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NASA NTRS1991

Patterns of discoloration and oxidation by direct and scattered fluxes, especially oxygen on silicon

A number of interesting discoloration patterns are clearly evident on M0002-1 which resides on three faces of LDEF: front face, rear face, and earth face. Most interesting is the pattern of blue oxidation on polished single crystal silicon apparently produced by once-scattered ram oxygen atoms along the earth face. Most of the other patterns are seen in the Thermal Control Paint. Also, severe oxidation of CR-39 polycarbonate occurred on the front face of LDEF, as expected. A complete explanation for the patterns has not yet been obtained.

Frederickson, A. R.↗

NASA NTRS1992

Patterns of discoloration and oxidation by direct and scattered fluxes on LDEF, including oxygen on silicon

A number of interesting discoloration patterns are clearly evident on MOOO2-1 which resides on the three faces of the Long Duration Exposure Facility (LDEF). Most interesting is the pattern of blue oxidation on polished single crystal silicon apparently produced by scattered or direct ram oxygen atoms along the earth face. A complete explanation for the patterns has not yet been obtained. All honeycomb outgassing holes have a small discoloration ring around them that varies in color. The shadow cast by a suspended wire on the earth face surface is not easily explained by either solar photons or by ram flux. The shadows and the dark/light regions cannot be explained consistently by the process of solar ultraviolet paint-darkening modulated by ram flux oxygen bleaching of the paint.

Frederickson, A. R.↗

NASA NTRS2004

Reliable and Affordable Control Systems Active Combustor Pattern Factor Control

Active, closed-loop control of combustor pattern factor is a cooperative effort between Honeywell (formerly AlliedSignal) Engines and Systems and the NASA Glenn Research Center to reduce emissions and turbine-stator vane temperature variations, thereby enhancing engine performance and life, and reducing direct operating costs. Total fuel flow supplied to the engine is established by the speed/power control, but the distribution to individual atomizers will be controlled by the Active Combustor Pattern Factor Control (ACPFC). This system consist of three major components: multiple, thin-film sensors located on the turbine-stator vanes; fuel-flow modulators for individual atomizers; and control logic and algorithms within the electronic control.

McCarty, Bob↗

NASA NTRS1990

Symmetry assessment of an air-blast atomizer spray

This study represents an evaluation of the extent to which conventional and recently introduced modern diagnostics can assess the symmetry of sprays formed by three atomizers of identical design. The conventional diagnostics include sheet-lit photography, patternation, and laser diffraction. The modern diagnostic is laser interferometry (phase Doppler). Symmetry is assessed in ambient conditions for four atomizer orientations, and comparisons are made between the diagnostic techniques. The results demonstrate that conventional and modern diagnostics are consistent in the assessment of symmetry, patternation and phase Doppler are most effective in establishing symmetry of mass flux, and phase Doppler, although more tedious to employ, provides the additional information necessary to establish the sources of detected asymmetries in terms of nonuniformities in droplet velocities, size distributions, volume flux, and concentration.

Mcdonnell, V. G.↗

NASA NTRS2004

Gardosian Patterns in Tribology

The following paper is a memorial retrospective on selected research of Dr. Michael N. Gardos. Dr. Gardos spent his professional career engaged in tribological research which often extended the scientific boundaries of the field. Several of the concepts he put forth into the tribology community were initially met with grave skepticism but over time his views have been largely embraced but not widely acknowledged. His approach to new research topics was often characterized by these qualities: 1) pioneering points of view, 2) the use of the model experiment, and 3) the presence of multiple research agendas for each single experiment. I have chosen to name his research approach as "Gardosian Patterns" in honor of his contributions to Tribology. Three specific examples of these patterns will be reviewed. One is the concept of atomic level tailoring of materials to control macroscopic properties. A second is the use of a model ball polishing experiment to identify high fracture toughness ceramics for use in rolling element bearings. A third Gardosian Pattern example is his pioneering work with the tribology of diamond and diamond films in which he proposed controlling friction via surface bond tailoring. In these examples, Gardos utilized conventional research tools in unconventional ways and, at times, even developed new tools which have become part of the mainstream. His remarkable career has left a positive and lasting mark on Tribology.

DellaCorte, Christopher↗

NASA NTRS1974

High energy galactic gamma radiation from cosmic rays concentrated in spiral arms

A model for the emission of high energy ( 100 MeV) gamma rays from the galactic disk was developed and compared to recent SAS-2 observations. In the calculation, it is assumed that (1) the high energy galactic gamma rays result primarily from the interaction of cosmic rays with galactic matter; (2) on the basis of theoretical and experimental arguments the cosmic ray density is proportional to the matter density on the scale of galactic arms; and (3) the matter in the galaxy, atomic and molecular, is distributed in a spiral pattern consistent with density wave theory and the experimental data on the matter distribution.

Bignami, G. F.↗

NASA NTRS1985

Satellite observations of 557.7 NM airglow as a diagnostic technique to study the dynamics of the lower thermosphere

Photometric observations of the airglow limb at 557.7 nm have been made from the ISIS 2 satellite since 1971. From an analysis of 32,000 airglow limb observations obtained during the first two years of operation, the major temporal and spatial characteristics of the night airglow have been identified. Maxima occur in mid-October and mid-April at all latitudes. There is a marked variation with latitude during the equinox periods, with peak intensities near 35 degrees in autumn and near 25 degrees in spring. It is possible to gain considerable insight into the behavior of the lower thermosphere by combining the airglow observations with a simple model of the photochemical and dynamical processes. In this way a pattern of the latitude and temporal variation of atomic oxygen concentration at the peak of the layer as well as the eddy diffusion in this altitude region have been inferred. The concentration of atomic oxygen shows midlatitude peaks near equinox, and minima about one month after solstice. Average values at midlatitudes are about 1.3 times those at the equator. The amplitude of the semiannual component is about 20% of the mean value at 35 degrees as compared to 10% at the equator, and the amplitude of 12-month component is about 12% at 35 deg and 5% at the equator. The semiannual component has a minimum that occurs approximately 3 weeks (plus or minus) after solstice at all latitudes, while the 12-month component peaks in the summer hemisphere at solstice (plus or minus 2 months).

Cogger, L. L.↗

NASA NTRS1995

Bulk Properties of Ni3Al(gamma') With Cu and Au Additions

The BFS method for alloys is applied to the study of 200 alloys obtained from adding Cu and Au impurities to a Ni3Al matrix. We analyze the trends in the bulk properties of these alloys (heat of formation, lattice parameter, and bulk modulus) and detect specific alloy compositions for which these quantities have particular values. A detailed analysis of the atomic interactions that lead to the preferred ordering patterns is presented.

Bozzolo, Guillermo↗

NASA NTRS1976

Interactions of satellite-speed helium atoms with satellite surfaces. 2: Energy distributions of reflected helium atoms

Energy transfer in collisions of satellite-speed (7,000 m/sec) helium atoms with a cleaned 6061-T6 satellite-type aluminum surface was investigated using the molecular-beam technique. The amount of energy transferred was determined from the measured energy of the molecular-beam and the measured spatial and energy distributions of the reflected atoms. Spatial distributions of helium atoms scattered from a 6061-T6 aluminum surface were measured. The scattering pattern exhibits a prominent backscattering, probably due to the gross surface roughness and/or the relative lattice softness of the aluminum surface. Energy distributions of reflected helium atoms from the same surface were measured for six different incidence angles. For each incidence angle, distributions were measured at approximately sixty scattering positions. At a given scattering position, the energy spectra of the reflected helium atoms and the background gas were obtained using the retarding-field energy analyzer.

Liu, S. M.↗

NASA NTRS1990

Down-to-earth studies of carbon clusters

Recent advances in supersonic beam experiments with laser-vaporization sources of clusters have provided some interesting new insights into the nature of the small clusters of carbon, and the processes through which carbon condenses. One cluster in particular, C(sub 60), appears to play a central role. It is argued that this cluster takes the shape of a soccerball: a hollow sphere composed of a shell of 60 carbon atoms connected by a lattice of hexagonal and pentagonal rings, in a pattern of overall icosahedral symmetry. Although C(sub 60) appears to be uniquely stable due to its perfect symmetry, all other even-numbered carbon clusters in the 32 to 100+ atom size range seem to favor similar closed spheroidal forms. These species are interpreted as relatively unreactive side products in condensation reactions of carbon vapor involving spiraling graphitic sheets. The prevalence of C(sub 60) in laser-vaporized carbon vapors and sooting flames suggests that it may be formed readily whenever carbon condenses. Such ready formation and extraordinary stability may have substantial astrophysical implications.

Smalley, R. E.↗

NASA NTRS1994

Coronal element abundances derived from solar energetic particles

The large gradual solar-energetic-particle (SEP) events, where abundances are commonly measured, are produced when coronal mass ejections (CMEs) drive shock waves through the corona and the interplanetary medium. The shock accelerates particles from the highly-ionized, approximately 1.5 MK, plasma in a manner that depends only weakly upon the Q/A of the ion, except at very high energies. Averaging the approximately 1 MeV/amu abundances over many events compensates for the acceleration effects to produce abundances that appear to correspond directly to those in the coronal source for all observed elements, including H. The resulting abundances reflect the 4 x enhancement of ions with low values of first ionization potential (FIP) arising from ion-neutral fractionation that occurs as the atoms are transported up from the photosphere. A different pattern of fractionation is found for ions that are shock-accelerated from the high speed solar wind emerging from coronal holes.

Reames, Donald V.↗

NASA NTRS1992

Preliminary investigations into UHCRE thermal control materials (A0178)

An overview of the initial work that was done in the ESTEC Materials and Processes Division to evaluate the effect of space environment on the thermal blankets of the Ultra-Heavy Cosmic Ray Nuclei Experiments (UHCRE) is presented. The topics covered include: (1) a preliminary survey of the perforations of the two-thirds of the thermal blanket returned to ESTEC; (2) thermo-optical properties and thickness recessions of three samples cut from each of the third center parts of the 16 thermal blankets were measured and effects of environments (sun illumination and atomic oxygen fluences); (3) contamination was analyzed on trays, external blanket and internal aluminized Kapton foil by IR technique and scanning electron microscopy SEM/EDX examination; (4) the pattern of contamination on the Al Kapton foils was observed, sketched, and related to atomic oxygen flow; and (5) the Long Duration Exposure Facility (LDEF) yaw angle misorientation was evaluated from the contaminated areas visible on some of the trays. In addition, impacts of micrometeoroids and space debris were experimentally simulated on spare flight thermal blankets. Relations between penetration/perforation hole characteristics and projectile parameters were established.

Levadou, Francois↗

NASA NTRS2003

Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)

Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.

Palosz, B.↗

NASA NTRS2005

Ferritin-Templated Quantum-Dots for Quantum Logic Gates

Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The work presented here offers a new method to develop quantum-dots using a bio-template, called ferritin, that ensures QD production in uniform size of nano-scale proportion. The bio-template for uniform yield of QD is based on a ferritin protein that allows reconstitution of core material through the reduction and chelation processes. One of the biggest challenges for developing QLG is the requirement of ordered and uniform size of QD for arrays on a substrate with nanometer precision. The QD development by bio-template includes the electrochemical/chemical reconsitution of ferritins with different core materials, such as iron, cobalt, manganese, platinum, and nickel. The other bio-template method used in our laboratory is dendrimers, precisely defined chemical structures. With ferritin-templated QD, we fabricated the heptagonshaped patterned array via direct nano manipulation of the ferritin molecules with a tip of atomic force microscope (AFM). We also designed various nanofabrication methods of QD arrays using a wide range manipulation techniques. The precise control of the ferritin-templated QD for a patterned arrangement are offered by various methods, such as a site-specific immobilization of thiolated ferritins through local oxidation using the AFM tip, ferritin arrays induced by gold nanoparticle manipulation, thiolated ferritin positioning by shaving method, etc. In the signal measurements, the current-voltage curve is obtained by measuring the current through the ferritin, between the tip and the substrate for potential sweeping or at constant potential. The measured resistance near zero bias was 1.8 teraohm for single holoferritin and 5.7 teraohm for single apoferritin, respectively.

Choi, Sang H.↗

NASA NTRS2003

Evaporative Cooling in a Holographic Atom Trap

We present progress on evaporative cooling of Rb-87 atoms in our Holographic Atom Trap (HAT). The HAT is formed by the interference of five intersecting YAG laser beams: atoms are loaded from a vapor-cell MOT into the bright fringes of the interference pattern through the dipole force. The interference pattern is composed of Talbot fringes along the direction of propagation of the YAG beams, prior to evaporative cooling each Talbot fringe contains 300,000 atoms at 50 micro-K and peak densities of 2 x 10(exp 14)/cu cm. Evaporative cooling is achieved through adiabatically decreasing the intensity of the YAG laser. We present data and calculations covering a range of HAT geometries and cooling procedures.

Newell, Raymond↗

NASA NTRS1991

Flow visualization of a rocket injector spray using gelled propellant simulants

A study was conducted at NASA-Lewis to compare the atomization characteristics of gelled and nongelled propellant simulants. A gelled propellant simulant composed of water, sodium hydroxide, and an acrylic acid polymer resin (as the gelling agent) was used to simulate the viscosity of an aluminum/PR-1 metallized fuel gel. Water was used as a comparison fluid to isolate the rheological effects of the water-gel and to simulate nongelled RP-1. The water-gel was injected through the central orifice of a triplet injector element and the central post of a coaxial injector element. Nitrogen gas flowed through the outer orifices of the triplet injector element and through the annulus of the coaxial injector element and atomized the gelled and nongelled liquids. Photographs of the water-gel spray patterns at different operating conditions were compared with images obtained using water and nitrogen. A laser light was used for illumination of the sprays. The results of the testing showed that the water sprays produced a finer and more uniform atomization than the water-gel sprays. Rheological analysis of the water-gel showed poor atomization caused by high viscosity of water-gel delaying the transition to turbulence.

Green, James M.↗

NASA NTRS1991

Flow visualization of a rocket injector spray using gelled propellant simulants

Green, James M.↗

NASA NTRS1986

Physics through the 1990s: Atomic, molecular and optical physics

The volume presents a program of research initiatives in atomic, molecular, and optical physics. The current state of atomic, molecular, and optical physics in the US is examined with respect to demographics, education patterns, applications, and the US economy. Recommendations are made for each field, with discussions of their histories and the relevance of the research to government agencies. The section on atomic physics includes atomic theory, structure, and dynamics; accelerator-based atomic physics; and large facilities. The section on molecular physics includes spectroscopy, scattering theory and experiment, and the dynamics of chemical reactions. The section on optical physics discusses lasers, laser spectroscopy, and quantum optics and coherence. A section elucidates interfaces between the three fields and astrophysics, condensed matter physics, surface science, plasma physics, atmospheric physics, and nuclear physics. Another section shows applications of the three fields in ultra-precise measurements, fusion, national security, materials, medicine, and other topics.

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