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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 361 records · Page 20
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NASA NTRS1972

Kinetic theory of a two-dimensional magnetized plasma. II - Balescu-Lenard limit.

The kinetic theory of a two-dimensional one-species plasma in a uniform dc magnetic field is investigated in the small plasma parameter limit. The plasma consists of charged rods interacting through the logarithmic Coulomb potential. Vahala and Montgomery earlier (1971) derived a Fokker-Planck equation for this system, but it contained a divergent integral, which had to be cut off on physical grounds. This cutoff is compared to the standard cutoff introduced in the two-dimensional unmagnetized Fokker-Planck equation. In the small plasma parameter limit, it is shown that the Balescu-Lenard collision term is zero in the long time average limit if only two-body interactions are considered. The energy transfer from a test particle to an equilibrium plasma is discussed and is also shown to be zero in the long time average limit. This supports the unexpected result of zero Balescu-Lenard collision term.

Vahala, G.↗
NASA NTRS1973

Low-energy electron experiment for Atmosphere Explorer-C and -D.

The low-energy electron experiment will provide differential measurements of the energy influx and angular distributions of electrons and protons on the Atmosphere Explorer-C and -D missions. The detectors consist of cylindrical electrostatic analyzers for species and energy selection and Spiraltron electron multipliers as particle sensors. The C version will contain three detectors, two measuring electrons and protons from 0.2 to 25 keV in 16 logarithmically spaced steps and one measuring 5 keV electrons continuously. Angular distributions will be acquired utilizing the spin of the spacecraft. The D version will contain 19 detectors, one proton-stepped energy analyzer, and two electron-stepped energy analyzers at two different angles, again over the energy range 0.2 to 25 keV.

Hoffman, R. A.↗
NASA NTRS1973

Observations of collisionless drift waves.

Velocity distribution functions of both the electron and the proton component of the magnetospheric plasma are measured in 62 logarithmically spaced steps from 50 eV to 50 keV by an instrument carried upon the ATS-5 spacecraft in circular synchronous orbit (6.6 earth radii). Oscillations which appear to be collisionless drift waves having periods of several minutes or longer are found in this data. Linearized wave theory can be used to predict the theoretical perturbation distribution function in terms of the perturbing fields and the equilibrium distribution function. The functional dependence of the theoretical perturbation distribution function upon particle energy can then be compared with that of the measured perturbation.

Laquey, R. E.↗
NASA NTRS1972

Development of soil on the lunar surface.

Discussion of the dynamic processes involved in the evolution of the lunar soil. Size, shape, and modal analyses of soil returned by Apollo 11, 12, 14, and 15, and Luna 16 indicate that the two most important dynamic processes resulting from meteorite impact are vitrification and comminution of the detrital material. The effects of the two processes are mutually opposed. As the glass content of the soil increases over an extended period of time, the statistical parameters of the mature soil tend to stabilize. Comminution probably plays a dominant role early in the development of the soil by reducing the median grain size and producing a logarithmic-normal grain-size distribution. The evolution of the soil does not necessarily progress in a regular manner. Both introduction of freshly comminuted bedrock material by small impact events, as well as local topographic effects, influence the development of the soil and reduce its maturity.

Lindsay, J. F.↗
NASA NTRS1973

Evaporation rate and vapor pressure of selected polymeric lubricating oils.

A recently developed ultrahigh-vacuum quartz spring mass sorption microbalance has been utilized to measure the evaporation rates of several low-volatility polymeric lubricating oils at various temperatures. The evaporation rates are used to calculate the vapor pressures by the Langmuir equation. A method is presented to accurately estimate extended temperature range evaporation rate and vapor pressure data for polymeric oils, incorporating appropriate corrections for the increases in molecular weight and the change in volatility of the progressively evaporating polymer fractions. The logarithms of the calculated data appear to follow linear relationships within the test temperature ranges, when plotted versus 1000/T. These functions and the observed effusion characteristics of the fluids on progressive volatilization are useful in estimating evaporation rate and vapor pressure changes on evaporative depletion.

Gardos, M. N.↗
NASA NTRS1973

Scale dependence of the 200-mb divergence inferred from EOLE data.

The EOLE experiment with 480 constant-volume balloons distributed over the Southern Hemisphere approximately at the 200-mb level, has provided a unique, highly accurate set of tracer trajectories in the general westerly circulation. The trajectories of neighboring balloons are analyzed to estimate the horizontal divergence from the Lagrangian derivative of the area of one cluster. The variance of the divergence estimates results from two almost comparable effects: the true divergence of the horizontal flow and eddy diffusion due to small-scale, two-dimensional turbulence. Taking this into account, the rms divergence is found to be of the order of 0.00001 per sec and decreases logarithmically with cluster size. This scale dependence is shown to be consistent with the quasi-geostrophic turbulence model of the general circulation in midlatitudes.

Morel, P.↗
NASA NTRS1973

Shear strength of lunar soil from Oceanus Procellarum.

Soil from the scoop of Surveyor 3, returned to earth by Apollo 12 astronauts, has been tested in a miniature shear box at five bulk densities, from 0.99 to 1.87 g/cu cm. Cohesion increased with bulk density from .03 to .3 N/sq cm; internal friction angle increased from 13 to 56 deg. Shear stress vs normal stress data fit a logarithmic relationship better than a linear one, at normal stresses of .003 to 3 N/sq cm. Results of these tests, in air, show no systematic differences from those for tests made elsewhere in vacuum and nitrogen. Results agree with those obtained in remotely controlled lunar surface operations with Surveyor 3 and other spacecraft provided that the bulk density was slightly underestimated for the on-surface measurements.

Jaffe, L. D.↗
NASA NTRS1973

Production of lunar fragmental material by meteoroid impact.

The rate of production of new fragmental lunar surface material is derived theoretically on the hypothesis that such material is excavated from a bedrock layer by meteoroid impacts. An overlaying regolith effectively shields the bedrock layer from small impacts, reducing the production rate of centimeter-sized and smaller blocks by a large factor. Logarithmic production rate curves for centimeter to motor-sized blocks are nonlinear for any regolith from centimeters to tens of meters in thickness, with small blocks relatively much less frequent for thicker (older) regoliths, suggesting the possibility of a statistical reverse bedding. Modest variations in the exponents of scaling laws for crater depth-diameter ratio and maximum block-diameter to crater diameter ratio are shown to have significant effects on the production rates. The production rate increases slowly with increasing size of the largest crater affecting the region.

Marcus, A. H.↗
NASA NTRS1973

Modeling of turbulent transport in the surface layer

The turbulence equations as written by Donaldson using the method of invariant modeling have been applied to the following limiting cases of the surface or constant flux layer of the planetary boundary layer: (1) Neutrally stable; (2) stable (above influence of surface roughness); (3) nearly neutrally stable; and (4) very unstable (free convection). For the neutrally stable case, the equations are shown to admit as a solution the familiar logarithmic profile. By use of this result, boundary conditions suitable for the surface layer are defined and are simple to apply to rough surfaces.

Smith, G. L.↗
NASA NTRS1973

Auger electron spectroscopy study of initial stages of oxidation in a copper - 19.6-atomic-percent-aluminum alloy

Auger electron spectroscopy was used to examine the initial stages of oxidation of a polycrystalline copper - 19.6 a/o-aluminum alloy. The growth of the 55-eV aluminum oxide peak and the decay of the 59-, 62-, and 937-eV copper peaks were examined as functions of temperature, exposure, and pressure. Pressures ranged from 1x10 to the minus 7th power to 0.0005 torr of O2. Temperatures ranged from room temperature to 700 C. A completely aluminum oxide surface layer was obtained in all cases. Complete disappearance of the underlying 937-eV copper peak was obtained by heating at 700 C in O2 at 0.0005 torr for 1 hr. Temperature studies indicated that thermally activated diffusion was important to the oxidation studies. The initial stages of oxidation followed a logarithmic growth curve.

Ferrante, J.↗
NASA NTRS1972

Unsteady viscous effects in the flow over an oscillating surface

A theoretical model for the interaction of a turbulent boundary layer with an oscillating wavy surface over which a fluid is flowing is developed, with an application to wind-driven water waves and to panel flutter in low supersonic flow. A systematic methodology is developed to obtain the surface pressure distribution by considering separately the effects on the perturbed flow of a mean shear velocity profile, viscous stresses, the turbulent Reynolds stresses, compressibility, and three-dimensionality. The inviscid theory is applied to the wind-water wave problem by specializing to traveling-wave disturbances, and the pressure magnitude and phase shift as a function of the wave phase speed are computed for a logarithmic mean velocity profile and compared with inviscid theory and experiment. The results agree with experimental evidence for the stabilization of the panel motion due to the influence of the unsteady boundary layer.

Lerner, J. I.↗
NASA NTRS1973

Temperature, illumination and fluence dependence of current and voltage in electron irradiated solar cells

Emperical equations have been derived from measurements of solar cell photovoltaic characteristics relating light generated current, IL, and open circuit voltage, VO, to cell temperature, T, intensity of illumination, W, and 1 Mev electron fluence, phi both 2 ohm-cm and 10 ohm-cm cells were tested. The temperature dependency of IL is similar for both resistivities at 140mw/sq cm; at high temperature the coefficient varies with fluence as phi 0.18, while at low temperatures the coefficient is relatively independent of fluence. Fluence dependent degration causes a decrease in IL at a rate proportional to phi 0.153 for both resistivities. At all intensities other than 560 mw/sq cm, a linear dependence of IL on illumination was found. The temperature coefficient of voltage was, to a good approximation, independent of both temperature and illumination for both resistivities. Illumination dependence of VOC was logarithmic, while the decrease with fluence of VOC varied as phi 0.25 for both resistivities.

Obenschain, A. F.↗
NASA NTRS1974

Curve fits of predicted inviscid stagnation-point radiative heating rates, cooling factors, and shock standoff distances for hyperbolic earth entry

Curve-fit formulas are presented for the stagnation-point radiative heating rate, cooling factor, and shock standoff distance for inviscid flow over blunt bodies at conditions corresponding to high-speed earth entry. The data which were curve fitted were calculated by using a technique which utilizes a one-strip integral method and a detailed nongray radiation model to generate a radiatively coupled flow-field solution for air in chemical and local thermodynamic equilibrium. The range of free-stream parameters considered were altitudes from about 55 to 70 km and velocities from about 11 to 16 km.sec. Spherical bodies with nose radii from 30 to 450 cm and elliptical bodies with major-to-minor axis ratios of 2, 4, and 6 were treated. Powerlaw formulas are proposed and a least-squares logarithmic fit is used to evaluate the constants. It is shown that the data can be described in this manner with an average deviation of about 3 percent (or less) and a maximum deviation of about 10 percent (or less). The curve-fit formulas provide an effective and economic means for making preliminary design studies for situations involving high-speed earth entry.

Suttles, J. T.↗
NASA NTRS1974

Report on objective ride quality evaluation

The correlation of absorbed power as an objective ride measure to the subjective evaluation for the bus data was investigated. For some individual bus rides the correlations were poor, but when a sufficient number of rides was used to give reasonable sample base, an excellent correlation was obtained. The following logarithmical function was derived: S = 1.7245 1n (39.6849 AP), where S = one subjective rating of the ride; and AP = the absorbed power in watts. A six-degree-of-freedom method developed for aircraft data was completed. Preliminary correlation of absorbed power with ISO standards further enhances the bus ride and absorbed power correlation numbers since the AP's obtained are of the same order of magnitude for both correlations. While it would then appear that one could just use ISO standards, there is no way to add the effect of three degrees of freedom. The absorbed power provides a method of adding the effects due to the three major directions plus the pitch and roll.

Wambold, J. C.↗
NASA NTRS1973

The Dirichlet problem for the two-dimensional Helmholtz equation for an open boundary

Development of a complete theory of the two-dimensional Dirichlet problem for an open boundary. It is shown that the solution of the Dirichlet problem for an open boundary requires the solution of a Fredholm integral equation of the first kind. Although a Fredholm integral equation of the first kind usually has no solution if the kernel is continuous, owing to the logarithmic singularity of the kernel, the equation in this case is converted to a singular integral equation with a Cauchy kernel. It is proven that the homogeneous adjoint equation of the singular integral equation has no nonzero solution. By virtue of this result, and with the aid of an existence theorem known in the theory of singular integral equations, the existence of solutions of the singular integral equation, and then of the unique solution of the Fredholm integral equation of the first kind is proved.

Hayashi, Y.↗
NASA NTRS1973

Observations from space of the solar corona/inner zodiacal light

Observations, from the Apollo 16 Spacecraft, in lunar orbit, of the total radiance of the K + F corona, from 3 to 55 solar radii are presented and discussed. The logarithmic slope of the K + F coronal radiance, at distances greater than 20 solar radii, is found to be n equals 1.93, slightly less steep than previous determinations. The photometric axis of the radiance is found to be displaced 3 plus or minus 1 deg north of the ecliptic, at distances greater than 20 solar radii, and this displacement is interpreted as an annual variation due to non-coincidence of the ecliptic and the symmetry axis of the zodiacal cloud.

Macqueen, R. M.↗
NASA NTRS1973

Permafrost - Relation between ice content and dielectric losses at 100 K

The dielectric response of permafrost at 100 K and vacuums of around 10 ntorr is analyzed, varying its percent ice content from 1 to 18.6. The distributions obtained correspond to dielectric relaxations of the Cole-Cole type, with maximum losses occurring in the 30- to 600-Hz frequency range. The logarithms of such maxima depend linearly on the permafrost ice content, two regions of linear variation being defined above and below 3.6% ice content. Such relations point out the feasibility of determining ice content in permafrost by electromagnetic means.

Alvarez, R.↗
NASA NTRS1973

Recent advances in elastomer service-life prediction

The mechanical properties of an elastomer, including rupture and its time dependence, are defined uniquely by a tensile property surface in normalized stress-strain-time coordinates. In practice, the property surface is determined from short-time constant strain-rate uniaxial tests. By using the time reduction properties of both temperature and cross-link density, an effective time scale of over ten decades of log time can be covered. Changes in cross-link density, filler content, or swelling do not affect the limits of the property surface when plotted in logarithmic coordinates but merely shift their positions. The shape, however, may be modified in certain cases. The service life of an elastomer in the absence of aging reactions can be estimated from the property surface and expected in-use conditions such as strains (static or dynamic).

Landel, R. F.↗