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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Equivalence of the generalized Lie-Hori method and the method of averaging

In this investigation, a comparison is made of two methods for developing perturbation theories for non-canonical dynamical systems. The methods compared are the generalized Lie-Hori method and the method of averaging. In the comparison presented here, the equivalence of the methods up to the second order in the small parameter is shown. However, the approach used can be extended to demonstrate the equivalence for higher orders. To illustrate the equivalence Duffing's equation, the van der Pol equation and the oscillator with quadratic damping problem are solved using each method.

Ahmed, A. H.↗
NASA NTRS1985

Average Spacing for Rings of Individual Multi-ring Basins Is 2.0(0.5)D

The mathematically regular spacing of the concentric rings of planetary impact basins are examined. It is shown that a constant radial increment of x (sub 0.5) D, where x is about 2.0 and D is ring diameter, separates adjacent statistical groups of rings and arcs of multiring basins on Mars, Mercury, and the Moon. Statistics of spacing for adjacent rings of individual basins on the three planets are presented, and single basins from ring measurements of newly-recognized basins on Mercury and Mars are revised. Analysis of ring rank: ring diameter for adjacent rings of individual basins also yields an average spacing of about 2.0 (sup 0.5) D, specifically (2.01 + or - 0.26) (sup 0.5) D.

Pike, R. J.↗
NASA NTRS1985

Ring-diameter Ratios for Multi-ring Basins Average 2.0(0.5)D

The spacing of the concentric rings of planetary impact basins was studied. It is shown that a radial increment of x (sup 0.5) D, where x is about 2.0 and D = ring diameter, separates both (1) adjacent least-squares groups of rings and arcs of multi-ring basins on Mars, Mercury, and the Moon; and (2) adjacent rings of individual basins on the three planets. Statistics for ratios of ring diameters are presented, the first and most-applied parameter of ring spacing. It is found that ratios excluding rings flanking the main ring also have a mean spacing increment of about 2.0. Ratios including such rings, as for the least-squares groups, and (1) above, have a larger increment, averaging 2.1. The F-test indicates, that these spacings of basin ring locations, and mode of ring formation are controlled by the mechanics of the impact event itself, rather than by crustal properties.

Pike, R. J.↗
NASA NTRS1985

On the possibility of the determining the average mass composition near 10 to the 14th power eV through the solar magnetic field

The discovery of primary ultrahigh energy (UHE) gamma-rays has spawned plans for a new generation of air shower experiments with unprecedented directional resolution. Such accuracy permits observation of a cosmic ray shadow due to the solar disc. Particle trajectory simulations through models of the large scale solar magnetic field were performed. The shadow is apparent above 10 to the 15th power eV for all cosmic ray charges /Z/ 26; at lower energies, trajectories close to the Sun are bent sufficiently for this shadow to be lost. The onset of the shadow is rigidity dependent, and occurs at an energy per nucleus of approx. Z x 10 to the 13th power eV. The possibility of determining the average mass composition near 10 to the 14th power eV from 1 year's observation at a mountain altitude array is investigated.

Lloyd-Evans, J.↗
NASA NTRS1985

When did the average cosmic ray flux increase?

A new 129 to 129 Xe method to obtain cosmic ray exposure ages and to study the average cosmic ray flux on a 10 to the 7th power to 10 to the 8th power year time-scale was developed. The method is based on secondary neutron reactions on Te in troilite and the subsequent decay of 129I, the reaction product to stable 129 Xe. The first measurements of 129 I and 129 Xe in aliquot samples of a Cape York troilite sample are reported.

Nishiizumi, K.↗
NASA NTRS1985

Dependence of the average spatial and energy characteristics of the hadron-lepton cascade on the strong interaction parameters at superhigh energies

A method for calculating the average spatial and energy characteristics of hadron-lepton cascades in the atmosphere is described. The results of calculations for various strong interaction models of primary protons and nuclei are presented. The sensitivity of the experimentally observed extensive air showers (EAS) characteristics to variations of the elementary act parameters is analyzed.

Boyadjian, N. G.↗
NASA NTRS1985

Error reduction in laser remote sensing - Combined effects of cross correlation and signal averaging

A systematic analysis is presented of the extent to which the accuracy of a differential-absorption lidar (DIAL) measurement may be improved by using the combined effects of signal averaging and temporal cross correlation. Previous studies which considered these effects separately are extended by incorporating both effects into a single analytical framework. In addition, experimental results involving lidar returns from a diffusely reflecting target using a dual-CO2 laser DIAL system with both heterodyne and direct detection are presented. These results are shown to be in good agreement with the theoretical analysis and help establish the limits of accuracy achievable under various experimental conditions.

Menyuk, N.↗
NASA NTRS1983

Survey of chondrule average properties in H-, L-, and LL-group chondrites - Are chondrules the same in all unequilibrated ordinary chondrites?

The petrogenetic properties of chondrules in different unequilibrated ordinary chondrites (UOCs) are compared to averaged chondrule-suite values obtained from recent analyses of several H-group, L-group, and LL-group chondrites. The purpose of the study was to develop a data base for future statistical analyses of chondrite characteristics. Mean end-member compositions of olivine (mol percent Fa) and pyroxene (mol percent Fs) were used as indices of the relative degree of 'equilibration' of each chondrule suite. It is found that the bulk chondrule geometric-mean abundances of Na, Mg, and Ni are the same from one UOC to another, and show no major systematic trends related to the H-group, L-group, of LL-group parentage of the host chondrites. The patterns of rare-earth element abundances in the chondrules are also examined, and the results are compared with statistical analyses. It is concluded that multivariate statistical analysis of pooled UOC chondrule data is justified for chondrule bulk compositions, as long as the statistical results are not misinterpreted as the primary petrogenetic features of chondrules.

Gooding, J. L.↗
NASA NTRS1985

Zonally averaged model of dynamics, chemistry and radiation for the atmosphere

A nongeostrophic theory of zonally averaged circulation is formulated using the nonlinear primitive equations on a sphere, taking advantage of the more direct relationship between the mean meridional circulation and diabatic heating rate which is available in isentropic coordinates. Possible differences between results of nongeostrophic theory and the commonly used geostrophic formulation are discussed concerning: (1) the role of eddy forcing of the diabatic circulation, and (2) the nonlinear nearly inviscid limit vs the geostrophic limit. Problems associated with the traditional Rossby number scaling in quasi-geostrophic formulations are pointed out and an alternate, more general scaling based on the smallness of mean meridional to zonal velocities for a rotating planet is suggested. Such a scaling recovers the geostrophic balanced wind relationship for the mean zonal flow but reveals that the mean meridional velocity is in general ageostrophic.

Tung, K. K.↗
NASA NTRS1985

Temperature averaging thermal probe

A thermal probe to average temperature fluctuations over a prolonged period was formed with a temperature sensor embedded inside a solid object of a thermally conducting material. The solid object is held in a position equidistantly spaced apart from the interior surfaces of a closed housing by a mount made of a thermally insulating material. The housing is sealed to trap a vacuum or mass of air inside and thereby prevent transfer of heat directly between the environment outside of the housing and the solid object. Electrical leads couple the temperature sensor with a connector on the outside of the housing. Other solid objects of different sizes and materials may be substituted for the cylindrically-shaped object to vary the time constant of the probe.

Kalil, L. F.↗
NASA NTRS1985

The zonally averaged transport characteristics of the atmosphere as determined by a general circulation model

Two dimensional modeling has become an established technique for the simulation of the global structure of trace constituents. Such models are simpler to formulate and cheaper to operate than three dimensional general circulation models, while avoiding some of the gross simplifications of one dimensional models. Nevertheless, the parameterization of eddy fluxes required in a 2-D model is not a trivial problem. This fact has apparently led some to interpret the shortcomings of existing 2-D models as indicating that the parameterization procedure is wrong in principle. There are grounds to believe that these shortcomings result primarily from incorrect implementations of the predictions of eddy transport theory and that a properly based parameterization may provide a good basis for atmospheric modeling. The existence of these GCM-derived coefficients affords an unprecedented opportunity to test the validity of the flux-gradient parameterization. To this end, a zonally averaged (2-D) model was developed, using these coefficients in the transport parameterization. Results from this model for a number of contrived tracer experiments were compared with the parent GCM. The generally good agreement substantially validates the flus-gradient parameterization, and thus the basic principle of 2-D modeling.

Plumb, R. A.↗
NASA NTRS1985

Development and testing of a simple assimilation technique to derive average wind fields from simulated scatterometer data

A simple algorithm is developed and tested to derive a regularly spaced wind field in a limited area from simulated multiorbit scatterometer data. The data are generated by sampling a time-varying known wind field, the 1000-mb FGGE data, from a simulated scatterometer. A simple assimilation technique is used to derive a regularly spaced (100-km grid) wind field representation of two-day averages from the simulated data. Several test cases are considered, and it is noted that the assimilation technique might be applicable to large-scale ocean or atmospheric models.

Legler, D. M.↗
NASA NTRS1985

An ISEE 3 study of average and substorm conditions in the distant magnetotail

Both average and substorm conditions in the distant magnetotail were investigated using ISEE 3 magnetic field and plasma observations. The diameter of the tail, the strength of the lobe magnetic fields, and their dependence on downstream distance were all found to agree well with the flaring tail models of magnetopause geometry and pressure balance. The gradual filling of the lobes by mantle plasma reported in previous ISEE 3 studies were further investigated, and the results were found to be in qualitative agreement with leaky magnetopause model of Pilipp and Morfill (1978). The variations of plasma parameters with X + or -Y, and AE in the plasma sheet were examined. At all distances, the greatest tailward flow speeds were found to be directly proportional to the embedded southward B(z). THe magnitudes of tailward V(x) and southward B(z) are directly proportional to the level of substorm activity near the earth as measured by the AE index.

Slavin, J. A.↗
NASA NTRS1985

Electron temperature and average density in spherical laser-produced plasmas - Ultraviolet plasma spectroscopy

The average values of the electron temperature Te and the electron density Ne in the corona plasmas of spherically irradiated high-Z targets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 microns) and the frequency-tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15-200 A. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency-tripled laser irradiation, Te = 2600 + or - 600 eV and Ne is greater than 6 x 10 to the 20th/cu cm. This is consistent with a 'flux limit' smaller than 0.1. The estimated values of Te and Ne are lower in the corona plasmas produced using the fundamental (1.06 micron) irradiation.

Goldsmith, S.↗
NASA NTRS1986

A new approximate LU factorization scheme for the Reynolds-averaged Navier-Stokes equations

A new approximate LU factorization scheme is developed to solve the steady state Reynolds-averaged Navier-Stokes (NS) equations. Central differencing is used for both implicit and explicit operator and special care is taken to obtain well-conditioned factors on the implicit side. The scheme is then analyzed and optimized according to a simple linear analysis. It is unconditionally stable for the model hyperbolic equation in both two- and three-dimensions. However, the requirement for well-conditioned factors has essentially limited the effective time step the scheme can achieve. Supersonic and transonic three-dimensinal flows past a hemisphere cylinder are computed to demonstrate the convergence characteristics of the scheme. A good convergence rate is achieved for the inviscid case. Finally, an explicit eigenvector annihilation procedure is adopted successfully to remove the stiffness caused by the fine grid spacing for viscous flows.

Pan, D.↗
NASA NTRS1986

Average power constraints in AlGaAs semiconductor lasers under pulse-position-modulation conditions

In some optical communications systems there are advantages to using low duty-cycle pulsed modulation formats such as pulse-position-modulation. However, because of intrinsic limitations of AlGaAs semiconductor lasers, the average power that they can deliver in a pulsed mode of operation is lower than in a CW mode. The magnitude of this problem and its implications are analyzed in this letter, and one possible solution is mentioned.

Katz, J.↗
NASA NTRS1986

Two-dimensional monthly average ozone balance from limb infrared monitor of the stratosphere and stratospheric and mesospheric sounder data

For many years, atmospheric scientists have been concerned with the balance of ozone production and loss terms in the upper stratosphere. Crutzen and Schmailzl (1983) found that the ozone loss was higher than the ozone production in the upper stratosphere. In the present investigation, previous studies are used as a basis in the conduction of a two-dimensional calculation of the production and loss of ozone. The monthly and zonally averaged loss and production rates for ozone are computed using recent Nimbus 7 satellite measurements of stratospheric constituents and accepted reaction and photodissociation rates. It is found that ozone has a loss rate which is about 40-60 percent higher than the production in the photochemical region.

Jackman, C. H.↗
NASA NTRS1986

Concentrations and uncertainties of stratospheric trace species inferred from limb infrared monitor of the stratosphere data. I - Methodology and application to OH and HO2. II - Monthly averaged OH, HO2, H2O2, and HO2NO2

Difficulties arise in connection with the verification of multidimensional chemical models of the stratosphere. The present study shows that LIMS data, together with a photochemical equilibrium model, may be used to infer concentrations of a variety of zonally averaged trace Ox, OHx, and NOx species over much of the stratosphere. In the lower stratosphere, where the photochemical equilibrium assumption for HOx species breaks down, inferred concentrations should still be accurate to about a factor of 2 for OH and 2.5 for HO2. The algebraic nature of the considered model makes it possible to see easily to the first order the effect of variation of any model input parameter or its uncertainty on the inferred concontration of the HOx species and their uncertainties.

Kaye, J. A.↗