deconvoluted temperatures and gas concentrations are compared with the synthetic data used for calculating the spectral radiation intensities. The deconvoluted temperatures and gas species concentrations are within 0.5 % of the synthetic data. The deconvolution algorithm is expected to provide combustion researchers with an easy method of obtaining the radial profiles of major gas species concentrations and temperatures in laminar flames non-intrusively using a mid-infrared spectrometer with a scanner.
Dated at approximately 3.9 billion years of age, carbonate disks, found within fractures of the host rock of Martian meteorite ALH84001, have been interpreted as secondary minerals that formed at low temperature in an aqueous medium. Heterogeneously distributed within these disks are magnetite nanocrystals that are of Martian origin. Approximately one quarter of these magnetites have morphological and chemical similarities to magnetite particles produced by magnetotactic bacteria strain MV-1, which are ubiquitous in aquatic habitats on Earth. Moreover, these types of magnetite particles are not known or expected to be produced by abiotic means either through geological processes or synthetically in the laboratory. The remaining three quarters of the ALH84001 magnetites are likely products of multiple processes including, but not limited to, precipitation from a hydrothermal fluid, thermal decomposition of the carbonate matrix in which they are embedded, and extracellular formation by dissimilatory Fe-reducing bacteria. We have proposed that the origins of magnetites in ALH84001 can be best explained as the products of multiple processes, one of which is biological. Recently the three-dimensional (3-D) external morphology of the purported biogenic fraction of the ALH84001 magnetites has been the subject of considerable debate. We report here the 3-D geometry of biogenic magnetite crystals extracted from MV-1 and of those extracted from ALH84001 carbonate disks using a combination of high resolution classical and tomographic transmission electron microscopy (TEM). We focus on answering the following questions: (1) which technique provides adequate information to deduce the 3-D external crystal morphology?; and, (2) what is the precise 3-D geometry of the ALH84001 and MV-1 magnetites?
We describe a novel synchronous detection approach to map the transmission of mechanical stresses within the cytoplasm of an adherent cell. Using fluorescent protein-labeled mitochondria or cytoskeletal components as fiducial markers, we measured displacements and computed stresses in the cytoskeleton of a living cell plated on extracellular matrix molecules that arise in response to a small, external localized oscillatory load applied to transmembrane receptors on the apical cell surface. Induced synchronous displacements, stresses, and phase lags were found to be concentrated at sites quite remote from the localized load and were modulated by the preexisting tensile stress (prestress) in the cytoskeleton. Stresses applied at the apical surface also resulted in displacements of focal adhesion sites at the cell base. Cytoskeletal anisotropy was revealed by differential phase lags in X vs. Y directions. Displacements and stresses in the cytoskeleton of a cell plated on poly-L-lysine decayed quickly and were not concentrated at remote sites. These data indicate that mechanical forces are transferred across discrete cytoskeletal elements over long distances through the cytoplasm in the living adherent cell.
The NASA Lewis Research Center recently codeveloped a state-of-the-art x-ray CT facility (designated SMS SMARTSCAN model 100-112 CITA by Scientific Measurement Systems, Inc., Austin, Texas). This multipurpose, modularized, digital x-ray facility includes an imaging system for digital radiography, CT, and computed laminography. The system consists of a 160-kV microfocus x-ray source, a solid-state charge-coupled device (CCD) area detector, a five-axis object-positioning subassembly, and a Sun SPARCstation-based computer system that controls data acquisition and image processing. The x-ray source provides a beam spot size down to 3 microns. The area detector system consists of a 50- by 50- by 3-mm-thick terbium-doped glass fiber-optic scintillation screen, a right-angle mirror, and a scientific-grade, digital CCD camera with a resolution of 1000 by 1018 pixels and 10-bit digitization at ambient cooling. The digital output is recorded with a high-speed, 16-bit frame grabber that allows data to be binned. The detector can be configured to provide a small field-of-view, approximately 45 by 45 mm in cross section, or a larger field-of-view, approximately 60 by 60 mm in cross section. Whenever the highest spatial resolution is desired, the small field-of-view is used, and for larger samples with some reduction in spatial resolution, the larger field-of-view is used.