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Results for “Higher-order interactions”

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 NTRS1986

Higher-order structure of rRNA

A comparative search for phylogenetically covarying basepair replacements within potential helices has been the only reliable method to determine the correct secondary structure of the 3 rRNAs, 5S, 16S, and 23S. The analysis of 16S from a wide phylogenetic spectrum, that includes various branches of the eubacteria, archaebacteria, eucaryotes, in addition to the mitochondria and chloroplast, is beginning to reveal the constraints on the secondary structures of these rRNAs. Based on the success of this analysis, and the assumption that higher order structure will also be phylogenetically conserved, a comparative search was initiated for positions that show co-variation not involved in secondary structure helices. From a list of potential higher order interactions within 16S rRNA, two higher-order interactions are presented. The first of these interactions involves positions 570 and 866. Based on the extent of phylogenetic covariation between these positions while maintaining Watson-Crick pairing, this higher-order interaction is considered proven. The other interaction involves a minimum of six positions between the 1400 and 1500 regions of the 16S rRNA. Although these patterns of covariation are not as striking as the 570/866 interaction, the fact that they all exist in an anti-parallel fashion and that experimental methods previously implicated these two regions of the molecule in tRNA function suggests that these interactions be given serious consideration.

Gutell, R. R.↗
NASA NTRS1977

Stability of higher-order Bragg interactions in active periodic media

The stability of waves in unbounded, longitudinally periodic media is studied for index and gain coupling. Time-independent periodic media are found to support both stable and absolutely unstable waves. The wave characteristics depend upon average gain or loss, coupling type, and Bragg order. The extended coupled waves equations provide explicit values of threshold, frequency, and temporal growth rate for instabilities at all Bragg resonances through the dispersion relation. Applications to multiharmonic periodicities and complex couplings are briefly discussed with particular note taken of possible reductions of the stability thresholds and removal of threshold degeneracies. Comparisons are made to the longitudinally bounded case of distributed feedback lasers.

Jaggard, D. L.↗
NASA NTRS1974

The role of higher-multipolar and repulsive forces in the calculation of collision-broadened line-widths of linear molecules

Collision-broadened line widths in CO-CO2 and CO-O2 collisions have been calculated by incorporating interactions due to octopoles and hexadecapoles and short-range repulsive interactions into Anderson's (1949) theory. It is shown how these higher-order interactions can be manipulated to yield good agreement with experimental data. A critical evaluation of this totally empirical manipulation suggests that a thorough revision of the theory is required for all but simple dipole-dipole interactions. In the process of the evaluation, the values of the multipole moments are discussed.

Varanasi, P.↗
NASA NTRS1984

An experimental study of a supercritical trailing-edge flow

An experimental study has been conducted of a transonic, turbulent, high-Reynolds-number blunt trailing-edge flow. The model shape and the surface pressure distribution are characteristics of a modern supercritical airfoil under shock-free conditions. Reynolds number and pressure gradient scaling of the boundary layer are relevant to airfoil applications. The data set is exceptionally accurate and consistent, with the momentum balance accounting for the flux of momentum to within 1 percent, except in the immediate vicinity of the blunt trailing edge. The experimental flow exhibits strong viscous-inviscid interaction and higher-order boundary-layer effects including strong adverse streamwise pressure gradient, significant normal pressure gradients associated with surface and streamline curvature, and significant wake curvature. Navier-Stokes calculations with a two-equation K-epsilon turbulence model predict the correct pressure distribution which demonstrates the utility of these engineering tools. The experiment approaches separation at the strailing edge. However, in comparison to the experiment, the calculations predict too high skin friction and insufficient displacement thickness growth. An analysis of the turbulent and mean flow fields reveals the turbulence model defects are likely in modeling the dissipation source and sink terms, and in the eddy viscosity relation.

Brown, J. L.↗
NASA NTRS1979

A progress report on a NASA research program for embedded computer systems software

The paper presents the results of the second stage of the Multipurpose User-oriented Software Technology (MUST) program. Four primary areas of activities are discussed: programming environment, HAL/S higher-order programming language support, the Integrated Verification and Testing System (IVTS), and distributed system language research. The software development environment is provided by the interactive software invocation system. The higher-order programming language (HOL) support chosen for consideration is HAL/S mainly because at the time it was one of the few HOLs with flight computer experience and it is the language used on the Shuttle program. The overall purpose of IVTS is to provide a 'user-friendly' software testing system which is highly modular, user controlled, and cooperative in nature.

Foudriat, E. C.↗
NASA NTRS1983

Interactive Graphics Analysis for Aircraft Design

Program uses higher-order far field drag minimization. Computer program WDES WDEM preliminary aerodynamic design tool for one or two interacting, subsonic lifting surfaces. Subcritical wing design code employs higher-order far-field drag minimization technique. Linearized aerodynamic theory used. Program written in FORTRAN IV.

Townsend, J. C.↗
NASA NTRS1982

Handling Qualities Specifications for U.S. Military Helicopters

Inadequacies in the military specification for helicopter handling qualities, MIL-H-8501A, have long been recognized, and the latest procurements by the U.S. Army used special Prime Item Development Specifications (PIDS). This paper assesses the efficacy of these PIDS and suggests that changes should be made. In particular, the structure developed in MIL-F-8785B (ASG) (the specification for flying qualities of piloted airplanes) should be incorporated. Improved requirements must be based on a systematic data base and concentrated on topics most important in preliminary design: static and dynamic stability, control power and sensitivity, and interaction with controllers and displays. Emphasis should be on current military helicopter missions and helicopter idiosyncrasies such as cross-coupling, nonlinearities, and higher-order dynamics.

Key, David L.↗
NASA NTRS1972

The induced magnetic field of the moon - Conductivity profiles and inferred temperature.

Electromagnetic induction in the moon driven by fluctuations of the interplanetary magnetic field is used to determine the lunar bulk electrical conductivity. The earlier data are now augmented by an order of magnitude. The present data clearly show the north-south and east-west transfer function difference as well as the high-frequency rollover suggested earlier. The difference is shown to be compatible over the midfrequency range (0.001 to 0.01 Hz) with a noise source associated with the compression of the local remanent field by solar wind dynamic pressure fluctuations. The rollover of the transfer functions is shown to result from higher order magnetic multipole radiation; electric multipoles appear supressed, although a vestigial TM interaction may still be present. Models for two, three, and four layer; current layer, double current layer, and core plus current layer moons are generated by inversion of the data, using a theory that incorporates higher-order multipoles.

Sonett, C. P.↗
NASA NTRS1979

Soft-photon emission effects and radiative corrections for electromagnetic processes at very high energies

Higher-order electromagnetic processes involving particles at ultrahigh energies are discussed, with particular attention given to Compton scattering with the emission of an additional photon (double Compton scattering). Double Compton scattering may have significance in the interaction of a high-energy electron with the cosmic blackbody photon gas. At high energies the cross section for double Compton scattering is large, though this effect is largely canceled by the effects of radiative corrections to ordinary Compton scattering. A similar cancellation takes place for radiative pair production and the associated radiative corrections to the radiationless process. This cancellation is related to the well-known cancellation of the infrared divergence in electrodynamics.

Gould, R. J.↗
NASA NTRS1974

Rarefied gas dynamics; Proceedings of the Eighth International Symposium, Stanford University, Stanford, Calif., July 10-14, 1972

Recent studies in the theory of rarefied gases (kinetic theory, shock structure, molecular forces and interactions, evaporation and condensation, expansions and jets, flow past bodies, gas-solid interactions) are presented along with descriptions of numerous experiments in these areas. Some of the topics covered include: singular limits of solutions of Boltzmann's equations, the Boltzmann and Klimontovich formalisms with reference to turbulent resolution, higher-order kinetic theory for the Lorentz gas, intermolecular potentials from shock structure experiments, cooling of particles in aerosol beams, hypersonic-subsonic transition in spherically symmetric expanding flows, absolute velocity measurements in a rarefied gas flow by an ion time-of-flight technique, the product distribution of gas-solid reactions from absolute rate theory, and relaxation of a gas with internal degrees of freedom. Individual items are announced in this issue.

Karamcheti, K.↗
NASA NTRS1974

Time response simulation of the 1975 Viking Orbiter digital tape recorder

The objective of the present study was to verify and understand in depth the performance of the speed control (frequency loop) servo of the 1975 Viking Orbiter (VO75) digital tape recorder (DTR). The time response method employed is written in the continuous system simulation language (CSSL) for the Univac 1108 computer system. In order to demonstrate the power and flexibility of the graphic interactive simulation program, four aspects of system dynamics are interactively adjusted to arrive at a number of stable system configurations that have significantly different tape transport and/or summing amplifier gain, larger static/dynamic Coulomb friction, and different system lag than envisioned in the nominal design by linear methods. Work is currently underway to derive a new higher-order DST transfer function and to simulate the servo using state-space variable techniques.

Mukhopadhyay, A. K.↗
NASA NTRS1986

Pre- and post-processing for Cosmic/NASTRAN on personal computers and mainframes

An interface between Cosmic/NASTRAN and GIFTS has recently been released, combining the powerful pre- and post-processing capabilities of GIFTS with Cosmic/NASTRAN's analysis capabilities. The interface operates on a wide range of computers, even linking Cosmic/NASTRAN and GIFTS when the two are on different computers. GIFTS offers a wide range of elements for use in model construction, each translated by the interface into the nearest Cosmic/NASTRAN equivalent; and the options of automatic or interactive modelling and loading in GIFTS make pre-processing easy and effective. The interface itself includes the programs GFTCOS, which creates the Cosmic/NASTRAN input deck (and, if desired, control deck) from the GIFTS Unified Data Base, COSGFT, which translates the displacements from the Cosmic/NASTRAN analysis back into GIFTS; and HOSTR, which handles stress computations for a few higher-order elements available in the interface, but not supported by the GIFTS processor STRESS. Finally, the versatile display options in GIFTS post-processing allow the user to examine the analysis results through an especially wide range of capabilities, including such possibilities as creating composite loading cases, plotting in color and animating the analysis.

Kamel, H. A.↗
NASA NTRS1985

Aspects of the design and performance of a 3-component LDV system

A conventional two color, two component Laser Doppler Velocimeter (LDV) has been converted into one capable of measuring all three components of velocity simultaneously in low-speed flows. All the Reynolds stresses and higher-order products can then be evaluated. The approach followed is to split one of the two colors and to focus a third pair of beams from an off axis direction. The third velocity component is computed from the known geometry of the system. This paper contains details of the system design with emphasis on the additional problems that are encountered through the introduction of the third component. Some preliminary measurements obtained in a vortex/mixing layer interaction are presented and compared directly with those obtained with a cross-wire system.

Bell, J. H.↗
NASA NTRS1985

A 3-component laser-Doppler velocimeter data acquisition and reduction system

A laser doppler velocimeter capable of measuring all three components of velocity simultaneously in low-speed flows is described. All the mean velocities, Reynolds stresses, and higher-order products can be evaluated. The approach followed is to split one of the two colors used in a 2-D system, thus creating a third set of beams which is then focused in the flow from an off-axis direction. The third velocity component is computed from the known geometry of the system. The laser optical hardware and the data acquisition electronics are described in detail. In addition, full operating procedures and listings of the software (written in BASIC and ASSEMBLY languages) are also included. Some typical measurements obtained with this system in a vortex/mixing layer interaction are presented and compared directly to those obtained with a cross-wire system.

Rodman, L. C.↗
NASA NTRS1986

A 3-component laser-Doppler velocimeter data acquisition and reduction system

This report describes a laser Doppler velocimeter capable of measuring all three components of velocity simultaneously in low-speed flows. All the mean velocities, Reynolds stresses, and higher-order products can then be evaluated. The approach followed is to split one of the colors used in a 2-D system, thus creating a third set of beams which is then focused in the flow from an off-axis direction. The third velocity component is computed from the known geometry of the system. In this report, the laser optical hardware and the data acquisition electronics are described in detail. In addition, full operating procedures and listings of the software (written in BASIC and assembly languages) are also included. Some typical measurements obtained with this system in a vortex/mixing layer interaction are presented and compared directly to those obtained with a cross-wire system.

Rodman, L. C.↗
NASA NTRS1977

Aspects of turbulent combustion

A complete second-order closure program for the investigation of chemically reacting turbulent flowfields is being developed. Many of the turbulence models being used have been developed and tested during previous studies of a variety of incompressible and compressible shear flows. A number of additional scalar correlations have to be modeled for chemically reacting flows, and a 'typical eddy' model has been developed for the joint probability density function for all the scalars. A simpler model in which higher-order scalar correlations are set zero is also being used. The program has been recently extended to multi-species, multi-step chemical reactions. Computations have been performed using the second-order closure program to study the turbulence-chemistry interaction in DF chemical laser flows and in a hydrogen-air diffusion flame. The results demonstrate the importance of the inclusion of the concentration and temperature fluctuation correlations in turbulent reacting flows.

Varma, A. K.↗
NASA NTRS1978

Two-photon excitation of atomic oxygen

A standard perturbation expansion in the atom-radiation-field interaction is used to calculate the two-photon excitation cross section for the 1s2 2s2 2p4 3p to 1s2 2s2 3(4S)3p 3P transition in atomic oxygen. The lowest-order summation over bound and continuum intermediate states is handled by solving the equivalent inhomogeneous differential equation. Higher-order electron-correlation effects are also examined.

Pindzola, M. S.↗
NASA NTRS1984

Higher-order parabolic approximations for sound propagation in stratified moving media

Asymptotic solutions of order k-n are developed for the equations governing the propagation of sound through a stratified moving medium. Here k is a dimensionless wave number and n is the arbitrary order of the approximation. These approximations are an extension of geometric acoustics theory and provide corrections to that theory in the form of multiplicative functions which satisfy parabolic partial differential equations. These corrections account for the diffraction effects caused by variation of the field normal to the ray path and the interaction of these transverse variations with the variation of the field along the ray. The theory is illustrated by application to simple examples.

Mcaninch, G. L.↗