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NASA NTRS1983

The effect of solar-wind convection on charged particle transport in interplanetary space

In the formulation of focused transport without convection, approximate solutions of the Boltzmann equation are described in terms of small perturbations of its two fundamental steady-state solutions. In the presence of convection, the same approach is applicable, provided that the analysis is carried out in a system moving with the solar wind. The approximate transport equations that apply in this system are very similar to those that apply in the absence of convection. The new equations assume that the wind blows in the direction of the guiding field and is constant in space and time. Nevertheless, these equations are more general than existing formulations, for they retain their validity when the solar wind velocity is large, and they describe the coherent modes of transport that appear when the mean free path is greater than 1 AU. An interesting implication of the new formulation is that coherent disturbances are swept along with the wind. In this respect, they differ from truly scatter-free modes, which are not affected by the wind.

Earl, J. A.↗

NASA NTRS1985

Far-field noise of a subsonic jet under controlled excitation

The role of large-scale coherent structures in broadband jet noise suppression and amplification under controlled excitation are studied experimentally. It is found that suppression occurs only at low Reynolds and Mach numbers, when the boundary layer at the jet exit is laminar; the optimum St(Theta) (St, based on the initial shear-layer momentum thickness) value is 0.017, at which the excitation results in a quick roll-up and transition of the laminar shear-layer vortices, yielding coherent structures similar to those existing at high speeds. At the asymptotic level the broadband jet noise can only be amplified by the excitation. The amplification is inferred to be maximum for excitation in the St(D) (St based on the jet diameter) range of 0.65-0.85. Finally, it is noted that the pairing process induced by the excitation is at the origin of the broadband noise amplification.

Zaman, K. B. M. Q.↗

NASA NTRS1986

Calculations on the production and use of superfine holographic X-ray gratings for astrophysical observations

Superfine holograhic X-ray gratings may be produced by transferring onto metal an interference pattern generated by two branches of a sufficiently coherent X-ray beam, emitted in the form of synchrotron radiation from high energy electron storage rings. Generation of the coherent beam requires restrictions on the beam size. A calculation is presented which allows an exact evaluation of this restriction. The effect of defocusing optics on the expected resolution is also studied.

Csonka, P. L.↗

NASA NTRS1986

Signal Detection Techniques for Diagnostic Monitoring of Space Shuttle Main Engine Turbomachinery

An investigation to develop, implement, and evaluate signal analysis techniques for the detection and classification of incipient mechanical failures in turbomachinery is reviewed. A brief description of the Space Shuttle Main Engine (SSME) test/measurement program is presented. Signal analysis techniques available to describe dynamic measurement characteristics are reviewed. Time domain and spectral methods are described, and statistical classification in terms of moments is discussed. Several of these waveform analysis techniques have been implemented on a computer and applied to dynamc signals. A laboratory evaluation of the methods with respect to signal detection capability is described. A unique coherence function (the hyper-coherence) was developed through the course of this investigation, which appears promising as a diagnostic tool. This technique and several other non-linear methods of signal analysis are presented and illustrated by application. Software for application of these techniques has been installed on the signal processing system at the NASA/MSFC Systems Dynamics Laboratory.

Coffin, Thomas↗

NASA NTRS1985

The influence of cobalt, tantalum, and tungsten on the microstructure of single crystal nickel-base superalloys

The influence of composition on the microstructure of single crystal nickel-base superalloys was investigated. Co was replaced by Ni, and Ta was replaced by either Ni or W, according to a matrix of compositions based on MAR-M247. Substitution of Ni for Co caused an increase in gamma-prime solvus temperature, an increase in gamma-gamma-prime lattice mismatch, and the precipitation of W-rich phases in the alloys with high refractory metal levels. Substitution of Ni for Ta caused large decreases in gamma-prime solvus temperature, gamma-prime volume fraction, and gamma-gamma-prime lattice mismatch, whereas substitution of W for Ta resulted in smaller decreases in these features. For the alloys with gamma-prime particles that remained coherent, substitution of Ni for Co caused an increase in gamma-prime coarsening rate. The two alloys with the largest magnitude of lattice mismatch possessed gamma-prime particles which lost coherency during unstressed aging and exhibited anomalously low coarsening rates. Creep exposure at 1000 C resulted in the formation of gamma-prime lamellae oriented perpendicular to the applied stress axis in all alloys.

Nathal, M. V.↗

NASA NTRS1985

An experimental study of organized motions in the turbulent plane mixing layer

Recent investigations suggest that turbulent shear flows are generally characterized by large-scale coherent structures. Little is currently known regarding the detailed characteristics and dynamical roles of these structures. The present study has been motivated by a number of questions which arise in connection with such structures, taking into account the education procedure, the topological characteristics, and the mechanics of the large-scale structures in a high-Reynolds-number plane mixing layer, originating from an initially fully turbulent boundary layer. Attention is given to the experimental apparatus, the initial conditions, the education scheme, and the coherent-structure properties.

Hussain, A. K. M. F.↗

NASA NTRS1985

Effect of a fibril magnetic field on solar p-modes

The dispersion relation is obtained for acoustic plane waves that scatter coherently from an ensemble of parallel magnetic flux tubes when the wave vector is perpendicular to the flux-tube axis. When the magnetic flux tubes are distributed uniformly and possess radii that are small compared with the wavelength, the frequency can be calculated exactly. The waves are damped slightly due to a loss of coherence and are shifted downward or upward in frequency relative to a medium devoid of magnetic fibrils, depending primarily on whether the flux tubes are more or less dense than their surroundings. It is suggested that the influence of the fibril magnetic fields observed at the solar surface cannot be ignored in the interpretation of high-1 surface p-mode data.

Bogdan, T. J.↗

NASA NTRS1985

A new type of VLF emission triggered at low altitude in the subauroral region by Siple Station VLF transmitter signals

The present paper has the objective to report the existence of a new phenomenon in which coherent VLF signals from the Siple Station VLF transmitter (Antarctica, 76 deg S, 84 deg W) are observed to trigger a new type of VLF emission, taking into account the propagation of these signals upward through the ionosphere and low-altitude magnetosphere to the ISIS 2 satellite at 1400 km altitude. The existence of the impulsive emission (IE) effect lends credence to the idea that coherent VLF signals can act as catalysts to trigger natural plasma instabilities in the subauroral ionosphere and lower magnetosphere. Controlled studies of these instabilities may, therefore, be possible.

Bell, T. F.↗

NASA NTRS1986

Combining beams from separated telescopes

In the present paper, work is discussed which arose in the context of optical design studies for the proposed space-based COSMIC (Coherent Optical System of Modular Interferometric Collectors) telescope. The operation of COSMIC involves the combination of a number of parallel beams with a central beam-combining telescope which forms an image of the sky. The paper is mainly concerned with the aspects of beam combination. The paraxial constraint condition is considered along with tolerances regarding the individual optical elements, and imaging as a nonshearing recombination. A first-order requirement for achieving a finite field of view is discussed, taking into account specifically the case of a coherent imaging optical system.

Traub, W. A.↗

NASA NTRS1985

A multiple scattering theory for EM wave propagation in a dense random medium

For a dense medium of randomly distributed scatterers an integral formulation for the total coherent field has been developed. This formulation accounts for the multiple scattering of electromagnetic waves including both the twoand three-particle terms. It is shown that under the Markovian assumption the total coherent field and the effective field have the same effective wave number. As an illustration of this theory, the effective wave number and the extinction coefficient are derived in terms of the polarizability tensor and the pair distribution function for randomly distributed small spherical scatterers. It is found that the contribution of the three-particle term increases with the particle size, the volume fraction, the frequency and the permittivity of the particle. This increase is more significant with frequency and particle size than with other parameters.

Karam, M. A.↗

NASA NTRS1986

Chaotic rotation of Hyperion?

Thomas et al. (1984) analyzed 14 Voyager 2 images of Saturn's satellite Hyperion and interpreted them to be consistent with a coherent (nonchaotic) rotation period of 13.1 days. This interpretation was criticized by Peale and Wisdom (1984), who argued that the low sampling frequency of Voyager data does not allow chaotic or nonchaotic rotation to be distinguished. New observations obtained with a higher sampling frequency are reported here which conclusively show that the 13.1 day period found by Thomas et al. was not due to coherent rotation.

Binzel, R. P.↗

NASA NTRS1985

Bit synchronization of differentially detected MSK and GMSK

The filter-square bit synchronizer has been previously proposed and shown to give near optimum performance for coherent PSK systems. In this paper, the same bit synchronization scheme is analyzed for a differentially detected GMSK system. It is shown that the filter-square bit synchronizer can successfully work in a differential phase detection receiver. By making linear approximations appropriate for high loop signal-to-noise ratio operation (the usual case of interest in tracking), it is demonstrated that the mean-square bit sync jitter of differentially detected GMSK system reveals striking similarities both qualitatively and quantitatively in comparison with that of a coherent PSK system.

Simon, M. K.↗

NASA NTRS1986

Ionospheric convection signatures observed by DE 2 during northward interplanetary magnetic field

Observations of the ionospheric convection signature at high latitudes are examined during periods of prolonged northward interplanetary magnetic field (IMF). The data from Dynamics Explorer 2 show that a four-cell convection pattern can frequently be observed in a region that is displaced to the sunward side of the dawn-dusk meridian regardless of season. In the eclipsed ionosphere, extremely structured or turbulent flow exists with no identifiable connection to a more coherent pattern that may simultaneously exist in the dayside region. The two highest-latitude convection cells that form part of the coherent dayside pattern show a dependence on the y component of the IMF. This dependence is such that a clockwise circulating cell displaced toward dawn dominates the high-latitude region when B(Y) is positive. Anti-clockwise circulation displaced toward dusk dominates the highest latitudes when B(Y) is negative. Examination of the simultaneously observed energetic particle environment suggests that both open and closed field lines may be associated with the high-latitude convection cells. On occasions these entire cells can exist on open field lines. The existence of closed field lines in regions of sunward flow is also apparent in the data.

Heelis, R. A.↗

NASA NTRS1987

Monolithic Isolated Single-Mode Ring Laser

MISER uses four-sided ring to lase nonreciprocally. Laser concept provides very-compact, efficient, and stable source of coherent radiation. Lasers of single, very-stable frequency desirable for number of purposes. Frequency stability makes possible coherent detection of laser radiation with low-bandwidth detector, useful for communications. Allows very-high-resolution spectroscopy. Any application where desired to use laser in way microwaves used traditionally enhanced if frequency very stable.

Kane, T. J.↗

NASA NTRS1987

Injection Phase-Locked Laser-Diode Array

Phase-coherent emission with negligible far-field supermodes produced by proposed surface-emitting laser-diode array stimulated by holographically directed emission from single master diode. To achieve same coherence and output power, single laser diode requires high power density, which substantially reduces working lifetime. Proposed integrated optical array useful in communications

Lesh, James R.↗

NASA NTRS1986

Progress in the MF radar system at Saskatoon

Two improvements were made to the radar system in the last year, one was the addition of O/X mode capability to the full antenna array used in the real-time wind system, and the other was the development of a coherent receiver. The design of the transmitter antenna is examined. The proposed coherent real-time wind system is also discussed.

Meek, C. E.↗

NASA NTRS1986

A single-board preprocessor and pulse generator

The Aeronomy Lab. of NOAA has designed and built a single board, programmable radar controller for use with VHF ST (stratosphere troposphere) radars. The controller consists of a coherent integrator preprocessor and a radar pulse generator, both of which are described, as well as interfaces to an antenna beam switch and a receiver bandwidth switch. The controller occupies a single slot in a Data General Nova of Eclipse computer. The integrator and pulse generator take advantage of high density, dual port FIFO chips such as the 512 x 9 Mostek MK 4501. These FIFOs have separate input and output ports and independent read and write cycles with cycle times of less than 200 ns, making them very fast and easy to interface. A simple block diagram of the coherent integrator is shown. The integrator is designed to handle inputs from one receiver (2 channels) with 1 sec sample spacing. The pulse generator is based on controllers designed by R. F. Woodman for the Arecibo and SOUSY radars us a recirculating memory scheme.

Carter, D. A.↗

NASA NTRS1986

Evaluation of diffuse-illumination holographic cinematography in a flutter cascade

Since 1979, the Lewis Research Center has examined holographic cinematography for three-dimensional flow visualization. The Nd:YAG lasers used were Q-switched, double-pulsed, and frequency-doubled, operating at 20 pulses per second. The primary subjects for flow visualization were the shock waves produced in two flutter cascades. Flow visualization was by diffuse-illumination, double-exposure, and holographic interferometry. The performances of the lasers, holography, and diffuse-illumination interferometry are evaluated in single-window wind tunnels. The fringe-contrast factor is used to evaluate the results. The effects of turbulence on shock-wave visualization in a transonic flow are discussed. The depth of field for visualization of a turbulent structure is demonstrated to be a measure of the relative density and scale of that structure. Other items discussed are the holographic emulsion, tests of coherence and polarization, effects of windows and diffusers, hologram bleaching, laser configurations, influence and handling of specular reflections, modes of fringe localization, noise sources, and coherence requirements as a function of the pulse energy. Holography and diffuse illumination interferometry are also reviewed.

Decker, A. J.↗