ESR investigation of photodamage to zinc oxide powders
Iron cyanide surface additives effect on photodamage to ZnO powder, using ESR method
Sancier, K. M.↗
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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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Severe weather, sea state, and selected climatologies
With the development of aerospace launch vehicles which are to be recovered by flying back to the earth's surface, additional climatic data are needed on specific landing sites. A short discussion is presented that includes tornadoes, hurricanes, tropical storms and effects of sea states.
Brown, S. C.↗
Doppler radar study of a warm frontal region
The paper presents a case study of the structure of a warm frontal region as deduced from Doppler radar observations. The precipitation occurring ahead of the surface warm front was banded. The dominant precipitation bands were oriented transverse to the mid-level winds, and they were spaced 110 km apart. It is suggested that these bands were formed by highly organized vertical circulations in a 2.5 km thick layer just above the warm frontal zone. The precipitation bands extended from this layer down to the surface. Near the surface additional circulations were produced by pressure perturbations resulting from cooling associated with melting snow. Some diagnostic calculations of ageostrophic winds, frontogenesis and vorticity production are presented. The frontogenesis calculation gives approximately a 2-4 h doubling time of the horizontal potential temperature gradient associated with the warm front, at mid-levels. The highly organized band-associated circulations suggest the importance of their inclusion in diagnostic calculations.
Heymsfield, G. M.↗
The Venus Orbiting Imaging Radar /VOIR/ mission
The VOIR mission will be devoted to obtaining synthetic aperture radar images of at least 70% of the Venus surface at resolutions of 600 m/line pair or better. High-resolution spot coverage, nested within the low-resolution data, will be obtained for up to 1% of the surface. Additional investigations will examine the shape and gravitational field of the planet, the character of its interior, the composition and dynamics of its atmosphere, and its interaction with the solar wind. This paper describes the VOIR mission as it is presently planned, and shows how the design of the spacecraft and the mission is responsive to the project science requirements as well as other programmatic constraints. In addition, several of the tradeoffs associated with the evolution of the present VOIR spacecraft and mission plan are reviewed.
Gardner, J. A.↗
Acoustic flight testing of advanced design propellers on a JetStar aircraft
Advanced turboprop-powered aircraft have the potential to reduce fuel consumption by 15 to 30 percent as compared with an equivalent technology turbofan-powered aircraft. An important obstacle to the use of advanced design propellers is the cabin noise generated at Mach numbers up to .8 and at altitudes up to 35,000 feet. As part of the NASA Aircraft Energy Efficiency Program, the near-field acoustic characteristics on a series of advanced design propellers are investigated. Currently, Dryden Flight Research Center is flight testing a series of propellers on a JetStar airplane. The propellers used in the flight test were previously tested in wind tunnels at the Lewis Research Center. Data are presented showing the narrow band spectra, acoustic wave form, and acoustic contours on the fuselage surface. Additional flights with the SR-3 propeller and other advanced propellers are planned in the future.
Lasagna, P.↗
Estimation of vegetation cover at subpixel resolution using LANDSAT data
The present report summarizes the various approaches relevant to estimating canopy cover at subpixel resolution. The approaches are based on physical models of radiative transfer in non-homogeneous canopies and on empirical methods. The effects of vegetation shadows and topography are examined. Simple versions of the model are tested, using the Taos, New Mexico Study Area database. Emphasis has been placed on using relatively simple models requiring only one or two bands. Although most methods require some degree of ground truth, a two-band method is investigated whereby the percent cover can be estimated without ground truth by examining the limits of the data space. Future work is proposed which will incorporate additional surface parameters into the canopy cover algorithm, such as topography, leaf area, or shadows. The method involves deriving a probability density function for the percent canopy cover based on the joint probability density function of the observed radiances.
Jasinski, Michael F.↗
A new boundary element formulation for two- and three-dimensional thermoelasticity using particular integrals
New two- and three-dimensional BEM formulations are developed for steady-state and transient uncoupled thermoelasticity. These new procedures differ from previous work in that additional surface of volume integration is not required to incorporate thermal loads in the analysis. Instead, thermal body forces are introduced in the BEM system via particular integrals. The present formulation is implemented in a general-purpose multiregion system, and examples are presented to demonstrate the accuracy and versatility of the method.
Henry, Donald P., Jr.↗
The effects of deuterium on static posture control
A significant operational problem impacting upon the Space Shuttle program involves the astronaut's ability to safely egress from the Orbiter during an emergency situation. Following space flight, astronauts display significant movement problems. One variable which may contribute to increased movement ataxia is deuterium (D2O). Deuterium is present in low levels within the Orbiter's water supply but may accumulate to significant physiological levels during lengthy missions. Deuterium was linked to a number of negative physiological responses, including motion sickness, decreased metabolism, and slowing of neural conduction velocity. The effects of D2O on static postural control in response to a range of dosage levels were investigated. Nine sugjects were divided into three groups of three subjects each. The groups were divided into a low, medium, and a high D2O dosage group. The subjects static posture was assessed with the use of the EquiTest systems, a commercially available postural control evaluation system featuring movable force plates and a visual surround that can be servoed to the subject's sway. In addition to the force plate information, data about the degree of subject sway about the hips and shoulders was obtained. Additionally, surface electromyographic (EMG) data from the selected lower limb muscles were collected along with saliva samples used to determine the amount of deuterium enrichment following D2O ingestion. Two baseline testing sessions were performed using the EquiTest testing protocol prior to ingestion of the D2O. Thirty minutes after dosing, subjects again performed the tests. Two more post-dosing tests were run with an interest interval of one hour. Preliminary data anlaysis indicates that only subjects in the igh dose group displayed any significant static postural problems. Future analyses of the sway and EMG is expected to reveal significant variations in the subject's postural control strategy following D2O dosing. While functionally significant static postural problems were not commonly observed, subjects in both the medium and high dosage groups displayed significant, and in some cases, severe voluntary movement problems.
Layne, Charles S.↗
Drag reduction in nature
Recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design. Consideration is given to form drag reduction (turbulent flow, vortex generation, mass transfer, and adaptations for body-intersection regions), skin-friction drag reduction (polymers, surfactants, and bubbles as surface 'additives'), reduction of the drag due to lift, drag-reduction studies on porpoises, and drag-reducing animal behavior (e.g., leaping out of the water by porpoises). The need for further research is stressed.
Bushnell, D. M.↗
A time-dependent incompressible viscous BEM for moderate Reynolds numbers
The boundary element method is applied to transient viscous incompressible flow. The time-domain formulation allows a boundary-only solution for linear Stokes flow. For higher speed flows in which the nonlinear convective effects cannot be ignored, a volume integral must be retained. However, the introduction of reference velocities often limits the nonlinear region to the vicinity of obstacles or boundary surfaces. Additionally, the volume terms are rewritten to eliminate the need for the calculation of velocity gradients. A general purpose numerical implementation of this new formulation then produces a very attractive tool for engineering analysis. This implementation includes a Newton-Raphson algorithm, permitting accurate solutions up to the moderate Reynolds number range. Several numerical examples are provided to validate the present approach.
Dargush, G. F.↗
The chemistry of dense interstellar clouds
The basic theme of this program is the study of molecular complexity and evolution in interstellar and circumstellar clouds incorporating the biogenic elements. Recent results include the identification of a new astronomical carbon-chain molecule, C4Si. This species was detected in the envelope expelled from the evolved star IRC+10216 in observations at the Nobeyama Radio Observatory in Japan. C4Si is the carrier of six unidentified lines which had previously been observed. This detection reveals the existence of a new series of carbon-chain molecules, C sub n Si (n equals 1, 2, 4). Such molecules may well be formed from the reaction of Si(+) with acetylene and acetylene derivatives. Other recent research has concentrated on the chemical composition of the cold, dark interstellar clouds, the nearest dense molecular clouds to the solar system. Such regions have very low kinetic temperatures, on the order of 10 K, and are known to be formation sites for solar-type stars. We have recently identified for the first time in such regions the species of H2S, NO, HCOOH (formic acid). The H2S abundance appears to exceed that predicted by gas-phase models of ion-molecule chemistry, perhaps suggesting the importance of synthesis on grain surfaces. Additional observations in dark clouds have studied the ratio of ortho- to para-thioformaldehyde. Since this ratio is expected to be unaffected by both radiative and ordinary collisional processes in the cloud, it may well reflect the formation conditions for this molecule. The ratio is observed to depart from that expected under conditions of chemical equilibrium at formation, perhaps reflecting efficient interchange between cold dust grains in the gas phase.
Irvine, W. M.↗
A new composite electrode architecture for energy storage devices
The research objective is to determine how the electrode microstructure (architecture) affect the performance of the nickel hydroxide electrochemical system. It was found that microstructure and additional surface area makes a difference. The best architectures are the FIBREX/nickel and nickel fiber composite electrodes. The conditioning time for full utilization was greatly reduced. The accelerated increase in capacity vs. cycling appears to be a good indicator of the condition of the electrode/active material microstructure and morphology. Conformal deposition of the active material may be indicated and important. Also higher utilizations were obtained; greater than 80 pct. after less than 5 cycles and greater than 300 pct. after more than 5 cycles using nickel fiber composite electrode assuming a 1 electron transfer per equivalent.
Ferro, Richard E.↗
Electromagnetic scattering from an inhomogeneous object by ray tracing
A 'shooting and bouncing ray' (SBR) formulation is presented for treating the electromagnetic scattering from electrically large, inhomogeneous objects. A dense grid of rays representing the incident plane wave is shot toward the inhomogeneous object. At the scatterer boundary, reflected rays and refracted rays are generated due to discontinuity of the medium parameters. The trajectory, amplitude, phase and polarization of the rays inside the inhomogeneous object are traced based on geometrical optics. Whenever the rays cross the scatterer surface, additional reflected/refracted rays are generated and are tracked. This process is repeated until the intensities of the refracted/reflected rays become negligible. The contributions of the exiting rays to the total scattered field are calculated by using the equivalence principle in conjunction with a ray-tube integration scheme. The ray formulation is applied to calculate the backscattering from cylinders and spheres and good agreement with the exact series solutions is observed in the high frequency range. In addition, the backscattering mechanisms in penetrable objects are interpreted in terms of simple ray pictures.
Kim, Hyeongdong↗
Evaluation of Equilibrium Turbulence for a Hypersonic Boundary Layer at Nonadiabatic Wall Conditions
This paper presents an experimental study to characterize the naturally developing compressible turbulent boundary layer produced along a flat plate measuring 9.7 feet long in the NASA Langley 8-Foot High Temperature Tunnel and to determine the test conditions necessary to achieve equilibrium turbulence. The measurements consist of pitot pressure, static pressure, and total temperature distributions in the boundary layer. In addition, surface measurements consisting of heat transfer and pressure distributions were obtained. The tests were conducted at a nominal free-stream Mach number of 6.5, total temperatures of 2700 and 3300 R, and angles of attack of 5 and 13 degrees. The corresponding nominal boundary-layer edge Mach numbers were 6.2 and 5.0. The nominal ratios of adiabatic wall temperature to cold wall temperature were 4.4 and 5.4 and the momentum thickness Reynolds numbers at the boundary layer probe locations ranged from 400 to 7800. The results of this study indicate that momentum thickness Reynolds numbers of at least 4000 are required to obtain an equilibrium turbulent boundary layer in the Langley 8-Foot High Temperature Tunnel. This evaluation is based primarily on the behavior of shape factors inferred from the boundary-layer measurements.
Albertson, Cindy W.↗
The three-dimensional flow past a rapidly rotating circular cylinder
The high Reynolds number (Re) flow past a rapidly rotating circular cylinder is investigated. The rotation rate of the cylinder is allowed to vary (slightly) along the axis of the cylinder, thereby provoking three-dimensional flow disturbances, which are shown to involve relatively massive (O(Re)) velocity perturbations to the flow away from the cylinder surface. Additionally, three integral conditions, analogous to the single condition determined in two dimensions by Batchelor, are derived, based on the condition of periodicity in the azimuthal direction.
Denier, James P.↗
Fluvial valleys in the heavily cratered terrains of Mars: Evidence for paleoclimatic change?
Whether the formation of the Martian valley networks provides unequivocal evidence for drastically different climatic conditions remains debatable. Recent theoretical climate modeling precludes the existence of a temperate climate early in Mars' geological history. An alternative hypothesis suggests that Mars had a globally higher heat flow early in its geological history, bringing water tables to within 350 m of the surface. While a globally higher heat flow would initiate ground water circulation at depth, the valley networks probably required water tables to be even closer to the surface. Additionally, it was previously reported that the clustered distribution of the valley networks within terrain types, particularly in the heavily cratered highlands, suggests regional hydrological processes were important. The case for localized hydrothermal systems is summarized and estimates of both erosion volumes and of the implied water volumes for several Martian valley systems are presented.
Gulick, V. C.↗
Backward-facing step measurements at low Reynolds number, Re(sub h)=5000
An experimental study of the flow over a backward-facing step at low Reynolds number was performed for the purpose of validating a direct numerical simulation (DNS) which was performed by the Stanford/NASA Center for Turbulence Research. Previous experimental data on back step flows were conducted at Reynolds numbers and/or expansion ratios which were significantly different from that of the DNS. The geometry of the experiment and the simulation were duplicated precisely, in an effort to perform a rigorous validation of the DNS. The Reynolds number used in the DNS was Re(sub h)=5100 based on step height, h. This was the maximum possible Reynolds number that could be economically simulated. The boundary layer thickness, d, was approximately 1.0 h in the simulation and the expansion ratio was 1.2. The Reynolds number based on the momentum thickness, Re(sub theta), upstream of the step was 610. All of these parameters were matched experimentally. Experimental results are presented in the form of tables, graphs and a floppy disk (for easy access to the data). An LDV instrument was used to measure mean velocity components and three Reynolds stresses components. In addition, surface pressure and skin friction coefficients were measured. LDV measurements were acquired in a measuring domain which included the recirculating flow region.
Jovic, Srba↗
Photodeposition of amorphous polydiacetylene films from monomer solutions onto transparent substrates
Polydiacetylenes are a very promising class of polymers for both photonic and electronic applications because of their highly conjugated structures. For these applications, high-quality thin polydiacetylene films are required. We have discovered a novel technique for obtaining such films of a polydiacetylene derivative of 2-methyl-4-nitroaniline using photodeposition from monomer solutions onto UV transparent substrates. This heretofore unreported process yields amorphous polydiacetylene films with thicknesses on the order of I micron that have optical quality superior to that of films grown by standard crystal growth techniques. Furthermore, these films exhibit good third-order nonlinear optical susceptibilities; degenerate four-wave mixing experiments give x(3) values on the order of 10(exp -8) - 10(exp -7) esu. We have conducted masking experiments which demonstrate that photodeposition occurs only where the substrate is directly irradiated, clearly indicating that the reaction occurs at the surface. Additionally, we have also been able to carry out photodeposition using lasers to form thin polymer circuits. In this work, we discuss the photodeposition of polydiacetylene thin films from solution, perform chemical characterization of these films, investigate the role of the substrate, speculate on the mechanism of the reaction, and make a preliminary determination of the third-order optical nonlinearity of the films. This simple, straightforward technique may ultimately make feasible the production of polydiacetylene thin films for technological applications.
Paley, M. S.↗