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This paper presents the results of determining fractional density fluctuations, which requires the measurement of absolute electron density as provided by dual-frequency observations of time delay or ranging conducted by the Ulysses Solar Corona Experiment.
Since radio propagation measurements using either natural or spacecraft radio signals are used for probing the solar wind in the vicinity of the sun, they represent a key tool for studying the interplanetary consequences of solar structure and dynamic phenomena. New information on the near sun consequences was obtained from radio scintillation observations of coherent spacecraft signals. The results covering density fluctuations, fractional density fluctuations, coronal streamers, heliospheric current sheets, coronal mass ejections and interplanetary shocks are reviewed. A joint ICE S-band (13 cm wavelength) Doppler scintillation measurement with the SOHO white-light coronograph (LASCO) is described.
Ultrasonic velocity/time-of-flight imaging that uses back surface reflections to gauge volumetric material quality is highly suited for quantitative characterization of microstructural gradients including those due to pore fraction, density, fiber fraction, and chemical composition variations. However, a weakness of conventional pulse-echo ultrasonic velocity/time-of-flight imaging is that the image shows the effects of thickness as well as microstructural variations unless the part is uniformly thick. This limits this imaging method's usefulness in practical applications. Prior studies have described a pulse-echo time-of-flight-based ultrasonic imaging method that requires using a single transducer in combination with a reflector plate placed behind samples that eliminates the effect of thickness variation in the image. In those studies, this method was successful at isolating ultrasonic variations due to material microstructure in plate-like samples of silicon nitride, metal matrix composite, and polymer matrix composite. In this study, the method is engineered for inspection of more complex-shaped structures-those having (hollow) tubular/curved geometry. The experimental inspection technique and results are described as applied to (1) monolithic mullite ceramic and polymer matrix composite 'proof-of-concept' tubular structures that contain machined patches of various depths and (2) as-manufactured monolithic silicon nitride ceramic and silicon carbide/silicon carbide composite tubular structures that might be used in 'real world' applications.
Ultrasonic velocity and time-of-flight (TOF) imaging that uses back surface reflections to gage volumetric material quality is highly suited for quantitative characterization of microstructural gradients including those due to pore fraction, density, fiber fraction, and chemical composition variations. However, a weakness of conventional pulse echo ultrasonic velocity and TOF imaging is that the image shows the effects of thickness as well as microstructural variations, unless the part is uniformly thick. This limits this imaging method's usefulness in practical applications. Prior studies have described a pulse echo TOF based ultrasonic imaging method that requires using a single transducer in combination with a reflector plate placed behind samples which, eliminates the effect of thickness variation in the image. In those studies, this method was successful at isolating ultrasonic variations due to material in plate like samples of silicon nitride, metal matrix composite, and polymer matrix composite. In this study, the method is engineered for inspection of more complex shaped structures- those having (hollow) tubular or curved geometry. The experimental inspection technique and results are described as applied to a polymer matrix composite "proof of concept" tube that contains machined patches of various depths and an as manufactured monolithic silicon nitride ceramic tube that might be used in "real world" applications.
The first measurements of fractional electron density fluctuations delta-n(sub e)/n(sub e), where delta-n(sub e) is rms electron density fluctuation and n(sub e) is the mean electron density, have been carried out inside 40 R(sub 0) using 1991 Ulysses dual-frequency S- and X-band (13 and 3.6 cm) ranging (time delay) measurements. In the frequency band of approximately 6 x 10(exp -5) - 8 x 10(exp -4) Hz (periods of 20 min to 5 hr), delta-n(sub e)/n(sub e) varies from a high near 20% in the slow wind close to the neutral line to a low of 1% in the fast wind far from the neutral line. For spatial wavenumber K approximately = 1.4 x 10(exp -6)/km (period of 5 hr at 250 km/s), delta-n(sub e)/n(sub e) is essentially independent of heliocentric distance over 0.03-1.0 AU in the slow wind; it is a factor of 30 lower in the fast wind than in the slow wind inside 0.1 AU, but exhibits dramatic growth with heliocentric distance inside 0.3 AU. This latter result reinforces current views of the evolution of MHD turbulence and the association of Alfven waves with high speed streams based on in situ fields and particles measurements beyond 0.3 AU. That regions of enhanced density fluctuations near or above the neutral line coincide with regions of enhanced density confirms previous conclusions that they are the interplanetary manifestation of the heliospheric current sheet and extensions of coronal streamers. While the regions of enhanced density fluctuations lie within those of enhanced density, they have boundaries that are distinctly more abrupt, suggesting the separation of plasma of different nature and origin.
Calculations of exospheric quantities (hydrogen atom density, satellite atom fractional density, kinetic temperature, and escape flux) at locations along the earth-sun axis in the noon and midnight directions have been extended to incorporate a plasmasphere characterized by a dipolar shape and an empirical temperature profile. This interaction, evaluated with parameter values corresponding to low-to-moderate solar conditions, results in an increased density at outer geocoronal positions; the effect is not dramatic, though, and the resulting exosphere mimics the evaporative case closely, in spite of the control of trajectory parcel content by charge exchange collisions. A careful discussion of the handling of plasmaspheric charge exchange collisions and solar ionization is included, and the effect on the exospheric kinetic distribution is analyzed in terms of pertinent examples.
We have measured C-, N-, and O-isotopic ratios of individual graphite grains from the Murchison density fractions KFB1 (2.1-2.15 g/cc) and KFC1 (2.15 -2.20 g/cc). According to the C-isotopic composition, KFC1 consists of two populations: one has light C while the other has heavy C. In addition to these two populations, KFB1 also contains grains whose C-isotopic ratios are approximately normal. In view of these isotopic distributions, it is difficult to understand why the Kr-isotopic compositions of these two separates are so different. In contrast to the lighter density fractions KE1 (1.6-2.05 g/cc) and KFA1 (2.05-2.10 g/cc), the separates KFB1 and KFC1 do not seem to contain many grains with significant O-18 excess.
A stepwise heating technique was used to analyze eight silicate samples from the Orgueil carbonaceous chondrite for He, Ne, Ar, and Xe. Six samples, of which two were etched with NaOH, were density fractions. The other two samples were grain-size fractions separated according to their ability to form a colloid at pH 11.5. Results showed the LiCl separation procedure to be gentler than the NaOH procedure. All fractions were found to be deficient in cosmogenic neon. Above 950 C the fractions gave low 20Ne/22Ne ratios particularly in the low-density and noncolloidal fraction. Compared to the other fractions the fraction from 2.35 to 2.45 g/cu cm contained less Xe and released it more rapidly at low temperatures.
Data from the Copernicus satellite's ultraviolet telescope were used to survey column densities of atomic and molecular hydrogen from a large sample of early-type stars; these data have bearing on an eventual understanding of diffuse and dense interstellar clouds. Column densities are derived by fitting damping profiles to the observed spectra, most of which exhibit strong damping lines in the lower rotational levels surveyed. Plots of dust column density, fractional abundance of molecular hydrogen, and the logarithm of fractional abundance versus total gas column density are given for many of the stars; stars with abnormally large or small hydrogen column densities, as well as some distant stars at high galactic latitudes, are considered. Equilibrium and nonequilibrium theories accounting for the abundance of interstellar hydrogen are compared, and support is found in the data for an account which balances hydrogen formation on interstellar grains with destruction through photodissociation. Overall averages for atomic and molecular hydrogen levels in the galactic plane are also calculated.
Silicon and oxygen data are presented for a number of Allende samples. It is found that based on oxygen and silicon isotopes, Allende samples EGG-1, EGG-6, BG1a, and 3529Yc are typical, unfractionated Allende inclusions. Where magnesium data are available, they indicate the same thing. EGG-3 is fractionated in both oxygen and silicon, as it is in magnesium. Sample D7 melilite is fractionated in oxygen by several per mil along the C2-matrix line, away from typical Allende melilites. Inclusion BG10a is a FUN inclusion with an inferred original oxygen isotopic fractionation of 8-9 per mille/amu relative to the Allende line. Silicon data for two density fractions of inclusion 3A with different mineralogies show a difference of about 2 per mille, which indicates that silicon, like oxygen, has been added to at least some mineral phases in Allende inclusions from a reservoir other than the one in which the inclusion first began to form.
This study presents an analysis of density measurements made using high-resolution accelerometers aboard several space shuttles at altitudes from 60 to 140 km during reentry into the earth's atmosphere. The observed density fluctuations are interpreted in terms of gravity waves and tides and provide evidence of the importance of such motions well into the thermosphere. Height profiles of fractional density variance reveal that wave amplitudes increase at a rate consistent with observations at lower levels up to about 90 km. The rate of amplitude growth decreases at greater heights, however, and appears to cease above about 110 km. Wave amplitudes are nevertheless large at these heights and suggest that gravity waves may play an important role in forcing of the lower thermosphere.
Current estimates of QSO luminosity, number density, evolution, and spectral index are used to study whether the diffuse cosmic ray background is (1) entirely due to thermal bremmstrahlung of the intergalactic medium (IGM), (2) completely supplied by QSO X-rays, or (3) a combination of both. The upper limits on an IGM fractional density with respect to closure are Omega = 0.26, 0.24, and 0.21 for pure collisional, photo/collisional, and pure photoionization, respectively. These calculations give emission spectra, Compton distortion of the microwave background, and optical depths to distant QSOs for comparison with relevant data.
Classification of blood hyperlipemias by electrophoresis or ultracentrifugation according to density fraction is described and therapeutic measures for humans with hyperlipoproteinemia are outlined. The statistically significant relationship between high serum cholesterol levels and incidence of coronary disease prescribes restricted caloric intake or physical exercise to burn excess calories as preventive measures.
The activity of long- and short-lived isotopes in a series of samples from a vertical column through the center of rock 14321 was measured. Rock 14321 is a 9 kg fragmental rock whose orientation was photographically documented on the lunar surface. Also investigated was a sample from the lower portion of rock 14310, where, in order to study target effects, two different density fractions (mineral separates) were analyzed. A few nuclides in a sample from the comprehensive fines 14259 were measured. This material has been collected largely from the top centimeter of the lunar soil. The study of the deep samples of 14321 and 14310 provided values for the activity of isotopes at points where only effects produced by galactic cosmic rays are significant.
Normal rates of dentinogenesis and osteogenesis in the body of the mandible were observed. The total calcium, inorganic phosphorus and hydroxyproline levels in the jaws and incisors of the flight rats were normal. Gravity density fractionation studies suggested, however, that spaceflight caused a delay in the normal maturation of bone mineral and matrix; normal values were reestablished by 6 days postflight. The teeth were spared. The circadian and ultradian patterns of dentin calcification were normal during spaceflight and recovery periods, but the enamel rhythms displayed a greater amplitude of sulfur concentrations and this abnormal calcium to sulfur ratios only during exposure to zero gravity. The rat mandible and teeth do not suffer the deficits of bone formation common to weight bearing parts of the skeleton during spaceflight. The only derangements detected were in the quality of the matrix and mineral moieties.
A well-validated quasi-one-dimensional computational fluid dynamics (CFD) code for the analysis of the internal ballistics of two-stage light gas guns is modified to explicitly calculate the ablation of steel from the gun bore and the incorporation of the ablated wall material into the hydrogen working cas. The modified code is used to model 45 shots made with the NASA Ames 0.5 inch light gas gun over an extremely wide variety of gun operating conditions. Good agreement is found between the experimental and theoretical piston velocities (maximum errors of +/-2% to +/-6%) and maximum powder pressures (maximum errors of +/-10% with good igniters). Overall, the agreement between the experimental and numerically calculated gun erosion values (within a factor of 2) was judged to be reasonably good, considering the complexity of the processes modelled. Experimental muzzle velocities agree very well (maximum errors of 0.5-0.7 km/sec) with theoretical muzzle velocities calculated with loading of the hydrogen gas with the ablated barrel wall material. Comparison of results for pump tube volumes of 100%, 60% and 40% of an initial benchmark value show that, at the higher muzzle velocities, operation at 40% pump tube volume produces much lower hydrogen loading and gun erosion and substantially lower maximum pressures in the gun. Large muzzle velocity gains (2.4-5.4 km/sec) are predicted upon driving the gun harder (that is, upon using, higher powder loads and/or lower hydrogen fill pressures) when hydrogen loading is neglected; much smaller muzzle velocity gains (1.1-2.2 km/sec) are predicted when hydrogen loading is taken into account. These smaller predicted velocity gains agree well with those achieved in practice. CFD snapshots of the hydrogen mass fraction, density and pressure of the in-bore medium are presented for a very erosive shot.
NASA Lewis Research Center's Life Prediction Branch, in partnership with Sonix, Inc., and Cleveland State University, recently advanced the development of, refined, and commercialized an advanced nondestructive evaluation (NDE) inspection method entitled the Single Transducer Thickness-Independent Ultrasonic Imaging Method. Selected by R&D Magazine as one of the 100 most technologically significant new products of 1996, the method uses a single transducer to eliminate the superimposing effects of thickness variation in the ultrasonic images of materials. As a result, any variation seen in the image is due solely to microstructural variation. This nondestructive method precisely and accurately characterizes material gradients (pore fraction, density, or chemical) that affect the uniformity of a material's physical performance (mechanical, thermal, or electrical). Advantages of the method over conventional ultrasonic imaging include (1) elimination of machining costs (for precision thickness control) during the quality control stages of material processing and development and (2) elimination of labor costs and subjectivity involved in further image processing and image interpretation. At NASA Lewis, the method has been used primarily for accurate inspections of high temperature structural materials including monolithic ceramics, metal matrix composites, and polymer matrix composites. Data were published this year for platelike samples, and current research is focusing on applying the method to tubular components. The initial publicity regarding the development of the method generated 150 requests for further information from a wide variety of institutions and individuals including the Federal Bureau of Investigation (FBI), Lockheed Martin Corporation, Rockwell International, Hewlett Packard Company, and Procter & Gamble Company. In addition, NASA has been solicited by the 3M Company and Allison Abrasives to use this method to inspect composite materials that are manufactured by these companies.
Smoke emissions have long been quantified after-the-fact by simple multiplication of burned area, biomass density, fraction of above-ground biomass, and burn efficiency. A new algorithm has been suggested, as described in Ichoku & Kaufman (2005), for use in calculating smoke emissions directly from fire radiative power (FRP) measurements such that the latency and uncertainty associated with the previously listed variables are avoided. Application of this new, simpler and more direct algorithm is automatic, based only on a fire's FRP measurement and a predetermined coefficient of smoke emission for a given location. Attaining accurate coefficients of smoke emission is therefore critical to the success of this algorithm. In the aforementioned paper, an initial effort was made to derive coefficients of smoke emission for different large regions of interest using calculations of smoke emission rates from MODIS FRP and aerosol optical depth (AOD) measurements. Further work had resulted in a first draft of a 1 1 resolution map of these coefficients. This poster will present the work done to refine this algorithm toward the first production of global smoke emission coefficients. Main updates in the algorithm include: 1) inclusion of wind vectors to help refine several parameters, 2) defining new methods for calculating the fire-emitted AOD fractions, and 3) calculating smoke emission rates on a per-pixel basis and aggregating to grid cells instead of doing so later on in the process. In addition to a presentation of the methodology used to derive this product, maps displaying preliminary results as well as an outline of the future application of such a product into specific research opportunities will be shown.