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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

An Automatic Phase-Change Detection Technique for Colloidal Hard Sphere Suspensions

Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. However, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time consuming. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The algorithm utilizes intelligent image processing techniques that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application where regions of interest are distinguished from the background by differing patterns of motion over time.

McDowell, Mark↗
NASA NTRS2004

Making Precise Resonators for Mesoscale Vibratory Gyroscopes

An alternative approach to the design and fabrication of vibratory gyroscopes is founded on the use of fabrication techniques that yield best results in the mesoscopic size range, which is characterized by overall device dimensions of the order of a centimeter. This approach stands in contradistinction to prior approaches in (1) the macroscopic size range (the size range of conventional design and fabrication, characterized by overall device dimensions of many centimeters) and (2) the microscopic size range [the size range of microelectromechanical systems (MEMS), characterized by overall device dimensions of the order of a millimeter or less]. The mesoscale approach offers some of the advantage of the MEMS approach (sizes and power demands smaller than those of the macroscale approach) and some of the advantage of the macroscale approach (the possibility of achieving relative dimensional precision greater than that of the MEMS approach). Relative dimensional precision is a major issue in the operation of a vibratory gyroscope. The heart of a vibratory gyroscope is a mechanical resonator that is required to have a specified symmetry in a plane orthogonal to the axis about which rotation is to be measured. If the resonator could be perfectly symmetrical, then in the absence of rotation, a free vibration of the resonator could remain fixed along any orientation relative to its housing; that is, the gyroscope could exhibit zero drift. In practice, manufacturing imprecision gives rise to some asymmetry in mass, flexural stiffness or dissipation, resulting in a slight drift or beating motion of an initial vibration pattern that cannot be distinguished from rotation. In the mesoscale approach, one exploits the following concepts: For a given amount of dimensional error generated in manufacturing, the asymmetry and hence the rate-of-rotation drift of the gyroscope can be reduced by increasing the scale. The decrease in asymmetry also reduces coupling of vibrations to the external environment. Mechanical thermal noise and electronic measurement noise and drift can also be reduced by increasing the size of the resonator and its associated sensors.

Yang, Eui-Hyeok↗
NASA NTRS1991

Preliminary micrometeoroid and debris effects on LDEF thermal control surfaces

Thermal control surfaces on the Long Duration Exposure Facility (LDEF) were exposed to 5.75 years of low-Earth orbit environments. Since LDEF was gravity gradient stabilized and directionally stable, the effects of each of the environments can be distinguished via changes in material responses to hypervelocity impacts. The extent of these effects are being visually and microscopically characterized using thermal control surfaces archived at Johnson Space Center in order to determine the the relationship between environment exposure and resulting ring sizes, delamination areas, and penetration diameters. The characterization of these affected areas will provide spacecraft system designers with the information they require to determine degradation of thermal control systems during satellite lifetimes.

Allbrooks, Martha K.↗
NASA NTRS2003

Raman-atomic force microscopy of the ommatidial surfaces of Dipteran compound eyes

The ommatidial lens surfaces of the compound eyes in several species of files (Insecta: Diptera) and a related order (Mecoptera) were analyzed using a recently developed Raman-atomic force microscope. We demonstrate in this work that the atomic force microscope (AFM) is a potentially useful instrument for gathering phylogenetic data and that the newly developed Raman-AFM may extend this application by revealing nanometer-scale surface chemistry. This is the first demonstration of apertureless near-field Raman spectroscopy on an intact biological surface. For Chrysopilus testaceipes Bigot (Rhagionidae), this reveals unique cerebral cortex-like surface ridges with periodic variation in height and surface chemistry. Most other Brachyceran flies, and the "Nematoceran" Sylvicola fenestralis (Scopoli) (Anisopodidae), displayed the same morphology, while other taxa displayed various other characteristics, such as a nodule-like (Tipula (Triplicitipula) sp. (Tipulidae)) or coalescing nodule-like (Tabanus punctifer Osten Sacken (Tabanidae)) morphology, a smooth morphology with distinct pits and grooves (Dilophus orbatus (Say) (Bibionidae)), or an entirely smooth surface (Bittacus chlorostigma MacLachlan (Mecoptera: Bittacidae)). The variation in submicrometer structure and surface chemistry provides a new information source of potential phylogenetic importance, suggesting the Raman-atomic force microscope could provide a new tool useful to systematic and evolutionary inquiry.

Eye/ultrastructure↗
NASA NTRS2008

New Techniques in Characterization of Ferroelectric Materials

Two new techniques have been developed to characterize Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) based ferroelectric single crystals: (i) electro-thermal imaging, and (ii) single crystal x-ray diffraction in the transmission mode. (i) Electro-thermal imaging is a remote sensing technique that can detect the polarization direction and poling state of a whole crystal slice. This imaging technique utilizes an IR camera to determine the field induced temperature change and does not require any special or destructive sample preparation. In the resulting images it is possible to distinguish regions of 180 deg domains. This powerful technique can be used remotely during poling to determine the poling state of the crystal to avoid over-poling that can result in inferior properties and/or cracking of the crystals. Electro-thermal imaging produced the first direct observations of polarization rotation. Under bipolar field, the domains near the corners were the first to switch direction. As the field increased above the coercive field, domains at the center part of the crystals switched direction. (ii) X-ray diffraction in the transmission mode has long been used in structure determination of organic crystals and proteins; however, it is not used much to characterize inorganic systems. 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals were examined by this XRD technique for the first time, and a never-before-seen super-lattice was revealed with a doubling of the unit cell in all three directions, giving a cell volume eight times that of a traditional perovskite unit cell. The significance of the super-lattice peaks increased with poling, indicating a structural contribution to ordering. Lack of such observations by electron diffraction in the transmission electron microscope examinations suggests the presence of a bulk effect.

Sehirlioglu, Alp↗
NASA NTRS2009

Detecting Phase Boundaries in Hard-Sphere Suspensions

A special image-data-processing technique has been developed for use in experiments that involve observation, via optical microscopes equipped with electronic cameras, of moving boundaries between the colloidal-solid and colloidal-liquid phases of colloidal suspensions of monodisperse hard spheres. During an experiment, it is necessary to adjust the position of a microscope to keep the phase boundary within view. A boundary typically moves at a speed of the order of microns per hour. Because an experiment can last days or even weeks, it is impractical to require human intervention to keep the phase boundary in view. The present image-data-processing technique yields results within a computation time short enough to enable generation of automated-microscope-positioning commands to track the moving phase boundary

McDowell, Mark↗
NASA NTRS1991

Design and analysis of aspherical multilayer imaging X-ray microscope

Spherical Schwarzschild microscopes for soft X-ray applications in microscopy and projection lithography employ two concentric spherical mirrors that are configured such that the third-order spherical aberration and coma are zero. Based on incoherent, sine-wave MTF calculations, the object-plane resolution of a magnification-factor-20 microscope is presently analyzed as a function of object height and numerical aperture of the primary for several spherical Schwarzschild, conic, and aspherical two-mirror microscope configurations.

Shealy, David L.↗
NASA NTRS1989

Ordering in the Fe-Ni system under electron irradiation

The disorder-order transformation was generated in a range of Fe-Ni alloys using 1 MeV electrons in a high voltage electron microscope. The experimental factors that influence the occurrence of the transformation were determined, and the critical disordering temperature, Tc, was determined as a function of composition. It was demonstrated that the irradiation enhanced the ordering reaction kinetics. A metastable, ordered phase transformation was not induced. From the results, it is possible to deduce new information about the Fe-Ni phase diagram below 350 C.

Reuter, K. B.↗
NASA NTRS1971

Earth physics and phase transformations program: A concept and proposal

A program to study the geophysical characteristics of the earth is presented as an integration of the different disciplines that constitute the earth sciences, through the foundation of a generalized geodynamic theory of earth physics. A program is considered for defining the physical constants of the earth's material which parametrize the hydrodynamic equation in the microscopic solid state behavior of the crystals of the lithosphere. In addition, in order to lay the foundation for a generalized theory in earth physics, specific research areas are considered, such as the nature of the kinetics of the phase transitions in mineral assemblages, the equilibrium thermodynamic properties of crystals which are major constituents of mineral assemblages, and the transport properties of pure crystals which are major constituents of mineral assemblages.

Bonavito, N. L.↗
NASA NTRS1984

Failure analysis of thin-film amorphous-silicon solar-cell modules

A failure analysis of thin film amorphous silicon solar cell modules was conducted. The purpose of this analysis is to provide information and data for appropriate corrective action that could result in improvements in product quality and reliability. Existing techniques were expanded in order to evaluate and characterize degradational performance of a-Si solar cells. Microscopic and macroscopic defects and flaws that significantly contribute to performance degradation were investigated.

Kim, Q.↗
NASA NTRS1995

Positron annihilation spectroscopic study of high performance semi-interpenetrating network polyimids

Semi-interpenetrating (S-IPN) network polyimids were made from different proportions of LaRC RP46 (a thermosetpolyimid) and LaRC BDTA-ODA (a thermoplastic polyimid). The ultimate goal of this networking is to improve the mechanical properties of the thermoset polyimid. Positron lifetime study was made to calculate lifetime based on second component of the life time spectra and the free volume & microvoid size. All these properties tend to decrease steadily with increasing thermoset content except at the 50 percent thermoset level where these properties show sudden drop. This result contradicts with the initial expectation that the blend properties should change gradually if it were a solid solution of thermoset (TSP) and thermoplastic (TPP) components. Thermal analyses (TMA, DSC, DMA & TGA) were run to complement the positron life time studies. The TMA and DSC studies confirm the contradiction mentioned above. Further experimentation with S-IPN polymers made at TSP/TTP content around 50/50 level are being conducted to explain this anomaly. Scanning electron microscope study of the S-IPN polyimid samples is under way in order to detect morphological differences which might help explain the phenomenon mentioned above.

Ray, Asit K.↗
NASA NTRS2001

Molecular Dynamic Simulations of Interaction of an AFM Probe with the Surface of an SCN Sample

Molecular dynamic (MD) simulations is conducted in order to estimate forces of probe-substrate interaction in the Atomic Force Microscope (AFM). First a review of available molecular dynamic techniques is given. Implementation of MD simulation is based on an object-oriented code developed at the University of Delft. Modeling of the sample material - succinonitrile (SCN) - is based on the Lennard-Jones potentials. For the polystyrene probe an atomic interaction potential is used. Due to object-oriented structure of the code modification of an atomic interaction potential is straight forward. Calculation of melting temperature is used for validation of the code and of the interaction potentials. Various fitting parameters of the probe-substrate interaction potentials are considered, as potentials fitted to certain properties and temperature ranges may not be reliable for the others. This research provides theoretical foundation for an interpretation of actual measurements of an interaction forces using AFM.

Bune, Adris↗
NASA NTRS2002

High-Fidelity Micromechanics Model Developed for the Response of Multiphase Materials

A new high-fidelity micromechanics model has been developed under funding from the NASA Glenn Research Center for predicting the response of multiphase materials with arbitrary periodic microstructures. The model's analytical framework is based on the homogenization technique, but the method of solution for the local displacement and stress fields borrows concepts previously employed in constructing the higher order theory for functionally graded materials. The resulting closed-form macroscopic and microscopic constitutive equations, valid for both uniaxial and multiaxial loading of periodic materials with elastic and inelastic constitutive phases, can be incorporated into a structural analysis computer code. Consequently, this model now provides an alternative, accurate method.

Aboudi, Jacob↗
NASA NTRS2019

Fine-Grained, Spinel-Rich Ca-Al-Rich Inclusions From The Reduced CV3 Chondrite Efremovka: A Genetic Link To Wark-Lovering Rims?

Fine-grained, spinel-rich Ca-Al-rich inclusions (FGIs) in carbonaceous chondrites, mostly CV3 chondrites, are interpreted as aggregates of nebular gas-solid condensates that escaped significant melting [1]. Multiple lines of evidence suggest a condensation origin for FGIs, including their layered structures and irregular shapes and the fine grain size of numerous spinel-cored nodules [e.g., 2,3], and the distinctive volatility-fractionated group II rare earth element patterns of bulk inclusions and their mineral constituents [e.g., 4,5]. The origin and nature of FGIs are poorly constrained because of their fine grain sizes and intimate intergrowths of refractory phases, combined with their susceptibility to secondary parent body alteration processes, making detailed mineralogical and petrologic characterizations difficult using scanning electron microscope (SEM) and electron microprobe techniques. In this study, we present preliminary transmission electron microscope (TEM) analyses of pristine FGIs from the reduced CV3 chondrite Efremovka in order to provide the detailed characterization of their micrometer- to nanometer-scale textures and chemical compositions. Our goals are to better understand the formation processes and conditions of FGIs in the early solar nebula and to explore their possible genetic relationship with other early-formed refractory inclusions and their rims.

Keller, L. P.↗
NASA NTRS1992

Design and analysis of soft X-ray imaging microscopes

The spherical Schwarzschild microscope for soft X-ray applications in microscopy and projection lithography consists of two concentric spherical mirrors configured such that the third-order spherical aberration and coma are zero. Since multilayers are used on the mirror substrates for X-ray applications, it is desirable to have only two reflecting surfaces in a microscope. To reduce microscope aberrations and increase the field of view, generalized mirror surface profiles are here considered. Based on incoherent and sine wave modulation transfer function calculations, the object plane resolution of a microscope has been analyzed as a function of the object height and numerical aperture (NA) of the primary for several spherical Schwarzschild, conic, and aspherical Head reflecting two-mirror microscope configurations. The Head microscope with a NA of 0.4 achieves diffraction limited performance for objects with a diameter of 40 microns. Thus, it seems possible to record images with a feature size less than 100 A with a 40x microscope when using 40 A radiation.

Shealy, David L.↗
NASA NTRS1972

Lunar sample analysis

A simple and convenient method of making quantitative magnetic separations of the lunar fines is described. The fractions obtained form groups containing distinctively different particle types; thus it appears that magnetic separation in itself may be a useful way of characterizing lunar fines. Mossbauer studies of fines 10084 show that the metal can not contain more than about 1.5% Ni implying that by far the bulk of it results from reduction rather than being a direct meteoritic addition. Mossbauer data also places an upper limit on the magnetite content of the fines at least an order of magnitude below that required to account for the characteristic ferromagnetic resonance observed. Microscopic examination of magnetic separates from the 15101 fines suggests that reduction of Fe accompanies every major impact event on the moon and also suggests that the bulk of the material at the collection site has at one time been in an impact plume.

Housley, R. M.↗
NASA NTRS1992

Preliminary micrometeoroid and debris effects on LDEF thermal control surfaces

Thermal control surfaces returned from space exhibited synergistic effects of simultaneous exposure to various natural environments. The thermal control surfaces of the Long Duration Exposure Facility (LDEF) were exposed to 5.75 years of low Earth orbit environments. Since LDEF was gravity-gradient stabilized and directionally stable (i.e., no rotation), the effects of each of the environments (meteoroid and space debris impacts, thermal cycling, atomic oxygen, and ultraviolet light exposure) can be distinguished via changes in material responses to hypervelocity impacts. The extent of these impacts are being visually and microscopically characterized using thermal control surfaces archived at NASA Johnson Space Center (JSC) in order to determine the relationship between environment exposure and resulting ring sizes, delamination areas, and penetration diameters. The characterization of these affected areas will provide spacecraft system designers with the information they require to determine degradation of thermal control systems during satellite lifetimes.

Allbrooks, Martha K.↗