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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 505 records · Page 28
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NASA NTRS1987

Properties of a large-scale interplanetary loop structure as deduced from low-energy proton anisotropy and magnetic field measurements

Correlated particle and magnetic field measurements by the ISEE 3 spacecraft are presented for the loop structure behind the interplanetary traveling shock event of Nov. 12, 1978. Following the passage of the turbulent shock region, strong bidirectional streaming of low-energy protons is observed for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magnetic field, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, a value of 3 AU is derived for the mean free path during the passage of the closed loop. It is inferred from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.

Tranquille, C.↗
NASA NTRS1987

Atmospheric optical depth effects on angular anisotropy of plant canopy reflectance

The effects of varying atmospheric aerosol optical depth on the bidirectional reflectance distribution of vegetation canopies is investigated. The reflectance distributions of two pasture grass canopies and one soya bean canopy under different sky irradiance distributions were measured, and the data were analyzed in the visible and IR spectral bands. It is observed that, for the pasture grass canopies, the change in reflectance is due to the percentage of shadowed area viewed by the sensor, and for the soya bean, the specular reflection effect and increased diffuse irradiance penetration into the canopy cause reflectance changes. It is detected that the reflectivity for the soya bean canopy on a hazy day is lower than on a clear day; however, the opposite change is observed for the pasture grass. It is also detected that the normalized difference vegetation index values differ under clear and hazy conditions for the same vegetation canopy conditions.

Deering, Donald W.↗
NASA NTRS1987

A survey of the cosmic ray diurnal variation during 1973-1979. I - Persistence of solar diurnal variation. II - Application of diffusion-convection model to diurnal anisotropy data

An analysis of data obtained with the vertical underground muon telescope at Embudo, NM shows that the solar diurnal variation in cosmic ray intensity is a persistent phenomenon over the 1973-1979 period. Assuming that the daily fluctuations in the amplitude and phase of the diurnal variation are random perturbations about the mean vector, the relative magnitude of the random component is determined. In the second part, the Diffusion-Convection model of cosmic ray transport is applied to high rigidity particles detected at the earth in order to deduce the behavior of the heliospheric transport parameters between 1973 and 1979. It is suggested that the diurnal variation observed at Embudo during 1979 may require a contribution from the charged particle drifts.

Riker, J. F.↗
NASA NTRS1988

Acousto-ultrasonics as a monitor of material anisotropy

This paper discusses experimental results obtained by performing the acousto-ultrasonic (AU) method at various azimuthal angles on the surface of fiber-reinforced composite plates. The use of an IBM-PC/data-acquisition board to obtain a digitized AU signal to be analyzed by specially developed software is described. An introduction is given to the use of AU parameters to quantify information evidenced in amplitude/frequency plots. A description of how the parameters are obtained by calculating various spectral moments and the area under particular ranges of the spectral density curve is presented. Results are given from voltage/time plots, amplitude/frequency plots, and plots showing the variation of calculated AU parameters with azimuthal angle. Finally, how the variation of AU parameters with azimuthal angle may be related to variation in material properties with azimuthal angle is discussed.

Duke, J. C., Jr.↗
NASA NTRS1988

Gamma-ray spectroscopic tests for the anisotropy of accelerated particles in solar flares

The profiles of 0.429 and 0.478 MeV gamma-ray lines from Be-7 and Li-7 (produced by interactions of flare-accelerated alpha particles with ambient He in the solar atmosphere) and of the 4.438 MeV line from C-12 (produced by inelastic scattering of C-12 by accelerated protons) depend on the angular distribution of the interacting accelerated particles. The line profiles resulting from various assumed accelerated-particle angular distributions are calculated and it is shown that it will be possible to distinguish among them using observations of gamma-ray spectra from solar flares obtained with high resolution detectors.

Murphy, R. J.↗
NASA NTRS1988

Origin and anisotropy of the cosmic submillimeter background

Some cosmological implications of the recently discovered submillimeter background (SMB) are discussed. Opacity and isotropy arguments show that if the background is due to dust emission it must originate at a high redshift z greater than about 10. Isotropy measurements are used to constrain the amplitude of dust optical-depth fluctuations and hence the scale of dust inhomogeneity. The observed flux, the inferred high z and high opacity imply that on small scales the mock gravitational instability driven by radiation pressure may have dominated gravitational effects.

Hogan, C. J.↗
NASA NTRS1989

The COBE cosmic 3 K anisotropy experiment: A gravity wave and cosmic string probe

Among the experiments to be carried into orbit next year, by the COBE satellite, are differential microwave radiometers. They will make sensitive all-sky maps of the temperature of the cosmic microwave background radiation at three frequencies, giving dipole, quadrupole, and higher order multipole measurements of the background radiation. The experiment will either detect, or place significant constraints on, the existence of cosmic strings and long wavelength gravity waves.

Bennett, Charles L.↗
NASA NTRS1990

Calculation of polarization and anisotropy of resonant and fluorescent scattering

Formulas are derived for the swift calculation of the angular intensity distribution and the degree of polarization associated with the resonant and fluorescent scattering of radiation by atoms which occurs in the rarefied upper atmospheres of planets during sunlit airglow phenomena. Attention is given to spectral lines with hyperfine structure, which are indicative of nuclear spin processes. The method employed involves summations over Zeeman components, allowing an evaluation of polarization through the addition of underlying simple resonant and fluorescent scattering channels.

Chamberlain, Joseph W.↗
NASA NTRS1990

Importance of anisotropy on design of compression-loaded composite corrugated panels

An investigation is conducted of the importance of anisotropic terms in the design of composite corrugated panels, for a range of axial compressive load intensities. The two panel configurations treated were panels with tailored laminates and panels with a continuous laminate; both are of interest to aircraft designers and prone to anisotropic effects which are of as-yet undetermined extent. The importance of the anisotropic terms is measured by the difference between the design load and the buckling load obtained from the ultimate structural analysis.

Gurdal, Zafer↗
NASA NTRS1990

The effects of transverse shearing and anisotropy on vibration frequencies of laminated cylinders

The natural vibration frequencies of orthotropic and anisotropic, simply supported right circular cylinders are predicted using a theory which takes into account higher-order transverse shear deformation effects. A comparison between results based on first-order transverse shear deformation theory and the higher-order theory indicates that an additional allowance for transverse shear deformation has a negligible effect on the predicted natural vibration frequencies associated with long wavelengths, but significantly reduces the natural vibration frequencies associated with short wavelengths. Results of a parametric study of ply orientation for two classes of laminates indicates that while stacking sequence affects natural vibration frequencies, cylinder geometry and mode shape are more important in accurately predicting transverse shear deformation effects. Transverse shearing effects are less important in predicting natural vibration frequencies associated with long wavelength than in predicting axial compressive buckling loads.

Jegley, D. C.↗
NASA NTRS1990

Out-of-ecliptic Lyman-alpha observations with Pioneer-Venus - Solar wind anisotropy degree in 1986

Measurements of interplanetary Lyman-alpha were made over a wide range of ecliptic latitudes by the Pioneer Venus Orbiter Ultraviolet Spectrometer during the tracking of Halley's comet from December 1985 to March 1986. By comparisons with models of the interstellar/interplanetary hydrogen wind, the total solar ionization lifetime at 1 AU is found to be 1.25-1.5 x 10 to the 6th sec, and its variation with solar latitude is found to be 30 + or - 5 percent. The solar wind mass flux variation with solar latitude is found to be very weak (0 + or - 10 percent). These values are appropriate to solar minimum. Comparison of the latitudinal variation with earlier measurements from 1973 to 1977 suggest that the asphericity of the solar wind may increase as solar activity passes through its minimum.

Lallement, R.↗
NASA NTRS1991

First results of the COBE satellite measurement of the anisotropy of the cosmic microwave background radiation

The concept and operation of the Differential Microwave Radiometers (DMR) instrument aboard NASA's Cosmic Background Explorer satellite are reviewed, with emphasis on the software identification and subtraction of potential systematic effects. Preliminary results obtained from the first six months of DMR data are presented, and implications for cosmology are discussed.

Smoot, G. F.↗
NASA NTRS1991

Temperature dependence of the anisotropy in magnetic relaxation in YBa2Cu3O(7-x) thin films

The relaxation of diamagnetic magnetization in the c-axis-aligned YBa2Cu3O(7-x) thin film is studied as a function of orientation and temperature in the range of 5-50 K at H = 0.2 T. The magnetization M(T,H) in the orientations H parallel to c and H perpendicular to c and at all the temperatures is found to decrease logarithmically with time t. The activation energy for the movement of flux lines U is found to be 30-110 meV in the range 5-50 K. For H parallel c, U increases continuously with T, whereas for H perpendicular c, U has two apparent maxima: at T = 10 K and T greater than 50 K. These results are discussed in terms of the thermally activated flux motion model.

Vitta, Satish↗
NASA NTRS1991

Anisotropy of thermal infrared exitance above and within plant canopies

Any significant angular dependence of the emitted long wave radiation could result in errors in remotely estimated energy budgets or evapotranspiration. Empirical data and thermal infrared radiation models are reviewed in reference to anisotropic emissions from the plant canopy. The biometeorological aspects of linking longwave models with plant canopy energy budgets and micrometeorology are discussed. A new soil plant atmosphere model applied to anisotropic longwave emissions from a canopy is presented. Time variation of thermal infrared emission measurements is discussed.

Pawu, Kyaw Tha↗
NASA NTRS1991

Chaotic inflationary universe and the anisotropy of the large-scale structure

It has been realized that the inflationary universe is in fact chaotic, that globally it is strongly inhomogeneous, and that the inflation in the universe as a whole is eternal. In such a picture the region available to modern observations is just a tiny part of the universe, in which inflation finished about 10(exp 10) years ago. In spite of the great popularity of the chaotic inflationary universe models, it is usually taken for granted that their specific features (such as strong global inhomogeneity of the universe) can hardly lead to any observable consequences. The argument is that all that is seen is just a tiny part of the universe, a region about 10(exp 28) cm, and the typical scales of considerable inhomogeneities are much greater than this size. In contrast to this opinion, an attempt is made to show that such observable consequences can really exist. The phenomenon closely connected with the origin of structure (galaxies, clusters, etc.) in the observable region is discussed. The main idea considered is the vacuum fluctuations evolution on the inhomogeneous background.

Chibisov, G. V.↗
NASA NTRS1991

Local anisotropy in strained turbulence at high Reynolds numbers

It is shown that the hypothesis of local isotropy is implausible in the presence of significant mean rates of strain. In fact, it appears that in uniform shear flow near equilibrium, local isotropy can never constitute a systematic approximation, even in the limit of infinite Reynolds number. An estimate of the level of mean strain rate for which local isotropy is formally a good approximation is provided.

Durbin, P. A.↗
NASA NTRS1989

South Pole studies of the anisotropy of the cosmic background radiation at one degree

A system is developed for making measurements of spatial fluctuations in the Cosmic Microwave Background at the 3-mm wavelength, on an angular scale of .5 to 5 degrees. The system includes a telescope with a Gaussian beam with an FWHM of 20 to 50 arcmin, an SIS coherent receiver operating around 90 GHz, and for balloon flights, a pointing system capable of 1 arc-minute RMS stabilization. Results are reported from ground-based measurements made from the South Pole station during December, 1988.

Meinhold, Peter R.↗