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Results for “SO(N) symmetry”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Low energy, left-right symmetry restoration in SO(N) GUTS

A general n step symmetry breaking pattern of SO(4K+2) down to SU sub C (3)xSU sub L (2)xU sub Y (1), which uses regular subgroups only, does not allow low energy left right symmetry restoration. In these theories, the smallest mass scale at which such restoration is possible is approximately one billion GeV as in the SO(10) case. The unification mass in SO(4K+2) GUTS must be at least as large as that in SU(5). These results assumed standard values of the Weinberg angle and strong coupling constant.

Holman, R.↗
NASA NTRS1992

Collisional broadening of rotational lines in the stimulated Raman pentad Q-branch of CD4

Self- and argon-broadening coefficients are reported for a number of Raman Q-branch transitions in the nu(1) and nu(2) + nu(4) bands of (C-12)D4 at room temperature (296 K). The coefficients display a variation with j and with C exp n (symmetry species A, E, F) that is essentially independent of collision partner and which is similar to the j- and C exp n-dependence found in previous measurements of the IR line-broadening coefficients. The rotationally inelastic collision rates previously measured by Foy et al. (1988) for (C-13)D4 (V4 = 0, 1) in collision with (C-13)D4 or Ar account for only a part of the Raman broadening rate, suggesting possibly significant contributions to the linewidths from efficient V-V transfer or elastic dephasing collisions.

Millot, G.↗
NASA NTRS1991

The formation and evolution of domain walls

Domain walls are sheet-like defects produced when the low energy vacuum has isolated degenerate minima. The researchers' computer code follows the evolution of a scalar field, whose dynamics are determined by its Lagrangian density. The topology of the scalar field determines the evolution of the domain walls. This approach treats both wall dynamics and reconnection. The researchers investigated not only potentials that produce single domain walls, but also potentials that produce a network of walls and strings. These networks arise in axion models where the U(1) Peccei-Quinn symmetry is broken into Z sub N discrete symmetries. If N equals 1, the walls are bounded by strings and the network quickly disappears. For N greater than 1, the network of walls and strings behaved qualitatively just as the wall network shown in the figures given here. This both confirms the researchers' pessimistic view that domain walls cannot play an important role in the formation of large scale structure and implies that axion models with multiple minimum can be cosmologically disastrous.

Press, William H.↗
NASA NTRSDate not supplied

Three-Dimensional Nonequilibrium Boundary Layer Stability & Transition Analysis For Martian Entry

In this work, we apply the boundary layer stability code LASTRAC, modified to include chemical and thermal nonequilibrium capabilities, to a simulated test case based on literature, with three-dimensional effects. LASTRAC provides Parabolized Stability Equations (PSE)as well as Linear Stability Theory (LST) to predict the stability of a boundary layer and transition with semiempirical eN methods. Tests of the Mars Science Laboratory (MSL)indicated a range of laminar to transitional flow conditions. In order to reduce the weight of Thermal Protection Systems (TPS), reliable prediction of transition and an understanding of the environmental factors that contribute to transition are necessary. This work is a step towards addressing this need, including the effects of thermochemical nonequilibrium but neglecting radiation, ablation, and ionization effects. Our results indicate that an oblique first mode produces maximum N-Factors on the symmetry plane, however with N-Factors too small to explain transition. Although we are able to show nonequilibrium three-dimensional PSE results inCO2, further study with improved mean flow solutions, accounting for some of the uncertainties inherent in this analysis, or evaluation of alternative transition mechanisms is needed to explain transition in the wind tunnel cases examined here.

H L Kline↗
NASA NTRS1992

Electron-impact excitation of the n 1P levels of helium - Theory and experiment

New experimental electron-energy-loss data have been used to extract differential and integral cross sections for excitation of the 2 1P level, and for the overlapping (3 1P, 3 1D, 3 3D) levels of helium, at 30-, 50-, and 100-eV incident electron energies. First-order many-body theory (FOMBT) has been used to calculate the differential and integral cross sections for excitation of the n 1P (n = 2,...,6) levels of helium by electron impact, for incident electron energies from threshold to 500 eV. Detailed comparisons between these two new sets of data are made as well as comparisons with appropriate published experimental and theoretical results. A simple scaling relationship is derived from the FOMBT results for n = 2,...,6 that provides differential and integral cross sections for all symmetry final levels of helium with n = 6 or greater.

Cartwright, David C.↗
NASA NTRS1981

The photometric center of the Gegenschein

Model calculations are employed to assess two factors that determine the position of the photometric center of the Gegenschein: (1) the increased scattering efficiency of the interplanetary dust near backscattering (at scattering angles of 165 to 180 deg); and (2) the spatial density distribution of the dust. Computer-generated brightness contours are used to examine which of these two factors dominates. It is found that the effect of the enhanced scattering of light by dust in the backscattering region is more important than the effect of the spatial density distribution of the dust. This means that the photometric center should be observed at the antisolar point at all times, except possibly when the antisolar point is at its maximum displacement from the symmetry plane.

Misconi, N. Y.↗
NASA NTRS1984

A numerical study of the stability of radiative shocks

Attention is given to the oscillatory instability of optically thin radiative shocks in time-dependent numerical calculations of accretion flows onto degenerate dwarfs. The present nonlinear calculations yield good quantitative agreement with the linear results obtained for oscillation frequencies, damping rates, and critical alpha-values. The fundamental mode and the first overtone in the shock radius and luminosity variations can be clearly identified, and evidence is sometimes seen for the second overtone. Time-dependent calculations are also performed which include additional physics relevant to degenerate dwarf accretion, such as electron thermal conduction, unequal electron and ion temperatures, Compton cooling, and relativistic corrections to the bremsstrahlung cooling law. All oscillatory modes are found to be damped, and hence stable, in the case of a 1-solar mass white dwarf accreting in spherical symmetry.

Imamura, J. N.↗
NASA NTRS1976

Molecular cluster theory for chemisorption of first row atoms on nickel /100/ surfaces

Self-consistent Hartree-Fock-Slater molecular cluster models for the chemisorption of first-row atoms on Ni(100) surfaces are presented. Energy levels and ground-state charge distributions are given for XNi5 clusters with the adatom X = H, C, N, O located in C4V symmetry at a fixed height of 2.0 au above the surface. The variation of properties with height was studied in detail for the case of oxygen. Theoretical results compare rather well with experimental photoelectron and energy-loss data. Local-densities-of-states diagrams are used to clarify the interaction between adsorbate levels and metal conduction bands.

Ellis, D. E.↗
NASA NTRS1973

The use of Levy-Lees variables in three-dimensional boundary-layer flows

A method for solving a general class of three-dimensional boundary layer flows is developed. In the development, Levy-Lees variables are extended to three dimensions and equations are placed in these similarity variables. An implicit finite difference scheme which is stable for negative transverse velocities is used to solve these equations. The method developed is applied to obtain solutions for sharp and spherically blunted circular cones at angle of attack. Longitudinal and transverse distributions are presented for these cases. Good agreement is found with the results obtained by other numerical schemes and the experimental data of Tracy, for sharp circular cones at angle of attack. For spherically blunted cones at angle of attack, the results are in good agreement with axisymmetric sphere results up to the region where spherical symmetry holds.

Vatsa, V. N.↗
NASA NTRS1992

Novel heterojunction varactors

An account is given of new varactor multiplier designs, for mm-wave and sub-mm-wave receiver systems, which have their bases in heterostructure layers and exhibit either stronger capacitance nonlinearity or a special symmetry of characteristics. While barrier-n-layer-n(+) C-V characteristics yield superior performance at low pump powers, the symmetric C-V characteristics of the single-barrier varactor devices yield efficient low-order harmonic generation. Capacitance nonlinearity in these devices is due to depletion of a semiconductor drift region.

Frerking, Margaret A.↗
NASA NTRS1994

Latitude variations of stratospheric trace gases

We present vertical column abundances of H2O, N2O, HNO3, NO2, O3, HF, HCl, and ClNO3, determined from solar absorption spectra measured by the JPL MkIV interferometer from the NASA DC-8 aircraft. These observations, taken in 1987 and 1992, covered latitudes ranging from 85 deg S to 85 deg N. Although most gases display latitude symmetry, large asymmetries in H2O, HNO3, and O3 are apparent, which can be ascribed to processes enhanced by the colder Antarctic winter temperatures.

Toon, G. C.↗
NASA NTRS2004

Linearity-Preserving Limiters on Irregular Grids

This paper examines the behavior of flux and slope limiters on non-uniform grids in multiple dimensions. We note that on non-uniform grids the scalar formulation in standard use today sacrifices k-exactness, even for linear solutions, impacting both accuracy and convergence. We rewrite some well-known limiters in a n way to highlight their underlying symmetry, and use this to examine both traditional and novel limiter formulations. A consistent method of handling stretched meshes is developed, as is a new directional formulation in multiple dimensions for irregular grids. Results are presented demonstrating improved accuracy and convergence using a combination of model problems and complex three-dimensional examples.

Berger, Marsha↗
NASA NTRS1992

Radar scattering properties of pancakelike domes on Venus

Magellan radar images have disclosed the presence of a large number of almost perfectly circular domes, presumably of volcanic origin, in many regions of Venus several with diameters of 30 km or more. Their high degree of symmetry has permitted measurements of their shape, as determined by the Magellan altimeter to be compared with models of dome production from the eruption of high-viscosity magmas. In this work, we examine in detail the radar images of domes in Rusalka Planitia (2.8 deg S, 150.9 deg E) and Tinatin Planitia (12.2 deg N, 7.5 deg E), selected for their circular symmetry and apparent absence of modification due to large-scale slumping or tectonic rifting.

Ford, P. G.↗
NASA NTRS1977

On the photometric axis of the zodiacal light

A model of the zodiacal cloud is used to predict the position of the photometric axis (the locus of points of maximum brightness) of the zodiacal light at any elongation angle from the sun for any time of the year for various symmetry planes: the orbital planes of Venus, Mars, and Jupiter, the invariable plane, and the solar equatorial plane. Using a scattering function which combines isotropic scattering and Fresnel reflection, the geocentric distance of the dust that contributes most of the brightness at each elongation angle is determined by computing the brightness contribution along the line of sight. A comparison of the predicted and observed positions shows that at elongation angles of 15 to 60 deg, the axis of symmetry appears to be close to the orbital plane of Venus. At angles of less than 10 deg, it is difficult to distinguish among the proposed planes of symmetry. Observations of the photometric axis at angles of 60 to 180 deg are scarce and do not permit precise determination of the axis of symmetry in that region.

Misconi, N. Y.↗
NASA NTRS1989

Effects of crystal-melt interfacial energy anisotropy on dendritic morphology and growth kinetics

Morphological and kinetic studies of succinonitrile, a BCC crystal with a low (0.5 percent) anisotropy and pivalic acid, and FCC crystal with relatively large (5 percent) anisotropy in solid-liquid interfacial energy, show clearly that anisotropy in the solid-liquid interfacial energy does not affect the tip radius-velocity relationship, but has a profound influence on the tip region and the rate of amplification of branching waves. Anisotropy of the solid-liquid interfacial energy may be one of the key factors by which the microstructural characteristics of cast structures reflect individual material behavior, especially crystal symmetry.

Glicksman, M. E.↗